Automobile side-module

Abstract

This automobile side-module is for reinforcing side outers of an automobile and is formed through hot-stamp molding of a plurality of integrated steel sheets. When S (m2) represents the minimum circumscribed rectangular area when viewed from the perpendicular direction of a reference plane, W0.2 (kg) represents the total weight of components each having a weight of 0.200 kg or more and W510 represents the total weight of components in each of which the minimum value of the Vickers hardness is HV510 or more among components of the automobile side-module, W0.2 / S is 7.7 or less, and W510 / W0.2 is more than 0.10.

Description

Automotive Side Module

[0001] The present invention relates to an automobile side module for reinforcing an outer side panel of an automobile. This application claims priority to Japanese Patent Application No. 2023-197287, filed on November 21, 2023, the contents of which are incorporated herein by reference.

[0002] Recently, from the viewpoint of preventing global warming, carbon dioxide (CO ２ It is becoming increasingly important to reduce emissions of greenhouse gases (Green House Gases, hereinafter referred to as GHGs), including CO₂. Under these circumstances, the emergence of electric vehicles, hybrid vehicles, and other vehicles that emit less GHG than conventional vehicles powered by internal combustion engines is expected to reduce GHG emissions from vehicles while they are in motion. In addition, the use of lightweight materials such as aluminum and carbon as materials for constructing vehicles is expected to reduce GHG emissions from vehicles while they are in motion.

[0003] Regarding automobile bodies, for example, Patent Document 1 listed below discloses a vehicle body structure with excellent productivity. Also, in relation to vehicle body structures, Patent Document 2 listed below discloses a method for manufacturing an automobile body side structural frame from a plurality of blanks. Furthermore, Patent Document 3 listed below discloses an automobile body that can reduce the total amount of GHG generated throughout the entire life cycle of an automobile, from its manufacture, use, and disposal.

[0004] International Publication No. 2021 / 001813 Japanese Patent Publication No. 2021-528248 International Publication No. 2022 / 250091

[0005] Considering the life cycle of an automobile, reducing GHGs only during vehicle use (driving) is insufficient to reduce the total amount of GHGs emitted into the global environment. Furthermore, no studies have been conducted to date to focus on reducing LC-GHGs (hereinafter referred to as life cycle GHGs or LC-GHGs) generated throughout the entire life cycle of an automobile side module, from its manufacture, use, and disposal.

[0006] Therefore, an object of the present invention is to provide an automobile side module that can reduce LC-GHG per unit area.

[0007] The gist of the present disclosure is as follows.

[0008] (1) A first aspect of the present invention is an automobile side module for reinforcing an outer side of an automobile, which is formed by hot stamping a plurality of integrated steel plates, and has a minimum circumscribed rectangular area S (m ２ ), the total weight of the components of the automobile side module that weigh 0.200 kg or more is W ０．２ (kg), and the total weight of the components with a minimum Vickers hardness of HV510 or more is W ５１０ When W ０．２ / S is 7.7 or less, and W ５１０ / W ０．２(2) The automobile side module described in (1) above may include at least one of elemental technology A1 and elemental technology A2, and at least one of elemental technology B1, elemental technology B2, elemental technology B3a, elemental technology B3b, elemental technology B4, elemental technology B5a, elemental technology B5b, and elemental technology B6. The elemental technology A1 has a chemical composition, in mass %, of 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%, and REM: 0 to 0.30%. and the balance being Fe and impurities; the hot stamped steel has a metallographic structure containing martensite, bainite, and tempered martensite in a total area ratio of 90% or more; in a texture from the surface to a position 1 / 4 of the sheet thickness from the surface, 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}<1-10> to {111}<-1-12> is less than 1.8; and in a texture from a position 1 / 4 of the sheet thickness from the surface to a position 1 / 2 of the sheet thickness from the surface, 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}<1-10> to {111}<-1-12> is less than 2.3.The elemental technology A2 has a chemical composition, in mass %, of 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%, and REM: 0 to 0.30%. and the balance being Fe and impurities, and the metallographic structure is composed of a total of 10 to 30% by area of ​​ferrite and granular bainite, and a balance composed of one or more of martensite, bainite, and tempered martensite, and in a texture from the surface to a position 1 / 4 of the plate thickness from the surface, 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}<1-10> to {111}<-1-12> is less than 1.8, In the texture from the surface to the position 1 / 4 of the sheet thickness from the surface to the position 1 / 2 of the sheet thickness from the surface, 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}<1-10> to {111}<-1-12> is less than 2.3.The elemental technology B1 is an lap hot stamped product comprising: a first Al-Fe alloy plated steel sheet having a thickness T1; and a second Al-Fe alloy plated steel sheet having a thickness T2 and having an area smaller than that of the first Al-Fe alloy plated steel sheet, the second Al-Fe alloy plated steel sheet being overlapped on and welded to the first Al-Fe alloy plated steel sheet, the lap hot stamped product satisfying the relationships of the following formulas (7) to (9): 25≦K1≦60 (7) 25≦K2≦60 (8) 0≦(D1−D2)×(K1 / K2)2≦5.0 (9) where, K1: the average value of the plating thickness of the Al-Fe-based alloy plating layer on the side in contact with the second Al-Fe-based alloy plated steel sheet and the plating thickness of the Al-Fe-based alloy plating layer on the side not in contact with the second Al-Fe-based alloy plated steel sheet, in the non-overlapping portion of the first Al-Fe-based alloy plated steel sheet; K2: the plating thickness of the Al-Fe-based alloy plating layer on the side not in contact with the first Al-Fe-based alloy plated steel sheet, in the overlapping portion of the second Al-Fe-based alloy plated steel sheet; D1: the average value of the thickness of a diffusion layer located in the Al-Fe-based alloy plating layer on the side in contact with the second Al-Fe-based alloy plated steel sheet so as to be in contact with the steel sheet substrate, and the thickness of a diffusion layer located in the Al-Fe-based alloy plating layer on the side not in contact with the second Al-Fe-based alloy plated steel sheet so as to be in contact with the steel sheet substrate. D2: the thickness of a diffusion layer located in the Al-Fe alloy plating layer so as to be in contact with the steel sheet substrate on the side of the second Al-Fe alloy plated steel sheet that is not in contact with the first Al-Fe alloy plated steel sheet, wherein the unit of the sheet thicknesses T1 and T2 is mm, and the unit of K1, K2, D1 and D2 is μm.The elemental technology B2 relates to an aluminum-plated steel sheet for hot stamping, the aluminum-plated steel sheet having: a base steel sheet; an aluminum plating layer having an Al content of 80 mass % or more provided on at least one surface of the base steel sheet; and a surface treatment film provided on the aluminum plating layer, wherein the surface treatment film contains a compound A containing carbon and a compound B which is an oxide or fluoride of a metal element M and has a rutile structure, the carbon concentration of the compound A being 80 mass % or more, and the concentration of the metal element M satisfying the following formulas (1) and (2), wherein 1≦C: ｂＭ ≦40...Formula (1) 1.5≦C ｂＭ / C ｔＭ ≦10.0...Equation (2) Here, when the average thickness of the surface treatment film is H, C in the above equation (2) ｔＭ is the concentration of the metal element M at a position 0.05H from the surface of the surface treatment film in mass %, and C in the above formula (1) and the above formula (2) ｂＭ is the concentration of the metal element M at a position 0.95H from the surface of the surface treatment film in mass %. The elemental technology B3a is a structural member comprising: a member body having an annular shape in a plan view, the member body being formed by a plurality of steel plates joined together, the first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate; ２ The elemental technology B3b is a structural member comprising: a component body having an annular shape in a plan view, the component body being formed by a plurality of steel plates joined together, the first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate; and a coating provided on the first steel plate, the coating containing carbon black at a concentration of 0.500 g / m ２and a coating containing the following: The elemental technology B4 is a structural member comprising: a component body having an annular shape in a plan view, the component body being formed by a plurality of steel plates joined together, the plurality of steel plates including a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate, the first steel plate and the second steel plate being plated steel plates each having an aluminum-based plating layer on both surfaces of a base steel plate, the thickness of the aluminum-based plating layer on the first steel plate being smaller than the thickness of the aluminum-based plating layer on the second steel plate. The elemental technology B5a is a structural member comprising: a member body formed by a plurality of steel plates joined together, the member body having an annular shape in a plan view, the member body including a first steel plate and a second steel plate having an end portion that is overlapped and joined to an end portion of the first steel plate to form an overlap portion together with the end portion of the first steel plate; and a metal oxide layer containing at least one oxide selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide at a concentration of 0.001 g / m on a surface of each of the first steel plate and the second steel plate positioned outside the overlap portion. ２ and a coating containing the above. The elemental technology B5b is a structural member comprising: a component body formed by a plurality of steel plates joined together, the component body having an annular shape in a plan view, the component body including a first steel plate and a second steel plate having an end portion that is overlapped and joined to an end portion of the first steel plate to form an overlap portion together with the end portion of the first steel plate; ２and a coating containing the following: The elemental technology B6 is a structural member comprising a component body formed by a plurality of steel plates joined together and having an annular shape in a plan view, the plurality of steel plates including a first steel plate, a second steel plate, and a third steel plate, an end of the first steel plate overlapping and joining to an end of the second steel plate to form, together with the end of the second steel plate, an overlap portion having the greatest plate thickness in the component body, at least one of the first steel plate and the second steel plate and the third steel plate are plated steel plates having aluminum-based plating layers on both surfaces of a base steel plate, and the thickness of the aluminum-based plating layer on at least one of the first steel plate and the second steel plate is smaller than the thickness of the aluminum-based plating layer on the third steel plate. (3) The automobile side module described in (2) above may comprise at least one of elemental technology A1 and elemental technology A2, and at least one of elemental technology B1 and elemental technology B2. (4) The automobile side module described in (2) above may include at least one of elemental technology A1 and elemental technology A2, and at least one of elemental technology B3a, elemental technology B3b, elemental technology B4, elemental technology B5a, elemental technology B5b, and elemental technology B6. (5) The automobile side module described in (2) above may include at least one of elemental technology A1 and elemental technology A2, at least one of elemental technology B1 and elemental technology B2, and at least one of elemental technology B3a, elemental technology B3b, elemental technology B4, elemental technology B5a, elemental technology B5b, and elemental technology B6.

[0009] According to the present disclosure, it is possible to provide an automobile side module that can reduce LC-GHG per unit area.

[0010] FIG. 1 is a characteristic diagram showing the environmental load (GHG emissions) during the manufacture of each material of an automobile side module. FIG. 2 is a perspective view showing an example of a frame having a monocoque structure of an automobile body to which the automobile side module according to the present embodiment is applied, the frame including an impact absorbing framework member. FIG. 3 is a plan view showing an automobile side module according to the present embodiment. FIG. 4 is a plan view showing an automobile side module according to a modified example. ５１０ / W ０．２ , W on the vertical axis ０．２ / S (kg / m ２ ) is plotted on the horizontal axis. ５１０ / W ０．２ The vertical axis is LC-GHG / S (kg, CO ２ -eq / m ２1 is a graph showing plots of the surface roughness of a hot-stamped laminated steel sheet and the surface roughness of a hot-stamped laminated steel sheet, respectively. FIG. 2 is an explanatory diagram schematically showing an example of an overlapping blank for hot stamping, a method for manufacturing an overlapping hot-stamped steel sheet, and an overlapping hot-stamped steel sheet according to an embodiment of the present invention. FIG. 3 is an explanatory diagram schematically showing a structure of an Al-based plated steel sheet having an Al-based plating layer on the surface of a base steel sheet, according to the overlapping blank for hot stamping according to the embodiment. FIG. 4 is an explanatory diagram schematically showing a structure of an Al-based plated steel sheet having an Al-based plating layer on the surface of a base steel sheet, according to the overlapping blank for hot stamping according to the embodiment. FIG. 5 is an explanatory diagram showing a structure of an Al-based plated steel sheet having an Al-based plating layer on the surface of a base steel sheet, according to the overlapping blank for hot stamping according to the embodiment. FIG. 6 is a diagram showing the result of observing, with an optical microscope, a cross section of an Al-based plated steel sheet having an Al-based plating layer on the surface of a base steel sheet, according to the overlapping blank for hot stamping according to the embodiment, after nital etching. 1 is an explanatory diagram schematically illustrating the structure of an Al-Fe alloy-plated steel sheet of the lap hot-stamped product according to the same embodiment, the Al-Fe alloy-plated steel sheet having an Al-Fe alloy plating layer on the surface of the base steel sheet, and a diffusion layer included in the Al-Fe alloy plating layer that is in contact with the steel sheet substrate.

[0033] FIG. 1 is a diagram showing the results of observing a cross section of the Al-Fe alloy-plated steel sheet of the hot-stamped product according to the same embodiment, the Al-Fe alloy plating layer on the surface of the base steel sheet, using an optical microscope after nital etching.

[0034] FIG. 1 is an explanatory diagram schematically illustrating the structure of an Al-Fe alloy-plated steel sheet of the lap hot-stamped product according to the same embodiment, the Al-Fe alloy plating layer (including a diffusion layer) on the surface of the base steel sheet, and Zn, Ti, Cu, and V in an upper layer thereon.

[0035] FIG. 16 is a plan view of a structural member according to a first embodiment of elemental technologies B3a and B3b.

[0036] FIG. 17 is a cross-sectional view taken along the line II-II of FIG. 16. Fig. 18A is a schematic diagram for manufacturing a structural member according to a first embodiment of elemental technologies B3a and B3b, showing a blank according to the first embodiment. Fig. 18B is a schematic diagram for manufacturing a structural member according to a first embodiment of elemental technologies B3a and B3b, showing a blank according to the first embodiment.FIG. 18C is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to elemental technologies B3a and B3b. FIG. 18D is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to elemental technologies B3a and B3b. FIG. 18E is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to elemental technologies B3a and B3b. FIG. 18F is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to elemental technologies B3a and B3b. FIG. 18G is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to elemental technologies B3a and B3b. FIG. 19 is a cross-sectional view of a structural member manufactured by the manufacturing method according to the first embodiment of elemental technologies B3a and B3b. FIG. 20 is a plan view of a blank according to the second embodiment of elemental technologies B3a and B3b. FIG. 21 is a cross-sectional view taken along line VI-VI of FIG. 20. FIG. 22 is a plan view of a structural member according to the second embodiment of elemental technologies B3a and B3b. FIG. 23 is a plan view of a structural member according to a modified example of each embodiment of elemental technologies B3a and B3b. FIG. 24A is a diagram showing a division pattern of a structural member in a first example of elemental technologies B3a and B3b. FIG. 24B is a diagram showing another division pattern of a structural member in a first example of elemental technologies B3a and B3b. FIG. 24C is a diagram showing yet another division pattern of a structural member in a first example of elemental technologies B3a and B3b. FIG. 24D is a diagram showing yet another division pattern of a structural member in a first example of elemental technologies B3a and B3b. FIG. 24E is a diagram showing yet another division pattern of a structural member in a first example of elemental technologies B3a and B3b. FIG. 24F is a diagram showing yet another division pattern of a structural member in a first example of elemental technologies B3a and B3b. FIG. 24G is a diagram showing yet another division pattern of a structural member in a first example of elemental technologies B3a and B3b. FIG. 25A is a diagram showing a division pattern of a structural member in a second example of elemental technologies B3a and B3b. Fig. 25B is a diagram showing another division pattern of the structural member in the second example of elemental technologies B3a and B3b. Fig. 25C is a diagram showing yet another division pattern of the structural member in the second example of elemental technologies B3a and B3b.FIG. 25D is a diagram showing yet another division pattern of a structural member in the second example of elemental technology B3a and B3b. FIG. 26 is a plan view of a structural member according to the first embodiment of elemental technology B4. FIG. 27 is a cross-sectional view taken along II-II in FIG. 1. FIG. 28A is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to elemental technology B4. FIG. 28B is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to elemental technology B4. FIG. 28C is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to elemental technology B4. FIG. 28D is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to elemental technology B4. FIG. 28E is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to elemental technology B4. FIG. 28F is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to elemental technology B4. FIG. 28G is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to elemental technology B4. FIG. 29A is a cross-sectional view of a structural member manufactured by the manufacturing method according to the first embodiment of elemental technology B4. FIG. 29B is another cross-sectional view of a structural member manufactured by the manufacturing method according to the first embodiment of elemental technology B4. FIG. 29C is yet another cross-sectional view of a structural member manufactured by the manufacturing method according to the first embodiment of elemental technology B4. FIG. 30 is a plan view of a blank according to the second embodiment of elemental technology B4. FIG. 31 is a cross-sectional view taken along line VI-VI of FIG. 30. FIG. 32 is a plan view of a structural member according to the second embodiment of elemental technology B4. FIG. 33 is a cross-sectional view of a blank according to the third embodiment of elemental technology B4. FIG. 34 is a cross-sectional view of a blank according to the fourth embodiment of elemental technology B4. FIG. 35 is a plan view of a structural member according to a modified example of each embodiment of elemental technology B4. FIG. 36A is a diagram showing a division pattern of a structural member according to the first example of elemental technology B4. FIG. 36B is a diagram showing another division pattern of a structural member according to the first example of elemental technology B4. FIG. 36C is a diagram showing yet another division pattern of a structural member according to the first example of elemental technology B4.FIG. 36D is a diagram showing yet another division pattern of a structural member in the first example of elemental technology B4. FIG. 36E is a diagram showing yet another division pattern of a structural member in the first example of elemental technology B4. FIG. 36F is a diagram showing yet another division pattern of a structural member in the first example of elemental technology B4. FIG. 36G is a diagram showing yet another division pattern of a structural member in the first example of elemental technology B4. FIG. 37A is a diagram showing a division pattern of a structural member in the second example of elemental technology B4. FIG. 37B is a diagram showing another division pattern of a structural member in the second example of elemental technology B4. FIG. 37C is a diagram showing yet another division pattern of a structural member in the second example of elemental technology B4. FIG. 37D is a diagram showing yet another division pattern of a structural member in the second example of elemental technology B4. FIG. 38 is a plan view of a structural member according to embodiments of elemental technologies B5a and B5b. FIG. 39 is a cross-sectional view taken along II-II in FIG. 38. FIG. 40A is a schematic diagram of a method for manufacturing a structural member according to an embodiment of elemental technologies B5a and B5b, showing a blank according to the embodiment. FIG. 40B is a schematic diagram of a method for manufacturing a structural member according to an embodiment of elemental technologies B5a and B5b, showing a blank according to the embodiment. FIG. 40C is a schematic diagram of a method for manufacturing a structural member according to an embodiment of elemental technologies B5a and B5b, showing a blank according to the embodiment. FIG. 40D is a schematic diagram of a method for manufacturing a structural member according to an embodiment of elemental technologies B5a and B5b, showing a blank according to the embodiment. FIG. 40E is a schematic diagram of a method for manufacturing a structural member according to an embodiment of elemental technologies B5a and B5b. FIG. 40F is a schematic diagram of a method for manufacturing a structural member according to an embodiment of elemental technologies B5a and B5b. FIG. 40G is a schematic diagram of a method for manufacturing a structural member according to an embodiment of elemental technologies B5a and B5b. FIG. 41 is a cross-sectional view of a structural member manufactured by a manufacturing method according to an embodiment of elemental technologies B5a and B5b. Fig. 42 is a plan view of a structural member according to a modification of the above-described embodiment of elemental technologies B5a and B5b. Fig. 43A is a diagram showing a division pattern of a structural member according to a first example of elemental technologies B5a and B5b.FIG. 43B is a diagram showing another division pattern of structural members in the first example of elemental technologies B5a and B5b. FIG. 43C is a diagram showing yet another division pattern of structural members in the first example of elemental technologies B5a and B5b. FIG. 43D is a diagram showing yet another division pattern of structural members in the first example of elemental technologies B5a and B5b. FIG. 43E is a diagram showing yet another division pattern of structural members in the first example of elemental technologies B5a and B5b. FIG. 43F is a diagram showing yet another division pattern of structural members in the first example of elemental technologies B5a and B5b. FIG. 43G is a diagram showing yet another division pattern of structural members in the first example of elemental technologies B5a and B5b. FIG. 44A is a diagram showing a division pattern of structural members in the second example of elemental technologies B5a and B5b. FIG. 44B is a diagram showing another division pattern of structural members in the second example of elemental technologies B5a and B5b. FIG. 44C is a diagram showing yet another division pattern of a structural member in the second example of elemental technologies B5a and B5b. FIG. 44D is a diagram showing yet another division pattern of a structural member in the second example of elemental technologies B5a and B5b. FIG. 45 is a plan view of a structural member according to the first embodiment of elemental technology B6. FIG. 46 is a cross-sectional view taken along II-II in FIG. 45. FIG. 47A is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to the first embodiment of elemental technology B6. FIG. 47B is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to the first embodiment of elemental technology B6. FIG. 47C is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to the first embodiment of elemental technology B6. FIG. 47D is a schematic diagram showing a blank according to the first embodiment of the manufacturing method for a structural member according to the first embodiment of elemental technology B6. FIG. 47E is a schematic diagram showing a blank according to the manufacturing method for a structural member according to the first embodiment of elemental technology B6. Fig. 47F is a schematic diagram for manufacturing a structural member according to the first embodiment of elemental technology B6. Fig. 47G is a schematic diagram for manufacturing a structural member according to the first embodiment of elemental technology B6.FIG. 48A is a cross-sectional view of a structural member manufactured by the manufacturing method according to the first embodiment of elemental technology B6. FIG. 48B is a cross-sectional view of a structural member manufactured by the manufacturing method according to the first embodiment of elemental technology B6. FIG. 48C is a cross-sectional view of a structural member manufactured by the manufacturing method according to the first embodiment of elemental technology B6. FIG. 49 is a cross-sectional view of a blank according to the second embodiment of elemental technology B6. FIG. 50 is a plan view of a structural member according to a modified example of the above embodiment of elemental technology B6. FIG. 51A is a diagram showing a division pattern of a structural member in the first example of elemental technology B6. FIG. 51B is a diagram showing another division pattern of a structural member in the first example of elemental technology B6. FIG. 51C is a diagram showing yet another division pattern of a structural member in the first example of elemental technology B6. FIG. 51D is a diagram showing yet another division pattern of a structural member in the first example of elemental technology B6. FIG. 51E is a diagram showing yet another division pattern of a structural member in the first example of elemental technology B6. FIG. 51F is a diagram showing yet another division pattern of a structural member in the first example of elemental technology B6. Fig. 51G is a diagram showing yet another division pattern of a structural member in the first example of elemental technology B6. Fig. 52A is a diagram showing a division pattern of a structural member in the second example of elemental technology B6. Fig. 52B is a diagram showing another division pattern of a structural member in the second example of elemental technology B6. Fig. 52C is a diagram showing yet another division pattern of a structural member in the second example of elemental technology B6. Fig. 52D is a diagram showing yet another division pattern of a structural member in the second example of elemental technology B6.

[0011] As mentioned above, when considering the life cycle of an automobile, reducing GHG emissions only while the vehicle is in use (while driving) is insufficient to reduce the total amount of GHG emitted into the global environment. Furthermore, since automobile side modules account for approximately 5-10% of the total weight of a vehicle, reducing GHG emissions related to automobile side modules will significantly contribute to reductions. Currently, the focus is on making automobiles multi-material by using materials such as aluminum and carbon to reduce their weight, but the inventors have focused on the following: 1. GHG generated in the production of materials for automobile side modules (hereinafter referred to as "material production GHG"); 2. GHG generated in the automobile side module manufacturing process (hereinafter referred to as "process GHG"); 3. The portion of GHG generated while the automobile is driving that is contributed to the automobile side module (hereinafter referred to as "driving GHG"); and 4. The present inventors have focused on four types of GHGs that are generated when automobile side modules are disposed of (hereinafter referred to as "disposal GHGs"), and have studied ways of reducing their total amount.

[0012] In this specification, the side module is a framework structural member provided inside the side outer panel to reinforce the side outer panel. The side module includes the A-pillar (front pillar), A-pillar (front pillar) lower, B-pillar (center pillar), C-pillar (rear pillar), side sill (rocker), and roof rail. Doors are not included in the side module. In addition, in this specification, the CO generated during the life cycle is ２ GHGs including CO are called LC-GHGs. ２ The amount is CO ２ GHGs other than CO are also calculated as equivalent masses and added together. ２ Other GHGs include methane, nitrous oxide, and ozone-depleting substances such as chlorofluorocarbon compounds. ２ The equivalent mass is calculated using the conversion factors listed in Table 1, which are set for each category of material, process, use, and recycling. ２ "equivalent" means "CO ２ Also referred to as "equivalent mass" and in this specification, "CO２ "equivalent", "CO ２ Equivalent mass” “CO ２ "CO equivalent" is defined as the same meaning. ２ The "equivalent mass" is CO ２ (global warming potential: 1) and CO ２ Gases other than methane CH ４ (Greenhouse effect per unit mass is CO ２ 25 times: Global warming potential 25), nitrous oxide N ２ O (greenhouse effect per unit mass is CO ２ 298 times the global warming potential (global warming potential 298), and then weighted by the global warming potential, CO ２ The converted mass is calculated.

[0013]

[0014] (GHG emissions in material manufacturing) Steel materials as raw materials have the smallest GHG emissions per unit of weight compared to other materials. Figure 1 is a characteristic diagram showing the environmental impact (GHG emissions) during the manufacturing of each material for automobile side modules. The vertical axis shows the materials for automobile side modules: ordinary steel plate, high-strength steel plate (steel plate with HV 510 or more), aluminum, and carbon fiber reinforced plastic (CFRP). The horizontal axis shows GHG emissions per equivalent function [kg-CO ２ As shown in Figure 1, steel materials (normal steel plate, high-strength steel plate) have overwhelmingly smaller GHG emissions than other materials (aluminum, carbon fiber reinforced plastic), and it can be seen that the primary use of steel materials as materials for constructing automobile side modules will contribute greatly to reducing LC-GHG.

[0015] (Process GHG) In the manufacture of automobile side modules, GHG is generated mainly in the welding process, heating process, painting process, etc. Therefore, appropriate process design while ensuring the performance required of automobile side modules can contribute to reducing LC-GHG.

[0016] (GHG during driving) Reducing the weight of the vehicle side module can reduce the load on the drive source such as an internal combustion engine, and therefore contribute to reducing LC-GHG.

[0017] (GHG emissions at the time of disposal) Steel reduces CO emissions by 1.60 kg per kg through scrap recycling ２ eq. Compared to aluminum, steel has a smaller effect on reducing emissions per kg, but when high-strength steel is used, the weight required to obtain the required strength is small, so it can be said that using high-strength steel can contribute to reducing LC-GHG. In other words, as with material manufacturing GHG, GHG emissions at disposal can be reduced by primarily using steel materials as the material that makes up the automobile side module, which can contribute to reducing LC-GHG.

[0018] As described above, in order to reduce LC-GHG, total GHG emissions must be reduced from four perspectives. For example, it is believed that there is a trade-off between "material production GHG, disposal GHG, and driving GHG." Furthermore, there is generally a tendency for "process GHG" to increase in the manufacture of lightweight, highly functional parts, and there is a trade-off between "process GHG" and "driving GHG." While methods for reducing GHG at each stage of a product's life cycle have been studied and discussed, no optimal examples of material selection and process design for reducing LC-GHG have been disclosed.

[0019] The inventors focused on reducing LC-GHG by taking into consideration the above four categories of GHG, which include trade-offs, and discovered that by controlling the weight of components per specified area and the weight of high-strength components with HV510 or higher within an appropriate range, it is possible to reduce the LC-GHG of an automobile side module while still satisfying the required strength (side impact resistance).

[0020] An automobile side module according to an embodiment of the present invention, which has been developed based on the above findings, will now be described with reference to the drawings. However, these descriptions are intended to merely exemplify preferred embodiments of the present invention, and are not intended to limit the present invention to such specific embodiments.

[0021] FIG. 2 shows a perspective view of an automobile body 1 to which the automobile side module 100 according to this embodiment is applied. The automobile body 1 is composed of a monocoque frame equipped with an impact-absorbing framework member. The automobile side module 100 according to this embodiment has a single door ring structure. FIG. 3 shows a plan view of the automobile side module 100. As shown in FIG. 3, the automobile side module 100 is configured with an integrated main body 110. The automobile side module 100 has a structure that is a single ring shape when viewed overall (a so-called single door ring structure).

[0022] The body 110 includes a B-pillar upper portion 111 , a B-pillar lower portion 112 , an A-pillar portion 113 , a front roof rail portion 114 , and a front side sill portion 115 .

[0023] Reinforcements (not shown) may be attached to the main body 110 for reinforcement. Examples of reinforcement members include a side sill reinforcement, a B-pillar reinforcement, an A-pillar reinforcement, and a front roof rail reinforcement.

[0024] The automobile side module 100 according to this embodiment is formed into an integrated component by hot stamping a single tailored blank. More specifically, the single tailored blank can be obtained, for example, by joining multiple hot-stamping steel sheets corresponding to the respective portions of the main body 110 together, and then overlapping and joining (patchwork joining) the hot-stamping steel sheets to be formed into the respective reinforcement members. Then, by hot stamping this single tailored blank, an automobile side module 100 can be obtained, with each portion having different characteristics (weight, hardness, strength, plate thickness). Note that additional reinforcing parts and brackets may be attached to the automobile side module 100 after hot stamping.

[0025] As described above, the automobile side module 100 according to this embodiment is constructed by hot stamping a plurality of integrated steel plates, which reduces material production GHG compared to press-forming each section, trimming unnecessary portions as needed, and then joining them by welding. Furthermore, when hot stamping each section and then welding them, the number of hot stamping heating processes and time are required. However, the automobile side module 100 according to this embodiment welds a plurality of steel plates and then hot stamps them, thereby reducing the number of heating processes and time required. Therefore, the automobile side module 100 according to this embodiment can reduce process GHG while still achieving the performance required of an automobile side module.

[0026] Furthermore, in the automobile side module 100 according to this embodiment, the weight of the components per minimum circumscribed rectangular area and the weight of the high-strength components of HV510 or higher are controlled within appropriate ranges, thereby making it possible to reduce the LC-GHG of the automobile side module.

[0027] Specifically, the minimum circumscribed rectangle area S (m ２ ), the total weight W of the components of the automobile side module that weigh 0.200 kg or more ０．２(kg), and the total weight W of components with a minimum Vickers hardness of HV 510 or more ５１０ But, W ０．２ / S≦7.7, and W ５１０ / W ０．２ By satisfying the condition of >0.10, it is possible to reduce LC-GHG emissions from the automobile side module. No automobile side module that satisfies this condition has existed to date, and this condition would not have been easily conceived without the above-mentioned findings of the inventors.

[0028] Here, the reference plane is a plane parallel to the flange surface of the vehicle underside of the side sill (rocker) of the automobile side module. In reality, it is a plane perpendicular to the vehicle width direction of the automobile side module when it is attached to the vehicle body. Also, the minimum circumscribed rectangular area S (m ２ ) is the minimum circumscribed rectangular area when viewed from the perpendicular direction of the reference plane of the automobile side module. In the example shown in Figure 3, it is the area of ​​the rectangle indicated by the dashed line. The weight of a component weighing 0.200 kg or more is defined as W ０．２ The reason for setting the weight at 0.200 kg is that components weighing less than 0.200 kg have a relatively small impact on GHG. For example, small components such as bolts and brackets weighing less than 0.200 kg are not taken into consideration.

[0029] W ０．２ The larger the vehicle body or side door module, the larger the value of W tends to be. ０．２ The value of W ０．２ / S (m ２ ) is used as an index. ０．２ When the value of / S is 7.7 or less, weight reduction according to the size of the side door module is realized, and it is possible to reduce GHG during driving. ０．２ The smaller the value of / S, the better, and it is preferably 6.9 or less, and more preferably 6.3 or less. ０．２ The lower limit of / S is set based on the required safety performance. ０．２ / S may be, for example, 5.0 or more in order to ensure both rigidity as a module and safety performance.

[0030] W ５１０ / W ０．２ When the value of W is more than 0.10, the proportion of high strength members with HV 510 or more used among the members used in the side door module is high, so it is possible to reduce GHG emissions in material production. ５１０ / W ０．２ The higher the value, the better, and it is preferably greater than 0.3, more preferably greater than 0.7.

