Title of invention: Structural material
Technical field
[0001]
　The present invention relates to a structural material including a plate portion that is superposed and joined.
Background technology
[0002]
　Conventionally, a structural material configured by stacking and joining a plurality of plates has been used. For example, the strength member described in Japanese Patent Application Laid-Open No. 8-337183 (Patent Document 1) has a structure in which two thin plate portions are opposed to each other in the left-right direction and are joined to form a closed cross section. A coupling flange is extended above and below each of the two thin plate portions. The flanges of the two thin plates are butted and joined by spot welding.
[0003]
　Further, Japanese Patent Laid-Open No. 2006-142905 (Patent Document 2) describes an energy absorbing member. This energy absorbing member includes a hat material and a plate-like closing plate that closes an open portion of the hat material. The hat material and the closing plate are joined to each other by spot welding.
Prior art documents
Patent literature
[0004]
Patent Document 1: Japanese Patent
Laid-Open No. 8-337183 Patent Document 2: Japanese Patent Laid-Open No. 2006-142905
Summary of the invention
Problems to be Solved by the Invention
[0005]
　In the above-mentioned conventional technique, the strength of the welded portions of the plates superposed by spot welding is not considered. When the superposed plates are formed of high-strength steel plates having a tensile strength of 980 MPa or more, a heat-affected zone softened by the heat during welding may occur around the weld. This heat affected zone becomes a weak point of the structural material. For example, when a B-pillar of an automobile collides with another automobile and is deformed, tensile stress is generated in the longitudinal direction of the B-pillar. At that time, the heat-affected zone of the flange breaks due to tensile stress.
[0006]
　Therefore, the present application discloses a structure material having a structure in which a steel plate having a tensile strength of 980 MPa or more is superposed on another metal plate and bonded by welding, and a structure in which breakage originating from the vicinity of a welded portion due to welding does not easily occur is disclosed. To do.
Means for solving the problem
[0007]
　The structural material according to the embodiment of the present invention includes a first member made of a steel plate having a tensile strength of 980 MPa or more, a second member made of a metal plate and superposed on the first plate portion, the first member and the first member. A plurality of welded portions connecting two members by welding, and a plurality of heat-affected zones formed in the first member around each of the plurality of welded portions and having a Vickers hardness lower than the Vickers hardness of the first member by 50 HV or more. And a pair of end portions of the first member extending between the heat-affected zones adjacent to each other and extending in a direction crossing a line connecting the welded portions adjacent to each other.
Effect of the invention
[0008]
　According to the embodiment of the present invention, in a structural material in which a steel plate having a tensile strength of 980 MPa or more is superposed on another metal plate and joined by welding, it is possible to prevent breakage from occurring near the welded portion. ..
Brief description of the drawings
[0009]
FIG. 1A is a perspective view showing a structure of a structural material in the present embodiment.
FIG. 1B is a plan view of the structural material shown in FIG. 1A as viewed from the z direction.
FIG. 1C is an enlarged view of a portion of circle B in FIG. 1B.
FIG. 1D is a sectional view taken along the line AA of FIG. 1C.
FIG. 2 is a diagram showing an example of a cross-sectional structure of a welded portion and a heat affected zone and hardness distribution.
FIG. 3 is a diagram for explaining an arrangement example of end portions between heat affected zones.
FIG. 4 is a diagram for explaining another arrangement example of the end portions between the heat affected zones.
FIG. 5 is a diagram for explaining another arrangement example of the end portions between the heat affected zones.
FIG. 6 is a view showing a modified example of the second member.
7 is a diagram showing a cross-sectional structure and hardness distribution in the modification shown in FIG.
FIG. 8A is a cross-sectional view showing a modified example of the cross-sectional shape of the structural material.
FIG. 8B is a cross-sectional view showing a modified example of the cross-sectional shape of the structural material.
FIG. 8C is a cross-sectional view showing a modified example of the cross-sectional shape of the structural material.
FIG. 9 is a cross-sectional view showing a modified example of the cross-sectional shape of the structural material.
FIG. 10 is a cross-sectional view showing a modified example of the cross-sectional shape of the structural material.
FIG. 11A is a cross-sectional view showing a modified example of the structural material.
FIG. 11B is a plan view of the structural material shown in FIG. 11A as viewed from the z direction.
FIG. 12 is a cross-sectional view showing a modified example of the cross-sectional shape of the structural material.
FIG. 13 is a cross-sectional view showing a modified example of the cross-sectional shape of the structural material.
FIG. 14 is a diagram showing a configuration example in the case where a closed cross section having a circular closed cross section is formed by one plate.
FIG. 15 is a diagram showing an example of a welded portion formed by arc welding.
FIG. 16 is a diagram for explaining a simulation model.
FIG. 17 is a view of the structural material of the model shown in FIG. 16 viewed from the z direction.
FIG. 18 is a cross-sectional view showing a cross section taken along the line AA in FIG.
FIG. 19 is an enlarged view of a region E in FIG.
FIG. 20A is a graph showing the analysis result when the length α of the notch in the y direction is changed.
FIG. 20B is a graph showing the analysis result when the length α is changed.
FIG. 20C is a graph showing analysis results when the length α is changed.
FIG. 21A is a graph showing an analysis result when the length S between the end portions 4 on both sides of the welded portion in the x direction is changed.
FIG. 21B is a graph showing analysis results when the length S is changed.
FIG. 21C is a graph showing the analysis result when the length S is changed.
FIG. 22A is a graph showing the analysis result when the radius of curvature R of the corner portion of the notch is changed.
FIG. 22B is a graph showing the analysis result when the radius of curvature R is changed.
FIG. 22C is a graph showing the analysis result when the radius of curvature R is changed.
MODE FOR CARRYING OUT THE INVENTION
[0010]
　Welding is often used as a method of superimposing and joining a first member of a steel plate and a second member of a metal plate. The inventors investigated the deformation behavior of the structural material composed of the first member and the second member joined to each other. When a force is applied to the structural material in a direction perpendicular to the plate surfaces of the first member and the second member, the structural material deforms and bends. It has been found that when the tensile strength of the material of the first member is increased and the structural material is deformed, the vicinity of the welded portion that joins the first member and the second member by welding is likely to break.
[0011]
　The inventors considered this phenomenon as follows. Heat is applied during welding to a portion where the first member and the second member are joined by welding, that is, a welded portion. The portion around the weld is also affected by heat during welding. When welded to a steel sheet having a tensile strength of 980 MPa or more, the periphery of the welded portion is softened by the heat during welding. A steel material having a tensile strength of 980 MPa or more contains a hard phase in order to achieve high tensile strength. Softening occurs because the heat during welding alters the hard phase. Specifically, martensite is transformed into ferrite. When the tensile stress in the in-plane direction becomes large, the first member or the second member breaks starting from the portion softened by heat during welding around the welded portion.
[0012]
　Based on the above consideration, the inventors studied a configuration for suppressing the softened portion generated around the welded portion from breaking due to tensile stress in the in-plane direction. As a result of repeating various analyzes and experiments, the inventors have come to the idea of ​​cutting between the softened portions around the welded portion of the steel sheet having a tensile strength of 980 MPa or more. That is, it was conceived to provide a pair of end portions between the softened portions around the welded portion of the steel sheet having a tensile strength of 980 MPa or more. It has been found that this makes it possible to prevent the portion around the welded portion from being the starting point and breaking when the tensile stress in the in-plane direction increases. Based on this knowledge, the following embodiments have been conceived.
