Automotive rear module

Abstract

The automobile rear module is configured by hot press forming a plurality of steel sheets integrated, for reinforcing a side outer panel of an automobile, wherein a projected area when viewed in a perpendicular direction from a reference plane is S, in units of m 2 , a total weight of the constituent parts of the automobile rear module is W, in units of kg, and a total weight of the constituent parts of the automobile rear module made of steel having a sheet thickness of 1.5 mm or less and a minimum value of Vickers hardness of HV230 or more is W A , wherein W / S is 24 or less, and W A / S is 0.30 or more.

Description

Technical Field

[0001] This invention relates to a rear module for reinforcing the side outer panel of a vehicle.

[0002] This application claims priority based on Japanese Patent Application No. 2024-045131, filed on March 21, 2024, the contents of which are incorporated herein by reference. Background Technology

[0003] Recently, from the perspective of preventing global warming, it has become more important to curb the emission of greenhouse gases (GHGs), primarily carbon dioxide (CO2).

[0004] In this context, the emergence of electric vehicles, hybrid vehicles, and other similar vehicles, which have reduced GHG emissions compared to traditional internal combustion engine-powered vehicles, raises expectations for reducing GHG emissions from vehicles during operation.

[0005] In addition, by using lightweight materials such as aluminum and carbon as raw materials for automobiles, it is expected that GHG emissions from automobiles during driving can be reduced.

[0006] Regarding automobile bodies, for example, a body structure with excellent productivity is disclosed in Patent Document 1 below.

[0007] In addition, regarding the vehicle body structure, Patent Document 2 disclosed below discloses a rear body structure and a manufacturing method including the step of forming a laser-welded blank into a desired shape, which provides improved impact resistance in the event of a rear impact on the vehicle.

[0008] Furthermore, Patent Document 3 disclosed below discloses a car body capable of reducing the total amount of GHG generated throughout the entire life cycle of a car, including its manufacturing, use, and disposal.

[0009] Existing technical documents Patent documents Patent Document 1: International Publication No. 2021 / 001813 Patent Document 2: Japanese Patent Publication No. 2019-503920 Patent Document 3: International Publication No. 2022 / 250091 Summary of the Invention

[0010] The problem that the invention aims to solve If we consider the entire life cycle of a vehicle, it is insufficient to focus solely on reducing GHG emissions during vehicle use (driving) in order to reduce the total amount of GHG emitted into the environment.

[0011] In addition, there is currently no research on reducing LC-GHG (hereinafter referred to as lifecycle GHG or LC-GHG) generated throughout the entire lifecycle of a vehicle, from its manufacturing and use to its disposal, by focusing on the post-modal modules.

[0012] Therefore, the object of the present invention is to provide an automotive rear module capable of reducing the LC-GHG per unit area.

[0013] Methods for solving problems The main points of this disclosure are as follows.

[0014] (1) The first technical solution of the present invention is a rear module for automobiles, which has an integrated component formed by hot stamping multiple integrated steel plates, and the projected area when viewed from the vertical direction of the reference plane is set as S(m 2 The total weight of the components in the rear module of the automobile is defined as W (kg), and the total weight of the components made of steel with a plate thickness of less than 1.5 mm and a minimum Vickers hardness of HV230 or higher is defined as W. A When W / S is below 24, W A / W is above 0.30.

[0015] (2) The automotive rear module described in (1) above may also include: element technology A1; and at least one of element technology B1, element technology C1, element technology C2, element technology D1 and element technology D2.

[0016] The aforementioned element technology A1 is a skeleton component formed by hot stamping a steel plate. The skeleton component has a closed section portion with a closed cross-section perpendicular to its length direction. The closed section portion has: at least two flat portions, each with a radius of curvature greater than the maximum external dimension of the cross-section; and concave reinforcing rib portions formed between the two flat portions. Each concave reinforcing rib portion has a pair of wall portions with a radius of curvature of 50 mm or more, protruding inwards from opposing ends of the two flat portions via a pair of curved portions bending inwards towards the closed section. The Vickers hardness at the center of the wall portion's thickness is 520 Hv or more, and the width of the wall portion is the effective width W calculated according to the Karman effective width formula. e The standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution of the surface layer of the wall by the standard deviation of the hardness frequency distribution of the center layer of the wall thickness is less than 1.0.

[0017] The element technology B1 is a structural component having a component body formed by multiple steel plates joined together, having a ring shape when viewed from above. The multiple steel plates include a first steel plate having the smallest plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate. The value of coefficient A calculated using the chemical composition of the first steel plate by the following formula (1) is greater than the value of coefficient A calculated using the chemical composition of the second steel plate by the following formula (1).

[0018] A=1.48×(2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr+2×Mo) 3.42 (1) In the above formula (1), the content (mass%) of the corresponding element is substituted into the element symbol.

[0019] The aforementioned element technology C1 is a structural member for a vehicle body, satisfying at least one of the following (C1a), (C1b), and (C1c): (C1a) the structural member includes a pair of side frames and a cross member connecting the side frames, the side frames and the cross member being formed of a plurality of steel plates joined together, the plurality of steel plates including a first steel plate having a minimum thickness and a second steel plate having a thickness greater than that of the first steel plate, and a coating (film) being provided on the first steel plate, the coating containing 0.001 g / m³. 2 The above refers to one or more oxides selected from the group consisting of Zr oxides, Zn oxides, and Ti oxides; (C1b) the structural member comprises a pair of side frames and a frame crossbeam connecting the side frames, the side frames and the frame crossbeam being formed of 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, wherein the first steel plate is provided with a content of 0.500 g / m 2 The following carbon black film; (C1c) The structural member has a pair of side frames and a frame crossbeam connecting the side frames, the side frames and the frame crossbeam being formed of 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 coated steel plates having an aluminum-based coating on two surfaces of a base steel plate, the thickness of the aluminum-based coating in the first steel plate being less than the thickness of the aluminum-based coating in the second steel plate.

[0020] The aforementioned element C2 is a structural component for a vehicle body, satisfying at least one of the following (C2a), (C2b), and (C2c): (C2a) the structural component includes a pair of side frames and a frame crossbeam connecting the side frames, the side frames and the frame crossbeam being formed from a plurality of steel plates joined together, the plurality of steel plates including a first steel plate and a second steel plate, the second steel plate having an end portion that overlaps with the end portion of the first steel plate and is joined thereto, forming an overlap portion together with the end portion of the first steel plate; a film is provided on the outer surface of each of the first and second steel plates, the film containing 0.001 g / m³. 2 The above refers to one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide; (C2b) the structural member has a pair of side frames and a frame crossbeam connecting the side frames, the structural member is formed of a plurality of steel plates joined together, the plurality of steel plates including a first steel plate and a second steel plate, the second steel plate having an end that overlaps with the end of the first steel plate by being overlapped and joined together, and on the surface of each of the first steel plate and the second steel plate located outside the overlap, a 0.500 g / m 2 The following carbon black film; (C2c) The structural member has a pair of side frames and a frame crossbeam connecting the side frames, the side frames and the frame crossbeam being formed by a plurality of steel plates joined together, the plurality of steel plates including a first steel plate, a second steel plate and a third steel plate, the second steel plate having an end that overlaps with the end of the first steel plate by being joined to form an overlap portion together with the end of the first steel plate, at least one of the first steel plate and the second steel plate and the third steel plate being coated steel plates having aluminum-based coatings on two surfaces of the base steel plate, the thickness of the aluminum-based coating in at least one of the first steel plate and the second steel plate being less than the thickness of the aluminum-based coating in the third steel plate.

[0021] The element technology D1 is a stamped forming part that joins multiple partial blanks made of steel sheet, satisfying at least one of the following (D1a) and (D1b): (D1a) At least two of the partial blanks are joined by multiple joining portions in an overlap formed by partial overlap; in a cross section perpendicular to the surface of the partial blank containing the outermost partial blank at the center of the joining portion, at a position 1 / 4 of the sheet thickness away from the surface of the partial blank in contact with other partial blanks, when the Vickers hardness at a position 15 mm or more from the center of the joining portion and not where the joining is not performed is set to Hvm, the difference between the maximum and minimum Vickers hardness, ΔHv, is less than 0.2H in the range within 5 mm (or within 12 mm) from the end of the joining portion toward the base material side for a portion of the multiple joining portions. The ΔHv of the other joint portions (joint portions other than the first portion) is 0.2Hvm or more, preferably 0.3Hvm, 0.4Hvm, or 0.5Hvm or more; (D1b) at least two of the partial blanks are joined by a plurality of spot welds in a partially overlapping overlap, and in a cross section including the center of the spot weld of the outermost partial blank, at a position 1 / 4 of the plate thickness from the surface of the partial blank, the hardness at a position 15 mm or more from the center of the spot weld and where the spot weld is not performed is set as Hvm, and for a portion of the plurality of spot welds, the difference between the maximum hardness and the minimum hardness within a radius of 12 mm from its center, i.e., ΔHv, is less than 0.2Hvm, and the ΔHv of the spot welds other than the first portion is 0.2Hvm or more.

[0022] The element technology D2 is a stamped part that satisfies at least one of the following (D2a) and (D2b): (D2a) the stamped part is joined at a joint by overlapping a patchwork made of steel sheet on the surface of a base blank, the stamped part having a bend, and the difference between the maximum hardness of the base blank surface within 2 mm outward from the outer edge of the joint and the hardness of the base material of the base blank being 7% or more of the hardness of the base material of the base blank; in the case of one bend, the bend exists only in a region on either side of the surface of the base blank, with the bend as the boundary; in the case of two or more bends, the bends exist only in the region between two adjacent bends on the surface of the base blank; (D2b) The stamped part is formed by overlapping welded parts made of steel plates on the surface of a base blank and joining them by spot welding at the joint point. The stamped part has a bent portion. The difference between the maximum hardness at a position 5 mm from the center of the joint point on the surface of the base blank and the hardness of the base material of the base blank is more than 7% of the hardness of the base material of the base blank. When there is one bent portion, the bent portion exists only in one area on the surface of the base blank, with the bent portion as the boundary. When there are two or more bent portions, the bent portions exist only in the area between two adjacent bent portions on the surface of the base blank.

[0023] (3) The automotive rear module described in (2) above may also include the element technology A1 and the element technology B1.

[0024] (4) The automotive rear module described in (2) above may also include: the element technology A1; and at least one of the element technology C1 and the element technology C2.

[0025] (5) The automotive rear module described in (2) above may also include: the element technology A1; and at least one of the element technology D1 and the element technology D2.

[0026] (6) The automotive rear module described in (2) above may also include: element technology A1; element technology B1; at least one of element technology C1 and element technology C2; and at least one of element technology D1 and element technology D2.

[0027] Invention Effects According to this disclosure, it is possible to provide an automotive rear module that can reduce the size of LC-GHG per unit area. Attached Figure Description

[0028] Figure 1 This is a characteristic graph representing the environmental impact (GHG emissions) of each raw material used in the manufacture of automotive aftermarket modules.

[0029] Figure 2 This is an exploded perspective view showing the rear module of the vehicle according to this embodiment.

[0030] Figure 3A It is a chart showing the weights of the various components in Example 1 of the invention.

[0031] Figure 3B This is a chart showing the weights of the various components in Comparative Example 1.

[0032] Figure 4A For the example, W is plotted on the horizontal axis. A / W, plot W / S (kg / m) on the vertical axis 2 (Charts)

[0033] Figure 4B For the example, W is plotted on the horizontal axis. A / W, plot LC-GHG / S (kg, CO2-eq / m) on the vertical axis. 2 The chart is represented by the graph.

[0034] Figure 5 This is a plan view of the structural components of the first embodiment.

[0035] Figure 6 yes Figure 5 Section II-II view.

[0036] Figure 7A This is a schematic diagram illustrating the manufacturing method of the structural member of the first embodiment, and a diagram showing the blank of the first embodiment.

[0037] Figure 7B This is a schematic diagram illustrating the manufacturing method of the structural member of the first embodiment, and a diagram showing the blank of the first embodiment.

[0038] Figure 7C This is a schematic diagram illustrating the manufacturing method of the structural member of the first embodiment, and a diagram showing the blank of the first embodiment.

[0039] Figure 7D This is a schematic diagram illustrating the manufacturing method of the structural member of the first embodiment, and a diagram showing the blank of the first embodiment.

[0040] Figure 7E This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment.

[0041] Figure 7FThis is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment.

[0042] Figure 7G This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment.

[0043] Figure 8 This is a cross-sectional view of the blank according to the second embodiment.

[0044] Figure 9 This is a cross-sectional view of the blank according to the third embodiment.

[0045] Figure 10A These are cross-sectional views of the blanks in various embodiments of the modified examples.

[0046] Figure 10B This is another cross-sectional view of the blank in a modified example of each embodiment.

[0047] Figure 10C This is another cross-sectional view of the blank in a modified example of each embodiment.

[0048] Figure 11 These are plan views of the structural components of various embodiments.

[0049] Figure 12A This is a diagram showing the segmentation pattern of the structural components in the first embodiment.

[0050] Figure 12B This is a diagram showing another division pattern of the structural components in the first embodiment.

[0051] Figure 12C This is a diagram showing another division pattern of the structural components in the first embodiment.

[0052] Figure 12D This is a diagram showing another division pattern of the structural components in the first embodiment.

[0053] Figure 12E This is a diagram showing another division pattern of the structural components in the first embodiment.

[0054] Figure 12F This is a diagram showing another division pattern of the structural components in the first embodiment.

[0055] Figure 12G This is a diagram showing another division pattern of the structural components in the first embodiment.

[0056] Figure 13A This is a diagram illustrating the segmentation pattern of the structural components in the second embodiment.

[0057] Figure 13B This is a diagram showing another division pattern of the structural components in the second embodiment.

[0058] Figure 13C This is a diagram showing another division pattern of the structural components in the second embodiment.

[0059] Figure 13D This is a diagram showing another division pattern of the structural components in the second embodiment.

[0060] Figure 14 This is an exploded perspective view of the structural components of the first embodiment.

[0061] Figure 15 yes Figure 14 The cross-sectional view of the side frames included in each structural component is shown.

[0062] Figure 16A This is a schematic diagram illustrating the manufacturing method of the structural member of the first embodiment, and it represents the... Figure 14 A diagram of the blank corresponding to one of the structural components shown.

[0063] Figure 16B This is a schematic diagram illustrating the manufacturing method of the structural member of the first embodiment. Figure 16A The cross-sectional view of the blank shown.

[0064] Figure 16C This is a schematic diagram illustrating the manufacturing method of the structural member of the first embodiment. Figure 16A Another cross-sectional view of the billet shown.

[0065] Figure 16D This is a schematic diagram illustrating the manufacturing method of the structural member of the first embodiment, and it represents the... Figure 14 A diagram of the blank corresponding to the other side of the structural component shown.

[0066] Figure 16E This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment.

[0067] Figure 16F This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment.

[0068] Figure 16G This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment.

[0069] Figure 17 This is a cross-sectional view of a structural member manufactured using the manufacturing method of the first embodiment.

[0070] Figure 18A This is a cross-sectional view of the blank according to the second embodiment.

[0071] Figure 18BThis is another cross-sectional view of the blank in the second embodiment.

[0072] Figure 19A This is a cross-sectional view of the structural component in the second embodiment.

[0073] Figure 19B This is another cross-sectional view of the structural component in the second embodiment.

[0074] Figure 19C This is another cross-sectional view of the structural component in the second embodiment.

[0075] Figure 20 This is a cross-sectional view of the blank in a modified example of the second embodiment.

[0076] Figure 21 This is a plan view of the blank in the third embodiment.

[0077] Figure 22 This is a cross-sectional view of the blank according to the third embodiment.

[0078] Figure 23 This is a cross-sectional view of the blank in a modified example of the third embodiment.

[0079] Figure 24 This is a cross-sectional view of the blank in another variation of the third embodiment.

[0080] Figure 25 This is an exploded perspective view of the structural components of the fourth embodiment.

[0081] Figure 26 This is a plan view of the blank according to the fourth embodiment.

[0082] Figure 27 This is a plan view of another blank in the fourth embodiment.

[0083] Figure 28 This is a plan view of the blank in a modified example of the first embodiment.

[0084] Figure 29 This is a plan view of the blank in another variation of the first embodiment.

[0085] Figure 30 This is a plan view of the blank in a modified example of the fourth embodiment.

[0086] Figure 31 This is a plan view of the blank in another variation of the fourth embodiment.

[0087] Figure 32 This is a plan view of the blank in another variation of the fourth embodiment.

[0088] Figure 33 This is a plan view of the blank in another variation of the fourth embodiment.

[0089] Figure 34 This is a plan view of the blank in another variation of the fourth embodiment.

[0090] Figure 35 This is a plan view of the blank in another variation of the fourth embodiment.

[0091] Figure 36 This is a plan view of the blank in another variation of the fourth embodiment.

[0092] Figure 37 This is a plan view of the blank in another variation of the fourth embodiment.

[0093] Figure 38 This is a plan view of the blank in another variation of the fourth embodiment.

[0094] Figure 39 This is a plan view of the blank in another variation of the fourth embodiment.

[0095] Figure 40 This is a plan view of the blank in another variation of the fourth embodiment.

[0096] Figure 41 This is a cross-sectional view of the side frame included in the structural member of each embodiment of the modified example.

[0097] Figure 42A This is a diagram illustrating the segmentation pattern of the structural components in the embodiment.

[0098] Figure 42B This is a diagram illustrating another division pattern of the structural components in the embodiment.

[0099] Figure 42C This is a diagram illustrating another division pattern of the structural components in the embodiment.

[0100] Figure 42D This is a diagram illustrating another division pattern of the structural components in the embodiment.

[0101] Figure 42E This is a diagram illustrating another division pattern of the structural components in the embodiment.

[0102] Figure 42F This is a diagram illustrating another division pattern of the structural components in the embodiment.

[0103] Figure 43 This is an exploded perspective view of the structural components of the first embodiment.

[0104] Figure 44 yes Figure 43 The cross-sectional view of the side frames included in each structural component is shown.

[0105] Figure 45A This is a schematic diagram illustrating the manufacturing method of the structural member of the first embodiment, and it represents the... Figure 43 A diagram of the blank corresponding to one of the structural components shown.

[0106] Figure 45B This is a schematic diagram illustrating the manufacturing method of the structural member of the first embodiment. Figure 45A The cross-sectional view of the blank shown.

[0107] Figure 45C This is a schematic diagram illustrating the manufacturing method of the structural member of the first embodiment. Figure 45A Another cross-sectional view of the billet shown.

[0108] Figure 45D This is a schematic diagram illustrating the manufacturing method of the structural member of the first embodiment, and a diagram showing the blank corresponding to the other side of the structural member shown in FIG45.

[0109] Figure 45E This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment.

[0110] Figure 45F This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment.

[0111] Figure 45G This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment.

[0112] Figure 46 This is a cross-sectional view of a structural member manufactured using the manufacturing method of the first embodiment.

[0113] Figure 47A This is a cross-sectional view of the blank according to the second embodiment.

[0114] Figure 47B This is another cross-sectional view of the blank in the second embodiment.

[0115] Figure 48A This is a cross-sectional view of the structural component in the second embodiment.

[0116] Figure 48B This is another cross-sectional view of the structural component in the second embodiment.

[0117] Figure 49 This is a cross-sectional view of the blank in a modified example of the second embodiment.

[0118] Figure 50 This is an exploded perspective view of the structural components of the third embodiment.

[0119] Figure 51This is a plan view of the blank in the third embodiment.

[0120] Figure 52 This is a plan view of another blank in the third embodiment.

[0121] Figure 53 This is a plan view of the blank in a modified example of the first embodiment.

[0122] Figure 54 This is a plan view of the blank in another variation of the first embodiment.

[0123] Figure 55 This is a plan view of the blank in another variation of the first embodiment.

[0124] Figure 56 This is a plan view of the blank in a modified example of the third embodiment.

[0125] Figure 57 This is a plan view of the blank in another variation of the third embodiment.

[0126] Figure 58 This is a plan view of the blank in another variation of the third embodiment.

[0127] Figure 59 This is a plan view of the blank in another variation of the third embodiment.

[0128] Figure 60 This is a plan view of the blank in another variation of the third embodiment.

[0129] Figure 61 This is a plan view of the blank in another variation of the third embodiment.

[0130] Figure 62 This is a plan view of the blank in another variation of the third embodiment.

[0131] Figure 63 This is a plan view of the blank in another variation of the third embodiment.

[0132] Figure 64 This is a plan view of the blank in another variation of the third embodiment.

[0133] Figure 65 This is a plan view of the blank in another variation of the third embodiment.

[0134] Figure 66 This is a plan view of the blank in another variation of the third embodiment.

[0135] Figure 67 This is a cross-sectional view of the side frame included in the structural member of each embodiment of the modified example.

[0136] Figure 68A This is a diagram illustrating the segmentation pattern of the structural components in the embodiment.

[0137] Figure 68B This is a diagram illustrating another division pattern of the structural components in the embodiment.

[0138] Figure 69 This is a schematic diagram showing the appearance of a car's integrated door ring.

[0139] Figure 70 This diagram illustrates the manufacturing process of conventional TWB stamping forming parts.

[0140] Figure 71 This is a schematic diagram illustrating the composition of the blank used for stamping door rings.

[0141] Figure 72 This is a conceptual diagram representing the stress analysis results of the overlapping part at the bottom of column A. Figure 72 (a) is a conceptual diagram showing the stress state of the lower part of column A when viewed from the outside, using a contour diagram. Figure 72 (b) is a conceptual diagram showing the stress state of the rocker when viewed from the inside, using a contour plot.

[0142] Figure 73 This is a conceptual diagram representing an example of a spot weld on the overlapping section at the bottom of the A-pillar. Figure 73 (a) shows an example of the spot weld location of the overlapping part at the bottom of column A. Figure 73 (b) is a conceptual diagram illustrating the locations of these spot welds, showing the parts at risk of breakage enclosed by solid lines and the parts at no risk of breakage enclosed by dashed lines.

[0143] Figure 74 This is a conceptual diagram representing the spot weld positions of the overlapping parts determined through simulation analysis. Figure 74 (a) shows an example of spot welding on the lower part of the A-pillar (L-shaped) and the lower part of the B-pillar (T-shaped) when viewed from the outside. Figure 74 (b) is a conceptual diagram representing the same area when viewed from the inside.

[0144] Figure 75 The results were obtained through FEM-based simulation. Figure 75 A conceptual diagram of the stress state of an integral blank after hot pressing. Figure 75 (a) is a conceptual diagram showing the stress state of the overlapping portion (L-shaped) at the bottom of column A and the overlapping portion (T-shaped) at the bottom of column B when viewed from the outside. Figure 75 (b) is a conceptual diagram representing the same area when viewed from the inside.

[0145] Figure 76 This is a diagram illustrating the manufacturing process of the stamped part of the TWB of the present invention.

[0146] Figure 77 This is an explanatory diagram used to illustrate the HAZ softening zone in spot welding.

[0147] Figure 78 This is a conceptual diagram illustrating an application example of the present invention in an automotive floor module.

[0148] Figure 79 This indicates the overlapping welding position of the overlapping portion, determined through analysis based on simulation, and represents the replacement... Figure 74 A conceptual diagram illustrating an example of overlapping welding performed through spot welding. Figure 79 (a) shows an example of the overlapping welding of the lower A-pillar (L-shaped) and the lower B-pillar (T-shaped) sections when viewed from the outside. Figure 79 (b) is a conceptual diagram representing the same area when viewed from the inside.

[0149] Figure 80 This is a diagram illustrating the present invention, showing an example of a stamped part (hat-shaped part) with a hat-shaped cross-section. Figure 80 (a) shows its appearance. Figure 80 (b) represents its cross-sectional view.

[0150] Figure 81 It means used for Figure 80 A schematic diagram of an example of a stamped blank (welded part blank) for a hat-shaped component.

[0151] Figure 82 It means in Figure 80 A schematic diagram of an example of a cross-section of a hat-shaped component with a concave portion on the top surface.

[0152] Figure 83 It means used for Figure 82 A schematic diagram of an example of a stamped blank (welded part blank) of a hat-shaped component with a concave top surface.

[0153] Figure 84 This is a diagram illustrating an example of a hat-shaped component manufactured using conventional methods. Figure 84 Image (a) shows its appearance. Figure 84 Figure (b) shows its cross-sectional view. Figure 84 (c) shows the representation used for Figure 84 A schematic diagram of an example of a stamped weldment blank for the hat-shaped component in (a).

[0154] Figure 85 This is a diagram illustrating an example of a cap-shaped component according to one aspect of the present invention. Figure 85Examples of joints based on spot welding are shown in (a) to (c). Figure 85 (a) is a schematic diagram showing its appearance. Figure 85 (b) is a schematic diagram showing its cross-sectional view. Figure 85 (c) indicates that it is used for Figure 85 A schematic diagram of an example of a stamped weldment blank for the hat-shaped component in (a).

[0155] Figure 86 This is a diagram illustrating an example of a cap-shaped component according to one aspect of the present invention. Figure 86 (d) to (f) are schematic diagrams illustrating an example of a weldment blank in which other joining methods are applied instead of spot welding in the same cap-shaped component. Figure 86 (d) indicates an example where lap fillet welding was used. Figure 86 (e) indicates an example where lap welding is used. Figure 86 In the example (f), an adhesive is applied before stamping and laser spot welding is applied after stamping.

[0156] Figure 87 This is a diagram illustrating an example of a cap-shaped component according to one aspect of the present invention, showing that... Figure 85 A schematic diagram of an example of a cap-shaped component where the welded part extends to the flange, as shown in (a).

[0157] Figure 88 This is a diagram illustrating an example of a cap-shaped component according to one aspect of the present invention. Figure 88 (a) indicates that there is no Figure 85 A schematic diagram of an example of a welded component on one side of the upright wall of the hat-shaped part shown in (a). Figure 88 (b) indicates that there is none. Figure 87 A schematic diagram illustrating an example of a welded component on one side of the upright wall of a hat-shaped part.

[0158] Figure 89 This is a diagram illustrating an example of a cap-shaped component according to one aspect of the present invention. Figure 89 (a) is a schematic diagram illustrating an example of a case where the top surface has a concave portion. Figure 89 (b) is a schematic diagram illustrating an example of a case where the top surface has a convex portion. Figure 89 (c) is a schematic diagram showing another example of a case where there is a protrusion on the top surface. Detailed Implementation

[0159] As mentioned above, considering the entire life cycle of a vehicle, it is insufficient to focus solely on reducing GHG emissions during vehicle use (driving) in order to reduce the total amount of GHG emitted into the environment.

[0160] In addition, the rear module accounts for approximately 3 to 10% of the vehicle's total weight, so the reduction contribution from reducing the GHG associated with the rear module is substantial.

[0161] Currently, the main focus is on using raw materials such as aluminum and carbon to make automobiles more lightweight. However, the inventors of this application focus on the following four types of GHG and study how to reduce their total amount: 1. GHG generated in the manufacturing of raw materials for the rear module of the automobile (hereinafter referred to as "raw material manufacturing GHG"); 2. GHG generated in the manufacturing process of the rear module of the automobile (hereinafter referred to as "process GHG"); 3. The contribution of the rear module of GHG generated when the automobile is in motion (hereinafter referred to as "in motion GHG"); and 4. GHG generated when the rear module of the automobile is discarded (hereinafter referred to as "discard GHG").

[0162] Furthermore, the rear module in this specification is a structural component assembly comprising the floor on the rear side of the vehicle body and the frame components that connect to it. The rear module mainly consists of an upper frame and a lower frame.

[0163] Furthermore, the rear module includes reinforcing or supplementary components that engage with these parts or components.

[0164] In addition, in this specification, GHG generated during the life cycle, with CO2 as the primary component, is referred to as LC-GHG. The CO2 quantity is defined as the total quantity that is equivalently converted to the mass of GHG other than CO2.

[0165] Other GHGs besides CO2 include methane, nitrous oxide, and CFCs, which are ozone-depleting substances. The equivalent mass of CO2 is calculated using the conversion factors listed in Table 1, which are set according to the categories of raw materials, processes, uses, and recycling.

[0166] "CO2 equivalent" is also called "CO2 equivalent mass". In this specification, "CO2 equivalent", "CO2 equivalent mass" and "CO2 conversion quantity" are defined with the same meaning.

[0167] "CO2 equivalent mass" is calculated by weighting CO2 (global warming potential: 1) and gases other than CO2, such as methane (CH4) (25 times the greenhouse effect of CO2 per unit mass: global warming potential 25) and nitrous oxide (N2O) (298 times the greenhouse effect of CO2 per unit mass: global warming potential 298), and then converting them into the mass of CO2.

[0168] (GGHG raw material manufacturing) Compared to other raw materials, steel, as a raw material, has the lowest GHG emissions per unit weight. Figure 1 This is a graph showing the environmental impact (GHG emissions) of each raw material used in the manufacture of automotive rear modules. The vertical axis represents the materials used in automotive rear modules: ordinary steel sheet, high-strength steel sheet, aluminum, and carbon fiber reinforced plastic (CFRP). The horizontal axis represents the GHG emissions per equivalent function [kg - CO2 equivalent / kg - equivalent component].

[0169] like Figure 1 As shown, steel raw materials (typical steel plates, high-strength steel plates) have an overwhelmingly lower GHG emission rate compared to other raw materials (aluminum, carbon fiber reinforced plastics). This demonstrates that the use of steel as the primary material for the construction of automotive rear modules greatly contributes to the reduction of LC-GHG emissions.

[0170] (Process GHG) In the manufacturing of automotive rear modules, GHG is mainly generated during welding, heating, and painting processes. Therefore, by ensuring the required performance of automotive rear modules while implementing appropriate process design, it is possible to reduce LC-GHG.

[0171] (GHG while driving) By reducing the weight of the rear module of a vehicle, the load on the drive source, such as the internal combustion engine, can be reduced. Therefore, reducing the weight of the rear module can contribute to the reduction of LC-GHG (lower atmospheric pressure).

[0172] (GHG when abandoned) Steel recycling can help reduce GHG by 1.60 kg-CO2eq per kg of waste. Compared to aluminum, steel has a smaller emission reduction effect per kg, but when using high-strength steel, less weight is required to achieve the necessary strength. Therefore, it can be said that using high-strength steel can contribute to the reduction of LC-GHG. That is, GHG at the time of disposal is the same as that used in the production of GHG from raw materials. As a raw material for constructing automotive aftermarket modules, steel is mainly used, thereby reducing emissions and contributing to the reduction of LC-GHG.

[0173] As mentioned above, in order to reduce LC-GHG, the total GHG emissions should be reduced from four perspectives, such as the trade-off between "raw material manufacturing GHG and waste disposal GHG" and "driving GHG". Furthermore, in general, there is a tendency for "process GHG" to increase in order to manufacture lightweight and high-performance components, and there is a trade-off between "process GHG" and "driving GHG".

[0174] Previous studies have explored and discussed GHG reduction methods across various lifecycles, but no optimal examples of material selection and process design for reducing LC-GHG have been publicly disclosed.

[0175] The inventors of this application focused on reducing LC-GHG by considering the above four categories of GHG with trade-offs, and found that by controlling the weight of the components per specified area and the weight of high-strength components with a plate thickness of 1.5 mm or less and a minimum Vickers hardness of HV230 or more within an appropriate range, it is possible to reduce the LC-GHG of the automotive rear module while meeting the necessary strength (crash resistance).

[0176] Hereinafter, a vehicle rear module according to an embodiment of the present invention, based on the above insights, will be described with reference to the accompanying drawings. However, these descriptions are merely illustrative of preferred embodiments of the present invention and do not imply that the present invention is limited to such specific embodiments.

[0177] The rear module 100 of this embodiment is applicable to automobile bodies constructed from a frame with a single-shell structure having shock-absorbing skeleton members.

