Vehicle frame components

Abstract

To facilitate an improvement effect of collision resistance performance per member unit mass by a high-strength material in a structure having a reinforcement member added to a hat-shaped member.SOLUTION: A vehicle skeleton member 10 has a hat-shaped member 1, a closing plate 2, a reinforcement member 6, and a plurality of welding parts 31. The hat-shaped member 1 has a first top plate 1a, two first vertical walls 1b and two flanges 1c. The reinforcement member 6 has a second top plate 6a and two second vertical walls 6b. A plurality of spot welding parts 31 join the first vertical wall 1b with the second vertical wall 6b. At least one of the hat-shaped member 1 and the reinforcement member 6 has a tensile strength exceeding 1.1 GPa. The whole of a HAZ softening part 31b of the spot welding part 31 on the vertical wall of the member having a tensile strength exceeding 1.1 GPa is positioned between a height position Lc of the center of the first vertical wall 1b and a ridge line 1ab between the first vertical wall 1b and the first top plate 1a, and is at a position that does reach an R-stop of the ridge line 1ab between the vertical wall and the top plate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a vehicle frame member including a reinforcing member. [Background technology]

[0002] For example, vehicle frame members such as B-pillars and side sills are required to have crashworthiness. A member having a hat-shaped cross-sectional shape to which a reinforcing member is joined may be used as a vehicle frame member. For example, JP 2013-189173 A (patent document) discloses a structural member for an automobile body in which a first molded body having a hat-shaped cross-sectional shape and a second molded body having a groove-shaped cross-sectional shape are closely attached to each other. By setting the cross-sectional perimeter of the vertical wall portion of the second molded body relative to the cross-sectional perimeter of the vertical wall portion of the first molded body to a specific range, early buckling of the vertical wall portion of the first molded body can be prevented. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-189173 A Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned conventional technology does not teach the relationship between the strength of a member having a hat-shaped cross-sectional shape (hereinafter referred to as a hat-shaped member) and a reinforcing member, and the arrangement of a HAZ softened portion around the spot weld that joins them. The inventors have studied how to improve the crash resistance per unit mass of the member by forming the hat-shaped member and the reinforcing member from a high-strength material. The crash resistance per unit mass of the member is represented, for example, by the maximum load and the amount of energy absorbed per unit mass of the member during a crash. In the study, it was found that when at least one of the hat-shaped member and the reinforcing member is formed from a high-strength material, the HAZ softened portion of the spot weld that joins the reinforcing member and the hat-shaped member is likely to be the starting point of a fracture. Hereinafter, such a fracture that starts from a HAZ softened portion is referred to as a HAZ fracture. The occurrence of a HAZ fracture can be a factor that reduces the effect of improving the crash resistance per unit mass of the member by using a high-strength material.

[0005] The present application discloses a vehicle frame component that can more easily achieve the effect of improving crash resistance per unit mass of the component by adding a reinforcing member to a hat-shaped component and suppressing the occurrence of HAZ fracture in a structure that uses a high-strength material for at least one of the hat-shaped component or the reinforcing member. [Means for solving the problem]

[0006] A vehicle frame member in an embodiment of the present invention includes a hat-shaped member, a closing plate, a reinforcing member, and a plurality of spot welds. The hat-shaped component includes a first top plate, two first vertical walls, and two flanges. The first top plate is disposed between the two first vertical walls. The first vertical walls are disposed between the first top plate and the flanges. The flanges are joined to the closing plate. The reinforcing member includes a second top plate and two second vertical walls, and the second top plate is disposed between the two second vertical walls. The first vertical wall and the second vertical wall are overlapped with each other, and the plurality of spot welds join the first vertical wall and the second vertical wall. At least one of the hat-shaped member and the reinforcing member has a tensile strength of more than 1.1 GPa. The entire HAZ softened portions of the multiple spot welds in the vertical walls of the hat-shaped member and the reinforcing member having a tensile strength exceeding 1.1 GPa are located, in a direction perpendicular to the face of the flange, between the center height of the first vertical wall and the R end of the ridge line between the first vertical wall and the first top plate on the first vertical wall side, and are located in a position that does not reach the R end of the vertical wall side of the ridge line between the vertical wall and the top plate of the member having a tensile strength exceeding 1.1 GPa. Effect of the Invention

[0007] According to the present disclosure, in a structure in which a reinforcing member is added to a hat-shaped member and a high-strength material is used for at least one of the hat-shaped member or the reinforcing member, the occurrence of HAZ fracture is suppressed, making it easier to obtain the effect of improving crash resistance per unit mass of the member by using a high-strength material. [Brief description of the drawings]

[0008] [Figure 1] 3 is a cross-sectional view showing the configuration of a structural member in the present embodiment. FIG. [Diagram 2] FIG. 2 is an enlarged view of the spot weld area of ​​the vertical wall in FIG. [Diagram 3] FIG. 2 is a side view of the structural member shown in FIG. [Figure 4] FIG. 2 is a diagram showing the hardness distribution of a spot weld of the structural member shown in FIG. [Diagram 5] 2 is a cross-sectional view showing a modified example of the structural member shown in FIG. [Figure 6] 1. FIG. 4 is a cross-sectional view showing another modified example of the structural member shown in FIG. [Figure 7] 1 is a diagram showing an example of application of a structural member according to the present embodiment to a vehicle frame. [Figure 8] FIG. 2 is a diagram showing a four-point bending model in this analysis example. [Figure 9] FIG. 9 is a diagram showing a model used in the four-point bending model of FIG. 8. [Figure 10]FIG. 10 is a diagram showing a stress field resulting from a four-point bending simulation performed on the model shown in FIG. [Figure 11] 10 is a graph showing the load-displacement relationship and the maximum load per unit mass as a result of a four-point bending simulation performed on the model shown in FIG. 9. [Figure 12] 10 is a graph showing the maximum load per unit mass of a member of the model shown in FIG. 9. [Figure 13] 10 is a graph showing the amount of energy absorbed per unit mass of a member of the model shown in FIG. 9. [Figure 14] FIG. 2 is a diagram showing the size of a test piece used in measuring tensile strength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The inventors have studied a configuration in which a closed cross-section structure having a hat-shaped member and a closing plate is reinforced with a groove-shaped reinforcing member as a vehicle frame member. It has been found that when at least one of the hat-shaped member and the reinforcing member is a high-strength member such as a hot-stamped material or a cold-pressed ultra-high tensile material, and the reinforcing member and the hat-shaped member are joined by spot welding, a HAZ softened portion exists in the spot weld. The HAZ softened portion is a region softened by the heat effect (tempering) during welding. For example, in a 1.5 GPa-class hot-stamped material, the hardness of the base material is about 450 HV in Vickers hardness, whereas the hardness of the softest part of the HAZ softened portion is reduced to about 300 HV.

[0010] As a result of investigations, the inventors found that when a high-strength member exceeding 1.1 GPa is used for a vehicle frame member, if a large tensile force is applied to the spot weld during a collision, strain is concentrated in the HAZ softened portion, making the member more likely to break. When such a HAZ break occurs, the effect of improving crash resistance per unit mass of the member by using a high-strength member is reduced, that is, the effect of improving crash resistance per unit mass of the member expected from a high-strength member is not easily achieved.