[0013]
　(Structure 1)
　The structural material in the structure 1 of the embodiment of the present invention includes a first member made of a steel plate having a tensile strength of 980 MPa or more, and a second member made of a metal plate, which is superposed on the first plate portion. A plurality of welded portions connecting the first member and the second member by welding and the first member around each of the plurality of welded portions are formed, and the Vickers hardness is 50 HV higher than the Vickers hardness of the first member. A plurality of lower heat-affected zones and a pair of end portions of the first member extending between the adjacent heat-affected zones and extending in a direction crossing a line connecting the adjacent welded portions are provided.
[0014]
　In the structural material of Configuration 1, a heat-affected zone having a Vickers hardness lower than the hardness of the first member by 50 HV or more is formed around each of the plurality of welded portions of the first member having a tensile strength of 980 MPa or more. The adjacent heat affected zones are cut off. That is, the pair of end portions of the first member are provided between the adjacent heat-affected zones of the first member. The pair of end portions extends in a direction crossing a line connecting the welded portions inside each of the adjacent heat-affected zones. That is, it extends in the direction crossing the line connecting the adjacent welded portions. With this configuration, when the structural material is deformed by receiving a force in a direction perpendicular to the plate surface of the first member, the in-plane tensile stress of the first member that acts on the heat-affected zone can be relaxed. Therefore, when the structural material is deformed, breakage from the heat-affected zone as the starting point can be less likely to occur. That is, in a structural material in which a steel plate having a tensile strength of 980 MPa or more is overlapped with another metal plate and joined by welding, it is possible to prevent breakage starting from the vicinity of the welded portion.
[0015]
　(Structure 2) In
　the structural material of Structure 1, the pair of end portions preferably cross a line connecting the centers of the adjacent welded portions. This makes it easier to obtain the effect of relaxing the tensile stress acting on the heat affected zone. The center of the weld is the midpoint of a line segment that bisects the weld in one direction when viewed from the direction perpendicular to the plate surface of the first member. Here, the plate surface of the first member is a surface of the first member that is in contact with the second member, that is, a mating surface with the second member.
[0016]
　(Structure 3) In
　the structural material according to Structure 2, it is preferable that the pair of end portions cross an end portion of a region between inner peripheral edges of the adjacent heat-affected zones. This makes it easier to obtain the effect of relaxing the tensile stress acting on the heat affected zone.
[0017]
　(Structure 4) In
　the structural material according to any one of Structures 2 and 3, it is preferable that the pair of end portions cross a region between the adjacent heat-affected zones. This makes it easier to obtain the effect of relaxing the tensile stress acting on the heat affected zone.
[0018]
　(Structure 5) In
　the structural material according to any one of Structures 1 to 4, it is preferable that the pair of end portions are edges of a hole formed in the first member. This is because it is easier to secure the strength of the first member when the ends of the first members between the adjacent heat-affected zones are used as the edges of the holes, as compared with the case where the holes are cut.
[0019]
　(Structure 6) In
　the structural material according to any one of Structures 1 to 5, the second member has a tensile strength of less than 1180 MPa, and the second member between the adjacent welds has no end portion. It is preferable. More preferably, the tensile strength of the second member is less than 980 MPa. More preferably, the tensile strength of the second member is less than 800 MPa. More preferably, the tensile strength of the second member is less than 720 MPa. By lowering the tensile strength of the second member in this way, it is possible to prevent the periphery of the welded portion from being softened by the heat of welding as compared with the hardness of the second member. By suppressing the softening of the periphery of the welded portion of the second member, breakage in the vicinity of the welded portion due to an increase in tensile stress in the in-plane direction is less likely to occur. Therefore, even if the second member is not provided with the pair of end portions of the second member disposed between the adjacent heat-affected zones, it is possible to prevent breakage near the welded portion from occurring easily. Further, by not providing the end portion between the adjacent welded portions of the second member, it becomes easy to secure the strength of the structural member.
[0020]
　(Structure 7) In
　the structural material according to any one of Structures 1 to 6, it is desirable that the second member is a steel plate having a tensile strength of 980 MPa or more. More preferably, the second member is preferably a steel plate having a tensile strength of 1180 MPa or more. Then, the strength of the member can be increased. However, in that case, a softened heat-affected zone may occur near the welded portion of the second member. As a countermeasure, by providing a pair of end portions of the second member between the adjacent welded portions, it is possible to prevent breakage from occurring near the welded portions.
[0021]
　(Structure 8) In
　the structural material according to any one of Structures 1 to 6, a heat-affected zone having a Vickers hardness lower than the hardness of the second member by 50 HV or more is provided in the second member around the plurality of welded portions. It is preferable not to have it. When there is no heat-affected zone around the welded portion of the second member, breakage near the welded portion is less likely to occur due to increase in tensile stress in the in-plane direction. Therefore, even if the second member is not provided with the pair of end portions of the second member disposed between the adjacent heat-affected zones, it is possible to prevent the breakage in the vicinity of the welded portion from occurring easily.
[0022]
　(Structure 9) In
　the structural material according to any one of Structures 1 to 8, the distance between the ones of the pair of end portions on both sides of the welded portion on the welded portion side is 6 times or less the diameter of the welded portion. Is preferred. In other words, the plurality of welded portions include a first welded portion by spot welding, a second welded portion adjacent to the first welded portion, and a third welded portion adjacent to the second welded portion. May be included. When viewed from a direction perpendicular to the plate surface of the first member, the end of the first member located between the second weld and the first weld is closest to the second weld. The sum of the distance to the position and the distance from the second weld to the closest position of the end of the first member between the second weld and the third weld, It is preferably 6 times or less the diameter of the first weld.
[0023]
　The configuration 9 can reduce the load on the first welded portion when the structural material is deformed by the force in the direction perpendicular to the plate surface of the first member. Further, the concentration of deformation on the first welded portion can be suppressed.
[0024]
　(Structure 10) In
　the structural material according to any one of the above structures 1 to 9, it is preferable that the radius of curvature of the locus of the end portion connecting the pair of end portions is 10 mm or less. In other words, when viewed from the direction perpendicular to the plate surface of the first member, the notch or hole corner of the first member formed by the pair of end portions of the first member between the adjacent heat-affected zones. The radius of curvature of the portion is preferably 10 mm or less. Accordingly, it is possible to suppress the concentration of deformation in the first member and the second member when the structural material is deformed by the force in the direction perpendicular to the plate surface of the first member.
[0025]
　(Structure 11) In
　the structural material according to any one of Structures 1 to 10, the first member includes a ridge line portion, and the pair of end portions and an end portion connected to the pair of end portions do not divide the ridge line portion. It is preferable. That is, the end portion of the first member formed between the pair of end portions of the first member between the adjacent heat-affected zones is preferably provided at a position that does not reach the ridge portion. By configuring the end portion of the first member so as not to divide the ridge line portion, the strength of the structural member can be increased as compared with the configuration in which the end portion of the first member divides the ridge line portion.
[0026]
　For example, at least one of the first member and the second member may have a bent portion that is bent in an out-of-plane direction. In this case, the bent portion becomes the ridge portion. The plurality of welded portions may be arranged, for example, in the extending direction of the ridge portion. It is desirable that the end portion between the pair of end portions of the first member between the adjacent heat-affected zones does not extend to the ridge portion. If the ridgeline is divided, the member is likely to bend there.
[0027]
　The structural material according to any one of the configurations 1 to 11 may form a closed cross section with the first member and the second member. The portion of the formed closed cross section is called a closed cross section. That is, at least two locations on the plate surface of the first member that are separated from each other may be in contact with the second member. In this case, the portion of the first member between the two points in contact with the second member is separated from the second member. The portion where the first member and the second member are overlapped is joined by welding. The portion where the first member and the second member are superposed and joined to each other forms a flange arranged inside or outside the closed cross-section. The flange extends in the axial direction of the closed cross section. For example, the first member may be a hat member and the second member may be a closing plate. The reason why the first member is the hat material is that the strength of the member is secured by the ridge line. The plate surface is easily deformed out-of-plane, while the ridge line is not easily deformed. If the ridgeline is formed of a high-strength material, it becomes a member having high strength.