[0178] Figure 2 This is an exploded perspective view of the rear vehicle module 100 according to this embodiment. Figure 2 As shown, the rear module 100 of the vehicle includes an integrated upper frame 10 and an integrated lower frame 20.

[0179] The integrated upper frame 10 is composed of a front rear beam 11, a rear rear beam 12, two frame crossbeams 13, a frame crossbeam extension 14 that connects to the frame crossbeams 13, a rear floor section 15, a rear floor side panel section 16, and a rear wheel arch section 17.

[0180] The integrated upper frame 10 is manufactured by hot stamping a tailored blank into an integrated component.

[0181] A welded blank can be obtained by joining multiple hot-stamped steel plates corresponding to various parts that are integrated components, and by overlapping and joining hot-stamped steel plates formed into reinforcing members as needed (welded part joining).

[0182] The integrated lower frame 20 consists of a front part 21 of the rear beam, a rear part 22 of the rear beam, three frame crossbeams 23, and a corresponding extension part 24 of the frame crossbeams that connects with the frame crossbeams 23.

[0183] The integrated lower frame 20 is manufactured by hot stamping a single welded blank to form an integrated component.

[0184] A welded blank can be obtained by joining multiple hot-stamped steel plates corresponding to various parts that are integrated components, and by overlapping and joining hot-stamped steel plates formed into reinforcing members as needed (welded part joining).

[0185] Thus, the rear module 100 of this embodiment has parts (integrated lower frame 110 and integrated upper frame 120) that are formed into integrated components by hot stamping of a single welded blank.

[0186] Moreover, by hot stamping the welded blanks, it is possible to obtain integrated parts with different characteristics (weight, hardness, strength, plate thickness) in different parts.

[0187] In addition, in the rear module 100 of the vehicle, reinforcing components and brackets are sometimes further installed after hot stamping.

[0188] Furthermore, the integrated components are not limited to the examples described above. For instance, in this embodiment, the rear floor portion 15, the rear floor side panel portion 16, and the rear wheel arch portion 17 are integrated with the upper frame 10. However, they can also be added after forming an integrated component consisting of the front portion 11 of the rear beam, the rear portion 12 of the rear beam, three frame crossbeams 13, and the corresponding extension portion 14 of the frame crossbeams that connect to the frame crossbeams 13. Additionally, the rear wheel arch portion 17 can also be integrated with the integrated lower frame 20.

[0189] Thus, in the rear automotive module 100 of this embodiment, since an integrated component is formed by hot stamping multiple hot-stamped steel sheets joined together, the material manufacturing GHG (Gas Heat Gauge) can be reduced compared to the case where each part is stamped separately and then welded together after appropriate trimming of unnecessary parts. Furthermore, when each part is hot-stamped and then welded, the number of heating processes and the time required for hot stamping are increased. However, in the rear automotive module 100 of this embodiment, by hot-stamping multiple steel sheets after welding, the number of heating processes and the time can be reduced. Therefore, the rear automotive module 100 of this embodiment can reduce the manufacturing GHG while achieving the performance required for a rear automotive module.

[0190] Furthermore, for the automotive rear module 100 of this embodiment, by controlling the weight of the constituent components per projected area and the weight of the high-strength constituent components with a plate thickness of 1.5 mm or less and a minimum Vickers hardness of HV230 or more within an appropriate range, the LC-GHG of the automotive rear module can be reduced.

[0191] Specifically, the projected area when viewed from the perpendicular direction of the reference plane is denoted as S(m). 2 In the components of the rear module of this automobile, the total weight of the components is set as W (kg), and the total weight of the components made of steel with a plate thickness of less than 1.5 mm and a minimum Vickers hardness of HV230 or higher is set as W. A At that time, by satisfying W / S less than 24, W AWith a / W ratio of 0.30 or higher, it is possible to reduce the LC-GHG of the rear module of the car.

[0192] The above-mentioned conditions for a rear-mounted vehicle module did not exist previously, and these conditions would not have been easily conceived without the insights of the inventors of this application.

[0193] In addition, the reference plane refers to the plane perpendicular to the vehicle height direction in the rear module of the car when it is installed on the vehicle body.

[0194] The larger the body and side door modules, the greater the W. A The value tends to be larger. Therefore, in this application, the value of W corresponding to the projected area S of the rear module of the vehicle is W / S (m²). 2 ) is used as an indicator.

[0195] With a W / S value of 24 or less, it is possible to achieve a weight reduction commensurate with the size of the side door module, thus reducing GHG during driving.

[0196] From the perspective of reducing GHG during driving, the smaller the W / S value, the better, preferably 23 or less, and even more preferably 22 or less.

[0197] The lower limit of W / S is set based on the required safety performance. To balance ensuring both the rigidity and safety performance of the module, a W / S of 5.0 or higher is acceptable.

[0198] In W A When the / W value is above 0.30, the proportion of high-strength components with a plate thickness of less than 1.5mm and a minimum Vickers hardness of HV230 or above is higher in the components used in the side door module, thus reducing the amount of raw materials used in GHG manufacturing.

[0199] From the perspective of reducing the raw materials used in GHG production, W A The higher the / W value, the better, preferably exceeding 0.40, and more preferably exceeding 0.45.

[0200] Furthermore, from the perspective of reducing raw material consumption in GHG manufacturing, the weight of components with a sheet thickness of 1.3mm or less and a minimum Vickers hardness of HV230 or higher is set as W. B At that time, W B The value of / W is preferably 0.18 or higher, and more preferably 0.20 or higher.

[0201] The method for determining Vickers hardness is as follows.

[0202] Samples with cross-sections perpendicular to the plate surface are collected from the flat portions of various locations. These cross-sections are prepared as the testing surface, which is then used for hardness testing. The preparation method of the testing surface is performed according to JIS Z 2244:2009. After grinding the testing surface using #600~#1500 silicon carbide paper, the surface is then polished to a mirror finish using a liquid prepared by dispersing diamond powder with a particle size of 1μm~6μm in a diluent such as alcohol and pure water. The hardness test is performed according to the method described in JIS Z 2244:2009. Using a micro Vickers hardness tester, 30 points are measured at 3 / 8 of the sample thickness, with a load of 1000gf and at intervals of at least three times the indentation length. The average value of these measurements is taken as the hardness at the center of the plate thickness.

[0203] In this application, at least one of (1) element technology A1 and (2) element technology B1, element technology C1, element technology C2, element technology D1 and element technology D2 is applied to the constituent parts of the rear module 100 of the automobile, thereby increasing the weight ratio of steel materials in the automobile body and reducing the GHG of the aforementioned raw materials, and reducing the GHG during driving by lightening the automobile body. As a result, a significant reduction in LC-GHG is achieved compared with conventional automobile bodies.

[0204] More preferably, the element technology A1 and the element technology B1 are applied.

[0205] More preferably, at least one of the element technology A1, element technology C1, and element technology C2 is applied.

[0206] More preferably, at least one of the element technology A1, element technology D1, and element technology D2 is applied.

[0207] More preferably, at least one of the element technology A1, the element technology B1, the element technology C1 and the element technology C2, and at least one of the element technology D1 and the element technology D2 are applied.

[0208] Furthermore, in this specification, the vehicle is described as having excellent rear-end collision safety. For example, a top rating in the IIHS (Insurance Institute for Highway Safety) rear-end collision neck injury protection test is sufficient evidence of its suitability for highway driving.

[0209] Furthermore, the vehicle body of the public road vehicle using the rear module of this embodiment is not limited to the body of an engine vehicle or an electric vehicle, but can also be the body of a hybrid vehicle, fuel cell vehicle, hydrogen engine vehicle, etc., which are driven by an internal combustion engine and an electric motor.

[0210] In addition, the car body that uses the rear module is not limited to a car body with a single-shell frame structure; it can also be a car body with a trapezoidal frame structure.

[0211] In addition, the types of vehicles used for road travel include passenger cars and commercial vehicles such as sedans, hatchbacks, station wagons, one-box vans, and pickup trucks.

[0212] Moreover, vehicles used for road travel include heavy-duty vehicles such as trucks.

[0213] (Example) The present invention is illustrated below with examples. Furthermore, the conditions of these examples are merely illustrative to confirm the feasibility and effectiveness of this disclosure, and the disclosure is not limited to these conditions. Various conditions can be employed to achieve the purpose of this disclosure without departing from its spirit.

[0214] Table 2 shows the calculated values ​​of various characteristic values ​​of the automotive rear module used as an example of the invention and a comparative example: • Number of constituent parts; • Weight ratio of steel plates; Projected area S (m 2 ); • Total weight W (kg) of the constituent components; W / S; • The total weight W of components with a sheet thickness of 1.5mm or less and a minimum Vickers hardness of HV230 or higher. A ; ·W A / W (kg / m 2 ); • The total weight W of the constituent parts with a sheet thickness of 1.3mm or less and a minimum Vickers hardness of HV230 or higher. B ; ·W B / W.

[0215] The rear module of the automobile in Invention Example 1 includes fifty-six components. Among them, four components are integrated.

[0216] The weight of each component, such as Figure 3A As shown in the chart.

[0217] exist Figure 3AIn the chart, the vertical axis represents the component weight for that location. The filled diagonal lines indicate locations meeting the criteria of a sheet thickness of 1.5mm or less and a minimum Vickers hardness of HV230 or higher. The filled dots indicate locations with a minimum Vickers hardness of HV230 or higher but a sheet thickness not less than 1.5mm. The horizontal axis is arranged from left to right in ascending order of sheet thickness. The area to the left of the dashed lines represents components with a sheet thickness of 1.5mm or less. Components No. 2, 3, 4, and 5 are integral components obtained by hot stamping from a single welded blank.

[0218] Furthermore, the same weight, plate thickness, and hardness were also implemented for Invention Examples 2-8.

[0219] The rear module of Comparative Example 1 comprises 129 components. There are no integrated components; each component is individually molded. The weight of each component is as follows: Figure 3B As shown in the chart.

[0220] exist Figure 3B In the chart, the vertical axis represents the component weight at that location. The filled diagonal lines indicate locations that meet the criteria of a sheet thickness of 1.5mm or less and a minimum Vickers hardness of HV230 or higher. The filled dots indicate locations with a minimum Vickers hardness of HV230 or higher but a sheet thickness not less than 1.5mm. The horizontal axis is arranged from left to right in ascending order of sheet thickness. The area to the left of the dashed lines represents components with a sheet thickness of 1.5mm or less.

[0221] In addition, the same weight, plate thickness, and hardness were applied to Comparative Examples 2 to 8.

[0222] The weights (kg) of the parts shown in Table 2 are the weights after the rear module of the automobile was cut along the weld lines of the welded blank. The weights in the comparative examples were determined by disassembling the body of a commonly used road vehicle and measuring and analyzing the data on its shape and weight. The weights in some comparative examples and invention examples were determined by measuring and analyzing design and development data based on CAD (Computer-Aided Design).

[0223] The hardness HV is calculated as follows.

[0224] Samples with cross-sections perpendicular to the plate surface are collected from the flat portions of various locations. These cross-sections are prepared as the testing surface, which is then used for hardness testing. The preparation method of the testing surface is performed according to JIS Z 2244:2009. After grinding the testing surface using #600~#1500 silicon carbide paper, the surface is then polished to a mirror finish using a liquid prepared by dispersing diamond powder with a particle size of 1μm~6μm in a diluent such as alcohol and pure water. The hardness test is performed according to the method described in JIS Z 2244:2009. Using a micro Vickers hardness tester, 30 points are measured at 3 / 8 of the sample thickness, with a load of 1000gf and at intervals of at least three times the indentation length. The average value of these measurements is taken as the hardness at the center of the plate thickness.

[0225] Table 3 shows the inventive examples and comparative examples, respectively. ·Total GHG emissions LC-GHG (kg, CO2-eq), and ·LC-GHG / S (kg, CO2-eq / m 2 The calculated value of ).

[0226] Total GHG emissions are calculated by summing the equivalent CO2 mass of GHG generated from raw materials, during manufacturing, during operation, and at the point of disposal. This is equivalent to the emissions of LC-GHG. The total GHG emissions are calculated using the method described later.

[0227] The characteristic values ​​of Examples 1-8 were obtained by the inventors of this application through measurement and analysis of the automobile body constructed by the inventors of this application using the above-mentioned element technologies.

[0228] In addition, the characteristic values ​​of Comparative Examples 1-8 were obtained by the inventors of this application through measurement and analysis of the car body of a commonly used road vehicle. For some comparative examples, the values ​​recorded as default values ​​on the website of the World Auto Steel Association (WAS) were used.

[0229] WAS is the automotive division of the World Steel Association (World Steel Federation), which consists of seventeen steel manufacturers worldwide.

[0230] In addition, 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".

[0231] (Calculation of raw materials for manufacturing GHG) The default settings of the GHG analysis software were used as the basic conditions. In these default settings, the scrap charge rate to the blast furnace was 11.9%, and the utilization rate of recycled scrap materials was set to 5% for plates, 85% for bars and wires, and 100% for cast iron based on statistical data. These were assumed as the basic conditions, and the values ​​were entered for calculation in the manner shown in Table 1 for the various raw material compositions.

[0232] (Calculation of process GHG) The default settings of the GHG parsing software are used as the basic conditions. Regarding the yield of raw materials in automotive parts production, it is assumed that steel plates are 55%, aluminum alloy plates are 52%, sheet, bar and wire are 75%, and cast iron, aluminum extrusion materials and aluminum casting materials are 80%. The values ​​are entered in the manner shown in Table 1 for calculation.

[0233] (Calculation of GHG during driving) For the powertrain type of the target vehicle, electric vehicles were selected. Based on the size and weight of the vehicles analyzed, a mid-size electric vehicle was chosen. The vehicle's driving mode was set to the following WLTP (Class 3b) mode.

[0234] WLTP mode Average speed…36.57 km / h; • Maximum speed…97.4 km / h; • Travel time…1477 seconds; • Driving distance…15.01km; • Idle speed ratio…15.4%; Cold start ratio…100%.

[0235] The driving range is assumed to be 110,000 km, and is set in a way that takes into account the weight reduction of the vehicle body and the size adjustment of the powertrain. In addition, the power consumption of the electric vehicle during driving is set to use electricity generated in Japan. The power consumption value of the contribution of the rear module obtained by the inventor through analysis is input and calculated.

[0236] (Calculation of GHG upon disposal) Based on the default settings of the GHG analysis software at the time of disposal, the recycling rate of steel is assumed to be 90.3% and the recycling rate of aluminum alloy is 78.6%. The settings are also taken into account as CO2 absorption, with the energy recovery from recycling to sources other than automobiles also taken into account.

[0237] Regarding the calculation of CO2 equivalent mass, GHG from the raw material manufacturing process, vehicle manufacturing process, fuel manufacturing and usage process, and raw material and vehicle recycling process shown in Table 1 is used as a coefficient for calculating CO2 equivalent mass. CO2 equivalent mass is determined using either weight or energy. These values ​​are the default settings for the GHG analysis software, based on statistical data on GHG emissions from various substances and processes.

[0238] Following the steps above, the equivalent mass of CO2 is calculated based on the GHG generated from raw materials, the GHG generated during the process, the GHG generated during operation, and the GHG generated during disposal. The LC-GHG recorded in Table 3 is then calculated by summing these values.

[0239] In Invention Examples 1-8, by increasing the steel usage ratio in the rear module of an automobile and combining the aforementioned technologies to form an integrated component, the result is that the W / S ratio can be reduced to 24 or less, and the W... A / W is above 0.30. This allows for the reduction of LC-GHG in the rear module of the vehicle.

[0240] On the other hand, in Comparative Examples 1-8, W A With a W / S ratio below 0.27, it is necessary to increase the W / S ratio to ensure collision performance, which cannot fully realize the reduction effect of GHG generated from raw materials and during driving.

[0241] In addition, in Comparative Examples 1 to 8, which did not adopt an integrated structure, each part was stamped and formed, and the unnecessary parts were trimmed and removed before being joined by welding. Therefore, the reduction effect of GHG during the manufacturing of raw materials and GHG during driving could not be fully obtained.

[0242] Figure 4A For the example, W is plotted on the horizontal axis. A / W, plot W / S (kg / m) on the vertical axis. 2 The resulting image.

[0243] Figure 4B For the specific implementation example, W is drawn on the horizontal axis. A / W, Plot LC-GHG / S (kg, CO2-eq / m) on the vertical axis. 2 The resulting chart.

[0244] These charts confirm that, according to the present invention, the LC-GHG is significantly reduced in size compared to existing structures.

[0245] Thus, according to the present invention, the projected area when viewed from a direction perpendicular to the reference plane is set as S(m 2 In the components of the rear module of this automobile, the total weight of the components is set as W (kg), and the total weight of the components made of steel with a plate thickness of 1.5mm or less and a minimum Vickers hardness of HV230 or more is set as W. A At that time, by satisfying W / S less than 24, W A With a / W ratio of 0.30 or higher, it is possible to reduce the LC-GHG of the rear module of the vehicle.

[0246] (Example 2) Table 4 shows the results of crash tests conducted on the Invention Example and the Comparative Example. In Table 4, the test results regarding the crashes are represented by evaluation values ​​A and B. In this evaluation, firstly, the test results from the IIHS rear-end collision test are disclosed. For the vehicle body of Comparative Example 6, which has the highest crash safety rating, numerical analysis of the rear-end collision test in the IIHS rear-end collision analytical model is performed, and the intrusion amount obtained is used as the benchmark (evaluation B).

[0247] Furthermore, the vehicle bodies of Comparative Examples 1-8 are also vehicle bodies that have obtained certification (type approval) in the regulations of various countries. In the comparison with Comparative Example 6, some of the safety performance evaluation results of the vehicle bodies are recorded.

[0248] For Invention Examples 1-8, numerical analysis of rear-end collision tests with only the rear module replaced was performed, and the safety performance was evaluated based on the relative intrusion of the rear module and the energy absorbed during the collision.

[0249] Furthermore, a rating of A is defined as a vehicle whose test results are superior to those of the vehicle with the highest rating in the IIHS rear-end collision simulation test (Comparative Example 6). A rating B is defined as a vehicle with the same safety test results as Comparative Example 6, where no component breakage occurs.

[0250] As shown in Table 4, in Invention Examples 1-8, regarding rear-end collisions, safety test results (rating A or rating B) of vehicles that received a "good" rating in the IIHS rear-end collision test were obtained.

[0251] Therefore, according to Examples 1-8 of the Invention, it is possible to reduce LC-GHG while meeting the safety test results of a vehicle that meets the "good" rating in the IIHS rear-end collision test.

[0252] The following is a summary of the technical elements of the automotive rear module 100 applicable to this embodiment.

[0253] Furthermore, the symbols for constituent elements, formulas, implementation methods, and examples in the descriptions of each element technology are assigned to each element technology for the purpose of brevity. Therefore, the same symbols are sometimes used in the descriptions of different element technologies. In addition, the term "invention" in the description of element technologies is replaced with "element technology".

[0254] Element A1 is a skeleton component formed by hot stamping a steel plate. The skeleton component has a closed section portion with a cross-section perpendicular to its length direction. The closed section portion has: at least two flat portions with radii of curvature larger than the maximum external dimension of the cross-section; and concave reinforcing rib portions formed between the two flat portions. Each concave reinforcing rib portion has a pair of wall portions with radii of curvature of 50 mm or more, protruding inwards from opposing ends of the two flat portions via a pair of curved portions bending inwards towards the closed section. The Vickers hardness at the center of the wall portion's thickness is 520 Hv or more, and the width of the wall portion is the effective width W calculated according to the Karman effective width formula. e The standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution of the surface layer of the wall by the standard deviation of the hardness frequency distribution of the center layer of the wall thickness is less than 1.0.

[0255] Element technology A1 is the technology disclosed in International Publication No. 2022 / 018963. According to this element technology A1, it is possible to provide a skeletal component with excellent energy absorption efficiency.

[0256] (Element Technology B1) The element technology B1 is a structural component having a component body formed by multiple steel plates joined together, having a ring shape when viewed from above, the multiple steel plates including a first steel plate having the smallest plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate, the value of coefficient A calculated using the chemical composition of the first steel plate by the following formula (1) is greater than the value of coefficient A calculated using the chemical composition of the second steel plate by the following formula (1).

[0257] A=1.48×(2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr+2×Mo) 3.42 (1) In the above formula (1), the content (mass%) of the corresponding element is substituted into the element symbol.

[0258] Based on element technology B1, structural components with excellent shock absorption performance can be provided.

[0259] For example, as recorded in "Ueno Masakatsu, Ito Kamitaro, 'A New Predictive Formula for Hardenability of Steel Replacing the Formula of GROSSMANN', Iron and Steel, Japan Iron and Steel Association, No. 6, 74 (1988), pp. 1073-1080", previously, the critical cooling rate V was used. c90 Critical cooling rate V is an indicator of the hardenability of steel. c90 It is the critical cooling rate (°C / s) for obtaining a martensitic structure with a volume fraction of over 90%, expressed as logV. c90 =2.94-0.75β. β is calculated from 2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr+2×Mo. β is based on the amount of Mn and represents the influence of each element on hardenability. The larger β is, the higher the critical cooling rate V. c90 The smaller the value, the better the hardenability of the steel.

[0260] There is a correlation between β, which represents the influence of each element on hardenability, and the time from the completion of heating the steel to the start of the diffusion phase transformation (phase transformation start time). The inventors of this application used the same hot-stamping steel plates A, B, C, and D (1.2 mm thick) as described in the embodiments below (Table 5). After holding them in a heating furnace at 900°C for 1 minute, they removed them from the furnace and air-cooled them, measuring the time until the phase transformation began (phase transformation start time). Then, using the measured phase transformation start time data, regression analysis was performed to construct a formula that converts β into the phase transformation start time: A = 1.48 × β 3.42 The A obtained by this formula is a coefficient (index value) that varies for each type of steel based on its chemical composition. The coefficient A corresponds to the phase transformation initiation time when only the influence of elements is considered; a larger coefficient A indicates better hardenability of the steel. The inventors of this application also used the coefficient A to study the appropriate configuration of steel in the billet. As a result, the inventors of this application completed the billet for the embodiment.

[0261] The hot stamping blank of the embodiment comprises multiple steel plates. The multiple steel plates are arranged and joined in a ring shape when viewed from above the blank. The multiple steel plates include a first steel plate and a second steel plate. The first steel plate has the smallest plate thickness among the multiple steel plates. The second steel plate has a plate thickness greater than that of the first steel plate. The value of coefficient A calculated using the chemical composition of the first steel plate by the following formula (1) is greater than the value of coefficient A calculated using the chemical composition of the second steel plate by the following formula (1) (first composition).

[0262] A=1.48×(2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr+2×Mo) 3.42 (1) In the above formula (1), the content (mass%) of the corresponding element is substituted into the element symbol.

[0263] For example, when the hardenability of materials in a first steel plate with the smallest thickness and a second steel plate with a thickness greater than that of the first steel plate are the same, the thinner first steel plate, after heating the billet for hot stamping, begins the phase transformation from austenite to ferrite (diffusion phase transformation) earlier than the thicker second steel plate. However, for the billet of the first composition, the coefficient A calculated based on its chemical composition for the first steel plate is greater than the coefficient A calculated based on its chemical composition for the second steel plate. That is, the first steel plate is composed of a material with higher hardenability than the second steel plate, in other words, a material whose diffusion phase transformation begins more slowly during cooling. Therefore, the delayed start of the diffusion phase transformation in the first steel plate after heating the billet reduces the difference in phase transformation start time between the first and second steel plates. As a result, when the billet is hot stamped, not only can the thicker second steel plate be quenched well, but the first steel plate with the smallest thickness can also be quenched well, making it easier to homogenize the hardness of the structural components formed from the billet. Furthermore, by properly quenching the first steel plate, the stress is offset by the phase transformation plasticity, and the residual stress is reduced. Therefore, in the annular structural member, the generation of torsion caused by the concentration of residual stress can be suppressed, and as a result, the deterioration of dimensional accuracy can be reduced.

[0264] Here, although the application of the invention in the annular door ring component of a car is described, it can also be used in the rear module of a car, etc., to suppress the occurrence of twisting, warping and the like caused by the concentration of residual stress.

[0265] Thus, in the first configuration, even though the annular blank contains a first steel plate that is thinner than the second steel plate, the hardness of the structural member formed by hot stamping from the blank can be made uniform, and the deterioration of dimensional accuracy can be suppressed. Therefore, the impact absorption performance (collision resistance) of annular structural members, especially large annular structural members or rear modules, can be improved.

[0266] In the first batch of blanks, the thickness of the first steel plate is set to t. min Let the largest thickness among the multiple steel plates be t. max When, it can be t max -t min ≥0.2 (mm) (Second component).

[0267] The manufacturing method of the structural member of the embodiment includes: a step of preparing a blank of the first or second configuration; a step of heating the plurality of steel plates contained in the blank to a temperature above the austenitic phase transformation completion temperature; and a step of forming the heated blank into a structural member that is ring-shaped in plan view using a mold and then quenching it (third configuration).

[0268] The structural member of the embodiment includes a member body. The member body is annular when viewed from above. The member body is formed by multiple steel plates that are joined together. The multiple steel plates include a first steel plate having the smallest plate thickness and a second steel plate having a plate thickness greater than that of the first steel plate. The value of coefficient A calculated using the chemical composition of the first steel plate by the following formula (1) is greater than the value of coefficient A calculated using the chemical composition of the second steel plate by the following formula (1) (fourth configuration).

[0269] A=1.48×(2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr+2×Mo) 3.42 (1) In the above formula (1), the content (mass%) of the corresponding element is substituted into the element symbol.

[0270] The fourth structural component can also be a car door ring assembly or a rear module. In the case of a car door ring assembly, the main body of the component can include the front pillar, the middle pillar, and the side beam connecting the front pillar and the middle pillar (the fifth component).

[0271] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the drawings, the same or equivalent components are labeled with the same symbols, and the same descriptions are not repeated.

[0272] <First Implementation Method> [Structural Components] Figure 5 This is a top-view (plan view) showing the structural member B1-10 of this embodiment placed on a horizontal plane. The structural member B1-10 is, for example, used in the body of a car. The structural member B1-10 is a typical car door ring component. In this embodiment, an example of the structural member B1-10 being a door ring component will be described.

[0273] Structural member B1-10 is a hot-stamped member. That is, structural member B1-10 is formed by hot stamping (hot pressing) a blank composed of multiple steel plates. Structural member B1-10 includes a member body B1-11. The member body B1-11 has a ring shape when viewed from above. The member body B1-11 includes a front pillar B1-111, a middle pillar B1-112, and a side beam B1-113. When structural member B1-10 is assembled into the vehicle body, the middle pillar B1-112 is positioned behind the front pillar B1-111. The middle pillar B1-112 extends generally along the vertical direction of the vehicle body. The front pillar B1-111 extends toward the middle pillar B1-112. When structural component B1-10 is assembled into the vehicle body, side beam B1-113 is positioned below the front pillar B1-111 and the middle pillar B1-112. Side beam B1-113 connects the front pillar B1-111 and the middle pillar B1-112.

[0274] In this embodiment, the main component B1-11 is formed by multiple steel plates B1-21, B1-22, and B1-23 that are joined together. Figure 5 In the example, the front column B1-111 is mainly composed of steel plates B1-21 and B1-22. The middle column B1-112 is mainly composed of steel plate B1-23. The side beam B1-113 is composed of steel plates B1-21 and B1-23.

[0275] Figure 6 yes Figure 5 Section II-II view. Figure 6 The image shows the cross-section of structural member B1-10 cut along the thickness of steel plate at the location of steel plate B1-21. Figure 6 As shown, steel plate B1-21 has an open section. In the cross-section of structural member B1-10, steel plate B1-21 has, for example, a generally cap-shaped form. More specifically, steel plate B1-21 includes a top plate B1-211, longitudinal walls B1-212 and B1-213, and flanges B1-214 and B1-215. Longitudinal wall B1-212 is disposed on the opposite side of longitudinal wall B1-213 relative to the top plate B1-211. In the cross-section of structural member B1-10, one end of longitudinal walls B1-212 and B1-213 is connected via the top plate B1-211. In the cross-section of structural member B1-10, flanges B1-214 and B1-215 are respectively connected to the other ends of longitudinal walls B1-212 and B1-213. Flanges B1-214 and B1-215 protrude from longitudinal walls B1-212 and B1-213 toward the outside of structural member B1-10, respectively.

[0276] In structural member B1-10, Figure 6 The width W of the steel plate B1-21 at the location shown is the width of the front pillar B1-111. Figure 5The width W of the lower part of the front column B1-111 can be more than 30 mm and less than 750 mm. The height H of the lower part of the front column B1-111 can be more than 25 mm and less than 150 mm. The width W is the distance in the cross section of the structural member B1-10 from the end point R of the longitudinal wall B1-212 side at the corner between the top plate B1-211 and the longitudinal wall B1-212 to the end point R of the longitudinal wall B1-213 side at the corner between the top plate B1-211 and the longitudinal wall B1-213. The height H is the distance from the top plate B1-211 to the flanges B1-214 and B1-215 along the thickness direction of the top plate B1-211. The equivalent of the side beam B1-113 in the steel plate B1-21 is... Figure 5 The width W of the portion of the steel plate B1-21 is, for example, 30mm or more and 300mm or less. The height of the portion of the steel plate B1-21 corresponding to the edge beam B1-113 can also be 25mm or more and 150mm or less.

[0277] Although the illustration is omitted, other steel plates B1-22 and B1-23 ( Figure 5 Like steel plate B1-21, steel plates B1-22 and B1-23 also have an open section. Steel plates B1-22 and B1-23 may also have, for example, a generally cap-shaped section when viewed in section of structural member B1-10. The portion of steel plate B1-22 corresponding to the upper part of the front column B1-111 may have a width of 15 mm or more and 300 mm or less. The portion of steel plate B1-22 corresponding to the upper part of the front column B1-111 may have a height of 10 mm or more and 150 mm or less. The portion of steel plate B1-23 corresponding to the middle column B1-112 may have a width of 15 mm or more and 300 mm or less. The portion of steel plate B1-23 corresponding to the middle column B1-112 may have a height of 10 mm or more and 150 mm or less.

[0278] When viewed from above, the size of the annular structural member B1-10 is, for example, 1.0m or more. The size of structural member B1-10 can be, for example, 4.0m or less. The size of structural member B1-10 refers to the length of the line segment connecting the two furthest points on the outer perimeter of structural member B1-10 when viewed vertically while the structural member B1-10 is placed on a horizontal plane.

[0279] [Manufacturing methods for structural components] The following is for reference Figures 7A-7G The manufacturing method of structural member B1-10 will be described. The manufacturing method of structural member B1-10 in this embodiment includes: a step of preparing blank B1-20; a step of heating blank B1-20; and a step of forming the heated blank B1-20 into structural member B1-10.

[0280] (Preparation process) like Figure 7A As shown, in the preparation process, a blank B1-20 is prepared, having the shape of the unfolded structural member B1-10. The blank B1-20 comprises multiple steel plates B1-21, B1-22, and B1-23. The steel plates B1-21, B1-22, and B1-23 are arranged and joined in a ring-like manner when viewed from above the blank B1-20.

[0281] Figure 7B , Figure 7C and Figure 7D This is a cross-sectional view of billet B1-20, which represents the joint of steel plates B1-21, B1-22, and B1-23. Figure 7B , Figure 7C and Figure 7D They are Figure 7A Sectional views IIIB-IIIB, IIIC-IIIC, and IIID-IIID. (Refer to...) Figure 7B and Figure 7C Steel plate B1-21 is butt-joined with steel plates B1-22 and B1-23 respectively. That is, these end faces are joined while the end face of steel plate B1-21 is in contact with the end face of steel plate B1-22, and then joined while the other end face of steel plate B1-21 is in contact with the end face of steel plate B1-23. (Refer to...) Figure 7D In addition to butt-joining with steel plate B1-21, steel plate B1-22 is also butt-joined with steel plate B1-23. The end face of steel plate B1-22 is joined to the end face of steel plate B1-23 in a state of abutment. Steel plates B1-21, B1-22, and B1-23 are joined, for example, by laser welding. In this embodiment, blank B1-20 is a so-called laser-welded blank.

