Structural members

Abstract

A structural member (100) comprises a member main body (10) and reinforcing plates (20). The member main body (10) includes a pair of vertical walls (111, 112) and a bottom plate (12). The pair of vertical walls (111, 112) face one other. The bottom plate (12) connects the vertical walls (111, 112) to one other. The bottom plate (12) includes protruding portions (121). The protruding portions (121) extend from one of the vertical walls (111, 112) to the other. The reinforcing plates (20) extend from one of the vertical walls (111, 112) to the other, and cover the protruding portions (121). The reinforcing plates (20) are joined to the member main body (10).

Description

[Technical Field]

[0001] This disclosure relates to structural components for vehicles. [Background technology]

[0002] Automobiles and other vehicles contain multiple structural members. Examples of structural members include bumper reinforcements, pillars, side sills, crash boxes, battery boxes, and floors.

[0003] For example, Patent Document 1 discloses a floor for a vehicle. The floor of Patent Document 1 includes a main floor panel and reinforcing patches. The reinforcing patches have greater ductility than the main floor panel. The reinforcing patches are placed on the main floor panel and joined to the main floor panel. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2021 / 094405 [Overview of the project] [Problems that the invention aims to solve]

[0005] When a vehicle collides, a collision load is applied to the structural members. From the perspective of ensuring collision resistance, other skeletal members such as cross members may be joined to structural members such as the battery box and floor. However, in this case, the number of parts in the vehicle increases, which may lead to increased complexity in the structure or manufacturing process. Therefore, it is preferable to maximize the collision resistance of the structural members themselves.

[0006] This disclosure aims to provide structural members for vehicles with good collision resistance. [Means for solving the problem]

[0007] The structural member for a vehicle according to the present disclosure includes a member main body and a reinforcing plate. The member main body includes a pair of vertical walls and a bottom plate. The pair of vertical walls face each other. The bottom plate connects the vertical walls. The bottom plate includes a convex portion. The convex portion extends from one of the vertical walls to the other. The reinforcing plate extends from one of the vertical walls to the other and covers the convex portion. The reinforcing plate is joined to the member main body.

Effect of the Invention

[0008] According to the present disclosure, the structural member for a vehicle itself can exhibit good collision resistance performance.

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a perspective view of the structural member according to the embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a part of the structural member shown in FIG. 1. [Figure 3] FIG. 3 is a partial cross-sectional view of the blank used for manufacturing the structural member. [Figure 4] FIG. 4 is a partial cross-sectional view of the structural member manufactured by hot stamping the blank shown in FIG. 3. [Figure 5] FIG. 5 is a cross-sectional view showing a part of the structural member according to the second embodiment. [Figure 6] FIG. 6 is another cross-sectional view showing a part of the structural member according to the second embodiment. [Figure 7] FIG. 7 is a cross-sectional view showing a part of the structural member according to a modification of each embodiment. [Figure 8] FIG. 8 is a diagram showing the deformation behavior of the structural member according to Example 6. [Figure 9] FIG. 9 is a diagram showing the deformation behavior of the structural member according to Comparative Example 6.

Mode for Carrying Out the Invention

[0010] The structural member for a vehicle according to this embodiment comprises a member body and a reinforcing plate. The member body includes a pair of vertical walls and a bottom plate. The pair of vertical walls face each other. The bottom plate connects the vertical walls. The bottom plate includes a protrusion. The protrusion extends from one vertical wall to the other. The reinforcing plate extends from one vertical wall to the other and covers the protrusion. The reinforcing plate is joined to the member body (first configuration).

[0011] In the first configuration, a protrusion is provided on the bottom plate of the main body of the member. The protrusion extends from one vertical wall to the other vertical wall of the main body of the member. Therefore, when a vehicle collides and a collision load is applied to the structural member, the collision load can be supported by the protrusion. Furthermore, in the first configuration, the protrusion is reinforced by covering it with a reinforcing plate. Since the reinforcing plate covers the protrusion from one vertical wall to the other vertical wall, the collision load is more easily supported by the protrusion. As a result, the structural member itself can exhibit good collision resistance.

[0012] In the structural member relating to the first configuration, the member body may be a tray for a battery box. In this case, the member body may further include a flange. The flange is connected to each of the vertical walls on the opposite side of the bottom plate. The flange protrudes outward from the member body (second configuration).

[0013] In the structural member relating to the second configuration, it is preferable that the reinforcing plate further covers the flange (third configuration).

[0014] Typically, a cover is attached to the flange of a battery box tray. The flange may deform downward due to gravity acting on it from the cover and vertical vibrations during vehicle operation. In the third configuration, the reinforcing plate covers the flange of the main component in addition to the protrusion, thus reinforcing the flange. Therefore, deformation of the flange is more easily suppressed.

[0015] In the structural member relating to the third configuration, the reinforcing plate may be joined to the outer surface of the member body (fourth configuration).

[0016] In the fourth configuration, since the reinforcing plate is provided on the outer surface of the main component, no step is created on the upper surface of the flange due to the reinforcing plate. Therefore, when the lid is attached to the main component, which serves as the tray for the battery box, and joined to the flange, it becomes easier to ensure a good seal between the main component and the lid.

[0017] In a structural member relating to any of the first to fourth configurations, the member body and the reinforcing plate may each be formed from plated steel sheets. The plated steel sheet, for example, has a base steel sheet and an aluminum-based plating layer. The aluminum-based plating layer covers both surfaces of the base steel sheet. In this case, the thickness of the aluminum-based plating layer in the reinforcing plate may be less than the thickness of the aluminum-based plating layer in the member body (fifth configuration).

[0018] In the structural member relating to the fifth configuration, the reinforcing plate may be joined to the inner surface of the member body (sixth configuration).

[0019] In the sixth configuration, a relatively thin plated reinforcing plate is placed inside the main body of the component. In this case, the reinforcing plate is less exposed to the outside air, making it less likely to rust or deteriorate.

[0020] In a structural member with a configuration relating to any of the first to sixth, the member body and the reinforcing plate may each be made of steel plate. In this case, the value of coefficient A calculated by the following formula (1) using the chemical composition of the steel plate forming the member body may be greater than the value of coefficient A calculated by the following formula (1) using the chemical composition of the steel plate forming the reinforcing plate (seventh configuration). A=1.48×(2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr+2×Mo) 3.42 (1) However, the elemental symbols in formula (1) above are substituted with the content (mass%) of the corresponding element.

