Structural member and production method therefor

Abstract

A structural member (10) comprises vertical walls (131, 132), first flange ridges (141, 142), first flanges (151, 152), second flange ridges (161, 162), and second flanges (171, 172). The first flanges (151, 152) are connected to the vertical walls (131, 132) via the first flange ridges (141, 142). The second flanges (171, 172) are connected to the vertical walls (131, 132), the first flange ridges (141, 142) and the first flanges (151, 152) via the second flange ridges (161, 162). In a cross-section of the structural member (10), when the radius of curvature of a portion of the second flange ridges (161, 162) adjacent to the first flange ridges (141, 142) is defined as RL, and the thickness of the structural member (10) is defined as t, RL / t < 23.0.

Description

Structural member and method for manufacturing the same 【0001】 The present disclosure relates to a structural member and a method for manufacturing the same. 【0002】 For example, a vehicle such as an automobile is formed using structural members. The structural members may be manufactured by press forming a blank. 【0003】 Patent Document 1 discloses a method for manufacturing a press-formed product. In Patent Document 1, the press-formed product is, for example, a floor cross member, a seat cross member, a side sill, or a side member for an automobile. The press-formed product includes a top plate, vertical walls, a lower flange, and end flanges. The vertical walls are provided on both sides of the top plate. The vertical walls are each connected to the top plate via a convex ridge line portion. A lower flange is connected to each of the vertical walls via a lower concave ridge line portion. The end flanges are connected to the ends of the top plate, the ends of the convex ridge line portions, and the ends of the vertical walls in the longitudinal direction of the press-formed product via end concave ridge line portions. The end flanges are also connected to the lower flange via a curved portion. 【0004】 In Patent Document 1, the press-formed product is formed by subjecting a blank to cold press working. In Patent Document 1, for example, a pad provided on a punch is used to bend a portion of the blank that becomes the top plate. Thereafter, portions of the blank that become the end concave ridge line portions, the top plate, the vertical walls, and the end flanges are constrained by the punch and the die to form the press-formed product. 【0005】 International Publication No. 2019 / 216317 【0006】 Some structural members are required to have energy absorption performance. For example, in the case of a structural member for a vehicle, it is required to absorb impact energy when the vehicle is subjected to an impact such as a collision. 【0007】 An object of the present disclosure is to provide a structural member capable of improving energy absorption performance. 【0008】The structural member according to the present disclosure includes a vertical wall, a top plate ridge line portion, a top plate, a first flange ridge line portion, a first flange, a second flange ridge line portion, and a second flange. The top plate ridge line portion is continuous with one end of the vertical wall in the height direction of the structural member. The top plate is connected to the vertical wall via the top plate ridge line portion. The first flange ridge line portion is continuous with the other end of the vertical wall in the height direction. The first flange is connected to the vertical wall via the first flange ridge line portion. The second flange ridge line portion is disposed at an end in the longitudinal direction of the structural member. The second flange ridge line portion is continuous with the vertical wall, the first flange ridge line portion, and the first flange. The second flange is connected to the vertical wall, the first flange ridge line portion, and the first flange via the second flange ridge line portion. In the cross section of the structural member, the radius of curvature of the portion of the second flange ridge line portion adjacent to the first flange ridge line portion is R Ｌ , when the plate thickness of the structural member is t, R Ｌ / t < 23.0. 【0009】 According to the present disclosure, the energy absorption performance of the structural member can be improved. 【0010】 FIG. 1 is a perspective view of a structural member according to an embodiment. FIG. 2 is another perspective view of the structural member according to the embodiment. FIG. 3 is a longitudinal sectional view (III-III sectional view) of the structural member shown in FIG. 1. FIG. 4 is a cross-sectional view (IV-IV sectional view) of the structural member shown in FIG. 1. FIG. 5A is a schematic diagram for explaining a manufacturing method of the structural member according to the embodiment. FIG. 5B is a schematic diagram for explaining a manufacturing method of the structural member according to the embodiment. FIG. 5C is a schematic diagram for explaining a manufacturing method of the structural member according to the embodiment. FIG. 5D is a schematic diagram for explaining a manufacturing method of the structural member according to the embodiment. FIG. 5E is a schematic diagram for explaining a manufacturing method of the structural member according to the embodiment. FIG. 6 is a perspective view of a structural member according to a modified example of the embodiment. FIG. 7 is a graph showing the relationship between R Ｌ / t and the energy absorption amount per unit weight of the structural member. FIG. 8 is a graph showing the relationship between R Ｕ / t and the energy absorption amount per unit weight of the structural member. FIG. 9 is a graph showing the relationship between θ and the energy absorption amount per unit weight of the structural member. FIG. 10 is a graph showing the energy absorption amount L of the structural member ＵIt is a graph shown for each case. 【0011】 The structural member according to the embodiment includes a vertical wall, a top plate ridge line portion, a top plate, a first flange ridge line portion, a first flange, a second flange ridge line portion, and a second flange. The top plate ridge line portion is continuous with one end of the vertical wall in the height direction of the structural member. The top plate is connected to the vertical wall via the top plate ridge line portion. The first flange ridge line portion is continuous with the other end of the vertical wall in the height direction. The first flange is connected to the vertical wall via the first flange ridge line portion. The second flange ridge line portion is disposed at an end in the longitudinal direction of the structural member. The second flange ridge line portion is continuous with the vertical wall, the first flange ridge line portion, and the first flange. The second flange is connected to the vertical wall, the first flange ridge line portion, and the first flange via the second flange ridge line portion. In the cross section of the structural member, the radius of curvature of the portion of the second flange ridge line portion adjacent to the first flange ridge line portion is R Ｌ , when the plate thickness of the structural member is t, R Ｌ / t < 23.0 (first configuration). 【0012】 The structural member according to the first configuration includes a first flange and a second flange. The first flange and the second flange are each connected to the vertical wall via the first flange ridge line portion and the second flange ridge line portion, and are also connected to each other via the second flange ridge line portion. With this configuration, when an impact is input to the structural member, for example, in the longitudinal direction, the impact energy is more easily absorbed. In addition, in the first configuration, the radius of curvature R Ｌ of the portion of the second flange ridge line portion adjacent to the first flange ridge line portion is set to satisfy R Ｌ / t < 23.0 together with the plate thickness t of the structural member. In this case, when the structural member receives an impact, the impact energy is more easily absorbed. Therefore, according to the first configuration, the energy absorption performance of the structural member can be improved. 