[0028]
　The structural material according to any one of the configurations 1 to 11 may include a closed cross-section portion that forms a closed cross-section with at least one plate. A plate forming a closed cross section includes the first member and the second member. In this case, both the first member and the second member are parts of the plate forming the closed cross section. The first member and the second member are superposed on each other and joined by welding. The superposed first member and second member may form a flange disposed inside or outside the closed cross section. Alternatively, the superposed first member and second member may form a part of the closed cross section.
[0029]
　In the structural material having any one of the above configurations 1 to 11, the metal structure of the first member has martensite as a main phase. To obtain a tensile strength of 980 MPa or more in a steel sheet, it is necessary to make martensite the main phase. That is, the area ratio of martensite in the first member is 25% or more. The area ratio of martensite in the first member may be 100%. The metal structure of the second member preferably has ferrite as the main phase. That is, the area ratio of the ferrite phase in the second member may be 30% or more. The upper limit of the area ratio of ferrite in the second member may be 95%. Alternatively, the area ratio of martensite of the second member may be 70% or less. By doing so, it is possible to avoid the appearance of a softened heat-affected zone in the second member around the weld.
[0030]
　[Embodiment]
　FIG. 1A is a perspective view showing a structural member 10 in the present embodiment. FIG. 1B is a plan view of the structural material 10 shown in FIG. 1A viewed from a direction (z direction) perpendicular to the longitudinal direction. FIG. 1C is an enlarged view of a portion of circle B in FIG. 1B. FIG. 1D is a sectional view taken along line AA in FIGS. 1B and 1C.
[0031]
　The structural material 10 is configured by combining a steel plate and a metal plate (not necessarily a steel plate). One of these is the hat member 1, and the other one is the closing plate 2. The hat member 1 has a hat-shaped cross section. The flange of the hat member 1 and a part of the closing plate 2 are superposed and joined to each other. The hat member 1 is an example of a first member. The closing plate 2 is an example of the second member.
[0032]
　As shown in FIG. 1A, the hat member 1 has a top surface portion 1a, a side wall 1b, and a flange 1c. The side walls 1b extend from both ends of the top surface portion 1a and face each other. The flange 1c is connected to each of the side walls 1b and extends in a direction away from the other end of the side wall 1b opposite to the one end on the top surface 1a side. That is, the two flanges 1c extend outward from the other end of the side wall 1b in the opposing direction of the side wall 1b. The closing plate 2 is provided by being joined to the flange 1c.
[0033]
　A boundary portion (shoulder portion) between the top surface portion 1a and the side wall 1b serves as a bent portion (first bent portion 1ab) of the hat member 1. The first bent portion 1ab forms a ridge line extending in the longitudinal direction (x direction) of the structural material 10. A boundary portion between each side wall 1b and each flange 1c becomes a second bent portion 1bc of the hat member 1. The second bent portion 1bc also forms a ridge line extending in the x direction.
[0034]
　The flange 1c and the closing plate 2 are superposed and joined. In this example, the flange 1c and the closing plate 2 are joined by spot welding. 1A to 1C, the position of the welded portion 3 where the flange 1c and the closing plate 2 are joined by welding is shown by a dotted line. As shown in FIG. 1D, the portion where the flange 1c and the closing plate 2 are integrated by welding is the welded portion 3.
[0035]
　The hat member 1 is formed of a steel plate having a tensile strength of 980 MPa or more. The hat member 1 is formed by molding a metal plate. The closing plate 2 is made of metal. The tensile strength of the closing plate 2 is not particularly limited.
[0036]
　As shown in FIG. 1D, the flange 1c and the closing plate 2 are superposed at two places. The flange 1c and the closing plate 2 that are overlapped with each other form a connecting plate portion 101. The coupling plate portion 101 is an example of a plate portion that is overlapped and bonded to each other. That is, the portion 2b of the closing plate 2 that is in contact with the flange 1c and the flange 1c are combined plate portions 101 that are overlapped and joined by the welded portion 3. The connecting plate portion 101 serves as a flange of the structural material 10. In FIG. 1D, there are two connecting plate portions 101. Between these connecting plate portions 101, there is a closed cross-section portion 102 in which the hat member 1 and the closing plate 2 extend apart from each other. That is, the closed member 102 is formed by the hat member 1 and the closing plate 2. The closed cross-section portion 102 is composed of a side wall 1b and a top surface portion 1a of the hat member 1 and a portion 2a between a portion 2b which is in contact with the flange 1c of the closing plate 2. That is, the closed cross-section portion 102 is formed by a plate portion that surrounds the hollow portion.
[0037]
　As described above, the structural member 10 has a closed cross-section portion 102 formed by a plate portion that surrounds the hollow portion, and a flange that is continuous with the closed cross-section portion 102 and that is arranged outside the closed cross-section portion 102 (coupling plate portion 101). Have and. The closed cross section 102 forms a tube. The portion where the flange 1c and the closing plate 2 are joined (that is, the connecting plate portion 101) is a flange protruding from the pipe.
[0038]
　In the example shown in FIGS. 1A to 1D, the axial direction of the tube formed by the closed cross section 102 is the x direction. The coupling plate portion 101, that is, the flange of the structural material 10 is formed to extend in the x direction. In this example, the extending direction (longitudinal direction) of the pipe formed by the closed cross section 102 and the extending direction of the flange of the structural material 10 are the same. Note that the extending direction of the flange of the structural material 10 does not necessarily have to be the same as the extending direction of the pipe formed by the closed cross section 102. For example, the hat materials having the side walls 1b whose height changes in the longitudinal direction may be combined.
[0039]
　As shown in FIG. 1C, the flange 1c and the closing plate 2 are joined by a plurality of welded portions 3, that is, a plurality of spot welds. There is a heat-affected zone 5 around each of the plurality of welded portions 3 on the flange 1c. The heat-affected zone 5 is a portion that is softened by the heat during welding of the welded portion 3. The heat-affected zone 5 is softer than the surroundings. A portion where the Vickers hardness is 50 HV or more lower than that of the hat member 1, that is, the base material is the heat-affected zone 5. That is, the Vickers hardness of the heat-affected zone 5 is lower than the Vickers hardness of the surrounding portion of the heat-affected zone 5 by 50 HV or more.
[0040]
　In the closing plate 2, there may or may not be a heat-affected zone around each of the plurality of welded sections 3. However, when the closing plate 2 has a heat-affected zone with a reduced tensile strength, a pair of ends of the closing plate are also provided between the heat-affected zones of the closing plate 2. Note that the heat-affected zone is omitted in FIG. 1B.
[0041]
　As shown in FIG. 1C, when viewed from the direction (z direction) perpendicular to the surface of the flange 1c in contact with the closing plate 2, the adjacent heats formed around the adjacent welds 3 among the plurality of welds 3. A pair of end portions 4 of the flange 1c are provided between the affected portions 5. The pair of end portions 4 of the flange 1c between the adjacent heat-affected zones 5 extend in a direction crossing a line connecting the adjacent weld portions 3.
[0042]
　In the example shown in FIG. 1C, a gap is formed between the adjacent heat-affected zones 5 by the pair of ends 4 of the flange 1 c between the adjacent heat-affected zones 5. The pair of end portions 4 may be in contact with each other. The pair of end portions 4 between the adjacent heat-affected zones 5 form a discontinuous portion between the adjacent heat-affected zones 5. Also in the closing plate 2, if there is a heat-affected zone 5 with a reduced tensile strength, the ends of the pair of closing plates 2 are arranged between the adjacent heat-affected zones 5. In this case, the pair of end portions between the adjacent heat-affected zones 5 of the flange 1c and the pair of end portions between the adjacent weld portions of the closing plate 2 are positioned so as to partially overlap each other when viewed from the z direction. They may be arranged, or may be arranged at positions that do not overlap each other.