[0021] Embodiments of this disclosure will be described below with reference to the drawings. In each drawing, the same or equivalent components are denoted by the same reference numerals, and the same description will not be repeated.

[0022] <First Embodiment> [Structural Member Composition] Figure 1 is a perspective view of the structural member 100 according to this embodiment. The structural member 100 is used in vehicles such as automobiles. The structural member 100 is, for example, a battery box or a floor. In this embodiment, an example in which the structural member 100 is a battery box will be described.

[0023] Referring to Figure 1, the structural member 100 comprises a member body 10 and a reinforcing plate 20.

[0024] The component body 10 is, for example, a tray for a battery box. In this case, the component body 10 has an overall concave shape so as to be able to accommodate battery cells. In the example in Figure 1, the component body 10 has a bottomed rectangular tube shape. Although not shown in the figure, the opening of the component body 10 may be sealed by a lid.

[0025] The main body 10 includes a pair of vertical walls 111, 112, a bottom plate 12, and a flange 13. In this embodiment, the main body 10 further includes vertical walls 141, 142.

[0026] The vertical walls 111 and 112 are arranged facing each other. For example, when the structural member 100 is incorporated into the vehicle, the vertical walls 111 and 112 are arranged to face each other in the vehicle width direction (left-right direction). The vertical walls 111 and 112 may also be arranged to face each other in the vehicle length direction (front-rear direction) when the structural member 100 is incorporated into the vehicle.

[0027] Vertical walls 111 and 112 are connected by other vertical walls 141 and 142. Specifically, one end of vertical walls 111 and 112 is connected by vertical wall 141, and the other end of vertical walls 111 and 112 is connected by vertical wall 142.

[0028] The base plate 12 connects the vertical walls 111 and 112 to each other. The base plate 12 also connects the vertical walls 141 and 142 to each other. The vertical walls 111, 112, 141, 142 and the base plate 12 define a space for arranging the battery cells. The vertical walls 111, 112, 141, 142 may be provided substantially perpendicular to the base plate 12, or they may be inclined relative to the base plate 12.

[0029] The base plate 12 includes at least one protrusion 121. The protrusion 121 has a shape that is convex to the inside or outside of the member body 10 compared to the rest of the base plate 12. In the example of Figure 1, the protrusion 121 has a shape that is convex to the inside of the member body 10. The protrusion 121 extends from one of the vertical walls 111, 112 to the other. That is, the protrusion 121 extends from vertical wall 111 toward vertical wall 112 and reaches both vertical walls 111, 112. The protrusion 121 is integrally formed with the rest of the base plate 12 and the vertical walls 111, 112.

[0030] In this embodiment, the base plate 12 includes a plurality of protrusions 121. The base plate 12 may include three or more protrusions 121. These protrusions 121 are arranged at intervals. The protrusions 121 may be arranged at substantially equal intervals.

[0031] The flange 13 is connected to each of the vertical walls 111 and 112 on the side opposite to the bottom plate 12. In this embodiment, the flange 13 is also connected to each of the vertical walls 141 and 142 on the side opposite to the bottom plate 12. The flange 13 protrudes outward from the vertical walls 111, 112, 141, and 142 of the member body 10. The flange 13 is provided on the member body 10 so as to surround the vertical walls 111, 112, 141, and 142 in a plan view of the member body 10. If the member body 10 is a tray for a battery box, a lid (not shown) is joined to the flange 13. To ensure the airtightness of the battery box, a gasket, O-ring, or known sealer (not shown) may be used between the flange 13 and the lid. The sealer is, for example, a coating agent mainly composed of resin.

[0032] In this embodiment, multiple reinforcing plates 20 are provided corresponding to multiple protrusions 121. The reinforcing plates 20 are arranged at intervals corresponding to the protrusions 121. Each of the reinforcing plates 20 extends from at least one of the vertical walls 111, 112 to the other, covering the corresponding protrusion 121. Each of the reinforcing plates 20 extends from the vertical wall 111 toward the vertical wall 112, and reaches both the vertical walls 111, 112, similar to each of the protrusions 121. Each of the reinforcing plates 20 covers the entirety of the corresponding protrusion 121.

[0033] Each of the reinforcing plates 20 is joined to the member body 10. In this embodiment, the reinforcing plates 20 are joined to the inner surface of the member body 10. Although not particularly limited, the reinforcing plates 20 are joined to the member body 10 by, for example, spot welding. Each of the reinforcing plates 20 covers the corresponding protrusion 121 from the inside of the member body 10.

[0034] In this embodiment, the reinforcing plate 20 includes a first portion 21 and a second portion 22. The first portion 21 covers the protrusion 121 and is joined to the bottom plate 12. The first portion 21 extends from one vertical wall 111 to the other vertical wall 112. The second portion 22 is provided continuously at both ends of the first portion 21 in the direction of extension. The second portion 22 is bent relative to the first portion 21 and is provided along either the vertical wall 111 or 112. The second portion 22 is joined to the vertical wall 111 or the vertical wall 112.

[0035] Figure 2 is a cross-sectional view taken along line II-II of Figure 1, showing the cross-section (a section perpendicular to the direction of extension) of the protrusion 121 provided on the base plate 12. Referring to Figure 2, the protrusion 121 of the base plate 12 is hollow and, for example, has a substantially arc shape in cross-sectional view. However, the protrusion 121 of the base plate 12 may have other cross-sectional shapes, such as a rectangular shape.

[0036] When the main component 10 is a tray for a battery box, it is preferable that the proportion of the protrusion 121 to the area of ​​the bottom plate 12 is small from the viewpoint of ensuring the battery mounting capacity. The width L1 of the protrusion 121 is, for example, 90 mm or less, preferably 70 mm or less, and more preferably 50 mm or less. The width L1 of the protrusion 121 may be 30 mm or more. The width L1 of the protrusion 121 is the maximum length of the protrusion 121 in the width direction, when the direction perpendicular to its extending direction and height direction is defined as the width direction. The protrusion 121 may have a substantially constant width L1 along its entire length in the extending direction, or it may have a width L1 that changes along the extending direction.

[0037] The height of the protrusion 121 is less than or equal to the height of the vertical walls 111, 112 (Figure 1). In this embodiment, the height of the protrusion 121 is less than the height of the vertical walls 111, 112. That is, the protrusion 121 does not reach the flange 13 (Figure 1) side edge of the vertical walls 111, 112. The protrusion 121 may have a substantially constant height along its entire length in the direction of extension, or it may have a height that varies along the direction of extension.

