RAW PIECE, PRODUCTION METHOD FOR STRUCTURAL ELEMENT AND STRUCTURAL ELEMENT

Description

1 / 65 RAW PIECE, PRODUCTION METHOD FOR STRUCTURAL ELEMENT AND STRUCTURAL ELEMENT TECHNICAL FIELD

[0001] The present invention relates to a blank for hot stamping. The present invention also relates to a production method for a structural element using the blank and the structural element. PREVIOUS TECHNIQUE

[0002] Structures such as a car body are formed by multiple structural elements. A structural element is produced by pressing a blank, for example. To ensure high strength and high dimensional accuracy, the structural element can be produced by a pressing method called hot stamping. Hot stamping is a technique that consists of heating a blank, which is a sheet of steel, to a temperature in the austenite zone, pressing the blank with pressing tools, and tempering the blank by holding it in the pressing tool for heat dissipation (rapid cooling).

[0003] Patent Literature 1 describes an overlapping blank for hot stamping. The overlapping blank of Patent Literature 1 includes a first steel sheet and a second steel sheet with an area smaller than the first steel sheet. The second steel sheet is overlapped onto a surface of the first steel sheet and welded to the first steel sheet. Both the first and second steel sheets are aluminum-clad steel sheets, and the amount of coating layer deposition on both surfaces is 20 g / m2 or more and 120 g / m2 or less.Given that the average amount of aluminum-based coating layer deposition on both surfaces of the first steel sheet is W1, the amount of aluminum-based coating layer deposition on the surface of the second steel sheet that is not in contact with the first steel sheet is W2, the thickness of the first steel sheet is t1 and the thickness of the second steel sheet is t2, the blank overlap of Patent Literature 1 satisfies the relations that 30 < (W1-W2) < 100 and (W1 / W2)2x(t1 / t2) > 1.5. According to Patent Literature 1, by satisfying these relations, the alloying reaction of the coating layer increases the emissivity. Petition 870260087749, dated 08 / 27 / 2026, page 80 / 154 2 / 65 can proceed quickly to the surface in the overlapping area between the first steel sheet and the second steel sheet during heating for hot stamping.

[0004] Patent Literature 2 describes a method for producing a side structural frame of an automobile body from multiple blanks. According to Patent Literature 2, multiple blanks are joined together to form a composite blank, and the composite blank is molded by pressing to produce a side structural frame of the body. In Patent Literature 2, the hot forming (hot stamping) of the composite blank is described. LIST OF QUOTES Patent Literature

[0005] Patent Literature 1: Japanese Patent No. 6642777

[0006] Patent Literature 2: Japanese Translation of the Application Publication International PCT No. 2021-528248 SUMMARY OF THE INVENTION TECHNICAL PROBLEM

[0007] In recent years, to simplify production processes for structures, the integration of two or more elements in the form of a blank has been studied. For example, Patent Literature 2 describes a composite blank with an annular shape in plan view that is subjected to hot stamping, thus producing an annular lateral structural frame, including a pillar, a rocker arm, and similar elements integrated together. Patent Literature 2 describes adjacent steel sheets in a composite blank that are overlapped and joined to each other by spot welding. When the composite blank includes such an overlapping part, it is difficult to guarantee a process window in the production of the structural element. Specifically, for hot stamping, the blank is heated until its microstructure is austenitized.However, the overlapping part formed by the partial overlapping of steel sheets has a greater sheet thickness than a part without overlap, and therefore the temperature of the overlapping part increases slowly. For example, when the raw piece includes a coated steel sheet, while the overlapping part has the greater thickness. Petition 870260087749, dated 08 / 27 / 2026, page 81 / 154 3 / 65 of the sheet in the raw piece is being heated to ensure the strength of the overlapping part by hot stamping. However, the alloy coating layer of a steel sheet (non-overlapping part) already heated to a desired temperature becomes excessive, the diffusion layer becomes thicker, and the corrosion resistance (rust resistance) due to the coating layer may deteriorate or be lost. Thus, when the raw piece includes an overlapping part, it is difficult to guarantee a process window for the heating condition. Furthermore, the heating rate of the overlapping part, with the greater sheet thickness in the raw piece, can be a bottleneck, and the productivity of the structural element may decrease.

[0008] One objective of the present invention is to provide a blank for hot stamping from which a structural element combining the strength of an overlapping part with the greater thickness of the sheet and a rust resistance function of each steel sheet can be produced. SOLUTION TO THE PROBLEM

[0009] A blank for hot stamping, according to the present invention, includes multiple steel sheets. The multiple steel sheets are arranged to form a ring in plan view of the blank and joined together. The multiple steel sheets include a first steel sheet, a second steel sheet, and a third steel sheet. An end portion of the first steel sheet overlaps and is joined to an end portion of the second steel sheet, thus forming an overlap portion with the end portion of the second steel sheet. The overlap portion has the greatest thickness of the sheet in the blank. At least one of the first steel sheet, the second steel sheet, and the third steel sheet is each a coated steel sheet. The coated steel sheet has a base steel sheet and an aluminum-based coating layer covering both surfaces of the base steel sheet.The amount of deposition (g / m2) of the aluminum-based coating layer on both surfaces of the base steel sheet of at least one of the first steel sheet and the second steel sheet is 60 or less and is less than the amount of deposition (g / m2) of the aluminum-based coating layer on both surfaces of the base steel sheet of the third steel sheet. Petition 870260087749, dated 08 / 27 / 2026, p. 82 / 154 4 / 65 ADVANTAGEOUS EFFECTS OF THE INVENTION

[00010] With a raw piece for hot stamping according to the present invention, a structural element that combines the strength of an overlapping part with the greater thickness of the sheet and a rust resistance function of each steel sheet can be produced. BRIEF DESCRIPTION OF THE DRAWINGS

[00011] Figure 1 is a plan view of a structural element according to a first embodiment.

[00012] Figure 2 is a cross-sectional view taken along line II-II in Figure 1.

[00013] Figure 3A is a schematic diagram to illustrate a production method for the structural element according to the first embodiment, showing a raw piece according to the first embodiment.

[00014] Figure 3B is a schematic diagram to illustrate the production method of the structural element according to the first method, showing the raw piece according to the first method.

[00015] Figure 3C is a schematic diagram to illustrate the production method of the structural element according to the first method, showing the raw piece according to the first method.

[00016] The 3D Figure is a schematic diagram to illustrate the production method of the structural element according to the first method, showing the raw piece according to the first method.

[00017] Figure 3E is a schematic diagram to illustrate the production method of the structural element according to the first modality.

[00018] Figure 3F is a schematic diagram to illustrate the production method of the structural element according to the first modality.

[00019] Figure 3G is a schematic diagram to illustrate the production method of the structural element according to the first modality.

[00020] Figure 4A is a cross-sectional view of the structural element produced using the production method according to the first modality. Petition 870260087749, dated 08 / 27 / 2026, page 83 / 154 5 / 65

[00021] Figure 4B is a cross-sectional view of the structural element produced using the production method according to the first modality.

[00022] Figure 4C is a cross-sectional view of the structural element produced using the production method according to the first modality.

[00023] Figure 5 is a cross-sectional view of a raw piece according to a second embodiment.

[00024] Figure 6 is a plan view of a structural element according to a variation of the modalities described above.

[00025] Figure 7A is a diagram showing a split pattern of a structural element in a first example.

[00026] Figure 7B is a diagram showing another pattern of division of the structural element in the first example.

[00027] Figure 7C is a diagram showing another pattern of division of the structural element in the first example.

[00028] Figure 7D is a diagram showing another pattern of division of the structural element in the first example.

[00029] Figure 7E is a diagram that shows another pattern of division of the structural element in the first example.

[00030] Figure 7F is a diagram that shows another pattern of division of the structural element in the first example.

[00031] Figure 7G is a diagram that shows another pattern of division of the structural element in the first example.

[00032] Figure 8A is a diagram showing a split pattern of a structural element in a second example.

[00033] Figure 8B is a diagram showing another pattern of division of the structural element in the second example.

[00034] Figure 8C is a diagram showing another pattern of division of the structural element in the second example.

[00035] Figure 8D is a diagram showing another division pattern of Petition 870260087749, dated 08 / 27 / 2026, page 84 / 154 6 / 65 structural element in the second example. DESCRIPTION OF THE MODALITIES

[00036] A raw part for hot stamping, according to one embodiment, includes multiple steel sheets. The multiple steel sheets are arranged to form an annular shape in plan view of the raw part and joined together. The multiple steel sheets include a first steel sheet, a second steel sheet, and a third steel sheet. An end portion of the first steel sheet is overlapped and joined to an end portion of the second steel sheet, thus forming an overlap portion with the end portion of the second steel sheet. The overlap portion has the greatest sheet thickness in the raw part. At least one of the first steel sheet, the second steel sheet, and the third steel sheet is each a coated steel sheet. The coated steel sheet has a base steel sheet and an aluminum-based coating layer covering both surfaces of the base steel sheet.The amount of deposition (g / m2) of the aluminum-based coating layer on both surfaces of the base steel sheet of at least one of the first steel sheet and the second steel sheet is 60 or less and is less than the amount of deposition (g / m2) of the aluminum-based coating layer on both surfaces of the base steel sheet of the third steel sheet (a first configuration).

[00037] The blank according to the first configuration includes the first steel sheet, the second steel sheet, and the third steel sheet. An end portion of the first steel sheet and an end portion of the second steel sheet form an overlap portion with the greater sheet thickness in the blank. The amount of aluminum-based coating layer deposition of at least one of the first and second steel sheets is less than the amount of aluminum-based coating layer deposition of the third steel sheet. The amount of aluminum-based coating layer deposition of at least one of the first and second steel sheets is 60 g / m2 or less.Since the first steel sheet and / or the second steel sheet are relatively thin steel sheets, when the sheet is heated for hot stamping, the alloy of the aluminum-based coating layer of the first steel sheet and / or the second steel sheet melts quickly, affecting both surfaces of the first and / or the second steel sheet. Petition 870260087749, dated 08 / 27 / 2026, page 85 / 154 7 / 65 steel sheets rapidly change color from silvery white to black or a color close to black. Therefore, the emissivity of the overlapping part formed by the first steel sheet and second steel sheet increases during the heating of the blank. As a result, the overlapping part can be heated more quickly to a temperature in the austenite zone, thus the heating time of the overlapping part can be reduced. Therefore, the heating of the blank required for hot stamping can be completed before the alloy of the aluminum-based coating layer of each steel sheet progresses excessively and the diffusion layer becomes thick. As a result, the strength of the overlapping part can be guaranteed by hot stamping, and the corrosion resistance (rust resistance) of each steel sheet can be guaranteed.

[00038] As described above, with the blank according to the first configuration, a structural element that combines the strength of the overlapping part with the greater sheet thickness and the rust resistance function of each steel sheet can be produced. That is, with the blank, the heating rate of the overlapping part with the greater sheet thickness can be increased, and a process window of heating conditions in the production of the structural element is more likely to be guaranteed. Furthermore, by increasing the heating rate of the overlapping part, the heating time of the blank for hot stamping can be reduced, and therefore the productivity of the structural element can be improved. In addition, as the heating time of the blank is reduced, the energy consumption of the production of the structural element is reduced, and greenhouse gas emissions during the heating of the blank for hot stamping can be reduced.

[00039] With the raw piece according to the first configuration, the amount of aluminum-based coating layer deposition on the third steel sheet is greater than the amount of aluminum-based coating layer deposition on at least one of the first and second steel sheets that form the overlapping part. That is, the third steel sheet exhibits superior rust resistance performance compared to the first and / or second steel sheets. Therefore, in the structural element produced from the raw piece, the rust resistance performance can be partially Petition 870260087749, dated 08 / 27 / 2026, page 86 / 154 8 / 65 increased. For example, by placing the third steel plate in a part of the structural element that requires relatively high rust resistance performance, the required rust resistance performance of the structural element as a whole can be guaranteed.

[00040] In the raw part according to the first configuration, the multiple steel sheets may include two or more steel sheets with different sheet thicknesses. In this case, provided that the sheet thickness of the overlapping part is tmax and the sheet thickness of a steel sheet with the smallest sheet thickness among the multiple steel sheets is tmin, it is preferable that tmax / tmin <3, 0 (a second configuration).

[00041] When the blank includes two or more steel sheets with different sheet thicknesses, the difference in sheet thickness between the overlapping part and the non-overlapping part is more significant compared to the case where all steel sheets included in the blank have the same sheet thickness. That is, the difference in sheet thickness between the overlapping part with the greatest sheet thickness in the blank and the steel sheet with the smallest sheet thickness is more significant. When the difference in sheet thickness is very large, when the structural element is produced from the blank by hot stamping, the overlapping part is heated more slowly than the steel sheet with the smallest sheet thickness, and it is likely that it will be difficult to guarantee a process window of the heating condition.In view of this, according to the second configuration, the ratio between the thickness of the overlapping sheet (tmax) and the smaller thickness of the sheet (tmin): tmax / tmin is defined as 3.0 or less. As a result, the heating of the overlapping sheet, which is the thicker part, will likely finish before the alloy of the coating layer of the thinner steel sheet progresses excessively, and the process window of the heating condition will likely be guaranteed.

