BODY FORMED BY HOT STAMPING

Abstract

This hot-stamped body has a predetermined chemical composition and a metallographic structure consisting, in area ratio, of a total of 10% to 30% granular ferrite and bainite and the remainder in the microstructure consisting of one or more martensite, bainite, and tempered martensite, and, in textures of a surface layer region and an interior region, the ratios between a pole density of an orientation group consisting of {001} <1-10> to {001} <-1-10> and a pole density of an orientation group consisting of {111} <1-10> to {111} <-1-12> are controlled.

Description

BODY FORMED BY HOT STAMPING TECHNICAL FIELD OF THE INVENTION [1] The present invention relates to a body formed by hot stamping. Priority is claimed over Japanese Patent Application No. 2020-084591, filed on May 13, 2020, the contents of which are incorporated herein by reference. BACKGROUND OF THE TECHNIQUE [2] In recent years, there has been a demand for a reduction in vehicle body weight for environmental protection and resource conservation, and high-strength steel sheet has been applied to vehicle members. Vehicle members are manufactured by pressure forming, but not only does the forming load increase, but formability also deteriorates as the strength of the steel sheet increases. For this reason, the formability of high-strength steel sheet in the shape of a member with a complex form becomes a problem. [3] To address this problem, the application of hot stamping techniques is underway. In this technique, pressure forming is performed after a steel sheet is heated to a high temperature within the austenite range, where the steel sheet softens. Hot stamping is gaining attention as a technique that achieves both the formability of a steel sheet into the shape of a vehicle component and the strength of the component by hardening the steel sheet in a die simultaneously with pressure working. [4] In order to achieve a greater effect of reducing the weight of a vehicle body from a vehicle member formed by hot stamping of a steel sheet, it is necessary to obtain a member that has high strength and also excellent collision characteristics. As a technique to improve the collision characteristics of a vehicle member, in particular, a technique to improve the foldability of the vehicle member is being studied. [5] Patent Document 1 discloses a high-strength stamped component having excellent shock-absorbing characteristics, wherein the hardness of the stamped component at the center of the sheet thickness is Hv400 or more, a soft layer having a hardness of Hv300 or less is provided on a surface layer of the stamped component, and the thickness of the soft layer is 20 to 200 pm. [6] Patent Document 2 discloses a high-strength cold-rolled steel sheet having excellent uniform elongation and hole expandability, in which the texture is controlled in the central portion of the steel sheet. [7] During bending distortion, distortion begins at the surface of a vehicle member and gradually progresses into the interior. Therefore, to further improve the bendability of the vehicle member, it is effective to first enhance the bending distortion capacity of the surface layer of the vehicle member and then enhance the bending distortion capacity of the interior of the vehicle member. Patent Documents 1 and 2 do not consider improvements in the bending distortion capacities of either the surface layer or the interior of the vehicle member. [8] Furthermore, when the surface layer of a vehicle member is softened to improve the member's pliability, a problem of ductility deterioration arises. Prior art document Patent Document [9] Patent Document 1: Unexamined Japanese patent application, first publication No. 2015-30890 Patent Document 2: International Publication PCT No. WO2012 / 144567 ινΐΛ / a / zuzz / uii DISCLOSURE OF THE INVENTION Problems to be solved by the invention

[10] The present invention has been made with view to the aforementioned problem. An object of the present invention is to provide a hot-formed body having excellent strength, foldability, and ductility. Means to solve the problem

[11] The essence of the present invention is as follows. (1) A body formed by hot stamping according to an aspect of the present invention contains, as a chemical composition, % by mass, C: 0.15 to 0.50%, Yes: 0.0010% to 3.000%, Mn: 0.30% to 3.00%, Al: 0.0002% to 2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0% to 0.15%, Ti: 0% to 0.15%, V: 0% to 0.15%, Mo: 0% to 1.0%, Cr: 0% to 1.0%, Cu: 0% to 1.0%, Ni: 0% to 1.0%, B: 0% to 0.0100%, Ca: 0% to 0.010%, REM: 0% to 0.30%, and the remainder consisting of Fe and an impurity, wherein the hot-formed body has a metallographic structure consisting, in area ratio, of a total of 10% to 30% granular ferrite and bainite and the remainder in the microstructure consisting of one or more martensite, bainite, and tempered martensite, in a texture between a surface and a position 1 / 4 sheet thickness from the surface, a ratio between a pole density of an orientation group consisting of {001} <1-10> to {001} <-1-10> and a pole density of an orientation group consisting of {111} <l-10>a {111} <-l12> is less than 1.8, and in a texture between the position of 1 / 4 sheet thickness from the surface and a position of 1 / 2 sheet thickness from the surface, a ratio between a pole density of an orientation group consisting of {001} <l-10>to {001} <-l-10> and a pole density of an orientation group consisting of {111} <l-10>a {111} <-l-12> is less than 2.3. (2) The body formed by hot stamping in accordance with (1) may additionally contain, as its chemical composition, % by mass, one or more of the group consisting of Nb: 0.05% to 0.15%, Ti: 0.05% to 0.15%, V: 0.05% to 0.15%, Mo: 0.05% to 1.0%, Cr: 0.05% to 1.0%, Cu: 0.05% to 1.0%, Ni: 0.05% to 1.0%, B: 0.0001% to 0.0100%, Ca: 0.001% to 0.010%, and REM: 0.001% to 0.30%. (3) The body formed by hot stamping in accordance with (1) or (2), in which a decarburization index may be 0.085 or more. Effects of the Invention

[12] In accordance with the above-mentioned aspect of the present invention, it is possible to provide a hot-stamped body that has excellent strength, foldability, and ductility. MODALITIES OF THE INVENTION

[13] The present inventors studied a method that allows not only obtaining a (maximum) tensile strength of 1.5 to 2.5 GPa and excellent pliability but also suppressing the deterioration of ductility after hot stamping. As a result, the present inventors found that, in a hot-stamped body, when the surface layer of the steel sheet is softened, and additionally, the texture is controlled at a predetermined position in the sheet thickness direction, it is possible to obtain higher strength and superior pliability than ever before and to suppress the deterioration of ductility.

[14] The texture is affected by the texture and carbon concentration of the metallographic structure before hot stamping. Accordingly, the present inventors found that, in order to obtain a desired texture in the hot-stamped body, it is effective to control the texture in the steel sheet after hot rolling and, additionally, to reduce the amount of carbon in the surface layer of the steel sheet during subsequent annealing.

[15] From now on, a hot-forming steel sheet for manufacturing a hot-formed body according to the present embodiment by hot stamping will be described in detail. First, the reasons for limiting the chemical composition of the hot-forming steel sheet will be described.

[16] The numerical limiting ranges expressed below using 'a' include the lower and upper limits in the ranges. Numerical values ​​expressed with 'greater than' and 'less than' are not included in the numerical ranges. With respect to chemical composition, % indicates % by mass in all cases.

[17] The hot-forming steel sheet for manufacturing the hot-formed body according to the present modality by hot stamping contains, as a chemical composition, % by mass, 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: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0% to 0.15%, Ti: 0% to 0.15%, V: 0% to 0.15%, Mo: 0% to 1.0%, Cr: 0% to 1.0%, Cu: 0% to 1.0%, Ni: 0% to 1.0%, B: 0% to 0.0100%, Ca: 0% to 0.010%, REM: 0% to 0.30%, and the remainder consisting of Fe and an impurity. From now on, each element will be described.

[18] C: 0.15% to 0.50% Carbon (C) is an element that improves the strength of hot-formed parts. When the carbon content is less than 0.15%, the desired strength of the hot-formed part cannot be achieved. For this reason, the carbon content is set at 0.15% or higher. The preferred carbon content is 0.17% or higher, 0.20% or higher, or 0.23% or higher. Furthermore, when the carbon content is greater than 0.50%, excellent pliability cannot be obtained. For this reason, the carbon content is set at 0.50% or lower. The preferred carbon content is 0.46% or lower, or 0.43% or lower.

[19] Yes: 0.0010% to 3.000% Silicon (Si) is an element that improves the strength of hot-formed bodies by strengthening the solid solution. When the Si content is less than 0.0010%, the desired strength cannot be achieved. For this reason, the Si content is set at 0.0010% or higher. The preferred Si content is 0.050% or higher, 0.100% or higher, 0.300% or higher, or 0.500% or higher. On the other hand, when the Si content is greater than 3.000%, the amount of ferrite increases, and the desired metallographic structure cannot be obtained. For this reason, the Si content is set at 3.000% or lower. The preferred Si content is 2.700% or lower, or 2.500% or lower.

[20] Mn: 0.30% to 3.00% Manganese (Mn) is an element that improves the hardenability of steel. To enhance hardenability and consequently obtain a desired amount of martensite after hot forging, the Mn content is set at 0.30% or more. The preferred 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 is likely to occur, and excellent pliability cannot be achieved. For this reason, the Mn content is set at 3.00% or less. The preferred Mn content is 2.70% or less, 2.50% or less, or 2.30% or less.

[21] Al: 0.0002% to 2.000% Aluminum (Al) is an element that improves the formability of molten steel by deoxidizing it, suppressing oxide formation, which is the source of fracture. It also improves the pliability of hot-formed parts. When the Al content is less than 0.0002%, deoxidation is insufficient, and a thick oxide layer forms, preventing the aforementioned effect. For this reason, the Al content is set at 0.0002% or higher. Preferably, the Al content is 0.001% or higher. Furthermore, when the Al content exceeds 2.000%, a thick oxide layer forms on the steel, impairing the pliability of hot-formed parts. Therefore, the Al content is set at 2.000% or lower. Preferably, the Al content is 1.700% or lower, or 1.500% or lower.

[22] P: 0.100% or less Phosphorus (P) is an impurity and can cause fracture by segregating at grain boundaries. For this reason, P content is limited to 0.100% or less. Preferably, P content is 0.050% or less. While the lower limit for P content is not strictly enforced, reducing it to less than 0.0001% significantly increases the cost of dephosphorization, which is not economically viable. Therefore, P content can be set at 0.0001% or higher.

[23] S: 0.1000% or less Sulfur (S) is an impurity element and forms an inclusion in steel. Because this inclusion serves as the source of fracture, the S content is limited to 0.1000% or less. The S content is preferably 0.0500% or less, or 0.0300% or less. The lower limit for the S content is not particularly restricted, but reducing the S content to less than 0.0001% significantly increases the cost of desulfurization, which is not economically desirable. For this reason, the S content can be set at 0.0001% or higher.

[24] N: 0.0100% or less Nitrogen (N) is an impurity element and forms nitride in steel. Because this nitride is the source of fracture, the N content is limited to 0.0100% or less. Ideally, the N content is 0.0050% or less. The lower limit for N content is not particularly restricted, but reducing it to less than 0.0001% significantly increases the cost of denitrification, which is not economically desirable. For this reason, the N content can be set at 0.0001% or higher.

[25] The remainder of the chemical composition of hot-formed steel sheet may be Fe and impurities. Elements that are inevitably mixed in from scrap or steel raw material and / or during steelmaking and are permitted within a range where the characteristics of the hot-formed body are not impaired are exemplary examples of impurities.

[26] Hot stamping steel sheet may contain the following elements as arbitrary elements in place of a portion of Fe. The contents of the following arbitrary elements, obtained in a case where the following arbitrary elements are not contained, are 0%.

[27] Nb: 0% to 0.15% Ti: 0% to 0.15% V: 0% to 0.15% Nitrogen (Nb) and titanium (Ti) enhance the strength of hot-formed parts through precipitation hardening by forming carbonitride in the steel. To reliably achieve this effect, the Nb, Ti, and V content is preferably set at 0.05% or higher. Conversely, if the Nb, Ti, and V content exceeds 0.15%, a significant amount of carbonitride forms in the steel, impairing the ductility of the hot-formed part. Therefore, the Nb, Ti, and V content is each set at 0.15% or lower.

