Title of invention: Skeleton member
Technical field
[0001]
　The present invention relates to a skeletal member.
　This application claims priority based on Japanese Patent Application No. 2018-193175 filed in Japan on October 12, 2018 and Japanese Patent Application No. 2019-0253666 filed in Japan on February 15, 2019. , The contents are used here.
Background technology
[0002]
　Conventionally, as a skeleton member of an automobile, a member obtained by processing a metal plate-shaped member into a predetermined cross-sectional shape has been used. These skeleton members are required to be lightweight and have a sufficient load capacity. Therefore, in recent years, a material having high strength such as a high-strength steel plate may be used. On the other hand, when an impact due to a collision is applied to a product having a skeleton member, the skeleton member is required to realize a desired deformation mode and efficiently absorb the impact.
[0003]
　In a skeleton member using a high-strength material such as a high-strength steel plate, it is required to improve both deformability and load capacity. For example, Patent Document 1 describes that a low hardness region and a high hardness region are provided in a product made of sheet metal by utilizing a technique for partially changing the hardness of a member.
Prior art literature
Patent documents
[0004]
Patent Document 1: International Publication No. 2012/118223
Outline of the invention
Problems to be solved by the invention
[0005]
　However, in the skeleton member whose hardness is partially changed as in Patent Document 1, when a softening layer for improving the deformability is simply provided, the deformability is guaranteed, but the load capacity can be further improved. There was a limit. That is, in applying a high-strength steel plate to a skeleton member, it is required to achieve both deformability and load capacity at a higher level.
[0006]
　Therefore, the present invention has been made in view of the above problems, and an object of the present invention is a novel and improved one capable of both ensuring deformability at the time of a collision and improving the load capacity. The purpose is to provide a skeletal member.
Means to solve problems
[0007]
　The gist of the present invention is as follows.
(1) The first aspect of the present invention is a skeleton member including a corner portion extending in the longitudinal direction and a vertical wall portion extending from an end portion in the lateral direction of the corner portion, and the corner portion of the corner portion. A softening layer is provided in the plate thickness direction from at least one surface of the bending inner side or the bending outer side, and the softening layer has a length of ½ or more of the length from the corner portion to the vertical wall portion in the lateral direction. The hardness of the central portion in the plate thickness direction in the portion extending over the vertical wall portion and provided with the softening layer is 400 Hv or more, and the softening layer is a portion provided with the softening layer. It is a region having a hardness at least 10 Hv lower than the hardness of the central portion in the plate thickness direction in the above, and the thickness of the softened layer is 2% or more and less than 20% of the plate thickness in the portion where the softened layer is provided. The hardness of the softened layer on the surface is 0.5 times or more and less than 0.9 times the hardness of the central portion in the plate thickness direction in the portion where the softened layer is provided, and the softened layer is said to be said. In the plate thickness direction, a first hardness change region which is a region from the surface to 40% of the thickness of the softened layer and a region of the softened layer which is not the first hardness change region. It has two hardness change regions, and the absolute value ΔHv1 of the hardness change in the plate thickness direction in the first hardness change region is the hardness change in the plate thickness direction in the second hardness change region. It is a skeleton member that is larger than the absolute value ΔHv2 and the bending radius R of the corner portion is R / t ≦ 2.5 with respect to the plate thickness t of the corner portion.
(2) In the skeleton member according to (1) above, the absolute value ΔHv1 of the hardness change in the plate thickness direction of the first hardness change region may be 100 Hv or more and less than 200 Hv.
(3) In the skeleton member according to the above (1) or (2), the softening layer may be provided on the bent outer side of the corner portion.
(4) In the skeleton member according to any one of (1) to (3) above, the softening layer may be provided on both the inside of the corner and the outside of the bend.
(5) In the skeleton member according to any one of (1) to (4) above, the vertical wall portion extends from one end of the corner portion, and the skeleton member is other than the corner portion. Further including a flat plate portion extending from the end portion, the softened layer extends from the corner portion to the flat plate portion over a region having a length of ½ or more of the lateral length of the flat plate portion. You may.
(6) In the skeleton member according to any one of (1) to (5) above, the vertical wall portion extends from one end of the corner portion, and the skeleton member is other than the corner portion. Further including the flat plate portion extending from the end portion, the hardness at a depth of 70 μm from the surface of the flat plate portion in the plate thickness direction of the center of the flat plate portion is the hardness of the central portion in the plate thickness direction. It may be 0.9 times or less.
(7) In the skeleton member according to (6) above, the surface of the flat plate portion may be a surface continuous with the bent inside of the corner portion in the flat plate portion.
Effect of the invention
[0008]
　According to the present invention, there is provided a skeleton member that has both an improvement in deformability at the time of a collision and an improvement in load capacity.
A brief description of the drawing
[0009]
FIG. 1 is a partial perspective view showing an example of a skeleton member according to the first embodiment of the present invention.
FIG. 2 is an XX plan sectional view of a region including a corner portion of the skeleton member according to the same embodiment.
FIG. 3 is a sectional view taken along line XX of the skeleton member according to the same embodiment.
FIG. 4 is a cross-sectional view taken along the line XX of the skeleton member according to the same embodiment.
FIG. 5 is a cross-sectional view taken along the line XX of the skeleton member according to the same embodiment.
FIG. 6A is a cross-sectional view showing the shape of a three-point bending simulation of a skeleton member according to the same embodiment.
FIG. 6B is a cross-sectional view showing the shape of a three-point bending simulation of a skeleton member according to the same embodiment.
FIG. 7 is a diagram showing an example of a hardness change between BB'in FIG. 2 of a softened layer of a skeleton member according to the same embodiment.
FIG. 8 is a load-stroke diagram for explaining the effect of the skeleton member according to the present embodiment.
FIG. 9 is an XX plan sectional view of a region including a corner portion according to a modified example of the same embodiment.
FIG. 10 is a partial perspective view showing an example of a skeleton member according to another modified example of the same embodiment.
FIG. 11 is an XX plan sectional view of a skeleton member according to another modification of the same embodiment.
FIG. 12A is a cross-sectional view taken along the line XX of the skeleton member according to the modified example.
12B is an enlarged view of a portion P in FIG. 12A.
[Fig. 13A] Fig. 13A is a diagram showing an example of deformation of a skeleton member according to the same deformation example.
FIG. 13B is a cross-sectional view taken along the line II'of FIG. 13A.
FIG. 14 is a partial perspective view showing an example of a skeleton member according to a second embodiment of the present invention.
FIG. 15 is a sectional view taken along line XX of the skeleton member according to the same embodiment.
FIG. 16 is a diagram showing an automobile skeleton as an example to which the skeleton member according to the embodiment of the present invention is applied.