[00042] In the raw part according to the first configuration, the multiple steel plates may include two or more steel plates with different plate thicknesses. Provided that the plate thickness of the overlapping part is tmax, and the plate thickness of a steel plate with the smallest plate thickness among the multiple steel plates is tmin, it is possible that tmax / tmin < 4.0. In this case, a surface of at least one of the first steel plate and the second steel plate Petition 870260087749, dated 08 / 27 / 2026, page 87 / 154 9 / 65 steel, which is located on an outer side of the overlapping part, is preferably coated with a film that is black in color (a third configuration).

[00043] According to the third configuration, in at least one of the first steel sheet and the second steel sheet that form the overlap, the surface located on the outside of the overlap is provided with a film that is black in color. In this way, the emissivity of the overlap can be increased in advance, and the heating of the overlap can be accelerated when the blank is heated for hot stamping. Therefore, even when the difference in sheet thickness between the overlap with the thickest sheet in the blank and the steel sheet with the thinnest sheet is more significant, the process window of the heating condition is more likely to be guaranteed. For example, even if the ratio between the thickness of the overlap sheet tmax and the thinnest sheet tmin: tmax / tmin is increased to 4.0, the process window will likely be guaranteed.

[00044] A production method for a structural element according to an embodiment includes a step of preparing the blank according to any of the first to third configurations, a step of heating the multiple steel sheets included in the blank to a temperature at completion of the austenite transformation or higher, and a step of molding and tempering the heated blank into a structural element with an annular shape in plan view with press tools (a fourth configuration).

[00045] A structural element, according to one embodiment, includes a main body of the element. The main body of the element is formed by multiple steel plates joined together. The main body of the element has an annular shape in plan view. The multiple steel plates include a first steel plate, a second steel plate, and a third steel plate. An end portion of the first steel plate is overlapped and joined to an end portion of the second steel plate, thus forming an overlap portion in the main body of the element with the end portion of the second steel plate. The overlap portion has the greater thickness of the plate in the main body of the element. At least one of the first steel plate, the second steel plate, and the third steel plate is each Petition 870260087749, dated 08 / 27 / 2026, page 88 / 154 10 / 65 a steel sheet coated with an aluminum-based coating layer on both surfaces of a base steel sheet. The thickness of the aluminum-based coating layer of at least one of the first and second steel sheets is less than the thickness of the aluminum-based coating layer of the third steel sheet (a fifth configuration).

[00046] With respect to the structural element according to the fifth configuration, in the overlapping part, provided that a maximum Vickers hardness value of a steel plate between the first steel plate and the second steel plate that is located on one side of the front surface of the main body of the element is HVmax, and a minimum Vickers hardness value is HVmin, HVmax - HVmin may be 30% or less of HVmax (a sixth configuration).

[00047] In the structural element according to the fifth or sixth configuration, the main body of the element may include a curved part. For example, the curved part is convexly curved outward from the main body of the element in plan view of the structural element. At least one of the first steel plate and the second steel plate may be located in the curved part (seventh configuration).

[00048] The structural element, according to any of the fifth to seventh configurations, may be a door ring piece from an automobile. In this case, the main body of the element may include a front pillar, a center pillar, and a rocker arm that connects the front pillar and the center pillar to each other (an eighth configuration).

[00049] The embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same components or corresponding components are indicated by the same reference numbers, and redundant descriptions will be omitted. First Mode Structural Element

[00050] Figure 1 is a diagram (plan view) showing a structural element 10, according to a first embodiment, positioned on a horizontal surface, viewed from above. The structural element 10 is used, for example, in the body of a car. The structural element 10 is typically a door ring piece of a car. This embodiment will be described with reference to an example in Petition 870260087749, dated 08 / 27 / 2026, p. 89 / 154 11 / 65 that structural element 10 is a door ring piece.

[00051] Structural element 10 is a hot-stamped element. That is, structural element 10 is produced by hot stamping (hot pressing work) on a blank formed from multiple steel sheets. Structural element 10 includes a main body of element 11. The main body of element 11 has an annular shape in plan view of structural element 10. The main body of element 11 includes a front pillar 111, a central pillar 112, and a rocker arm 113.

[00052] When structural element 10 is mounted on the car body, the center pillar 112 is positioned behind the front pillar 111. The center pillar 112 generally extends upwards and downwards from the body. The front pillar 111 extends towards the center pillar 112. The front pillar 111 includes a curved section 111a. The curved part 111a is a part that is convexly curved outward from the main body of element 11 in plan view of structural element 10. In the example of Figure 1, the curved part 111a is located on an upper part (an upper part of the front pillar) of the front pillar 111. When structural element 10 is mounted on the car body, the rocker arm 113 is arranged below the front pillar 111 and the center pillar 112. The rocker arm 113 connects the front pillar 111 and the center pillar 112 to each other.

[00053] In this embodiment, the main body of element 11 is formed by multiple steel plates 21, 22 and 23 joined together. In the example of Figure 1, the front pillar 111 is formed mainly by steel plates 21 and 23. Steel plate 21 is located in the curved part 111a of the front pillar 111. That is, at least a part of steel plate 21 forms part or all of the curved part 111a. The central pillar 112 is formed mainly by steel plate 22. The rocker arm 113 is formed by steel plates 22 and 23.

[00054] Figure 2 is a cross-sectional view taken along line II-II in Figure 1. Figure 2 shows a cross-section of structural element 10 taken at the position of steel plate 21 along the direction of the plate thickness. As shown in Figure 2, steel plate 21 has an open cross-section. Steel plate 21 generally has a hat-like shape in the cross-sectional view of structural element 10, for example. More specifically, steel plate 21 includes a top plate 211, vertical walls Petition 870260087749, dated 08 / 27 / 2026, page 90 / 154 12 / 65 212 and 213 and flanges 214 and 215. Vertical wall 212 is located on the opposite side of top plate 211 to vertical wall 213. In the cross-sectional view of structural element 10, one end of vertical walls 212 and 213 is connected to top plate 211. In the cross-sectional view of structural element 10, the other ends of vertical walls 212 and 213 are connected to flanges 214 and 215, respectively. Flanges 214 and 215 project outwards from vertical walls 212 and 213 of structural element 10, respectively.

[00055] In structural element 10, the width W of the steel plate 21, that is, the part of the structural element 10 that is located at the top of the front pillar 111 (Figure 1), can be 15 mm or more and 300 mm or less. The height H of the steel plate 21, that is, the part of the structural element 10 that is located at the top of the front pillar 111, can be 10 mm or more and 150 mm or less. The width W is the distance from end R on the side of the vertical wall 212 of the corner section between the top plate 211 and the vertical wall 212 to end R on the side of the vertical wall 213 of the corner section between the top plate 211 and the vertical wall 213, in the cross-section of structural element 10. The height H is the distance from the top plate 211 to the flange 214 or 215 in the direction of the thickness of the top plate 211.

[00056] Although not shown, the other steel plates 22 and 23 have an open cross-section, like steel plate 21. Steel plates 22 and 23 may also have a shape generally similar to a hat in the cross-sectional view of structural element 10. The width of a portion of steel plate 22 that corresponds to the central column 112 (Figure 1) may be 15 mm or more and 300 mm or less. The height of the portion of steel plate 22 that corresponds to the central column 112 may be 10 mm or more and 150 mm or less. The width of a portion of steel plate 23 that corresponds to a lower part of the front column 111 (Figure 1) is 30 mm or more and 750 mm or less, for example. The height of the steel plate section 23 that corresponds to the lower part of the front pillar 111 can be 25 mm or more and 150 mm or less. The width of a section of the steel plate 23 that corresponds to the rocker arm 113 (Figure 1) is 30 mm or more and 300 mm or less, for example.The height of the part of the steel plate 23 that corresponds to the rocker arm 113 can be 25 mm or more and 150 mm or less.

[00057] The size of the annular structural element 10 in plan view Petition 870260087749, dated 08 / 27 / 2026, page 91 / 154 13 / 65 is 1.0 m or more, for example. The size of structural element 10 can be 4.0 m or less, for example. The size of structural element 10 means the length of the line segment connecting two points that are the furthest apart from each other between any two points on the outer circumference of structural element 10 when structural element 10 placed on a horizontal surface is viewed in the vertical direction. Production Method for Structural Element

[00058] Next, a production method for structural element 10 will be described with reference to Figures 3A to 3G. The production method for structural element 10, according to this embodiment, includes a preparation step of a blank 20, a heating step of the blank 20, and a molding step of the heated blank 20 into structural element 10. Preparation Stage

[00059] As shown in Figure 3A, in the preparation stage, a blank 20 with the expanded shape of the structural element 10 is prepared. The blank 20 includes multiple steel plates 21, 22 and 23. The steel plates 21, 22 and 23 are arranged to form an annular shape in the plan view of the blank 20 and joined together.

[00060] Figures 3B, 3C, and 3D are cross-sectional views of the raw piece 20, showing the junctions between steel plates 21, 22, and 23. Figures 3B, 3C, and 3D are cross-sectional views taken along lines IIIB-IIIB, IIIC-IIIC, and IIID-IIID in Figure 3A, respectively. With reference to Figures 3B and 3C, steel plate 21 is superimposed on each of steel plates 22 and 23 and joined to them. That is, one end portion of steel plate 21 is overlapped onto an end portion of steel plate 22 and joined to it, thus forming an overlap portion 241 with the end portion of steel plate 22. Similarly, another end portion of steel plate 21 is overlapped onto an end portion of steel plate 23 and joined to it, thus forming an overlap portion 242 with the end portion of steel plate 23. With reference to Figure 3D, steel plate 22 is joined by overlap not only to steel plate 21, but also to steel plate 23.One end portion of steel plate 22 is overlapped onto and joined to one end portion of steel plate 23, thus forming a part of... Petition 870260087749, dated 08 / 27 / 2026, page 92 / 154 14 / 65 overlap 243 with the end part of the steel plate 23. Steel plates 21, 22 and 23 are joined by spot welding or laser welding, for example.

[00061] With reference to Figures 3B to 3D, steel plate 21 has a thickness of plate t1. Steel plate 22 has a thickness of plate t2. Steel plate 23 has a thickness of plate t3. In this example, the thickness of sheet t1 of steel sheet 21 and the thickness of sheet t2 of steel sheet 22 are greater than the thickness of sheet t3 of steel sheet 23. Therefore, the overlapping part 241 between steel sheets 21 and 22 has the greatest sheet thickness tmax in the raw piece 20. The sheet thickness tmax of the overlapping part 241 is greater than the sheet thickness of the overlapping part 242 between steel sheets 21 and 23 and the sheet thickness of the overlapping part 243 between steel sheets 22 and 23. The sheet thickness t3 of steel sheet 23 is the smallest sheet thickness tmin among the multiple steel sheets 21, 22, and 23 included in the raw piece 20.

[00062] When the multiple steel plates 21, 22, and 23 have different plate thicknesses t1, t2, and t3, as in this embodiment, the ratio between the largest plate thickness tmax and the smallest plate thickness tmin in the raw piece 20: tmax / tmin is greater than 2.0. In this case, the largest plate thickness tmax and the smallest plate thickness tmin satisfy a relationship such that tmax / tmin < 3.0, for example. The largest plate thickness tmax and the smallest plate thickness tmin may satisfy a relationship such that tmax / tmin > 2.5. The largest plate thickness tmax is 4.2 mm or less, for example. The plate thickness tmax may be 1.6 mm or more.

[00063] Each of the steel plates 21, 22 and 23 is a coated steel plate, more specifically, an aluminum-clad steel plate. Steel plate 21 has a base steel plate 21a and an aluminum-based coating layer 21b. Steel plate 22 has a base steel plate 22a and an aluminum-based coating layer 22b. Steel plate 23 has a base steel plate 23a and an aluminum-based coating layer 23b. The thickness of sheet t1 of steel sheet 21 is the total thickness of the base steel sheet 21a and the aluminum-based coating layer 21b, and is the average thickness of the sheet of steel sheet 21. The thickness of sheet t2 of steel sheet 22 is the total thickness of the base steel sheet 22a and the aluminum-based coating layer 22b, and is the average thickness of the sheet of steel sheet 22. The thickness of sheet tada of steel sheet 23 is the total thickness of the base steel sheet 23a. Petition 870260087749, dated 08 / 27 / 2026, p. 93 / 154 15 / 65 and the aluminum-based coating layer 23b and is the average thickness of the steel sheet 23.

[00064] In steel sheet 21, the aluminum-based coating layer 21b covers both surfaces of the base steel sheet 21a. The aluminum-based coating layer 21b is provided over all or practically all of both surfaces of the base steel sheet 21a. Similarly, in steel sheet 22, the aluminum-based coating layer 22b covers both surfaces of the base steel sheet 22a. The aluminum-based coating layer 22b is provided over all or practically all of both surfaces of the base steel sheet 22a. Furthermore, in steel sheet 23, the aluminum-based coating layer 23b covers both surfaces of the base steel sheet 23a. The aluminum-based coating layer 23b is provided over all or practically all of both surfaces of the base steel sheet 23a.

[00065] The chemical composition of aluminum-based coating layers 21b, 22b, and 23b is not particularly limited. As aluminum-based coating layers 21b, 22b, and 23b, a well-known aluminum-based coating layer (a coating layer containing primarily aluminum) can be used. Although this is not intended to be limiting, aluminum-based coating layers 21b, 22b, and 23b are, for example, Al-Si-based coating layers. Each of the aluminum-based coating layers 21b, 22b, and 23b can be the same as or different from the aluminum-based coating layers of the other steel sheets.