[0038] The first portion 21 of the reinforcing plate 20 covers at least the protrusion 121. The first portion 21 may further cover the portion of the base plate 12 adjacent to the protrusion 121. In the example of Figure 2, the first portion 21 includes a protrusion 211 and a flat portion 212. The protrusion 211 has a shape corresponding to the protrusion 121 of the base plate 12 and is positioned on the protrusion 121. The protrusion 211 may be in contact with the entire protrusion 121 of the base plate 12. The flat portion 212 is provided continuously on both sides of the protrusion 211. From the viewpoint of moldability of the member body 10 and the reinforcing plate 20, the width L2 of the flat portion 212 is, for example, 10 mm or more. The width L2 of the flat portion 212 may be 40 mm or less. The width L2 of the flat portion 212 is the maximum length of the flat portion 212 in the width direction of the protrusion 121 of the base plate 12. The width L2 of the flat portion 212 may be substantially constant along the extending direction of the protrusion 121 of the base plate 12, or it may vary.

[0039] The main body 10 and the reinforcing plate 20 may each be made of steel plate to ensure their strength. The main body 10 and the reinforcing plate 20 may be made of, for example, plated steel plate. Specifically, the main body 10 and the reinforcing plate 20 may each be made of aluminum-plated steel plate.

[0040] The thickness of the main body 10 and the reinforcing plate 20 is, for example, 0.4 mm or more and 2.0 mm or less, preferably 1.0 mm or more and 1.8 mm or less. The thickness of the reinforcing plate 20 is preferably greater than the thickness of the main body 10. However, the thickness of the reinforcing plate 20 may be less than or equal to the thickness of the main body 10.

[0041] The main component 10 and the reinforcing plate 20 can have a tensile strength of, for example, 980 MPa or more and 2200 MPa or less. The tensile strength of the reinforcing plate 20 may be the same as that of the main component 10, or it may be different from that of the main component 10.

[0042] The structural member 100 is manufactured by press working on a blank. The structural member 100 can be manufactured by hot stamping (hot press working). For example, the blank 30 shown in Figure 3 is manufactured at the austenite transformation completion temperature (A c3 After heating to a certain temperature (1.5°C or higher), the heated blank 30 can be molded into a structural member 100 using a mold and then hardened to manufacture the structural member 100.

[0043] Figure 3 is a partial cross-sectional view of the blank 30. As shown in Figure 3, the blank 30 includes a steel plate 31 and a steel plate 32. Steel plate 31 is a steel plate for forming the member body 10 (Figures 1 and 2). Steel plate 32 is a steel plate for forming the reinforcing plate 20 (Figures 1 and 2). In the blank 30, steel plate 32 is joined to steel plate 31 by overlapping them. Steel plate 32 is joined to steel plate 31, for example, by spot welding. The thickness of each of the steel plates 31 and 32 is, for example, 0.4 mm or more and 2.0 mm or less, preferably 1.0 mm or more and 1.8 mm or less. It is preferable that the thickness of steel plate 32 is greater than the thickness of steel plate 31. However, the thickness of steel plate 32 may be less than or equal to the thickness of steel plate 31.

[0044] Steel sheets 31 and 32 are, for example, aluminum-plated steel sheets. Steel sheet 31 has a base steel sheet 31a and an aluminum-plated layer 31b. The aluminum-plated layer 31b covers both surfaces of the base steel sheet 31a. Steel sheet 32 ​​has a base steel sheet 32a and an aluminum-plated layer 32b. The aluminum-plated layer 32b covers both surfaces of the base steel sheet 32a.

[0045] The chemical composition of the aluminum-based plating layers 31b and 32b is not particularly limited. Known aluminum-based plating layers (plating layers mainly composed of aluminum) can be used as the aluminum-based plating layers 31b and 32b. Although not particularly limited, the aluminum-based plating layers 31b and 32b are, for example, Al-Si-based plating layers. The aluminum-based plating layer 31b of the steel sheet 31 may be the same as or different from the aluminum-based plating layer 32b of the steel sheet 32. Similarly, the types of base steel sheets 31a and 32a are not particularly limited. The base steel sheet 31a may be the same as or different from the base steel sheet 32a.

[0046] In this embodiment, the amount of aluminum-based plating layer 32b adhering to the steel plate 32 is W2 (g / m²). 2 ) is the amount of aluminum-based plating layer 31b deposited on the steel plate 31 W1 (g / m²). 2Less than. The deposition amount W1 of the aluminum-based plating layer 31b on the steel sheet 31 is the average deposition amount on both surfaces of the base steel sheet 31a. Similarly, the deposition amount W2 of the aluminum-based plating layer 32b on the steel sheet 32 is the average deposition amount on both surfaces of the base steel sheet 32a. The deposition amounts W1 and W2 are, respectively, 20 g / m 2 or more and 120 g / m 2 or less. The deposition amounts W1 and W2 are, respectively, preferably 30 g / m 2 or more, and more preferably 35 g / m 2 or more. The deposition amounts W1 and W2 are, respectively, preferably 115 g / m 2 or less, and more preferably 100 g / m 2 or less. The difference between the deposition amounts W1 and W2: W1 - W2 is, for example, 10 (g / m 2 ) or more. W1 - W2 is preferably 20 (g / m 2 ) or more, and more preferably 30 (g / m 2 ) or more. W1 - W2 may be 80 (g / m 2 ) or less. W1 - W2 is preferably 70 (g / m 2 ) or less, and more preferably 60 (g / m 2 ) or less. Also, the deposition amounts W1 and W2 satisfy the relationship W1 / W2 > 1.0. W1 / W2 is preferably 1.2 or more, and more preferably 1.5 or more.

[0047] The method for forming the aluminum-based plating layer on the base steel sheet is not particularly limited, but for example, it is a common molten plating method. That is, by immersing the base steel sheet 31a in a molten aluminum plating bath and performing gas wiping with nitrogen, air, etc., a plated steel sheet 31 with the deposition amount W1 of the aluminum-based plating layer 31b adjusted can be obtained. Similarly, by immersing the base steel sheet 32a in a molten aluminum plating bath and performing gas wiping with nitrogen, air, etc., a plated steel sheet 32 with the deposition amount W2 of the aluminum-based plating layer 32b adjusted can be obtained. When forming the aluminum-based plating layer by the molten plating method, an Al-Fe alloy layer is formed at the interface between the base steel sheet and the aluminum-based plating layer due to the elution of Fe during the molten plating process.

