Impact absorbing member and vehicle body

Abstract

The impact absorbing member is provided on a vehicle body, and includes a closed cross-sectional portion formed along a predetermined longitudinal direction, and a cross-section perpendicular to the longitudinal direction has a closed cross-sectional shape. The impact absorbing member includes a low strength portion, a high strength portion having a central portion in the thickness direction that is aligned with the low strength portion and has a Vickers hardness higher than the Vickers hardness of the central portion in the thickness direction of the low strength portion, and a joint portion that joins the low strength portion and the high strength portion. The maximum bending angle of the high strength portion is set according to the maximum bending angle of the low strength portion.

Description

[Technical field]

[0001] The present invention relates to an impact absorbing member and a vehicle body. [Background technology]

[0002] Automobiles are CO 2 While emissions reduction is required, the standard values ​​for collision safety are becoming stricter. Therefore, for automobile components, for example, shock absorbing components, weight reduction and improved collision safety are required, and material selection and structural design of the shock absorbing components are important. In particular, for the center pillar, which is an important component for protecting occupants during a side collision of an automobile, more advanced material selection and structural design knowledge are required. From the viewpoint of occupant protection, the upper part of the center pillar is required to have high strength so as not to deform, so the application of high-strength materials is effective. On the other hand, the lower part of the center pillar is required to absorb energy, so a material with a good balance between strength and fracture resistance is required. Therefore, from the viewpoint of weight reduction, tailor weld blanks (TWBs), which can arrange two different materials in one blank, are useful as materials for center pillars. As an example of TWB materials, the TWB materials described in Patent Document 1 can be given. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-55526 A Summary of the Invention [Problem to be solved by the invention]

[0004] CO 2From the viewpoint of reducing emissions, automakers are rapidly developing electric vehicles. In automobiles that transmit the output rotation of the internal combustion engine to the wheels, such as gasoline and diesel engine vehicles, the structure of the side sill means that in the event of a side collision, the side sill connected to the lower part of the center pillar tends to deform significantly as it rotates, while the center pillar also tends to deform. For this reason, the deformation of the center pillar is localized.

[0005] On the other hand, in an electric vehicle, a battery is disposed on the side of the side sill. In order to protect the battery, a shock absorbing member for protecting the battery is installed in the side sill to reinforce the side sill, and the side sill is structured to be less likely to deform. In this way, in an electric vehicle in which the side sill tends to be less likely to deform due to the structure of the battery protection, the deformation amount of the side sill is relatively small during a side collision, and the deformation amount of the center pillar tends to increase due to shock absorption. In particular, in a center pillar outer formed from a TWB and having a higher tensile strength in the upper part compared to the tensile strength in the lower part, the lower end part (the part near the weld line with the lower part) of the high strength upper part is also significantly deformed due to the deformation of the lower part with low strength, and there is a possibility that the base material fracture occurs. Since it is preferable that the possibility of the base material fracture does not occur from the viewpoint of ensuring the shock absorbing performance, it is preferable to suppress such a possibility of the base material fracture. In order to suppress the possibility of the base material fracture, it is possible to increase the plate thickness of the center pillar outer, but increasing the plate thickness of the center pillar outer is not preferable because it increases the weight of the center pillar outer. In order to make the center pillar outer lightweight while improving its impact absorption performance in the event of a side collision, it is preferable to make the steel plate that constitutes the center pillar outer thin while increasing its strength, and further to reduce the possibility of the component breaking in the event of a side collision.

[0006] An object of the present invention is to provide an impact absorbing member that is lighter in weight and can achieve high crash resistance, and a vehicle body equipped with the impact absorbing member. [Means for solving the problem]

[0007] The present invention relates to the following shock absorbing member and vehicle body.

[0008] (1) An impact absorbing member provided on a vehicle body, formed along a predetermined longitudinal direction, and including a portion having a cross section perpendicular to the longitudinal direction that has a closed cross-sectional shape, A low strength portion; A high strength portion is arranged in the longitudinal direction of the low strength portion and has a central portion in the thickness direction having a Vickers hardness higher than a Vickers hardness of a central portion in the thickness direction of the low strength portion; a joining portion joining the low strength portion and the high strength portion; Equipped with An impact absorbing member, wherein the maximum bending angle of the high strength portion is set according to the maximum bending angle of the low strength portion.

[0009] According to this configuration, for example, by increasing the maximum bending angle of the material of the high strength portion, the difference between the maximum bending angle of the material of the high strength portion and the maximum bending angle of the material of the low strength portion can be reduced. By setting such a bending angle, the material of the high strength portion, which has high strength due to its high Vickers hardness, can also exhibit high bending performance. Therefore, even when the high strength portion is relatively largely plastically deformed due to the influence of the plastic deformation of the low strength portion during a side collision, the deformability of the high strength portion can be increased, and the possibility of fracture of the high strength portion near the joint can be suppressed. In addition, the high strength portion can be applied to a portion where high strength is required from the viewpoint of passenger protection. Here, if a material with low Vickers hardness (low strength) is used to ensure high bending properties, it is necessary to increase the plate thickness in order to reduce the amount of deformation toward the passenger side, which leads to an increase in mass. On the other hand, according to the above configuration, the high strength portion has high strength because the Vickers hardness of the high strength portion is high, and while improving the impact absorption performance during a collision such as a side collision, the high strength portion can be made thinner to achieve a reduction in weight of the impact absorbing member. In this way, by using a material that combines Vickers hardness (strength) and bendability as the high-strength portion, it is possible to realize an impact absorbing component that is lightweight and has high impact absorbing performance by reducing the possibility of breakage.

[0010] (2) The impact absorbing member according to (1) above, wherein the difference between the maximum bending angle of the high strength portion and the maximum bending angle of the low strength portion is 100 degrees or less.

[0011] According to this configuration, it is possible to more reliably suppress the possibility of breakage of the high strength portion that follows the bending deformation of the low strength portion during a side collision of the vehicle, thereby realizing an impact absorbing member having high impact absorbing performance through suppression of the possibility of breakage.

[0012] (3) The impact absorbing component according to (1) or (2), wherein the Vickers hardness of the central portion of the high strength portion in the plate thickness direction is 500 HV or more.

[0013] According to this configuration, the strength difference (strength ratio) between the high strength portion and the low strength portion is large, and the difference between the bendability of the material of the high strength portion and the bendability of the material of the low strength portion tends to be large. That is, when the Vickers hardness of the high strength portion is 500 HV or more, the high strength portion is likely to be broken due to the bending deformation of the high strength portion following the bending deformation of the low strength portion during a side collision. In this way, when the Vickers hardness of the high strength portion is 500 HV or more, the problem of the possibility of breaking in the high strength portion is significantly generated. Even in such a case, the possibility of breaking in the high strength portion during a side collision can be suppressed by setting the maximum bending angle of the high strength portion according to the maximum bending angle of the low strength portion.

[0014] (4) The impact absorbing component according to any one of (1) to (3), wherein the Vickers hardness of the central portion in the plate thickness direction of the low strength portion is 150 HV or more.

[0015] With this configuration, in the event of a side collision, the impact energy absorption effect due to plastic deformation of the low strength parts can be increased while excessive plastic deformation of the high strength parts can be suppressed, thereby improving impact absorption performance while reducing the amount of penetration of the high strength parts into the cabin side of the vehicle body.

[0016] (5) The Vickers hardness HV of the center portion of the high strength portion in the thickness direction 1and the Vickers hardness HV 2 Relative to HV 1 / HV 2 The impact absorbing member according to any one of (1) to (4), wherein is 1.3 or more.

[0017] According to this configuration, the difference in strength (strength ratio) between the high strength portion and the low strength portion is large, and the difference in bendability between the material of the high strength portion and the material of the low strength portion tends to be large. 1 / HV 2 When the Vickers hardness is 1.3 or more, the high strength part with high Vickers hardness is likely to break during a side collision due to the bending deformation of the high strength part following the bending deformation of the low strength part. 1 / HV 2 When the bending angle of the high strength portion is 1.3 or more, the need to suppress the possibility of fracture in the high strength portion becomes evident. Even in such a case, the possibility of fracture in the high strength portion during a side collision can be suppressed by setting the maximum bending angle of the high strength portion according to the maximum bending angle of the low strength portion.

[0018] (6) The impact absorbing member according to any one of (1) to (5), wherein the difference between the maximum bending angle of the low strength portion and the maximum bending angle of the high strength portion is 30 degrees or less.

[0019] With this configuration, the high strength portion can bend and deform sufficiently to follow the bending deformation of the low strength portion during a side collision, thereby reducing the possibility of the high strength portion breaking during a side collision.

[0020] (7) The impact absorbing member is a center pillar that includes an inner pillar and an outer pillar and is disposed along the vertical direction of the vehicle body, The pillar outer includes the low strength portion, the joint portion, and the high strength portion, The impact absorbing member according to any one of (1) to (6), wherein the high strength portion is disposed above the low strength portion.

[0021] With this configuration, in the case of a side collision, the outer pillar portion of the center pillar receives most of the impact load, and the high strength portion disposed above the low strength portion has high bendability, which more reliably prevents the high strength portion from breaking, thereby more reliably protecting the occupant from being broken.

[0022] (8) The center pillar is provided with a pair of upper and lower brackets for supporting a door installed behind the center pillar, The impact absorbing member according to (7) above, wherein the joint is positioned at a position lower than the height position of the lower end of the upper bracket.

[0023] With this structure, the impact load input to the center pillar from the upper bracket (the input point of the impact load) located far from the side sill can be received by the high strength portion, thereby reducing the amount of deformation of the center pillar toward the occupant in a side collision.

[0024] (9) The impact absorbing member according to (8) above, wherein the joint is positioned at a height position higher than the height position of the upper end of the lower bracket.

[0025] This configuration ensures a sufficient range for the low strength portion, which makes it possible to achieve both shock absorption by the low strength portion in cooperation with the side sill in the early stage of a side collision and suppression of deformation of the center pillar toward the occupant in the later stage of a side collision by the high strength portion receiving the impact load from the upper bracket.

[0026] (10) The impact absorbing member according to (8) above, wherein the joint is positioned at a position lower than the height position of the lower end of the lower bracket.

[0027] During a side collision, the side sill may undergo torsional deformation around an axis along the front-to-rear direction. In cases where the side sill undergoes torsional deformation in this manner, by locating the joint at a position lower than the height position of the lower end of the lower bracket, the high-strength portion can be installed close to the side sill, which experiences a large amount of deformation during a side collision. Therefore, during a side collision, the high-strength portion can suppress deformation of the center pillar that follows the intrusion of the side sill into the cabin due to the torsional deformation of the side sill. As a result, the amount by which the center pillar intrudes into the cabin can be reduced, and torsional deformation of the side sill can be suppressed.

[0028] (11) The vehicle body further includes a side sill joined to a lower portion of the center pillar, disposed along a front-rear direction of the vehicle body, and having a closed cross-sectional shape in a cross section perpendicular to the front-rear direction, The side sill includes an outer wall disposed on the outer side of the side sill in a width direction of the vehicle body, The lower part of the center pillar has an overlapping portion arranged to cover the side sill at a connection point with the side sill, The impact absorbing member according to any one of (7) to (9), wherein the overlapping portion is arranged along a portion below half the height of the outer wall of the side sill in the up-down direction.

[0029] According to this configuration, the joint area between the center pillar and the side sill can be increased, so that the stress acting between the side sill and the center pillar during a side collision can be reduced. In addition, the load transmitted from the center pillar to the side sill during a side collision is mainly received by the vehicle body as a torsional moment. Therefore, the closed cross-sectional shape of the side sill, particularly the outer side sill, can be prevented from being deformed. Even if a side collision occurs, the original closed cross-sectional shape of the side sill before the collision is unlikely to change, so the side sill has high torsional rigidity and the torsional angle of the side sill during a side collision can be reduced. This reduces the amount of intrusion of the center pillar and the side sill into the cabin. On the other hand, for example, by devising an arrangement so that the center pillar does not reach the lower end of the side sill, the center pillar does not become unnecessarily heavy, and a high level of balance can be achieved between the improvement of the reinforcing effect of the side sill due to the lower shape of the center pillar and the suppression of the weight increase of the center pillar.

[0030] (12) An impact absorbing component according to any one of (1) to (11), wherein the Vickers hardness at the surface in the plate thickness direction of the high strength portion is at least 100 HV lower than the Vickers hardness at the central portion in the plate thickness direction of the high strength portion.

[0031] With this configuration, the maximum bending angle of the high strength portion can be increased, which allows the high strength portion to more reliably follow the bending deformation of the low strength portion during a side collision, thereby suppressing the possibility of breakage of the high strength portion and improving the impact absorption performance.

[0032] (13) The high strength portion has a high strength portion softened layer provided from the surface in the plate thickness direction, The Vickers hardness of the central portion in the plate thickness direction in the portion where the high strength portion softened layer is provided in the high strength portion is 500 HV or more, The thickness of the high strength portion softened layer is 80 μm or more, and is 5% to 20% of the plate thickness at the portion where the high strength portion softened layer is provided, The Vickers hardness of the high strength portion softened layer on the surface is 0.5 times or more and less than 0.9 times the Vickers hardness of the central portion in the plate thickness direction in the portion where the high strength portion softened layer is provided, The high-strength portion softened layer has, in the plate thickness direction, a first hardness change region that is a region from the surface to 40% of the thickness of the high-strength portion softened layer, and a second hardness change region that is a region of the high-strength portion softened layer that is not the first hardness change region, The impact absorbing member according to (12), wherein an absolute value ΔHV1 of the hardness change in the thickness direction in the first hardness change region is greater than an absolute value ΔHV2 of the hardness change in the thickness direction in the second hardness change region.

[0033] According to this configuration, the Vickers hardness of the high-strength portion at the center in the plate thickness direction is 500HV or more, so that the effect of improving the deformability by the softened layer in the high-strength portion is remarkable. In addition, if the thickness of the high-strength portion softened layer is 20% or less of the plate thickness, the ratio of the high-strength portion softened layer to the steel plate, which is the material of the high-strength portion, is small, so that the load resistance required for the high-strength portion can be maintained. On the other hand, if the thickness of the high-strength portion softened layer is 80 μm or more and 5% or more of the plate thickness, the deformability by the high-strength portion softened layer can be fully exhibited. In addition, if the Vickers hardness of the surface of the high-strength portion is 0.5 times or more the Vickers hardness of the center in the plate thickness direction, the load resistance during a collision, especially in the later part of the stroke during a collision, can be improved. On the other hand, if the Vickers hardness of the surface of the high-strength portion is less than 0.9 times the Vickers hardness of the center in the plate thickness direction, the deformability can be fully improved. In addition, if ΔHV1 is larger than ΔHV2, sufficient load characteristics can be obtained.

[0034] (14) An impact absorbing component according to any one of (1) to (13), wherein the Vickers hardness at the surface in the thickness direction of the low strength portion is at least 100 HV lower than the Vickers hardness at the central portion in the thickness direction of the low strength portion.