【0013】The structural member relating to the first configuration may further include a third flange ridge and a third flange. The third flange ridge is continuous with the second flange ridge and also continuous with the top plate and the top plate ridge. The third flange is connected to the top plate and the top plate ridge via the third flange ridge. The third flange is continuous with the second flange (second configuration). 【0014】 The structural member relating to the second configuration is provided with a third flange continuous with the second flange. The third flange is connected to the top plate and the top plate edge via the third flange ridge. In this case, when an impact is applied to the structural member, for example in the longitudinal direction, the impact energy is absorbed more easily. Therefore, the energy absorption performance of the structural member is more easily improved. 【0015】 In the structural member relating to the second configuration, the radius of curvature of the portion of the top plate ridge adjacent to the third flange ridge in the cross-section of the structural member is R Ｕ When the thickness of the structural member is t, R Ｕ / t ≤ 8.0 is also acceptable (third configuration). 【0016】 In the structural member relating to the second or third configuration, the angle that the third flange makes with the top plate may be 90° or more and less than 140° (fourth configuration). 【0017】 In the fourth configuration, the angle between the third flange and the top plate is between 90° and 140°. This makes it easier to further improve the energy absorption performance of the structural members. 【0018】 In a structural member relating to any of the second to fourth configurations, the length from the end of the third flange on the third flange ridge side to the opposite end may be 10 mm or more (fifth configuration). 【0019】In the fifth configuration, the length of the third flange from one end on the ridge side to the other end is 10 mm or more. In this case, a larger space can be secured in the third flange for arranging joints between the structural member and other members. Therefore, for example, the number of joints between the structural member and other members can be increased. This makes it easier to improve the energy absorption performance of the structural member. In addition, the rigidity of the structural member can also be increased. 【0020】 A structural member relating to any of the first to fifth configurations may have a Vickers hardness of 250 HV or more (sixth configuration). 【0021】 In a structural member relating to any of the first to sixth configurations, the top plate may have a width of 200 mm or less (seventh configuration). 【0022】 A method for manufacturing a structural member according to an embodiment comprises the steps of preparing a blank and forming a structural member from the blank using a mold including an upper mold and a lower mold. The structural member includes a vertical wall, a top plate ridge, a top plate, a first flange ridge, a first flange, a second flange ridge, and a second flange. The top plate ridge is continuous with one end of the vertical wall in the height direction of the structural member. The top plate is connected to the vertical wall via the top plate ridge. The first flange ridge is continuous with the other end of the vertical wall in the height direction. The first flange is connected to the vertical wall via the first flange ridge. The second flange ridge is located at the end of the structural member in the longitudinal direction. The second flange ridge is continuous with the vertical wall, the first flange ridge, and the first flange. The second flange is connected to the vertical wall, the first flange ridge, and the first flange via the second flange ridge. In the molding process, the upper mold is brought close to the lower mold from the outside in the width direction of the lower mold, and the blank is clamped between the upper and lower molds. In the cross-section of the structural member, the radius of curvature of the portion of the second flange ridge adjacent to the first flange ridge is R Ｌ When the thickness of the structural member is t, R Ｌ / t < 23.0 (the eighth configuration). 【0023】In the manufacturing method relating to the eighth configuration, the upper die is brought close to the lower die from the outside in the width direction, and the blank is press-formed to create a structural member including the first flange and the second flange. By operating the die in this manner, the material flows more easily from the outside to the inside of the blank when forming the structural member. Therefore, cracks are less likely to occur in the structural member during forming. In particular, the reduction in plate thickness is easily suppressed in the portion of the second flange ridge adjacent to the first flange ridge. Therefore, the radius of curvature R of the portion of the second flange ridge adjacent to the first flange ridge Ｌ When R is relatively small relative to the plate thickness t, specifically R Ｌ Even when / t < 23.0, the structural member can be formed while suppressing cracking in that area. 【0024】 In the manufacturing method relating to the eighth configuration, the structural member may be formed by hot pressing of the blank during the molding process (ninth configuration). 【0025】 In the ninth configuration, the structural members are formed by hot pressing of the blanks. In this case, cracking of the structural members is less likely to occur during forming. 【0026】 Embodiments of this disclosure will be described below with reference to the drawings. In these drawings, the same or equivalent components are denoted by the same reference numerals, and the same description will not be repeated. 【0027】 [Structural Member Composition] Figures 1 and 2 are perspective views of the structural member 10 according to this embodiment. As shown in Figures 1 and 2, the structural member 10 is a long, rectangular member. The structural member 10 is formed from, for example, a metal plate. The structural member 10 may also be formed from a steel plate. 【0028】 The structural member 10 is used, for example, in a vehicle. The structural member 10 may be a cross member for a battery pack. In this case, the structural member 10 is placed inside the battery box and can extend in the left-right direction of the vehicle. Alternatively, the structural member 10 may be a cross member for the floor. In this case, the structural member 10 is placed on the floor and can extend in the left-right direction of the vehicle. However, the applications of the structural member 10 are not limited to these. 【0029】 The structural member 10 comprises a top plate 11, top plate ridges 121, 122, vertical walls 131, 132, first flange ridges 141, 142, first flanges 151, 152, second flange ridges 161, 162, and second flanges 171, 172. The structural member 10 may further comprise a third flange ridge 18 and a third flange 19. 【0030】 Referring to Figure 1, the top plate 11 extends in the longitudinal direction of the structural member 10. The top plate 11 is connected to the vertical wall 131 via the top plate ridge 121. That is, the top plate ridge 121 is positioned between the top plate 11 and the vertical wall 131. The top plate ridge 121 is continuous with the top plate 11 on one side in the width direction of the structural member 10. The top plate ridge 121 extends along the top plate 11 in the longitudinal direction of the structural member 10. The top plate ridge 121 is continuous with one end of the vertical wall 131 in the height direction of the structural member 10. The vertical wall 131 extends along the top plate ridge 121 in the longitudinal direction of the structural member 10. 【0031】 The first flange 151 is connected to the vertical wall 131 via the first flange ridge 141. That is, the first flange ridge 141 is positioned between the vertical wall 131 and the first flange 151. The first flange ridge 141 is the corner portion between the vertical wall 131 and the first flange 151. The first flange ridge 141 is continuous with the other end of the vertical wall 131 in the height direction of the structural member 10. In other words, the first flange ridge 141 is continuous with the vertical wall 131 on the opposite side of the top plate ridge 121. The first flange ridge 141 extends along the vertical wall 131 in the longitudinal direction of the structural member 10. The first flange ridge 141 is also continuous with the first flange 151. The first flange 151 protrudes outward from the first flange ridge 141 in the width direction of the structural member 10. The first flange 151 extends along the first flange ridge 141 in the longitudinal direction of the structural member 10. 