[0011] As a result of further trial and error, the inventors discovered that HAZ fracture can be suppressed by positioning the HAZ softened portion of the spot weld in a high-strength component exceeding 1.1 GPa closer to the top plate of the hat-shaped component than the height of the center of the vertical wall of the hat-shaped component, and by positioning it in an area that does not reach the R end of the vertical wall side of the ridge between the vertical wall and the top plate of the high-strength component exceeding 1.1 GPa.

[0012] A vehicle frame member in an embodiment of the present invention includes a hat-shaped member, a closing plate, a reinforcing member, and a plurality of spot welds. The hat-shaped component includes a first top plate, two first vertical walls, and two flanges. The first top plate is disposed between the two first vertical walls. The first vertical walls are disposed between the first top plate and the flanges. The flanges are joined to the closing plate. The reinforcing member includes a second top plate and two second vertical walls, and the second top plate is disposed between the two second vertical walls. The first vertical wall and the second vertical wall are overlapped with each other, and the plurality of spot welds join the first vertical wall and the second vertical wall. At least one of the hat-shaped member and the reinforcing member has a tensile strength of more than 1.1 GPa. The entire HAZ softened portions of the multiple spot welds in the vertical walls of the hat-shaped member and the reinforcing member having a tensile strength exceeding 1.1 GPa (the first vertical wall and the second vertical wall having a tensile strength exceeding 1.1 GPa in portions other than the spot welds) are located, in a direction perpendicular to the face of the flange, between the height of the center of the first vertical wall and the R end of the ridge line between the first vertical wall and the first top plate, and are located in a position that does not reach the R end of the vertical wall side of the ridge line between the vertical wall and the top plate (the first top plate and the second top plate having a tensile strength exceeding 1.1 GPa) of the member having a tensile strength exceeding 1.1 GPa.

[0013] According to the above configuration, by using a material having a strength of more than 1.1 GPa for at least one of the hat-shaped member and the reinforcing member, and by arranging the spot welds and the HAZ softened portion in the above configuration, it is possible to suppress HAZ fracture in the high-strength member during a collision in which a load is applied to the first top plate. This makes it easier to obtain the effect of improving the crashworthiness per unit mass of the member by using a high-strength member. As a result, it is possible to realize a crash-resistant member with high mass efficiency.

[0014] More specifically, in the above configuration, the entire HAZ softened portion of the plurality of spot welds in the vertical wall of the member having a tensile strength exceeding 1.1 GPa is located between the position of the center height of the first vertical wall of the hat-shaped member and the R end of the ridgeline between the first vertical wall and the first top plate on the first vertical wall side. Here, the HAZ softened portion is defined as a region around the nugget of the spot weld where the Vickers hardness is 30 HV or more lower than the Vickers hardness of the member. The spot weld includes the nugget and its surrounding heat affected zone (HAZ). The HAZ softened portion is included in the heat affected zone. The nugget is a portion that is melted during welding. The center of the spot weld is defined as the center of the nugget when viewed from the plate thickness direction of the first vertical wall.

[0015] When a load is applied to the first top plate due to a collision, the vehicle frame member is deformed by receiving a bending moment. This bending moment applies a compressive bending to the first top plate side and a tensile bending to the closing plate side. In the region on the first top plate side from the center of the height of the first vertical wall, a compressive force is likely to occur in the longitudinal direction in both the first vertical wall and the second vertical wall. That is, in the above region, the tensile force in the longitudinal direction tends not to occur or to be small. By arranging the spot welds as described above, a compressive force rather than a tensile force is likely to occur in the HAZ softened portion during a collision. When a large tensile force in the longitudinal direction is applied to the HAZ softened portion, a HAZ fracture is likely to occur in the HAZ softened portion, whereas a HAZ fracture is unlikely to occur even if a compressive force in the longitudinal direction is applied to the HAZ softened portion. Therefore, the above spot weld arrangement structure suppresses HAZ fracture in members exceeding 1.1 GPa. As a result, the collision resistance performance per unit mass of the member of the vehicle frame member can be improved.

[0016] The position of the central height of the first vertical wall is determined by taking the height of the first vertical wall from the R end of the ridgeline between the first vertical wall and the first top plate on the first top plate side to the R end of the ridgeline between the first vertical wall and the flange on the flange side in a cross section that passes through the centers of the respective welding spots and is perpendicular to the longitudinal direction of the hat-shaped member. The height direction of the first vertical wall is the direction perpendicular to the surface of the flange that extends from the first vertical wall via the ridgeline in the cross section. That is, the height of the first vertical wall is the height of the part including the ridgelines at both ends of the first vertical wall. More specifically, the height of the first vertical wall is the dimension from the R end of the boundary between the lower surface of the flange and the ridgeline to the R end of the boundary between the upper surface of the first top plate and the ridgeline in the direction perpendicular to the surface of the flange that extends from the first vertical wall via the ridgeline. If the upper surface and the lower surface of the flange are not parallel, the direction perpendicular to the lower surface of the flange is the direction perpendicular to the surface of the flange. The above upper and lower surfaces are the upper and lower surfaces in the height direction of the first vertical wall when the up-down direction is defined with the first vertical wall as the reference, the first top plate as the top, and the flange as the bottom. The height of the first vertical wall is determined for each of the two first vertical walls in one hat-shaped component. The height of each first vertical wall is the height of the part including the ridge lines at both ends of each first vertical wall.

[0017] In a spot weld, the area where the Vickers hardness is 30HV or more lower than the Vickers hardness of the component is defined as the HAZ softened area. The Vickers hardness of the component is the Vickers hardness of the part other than the spot weld of the component. The HAZ softened area in the vertical wall of a hat-shaped component or a reinforcing component is defined as the area where the Vickers hardness is 30HV or more lower than the part other than the spot weld of the vertical wall. The Vickers hardness in the vertical wall of a hat-shaped component or a reinforcing component whose tensile strength exceeds 1.1 GPa is measured at a position 1 / 4 of the plate thickness from the interface between the first vertical wall and the second vertical wall (if there is a small gap between the first vertical wall and the second vertical wall, the surface in contact with the gap of the first vertical wall or the second vertical wall whose tensile strength exceeds 1.1 GPa) to the first vertical wall or the second vertical wall whose tensile strength exceeds 1.1 GPa on the cut surface including the spot weld of the first vertical wall and the second vertical wall. The method for measuring Vickers hardness is in accordance with the Vickers hardness test method specified in JIS Z 2244-1:2020. The conditions for measuring Vickers hardness are a load (test force) of 3N and a measurement pitch of 0.5mm. The Vickers hardness of the component is measured at five points that are 10mm or more away from the spot weld. The average value of the Vickers hardness measured at these five points is the Vickers hardness of the component.

[0018] The tensile strength of the hat-shaped member and the reinforcing member shall be the tensile strength obtained by measuring the test pieces taken from the parts of the hat-shaped member and the reinforcing member excluding the spot welds and other parts where the strength has changed locally. The test pieces shall be ASTM half-size test pieces shown in Figure 14. The units of the dimensions shown in Figure 14 are mm. The plate thickness of the test pieces shall be the plate thickness of the member. The tensile strength shall be measured in accordance with JIS Z 2241 (2011), and a tensile test shall be performed at a tensile speed (crosshead displacement speed) of 10 mm / min. The test pieces may be taken from either the vertical wall or the top plate. The form in which the tensile strength of the member exceeds 1.1 GPa includes the case where the tensile strength exceeds 1.1 GPa in all areas except the spot welds of the member, as well as the case where the tensile strength of the member as a whole is considered to be equivalent to a strength of more than 1.1 GPa, even though there are some small areas in the member where the tensile strength does not exceed 1.1 GPa.