[0035] According to this configuration, the maximum bending angle of the low strength portion can be increased. Therefore, the occurrence of cracks in the low strength portion during a side collision can be suppressed, and the impact absorption performance can be improved. As a result, since the high strength portion has a high Vickers hardness and high strength, the amount of penetration into the vehicle interior can be suppressed, and the occupant protection effect can be enhanced, and while the amount of absorption of impact energy in the low strength portion is ensured, the plate thickness of the low strength portion can be further reduced to reduce the weight of the vehicle body. In addition, even if the low strength portion is formed from a high strength material with a higher Vickers hardness, the possibility of fracture of the low strength portion can be suppressed, and the amount of penetration of the low strength portion into the inside of the vehicle body during a side collision can be reduced.

[0036] (15) The low strength portion has a low strength portion softened layer provided from the surface in the plate thickness direction, The Vickers hardness of the central portion in the plate thickness direction in the portion where the low strength portion softened layer is provided in the low strength portion is 150 HV or more, The thickness of the low-strength portion softened layer is 80 μm or more, and is 5% to 20% of the plate thickness at the portion where the low-strength portion softened layer is provided, The Vickers hardness of the low-strength portion softened layer on the surface is 0.5 times or more and less than 0.9 times the Vickers hardness of the central portion in the plate thickness direction in the portion where the low-strength portion softened layer is provided, The low-strength portion softened layer has, in the plate thickness direction, a first hardness change region that is a region from the surface to 40% of the thickness of the low-strength portion softened layer, and a second hardness change region that is a region of the low-strength portion softened layer that is not the first hardness change region, The impact absorbing member according to (14), wherein an absolute value ΔHV1' of the hardness change in the thickness direction in the first hardness change region is greater than an absolute value ΔHV2' of the hardness change in the thickness direction in the second hardness change region.

[0037] According to this configuration, the Vickers hardness of the low-strength portion at the center in the plate thickness direction is 150HV or more, so that the effect of improving the deformability by the low-strength portion softened layer in the low-strength portion is remarkable. In addition, if the thickness of the low-strength portion softened layer is 20% or less of the plate thickness, the ratio of the low-strength portion softened layer to the steel plate that is the material of the low-strength portion is small, so that the load resistance required for the low-strength portion can be maintained. On the other hand, if the thickness of the low-strength portion softened layer is 80 μm or more and 5% or more of the plate thickness, the deformability by the low-strength portion softened layer can be fully exhibited. In addition, if the Vickers hardness of the surface of the low-strength portion is 0.5 times or more the Vickers hardness of the center in the plate thickness direction, the load resistance during a collision, especially in the later part of the stroke during a collision, can be improved. On the other hand, if the Vickers hardness of the surface of the low-strength portion is less than 0.9 times the Vickers hardness of the center in the plate thickness direction, the deformability can be fully improved. In addition, if ΔHV1′ is larger than ΔHV2′, sufficient load characteristics can be obtained.

[0038] (16) A vehicle body having a center pillar and a side sill joined to a lower portion of the center pillar, At least one of the center pillar and the side sill is the impact absorbing member according to any one of (1) to (15).

[0039] This configuration makes it possible to realize a vehicle body that is lighter in weight and has high crashworthiness. Effect of the Invention

[0040] According to the present invention, it is possible to realize a shock absorbing member that is lighter in weight and can achieve high crash resistance. [Brief description of the drawings]

[0041] [Figure 1] FIG. 1 is a schematic left side view showing a main part of a vehicle body to which a shock absorbing member according to one embodiment of the present invention is applied. [Diagram 2]FIG. 2 is a cross-sectional view of the closed cross-sectional portion of the center pillar taken along line II-II in FIG. 1, perpendicular to the up-down direction, with the back side of the cross-section not shown. [Diagram 3] FIG. 3 is a schematic cross-sectional view of the main parts for explaining the joining state between the side sill outer and the pillar outer of the center pillar, taken along line III-III in FIG. 1, and shows a cross section perpendicular to the fore-and-aft direction of the vehicle body. [Figure 4] 4A and 4B are schematic diagrams for explaining the bending test, where FIG. 4A is a plan view of the test piece before the test, and FIG. 4B shows the test piece, a punch, and a roll. [Diagram 5] FIG. 5 is a vertical cross-sectional view of the outer pillar in the vicinity of a joint in the first modified example, taken along the plate thickness direction and the up-down direction, with the back side of the cross-section not shown. [Figure 6] FIG. 6 is an image diagram for explaining an example of a method for measuring the boundary between the high-strength portion softened layer and the central portion. [Figure 7] FIG. 7 is an image diagram for explaining an example of a change in Vickers hardness in the softened layer. [Figure 8] FIG. 8 is a vertical cross-sectional view of the outer pillar in the vicinity of a joint in the plate thickness direction and the up-down direction in the second modified example, with the back side of the cross-section not shown. [Figure 9] FIG. 9 is a schematic left side view for explaining a third modification in which no reinforcing member is provided within the side sill. [Figure 10] FIG. 10 is a schematic cross-sectional view of a main portion of a fourth modified example relating to a modified overlapping portion of the outer pillar, showing a cross section perpendicular to the front-rear direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a shock absorbing member applied to an automobile will be described.

[0043] Fig. 1 is a schematic left side view showing a main part of a vehicle body 1 to which a shock absorbing member according to an embodiment of the present invention is applied. Fig. 2 is a cross-sectional view of the closed cross-sectional part 46 of the center pillar 4 perpendicular to the up-down direction Z along the line II-II in Fig. 1, and the illustration of the back side of the cross-section is omitted. Fig. 3 is a schematic cross-sectional view of the main part for explaining the joining state between the side sill outer 15 and the pillar outer 41 of the center pillar 4 along the line III-III in Fig. 1, and shows a cross section perpendicular to the front-rear direction X of the vehicle body 1. In the following, unless otherwise specified, explanation will be given while referring to Figs. 1 to 3 as appropriate.

[0044] The vehicle body 1 is a part of a vehicle, and an example of the vehicle is an automobile. An example of an automobile is a passenger car. Examples of the passenger car include a sedan type passenger car, a coupe type passenger car, a hatchback type passenger car, a minivan type passenger car, and an SUV (Sport Utility Vehicle) type passenger car. In this embodiment, a configuration in which the vehicle is a BEV (Battery Electric Vehicle) will be described as an example.

[0045] In this embodiment, the vehicle body 1 is formed of a material including a steel plate. An example of the steel plate is an aluminum-plated steel plate, but other steel types such as a zinc-plated steel plate may also be used. The plating of the plated steel plate is not particularly limited, but examples include hot-dip galvanizing, alloyed hot-dip galvanizing, electrogalvanizing, Zn-Ni plating (electric alloy zinc plating), Sn plating, Al-Si plating, alloyed electrogalvanizing, hot-dip zinc-aluminum alloy plating, hot-dip zinc-aluminum-magnesium alloy plating, hot-dip zinc-aluminum-magnesium-Si alloy plating, and zinc vapor deposition Al plating. The plating process can be performed by passing the plate through a continuous line.

[0046] The vehicle body 1 includes a front pillar 2, a roof rail 3, a center pillar 4, a side sill 5, and a side sill rear 6.

[0047] The front pillar 2 has an endless closed shape (closed cross-sectional shape) in a cross section perpendicular to the longitudinal direction of the front pillar 2. The front pillar 2 has a front pillar upper 11 that extends upward and then toward the rear and is joined to the roof rail 3, and a front pillar lower 12 that is disposed below the front pillar upper 11. The front pillar lower 12 is formed, for example, in an L-shape in side view. A lower rear edge 12a of the front pillar lower 12 opens toward the rear.

[0048] The roof rail 3 is disposed on the roof portion of the vehicle body 1 and extends rearward from the front pillar upper portion 11.

[0049] The side sill 5 is provided at the lower part of the outer portion of the vehicle body 1 in the width direction Y. The side sill 5 is joined to the lower part (lower overlapping part 47) of the center pillar 4 and is disposed along the front-rear direction X of the vehicle body 1. The side sill 5 has an endless closed cross-sectional shape in a cross section perpendicular to the front-rear direction X.

[0050] The side sill 5 has a side sill outer 15 and a side sill inner 16 aligned in the width direction Y.

[0051] The side sill outer 15 and the side sill inner 16 each have a hat-shaped cross section perpendicular to the front-rear direction X, and cooperate to form a closed cross section of the side sill 5. The side sill outer 15 is disposed outboard of the side sill inner 16 in the width direction Y.

[0052] The side sill outer 15 and the side sill inner 16 are formed of, for example, a steel plate. The tensile strength of the side sill outer 15 and the side sill inner 16 is not particularly limited, but can be, for example, a value of 980 MPa or more.

[0053] The side sill outer 15 has an upper flange 151, an upper wall 152 extending outward in the width direction Y from the upper flange 151, an outer wall 153 extending downward from the upper wall 152 and positioned at the outermost position in the width direction Y of the side sill 5, a lower wall 154 extending inward in the width direction Y from the outer wall 153, and a lower flange 155 extending downward from the lower wall 154.

[0054] The side sill inner 16 has an upper flange 161, an upper wall 162 extending inward in the width direction Y from the upper flange 161, an inner wall 163 extending downward from the upper wall 162, a lower wall 164 extending outward in the width direction Y from the inner wall 163, and a lower flange 165 extending downward from the lower wall 164.

[0055] The upper flanges 151, 161 are joined to each other by welding, adhesive, etc. Similarly, the lower flanges 155, 165 are joined to each other by welding, adhesive, etc.

[0056] A front portion 5a of the side sill 5 fits into a front pillar lower section 12 of the front pillar 2 and is joined to the front pillar lower section 12 by welding, adhesive, or the like. The side sill 5 extends rearward from a lower rear end edge section 12a of the front pillar lower section 12. A rear portion 5b of the side sill 5 fits into a side sill rear section 6 and is joined to the side sill rear section 6 by welding, adhesive, or the like.

[0057] The side sill rear 6 is disposed behind the side sill 5. The side sill rear 6 is a hollow member extending along the front-rear direction X. The cross-sectional shape of the side sill rear 6 in a cross section perpendicular to the longitudinal direction of the side sill rear 6 is formed into a closed shape (closed cross-sectional shape) such as a rectangle. The side sill 5 extends forward from a front end edge portion 6a of the side sill rear 6.

[0058] The battery unit 18 is installed at a location (on the side of the side sill 5) that is located inward in the width direction Y from the side sill 5. The battery unit 18 is arranged below the floor panel 7 that extends inward in the width direction Y from the side sill 5. The battery unit 18 has a battery case 18a and a battery 18b accommodated in the battery case 18a. The battery 18b supplies power to an electric motor for driving wheels (not shown) via a cable or the like. The battery case 18a is fixed to a member of the vehicle body 1, such as the floor panel 7, by a fixing member such as a bolt (not shown). The battery unit 18 is also installed near the center pillar 4, and is aligned in the width direction Y with a lower overlapping portion 47 of the center pillar 4 (described later). The battery unit 18 is arranged adjacent to the side sill 5 in the width direction Y (for example, at a short distance of less than 10 cm). The battery case 18a protects the battery 18b in cooperation with the side sill 5 and the center pillar 4 during a side collision.

[0059] A reinforcing member 20 is disposed within the side sill 5. The reinforcing member 20 is provided to suppress the transmission of impact to the battery unit 18 during a side collision. The specific shape of the reinforcing member 20 is not limited. When an impact load of a certain level or more acts from the side sill outer 15 toward the inside in the width direction Y (toward the cabin 10), the reinforcing member 20 absorbs the impact by being crushed while undergoing plastic deformation toward the inside in the width direction Y. In this embodiment, the reinforcing member 20 is disposed so as to be aligned with the battery unit 18 in the width direction Y, and the cross-sectional shape perpendicular to the front-rear direction X is a shape in which a plurality of rectangles are arranged in the width direction Y. The reinforcing member 20 is fixed to, for example, the inner wall 163 of the side sill inner 16. The reinforcing member 20 is disposed, for example, in at least a part of the side sill 5 in the front-rear direction X, and may be disposed over the entire area of ​​the side sill 5.

[0060] Additionally, a floor cross member (not shown) is disposed around the center pillar 4 and on the side of the side sill 5 .

[0061] During a side collision at the side sill 5, particularly at the lower overlapping portion 47 between the center pillar 4 and the side sill 5, the side sill 5 receives an impact load from an object with the lower rear end edge 12a of the front pillar 2 as the front fastening position, the lower overlapping portion 47 of the center pillar 4 as the intermediate fastening position, the front end edge 6a of the side sill rear 6 as the rear fastening position, and the location where the floor cross member is located as the inner fastening position. When the impact load is equal to or greater than a certain level, the side sill 5 absorbs the impact load by plastically deforming inward in the width direction Y.

[0062] By installing the reinforcing member 20 inside the side sill 5, a larger impact load is required to deform the reinforced side sill 5 during a side collision. Therefore, the bending deformation and twisting deformation of the side sill 5 are both small. On the other hand, the center pillar 4 receives a correspondingly larger impact load, and is therefore plastically deformed significantly toward the cabin 10.

[0063] In this embodiment, the side sill rear 6 is described as a member constituting the rear fastening position. However, this is not necessarily the case. For example, another member, such as the lower end of the C-pillar connected to the rear end of the side sill 5, may constitute the rear fastening position. The rear fastening position may be a rear fastening point when the side sill 5 is subjected to an impact load during a side collision and plastically deforms, and specific examples of members constituting the rear fastening position are not limited. Similarly, specific examples of members constituting the front fastening position are not limited for the front fastening position. When a member other than the side sill rear 6 constitutes the rear fastening position, the side sill rear 6 may not be present in the vehicle body 1.

[0064] The center pillar 4 is disposed behind the front pillar 2, and is formed along the vertical direction Z (a predetermined longitudinal direction) from the roof rail 3 to the side sill 5. The center pillar 4 is an impact absorbing member that absorbs impact when the vehicle body 1 is hit by a side collision.

[0065] The center pillar 4 has an upper overlapping portion 45 that is joined to the roof rail 3, a closed cross-sectional portion 46 that is positioned below the upper overlapping portion 45 and above the side sill 5, and a lower overlapping portion 47 that serves as a lower portion that is positioned below the closed cross-sectional portion 46 and arranged to cover the outer surface of the side sill 5 at the connection point with the side sill 5.

[0066] The center pillar 4 also includes an outer pillar 41 and an inner pillar 42 aligned in the width direction Y, and a reinforcing patch 43 disposed between the outer pillar 41 and the inner pillar 42. The outer pillar 41 and the inner pillar 42 form an upper overlapping portion 45, a closed cross-sectional portion 46, and a lower overlapping portion 47. The patch 43 is a member formed by pressing a blank, and is joined to at least one of the outer pillar 41 and the inner pillar 42. The patch 43 is not essential.