[00066] With reference to Figure 3B, steel plates 21 and 22 form the overlapping part 241 with the greatest plate thickness tmax in the raw piece 20. The amount of deposition W1 (g / m2) of the aluminum-based coating layer 21b of steel plate 21 is less than the amount of deposition W3 (g / m2) of the aluminum-based coating layer 23b of steel plate 23 (Figures 3C and 3D). Furthermore, the amount of deposition W2 (g / m2) of the aluminum-based coating layer 22b of steel plate 22 is also less than the amount of deposition W3 of the aluminum-based coating layer 23b of steel plate 23.

[00067] On steel plate 21, the amount of deposition W1 is the amount of Petition 870260087749, dated 08 / 27 / 2026, page 94 / 154 16 / 65 deposition of the aluminum-based coating layer 21b on both surfaces of the base steel sheet 21a and an average amount of deposition on both surfaces of the base steel sheet 21a. Typically, the amount of deposition (g / m2) of the aluminum-based coating layer 21b on one surface of the base steel sheet 21a is substantially equal to the amount of deposition (g / m2) of the aluminum-based coating layer 21b on the other surface of the base steel sheet 21a. However, the amount of deposition of the aluminum-based coating layer 21b may vary between the front and back surfaces of the base steel sheet 21a due to production conditions, for example. The amount of deposition of the aluminum-based coating layer 21b may be different between one surface and the other surface of the base steel sheet 21a.Similarly, in steel sheet 22, the deposition quantity W2 is the deposition quantity of the aluminum-based coating layer 22b on both surfaces of the base steel sheet 22a and an average deposition quantity on both surfaces of the base steel sheet 22a. Typically, the deposition quantity (g / m2) of the aluminum-based coating layer 22b on one surface of the base steel sheet 22a is substantially equal to the deposition quantity (g / m2) of the aluminum-based coating layer 22b on the other surface of the base steel sheet 22a. However, the deposition quantity of the aluminum-based coating layer 22b may vary between the front and back surfaces of the base steel sheet 22a due to production conditions, for example. The deposition quantity of the aluminum-based coating layer 22b may be different between one surface and the other surface of the base steel sheet 22a.In steel sheet 23, the deposition quantity W3 is the amount of aluminum-based coating layer 23b deposited on both surfaces of base steel sheet 23a and an average amount of deposition on both surfaces of base steel sheet 23a. Typically, the amount of aluminum-based coating layer 23b deposited on one surface of base steel sheet 23a is substantially equal to the amount of aluminum-based coating layer 23b deposited on the other surface of base steel sheet 23a. However, the amount of aluminum-based coating layer 23b deposited may vary between the front and back surfaces of base steel sheet 23a due to production conditions, for example. The amount of aluminum-based coating layer 23b deposited may be different between one. Petition 870260087749, dated 08 / 27 / 2026, page 95 / 154 17 / 65 surface and the other surface of the base steel plate 23a.

[00068] The deposition quantity W1 of the aluminum-based coating layer 21b of the steel sheet 21 and the deposition quantity W2 of the aluminum-based coating layer 22b of the steel sheet 22 are each 60 g / m2 or less, and preferably 50 g / m2 or less. The deposition quantities W1 and W2 are each 10 g / m2 or more, for example, and preferably 20 g / m2 or more. The deposition quantity W3 of the aluminum-based coating layer 23b of the steel sheet 23 is, for example, 20 g / m2 or more and, for example, 120 g / m2 or less. W3 is preferably 30 g / m2 or more, and more preferably 35 g / m2 or more. However, the deposition quantity W3 is greater than the deposition quantities W1 and W2. The amount of W3 deposition is preferably 115 g / m2 or less, and more preferably 100 g / m2 or less.The difference between the deposition quantity W1 of the aluminum-based coating layer 21b of the steel sheet 21 and the deposition quantity W3 of the aluminum-based coating layer 23b of the steel sheet 23: W3-W1 is 20 (g / m2) or more, for example. W3W1 can be 80 (g / m2) or less. Similarly, the difference between the deposition quantity W2 of the aluminum-based coating layer 22b of the steel sheet 22 and the deposition quantity W3 of the aluminum-based coating layer 23b of the steel sheet 23: W3-W2 is 20 (g / m2) or more, for example. W3-W2 can be 80 (g / m2) or less.

[00069] Although the method of forming the aluminum-based coating layers 21b, 22b and 23b on the base steel sheets 21a, 22a and 23a, respectively, is not particularly limited, a common hot-dip process is used, for example. Specifically, the aluminum-coated steel sheet 21 with an adjusted deposition quantity W1 of the aluminum-based coating layer 21b can be obtained by immersing the base steel sheet 21a in a molten aluminum coating bath and then performing gas cleaning with nitrogen or atmosphere, for example. Similarly, the aluminum-coated steel sheet 22 with an adjusted deposition quantity W2 of the aluminum-based coating layer 22b can be obtained by immersing the base steel sheet 22a in a molten aluminum coating bath and then performing gas cleaning with nitrogen or atmosphere, for example.In addition, the aluminum-clad steel sheet 23 with an adjusted deposition quantity W3 of. Petition 870260087749, dated 08 / 27 / 2026, page 96 / 154 18 / 65 aluminum-based coating layer 23b can be obtained by immersing the base steel sheet 23a in a molten aluminum coating bath and then performing gas cleaning, for example with nitrogen or atmosphere. When the aluminum-based coating layer is formed in the hot-dip process, an Al-Fe-based alloy layer is formed at the interface between the base steel sheet and the aluminum-based coating layer as a result of Fe elution in the hot-dip process.

[00070] The method for measuring the deposition quantities W1, W2, and W3 of the aluminum-based coating layers 21b, 22b, and 23b may be the sodium hydroxide-hexamethylenetetramine hydrochloric acid stripping weighing method described in JIS G 3314: 2019, for example. Specifically, according to JIS G 3314: 2019, five or more test specimens with a predetermined surface area S (mm2) (such as 50 mm ± x50 mm) are taken from each of the steel sheets 21, 22, and 23b of the blank 20, and the weight w1 (g) of each test specimen is measured. Next, each test specimen is immersed in a sodium hydroxide solution and, after verifying that gasification due to coating dissolution has ceased, the test specimen is removed from the sodium hydroxide solution and rinsed with water.Next, each test specimen, still wet after rinsing, is immersed in a hydrochloric acid solution with added hexamethylenetetramine until gasification due to coating dissolution ceases. Each test specimen removed from the hexamethylenetetramine hydrochloric acid solution is rinsed with water and dried immediately, and the weight w2 (g) of the test specimen is measured again. The amount of deposition W (g / m2) of the aluminum-based coating layer of each test specimen can be determined according to {(w1-w2) / S} x106. An average value of the amounts of deposition W of the five or more test specimens taken from each steel plate is considered as the amount of deposition of the aluminum-based coating layer of the steel plate.

[00071] However, when the test specimens taken from each of the steel plates 21, 22 and 23b are small in size, the cross-section of each of the aluminum-based coating layers 21b, 22b and 23b can be observed with an optical microscope (area: 100 µm x 100 µm), the thickness (µm) of the coating layer can be measured in three visual fields, and an average value Petition 870260087749, dated 08 / 27 / 2026, page 97 / 154 19 / 65 of the thicknesses measured in the three visual fields can be multiplied by three and converted to the amount of deposition. In this case, for each of the steel sheets 21, 22, and 22b, the amount of deposition is calculated for each surface of the base steel sheet, and an average value of the calculated amounts of deposition (average value for both surfaces) is considered as the amount of deposition of the aluminum-based coating layer. When there is an Al-Fe-based alloy layer at the interface between the base steel sheet and the aluminum-based coating layer, the thickness of the aluminum-based coating layer includes the thickness of the Al-Fe-based alloy layer. The thicknesses of the aluminum-based coating layers 21b and 22b of the steel sheets 21 and 22b that form the thickest overlapping part 241 are less than the thickness of the aluminum-based coating layer 23b of the other steel sheet 23.The thickness of the aluminum-based coating layer 21b of the steel sheet 21 may be the same as or different from the thickness of the aluminum-based coating layer 22b of the steel sheet 22. Heating Stage

[00072] The prepared blank 20 is molded into the structural element 10 (Figures 1 and 2) by hot stamping (hot pressing work). For hot stamping, the blank 20 undergoes a heating step. With reference to Figure 3E, in the heating step, the blank 20 is heated in a heating furnace 30, for example. The multiple steel sheets 21, 22 and 23 included in the blank 20 are heated to a temperature at the completion of the austenite transformation (Ac3 point) or higher. The steel sheets 21, 22 and 23 are heated to 900 °C or more, for example. In this way, all or substantially all of the microstructure of the steel sheets 21, 22 and 23 is transformed into the austenite phase, for example. Forming Stage

[00073] With reference to Figure 3F, in the forming stage, using the press tool 40, the heated raw part 20 is molded into the structural element 10, which has an annular shape in plan view (Figures 1 and 2), and tempered. The raw part 20 heated in the heating stage is removed from the heating furnace 30 (Figure 3E) and transported to the press tool 40. Petition 870260087749, dated 08 / 27 / 2026, p. 98 / 154 20 / 65 The press tool 40 is attached to a known press device. The press tool 40 includes, for example, a punch 41 and a die 42. The blank 20 is placed between the punch 41 and the die 42.

[00074] With reference to Figure 3G, after the blank 20 is placed between the punch 41 and the die 42, the die 42 approaches relatively close to the punch 41. The blank 20 is pressed between the punch 41 and the die 42 and shaped into a form that adapts to the forming surfaces of the punch 41 and the die 42. The blank 20 is held pressed between the punch 41 and the die 42. The blank 20 is designed to dissipate heat (rapid cooling) in the pressing tool 40, and thus its microstructure is transformed into martensite. In this way, the structural element 10 can be produced from the blank 20.

[00075] Figures 4A to 4C are cross-sectional views of structural element 10 after hot stamping. Figure 4A shows a cross-section of structural element 10 at the position of the overlapping part 241 with the greatest sheet thickness tmax. Figures 4B and 4C show cross-sections of structural element 10 at the positions of the other overlapping parts 242 and 243.

[00076] With reference to Figure 4A, also in structural element 10, after hot stamping, steel sheet 21 is a steel sheet coated with aluminum-based coating layers 21b on both surfaces of base steel sheet 21a. Similarly, steel sheet 22 is also a steel sheet coated with aluminum-based coating layers 22b on both surfaces of base steel sheet 22a. With reference to Figures 4B and 4C, in structural element 10, after hot stamping, steel sheet 23 is a steel sheet coated with aluminum-based coating layers 23b on both surfaces of base steel sheet 23a. However, the aluminum-based coating layers 21b, 22b and 23b in structural element 10 are more bonded to the iron during the heating stage than those in the blank 20 (Figures 3B to 3D).

[00077] With reference to Figures 4A to 4C, the thicknesses K1 and K2 of the aluminum-based coating layers 21b and 22b of the steel sheets 21 and 22 that form the thickest overlapping part 241 are each smaller than the thickness K3 of the aluminum-based coating layer 23b of the other steel sheet 23. In steel sheet 21, the thickness K1 is the average thickness of the layer of Petition 870260087749, dated 08 / 27 / 2026, p. 99 / 154 21 / 65 aluminum-based coating 21b on both surfaces of base steel sheet 21a. On steel sheet 22, thickness K2 is the average thickness of the aluminum-based coating layer 22b on both surfaces of base steel sheet 22a. On steel sheet 23, thickness K3 is the average thickness of the aluminum-based coating layer 23b on both surfaces of base steel sheet 23a. The difference between the thickness K1 of the aluminum-based coating layer 21b of steel sheet 21 and the thickness K3 of the aluminum-based coating layer 23b of steel sheet 23: K3-K1 is 7 (µm) or more, for example. K3-K1 can be 33 (µm) or less. Similarly, the difference between the thickness K2 of the aluminum-based coating layer 22b of the steel sheet 22 and the thickness K3 of the aluminum-based coating layer 23b of the steel sheet 23: K3-K2 is 7 (pm) or more, for example. K3-K2 can be 33 (pm) or less.The thickness K1 of the aluminum-based coating layer 21b of the steel sheet 21 may be equal to or different from the thickness K2 of the aluminum-based coating layer 22b of the steel sheet 22.

[00078] The thicknesses K1, K2 and K3 of the aluminum-based coating layers 21b, 22b and 23b of structural element 10 can be measured as follows. That is, a part of a car body is disassembled to obtain the annular structural element 10, and a specimen for analysis is obtained from structural element 10 by laser cutting, for example. For example, a specimen for analysis is obtained from each of the multiple steel plates included in structural element 10. The specimen for analysis is taken from a central part or from near the top plate of each of the open cross-section steel plates.For the test specimen taken from each of the multiple steel plates, the cut surface of the aluminum-based coating layer is etched with nital and then observed with an optical microscope (area: 100 pm χ x 100 pm), the coating layer thickness is measured in three visual fields, and an average value of the coating layer thicknesses measured in the three visual fields can be considered as the coating thickness. In the outermost layer of structural element 10, there is often an electrodeposition film or similar, for example. In this case, the coating layer that exists under the electrodeposition film layer and on the base steel plate is observed.