[0282] Reference Figures 7B-7D Steel plate B1-21 has a thickness t1. Steel plate B1-22 has a thickness t2. Steel plate B1-23 has a thickness t3. The thicknesses t2 and t3 of steel plates B1-22 and B1-23 are greater than the thickness t1 of steel plate B1-21. That is, the thickness t1 of steel plate B1-21 is the smallest among steel plates B1-21, B1-22, and B1-23. min In this embodiment, the thickness t2 of steel plate B1-22 is greater than the thickness t3 of steel plate B1-23. Therefore, the thickness t2 of steel plate B1-22 is the largest among steel plates B1-21, B1-22, and B1-23. max However, it is also possible that steel plate B1-22 does not necessarily have the largest plate thickness t among steel plates B1-21, B1-22, and B1-23. max The thickness t2 of steel plate B1-22 can also be less than or equal to the thickness t3 of other steel plates B1-23.

[0283] The smallest plate thickness t among steel plates B1-21, B1-22, and B1-23 min and the largest plate thickness t max For example, satisfying t max -t min ≥0.2 (mm). Plate thickness t min t max It can also satisfy t max -t min ≤3.2 (mm). Thickness t of steel plate B1-21 min For example, less than 1.4 mm. Plate thickness t min It can also be 0.8mm or more. The maximum plate thickness t max For example, less than 4.0 mm. Plate thickness t max It can also be 1.4mm or more.

[0284] Steel plates B1-21, B1-22, and B1-23 may have chemical compositions known for use as steel plates for hot stamping. For example, the chemical compositions of steel plates B1-21, B1-22, and B1-23, by mass%, contain C: 0.05~0.50%, Si: 0.020~1.000%, Mn: 0.20~2.50%, Ni: 0~0.50%, Cr: 0~0.50%, Mo: 0~0.5%, and B: 0.0005~0.0050%. The chemical composition of steel plates B1-21, B1-22, and B1-23 may also contain, by mass%, one or more of the following components selected from the group consisting of Cu: 0.005~3.000%, Co: 0.005~0.500%, Sn: 0.005~0.500%, Ca: 0.0005~0.0050%, Mg: 0.0005~0.0050%, REM: 0.0005~0.0050%, and Sb: 0.0005~0.0200%.

[0285] Among steel plates B1-21, B1-22, and B1-23, the smallest plate thickness t is... min The chemical composition of steel plate B1-21 is different from that of the thicker steel plates B1-22 and B1-23. The value of coefficient A calculated using the chemical composition of steel plate B1-21 by the following formula (1) is different from the value of coefficient A calculated using the chemical composition of steel plates B1-22 and B1-23 by formula (1).

[0286] A=1.48×(2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr+2×Mo) 3.42 (1) Substitute the corresponding element content (mass%) into the element symbols in equation (1). That is, the coefficient A of steel plate B1-21 is calculated by substituting the content (mass%) of each element in the chemical composition of steel plate B1-21 into the corresponding element symbols in equation (1). Similarly, the coefficient A of steel plate B1-22 is calculated by substituting the content (mass%) of each element in the chemical composition of steel plate B1-22 into the corresponding element symbols in equation (1). The value of coefficient A calculated by equation (1) using the chemical composition of steel plate B1-21 is greater than the value of coefficient A calculated by equation (1) using the chemical composition of steel plate B1-22. The coefficient A of steel plate B1-22 is the smallest coefficient among the coefficients A calculated by equation (1) for steel plates B1-22 and B1-23 other than steel plate B1-21. When the coefficient A of steel plate B1-21 is set as A1 and the coefficient A of steel plate B1-22 is set as A2, A1-A2 is preferably 0.10 or more, more preferably 0.20 or more. For example, A1-A2 can be 11.50 or less.

[0287] The coefficient A of steel plate B1-23 is calculated by substituting the content (mass%) of each element in the chemical composition of steel plate B1-23 into the corresponding element symbols in formula (1). The value of coefficient A calculated by formula (1) using the chemical composition of steel plate B1-23 is greater than the value of coefficient A calculated by formula (1) using the chemical composition of steel plate B1-22. The value of coefficient A of steel plate B1-23 is preferably less than that of the minimum plate thickness t. min The value of coefficient A for steel plate B1-21. That is, among the multiple steel plates B1-21, B1-22, and B1-23 contained in billet B1-20, the one with the smallest plate thickness t is preferred. min The coefficient A of steel plate B1-21 is the largest. When the coefficient A of steel plate B1-21 is set as A1 and the coefficient A of steel plate B1-23 is set as A3, A1-A3 is preferably 0.10 or more, more preferably 0.20 or more. Although not particularly limited, A1-A3 can be 11.50 or less. However, the coefficient A3 of steel plate B1-23 can also be greater than or equal to the coefficient A1 of steel plate B1-21 (A1-A3≤0).

[0288] The chemical composition of steel plates B1-21, B1-22, and B1-23 contained in billet B1-20 can be determined using general analytical methods. For example, analytical test pieces can be extracted from steel plates B1-21, B1-22, and B1-23 respectively, and the chemical composition of steel plates B1-21, B1-22, and B1-23 can be obtained by using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). In each analytical test piece, carbon (C) can be determined using combustion-infrared absorption spectrometry.

[0289] (Heating process) The prepared blank B1-20 is formed into structural component B1-10 by hot stamping (hot pressing). Figure 5 and Figure 6 During hot stamping, blank B1-20 is fed into the heating process. (See reference...) Figure 7E In the heating process, for example, billet B1-20 is heated in heating furnace B1-30. The multiple steel plates B1-21, B1-22, and B1-23 contained in billet B1-20 are heated to the austenitic phase transformation completion temperature (A). c3 (Points) and above. Steel plates B1-21, B1-22, and B1-23 are, for example, heated to above 900°C. As a result, the microstructure of steel plates B1-21, B1-22, and B1-23 is, for example, wholly or substantially transformed into the austenitic phase.

[0290] (Forming process) Reference Figure 7F In the forming process, mold B1-40 is used to form the heated blank B1-20 into a ring-shaped structural component B1-10 when viewed from above. Figure 5 and Figure 6 The billet B1-20, after being heated through the heating process, is then removed from the heating furnace B1-30 (and quenched). Figure 7E The blank B1-20 is removed and fed into die B1-40. Die B1-40 is mounted on a known stamping device. Die B1-40 includes, for example, a punch B1-41 and a die B1-42. The blank B1-20 is disposed between the punch B1-41 and the die B1-42.

[0291] Reference Figure 7G After the blank B1-20 is positioned between the punch B1-41 and the die B1-42, the die B1-42 approaches the punch B1-41 relatively. The blank B1-20 is clamped (stamped) by the punch B1-41 and the die B1-42 and is formed into a shape along the forming surfaces of the punch B1-41 and the die B1-42. The blank B1-20 is held in the clamped state by the punch B1-41 and the die B1-42. The blank B1-20 is cooled by the die B1-40, and its microstructure transforms into martensite. Thus, structural component B1-10 can be manufactured from the blank B1-20.

[0292] Refer again Figure 5 The chemical composition of steel plates B1-21, B1-22, and B1-23 remains unchanged before and after hot stamping. Therefore, in structural member B1-10, a plate with a minimum thickness t is used. minThe value of coefficient A calculated from the above formula (1) for the chemical composition of steel plate B1-21 is greater than the value of coefficient A calculated from the formula (1) for the chemical composition of steel plate B1-22. Preferably, the value of coefficient A calculated from the formula (1) for the chemical composition of steel plate B1-21 is greater than the value of coefficient A calculated from the formula (1) for the chemical composition of steel plate B1-23. However, the value of coefficient A calculated from the formula (1) for the chemical composition of steel plate B1-21 may also be less than or equal to the value of coefficient A calculated from the formula (1) for the chemical composition of steel plate B1-23.

[0293] The chemical composition of steel plates B1-21, B1-22, and B1-23 in the hot-stamped structural component B1-10 can be obtained using the same analytical method as that used for the steel plates B1-21, B1-22, and B1-23 in the stage of billet B1-20.

[0294] Reference Figure 6 With the minimum plate thickness t min When the deviation of the martensite fraction is obtained by subtracting the minimum martensite fraction from the maximum martensite fraction (%) in the cross-section of structural member B1-10 at the location of steel plate B1-21, the deviation of the martensite fraction is, for example, 20% or less. The deviation of the martensite fraction is preferably 15% or less, more preferably 10% or less. The deviation of the martensite fraction can be determined as follows: that is, within the minimum plate thickness t... min From the cross-section of structural member B1-10 at position B1-21 of steel plate, at least ten analytical samples (e.g., approximately 10 mm in size on the long side) were cut from positions at least 20 mm from the end and at least 10 mm apart. Each sample was then mirror-polished with the plate thickness as the observation surface, and etched using Lepera reagent. Then, for the area at a depth of 1 / 4 of the plate thickness from the surface (from 1 / 8 to 3 / 8 of the plate thickness from the surface), 30 tissue photographs were taken using an optical microscope at 1000x magnification, with each field of view measuring 2400 μm. 2 The above describes the image analysis of the obtained tissue photographs.

[0295] As an image analysis method, the maximum brightness value Lmax and minimum brightness value Lmin of the image are obtained. Pixels with brightness values ​​between Lmax-0.3(Lmax-Lmin) and Lmax are designated as white regions. The proportion of pixels in the white regions to the total number of pixels is calculated to determine the martensite fraction. This image analysis is performed on a total of 30 observation fields for each analytical sample to determine the martensite fraction, and the average value is taken as the martensite fraction of each analytical sample. Furthermore, the difference between the maximum and minimum martensite fractions among ten or more analytical samples is defined as the value with the minimum plate thickness t. minThe deviation of the martensite fraction in the cross-section of structural member B1-10 at the location of steel plate B1-21. The structural member B1-10 has the minimum plate thickness t. min When there are multiple steel plates, the martensite fraction is calculated by analyzing each steel plate, and the deviation of the largest martensite fraction among these steel plates is taken as the deviation of the martensite fraction in structural member B1-10.

[0296] Furthermore, depending on the steel plate, the martensite area ratio obtained through image analysis, i.e., the area ratio of the white region, may sometimes contain a few percentage points of retained austenite area ratio. However, since the deviation in the martensite fraction is calculated using differentials, its impact is minor.

[0297] After the forming process (hot stamping), steel sheet B1-21 can, for example, have a tensile strength of 0.5 GPa or more, preferably 1.0 GPa or more. Similarly, after the forming process (hot stamping), steel sheets B1-22, 23 ( Figure 5 For example, it can have a tensile strength of 0.5 GPa or higher, preferably 1.0 GPa or higher. At least one of steel plates B1-21, B1-22, and B1-23 can also have a tensile strength of 1.5 GPa or higher after the forming process. The tensile strength of each of steel plates B1-21, B1-22, and B1-23 can be the same as or different from the tensile strength of the other steel plates.

[0298] [Effect] For the blank B1-20 in this embodiment, it has the smallest plate thickness t min The coefficient A1 of the thicker steel plate B1-21 is greater than the coefficient A2 of the thicker steel plate B1-22. The coefficients A1 and A2 are based on the chemical composition of steel plates B1-21 and B1-22 respectively, for formula (1): A=1.48×(2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr+2×Mo) 3.42 The values ​​are obtained through calculation. Coefficients A1 and A2 correspond to the time (phase transformation start time) from the time the billet B1-20 for hot stamping is heated in the heating furnace B1-30 until the diffusion phase transformation begins in steel plates B1-21 and B1-22, respectively. Coefficients A1 and A2 are values ​​corresponding to the phase transformation start time when only the elemental effect is considered for steel plates B1-21 and B1-22, without considering the plate thickness. When coefficient A1 is greater than coefficient A2, it means that steel plate B1-21 is made of a material with higher hardenability than steel plate B1-22, in other words, a material whose diffusion phase transformation begins later during cooling. By setting coefficients A1 > A2 as in this embodiment, it is possible to achieve a minimum plate thickness t. minThe delayed onset of the diffusion phase transformation in steel plate B1-21, compared to cases where coefficient A1 is below coefficient A2, reduces the difference in phase transformation onset time between steel plates B1-21 and B1-22. Therefore, during hot stamping of billet B1-20, not only can the thicker steel plate B1-22 be effectively quenched, but the minimum plate thickness t can also be improved. min Proper quenching of steel plate B1-21 facilitates the homogenization of hardness in structural components formed from billet B1-20. Furthermore, by effectively quenching steel plate B1-21, stress is offset by phase transformation plasticity, resulting in reduced residual stress. Therefore, in the annular structural component B1-10, the generation of torsion caused by the concentration of residual stress can be suppressed. Consequently, the deterioration of the dimensional accuracy of structural component B1-10 can be reduced.

[0299] Thus, in this embodiment, even though the annular blank B1-20 includes a steel plate B1-21 that is thinner than the steel plate B1-22, the hardness of the structural member B1-10 formed from the blank B1-20 by hot stamping can be made uniform, and the deterioration of dimensional accuracy can be suppressed. Therefore, the impact absorption performance (collision resistance) of the annular structural member B1-10, especially large and annular structural members B1-10, can be improved.

[0300] In this embodiment, by improving the hardenability of the relatively thin steel plate B1-21, the hardness of the structural member B1-10 formed from the billet B1-20 can be made more uniform. More specifically, for a plate with the minimum thickness t... min The steel plate B1-21 is also well quenched, thus ensuring that the deviation of the martensite fraction in the steel plate B1-21 is less than 20%. Therefore, for example, when a collision load is applied to the structural member B1-10, deformation concentration is less likely to occur, and the structural member B1-10 easily exhibits high impact absorption performance. Therefore, even in the case of forming annular structural members B1-10 from the billet B1-20 that include thin steel plates B1-21, especially large and annular structural members B1-10, the weakness of the structural member B1-10 can be reduced, and the impact absorption performance of the structural member B1-10 can be improved.

[0301] The smaller the deviation in martensite fraction, the less uneven the mechanical properties within structural member B1-10, which is preferable from a functional perspective. On the other hand, a large deviation in martensite fraction indicates the presence of areas with insufficient hardenability (i.e., insufficient hardness) within structural member B1-10. During impact deformation, deformation tends to concentrate in these areas, thus reducing the functionality of structural member B1-10.

[0302] <Second Implementation Method> Figure 8 This is a cross-sectional view of the blank B1-20A according to the second embodiment. Figure 8 The figure shows the plate with the minimum thickness t. min The joint between steel plate B1-21 and steel plate B1-22, which has a larger plate thickness t2. The billet B1-20A of this embodiment has a substantially the same structure as the billet B1-20 of the first embodiment, but differs from the billet B1-20 of the first embodiment in that a film (coating) B1-24 is provided on the steel plate B1-21. Figure 8 In the example, the smallest plate thickness t min The steel plate B1-21 has one surface covered by a film B1-24.

[0303] Film B1-24 is essentially a black film. For example, the lightness L from the surface of film B1-24... The value (CIE 1976 lightness index L as specified in JIS Z8781-4 (2013)) If the value is below 60, it can be determined that film B1-24 is black. Film B1-24 can be a carbon-based surface treatment film (a film containing carbon (C)).

[0304] Films B1-24 may contain, for example, carbon black. Films B1-24 may further contain metal oxides. The metal oxides may be, for example, one or more oxides selected from the group consisting of Zr oxides, Zn oxides, and Ti oxides. Films B1-24 may also contain silicon dioxide.

[0305] As the coating B1-24, for example, the surface treatment coating described in International Publication No. 2022 / 215229 can be used. That is, the coating B1-24 can replace carbon black or contain graphite or carbon soot in addition to carbon black. Alternatively, the coating B1-24 may also contain, for example, needle-like compounds with an aspect ratio of 4 or more and 50 or less and a hexagonal crystal structure. A typical compound with a hexagonal crystal structure is graphite (C), but it can also be lanthanum silicate, magnesium diboride, beryllium oxide (BeO), zinc oxide, β-quartz, goethite (NiS), wurtzite (ZnS), etc.

[0306] In this embodiment, the blank B1-20A is formed into a ring-shaped structural member B1-10 using the same manufacturing method as in the first embodiment. Figure 5 and Figure 6In billet B1-20A, the emissivity of the steel sheet B1-21 is increased by applying a substantially black film B1-24 to its surface. The surface of the steel sheet B1-21 covered by film B1-24 exhibits, for example, an emissivity of over 60% at a measurement temperature of 25°C and a wavelength of 8.0 μm. This increases the emissivity to achieve the minimum sheet thickness t. min The emissivity of steel sheet B1-21 allows for faster heating of steel sheet B1-21 when billet B1-20A is heated during hot stamping. Therefore, steel sheet B1-21 can be rapidly heated to the austenitic region temperature, ensuring a longer high-temperature holding time. As a result, the austenite grains in the microstructure of steel sheet B1-21 coarsen, further delaying the diffusion phase transformation of steel sheet B1-21 after the heating process. Therefore, quenching can be effectively performed using steel sheet B1-21. At least a portion of the film B1-24 can remain on the surface of steel sheet B1-21 after hot stamping.

[0307] In this embodiment, one surface of steel plate B1-21 is covered by film B1-24. However, both surfaces of steel plate B1-21 may also be substantially covered by black film B1-24. Film B1-24 may also be provided on one or both surfaces of other steel plates B1-22 and B1-23, or it may not be provided. However, based on the viewpoint of ensuring a longer period of high temperature maintenance for steel plate B1-21 from the start of heating of billet B1-20A to completion, it is preferable that at least one of the other steel plates B1-22 and B1-23 is not provided with film B1-24.

[0308] <Third Implementation Method> Figure 9 This is a cross-sectional view of the blank B1-20B according to the third embodiment. Figure 9 The figure shows the plate with the minimum thickness t. min The joint between steel plate B1-21 and steel plate B1-22, which has a larger plate thickness t2. The blank B1-20B of this embodiment has a composition that is substantially the same as that of blank B1-20 of the first embodiment, but it differs from blank B1-20 of the first embodiment in that steel plates B1-21 and B1-22 are plated steel plates.

[0309] exist Figure 9In the example, steel plate B1-21 has a base steel plate B1-21a and an aluminum-based coating B1-21b. The aluminum-based coating B1-21b covers both surfaces of the base steel plate B1-21a. The aluminum-based coating B1-21b is provided for the entirety or substantially the entirety of both surfaces of the base steel plate B1-21a. Similarly, steel plate B1-22 has a base steel plate B1-22a and an aluminum-based coating B1-22b. The aluminum-based coating B1-22b covers both surfaces of the base steel plate B1-22a. The aluminum-based coating B1-22b is provided for the entirety or substantially the entirety of both surfaces of the base steel plate B1-22a. In this embodiment, the plate thickness t of steel plate B1-21 is... min The thickness t2 of steel plate B1-21a includes both the base steel plate B1-21a and the aluminum coating B1-21b. Additionally, the thickness t2 of steel plate B1-22 includes both the base steel plate B1-22a and the aluminum coating B1-22b.

[0310] The chemical composition of aluminum-based coatings B1-21b and B1-22b is not particularly limited. Known aluminum-based coatings (coatings with aluminum as the main component) can be used as aluminum-based coatings B1-21b and B1-22b. Although not particularly limited, aluminum-based coatings B1-21b and B1-22b can be, for example, Al-Si based coatings. The chemical compositions of aluminum-based coatings B1-21b and B1-22b can be the same or different.

[0311] The adhesion amount of the aluminum-based coating B1-21b in steel plate B1-21 is set as W1 (g / m). 2 The adhesion amount of the aluminum-based coating B1-22b in steel plate B1-22 is set as W2 (g / m). 2 When the adhesion amounts W1 and W2 are 20 g / m, the amounts can also be 20 g / m. 2 Above and 120g / m 2 Below, the adhesion amount W1 of the aluminum-based coating B1-21b is the average adhesion amount on the two surfaces of the base steel plate B1-21a. The adhesion amount W2 of the aluminum-based coating B1-22b is the average adhesion amount on the two surfaces of the base steel plate B1-22a.

[0312] The preferred adhesion amounts W1 and W2 are 30 g / m². 2 The above, more preferably 35g / m 2 The above. The preferred adhesion amounts W1 and W2 are 115 g / m². 2 The following is more preferably 100g / m 2 Below. However, the minimum plate thickness t min The amount of aluminum-based coating B1-21b adhering to steel plate B1-21, W1, is less than the amount of aluminum-based coating B1-22b adhering to steel plate B1-22, which has a thicker plate thickness t2. The difference between the adhering amounts W1 and W2, W2-W1, is, for example, 10 (g / m²).2 ) or above. W2-W1 is preferably 20 (g / m³). 2 ) or more, more preferably 30 (g / m 2 Above 80 (g / m³). W2-W1 can be 80 (g / m³). 2 Below 70 (g / m³). W2-W1 is preferably 70 (g / m³). 2 ) or less, more preferably 60 (g / m 2 The following applies: The adhesion amounts W1 and W2 satisfy the relationship that W2 / W1>1.0. Preferably, the adhesion amounts W1 and W2 satisfy the relationship that W2 / W1≥1.2, and more preferably, the relationship that W2 / W1≥1.5.

[0313] When steel plates B1-21 and B1-22 are clad steel plates, coefficients A1 and A2 are calculated using the chemical composition of the base steel plates B1-21a and B1-22a. That is, the content (mass%) of each element in the chemical composition of the base steel plate B1-21a is substituted into the above formula (1) to calculate the coefficient A1 of steel plate B1-21. Similarly, the content (mass%) of each element in the chemical composition of the base steel plate B1-22a is substituted into formula (1) to calculate the coefficient A2 of steel plate B1-22. In this embodiment, as in the first embodiment, the coefficient A1 of steel plate B1-21 is greater than the coefficient A2 of steel plate B1-22. The coefficient A2 of steel plate B1-22 is the smallest coefficient A among the coefficients A calculated by formula (1) for each of the multiple steel plates contained in billet B1-20B.

[0314] In this embodiment, the blank B1-20B is formed into a ring-shaped structural member B1-10 using the same manufacturing method as in the first embodiment. Figure 5 and Figure 6 In the blanks B1-20B of this embodiment, the minimum plate thickness t is obtained. minThe amount W1 of the aluminum-based coating B1-21b on steel sheet B1-21 is less than the amount W2 of the aluminum-based coating B1-22b on steel sheet B1-22, which has a greater plate thickness t2. Therefore, when the billet B1-20B is heated during hot stamping, the heating rate of steel sheet B1-21 is significantly higher than that of steel sheet B1-22. Specifically, the aluminum-based coating B1-21b on the surface of steel sheet B1-21 becomes thinner, so when the billet B1-20B is heated, the alloying of the aluminum-based coating B1-21b with the iron contained in the base steel sheet B1-21a rapidly advances to the surface of steel sheet B1-21, causing both surfaces of steel sheet B1-21 to change to a black or near-black color. That is, the emissivity of both surfaces of steel sheet B1-21 increases during the heating process. Therefore, steel plate B1-21 can be rapidly heated to the temperature of the austenitic region, ensuring a longer high-temperature holding time. As a result, the austenite grains in the microstructure of steel plate B1-21 become coarser, further delaying the diffusion phase transformation of steel plate B1-21 after the heating process. Therefore, quenching can be effectively performed using steel plate B1-21.

[0315] In the structural component B1-10 formed from blank B1-20B ( Figure 5 and Figure 6 In the above, when the average thickness (coating thickness) of the aluminum-based coating B1-21b on both surfaces of steel plate B1-21 is set as K1 (μm), and the average thickness (coating thickness) of the aluminum-based coating B1-21b on both surfaces of steel plate B1-22 is set as K2 (μm), the coating thickness K1 of steel plate B1-21 is smaller than the coating thickness K2 of steel plate B1-22. The difference between coating thicknesses K1 and K2: K2-K1 is, for example, 7 (μm) or more. K2-K1 can be 33 (μm) or less. In addition, the coating thicknesses K1 and K2 can satisfy the relationship K2 / K1>1.0. K2 / K1 is preferably 1.2 or more, and more preferably 1.5 or more.

[0316] In this embodiment, steel plate B1-23 ( Figure 7C as well as Figure 7DThe plate B1-23 can be a clad steel plate having a base steel plate and a coating, similar to steel plates B1-21 and B1-22, or it can be a bare steel plate without a coating. When steel plate B1-23 is a clad steel plate, its coating can be an aluminum-based coating or a coating of a metal other than aluminum. When steel plate B1-23 is a clad steel plate, there are no particular limitations on the amount and thickness of the coating relative to the base steel plate. When steel plate B1-23 is a clad steel plate, the coefficient A3 of steel plate B1-23 is calculated by substituting the content (mass%) of each element in the chemical composition of the base steel plate into the above formula (1). When steel plates B1-21, B1-22, and B1-23 are clad steel plates, the chemical composition of steel plates B1-21, B1-22, and B1-23 can also be determined using the general analytical methods described in the first embodiment. The analysis of the chemical composition of steel plates B1-21, B1-22, and B1-23 can be carried out after the coating on their surface is removed by mechanical grinding.

[0317] The composition of the blank B1-20B in this embodiment can also be combined with the blanks B1-20 and B1-20A in the first and second embodiments, respectively. That is, in each of the blanks B1-20 and B1-20A, the steel plate B1-21 is a coated steel plate having a base steel plate B1-21a and an aluminum-based coating B1-21b, and the steel plate B1-22 is a coated steel plate having a base steel plate B1-22a and an aluminum-based coating B1-22b, wherein the amount W1 of the aluminum-based coating B1-21b in the steel plate B1-21 is less than the amount W2 of the aluminum-based coating B1-22b in the steel plate B1-22.

[0318] However, in the first and second embodiments, the amount W1 of the aluminum-based coating B1-21b on the steel plate B1-21 can be greater than or equal to the amount W2 of the aluminum-based coating B1-22b on the steel plate B1-22. Furthermore, in the first and second embodiments, the coatings on the steel plates B1-21 and B1-22 can be metal coatings other than aluminum, and the steel plates B1-21 and B1-22 can also be bare steel plates (bare materials) without any coating on their surfaces.

[0319] The embodiments of this disclosure have been described above, but this disclosure is not limited to the above embodiments. Various changes can be made as long as they do not depart from its spirit.

[0320] In the above embodiments, billets B1-20, B1-20A, and B1-20B each comprise three steel plates B1-21, B1-22, and B1-23, respectively. However, the number of steel plates contained in billets B1-20, B1-20A, and B1-20B is not limited thereto. Billets B1-20, B1-20A, and B1-20B may be composed of two steel plates B1-21 and B1-22, or may contain four or more steel plates. Billets B1-20, B1-20A, and B1-20B shall contain at least a minimum plate thickness t. min Steel plate B1-21 and having a thickness t greater than the plate thickness min For large plates with a thickness of t2, B1-22 steel plates are sufficient.

[0321] The annular billets B1-20, B1-20A, and B1-20B, when viewed from above, typically contain more than three steel plates. Steel plate B1-21 is joined directly or indirectly to steel plate B1-22. The arrangement of multiple steel plates, including steel plates B1-21 and B1-22, in billets B1-20, B1-20A, and B1-20B is not particularly limited. In billets B1-20, B1-20A, and B1-20B, the coefficient A1 of steel plate B1-21 is greater than the coefficient A calculated using equation (1) for the other steel plates B1-2i. i The coefficient A2 of the smallest steel plate B1-22 in (i=2,3,...). There exist multiple plates with the smallest thickness t in any of the billets B1-20, B1-20A, and B1-20B. min In the case of steel plate B1-21, it is preferable that the coefficient A1 of all steel plates B1-21 is greater than the coefficient A2 of steel plate B1-22. When billets B1-20, B1-20A, and B1-20B contain three or more steel plates, the coefficient A of the steel plates other than B1-21 and B1-22 should be greater than or equal to the coefficient A2 of steel plate B1-22.

[0322] In the above embodiment, steel plate B1-21 is butt-joined with steel plates B1-22 and B1-23 respectively. Steel plate B1-22 is butt-joined with steel plate B1-23. However, steel plate B1-21 may also overlap with at least one of steel plates B1-22 and B1-23. That is, as shown... Figure 10A As shown, steel plate B1-21 can also be joined to the end of steel plate B1-22 by means of, for example, spot welding or laser welding, with the end of steel plate B1-21 overlapping the end of steel plate B1-22, thereby forming an overlapping portion B1-25 between steel plates B1-21 and B1-22. Similarly, as Figure 10B As shown, steel plate B1-21 can also be joined to the end of steel plate B1-23 by means of spot welding or laser welding, whereby steel plates B1-21 and B1-23 overlap to form an overlapping portion B1-25. Additionally, as... Figure 10C As shown, steel plate B1-22 can also be joined to the end of steel plate B1-23 by means of spot welding or laser welding, whereby steel plates B1-22 and B1-23 overlap to form an overlapping portion B1-25. In billets B1-20, B1-20A, and B1-20B, the joining method for adjacent steel plates can be butt joint or overlap joint.

[0323] In each of the billets B1-20, B1-20A, and B1-20B described in the above embodiments, the plurality of steel plates arranged in a ring shape when viewed from above can be a single layer or multiple layers. That is, the plurality of steel plates can be a single steel plate or a plate composed of multiple steel plates stacked together.

[0324] In the above embodiments, the die B1-40 used for hot stamping of blanks B1-20, B1-20A, and B1-20B includes a punch B1-41 and a die B1-42. However, the structure of the die B1-40 is not limited to the example described in the above embodiments. The die B1-40 may also include, for example, a liner and a pressure ring.

[0325] In the above embodiment, the main body B1-11 of structural member B1-10 includes a front column B1-111, a middle column B1-112, and a side beam B1-113. However, the main body B1-11 may also include other constituent elements. For example, such as... Figure 11 As shown, the main body of component B1-11 may also include a rear pillar B1-114. The structural component B1-10 in the above embodiment is a door ring component (one-piece door ring component) with a single-ring shape. On the other hand, Figure 11 The structural component shown is a door ring component with a double-ring shape (double door ring component). When manufacturing the double door ring component, the blank used as its raw material also has a double-ring shape.

[0326] The present disclosure will be further described in detail below through embodiments. However, the present disclosure is not limited to the following embodiments.

[0327] [First Embodiment] To confirm the effectiveness of this disclosure, CAE analysis was performed using commercially available software (AUTOFORM R.10, manufactured by AUTOFORM Corporation) on the stamping (hot stamping) of the structural member as an integral door ring component, while changing the steel plate included in the structural member and the segmentation pattern of the structural member.

[0328] Table 5 shows the types of steel plates (raw materials) used in this analysis. In Table 5, for each raw material, the content (mass%) of each element in the base material, the type of coating, and the coefficient A calculated by the above formula (1) are shown.

[0329] The segmentation pattern of structural components in Figures 12A-12G Displayed in [the context]. Figures 12A-12G The diagram shows the number of steel plates (raw materials) included in the structural member of the integrated door ring component, as well as the positions of the joints between the steel plates in the structural member. Figures 12A-12G In the diagram, the numbers for each steel plate are marked in parentheses.

[0330] Referring to Table 6, in Example 1, the material with the smallest plate thickness t among raw materials (1) to (3) is... min For raw material (3) with a thickness of 1.2 mm, the value of coefficient A is the largest. In Example 1, the coefficient A1 of the thinnest raw material (3) is significantly greater than the smallest coefficient A2 among the other raw materials (1) and (2). In Example 2, the raw materials (1) to (3) have the smallest plate thickness t. min The coefficient A1 of raw material (1) with a thickness of 1.2 mm is also significantly greater than the smallest coefficient A2 among the other raw materials (2) and (3). In Example 3, the material with the smallest plate thickness t among raw materials (1) to (3) is... min For the 1.2mm raw material (2), the value of coefficient A is the largest. In Example 3, the coefficient A1 of the thinnest raw material (2) is also significantly greater than the smallest coefficient A2 among the other raw materials (1) and (3). In contrast, in Comparative Examples 1 and 2, the coefficient A1 of the thinnest raw material is less than the coefficient A of the other raw materials.