FIG. 17 shows an example of a load-stroke diagram obtained as a result of a simulation according to this embodiment.
FIG. 18 shows an example of a load-stroke diagram obtained as a result of the simulation according to this embodiment.
Mode for carrying out the invention
[0010]
　Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.
[0011]
　<1. First Embodiment>
　[Overall Structure of Skeleton Member]
　First, with reference to FIG. 1, a partial structure of an example of the skeleton member according to the first embodiment of the present invention will be described. FIG. 1 is a partial perspective view showing an example of a skeleton member according to the present embodiment. As an example, the skeleton member 10 is a member that extends in the Y direction shown in FIG. 1 as the longitudinal direction and has a substantially hat shape in which the longitudinal cross section (XX plane) is opened in the X direction. As an example, the skeleton member 10 has a flat plate portion 11, a vertical wall portion 15 as a wall portion extending from the flat plate portion 11 via a corner portion 13, and a side opposite to the corner portion 13 of the vertical wall portion 15. It includes a flange portion 17 bent from the end portion. Further, in the skeleton member 10, at least the corner portion 13 and the vertical wall portion 15 have a softening layer 20 described later.
[0012]
　The skeleton member 10 forms the skeleton of the entire product or a part by being fixed or connected to other members. For example, when a load is applied to the skeleton member 10 in a direction perpendicular to the longitudinal direction (X direction or Z direction in FIG. 1), bending deformation may occur. Further, for example, when a load in the axial direction is applied to the skeleton member 10 in the longitudinal direction (Y direction in FIG. 1), deformation due to axial crushing may occur.
[0013]
　The skeleton member 10 may be composed of various metal plate-shaped members. In particular, the skeleton member 10 may be made of a steel plate. As an example, a steel material having a tensile strength of 1470 MPa or more (for example, 1.5 GPa class or 1.8 GPa class or more) can be mentioned. The thickness of the steel plate used for the skeleton member 10 is about 0.5 to 3.5 mm or about 1.0 to 2.9 mm. The skeleton member 10 can be formed by applying various processing techniques, which are known techniques, to a metal plate-shaped member (blank material).
[0014]
　[Structure of corner portion of skeleton member]
　Next, the configuration of the region including the corner portion 13 according to the present embodiment will be described with reference to FIGS. 2 to 5, 6A, and 6B. FIG. 2 is a cross-sectional view taken along the line XX of the region including the corner portion 13 according to the present embodiment. 3 to 5 are cross-sectional views taken along the line XX of the skeleton member according to the present embodiment. The corner portion 13 is a bent portion existing between the flat plate portion 11 and the vertical wall portion 15, and has a predetermined bending radius R described later. As shown in FIG. 2, the corner portion 13 is formed in a region defined by R stop points A1 and A2 on the inside of the bend and R stop points A3 and A4 on the outside of the bend in the XZ plan cross-sectional view.
[0015]
　The bending radius R is set to a value that satisfies the relational expression of R / t ≦ 2.5 with respect to the plate thickness t at the corner portion 13. When R / t ≦ 2.5 or less, the vertical wall portion 15 is less likely to bend during bending deformation at the time of collision, and the load capacity of the corner portion 13 at the initial stage of the stroke increases. Along with this, a high load capacity can be maintained even in the middle and late strokes. Further, in combination with the effect that the softening layer 20 described later is formed in the corner portion 13, an excellent load bearing capacity can be exhibited especially in the latter stage of the stroke, and the deformability and the load bearing capacity at the time of collision can be improved. Become.
[0016]
　The lower limit of R / t is not particularly limited, but from the viewpoint of moldability, R / t ≧ 0.5 is preferable, and R / t ≧ 0.9 is more preferable. The bending radius R is set to half the distance between the R stop points A1 and A2 and the bending center point of the corner portion 13 (at the corner portion 13 between the R stop points A1 and A2) from the image of the cross section of the corner portion 13 inside the bend. It can be obtained by finding three points (points to be located) and finding the curvature from these three points by a known mathematical method.
　When manufacturing a skeleton member 10 having a tensile strength of 1470 MPa or more (for example, 1.5 GPa class or 1.8 GPa class or more), in order to obtain a corner portion 13 satisfying R / t ≦ 2.5, It is preferable to use the hot stamping method.
[0017]
　The corner portion 13 has a softening layer 20. The softening layer 20 is on the surface side of the skeleton member 10, and may be provided on either the bending inner side or the bending outer side of the corner portion 13, or both the bending inner side and the bending outer side. In particular, as shown in FIG. 4, the softening layer 20 may be provided on the bent outer side of the corner portion 13. Further, as shown in FIG. 5, the softening layer 20 may be provided on the entire surface of the skeleton member 10.
[0018]
　[Structure of vertical wall portion of skeleton member] The
　vertical wall portion 15 extends in a direction orthogonal to the plate thickness direction from the end portion including the R stop of the corner portion 13. The end portion of the vertical wall portion 15 opposite to the corner portion 13 is bent outward, and the flange portion 17 may extend through the bent portion. That is, the skeleton member 10 can be formed in a substantially hat shape in the XX cross section in FIG.
[0019]
　The vertical wall portion 15 has a softening layer 20 like the corner portion 13. As shown in FIG. 3, in the vertical wall portion 15, the softening layer 20 is 1/2 of the length of the vertical wall portion 15 in the lateral direction from the R stop which is the connecting portion of the corner portion 13 with the vertical wall portion 15. It extends over a region of the above length. The reason why the softened layer 20 is a region having a length of 1/2 or more of the length in the lateral direction of the vertical wall portion 15 is the three points of the skeleton member 10 by the present inventors shown in FIGS. 6A and 6B. Based on the results of bending simulation. That is, when a three-point bending simulation is performed from the initial state of FIG. 6A, as shown in FIG. 6B, a region having a length of 1/2 of the length of the corner portion 13 and the vertical wall portion 15 from the R stop in the lateral direction. It was found that the maximum principal strain was higher than that of other parts. Therefore, by providing the softening layer 20 in a region having a length of at least 1/2 of the length in the lateral direction of the vertical wall portion 15 from the R stop, it is possible to prevent cracking in this region at the time of collision.
[0020]
　The lateral direction of the vertical wall portion 15 is the extending direction of the vertical wall portion 15 when the longitudinal direction of the skeleton member 10 (Y direction in FIG. 1) is the longitudinal direction of the vertical wall portion 15. The direction is orthogonal to the longitudinal direction (approximately X direction in FIG. 1). The length of the vertical wall portion 15 in the lateral direction is the vertical wall of the bent portion between the vertical wall portion 15 and the flange portion 17 from the R stop on the vertical wall portion 15 side of the corner portion 13 in the XZ plane cross section. Refers to the distance between the R stops on the portion 15 side.