[0043]
　The welded portions 3 are arranged side by side in the x direction, that is, in the direction in which the ridge lines of the first bent portion 1ab and the second bent portion 1bc extend. Between the heat-affected zones 5 adjacent to each other, the flange 1c is divided by the discontinuous portion formed by the pair of end portions 4.
[0044]
　The pair of ends 4 between the adjacent heat-affected zones 5 prevent the force applied to the flange 1 c from being transmitted between the adjacent heat-affected zones 5. For example, when the structural material 10 is deformed by an external force, a force that deforms the flange 1c acts on a certain one welded portion 3 and the heat-affected zone 5 around it. Between one heat-affected zone 5 and the heat-affected zone 5 adjacent to the heat-affected zone 5, there is an end 4 of the pair of flanges 1c, that is, a discontinuous portion. Due to this discontinuous portion, the force applied to one heat-affected zone 5 is less likely to be transmitted to the adjacent heat-affected zone 5. Therefore, the adjacent heat-affected zones 5 can be deformed without restraining each other. As a result, the load on each heat-affected zone 5 is reduced, and the heat-affected zone 5 is less likely to break.
[0045]
　As shown in FIG. 1D, the first bent portion 1ab and the second bent portion 1bc of the hat member 1 have round and curved shapes, and the surfaces of the first bent portion 1ab and the second bent portion 1bc include curved surfaces. That is, R (curved portion) is formed in the first bent portion 1ab and the second bent portion 1bc. In FIG. 1C and FIG. 1D, the end of the R (curved portion) of the first bent portion 1ab on the side of the top surface 1a is defined as an R boundary (R stop) 1e, and the R (curved portion) of the second bent portion 1bc is on the flange 1c side. Is defined as the R boundary (R stop) 1f. The ridgeline of the first bent portion 1ab extends in the same direction (x direction) as the R boundary 1e. The ridgeline of the second bent portion 1bc extends in the same direction (x direction) as the R boundary 1f. The R boundary is a boundary between the bent portion and a surface adjacent to the bent portion. The point where the direction of the surface changes from the adjacent surface to the bent portion is regarded as the R boundary.
[0046]
　As shown in FIG. 1C, when viewed from the z direction (direction perpendicular to the joint surface), the end portions 4 of the pair of flanges 1c between the adjacent heat-affected zones 5 are located inside (side wall 1b) from the end portions of the flange 1c. ) Is a part of the notch (slit). The notch of the flange 1c does not extend to the side wall 1b. More specifically, the end portion connecting the end portions 4 of the pair of flanges 1c between the adjacent heat-affected zones 5 does not extend to the second bent portion 1bc at the boundary between the flange 1c and the side wall 1b (also in FIG. 1D). reference). In other words, the end portion connecting the end portions 4 of the pair of flanges 1c between the adjacent heat-affected zones 5 extends to the ridge line formed between the closed cross-section portion 102 and the flange of the structural member 10. do not do. As a specific example, the end portion 4 of the pair of flanges 1c between the adjacent heat-affected zones 5 and the end portion of the flange 1c connecting the pair of end portions 4 are R boundary lines on the flange 1c side of the second bent portion 1bc. It is arranged closer to the flange 1c than to 1f. That is, when viewed from the z direction (direction perpendicular to the joint surface), the end portion connecting between the end portions 4 of the pair of flanges 1c between the adjacent heat-affected portions 5 does not intersect the second bent portion 1bc. It is provided in. The reason for doing so is to prevent the member from easily bending at a portion where the ridge line is divided. The end portion connecting the pair of end portions between the adjacent welded portions 3 of the closing plate 2 may or may not intersect the second bent portion 1bc when viewed from the z direction.
[0047]
　
　FIG. 2 is a diagram showing an example of the cross-sectional structure and hardness distribution of the weld zone 3 and the heat affected zone 5. The upper part of FIG. 2 is a sectional view of a portion including the welded portion 3 and the heat-affected zone 5. The lower part of FIG. 2 is a graph showing the distribution of Vickers hardness along the line S in the sectional view. In FIG. 2, the first member and the second member are made of the same material. The welded portion 3 is heated until it is melted during welding and then cooled. Since the welding part 3 is deheated by the electrode, the cooling rate is very high. As a result, the weld 3 is hardened. As a result of quenching, the weld zone 3 and the heat-affected zone adjacent to the weld zone 3 have the same hardness as the first member. Around the periphery of the welded portion 3, there is a heat-affected zone in which the reinforced structure of the first member is deteriorated and softened by heat during welding. This softened heat-affected zone is a zone where the cooling rate is slow. The softened portion around the welded portion 3 shown in FIG. 2 is particularly called a heat-affected zone 5. Here, the hardness of the first member 1 at a distance SD=10 mm or more from the welded portion 3 is regarded as the hardness of the first member. The same applies to the second member. The heat-affected zone 5 of the first member is a portion whose Vickers hardness is lower than the hardness of the first member by 50 HV or more. The hardness of the portion of the first member separated from the welded portion 3 by the distance SD or more becomes the hardness of the first member. The distance SD changes depending on the material and plate thickness of the first member. When the first member is a steel plate having a plate thickness of about 1 to 2 mm for automobile use, it is considered that SD=10 mm. The same applies when the heat-affected zone appears in the second member. That is, the heat-affected zone of the second member is a portion whose Vickers hardness is lower than the hardness of the second member by 50 HV or more. The hardness of the portion of the second member separated from the welded portion 3 by the distance SD or more is the hardness of the second member.
[0048]
　
　FIG. 3 is a diagram showing an example of arrangement of the ends 4 of the pair of flanges 1c between the adjacent heat-affected zones 5 of the flange 1c. FIG. 3 is a view seen from a direction (z direction) perpendicular to a surface of the flange 1c in contact with the closing plate 2. As shown in FIG. 3, in the present embodiment, when viewed from the z direction, a line LC1 that connects the centers C1 and C2 of the adjacent welding portions 31 and 32 is crossed between the adjacent heat-affected portions 51 and 52. Two end portions 4 of the flange 1c extending in the direction are arranged.
[0049]
　Here, between adjacent heat-affected zones is the area between the outer peripheral edge 51g of the heat-affected zone 51 and the outer peripheral edge 52g of the adjacent heat-affected zone 52. In the example of FIG. 3, the regions surrounded by the outer peripheral edges 51g and 52g of the heat-affected zone 51, the line LG1, and the line LG2 are between the adjacent heat-affected zones.
[0050]
　The direction crossing the line LC1 connecting the centers C1 and C2 of the adjacent welded portions 31 and 32 is a direction having an angle with respect to the line LC1. The direction is not limited to the direction perpendicular to the line LC1. Further, the end portions 4 of the pair of flanges 1c may or may not intersect the line LC1 connecting the centers of the adjacent welded portions.
[0051]
　As shown in FIG. 3, the pair of end portions 4 of the flange 1c between the adjacent heat-affected portions 51 and 52 form a line LC1 connecting the centers C1 and C2 of the adjacent weld portions 31 and 32 when viewed in the z direction. It is preferable to traverse. The width of the heat-affected zones 51, 52 in the direction of the line LC1 is the shortest at the portion where the line LC1 and the heat-affected zones 51, 52 overlap. That is, the load is most likely to be concentrated on the heat-affected zones 51 and 52 on the line LC1. Therefore, the line LC1 connecting the centers C1 and C2 of the adjacent welded portions 31 and 32 and the pair of end portions 4 of the flange 1c intersect with each other, so that the load on the heat-affected zones 51 and 52 when the flange 1c is deformed. It can be effectively suppressed.