[0048] In the example shown in Figure 3, a coating 32c is provided on the steel plate 32. Of the two surfaces of the steel plate 32, the surface opposite to the steel plate 31 is covered with the coating 32c. On the other hand, the steel plate 31 is not covered with the coating 32c. The coating 32c is substantially black. For example, the brightness L from the surface of the coating 32c * Value (CIE 1976 Lightness Index L as defined in JIS Z8781-4:2013) * If the value is 60 or less, the coating 32c can be determined to be substantially black. The coating 32c may be a carbon-based surface treatment coating (a coating containing carbon (C)). For example, the surface treatment coating described in International Publication No. 2022 / 215229 can be used as the coating 32c.

[0049] Figure 4 is a partial cross-sectional view of a structural member 100 manufactured by hot stamping of a blank 30. Referring to Figure 4, a protrusion 121 is formed on the steel plate 31 (Figure 3) and a protrusion 211 is formed on the steel plate 32 (Figure 3) by hot stamping. Even after hot stamping, the structural member 100 is a plated steel sheet having a base steel sheet 31a and an aluminum-based plating layer 31b. The reinforcing plate 20 is a plated steel sheet having a base steel sheet 32a and an aluminum-based plating layer 32b. However, compared to the state of the blank 30 (Figure 3), the aluminum-based plating layers 31b and 32b in the structural member 100 undergo alloying with iron due to heating during hot stamping. The reinforcing plate 20 may further have a coating 32c. The composition of the coating 32c on the reinforcing plate 20 may change after hot stamping.

[0050] In this embodiment, the thickness of the aluminum-based plating layer 32b on the reinforcing plate 20 is smaller than the thickness of the aluminum-based plating layer 31b on the member body 10. When the average thickness (plating thickness) of the aluminum-based plating layer 31b on both surfaces of the steel plate 31 is K1 (μm), and the average thickness (plating thickness) of the aluminum-based plating layer 31b on both surfaces of the steel plate 32 is K2 (μm), the plating thickness K2 of the steel plate 32 is smaller than the plating thickness K1 of the steel plate 31. The difference between the plating thicknesses K1 and K2: K1-K2 is, for example, 7 (μm) or more. K1-K2 may also be 33 (μm) or less. Furthermore, the plating thicknesses K1 and K2 can satisfy the relationship K1 / K2 > 1.0. K1 / K2 is preferably 1.2 or more, more preferably 1.5 or more.

[0051] The thickness of the aluminum-based plating layer 31b on the main body 10 and the thickness of the aluminum-based plating layer 32b on the reinforcing plate 20 can be measured as follows. Specifically, the vehicle is dismantled to obtain the structural members 100, and analytical samples are obtained from these structural members 100, for example, by laser cutting. For example, analytical samples are obtained from both the main body 10 and the reinforcing plate 20 of the structural member 100. For the analytical samples obtained from both the main body 10 and the reinforcing plate 20, the cross-section of the aluminum-based plating layer is etched with Nital, and then observed with an optical microscope (area: 100 μm × 100 μm). The thickness of the plating layer is measured in three fields of view, and the average value of the plating layer thickness measured in the three fields of view can be taken as the plating thickness. In many cases, the outermost layer of the structural member 100 has, for example, an electrodeposited coating. In that case, the plating layer that is below the electrodeposited coating layer and above the base steel plate is observed.

[0052] In this embodiment, the steel plates 31 and 32 (Figure 3) are integrated by welding before hot stamping. A structural member 100, including the member body 10 and reinforcing plate 20, is formed as a single part from a blank 30 (Figure 3) containing the steel plates 31 and 32. In this case, even if softening of the heat-affected zone (HAZ softening) occurs during welding before forming, the heat treatment of hot stamping reduces the HAZ softening, and the hardness difference between the heat-affected zone and the unwelded parts in the resulting structural member 100 becomes smaller. Therefore, in at least one reinforcing plate 20 of the structural member 100 shown in Figure 1, the minimum value of the Vickers hardness of the heat-affected zone of the welded part is set to HV weld When the Vickers hardness of the non-welded area is HV, HV-HV weld For example, this is less than 30% of HV.

[0053] The Vickers hardness of the heat-affected zone and non-welded area of ​​the reinforcing plate 20 can be measured by the Vickers hardness test specified in JIS Z 2244-1:2020. Specifically, first, a test piece including the member body 10, the reinforcing plate 20, and the weld is obtained by laser cutting or the like at a position passing through the weld center of the weld of the structural member 100. Then, the test piece is embedded in resin so that the cross-section passing through the weld center of the member body 10, the reinforcing plate 20, and the weld is positioned on the surface, and the cross-section is polished. Subsequently, the Vickers hardness is measured at a position 1 / 4 of the plate thickness from the surface on the weld center side of the reinforcing plate 20, up to a position 12.0 mm outward from the weld center, in accordance with JIS Z 2244-1:2020, for example, with a test force of 0.49 N and a measurement interval (pitch) of 0.1 to 0.2 mm. The minimum value among the measured Vickers hardness is taken as the minimum Vickers hardness of the heat-affected zone of the reinforcing plate 20. Furthermore, at a position at least 15.0 mm away from the weld center of the welded joint, and at a position 1 / 4 of the way from the surface of the reinforcing plate 20 on the weld center side of the welded joint in the plate thickness direction, the Vickers hardness is measured in accordance with JIS Z 2244-1:2020, for example, with a test force of 0.49 N. This Vickers hardness is taken as the Vickers hardness of the non-welded part of the reinforcing plate 20.

[0054] [effect] In the structural member 100 according to this embodiment, a protrusion 121 is provided on the bottom plate 12 of the member body 10. The protrusion 121 extends from one of the vertical walls 111, 112 to the other on the member body 10. Therefore, when a vehicle collides and a collision load is applied to the structural member 100, the collision load can be supported by the protrusion 121. Furthermore, in the structural member 100, the protrusion 121 is reinforced by a reinforcing plate 20 covering the protrusion 121. Since the reinforcing plate 20 extends at least from one of the vertical walls 111, 112 to the other and covers the protrusion 121, the collision load is more easily supported by the protrusion 121. As a result, collision resistance is imparted to the structural member 100, and the structural member 100 itself can exhibit good collision resistance.

[0055] In this embodiment, the component body 10 is a tray for a battery box. The component body 10 includes flanges 13 that protrude outward from the vertical walls 111, 112, 141, and 142. When a lid is attached to the component body 10, the lid is joined to the flanges 13, thereby sealing the component body 10 and ensuring a good seal between it and the lid.

