Automobile body

Abstract

The vehicle body is derived from a road-going vehicle with excellent collision safety by removing the battery, tires, and liquids containing water or oil. This road-going vehicle is constructed from at least steel materials including steel plates with a tensile strength of 1180 MPa or higher, non-ferrous metal materials, and resin materials. The mass m of the steel plates with a tensile strength of 1180 MPa or higher is specified. h The ratio of (kg) to the mass m (kg) of the aforementioned vehicle body is 9% or more, where the mass of the aforementioned vehicle body is set as m (kg) and the projected area of ​​the aforementioned vehicle body from above is set as s (m²). 2 When ), the following equations (1) and (2) are satisfied. 6

Description

Technical Field

[0001] This invention relates to automobile bodies.

[0002] This application claims priority based on Japanese Patent Application No. 2021-088012 filed on May 25, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] Recently, from the perspective of preventing global warming, reducing greenhouse gas emissions has become more important. In this context, it is hoped that the emergence of electric vehicles, hybrid vehicles, and the like, which reduce emissions of greenhouse gases such as carbon dioxide (CO2) compared to existing internal combustion engine-powered vehicles, will reduce the amount of greenhouse gases emitted from vehicles during operation. Furthermore, it is hoped that the use of lightweight materials such as aluminum and carbon as raw materials for automobile construction will further reduce the amount of greenhouse gases emitted from vehicles during operation.

[0004] Regarding automobile bodies, for example, Patent Document 1 discloses a body structure with excellent productivity. Furthermore, Non-Patent Document 1 discloses that, regarding the proportion of high-strength steel in the body-in-white (BIW) of an automobile, the same 1180MPa grade steel sheet accounts for 0% to 17% in current vehicles, the same 1310MPa grade steel sheet accounts for 0% to 5%, and the same 1470MPa grade steel sheet accounts for 6%. Generally, the weight ratio of BIW to vehicle weight is about 30%. If converted to the weight ratio of high-strength steel to vehicle weight, the proportion of steel sheet of 1180MPa grade or higher is less than 9%, and the proportion of the same 1470MPa grade steel sheet is less than 2%.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2021 / 001813

[0008] Non-patent literature

[0009] Non-patent literature 1: Nikkan Kogyo Shimbun, October 12, 2017 report: https: / / www.nikkan.co.jp / articles / view / 00446307 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] However, if we consider the life cycle of a car, it is insufficient to focus solely on reducing greenhouse gas emissions during vehicle use (driving) as described above in order to reduce the total amount of greenhouse gases emitted into the Earth's environment. It is necessary to reduce the total amount of greenhouse gases, including "1. greenhouse gases generated during the manufacture of materials that make up a car", "2. greenhouse gases generated during the manufacture of a car", "3. greenhouse gases generated during the use of a car", and "4. greenhouse gases generated when a car is scrapped".

[0012] Therefore, the object of the present invention is to provide a vehicle body capable of reducing the total amount of greenhouse gases generated throughout the entire life cycle of a car, including its manufacture, use and disposal.

[0013] means for solving problems

[0014] The subject of this application is as follows.

[0015] (1) The first aspect of the present invention relates to a car body, which is a car body obtained by removing the battery, tires, and liquid containing water or oil from a road-going vehicle with excellent collision safety. The road-going vehicle is at least composed of steel material comprising steel plates with a tensile strength of 1180 MPa or more, non-ferrous metal material, and resin material, wherein the mass m of the steel plates with a tensile strength of 1180 MPa or more is... h The ratio of (kg) to the mass m (kg) of the aforementioned vehicle body is 9% or more, where the mass of the aforementioned vehicle body is set as m (kg) and the projected area of ​​the aforementioned vehicle body from above is set as s (m²). 2 When ), the following equations (1) and (2) are satisfied.

[0016] 6 <s<11 (1)

[0017] m<(272.37×s-835)×0.98 (2)

[0018] (2) A second aspect of the present invention relates to a car body, which is a car body obtained by removing the battery, tires, and liquids containing water or oil from a road-going vehicle with excellent collision safety. The road-going vehicle is constructed of at least steel material comprising steel plates with a tensile strength of 1180 MPa or more, non-ferrous metal material, and resin material, wherein the mass m of the steel plates with a tensile strength of 1180 MPa or more is... h The ratio of (kg) to the mass m (kg) of the aforementioned automobile body is 9% or more. Let M be the sum of CO2 emissions during manufacturing, use, and disposal, calculated from the raw materials of the aforementioned automobile body, and let s (m²) be the projected area of ​​the aforementioned automobile body from above. 2When the height of the above-mentioned car body is set to h (m), the following equations (3) and (4) are satisfied.

[0019] 9 <s×h<19 (3)

[0020] M<(1925.1×s×h-81.4)×0.98 (4)

[0021] (3) The automobile body according to (1) or (2) above, wherein the mass m of the steel material described above may be: s The total mass of sheet metal parts made of the aforementioned steel plates with a tensile strength of 1.9 GPa or higher, where the ratio of the mass m (kg) to the mass m (kg) of the aforementioned automobile body is 64% or more. hs The ratio of (kg) to the mass m (kg) of the aforementioned automobile body is 9% or more.

[0022] (4) The automobile body according to (1) or (2) above, wherein the total mass m of the sheet metal parts made of the steel plate with a tensile strength of 1180 MPa or more is... ht (kg) relative to the body weight of the aforementioned automobile body (m) b The ratio (kg) can also be 24% or more.

[0023] (5) The automobile body according to (1) or (2) above, wherein the total mass m of sheet metal parts containing more than 0.013% Cu, more than 0.018% Ni and more than 0.002% Sn sc (kg) The total mass of the sheet metal parts of the above-mentioned automobile body (m) sp The ratio (kg) can also be 20% or more.

[0024] (6) The automobile body according to (3) above may also have: a hot-stamped formed body, the chemical composition of which, in mass %, contains: C: 0.30-0.50%, Si: 0.50-3.00%, Mn: 0.50-3.00%, Al: 0.0002-2.000%, P: less than 0.100%, S: less than 0.1000%, N: less than 0.0100%, Nb: 0-0.150%, Ti: 0-0.150%, Co: 0-2.00%, Mo: 0-1.00%, Cr: 0-1.00%, Cu: 0-1.00%, V: 0- The hot-stamped body contains 1.00% W, 0-1.00% Ni, 0-3.00% Mg, 0-1.00% Zr, 0-1.00% Sb, 0-1.00% Ca, 0-0.10% REM, 0-0.30% B, and the remainder includes Fe and impurities. The microstructure of the hot-stamped body is as follows: containing 5% to less than 10% retained austenite, bainite and tempered martensite totaling more than 90% to less than 95% by area, and less than 5% remaining microstructure. At the grain boundaries of the bainite and tempered martensite grains, relative to the area of… <011> The total length of grain boundaries with a rotation angle of 4° to 12° along the rotation axis, the length of grain boundaries with a rotation angle of 49° to 54°, and the length of grain boundaries with a rotation angle of 55° to 75°, wherein the proportion of the length of grain boundaries with a rotation angle of 55° to 75° is 30% or more, and the tensile strength of the hot-stamped formed body is 1500 MPa or more; a skeleton member formed by hot stamping a steel sheet, the skeleton member having a closed section portion with a closed section perpendicular to the length direction, the closed section portion having at least one flat portion having a radius of curvature larger than the maximum external dimension of the section, and the flat portion having the largest width relative to the effective width calculated by the Karman formula among the at least one flat portion is defined as a reference flat portion. At that time, the Vickers hardness of the center portion of the plate thickness at the aforementioned reference flat portion is 300 Hv or more, the width of the aforementioned reference flat portion is less than 2.0 times the aforementioned effective width, and the standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution at the surface portion of the aforementioned reference flat portion by the standard deviation of the hardness frequency distribution at the center portion of the plate thickness of the aforementioned reference flat portion is less than 1.0; and the hot-stamped formed body, the chemical composition of which, in mass % contains: C: 0.15 to 0.50%, Si: 0.0010 to 3.000%, Mn: 0.30 to 3.00%, Al: 0.0002 to 2.000%, P: less than 0.100%, S: less than 0.1000%, N: less than 0.0100%, Nb: 0 to 0.15%, Ti: 0 to 0.15%, V: 0 to 0.15%, Mo: 0 to 1.0%, Cr: 0-1.0%, Cu: 0-1.0%, Ni: 0-1.0%, B: 0-0.0100%, Ca: 0-0.010%, and REM: 0-0.30%, with the remainder containing Fe and impurities. The hot-stamped body has a metallic structure comprising martensite, bainite, and tempered martensite comprising more than 90% by area. In the texture from the surface to a position 1 / 4 of the plate thickness away from the surface, it consists of {001}<1-10> to {001}<-1-1. The ratio of the extreme density of the orientation group formed by {001}<1-10> to {111}<-1-12> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is less than 1.8. In the texture at a distance of 1 / 4 to 1 / 2 of the plate thickness from the surface, the ratio of the extreme density of the orientation group formed by {001}<1-10> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is less than 2.3.

[0025] (7) The automobile body according to (3) above may also have: a hot-stamped formed body, the chemical composition of which, in mass %, contains: C: 0.15-0.50%, Si: 0.0010-3.000%, Mn: 0.30-3.00%, Al: 0.0002-2.000%, P: less than 0.100%, S: less than 0.1000%, N: less than 0.0100%, Nb: 0-0.15%, Ti: 0-0.15%. The hot-stamped body contains 0-1.0% of the following components: V: 0-0.15%, Mo: 0-1.0%, Cr: 0-1.0%, Cu: 0-1.0%, Ni: 0-1.0%, B: 0-0.0100%, Ca: 0-0.010%, and REM: 0-0.30%, with the remainder being Fe and impurities. The hot-stamped body has a metallic microstructure comprising at least 90% martensite, bainite, and tempered martensite by area, with the microstructure extending from the surface to a distance of 1 / 4 of the plate thickness. In the texture of the position, the ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is less than 1.8. In the texture at a distance of 1 / 4 to 1 / 2 of the plate thickness from the surface, the ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10> is less than 1.8. The ratio of the extreme densities of the orientation groups formed by {111}<1-10>~{111}<-1-12> is less than 2.3; and a skeleton member formed by hot stamping a steel plate, the skeleton member having a closed section portion with a cross section perpendicular to the length direction, the closed section portion having at least two flat portions as portions with a radius of curvature larger than the maximum external dimension in the cross section and a recessed reinforcing rib portion formed between the two flat portions, the recessed reinforcing rib portion having a pair of wall portions with a radius of curvature of 50 mm or more, the pair of wall portions protruding from the opposing ends of the two flat portions toward the inside of the closed section portion by a pair of curved portions bending toward the inside of the closed section portion, the Vickers hardness of the center portion of the plate thickness of the wall portion being 520 Hv or more, and the width of the wall portion being the effective width W obtained by the Karman effective width formula. e The standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution at the surface layer of the wall by the standard deviation of the hardness frequency distribution at the center of the wall thickness is less than 1.0.

[0026] (8) The automobile body according to (3) above may also have: a skeleton member formed by cold pressing of a steel sheet, the skeleton member having a closed section portion with a closed section perpendicular to the length direction, the closed section portion having at least one flat portion having a radius of curvature larger than the maximum external dimension in the section, and when the flat portion having the largest width relative to the effective width calculated by the effective width formula of the at least one flat portion is defined as a reference flat portion, the Vickers hardness of the center of the plate thickness at the reference flat portion is 300 Hv or more. The width of the aforementioned reference flat portion is less than 2.0 times the aforementioned effective width, and the standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution at the surface portion of the aforementioned reference flat portion by the standard deviation of the hardness frequency distribution at the center of the plate thickness of the aforementioned reference flat portion is greater than 1.0; the skeleton member formed by hot stamping a steel plate has a closed section portion with a closed section perpendicular to the length direction, and the closed section portion has at least one flat portion with a radius of curvature larger than the maximum external dimension in the section, wherein the at least one flat portion has a relative to the through When the flat portion that is the largest in proportion to the effective width obtained by the effective width formula of the kamen method is defined as the reference flat portion, the Vickers hardness at the center of the plate thickness at the reference flat portion is 300 Hv or more, the width of the reference flat portion is less than 2.0 times the effective width, and the standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution at the surface of the reference flat portion by the standard deviation of the hardness frequency distribution at the center of the plate thickness at the reference flat portion is less than 1.0; and the skeleton member formed by hot stamping the steel plate, the skeleton member having a cross section perpendicular to the length direction is The closed section of the closed section has at least two flat portions, each having a radius of curvature larger than the maximum external dimension of the section, and a concave reinforcing rib formed between the two flat portions. The concave reinforcing rib has a pair of wall portions with a radius of curvature of 50 mm or more. These wall portions protrude inwards from opposite ends of the two flat portions via a pair of curved portions bending toward the interior of the closed section. The Vickers hardness at the center of the wall portion is 520 Hv or more. The width of the wall portion is the effective width W calculated using the Karman formula. e The standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution at the surface layer of the wall by the standard deviation of the hardness frequency distribution at the center of the wall thickness is less than 1.0.

[0027] (9) According to the automobile body described in (8) above, it may also have: a structural member for automobile body, which extends along a predetermined direction and has a top plate portion, a ridge portion continuous with the top plate portion, and a longitudinal wall portion continuous with the ridge portion. The structural member for automobile body is made of a pressed steel sheet with a cross section that is approximately channel-shaped, intersecting the predetermined direction. The structural member for automobile body has at least one groove portion formed at the end of the top plate portion extending along the predetermined direction and an outward flange formed at least within the ridge portion at the end portion. The depth (h), width (w), and thickness (t) of the steel sheet at the end portion satisfy the following relationship:

[0028] 0.2×H0≤h≤3.0×H0、

[0029] H0 = (0.037t - 0.25) × w - 5.7t + 29.2; and

[0030] High-strength frame components, which have L-shaped and T-shaped features.

[0031] (10) The automobile body according to (3) above may also have: a hot-stamped formed body, the chemical composition of which, in mass %, contains: C: 0.15-0.50%, Si: 0.0010-3.000%, Mn: 0.30-3.00%, Al: 0.0002-2.000%, P: less than 0.100%, S: less than 0.1000%, N: less than 0.0100%, Nb: 0-0.15%, Ti: 0-0.15%, V: 0-0.15%, Mo: 0-1.0%, Cr: 0-1.0%, Cu: 0-1.0%, Ni: 0-1.0%, B: 0-0.0100%, C a: 0-0.010% and REM: 0-0.30%, the remainder containing Fe and impurities. The hot-stamped formed body has a metallic structure containing martensite, bainite, and tempered martensite totaling more than 90% by area. In the texture from the surface to a position 1 / 4 of the plate thickness away from the surface, the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is less than 1.8. In the texture from a position 1 / 4 of the plate thickness away from the surface to a position 1 / 2 of the plate thickness away from the surface, the ratio of the extreme density of the orientation group formed by {001}<1-10> to {111}<-1-12> is less than 1.8. The ratio of the extreme density of the orientation group formed by -10>~{001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10>~{111}<-1-12> is less than 2.3; and a skeleton member, which is a skeleton member joined by spot welding a first steel plate member and a second steel plate member at a spot weld portion, the skeleton member having a cross-sectional region with a closed cross-section perpendicular to the length direction of the skeleton member, the first steel plate member having a tensile strength of 1900 MPa or more, the spot weld portion having a molten metal portion formed by the spot weld and a heat-affected portion adjacent to the outside of the molten metal portion, the molten metal portion being included in the... In a cross-section perpendicular to the length direction at the center point, the region corresponding to the molten metal portion is defined as a first region, the region corresponding to the heat-affected zone is defined as a second region, and the region formed by the region from the boundary between the first and second regions to a distance of 100 μm towards the first region and the region from the boundary to a distance of 100 μm towards the second region is defined as a third region. When measuring Vickers hardness at 15 μm intervals with a load of 10 gf along an imaginary straight line extending from the center of the first region towards the second region, the average Vickers hardness Hv at the measurement location corresponding to the first region on the imaginary straight line is... Ave The lowest Vickers hardness Hv at the measurement location corresponding to the third region on the hypothetical straight line described above. Min Satisfy Hv Ave -Hv Min≤100.

[0032] (11) According to the automobile body described in (10) above, it may also have: a structural member for automobile body, which is formed extending along a predetermined direction and has a top plate portion, a ridge portion continuous with the top plate portion and a longitudinal wall portion continuous with the ridge portion. The structural member for automobile body is made of a pressed and formed steel sheet with a cross section forming a generally channel-shaped cross section intersecting the predetermined direction. The structural member for automobile body has at least one groove portion formed extending along the predetermined direction from the end of the top plate portion from the predetermined direction and an outward flange formed in the end portion with a range of at least the ridge portion. The depth (h), the width (w), and the thickness (t) of the steel sheet in the end portion satisfy the following relationship:

[0033] 0.2×H0≤h≤3.0×H0、

[0034] H0 = (0.037t - 0.25) × w - 5.7t + 29.2; and

[0035] High-strength frame components, which have L-shaped and T-shaped features.

[0036] (12) The automobile body according to (10) above may also have a hot-stamped formed article, wherein the hot-stamped formed article has a base steel sheet having the following chemical composition: containing, by mass %: C: more than 0.40% and less than 0.70%, Si: less than 2.00%, Mn: more than 0.01% and less than 0.50%, P: less than 0.200%, S: less than 0.0200%, sol.Al: 0.001 to 1.000%, N: less than 0.0200%, Mo: more than 0.01% and less than 0.50%, B: 0.0002 to 0.0200%, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0 to 0.000%. 0.200%, Zr: 0-0.200%, Cr: 0-2.00%, W: 0-2.00%, Cu: 0-2.00%, Ni: 0-2.00%, Ca: 0-0.0100%, Mg: 0-0.0100%, REM: 0-0.1000%, Bi: 0-0.0500%, and the remainder being Fe and impurities. When determining the Mo content of the base steel plate using EPMA line analysis, within a 0.05 mm range along the thickness direction centered at a depth of 1 / 4 of the plate thickness from the surface of the base steel plate, the maximum, minimum, and average Mo content were set as follows:

[0037] [Mo] mMAX Maximum Mo content (mass%) in the base steel plate

[0038] [Mo] mMIN Minimum Mo content (mass%) in the base steel plate.

[0039] [Mo] mAVE : Average Mo content (mass %) of the base steel plate

[0040] Satisfy ([Mo]) mMAX -[Mo] mMIN ) / [Mo] mAVE <0.50, the metal structure of the aforementioned base steel plate contains more than 90.0% martensite, the standard deviation of Vickers hardness in a region 0.3 mm along the thickness direction and 0.6 mm in a direction orthogonal to the thickness direction, centered at a depth of 1 / 4 of the thickness of the aforementioned base steel plate, is less than 20 (Hv), and the tensile strength of the aforementioned base steel plate is more than 2300 MPa.

[0041] (13) The automobile body according to (11) above may also have a hot-stamped formed article, wherein the hot-stamped formed article has a base steel sheet having the following chemical composition: containing, by mass %: C: more than 0.40% and less than 0.70%, Si: less than 2.00%, Mn: more than 0.01% and less than 0.50%, P: less than 0.200%, S: less than 0.0200%, sol.Al: 0.001 to 1.000%, N: less than 0.0200%, Mo: more than 0.01% and less than 0.50%, B: 0.0002 to 0.0200%, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0 to 0.000%. 0.200%, Zr: 0-0.200%, Cr: 0-2.00%, W: 0-2.00%, Cu: 0-2.00%, Ni: 0-2.00%, Ca: 0-0.0100%, Mg: 0-0.0100%, REM: 0-0.1000%, Bi: 0-0.0500%, and the remainder being Fe and impurities. When determining the Mo content of the base steel plate using EPMA line analysis, within a 0.05 mm range along the thickness direction centered at a depth of 1 / 4 of the plate thickness from the surface of the base steel plate, the maximum, minimum, and average Mo content were set as follows:

[0042] [Mo] mMAX Maximum Mo content (mass%) in the base steel plate

[0043] [Mo] mMIN Minimum Mo content (mass%) in the base steel plate.

[0044] [Mo] mAVE : Average Mo content (mass %) of the base steel plate

[0045] Satisfy ([Mo]) mMAX -[Mo] mMIN ) / [Mo] mAVE <0.50, the metal structure of the aforementioned base steel plate contains more than 90.0% martensite, the standard deviation of Vickers hardness in a region 0.3 mm along the thickness direction and 0.6 mm in a direction orthogonal to the thickness direction, centered at a depth of 1 / 4 of the thickness of the aforementioned base steel plate, is less than 20 (Hv), and the tensile strength of the aforementioned base steel plate is more than 2300 MPa.

[0046] (14) The automobile body according to (3) above may also have: a hot-stamped formed body, the chemical composition of which, in mass %, contains: C: 0.15-0.50%, Si: 0.0010-3.000%, Mn: 0.30-3.00%, Al: 0.0002-2.000%, P: less than 0.100%, S: less than 0.1000%, N: less than 0.0100%, Nb: 0-0.15%, Ti: 0-0.15%, V: 0-0.15%, Mo: 0-1%. 0%, Cr: 0-1.0%, Cu: 0-1.0%, Ni: 0-1.0%, B: 0-0.0100%, Ca: 0-0.010%, and REM: 0-0.30%, with the remainder containing Fe and impurities. The hot-stamped body described above has a metallic microstructure comprising martensite, bainite, and tempered martensite, totaling over 90% by area. In the texture from the surface to a position 1 / 4 of the plate thickness away from the surface, the orientation groups formed by {001}<1-10> to {001}<-1-10> are extremely... The ratio of the density to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is less than 1.8; in the texture at a distance of 1 / 4 to 1 / 2 of the plate thickness from the surface, the ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is less than 2.3; and the side member structure of the vehicle body, which has a structure along the vehicle body The cylinder extends in the longitudinal direction and an impact-absorbing member is disposed inside the cylinder. The impact-absorbing member has a web extending in the longitudinal direction and being flat in the vehicle width direction, an outer flange that engages with the outer end of the web and extends in the longitudinal direction, and an inner flange that engages with the inner end of the web and extends in the longitudinal direction. The outer flange and the inner flange have ribs that are arranged to clamp the web from above and below and extend in the longitudinal direction.

[0047] (15) According to the automobile body described in (14) above, it may also have: a structural member for automobile body, which extends along a predetermined direction and has a top plate portion, a ridge portion continuous with the top plate portion, and a longitudinal wall portion continuous with the ridge portion. The structural member for automobile body is made of a pressed steel sheet with a cross section that is approximately groove-shaped and intersects the predetermined direction. The structural member for automobile body has at least one groove portion formed at the end of the top plate portion extending along the predetermined direction and an outward flange formed at least in the range of the ridge portion at the end portion. The depth (h), the width (w), and the thickness (t) of the steel sheet in the end portion satisfy the following relationship:

[0048] 0.2×H0≤h≤3.0×H0、

[0049] H0 = (0.037t - 0.25) × w - 5.7t + 29.2; and

[0050] High-strength frame components, which have L-shaped and T-shaped features.

[0051] (16) The automobile body according to (14) above may also have steel components, the steel components having a steel sheet substrate and a coating containing Al and Fe formed on the surface of the steel sheet substrate, the steel sheet substrate having the following chemical composition: containing, by mass %: C: 0.10-0.65%, Si: 0.10-2.00%, Mn: 0.30-3.00%, P: less than 0.050%, S: less than 0.0100%, N: less than 0.010%, O: less than 0.010%, Ti: 0-0.100%, B: 0-0.0100%, Cr: 0-1.00%, Mo: 0-1.00%, Ni: 0-1.00%, Nb: 0-0.10%, Cu: 0-1.00%. The steel plate substrate contains 0-1.00% V, 0-0.010% Ca, 0-0.010% Mg, 0-1.00% Al, 0-1.00% Sn, 0-1.00% W, 0-1.00% Sb, 0-1.00% Zr, 0-1.00% Co, 0-1.00% REM, and the remainder contains Fe and impurities. The steel plate substrate has a decarburized layer formed on the coated side, and the decarburized layer has an internal oxide layer formed on the coated side. The depth of the decarburized layer from the interface between the steel plate substrate and the coated side is 30 μm or more, and the depth of the internal oxide layer from the interface is less than 20 μm. There is no oxide scale between the steel plate substrate and the coated side containing Al and Fe.

[0052] (17) The automobile body according to (15) above may also have steel components, the steel components having a steel sheet substrate and a coating containing Al and Fe formed on the surface of the steel sheet substrate, the steel sheet substrate having the following chemical composition: containing, by mass %: C: 0.10-0.65%, Si: 0.10-2.00%, Mn: 0.30-3.00%, P: less than 0.050%, S: less than 0.0100%, N: less than 0.010%, O: less than 0.010%, Ti: 0-0.100%, B: 0-0.0100%, Cr: 0-1.00%, Mo: 0-1.00%, Ni: 0-1.00%, Nb: 0-0.10%, Cu: 0-1.00%. The steel plate substrate contains 0-1.00% V, 0-0.010% Ca, 0-0.010% Mg, 0-1.00% Al, 0-1.00% Sn, 0-1.00% W, 0-1.00% Sb, 0-1.00% Zr, 0-1.00% Co, 0-1.00% REM, and the remainder contains Fe and impurities. The steel plate substrate has a decarburized layer formed on the coated side, and the decarburized layer has an internal oxide layer formed on the coated side. The depth of the decarburized layer from the interface between the steel plate substrate and the coated side is 30 μm or more, and the depth of the internal oxide layer from the interface is less than 20 μm. There is no oxide scale between the steel plate substrate and the coated side containing Al and Fe.

[0053] (18) According to the automobile body described in (14) above, it may also have a tray manufactured by a manufacturing method comprising: a welding process in which a high-strength portion having high tensile strength is welded to a low-strength portion having a lower tensile strength than the high-strength portion; and a forming process in which the low-strength portion is pressed in such a way that it includes a recess, the recess having an angle between the inner surfaces of the first sidewall of the first sidewall and the inner surfaces of the second sidewall of the second sidewall, which are adjacent to each other at an acuminate angle, and an angle between the inner surfaces of the first sidewall and the inner surfaces of the second sidewall of the second sidewall and the inner surfaces of the first sidewall in relation to the angle. The tray has a corner portion on the upper surface of a bottom wall with a sub-oblique angle, wherein the tray has a bottom wall and a peripheral side wall vertically disposed from the outer periphery of the bottom wall, and the tray has a high-strength portion having high tensile strength and a low-strength portion having lower tensile strength than the high-strength portion. The low-strength portion is formed by including a recess, and the recess has a corner portion in the inner surface of the first side wall of the first side wall and the inner surface of the second side wall of the second side wall that are adjacent to each other at a sub-oblique angle, and a corner portion in the upper surface of the bottom wall that is at a sub-oblique angle relative to the inner surface of the first side wall and the inner surface of the second side wall.

[0054] (19) According to the automobile body described in (15) above, it may also have a tray manufactured by a manufacturing method comprising: a welding process in which a high-strength portion having high tensile strength is welded to a low-strength portion having a lower tensile strength than the high-strength portion; and a forming process in which the low-strength portion is pressed in such a way that it includes a recess, the recess having an angle between the inner surfaces of the first sidewall of the first sidewall and the inner surfaces of the second sidewall of the second sidewall, which are adjacent to each other at an acuminate angle, and an angle between the inner surfaces of the first sidewall and the inner surfaces of the second sidewall of the second sidewall and the inner surfaces of the first sidewall in relation to the angle. The tray has a corner portion on the upper surface of a bottom wall with a sub-oblique angle, wherein the tray has a bottom wall and a peripheral side wall vertically disposed from the outer periphery of the bottom wall, and the tray has a high-strength portion having high tensile strength and a low-strength portion having lower tensile strength than the high-strength portion. The low-strength portion is formed by including a recess, and the recess has a corner portion in the inner surface of the first side wall of the first side wall and the inner surface of the second side wall of the second side wall that are adjacent to each other at a sub-oblique angle, and a corner portion in the upper surface of the bottom wall that is at a sub-oblique angle relative to the inner surface of the first side wall and the inner surface of the second side wall.

[0055] (20) According to the automobile body described in (16) above, it may also have a tray manufactured by a manufacturing method comprising: a welding process in which a high-strength portion having high tensile strength is welded to a low-strength portion having a lower tensile strength than the high-strength portion; and a forming process in which the low-strength portion is pressed in such a way that it includes a recess, the recess having a corner portion of the inner surface of the first sidewall of the first sidewall and the inner surface of the second sidewall of the second sidewall that are adjacent to each other at an acuminate angle, and a corner portion of the inner surface of the first sidewall and the inner surface of the second sidewall relative to the corner portion. The tray has a corner portion on the upper surface of a bottom wall with a sub-oblique angle, wherein the tray has a bottom wall and a peripheral side wall vertically disposed from the outer periphery of the bottom wall, and the tray has a high-strength portion having high tensile strength and a low-strength portion having lower tensile strength than the high-strength portion. The low-strength portion is formed by including a recess, and the recess has a corner portion in the inner surface of the first side wall of the first side wall and the inner surface of the second side wall of the second side wall that are adjacent to each other at a sub-oblique angle, and a corner portion in the upper surface of the bottom wall that is at a sub-oblique angle relative to the inner surface of the first side wall and the inner surface of the second side wall.

[0056] (21) According to the automobile body described in (17) above, it may also have a tray manufactured by a manufacturing method comprising: a welding process in which a high-strength portion having high tensile strength is welded to a low-strength portion having a lower tensile strength than the high-strength portion; and a forming process in which the low-strength portion is pressed in such a way that it includes a recess, the recess having an angle between the inner surfaces of the first sidewall of the first sidewall and the inner surfaces of the second sidewall of the second sidewall, which are adjacent to each other at an acuminate angle, and an angle between the inner surfaces of the first sidewall and the inner surfaces of the second sidewall of the second sidewall and the inner surfaces of the first sidewall in relation to the angle. The tray has a corner portion on the upper surface of a bottom wall with a sub-oblique angle, wherein the tray has a bottom wall and a peripheral side wall vertically disposed from the outer periphery of the bottom wall, and the tray has a high-strength portion having high tensile strength and a low-strength portion having lower tensile strength than the high-strength portion. The low-strength portion is formed by including a recess, and the recess has a corner portion in the inner surface of the first side wall of the first side wall and the inner surface of the second side wall of the second side wall that are adjacent to each other at a sub-oblique angle, and a corner portion in the upper surface of the bottom wall that is at a sub-oblique angle relative to the inner surface of the first side wall and the inner surface of the second side wall.

[0057] Invention Effects

[0058] According to the present invention, a vehicle body can be provided that can reduce the total amount of greenhouse gases generated throughout the entire life cycle of a vehicle, including its manufacture, use and disposal. Attached Figure Description

[0059] Figure 1 It is a characteristic graph representing the environmental impact (greenhouse gas production) of each raw material used in the manufacture of automobiles.

[0060] Figure 2 This is an exploded perspective view of the vehicle body of the road-driving automobile of this embodiment.

[0061] Figure 3 This is an exploded perspective view of the vehicle body of the road-driving automobile of this embodiment.

[0062] Figure 4 This is a perspective view showing the exterior panel of the automobile body according to this embodiment.

[0063] Figure 5 This is a perspective view showing an example of a frame of a single-shell structure for an automobile body according to this embodiment, the frame having an impact-absorbing skeleton member.

[0064] Figure 6 This is a perspective view showing an example of a frame of a single-shell structure for a car body according to this embodiment, the frame having a cockpit frame component.

[0065] Figure 7This is a perspective view of the floor frame components of the single-shell structure of the car body of an electric vehicle when the car is an electric vehicle used for road travel.

[0066] Figure 8 This is a graph showing the relationship between the projected area s of the car body and the vehicle weight, as shown in Table 1.

[0067] Figure 9 This is a characteristic diagram showing the results of comparing the mass (equivalent mass) per unit projected area of ​​the automobile body with Invention Example 5, Comparative Example 1, and Comparative Example 8.

[0068] Figure 10 This is a graph showing the relationship between the volume v of the car body and the total greenhouse gas (GHG) emissions obtained by converting CO2 equivalent mass as shown in Table 1.

[0069] Figure 11 This is a characteristic diagram showing the results of comparing torsional stiffness with Invention Example 5, Comparative Example 1, and Comparative Example 9.

[0070] Figure 12 This is a characteristic diagram showing the results of comparing the amount of intrusion of the center pillar of the car body into the inside of the car body during a side collision using numerical simulation for Invention Example 5 and Comparative Example 1.

[0071] Figure 13 This is a schematic diagram used to illustrate the amount of energy absorbed.

[0072] Figure 14 This is a perspective view of the skeleton component A10 representing one embodiment of element technology A.

[0073] Figure 15 yes Figure 14 The cross-sectional view of the cut line A1-A1.

[0074] Figure 16 This is a graph showing the relationship between the standard deviation of hardness and the VDA bending angle ratio in the VDA bending test for cold-rolled steel sheets with a tensile strength of 980 MPa or higher.

[0075] Figure 17 This is a perspective view of the skeleton component A20 in the modified example.

[0076] Figure 18 yes Figure 17 The cross-sectional view of the cut line A2-A2.

[0077] Figure 19 This is a perspective view of the car frame A100 as an example of an applied structural component.

[0078] Figure 20This is a schematic diagram used to illustrate the cross-sectional shape of the square tube material used in the embodiments.

[0079] Figure 21 This is a graph obtained by plotting the relationship between the effective width ratio and energy absorption efficiency of the experimental examples.

[0080] Figure 22 This is a graph showing an example of an FS curve obtained through a bending test.