【0032】The second flange ridge section 161 is positioned at the longitudinal end of the structural member 10. The second flange ridge section 161 is continuous with the vertical wall 131, the first flange ridge section 141, and the first flange 151. The second flange ridge section 161 includes ridge section bodies 161a and 161b and a corner section 161c. 【0033】 The ridge section body 161a is the portion of the second flange ridge section 161 adjacent to the vertical wall 131. The ridge section body 161a extends along the vertical wall 131 in the height direction of the structural member 10. The ridge section body 161b is the portion of the second flange ridge section 161 adjacent to the first flange 151. The ridge section body 161b extends along the first flange 151 in the width direction of the structural member 10. The ridge section bodies 161a and 161b are connected by a corner section 161c. The corner section 161c is the portion of the second flange ridge section 161 adjacent to the first flange ridge section 141. 【0034】 The second flange 171, like the second flange ridge 161, is positioned at the longitudinal end of the structural member 10. The second flange 171 is connected to the vertical wall 131, the first flange ridge 141, and the first flange 151 via the second flange ridge 161. The second flange ridge 161 is a corner portion that connects the second flange 171 to the vertical wall 131, the first flange ridge 141, and the first flange 151. The second flange 171 is provided continuously with the second flange ridge 161. The second flange 171 protrudes outward from the second flange ridge 161 in the width direction of the structural member 10. 【0035】 The third flange ridge portion 18 and the third flange 19 are positioned at the longitudinal end of the structural member 10, similar to the second flange ridge portion 161 and the second flange 171. The third flange ridge portion 18 is continuous with the second flange ridge portion 161. The third flange ridge portion 18 is also continuous with the top plate 11 and the top plate ridge portion 121. 【0036】The third flange 19 is connected to the top plate 11 via the third flange ridge 18. The third flange 19 protrudes outward from the third flange ridge 18 in the height direction of the structural member 10. The third flange 19 is also connected to the top plate ridge 121 via the third flange ridge 18. The third flange 19 is continuous with the second flange 171. 【0037】 When the structural member 10 is used in a vehicle, the height direction of the structural member 10 corresponds to the vertical direction of the vehicle. The width direction of the structural member 10 is perpendicular to the longitudinal direction and height direction of the structural member 10. When the structural member 10 is used in a vehicle, the longitudinal direction of the structural member 10 may correspond to the left-right direction of the vehicle. In this case, the width direction of the structural member 10 corresponds to the front-rear direction of the vehicle. Alternatively, the longitudinal direction of the structural member 10 may correspond to the front-rear direction of the vehicle. In this case, the width direction of the structural member 10 corresponds to the left-right direction of the vehicle. 【0038】 Referring to Figure 2, the top plate 11 is connected to the vertical wall 132 via the top plate ridge 122. That is, the top plate ridge 122 is positioned between the top plate 11 and the vertical wall 132. The top plate ridge 122 is continuous with the top plate 11 on the opposite side of the top plate ridge 121 in the width direction of the structural member 10. The top plate ridge 122 extends along the top plate 11 in the longitudinal direction of the structural member 10. The top plate ridge 122 is continuous with one end of the vertical wall 132 in the height direction of the structural member 10. The vertical wall 132 extends along the top plate ridge 122 in the longitudinal direction of the structural member 10. 【0039】The first flange 152 is connected to the vertical wall 132 via the first flange ridge 142. That is, the first flange ridge 142 is positioned between the vertical wall 132 and the first flange 152. The first flange ridge 142 is the corner portion between the vertical wall 132 and the first flange 152. The first flange ridge 142 is continuous with the other end of the vertical wall 132 in the height direction of the structural member 10. In other words, the first flange ridge 142 is continuous with the vertical wall 132 on the opposite side of the top plate ridge 122. The first flange ridge 142 extends along the vertical wall 132 in the longitudinal direction of the structural member 10. The first flange ridge 142 is also continuous with the first flange 152. The first flange 152 protrudes outward from the first flange ridge 142 in the width direction of the structural member 10. The first flange 152 extends along the first flange ridge 142 in the longitudinal direction of the structural member 10. 【0040】 The second flange ridge section 162 and the second flange 172 are positioned at the longitudinal end of the structural member 10, similar to the second flange ridge section 161 and the second flange 171 (Figure 1). The second flange ridge section 162 is continuous with the vertical wall 132, the first flange ridge section 142, and the first flange 152. The second flange ridge section 162 includes ridge section bodies 162a and 162b and corner sections 162c. 【0041】 The ridge section body 162a is the portion of the second flange ridge section 162 adjacent to the vertical wall 132. The ridge section body 162a extends along the vertical wall 132 in the height direction of the structural member 10. The ridge section body 162b is the portion of the second flange ridge section 162 adjacent to the first flange 152. The ridge section body 162b extends along the first flange 152 in the width direction of the structural member 10. The ridge section bodies 162a and 162b are connected by a corner section 162c. The corner section 162c is the portion of the second flange ridge section 162 adjacent to the first flange ridge section 142. 【0042】The second flange 172 is connected to the vertical wall 132, the first flange ridge 142, and the first flange 152 via the second flange ridge 162. The second flange ridge 162 is a corner portion that connects the second flange 172 to the vertical wall 132, the first flange ridge 142, and the first flange 152. The second flange 172 is provided continuously with the second flange ridge 162. The second flange 172 protrudes outward from the second flange ridge 162 in the width direction of the structural member 10. 【0043】 In this embodiment, the third flange ridge portion 18 is continuous with the top plate 11, the top plate ridge portion 121, and the second flange ridge portion 161 (Figure 1), as well as the top plate ridge portion 122 and the second flange ridge portion 162. The third flange 19 is connected to the top plate ridge portion 122 via the third flange ridge portion 18. The third flange 19 is continuous with the second flange 172. 【0044】 Figure 3 is a longitudinal cross-sectional view (III-III cross-section) of the structural member 10 shown in Figure 1. The longitudinal cross-section of the structural member 10 refers to the cross-section obtained when the structural member 10 is cut along its longitudinal and height directions. In Figure 3, the longitudinal cross-section of the structural member 10 at the center position in the width direction of the top plate 11 is shown. 