[00079] With reference to Figure 4A, in structural element 10, the part of Petition 870260087749, dated 08 / 27 / 2026, pp. 100 / 154 22 / 65 overlap 241 with the greater thickness of the sheet tmax is the junction between the two adjacent steel sheets 21 and 22. Since a maximum and a minimum Vickers hardness value of the steel sheet on the front surface side of the main body of element 11 between the steel sheets 21 and 22 that form the overlap part 241 are HVmax and HVmin, respectively, HVmax-HVmin is 30% or less of HVmax. In the production method according to this embodiment, after the relatively thinner coated steel sheets 21 and 22 are joined together to form the overlap part 241, the steel sheets 21 and 22 are subjected to hot stamping. In the overlapping section 241 after hot stamping, the maximum HVmax and minimum HVmin Vickers hardness values ​​of at least the steel sheet located on the front surface side of the main body of element 11 between steel sheets 21 and 22 satisfy a relationship such that HVmax-HVmin < HVmax x30%.In this embodiment, steel plate 22, not steel plate 21, is arranged on the front surface (outer side) of the main body of element 11. However, steel plate 21, instead of steel plate 22, may be arranged on the front surface (outer side) of the main body of element 11.

[00080] The maximum HVmax and minimum HVmin Vickers hardness values ​​of the overlapping part 241 can be measured as follows. First, a test specimen is taken from the structural element 10 by laser cutting, the test specimen including a cut surface of the steel plate located on the front surface side of the main body of the element 11, between the steel plates 21 and 22 that form the overlapping part 241. According to JIS Z 2244: 2020, the cut surface of the steel plate (base steel plate) is set as the test surface, and the Vickers hardness test is performed at thirty arbitrary points on the test surface, spaced apart by the total thickness of the overlapping part 241 plate or more, under conditions where the test force is 10 kgf (98.07 N) and the test force retention time is 10 s.Among the thirty Vickers hardness values ​​(HV) obtained in this way, the maximum Vickers hardness can be used as HVmax, and the minimum Vickers hardness can be used as HVmin.

[00081] With reference to Figure 4B, in structural element 10, the overlapping part 242 is the junction between the two adjacent steel plates 21 and 23. With reference to Figure 4C, the overlapping part 243 is the junction between the two adjacent steel plates 22 and 23. Just as the overlapping part 241 has the largest Petition 870260087749, dated 08 / 27 / 2026, pp. 101 / 154 23 / 65 thickness, provided that in each of the overlapping parts 242 and 243, the maximum and minimum Vickers hardness values ​​are HVmax and HVmin, respectively, HVmax-HVmin being 30% or less of HVmax, for example. In the production method according to this embodiment, after the overlapping part 242 is formed, the steel sheets 21 and 23 are subjected to hot stamping, and after the overlapping part 243 is formed, the steel sheets 22 and 23 are subjected to hot stamping. In the overlapping parts 242 and 243 after hot stamping, the maximum HVmax and minimum HVmin Vickers hardness values ​​satisfy a relationship such that HVmax - HVmin < HVmax x 30%.

[00082] The maximum HVmax and minimum HVmin Vickers hardness values ​​of overlapping part 242 are measured on the steel plate located on the front surface side of the main body of element 11, between steel plates 21 and 23 in overlapping part 242. The maximum HVmax and minimum HVmin Vickers hardness values ​​of overlapping part 243 are measured on the steel plate located on the front surface side of the main body of element 11, between steel plates 22 and 23 in overlapping part 243. The maximum HVmax and minimum HVmin Vickers hardness values ​​of overlapping parts 242 and 243 can be measured in the same way as overlapping part 241.

[00083] After the forming stage (hot stamping), steel sheets 21, 22 and 23 may have a tensile strength of 0.5 GPa or more, for example, and preferably a tensile strength of 1.0 GPa or more. At least one of the steel sheets 21, 22 and 23 may have a tensile strength of 1.5 GPa or more after the forming stage. The tensile strength of each of the steel sheets 21, 22 and 23 may be equal to or different from the tensile strength of the other steel sheets. Effects

[00084] When the blank 20 is heated for hot stamping, in the steel sheets 21, 22 and 23, iron is diffused from the base steel sheets 21a, 22a and 23a to the aluminum-based coating layers 21b, 22b and 23b, forming a diffusion layer. The thickness of the diffusion layer increases as the heating time of the blank 20 increases, and the corrosion resistance or weldability due to the aluminum-based coating layers 21b, 22b and 23b Petition 870260087749, dated 08 / 27 / 2026, pp. 102 / 154 24 / 65 of steel plates 21, 22 and 23 may deteriorate. To ensure the corrosion resistance and weldability of steel plates 21, 22 and 23, the thickness of the diffusion layer is preferably maintained at a predetermined value or lower. For example, when steel plates 21, 22 and 23 are heavy-clad aluminum-coated steel plates having a basis weight of approximately 50 to 80 g / m2, the thickness of the diffusion layer is preferably 15 µm or less. Furthermore, when steel plates 21, 22 and 23 are light-clad aluminum-coated steel plates having a basis weight of approximately 40 to 50 g / m2, for example, the thickness of the diffusion layer is preferably 10 µm or less.With the blank 20 according to this embodiment, the deposition amounts W1 and W2 of the aluminum-based coating layers 21b and 22b on the base steel sheets 21a and 22a of the steel sheets 21 and 22 that form the overlapping part 241 with the greater sheet thickness tmax are less than the deposition amount W3 of the aluminum-based coating layer 23b on the base steel sheet 21a of the other steel sheet 23. The deposition amounts W1 and W2 are 60 g / m2 or less. As a result, when the blank 20 is heated for hot stamping, the heating rate of the overlapping part 241 can be increased and the heating time of the overlapping part 241 can be reduced.Specifically, since the aluminum-based coating layers 21b and 22b on the surface layers of the steel sheets 21 and 22 are as thin as 60 g / m2 or less in terms of deposition quantity, when the blank 20 is heated, the alloy of the aluminum-based coating layers 21b and 22b with the iron contained in the base steel sheets 21a and 22a rapidly progresses to the surfaces of the steel sheets 21 and 22, and both surfaces of the steel sheets 21 and 22, including the overlapping part 241, change color to black or a color close to black relatively quickly. Therefore, the heating of the overlapping part 241 can be accelerated and the heating time of the overlapping part 241 can be reduced. Therefore, the heating of the raw piece 20 can be stopped before the alloying of the aluminum-based coating layers 21b, 22b and 23b of the steel sheets 21, 22 and 23 proceeds excessively and the diffusion layer exceeds the predetermined thickness.As a result, the strength of the overlapping part 241 with the greater thickness of the sheet tmax can be guaranteed by hot stamping, and the corrosion resistance (rust resistance) of the steel sheets 21, 22. Petition 870260087749, dated 08 / 27 / 2026, pp. 103 / 154 25 / 65 and 23 can be assured. Furthermore, by keeping the diffusion layer thickness small, the weldability of steel plates 21, 22, and 23 will likely be guaranteed.

[00085] With the blank 20, according to this embodiment, as described above, the heating rate of the overlapping part 241, with the greater sheet thickness tmax, can be increased. Therefore, the entire blank 20 can be heated to a temperature required for hot stamping before the alloy of the aluminum-based coating layers 21b, 22b and 23b of the steel sheets 21, 22 and 23 proceeds excessively, and a process window of the heating conditions in the production of the structural element 10 can be guaranteed. Therefore, it is possible to produce the structural element 10 which combines the strength of the overlapping part 241, with the greater thickness of the sheet tmax, and the rust resistance function of the steel sheets 21, 22 and 23. Furthermore, by increasing the heating rate of the overlapping part 241, the heating time of the blank 20 can be reduced and, therefore, the productivity of the structural element 10 can be improved.Furthermore, since the heating time of the raw piece 20 is reduced, the energy consumption in the production of the structural element 10 can be reduced, and greenhouse gas emissions during heating can be reduced.

[00086] In this embodiment, the amount of deposition W3 of the aluminum-based coating layer 23b on the steel plate 23 is greater than the amount of deposition on the steel plates 21 and 22 that form the thicker overlapping part 241. That is, the steel plate 23 exhibits superior rust resistance performance compared to the steel plates 21 and 22. The steel plate 23 is typically arranged in a part of the structural element 10 that requires relatively high rust resistance performance. In this way, the rust resistance performance required for the annular structural element 10 can be guaranteed.

[00087] In this embodiment, the deposition amounts W1 and W2 of the aluminum-based coating layers 21b and 22b of the steel sheets 21 and 22 may be equal or different. However, from the point of view of uniform heating of the blank 20, the deposition amount W1 of the aluminum-based coating layer 21b of the steel sheets 21 is preferably substantially equal to the deposition amount W2 of the aluminum-based coating layer 22b of the steel sheet 22. Petition 870260087749, dated 08 / 27 / 2026, pp. 104 / 154 26 / 65

[00088] In this embodiment, during the heating stage, the steel plate 23 with the smallest thickness (tmin) in the blank 20 first reaches a temperature in the austenite zone, and then the other parts reach the temperature in the austenite zone in ascending order of plate thickness. The overlapping part 241 with the largest thickness (tmax) is the last part to reach the temperature in the austenite zone. When the steel plates 21, 22, and 23 included in the blank 20 have different plate thicknesses, as in this embodiment, if the smallest thickness (tmin) and the largest thickness (tmax) are excessively different, the heating of the overlapping part 241 with the largest thickness (tmax) is substantially delayed compared to the steel plate 23 with the thickness (tmin), and the process window of the heating condition may not be guaranteed.In view of this, the ratio between the greater thickness of the sheet tmax and the smaller thickness of the sheet tmin: tmax / tmin is preferably equal to or less than 3.0. In this way, even if the steel sheets 21, 22 and 23 have different sheet thicknesses, the overlapping part 241 can be heated sufficiently for the austenite phase transformation to be completed before the alloy of the aluminum-based coating layer 23b of the thinner steel sheet 23 proceeds and its corrosion resistance is lost. Therefore, a process window is likely to be guaranteed in the production of the structural element 10. Second Mode

[00089] Figure 5 is a cross-sectional view of a blank 20A according to a second embodiment. Figure 5 shows an overlapping part 241 formed by steel sheets 21 and 22. The blank 20A according to this embodiment differs from the blank 20 of the first embodiment in that the overlapping part 241, with the greater sheet thickness tmax, is provided with a film 25.

[00090] The surface of each of the steel plates 21 and 22 located on the outside of the overlapping part 241 is coated with film 25. With steel plate 21, the entire surface opposite the other steel plate 22 is coated with film 25. With steel plate 22, the entire surface opposite the other steel plate 21 is coated with film 25. That is, the surfaces of steel plates 21 and 22 that form the front and rear surfaces of the overlapping part 241 are each coated with film 25. Petition 870260087749, dated 08 / 27 / 2026, pp. 105 / 154 27 / 65

[00091] Film 25 is a film that is substantially black in color. For example, when the surface luminosity value L* of film 25 (luminosity index L* CIE 1976 defined in JIS Z8781-4: 2013) is equal to or less than 60, film 25 can be considered black. Film 25 may be a carbon-based film with a treated surface (a film containing carbon (C)).

[00092] As with film 25, for example, a treated surface film described in International Application Publication No. WO2022 / 215229 may be used. Specifically, film 25 may contain, for example, carbon black. Film 25 may also contain a metal oxide. The metal oxide is one or more oxides selected from the group consisting of Zr oxide, Zn oxide and Ti oxide, for example. Film 25 may contain silica.

[00093] Film 25 may contain graphite, soot, or similar material instead of or in addition to carbon black. Alternatively, to increase the emissivity of steel sheet 21, film 25 may contain an acicular compound with a hexagonal crystal structure and an aspect ratio of 4 or more and 50 or less, for example. The compound with a hexagonal crystal structure is typically graphite (C). However, the compound may be lanthanum silicate, magnesium diboride, beryllium oxide (beryllium), zinc oxide, β-quartz, millerite (NiS), wurtzite (ZnS), or similar material.

[00094] The thickness of film 25 is 0.5 pm or more and 5.0 pm or less, for example. The thickness of film 25 is preferably 1.0 pm or more and 3.0 pm or less. The thickness of film 25 is small enough to be negligible compared to the thickness of the sheet of each of the steel sheets 21, 22 and 23. Therefore, the measured sheet thickness, including the thickness of film 25, can be treated as the tmax sheet thickness of the overlapping part 241.

[00095] In this embodiment, as the surface of each of the steel plates 21 and 22, which are located on the outer side of the overlapping part 241, is provided with film 25, which is substantially black, the emissivity of both outer surfaces of the overlapping part 241 can be increased. For example, in each of the steel plates 21 and 22, the surface coated with film 25 has an emissivity of 60% or more at a measuring temperature of 25°C and a wavelength of 8.0 pm. As a result of being provided with film 25, the surfaces of the steel plates 21 and 22, located on the outer side of the overlapping part Petition 870260087749, dated 08 / 27 / 2026, pp. 106 / 154 28 / 65 overlap 241, have an emissivity greater than 5%, preferably greater than 10%, or more preferably greater than 20%, of the emissivity of the other steel sheet that is not provided with film 25 at a temperature of 25°C and a wavelength of 8.0 pm, for example. By increasing the emissivity of the overlap 241 portion in advance, the heating of the overlap 241 portion can be accelerated when the blank 20A is heated for hot stamping. Therefore, even when the overlap 241 portion, with the greater sheet thickness tmax, and the steel sheet 23, with the smaller sheet thickness tmin (Figures 3C and 3D) in the blank 20A have significantly different sheet thicknesses, a process window of the heating condition is likely to be guaranteed.