[0021]
　[Structure of softening layer] On
　the surface side of the skeleton member 10, the softening layer 20 is formed at least on the corner portion 13 and the vertical wall portion 15. The softening layer 20 may be continuously formed or partially formed over the longitudinal direction (Y direction in FIG. 1) of the skeleton member 10. Further, the softening layer 20 is formed from the surface of the skeleton member 10 to a predetermined depth in the plate thickness direction. In the skeleton member 10 according to the present embodiment, the thickness of the softening layer 20 is 2% or more and less than 20% of the plate thickness of the skeleton member 10. Here, the plate thickness refers to the total thickness of the skeleton member 10 in the plate thickness direction, including the softened layer 20 and the central portion 30 in the plate thickness direction, which will be described later.
[0022]
　When the thickness of the softening layer 20 is 20% or more of the plate thickness of the skeleton member 10, the proportion of the softening layer 20 in the skeleton member 10 increases, and the load capacity required for the skeleton member 10 cannot be maintained. The thickness of the softening layer 20 is preferably 17% or less, more preferably 14% or less of the plate thickness of the skeleton member 10.
　On the other hand, when the thickness of the softening layer 20 is less than 2% of the plate thickness of the skeleton member 10, the proportion of the softening layer 20 in the skeleton member 10 is small, and the deformability is not sufficiently exhibited. The thickness of the softening layer 20 is preferably 5% or more, more preferably 8% or more of the plate thickness of the skeleton member 10.
[0023]
　The central side of the skeleton member 10 in the plate thickness direction (the region in the plate thickness direction excluding the softening layer 20 of the skeleton member 10) is the central portion 30 in the plate thickness direction. The softened layer 20 is a region having a hardness at least 10 Hv lower than the hardness of the central portion 30 in the plate thickness direction.
[0024]
　The softened layer 20 has a hardness of 0.5 times or more and less than 0.9 times the hardness of the central portion 30 in the plate thickness direction on the surface of the skeleton member 10. Here, the surface of the skeleton member 10 refers to the surface of the base material of the skeleton member 10 excluding the coating film and the plating layer. The hardness of the surface of the skeleton member 10 is measured with respect to the cross section of the base metal by the Vickers hardness test described in JIS Z 2244: 2009. At that time, the measurement point is measured so that the depth is within 20 μm from the surface of the base material and the indentation is 10 μm or less. When the hardness of the surface is less than 0.5 times the hardness of the central portion 30 in the plate thickness direction, the surface layer portion of the member becomes too soft, and the load capacity at the time of collision, especially in the latter half of the stroke, can be improved. It disappears. The softening layer 20 preferably has a hardness of 0.6 times or more with respect to the hardness of the central portion 30 in the plate thickness direction on the surface of the skeleton member 10.
　On the other hand, when the hardness of the surface is 0.9 times or more the hardness of the central portion 30 in the plate thickness direction, it becomes difficult to sufficiently improve the deformability. The softening layer 20 preferably has a hardness of less than 0.8 times the hardness of the central portion 30 in the plate thickness direction on the surface of the skeleton member 10.
[0025]
　The hardness of the central portion 30 in the plate thickness direction is Vickers hardness of 400 Hv or more. In a steel material having a Vickers hardness of 400 Hv or more, it becomes difficult to maintain the deformability at the time of collision. That is, when the Vickers hardness of the central portion 30 of the skeleton member 10 in the plate thickness direction is 400 Hv or more, the effect of improving the deformability by the softened layer 20 according to the present embodiment becomes remarkable. The Vickers hardness of the central portion 30 of the skeleton member 10 in the plate thickness direction is preferably 500 Hv or more, and more preferably 600 Hv or more.
　The upper limit of the hardness of the central portion 30 in the plate thickness direction is not particularly specified, but it is preferably 800 Hv, more preferably 700 Hv, in view of the moldability of the skeleton member 10.
[0026]
　For example, within the hardness range of the central portion 30 in the plate thickness direction described above, the hardness of the softened layer 20 on the surface of the skeleton member 10 can be 250 Hv or more in terms of Vickers hardness. Further, within the hardness range of the central portion 30 in the plate thickness direction described above, the hardness of the softened layer 20 on the surface of the skeleton member 10 can be 500 Hv or less in terms of Vickers hardness. The details of the method for measuring the hardness of the surface of the softened layer 20 region of the skeleton member 10 and the hardness of the central portion 30 in the plate thickness direction will be described later.
[0027]
　The softened layer 20 can be formed on the surface side of the skeleton member 10 by applying various surface treatment, surface treatment or heat treatment techniques which are known techniques. As an example of the method of forming the softened layer 20, laser heating to the region corresponding to the corner portion 13 and the vertical wall portion 15 and partial tempering by high frequency heating can be mentioned. Further, by processing the blank material on which the above-mentioned softening layer is previously formed on the surface layer, a skeleton member 10 having the softening layer 20 in a predetermined region can be formed.
[0028]
　FIG. 7 is a diagram showing an example of a hardness change between BB'in FIG. 2 of the softened layer 20 of the skeleton member 10 according to the present embodiment. FIG. 7 is formed by molding the skeleton member 10 according to the present embodiment into a hat shape having a tensile strength of 2.0 GPa class by hot stamping using a steel material for hot stamping, and is formed in the thickness direction of the softened layer 20. It is the result of plotting the Vickers hardness. As shown in FIG. 7, the softening layer 20 is formed between the first hardness changing region 21 existing on the surface side of the skeleton member 10 and the first hardness changing region 21 and the central portion 30 in the plate thickness direction. It has a second hardness changing region 22 existing in. The second hardness change region 22 is a region of the softening layer 20 that is not the first hardness change region 21. The first hardness change region 21 and the second hardness change region 22 are both regions in which the hardness in the plate thickness direction changes with a predetermined gradient, and the first hardness change region 21 and the second hardness change region 21 The second hardness change region 22 has different absolute values ​​of hardness change ΔHv1 and ΔHv2, respectively.
[0029]
　As shown in FIG. 7, the first hardness change region 21 extends from the surface of the skeleton member 10 to 40% of the total thickness of the softening layer 20. The second hardness change region 22 is continuous from the first hardness change region 21 of the softening layer 20 to the central portion 30 of the skeleton member 10 in the plate thickness direction. That is, the second hardness change region 22 is a region of the softening layer 20 that is not the first hardness change region 21.
[0030]
　Further, as shown in FIG. 7, the absolute value ΔHv1 of the hardness change in the first hardness change region 21 is larger than the absolute value ΔHv2 of the hardness change in the second hardness change region 22. This is because if ΔHv2 is larger than ΔHv1, the skeleton member 10 becomes too soft and sufficient load characteristics cannot be obtained.