[0052]
　Further, in the example shown in FIG. 3, the pair of end portions 4 of the flange 1c between the heat-affected zones 51 and 52 cross the line LC1 and the line LN2. The lines LN1 and LN2 are end portions of a region between the inner peripheral edge 51n of the heat-affected zone 51 and the inner peripheral edge 52n of the heat-affected zone 52 adjacent thereto. The pair of ends 4 of the flange 1c between the heat-affected zones 51 and 52 preferably cross the line LC1 and at least one of the two lines LN1 and LN2. As a result, the load on the heat-affected parts 51 and 52 when the flange 1c is deformed can be effectively suppressed.
[0053]
　The end portions 4 of the pair of flanges 1c between the heat-affected zones 51 and 52 cross the line LC1 connecting the centers C1 and C2 of the welded portions 31 and 32 and do not cross the two lines LN1 and LN2. It may be configured. In the example shown in FIG. 4, the ends 4 of the pair of flanges 1c between the heat-affected zones 51 and 52 cross the line LC1 and do not cross the two lines LN1 and LN2. The ends 4 of the pair of flanges 1c are part of the edges of the holes formed in the flanges 1c.
[0054]
　Further, the end portions 4 of the pair of flanges 1c between the heat-affected zones 51 and 52 cross the line LC1 connecting the centers C1 and C2 of the welded portions 31 and 32, and further, two lines LN1 and LN2. The structure may be crossed. In the example shown in FIG. 5, the end portions 4 of the pair of flanges 1c between the heat-affected zones 51 and 52 cross the line LC1 and also the two lines LN1 and LN2.
[0055]
　In the example shown in FIG. 5, the end portions 4 of the pair of flanges 1c between the heat-affected zones 51 and 52 cross the two lines LG1 and LG2. The lines LG1 and LG2 are end portions of a region between the outer peripheral edge 51g of the heat affected zone 51 and the outer peripheral edge 52g of the heat affected zone 52 adjacent thereto. In this case, the end portions 4 of the pair of flanges 1c between the heat-affected zones 51 and 52 cross the region between the adjacent heat-affected zones 51 and 52. As a result, the load on the heat-affected parts 51 and 52 when the flange 1c is deformed can be effectively suppressed.
[0056]
　
　FIG. 6 is a view showing a modification of the closing plate 2 which is an example of the second member. If the closing plate does not have a heat-affected zone with a reduced tensile strength, as shown in FIG. Even with this configuration, it is possible to suppress the load on the heat-affected parts 51 and 52 when the flange 1c is deformed. The tensile strength of the material of the closing plate 2 is preferably less than 980 MPa. This is because the periphery of the welded portion 3 is less likely to be softened by the heat during welding. As described above, it is preferable to select, as the material of the closing plate 2, a material that does not cause a portion to be softened by the heat of welding. That is, it is preferable that the closing plate 2 has no heat-affected zone around the welded portion 3. This is because if there is no heat-affected zone with a reduced tensile strength, no fracture occurs that originates from the heat-affected zone when the closing plate 2 is deformed.
[0057]
　As described above, the hat member 1 is made of a high strength material having a tensile strength of 980 MPa or more. Therefore, in the hat member 1, the end portions of the pair of flanges 1c are arranged between the heat-affected zones 51 and 52 of the flange 1c. On the other hand, the closing plate 2 is made of a material that does not cause a heat-affected zone. In the closing plate 2, no end portion is provided between the welded portions 3. This makes it possible to secure the strength of the structural member 10 by using a high-strength material for the hat member 1. Further, it is possible to suppress breakage caused by the softened portion generated by using the high-strength material.
[0058]
　FIG. 7 is a diagram showing an example of a cross section in the vicinity of the welded portion and a Vickers hardness distribution when the tensile strength of the closing plate 2 is less than 1180 MPa. In FIG. 7, the upper part of FIG. 7 is a sectional view of a portion including the welded portion 3. The lower part of FIG. 7 is a graph showing the distribution of Vickers hardness on line S and line S1 in the cross-sectional view. In this bluff, the line T1 shows the distribution of Vickers hardness on the line S, and the line T2 shows the distribution of Vickers hardness on the line S1.
[0059]
　As shown in FIG. 7, the tensile strength of the weld 3 is lower than the hardness of the hat member 1. This is because in the welded portion 3, the hat member 1 and the closing plate 2 are melted and mixed with each other, and the hardness is lower than that of the hat member 1. The area adjacent to the welded portion 3 of the hat member 1 which is affected by heat has the same hardness as the hat member 1 (base material). The hardness of the region of the hat member 1 separated from the welded portion 3 and affected by heat is lower than that of the hat member 1. The hardness distribution of the heat affected zone 5 of the hat member 1 is the same as in FIG. The hardness of the welded portion 3 on the closing plate 2 side is equal to the hardness of the hat member 1. The hardness of the region affected by the heat around the welded portion 3 on the side of the closing plate 2 decreases as the distance from the welded portion 3 increases. This is because the cooling rate after welding decreases as the distance from the welded portion 3 increases. The high cooling rate in the region close to the welded portion 3 is due to heat removal by the electrode in spot welding. The closing plate 2 does not have a heat-affected zone whose hardness is 50 Hv or more lower than that of the closing plate 2.
[0060]
　
　FIG. 8A is a cross-sectional view showing a modification of the cross-sectional shape of the structural material. The cross-sectional shape of the structural material 10a shown in FIG. 1D is symmetrical with respect to the perpendicular bisector of the closing plate 2 (the surface including the x axis). On the other hand, the structural material 10a shown in FIG. 8A is asymmetric with respect to the vertical bisector of the closing plate 2. The hat member 1 of the structural material 10a shown in FIG. 8A has two side walls 1b having different shapes. The two side walls 1b have different angles with respect to the flange 1c and heights HR and HL in the z direction.
[0061]
　In the example shown in FIG. 8A, one side wall 1b of the two side walls 1b has a step. The other side wall 1b of the two side walls 1b has a round and curved shape. Specifically, R (roundness) is formed in a portion extending from the first bent portion 1ab of the other side wall 1b.
[0062]
　Although not shown, at least one surface of the top surface portion 1a, the side wall 1b, the flange 1c, and the closing plate 2 may be a curved surface instead of a flat surface. That is, at least one of the top surface portion 1a, the side wall 1b, the flange 1c, and the closing plate 2 may be curved.
[0063]
　In FIG. 8A, illustration of the heat-affected zone is omitted. Hereinafter, also in FIGS. 9A to 14 (excluding FIG. 11B), illustration of the heat-affected zone is omitted.
[0064]
　Further, in the example shown in FIG. 8A, the closing plate 2 has a shape protruding in a direction away from the hat member 1. Specifically, the closing plate 2 includes a portion 2b that overlaps the flange 1c of the hat member 1 and a portion 2a between these portions 2b. This portion 2 a has a shape protruding in a direction away from the hat member 1. In this example, the closing plate 2 has a hat-shaped cross section. This constitutes a so-called double-hat shaped structural material. In the configuration shown in FIG. 8A, the hat member 1 may be the first member and the closing plate 2 may be the second member, or the hat member 1 may be the second member and the closing plate 2 may be the first member.