[0031] The Vickers hardness measurement method is as follows. A sample having a cross section perpendicular to the plate surface is taken from the flat portion of each portion, and the cross section is prepared as the measurement surface, which is then subjected to a hardness test. The measurement surface is prepared in accordance with JIS Z 2244:2009. The measurement surface is polished using silicon carbide paper of #600 to #1500, and then the measurement surface is mirror-finished using a liquid in which diamond powder with a particle size of 1 μm to 6 μm is dispersed in a diluted solution such as alcohol or pure water. The hardness test is performed according to the method described in JIS Z 2244:2009. Using a micro Vickers hardness tester, measurements are taken at 30 points at 3 / 8 of the plate thickness of the sample, with a load of 1000 gf, at intervals of at least three times the indentation, and the average value is the hardness at the center of the plate thickness.

[0032] In the present application, by applying at least one of elemental technology A1 and elemental technology A2, and at least one of elemental technology B1, elemental technology B2, elemental technology B3a, elemental technology B3b, elemental technology B4, elemental technology B5a, elemental technology B5b, and elemental technology B6, the weight ratio of steel material in the automobile body 1 is increased to reduce the material production GHG, and GHG during driving is reduced by reducing the weight of the automobile body 1, resulting in a significant reduction in LC-GHG compared to conventional automobile bodies. The above elemental technologies can be applied mainly to the B-pillar upper portion 111, the B-pillar lower portion 112, the A-pillar portion 113, the front roof rail portion 114, and the front side sill portion 115 of the components of the automobile side module 100.

[0033] It is more preferable to apply at least one of elemental technology A1 and elemental technology A2, and at least one of elemental technology B1 and elemental technology B2, It is more preferable to apply at least one of elemental technology A1 and elemental technology A2, and at least one of elemental technology B3a, elemental technology B3b, elemental technology B4, elemental technology B5a, elemental technology B5b, and elemental technology B6, It is more preferable to apply at least one of elemental technology A1 and elemental technology A2, and at least one of elemental technology B1 and elemental technology B2, and at least one of elemental technology B3a, elemental technology B3b, elemental technology B4, elemental technology B5a, elemental technology B5b, and elemental technology B6.

[0034] In this specification, the term "automobile" refers to an automobile for driving on public roads. An automobile for driving on public roads is an automobile that meets the safety standards of the laws and regulations (type approval) of each country and has excellent collision safety performance ratings in each collision test in the collision safety performance evaluation of the NCAP (New Car Assessment Programme), which is an assessment test of each country. The assessment tests are stricter than the laws and regulations of each country, and if a vehicle receives the highest rating (5-star rating) in the assessment test, it can be said that it is fully suitable for driving on public roads.

[0035] Furthermore, the automobile body of a road-legal automobile to which the automobile side module according to this embodiment is applicable is not limited to an internal combustion engine or an electric automobile, but may also be a hybrid automobile, a fuel cell automobile, a hydrogen engine automobile, or the like, which is driven by an internal combustion engine and an electric motor. While FIG. 2 shows an automobile body having a monocoque frame, the automobile body 1 is not limited to an automobile body having a monocoque frame, but may also be an automobile body having a ladder frame structure. Furthermore, automobile models for road-legal automobiles include passenger cars and commercial vehicles such as sedans, hatchbacks, station wagons, minivans, and pickup trucks. Furthermore, automobiles for road-legal automobiles also include loaded vehicles such as trucks.

[0036] Fig. 4 is a plan view of a modified automobile side module 200. The automobile side module 200 has a structure in which two rings are connected together (a so-called double door ring structure) when viewed from above. As shown in Fig. 4, the automobile side module 200 may have a double door ring structure in which its main body includes a B-pillar upper portion 211, a B-pillar lower portion 212, an A-pillar portion 213, a front roof rail portion 214, a front side sill portion 215, a rear roof rail portion 216, a C-pillar upper portion 217, and a C-pillar lower portion 218.

[0037] In the automobile side module 200 having such a double door ring structure, similarly to the automobile side module 100, the minimum circumscribed rectangular area S (m ２ ), the total weight W of the components of the automobile side module that weigh 0.200 kg or more ０．２ (kg), and the total weight W of components with a minimum Vickers hardness of HV510 or more ５１０ But, W ０．２ / S≦7.7, and W ５１０ / W ０．２ By satisfying the condition >0.10, it becomes possible to reduce LC-GHG of the automobile side module.

[0038] (Examples) The present invention will be specifically described below by way of examples. Note that the conditions in the examples are examples adopted to confirm the feasibility and effects of the present disclosure, and the present disclosure is not limited to the conditions in the examples. Various conditions may be adopted in the present disclosure as long as they do not deviate from the gist of the disclosure and the purpose is achieved.

[0039] Tables 2 and 3 show various property values ​​of the automobile side modules according to the invention examples and comparative examples. Table 2 shows the weight (kg) and hardness HV of each integrated part constituting the automobile side module. Table 3 shows the weight (kg) and hardness HV of the separate parts (i.e., parts attached after hot stamping) constituting the automobile side module. The automobile side modules of invention examples 1 to 7 and comparative examples 1, 3, and 4 are automobile side modules in which hot stamping steel sheets having shapes corresponding to the pre-forming shapes of multiple parts shown in Table 2 (seven parts in the case of invention example 1) are joined to form a tailored blank, and multiple separate parts shown in Table 3 (five parts in the case of invention example 1) are joined to the main body obtained by hot stamping. The automobile side modules of comparative examples 2 and 5 to 11 are automobile side modules in which multiple separate parts shown in Table 3 are joined. The separate parts are basically steel members, but separate part No. 8 of comparative example 8 and separate part No. 10 of comparative example 10 are aluminum extrusions.

[0040] The weights (kg) of the parts shown in Table 2 are the weights when the automobile side module is cut along the weld lines of the tailored blank. The weights in the comparative examples were determined by disassembling the body of a commonly available road-legal automobile and measuring and analyzing the shape and weight data. The weights in some comparative examples and inventive examples were determined by measuring and analyzing design and development data using CAD (Computer-Aided Design). The hardness HV was determined as follows: A sample having a cross section perpendicular to the plate surface was taken from the flat portion of each part, and the cross section was prepared as the measurement surface, which was then subjected to the hardness test. The measurement surface was prepared in accordance with JIS Z 2244:2009. The measurement surface was polished using #600 to #1500 silicon carbide paper, and then mirror-finished using a liquid in which diamond powder with a particle size of 1 μm to 6 μm was dispersed in a diluted solution such as alcohol or pure water. The hardness test was carried out according to the method described in JIS Z 2244: 2009. Using a micro-Vickers hardness tester, measurements were taken at 30 points at 3 / 8 of the thickness of the sample, with a load of 1000 gf, and at intervals of at least three times the indentation, and the average value was taken as the hardness at the center of the thickness.

[0041] Table 4 shows the minimum circumscribed rectangle area S (m ２ ), the total weight W of components weighing 0.200 kg or more ０．２ (kg), the total weight W of components with a minimum Vickers hardness of HV510 or more ５１０ (kg), and Total GHG emissions LC-GHG (kg, CO ２ -eq) in addition to W ５１０ / W ０．２ (-), ・W ０．２ / S (kg / m ２ ), and LC-GHG / S (kg, CO ２ -eq / m ２ ) are shown as calculated values.

[0042] The total GHG emissions are calculated by subtracting the CO from the above-mentioned GHGs from the material manufacturing GHGs, process GHGs, GHGs during driving, and GHGs during disposal. ２The equivalent mass is calculated and summed up, which corresponds to the amount of LC-GHG emissions. The total GHG emissions is a value calculated using the method described below.

[0043] The characteristic values ​​of Examples 1-7 were obtained by measuring and analyzing the automobile body 1 constructed by the inventors using the above-mentioned elemental technologies. The characteristic values ​​of Comparative Examples 1-7 were obtained by measuring and analyzing the automobile body of a publicly available road-legal automobile. For some Comparative Examples, default values ​​listed on the World Auto Steel (WAS) website were used. WAS is the Automotive Subcommittee of the World Steel Association, consisting of 17 steel manufacturers worldwide. The analysis of LC-GHG emissions was based on "Roland Geyer, Parametric Assessment of Climate Change Impacts of Automotive Material Substitution, Environmental Science & Technology 2008 42 (18), 6973-6979, DOI: 10.1021 / es800314w."

[0044] (Calculation of GHG emissions from material production) The default settings of the GHG analysis software were used as the basic conditions. With these default settings, the scrap charging rate to the blast furnace was 11.9%, and the usage rates of recycled materials made from scrap were set based on statistical data as follows: plate material 5%, wire rod 85%, and cast iron 100%. Assuming these as the base conditions, values ​​were entered to obtain the various material compositions shown in Table 1, and calculations were performed.

[0045] (Calculation of process GHG) The default settings of the GHG analysis software were used as the basic conditions. The material yield in automobile part production was assumed to be 55% for steel plate, 52% for aluminum alloy plate, 75% for plate, bar, and wire rod, and 80% for cast iron, aluminum extrusion, and aluminum casting. Calculations were performed by inputting values ​​for the various material compositions shown in Table 1.

[0046] (Calculation of Driving GHG) An electric vehicle was selected as the powertrain type for the target vehicle. A mid-size electric vehicle was selected based on the size and weight of each vehicle to be analyzed. The vehicle's driving pattern was set to the following WLTP (Class 3b) mode. WLTP mode: Average speed: 36.57 km / h; Maximum speed: 97.4 km / h; Driving time: 1,477 seconds; Driving distance: 15.01 km; Idling ratio: 15.4%; Cold start ratio: 100%. The driving distance was assumed to be 110,000 km, and the settings were made to take into account the weight reduction of the vehicle body and resize the powertrain. The electric vehicle's power consumption during driving was set to be generated in Japan, and the calculation was performed by inputting the power consumption contribution of the side module obtained by the inventors' analysis.

[0047] (Calculation of GHG at disposal) The default settings of the software for GHG analysis at disposal are used as the basic conditions, and the recycling rate of steel is assumed to be 90.3%, and that of aluminum alloy material is 78.6%. Energy recovery from recycling other than automobiles is also calculated as CO2. ２ This setting is taken into consideration as the amount of absorption.

[0048] CO ２ The calculation of the equivalent mass is based on the GHG emissions from the material manufacturing process, vehicle manufacturing process, fuel manufacturing and use process, and material and vehicle recycling process shown in Table 1. ２ Use a coefficient to calculate the equivalent mass, and use the weight or energy amount to calculate CO ２ These values ​​are the default settings of the GHG analysis software, and are set based on statistical data on GHG emissions for each substance and each process. By following the above procedure, CO2 can be calculated from the material production GHG, process GHG, GHG during driving, and GHG during disposal. ２ The equivalent masses were calculated and summed to calculate the LC-GHGs listed in Table 4.

[0049]

[0050] (*1) is the weight of the aluminum extrusion.

[0051]

[0052] In invention examples 1-7, the proportion of steel used in the automobile side module was increased, and the above-mentioned elemental technologies were combined and applied to form an integrated part. As a result, ０．２ / S is 7.7 or less, and W ５１０ / W ０．２ This enabled us to reduce the LC-GHG of the automobile side module.

[0053] On the other hand, in Comparative Examples 1 to 5 and 8, W ５１０ / W ０．２ is 0.00, and W ０．２ Therefore, it was necessary to increase the / S, and it was not possible to obtain a sufficient reduction effect in GHG during material production and GHG during driving.

[0054] Furthermore, in Comparative Examples 2 and 5 to 11, which did not employ an integrated structure, each section was press-formed, and unnecessary sections were trimmed and removed before being joined by welding, so it was not possible to obtain a sufficient effect in reducing material production GHG and running GHG. In particular, in Comparative Examples 7, 9, and 10, although two or more sections having a hardness of HV 510 or higher were obtained by hot stamping, the lack of an integrated structure meant that it was not possible to obtain a sufficient effect in reducing material production GHG and a sufficient effect in reducing LC-GHG.

[0055] FIG. 5 shows the results of the embodiment, with the horizontal axis representing W ５１０ / W ０．２ , W on the vertical axis ０．２ / S (kg / m ２ 6 is a graph plotting the W ５１０ / W ０．２ The vertical axis is LC-GHG / S (kg, CO ２ -eq / m ２ ) are plotted. From these graphs, it can be seen that the example of the present invention reduces LC-GHG by about 5 to 30% compared to the conventional structure. Thus, according to the present invention, the minimum circumscribed rectangular area S (m２ ), the total weight W of the components of the automobile side module that weigh 0.200 kg or more ０．２ (kg), and the total weight W of components with a minimum Vickers hardness of HV510 or more ５１０ But, W ０．２ / S≦7.7, and W ５１０ / W ０．２ By satisfying the condition >0.10, it is possible to reduce LC-GHG of the automobile side module.

[0056] (Example 2) Table 5 shows the results of side collision tests conducted on the invention examples and comparative examples. Table 5 shows the test results for side collisions, with evaluation scores A to C. In this evaluation, the test results of the IIHS side collision test were first disclosed. For the vehicle body of Comparative Example 2, which received a good evaluation for collision safety performance, a numerical analysis of the collision test was conducted using the IIHS collision analysis model, and the resulting intrusion amount was used as the standard (evaluation B). Note that the vehicle bodies of Comparative Examples 1 and 3-11 are also certified (type approved) under the laws and regulations of each country. The safety performance evaluation results of some vehicle bodies are listed in comparison with Comparative Example 2. For Inventive Examples 1-7, a numerical analysis of a side collision test was conducted with only the front side and outer R / F modules swapped, and safety performance was evaluated based on the relative intrusion amount of the center pillar into the cabin. Then, vehicles with test results superior to the vehicle (Comparative Example 2) that received a 5-star evaluation in the IIHS crash simulation test were given an evaluation of A. Furthermore, the safety test results were inferior to those of Comparative Example 2, but no separation of the parts occurred, and the evaluation was C.

[0057]

[0058] As shown in Table 5, inventive examples 1-7, results (rating A or B) for side collisions were obtained that were equal to or better than the safety test results of vehicles that received a good rating in the IIHS side impact test.

[0059] Therefore, according to Examples 1-7, it is possible to reduce LC-GHG while satisfying the vehicle safety test results of a good rating in the IIHS side impact test.

[0060] The outline of the elemental technologies applied to the automobile side module 100 according to this embodiment is as follows. Note that the symbols for components, formulas, examples, etc. in the explanation of each elemental technology are assigned to each elemental technology for the sake of simplicity. Therefore, the same symbols may be assigned in the explanation of different elemental technologies. Also, the word "invention" in the description of the elemental technology can be read as "elemental technology."

[0061] <<Elemental Technology A1>> Elemental technology A1 has a chemical composition, in mass%, of 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%, and REM: 0 to 0.30%. and the balance being Fe and impurities; the hot stamped steel has a metallographic structure containing martensite, bainite, and tempered martensite in a total area ratio of 90% or more; in a texture from the surface to a position 1 / 4 of the sheet thickness from the surface, 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}<1-10> to {111}<-1-12> is less than 1.8; and in a texture from a position 1 / 4 of the sheet thickness from the surface to a position 1 / 2 of the sheet thickness from the surface, 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}<1-10> to {111}<-1-12> is less than 2.3.

[0062] Elemental technology A1 is a technology disclosed in International Publication No. 2021 / 230150. This elemental technology A1 makes it possible to provide a hot-stamped steel sheet having excellent strength and bendability and high load capacity.

[0063] <<Elemental Technology A2>> Elemental Technology A2 has a chemical composition, in mass%, of 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%, and REM: 0 to 0.30%. and the balance being Fe and impurities, and the metallographic structure is composed of a total of 10 to 30% by area of ​​ferrite and granular bainite, and a balance composed of one or more of martensite, bainite, and tempered martensite, and in a texture from the surface to a position 1 / 4 of the plate thickness from the surface, 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}<1-10> to {111}<-1-12> is less than 1.8, In the texture from the surface to the position 1 / 4 of the sheet thickness from the surface to the position 1 / 2 of the sheet thickness from the surface, 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}<1-10> to {111}<-1-12> is less than 2.3.

[0064] Elemental technology A2 is a technology disclosed in WO 2021 / 230149. This elemental technology A2 makes it possible to provide a hot-stamped steel sheet having excellent strength, bendability, and ductility.

[0065] <<Elemental Technology B1>> The elemental technology B1 is a hot-stamped lap steel sheet including a first Al-Fe alloy plated steel sheet having a thickness T1 and a second Al-Fe alloy plated steel sheet having a thickness T2 and having an area smaller than that of the first Al-Fe alloy plated steel sheet, the second Al-Fe alloy plated steel sheet being overlapped on and welded to the first Al-Fe alloy plated steel sheet, and the hot-stamped lap steel sheet satisfies the relationships of the following formulas (7) to (9): 25≦K1≦60 (formula (7)) 25≦K2≦60 (formula (8)) 0≦(D1-D2)×(K1 / K2) ２ ≦5.0 ...Equation (9) wherein, K1: average value of the plating thickness of the Al-Fe-based alloy plating layer on the side in contact with the second Al-Fe-based alloy plated steel sheet and the plating thickness of the Al-Fe-based alloy plating layer on the side not in contact with the second Al-Fe-based alloy plated steel sheet, in the non-overlapping portion of the first Al-Fe-based alloy plated steel sheet; K2: plating thickness of the Al-Fe-based alloy plating layer on the side not in contact with the first Al-Fe-based alloy plated steel sheet, in the overlapping portion of the second Al-Fe-based alloy plated steel sheet; D1: average value of the thickness of a diffusion layer located in the Al-Fe-based alloy plating layer on the side in contact with the second Al-Fe-based alloy plated steel sheet so as to be in contact with the steel sheet substrate, and the thickness of a diffusion layer located in the Al-Fe-based alloy plating layer on the side not in contact with the second Al-Fe-based alloy plated steel sheet so as to be in contact with the steel sheet substrate. D2: the thickness of a diffusion layer located in the Al-Fe alloy plating layer so as to be in contact with the steel sheet substrate on the side of the second Al-Fe alloy plated steel sheet that is not in contact with the first Al-Fe alloy plated steel sheet. The sheet thicknesses T1 and T2 are in mm, and the units of K1, K2, D1, and D2 are in μm.

[0066] According to elemental technology B1, when an Al-based plated steel sheet is used as the raw material, it is possible to provide an overlapping blank for hot stamping and an overlapping hot-stamped product that can improve both the slow temperature rise rate in the overlapping portion and the difference in temperature rise rate between the overlapping portion and the single-piece portion.

[0067] The present inventors have conducted extensive research to solve the above problems, and have found that the lightness L of the surface of an Al-based plated steel sheet as defined in JIS Z 8781-4 ＊ As a result of focusing on this, it was confirmed that the lower the lightness, the higher the heating rate during hot stamping of Al-based plated steel sheets. This is thought to be because a lower lightness value indicates a darker surface of the Al-based plated steel sheet, which is more likely to absorb heat. In particular, it was found that to improve the slow heating rate at the overlapping portion of a patchwork, it is important to reduce the lightness of the overlapping portion relative to the sheet thickness of the overlapping portion (i.e., the total thickness of the two steel sheets). Furthermore, it was found that to improve the difference in heating rate between the overlapping portion and the single portion, it is important to create a difference in lightness between the overlapping portion and the single portion (i.e., lowering the surface lightness at the thicker overlapping portion and increasing the surface lightness at the single portion).

[0068] The inventors also found that by using an Al-based plated steel sheet, high brightness can be obtained due to the surface having a silvery-white metallic luster, and that by increasing the thickness of the Al-based plated layer, blackening of the plated surface, which occurs when alloying of the plating reaches the surface, can be suppressed, and high brightness can be maintained even during heating in hot stamping.

[0069] They also found that the brightness can be reduced by using a carbon-based black coating on the top layer of an Al-based plated steel sheet. In particular, they found that because the carbon-based black coating is burned away by combustion due to an oxidation reaction during heating in hot stamping, it is possible to suppress the deterioration of spot weldability of lap hot stamped parts due to the remaining carbon-based black coating.

[0070] Preferred embodiments of the present technology will be described in detail below with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0071] FIG. 7 is an explanatory view schematically illustrating an example of a hot stamping overlap blank and a hot stamped overlap body according to an embodiment of the present technology.

[0072] The overlapping blank for hot stamping according to the present embodiment is a type of tailored blank and is also called a patchwork blank. The overlapping blank for hot stamping according to the present embodiment is used as a raw material for a hot-stamped overlapping compact.

[0073] As schematically shown in Fig. 7 , an overlapping blank for hot stamping 4 according to this embodiment is formed by welding 3 a first Al-based plated steel sheet 1 and a second Al-based plated steel sheet 2 having an area smaller than that of the first Al-based plated steel sheet 1. In this case, in the overlapping blank for hot stamping 4, a portion where the second Al-based plated steel sheet 2 is overlapped is called an overlapping portion 4a, and a portion where the second Al-based plated steel sheet 2 is not overlapped is called a single portion 4b. In the overlapping blank for hot stamping 4 according to this embodiment, the second Al-based plated steel sheet 2 is preferably positioned more inward than the outer edge of the first Al-based plated steel sheet 1 so that no portion of the second Al-based plated steel sheet 2 protrudes from the first Al-based plated steel sheet 1, as schematically shown in Fig. 7 .

[0074] Moreover, an Al-based plating layer is applied to both surfaces of the first Al-based plated steel sheet 1, i.e., a surface 1a that comes into contact with the second Al-based plated steel sheet 2 and a surface 1b that does not come into contact with the second Al-based plated steel sheet 2, and similarly, an Al-based plating layer is applied to both surfaces of the second Al-based plated steel sheet 2, i.e., a surface 2a that comes into contact with the first Al-based plated steel sheet 1 and a surface 2b that does not come into contact with the first Al-based plated steel sheet 1. Furthermore, a carbon-based black coating (not shown) is provided on top of the Al-based plating layer on the surface 2b of the second Al-based plated steel sheet 2 that does not come into contact with the first Al-based plated steel sheet 1.

[0075] In the method for manufacturing the overlap hot-stamped steel sheet according to this embodiment, the overlap blank for hot stamping 4 is heated to the Ac3 point or higher in a heating furnace 5, whereby the steel sheet is austenitized, and immediately after removal from the furnace, is press-formed in a die 6 and quenched, whereby the steel sheet is transformed into martensite. As a result, the overlap blank for hot stamping 4 becomes the overlap hot-stamped steel sheet 12 according to this embodiment, which has excellent crash resistance. At this time, at least a part of the overlap portion 4a has a portion that will become the bent portion 8 when the overlap hot-stamped steel sheet 12 is obtained.

[0076] 7 illustrates a product formed using a hat-shaped die as an example of the overlapped hot-stamped body 12. Here, the parts of the hot-stamped body 12 are referred to as a head vertex portion 7, a bent portion 8 of the head vertex, a vertical wall portion 10, a flange portion 11, and a bent portion 9 of the flange portion.

[0077] In FIG. 7 , the second Al-based plated steel sheet 2 according to this embodiment is arranged on the outer side of the vertex portion 7, but the object of this elemental technology can also be achieved by arranging the second Al-based plated steel sheet 2 on the inner side of the vertex portion 7.

[0078] (1. Laminated Blank for Hot Stamping) Hereinafter, the laminated blank for hot stamping 4 according to this embodiment will be described in detail.

[0079] As described above, the overlapping blank for hot stamping 4 according to this embodiment includes the first Al-based plated steel sheet 1 and the second Al-based plated steel sheet 2 welded to the first Al-based plated steel sheet 1 and having an area smaller than that of the first Al-based plated steel sheet 1, and both surfaces of each of the first Al-based plated steel sheet 1 and the second Al-based plated steel sheet 2 are coated with Al-based plating. That is, the first Al-based plated steel sheet 1 and the second Al-based plated steel sheet 2 according to this embodiment are aluminum-plated steel sheets having Al-based plating layers on both surfaces of the base steel sheet.

[0080] <Base Steel Sheet> In the overlapping blank for hot stamping 4 according to this embodiment, the chemical composition of the base steel sheet in each of the first Al-based plated steel sheet 1 and the second Al-based plated steel sheet 2 is not particularly limited. However, for the purpose of obtaining a tensile strength of, for example, 1500 MPa or more (Vickers hardness (i.e., HV1 in JIS Z2244-1:2020) of about 400 or more when the test force is 9.8107 N), the chemical composition may be, in mass %, C: 0.19 to 0.50%, Si: 0.01 to 1.50%, Mn: 0.4 to 2.0%, Cr: 0.01 to 1.00%, Ti: 0.001 to 0.100%, B: 0.0005 to 0.0100%, and P: 0.100% or more. It is preferable to use a base steel sheet containing 0.100% or less S, 0 to 1.000% Al, 0.0100% or less N, 0 to 0.100% Nb, 0 to 0.500% Mo, Ni, Cu, Co, W, Sn, V, and Sb, 0 to 0.0100% or less Mg, Ca, Zr, REM, and O, with the balance being Fe and impurities. Furthermore, within the above-mentioned chemical composition ranges, the chemical composition of the base steel sheet of the first Al-based plated steel sheet 1 and the chemical composition of the base steel sheet of the second Al-based plated steel sheet 2 may be the same as or different from each other.

[0081] The method for producing an Al-based plated steel sheet using the above-mentioned base steel sheet chemical composition is not particularly limited. For example, a steel sheet produced through a conventional ironmaking process and steelmaking process, followed by hot rolling, pickling, cold rolling, and Sendzimir hot-dip aluminizing can be used as the above-mentioned aluminum-plated steel sheet.

[0082] In this embodiment, the sheet thickness t1 (mm) of the first Al-based plated steel sheet 1 and the sheet thickness t2 (mm) of the second Al-based plated steel sheet 2 are each preferably selectively set to 0.5 mm or more and 3.2 mm or less. By setting the sheet thickness to 0.5 mm or more, it becomes possible to maintain desired productivity in the hot rolling and cold rolling processes. Furthermore, by setting the sheet thickness to 3.2 mm or less, it becomes possible to prevent a phenomenon in which the cooling rate during die quenching in hot stamping is reduced, resulting in insufficient hardenability and making it impossible to obtain the desired tensile strength.

[0083] The sheet thickness t1 of the first Al-based plated steel sheet 1 and the sheet thickness t2 of the second Al-based plated steel sheet 2 can be measured, for example, using a micrometer in accordance with JIS B7502: 2016. The sheet thicknesses t1 and t2 include the thickness of the base steel sheet as well as the thickness of the Al-based plated layers provided on both sides.

[0084] <Al-based plating layer> The coating weight of the Al-based plating layer applied to both surfaces of the first Al-based plated steel sheet 1 is W1a (g / m) on the surface 1a on the side in contact with the second Al-based plated steel sheet 2. ２ ) on the surface 1b on the side not in contact with the second Al-based plated steel sheet 2, W1b (g / m ２ The coating weight of the Al-based plating layer applied to both surfaces of the second Al-based plated steel sheet 2 is W2b (g / m) on the surface 2b on the side not in contact with the first Al-based plated steel sheet 1. ２ ) where W1a, W1b, and W2b each independently have a value of 20 g / m per side. ２ 120g / m or more ２ That is, W1a, W1b, and W2b satisfy the following formulas (3), (4), and (5), respectively: 20≦W1a≦120 (formula (3)) 20≦W1b≦120 (formula (4)) 20≦W2b≦120 (formula (5))

[0085] Here, the average deposition amount of the Al-based plating layer on the non-overlapped portion (single portion 4b) of the overlapping blank for hot stamping 4 is defined as W1 (g / m) per side. ２ ) of the first Al-based plated steel sheet 1, the coating weight of the Al-based plated layer on one surface of the surface in contact with the second Al-based plated steel sheet 2 is W1a (g / m ２ ), and the coating weight of the Al-based plating layer on one side of the surface not in contact with the second Al-based plated steel sheet 2 is W1b (g / m ２ ), W1 = 0.5 × (W1a + W1b). In addition, the average coating weight of the Al-based plating layer in the overlapping portion 4a of the overlapping blank 4 for hot stamping is set to W2 (g / m) per side. ２) is the coating weight of the Al-based plating layer on one side of the surface 1b of the first Al-based plated steel sheet 1 that is not in contact with the second Al-based plated steel sheet 2, W1b (g / m ２ ), and the coating weight of the Al-based plating layer on one surface of the second Al-based plated steel sheet 2 that is not in contact with the first Al-based plated steel sheet 1 is W2b (g / m ２ ), then W2 = 0.5 × (W1b + W2b).

[0086] Note that, in the first Al-based plated steel sheet 1, surface 1a on the side that comes into contact with the second Al-based plated steel sheet 2, surface 1b on the side that does not come into contact with the second Al-based plated steel sheet 2, and surface 2b on the side that does not come into contact with the first Al-based plated steel sheet 1 in the second Al-based plated steel sheet 2 are surfaces that are exposed to a heat source when the produced overlapping blank is heated for hot stamping, and are important surfaces for controlling the rate of temperature rise during heating in hot stamping.

[0087] The Al-based plating layer according to this embodiment is required to have the following characteristics: (a) suppress the generation of Fe scale during hot stamp heating; and (b) suppress the occurrence of chipping or dents in the plating due to slippage of the plating (also referred to as powdering) during hot stamp forming.

[0088] Powdering occurs due to compressive stress applied to the plating on the inner surface of the bent portion during forming, and shear stress applied to the plating due to sliding from the mold during forming. ２ If the coating weight W1 is less than 20 g / m, the thickness of the coating will be thin, resulting in a problem of insufficient suppression of Fe scale. ２ The coating weights W1 and W2 of the Al-based plating layer of each Al-based plated steel sheet are each independently preferably 30 g / m ２ More preferably, it is 35 g / m or more. ２ Above, 40g / m ２ Above, 45g / m ２ or more, or 50 g / m ２ That's all.

[0089] On the other hand, the coating weights W1 and W2 of the Al-based plated steel sheets on one side were 120 g / m ２ If the coating weight W1 exceeds 120 g / m, the powdering may not be sufficiently suppressed. Therefore, in this embodiment, the coating weights W1 and W2 of the coating on one side of each Al-based plated steel sheet are each independently set to 120 g / m or less. ２ The coating weights W1 and W2 of each Al-based plated steel sheet per side are preferably 110 g / m or less. ２ More preferably, it is 100 g / m or less, in order of preference. ２ Below, 95g / m ２ Below, 90g / m ２ The following is a description thereof. Note that the coating weight of the Al-based plating layer on the surface of the second Al-based plated steel sheet 2 that comes into contact with the first Al-based plated steel sheet 1 is not particularly limited.

[0090] The thickness (μm) of the Al-based plating layer on each Al-based plated steel sheet was calculated based on the coating weight (g / m ２ The thickness (μm) of the Al-based plating layer of each Al-based plated steel sheet depends on the chemical composition of the Al-based plating layer, but can generally be calculated by the following formula (10):

[0091] (Plating thickness) = (Plating weight) / 3 Equation (10)

[0092] 8 is a schematic diagram showing the layer structure of one side of a plated steel sheet B1-13 in which an Al-based plating layer according to this embodiment is provided on the surface of a base steel sheet. When the Al-based plating layer according to this embodiment is produced by a hot-dip galvanizing method, an aluminum-iron (Al—Fe) alloy layer (not shown) is formed near the boundary between the Al-based plating layer B1-14 and the base steel sheet B1-15.

[0093] According to a hot-dip galvanizing method, which is a common method for applying an Al-based coating to a base steel sheet, an Al-based coated steel sheet with an adjusted coating weight can be produced by immersing the base steel sheet in a hot-dip aluminum coating bath and gas wiping with nitrogen, air, or the like. As a result, an aluminum-iron-based alloy layer is inevitably formed at the interface between the Al-based coating layer B1-14 and the base steel sheet B1-15 in Figure 8 due to the elution of Fe during hot-dip galvanizing. In this specification, the Al-based coating layer B1-14 in Figure 8 also includes the aluminum-iron-based alloy layer.

[0094] The chemical composition of the hot-dip aluminum plating bath for forming the Al-based plating layer (i.e., the chemical composition is substantially the same as that of the Al-based plating layer B1-14, excluding Fe) is not particularly limited. However, in order to obtain excellent heat resistance required during hot stamp heating, the Al content of the hot-dip aluminum plating bath is preferably 80 mass % or more. In addition, in order to easily control the thickness of the aluminum-iron alloy layer, the Si content of the hot-dip aluminum plating bath is preferably 2 mass % or more. By setting the Si content to 2 mass % or more, it is possible to prevent the aluminum-iron alloy layer from becoming too thick, which would result in a decrease in formability. On the other hand, by setting the Si content of the hot-dip aluminum plating bath to 15 mass % or less, it is possible to prevent a decrease in hot stamping productivity due to a slowdown in the alloying reaction during hot stamp heating.