[0081] Figure 23 This is a schematic diagram used to illustrate the amount of energy absorbed.

[0082] Figure 24 This is a perspective view of the skeleton component C10 representing one embodiment of element technology C.

[0083] Figure 25 yes Figure 24 The cross-sectional view of the cut line A1-A1.

[0084] Figure 26 This is a graph showing the relationship between the standard deviation of hardness and the VDA bending angle ratio in the VDA bending test for 2.0 GPa grade materials.

[0085] Figure 27 This is a perspective view of the skeleton component C20 in a modified example.

[0086] Figure 28 yes Figure 27 The cross-sectional view of the cut line A2-A2.

[0087] Figure 29 This is a perspective view of the car frame C100 as an example of an applied structural component.

[0088] Figure 30 This is a schematic diagram used to illustrate the cross-sectional shape of the square tube material used in the embodiments.

[0089] Figure 31 This is a graph obtained by plotting the relationship between the effective width ratio and energy absorption efficiency of the experimental examples.

[0090] Figure 32 This is a schematic diagram illustrating an example of a steel plate according to this embodiment.

[0091] Figure 33 This is a schematic diagram illustrating an example of a steel component according to this embodiment.

[0092] Figure 34 This is a schematic diagram illustrating an example of another type of steel member (covered steel member) of this embodiment.

[0093] Figure 35This is a schematic diagram showing the location for measuring the hardness of steel plates used in hot stamping.

[0094] Figure 36 This is a schematic diagram illustrating an example of the shape of a hot-stamped product.

[0095] Figure 37 This is a schematic diagram showing the shape of a 3-point bending test specimen.

[0096] Figure 38 This is a schematic diagram showing the configuration of the testing machine and the test specimen in a 3-point bending test.

[0097] Figure 39 This is a perspective view of the skeleton components of one embodiment of element technology G.

[0098] Figure 40 yes Figure 39 The cross-sectional view of the cut line A1-A1.

[0099] Figure 41 yes Figure 40 A magnified view of the area enclosed by A.

[0100] Figure 42 This is a graph showing the relationship between the standard deviation of hardness and the bending angle ratio in the VDA bending test for 2.0 GPa grade materials.

[0101] Figure 43 It is a three-dimensional view showing the skeleton components of a modified example.

[0102] Figure 44 yes Figure 43 The cross-sectional view of the cut line A2-A2.

[0103] Figure 45 yes Figure 43 A magnified view of the area enclosed by B.

[0104] Figure 46 This is a cross-sectional view showing a deformed example of a skeleton component.

[0105] Figure 47 This is a schematic diagram showing a deformation example of the concave reinforcing rib.

[0106] Figure 48 This is a schematic diagram showing another variation of the concave reinforcing rib area.

[0107] Figure 49 This is a perspective view of a car frame as an example of an applied skeletal component.

[0108] Figure 50 This is a schematic diagram used to illustrate the cross-sectional shape of the square tube component used in the first embodiment.

[0109] Figure 51 The graph is obtained by plotting the relationship between the effective width ratio and the energy absorption efficiency of the first experimental example.

[0110] Figure 52 This is a schematic diagram used to illustrate the cross-sectional shape of the square tube component used in the second embodiment.

[0111] Figure 53 This is a perspective view of the skeleton components representing one embodiment of element technology H.

[0112] Figure 54 This is a schematic cross-sectional view showing the vicinity of the spot weld portion of the skeleton member in the above embodiment.

[0113] Figure 55 It means Figure 54 The curve showing the hardness distribution along the imaginary straight line a.

[0114] Figure 56 This is a schematic cross-sectional view of the vicinity of the spot weld of a skeleton component of a steel plate component using a Mn content of 1.27% by mass.

[0115] Figure 57 It means Figure 56 The curve showing the hardness distribution along the imaginary straight line a.

[0116] Figure 58 This is a schematic diagram used to illustrate the cross-sectional shape of the components used in the embodiments.

[0117] Figure 59 This is a schematic diagram used to illustrate the three-point bending test conditions of the experimental example.

[0118] Figure 60 This is a schematic diagram illustrating the state of spot fracture caused by a 3-point bending test, showing the state of spot fracture occurring at 5 locations on one side.

[0119] Figure 61 This is a schematic diagram showing the state of solder joint fracture caused by a 3-point bending test, illustrating the state of solder joint fracture occurring at one location on one side.

[0120] Figure 62 It is an exploded perspective view showing a part of the vehicle body.

[0121] Figure 63 This refers to the side member structure of the first embodiment. Figure 62 A-direction view in the diagram.

[0122] Figure 64 This is a cross-sectional perspective view showing a portion of the side member structure of the first embodiment.

[0123] Figure 65 This is an exploded perspective view showing a portion of the side member structure of the first embodiment.

[0124] Figure 66 This is a side view showing a portion of the web of the first embodiment.

[0125] Figure 67 This diagram illustrates the distribution of bending moment acting on the side member structure of the first embodiment and the deformation mode of the side member structure. Figure 67 (A) is a top-down view. Figure 67 (B) is a side view.

[0126] Figure 68 This refers to the side member structure of the second embodiment. Figure 62 A-direction view in the diagram.

[0127] Figure 69 This is a cross-sectional perspective view showing a portion of the side member structure of the second embodiment.

[0128] Figure 70 This is an exploded perspective view showing a portion of the side member structure of the second embodiment.

[0129] Figure 71 This is a side view showing a portion of the web of the second embodiment.

[0130] Figure 72 This is a graph representing the numerical analysis results of the intrusion amount.

[0131] Figure 73 This is an explanatory diagram of the tray used in the implementation method.

[0132] Figure 74 This is a perspective view of the tray in the implementation method.

[0133] Figure 75 This is a top view of the tray in the implementation method.

[0134] Figure 76 yes Figure 75 A-direction view in the diagram.

[0135] Figure 77 This is a diagram illustrating an example of a single-shell structure frame for the automobile body and a cabin frame component according to this embodiment.

[0136] Figure 78 This is a diagram illustrating an example of a single-shell structure frame for the automobile body of this embodiment, and a high-strength frame member having L-shaped and T-shaped features in the cabin frame member. Detailed Implementation

[0137] Hereinafter, several embodiments of the present invention will be described with reference to the figures. However, these descriptions are merely illustrative of preferred embodiments of the present invention and are not intended to limit the present invention to such specific embodiments.

[0138] As mentioned above, considering the entire lifecycle of a vehicle, reducing the total amount of greenhouse gases (GHG) emitted into the Earth's environment by focusing solely on reductions during vehicle use (driving) is insufficient. It is necessary to reduce the total amount of GHG emitted, including: 1. GHG generated during the manufacture of materials constituting the vehicle; 2. GHG generated during vehicle manufacturing; 3. GHG generated during vehicle use; and 4. GHG generated when the vehicle is scrapped. It should be noted that in this specification, greenhouse gases represented by CO2 generated during the vehicle's lifecycle, considered from this perspective, are referred to as "lifecycle greenhouse gases." The CO2 quantity is defined as the total amount after equivalent mass conversion of other greenhouse gases besides CO2. Examples of greenhouse gases besides CO2 include methane, nitrous oxide, and CFCs, which deplete the ozone layer. The method for calculating the equivalent mass of CO2 will be described below.

[0139] Regarding the aforementioned "1. Greenhouse gases generated during the manufacture of raw materials that constitute automobiles", steel, as a raw material, emits the least amount of greenhouse gases per automobile compared to other raw materials. Figure 1 This is a graph representing the environmental impact (greenhouse gas emissions) of each raw material used in the manufacture of automobiles. The vertical axis represents the materials used in automobiles (typically steel sheets, high-strength steel sheets, aluminum, carbon fiber reinforced plastics (CFRP)), and the horizontal axis represents the greenhouse gas emissions per equivalent function [kg - CO2 equivalent / kg - equivalent component]. For example... Figure 1As shown, steel raw materials (typically steel plates and high-strength steel plates) produce significantly less greenhouse gas emissions compared to other raw materials (aluminum, carbon fiber reinforced plastics). By primarily using steel as the raw material for automobiles, greenhouse gas emissions are reduced, greatly contributing to life-cycle greenhouse gas reduction. It should be noted that "CO2 equivalent" is also called "CO2 equivalent mass." In this specification, "CO2 equivalent," "CO2 equivalent mass," and "CO2 conversion" are defined with the same meaning. "CO2 equivalent mass" is calculated by weighting CO2 (global warming coefficient: 1) with gases other than CO2, such as methane (CH4) (25 times the greenhouse effect of CO2 per unit mass: global warming coefficient 25) and nitrous oxide (N2O) (298 times the greenhouse effect of CO2 per unit mass: global warming coefficient 298), and then converting the equivalent mass into CO2. It should be noted that in this specification, the "CO2 equivalent mass" is calculated by using the conversion factor (the conversion factor recorded in Table 4 below) set for the "CO2 equivalent mass" of each raw material.

[0140] Furthermore, regarding the aforementioned "3. Greenhouse gases generated during automobile use," from the perspective of reducing the load on internal combustion engines and other drive sources by making automobiles lighter and thus reducing greenhouse gases, the current focus is mainly on using raw materials such as aluminum and carbon to make automobiles more multi-material and lighter. Therefore, in reality, this is achieved through methods such as... Figure 1 The proposed method of reducing the amount of greenhouse gases produced by raw materials with relatively high greenhouse gas emissions does not take into account both the reduction of greenhouse gases produced during the use of automobiles ("3. Greenhouse gases produced during automobile use") and the reduction of greenhouse gases produced during the manufacture of raw materials that constitute automobiles. The main reason is that, currently, it is believed that the reduction of greenhouse gases produced during the manufacture of raw materials that constitute automobiles and the reduction of greenhouse gases produced during automobile use are in a compromise relationship, and there is no intention to simultaneously reduce both.

[0141] The inventors of this invention, aiming to reduce life-cycle greenhouse gases by simultaneously reducing "1. greenhouse gases generated during the manufacture of raw materials constituting the automobile" and "3. greenhouse gases generated during the use of the automobile," have conducted in-depth research on the essential technologies of the automobile body 100, particularly its materials and structure. The inventors of this invention have applied new materials (high-strength steel) and novel structures corresponding to the functions of each part of the automobile body 100. More specifically, the inventors of this invention have constructed the automobile body 100 primarily of steel, applied new steel materials to each part of the automobile body 100, and applied novel structures in each part to compensate for the insufficient body rigidity caused by the accompanying thinning of the steel plates. Thus, the automobile body 100 of the road-going automobile of this embodiment achieves both lightweighting and high rigidity resulting from the thinning of the steel plates, and is able to reduce life-cycle greenhouse gases while meeting the necessary strength requirements.

[0142] Figure 2 and Figure 3 This is an exploded perspective view of the vehicle body 100 of the road-driving vehicle according to this embodiment. Figure 2 The vehicle body 100 of a car (engine vehicle) powered by an internal combustion engine 1 is shown. Additionally, Figure 3 The vehicle body 100 of an electric vehicle powered by an electric motor 2 is shown. Figure 2 and Figure 3 The car body 100 shown has an exterior panel 10 and a single-shell frame 20, and the exterior panel 10 is mounted on the single-shell frame 20. It should be noted that the exterior panel 10 includes an engine hood 12, doors 14, a roof 16, mudguards 18, a trunk lid 19, etc. Figure 2 and Figure 3 The car bodies 100 shown are all obtained from road-going cars after removing the batteries, tires, and liquids containing water or oil.

[0143] It should be noted that, in Figure 2 The engine vehicle shown has a car body 100 and Figure 3 In the electric vehicle body 100 shown, the electric vehicle has a large-capacity battery mounted near the floor of the body, so the main difference lies in the composition of the floor components. In the engine vehicle body 100, the floor 15 is provided on the frame 20, and the internal combustion engine 1, suspension 3, etc. are mounted on the frame 20. Regarding the electric vehicle body 100, it may also have a structure similar to the engine vehicle, with the engine 2, suspension 3, etc. mounted on the frame 20, but it may also be as follows: Figure 3As shown, the structure includes an engine 2, suspension 3, etc., mounted on the floor frame member 30. Furthermore, the electric vehicle body 100 differs from the engine vehicle body 100 in that it has a battery box 40 for mounting the battery on the floor frame member 30. Additionally, in... Figure 3 The diagram shows a structure in which the floor 15 is mounted on the frame 20, but the floor 15 can also be mounted on the battery box 40, or the upper surface of the battery box 40 can also serve as the floor.

[0144] The vehicle body 100 of the highway driving vehicle of this embodiment, by applying new materials and a new structure, can meet the specified conditions that existing vehicle bodies cannot meet. Specifically, the vehicle body 100 of the highway driving vehicle of this embodiment is a vehicle body 100 of a highway driving vehicle with excellent collision safety after removing the battery, tires, and liquids containing water or oil. The aforementioned highway driving vehicle is at least composed of steel materials including steel plates with a tensile strength of 1180 MPa or more, non-ferrous metal materials, and resin materials, wherein the mass m of the steel plates with a tensile strength of 1180 MPa or more is... h The ratio of the mass (kg) to the mass m (kg) of the vehicle body 100 is 9% or more, where the mass of the vehicle body 100 is set as m (kg) and the projected area of ​​the vehicle body 100 from above is set as s (m²). 2 When ), the following equations (1) and (2) are satisfied.

[0145] 6 <s<11 (1)

[0146] m<(272.37×s-835)×0.98 (2)

[0147] More preferably, the mass m of steel plates with a tensile strength of 1470 MPa or higher h The ratio of (kg) to the mass m (kg) of the aforementioned automobile body 100 is 9% or more.

[0148] It should be noted that the coefficient 0.98 is the value when taking a 2% margin, and it is more preferable to set the coefficient to 0.972 and take a 2.8% margin. Furthermore, it is more preferable to set the coefficient to 0.965 and take a 3.5% margin.

[0149] Furthermore, the vehicle body 100 of the highway driving vehicle in this embodiment is a vehicle body 100 of a highway driving vehicle with excellent collision safety, after removing the battery, tires, and liquids containing water or oil. The highway driving vehicle is constructed of at least steel material comprising steel plates with a tensile strength of 1180 MPa or more, non-ferrous metal materials, and resin materials. The mass m of the steel plates with a tensile strength of 1180 MPa or more is... hThe ratio of (kg) to the mass m (kg) of the car body 100 is 9% or more. Let M be the sum of the CO2 equivalent masses of various greenhouse gas emissions during manufacturing, use, and disposal, calculated from the raw material composition of the car body 100. Let s (m²) be the projected area of ​​the car body 100 from above. 2 When the height of the car body 100 is set to h (m), the following equations (3) and (4) are satisfied.

[0150] 9 <s×h<19 (3)

[0151] M<(1925.1×s×h-81.4)×0.98 (4)

[0152] More preferably, the mass m of steel plates with a tensile strength of 1470 MPa or higher h The ratio of (kg) to the mass m (kg) of the aforementioned automobile body 100 is 9% or more.

[0153] It should be noted that the coefficient 0.98 is the value with a 2% margin, and it is more preferable to set the coefficient to 0.975 with a 2.5% margin. It is even more preferable to set the coefficient to 0.97 with a 3% margin.

[0154] Furthermore, regarding the vehicle body 100 of the road-driving vehicle in this embodiment, the mass m of the aforementioned steel material... s The ratio of (kg) to the mass m (kg) of the car body 100 is 64% or more.

[0155] Furthermore, regarding the vehicle body 100 of the road-driving vehicle in this embodiment, the total mass m of the sheet metal parts made of steel plates with a tensile strength of 1180 MPa or higher is... ht (kg) relative to the body weight (m) of the car body 100 b The total mass of sheet metal parts made of steel plates with a tensile strength of 1.9 GPa or higher, comprising 24% or more of the total mass (kg), is m. hs (kg) relative to the body weight (m) of the car body 100 b The ratio (kg) is 9% or more. More preferably, the total mass m of sheet metal parts made of steel plates with a tensile strength of 1470 MPa or more is... ht (kg) relative to the body weight (m) of the car body 100 b The ratio (kg) is 24% or more.

[0156] Furthermore, regarding the vehicle body 100 of the road-driving vehicle in this embodiment, the total mass m of sheet metal parts containing 0.013% or more Cu, 0.018% or more Ni, and 0.002% or more Sn sc(kg) The total mass of sheet metal parts relative to 100 of the car body (m) sp The ratio (kg) is 20% or more.

[0157] It should be noted that "road vehicles with excellent crash safety" include "vehicles that meet the crash safety standards of various countries around the world, such as USNCAP, and are subject to the New Vehicle Assessment Program".

[0158] Although these conditions will be explained in detail later, they are satisfied by the novel materials and structures of the vehicle body 100 of this embodiment, which cannot be satisfied by existing vehicle bodies that do not possess these novel materials and structures. It should be noted that the vehicle body 100 of this embodiment can ultimately be implemented (achieved) by appropriately combining multiple technologies from elements A to L described later. Furthermore, it is desirable that the vehicle body 100 of this embodiment preferably employs three or more technologies from elements A to L.

[0159] In particular, in order to meet the quality requirements of the aforementioned steel materials m s The total mass of sheet metal parts made of the aforementioned steel plates with a tensile strength of 1.9 GPa or higher, wherein the ratio of the mass m (kg) to the mass m (kg) of the automobile body is 64% or more. hs For a car body where the ratio of mass m (kg) to mass m (kg) of the car body is 9% or more, it is preferable to combine the element technologies A to L as described below.

[0160] Combining 1 element technology B+C+E

[0161] Combining 2-Element Technology E+G

[0162] Combining the three elements of technology A+C+G

[0163] Combining 3-1 element technologies A+C+G+K+L

[0164] Combining the four elements of technology E+H

[0165] Combining 4-1 elements of technology E+H+K+L

[0166] Combining 4-2-1 element technology E+H+F

[0167] Combining the 4-2-2 element technology E+H+K+L+F

[0168] Combining the 5 elements of technology E+I

[0169] Combining 5-1 elements of technology E+I+K+L

[0170] Combining the 5-2-1 elements of technology E+I+D

[0171] Combining the 5-2-2 elements of technology: E+I+K+L+D

[0172] Combining 5-3-1 elements of technology E+I+J

[0173] Combining the 5-3-2 elements of technology: E+I+K+L+J

[0174] Combining the 5-3-3 elements of technology: E+I+D+J

[0175] Combining the 5-3-4 elements of technology: E+I+K+L+D+J

[0176] It should be noted that, in this manual, "road-going vehicle" refers to a vehicle that meets the safety standards of various countries' regulations (type certification) and achieves excellent crash safety ratings in all crash tests conducted by NCAP (New Car Assessment Program) in those countries. It should be noted that these assessment tests are more stringent than the regulations of various countries; if a vehicle receives the highest rating (5-star rating) in these tests, it can be said to be fully capable of road driving.

[0177] Furthermore, the vehicle body 100 of the road-driving vehicle in this embodiment is not limited to... Figure 2 The engine vehicle shown or Figure 3 The electric vehicle body shown can also be the body of a hybrid electric vehicle, fuel cell vehicle, or hydrogen engine vehicle, which uses an internal combustion engine and an electric motor as propulsion sources. Additionally, in Figure 2 and Figure 3 The image shows a car body with a single-shell frame 20, but the car body 100 is not limited to a car body with a single-shell frame 20; it can also be a car body with a trapezoidal frame structure. Furthermore, types of vehicles used for road travel include passenger cars or commercial vehicles such as sedans, hatchbacks, station wagons, one-box vans, and pickup trucks. In addition, vehicles used for road travel include heavy-duty vehicles such as trucks.

[0178] The outline of the element technologies used in the automobile body 100 of this embodiment is described below. It should be noted that details regarding each element technology will be described later.

[0179] 1. Outer panel

[0180] Figure 4This is a perspective view showing an example of the exterior panel 10 of the automobile body 100 according to this embodiment. Specifically, the exterior panel 10 includes the hood 12, door 14, roof 16, etc., and is designed to have excellent surface quality and appearance after pressing and forming. As the raw material for the exterior panel 10, cold-rolled high-strength steel with a tensile strength of 590MPa to 780MPa is mainly used.

[0181] 2. Impact-absorbing skeleton components (Technical elements A, B, and C)

[0182] Figure 5 This is a perspective view showing an example of a frame 20 of a single-shell structure for an automobile body 100 according to this embodiment, which includes an impact-absorbing skeleton member 22. The impact-absorbing skeleton member 22 is located at the area marked with gray density in the figure; it deforms during a collision to absorb impact energy. Details of the material and structure of the impact-absorbing skeleton member 22 are shown below.

[0183] 2.1. Structure using cold-rolled high-strength steel with a tensile strength of 980 MPa or higher (Element Technology A)

[0184] 2.2. Hot-stamped formed bodies with a tensile strength of 1470 MPa or higher (Element Technology B)

[0185] 2.3. Skeleton components with excellent energy absorption efficiency (Element Technology C)

[0186] 2.4. Skeleton components with continuous flanges and their manufacturing methods (Element Technology K)

[0187] 3. Cockpit frame components and floor frame components (technical elements D, E, F, G, H)

[0188] Figure 6 This is a perspective view showing an example of a frame 20 of a single-shell structure for a car body 100 according to this embodiment, which includes a cabin frame member 24. The cabin frame member 24 is located in areas marked with gray density in the figure. It should be noted that, in the case of a motor vehicle, the cabin frame member 24a located on the floor portion is only located on the upper part of the floor 15, while in the case of an electric vehicle, it is located on both the upper and lower parts of the floor 15. Furthermore, Figure 7 This is a perspective view showing the integrated state in which the floor frame member 30 is connected to the single-shell structure frame 20 of the electric vehicle body 100 when the vehicle is an electric car for road use. Details of the materials and structure of the cabin frame member 24 and the floor frame member 30 are shown below.

[0189] 3.1. Materials

[0190] 3.1.1. High-strength steel components with excellent bending and weldability, and preferred steel as the raw material for such steel components (rust-proof components in the lower part of the vehicle body, improved spot weldability) (Element Technology D)

[0191] 3.1.2. Hot-stamped formed bodies with excellent strength and flexibility, and high load-bearing capacity (Element Technology E)

[0192] 3.1.3. Hot stamping steel sheet with excellent impact resistance, preferred as a raw material for hot stamping formed articles with a tensile strength of 2300 MPa or higher (Element Technology F).

[0193] 3.2. Structure

[0194] 3.2.1. Skeleton components with excellent energy absorption efficiency (Element Technology G)

[0195] 3.2.2. A skeleton component that can exhibit excellent energy absorption performance commensurate with its high strength by suppressing the fracture of spot welds during impact. (Element Technology H)

[0196] 3.2.3. Skeleton components with continuous flanges and their manufacturing methods (Element Technology K)

[0197] 3.2.4. Manufacturing method of high-strength frame components of L-shaped and T-shaped structures (Element Technology L)

[0198] 4. Side beams and battery box (Technical Elements I and J)

[0199] like Figure 7 As shown, side beams 28 are provided on the left and right sides of the single-shell frame 20. The side beams 28, also called rockers, are components that connect the front and rear sides of the vehicle's floor. In the case of electric vehicles, the battery box is mounted on the floor frame member 30. Details of the materials and structure of the side beams 28 and the battery box are shown below.

[0200] 4.1. Side body structure (side beam) that can suppress local deformation while maintaining impact absorption capacity (Element Technology I)

[0201] 4.2. High-impact battery box (Element Technology J)

[0202] It can be used in battery box covers, floor components, etc., eliminating the painting process and reducing greenhouse gas emissions during manufacturing.

[0203] The aforementioned elements A through L are all characterized in the steel sheet material itself or in the structure using the steel sheet material. This embodiment reduces the aforementioned "1. greenhouse gases generated during the manufacture of raw materials constituting the automobile" by increasing the weight ratio of steel material in the automobile body 100 through the adoption of these materials and structures. At the same time, it reduces the aforementioned "3. greenhouse gases generated during the use of the automobile" by making the automobile body 100 lighter. As a result, a significant reduction in life-cycle greenhouse gases is achieved compared to existing automobile bodies.

[0204] (Example)

[0205] The following examples illustrate the present invention in detail. It should be noted that the conditions of the examples are merely one example adopted to confirm the feasibility and effectiveness of this application, and the present application is not limited to the conditions of the examples. Various conditions can be adopted by the present application as long as they do not depart from the spirit and purpose of the application.

[0206] Tables 1 and 2 show various characteristic values ​​of the vehicle body of the road-driving vehicle of the present invention (Examples 1-12) and the vehicle body of the comparative examples (Comparative Examples 1-8). Table 1 shows the characteristic values ​​of the road-driving vehicle (total weight or mass, the same below), vehicle body weight, width w, height h, length l, projected area s, volume v, weight % of ferrous alloy, weight % of aluminum alloy, weight % of other non-ferrous metals, weight % of resin material, weight % of other materials, weight % of ultra-high strength steel, weight of ultra-high strength steel, waste ratio, type of power transmission system, and total greenhouse gas emissions (recorded as GHG emissions in the table).

[0207] The gross vehicle weight (GVW) of a car for road use is the weight of the car itself when it is carrying passengers and capable of driving on a public road. GVW includes the total weight of a car, such as the body, interior, seats, accessories like the navigation system, electronic components like the battery and wiring, suspension, engine, electric generator, transmission, braking system, heating and cooling system, air conditioning, steering system, safety devices like airbags, pedal systems for acceleration and deceleration, and fluids like oil, fuel, and refrigerant.

[0208] The weight of a car body is the weight obtained by subtracting the battery, tires, and liquids containing water or oil (all fluids in a road-driving car, such as coolant, air conditioning refrigerant, brake fluid, engine oil, differential oil, and cleaning fluid) from the total weight of the car.

[0209] Regarding the weights in the comparative examples, the weights were determined by disassembling the body of a commonly used road vehicle and measuring and analyzing the data obtained from shape and weight measurements. Regarding the weights in some of the comparative and inventive examples, the weights were determined by measuring and analyzing design and development data obtained using CAD (Computer-Aided Design).

[0210] Width w, height h, and length l are the full width, full height, and full length specified by Japanese Industrial Standard JISD 0302-1996, "Method for Measurement of External Dimensions of Automobiles".

[0211] Furthermore, the projected area s is the area of ​​the vehicle body projected from above, and there exists a relationship between projected area s = width w × length l. Additionally, the volume v described in this specification is an indicator of the vehicle's dimensions, defined as volume v = projected area s × height h.

[0212] The weight percentage of ferroalloys is the ratio of the total weight of components made of iron (plates, bars, rods, wires, pipes, profiles, forgings, cast iron, etc.) to the weight of the aforementioned automobile body.

[0213] The percentage by weight of aluminum alloy refers to the ratio of the total weight of components made of aluminum (sheets, bars, rods, wires, tubes, profiles, forgings, aluminum castings, etc.) to the weight of the aforementioned automobile body.

[0214] The percentage of other non-ferrous metals by weight is the ratio of the total weight of components made of non-ferrous metals other than iron and aluminum to the weight of the aforementioned automobile body.

[0215] The weight of ultra-high strength steel refers to the total weight of components made from materials with a strength of 1180 MPa or higher. The aforementioned component strength is the tensile strength σ obtained by taking JIS 5 test specimens from the component and measuring them according to JIS Z2241:2011, the method for tensile testing of metallic materials. ts The value of . In the absence of JIS 5 test piece from the component, the Vickers hardness obtained by measuring with a test load of 50 kg is used according to JIS Z2244:2009 Vickers hardness test - test method. The tensile strength is calculated from the Vickers hardness HV using the following formula (5) and is used as the strength of the component.

[0216] Tensile strength σ ts =HV×3.27(5)

[0217] Furthermore, the scrap ratio is the utilization rate of steel plates obtained from recycling scrap, and is the ratio of the total mass of sheet metal parts containing more than 0.013% Cu, more than 0.018% Ni, and more than 0.002% Sn to the total mass of sheet metal parts. The inventors conducted repeated and in-depth studies by performing chemical analyses on parts using blast furnace materials and parts using recycled scrap materials. The results showed that, based on the aforementioned chemical composition of Cu, Ni, and Sn, it is possible to determine whether parts are obtained from recycled scrap. The range of chemical components that cannot be detected in raw materials using blast furnace materials is: Cu 0.013% or more, Ni 0.018% or more, and Sn 0.002% or more. It can be determined that these elements are unavoidably mixed in from the scrap. Other impurity elements that may be present in scrap include H, Na, Cl, Co, Zn, Ga, Ge, As, Se, Y, Tc, Ru, Rh, Pd, Ag, Cd, In, Te, Cs, Ta, Re, Os, Ir, Pt, Au, Pb, Bi, and Po. The upper limit for Cu content is 1.0% or less. When manufacturing steel plates from scrap, if Cu exceeds 1.0%, hot working cracking occurs, reducing manufacturability. Similarly, the upper limit for Sn content is 0.5% or less. When manufacturing steel plates from scrap, if Sn exceeds 0.5%, hot working cracking occurs, reducing manufacturability. Furthermore, the upper limit for Ni content is 5.0% or less. Ni is added to neutralize Cu and Sn, but adding more than 5.0% Ni increases costs.

[0218] Total greenhouse gas emissions (GHG emissions) are calculated by summing the equivalent mass of CO2 from the following categories: "1. Greenhouse gases produced during the manufacture of raw materials for automobiles," "2. Greenhouse gases produced during automobile manufacturing," "3. Greenhouse gases produced during automobile use," and "4. Greenhouse gases produced when automobiles are scrapped." This represents the total life-cycle emissions of greenhouse gases. The total greenhouse gas emissions (GHG emissions) are calculated using the method described later.

[0219] The characteristic values ​​of Examples 1-12 were obtained by the inventors of this invention through measurement and analysis of a car body 100, which was constructed by the inventors of this invention using the aforementioned element technologies. Furthermore, the characteristic values ​​of Comparative Examples 1-8 were obtained by the inventors of this invention through measurement and analysis of the car bodies of commonly used road vehicles. However, for some of the comparative examples, values ​​recorded as default values ​​on the website of the World Automotive Steel Association (WAS). WAS is the automotive division of the World Steel Association (World Steel Federation), composed of 17 steel manufacturers worldwide. It should be noted that in the analysis of the aforementioned life-cycle greenhouse gas emissions, the analysis software (hereinafter referred to as WAS analysis software) in Excel format downloaded from the WAS homepage (https: / / www.worldautosteel.org / life-cycle-thinking / case-studies / comparing-material-usage-in-production-vehicle-efficient-designs / ) was appropriately used.

[0220] Regarding the calculation of "1. Greenhouse gases generated during the manufacture of raw materials constituting automobiles," the default settings of the WAS analysis software were used as the basic conditions. In these default settings, the waste charging rate into the blast furnace was 11.9%, and the utilization rate of recycled materials utilizing waste was set at 5% for plates, 85% for bars and wires, and 100% for cast iron, based on statistical data. These assumptions were used as the basic conditions, and values ​​were input in the manner shown in Table 1 for the various raw material compositions, and calculations were performed. By using the above-described techniques, the utilization rate of recycled materials utilizing waste can be increased. Therefore, in Invention Examples 6, 7, 9, and 10, the utilization rate of recycled materials was set and analyzed for plates with a tensile strength of 1180 MPa or less.

[0221] Regarding the calculation of "2. Greenhouse gases generated during automobile manufacturing", the default settings of the WAS analysis software were also used as the basic conditions. In terms of the yield of raw materials in automobile parts production, it was assumed that the yield of steel plates was 55%, aluminum alloy plates was 52%, plates, bars and wires was 75%, and cast iron, aluminum extruded materials and aluminum castings were 80%. The values ​​were entered and calculated in the manner shown in Table 1 for the various raw material compositions.

[0222] In the calculation of "3. Greenhouse gases generated when using automobiles", the powertrain type of each vehicle type was selected (gasoline engine vehicle, diesel engine vehicle, hybrid vehicle, electric vehicle). The vehicle types (small car, mid-size car, SUV, electric vehicle class) were classified and set according to the size and weight of each analyzed vehicle. The driving mode of the vehicle was set to the following WLTP (Level 3b) mode.

[0223] WLTP mode

[0224] · Average speed: 36.57 km / h

[0225] · Top speed: 97.4 km / h

[0226] · Driving time: 1477 seconds

[0227] · Driving distance: 15.01km

[0228] · Idle speed ratio: 15.4%

[0229] · Cold start ratio: 100%

[0230] The driving distance is assumed to be 100,000 km, and the setting is based on incorporating vehicle weight reduction and considering adjustments to the powertrain dimensions. Furthermore, the electric vehicle's power is set to use electricity generated in Japan, and the vehicle weight values ​​obtained from the inventors' analysis, as shown in Table 1, are input and calculated.

[0231] In the calculation of “4. Greenhouse gases generated when vehicles are abandoned”, the default settings of the WAS analysis software are also used as the basic conditions. It is assumed that the recycling rate of steel is 90.3% and the recycling rate of aluminum alloy is 78.6%. The energy recovery from recycling outside the vehicle is also taken into account as the CO2 absorption.

[0232] Regarding the calculation of CO2 equivalent mass, the greenhouse gas emissions from the raw material manufacturing process, vehicle manufacturing process, fuel manufacturing and usage process, and raw material and vehicle recycling process shown in Table 3 are used as coefficients for calculating CO2 equivalent mass. The CO2 equivalent mass is calculated using weight or energy. These values ​​are the default settings for the WAS analysis software, based on statistical data on greenhouse gas emissions from various substances and processes.