[28] Mo: 0% to 1.0% Cr: 0% to 1.0% Cu: 0% to 1.0% Ni: 0% to 1.0% Molybdenum (Mo) and chromium (Cr) increase the strength of hot-formed parts by forming a solid solution with the pre-formed austenite grains during preheating. To reliably achieve this effect, the content of each Mo, Cr, Cu, and Ni is preferably set at 0.05% or higher. However, because the effect saturates even with higher concentrations of Mo, Cr, Cu, and Ni, the Mo, Cr, Cu, and Ni contents are preferably set at 1.0% or lower each.

[29] B: 0% to 0.0100% Boron (B) is an element that improves the hardenability of steel. To reliably achieve this effect, the B content is preferably set at 0.0001% or higher. However, even when the B content is set above 0.0100%, the effect on hardenability improvement is saturated. For this reason, the B content is typically set at 0.0100% or lower.

[30] Ca: 0% to 0.010% REM: 0% to 0.30% Calcium (Ca) and mineral spirits (MS) are elements that improve distortion capacity by suppressing the formation of an oxide that serves as the origin of fracture, thus enhancing the foldability of the hot-formed body. To reliably achieve this effect, the Ca and MS content is preferably set at 0.001% or higher. However, because the effect saturates even with a high concentration of Ca and MS, the Ca content is set at 0.010% or lower, and the MS content at 0.30% or lower.

[31] In this modality, REM refers to a total of 17 elements composed of Se, Y, and lanthanides and the content of REM refers to the total content of these elements.

[32] The aforementioned chemical composition of hot-formed steel sheet can be measured using ordinary analytical methods. For example, the chemical composition of the aforementioned hot-formed body can be measured using inductively coupled plasma atomic emission spectrometry (ICP-AES). Carbon and sulfur can be measured using an infrared combustion absorption method, and nitrogen can be measured using an inert gas fusion thermal conductivity method. In cases where a plating layer is applied to the surface of the hot-formed steel sheet, the chemical composition can be analyzed after the plating layer is removed by mechanical grinding.

[33] The metallographic structure of the hot-stamped steel sheet for manufacturing the hot-stamped body according to the present modality by hot stamping will now be described. Hot stamping steel sheet has a metallographic structure consisting, by area, of 20% to 80% ferrite, granular bainite, bainite, and martensite, with the remainder comprising a microstructure of pearlite and a carbide. With respect to the metallographic structure described below, % indicates % by area in all cases.

[34] Ferrite, granular bainite, bainite, and martensite: 20% to 80% Ferrite, granular bainite, bainite, and martensite are structures necessary to achieve a desired texture in a hot-formed body. When the total area ratio of these structures is less than 20%, it is not possible to obtain a desired texture in the hot-formed body. For this reason, the ferrite area ratio is set at 20% or higher. The ferrite area ratio is preferably 30% or higher, or 40% or higher. On the other hand, when the area ratio of these structures is greater than 80%, the carbon is concentrated in the pearlite, which is the remaining material. This makes it difficult for a carbide to dissolve during the hot-forming heating process, and the carbide becomes the source of cracking during distortion. Consequently, the area ratio is set at 80% or lower. The area ratio is preferably 70% or lower, or 60% or lower.

[35] Remainder in the microstructure: Pearlite and carbide The remainder of the metallographic structure of hot-stamped steel sheet consists of pearlite and a carbide. Since the metallographic structure of hot-stamped steel sheet does not contain structures other than the aforementioned pearlite and carbide, the area ratio of the remainder in the microstructure can be established at 20% to 80%.

[36] Method for measuring the metallographic structure of hot stamping steel sheet A sample is cut from an arbitrary position 50 mm or more away from an extreme surface of the hot-forming steel sheet (a position that avoids an extreme portion in a case where the sample cannot be collected at that position) so that a cross-section of sheet thickness parallel to a rolling direction can be observed. The size of the sample also depends on a measuring device, but it is set to a size that allows observation for approximately 10 mm in the rolling direction.

[37] After polishing using silicon carbide paper with an abrasive grit of #600 to #1500, the cross-section of the sample is finished to a mirror surface using a liquid in which diamond powder with a grain size in the range of 1 µm to 6 µm is dispersed in a dilute solution of alcohol or similar solvent or pure water and polished to a finish using a colloidal silica solution. Analysis is then performed on a region 50 µm long, located between a depth corresponding to 1 / 8 of the sheet thickness from the surface and a depth corresponding to 3 / 8 of the sheet thickness from the surface at an arbitrary position in the cross-section of the sample in a longitudinal direction at an analysis rate of 200 to 300 points / second using an EBSD analyzer including a Schottky emission scanning electron microscope (JSM-7001F manufactured by JEOL Ltd.).and an EBSD detector (DVC 5 type detector manufactured by TSL Solutions). The area ratio of a region where the crystal structure is bcc is calculated using a phase map function installed in the OIM Analysis software (registered trademark) included in an EBSD analyzer, so the total area ratio of ferrite, granular bainite, bainite, and martensite can be obtained.

[38] Pearlite and carbide can be identified by the following method. After polishing using silicon carbide paper having an abrasive of #600 to #1500, the cross-section of the sample is finished to a mirror surface using a liquid in which diamond powder having a grain size in the range of 1 µm to 6 µm is dispersed in a dilute solution of alcohol or similar or pure water, and etched with Nital. Photographs having a plurality of fields of view are then taken using a Schottky emission scanning electron microscope (JSM-7001F manufactured by JEOL Ltd.) in a region that has a length of 50 µm and is present between a depth corresponding to 1 / 8 of the sheet thickness from the surface and a depth corresponding to 3 / 8 of the sheet thickness from the surface at an arbitrary position in the cross-section of the sample in a longitudinal direction.Uniformly spaced grids are drawn on the photographs, and structures are identified at the grid points. The number of grid points corresponding to each structure is calculated and divided by the total number of grid points, yielding the area ratio for that structure. The area ratio can be obtained more precisely as the total number of grid points increases. In this method, the grid spacing is set to 2 pm × 2 pm, and the total number of grid points is set to 1500. Particles with a bright luster are considered to be carbide, and a region where these lustrous particles are arranged in a sheet-like or granular form, as well as in a sheet-like form, is considered to be pearlite.

[39] The texture of the hot stamping steel sheet for making the hot stamped body according to the present modality by hot stamping will now be described. In hot stamping steel sheet, the ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12> is less than 1.5 in the texture between the surface and the position 1 / 4 sheet thickness from the surface, and the ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12> is less than 2.0 in the texture between the position of 1 / 4 sheet thickness from the surface and the position of 1 / 2 sheet thickness from the surface.

[40] The orientation group consisting of {001} <l-10>{001} <-l-10> includes crystal orientations of {001} <1 ινΐΛ / a / zuzz / uii 1Ο>, {001} <1-20>, {001} <0-10>, and {001} <-1-10>. The orientation group consisting of {111} <l-10>a {111} <-l-12> includes crystal orientations of {111} <l-10> , {111} <l-20>, {111} <0-10>, and {111} <-l-12>.

[41] Texture between the surface and the position 1 / 4 sheet thickness from the surface: Ratio between the pole density of the orientation group consisting of {001} <1-10> to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12> which is less than 1.5 In the texture between the surface and the position 1 / 4 sheet thickness from the surface (hereafter referred to as the surface layer region in some cases), the ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12> is set to less than 1.5.

[42] When the texture in the surface layer region of the hot-forming steel sheet is preferably controlled, it is possible to suppress carbon recovery in the surface layer region (carbon diffusion from the interior region to the surface layer region having a low concentration of C) during heating for hot forming, and, when a texture is developed that readily relaxes the stress introduced by bending distortion in the surface layer region where the energy attributed to distortion is absorbed, such as in proximity to the surface of the steel sheet, it is possible to obtain a hot-forming steel sheet that has excellent pliability after hot forming.

[43] When the relationship between the density of poles of the orientation group consisting of {001} <l-10>to {001} <-l10> and the pole density of the orientation group consisting of {111} <l-10>If the {111} <-l-12> of the texture in the surface layer region is 1.5 or more, the aforementioned effect cannot be obtained. Therefore, the relationship between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>The {111} <-l-12> of the texture in the surface layer region is set to less than 1.5. The ratio is preferably less than 1.2.

[44] The relationship between the density of poles of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>The {111} <-l-12> texture in the surface layer region can be set to 0.4 or more from the point of view of ensuring the strength of the hot-stamped body.

[45] Texture between the position of 1 / 4 sheet thickness from the surface and the position of 1 / 2 sheet thickness from the surface: Ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l10> and the pole density of the orientation group consisting of {111} <1-10> to {111} <-l-12> which is less than 2.0 In the texture between the position 1 / 4 sheet thickness from the surface and the position 1 / 2 sheet thickness from the surface (hereafter referred to as the interior region in some cases), the ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12> is set to less than 2.0.

[46] When the texture in the interior region of the hot-forming steel sheet is preferably controlled, it is possible to develop a texture that includes grain boundaries that do not easily fracture in a region that resists a load, such as the near-interior of the steel sheet, and also improve load-bearing capacity while maintaining excellent pliability. When the ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>If the {111} <-l-12> of the texture in the interior region is 2.0 or more, the aforementioned effect cannot be obtained. Therefore, the relationship between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>The {111} <-l-12> of the texture in the interior region is set to less than 2.0. The ratio is preferably less than 1.6.

[47] The relationship between the density of poles of the orientation group consisting of {001} <l-10>a {001} <-l-10> and the pole density of the orientation group consisting of {111} <1-10> to {111} <-l-12> of the texture in the interior region can be set to 0.4 or more from the point of view of ensuring toughness.

[48] ​​Method for measuring pole density The pole densities of the surface layer region and the interior region are measured using the following method. The pole densities of the surface layer region and the interior region can be obtained from an orientation distribution function (ODF) that displays a computationally calculated three-dimensional texture, using spherical harmonics, orientation data measured by an electron backscatter diffraction (EBSD) method using a device in which a scanning electron microscope and an EBSD analyzer are combined, and OIM Analysis (registered trademark) manufactured by TSL Solutions.

[49] The measurement ranges are a region between the surface and the position 1 / 4 sheet thickness from the surface (a region between the surface as the starting point and the position 1 / 4 sheet thickness in the sheet thickness direction from the surface as the ending point) for the surface layer region and a region between the position 1 / 4 sheet thickness from the surface and the position 1 / 2 sheet thickness from the surface (a region between the position 1 / 4 sheet thickness in the sheet thickness direction from the surface as the starting point and the position 1 / 2 sheet thickness in the sheet thickness direction from the surface as the ending point) for the interior region. The measurement steps are set at 5 pm / stage.

[50] A value obtained by dividing the average value of the pole densities of the orientation group consisting of {001} <1-10> to {001} <-l-10> by the average value of the pole densities of the orientation group consisting of {111} <1-10> to {111} <-l-12> is considered to be the ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12>.

[51] It should be noted that {hkl} indicates a glass plane parallel to a laminated surface and <uvw>indicates a crystal direction parallel to a rolling direction. That is, {hkl} <uvw>indicates a crystal in which {hkl} is oriented in the normal direction to the sheet surface and <uvw>It is oriented in the direction of rolling.

[52] The hot-forming steel sheet mentioned above may have a plating layer on its surface. The plating layer provided on the surface makes it possible to improve corrosion resistance after hot-forming. Such plating layers include aluminum plating, aluminum-zinc plating, aluminum-silicon plating, hot-dip galvanizing, electrogalvanizing, hot-dip electroannealing, or similar coatings.