【0045】 As shown in Figure 3, the structural member 10 according to this embodiment is provided with a third flange 19. A third flange ridge 18 is positioned between the third flange 19 and the top plate 11. The third flange ridge 18 is the corner portion between the third flange 19 and the top plate 11. At least the portion of the third flange 19 adjacent to the third flange ridge 18 has a straight shape in a longitudinal cross-sectional view of the structural member 10. The third flange 19 may have a straight shape overall in a longitudinal cross-sectional view of the structural member 10. At least the portion of the top plate 11 adjacent to the third flange ridge 18 has a straight shape in a longitudinal cross-sectional view of the structural member 10. The third flange ridge 18 is smoothly connected to the top plate 11 and the third flange 19. The third flange ridge 18 may have a substantially arc shape in a longitudinal cross-sectional view of the structural member 10. 【0046】The third flange 19 stands upright in the height direction of the structural member 10 relative to the top plate 11. The third flange 19 forms an angle θ with the top plate 11. The angle θ is the angle that the third flange 19 forms with the top plate 11 in the vertical cross-section of the structural member 10 at the center of the width direction of the top plate 11. The angle θ is, for example, 90° or more and 150° or less, preferably 90° or more and less than 140°. The angle θ is more preferably 90° or more and less than 120°, and even more preferably 90° or more and less than 110°. Particularly preferably, the angle θ is 90° or more and less than 100°. The angle θ may be 90° or more and 130° or less, or 90° or more and 110° or less. 【0047】 The third flange 19 has a length L Ｕ It has length L. Ｕ It may be 10 mm or more. Length L Ｕ The length L is preferably 15 mm or more. Ｕ For example, it is 50 mm or less, and preferably 30 mm or less. 【0048】 Length L Ｕ L is the length from the end of the third flange 19 on the third flange ridge 18 side to the opposite end (open end). The end of the third flange 19 on the third flange ridge 18 side is the R-end of the third flange ridge 18 on the third flange 19 side. Ｕ This can be measured along the outer surface of the third flange 19 in the longitudinal cross-section of the structural member 10 at the center position in the width direction of the top plate 11. 【0049】Figure 4 is a cross-sectional view (IV-IV section) of the structural member 10 shown in Figure 1. The cross-section of the structural member 10 refers to the cross-section obtained when the structural member 10 is cut intersecting its longitudinal direction. Figure 4 shows the cross-section of the structural member 10 when cut along one end in the longitudinal direction of the top plate 11 and the vertical walls 131 and 132. In this embodiment, one end in the longitudinal direction of the top plate 11 is the boundary between the third flange ridge 18 and the top plate 11, that is, the R-end of the third flange ridge 18 on the top plate 11 side. One end in the longitudinal direction of the vertical wall 131 is the boundary between the second flange ridge 161 and the vertical wall 131, that is, the R-end of the second flange ridge 161 on the vertical wall 131 side. One end of the vertical wall 132 in the longitudinal direction is the boundary between the second flange ridge portion 162 and the vertical wall 132, that is, the end of the R-shaped portion of the second flange ridge portion 162 on the vertical wall 132 side. 【0050】 As shown in Figure 4, the top plate 11 is connected to the vertical walls 131 and 132 via top plate edges 121 and 122. The top plate 11 has a straight shape in cross-sectional view of the structural member 10, at least in the portion adjacent to the top plate edges 121 and 122. The vertical walls 131 and 132 each have a straight shape in cross-sectional view of the structural member 10, at least in the portion adjacent to the top plate edges 121 and 122. The top plate edge 121 is the corner portion between the top plate 11 and the vertical wall 131. The top plate edge 122 is the corner portion between the top plate 11 and the vertical wall 132. The top plate edges 121 and 122 are smoothly connected to the top plate 11 and the vertical walls 131 and 132, respectively. The top plate edges 121 and 122 may have a substantially arc shape in cross-sectional view of the structural member 10. 【0051】 The top plate 11 has a width W. The width W is the distance in the width direction of the structural member 10 on the outer surface of the structural member 10 from the boundary between the top plate 11 and the top plate ridge portion 121 to the boundary between the top plate 11 and the top plate ridge portion 122. The boundary between the top plate 11 and the top plate ridge portion 121 is the end of the radius on the top plate 11 side of the top plate ridge portion 121. The boundary between the top plate 11 and the top plate ridge portion 122 is the end of the radius on the top plate 11 side of the top plate ridge portion 122. If the distance in the width direction of the structural member 10 from the boundary between the top plate 11 and the top plate ridge portion 121 to the boundary between the top plate 11 and the top plate ridge portion 122 changes along the longitudinal direction of the structural member 10, the minimum value of this distance is taken as the width W of the top plate 11. 【0052】 The width W is, for example, 200 mm or less. The width W may be 100 mm or less, or 50 mm or less. The width W may be 30 mm or less, or 15 mm or less. The width W is, for example, 5 mm or more. 【0053】 In the cross-section of the structural member 10, the radius of curvature of the portions of the top plate ridges 121 and 122 adjacent to the third flange ridge 18 is R Ｕ When the plate thickness of the structural member 10 is t, R Ｕ / t ≤ 12.0 is also acceptable. Radius of curvature R Ｕ And the plate thickness t is R Ｕ It is preferable that / t ≤ 8.0. The radius of curvature R is not particularly limited. Ｕ And the plate thickness t is 0.5 ≤ R Ｕ / t can be satisfied. 【0054】 Radius of curvature R of the top plate ridges 121 and 122 Ｕ This is measured in the cross-section of the structural member 10 when cut along the longitudinal ends of the top plate 11 and vertical walls 131, 132. Radius of curvature R of the top plate ridge 121 Ｕ This is the radius of curvature of the arc passing through one end of the top plate ridge portion 121 on the inner surface of the bend in the cross-section of the structural member 10, the other end of the top plate ridge portion 121, and the midpoint between them. One end of the top plate ridge portion 121 is the boundary between the top plate ridge portion 121 and the top plate 11, that is, the end of the radius R on the top plate 11 side of the top plate ridge portion 121. The other end of the top plate ridge portion 121 is the boundary between the top plate ridge portion 121 and the vertical wall 131, that is, the end of the radius R on the vertical wall 131 side of the top plate ridge portion 121. Similarly, the radius of curvature R of the top plate ridge portion 122 Ｕ This is the radius of curvature of the arc passing through one end of the top plate ridge portion 122 on the inner surface of the bend, the other end of the top plate ridge portion 122, and the midpoint between them in the cross-section of the structural member 10. One end of the top plate ridge portion 122 is the boundary between the top plate ridge portion 122 and the top plate 11, that is, the end of the radius on the top plate 11 side of the top plate ridge portion 122. The other end of the top plate ridge portion 122 is the boundary between the top plate ridge portion 122 and the vertical wall 132, that is, the end of the radius on the vertical wall 132 side of the top plate ridge portion 122. 【0055】 radius of curvature R ＵThe radius of curvature R is, for example, 0.3 mm or more, and preferably 2.0 mm or more. Ｕ For example, it is 40.0 mm or less, preferably 20.0 mm or less. Radius of curvature R of the top plate ridge portion 122 Ｕ The radius of curvature R of the top plate edge portion 121 Ｕ It may be the same as, or it may be different from, it may be. 