[0019] The end of the R on the vertical wall side of the ridgeline between the vertical wall and the top plate in a hat-shaped member or reinforcing member is the end on the vertical wall side (not the top plate side) of the rounded portion between the vertical wall and the top plate, i.e., the R-shaped portion (R portion) in a cross section perpendicular to the ridgeline of the hat-shaped member or reinforcing member. When two members are overlapped, the two members are in contact at least partially.

[0020] In the above configuration, the reinforcing member may have a tensile strength of more than 1.1 GPa, and the hat-shaped member may have a tensile strength of 1.1 GPa or less. This allows the hat-shaped member to have a tensile strength of 1.1 GPa or less to ensure ductility, while a reinforcing member having a tensile strength of more than 1.1 GPa can be disposed in a portion where deformation resistance (resistance to deformation) against a collision load is desired to be improved. This makes it possible to appropriately dispose a portion that is made ductile and less susceptible to material fracture, and a portion that is made less susceptible to deformation by the reinforcing member, thereby further improving the collision resistance performance as a whole. In addition, the occurrence of fracture originating from the HAZ softened portion (HAZ fracture) can be further suppressed in the spot welded portion in the first vertical wall of the hat-shaped member.

[0021] For example, the tensile strength of the hat-shaped member may be 980 MPa or more and less than 1.1 GPa. This allows the hat-shaped member to have appropriate strength and to more easily ensure ductility. By ensuring ductility, material fracture can be suppressed.

[0022] In the above configuration, the hat-shaped member and the reinforcing member may both have a tensile strength of more than 1.1 GPa, thereby ensuring higher crash resistance for the entire vehicle frame member.

[0023] In a cross section in a plane passing through the center of each of the plurality of spot welds and perpendicular to the longitudinal direction of the hat-shaped member, it is preferable that the distance from the end of the R on the vertical wall side of the ridgeline between the first vertical wall and the first top plate to the end of the second vertical wall in the direction perpendicular to the surface of the flange is one-third or less of the height of the first vertical wall. This allows the spot welds to be disposed close to the ridgeline between the first vertical wall and the first top plate and at a position that does not interfere with crashworthiness. As a result, it is possible to further improve the crashworthiness per unit mass of the member against bending of the vehicle frame member due to a collision. From this viewpoint, it is more preferable that the distance is one-quarter or less of the height of the first vertical wall.

[0024] When a vehicle frame member including a hat-shaped member and a reinforcing member is collided from the top plate side, the vehicle frame member receives a bending moment due to the collision load that applies a compressive bending to the top plate side. In the deformation due to this collision load, the inventor has found that the top plate and the ridge line mainly bear the load. In such bending deformation, the contribution of the vertical wall to the load capacity is considered to be lower than that of the top plate and the ridge line. In addition, the inventor has found that when the tensile strength of at least one of the hat-shaped member and the reinforcing member exceeds 1.1 GPa, the spot welded portion can be arranged in a position close to the ridge line, making it difficult for the spot welded portion to peel off during cross-sectional deformation, thereby making it difficult for the reinforcing member to come off from the hat-shaped member. Based on this knowledge, by arranging the spot welded portion in a position close to the ridge line, the stress applied to the spot welded portion in the peeling direction (direction perpendicular to the vertical wall) can be reduced, and peeling of the spot welded portion can be suppressed. This improves the amount of energy absorption during the deformation period after the maximum load is reached. Note that the higher the strength of the member, the easier it is for peeling of the spot welded portion to occur. Therefore, in a configuration in which the tensile strength of at least one of the hat-shaped member and the reinforcing member exceeds 1.1 GPa, the effect of preventing peeling due to the arrangement of the spot welds is more pronounced. In a configuration in which the tensile strength of both the hat-shaped member and the reinforcing member exceeds 1.1 GPa, peeling of the spot welds is more likely to occur than in a configuration in which the tensile strength of only one of them exceeds 1.1 GPa, so the effect of preventing peeling due to the arrangement of the spot welds is even more pronounced.

[0025] From the viewpoint of the maximum load and energy absorption per unit mass of the member, the distance from the end of the R on the vertical wall side of the ridgeline between the first vertical wall and the first top plate in the above cross section to the end of the second vertical wall is preferably, for example, 10 to 50 mm. From the same viewpoint, the minimum value of this distance is more preferably 15 mm or more, and even more preferably 20 mm or more. The maximum value of this distance is more preferably 40 mm or less, and even more preferably 30 mm or less. The centers of the multiple welding spots are preferably located 5 to 15 mm from the end of the R on the vertical wall side of the ridgeline between the vertical wall and the top plate of the member having a tensile strength of more than 1.1 GPa among the hat-shaped member and the reinforcing member. This allows the spot welds to be positioned close to the ridgeline while avoiding reaching the HAZ softened portion and the ridgeline.

[0026] The centers of the plurality of spot welds are preferably located 5 to 15 mm from the end of the second vertical wall of the reinforcing member. Here, the end of the second vertical wall of the reinforcing member is an end on the opposite side of the ridgeline between the second vertical wall and the second top plate with respect to the spot welds. That is, the spot welds are disposed between the end of the reinforcing member and the ridgeline. The ridgeline side portion from the spot welds to the ridgeline between the second vertical wall and the second top plate of the reinforcing member contributes to a certain degree to the load-bearing performance. In contrast, the end side portion from the spot welds to the end of the second vertical wall of the reinforcing member is considered to contribute less to the load-bearing performance. Therefore, by making this end side portion smaller, the load-bearing performance relative to the weight of the vehicle frame member can be improved. On the other hand, from the viewpoint of ensuring the joint strength of the spot welds, it is preferable to secure a sufficient area for the spot welds in the reinforcing member. From these viewpoints, the inventor has come up with a configuration in which the centers of the plurality of spot welds are located 5 to 15 mm from the end of the second vertical wall of the reinforcing member.

[0027] The end of the second vertical wall of the reinforcing member may be disposed between the position of the center height of the first vertical wall and the ridgeline between the first vertical wall and the first top plate in the direction perpendicular to the surface of the flange. The inventors have found that it is important that the first top plate does not buckle against the bending moment during a collision in which a load is applied to the first top plate, and that for this purpose, strengthening the first top plate and the vicinity of the ridgelines at both ends is effective. By locating the end of the reinforcing member between the position of the center height of the first vertical wall and the ridgeline between the first vertical wall and the first top plate, the weight of the reinforcing member can be reduced while ensuring a higher load-bearing performance during a collision by the reinforcing member. Furthermore, the part of the second vertical wall on the ridgeline side of the spot welded part contributes more to the load-bearing performance than the part of the second vertical wall on the flange side of the spot welded part. Therefore, in addition to the above-mentioned arrangement of the end of the second vertical wall, the center of the plurality of spot welded parts can be located 5 to 15 mm from the end of the second vertical wall of the reinforcing member, thereby further enhancing the effect of reducing the weight of the reinforcing member while ensuring a higher load-bearing performance.