[0056] In this embodiment, the structural member 100 is manufactured by hot stamping a blank 30. The portion of the steel plate 31 corresponding to the member body 10 to which the steel plate 32 that will become the reinforcing plate 20 is joined has a greater thickness and heat capacity compared to other portions, and therefore does not heat up easily when heated during hot stamping. However, in this embodiment, the amount W2 (thickness) of the aluminum-based plating layer 32b on the steel plate 32 is less than the amount W1 (thickness) of the aluminum-based plating layer 31b on the steel plate 31. In this case, when the blank 30 is heated during hot stamping, the alloying of the aluminum-based plating layer 32b and iron on the steel plate 32 proceeds faster than on the steel plate 31, and the surface of the steel plate 32 changes from silvery white to black or a similar color. As a result, the emissivity of the steel plate 32 increases, which can increase the heating rate of the portion of the blank 30 to which the steel plate 32 is superimposed on the steel plate 31, and shorten the heating time for hot stamping. Therefore, the productivity of the structural member 100 can be improved. Furthermore, by shortening the heating time of the blank 30, energy consumption in the heating process is suppressed, which reduces the cost and greenhouse gas emissions in the manufacturing of the structural member 100.

[0057] In this embodiment, the thickness of the aluminum-based plating layer 31b on the member body 10 is greater than the thickness of the aluminum-based plating layer 32b on the reinforcing plate 20. This ensures the corrosion resistance of the member body 10. Furthermore, in this embodiment, the reinforcing plate 20, which has a relatively small thickness of aluminum-based plating layer 32b, is provided on the inside of the member body 10. In this case, the reinforcing plate 20 is less exposed to the outside air, making it less likely for the reinforcing plate 20 to rust or otherwise deteriorate.

[0058] In this embodiment, since a substantially black coating 32c is applied to the surface of the steel plate 32, the emissivity of the surface of the steel plate 32 can be increased. By increasing the emissivity of the surface of the steel plate 32 in advance, when the blank 30 is heated during hot stamping, the heating of the portion of the blank 30 in which the steel plate 32 is overlapped with the steel plate 31 can be accelerated.

[0059] In the structural member 100 according to this embodiment, the heights of the vertical walls 111, 112, 141, and 142 are greater than the height of the protrusion 121. That is, the depth of the member body 10 is greater than the height of the protrusion 121 provided on the bottom plate 12. In this case, the battery mounting capacity of the member body 10 is increased, and the design flexibility of the housing section of the member body 10 can be increased.

[0060] <Second Embodiment> Figure 5 is a cross-sectional view of the structural member 100A according to the second embodiment at the position of the protrusion 121. The structural member 100A according to this embodiment differs from the structural member 100 of the first embodiment in the arrangement of the reinforcing plate 20.

[0061] Referring to Figure 5, in the structural member 100A according to this embodiment, the reinforcing plate 20 is joined to the outer surface of the member body 10. The reinforcing plate 20 covers the protrusion 121 of the bottom plate 12 from the outside of the member body 10. More specifically, the protrusion 121 is covered from the outside of the bottom plate 12 by the first portion 21 of the reinforcing plate 20. The first portion 21 of the reinforcing plate 20 may include a protrusion 211 and a flat portion 212, similar to the first embodiment.

[0062] Figure 6 is a cross-sectional view (vertical section) of the structural member 100A according to this embodiment, cut perpendicular to the width direction of the protrusion 121. Referring to Figure 6, the reinforcing plate 20 further covers the vertical wall 111 or vertical wall 112 (Figure 1) and the flange 13 from the outside of the member body 10, in addition to the protrusion 121 of the bottom plate 12. More specifically, the reinforcing plate 20 further includes a third portion 23. The third portion 23 is continuous with the second portion 22 on the opposite side of the first portion 21. The third portion 23 is joined to the flange 13, for example, by spot welding. In the example shown in Figure 6, the third portion 23 may extend from the second portion 22 to the free end of the flange 13 in a vertical section view.

[0063] If the main body 10 is a battery box tray, when the lid is joined to the flange 13, the flange 13 may deform downward due to gravity acting on the lid and vibrations in the vertical direction when the vehicle is running. In this embodiment, since the third portion 23 of the reinforcing plate 20 covers the flange 13, the flange 13 can be reinforced by the reinforcing plate 20. Therefore, deformation of the flange 13 is more easily suppressed. Also, in this embodiment, since the reinforcing plate 20 is provided on the outer surface of the main body 10, no step is created on the upper surface of the flange 13 due to the reinforcing plate 20. Therefore, when the lid is joined to the flange 13, it is easier to ensure a good seal between the main body 10 and the lid.

[0064] <Third Embodiment> In the first embodiment described above, an example was described in which the amount (thickness) of the aluminum-based plating layer 32b on the steel plate 32 corresponding to the reinforcing plate 20 is reduced compared to the steel plate 31 corresponding to the main body 10. In this embodiment, an example is described in which the steel plate 31 is made of a highly hardened material, either as an alternative or in addition to the above.

[0065] Referring again to Figures 3 and 4, in the blank 30 and the structural member 100 formed therefrom, the portion of the steel plate 31 forming the member body 10 that is not overlapped with the steel plate 32 forming the reinforcing plate 20 is thinner than the portion where the steel plate 32 is overlapped. The chemical composition of the steel plate 31 may differ from that of the steel plate 32. More specifically, the value of coefficient A calculated using the chemical composition of the steel plate 31 in the following formula (1) may differ from the value of coefficient A calculated using the chemical composition of the steel plate 32 in the formula (1). A=1.48×(2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr+2×Mo) 3.42 (1)

[0066] The meaning of the coefficient A calculated in equation (1) is explained below. For example, as described in "Masakatsu Ueno, Kametaro Ito, "A New Predictive Formula for Steel Hardenability Replacing GROSSMANN's Formula", Iron and Steel, The Iron and Steel Institute of Japan, 74th (1988) No. 6, pp. 1073-1080", the critical cooling rate V has traditionally been used as an indicator of the hardenability of steel. c90 The critical cooling rate V is used. c90 This is the critical cooling rate (°C / s) at which a martensitic structure with a volume fraction of 90% or more is obtained, and logV c90 It is expressed by the formula = 2.94 - 0.75β. β is calculated as 2.7 × C + 0.4 × Si + Mn + 0.45 × Ni + 0.8 × Cr + 2 × Mo. β represents the degree of influence of each element on hardenability, based on the amount of Mn. The larger β, the higher the critical cooling rate V. c90 This reduces the size of the material, resulting in improved hardenability of the steel.