[0233] Following the steps above, calculate the equivalent mass of CO2 based on "1. Greenhouse gases generated during the manufacture of raw materials for automobiles", "2. Greenhouse gases generated during automobile manufacturing", "3. Greenhouse gases generated during automobile use", and "4. Greenhouse gases generated during automobile disposal", and sum them up to calculate the total greenhouse gas emissions (GHG emissions) recorded in Table 1.

[0234] [Table 1]

[0235]

[0236] [Table 2]

[0237]

[0238] [Table 3]

[0239]

[0240] In Invention Examples 1-12, in order to reduce the greenhouse gases generated during the manufacture of raw materials constituting automobiles, steel materials were used through the aforementioned techniques. As a result, the weight ratio of iron to vehicle weight (weight % of iron alloy) increased. As shown in Table 1, in Invention Examples 1-12, the weight % of iron alloy was 64% or more. On the other hand, Comparative Examples 1-8 included those with an iron alloy weight % of 64% or more and those with an iron alloy weight % of less than 64%.

[0241] Furthermore, in Invention Examples 1-12, by applying the aforementioned element technology, it became possible to achieve a higher weight percentage of ultra-high-strength steel than in the comparative examples. As shown in Table 1, in Invention Examples 1-12, the weight percentage of ultra-high-strength steel was 9% or more. On the other hand, in Comparative Examples 1-8, the maximum weight percentage of ultra-high-strength steel was 4% (Comparative Examples 1 and 3). Additionally, the minimum weight of the ultra-high-strength steel in the Invention Examples was 102.3 kg. In Invention Example 5, the weight percentage of ultra-high-strength steel with a strength of 1180 MPa or higher was 14%, but the weight percentage of ultra-high-strength steel with a strength of 1470 MPa or higher was 8%. On the other hand, in Invention Example 11, the weight percentage of ultra-high-strength steel with a strength of 1180 MPa or higher was also 14%, but the weight percentage of ultra-high-strength steel with a strength of 1470 MPa or higher was 9%. Comparing Invention Example 11 with Invention Example 5, it can be seen that although the volume v is the same, Invention Example 11 is more capable of reducing life-cycle greenhouse gases. Therefore, it can be said that the preferred mass m of steel plates with a tensile strength of 1470 MPa or higher is... h The ratio of (kg) to the mass m (kg) of the aforementioned automobile body 100 is 9% or more.

[0242] Furthermore, in Invention Examples 6, 7, 9, and 10, by applying the aforementioned element technology, the strength and performance of ultra-high strength steel components with a strength of 1180 MPa or higher can be ensured, thereby increasing the utilization rate of recycled waste materials in addition to the aforementioned ultra-high strength steel components. Therefore, in Invention Examples 6, 7, 9, and 10, the total mass m of the sheet metal component containing 0.015% or more Cu, 0.01% or more Ni, and 0.004% or more Sn... sc (kg) relative to the total mass of sheet metal parts (m) sp The proportion of recycled materials used in components is significantly increased compared to Comparative Examples 1-8, with a waste ratio of 20% or more. Comparing Examples 8 and 10, it is evident that by increasing the waste ratio from 6% to 20%, a reduction of 47 kg CO2-eq in lifecycle greenhouse gases, taking into account recycling outside of automobiles, can be achieved. Furthermore, comparing Examples 5 and 7, it is evident that by increasing the waste ratio from 5% to 60%, a reduction of 94 kg CO2-eq in lifecycle greenhouse gases, taking into account recycling outside of automobiles, can be achieved. Therefore, a higher waste ratio is preferable, with a more preferred value range of 20% or more. In addition, the inventors' in-depth research has shown that when the waste ratio exceeds 60%, the formability and performance of the components are compromised, and a decrease in vehicle performance during a collision has been observed. Therefore, the upper limit for the waste ratio is 60%.

[0243] Figure 8 This is a graph showing the relationship between the projected area *s* of the car body and its weight, as shown in Table 1. The horizontal axis represents the projected area *s* of the car body, and the vertical axis represents the vehicle weight. (As shown...) Figure 8 As shown, the larger the projected area s becomes, the greater the vehicle weight becomes. It should be noted that in Invention Examples 1-12 and Comparative Examples 1-8, the projected area of ​​the vehicle body from above is set to s(m²). 2 When ), the projected area s is greater than 6 and less than 11, which satisfies the condition of equation (1).

[0244] like Figure 8 As shown, in Invention Examples 1-12 that utilize the aforementioned technological elements, the utilization rate of new raw materials (ultra-high strength steel) is increased, thus the vehicle weight corresponding to the projected area s is lower than that in Comparative Examples 1-8. More specifically, when the vehicle weight is set as y and the projected area as x, for each of Invention Examples 1-12, if the projected area s and vehicle weight are substituted... Figure 8 If the points marked with 〇 are plotted on the horizontal and vertical axes, then each point on the attached figure is located lower than the straight line L1 shown in the following equation (6).

[0245] y = 272.37 × x - 840 (6)

[0246] On the other hand, for each of Comparative Examples 1-8, if we substitute the vehicle weight and projected area... Figure 8 Points marked with △ and □ are plotted on the horizontal and vertical axes. In the attached figure, each point is located on or above the straight line L1 shown in Equation (6). It should be noted that the △ mark indicates Comparative Examples 1-5 where the weight percentage of the ferroalloy is 64% or more, and the □ mark indicates Comparative Examples 6-8 where the weight percentage of the ferroalloy is less than 64%.

[0247] Here, let the weight (mass) of any car body be m (kg) and its projected area be s (m²). 2 When ), substitute the vehicle's weight m and projected area s into... Figure 8 The condition that the point drawn on the horizontal and vertical axes is located below the line L1 is such that if a 2% margin is taken, then m is 0.98 times smaller than the value of y obtained by substituting the projected area s into x in equation (6). Therefore, Invention Examples 1-12 satisfy the condition of equation (2) above. It should be noted that the margin value can also be 3.5% as described above.

[0248] As described above, the result of applying the aforementioned technical elements is that the vehicle body 100 of Invention Examples 1-12 has a lower weight corresponding to its projected area compared to the vehicle bodies of Comparative Examples 1-8. More specifically, the vehicle body 100 of Invention Examples 1-12 is constructed primarily of steel, with new steel materials applied in various parts, and novel structures applied in various parts to compensate for the insufficient body rigidity caused by the accompanying thinning of steel plates. Therefore, compared to the vehicle bodies of Comparative Examples 1-8, the weight corresponding to its projected area is reduced. Thus, according to Invention Examples 1-12, in particular, the aforementioned "1. greenhouse gases generated during the manufacture of raw materials constituting the vehicle" and "3. greenhouse gases generated during the use of the vehicle" are reduced, thereby reducing life-cycle greenhouse gases.

[0249] Figure 9 This is a characteristic diagram showing the results of comparing the mass per unit projected area (equivalent mass) of the automobile body 100 with Invention Example 5, Comparative Example 1, and Comparative Example 8. As shown in Table 1, Comparative Example 8 is an aluminum multi-purpose vehicle body with a weight percentage as low as 59% for iron alloy and as high as 16% for aluminum alloy, using a large amount of aluminum. On the other hand, Comparative Example 1 is a vehicle body with a weight percentage as high as 77% for iron alloy and as low as 6% for aluminum alloy, using a large amount of steel. Therefore, as... Figure 9As shown, compared to Comparative Examples 1 and 5, Comparative Example 8 has a smaller equivalent mass compared to Comparative Example 1. Although Invention Example 5 has a high iron alloy content of up to 75% by weight and is primarily composed of steel, it utilizes new steel materials in various parts and employs novel structures in each part to compensate for insufficient body rigidity caused by the accompanying thinning of steel plates. Therefore, it can be seen that Invention Example 5 has a sufficiently smaller equivalent mass compared to Comparative Example 1, possessing an equivalent mass comparable to that of Comparative Example 8, which is an aluminum multi-purpose vehicle body, and has been lightweighted to the same level as the aluminum multi-purpose vehicle body.

[0250] Figure 10 This is a graph showing the relationship between the volume v of the car body and the total greenhouse gas emissions calculated using the equivalent mass of CO2, as shown in Table 1. The horizontal axis represents the volume v of the car body, and the vertical axis represents the emissions based on the aforementioned equivalent mass of CO2. Figure 10 As shown, the larger the volume v becomes, the more materials such as steel, non-ferrous metals, and resins are used in the automobile body 100, thus increasing the amount of greenhouse gas emissions. It should be noted that in Invention Examples 1-12 and Comparative Examples 1-8, the projected area of ​​the automobile body from above is set to s(m²). 2 When the height of the car body is set to h (m), the volume v (=s×h)(m) 3 The values ​​of all of them are greater than 9 and less than 19, which satisfies the condition of equation (3).

[0251] like Figure 10 As shown, in Invention Examples 1-12 that utilize the aforementioned technological elements, by increasing the weight ratio of iron to vehicle weight (weight %) and decreasing the weight ratio of materials such as aluminum and carbon fiber reinforced plastic (CFRP) to vehicle weight, greenhouse gas emissions based on the aforementioned CO2 equivalent mass are reduced compared to Comparative Examples 1-8. More specifically, when the greenhouse gas emissions based on the aforementioned CO2 equivalent mass are set as y and the volume of the vehicle body is set as x, for each of Invention Examples 1-12, if the volume and the greenhouse gas emissions based on the aforementioned CO2 equivalent mass are substituted... Figure 10 If the points marked with 〇 are plotted on the horizontal and vertical axes, then each point on the attached figure is located lower than the straight line L2 shown in the following equation (7).

[0252] y = 1925.1 × x - 121.4 (7)

[0253] On the other hand, for each of Comparative Examples 1-8, if the volume and greenhouse gas emissions based on the above-mentioned CO2 equivalent mass are substituted into... Figure 10Points marked with △ and □ are plotted on the horizontal and vertical axes. In the attached figure, each point is located on or above the straight line L2 shown in equation (6). It should be noted that the △ mark indicates Comparative Examples 1-5 where the weight percentage of the ferroalloy is 64% or more, and the □ mark indicates Comparative Examples 6-8 where the weight percentage of the ferroalloy is less than 64%.

[0254] Here, the volume of any car body is v(m) 3 When the greenhouse gas emission amount based on the equivalent mass of CO2 is M, how to substitute the volume v of the car body and the greenhouse gas emission amount M into... Figure 10 The condition that the point drawn on the horizontal and vertical axes is located below the line L2 on the attached drawing is such that if a 2% margin is taken, then M is 0.98 times smaller than the value of y obtained by substituting the volume v (=projected area s×height h) into x in equation (7). Therefore, Invention Examples 1-12 satisfy the condition of equation (4) above. It should be noted that the margin value can also be 2.5%, as described above.

[0255] As described above, the result of applying the aforementioned technical elements is that the automobile body 100 of Invention Examples 1-12 reduces the greenhouse gas emissions corresponding to volume v compared to the automobile bodies of Comparative Examples 1-8. More specifically, the automobile body 100 of Invention Examples 1-12 is constructed primarily of steel, employing new steel materials in various parts, and utilizing novel structures in each part to compensate for insufficient body rigidity caused by the accompanying thinning of steel plates. Therefore, compared to the automobile bodies of Comparative Examples 1-8, the greenhouse gas emissions corresponding to volume v are reduced. Thus, according to Invention Examples 1-12, it is possible to reduce life-cycle greenhouse gas emissions.

[0256] Table 2 shows the characteristic values ​​of the vehicle body weight, aluminum alloy weight % of total weight, resin material weight % of total weight, iron alloy weight % of total weight, high-strength steel with a tensile strength of 1.9 GPa or more weight % of total weight, high-strength steel with a tensile strength of 1180 MPa or more but less than 1.9 GPa weight % of total weight, high-strength steel with a tensile strength of 780 MPa or more but less than 1180 MPa weight % of total weight, high-strength steel with a tensile strength of 590 MPa or more but less than 780 MPa weight % of total weight, and high-strength steel with a tensile strength of 390 MPa or more but less than 590 MPa weight % of total weight.

[0257] In Table 2, the vehicle body weight is calculated as a subset of the frame 20, which consists of sheet metal parts, and the components that make up the vehicle body. Figure 1 and Figure 2The total mass of the components shown, including the frame 20, engine hood 12 and trunk lid 19, mudguards 18 and bumper 17 (including components other than sheet metal parts (interior parts, built-in parts, etc.)). The percentage by weight of aluminum alloy, resin material, ferrous alloy, and each high-strength steel is the ratio of the mass of aluminum alloy, resin material, ferrous alloy, and each high-strength steel to the vehicle body weight.

[0258] As shown in Table 2, it can be seen that, in Invention Examples 1-12, the weight percentage of each high-strength steel is higher compared to Comparative Examples 1-8. For example, in Invention Examples 1-12, the minimum weight percentage of high-strength steel with a tensile strength of 1.9 GPa or higher is 9% (Invention Example 2). On the other hand, in Comparative Examples 1-8, no high-strength steel with a tensile strength of 1.9 GPa or higher was used, and the weight percentage of high-strength steel with a tensile strength of 1.9 GPa or higher was 0%. In addition, in Invention Examples 1-12, the minimum weight percentage of high-strength steel with a tensile strength of 1180 MPa or higher but lower than 1.9 GPa is 8% (Invention Examples 3 and 6). On the other hand, in Comparative Examples 1-8, the maximum weight percentage of high-strength steel with a tensile strength of 1180 MPa or higher but lower than 1.9 GPa is 7% (Comparative Example 4). If the weight percentage of the high-strength steel with a tensile strength of 1.9 GPa or more and the weight percentage of the high-strength steel with a tensile strength of 1180 MPa or more but less than 1.9 GPa are summed and defined as the weight percentage of the high-strength steel with a tensile strength of 1180 MPa or more, then for Invention Examples 1-12, the minimum is 24% (Invention Examples 3 and 6).

[0259] Regarding Examples 1-12, the application of the aforementioned technical elements results in an increase in the proportion of high-strength steel with a tensile strength of 1.9 GPa or higher and 1180 MPa or higher but lower than 1.9 GPa, which contributes to weight reduction. Therefore, as shown in Table 1, it can be seen that, according to Examples 1-12, it becomes possible to reduce life-cycle greenhouse gas emissions. From the results in Tables 1 and 2, it can be seen that the weight percentage of high-strength steel with a tensile strength of 1180 MPa or higher relative to the vehicle body weight is 24% or higher, more preferably 38% or higher. Furthermore, the weight percentage of high-strength steel with a tensile strength of 1.9 GPa or higher relative to the vehicle body weight is 9% or higher, more preferably 16% or higher.

[0260] In Invention Example 5, the weight percentage of ultra-high strength steel with a tensile strength of 1180 MPa or higher relative to the vehicle body weight is 40%, but the weight percentage of ultra-high strength steel with a tensile strength of 1470 MPa or higher relative to the vehicle body weight is 23%. On the other hand, in Invention Example 11, the weight percentage of ultra-high strength steel with a tensile strength of 1180 MPa or higher relative to the vehicle body weight is 41%, but the weight percentage of ultra-high strength steel with a tensile strength of 1470 MPa or higher relative to the vehicle body weight is 24%. Comparing Invention Example 11 and Invention Example 5, it can be seen that although the volume v is the same, Invention Example 11 is more effective at reducing greenhouse gases over the life cycle. Therefore, it can be said that a more preferable ratio of the mass (kg) of steel sheet with a tensile strength of 1470 MPa or higher relative to the aforementioned vehicle body weight is 24% or more.

[0261] Table 3 shows the results of crash tests conducted on Invention Examples 1-12 and Comparative Examples 1-8. In Table 3, the test results for frontal collision, offset collision, side collision, pole collision, and rear-end collision are represented by evaluation values ​​A to D. In this evaluation, the vehicle body of Comparative Example 1, which has obtained certification (type certification) in the regulations of various countries and has published a 5-star rating report in the European New Car Assessment Programme (EURO NCAP) tests, is used as the benchmark (evaluation B). It should be noted that the vehicle bodies of Comparative Examples 2-8 are also vehicle bodies that have obtained certification (type certification) in the regulations of various countries, but the safety performance evaluation results are recorded by comparing them with Comparative Example 1.

[0262] Numerical simulations were used to evaluate the deformation and energy absorption of the cabin frame in frontal, offset, side, pole, and rear-end collisions, respectively. The test results were compared with those of Comparative Example 1 to evaluate the safety performance. In frontal and offset collisions, the relative intrusion of the front pole into the cabin was compared; in side collisions, the relative intrusion of the middle pole into the cabin was compared; in pole collisions, the intrusion of the side beam (rocker panel) into the cabin was compared; and in rear-end collisions, the intrusion of the rear pole into the cabin was compared.

[0263] Then, vehicles whose test results were better than those of the European New Car Assessment Programme (Euro NCAP) 5-star rating (Comparative Example 1) were designated as rating A. Vehicles with worse safety test results than Comparative Example 1 but without component breakage were designated as rating C. Furthermore, vehicles with worse safety test results than Comparative Example 1 and with component breakage were designated as rating D. It should be noted that even a rating of D represents the level of obtaining certification (type approval) under the regulations of various countries, indicating that the vehicle is safe for road use.

[0264] [Table 4]

[0265] Invention Example 1 A A B B A Invention Example 2 C C B B A Invention Example 3 B A B A A Invention Example 4 B B A A B Invention Example 5 B B B B B Invention Example 6 B B B B B Invention Example 7 B C B B B Invention Example 8 B B A A B Invention Example 9 B B B B A Invention Example 10 B B B A B Invention Example 11 B B B B B Invention Example 12 B B B B B Comparative Example 1 B B B B B Comparative Example 2 C C B D C Comparative Example 3 C C B B A Comparative Example 4 B B B C C Comparative Example 5 B B B A A Comparative Example 6 B B A A B Comparative Example 7 B B B B A Comparative Example 8 A A B B A

[0266] As shown in Table 3, for Invention Examples 1, 3-6, and 8-12, the safety test results for frontal collisions, offset collisions, side collisions, pole collisions, and rear-end collisions were all equivalent to or higher than the safety test results of vehicles with a 5-star rating in the Euro NCAP tests (Rating A or Rating B). Regarding Invention Example 2, only the frontal and offset collisions received a Rating C, but the safety test results for side collisions, pole collisions, and rear-end collisions were all equivalent to or higher than the safety test results of vehicles with a 5-star rating in the Euro NCAP tests (Rating A or Rating B). Furthermore, regarding Invention Example 7, only the offset collision received a Rating C, but the safety test results for frontal collisions, side collisions, pole collisions, and rear-end collisions were all equivalent to or higher than the safety test results of vehicles with a 5-star rating in the Euro NCAP tests (Rating A or Rating B).

[0267] Therefore, according to Examples 1-12 of the invention, it is possible to reduce the aforementioned life-cycle greenhouse gases while meeting the same or higher level of crash test performance as vehicles that have achieved a 5-star rating in the European New Car Assessment Programme (Euro NCAP) tests.

[0268] Figure 11 and Figure 12 This is a characteristic diagram showing that the rigidity and collision safety performance of the vehicle in the invention example are equivalent to those of Comparative Example 1. Figure 11 This is a characteristic diagram showing the results of comparing the torsional stiffness of Invention Example 5, Comparative Example 1, and Comparative Example 9. For example... Figure 11 As shown, although the invention example 5 uses ultra-high strength steel in thin sheet form, it has the same torsional stiffness as comparative example 1. Figure 11 Comparative Example 9 illustrates the following situation: without using the novel structure employed in Invention Example 5, Comparative Example 1 is simply made lighter by increasing its strength and thinning its walls. Comparing Invention Example 5 and Comparative Example 9, it can be seen that, according to Invention Example 5, by applying the novel structure, the torsional rigidity becomes the same as that of Comparative Example 1, thus ensuring the rigidity of the vehicle.

[0269] Figure 12 The results of numerical simulation comparing the intrusion amount of the center pillar 26 of the car body 100 into the interior of the vehicle body during a side collision are shown for Invention Example 5 and Comparative Example 1. It should be noted that the center pillar 26, as... Figure 6 As shown, this constitutes the cockpit frame component 24. In Figure 12 In the diagram, the horizontal axis represents the intrusion amount of the center pillar 26 during a side impact, and the vertical axis represents the position of the center pillar 26 in the height direction. For example... Figure 12As shown, it can be seen that, particularly in the height direction of the center pillar 26 within the range of 430–1150 mm, the intrusion of the center pillar is reduced in Invention Example 5 compared to Comparative Example 1. It can be seen that, according to Invention Example 5, by applying new raw materials and structure, the intrusion of the center pillar is equal to that of Comparative Example 1, thus achieving a crash safety performance equivalent to or better than a vehicle achieving a 5-star rating in the European New Car Assessment Programme (Euro NCAP) tests.

[0270] Next, the details of each of the above-mentioned element technologies A to L will be explained. It should be noted that, for the sake of simplicity, the symbols for constituent elements, formulas, embodiments, etc., in the description of each element technology are assigned according to each element technology. Therefore, sometimes the same symbol may be used.

[0271] (Element Technology A)

[0272] Element A is a skeleton component formed by cold pressing a steel plate. The skeleton component has a closed section portion with a closed section perpendicular to the length direction. The closed section portion has at least one flat portion with a radius of curvature larger than the maximum external dimension of the section. When the flat portion with the largest width relative to the effective width calculated by the Karman formula is defined as the reference flat portion, the Vickers hardness at the center of the plate thickness at the reference flat portion is 300 Hv or more, the width of the reference flat portion is less than 2.0 times the effective width, and the standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution at the surface portion of the reference flat portion by the standard deviation of the hardness frequency distribution at the center of the plate thickness at the reference flat portion is greater than 1.0.

[0273] According to the aforementioned element technology A, by controlling the ratio of width and hardness standard deviations within an appropriate range in the reference flat region, it is possible to suppress elastic buckling while preventing fracture during wrinkling deformation caused by axial loads. Therefore, even when using high-strength thin-walled components, high energy absorption performance can be achieved. Thus, excellent energy absorption efficiency can be achieved.

[0274] The inventors of this invention have conducted in-depth research on the construction of skeletal components that can achieve excellent energy absorption efficiency.

[0275] First, a certain yield strength is important to achieve excellent energy absorption efficiency. When an axial input load is applied due to a collision, elastic buckling may sometimes occur in the flat areas during the initial stage of deformation. If elastic buckling occurs, the necessary yield strength may not be obtained, and excellent energy absorption efficiency cannot be achieved.

[0276] In addition, to achieve excellent energy absorption efficiency, the following is also important: after an axial input load is applied due to a collision, the impact energy is efficiently absorbed by folding deformation in the desired deformation mode through the skeleton members. In particular, if fracture occurs during the folding deformation process caused by axial load (fracture at the fold), excellent energy absorption efficiency may not be achieved.

[0277] Therefore, it can be said that if the cross-sectional design is set to be less prone to elastic buckling in flat areas and given high bending performance that is not easy to break, then excellent energy absorption efficiency can be achieved.

[0278] Here, when components are made stronger and thinner as a method to achieve lightweighting, the following problems occur.

[0279] • Due to the thinning of the wall, elastic buckling becomes more likely to occur in the flat parts of the component, making it difficult to obtain the necessary yield strength.

[0280] • Due to the increased strength, the bending performance of the steel plate is reduced, and the folded part after deformation begins is prone to breakage, making it difficult to efficiently absorb impact energy.

[0281] The inventors of this invention have identified the aforementioned problems as the main reasons hindering the further increase in strength and thinness of high-strength steel plates.

[0282] The inventors of this invention, through further research, discovered that by controlling the ratio of width to hardness standard deviation within an appropriate range in the reference flat area, it is possible to suppress elastic buckling while preventing fracture during the wrinkling deformation process caused by axial loads. It was found that through such control, the aforementioned problems that were concerning when using high-strength steel plates can be eliminated, resulting in excellent energy absorption efficiency, thus completing element technology A.

[0283] The skeleton component A10 of the first embodiment of element technology A, which is based on the above insights, will be described below.

[0284] It should be noted that in this specification and accompanying drawings, constituent elements that have essentially the same function are omitted from repeated descriptions by using the same symbols.

[0285] First, let's explain the statements in this instruction manual.

[0286] "Length direction" refers to the material axis direction of the skeleton component, that is, the direction in which the axis extends.

[0287] A "flat section" refers to a straight section in a cross-section of a skeletal component that is perpendicular to its length; specifically, it refers to a section whose radius of curvature is larger than the maximum external dimension of the cross-section. The maximum external dimension is the length of the straight line that makes the distance between the ends of any two points in the cross-section the greatest.

[0288] "Corner section" refers to a non-linear section of a skeletal component in a cross-section perpendicular to its length direction, excluding flat sections.

[0289] "Width" refers to the length of the line along the circumference of the closed section, while "width of the flat section" refers to the length of the line between one end and the other end of the flat section.

[0290] The "effective width" is the effective width W obtained by applying the following equation (A1), based on Karman's effective width theory, i.e., Karman's effective width equation. e .

[0291] W e =t(4π) 2 E / 12(1-ν 2 )σ y ) 1 / 2 (A1)

[0292] in,

[0293] σ y Yield stress (MPa) in the flat region

[0294] E: Young's modulus (MPa) of the flat region

[0295] t: Thickness of the plate in the flat section (mm)

[0296] ν: Poisson's ratio for flat areas.

[0297] Furthermore, in steel plates, the Young's modulus and Poisson's ratio of the flat portions can be obtained using general physical property values. Alternatively, the yield stress of the flat portions can be replaced with the Vickers hardness at the center of the plate thickness, thereby allowing the yield stress to be determined by W. e The effective width W can be calculated using the formula =577t / √h. e .

[0298] in,

[0299] t: Thickness of the plate in the flat section (mm)

[0300] h: Vickers hardness (Hv) at the center of the plate thickness in the flat section.

[0301] The effective width W is difficult to determine using equation (A1). e In this case, it can be obtained using the above formula.

[0302] "Effective width ratio" refers to the width W of the flat portion relative to the effective width W0. e The ratio is determined by W / W e The calculated value. It can be said that the smaller the effective width ratio, the less likely the cross-sectional shape is to experience elastic buckling.

[0303] "Reference flat section" refers to the flat section with the largest effective width ratio among the flat sections in a closed cross section at any position in the length direction.

[0304] "Surface portion" refers to the area between a depth position that is 1% of the thickness of the steel plate in the thickness direction from the surface of the steel plate and a depth position that is 5% of the thickness of the steel plate in the thickness direction from the surface of the steel plate.

[0305] "Center of plate thickness" refers to the depth position at a distance of 3 / 8 of the plate thickness in the thickness direction from the surface of the steel plate.

[0306] The "surface of the steel plate" used as a reference for depth positioning refers to the surface of the base steel plate. For example, in cases where plating or painting has been applied, or where rust has formed, the surface of the steel plate after the plating, painting, and rust have been removed is used as the reference for depth positioning. It should be noted that when a surface coating such as plating, painting, or rust has formed on the surface of the base steel plate, the boundary between this surface coating and the surface of the base steel plate can be easily identified using various known methods.

[0307] "Energy absorption" is calculated based on the relationship between the impactor's reaction force (load) and the stroke when the frame component undergoes wrinkling deformation. For example... Figure 13 As shown, the impactor reaction force (load) and stroke can be obtained as follows: the skeleton members are arranged in a manner where the length direction is vertical, and the rigid plane impactor is made to collide from the upper side along the direction of the hollow arrow while the lower end side is fully constrained.

[0308] "Energy absorption efficiency" is the energy absorption per unit cross-sectional area (plate thickness × section length) of a frame component. When frame components do not have uniform cross-sections along their length, it refers to the energy absorption per unit cross-sectional area (plate thickness × section length) of the closed section perpendicular to the component's length direction.

[0309] Figure 14 This is a perspective view of the skeleton component A10. Skeleton component A10 is a hollow cylindrical component extending along its length.

[0310] Figure 15 yes Figure 14 The cross-sectional view of the cut line A1-A1. (As shown...) Figure 15As shown, the skeleton member A10 forms a roughly rectangular closed cross section through four flat parts A11 and four corner parts C.

[0311] Specifically, the closed cross-section is formed in the following manner: it has a first flat portion A11a, a second flat portion A11b connected to the first flat portion A11a via a corner portion C, a third flat portion A11c connected to the second flat portion A11b via a corner portion C, and a fourth flat portion A11d connected to the third flat portion A11c via a corner portion C, and the fourth flat portion A11d is connected to the first flat portion via a corner portion C.

[0312] All four corner sections C have the same radius of curvature r. For example, if the maximum external dimension is 140 mm, the radius of curvature r can be less than 140 mm. The radii of curvature of the four corner sections C do not need to be the same, and they can also be different from each other. There is no specific upper limit for the radius of curvature, but sections with a radius of curvature greater than the maximum external dimension of the cross-section are considered as separate flat sections or part of adjacent flat sections, and are not considered as corner sections. Therefore, it can be said that the upper limit of the radius of curvature of the corner section C is essentially "below the maximum external dimension of the cross-section".

[0313] In this application, the reference flat portion is defined as the flat portion with the largest effective width ratio among the flat portions in the closed cross section.

[0314] The first flat region A11a, the second flat region A11b, the third flat region A11c, and the fourth flat region A11d all have the same yield stress σ. y Young's modulus E, plate thickness t, and Poisson's ratio ν.

[0315] Therefore, for each flat portion A11, the width W / effective width W e The calculated effective width ratio depends only on the width W of each flat section A11.

[0316] Therefore, in this embodiment, the first flat portion A11a and the third flat portion A11c, which have the largest width W in the closed cross section, are set as the reference flat portions.

[0317] In the reference flat region, when the skeleton member A10 is subjected to axial compressive force, elastic buckling is most likely to occur in the early stage of deformation. Therefore, if the width W of this reference flat region... S If the width is too large, the necessary yield strength cannot be obtained, making it difficult to achieve excellent energy absorption efficiency. Therefore, the width W of the reference flat section... S The upper limit is set to the effective width W. e Less than 2.0 times.

[0318] It should be noted that the width W of the reference flat area S The lower limit is not specifically set, but if the width W of the reference flat part is... S If the area is too small, the area of ​​the closed section of the skeleton member A10 will decrease, making it difficult to ensure the yield strength.

[0319] Therefore, the width W of the reference flat portion S The preferred effective width W e More than 0.1 times.

[0320] From the perspective of lightweight design, the thickness of the plate in the reference flat area is preferably less than 4.2 mm.

[0321] On the other hand, when the plate thickness of the reference flat section is less than 0.4 mm, elastic buckling of the reference flat section becomes more likely to occur, therefore the width W of the reference flat section... S The limitations on the setting range become larger. Therefore, the thickness of the plate in the reference flat area is preferably 0.4 mm or more.

[0322] The skeleton member A10 is formed by pressing a cold-rolled steel sheet with a tensile strength of 980 MPa or more into a specified shape, and then joining the end faces. The skeleton member A10 thus formed has a strength of 980 MPa or more in terms of tensile strength. Furthermore, by forming it in this way, the Vickers hardness of the center of the sheet thickness at the reference flat portion of the skeleton member A10 becomes 300 Hv or more in a hardness test performed according to the method described in JIS Z 2244:2009, with the test load set to 300 gf (2.9 N).

[0323] In this application, in order to improve the deformation capacity and exert excellent energy absorption efficiency with high strength as a premise, the hardness of the center of the plate thickness at the reference flat part is specified as 300Hv or more by Vickers hardness tester.

[0324] There is no specific upper limit for the hardness of the center of the plate thickness, but it can be set to below 900 Hv using a Vickers hardness tester.

[0325] The method for determining the hardness of the center of the plate thickness is as follows.

[0326] A specimen with a cross-section perpendicular to the plate surface is collected from the skeleton component, and this cross-section is used as the measurement surface for preparation. This measurement surface is then used for hardness testing.

[0327] The size of the measuring surface also depends on the measuring device, but it can be around 10mm × 10mm.

[0328] The preparation method of the test surface was performed according to JIS Z 2244:2009. After grinding the test surface with #600 to #1500 silicon carbide paper, it was then finished to a mirror finish using a liquid obtained by dispersing diamond powder with a particle size of 1μm to 6μm in a diluent such as alcohol or pure water. The hardness test was performed according to the method described in JIS Z 2244:2009. Using a micro Vickers hardness tester, 30 points were measured at 3 / 8 of the sample thickness, with a load of 300gf and intervals of at least three times the indentation length. The average value of these measurements was taken as the hardness at the center of the sample thickness.

[0329] As described above, the width W of the reference flat portion S For the effective width W e At a strength less than 2.0 times that of steel, elastic buckling can be suppressed. However, for high-strength materials, such as cold-rolled steel sheets with a tensile strength of 980 MPa or higher, even by controlling the effective width W... e However, if elastic buckling is suppressed and bending performance is insufficient, fracture may occur during the process of wrinkling deformation caused by axial load, thus failing to achieve excellent energy absorption efficiency.

[0330] In the past, the standard deviation of the hardness frequency distribution at the center of the plate thickness in the flat part of the reference plate was almost the same as that at the surface part, and the ratio of the hardness standard deviations was 1.0.

[0331] However, in the skeleton member A10 of this embodiment, the bending performance is improved by appropriately controlling the ratio of the standard deviation of the hardness frequency distribution at the center of the plate thickness at the reference flat part to the standard deviation of the hardness frequency distribution at the surface part.

[0332] Therefore, even when using high-strength materials, it can suppress breakage during the wrinkling and deformation process, and achieves exceptionally high energy absorption efficiency compared to the past.

[0333] Specifically, in the skeleton member A10 of this embodiment, control is performed in the following manner: in the reference flat area, the standard deviation of the hardness frequency distribution at the surface layer is divided by the standard deviation of the hardness frequency distribution at the center of the plate thickness, i.e., the hardness standard deviation ratio, becomes greater than 1.0.