[0028] The HAZ softened portion of the vertical wall of the hat-shaped member and the reinforcing member having a tensile strength exceeding 1.1 GPa may have a large softened region having a Vickers hardness that is 50 HV or more lower than the Vickers hardness of the portion of the vertical wall other than the spot welds. When the difference in Vickers hardness between the HAZ softened portion of the vertical wall and the portion of the vertical wall other than the spot welds is 50 HV or more, strain concentration is likely to occur in the HAZ softened portion under conditions where a tensile force is applied, and fracture (HAZ fracture) originating from the HAZ softened portion is likely to occur. By arranging the HAZ softened portion having a Vickers hardness difference of 50 HV or more with the portion of the vertical wall other than the spot welds on the compression side, the effect of suppressing HAZ fracture becomes significant.

[0029] A vehicle frame including the vehicle frame member having the above-mentioned configuration is also included in the embodiments of the present invention. In this case, the first top plate may be disposed on the outer side of the vehicle, and the closing plate may be disposed on the inner side of the vehicle. This makes it possible to form a vehicle frame having improved collision resistance against a collision load from the outside of the vehicle.

[0030] The reinforcing member may be disposed outside the closed cross-sectional structure formed by the hat-shaped member and the closing plate, or may be disposed inside the closed cross-sectional structure, i.e., between the hat-shaped member and the closing plate.

[0031] The second top plate may be located closer to the first top plate than the center height of the first vertical wall. The second top plate may be disposed between the center height of the first vertical wall and the first top plate. This improves the reinforcing effect of the reinforcing member on the ridge between the first vertical wall and the first top plate. As a result, the vehicle frame member can more efficiently absorb energy during bending and crushing deformation.

[0032] The neutral axis of the vehicle frame member is a position where, when a bending moment occurs in the member, the tension and compression forces in the longitudinal direction of the member are balanced and the stress becomes zero. When a bending moment occurs in the member, the stress at the neutral axis becomes zero, and the tension force increases as the distance from the neutral axis to the tension side increases, and the compression force increases as the distance from the neutral axis to the compression side increases. The position of the neutral axis in the member changes depending on the structural conditions such as the shape of the member. The inventors have found that, due to the structure of the vehicle frame member, the position of the neutral axis is often located near the height of the center of the first vertical wall of the hat-shaped member or on the closing plate side. Based on this, they have conceived that by arranging the entire HAZ softened portion based on the position of the height of the center of the first vertical wall as in the embodiment of the present invention, it is possible to load a compressive force or a relatively small tensile force on the HAZ softened portion during a collision even under various structural conditions. That is, according to the embodiment of the present invention, HAZ fracture in a high-strength member can be suppressed under various structural conditions.

[0033] The inventors' study has revealed that when a HAZ softened portion is disposed on a ridgeline between a vertical wall and a top plate, the strength of the ridgeline is reduced. Therefore, it is preferable that the spot welds are disposed so that the HAZ softened portion is not present on either the ridgeline between the first vertical wall and the first top plate or the ridgeline between the second vertical wall and the second top plate. From the same viewpoint, the spot welds may also be disposed so that the nugget and the HAZ softened portion are not present on either ridgeline. It is also preferable to dispose the spot welds 31 so that the difference between the Vickers hardness of the R-stopping portion on the vertical wall side of the ridgeline and the Vickers hardness of the portion of the vertical wall other than the spot welds is 30 HV or less.

[0034] In the above configuration, the first top plate and the second top plate may be overlapped. This can further enhance the reinforcing effect of the reinforcing member. In this case, a top plate spot weld may be provided to join the first top plate and the second top plate. In the hat-shaped member, the first vertical wall, the first top plate, and the flange are integrally formed from the same plate material. In the reinforcing member, the second vertical wall and the second top plate are integrally formed from the same plate material. Therefore, at least one of the first top plate and the second top plate has a tensile strength of more than 1.1 GPa. The top plate spot weld may be arranged so that the HAZ softened portion of the top plate spot weld does not reach the R end on the top plate side of the ridge between the top plate and the vertical wall of the member having a tensile strength of more than 1.1 GPa among the hat-shaped member and the reinforcing member. This can further enhance the effect of suppressing HAZ fracture in high-strength members.

[0035] The manufacturing method of the vehicle frame member having the above-mentioned configuration is also included in the embodiment of the present invention. The manufacturing method of this embodiment includes a step of forming the hat-shaped member by press forming, a step of forming the reinforcing member by press forming separately from the hat-shaped member, a step of joining the first vertical wall of the hat-shaped member and the second vertical wall of the reinforcing member by spot welding, and a step of joining the closing plate to the flange of the hat-shaped member. In the joining of the hat-shaped member and the reinforcing member, by spot welding so that the HAZ softened portion is located as described above, it is possible to provide a vehicle frame member that is easy to obtain the effect of improving the collision resistance per unit mass of the member by using a high-strength member. At least one of the hat-shaped member and the reinforcing member can be made into a member having a tensile strength exceeding 1.1 GPa by, for example, quenching during press forming by hot stamping (hot press). Alternatively, a hat-shaped member or a reinforcing member having a tensile strength exceeding 1.1 GPa can be obtained by forming an ultra-high tensile material by cold press. The closing plate is not particularly limited, but may be formed by, for example, hot press or cold press. For example, a closing plate can be obtained by cold pressing a high tensile steel material.

[0036] [Embodiment] FIG 1 is a cross-sectional view showing the configuration of a vehicle frame member (hereinafter simply referred to as "structural member") 10 in this embodiment. FIG 2 is an enlarged view of the vicinity of the spot weld of the vertical wall in FIG 1. FIG 3 is a side view of the structural member 10 shown in FIG 1. FIG 1 is a cross-section of a surface perpendicular to the longitudinal direction of the structural member 10 (i.e., the longitudinal direction of the hat-shaped member 1). FIG 3 is a side view of the structural member 10 shown in FIG 1 as seen from a direction perpendicular to the longitudinal direction (x direction) and height direction (z direction), i.e., the width direction (y direction).

[0037] The structural member 10 comprises a hat-shaped member 1, a closing plate 2, and a reinforcing member 6. The hat-shaped member 1 has a hat-shaped cross-sectional shape. A part of the hat-shaped member 1 and a part of the closing plate 2 are overlapped and joined to each other. The hat-shaped member 1 and the closing plate 2 are joined to each other to form a closed cross-sectional structure. A part of the reinforcing member 6 and a part of the hat-shaped member 1 are joined to each other.

[0038] As shown in FIG. 1 and FIG. 3, the hat-shaped member 1 has a first top plate 1a, two first vertical walls 1b, and two flanges 1c. The two first vertical walls 1b extend from both ends of the first top plate 1a in the width direction via a ridge line 1ab and face each other. The two flanges 1c extend from the other end of the first vertical wall 1b opposite to the one end of the first top plate 1a side of the first vertical wall 1b in a direction away from each other. That is, the two flanges 1c extend outward from the other end of the two first vertical walls 1b in the opposing direction of the two first vertical walls 1b via a ridge line 1bc. The two flanges 1c and the closing plate 2 are joined together in an overlapping manner. The closing plate 2 and the two flanges 1c are joined by a plurality of flange spot welds 33.

[0039] The boundaries (shoulders) between the first top panel 1a and the two first vertical walls 1b form the bent portions of the hat-shaped member 1. These bent portions form ridge lines 1ab extending in the longitudinal direction (x-direction) of the structural member 10. The boundaries between each of the two first vertical walls 1b and each flange 1c form the bent portions of the hat-shaped member 1. These bent portions also form ridge lines 1bc extending in the x-direction.