[53] decarburization index of hot stamping steel sheet that is 0.085 or more By controlling the decarburization index of hot-forming steel sheet, it is possible to promote the development of textures that include grain boundaries that do not easily fracture in load-bearing regions, such as the near-inner area of ​​the steel sheet. This also improves load-bearing capacity while maintaining excellent pliability. The decarburization index is preferably 0.140 or higher, and even more preferably 0.180 or higher. Due to the method used to calculate the decarburization index, the upper limit becomes 1.000.

[54] Method for measuring the decarburization index The decarburization index quantifies the amount of carbon reduced in the surface layer of the steel sheet and can be calculated using the following method. The concentration distribution of elements along the sheet thickness direction in the hot-forming steel sheet is measured using light discharge optical emission spectrometry (GD-OES). The measurement range is set to a depth of 200 pm from the outermost surface of the steel sheet, and the measurement intervals are set to 0.02 pm or less. All elements contained in the hot-forming steel sheet are measured.

[55] For steel sheets having a plating layer, coating film, or the like on the surface, part or all of the plating layer, coating, or the like is removed by mechanical or chemical polishing so that measurement becomes possible to a depth of 200 pm from the outermost surface of the steel sheet, and the GD-OES measurement is performed. In the GD-OES measurement, a region where the iron concentration becomes 90% by mass or more is determined to be the steel sheet, and a measurement point where the iron concentration becomes 90% by mass is defined as the position on the outermost surface of the steel sheet.

[56] Next, the average value of the measurement values ​​(1000 points or more) of the carbon concentration of the position of the outermost surface of the steel sheet at a depth of 180 pm to a depth of 200 pm is calculated, and this average value is considered to be the carbon concentration of the base metal of the steel sheet. Alternatively, with respect to the measurement value of the carbon concentration in a region of 20 pm from the deepest portion towards the surface layer, in a case where the absolute value of the difference between the average value of the carbon concentrations in the regions of 20 pm from the deepest portion towards the surface layer and the maximum value of the measurement values ​​of the carbon concentrations in the regions of 20 pm from the deepest portion towards the surface layer is 0.1% or less, and the absolute value of the difference between the average value of the carbon concentrations in the regions of 20 pm from the deepest portion towards the surface layer and the minimum value of the measurement values ​​of the carbon concentrations in the regions of 20 pm from the deepest portion towards the surface layer is 0.1% or less, the average value of carbon concentrations in the 20 pm regions from the deepest portion towards the surface layer can be considered as the carbon concentration of the base metal of the steel sheet. The unit depth is 20 pm, and the deepest portion refers to each deep position in a case where the positions are marked at each unit depth from the outermost surface of the steel sheet down to a depth of 200 pm. For example, in a case where the deepest portion is 120 pm, the carbon concentration measurement value in the 20 pm region from the deepest portion toward the surface layer means the carbon concentration at a measurement point that is between the 100 pm and 120 pm positions.

[57] The amount of carbon concentration decreased per unit depth (a value obtained by subtracting the carbon concentration at each measurement point from the carbon concentration of the base metal) is calculated from the position of the outermost surface of the steel sheet to the depth position of 200 pm, and the integrated value of the product of the unit depth and the amount of carbon concentration decreased is obtained and considered as the area of ​​a carbon-deficient region (area A). Then, the product of the carbon concentration of the base metal and 200 pm is considered as a reference area (area B), and a value obtained by dividing the carbon-deficient area (area A) by the reference area (area B) is considered as the decarburization index.

[58] The hot-formed body according to the present embodiment will now be described. The hot-formed body according to the present embodiment can be obtained by applying a manufacturing method to be described below to the hot-formed steel sheet described above. In the hot-formed body according to the present embodiment, the texture changes between the surface layer region and the interior region, thereby improving the foldability of the metallographic structure in the surface layer region, and one or more granular ferrite and bainite layers are formed to increase the ductility of the surface layer region.Specifically, in the surface layer region where the energy attributed to bending distortion is absorbed, a texture develops in which the stress introduced by bending distortion is easily relieved. In the interior region, which influences load-bearing capacity, a texture develops that includes grain boundaries that do not fracture easily. The chemical composition of the hot-formed body produced according to the present method is the same as the chemical composition of the hot-formed steel sheet described above and will therefore not be described again.

[59] The body formed by hot stamping according to the present modality has a metallographic structure consisting, in area ratio, of a total of 10% to 30% granular ferrite and bainite and the remainder in the microstructure consisting of one or more martensite, bainite and tempered martensite, the ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12> is less than 1.8 in the texture between the surface and the position 1 / 4 sheet thickness from the surface, and the ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12> is less than 2.3 in the texture between the position of 1 / 4 sheet thickness from the surface and the position of 1 / 2 sheet thickness from the surface. With respect to the metallographic structure to be described below, % indicates % by area in all cases.

[60] Granular ferrite and bainite: Total from 10% to 30% Ferrite and granular bainite are soft structures with excellent ductility. When the total area ratio of ferrite to granular bainite is less than 10%, the desired ductility cannot be achieved. Therefore, in the body formed by hot stamping according to the present method, the total area ratio of ferrite to granular bainite is set at 10% or more. The area ratio is preferably 15% or more, or 20% or more. Furthermore, when the total ferrite-to-bainite area ratio exceeds 30%, the desired strength cannot be achieved. Therefore, the total ferrite-to-bainite area ratio is set at 30% or less. Preferably, the area ratio is 27% or less, or 25% or less.

[61] In the present form, it may contain a total of 10% to 30% of granular ferrite and bainite or it may contain 10% to 30% of granular ferrite or bainite.

[62] Remainder in the microstructure: One or more of martensite, bainite, and tempered martensite The body formed by hot stamping according to the present embodiment has the remainder in the microstructure consisting of one or more layers of martensite, bainite, and tempered martensite. The area ratio of this remainder in the microstructure is preferably set at 70% or more in order to obtain a desired strength. The area ratio is preferably 73% or more or 75% or more. In addition, in order to obtain the desired ductility, the area ratio of this remainder in the microstructure may be set at 90% or less, 85% or less, or 80% or less.

[63] Method for measuring the area ratio of the metallographic structure A sample is cut from an arbitrary position 50 mm or more away from an extreme surface of the hot-formed body (a position that avoids an extreme portion in a case where the sample cannot be collected in that position) so that a cross-section of sheet thickness parallel to a rolling direction can be observed. The size of the sample also depends on a measuring device, but is set to a size that allows observation for approximately 10 mm in the rolling direction.

[64] After polishing using silicon carbide paper with an abrasive grit of #600 to #1500, the cross-section of the sample is finished to a mirror surface using a liquid in which diamond powder with a grain size in the range of 1 µm to 6 µm is dispersed in a dilute solution of alcohol or similar solvent or pure water. The sample is then polished for 8 minutes using colloidal silica containing no alkali solution at room temperature, thereby removing the stress introduced into the surface layer of the sample. A region, which is 50 µm long and located between a depth corresponding to 1 / 8 of the sheet thickness from the surface and a depth corresponding to 3 / 8 of the sheet thickness from the surface, is measured at a measurement interval of 0.1 pm at an arbitrary position in the cross-section of the sample in a longitudinal direction using an electron backscatter diffraction method, thus obtaining crystal orientation information. An EBSD analyzer consisting of a Schottky emission scanning electron microscope (JSM-7001F manufactured by JEOL Ltd.) and an EBSD detector (DVC 5 type detector manufactured by TSL Solutions) is used for the measurement. In this case, the vacuum level in the EBSD analyzer is set to 9.6 * 10⁻⁵ Pa or less, the accelerating voltage is set to 15 kV, the irradiation current level is set to 13, and the electron beam irradiation level is set to 62.

[65] A region where the crystal structure is bcc is specified using the obtained crystal orientation information and the phase map function of the OIM Analysis software (registered trademark) included in an EBSD analyzer. Regions where the crystal structure is bcc are determined to be martensite, bainite, tempered martensite, granular bainite, and ferrite. In these regions, areas where the average grain orientation misorientation value is greater than 3.0° are determined to be martensite, bainite, and tempered martensite using the average grain misorientation function of the OIM Analysis software (registered trademark) included in the EBSD analyzer, and the sum of these area ratios is calculated, thereby obtaining the total area ratio of martensite, bainite, and tempered martensite. Regions where the average grain misorientation value is 3.0° or less are determined as granular ferrite and bainite, and the total of these area ratios is calculated, thus obtaining the total area ratio of granular ferrite and bainite.

[66] Texture between the surface and the position 1 / 4 sheet thickness from the surface: Ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12> which is less than 1.8 In the texture between the surface and the position 1 / 4 sheet thickness from the surface (surface layer region), when the ratio between the pole density of the orientation group consisting of {001} <l-10>If the ratio of the pole density of the orientation group consisting of {001} <-l10> to {111} <1-10> to {111} <-l-12> is less than 1.8, foldability can be improved. Consequently, in the surface layer region texture, the ratio of the pole density of the orientation group consisting of {001} <1—10> to {001} <—1—10> to the pole density of the orientation group consisting of {111} <-l-12> is less than 1.8. <l-10>a {111} <-l-12> is set to less than 1.8. The ratio is preferably less than 1.7 or less than 1.6.

[67] The relationship between the density of poles of the orientation group consisting of {001} <l-10>a {001} <-l-10> and the pole density of the orientation group consisting of {111} <1-10> to {111} <-l-12> of the surface layer region texture can be set to 0.4 or more from the point of view of ensuring strength.

[68] Texture between the position of 1 / 4 sheet thickness from the surface and the position of 1 / 2 sheet thickness from the surface: Ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l10> and the pole density of the orientation group consisting of {111} <1-10> to {111} <-l-12> which is less than 2.3 In the texture between the position of 1 / 4 sheet thickness from the surface and the position of 1 / 2 sheet thickness from the surface (interior region), when the ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>If {111} <-l-12> is set to less than 2.3, ductility can be improved. Consequently, in the texture of the interior region, the relationship between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12> is set to less than 2.3. The relation is preferably less than 2.2 or less than 2.1.

[69] The relationship between the density of poles of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <1-10> to {111} <-l-12> of the texture of the interior region can be set to 0.4 or more from the point of view of ensuring toughness.

[70] The pole densities of the surface layer region and the interior region can be measured using the same method as for hot-formed steel sheet. However, the rolling direction in the hot-formed body can be determined using the following method. First, a test piece is collected in such a way that the cross-section of the sheet thickness of the hot-stamped body can be observed. The cross-section of the collected sheet thickness sample is finished by mirror polishing and then observed using an optical microscope. The observation range is set to the overall thickness of the sheet, and a region where the gloss is dark is identified as an inclusion. Among inclusions, for those with a major axis length of 40 pm or more, a direction parallel to the direction in which the inclusion extends is determined to be the rolling direction.

[71] The body formed by hot stamping according to the present embodiment may have a plating layer on one surface. The plating layer provided on the surface makes it possible to improve corrosion resistance after hot stamping. Such plating layer includes, for example, an aluminum plating layer, an aluminum-zinc plating layer, an aluminum-silicon plating layer, a hot-dip galvanized layer, an electrogalvanized layer, a hot-dip electroannealed layer, or the like.

[72] decarburization index of the hot-formed body that is 0.085 or more By carefully controlling the decarburization index of the hot-formed body, it is possible to promote the development of a texture that includes grain boundaries that do not easily fracture in a load-bearing region, such as near the interior of the steel sheet. This also improves load-bearing capacity while maintaining excellent pliability. The decarburization index is preferably 0.140 or higher, and more preferably 0.180 or higher. Due to the method used to calculate the decarburization index, the upper limit becomes 1.000; however, to further improve load-bearing capacity while maintaining excellent pliability, the upper limit is preferably 0.500 or lower, and more preferably 0.040 or lower.

[73] The decarburization index of the hot-formed body can be measured by the same method as that for hot-formed steel sheet.

[74] Method of manufacturing steel sheet for hot stamping From now on, a preferred method of manufacturing hot stamping steel sheet for manufacturing the hot stamped body according to the present modality by hot stamping will be described.