【0056】 radius of curvature R Ｕ If the cross-section of the structural member 10 on which the radius of curvature is measured is a cross-section passing through the first flanges 151 and 152, the plate thickness t is the plate thickness of the structural member 10 measured at the first flange 151 or 152 in that cross-section. The plate thickness t is measured in the cross-section of the structural member 10 at a position, for example, 1.0 mm or more away from the open end of the first flange 151 or 152. Radius of curvature R Ｕ When the cross-section of the structural member 10 on which the thickness is measured passes through the second flange ridge sections 161 and 162, the plate thickness t is the plate thickness of the structural member 10 measured at the ridge section body 161b of the second flange ridge section 161 or the ridge section body 162b of the second flange ridge section 162 in the said cross-section. The plate thickness t is measured in the cross-section of the structural member 10 at a position, for example, 5.0 mm or more away from the open end of the ridge section body 161b or 162b. The plate thickness t is, for example, 0.1 mm or more, preferably 0.8 mm or more. The plate thickness t is, for example, 5.0 mm or less, preferably 2.6 mm or less. 【0057】 When a cross-section of the structural member 10 is obtained along the longitudinal ends of the top plate 11 and vertical walls 131, 132, this cross-section includes the corner portions 161c, 162c of the second flange ridge portions 161, 162. The corner portions 161c, 162c may each have a substantially arc shape in the cross-sectional view of the structural member 10. In the cross-section of the structural member 10, the radius of curvature of the corner portions 161c, 162c is R Ｌ When the plate thickness of the structural member 10 is t, R Ｌ / t < 23.0. Radius of curvature R Ｌ And the plate thickness t is R Ｌ It is preferable that / t ≤ 20.0, and R ＬIt is more preferable that / t ≤ 8.0. While not particularly limited, the radius of curvature R is also important. Ｌ And the plate thickness t is 0.5 ≤ R Ｌ / t can be satisfied. 【0058】 Radius of curvature R of corner sections 161c and 162c Ｌ This is measured in the cross-section of the structural member 10 when cut along the longitudinal ends of the top plate 11 and vertical walls 131, 132. The radius of curvature R of the corner portion 161c. Ｌ This is the radius of curvature of the arc passing through one end of the corner portion 161c, the other end of the corner portion 161c, and the midpoint between them on the inner surface of the bend in the cross-section of the structural member 10. One end of the corner portion 161c is the R-end on the ridge portion body 161a side of the corner portion 161c. The other end of the corner portion 161c is the R-end on the ridge portion body 161b side of the corner portion 161c. Similarly, the radius of curvature R of the corner portion 162c Ｌ This is the radius of curvature of the arc passing through one end of the corner portion 162c, the other end of the corner portion 162c, and the midpoint between them on the inner surface of the bend in the cross-section of the structural member 10. One end of the corner portion 162c is the R-end on the ridge portion body 162a side of the corner portion 162c. The other end of the corner portion 162c is the R-end on the ridge portion body 162b side of the corner portion 162c. 【0059】 radius of curvature R Ｌ The radius of curvature R is, for example, 0.3 mm or more, and preferably 2.0 mm or more. Ｌ For example, it is 50.0 mm or less, preferably 20.0 mm or less. The radius of curvature R of the corner portion 161c Ｌ The radius of curvature R of the corner section 162c Ｌ It may be the same as or different from the same. The radius of curvature R of the corner portion 161c Ｌ The radius of curvature R of the top plate edge portion 121 Ｕ It may be larger than this. Radius of curvature R of corner section 162c Ｌ The radius of curvature R of the top plate edge portion 122 Ｕ It can be larger than that. 【0060】 Radius of curvature R of corner sections 161c and 162c ＬThe radius of curvature R of the top plate ridges 121 and 122. Ｕ It is measured on the same cross-section. The plate thickness t and its measurement method are as described above. 【0061】 The structural member 10 has a Vickers hardness of, for example, 300 HV or more, preferably 400 HV or more. The structural member 10 may have a Vickers hardness of 250 HV or more, or 270 HV or more, or 280 HV or more. The structural member 10 can have a tensile strength of 980 MPa or more, preferably 1180 MPa or more. 【0062】 The Vickers hardness of the structural member 10 can be obtained by performing a Vickers hardness test in accordance with JIS Z 2244:2024. Specifically, a test piece for the Vickers hardness test is cut from the flat portion of the structural member 10. The test piece can be cut, for example, from the top plate 11 of the structural member 10. Then, using this test piece, a Vickers hardness test is performed on a cross section along the thickness direction in accordance with JIS Z 2244:2024. More specifically, the Vickers hardness is measured at the center or near the center in the thickness direction of the cross section, and at a position 1 / 4 of the thickness from each of the front and back surfaces, with a test force of 300 gf (2.9 N). The average of the obtained Vickers hardness values ​​is the Vickers hardness of the structural member 10. 【0063】 [Method for Manufacturing Structural Members] Next, the method for manufacturing the structural member 10 will be described with reference to Figures 5A to 5E. The manufacturing method according to this embodiment comprises a preparation step and a molding step. The manufacturing method may further include a heating step. 【0064】 (Preparation Step) Referring to Figure 5A, the blank 20 is prepared in the preparation step. The blank 20 has the shape of the structural member 10 (Figures 1 to 4) unfolded. The blank 20 is formed from at least one metal plate. The metal plate may be a steel plate. 【0065】(Heating process) In the heating process, the blank 20 is heated. The blank 20 is heated to a temperature suitable for hot press working, for example, using a heating furnace. If the blank 20 is made of one or more steel plates, the blank 20 is heated to the austenite transformation completion temperature (A ｃ３ The temperature is heated to a certain level (10°C or higher). If the heating process is performed, in the subsequent molding process, the structural member 10 (Figures 1 to 4) is formed by hot stamping of the blank 20. 【0066】 (Molding Process) Referring to Figures 5B to 5E, in the molding process, a mold 30 is used to mold the structural member 10 from the blank 20. If a heating process is performed before the molding process, in the molding process, the heated blank 20 is molded into the structural member 10. 【0067】 First, the configuration of the mold 30 used in the molding process will be explained. As shown in Figure 5B, the mold 30 includes a lower mold 31 and upper molds 321 and 322. 【0068】 The lower mold 31 has a molding surface 311 with a shape corresponding to the structural member 10. More specifically, the molding surface 311 has portions corresponding to the top plate 11, top plate ridges 121, 122, vertical walls 131, 132, first flange ridges 141, 142, first flanges 151, 152, second flange ridges 161, 162, and second flanges 171, 172 of the structural member 10 (Figures 1 to 4). In this embodiment, the molding surface 311 further has portions corresponding to the third flange ridge 18 and third flange 19 of the structural member 10. 【0069】The upper molds 321 and 322 are configured to clamp the blank 20 together with the lower mold 31. The upper molds 321 and 322 are separate parts. The upper molds 321 and 322 each have molding surfaces 321a and 322a that correspond to a part of the structural member 10. The molding surface 321a of the upper mold 321 corresponds to at least the top plate ridge 121, vertical wall 131, first flange ridge 141, first flange 151, second flange ridge 161, and second flange 171 of the structural member 10 (Figures 1 to 4). The molding surface 322a of the upper mold 322 corresponds to at least the top plate ridge 122, vertical wall 132, first flange ridge 142, first flange 152, second flange ridge 162, and second flange 172 of the structural member 10. In this embodiment, the molded surfaces 321a and 322a further correspond to the third flange ridge 18 and a part of the third flange 19 of the structural member 10. 【0070】 Figures 5C to 5E show cross-sectional views of the mold 30 perpendicular to the longitudinal direction (Figures 1 to 4) of the structural member 10. Referring to Figure 5C, in the molding process, first, the blank 20 is placed between the lower mold 31 and the upper molds 321 and 322. If the lower mold 31 is positioned below the upper molds 321 and 322, the blank 20 may be placed on the lower mold 31. 