[0095] When the hot-dip aluminum coating bath contains 2% by mass or more and 15% by mass or less of Si, the Al-based coating layer B1-14 formed using such a coating bath forms a eutectic structure of Al and Si based on the phase diagram. When using a hot-dip coating method, the base steel sheet may inevitably contain 1% by mass or more and 5% by mass or less of Fe as a component eluted from the base steel sheet. Other unavoidable impurities include elements such as Cr, Mn, Zn, V, Ti, Sn, Ni, Cu, W, Bi, Mg, and Ca, which are derived from components eluted from the hot-dip coating equipment or impurities in the ingots used in the hot-dip aluminum coating bath, and these elements may be contained in an amount of less than 1% by mass.

[0096] That is, the chemical composition (average chemical composition) of the Al-based plating layer B1-14 according to this embodiment may be, in mass %, 80 to 97% Al, 2 to 15% Si, 1 to 15% Fe, 0% to less than 1% Cr, 0% to less than 1% Mo, 0% to less than 1% Zn, 0% to less than 1% V, 0% to less than 1% Ti, 0% to less than 1% Sn, 0% to less than 1% Ni, 0% to less than 1% Cu, 0% to less than 1% W, 0% to less than 1% Bi, 0% to less than 1% Mg, and 0% to less than 1% Ca, with the remainder being impurities. Here, as described above, a hot-dip aluminum plating bath may inevitably contain 1% to 5% by mass of Fe, whereas an aluminum-iron alloy layer is formed in the Al-based plating layer, resulting in a higher Fe content. Therefore, the chemical composition of the Al-based plating layer B1-14 may be Fe: 1 to 15%.

[0097] The metal structure of the aluminum-iron alloy layer is a θ phase (FeAl ３ ), η phase (Fe ２ Al ５ ), ζ phase (FeAl ２ ), Fe ３ The aluminum-iron alloy layer is made up of a combination of these plating phases. When Si is contained, the metal structure of the aluminum-iron alloy layer is a τ1 phase (Al ２ Fe ３ Si ３ ), τ2 phase (Al ３ FeSi), τ3 phase (Al ２ FeSi), τ4 phase (Al ３ FeSi ２ ), τ5 phase (Al ８ Fe ２ Si), τ6 phase (Al ９ Fe ２ Si ２ ), τ7 phase (Al ３ Fe ２ Si ３ ), τ8 phase (Al ２ Fe ３ Si ４ ), τ10 phase (Al ４ Fe １．７ Si), τ11 phase (Al５ Fe ２ Si) (however, each phase may not have a stoichiometric composition), and the metal structure of the aluminum-iron based alloy layer is often mainly composed of the τ5 phase or the θ phase.

[0098] The coating weight of the Al-based plating layer per side is measured using the method of JIS G 3314:2019 JB.3 (sodium hydroxide-hexamethylenetetramine-hydrochloric acid stripping weight method) after protecting the Al-based plating layer on one side with a seal in advance.

[0099] <Lightness> Below, lightness, which is important in this elemental technology, will be described with reference to Fig. 7. The lightness is measured using the CIE 1976 lightness index L as defined in JIS Z8781-4:2013, 3.3. ＊ (CIE 1976 lightness), and will be referred to simply as "lightness" or "lightness L" hereinafter. ＊ "

[0100] Lightness L of the surface of the first Al-plated steel sheet 1 ＊ Regarding the surface 1a on the side in contact with the second Al-based plated steel sheet 2, ＊ 1a, and the surface 1b on the side not in contact with the second Al-plated steel sheet 2 is denoted by L ＊ Furthermore, the surface brightness L of the second Al-plated steel sheet 2 is expressed as ＊ Regarding the surface 2b on the side not in contact with the first Al-based plated steel sheet 1, ＊ 2b. Then, L ＊ 1 = 0.5 × (L ＊ 1a+L ＊ 1b), L ＊ 2 = 0.5 × (L ＊ 1b+L ＊ In this case, the overlapping blank 4 for hot stamping satisfies the following formulas (1) and (2). Note that, in the second Al-based plated steel sheet 2, the surface lightness of the Al-based plated layer on the surface 2a on the side in contact with the first Al-based plated steel sheet 1 is not particularly specified.

[0101] 14.0≦(L ＊ 1-L ＊2) × (W1 / W2) ２ ≦32.0 ... Formula (1) 0.86≦{t1 / (t1+t2)}×(L ＊ 1 / L ＊ 2) ２ ... Formula (2)

[0102] Here, L ＊ 1 means the average surface brightness of the Al-based plating layer of the non-overlapped portion (single portion 4b) of the overlapping blank 4 for hot stamping. ＊ 2 means the average brightness of the surface of the Al-based plating layer of the overlapping portion 4 a in the overlapping blank 4 for hot stamping.

[0103] [(L ＊ 1-L ＊ 2) × (W1 / W2) ２ : 14.0 or more and 32.0 or less] The lower the lightness value, the higher the temperature rise rate during heating during hot stamping of the aluminum-plated steel sheet. This is thought to be because the lower the lightness value, the more blackened the surface of the aluminum-plated steel sheet is, and therefore the aluminum-plated steel sheet is likely to have a property of absorbing heat more easily. That is, in this embodiment, lightness is used as an index for evaluating the temperature rise rate during heating during hot stamping. In particular, to improve the difference in the temperature rise rate between the overlapping portion and the single portion, a difference is made in the lightness of the overlapping portion and the single portion, and (L ＊ 1-L ＊ 2) is important (i.e., it is important to lower the surface brightness in the overlapping portion where the plate thickness is thick, and conversely, to increase the surface brightness in the single portion).

[0104] Furthermore, we have found that the use of an Al-based plated steel sheet can achieve high brightness due to the silver-white metallic luster of the surface, and that increasing the thickness of the Al-based plated layer (which can also be considered as the coating mass of the Al-based plated layer) can suppress blackening of the plated surface caused by alloying of the plated layer reaching the surface, thereby maintaining high brightness even during heating in hot stamping. In other words, it is important to increase the ratio (W1 / W2) of the coating mass W1 of the Al-based plated layer in the single-piece portion 4b to the coating mass W2 of the Al-based plated layer in the overlapping portion 4a. Furthermore, the use of a carbon-based black coating on the Al-based plated steel sheet can reduce brightness. Thus, by appropriately controlling the Al-based plated layer and the carbon-based black coating used in the Al-based plated steel sheet, it is possible to adjust the brightness to a desired value.

[0105] From the above, in order to improve the difference in the temperature rise rate between the overlapping part and the single part, since the brightness and the adhesion amount are mutually related, (L ＊ 1-L ＊ 2) and (W1 / W2) ２ It is important to control the product of and within a certain range.

[0106] (L ＊ 1-L ＊ 2) × (W1 / W2) ２ If the value of (L) is less than 14.0, the temperature rise rate during heating during hot stamping is not sufficiently improved, and further, the difference in the temperature rise rate between the overlapping portion and the single portion is not sufficiently improved, resulting in a decrease in the spot weldability of the lap hot stamped body. ＊ 1-L ＊ 2) × (W1 / W2) ２ The value of L is 14.0 or more. ＊ 1-L ＊ 2) × (W1 / W2) ２ The value of is preferably 16.0 or more, more preferably 18.0 or more.

[0107] Also, (L ＊ 1-L ＊ 2) × (W1 / W2) ２If the value of (L ＊ 1-L ＊ 2) × (W1 / W2) ２ The value of L is 32.0 or less. ＊ 1-L ＊ 2) × (W1 / W2) ２ The value of is preferably 31.0 or less, more preferably 30.0 or less, 29.0 or less, 28.0 or less, 27.0 or less, or 26.0 or less.

[0108] [{t1 / (t1+t2)}×(L ＊ 1 / L ＊ 2) ２ : 0.86 or more] The lower the lightness value, the higher the temperature rise rate during heating during hot stamping of the aluminum-plated steel sheet. This is thought to be because the lower the lightness value, the more blackened the surface of the aluminum-plated steel sheet is, and therefore the aluminum-plated steel sheet is more likely to absorb heat. In particular, to improve the slow temperature rise rate at the overlapping portion of the patchwork, it is important to reduce the lightness of the overlapping portion relative to the sheet thickness of the overlapping portion (i.e., the sum t1 + t2 of the sheet thickness t1 of the first Al-plated steel sheet 1 and the sheet thickness t2 of the second Al-plated steel sheet 2). In the above formula (2), the exponent of the sheet thickness ratio t1 / (t1 + t2) is 1, while the lightness ratio (L ＊ 1 / L ＊ 2) is 2. Therefore, in this elemental technology, the ratio of brightness (L ＊ 1 / L ＊ 2) is more important than the thickness ratio t1 / (t1+t2).

[0109] Furthermore, to improve the difference in the rate of temperature rise between the overlapping portion and the single portion, it is important to lower the surface brightness in the overlapping portion, which has a thicker plate thickness, and conversely, to increase the surface brightness in the single portion.

[0110] That is, the lightness L of the overlapping portion is calculated based on the sheet thickness t1 of the first Al-based plated steel sheet 1 and the sheet thickness t2 of the second Al-based plated steel sheet 2, and is expressed as t1 / (t1+t2) of the sheet thickness (t1) of the overlapping portion to the sheet thickness t1 of the single sheet portion. ＊ 2 and the brightness of one piece L ＊ The ratio to 1 (L ＊ 1 / L ＊ It is important that the square of {t1 / (t1+t2)}×(L ＊ 1 / L ＊ 2) ２ If the value of {t1 / (t1+t2)}×(L ＊ 1 / L ＊ 2) ２ The higher the value of is, the more preferable. Therefore, the lower limit may be set to 0.90 or more, 0.94 or more, 0.98 or more, or 1.02 or more, as necessary. However, {t1 / (t1+t2)}×(L ＊ 1 / L ＊ 2) ２ There is no particular upper limit for the value of {t1 / (t1+t2)}×(L ＊ 1 / L ＊ 2) ２ The upper limit of the value of {t1 / (t1+t2)}×(L ＊ 1 / L ＊ 2) ２ The value of is preferably 2.50 or less, more preferably 2.00 or less, and even more preferably 1.50 or less.

[0111] The brightness can be measured, for example, by cutting out a test piece measuring 50 x 50 mm and measuring it using a spectrophotometer (SC-T-GV5 manufactured by Suga Test Instruments, including specular reflection light) with a measurement beam diameter of 15 mm.

[0112] The above formulas (1) and (2) were established by conducting a series of verifications in which lap blanks were prepared while changing the sheet thickness of the Al-based plated steel sheet, the coating weight of the Al-based plated layer, etc., and hot stamping was actually performed to evaluate the obtained lap hot-stamped bodies. In these verifications, each of the obtained lap hot-stamped bodies was evaluated from the viewpoints of the heating rate of the lap portion and spot weldability, and the relationships satisfied by those that showed good evaluation results were experimentally formulated.

[0113] <Carbon-based black coating> Fig. 9 schematically shows the layer structure of one side of an Al-based plated steel sheet B1-16 in this embodiment, in which an Al-based plating layer B1-14 is provided on the surface of a base steel sheet B1-15 and a carbon-based black coating B1-17 is further provided thereon, or the layer structure of one side of an Al-based plated steel sheet B1-16 in which a carbon-based black coating B1-17 further containing Zn, Ti, Cu, and V is selectively provided thereon.

[0114] In the second Al-plated steel sheet 2, a carbon-based black coating B1-17 is provided on the upper layer of the Al-plated layer located on the surface 2b on the side not in contact with the first Al-plated steel sheet 1. The Al-plated steel sheet has a surface with a silvery-white metallic luster, resulting in high brightness. Here, by providing a carbon-based black coating on the upper layer of the Al-plated steel sheet, it is possible to reduce the brightness. In particular, the carbon-based black coating B1-17 is burned away by combustion due to an oxidation reaction during heating during hot stamping, and CO ２ As a result, it is possible to suppress a decrease in the spot weldability of the lap hot stamped product due to the carbon-based black coating B1-17 remaining.

[0115] In addition, as a means for further increasing the brightness of an Al-based plated steel sheet having a silvery-white metallic luster, for example, the Al-based plated steel sheet is heated to about 600° C. to oxidize the surface and thereby whiten it, which makes it possible to further increase the brightness of the surface of the Al-based plated steel sheet.

[0116] [Film Thickness of Carbon-Based Black Coating B1-17] The film thickness of the carbon-based black coating B1-17 is preferably 0.3 μm or more and 10 μm or less. By making the film thickness of the carbon-based black coating B1-17 0.3 μm or more, it is possible to suppress an increase in lightness and increase the temperature rise rate of the overlapping portion. The film thickness of the carbon-based black coating B1-17 is more preferably 0.3 μm or more, even more preferably 0.4 μm or more, and even more preferably, in order of preference, 0.5 μm or more, 0.6 μm or more, and 0.7 μm or more. On the other hand, by making the film thickness of the carbon-based black coating B1-17 10 μm or less, it is possible to reduce the lightness while ensuring economic efficiency, and it is possible to ensure spot weldability without leaving any film remaining after heating for hot stamping. The film thickness of the carbon-based black coating B1-17 is more preferably 8 μm or less, and even more preferably, in order of preference, 6 μm or less, 5 μm or less, and 4 μm or less.

[0117] The film thickness of the carbonaceous black coating B1-17 can be determined by observing the cross section of the plating with an optical microscope (for example, area: 100 μm × 100 μm) (without etching), measuring the thickness of the coating on top of the aluminum plating layer in three fields of view as shown in Figure 9, and calculating the average value of the film thicknesses measured in each of the three fields of view. At this time, the cross section of the coating is analyzed with an electron probe microanalyzer (EPMA), and if the carbon content is 30 mass% or more, it is determined to be a carbonaceous black coating. A black coating is defined as a coating that has a lightness L from the surface. ＊ This is judged based on the value being 60 or less.

[0118] [Binder] The carbon-based black coating B1-17 may optionally contain a resin as a binder to enhance adhesion with the Al-based plating layer. The type of resin is not particularly limited, and examples thereof include polyethylene resin, polyolefin resin, polyacrylic resin, polymethacrylic acid resin, polyepoxy resin, polyurethane resin, and polycarbonate resin.

[0119] [Nitrogen Content of Carbon-Based Black Coating] The carbon-based black coating B1-17 preferably has a nitrogen content of 2% by mass or more and 18% by mass or less. Generally, when a carbon-based coating is applied to an aluminum plating, the adhesion between the coating and the plating decreases. However, by increasing the nitrogen content, for example, by using a nitrogen-containing polyurethane resin as a binder component or by mixing ammonia, the adhesion with the aluminum plating layer can be further improved. This allows the temperature rise rate of the overlapping portion to be further increased.

[0120] Since this effect of improving adhesion with the Al-based plating layer can be achieved by setting the nitrogen content to 2% by mass or more, the nitrogen content of the carbon-based black coating B1-17 is preferably 2% by mass or more. Furthermore, by setting the nitrogen content of the carbon-based black coating B1-17 to 18% by mass or less, it is possible to suppress the decomposition reaction of the resin and prevent peeling of the coating. The nitrogen content can be determined by analyzing the cross-section of the coating with an electron probe microanalyzer (EPMA).

[0121] [Containing at least one of Zn, Ti, Cu, and V in carbon-based black coating] At least one of Zn, Ti, Cu, and V is selectively contained in a total amount of 0.2 g / m for the carbon-based black coating B1-17 located further above the Al-based plating layer applied to the surface of the second steel sheet 2. ２ 3.0g / m or more ２The following elements are preferably contained. The deposition amount shown here refers to the amount of Zn, Ti, Cu, or V deposited per unit area. Zn, Ti, Cu, and V are elements that not only improve emissivity but also form oxides with good infrared absorption. Therefore, by providing the carbon-based black coating layer 17 containing such elements, the difference in temperature rise rate between the overlapping portion, which has a slow temperature rise rate, and the single portion, which has a fast temperature rise rate, which is an issue when used as an overlapping blank, can be suppressed. In particular, while the carbon-based black coating layer 17 is burned away during hot stamping, Zn, Ti, Cu, or V remains even during hot stamping. Therefore, the carbon-based black coating layer 17 containing such elements can further contribute to improving the temperature rise rate at high temperatures. Furthermore, Zn, Ti, Cu, and V may be contained in either a metallic state or an oxide state. This is because they all become oxides during the temperature rise process, contributing to improving the emissivity.

[0122] The effect of suppressing the difference in the rate of temperature rise as described above is obtained when the total deposition amount of the elements is 0.2 g / m ２ Therefore, the total amount of these elements deposited in the carbon-based black coating layer 17 is 0.2 g / m ２ The total amount of these elements in the carbon-based black coating layer 17 is more preferably 0.4 g / m or more. ２ More preferably, it is 0.6 g / m or more. ２ That's all.

[0123] On the other hand, the total deposition amount of these elements in the carbon-based black coating layer 17 is 3.0 g / m ２ By setting the total amount of Zn, Ti, Cu, or V in the carbon-based black coating layer 17 to 3.0 g / m or less, it is possible to achieve the suppression effect of the difference in the temperature rise rate as described above without saturating the effect. ２ By setting the total deposition amount of these elements in the carbon-based black coating layer 17 to 2.8 g / m or less, it is possible to maintain the spot weldability of the hot stamped product. ２More preferably, it is 2.6 g / m or less. ２ The following is the result.

[0124] The deposition amounts (contents) of Zn, Ti, Cu, and V can be determined by, for example, performing elemental analysis from the surface using an X-ray fluorescence analyzer (ZSX Primus, manufactured by RIGAKU Corporation) and quantifying the deposition amounts of Zn, Ti, Cu, and V.

[0125] The method for treating the carbon-based black coating layer 17 described above is not particularly limited. For example, the carbon-based black coating layer 17 can be produced by preparing an aqueous coating solution in which water-dispersed carbon black (e.g., RCF#52 manufactured by Mitsubishi Chemical Corporation), zinc oxide (e.g., NanoTek manufactured by C.I. Chemical Co., Ltd.), titanium oxide (e.g., NanoTek manufactured by C.I. Chemical Co., Ltd.), copper oxide (e.g., NanoTek manufactured by C.I. Chemical Co., Ltd.), or vanadium oxide (manufactured by Hongwu International Group Ltd.) is dispersed in water, and the resulting solution is applied using a roll coater after the above-mentioned hot-dip aluminum plating treatment, followed by a drying and baking treatment. Alternatively, the carbon-based black coating layer 17 can be produced by vacuum-depositing Zn, Ti, Cu, or V onto an aluminum-plated steel sheet.

[0126] In another embodiment of the present embodiment, both the carbon-based black coating layer 17 and a coating layer 17' containing at least one of Zn, Ti, Cu, and V (more specifically, these elements in a metallic state or an oxide of these elements) may be provided on the Al-based plating layer. In this case, the order in which the carbon-based black coating layer 17 and the coating layer 17' containing at least one of Zn, Ti, Cu, and V are arranged is not particularly limited. The carbon-based black coating layer 17 may be located above the coating layer 17' containing at least one of Zn, Ti, Cu, and V, or the coating layer 17' containing at least one of Zn, Ti, Cu, and V may be located above the carbon-based black coating layer 17.

[0127] Even when a coating layer 17′ containing at least one of Zn, Ti, Cu, and V is located below the carbon-based black coating layer 17, fluorescent X-rays can easily pass through the carbon-based black coating layer 17 as long as the carbon-based black coating layer 17 has a thickness according to this embodiment. Therefore, even when a coating layer 17′ containing at least one of Zn, Ti, Cu, and V is located below the carbon-based black coating layer 17, the amounts of Zn, Ti, Cu, and V deposited can be measured by fluorescent X-ray analysis.

[0128] Furthermore, such a carbon-based black coating layer 17 or a coating layer 17′ containing at least one of Zn, Ti, Cu, and V may be provided on both sides of the base steel sheet, but it is more preferable that it be provided only on the side of the base steel sheet that is exposed to the heat source during heating for hot stamping.

[0129] The first Al-based plated steel sheet 1 may have the above-described black carbon-based coating as an upper layer of the Al-based plating layer on the side not in contact with the second Al-based plated steel sheet 2 .

[0130] <Welding> In the overlapping blank for hot stamping 4 in which the first Al-based plated steel sheet 1 and the second Al-based plated steel sheet 2 are overlapped and welded, the type of welding can be selected from spot welding, seam welding, braze welding, laser welding, plasma welding, arc welding, etc. Here, in terms of achieving good contact at the overlapping portions, spot welding is more preferred, as it allows contact at multiple points up to the inside of the overlapping portions and allows direct joining by applying pressure between the steel sheets.

[0131] (2. Laptop Hot-Stamped Body) In the method for producing a hot-stamped body according to this embodiment, as shown in FIG. 7 , the above-described overlapping blank for hot stamping 4 is heated and formed immediately after the heating, whereby a bent portion is provided by bending at least a portion of the overlapping portion, thereby producing the overlapping hot-stamped body 12 according to this embodiment.

[0132] The heating temperature is not particularly limited, but is generally in the range of from the Ac3 point (e.g., 800°C) to 1000°C. During forming immediately after heating, cooling is performed using a mold or a refrigerant such as water to obtain a hot-stamped laminated body 12 with excellent impact resistance. The time for which the hot-stamping laminated blank 4 is kept at the heating temperature is not particularly limited, but may be, for example, from 4 minutes to 20 minutes.

[0133] For example, a preliminary test may be conducted to measure the heating time or temperature rise rate of a hot stamping overlapping blank 4 of interest to a temperature of not less than the Ac3 point and not more than 1000°C, and the holding time may be determined using the obtained preliminary test results. In this way, for example, a condition such as "holding a temperature of 910 to 920°C for 250 to 1200 seconds" may be determined.

[0134] The heating temperature refers to the maximum temperature that the steel sheets reach at the overlapping portion. Examples of the heating method include heating with an electric furnace, gas furnace, far-infrared furnace, near-infrared furnace, etc., electrical heating, high-frequency heating, and induction heating.

[0135] The lap hot-stamped steel body 12 according to the present embodiment produced as described above includes a first Al-Fe-based alloy-plated steel sheet having a thickness T1 (mm), and at least one second Al-Fe-based alloy-plated steel sheet which is overlapped on and welded to the first Al-Fe-based alloy-plated steel sheet, has an area smaller than that of the first Al-Fe-based alloy-plated steel sheet, and has a thickness T2 (mm).

[0136] As described above, the hot-stamped steel 12 is produced by heating the overlapping hot-stamping blank 4, which is made by overlapping and welding the first Al-plated steel sheet 1 and the second Al-plated steel sheet 2, and then further subjecting the sheet to bending or the like. Therefore, the first Al-Fe alloy-plated steel sheet and the second Al-Fe alloy-plated steel sheet constituting the hot-stamped steel 12 do not necessarily have a flat shape. For example, as shown in FIG. 7 , the first Al-Fe alloy-plated steel sheet has a bent portion 8 at the apex, and the second Al-Fe alloy-plated steel sheet has a bent portion 8 at the apex and a bent portion 9 at the flange. Although the term "steel sheet" is used, the sheet does not necessarily have a flat shape. In this embodiment, in order to distinguish between the steel sheet constituting the hot-stamped body 12 and the steel sheet constituting the overlapping blank 4, for convenience, the former will be referred to as an alloy-plated steel sheet (for example, an Al-Fe-based alloy-plated steel sheet), and the latter will be referred to as a plated steel sheet (for example, an Al-based plated steel sheet) (without the term "alloy").

[0137] The first Al-Fe alloy plated steel sheet in the overlap hot-stamped steel sheet 12 is a plated steel sheet having an Al-Fe alloy plating layer with an average plating thickness of K1 (μm) on both sides of the first Al-Fe alloy plated steel sheet. Here, K1 is the average value of the plating thickness of the Al-Fe alloy plating layer on the side in contact with the second Al-Fe alloy plated steel sheet and the plating thickness of the Al-Fe alloy plating layer on the side not in contact with the second Al-Fe alloy plated steel sheet in the non-overlapping portion of the first Al-Fe alloy plated steel sheet.

[0138] The second Al-Fe alloy plated steel sheet in the overlap hot-stamped product 12 is a plated steel sheet having an Al-Fe alloy plating layer with a plating thickness of K2 (μm) on the surface on the side not in contact with the first Al-Fe alloy plated steel sheet. Here, K2 refers to the plating thickness of the Al-Fe alloy plating layer on the side not in contact with the first Al-Fe alloy plated steel sheet in the overlapping portion of the second Al-Fe alloy plated steel sheet.

[0139] In addition, the plating thickness of the Al—Fe alloy plating layer on the surface of the second Al—Fe alloy plated steel sheet that comes into contact with the first Al—Fe alloy plated steel sheet is not particularly specified.

[0140] Here, the average plating thicknesses K1 and K2 of the Al-Fe alloy plating layer on each Al-Fe alloy plated steel sheet of the lap hot-stamped body 12 are each independently 25 μm or more. Also, the average plating thicknesses K1 and K2 of the Al-Fe alloy plating layer on each Al-Fe alloy plated steel sheet are each independently 60 μm or less. That is, K1 and K2 satisfy the following formulas (7) and (8): 25≦K1≦60... formula (7) 25≦K2≦60... formula (8)

[0141] Furthermore, the average plating thicknesses K1 and K2 of the Al-Fe alloy plating layer in each of the Al-Fe alloy plated steel sheets are each independently preferably 30 μm or more, and more preferably 35 μm or more.

[0142] The average plating thicknesses K1 and K2 of the Al—Fe alloy plating layer in each Al—Fe alloy plated steel sheet are each independently preferably 58 μm or less, more preferably 56 μm or less, 52 μm or less, or 48 μm or less.

[0143] When the plating thicknesses of the Al-Fe-based alloy plating layers of the first Al-Fe-based alloy plated steel sheet and the second Al-Fe-based alloy plated steel sheet are within the above-mentioned ranges, the spot weldability of the hot-stamped lap body 12 can be maintained in a good condition.

[0144] The above-mentioned plating thickness can be determined as the average value of the plating thicknesses measured in three visual fields, by observing the cross section of the plating with an optical microscope (area: 100 μm × 100 μm) after nital etching, and measuring the plating thickness in each of the three visual fields. Note that the plating thickness of the first Al-Fe-based alloy-plated steel sheet is measured at a position 4b of the single-piece portion and at a position 4a of the overlapping portion in contact with the second Al-Fe-based alloy-plated steel sheet, but the plating thickness of the first Al-Fe-based alloy-plated steel sheet is measured from the single-piece portion because the heating rate is fast, the heating time in hot stamping is longest, and spot weldability is likely to deteriorate.

[0145] The Al-Fe alloy plating layer is a layer formed as a result of Fe diffusing to the surface of the Al-based plating layer due to heating during hot stamping (in other words, an alloy plating layer containing at least Al and Fe). The Al-Fe alloy plating layer is a θ phase (FeAl ３ ), η phase (Fe ２ Al ５ ), ζ phase (FeAl ２ ), Fe ３ It is composed of a combination of phases such as Al, FeAl, and Al-dissolved Fe. When Si is contained in the plating, the Al-Fe alloy plating layer has a τ1 phase (Al ２ Fe ３ Si ３ ), τ2 phase (Al ３ FeSi), τ3 phase (Al ２ FeSi), τ4 phase (Al ３ FeSi ２ ), τ5 phase (Al ８ Fe ２ Si), τ6 phase (Al ９ Fe ２ Si ２ ), τ7 phase (Al ３ Fe ２ Si ３ ), τ8 phase (Al ２ Fe ３ Si ４ ), τ10 phase (Al ４ Fe １．７ Si), τ11 phase (Al ５ Fe ２Si) (however, each phase may not have a stoichiometric composition), and the Al-Fe alloy plating layer is mainly composed of the τ1 phase (Al ２ Fe ３ Si ３ ), η phase (Fe ２ Al ５ ), an FeAl phase, or a BCC phase of Fe with Al as a solid solution, or a combination of these phases.

[0146] In particular, heating during hot stamping causes interdiffusion of Al in the Al-based coating and Fe in the base steel sheet. Therefore, as a phase formed by diffusion of Al into the base steel sheet, a layer containing a BCC phase of Fe with Al solid solution and an FeAl phase is formed, in that order from the base steel sheet side. A layer containing these phases is also called a diffusion layer. Here, as described below, such a diffusion layer can be identified by observing a cross section after nital etching treatment with an optical microscope. Furthermore, if the diffusion layer cannot be identified by observation with an optical microscope, it can be identified by analyzing the cross section with an electron probe microanalyzer (EPMA). In this case, a layer containing 30 mass % or less of Al and 70 mass % or more of Fe according to the EPMA analysis results can be defined as the diffusion layer 20.

[0147] 11 and 12, in the hot-stamped lap body B1-18, layer B1-19 is an Al—Fe alloy plating layer and includes a diffusion layer B1-20. The thickness of the Al—Fe alloy layer is measured as the thickness of layer B1-19, and the thickness of the diffusion layer is measured as the thickness of layer 20. For example, an example of a cross section observed with an optical microscope after nital etching is shown in FIG.

[0148] The thickness of the diffusion layer contained in the Al-Fe alloy plating layer of the first Al-Fe alloy plated steel sheet in the portion not overlapped with the second Al-Fe alloy plated steel sheet is denoted as D1 (μm), and the thickness of the diffusion layer contained in the Al-Fe alloy plating layer of the second Al-Fe alloy plated steel sheet is denoted as D2 (μm). In this case, the difference (D1-D2) between D1 (μm) and D2 (μm) and the ratio (K1 / K2) of the plating thickness K1 of the portion not overlapped with the first Al-Fe alloy plated steel sheet to the plating thickness K2 of the portion overlapped with the second Al-Fe alloy plated steel sheet are expressed as ２ and the product (D1-D2) x (K1 / K2) ２ is 5.0 μm or less.

[0149] Here, D1 is the average value of the thickness of a diffusion layer located in the Al-Fe alloy plating layer on the side of the first Al-Fe alloy plated steel sheet that contacts the second Al-Fe alloy plated steel sheet so as to be in contact with the steel sheet substrate, and the thickness of a diffusion layer located in the Al-Fe alloy plating layer on the side not in contact with the second Al-Fe alloy plated steel sheet so as to be in contact with the steel sheet substrate. D2 is the thickness of a diffusion layer located in the Al-Fe alloy plating layer on the side of the second Al-Fe alloy plated steel sheet that is not in contact with the first Al-Fe alloy plated steel sheet so as to be in contact with the steel sheet substrate.

[0150] In the Al-Fe-based plating layer, the Al-Fe binary alloy (FeAl ３ , Fe ２ Al ５ , FeAl ２ ) contains a phase with a relatively low melting point of more than 30 mass % Al and less than 70 mass % Fe, and a phase with a relatively high melting point of 30 mass % or less Al and 70 mass % or more Fe. When the heating time or heating temperature of hot stamping is long or high, the diffusion layer increases, and conversely, the binary alloy (FeAl ３ , Fe ２ Al ５ , FeAl ２ In terms of spot weldability, the presence of a plating layer with a low melting point promotes sufficient fusion between materials, so when the diffusion layer is thick, the binary alloy (FeAl ３ , Fe ２ Al５ , FeAl ２ ) decreases, and spot weldability is known to deteriorate.

[0151] (D1-D2)×(K1 / K2) ２ If the value of (D1-D2) x (K1 / K2) exceeds 5.0 μm, the above-mentioned diffusion layer of the first Al-Fe alloy plated steel sheet increases, and conversely, the Al-Fe binary alloy becomes thin, resulting in a decrease in spot weldability. ２ It is important for the spot weldability of the overlapping portion to keep the thickness (D1-D2) x (K1 / K2) to 5.0 μm or less. ２ The value of is preferably 4.5 μm or less, and more preferably 4.0 μm or less.

[0152] On the other hand, (D1-D2) x (K1 / K2) ２ The lower limit of (D1-D2) x (K1 / K2) is 0 μm. ２ When the value is less than 0.5 μm, the effect is saturated.