[0031]
　Further, the absolute value ΔHv1 of the hardness change in the first hardness change region 21 is 100 Hv or more and less than 200 Hv. When ΔHv1 is 100 Hv or more, the stress concentration at the time of bending deformation can be further relaxed, and the bending characteristics can be further improved. Further, when ΔHv1 is less than 200 Hv, the effect of relaxing the stress concentration at the time of bending deformation is further enhanced, and better bending characteristics can be obtained. Therefore, when ΔHv1 is 100 Hv or more and less than 200 Hv, good bending characteristics can be obtained and the deformability of the skeleton member 10 can be improved. Specifically, in the latter half of the stroke at the time of collision, it is possible to moderate the drop of the load immediately after the load peak. Therefore, as described above, the absolute value ΔHv1 of the hardness change in the first hardness change region 21 is preferably 100 Hv or more and less than 200 Hv.
[0032]
[Hardness measurement method and hardness change calculation method]
　The hardness measurement method of the central portion 30 in the plate thickness direction is as follows. A cross section perpendicular to the plate surface of the sample is taken, the sample of the measurement surface is prepared, and the sample is subjected to a hardness test. The method for preparing the measurement surface is carried out according to JIS Z 2244: 2009. After polishing the measurement surface with # 600 to # 1500 silicon carbide paper, a mirror surface is finished using a diluted solution such as alcohol or a liquid in which diamond powder having a particle size of 1 μm to 6 μm is dispersed in pure water. The hardness test is carried out by the method described in JIS Z 2244: 2009. Using a Micro Vickers hardness tester, 10 points were measured at 1/2 of the sample plate thickness at a load of 1 kgf at intervals of 3 times or more the indentation, and the average value was measured at the center 30 in the plate thickness direction. Hardness.
[0033]
　Next, a method for measuring the hardness of the first hardness change region 21 and the second hardness change region 22 will be described. A cross section perpendicular to the plate surface of the sample is taken, the sample is prepared on the measurement surface, and then subjected to a hardness test. In order to accurately measure the hardness near the surface of the sample, the measurement surface is prepared so that the unevenness is as small as possible and no drool is generated near the surface. Here, the measurement surface is sputtered by an argon ion beam using a cross-section polisher manufactured by JEOL Ltd. At this time, for the purpose of suppressing the occurrence of streaky irregularities on the measurement surface, the measurement surface is irradiated with an argon ion beam from the 360-degree direction using a sample rotation holder manufactured by JEOL Ltd.
[0034]
　The hardness of the sample whose measurement surface has been prepared is measured using a Micro Vickers hardness tester. The region corresponding to the softened layer of the sample from the surface of the sample is measured in a direction perpendicular to the plate surface (plate thickness direction) with a load of 1 kgf and at intervals of 3 times or more of the indentation. At this time, the total number of measurement points differs depending on the plate thickness of the sample, but the number of measurement points for calculating ΔHv1 and ΔHv2, which will be described later, is based on the description of JIS Z 2244: 2009 to the extent that there is no influence of indentation. Set as many measurement points as possible while ensuring the interval between. The measurement position on the outermost surface side of the sample should be within 20 μm from the plate surface (if there is a plating layer, directly below the plating layer or directly below the alloy layer between the plating layer and the base material). To do. This is because the outermost surface portion of the base metal surface has a large amount of soft phase structure.
[0035]
　In the case of a sample in which the softening layers 20 are arranged on both sides of the central portion 30 in the plate thickness direction, the same measurement is performed from the first surface side of the sample, and further, the second surface side opposite to the first surface. Also do from.
[0036]
　Next, a method for calculating ΔHv1 will be described. That is, from all the measurement points included in the region from the surface of the sample to the thickness of the entire softened layer up to 40% (first hardness change region 21), the first hardness change region 21 according to the equation (1). The hardness gradient Δa is calculated. Here, a i is the ratio of the distance from the surface in the i-th measurement point occupies in the total thickness of the softened layer (%), c i is a i Vickers hardness in (Hv), n is softened layer from the surface It is the total of all the measurement points included in the region up to 40% of the total thickness (first hardness change region 21).
[0037]
[Number 1]

[0038]
　Here,
.DELTA.a: first plate in hardness change region thickness direction of the gradient of the hardness variation (Hv /%) a i
: the distance from the surface in the i-th
c i : Vickers hardness (Hv) in ai
n: The total
of all measurement points included in the first hardness change region on the first surface side .
[0039]
　In the case of a sample in which the softening layers 20 are arranged on both sides of the central portion 30 in the plate thickness direction, Δa1 on the first surface side is calculated based on the hardness measurement result from the first surface side, and further. Based on the hardness measurement result from the second surface side, Δa2 on the second surface side is calculated. The arithmetic mean of Δa1 and Δa2 can be Δa.
[0040]
　ΔHv1 can be obtained by multiplying Δa obtained by the formula (1) by the ratio of the thickness of the first hardness change region 21 to the total thickness of the softened layer in the plate thickness direction.
[0041]
　Next, a method for calculating ΔHv2 will be described. That is, from all the measurement points included in the region from 40% to 100% of the thickness of the entire softened layer on the surface side of the sample (second hardness change region 22), the second hardness according to the formula (2). The hardness gradient ΔA of the change region 22 is calculated. Here, A i is the ratio of the distance from the surface in the i-th measurement point occupies in the total thickness of the softened layer (%), C i is A i Vickers hardness in (Hv), N is softened at the surface side It is the sum of all the measurement points included in the region from 40% to 100% of the thickness of the entire layer (second hardness change region 22).
[0042]
[Number 2]

[0043]
　Here,
ΔA: Gradient of change in hardness in the plate thickness direction in the second hardness change region (Hv /%)
A i : Distance from the surface at the i-th measurement point occupies the thickness of the entire softened layer. Ratio (%)
C i : Vickers hardness (Hv) in A i
N: The total
of all measurement points included in the first surface side second hardness change region .
[0044]
　In the case of a sample in which the softening layers 20 are arranged on both sides of the central portion 30 in the plate thickness direction, ΔA1 on the first surface side is calculated based on the hardness measurement result from the first surface side, and further. Based on the hardness measurement result from the second surface side, ΔA2 on the second surface side is calculated. The arithmetic mean of ΔA1 and ΔA2 can be ΔA.
[0045]
　ΔHv2 can be obtained by multiplying ΔA obtained by the formula (2) by the ratio of the thickness of the second hardness change region 22 to the total thickness of the softened layer in the plate thickness direction.
[0046]
　(Action and Effect)
　FIG. 8 is a load-stroke diagram for explaining the action and effect of the skeleton member 10 according to the present embodiment.