[0067] In the closed cross-sectional portion 46, the pillar outer 41 and the pillar inner 42 each have a hat-shaped cross-sectional shape perpendicular to the up-down direction Z. Since the pillar outer 41 and the pillar inner 42 are joined to each other, the closed cross-sectional portion 46 has a closed cross-sectional shape perpendicular to the up-down direction Z. The pillar outer 41 is disposed outside the pillar inner 42 in the width direction Y.

[0068] The pillar outer 41 in the closed cross-section portion 46 has a front flange 411, a front wall 412 extending outward in the width direction Y from the front flange 411, a side wall 413 extending rearward from the front wall 412, a rear wall 414 extending inward in the width direction Y from the side wall 413, and a rear flange 415 extending rearward from the rear wall 414.

[0069] The pillar inner 42 in the closed cross-sectional portion 46 has a front flange 421, a front wall 422 extending inward in the width direction Y from the front flange 421, a side wall 423 extending rearward from the front wall 422, a rear wall 424 extending outward in the width direction Y from the side wall 423, and a rear flange 425 extending rearward from the rear wall 424. Note that the pillar inner 42 may have a flat plate shape such that the cross-sectional shape perpendicular to the up-down direction Z is substantially straight in the front-rear direction X. In this case, the front wall 422 and the rear wall 424 are omitted, and the front flange 421, the side wall 423, and the rear flange 425 are aligned along the front-rear direction X.

[0070] The front flanges 411, 421 are joined to each other by welding, adhesive, etc. Similarly, the rear flanges 415, 425 are joined to each other by welding, adhesive, etc.

[0071] A more specific configuration of the closed cross-sectional portion 46 will be described later.

[0072] Next, a more specific description will be given of the configuration of the lower overlap portion 47. The pillar inner member 42 at the lower overlap portion 47 is joined to the side sill inner member 16 by welding, adhesive, or the like.

[0073] In this embodiment, the pillar outer 41 at the lower overlapping portion 47 may be simply referred to as the overlapping portion 47.

[0074] The overlapping portion 47 is disposed in the pillar outer portion 41 of the center pillar 4 at a connection portion between the side sill 5 and the pillar outer portion 41 so as to cover the outer surface of the side sill 5 from the outside in the width direction Y.

[0075] The overlapping portion 47 has an upper flange 471, an upper wall 472 extending outward in the width direction Y from the upper flange 471, and an outer wall 473 extending downward from the upper wall 472.

[0076] The upper flange 471 is joined to the outer surface 151a of the upper flange 151 of the side sill outer 15 by welding, adhesive, or the like.

[0077] The upper wall 472 is preferably in contact with the upper surface 152a of the upper wall 152 of the side sill outer 15 along the length thereof, and may or may not be joined to this upper surface 152a by welding, adhesive, or the like.

[0078] The outer wall 473 is preferably in contact with the outer surface 153a of the outer wall 153 of the side sill outer 15 along the outer surface 153a, and may or may not be joined to the outer surface 153a by welding, adhesive, or the like. In this embodiment, the lower end 473b of the outer wall 473 is the lower end of the overlapping portion 47. The lower end 473b of the overlapping portion 47 may be aligned along the upper wall 152 without being aligned along the outer wall 153 of the side sill outer 15.

[0079] As shown by the two-dot chain line in FIG. 3, it is preferable that the lower end 473b (overlapped portion 47) of the outer wall 473 is aligned downward from a height position 153b that is halfway in the vertical direction Z of the outer wall 153 of the side sill 5. The height position 153b is the center position of the length in the vertical direction Z at a portion of the outer wall 153 that overlaps with the central portion of the outer wall 473 in the front-rear direction X. The length in the vertical direction Z of the outer wall 153 is the length between the upper end 153c and the lower end 153d in the vertical direction Z at a portion of the outer wall 153 that overlaps with the central portion of the outer wall 473 in the front-rear direction X. The upper end 153c of the outer wall 153 is the curvature start point of the curved portion extending from the outer wall 153 to the upper wall 152 of the side sill outer 15. The lower end 153d of the outer wall 153 is a curve start point of a curved portion extending from the outer wall 153 to the lower wall 154 of the side sill outer 15. When the lower end 473b of the outer wall 473 is aligned downward from the height position 153b, the lower end 473b may be disposed lower than a position 1 / 6 of the length of the outer wall 153 in the vertical direction Z from the height position 153b (a position 1 / 3 of the length of the outer wall 153 in the vertical direction Z from the bottom), may be disposed lower than a position 1 / 4 of the length of the outer wall 153 in the vertical direction Z from the height position 153b (a position 1 / 4 of the length of the outer wall 153 in the vertical direction Z from the bottom), or may be disposed lower than a position 1 / 3 of the length of the outer wall 153 in the vertical direction Z from the height position 153b (a position 1 / 6 of the length of the outer wall 153 in the vertical direction Z from the bottom).

[0080] By disposing the overlapping portion 47 in this way, the joint area between the center pillar 4 and the side sill 5 can be increased, so that the stress acting between the side sill 5 and the center pillar 4 during a side collision can be reduced. In addition, the load transmitted from the center pillar 4 to the side sill 5 during a side collision is mainly received by the vehicle body 1 as a torsional moment. Therefore, the closed cross-sectional shape of the side sill 5, particularly the side sill outer 15, can be prevented from being deformed. Even if a side collision occurs, the original closed cross-sectional shape of the side sill 5 before the collision is unlikely to change, so the side sill 5 has high torsional rigidity and can reduce the torsional angle of the side sill 5 during a side collision. This reduces the amount of intrusion of the center pillar 4 and the side sill 5 into the cabin 10. On the other hand, if the center pillar 4 is disposed so that it does not reach the lower end (lower flange 155) of the side sill 5, the center pillar 4 does not become unnecessarily heavy, and a high level of balance can be achieved between the improvement of the reinforcing effect of the side sill 5 due to the lower shape of the center pillar 4 and the suppression of the weight increase of the center pillar 4.

[0081] It is preferable that the lower end 473b of the overlapping portion 47 is a linear end portion along the fore-and-aft direction X. With this configuration, the vehicle body 1 can receive the load transmitted from the center pillar 4 to the side sill 5 during a side collision as a torsional moment over the entire area where the overlapping portion 47 is disposed in the fore-and-aft direction X. This makes it possible to more reliably prevent the closed cross-sectional shape of the side sill 5, and in particular the side sill outer 15, from being crushed.

[0082] The center pillar 4 is provided with a pair of upper and lower brackets 61, 62 for supporting a door 8 disposed behind the center pillar 4.

[0083] Each bracket 61, 62 may be a plate-like member formed by pressing a steel plate, or may be a block-like member formed by cutting a steel material or the like. Each bracket 61, 62 constitutes a part of a hinge mechanism that connects the center pillar 4 and the door 8. Door shafts 63, 64 are provided between each bracket 61, 62 and the door 8. In addition, a pair of upper and lower brackets 65, 66 corresponding to the brackets 61, 62 are provided on the door 8. The brackets 61, 62 and the corresponding brackets 65, 66 are connected via the corresponding door shafts 63, 64. The door 8 moves around the door shafts 63, 64 to open and close.

[0084] Each bracket 61, 62 is fixed to the pillar outer 41 of the center pillar 4 by welding or a fixing member such as a bolt. Each bracket 61, 62 is preferably fixed to the pillar outer 41, particularly to the side wall 413. With this configuration, the impact absorbing effect of the center pillar 4 can be improved by providing the high-strength portion 53 formed of a material having high hardness and high bending deformability against an impact load input to the pillar outer 41 through each bracket 61, 62. The lower bracket 62 is installed in the closed cross-sectional portion 46 near the overlapping portion 47 of the center pillar 4. The upper bracket 61 is installed above the lower bracket 62 and is separated from the lower bracket 62. The upper bracket 61 is installed, for example, near the lower end 8a of the window opening of the door 8.

[0085] (More detailed structure of pillar outer) The material of the pillar outer 41 is a tailor weld blank (TWB) made into one member by joining two separately formed blanks. The pillar outer 41 is formed by pressing this material.

[0086] As described above, the pillar outer 41 of the center pillar 4 includes the low strength portion 51, the joint portion 52, and the high strength portion 53. The lower portion of the pillar outer 41 is constituted by the low strength portion 51, and the upper portion is constituted by the high strength portion 53. In this embodiment, in the pillar outer 41 which receives most of the impact load of the center pillar 4 during a side collision, the material of the high strength portion 53 arranged above the low strength portion 51 has high bendability, so that the possibility of the high strength portion 53 breaking can be more reliably prevented. Therefore, the occupant protection effect of the center pillar 4 can be more reliably achieved.

[0087] As described above, the pillar outer 41 has the low strength portion 51 and the low strength portion 51 arranged in the vertical direction Z. 2 Higher Vickers hardness HV 1 and a joining portion 52 that joins the low strength portion 51 and the high strength portion 53. In this embodiment, the low strength portion 51 has a Vickers hardness HV 2 , and Vickers hardness HV of high strength section 53 1 and mean the Vickers hardness of the center in the sheet thickness direction of the low strength portion 51, and the Vickers hardness of the center in the sheet thickness direction of the high strength portion 53, respectively. In this embodiment, the center portion refers to most of the steel sheet part when no coating layer is present, and refers to most of the steel sheet base material directly below the coating layer when a coating layer is present. When an alloy layer is present between the coating layer and the steel sheet base material in addition to the coating layer, most of the steel sheet base material directly below the alloy layer is referred to as the center portion.

[0088] Here, a layer including at least one of a plating layer and an alloy layer is referred to as a plating film. When a plating film is present, the thickness of the plating film is measured, and the position corresponding to the thickness of the plating film in the thickness direction from the surface of the steel sheet including the plating film is regarded as the boundary position between the plating film and the base material of the steel sheet. In this embodiment, the "thickness" refers to the thickness of the base material portion obtained by subtracting the thickness of the plating film on the front surface side of the steel sheet and the thickness of the plating film on the back surface side of the steel sheet from the total thickness of the steel sheet including the plating film. In addition, unless otherwise specified, the surface of the low strength portion 51 and the surface of the high strength portion 53 refer to the surface of the base material of the steel sheet. In addition, the thickness of the plating film is measured by a high frequency glow discharge optical emission surface analyzer (GDS). A specific measurement method is described below.

[0089] Three arbitrary measurement positions are determined from the region having the plated coating of the low-strength portion 51 or the high-strength portion 53. The element concentrations of Fe, Mn, Zn, Si, Al, O, Cr, Ni, Mg, Cu, and Sn are measured at each measurement point while sputtering is performed from the surface of the plated coating.

[0090] The content of each element is analyzed in the depth direction, and the depth at which the Fe concentration first becomes 90 mass% or more is determined. Then, the average depth at each measurement point is calculated, and the average is set as the plating film thickness of the low strength part 51 or the high strength part 53. If the Fe concentration does not become 90 mass% or more by the depth that can be analyzed by one GDS measurement, that is, if the plating film thickness is larger than the measured depth, the plating film equivalent to 80% to 90% of the previous measured depth is removed by polishing at an arbitrary position other than the measured position in the same area, and the depth of the plating film removed by polishing is determined from the change in sheet thickness before and after polishing, and a new GDS analysis is performed from the polished surface, and the plating film thickness is measured by combining the first and second measurement results. Even if a structure other than the plating film exists on the surface of the steel sheet base material, the boundary position between the steel sheet base material and the other structure can be measured by the above-mentioned measurement method.

[0091] As a measuring device for GDS, for example, a Marcus type high frequency glow discharge optical emission spectrometer GD-Profiler2 (manufactured by HORIBA) is used. In this case, for example, the discharge conditions are 35 W, the Ar pressure during measurement is 600 Pa, the discharge range is 4 mm in diameter, the electrode distance is 0.15 mm to 0.25 mm, and the measurement pitch in the plate thickness direction is 0.01 μm to 0.05 μm.

[0092] (Maximum bending angle of high strength and low strength parts) Maximum bending angle θ of the high strength portion 53 1 is the maximum bending angle θ of the low strength portion 51 2The maximum bending angle is set according to the above. The maximum bending angle can be obtained by the VDA bending test (VDA238-100:2017) standardized by the German Association of the Automotive Industry (VDA). Figures 4A and 4B are schematic diagrams for explaining the bending test, in which Figure 4A is a plan view of the test piece S before the test, and Figure 4B shows the test piece S, the punch P, and the roll R. As shown in Figures 4A and 4B, this VDA bending test is a test in which the test piece S placed on two rolls R, R is pushed between the rolls R, R with a punch P having a tip radius of 0.4 mm to deform the test piece S into a V-shape. The length of the test piece S is in the range from the value obtained by adding 10 mm to the distance between the centers of the rolls R, R to 60 mm. The width of the test piece S is in the range from 10 mm to 60 mm. The test piece S is taken from the high strength portion 53 so that the direction in which the radius of curvature is 500 mm or more is the length direction of the test piece S. As shown in FIG. 4B, the test piece S is deformed so as to have a V-shape when viewed along the width direction. The ridge line L generated by the bending of the test piece S at this time is a line along the width direction of the test piece S. The load of the punch P and the stroke of the punch P at this time are measured. Then, the fracture resistance of the test piece S is evaluated by calculating the maximum bending angle from the stroke when the load of the punch P, which increased with the start of the test, decreases by 60 N from the maximum load due to the occurrence of fracture at the apex of the bend of the test piece S. The formula for calculating the maximum bending angle from the stroke is the formula described in Annex D of VDA238-100 mentioned above. Note that, when the test piece S does not break even with a stroke of 14 mm, the value obtained by the formula for calculating the maximum bending angle from the bending angle at a stroke of 14 mm is regarded as the maximum bending angle of the test piece S.

[0093] In this embodiment, a part of the high strength portion 53, for example, in the vicinity of the upper bracket 61, is cut out as a test piece S and subjected to a VDA bending test, so that the maximum bending angle θ 1 In addition, by cutting out a part of the low strength portion 51, for example, in the vicinity of the lower bracket 62 as a test piece S and performing a VDA bending test, the maximum bending angle θ of the low strength portion 51 can be calculated. 2The number of tests for the high strength portion 53 in the VDA bending test was three, and the average value of the measurement results of the three test pieces S was calculated as the maximum bending angle θ of the high strength portion 53. 1 Similarly, the number of tests for the low strength portion 51 in the VDA bending test is three, and the average value of the measurement results of the three test pieces S is defined as the maximum bending angle θ of the low strength portion 51. 2 Let us assume that.