[0065]
　FIG. 8B is a cross-sectional view showing another modification of the cross-sectional shape of the structural material. In the example shown in FIG. 8B, a groove-shaped member including one flange is used instead of the hat member including two flanges. The structural material 10b shown in FIG. 8B has a groove-shaped groove-shaped member 13, a closing plate 2, and welded portions 3r and 3h for joining the groove-shaped member 13 and the closing plate 2. The groove-shaped member 13 includes a top surface portion 1a, a first side wall 1br and a second side wall 1bh extending from both ends of the top surface portion 1a. The first side wall 1br and the second side wall 1bh face each other.
[0066]
　A flange 1c extends outward from the end of the first side wall 1b opposite to the top surface 1a. There is a bent portion 1bcr at the boundary between the first side wall 1br and the flange 1c. The flange 1c is superposed on the closing plate 2 and joined by the welded portion 3r. The closing plate 2 is superposed on the portion 1bhd including the end portion on the opposite side of the top surface portion 1a of the second side wall 1bh. The portion 1bhd and the closing plate 2 are joined by the welded portion 3h. The closing plate 2 has a bent portion 2abh at the inner end of the portion 2bh that is overlapped with the second side wall 1bh.
[0067]
　The groove-shaped member 13 may be configured without a flange. In the configuration shown in FIG. 8B, the groove member 13 is an example of the first member, and the closing plate 2 is an example of the second member. The structural material 10b includes a closed cross section 102 and flanges 101r and 101h arranged outside the closed cross section 102. Welds 3r and 3h are formed on the flanges 101r and 101h. There is a heat-affected zone (not shown) in the groove-shaped member 13 around the welded portions 3r and 3h.
[0068]
　As shown in FIG. 8C, the flange 101 on which the welded portion 3 is formed may be arranged inside the closed cross section 102. In the structural material 10c shown in FIG. 8C, the flange 101 constitutes a part of the closed cross section 102. The structural material 10c includes a groove-shaped member 13 and a closing plate 2. The groove-shaped member 13 includes a top surface portion 1a, side walls 1b extending from both ends of the top surface portion 1a so as to face each other, and a flange 1c extending from the side of the side wall 1b opposite to the top surface portion 1a so as to approach each other. The flange 1c is superposed on the closing plate 2. In the configuration shown in FIG. 8C, the hat member 1 is an example of the first member, and the closing plate 2 is an example of the second member.
[0069]
　FIG. 9: is sectional drawing which shows the example of the structural material comprised by joining three plates. The structural material 10d shown in FIG. 8 has a configuration in which another hat member 11 is further provided on the side opposite to the hat member 1 with the closing plate 2 interposed therebetween with respect to the structural material 10 shown in FIG. 1D. Like the hat member 1, the hat member 11 has a top surface portion 11a, a side wall 11b, and a flange 11c. The flange 1c of the hat member 1, the closing plate 2 and the flange 11c of the hat member 11 are overlapped and joined by the welded portion 3. As described above, the number of plates constituting the structural material is not limited to two. Further, the number of plate portions that are overlapped and joined is not limited to two. The structural material may have a configuration in which three or more plates are stacked and joined by a weld. In the configuration shown in FIG. 9, at least one of the hat members 1 and 11 may be the first member and the closing plate 2 may be the second member.
[0070]
　FIG. 10: is sectional drawing of the structural material which concerns on a modification. The structural material 10e shown in FIG. 10 includes a first plate 12 having three bent portions 12bb and 12bc and a second plate 22 which is a flat plate having no bent portions. The structural material 10e includes a closed cross section 102 and a coupling plate section 101 protruding outside the closed cross section 102. In the connecting plate portion 101, the first plate 12 and the second plate 22 are superposed and joined by welding. In the configuration shown in FIG. 10, the first plate 12 may be the first member and the second plate 22 may be the second member, or the first plate 12 may be the second member and the second plate 22 may be the second member. May be the first member. Thus, the plate forming the closed cross section is not limited to the plate having the top surface 1a shown in FIGS. 1A to 1D. The closed cross section can be formed by using a plate having another bent portion.
[0071]
　
　FIG. 11A is a sectional view of a structural material according to a modification. FIG. 11B is a plan view of the structural material shown in FIG. 11A as viewed from the z direction. The structural material 10f shown in FIGS. 11A and 11B has a structure without a closed cross section. The structural material 10f has a first plate 13 having a bent portion 13bc and a second plate 23 having no bent portion. The first plate 13 and the second plate 23 are overlapped with each other and are configured by the welded portion 3. The tensile strength of the first plate 13 is 980 MPa or more.
[0072]
　The first plate 13 includes a first coupling plate portion 13c and a first spacing plate portion 13b. The first coupling plate portion 13c is overlaid and joined to the second plate 23. The first spacing plate portion 13b is a surface that has a predetermined angle (in this example, a substantially right angle) from the end of the first coupling plate portion 13c to the joint surface of the first plate 13 and the second plate 23. Extending in the direction of. The boundary between the first coupling plate portion 13c and the first spacing plate portion 13b becomes the bent portion 13bc of the first plate 13.
[0073]
　The first coupling plate portion 13c and the second plate 23 are in contact with each other and are joined by the welding portion 3. The welded portion 3 is a portion where a part of the first plate 13 and a part of the second plate 23 are integrated by welding, that is, a welded part. As shown in FIG. 11B, a plurality of welded portions 3 (spot welded portions) are provided on the first coupling plate portion 13c and the second plate 23. There is a heat-affected zone 5 around each of the plurality of welded portions 3 of the first coupling plate portion 13c. The pair of end portions 4 of the first coupling plate portion 13c are arranged between the adjacent heat-affected zones 5. The pair of end portions 4 of the first coupling plate portion 13c form a discontinuous portion between the adjacent heat-affected zones 5.
[0074]
　The plurality of welded portions 3 and the heat-affected zone 5 are arranged side by side in the direction (x direction) in which the ridgeline of the bent portion 13bc extends. The pair of end portions 4 of the first coupling plate portion 13c are a part of slits (notches) that enter from the end portion of the first coupling plate portion 13c on the side opposite to the bending portion 13bc toward the bending portion 13bc. The slit does not extend to the bent portion 13bc. Specifically, the slits are formed in the curved portion between the first coupling plate portion 13c and the first spacing plate portion 13b and the region that does not overlap with each other when viewed in the z direction. That is, the end portion connecting between the pair of end portions 4 of the first coupling plate portions 13c between the adjacent heat-affected zones does not intersect the R end portion 13f of the bent portion 13bc on the side of the first coupling plate portion 13c. Is arranged as follows.
[0075]
　Thus, the structural material may have a structure that does not have a closed cross section. Further, the structural material may be formed by a plate having no bent portion. For example, in the configuration shown in FIG. 11A, the first plate 13 may be replaced with a flat plate having no bent portion. In this case, the weld 3 and the pair of ends 4 may be arranged, for example, in the same manner as in FIG. 11B. In the configurations shown in FIGS. 11A and 11B, the first plate 13 may be the first member and the second plate 23 may be the second member, or the first plate 13 may be the second member and the second member may be the second member. The plate 23 may be used as the first member.
[0076]
　FIG. 12: is sectional drawing of the structural material which concerns on a modification. The structural material 10g shown in FIG. 12 is formed by bending a single plate 14 to form a tubular portion (closed cross-section portion 102).
[0077]
　One plate 14 that constitutes the structural material 10g includes a first plate portion 14a and a second plate portion 14e as plate portions that are overlapped and joined to each other. The first plate portion 14a and the second plate portion 14e are portions including the end portion of one plate 14. The first plate portion 14a and the second plate portion 14e that are overlapped with each other form a flange 101 that is continuous with the closed cross-section portion 102 and that is disposed outside the closed cross-section portion 102. That is, in the example shown in FIG. 12, the closed cross section 102 and the flange 101 are formed by one plate 14.