　The curve a is a load-stroke diagram assuming a skeleton member in which an appropriate softening layer is provided, R / t is set to 2.0, and the absolute value ΔHv1 is set to 150 Hv.
　The curve b is a load-stroke diagram assuming a skeleton member in which an appropriate softening layer is provided, R / t is set to 2.0, and the absolute value ΔHv1 is set to 70Hv.
　The curve c is a load-stroke diagram assuming a skeleton member in which an appropriate softening layer is provided, R / t is set to 5.0, and the absolute value ΔHv1 is set to 150 Hv.
　The curve d is a load-stroke diagram assuming a skeleton member in which a softening layer is not provided and R / t is set to 2.0.
　According to the skeleton member 10 according to the present embodiment, the R / t is set to 2.5 or less, and the softening layer 20 is provided on the corner portion 13 and at least a part of the vertical wall portion 15, so that the curve a Alternatively, as shown in the curve b, the bending characteristics at the time of collision are improved from the initial stage of the stroke to the latter stage of the stroke, and the load can be dropped with a gentle curve in the latter stage of the stroke. That is, the deformability can be improved.
[0047]
　Further, by setting the hardness of the central portion 30 in the plate thickness direction to 400 Hv or more in Vickers hardness, a high load capacity is maintained especially in the latter half of the stroke. Further, since the absolute value ΔHv1 of the hardness change in the first hardness change region was made larger than the absolute value ΔHv2 of the hardness change in the second hardness change region, the softened portion on the surface side of the skeleton member 10. Is secured and the bending characteristics are improved. Further, by making ΔHv2 smaller than ΔHv1, the sudden change in the gradient of the hardness change in the plate thickness direction is eliminated, the stress concentration is relaxed, and cracks and cracks are suppressed. As a result, it is possible to moderate the drop of the load capacity immediately after the peak in the latter half of the stroke. Therefore, the skeleton member 10 can obtain excellent impact resistance characteristics.
[0048]
　When ΔHv1 is 100 Hv to 200 Hv, a sufficiently softened portion on the surface side of the skeleton member 10 is sufficiently secured, so that the bending characteristics of the softened layer 20 are sufficiently improved. That is, comparing the curve a in which ΔHv1 is 150 Hv and the curve b in which ΔHv1 is 70 Hv, the curve a sets ΔHv1 in the range of 100 Hv to 200 Hv, so that the load capacity drops immediately after the peak in the latter half of the stroke. It can be made even more gradual.
[0049]
　Further, according to the skeleton member 10 according to the present embodiment, by setting the R / t of the corner portion 13 to 2.5 or less, a high load capacity can be maintained from the initial stage of the stroke to the latter stage of the stroke. In particular, in the latter half of the stroke, in combination with the effect that the softened layer 20 is formed on the corner portion 13, a particularly excellent load capacity can be exhibited, and the deformability and load capacity at the time of collision can be improved. It will be possible.
[0050]
　Therefore, the skeleton member 10 according to the present embodiment can maintain a high load capacity against a collision, is less likely to crack due to a collision, and can sufficiently secure a deformability. This makes it possible to achieve both load capacity and bending characteristics at a high level compared to conventional skeletal members.
[0051]
　Here, when the skeleton member 10 is input in the direction including the X-direction component in FIG. 1 from the outside, that is, when there is a collision with the flat plate portion 11 or the closing plate joined to the flange portion 17, the vertical direction is obtained. The wall portion 15 may buckle and deform. At this time, in the vertical wall portion 15, the softening layer 20 extends from the corner portion 13 over a region having a length of ½ or more of the length in the lateral direction of the vertical wall portion 15. The vertical wall portion 15 is effectively deformed. That is, when an external force is applied to the skeleton member 10 due to a collision in the direction including the X-direction component, the portion of the vertical wall portion 15 on the corner portion 13 side is bent and deformed. The portion includes a region provided with the softening layer 20. Therefore, when the softening layer 20 is provided in the region, the skeleton member 10 is flexibly bent by the softening layer 20, so that the buckling deformation of the vertical wall portion 15 at a small pitch is promoted. Thereby, the deformability of the skeleton member 10 can be improved and the shock absorption energy can be increased.
[0052]
　Further, by providing the softening layer 20 on both the inside and outside of the bending of the corner portion 13, the bending characteristics can be further improved and the deformability can be improved.
[0053]
　(Modification Example 1) The
　skeleton member according to the first embodiment of the present invention has been described above. From here, a modified example of the present embodiment will be described with reference to FIG. The present modification is characterized in that the flat plate portion 11 extending between the corner portions 13 of the skeleton member 10 has the softening layer 20.
[0054]
　FIG. 9 is an XX plan sectional view of a region including a corner portion according to a modification of the present embodiment. As shown in FIG. 9, in the corner portion 13, the flat plate portion 11 as the second wall portion from the other end on the side opposite to the extended one end portion of the vertical wall portion 15 as the first wall portion. Is extended, and a softening layer 20 is also formed on the flat plate portion 11. In this modification, since the softening layer 20 is also present in the flat plate portion 11, the surface portion of the flat plate portion 11 is also softened, so that the bending characteristics at the time of collision can be improved and the deformability can be improved. it can.
[0055]
　Further, in the flat plate portion 11, the softening layer 20 may be formed over the entire area of ​​the flat plate portion 11. As a result, the bending characteristics of the flat plate portion 11 are improved, so that the deformability of the skeleton member 10 can be further improved.
[0056]
　Further, the configuration in which the softening layer 20 is provided over the entire area of ​​the flat plate portion 11 is also effective when the skeleton member 10 is used as a shock absorbing skeleton. In particular, it is effective when the input to the skeleton member 10 is axial compression. In this case, the skeleton member 10 is crushed by the load in the longitudinal direction (Y direction shown in FIG. 1), but buckling occurs in the flat plate portion 11 because the flat plate portion 11 has the softening layer 20 as a whole. It is possible to prevent the flat plate portion 11 from cracking.
[0057]
　Further, the softening layer 20 may be provided over the entire area of ​​the flat plate portion 11, the vertical wall portion 15, and the flange portion 17. As a result, the bending characteristics of the entire skeleton member 10 are improved, so that the deformability of the skeleton member 10 can be further improved.
[0058]
(Modification 2) The modification according to
　the first embodiment of the present invention has been described above. From here, another modification of the present embodiment will be described with reference to FIGS. 10 and 11. This modification is characterized in that the patch material 40 is attached to the inside of the corner portion 13 bent.