[0331] As mentioned above, coefficient A corresponds to the phase transformation start time of each raw material when only the influence of elements is considered. However, the actual phase transformation start time of each raw material is also affected by the plate thickness. The smaller the plate thickness, the shorter the phase transformation start time. The “phase transformation start time” in Table 6 refers to the shortest time from when the billet is heated at a furnace temperature of 920°C for 5 minutes and 30 seconds and taken out of the furnace until the phase transformation to ferrite begins (the time until the thinnest raw material begins to transform). As shown in Table 6, in Examples 1 to 3, the phase transformation start time is longer compared to Comparative Examples 1 and 2. For example, comparing Example 3 and Comparative Example 2, which are identical except for the material of the thinnest raw material (2), it can be seen that the phase transformation start time is slower in Example 3 than in Comparative Example 2. In Example 3, the coefficient A1 of the thinnest raw material (2) is larger than the smallest coefficient A2 of the other raw materials (1) and (3), and the hardenability of the thinnest raw material is higher than that of the other raw materials. On the other hand, in Comparative Example 2, the coefficient A1 of the thinnest raw material (2) is less than or equal to the coefficient A2 of the other raw materials (1) and (3), and the hardenability of the thinnest raw material is equal to or less than that of the other raw materials. In Example 3, by making the hardenability of the thinnest raw material higher than that of the other raw materials, compared with Comparative Example 2, the phase transformation start time of the thinnest raw material is prolonged, and the phase transformation start time of the thinnest raw material is made more uniform with that of the other, thicker raw materials. Therefore, in Example 3, after the billet is heated, it is easier to start forming before the phase transformation to ferrite begins in the thinnest raw material, and it is easier to uniformly quench the structural components.

[0332] about Figure 12C as well as Figure 12D The segmentation patterns 3 and 4 shown are illustrated in Table 7, with the parsing conditions and results displayed therein. Figure 12C and Figure 12D In the middle, the structural components are formed from four raw materials (1) to (4).

[0333] Referring to Table 7, in Examples 4-11, the raw materials (1)-(4) have the smallest plate thickness t. min The coefficient A1 of the raw material is greater than the smallest coefficient A2 among the other thicker raw materials. In contrast, in Comparative Examples 3-7, the smallest plate thickness t among raw materials (1)-(4) is... min The coefficient A1 is less than or equal to the smallest coefficient A2 among other relatively thick raw materials. The smallest plate thickness t is found in each embodiment and comparative example. min When multiple raw materials are available, the one with the smallest plate thickness t will be selected. min The smallest value among the coefficients A of the raw materials is set as coefficient A1, and compared with the coefficients A2 of the other raw materials.

[0334] Comparing each embodiment with the corresponding comparative example reveals that the phase transition start time is prolonged. For example, comparing Embodiment 6 and Comparative Example 5, which are identical except for the material of the thinnest raw material (4), the phase transition start time in Embodiment 6 is slower than that in Comparative Example 5. In Embodiment 6, the coefficient A1 of the thinnest raw material (4) is larger than the smallest coefficient A2 among the other raw materials (1) to (3), and the hardenability of the thinnest raw material is higher than that of the other raw materials. On the other hand, in Comparative Example 5, the coefficient A1 of the thinnest raw material (4) is less than or equal to the smallest coefficient A2 among the other raw materials (1) to (3), and the hardenability of the thinnest raw material is equal to or lower than that of the other raw materials. In Embodiment 6, by making the hardenability of the thinnest raw material higher than that of the other raw materials, the phase transition start time of the thinnest raw material is prolonged compared to Comparative Example 5, and the phase transition start time of the thinnest raw material is homogenized with that of the thicker other raw materials. Therefore, in Example 6, after the billet is heated, it is easy to start forming before the phase transformation to ferrite begins in the thinnest raw material, and it is easy to uniformly quench the structural components.

[0335] about Figures 12E-12G The segmentation patterns 5-7 shown are illustrated in Table 8, with the parsing conditions and results displayed therein. Figures 12E-12G In the middle, the structural components are formed from five raw materials (1) to (5).

[0336] Referring to Table 8, in Examples 12-17, the raw materials (1) to (5) have the smallest plate thickness t. min The coefficient A1 of the raw material is greater than the smallest coefficient A2 among the other thicker raw materials. In contrast, in Comparative Examples 8-11, the raw materials (1)-(5) have the smallest plate thickness t. min The coefficient A1 of the raw material is less than or equal to the smallest coefficient A2 among other relatively thick raw materials. The smallest plate thickness t is found in each embodiment and comparative example. min When multiple raw materials are available, the one with the smallest plate thickness t will be selected. min The smallest value among the coefficients A of the raw materials is set as coefficient A1, and compared with the coefficients A2 of the other raw materials.

[0337] Comparing each embodiment with the corresponding comparative example reveals that the phase transition start time is prolonged. For example, comparing Embodiment 12 and Comparative Example 8, which are identical except for the materials of the thinnest raw materials (1) and (4), the phase transition start time in Embodiment 12 is delayed compared to Comparative Example 8. In Embodiment 12, the coefficient A1 of the thinnest raw materials (1) and (4) is larger than the smallest coefficient A2 among the other raw materials (2), (3), and (5), and the hardenability of the thinnest raw material is higher than that of more than one of the other raw materials. In Embodiment 12, the coefficient A1 of the thinnest raw materials (1) and (4) is greater than all coefficients A of the other raw materials (2), (3), and (5). On the other hand, in Comparative Example 8, the coefficient A1 of the thinnest raw materials (1) and (4) is less than or equal to the smallest coefficient A2 among the other raw materials (2), (3), and (5), and the hardenability of the thinnest raw material is equal to or less than that of the other raw materials. In Example 12, by making the hardenability of the thinnest raw material higher than that of the other raw materials, the phase transformation initiation time of the thinnest raw material is prolonged compared to Comparative Example 8, and the phase transformation initiation time of the thinnest raw material is homogenized with that of the thicker raw materials. Therefore, in Example 12, after the billet heating is completed, forming can be easily started before the phase transformation to ferrite begins in the thinnest raw material, and the structural components can be easily and uniformly quenched.

[0338] Furthermore, for example, when comparing Example 13 and Comparative Example 9, which are identical except for the materials of the thinnest raw materials (1), (3), and (5), the phase transformation start time is delayed in Example 13 compared to Comparative Example 9. In Example 13, the smallest coefficient A1 among the thinnest raw materials (1), (3), and (5) is greater than the smallest coefficient A2 among the other raw materials (2) and (4), and the hardenability of the thinnest raw material is higher than that of the other raw materials. In Example 13, the coefficient A of all the thinnest raw materials (1), (3), and (5) is larger than the coefficient A of the other raw materials (2) and (4). On the other hand, in Comparative Example 9, the smallest coefficient A1 among the thinnest raw materials (1), (3), and (5) is less than or equal to the hardenability of the other raw materials. In Example 13, by making the hardenability of the thinnest raw material higher than that of the other raw materials, the phase transformation initiation time of the thinnest raw material is prolonged compared to Comparative Example 9, and the phase transformation initiation time of the thinnest raw material is homogenized with that of the thicker raw materials. Therefore, in Example 13, after the billet heating is completed, forming can be easily started before the phase transformation to ferrite begins in the thinnest raw material, and the structural components can be easily and uniformly quenched.

[0339] In the embodiments and comparative examples shown in Tables 6 to 8, the raw materials are joined together by laser bonding (butt bonding) after butt welding. On the other hand, in the embodiments and comparative examples shown in Table 9 below, a portion of the raw materials are joined, for example, by spot welding to form an overlap.

[0340] Refer to Table 9 and Figure 12F In Example 18 and Comparative Example 12, raw material (2) and raw material (5), raw material (3) and raw material (4), and raw material (4) and raw material (5) respectively form overlapping portions at their joints. Refer to Table 9 and Figure 12E In Example 19 and Comparative Example 13, raw material (2) and raw material (5), as well as raw material (3) and raw material (4), respectively form overlapping portions at their joints.

[0341] As shown in Table 9, in Examples 18 and 19, the raw materials (1) to (5) have the smallest plate thickness t. min The coefficient A1 of the raw material is greater than the smallest coefficient A2 among the other thicker raw materials. In contrast, in Comparative Examples 12 and 13, the smallest plate thickness t among raw materials (1) to (5) is... min The coefficient A1 is less than the smallest coefficient A2 among other relatively thick raw materials.

[0342] According to Table 9, for Examples 18 and 19, the phase transformation start time is delayed compared to Comparative Examples 12 and 13. Therefore, it is confirmed that even when there is an overlap in the billet, by making the coefficient A1 of the thinnest raw material greater than the smallest coefficient A2 among the other raw materials, the phase transformation start time of each raw material in the billet can be homogenized.

[0343] [Second Embodiment] Regarding the stamping (hot stamping) of the structural member that serves as the double door ring component, the same analysis as in the first embodiment was performed while changing the material and sheet thickness of the raw materials included in the structural member and the segmentation pattern of the structural member.

[0344] The steel plates used as raw materials are selected from those shown in Table 5, as in the first embodiment. The segmentation pattern of the structural components is as follows: Figures 13A-13D As shown. In Figures 13A-13D The diagram shows the number of steel plates (raw materials) included in the structural member of the double door ring component, as well as the positions of the joints between the steel plates in the structural member. Figures 13A-13D In the text, the numbers for each steel plate used as raw material are marked in parentheses.

[0345] about Figure 13A as well as Figure 13BThe segmentation patterns 8 and 9 shown are illustrated in Table 10, which displays the parsing conditions and results. Figure 13A and Figure 13B In the middle, the structural components are formed from six raw materials (1) to (6).

[0346] Referring to Table 10, in Examples 20 and 21, the minimum plate thickness t among raw materials (1) to (6) is... min The coefficient A1 is greater than the smallest coefficient A2 among the other thicker raw materials. In contrast, in Comparative Examples 14 and 15, the smallest plate thickness t among raw materials (1) to (6) is... min The coefficient A1 is less than the smallest coefficient A2 among the thicker raw materials.

[0347] As shown in Table 10, in Examples 20 and 21 where A1-A2>0, the phase transformation initiation time is prolonged compared to Comparative Examples 14 and 15 where A1-A2≤0. Therefore, by making the hardenability of the thinnest raw material higher than that of the other raw materials, it is easy to start billet forming before the phase transformation to ferrite begins in the thinnest raw material, and it can be said that structural components can be quenched uniformly.

[0348] about Figure 13C and Figure 13D The segmentation patterns 10 and 11 shown are illustrated in Table 11, with the parsing conditions and results displayed therein. Figure 13C and Figure 13D In the middle, the structural components are formed from seven raw materials (1) to (7).

[0349] Referring to Table 11, in Examples 22-24, the raw materials (1) to (7) have the smallest plate thickness t. min The smallest coefficient A1 among the raw materials is greater than the smallest coefficient A2 among the other relatively thick raw materials. In contrast, in Comparative Examples 16 and 17, the raw materials (1) to (7) have the smallest plate thickness t. min The smallest coefficient A1 among the raw materials is less than the smallest coefficient A2 among the other relatively thick raw materials.

[0350] As shown in Table 11, for Examples 22-24 where A1-A2>0, the phase transformation initiation time is prolonged compared to Comparative Examples 16 and 17 where A1-A2≤0. Therefore, by making the hardenability of the thinnest raw material higher than that of the other raw materials, it is easy to start billet forming before the phase transformation to ferrite begins in the thinnest raw material, and it can be said that structural components can be quenched uniformly.

[0351] [Third Embodiment] After heating the billet to 910°C in a furnace at 920°C, it is fed to a stamping device for 17 seconds and hot-stamped at a forming speed of 40 mm / s. While under pressure of 3000 kN, it is held at the bottom dead center for 20 seconds to obtain a hot-stamped structural component. Samples are collected and analyzed from the thinnest part of these structural components using the method described in the above embodiments to determine the deviation of the martensite fraction. Furthermore, shape accuracy and impact absorption performance are measured for these structural components. The evaluation results are shown in Table 12.

[0352] Examples 14 and 16 in Table 12 are examples under the same conditions as Examples 14 and 16 shown in Table 8. The division pattern and raw material combination of Example 15A are the same as those of Example 15 shown in Table 8, but some of the raw materials form overlapping portions at the joints. The division pattern and raw material combination of Comparative Example 10A are the same as those of Comparative Example 10 shown in Table 8, but some of the raw materials form overlapping portions at the joints. In Examples 15A and Comparative Example 10A, raw materials (1) and (2), raw materials (1) and (3), raw materials (2) and (5), and raw materials (4) and (5) respectively form overlapping portions at their joints. Comparative Example 11 is a comparative example under the same conditions as Comparative Example 11 shown in Table 8.

[0353] In Table 12, the deviation of the martensite fraction refers to, as explained in the above embodiments, the deviation within the minimum plate thickness t. min The value obtained by subtracting the minimum martensite fraction (%) from the maximum martensite fraction (%) in the cross section of the structural member at the location of the raw material.

[0354] Regarding shape accuracy, when installing a structural member that is roughly cap-shaped in cross-section onto other members, the evaluation is based on the degree of separation between the structural member and the other member at the overlapping portion. In Table 12, cases within ±2.0 mm of the surface of the other member are indicated by ○, cases exceeding ±2.0 mm but within ±3.0 mm are indicated by △, and cases exceeding ±3.0 mm are indicated by ×.

[0355] Regarding impact absorption performance, door ring assembly components were fabricated by spot welding the inner door ring components to the structural members (outer door ring components) of the embodiments and comparative examples shown in Table 12, and these were used as test subjects for partial structural evaluation. Furthermore, each test subject was fixed around its perimeter using constraint fixtures to reproduce the deformation during a vehicle collision, and an obstacle was allowed to collide from the outer door ring component side (side of the vehicle body). The maximum intrusion amount at this point was used as the impact absorption performance for evaluation. Impact absorption performance was evaluated by comparing the impact absorption performance of the outer door ring component, which was fabricated by hot stamping and then joining the raw materials, with the impact absorption performance relative to the benchmark. In Table 12, "good" indicates impact absorption performance equivalent to the benchmark, "better" indicates impact absorption performance superior to the benchmark, "marginal" indicates impact absorption performance slightly lower than the benchmark, and "poor" indicates even lower impact absorption performance. The comprehensive evaluation of shape accuracy and impact absorption performance is also expressed in four levels: "poor", "marginal", "good" and "better".

[0356] The embodiments shown in Table 12 satisfy A1-A2>0, while in the comparative examples, A1-A2≤0. In Comparative Examples 10A and 11, the deviation of the martensite fraction exceeds 20%, while in Examples 14, 15A, and 16, the deviation of the martensite fraction is less than 20%. In Examples 14, 15A, and 16, the deviation of the martensite fraction is reduced to less than 15%. In Examples 14, 15A, and 16, the shape accuracy is also good compared to Comparative Examples 10A and 11.

[0357] For Examples 14, 15A, and 16, where the deviation in martensite fraction is small, the impact absorption performance is also improved compared to Comparative Examples 10A and 11. In particular, in Examples 14 and 15A, where the deviation in martensite fraction is less than 10%, impact absorption performance above the baseline can be ensured. That is, although multiple raw materials are integrally formed into a ring-shaped structural member at the blank stage, impact absorption performance of equal or greater than that of a structural member obtained by stamping and joining the raw materials separately can be ensured.

[0358] Furthermore, while the present invention has been described so far with regard to the annular door ring of a car, it can also be used for other modules, thereby improving dimensional accuracy and ensuring impact absorption performance.

[0359] (Element Technology C1) The aforementioned element C1 is a structural member for a vehicle body, satisfying at least one of the following (C1a), (C1b), and (C1c): (C1a) the structural member comprises a pair of side frames and a frame crossbeam connecting the side frames, the side frames and the frame crossbeam being formed of a plurality of steel plates joined together, the plurality of steel plates including a first steel plate having a minimum thickness and a second steel plate having a thickness greater than that of the first steel plate, and a coating (film) being provided on the first steel plate, the coating containing 0.001 g / m³. 2 The above refers to one or more oxides selected from the group consisting of Zr oxides, Zn oxides, and Ti oxides; (C1b) the structural member comprises a pair of side frames and a frame crossbeam connecting the side frames, the side frames and the frame crossbeam being formed of 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, wherein the first steel plate is provided with a content of 0.500 g / m 2 The following carbon black film; (C1c) The structural member has a pair of side frames and a frame crossbeam connecting the side frames, the side frames and the frame crossbeam being formed of 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 coated steel plates having an aluminum-based coating on two surfaces of a base steel plate, the thickness of the aluminum-based coating in the first steel plate being less than the thickness of the aluminum-based coating in the second steel plate.

[0360] Based on element technology C1, structural components with excellent shock absorption performance can be provided.

[0361] The hot stamping blank of the embodiment comprises multiple steel plates. The multiple steel plates are arranged and joined in such a way that they form two elongated portions and a connecting portion. The elongated portions are arranged transversely in a top view of the blank. The connecting portion connects the elongated portions to each other. The multiple steel plates include a first steel plate and a second steel plate. The first steel plate has the smallest thickness among the multiple steel plates. The second steel plate has a thickness greater than that of the first steel plate. At least one of the two surfaces of the first steel plate is subjected to a treatment (first configuration) to increase emissivity compared to the two surfaces of the second steel plate.

[0362] The first constituent billet includes a first steel plate with the smallest thickness and a second steel plate with a thickness greater than that of the first steel plate. At least one surface of the first steel plate is treated to increase emissivity compared to both surfaces of the second steel plate. Therefore, when the billet is heated during hot stamping, the heating rate of the first steel plate, which is a thin-walled portion, can be increased. Consequently, the first steel plate can be heated to the austenitic region temperature more quickly, ensuring a longer holding time at that temperature. This allows for coarsening of the austenitic grains in the first steel plate. As a result, the ferrite transformation region (ferrite nose) in the CCT diagram shifts towards the longer-time side, thus delaying the onset of the ferrite transformation in the first steel plate after billet heating, allowing billet forming to begin while maintaining the microstructure of the first steel plate in an austenitic phase. In other words, the hardenability of the thinner first steel plate can be improved. Furthermore, the concept of "implementing a treatment to increase emissivity" includes not only the case where the emissivity of at least one surface of the first steel plate is higher than that of the two surfaces of the second steel plate before the billet is heated, but also the case where the emissivity of at least one surface of the first steel plate is higher than that of the two surfaces of the second steel plate during the heating of the billet.

[0363] For the billet of the first component, the improved hardenability of the thinner first steel plate allows for effective quenching during the hot stamping process of forming structural components from the billet. This results in more uniform hardness of the structural component, suppressing localized strength reduction. Furthermore, stress unevenness is less likely to occur within the structural component, thus minimizing the risk of twisting or warping even in large structural members, ensuring good dimensional accuracy. Therefore, when forming structural components, particularly large ones, from a billet including a thinner first steel plate compared to the second steel plate, it reduces strength and dimensional inaccuracies, and improves impact absorption (collision resistance).

[0364] In the first-formed billet, the first steel plate with the smallest plate thickness undergoes a treatment to increase emissivity compared to the second steel plate with a larger plate thickness. In this case, when the billet is heated during hot stamping, the first steel plate heats up faster than the second steel plate. Compared to a case where the first steel plate has the same emissivity as the second steel plate, the time for holding the first steel plate at its high temperature—that is, the time from when the first steel plate reaches the austenitic region until the second steel plate and the entire billet reach the austenitic region—is longer. This reduces the inhomogeneity of phase transformation caused by the difference in cooling rates between the steel plates after the billet heating is completed. Specifically, for the first steel plate with the smallest plate thickness, the onset of the phase transformation from austenite to ferrite can be delayed, and the difference in phase transformation onset time between the first steel plate with the smallest plate thickness and other steel plates becomes smaller. As a result, hardenability can be homogenized between the first steel plate with the smallest plate thickness and other steel plates.

[0365] In the first composition of the billet, the first steel plate may have a plate thickness of less than 1.4 mm (second composition).

[0366] When the thickness of the first steel plate is less than 1.4 mm, as in the second configuration, the first steel plate dissipates heat particularly easily after the billet is heated, making it more prone to deterioration of its hardenability. However, even if the thickness of the first steel plate is less than 1.4 mm, by performing a treatment on at least one surface of the first steel plate to increase its emissivity compared to the thicker second steel plate, and by heating the billet during hot stamping, it is possible to promote the temperature rise of the first steel plate and ensure a longer high-temperature holding time. Therefore, the hardenability of the first steel plate can be improved.

[0367] In the first or second composition of the billet, the first steel sheet may be a clad steel sheet. The clad steel sheet may have a base steel sheet and an aluminum-based coating disposed on the base steel sheet (third composition).

[0368] In the case where the first steel sheet, as in the third configuration, is a coated steel sheet with an aluminum-based coating, the heating rate of the first steel sheet tends to be slow when the billet is heated during hot stamping. The aluminum-based coating is nearly white, thus easily reflecting heat and hindering the heating of the first steel sheet. However, even if the first steel sheet is a coated steel sheet with an aluminum-based coating, by performing a treatment on at least one surface of the first steel sheet to increase emissivity compared to a thicker second steel sheet, the heating of the first steel sheet can be promoted when the billet is heated during hot stamping. Therefore, a longer high-temperature holding time for the first steel sheet can be ensured, and the hardenability of the first steel sheet can be improved.

[0369] In any of the first to third configurations of the billet, a film may be formed on at least one surface of the first steel plate as a treatment to improve emissivity. The emissivity of this film at a wavelength of 8.0 μm at 25°C may be 60% or more (fourth configuration).

[0370] In any of the first to third configurations of the billet, a film may be formed on at least one surface of the first steel plate as a treatment to improve emissivity. The film may contain: carbon black; one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide; and 0~0.30 g / m 2 Silica. In this case, the carbon black content in the film is set as X. CB (g / m 2 Let the content of oxides be X. Oxide (g / m 2 When X CB and X Oxide It can satisfy the following equation (1) (refer to Patent Document 1) (Fifth Structure).

[0371] 118.9≤24280 / {6700 / (100+76×X CB ) + 18000 / (130 + 65 × X) Oxide )}≤332.0 (1) In any of the first to fifth configurations of the billet, the first steel plate and the second steel plate may each be a clad steel plate. The clad steel plate may have a base steel plate and an aluminum-based coating covering both surfaces of the base steel plate. As a treatment to improve emissivity, the amount of aluminum-based coating in the first steel plate adhering to both surfaces of the base steel plate (g / m²) is... 2 The amount of aluminum coating in the second steel plate adhering to both surfaces of the base steel plate can be less than the amount (g / m) of the coating on both surfaces of the base steel plate. 2 (Sixth component).

[0372] In the sixth configuration, both the first and second steel plates are coated steel plates with aluminum-based coatings. However, the amount of aluminum-based coating adhering to both surfaces of the base steel plates is less in the first steel plate than in the second steel plate. Therefore, when the billet is heated during hot stamping, the alloying of the aluminum-based coating with iron progresses to the surface of the thin-walled first steel plate before the thicker second steel plate, causing both surfaces of the first steel plate to change from silvery-white to black or near-black. Consequently, during billet heating, the emissivity of both surfaces of the first steel plate is higher than that of the second steel plate. This allows the first steel plate to be heated to the austenitic region temperature more quickly, ensuring a longer holding time at that temperature. Consequently, the austenite grains in the first steel plate can be coarsened. As a result, the ferrite transformation region (ferrite nose) in the CCT diagram shifts towards the longer-term side, thus delaying the onset of the ferrite transformation in the first steel plate after billet heating is complete. Therefore, it can improve the hardenability of the first steel plate.

[0373] In any of the first to sixth configurations of the billet, the first steel plate may be a coated steel plate having a base steel plate and a coating disposed on the base steel plate. In this case, the thickness of the first steel plate is set as t. min Let the thickness of the steel plate with the largest thickness among multiple steel plates be t. max When t < 1.0, it is preferable to have 1.0 < t. max / t min ≤3.2 (Seventh component).

[0374] The billet contains multiple steel plates with the smallest plate thickness t. min The first steel plate with the largest plate thickness t max When there are significant thickness differences between other steel plates, it is difficult to ensure the process window during the manufacturing of structural components. For example, in the case of minimum plate thickness t min With maximum plate thickness t max When the difference is large, and the billet is heated during hot stamping, while waiting for the maximum plate thickness t... max During the period when the steel plate reaches the temperature of the austenitic region, the alloying of the coating of the first steel plate, which is heated to the temperature of the austenitic region first, is advanced, and the diffusion layer becomes thicker. Sometimes, it is not possible to ensure the corrosion resistance or weldability of the first steel plate based on the coating. Therefore, in the seventh configuration, the maximum plate thickness t is... max Relative to minimum plate thickness t min The ratio is set to 3.2 or less. Therefore, the maximum plate thickness t is achieved. max The heating rate of the steel plate is related to the minimum plate thickness t minThe heating rate of the first steel plate does not deviate excessively, thus allowing the heating of other steel plates to be completed before the alloying of the coating on the first steel plate is overly advanced. Therefore, structural components can be manufactured while maintaining the corrosion resistance or weldability of the first steel plate, ensuring a smooth manufacturing process.

[0375] In any of the first to seventh configurations of the billet, the first steel plate may be a plated steel plate having a base steel plate and a coating disposed on the base steel plate. Furthermore, the billet may have an overlapping portion. The overlapping portion is formed by overlapping the ends of two adjacent steel plates, which are other than the second steel plate, with each other. The overlapping portion may have a total plate thickness of 4.0 mm or less. Alternatively, a treatment to increase emissivity compared to the two surfaces of the second steel plate may be applied to the outer surface of each of the two steel plates located at the overlapping portion (eighth configuration).

[0376] In cases where two steel plates overlap at their ends in a blank, the manufacturing process window for the structural member can sometimes be compromised. Specifically, when the blank is heated during hot stamping, while waiting for the overlap to reach the temperature of the austenitic region, the alloying of the coating on the first steel plate with the smallest plate thickness progresses, the diffusion layer thickens, and the corrosion resistance or weldability of the first steel plate based on the coating can sometimes be compromised. Therefore, in the eighth configuration, the outer surface of the overlap is treated to increase emissivity in each of the two steel plates forming the overlap. This promotes the heating of the overlap, allowing the heating of the overlap to be completed before the alloying of the coating on the first steel plate progresses excessively, and enabling the structural member to be manufactured while maintaining the corrosion resistance or weldability of the first steel plate. That is, the manufacturing process window for the structural member is easily secured. However, even with increased emissivity of the overlap, if the total plate thickness of the overlap becomes too large, it is difficult to secure the manufacturing process window; therefore, the total plate thickness of the overlap is preferably 4.0 mm or less.

[0377] In the eighth composition of the billet, the second steel plate and the two aforementioned steel plates may each be a base steel plate and an aluminum-based coating covering both surfaces of the base steel plate, respectively. In this case, the amount of aluminum-based coating adhering to the two surfaces of the base steel plate in each of the two steel plates (g / m²) is... 2 It can also be compared to the adhesion amount (g / m) of the aluminum-based coating in the second steel plate to both surfaces of the base steel plate. 2 Less (the ninth component).

[0378] In the ninth configuration, the two steel plates forming the overlapping section and the second steel plate are aluminized steel plates. The amount of aluminum coating adhering to the two surfaces of the base steel plates forming the overlapping section is less than that adhering to the second steel plate. Therefore, when the blank is heated during hot stamping, the alloying of the aluminum coating with iron in the overlapping section progresses more rapidly to the surface, and the two surfaces of the overlapping section change from silvery-white to black or near-black. That is, the emissivity of the two surfaces of the overlapping section increases during the heating of the blank. As a result, the temperature rise of the overlapping section can be accelerated, thus easily ensuring the process window during the manufacturing of the structural member.

[0379] The manufacturing method of the structural member of the embodiment includes: a step of preparing a blank of any one of the first to ninth configurations; a step of heating the plurality of steel plates contained in the blank to a temperature above the austenitic phase transformation completion temperature; and a step of forming the heated blank using a mold and quenching it (tenth configuration).

[0380] The vehicle body structural member of the embodiment includes a pair of side frames and a frame crossbeam. The frame crossbeam connects the side frames. The side frames and the frame crossbeam are formed by multiple steel plates that are joined together. The multiple steel plates include a first steel plate with a minimum thickness and a second steel plate with a thickness greater than that of the first steel plate. A membrane is provided on the first steel plate. The membrane contains 0.001 g / m³. 2 The above refers to one or more oxides selected from the group consisting of Zr oxides, Zn oxides and Ti oxides (Eleventh Composition).

[0381] In another embodiment, the structural member for the vehicle body includes a pair of side frames and a frame crossbeam. The frame crossbeam connects the side frames. The side frames and the frame crossbeam are formed by multiple steel plates joined together. The multiple steel plates include a first steel plate with a minimum thickness and a second steel plate with a thickness greater than that of the first steel plate. A membrane is provided on the first steel plate. The membrane contains 0.500 g / m³ of... 2 The following carbon black (component number 12).

[0382] In another embodiment, the structural member for the vehicle body includes a pair of side frames and a frame crossbeam. The frame crossbeam connects the side frames. The side frames and the frame crossbeam are formed by multiple steel plates joined together. The multiple steel plates include a first steel plate with a minimum thickness and a second steel plate with a thickness greater than that of the first steel plate. The first steel plate and the second steel plate are coated steel plates having an aluminum-based coating on two surfaces of the base steel plate, respectively. The thickness of the aluminum-based coating in the first steel plate is less than the thickness of the aluminum-based coating in the second steel plate (thirteenth configuration).

[0383] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In each drawing, the same or equivalent structures are labeled with the same symbols, and the same descriptions are not repeated.

[0384] <First Implementation Method> [Structural Components] Figure 14 This is an exploded perspective view of structural components C1-10 and C1-20 in this embodiment. Structural components C1-10 and C1-20 are used in the body of automobiles, etc. Figure 14 In the example shown, structural components C1-10 and C1-20 constitute the front under module of the vehicle body.

[0385] Structural member C1-10 is the upper module. That is, structural member C1-10 is positioned above structural member C1-20 when assembled into the vehicle body. Structural member C1-10 has a pair of side frames C1-11L and C1-11R and at least one frame crossbeam C1-12. The side frames C1-11L and C1-11R and the frame crossbeam C1-12 are each elongated.

[0386] With structural member C1-10 assembled to the vehicle body, side frames C1-11L and C1-11R are arranged along the left-right direction of the vehicle body. Side frames C1-11L and C1-11R extend in the front-rear direction of the vehicle body, respectively. Each side frame C1-11L and C1-11R includes a front portion C1-111 and a rear portion C1-112. With structural member C1-10 assembled to the vehicle body, the rear portion C1-112 is positioned behind the front portion C1-111.

[0387] With structural member C1-10 assembled into the vehicle body, frame crossbeam C1-12 extends in the left-right direction of the vehicle body. Frame crossbeam C1-12 extends from side frame C1-11L to side frame C1-11R. Frame crossbeam C1-12 connects side frames C1-11L and C1-11R. Figure 14 In the example shown, the frame crossbeam C1-12 connects the side frames C1-11L and C1-11R to each other at one end along their length. With the structural member C1-10 assembled to the vehicle body, the frame crossbeam C1-12 is, for example, positioned at the rear end of the structural member C1-10. However, the frame crossbeam C1-12 may also connect the middle portions of the side frames C1-11L and C1-11R.

[0388] Structural member C1-20 is the lower module. That is, structural member C1-20 is positioned below structural member C1-10 when assembled into the vehicle body. Structural member C1-20 has a pair of side frames C1-21L and C1-21R and at least one frame crossbeam C1-22. The side frames C1-21L and C1-21R and the frame crossbeam C1-22 are each elongated.