[0334] The inventors of this invention discovered through experiments that when using cold-rolled steel sheets with a tensile strength of 980 MPa or higher, and setting the hardness standard deviation ratio to a value greater than 1.0, the maximum bending angle in the VDA bending test based on the VDA standard (VDA238-100) specified by the German Association of the Automotive Industry can be significantly increased.

[0335] Figure 16 This graph shows the results of VDA bending tests using cold-rolled steel sheets of 1470MPa, 1180MPa, and 980MPa grades with a thickness of 1.6mm. It reveals that, for steel sheets of each strength grade, compared to steel sheets with a hardness standard deviation ratio of 1.0 (as in the past), steel sheets with a hardness standard deviation ratio greater than 1.0 exhibit a higher maximum bending angle (°) and a higher VDA angle ratio in the VDA bending test. In other words, with a hardness standard deviation ratio greater than 1.0, the steel becomes less prone to fracture during wrinkling deformation under axial loads, thus exhibiting excellent energy absorption efficiency.

[0336] Therefore, the standard deviation of hardness is preferably greater than 1.05, and more preferably greater than 1.20.

[0337] Even when the hardness standard deviation ratio is greater than 3.0, the effect of improving flexibility becomes saturated. Therefore, the hardness standard deviation ratio is preferably below 3.0.

[0338] Here, the hardness frequency distribution at the center of the plate thickness and the hardness frequency distribution at the surface are obtained by Vickers hardness test.

[0339] A specimen with a cross-section perpendicular to the plate surface is collected from the skeleton component, and this cross-section is used as the measurement surface for preparation. This measurement surface is then used for hardness testing.

[0340] The size of the measuring surface also depends on the measuring device, but it can be around 10mm × 10mm.

[0341] The preparation method of the measuring surface was carried out in accordance with JIS Z 2244:2009. After grinding the measuring surface with silicon carbide paper of #600 to #1500, the measuring surface was polished to a mirror finish using a liquid obtained by dispersing diamond powder with a particle size of 1μm to 6μm in a diluent such as alcohol or pure water.

[0342] For the test surface that has been so finely machined into a mirror finish, the hardness test shall be performed according to the method described in JIS Z 2244:2009.

[0343] The hardness of the surface layer was measured using a micro Vickers hardness tester.

[0344] The hardness frequency distribution at the surface layer was determined by measuring 30 points at intervals of more than 3 times the indentation with a load of 300 gf.

[0345] Similarly, at a depth of 3 / 8 of the plate thickness, 30 points were measured at intervals of more than 3 times the indentation with a load of 300gf to determine the hardness frequency distribution at the center of the plate thickness.

[0346] In addition, in order to determine the standard deviation of the hardness frequency distribution at the center of the plate thickness and the hardness frequency distribution at the surface obtained from the Vickers hardness test results mentioned above, known statistical methods were used.

[0347] When the metal structure of the center and surface of a cold-rolled steel sheet with a tensile strength of 980 MPa or higher is the same as in the past, the hardness frequency distribution in the surface becomes the same as that in the center of the sheet, and the hardness standard deviation ratio becomes 1.0.

[0348] On the other hand, when only the surface layer and the surrounding metal structure are modified, the hardness standard deviation ratio becomes a value different from 1.0.

[0349] In the skeleton member A10 formed from the cold-rolled steel sheet with a tensile strength of 980 MPa or more according to this embodiment, by modifying only the metal structure of the surface layer and its vicinity, the metal structure of the surface layer becomes a structure close to a two-phase structure. Therefore, the distribution and unevenness of hardness in the surface layer increases, and the ratio of the standard deviation of hardness between the surface layer and the center of the sheet thickness is greater than 1.0.

[0350] Specifically, the hardness standard deviation ratio can be controlled by adjusting the maximum heating temperature and holding time during decarburization annealing of the steel sheet, which is a known technique. The preferred decarburization annealing conditions are: in a humid atmosphere containing hydrogen, nitrogen, or oxygen, setting the decarburization annealing temperature (the maximum temperature reached by the steel sheet) to 700–950°C, and setting the holding time within the temperature range of 700–950°C to 5–1200 seconds.

[0351] Furthermore, by setting the annealing temperature to a higher temperature range and limiting the dwell temperature to a longer time range within this condition, it is possible to achieve a hardness standard deviation ratio greater than 1.20.

[0352] It should be noted that it is sufficient for at least one surface portion of the skeleton member A10 to meet the above-mentioned condition of hardness standard deviation ratio. However, it is preferable that the surface portions on both sides of the skeleton member A10 meet the above-mentioned condition of hardness standard deviation ratio.

[0353] Thus, according to the skeleton member A10 of this embodiment, the width W of the reference flat portion is controlled by the reference flat portion. S It can suppress elastic buckling, and by controlling the standard deviation ratio of hardness, it can suppress fracture during the wrinkling deformation process.

[0354] Therefore, even if the Vickers hardness of the center of the plate thickness in the reference flat area is sufficient to reach 300 Hv or more, it can still significantly improve energy absorption efficiency.

[0355] The preferred embodiments of element technology A have been described in detail above with reference to the accompanying drawings, but element technology A is not limited to the above examples.

[0356] Obviously, anyone with ordinary knowledge of the technical field to which element technology A belongs can conceive of various modifications or alterations within the scope of the technical concept of this application, and these are of course also understood to fall within the technical scope of element technology A.

[0357] For example, the aforementioned skeleton component A10 may be composed of a single component, but it may also be composed of multiple components. Figure 17 This is a perspective view of the skeleton component A20 in the modified example. Figure 18 yes Figure 17 The cross-sectional view of the cut line A2-A2.

[0358] The skeleton member A20 includes a first skeleton member A20A extending along the length direction and a second skeleton member A20B extending along the length direction and engaging with the first skeleton member A20A. Moreover, a closed section is formed by the first skeleton member A20A and the second skeleton member A20B.

[0359] The first skeleton component A20A is a component with an open cross-section that is approximately hat-shaped, formed by cold pressing a steel plate with a thickness of 1.2 mm.

[0360] like Figure 18 As shown, the cross-section perpendicular to the length direction of the first skeleton member A20A has five flat parts A21 and four corner parts C.

[0361] Specifically, the cross-section perpendicular to the length direction of the first skeleton member A20A includes: a first flat portion A21a, a second flat portion A21b connected to the first flat portion A21a via a corner portion C, a third flat portion A21c connected to the second flat portion A21b via a corner portion C, a fourth flat portion A21d connected to the third flat portion A21c via a corner portion C, and a fifth flat portion A21e connected to the fourth flat portion A21d via a corner portion C.

[0362] The second frame member A20B is a member with an open cross-section that is approximately hat-shaped, formed by cold pressing a steel plate with a thickness of 0.8 mm.

[0363] like Figure 18 As shown, the cross-section perpendicular to the length direction of the second skeleton member A20B has five flat parts A23 and four corner parts C.

[0364] Specifically, the cross-section perpendicular to the length direction of the second skeleton member A20B includes: a first flat portion A23a, a second flat portion A23b connected to the first flat portion A23a via a corner portion C, a third flat portion A23c connected to the second flat portion A23b via a corner portion C, a fourth flat portion A23d connected to the third flat portion A23c via a corner portion C, and a fifth flat portion A23e connected to the fourth flat portion A23d via a corner portion C.

[0365] Furthermore, the first flat portion A21a and the fifth flat portion A21e of the first frame member A20A are joined to the first flat portion A23a and the fifth flat portion A23e of the second frame member A20B by spot welding.

[0366] By constructing it in this way, the cross section of the skeleton member A20 perpendicular to the length direction has a closed section.

[0367] In this application, the reference flat portion is defined as the flat portion with the largest effective width ratio among the flat portions in the closed cross section.

[0368] The flat portion A21 of the first skeleton member A20A and the flat portion A23 of the second skeleton member A20B both have the same yield stress σ. y Young's modulus E and Poisson's ratio ν. Therefore, for each flat part A21, A23, the width W / effective width W is used. e The calculated effective width ratio depends on the width W and plate thickness t of each flat section A21 and A23.

[0369] In this closed cross-section, both the third flat portion A21c of the first skeleton member A20A and the third flat portion A23c of the second skeleton member A20B have the largest width among all flat portions. However, since the plate thickness of the third flat portion A23c of the second skeleton member A20B is smaller than that of the third flat portion A21c of the first skeleton member A20A, the effective width ratio of the third flat portion A23c of the second skeleton member A20B is the largest. Therefore, the third flat portion A23c of the second skeleton member A20B is the reference flat portion.

[0370] Therefore, in the modified skeleton member A20, by controlling the Vickers hardness of the center of the plate thickness to 300Hv or more for the third flat portion A23c of the second skeleton member A20B, which serves as the reference flat portion, and by controlling the width W... s Controlled to effective width W e The standard deviation ratio is controlled to be greater than 1.0 when the standard deviation is less than 2.0 times that of the standard deviation ratio, thereby achieving excellent energy absorption efficiency.

[0371] It should be noted that the skeleton member A10 has a roughly rectangular cross-sectional shape with opposite sides having the same width, but it may also have a roughly square cross-sectional shape with four flat parts A11 having the same width.

[0372] In addition, there is no particular limit to the number of flat parts A11, but at least one is required.

[0373] Furthermore, the skeleton member A10 of the embodiment has the same cross-sectional shape along its entire length, but it may not have the same cross-sectional shape along its entire length. The closed section with the smallest cross-sectional area (plate thickness × section line length) in the closed section perpendicular to the length direction of the member is the closed section portion described above, which may exist in a portion of the entire length direction. However, it is preferable that the closed section portion exists in 50% or more of the entire length direction, and more preferably 80% or more.

[0374] It should be noted that the skeleton components A10 and A20 are structural components of the automobile body that are expected to be compressed primarily in the axial direction during a collision. Figure 19 This is a diagram showing an automobile frame A100 as an example of the application of frame components A10 and A20.

[0375] If you refer to this Figure 19 Then, the frame members A10 and A20 can be applied to the front side member A101, rear side member A103, side beam A105, A-pillar A107, B-pillar A109, roof rail A111, floor cross A113, roof cross A115, and under reinforcement A117 in the structural components of the automobile body.

[0376] (Example)

[0377] Steel plates A and B are prepared as 1470MPa grade cold-rolled steel plates with a thickness of 1.6mm, steel plate C is prepared as 1180MPa grade cold-rolled steel plates with a thickness of 1.6mm, and steel plate D is prepared as 980MPa grade cold-rolled steel plates with a thickness of 1.6mm.

[0378] For steel plates B, C, and D, by setting the decarburization annealing temperature (the highest temperature reached by the steel plate) to 700–900°C in a humid atmosphere mixed with hydrogen and nitrogen during decarburization annealing, and setting the residence time in the temperature range of 700–900°C to 60–600 seconds, the metal structure of only the surface layer and its vicinity is modified.

[0379] By cold-pressing the aforementioned steel plates A, B, C, and D, and welding their end faces together, a 300mm high square tube component made from each steel plate was obtained.

[0380] Steel plate A has the same microstructure in its center and surface regions. Therefore, the standard deviation of the hardness frequency distribution in the center of the reference flat region is equal to the standard deviation of the hardness frequency distribution in the surface region of the reference flat region, resulting in a hardness standard deviation ratio of 1.0. On the other hand, steel plates B, C, and D modify the microstructure of their surface regions but not their center regions, thus altering the hardness frequency distribution in their surface regions and adjusting the standard deviation of the surface regions. Consequently, the hardness standard deviation ratio of the surface region relative to the center region in the reference flat region of steel plate B is 2.37, that of steel plate C is 1.25, and that of steel plate D is 1.28.

[0381] The material properties of the flattened portion after pressing are shown in Table 5.

[0382] [Table 5]

[0383]

[0384] like Figure 20 As shown, the cross-section perpendicular to the length direction of the square tube component is designed as an approximately square cross-section with four flat sections of equal width. That is, in each square tube component, all four flat sections are reference flat sections with the largest effective width-to-width ratio. Based on this condition, the width W of the reference flat section is set for each experimental example. S It should be noted that the radius of curvature of all four corners C is designed to be 5mm.

[0385] For these rectangular tube components, with the lower end fully constrained, a rigid planar impactor was driven at 90 km / h from the upper end. The absorbed energy was calculated and compared based on the deformation state, fracture occurrence, impactor reaction force (load), and stroke. The setup conditions and results for each experimental example are shown in Table 6.

[0386] [Table 6]

[0387]

[0388] It should be noted that, Figure 21The graph in Table 6 compares the energy absorption efficiency with the effective width ratio based on the experimental results shown. As the graph shows, it can be seen that simply reducing the effective width ratio does not result in an increase in energy absorption efficiency. However, when the hardness standard deviation ratio is appropriately controlled, as in this application, reducing the effective width ratio significantly improves the energy absorption efficiency.

[0389] (Element Technology B)

[0390] Element technology B is a hot-stamped formed body whose chemical composition, by mass%, contains: C: 0.30–0.50%, Si: 0.50–3.00%, Mn: 0.50–3.00%, Al: 0.0002–2.000%, P: less than 0.100%, S: less than 0.1000%, N: less than 0.0100%, Nb: 0–0.150%, Ti: 0–0.150%, Co: 0–2.00%, Mo: 0–1.00%, Cr: 0–1.00%, Cu: 0–1.00%, V: 0–1.00%, W: The hot-stamped body contains 0-1.00% Ni, 0-3.00% Mg, 0-1.00% Zr, 0-1.00% Sb, 0-1.00% Ca, 0-0.10% REM, 0-0.30% B, and the remainder includes Fe and impurities. The microstructure of the hot-stamped body is as follows: containing 5% to less than 10% retained austenite, bainite and tempered martensite totaling more than 90% to less than 95% by area, and less than 5% remaining microstructure. At the grain boundaries of the bainite and tempered martensite grains, relative to the area... <011> The total length of the grain boundary with a rotation angle of 4° to 12° along the rotation axis, the length of the grain boundary with a rotation angle of 49° to 54°, and the length of the grain boundary with a rotation angle of 55° to 75°, wherein the proportion of the length of the grain boundary with a rotation angle of 55° to 75° is 30% or more, and the tensile strength of the hot-stamped formed body is 1500 MPa or more.

[0391] According to element technology B, hot stamping formed bodies with excellent strength and impact characteristics can be obtained.

[0392] The inventors of this invention have discovered that in the microstructure of a hot-stamped body, by including a specified amount of retained austenite, bainite, and tempered martensite, and at the grain boundaries of the bainite and tempered martensite grains, relative to the... <011> The total length of grain boundaries with a rotation angle of 4° to 12° along the rotation axis, the length of grain boundaries with a rotation angle of 49° to 54°, and the length of grain boundaries with a rotation angle of 55° to 75° (hereinafter, sometimes referred to as large-angle grain boundaries) is such that the proportion of the length of grain boundaries with a rotation angle of 55° to 75° (large-angle grain boundaries) is 30% or more, thereby improving the collision characteristics while maintaining high strength.

[0393] It should be noted that, in this embodiment, excellent collision characteristics refer to excellent uniform deformation capability and excellent crack propagation suppression capability.

[0394] Large-angle grain boundaries are the highest-angle grain boundaries found within bainitic and tempered martensite grains. During the austenitic-to-bainitic or martensitic phase transformation, strain occurs accompanying the transformation. When the austenite before the transformation is of high hardness, or when the original austenite is in a deformable state, it becomes easier to form large-angle grain boundaries that effectively mitigate strain. The inventors of this invention have discovered that by applying pressure within a specified temperature range after hot stamping to render the austenite in a deformable state, and then transforming the austenite into bainitic or martensitic phase, a large number of large-angle grain boundaries can be formed.

[0395] The hot-stamped formed article of this embodiment will now be described in detail. First, the reasons for limiting the chemical composition of the hot-stamped formed article of this embodiment will be explained.

[0396] It should be noted that for the numerical ranges specified by the "~" in the following description, both the lower and upper limits are included within that range. Values ​​expressed as "lower than" or "higher than" are not included in the numerical range. All "%" values ​​related to chemical composition represent "mass %".

[0397] The chemical composition of the hot-stamped formed article of this embodiment, by mass%, contains: C: 0.30-0.50%, Si: 0.50-3.00%, Mn: 0.50-3.00%, Al: 0.0002-2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, and the remainder: Fe and impurities. The details of each element are described below.

[0398] C: 0.30-0.50%

[0399] Carbon (C) is an element that improves the strength of hot-stamped formed articles. Additionally, C is also an element that stabilizes retained austenite. When the C content is below 0.30%, the desired strength cannot be obtained in hot-stamped formed articles. Therefore, the C content is set to 0.30% or more. The C content is preferably 0.32% or more, or 0.35% or more. On the other hand, when the C content exceeds 0.50%, excellent uniform deformation ability cannot be obtained. Therefore, the C content is set to 0.50% or less. Preferably, the C content is 0.46% or less, 0.43% or less, or 0.40% or less.

[0400] "Si: 0.50~3.00%"

[0401] Si is an element that stabilizes retained austenite. When the Si content is below 0.50%, the above-mentioned effect cannot be obtained, the stabilization of retained austenite becomes insufficient, and the desired amount of retained austenite cannot be obtained. Therefore, the Si content is set to 0.50% or more. The Si content is preferably 1.00% or more or 1.10% or more. On the other hand, when the Si content exceeds 3.00%, the amount of ferrite increases, and the desired microstructure cannot be obtained. Therefore, the Si content is set to 3.00% or less. The Si content is preferably 2.70% or less, 2.30% or less, or 2.00% or less.

[0402] Mn: 0.50~3.00%

[0403] Mn is an element that segregates at the original austenite grain boundaries, thereby suppressing the formation of ferrite and pearlite. When the Mn content is below 0.50%, ferrite and pearlite are formed in large quantities, making it impossible to obtain the desired microstructure. Therefore, the Mn content is set to 0.50% or more. The Mn content is preferably 0.70% or more or 1.00% or more. On the other hand, when the Mn content exceeds 3.00%, excellent uniform deformation ability cannot be obtained. Therefore, the Mn content is set to 3.00% or less. Preferably, the Mn content is 2.50% or less or 2.00% or less.

[0404] "Al: 0.0002~2.000%"

[0405] Al is an element that improves deformability and collision characteristics of hot-stamped formed articles by deoxidizing molten steel and suppressing the formation of oxides that become the starting point of damage. When the Al content is below 0.0002%, deoxidation cannot be fully carried out, resulting in the formation of coarse oxides, and the above-mentioned effects cannot be obtained. Therefore, the Al content is set to 0.0002% or more. The Al content is preferably 0.001% or more, 0.050% or more, 0.100% or more, or 0.300% or more. On the other hand, if the Al content exceeds 2.000%, coarse oxides are formed in the steel, and the collision characteristics of the hot-stamped formed articles decrease. Therefore, the Al content is set to 2.000% or less. The Al content is preferably 1.700% or less, 1.500% or less, 1.000% or less, or 0.800% or less.

[0406] "P: Below 0.100%"

[0407] Phosphorus (P) is an impurity element that becomes the starting point for degradation through segregation at grain boundaries. Therefore, the P content is set to be 0.100% or less. Preferably, the P content is 0.050% or less, or 0.030% or less. While there is no particular limitation on the lower limit of the P content, reducing it below 0.0001% significantly increases the cost of P removal, making it economically undesirable. Therefore, in practice, 0.0001% can also be used as the lower limit.

[0408] "S: Below 0.1000%"

[0409] Sulfur (S) is an impurity element that forms inclusions in steel. Since these inclusions are the starting point for damage, the S content is set to be below 0.1000%. Preferably, the S content is below 0.0500%, 0.0300%, or 0.0100%. There is no particular limitation on the lower limit of the S content, but if it is reduced below 0.0001%, the cost of desulfurization increases significantly, which is not economically desirable. Therefore, in practice, 0.0001% can also be used as the lower limit.

[0410] "N: Below 0.0100%"

[0411] Nitrogen (N) is an impurity element that forms nitrides in steel. Since these nitrides are the starting point for degradation, the N content is set to be below 0.0100%. Preferably, the N content is below 0.0050%. There is no particular limitation on the lower limit of the N content, but if it is reduced below 0.0001%, the cost of nitrogen removal increases significantly, which is not economically desirable. Therefore, in practice, 0.0001% can also be used as the lower limit.

[0412] The remaining portion of the chemical composition of the hot-stamped formed article of this embodiment may also be Fe and impurities. Examples of impurities include elements that are unavoidably mixed in from steel raw materials or scrap and / or during the steelmaking process, and are permitted within a range that does not impair the characteristics of the hot-stamped formed article of this embodiment.

[0413] The hot-stamped formed article of this embodiment may also contain the following elements as optional elements to replace a portion of the Fe. The content of the following optional elements is 0% when they are not present.

[0414] "Nb: 0~0.150%"

[0415] "Ti: 0~0.150%"

[0416] Nb and Ti increase the proportion of large-angle grain boundaries by refining the original austenite grains during heating before hot stamping and suppressing the deformation of the original austenite during the phase transformation from austenite to bainite or martensite. To ensure this effect is reliably achieved, it is preferable to set the content of either Nb or Ti to 0.010% or more. On the other hand, even if the content of either Nb or Ti exceeds 0.150%, the above effect saturates; therefore, it is preferable to set the content of Nb and Ti to 0.150% or less respectively.

[0417] Co: 0-2.00%

[0418] "Mo: 0~1.00%"

[0419] "Cr: 0~1.00%"

[0420] "Cu: 0~1.00%"

[0421] "V: 0~1.00%"

[0422] "W: 0~1.00%"

[0423] "Ni: 0~3.00%"

[0424] Co, Mo, Cr, Cu, V, W, and Ni have the following effect: by dissolving in the original austenite grains during heating before hot stamping, they improve the strength of the hot-stamped body. Therefore, during the austenite-to-bainite or martensite phase transformation, deformation of the original austenite grains can be suppressed, increasing the proportion of large-angle grain boundaries. To reliably obtain this effect, it is preferable to contain any one or more of the following: Co: 0.01% or more, Mo: 0.005% or more, Cr: 0.005% or more, Cu: 0.001% or more, V: 0.0005% or more, W: 0.001% or more, and Ni: 0.001% or more. On the other hand, even with a large amount of these elements, the above effect is saturated; therefore, it is preferable to set the Co content to 2.00% or less, the Mo, Cr, Cu, V, and W contents to 1.00% or less, and the Ni content to 3.00% or less.

[0425] Mg: 0-1.00%

[0426] Zr: 0~1.00%

[0427] "Sb: 0~1.00%"

[0428] "Ca: 0~0.10%"

[0429] REM: 0-0.30%

[0430] Mg, Zr, Sb, Ca, and REM are elements that improve deformability and collision characteristics of hot-stamped parts by suppressing the formation of oxides that become the starting point of damage. To reliably obtain this effect, it is preferable to set the content of any one of Mg, Zr, Sb, Ca, and REM to 0.001% or more. On the other hand, even with a large content of these elements, the above effect becomes saturated; therefore, it is preferable to set the Mg content, Zr content, and Sb content to 1.00% or less, the Ca content to 0.10% or less, and the REM content to 0.30% or less, respectively.

[0431] It should be noted that in this embodiment, REM refers to a total of 17 elements including Sc, Y and lanthanides, and the content of REM refers to the total content of these elements.

[0432] "B: 0~0.0100%"

[0433] Bode (B) is an element that segregates at the original austenite grain boundaries, thereby suppressing the formation of ferrite and pearlite. To reliably achieve this effect, the B content is preferably set to 0.0005% or more. On the other hand, even if the B content exceeds 0.0100%, the above effect saturates; therefore, the B content is preferably set to 0.0100% or less.

[0434] The chemical composition of the hot-stamped formed body can be determined using general analytical methods. For example, it can be determined using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). It should be noted that C and S can be determined using combustion-infrared absorption spectroscopy, and N can be determined using inert gas melting-thermal conductivity spectroscopy. When the hot-stamped formed body has a coating on its surface, the chemical composition can be analyzed after removing the coating by mechanical grinding.

[0435] Next, the microstructure of the hot-stamped formed article of this embodiment will be described.

[0436] The hot-stamped formed body of this embodiment has the following microstructure: containing 5% or more but less than 10% retained austenite, bainite and tempered martensite totaling more than 90% but less than 95% by area, and less than 5% residual microstructure. At the grain boundaries of the bainite and tempered martensite grains, relative to the area of… <011> The total length of grain boundaries with a rotation angle of 4° to 12° along the rotation axis, the length of grain boundaries with a rotation angle of 49° to 54°, and the length of grain boundaries with a rotation angle of 55° to 75° (large dip angle grain boundaries) shall account for more than 30% of the total length of the aforementioned grain boundaries with a rotation angle of 55° to 75°.

[0437] It should be noted that, in this embodiment, the microstructure at a depth of 1 / 4 of the sheet thickness (the region from 1 / 8 to 3 / 8 of the sheet thickness from the surface) of the hot-stamped body is defined. This is because this depth is the midpoint between the surface of the hot-stamped body and the center of the sheet thickness, and the microstructure at this location represents the steel structure of the hot-stamped body (representing the average microstructure of the entire hot-stamped body).

[0438] "Retained austenite: 5% or more but less than 10%"

[0439] Retained austenite improves the impact characteristics of hot-stamped articles. If the retained austenite content is less than 5%, the desired uniform deformation capacity cannot be obtained. Therefore, the retained austenite content is set to 5% or more, preferably 6% or more or 7% or more. On the other hand, if the retained austenite content is 10% or more, the desired strength cannot be obtained. Therefore, the retained austenite content is set to less than 10%, preferably 9% or less or 8% or less.

[0440] "Bainite and tempered martensite: totaling more than 90% but less than 95%"

[0441] Bainite and tempered martensite improve the strength of hot-stamped parts. If the total content of bainite and tempered martensite is less than 90%, the desired strength cannot be obtained. Therefore, the total content of bainite and tempered martensite is set to be more than 90%. Preferably, it is 91% or more or 92% or more. On the other hand, if the total content of bainite and tempered martensite exceeds 95%, the desired uniform deformation capability cannot be obtained. Therefore, the total content of bainite and tempered martensite is set to be 95% or less. Preferably, it is 94% or less or 93% or less.

[0442] "Remaining tissue: less than 5%"

[0443] In the microstructure of the hot-stamped formed article of this embodiment, the residual structure sometimes includes ferrite, pearlite, primary martensite, and granular bainite. If the area ratio of the residual structure is high, the desired strength and impact properties cannot be obtained. Therefore, the residual structure is set to be less than 5%. Preferably, it is 3% or less, or 1% or less.

[0444] "Determination of the area ratio of retained austenite, bainite, and tempered martensite"

[0445] The sample is cut from any position more than 50 mm away from the end face of the hot-stamped body (to avoid the end face if it is not possible to take a sample from that position), in a way that allows observation of a cross-section (plate thickness section) perpendicular to the surface. The size of the sample also depends on the measuring device, but is set to be about 10 mm in size that can be observed in the rolling direction.

[0446] The cross-section of the above samples was ground using #600 to #1500 silicon carbide paper, and then mirror-finished using a liquid polishing process. This liquid was obtained by dispersing diamond powder with a particle size of 1–6 μm in a diluent such as alcohol or pure water. Next, the samples were ground for 8 minutes at room temperature using colloidal silica without an alkaline solution to remove strain introduced into the sample surface. At any location along the length of the sample cross-section, regions with a length of 50 μm and a depth from 1 / 8 to 3 / 8 of the plate thickness from the surface were measured using electron backscatter diffraction at intervals of 0.1 μm to obtain crystal orientation information. The measurements were performed using an EBSD apparatus consisting of a thermal field emission scanning electron microscope (JEOL JSM-7001F) and an EBSD detector (TSL DVC5 detector). The vacuum level within the EBSD apparatus was maintained at 9.6 × 10⁻⁶. -5The conditions were: Pa below 1, accelerating voltage 15 kV, irradiation current level 13, and electron beam irradiation level 62. The obtained crystal orientation information was used to calculate the area ratio of retained austenite using the "Phase Map" function in the "OIM Analysis" software (registered trademark) attached to the EBSD analysis device. The phase with the fcc crystal structure was identified as retained austenite.

[0447] Next, the phases with a bcc crystal structure were classified as bainite, tempered martensite, primary martensite, granular bainite, and ferrite. For these regions, the "Grain Average Misorientation" function in the "OIM Analysis" software (registered trademark) attached to the EBSD analysis device was used. Regions with a Grain Average Image Quality value below 60000 were classified as bainite, tempered martensite, and primary martensite. The total area ratio of these regions was calculated to obtain the total area ratio of "bainite, tempered martensite, and primary martensite". The total area ratio of "bainite and tempered martensite" was obtained by subtracting the area ratio of primary martensite obtained by the method described later from the total area ratio of "bainite, tempered martensite, and primary martensite" obtained by the above method.

[0448] "Determination of the area ratio of remaining tissue"

[0449] The sample is cut from any position more than 50 mm away from the end face of the hot-stamped body (to avoid the end face if it is not possible to take a sample from that position), in a way that allows observation of a cross-section (plate thickness section) perpendicular to the surface. The size of the sample also depends on the measuring device, but is set to be about 10 mm in size that can be observed in the rolling direction.

[0450] The cross-section of the above sample was polished using #600 to #1500 silicon carbide paper, then mirror-finished using liquid finishing, and etched with nitric acid ethanol. This liquid was obtained by dispersing diamond powder with a particle size of 1 to 6 μm in a diluent such as alcohol or pure water. Next, multiple fields of view were photographed using a thermal field emission scanning electron microscope (JEOL JSM-7001F) at arbitrary locations along the length of the sample cross-section, with a length of 50 μm and a depth from 1 / 8 to 3 / 8 of the plate thickness from the surface. Equally spaced grids were drawn on the photographs to determine the microstructure at each grid point. The area fraction of each microstructure was obtained by calculating the number of grid points belonging to each microstructure and dividing by the total number of grid points. A higher total number of grid points allows for a more accurate determination of the area fraction. In this embodiment, the grid spacing was set to 2 μm × 2 μm, and the total number of grid points was set to 1500.

[0451] Regions where cementite precipitates in lamellar form within the grains are identified as pearlite. Regions with low brightness and no underlying microstructure are identified as ferrite. Regions with high brightness and no underlying microstructure due to etching are identified as primary martensite and retained austenite. Regions not belonging to any of the above categories are identified as granular bainite. The area ratio of primary martensite is obtained by subtracting the area ratio of retained austenite obtained from the EBSD analysis from the area ratios of primary martensite and retained austenite obtained from the photographs.

[0452] "In the grain boundaries of bainite and tempered martensite, relative to the grains of..." <011> The total length of grain boundaries with a rotation angle of 4°–12° along the rotation axis, the length of grain boundaries with a rotation angle of 49°–54°, and the length of grain boundaries with a rotation angle of 55°–75°, with the proportion of grain boundaries with a rotation angle of 55°–75° (large dip angle grain boundaries) being more than 30%

[0453] Large-angle grain boundaries are the highest-angle grain boundaries found within bainite and tempered martensite grains. Large-angle grain boundaries are highly effective at suppressing the propagation of cracks generated during impacts. If the length proportion of large-angle grain boundaries is less than 30%, the desired impact characteristics cannot be obtained in the hot-stamped formed article. Therefore, the length proportion of large-angle grain boundaries is set to 30% or more. Preferably, it is 35% or more, 40% or more, or 45% or more. While there is no specific upper limit for the length proportion of large-angle grain boundaries, based on the chemical composition and manufacturing method of this embodiment, a practically upper limit of 90% is achieved.

[0454] Method for determining the length ratio of large-angle grain boundaries

[0455] From a position more than 50 mm away from the end face of the hot-stamped body (or, if this position is not possible, to avoid the end face), a sample is cut out in a way that allows observation of a cross-section perpendicular to the surface (thickness section). The sample length also depends on the measuring device, but is set to be approximately 10 mm long that can be observed in the rolling direction. For the cut sample, EBSD analysis is performed at a depth of 1 / 4 of the thickness (the region from 1 / 8 to 3 / 8 of the thickness from the surface) at measurement intervals of 0.1 μm to obtain crystal orientation information. Here, EBSD analysis is performed using an EBSD apparatus consisting of a thermal field emission scanning electron microscope (JEOL JSM-7001F) and an EBSD detector (TSL DVC5 detector), with the electron beam irradiation level set to 62.

[0456] Next, using the "Grain Average Image Quality" function within the "OIM Analysis" software (registered trademark) attached to the EBSD analysis device, regions with a Grain Average Image Quality value below 60000 were identified as bainite, tempered martensite, and primary martensite grains. For the grain boundaries of bainite and tempered martensite grains within these grain boundaries, the values ​​were calculated... <011> The lengths of grain boundaries with rotation angles of 4°–12°, 49°–54°, and 55°–75° are calculated. The length of the grain boundary with a rotation angle of 55°–75° is then determined relative to the sum of the lengths of all individual grain boundaries. This yields the ratio of the length of the grain boundary with a rotation angle of 55°–75° to the sum of the lengths of all individual grain boundaries within the bainite and tempered martensite grains. <011> The length of a grain boundary with a rotation angle of 4° to 12° is the proportion of the total length of a grain boundary with a rotation angle of 49° to 54° and a rotation angle of 55° to 75° (large dip angle grain boundary).

[0457] It should be noted that photographs are obtained using the same method as for determining the area ratio of the remaining microstructure. Primary martensite is identified from the grains of bainite, tempered martensite, and primary martensite, and then removed from these grains. Grain boundaries that do not contain primary martensite in the determination of large-angle grain boundaries are because primary martensite has high hardness and becomes the starting point for damage.