[75] First, it is preferable that a casting be heated to 1200 °C or higher and held for 20 minutes or more, and then, in a hot rolling process, a roll that is one pass before a final roll is carried out in a temperature range of 850 °C to 900 °C with a roll reduction of 8% to 30%. The hot rolling is then preferably completed in a temperature range of 800 °C or higher and lower than 850 °C with a roll reduction of 6% to 12%. That is, the final roll of the hot roll is preferably carried out in a temperature range of 800 °C or higher and lower than 850 °C with a roll reduction of 6% to 12%.

[76] It is preferable that, after 2.5 seconds or more have elapsed since the end of hot rolling, cooling be carried out at an average cooling rate, in a temperature range from the final hot-rolling temperature down to 450 °C, of ​​less than 10 °C / s. After that, the hot-rolled steel sheet is preferably coiled at a temperature range of 700 °C or lower. Additionally, it is preferable that decarburizing annealing be performed, thereby producing a hot-forming steel sheet having the chemical composition described above.

[77] The present inventors found that a texture that improves bending distortion capability and load-bearing capacity after hot stamping is developed by the transformation of austenite, including a small amount of dislocation, to granular ferrite or bainite. Consequently, when the rolling one pass prior to the final rolling is carried out at less than 850 °C or at a rolling reduction of more than 30%, there is a case where the casting is finally rolled while the austenite dislocation remains unrecovered prior to the transformation, the transformation of austenite, including the dislocation, to ferrite occurs, and the development of a desired texture is impaired.

[78] On the other hand, when the rolling one pass before the final rolling is done at more than 900 °C or is done at a rolling reduction of less than 8%, there is a case where dislocation recovery is excessively promoted, the dislocation density in the austenite becomes too low, and a desired texture cannot be obtained. Therefore, the one-pass rolling before the final rolling in hot rolling is preferably carried out in a temperature range of 850 °C to 900 °C at a rolling reduction of 8% to 30%.

[79] When the final rolling is done at less than 800 °C or is done at a rolling reduction greater than 12%, there is a case where the casting is finally rolled while the austenite dislocation remains unrecovered before the transformation, the austenite transformation occurs which includes the dislocation to ferrite, and the development of a desired texture deteriorates.

[80] On the other hand, when the final rolling is done at 850 °C or higher or is done at a rolling reduction of less than 6%, there is a case where dislocation recovery is excessively promoted, and in this way the dislocation density in the austenite becomes too low, and a desired texture cannot be obtained. Therefore, the final rolling of hot rolling is preferably carried out in a temperature range of 800 °C or higher and lower than 850 °C at a rolling reduction of 6% to 12%.

[81] It is preferable to begin cooling after 2.5 seconds or more have elapsed since the end of hot rolling. When a time of 2.5 seconds or more is ensured before the start of cooling, the phase transformation to granular ferrite or bainite is promoted, and a desired texture can be sufficiently developed. When the elapsed time is less than 2.5 seconds, there is a case where a desired texture cannot be obtained.

[82] After 2.5 seconds or more have elapsed since the completion of hot rolling, when the average cooling rate over a temperature range from the final hot rolling temperature to 450 °C is established at less than 10 °C / s, the phase transformation to granular ferrite or bainite is promoted, and a desired texture can be sufficiently developed. When the average cooling rate over the above-described temperature range is 10 °C / s or greater, a desired texture cannot be obtained. The average cooling rate mentioned here is defined as a value obtained by dividing a temperature difference between the starting point and the ending point of a set range by the time elapsed from the starting point to the ending point.

[83] When the winding temperature is greater than 700 °C, there is a case where dislocation recovery is excessively promoted and a desired texture is not developed. Therefore, the winding temperature is preferably set at 700 °C or lower. Hot stamping steel sheet is obtained using the above method.

[84] It is preferable to perform decarburization annealing on the hot-forming steel sheet obtained by the above method. Before decarburization annealing, a softening heat treatment may be performed as required, and additionally, cold rolling may be carried out at a cumulative roll reduction (= {1 - (sheet thickness after cold rolling / sheet thickness before cold rolling)} × 100) of 30% to 70%. Plating may be performed on a decarburization annealing line, or a plating annealing line may be re-steered after the completion of decarburization annealing.Such as a plating layer imparted to the surface of hot-stamped steel sheet, an aluminum plating layer, an aluminum-zinc plating layer, an aluminum-silicon plating layer, a hot-dip galvanized layer, an electrogalvanized layer, a hot-dip electroannealed layer, or similar is an exemplary example.

[85] Decarburization annealing reduces the amount of carbon in the surface layer region of hot-forming steel sheet. Under decarburization annealing conditions, it is preferable that the atmosphere be humidified and contain hydrogen, nitrogen, or oxygen. The decarburization annealing temperature (the maximum achievable temperature of the steel sheet) is set at 700 °C to 950 °C, and the residence time in the temperature range of 700 °C to 950 °C is set at 5 seconds to 1200 seconds. The residence time mentioned here refers to the time from when the temperature of the steel sheet rises and reaches 700 °C until the temperature of the steel sheet, held between 700 °C and 950 °C, decreases and reaches 700 °C.

[86] When the maximum achievable temperature is less than 700 °C and the residence time in the temperature range of 700 °C to 950 °C is less than 5 seconds, because C diffusion is not sufficiently promoted, there is a case where decarburization does not occur and the texture of the surface layer region cannot be controlled. On the other hand, when the maximum achievable temperature is greater than 950 °C and the residence time in the temperature range of 700 °C to 950 °C is greater than 1200 seconds, there is a case where decarburization proceeds excessively and, in the texture of the surface layer region of the hot-formed steel sheet, the ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12> cannot be controlled at less than 1.5.

[87] A preferred method of manufacturing the hot-stamped body in accordance with the present embodiment using the hot-stamping steel sheet described above will now be described.

[88] First, it is preferable that the hot-forming steel sheet be heated and held at a temperature range of 800 °C to 1000 °C for 60 to 600 seconds. The average heating rate during heating can be set at 0.1 °C / second higher or 200 °C / second lower. The average heating rate mentioned here is a value obtained by dividing the temperature difference between the surface temperature of a steel sheet at the start of heating and a holding temperature by the time difference from the start of heating until the temperature reaches the holding temperature. Furthermore, during holding, the temperature of a steel sheet may fluctuate within the range of 800 °C to 1000 °C or it may remain constant.

[89] When the heating temperature is below 800 °C and the holding time is less than 60 seconds, there is a case where the dissolution of a carbide becomes impure and the remaining carbide acts as a starting point for cracking, degrading the foldability. When the heating temperature is above 1000 °C and the holding time is above 600 seconds, there is a case where the diffusion of C is excessively promoted, and the ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12> of the texture of the interior region cannot be set to less than 2.3.

[90] Exemplary examples of a heating method to ML / a / ZUZZ / U 1 I to be performed prior to hot stamping include heating using an electric oven, a gas oven, or similar, flame heating, energizing heating, high frequency heating, induction heating, and the like.

[91] After the steel sheet has been held within the temperature range described above, hot stamping is performed. In the method of manufacturing the hot-stamped body according to the present embodiment, the forming is preferably carried out at 300 °C or higher and lower than 650 °C. After hot stamping, it is preferable to cool the steel sheet to a temperature range of 300 °C or lower at a rate of 10 °C / s faster.

[92] In the hot-forming method of manufacturing the body according to the present embodiment, when the forming temperature is 650 °C or higher, the ratio of total ferrite to granular bainite area becomes less than 10%, and the desired ductility cannot be obtained. When the forming temperature is less than 300 °C, the forming load becomes too high, and there is a case where a die breaks.

[93] The hot-stamped body is obtained using the above method. After hot stamping, an annealing treatment can be carried out at 150 °C to 600 °C. In addition, a portion of the hot-stamped body can be tempered by laser irradiation or similar means to partially provide a softened region. EXAMPLES

[94] Examples of the present invention will now be described. The conditions in the examples are exemplary of the conditions adopted to confirm the feasibility and effect of the present invention, and the present invention is not limited to the exemplified conditions. The present invention is capable of adopting a variety of conditions, provided that the object of the present invention is achieved without departing from the essence of the present invention.

[95] Steel parts manufactured by casting molten steel having a chemical composition shown in Table 1-1 and Table 1-2 were held at a temperature of 1200°C or higher for 20 minutes or more, and then hot rolling, cold rolling, and decarburization annealing were performed under the conditions shown in Table 2-1 through Table 2-6. A softening heat treatment was performed prior to decarburization annealing as required. In addition, plating and plating annealing were performed as required. Accordingly, the hot-forming steel sheets shown in Table 3-1 through Table 3-3 were obtained.

[96] Hot stamping was performed on the obtained hot stamping steel sheet under the conditions shown in Tables 4-B1 to 4-B3, resulting in hot stamped parts. Some of the hot stamped parts underwent an annealing treatment at 150 °C to 600 °C after hot stamping. In addition, some of the hot stamped parts were partially irradiated with a laser, resulting in partially softened regions. Tables 5-B1 to 5-B3 show the microstructures and mechanical properties of the resulting hot stamped parts.

[97] The underlined values ​​in the tables indicate that the values ​​are outside the scope of the present invention, the preferred manufacturing conditions are not met, or the property values ​​are not preferred. Furthermore, the pole density ratio in the surface layer region texture in Table 5-B1 to Table 5-B3 indicates the ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12> in the texture between the surface and the position 1 / 4 sheet thickness from the surface, and the pole density ratio in the texture of the interior region indicates the ratio between the pole density of the orientation group consisting of {001} <l-10>to {001} <-l-10> and the pole density of the orientation group consisting of {111} <l-10>a {111} <-l-12> in the texture between the position of 1 / 4 sheet thickness from the surface and the position of 1 / 2 sheet thickness from the surface.

[98] The metallographic structures and textures of the hot-stamped steel sheet and hot-stamped bodies were measured using the measurement method described above. In addition, the mechanical properties of the hot-stamped body were evaluated using the following methods.

[99] Tensile strength and uniform elongation The tensile strength (maximum) and uniform elongation (uEl) of the hot-formed body were obtained by producing a test piece No. 5 from an arbitrary position of the hot-formed body in accordance with JIS Z 2241: 2011 and performing a tensile test. The crosshead speed was set to 3 mm / min.

[100] In a case where the tensile strength TS was 1500 MPa or more, the hot-formed body was determined to be acceptable due to its excellent strength, and, in a case where the tensile strength TS was less than 1500 MPa, the hot-formed body was determined to be unacceptable due to its poor strength. Furthermore, in a case where the product of the tensile strength TS and the uniform elongation uEl (TS x UuEl) was 6000 MPa-% or more, the hot-formed body was determined to be acceptable due to its excellent ductility, and, in a case where the product was less than 6000 MPa-%, the hot-formed body was determined to be unacceptable due to its poor ductility.

[101] Angle of bending The bending angle was evaluated using the following method based on the VDA standard (VDA238-100) specified by the Verband der Automobilindustrie. In the examples presented, the displacement under the maximum load obtained in a bending test was converted to an angle based on the VDA standard, thus obtaining the maximum bending angle α (°). In cases where the product (TS χ α) of the tensile strength TS and the maximum bending angle α obtained using the method described above was 75,000 MPa · ° or higher, the hot-formed body was deemed acceptable due to its excellent pliability. In cases where the product was less than 75,000 MPa · °, the hot-formed body was deemed unacceptable due to its poor pliability.