[00096] With the blank 20 according to this embodiment, the ratio between the larger sheet thickness tmax and the smaller sheet thickness tmin: tmax / tmin is 2.5 or more, for example. tmax / tmin can be greater than 3.0. In this embodiment, as the emissivity of the overlapping part 241 is increased in advance by the film 25, which is substantially black in color, the heating of the overlapping part 241 is accelerated when the blank 20A is heated for hot stamping. Therefore, even when tmax / tmin is high, for example, even when tmax / tmin is greater than 3.0, the heating of the overlapping part 241, which is the thicker one, will probably finish before the alloy of the aluminum-based coating layer 23b of the thinner steel sheet 23 (Figures 3C and 3D) proceeds excessively, and a process window of the heating condition can be guaranteed.From the point of view of ensuring a more reliable heating condition process window, the greater sheet thickness tmax and the smaller sheet thickness tmin of the raw part 20A preferably satisfy a ratio where tmax / tmin <4.0.

[00097] In the example in Figure 5, the surface of each of the steel plates 21 and 22, which is located on the outside of the overlapping part 241, is coated with film 25, which is substantially black in color. However, it is also possible that the surface of one of the steel plates 21 and 22, which is located on the outside of the overlapping part 241, is coated with film 25, and the surface of the other steel plates 21 and 22, which is located on the outside of the overlapping part 241, is not coated with film 25. Furthermore, in the example Petition 870260087749, dated 08 / 27 / 2026, pp. 107 / 154 29 / 65 shown in Figure 5, the surface of each of the steel sheets 21 and 22, which is located on the inner side of the overlapping part 241, is not coated with film 25, which is substantially black in color. However, the surface of each of the steel sheets 21 and 22 that is located on the inner side of the overlapping part 241 may also be coated with film 25. However, from the point of view of making the heating of the blank 20A uniform for hot stamping, it is preferable that the surface of each of the steel sheets 21 and 22 that is located on the outer side of the overlapping part 241 be coated with film 25, and the surface located on the inner side of the overlapping part 241 not be coated with film 25.

[00098] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the present invention.