[0458] The length of the aforementioned grain boundaries can be easily calculated, for example, using the "Inverse Pole Figure Map" and "Axis Angle" functions of the "OIM Analysis" software (registered trademark) included with the EBSD analysis device. With these functions, for bainite and tempered martensite grains, by specifying a particular rotation angle with an arbitrary rotation axis, the total length of the grain boundary can be calculated. Performing the above analysis on all grains contained in the measurement region, the length of the grain boundary in the bainite and tempered martensite grains can be calculated using... <011> Using the direction as the axis of rotation, the lengths of the three types of grain boundaries can be calculated.

[0459] Plate thickness and tensile strength

[0460] The sheet thickness of the hot-stamped formed body in this embodiment is not particularly limited, but from the viewpoint of lightweight vehicle body, it is preferably set to 0.5 to 3.5 mm. Furthermore, from the viewpoint of lightweight vehicle body, the tensile strength of the hot-stamped formed body is set to 1500 MPa or more. Preferably, it is 1800 MPa or more, or 2000 MPa or more. The upper limit of the tensile strength is not particularly specified, but it can also be set to 2600 MPa or less, or 2550 MPa or less.

[0461] "Coating"

[0462] For purposes such as improving corrosion resistance, the hot-stamped formed body of this embodiment may also have a coating formed on its surface. The coating may be either an electroplated coating or a hot-dip coating. Examples of electroplated coatings include electroplated zinc layers and electroplated Zn-Ni alloy layers. Examples of hot-dip coatings include: hot-dip zinc layers, alloyed hot-dip zinc layers, hot-dip aluminum layers, hot-dip Zn-Al alloy layers, hot-dip Zn-Al-Mg alloy layers, and hot-dip Zn-Al-Mg-Si alloy layers. The amount of coating applied is not particularly limited and can be a general amount.

[0463] "Manufacturing method of hot stamped parts"

[0464] Next, a preferred manufacturing method for the hot stamping formed article of this embodiment will be described.

[0465] The hot-stamped formed body of this embodiment can be manufactured by hot stamping a cold-rolled steel sheet manufactured by conventional methods or a cold-rolled steel sheet with a coating on its surface, holding it under pressure within a specified temperature range after hot stamping, and then cooling it.

[0466] Heating and holding before hot stamping

[0467] Preferably, the temperature is held at 800–1000°C for 60–600 seconds before hot stamping. If the heating temperature is below 800°C or the holding time is below 60 seconds, sufficient austenitization may not occur, and the desired amount of bainite and tempered martensite cannot be obtained in the hot-stamped body. If the heating temperature exceeds 1000°C or the holding time exceeds 600 seconds, the austenite grain size may coarsen, delaying the phase transformation to bainite and tempered martensite, thus failing to obtain the desired amount of bainite and tempered martensite.

[0468] The average heating rate should be between 0.1°C / second and 200°C / second. This average heating rate is calculated by dividing the temperature difference between the initial surface temperature of the steel plate and the holding temperature by the time difference between the start of heating and the reaching of the holding temperature. Furthermore, during the holding period, the steel plate temperature can be varied within a range of 800 to 1000°C, or it can be set to a constant temperature.

[0469] Methods for heating before hot stamping include heating via electric furnaces, gas furnaces, flame heating, electric heating, high-frequency heating, and induction heating.

[0470] Cooling after hot stamping

[0471] After the aforementioned heating and holding, hot stamping is performed. Preferably, after hot stamping, cooling is carried out at an average cooling rate of 1.0–100 °C / s until a temperature range of 200–400 °C is reached. During cooling after hot stamping, if the cooling stop temperature is below 200 °C, the stabilization of retained austenite may not be promoted, and the desired amount of retained austenite cannot be obtained. If the cooling stop temperature exceeds 400 °C, the hardness of the original austenite grains may decrease, making it impossible to form the desired amount of large-angle grain boundaries. Furthermore, if the average cooling rate is below 1.0 °C / s, phase transformations to ferrite, granular bainite, and pearlite may be promoted, making it impossible to obtain the desired amount of bainite and tempered martensite. If the average cooling rate exceeds 100 °C / s, the driving force for phase transformations to tempered martensite and bainite increases, while the effect of mitigating the strain introduced by the phase transformation decreases, making it difficult to obtain the desired amount of large-angle grain boundaries.

[0472] It should be noted that the so-called average cooling rate here refers to the value obtained by dividing the temperature difference between the steel plate surface temperature at the start of cooling and the temperature at the end of cooling by the time difference from the start of cooling to the end of cooling.

[0473] "Pressure maintenance"

[0474] Within a temperature range of 200–400°C, a pressure holding time of 30 to 3600 seconds is maintained at a surface pressure P (MPa) satisfying Equation (B1).

[0475] If the holding time is less than 30 seconds, carbon may not be sufficiently distributed from martensite to untransformed austenite, resulting in the undesirable amount of retained austenite. If the holding time exceeds 3600 seconds, bainite or tempered martensite may soften, preventing the attainment of the desired strength. If the surface pressure P is lower than the left side of equation (B1), deformation of the original austenite grains may not be adequately suppressed, leading to a reduction in the proportion of large-angle grain boundaries.

[0476] There is no particular upper limit to the surface pressure P, but for the material of the strength grade in this embodiment, 300 MPa is a practical upper limit in order not to damage the equipment. When maintaining pressure, the temperature of the steel plate can be varied within the temperature range of 200 to 400°C, or it can be set to be constant.

[0477] Pressurization can be achieved simply by transferring the formed steel sheet from the hot stamping and subsequent cooling mold to another mold with heating capabilities.

[0478] It should be noted that if the temperature is heated to a range of 400°C or higher after hot stamping and cooling but before pressure holding, bainite is formed, resulting in the inability to obtain the desired amount of large-angle grain boundaries. Therefore, when manufacturing the hot-stamped formed article of this embodiment, it is not preferable to heat it to a temperature range of 400°C or higher after hot stamping and cooling but before pressure holding.

[0479] -1.85×Ms+755≤P≤300 (Equation B1)

[0480] Ms (°C) = 539 - 423 × C - 30 × Mn - 12 × Cr - 17 × Ni - 7.5 × Mo (Formula B2)

[0481] It should be noted that the element symbols in the above formula (B2) represent the content of each element in terms of mass % and should be replaced with 0 if the element is not present.

[0482] Cooling after pressurization

[0483] Ideally, after pressurization and holding, the temperature should be cooled to below 80°C at an average cooling rate of 1.0–100°C / second. If the average cooling rate is below 1.0°C / second, the retained austenite may decompose. If the average cooling rate exceeds 100°C / second, it will place a load on the equipment, and the retained austenite may decompose. The average cooling rate referred to here is the temperature difference between the steel plate surface temperature at the start of cooling after pressurization and holding and the cooling stop temperature, divided by the time difference from the start to the stop of cooling.

[0484] Next, embodiments of element technology B will be described. The conditions in these embodiments are examples used to confirm the feasibility and effectiveness of element technology B; element technology B is not limited to these single examples. Without departing from the essence of element technology B, various conditions can be employed as long as the purpose of element technology B can be achieved.

[0485] Cold-rolled steel sheets are obtained by hot-rolling and cold-rolling steel billets manufactured from molten steel with the chemical compositions shown in Tables 7 and 8 through casting, and by applying a coating as needed. Next, the cold-rolled steel sheets are used to manufacture the hot-stamped forms shown in Tables 9 and 10 under the conditions shown in Tables 9 and 10.

[0486] It should be noted that the average heating rate during the heating before hot stamping is set to 0.1 to 200°C / second, the cooling after hot stamping continues until the temperature reaches 200 to 400°C, and the cooling after pressurization continues until the temperature drops below 80°C.

[0487] In addition, a hot-dip aluminized layer is applied to Manufacturing No. 16 in Table 9, and a hot-dip galvanized layer is applied to Manufacturing No. 17.

[0488] Manufacturing No. 55 in Table 10 was subjected to the pressure holding shown in Table 10 after hot stamping and cooling and before pressure holding, and held at a temperature range of 410–560°C for 30 seconds.

[0489] In Tables 9 and 10, γr represents retained austenite, B represents bainite, and TM represents tempered martensite.

[0490] The area ratio of each microstructure and the proportion of large-angle grain boundaries were determined using the methods described above. Furthermore, the mechanical properties of the hot-stamped body were evaluated using the following methods.

[0491] "tensile strength"

[0492] Regarding the tensile strength of the hot-stamped formed body, test piece No. 5 as described in JIS Z 2241:2011 was prepared from any location on the hot-stamped formed body, and the strength was determined according to the test method described in JIS Z 2241:2011. It should be noted that the crosshead speed was set to 3 mm / min. A tensile strength of 1500 MPa or higher was considered acceptable, while a tensile strength lower than 1500 MPa was considered unacceptable.

[0493] "Collision characteristics (uniform deformation capability and crack propagation suppression effect)"

[0494] The impact characteristics of hot-stamped parts are evaluated based on the VDA standard (VDA238-100) specified by the German Association of the Automotive Industry, using the following methods.

[0495] In this embodiment, the results obtained from the bending test are as follows: Figure 22The FS curve (load-bending angle graph) shown is used to determine the absorbed energy S1 as an indicator of uniform deformation capacity, and S2 is used to determine the crack propagation suppression effect. Regarding S1, based on the slope of the FS curve, the increase in load per unit bending angle from the start of the test to reaching the maximum load is calculated, and this is used as the integral value (absorbed energy S1) over these small areas. Regarding S2, based on the slope of the FS curve, the change in load per unit bending angle from reaching the maximum load to reducing to half of the maximum load is calculated, and this is used as the integral value (absorbed energy S2) over these small areas.

[0496] In this embodiment, a value of S1 of 100 (°·kN) or higher is considered excellent in terms of uniform deformation capability and is thus deemed acceptable; a value of 100 (°·kN) or higher is considered "acceptable"; a value of 120 (°·kN) or higher is considered "good"; and a value of 180 (°·kN) or higher is considered "very good," as recorded in Tables 9 and 10. A value below 100 (°·kN) is considered poor in terms of uniform deformation capability and is thus deemed unacceptable, as recorded as "poor" in Tables 9 and 10.

[0497] Values ​​obtained by dividing S2 by the sum of S1 and S2 (S2 / (S1+S2)) of 0.01 or higher are considered excellent in crack propagation suppression and are deemed acceptable. Values ​​of 0.01 or higher are considered "acceptable," 0.02 or higher are considered "good," and 0.07 or higher are considered "very good," and are recorded in Tables 9 and 10. Values ​​below 0.01 are considered poor in crack propagation suppression and are deemed unacceptable, and are recorded as "poor" in Tables 9 and 10.

[0498] The conditions for the bending test are as follows.

[0499] Test piece dimensions: 60mm (rolling direction) × 30mm (parallel to the plate width direction)

[0500] Test piece thickness: 1.01~1.05mm (both sides were ground to equal thickness).

[0501] Curved edge: A direction parallel to the width of the plate.

[0502] Test method: roller support, punch pressing

[0503] Roller diameter: φ30mm

[0504] Punch shape: Front end R = 0.4mm

[0505] Roller spacing: 2.0 × plate thickness (mm) + 0.5mm

[0506] Pressing speed: 20mm / minute

[0507] Testing machine: Shimadzu Corporation AG-100KNI [Table 7]

[0508]

[0509] [Table 8]

[0510]

[0511] [Table 9]

[0512]

[0513] [Table 10]

[0514]

[0515] (Element Technology C)

[0516] Element technology C is a skeleton component formed by hot stamping of steel sheet. The skeleton component has a closed section portion with a closed section perpendicular to the length direction. The closed section portion has at least one flat portion with a radius of curvature larger than the maximum external dimension of the section. When the flat portion with the largest width relative to the effective width calculated by the Karman formula is defined as the reference flat portion, the Vickers hardness at the center of the plate thickness at the reference flat portion is 300 Hv or more, the width of the reference flat portion is less than 2.0 times the effective width, and the standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution at the surface portion of the reference flat portion by the standard deviation of the hardness frequency distribution at the center of the plate thickness at the reference flat portion is less than 1.0.

[0517] According to element technology C, by controlling the ratio of width and hardness standard deviations within an appropriate range in the reference flat area, it is possible to suppress elastic buckling while preventing fracture during wrinkling deformation caused by axial loads. Therefore, even when using high-strength thin-walled components, high energy absorption performance can be achieved. Thus, excellent energy absorption efficiency can be achieved.

[0518] The inventors of this invention have conducted in-depth research on the construction of skeletal components that can achieve excellent energy absorption efficiency.

[0519] First, a certain yield strength is important to achieve excellent energy absorption efficiency. When an axial input load is applied due to a collision, elastic buckling may sometimes occur in the flat areas during the initial stage of deformation. If elastic buckling occurs, the necessary yield strength may not be obtained, and excellent energy absorption efficiency cannot be achieved.

[0520] In addition, to achieve excellent energy absorption efficiency, the following is also important: after an axial input load is applied due to a collision, the impact energy is efficiently absorbed by folding deformation in the desired deformation mode through the skeleton members. In particular, if fracture occurs during the folding deformation process caused by axial load (fracture at the fold), excellent energy absorption efficiency may not be achieved.

[0521] Therefore, it can be said that if the cross-sectional design is set to be less prone to elastic buckling in flat areas and given high bending performance that is not easy to break, then excellent energy absorption efficiency can be achieved.

[0522] Here, when components are made stronger and thinner as a method to achieve lightweighting, the following problems occur.

[0523] • Due to the thinning of the wall, elastic buckling becomes easier to occur in the flat parts of the component, making it difficult to obtain the necessary yield strength.

[0524] • Due to the increased strength, the bending performance of the steel plate is reduced, and the folded part after deformation begins is prone to breakage, making it difficult to efficiently absorb impact energy.

[0525] The inventors of this invention have identified the aforementioned problems as the main reasons hindering the further increase in strength and thinness of high-strength steel plates.

[0526] Through further research, the inventors of this invention discovered that by controlling the ratio of width to hardness standard deviation within an appropriate range in the reference flat area, it is possible to suppress elastic buckling while preventing fracture during the wrinkling deformation process caused by axial loads. They found that this control eliminates the aforementioned problems that are concerning when using high-strength steel plates, achieving excellent energy absorption efficiency, thus completing element technology C.

[0527] The skeleton component C10 of the first embodiment of the element technology C based on the above insights will be described below.

[0528] It should be noted that in this specification and accompanying drawings, constituent elements that have essentially the same function are omitted from repeated descriptions by using the same symbols.

[0529] First, let's explain the statements in this instruction manual.

[0530] "Length direction" refers to the material axis direction of the skeleton component, that is, the direction in which the axis extends.

[0531] A "flat section" refers to a straight section in a cross-section of a skeletal component that is perpendicular to its length; specifically, it refers to a section whose radius of curvature is larger than the maximum external dimension of the cross-section. The maximum external dimension is the length of the straight line that makes the distance between the ends of any two points in the cross-section the greatest.

[0532] "Corner section" refers to a non-linear section of a skeletal component in a cross-section perpendicular to its length direction, excluding flat sections.

[0533] "Width" refers to the length of the line along the circumference of the closed section, while "width of the flat section" refers to the length of the line between one end and the other end of the flat section.

[0534] The "effective width" is the effective width W obtained by applying the following equation (C1), based on Karman's effective width theory, i.e., Karman's effective width equation. e .

[0535] W e =t(4π) 2 E / 12(1-ν 2 )σ y ) 1 / 2 (C1) formula

[0536] in,

[0537] σ y Yield stress (MPa) in the flat region

[0538] E: Young's modulus (MPa) of the flat region

[0539] t: Thickness of the plate in the flat section (mm)

[0540] ν: Poisson's ratio for flat areas.

[0541] Furthermore, in steel plates, the Young's modulus and Poisson's ratio of the flat portions can be obtained using general physical property values. Alternatively, the yield stress of the flat portions can be replaced with the Vickers hardness at the center of the plate thickness, thereby allowing the yield stress to be determined by W. e The effective width W can be calculated using the formula =577t / √h. e .

[0542] in,

[0543] t: Thickness of the plate in the flat section (mm)

[0544] h: Vickers hardness (Hv) at the center of the plate thickness in the flat section.

[0545] The effective width W is difficult to determine using equation (C1). e In this case, it can be obtained using the above formula.

[0546] "Effective width ratio" refers to the width W of the flat portion relative to the effective width W0. e The ratio is determined by W / W e The calculated value. It can be said that the smaller the effective width ratio, the less likely the cross-sectional shape is to experience elastic buckling.

[0547] "Reference flat section" refers to the flat section with the largest effective width ratio among the flat sections in a closed cross section at any position in the length direction.

[0548] "Surface portion" refers to the area between a depth position that is 1% of the thickness of the steel plate in the thickness direction from the surface of the steel plate and a depth position that is 5% of the thickness of the steel plate in the thickness direction from the surface of the steel plate.

[0549] "Center of plate thickness" refers to the depth position at a distance of 3 / 8 of the plate thickness in the thickness direction from the surface of the steel plate.

[0550] The "surface of the steel plate" used as a reference for depth positioning refers to the surface of the base steel plate. For example, in cases where plating or painting has been applied, or where rust has formed, the surface of the steel plate after the plating, painting, and rust have been removed is used as the reference for depth positioning. It should be noted that when a surface coating such as plating, painting, or rust has formed on the surface of the base steel plate, the boundary between this surface coating and the surface of the base steel plate can be easily identified using various known methods.

[0551] "Energy absorption" is calculated based on the relationship between the impactor's reaction force (load) and the stroke when the frame component undergoes wrinkling deformation. For example... Figure 23 As shown, the impactor reaction force (load) and stroke can be obtained as follows: the skeleton members are arranged in a manner where the length direction is vertical, and the rigid plane impactor is made to collide from the upper side along the direction of the hollow arrow while the lower end side is fully constrained.

[0552] "Energy absorption efficiency" is the energy absorption per unit cross-sectional area (plate thickness × section length) of a frame component. When frame components do not have uniform cross-sections along their length, it refers to the energy absorption per unit cross-sectional area (plate thickness × section length) of the closed section perpendicular to the component's length direction.

[0553] Figure 24 This is a perspective view of the skeleton component C10. The skeleton component C10 is a hollow cylindrical component extending along its length.

[0554] Figure 25 yes Figure 24 The cross-sectional view of the cut line A1-A1. (As shown...) Figure 25As shown, the skeleton component C10 forms a roughly rectangular closed cross section through four flat parts C11 and four corner parts C.

[0555] Specifically, the closed cross-section is formed in the following manner: it has a first flat portion C11a, a second flat portion C11b connected to the first flat portion C11a via a corner portion C, a third flat portion C11c connected to the second flat portion C11b via a corner portion C, and a fourth flat portion C11d connected to the third flat portion C11c via a corner portion C, and the fourth flat portion C11d is connected to the first flat portion via a corner portion C.

[0556] All four corner sections C have the same radius of curvature r. For example, if the maximum external dimension is 140 mm, the radius of curvature r can be less than 140 mm. The radii of curvature of the four corner sections C do not need to be the same, and they can also be different from each other. There is no specific upper limit for the radius of curvature, but sections with a radius of curvature greater than the maximum external dimension of the cross-section are considered as separate flat sections or part of adjacent flat sections, and are not considered as corner sections. Therefore, it can be said that the upper limit of the radius of curvature of the corner section C is essentially "below the maximum external dimension of the cross-section".

[0557] In this application, the reference flat portion is defined as the flat portion with the largest effective width ratio among the flat portions in the closed cross section.

[0558] The first flat region C11a, the second flat region C11b, the third flat region C11c, and the fourth flat region C11d all have the same yield stress σ. y Young's modulus E, plate thickness t, and Poisson's ratio ν.

[0559] Therefore, for each flat section C11, the width W / effective width W is used. e The calculated effective width ratio depends only on the width W of each flat section C11.

[0560] Therefore, in this embodiment, the first flat portion C11a and the third flat portion C11c, which have the largest width W in the closed cross section, are set as the reference flat portions.

[0561] In the reference flat region, when the skeleton member C10 is subjected to axial compressive force, elastic buckling is most likely to occur in the early stage of deformation. Therefore, if the width W of this reference flat region... S If the width is too large, the necessary yield strength cannot be obtained, making it difficult to achieve excellent energy absorption efficiency. Therefore, the width W of the reference flat section... S The upper limit is set to the effective width W. e Less than 2.0 times.

[0562] It should be noted that the width W of the reference flat area S The lower limit is not specifically set, but if the width W of the reference flat part is... S If the area is too small, the area of ​​the closed section of the skeleton member C10 will decrease, making it difficult to ensure the yield strength.

[0563] Therefore, the width W of the reference flat portion S The preferred effective width W e More than 0.1 times.

[0564] From the perspective of lightweight design, the thickness of the plate in the reference flat area is preferably less than 4.2 mm.

[0565] On the other hand, when the plate thickness of the reference flat section is less than 0.4 mm, elastic buckling of the reference flat section becomes more likely to occur, therefore the width W of the reference flat section... S The limitations on the setting range become larger. Therefore, the thickness of the plate in the reference flat area is preferably 0.4 mm or more.

[0566] The skeleton member C10 is formed by hot-pressing a hot-stamped steel sheet into a specified shape and then joining the end faces. The skeleton member C10 thus formed has a strength of 1.5 GPa or more in tensile strength. Furthermore, by forming it in this way, the Vickers hardness of the center of the plate thickness at the reference flat portion of the skeleton member C10 becomes 300 Hv or more in a hardness test performed according to the method described in JIS Z 2244:2009, with the test load set to 300 gf (2.9 N).

[0567] In this application, in order to improve the deformation capacity and exert excellent energy absorption efficiency with high strength as a premise, the hardness of the center of the plate thickness at the reference flat part is specified as 300Hv or more by Vickers hardness tester.

[0568] There is no specific upper limit for the hardness of the center of the plate thickness, but it can be set to below 900 Hv using a Vickers hardness tester.

[0569] The method for determining the hardness of the center of the plate thickness is as follows.

[0570] A specimen with a cross-section perpendicular to the plate surface is collected from the skeleton component, and this cross-section is used as the measurement surface for preparation. This measurement surface is then used for hardness testing.

[0571] The size of the measuring surface also depends on the measuring device, but it can be around 10mm × 10mm.

[0572] The preparation method of the test surface was performed according to JIS Z 2244:2009. After grinding the test surface with #600 to #1500 silicon carbide paper, it was then finished to a mirror finish using a liquid obtained by dispersing diamond powder with a particle size of 1μm to 6μm in a diluent such as alcohol or pure water. The hardness test was performed according to the method described in JIS Z 2244:2009. Using a micro Vickers hardness tester, 30 points were measured at 3 / 8 of the sample thickness, with a load of 300gf and intervals of at least three times the indentation length. The average value of these measurements was taken as the hardness at the center of the sample thickness.

[0573] As described above, the width W of the reference flat portion S For the effective width W e When the tensile strength is less than 2.0 times, elastic buckling can be suppressed. However, for high-strength materials, such as hot-stamped materials (hot-stamped formed bodies) with a tensile strength of 1.5 GPa or higher, even by controlling the effective width W... e However, if elastic buckling is suppressed and bending performance is insufficient, fracture may occur during the process of wrinkling deformation caused by axial load, thus failing to achieve excellent energy absorption efficiency.

[0574] In the past, the standard deviation of the hardness frequency distribution at the center of the plate thickness in the flat part of the reference plate was almost the same as that at the surface part, and the ratio of the hardness standard deviations was 1.0.

[0575] However, in the skeleton member C10 of this embodiment, the bending performance is improved by appropriately controlling the ratio of the standard deviation of the hardness frequency distribution at the center of the plate thickness at the reference flat part to the standard deviation of the hardness frequency distribution at the surface part.

[0576] Therefore, even when using high-strength materials, it can suppress breakage during the wrinkling and deformation process, and achieves exceptionally high energy absorption efficiency compared to the past.

[0577] Specifically, in the skeleton member C10 of this embodiment, control is performed in the following manner: in the reference flat area, the standard deviation ratio of hardness frequency distribution at the surface layer divided by the standard deviation of hardness frequency distribution at the center of the plate thickness becomes less than 1.0.

[0578] The inventors of this invention discovered through experiments that when using hot-stamped materials with a tensile strength of 1.5 GPa or higher, setting the hardness standard deviation ratio to a value less than 1.0 can significantly increase the maximum bending angle in the VDA bending test based on the VDA standard (VDA238-100) specified by the German Association of the Automotive Industry.

[0579] Figure 26 This graph shows the results of the VDA bending test using a steel plate with a thickness of 1.4 mm and a 2.0 GPa grade material. It indicates that the smaller the standard deviation ratio of the hardness is (less than 1.0), the higher the maximum bending angle (°) and the higher the VDA bending angle ratio in the VDA bending test. In other words, when the standard deviation ratio of the hardness is less than 1.0, it becomes less prone to fracture during wrinkling deformation under axial load, thus exhibiting excellent energy absorption efficiency.

[0580] Therefore, the standard deviation of hardness is preferably less than 0.95, and more preferably less than 0.80.

[0581] A smaller hardness standard deviation ratio is preferred, but even if it is less than 0.01, the effect of improving flexibility is saturated. Therefore, a hardness standard deviation ratio of 0.01 or higher is preferred.

[0582] Here, the hardness frequency distribution at the center of the plate thickness and the hardness frequency distribution at the surface are obtained by Vickers hardness test.

[0583] A specimen with a cross-section perpendicular to the plate surface is collected from the skeleton component, and this cross-section is used as the measurement surface for preparation. This measurement surface is then used for hardness testing.

[0584] The size of the measuring surface also depends on the measuring device, but it can be around 10mm × 10mm.

[0585] The preparation method of the measuring surface was carried out in accordance with JIS Z 2244:2009.

[0586] After grinding the measuring surface with silicon carbide paper of #600 to #1500, the measuring surface is then finished into a mirror finish using a liquid obtained by dispersing diamond powder with a particle size of 1μm to 6μm in a diluent such as alcohol or pure water.

[0587] For the test surface that has been so finely machined into a mirror finish, the hardness test shall be performed according to the method described in JIS Z 2244:2009.

[0588] The hardness of the surface layer was measured using a micro Vickers hardness tester.

[0589] The hardness frequency distribution at the surface layer was determined by measuring 30 points at intervals of more than 3 times the indentation with a load of 300 gf.

[0590] Similarly, at a depth of 3 / 8 of the plate thickness, 30 points were measured at intervals of more than 3 times the indentation with a load of 300gf to determine the hardness frequency distribution at the center of the plate thickness.

[0591] In addition, in order to determine the standard deviation of the hardness frequency distribution at the center of the plate thickness and the hardness frequency distribution at the surface obtained from the Vickers hardness test results mentioned above, known statistical methods were used.

[0592] When the metal structure of the hot-stamped steel sheet is the same in the center and the surface as in the past, the hardness frequency distribution in the surface becomes the same as that in the center, and the hardness standard deviation ratio becomes 1.0.

[0593] On the other hand, when only the surface layer and the surrounding metal structure are modified, the hardness standard deviation ratio becomes a value different from 1.0.

[0594] In the skeleton member C10 formed from the hot-stamped steel sheet of this embodiment, by modifying only the metal structure of the surface layer and its vicinity, the distribution and unevenness of hardness at the surface layer can be suppressed, and the ratio of the standard deviation of hardness between the surface layer and the center of the sheet thickness is less than 1.0.

[0595] Specifically, the hardness standard deviation ratio can be controlled by adjusting the maximum heating temperature and holding time during decarburization annealing of hot-stamping steel sheets, which is a known technique. The preferred decarburization annealing conditions are: in a humid atmosphere containing hydrogen, nitrogen, or oxygen, setting the decarburization annealing temperature (the maximum temperature reached by the steel sheet) to 700–950°C, and setting the holding time within the temperature range of 700–950°C to 5–1200 seconds.

[0596] In addition, by setting the annealing temperature to a higher temperature range and limiting the dwell temperature to a longer time range within this condition, it is possible to make the hardness standard deviation ratio less than 0.80.

[0597] It should be noted that it is sufficient for at least one surface portion of the skeleton member C10 to meet the above-mentioned condition of the hardness standard deviation ratio. However, it is preferable that the surface portions on both sides of the skeleton member C10 meet the above-mentioned condition of the hardness standard deviation ratio.

[0598] Thus, according to the skeleton member C10 of this embodiment, the width W of the reference flat portion is controlled at the reference flat portion. S It can suppress elastic buckling, and by controlling the standard deviation ratio of hardness, it can suppress fracture during the wrinkling deformation process.

[0599] Therefore, even if the Vickers hardness of the center of the plate thickness in the reference flat area is sufficient to reach 300 Hv or more, it can still significantly improve energy absorption efficiency.

[0600] The preferred embodiments of element technology C have been described in detail above with reference to the accompanying drawings, but element technology C is not limited to the examples described above.

[0601] Obviously, anyone with ordinary knowledge of the technical field to which element technology C belongs can conceive of various modifications or alterations within the scope of the technical concept of this application, and these are of course also understood to fall within the technical scope of element technology C.

[0602] For example, the aforementioned skeleton component C10 may be composed of a single component, but it may also be composed of multiple components. Figure 27 This is a perspective view of the skeleton component C20 in a modified example. Figure 28 yes Figure 27 The cross-sectional view of the cut line A2-A2.

[0603] The skeleton member C20 includes a first skeleton member C20A extending along the length direction and a second skeleton member C20B extending along the length direction and engaging with the first skeleton member C20A. Moreover, a closed section is formed by the first skeleton member C20A and the second skeleton member C20B.

[0604] The first frame component C20A is a component with an open cross-section that is approximately hat-shaped, formed by hot stamping a steel plate with a thickness of 1.2 mm.

[0605] like Figure 28 As shown, the cross-section perpendicular to the length direction of the first skeleton member C20A has five flat parts C21 and four corner parts C.

[0606] Specifically, the cross-section perpendicular to the length direction of the first skeleton member C20A includes: a first flat portion C21a, a second flat portion C21b connected to the first flat portion C21a via a corner portion C, a third flat portion C21c connected to the second flat portion C21b via a corner portion C, a fourth flat portion C21d connected to the third flat portion C21c via a corner portion C, and a fifth flat portion C21e connected to the fourth flat portion C21d via a corner portion C.

[0607] The second frame member C20B is a member with an open cross-section that is approximately hat-shaped, formed by hot stamping a steel plate with a thickness of 0.8 mm.

[0608] like Figure 28 As shown, the cross-section perpendicular to the length direction of the second skeleton member C20B has five flat parts C23 and four corner parts C.

[0609] Specifically, the cross-section perpendicular to the length direction of the second skeleton member C20B includes: a first flat portion C23a, a second flat portion C23b connected to the first flat portion C23a via the corner portion C, a third flat portion C23c connected to the second flat portion C23b via the corner portion C, a fourth flat portion C23d connected to the third flat portion C23c via the corner portion C, and a fifth flat portion C23e connected to the fourth flat portion C23d via the corner portion C.

[0610] Furthermore, the first flat portion C21a and the fifth flat portion C21e of the first frame member C20A are joined to the first flat portion C23a and the fifth flat portion C23e of the second frame member C20B by spot welding.

[0611] By constructing it in this way, the cross section of the skeleton member C20 perpendicular to the length direction has a closed section.

[0612] In this application, the reference flat portion is defined as the flat portion with the largest effective width ratio among the flat portions in the closed cross section.

[0613] The flat portion C21 of the first skeleton member C20A and the flat portion C23 of the second skeleton member C20B both have the same yield stress σ. y Young's modulus E and Poisson's ratio ν. Therefore, for each flat part C21, C23, the width W / effective width W is used. e The calculated effective width ratio depends on the width W and plate thickness t of each flat section C21 and C23.

[0614] In this closed cross-section, the third flat portion C21c of the first skeleton member C20A and the third flat portion C23c of the second skeleton member C20B both have the largest width among all flat portions C21 and C23. However, the plate thickness of the third flat portion C23c of the second skeleton member C20B is smaller than that of the third flat portion C21c of the first skeleton member C20A, therefore the effective width ratio of the third flat portion C23c of the second skeleton member C20B is the largest. Therefore, the third flat portion C23c of the second skeleton member C20B is the reference flat portion.

[0615] Therefore, in the modified skeleton member C20, by controlling the Vickers hardness of the center of the plate thickness to 300Hv or more for the third flat portion C23c of the second skeleton member C20B, which serves as the reference flat portion, the width W is... s Controlled to effective width W e By controlling the standard deviation ratio to less than 1.0, which is less than 2.0 times that of the standard deviation ratio, excellent energy absorption efficiency can be achieved.

[0616] It should be noted that the skeleton member C10 has a roughly rectangular cross-sectional shape with opposite sides having the same width, but it may also have a roughly square cross-sectional shape with four flat parts C11 having the same width.

[0617] In addition, there is no particular limit to the number of flat C11 parts, but at least one is required.

[0618] Furthermore, the skeleton member C10 of the embodiment has the same cross-sectional shape throughout its entire length, but it may not have the same cross-sectional shape throughout its entire length. The closed section with the smallest cross-sectional area (plate thickness × section line length) in the closed section perpendicular to the length direction of the member is the aforementioned closed section portion, which may exist in a portion of the entire length direction. However, it is preferable that the aforementioned closed section portion exists in 50% or more of the entire length direction, and more preferably in 80% or more.

[0619] It should be noted that the skeleton components C10 and C20 are structural components of automobile bodies that are expected to be primarily compressed by axial loads during a collision. Figure 29 This is a diagram showing an automobile frame C100 as an example of the application of frame components C10 and C20.