[102] The conditions in the flexural test were as described below. Dimensions of the test piece: 60 mm (rolling direction) * 30 mm (a direction parallel to a sheet width direction) Sheet thickness of the test piece: 1.6 mm Flexure flange: A direction parallel to a sheet width direction Test method: Supported by rollers and stamped by a punch Roller diameter: φ 30 mm Punch shape: Tip R = 0.4 mm Distance between rollers: 2.0 * sheet thickness (mm) + 0.5 mm Pressing speed: 20 mm / min Tester: SHIMADZU AUTOGRAPH 20 kN

[103] From Table 5-B1 to Table 5-B-3, it is found that the hot-formed bodies that were the examples of the present invention had excellent strength, foldability, and ductility. On the other hand, it is found that the hot-formed bodies that were the comparative examples were poor in one or more of these properties.

[104] Table 1-1 ινΐΛ / a / zuzz / uiui Steel No. Chemical composition (% by mass), remainder: Fe and impurities Note C Si Mn Al PSN Nb Ti V Mo Cr Cu Ni B Ca REM 1 0.12 0.200 1.60 0.026 0.010 0.0012 0.0056 Comparative steel 2 0.21 0.130 1.20 0.026 0.012 0.0010 0.0081 Steel of the present invention 3 0.31 0.300 1.30 0.031 0.009 0.0036 0.0030 Steel of the present invention 4 0.36 0.200 1.40 0.030 0.015 0.0029 0.0047 Steel of the present invention 5 0.45 0.120 1.60 0.031 0.015 0.0025 0.0059 Steel of the present invention 6 0.51 0.210 1.70 0.040 0.013 0.0031 0.0086 Comparative steel 7 0.18 0.0005 1.30 0.038 0.015 0.0026 0.0044 Comparative steel 8 0.35 0.005 1.20 0.029 0.009 0.0011 0.0044 Steel of the present invention 9 0.35 0.200 1.00 0.027 0.011 0.0037 0.0094 Steel of the present invention 10 0.35 1.000 1.40 0.029 0.015 0.0019 0.0032 Steel of the present invention 11 0.35 3.200 1.60 0.033 0.015 0.0018 0.0095 Comparative steel 12 0.35 0.240 0.20 0.028 0.014 0.0015 0.0098 Comparative steel 13 0.35 0.220 0.50 0.039 0.012 0.0015 0.0086 Steel of the present invention 14 0.35 0.180 1.30 0.044 0.014 0.0008 0.0065 Steel of the present invention 15 0.35 0.290 2.00 0.037 0.013 0.0026 0.0047 Steel of the present invention 16 0.35 0.280 3.20 0.027 0.010 0.0014 0.0030 Comparative steel 17 0.35 0.260 1.50 0.000 0.012 0.0030 0.0069 Comparative steel 18 0.35 0.220 1.70 0.001 0.009 0.0040 0.0047 Steel of the present invention 19 0.35 0.280 1.00 0.030 0.014 0.0040 0.0070 Steel of the present invention 20 0.35 0.230 1.50 1.700 0.013 0.0023 0.0060 Steel of the present invention 21 0.35 0.120 1.90 2.200 0.014 0.0007 0.0038 Comparative steel 22 0.35 0.190 1.70 0.045 0.001 0.0018 0.0073 Steel of the present invention. The underlines indicate that the corresponding values ​​are outside the scope of the present invention.

[105] Table 1-2 ινΐΛ / a / zuzz / uiu óz i Steel No. Chemical composition (% by mass), remainder: Fe and impurity Note C Si Mn Al PSN Nb Ti V Mo Cr Cu Ni B Ca REM 23 0.35 0.120 1.30 0.035 0.008 0.0020 0.0094 Steel of the present invention 24 0.35 0.220 2.00 0.039 0.150 0.0035 0.0036 Comparative steel 25 0.35 0.110 1.30 0.043 0.014 0.0003 0.0070 Steel of the present invention 26 0.35 0.150 1.30 0.041 0.008 0.0030 0.0065 Steel of the present invention 27 0.35 0.250 1.10 0.030 0.011 0.1500 0.0057 Comparative steel 28 0.35 0.270 1.50 0.035 0.013 0.0013 0.0008 Steel of the present invention 29 0.35 0.280 1.40 0.030 0.009 0.0016 0.0040 Steel of the present invention 30 0.35 0.240 1.70 0.035 0.012 0.0032 0.1200 Comparative steel 31 0.37 0.240 1.00 0.028 0.011 0.0038 0.0093 0.05 Steel of the present invention 32 0.37 0.110 2.00 0.036 0.009 0.0015 0.0072 0.05 Steel of the present invention 33 0.37 0.190 1.30 0.038 0.015 0.0034 0.0031 0.05 Steel of the present invention 34 0.37 0.220 1.20 0.025 0.009 0.0017 0.0076 0.2 Steel of the present invention 35 0.37 0.140 1.20 0.030 0.015 0.0033 0.0083 0.4 Steel of the present invention 36 0.37 0.110 1.40 0.041 0.009 0.0020 0.0089 0.3 Steel of the present invention 37 0.37 0.270 1.30 0.045 0.012 0.0020 0.0082 0.4 Steel of the present invention 38 0.35 0.100 1.10 0.045 0.013 0.0033 0.0038 0.0025 Steel of the present invention 39 0.35 0.150 1.30 0.028 0.011 0.0026 0.0061 0.006 Steel of the present invention 40 0.35 0.170 1.40 0.028 0.012 0.0036 0.0067 0.20 Steel of the present invention 41 0.35 2.890 1.42 0.030 0.014 0.0022 0.0039 Steel of the present invention 42 0.35 0.297 2.78 0.031 0.012 0.0024 0.0044 Steel of the present invention 43 0.35 0.124 1.31 0.037 0.091 0.0025 0.0097 Steel of the present invention 44 0.35 0.147 1.29 0.045 0.008 0.0870 0.0059 Steel of the present invention. The underlines indicate that the corresponding values ​​are outside the scope of the present invention.

[106] Table 2-1 ινΐΛ / a / zuzz / uii Steel Sheet No. Steel No. Hot Rolled Rolling temperature one pass before final rolling (°C) Rolling reduction one pass before final rolling (%) Final rolling temperature (°C) Rolling reduction of final rolling (%) Time elapsed from end of hot rolling to start of cooling (seconds) Average cooling rate in the temperature range from final hot rolling temperature to 450°C (°C / s) Winding temperature (°C) 1 1 856 23 831 10 4.2 7 691 2 2 858 19 807 8 2.5 5 675 3 3 857 21 807 6 3.6 8 686 4 4 873 17 819 12 4.0 9 682 5 5 875 17 825 6 3.6 9 634 6 6 867 17 813 6 4.3 9 609 7 7 872 18 824 10 3.3 8 604 8 8 875 22 835 10 4.4 5 614 9 9 853 23 819 6 3.0 6 682 10 10 860 18 805 11 3.3 6 694 11 11 876 20 832 9 4.4 6 614 12 12 867 22 810 12 4.3 6 680 13 13 855 17 807 8 4.5 7 658 14 14 870 22 820 6 4.0 9 647 15 15 862 21 831 10 3.1 8 609 16 16 854 23 828 6 3.6 7 633 17 17 875 19 808 10 4.1 6 623 18 18 872 23 825 10 4.2 6 680 19 19 858 18 807 8 2.9 9 642 20 20 862 18 810 12 4.1 6 651 21 21 860 20 824 9 3.7 5 645 22 22 852 23 812 10 3.2 6 699 23 23 872 21 818 7 3.0 5 646 24 24 875 19 831 12 3.9 5 622 25 25 864 22 811 9 2.8 5 625 26 26 869 19 820 10 4.1 7 695 27 27 866 22 810 7 3.9 9 603 28 28 857 22 808 12 4.5 6 641 29 29 862 23 824 11 4.5 5 699 30 30 868 23 829 10 3.6 6 696. The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the manufacturing conditions are not preferable.

[107] Table 2-2 ινΐΛ / a / zuzz / uiu óz i Steel Sheet No. Steel No. Hot Rolled Rolling temperature one pass before final roll (T) Rolling reduction one pass before final roll (%) Final roll temperature (°C) Rolling reduction of final roll (%) Time elapsed from end of hot roll to start of cooling (seconds) Average cooling rate in the temperature range from final hot roll temperature to 450°C (°C / s) Winding temperature (°C) 31 31 867 19 817 11 4.3 6 689 32 32 866 21 822 9 3.0 6 679 33 33 868 23 819 11 4.1 7 629 34 34 867 19 808 10 3.2 5 671 35 35 876 ​​19 826 7 2.5 7 625 36 36 859 18 816 9 2.7 7 638 37 37 851 19 815 6 3.6 6 689 38 38 868 22 822 8 2.6 9 685 39 39 854 22 822 7 2.7 6 618 40 40 864 19 808 9 3.8 8 699 41 4 800 22 820 9 3.7 9 616 42 4 860 19 820 8 3.0 9 689 43 4 950 21 825 7 3.7 9 684 44 4 873 7 828 8 3.9 6 679 45 4 872 20 825 9 3.2 7 671 46 4 854 35 810 8 3.0 6 615 47 4 850 23 770 9 3.0 5 682 48 4 873 21 820 10 2.5 8 632 49 4 853 23 870 12 4.4 5 672 50 4 853 21 818 4 2.8 7 639 51 4 873 23 823 8 4.3 7 603 52 4 861 22 831 18 2.8 5 689 53 4 862 18 825 6 1.5 9 694 54 4 856 18 827 11 3.5 5 692 55 4 875 21 830 8 6.7 6 611 56 4 875 18 832 10 2.8 7 690 57 4 869 20 813 8 2.5 9 665 58 4 866 22 808 6 3.0 15 617 59 4 872 23 810 7 4.4 5 550 60 4 887 19 808 11 4.2 8 650. The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the manufacturing conditions are not preferable.

[108] Table 2-3 ινΐΛ / a / zuzz / ui uóz i Steel Sheet No. Steel No. Hot Rolling Temperature of one pass before final rolling (°C) Reduction of one pass before final rolling (%) Final Rolling Temperature (°C) Reduction of final rolling (°C) Time elapsed from end of hot rolling to start of cooling (seconds) Average cooling rate in the temperature range from final hot rolling temperature to 450°C (°C / s) Winding Temperature (T) 61 4 866 20 823 7 2.5 9 750 62 4 856 21 834 10 2.5 5 630 63 4 860 20 834 8 4.5 9 681 64 4 855 20 817 9 4.1 7 603 65 4 850 17 812 11 2.9 7 685 66 4 856 23 832 11 4.5 6 699 67 4 870 23 832 8 4.4 6 685 68 4 855 21 821 12 4.4 6 676 69 4 867 23 814 9 3.6 6 638 70 4 867 22 831 7 4.4 8 657 71 4 875 18 832 8 4.1 9 663 72 4 864 17 805 11 3.0 7 653 73 4 866 21 809 12 3.0 9 628 74 4 871 22 812 7 3.6 5 636 75 4 857 22 807 8 4.0 9 602 76 4 873 18 822 8 3.8 5 691 77 4 873 22 830 9 3.1 8 674 78 4 866 21 822 11 3.3 6 660 79 4 865 19 826 6 4.2 8 693 80 4 865 17 811 12 3.0 8 631 81 4 858 21 811 7 3.2 9 642 82 4 854 22 820 11 3.8 7 668 83 4 868 20 827 8 4.2 9 686 84 4 875 19 833 9 3.2 7 669 85 4 860 22 821 6 3.0 7 686 86 4 859 19 821 9 4.4 6 616 87 41 856 18 811 10 2.9 6 698 88 42 855 23 821 11 2.7 8 609 89 43 875 22 814 8 3.4 4 651 90 44 879 20 828 9 4.2 7 697. The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the manufacturing conditions are not preferable.