[00099] With blanks 20 and 20A according to the embodiments described above, in both steel sheets 21 and 22 that form the overlapping part 241 having the greater sheet thickness tmax, the deposition amounts W1 and W2 of the aluminum-based coating layers 21b and 22b are 60 g / m2 or less and are less than the deposition amount W3 of the aluminum-based coating layer 23b of the other steel sheet 23. However, in blanks 20 and 20A, the deposition amount of the aluminum-based coating layer of only at least one of the steel sheets 21 and 22 has to be 60 g / m2 or less and less than the deposition amount W3 of the aluminum-based coating layer 23b of the other steel sheet 23.For example, when the deposition quantity W1 of the aluminum-based coating layer 21b of the steel sheet 21 is 60 g / m2 or less, the deposition quantity W2 of the aluminum-based coating layer 22b of the steel sheet 22 may be greater than 60 g / m2. In this case, the deposition quantity W2 may be equal to or greater than the deposition quantity W3 of the aluminum-based coating layer 23b of the steel sheet 23. Similarly, when the deposition quantity W2 of the aluminum-based coating layer 22b of the steel sheet 22 is 60 g / m2 or less, the deposition quantity W1 of the aluminum-based coating layer 21b of the steel sheet 21 may be greater than 60 g / m2. In this case, the deposition quantity W1 may be equal to or greater than the deposition quantity W3 of the coating layer. Petition 870260087749, dated 08 / 27 / 2026, pp. 108 / 154 30 / 65 aluminum 23b steel sheet 23. [000100] With the structural elements 10 in accordance with the embodiments described above, both steel plates 21 and 22 that form the overlapping part 241 having the greater plate thickness tmax, the thicknesses K1 and K2 of the aluminum-based coating layers 21b and 22b are less than the thickness K3 of the aluminum-based coating layer 23b of the other steel plate 23. However, in the structural elements 10, the thickness of the aluminum-based coating layer of only at least one of the steel plates 21 and 22 must be less than the thickness K3 of the aluminum-based coating layer 23b of the other steel plate 23.For example, when the thickness K1 of the aluminum-based coating layer 21b of the steel sheet 21 is less than the thickness K3 of the aluminum-based coating layer 23b of the steel sheet 23, the thickness K2 of the aluminum-based coating layer 22b of the steel sheet 22 can be equal to or greater than the thickness K3 of the aluminum-based coating layer 23b of the steel sheet 23. Similarly, when the thickness K2 of the aluminum-based coating layer 22b of the steel sheet 22 is less than the thickness K3 of the aluminum-based coating layer 23b of the steel sheet 23, the thickness K1 of the aluminum-based coating layer 21b of the steel sheet 21 can be equal to or greater than the thickness K3 of the aluminum-based coating layer 23b of the steel sheet 23. [000101] In the embodiments described above, both steel plates 21 and 22 that form the overlapping part 241 with the greater thickness of the plate tmax are aluminum-clad steel plates. That is, steel plates 21 and 22 have base steel plates 21a and 22a and aluminum-based cladding layers 21b and 22b, respectively. However, only at least one of the steel plates 21 and 22 needs to be a steel plate clad with a base steel plate and an aluminum-based cladding layer. In other words, neither of the steel plates 21 and 22 needs to be an aluminum-clad steel plate. When one of the steel plates 21 and 22 is an aluminum-clad steel plate, the other of the steel plates 21 and 22 may be a zinc-clad steel plate, for example. [000102] With the raw pieces 20 and 20A, according to the embodiments described above, the end parts of the steel plates 21 and 22 are joined by overlapping to form the overlapping part 241. Similarly, the parts Petition 870260087749, dated 08 / 27 / 2026, pp. 109 / 154 31 / 65 of the ends of steel plates 21 and 23 are joined by overlapping to form the overlap part 242. Furthermore, the end parts of steel plates 22 and 23 are joined by overlapping to form the overlap part 243. However, blanks 20 and 20A need only include at least one overlap part. That is, steel plate 23 does not need to be joined by overlapping to steel plates 21 and 22. Steel plate 23 can be joined by butt to one or both steel plates 21 and 22. [000103] In the embodiments described above, the steel sheets 21, 22 and 23 included in the raw piece 20 or 20A may be single-layer or multi-layer. That is, each of the steel sheets 21, 22 and 23 may be a single steel sheet or a material formed by multiple steel sheets superimposed on one another. [000104] In the embodiments described above, blanks 20 and 20A each include three steel plates 21, 22, and 23. However, the number of steel plates included in blanks 20 and 20A is not limited to this. Blank 20 or 20A may include four or more steel plates. When blank 20 or 20A includes four or more steel plates, the steel plates, except for steel plates 21, 22, and 23, may be aluminum-clad steel plates, other clad steel plates, or steel plates without cladding layers (bare materials). When steel sheets, except for steel sheets 21, 22 and 23, are coated steel sheets, the amount of coating layer deposition on the steel sheets may be equal to or different from any of the W1, W2 and W3 deposition amounts of the aluminum-based coating layers 21b, 22b and 23b of steel sheets 21, 22 and 23. [000105] With blanks 20 and 20A according to the embodiments described above, the steel plate 23 that does not form the overlapping part 241, having the greatest thickness of the plate tmax, has the smallest thickness of the plate tmin. However, one or both of the steel plates 21 and 22 that form the overlapping part 241, having the greatest thickness of the plate tmax, may be steel plates that have the smallest thickness of the plate tmin in the annular blanks 20 and 20A. Alternatively, when the blank 20 or 20A includes four or more steel plates, a steel plate other than steel plates 21, 22 and 23 may have the smallest thickness of the plate tmin. [000106] In the modalities described above, the raw pieces 20 and 20A have Petition 870260087749, dated 08 / 27 / 2026, pp. 110 / 154 32 / 65 only one overlapping part 241 with the largest sheet thickness tmax. However, the raw part 20 or 20A may have multiple overlapping parts with the largest sheet thickness tmax. In this case, for all overlapping parts with the largest sheet thickness tmax, the amount of aluminum-based coating layer deposition on at least one of the two steel sheets forming the overlapping part is preferably 60 g / m2 or less. [000107] With the blanks 20 and 20A, according to the embodiments described above, the multiple steel plates 21, 22 and 23 have different plate thicknesses. However, among the three or more steel plates included in each of the blanks 20 and 20A, two or more steel plates may have the same thickness, or all steel plates may have the same thickness. When all steel plates included in the blanks 20 and 20A have the same thickness, tmax / tmin is 2.0. [000108] In the embodiments described above, the press tool 40 used for hot stamping of the raw part 20 includes the punch 41 and the die 42. However, the configuration of the press tool 40 is not limited to the example described in the embodiments above. The press tool 40 may also include a pad or a support for the raw part, for example. [000109] In the embodiments described above, the main body 11 of the structural element 10 includes the front pillar 111, the central pillar 112, and the rocker arm 113. However, the main body of the element 11 may also include another component. For example, as shown in Figure 6, the main body of the element 11 may also include a rear pillar 114. The rear pillar 114 may include a curved part 114a that is convexly curved outward from the main body of the element 11 in plan view of the structural element 10. In the example in Figure 6, the curved part 114a is arranged in an upper part (upper part of the rear pillar) of the rear pillar 114. The structural elements 10, according to the embodiments described above, are door ring pieces (single door ring pieces) with a single ring shape. On the other hand, the structural element shown in Figure 6 is a door ring piece (double door ring piece) with a double ring shape.When producing the double door ring component, the raw piece used as starting material also has a double ring shape. Petition 870260087749, dated 08 / 27 / 2026, pp. 111 / 154 33 / 65 [000110] In structural element 10, according to the first embodiment described above, steel plate 21, with a relatively small amount of aluminum-based coating layer 21b deposition, is arranged on the curved part 111a of the front pillar 111. However, steel plate 22, which forms the overlapping part 241 with steel plate 21, can be arranged on the curved part 111a. In the case of the structural element shown in Figure 6, at least one of the steel plates 21 and 22 can be arranged on the curved part 114a of the rear pillar 114. In the door ring piece, the curved parts 111a and 114a are parts that must exhibit relatively low rust resistance performance. Thin coated steel sheets 21 and / or 22 exhibit lower rust resistance performance than thick coated steel sheets and are therefore preferably placed in the curved section 111a or 114a, which does not need to exhibit high rust resistance performance.However, the positions of steel plates 21 and 22 are not limited to this. Steel plates 21 and 22 can be arranged on a lower part (lower part of the front pillar) of the front pillar 111, a lower part (lower part of the front pillar) of the rear pillar 114, or on the central pillar 112. EXAMPLES [000111] The present invention will now be described in more detail with reference to examples. However, the present invention is not limited to the examples described below. First Example [000112] To verify the effects of the present invention, using commercially available software (AUTOFORM R. 10 available from AUTOFORM), CAE analysis was performed on the press forming (hot stamping) of structural elements that were single door ring parts for different types (starting material types) and sheet thicknesses of steel sheets included in the structural elements and different split patterns of the structural elements. [000113] Table 1 shows the steel plates used in this analysis. TABLE 1 Petition 870260087749, dated 08 / 27 / 2026, pp. 112 / 154 34 / 65 Symbol | Starting material type | Base material | Coating quantity on one side, g / m2 | A120 Al-Si 1.5G HS | Hot stamping steel sheet, class 1.5 GPa | 120 | A80 Al-Si 1.5G HS | Hot stamping steel sheet, class 1.5 GPa | 80 | A80-1 | Black film (one side) | Al-Si 1.5G HS | Hot stamping steel sheet, class 1.5 GPa | 80 | A60 Al-Si 1.5G HS | Hot stamping steel sheet, class 1.5 GPa | 60 | A50 Al-Si 1.5G HS | Hot stamping steel sheet, class 1.5 GPa | 50 | A40 Al-Si 1.5G HS | Hot stamping steel sheet, class 1.5 GPa | 40 | A40-1 | Black film (one side) | Al-Si 1.5G HS Hot stamping steel sheet, class 1.5 GPa 40 A60-G GA 1.5G HS Hot stamping steel sheet, class 1.5 GPa 60 B120 Al-Si 2.0G HS Hot stamping steel sheet, class 2.0 GPa 120 Petition 870260087749, dated 08 / 27 / 2026, pp. 113 / 154 35 / 65 Symbol | Starting Material Type | Base Material | Coating Quantity on One Side, g / m2 | B80 Al-Si 2.0G HS | 2.0 GPa Class 80 Hot Stamping Steel Sheet | B60 Al-Si 2.0G HS | 2.0 GPa Class 60 Hot Stamping Steel Sheet | B40 Al-Si 2.0G HS | 2.0 GPa Class 40 Hot Stamping Steel Sheet | B40-1 Black Film (One Side) | Al-Si 2.0G HS | 2.0 GPa Class 40 Hot Stamping Steel Sheet | B60-G GA 2.0G HS | 2.0 GPa Class 60 Hot Stamping Steel Sheet | C80 Al-Si 2.5G HS | 2.5 GPa Class 80 Hot Stamping Steel Sheet | C40 Al-Si 2.5G HS | Hot Stamping Steel Sheet Hot stamping steel sheet, class 2.5 GPa 40 C40-1 Black film (one side) Al-Si 2.5G HS Hot stamping steel sheet, class 2.5 GPa 40 D80 Al-Si 1.0G HS Hot stamping steel sheet, class 1.0 GPa 80 Petition 870260087749, dated 08 / 27 / 2026, pp. 114 / 154 36 / 65 Symbol | Starting Material Type | Base Material | Coating Quantity on One Side, g / m2 | D80-2 | Black Film (Both Sides) | Al-Si 1.0G HS | Hot Stamping Steel Sheet, Class 1.0 GPa | 80 | D40 | Al-Si 1.0G HS | Hot Stamping Steel Sheet, Class 1.0 GPa | 40 | D40-1 | Black Film (One Side) | Al-Si 1.0G HS | Hot Stamping Steel Sheet, Class 1.0 GPa | 40 | E80 | Al-Si 0.5G HS | Hot Stamping Steel Sheet, Class 0.5 GPa | 80 | E40 | Al-Si 0.5G HS | Hot Stamping Steel Sheet, Class 0.5 GPa | 40 | E40-1 | Black Film (One Side) | Al-Si 0.5G HS | Hot Stamping Steel Sheet, Class 0.5 GPa | 40 | [000114] In Table 1, the starting material type shows the coating type, tensile strength, and use (hot stamping) in that order. However, for cases where a black film containing carbon (C) is provided over a coating layer, the term black film (one side) or black film (both sides) is presented before the starting material type. Black film (one side) means that the entire surface of the coated steel sheet is coated with a black film. Black film (both sides) means that the entire surface of both coated steel sheets is coated with a black film. Although Table 1 shows the values ​​of the amount of coating layer deposition per side, the amount of coating layer deposition is the same on both surfaces of the Petition 870260087749, dated 08 / 27 / 2026, pp. 115 / 154 37 / 65 starting material in this analysis. [000115] Figures 7A to 7G show the division patterns of the structural element. Figures 7A to 7G show the number of steel plates (starting materials) included in the structural elements that are single-port ring pieces and the positions of the junctions between the steel plates in the structural elements. In Figures 7A to 7G, each steel plate is indicated by a number in parentheses. [000116] Table 2 shows the analysis conditions and results for split patterns 1 and 2 shown in Figures 7A and 7B. In Figures 7A and 7B, the structural element is formed by three starting materials (1) to (3). Starting materials (1) to (3) are joined by overlapping adjacent starting materials. Petition 870260087749, dated 08 / 27 / 2026, pp. 116 / 154 38 / 65 TABLE 2 Standard Division Symbol Starting Material (1) Starting Material (2) Starting Material (3) Smallest sheet thickness tmin, mm Largest sheet thickness tmax, mm Time required to reach 910°C, s Heating completion time, s PW, s Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Example 1 1 B40 1.4 D40 1.4 B80 1.2 1.2 2.8 149.5 301.5 93.0 Example 2 1 B80 1.2 D40 1.3 A40 1.6 1.2 2.9 149.5 312.3 82.2 Example 3 2 A40 1.6 D80 1.2 A40 1.8 1.2 3.4 149.5 366.0 28.5 Comparative example 1 1 B80 1.4 D80 1.4 B80 1.2 1.2 2.8 149.5 349.5 45.0 Comparative example 2 2 A80 1.6 D80 1.2 A80 1.8 1.2 3.4 149.5 424.5 -30.0 Petition 870260087749, dated 08 / 27 / 2026, pp. 117 / 154 39 / 65 [000117] In Table 2, time required to reach 910°C means the time required for the starting material with the smallest sheet thickness tmin among the starting materials included in the blank to reach 910°C (point Ac3 or higher) after the start of heating the blank. Heating completion time means the time required for a part with the slowest temperature in the blank to reach 910°C so that hot stamping can be performed after the start of heating the blank. Process window (PW) means a value obtained by subtracting the heating completion time from the sum of the allowable heating time (245 seconds) after the starting material with the smallest sheet thickness tmin reaches 910°C and the time required to reach 910°C. The larger this value, the larger the process window of the heating condition in the hot stamping of the structural element. [000118] With reference to Table 2 and Figure 7A, in Example 1, starting material (1) and starting material (2) form an overlapping part with the largest plate thickness tmax = 2.8 mm. In Example 1, the amount of aluminum-based coating layer deposition of both starting materials (1) and (2) was 40 g / m2 and was less than the amount of aluminum-based coating layer deposition of the other starting material (3). In Comparative Example 1, where the combination of starting material type and plate thickness was the same as in Example 1, the amount of aluminum-based coating layer deposition was the same, 80 g / m2, for starting materials (1) to (3).In Example 1, the overlapping part, which was the thickest part, was a thinly coated part, so the heating of the overlapping part was promoted, and the completion time for heating the raw part was substantially reduced compared to Comparative Example 1. As a result, in Example 1, the process window was extended by almost 50 seconds compared to Comparative Example 1. [000119] With reference to Table 2 and Figure 7B, in Example 3, starting material (1) and starting material (3) form an overlapping part with the largest sheet thickness tmax = 3.4 mm. In Example 3, the amount of aluminum-based coating layer deposition of both starting materials (1) and (3) was 40 g / m2 and was less than the amount of aluminum-based coating layer deposition of the other starting material (2). In Example Petition 870260087749, dated 08 / 27 / 2026, pp. 118 / 154 40 / 65 Comparative Example 2, where the combination of starting material type and sheet thickness was the same as in Example 3, the amount of aluminum-based coating layer deposition was the same, 80 g / m2, for starting materials (1) to (3). In Example 3, the overlapping part, which was the thickest part, was a thinly coated part, so the heating of the overlapping part was promoted, and the completion time of the raw part heating was substantially reduced compared to Comparative Example 2. As a result, in Example 3, the process window was extended by 50 seconds or more compared to Comparative Example 2. [000120] In Example 2, starting material (2) and starting material (3) form an overlapping part with the largest sheet thickness tmax — 2.9 mm. In Example 2, the amount of aluminum-based coating layer deposition of starting materials (2) and (3) was 40 g / m2 and was less than the amount of aluminum-based coating layer deposition of the other starting material (1). In Example 2, again, it was found that a sufficient process window was ensured. [000121] Table 3 shows the analysis conditions and results for split patterns 3 and 4 shown in Figures 7C and 7D. In Figures 7C and 7D, the structural element is formed by four starting materials (1) to (4). Starting materials (1) to (4) are joined by overlapping adjacent starting materials. Petition 870260087749, dated 08 / 27 / 2026, pp. 119 / 154 41 / 65 TABLE 3 Standard Division Symbol Starting Material (1) Starting Material (2) Starting Material (3) Starting Material (4) Smallest sheet thickness tmin, mm Largest sheet thickness tmax, mm Time required to reach 910 °C, s Heating completion time, s PW, s Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Example 4 3 C40 2.0 A40 1.6 A40 1.6 A80 1.4 1.4 3.6 174.5 387.5 32.0 Example 5 4 B40 1.4 B80 1.4 B40 1.6 Example 6: 4 B40 1.6 A80 1.6 A40 1.8 A40 1.4 1.4 3.4 150.5 366.0 29.5 Example 7: 3 B40 1.6 D80 1.4 B40 2.0 D40 1.6 1.4 3.6 174.5 387.5 32.0 Example 8: 4 A40 1.8 C40 1.6 B40 2.0 A80 1.4 1.4 3.8 174.5 409.0 10.5 Example 9: 4 A40 1.2 B80 1.4 B40 1.4 D40 1.2 1.2 Example 3: C40 1.6, A80 1.2, C40 2.0, E40 1.6, 1.2, 3.6, 149.5, 387.5, 7.0 Petition 870260087749, dated 08 / 27 / 2026, pp. 120 / 154 42 / 65 Standard Division Symbol Starting Material (1) Starting Material (2) Starting Material (3) Starting Material (4) Smallest sheet thickness tmin, mm Largest sheet thickness tmax, mm Time required to reach 910 °C, s Heating completion time, s PW, s Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm 10 Example 11 4 A80 1.6 A60-G 1.6 B40 2.0 A40 1.6 1.6 3.6 171.5 387.5 29.0 Comparative example 3 3 C80 1.6 A80 1.6 B80 2.0 A80 1.6 1.6 3.6 199.5 449.5 -5.0 Comparative example 4 4 ​​A80 1.8 C80 1.6 B80 2.0 A80 1.4 1.4 3.8 174.5 474.5 -55.0 Petition 870260087749, dated 08 / 27 / 2026, pp. 121 / 154 43 / 65 Standard Division Symbol Starting Material (1) Starting Material (2) Starting Material (3) Starting Material (4) Smallest sheet thickness tmin, mm Largest sheet thickness tmax, mm Time required to reach 910 °C, s Heating completion time, s PW, s Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Comparative example 5 4 B80 1.6 A80 1.6 A80 1.8 A80 1.4 1.4 3.4 174.5 424.5 -5.0 Comparative example 6 3 B80 1.6 D80 1.4 B80 2.0 D80 1.6 1.4 3.6 174.5 449.5 -30.0 Comparative example 7 4 A80 1.2 B80 1.4 B80 1.4 D80-2 1.2 1.2 2.6 115.0 324.5 35.5 Petition 870260087749, dated 08 / 27 / 2026, pp. 122 / 154 44 / 65 [000122] In Examples 4 to 11 shown in Table 3, as well as in Examples 1 to 3 (Table 2), the amount of aluminum-based coating layer deposition on the starting materials forming the thickest overlapping part of the sheet tmax was 40 g / m2e and was less than the amount of deposition on another starting material. Therefore, in Examples 4 to 11, it was again possible to guarantee a process window under heating conditions. As can be observed, the process window in each example was enlarged compared to a corresponding comparative example. [000123] For example, in Example 8, starting material (1) and starting material (3) form an overlap part with the largest plate thickness tmax = 3.8 mm. In Example 8, the amount of aluminum-based coating layer deposition of each of the starting materials (1) and (3) was 40 g / m2 and was less than the amount of aluminum-based coating layer deposition of starting material (4) (Table 3 and Figure 7D). On the other hand, in Comparative Example 4, although the combination of starting material type and plate thickness was the same as in Example 8, the amount of aluminum-based coating layer deposition was the same, 80 g / m2, for all starting materials. In Example 8, the heating of the overlap part, which was a thinly coated part, was promoted, and the completion time for heating the blank was substantially reduced compared to Comparative Example 4.In Example 8, the process window was extended by 60 seconds or more compared to Comparative Example 4. In Comparative Example 4, the process window for the heating condition was lost (negative). [000124] For example, in Example 9, starting material (3) and starting material (4) form an overlap part with the largest plate thickness tmax = 2.6 mm. In Example 9, the amount of aluminum-based coating layer deposition of each of the starting materials (3) and (4) was 40 g / m2 and was less than the amount of aluminum-based coating layer deposition of starting material (2) (Table 3 and Figure 7D). On the other hand, in Comparative Example 7, although the combination of starting material type and plate thickness was the same as in Example 9, the amount of aluminum-based coating layer deposition was the same, 80 g / m2, for all starting materials. In Example 9, heating the overlap part, which was a part Petition 870260087749, dated 08 / 27 / 2026, pp. 123 / 154 45 / 65 finely coated, was promoted, and the completion time for heating the raw part was substantially reduced compared to Comparative Example 7. In Example 9, the process window was extended by almost 60 seconds compared to Comparative Example 7. In Comparative Example 7, both surfaces of the thinner starting material (4) were provided with a black film, and although the time required to reach 910°C was slightly more than 10 seconds earlier than in Example 9, the completion time for heating the raw part was reduced by 45 seconds in Example 9 compared to Comparative Example 7. Therefore, it can be said that the process window was extended compared to Comparative Example 7, even if the difference in the time required to reach 910°C was taken into account. [000125] Table 4 shows the analysis conditions and results for split patterns 5 to 7 shown in Figures 7E to 7G. In Figures 7E to 7G, the structural element is formed by five starting materials (1) to (5). Starting materials (1) to (5) are joined by overlapping adjacent starting materials. Petition 870260087749, dated 08 / 27 / 2026, pp. 124 / 154 46 / 65 Table 4 Standard Division Symbol Starting Material (1) Starting Material (2) Starting Material (3) Starting Material (4) Starting Material (5) Smallest sheet thickness tmin, mm Largest sheet thickness tmax, mm Time required to reach 910°C, s Heating completion time, s PW, s Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Example 