【0071】 Referring to Figure 5D, the upper molds 321 and 322 are then brought relatively closer to the lower mold 31. The upper molds 321 and 322 approach the lower mold 31 from the outside in the width direction. More specifically, as shown by the white arrows in Figure 5D, the upper molds 321 and 322 approach the lower mold 31 along a direction that is inclined with respect to both the width and height directions of the lower mold 31. For example, by using a cam mechanism, the upper molds 321 and 322 can be brought closer to the lower mold 31 along a direction that is inclined with respect to the width and height directions of the lower mold 31. The width and height directions of the lower mold 31 correspond to the width and height directions of the structural member 10 (Figures 1 to 4). 【0072】Referring to Figures 5D and 5E, in the molding process, the upper molds 321 and 322 are brought close to the lower mold 31 from the outside in the width direction of the lower mold 31, and the blank 20 is sandwiched between the upper molds 321 and 322 and the lower mold 31. By sandwiching the blank 20 between the molding surface 321a of the upper mold 321 and the molding surface 311 of the lower mold 31, the top plate ridge portion 121, the vertical wall 131, the first flange ridge portion 141, and the first flange 151 (Figure 1) of the structural member 10 are formed. The molding surface 321a of the upper mold 321 and the molding surface 311 of the lower mold 31 also form the second flange ridge portion 161 and the second flange 171 (Figure 1) of the structural member 10. Furthermore, the blank 20 is sandwiched between the molding surface 322a of the upper mold 322 and the molding surface 311 of the lower mold 31, thereby forming the top plate ridge 122, vertical wall 132, first flange ridge 142, and first flange 152 (Figure 2) of the structural member 10. The molding surface 322a of the upper mold 322 and the molding surface 312 of the lower mold 31 also form the second flange ridge 162 and second flange 172 (Figure 2) of the structural member 10. In addition, when the upper molds 321, 322 and the lower mold 31 are closed, a portion of the blank 20 is formed along the molding surface 311 of the lower mold 31 into the top plate 11, third flange ridge 18, and third flange 19 (Figures 1 and 2) of the structural member 10. This completes the manufacturing of the structural member 10. 【0073】 If a heating process is performed before the molding process, the structural member 10 remains held between the upper molds 321, 322 and the lower mold 31. The structural member 10 is then cooled (rapidly cooled) by the upper molds 321, 322 and the lower mold 31, and its microstructure transforms from austenite to martensite. 【0074】 [Effect] The structural member 10 according to this embodiment includes second flanges 171 and 172 in addition to the first flanges 151 and 152. The second flanges 171 and 172 are connected to the first flanges 151 and 152 and the vertical walls 131 and 132, respectively, at one end in the longitudinal direction of the structural member 10 via the second flange ridges 161 and 162. This makes it easier to absorb impact energy when an impact is applied to the structural member 10 in the longitudinal direction. In addition, in this embodiment, the radius of curvature R of the corner portion 161c of the second flange ridge portion 161 and the corner portion 162c of the second flange ridge portion 162Ｌ The thickness t of the structural member 10 is R Ｌ The condition / t < 23.0 is satisfied. In this case, when the structural member 10 is subjected to an impact in the longitudinal direction, the impact energy is absorbed more easily. Therefore, the energy absorption performance of the structural member 10 can be improved. 【0075】 The structural member 10 according to this embodiment further includes a third flange 19. The third flange 19 is continuous with the second flanges 171 and 172 at one end in the longitudinal direction of the structural member 10, and is connected to the top plate 11 and the top plate edges 121 and 122 via the third flange edge 18. In this case, when an impact is applied to the structural member 10 in the longitudinal direction, the impact energy is absorbed more easily. Therefore, the energy absorption performance of the structural member 10 can be improved. 【0076】 In this embodiment, the angle θ that the third flange 19 makes with the top plate 11 is preferably 90° or more and less than 140°. This makes it easier to further improve the energy absorption performance of the structural member 10. 【0077】 In this embodiment, the third flange 19 has a length L of 10 mm or more. Ｕ This allows for a wider space to be secured in the third flange 19 for arranging the joint between the structural member 10 and other members. Length L of the third flange 19 Ｕ By making the gap 10 mm or larger, for example, multiple spot welds can be placed on the third flange 19. Therefore, the energy absorption performance of the structural member 10 can be further enhanced. In addition, the rigidity of the structural member 10 during use can also be easily improved. 【0078】 The structural member 10 according to this embodiment may have a Vickers hardness of 250 HV or higher. This can improve the impact resistance of the structural member 10. 【0079】In the manufacturing method of the structural member 10 according to this embodiment, the upper dies 321 and 322 are brought close to the lower die 31 from the outside in the width direction, and the blank 20 is press-formed to create the structural member 10. By operating the die in this manner, the material flows more easily from the outside to the inside of the blank 20 during the molding process. Therefore, cracks are less likely to occur in the structural member 10 during the molding process. In particular, the reduction in plate thickness is easily suppressed at the corner portion 161c of the second flange ridge portion 161 adjacent to the first flange ridge portion 141. Similarly, the reduction in plate thickness is easily suppressed at the corner portion 162c of the second flange ridge portion 162 adjacent to the first flange ridge portion 142. Therefore, the radius of curvature R of the corner portions 161c and 162c relative to the plate thickness t Ｌ Even when the radius is relatively small, the structural member 10 can be formed while suppressing cracking at the corners 161c and 162c. Specifically, R Ｌ Even when / t < 23.0, cracking is less likely to occur at the corners 161c and 162c. 【0080】 The manufacturing method of the structural member 10 according to this embodiment may include a heating step. In this case, the structural member 10 is formed by hot stamping of the blank 20. When the structural member 10 is formed by hot stamping, cracking of the structural member 10 during the forming process becomes less likely. Specifically, while suppressing cracking, R Ｌ It is possible to form corner sections 161c and 162c with a small / t. 【0081】In the manufacturing method of the structural member 10 according to this embodiment, the mold 30 does not need to include a pad for holding down the top plate 11. If the width W of the top plate 11 is small and sufficient space cannot be secured between the upper mold 321 and the upper mold 322, the mold 30 does not need to include a pad. For example, if the structural member 10 is a cross member for a battery pack, it is preferable that the width W of the top plate 11 be small from the viewpoint of securing the capacity of the battery in the battery pack. Therefore, the width W of the top plate 11 may be 50 mm or less. In this case, the mold 30 does not need to include a pad. However, if the width W of the top plate 11 is relatively large and space can be secured between the upper mold 321 and the upper mold 322, the mold 30 may include a pad. 【0082】 In the manufacturing method of the structural member 10 according to this embodiment, a mold 30 including a lower mold 31 and upper molds 321 and 322 is used. The mold 30 may further include a holder. In this case, the holder is positioned to face the portion of the molding surface 321a of the upper mold 321 that is used to form the first flange 151. The holder is also positioned to face the portion of the molding surface 322a of the upper mold 322 that is used to form the first flange 152. 