[0094] The low-strength portion 51 forms the overlapping portion 47 and a part of the overlapping portion 47 side (lower side) of the closed cross-sectional portion 46 in the pillar outer 41. The joint portion 52 is a portion formed by joining the material of the low-strength portion 51 and the material of the high-strength portion 53. The joint portion 52 exists as a portion joining the material of the low-strength portion 51 and the material of the high-strength portion 53 even before the material of the low-strength portion 51 and the material of the high-strength portion 53 are press-molded to form the pillar outer 41. When the low-strength portion 51 and the high-strength portion 53 are joined by laser welding, the low-strength portion 51 and the high-strength portion 53 face each other in the longitudinal direction of the pillar outer 41 near the joint portion 52. On the other hand, when the low-strength portion 51 and the high-strength portion 53 are joined by spot welding, the low-strength portion 51 and the high-strength portion 53 face each other in the plate thickness direction of the pillar outer 41 near the joint portion 52. The joint 52 is preferably disposed straight in the front-rear direction X. This allows the strength distribution of the pillar outer 41 in the front-rear direction X to be more uniform around the joint 52. The joint 52 does not have to be straight in the front-rear direction X. The joint 52 only needs to join at least a part of the low-strength portion 51 and the high-strength portion 53 in the front-rear direction X. The low-strength portion 51 is disposed below the joint 52, and the high-strength portion 53 is disposed above the joint 52. The high-strength portion 53 forms a part of the closed cross-sectional portion 46 on the upper overlap portion 45 side and the upper overlap portion 45 in the pillar outer 41.

[0095] In this embodiment, since the side sill 5 is reinforced by the reinforcing member 20, the deformation amount of the side sill 5 is small during a side collision, and the bending deformation of the center pillar 4 is more dominant than the torsional deformation of the side sill 5. Since the plastic deformation amount of the side sill 5 is small, the center pillar 4 is largely plastically deformed to absorb the impact. At this time, the low strength portion 51 is largely plastically deformed inward in the width direction Y to absorb the impact. Since the high strength portion 53 has high strength to suppress a collision with an occupant, the amount of plastic deformation inward in the width direction Y tends to be smaller than the amount of plastic deformation of the low strength portion 51. On the other hand, in the vicinity of the joint portion 52, the amount of plastic deformation of the high strength portion 53 is also increased in accordance with the plastic deformation inward in the width direction Y by the low strength portion 51.

[0096] Therefore, in this embodiment, the maximum bending angle θ of the high strength portion 53 1 is the maximum bending angle θ of the low strength portion 51 2 As a result, for example, the maximum bending angle θ 1 By increasing the maximum bending angle θ of the material of the high strength portion 53, 1 and the maximum bending angle θ of the material of the low strength portion 51 2The difference between the hardness and the strength is reduced. By setting the bending angle in this way, the high strength portion 53 can exhibit high bending performance even in a material having high strength due to its high Vickers hardness. Therefore, even when the high strength portion 53 is plastically deformed relatively greatly due to the influence of the plastic deformation of the low strength portion 51 of the pillar outer 41 during a side collision, the deformability of the high strength portion 53 can be increased, and the possibility of breakage of the pillar outer 41 (high strength portion 53) near the joint 52 can be suppressed. In addition, the upper portion of the center pillar 4 is required to have high strength from the viewpoint of protecting the occupant. Here, if a material having a low Vickers hardness (low strength) is used in the member above the joint 52 to ensure high bending properties, it is necessary to increase the plate thickness in order to reduce the amount of deformation toward the occupant side, which leads to an increase in mass. On the other hand, in this embodiment, the high strength portion 53 has high strength because the Vickers hardness of the high strength portion 53 is high, and the weight of the pillar outer 41 can be reduced by making the high strength portion 53 thinner while increasing the impact absorption performance during a collision such as a side collision. In this way, by applying a material that combines Vickers hardness (strength) and bendability as the high-strength portion 53 to the upper portion of the center pillar 4, it is possible to realize a center pillar 4 that is lightweight and has high impact absorption performance by reducing the possibility of breakage.

[0097] Maximum bending angle θ of the high strength portion 53 1 and the maximum bending angle θ of the low strength portion 51 2 The difference Δθ between the low strength portions 51 and the high strength portions 53 is preferably 100 degrees or less. By making the difference Δθ between the bending angles 100 degrees or less, it is possible to more reliably achieve bending deformation of the high strength portions 53 following the bending deformation of the low strength portions 51 during a side collision of the vehicle. This makes it possible to realize a center pillar 4 having high impact absorbing performance by suppressing the possibility of breakage.

[0098] (Thickness of low and high strength parts) The plate thickness of the low strength portion 51 and the high strength portion 53 may be the same or different. The plate thickness of the low strength portion 51 and the high strength portion 53 can be, for example, 0.8 mm to 2.6 mm. By making the plate thickness 0.8 mm or more, the strength of the pillar outer 41 can be sufficiently increased, and the amount of deformation of the center pillar 4 toward the inside in the width direction Y during a side collision can be reduced. By making the plate thickness 2.6 mm or less, it is possible to prevent the center pillar 4 from becoming too heavy.

[0099] Examples of lower limits of the plate thickness of each of the low-strength portion 51 and the high-strength portion 53 are 0.8 mm, 1.0 mm, and 1.2 mm, and examples of upper limits are 1.6 mm, 1.8 mm, 2.0 mm, 2.2 mm, 2.3 mm, and 2.5 mm. As is clear from the above, the plate thickness of each of the low-strength portion 51 and the high-strength portion 53 is preferably 1.0 mm to 2.5 mm, 1.2 mm to 2.3 mm, 1.2 mm to 2.2 mm, 1.2 mm to 2.0 mm, 1.2 mm to 1.8 mm, or 1.2 mm to 1.6 mm.

[0100] (Vickers hardness of low strength part) Vickers hardness HV at the center of the low strength portion 51 in the thickness direction 2 In order to exhibit high impact absorbing performance, the Vickers hardness HV of the low strength portion 51 may be 150HV or more, 300HV or more, 400HV or more, or 500HV or more. 2 The upper limit of the Vickers hardness HV of the low strength portion 51 is not particularly limited, but from the viewpoint of more reliably suppressing the possibility of breakage during a side collision, it can be 500HV, 400HV, or 300HV. 2 An example of this is 150HV to 500HV.

[0101] (Vickers hardness of high strength part) Vickers hardness HV at the center of the thickness direction of high strength section 53 1From the viewpoint of reducing the amount of displacement of the high strength portion 53 toward the cabin 10 (inner side in the width direction Y) during a side collision, the Vickers hardness HV of the high strength portion 53 is preferably 300HV or more, and may be 400HV or more, 500HV or more, 600HV or more, 750HV or more, 800HV or more, 900HV or more, 950HV or more, 1000HV or more, 1050HV or more, or 1100HV or more. 1 The upper limit of the Vickers hardness HV of the high strength portion 53 is not particularly limited, but from the viewpoint of more reliably suppressing the possibility of breakage during a side collision, examples of the upper limit include 1100HV, 1050HV, 1000HV, 950HV, 900HV, 800HV, 750HV, 650HV, 600HV, 550HV, and 500HV. 1 A preferred example of the hardness is 300HV to 1100HV, and a more preferred example of the hardness is 500HV to 1100HV.

[0102] (Method for measuring Vickers hardness of low strength and high strength parts) In this embodiment, the method for measuring the Vickers hardness of the low strength portion 51 or the high strength portion 53 at the center in the plate thickness direction is as follows. A cross section perpendicular to the plate surface of a sample cut from a part of the low strength portion 51 near the lower bracket 62, for example, or a part of the high strength portion 53 near the upper bracket 61, for example, is taken, and the sample of the measurement surface is prepared and subjected to a hardness test. The measurement surface is prepared in accordance with JIS Z 2244:2020. After polishing the measurement surface using silicon carbide paper of #600 to #1500, a diamond powder with a grain size of 1 μm to 6 μm is dispersed in a diluent such as alcohol or pure water to give a mirror finish. The hardness test is performed in accordance with JIS Z 2244:2020. Using a micro Vickers hardness tester, measurements are taken at 10 points at 1 / 2 the thickness of the sample, with a test force of 1 kgf, so that the distance between the centers of the indentations is at least three times the average diagonal length of the indentations, and the average value is taken as the Vickers hardness of the low strength portion 51 or the high strength portion 53.

[0103] Furthermore, the Vickers hardness HV of the low strength part 51 2 The Vickers hardness of the high-strength part is 53 HV or more. 1 By setting the hardness to 500 HV or more, it is possible to increase the impact energy absorption effect due to plastic deformation of the low strength portion 51 during a side collision while suppressing excessive plastic deformation of the high strength portion 53, thereby reducing the amount by which the upper portion of the center pillar 4 penetrates into the cabin 10 while improving the impact absorption performance.

[0104] In particular, the Vickers hardness of the high-strength section is 53 HV 1 When the Vickers hardness HV of the high strength portion 53 is 500 HV or more, the strength difference (strength ratio) between the high strength portion 53 and the low strength portion 51 is large, and the difference between the bending property of the material of the high strength portion 53 and the bending property of the material of the low strength portion 51 tends to be large. 1 When the Vickers hardness HV of the high strength portion 53 is 500 HV or more, the high strength portion 53 is likely to be broken due to bending deformation of the high strength portion 53 following the bending deformation of the low strength portion 51 during a side collision. 1 When the bending strength of the high-strength portion 53 is 500 HV or more, the problem of the possibility of fracture in the high-strength portion 53 occurs significantly. 1 The maximum bending angle θ of the low strength portion 51 2 By setting the height in accordance with this, the possibility of the high strength portion 53 breaking during a side collision can be reduced.

[0105] (An example of a combination of Vickers hardness of low strength parts and Vickers hardness of high strength parts) Vickers hardness HV of low strength section 51 2 and Vickers hardness HV of high strength part 53 1 As an example of the combination, the Vickers hardness HV 1 The Vickers hardness of the low strength part is 480HV~750HV, and the Vickers hardness of the low strength part is 51HV 2 Vickers hardness of 150HV~480HV (high strength part 53HV 1More specifically, the following three combinations can be given as preferred combinations: Example 1) Vickers hardness HV of high strength part 53 1 and Vickers hardness HV of low strength part 51 2 :600HV and 350HV Example 2) Vickers hardness HV of high strength part 53 1 and Vickers hardness HV of low strength part 51 2 :600HV and 420HV Example 3) Vickers hardness HV of high strength part 53 1 and Vickers hardness HV of low strength part 51 2 :720HV and 480HV

[0106] In all three of the above examples, the Vickers hardness of the high-strength portion is 53 HV 1 and Vickers hardness HV of low strength part 51 2 Relative to HV 1 / HV 2 is 1.3 or more. Thus, HV 1 / HV 2 When HV is 1.3 or more, the strength difference (strength ratio) between the high strength portion 53 and the low strength portion 51 is large, and the difference between the bending property of the material of the high strength portion 53 and the bending property of the material of the low strength portion 51 tends to be large. 1 / HV 2 When the Vickers hardness is 1.3 or more, the high strength portion 53 having a high Vickers hardness is likely to break due to bending deformation of the high strength portion 53 following the bending deformation of the low strength portion 51 during a side collision. 1 / HV 2 When the maximum bending angle θ of the high strength portion 53 is 1.3 or more, the problem of the need to suppress the possibility of fracture in the high strength portion 53 occurs significantly. 1 The maximum bending angle θ of the low strength portion 51 2 By setting the high strength portion 53 in accordance with HV 1 / HV 2 is preferably 1.4 or more, and more preferably 1.5 or more.

[0107] High strength section: Vickers hardness HV 53 1 The higher the Vickers hardness and plate thickness, the smaller the plate thickness required for the required impact absorbing performance, but the more likely cracks will occur during press working of the low strength portion 51 and the high strength portion 53 and during a side collision. Therefore, it is necessary to appropriately set the Vickers hardness and plate thickness, and further, to set the maximum bending angle θ of the high strength portion 53. 1 By improving this, it is possible to create a center pillar 4 that is lightweight and has excellent impact absorption performance.

[0108] (Combination of maximum bending angle of low strength part and maximum bending angle of high strength part) Maximum bending angle θ of low strength portion 51 2 The maximum bending angle θ of the high-strength portion 53 is, for example, 135 degrees to 50 degrees, and within this range, 135 degrees, 70 degrees, 60 degrees, and 50 degrees can be exemplified. 1 The maximum bending angle θ of the high-strength portion 53 can be exemplified as 60 degrees to 40 degrees, and within this range, 60 degrees, 50 degrees, and 40 degrees can be exemplified. 1 and the maximum bending angle θ of the low strength portion 51 2 The difference Δθ from may be 95 degrees or less, 85 degrees or less, 75 degrees or less, 30 degrees or less, 20 degrees or less, 10 degrees or less, or 0 degrees. The minimum value of the difference Δθ is 0 degrees.

[0109] Maximum bending angle θ of the high strength portion 53 1 and the maximum bending angle θ of the low strength portion 51 2 Ratio θ 1 / θ 2 may be 40 / 135=about 0.30 or more, 50 / 135=about 0.37 or more, 60 / 135=about 0.44 or more, 40 / 70=about 0.57 or more, 40 / 60=about 0.67 or more, 50 / 70=about 0.71 or more, 50 / 60=about 0.83 or more, or 60 / 70=about 0.86 or more. 1 / θ 2 The upper limit of the ratio θ is, for example, 1.00. 1 / θ 2The upper limit of the ratio θ may be 0.95 or 0.90. 1 / θ 2 may be 0.30 to 1.00, may be 0.37 to 0.95, may be 0.44 to 0.90, may be 0.57 to 0.90, may be 0.67 to 0.90, may be 0.71 to 0.90, or may be 0.86 to 0.90.

[0110] (Combination of Vickers hardness and maximum bending angle) Regarding the above-mentioned examples 1) to 3) of the preferable combinations of the high-strength portion 53 and the low-strength portion 51, the maximum bending angle θ 2 and the maximum bending angle θ of the high strength portion 53 1 The difference Δθ between these will be described. Example 1) Vickers hardness HV of high strength part 53 1 and Vickers hardness HV of low strength part 51 2 : Maximum bending angle θ of low strength portion 51 in the case of 600HV and 350HV 2 and the maximum bending angle θ of the high strength portion 53 1 The difference Δθ is 30 degrees. Example 2) Vickers hardness HV of high strength part 53 1 and Vickers hardness HV of low strength part 51 2 : In the case of 600HV and 420HV, the maximum bending angle θ of the low strength portion 51 2 and the maximum bending angle θ of the high strength portion 53 1 The difference Δθ is 20 degrees. Example 3) Vickers hardness HV of high strength part 53 1 and Vickers hardness HV of low strength part 51 2 : In the case of 720HV and 480HV, the maximum bending angle θ of the low strength portion 51 2 and the maximum bending angle θ of the high strength portion 53 1 The difference Δθ is less than 15 degrees.

[0111] As is clear from the above description, the maximum bending angle θ of the low strength portion 51 2 and the maximum bending angle θ of the high strength portion 53 1It is preferable that the difference Δθ between the low-strength portions 51 and 51a is 30 degrees or less. With this configuration, the high-strength portions 53 can bend and deform sufficiently to follow the bending deformation of the low-strength portions 51 during a side collision. As a result, the possibility of the high-strength portions 53 breaking during a side collision can be reduced.

[0112] The maximum bending angle θ of the high strength portion 53 1 and the maximum bending angle θ of the low strength portion 51 2 The difference Δθ between the Vickers hardness HV of the high strength part 53 1 and Vickers hardness HV of low strength part 51 2 In this case, the Vickers hardness HV of the high strength portion 53 is preferably set according to 1 and Vickers hardness HV of low strength part 51 2 The larger the difference between the bending angles Δθ, the larger the bending angle difference Δθ tends to be. On the other hand, within the range of the difference Δθ, 1 and the maximum bending angle θ of the low strength portion 51 2 is set.