[0153] The plating thicknesses K1 and K2 of the Al-Fe alloy plating layer and the thicknesses D1 and D2 of the diffusion layer are determined by: A cross-section of the plating is subjected to nital etching in a 100 μm × 100 μm field of view, and the cross-section is then observed using an optical microscope. As shown in FIG. 12 , the plating thickness and the diffusion layer thickness are measured using an optical microscope. More specifically, the cross-section of the plating is observed at least three times using the above method, and the plating thickness and the diffusion layer thickness at each observation point are identified. The average of the thicknesses is then calculated, and this average value is used as the plating thickness and the diffusion layer thickness. However, if the diffusion layer cannot be identified by optical microscope observation, an electron probe microanalyzer (EPMA) is used to measure the thickness of a layer containing 30% or less by mass of Al and 70% or more by mass of Fe at least three times, and the average value is used as the thickness of the diffusion layer B1-20.

[0154] Since the above-described diffusion layer is formed by inward diffusion within the Al-based plating layer, the thicknesses D1 and D2 of the diffusion layers are largely influenced only by the heating conditions of hot stamping and are not affected by the initial plating thickness. Furthermore, even if the coating weight of the second Al-based plated steel sheet is increased, the thickness D2 of the diffusion layer of the second Al-Fe alloy-plated steel sheet, which has a slower heating rate, cannot be made substantially the same as the thickness D1 of the diffusion layer of the first Al-Fe alloy-plated steel sheet. When a hot stamping lap blank satisfying formulas (1) to (5) is subjected to a conventional hot stamping process, a hot-stamped lap body satisfying formulas (7) to (9) can be easily obtained.

[0155] The plating thicknesses K1 and K2 of the Al-Fe alloy plating layer are affected not only by the plating adhesion before hot stamping but also by the heating conditions (heating temperature and holding time) of hot stamping. Furthermore, the plating thicknesses K1 and K2 of the Al-Fe alloy plating layer are affected not only by these influences but also by the sheet thickness and lightness, which affect the heating time at high temperature, and therefore are not only affected by the initial plating thickness.

[0156] The above-mentioned relational expression was established through a series of verifications in which lap blanks were prepared while changing the sheet thickness of the Al-based plated steel sheet, the coating weight of the Al-based plated layer, etc., and hot stamping was actually performed, and the obtained lap hot-stamped bodies were evaluated. In these verifications, each of the obtained lap hot-stamped bodies was evaluated from the viewpoints of the heating rate of the lap portion and spot weldability, and the relationship satisfied by those that showed good evaluation results was experimentally formulated.

[0157] Furthermore, a layer containing at least one of Zn, Ti, Cu, and V may be selectively provided on the Al-Fe alloy plating layer applied to the surface of the second Al-Fe alloy plated steel sheet. In this case, the coating amount (content) of at least one of Zn, Ti, Cu, and V is 0 g / m ２ The amount (content) of at least one of Zn, Ti, Cu, and V is more preferably 0.2 g / m ２3.0g / m or more ２ The layer containing Zn, Ti, Cu, and V can be obtained by providing a layer containing these elements in a metallic or oxidized state before the heating of hot stamping. Most of these elements become oxides during the temperature rise process, but some of the metallic state may remain.

[0158] The deposition amount (content) shown here refers to the amount of Zn, Ti, Cu, or V deposited per unit area.

[0159] 13 schematically shows the structure of an Al-Fe alloy-plated steel sheet in which a layer containing at least one of Zn, Ti, Cu, and V is provided on top of the Al-Fe alloy plating layer applied to the surface of a second Al-Fe alloy-plated steel sheet in a lap hot-stamped product B1-22. This Al-Fe alloy-plated steel sheet has, on the surface of a base steel sheet B1-21, an Al-Fe alloy plating layer B1-19 (including a diffusion layer B1-20) and a coating layer B1-23 containing at least one of Zn, Ti, Cu, and V. This coating layer B1-23 is preferably provided on the Al-Fe alloy plating layer B1-19 on the surface of the second Al-Fe alloy-plated steel sheet that is not in contact with the first Al-Fe alloy-plated steel sheet.

[0160] Zn, Ti, Cu, and V not only improve emissivity, but also have good infrared absorption when in the form of oxides. Therefore, by providing such layers, it is possible to suppress the difference in temperature rise rate between the overlapping portion (which has a slow temperature rise rate) and the single portion (which has a fast temperature rise rate), which is an issue when using a laminated blank. As a result, excessive heating of the single portion is suppressed, and the spot weldability of the single portion of the hot-stamped body can be improved.

[0161] In particular, oxides of Zn, Ti, Cu, or V remain even during heating during hot stamping. Therefore, such a coating layer B1-23 can further contribute to improving the temperature rise rate at high temperatures. When the coating layer B1-23 is provided on the surface of the Al-Fe alloy plating layer B1-19 applied to the surface of the second Al-Fe alloy plated steel sheet, the coating weight of the coating layer B1-23 is set to 0.2 g / m.２ By setting the coating amount to 0.4 g / m or more, it is possible to fully exert the effect of suppressing the difference in the temperature rise rate. ２ More preferably, it is 0.6 g / m or more. ２ On the other hand, the coating weight of the coating layer B1-23 was 3.0 g / m ２ By setting the amount of Zn, Ti, Cu, or V to 3.0 g / m or less, it is possible to achieve this effect without saturating. ２ By setting the coating weight of the coating layer B1-23 to 2.8 g / m or less, it is possible to prevent a decrease in the spot weldability of the hot stamped product. ２ More preferably, it is 2.6 g / m or less. ２ The following is the result.

[0162] In addition, when the coating layer B1-23 is not provided on the surface of the Al-Fe alloy plating layer B1-19 applied to the surface of the second Al-Fe alloy plated steel sheet, the coating amount (content) of Zn, Ti, Cu, or V is 0 g / m ２ This becomes:

[0163] Furthermore, in the first Al-Fe alloy plated steel sheet, a layer containing at least one of Zn, Ti, Cu, and V may be selectively provided on the Al-Fe alloy plated layer on the surface not in contact with the second Al-Fe alloy plated steel sheet. In this case, the coating amount (content) of at least one of Zn, Ti, Cu, and V is 0 g / m ２ The amount (content) of at least one of Zn, Ti, Cu, and V is more preferably 0.2 g / m ２ 3.0g / m or more ２ When a layer containing at least one of Zn, Ti, Cu, and V is not provided, the deposition amount (content) of Zn, Ti, Cu, or V is 0 g / m or less. ２ This becomes:

[0164] The deposition amount of the layer containing Zn, Ti, Cu, or V can be determined by, for example, performing elemental analysis from the surface using an X-ray fluorescence analyzer (ZSX Primus, manufactured by RIGAKU Corporation) and quantifying the amounts of Zn, Ti, Cu, and V.

[0165] As described above, in the lap hot-stamped steel according to the present embodiment, the second Al-Fe alloy plated steel sheet has an Al-Fe alloy plated layer on the surface that is not in contact with the first Al-Fe alloy plated steel sheet, and the total of the Zn content, Ti content, Cu content and V content is 0.2 to 3.0 g / m ２ and a layer having a total content of Zn, Ti, Cu and V of 0 to 3.0 g / m on the Al-Fe alloy plating layer on the surface of the first Al-Fe alloy plated steel sheet that is not in contact with the second Al-Fe alloy plated steel sheet. ２ A layer may be located in which

[0166] When the overlap hot-stamped body 12 of this embodiment is used as an automobile part, it is generally subjected to welding, phosphate-based chemical conversion treatment, electrodeposition coating, etc. Therefore, for example, a zinc phosphate coating and a phosphate coating may be formed on the surface of the hot-stamped body 12 by phosphate-based chemical conversion treatment, and an organic coating having a thickness of 5 μm to 50 μm may be formed on the surface of such a coating by electrodeposition coating. After electrodeposition coating, further coatings such as an undercoat and a topcoat may be applied to improve appearance quality and corrosion resistance. (Example)

[0167] The present elemental technology will be described in more detail below using examples.

[0168] Example 1 A first Al-based plated steel sheet 1 and a second Al-based plated steel sheet 2 shown in Table 6 were produced by the method described below, and spot-welded 3 as shown in FIG. 7 to produce a hot stamping overlap blank 4. A cold-rolled steel sheet (chemical composition: by mass, C: 0.23%, Si: 0.30%, Mn: 1.2%, P: 0.010%, S: 0.002%, Cr: 0.25%, Ti: 0.020%, Al: 0.042%, N: 0.0030%, B: 0.0020%, balance: Fe and impurities) that had been subjected to a conventional hot-rolling process and a cold-rolling process was used as the first Al-based plated steel sheet 1. Both surfaces of the cold-rolled steel sheet were aluminum-plated in a Sendzimir hot-dip aluminum plating line. After plating, the coating weight was adjusted by gas wiping, and the steel sheet was then cooled to produce the first Al-based plated steel sheet 1. The plating bath composition was 89% by mass Al-9% by mass Si-2% by mass Fe. A second Al-based plated steel sheet 2 was also prepared in the same manner as the first Al-based plated steel sheet 1, and a carbon-based black coating was applied thereto.

[0169] This blank was hot stamp heated at 920°C to investigate the temperature rise rate of the overlapping portion, and the overlapping portion was heated for 300 seconds at a temperature between 910 and 920°C, followed by immediate die cooling to obtain a hot-stamped overlapping body 12. Two flange portions 11 were cut out from the non-overlapping portion (single-piece portion), and spot weldability was investigated using the same type of plate assembly.

[0170] In Table 6, the levels are shown as A3 to A7, A10, A11, A13, A20, A21, and A23 for the invention examples of the present application (hereinafter simply referred to as "invention examples"), and A1, A2, A8, A9, A12, A15 to A19, and A22 for the comparative examples.

[0171] The thicknesses t1 and t2 of the steel sheets were measured using a micrometer in accordance with JIS B7502:2016, as described above. The coating weights W1a, W1b, and W2b per side were measured using the method of JIS G 3314:2019 JB.3 after applying a seal to the surface behind the surface to be measured. The lightness L ＊ 1a, L ＊ 1b, L ＊For 2b, a 50 x 50 mm test piece was cut out, and measurements were taken using a spectrophotometer (SC-T-GV5 manufactured by Suga Test Instruments, including specular reflection light) with a measurement beam diameter of φ = 15 mm. The film thickness of the carbonaceous black coating was measured by cross-sectional observation as described above.

[0172] To investigate the temperature rise rate at the overlapping portion of the blank, a K-type thermocouple was welded to the center of the overlapping portion of the hot stamping overlapping blank 4 shown in FIG. 7 . The temperature rise time was then determined, and the temperature rise rate was evaluated. The temperature rise time was calculated from the time it took to reach 910°C, and the evaluation was performed. The evaluation criteria were that the temperature rise time was shortened as follows, using Comparative Example A15, in which the second Al-based plated steel sheet did not have a carbon-based black coating, as the standard. A rating of G3 (Good 3) was judged as good, G2 (Good 2) as even better, G1 (Good 1) as particularly good, and a rating of NG (No Good) as poor. The entry in the "Temperature rise rate at the overlapping portion" column for Comparative Example A15, which served as the evaluation standard, was marked with "-" to indicate that it was a standard.

[0173] <Evaluation criteria> G1: Reduction of temperature rise time by 90 seconds or more G2: Reduction of temperature rise time by 60 seconds or more but less than 90 seconds G3: Reduction of temperature rise time by 30 seconds or more but less than 60 seconds NG: Reduction of temperature rise time by less than 30 seconds, or extension of temperature rise time

[0174] To investigate the spot weldability of the hot stamping overlap blank after heating, the hot stamping overlap blank 4 shown in FIG. 7 was hot stamped at 920°C to investigate the temperature rise rate of the overlapping portion. The overlapping portion was heated between 910 and 920°C for 300 seconds, and then immediately cooled by the die to obtain a hot stamped overlapping body 12. Two flange portions 11 of the non-overlapping portion (one-piece portion) were cut out, and the spot weldability of the same plate assembly was investigated under the welding conditions shown below. The evaluation criteria were the range (referred to as the appropriate current range) between the welding current value at which the weld nugget diameter during spot welding was 4√t (t is the plate thickness) and the welding current value at which splash occurs. A rating of G3 (Good 3) was judged as good, G2 (Good 2) as even better, G1 (Good 1) as particularly good, and NG (No Good) as poor.

[0175] <Evaluation criteria> G1: Appropriate current range is 2.0 kA or more G2: Appropriate current range is 1.5 kA or more and less than 2.0 kA G3: Appropriate current range is 1.0 kA or more and less than 1.5 kA NG: Appropriate current range is less than 1.0 kA

[0176] Welding power source: DC inverter, electrode pressure: 400 kgf, electrode shape: DR, tip diameter 6φ (R40) (material: chromium copper), initial pressure time: 60 cycles, welding time 22 cycles, holding time 10 cycles, welding current value: 4 kA to 15 kA, welding at 0.2 kA intervals

[0177] A comprehensive evaluation was performed based on the evaluation results for the temperature rise rate of the blank overlap portion and the evaluation results for the spot weldability after hot stamping (HS). More specifically, the evaluation value was determined by multiplying the scores "Gx" (x is an integer from 1 to 3) for each item. A sample with an evaluation score of "9" or a sample with an evaluation result of "NG" for at least one item was given an overall evaluation of "NG." Furthermore, since Comparative Example A15 serves as the evaluation standard for the temperature rise rate, the above-described comprehensive evaluation was not performed, and "-" was entered in the overall evaluation column.

[0178] Table 6 summarizes the evaluation results of investigating the temperature rise rate of the overlapping portion of the blank and the spot weldability after hot stamping (HS).

[0179]

[0180] The invention examples A3 to A7, A10, A11, A13, A20, A21, and A23 had coating weights within the range of the present application, had a carbon-based black coating, and the relationship between plate thickness, coating weight, and brightness satisfied formulas (1) and (2), so the heating rate of the overlapping portion and spot weldability after hot stamping were good. The comparative example A1 had a carbon-based black coating but did not satisfy formulas (1) and (2), so both the heating rate of the overlapping portion and spot weldability after hot stamping were poor. The comparative examples A8, A9, and A12 did not satisfy formula (1), so their spot weldability after hot stamping was poor. Furthermore, the comparative examples A2 and A22 had a carbon-based black coating but did not satisfy formula (2), so the overall evaluation was NG (No Good). Furthermore, the coating weight was 20 g / m ２ In Comparative Examples A16 and A18, scale was formed and the thickness was less than 120 g / m ２ It is believed that the deterioration of spot weldability was also due to the influence of powdering that occurred during press forming in Comparative Examples A17 and A19. Note that Comparative Example A15 did not have a carbon-based black coating and did not satisfy formulas (1) and (2), and therefore had poor spot weldability after hot stamping.

[0181] Example 2 A first Al-based plated steel sheet and a second Al-based plated steel sheet having sheet thicknesses of 1.0 mm, 1.6 mm, and 2.0 mm were produced to prepare overlapping blanks for hot stamping under the same production conditions as those in Example 1 shown in Table 7. A first Al-based plated steel sheet 1 and a second Al-based plated steel sheet 2 were produced by the method described below, and spot-welded 3 as shown in Fig. 7 to prepare overlapping blanks 4 for hot stamping.

[0182] This blank was hot stamped at 920°C in the same manner as in Example 1 to investigate the temperature rise rate of the overlapping portion. The overlapping portion was heated between 910 and 920°C for 300 seconds, and then immediately cooled in the mold to obtain a hot-stamped lapped body 12. Two flange portions 11 were cut out from the non-overlapping portion (one-piece portion), and spot weldability was investigated using a homogeneous plate assembly. In Table 7, the levels are indicated as B1, B5, and B6 for the invention examples, and B2, B3, B4, and B7 for the comparative examples.

[0183] In investigating the temperature rise rate of the overlapping portion of the blank, the temperature rise time was determined and evaluated in the same manner as in Example 1. The evaluation criteria for B1 were that the temperature rise time be shortened as follows relative to Comparative Example B2, which had the same sheet thicknesses of the first and second Al-plated steel sheets but did not have a carbon-based black coating on the second Al-plated steel sheet. Similarly, for B3, the temperature rise time be shortened as follows relative to Comparative Example B4, which had the same sheet thicknesses of the first and second Al-plated steel sheets but did not have a carbon-based black coating on the second Al-plated steel sheet. Furthermore, for B5 and B6, the temperature rise time be shortened as follows relative to Comparative Example B7, which had the same sheet thicknesses of the first and second Al-plated steel sheets but did not have a carbon-based black coating on the second Al-plated steel sheet. A rating of G3 (Good 3) was judged as good, G2 (Good 2) as even better, G1 (Good 1) as particularly good, and a rating of NG (No Good) as bad. Note that for each comparative example serving as the standard for evaluation, the entry in the column "Temperature rise rate of overlapping portion" was marked with "-" to indicate that it was a standard.

[0184] <Evaluation criteria> G1: Reduction of temperature rise time by 90 seconds or more G2: Reduction of temperature rise time by 60 seconds or more but less than 90 seconds G3: Reduction of temperature rise time by 30 seconds or more but less than 60 seconds NG: Reduction of temperature rise time by less than 30 seconds, or extension of temperature rise time

[0185] The spot weldability of the overlapping blank for hot stamping after heating was evaluated using the same examination method and evaluation criteria as in Example 1.

[0186] A comprehensive evaluation was performed based on the evaluation results for the temperature rise rate of the blank overlap portion and the evaluation results for the spot weldability after hot stamping (HS). More specifically, the evaluation value was determined by multiplying the scores "Gx" (x is an integer from 1 to 3) for each item. A test piece with an evaluation score of "9" or an evaluation result of at least one item being "NG" was given an overall evaluation of "NG." Furthermore, for each comparative example that served as the basis for the evaluation of the temperature rise rate, the above-described comprehensive evaluation was not performed, and a "-" was entered in the overall evaluation column.

[0187]

[0188] The invention examples B1, B5, and B6 had coating weights within the range of the present invention, had a carbon-based black coating, and the relationship between plate thickness, coating weight, and brightness satisfied formulas (1) and (2), so the heating rate of the overlapping portion and spot weldability after hot stamping were good. Comparative example B3 had a carbon-based black coating but did not satisfy formula (2), so the heating rate of the overlapping portion was poor compared to B4. Comparative examples B2, B4, and B7 did not have a carbon-based black coating and did not satisfy formulas (1) and (2), so the spot weldability after hot stamping was evaluated as poor.

[0189] Example 3: A first Al-plated steel sheet and a second Al-plated steel sheet were produced under the same manufacturing conditions as Level A3 of Example 1. Zn, V, Ti, and Cu were formed (by vacuum deposition) on the second Al-plated steel sheet, and a carbon-based black coating was then formed thereon to produce invention examples C1 to C4. Furthermore, water-dispersed sols of Zn oxide, V oxide, Ti oxide, and Cu oxide were added to the carbon-based black coating to produce invention examples C5 to C10. These were then spot-welded 3 as shown in FIG. 7 to produce overlapping blanks 4 for hot stamping. Details of invention examples C1 to C10 are shown in Table 8.

[0190] This blank was hot stamp heated at 920°C in the same manner as in Example 1 to investigate the temperature rise rate of the overlapping portion (evaluation criteria were the same as in Example 1, and were based on Comparative Example A15, in which the second Al-based plated steel sheet did not have a carbon-based black coating). The overlapping portion was heated to a temperature between 910 and 920°C for 300 seconds, and then immediately cooled in the mold to obtain a hot-stamped overlapping body 12. Two flange portions 11 were cut out from the non-overlapping portion (single-piece portion), and spot weldability was investigated using a homogeneous sheet assembly (evaluation criteria were the same as in Example 1). The results are also shown in Table 8.

[0191]

[0192] Inventive examples C1 to C10 are preferable coatings containing Zn, V, Ti, and Cu in a carbon-based black coating, and therefore showed better results than A3 in terms of the temperature rise rate at the overlapping portion and spot weldability after HS.

[0193] Example 4 A first Al-based plated steel sheet and a second Al-based plated steel sheet were produced under the same production conditions as level A3 in Example 1, and a carbon-based black coating was formed on the second Al-based plated steel sheet. The sample with a nitrogen content of 1% was designated D1, and samples with a nitrogen content of 2%, 5%, 8%, 18%, and 20% were designated D2, D3, D4, D5, and D6, respectively, and a tape peeling test was performed on these samples (tape: CT405AP-24 manufactured by Nichiban Co., Ltd.). As a result, peeling of the coating was observed in D1 with a nitrogen content of 1% and D6 with a nitrogen content of 20%, but no peeling was observed in the other samples D2, D3, D4, and D5.

[0194] Example 5 Lap-hot-stamped bodies were produced under the same production conditions as those for Levels A3, A7, A10, A12, A13, A15, and A16 of Example 1 and Levels C5, C6, C9, and C10 of Example 3, as shown in Table 9. These levels were designated E1, E6, E7, E8, E9, E10, and E11, and E2, E3, E4, and E5, respectively. Furthermore, Al-based plated steel sheets having carbon-based black coatings containing Zn oxide, V oxide, Ti oxide, and Cu oxide, which were used for the second Al-based plated steel sheets E2, E3, E4, and E5, were used as both the second Al-based plated steel sheet and the first Al-based plated steel sheet, and lap-hot-stamped bodies were produced under the same production conditions as those for Example 3. These levels were designated E12, E13, E14, and E15, respectively. The manufacturing conditions used in Examples 1 and 3 to obtain the overlap hot-stamped compacts of each level E1 to E15 are listed in Table 9 under the heading "Applied Manufacturing Conditions." Two non-overlapping sections (single-piece sections) were cut out and the spot weldability was investigated using the same sheet combination. The levels in Table 9 are shown as E1 to E5, E7, E9, and E12 to E15 for the invention examples, and E6, E8, E10, and E11 for the comparative examples. The evaluation method and criteria for spot weldability after hot stamping were the same as those in Example 1.

[0195] The plating thickness K1 of the Al-Fe alloy plating layer and the thickness D1 of the diffusion layer of the first Al-Fe alloy-plated steel sheet, and the plating thickness K2 of the Al-Fe alloy plating layer and the thickness D2 of the diffusion layer of the second Al-Fe alloy-plated steel sheet were measured by cross-sectional observation with an optical microscope as described above (each was measured at three locations and the average value was calculated).

[0196]

[0197] Inventive examples E1 to E5, E7, E9, and E12 to E15, the plating thicknesses K1 and K2 of the Al-Fe alloy plating layer were within the range of the present invention, and the plating thicknesses of the Al-Fe alloy plating layer and the diffusion layer satisfied formula (9), so the spot weldability after hot stamping was good. Comparative examples E6, E8, and E10 did not satisfy formula (9), so the spot weldability after hot stamping was poor. Comparative example E11 had a plating thickness of the Al-Fe alloy plating layer of less than 25 μm, so it did not satisfy formula (9), so both the plating thickness and the diffusion layer thickness were poor.

[0198] Furthermore, inventive examples E2, E3, E4, and E5 had oxides of Zn, V, Ti, and Cu on the Al-Fe alloy plating layer of the second Al-Fe alloy plated steel sheet, and therefore showed better spot weldability after HS than E1.

[0199] Furthermore, inventive examples E12, E13, E14, and E15 each had oxides of Zn, V, Ti, and Cu on the Al-Fe-based alloy plating layer of the first Al-Fe-based alloy-plated steel sheet and on the Al-Fe-based alloy plating layer of the second Al-Fe-based alloy-plated steel sheet, respectively, and therefore showed better spot weldability after HS than E1.

[0200] (Example 6) Focusing again on levels A2, A3, A5, and A15 of Example 1 shown in Table 6, a laminated blank 4 for hot stamping was produced by manufacturing under the same manufacturing conditions as those of these levels, except that a carbon-based black coating was further provided on the first Al-based plating layer, and spot welding 3 was performed as shown in FIG. 7 .

[0201] This blank was hot stamp heated at 920°C in the same manner as in Example 1, and the temperature rise rate of the overlapping portion was investigated (the evaluation criteria were the same as in Example 1, and the evaluation was based on Comparative Example A15, in which the second Al-based plated steel sheet did not have a carbon-based black coating). The overlapping portion was heated for 300 seconds at a temperature between 910 and 920°C, and then immediately cooled in the mold, to obtain a hot-stamped overlapping body 12. Two flange portions 11 were cut out from the non-overlapping portion (single-piece portion), and spot weldability was investigated using the same type of sheet assembled together (the evaluation criteria were the same as in Example 1).

[0202] The levels in Table 10 are indicated as F1 to F4. Level F1 is a first Al-based plated steel sheet of level A2 on which a carbon-based black coating is further provided, level F2 is a first Al-based plated steel sheet of level A3 on which a carbon-based black coating is further provided, level F3 is a first Al-based plated steel sheet of level A5 on which a carbon-based black coating is further provided, and level F4 is a first Al-based plated steel sheet of level A15 on which a carbon-based black coating is further provided.

[0203]

[0204] As is clear from Table 10 above, F1 to F4 have a higher temperature rise rate at the overlapping portion than the corresponding A2, A3, A5, and A15, and therefore have better evaluation results.

[0205] <<Elemental Technology B2>> Elemental Technology B2 is a hot-stamped product formed using an aluminum-plated steel sheet for hot stamping, the hot-stamped product comprising: a base steel sheet; an aluminum plating layer having an Al content of 80 mass % or more formed on at least one surface of the base steel sheet; and a surface treatment film formed on the aluminum plating layer, wherein the surface treatment film contains a compound A containing carbon and a compound B which is an oxide or fluoride of a metal element M and has a rutile structure, the carbon concentration of the compound A being 80 mass % or more, and the concentration of the metal element M satisfying the following formulas (1) and (2): 1≦CｂＭ ≦40...Formula (1) 1.5≦C ｂＭ / C ｔＭ ≦10.0...Equation (2) Here, when the average thickness of the surface treatment film is H, C in the above equation (2) ｔＭ is the concentration of the metal element M at a position 0.05H from the surface of the surface treatment film in mass %, and C in the above formula (1) and the above formula (2) ｂＭ is the concentration of the metal element M in mass % at a position 0.95H from the surface of the surface treatment film.

[0206] The objective of elemental technology B2 is to provide a steel sheet for hot stamping that can further improve the productivity of hot stamped members.

[0207]

[0005] In order to solve the above problems, the present inventors conducted extensive research. As a result, they found that, when manufacturing a hot-stamped member using a steel sheet for hot stamping, if the heating rate when the steel sheet is heated to a desired temperature (e.g., Ac3 point or higher) can be increased, the heating time can be shortened, contributing to improved productivity. Specifically, they found that the heating rate can be significantly increased by providing, on a coating layer, a surface treatment coating containing: compound A having a carbon concentration of 80 mass% or more; and compound B, which is an oxide or fluoride of metal element M and has a rutile structure; and controlling the concentration range of metal element M within a predetermined range.

[0208] (Aluminum-plated steel sheet for hot stamping) An aluminum-plated steel sheet for hot stamping (hereinafter also referred to as "aluminum-plated steel sheet for HS") according to an embodiment of the present elemental technology makes it possible to increase the temperature rise rate when heating the aluminum-plated steel sheet for HS when producing a hot-stamped member using the aluminum-plated steel sheet for HS. In other words, by using the aluminum-plated steel sheet for HS according to the present embodiment, which can increase the temperature rise rate during heating, it becomes possible to improve the productivity of hot-stamped members.

[0209] The aluminum-plated steel sheet for hot stamping according to this embodiment has a surface treatment film containing a predetermined compound on at least one surface of the plated steel sheet on which an aluminum plating layer is formed, in order to improve the temperature rise rate when the aluminum-plated steel sheet for HS is heated. By providing a surface treatment film containing a predetermined compound on at least one surface of the plated steel sheet on which an aluminum plating layer is formed, the temperature rise rate of the resulting aluminum-plated steel sheet for HS can be increased when it is heated. The surface treatment film may be formed on both surfaces of the plated steel sheet on which the aluminum plating layer is formed, or on only one surface. The surface treatment film may be formed on the entire surface of the plated steel sheet on which the aluminum plating layer is formed, or on a part of the surface. From the viewpoint of further improving the productivity of hot stamping members, it is preferable that the surface treatment film be formed on the entire surface of the plated steel sheet on which the aluminum plating layer is formed.

[0210] In the aluminum-plated steel sheet for hot stamping according to this embodiment, the type of steel sheet (base steel sheet) serving as a base material is not particularly limited. Examples of the base steel sheet include various hot-rolled steel sheets and cold-rolled steel sheets. The plated steel sheet constituting the aluminum-plated steel sheet for hot stamping according to this embodiment has a plating layer on at least one surface of such a base steel sheet. Examples of the plated steel sheet include steel sheets that have been subjected to hot-dip aluminum plating. However, the plating layer according to this embodiment is not limited to hot-dip aluminum plating as long as it is applicable to hot stamping.

[0211] Conventionally, most of the steel sheets used for automotive frame parts and the like have been hot-rolled steel sheets, cold-rolled steel sheets, or plated steel sheets coated with aluminum, zinc, etc. These conventional steel sheets have low emissivity, and therefore their temperature rise rate in response to radiant heating is low.

[0212] In the aluminum-plated steel sheet for hot stamping of this embodiment, by providing a predetermined surface treatment film, which will be described later, on the entire surface of at least one surface of the plating layer, the temperature rise rate during hot stamping heating can be increased. Specifically, by heating the aluminum-plated steel sheet for HS having the predetermined surface treatment film and hot stamping the heated aluminum-plated steel sheet for hot stamping, the productivity of hot-stamped members can be further improved.

[0213] <Surface Treatment Film> FIG. 14 shows a cross-sectional schematic view of a surface portion of one of the surfaces of the aluminum-plated steel sheet for hot stamping according to this embodiment.

[0214] As shown in FIG. 14 , the aluminum-plated steel sheet for hot stamping B2-10 according to this embodiment includes, for example, a base steel sheet B2-11, an aluminum plating layer (Al plating layer) B2-12 provided on at least one surface of the base steel sheet B2-11, and a surface treatment film 13 provided on the aluminum plating layer B2-12. In the aluminum-plated steel sheet for hot stamping B2-10 according to this embodiment, the surface on which the surface treatment film 13 is applied (i.e., the surface of the surface treatment film B2-13) has a high emissivity. This allows for a high temperature rise rate during hot stamping heating, thereby further improving the productivity of hot-stamped members. Note that FIG. 14 is a schematic diagram for illustrative purposes, and the dimensions of the surface treatment film 13 and the aluminum plating layer B2-12, etc., do not necessarily represent preferred embodiments, and are not limited to the dimensions shown in FIG. 14 .

[0215] The surface treatment film B2-13 according to this embodiment contains a compound A containing carbon and a compound B which is an oxide or fluoride of a metal element M and has a rutile structure. The surface treatment film B2-13 according to this embodiment may further contain a binder component as necessary. The surface treatment film B2-13 according to this embodiment may also contain silica. Furthermore, in this embodiment, the temperature rise rate (heating efficiency) during hot stamp heating can be improved by adjusting the contents of compound A and compound B in the surface treatment film B2-13, the concentration distribution of the metal element M, the application and drying methods of the surface treatment film B2-13, and the film thickness, etc.

[0216] Furthermore, in the surface treatment coating B2-13 according to this embodiment, the compound B has a predetermined concentration distribution. Specifically, the concentration of the metal element M constituting the compound B in the coating has a concentration distribution (concentration gradient) in which the concentration in the coating is higher in the coating layer side than in the surface side of the coating in the film thickness direction. The presence of the metal element M in such a predetermined concentration distribution makes it possible to further improve the heating efficiency of the surface treatment coating B2-13. When the hot stamping steel sheet according to this embodiment is hot stamped, radiant heat from the heating atmosphere can be efficiently absorbed. In addition, heat can also be efficiently absorbed by thermal conduction through contact with the heated atmospheric gas. As a result, it becomes possible to rapidly heat the entire surface treatment coating. The constituent elements of the surface treatment coating B2-13 are described in detail below.

[0217] [Compound A] The carbon concentration of compound A contained in surface treatment film B2-13 is 80% by mass or more. If the carbon concentration of compound A is less than 80% by mass, compound A may be decomposed and oxidized even at relatively low temperatures when the aluminum-plated steel sheet for HS is heated in the hot stamping process, resulting in the risk of compound A disappearing from the film. If compound A disappears from the film, the effect of improving the temperature rise characteristics cannot be maintained up to high temperatures. Therefore, the carbon concentration of compound A is set to 80% by mass or more. Preferably, the carbon concentration of compound A is 82% by mass or more, and more preferably 85% by mass or more. The carbon concentration of compound A may be 100% by mass. Examples of compound A include carbon black (CB), graphite, and soot.