[109] Table 2-4 ινΐΛ / a / zuzz / uii Steel Sheet No. Steel No. Presence or absence of softening heat treatment Cold rolling Decarburization annealing Plating Note Cumulative rolling reduction (%) Maximum achievable temperature (°C) Residence time in the temperature range of 700°C to 950°C (seconds) Presence or absence of plating Plating annealing after decarburization annealing 1 1 Absent 69 830 151 Comparative example 2 2 Absent 66 818 166 Example of the present invention 3 3 Absent 36 784 172 Example of the present invention 4 4 Absent 30 773 135 Example of the present invention 5 5 Absent 41 808 216 Example of the present invention 6 6 Absent 39 811 268 Comparative example 7 7 Absent 45 789 231 Comparative example 8 8 Absent 45 818 273 Example of the present invention 9 9 Absent 33 801 237 Example of the present invention 10 10 Absent 64 818 228 Example of the present invention 11 11 Absent 44 801 277 Comparative example 12 12 Absent 66 775 209 ExampleComparative 13 13 Absent 65 795 219 Example of the present invention 14 14 Absent 63 776 197 Example of the present invention 15 15 Absent 40 803 183 Example of the present invention 16 16 Absent 54 805 250 Comparative example 17 17 Absent 64 810 177 Comparative example 18 18 Absent 66 828 216 Example of the present invention 19 19 Absent 33 826 248 Example of the present invention 20 20 Absent 54 824 280 Example of the present invention 21 21 Absent 32 822 179 Comparative example 22 22 Absent 31 827 167 Example of the present invention 23 23 Absent 40 786 197 Example of the present invention 24 24 Absent 32 823 167 Comparative example 25 25 Absent 49 787 258 Example of the present invention 26 26 Absent 70 800 150 Example of the present invention 27 27 Absent 52 787 187 Comparative example 28 28 Absent 43 817 140 Example of the present invention 29 29 Absent 49 808 148 Example of the present invention 30 30 Absent 46 813 265 Comparative example The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the manufacturing conditions are not preferable.

[110] Table 2-5 ινΐΛ / a / zuzz / uiui Steel Sheet No. Steel No. Presence or absence of softening heat treatment Cold rolling Decarburization annealing Plating Note Cumulative rolling reduction (%) Maximum achievable temperature (°C) Residence time in the temperature range of 700°C to 950°C (seconds) Presence or absence of plating Plating annealing after decarburization annealing 31 31 Absent 51 808 209 Example of the present invention 32 32 Absent 55 778 270 Example of the present invention 33 33 Absent 46 792 167 Example of the present invention 34 34 Absent 57 819 246 Example of the present invention 35 35 Absent 54 815 267 Example of the present invention 36 36 Absent 69 774 275 Example of the present invention 37 37 Absent 43 804 240 Example of the present invention 38 38 Absent 65 822 238 Example of the present invention 39 39 Absent 56 784 209 Example of the present invention 40 40 Absent 58 824 130 Example of the present invention 41 4 Absent 41 775 251Comparative example 42 4 Absent 39 828 151 Example of the present invention 43 4 Absent 61 814 241 Comparative example 44 4 Absent 37 828 173 Comparative example 45 4 Absent 62 789 166 Example of the present invention 46 4 Absent 48 775 211 Comparative example 47 4 Absent 40 806 265 Comparative example 48 4 Absent 70 817 165 Example of the present invention 49 4 Absent 45 798 130 Comparative example 50 4 Absent 44 811 232 Comparative example 51 4 Absent 37 775 225 Example of the present invention 52 4 Absent 42 812 262 Comparative Example 53 4 Absent 33 817 255 Comparative Example 54 4 Absent 48 814 275 Example of the present invention 55 4 Absent 61 792 137 Example of the present invention 56 4 Absent 58 800 273 Example of the present invention 57 4 Absent 62 792 197 Example of the present invention 58 4 Absent 52 814 149 Comparative Example 59 4 Absent 37 812 215 Example of the present invention 60 4 Absent 67 779 276 Example of the present invention The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the manufacturing conditions are not preferable.

[111] Table 2-6 ινΐΛ / a / zuzz / uii Steel Sheet No. Steel No. Presence or absence of softening heat treatment Cold rolling Decarburization annealing Plating Note Cumulative rolling reduction (%) Maximum achievable temperature (°C) Residence time in the temperature range of 700°C to 950°C (seconds) Presence or absence of plating Plating annealing after decarburization annealing 61 4 Absent 44 785 234 Comparative example 62 4 Present 59 809 267 Example of the present invention 63 4 Absent 40 814 272 Example of the present invention 64 4 Absent 55 660 155 Comparative example 65 4 Absent 31 720 269 Example of the present invention 66 4 Absent 64 800 263 Example of the present invention 67 4 Absent 61 900 247 Example of the present invention 68 4 Absent 50 970 263 Comparative example 69 4 Absent 56 806 3 Comparative example 70 4 Absent 62 770 60 Example of the present invention 71 4 Absent 54 770 180 Example of the present invention 72 4 Absent 45 812 900 Example ofthe present invention 73 4 Absent 54 793 1300 Comparative example 74 4 Absent 44 803 234 Present Example of the present invention 75 4 Absent 56 773 189 Present Example of the present invention 76 4 Absent 67 777 268 Example of the present invention 77 4 Absent 58 798 138 Example of the present invention 78 4 Absent 35 829 246 Example of the present invention 79 4 Absent 52 799 211 Example of the present invention 80 4 Absent 33 801 151 Example of the present invention 81 4 Absent 37 805 203 Example of the present invention 82 4 Absent 49 823 179 Example of the present invention 83 4 Absent 31 821 276 Example of the present invention 84 4 Absent 64 802 163 Example of the present invention 85 4 Absent 46 801 176 Example of the present invention 86 4 Absent 67 801 146 Example of the present invention 87 41 Absent 66 828 216 Example of the present invention 88 42 Absent 42 794 189 Example of the present invention 89 43 Absent 38 782 188 Example of the present invention90 44 Absent 64 802 135 Example of the present invention The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the manufacturing conditions are not preferable.

[112] Table 3-1 ινΐΛ / a / zuzz / uii Steel Sheet No. Steel No. Hot Stamping Steel Sheet Note Ferrite, granular bainite, bainite, and martensite (% by area) Pearlite and carbide (% by area) Ratio of pole density of the orientation group consisting of {001} <1-10 to {001} <-1-10> and pole density of the orientation group consisting of {111} <110> to {111} <-1-12> in the surface layer region texture. Relationship between the pole density of the orientation group consisting of {001} <1-10 to {001} <-1-10 and the pole density of the orientation group consisting of {111} <110> a {111} <-1-12> in the texture of the inner region decarburization index Sheet thickness (mm) 1 1 28 72 1.3 1.9 0.174 1.6 Comparative example 2 2 52 48 1.2 1.6 0.198 1.6 Example of the present invention 3 3 74 26 1.3 1.8 0.244 1.6 Example of the present invention 4 4 22 78 1.3 1.7 0.270 1.6 Example of the present invention 5 5 37 63 1.2 1.7 0.320 1.6 Example of the present invention 6 6 68 32 1.3 1.9 0.376 1.6 Comparative example 7 7 22 78 1.3 1.7 0.283 1.6 Comparative example 8 8 43 57 1.3 1.6 0.267 1.6 Example of the present invention 9 9 41 59 1.2 1.7 0.250 1.6 Example of the present invention 10 10 56 44 1.2 1.8 0.236 1.6 Example of the present invention 11 11 60 40 1.2 1.9 0.243 1.6 Comparative example 12 12 43 57 1.3 1.8 0.241 1.6 Comparative example 13 13 60 40 1.3 1.6 0.266 1.6 Example of the present invention 14 14 77 23 1.2 1.8 0.285 1.6 Example of the present invention 15 15 30 70 1.2 1.8 0.279 1.6 Example of the present invention 16 16 50 50 1.2 1.6 0.279 1.6 Comparative example 17 17 21 79 1.3 1.7 0.261 1.6 Comparative example 18 18 31 69 1.3 1.9 0.280 1.6 Example of the present invention 19 19 51 49 1.3 1.8 0.279 1.6 Example of the present invention 20 20 34 66 1.2 1.9 0.277 1.6 Example of the present invention 21 21 60 40 1.2 1.6 0.248 1.6 Comparative example 22 22 28 72 1.3 1.6 0.268 1.6 Example of the present invention 23 23 66 34 1.2 1.7 0.280 1.6 Example of the present invention 24 24 25 75 1.2 1.7 0.257 1.6 Comparative example 25 25 54 46 1.2 1.7 0.260 1.6 Example of the present invention 26 26 75 25 1.2 1.6 0.261 1.6 Example of the present invention 27 27 52 48 1.2 1.8 0.273 1.6 Comparative example 28 28 39 61 1.3 1.8 0.261 1.6 Example of the present invention 29 29 55 45 1.3 1.7 0.260 1.6 Example of the present invention 30 30 71 29 1.2 1.7 0.236 1.6 Example comparative. The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the manufacturing conditions are not preferable.

[113] Table 3-2 ινΐΛ / a / zuzz / uii Steel Sheet No. Steel No. Hot Stamping Steel Sheet Note Ferrite, granular bainite, bainite, and martensite (% by area) Pearlite and carbide (% by area) Ratio of pole density of the orientation group consisting of {001} <1-10> to {001} <-1-10> and pole density of the orientation group consisting of {111} <110> to {111} <-1-12> in the surface layer region texture. Relationship between the pole density of the orientation group consisting of {001} <1-10> to {001} <-1-10> and the pole density of the orientation group consisting of {111} <110> a {111} <-1-12> in the texture of the inner region decarburization index Sheet thickness (mm) 31 31 70 30 1.2 1.6 0.271 1.6 Example of the present invention 32 32 24 76 1.3 1.6 0.280 1.6 Example of the present invention 33 33 23 77 1.2 1.6 0.259 1.6 Example of the present invention 34 34 76 24 1.2 1.8 0.249 1.6 Example of the present invention 35 35 28 72 1.3 1.7 0.251 1.6 Example of the present invention 36 36 76 24 1.3 1.9 0.284 1.6 Example of the present invention 37 37 55 45 1.3 1.8 0.241 1.6 Example of the present invention 38 38 28 72 1.2 1.7 0.231 1.6 Example of the present invention 39 39 57 43 1.2 1.7 0.261 1.6 Example of the present invention 40 40 38 62 1.2 1.6 0.236 1.6 Example of the present invention 41 4 40 60 1.8 2.4 0.254 1.6 Comparative example 42 4 58 42 1.2 1.5 0.275 1.6 Example of the Present invention 43 4 37 63 1.8 2.2 0.277 1.6 Comparative example 44 4 26 74 1.9 2.6 0.248 1.6 Comparative example 45 4 49 51 0.8 1.1 0.239 1.6 Example of the present invention 46 4 40 60 1.9 2.4 0.239 1.6 Comparative example 47 4 51 49 1.9 2.6 0.243 1.6 Comparative example 48 4 72 28 1.1 1.1 0.268 1.6 Example of the present invention 49 4 57 43 1.9 2.3 0.243 1.6 Comparative example 50 4 23 77 1.7 2.4 0.239 1.6 Comparative example 51 4 69 31 1.1 1.5 0.263 1.6 Example of the present invention 52 4 21 79 1.9 2.3 0.251 1.6 Comparative example 53 4 68 32 1.7 2.4 0.232 1.6 Comparative example 54 4 43 57 1.3 1.7 0.274 1.6 Example of the present invention 55 4 27 73 1.2 1.4 0.260 1.6 Example of the present invention 56 4 69 31 0.9 1.2 0.246 1.6 Example of the present invention 57 4 31 69 1.3 1.8 0.230 1.6 Example of the present invention 58 4 33 67 1.8 2.6 0.243 1.6 Comparative example 59 4 42 58 1.2 1.5 0.239 1.6 Example of the present invention 60 4 45 55 1.2 1.8 0.234 1.6 Example of the present invention. The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the manufacturing conditions are not preferable.