[0067] A correlation exists between β, which represents the degree of influence of each element on hardenability, and the time from the completion of heating of the steel material until diffusion transformation begins (transformation onset time). The inventors conducted tests on multiple hot-stamping steel materials and performed regression analysis using the test results, and found the following formula to convert β to transformation onset time: A = 1.48 × β 3.42 The following formula was constructed. The value A obtained from this formula is a coefficient (index value) that differs for each type of steel depending on its chemical composition. Coefficient A corresponds to the transformation onset time when only the influence of elements is considered, and a larger coefficient A means that the steel has better hardenability. Coefficient A roughly corresponds to the transformation onset time when the steel plate thickness is 1.2 mm.

[0068] In equation (1), the elemental symbols are substituted with the corresponding elemental content (mass%). That is, the coefficient A for steel sheet 31 is calculated by substituting the content (mass%) of each element in the chemical composition of steel sheet 31 into the corresponding elemental symbols in equation (1). If steel sheet 31 is a plated steel sheet, the coefficient A for steel sheet 31 is calculated by substituting the content (mass%) of each element in the chemical composition of base steel sheet 31a into equation (1). Similarly, the coefficient A for steel sheet 32 ​​is calculated by substituting the content (mass%) of each element in the chemical composition of steel sheet 32 ​​into the corresponding elemental symbols in equation (1). If steel sheet 32 ​​is a plated steel sheet, the coefficient A for steel sheet 32 ​​is calculated by substituting the content (mass%) of each element in the chemical composition of base steel sheet 32a into equation (1). The chemical composition of steel sheets 31 and 32 does not change before and after hot stamping.

[0069] In the blank 30 and the structural member 100 formed therefrom, the value of coefficient A calculated using formula (1) with respect to the chemical composition of steel plate 31 is preferably greater than the value of coefficient A calculated using formula (1) with respect to the chemical composition of steel plate 32. When coefficient A for steel plate 31 is denoted as A1 and coefficient A for steel plate 32 is denoted as A2, A1-A2 is preferably 0.10 or more, and more preferably 0.20 or more. A1-A2 may also be, for example, 11.50 or less.

[0070] The steel sheets 31 and 32 may have chemical compositions known for hot stamping. For example, the chemical compositions of steel sheets 31 and 32 are, by mass%, C: 0.05-0.50%, Si: 0.020-1.000%, Mn: 0.20-2.50%, Ni: 0-0.50%, Cr: 0-0.50%, Mo: 0-0.5%, and B: 0.0005-0.0050%. The chemical compositions of steel sheets 31 and 32 may further contain, in mass%, one or more elements selected from the group consisting of Cu: 0.005 to 3.000%, Co: 0.005 to 0.500%, Sn: 0.005 to 0.500%, Ca: 0.0005 to 0.0050%, Mg: 0.0005 to 0.0050%, REM: 0.0005 to 0.0050%, and Sb: 0.0005 to 0.0200%.

[0071] The chemical composition of steel plates 31 and 32 contained in the blank 30 can be measured by a general analytical method. For example, the chemical composition of steel plates 31 and 32 can be obtained by taking analytical specimens from each of the steel plates 31 and 32 and measuring them using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). In each analytical specimen, carbon (C) can be measured using the combustion-infrared absorption method. The chemical composition of steel plates 31 and 32 in the structural member 100 after hot stamping can be obtained by the same analytical method as for the blank 30.

[0072] If the hardenability of the steel plate 31 corresponding to the main body 10 and the steel plate 32 corresponding to the reinforcing plate 20 is the same, then after the blank 30 is heated for hot stamping, the thin portion of the steel plate 31 that is not overlapped with the steel plate 32 will begin phase transformation (diffusion transformation) from austenite to ferrite relatively quickly. However, in this embodiment, the coefficient A1 calculated for the steel plate 31 based on its chemical composition is larger than the coefficient A2 calculated for the steel plate 32 based on its chemical composition. That is, the steel plate 31 forming the main body 10 is made of a material with higher hardenability compared to the steel plate 32 forming the reinforcing plate 20, in other words, a material that starts diffusion transformation later when cooled. Therefore, after the blank 30 is heated, the start of diffusion transformation in the thin portion of the steel plate 31 that is not overlapped with the steel plate 32 can be delayed. As a result, when the blank 30 is hot stamped, the thin portion can also be hardened well, making it easier to achieve uniform hardness in the structural member 100.

[0073] The configuration of the steel plates 31 and 32 in this embodiment can also be applied to the structural member 100A according to the second embodiment.

[0074] While embodiments relating to this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible as long as they do not deviate from its spirit.

[0075] In the above embodiments, examples of the shape of the member body 10 are shown, but the shape of the member body 10 is not limited to the examples in the above embodiments. For example, in the examples of the above embodiments, the heights of the vertical walls 111, 112, 141, and 142 are greater than the height of the protrusion 121. However, as shown in Figure 7, the height of the protrusion 121 may be substantially the same as the heights of the vertical walls 111 and 112.

[0076] In the embodiments described above, examples were given in which the structural members 100 and 100A are battery boxes. However, the structural members 100 and 100A are not limited to this and may be, for example, the floor of a vehicle. That is, the member body 10 may be a floor panel. In this case, the member body 10 includes at least a pair of vertical walls 111 and 112 and a bottom plate 12. The member body 10 may further include flanges 13 continuous with the vertical walls 111 and 112. The member body 10 may not include vertical walls 141 and 142. [Examples]

[0077] The present disclosure will be further described below with reference to examples. However, the present disclosure is not limited to the following examples.

[0078] [First Embodiment] To confirm the effects of this disclosure, CAE analysis was performed using commercially available software (AUTOFORM R.10, manufactured by AUTOFORM) while changing the type and thickness of the steel plates forming the structural members for the vehicle.

[0079] [Table 1]

[0080] Table 1 shows the types of steel sheets (materials) used in this analysis. For each material, Table 1 shows the content (mass%) of each element in the base material and the coefficient A calculated by the above formula (1).

[0081] The conditions and results of the analysis in this embodiment are shown in Table 2. In Table 2, material (1) forms the main body of the structural member, and material (2) forms the reinforcing plate of the structural member. The thickness of material (1) is 1.0 mm, and the thickness of material (2) is 1.2 mm.