[0059]
　FIG. 10 is a partial perspective view showing an example of the skeleton member according to the present modification. FIG. 11 is a cross-sectional view taken along the line XX of the skeleton member according to the present modification. As shown in FIG. 10, in this modification, the patch material 40, which is a separate component from the skeleton member 10, is attached to the inside of the corner portion 13 bent. As shown in FIG. 11, the patch material 40 is a member having an L-shaped cross section. The patch material 40 may be made of the same material as the skeleton member 10, or may be made of a different material. The length of the patch material 40 in the longitudinal direction may be the same as or shorter than that of the skeleton member 10. The patch material 40 is attached so as to cover at least the bent inner portion of the corner portion 13. The patch material 40 can be attached to the inside of the bent corner portion 13 by various known techniques.
[0060]
　In this modification, the patch material 40 is attached to the inside of the corner portion 13 of the skeleton member 10 so that the load capacity of the skeleton member 10 can be further improved.
[0061]
(Modification 3)
　Above, some modifications according to the first embodiment of the present invention have been described. From here, other modifications of the present embodiment will be described with reference to FIGS. 12A, 12B, 13A, and 13B. This modification is characterized in that the hardness is set in a predetermined range at a depth of 70 μm from the surface in the plate thickness direction at the center of the flat plate portion 11.
[0062]
　FIG. 12A is a sectional view taken along line XX of the skeleton member 10 according to the present modification. Further, FIG. 12B is an enlarged view of a portion (that is, a portion P in FIG. 12A) including the center position S of the flat plate portion 11 in the XZ plane cross section of the skeleton member 10 according to the present modification. FIG. 13A is a diagram showing an example of the deformation of the skeleton member 10 according to the present modification. FIG. 13B is a cross-sectional view taken along the line I'I'of FIG. 13A. As shown in FIG. 12A, in this modification, the hardness is set in a predetermined range at the center position S of the flat plate portion 11 in the lateral direction of the skeleton member (X direction in FIG. 12A). Here, the center position S is a position separated from both ends of the flat plate portion 11 in the lateral direction by an equal distance L. Further, the hardness is within a predetermined range at a position at a predetermined depth from the surface at the center position S. As shown in FIG. 12B, the depth (distance in the plate thickness direction) d from the surface of the flat plate portion 11 at the position C where the hardness is set in a predetermined range is 70 μm. Further, the hardness of the position C is set to be 0.9 times or less with respect to the hardness of the central portion 30 of the flat plate portion 11 in the plate thickness direction.
[0063]
　Here, as shown in FIG. 13A, when a load is input to the flat plate portion 11 of the skeleton member 10, the deformation is started from the periphery of the center position S of the flat plate portion 11. At this time, cracks may occur and propagate in the flat plate portion 11, and finally cracks may occur during the deformation of the skeleton member 10. The occurrence of cracks during deformation reduces the amount of energy absorbed by the skeleton member 10 and affects the shock absorption characteristics.
[0064]
　In particular, as shown in FIG. 13B, when a load is applied to the flat plate portion 11 of the skeleton member 10, the flat plate portion 11 is locally deformed into a concave shape. At this time, a tensile load is generated on the surface side of the flat plate portion 11 continuous with the bending inside of the corner portion 13 (see the arrow in FIG. 13B), cracks grow, and cracks are likely to occur.
[0065]
　Therefore, as a result of diligent studies by the present inventors, it has been clarified that cracks are likely to occur in a region including a position at a depth of 70 μm from the surface of the central position S of the flat plate portion 11. In this modification, the hardness at a depth of 70 μm from the surface of the center position S of the flat plate portion 11 is set to be 0.9 times or less the hardness of the center portion 30 in the plate thickness direction. .. As a result, the hardness is reduced at the center position S of the flat plate portion 11, so that the growth of cracks is suppressed. As a result, the occurrence of cracks during the deformation of the skeleton member 10 is suppressed, the amount of energy absorbed by the skeleton member 10 is increased, and the shock absorption characteristics are further improved.
[0066]
　In particular, at a position of the flat plate portion 11 at a depth of 70 μm from the surface continuous with the bending inside of the corner portion 13, the hardness is 0.9 times or less the hardness of the central portion 30 in the plate thickness direction. There is. As a result, in the flat plate portion 11, the hardness of the surface continuous from the bending inside of the corner portion 13 in which the tensile load that propagates the crack is generated is controlled. As a result, the occurrence of cracks during the deformation of the skeleton member 10 is suppressed, the amount of energy absorbed by the skeleton member 10 is increased, and the shock absorption characteristics are further improved.
[0067]
　Further, the hardness of the position C where the hardness is controlled may be set to be 0.1 times or more the hardness of the central portion 30 in the plate thickness direction of the flat plate portion 11. As a result, the hardness ratio of the flat plate portion 11 is set to a predetermined value or more, so that a high load capacity can be maintained.
[0068]
<2. Second Embodiment>
　Subsequently, the skeleton member according to the second embodiment of the present invention will be described with reference to FIGS. 14 and 15. The skeleton member according to the present embodiment and the skeleton member according to the first embodiment are different in the shape of the cross section in the lateral direction of the skeleton member.
[0069]
　FIG. 14 is a partial perspective view showing an example of the skeleton member according to the present embodiment. FIG. 15 is a sectional view taken along line XX of the skeleton member according to the present embodiment. As shown in FIG. 14, the skeleton member 100 according to the present embodiment has a shape in which the cross section (XX plane) of the skeleton member 100 in the lateral direction is a closed cross section. As an example, the skeleton member 100 is a so-called square tubular member, and the cross-sectional shape is a hollow rectangle.
[0070]
　As an example, the skeleton member 100 extends in the Y direction shown in FIG. 14 as the longitudinal direction. As shown in FIG. 15, the skeleton member 100 is a member having a hollow rectangular cross section (XX plane) in the lateral direction having a closed cross section. The skeleton member 100 has a flat plate portion 151, a vertical wall portion 153, and a corner portion 130 bent so as to connect the flat plate portion 151 and an adjacent vertical wall portion 153. That is, the skeleton member 100 includes a vertical wall portion 153 extending from one end having an R stop of the corner portion 130, and a flat plate portion 151 extending from the other end having an R stop of the corner portion 130. Consists of.
[0071]
　In this embodiment, at least the corner portion 130 has a softening layer 200. The softening layer 200 does not have to be provided in all the corner portions 130, and may be provided in at least one corner portion 130.
[0072]
　Further, the softening layer 200 extends from the corner portion 130 to the vertical wall portion 153. The softening layer 200 extends over a length of ½ or more of the length of the vertical wall portion 153 in the lateral direction. Further, the softening layer 200 may be formed over the entire area of ​​the vertical wall portion 153.
[0073]
　Further, the softening layer 200 may extend over a length of ½ or more of the length in the lateral direction of the flat plate portion 151. Further, the softening layer 200 may be formed over the entire area of ​​the flat plate portion 151.