[0218] The carbon concentration of compound A can be measured by cross-sectional analysis of the surface treatment film using a transmission electron microscope (TEM), energy dispersive X-ray spectroscopy (EDS), and electron beam diffraction. Specifically, the spectrum of characteristic X-rays during electron beam irradiation is measured, the detection intensity for each energy is calculated, and the elements constituting the compound to be measured can be identified from the energy value. Then, using a calibration curve prepared in advance from the relationship between substances with known element concentrations and the corresponding detection intensity data, the concentration of each element in the compound to be measured is calculated from the detection intensity of each element constituting the compound. Measurements are performed at 10 locations within the same compound, and if the maximum concentration of each element falls within a range of 1.0 to 1.3 times the minimum concentration of each element, the compound is considered to be the same. That is, 10 points are measured for a compound observed by TEM-EDS, and if the maximum concentration value of all elements constituting the compound is between 1.0 and 1.3 times the minimum value, the compound is considered to be the same. TEM observation samples are prepared by the FIB sampling method using a focused ion beam (FIB) processing and observation device (e.g., "NB5000" manufactured by Hitachi High-Tech Corporation). The accelerating voltage during processing is 40 kV.

[0219] The carbon concentration of compound A is defined as follows: In a cross-sectional analysis of a surface treatment film, measurements are taken at 10 locations within the same compound within an area encompassed by the film thickness and a length of 5 μm in the direction perpendicular to the film thickness. The carbon concentration of compound A is the median value between the maximum and minimum carbon concentrations. If multiple compounds A are present within the above range, the median value is calculated for each compound A, and the average of the resulting median values ​​is taken as the carbon concentration of compound A. This method can be used to analyze the concentrations of elements such as carbon that constitute compound A. Compound A, which is primarily composed of carbon, and compound B, which is an oxide or fluoride of metal element M, can be distinguished by their different carbon concentrations.

[0220] Furthermore, in this embodiment, the content of compound A having a carbon concentration of 80 mass % or more is preferably 10 to 90% or 20 to 90%, and more preferably 30 to 80%, at a position 0.90H from the surface of the surface treatment film (hereinafter also referred to as the "interface-side position P." This interface-side position P can be said to be a position 0.10H from the interface between the surface treatment film and the Al plating layer), where H (μm) is the average thickness of the surface treatment film.

[0221] Compound A having a carbon concentration of 80% by mass or more has a strong effect of absorbing radiant heat. Furthermore, because of its high carbon concentration, such compound A is less likely to be decomposed or volatilized by heating and disappear from the surface treatment film. Therefore, even when the temperature of the outermost surface of the aluminum-plated steel sheet for HS rises due to hot stamping, the absorption of radiant heat can be enhanced up to a high temperature range. To achieve this effect, it is effective to increase the content of compound A. In this embodiment, the content of compound A at the interface-side position P is preferably 10% or more, or 20% or more, and more preferably 30% or more, to further improve the temperature rise rate during hot stamping. Meanwhile, compound A itself in the surface treatment film does not have the effect of improving film adhesion. Therefore, it is preferable to limit the content of compound A in the surface treatment film, particularly at the interface-side position P on the Al plating layer side, to a predetermined amount or less. Specifically, the content of compound A at the interface-side position P is preferably 90% or less, more preferably 80% or less, to improve the adhesion between the surface treatment film and the Al plating layer. The mechanism by which the content of compound A at the interface side position P is improved by preferably setting it to 90% or less, and more preferably 80% or less, is thought to be that chemical and physical bonds between the highly polar rutile compound and binder resin contained in the surface treatment film and the aluminum plating layer can be ensured, resulting in an effect of improving film adhesion.

[0222] The content of compound A at the interface-side position P is determined by the following method. First, compound A with a carbon concentration of 80% or more is detected at the interface-side position P by EDS using TEM observation. For example, when the average thickness H of the surface treatment film is 5 μm, the "0.90H position" is a position 4.5 μm deep (thickness) from the surface of the surface treatment film (i.e., a position 0.5 μm deep (thickness) from the interface between the surface treatment film and the Al plating layer toward the film side). Next, in a TEM image of a sample described below, when 10 points are observed at 30 nm intervals in a direction perpendicular to the thickness direction of the surface treatment film layer (a direction parallel to the interface between the aluminum plating layer and the surface treatment film and perpendicular to the thickness direction of the sample), if the presence of compound A is observed at three points, the content of compound A at the interface-side position P is defined as 30%. Similarly, if the presence of compound A is observed at four points, the content of compound A is defined as 40%, and the same applies hereinafter. Therefore, when compound A with a carbon concentration of 80% or more is observed at three or more points and eight or fewer points, this means that the compound A content is 30 to 80%. The TEM observation sample used in calculating the compound A content is prepared by the FIB sampling method using a focused ion beam (FIB) processing and observation device (e.g., the "NB5000" manufactured by Hitachi High-Tech Corporation). The acceleration voltage during processing is 40 kV. The sample thickness is 100 nm ± 10 nm. As described above, the compound A content is a percentage (%) calculated from the ratio of the number of points where compound A is observed (present) to the number of points where compound A is present / 10 in a specific direction (parallel to the surface of the surface treatment film and perpendicular to the thickness direction of the sample) in a TEM image of a sample with a thickness of 100 ± 10 nm. For this reason, the unit of content is not volume % or area %, but rather a dimensionless %.

[0223] [Compound B] Compound B is an oxide or fluoride of a metal element M and has a rutile structure. Examples of the metal element M include Ti, V, Mn, Ru, Cs, Ir, Ge, Cu, Ag, and Ni. If necessary, only one or a plurality of the above elements may be used as the metal element M. In addition, examples of such compound B include TiO ２ , V.O. ２ , β-MnO２ , RuO ２ , CsO ２ , IrO ２ , GeO ２ , CuO ２ , AgO ２ , NiF ２ If necessary, only one or a plurality of the above compounds may be used as the compound B.

[0224] Incorporating compound B having a rutile-type compound structure into a coating can increase the heating rate during hot stamping. While the reason for this is unclear, it is presumed as follows. The rutile-type structure is a structure in which anions have a distorted hexagonal close-packed structure, with cations located in the six-coordinated spaces (six-coordinated gaps). Furthermore, it is presumed that the inclusion of compound B having such a rutile-type compound structure in a coating increases the inter-ionic distance that is active for radiation from infrared or near-infrared electromagnetic waves, the main heating factor during hot stamping. The crystal structure and type of compound B (whether oxide or fluoride) can be determined by cross-sectional analysis of the surface treatment coating using TEM, EDS, and electron diffraction. Specifically, the electron diffraction image obtained during electron beam irradiation is compared with a pre-existing database. If the compound is classified as having a rutile-type structure, it can be determined that the compound has a rutile-type structure. Furthermore, EDS can identify compounds from the ratio of element concentrations, and if the ratio of oxygen or fluorine is 10 mass % or more, the compound can be determined to be an oxide or a fluoride.

[0225] In this embodiment, the concentration of the metal element M in the compound B satisfies the following formula (1) and formula (2).

[0226] 1≦C ｂＭ ≦40...Formula (1) 1.5≦C ｂＭ / C ｔＭ ≦10.0...Equation (2) Here, when the average thickness of the surface treatment film is H (μm), C in the above equation (2) ｔＭis the concentration (mass %) of the metal element M at a position 0.05H from the surface of the surface treatment film B2-13, and C in the above formula (1) and the above formula (2) ｂＭ is the concentration (mass %) of the metal element M at a position 0.95H from the surface of the surface treatment film B2-13.

[0227] As shown in FIG. 14, when the thickness of the surface treatment film B2-13 is H (μm), the concentration C of the metal element M at 0.95H from the surface of the surface treatment film B2-13 is ｂＭ is 1% or more and 40% or less in mass %. ｂＭ If C is less than 1%, it becomes difficult to improve the temperature rise characteristics, particularly in the high temperature range, during heating by hot stamping. ｂＭ must be 1% or more. ｂＭ is preferably 5% or more, more preferably 8% or more. ｂＭ By making C 8% or more, the temperature rise rate during hot stamping can be further increased. ｂＭ When the concentration C in the surface treatment film B2-13 near the Al plating layer B2-12 exceeds 40%, the temperature rise rate during heating in hot stamping becomes saturated, while the adhesion between the surface treatment film B2-13 and the Al plating layer B2-12 decreases. ｂＭ This is because, when C increases, the ability of the surface treatment film B2-13 to conform to the fine irregularities on the surface of the Al plating layer B2-12 decreases. ｂＭ This allows the temperature rise rate during hot stamping to be increased and also improves the coating adhesion. ｂＭ is preferably 35% or less, more preferably 30% or less, and further preferably 20% or less. ｂＭ By making the ratio 20% or less, the adhesion of the surface treatment film B2-13 to the aluminum plating layer B2-12 can be further improved.

[0228] Furthermore, as shown in the above formula (2), C ｂＭ / C ｔＭ The concentration of the metal element M is high near the interface between the Al plating layer B2-12 and the surface treatment film B2-13, and CｂＭ / C ｔＭ When C is 1.5 or more, the metallic luster of the surface of the Al plating layer B2-12 can be concealed and the reflection of radiant heat can be suppressed. ｂＭ / C ｔＭ is preferably 2.0 or more, more preferably 3.0 or more. ｂＭ / C ｔＭ If C exceeds 10.0, the heat absorption on the surface side of the surface treatment film B2-13 is insufficient, and as a result, the temperature rise rate during hot stamping cannot be increased. ｂＭ / C ｔＭ is set to 10.0 or less. This makes it possible to appropriately control the reflection of radiant heat on the surface of the Al plating layer B2-12 and the heat absorption state on the surface side of the surface treatment film B2-13, thereby increasing the temperature rise rate. ｂＭ / C ｔＭ is preferably 8.0 or less, more preferably 6.0 or less.

[0229] Concentration (mass%) of metal element M at 0.05H from the surface of surface treatment film B2-13 ｔＭ , and the concentration C of the metal element M at 0.95H from the surface of the surface treatment film B2-13 ｂＭ As shown in FIG. 14, when the thickness of the surface treatment film B2-13 is H (μm), C can be measured by X-ray fluorescence analysis and glow discharge optical emission spectroscopy (GDS). ｂＭ and C ｔＭ We will explain in detail how to calculate this.

[0230] First, the average concentration (mass %) of the metal element M is determined as follows: Using an aluminum-plated steel sheet provided with a surface treatment film containing compound A and compound B (oxide or fluoride of the metal element M), the detection intensity (kcps, 10 ３ The adhesion amount (g / m) of the metal element M in the surface treatment film is determined in advance by fluorescent X-rays in accordance with JIS K 0119 (2008). ２A calibration curve of the detection intensity (kcps) of the metal element M is prepared in advance. Using this calibration curve, the adhesion amount P (g / m) of the metal element M in the surface treatment film is calculated from the detection intensity (kcps) of the metal element M obtained by X-ray fluorescence analysis. ２ ) is obtained. When determining the detection intensity of the metal element M in the surface treatment film by X-ray fluorescence analysis, the concentration of the metal element M in the base steel material does not have an effect, that is, it can be ignored. In other words, since fluorescent X-rays are significantly attenuated by the metal elements in the aluminum plating layer and the surface treatment film, elements in the base steel material at a position deeper than the aluminum plating layer and the surface treatment film can be considered not to have an effect on the detection intensity of the metal element M in the surface treatment film.

[0231] Next, the metal element M is measured in the depth direction of the surface treatment film B2-13 by GDS, and the location where the strength of the metal element M is less than half on the base steel sheet side of the depth (thickness) position where the strength is maximum is defined as the interface between the surface treatment film and the Al plating layer, and the thickness of the surface treatment film B2-13 is determined. This thickness is measured at five locations, and the average of the obtained thicknesses is defined as the thickness H (μm) of the surface treatment film B2-13. The deposition amount P of the metal element M is then divided by H, and the result is multiplied by 100 to obtain "P × 100 / H," which is considered to be the average concentration (mass %) of the metal element M in the surface treatment film in the entire depth direction.

[0232] On the other hand, by utilizing the fact that the relationship between the average value of the intensity of the metal element M measured by GDS from the surface of the surface treatment film to the interface with the Al plating layer and the above-mentioned average concentration P×100 / H is proportional to one to one, the concentration of the metal element M at any position in the depth direction of the surface treatment film can be determined. That is, P×100 / H, which is the average concentration (mass%) of the metal element M in the entire film thickness, and the average value α of the intensity of the metal element M from the surface to the interface with the Al plating layer can be determined. On the other hand, if the intensity (kcps) of the metal element M at any position X in the depth direction is β, the concentration C of the metal element M at that position X can be determined by ＸＭ (mass %) can be calculated using the following formula (3) by utilizing a proportional relationship.

[0233] C ＸＭ= P / H × 100 × (β / α) (3) The average concentration (mass%) of the metal element M in 0.05H obtained using this formula (3) is expressed as C ｔＭ , the concentration (mass%) of the metal element M at a position 0.95H from the surface is C ｂＭ Let's say.

[0234] In this embodiment, compound B is rutile-type TiO ２ It is preferable that the compound B is rutile type TiO ２ In this case, the temperature rise rate during hot stamping can be further increased. The reason for this is unclear, but is presumed to be as follows. ２ O ３ Rutile TiO ２ can maintain a high emissivity even in the high temperature range from 300 to 900°C. Therefore, it is presumed that the amount of heat input by radiation can be increased. Furthermore, when the temperature is raised to a higher temperature range, rutile-type TiO ２ and Al ２ O ３ There is a possibility that a complex oxide with this rutile-type TiO ２ and Al ２ O ３ The fact that the emissivity of the composite oxide of Cr is higher than that of other oxides is also presumably a factor that can further increase the temperature rise rate during hot stamping.

[0235] The compound B is an oxide or fluoride of the metal element M, but the compound B may be composed of two or more compounds. For example, the compound B may be TiO ２ and V.O. ２ In addition, when two or more compounds are contained as compound B in the surface treatment film, it is sufficient that the compound contained in the greatest amount has the desired concentration and distribution that satisfies the above (1) and (2).

[0236] In addition, when a laminated film is formed by separately preparing a treatment solution containing compound A, compound B which is an oxide or fluoride of metal element M and has a rutile structure, and a treatment solution containing an organic or inorganic substance such as a resin serving as a binder component, and applying these treatment solutions separately to an aluminum plating layer, compound B does not exist in the predetermined concentration distribution as described above. Furthermore, when attempting to form a multi-layer surface treatment film using multiple treatment solutions in this manner, the second layer must be formed after the first layer has been formed, which increases the size of the manufacturing equipment and the manufacturing cost. Therefore, the surface treatment film B2-13 of this embodiment needs to have a single layer structure, not a multi-layer structure.

[0237] The aluminum-plated steel sheet for hot stamping B2-10 according to this embodiment is provided with the surface treatment film B2-13 having the above-described characteristics, and thus can improve the temperature rise rate during hot stamping. Therefore, by using the aluminum-plated steel sheet for hot stamping B2-10 according to this embodiment as a raw material, the productivity of hot stamped materials can be improved.

[0238] Although it is not clear why the provision of the surface treatment film B2-13 according to this embodiment enables the temperature rise rate of the steel sheet to be improved during hot stamping, one possible reason is that there are many bonds active against infrared rays with wavelengths of 1 to 10 μm, which are particularly effective in absorbing radiant heat.

[0239] In addition to the above-mentioned Compound A and Compound B, the surface treatment film B2-13 according to this embodiment can contain various resins and additives as binder components. By containing a resin, the adhesion between the surface treatment film B2-13 and the Al plating layer B2-12 can be improved. Examples of additives contained in the surface treatment film B2-13 include a leveling agent, an antifoaming agent, a colorant, a viscosity modifier, and an ultraviolet absorber. The coating liquid for forming the surface treatment film B2-13 is preferably obtained by dispersing or dissolving the above-mentioned components in water or a solvent.

[0240] In this embodiment, specific methods for applying the surface treatment film B2-13 include, but are not limited to, coating and lamination. The surface treatment film B2-13 may be applied to only one surface of the aluminum-plated steel sheet, or may be applied to both surfaces of the aluminum-plated steel sheet.

[0241] When applying the surface treatment film B2-13 to the entire surface of the aluminum plating layer B2-12 by coating, first, a treatment liquid is prepared containing, for example, compound A having a carbon concentration of 80% by weight or more and compound B which is an oxide or fluoride of metal element M and has a rutile structure. The treatment liquid is then applied to the entire surface of the aluminum plating layer B2-12 using a roll coater, curtain coater, inkjet, or the like, and the volatile components in the treatment liquid are then dried to apply the surface treatment film B2-13. Inkjet coating is particularly preferred because it allows the film thickness to be continuously changed.

[0242] Here, in the past (for example, JP 2011-149084 A, etc.), when a surface treatment film contains organic substances such as carbon pigments, when the plated steel sheet is heated to a high temperature range (for example, 750°C or higher), all of the organic substances disappear, resulting in a problem of a deterioration in the temperature rise characteristics (heat rise rate). However, the present inventors have discovered that in the case of the surface treatment film B2-13 according to this embodiment, it is possible to efficiently heat up to a high temperature range even if the organic substances disappear. Although the mechanism by which it is possible to heat up to a high temperature range even if the organic substances disappear is not clear, it is presumed that the compound B (oxide or fluoride of metal element M) contained in the film increases the heat input by radiation at high temperatures.

[0243] [Binder Component (Resin)] The content of the binder component (resin) that can be contained in the surface treatment film B2-13 according to this embodiment is preferably 40% by volume or more relative to the total volume of the surface treatment film B2-13. Various known resins can be used as the binder component.

[0244] The resin used as the binder component is not particularly limited. Examples include polyurethane resin, polyester resin, acrylic resin, epoxy resin, fluororesin, polyamide resin, polyolefin resin, and polymer compounds obtained by hydrolysis and condensation polymerization of a silane coupling agent. Examples of the resin include butylated melamine resin, methylated melamine resin, butylmethyl-mixed melamine resin, urea resin, isocyanate resin, or a resin obtained by crosslinking these resins with a crosslinking agent component of a mixed system thereof. Examples also include electron beam curable resins and ultraviolet curable resins. Among these, the resin used as the binder component is preferably one or more of polyester resin, epoxy resin, acrylic resin, and polyurethane resin. These resins used as the binder component may be used alone or in combination of two or more.

[0245] When a polyurethane resin is used as the binder component, for example, the polyurethane resin is preferably a polyether-based polyurethane resin, because the use of a polyether-based polyurethane resin can prevent the occurrence of hydrolysis due to acid or alkali compared to a polyester-based polyurethane resin, and because the use of a polyether-based polyurethane resin can suppress the formation of a hard and brittle film compared to a polycarbonate-based polyurethane resin, thereby ensuring adhesion during processing and corrosion resistance of the processed part.

[0246] Whether or not a polyurethane resin is contained can be determined by detecting a peak at 3330 cm in an infrared absorption spectrum obtained by infrared spectroscopy. －１ (NH telescopic), 1730cm －１ (C=O expansion / contraction), 1530cm －１ (CN), 1250cm －１ This can be determined based on whether the characteristic absorption of (C-O) is observed. Furthermore, the content of polyurethane resin can also be determined from the obtained characteristic absorption intensity by creating a calibration curve showing the relationship between the content and the characteristic absorption intensity using samples with known contents.

[0247] Furthermore, for resins other than the polyurethane resins described above, it is possible to determine the presence or absence and amount of the resin, similarly to the polyurethane resins, by focusing on the characteristic absorption derived from the functional groups specific to each resin. Water or a solvent can be used as a component in the treatment liquid for dispersing or dissolving the resin.

[0248] [Additives] The surface treatment film B2-13 according to this embodiment can contain various additives, such as a leveling agent, a water-soluble solvent, a metal stabilizer, an etching inhibitor, etc., as additives used in preparing the treatment liquid prior to film formation, within a range that does not impair the effects of this fundamental technology.

[0249] The leveling agent may be a nonionic or cationic surfactant, such as a polyethylene oxide or polypropylene oxide adduct, or an acetylene glycol compound.

[0250] Examples of the water-soluble solvent include alcohols such as ethanol, isopropyl alcohol, t-butyl alcohol, and propylene glycol; cellosolves such as ethylene glycol monobutyl ether and ethylene glycol monoethyl ether; esters such as ethyl acetate and butyl acetate; and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone.

[0251] Examples of metal stabilizers include chelating compounds such as EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid).

[0252] Examples of etching inhibitors include amine compounds such as ethylenediamine, triethylenepentamine, guanidine, and pyrimidine.

[0253] The contents of the binder components and additives can also be measured in the same manner as in the case of the compounds A and B.

[0254] [Silica] The surface treatment film B2-13 according to this embodiment may contain silica. When silica is contained, the content of silica is 0.01 to 0.3 g / m ２Silica is preferably 0.01 g / m ２ By containing silica at a content of 0.3 g / m or more, it is possible to prevent scratches on the coating due to contact with other steel sheets or equipment. ２ If the content exceeds 0.3 g / m, the temperature rise effect cannot be expected and the cost becomes high, which is not preferable from the economic point of view. ２ If the silica content exceeds 0.10 g / m, it is not preferable in terms of weldability after hot stamping. When silica is contained, the smaller the silica content in the surface treatment film B2-13, the better. The silica content of the surface treatment film is more preferably 0.10 g / m ２ More preferably, it is 0.05 g / m or less. ２ The following is the result.

[0255] [Thickness of Surface Treatment Film] The average film thickness H of the surface treatment film B2-13 containing the above components is preferably 0.5 to 15.0 μm, for example. If the average film thickness of the surface treatment film B2-13 is less than 0.5 μm, the absorption of radiant heat is insufficient, making it impossible to sufficiently increase the temperature rise rate during hot stamping. On the other hand, if the average film thickness of the surface treatment film B2-13 exceeds 15.0 μm, the heat capacity of the surface treatment film B2-13 itself increases, acting as a barrier to heat transfer to the aluminum plating layer B2-12. As a result, the temperature rise rate cannot be sufficiently improved, and costs increase, which is undesirable from an economic standpoint. By setting the average film thickness of the surface treatment film B2-13 in the range of 0.5 to 15.0 μm, the temperature rise rate can be improved. The average film thickness of the surface treatment film B2-13 is more preferably 1.0 to 7.0 μm.

[0256] <Undercoat Treatment Film> A undercoat treatment film (chemical conversion layer) B2-14 may be applied between the surface treatment film B2-13 and the aluminum plating layer B2-12 to improve the adhesion of the surface treatment film B2-13, as shown in Fig. 15. Note that Fig. 15 is a schematic diagram for explanation, and the dimensions of the surface treatment film 13, aluminum plating layer B2-12, and undercoat treatment film 14 do not necessarily represent a preferred embodiment, and are not limited to the dimensions shown in Fig. 15.

[0257] The base treatment coating B2-14 may contain one or more selected from resins, silane coupling agents, zirconium compounds, silica, phosphoric acid and its salts, fluorides, and vanadium compounds. The inclusion of these substances further improves the film-forming properties after application of the chemical conversion treatment agent, the barrier properties (density) of the coating against corrosive factors such as moisture and corrosive ions, and the adhesion of the coating to the plating surface, thereby contributing to improving the corrosion resistance of the coating. In particular, when the chemical conversion treatment layer contains one or more of a silane coupling agent and a zirconium compound, a crosslinked structure is formed in the coating, further strengthening the bond with the plating surface, thereby improving the adhesion and barrier properties of the coating. Furthermore, when the base treatment coating B2-14 contains one or more of silica, phosphoric acid and its salts, fluorides, and vanadium compounds, they act as inhibitors to form precipitate films or passivation films on the plating surface and the base steel sheet surface, thereby improving corrosion resistance.

[0258] [Adhesion amount of base treatment film B2-14] The adhesion amount of the base treatment film B2-14 per one side of the plating layer is 10 to 1000 mg / m in terms of solid content. ２ The coating amount of the base treatment film B2-14 is preferably 10 mg / m ２ If the coating weight is less than 1000 mg / m, sufficient adhesion and corrosion resistance cannot be ensured. ２ If the coating weight exceeds 2000 mg / m, the adhesion may be reduced. ２ , more preferably 50 to 600 mg / m ２ is.

[0259] <Aluminum Plating Layer> The aluminum-plated steel sheet for hot stamping B2-10 according to this embodiment preferably has an aluminum plating layer B2-12 on at least one surface of the base steel sheet B2-11. By having the aluminum plating layer B2-12, the corrosion resistance after painting after hot stamping can be further improved. Furthermore, the presence of the aluminum plating layer B2-12 between the base steel sheet B2-11 and the surface treatment coating B2-13 can prevent iron scale from forming due to heating during hot stamping. Iron scale contaminates heating furnaces and adheres to rolls used for transportation, thereby imposing a burden on manufacturing. Therefore, if iron scale does form, a process such as shot blasting is required to remove the iron scale, which is economically undesirable.

[0260] The type of the aluminum plating layer is not particularly limited, and the composition of the aluminum plating layer may be aluminum plating, Al—Si plating, Al—Si—Mg plating, Al—Si—Ca plating, or the like. For example, the aluminum plating layer may have a chemical composition (average chemical composition) containing, in mass %, Al: 80.0 to 95.0%, Si: 2.0 to 15.0%, Fe: 1 to 15.0%, Cr: 0% or more and less than 1.0%, Mo: 0% or more and less than 1.0%, Zn: 0% or more and less than 1.0%, V: 0% or more and less than 1.0%, Ti: 0% or more and less than 1.0%, Sn: 0% or more and less than 1.0%, Ni: 0% or more and less than 1.0%, Cu: 0% or more and less than 1.0%, W: 0% or more and less than 1.0%, Bi: 0% or more and less than 1.0%, Mg: 0% or more and less than 1.0%, and Ca: 0% or more and less than 1.0%, with the remainder being impurities.

[0261] If the Al content in the aluminum plating layer is less than 80.0%, the corrosion resistance after hot stamping (corrosion resistance of the hot-stamped body) deteriorates. Therefore, the Al content is preferably 85.0% or more. The Al content is more preferably 88.0% or more. On the other hand, if the Al content in the aluminum plating layer exceeds 95.0%, the plating adhesion may deteriorate. Therefore, the Al content is preferably 95.0% or less. The Al content is more preferably 92.0% or less.

[0262] If the Si content in the aluminum plating layer is less than 2.0%, plating adhesion may deteriorate. Therefore, the Si content is preferably 2.0% or more. The Si content is more preferably 3.0% or more, and even more preferably 4.0% or more. On the other hand, if the Si content in the aluminum plating layer is more than 15.0%, plating adhesion may deteriorate. Therefore, the Si content is preferably 15.0% or less. The Si content is more preferably 13.0% or less.

[0263] The Fe content is preferably 1.0% or more and 15.0% or less.

[0264] The chemical composition of the aluminum plating layer can be measured by X-ray fluorescence spectroscopy in accordance with JIS G K 0119:2008. That is, using a sample with a known content of the target element, the relationship between X-ray intensity and content is determined in advance. From a calibration curve created based on this, the content of each element, i.e., the chemical composition, of an unknown sample can be determined.

[0265] [Aluminum plating layer deposition mass] The aluminum plating layer B2-12 is applied to one or both sides of the base steel sheet B2-11. The deposition mass is 5 g / m per side. ２ ~140g / m ２ The amount of adhesion per side is preferably 5 g / m ２ If the adhesion amount is less than 140 g / m, iron scale will form on the surface of the base steel sheet during the heating step of hot stamping, and a step of removing the scale will be required. ２If the coating weight of the aluminum plating layer B2-12 is more than 5 g / m per side, it takes time to proceed with the alloying reaction between Al and Fe in the hot stamp heating step, which is necessary to improve corrosion resistance after painting, and this is therefore not preferable from the viewpoint of productivity. ２ ~140g / m ２ is preferred.

[0266] <Base Steel Sheet> Next, a base steel sheet B2-11 of the aluminum-plated steel sheet for hot stamping B2-10 according to this embodiment will be described. The base steel sheet B2-11 is not particularly limited as long as it is a steel sheet that can be suitably used in hot stamping. The chemical composition of the base steel sheet B2-11 applicable to the aluminum-plated steel sheet for hot stamping B2-10 according to this embodiment is, for example, in mass %, C: 0.03 to 0.60%, Si: 0.01 to 0.60%, Mn: 0.50 to 3.00%, P: 0.050% or less, S: 0.020% or less, Al: 0.100% or less, Ti: 0.01 to 0.10%, B: 0.0001 to 0.0100%, N: 0.010% or less, Cr: 0 to 1.00%, Ni: 0 to 2.00%, Cu: 0 to 1.000%, Mo: 0 to 1.00%, V: 0 to 1.00%, Nb: 0 to 1.00%, Sn: 0 to 1.00%, The base steel sheet B2-11 may contain W: 0 to 1.00%, Ca: 0 to 0.010%, REM: 0 to 0.30%, and the balance may be Fe and impurities. Examples of the form of the base steel sheet B2-11 include hot-rolled steel sheets and cold-rolled steel sheets. The preferred ranges of each element in the base steel sheet B2-11 for the aluminum-plated steel sheet B2-10 for hot stamping and the reasons for this will be described in detail below. In the following description of the chemical composition of the base steel sheet B2-11, the notation "%" means "mass %" unless otherwise specified.

[0267] [C: 0.03 to 0.60%] C is contained to ensure the desired mechanical strength. When the C content is 0.03% or more, a sufficient improvement in mechanical strength is obtained, and the effect of containing C is fully achieved. Therefore, the C content is preferably 0.03% or more. The C content is more preferably 0.20% or more. On the other hand, when the C content is 0.60% or less, the strength of the steel sheet can be hardened and improved while suppressing a decrease in elongation and reduction of area. Therefore, the C content is preferably 0.60% or less. The C content is more preferably 0.40% or less.

[0268] [Si: 0.01 to 0.60%] Si is one of the strength-improving elements that improves mechanical strength, and like C, is contained to ensure the desired mechanical strength. When the Si content is 0.01% or more, the strength-improving effect is fully exerted, and a sufficient improvement in mechanical strength is obtained. Therefore, the Si content is preferably 0.01% or more. The Si content is more preferably 0.10% or more. On the other hand, since Si is also an easily oxidizable element, when the Si content is 0.60% or less, a decrease in wettability during hot-dip Al plating due to the influence of Si oxides formed on the steel sheet surface layer is suppressed, and the occurrence of bare spots can be suppressed. Therefore, the Si content is preferably 0.60% or less. The Si content is more preferably 0.40% or less.

[0269] [Mn: 0.50 to 3.00%] Mn is one of the strengthening elements that strengthen steel and is also one of the elements that improve hardenability. Furthermore, Mn is an element that is effective in preventing hot embrittlement caused by S, an impurity. A Mn content of 0.50% or more sufficiently achieves these effects. Therefore, to ensure the above effects, the Mn content is preferably 0.50% or more. The Mn content is more preferably 0.80% or more. On the other hand, since Mn is an austenite-forming element, a Mn content of 3.00% or less prevents the amount of retained austenite phase from becoming too large, thereby suppressing a decrease in strength. Therefore, the Mn content is preferably 3.00% or less. The Mn content is more preferably 1.50% or less.

[0270] [P: 0.050% or less] P is an impurity contained in steel. By setting the P content to 0.050% or less, it is possible to prevent P contained in the steel sheet from segregating at the grain boundaries of the steel sheet and reducing the toughness of the base material of the hot-stamped body, thereby suppressing a decrease in the delayed fracture resistance of the steel sheet. Therefore, the P content is preferably 0.050% or less, and it is preferable to reduce the P content as much as possible. If necessary, the P content may be set to 0.045% or less or 0.040% or less. The lower limit of the P content is 0%, but the lower limit may also be set to 0.001% or 0.005%.

[0271] [S: 0.020% or less] S is an impurity contained in steel. By setting the S content to 0.020% or less, it is possible to prevent the S contained in the steel sheet from forming sulfides, which reduces the toughness of the steel sheet, and to prevent a decrease in the delayed fracture resistance of the steel sheet. Therefore, the S content is preferably 0.020% or less, and it is preferable to reduce the S content as much as possible. If necessary, the S content may be set to 0.015% or less or 0.010% or less. The lower limit of the S content is 0%, but the lower limit may also be set to 0.001% or 0.002%.