[0082] [Table 2]

[0083] In Table 2, "Time to reach 910°C" refers to the time it takes for the material (1) to reach 910°C (A) from the start of heating the blank. c3 This is the time required to reach a temperature of 910°C or higher. "Heating completion time" is the time required for the slowest heating point in the blank to reach 910°C from the start of heating of the blank until it is ready for hot stamping. "Process window (PW)" is the value obtained by subtracting the heating completion time from the time obtained by adding the allowable heating time (250 seconds) after the material (1) reaches 910°C to the time to reach 910°C. The larger this value, the wider the process window for heating conditions in hot stamping of structural members.

[0084] Referring to Table 2, in Example 1, the amount of aluminum-based plating layer attached to material (2) was 40 g / m². 2 This is less than the amount of aluminum-based plating layer attached to material (1). Similarly, in Example 3, the amount of aluminum-based plating layer attached to material (2) was 60 g / m². 2 This is less than the amount of aluminum-based plating layer attached to material (1). On the other hand, in Comparative Example 1, where the combination of material types is the same as in Examples 1 and 3, the amount of aluminum-based plating layer attached to materials (1) and (2) was 80 g / m². 2 They are identical. In Examples 1 and 3, since material (2) was thinly plated, the heating of the overlapping area between material (1) and material (2) was accelerated, and the time required to complete heating of the blank was shortened compared to Comparative Example 1. As a result, in Example 1, the process window was extended by 25 seconds compared to Comparative Example 1. In Example 3, the process window was extended by 10 seconds compared to Comparative Example 1.

[0085] In Example 2, the amount of aluminum-based plating layer adhering to material (2) was 40 g / m². 2 This is less than the amount of aluminum-based plating layer deposited on material (1). In Comparative Example 2, where the combination of material types is the same as in Example 2, the amount of aluminum-based plating layer deposited on materials (1) and (2) was 80 g / m². 2 They are identical. In Example 2, since material (2) was thinly plated, the heating of the overlapping area between material (1) and material (2) was accelerated, and the time required to complete heating of the blank was shortened compared to Comparative Example 2. As a result, in Example 2, the process window was extended by 25 seconds compared to Comparative Example 2.

[0086] For Example 1 and Comparative Example 1, the productivity of structural members and the ratio of greenhouse gas emissions were evaluated. The evaluation results are shown in Table 3.

[0087] [Table 3]

[0088] As shown in Table 3, in Example 1, the time required to complete the heating of the blanks was shortened compared to Comparative Example 1 (Table 2), resulting in improved productivity of structural members compared to Comparative Example 1. In addition, in Example 1, the time required to complete the heating of the blanks was shortened compared to Comparative Example 1, and the energy consumption required for manufacturing the structural members was reduced, thus reducing the greenhouse gas emission ratio during manufacturing. In Table 3, "productivity" refers to the number of blanks (structural members) that can be heated per minute in the heating furnace. "Greenhouse gas emission ratio" is the ratio of greenhouse gas emissions to those in Comparative Example 1. The amount of greenhouse gas emissions during the heating process was calculated by assuming the production of components at the productivity shown in Table 3, with a multi-stage electric heating furnace for hot stamping blanks having a power consumption of 450 kWh per hour, a furnace temperature of 920°C, a daily operating time of 15 hours, and a heating and waiting time of 3 hours inside the furnace. This was then allocated to the power consumption per structural component and multiplied by the greenhouse gas intensity per kWh of average Japanese electricity in 2018 (LCA database, AIST IDEAv3.2). Other greenhouse gas emissions (excluding the heating process) during the production of structural components were calculated using the method described in the publicly available literature on LCA calculations for automotive parts (Masahiro Kubo, et al., "Evaluation of Greenhouse Gas Emissions in the Life Cycle of Lightweight Steel Body and Parts," Proceedings of the Spring Conference, Society of Automotive Engineers of Japan, 2022).

[0089] [Second Example] The same analysis as in the first embodiment was performed while changing the type (material type) and thickness of the steel plate used to form the structural members of the vehicle. The steel plate used as the material was selected from those shown in Table 1, as in the first embodiment.

[0090] Table 4 shows the analysis conditions and results for this embodiment. Similar to the first embodiment, material (1) forms the main body of the structural member, and material (2) forms the reinforcing plate of the structural member. The thickness of material (1) is 1.0 mm, and the thickness of material (2) is 1.2 mm.

[0091] [Table 4]

[0092] As shown in Table 4, in Examples 4 and 5, the coefficient A1 of material (1) is greater than the coefficient A2 of material (2). In contrast, in Comparative Examples 3 and 4, the coefficient A1 of material (1) is equal to the coefficient A2 of material (2). The coefficient A1 of material (1) in Comparative Examples 3 and 4 is equal to the coefficient A2 of material (2) in Examples 4 and 5, respectively.

[0093] As mentioned above, coefficient A corresponds to the transformation onset time for each material when only the influence of the elements is considered. However, the actual transformation onset time for each material is also affected by the plate thickness, and becomes shorter as the plate thickness decreases. The "phase transformation onset time" in Table 4 is the shortest time from when the blank is heated at a furnace temperature of 920°C for 5 minutes and 30 seconds and removed from the furnace until the phase transformation to ferrite begins (the time until the thinnest material begins the phase transformation). As shown in Table 4, the phase transformation onset times were longer in Examples 4 and 5 compared to Comparative Examples 3 and 4. For example, comparing Example 4 and Comparative Example 3, which are under the same conditions except for the material of material (1), it can be seen that the phase transformation onset time in Example 4 is later than in Comparative Example 3. In Example 4, the coefficient A1 of material (1) is larger than the coefficient A2 of material (2), and the hardenability of material (1) is higher than that of material (2). On the other hand, in Comparative Example 3, the coefficient A1 of material (1) is equal to the coefficient A2 of material (2), and the hardenability of material (1) is equivalent to that of material (2). In Example 4, by making the hardenability of material (1) higher than that of material (2), the phase transformation start time of material (1) was extended compared to Comparative Example 3, and the phase transformation start time of material (1) and the phase transformation start time of the relatively thick material (2) were made uniform. Therefore, in Example 4, after the heating of the blank is completed, it becomes easier to start forming before the phase transformation to ferrite begins in material (1) that has parts that do not overlap with other materials (2), and the structural members become more uniformly hardened. The same can be said for Example 5 and Comparative Example 4, which are under the same conditions except for the material of material (1).