[0113] For example, the Vickers hardness HV of the low strength portion 51 2 The Vickers hardness of the high-strength part is 200HV and that of the high-strength part is 53HV. 1 In the case where the Vickers hardness HV of the low strength portion 51 is 600 HV, the difference in bending angle Δθ may be 90 degrees or less. 2 The Vickers hardness of the high-strength part is 200HV and that of the high-strength part is 53HV. 1 When the hardness is 480HV, the difference in bending angle Δθ may be 85 degrees or less.

[0114] Vickers hardness HV of low strength section 51 2 The Vickers hardness of the high-strength part is 350HV and that of the high-strength part is 53HV. 1 In the case where the Vickers hardness HV of the low strength portion 51 is 600 HV, the difference in bending angle Δθ may be 30 degrees or less. 2 The Vickers hardness of the high-strength part is 350HV and that of the high-strength part is 53HV. 1 When the hardness is 480HV, the difference in bending angle Δθ may be 20 degrees or less.

[0115] Vickers hardness HV of low strength section 512 The Vickers hardness of the high-strength part is 420HV and that of the high-strength part is 53HV. 1 In the case where the Vickers hardness HV of the low strength portion 51 is 600 HV, the difference in bending angle Δθ may be 20 degrees or less. 2 The Vickers hardness of the high-strength part is 420HV and that of the high-strength part is 53HV. 1 When the hardness is 480HV, the difference in bending angle Δθ may be 10 degrees or less.

[0116] When the Vickers hardness of the low-strength portion 51 is 350HV to 470HV and the Vickers hardness of the high-strength portion 53 is 430HV to 530HV, the difference Δθ in bending angles may be 25 degrees or less, 20 degrees or less, 15 degrees or less, or 10 degrees or less. With such a relationship between the Vickers hardness and the difference Δθ in bending angles of the low-strength portion 51 and the high-strength portion 53, the high-strength portion 53 can bend and deform in a manner sufficiently following the bending deformation of the low-strength portion 51 during a side collision. As a result, the possibility of the high-strength portion 53 breaking during a side collision can be suppressed. In this case, the lower limit of the difference Δθ in bending angles is 0 degrees.

[0117] (Height of joint) During a side collision, the impact load acts on the pillar outer 41 from the door 8 via the brackets 61, 62, 65, and 66. Therefore, in the pillar outer 41, the joint portion between the brackets 61 and 62 becomes the input point of the impact load during the side collision. More specifically, when another vehicle collides with the vehicle from the side as the colliding vehicle, the input from the colliding vehicle to the lower side of the vehicle tends to be large in the early stage of the collision due to the shape of the colliding vehicle (the shape in which the front lower part of the colliding vehicle protrudes forward from the front upper part of the vehicle). Therefore, in the early stage of the collision, the impact needs to be absorbed by the part of the center pillar 4 near the side sill 5 in addition to the side sill 5, and it is desirable that the lower part of the center pillar 4 can be plastically deformed largely. Therefore, it is preferable that the input from the lower bracket 62, which receives more impact in the early stage of the collision among the brackets 61 and 62 for the door 8, is received by the low strength portion 51 as in this embodiment. On the other hand, in the later stage of the collision, the upper part of the colliding vehicle also collides with the vehicle, so that the impact is also input to the upper bracket 61 of the brackets 61 and 62. From the viewpoint of passenger protection, it is desirable to suppress plastic deformation as much as possible of the center pillar 4 near the upper bracket 61. Therefore, it is preferable that the impact load from the upper bracket 61 be borne by the high strength portion 53 as in this embodiment.

[0118] In this embodiment, the joint 52 is disposed at a position lower than the height position of the lower end 61b of the upper bracket 61. This allows the high strength portion 53 to receive the impact load input to the center pillar 4 from the upper bracket 61 (the input point of the impact load) located far from the side sill 5. This makes it possible to reduce the amount of deformation of the center pillar 4 toward the occupant due to a side collision.

[0119] Preferably, as in this embodiment, the joint 52 is disposed at a height position between the lower end 61b of the upper bracket 61 and the upper end 62a of the lower bracket 62 in the vertical direction Z of the vehicle body 1. This makes it possible to sufficiently secure the range of the low strength portion 51. This makes it possible to simultaneously absorb the impact by the low strength portion 51 in cooperation with the side sill 5 in the early stage of a side collision, and suppress deformation of the center pillar 4 toward the cabin 10 caused by the high strength portion 53 receiving the impact load from the upper bracket 61 in the later stage of the side collision.

[0120] The embodiment of the present invention has been described above. However, the present invention is not limited to the above embodiment. Various modifications of the present invention are possible within the scope of the claims. In the following, the configurations different from the above embodiment and modified examples will be mainly described, and similar configurations will be denoted by similar reference numerals and detailed description will be omitted.

[0121] <Variation 1> In the above embodiment, the steel plate base material is described as an example of a configuration in which there is substantially no difference in strength distribution in the thickness direction. However, this does not have to be the case. FIG. 5 is a longitudinal cross-sectional view of the pillar outer 41 in the plate thickness direction and the vertical direction Z in the vicinity of the joint 52 in the first modification, and the illustration of the inner side of the cross section is omitted. As shown in FIG. 5, a high-strength portion softened layer 55 may be present in at least one of the vicinity of the outer surface 53a and the vicinity of the inner surface 53b of the high-strength portion 53. In the first modification, the high-strength portion softened layer 55 is present both in the vicinity of the outer surface 53a and the vicinity of the inner surface 53b, and a central portion 56 is present between the high-strength portion softened layers 55.

[0122] (Extent of softened layer in high strength area) It is preferable that each high-strength portion softening layer 55 is directly connected to the entire region of the joint 52 in order to enhance the effect of suppressing the possibility of breakage in the vicinity of the joint 52 during a side collision. It is preferable that each high-strength portion softening layer 55 exists near the joint 52 even if it is not directly connected to the joint 52. In either case where each high-strength portion softening layer 55 is directly connected to the joint 52 or not, each high-strength portion softening layer 55 preferably exists from the vicinity of the joint 52 to a position higher than the upper end 61a of the upper bracket 61. This can enhance the bending deformation ability of the high-strength portion 53 accompanying the bending deformation of the low-strength portion 51 during a side collision, thereby suppressing the possibility of breakage of the high-strength portion 53. In particular, when each high-strength portion softening layer 55 is connected to the joint 52 over the entire region in the longitudinal direction (front-rear direction X) of the joint 52, the effect of suppressing the possibility of breakage of the high-strength portion 53 can be enhanced. When each high-strength portion softened layer 55 is formed over the entire area of ​​the high-strength portion 53 in the up-down direction Z, the effect of suppressing the possibility of the high-strength portion 53 breaking can be further enhanced.

[0123] (Overview of thickness range of softened layer in high strength section) Each high-strength portion softened layer 55 is formed, for example, by reducing the carbon content in the vicinity of the portion that will become the outer surface 53a and the portion that will become the inner surface 53b (portions that will become the high-strength portion softened layer 55) of the blank, which is the material of the high-strength portion 53, compared to the portion that will become the central portion 56 of the blank. There are no particular limitations on the method of forming the high-strength portion softened layer 55, and any method may be used. In this modified example, each high-strength portion softened layer 55 is provided with a predetermined thickness from the corresponding surface 53a, 53b, for example, in accordance with the maximum bending angle θ of the high-strength portion 53. 1 This is preferable in that it is possible to increase the thickness while sufficiently ensuring the strength of the high-strength portion 53. The lower limit of the above-mentioned predetermined thickness is, for example, 80 μm, and the upper limit is, for example, 200 μm.

[0124] (Summary of the distribution of Vickers hardness in the softened layer of the high strength section and summary of the Vickers hardness in the center) In each high strength portion softened layer 55, the Vickers hardness decreases with increasing distance from the 1 / 2 plate thickness position of the high strength portion 53. In each high strength portion softened layer 55, the portions that become the surfaces 53a and 53b have the lowest Vickers hardness in the high strength portion 53, and are lower than the Vickers hardness of the central portion 56 by, for example, at least 100 HV. Examples of the upper limit of the difference in Vickers hardness between the surfaces 53a and 53b of the high strength portion 53 and the central portion 56 include 250 HV, 300 HV, 350 HV, 400 HV, 500 HV, 550 HV, 600 HV, and 650 HV. Note that when simply referring to the "Vickers hardness of the high strength portion 53," the Vickers hardness at the central portion 56 is referred to.

[0125] In the present modified example 1 in which the high-strength portion softened layers 55 are provided in the high-strength portions 53, the maximum bending angle θ 1 can be increased by, for example, about 20 degrees.

[0126] In this manner, the Vickers hardness of the surfaces 53a and 53b in the thickness direction of the high strength portion 53 is set to be at least 100 HV lower than the Vickers hardness of the central portion 56 in the thickness direction of the high strength portion 53. As a result, the maximum bending angle θ of the high strength portion 53 1 Therefore, the high strength portion 53 can more reliably follow the bending deformation of the low strength portion 51 during a side collision, and the occurrence of cracks in the high strength portion 53 can be suppressed, thereby improving the impact absorbing performance.

[0127] An example of the configuration of the high-strength portion 53 will be described more specifically.

[0128] (Vickers hardness at the center of the high strength part) The Vickers hardness of the central portion 56 in the plate thickness direction in the portion where the high strength portion softening layer 55 is provided is preferably 500HV or more. When the Vickers hardness of the central portion 56 is 500HV or more, the effect of improving the deformability of the high strength portion 53 by the high strength portion softening layer 55 becomes significant. The Vickers hardness of the central portion 56 is preferably 600HV or more, and more preferably 700HV or more. There is no particular upper limit to the Vickers hardness of the central portion 56, but in consideration of formability, etc., it is preferably 900HV or less, and more preferably 800HV or less. Thus, examples of preferred lower limits of the Vickers hardness of the central portion 56 include 500HV, 550HV, 600HV, 700HV, 720HV, and 750HV. Also, examples of preferred upper limits of the Vickers hardness of the central portion 56 include 1100HV, 1050HV, 1000HV, 950HV, 900HV, 850HV, and 800HV. As is clear from the above, the Vickers hardness of the central portion 56 may be 500HV to 1100HV, 550HV to 1050HV, 600HV to 1000HV, 700HV to 950HV, 720HV to 900HV, 750HV to 850HV, or 750HV to 800HV. The Vickers hardness of the central portion 56 may be 550HV to 1000HV, 550HV to 950HV, 550HV to 900HV, 550HV to 850HV, or 550HV to 800HV.

[0129] (Combination of Vickers hardness at the center and maximum bending angle difference) The Vickers hardness of the low-strength portion 51 (the central portion of the low-strength portion 51) in the first modification can be 350HV to 530HV. When the Vickers hardness of the low-strength portion 51 is 350HV to 530HV and the Vickers hardness of the central portion 56 of the high-strength portion 53 is 550HV to 1050HV, the difference Δθ in bending angles may be 30 degrees or less, 25 degrees or less, 20 degrees or less, 15 degrees or less, 10 degrees or less, or 5 degrees or less. The lower limit of the difference Δθ in bending angles is preferably 0 degrees. With such a relationship between the Vickers hardness and the difference Δθ in bending angles at the central portions of the low-strength portion 51 and the high-strength portion 53, the high-strength portion 53 can bend and deform in a manner sufficiently following the bending deformation of the low-strength portion 51 during a side collision. As a result, the possibility of the high-strength portion 53 breaking during a side collision can be suppressed. The Vickers hardness of the central portion 56 of the high strength portion 53 may be in the range of 350 HV to 770 HV.

[0130] (Details of the thickness of the softened layer in each high strength section) The thickness of each high-strength portion softened layer 55 in the plate thickness direction is preferably 80 μm or more and 5% to 20% of the plate thickness at the portion where each high-strength portion softened layer 55 is provided. If the thickness of each high-strength portion softened layer 55 is 20% or less of the plate thickness, the proportion of each high-strength portion softened layer 55 in the steel plate that is the material of the high-strength portion 53 is small, so that the load resistance required for the high-strength portion 53 can be maintained. The thickness of each high-strength portion softened layer 55 is preferably 17% or less of the plate thickness, and more preferably 14% or less. On the other hand, when the high-strength portion softened layer 55 is provided on the entire surface of the steel plate that is the material of the high-strength portion 53, if the thickness of each high-strength portion softened layer 55 is 80 μm or more and 5% or more of the plate thickness, the deformability due to the high-strength portion softened layer 55 can be fully exhibited. The thickness of each high-strength portion softened layer 55 is more preferably 8% or more of the plate thickness. As is clear from the above, the thickness of each high-strength portion softened layer 55 may be 5% to 17% of the above plate thickness, or 5% to 14%, or 8% to 20%, or 8% to 17%, or 8% to 14%.

[0131] (Method for measuring the thickness position of the boundary between the softened layer of the high strength part and the center part) Next, a method for measuring the boundary between the high-strength softened layer 55 and the central portion 56 will be described. FIG. 6 is an image diagram for explaining an example of a method for measuring the boundary between the high-strength softened layer 55 and the central portion 56. A cross section perpendicular to the plate surface of the sample taken from the high-strength portion 53 is taken, and the sample of the measurement surface is prepared and then subjected to a hardness test. The measurement surface is prepared so that the irregularities are as small as possible and no sagging occurs near the surface in order to accurately measure the Vickers hardness near the surface of the sample. Here, the measurement surface is sputtered with an argon ion beam using a cross-section polisher manufactured by JEOL. At this time, in order to suppress the generation of streaky irregularities on the measurement surface, an argon ion beam is irradiated to the measurement surface from 360 degrees using a sample rotating holder manufactured by JEOL.

[0132] The Vickers hardness of the sample with the prepared measurement surface is measured using a micro Vickers hardness tester. The area from the surface of the sample to the softened layer of the sample is measured in the direction perpendicular to the surface (thickness direction) with a test force of 50 gf.

[0133] The measurement position on the most surface side of the sample is a position 20 μm thick from either of the two surfaces 53a and 53b (if a plating layer exists, this refers to the surface of the steel sheet base material directly below the plating layer, and if an alloy layer exists between the plating layer and the steel sheet base material in addition to the plating layer, this refers to the surface of the steel sheet base material directly below the alloy layer). The measurement points when measuring the boundary between the high-strength portion softened layer 55 and the central portion 56 are equally spaced at intervals of 5 μm to 15 μm in the sheet thickness direction, and the distance between the centers of the dents is at least three times the average diagonal length of the dents. Depending on the average diagonal length of the dents, it may not be possible to ensure a center distance of at least three times the average diagonal length of the dents in a row along the sheet thickness direction. In this case, measurements are made at different positions in the sheet thickness direction while varying the positions in the direction perpendicular to the sheet thickness direction. This makes it possible to meet the measurement conditions of having dimples spaced at equal intervals of 5 μm to 15 μm in the thickness direction and having the distance between the centers of the dimples be at least three times the average diagonal length of the dimples. Measurements are taken from a thickness position 20 μm from the surface to a position halfway along the thickness direction.