[0040] The reinforcing member 6 is a groove-shaped member including a second top plate 6a and two second vertical walls 6b. The two second vertical walls 6b extend from both ends of the second top plate 6a in the width direction via ridge lines 6ab. That is, the second top plate 6a is disposed between the two second vertical walls 6b. The two second vertical walls 6b face each other.

[0041] The boundary portions (shoulder portions) between the second top plate 6a and the two second vertical walls 6b become bent portions of the reinforcing member 6. These bent portions form a ridge line 6ab that extends in the longitudinal direction (x direction) of the structural member 10.

[0042] The ridge lines 1ab, 1bc, and 6ab have an R-shape in a cross section perpendicular to the longitudinal direction of the hat-shaped member. The ends of the R-shape end in an R-shape. In FIG. 1, the R-points of the ridge lines 1ab, 6ab, and 1bc are indicated by dashed lines. As shown in FIG. 2, in this cross section, the ridge line 1ab is the portion between the R-point 1ab1 on the vertical wall side and the R-point 1ab2 on the top plate side. The ridge line 6ab is the portion between the R-point 6ab1 on the vertical wall side and the R-point 6ab2 on the top plate side.

[0043] The second top plate 6a is overlapped with the first top plate 1a of the hat-shaped member 1. The second vertical wall 6b of the second top plate 6a is overlapped with the first vertical wall 1b. The second vertical wall 6b is joined to the first vertical wall 1b of the hat-shaped member 1 by a plurality of spot welds 31. The first top plate 1a and the second top plate 6a may be joined by spot welds.

[0044] 1 to 3, the hat-shaped member 1 and the reinforcing member 6 are both made of a material having a tensile strength of more than 1.1 GPa. Therefore, the flange 1c, the first top plate 1a, the second top plate 6a, the first vertical wall 1b, and the second vertical wall 6b all have a tensile strength of more than 1.1 GPa except for the spot welds 31, 33.

[0045] As shown in FIG. 2, in the first vertical wall 1b and the second vertical wall 6b, the spot weld 31 includes a nugget 31c, a HAZ hardened portion 31a around the nugget 31c, and a HAZ softened portion 31b around the HAZ hardened portion 31a. Similarly, the flange spot weld 33 includes a nugget, a HAZ hardened portion, and a HAZ softened portion. The nugget is a portion that melts and solidifies during welding. In the spot weld, the nugget mainly contributes to the joining. In some cases, a part of the HAZ hardened portion contributes to the joining.

[0046] In the example shown in Figs. 1 and 3, the neutral axis G1 passes through the center of the height H in a direction perpendicular to the lower surface of the flange 1c extending from the first vertical wall 1b via the ridge line 1bc.

[0047] As shown in FIG. 2, the HAZ softened portion 31b of the multiple spot welds 31 joining the first vertical wall 1b and the second vertical wall 6b is located between the position Lc of the center height of the first vertical wall 1b and the ridgeline 1ab between the first vertical wall 1b and the first top plate 1a, and is located at a position that does not reach the R end of the ridgeline of the first vertical wall 1b and the first top plate 1a. The position Lc of the center height of the first vertical wall 1b is a position that is 1 / 2 the height H of the first vertical wall (a position at a height of H / 2). The height H of the first vertical wall is the dimension from the R end of the boundary between the lower surface of the flange 1c and the ridgeline 1bc to the R end of the boundary between the upper surface of the first top plate 1a and the ridgeline 1ab in a direction perpendicular to the lower surface of the flange 1c extending from the first vertical wall 1b via the ridgeline 1bc.

[0048] Fig. 4 is a diagram showing an example of the cross-sectional structure and hardness distribution of the HAZ softened portion 31b in the spot welded portion 31. The upper part of Fig. 4 is a cross-sectional view of a portion including the nugget 31c, the HAZ hardened portion 31a, and the HAZ softened portion 31b in the spot welded portion 31. The lower part of Fig. 4 is a graph showing an example of the distribution of Vickers hardness along a line S2 in the cross-sectional view. The line S2 is a line located at a distance of 1 / 4 of the plate thickness t of the first vertical wall 1b from the interface 16b between the first vertical wall 1b and the second vertical wall 6b.

[0049] In FIG. 4, the spot welded portion 31 is heated to melt during welding, and then cooled. The nugget 31c is a portion that melts and solidifies during welding, that is, a molten portion. After melting during welding, the nugget 31c is heat-removed by an electrode or a steel plate portion and quenched. At this time, the periphery of the nugget 31c also reaches the A3 point or higher and is austenitized, and then heat-removed and quenched. As a result, the nugget 31c and the area adjacent to the periphery thereof have approximately the same hardness as the vertical walls 1b and 6b. This forms a HAZ hardened portion 31a around the nugget 31c. Around the nugget 31c, a HAZ softened portion 31b is formed, in which the structure is transformed and softened by the heat during welding. This HAZ softened portion 31b is a portion that is softened by tempering (hard phase is softened). The hardness distribution of the spot welded portion is not limited to the example shown in FIG. 4. For example, the hardness of the nugget may vary depending on the composition of the hat member and the reinforcing member.

[0050] Here, the Vickers hardness measured on the first vertical wall 1b and the second vertical wall 6b at a distance SD = 10 mm or more away from the spot weld 31 is regarded as the Vickers hardness of the portions of the first vertical wall 1b and the second vertical wall 6b other than the HAZ softened portions. The HAZ softened portion 31b of the first vertical wall 1b is defined as a portion having a Vickers hardness 30 HV or more lower than the Vickers hardness H1 of the base material of the first vertical wall 1b. The HAZ softened portion 31b of the second vertical wall 6b is defined as a portion having a Vickers hardness 30 HV or more lower than the base material of the second vertical wall 6b.

[0051] The Vickers hardness is measured on a cut surface including the center of the spot welded portion 31 of the first vertical wall 1b and the second vertical wall 6b (i.e., the center of the nugget 31c) at a position 1 / 4 of the plate thickness t from the interface 16b between the first vertical wall 1b and the second vertical wall 6b toward the member of the first vertical wall 1b and the second vertical wall 6b whose tensile strength exceeds 1.1 GPa (t / 4). If there is a small gap between the first vertical wall 1b and the second vertical wall 6b, the Vickers hardness is measured at a position 1 / 4 of the plate thickness t (t / 4) from the surface in contact with the gap of the member of the first vertical wall 1b and the second vertical wall 6b whose tensile strength exceeds 1.1 GPa toward the plate thickness direction of the member. The measurement conditions for Vickers hardness are a load of 3N and a measurement pitch of 0.5 mm. In the case of FIG. 4, since both the first vertical wall 1b and the second vertical wall 6b exceed 1.1 GPa, the Vickers hardness is measured on both the first vertical wall 1b and the second vertical wall 6b.

[0052] The HAZ softened portion 31b of the first vertical wall 1b and the second vertical wall 6b is located between the position Lc of the center height of the first vertical wall 1b and the ridgeline 1ab between the first vertical wall 1b and the first top plate 1a in the direction perpendicular to the surface of the flange 1c. Furthermore, the spot welds 31 are formed so that the HAZ softened portion 31b is located at a position that does not reach the R end of the ridgeline 1ab between the first vertical wall 1b and the first top plate 1a on the vertical wall side, and at a position that does not reach the R end of the ridgeline 6ab between the second vertical wall 6b and the second top plate 6a on the vertical wall side. That is, in both the hat-shaped member 1 and the reinforcing member 6, the entire HAZ softened portion 31b is located on the vertical wall side from the R end of the ridgeline between the vertical wall and the top plate on the vertical wall side. Furthermore, in both the hat-shaped member 1 and the reinforcing member 6, the HAZ softened portion 31b is located on the compression side of the neutral axis G1 of bending due to the load on the first top plate 1a. As a result, when the structural member 10 is deformed by the load on the first top plate 1a, a compressive force is generated in the HAZ softened portion 31b, which makes it difficult for HAZ fracture to occur starting from the HAZ softened portion 31b.