[0272] [Al: 0.100% or less] Al is generally used for the purpose of deoxidizing steel. On the other hand, an Al content of 0.100% or less suppresses an increase in the Ac3 point of the steel sheet, thereby reducing the heating temperature required to ensure the hardenability of the steel during hot stamping, which is desirable for hot stamping production. Therefore, the Al content of the steel sheet is preferably 0.100% or less, more preferably 0.050% or less, and even more preferably 0.030% or less. The lower limit of the Al content is 0%, but the lower limit may be 0.001%, 0.003%, or 0.007%.

[0273] [Ti: 0.01 to 0.10%] Ti is one of the strength-enhancing elements. When the Ti content is 0.01% or more, the strength-improving effect and the oxidation resistance-improving effect can be sufficiently obtained. Therefore, in order to reliably realize the above effects, the Ti content is preferably 0.01% or more. The Ti content is more preferably 0.03% or more. On the other hand, when the Ti content is 0.10% or less, for example, the formation of carbides and nitrides is suppressed, which can suppress softening of the steel and ensure that the desired mechanical strength can be sufficiently obtained. Therefore, the Ti content is preferably 0.10% or less. The Ti content is more preferably 0.08% or less.

[0274] [B: 0.0001 to 0.0100%] B acts during quenching to improve strength. When the B content is 0.0001% or less, this strength-improving effect can be sufficiently obtained. Therefore, the B content is preferably 0.0001% or more. The B content is more preferably 0.0010% or more. On the other hand, when the B content is 0.0100% or less, the formation of inclusions is reduced, which suppresses embrittlement of the steel sheet and can suppress a decrease in fatigue strength. Therefore, the B content is preferably 0.0100% or less. The B content is more preferably 0.0040% or less.

[0275] [N: 0.010% or less] N is an impurity contained in steel. By setting the N content to 0.010% or less, the formation of nitrides due to N contained in the steel sheet is suppressed, thereby suppressing a decrease in the toughness of the steel sheet. Furthermore, when B is contained in the steel sheet, the N contained in the steel sheet is prevented from combining with B to reduce the amount of solute B, thereby suppressing a decrease in the hardenability-improving effect of B. Therefore, the N content is preferably 0.010% or less, and it is more preferable to reduce the N content as much as possible.

[0276] Furthermore, the base steel sheet of the steel sheet for hot stamping according to this embodiment may further contain, as an optional element, one or more elements selected from the group consisting of Cr, Mo, Ni, Cu, V, Nb, Sn, W, Ca, and REM. The lower limit of the content of these elements is 0%.

[0277] [Cr: 0 to 1.00%] Cr is an element that improves the hardenability of steel sheet. To fully obtain this effect, the Cr content is preferably 0.01% or more. On the other hand, by setting the Cr content to 1.00% or less, the effect can be fully obtained while suppressing increases in costs. Therefore, when Cr is contained, the Cr content is preferably 1.00% or less. If necessary, the Cr content may be set to 0.70% or less or 0.50% or less.

[0278] [Ni: 0 to 2.00%] Ni is an element that improves the hardenability of steel and enables the strength of steel plate members to be stably ensured after quenching. In order to fully realize this effect, the Ni content is preferably 0.10% or more. On the other hand, by setting the Ni content to 2.00% or less, the above effects can be fully obtained while improving economic efficiency. Therefore, when Ni is contained, the Ni content is preferably 2.00% or less. If necessary, the Ni content may be 1.20% or less, 0.80% or less, or 0.50% or less.

[0279] [Cu: 0 to 1.000%] Cu is an element that improves the hardenability of steel and enables the strength of steel plate members to be stably ensured after quenching. Cu also improves pitting corrosion resistance in corrosive environments. In order to fully realize this effect, the Cu content is preferably 0.100% or more. On the other hand, by setting the Cu content to 1.000% or less, the above effects can be fully obtained while improving economic efficiency. Therefore, when Cu is contained, the Cu content is preferably 1.000% or less. If necessary, the Cu content may be 0.600% or less, 0.400% or less, or 0.200% or less.

[0280] [Mo: 0 to 1.00%] Mo is an element that improves the hardenability of steel and enables the strength of steel plate members to be stably ensured after quenching. To fully realize this effect, the Mo content is preferably 0.10% or more. On the other hand, by setting the Mo content to 1.00% or less, the above effects can be fully obtained while improving economic efficiency. Therefore, when Mo is contained, the Mo content is preferably 1.00% or less. If necessary, the Mo content may be 0.60% or less, 0.40% or less, or 0.20% or less.

[0281] [V: 0 to 1.00%] V is an element that improves the hardenability of steel and enables the strength of steel plate members to be stably ensured after quenching. In order to fully realize this effect, the V content is preferably 0.10% or more. On the other hand, by setting the V content to 1.00% or less, the above-mentioned effect can be fully obtained while improving economic efficiency. Therefore, when V is contained, the V content is preferably 1.00% or less. If necessary, the V content may be 0.60% or less, 0.40% or less, or 0.20% or less.

[0282] [Nb: 0 to 1.00%] Nb is an element that improves the hardenability of steel and enables the strength of steel plate members to be stably ensured after quenching. In order to fully realize this effect, the Nb content is preferably 0.01% or more. On the other hand, by setting the Nb content to 1.00% or less, the above-mentioned effects can be fully obtained while improving economic efficiency. Therefore, when Nb is contained, the Nb content is preferably 1.00% or less. If necessary, the Nb content may be 0.50% or less, 0.20% or less, or 0.10% or less.

[0283] [Sn: 0 to 1.00%] Sn is an element that improves pitting corrosion resistance in a corrosive environment. To fully exert this effect, the Sn content is preferably 0.01% or more. On the other hand, when the Sn content is 1.00% or less, a decrease in grain boundary strength is suppressed, and a decrease in toughness can be suppressed. Therefore, when Sn is contained, the Sn content is preferably 1.00% or less. If necessary, the Sn content may be 0.40% or less, 0.10% or less, or 0.05% or less.

[0284] [W: 0 to 1.00%] W is an element that improves the hardenability of steel and enables the strength of steel plate members to be stably ensured after quenching. W also improves pitting corrosion resistance in corrosive environments. In order to fully exert this effect, the W content is preferably 0.01% or more. On the other hand, by setting the W content to 1.00% or less, the above effects can be fully obtained while improving economic efficiency. Therefore, when W is contained, the W content is preferably 1.00% or less. If necessary, the W content may be 0.60% or less, 0.40% or less, or 0.20% or less.

[0285] [Ca: 0 to 0.010%] Ca is an element that has the effect of refining inclusions in steel and improving toughness and ductility after quenching. In order to fully exert this effect, the Ca content is preferably 0.001% or more, and more preferably 0.002% or more. On the other hand, a Ca content of 0.010% or less can fully obtain this effect while suppressing costs. Therefore, when Ca is contained, the Ca content is preferably 0.010% or less, and more preferably 0.004% or less. If necessary, the Ca content may be 0.008% or less, 0.006% or less, or 0.0004% or less.

[0286] [REM: 0 to 0.30%] Like Ca, REM is an element that has the effect of refining inclusions in steel and improving toughness and ductility after quenching. In order to fully exert this effect, the REM content is preferably 0.001% or more, and more preferably 0.002% or more. On the other hand, by setting the REM content to 0.30% or less, the effect can be fully obtained while reducing costs. Therefore, when REM is contained, the REM content is preferably 0.30% or less, and more preferably 0.20% or less. If necessary, the REM content may be 0.10% or less, 0.05% or less, or 0.02% or less.

[0287] Here, REM refers to a total of 17 elements, including Sc, Y, and lanthanoids, and the REM content refers to the total content of these elements. REM is added to molten steel using, for example, an Fe—Si—REM alloy, and this alloy contains, for example, Ce, La, Nd, and Pr.

[0288] The balance other than the above components is Fe and impurities. In addition to the above components, the base steel plate B2-11 may also contain impurities that are mixed in during the manufacturing process, etc., as long as they do not impair the effects of this elemental technology. Examples of such impurities include Zn (zinc) and Co (cobalt).

[0289] The chemical composition of the base steel sheet B2-11 of the aluminum-plated steel sheet for hot stamping B2-10 described above may be measured by a general analytical method. For example, it may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). C and S may be measured using a combustion-infrared absorption method, N may be measured using an inert gas fusion-thermal conductivity method, and O may be measured using an inert gas fusion-non-dispersive infrared absorption method. When the steel sheet for hot stamping has a plating layer on its surface, the plating layer on the surface may be removed by mechanical grinding before analyzing the chemical composition.

[0290] The surface of the plated steel sheet B2-11 having the above-mentioned chemical composition and the aluminum plating layer B2-12, on which the surface treatment film B2-13 is applied, can be made into a hot stamped member having high tensile strength by heating and quenching using a hot stamping method. In addition, the hot stamping method allows press working to be performed in a softened state at high temperatures, making it easy to form.

[0291] (Method for manufacturing aluminum-plated steel sheet for hot stamping) Hereinafter, an example of a method for manufacturing an aluminum-plated steel sheet for hot stamping according to this embodiment will be described. Note that the method for manufacturing the aluminum-plated steel sheet for hot stamping according to this embodiment is not particularly limited as long as it has the above-described configuration. The manufacturing method described below is one example for manufacturing the aluminum-plated steel sheet for hot stamping according to this embodiment, and is a suitable example of the method for manufacturing the aluminum-plated steel sheet for hot stamping according to this embodiment.

[0292] <Base Steel Sheet> The base steel sheet to be subjected to aluminum plating is not particularly limited as long as it is a steel sheet that can be suitably used in hot stamping. Examples of the form of the base steel sheet include a hot-rolled steel sheet and a cold-rolled steel sheet.

[0293] <Formation of Aluminum Plating Layer> Methods for forming an aluminum plating layer include, but are not limited to, hot-dip plating, electroplating, physical vapor deposition, chemical vapor deposition, etc. An aluminum plating layer is formed on the surface of a base steel sheet by a known method.

[0294] <Method for Producing Surface Treatment Film> The method for producing the surface treatment film is not particularly limited, but examples include a method in which the respective film-forming components are mixed, stirred with a disperser, dissolved or dispersed, and the resulting mixed treatment liquid is applied to the plating layer, followed by drying. The mixed treatment liquid is produced, for example, by preparing a treatment liquid of compound A and a treatment liquid of compound B, adjusting the pH, and then mixing each treatment liquid with other optional components such as a resin. A specific description will be given below.

[0295] Examples of the compound A contained in the surface treatment film include carbon black, graphite, soot, etc. In the method for producing the surface treatment film, it is preferable to use a treatment liquid in which powders of these compounds are dispersed in water or the like.

[0296] Compound A is pulverized by a machine or the like to a powder diameter (particle size) of 30 to 300 nm, and then compound A is introduced into a treatment solution containing sodium hydroxide and adjusted to a pH of 9.0 to 13.0. The treatment solution containing compound A is then stirred at 50 to 80°C for 1 to 4 days as a pretreatment, thereby enabling compound A with particle sizes of 30 to 300 nm to be more stably dispersed in the treatment solution. Furthermore, when a surface treatment film is formed, compound A can be uniformly present in the film layer, thereby improving the temperature rise characteristics.

[0297] Furthermore, the carbon concentration of compound A in the coating can be increased by heating a treatment solution containing compound A at a pH of 9.0 to 13.0 at 50 to 80°C for one to four days (i.e., by satisfying the pretreatment conditions described above). When the treatment solution is subjected to this pretreatment, areas of low carbon concentration on the outside of the compound A particles (e.g., areas with high ratios of oxygen (O), nitrogen (N), sulfur (S), etc.) are dissolved by the treatment solution containing sodium hydroxide, leaving areas of high carbon concentration on the inside of the particles. This can also increase the carbon concentration of compound A in the coating. On the other hand, if the pretreatment conditions described above are not satisfied (e.g., if the stirring time is less than one day), the amount of dissolution of the areas of low carbon concentration on the outside of the compound A particles decreases, resulting in a relative decrease in the carbon concentration of compound A in the coating. Therefore, in order to sufficiently increase the carbon concentration of compound A in the coating, it is necessary to control the pretreatment conditions described above before applying the treatment solution.

[0298] Similarly, the compound B, which is an oxide or fluoride of the metal element M and has a rutile structure, may be used in the form of a powder or a treatment liquid dispersed in water or a solvent.

[0299] Compound B is pulverized by a machine or the like to a powder diameter (particle size) of 10 to 300 nm, and then introduced into a treatment solution containing sodium fluoride and adjusted to a pH of 3 to 7, followed by stirring at 50 to 80°C for 4 to 24 hours as a pretreatment. This allows compound B with a particle size of 10 to 300 nm to be more stably dispersed in the treatment solution. As a result, when a surface treatment film is formed, compound B can be present in the film in the form described below, thereby improving the temperature rise characteristics.

[0300] The surface treatment film of this embodiment can be obtained by using a mixed treatment liquid in which a binder component (resin) is appropriately added to the raw materials and treatment liquid screened in this manner.

[0301] The method for producing a mixed treatment liquid by combining a treatment liquid of compound A and a treatment liquid of compound B is not particularly limited. For example, the treatment liquid containing compound A and the treatment liquid containing compound B obtained by the above method are mixed, stirred with a disperser to dissolve or disperse the mixture, and then a binder (resin) or silica is added as needed. A known hydrophilic solvent or the like may be added as needed to improve the solubility or dispersibility of each film-forming component. An acid, alkali, or the like may be added to the treatment liquid to adjust the pH, as long as the performance of the treatment liquid is not impaired. The method for producing a mixed treatment liquid is specifically described below.

[0302] To achieve a surface treatment film that satisfies the above formulas (1) and (2), first, compound A and compound B are each dispersed in water or a mixed solution of water and a solvent such as ethanol, and each treatment liquid is prepared by the above-mentioned preparation method. Then, a binder component (e.g., resin) and the treatment liquid of compound A are mixed, followed by mixing with the treatment liquid of compound B to prepare a mixed treatment liquid. After stirring the treatment liquid of compound B at pH 3 to 7 for 4 to 25 hours at 30 to 50°C, the pH of the treatment liquid of compound B is adjusted to 8 or higher using ammonia water or the like just before mixing with the treatment liquid of compound A. Furthermore, when silica is to be contained in the surface treatment film, it is advisable to add the silica after mixing the treatment liquid of compound B with the mixed solution. In order to achieve a compound A content of 30% or higher at the interface side position P of the surface treatment film, the concentration (content) of compound A in the mixed treatment liquid is set to 15% by dry weight (mass) or higher. In order to achieve a compound A content of 80% or less at the interface side position P of the surface treatment film, the concentration (content) of compound A in the mixed treatment liquid is set to 50 mass% or less in terms of dry weight (mass). In order to satisfy formulas (1) and (2) regarding the concentration of metal element M, the concentration (content) of compound B in the mixed treatment liquid is set to 3 to 50 mass% in terms of dry weight (mass). The total concentration (content) of compound A and compound B in the mixed treatment liquid is set to 18 to 90% in terms of dry weight (mass). Next, it is preferable to stir the obtained mixed treatment liquid at 150 rpm to 300 rpm immediately before coating, and to apply the mixed treatment liquid after stirring within 5 seconds.

[0303] In order to realize a surface treatment film that satisfies the above formulas (1) and (2), a shear rate of 10 －３ The dynamic viscosity of the mixed treatment liquid at 2000 kJ / s is set to 3 to 16 mPa·s, and the surface tension is set to 20 to 60 mN / m. When the dynamic viscosity is less than 3 mPa·s, ｂＭ / C ｔＭ If the dynamic viscosity exceeds 16 mPa·s, the desired temperature rise rate may not be obtained. Therefore, the dynamic viscosity of the mixed treatment liquid is set to 3 mPa·s or more, and preferably 6 mPa·s or more. On the other hand, if the dynamic viscosity exceeds 16 mPa·s, the C ｂＭ / C ｔＭIf the dynamic viscosity of the mixed treatment liquid is less than 1.5, the desired temperature rise rate may not be obtained. Therefore, the dynamic viscosity of the mixed treatment liquid is set to 16 mPa·s or less, and preferably 12 mPa·s or less.

[0304] In addition, when the surface tension of the mixed treatment liquid is less than 20 mN / m, C ｂＭ If the surface tension of the mixed treatment liquid is less than 1 mass %, the desired rate of temperature rise cannot be obtained. Therefore, the surface tension of the mixed treatment liquid is set to 20 mN / m or more, and preferably 30 mN / m or more. On the other hand, if the surface tension exceeds 60 mN / m, the desired rate of temperature rise cannot be obtained. Therefore, the surface tension of the mixed treatment liquid is set to 60 mN / m or less, and preferably 40 mN / m or less.

[0305] To form the surface treatment film layer, a treatment solution is applied to the aluminum plating layer (or chemical conversion treatment layer) and the applied film is dried by heating. The method for applying the treatment solution is not particularly limited, and generally known application methods such as roll coating and immersion are possible.

[0306] In order to control compound B to have a predetermined concentration distribution as represented by formula (1) and formula (2), the ultimate heating and drying temperature after application is set to 55°C to 120°C. Here, the "ultimate temperature" refers to the temperature of the surface of the base steel sheet. If the ultimate temperature is less than 55°C, the evaporation rate of water is slow and sufficient film formation is not achieved, which may result in insufficient film adhesion. Furthermore, if the ultimate temperature is too low, the evaporation rate of the treatment solution is slow, so that the metal element M in compound B concentrates on the Al plating layer side, and C ｂＭ / C ｔＭ becomes excessively high. As a result, heat absorption on the surface side of the surface treatment film B2-13 is insufficient, which may result in deterioration of the temperature rise characteristics during hot stamping. On the other hand, if the ultimate temperature exceeds 120°C, the binder components may be denatured due to thermal decomposition or the like, which may result in a decrease in adhesion and corrosion resistance. The ultimate temperature is more preferably 65 to 100°C.

[0307] In addition, if the time taken for the temperature of the surface of the base steel sheet to reach 65°C from 25°C is t1 (or the final temperature of the base material if it does not reach 65°C), and the time taken for the temperature to drop from 65°C (or the final temperature of the base material) to 40°C by cooling is t2, t1 is set to 1.5 to 14.0 seconds, t2 is set to 0.5 to 8.6 seconds, and t1 / t2 is set to the range of 0.35 to 10.0. As a result, the concentration distribution C of compound B in the surface treatment film ｂＭ / C ｔＭ This makes it easier to control the temperature, and the temperature rise rate is further improved.

[0308] Furthermore, when the time required for the temperature of the surface of the base steel sheet to reach 55°C from 25°C is t3, t3 is set to 5.0 seconds to 12.0 seconds, thereby making it possible to set the content of compound A at the interface side position P to 30 to 80%.

[0309] The method for heating and drying the treatment liquid after application is not particularly limited, and examples thereof include hot air, induction heating, near infrared rays, direct flame, etc., either alone or in combination. Water or a solvent can be used as a component in the treatment liquid that disperses or dissolves the resin.

[0310] (Method for manufacturing hot-stamped member) Various hot-stamped members, such as automotive frame parts, can be manufactured using an aluminum-plated steel sheet for hot stamping having the above-described surface treatment film applied to the entire surface of at least one surface.

[0311] First, for example, an aluminum-plated steel sheet provided with a surface treatment film is subjected to various processes such as cutting or punching with a press to obtain the aluminum-plated steel sheet for hot stamping according to this embodiment. Alternatively, the aluminum-plated steel sheet for hot stamping according to this embodiment can also be obtained by providing a surface treatment film on an aluminum-plated steel sheet that has been cut or punched with a press. Furthermore, by partially reducing the thickness of the surface treatment film, for example, in applications where multiple steel sheets are welded together before hot stamping, current can be more easily passed through the surface, thereby improving spot weldability.

[0312] The aluminum-plated steel sheet for hot stamping having the surface treatment film applied thereto as described above is hot stamped. Examples of heating devices include an electric heating furnace, a gas heating furnace, a far-infrared furnace, and a conventional heating device equipped with an infrared heater. The surface on which the surface treatment film is applied and has increased emissivity has a high heat-up rate due to a large heat transfer effect caused by radiation. Therefore, the temperature is rapidly raised to a temperature equal to or higher than the Ac3 point at which the metal structure transforms to the austenite phase. Thus, the method for producing a hot-stamped member according to this embodiment can shorten the heating time, thereby further improving the productivity of hot-stamped members. In this embodiment, the specific heating conditions are not particularly limited, and the heating device used may be appropriately controlled.

[0313] Next, the heated steel sheet is formed and cooled. The portion heated to or above the Ac3 point temperature at which the metal structure of the steel material transforms into an austenite phase is quenched simultaneously with forming, thereby increasing the strength. This allows a hot-stamped part with improved strength to be obtained. (Example)

[0314] While examples of the present elemental technology are described below, the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present elemental technology, and the present invention is not limited to these examples. Various conditions may be adopted for the present elemental technology as long as they do not deviate from the gist of the present elemental technology and achieve the purpose of the present elemental technology.

[0315] It is preferable to use a steel sheet having high mechanical strength (meaning various properties related to mechanical deformation and fracture, such as tensile strength, yield point, elongation, reduction of area, hardness, impact value, fatigue strength, etc.) as the base steel sheet. The chemical compositions of the base steel sheets before plating used in the hot stamping steel sheets shown in the following examples are shown in Table 11 below.

[0316]

[0317] For base steel sheets (steel Nos. S1 to S10) having the chemical compositions shown in Table 11, steel sheets (base steel sheets) measuring 100 mm in width, 200 mm in length, and 2.3 mm in thickness were prepared, and an aluminum plating layer and a surface treatment film were applied to the entire surfaces of both sides of the base steel sheets by the method described below. Here, the notation "-" in Table 11 means that the content of the corresponding element is 0% in significant figures (numerical values ​​down to the least significant digit) specified in this embodiment.

[0318] First, an aqueous treatment liquid (solvent: water) containing at least one of carbon black (CB), graphite, and soot, pulverized to a powder diameter (particle size) of 30 to 300 nm, was prepared as Compound A. Another aqueous treatment liquid (solvent: water) containing a metal oxide or metal fluoride, pulverized to a powder diameter (particle size) of 30 to 300 nm, was prepared as Compound B. The two treatment liquids were then mixed, and a polyurethane resin was added to the resulting solution. This treatment liquid was then applied to the aluminum plating layer and dried to form a surface treatment film. The thickness of the surface treatment film was within the range of 1.0 to 2.5 μm, and the same type of film was applied to both sides.

[0319] Tables 12A and 12B list the methods for producing surface treatment films, including the types of compounds and additives used. In all of the production methods shown in Tables 12A and 12B, polyurethane resin was added so that its solid content in the treatment solution was 10 to 92 mass %. In addition, in all of the production methods shown in Tables 12A and 12B, sodium fluoride was used as an additive when preparing compound B. When compound A and compound B were mixed, the treatment solutions were adjusted to have the dry weight ratios shown in Tables 12A and 12B. Note that underlines in Tables 12A and 12B indicate conditions outside the preferred conditions of the production method of this elemental technology. In addition, the dynamic viscosity (mPa s) shown in Tables 12A and 12B was measured at a shear rate of 10 －３ "Time t1", "Time t2", and "Time t3" shown in Tables 12A and 12B respectively indicate "the time until the temperature of the surface of the base steel plate reaches 65°C from 25°C", "the time until the temperature of the surface of the base steel plate falls from 65°C to 40°C", and "the time until the temperature of the surface of the base steel plate reaches 55°C from 25°C".

[0320]

[0321]

[0322] Thereafter, a thermocouple was connected to the surface of the aluminum-plated steel sheet (aluminum-plated steel sheet for HS) to which the surface treatment film had been applied so that the temperature at each position could be measured. The aluminum-plated steel sheet for HS was then heated in an electric heating furnace set at a temperature of 940°C, and when the surface temperature reached 930°C, the aluminum-plated steel sheet for HS was removed from the heating furnace. Thereafter, the aluminum-plated steel sheet for HS was rapidly cooled using a flat die to obtain a hot-stamped member.

[0323] In this example, the base steel sheet was plated with Al-10 mass% Si by hot-dip galvanization, and then the above-mentioned surface treatment film was applied. In the case of the hot-dip galvanization, the base steel sheet was immersed in a plating bath, and then the coating amount was adjusted to 100 g / m per side by gas wiping. ２ was adjusted to.

[0324] The coating composition, temperature rise rate (temperature rise characteristics), and coating adhesion of the surface treatment coating were investigated. Note that hot stamped components are not necessarily used as components that are subjected to sliding, etc. Therefore, in this example, coating adhesion is not an essential characteristic that hot stamped components must have, but is a preferable characteristic that they should have.

[0325] The evaluation methods for each evaluation item were as follows.

[0326] (1) Heating Rate (Heating Characteristics) (Rating Score) The heating rate of each aluminum-plated steel sheet for HS was calculated from the temperature change obtained from the thermocouple attached to the aluminum-plated steel sheet for HS and the heating time in the electric heating furnace, and evaluation was performed. Specifically, the heating rate from room temperature to 910°C was calculated, and evaluation was performed based on the following evaluation criteria. A rating of "2" or higher was considered to be acceptable.

[0327] (Rating) 4: Temperature rise rate of 5.7°C / s or more 3: Temperature rise rate of 4.3°C / s or more and less than 5.7°C / s 2: Temperature rise rate of 3.5°C / s or more and less than 4.3°C / s 1: Temperature rise rate less than 2.5°C / s

[0328] (2) Film Adhesion The obtained hot stamped molded body was placed in a rubbing tester (Imoto Manufacturing Co., Ltd., "Rubbing Tester 1509"), and then absorbent cotton impregnated with ethanol was rubbed against the surface with a stroke distance of 100 mm, a speed of 30 reciprocations per minute, and a load of 0.5 kgf / cm. ２ After sliding (back and forth) 10 times, the film condition was evaluated according to the following criteria.

[0329] (Rating) 3: No marks at all on the entire sliding portion 2: Slight marks on part of the sliding portion 1: No coating on the sliding portion

[0330] Example 1 In Table 13, B1 to B16 are invention examples, and b1 to b10 are comparative examples. In this example, when preparing the aqueous treatment liquid, carbon black (CB), graphite, soot powder, and an aqueous dispersion were used as compounds other than the binder component.

[0331] In Comparative Example b1, the carbon concentration of Compound A was low at 71%. In Comparative Examples b2 to b4, Compound B did not have a rutile structure. In Comparative Examples b5, b8, and b10, formula (1) was not satisfied. In Comparative Examples b5, b6, b7, b8, and b9, formula (2) was not satisfied. In Comparative Examples b1 to b10, the temperature rise rate was scored as 1, whereas in Invention Examples B1 to B16, the temperature rise rate was scored as 2 or 3.

[0332]

[0333] Example 2 As shown in Table 14, invention examples C2 to C11, in which the compound A content at a position 0.90H from the surface of the surface treatment film (i.e., interface-side position P) was 30 to 90%, had a superior heating rate to example C1, in which the compound A content at the same position was 20%.

[0334]

[0335] Example 3 As shown in Table 15, compound B was replaced with TiO ２ Inventive Examples D6 to D9, Compound B was IrO ２ Compound B was replaced with GeO ２ The temperature rise rate was superior to that of invention example D5.

[0336]

[0337] <<Elemental Technologies B3a and B3b>> The elemental technology B3a is a structural member comprising: a member body formed by a plurality of steel plates joined together, the member body having an annular shape in a plan view, the plurality of steel plates including a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate; and a metal oxide layer formed on the first steel plate, the metal oxide layer containing at least one oxide selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide at a concentration of 0.001 g / m ２ The elemental technology B3b is a structural member comprising: a component body having an annular shape in a plan view, the component body being formed by a plurality of steel plates joined together, the first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate; and a coating provided on the first steel plate, the coating containing carbon black at a concentration of 0.500 g / m ２ and a coating containing the following:

[0338] The objective of elemental technologies B3a and B3b is to provide a hot stamping blank that can improve the performance of an annular structural component, particularly a large annular structural component, when the component is formed from a steel plate having a thickness smaller than that of other steel plates.

[0339] A hot stamping blank according to an embodiment includes a plurality of steel plates. The plurality of steel plates are arranged and joined to form an annular shape in a plan view of the blank. The plurality of steel plates include a first steel plate and a second steel plate. The first steel plate has the smallest thickness among the plurality of steel plates. The second steel plate has a thickness greater than that of the first steel plate. The first steel plate is configured so that the emissivity of at least one of both surfaces of the first steel plate is greater than the emissivity of both surfaces of the second steel plate (first configuration).

[0340] The blank according to the first configuration includes a first steel plate having a minimum thickness and a second steel plate having a thickness greater than that of the first steel plate. The emissivity of at least one surface of the first steel plate is greater than the emissivity of both surfaces of the second steel plate. This allows for an increased heating rate of the thin-walled portion of the first steel plate when the blank is heated during hot stamping. Therefore, the first steel plate can be heated to the austenite temperature more quickly, ensuring a longer holding time for the first steel plate at that temperature. This allows for coarsening of austenite grains in the first steel plate. As a result, the ferrite transformation region (ferrite nose) in the CCT diagram shifts to the long-time side, delaying the onset of ferrite transformation in the first steel plate after heating of the blank is completed. This allows blank forming to begin while maintaining the microstructure of the first steel plate in the austenite phase. In other words, the hardenability of the thin-walled first steel plate can be improved.

[0341] In the blank according to the first configuration, the hardenability of the first steel plate having a smaller thickness is improved, and therefore the first steel plate can be well hardened when a structural component is formed from the blank by hot stamping. This facilitates uniform hardness in the structural component, thereby preventing partial reductions in the structural component's strength. Furthermore, because uneven stress is less likely to occur in the structural component, twisting is less likely to occur even when the formed structural component is annular, ensuring good dimensional accuracy in the structural component. Therefore, when an annular structural component, particularly a large annular structural component, including a first steel plate having a smaller thickness than the second steel plate is formed from the blank, poor strength and dimensional accuracy of the structural component can be reduced, and the impact absorption performance (crash resistance) of the structural component can be improved.

[0342] In the blank according to the first configuration, the emissivity of the first steel sheet with the minimum thickness is higher than that of the second steel sheet with a relatively large thickness. In this case, the first steel sheet heats up faster than the second steel sheet, and the high-temperature holding time of the first steel sheet, i.e., the time from when the first steel sheet reaches the austenite temperature range until the second steel sheet and the entire blank reach the austenite temperature range, is longer than when the first steel sheet has the same emissivity as the second steel sheet. This reduces non-uniformity in phase transformation due to differences in cooling rates between the steel sheets after the blank is heated. Specifically, the initiation of the austenite-to-ferrite phase transformation in the first steel sheet with the minimum thickness can be delayed, thereby reducing the difference in the phase transformation initiation time between the first steel sheet with the minimum thickness and the other steel sheets. As a result, the hardenability can be made uniform between the first steel sheet with the minimum thickness and the other steel sheets.

[0343] In the first configuration, the first steel plate may have a plate thickness of less than 1.4 mm (second configuration).

[0344] When the thickness of the first steel plate is less than 1.4 mm as in the second configuration, the first steel plate is particularly susceptible to heat dissipation after the heating of the blank is completed, making the hardenability of the first steel plate more likely to deteriorate. However, even when the thickness of the first steel plate is less than 1.4 mm, by increasing the emissivity of at least one surface of the first steel plate compared to the relatively thick second steel plate, it is possible to promote the temperature rise of the first steel plate when the blank is heated during hot stamping, thereby ensuring a long high-temperature holding time for the first steel plate. Therefore, the hardenability of the first steel plate can be improved.

[0345] In the first or second configuration, the first steel sheet may be a plated steel sheet. In this case, the first steel sheet may have a base steel sheet and an aluminum-based plating layer provided on the base steel sheet (third configuration).

[0346] When the first steel sheet is a plated steel sheet having an aluminum-based plating layer, as in the third configuration, the temperature rise rate of the first steel sheet tends to be slow when the blank is heated during hot stamping. Because the aluminum-based plating layer is nearly white, it tends to reflect heat energy and inhibit the temperature rise of the first steel sheet. However, even when the first steel sheet is a plated steel sheet having an aluminum-based plating layer, by increasing the emissivity of at least one surface of the first steel sheet compared to that of a relatively thick second steel sheet, the temperature rise of the first steel sheet can be promoted when the blank is heated during hot stamping. This allows the first steel sheet to be held at a high temperature for a long time, thereby improving the hardenability of the first steel sheet.