[0094] For Example 4 and Comparative Example 3, the variation in martensite fraction was measured. Separately, shape accuracy measurements were performed on these structural members. The results of each evaluation are shown in Table 5.

[0095] [Table 5]

[0096] The variation in martensite fraction was measured as follows: Ten or more analytical samples (for example, approximately 10 mm in size on the longer side) were cut from the cross-section of the structural member at the flange position of the structural member, at a distance of 20 mm or more from the end and at a distance of 10 mm or more from each other. Each sample was then polished and etched with a repelling agent so that the thickness direction was the observation surface. After that, an optical microscope was used to observe the analytical sample at a position 1 / 4 of the way from the surface in the thickness direction at a magnification of 1000x, and an optical microscope image was obtained. The obtained optical microscope image was analyzed using commercially available image analysis software (Photoshop CS5, Adobe), for example, to determine the martensite area ratio and use it as the martensite fraction.

[0097] As an image analysis method, the maximum brightness value L of the image is used. max and minimum brightness value L min The values ​​are obtained from the image, and the brightness is L max -0.3(L max -L min ) from L max The area containing up to a certain number of pixels was defined as the white region, and the martensite fraction was measured by calculating the ratio of the number of pixels in the white region to the total number of pixels. This image analysis was performed on a total of 10 observation fields for each analysis sample to determine the martensite fraction, and the average value was taken as the martensite fraction for each analysis sample. Furthermore, the difference between the maximum and minimum values ​​of the martensite fraction in 10 or more analysis samples was defined as the variation in the martensite fraction in the cross-section of the structural member at the flange position of the structural member.

[0098] Shape accuracy was evaluated by measuring the distance between the structural member and the mating member at the overlapping portion when the structural member was attached to another member. In Table 5, ○ indicates a distance of ±2.0 mm or less from the surface of the mating member, and △ indicates a distance greater than ±2.0 mm but within ±3.0 mm.

[0099] In Example 4, shown in Table 5, A1-A2>0 is satisfied, whereas in Comparative Example 3, A1-A2=0. In Comparative Example 3, the variation in martensite fraction was 15%, while in Example 4, the variation in martensite fraction was reduced to 5% or less. In Example 4, the shape accuracy was also better compared to Comparative Example 3.

[0100] [Third Embodiment] We investigated the collision resistance performance of structural members by performing load-load simulation analysis using general-purpose structural analysis software (LS-DYNA, manufactured by Ansys). In this analysis, we examined the deformation of structural members by impacting them with an object from the side. The conditions and results of this analysis are shown in Table 6.

[0101] [Table 6]

[0102] Referring to Table 6, the structural member in Example 6 includes the member body and reinforcing plates. The structural members in Comparative Examples 5 and 6 are formed only from the member body and do not include reinforcing plates. The structural members in Example 6 and Comparative Example 5 were manufactured by hot stamping on hot-stamping steel plates. The structural member in Comparative Example 6 was manufactured by cold-pressing mild steel. In Example 6, the tensile strength of the member body and reinforcing plates after hot stamping is 1500 MPa. The tensile strength of the member body in Comparative Example 5 is 1500 MPa, and the tensile strength of the member body in Comparative Example 6 is 270 MPa. The thickness of the member body was 0.8 mm, and the thickness of the reinforcing plate was 1.0 mm.

[0103] In Example 6 and Comparative Example 6, a protrusion is provided on the bottom plate of the member body, but in Comparative Example 5, no protrusion is provided. The width of the protrusion in Example 6 is 50 mm and the height of the protrusion is 25 mm. The width of the protrusion in Comparative Example 6 is 50 mm and the height of the protrusion is 10 mm.

[0104] Figure 8 shows the deformation behavior of the structural member according to Example 6. Figure 9 shows the deformation behavior of the structural member according to Comparative Example 6. As shown in Figure 8 and Table 6, in Example 6, in which a protrusion was provided on the bottom plate of the member body and the protrusion was covered with a reinforcing plate, almost no deformation of the structural member occurred even when an object collided with it from the direction of extension of the protrusion. In Example 6, a maximum load of 100kN or more was confirmed.

[0105] On the other hand, as shown in Figure 9, in Comparative Example 6, where a protrusion is provided on the bottom plate of the member body but there is no reinforcing plate, deformation occurred in which the member body bent at the point of impact with the structural member. Therefore, in Comparative Example 6, the load on the structural member during impact was significantly lower compared to Example 6. The same results were obtained for Comparative Example 5, which does not have a protrusion on the bottom plate of the member body and also does not have a reinforcing plate.

[0106] This analysis confirmed that by providing a protrusion on the bottom plate of the main body of the structural member and covering the protrusion with a reinforcing plate, the structural member exhibits good collision resistance. [Explanation of Symbols]

[0107] 100, 100A: Structural members 10: Main body component 111,112: Vertical wall 12: Bottom plate 121: Convex part 13: Flange 20: Reinforcement plate

Claims

1. A structural component for a vehicle, A member body including a pair of opposing vertical walls, a base plate connecting the vertical walls and including a protrusion extending from one vertical wall to the other, The system includes a reinforcing plate that extends from one vertical wall to the other, covering the protrusion, and is joined to the main body of the member, The member body is a tray for a battery box, and further includes a flange that is connected to each of the vertical walls on the opposite side of the bottom plate and protrudes outward from the member body.

2. A structural member according to claim 1, The reinforcing plate is a structural member that further covers the flange.

3. A structural member according to claim 2, The reinforcing plate is a structural member that is joined to the outer surface of the main body of the member.

4. A structural member according to claim 1, The member body and the reinforcing plate are each formed from a plated steel sheet having a base steel sheet and an aluminum-based plating layer covering both surfaces of the base steel sheet. A structural member wherein the thickness of the aluminum-based plating layer on the reinforcing plate is smaller than the thickness of the aluminum-based plating layer on the main body of the member.

5. A structural member according to claim 4, The reinforcing plate is a structural member that is joined to the inner surface of the main body of the member.

6. A structural member according to claim 1, The main body of the member and the reinforcing plate are each formed from steel plates. A structural member wherein the value of coefficient A calculated by the following formula (1) using the chemical composition of the steel plate forming the main body of the member is greater than the value of coefficient A calculated by the following formula (1) using the chemical composition of the steel plate forming the reinforcing plate. A=1.48×(2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr+2×Mo) ３．４２ (1) However, the elemental symbols in formula (1) above are substituted with the content (mass%) of the corresponding element.

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