[0053] The inventors' research has revealed that when the hardness difference ΔHV between the minimum hardness of the HAZ softened portion of the vertical wall and the hardness of the portion of the vertical wall other than the spot weld is 50 HV or more, strain concentration is more likely to occur in the HAZ softened portion under tensile load conditions, and as a result, fracture originating from the HAZ softened portion is more likely to occur. Figure 4 shows an example in which the HAZ softened portion 31b includes a portion where the hardness difference ΔHV is 50 HV or more. In such a case, by arranging the spot welds so that the HAZ softened portion 31b is located on the compression side of the bend, HAZ fracture in high-strength members can be effectively suppressed.

[0054] 1 to 4 show examples in which the tensile strength exceeds 1.1 GPa in both the hat-shaped member and the reinforcing member. The tensile strength of one of the hat-shaped member and the reinforcing member may exceed 1.1 GPa, and the tensile strength of the base material of the other may be 1.1 GPa or less. For example, the tensile strength of one of the hat-shaped member 1 and the reinforcing member 6 may exceed 1.1 GPa, and the tensile strength of the base material of the other may be 1.1 GPa or less.

[0055] FIG. 5 is a cross-sectional view showing an example in which the tensile strength of the reinforcing member 6 exceeds 1.1 GPa and the tensile strength of the hat-shaped member 1 is 1.1 GPa or less. In the example shown in FIG. 4, the spot welds 31 of the first vertical wall 1b and the first top plate 1a of the hat-shaped member 1 do not have a HAZ softened portion with a hardness difference of 30 HV or more from the portion other than the spot welds of the vertical wall. That is, no HAZ softened portion that can be the starting point of HAZ fracture is formed. In such a case, the spot welds 31 are arranged so that the HAZ softened portion 31b does not reach the R end of the vertical wall side of the ridge line 6ab between the second vertical wall 6b and the second top plate 6a in the second vertical wall 6b of the reinforcing member 6, which exceeds 1.1 GPa, and the entire HAZ softened portion 31b is located on the first top plate 1a side from the position Lc at the height of the center of the first vertical wall (i.e., on the compression side from the neutral axis G1). This makes it possible to effectively suppress HAZ fracture in high-strength members.

[0056] FIG. 6 is a cross-sectional view showing an example in which the tensile strength of the base material of the hat-shaped member 1 exceeds 1.1 GPa, and the tensile strength of the base material of the reinforcing member 6 is 1.1 GPa or less. In the example shown in FIG. 6, the spot weld 31 of the second vertical wall 6b of the reinforcing member 6 does not have a HAZ softened portion that can be the starting point of HAZ fracture. In such a case, the spot weld 31 is arranged so that the HAZ softened portion 31b does not reach the R end of the vertical wall side of the ridge line 6ab between the first vertical wall 1b and the first top plate 1a in the first vertical wall 1b of the hat-shaped member 1, which exceeds 1.1 GPa, and the entire HAZ softened portion 31b is located on the first top plate 1a side (i.e., on the compression side of the neutral axis G1) from the position Lc of the height of the center of the first vertical wall 1b. This makes it possible to effectively suppress HAZ fracture in high-strength members.

[0057] In the examples of Figures 1, 2, 5, and 6, the first top plate 1a and the second top plate 6a are in contact with each other. The first top plate 1a and the second top plate 6a may be joined by spot welding. Alternatively, the first top plate 1a and the second top plate 6a may not be joined and may be spaced apart from each other.

[0058] The neutral axis G1 is located near the center height of each of the two first vertical walls 1b, or on the closing plate 2 side of the center height of each of the two first vertical walls 1b, in a cross section perpendicular to the longitudinal direction of the hat-shaped member 1. Therefore, in the structural member 10, the same effect can be obtained even if the center height of the first vertical wall 1b is replaced with the neutral axis. When the structural conditions of the structural member 10, such as the shape, change, the position of the neutral axis G1 also changes. Here, for example, as shown in FIG. 1 and FIG. 2, in a cross section in a plane perpendicular to the longitudinal direction of the hat-shaped member 1, the entire HAZ softened portion 31b of the spot welded portion 31 is located between the center height position Lc of the first vertical wall 1b and the R end of the ridgeline 1ab between the first vertical wall 1b and the first top plate 1a on the first vertical wall 1b side, and the spot welded portion 31 can be arranged so that it is located at a position that does not reach the R end of the ridgeline between the vertical wall and the top plate of a member having a tensile strength exceeding 1.1 GPa on the vertical wall side. This allows a compressive force or a relatively small tensile force to be applied to the HAZ-softened portion during a collision under various structural conditions. Therefore, HAZ fracture in high-strength components can be suppressed under various structural conditions. In other words, it is possible to more easily obtain the effect of improving the crashworthiness per unit mass of a component by using a high-strength component under various structural conditions.

[0059] In a cross section passing through the center of each of the spot welds 31 and perpendicular to the longitudinal direction of the hat-shaped member 1, the distance h1 in the direction perpendicular to the flange surface from the end of the R on the vertical wall side of the ridgeline 1ab between the first vertical wall 1b and the first top plate 1a to the end 6bt of the second vertical wall 6b is preferably one third or less (h1≦(H / 3)) of the height H in the direction perpendicular to the flange surface of the first vertical wall 1b. This makes it possible to improve both the maximum load per unit mass of the structural member 10 against moment bending and the amount of energy absorbed per unit mass of the structural member 10. From the same viewpoint, it is more preferable to make h1≦(H / 4). For example, the distance h1 in the direction perpendicular to the flange surface 1c from the end of the R on the vertical wall side of the ridgeline 1ab between the first vertical wall 1b and the first top plate 1a to the end 6bt of the second vertical wall 6b can be 10 to 50 mm. Furthermore, for example, the distance s1 from the end of the R on the vertical wall side of the ridgeline between the vertical wall and the top plate of the hat-shaped member 1 or the reinforcing member 6 having a tensile strength exceeding 1.1 GPa to the center of the spot welded portion 31 can be 5 to 15 mm. Here, the center of the spot welded portion 31 is the center of the nugget 31c when viewed from the plate thickness direction of the first vertical wall 1b.

[0060] Next, an example of the positional relationship between the spot weld 31 and the end 6bt of the reinforcing member 6 will be described with reference to Figs. 1 and 2. The distance s between the center of the spot weld 31 and the end 6bt of the second vertical wall 6b of the reinforcing member 6 can be, for example, 5 to 15 mm. It is considered that the portion from the spot weld 31 to the end 6bt of the second vertical wall 6b hardly contributes to the load-bearing performance. Therefore, by making this portion smaller, the weight of the reinforcing member 6 can be reduced. As a result, the load-bearing performance relative to the weight of the structural member 10 can be further improved.