[0389] With structural member C1-20 assembled to the vehicle body, side frames C1-21L and C1-21R are arranged along the left-right direction of the vehicle body. Side frames C1-21L and C1-21R extend in the front-rear direction of the vehicle body, respectively. Each side frame C1-21L and C1-21R includes a front portion C1-211 and a rear portion C1-212. With structural member C1-10 assembled to the vehicle body, the rear portion C1-212 is positioned behind the front portion C1-211.

[0390] The lower side frames C1-21L and C1-21R are connected to the upper side frames C1-11L and C1-11R, respectively. The side frames C1-21L and C1-21R together form a closed section. Figure 15 The closed sections formed by side frames C1-21L and C1-21R together with side frames C1-11L and C1-11R are shown. Hereinafter, unless there is a specific distinction between side frames C1-11L and C1-11R, they will be collectively referred to as side frame C1-11. Similarly, unless there is a specific distinction between side frames C1-21L and C1-21R, they will be collectively referred to as side frame C1-21.

[0391] Figure 15 This is a cross-sectional view (section view) obtained by cutting side frames C1-11 and C1-21 with a plane perpendicular to the length direction. Figure 15 In the example, the side frames C1-11 and C1-21 each have a hat-shaped cross-section.

[0392] Reference Figure 15 The side frame C1-11 includes a top plate C1-113, longitudinal walls C1-114 and C1-115, and flanges C1-116 and C1-117. In a cross-sectional view of the side frame C1-11, one end of the longitudinal walls C1-114 and C1-115 is connected to the top plate C1-113. In a cross-sectional view of the side frame C1-11, flanges C1-116 and C1-117 are respectively connected to the other ends of the longitudinal walls C1-114 and C1-115. Flanges C1-116 and C1-117 protrude outward from the longitudinal walls C1-114 and C1-115, respectively.

[0393] The side frame C1-21 includes a top plate C1-213, longitudinal walls C1-214 and C1-215, and flanges C1-216 and C1-217. In a cross-sectional view of the side frame C1-21, one end of the longitudinal walls C1-214 and C1-215 is connected to the top plate C1-213. In a cross-sectional view of the side frame C1-21, flanges C1-216 and C1-217 are respectively connected to the other ends of the longitudinal walls C1-214 and C1-215. Flanges C1-216 and C1-217 protrude outward from the longitudinal walls C1-214 and C1-215, respectively.

[0394] The top plate C1-213 of the lower side frame C1-21 is configured to oppose the top plate C1-113 of the upper side frame C1-11. In the cross-sectional view of the side frames C1-11 and C1-21, the longitudinal walls C1-214 and C1-215 of the side frame C1-21 extend from the top plate C1-213 toward the side frame C1-11. The flanges C1-216 and C1-217 of the side frame C1-21 are respectively joined to the flanges C1-116 and C1-117 of the side frame C1-11. The flanges C1-216 and C1-217 are joined to the flanges C1-116 and C1-117, for example, by spot welding. Figure 15 In the example, the flanges C1-116 and C1-117 of the upper side frame C1-11 are directly joined to the flanges C1-216 and C1-217 of the lower side frame C1-21. However, other components, such as floor panels, can also be provided between the side frames C1-11 and C1-21.

[0395] Return to Figure 14 With structural member C1-20 assembled into the vehicle body, frame crossbeam C1-22 extends in the left-right direction of the vehicle body. Frame crossbeam C1-22 extends from side frame C1-21L to side frame C1-21R. Frame crossbeam C1-22 connects side frames C1-21L and C1-21R. Figure 14 In the example shown, the frame crossbeam C1-22 connects the side frames C1-21L and C1-21R to each other at one end along their length. Like the upper frame crossbeam C1-12, the frame crossbeam C1-22 is positioned, for example, at the rear end of the structural member C1-20 when the structural member C1-20 is assembled to the vehicle body. However, the frame crossbeam C1-22 can also connect the middle portions of the side frames C1-21L and C1-21R. The frame crossbeam C1-22 can also be joined to the upper frame crossbeam C1-12, for example, by spot welding.

[0396] Structural components C1-10 and C1-20 are hot-stamped components. That is, structural component C1-10 is formed by hot stamping (hot pressing) a blank made of multiple steel plates (sub-blanks). Similarly, structural component C1-20 is formed by hot stamping a blank made of multiple steel plates.

[0397] In the upper structural members C1-10, for example, the side frames C1-11L and C1-11R can also be formed from multiple steel plates C1-31 and C1-32, respectively. In each of the side frames C1-11L and C1-11R, for example, the front part C1-111 can be formed from steel plate C1-31, and the rear part C1-112 can be formed from steel plate C1-32. The thickness of the steel plate C1-32 forming the rear part C1-112 can be greater than the thickness of the steel plate C1-31 forming the front part C1-111. Furthermore, the tensile strength of steel plate C1-32 can also be greater than the tensile strength of steel plate C1-31. The frame crossbeam C1-12 can also be mainly formed from steel plate C1-33, which is different from the steel plates C1-31 and C1-32 forming the side frames C1-11L and C1-11R. Adjacent steel plates in steel plates C1-31, C1-32, and C1-33 are joined together by welding.

[0398] Similarly, in the lower structural members C1-20, for example, the side frames C1-21L and C1-21R can also be formed from multiple steel plates C1-41 and C1-42, respectively. In each of the side frames C1-21L and C1-21R, for example, the front part C1-211 can be formed from steel plate C1-41, and the rear part C1-212 can be formed from steel plate C1-42. The thickness of the steel plate C1-42 forming the rear part C1-212 can be greater than the thickness of the steel plate C1-41 forming the front part C1-211. Furthermore, the tensile strength of steel plate C1-42 can also be greater than the tensile strength of steel plate C1-41. The frame crossbeam C1-22 can also be mainly formed from steel plate C1-43, which is different from the steel plates C1-41 and C1-42 forming the side frames C1-21L and C1-21R. Adjacent steel plates in steel plates C1-41, C1-42, and C1-43 are joined together by welding.

[0399] [Manufacturing methods for structural components] The following is for reference Figures 16A-16GThe manufacturing methods for structural members C1-10 and C1-20 of this embodiment will be described. The manufacturing method for structural member C1-10 includes: a step of preparing a blank C1-30; a step of heating the blank C1-30; and a step of forming the heated blank C1-30 into structural member C1-10. Similarly, the manufacturing method for structural member C1-20 includes: a step of preparing a blank C1-40; a step of heating the blank C1-40; and a step of forming the heated blank C1-40 into structural member C1-20.

[0400] (Preparation process) like Figure 16A As shown, in manufacturing the upper structural component C1-10 ( Figure 14 In the preparation process, a billet C1-30 is prepared. The billet C1-30 has a shape formed by unfolding the structural member C1-10. The billet C1-30 comprises a plurality of steel plates (sub-bills) C1-31, C1-32, and C1-33. The steel plates C1-31, C1-32, and C1-33 are arranged and joined in such a way that they form two elongated sections C1-34L and C1-34R and at least one connecting section C1-35.

[0401] The elongated sections C1-34L and C1-34R are arranged transversely in a top view of the billet C1-30. The elongated section C1-34L is equivalent to the side frame C1-11L in the billet C1-30. Figure 14 The long strip C1-34R is the equivalent of the side frame C1-11R in the blank C1-30. Figure 14 (part of the text). Figure 16A In the example, the long strips C1-34L and C1-34R are formed from steel plates C1-31 and C1-32, respectively.

[0402] Connecting part C1-35 connects the long strips C1-34L and C1-34R to each other. Connecting part C1-35 is equivalent to the frame crossbeam C1-12 in the blank C1-30. Figure 14 (part of the text). Figure 16A In the example, the connecting part C1-35 includes steel plate C1-33. The connecting part C1-35 may also include a portion of steel plate C1-32.

[0403] Figure 16B and Figure 16C This is a cross-sectional view of the blank C1-30 representing the joint of steel plates C1-31, C1-32, and C1-33. Figure 16B and Figure 16C They are Figure 16A Sectional views IIIB-IIIB and IIIC-IIIC are shown. (Refer to...) Figure 16BSteel plate C1-31 is butt-jointed with steel plate C1-32. That is, the end faces of steel plate C1-31 are joined together with the end faces of steel plate C1-32 in contact. (Refer to...) Figure 16C Steel plate C1-32 is butt-jointed with steel plate C1-33. That is, these end faces are joined with the other end face of steel plate C1-32 abutting against the end face of steel plate C1-33. Steel plates C1-31, C1-32, and C1-33 are joined, for example, by laser welding. In this embodiment, the blank C1-30 is a so-called laser-welded blank.

[0404] However, steel plates C1-31, C1-32, and C1-33 can also be joined to adjacent steel plates with their ends overlapping (overlapping joining). In this case, steel plates C1-31, C1-32, and C1-33 can also be joined by spot welding. In particular, the frame crossbeam C1-12 extending along the left-right direction of the vehicle body ( Figure 14 ) and the side frames C1-11L and C1-11R extending along the front and rear directions of the vehicle body. Figure 14 The intersections of ) are sometimes made into overlapping structures as needed.

[0405] Reference Figure 16B and Figure 16C Steel plate C1-31 has a thickness t1. Steel plate C1-32 has a thickness t2. Steel plate C1-33 has a thickness t3. In this embodiment, t1 of steel plate C1-31 is the smallest thickness t among steel plates C1-31, C1-32, and C1-33. min The thickness t2 of steel plate C1-32 is greater than the thickness t1 of steel plate C1-31. The thickness t3 of steel plate C1-33 is greater than or equal to the thickness t1 of steel plate C1-31. In this embodiment, the thickness t2 of steel plate C1-32 is the largest thickness t among steel plates C1-31, C1-32, and C1-33. max However, the thickness t3 of steel plate C1-33 can also be the largest thickness t among steel plates C1-31, C1-32, and C1-33. max That is, the thickness t3 of steel plate C1-33 can be greater than or equal to the thickness t2 of steel plate C1-32.

[0406] The thickness t of steel plate C1-31 min Typically, it is less than 1.4 mm. Plate thickness t min For example, it can be 0.8mm or more. Plate thickness t min and plate thickness t max Preferably, 1.0 < t max / t min ≤3.2, more preferably 1.3≤t max / t min≤3.2.

[0407] For the plate with the smallest thickness t min At least one of the two surfaces of the steel plate C1-31 is subjected to a treatment to increase emissivity compared to the two surfaces of the thicker-walled steel plate C1-32. In this embodiment, the emissivity of at least one surface of the steel plate C1-31 is higher than that of the two surfaces of the steel plate C1-32 even before the heating process of the billet C1-30.

[0408] For example, the emissivity at 8.0 μm at 25°C is 60% or more on one or both surfaces of steel plate C1-31, and less than 60% on both surfaces of steel plate C1-32. More preferably, the emissivity at 8.0 μm at 25°C on one or both surfaces of steel plate C1-31 is 70% or more, and even more preferably 80% or more. This results in a minimum plate thickness t. min The difference in emissivity at 8.0 μm at 25°C between steel plate C1-31 and other steel plates C1-32 is preferably greater than 5%, more preferably greater than 10%, and even more preferably greater than 20%. The emissivity can be measured according to JIS R 1801:2002. In this case, the sample collected from the steel plate being measured is set in a Fourier transform infrared spectrometer, and the radiation intensity at 8.0 μm at 25°C is measured to calculate the emissivity. Alternatively, a radiation thermometer with the measurement wavelength set to 8.0 μm can be used to measure the radiation intensity of the area of ​​interest at 25°C, and the emissivity can be calculated based on the ratio of the radiation intensity to that of a blackbody.

[0409] In this embodiment, a film C1-50 is formed on one surface of the steel plate C1-31 as a treatment to improve emissivity. For example, the entire surface of the steel plate C1-31 is covered by the film C1-50. On the other hand, the film C1-50 is not provided on either of the two surfaces of the steel plate C1-32. Therefore, the emissivity of one surface of the steel plate C1-31 is higher than the emissivity of both surfaces of the steel plate C1-32. However, the film C1-50 may also be provided on both surfaces of the steel plate C1-31.

[0410] The film C1-50 is, for example, essentially a black film. For example, the lightness L from the surface of the film C1-50... Value (CIE 1976 Lightness Index L as specified in JIS Z8781-4:2013) When the emissivity is 60 or less, it can be determined that the film C1-50 is substantially black. The film C1-50 can be a carbon-based surface treatment film (a film containing carbon (C)). The emissivity of the film C1-50 at 25°C and a wavelength of 8.0 μm is 60% or more, preferably 70% or more, and more preferably 80% or more. That is, the emissivity of the surface of the steel plate C1-31 to which the film C1-50 is applied at 25°C and a wavelength of 8.0 μm is 60% or more, preferably 70% or more, and more preferably 80% or more. The emissivity of the film C1-50 at 700°C and a wavelength of 8.0 μm can be 60% or more. For example, the surface treatment film described in Patent Document 1 can be used as the film C1-50. Specifically, the film C1-50 can contain carbon black and one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide. The C1-50 film may or may not contain silica. Specifically, the silica content of the C1-50 film is 0 g / m³. 2 The silica content of the C1-50 film can be 0.30 g / m³. 2 The silica content is more preferably 0.10 g / m³. 2 The following is a further preferred value: 0.05 g / m 2 the following.

[0411] Carbon black and oxides can be dispersed throughout the film C1-50 in a plane perpendicular to the thickness direction of the steel plate C1-31. Let the carbon black content be X. CB (g / m 2 X is defined as the content of one or more oxides (metal oxides) selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide. Oxide (g / m 2 When X CB and X Oxide It is preferable to satisfy the following equation (1).

[0412] 118.9≤24280 / {6700 / (100+76×X CB ) + 18000 / (130 + 65 × X) Oxide )}≤332.0 (1) In equation (1), the middle equation is: 24280 / {6700 / (100+76×X)} CB ) + 18000 / (130 + 65 × X) OxideThe calculated value is preferably 119.0 or higher, more preferably 170.0 or higher, and even more preferably 220.0 or higher. The value calculated from the intermediate formula is preferably 330.0 or lower, more preferably 310.0 or lower, and even more preferably 300.0 or lower.

[0413] The dispersion state of carbon black and metal oxides in the C1-50 film can be confirmed by surface analysis of the C1-50 film using an electron probe microanalyzer (EPMA) to determine the elemental composition of carbon black (e.g., C) and the elemental composition of oxides (Zr, Zn, and Ti). Carbon black content X CB The C1-50 film can be determined by cross-sectional analysis using a transmission electron microscope (TEM). Specifically, TEM-EDS analysis is performed on a cross-section of the C1-50 film of a specified size (film thickness × 5 μm) to determine the film thickness and the area fraction of particles with a carbon content of 70% by mass or higher in that region. Let the density of the carbon black be ρ (tons / m³). 3 When the film thickness is d (μm) and the area fraction is a (%), the value expressed as ρ×d×a is the carbon black content X. CB (g / m) 2 Oxide content X Oxide Elemental analysis of the C1-50 film can be performed using a fluorescence X-ray analysis device (RIGAKU Corporation, ZSXPrimus) to quantitatively determine the metals Zr, Zn, and Ti.

[0414] The carbon black content X in the film C1-50 CB The preferred value is 0.030 g / m 2 The above, more preferably 0.100 g / m 2 That's all. Content X CB The value can be set within the range that satisfies formula (1), preferably 0.800 g / m 2 The preferred value is 0.600 g / m³. 2 the following.

[0415] The film C1-50 may contain 5.0% or more carbon black by volume, preferably 8.0% or more carbon black by volume. In addition, the film C1-50 may contain 40.0% or less carbon black by volume, preferably 30.0% or less carbon black by volume.

[0416] The content of metal oxides X in the film C1-50 Oxide The preferred value is 0.030 g / m2 The above, more preferably 0.060 g / m 2 That's all. Content X Oxide The value can be set within the range that satisfies formula (1), preferably 0.500 g / m 2 The following is more preferably 0.300 g / m 2 the following.

[0417] The film C1-50 may contain 1.0 or more metal oxides by volume%. In addition, the film C1-50 may contain 30.0 or less metal oxides by volume, preferably 25.0 or less metal oxides by volume.

[0418] Carbon black content X CB (g / m 2 ) and the content of metal oxides X Oxide (g / m 2 The ratio of X: Oxide / X CB Preferably, the value is above 0.20 and below 200.00. X Oxide / X CB More preferably, the value is 0.40 or higher and 10.00 or lower, and even more preferably, it is 0.60 or higher and 5.00 or lower.

[0419] In addition to the carbon black and metal oxides mentioned above, the film C1-50 may also contain various adhesive components and additives.

[0420] The adhesive component is preferably a water-dispersible or water-soluble resin. The content of the adhesive component is preferably 40% by volume or more relative to the total volume of the film C1-50. Various known resins exhibiting water dispersibility or water solubility can be used as the adhesive component selected from the water-dispersible or water-soluble resins. Examples of such water-dispersible or water-soluble resins include polyurethane resins, polyester resins, acrylic resins, epoxy resins, fluoropolymers, polyamide resins, polyolefin resins, and polymer compounds obtained by hydrolysis and condensation of a silane coupling agent. More preferably, the adhesive component is one or more resins selected from the group consisting of polyester resins, polyurethane resins, polyolefin resins, acrylic resins, epoxy resins, fluoropolymers, and polyamide resins. When using a polyurethane resin as the adhesive component, a polyether-based polyurethane resin is preferred.

[0421] Additives include, for example, leveling agents, water-soluble solvents, metal stabilizers, and etching inhibitors. Leveling agents include, for example, nonionic or cationic surfactants. Examples of nonionic or cationic surfactants include polyethylene oxide or polypropylene oxide adducts and acetylenic diol compounds. Examples of water-soluble solvents include, for example, alcohols such as ethanol, isopropanol, tert-butanol, and propylene glycol; cellosol agents 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, for example, chelating compounds such as EDTA (ethylenediaminetetraacetic acid) and DTPA (diethyltriaminepentaacetic acid). Examples of etching inhibitors include, for example, amine compounds such as ethylenediamine, triethylenepentamine, guanidine, and pyrimidine.

[0422] The coating C1-50 can be formed, for example, by applying an organic or inorganic treatment solution containing carbon black and metal oxides to the entire surface of the steel plate C1-31, followed by drying the volatile components in the treatment solution. The treatment solution can be applied to the surface of the steel plate C1-31 using a roller coater, curtain coater, or inkjet printer, for example. In the case of inkjet printing, the film thickness of the coating C1-50 can be continuously varied. The film thickness of the coating C1-50 is, for example, 0.5 μm or more and 5.0 μm or less. Preferably, the film thickness of the coating C1-50 is 1.0 μm or more and 3.0 μm or less. The film thickness of the coating C1-50 is related to the thickness t of the steel plate C1-31. min Compared to a negligible level, the thickness of the steel plate C1-31, measured in a manner that includes the film C1-50, can be taken as the thickness t of the steel plate C1-31. min To handle it.

[0423] Steel plate C1-31 can also be clad steel plate. In this case, steel plate C1-31 has a base steel plate C1-31a and a coating C1-31b. The type of base steel plate C1-31a is not particularly limited. The coating C1-31b is applied to the base steel plate C1-31a. The coating C1-31b covers both sides of the base steel plate C1-31a entirely or substantially entirely. The coating C1-31b is a metallic coating. For example, the coating C1-31b can be a hot-dip aluminized layer, a hot-dip galvanized layer, an alloyed hot-dip galvanized layer, or an electro-galvanized layer. Known aluminized steel plates, galvanized steel plates, etc., can be used as steel plate C1-31.

[0424] Coating C1-31b is typically an aluminum-based coating (aluminum-based coating). The composition of aluminum-based coatings is not particularly limited. Known aluminum-based coatings can be used as coating C1-31b. When the steel plate C1-31 is a coated steel plate, the thickness t of the steel plate C1-31... min It is the combined thickness of the base steel plate C1-31a and the coating C1-31b.

[0425] Like steel plate C1-31, steel plates C1-32 and C1-33 can be known clad steel plates. Steel plates C1-32 and C1-33 can be aluminized steel plates or galvanized steel plates. Steel plates C1-32 and C1-33 can be clad steel plates of the same type as steel plate C1-31, or they can be clad steel plates of a different type. Similarly, steel plate C1-32 can be clad steel plates of the same type as steel plate C1-33, or it can be a different type. When steel plate C1-32 is a clad steel plate, its thickness t2 becomes the thickness of the base steel plate and the coating combined. Similarly, when steel plate C1-33 is a clad steel plate, its thickness t3 becomes the thickness of the base steel plate and the coating combined. When two or more of the steel plates C1-31, C1-32, and C1-33 are coated steel plates, the unit area weight of the coating on each steel plate can be the same as or different from the other steel plates. However, in this embodiment, the steel plates C1-31, C1-32, and C1-33 can also be steel plates (bare materials) without a coating on their surface.

[0426] like Figure 16D As shown, in the lower structural member C1-20 ( Figure 14 During the manufacture of [the component], in the preparation process, a blank C1-40 is prepared. The blank C1-40 has a shape formed by unfolding the structural member C1-20. The blank C1-40 comprises multiple steel plates (sub-blanks) C1-41, C1-42, and C1-43. The steel plates C1-41, C1-42, and C1-43 are arranged and joined in such a manner that they form two elongated portions C1-44L and C1-44R and at least one connecting portion C1-45.

[0427] The elongated sections C1-44L and C1-44R are arranged transversely in a top view of the billet C1-40. The elongated section C1-44L is equivalent to the side frame C1-21L in the billet C1-40. Figure 14 The long strip C1-44R is the equivalent of the side frame C1-21R in the blank C1-40. Figure 14 (part of the text). Figure 16D In the example, the long strips C1-44L and C1-44R are formed from steel plates C1-41 and C1-42, respectively.

[0428] Connecting part C1-45 connects the long strips C1-44L and C1-44R to each other. Connecting part C1-45 is equivalent to the frame crossbeam C1-22 in the blank C1-40. Figure 14 (part of the text). Figure 16DIn the example, the connecting part C1-45 includes steel plate C1-43. The connecting part C1-45 may also include a portion of steel plate C1-42.

[0429] Regarding billet C1-40, and steel plates C1-41, C1-42, and C1-43, and billet C1-30 ( Figure 16B and Figure 16C Similarly, the steel plates C1-31, C1-32, and C1-33 of billet C1-30 are constructed in the same way. Figure 16B as well as Figure 16C This method can be directly applied to steel plates C1-41, C1-42, and C1-43. Therefore, detailed descriptions of the composition of steel plates C1-41, C1-42, and C1-43 are omitted.

[0430] (Heating process) The prepared blanks C1-30 and C1-40 are hot-stamped into structural components C1-10 and C1-20, respectively. Figure 14 During hot stamping, blanks C1-30 and C1-40 are provided for the heating process. (See reference...) Figure 16E In the heating process, for example, the billet C1-30 is heated in a heating furnace. The multiple steel plates C1-31, C1-32, and C1-33 contained in the billet C1-30 are heated to the austenitic phase transformation completion temperature (A). c3 Above 900°C. Steel plates C1-31, C1-32, and C1-33 are, for example, heated to above 900°C. Consequently, the microstructure of steel plates C1-31, C1-32, and C1-33 transforms into austenitic phase. Although the illustration is omitted, the billet C1-40 contains multiple steel plates C1-41, C1-42, and C1-43 (…). Figure 16D It is also heated to the austenite phase transformation completion temperature (A) during the heating process. c3 point) above.

[0431] (Forming process) Reference Figure 16F In the forming process, mold C1-60 is used to form the heated blank C1-30 into structural component C1-10. Figure 14 The billet C1-30, heated by the heating process, is removed from the furnace and fed into the die C1-60. The die C1-60 can also be installed in a known stamping device. The die C1-60 includes, for example, a punch C1-61 and a die C1-62. The billet C1-30 is positioned between the punch C1-61 and the die C1-62.

[0432] Reference Figure 16GAfter the blank C1-30 is positioned between the punch C1-61 and the die C1-62, the die C1-62 approaches the punch C1-61 relatively. The blank C1-30 is clamped (stamped) by the punch C1-61 and the die C1-62, and is formed into a shape along the forming surfaces of the punch C1-61 and the die C1-62. The blank C1-30 is held in the clamped state by the punch C1-61 and the die C1-62. The blank C1-30 is cooled by the die C1-60, and its microstructure transforms into martensite. Thus, structural component C1-10 can be manufactured from the blank C1-30.

[0433] Although the illustration is omitted, Figure 16D The blank C1-40 shown is also supplied for the same forming process as blank C1-30. That is, the heated blank C1-40 is formed into structural component C1-20 using a mold. Figure 14 And then quenched. Structural component C1-20, for example, is welded to structural component C1-10 ( Figure 14 ) join.

[0434] Figure 17 This is a cross-sectional view of structural component C1-10 after hot stamping. Figure 17 The image shows a steel plate C1-31 that was given a black film C1-50 during the billet C1-30 stage. Figure 16B The cross-section of structural member C1-10 at the location of ). Figure 17 In the example, structural member C1-10 includes a membrane C1-13. Membrane C1-13 is disposed on steel plate C1-31. A black membrane C1-50 is applied to steel plate C1-31 in billet C1-30. Figure 16B The film C1-13 is formed by hot stamping. The film C1-13 is disposed on at least one surface of the steel plate C1-31. If the film C1-50 before hot stamping contains carbon black, the carbon black is almost eliminated due to the high temperature during hot stamping, but sometimes it remains. If the film C1-50 before hot stamping satisfies the above formula (1), the film C1-13 after hot stamping sometimes does not contain carbon black, and sometimes contains 0.500 g / m 2 The following carbon black. However, if the film C1-50 before hot stamping satisfies the above formula (1), the film C1-13 after hot stamping preferably contains 0.500 g / m 2 The following carbon black. In the case of carbon black in the hot-stamped film C1-13, the carbon black content in film C1-13 exceeds 0 g / m. 2 More preferably, it is 0.001 g / m 2 The above. A film C1-50 is provided on the steel plate C1-31 before hot stamping, with the film C1-13 containing carbon black after hot stamping. Figure 16B In the case of carbon black, even in the later stages of the heating process, carbon black is present on steel plate C1-31, ensuring the emissivity of steel plate C1-31. Therefore, even in the later stages of the heating process, it has the minimum plate thickness t. min Steel plate C1-31 is also easily heated. Furthermore, when steel plate C1-31 is a coated steel plate, the film C1-13 after the heating process contains carbon black, which, during the forming process (hot stamping), can suppress the formation of coating C1-31b (…). Figure 16B Adhesion to mold C1-60, reducing the adhesion between steel plate C1-31 and mold C1-60 ( Figure 16F as well as Figure 16G The coefficient of friction. When the film C1-50 before hot stamping satisfies the above formula (1), for the film C1-13 after hot stamping, the intermediate formula is: 24280 / {6700 / (100+76×X) CB ) + 18000 / (130 + 65 × X) Oxide The calculated value is, for example, above 120.0 and below 150.0.

[0435] C1-50 film before hot stamping ( Figure 16B Under the condition that the above formula (1) is satisfied, the hot-stamped film C1-13 contains, for example, more than 0 g / m 2 More preferably, it is 0.001 g / m 2 The above refers to one or more oxides (metal oxides) selected from the group consisting of Zr oxides, Zn oxides, and Ti oxides. The content of the metal oxide in the film C1-13 is, for example, 0.500 g / m³. 2 Therefore, in the case where metal oxides remain in structural member C1-10, i.e., when the film C1-13 contains more than 0 g / m 2 In the case of metal oxides, the corrosion resistance of structural component C1-10 is improved, and therefore preferred. When the film C1-50 before hot stamping satisfies the above formula (1), the film C1-13 after hot stamping contains 0~0.30 g / m 2 Silica.

[0436] The content of carbon black, metal oxides, and silicon dioxide in the film C1-13 can be compared with the film C1-50 in the billet C-30 stage. Figure 16BSimilarly, the determination is performed. Specifically, the body parts are disassembled to obtain structural members C1-10, and analytical samples are obtained from these structural members C1-10, for example, by laser cutting. For example, analytical samples are obtained from each of the multiple steel plates contained in the structural member C1-10. The analytical samples are obtained, for example, at or near the center of the top plate of each steel plate with an open cross section. The obtained analytical samples are adjusted by grinding the cross section to the outside of the heat-affected zone during laser cutting to prepare a sample for film analysis. For this sample, the surface analysis of the film C1-13 is performed by EPMA to determine the dispersion state of carbon black and metal oxides in the film C1-13. Depending on the location of the structural member C1-10, the film C1-13 exists on the surface and / or back side of the structural member C1-10, therefore the surface and back sides of the analytical sample are analyzed.

[0437] In structural components C1-10, the outermost layer often contains an electrodeposited coating film. In this case, we analyze the film layer that exists beneath the electrodeposited coating film and above the alloyed metal plating layer. The carbon black content X in film C1-13 is... CB This can be determined through cross-sectional analysis of the C1-50 film using TEM. Specifically, a cross-sectional analysis of the C1-13 film (film thickness of C1-13 × 5 μm) is performed on a region of a specified size using TEM-EDS, determining the film thickness of C1-13 and the area fraction of particles with a carbon content of 70% by mass or higher in that region. Let the density of the carbon black be ρ (tons / m³). 3 When the film thickness is d (μm) and the area fraction is a (%), the value expressed as ρ×d×a is the carbon black content X. CB (g / m 2 Oxide content X Oxide The elemental analysis of Zr, Zn, and Ti can be quantitatively determined by using the aforementioned fluorescence X-ray analysis device to analyze the upper layer of the alloyed metal coating layer, which is located below the electrodeposited coating layer.

[0438] With the minimum plate thickness t min In the cross-section of structural member C1-10 at position C1-31 of steel plate, the value obtained by subtracting the minimum martensite fraction from the maximum martensite fraction (%) is taken as the deviation of the martensite fraction. For example, the deviation of the martensite fraction is 15% or less. Preferably, the deviation of the martensite fraction is 10% or less. The deviation of the martensite fraction can be determined as follows: that is, within the minimum plate thickness t... minFrom the cross-section of structural member C1-10 at position C1-31 of the steel plate, at least ten analytical samples (e.g., approximately 10 mm in size on the long side) were cut from positions at least 20 mm from the end and at least 10 mm apart. These samples were then mirror-polished with the plate thickness as the observation surface, and etched using Lepera reagent. Next, for the area at a depth of 1 / 4 of the plate thickness from the surface (from 1 / 8 to 3 / 8 of the plate thickness from the surface), 30 fields of view tissue photographs were taken using an optical microscope at 1000x magnification, with each field of view measuring 2400 μm. 2 The above describes the image analysis of the obtained tissue photographs.

[0439] As an image analysis method, the maximum brightness value Lmax and minimum brightness value Lmin of the image are obtained. Pixels with brightness values ​​between Lmax-0.3(Lmax-Lmin) and Lmax are designated as white regions. The proportion of pixels in the white regions to the total number of pixels is calculated to determine the martensite fraction. This image analysis is performed on a total of 30 observation fields for each analytical sample to determine the martensite fraction, and the average value is taken as the martensite fraction of each analytical sample. Furthermore, the difference between the maximum and minimum martensite fractions among ten or more analytical samples is defined as the value with the minimum plate thickness t. min The deviation of the martensite fraction in the cross-section of structural member C1-10 at the location of steel plate C1-31. The structural member C1-10 has the minimum plate thickness t. min When there are multiple steel plates, the martensite fraction is calculated by analyzing each steel plate, and the deviation of the largest martensite fraction among these steel plates is taken as the deviation of the martensite fraction in structural member C1-10.

[0440] Furthermore, depending on the steel plate, the martensite area ratio obtained through image analysis, i.e., the area ratio of the white region, sometimes contains a few percentage points of retained austenite area ratio. However, since the deviation in the martensite fraction is calculated using differentials, its impact is minor.