[0074]
　In the skeleton member 100, the softening layer 200 may be formed on the entire surface of the skeleton member 100.
[0075]
　By having the softening layer 200 in the corner portion 130 and the vertical wall portion 153, the skeleton member 100 according to the present embodiment can further improve the deformability while ensuring the load capacity. The portion where the softening layer 200 is provided is selected according to the application target of the skeleton member 100.
[0076]
　[Application Example of Skeleton Member According to the Embodiment of the Present
　Invention ] The preferred embodiment of the present invention has been described in detail above. From here, an application example of the skeleton member according to the embodiment of the present invention will be described with reference to FIG. FIG. 16 is a diagram showing an automobile skeleton as an example to which the skeleton members 10 and 100 according to the embodiment of the present invention are applied. Skeleton members 10 and 100 may constitute an automobile skeleton as a cabin skeleton or a shock absorbing skeleton. Examples of applications of the skeleton members 10 and 100 as the cabin skeleton are roof center lean force 201, roof side rail 203, B pillar 207, side sill 209, tunnel 211, A pillar lower 213, A pillar upper 215, kick clean force 227, and floor. Examples thereof include a cross member 229, an under lean force 231 and a front header 233.
[0077]
　Examples of applications of the skeleton members 10 and 100 as the shock absorbing skeleton include a rear side member 205, an apron upper member 217, a bumperin force 219, a crash box 221 and a front side member 223.
[0078]
　Since the skeleton members 10 and 100 are used as a cabin skeleton or a shock absorbing skeleton, the skeleton members 10 and 100 have a sufficient load capacity, so that deformation at the time of collision can be reduced. Further, the skeleton members 10 and 100 have improved deformability, and even when an input such as a side collision is input to the automobile skeleton, the impact can be absorbed by sufficient deformation to protect the inside of the skeleton.
Example
[0079]
　A three-point bending crush simulation of an automobile structural member was carried out. Table 1 below shows the conditions and evaluation results of the analysis model used in the simulation.
[0080]
[table 1]

[0081]
　The shapes of the analysis model were "hat material" and "square tube". The “hat material” means a closed cross-section hat member having a closed cross section by joining a closing plate to the flange portion 17 of the skeleton member 10 shown in FIGS. 1 and 4. “Square tube” means a square member as shown in FIGS. 14 and 15. The length of these "hat material" and "square tube" in the longitudinal direction was set to 500 mm. The height of each model (corresponding to the heights of the vertical wall portions 15 and 153) was 60 mm, and the length in the width direction (corresponding to the lengths of the flat plate portions 11 and 151 in the width direction) was 80 mm. The plate thickness was 1.6 mm.
[0082]
　The tensile strength of each model was 1.5 GPa, 1.8 GPa, and 2.0 GPa. Regarding the region where the softening layer is provided, the "corner portion" means a region corresponding to the corner portions 13 and 130 in the "hat material". Further, as shown in FIG. 3, the “vertical wall” means a region having a length of 1/2 of the length of the vertical wall portion 15 in the lateral direction from the R stop of the corner portion 13. Further, the “flat plate” means a region having a length of 1/2 of the length in the lateral direction of the flat plate portion 151 from the R stop of the corner portion 130. Further, "whole" means that a softening layer is provided on the entire surface including the corner portion. "Double-sided" means that the softening layer is provided on both sides, and "single-sided" means that the softening layer is provided on the bent outer surface of the corner portion.
[0083]
　Table 1 shows R / t, the thickness of the softened layer, ΔHv1, ΔHv2, and the ratio of the surface hardness to the central hardness.
[0084]
　A three-point bending crush simulation was performed on these analysis models. The results are shown in Table 1.
　On the opposite side of the flat plate portions 11 and 151 of the skeleton members 10 and 100, the skeleton members 10 and 100 are supported with a distance between fulcrums of 600 mm, and an impactor having a radius of 150 mm is quasi-statically pushed into the flat plate portions 11 and 151 sides. , The push-in amount and the load value were calculated to obtain the energy absorption amount. In addition, it was also determined whether or not the vertical wall portion was cracked in the middle stroke, which will be described later, at the time of pushing. The evaluation criteria for load characteristics, which are indicators of load capacity, and energy absorption characteristics, which are indicators of load capacity and deformability, are as follows.
[0085]
Load characteristics:
· A: Shows the first peak at the beginning of the stroke, maintains a high load capacity throughout the middle and late strokes, and shows the second peak at the late stroke. After the second peak, the load capacity gradually decreases.
B: Shows the first peak at the beginning of the stroke, maintains a high load capacity throughout the middle and late strokes, and shows the second peak at the late stroke.
-C: Maintains a high load in the middle and late strokes and shows a peak in the late strokes.
-D: Maintain a high load in the middle and late strokes.
-E: Shows a low load in any period, or the maximum load is low due to the occurrence of cracks.
　In addition, A to C were set as the passing level.
[0086]
Energy absorption performance:
・ A: A level at which sufficient energy can be absorbed as a result of maintaining a high load over the entire stroke.
-B: A level at which sufficient energy cannot be absorbed as a result of not being able to maintain a high load over the entire stroke.
-C: A level at which a low load cannot be maintained over the entire stroke or sufficient energy cannot be absorbed due to the occurrence of cracks.
　In addition, A was set as the passing level.
[0087]
　As shown in Table 1, in Examples 1 to 9, peaks were obtained in the early and late strokes, and overall sufficient load characteristics and energy absorption characteristics were shown.
　Further, in Example 9, sufficient load characteristics and energy absorption characteristics were obtained even when the softening layer was provided only on one side.
[0088]
　FIG. 17 shows an example of a load-stroke diagram obtained as a result of the simulation according to this embodiment. As shown in FIG. 17, for example, in Example 2, the first peak was shown at the beginning of the stroke, the high load was maintained throughout the middle and late strokes, and the second peak was shown at the late stroke. In Comparative Example 11, since R / t was 5.0, no peak was observed at the beginning of the stroke. Further, although the softened layer is present, the second peak in the late stroke is lower than that in Example 2.
[0089]
　On the other hand, in Comparative Examples 1 and 2, since the softening layer was not provided, cracks occurred before the theoretically assumed maximum load was reached, so that sufficient load characteristics and energy absorption characteristics could not be obtained.
[0090]
　In Comparative Example 3, since the softening layer was provided only at the corner portion, cracks occurred at the vertical wall portion before the maximum load was reached. As a result, sufficient load characteristics and energy absorption characteristics could not be obtained.
　In Comparative Example 4, since the softening layer was provided at only 1% of the plate thickness, cracks occurred before the maximum load was reached. Therefore, sufficient load characteristics and energy absorption characteristics could not be obtained.