【0083】 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. 【0084】 In the above embodiment, the structural member 10 includes a third flange ridge portion 18 and a third flange 19. Therefore, the second flange ridge portions 161 and 162 are connected by the third flange ridge portion 18, and the second flanges 171 and 172 are connected by the third flange 19. However, the structural member 10 does not necessarily have to include a third flange ridge portion 18 and a third flange 19. In the example of the above embodiment, the second flange ridge portion 161 and the second flange 171 may be divided in the width direction of the structural member 10 into the second flange ridge portion 162 and the second flange 172. 【0085】In the structural member 10 according to the above embodiment, a top plate ridge 121, a vertical wall 131, a first flange ridge 141, a first flange 151, a second flange ridge 161, and a second flange 171 are provided on one side of the top plate 11 in the width direction, and a top plate ridge 122, a vertical wall 132, a first flange ridge 142, a first flange 152, a second flange ridge 162, and a second flange 172 are provided on the other side of the top plate 11. However, as shown in Figure 6, the structural member 10 may include a top plate ridge 121, a vertical wall 131, a first flange ridge 141, a first flange 151, a second flange ridge 161, and a second flange 171, but may not include a top plate ridge 122, a vertical wall 132, a first flange ridge 142, a first flange 152, a second flange ridge 162, and a second flange 172. Alternatively, the structural member 10 may include a top plate ridge 122, a vertical wall 132, a first flange ridge 142, a first flange 152, a second flange ridge 162, and a second flange 172, while not including a top plate ridge 121, a vertical wall 131, a first flange ridge 141, a first flange 151, a second flange ridge 161, and a second flange 171. In these cases, the mold 30 for forming the structural member 10 does not include either the upper mold 321 or 322. 【0086】 In the above embodiment, the second flange ridges 161, 162 and the second flanges 171, 172 are provided at one end of the structural member 10 in the longitudinal direction. However, the second flange ridges 161, 162 and the second flanges 171, 172 may be provided at both ends of the structural member 10 in the longitudinal direction, respectively. In this case, the third flange ridges 18 and the third flange 19 may be provided at both ends of the structural member 10 in the longitudinal direction, or the third flange ridges 18 and the third flange 19 may be provided only at one end of the structural member 10 in the longitudinal direction. Alternatively, the third flange ridges 18 and the third flange 19 may not be provided at any end of the structural member 10 in the longitudinal direction. 【0087】 The present disclosure will be further described below with reference to examples. However, the present disclosure is not limited to the following examples. 【0088】[First Embodiment] To confirm the effects of the present disclosure, commercially available analysis software (LS-Dyna, manufactured by Ansys) was used to perform an analysis on a structural member 10 having the shape shown in Figures 1 and 2. The analysis involved constraining one end in the longitudinal direction and pushing a rigid wall from the other end in the longitudinal direction (the second flanges 171, 172 and the third flange 19 side) to evaluate the energy absorption performance of the structural member 10. The material of the structural member 10 was assumed to be a steel plate with a Vickers hardness of 450 HV. In this analysis, the radius of curvature R of the corner portions 161c and 162c of the second flange ridge portions 161 and 162 was used. Ｌ And by changing the ratio of plate thickness t, the R of energy absorption performance is affected. Ｌ The effect of / t was evaluated. The conditions and results of this analysis are shown in Table 1 and Figure 7. 【0089】 【0090】 In this analysis, the amount of energy absorbed per unit weight (EA) of the structural member 10 at a stroke of 100 mm was obtained, and the energy absorption performance of the structural member 10 was evaluated based on this. As shown in Table 1 and Figure 7, R Ｌ In analyses No. 1-1 to 1-5, where / t < 23.0, R Ｌ Compared to analysis No. 1-6, where / t = 23.0, the energy absorption per unit weight was significantly larger. Therefore, R Ｌ By satisfying the condition / t < 23.0, it can be said that the energy absorption performance of the structural member 10 is improved. 【0091】 [Second Example] R for energy absorption performance Ｕ To evaluate the effect of / t, the radius of curvature R of the top plate edges 121 and 122 is determined. Ｕ Furthermore, the same analysis as in the first embodiment was performed while varying the ratio of the plate thickness t. The conditions and results of this analysis are shown in Table 2 and Figure 8. 【0092】 【0093】In this analysis, the amount of energy absorbed per unit weight (EA) of the structural member 10 at a stroke of 100 mm was obtained, and the energy absorption performance of the structural member 10 was evaluated based on this. As shown in Table 2 and Figure 8, R Ｕ It was confirmed that sufficient energy absorption per unit weight is ensured when / t ≤ 12.0. Ｕ In analysis No. 2-2, where / t = 8.0, R Ｕ Compared to analysis No. 2-3, where / t = 12.0, the energy absorption performance of structural member 10 was improved. 【0094】 [Third Embodiment] To evaluate the effect of the angle θ of the third flange 19 with respect to the top plate 11 on the energy absorption performance, the same analysis as in the first embodiment was performed while varying the angle θ. The conditions and results of this analysis are shown in Table 3 and Figure 9. 【0095】 【0096】 In this analysis, the energy absorption per unit weight (EA) of the structural member 10 was obtained when the indentation amount (stroke) was 50 mm, and the energy absorption performance of the structural member 10 was evaluated based on this. As shown in Table 3 and Figure 9, in analyses No. 3-1 to 3-3, where θ was between 90° and less than 140°, the energy absorption per unit weight was greater compared to analyses No. 3-4 and 3-5, where θ was 140° or more. Therefore, it can be said that the energy absorption performance of the structural member 10 is further improved by setting θ to between 90° and less than 140°. 【0097】 [Fourth Embodiment] To confirm the effect of the presence or absence of a joint in the third flange 19 on the energy absorption performance, the same analysis as in the first embodiment was performed for both the case where a joint is present in the third flange 19 and the case where it is not. The conditions and results of this analysis are shown in Table 4 and Figure 10. 【0098】 【0099】 In analysis No. 4-1, the length L of the third flange 19 is... ＵThe length was set to 10 mm, and multiple spot welds were placed on the third flange 19 as joints between the structural member 10 and other members. On the other hand, in analysis No. 4-2, the length L of the third flange 19 was set to 10 mm. Ｕ Because the depth was set to 5 mm, it was not possible to place a spot weld on the third flange 19. In this analysis, for each of analyses No. 4-1 and 4-2, the energy absorption amount (EA) of the structural member 10 was obtained when the indentation amount (stroke) was 100 mm. 【0100】 As shown in Table 4 and Figure 10, the energy absorption in analysis No. 4-1 was significantly larger compared to analysis No. 4-2. Therefore, the length L of the third flange 19 Ｕ By ensuring a gap of 10 mm or more and joining the third flange 19 to other members, the energy absorption performance of the structural member 10 can be said to be improved. 【0101】 10: Structural member 11: Top plate 121, 122: Top plate edge section 131, 132: Vertical wall 141, 142: First flange edge section 151, 152: First flange 161, 162: Second flange edge section 161c, 162c: Corner section 171, 172: Second flange 18: Third flange edge section 19: Third flange 20: Blank 30: Mold 31: Lower mold 321, 322: Upper mold