[0620] If you refer to this Figure 29 Then, the skeleton components C10 and C20 can be applied to the front longitudinal beam C101, rear longitudinal beam C103, side beam C105, A-pillar C107, B-pillar C109, upper side beam C111, floor crossbeam C113, roof crossbeam C115 and underbody reinforcement C117 in the structural components of the automobile body.

[0621] (Example)

[0622] Prepare steel plates A, B, and C, each with a thickness of 1.6 mm.

[0623] For steel plates B and C, by setting the decarburization annealing temperature (the highest temperature reached by the steel plate) to 700–900°C in a humid atmosphere mixed with hydrogen and nitrogen during decarburization annealing, and setting the residence time in the temperature range of 700–900°C to 60–600 seconds, the metal structure of only the surface layer and its vicinity is modified.

[0624] By heating the aforementioned steel plates A, B, and C at a temperature range of 900°C and rapidly cooling them in a mold, hot stamping is performed. By welding the end faces together, a 300mm high square tube component made from each steel plate is obtained.

[0625] Steel plate A has the same microstructure in its center and surface regions. Therefore, the standard deviation of the hardness frequency distribution in the center of the reference flat region is equal to the standard deviation of the hardness frequency distribution in the surface region of the reference flat region, resulting in a hardness standard deviation ratio of 1.0. On the other hand, steel plates B and C modify the microstructure of their surface regions but not their center regions, thus altering the hardness frequency distribution in their surface regions and adjusting the standard deviation of the surface regions. Consequently, the hardness standard deviation ratio of the surface region relative to the center region in the reference flat region of steel plate B is 0.65, and the hardness standard deviation ratio in the reference flat region of steel plate C is 0.80.

[0626] The material properties of the flattened portion after hot stamping are shown in Table 11.

[0627] [Table 11]

[0628]

[0629] like Figure 30 As shown, the cross-section perpendicular to the length direction of the square tube component is designed as an approximately square cross-section with four flat sections of equal width. That is, in each square tube component, all four flat sections are reference flat sections with the largest effective width-to-width ratio. Based on this condition, the width W of the reference flat section is set for each experimental example. S .

[0630] It should be noted that the radius of curvature of the four corners C is designed to be 5mm.

[0631] For these rectangular tube components, with the lower end fully constrained, a rigid planar impactor was driven at 90 km / h from the upper end. The absorbed energy was calculated and compared based on the deformation state, fracture occurrence, impactor reaction force (load), and stroke. The setup conditions and results for each experimental example are shown in Table 12.

[0632] [Table 12]

[0633]

[0634] It should be noted that, Figure 31 This is a graph comparing the energy absorption efficiency with the effective width ratio to the experimental results shown in Table 12. As the graph shows, it can be seen that simply reducing the effective width ratio does not result in an increase in energy absorption efficiency. However, when the hardness standard deviation ratio is properly controlled, as in this application, reducing the effective width ratio significantly improves the energy absorption efficiency.

[0635] (Element Technology D)

[0636] Element technology D is a steel component having a steel plate substrate and a coating containing Al and Fe formed on the surface of the steel plate substrate. The steel plate substrate has the following chemical composition (in mass percent): C: 0.10–0.65%, Si: 0.10–2.00%, Mn: 0.30–3.00%, P: less than 0.050%, S: less than 0.0100%, N: less than 0.010%, O: less than 0.010%, Ti: 0–0.100%, B: 0–0.0100%, Cr: 0–1.00%, Mo: 0–1.00%, Ni: 0–1.00%, Nb: 0–0.10%, Cu: 0–1.00%, V: 0–1.00%. Ca: 0-0.010%, Mg: 0-0.010%, Al: 0-1.00%, Sn: 0-1.00%, W: 0-1.00%, Sb: 0-1.00%, Zr: 0-1.00%, Co: 0-1.00%, and REM: 0-0.30%, with the remainder containing Fe and impurities. The steel plate substrate has a decarburized layer formed on the coated side, and the decarburized layer has an internal oxide layer formed on the coated side. The depth of the decarburized layer from the interface between the steel plate substrate and the coated side is 30 μm or more, and the depth of the internal oxide layer from the interface is less than 20 μm. No oxide scale is present between the steel plate substrate and the coated side containing Al and Fe.

[0637] According to element technology D, it is possible to provide steel components (including covered steel components) with high strength and excellent bending and weldability, and steel plates preferred as raw materials for such steel components.

[0638] Hereinafter, a preferred manufacturing method of a steel plate (the steel plate of this embodiment) and a steel component (including a covered steel component) (the steel component of this embodiment) according to an embodiment of element technology D will be described.

[0639] First, the steel plate used in this embodiment will be described. For example... Figure 32 As shown, the steel plate D10 of this embodiment includes: a base steel plate D11 having the chemical composition shown below; and an oxide scale D12 formed on the surface of the base steel plate D11 containing 80% by mass or more of Fe. Furthermore, the base steel plate D11 has a decarburized layer D13 of a predetermined depth on the interface side (the area in contact with the interface) with the oxide scale D12, and the decarburized layer D13 has an internal oxide layer D14 on the interface side between the base steel plate D11 and the oxide scale D12.

[0640] exist Figure 32 The diagram only shows a single-sided oxide scale, but oxide scale can also be formed on both sides. In this case, the decarburized layer D13 and the inner oxide layer D14 are formed in the area where the interface with the parent steel plate D11 is in contact with both sides of the oxide scale.

[0641] In this embodiment, "oxetine scale side" refers to "the oxide scale side in the thickness direction of the base steel plate", and "interface side with oxide scale" refers to "the interface side between the base steel plate and the oxide scale in the thickness direction of the base steel plate (the area in contact with the interface)".

[0642] <Base Material Steel Plate>

[0643] [Chemical Composition]

[0644] For the numerical range specified by the bracket "~" below, the values ​​at both ends are included as the lower and upper limits within the range. However, values ​​expressed as "more than" or "less than" are not included in the numerical range. Unless otherwise specified, the "%" for the content of each element refers to "mass %".

[0645] C: 0.10–0.65%

[0646] Carbon (C) is an element that improves the hardenability of steel and the strength of hot-stamped steel components (steel components obtained by hot stamping steel sheets). However, when the C content is below 0.10%, it becomes difficult to ensure sufficient strength (exceeding 1.0 GPa) in hot-stamped steel components. Therefore, the C content is set to 0.10% or more. The C content is preferably 0.15% or more, and more preferably 0.26% or more.

[0647] On the other hand, if the carbon content exceeds 0.65%, the strength of the hot-stamped steel component becomes excessively high, and the deterioration of its bending properties becomes significant. Furthermore, weldability also deteriorates. Therefore, the carbon content is set to 0.65% or less. Preferably, the carbon content is 0.60% or less.

[0648] Si: 0.10–2.00%

[0649] Si is an effective element for improving the hardenability of steel and ensuring stable strength in steel components after hot stamping. To achieve this effect, the Si content needs to be set to 0.10% or more. The Si content is preferably 0.35% or more.

[0650] On the other hand, if the Si content in the steel sheet exceeds 2.00%, the heating temperature required for austenitic phase transformation during heat treatment becomes significantly higher. This sometimes increases the cost of heat treatment. Furthermore, if the Si content exceeds 2.00%, the toughness of the quenched portion deteriorates. Therefore, the Si content is set to 2.00% or less. Preferably, the Si content is 1.60% or less.

[0651] Mn: 0.30~3.00%

[0652] Manganese (Mn) is a highly effective element for improving the hardenability of steel and ensuring stable strength in hot-stamped steel components. Mn also lowers the Ac3 point and promotes lower quenching temperatures. Furthermore, Mn has the effect of improving corrosion resistance through diffusion in Al-Fe coatings. These effects are insufficient when the Mn content is below 0.30%, therefore the Mn content is set to 0.30% or more. The preferred Mn content is 0.40% or more.

[0653] On the other hand, if the Mn content exceeds 3.00%, the above-mentioned effects saturate, and the toughness and flexibility of the quenched part deteriorate. Therefore, the Mn content is set to 3.00% or less. The Mn content is preferably 2.80% or less, and more preferably 2.50% or less.

[0654] P: below 0.050%

[0655] Phosphorus (P) is an element that degrades the toughness of hot-stamped steel components. In particular, if the P content exceeds 0.050%, the degradation of toughness becomes significant. Therefore, the P content is limited to 0.050% or less. The P content is preferably limited to 0.005% or less. The P content is preferably low, and therefore can be 0%, but from a cost perspective, it can also be set to 0.001% or more.

[0656] S: below 0.0100%

[0657] Sulfur (S) is an element that degrades the toughness and bending properties of hot-stamped steel components. In particular, if the S content exceeds 0.0100%, the degradation of toughness and bending properties becomes significant. Therefore, the S content is limited to 0.0100% or less. The S content is preferably limited to 0.0050% or less. The S content is preferably low, and therefore can be 0%, but from a cost perspective, it can also be set to 0.0001% or more.

[0658] N: below 0.010%

[0659] Nitrogen (N) is an element that degrades the toughness of hot-stamped steel components. In particular, if the N content exceeds 0.010%, coarse nitrides form in the steel, significantly worsening toughness. Therefore, the N content is set below 0.010%. While a specific lower limit for the N content is not necessary, and it could be 0%, setting the N content below 0.0002% would increase steelmaking costs, which is not economically preferable. Therefore, the N content can also be set above 0.0002% or above 0.0008%.

[0660] O: below 0.010%

[0661] Oxygen (O) is an element that degrades the toughness of hot-stamped steel components. In particular, if the O content exceeds 0.010%, coarse oxides form in the steel, significantly worsening toughness. Therefore, the O content is set below 0.010%. While a specific lower limit for the O content is not necessary, and it could be 0%, setting the O content below 0.0002% would increase steelmaking costs, which is not economically preferable. Therefore, the O content can also be set above 0.0002% or above 0.0008%.

[0662] To improve the strength, toughness, bending performance, corrosion resistance, and deoxidation properties of the steel components in this embodiment, in addition to the elements mentioned above, one or more elements selected from the following: Ti, B, Cr, Mo, Ni, Nb, Cu, V, Ca, Mg, Al, Sn, W, Sb, Zr, Co, and REM. These elements are optional and not mandatory; therefore, the lower limit is 0%.

[0663] Ti: 0~0.100%

[0664] Ti is an element that inhibits recrystallization during heat treatment of steel sheets at temperatures above Ac3 and forms fine carbides to suppress grain growth, thereby producing fine-grained austenite grains. Therefore, by including Ti, the toughness of hot-stamped steel components can be significantly improved. Furthermore, Ti preferentially combines with nitrogen in the steel to suppress boron consumption caused by boron (BN) precipitation and promotes the improved hardenability (described later) due to boron. Therefore, Ti can also be included. To fully obtain the above effects, the Ti content is preferably set to 0.010% or more. More preferably, the Ti content is 0.020% or more.

[0665] On the other hand, if the Ti content exceeds 0.100%, the amount of TiC precipitation increases, thus consuming C, and consequently reducing the strength of the steel component after hot stamping. Therefore, the Ti content is set to 0.100% or less. The Ti content is preferably 0.080% or less.

[0666] B: 0~0.0100%

[0667] Boron (B) is an element that significantly improves the hardenability of steel, even in trace amounts. Furthermore, B enhances toughness by strengthening grain boundaries through segregation at grain boundaries and inhibits austenite grain growth during steel sheet heating. Therefore, B may be included. To fully obtain the above-mentioned effects, the B content is preferably set to 0.0010% or more. More preferably, the B content is 0.0020% or more.

[0668] On the other hand, if the boron content exceeds 0.0100%, large amounts of coarse compounds precipitate out, deteriorating the toughness of the steel component after hot stamping. Therefore, in the case of boron content, the boron content is set to 0.0100% or less. The boron content is preferably 0.0080% or less.

[0669] Cr: 0–1.00%

[0670] Cr is an effective element for improving the hardenability of steel and ensuring the stable strength of steel components after hot stamping. Therefore, Cr may be included. To achieve the above-mentioned effects, the Cr content is preferably set to 0.01% or more. The Cr content is more preferably 0.05% or more, and even more preferably 0.08% or more.

[0671] On the other hand, if the Cr content exceeds 1.00%, the aforementioned effects become saturated, and costs increase. Furthermore, Cr has a stabilizing effect on iron carbides; therefore, if the Cr content exceeds 1.00%, large iron carbides may remain undissolved during steel sheet heating, leading to a deterioration in the toughness of the hot-stamped steel component. Therefore, in cases where Cr is present, the Cr content is set to 1.00% or less. The Cr content is preferably 0.80% or less.

[0672] Mo: 0–1.00%

[0673] Mo is an effective element for improving the hardenability of steel and ensuring the stable strength of steel components after hot stamping. Therefore, it may contain Mo. To achieve the above-mentioned effects, the Mo content is preferably set to 0.01% or more. The Mo content is more preferably 0.05% or more.

[0674] On the other hand, if the Mo content exceeds 1.00%, the aforementioned effects become saturated, and costs increase. Furthermore, Mo has a stabilizing effect on iron carbides; therefore, if the Mo content exceeds 1.00%, large iron carbides may remain undissolved during steel sheet heating, leading to a deterioration in the toughness of the hot-stamped steel component. Therefore, in cases where Mo is present, the Mo content is set to 1.00% or less. The Mo content is preferably 0.80% or less.

[0675] Ni: 0~1.00%

[0676] Ni is an effective element for improving the hardenability of steel and ensuring the stable strength of steel components after hot stamping. Therefore, Ni may be included. To achieve the above-mentioned effects, it is preferable to set the Ni content to 0.01% or more. More preferably, the Ni content is 0.10% or more.

[0677] On the other hand, if the Ni content exceeds 1.00%, the above-mentioned effect saturates, and the economic efficiency decreases. Therefore, in the case of Ni, the Ni content is set to 1.00% or less.

[0678] Nb: 0–0.10%

[0679] Nitrogen (Nb) is an element that forms fine carbides, thereby improving the toughness of steel through its grain-refining effect. Therefore, Nb may be included in steel. To fully obtain the above-mentioned effects, it is preferable to set the Nb content to 0.02% or more. More preferably, the Nb content is 0.03% or more.

[0680] On the other hand, if the Nb content exceeds 0.10%, the carbides become coarse, and the toughness of the steel component deteriorates. Therefore, the Nb content is set to 0.10% or less. The Nb content is preferably 0.08% or less.

[0681] Cu: 0~1.00%

[0682] Cu is an effective element for improving the hardenability of steel and ensuring the stable strength of steel components after hot stamping. Therefore, Cu may be included. In addition, Cu is an element that improves the corrosion resistance of steel components. To obtain the above effects, it is preferable to set the Cu content to 0.01% or more. The Cu content is more preferably 0.05% or more.

[0683] On the other hand, if the Cu content exceeds 1.00%, the above-mentioned effects become saturated, and the cost increases. Therefore, in cases containing Cu, the Cu content is set to 1.00% or less. The Cu content is preferably 0.80% or less.

[0684] V: 0~1.00%

[0685] V is an element that forms fine carbides, thereby improving the toughness of steel through its grain-refining effect. Therefore, V may be included. To achieve the above-mentioned effect, it is preferable to set the V content to 0.01% or more. The V content is more preferably 0.10% or more.

[0686] On the other hand, if the vitamin C content exceeds 1.00%, the aforementioned effects become saturated, thus reducing economic efficiency. Therefore, in cases containing vitamin C, the vitamin C content is set to 1.00% or less.

[0687] Ca: 0–0.010%

[0688] Ca is an element that can refine inclusions in steel and improve toughness after hot stamping. Therefore, it may contain Ca. To obtain the above-mentioned effects, it is preferable to set the Ca content to 0.001% or more. The Ca content is more preferably 0.002% or more.

[0689] On the other hand, if the Ca content exceeds 0.010%, its effect saturates, and the cost increases. Therefore, in the case of Ca, the Ca content is set to 0.010% or less. The Ca content is preferably 0.005% or less, and more preferably 0.004% or less.

[0690] Mg: 0–0.010%

[0691] Mg is an element that can refine inclusions in steel and improve the toughness of steel components after hot stamping. Therefore, Mg may be included. To obtain the above-mentioned effects, it is preferable to set the Mg content to 0.001% or more. More preferably, the Mg content is 0.002% or more.

[0692] On the other hand, if the Mg content exceeds 0.010%, its effect becomes saturated, and the cost increases. Therefore, in cases where Mg is present, the Mg content is set to 0.010% or less. The Mg content is preferably 0.005% or less, and more preferably 0.004% or less.

[0693] Al: 0~1.00%

[0694] Al is an element commonly used as a deoxidizer for steel. Therefore, it can be contained in steel. To achieve the aforementioned effects, it is preferable to set the Al content to 0.01% or more.

[0695] On the other hand, if the Al content exceeds 1.00%, the aforementioned effect becomes saturated, thus reducing economic efficiency. Therefore, in cases containing Al, the Al content is set to 1.00% or less.

[0696] Sn: 0~1.00%

[0697] Sn is an element that improves corrosion resistance in corrosive environments. Therefore, it is also possible to include Sn. To achieve the above-mentioned effects, it is preferable to set the Sn content to 0.01% or more.

[0698] On the other hand, if the Sn content exceeds 1.00%, the grain boundary strength decreases, and the toughness of the steel component after hot stamping deteriorates. Therefore, in the case of Sn, the Sn content is set to be below 1.00%.

[0699] W: 0~1.00%

[0700] W is an element that can improve the hardenability of steel and stably ensure the strength of steel components after hot stamping. Therefore, it may contain W. In addition, W is an element that improves corrosion resistance in corrosive environments. To obtain the above effects, it is preferable to set the W content to 0.01% or more.

[0701] On the other hand, if the W content exceeds 1.00%, the aforementioned effect saturates, thus reducing economic efficiency. Therefore, in cases containing W, the W content is set to 1.00% or less.

[0702] Sb: 0~1.00%

[0703] Sb is an element that improves corrosion resistance in corrosive environments. Therefore, it may contain Sb. To achieve the above-mentioned effects, it is preferable to set the Sb content to 0.01% or more.

[0704] However, if the Sb content exceeds 1.00%, the grain boundary strength decreases, and the toughness of the steel component after hot stamping deteriorates. Therefore, in the case of Sb, the Sb content is set to below 1.00%.

[0705] Zr: 0~1.00%

[0706] Zr is an element that improves corrosion resistance in corrosive environments. Therefore, it may contain Zr. To achieve the above-mentioned effects, it is preferable to set the Zr content to 0.01% or more.

[0707] On the other hand, if the Zr content exceeds 1.00%, the grain boundary strength decreases, and the resistance to hydrogen embrittlement of the steel components after hot stamping decreases. Therefore, in the case of Zr, the Zr content is set to below 1.00%.

[0708] Co: 0~1.00%

[0709] Co is an element that improves corrosion resistance in corrosive environments. Therefore, it may contain Co. To achieve the above-mentioned effects, it is preferable to set the Co content to 0.01% or more.

[0710] On the other hand, if the Co content exceeds 1.00%, the aforementioned effect becomes saturated, thus reducing economic efficiency. Therefore, in cases containing Co, the Co content is set to 1.00% or less.

[0711] REM: 0–0.30%

[0712] REM, like Ca, is an element that refines inclusions in steel and improves the toughness of steel components after hot stamping. Therefore, REM may also be included. To achieve the above-mentioned effects, it is preferable to set the REM content to 0.01% or more. The REM content is more preferably 0.02% or more.

[0713] On the other hand, if the REM content exceeds 0.30%, its effect becomes saturated, and the cost increases. Therefore, in cases containing REM, the REM content is set to 0.30% or less. The REM content is preferably 0.20% or less.

[0714] Here, REM refers to a total of 17 elements, including Sc, Y, and lanthanide elements such as La and Nd. The REM content refers to the total content of these elements. REM is added to molten steel, for example, using an Fe-Si-REM alloy, which may contain elements such as La, Nd, Ce, and Pr.

[0715] In the chemical composition of the base steel plate of the steel plate in this embodiment, apart from the elements mentioned above, the remaining part is Fe and impurities.

[0716] Here, "impurities" refers to components that are mixed in during the industrial manufacturing of steel plates through raw materials such as ores and waste, as well as various factors in the manufacturing process, and are permitted within a range that does not adversely affect the characteristics of the steel plate or the steel component of this embodiment.

[0717] The chemical composition of the base steel plate can be determined using the following methods.

[0718] Analytical samples were cut from the base steel plate and obtained by elemental analysis, including ICP (inductively coupled plasma) luminescence spectrophotometry. C and S were determined using the combustion-infrared absorption method, N using the inert gas melting-thermal conductivity method, and O using the inert gas melting-non-dispersive infrared absorption method.

[0719] The analytical samples were collected as described in JIS G 0417:1999, in a manner that yielded the average chemical composition of the entire thickness of the base steel plate. Specifically, the analytical samples were collected from a position one-quarter of the thickness of the plate in the thickness direction, avoiding the ends of the base steel plate in the width direction.

[0720] [Decarburized layer]

[0721] [Internal Oxide Layer]

[0722] like Figure 32 As shown, the steel plate D10 of this embodiment has a decarburized layer D13 on the oxide scale D12 side (the interface side between the base steel plate D11 and the oxide scale D12). That is, a portion of the oxide scale D12 side of the base steel plate D11 is the decarburized layer D13. Furthermore, the decarburized layer D13 has an internal oxide layer D14 on the oxide scale D12 side. That is, a portion of the oxide scale D12 side of the decarburized layer D13 is the internal oxide layer D14. The depth of the internal oxide layer D14 in the thickness direction section from the interface between the base steel plate D11 and the oxide scale D12 (distance in the thickness direction from the interface) is less than 30 μm. The depth of the decarburized layer D13 in the thickness direction section from the interface between the base steel plate D11 and the oxide scale D12 (distance in the thickness direction from the interface) is 90 μm or more.

[0723] In steel components obtained by hot stamping of steel plates, decarburizing and softening the surface layer is extremely effective in improving bending resistance. Since the stress and strain generated are greater on the outermost surface layer during bending deformation, softening the surface layer increases the failure limit, thereby improving bending resistance.

[0724] In the steel plate D10 of this embodiment, in order to form a decarburized layer on the surface of the hot-stamped steel component, a decarburized layer D13 with a depth (thickness) of 90 μm or more is formed on the interface side between the base steel plate D11 and the oxide scale D12 (described later). When the depth (thickness) of the decarburized layer D13 is less than 90 μm, a sufficiently deep decarburized layer will not be formed in the steel plate substrate of the hot-stamped steel component, and the bending of the steel component will decrease. Hot stamping causes recarburization on the surface of the base steel plate, reducing the depth of the decarburized layer. However, by setting the decarburized layer depth of the base steel plate D11 to 90 μm or more, it is possible to set the decarburized layer depth of the hot-stamped steel component to 60 μm or more under normal hot stamping conditions.

[0725] As mentioned above, a known technique for decarburizing the surface of steel sheets is annealing the steel sheet at a high dew point and using H2O in an atmosphere for decarburization (high dew point annealing). However, the inventors of this invention conducted research and found that, under such high dew point annealing conditions, internal oxidation (oxidation of easily oxidizable elements such as Si and Mn in the steel) that occurs simultaneously with decarburization causes various problems. Specifically, it has been found that in steel components obtained by hot stamping, sometimes an oxide scale (internal oxide scale) is generated inside the steel sheet during hot stamping, starting from an internal oxide layer, and this oxide scale generated inside the steel sheet hinders weldability.

[0726] The inventors of this invention conducted further research and discovered that by setting the depth of the internal oxide layer D14 in the steel sheet (base steel sheet D11) supplied for hot stamping to less than 30 μm, the formation of oxide scale inside the steel sheet during hot stamping can be suppressed. Therefore, in the steel sheet D10 of this embodiment, the depth (thickness) of the internal oxide layer D14 of the base steel sheet D11 from the interface between the base steel sheet D11 and the oxide scale D12 is set to less than 30 μm.

[0727] The depth of the internal oxide layer is preferably less than 5 μm. In this case, flexibility becomes even more advantageous.

[0728] To ensure the depth of the decarburized layer 13 and to suppress the depth of the internal oxide layer D14, the annealing conditions need to be controlled as described later.

[0729] Furthermore, the ratio of the depth (thickness) of the decarburized layer to the depth (thickness) of the inner oxide layer preferably satisfies a relationship of 3 or more (thickness of the decarburized layer / thickness of the inner oxide layer ≥ 3). In this case, the flexibility described later becomes even more advantageous. More preferably, the above ratio is 10 or more. More preferably, the above ratio is 20 or more.

[0730] The depth of the decarburized layer D13 from the interface between the base steel plate D11 and the oxide scale D12 can be determined using GDS using the following method.

[0731] GDS (Glow Discharge Analysis) is performed along the thickness direction from the surface of the steel plate to determine the depth of the decarburized layer. GDS measurements are taken at intervals of 50 nm or less, starting from a position 1 / 4 of the plate width away from the end of the steel plate in the width direction, moving from the surface (surface of the oxide scale) towards the thickness direction. The position where the Fe content begins to reach 95% or more is defined as the interface between the base steel plate and the oxide scale. Furthermore, the position where the C content obtained through GDS analysis is located at the aforementioned position 1 / 4 of the plate thickness away from the surface of the base steel plate is defined as the deepest point of the decarburized layer. The distance from the interface between the base steel plate and the oxide scale to the deepest point of the decarburized layer is defined as the depth of the decarburized layer from the interface between the base steel plate and the oxide scale (the thickness of the decarburized layer). The above measurements are performed 5 times at different locations, and the average of the 5 measurements is defined as the depth of the decarburized layer of the steel plate in this embodiment from the interface between the base steel plate and the oxide scale (also called the total decarburization depth).

[0732] When the decarburized layer is deeper than the GDS measurement limit, the depth of the decarburized layer can also be determined by microscopic observation as described in JIS G 0558 (2007). In this case, a cross-sectional sample is collected at a position 1 / 4 of the plate width (width) from the end of the steel plate in the width direction. The sample is etched with nitric acid ethanol, and the cross-section is observed using an optical microscope. The depth of the microstructure at a position equal to 1 / 4 of the plate thickness from the surface (interface with the oxide scale) of the base steel plate is measured, and the depth at this position is set as the depth of the decarburized layer. The measurement is performed 5 times at different locations, and the average of the 5 measurements is set as the depth of the decarburized layer.

[0733] The depth of the internal oxide layer at the interface between the base steel plate and the oxide scale is determined by SEM (scanning electron microscope) observation of the steel plate cross-section.

[0734] A cross-sectional sample was collected at a position one-quarter of the plate width from the end of the steel plate in the width direction, and a COMPO image was observed using SEM. Regarding internal oxidation, it occurs deeper at the grain boundaries compared to within the grains, and is reflected darker in the COMPO image than in the constant portion (high Fe content) of the base steel plate. Therefore, the internal oxide layer was determined by the difference in color, and the depth of the deepest internal oxide layer was measured at the interface between the base steel plate and the oxide scale. This measurement was performed five times at different locations, and the average of the five measurements was set as the depth of the distance between the internal oxide layer and the oxide scale interface of the steel plate in this embodiment.

[0735] [Oxide Skin]

[0736] The steel sheet of this embodiment has an oxide scale formed on the surface of the base steel sheet. As described later, the steel sheet of this embodiment effectively utilizes the oxygen (O) from the oxide scale formed on the surface of the base steel sheet during rolling or the like to decarburize the base steel sheet. Therefore, regarding the oxide scale after decarburization, the O content is significantly reduced compared to the typical oxide scale formed during hot rolling or the like, which is composed of FeO, Fe2O3, Fe3O4, etc., and becomes more than 80% Fe by mass%.

[0737] That is, by decarburizing under conditions where the Fe content of the oxide scale is 80% or more, steel plates with the aforementioned depth of internal oxide layer and decarburized layer can be obtained.

[0738] In other words, the oxide scale may be removed or peeled off during processing, but it can also be considered that steel plates with an internal oxide layer and decarburized layer depth within the above range have an oxide scale equivalent to that of the steel plate of this embodiment.

[0739] Furthermore, considering the supply of oxygen for decarburization, the thickness of the oxide scale is preferably set to 5 μm or more. More preferably, it is 8 μm or more, and even more preferably, it is 10 μm or more. Considering the yield of the steel sheet, the thickness of the oxide scale is preferably less than 100 μm. More preferably, it is 50 μm or less or 30 μm or less.

[0740] The oxide scale of the steel plate in this embodiment preferably comprises: a first region containing at least 80% Fe and at least 0.1% and less than 3.0% Si by mass; and a second region containing at least 65% and less than 80% Fe and at least 0.8% and less than 7.5% Mn. It is preferable that the scale is substantially formed by the first and second regions. However, the oxide scale may sometimes also contain impurities, oxides mainly composed of Cr and Si, or elemental substances of difficult-to-oxidize elements such as Cu as "other regions" on the outermost layer.

[0741] By having an oxide scale with such a structure, the current limit at which spatter occurs can be increased during spot welding when assembling the vehicle body, resulting in a steel sheet with a wide appropriate current range and good weldability.

[0742] In region 1, in addition to Fe, Si, and O, C, Ni, Cr, Mo, etc. are sometimes also included. In region 2, in addition to Fe, Mn, and O, C, Ni, etc. are sometimes also included.

[0743] In the presence of a first region and a second region, the second region typically takes the following form: it exists as an island within the first region, which serves as the matrix. There are cases where the second region is dispersed as islands, and cases where several islands are combined. In either case, the first and second regions can be distinguished using methods described later.

[0744] The Fe content of the oxide scale is determined using the following method. GDS (Glow Discharge Analysis) is performed from the surface along the thickness direction at a position one-quarter of the width of the steel plate, extending from the end in the width direction. The Fe and O contents of the oxide scale are then determined. Areas with an O content of 0.1% or higher are removed as impurities. The average Fe content in areas with an O content below 0.1% is measured from the surface. This measurement is performed five times at different locations, and the average of the five measurements is taken as the Fe content of the oxide scale.

[0745] The Fe and Si contents in region 1 of the oxide scale, and the Fe and Mn contents in region 2, were determined using SEM (Scanning Electron Microscopy) and an electron probe microanalyzer (EPMA). Samples were collected at a position one-quarter of the width of the steel plate from its width-direction end, with the thickness-direction of the steel plate observable. For this sample, a COMPO image was obtained using a scanning electron microscope to confirm the presence of two contrasting microstructures constituting the oxide scale. Region 1, containing more Fe (a heavy element) than Region 2, was observed brighter. Therefore, the relatively bright region was designated as Region 1, and the relatively dark region as Region 2. Elemental analysis of the two microstructures (Regions 1 and 2) using an electron probe microanalyzer (EPMA) with a beam diameter of less than 1 μm was performed to determine the Fe and Si contents in Region 1 and the Fe and Mn contents in Region 2. During the measurement, analyses were performed at 10 points, and the average value was set as the Fe and Si content in region 1 of the oxide scale and the Fe and Mn content in region 2. Oxide scale may also include "other regions" as described above. Regions containing 10% by mass or more of Cr, Si, or Cu are defined as the aforementioned "other regions".

[0746] The thickness of the oxide scale was determined using SEM. A cross-sectional sample was collected at a position 1 / 4 of the width of the steel plate from its width-direction end, and composite images were obtained using SEM. The thickness of the oxide scale at 10 locations where it had not peeled off was measured, and the average value was set as the thickness of the oxide scale.

[0747] <Steel Components>

[0748] like Figure 33 As shown, the steel component D110 of this embodiment includes: a steel plate substrate D111 having a predetermined chemical composition; and an oxide scale D112 formed on the surface of the steel plate substrate D111 containing 70% by mass or more of Fe. Furthermore, the steel plate substrate D111 has a decarburized layer D113 formed at a predetermined depth on the oxide scale D112 side (the interface side with the oxide scale D112), and this decarburized layer D113 has an internal oxide layer D114 formed on the oxide scale D112 side.

[0749] In addition, the steel component D110 of this embodiment can be obtained by subjecting the steel plate D10 of this embodiment to heat treatment (and processing) such as hot stamping.

[0750] In the figure, the steel component D110 of this embodiment is shown in the form of a flat plate, but the component obtained by hot stamping is not limited to a flat plate.

[0751] [Chemical Composition]

[0752] Since the chemical composition of the steel plate does not change substantially through hot stamping, the chemical composition of the steel plate substrate D111 of the steel component D110 in this embodiment is the same as the chemical composition of the parent steel plate D11 of the steel plate D10 in this embodiment, and can be measured by the same measurement method as the parent steel plate.

[0753] [Decarburized layer]

[0754] [Internal Oxide Layer]

[0755] In this embodiment, the steel component D110 has a decarburized layer at the interface between the steel substrate D111 and the oxide scale D112, and an internal oxide layer D114 at the interface between the decarburized layer D113 and the oxide scale D112. Furthermore, the depth of the decarburized layer D113 from the interface between the steel substrate D111 and the oxide scale D112 is 60 μm or more, and the depth of the internal oxide layer D114 from the interface between the steel substrate D111 and the oxide scale D112 is less than 40 μm.

[0756] In steel components, decarburizing and softening the surface layer is extremely effective in improving bending resistance. The further the bending deformation extends from the surface layer, the greater the stress and strain generated. Therefore, by softening the surface layer, the failure limit can be increased, thereby improving bending resistance.

[0757] If the depth (thickness) of the decarburized layer D113 formed on the surface of the steel member D110 in this embodiment is 60 μm or more, the flexibility is improved. Therefore, the depth of the decarburized layer D113 from the interface between the steel plate substrate D111 and the oxide scale D112 is set to 60 μm or more.