[0441] After the forming process (hot stamping), steel sheet C1-31 can, for example, have a tensile strength of 0.5 GPa or more, preferably 1.0 GPa or more. Similarly, after the forming process (hot stamping), steel sheets C1-32 and C1-33 ( Figure 14For example, it can have a tensile strength of 0.5 GPa or higher, preferably 1.0 GPa or higher. At least one of steel plates C1-31, C1-32, and C1-23 can have a tensile strength of 1.5 GPa or higher after the forming process. The tensile strength of each of steel plates C1-31, C1-32, and C1-33 can be the same as or different from the tensile strength of the other steel plates.

[0442] Although the illustration is omitted, the lower structural member C1-20 ( Figure 14 It is also possible to include the same membrane C1-13 as the upper structural member C1-10 after hot stamping. The membrane C1-13 is, for example, disposed in the structural member C1-20 at a minimum plate thickness t. min At least one surface of the steel plate. For structural member C1-20, the minimum plate thickness t... min The deviation of the martensite fraction at the location of the steel plate is also the same as that of structural member C1-10, for example, less than 15%, more preferably less than 10%.

[0443] [Effect] In this embodiment, the blank C1-30 has the smallest plate thickness t. min The emissivity of one surface of steel plate C1-31 is greater than that of both surfaces of steel plate C1-32, which has a greater plate thickness t2. That is, the surface of steel plate C1-31 has undergone a treatment to increase emissivity compared to the two surfaces of steel plate C1-32. Therefore, when the billet C1-30 is heated during hot stamping, the heating rate of steel plate C1-31 is significantly higher than that of steel plate C1-32. Consequently, during the heating process, steel plate C1-31 can be rapidly heated to the temperature of the austenitic region, ensuring a longer high-temperature holding time. As a result, the austenite grains in the microstructure of steel plate C1-31 become coarser, and the ferrite phase transformation region (ferrite nose) in the CCT diagram shifts towards the longer-time side. Therefore, it is possible to prevent the austenitic phase from transforming into ferrite in the steel sheet C1-31 during the period from when the billet C1-30 is removed from, for example, a heating furnace until the start of forming based on the die C1-60. Thus, it is possible to begin forming the billet C1-30 based on the die C1-60 while maintaining the microstructure of the steel sheet C1-31 in an austenitic phase state, thereby improving the sheet thickness t to a minimum. min The hardenability of C1-31 steel plate.

[0444] In this embodiment, by improving the hardenability of the thinner steel plate C1-31, the hardness of the structural member C1-10 formed from the billet C1-30 can be made more uniform. More specifically, for the smallest plate thickness t... minThe C1-31 steel sheet is also well quenched, thus ensuring that the martensite fraction deviation in the C1-31 steel sheet is less than 15%. Therefore, for example, when a collision load is applied to the structural member C1-10, deformation concentration is less likely to occur, and the structural member C1-10 easily exhibits high impact absorption performance. Therefore, even when forming structural members C1-10 from billet C1-30, including relatively large structural members C1-10 such as those used in vehicle bodies, the strength defects of the structural member C1-10 can be reduced, and the impact absorption performance of the structural member C1-10 can be improved.

[0445] The smaller the deviation in martensite fraction, the less uneven the mechanical properties within structural member C1-10, which is preferable from a functional perspective. On the other hand, a large deviation in martensite fraction indicates that there is a predominance of insufficient hardenability, i.e., insufficient hardness, within structural member C1-10. During impact deformation of structural member C1-10, deformation tends to concentrate in the areas with insufficient hardness, thus reducing the functionality of structural member C1-10.

[0446] In this embodiment, by improving the hardenability of the thinner steel plate C1-31, stress unevenness is less likely to occur in the structural member C1-10. Therefore, even when forming, for example, a large structural member C1-10 from the blank C1-30, the structural member C1-10 is less prone to twisting, warping, etc. Therefore, even when forming a large structural member C1-10 from the blank C1-30, including a thin steel plate C1-31, dimensional inaccuracies in the structural member C1-10 can be reduced, and the impact absorption performance of the structural member C1-10 can be improved.

[0447] In the billet C1-30 of this embodiment, the minimum plate thickness t min The surface of steel plate C1-31 is essentially covered by a black film C1-50, while steel plate C1-32, which has a thickness t2 greater than steel plate C1-31, does not have the film C1-50. Therefore, the emissivity of the surface of steel plate C1-31 is inherently greater than the emissivity of both surfaces of steel plate C1-32. In this case, when the billet C1-30 is heated during hot stamping, steel plate C1-31 heats up faster than steel plate C1-32, thus the high-temperature holding time of steel plate C1-31 is longer compared to the case where steel plate C1-31 has the same emissivity as steel plate C1-32. Therefore, after the billet C1-30 is heated, the inhomogeneity of the phase transformation caused by the difference in cooling rates between steel plates C1-31, C1-32, and C1-33 can be reduced. Specifically, for the minimum thickness t... minSteel plate C1-31 can delay the onset of the phase transformation from austenite to ferrite, thus reducing the difference in phase transformation onset time between steel plate C1-31 and other steel plates C1-32 and C1-33. As a result, the hardenability of steel plates C1-31, C1-32, and C1-33 contained in billet C1-30 can be homogenized.

[0448] For example, when the coating C1-31b of the steel sheet C1-31 is an aluminum-based coating, the heating rate of the steel sheet C1-31 tends to be slow during the heating process. Aluminum-based coatings are white and therefore easily reflect heat, hindering the heating of the steel sheet C1-31. However, in the billet C1-30 of this embodiment, the surface of the steel sheet C1-31 is treated to increase its emissivity. Therefore, even if the steel sheet C1-31 is a coated steel sheet with an aluminum-based coating, the heating process of the steel sheet C1-31 can be accelerated, ensuring a longer high-temperature holding time for the steel sheet C1-31. Therefore, the hardenability of the thin-walled steel sheet C1-31 can be ensured.

[0449] In this embodiment, during the heating process, the plate with the minimum thickness t is first selected. min Steel plate C1-31 reaches the temperature of the austenitic region. Subsequently, steel plates C1-32 and C1-33 reach the temperature of the austenitic region in ascending order of thickness. Here, among steel plates C1-31, C1-32, and C1-33, the smallest thickness t... min With the largest plate thickness t max The ratio: t max / t min Preferably, it is 3.2 or less. Therefore, the plate thickness t increases due to heating. min Before the alloying of the C1-31b coating on the C1-31 steel plate is excessively advanced, and the diffusion layer grows, causing it to lose its corrosion resistance or weldability, it is possible to achieve a plate thickness of t. max The C1-33 steel plate is fully heated until the austenitic phase transformation is complete. Therefore, the process window can be ensured in the manufacture of structural components C1-10.

[0450] In this embodiment, to improve the emissivity of the steel plate C1-31, a film C1-50 can be applied to the steel plate C1-31. The emissivity of the film C1-50 (at a temperature of 25°C and a wavelength of 8.0 μm) is, for example, 60% or more. Therefore, the steel plate C1-31 can be radiatively heated efficiently, and the heating rate of the steel plate C1-31 can be more easily increased during the heating process.

[0451] In this embodiment, the film C1-50 may contain: carbon black; one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide; and 0~0.30 g / m 2 The following is about silicon dioxide. The carbon black content is X.CB (g / m 2 The content of ) and oxides X Oxide (g / m 2 Preferably, the above formula (1) is satisfied. As described in Patent Document 1, formula (1) specifies the ratio of the increase rate (°C / s) of heating rate (%) to the carbon black content X. CB And the content of oxides X Oxide The relationship is expressed by equation (1). Equation (1) indicates that carbon black mainly functions as a heat-absorbing material up to 700°C, while oxides mainly function as a heat-absorbing material above 700°C. By making the film C1-50 satisfy equation (1), the emissivity of the steel plate C1-31 with the film C1-50 applied at 25°C at a wavelength of 8.0 μm easily becomes more than 60%.

[0452] Carbon black and oxides can be dispersed throughout the film C1-50 in a plane perpendicular to the thickness direction of the steel plate C1-31. This facilitates the homogenization of the emissivity of the steel plate C1-31 surface. Therefore, during the heating process, a plate with a minimum thickness t can be heated rapidly and uniformly. min C1-31 steel plate.

[0453] However, the composition of the C1-50 coating is not limited to this. The C1-50 coating improves the emissivity of the C1-31 steel sheet compared to the untreated case, so any substantially black coating is acceptable. For example, the C1-50 coating can replace carbon black or contain graphite or soot in addition to carbon black. Alternatively, to improve the emissivity of the C1-31 steel sheet, the C1-50 coating can, for example, contain needle-like compounds with an aspect ratio of 4 or more and 50 or less and a hexagonal crystal structure. A typical hexagonal crystal structure compound is graphite (C), but it can also be lanthanum silicate, magnesium diboride, beryllium oxide (BeO), zinc oxide, β-quartz, goethite (NiS), wurtzite (ZnS), etc.

[0454] The lower structural member C1-20 and the blank C1-40 have the same configuration as the upper structural member C1-10 and the blank C1-30. Therefore, the lower structural member C1-20 and the blank C1-40 can achieve the same effect as described above.

[0455] <Second Implementation Method> [Burnt Material] Figure 18A and Figure 18B This is a cross-sectional view of the blank C1-30A according to the second embodiment. Figure 18A and Figure 18B This is a cross-sectional view of the blank C1-30 in the first embodiment. Figure 16B and Figure 16C The corresponding figure. In the first embodiment, among the blanks C1-30 used for structural members C1-10, the one with the smallest plate thickness t is selected. min At least one surface of steel plate C1-31 is treated to ensure that the emissivity of the surface of steel plate C1-31 is higher than that of other steel plates C1-32 before the heating process. In a first embodiment, for example, a film C1-50 for improving emissivity is formed on one or both sides of steel plate C1-31. Figure 16B On the other hand, in this embodiment, the surface of steel plate C1-31 is treated in billet C1-30A in such a way that the emissivity of the surface of steel plate C1-31 is higher than that of the surface of steel plate C1-32 during the heating process.

[0456] Reference Figure 18A and Figure 18B In this embodiment, steel plates C1-31, C1-32, and C1-33 are clad steel plates. More specifically, steel plates C1-31, C1-32, and C1-33 are all aluminized steel plates. Steel plate C1-31 has a base steel plate C1-31a and an aluminum-based coating C1-31b. Steel plate C1-32 has a base steel plate C1-32a and an aluminum-based coating C1-32b. Steel plate C1-33 has a base steel plate C1-33a and an aluminum-based coating C1-33b.

[0457] In steel plate C1-31, an aluminum-based coating C1-31b covers both surfaces of the base steel plate C1-31a. The aluminum-based coating C1-31b is applied to the entirety or substantially the entirety of both surfaces of the base steel plate C1-31a. Similarly, in steel plate C1-32, an aluminum-based coating C1-32b covers both surfaces of the base steel plate C1-32a. The aluminum-based coating C1-32b is applied to the entirety or substantially the entirety of both surfaces of the base steel plate C1-32a. Furthermore, in steel plate C1-33, an aluminum-based coating C1-33b covers both surfaces of the base steel plate C1-33a. The aluminum-based coating C1-33b is applied to the entirety or substantially the entirety of both surfaces of the base steel plate C1-33a.

[0458] The chemical composition of aluminum-based coatings C1-31b, C1-32b, and C1-33b is not particularly limited. Known aluminum-based coatings (coatings with aluminum as the main component) can be used as aluminum-based coatings C1-31b, C1-32b, and C1-33b. Although not particularly limited, aluminum-based coatings C1-31b, C1-32b, and C1-33b can be, for example, Al-Si based coatings. Aluminum-based coatings C1-31b, C1-32b, and C1-33b can be the same as or different from aluminum-based coatings on other steel plates C1-31, C1-32, and C1-33.

[0459] There are no particular restrictions on the types of base steel plates C1-31a, C1-32a, and C1-33a. Base steel plates C1-31a, C1-32a, and C1-33a can be the same as or different from other base steel plates.

[0460] Reference Figure 18A and Figure 18B Similar to the first embodiment, steel plate C1-31 has the smallest plate thickness t among steel plates C1-31, C1-32, and C1-33. min Steel plate C1-32 has a thickness t greater than steel plate C1-31. min Larger plate thickness t2. Steel plate C1-33 has the same plate thickness t as steel plate C1-31. min The above refers to plate thickness t3. The plate thickness t of steel plate C1-31 is... min The thickness t2 of steel plate C1-32 is the combined thickness of the base steel plate C1-32a and the aluminum coating C1-32b, and is the average thickness of steel plate C1-31. The thickness t3 of steel plate C1-33 is the combined thickness of the base steel plate C1-33a and the aluminum coating C1-33b, and is the average thickness of steel plate C1-32.

[0461] Reference Figure 18A In relation to the plate with the smallest thickness t min The amount of aluminum coating C1-31b adhering to the two surfaces of the base steel plate C1-31a in steel plate C1-31 is set as W1 (g / m). 2 The amount of aluminum coating C1-32b applied relative to the two surfaces of the base steel plate C1-32a in the steel plate C1-32 with a greater plate thickness t2 is defined as W2 (g / m). 2 When the aluminum coating C1-31b in steel plate C1-31 is less than the aluminum coating C1-32b in steel plate C1-32, the adhesion amount W1 is less. The adhesion amount W1 of the aluminum coating C1-31b in steel plate C1-31 is the average adhesion amount on both surfaces of the base steel plate C1-31a. Typically, the adhesion amount (g / m²) of the aluminum coating C1-31b relative to one surface of the base steel plate C1-31a is... 2 The amount of aluminum coating C1-31b adhered to relative to the other surface of the base steel plate C1-31a (g / m²) 2The amounts of aluminum-based coating C1-31b are essentially equal. However, due to factors such as manufacturing conditions, the amount of aluminum-based coating C1-31b may vary between the front and back surfaces of the base steel plate C1-31a. The amount of aluminum-based coating C1-31b may also differ between one and the other surface of the base steel plate C1-31a. Similarly, the amount of aluminum-based coating C1-32b W2 in steel plate C1-32 is the average amount of aluminum-based coating C1-32b on both surfaces of the base steel plate C1-32a. The amount of aluminum-based coating C1-32b (g / m²) relative to one surface of the base steel plate C1-32a is... 2 The amount of aluminum coating C1-32b typically adhered to relative to the other surface of the base steel sheet C1-32a (g / m²) 2 They are essentially equal. However, due to factors such as manufacturing conditions, the amount of aluminum-based coating C1-32b may vary between the front and back surfaces of the base steel plate C1-32a. The amount of aluminum-based coating C1-32b may also differ between one surface and the other.

[0462] The adhesion amount W1 of the aluminum-based coating C1-31b in steel plate C1-31 and the adhesion amount W2 of the aluminum-based coating C1-32b in steel plate C1-32 can also be 20g / m². 2 Above and 120g / m 2 The following are preferred adhesion amounts: W1 and W2 are both 30 g / m². 2 The above, more preferably 35g / m 2 The above. The preferred adhesion amounts W1 and W2 are 115 g / m². 2 The following is more preferably 100g / m 2 The following is the difference between the adhesion amounts W1 and W2: W2 - W1 is, for example, 10 (g / m³). 2 ) or above. W2-W1 is preferably 20 (g / m³). 2 ) or more, more preferably 30 (g / m 2 Above 80 (g / m³). W2-W1 can be 80 (g / m³). 2 Below 70 (g / m³). W2-W1 is preferably 70 (g / m³). 2 ) or less, more preferably 60 (g / m 2 Below that. Furthermore, the adhesion amounts W1 and W2 satisfy the relationship that W2 / W1 > 1.0. Preferably, the adhesion amounts W1 and W2 satisfy the relationship that W2 / W1 ≥ 1.2, and more preferably, the relationship that W2 / W1 ≥ 1.5.

[0463] Reference Figure 18B The amount of aluminum-based coating C1-33b applied relative to the two surfaces of the base steel plate C1-33a in the steel plate C1-33 with a plate thickness t3 is set as W3 (g / m). 2When the aluminum coating C1-33b in steel plate C1-33 is less than the aluminum coating C1-32b in steel plate C1-32, the adhesion amount W3 can be less. The adhesion amount W3 of the aluminum coating C1-33b is the average adhesion amount on both surfaces of the base steel plate C1-33a. Typically, the adhesion amount (g / m²) of the aluminum coating C1-33b relative to one surface of the base steel plate C1-33a is... 2 The amount of aluminum coating C1-33b adhered to relative to the other surface of the base steel plate C1-33a (g / m²) 2 They are essentially equal. However, due to factors such as manufacturing conditions, the amount of aluminum-based coating C1-33b may vary between the front and back surfaces of the base steel plate C1-33a. The amount of aluminum-based coating C1-33b may also differ between one and the other surface of the base steel plate C1-33a.

[0464] The adhesion amount W3 of the aluminum-based coating C1-33b in steel plate C1-33 is the same as that in steel plates C1-31 and C1-32, for example, it can be 20g / m². 2 Above and 120g / m 2 The following is a preferred adhesion amount W3: 30 g / m³. 2 The above, more preferably 35g / m 2 The above. The preferred adhesion amount W3 is 115 g / m³. 2 The following is more preferably 100g / m 2 Below. When W2 > W3, the difference between the adhesion amounts W2 and W3: W2 - W3 is, for example, 10 (g / m³). 2 ) or above. W2-W3 is preferably 20 (g / m³). 2 ) or more, more preferably 30 (g / m 2 W2-W3 can be 80 (g / m³) or above. 2 Below ) . W2-W3 is preferably 70 (g / m 2 ) or less, more preferably 60 (g / m 2 The following applies. The adhesion amount W3 of the aluminum-based coating C1-33b in steel plate C1-33 can be compared with the minimum plate thickness t. min The amount of aluminum coating C1-31b on the steel plate C1-31 is equal to or greater than the amount of aluminum coating C1-31b.

[0465] The method for forming aluminum-based coatings C1-31b, C1-32b, and C1-33b on base steel plates C1-31a, C1-32a, and C1-33a is not particularly limited; for example, it can be a general hot-dip galvanizing process. Specifically, by immersing the base steel plate C1-31a in a hot-dip aluminizing bath and wiping it with nitrogen or atmospheric gas, an aluminized steel plate C1-31 with an adjusted adhesion amount W1 of the aluminum-based coating C1-31b can be obtained. Similarly, by immersing the base steel plate C1-32a in a hot-dip aluminizing bath and wiping it with nitrogen or atmospheric gas, an aluminized steel plate C1-32 with an adjusted adhesion amount W2 of the aluminum-based coating C1-32b can be obtained. Furthermore, by immersing the base steel sheet C1-33a in a hot-dip aluminizing bath and wiping it with gases such as nitrogen and atmosphere, an aluminized steel sheet C1-33 with an adjusted adhesion amount W3 of the aluminum-based coating C1-33b can be obtained. In the case of forming an aluminum-based coating through hot-dip galvanizing, an Al-Fe alloy layer is formed at the interface between the base steel sheet and the aluminum-based coating through the dissolution of Fe during the hot-dip galvanizing process.

[0466] As a method for determining the adhesion amounts W1, W2, and W3 of aluminum-based coatings C1-31b, C1-32b, and C1-33b, for example, the sodium hydroxide-hexamethylenetetramine-hydrochloric acid peeling gravimetric method described in JIS G 3314:2019 can be cited. Specifically, according to JIS G 3314:2019, five or more specified surface areas S (mm²) are collected from each of the steel plates C1-31, C1-32, and C1-32 of billet C1-30A. 2 Test pieces (e.g., 50mm × 50mm) were used, and the weight w1 (g) of each test piece was measured. Then, each test piece was immersed in a sodium hydroxide aqueous solution. After confirming the foaming caused by the dissolution of the coating had subsided, the test pieces were removed from the sodium hydroxide aqueous solution and washed with water. Next, the washed and wetted test pieces were immersed in a hydrochloric acid aqueous solution containing hexamethylenetetramine until the foaming caused by the dissolution of the coating was complete. The test pieces removed from the hexamethylenetetramine hydrochloric acid aqueous solution were immediately washed with water and dried, and the weight w2 (g) of the test piece was measured again. The adhesion amount W (g / m²) of the aluminum-based coating on each test piece was determined. 2 ) can be obtained by {(w1-w2) / S}×10 6 The average value of the adhesion amount W from five or more test pieces collected from each steel plate is taken as the adhesion amount of the aluminum-based coating in that steel plate.

[0467] However, when the test pieces collected from steel plates C1-31, C1-32, and C1-33 are relatively small, the cross-sections of the aluminum-based coatings C1-31b, C1-32b, and C1-33b are observed using an optical microscope (area: 100μm × 100μm). The thickness (μm) of the coating is measured in the same way in three fields of view. By multiplying the average thickness measured in the three fields of view by a factor of 3, the adhesion amount can be converted. At this time, for each steel plate C1-31, C1-32, and C1-33, the adhesion amount is calculated for each single side of the base steel plate, and the average value of the obtained adhesion amount (the average value of both sides) is taken as the adhesion amount of the aluminum-based coating. When an Al-Fe alloy layer exists at the interface between the base steel plate and the aluminum-based coating, the thickness of the aluminum-based coating also includes the thickness of the Al-Fe alloy layer. The thickness of the aluminum-based coating C1-31b on the thinnest steel plate C1-31 is smaller than the thickness of the aluminum-based coating C1-32b on the other steel plates C1-32. In this embodiment, the thickness of the aluminum-based coating C1-33b on the steel plate C1-33 is also smaller than the thickness of the aluminum-based coating C1-32b on the steel plate C1-32. The thicknesses of the aluminum-based coatings C1-31b and C1-33b can be different or the same.

[0468] [Structural Components] The blank C1-30A is provided with the same heating and forming processes as in the first embodiment. Thus, as... Figures 19A-19C As shown, structural member C1-10A, the same as in the first embodiment, is manufactured from blank C1-30A. Figures 19A-19C This is a cross-sectional view of structural component C1-10A after the forming process (hot stamping). Figure 19A This indicates the minimum plate thickness t. min The cross section of structural member C1-10A at the location of steel plate C1-31. Figure 19B This indicates a plate thickness t greater than that of steel plate C1-31. min The cross section of structural member C1-10A at the location of steel plate C1-32 with a large plate thickness t2. Figure 19C This indicates the thickness t of steel plate C1-31. min The cross section of structural member C1-10A at the location of steel plate C1-33 with a plate thickness of t3.

[0469] Reference Figure 19A In the hot-stamped structural component C1-10A, the steel plate C1-31 is also a coated steel plate with an aluminum-based coating C1-31b on both surfaces of the base steel plate C1-31a. (Refer to...) Figure 19B Steel plate C1-32 is a coated steel plate with an aluminum-based coating C1-32b on both surfaces of the base steel plate C1-32a. (Refer to...) Figure 19CSteel plate C1-33 is a coated steel plate with aluminum-based coatings C1-33b on both surfaces of the base steel plate C1-33a. However, the aluminum-based coatings C1-31b, C1-32b, and C1-33b in structural member C1-10A are different from those in billet C1-30A ( Figure 18A as well as Figure 18B Compared to the state of ), alloying with iron is carried out through a heating process.

[0470] Reference Figure 19A and Figure 19B When the average thickness (coating thickness) of the aluminum-based coating C1-31b on both surfaces of steel plate C1-31 is set as K1 (μm), and the average thickness (coating thickness) of the aluminum-based coating C1-32b on both surfaces of steel plate C1-32 is set as K2 (μm), the coating thickness K1 of steel plate C1-31 is smaller than the coating thickness K2 of steel plate C1-32. The difference between coating thicknesses K1 and K2: K2-K1 is, for example, 7 (μm) or more. K2-K1 can be 33 (μm) or less. In addition, the coating thicknesses K1 and K2 can satisfy the relationship K2 / K1 > 1.0. K2 / K1 is preferably 1.2 or more, and more preferably 1.5 or more.

[0471] Reference Figure 19B as well as Figure 19C When the average thickness (coating thickness) of the aluminum-based coating C1-33b on both surfaces of the steel plate C1-33 is set to K3 (μm), in this embodiment, the coating thickness K3 of the steel plate C1-33 is smaller than the coating thickness K2 of the steel plate C1-32. The difference between coating thicknesses K2 and K3: K2-K3 is, for example, 7 (μm) or more. K2-K3 can be 33 (μm) or less.

[0472] The thicknesses K1, K2, and K3 of the aluminum-based coatings C1-31b, C1-32b, and C1-33b in structural member C1-10A can be measured as follows: Structural member C1-10A is obtained by disassembling the vehicle body component, and analytical samples are obtained from it, for example, by laser cutting. For example, analytical samples are obtained from multiple steel plates contained in structural member C1-10A. The analytical samples are obtained at or near the center of the top plate of each steel plate with an open cross-section. For the test pieces obtained from multiple steel plates, the cross-section of the aluminum-based coating is etched with nitric acid ethanol, and then observed using an optical microscope (area: 100μm × 100μm). The thickness of the coating is measured in three fields of view, and the average thickness of the coating measured in the three fields of view can be taken as the coating thickness. In many cases, an electrodeposited coating film exists on the outermost layer of structural member C1-10A. In this case, observe the coating layer that exists below the electrodeposited coating film layer and above the base steel plate.

[0473] In the structural member C1-10A of this embodiment, similar to the first embodiment, it has a minimum plate thickness t. min The deviation of the martensite fraction at the cross-section of the steel plate at position C1-31 is, for example, 15% or less, more preferably 10% or less. The deviation of the martensite fraction can be measured by the method described in the first embodiment.

[0474] Although the illustration is omitted, the blank C1-40 used for structural component C1-20 ( Figure 14 and Figure 16D The same structure as billet C1-30A can be used. That is, the structure of steel plates C1-31, C1-32, and C1-33 in billet C1-30A can be directly applied to steel plates C1-41, C1-42, and C1-43 in billet C1-40. Figure 16D In this case, in the structural member C1-20 manufactured from the blank C1-40 through the heating and forming processes, steel plates C1-41, C1-42, and C1-43 become... Figures 19A-19C The steel plates C1-31, C1-32, and C1-33 of the structural component C1-10A shown have the same structure.

[0475] [Effect] In the billet C1-30A of this embodiment, the treatment used to increase the emissivity of the surface of steel plate C1-31 compared to the two surfaces of steel plate C1-32 results in the smallest possible plate thickness t. minThe amount of aluminum-based coating C1-31b adhering to steel plate C1-31, W1, is less than the amount of aluminum-based coating C1-32b adhering to steel plate C1-32, which has a greater plate thickness t2. Therefore, when the billet C1-30A is heated during hot stamping, the heating rate of steel plate C1-31 is significantly higher than that of steel plate C1-32. Specifically, the aluminum-based coating C1-31b on the surface of steel plate C1-31 becomes thinner, so when the billet C1-30A is heated, the alloying of the aluminum-based coating C1-31b with the iron contained in the base steel plate C1-31a rapidly advances to the surface of steel plate C1-31, causing both surfaces of steel plate C1-31 to change to a black color or a similar color. That is, the emissivity of both surfaces of steel plate C1-31 increases during the heating process. Therefore, steel sheet C1-31 can be heated to the austenitic region temperature more quickly, ensuring a longer high-temperature holding time. As a result, the austenite grains in the microstructure of steel sheet C1-31 coarsen, and the ferrite phase transformation region (ferrite nose) in the CCT diagram shifts towards the longer-term side. Therefore, the austenite phase transformation to ferrite in steel sheet C1-31 can be prevented from occurring between removal from the furnace and the start of forming based on die C1-60. Thus, forming of billet C1-30A based on die C1-60 can begin while maintaining the microstructure of steel sheet C1-31 in an austenitic phase state, improving the sheet thickness t to a minimum. min The hardenability of C1-31 steel plate.

[0476] In this embodiment, by improving the hardenability of the thinner steel plate C1-31, the hardness of the structural member C1-10A formed from the billet C1-30A can be made more uniform. More specifically, in this embodiment, the hardness of the plate with the minimum thickness t is also optimized. min The steel plate C1-31 is properly quenched, thus the deviation of the martensite fraction of the steel plate C1-31 can be kept below 15%. Therefore, as described in the first embodiment, the strength defects of the structural member C1-10A can be reduced, and the impact absorption performance of the structural member C1-10A can be improved.

[0477] Similar to the first embodiment, by improving the hardenability of the thinner steel sheet C1-31, stress unevenness is less likely to occur in the structural member C1-10A. Therefore, even when forming, for example, a large structural member C1-10A from a blank C1-30A containing the steel sheet C1-31, dimensional inaccuracies in the structural member C1-10A can be reduced, and the impact absorption performance of the structural member C1-10A can be improved.

[0478] In the billet C1-30A of this embodiment, the minimum plate thickness t minThe amount W1 of aluminum-based coating C1-31b in steel plate C1-31 is less than the amount W2 of aluminum-based coating C1-32b in steel plate C1-32, which is thicker than steel plate C1-31. Therefore, steel plate C1-31 can heat up faster than steel plate C1-32, and thus the high-temperature holding time of steel plate C1-31 is longer compared to cases where the amount W1 of aluminum-based coating C1-31b in steel plate C1-31 and the amount W2 of aluminum-based coating C1-32b in steel plate C1-32 are the same or greater. Therefore, after the billet C1-30A is heated, the inhomogeneity of the phase transformation caused by the difference in cooling rates between steel plates C1-31, C1-32, and C1-33 can be reduced. Specifically, for the minimum plate thickness t... min Steel plate C1-31 can delay the onset of the phase transformation from austenite to ferrite, thus reducing the difference in phase transformation onset time between steel plate C1-31 and other steel plates C1-32 and C1-33. As a result, the hardenability of steel plates C1-31, C1-32, and C1-33 contained in billet C1-30 can be homogenized.

[0479] like Figure 20 As shown, in the blank C1-30A of this embodiment, it is also possible to have a minimum plate thickness t. min The steel plate C1-31 is provided with the same coating C1-50 as in the first embodiment. The coating C1-50 can be provided on at least one surface of the steel plate C1-31. That is, the coating C1-50 can cover only one surface of the steel plate C1-31, or it can cover both surfaces of the steel plate C1-31. This allows for a pre-increase in the surface emissivity of the steel plate C1-31, resulting in a faster temperature rise when the billet C1-30A is heated during hot stamping. Therefore, a longer high-temperature holding time for the steel plate C1-31 can be ensured. Consequently, the hardenability of the thinnest steel plate C1-31 can be further improved.

[0480] In the case where a film C1-50 is provided on the thinnest steel plate C1-31 in the blank C1-30A, in the formed structural member C1-10A, a film C1-13, the same as in the first embodiment, exists on the steel plate C1-31. Figure 17 ).

[0481] The lower structural member C1-20 ( Figure 14 ) and billet C1-40 ( Figure 16D The structure can have the same configuration as the upper structural member C1-10A and the blank C1-30A in this embodiment. Therefore, the lower structural member C1-20 and the blank C1-40 can also achieve the same effect as described above.

[0482] <Third Implementation Method> Figure 21 This is a plan view of the blank C1-30B in the third embodiment. The blanks C1-30 and C1-30A in the first and second embodiments are welded blanks formed by butt-jointing steel plates C1-31, C1-32, and C1-33. The blank C1-30B in this embodiment differs from the first and second embodiments mainly in the arrangement of the steel plates and the shape of the joints.

[0483] Reference Figure 21 The billet C1-30B comprises multiple steel plates C1-31, C1-32, C1-33, and C1-36. In Figure 21 In the example, steel plates C1-31, C1-32, C1-33, and C1-36 are configured and joined in such a manner that they form elongated sections C1-34L and C1-34R and multiple connecting sections C1-35. For a plate with a minimum thickness t... min At least one surface of the steel plate C1-31 is treated to increase emissivity compared to the two surfaces of the steel plate C1-32. That is, at least one surface of the steel plate C1-31 is treated in the same way as in the first or second embodiment, such that its emissivity increases compared to the steel plate C1-32 before or during heating. Therefore, the billet C1-30B of this embodiment can also achieve the same effect as in the first embodiment.