[114] Table 3-3 Steel Sheet No. Steel No. Hot Stamping Steel Sheet Note Ferrite, granular bainite, bainite, and martensite (% by area) Pearlite and carbide (% by area) Ratio of pole density of the orientation group consisting of {001} <1-10> to {001} <-1-10> and pole density of the orientation group consisting of {111} <110> to {111} <-1-12> in the surface layer region texture. Relationship between the pole density of the orientation group consisting of {001} <1-10> to {001} <-110> and the pole density of the orientation group consisting of {111} <110> a {111} <-1-12> in the texture of the inner region decarburization index Sheet thickness (mm) 61 4 69 31 1.9 2.2 0.271 1.6 Comparative example 62 4 26 74 1.2 1.6 0.260 1.6 Example of the present invention 63 4 71 29 1.2 1.7 0.270 1.6 Example of the present invention 64 4 55 45 1.7 1.9 0.078 1.6 Comparative example 65 4 25 75 1.2 1.7 0.159 1.6 Example of the present invention 66 4 57 43 0.9 1.2 0.221 1.6 Example of the present invention 67 4 80 20 1.2 1.7 0.342 1.6 Example of the present invention 68 4 35 65 1.9 1.6 0.520 1.6 Comparative example 69 4 64 36 1.8 1.7 0.016 1.6 Comparative example 70 4 72 28 1.3 1.8 0.097 1.6 Example of the present invention 71 4 36 64 0.9 1.3 0.261 1.6 Example of the present invention 72 4 75 25 1.3 1.7 0.423 1.6 Example of the present invention 73 4 72 28 1.6 1.8 0.514 1.6 Comparative example 74 4 28 72 1.2 1.8 0.244 1.6 Example of the present invention 75 4 77 23 1.3 1.8 0.289 1.6 Example of the present invention 76 4 70 30 1.2 1.6 0.273 1.6 Example of the present invention 77 4 24 76 1.2 1.9 0.265 1.6 Example of the present invention 78 4 74 26 1.2 1.6 0.264 1.6 Example of the present invention 79 4 21 79 1.3 1.8 0.275 1.6 Example of the present invention 80 4 43 57 1.2 1.6 0.281 1.6 Example of the present invention 81 4 21 79 1.2 1.8 0.271 1.6 Example of the present invention 82 4 47 53 1.3 1.8 0.247 1.6 Example of the present invention 83 4 50 50 1.2 1.8 0.246 1.6 Example of the present invention 84 4 59 41 1.3 1.9 0.282 1.6 Example of the present invention 85 4 39 61 1.3 1.6 0.246 1.6 Example of the present invention 86 4 76 24 1.2 1.8 0.235 1.6 Example of the present invention 87 41 55 40 1.2 1.7 0.275 1.6 Example of the present invention 88 42 29 66 1.1 1.7 0.291 1.6 Example of the present invention 89 43 64 36 1.1 1.6 0.254 1.6 Example of the present invention 90 44 75 28 1.1 1.5 0.270 1.6 Example of the present invention. The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the manufacturing conditions are not preferable.

[115] Table 4-Bl ινΐΛ / a / zuzz / uii Manufacturing No. Steel Sheet No. Steel No. Hot Stamping Conditions Tempering Treatment Partially Softened Region Note Heating Temperature (°C) Holding Time (s) Forming Temperature (°C) Cooling Rate to Temperature Range of 300°C or Lower (°C / s) 1 1 1 880 306 585 21 Comparative Example 2 2 2 890 325 602 31 Example of the Present Invention 3 3 3 960 231 600 42 Example of the Present Invention 4 4 4 930 330 605 48 Present Example of the Present Invention 5 5 5 880 295 625 25 Example of the Present Invention 6 6 6 970 322 576 35 Comparative Example 7 7 7 870 315 571 38 Comparative Example 8 8 8 870 324 569 27 Example of the present invention 9 9 9 920 237 600 37 Example of the present invention 10 10 10 870 192 544 28 Example of the present invention 11 11 11 940 293 596 44 Comparative Example 12 12 12 940 190 547 40 Comparative Example 13 13 13 970 251 634 34 Present Example of the present invention 14 14 14 900 225 630 37Example of the present invention 15 15 15 910 294 633 25 Example of the present invention 16 16 16 870 316 600 37 Comparative example 17 17 17 960 322 548 42 Comparative example 18 18 18 940 293 543 43 Example of the present invention 19 19 19 930 192 616 35 Present Example of the present invention 20 20 20 940 282 588 42 Example of the present invention 21 21 21 960 270 582 49 Comparative example 22 22 22 900 291 547 48 Example of the present invention 23 23 23 900 232 592 36 Example of the present invention 24 24 24 960 292 542 24 Comparative example 25 25 25 960 238 547 18 Example of the present invention 26 26 26 920 214 626 17 Example of the present invention 27 27 27 890 206 579 19 Comparative example 28 28 28 920 243 593 21 Example of the present invention 29 29 29 900 193 540 32 Example of the present invention 30 30 30 920 263 616 47 Comparative example The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the manufacturing conditions are not preferable.

[116] Table 4-B-2 ινΐΛ / a / zuzz / uii Manufacturing No. Steel Sheet No. Steel No. Hot Stamping Conditions Tempering Treatment Partially Softened Region Note Heating Temperature (°C) Holding Time (s) Forming Temperature (°C) Cooling Rate to Temperature Range of 300°C or Lower (°C / s) 31 31 31 910 311 551 22 Example of the present invention 32 32 32 940 307 623 35 Example of the present invention 33 33 33 890 301 568 26 Example of the present invention 34 34 34 950 338 608 45 Example of the present invention 35 35 35 970 233 542 16 Example of the present invention 36 36 36 890 313 580 49 Example of Example of the present invention 37 37 37 930 251 559 30 Example of the present invention 38 38 38 920 301 615 32 Example of the present invention 39 39 39 890 329 606 36 Example of the present invention 40 40 40 880 324 598 38 Example of the present invention 41 41 4 910 291 600 34 Comparative example 42 42 4 970 330 581 29 Example of the present invention 43 43 4 950 280 62017 Comparative example 44 44 4 920 323 599 46 Comparative example 45 45 4 900 221 556 49 Example of the present invention 46 46 4 890 339 532 23 Comparative example 47 47 4 920 228 603 20 Comparative example 48 48 4 870 227 612 35 Example of the present invention 49 49 4 940 258 563 27 Comparative example 50 50 4 960 204 637 34 Comparative example 51 51 4 920 253 538 20 Example of the present invention 52 52 4 870 262 534 30 Comparative example 53 53 4 870 299 599 28 Comparative example 54 54 4 920 192 543 15 Example of the present invention 55 55 4 930 339 593 19 Example of the present invention 56 56 4 960 302 596 50 Present Example of the present invention 57 57 4 920 273 637 48 Example of the present invention 58 58 4 900 259 591 21 Comparative example 59 59 4 920 227 561 20 Example of the present invention 60 60 4 920 309 587 30 Example of the present invention The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the manufacturing conditions are not preferable.

[117] Table 4-B-3 ινΐΛ / a / zuzz / uii Manufacturing No. | Steel Sheet No. Steel No. Hot Stamping Conditions Tempering Treatment Partially Softened Region Note Heating Temperature (°C) Holding Time (s) Forming Temperature (°C) Cooling Rate to Temperature Range of 300°C or Lower (°C / s) 61 61 4 960 312 574 28 Comparative Example 62 62 4 880 249 612 26 Example of the Present Invention 63 63 4 940 237 637 41 Example of the Present Invention 64 64 4 960 197 629 34 Comparative Example 65 65 4 960 304 576 23 Example of the Present Invention 66 66 4 910 322 597 19 Example of the Present Invention 67 67 4 890 336 534 20 Example of the present invention 68 68 4 920 308 534 39 Comparative example 69 69 4 940 227 556 21 Comparative example 70 70 4 960 240 588 15 Example of the present invention 71 71 4 960 280 556 35 Present Example of the present invention 72 72 4 910 225 544 27 Example of the present invention 73 73 4 970 207 532 47 Comparative example 74 74 4 900 331605 43 Example of the present invention 75 75 4 920 261 576 34 Example of the present invention 76 76 4 770 303 538 40 Comparative example 77 77 4 920 238 531 21 Example of the present invention 78 78 4 1030 339 604 48 Comparative example 79 79 4 910 45 534 49 Comparative example 80 80 4 920 240 621 23 Example of the present invention 81 81 4 880 630 606 36 Comparative example 82 82 4 960 290 538 32 Example of the present invention 83 83 4 870 316 569 16 Example of the present invention 84 84 4 970 316 535 47 Example of the present invention 85 85 4 890 212 630 22 Example of the present invention 86 86 4 880 331 710 20 Comparative example 87 87 41 877 185 535 23 Example of the present invention 88 88 42 920 296 638 22 Example of the present invention 89 89 43 908 240 593 32 Example of the present invention 90 90 44 925 212 622 16 Example of the present invention The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the manufacturing conditions are not preferable.

[118] Table 5-Bl ινΐΛ / a / zuzz / uiui Manufacturing No. Steel Sheet No. Steel No. Microstructures Textures Amount of decarburization Mechanical properties Note Granular ferrite and bainite (% by area) Martensite, bainite, and tempered martensite (% by area) Ratio of pole density of the orientation group consisting of {1001} <1 -10> to {001} <-1-10> and the pole density of the orientation group consisting of {111} <1-10> to {1Ή} <-1-12> in the surface layer region texture Ratio of pole density of the orientation group consisting of {001} <1-10> to {001} <-1-10> and the pole density of the orientation group consisting of {111} <1-10> to {1Í1} <-1-12> in the interior region texture Decarburization index Strength TS in tension (MPa) Maximum bending angle a (°) TS xa (MPa-°) Uniform elongation uEL (%) TS x uEL (MPa-%) 1 1 1 12 88 1.7 2.2 0.220 1313 97 127361 4.8 6115 Comparative example 2 2 2 21 79 1.7 2.0 0.260 1533 75 114975 4.6 6831 Example of the present invention 3 3 3 25 75 1.7 2.1 0.306 1821 53 96513 5.4 9331 Example of the present invention 4 4 4 25 75 1.6 2.2 0.329 2033 57 115881 5.0 9600 Example of the present invention 5 5 5 17 83 1.5 2.2 0.375 2486 51 126786 5.4 12960 Example of the present invention 6 6 6 26 74 1.6 2.1 0.428 2617 27 70659 2.2 5757 Comparative example 7 7 7 10 90 1.6 2.1 0.341 1289 99 127611 5.7 7347 Comparative example 8 8 8 15 85 1.7 2.0 0.322 2200 54 118800 5.1 10659 Example of the present invention 9 9 9 17 83 1.7 2.2 0.299 2215 72 159480 6.1 13286 Example of the present invention 10 10 10 18 82 1.6 1.9 0.299 2221 51 113271 5.4 11405 Example of the present invention 11 11 11 22 78 1.5 2.0 0.291 1334 85 113390 6.4 8538 Comparative example 12 12 12 20 80 1.7 2.3 0.300 1308 98 128184 6.6 8633 Comparative example 13 13 13 25 75 1.7 2.1 0.323 2042 55 112310 5.0 10000 Example of the present invention 14 14 14 22 78 1.7 1.9 0.333 2243 81 181683 6.1 12749 Example of the present invention 15 15 15 24 76 1.7 1.9 0.331 2025 55 111375 5.0 9900 Example of the present invention 16 16 1θ 23 77 1.7 2.1 0.334 2020 33 66660 5.8 11252 Comparative example 17 17 17 14 86 1.5 2.0 0.309 2019 33 66627 5.5 10450 Comparative example 18 18 18 22 78 1.7 1.9 0.326 2036 56 114016 5.2 10192 Example of the present invention 19 19 19 15 85 1.7 2.2 0.328 2049 50 102450 5.8 11484 Example of the present invention 20 20 20 19 81 1.5 2.1 0.340 2039 54 110106 5.4 10584 Example of the present invention 21 21 21 20 80 1.6 2.2 0.311 1996 33 65868 6.9 13524 Comparative example 22 22 22 14 86 1.5 2.2 0.313 1986 89 176754 5.7 11172 Example of the present invention 23 23 23 24 76 1.6 1.9 0.342 2032 57 115824 5.2 10296 Example of the present invention 24 24 24 22 78 1.6 1.9 0.310 2032 27 54864 5.0 10000 Comparative example 25 25 25 27 73 1.7 2.2 0.323 1985 89 176665 6.8 13192 Example of the present invention 26 26 26 15 85 1.6 1.9 0.316 1996 54 107784 5.0 9600 Example of the present invention 27 27 27 17 83 1.7 2.2 0.329 2005 33 66165 5.3 10282 Comparative example 28 28 28 23 77 1.7 2.2 0.311 2017 79 159343 6.6 12540 Example of the present invention 29 29 29 24 76 1.6 1.9 0.315 2014 51 102714 5.1 9996 Example of the present invention 30 30 30 25 75 1.7 2.2 0.293 2002 35 70070 5.4 10800 Comparative example. The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the characteristics are not preferable.