[0134] (Method of calculating the slope of Vickers hardness at each thickness position after measuring the boundary between the high strength softened layer and the center) The slope of the Vickers hardness at each thickness position after the Vickers hardness measurement at the boundary between the high-strength portion softened layer 55 and the central portion 56 is, for example, a slope Δbi obtained from the Vickers hardness at multiple consecutive points (three points). The slope Δbi is calculated from the following formula (1).

number

[0135] Of the three measurement points at which the gradient Δbi calculated by equation (1) from the surface side of the high strength portion 53 first becomes 0.5 (HV / μm) or less, the thickness position of the measurement point closest to the steel plate surface is determined to be the thickness position of the boundary between the high strength portion softened layer 55 and the central portion 56.

[0136] (Relationship between Vickers hardness of the softened layer of the high strength part and the Vickers hardness of the center part) The Vickers hardness of the high-strength portion softened layer 55 on the surfaces 53a, 53b of the high-strength portion 53 is preferably 0.5 to less than 0.9 times the Vickers hardness of the central portion 56 where the high-strength portion softened layer 55 is provided.

[0137] (Method for measuring Vickers hardness at the center of high strength part) The method for measuring the Vickers hardness of the central portion 56 is as follows. A cross section perpendicular to the plate surface of the sample cut out from the high strength portion 53 is taken, and the sample of the measurement surface is prepared and subjected to a hardness test. The measurement surface is prepared in accordance with JIS Z 2244:2020. After polishing the measurement surface using silicon carbide paper of #600 to #1500, it is finished to a mirror surface using a liquid in which diamond powder with a grain size of 1 μm to 6 μm is dispersed in a dilution such as alcohol or pure water. The hardness test is performed in accordance with JIS Z 2244:2020. Using a micro Vickers hardness tester, 10 indentations are measured at a center-to-center distance of at least three times the average diagonal length of the indentations at a position 1 / 2 the plate thickness of the sample with a test force of 1 kgf, and the average value is taken as the Vickers hardness of the central portion 56.

[0138] (Method for measuring Vickers hardness of the surface of high strength parts) The Vickers hardness of the surface of the high strength portion 53 is measured on a cross section obtained by cutting the high strength portion 53 along the plate thickness direction in accordance with the Vickers hardness test described in JIS Z 2244:2020.

[0139] After the above-mentioned cross section is subjected to sample preparation of the measurement surface, it is subjected to hardness testing. The measurement surface is prepared so that the irregularities are as small as possible and no sagging occurs near the surface in order to accurately measure the Vickers hardness near the surface of the sample. Here, the measurement surface is sputtered with an argon ion beam using a cross-section polisher manufactured by JEOL. At this time, in order to prevent streaky irregularities from occurring on the measurement surface, an argon ion beam is irradiated onto the measurement surface from 360 degrees using a sample rotating holder manufactured by JEOL.

[0140] The Vickers hardness of the sample with the prepared measurement surface is measured using a micro Vickers hardness tester. At this time, the measurement point is a thickness position 20 μm from the surface of the high strength part 53. If a plating layer exists in the high strength part 53, the measurement point is a thickness position 20 μm from the surface of the steel sheet base material directly below the plating layer. If an alloy layer exists between the plating layer and the steel sheet base material in addition to the plating layer in the high strength part 53, the measurement point is a thickness position 20 μm from the surface of the steel sheet base material directly below the alloy layer. At the locations at the above-mentioned thickness positions from the surface of the sample, 10 indentations are measured in a direction perpendicular to the sheet surface (sheet thickness direction) with a test force of 10 gf at a center-to-center distance of at least three times the average diagonal length of the indentations, and the average value is taken as the Vickers hardness of the surface of the high strength part 53.

[0141] If the Vickers hardness of the surface of the high-strength portion 53 is 0.5 times or more the Vickers hardness of the central portion 56, the load resistance during a collision, particularly during the later part of the stroke during a collision, can be improved. It is more preferable that the Vickers hardness of the high-strength portion softened layer 55 is 0.6 times or more the Vickers hardness of the central portion 56 on the surface of the high-strength portion 53. On the other hand, if the Vickers hardness of the surface of the high-strength portion 53 is less than 0.9 times the Vickers hardness of the central portion 56, the deformability can be sufficiently improved. It is more preferable that the Vickers hardness of the high-strength portion softened layer 55 is less than 0.8 times the Vickers hardness of the central portion 56 on the surface of the high-strength portion 53.

[0142] (Changes in Vickers hardness in the softened layer of the high strength part) FIG. 7 is an image diagram for explaining an example of the Vickers hardness change in the high-strength portion softened layer 55. As shown in FIG. 7, the high-strength portion softened layer 55 preferably has a first hardness change region that is a region from the surfaces 53a, 53b to 40% of the thickness of the high-strength portion softened layer 55 in the sheet thickness direction, and a second hardness change region that is a region of the high-strength portion softened layer 55 that is not the first hardness change region. The absolute value ΔHV1 of the hardness change in the sheet thickness direction in the first hardness change region is preferably larger than the absolute value ΔHV2 of the hardness change in the sheet thickness direction in the second hardness change region. If ΔHV1 is larger than ΔHV2, sufficient load characteristics can be obtained.

[0143] The absolute value ΔHV1 of the hardness change in the first hardness change region is preferably 100HV or more and less than 200HV. If ΔHV1 is 100HV or more, the stress concentration during bending deformation can be further alleviated, and the bending characteristics can be further improved. If ΔHV1 is less than 200HV, the effect of alleviating the stress concentration during bending deformation can be further enhanced, and better bending characteristics can be obtained. Therefore, when ΔHV1 is 100HV or more and less than 200HV, good bending characteristics can be obtained, and the deformability of the high strength portion 53 can be improved. Specifically, in the latter part of the stroke during the collision, the load drop immediately after the load peak can be made gentle. Therefore, as described above, the absolute value ΔHV1 of the hardness change in the first hardness change region is preferably 100HV or more and less than 200HV. It should be noted that the lower limit of ΔHV1 is preferably 100 HV, while the upper limit may be less than 200 HV, less than 300 HV, or less than 400 HV.

[0144] (Method of measuring Vickers hardness of first and second hardness change regions of the high strength portion softened layer) Next, a method for measuring the hardness of the first hardness change region and the second hardness change region will be described. A cross section perpendicular to the plate surface of the sample taken from the high strength portion 53 is taken, and the sample is prepared for the measurement surface, and then the sample is subjected to a hardness test. The measurement surface is prepared so that the irregularities are as small as possible and no sagging occurs near the surface in order to accurately measure the Vickers hardness near the surface of the sample. Here, the measurement surface is sputtered with an argon ion beam using a cross-section polisher manufactured by JEOL. At this time, in order to suppress the occurrence of streaky irregularities on the measurement surface, an argon ion beam is irradiated to the measurement surface from 360 degrees using a sample rotating holder manufactured by JEOL.

[0145] The Vickers hardness is measured on the sample with the prepared measurement surface using a micro Vickers hardness tester. The area from the surface of the sample corresponding to the softened layer of the sample is measured in the direction perpendicular to the plate surface (plate thickness direction) with a test force of 10 gf. The total number of measurement points varies depending on the plate thickness of the sample, but the number of measurement points for calculating ΔHV1 and ΔHV2 described below is set in accordance with the description of JIS Z 2244:2020.

[0146] The thickness of the high-strength portion softened layer 55 is 80 μm or more and is 5% to 20% of the plate thickness at the portion where the high-strength portion softened layer 55 is provided. The first hardness change region is a region from the surface of the high-strength portion softened layer 55 to 40% of the thickness, and in this embodiment, it exists at a thickness position from the surface of the high-strength portion 53 to a minimum of, for example, 40 μm and a maximum of, for example, 80 μm.

[0147] The measurement position on the most surface side of the sample is a position 20 μm thick from the surface (if a plating layer exists, this refers to the surface of the steel sheet base material directly below the plating layer, and if an alloy layer exists between the plating layer and the steel sheet base material in addition to the plating layer, this refers to the surface of the steel sheet base material directly below the alloy layer). The measurement point at this 20 μm thick position is a different point from the measurement point at the time of measuring the Vickers hardness of the surface of the high strength portion 53 described above. The measurement of the first hardness change region is performed by measuring the indentations at at least two points in the thickness direction at equal intervals of 15 μm or less in the thickness direction and with a center-to-center distance of three or more times the average diagonal length of the indentations. Depending on the average diagonal length of the indentations, it may be possible to measure only one point in the row along the thickness direction for the first hardness change region. In this case, the measurement is performed at different positions in the thickness direction while varying the positions in the direction perpendicular to the thickness direction. This allows the Vickers hardness to be measured at at least two points in the first hardness change region while satisfying the measurement conditions that the depressions are spaced at equal intervals of 15 μm or less in the plate thickness direction and the distance between the centers of the depressions is at least three times the average diagonal length of the depressions.

[0148] The thickness of the high strength portion softened layer 55 is 80 μm or more, and is 5% to 20% of the sheet thickness at the portion where the high strength portion softened layer 55 is provided. The Vickers hardness of the second hardness change region is measured in this thickness range excluding the first hardness change region. When the thickness of the high strength portion softened layer 55 is 80 μm to 200 μm, the second hardness change region is present in a thickness position range of 32 μm to 80 μm at minimum (48 μm thickness range) and 80 μm to 200 μm at maximum (120 μm thickness range) starting from the surface of the high strength portion 53. The second hardness change region is measured at at least two locations in the sheet thickness direction at equal intervals of 15 μm or less in the sheet thickness direction and with a center-to-center distance of three times or more the average diagonal length of the indentations. Depending on the average diagonal length of the indentations, it may not be possible to measure two adjacent points at a fixed interval in a row along the plate thickness direction for the second hardness change region. In this case, measurements are performed at different positions in the plate thickness direction while varying positions in the direction perpendicular to the plate thickness direction. This allows the Vickers hardness of the second hardness change region to be measured while satisfying the measurement conditions of being spaced at equal intervals of 15 μm or less in the plate thickness direction and the distance between the centers of the indentations being three times or more the average diagonal length of the indentations. The second hardness change region may be measured on the same row as the first hardness change region. The second hardness change region may be measured at a total of four points, for example, one point near the boundary with the first hardness change region, one point near the boundary with the central portion 58, and two points between these two points. When the second hardness change region exists up to 200 μm from the steel plate surface, the measurement points of the first hardness change region and the second hardness change region can be measured at each thickness position from the steel plate surface, for example, 20 μm, 35 μm, 50 μm, 65 μm, 80 μm, 95 μm, 110 μm, 125 μm, 140 μm, 155 μm, 170 μm, 185 μm, and 200 μm.

[0149] In the case of a sample in which high-strength portion softened layers 55 are arranged on both sides of the central portion 56 of the high-strength portion 53, similar measurements are performed from the first surface side of the sample, and also from the second surface side opposite the first surface.

[0150] (Method of calculating absolute value ΔHV1 of hardness change after measurement of first hardness change region) ΔHV1 is calculated by the following procedure. That is, from all measurement points included in the region (first hardness change region) from the surface of the sample cut out from the high strength portion 53 to 40% of the entire thickness of the high strength portion softened layer 55, the hardness gradient Δa of the first hardness change region is calculated by formula (2). Here, ai is the percentage (%) of the distance from the surface at the i-th measurement point to the entire thickness of the softened layer, ci is the Vickers hardness (HV) at ai, and n is the sum of all measurement points included in the region (first hardness change region) from the surface to 40% of the entire thickness of the softened layer.

[0151]

number

[0152] Where: Δa: Gradient of hardness change in the thickness direction in the first hardness change region (HV / %) ai: The percentage of the distance from the surface at the i-th measurement point to the total thickness of the softened layer (%) ci: Average value of Vickers hardness at three different points at the i-th measurement thickness position (HV) n: the sum of all measurement points included in the first hardness change region on the first surface side It is.

[0153] In the case of a sample in which high-strength portion softened layers 55 are arranged on both sides of center portion 56, Δa1 on the first surface side is calculated from equation (2) based on the results of measuring the Vickers hardness from the first surface side, and Δa2 on the second surface side is calculated from equation (2) based on the results of measuring the Vickers hardness from the second surface side. The arithmetic average of Δa1 and Δa2 can be taken as Δa.

[0154] ΔHV1 can be obtained by multiplying Δa obtained by formula (2) by the ratio of the thickness in the sheet thickness direction of the first hardness change region to the entire thickness of the softened layer.

[0155] (Method of calculating absolute value ΔHV2 of hardness change after measuring second hardness change region) ΔHV2 is calculated by the following procedure. That is, from all measurement points included in the region (second hardness change region) from 40% to 100% of the total thickness of the high-strength softened layer 55 on the surface side of the sample, the hardness gradient ΔA of the second hardness change region is calculated by formula (3). Here, Ai is the percentage (%) of the distance from the surface at the i-th measurement point to the total thickness of the softened layer, Ci is the Vickers hardness (HV) at Ai, and N is the sum of all measurement points included in the region (second hardness change region) from 40% to 100% of the total thickness of the softened layer on the surface side.

[0156]

number

[0157] Where: ΔA: Gradient of hardness change in the thickness direction in the second hardness change region (HV / %) Ai: The percentage of the distance from the surface at the i-th measurement point to the total thickness of the softened layer (%) Ci: Average Vickers hardness (HV) at three different points at the i-th measurement thickness position N: The sum of all measurement points included in the second hardness change region on the first surface side It is.

[0158] In the case of a sample in which high-strength portion softened layers 55 are arranged on both sides of center portion 56, ΔA1 on the first surface side is calculated from equation (3) based on the results of measuring the Vickers hardness from the first surface side, and ΔA2 on the second surface side is calculated from equation (3) based on the results of measuring the Vickers hardness from the second surface side. The arithmetic average of ΔA1 and ΔA2 can be taken as ΔA.

[0159] ΔHV2 can be calculated by multiplying ΔA calculated by formula (3) by the ratio of the thickness in the sheet thickness direction of the second hardness change region to the total thickness of the softened layer.

[0160] In addition, the maximum bending angle θ 1It is mainly the high-strength portion softened layer 55 on the outer surface 53a side that can exhibit the effect of preventing cracks due to its large Vickers hardness. Therefore, the high-strength portion softened layer 55 does not need to be provided on the inner surface 53b side. In this case, the inner surface 53b side has the same Vickers hardness as the central portion 56, and the high-strength portion softened layer 55 is present only on the outer surface 53a side.