[0091]
　In Comparative Examples 5 to 7, since the amount of softening in the softened layer was large, cracks did not occur, but a sufficient load could not be maintained, and as a result, sufficient energy absorption characteristics could not be obtained.
[0092]
　In Comparative Example 8, since the surface hardness was not sufficiently smaller than the hardness of the central portion, cracks occurred in the vertical wall portion before reaching the maximum load. As a result, sufficient load characteristics and energy absorption characteristics could not be obtained.
　In Comparative Examples 9 to 11, since the R / t was more than 2.5, a high load could not be maintained from the early stage of the stroke to the late stage of the stroke.
　In Comparative Example 12, although the R / t was 2.5 or less, it did not have a softening layer, so that cracks occurred in the latter half of the stroke, and a high maximum load could not be secured. As a result, sufficient load characteristics and energy absorption characteristics could not be obtained.
[0093]
　Referring to FIG. 17, in Comparative Example 1, the maximum load could not be obtained because the crack occurred in the middle of the stroke. Further, in Comparative Example 5, it was shown that although cracking did not occur until the latter half of the stroke, a sufficient load could not be maintained.
[0094]
　Further, in order to evaluate the performance of the skeleton member whose hardness was controlled at the center position S, a three-point bending crushing simulation of the automobile structural member was carried out. The conditions of the analysis model used in the simulation are shown in Table 2 below.
[0095]
[Table 2]

[0096]
　The description of the shape, tensile strength, R / t, and softened layer in Table 2 is the same as the description in Table 1. In Table 2, with respect to the hardness distribution at the center position S, the depth from the surface shows the value of the depth d in FIG. 12B. Further, when the hardness is controlled at a predetermined depth position from the surface continuous to the bending inner side of the corner portion, the surface is defined as "inside" and the hardness is set at a predetermined depth position from the surface continuous to the bending outer side of the corner portion. When is controlled, the surface is defined as "outside". Further, when the hardness is controlled at a predetermined depth position from both surfaces, it is defined as "both sides". Further, the ratio of the hardness of the predetermined depth position C at the center position S to the hardness of the central portion 30 in the plate thickness direction is as shown in Table 2.
[0097]
　For these analysis models, simulations were performed under the same conditions as the three-point crushing simulation performed for the analysis models in Table 1. The evaluation results are shown in Table 2. The evaluation criteria are the same as the evaluation criteria in Table 1.
[0098]
　As shown in Table 2, in Examples 10 to 12, since the hardness was controlled at a predetermined depth of the center position S of the flat plate portion 11, flat plate cracking did not occur. On the other hand, in Reference Example 1 and Reference Example 2, since the hardness was not controlled at the center position S of the flat plate portion 11, the flat plate portion 11 was cracked in the latter stage of deformation.
[0099]
　FIG. 18 shows an example of a load-stroke diagram obtained as a result of the simulation according to the embodiment shown in Table 2. As shown in FIG. 18, in Example 10, a high load was maintained throughout the late stroke, and a second peak was shown in the late stroke.
[0100]
　On the other hand, in Reference Example 1, although a high peak is shown in the latter half of the stroke, as compared with Example 10, the flat plate portion 11 is broken in the middle of the latter half of the stroke, and a high load can be maintained until the end of the latter half of the stroke. There wasn't. Therefore, it was shown that the skeleton member whose hardness is controlled at the center position S can maintain a high load until the end of the latter half of the stroke and can obtain higher shock absorption characteristics.
[0101]
　Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical idea described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.
Industrial applicability
[0102]
　According to the present invention, there is provided a skeleton member that has both improved deformability at the time of collision and improved load capacity.
Code description
[0103]
10 Skeleton member
11 Flat plate portion
13 Corner portion
15 Vertical wall portion
17 Flange portion
20 Softening layer
21 First hardness change region
22 Second hardness change region
30 Central portion in the plate thickness direction
The scope of the claims
[Claim 1]
　A skeleton member including a corner portion extending in the longitudinal direction and a vertical wall portion extending from an end portion in the
　lateral direction of the corner portion, and at least one surface of the corner portion inside or outside bending. A softening layer is provided in the plate thickness direction, and the softening layer extends from the
　corner portion to the vertical wall portion over a region having a length of ½ or more of the lateral length of the vertical wall portion. and,
　the hardness of the center of the plate thickness direction at a portion where the softened layer is provided is at least 400 Hv, the softened layer, than the hardness of the center of the plate thickness direction at a portion where the softened layer is provided It is a region having a hardness as low as at least 10 Hv,
　the thickness of the softened layer is 2% or more and less than 20% of the plate thickness in the portion where the softened layer is provided, and
　the hardness of the softened layer on the surface is as follows . The hardness of the central portion in the plate thickness direction in the portion where the softening layer is provided is 0.5 times or more and less than 0.9 times, and the
　softening layer is formed from the surface to the softening layer in the plate thickness direction. has a first hardness change area which is an area of up to 40% of the thickness, and a second hardness change area which is an area not the first hardness change region of the softened layer,
　wherein The absolute value ΔHv1 of the hardness change in the plate thickness direction in the first hardness change region is larger than the absolute value ΔHv2 of the hardness change in the plate thickness direction in the second hardness change region
　, and the bending of the corner portion. A
skeleton member having a radius R of R / t ≦ 2.5 with respect to the plate thickness t of the corner portion .
[Claim 2]
　The skeleton member according to claim 1, wherein the absolute value ΔHv1 of the hardness change in the plate thickness direction of the first hardness change region is 100 Hv or more and less than 200 Hv.
[Claim 3]
　The skeleton member according to claim 1 or 2, wherein the softened layer is provided on the bent outer side of the corner portion.
[Claim 4]
　The skeleton member according to any one of claims 1 to 3, wherein the softening layer is provided on both the inside of the corner and the outside of the bend.
[Claim 5]
　The vertical wall portion extends from one end of the corner portion, the
　skeleton member further includes a flat plate portion extending from the other end of the corner portion, and the
　softening layer extends from the corner portion to the corner portion. The skeleton member according to any one of claims 1 to 4, which extends over the flat plate portion over a region having a length of ½ or more of the length in the lateral direction of the flat plate portion.
[Claim 6]
　The vertical wall portion extends from one end of the corner portion, and the
　skeleton member further includes a flat plate portion extending from the other end of the corner portion in
　the plate thickness direction of the center of the flat plate portion. The skeleton member according to any one of claims 1 to 5, wherein the hardness at a depth of 70 μm from the surface of the flat plate portion is 0.9 times or less the hardness of the central portion in the plate thickness direction. ..
[Claim 7]
　The skeleton member according to claim 6, wherein the surface of the flat plate portion is a surface continuous with the bent inside of the corner portion in the flat plate portion.