[0484] The billet C1-30B has an overlapping portion C1-37. Figure 22 yes Figure 21 The IX-IX cross-sectional view shows the cross-section of the overlapping portion C1-37. In this embodiment, the overlapping portion C1-37 is formed by overlapping the ends of two adjacent steel plates C1-33 and C1-36. The ends of steel plate C1-33 are joined together in an overlapping state with the ends of steel plate C1-36. Steel plates C1-33 and C1-36 are joined together, for example, by spot welding or laser welding.

[0485] The overlapping portion C1-37 has a total plate thickness t. The total plate thickness t is the thickness obtained by adding the plate thickness t3 of steel plate C1-33 to the plate thickness t6 of steel plate C1-36. If at least one of steel plates C1-33 or C1-36 is a clad steel plate, the total plate thickness t also includes the thickness of the cladding. The total plate thickness t of the overlapping portion C1-37 is, for example, 4.0 mm or less. The total plate thickness t of the overlapping portion C1-37 may also be greater than 2.5 mm.

[0486] On the outer surface of the overlapping portion C1-37 in steel plates C1-33 and C1-36 respectively, a coating was applied with that of steel plate C1-32 ( Figure 16BThe emissivity of the two surfaces is increased by comparing them. In each of steel plates C1-33 and C1-36, the surface located outside the overlapping portion C1-37 is treated, for example, throughout the entire surface. For example, the emissivity of the surface of steel plate C1-33 located outside the overlapping portion C1-37, i.e., the surface located on the opposite side of the other steel plate C1-36, is pre-set to be greater than the emissivity of the two surfaces of steel plate C1-32. Similarly, the emissivity of the surface of steel plate C1-36 located outside the overlapping portion C1-37, i.e., the surface located on the opposite side of the other steel plate C1-33, is pre-set to be greater than the emissivity of the two surfaces of steel plate C1-32. For example, at 25°C and a wavelength of 8.0 μm, the emissivity of the surface of steel plates C1-33 and C1-36 located outside the overlapping portion C1-37 is 60% or more, preferably 70% or more, and more preferably 80% or more. The difference in emissivity at 25°C and wavelength of 8.0 μm between the outer surface of the overlapping portion C1-37 in steel plates C1-33 and C1-36 and the two surfaces of other steel plates C1-32 is preferably greater than 5%, more preferably greater than 10%, and even more preferably greater than 20%. In steel plates C1-33 and C1-36, the emissivity of the surface located on the inner side of the overlapping portion C1-37 can be greater than or less than the emissivity of the two surfaces of steel plate C1-32.

[0487] For example, using the film C1-50 described in the first embodiment, the surface located outside the overlapping portion C1-37 in each of the steel plates C1-33 and C1-36 can also have a larger surface area than that of the steel plate C1-32. Figure 16B High emissivity. The film C1-50 is disposed on at least the outer (surface) surface of the overlapping portion C1-37 of one of the two surfaces of the steel plate C1-33, completely covering that surface. Additionally, the film C1-50 is disposed on at least the outer (surface) surface of the overlapping portion C1-37 of one of the two surfaces of the steel plate C1-36, completely covering that surface. The film thickness of the film C1-50 is very small, as described in the first embodiment; therefore, the plate thickness measured including the film C1-50 can be treated as the total plate thickness t for the overlapping portion C1-37.

[0488] Alternatively, the outer surface of the overlapping portion C1-37 in steel plates C1-33 and C1-36 can also be heated by heating the billet C1-30 to overlap with steel plate C1-32 ( Figure 21 The two surfaces were treated in a way that increased their emissivity compared to each other. For example, Figure 23 As shown, steel plates C1-33 and C1-36 can also be the same as steel plate C1-32 ( Figure 18ACompared to thin-coated steel sheets, steel sheets C1-33 are coated steel sheets with a base steel sheet C1-33a and an aluminum-based coating C1-33b, similar to the second embodiment. Steel sheet C1-36 is also a coated steel sheet with a base steel sheet C1-36a and an aluminum-based coating C1-36b. The base steel sheets C1-33a and C1-36a can be the same type of steel sheet or different types of steel sheet. Similarly, the aluminum-based coatings C1-33b and C1-36b can be the same type of coating or different types of coating. Other steel sheets C1-31, C1-32 ( Figure 18A and Figure 18B They are also coated steel sheets having base steel plates C1-31a, C1-32a and aluminum coating C1-33b, respectively, and have the same structure as the second embodiment.

[0489] When steel plates C1-33 and C1-36 are clad steel plates, the total plate thickness t of the overlapping portion C1-37 also includes the thickness of the cladding layers C1-33b and C1-36b. Figure 23 In the example, the amount of aluminum coating C1-33b applied relative to the two surfaces of the base steel plate C1-33a is set as W3 (g / m²). 2 The amount of aluminum coating C1-36b applied relative to the two surfaces of the parent steel plate C1-36a is set as W6 (g / m). 2 When the adhesion amounts W3 and W6 are relative to the two surfaces of the base steel plate C1-32a, the aluminum coating C1-32b ( Figure 18A The amount of W2 adhering to it is small.

[0490] As described in the second embodiment, the adhesion amount W3 of the aluminum-based coating C1-33b in steel plate C1-33 is the average adhesion amount on both surfaces of the base steel plate C1-33a. Similarly, the adhesion amount W6 of the aluminum-based coating C1-36b in steel plate C1-36 is the average adhesion amount on both surfaces of the base steel plate C1-36a. Typically, the adhesion amount (g / m²) of the aluminum-based coating C1-36b relative to one surface of the base steel plate C1-36a is... 2 The amount of aluminum coating C1-36b adhered to relative to the other surface of the base steel plate C1-36a (g / m²) 2 They are essentially equal. However, due to factors such as manufacturing conditions, the amount of aluminum-based coating C1-36b may vary between the front and back surfaces of the base steel plate C1-36a. The amount of aluminum-based coating C1-36b may also differ between one and the other surface of the base steel plate C1-36a. The amounts W3 and W6 may also be 20 g / m². 2 Above and 120g / m2 The following are preferred adhesion amounts: W3 and W6 are each 30 g / m³. 2 The above, more preferably 35g / m 2 The above. The preferred adhesion amounts W3 and W6 are 115 g / m³. 2 The following is more preferably 100g / m 2 The following is the difference between the adhesion amounts W2 and W3 between steel plates C1-32 and C1-33: W2-W3 is, for example, 20 (g / m²). 2 W2-W3 can be 80 (g / m³) or above. 2 Similarly, the difference in adhesion amount W2 and W6 between steel plates C1-32 and C1-36: W2-W6 is, for example, 20 (g / m²). 2 Above 80 (g / m³). W2-W6 can be 80 (g / m³). 2 The following applies: The adhesion amount W3 of the aluminum-based coating C1-33b on steel plate C1-33 and the adhesion amount W6 of the aluminum-based coating C1-36b on steel plate C1-36 can be the same or different. Furthermore, the plate thickness t3 of steel plate C1-33 and the plate thickness t6 of steel plate C1-36 can be the same or different. The plate thickness t3 of steel plate C1-33 and the plate thickness t6 of steel plate C1-36 are the average plate thicknesses of steel plates C1-33 and C1-36, respectively, and also include the thicknesses of the aluminum-based coatings C1-33b and C1-36b.

[0491] The amount of aluminum coating C1-33b adhering to steel plate C1-33 and the amount of aluminum coating C1-36b adhering to steel plate C1-36 can be determined by the method described in the second embodiment.

[0492] When the total thickness t of the overlapping portion C1-37 exceeds, for example, 2.5 mm, the overlapping portion C1-37 is difficult to heat up. Therefore, when the blank C1-30B is heated during hot stamping, the overlap portion C1-37 has a minimum thickness t until it reaches the temperature of the austenitic region. min C1-31b coating on steel plate C1-31 ( Figure 16B and Figure 18A Alloying thickens the diffusion layer, compromising the corrosion resistance or weldability of the C1-31 steel plate. However, in Figure 22 In some examples, the emissivity of the overlapping portion C1-37 is pre-enhanced by the film C1-50, which promotes the temperature rise of the overlapping portion C1-37 during the heating process. Figure 23In the example, by making the adhesion amounts W3 and W6 of the coatings C1-33b and C1-36b in the overlapping portion C1-37 less than the adhesion amount W2 of the coating C1-32b in the other steel plate C1-32, the emissivity of the overlapping portion C1-37 becomes higher during heating compared to the steel plate C1-32, thus promoting the temperature rise of the overlapping portion C1-37. Therefore, even when the total plate thickness t of the overlapping portion C1-37 is greater than 2.5 mm, the overlapping portion C1-37 can be sufficiently heated to complete the austenitic phase transformation before the alloying of the coating C1-31b in the steel plate C1-31 progresses, the diffusion layer thickens, and the corrosion resistance or weldability is lost. Therefore, the process window in the manufacturing of structural components can be ensured.

[0493] like Figure 24 As shown, when steel plates C1-33 and C1-36 are coated steel plates with aluminum-based coatings C1-33b and C1-36b, a film C1-50 may be provided on the outer surface of at least one of the steel plates C1-33 and C1-36 located at the overlapping portion C1-37. The film C1-50 may also be provided on the outer surface of either steel plate C1-33 or C1-36 located at the overlapping portion C1-37. The inner surface of each of the steel plates C1-33 and C1-36 located at the overlapping portion C1-37 may also be covered by the film C1-50, but from the viewpoint of homogenizing the heating of the billet C1-30B, it is preferable that it is not covered by the film C1-50.

[0494] Therefore, the emissivity of the overlapping portion C1-37 can be increased in advance, thus further accelerating the heating of the overlapping portion C1-37 when the blank C1-30B is heated during hot stamping. Therefore, with a plate thickness t... min C1-31 steel plate ( Figure 16B and Figure 18A Before the alloying of the C1-31b coating is excessively advanced, the overlapping portion C1-37 can be easily heated to the temperature of the austenitic region, enabling the manufacture of structural components while maintaining the corrosion resistance or weldability of the C1-31 steel sheet. Therefore, it is easy to ensure the process window during the manufacture of structural components.

[0495] In the billet C1-30B of this embodiment, steel plate C1-31 can be butt-joined with steel plate C1-32, or it can form an overlapping portion with steel plate C1-32, as with steel plates C1-33 and C1-36. Steel plate C1-32 can be butt-joined with steel plate C1-36, or it can form an overlapping portion with steel plate C1-36, as with steel plates C1-33 and C1-36.

[0496] The lower billet C1-40 ( Figure 16DIt can have the same configuration as the upper blank C1-30B in this embodiment. In this case, the lower blank C1-40 can also achieve the same effect as described above.

[0497] <Fourth Implementation Method> Figure 25 This is an exploded perspective view of structural components C1-10C and C1-20C in this embodiment. The structural components C1-10, C1-10A, and C1-20 of the above embodiment constitute the front under-module of the vehicle body. On the other hand, the structural components C1-10C and C1-20C of this embodiment constitute the rear under-module of the vehicle body.

[0498] Reference Figure 25 Structural member C1-10C, like in the above embodiment, includes a pair of side frames C1-11L and C1-11R and at least one frame crossbeam C1-12. Structural member C1-20C, also like in the above embodiment, includes a pair of side frames C1-21L and C1-21R and at least one frame crossbeam C1-22. Figure 25 In the example shown, the frame crossbeam C1-12 connects the middle portions of the side frames C1-11L and C1-11R. Similarly, the frame crossbeam C1-22 connects the middle portions of the side frames C1-21L and C1-21R. The configurations of structural members C1-10, C1-10A, and C1-20 described in other embodiments can be applied to structural members C1-10C and C1-20C of this embodiment, respectively.

[0499] Structural components C1-10C can be manufactured using the same manufacturing method as described in the first embodiment. Figure 26 The billet C1-30C shown is manufactured from steel plates C1-31, C1-32, and C1-33. The steel plates C1-31, C1-32, and C1-33 are configured and joined to form two elongated portions C1-34L and C1-34R, and at least one connecting portion C1-35. The billet C1-30C may have the same configuration as any of the billets C1-30, C1-30A, and C1-30B described in other embodiments.

[0500] In this embodiment, the rear portions C1-112 of the side frames C1-11L and C1-11R are formed. Figure 25 The thickness ratio of steel plate C1-31 to form front C1-111 ( Figure 25The steel plate C1-32 has a smaller plate thickness. The tensile strength of steel plate C1-31 can be less than that of steel plate C1-32. In this embodiment, structural member C1-10C and in other embodiments, structural members C1-10 and C1-10A (…) Figure 14 and Figures 19A-19C In the structural members C1-10, C1-10A, and C1-10C, the outermost steel plate in the longitudinal direction of the vehicle body preferably has a smaller plate thickness and / or tensile strength than the innermost steel plate. Therefore, when a longitudinal collision load is applied to the vehicle body, the outermost portion of the vehicle body deforms to absorb the collision energy, while the innermost portion is less prone to deformation, thus protecting surrounding components.

[0501] Structural components C1-20C can be manufactured using the same manufacturing method as described in the first embodiment. Figure 27 The billet C1-40C shown is manufactured from steel plates C1-41, C1-42, and C1-43. The steel plates C1-41, C1-42, and C1-43 are configured and joined to form two elongated portions C1-44L and C1-44R, and at least one connecting portion C1-45. The billet C1-40C can have the same configuration as any of the billets C1-30, C1-30A, and C1-30B described in other embodiments.

[0502] In this embodiment, the rear portions C1-212 of the side frames C1-21L and C1-21R are formed. Figure 25 The thickness ratio of steel plate C1-41 to form front C1-211 () Figure 25 Steel plate C1-42 has a smaller plate thickness. The tensile strength of steel plate C1-41 can be less than that of steel plate C1-42. In the lower structural members C1-20 and C1-20C... Figure 14 and Figure 25 In the same manner as above, it is preferable that the thickness and / or tensile strength of the outermost steel plate in the longitudinal direction of the vehicle body is smaller than that of the innermost steel plate. Therefore, when a longitudinal collision load is applied to the vehicle body, in structural members C1-20 and C1-20C, the outermost portion of the vehicle body deforms to absorb the collision energy, while the innermost portion of the vehicle body is less prone to deformation, thus protecting surrounding components.

[0503] The embodiments of this disclosure have been described above, but this disclosure is not limited to the above embodiments. Various changes can be made as long as they do not depart from its spirit.

[0504] In the blanks C1-30 of the first embodiment described above, as a material for achieving the minimum plate thickness t minThe treatment to increase the emissivity of the surface of steel plate C1-31 compared to other steel plates C1-32 involves forming a film C1-50 on at least one surface of steel plate C1-31. In the blank C1-30A of the second embodiment described above, as a treatment to increase the emissivity of the surface of steel plate C1-31 compared to other steel plates C1-32, the amount W1 of the aluminum-based coating C1-31b on both surfaces of steel plate C1-31 is less than the amount W2 of the aluminum-based coating C1-32b on other steel plates C1-32. However, the treatment for increasing the emissivity of steel plate C1-31 is not limited to this. For example, by making the surface roughness of at least one surface of steel plate C1-31 greater than the surface roughness of the two surfaces of steel plate C1-32, it is also possible to make the emissivity of at least one surface of steel plate C1-31 higher than that of steel plate C1-32. Similarly, in the billet C1-30B of the third embodiment, the treatment of improving emissivity on the outer surface of the overlapping portion C1-37 of the steel plates C1-33 and C1-36 is not limited to the method described in this embodiment.

[0505] In the second embodiment described above, it is explained that not only does it have a minimum plate thickness t min The amount of aluminum coating adhered in steel plate C1-31 is such that the amount of aluminum coating C1-33b adhered in steel plate C1-33 with a plate thickness t3 is also less than the amount of aluminum coating C1-32b adhered in other steel plates C1-32. However, this is only true for the multiple steel plates C1-31, C1-32, and C1-33 constituting billet C1-30 that have at least a minimum plate thickness t. min The amount of aluminum-based coating C1-31b adhering to steel plate C1-31, W1, can be less than the amount of aluminum-based coating C1-32b adhering to steel plate C1-32. The amount of aluminum-based coating C1-33b adhering to steel plate C1-33 (other than steel plate C1-32) can also be set to be greater than or equal to the amount of aluminum-based coating C1-32b adhering to steel plate C1-32. In this case, in the hot-stamped structural member C1-10A, the coating thickness K3 of steel plate C1-33 is also greater than or equal to the coating thickness K2 of steel plate C1-32. In the second embodiment described above, steel plates other than C1-31 and C1-32 do not necessarily need to be aluminized steel plates.

[0506] In the first embodiment described above, the billet C1-30 includes steel plates C1-31 and C1-32, respectively corresponding to the elongated sections C1-34L and C1-34R (side frames C1-11L and C1-11R), and a steel plate C1-33, corresponding to the connecting section C1-35 (frame crossbeam C1-12). However, the number and arrangement of steel plates contained in the billet C1-30 and the structural member C1-10 manufactured from the billet C1-30 are not limited thereto. Figure 28 and Figure 29As shown, the quantity and configuration of the steel plates can be changed appropriately.

[0507] like Figure 28 as well as Figure 29 As shown, in the structural component C1-10 of the lower front module ( Figure 14 In the corresponding blank C1-30, the elongated portions C1-34L and C1-34R can also be each composed of a single steel plate C1-31. In the blank C1-30, the connecting portion C1-35 can connect one end of the elongated portions C1-34L and C1-34R to each other in the longitudinal direction, similar to the first embodiment described above. That is, when the structural member C1-10 is assembled into the vehicle body, the elongated portions C1-34L and C1-34R can also be connected via the connecting portion C1-35 at the end side positioned at the front or rear. Figure 29 As shown, the billet C1-30 can also include multiple connecting parts C1-35. These connecting parts C1-35 are formed by separate steel plates C1-32 and C1-33.

[0508] Although figures are omitted, the quantity and arrangement of steel plates for structural members C1-10A and blanks C1-30A, C1-30B, the lower structural member C1-20 and blank C1-40 in other embodiments are not particularly limited. Structural members C1-10, C1-10A, C1-20 and blanks C1-30, C1-30A, C1-30B, C1-40 need only each contain two or more joined steel plates. Structural members C1-10, C1-10A, C1-20 and blanks C1-30, C1-30A, C1-30B, C1-40 preferably each contain three or more steel plates. Each of blanks C1-30, C1-30A, C1-30B, and C1-40 contains at least a minimum plate thickness t. min The first steel plate, and having a thickness t greater than the plate min A thicker second steel plate is acceptable. The first and second steel plates are joined directly or indirectly via other steel plates. One or both sides of the first steel plate undergo a treatment to improve emissivity compared to both sides of the second steel plate. For other steel plates, this treatment may or may not be performed. The smallest plate thickness t is found among the billets C1-30, C1-30A, C1-30B, and C1-40. min When multiple steel plates exist, it is preferable to apply a treatment to one or two sides of all of these steel plates to improve emissivity compared to the two sides of a steel plate with a greater plate thickness.

[0509] In the fourth embodiment described above, the blank C1-30C corresponds to the structural member C1-10C of the rear lower module. The blank C1-30C includes steel plates C1-31 and C1-32, corresponding to the long strips C1-34L and C1-34R (side frames C1-11L and C1-11R), and a steel plate C1-33, corresponding to the connecting part C1-35 (frame crossbeam C1-12). However, the number and arrangement of the steel plates contained in the blank C1-30C and the structural member C1-10C manufactured from the blank C1-30C are not limited thereto. Figures 30-40 As shown, the quantity and configuration of the steel plates can be changed appropriately.

[0510] For example, such as Figure 30 and Figure 31 As shown, in billet C1-30C, the long strips C1-34L and C1-34R can also be each composed of a single steel plate C1-31. In this case, the connecting part C1-35 can also connect the long strips C1-34L and C1-34R at one end along the length direction. For example, in structural member C1-10C ( Figure 25 When assembled onto the vehicle body, the elongated sections C1-34L and C1-34R, located at the front end, can also be connected via the connecting section C1-35. The elongated sections C1-34L and C1-34R can be connected at their middle section via the connecting section C1-35.

[0511] like Figure 32 As shown, in billet C1-30C, when the long strips C1-34L and C1-34R are formed from multiple steel plates C1-31 and C1-32, in structural member C1-10C ( Figure 25 When assembled onto the vehicle body, the long strips C1-34L and C1-34R, located at the front end, can also be connected via the connecting part C1-35. For example, at the front part C1-111 (corresponding to the side frames C1-11L and C1-11R)... Figure 25 The portion is formed of steel plate C1-31, equivalent to the rear C1-112 ( Figure 25 When the portion of the steel plate C1-32 is formed, the connecting portion C1-35 can be as follows: Figure 32 as well as Figure 33 As shown, it can be joined with steel plate C1-31, or as... Figure 34 It is shown to be joined with steel plate C1-32.

[0512] In the fourth embodiment described above, in structural member C1-10C ( Figure 25The structure has a single frame crossbeam C1-12, therefore the blank C1-30C used for structural member C1-10C also includes a single connecting part C1-35. However, structural member C1-10C can include multiple frame crossbeams C1-12. In this case, such as Figures 35-40 As shown, billet C1-30C also includes multiple connecting portions C1-35. The connecting portions C1-35 are formed from separate steel plates C1-32, C1-33, C1-33, C1-36, or steel plates C1-32, C1-33, C1-36. In this case, the elongated portions C1-34L and C1-34R can be as follows: Figure 35 , Figure 36 as well as Figure 40 As shown, they are formed from single steel plates C1-31, or as... Figures 37-39 As shown, it is formed by multiple steel plates C1-31 and C1-32 respectively.

[0513] Although the illustrations are omitted, in the fourth embodiment, the number and arrangement of steel plates for the lower structural members C1-20C and billets C1-40C are not particularly limited. Structural members C1-10C and C1-20C, and billets C1-30C and C1-40C each may consist of two or more joined steel plates. Preferably, structural members C1-10C and C1-20C, and billets C1-30C and C1-40C each consist of three or more steel plates. Each of billets C1-30C and C1-40C contains at least a minimum plate thickness t. min The first steel plate, and having a thickness t greater than the plate min A thicker second steel plate is acceptable. The first and second steel plates are joined directly or indirectly via other steel plates. One or both sides of the first steel plate undergo a treatment to improve emissivity compared to both sides of the second steel plate. For other steel plates, this treatment to improve emissivity may or may not be performed. Within each of the billets C1-30C and C1-40C, there are multiple plates with a minimum thickness t. min In the case of steel plates, it is preferable to apply a treatment to one or both sides of all of these steel plates to improve emissivity compared to the two sides of a steel plate with a greater plate thickness.

[0514] In the above embodiments, each billet and each structural component contains multiple steel plates (sub-bills), which can be single-layered or multi-layered. That is, the sub-bills can be single steel plates or plates composed of multiple overlapping steel plates.

[0515] In the above embodiments, the mold C1-60 used in the forming process includes a punch C1-61 and a die C1-62. However, the structure of the mold C1-60 is not limited to the example described in the above embodiments. The mold C1-60 may also include, for example, a liner and a pressure ring. The mold C1-60 can be constructed as long as it is based on the structural components that are the target.

[0516] In the structural members C1-10, C1-10A, C1-10C, C1-20, and C1-20C of the above embodiments, the side frames C1-11 and C1-21 substantially have a cap-shaped cross-section. However, the shape of the cross-section of the side frames C1-11 and C1-21 is not limited thereto. For example, as Figure 41 As shown, side frames C1-11 and C1-21 can also have a shape that is open on one side in the width direction in the cross-sectional view. In this case, other components (not shown) can be joined to the open portion of side frames C1-11 and C1-21, forming a closed section by side frames C1-11, C1-21 and other components. Similarly, frame crossbeams C1-12 and C1-22 can also have substantially hat-shaped cross sections, or other cross sections.

[0517] The present disclosure will be further described in detail below through embodiments. However, the present disclosure is not limited to the following embodiments.

[0518] To confirm the effectiveness of this disclosure, regarding the stamping (hot stamping) of structural members serving as front or rear lower modules, the type (raw material type) and thickness of the steel plates contained in the structural members, as well as the segmentation pattern of the structural members, were changed, and CAE analysis was performed using commercially available software (AUTOFORM R.10, manufactured by AUTOFORM Corporation).

[0519] The steel plates (raw material types) used in this analysis are shown in Table 13.

[0520] In Table 13, raw material types are marked in the order of coating type, tensile strength, and application (hot stamping). Regarding coating specifications, black coating is a black coating containing carbon black and metal oxides. "Black coating - single-sided" means that one side of the steel plate is completely covered by black coating. "Black coating - double-sided" means that both sides of the steel plate are completely covered by black coating. In this analysis, the raw material types selected from Table 13 constitute the structural components of the object.

[0521] The segmentation pattern of the structural components is shown in Figures 42A-42F . Figure 42A The structural component shown is the upper or lower structural component of the front lower module. Figures 42B-42FThe structural member shown is the upper or lower structural member of the rear lower module. Figures 42A-42F The diagram shows the number of steel plates (raw materials) contained in the structural member, as well as the locations of the joints between the steel plates in the structural member. Figures 42A-42F In the diagram, numbers are marked in parentheses for each steel plate.

[0522] about Figure 42A and Figure 42B The structural components shown are illustrated in Table 14, with the analytical conditions and results presented. Figure 42A and Figure 42B In the structure, the side frames of the structural components are formed from two raw materials (1) and (2). The crossbeams of the frame are formed from raw material (3). Raw materials (1) to (3) are joined to the adjacent raw materials respectively.

[0523] Refer to Table 14 and Figure 42A and Figure 42B Examples 1 and 2, and Comparative Examples 1 and 2, are structural members on the upper side of the rear lower module, while Examples 3 and Comparative Examples 3 are structural members on the upper side of the front lower module. In Example 1, the material with the smallest plate thickness t among the raw materials (1) to (3) is... min A black film is applied to both sides of the raw material (3) with a thickness of 1.0 mm. In Example 2, the raw materials (1) to (3) have the smallest plate thickness t. min A black film is applied to one side of the raw material (3) with a thickness of 1.0 mm. In Example 3, the material with the smallest plate thickness t among the raw materials (1) to (3) is... min A black film was applied to one side of the raw material (2) with a thickness of 1.0 mm. On the other hand, in Comparative Examples 1 to 3, the raw materials (1) to (3) were not coated with a black film. In Comparative Examples 1 to 3, for the material with the smallest plate thickness t min The 1.0mm raw material was not given a black film.

[0524] In Table 14, "Time to reach 910°C" refers to the earliest temperature reached by the raw materials contained in the billet (A). c3The time required for the raw material (above 920°C) to reach 910°C from the start of billet heating. "Phase transformation start time" refers to the shortest time from when the billet is heated at 920°C for 5 minutes and 30 seconds and removed from the furnace until the ferrite phase transformation begins. According to Table 14, in Examples 1-3, where the emissivity of the thinnest raw material was improved using a black film, the time to reach 910°C was shortened by approximately 20 seconds compared to Comparative Examples 1-3, resulting in a higher heating rate for the thinnest raw material during the heating process. Furthermore, in Examples 1-3, the phase transformation start time was later than in Comparative Examples 1-3, making it easier to begin billet forming before the ferrite phase transformation begins, and allowing for uniform quenching of the billet during the forming process.

[0525] about Figures 42C-42F The structural components shown are illustrated in Tables 15 and 16, with the analytical conditions and results presented. Examples 4-16 and Comparative Examples 4-16 in Tables 15 and 16 are all lower rear modules, but Examples 4-8 and 14-16, and Comparative Examples 4-8 and 14-16 are upper structural components, while Examples 9-13 and Comparative Examples 9-13 are lower structural components. Figures 42C-42E In the middle, the side frames of the structural components are formed by two raw materials (1) and (2). Figures 42C-42E The structural components include multiple frame crossbeams formed from raw material (3) or raw material (4). Figure 42F In the middle, the side frame of the structural component is formed from a single raw material (1). Figure 42F The structural components include multiple frame beams formed from any one of the raw materials (2) to (4). The raw materials (1) to (4) are respectively joined to the adjacent raw materials.

[0526] Referring to Table 15, in Examples 4-13, the material with the smallest plate thickness t among raw materials (1)-(4) is selected. min The black film is made from 1.0 mm thick raw material. In Examples 4-13, the black film achieves the minimum plate thickness t. min The raw material is covered on one or both sides. With a minimum plate thickness t min When multiple raw materials exist, all of them are coated with a black film. On the other hand, in Comparative Examples 4-13, raw materials (1) to (4) are not coated with a black film. That is, in Comparative Examples 4-13, no material with the smallest plate thickness t is coated with a black film. min The 1.0mm thick raw material gives the black film its color.

[0527] As shown in Table 15, in Examples 4-13, compared with Comparative Examples 4-13, the time to reach 910°C was shortened by about 20 seconds, and the heating rate of the thinnest raw material in the heating process was increased. Furthermore, in Examples 4-13, the phase transformation started later than in Comparative Examples 4-13, making it easier to start billet forming before the ferrite phase transformation begins, and allowing for uniform quenching of the billet during the forming process.

[0528] Referring to Table 16, in Examples 14-16, the material with the smallest plate thickness t among raw materials (1)-(4) is selected. min The black film is made of 1.2mm thick raw material. In Examples 14-16, the black film has the smallest plate thickness t min The raw materials are covered on one or both sides. On the other hand, in Comparative Examples 14-16, the raw materials (1) to (4) were not coated with a black film. In Comparative Examples 14-16, for the smallest plate thickness t min The 1.2mm raw material was not given a black film.

[0529] As shown in Table 16, in Examples 14-16, compared with Comparative Examples 14-16, the time to reach 910°C was shortened by more than 45 seconds, and the heating rate of the thinnest raw material in the heating process was increased. Furthermore, in Examples 14-16, the phase transformation initiation time exceeded 20 seconds, which was delayed compared to Comparative Examples 14-16. Therefore, it is easier to start billet forming before the ferrite phase transformation begins, and the billet can be uniformly quenched during the forming process.

[0530] For Examples 6, 11, and 16, and Comparative Examples 6, 11, and 16, analytical samples were collected from the thinnest part of the structural members using the methods described in the above embodiments, and the deviation of the martensite fraction was measured. In addition, shape accuracy and impact absorption performance were measured separately for these structural members. The evaluation results are shown in Table 17.

[0531] In Table 17, the deviation of the martensite fraction refers to, as described in the above embodiments, the deviation at the minimum plate thickness t. min The value obtained by subtracting the minimum martensite fraction (%) from the maximum martensite fraction (%) in the cross section of the structural member at the location of the raw material.

[0532] Regarding shape accuracy, when installing structural members onto other members, the evaluation is based on the degree of separation between the structural member and the other member at the overlapping portion. In Table 17, cases within ±2.0 mm of the surface of the other member are represented by ○, cases exceeding ±2.0 mm but within ±3.0 mm are represented by △, and cases exceeding ±3.0 mm are represented by ×.

[0533] Regarding impact absorption performance, rear-end and side-end collisions were simulated with the structural components assembled in the vehicle. The impactor of the simulated vehicle collided with the structural components, and the maximum intrusion volume was evaluated for both rear-end and side-end collisions. Impact absorption performance was evaluated by comparing it to the impact absorption performance of a structure formed by hot-stamping and joining the various materials to create the rear lower module. In Table 17, "good" indicates impact absorption performance equivalent to the benchmark, "better" indicates impact absorption performance superior to the benchmark, "marginal" indicates impact absorption performance slightly lower than the benchmark, and "poor" indicates even lower impact absorption performance.

[0534] As described above, in Examples 6, 11, and 16, a black film was applied to the surface of the thinnest raw material. On the other hand, in Comparative Examples 6, 11, and 16, no black film was applied to any of the raw materials, including the thinnest raw material. As shown in Table 17, the deviation of the martensite fraction in Examples 6, 11, and 16 was less than 15%, a significant reduction compared to Comparative Examples 6, 11, and 16. In Examples 6, 11, and 16, the shape accuracy was also good compared to Comparative Examples 6, 11, and 16.