[0347] In any of the first to third configurations, at least one surface of the first steel plate may be coated with a coating having an emissivity of 60% or more at a wavelength of 8.0 μm at 25°C (fourth configuration).

[0348] In any one of the first to third configurations, at least one surface of the first steel plate may be coated with a coating, which comprises carbon black, one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide, and a 0 to 0.30 g / m ２ The content of carbon black in the coating can be X ＣＢ (g / m ２ ), the oxide content is X Ｏｘｉｄｅ (g / m ２ ) and then X ＣＢ and X Ｏｘｉｄｅ It is preferable that the following formula (1) (see International Publication No. 2022 / 215229) is satisfied (fifth configuration): 118.9≦24280 / {6700 / (100+76×X ＣＢ ) + 18000 / (130 + 65 x X Ｏｘｉｄｅ )≦332.0 (1)

[0349] In any one of the first to fifth configurations, the first steel sheet may be a plated steel sheet having a base steel sheet and a plating layer provided on the base steel sheet. In this case, the plate thickness of the first steel sheet may be t ｍｉｎThe thickness of the steel plate having the largest thickness among the plurality of steel plates is t ｍａｘ When 1.0<t ｍａｘ / t ｍｉｎ It is preferable that the ratio is ≦3.2 (sixth configuration).

[0350] Among the multiple steel plates included in the blank, the smallest plate thickness t ｍｉｎ The first steel plate having a maximum plate thickness t ｍａｘ When the difference in thickness between the steel plate and other steel plates having the minimum thickness t is large, it becomes difficult to ensure the process window in the manufacture of structural members. ｍｉｎ and maximum plate thickness t ｍａｘ If the difference is large, when the blank is heated during hot stamping, the maximum plate thickness t ｍａｘ While waiting for the steel sheet having the minimum sheet thickness t to reach the austenite temperature range, alloying of the coating layer of the first steel sheet, which has been heated to the austenite temperature range in advance, progresses, and the diffusion layer becomes thick, which may make it impossible to ensure the corrosion resistance or weldability of the first steel sheet due to the coating layer. ｍｉｎ Maximum plate thickness t ｍａｘ The ratio is set to 3.2 or less. ｍａｘ The temperature rise rate and minimum plate thickness t of the steel plate ｍｉｎ Since the heating rate of the first steel sheet does not deviate too much from the heating rate of the other steel sheet, heating of the other steel sheet can be completed before excessive alloying of the coating layer of the first steel sheet progresses. Therefore, a structural component can be manufactured while maintaining the corrosion resistance or weldability of the first steel sheet, and a process window can be secured in the manufacture of the structural component.

[0351] In any one of the first to sixth configurations, the first steel sheet may be a plated steel sheet having a base steel sheet and a plating layer provided on the base steel sheet. The blank may further include an overlap portion. The overlap portion is formed by overlapping the ends of two adjacent steel sheets among the plurality of steel sheets, the steel sheets being other than the second steel sheet. The overlap portion may have a total thickness of greater than 2.5 mm and not greater than 4.0 mm. In this case, it is preferable that the emissivity of each of the two steel sheets at the surface located outside the overlap portion is greater than the emissivity of both surfaces of the second steel sheet (seventh configuration).

[0352] When a blank has an overlap portion formed by overlapping the ends of two steel sheets, it may be impossible to ensure a process window for manufacturing a structural component. Specifically, if the steel sheets included in the blank have different thicknesses and the total thickness of the overlap portion exceeds 2.5 mm, when the blank is heated during hot stamping, alloying of the coating layer of the first steel sheet with the smallest thickness may progress while waiting for the overlap portion to reach the austenite temperature range, resulting in a thick diffusion layer, making it impossible to ensure the corrosion resistance or weldability of the first steel sheet. Therefore, in the seventh configuration, the emissivity of the outer surface of the overlap portion is increased on each of the two steel sheets forming the overlap portion. This accelerates the temperature rise of the overlap portion, allowing heating of the overlap portion to be completed before excessive alloying of the coating layer of the first steel sheet progresses, thereby enabling the structural component to be manufactured while maintaining the corrosion resistance or weldability of the first steel sheet. In other words, it is easier to ensure a process window for manufacturing a structural component. However, even if the emissivity of the overlapping portion is increased, if the total thickness of the overlapping portion becomes excessively large, it becomes difficult to ensure a process window, so it is preferable that the total thickness of the overlapping portion be 4.0 mm or less.

[0353] A method for manufacturing a structural component according to an embodiment includes the steps of preparing a blank according to any one of the first to seventh configurations, heating a plurality of steel plates included in the blank to a temperature equal to or higher than the austenite transformation completion temperature, and using a mold to form the heated blank into a structural component that is annular in plan view and quenching it (eighth configuration).

[0354] A structural member according to an embodiment includes a member body and a coating. The member body is formed by a plurality of steel plates joined together and has an annular shape in plan view. The plurality of steel plates include a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate. The coating is provided on the first steel plate. The coating contains one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide at a concentration of 0.001 g / m ２ or more (ninth configuration).

[0355] A structural member according to an embodiment includes a member body and a coating. The member body is formed by a plurality of steel plates joined together and has an annular shape in plan view. The plurality of steel plates includes a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate. The coating is provided on the first steel plate. The coating contains carbon black at a concentration of 0.500 g / m. ２ The following is contained (tenth configuration).

[0356] In the ninth or tenth configuration, the structural member may be a door ring part of an automobile. In this case, the member body may include a front pillar, a center pillar, and a rocker connecting the front pillar and the center pillar (eleventh configuration).

[0357] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or equivalent components are designated by the same reference numerals, and the same description will not be repeated.

[0358] <First embodiment> [Structural member] Fig. 16 is a diagram (plan view) of a structural member B3-10 according to this embodiment, viewed from above when placed on a horizontal surface. The structural member B3-10 is used, for example, in the body of an automobile. The structural member B3-10 is typically a door ring component of an automobile. In this embodiment, an example in which the structural member B3-10 is a door ring component will be described.

[0359] The structural member B3-10 is a hot-stamped member. That is, the structural member B3-10 is formed by hot stamping (hot press processing) a blank made of multiple steel plates. The structural member B3-10 includes a member body B3-11. The member body B3-11 has an annular shape in a plan view of the structural member B3-10. The member body B3-11 includes a front pillar B3-111, a center pillar B3-112, and a rocker B3-113. When the structural member B3-10 is assembled to the body of an automobile, the center pillar B3-112 is disposed behind the front pillar B3-111. The center pillar B3-112 extends generally in the vertical direction of the vehicle body. The front pillar B3-111 extends toward the center pillar B3-112. When the structural member B3-10 is mounted on the body of an automobile, the rocker B3-113 is disposed below the front pillar B3-111 and the center pillar B3-112. The rocker B3-113 connects the front pillar B3-111 and the center pillar B3-112.

[0360] In this embodiment, the member body B3-11 is formed of multiple steel plates B3-21, 22, and 23 joined together. In the example of Fig. 16, the front pillar B3-111 is mainly formed of steel plates B3-21 and 22. The center pillar B3-112 is mainly formed of steel plate B3-23. The rocker B3-113 is also formed of steel plates B3-21 and 23.

[0361] Figure 17 is a cross-sectional view taken along line II-II of Figure 16. Figure 17 shows a cross-section of the structural member B3-10 cut along the thickness direction at the position of the steel plate B3-21. As shown in Figure 17, the steel plate B3-21 has an open cross-section. In a cross-sectional view of the structural member B3-10, the steel plate B3-21 has, for example, a roughly hat-like shape. More specifically, the steel plate B3-21 includes a top plate B3-211, vertical walls B3-212 and B3-213, and flanges B3-214 and B3-215. The vertical wall B3-212 is located on the opposite side of the vertical wall B3-213 from the top plate B3-211. In a cross-sectional view of the structural member B3-10, one end of the vertical walls B3-212 and B3-213 is connected by the top plate B3-211. In a cross-sectional view of the structural member B3-10, flanges B3-214 and 215 are connected to the other ends of the vertical walls B3-212 and 213, respectively. The flanges B3-214 and 215 protrude from the vertical walls B3-212 and 213, respectively, to the outside of the structural member B3-10.

[0362] In the structural member B3-10, the width W of the steel plate B3-21 may be 30 mm or more and 750 mm or less. The height H of the steel plate B3-21 may be 25 mm or more and 150 mm or less. The width W is the distance from the end of the R on the vertical wall B3-212 side of the corner portion between the top plate B3-211 and the vertical wall B3-212 to the end of the R on the vertical wall B3-213 side of the corner portion between the top plate B3-211 and the vertical wall B3-213 in the cross section of the structural member B3-10. The height H is the distance from the top plate B3-211 to the flanges B3-214 and B3-215 along the thickness direction of the top plate B3-211.

[0363] Although not shown in the figures, the other steel plates B3-22 and B3-23 also have an open cross section similar to the steel plate B3-21. The steel plates B3-22 and B3-23 may also have, for example, a generally hat-shaped cross section of the structural member B3-10. The width of the steel plates B3-22 and B3-23 may be 15 mm or more and 300 mm or less. The height of the steel plates B3-22 and B3-23 may be 10 mm or more and 150 mm or less.

[0364] The size of the annular structural member B3-10 in a plan view is, for example, 1.0 m or more. The size of the structural member B3-10 may be, for example, 4.0 m or less. The size of the structural member B3-10 is the length of the line segment connecting the two farthest points on the outer periphery of the structural member B3-10 when the structural member B3-10 is placed on a horizontal surface and viewed vertically.

[0365] [Method for manufacturing a structural member] A method for manufacturing a structural member B3-10 will be described below with reference to Figures 18A to 18G. The method for manufacturing a structural member B3-10 according to this embodiment includes the steps of preparing a blank B3-20, heating the blank B3-20, and forming the heated blank B3-20 into a structural member B3-10.

[0366] 18A, in the preparation step, a blank B3-20 having a shape obtained by unfolding the structural member B3-10 is prepared. The blank B3-20 includes a plurality of steel plates B3-21, 22, and 23. The steel plates B3-21, 22, and 23 are arranged and joined so as to have an annular shape in a plan view of the blank B3-20.

[0367] Figures 18B, 18C, and 18D are cross-sectional views of blank B3-20 showing the joints of steel plates B3-21, 22, and 23. Figures 18B, 18C, and 18D are cross-sectional views taken along lines IIIB-IIIB, IIIC-IIIC, and IIID-IIID in Figure 18A, respectively. Referring to Figures 18B and 18C, steel plate B3-21 is butt-joined to each of steel plates B3-22 and B3-23. That is, the end faces of steel plate B3-21 are joined with the end face of steel plate B3-22 abutting against the end face of steel plate B3-22, and the other end face of steel plate B3-21 is joined with the end face of steel plate B3-23 abutting against the end face of steel plate B3-23. Referring to Figure 18D, steel plate B3-22 is butt-joined to steel plate B3-21 as well as steel plate B3-23. The end face of the steel plate B3-22 is joined to the end face of the steel plate B3-23 in a state of contact with the end face. The steel plates B3-21, 22, and 23 are joined by, for example, laser welding. In this embodiment, the blank B3-20 is a so-called tailor weld blank.

[0368] 18B and 18C, among the steel plates B3-21, 22, and 23, the steel plate B3-21 has the smallest plate thickness t ｍｉｎ The steel plate B3-22 has a thickness t ｍｉｎ The steel plate B3-23 has a thickness t ｍｉｎ In this embodiment, the thickness of each of the steel plates B3-22 and B3-23 is equal to or greater than the thickness t ｍｉｎ In this embodiment, the steel plate B3-23 has the largest plate thickness t ｍａｘ The steel plate B3-22 has a thickness t ｍｉｎ is larger than the thickness t of steel plate B3-23 ｍａｘ Plate thickness t smaller than ｍｉｄ However, the steel plate B3-22 can have a thickness equal to or greater than that of the steel plate B3-23. That is, among the steel plates B3-21, 22, and 23, the steel plate B3-22 has the maximum thickness t ｍａｘ It can also have:

[0369] Steel plate B3-21 thickness t ｍｉｎ is typically less than 1.4 mm. ｍｉｎ The thickness t of the steel plate B3-21 may be, for example, 0.8 mm or more. ｍｉｎ and the thickness t of steel plate B3-23 ｍａｘ is 1.0<t ｍａｘ / t ｍｉｎ ≦3.2, and 1.3≦t ｍａｘ / t ｍｉｎ It is more preferable that the ratio ≦3.2 is satisfied.

[0370] Minimum thickness t for blank B3-20 ｍｉｎThe steel plate B3-21 having the above structure is configured so that the emissivity of at least one of its two surfaces is greater than the emissivity of both surfaces of the steel plate B3-22. For example, the emissivity at a wavelength of 8.0 μm at 25°C is 60% or more on one or both surfaces of the steel plate B3-21, and less than 60% on both surfaces of the steel plate B3-22. The emissivity at a wavelength of 8.0 μm at 25°C on one or both surfaces of the steel plate B3-21 is more preferably 70% or more, and even more preferably 80% or more. The minimum plate thickness t ｍｉｎ The difference in emissivity at a wavelength of 8.0 μm at 25°C between steel sheet B3-21 having the above formula and other steel sheet B3-22 is preferably greater than 5%, more preferably greater than 10%, and even more preferably greater than 20%. The emissivity can be measured in accordance with JIS R 1801 (2002). In this case, a sample taken from the steel sheet to be measured is placed in a Fourier transform infrared spectrophotometer, and the radiation intensity at a wavelength of 8.0 μm at 25°C is measured to calculate the emissivity. Alternatively, it is also possible to measure the radiation intensity of a target area at 25°C using a radiation thermometer set to a measurement wavelength of 8.0 μm, and calculate the emissivity from the ratio to the radiation intensity of a blackbody.

[0371] In this embodiment, one surface of the steel plate B3-21 is coated with the coating B3-26. On the other hand, the steel plate B3-22 is not provided with the coating B3-26. As a result, the emissivity of the one surface of the steel plate B3-21 is higher than the emissivity of both surfaces of the steel plate B3-22.

[0372] The coating B3-26 is, for example, a black coating. For example, the lightness L ＊ Value (CIE 1976 lightness index L defined in JIS Z8781-4 (2013) ＊) is 60 or less, the coating B3-26 can be determined to be black. The coating B3-26 may be a carbon-based surface treatment coating (a coating containing carbon (C)). The emissivity of the coating B3-26 at a wavelength of 8.0 μm at 25°C is 60% or more, preferably 70% or more, and more preferably 80% or more. That is, the emissivity of the surface of the steel sheet B3-21 to which the coating B3-26 is applied at a wavelength of 8.0 μm at 25°C is 60% or more, preferably 70% or more, and more preferably 80% or more. The coating B3-26 may have an emissivity of 60% or more at a wavelength of 8.0 μm at 700°C. For example, the surface treatment coating described in Patent Document 1 can be used as the coating B3-26. Specifically, the coating B3-26 can contain carbon black and one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide. The coating B3-26 may or may not contain silica. That is, the silica content of the coating B3-26 is 0 g / m ２ The silica content of the coating B3-26 is 0.30 g / m ２ The silica content may be more preferably 0.10 g / m or less. ２ More preferably, it is 0.05 g / m or less. ２ The following is the result.

[0373] The carbon black and oxides can be dispersed throughout the entire surface of the coating B3-26 that is perpendicular to the thickness direction of the steel sheet B3-21. ＣＢ (g / m ２ ), the content of one or more oxides (metal oxides) selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide is X Ｏｘｉｄｅ (g / m ２ ) and then X ＣＢ and X Ｏｘｉｄｅ It is preferable that the following formula (1) is satisfied: 118.9≦24280 / {6700 / (100+76×X ＣＢ ) + 18000 / (130 + 65 x X Ｏｘｉｄｅ )≦332.0 (1)

[0374] In formula (1), the central formula: 24280 / {6700 / (100+76×X ＣＢ ) + 18000 / (130 + 65 x X Ｏｘｉｄｅ )) is preferably 119.0 or more, more preferably 170.0 or more, and even more preferably 220.0 or more. The value calculated by the middle formula is preferably 330.0 or less, more preferably 310.0 or less, and even more preferably 300.0 or less.

[0375] The dispersion state of the carbon black and metal oxide in the coating B3-26 can be confirmed by performing an area analysis of the coating B3-26 with an electron probe microanalyzer (EPMA) for elements derived from the carbon black (e.g., C) and elements derived from the oxide (Zr, Zn, and Ti). ＣＢ can be measured by cross-sectional analysis of the coating B3-26 using a transmission electron microscope (TEM). That is, a cross-sectional analysis of the coating B3-26 is performed by TEM-EDS analysis in an area of ​​a predetermined size (thickness of the coating B3-26 × 5 μm), and the thickness of the coating B3-26 and the area ratio of particles with a carbon content of 70 mass % or more in that area are measured. The density of the carbon black is defined as ρ (ton / m ３ ), the film thickness is d (μm), and the area ratio is a (%), the value expressed by ρ×d×a is the carbon black content X ＣＢ (g / m ２ ) The oxide content X Ｏｘｉｄｅ can be determined by performing elemental analysis on the surface of the coating B3-26 using an X-ray fluorescence analyzer (ZSX Primus, manufactured by RIGAKU Corporation) and quantifying the amounts of metal Zr, metal Zn, and metal Ti.

[0376] Carbon black content X in film B3-26 ＣＢ is 0.030 g / m ２ It is preferable that the content is 0.100 g / m or more. ２ It is more preferable that the content X is equal to or greater than this.ＣＢ is set within a range that satisfies the formula (1), but is preferably 0.800 g / m ２ or less, more preferably 0.600 g / m ２ The following is the result.

[0377] Coating B3-26 may contain 5.0% or more, preferably 8.0% or more, by volume of carbon black. Coating B3-26 may contain 40.0% or less, preferably 30.0% or less, by volume of carbon black.

[0378] Metal oxide content X in coating B3-26 Ｏｘｉｄｅ is 0.030 g / m ２ It is preferable that the content is 0.060 g / m or more. ２ It is more preferable that the content X is equal to or greater than this. Ｏｘｉｄｅ is set within a range that satisfies the formula (1), but is preferably 0.500 g / m ２ More preferably, it is 0.300 g / m or less. ２ The following is the result.

[0379] The coating B3-26 may contain 1.0% or more of metal oxide by volume, and 30.0% or less of metal oxide by volume, preferably 25.0% or less of metal oxide by volume.

[0380] Carbon black content X ＣＢ (g / m ２ ) and the metal oxide content X Ｏｘｉｄｅ (g / m ２ ) ratio: X Ｏｘｉｄｅ / X ＣＢ is preferably 0.20 or more and 200.00 or less. Ｏｘｉｄｅ / X ＣＢ is more preferably 0.40 or more and 10.00 or less, and further preferably 0.60 or more and 5.00 or less.

[0381] The coating B3-26 may contain various binder components and additives in addition to the carbon black and metal oxides described above.

[0382] The binder component is preferably a water-dispersible or water-soluble resin. The content of the binder component is preferably 40% by volume or more relative to the total volume of the coating B3-26. As the binder component selected from water-dispersible or water-soluble resins, various known resins exhibiting water dispersibility or water solubility can be used. Examples of such water-dispersible or water-soluble resins include polyurethane resins, polyester resins, acrylic resins, epoxy resins, fluororesins, polyamide resins, polyolefin resins, and polymer compounds obtained by hydrolysis and condensation polymerization of silane coupling agents. It is more preferable that the binder component be one or more selected from the group consisting of polyester resins, polyurethane resins, polyolefin resins, acrylic resins, epoxy resins, fluororesins, and polyamide resins. When a polyurethane resin is used as the binder component, the polyurethane resin is preferably a polyether-based polyurethane resin.

[0383] Examples of additives include leveling agents, water-soluble solvents, metal stabilizers, and etching inhibitors. The leveling agent is, for example, a nonionic or cationic surfactant. Examples of nonionic or cationic surfactants include polyethylene oxide or polypropylene oxide adducts, acetylene glycol compounds, and the like. Examples of water-soluble solvents include alcohols such as ethanol, isopropyl alcohol, t-butyl alcohol, and propylene glycol; cellosolves such as ethylene glycol monobutyl ether and ethylene glycol monoethyl ether; esters such as ethyl acetate and butyl acetate; and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone. Examples of metal stabilizers include chelate compounds such as EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid). Examples of etching inhibitors include amine compounds such as ethylenediamine, triethylenepentamine, guanidine, and pyrimidine.

[0384] The coating B3-26 can be formed by applying an organic or inorganic treatment liquid containing, for example, carbon black and a metal oxide to the entire surface of the steel sheet B3-21, and then drying the volatile components in the treatment liquid. The treatment liquid can be applied to the surface of the steel sheet B3-21, for example, by a roll coater, a curtain coater, or an inkjet. In the case of inkjet coating, the thickness of the coating B3-26 can be continuously changed. The thickness of the coating B3-26 is, for example, 0.5 μm or more and 5.0 μm or less. The thickness of the coating B3-26 is preferably 1.0 μm or more and 3.0 μm or less. The thickness of the coating B3-26 is determined by the thickness t of the steel sheet B3-21. ｍｉｎ Therefore, the thickness of the steel plate B3-21 measured with the coating B3-26 included is ｍｉｎ can be treated as

[0385] The steel sheet B3-21 may be a plated steel sheet. In this case, the steel sheet B3-21 has a base steel sheet B3-216 and a plated layer B3-217. The type of base steel sheet B3-216 is not particularly limited. The plated layer B3-217 is provided on the base steel sheet B3-216. The plated layer B3-217 covers the entire or almost the entire surface of both sides of the base steel sheet B3-216. The plated layer B3-217 is a metal plated layer. The plated layer B3-217 may be, for example, hot-dip aluminum plating, hot-dip galvanneal plating, or electrogalvanized plating. Known aluminum-plated steel sheets, zinc-plated steel sheets, etc. can be used as the steel sheet B3-21.

[0386] The plating layer B3-217 is typically a plating layer containing aluminum as a main component (aluminum-based plating layer). The configuration of the aluminum-based plating layer is not particularly limited. A known aluminum-based plating layer can be adopted as the plating layer B3-217. When the steel sheet B3-21 is a plated steel sheet, the sheet thickness t ｍｉｎ is the combined thickness of the base steel plate B3-216 and the plating layer B3-217.

[0387] Like the steel sheet B3-21, the steel sheets B3-22 and B3-23 may be known plated steel sheets. The steel sheets B3-22 and B3-23 may be aluminum-plated steel sheets or zinc-plated steel sheets. The steel sheets B3-22 and B3-23 may be plated steel sheets of the same type as the steel sheet B3-21, or may be plated steel sheets of a different type from the steel sheet B3-21. Furthermore, the steel sheet B3-22 may be plated steel sheets of the same type as the steel sheet B3-23, or may be plated steel sheets of a different type from the steel sheet B3-23. When the steel sheet B3-22 is a plated steel sheet, the thickness t ｍｉｄ Similarly, when the steel sheet B3-23 is a plated steel sheet, the thickness t ｍａｘ is the combined thickness of the base steel sheet and the plating layer. When two or more of the steel sheets B3-21, 22, and 23 are plated steel sheets, the coating weight of each steel sheet may be the same as or different from that of the other steel sheets.

[0388] (Heating Step) The prepared blank B3-20 is formed into a structural member B3-10 (FIGS. 16 and 17) by hot stamping (hot press working). During the hot stamping, the blank B3-20 is subjected to a heating step. Referring to FIG. 18E, in the heating step, the blank B3-20 is heated, for example, by a heating furnace B3-30. The plurality of steel plates B3-21, 22, and 23 included in the blank B3-20 are heated to an austenite transformation completion temperature (A ｃ３ The steel plates B3-21, 22, and 23 are heated to, for example, 900° C. or higher, so that the microstructures of the steel plates B3-21, 22, and 23 are transformed entirely or almost entirely into the austenite phase.

[0389] (Forming Process) Referring to Figure 18F, in the forming process, a mold B3-40 is used to form the heated blank B3-20 into a structural member B3-10 (Figures 16 and 17) that is annular in plan view and then quenched. The blank B3-20 heated in the heating process is removed from the heating furnace B3-30 (Figure 18E) and transported to the mold B3-40. The mold B3-40 is attached to a known press device. The mold B3-40 includes, for example, a punch B3-41 and a die B3-42. The blank B3-20 is placed between the punch B3-41 and the die B3-42.

[0390] Referring to Figure 18G, after the blank B3-20 is placed between the punch B3-41 and the die B3-42, the die B3-42 moves relatively close to the punch B3-41. The blank B3-20 is clamped (pressed) between the punch B3-41 and the die B3-42 and formed into a shape that conforms to the forming surfaces of the punch B3-41 and the die B3-42. The blank B3-20 remains clamped between the punch B3-41 and the die B3-42. The blank B3-20 is cooled (quenched) by the die B3-40, and its microstructure is transformed to martensite. This allows the structural member B3-10 to be manufactured from the blank B3-20.

[0391] Figure 19 is a cross-sectional view of the structural member B3-10 after hot stamping. Figure 19 shows a cross-section of the structural member B3-10 at the position of the steel plate B3-21 (Figures 18B and 18C) to which the black coating B3-26 was applied at the blank B3-20 stage. This structural member B3-10 includes a member body B3-11 and a coating B3-12. The coating B3-12 is provided on the steel plate B3-21. The black coating B3-26 (Figures 18B and 18C) applied to the steel plate B3-21 in the blank B3-20 becomes the coating B3-12 after hot stamping. If the coating B3-26 contains carbon black, this carbon black is almost entirely eliminated by the high-temperature heating during hot stamping, but may remain on the member body B3-11. When the coating B3-26 before hot stamping satisfies the above formula (1), the coating B3-12 after hot stamping may not contain carbon black or may contain 0.500 g / m２ If the coating B3-12 after hot stamping contains carbon black, the carbon black content in the coating B3-12 is 0 g / m ２ Furthermore, when the coating B3-26 before hot stamping satisfies the above formula (1), the coating B3-12 after hot stamping satisfies the central formula: 24280 / {6700 / (100+76×X ＣＢ ) + 18000 / (130 + 65 x X Ｏｘｉｄｅ )} is, for example, 120.0 or more and 150.0 or less.

[0392] When the coating B3-26 (FIGS. 18B and 18C) before hot stamping satisfies the above formula (1), the coating B3-12 after hot stamping contains one or more oxides (metal oxides) selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide at a concentration of, for example, 0 g / m ２ More preferably, 0.001 g / m ２ The metal oxide content of the coating B3-12 is, for example, 0.500 g / m ２ In this way, when the metal oxide remains on the structural member B3-10, that is, when the coating B3-12 is 0 g / m or less, ２ When the coating B3-26 before hot stamping satisfies the above formula (1), the coating B3-12 after hot stamping has a metal oxide content of 0 to 0.30 g / m or more, which is more preferable because the corrosion resistance of the structural member B3-10 is improved. ２ Contains silica.

[0393] The carbon black content, metal oxide content, and silica content of the coating B3-12 can be measured in the same manner as for the coating B3-26 at the blank B3-20 stage. Specifically, a vehicle body part is disassembled to obtain an annular structural member B3-10, and an analytical sample is obtained from this structural member B3-10, for example, by laser cutting. For example, an analytical sample is obtained from each of the multiple steel plates included in the structural member B3-10. The analytical sample is obtained from the center or its vicinity of the top plate of each steel plate having an open cross section. The cross section of the obtained analytical sample is adjusted, for example, by polishing the cross section to outside the heat-affected zone during laser cutting, to prepare a coating analysis sample. The surface analysis of the coating B3-12 using EPMA for elements derived from carbon black (e.g., C) and elements derived from oxides (Zr, Zn, and Ti) can be confirmed to confirm the dispersion state of the carbon black and metal oxide in the coating B3-12.

[0394] In many cases, the outermost surface layer of the structural member B3-10 is, for example, an electrodeposition coating film. In such cases, the coating layer that is below the electrodeposition coating film layer and above the alloyed metal plating layer is analyzed. The carbon black content X in the coating B3-12 ＣＢ can be measured by cross-sectional analysis of the coating B3-26 using a TEM. That is, a cross-sectional analysis of the coating B3-12 is performed by TEM-EDS analysis in an area of ​​a predetermined size (thickness of the coating B3-12 × 5 μm), and the thickness of the coating B3-12 and the area ratio of particles with a carbon content of 70 mass % or more in that area are measured. The density of carbon black is defined as ρ (ton / m ３ ), the film thickness is d (μm), the area ratio is a (%), and the value expressed by ρ×d×a is the carbon black content X ＣＢ (g / m ２ ) The oxide content X Ｏｘｉｄｅ can be determined by performing elemental analysis of the coating layer that is present below the electrodeposition coating layer and above the alloyed metal plating layer using the above-mentioned X-ray fluorescence analyzer, and quantifying the amounts of metal Zr, metal Zn, and metal Ti.

[0395] Minimum plate thickness t ｍｉｎIn the cross section of the structural member B3-10 at the position of the steel plate B3-21 having the minimum martensite fraction (%), the martensite fraction variation is, for example, 20% or less. The martensite fraction variation is preferably 15% or less, and more preferably 10% or less. The martensite fraction variation can be measured as follows. That is, ｍｉｎ Ten or more analysis samples (for example, a length of about 10 mm) were cut out from the cross section of the structural member B3-10 at the position of the steel plate B3-21 having the above structure, at positions 20 mm or more away from the end and 10 mm or more away from each other, and then each was mirror-polished and etched with LePeller's reagent so that the observation surface was in the thickness direction. Then, an optical microscope was used to observe the area from the steel plate surface to a depth of 1 / 4 of the plate thickness (the area from the steel plate surface to a depth of 1 / 8 of the plate thickness to a depth of 3 / 8 of the plate thickness) at a magnification of 1000x, with one field of view of 2,400 μm ２ The above structural photographs are taken from 30 fields of view, and the obtained structural photographs are subjected to image analysis.

[0396] The image analysis method involves obtaining the maximum brightness value Lmax and minimum brightness value Lmin from the image, designating the area with pixels whose brightness ranges from Lmax-0.3 (Lmax-Lmin) to Lmax as a white area, and calculating the ratio of the number of pixels in the white area to the total number of pixels to measure the martensite fraction. This type of image analysis is performed on a total of 30 observation fields of each analysis sample to determine the martensite fraction, and the average value is used as the martensite fraction for each analysis sample. Furthermore, the difference between the maximum and minimum martensite fractions in 10 or more analysis samples is calculated based on the minimum plate thickness t ｍｉｎ The variation in martensite fraction in the cross section of the structural member B3-10 at the position of the steel plate B3-21 having the minimum plate thickness t ｍｉｎ When there are multiple steel plates having the above structure, such analysis is performed on each steel plate to determine the martensite fraction, and the maximum variation in martensite fraction among these steel plates is taken as the variation in martensite fraction in the structural member B3-10.

[0397] In some steel sheets, the area fraction of martensite obtained by image analysis, i.e., the area fraction of the white region, may contain a few percent of the area fraction of retained austenite. However, since the variation in the martensite fraction is calculated as a difference, the impact is minor.

[0398] After the forming process (hot stamping), steel plate B3-21 can have a tensile strength of, for example, 0.5 GPa or more, and preferably has a tensile strength of 1.0 GPa or more. Similarly, after the forming process (hot stamping), steel plates B3-22 and B3-23 (FIG. 16) can have a tensile strength of, for example, 0.5 GPa or more, and preferably has a tensile strength of 1.0 GPa or more. At least one of steel plates B3-21, B3-22, and B3-23 may have a tensile strength of 1.5 GPa or more after the forming process. The tensile strength of each of steel plates B3-21, B3-22, and B3-23 may be the same as or different from the tensile strength of the other steel plates.

[0399] [Effect] In the blank B3-20 according to this embodiment, the minimum plate thickness t ｍｉｎ The emissivity of one surface of steel sheet B3-21 having a thickness of 1.0 mm is higher than the emissivity of both surfaces of steel sheet B3-22 having a greater thickness. That is, the surface of steel sheet B3-21 is treated to increase the emissivity. As a result, when blank B3-20 is heated during hot stamping, the temperature rise rate of steel sheet B3-21 is significantly higher than that of steel sheet B3-22. Therefore, in the heating process, steel sheet B3-21 can be rapidly heated to the austenite range temperature, ensuring a long high-temperature holding time for steel sheet B3-21. As a result, austenite grains in the microstructure of steel sheet B3-21 coarsen, and the ferrite transformation region (ferrite nose) in the CCT diagram shifts to the longer time side. This prevents the transformation of austenite to ferrite in steel sheet B3-21 between removal from heating furnace B3-30 and the start of forming using mold B3-40. Therefore, it is possible to start forming the blank B3-20 using the die B3-40 while maintaining the microstructure of the steel plate B3-21 in the austenite phase, and the minimum plate thickness tｍｉｎ The hardenability of the steel plate B3-21 having the above properties can be improved.