[0758] Furthermore, in steel components, if the depth of the internal oxide layer exceeds 40 μm, the weldability will decrease due to the oxide scale generated inside the steel sheet during hot stamping. Therefore, the depth of the internal oxide layer D114 is set to be less than 40 μm.

[0759] Oxidized Skin

[0760] The steel component D110 of this embodiment has an oxide scale D112 formed on the surface of the steel sheet substrate D111. The steel component D110 of this embodiment is obtained by hot stamping a steel sheet having an oxide scale containing 80% by mass or more of Fe. Although the oxide scale undergoes surface oxidation due to hot stamping, the oxide scale D112 of the steel component D110 of this embodiment contains 70% by mass or more of Fe.

[0761] In another embodiment of element technology D, the steel component can also be a coated steel component, which is obtained by: subjecting the steel plate of this embodiment described above to pickling or the like to remove the oxide scale on the surface, forming an Al-containing coating or the like to produce a coated steel plate, and subjecting the coated steel plate to heat treatment such as hot stamping.

[0762] In this case, such as Figure 34 As shown, in another embodiment of element technology D, the steel component (coated steel component) D210 has a steel plate substrate D211 and an Al and Fe-containing coating D215 formed on the surface of the steel plate substrate D211, with no oxide scale between the steel plate substrate D211 and the Al and Fe-containing coating D215.

[0763] In addition, the steel plate substrate D211 has a decarburized layer D213 formed on the side covered by D215, the decarburized layer D213 has an internal oxide layer D214 formed on the side covered by D215, the depth of the decarburized layer D213 from the interface between the steel plate substrate D211 and the covered by D215 is more than 30 μm, and the depth of the internal oxide layer D214 from the interface between the steel plate substrate D211 and the covered by D215 is less than 20 μm.

[0764] If the depth (thickness) of the decarburized layer D213 is 30 μm or more, the flexibility is improved. Conversely, if the depth of the inner oxide layer D214 is less than 20 μm, the weldability is improved.

[0765] In the case of coated steel components, the depth of the decarburized layer and the depth of the internal oxide layer are different because the surface oxidation state during heat treatment such as hot stamping is different from that of the aforementioned steel components without coating.

[0766] <Manufacturing Method>

[0767] Regardless of the manufacturing method, the steel plate and steel components of this embodiment can achieve the desired effect as long as they possess the aforementioned characteristics. However, a manufacturing method that includes the following steps (I) to (IV) for the steel plate and (I) to (V) for the steel components can be manufactured stably and is therefore preferred.

[0768] (I) Steel billet manufacturing process for producing steel billets with a specified chemical composition

[0769] (II) Hot rolling process of heating and hot rolling the above-mentioned steel billet to produce hot-rolled steel plate

[0770] (III) The coiling process of coiling the above-mentioned hot-rolled steel sheet to form hot-rolled coil.

[0771] (IV) The hot-rolled coil with the hot-rolled oxide scale formed is subjected to a box annealing (BAF) annealing process.

[0772] (V) A blank of a specified size is cut from the hot-rolled coil after the above annealing process and subjected to heat treatment to obtain the heat treatment process of the steel component.

[0773] The following describes each process. Processes and conditions not described below can be performed using appropriately known methods.

[0774] (I) Steel billet manufacturing process

[0775] In the billet manufacturing process, steel billets such as slabs having the aforementioned preferred chemical composition are manufactured. This can be achieved by continuously casting or similar methods using molten steel with the specified chemical composition under known conditions.

[0776] (II) Hot rolling process

[0777] In the hot rolling process, hot-rolled steel sheets are produced by heating and hot rolling the obtained steel billets. During the hot rolling process, an oxide scale (hot-rolled oxide scale) is formed on the surface of the steel sheet.

[0778] There are no particular limitations on hot rolling conditions; they can be set appropriately within the known range of conditions based on the required characteristics of the steel plate.

[0779] (III) Winding process

[0780] In the coiling process, the hot-rolled steel sheet obtained in the hot rolling process is coiled into a coil shape to produce hot-rolled coil.

[0781] There are no special restrictions on winding temperature and other conditions.

[0782] (IV) Annealing process

[0783] In the annealing process, for hot-rolled coils with hot-rolled oxide scale formed on the surface, box annealing (BAF) is performed without removing the oxide scale (in the so-called black scale state).

[0784] During annealing, the annealing atmosphere is set to an inert gas atmosphere (N2 atmosphere, H2 atmosphere, etc.), and annealing is carried out at 650–900°C for 4–16 hours. In conventional decarburization annealing, high dew point annealing is performed, using H2O in the atmosphere as the decarburization source. In contrast, in this embodiment, decarburization is carried out by annealing hot-rolled coils with hot-rolled oxide scale, thereby using O in the oxide scale as the decarburization source. Specifically, decarburization occurs by the reaction of C in the outermost layer of the base steel plate with O in the oxide scale to become CO gas. Furthermore, insufficient C is then supplied from the interior of the base steel plate to the outermost layer, where it becomes CO gas, further advancing the decarburization reaction. At this time, O in the oxide scale is consumed, and the Fe content in the oxide scale increases.

[0785] However, if the annealing temperature is below 650°C or the annealing time is less than 4 hours, decarburization will not be sufficient. On the other hand, if the annealing temperature exceeds 900°C or the annealing time exceeds 16 hours, the reduction reaction of the oxide scale ends, and carbon continues to be supplied from the interior of the steel plate to the surface, resulting in shallow decarburization. Furthermore, if the generated CO gas remains around the oxide scale, further decarburization will not occur, and a deep decarburized layer cannot be obtained. Therefore, in the steel plate manufacturing method of this embodiment, it is important to move the gas within the annealing furnace to prevent the generated CO gas from remaining around the oxide scale. Specifically, this is achieved by installing a fan or similar device within the annealing furnace and setting its airflow to 250 m³ / h. 3 An airflow rate of at least 100 m³ / h is sufficient to ensure adequate flow within the annealing furnace for the decarburization reaction. An airflow rate below 250 m³ / h is also acceptable. 3 At a speed of [insert speed here], the retention of CO gas around the oxide scale cannot be sufficiently suppressed, resulting in incomplete decarburization. The air volume is set to the air volume around the hot-rolled coil, or multiple fans can be set according to the size of the annealing furnace to obtain the specified air volume. The preferred dimensions of the hot-rolled coil are: thickness less than 9mm, width less than 2100mm, diameter less than 2000mm, and weight of one coil less than 30 tons.

[0786] Compared to using H2O in the atmosphere as the decarburization source in high dew point annealing, when using O in the oxide scale as the decarburization source, the O from the decarburization source does not easily penetrate into the interior of the base steel plate, resulting in less internal oxidation.

[0787] That is, by applying the hot-rolled coil in its black-skinned state as described above to an inert gas atmosphere at an airflow rate of 250m³, 3 By supplying air at a rate of 1 / hour or more for box annealing, the desired decarburized layer depth, internal oxide layer depth, and Fe content in the oxide scale as described in the steel sheet of this embodiment can be obtained.

[0788] (V) Heat treatment process

[0789] In the heat treatment process, blanks of a specified size are cut from the hot-rolled coil after the annealing process, and the blanks are heat-treated to make steel components.

[0790] The heat treatment is preferably carried out under the following conditions: heating to Ac3 point to (Ac3 point + 300)℃ at an average heating rate of 1.0 to 1000℃ / second, and cooling to Ms point (℃) or below at an average cooling rate of at least the upper critical cooling rate.

[0791] If the heating rate is less than 1.0 °C / s, the productivity of heat treatment decreases, which is therefore undesirable. On the other hand, if the heating rate exceeds 1000 °C / s, a mixed-particle structure is formed, resulting in a decrease in the limiting hydrogen content, which is also undesirable.

[0792] Furthermore, if the heat treatment temperature is below the Ac3 point (°C), ferrite will remain after cooling, resulting in lower strength, which is therefore undesirable. On the other hand, if the heat treatment temperature exceeds (Ac3 point + 300)°C, the microstructure will become coarse-grained, thereby reducing the limiting hydrogen content, which is also undesirable.

[0793] The upper critical cooling rate refers to the minimum cooling rate at which austenite is supercooled to form martensite without precipitating ferrite and pearlite in the microstructure. If cooling is performed at an average cooling rate lower than the upper critical cooling rate, ferrite and pearlite will be formed, resulting in insufficient strength.

[0794] During heating, the temperature can be maintained for 1 to 300 seconds within a range of ±10°C.

[0795] In addition, after cooling to a temperature below Ms point, tempering treatment can be performed in a temperature range of about 100 to 600°C to adjust the strength of the steel.

[0796] During this heat treatment, processing can also be performed simultaneously. That is, so-called hot stamping can also be performed.

[0797] Alternatively, the steel component (including the covered steel component) in this embodiment may also be a steel component with different strength regions obtained by hot forming or heat treating a portion of a steel plate that serves as raw material.

[0798] (VI) Pickling, cold rolling and coating

[0799] When steel components are made into coated steel components, hot-rolled coils can be pickled and cold-rolled between the annealing and heat treatment processes to form an Al-containing coating on the surface.

[0800] In this case, pickling, cold rolling, and coating can be performed under known conditions. If the oxide scale is not sufficiently removed during pickling, shot peening can be performed before pickling to mechanically promote its removal. For example, a shot peening grit size of #60 can be used.

[0801] (Example)

[0802] First, steel with the chemical composition shown in Table 13 is melted to obtain a hot-rolled slab.

[0803] <Example 1>

[0804] The obtained slab is hot-rolled to produce a hot-rolled steel plate with a thickness of 3.2 mm and a width of 1000 mm. The hot-rolled steel plate is then coiled at a temperature below 800℃ to produce a hot-rolled coil with a diameter of 1700 mm and a weight of 14 tons per coil.

[0805] The obtained hot-rolled coils were subjected to box annealing under the conditions (temperature, time, air volume) recorded in Tables 14 to 16. The annealing atmosphere was set to nitrogen.

[0806] [Table 13]

[0807]

[0808] [Table 14]

[0809]

[0810] [Table 15]

[0811]

[0812] [Table 16]

[0813]

[0814] Steel plates (bills) of specified dimensions were cut from the annealed hot-rolled coils. GDS (Glow Discharge Luminescence Analysis), SEM (Sequencing Electron Microscopy), EPMA (Electroluminescence Spectroscopy), and optical microscopy were performed using the methods described above to evaluate the decarburized layer depth, internal oxide layer depth, oxide scale thickness, and Fe content of the oxide scale. Furthermore, the Fe and Si contents in the first region and the Fe and Mn contents in the second region constituting the oxide scale were evaluated using the methods described above. The evaluation results are shown in Tables 2-1 to 2-3.

[0815] In addition, the chemical composition of the steel plate at a position 1 / 4 of the plate thickness away from the surface in the thickness direction is the same as that of the slab.

[0816] <Example 2>

[0817] The steel plates shown in Tables 14 to 16 were subjected to heat treatment under the conditions shown in Tables 17 to 19 to obtain steel components.

[0818] The obtained steel components are cut and subjected to GDS (glow discharge luminescence analysis), SEM, and optical microscopy observations using the above-mentioned techniques to determine the decarburized layer depth, internal oxide layer depth, and Fe content of the oxide scale.

[0819] The results are shown in Tables 17 to 19.

[0820] In addition, the obtained steel components are evaluated by tensile tests, bending tests, and spot welding tests using the following methods to evaluate tensile strength, bending properties, and weldability (within the appropriate welding current range).

[0821] <Tensile Strength>

[0822] The tensile test was performed in accordance with ASTM standard E8.

[0823] After grinding the homogenized section of the steel component to a thickness of 1.2 mm, half-size plate test pieces (parallel section length: 32 mm, parallel section width: 6.25 mm) of ASTM standard E8 were collected with the test direction parallel to the rolling direction. Then, room temperature tensile tests were performed at a strain rate of 3 mm / min to determine the tensile strength (maximum strength).

[0824] In this embodiment, a tensile strength exceeding 1000 MPa is evaluated as high strength.

[0825] <Flexibility>

[0826] The bending test was conducted according to VDA238-100. Bending test pieces were collected from the homogenization zone of the steel member, 60 mm parallel to the rolling direction and 30 mm perpendicular to it. The bending punch was aligned so that it became perpendicular to the rolling direction, and the bending angle at maximum load was measured. Since the bending angle is correlated with strength, in this embodiment, bending angles exceeding 55 degrees for tensile strengths below 2100 MPa and bending angles exceeding 45 degrees for tensile strengths above 2100 MPa were evaluated as having superior bending performance compared to existing technologies.

[0827] <Appropriate current range>

[0828] Spot welding was performed according to JIS Z 3001-6:2013. A single-phase AC power supply of 60Hz was used, with electrodes having a tip diameter of 8mm, and the welding time was set to 10 cycles. Test pieces for spot welding were collected from the homogenization area of ​​the steel component, 40mm in the rolling direction and 30mm vertically. These pieces were bonded together, and the range of welding current from a weld nugget diameter of 3√t to the upper limit of the current that prevents spatter was determined and set as an appropriate current range.

[0829] The weld nugget diameter was set to the peel diameter obtained from the peel test. Five welding test pieces were collected under each current, and the average value of these peel diameters was set as the weld nugget diameter.

[0830] If the appropriate current range is above 2.5kA, it is judged to have excellent weldability.

[0831] [Table 17]

[0832]

[0833] [Table 18]

[0834]

[0835] [Table 19]

[0836]

[0837] <Example 3>

[0838] Pickling, cold rolling, and hot-dip Al galvanizing were performed on the steel plates shown in Tables 14 to 16 above to obtain coated steel plates with a thickness of 2.0 mm. The coated steel plates were then subjected to heat treatment under the conditions shown in Tables 20 to 22 to obtain coated steel components.

[0839] The obtained steel components are cut and subjected to GDS (glow discharge luminescence analysis), SEM, and optical microscopy observations using the above-mentioned techniques to determine the decarburized layer depth, internal oxide layer depth, and Fe content in the oxide scale.

[0840] In addition, the obtained steel components were subjected to tensile tests, bending tests, and spot welding tests using the same procedures as in Example 2 to evaluate their tensile strength, bending properties, and weldability.

[0841] The results are shown in Tables 20 to 22.

[0842] [Table 20]

[0843]

[0844] [Table 21]

[0845]

[0846] [Table 22]

[0847]

[0848] (Element Technology E)

[0849] Element technology E is a hot-stamped formed body whose chemical composition, by mass percent, contains: C: 0.15–0.50%, Si: 0.0010–3.000%, Mn: 0.30–3.00%, Al: 0.0002–2.000%, P: less than 0.100%, S: less than 0.1000%, N: less than 0.0100%, Nb: 0–0.15%, Ti: 0–0.15%, V: 0–0.15%, Mo: 0–1.0%, Cr: 0–1.0%, Cu: 0–1.0%, Ni: 0–1.0%, B: 0–0.0100%, Ca: 0–0.010%, and REM: 0–0.30%, with the remainder being Fe and impurities. The above-mentioned hot-stamped formed body possesses… The metal structure contains at least 90% martensite, bainite, and tempered martensite in terms of area ratio. In the texture from the surface to a position 1 / 4 of the plate thickness away from the surface, the ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is less than 1.8. In the texture from a position 1 / 4 of the plate thickness away from the surface to a position 1 / 2 of the plate thickness away from the surface, the ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is less than 2.3.

[0850] According to element technology E, it is possible to provide hot stamped parts with excellent strength and flexibility, and high load-bearing capacity.

[0851] The inventors of this invention have studied a method for achieving not only a tensile (maximum) strength of 1.5–2.5 GPa and excellent bending properties after hot stamping, but also for suppressing the deterioration of load-bearing capacity. As a result, the inventors discovered that by softening not only the surface layer of the steel sheet but also controlling the texture at specified positions along the thickness direction in a hot-stamped formed body, high strength and superior bending properties compared to previous methods can be obtained, while suppressing the deterioration of load-bearing capacity.

[0852] Texture is affected by the texture of the metal structure and carbon concentration before hot stamping. Therefore, the inventors of this invention have found that in order to obtain the desired texture in the hot-stamped part, it is effective to control the texture in the hot-rolled steel sheet and then reduce the carbon content on the surface of the steel sheet during subsequent annealing.

[0853] The hot-stamping steel sheet and the hot-stamped formed body of this embodiment will be described in detail below. First, the reasons for limiting the chemical composition of the hot-stamping steel sheet of this embodiment will be explained.

[0854] It should be noted that for the numerical ranges specified by the "~" in the following description, both the lower and upper limits are included within that range. Values ​​expressed as "lower than" or "higher than" are not included in the numerical range. All "%" values ​​related to chemical composition represent "mass %".

[0855] The hot-stamping steel sheet of this embodiment contains, by mass%, the following: C: 0.15-0.50%, Si: 0.0010-3.000%, Mn: 0.30-3.00%, Al: 0.0002-2.000%, P: less than 0.100%, S: less than 0.1000%, N: less than 0.0100%, Nb: 0-0.15%, Ti: 0-0.15%, V: 0-0.15%, Mo: 0-1.0%, Cr: 0-1.0%, Cu: 0-1.0%, Ni: 0-1.0%, B: 0-0.0100%, Ca: 0-0.010%, and REM: 0-0.30%, with the remainder being Fe and impurities.

[0856] The following is an explanation of each element.

[0857] C: 0.15~0.50%

[0858] Carbon (C) is an element that improves the strength of hot-stamped formed articles. When the C content is below 0.15%, the desired strength cannot be obtained in the hot-stamped formed article. Therefore, the C content is set to 0.15% or more. The C content is preferably 0.17% or more, 0.20% or more, or 0.23% or more. On the other hand, when the C content exceeds 0.50%, excellent flexibility cannot be obtained. Therefore, the C content is set to 0.50% or less. Preferably, the C content is 0.46% or less or 0.43% or less.

[0859] Si: 0.0010~3.000%

[0860] Si is an element that improves the strength of hot-stamped parts through solid solution strengthening. When the Si content is below 0.0010%, the desired strength cannot be obtained. Therefore, the Si content is set to 0.0010% or more. Preferably, the Si content is 0.050% or more, 0.100% or more, 0.300% or more, or 0.500% or more. On the other hand, when the Si content exceeds 3.000%, the ferrite content increases, and the desired metallic structure cannot be obtained. Therefore, the Si content is set to 3.000% or less. Preferably, the Si content is 2.700% or less or 2.500% or less.

[0861] Mn: 0.30~3.00%

[0862] Mn is an element that improves the hardenability of steel. To improve hardenability and obtain the desired amount of martensite after hot stamping, the Mn content is set to 0.30% or more. Preferably, the Mn content is 0.50% or more, 0.70% or more, or 1.00% or more. On the other hand, when the Mn content exceeds 3.00%, cracking due to Mn segregation becomes more likely, making it difficult to obtain excellent bending properties. Therefore, the Mn content is set to 3.00% or less. Preferably, the Mn content is 2.70% or less, 2.50% or less, or 2.30% or less.

[0863] Al: 0.0002~2.000%

[0864] Al is an element that improves deformability and flexibility of hot-stamped formed articles by deoxidizing molten steel and suppressing the formation of oxides that become the starting point of damage. When the Al content is below 0.0002%, deoxidation cannot be sufficiently achieved, resulting in the formation of coarse oxides, and the aforementioned effects cannot be obtained. Therefore, the Al content is set to 0.0002% or more. The Al content is preferably 0.001% or more. On the other hand, if the Al content exceeds 2.000%, coarse oxides are formed in the steel, and the flexibility of the hot-stamped formed article decreases. Therefore, the Al content is set to 2.000% or less. The Al content is preferably 1.700% or less or 1.500% or less.

[0865] P: below 0.100%

[0866] Phosphorus (P) is an impurity element that becomes the starting point for destruction through segregation at grain boundaries. Therefore, the P content is limited to 0.100% or less. The P content is preferably 0.050% or less. While there is no particular lower limit for the P content, reducing it below 0.0001% significantly increases the cost of P removal, making it economically undesirable. Therefore, the P content can also be set to 0.0001% or more.

[0867] S: Below 0.1000%

[0868] Sulfur (S) is an impurity element that forms inclusions in steel. Since these inclusions are the starting point for damage, the S content is limited to 0.1000% or less. The S content is preferably 0.0500% or less, or 0.0300% or less. There is no particular lower limit for the S content, but if it is reduced below 0.0001%, the cost of desulfurization increases significantly, which is not economically desirable. Therefore, the S content can also be set to 0.0001% or more.

[0869] N: below 0.0100%

[0870] Nitrogen (N) is an impurity element that forms nitrides in steel. Since these nitrides are the starting point for degradation, the N content is limited to 0.0100% or less. The preferred N content is 0.0050% or less. While there is no particular lower limit for the N content, reducing it below 0.0001% significantly increases the cost of nitrogen removal, making it economically undesirable. Therefore, the N content can also be set above 0.0001%.

[0871] The remaining portion of the chemical composition of the hot-stamping steel sheet of this embodiment may also be Fe and impurities. Examples of impurities include elements that are unavoidably mixed in from steel raw materials or scrap and / or during the steelmaking process, and that are permitted within a range that does not impair the characteristics of the hot-stamping steel sheet of this embodiment.

[0872] The hot-stamping steel sheet of this embodiment may also contain the following elements as optional elements to replace a portion of Fe. The content of the following optional elements is 0% when they are not present.

[0873] Nb: 0–0.15%

[0874] Ti: 0–0.15%

[0875] V: 0~0.15%

[0876] Nb and Ti have the effect of forming carbonitrides in steel, thereby increasing the strength of the hot-stamped form through precipitation reinforcement. To reliably achieve this effect, it is preferable to set the content of even one of Nb, Ti, and V to 0.05% or more. On the other hand, if the content of even one of Nb, Ti, and V is set to exceed 0.15%, a large amount of carbonitrides will be formed in the steel, thus reducing the ductility of the hot-stamped form. Therefore, the Nb content, Ti content, and V content are each set to 0.15% or less.

[0877] Mo: 0–1.0%

[0878] Cr: 0–1.0%

[0879] Cu: 0–1.0%

[0880] Ni: 0–1.0%

[0881] Mo and Cr have the following effect: by dissolving in the original austenite grains during heating before hot stamping, they improve the strength of the hot-stamped body. To reliably obtain this effect, it is preferable to set the content of even one of Mo, Cr, Cu, and Ni to 0.05% or more. On the other hand, even with a large content of Mo, Cr, Cu, and Ni, the above effect becomes saturated; therefore, the content of Mo, Cr, Cu, and Ni is preferably set to 1.0% or less each.

[0882] B: 0~0.0100%

[0883] Boron (B) is an element that improves the hardenability of steel. To reliably achieve this effect, the B content is preferably set to 0.0001% or more. On the other hand, even if the B content is set to exceed 0.0100%, the effect of improving hardenability becomes saturated. Therefore, the B content is set to 0.0100% or less.

[0884] Ca: 0–0.010%

[0885] REM: 0–0.30%

[0886] Ca and REM are elements that improve deformability and flexibility of hot-stamped parts by suppressing the formation of oxides that become the starting point of damage. To reliably obtain this effect, it is preferable to set the content of even one of Ca and REM to 0.001% or more. On the other hand, even with a large content of Ca and REM, the above effect is saturated; therefore, the Ca content is set to 0.010% or less, and the REM content is set to 0.30% or less.

[0887] It should be noted that in this embodiment, REM refers to a total of 17 elements including Sc, Y and lanthanides, and the content of REM refers to the total content of these elements.

[0888] The chemical composition of the aforementioned hot-stamping steel sheet can be determined using general analytical methods. For example, it can be determined using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). It should be noted that C and S can be determined using the combustion-infrared absorption method, and N can be determined using the inert gas melting-thermal conductivity method. When the surface of the hot-stamping steel sheet has a coating, the chemical composition can be analyzed after removing the coating by mechanical grinding.

[0889] Next, the metal structure of the hot stamping steel sheet of this embodiment will be described.

[0890] The hot-stamping steel sheet of this embodiment has a metallic microstructure comprising 20-80% ferrite, granular bainite, bainite, and martensite in total by area; and the remaining microstructure comprising pearlite and carbides. All percentages of the metallic microstructure described below refer to "area %".

[0891] Ferrite, granular bainite, bainite, martensite: 20–80%

[0892] Ferrite, granular bainite, bainite, and martensite are the microstructures required to obtain the desired texture in hot-stamped formed articles. If the combined area fraction of these microstructures is less than 20%, the desired texture cannot be obtained in the hot-stamped formed article. Therefore, the area fraction of ferrite is set to 20% or more, preferably 30% or more, or 40% or more. On the other hand, if the area fraction of these microstructures exceeds 80%, carbon concentrates in the remaining pearlite, making the carbides less fusible during hot stamping heating and becoming the starting point for cracking during deformation. Therefore, it is set to 80% or less, preferably 70% or less, or 60% or less.

[0893] Remaining tissue: pearlite and carbides

[0894] The residual microstructure of hot-stamping steel sheet includes pearlite and carbides. Since the microstructure of hot-stamping steel sheet does not contain any microstructure other than the above-mentioned microstructure and pearlite and carbides, the area ratio of the residual microstructure can be set to 20% to 80%.

[0895] Methods for determining the microstructure of hot-stamped steel sheets

[0896] A sample is cut from any position at least 50 mm from the end face of the hot-stamped steel sheet (avoiding positions where sample collection is not possible at that position), in a manner that allows observation of the sheet thickness section parallel to the rolling direction. The size of the sample also depends on the measuring device, but is set to be approximately 10 mm in size that can be observed in the rolling direction.

[0897] The cross-section of the above sample was ground using #600 to #1500 silicon carbide paper, then refined to a mirror finish using the following liquid, and further refined using a colloidal silica solution. This liquid was obtained by dispersing diamond powder with a particle size of 1 to 6 μm in a diluent such as alcohol or pure water. Next, in a region 50 μm long along the longitudinal direction of the sample cross-section, at a depth of 1 / 8 to 3 / 8 of the plate thickness from the surface, an EBSD analysis was performed using an EBSD analyzer consisting of a thermal field emission scanning electron microscope (JEOL JSM-7001F) and an EBSD detector (TSL DVC5 detector), at a resolution speed of 200 to 300 points per second. Using the "Phase Map" function in the "OIM Analysis" software (registered trademark) included with the EBSD analyzer, the area fraction of the bcc crystal structure was calculated, yielding the total area fraction of ferrite, granular bainite, bainite, and martensite.

[0898] Pearlite and carbides can be determined using the following method. The cross-section of the sample is polished using #600 to #1500 silicon carbide paper, then refined to a mirror finish using a liquid containing nitric acid and ethanol (obtained by dispersing diamond powder with a particle size of 1–6 μm in a diluent such as alcohol or pure water). Next, multiple fields of view are captured using a thermal field emission scanning electron microscope (JEOL JSM-7001F) at arbitrary locations along the length of the sample cross-section, within a region 50 μm in length and at a depth from 1 / 8 to 3 / 8 of the plate thickness from the surface. Equally spaced grids are drawn on the photographs to determine the microstructure at each grid point. The area fraction of each microstructure is obtained by calculating the number of grid points belonging to each microstructure and dividing by the total number of grid points. A higher total number of grid points allows for a more accurate determination of the area fraction. In this embodiment, the grid spacing is set to 2μm × 2μm, and the total number of grid points is set to 1500. Bright particles are considered as carbides, and bright regions arranged in granular or plate-like and lamellar shapes are considered as pearlites.

[0899] Next, the texture of the hot-stamping steel sheet of this embodiment will be described.

[0900] In this embodiment, the ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> in the texture from the surface to a position 1 / 4 of the thickness from the surface of the hot stamping steel sheet is less than 1.5. In the texture from a position 1 / 4 of the thickness from the surface to a position 1 / 2 of the thickness from the surface of the sheet, the ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is less than 2.0.

[0901] It should be noted that the orientation group formed by {001}<1-10> to {001}<-1-10> includes crystal orientations of {001}<1-10>, {001}<1-20>, {001}<0-10>, and {001}<-1-10>. Similarly, the orientation group formed by {111}<1-10> to {111}<-1-12> includes crystal orientations of {111}<1-10>, {111}<1-20>, {111}<0-10>, and {111}<-1-12>.

[0902] Texture at a distance of 1 / 4 of the plate thickness from the surface: The ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is less than 1.5.

[0903] In the texture at a distance of 1 / 4 of the plate thickness from the surface (hereinafter sometimes referred to as the surface region), the ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is set to be less than 1.5.

[0904] By preferably controlling the texture of the surface region of the hot-stamping steel sheet, carbon recarburization into the surface region (carbon diffusion from the interior region to the surface region with low C concentration) can be suppressed during the heating of hot stamping. Furthermore, by developing a texture in the surface region, which bears the energy absorption caused by deformation, such as near the surface of the steel sheet, that facilitates the mitigation of strain introduced by bending deformation, a hot-stamping steel sheet with excellent bending properties can be obtained after hot stamping.

[0905] If the extreme density of the orientation groups formed by {001}<1-10> to {001}<-1-10> in the surface region texture is greater than or equal to the extreme density of the orientation groups formed by {111}<1-10> to {111}<-1-12>, the aforementioned effect cannot be obtained. Therefore, the ratio of the extreme density of the orientation groups formed by {001}<1-10> to {001}<-1-10> in the surface region texture to the extreme density of the orientation groups formed by {111}<1-10> to {111}<-1-12> is set to be less than 1.5. Preferably, it is less than 1.2.

[0906] The ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> in the surface region to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> can be set to 0.4 or higher from the viewpoint of ensuring the strength in the hot stamped body.

[0907] Texture at a distance of 1 / 4 to 1 / 2 of the plate thickness from the surface: The ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is less than 2.0.

[0908] In the texture at a distance of 1 / 4 to 1 / 2 of the plate thickness from the surface (hereinafter sometimes referred to as the internal region), the ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is set to be less than 2.0.

[0909] By preferably controlling the texture of the internal region of the hot-stamped steel sheet, a texture with durable grain boundaries can be developed in load-bearing regions, such as the area near the interior of the steel sheet, thereby improving load-bearing capacity while maintaining excellent flexibility. If the ratio of the extreme density of orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of orientation groups formed by {111}<1-10> to {111}<-1-12> in the internal region texture is 2.0 or higher, the aforementioned effect cannot be obtained. Therefore, the ratio of the extreme density of orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of orientation groups formed by {111}<1-10> to {111}<-1-12> in the internal region texture is set to be less than 2.0. Preferably, it is less than 1.6.

[0910] The ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> in the internal region to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> can also be set to 0.4 or higher from the point of view of ensuring toughness.

[0911] Methods for determining extreme density

[0912] The extreme densities of the surface and interior regions were determined using the following methods.

[0913] The extreme densities of the surface and internal regions can be determined as follows: using a device combining a scanning electron microscope and an EBSD analysis apparatus, and an OIM Analysis (registered trademark) manufactured by TSL Corporation, orientation data are determined by EBSD (Electron Back Scattering Diffraction). The obtained orientation data is then used to calculate the crystal orientation distribution function (ODF) representing the three-dimensional texture using spherical harmonic functions. The crystal orientation distribution function is then used to determine the orientation data.

[0914] Regarding the measurement range, for the surface region, it is set to the area from the surface to a position 1 / 4 of the plate thickness away from the surface (the surface is set as the starting point, and a position 1 / 4 of the plate thickness away from the surface in the thickness direction is set as the ending point). For the internal region, it is set to the area from a position 1 / 4 of the plate thickness away from the surface to a position 1 / 2 of the plate thickness away from the surface (the position 1 / 4 of the plate thickness away from the surface in the thickness direction is set as the starting point, and a position 1 / 2 of the plate thickness away from the surface in the thickness direction is set as the ending point). The measurement interval is set to 5 μm / step.

[0915] The value obtained by dividing the average value of the polar density of the orientation group formed by {001}<1-10> to {001}<-1-10> by the average value of the polar density of the orientation group formed by {111}<1-10> to {111}<-1-12> is set as the ratio of the polar density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the polar density of the orientation group formed by {111}<1-10> to {111}<-1-12>.

[0916] It should be noted that {hkl} represents a crystal plane parallel to the rolling plane. <uvw>This indicates the crystal orientation parallel to the rolling direction. That is, {hkl} <uvw>This indicates that {hkl} is oriented towards the normal direction of the board surface. <uvw>Crystals oriented towards the rolling direction.

[0917] The hot-stamping steel sheet of this embodiment may also have a coating on its surface. By having a coating on the surface, corrosion resistance can be improved after hot stamping. Examples of coatings include aluminum coatings, aluminum-zinc coatings, aluminum-silicon coatings, hot-dip galvanized coatings, electro-galvanized coatings, and alloyed hot-dip galvanized coatings.

[0918] The decarburization index of hot-stamping steel sheets is above 0.085.

[0919] By preferably controlling the decarburization index of hot-stamping steel sheets, the development of a texture with resilient grain boundaries can be promoted in load-bearing regions, such as the area near the interior of the steel sheet, thereby improving load-bearing capacity while maintaining excellent bending properties. The decarburization index of the hot-stamping steel sheet is preferably 0.140 or higher, more preferably 0.180 or higher. According to the method for calculating the decarburization index, the upper limit is 1.000.

[0920] Determination method of decarbonization index

[0921] The decarburization index is a quantitative indicator of the reduction in carbon in the surface layer of steel sheets, and it can be calculated using the following method. A glow discharge optical emission spectrometry (GD-OES) device is used to determine the elemental concentration distribution along the thickness of the hot-stamping steel sheet. Here, the measurement range is set to the outermost surface of the steel sheet up to a depth of 200 μm, and the measurement interval is set to less than 0.02 μm. Measurements are performed on all elements contained in the hot-stamping steel sheet.