[0078]
　The first plate portion 14a and the second plate portion 14e are joined by the welded portion 3. Although not shown in FIG. 12, a plurality of welds 3 are provided. Heat-affected zones are formed around the welded portions 3 of the first plate portion 14a and the second plate portion 14e. A pair of end portions of the first plate portion 14a is provided between the adjacent heat-affected zones of the first plate portion 14a. A pair of end portions of the second plate portion 14e is provided between the adjacent heat-affected zones of the second plate portion 14e. In the first plate portion 14a and the second plate portion 14e, the configurations of the welded portion 3, the heat-affected zone, and the pair of end portions are, for example, the configurations of the first member in FIGS. 1B, 1C, and 2 to 6 above. Can be similar to
[0079]
　The plate 14 has a plurality of bent portions 14ab, 14bc, 14cd, 14de between the first plate portion 14a and the second plate portion 14e. The ridgeline formed by these bent portions 14ab, 14bc, 14cd, 14de extends in the x direction. Although not shown, the x direction may be the longitudinal direction of the structural material 10g. In this case, the structural material 10g has a tubular portion extending in the x direction. Further, the plurality of welded portions 3 are arranged in the extending direction of the ridgelines of the bent portions 14ab, 14bc, 14cd, 14de. An end portion connecting a pair of end portions formed between the adjacent heat-affected portions of the first plate portion 14a is formed so as not to extend to the bent portion 14ab.
[0080]
　The shape of the closed cross section of the structural material is not limited to a quadrangle, and may be a shape including another polygon or a curve. Further, in the example shown in FIG. 12, the flange 101, which is a plate portion that is overlapped with each other, is arranged outside the closed cross-section portion 102. Alternatively, as shown in FIGS. 13 and 14, the plate portions that are overlapped with each other may be formed in the closed cross-section portion 102.
[0081]
　In the structural material 10h shown in FIG. 13, the closed cross-section portion 102 includes plate portions 14a and 14e that are overlapped with each other. The plate portions 14 a and 14 e that are overlapped with each other are joined by the weld portion 3. Although not shown in FIG. 13, a plurality of welded portions 3 are arranged side by side in the x direction. There is a heat-affected zone around each of the plate portions 14a and 14e of the plurality of welded portions 3. In the plate portions 14a and 14e, a pair of end portions are arranged between adjacent heat-affected zones. The configuration of the pair of end portions can be similar to, for example, the above-described FIGS. 1B, 1C, and 2 to 6. The end portions connecting the pair of end portions of the plate portion 14a and the plate portion 14e are formed so as not to extend to the bent portions 14ab and 14de of the plate 14.
[0082]
　Moreover, the closed cross-sectional shape of the closed cross-section portion formed by one plate 14 is not limited to a quadrangle. For example, a closed cross section having a closed cross section of any shape such as a polygon, a circle, and an ellipse can be formed by one plate 14. FIG. 14 is a diagram showing a configuration example in the case where the closed cross section 102 having a circular closed cross section is formed by one plate 14.
[0083]
　 The
　welding for forming the welded part is not limited to spot welding. For example, the weld may be formed by laser welding or arc welding. In both cases of arc welding and welding by laser, when the tensile strength of the first member is 980 MPa or more, a heat-affected zone may occur around the weld. In this case, it is preferable to arrange a pair of end portions of the first member between the adjacent heat-affected zones of the first member, as in the above embodiment. This makes it possible to suppress breakage starting from the heat-affected zone.
[0084]
　FIG. 15: is a figure which shows the example of the welding part by arc welding. In the example shown in FIG. 15, there are heat-affected zones 51, 52 around the welded zones 31, 32 by arc welding. The pair of end portions 4 of the first member 1c are arranged between the adjacent heat-affected zones 51 and 52. The longitudinal direction of the welded portion by arc welding is defined as the length direction LB, and the direction perpendicular to the longitudinal direction is defined as the width direction LW. The midpoints of the line that divides the welded portions 31 and 32 into two in the length direction are defined as the centers C1 and C2 of the welded portions 31 and 32. In the example shown in FIG. 15, the pair of end portions 4 are arranged so as to cross a line connecting the centers of the welded portions 31 and 32. The end portion 4a connecting the pair of end portions 4 does not divide the ridge line portion 1f of the first member.
[0085]
　
　The joint surface of the steel plates joined by the welded portion may be curved. The structural material may be curved, for example, in a direction perpendicular to the joint surface of the steel plate (or plate portion) or in a direction parallel to the joint surface (in-plane direction). When the structural material is formed of a plate including a bent portion, the ridgeline formed by the bent portion may be linear or curved.
[0086]
　As an example of the configuration in which the plurality of welded portions are arranged side by side in the direction in which the ridgeline of the bent portion extends, at least the welded portions of the plurality of welded portions may be displaced in the direction perpendicular to the ridgeline. The plurality of welded portions may be arranged side by side in a direction perpendicular to the direction in which the ridgeline of the bent portion extends.
[0087]
　[Simulation Results] The
　inventors performed a simulation using a model of a structural material including a hat member and a closing plate, and analyzed the deformation behavior of the structural material when a shock was applied. The simulation was performed using a plurality of models in which the structure of the flange end of the structural material was changed. The simulation was performed when the indenter was made to collide with the hat member 1 in the z direction.
[0088]
　FIG. 16 is a diagram showing a model used for the simulation. FIG. 17 is a view of the structural member in the model shown in FIG. 16 seen from above (z direction). FIG. 18 is a cross-sectional view showing a cross section taken along the line AA shown in FIG. FIG. 19 is an enlarged view of the area E shown in FIG.
[0089]
　In the model shown in FIG. 16, the impactor 17 is made to collide from above the structural material having the hat member 41 and the closing plate 42. The structural material is placed on the table 19 arranged in the longitudinal direction of the hat member 41. The cover 18 covers the central portion of the hat member 41 between the bases 19 upward. The hat member 41 has a top surface portion 41a, a side wall 41b, and a flange 41c. The flange 41c is superposed on the closing plate 42 and joined by spot welding. The cover 18 contacts the top surface portion 18. The impactor 17 advances in the z direction and collides with the cover 18.
[0090]
　As shown in FIG. 17, a plurality of welded portions 43 by spot welding are arranged in the same direction as the extending direction (x direction) of the ridgeline 41bc between the flange 41c and the side wall 41b. There is a heat-affected zone 45 around each of the plurality of welds 43. The strength of the heat-affected zone 45 is set lower than the strength of the base material of the hat member.
[0091]
　As shown in FIG. 18, a reinforcing member 46 that is in contact with the hat member 41 is arranged inside the space surrounded by the hat member 41 and the closing plate 42. The reinforcing member 46 is joined to the side wall 41b of the hat member 41 and the top surface portion 41a by welding. The closing plate 42 is bent along the bent portion between the flange 41c and the side wall 41b of the hat member 41. The tensile strength of the metal plate of the hat member 41 and the closing plate 42 in FIG. 17 is 1470 MPa, and the plate thickness is 1.4 mm. The tensile strength of the metal plate of the reinforcing member 46 is 1470 MPa, and the plate thickness is 2.0 mm.
[0092]
　As shown in FIG. 19, the flange 41c is provided with a notch. That is, the pair of end portions 44 of the flange 41c are arranged between the adjacent heat-affected zones 45. The end portion 44 extends in the y direction. The pair of end portions 44 of the flange 41c between the adjacent heat-affected zones 45 are a part of the notch. The diameter ND of the welded portion 43, the distance C between the centers of the welded portions 43, the length S between the ends 44 of the flanges 41c on both sides of the welded portion 43 in the x direction, the length α of the notch in the y direction, that is, the notch. The depth α, the length F of the flange 41c in the y direction, and the radius of curvature R of the corner of the notch are included in the simulation parameters. The radius of curvature R is the radius of curvature of the locus of the end portion connecting the pair of end portions 44.