12 5 A40 1.2 A80 1.4 C80 1.2 A40 1.8 A40 Example 13: 5 A40-1 1.4 B80 1.2 C40 1.6 D80 1.2 B40-1 1.4 1.2 3.0 110.0 323.0 32.0 Example 14: 6 A40 1.6 C40 1.6 A80 1.2 B40 1.8 D80 1.2 1.2 3.2 149.5 344.5 50.0 Example 15: 5 C40-1 1.6 B40 1.6 B80 1.4 A40 1.2 A120 1.2 1.2 3.2 131.5 344.5 32.0 Petition 870260087749, dated 08 / 27 / 2026, pp. 125 / 154 47 / 65 Standard Division Symbol Starting Material (1) Starting Material (2) Starting Material (3) Starting Material (4) Starting Material (5) Smallest sheet thickness tmin, mm Largest sheet thickness tmax, mm Time required to reach 910°C, s Heating completion time, s PW, s Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Example 16 6 B40 1.2 B80 1.2 A40 1.8 D40 1.2 B80 Example 17: 5 B60-G 1.4 D80 1.2 B40 1.6 E40 1.0 A40 1.2 1.0 3.0 107.0 323.0 29.0 Example 18: 5 A50 1.2 B80 1.6 B40 2.0 A50 1.2 A80 1.4 1.2 3.2 129.0 352.1 21.9 Example 19: 5 A60 1.2 B80 1.6 B40 2.0 A60 1.2 A80 1.4 1.2 3.2 129.0 363.0 11.0 Example 5 A60 1.2 B80 1.4 B60 1.8 A80 1.2 A80 1.4 1.2 3.0 129.0 362.0 12.0 Petition 870260087749, dated 08 / 27 / 2026, pp. 126 / 154 48 / 65 Standard Division Symbol Starting Material (1) Starting Material (2) Starting Material (3) Starting Material (4) Starting Material (5) Smallest sheet thickness tmin, mm Largest sheet thickness tmax, mm Time required to reach 910°C, s Heating completion time, s PW, s Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm 20 Example 21 5 A80-1 1.2 B80 1.6 B60 2.0 A80-1 Comparative example 8 5 A80 1.4 A80 1.2 C80 1.8 A80 1.4 A80 1.4 1.2 3.2 149.5 399.5 -5.0 Comparative example 9 6 A80 1.6 C80 1.6 A80 1.2 B80 1.8 D80 1.2 1.2 3.2 149.5 399.5 -5.0 Petition 870260087749, dated 08 / 27 / 2026, pp. 127 / 154 49 / 65 Standard Division Symbol Starting Material (1) Starting Material (2) Starting Material (3) Starting Material (4) Starting Material (5) Smallest sheet thickness tmin, mm Largest sheet thickness tmax, mm Time required to reach 910°C, s Heating completion time, s PW, s Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Type of starting material Sheet thickness, mm Comparative example 10 5 C80 1.6 B80 1.6 B80 1.4 A80 1.2 A80 1.2 1.2 3.2 149.5 399.5 -5.0 Comparative example 11 6 B80 1.2 B80 1.2 A80 1.8 D80 1.2 B80 1.2 1.2 3.0 149.5 374.5 20.0 Petition 870260087749, dated 08 / 27 / 2026, pp. 128 / 154 50 / 65 [000126] In Examples 12 to 21, shown in Table 4, the amount of aluminum-based coating layer deposition on at least one of the two starting materials forming the thickest overlapping part of the sheet tmax was 60 g / m2 or less, and was less than the amount of deposition on the other starting material. In Examples 12 to 21, again, it was possible to ensure a sufficient process window for the heating condition. As can be observed, the process window in each example was enlarged compared to a corresponding comparative example. [000127] For example, in Example 14, starting material (1) and starting material (2) form an overlapping part with the largest plate thickness tmax — 3.2 mm. In Example 14, the amount of aluminum-based coating layer deposition of each of the starting materials (1) and (2) was 40 g / m2 or less and was less than the amount of aluminum-based coating layer deposition of starting materials (3) and (5) (Table 4 and Figure 7F). On the other hand, in Comparative Example 9, although the combination of starting material type and plate thickness was the same as in Example 14, the amount of aluminum-based coating layer deposition was the same, 80 g / m2 or less, for all starting materials. In Example 14, the heating of the overlay part, which was a thinly coated part, was promoted, and the completion time for heating the raw piece was substantially reduced compared to Comparative Example 9.In Example 14, the process window was extended by 50 seconds or more compared to Comparative Example 9. In Comparative Example 9, the process window for the heating condition was lost (negative). [000128] For example, in Example 16, starting material (1) and starting material (3) form an overlapping part with the largest sheet thickness tmax — 3.0 mm. In Example 16, the amount of aluminum-based coating layer deposition of each of the starting materials (1) and (3) was 40 g / m2 and was less than the amount of aluminum-based coating layer deposition of each of the starting materials (2) and (5) (Table 4 and Figure 7F). In Example 16, additionally, starting material (3) and starting material (4) form an overlapping part with the largest sheet thickness tmax — 3.0 mm. In Example 16, the amount of aluminum-based coating layer deposition of each of the starting materials (3) and (4) was 40 g / m2 and was less than the amount of Petition 870260087749, dated 08 / 27 / 2026, pp. 129 / 154 51 / 65 deposition of the aluminum-based coating layer of each of the starting materials (2) and (5). On the other hand, in Comparative Example 11, although the combination of starting material type and sheet thickness was the same as in Example 16, the amount of aluminum-based coating layer deposition was the same, 80 g / m2, for all starting materials. In Example 16, the heating of the overlay part, which was a thinly coated part, was promoted, and the completion time for heating the blank was substantially reduced compared to Comparative Example 11. In Example 16, the process window was extended by 30 seconds or more compared to Comparative Example 11. [000129] In Example 19, starting materials (1) and (3) and starting materials (3) and (4) each form an overlapping part with the largest plate thickness tmax — 3.2 mm. In Example 19, the amount of aluminum-based coating layer deposition of starting material (3) was 40 g / m2, and the amount of aluminum-based coating layer deposition of each of starting materials (1) and (4) was 60 g / m2. In Example 19, again, the heating of the overlapping parts, which were thinly coated parts, was promoted, and the completion time for heating the blank was reduced compared to the comparative examples. In Example 18, the completion time for heating the blank was further reduced compared to Example 19.In Example 18, the amount of aluminum-based coating layer deposition of each of the starting materials (1) and (4) that form an overlap part having the largest sheet thickness tmax with starting material (3) was 50 g / m2. [000130] In Example 20, starting materials (1) and (3) and starting materials (3) and (4) each form an overlap part with the largest plate thickness tmax — 3.0 mm. In Example 20, the amount of aluminum-based coating layer deposition of starting material (4) was 80 g / m2, and the amount of aluminum-based coating layer deposition of starting materials (1) and (3) was 60 g / m2. In Example 20, again, as at least one of the two starting materials forming the overlap part was a thinly coated part with a deposition amount of 60 g / m2 or less, the heating of the overlap part was promoted, and the completion time for heating the blank was reduced by Petition 870260087749, dated 08 / 27 / 2026, pp. 130 / 154 52 / 65 comparison with the comparative examples. [000131] In Example 21, starting materials (1) and (3) and starting materials (3) and (4) each form an overlay part with the largest plate thickness tmax = 3.2 mm. In Example 21, the amount of aluminum-based coating layer deposition of starting materials (1) and (4) was 80 g / m2, and the amount of aluminum-based coating layer deposition of starting material (3) was 60 g / m2. In Example 21, again, as at least one of the two starting materials forming the overlay part was a thinly coated part with a deposition amount of 60 g / m2 or less, the heating of the overlay part was promoted, and the completion time of the raw part heating was reduced compared to the comparative examples.In Example 21, starting materials (1) and (4) were provided with a black film to increase the emissivity of the overlay part beforehand, which further reduced the completion time of heating the blank compared with Example 20. Second Example [000132] The same analysis from the first example was performed on the press forming (hot stamping) of structural elements that were double-door ring parts for different types and thicknesses of sheet metal of the initial materials included in the structural elements and different split patterns of the structural elements. [000133] The steel plates as starting materials were selected from those shown in Table 1, as in the first modality. The division patterns of the structural elements are shown in Figures 8A to 8D. Figures 8A to 8D show the number of steel plates (starting materials) included in the structural elements that are double-door ring pieces and the positions of the junctions between the steel plates in the structural elements. In Figures 8A to 8D, each steel plate as starting material is indicated by a number in parentheses. [000134] Table 5 shows the analysis conditions and results for split patterns 8 and 9 shown in Figures 8A and 8B. In Figures 8A and 8B, the structural element is formed by six starting materials (1) to (6). Starting materials (1) to (6) are each joined by overlapping adjacent starting materials. Petition 870260087749, dated 08 / 27 / 2026, pp. 131 / 154 53 / 65 Table 5 Standard Division Symbol Starting Material (1) Starting Material (2) Starting Material (3) Starting Material (4) Starting Material (5) Starting Material (6) Smaller sheet thickness tmin, mm Larger sheet thickness tmax, mm Time required to reach 910°C, s Heating completion time, s PW, s Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Petition 870260087749, dated 08 / 27 / 2026, pp. 132 / 154 54 / 65 Example 22 8 C40 1.4 A80 1.4 A40 1.8 D40 1.4 B4 0 1.0 D4 0 1.2 1.0 3.2 107, 0 344.5 7, 5 Example 23 8 A40 1.6 B80 1.3 B40-1 1.8 A40 1.4 A8 0 1.2 A8 0 1.0 1.0 3.4 124.5 306.0 63.5 Example 24 9 B40-1 1.4 A80 1.4 C40 1.6 B40 1.4 B4 0-1 1.0 A4 0-1 1.0 1.0 3.0 95.5 323.0 17 .5 Comparative example 12 8 C80 1.4 A80 1.4 A80 1.8 D80 1.4 B8 0 1.0 D8 0 1.2 1.0 3.2 124.5 399.5 - 30.0 Comparative example 13 9 B80 1.4 A80 1.4 C80 1.6 B80 1.4 B8 0 1.0 A8 0 1.0 1.0 3.0 124.5 374.5 - 5.0 Petition 870260087749, dated 08 / 27 / 2026, pp. 133 / 154 55 / 65 [000135] With reference to Table 5, in Example 22, starting materials (1) and (3) and starting materials (3) and (4) each form an overlap portion with the largest sheet thickness tmax = 3.2 mm, and the amount of aluminum-based coating layer deposition of each of starting materials (1), (3) and (4) was less than the amount of aluminum-based coating layer deposition of starting material (2). In Example 23, starting material (1) and starting material (3) form an overlap portion with the largest sheet thickness tmax = 3.4 mm, and the amount of aluminum-based coating layer deposition of each of starting materials (1) and (3) was less than the amount of aluminum-based coating layer deposition of starting materials (2), (5) and (6).In Example 24, starting materials (1) and (3) and starting materials (3) and (4) each form an overlap portion having the greatest sheet thickness tmax = 3.0 mm, and the amount of aluminum-based coating layer deposition of each of starting materials (1), (3) and (4) was less than the amount of aluminum-based coating layer deposition of starting material (2). In Examples 22 to 24, the amount of aluminum-based coating layer deposition of the starting materials forming the overlap portion, which was the thickest portion, was 40 g / m2. On the other hand, in Comparative Examples 12 and 13, the amount of aluminum-based coating layer deposition was the same, 80 g / m2, for all starting materials. [000136] As can be seen in Table 5, in Examples 22 to 24, since the overlapping part with the greatest sheet thickness tmax was a thinly coated part, the heating of the overlapping part was promoted, and the completion time of the raw part heating was substantially reduced compared to Comparative Examples 12 and 13. As a result, in Examples 22 to 24, the process window of the heating condition was significantly widened compared to Comparative Examples 12 and 13. [000137] Table 6 shows the analysis conditions and results for split patterns 10 and 11 shown in Figures 8C and 8D. In Figures 8C and 8D, the structural element is formed by seven starting materials (1) to (7). Starting materials (1) to (7) are each joined by overlapping adjacent starting materials. Petition 870260087749, dated 08 / 27 / 2026, pages 134 / 154 56 / 65 Table 6 Standard Division Symbol Starting Material (1) Starting Material (2) Starting Material (3) Starting Material (4) Starting Material (5) Starting Material (6) Starting Material (7) Minimum sheet thickness tmin, mm Maximum sheet thickness tmax, mm Time required to reach 910 °C, s Heating completion time, s PW, s Type of material Sheet thickness, Type of starting material Thickness Type of starting material Thickness Type of starting material Thickness Type of material Sheet thickness, Type of material Thickness Type of material Thickness Petition 870260087749, dated 08 / 27 / 2026, pages 135 / 154 57 / 65 part mm cha cha cha part mm teri cha teri cha pa, pa, pa, al pa, al pa, mm mm mm de mm de mm par par tid tid aa Example 25 10 C40 1.6 A80 1.4 A40-1 1.8 D40-1 1.2 D80 1.4 B4 0 1.2 D4 0-1 1.0 1.0 3.4 89.5 30 6.0 28.5 Example 26 10 A40 1.6 A80 1.4 B40-1 1.8 A40 1.2 B40 1.2 A4 0 1.2 A4 0 1.2 1.2 3.4 128.5 30 6.0 67.5 Example 27 11 B40 1.6 B80 1.3 C40-1 1.8 E40 1.2 A80-1 1.2 B4 0-1 1.2 A4 0-1 1.0 1.0 3.4 95.5 30 6.0 34.5 Comparative example 14 10 C80 1.6 A80 1.4 A80 1.8 D80 1.2 D80 1.4 B8 0 1.2 D8 0 1.2 1.2 3.4 124.5 42 4.5 - 55.0 Comparative example 15 11 B80 1.6 A80 1.4 C80 1.8 E80 1.2 A80 1.2 B8 0 1.2 A8 0 1.0 1.0 3.4 124.5 42 4.5 - 55.0 Petition 870260087749, de 27 / 08 / 2026, pág. 136 / 154 58 / 65 [000138] With reference to Table 6, in Examples 25 and 27, starting material (1) and starting material (3) form an overlapping part with the largest sheet thickness tmax = 3.4 mm, and the amount of aluminum-based coating layer deposition of each of starting materials (1) and (3) was less than the amount of aluminum-based coating layer deposition of each of starting materials (2) and (5). In Example 26, starting material (1) and starting material (3) form an overlapping part with the largest sheet thickness tmax = 3.4 mm, and the amount of aluminum-based coating layer deposition of each of starting materials (1) and (3) was less than the amount of aluminum-based coating layer deposition of starting material (2).In Examples 25 to 27, the amount of aluminum-based coating layer deposited on the starting materials forming the overlap, which was the thickest part, was 40 g / m2. On the other hand, in Comparative Examples 14 and 15, the amount of aluminum-based coating layer deposited was the same, 80 g / m2, for all starting materials. [000139] As can be seen in Table 6, in Examples 25 to 27, since the overlapping part with the greatest sheet thickness tmax was a thinly coated part, the heating of the overlapping part was promoted, and the completion time of the raw part heating was substantially reduced compared to Comparative Examples 14 and 15. As a result, in Examples 25 to 27, the process window of the heating condition was significantly widened compared to Comparative Examples 14 and 15. Third Example [000140] To verify the effect of the difference between the largest sheet thickness tmax and the smallest sheet thickness tmin on the press forming (hot stamping) of structural elements that are single-door ring parts, the same analysis from the first example was performed for different tmax / tmin values. Table 7 shows the analysis conditions and results. Petition 870260087749, dated 08 / 27 / 2026, pp. 137 / 154 59 / 65 Table 7 Starting Material (1) Starting Material (2) Starting Material (3) Starting Material (4) Starting Material (5) Division Symbol Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Starting Material Type Sheet Thickness, mm Minimum Sheet Thickness tmin, mm Maximum Sheet Thickness tmax, mm Sheet Thickness Ratio tmax / tmin Time Required to Reach 910°C, s Heating Completion Time, s PW, s Example of Test 1 7- Overlap A40 1.6 A40 1.4 C40 1.4 A40 1.2 A80 1.4 1.2 3.0 2.5 129.0 323.0 51.0 Test example 2 5- overlays C40 1.2 B80 1.6 B40 2.2 A40 1.2 A80 1.6 1.2 3.4 2.8 129.0 366.0 8.0 Petition 870260087749, dated 08 / 27 / 2026, pp. 138 / 154 60 / 65 Example of proof 3 7- superposition C40 -1 1.8 B80 1.6 B40- 1 2.6 A40 1.2 A80 1.6 1.2 4.4 3.7 129.0 358.5 15.5 Example of proof 4 5- superposition A40 1.0 A80 1.4 A40 2.6 A40 1.0 A80 1.4 1.0 3.6 3.6 124.5 387.5 -18.0 Example of proof 5 7- superposition A40 -1 1.0 A80 1.4 A40- 1 3.5 A40- 1 1.0 A80 1.4 1.0 4.5 4.5 124.5 369.3 0.3 Example of reference 5 - overlap C80 1.4 A80 1.4 A80 1.4 D80 1.4 B80 1.4 1.4 2.8 2.0 174.5 305.0 114.5 Example 7 - overlap A80 1.6 A80 1.4 C80 1.6 A80 1.2 A80 1.4 1.2 3.2 2.7 149.5 399.5 -5.0 Petition 870260087749, dated 08 / 27 / 2026, pp. 139 / 154 61 / 65 Comparative active 16 eposition Petition 870260087749, dated 08 / 27 / 2026, pages 140 / 154 62 / 65 [000141] The split pattern in Test Examples 1, 3 and 5 and in Comparative Example 16 was split pattern 7 shown in Figure 7G. In Test Examples 1 and 3, starting materials (1) and (3) form an overlapping part with the largest sheet thickness tmax. In Test Examples 1 and 3, the amount of aluminum-based coating layer deposition of each of the starting materials (1) and (3) was 60 g / m2 or less and was less than the amount of aluminum-based coating layer deposition of at least one of the other starting materials. In Test Example 5, starting materials (1) and (3) and starting materials (3) and (4) each form an overlapping part with the largest sheet thickness tmax.Furthermore, in Test Example 5, the amount of aluminum-based coating layer deposition of each of the starting materials (1), (3), and (4) was 60 g / m2 or less and was less than the amount of aluminum-based coating layer deposition of the other starting materials. In Test Example 3, the surfaces of starting materials (1) and (3) that were located on the outer sides of the overlapping part were coated with a black film. In Test Example 5, the surfaces of starting materials (1), (3), and (4) that were located on the outer sides of the overlapping part were coated with a black film. In Comparative Example 16, the amount of aluminum-based coating layer deposition was the same, 80 g / m2, for all starting materials. [000142] The split pattern in Test Examples 2 and 4 and in the Reference Example was split pattern 5 shown in Figure 7E. In Test Examples 2 and 4, starting materials (1) and (3) and starting materials (3) and (4) each form an overlapping part with the largest plate thickness tmax. Furthermore, in Test Examples 2 and 4, the amount of aluminum-based coating layer deposition of each of the starting materials (1), (3) and (4) was 60 g / m2 or less and was less than the amount of aluminum-based coating layer deposition of the other starting materials. In the Reference Example, all starting materials (1) to (5) had equal plate thickness and equal amount of aluminum-based coating layer deposition of 80 g / m2. [000143] In the Reference Example, there was no difference in sheet thickness between starting materials (1) to (5), and the ratio of the largest sheet thickness tmax Petition 870260087749, dated 08 / 27 / 2026, pages 141 / 154 63 / 65 (sheet thickness of the overlapping part) for the smallest sheet thickness tmin (sheet thickness of the starting materials (1) to (5)): tmax / tmin was 2.0. In the Reference Example, the difference (tmax / tmin) between the largest sheet thickness tmax and the smallest sheet thickness tmin was not large, so that even when the amount of aluminum-based coating layer deposition on the overlapping part was as high as 80 g / m2, a process window of the heating condition was possible to guarantee. On the other hand, when there is a difference in sheet thickness between the starting materials (1) to (5), the difference (tmax / tmin) between the largest sheet thickness tmax and the smallest sheet thickness tmin was greater than 2.0. In this case, the effect of forming the overlapping part as a thinly coated part would likely manifest itself markedly. [000144] As can be seen in Table 7, when the amount of aluminum-based coating layer deposition of the starting materials forming the thickest overlapping part of the sheet tmax was 60 g / m2 or less, even if tmax / tmin was on the order of 3.0, the heating completion time was less likely to be long, and a process window could be guaranteed (Test Examples 1 and 2). Furthermore, when the outer side of the thickest overlapping part of the sheet tmax was provided with a black film, even if tmax / tmin was greater than 3.0, the heating completion time would hardly be long, and a process window could be guaranteed (Test Example 3). However, even when each of the starting materials that form the overlapping part with the greatest thickness of the tmax sheet was provided with a black film, it was difficult to guarantee the process window if tmax / tmin was greater than 4.0 (Test Example 5). [000145] Under the conditions of this analysis, it can be said that when there is a difference in sheet thickness between the starting materials, it is preferable that tmax / tmin < 3.0. However, when the outer side of the overlapping part with the greater sheet thickness tmax is provided with a black film, it is possible that tmax / tmin < 4.0. [000146] For Test Examples 1 and 3 and Comparative Example 16, the productivity of the structural element and the rate of greenhouse gas emissions were evaluated. Table 8 presents the results of the evaluation. Table 8 Petition 870260087749, dated 08 / 27 / 2026, pages 142 / 154 64 / 65 Standard symbol for division Productivity, items / min Greenhouse gas emission rate during production Example Proof 1 7- overlap 3.71 82% Example Proof 3 7- overlap 3.34 91% Comparative Example 16 7- overlap 3.00 100% [000147] As shown in Table 8, in Proof Examples 1 and 3, the productivity of the structural element was improved compared to Comparative Example 16, since the heating time of the raw part was reduced compared to Comparative Example 16 (Table 7). Furthermore, in Proof Examples 1 and 3, the heating time of the raw part was reduced compared to Comparative Example 16, and the energy consumption required for the production of the structural element was reduced, so the rate of greenhouse gas emissions during production was also reduced. Productivity in Table 8 means the number of raw parts (structural elements) that can be heat-treated in a heating furnace in one minute. Rate of greenhouse gas emissions means the rate of greenhouse gas emissions relative to Comparative Example 16.Greenhouse gas emissions in the heating stage were determined by multiplying the greenhouse gas emissions per kWh of electricity from Japan's average power output in 2018 (LCA database, National Institute of Advanced Industrial Science and Technology, IDEAv3.2) by the energy consumption per allocated structural element, assuming that the hourly energy consumption of the multi-stage electric heating furnace for heating hot-stamped raw parts was 450 kWh, the furnace temperature was 920°C, the daily operating time was 15 hours, the heating and waiting time for the heating furnace was 3 hours, and the elements were produced with the productivity described in Table 8. Greenhouse gas emissions in the other stages (besides the heating stage) in the production of the structural element were calculated using the method described in a. Petition 870260087749, dated 08 / 27 / 2026, pages 143 / 154 65 / 65 published literature on LCA calculation for automotive parts (Masahiro Kubo et al., Life Cycle Assessment of Greenhouse Gas (GHG) Emissions of a Light Steel Body and Part, Proceedings of the JSAE Annual Congress (Spring), Japan Society of Automotive Engineers, Inc., 2022). LIST OF REFERENCE SIGNS 10: structural element 11: main body of the element 20, 20A: raw piece 21: steel plate (first steel plate) 21a: base steel plate 21b: aluminum-based coating layer 22: steel plate (second steel plate) 22a: base steel plate 22b: aluminum-based coating layer 23: steel plate (third steel plate) 23a: base steel plate 23b: aluminum-based coating layer 25: movie 40: Pressing tools 111: front pillar 112: central pillar 113: rocker 111a, 114a: curved part 241, 242, 243: overlapping part Petition 870260087749, dated 08 / 27 / 2026, pages 144 / 154