[0400] In this embodiment, the hardenability of the relatively thin steel plate B3-21 is improved, so that the hardness of the structural member B3-10 formed from the blank B3-20 can be made uniform. More specifically, the minimum plate thickness t ｍｉｎ Since the steel plate B3-21 having the above structure is also well quenched, the variation in martensite fraction in the steel plate B3-21 can be reduced to 20% or less. This reduces the likelihood of concentrated deformation when a collision load is applied to the structural member B3-10, making it easier for the structural member B3-10 to exhibit high impact absorption performance. Therefore, even when an annular structural member B3-10 including the thin steel plate B3-21, particularly a large annular structural member B3-10, is formed from the blank B3-20, the strength defect of the structural member B3-10 can be reduced, and the impact absorption performance of the structural member B3-10 can be improved.

[0401] The smaller the variation in the martensite fraction, the less non-uniformity there is in the mechanical properties within the structural member B3-10, which is preferable from the viewpoint of the functionality of the structural member B3-10. On the other hand, a large variation in the martensite fraction indicates that there are unevenly distributed hardenable insufficient parts, i.e., hardness insufficient parts, within the structural member B3-10, and when the structural member B3-10 is deformed by impact, deformation tends to concentrate in the hardness insufficient parts, thereby reducing the functionality of the structural member B3-10.

[0402] In this embodiment, the improved hardenability of the relatively thin steel plate B3-21 reduces the likelihood of non-uniform stress in the structural member B3-10. Therefore, even when the annular structural member B3-10 is formed from an annular blank B3-20, twisting of the structural member B3-10 is unlikely to occur. Therefore, even when a structural member B3-10 including a thin steel plate B3-21, particularly a large annular structural member B3-10, is formed from the blank B3-20, poor dimensional accuracy of the structural member B3-10 can be reduced, and the impact absorption performance of the structural member B3-10 can be improved.

[0403] In the blank B3-20 according to this embodiment, the minimum plate thickness t ｍｉｎ The surface of the steel plate B3-21 is substantially coated with a black coating B3-26, while the steel plate B3-22, which has a thickness greater than that of the steel plate B3-21, is not provided with the coating B3-26. Therefore, the emissivity of the surface of the steel plate B3-21 is greater than the emissivity of both surfaces of the steel plate B3-22. In this case, the steel plate B3-21 heats up faster than the steel plate B3-22, and therefore the high-temperature holding time of the steel plate B3-21 is longer than when the steel plate B3-21 and the steel plate B3-22 have the same emissivity. This reduces the non-uniformity of the phase transformation due to the difference in cooling rate between the steel plates B3-21, 22, and 23 after the heating of the blank B3-20 is completed. Specifically, the minimum plate thickness t ｍｉｎ This delays the start of the austenite-to-ferrite phase transformation in the steel plate B3-21, thereby reducing the difference in the phase transformation start time between the steel plate B3-21 and the other steel plates B3-22 and 23. As a result, the hardenability of the steel plates B3-21, 22, and 23 included in the blank B3-20 can be made uniform.

[0404] For example, if the plating layer B3-217 of the steel sheet B3-21 is an aluminum-based plating layer, the temperature rise rate of the steel sheet B3-21 during the heating process tends to be slow. Because the aluminum-based plating layer is white, it tends to reflect heat energy, inhibiting the temperature rise of the steel sheet B3-21. However, in the blank B3-20 according to this embodiment, the surface of the steel sheet B3-21 is treated to increase the emissivity. Therefore, even if the steel sheet B3-21 is a plated steel sheet having an aluminum-based plating layer, the temperature rise of the steel sheet B3-21 during the heating process can be accelerated and the high-temperature holding time of the steel sheet B3-21 can be extended. Therefore, the hardenability of the thin-walled steel sheet B3-21 can be ensured.

[0405] In this embodiment, in the heating process, first, the minimum plate thickness t ｍｉｎ The steel plate B3-21 having the above temperature reaches the austenite region, and then the intermediate thickness t ｍｉｄ Steel plate B3-22 and maximum plate thickness t ｍａｘ The steel plate B3-23 having the minimum thickness tｍｉｎ and maximum plate thickness t ｍａｘ Ratio to: t ｍａｘ / t ｍｉｎ It is preferable that the thickness t ｍｉｎ The alloying of the plating layer B3-217 of the steel plate B3-21 having the thickness t ｍａｘ The steel plate B3-23 having the above-mentioned structure can be heated sufficiently until the phase transformation to austenite is completed, thereby ensuring a process window in the production of the structural member B3-10.

[0406] In this embodiment, a coating B3-26 can be applied to the steel sheet B3-21 to increase its emissivity. The emissivity of the coating B3-26 (at a temperature of 25°C and a wavelength of 8.0 μm) is, for example, 60% or more. This allows the steel sheet B3-21 to be efficiently radiated and makes it easier to increase the temperature rise rate of the steel sheet B3-21 during the heating process.

[0407] In this embodiment, the coating B3-26 is a coating containing carbon black, one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide, and 0 to 0.30 g / m ２ The carbon black content X may be the following: ＣＢ (g / m ２ ), and the oxide content X Ｏｘｉｄｅ (g / m ２ ) preferably satisfies the above formula (1). Formula (1) is a relationship between the rate of increase (%) of temperature rise (°C / s) and the carbon black content X ＣＢ and oxide content X Ｏｘｉｄｅ Formula (1) defines the relationship between the carbon black and oxides. Formula (1) indicates that carbon black primarily functions as a heat absorbing material in the temperature range up to 700°C, and oxides primarily function as heat absorbing materials in the temperature range of 700°C or higher. When coating B3-26 satisfies formula (1), the surface of steel sheet B3-21 to which coating B3-26 is applied tends to have an emissivity of 60% or more at a wavelength of 8.0 μm at 25°C.

[0408] The carbon black and oxides can be dispersed throughout the entire surface of the coating B3-26 that is perpendicular to the thickness direction of the steel sheet B3-21. This makes it easier to make the emissivity of the surface of the steel sheet B3-21 uniform. Therefore, in the heating process, the emissivity of the steel sheet B3-21 can be uniform even at the minimum thickness t ｍｉｎ The steel plate B3-21 having the above properties can be heated quickly and uniformly.

[0409] However, the configuration of the coating B3-26 is not limited to this. The coating B3-26 may be a substantially black coating in order to increase the emissivity of the steel sheet B3-21 compared to an untreated steel sheet. For example, the coating B3-26 may contain graphite or soot instead of or in addition to carbon black. Alternatively, the coating B3-26 may contain, for example, an acicular compound having a hexagonal crystal structure with an aspect ratio of 4 to 50 inclusive in order to increase the emissivity of the steel sheet B3-21. The compound having a hexagonal crystal structure is typically graphite (C), but may also be lanthanum silicate, magnesium diboride, beryllium oxide (beryllia), zinc oxide, β-quartz, goethite (NiS), wurtzite (ZnS), or the like.

[0410] <Second embodiment> Figure 20 is a plan view of a blank B3-20A according to the second embodiment. The blank B3-20 according to the first embodiment is a tailored blank in which steel plates B3-21, 22, and 23 are butt-joined to one another. The blank B3-20A according to this embodiment differs from the first embodiment mainly in the form of the joint between the steel plates.

[0411] 20, the blank B3-20A includes a plurality of steel plates B3-21, 22, 23, 24, and 25. The steel plates B3-21, 22, 23, 24, and 25 are arranged and joined to form an annular shape in a plan view of the blank B3-20. As in the first embodiment, the steel plate B3-21 has a minimum plate thickness t ｍｉｎ The blank B3-20A according to this embodiment has an emissivity greater than that of the steel plate B3-22 on at least one surface thereof, and is configured so that the emissivity of the blank B3-20A on at least one surface thereof is greater than that of the steel plate B3-22 on both surfaces thereof. Therefore, the blank B3-20A according to this embodiment can also achieve the same effects as those of the first embodiment.

[0412] The blank B3-20A has an overlap portion B3-27. Figure 21 is a cross-sectional view taken along line VI-VI in Figure 20, showing a cross section of the overlap portion B3-27. In this embodiment, the overlap portion B3-27 is formed by overlapping the ends of two adjacent steel plates B3-23 and B3-24. The end of the steel plate B3-23 is joined to the end of the steel plate B3-24 in an overlapping state. The steel plates B3-23 and B3-24 are joined to each other by, for example, spot welding or laser welding.

[0413] The overlap portion B3-27 has a total thickness t. The total thickness t is the sum of the thicknesses of the steel plates B3-23 and B3-24. If at least one of the steel plates B3-23 and B3-24 is a plated steel plate, the total thickness t also includes the thickness of the plating layer. The total thickness t of the overlap portion B3-27 is, for example, greater than 2.5 mm and less than 4.0 mm. In this case, the steel plate B3-23 is configured so that the emissivity of the surface located outside the overlap portion B3-27, i.e., the surface opposite the steel plate B3-24, is greater than the emissivity of both surfaces of the steel plate B3-22 (Figure 20). The steel plate B3-24 is configured so that the emissivity of the surface located outside the overlap portion B3-27, i.e., the surface opposite the steel plate B3-23, is greater than the emissivity of both surfaces of the steel plate B3-22. That is, in each of the steel plates B3-23 and 24, the surface located outside the overlap portion B3-27 is treated to increase the emissivity throughout its entirety. For example, the emissivity at 25°C at a wavelength of 8.0 μm is 60% or more, preferably 70% or more, and more preferably 80% or more, for the surface of the steel plates B3-23 and 24 located outside the overlap portion B3-27. The difference in emissivity at a wavelength of 8.0 μm at 25°C between the surface of the steel plates B3-23 and 24 located outside the overlap portion B3-27 and both surfaces of the other steel plate B3-22 is preferably greater than 5%, more preferably greater than 10%, and even more preferably greater than 20%. In the steel plates B3-23 and 24, the emissivity of the surface located inside the overlap portion B3-27 may be greater than the emissivity of both surfaces of the steel plate B3-22, or may be less than the emissivity of both surfaces of the steel plate B3-22.

[0414] In steel plates B3-23 and B3-24, the surface located outside the overlap portion B3-27 may be covered with a coating B3-26, thereby increasing the emissivity of the surface compared to steel plate B3-22 (FIG. 20). The coating B3-26 used on steel plates B3-23 and B3-24 may have a similar configuration to the coating B3-26 used on steel plate B3-21. As described above, the thickness of the coating B3-26 is very small, so the total thickness t of the overlap portion B3-27 can be the thickness measured including the coating B3-26.

[0415] If the total thickness t of the overlap portion B3-27 exceeds, for example, 2.5 mm, the overlap portion B3-27 is difficult to heat up, so when the blank B3-20A is heated during hot stamping, the overlap portion B3-27 reaches the minimum thickness t ｍｉｎ In some cases, the plating layer B3-217 (FIGS. 18B and 18C) of the steel sheet B3-21 having the above-mentioned structure may be alloyed, causing a diffusion layer to grow, resulting in the corrosion resistance or weldability of the steel sheet B3-21 being compromised. However, in this embodiment, the emissivity of the overlap portion B3-27 is increased to facilitate heating. Therefore, even if the total thickness t of the overlap portion B3-27 is greater than 2.5 mm, the overlap portion B3-27 can be heated sufficiently until the phase transformation to austenite is complete before the alloying of the plating layer B3-217 of the steel sheet B3-21 progresses and the diffusion layer thickens, resulting in a loss of corrosion resistance or weldability. This ensures a process window for the manufacture of structural components.

[0416] In the blank B3-20A according to this embodiment, the steel plate B3-21 may be butt-joined to the steel plates B3-22 and B3-23, or may form an overlap portion B3-27 with one or both of the steel plates B3-22 and B3-23. The steel plate B3-25 may be butt-joined to the steel plates B3-22 and B3-24, or may form an overlap portion B3-27 with one or both of the steel plates B3-22 and B3-24. When the steel plates B3-21 and B3-23 form the overlap portion B3-27 and the total thickness t of the overlap portion B3-27 exceeds 2.5 mm, the steel plates B3-21 and B3-23 may be configured so that the emissivity of the surface located outside the overlap portion B3-27 is greater than the emissivity of both surfaces of the steel plate B3-22. Similarly, when steel plates B3-24 and 25 form an overlap portion B3-27 and the total thickness t of the overlap portion B3-27 exceeds 2.5 mm, steel plates B3-24 and 25 may be configured so that the emissivity of the surface located outside the overlap portion B3-27 is greater than the emissivity of both surfaces of steel plate B3-22.

[0417] Figure 22 is a plan view of a structural member B3-10A manufactured from a blank B3-20A. The structural member B3-10A has roughly the same configuration as the structural member B3-10 of the first embodiment (Figures 16 and 17). However, in the structural member B3-10A, the member body B3-11 is formed from five steel plates B3-21, 22, 23, 24, and 25. The method of manufacturing the structural member B3-10A from the blank B3-20A is the same as in the first embodiment.

[0418] The structural member B3-10A can have a size similar to that of the structural member B3-10 according to the first embodiment. That is, the size of the structural member B3-10A, which is annular in plan view, is, for example, 1.0 m or more and 4.0 mm or less. In the structural member B3-10A, each of the steel plates B3-21, 22, 23, 24, and 25 has an open cross section similar to that of the first embodiment. Each of the steel plates B3-21, 22, 23, 24, and 25 can have, for example, a generally hat-shaped cross section of the structural member B3-10A.

[0419] Although not shown, in the structural member B3-10A, the width of the steel plate B3-21 arranged on the upper part of the front pillar B3-111 is, for example, 15 mm or more and 300 mm or less. The height of the steel plate B3-21 may be 10 mm or more and 150 mm or less. In the structural member B3-10A, the width of the steel plate B3-22 arranged on the lower part of the front pillar B3-111 is, for example, 30 mm or more and 750 mm or less. The height of the steel plate B3-22 may be 25 mm or more and 150 mm or less. In the structural member B3-10A, the width of the steel plates B3-23, 24 arranged at the position of the center pillar B3-112 is, for example, 15 mm or more and 300 mm or less. The height of the steel plates B3-23, 24 may be 10 mm or more and 150 mm or less. In the structural member B3-10A, the width of the steel plate B3-25 arranged at the position of the locker B3-113 is, for example, 30 mm or more and 300 mm or less. The height of the steel plate B3-25 may be 25 mm or more and 150 mm or less.

[0420] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0421] In each of the above embodiments, the minimum plate thickness t ｍｉｎ In order to increase the emissivity of the surface of steel plate B3-21 having a roughness greater than that of steel plate B3-22, the surface of steel plate B3-21 is coated with coating B3-26. However, the method for increasing the emissivity of the surface of steel plate B3-21 is not limited to coating B3-26. For example, the emissivity of the surface of steel plate B3-21 can be increased compared to that of steel plate B3-22 by increasing the surface roughness of steel plate B3-21 more than that of steel plate B3-22. Similarly, the method for increasing the emissivity of the outer surface of overlap portion B3-27 is not limited to coating B3-26.

[0422] In each of the above embodiments, the minimum plate thickness t ｍｉｎIn the above example, the emissivity of only one of the two surfaces of steel plate B3-21 having a thickness of 1000 nm or less is higher than that of steel plate B3-22. However, the emissivity of both surfaces of steel plate B3-21 may be higher than that of steel plate B3-22. For example, both surfaces of steel plate B3-21 may be coated with coating B3-26. Alternatively, the surface roughness of both surfaces of steel plate B3-21 may be higher than that of steel plate B3-22.

[0423] In the first embodiment, the steel plates B3-21, 22, and 23 included in the blank B3-20 may each be single-layered or multi-layered. That is, the steel plates B3-21, 22, and 23 may each be a single steel plate or a plate material formed by stacking multiple steel plates. Similarly, in the second embodiment, the steel plates B3-21, 22, 23, 24, and 25 may each be single-layered or multi-layered.

[0424] In the first embodiment, the blank B3-20 includes three steel plates B3-21, 22, and 23. In the second embodiment, the blank B3-20A includes five steel plates B3-21, 22, 23, 24, and 25. However, the number of steel plates included in the blanks B3-20 and 20A is not limited to this. The blanks B3-20 and 20A have at least a minimum plate thickness t ｍｉｎ Steel plate B3-21 having a plate thickness t ｍｉｎ and a steel plate B3-22 having a thickness greater than t. The emissivity of one or both sides of the steel plate B3-21 is greater than the emissivity of both sides of the steel plate B3-22. The steel plate B3-21 is joined directly or indirectly to the steel plate B3-22. The blank B3-20, 20A, which is annular in plan view, can typically include three or more steel plates. In the blank B3-20, 20A, the steel plates other than the steel plates B3-21, 22 may or may not be treated to increase the emissivity. In either blank B3-20, 20A, the minimum thickness t ｍｉｎWhen there are a plurality of steel plates B3-21 having the above-mentioned emissivity, it is preferable that the emissivity of one or both sides of all of the steel plates B3-21 is higher than the emissivity of both sides of the other steel plates B3-22. In the annular blanks B3-20 and B3-20A, the arrangement of the plurality of steel plates including the steel plates B3-21 and B3-22 is not particularly limited.

[0425] In each of the above embodiments, the minimum plate thickness t ｍｉｎ In the above example, the steel sheet B3-21 having the above-mentioned properties is a plated steel sheet. However, the steel sheet B3-21 does not necessarily have to be a plated steel sheet. The steel sheet B3-21 may be a steel sheet (bare material) that does not have a plated layer on its surface. Similarly, steel sheets other than the steel sheet B3-21 may also be plated steel sheets or bare materials.

[0426] In the first embodiment, the mold B3-40 used for hot stamping the blank B3-20 includes a punch B3-41 and a die B3-42. However, the configuration of the mold B3-40 is not limited to the example described in the first embodiment. The mold B3-40 may further include, for example, a pad and a blank holder.

[0427] In the above embodiment, the main body 11 of the structural member B3-10, 10A includes a front pillar B3-111, a center pillar B3-112, and a rocker B3-113. However, the member main body B3-11 can further include other components. For example, as shown in FIG. 23, the member main body B3-11 can further include a rear pillar B3-114. The structural members B3-10, 10A according to the above embodiment are door ring components (single door ring components) having a single ring shape. On the other hand, the structural member shown in FIG. 23 is a door ring component (double door ring component) having a double ring shape. When manufacturing double door ring components, the blank used as the material also has a double ring shape. (Example)

[0428] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0429] [First Example] In order to confirm the effects of the present disclosure, a CAE analysis was performed on a press-formed (hot stamped) structural member that is a single door ring part, using commercially available software (AUTOFORM R.10, manufactured by AUTOFORM) while changing the type (material type) and thickness of the steel plate included in the structural member, as well as the division pattern of the structural member.

[0430] The steel plates used in this analysis are shown in Table 16.

[0431]

[0432] In Table 16, the material type is listed in the order of plating type, tensile strength, and application (hot stamping). Regarding the coating specifications, the black coating is a black coating containing carbon black and metal oxide. "Black coating - one side" means that one entire side of the steel sheet is coated with a black coating. "Black coating - both sides" means that both entire sides of the steel sheet are coated with a black coating.

[0433] The division patterns of the structural members are shown in Figures 24A to 24G. Figures 24A to 24G show the number of steel plates (materials) included in the structural member, which is a single door ring part, and the positions of the joints between the steel plates in the structural member. In Figures 24A to 24G, each steel plate is given a number in parentheses.

[0434] The analysis conditions and results for division patterns 1 and 2 shown in Figures 24A and 24B are shown in Table 17. In Figures 24A and 24B, the structural member is formed from three pieces of material (1) to (3).

[0435]

[0436] Referring to Table 17, in Example 1, the minimum plate thickness t ｍｉｎ In Example 2, the material (3) having the smallest thickness t of the materials (1) to (3) is provided with a black coating on both sides. ｍｉｎ In Example 3, a black coating is applied to one side of the material (1) having a thickness of 1.2 mm. ｍｉｎ: A black coating is applied to both sides of the material (2) having a thickness of 1.2 mm. On the other hand, in Comparative Examples 1 and 2, a black coating is not applied to any of the materials (1) to (3). In Comparative Examples 1 and 2, ｍｉｎ : No black coating was applied to the material having a thickness of 1.2 mm.

[0437] In Table 17, the "time to reach 910°C" indicates the time to reach 910°C (A ｃ３ The "phase transformation start time" is the time required for a blank heated to 910°C from the start of heating to reach 910°C for a material heated to a furnace temperature of 920°C for 5 minutes and 30 seconds and then removed from the heating furnace. Table 17 shows that in Examples 1 to 3, in which the emissivity of the thinnest material was increased by a black coating, the time to reach 910°C was 20 seconds or more shorter than in Comparative Examples 1 and 2, and the heating rate of the thinnest material in the heating process was higher. Furthermore, in Examples 1 to 3, the phase transformation start time exceeded 20 seconds, making the phase transformation start time slower than in Comparative Examples 1 and 2. This makes it easier to start forming the blank before the onset of ferrite transformation, enabling the blank to be uniformly quenched during the forming process.

[0438] The analysis conditions and results for division patterns 3 and 4 shown in Figures 24C and 24D are shown in Table 18. In Figures 24C and 24D, the structural member is formed from four pieces of material (1) to (4).

[0439]

[0440] Referring to Table 18, in Examples 4 to 10, the minimum plate thickness t ｍｉｎ In Examples 4 to 10, a black coating is applied to a material having a minimum plate thickness t ｍｉｎ The material is covered with a black coating on one or both sides. ｍｉｎ In the case where there are multiple blanks having the same thickness, all of these blanks are provided with a black coating. On the other hand, in Comparative Examples 3 to 7, none of the blanks (1) to (4) are provided with a black coating. In Comparative Examples 3 to 7, ｍｉｎNo black coating is applied to the material having the above.

[0441] Table 18 shows that in Examples 4 to 10, the time to reach 910°C was 20 seconds or more shorter than in Comparative Examples 3 to 7, and the temperature rise rate of the thinnest material in the heating process was higher. Furthermore, in Examples 4 to 10, the phase transformation start time exceeded 20 seconds, which was later than in Comparative Examples 3 to 7. This makes it easier to start forming the blank before the onset of ferrite transformation, and enables the blank to be uniformly quenched in the forming process.

[0442] The analysis conditions and results for division patterns 5 to 7 shown in Figures 24E to 24G are shown in Table 19. In Figures 24E to 24G, the structural member is formed from five pieces of material (1) to (5).

[0443]

[0444] Referring to Table 19, in Examples 11 to 15, the minimum plate thickness t ｍｉｎ In Examples 11 to 15, a black coating is applied to a material having a minimum plate thickness t ｍｉｎ The material is covered with a black coating on one or both sides. ｍｉｎ In the case where there are multiple blanks having the minimum thickness t ｍｉｎ No black coating is applied to the material having the above.

[0445] Table 19 shows that in Examples 11 to 15, the time to reach 910°C was 20 seconds or more shorter than in Comparative Examples 8 to 11, and the temperature rise rate of the thinnest material in the heating process was higher. Furthermore, in Examples 11, 12, 14, and 15, the phase transformation start time exceeded 20 seconds, which was later than in Comparative Examples 8 to 11. In Example 13, the phase transformation start time was also later than in Comparative Examples 8 to 11. Therefore, it became easier to start forming the blank b...

Claims

1. An automobile side module for reinforcing the outer side of an automobile, which is made by hot stamping a plurality of integrated steel plates, and the minimum circumscribed rectangular area when viewed from the perpendicular direction of a reference plane is S (m ２ ), the total weight of the components of the automobile side module that weigh 0.200 kg or more is W ０．２ (kg), the total weight of the components having a minimum Vickers hardness of HV510 or more is W ５１０ Then, W ０．２ / S is 7.7 or less, W ５１０ / W ０．２ An automobile side module, characterized in that:

2. At least one of elemental technology A1 and elemental technology A2, and at least one of elemental technology B1, elemental technology B2, elemental technology B3a, elemental technology B3b, elemental technology B4, elemental technology B5a, elemental technology B5b, and elemental technology B6, wherein elemental technology A1 has a chemical composition, in mass %, of C: 0.15-0.50%, Si: 0.0010-3.000%, Mn: 0.30-3.00%, Al: 0.0002-2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0-0.15%, Ti: 0-0.15%, V: 0-0.15%, the steel sheet has a metallographic structure containing 90% or more of martensite, bainite and tempered martensite in total in terms of area ratio, in a texture from the surface to a position 1 / 4 of the sheet thickness from the surface, a ratio of the pole density of an orientation group consisting of {001}<1-10> to {001}<-1-10> to the pole density of an orientation group consisting of {111}<1-10> to {111}<-1-12> is less than 1.8, a ratio of a pole density of an orientation group consisting of {001}<1-10> to {001}<-1-10> to a pole density of an orientation group consisting of {111}<1-10> to {111}<-1-12> is less than 2.3 in a texture from the surface to a position 1 / 4 of the sheet thickness from the surface to a position 1 / 2 of the sheet thickness from the surface, and the elemental technology A2 has a chemical composition, in mass %, of: 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: 0-0.15%, Mo: 0-1.0%, Cr: 0-1.0%, Cu: 0-1.0%, Ni: 0-1.0%, B: 0-0.0100%, Ca: 0-0.010%, and REM: 0-0.30%, with the balance being Fe and impurities;a hot stamped steel having a metal structure consisting of 10 to 30% in total of ferrite and granular bainite, in terms of area ratio, and a residual structure consisting of one or more of martensite, bainite, and tempered martensite, wherein in a texture from the surface to a position 1 / 4 of the sheet thickness from the surface, a 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}<1-10> to {111}<-1-12> is less than 1.8, and in a texture from a position 1 / 4 of the sheet thickness from the surface to a position 1 / 2 of the sheet thickness from the surface, a 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}<1-10> to {111}<-1-12> is less than 2.3, The elemental technology B1 is a lap hot stamped product comprising a first Al-Fe alloy plated steel sheet having a thickness T1, and a second Al-Fe alloy plated steel sheet having a thickness T2 and having an area smaller than that of the first Al-Fe alloy plated steel sheet, the second Al-Fe alloy plated steel sheet being overlapped on and welded to the first Al-Fe alloy plated steel sheet, the lap hot stamped product satisfying the relationships of the following formulas (7) to (9): 25≦K1≦60 ... formula (7) 25≦K2≦60 ... formula (8) 0≦(D1-D2)×(K1 / K2)2≦5.0 ... formula (9) where, K1: an average value of a plating thickness of the Al-Fe-based alloy plating layer on a side in contact with the second Al-Fe-based alloy plated steel sheet and a plating thickness of the Al-Fe-based alloy plating layer on a side not in contact with the second Al-Fe-based alloy plated steel sheet, in a portion where the first Al-Fe-based alloy plated steel sheet is not overlapped; K2: a plating thickness of the Al-Fe-based alloy plating layer on a side not in contact with the first Al-Fe-based alloy plated steel sheet, in a portion where the second Al-Fe-based alloy plated steel sheet is overlapped; D1: an average value of a thickness of a diffusion layer located in the Al-Fe-based alloy plating layer on a side in contact with the second Al-Fe-based alloy plated steel sheet so as to be in contact with a steel sheet substrate, in the first Al-Fe-based alloy plated steel sheet, and a thickness of a diffusion layer located in the Al-Fe-based alloy plating layer on a side not in contact with the second Al-Fe-based alloy plated steel sheet so as to be in contact with a steel sheet substrate, in the first Al-Fe-based alloy plated steel sheet.D2: a thickness of a diffusion layer located in the Al-Fe alloy plating layer so as to be in contact with a steel sheet substrate on a side of the second Al-Fe alloy plated steel sheet not in contact with the first Al-Fe alloy plated steel sheet, wherein the unit of the sheet thickness T1 and the sheet thickness T2 is mm, and the unit of the K1, the K2, the D1 and the D2 is μm, and the elemental technology B2 is an aluminum-plated steel sheet for hot stamping, comprising: a base steel sheet; an aluminum plating layer having an Al content of 80 mass% or more provided on at least one surface of the base steel sheet; and a surface treatment film provided on the aluminum plating layer, wherein the surface treatment film contains a compound A containing carbon, and a compound B which is an oxide or fluoride of a metal element M and has a rutile structure, A hot stamped product formed using an aluminum-plated steel sheet for hot stamping, characterized in that the concentration of the metal element M satisfies the following formula (1) and the following formula (2), ｂＭ ≦40...Formula (1) 1.5≦C ｂＭ / C ｔＭ ≦10.0...Equation (2) Here, when the average thickness of the surface treatment film is H, C in the above equation (2) ｔＭ is the concentration of the metal element M at a position of 0.05H from the surface of the surface treatment film in mass %, and C in the above formula (1) and the above formula (2) ｂＭ is the concentration of the metal element M in mass % at a position of 0.95H from the surface of the surface treatment film, and the element technology B3a is a structural member, comprising: a member body having an annular shape in a plan view, the member body being formed by a plurality of steel plates joined together, the member body including a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate; and a component body having an annular shape in a plan view, the component body being formed by a plurality of steel plates joined together, the component body including: a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate; ２ and a coating containing 0.500 g / m or more of carbon black. The elemental technology B3b is a structural member comprising: a component body formed by a plurality of steel plates joined together, the component body including a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate, the component body having an annular shape in a plan view; and a coating provided on the first steel plate, the coating containing 0.500 g / m or more of carbon black. ２ and a coating containing the following: said elemental technology B4 is a structural member comprising a component main body formed by a plurality of steel plates joined to each other, including a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate, and having an annular shape in a plan view, said first steel plate and said second steel plate are plated steel plates each having an aluminum-based plating layer on both surfaces of a base steel plate, and a thickness of the aluminum-based plating layer on the first steel plate is smaller than a thickness of the aluminum-based plating layer on the second steel plate; said elemental technology B5a is a structural member comprising a component main body formed by a plurality of steel plates joined to each other, having an annular shape in a plan view, said component main body comprising a first steel plate and a second steel plate having an end portion that is overlapped and joined to an end portion of the first steel plate to form an overlap portion together with the end portion of the first steel plate, a first steel plate and a second steel plate, the first steel plate and the second steel plate being provided on a surface located outside the overlap portion ... ２ and a coating containing at least one of the above carbon black and carbon monoxide. The elemental technology B5b is a structural member comprising: a component body formed of a plurality of steel plates joined together, the component body having an annular shape in a plan view, the component body including a first steel plate and a second steel plate having an end portion that is overlapped and joined to an end portion of the first steel plate to form an overlap portion together with the end portion of the first steel plate, the component body being formed of a plurality of steel plates joined together, the component body having an annular shape in a plan view, and ２ and a coating containing the following: wherein the element technology B6 is a structural member comprising a component main body formed by a plurality of steel plates joined to each other and having an annular shape in a plan view, the plurality of steel plates include a first steel plate, a second steel plate, and a third steel plate, an end of the first steel plate is overlapped and joined to an end of the second steel plate to form, together with the end of the second steel plate, an overlap portion having the maximum sheet thickness in the component main body, at least one of the first steel plate and the second steel plate, and the third steel plate are each a plated steel plate having an aluminum-based plating layer on both surfaces of a base steel plate, and a thickness of the aluminum-based plating layer on at least one of the first steel plate and the second steel plate is smaller than a thickness of the aluminum-based plating layer on the third steel plate.

3. The automobile side module according to claim 2, characterized in that it comprises at least one of element technology A1 and element technology A2, and at least one of element technology B1 and element technology B2.

4. The automobile side module according to claim 2, characterized in that it comprises at least one of element technology A1 and element technology A2, and at least one of element technology B3a, element technology B3b, element technology B4, element technology B5a, element technology B5b, and element technology B6.

5. The automobile side module according to claim 2, characterized in that it comprises at least one of element technology A1 and element technology A2, at least one of element technology B1 and element technology B2, and at least one of element technology B3a, element technology B3b, element technology B4, element technology B5a, element technology B5b, and element technology B6.

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