[0161] <Variation 2> In the above-mentioned embodiment, the low-strength portion 51 is not formed with a softened layer. However, this is not necessarily the case. FIG. 8 is a longitudinal cross-sectional view of the pillar outer 41 in the thickness direction and the vertical direction Z in the vicinity of the joint 52 in the second modified example, and the illustration of the inner side of the cross section is omitted. As shown in FIG. 8, the low-strength portion 51 may have a low-strength portion softened layer 57. In this case, the low-strength portion softened layer 57 is present both near the outer surface 51a and near the inner surface 51b of the low-strength portion 51. In this case, the low-strength portion softened layer 57 is present on both sides in the thickness direction of the low-strength portion 51, and a central portion 58 is present between the low-strength portion softened layers 57.

[0162] (Vickers hardness at the center of the low strength part) Even when the Vickers hardness of the central portion 58 exceeds 300HV, for example, 400HV, the low-strength portion 51 may be able to avoid the possibility of fracture during a side collision. However, in a configuration in which the Vickers hardness of the central portion 58 exceeds 300HV, the presence of the low-strength portion softening layer 57 can significantly increase the effect of suppressing the possibility of fracture of the low-strength portion 51 during a side collision. Examples of preferred lower limits of the Vickers hardness of the central portion 58 include 300HV, 350HV, 400HV, 420HV, and 450HV. Examples of preferred upper limits of the Vickers hardness of the central portion 58 include 530HV, 500HV, 480HV, and 450HV. As is clear from the above, the Vickers hardness of the central portion 58 may be 300HV to 530HV, 350HV to 500HV, 400HV to 480HV, or 420HV to 450HV.

[0163] (Combination of Vickers hardness at the center and maximum bending angle difference) When the Vickers hardness of the low strength portion 51 is 420HV to 530HV and the Vickers hardness of the central portion 56 of the high strength portion 53 is 550HV to 1050HV, the difference Δθ in bending angles may be 50 degrees or less, 45 degrees or less, 40 degrees or less, 35 degrees or less, 30 degrees or less, or 25 degrees or less. The lower limit of the difference Δθ in bending angles is preferably 0 degrees. With such a relationship between the Vickers hardness and the difference Δθ in bending angles at the respective central portions of the low strength portion 51 and the high strength portion 53, the high strength portion 53 can bend and deform in a side collision by sufficiently following the bending deformation of the low strength portion 51. As a result, the possibility of breakage of the high strength portion 53 in a side collision can be suppressed. The Vickers hardness of the central portion 56 of the high strength portion 53 described above may be in the range of 550HV to 770HV.

[0164] (Area of ​​existence of softened layer in low strength area) When the joint 52 is at a height position between the lower end 61b of the upper bracket 61 and the upper end 62a of the lower bracket 62 (when it is at the position shown in FIG. 1), it is preferable that each low-strength portion softened layer 57 on each surface 51a, 51b of the low-strength portion 51 exists from a position higher than the upper end 62a of the lower bracket 62 to a position lower than the lower end 62b of the lower bracket 62. This allows each low-strength portion softened layer 57 to be arranged so as to cover the lower bracket 62 that deforms the most in the vehicle body 1 during a side collision, and each low-strength portion softened layer 57 can improve the bending deformation ability of the low-strength portion 51, thereby suppressing the possibility of breakage of the low-strength portion 51 and improving the impact energy absorption amount of the low-strength portion 51. The low-strength portion softened layer 57 may be formed over the entire area of ​​the low-strength portion 51 in the vertical direction Z. In particular, as described below, when the joint 52 is located lower than the lower end 62b of the lower bracket 62 (when located in the position shown in FIG. 9 ), it is preferable that the low-strength portion softened layer 57 is formed over the entire area of ​​the low-strength portion 51 in the up-down direction Z. In this case, the range of the low-strength portion 51 is relatively narrow in the center pillar 4, and the entire area of ​​the low-strength portion 51 tends to deform during a side collision. Therefore, it is possible to suppress the possibility of breakage of the low-strength portion 51 and improve the amount of impact energy absorption of the low-strength portion 51 by improving the bending deformability of the low-strength portion 51 due to the low-strength portion softened layer 57.

[0165] (Overview of thickness range of softened layer in low strength area) Each low-strength portion softened layer 57 is formed, for example, by reducing the carbon content in the vicinity of the portion that will become the outer surface 51a and the portion that will become the inner surface 51b (portion that will become the low-strength portion softened layer 57) of the blank, which is the material of the low-strength portion 51, compared to the portion that will become the central portion 58 of the blank. The method of forming the low-strength portion softened layer 57 is not particularly limited, and any method may be used. In this modification, it is preferable that each low-strength portion softened layer 57 is provided with a predetermined thickness from the corresponding surface 51a, 51b, for example, in that the strength of the low-strength portion 51 can be sufficiently secured while increasing the maximum bending angle of the low-strength portion 51. The lower limit of the above-mentioned predetermined thickness is, for example, 80 μm, and the upper limit is, for example, 200 μm.

[0166] (Summary of the distribution of Vickers hardness in the softened layer of the low strength area and summary of the Vickers hardness in the center) In each low-strength portion softened layer 57, the Vickers hardness decreases with increasing distance from the 1 / 2 plate thickness position of the low-strength portion 51. In each low-strength portion softened layer 57, the portions that become the surfaces 51a, 51b have the lowest Vickers hardness in the low-strength portion 51, and are lower than the Vickers hardness of the central portion 58 by, for example, at least 100 HV to 250 HV. In this case, the Vickers hardness of the low-strength portion 51 refers to the Vickers hardness of the central portion 58.

[0167] In this variant example 2 in which each low-strength portion 51 is provided with a low-strength portion softening layer 57, the maximum bending angle of the low-strength portion 51 can be made higher by, for example, about 20 degrees compared to the case in which the low-strength portion softening layer 57 is not provided (embodiment).

[0168] In this way, the Vickers hardness of the low-strength portion 51 at the surfaces 51a and 51b in the thickness direction is set to be at least 100 HV lower than the Vickers hardness of the central portion 58 in the thickness direction of the low-strength portion 51. This allows the maximum bending angle of the low-strength portion 51 to be increased. Therefore, the low-strength portion 51 can more reliably follow the bending deformation of the center pillar 4 during a side collision, and the occurrence of cracks in the low-strength portion 51 can be suppressed, thereby improving the impact absorption performance. As a result, since the high-strength portion 53 has a high Vickers hardness and high strength, the amount of intrusion into the vehicle interior can be suppressed, thereby improving the occupant protection effect, and the low-strength portion 51 can further reduce the thickness of the low-strength portion 51 to reduce the weight of the vehicle body 1 while ensuring the absorption amount of impact energy in the low-strength portion 51. In addition, even if the low-strength portion 51 is formed of a high-strength material with a higher Vickers hardness, the possibility of fracture of the low-strength portion 51 can be suppressed, so that the amount of intrusion of the low-strength portion 51 into the inside of the vehicle body during a side collision can be reduced.

[0169] An example of the configuration of the low-strength portion 51 will be described more specifically.

[0170] (Vickers hardness at the center of the low strength part) The Vickers hardness of the central portion 58 in the plate thickness direction in the portion where the low strength portion softening layer 57 is provided is preferably 150 HV or more. When the Vickers hardness of the central portion 58 is 150 HV or more, the strength of the low strength portion 51 during a side collision can be sufficiently ensured. The Vickers hardness of the central portion 58 may be greater than 200 HV, may be 250 HV or more, may be 300 HV or more, may be 400 HV or more, or may be 500 HV or more. There is no particular upper limit to the Vickers hardness of the central portion 58, but in consideration of the ability to follow the deformation of the center pillar 4 during a side collision, it is preferably 500 HV or less.

[0171] (Details of thickness range of softened layer in each low strength part) The thickness of each low-strength portion softened layer 57 in the plate thickness direction is preferably 80 μm or more and 5% to 20% of the plate thickness at the portion where each low-strength portion softened layer 57 is provided. If the thickness of each low-strength portion softened layer 57 is 20% or less of the plate thickness, the proportion of each low-strength portion softened layer 57 in the steel plate that is the material of the low-strength portion 51 is small, so that the load resistance required for the low-strength portion 51 can be maintained. The thickness of each low-strength portion softened layer 57 is preferably 17% or less of the plate thickness, and more preferably 14% or less. On the other hand, when the low-strength portion softened layer 57 is provided on the entire surface of the steel plate that is the material of the low-strength portion 51, if the thickness of each low-strength portion softened layer 57 is 80 μm or more and 5% or more of the plate thickness, the deformability due to the low-strength portion softened layer 57 can be fully exhibited. The thickness of each low-strength portion softened layer 57 is more preferably 8% or more of the plate thickness. As is clear from the above, the thickness of each low-strength portion softened layer 57 may be 5% to 17% of the above plate thickness, or 5% to 14%, or 8% to 20%, or 8% to 17%, or 8% to 14%.

[0172] (Method for measuring the thickness position of the boundary between the softened layer of the low strength part and the center part) The method for measuring the boundary between the low-strength portion softened layer 57 and the central portion 58 is the same as the method for measuring the boundary between the high-strength portion softened layer 55 and the central portion 56 .

[0173] (Method of calculating the slope of Vickers hardness at each thickness position after measuring the boundary between the softened layer of the low strength portion and the center portion) The method for calculating the slope of the Vickers hardness at each thickness position after Vickers hardness measurement when measuring the boundary between the low-strength softened layer 57 and the central portion 58 is the same as the method for calculating the slope of the Vickers hardness at each thickness position after Vickers hardness measurement when measuring the boundary between the high-strength softened layer 55 and the central portion 56.

[0174] (Relationship between the Vickers hardness of the softened layer in the low strength area and the Vickers hardness of the center area) The Vickers hardness of the low-strength portion softened layer 57 on the surfaces 51a, 51b of the low-strength portion 51 is preferably 0.5 to less than 0.9 times the Vickers hardness of the central portion 58 where the low-strength portion softened layer 57 is provided.

[0175] (Method for measuring Vickers hardness at the center of low strength part) The method for measuring the Vickers hardness of the central portion 58 of the low strength portion 51 is similar to the method for measuring the Vickers hardness of the central portion 56 of the high strength portion 53.

[0176] (Method for measuring Vickers hardness of the surface of low strength parts) The method for measuring the Vickers hardness of the surface of the low strength portion 51 is similar to the method for measuring the Vickers hardness of the surface of the high strength portion 53 .

[0177] If the Vickers hardness of the surface of the low-strength portion 51 is 0.5 times or more the Vickers hardness of the central portion 58, the load resistance during a collision, particularly during the later part of the stroke during a collision, can be improved. It is more preferable that the Vickers hardness of the low-strength portion softened layer 57 is 0.6 times or more the Vickers hardness of the central portion 58 on the surface of the low-strength portion 51. On the other hand, if the Vickers hardness of the surface of the low-strength portion 51 is less than 0.9 times the Vickers hardness of the central portion 58, the deformability can be sufficiently improved. It is more preferable that the Vickers hardness of the low-strength portion softened layer 57 is less than 0.8 times the Vickers hardness of the central portion 58 on the surface of the low-strength portion 51.

[0178] (Change in Vickers hardness in the softened layer of the low strength part) FIG. 7 is also an image diagram for explaining an example of the Vickers hardness change in the low-strength portion softened layer 57. As shown in FIG. 7, the low-strength portion softened layer 57 preferably has a first hardness change region that is a region from the surfaces 51a, 51b to 40% of the thickness of the low-strength portion softened layer 57 in the plate thickness direction, and a second hardness change region that is a region of the low-strength portion softened layer 57 that is not the first hardness change region. The absolute value ΔHV1' of the hardness change in the plate thickness direction in the first hardness change region is preferably larger than the absolute value ΔHV2' of the hardness change in the plate thickness direction in the second hardness change region. If ΔHV1' is larger than ΔHV2', sufficient load characteristics can be obtained.

[0179] The absolute value ΔHV1' of the hardness change in the first hardness change region is preferably 100HV or more and less than 200HV. If ΔHV1' is 100HV or more, the stress concentration during bending deformation can be further alleviated, and the bending characteristics can be further improved. If ΔHV1' is less than 200HV, the effect of alleviating the stress concentration during bending deformation can be further enhanced, and better bending characteristics can be obtained. Therefore, when ΔHV1' is 100HV or more and less than 200HV, good bending characteristics can be obtained, and the deformability of the low strength portion 51 can be improved. Specifically, in the latter part of the stroke during the collision, the load drop immediately after the load peak can be made gentle. Therefore, as described above, the absolute value ΔHV1' of the hardness change in the first hardness change region is preferably 100HV or more and less than 200HV. It is preferable that the upper limit of ΔHV1′ is less than 200HV, while the lower limit may be 50HV, may be more than 50HV, may be 55HV, may be 60HV, or may be 100HV.

[0180] (Method of measuring Vickers hardness of first and second hardness change regions of low strength portion softened layer) The method for measuring the hardness of the first hardness change region and the second hardness change region in the low-strength portion 51 is similar to the method for measuring the hardness of the first hardness change region and the second hardness change region in the high-strength portion 53.

[0181] In the case of a sample in which low-strength portion softened layers 57 are arranged on both sides of the central portion 58 of the low-strength portion 51, similar measurements are performed from the first surface side of the sample, and also from the second surface side opposite the first surface.

[0182] (Method of calculating absolute values ​​ΔHV1' and ΔHV2' of hardness change after measuring first and second hardness change regions) The method of calculating ΔHV1′ and ΔHV2′ in the low-strength portion 51 is similar to the method of calculating ΔHV1 and ΔHV2 in the high-strength portion 53.

[0183] In addition, it is mainly the low-strength portion softened layer 57 on the outer surface 51a side that can exhibit the effect of preventing cracking due to the large maximum bending angle during a side collision. Therefore, the low-strength portion softened layer 57 does not need to be provided on the inner surface 51b side. In this case, the inner surface 51b side has the same Vickers hardness as the central portion 58, and the low-strength portion softened layer 57 exists only on the outer surface 51a side.

[0184] In addition, in this modified example 2, high strength portion softened layer 55 does not have to be provided in high strength portion 53. In this case, most of the steel sheet base material in high strength portion 53 is formed by central portion 56. When a plating layer is present in high strength portion 53, the steel sheet base material begins immediately below the plating layer, and when an alloy layer is present between the plating layer and the steel sheet base material in addition to the plating layer in high strength portion 53, the steel sheet base material begins immediately below the alloy layer.

[0185] <Variation 3> In the above embodiment, the vehicle is a BEV, and the reinforcing member 20 for protecting the battery 18b from a side collision is provided in the side sill 5. However, this is not necessarily the case. FIG. 9 is a schematic left side view for explaining Modification 3 in which the reinforcing member 20 is not provided in the side sill 5. As shown in FIG. 9, when the vehicle is equipped with an internal combustion engine such as a gasoline engine or a diesel engine, and the battery is not provided on the side of the side sill 5 (inside the width direction Y), the reinforcing member 20 may not be provided in the side sill 5. It is common to provide a reinforcing member in the side sill 5 even in a vehicle equipped with an internal combustion engine. The vehicle shown in FIG. 9 may be a PHEV (Plug-in Hybrid Electric Vehicle). When the vehicle is a PHEV, the driving battery for driving the wheels is fixed to the floor panel 7 or the like at a relatively large distance (for example, a distance greater than 10 cm) from the side sill 5 in the width direction Y.