Claims

1 / 3 CLAIMS 1. A raw part for hot stamping, characterized in that it comprises: multiple steel sheets arranged to form an annular shape in the plan view of the raw part and joined together, wherein the multiple steel sheets include a first steel sheet, a second steel sheet and a third steel sheet, an end portion of the first steel sheet is overlapped and joined to an end portion of the second steel sheet, thus forming an overlap portion having a greater sheet thickness in the raw part than the end portion of the second steel sheet, at least one of the first steel sheet and the second steel sheet and the third steel sheet are each a coated steel sheet having a base steel sheet and an aluminum-based coating layer covering both surfaces of the base steel sheet,and a deposition quantity (g / m2) of the aluminum-based coating layer on both surfaces of the base steel sheet of at least one of the first steel sheet and the second steel sheet is 60 or less and is less than a deposition quantity (g / m2) of the aluminum-based coating layer on both surfaces of the base steel sheet of the third steel sheet.

2. A raw piece, according to claim 1, characterized in that the multiple steel plates include two or more steel plates with different plate thicknesses, and provided that the plate thickness of the overlapping part is tmax, and the plate thickness of a steel plate with the smallest plate thickness among the multiple steel plates is tmin, tmax / tmin < 3.

0.

3. A raw part, according to claim 1, characterized in that the multiple steel plates include two or more steel plates with different plate thicknesses, provided that the plate thickness of the overlapping part is tmax, and the plate thickness of a steel plate with the smallest plate thickness among the multiple steel plates is tmin, tmax / tmin < 4.0, and a surface of at least one of the first steel plate and the second steel plate that is located on an outer side of the overlapping part is coated with a film that is black in color.

4. Production method for a structural element, characterized in that it comprises: a step of preparing the blank, as defined in any one of claims 1 to 3; a step of heating the multiple steel sheets included in the blank to a temperature at or above the completion of the austenite transformation; and a step of molding and tempering the heated blank into a structural element with an annular shape in plan view using press tools.

5. Structural element, characterized in that it comprises: a main body of the element which is formed by multiple steel plates joined together and has an annular shape in plan view, wherein the multiple steel plates include a first steel plate, a second steel plate and a third steel plate, an end portion of the first steel plate is overlapped and joined to an end portion of the second steel plate, thus forming an overlap portion having a greater thickness of plate in the main body of the element than the end portion of the second steel plate, at least one of the first steel plate and the second steel plate and the third steel plate are each steel plates coated with an aluminum-based coating layer on both surfaces of a base steel plate,and the thickness of the aluminum-based coating layer of at least one of the first steel sheet and the second steel sheet is less than the thickness of the aluminum-based coating layer of the third steel sheet.

6. Structural element, according to claim 5, characterized in that in the overlapping part, provided that a maximum Vickers hardness value of a steel plate between the first steel plate and the second steel plate located on one side of the front surface of the main body of the element is HVmax, and a minimum Vickers hardness value is HVmin, HVmax-HVmin is 30% or less of HVmax.

7. Structural element, according to claim 5, characterized in that the main body of the element includes a curved part that is convexly curved outward from the main body of the element in plan view of the structural element, and at least one of the first steel plate and the second steel plate is located in the curved part.

8. Structural element, according to any one of claims 5 to 7, characterized in that the structural element is a door ring piece of an automobile, and the main body of the element includes a front pillar, a central pillar, and a rocker arm connecting the front pillar and the central pillar to each other. Petition 870260087749, dated 08 / 27 / 2026, pp. 147 / 154

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