[0535] In Examples 6, 11, and 16, where the deviation in martensite fraction is small, the impact absorption performance is also improved compared to Comparative Examples 6, 11, and 16. In Examples 6, 11, and 16, although multiple raw materials are integrally formed into structural components at the blank stage, it is possible to ensure impact absorption performance equal to or better than that of structural components formed by stamping raw materials separately and then joining them together.

[0536] (Element Technology C2) The aforementioned element C2 is a structural component for a vehicle body, satisfying at least one of the following (C2a), (C2b), and (C2c): (C2a) the structural component includes a pair of side frames and a frame crossbeam connecting the side frames, the side frames and the frame crossbeam being formed from a plurality of steel plates joined together, the plurality of steel plates including a first steel plate and a second steel plate, the second steel plate having an end that overlaps with and is joined to the end of the first steel plate to form an overlap portion together with the end of the first steel plate, a film being provided on the outer surface of each of the first steel plate and the second steel plate, the film containing 0.001 g / m³. 2The above refers to one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide; (C2b) the structural member has a pair of side frames and a frame crossbeam connecting the side frames, the structural member is formed of a plurality of steel plates joined together, the plurality of steel plates including a first steel plate and a second steel plate, the second steel plate having an end that overlaps with the end of the first steel plate and is joined to form an overlap portion together with the end of the first steel plate, and on the surface of each of the first steel plate and the second steel plate located outside the overlap portion, a 0.500 g / m 2 The following carbon black film; (C2c) The structural member has a pair of side frames and a frame crossbeam connecting the side frames, the side frames and the frame crossbeam being formed by a plurality of steel plates joined together, the plurality of steel plates including a first steel plate, a second steel plate and a third steel plate, the second steel plate having an end that overlaps with the end of the first steel plate by being overlapped and joined together, at least one of the first steel plate and the second steel plate and the third steel plate are respectively coated steel plates having an aluminum-based coating on two surfaces of a base steel plate, the thickness of the aluminum-based coating in at least one of the first steel plate and the second steel plate being less than the thickness of the aluminum-based coating in the third steel plate.

[0537] According to element technology C2, it is possible to provide structural components that combine the strength of the overlapping section with the largest plate thickness and rust prevention.

[0538] The hot stamping blank of the embodiment comprises multiple steel plates. The multiple steel plates are arranged and joined in such a way that they form two elongated portions and a connecting portion. The elongated portions are arranged laterally in a top view of the blank. The connecting portion connects the elongated portions to each other. The multiple steel plates include a first steel plate and a second steel plate. The second steel plate has an end that overlaps with the end of the first steel plate to form an overlapping portion. The overlapping portion has the largest plate thickness in the blank. At least one of the multiple steel plates is a plated steel plate having a base steel plate and a coating disposed on the base steel plate. A treatment (first configuration) is performed on the surface of at least one of the first and second steel plates located outside the overlapping portion to increase emissivity compared to at least one other surface of the multiple steel plates.

[0539] In the first-formed billet, the ends of the first steel plate and the second steel plate form an overlap with the largest plate thickness in the billet. The surface of at least one of the first and second steel plates located outside the overlap is treated to increase emissivity compared to at least one other surface among the plurality of steel plates included in the billet. Therefore, when the billet is heated during hot stamping, the heating rate of the overlap can be increased, thus shortening the heating time of the overlap. Consequently, the heating of the billet required for hot stamping can be completed before the alloying of the plating in the coated steel sheet included in the billet progresses excessively and the diffusion layer thickens. As a result, in structural members formed from the billet, the strength of the overlap can be ensured by hot stamping, and corrosion resistance (rust prevention) can be ensured. Furthermore, the concept of "implementing a treatment to increase emissivity" includes not only the case where the emissivity of the surface located outside the overlapping portion of at least one of the first and second steel plates is higher than that of other surfaces before the billet is heated, but also the case where the emissivity of the surface located outside the overlapping portion of at least one of the first and second steel plates is higher than that of other surfaces during the heating of the billet.

[0540] Thus, based on the blank of the first configuration, it is possible to manufacture structural components that combine the strength of the overlapping section with the maximum plate thickness and the rust-resistant function of the clad steel portion. Specifically, based on this blank, the heating rate of the overlapping section with the maximum plate thickness can be increased, resulting in a process window for ensuring heating conditions during the manufacture of the structural components. Furthermore, by increasing the heating rate of the overlapping section, the heating time of the blank used for hot stamping can be shortened, thereby increasing the productivity of the structural components. In addition, by shortening the heating time of the blank, energy consumption during the manufacture of the structural components can be suppressed, and the generation of greenhouse gases during the heating of the blank during hot stamping can be reduced.

[0541] In the first constituent billet, the steel plate with the smallest plate thickness among the multiple steel plates constituting the billet may be a galvanized steel plate (second constituent).

[0542] When the billet is heated during hot stamping, the steel sheet with the smallest thickness heats up faster. Therefore, if the steel sheet with the smallest thickness in the billet is a coated steel sheet, during the heating of the overlap portion to ensure the strength of the overlap portion with the largest thickness through hot stamping, the alloying of the coating is easily advanced in the coated steel sheet with the smallest thickness that has been heated first, and the corrosion resistance provided by the coating may sometimes decrease or disappear. However, in the billet of the embodiment, at least one of the first and second steel sheets has undergone a treatment to increase emissivity on the surface located on the outer side of the overlap portion. Therefore, the heating rate of the overlap portion can be increased and its heating time shortened, and the heating of the billet required for hot stamping can be completed before the alloying of the coating in the steel sheet with the smallest thickness that has been heated first is excessively advanced. Therefore, even if the steel sheet with the smallest thickness is a coated steel sheet as in the second configuration, its corrosion resistance can be ensured.

[0543] In the first or second configuration of the billet, the outer surface of the first and second steel plates located at the overlap may be subjected to a treatment to improve emissivity compared to at least one other surface among the plurality of steel plates (third configuration).

[0544] In the third-component billet, on both the first and second steel plates, a treatment is applied to the outer surfaces of the overlapping portion to increase emissivity. That is, the emissivity of the two outer surfaces of the overlapping portion is higher than that of other surfaces before heating the billet, or higher than that of other surfaces during heating the billet. In this case, the heating rate of the overlapping portion can be further increased during billet heating, and the heating time of the overlapping portion can be further shortened. Therefore, it is easier to ensure the process window for heating conditions during the manufacture of structural components.

[0545] In any of the first to third components of the billet, the multiple steel plates can be clad steel plates (fourth component).

[0546] In the fourth configuration, each steel sheet included in the billet is a clad steel sheet. In this case, when the billet is formed into a structural component by hot stamping, the formation of oxide scale can be suppressed. Therefore, after hot stamping, it is not necessary to perform treatments such as shot peening to remove oxide scale on the structural component. As a result, the productivity of structural components can be improved. In addition, by using clad steel sheets, the corrosion resistance of the structural component is also easily ensured.

[0547] In the fourth component of the billet, the coating of each steel plate is an aluminum-based coating (fifth component).

[0548] In cases where each steel sheet, as in the fifth configuration, is an aluminum-coated steel sheet, a difference in heating rate can easily occur, particularly between the overlapping and non-overlapping sections where the sheet thickness is greatest, when the billet is heated during hot stamping. Since the aluminum-coated layer is nearly white, it easily reflects heat, hindering the heating of the overlapping section. However, even if each steel sheet is an aluminum-coated steel sheet, by applying a treatment to at least one of the outer surfaces of the overlapping section to increase emissivity, the heating of the overlapping section can be promoted during hot stamping when the billet is heated, thus shortening the heating time. Therefore, corrosion resistance in the coated steel sheet portion can be ensured, and the productivity of structural components manufactured from the billet can be improved.

[0549] In any of the third to fifth configurations of the billet, a film may be formed on the outer surface of the overlapping portion of the first and second steel plates as a treatment to improve emissivity. The emissivity of this film at a wavelength of 8.0 μm at 25°C may be 60% or more (sixth configuration).

[0550] In any of the third to fifth configurations of the billet, a film may be formed on the outer surface of the overlapping portion of both the first and second steel plates as a treatment to improve emissivity. This film may contain: carbon black; one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide; and 0~0.30 g / m 2 Silica. In this case, the carbon black content in the film is set as X. CB (g / m 2 Let the content of oxides be X. Oxide (g / m 2 When X CB and X Oxide It can satisfy the following equation (1) (refer to Patent Document 1) (Seventh Structure).

[0551] 118.9≤24280 / {6700 / (100+76×X CB ) + 18000 / (130 + 65 × X) Oxide )}≤332.0 (1) In any of the third to seventh configurations of the billet, it is also possible for multiple steel plates to comprise two or more steel plates with different thicknesses. In this case, the thickness of the overlapping portion is set as t. max Let the thickness of the steel plate comprising the portion of the billet with the smallest plate thickness be t. min When, it can be t max / t min ≤3.2 (Eighth component).

[0552] When a billet contains two or more steel plates with different thicknesses, the thickness difference between the overlapping portion and the steel plate constituting the portion with the smallest thickness in the billet increases compared to the case where all steel plates in the billet have the same thickness. When the thickness difference is too large, the overlapping portion heats up more slowly when manufacturing structural components from the billet by hot stamping compared to the steel plate constituting the portion with the smallest thickness in the billet. Therefore, for example, if the thinnest steel plate is a galvanized steel plate, the alloying of the coating in the thinnest steel plate may be over-promoted, making it more difficult to ensure adequate heating conditions within the process window. However, in the eighth configuration, the thickness t of the overlapping portion... max With the minimum plate thickness t min The ratio: t max / t min It is set to 3.2 or below. Therefore, even when the billet contains two or more steel plates with different thicknesses, it is easy to complete the heating of the thickest overlap before the alloying of the coating is over-progressed, and the process window for heating conditions is easily ensured.

[0553] In the first constituent billet, the plurality of steel plates may further include a third steel plate. At least one of the first and second steel plates and the third steel plate may be coated steel plates having an aluminum-based coating on both surfaces of the base steel plate. In this case, as a treatment to make the emissivity of the surface located on the outer side of the overlapping portion higher than the emissivity of the surface of the third steel plate, for example, the amount (g / m²) of the aluminum-based coating adhered to at least one of the first and second steel plates relative to the two surfaces of the base steel plate is... 2 The value can be below 60, which refers to the amount of aluminum coating (g / m²) adhered to the third steel plate relative to the two surfaces of the base steel plate. 2 Less (the ninth component).

[0554] The ninth component of the billet includes a first steel plate, a second steel plate, and a third steel plate. At least one of the first and second steel plates, and the third steel plate, are aluminized steel plates. The amount of aluminum coating on at least one of the first and second steel plates is less than the amount of aluminum coating on the third steel plate, and is 60 g / m². 2The following describes a process where the first and / or second steel plates are thinly coated. During hot stamping, when the billet is heated, the alloying of the aluminum-based coating with iron in the first and / or second steel plates progresses rapidly, causing both surfaces to quickly change from silvery-white to black or near-black. Therefore, during billet heating, the emissivity of the overlap formed by the first and second steel plates is higher than that of the third steel plate. This allows the overlap to heat up to the austenitic region temperature more quickly, thus shortening the heating time. Consequently, the billet heating required for hot stamping can be completed before the alloying of the aluminum-based coating in each steel plate becomes excessive and the diffusion layer thickens. As a result, the strength of the overlap can be ensured through hot stamping, and the corrosion resistance (rust prevention) of each steel plate can be guaranteed.

[0555] In the ninth constituent billet, the amount of aluminum-based coating adhering to the third steel plate is greater than that of at least one of the first and second steel plates forming the overlapping portion. That is, the third steel plate has higher rust resistance compared to the first and / or second steel plates. Therefore, in structural members formed from the billet, rust resistance can be locally improved. For example, by placing the third steel plate in areas of the structural member where higher rust resistance is required, the overall rust resistance required for the structural member can be ensured.

[0556] In the ninth composition of the billet, it is also possible that multiple steel plates include two or more steel plates with different thicknesses. In this case, the thickness of the overlapping portion is set as t. max Let the thickness of the steel plate with the smallest thickness among multiple steel plates be t. min When, it can be t max / t min ≤3.0 (tenth component).

[0557] When a billet contains two or more steel plates with different thicknesses, the thickness difference between the overlapping and non-overlapping portions increases compared to the case where all steel plates in the billet have the same thickness. That is, the thickness difference between the overlapping portion with the largest thickness and the steel plate with the smallest thickness in the billet increases. When the thickness difference is too large, the overlapping portion heats up more slowly than the steel plate with the smallest thickness when manufacturing structural components from the billet by hot stamping. Therefore, for example, if the thinnest steel plate is a coated steel plate, alloying of the coating in the thinnest steel plate may be over-promoted, making it difficult to ensure the process window for heating conditions. Therefore, in the tenth configuration, when the first and / or second steel plates forming the overlapping portion are thinner coated steel plates, the thickness t of the overlapping portion... max With the minimum plate thickness t min The ratio: t max / t minIt is set to 3.0 or below. This allows for easy heating of the thickest overlap before the alloying of the coatings in each plated steel sheet becomes excessive, easily ensuring the process window for heating conditions.

[0558] In the ninth composition of the billet, multiple steel plates may include two or more steel plates with different thicknesses. In this case, the thickness of the overlapping portion is set as t. max Let the thickness of the steel plate with the smallest thickness among multiple steel plates be t. min When, it can be t max / t min ≤4.0. Furthermore, the outer surface of at least one of the first steel plate and the second steel plate located at the overlapping portion may be covered with a black film (eleventh configuration).

[0559] In the eleventh configuration, besides the first and / or second steel plates forming the overlapping portion being relatively thin-coated steel plates, at least one of the first and second steel plates has a substantially black film applied to the surface located on the outer side of the overlapping portion. This allows for a pre-increased emissivity of the overlapping portion, further accelerating the heating of the overlapping portion when the billet is heated during hot stamping. Therefore, even when the thickness difference between the overlapping portion with the largest thickness and the steel plate with the smallest thickness in the billet is large, it is easy to ensure a suitable process window for heating conditions. For example, even if the thickness t of the overlapping portion is... max With the minimum plate thickness t min The ratio: t max / t min Expanding to 4.0 also makes it easier to ensure the process window.

[0560] The manufacturing method of the structural member of the embodiment includes: a step of preparing a blank of any one of the first to eleventh configurations; a step of heating the plurality of steel plates contained in the blank to a temperature above the austenitic phase transformation completion temperature; and a step of forming the heated blank using a mold and quenching it (twelfth configuration).

[0561] The vehicle body structural member of the embodiment can have a pair of side frames and a frame crossbeam. The frame crossbeam connects the side frames. The side frames and the frame crossbeam are formed by multiple steel plates that are joined together. The multiple steel plates include a first steel plate and a second steel plate. The second steel plate has an end that is joined to the end of the first steel plate by overlapping with the end of the first steel plate, thereby forming an overlap portion together with the end of the first steel plate. A film is provided on the outer surface of each of the first and second steel plates located at the overlap portion. The film contains 0.001 g / m 2 The above refers to one or more oxides selected from the group consisting of Zr oxides, Zn oxides and Ti oxides (the thirteenth group).

[0562] In another embodiment, the structural member for the vehicle body may include a pair of side frames and a frame crossbeam. The frame crossbeam connects the side frames. The side frames and the frame crossbeam are formed by multiple steel plates that are joined together. The multiple steel plates include a first steel plate and a second steel plate. The second steel plate has an end that is joined to the end of the first steel plate by overlapping with the end of the first steel plate, thereby forming an overlap portion together with the end of the first steel plate. A film is provided on the outer surface of each of the first and second steel plates located at the overlap portion. The film contains 0.500 g / m³. 2 The following carbon black (Fourteenth Composition).

[0563] In another embodiment, the structural member for the vehicle body may include a pair of side frames and a frame crossbeam. The frame crossbeam connects the side frames. The side frames and the frame crossbeam are formed by multiple steel plates that are joined together. The multiple steel plates include a first steel plate, a second steel plate, and a third steel plate. The second steel plate has an end that is joined to the end of the first steel plate by overlapping with the end of the first steel plate, thereby forming an overlap portion together with the end of the first steel plate. At least one of the first steel plate and the second steel plate, as well as the third steel plate, are coated steel plates having aluminum-based coatings on two surfaces of the base steel plate. The thickness of the aluminum-based coating on at least one of the first steel plate and the second steel plate is less than the thickness of the aluminum-based coating on the third steel plate (fifteenth configuration).

[0564] In the fifteenth structural member, it is also possible that, in the overlapping portion, the maximum value of the Vickers hardness of the steel plate located on the surface side of the structural member in the first and second steel plates is set as HV. max Set the minimum Vickers hardness to HV. min At that time, HV max -HV min For HV max Less than 30% (the sixteenth component).

[0565] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the drawings, the same or equivalent components are labeled with the same symbols, and the same descriptions are not repeated.

[0566] <First Implementation Method> [Structural Components] Figure 43 This is an exploded perspective view of structural components C2-10 and C2-20 in this embodiment. Structural components C2-10 and C2-20 are used in the body of automobiles, etc. Figure 43 In the example shown, structural components C2-10 and C2-20 constitute the lower front module of the vehicle body.

[0567] Structural member C2-10 is the upper module. That is, structural member C2-10 is positioned above structural member C2-20 when assembled in the vehicle body. Structural member C2-10 has a pair of side frames C2-11L and C2-11R, and at least one frame crossbeam C2-12. The side frames C2-11L and C2-11R and the frame crossbeam C2-12 are each elongated.

[0568] With structural member C2-10 assembled into the vehicle body, side frames C2-11L and C2-11R are arranged along the left-right direction of the vehicle body. Side frames C2-11L and C2-11R extend along the front-rear direction of the vehicle body, respectively. Side frames C2-11L and C2-11R each include a front portion C2-111 and a rear portion C2-112. With structural member C2-10 assembled into the vehicle body, the rear portion C2-112 is positioned behind the front portion C2-111.

[0569] With structural component C2-10 assembled to the vehicle body, frame crossbeam C2-12 extends along the left-right direction of the vehicle body. Frame crossbeam C2-12 extends from side frame C2-11L to side frame C2-11R. Frame crossbeam C2-12 connects side frames C2-11L and C2-11R. Figure 43 In the example shown, a frame crossbeam C2-12 connects the side frames C2-11L and C2-11R to each other at one end along their length. With structural member C2-10 assembled to the vehicle body, the frame crossbeam C2-12 is, for example, positioned at the rear end of structural member C2-10. However, the frame crossbeam C2-12 may also connect the middle portions of the side frames C2-11L and C2-11R.

[0570] Structural member C2-20 is the lower module. That is, structural member C2-20 is positioned below structural member C2-10 when assembled into the vehicle body. Structural member C2-20 has a pair of side frames C2-21L and C2-21R, and at least one frame crossbeam C2-22. The side frames C2-21L and C2-21R and the frame crossbeam C2-22 are each elongated.

[0571] With structural member C2-20 assembled to the vehicle body, side frames C2-21L and C2-21R are arranged along the left-right direction of the vehicle body. Side frames C2-21L and C2-21R extend along the front-rear direction of the vehicle body, respectively. Side frames C2-21L and C2-21R each include a front portion C2-211 and a rear portion C2-212. With structural member C2-10 assembled to the vehicle body, the rear portion C2-212 is positioned behind the front portion C2-211.

[0572] The lower side frames C2-21L and C2-21R are connected to the upper side frames C2-11L and C2-11R, respectively. The side frames C2-21L and C2-21R together form a closed section. Figure 44 The symbols represent the closed sections formed by side frames C2-21L and C2-21R together with side frames C2-11L and C2-11R, respectively. Hereinafter, unless there is a specific distinction between side frames C2-11L and C2-11R, they will be collectively referred to as side frame C2-11. Similarly, unless there is a specific distinction between side frames C2-21L and C2-21R, they will be collectively referred to as side frame C2-21.

[0573] Figure 44 This is a cross-sectional view (section view) of side frames C2-11 and C2-21 when cut with a plane perpendicular to the length direction. Figure 44 In the example, side frames C2-11 and C2-21 each have a substantially cap-shaped cross-section.

[0574] Reference Figure 44 The side frame C2-11 includes a top plate C2-113, longitudinal walls C2-114 and C2-115, and flanges C2-116 and C2-117. In a cross-sectional view of the side frame C2-11, one end of the longitudinal walls C2-114 and C2-115 is connected to the top plate C2-113. In a cross-sectional view of the side frame C2-11, flanges C2-116 and C2-117 are respectively connected to the other ends of the longitudinal walls C2-114 and C2-115. Flanges C2-116 and C2-117 protrude outward from the longitudinal walls C2-114 and C2-115, respectively.

[0575] Side frame C2-21 includes a top plate C2-213, longitudinal walls C2-214 and C2-215, and flanges C2-216 and C2-217. In a cross-sectional view of side frame C2-21, one end of longitudinal walls C2-214 and C2-215 is connected to the top plate C2-213. In a cross-sectional view of side frame C2-21, flanges C2-216 and C2-217 are respectively connected to the other ends of longitudinal walls C2-214 and C2-215. Flanges C2-216 and C2-217 protrude outward from longitudinal walls C2-214 and C2-215, respectively.

[0576] The top plate C2-213 of the lower side frame C2-21 is configured to oppose the top plate C2-113 of the upper side frame C2-11. In the cross-sectional view of the side frames C2-11 and C2-21, the longitudinal walls C2-214 and C2-215 of the side frame C2-21 extend from the top plate C2-213 toward the side frame C2-11. The flanges C2-216 and C2-217 of the side frame C2-21 are respectively joined to the flanges C2-116 and C2-117 of the side frame C2-11. The flanges C2-216 and C2-217 are joined to the flanges C2-116 and C2-117, for example, by spot welding. Figure 44 In the example, the flanges C2-116 and C2-117 of the upper side frame C2-11 are directly joined to the flanges C2-216 and C2-217 of the lower side frame C2-21. However, other components, such as floor panels, can also be placed between the side frames C2-11 and C2-21.

[0577] return Figure 43 With structural component C2-20 assembled to the vehicle body, frame crossbeam C2-22 extends along the left-right direction of the vehicle body. Frame crossbeam C2-22 extends from side frame C2-21L to side frame C2-21R. Frame crossbeam C2-22 connects side frames C2-21L and C2-21R. Figure 43 In the example shown, at one end of the side frames C2-21L and C2-21R along their length, a frame crossbeam C2-22 connects the side frames C2-21L and C2-21R to each other. Like the upper frame crossbeam C2-12, the frame crossbeam C2-22 is positioned, for example, at the rear end of the structural member C2-20 when the structural member C2-20 is assembled into the vehicle body. However, the frame crossbeam C2-22 can also connect the middle portions of the side frames C2-21L and C2-21R. The frame crossbeam C2-22 can also be joined to the upper frame crossbeam C2-12, for example, by spot welding.

[0578] Structural components C2-10 and C2-20 are hot-stamped components. That is, structural component C2-10 is formed by hot stamping (hot pressing) a blank made of multiple steel plates (sub-blanks). Similarly, structural component C2-20 is formed by hot stamping a blank made of multiple steel plates.

[0579] In the upper structural member C2-10, for example, the side frames C2-11L and C2-11R can also be formed from multiple steel plates C2-31 and C2-32, respectively. In each of the side frames C2-11L and C2-11R, for example, the rear portion C2-112 can be formed from steel plate C2-31, and the front portion C2-111 can be formed from steel plate C2-32. At least one of the plate thickness and tensile strength of the steel plate C2-31 forming the rear portion C2-112 can be greater than that of the ...

Claims

1. A rear module for automobiles, comprising an integrated component formed by hot stamping multiple integral steel plates. The rear module of the vehicle is characterized in that... Let S be the projected area when viewed from the perpendicular direction of the reference plane, with units of m. 2 Let W be the total weight of the components of the rear module of the vehicle, in kg. Let W also be the total weight of the steel components of the rear module that are less than 1.5 mm thick and have a minimum Vickers hardness of HV230 or higher. A In this case, W / S is below 24, W A / W is above 0.

30.

2. The automotive rear module as described in claim 1, characterized in that, have: Element technology A1; and At least one of factor technology B1, factor technology C1, factor technology C2, factor technology D1, and factor technology D2. The element technology A1 is a skeleton component formed by hot stamping of a steel plate. The skeleton component has a closed section portion with a closed section perpendicular to the length direction. The closed section portion has at least two flat parts, which are parts with a large radius of curvature compared to the maximum external dimension in the section. A concave reinforcing rib is formed between the two flat portions. The concave reinforcing rib has a pair of walls with a radius of curvature of 50 mm or more, protruding from opposite ends of the two flat portions towards the inside of the closed section via a pair of curved portions bending inwards. The Vickers hardness at the center of the wall thickness is 520 Hv or more, and the width of the wall is the effective width W calculated according to the Karman effective width formula. e The standard deviation ratio obtained by dividing the standard deviation of the hardness frequency distribution of the surface layer of the wall portion by the standard deviation of the hardness frequency distribution of the center layer of the wall portion is less than 1.

0. This ratio is greater than 0.5 times but less than 2.5 times. The element technology B1 is a structural component having a main body. The main body is formed by a plurality of steel plates joined together, including 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 main body has a ring shape when viewed from above. The value of coefficient A calculated using the chemical composition of the first steel plate by the following formula (1) is greater than the value of coefficient A calculated using the chemical composition of the second steel plate by the following formula (1). A=1.48×(2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr+2×Mo) 3.42 (1), In the above formula (1), the element symbols are replaced with the content of the corresponding element in terms of mass%. The aforementioned element technology C1 is a structural component for a vehicle body, which satisfies at least one of (C1a), (C1b), and (C1c). (C1a) The structural member comprises a pair of side frames and a frame crossbeam connecting the side frames. The side frames and the frame crossbeam are formed of a plurality of steel plates, including a first steel plate having a minimum thickness and a second steel plate having a thickness greater than that of the first steel plate, and which are joined together. The first steel plate is provided with a coating containing 0.001 g / m³. 2 The above refers to films of one or more oxides selected from the group consisting of Zr oxide, Zn oxide and Ti oxide; (C1b) The structural member comprises a pair of side frames and a frame crossbeam connecting the side frames. The side frames and the frame crossbeam are formed of a plurality of steel plates, including a first steel plate having a minimum thickness and a second steel plate having a thickness greater than that of the first steel plate, and which are joined together. The first steel plate is provided with a coating containing 0.500 g / m³. 2 The following is the film of carbon black; (C1c) The structural member comprises a pair of side frames and a frame crossbeam connecting the side frames. The side frames and the frame crossbeam are formed by a plurality of steel plates, each comprising a first steel plate having a minimum thickness and a second steel plate having a thickness greater than that of the first steel plate, and which are joined together. The first steel plate and the second steel plate are coated steel plates having an aluminum-based coating on two surfaces of a base steel plate, respectively. The thickness of the aluminum-based coating in the first steel plate is smaller than the thickness of the aluminum-based coating in the second steel plate. The aforementioned element technology C2 is a structural component for a vehicle body, which satisfies at least one of (C2a), (C2b), and (C2c). (C2a) The structural member comprises a pair of side frames and a frame crossbeam connecting the side frames. The side frames and the frame crossbeam are formed of a plurality of steel plates, including a first steel plate and a second steel plate, which are joined together. The second steel plate has an end that overlaps and joins with the end of the first steel plate to form an overlapping portion together with the end of the first steel plate. On the surface of each of the first steel plate and the second steel plate located outside the overlapping portion, a coating containing 0.001 g / m³ is provided. 2 The above refers to films of one or more oxides selected from the group consisting of Zr oxide, Zn oxide and Ti oxide; (C2b) The structural member includes a pair of side frames and a frame crossbeam connecting the side frames. The structural member is formed of a plurality of steel plates, including a first steel plate and a second steel plate, which are joined together. The second steel plate has an end that overlaps and joins with the end of the first steel plate to form an overlapping portion together with the end of the first steel plate. On the outer surface of each of the first steel plate and the second steel plate, a coating containing 0.500 g / m³ is provided. 2 The following is the film of carbon black; (C2c) The structural member includes a pair of side frames and a frame crossbeam connecting the side frames. The side frames and the frame crossbeam are formed of a plurality of steel plates, including a first steel plate, a second steel plate, and a third steel plate, which are joined together. The second steel plate has an end that overlaps with and joins the end of the first steel plate to form an overlapping portion together with the end of the first steel plate. At least one of the first steel plate and the second steel plate, and the third steel plate, are coated steel plates having an aluminum-based coating on two surfaces of the base steel plate. The thickness of the aluminum-based coating in at least one of the first steel plate and the second steel plate is smaller than the thickness of the aluminum-based coating in the third steel plate. The element technology D1 is a stamped forming part that joins multiple partial blanks made of steel sheet, the stamped forming part satisfying at least one of (D1a) and (D1b). (D1a) At least two of the said partial blanks are joined by a plurality of joint portions in an overlapping portion formed by partially overlapping, wherein, in a cross section perpendicular to the surface of the part blank containing the center of the joint portion of the partial blanks, at a position 1 / 4 of the plate thickness from the surface of the partial blanks that contacts the other partial blanks, and at a position where the Vickers hardness is set to Hvm at a position 15 mm or more from the center of the joint portion and where the joining is not performed, for the joint portion of a part of the plurality of joint portions, the difference between the maximum hardness and the minimum hardness, i.e., ΔHv, is less than 0.2Hvm, preferably less than 0.1Hvm, in the range of 5 mm or less from the end of the joint portion toward the base material side, or 12 mm or less from the center of the joint portion; for the other joint portions of the plurality of joint portions, i.e., the joint portions other than the joint portions of the said part, the ΔHv is 0.2Hvm or more, preferably 0.3Hvm, 0.4Hvm or 0.5Hvm or more; (D1b) At least two of the said partial blanks are joined by a plurality of spot welds in an overlap obtained by partially overlapping. In a cross-section including the center of the spot weld of the outermost partial blank, at a position 1 / 4 of the plate thickness from the surface of the partial blank, and with the hardness defined as Hvm at a position 15 mm or more from the center of the spot weld and where no spot weld has been performed, for a spot weld of a portion of the plurality of spot welds, the difference between the maximum and minimum hardness, i.e., ΔHv, is less than 0.2Hvm; for spot welds other than the spot weld of the portion of the portion, the ΔHv is 0.2Hvm or more. The element technology D2 is a stamped part that satisfies at least one of (D2a) and (D2b). (D2a) The stamping forming component overlaps a welded part made of steel plate on the surface of a base blank made of steel plate and joins it at the joint. The stamping forming component has a bent portion. For the joint where the difference between the maximum hardness of the base blank within 2 mm from the outer edge of the joint and the hardness of the base material of the base blank is more than 7% of the hardness of the base material of the base blank, in the case of one bent portion, the bent portion is the boundary of the area on one side of the surface of the base blank. In the case of two or more bent portions, the bent portions are the boundary of the area between two adjacent bent portions on the surface of the base blank. (D2b) The stamping forming component overlaps a welded part made of steel plate on the surface of a base blank made of steel plate and is joined by spot welding at the joint point. The stamping forming component has a bent portion. For the joint where the difference between the maximum hardness at a position 5 mm from the center of the joint point on the surface of the base blank and the hardness of the base material of the base blank is more than 7% of the hardness of the base material of the base blank, in the case of one bent portion, the bent portion is the boundary of the area on one side of the surface of the base blank, and in the case of two or more bent portions, the bent portions are the boundary of the area between two adjacent bent portions on the surface of the base blank.

3. The automotive rear module as described in claim 2, characterized in that, It possesses the aforementioned element technology A1 and the aforementioned element technology B1.

4. The automotive rear module as described in claim 2, characterized in that, have: The element technology A1; and At least one of the element technology C1 and the element technology C2.

5. The automotive rear module as described in claim 2, characterized in that, have: The element technology A1; and At least one of the element technology D1 and the element technology D2.

6. The automotive rear module as described in claim 2, characterized in that, have: The element technology A1; The element technology B1; At least one of the element technology C1 and the element technology C2; and At least one of the element technology D1 and the element technology D2.

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