[0093]
　20A to 20C are graphs showing simulation results at the time of impactor collision when the length α of the notch in the y direction is changed. These graphs show that α=0, α=(1/4)F, α=(1/2)F, α=(3/4)F, α=(1/2)F+(ND+1), α= The calculated values ​​for each of F and α=(5/4)F are shown. FIG. 20A shows the maximum shear force up to the impactor maximum load stroll. FIG. 20B shows the equivalent plastic strain of the deformation concentrated portion. FIG. 20C shows the equivalent plastic strain of the heat affected zone.
[0094]
　From the results shown in FIG. 20A, when the length α of the notch in the y direction becomes larger than the distance in the y direction between the center of the welded portion 43 and the edge of the flange 41c (α>(1/2)F), the welding is performed. It was found that the burden on the club would decrease. From the results shown in FIG. 20B, it was found that the deeper the notch, the less the load on the heat-affected zone. In particular, when the length α of the notch in the y direction is larger than the distance between the center of the welded portion 43 and the edge of the flange 41c in the y direction (α>(1/2)F), the load on the heat-affected zone is increased. Drastically reduced. From the results shown in FIG. 20C, it was found that the deeper the notch depth, the greater the concentration of deformation on the flange.
[0095]
　21A to 21C are graphs showing simulation results at the time of impactor collision when the length S between the end portions 44 on both sides of the welded portion 43 in the x direction is changed. These graphs show the calculated values ​​for S=26.6 mm and S=15.3 mm, respectively. FIG. 21A shows the maximum shear force to the impactor maximum load stroll. FIG. 21B shows the equivalent plastic strain in the deformation concentrated portion. FIG. 21C shows the equivalent plastic strain of the heat affected zone.
[0096]
　From the results shown in FIG. 21A, it was found that the larger the length S, the more the load on the welded portion. From the result shown in FIG. 21B, it was found that the larger the length S, the more the deformation concentration on the flange. From the results shown in FIG. 21C, it was found that there was almost no effect of the load on the heat-affected zone of length S.
[0097]
　22A to 22C are graphs showing simulation results at the time of impactor collision when the radius of curvature R of the corner portion of the notch is changed. These graphs show the calculated values ​​for R=0, R=5 mm, and R=10 mm, respectively. FIG. 22A shows the maximum shear force up to the impactor maximum load stroll. FIG. 22B shows the equivalent plastic strain in the deformation concentrated portion. FIG. 22C shows the equivalent plastic strain of the heat affected zone.
[0098]
　From the results shown in FIG. 22A, it was found that the radius of curvature R of the corner portion of the notch had almost no effect on the welded portion. From the results shown in FIG. 22B, it was found that the larger the radius of curvature R of the corner portion of the notch, the greater the concentration of deformation on the flange. From the results shown in FIG. 22C, it was found that there was almost no effect of the load on the heat-affected zone of the radius of curvature R of the corner portion of the notch.
[0099]
　The above-mentioned structural material can be suitably used as a structural material that is expected to be deformed or destroyed. In particular, when the present invention is applied to a structural material that is expected to be deformed or destroyed, the welded portion is unlikely to break, so that a structural material that is not easily destroyed can be obtained. A structural material for vehicles is an example of a structural material that is expected to be deformed or destroyed. As a structural material for a vehicle, specifically, a vehicle structure such as a front frame, a rear frame, a side sill, a front pillar, a center pillar, a cross member, a side rail, a tunnel, a bumper reinforcement, and various reinforcements (reinforcing members). Frame-based parts are included. Further, the present invention may be applied to panel-based parts for automobile structures such as side panels, fenders, dash panels, floor panels, and center panels. Since these automobile structures are deformed and destroyed when the automobile collides, the present invention is effective.
[0100]
　When the structural material of the present invention is used as a structural material for a vehicle, for example, the structural material may be arranged so that the direction in which the welded portions of the structural material are arranged or the direction in which the bent portion extends extends along the outer shape of the vehicle. That is, the structural material may be arranged so that the direction in which the welded portions of the structural material are arranged or the direction in which the bent portion extends is substantially orthogonal to the impact from the outside of the vehicle. Thereby, when the structural material receives an impact from the outside of the vehicle, it is possible to make the welded portion more difficult to break. As described above, a vehicle in which the above structural material is used and a vehicle including the above structural material are also included in the embodiments of the present invention.
[0101]
　Further, in the structural material of the present invention, there may be a plurality of pairs of adjacent welded portions. That is, there may be a plurality of pairs of adjacent heat-affected zones of the first member. In this case, in at least a part of the plurality of heat-affected zone pairs, the pair of end portions of the first member are provided between the adjacent heat-affected zones. The material of the second member is not limited to steel. For example, the material of the second member can be steel, aluminum or other metal.
[0102]
　Although one embodiment of the present invention has been described above, the above embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments without departing from the spirit thereof.
Explanation of symbols
[0103]
　1: Hat member (first plate)
　2: Closing plate (second plate) 3,
　31, 32: Welded parts 5,
　51, 52: Heat-affected parts
　10, 10a, 10b, 10c: Structural material
　1a: Top 　Surface portion
　1b: Side wall
　1c: Flange
1ab, 1bc: Bent portion
The scope of the claims
[Claim 1]
　A first member of a steel plate having a tensile strength of 980 MPa or more, a
　second member of a metal plate, which is overlapped with the first plate portion, and
　a plurality of welds for connecting the first member and the second member by welding. And a
　plurality of heat-affected zones formed on the first member around each of the plurality of welded sections and having a Vickers hardness lower than the Vickers hardness of the first member by 50 HV or more, and between the
　adjacent heat-affected zones. And a pair of end portions of the first member extending in a direction crossing a line connecting the adjacent welded portions
.
[Claim 2]
　The structural material according to claim 1,
　wherein the pair of end portions cross a line connecting the centers of the adjacent welded portions.
[Claim 3]
　The structural material according to claim 2,
　wherein the pair of end portions cross an end portion of a region between the inner peripheral edges of the adjacent heat-affected zones.
[Claim 4]
　The structural material according to claim 3,
　wherein the pair of end portions traverses a region between the adjacent heat-affected zones.
[Claim 5]
　The structural material according to any one of claims 1 to 4,
　wherein the pair of end portions are edges of a hole formed in the first member.
[Claim 6]
　The structural material according to any one of claims 1 to 5,
　wherein a tensile strength of the second member is less than 1180 MPa, and an
　end portion of the second member between the adjacent welded portions is formed. There is no structure material.
[Claim 7]
　The structural material according to any one of claims 1 to 5,
　wherein the second member is a steel plate having a tensile strength of 980 MPa or more, and the
　adjacent welded portions are provided between the adjacent welded portions. A structural member further comprising a pair of end portions of the second member extending in a direction crossing a line connecting the two.
[Claim 8]
　The structural material according to any one of claims 1 to 6,
　wherein the second member around the plurality of welds has a Vickers hardness that is lower than the hardness of the second member by 50 HV or more. Structural material without parts.
[Claim 9]
　The structural member according to any one of claims 1 to 8,
　wherein a distance between the ones of the pair of end portions on both sides of the welded portion on the welded portion side is 6 times a diameter of the welded portion. A structural material that is less than or equal to twice.
[Claim 10]
　The structural material according to any one of claims 1 to 9,
　wherein a radius of curvature of an end portion connecting the pair of end portions is 10 mm or less.
[Claim 11]
　The structural material according to any one of claims 1 to 10,
　wherein the first member includes a ridge line portion, and the pair of end portions and an end portion connected to the pair of end portions have the ridge line portion. Structural material that does not divide.