[0061] The end 6bt of the second vertical wall 6b of the reinforcing member 6 may be located closer to the first top plate 1a than the position Lc at the center height of the first vertical wall 1b in the direction perpendicular to the flange surface. In this case, the reinforcing effect of the reinforcing member 6 can be obtained. As an example, a portion that is not actively crushed, such as a vehicle frame member such as a B-pillar upper, is assumed. In this case, it is important that the top plate does not buckle against the bending moment applied during a collision with the top plate. In order to withstand this buckling, it is effective to strengthen the top plate and the ridgeline. For example, it is effective to reinforce the vicinity of the ridgeline 1ab between the first top plate 1a and the first vertical wall 1b of the hat-shaped member 1 with the reinforcing member 6. This is because the contribution to improving the impact resistance performance by reinforcing the first vertical wall 1b up to the flange 1c side is lower than the contribution by reinforcing the ridgeline 1ab of the first vertical wall 1b and the first top plate 1a. Therefore, even if the length of the second vertical wall 6b of the reinforcing member 6 is arranged only on the compression side (first top plate 1a side) of the neutral axis, it is possible to improve the collision resistance. Also, with this configuration, the reinforcing member 6 can be shortened and made lighter.

[0062] <Application to vehicles> FIG. 7 is a diagram showing an example of a state in which a structural member 10 having the characteristics shown in FIGS. 1 to 6 is mounted on a vehicle as a vehicle frame. In the example of FIG. 7, the structural member 10 is used as a B-pillar (center pillar). The structural member 10 is mounted so that the hat-shaped member 1 is disposed on the outer side of the vehicle and the closing plate 2 is disposed on the inner side of the vehicle. The first top plate 1a surface of the hat-shaped member 1 faces the outer side of the vehicle. The reinforcing member 6 is provided at a position covering the center of the hat-shaped member 1 in the longitudinal direction. The second top plate 6a surface of the reinforcing member 6 also faces the outer side of the vehicle.

[0063] In the example shown in FIG. 7, it is assumed that an object collides with the structural member 10 from the outside of the side of the vehicle. During a collision, a bending moment is generated in the structural member 10 due to a load on the first top plate 1a of the hat-shaped member 1. As an example, a bending moment is generated in the structural member 10 due to a collision load. A four-point bending test is known as a test method for reproducing and evaluating such bending moments. In a four-point bending test, a region where the bending moment is constant can be generated. In a four-point bending test, the collision performance of the B-pillar can be evaluated by applying the maximum bending moment generated during collision deformation.

[0064] In the example shown in FIG. 7, the central portion B2 of the B-pillar is provided with the reinforcing member 6, so that the load-bearing performance against the load due to the collision is high, and deformation toward the inside of the vehicle is suppressed. The base material of the reinforcing member 6 is formed of a material exceeding 1.1 GPa, for example. On the other hand, the lower portion B1 of the B-pillar is not provided with the reinforcing member 6. Therefore, it is more likely to be crushed by the collision load than the central portion B2. The lower portion B1 absorbs the collision load by being crushed and deformed. For example, the hat-shaped member 1 is formed of a base material of 1.1 GPa or less. In this way, by appropriately arranging the reinforcing member 6 according to the expected collision, the deformation behavior at the time of the collision can be made closer to the target. Note that the form of the structural member 10 is not limited to the above example. The structural member 10 may be used not only for the B-pillar, but also for other vehicle frame members, such as A-pillars, roof rails, bumpers, door beams, etc. In addition, the combination of the tensile strengths of the hat-shaped member 1 and the reinforcing member 6 is not limited to the above example. For example, both the hat-shaped member 1 and the reinforcing member 6 may have a tensile strength of more than 1.5 GPa.

[0065] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, the hat-shaped member and the reinforcing member may be curved in the longitudinal direction. In this case, at least one of the ridgeline between the first top plate and the first vertical wall of the hat-shaped member and the ridgeline between the first vertical wall and the flange extends in a curved manner. The ridgeline between the first top plate and the first vertical wall of the hat-shaped member and the ridgeline between the first vertical wall and the flange may or may not be parallel.

[0066] The first top plate and the first vertical wall of the hat-shaped member may be formed of a flat plate, or may have a shape with a part of the flat plate having an uneven surface. The second top plate and the second vertical wall of the reinforcing member may be formed of a flat plate, or may have a shape with a part of the flat plate having an uneven surface. The first top plate and the flange of the hat-shaped member may be parallel or not parallel. The closing plate is not limited to a flat plate. For example, the closing plate may have a top plate, two vertical walls extending from both ends of the top plate via a ridge line, and a flange extending from the end of the vertical wall via a ridge line. In this case, the flange of the hat-shaped member and the flange of the closing plate are joined. The first vertical wall of the hat-shaped member and the vertical wall of the closing plate extend from the flange in opposite directions to each other. That is, the cross-sectional shape of the closing plate may be hat-shaped. In this case, the hat-shaped member and the closing plate constitute a structural member having a closed cross-sectional structure of a so-called double hat shape.

[0067] <Analysis example> FIG. 8 is a diagram showing a four-point bending model used in the analysis. The structural member 10E to be analyzed includes a hat-shaped member 1E, a reinforcing member, and a closing plate 2E. Note that the reinforcing member is omitted in FIG. 8. As shown in FIG. 8, in four-point bending, the lower surface of the structural member 10E is supported by two support parts SE spaced apart in the longitudinal direction, and a load is applied to the upper surface of the structural member 10E by two indenters PE spaced apart in the longitudinal direction between the two support parts SE. The reinforcing members are provided over the entire longitudinal direction of the structural member 10E. The two support parts SE serve as two fulcrums, and the points where the two indenters PE contact the upper surface serve as force points. In four-point bending, a bending moment due to the load is generated between the two fulcrums. Between the two force points, the bending moment is constant and maximum. For example, as shown in FIG. 10 described later, this bending moment generates a compressive force on the top plate side and a tensile force on the closing plate side between two fulcrums in the vertical wall of the hat-shaped member. The bending of the structural member occurs largely between the two force points. FIG. 9 is a diagram showing a model of the structural member 10E used in the four-point bending model of FIG. 8. Models A to E in FIG. 9 are a group of models in which the spot welding positions (spot positions) on the vertical walls of the hat-shaped member 1E and the reinforcing member 6E and the length of the vertical wall of the reinforcing member 6E are variously changed. In FIG. 9, the positions of the spot welds are represented by squares. In models A and B, the spot welds are located between the position Lc at the center height of the first vertical wall of the hat-shaped member 1E and the flange. In models C and D, the spot welds are located between the position Lc at the center height of the first vertical wall and the first top plate. The position of the spot welds on the vertical wall of model D is located farther from the position Lc at the center height of the first vertical wall than the position of the spot welds on the vertical wall of model C. The position of the spot weld of the vertical wall of model E reaches both the R end of the ridgeline between the first vertical wall and the first top plate on the vertical wall side and the R end of the ridgeline between the second vertical wall and the second top plate on the vertical wall side. In all of models A to D, the distance s from the end of the second vertical wall to the position of the center of the spot weld is s = 5 mm, which is within the range of 5 to 15 mm. In models A to C, the end of the second vertical wall is on the closing plate side of the position Lc at the height of the center of the first vertical wall.In Models D and E, the end of the second vertical wall of the reinforcing member 6E is located closer to the second top plate than the position Lc at the height of the center of the first vertical wall. The distance h1 from the end of the R on the vertical wall side of the ridge line 1ab between the first vertical wall 1b and the first top plate 1a to the end 6bt of the second vertical wall 6b is as follows. In Model A, h1=50 mm, in Model B, h1=32 mm, in Model C, h1=24 mm, and in Model D, h1=12 mm. In Model E, h1=12 mm. That is, in Models A to C, h1>(H / 3), and in Models D and E, h1≦(H / 3). In Models A to E, the height H of the first vertical wall is 60 mm. In Models A to E, the tensile strength of the hat-shaped member 1E is 1.5 GPa, and the plate thickness of the hat-shaped member 1E is 2.0 mm. The tensile strength of the reinforcing member 6E is 1.5 GPa, and the plate thickness of the reinforcing member 6E is 1.6 mm. The tensile strength of the closing plate 2E is 780 MPa, and the plate thickness is 1.2 mm. In models A to E, spot welds are provided to join the first top plate and the second top plate, and spot welds are provided to join the flange of the hat-shaped member 1E and the closing plate 2E. The four-point bending simulation shown in FIG. 8 was performed using models A to E shown in FIG. 9.