[0186] In such a configuration, the deformation amount of the side sill 5 tends to be large during a side collision, and further, the side sill 5 undergoes torsional deformation. Since the plastic deformation amount of the side sill 5 is relatively large, the impact energy absorption amount by the side sill 5 is large, and the side sill 5 and the center pillar 4 share the impact energy absorption. When the impact energy absorption amount shared by the center pillar 4 is small, in order to suppress contact between the vehicle body 1 and the occupant, it is preferable to narrow the range of the low-strength portion 51 that undergoes large plastic deformation inward in the width direction Y to absorb the impact, and to arrange the high-strength portion 53 that reduces the amount of plastic deformation of the vehicle body 1 inward in the width direction Y close to the side sill 5.

[0187] Therefore, in this modification, the joint 52 is disposed at a height position lower than the upper end 62a of the lower bracket 62 in the vertical direction Z, and is preferably disposed at a height position lower than the lower end 62b of the lower bracket 62 in the vertical direction Z. The joint 52 is disposed, for example, above the side sill 5 below the lower end 62b. In the vehicle shown in FIG. 9, the side sill 5 undergoes torsional deformation about an axis along the front-rear direction X during a side collision. In this case where the side sill 5 undergoes torsional deformation, the joint 52 is disposed as described above, so that the high-strength portion 53 can be provided close to the side sill 5, which is subject to a large amount of deformation during a side collision. Therefore, during a side collision, the deformation of the pillar outer 41 that follows the intrusion of the side sill 5 into the cabin 10 due to the torsional deformation of the side sill 5 can be suppressed by the high-strength portion 53. As a result, the amount of intrusion of the center pillar 4 into the cabin 10 can be reduced, and the torsional deformation of the side sill 5 can be suppressed.

[0188] <Variation 4> In the above embodiment, the lower end 473b of the overlapping portion 47 of the pillar outer 41 is aligned along the outer side wall 153 of the side sill outer 15. However, this does not have to be the case. Fig. 10 is a schematic cross-sectional view of a main portion of Variation 4 relating to a variation of the overlapping portion 47 of the pillar outer 41, showing a cross section perpendicular to the front-rear direction.

[0189] The overlapping portion 47 of the fourth modification has, in addition to an upper flange 471, an upper wall 472, and an outer wall 473, a lower wall 474 extending inward in the width direction Y from the outer wall 473.

[0190] The outer wall 473 is disposed up to the lower end of the outer surface 153 a of the outer wall 153 of the side sill outer 15 .

[0191] The lower wall 474 is preferably in contact with the lower surface 154a of the lower wall 154 of the side sill outer 15 along the length thereof, and is joined to the lower surface 154a by welding, adhesive, or the like. In this embodiment, a lower end 474b (lower tip) of the lower wall 474 is the lower end of the overlapping portion 47.

[0192] In this way, the overlapping portion 47 is extended to the lower wall 474 of the side sill outer 15, so that the center pillar 4 is configured to hold the lower part of the side sill 5. This makes it possible to increase the joint area between the center pillar 4 and the side sill 5, so that the stress acting between the side sill 5 and the center pillar 4 during a side collision can be reduced. In addition, the load transmitted from the center pillar 4 to the side sill 5 during a side collision is received by the vehicle body 1 as a torsional moment. Therefore, deformation of the closed cross-sectional shape of the side sill 5, particularly the side sill outer 15, can be suppressed. Even if a side collision occurs, the original closed cross-sectional shape of the side sill 5 before the collision is unlikely to change, so the side sill 5 has high torsional rigidity and can reduce the torsional angle of the side sill 5 during a side collision. This makes it possible to reduce the amount of intrusion of the center pillar 4 and the side sill 5 into the cabin 10. On the other hand, by devising an arrangement in which the center pillar 4 does not reach the lower end (lower flange 155) of the side sill 5, the center pillar 4 does not become unnecessarily heavy, and it is possible to achieve an excellent balance between improving the reinforcing effect of the side sill 5 due to the lower shape of the center pillar 4 and suppressing the weight increase of the center pillar 4.

[0193] The lower end 474b of the overlapping portion 47 is, for example, a linear end portion along the front-rear direction X. With this configuration, the vehicle body 1 can receive the load transmitted from the center pillar 4 to the side sill 5 during a side collision as a torsional moment over the entire area where the overlapping portion 47 is disposed in the front-rear direction X. This makes it possible to more reliably prevent the closed cross-sectional shape of the side sill 5, and in particular the side sill outer 15, from being crushed.

[0194] In the fourth modification, as described in the embodiment, the height position of the joint 52 is preferably between the height position of the lower end 61b of the upper bracket 61 and the height position of the upper end 62a of the lower bracket 62. Since the overlapping portion 47 is extended to the lower wall 474 of the side sill outer 15, the overlapping portion 47 acts in the same manner as the reinforcing member 20 during a side collision, and deformation of the side sill 5 is suppressed. In this case, by setting the height position of the joint 52 to the above-mentioned position, the range of the low strength portion 51 can be sufficiently secured. Therefore, it is possible to achieve both the absorption of impact by the low strength portion 51 in cooperation with the side sill 5 in the early stage of the side collision and the suppression of deformation of the center pillar 4 toward the cabin 10 side due to the high strength portion 53 receiving the impact load from the upper bracket 61 in the later stage of the side collision.

[0195] In addition, in the fourth modification, the height position of the joint 52 may be disposed at a position lower than the height position of the lower end 62b of the lower bracket 62. In addition, although the reinforcing member 20 is illustrated in Fig. 10 showing the fourth modification, the reinforcing member 20 may be omitted.

[0196] <Other Modifications> In the above-mentioned embodiment and modified example, the center pillar has been described as an example of the impact absorbing member of the present invention. However, this is not necessarily the case. A side sill may be adopted as the impact absorbing member of the present invention. In this case, for example, the side sill outer 15 has a low strength portion 51 near the overlapping portion 47, and a high strength portion 53 is disposed at the front fastening position or the rear fastening position side of the side sill 5. In this case, during a side collision, the impact absorbing effect is exerted near the overlapping portion 47 of the side sill 5, while the high strength portion at the front portion or the rear portion of the side sill 5 can more reliably prevent the side sill 5 from entering the cabin 10. The impact absorbing member of the present invention may be applied to other than the center pillar and the side sill. EXAMPLES

[0197] A model of the vehicle body 1 described in the embodiment (FIGS. 1 to 3) was created by a computer. The configurations of the vehicle body 1 model in the example and the comparative example are as follows. (Configuration of the embodiment) Vickers hardness HV of high strength part 53 of pillar outer 41 1 and plate thickness: 600HV, 1.2 mm. High strength portion 53 is made of the material described in modification 1, and includes high strength portion softened layer 55. Vickers hardness HV of low strength portion 51 of pillar outer 41 2 and plate thickness: 350HV, 1.4mm (Configuration of Comparative Example) Vickers hardness HV of high strength part 53 of pillar outer 41 1 and plate thickness: 1000 HV, 1.2 mm. High strength portion 53 does not include high strength portion softened layer 55 described in the first modified example. Vickers hardness HV of low strength portion 51 of pillar outer 41 2 and plate thickness: 150HV, 1.4mm (Common configuration between the examples and comparative examples) Vickers hardness and thickness of Pillar Inner 42: 350HV, 1.3mm Patch 43 Vickers hardness and thickness: 600HV, 1.2mm

[0198] The comparative example and the embodiment are different in the following respects. Maximum bending angle θ of high strength portion 53 in comparative example 1 and the maximum bending angle θ of the low strength portion 51 2 Difference Δθ: 105 degrees Maximum bending angle θ of the high strength portion 53 in the embodiment 1 and the maximum bending angle θ of the low strength portion 51 2 Difference Δθ: 20 degrees

[0199] For the comparative example and the example, the presence or absence of cracks in the pillar outer 41 when a side collision occurs to the vehicle body 1 was measured by computer simulation. The side collision conditions were set in accordance with the Insurance Institute for Highway Safety (IIHS). Specifically, the test conditions were set so that a collision load was applied to the center pillar under conditions assuming a full-car collision.

[0200] As a result, in the comparative example, cracks occurred in the front wall 412 and the rear wall 414 of the high strength portion 53 near the joint 52. On the other hand, no cracks occurred in the example. Thus, the example was thin and lightweight, and did not crack even during a side collision, and impact absorption performance was ensured by suppressing cracks. [Industrial Applicability]

[0201] The present invention can be widely applied as a shock absorbing member. [Explanation of symbols]

[0202] 1. Vehicle body 4 Center pillar (shock absorbing material) 5 Side sill 8 Doors 20 Reinforcement member 41 Pillar outer 42 Pillar inner 47 Overlap 51 Low strength section 52 Joint 53 High strength section 61 Bracket 61a Top end of upper bracket 62 Bracket 153 Outside wall Z Up / Down (Longitudinal) θ 1 Maximum bending angle of high strength section θ 2 Maximum bending angle of low strength part

Claims

1. An impact absorbing member provided on a vehicle body, formed along a predetermined longitudinal direction, and including a portion having a cross section perpendicular to the longitudinal direction that has a closed cross-sectional shape, A low strength portion; A high strength portion is arranged in the longitudinal direction of the low strength portion and has a central portion in the thickness direction having a Vickers hardness higher than a Vickers hardness of a central portion in the thickness direction of the low strength portion; a joining portion joining the low strength portion and the high strength portion; Equipped with The difference between the maximum bending angle of the low strength portion and the maximum bending angle of the high strength portion is 85 degrees or less, A shock absorbing component, wherein a ratio HV 1 / HV 2 of the Vickers hardness HV 1 of the central portion in the plate thickness direction of the high strength portion to the Vickers hardness HV 2 of the central portion in the plate thickness direction of the low strength portion is 1.3 or more.

2. The impact absorbing component according to claim 1 , wherein a difference between the maximum bending angle of the high strength portion and the maximum bending angle of the low strength portion is 75 degrees or less.

3. An impact absorbing member as described in claim 1, wherein the difference between the maximum bending angle of the high strength portion and the maximum bending angle of the low strength portion is 50 degrees or less.

4. 2. The impact absorbing component according to claim 1, wherein the Vickers hardness of the central portion in the plate thickness direction of the high strength portion is 500 HV or more.

5. The impact absorbing component according to claim 4 , wherein the Vickers hardness of the central portion in the plate thickness direction of the low strength portion is 150 HV or more.

6. The Vickers hardness HV １ and the Vickers hardness HV ２ Relative HV １ / HV ２ The impact absorbing member according to claim 1, wherein the elastic modulus is 1.5 or more.

7. The impact absorbing member according to claim 1, wherein a ratio HV 1 / HV 2 of the Vickers hardness HV 1 of the central portion in the plate thickness direction of the high strength portion to the Vickers hardness HV 2 of the central portion in the plate thickness direction of the low strength portion is 2.0 or more.

8. 2. The impact absorbing component according to claim 1, wherein a difference between the maximum bending angle of the low strength portion and the maximum bending angle of the high strength portion is 30 degrees or less.

9. the impact absorbing member is a center pillar that includes a pillar inner and a pillar outer and is disposed along the up-down direction of the vehicle body, The pillar outer includes the low strength portion, the joint portion, and the high strength portion, The impact absorbing member according to any one of claims 1 to 8, wherein the high strength portion is disposed above the low strength portion.

10. The center pillar is provided with a pair of upper and lower brackets for supporting a door installed behind the center pillar, The shock absorbing member according to claim 9 , wherein the joint portion is disposed at a position lower than a height position of a lower end of the upper bracket.

11. The shock absorbing member according to claim 10 , wherein the joint portion is disposed at a position higher than a height position of an upper end of the lower bracket.

12. The shock absorbing member according to claim 10 , wherein the joint portion is disposed at a position lower than a height position of a lower end of the lower bracket.

13. The vehicle body further includes a side sill joined to a lower portion of the center pillar, disposed along a front-rear direction of the vehicle body, and having a closed cross-sectional shape in a cross section perpendicular to the front-rear direction, The side sill includes an outer wall disposed on the outer side of the side sill in a width direction of the vehicle body, The lower part of the center pillar has an overlapping portion arranged to cover the side sill at a connection point with the side sill, The impact absorbing member according to claim 9 , wherein the overlapping portion is disposed below a half-height position of the outer wall of the side sill in the up-down direction.

14. 2. The impact absorbing component according to claim 1, wherein a Vickers hardness at a surface of the high strength portion in the plate thickness direction is at least 100 HV lower than a Vickers hardness at a central portion of the high strength portion in the plate thickness direction.

15. The high strength portion has a high strength portion softened layer provided from the surface in the plate thickness direction, The Vickers hardness of the central portion in the plate thickness direction in the portion where the high strength portion softened layer is provided in the high strength portion is 500 HV or more, The thickness of the high strength portion softened layer is 80 μm or more, and is 5% to 20% of the plate thickness at the portion where the high strength portion softened layer is provided, The Vickers hardness of the high strength portion softened layer on the surface is 0.5 times or more and less than 0.9 times the Vickers hardness of the central portion in the plate thickness direction in the portion where the high strength portion softened layer is provided, The high strength portion softened layer has, in the plate thickness direction, a first hardness change region that is a region from the surface to 40% of the thickness of the high strength portion softened layer, and a second hardness change region that is a region of the high strength portion softened layer that is not the first hardness change region, The impact absorbing component according to claim 14, wherein an absolute value ΔHV1 of the hardness change in the thickness direction in the first hardness change region is greater than an absolute value ΔHV2 of the hardness change in the thickness direction in the second hardness change region.

16. 2. The impact absorbing component according to claim 1, wherein a Vickers hardness at a surface in the plate thickness direction of the low strength portion is at least 100 HV lower than a Vickers hardness at a central portion in the plate thickness direction of the low strength portion.

17. The low strength portion has a low strength portion softened layer provided from the surface in the plate thickness direction, The Vickers hardness of the central portion in the plate thickness direction in the portion where the low strength portion softened layer is provided in the low strength portion is 150 HV or more, The thickness of the low-strength portion softened layer is 80 μm or more, and is 5% to 20% of the plate thickness at the portion where the low-strength portion softened layer is provided, The Vickers hardness of the low-strength portion softened layer on the surface is 0.5 times or more and less than 0.9 times the Vickers hardness of the central portion in the plate thickness direction in the portion where the low-strength portion softened layer is provided, The low-strength portion softened layer has, in the plate thickness direction, a first hardness change region that is a region from the surface to 40% of the thickness of the low-strength portion softened layer, and a second hardness change region that is a region of the low-strength portion softened layer that is not the first hardness change region, The impact absorbing member according to claim 16, wherein an absolute value ΔHV1′ of the hardness change in the thickness direction in the first hardness change region is greater than an absolute value ΔHV2′ of the hardness change in the thickness direction in the second hardness change region.

18. A center pillar and a side sill joined to a lower portion of the center pillar, A vehicle body, wherein at least one of the center pillar and the side sill is the impact absorbing member according to claim 1.

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