Claims

1. A structural member comprising: a vertical wall; a top plate ridge portion continuous with one end of the vertical wall in the height direction of the structural member; a top plate connected to the vertical wall via the top plate ridge portion; a first flange ridge portion continuous with the other end of the vertical wall in the height direction; a first flange connected to the vertical wall via the first flange ridge portion; a second flange ridge portion disposed at the longitudinal end of the structural member and continuous with the vertical wall, the first flange ridge portion, and the first flange; and a second flange connected to the vertical wall, the first flange ridge portion, and the first flange via the second flange ridge portion, wherein in the cross-section of the structural member, the radius of curvature of the portion of the second flange ridge portion adjacent to the first flange ridge portion is R Ｌ When the plate thickness of the structural member is t, R Ｌ A structural member where / t < 23.

0.

2. A structural member according to claim 1, further comprising: a third flange ridge portion that is continuous with the second flange ridge portion and is continuous with the top plate and the top plate ridge portion; and a third flange that is connected to the top plate and the top plate ridge portion via the third flange ridge portion and is continuous with the second flange.

3. A structural member according to claim 2, wherein in the cross-section of the structural member, the radius of curvature of the portion of the top plate ridge adjacent to the third flange ridge is R Ｕ When the plate thickness of the structural member is t, R Ｕ A structural member where t ≤ 8.

0.

4. A structural member according to claim 2, wherein the angle between the third flange and the top plate is 90° or more and less than 140°.

5. A structural member according to claim 2, wherein the length of the third flange from the end on the third flange ridge side to the opposite end is 10 mm or more.

6. A structural member according to claim 1, wherein the structural member has a Vickers hardness of 250 HV or more.

7. A structural member according to claim 1, wherein the top plate has a width of 200 mm or less.

8. A method for manufacturing a structural member, comprising: a step of preparing a blank; and a step of forming the structural member from the blank using a mold including an upper mold and a lower mold, the structural member comprising a vertical wall, a top plate ridge portion continuous with one end of the vertical wall in the height direction of the structural member, a top plate connected to the vertical wall via the top plate ridge portion, a first flange ridge portion continuous with the other end of the vertical wall in the height direction, a first flange connected to the vertical wall via the first flange ridge portion, a second flange ridge portion disposed at the longitudinal end of the structural member and continuous with the vertical wall, the first flange ridge portion and the first flange, and a second flange connected to the vertical wall, the first flange ridge portion and the first flange via the second flange ridge portion, wherein in the forming step, the upper mold is brought close to the lower mold from the outside in the width direction of the lower mold and the blank is sandwiched between the upper mold and the lower mold. In the cross-section of the structural member, the radius of curvature of the portion of the second flange ridge adjacent to the first flange ridge is R Ｌ When the plate thickness of the structural member is t, R Ｌ A manufacturing method in which / t < 23.

0.

9. A manufacturing method according to claim 8, wherein in the molding step, the structural member is formed by hot pressing of the blank.

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