[0068] FIG. 10 is a diagram showing the stress field calculated as a result of performing a four-point bending simulation in models A to D shown in FIG. 9. In FIG. 10, the illustration of the reinforcing member 6E and the spot welds of the top plate and the flange are omitted. In FIG. 10, the area where tensile force occurs is not hatched, and the area where compressive force occurs is indicated by dots. In FIG. 10, the spot welds of the vertical walls are indicated by circles. In the results shown in FIG. 10, in models A and B where a large tensile force occurs in the spot welds, the spot welds break (HAZ break). In models A and B, tensile force occurs in the spot welds between the two force points (see FIG. 8). On the other hand, in the cases of models C and D, there was no break (HAZ break) in the spot welds. In model C, tensile force and compressive force are almost zero in the spot welds between the two force points. In model D, compressive force occurs in the spot welds. From this, it was found that fracture of the spot weld (HAZ fracture) can be avoided by locating the spot weld between the position Lc at the center height of the first vertical wall and the first top plate.

[0069] Fig. 11 is a graph showing the load-displacement relationship of models A to E. In the results shown in Fig. 11, in models A and B, a large tensile force was generated in the HAZ-softened portion, and strain was concentrated in the HAZ-softened portion, causing HAZ fracture before the maximum load was reached. The tensile force in model A was even greater than that in model B. Model A fractured in the HAZ earlier than model B. In model C, after the maximum load was reached, the reinforcing member came off the hat-shaped member due to peeling of the spot weld. In model C, the load dropped rapidly after this peeling.

[0070] Fig. 12 is a graph showing the maximum load per unit mass of the member for models A to E. From this graph, it is found that models C and D, which have shorter vertical walls of the reinforcing members, have a higher maximum load per unit mass of the member than models A and B, which have longer vertical walls. Also, model D, where h1 ≦ (H / 3), has a significantly higher maximum load per unit mass of the member than model C, where h1 > (H / 3). Model E, which has a configuration in which the spot welds reach the ridgeline, has a significantly lower maximum load per unit mass of the member.

[0071] Fig. 13 is a graph showing the energy absorption amount per unit mass of the member of models A to E. From this graph, it was found that models C and D, which have shorter vertical walls of the reinforcing members, have a higher energy absorption amount (energy absorption efficiency) per unit mass of the member than models A and B, which have longer vertical walls. Also, model D, where h1 ≦ (H / 3), has a significantly higher energy absorption amount (energy absorption efficiency) per unit mass of the member than model C, where h1 > (H / 3). Model E, which has a configuration in which the spot welds reach the ridgeline, has a lower energy absorption amount (energy absorption efficiency) than model D.

[0072] In this analysis example, by positioning the spot welds between the reinforcing member and the hat-shaped member closer to the ridgeline than the center height of the first vertical wall, but not reaching the ridgeline, it is possible to suppress HAZ fracture originating from the HAZ softened part of the spot weld under bending moment loading conditions. As a result, it was found that the maximum load and energy absorption per unit mass of the member, i.e., the crashworthiness per unit mass of the member, can be improved by using high-strength materials for the reinforcing member and the hat-shaped member, that is, it is possible to realize a reinforcement structure with excellent mass efficiency. In particular, it was found that the maximum load and energy absorption per unit mass of the member can be further improved by positioning the spot welds so that h1≦(H / 3) and the HAZ softened part does not reach the ridgeline.

[0073] Although one embodiment of the present invention has been described above, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and carried out without departing from the spirit of the present invention. [Explanation of symbols]

[0074] 1: Hat-shaped component 2: Closing plate 31, 33: Joint 6: Reinforcement member 10: Structural members 1a: First tabletop 1b: 1st vertical wall 1c: Flange 6a: 2nd top plate 6b: Second vertical wall

Claims

1. A vehicle frame member, A hat-shaped member; Closing plate and A reinforcing member; Multiple spot welds and Equipped with The hat-shaped member includes a first top plate, two first vertical walls, and two flanges. The first top plate is disposed between the two first vertical walls, The first vertical wall is disposed between the first top plate and the flange, The flange is joined to the closing plate, The reinforcing member includes a second top plate and two second vertical walls, The second top plate is disposed between the two second vertical walls, The first vertical wall and the second vertical wall are overlapped with each other, the plurality of spot welds join the first vertical wall and the second vertical wall, At least one of the hat-shaped member and the reinforcing member has a tensile strength of more than 1.1 GPa; A vehicle frame member, wherein the entire HAZ softened portion of the plurality of spot welds in the vertical wall of the hat-shaped member and the reinforcing member having a tensile strength exceeding 1.1 GPa is located, in a direction perpendicular to the face of the flange, between the center height of the first vertical wall and the R end of the ridge line between the first vertical wall and the first top plate on the first vertical wall side, and is located at a position that does not reach the R end of the ridge line between the vertical wall and the top plate of the member having a tensile strength exceeding 1.1 GPa on the vertical wall side.

2. The tensile strength of the reinforcing member is greater than 1.1 GPa; The tensile strength of the hat-shaped member is 1.1 GPa or less. The vehicle frame member according to claim 1 .

3. The tensile strength of both the hat-shaped member and the reinforcing member is greater than 1.1 GPa; The vehicle frame member according to claim 1 or 2.

4. In a cross section in a plane passing through the center of each of the plurality of spot welds and perpendicular to the longitudinal direction of the hat-shaped member, in a direction perpendicular to the surface of the flange, a distance from an R end of a ridge line between the first vertical wall and the first top plate on the vertical wall side to an end of the second vertical wall of the reinforcing member is one-third or less of a height of the first vertical wall. The vehicle frame member according to any one of claims 1 to 3.

5. The centers of the plurality of spot welds are located 5 to 15 mm from the end of the second vertical wall of the reinforcing member. The vehicle frame member according to any one of claims 1 to 4.

6. The HAZ softened portion of the vertical wall of the hat-shaped member and the reinforcing member having a tensile strength exceeding 1.1 GPa has a large softened region in which the Vickers hardness is 50 HV or more lower than the Vickers hardness of the portion other than the spot weld of the vertical wall. The vehicle frame member according to any one of claims 1 to 5.

7. A vehicle frame member according to any one of claims 1 to 6, The first top plate is disposed on the outer side of the vehicle, A vehicle frame, wherein the closing plate is disposed on an inner side of the vehicle.

Images