[119] Table 5-B-2 ινΐΛ / a / zuzz / uiui Manufacturing No. Steel Sheet No. Steel No. Microstructures Textures Amount of decarburization Mechanical properties Note Granular ferrite and bainite (% by area) Martensite, bainite, and tempered martensite (% by area) Ratio of pole density of the orientation group consisting of {1001} <1 -10> to {001} <-1-10> and pole density of the orientation group consisting of {111} <1-10> to {111} <-1-12> in the surface layer region texture Ratio of pole density of the orientation group consisting of {001} <1-10> to {001} <-1-10> and pole density of the orientation group consisting of {111} <1-10> to {111} <-1-12> in the interior region texture Decarburization index Strength TS in tension (MPa) Maximum bending angle a (°) TS * a (MPa-°) Uniform elongation uEL (%) TS x uEL (MPa-%) 31 31 31 15 85 1.5 2.0 0.317 2306 65 149890 6.6 14573 Example of the present invention 32 32 32 12 88 1.5 2.0 0.335 2318 78 180804 6.1 13469 Example of the present invention 33 33 33 26 74 1.5 2.1 0.304 2323 83 192809 6.9 15553 Example of the present invention 34 34 34 17 83 1.6 1.9 0.304 2313 80 185040 6.3 14055 Example of the present invention 35 35 35 20 80 1.6 2.2 0.303 2330 73 170090 6.3 13910 Example of the present invention 36 36 36 27 73 1.5 2.2 0.345 2349 65 152685 6.4 14426 Example of Example of the present invention 37 37 37 28 72 1.5 2.1 0.286 2299 67 154033 7.0 15617 Example of the present invention 38 38 38 11 89 1.7 2.2 0.286 2207 59 130213 5.2 10868 Example of the present invention 39 39 39 24 76 1.5 2.0 0.306 2040 72 146880 6.9 13386 Example of the present invention 40 40 40 25 75 1.7 2.1 0.295 2018 63 127134 6.4 12160 Example of the present invention 41 41 4 15 85 2.2 2.5 0.310 2033 27 54891 5.4 10692 Comparative example 42 42 4 28 72 0.9 1.7 0.337 2044 78 159432 7.0 13720 Example of the present invention 43 43 4 22 78 2.0 2.5 0.324 2028 35 70980 5.3 10388 Comparative example 44 44 4 10 90 2.3 2.7 0.310 1969 36 70884 5.0 9600 Comparative example 45 45 4 28 72 0.9 1.5 0.303 2040 66 134640 5.8 11020 Example of the present invention 46 46 4 11 89 2.0 2.6 0.284 2033 30 60990 5.4 10368 Comparative example 47 47 4 16 84 2.1 2.5 0.299 1989 31 61659 5.4 10692 Comparative example 48 48 4 22 78 1.4 1.8 0.325 2010 65 130650 6.7 12864 Example of the present invention 49 49 4 10 90 2.1 2.6 0.288 1994 26 51844 5.3 10070 Comparative example 50 50 4 20 80 2.2 2.6 0.297 2025 27 54675 5.2 10400 Comparative example 51 51 4 18 82 1.4 1.5 0.311 2033 77 156541 5.5 11000 Example of the present invention 52 52 4 21 79 2.1 2.8 0.306 2035 31 63085 5.0 9900 Comparative example 53 53 4 19 81 2.2 2.6 0.294 2017 35 70595 5.2 10088 Comparative example 54 54 4 24 76 1.6 2.1 0.326 2048 50 102400 5.0 9900 Example of the present invention 55 55 4 15 85 0.8 1.8 0.308 2015 77 155155 6.6 12936 Example of the present invention 56 56 4 14 86 1.4 1.5 0.309 1996 88 175648 6.5 12740 Example of the present invention 57 57 4 24 76 1.6 2.2 0.281 2023 59 119357 5.1 9792 Example of the present invention 58 58 4 14 86 2.0 2.7 0.290 2015 36 72540 5.2 9984 Comparative example 59 59 4 17 83 0.8 1.7 0.291 2025 89 180225 6.1 11712 Example of the present invention 60 60 4 18 82 1.6 2.0 0.283 2032 51 103632 5.3 10282 Example of the present invention. The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the characteristics are not preferable.

[120] Table 5-B-3 ινΐΛ / a / zuzz / uii Manufacturing No. Steel Sheet No. Steel No. Microstructures Textures Amount of decarburization Mechanical properties Note Granular ferrite and bainite (% by area) Martensite, bainite, and tempered martensite (% by area) Ratio of pole density of the orientation group consisting of {1001} <1 -10> to {001} <-1-10> and the pole density of the orientation group consisting of {111} <1-10> to {111} <-1-12> in the surface layer region texture Ratio of pole density of the orientation group consisting of {001} <1-10> to {001} <-1-10> and the pole density of the orientation group consisting of {111} <1-10> to {111} <-1-12> in the interior region texture Decarburization index Strength TS in tension (MPa) Maximum bending angle a (°) TS xa (MPa-°) Uniform elongation uEL (%) TS x uEL (MPa-%) 61 61 4 19 81 2.0 2.8 0.330 2000 28 56000 5.1 9894 Comparative example 62 62 4 12 88 1.7 2.2 0.321 1992 53 105576 5.4 10368 Example of the present invention 63 63 4 14 86 1.7 2.2 0.324 2039 50 101950 5.2 10088 Example of the present invention 64 64 4 18 82 2.3 2.0 0.080 1988 36 71568 5.3 10070 Comparative example 65 65 4 10 90 1.7 2.0 0.206 2037 57 116109 5.3 10282 Example of the present invention 66 66 4 14 86 1.1 1.4 0.269 2029 83 168407 6.7 13132 Example of the present invention 67 67 4 14 86 1.6 2.1 0.381 2043 54 110322 5.0 9500 Example of the present invention 68 68 4 17 83 2.0 1.9 0.568 2011 36 73210 4.9 6115 Comparative example 69 69 4 26 74 2.1 2.0 0.060 2000 32 64000 5.4 10692 Comparative example 70 70 4 23 77 1.7 2.2 0.147 2011 52 104572 5.4 10800 Example of the present invention 71 71 4 25 75 1.3 1.8 0.299 2009 75 150675 6.0 11880 Example of the present invention 72 72 4 13 87 1.5 1.9 0.481 2022 53 107166 5.1 9690 Example of the present invention 73 73 4 21 79 2.3 2.3 0.565 2014 37 74520 6.7 13494 Comparative example 74 74 4 25 75 1.7 1.9 0.295 2028 50 101400 5.3 10388 Example of the present invention 75 75 4 24 76 1.5 2.2 0.348 2050 58 118900 5.0 9900 Example of the present invention 76 76 4 21 79 2.0 2.7 0.318 2001 33 66033 5.2 10296 Comparative example 77 77 4 14 86 1.7 2.0 0.322 2047 56 114632 5.1 9690 Example of the present invention 78 78 4 27 73 1.6 2.9 0.314 2009 28 56252 5.4 10692 Comparative example 79 79 4 23 77 1.9 2.6 0.335 2036 28 57008 5.0 9800 Comparative example 80 80 4 25 75 1.7 2.2 0.329 1996 52 103792 5.0 9700 Example of the present invention 81 81 4 21 79 1.6 2.7 0.324 1988 36 71568 5.4 10692 Comparative example 82 82 4 20 80 1.7 1.9 0.301 1988 50 99400 5.2 10192 Example of the present invention 83 83 4 14 86 1.7 2.1 0.303 2050 55 112750 5.4 10692 Example of the present invention 84 84 4 18 82 1.5 2.2 0.342 2020 52 105040 5.2 9984 Example of the present invention 85 85 4 15 85 1.5 2.0 0.306 2024 52 105248 5.4 10368 Example of the present invention 86 86 4 5 95 1.6 2.0 0.281 1990 57 113430 2.9 5771 Comparative example 87 87 41 19 81 1.6 1.9 0.320 2057 51 104907 5.5 11314 Example of the present invention 88 88 42 24 76 1.6 2.0 0.352 2025 55 111375 5.1 10328 Example of the present invention 89 89 43 23 77 1.6 1.8 0.301 2037 54 109998 5.3 10796 Example of the present invention 90 90 44 14 86 1.5 2.0 0.322 1990 52 103480 4.9 9751 Example of the present invention. The underlines indicate that the corresponding values ​​are outside the scope of the present invention and that the characteristics are not preferable. INDUSTRIAL APPLICABILITY

[121] According to the above-mentioned aspect of the present invention, it is possible to provide a hot-stamped body that has excellent strength, foldability, and ductility. < / uvw> < / uvw> < / uvw> < / l-10>

Claims

1. A hot-stamped body comprising, as a chemical composition, % by mass: 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: 0.100% or less; S: 0.1000% or less; N: 0.0100% or less; Nb: 0% to 0.15%; Ti: 0% to 0.15%; V: 0% to 0.15%; Mo: 0% to 1.0%; Cr: 0% to 1.0%; Cu: 0% to 1.0%; Ni: 0% to 1.0%; B: 0% to 0. 0100%; Ca: 0% to 0.010%; REM: 0% to 0.30%; and the remainder consisting of Fe and an impurity, wherein the hot-formed body has a metallographic structure consisting, in area ratio, of a total of 10% to 30% granular ferrite and bainite and the remainder in the microstructure consisting of one or more martensite, bainite, and tempered martensite, in a texture between a surface and a position 1 / 4 sheet thickness from the surface, a ratio between a pole density of an orientation group consisting of {001} <1—10> to {001} <-l-10> and a pole density of an orientation group consisting of {111}. <l-10>a {111} <-l12> is less than 1.8, and in a texture between the position of 1 / 4 sheet thickness from the surface and a position of 1 / 2 sheet thickness from the surface, a ratio between a pole density of an orientation group consisting of {001} <l-10>to {001} <-l-10> and a pole density of an orientation group consisting of {111} <l-10>a {111} <-l-12> is less than 2.

3.

2. The body formed by hot stamping according to claim 1, further comprising, as the chemical composition, % by mass, one or more of the group consisting of: Nb: 0.05% to 0.15%, Ti: 0.05% to 0.15%, V: 0.05% to 0.15%, Mo: 0.05% to 1.0%, Cr: 0.05% to 1.0%, Cu: 0.05% to 1.0%, Ni: 0.05% to 1.0%, B: 0.0001% to 0.0100%, Ca: 0.001% to 0.010%, and REM: 0.001% to 0.30%.

3. The body formed by hot stamping according to claim 1 or 2, wherein a decarburization index is 0.085 or more.