[0922] For steel sheets with coatings or plating on their surface, the coatings or plating are partially or completely removed by mechanical or chemical grinding to allow for measurements from the outermost surface of the steel sheet to a depth of 200 μm before being subjected to GD-OES testing. In GD-OES testing, areas where the iron concentration is 90% by mass or higher are defined as steel sheets, and the measurement point where the iron concentration reaches 90% by mass is set as the outermost surface of the steel sheet.

[0923] Next, the average value of the carbon concentration measured at depths of 180 μm to 200 μm from the outermost surface of the steel plate (more than 1000 points) was calculated, and this average value was regarded as the carbon concentration of the steel plate base material.

[0924] Alternatively, if the measured carbon concentration in the region from the deepest point to the surface side up to 20 μm is as follows, the average carbon concentration in the region from the deepest point to the surface side up to 20 μm may be set as the carbon concentration of the steel sheet base material: the absolute value of the difference between the average carbon concentration in the region from the deepest point to the surface side up to 20 μm and the maximum value of the measured carbon concentration in the region from the deepest point to the surface side up to 20 μm is 0.1% or less, and the absolute value of the difference between the average carbon concentration in the region from the deepest point to the surface side up to 20 μm and the minimum value of the measured carbon concentration in the region from the deepest point to the surface side up to 20 μm is 0.1% or less.

[0925] The unit depth is 20 μm. The so-called deepest part refers to the deepest position within a range of 200 μm from the outermost surface of the steel plate, marked with positions per unit depth. For example, in the case where the deepest part is 120 μm, "the measured value of carbon concentration in the region from the deepest part to the surface side up to 20 μm" refers to the carbon concentration at the measurement points within the range of 100 μm to 120 μm.

[0926] Within a depth of approximately 200 μm from the outermost surface of the steel plate, the reduction in carbon concentration per unit depth is calculated (the value obtained by subtracting the carbon concentration at each measurement point from the carbon concentration of the base material). The integral value of the product of the reduction in carbon concentration per unit depth is then calculated and set as the area of ​​the carbon-deficient region (area A). Next, the product of the carbon concentration of the base material and 200 μm is set as the reference area (area B). The value obtained by dividing the carbon-deficient area (area A) by the reference area (area B) is set as the decarburization index.

[0927] Next, a hot-stamped formed article that can be obtained by applying the manufacturing method described later to the hot-stamping steel sheet described above will be explained. The hot-stamped formed article of this embodiment is characterized by improving the deformability of the metal structure in the surface region and simultaneously improving the load-bearing capacity of the interior by changing the texture in both the surface and interior regions. Furthermore, the chemical composition of the hot-stamped formed article of this embodiment is the same as that of the hot-stamping steel sheet described above, therefore, its description is omitted.

[0928] The hot-stamped formed body of this embodiment has a metallic structure comprising martensite, bainite, and tempered martensite, totaling 90% or more in area. In the texture from the surface to a position one-quarter of the plate thickness away from the surface, the ratio of the extreme density of orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of orientation groups formed by {111}<1-10> to {111}<-1-12> is less than 1.8. In the texture from a position one-quarter of the plate thickness away from the surface to a position one-half of the plate thickness away from the surface, the ratio of the extreme density of orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of orientation groups formed by {111}<1-10> to {111}<-1-12> is less than 2.3. Furthermore, all "%" in the following description of the metallic structure refers to "area %".

[0929] Martensite, bainite, and tempered martensite: totaling over 90%.

[0930] Martensite, bainite, and tempered martensite are the microstructure required to obtain the desired strength. If the combined area ratio of martensite, bainite, and tempered martensite is less than 90%, the desired strength cannot be obtained. Therefore, the combined area ratio of martensite, bainite, and tempered martensite is set to 90% or more. Preferably, it is 93% or more, or 95% or more. A higher area ratio of martensite, bainite, and tempered martensite is preferred; therefore, the area ratio of martensite, bainite, and tempered martensite can also be set to 100%.

[0931] It should be noted that in this embodiment, the total content may include more than 90% of two or more of martensite, bainite and tempered martensite, or it may include more than 90% of one of martensite, bainite or tempered martensite.

[0932] The hot-stamped formed article of this embodiment may contain one or more of ferrite and granular bainite as residual microstructure. If the area ratio of these residual microstructures exceeds 10%, the desired load-bearing capacity cannot be obtained. Therefore, the area ratio of the residual microstructure can also be set to 10% or less. The lower the area ratio of the residual microstructure, the better; therefore, the area ratio of the residual microstructure can also be set to 7% or less, 5% or less, or 0%.

[0933] Methods for determining the area ratio of martensite, bainite, and tempered martensite

[0934] The metal structure of the hot-stamped formed body in this embodiment was determined by the following method.

[0935] The sample is cut from any position more than 50 mm away from the end face of the hot-stamped body (to avoid the end position if it is not possible to collect the sample from that position), in a way that allows observation of the sheet thickness section parallel to the rolling direction. The size of the sample also depends on the measuring device, but is set to be about 10 mm in size that can be observed in the rolling direction.

[0936] The cross-section of the above samples was ground using #600 to #1500 silicon carbide paper, and then mirror-finished using a liquid polishing process. This liquid was obtained by dispersing diamond powder with a particle size of 1–6 μm in a diluent such as alcohol or pure water. Next, the samples were ground for 8 minutes at room temperature using colloidal silica without an alkaline solution to remove strain introduced into the sample surface. At any location along the length of the sample cross-section, regions with a length of 50 μm and a depth from 1 / 8 to 3 / 8 of the plate thickness from the surface were measured using electron backscatter diffraction at intervals of 0.1 μm to obtain crystal orientation information. The measurements were performed using an EBSD analysis apparatus consisting of a thermal field emission scanning electron microscope (JEOL JSM-7001F) and an EBSD detector (TSL DVC5 detector). The vacuum level within the EBSD analysis apparatus was set to 9.6 × 10⁻⁶. -5 Below Pa, the accelerating voltage is set to 15kV, the irradiation current level is set to 13, and the electron beam irradiation level is set to 62.

[0937] The obtained crystal orientation information was used in the "Phase Map" function of the "OIM Analysis (registered trademark)" software included with the EBSD analysis device to identify regions with a bcc crystal structure. These bcc crystal structures were then classified as bainite, tempered martensite, martensite, granular bainite, and ferrite. For these regions, the "Grain Average Misorientation" function of the "OIM Analysis (registered trademark)" software was used to classify regions with a Grain Average Misorientation value exceeding 3.0° as martensite, bainite, and tempered martensite. The sum of these area ratios was then calculated to obtain the total area ratio of "martensite, bainite, and tempered martensite".

[0938] The area ratio of the remaining structure can be obtained by subtracting the sum of the area ratios of "martensite, bainite and tempered martensite" from 100%.

[0939] Texture at a distance of 1 / 4 of the plate thickness from the surface: The ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> is less than 1.8.

[0940] In the texture extending from the surface to a position one-quarter of the plate thickness away from the surface (surface region), bending flexibility can be improved by setting the ratio of the extreme density of the orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation groups formed by {111}<1-10> to {111}<-1-12> to less than 1.8. Therefore, in the texture of the surface region, the ratio of the extreme density of the orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of the orientation groups formed by {111}<1-10> to {111}<-1-12> is set to less than 1.8. Preferably, it is less than 1.7 or less than 1.6.

[0941] The ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> in the surface region to the extreme density of the orientation group formed by {111}<1-10> to {111}<-1-12> can be set to 0.4 or higher from the point of view of ensuring strength.

[0942] Texture at a distance of 1 / 4 to 1 / 2 of the plate thickness from the surface: The ratio of the extreme density of the orientation group formed by {001}<1-10> to {001}<-1-10> to the extreme density of the or...

Claims

1. A vehicle body, comprising a battery, tires, and liquids containing water or oil, removed from a road-going vehicle with excellent collision safety, wherein the road-going vehicle is composed of at least steel material comprising steel plates with a tensile strength of 1180 MPa or more, non-ferrous metal material, and resin material. in, The mass (m) of the steel plate having a tensile strength of 1180 MPa or higher in kg h The ratio of the mass m (in kg) of the vehicle body to the total mass of the vehicle body is 9% or more. Let the mass of the car body be expressed in kg as m, and the projected area of ​​the car body from above be expressed in m. 2 When the value is set to s, the following equations (1) and (2) are satisfied. 6<s<11 (1) m<(272.37×s-835)×0.98 (2).

2. A vehicle body, which is a vehicle body derived from a road-going vehicle with excellent collision safety after removing the battery, tires, and liquids containing water or oil, wherein the road-going vehicle is composed of at least steel material comprising steel plates with a tensile strength of 1180 MPa or more, non-ferrous metal materials, and resin materials. in, The mass (m) of the steel plate having a tensile strength of 1180 MPa or higher in kg h The ratio of the mass m (in kg) of the vehicle body to the total mass of the vehicle body is 9% or more. Let M be the sum of CO2 emissions calculated from the raw materials of the vehicle body during manufacturing, use, and disposal; and let m be the projected area of ​​the vehicle body from above. 2 When the height of the vehicle body is set to h (in meters), the following equations (3) and (4) are satisfied. 9 <s×h<19 (3) M<(1925.1×s×h-81.4)×0.98 (4).

3. The vehicle body according to claim 1 or 2, wherein, The mass m of the steel material in kg s The ratio of the mass m (in kg) of the vehicle body to the total mass of the vehicle body is 64% or more. The total mass (in kg) of sheet metal parts made from the steel plate with a tensile strength of 1.9 GPa or higher. hs The ratio of the mass m in kg to the vehicle body is 9% or more.

4. The vehicle body according to claim 1 or 2, wherein, The total mass (in kg) of sheet metal parts made from the steel plate with a tensile strength of 1180 MPa or higher. ht relative to the vehicle body weight (in kg) m b The ratio is over 24%.

5. The vehicle body according to claim 1 or 2, wherein, The total mass (in kg) of sheet metal parts containing more than 0.013% Cu, more than 0.018% Ni, and more than 0.002% Sn. sc The total mass (in kg) of the sheet metal components of the vehicle body relative to the total mass of the sheet metal components of the vehicle body. sp The ratio is over 20%.

6. The automobile body according to claim 3, comprising: The hot-stamped formed body has the following chemical composition (by mass%): C: 0.30–0.50%, Si: 0.50–3.00%, Mn: 0.50–3.00%, Al: 0.0002–2.000%, P: less than 0.100%, S: less than 0.1000%, N: less than 0.0100%, Nb: 0–0.150%, Ti: 0–0.150%, Co: 0–2.00%, Mo: 0–1.00%, Cr: 0–1.00%, Cu: 0–1.00%, V: 0–1.00%, W: 0–1. 0.00%, Ni: 0-3.00%, Mg: 0-1.00%, Zr: 0-1.00%, Sb: 0-1.00%, Ca: 0-0.10%, REM: 0-0.30%, and B: 0-0.0100%, with the remainder containing Fe and impurities. The hot-stamped body has the following microstructure: containing more than 5% and less than 10% retained austenite, more than 90% and less than 95% bainite and tempered martensite in total, and less than 5% of the remaining microstructure, at the grain boundaries of the bainite and the tempered martensite grains, relative to the area of… <011> The total length of the grain boundary with a rotation angle of 4° to 12° along the rotation axis, the length of the grain boundary with a rotation angle of 49° to 54°, and the length of the grain boundary with a rotation angle of 55° to 75°, wherein the proportion of the length of the grain boundary with a rotation angle of 55° to 75° is 30% or more, and the tensile strength of the hot-stamped formed body is 1500 MPa or more. A skeleton member, formed by hot stamping a steel plate, has a closed section portion with a closed cross-section perpendicular to its length direction. The closed cross-section portion has at least one flat portion whose radius of curvature is larger than the maximum external dimension of the cross-section. When defining a reference flat portion as the flat portion having the largest width proportional to the effective width calculated using the Karman formula, the Vickers hardness at the center of the plate thickness at the reference flat portion is 300 Hv or higher, the width of the reference flat portion is less than 2.0 times the effective width, and the standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution at the surface portion of the reference flat portion by the standard deviation of the hardness frequency distribution at the center of the plate thickness at the reference flat portion is less than 1.0; and The hot-stamped formed body has the following chemical composition (by mass%): C: 0.15–0.50%, Si: 0.0010–3.000%, Mn: 0.30–3.00%, Al: 0.0002–2.000%, P: less than 0.100%, S: less than 0.1000%, N: less than 0.0100%, Nb: 0–0.15%, Ti: 0–0.15%, V: 0–0.15%, Mo: 0–1.0%, Cr: 0–1.0%, Cu: 0–1.0%, Ni: 0–1.0%, B: 0–0.0100%, Ca: 0–0.010%, and REM: 0–0.30%, with the remainder being Fe and impurities. The hot-stamped formed body contains: For a metallic microstructure consisting of martensite, bainite, and tempered martensite with a total area ratio of 90% or more, in the texture from the surface to a position 1 / 4 of the plate thickness away from the surface, the ratio of the extreme density of orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of orientation groups formed by {111}<1-10> to {111}<-1-12> is less than 1.8; and in the texture from a position 1 / 4 of the plate thickness away from the surface to a position 1 / 2 of the plate thickness away from the surface, the ratio of the extreme density of orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of orientation groups formed by {111}<1-10> to {111}<-1-12> is less than 2.

3.

7. The automobile body according to claim 3, comprising: The hot-stamped formed body has the following chemical composition (by mass%): C: 0.15–0.50%, Si: 0.0010–3.000%, Mn: 0.30–3.00%, Al: 0.0002–2.000%, P: less than 0.100%, S: less than 0.1000%, N: less than 0.0100%, Nb: 0–0.15%, Ti: 0–0.15%, V: 0–0.15%, Mo: 0–1.0%, Cr: 0–1.0%, Cu: 0–1.0%, Ni: 0–1.0%, B: 0–0.0100%, Ca: 0–0.010%, and REM: 0–0.30%, with the remainder being Fe and impurities. The hot-stamped formed body has a surface... For a metallic microstructure comprising martensite, bainite, and tempered martensite with a total product of 90% or more, in the texture from the surface to a position 1 / 4 of the plate thickness away from the surface, the ratio of the extreme density of orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of orientation groups formed by {111}<1-10> to {111}<-1-12> is less than 1.8; and in the texture from a position 1 / 4 of the plate thickness away from the surface to a position 1 / 2 of the plate thickness away from the surface, the ratio of the extreme density of orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of orientation groups formed by {111}<1-10> to {111}<-1-12> is less than 2.3; and A skeleton member, formed by hot stamping of steel plate, has a closed section portion with a closed cross-section perpendicular to its length direction. The closed section portion has at least two flat portions, each with a radius of curvature larger than the maximum external dimension of the section, and a concave reinforcing rib portion formed between the two flat portions. The concave reinforcing rib portion has a pair of wall portions with a radius of curvature of 50 mm or more. These wall portions protrude inwards from opposite ends of the two flat portions via a pair of curved portions bending inwards towards the closed section. The Vickers hardness at the center of the plate thickness of the wall portions is 520 Hv or more. The width of the wall portions is the effective width W obtained using the Karman formula. e The standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution at the surface layer of the wall by the standard deviation of the hardness frequency distribution at the center of the wall thickness is less than 1.

0.

8. The automobile body according to claim 3, comprising: A skeleton member formed by cold pressing a steel plate has a closed section portion with a closed section perpendicular to the length direction. The closed section portion has at least one flat portion with a radius of curvature larger than the maximum external dimension of the section. When the flat portion with the largest width relative to the effective width calculated by the Karman formula is defined as the reference flat portion, the Vickers hardness at the center of the plate thickness at the reference flat portion is 300 Hv or more, the width of the reference flat portion is less than 2.0 times the effective width, and the standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution at the surface portion of the reference flat portion by the standard deviation of the hardness frequency distribution at the center of the plate thickness at the reference flat portion is greater than 1.

0. A skeleton member formed by hot stamping a steel plate, the skeleton member having a closed section portion with a closed section perpendicular to the length direction, the closed section portion having at least one flat portion whose radius of curvature is larger than the maximum external dimension of the section, when defining the flat portion having the largest width relative to the effective width calculated by the Karman formula among the at least one flat portion as a reference flat portion, the Vickers hardness at the center of the plate thickness at the reference flat portion is 300 Hv or more, the width of the reference flat portion is less than 2.0 times the effective width, and the standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution at the surface portion of the reference flat portion by the standard deviation of the hardness frequency distribution at the center of the plate thickness at the reference flat portion is less than 1.0; and A skeleton member formed by hot stamping a steel plate has a closed section portion with a closed cross-section perpendicular to its length direction. The closed section portion has at least two flat portions with a radius of curvature larger than the maximum external dimension of the cross-section, and a concave reinforcing rib portion formed between the two flat portions. The concave reinforcing rib portion has a pair of wall portions with a radius of curvature of 50 mm or more. These wall portions protrude inwards from opposite ends of the two flat portions via a pair of curved portions bending inwards towards the closed section. The Vickers hardness at the center of the plate thickness of the wall portions is 520 Hv or more. The width of the wall portions is the effective width W obtained using the Karman formula. e The standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution at the surface layer of the wall by the standard deviation of the hardness frequency distribution at the center of the wall thickness is less than 1.

0.

9. The automobile body according to claim 8, comprising: A structural member for an automobile body extends along a predetermined direction and has a top plate portion, a ridge portion continuous with the top plate portion, and a longitudinal wall portion continuous with the ridge portion. The structural member is made of a pressed steel sheet with a generally channel-shaped cross-section intersecting the predetermined direction. The structural member includes at least one groove extending along the predetermined direction from an end portion of the top plate portion and an outward flange formed at least within the ridge portion at the end portion. The depth (h), width (w), and thickness (t) of the groove at the end portion satisfy the following relationship: 0.2×H0≤h≤3.0×H0、 H0 = (0.037t - 0.25) × w - 5.7t + 29.2; and High-strength frame components, which have L-shaped and T-shaped features.

10. The automobile body according to claim 3, comprising: The hot-stamped formed body has the following chemical composition (by mass%): C: 0.15–0.50%, Si: 0.0010–3.000%, Mn: 0.30–3.00%, Al: 0.0002–2.000%, P: less than 0.100%, S: less than 0.1000%, N: less than 0.0100%, Nb: 0–0.15%, Ti: 0–0.15%, V: 0–0.15%, Mo: 0–1.0%, Cr: 0–1.0%, Cu: 0–1.0%, Ni: 0–1.0%, B: 0–0.0100%, Ca: 0–0.010%, and REM: 0–0.30%, with the remainder being Fe and impurities. The hot-stamped formed body has a surface... For a metallic microstructure comprising martensite, bainite, and tempered martensite with a total product of 90% or more, in the texture from the surface to a position 1 / 4 of the plate thickness away from the surface, the ratio of the extreme density of orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of orientation groups formed by {111}<1-10> to {111}<-1-12> is less than 1.8; and in the texture from a position 1 / 4 of the plate thickness away from the surface to a position 1 / 2 of the plate thickness away from the surface, the ratio of the extreme density of orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of orientation groups formed by {111}<1-10> to {111}<-1-12> is less than 2.3; and A skeleton member is a skeleton member joined by spot welding a first steel plate member and a second steel plate member at a spot weld joint. The skeleton member has a cross-sectional area with a closed section perpendicular to its length direction. The first steel plate member has a tensile strength of 1900 MPa or more. The spot weld joint has a molten metal portion formed by the spot weld and a heat-affected zone adjacent to the outer side of the molten metal portion. In a cross-section perpendicular to the length direction containing the center point of the molten metal portion, the area corresponding to the molten metal portion is defined as a first region, the area corresponding to the heat-affected zone is defined as a second region, and the region formed by the area from the boundary between the first and second regions to a distance of 100 μm towards the first region and the area from the boundary to a distance of 100 μm towards the second region is defined as a third region. The average Vickers hardness Hv at the measurement location corresponding to the first region on an imaginary straight line extending from the center of the first region towards the second region is determined by a load of 10 gf at 15 μm intervals. Ave The lowest Vickers hardness Hv at the measurement location corresponding to the third region on the imaginary straight line. Min Satisfy Hv Ave -Hv Min ≤100.

11. The automobile body according to claim 10, comprising: A structural member for an automobile body extends along a predetermined direction and has a top plate portion, a ridge portion continuous with the top plate portion, and a longitudinal wall portion continuous with the ridge portion. The structural member is made of a pressed steel sheet with a generally channel-shaped cross-section intersecting the predetermined direction. The structural member includes at least one groove extending along the predetermined direction from an end portion of the top plate portion and an outward flange formed at least within the ridge portion at the end portion. The depth (h), width (w), and thickness (t) of the groove at the end portion satisfy the following relationship: 0.2×H0≤h≤3.0×H0、 H0 = (0.037t - 0.25) × w - 5.7t + 29.2; and High-strength frame components, which have L-shaped and T-shaped features.

12. The automobile body according to claim 10, comprising a hot-stamped formed article, the hot-stamped formed article having a base steel sheet having the following chemical composition in mass percent: C: more than 0.40% and less than 0.70%, Si: less than 2.00%, Mn: more than 0.01% and less than 0.50%, P: less than 0.200%, S: less than 0.0200%, sol.Al: 0.001 to 1.000%, N: less than 0.0200%, Mo: more than 0.01% and less than 0.50%, B: 0.0002 to 0.0200%, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0 to 0.2%. 0.00%, Zr: 0-0.200%, Cr: 0-2.00%, W: 0-2.00%, Cu: 0-2.00%, Ni: 0-2.00%, Ca: 0-0.0100%, Mg: 0-0.0100%, REM: 0-0.1000%, Bi: 0-0.0500%, Remaining: Fe and impurities. When determining the Mo content of the base steel plate using EPMA line analysis, within a 0.05 mm range along the thickness direction centered at a depth of 1 / 4 of the base steel plate's thickness from the surface, the maximum, minimum, and average Mo content are set as follows: [Mo] mMAX The maximum value of Mo content in the base steel plate, expressed as a percentage by mass. [Mo] mMIN Minimum Mo content (in mass percent) of the base steel plate [Mo] mAVE The average Mo content (in mass percent) of the base steel plate. Satisfy ([Mo]) mMAX -[Mo] mMIN ) / [Mo] mAVE <0.50, the microstructure of the base steel plate contains more than 90.0% martensite, the standard deviation of Vickers hardness in a region 0.3 mm along the thickness direction and 0.6 mm in a direction orthogonal to the thickness direction, centered at a depth of 1 / 4 of the thickness of the base steel plate, is less than 20 Hv, and the tensile strength of the base steel plate is more than 2300 MPa.

13. The automobile body according to claim 11, comprising a hot-stamped formed article, the hot-stamped formed article having a base steel sheet having the following chemical composition in mass percent: C: more than 0.40% and less than 0.70%, Si: less than 2.00%, Mn: more than 0.01% and less than 0.50%, P: less than 0.200%, S: less than 0.0200%, sol.Al: 0.001 to 1.000%, N: less than 0.0200%, Mo: more than 0.01% and less than 0.50%, B: 0.0002 to 0.0200%, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0 to 0.2%. 0.00%, Zr: 0-0.200%, Cr: 0-2.00%, W: 0-2.00%, Cu: 0-2.00%, Ni: 0-2.00%, Ca: 0-0.0100%, Mg: 0-0.0100%, REM: 0-0.1000%, Bi: 0-0.0500%, Remaining: Fe and impurities. When determining the Mo content of the base steel plate using EPMA line analysis, within a 0.05 mm range along the thickness direction centered at a depth of 1 / 4 of the base steel plate's thickness from the surface, the maximum, minimum, and average Mo content are set as follows: [Mo] mMAX The maximum value of Mo content in the base steel plate, expressed as a percentage by mass. [Mo] mMIN Minimum Mo content (in mass percent) of the base steel plate [Mo] mAVE The average Mo content (in mass percent) of the base steel plate. Satisfy ([Mo]) mMAX -[Mo] mMIN ) / [Mo] mAVE <0.50, the microstructure of the base steel plate contains more than 90.0% martensite, the standard deviation of Vickers hardness in a region 0.3 mm along the thickness direction and 0.6 mm in a direction orthogonal to the thickness direction, centered at a depth of 1 / 4 of the thickness of the base steel plate, is less than 20 Hv, and the tensile strength of the base steel plate is more than 2300 MPa.

14. The automobile body according to claim 3, comprising: The hot-stamped formed body has the following chemical composition (by mass%): C: 0.15–0.50%, Si: 0.0010–3.000%, Mn: 0.30–3.00%, Al: 0.0002–2.000%, P: less than 0.100%, S: less than 0.1000%, N: less than 0.0100%, Nb: 0–0.15%, Ti: 0–0.15%, V: 0–0.15%, Mo: 0–1.0%, Cr: 0–1.0%, Cu: 0–1.0%, Ni: 0–1.0%, B: 0–0.0100%, Ca: 0–0.010%, and REM: 0–0.30%, with the remainder being Fe and impurities. The hot-stamped formed body has a surface... For a metallic microstructure comprising martensite, bainite, and tempered martensite with a total product of 90% or more, in the texture from the surface to a position 1 / 4 of the plate thickness away from the surface, the ratio of the extreme density of orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of orientation groups formed by {111}<1-10> to {111}<-1-12> is less than 1.8; and in the texture from a position 1 / 4 of the plate thickness away from the surface to a position 1 / 2 of the plate thickness away from the surface, the ratio of the extreme density of orientation groups formed by {001}<1-10> to {001}<-1-10> to the extreme density of orientation groups formed by {111}<1-10> to {111}<-1-12> is less than 2.3; and The side component structure of the vehicle body includes a cylindrical body extending along the longitudinal direction of the vehicle body and an impact-absorbing member disposed inside the cylindrical body. The impact-absorbing member has a web extending along the longitudinal direction and being flat in the vehicle width direction, an outer flange engaging with the outer end of the web and extending along the longitudinal direction, and an inner flange engaging with the inner end of the web and extending along the longitudinal direction. The outer flange and the inner flange have ribs arranged to clamp the web from above and below and extending along the longitudinal direction.

15. The automobile body according to claim 14, comprising: A structural member for an automobile body extends along a predetermined direction and has a top plate portion, a ridge portion continuous with the top plate portion, and a longitudinal wall portion continuous with the ridge portion. The structural member is made of a pressed steel sheet with a generally channel-shaped cross-section intersecting the predetermined direction. The structural member includes at least one groove extending along the predetermined direction from an end portion of the top plate portion and an outward flange formed at least within the ridge portion at the end portion. The depth (h), width (w), and thickness (t) of the groove at the end portion satisfy the following relationship: 0.2×H0≤h≤3.0×H0、 H0 = (0.037t - 0.25) × w - 5.7t + 29.2; and High-strength frame components, which have L-shaped and T-shaped features.

16. The automobile body according to claim 14, comprising a steel component having a steel sheet substrate and a coating containing Al and Fe formed on the surface of the steel sheet substrate, the steel sheet substrate having the following chemical composition (in mass%): C: 0.10–0.65%, Si: 0.10–2.00%, Mn: 0.30–3.00%, P: less than 0.050%, S: less than 0.0100%, N: less than 0.010%, O: less than 0.010%, Ti: 0–0.100%, B: 0–0.0100%, Cr: 0–1.00%, Mo: 0–1.00%, Ni: 0–1.00%, Nb: 0–0.10%, Cu: 0–1.00%, V The composition of the steel plate substrate is as follows: 0-1.00%, Ca: 0-0.010%, Mg: 0-0.010%, Al: 0-1.00%, Sn: 0-1.00%, W: 0-1.00%, Sb: 0-1.00%, Zr: 0-1.00%, Co: 0-1.00%, and REM: 0-0.30%, with the remainder containing Fe and impurities. The steel plate substrate has a decarburized layer formed on the coated side, the decarburized layer has an internal oxide layer formed on the coated side, the depth of the decarburized layer from the interface between the steel plate substrate and the coated side is more than 30 μm, the depth of the internal oxide layer from the interface is less than 20 μm, and there is no oxide scale between the steel plate substrate and the coated side containing Al and Fe.

17. The automobile body according to claim 15, comprising a steel component having a steel sheet substrate and a coating containing Al and Fe formed on the surface of the steel sheet substrate, the steel sheet substrate having the following chemical composition (in mass%): C: 0.10–0.65%, Si: 0.10–2.00%, Mn: 0.30–3.00%, P: less than 0.050%, S: less than 0.0100%, N: less than 0.010%, O: less than 0.010%, Ti: 0–0.100%, B: 0–0.0100%, Cr: 0–1.00%, Mo: 0–1.00%, Ni: 0–1.00%, Nb: 0–0.10%, Cu: 0–1.00%, V The composition of the steel plate substrate is as follows: 0-1.00%, Ca: 0-0.010%, Mg: 0-0.010%, Al: 0-1.00%, Sn: 0-1.00%, W: 0-1.00%, Sb: 0-1.00%, Zr: 0-1.00%, Co: 0-1.00%, and REM: 0-0.30%, with the remainder containing Fe and impurities. The steel plate substrate has a decarburized layer formed on the coated side, the decarburized layer has an internal oxide layer formed on the coated side, the depth of the decarburized layer from the interface between the steel plate substrate and the coated side is more than 30 μm, the depth of the internal oxide layer from the interface is less than 20 μm, and there is no oxide scale between the steel plate substrate and the coated side containing Al and Fe.

18. The automobile body according to claim 14, having a pallet manufactured by a method comprising: The process includes a welding step, which welds a high-strength portion having high tensile strength to a low-strength portion having lower tensile strength than the high-strength portion; and a forming step, which presses the low-strength portion to include a recess, the recess having a corner portion in the inner surfaces of the first sidewall and the second sidewall of a first sidewall that are adjacent to each other at an inferior angle, and a corner portion in the upper surface of a bottom wall that is at an inferior angle relative to the inner surfaces of the first and second sidewalls, respectively, wherein the... The tray has a bottom wall and peripheral side walls that are vertically disposed from the outer periphery of the bottom wall. The tray also has a high-strength portion having high tensile strength and a low-strength portion having lower tensile strength than the high-strength portion. The low-strength portion is formed by including a recess. The recess has a corner portion of the inner surfaces of the first side wall and the second side wall of the first side wall that are adjacent to each other at an inferior angle, and a corner portion of the upper surface of the bottom wall that forms an inferior angle with respect to the inner surfaces of the first and second side walls, respectively.

19. The automobile body according to claim 15, having a pallet manufactured by a method comprising: The process includes a welding step, which welds a high-strength portion having high tensile strength to a low-strength portion having lower tensile strength than the high-strength portion; and a forming step, which presses the low-strength portion to include a recess, the recess having a corner portion in the inner surfaces of the first sidewall and the second sidewall of a first sidewall that are adjacent to each other at an inferior angle, and a corner portion in the upper surface of a bottom wall that is at an inferior angle relative to the inner surfaces of the first and second sidewalls, respectively, wherein the... The tray has a bottom wall and peripheral side walls that are vertically disposed from the outer periphery of the bottom wall. The tray also has a high-strength portion having high tensile strength and a low-strength portion having lower tensile strength than the high-strength portion. The low-strength portion is formed by including a recess. The recess has a corner portion of the inner surfaces of the first side wall and the second side wall of the first side wall that are adjacent to each other at an inferior angle, and a corner portion of the upper surface of the bottom wall that forms an inferior angle with respect to the inner surfaces of the first and second side walls, respectively.

20. The automobile body according to claim 16, having a pallet manufactured by a method comprising: The process includes a welding step, which welds a high-strength portion having high tensile strength to a low-strength portion having lower tensile strength than the high-strength portion; and a forming step, which presses the low-strength portion to include a recess, the recess having a corner portion in the inner surfaces of the first sidewall and the second sidewall of a first sidewall that are adjacent to each other at an inferior angle, and a corner portion in the upper surface of a bottom wall that is at an inferior angle relative to the inner surfaces of the first and second sidewalls, respectively, wherein the... The tray has a bottom wall and peripheral side walls that are vertically disposed from the outer periphery of the bottom wall. The tray also has a high-strength portion having high tensile strength and a low-strength portion having lower tensile strength than the high-strength portion. The low-strength portion is formed by including a recess. The recess has a corner portion of the inner surfaces of the first side wall and the second side wall of the first side wall that are adjacent to each other at an inferior angle, and a corner portion of the upper surface of the bottom wall that forms an inferior angle with respect to the inner surfaces of the first and second side walls, respectively.

21. The automobile body according to claim 17, having a pallet manufactured by a method comprising: The process includes a welding step, which welds a high-strength portion having high tensile strength to a low-strength portion having lower tensile strength than the high-strength portion; and a forming step, which presses the low-strength portion to include a recess, the recess having a corner portion in the inner surfaces of the first sidewall and the second sidewall of a first sidewall that are adjacent to each other at an inferior angle, and a corner portion in the upper surface of a bottom wall that is at an inferior angle relative to the inner surfaces of the first and second sidewalls, respectively, wherein the... The tray has a bottom wall and peripheral side walls that are vertically disposed from the outer periphery of the bottom wall. The tray also has a high-strength portion having high tensile strength and a low-strength portion having lower tensile strength than the high-strength portion. The low-strength portion is formed by including a recess. The recess has a corner portion of the inner surfaces of the first side wall and the second side wall of the first side wall that are adjacent to each other at an inferior angle, and a corner portion of the upper surface of the bottom wall that forms an inferior angle with respect to the inner surfaces of the first and second side walls, respectively.

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