CN-116761691-B - Skeleton member

Abstract

The frame member is joined by spot welding the first steel plate member and the second steel plate member at spot welded portions. The skeleton member has a cross-sectional area having a closed cross-section perpendicular to a longitudinal direction of the skeleton member, the first steel plate member has a tensile strength of 1900MPa or more, and the spot-welded portion has a molten metal portion formed by the spot welding and a heat-affected portion adjacent to an outer side of the molten metal portion. The average vickers hardness Hv Ave at the measurement portion corresponding to the first region on the virtual straight line and the lowest vickers hardness Hv Min at the measurement portion corresponding to the third region on the virtual straight line satisfy Hv Ave -Hv Min +≤100.

Inventors

• KATO TAKASHI
• Xiang Tengxiaobo
• FUJINAKA SHINGO
• TODA YURI

Assignees

• 日本制铁株式会社

Dates

Publication Date

20260512

Application Date

20220414

Priority Date

20210422

Claims (3)

1. 1. A frame member is characterized in that the frame member is joined by spot welding a first steel plate member and a second steel plate member at spot welding portions, The skeleton member has a cross-sectional area in which a cross-section perpendicular to a longitudinal direction of the skeleton member is a closed cross-section, The first steel plate member has a tensile strength of 1900MPa or more, The spot-welded portion has a molten metal portion formed by the spot welding and a heat-affected portion adjacent to an outer side of the molten metal portion, In a cross section perpendicular to the longitudinal direction including a center point of the molten metal portion, a region corresponding to the molten metal portion is defined as a first region, a region corresponding to the heat-affected portion is defined as a second region, a region consisting of a region from a boundary between the first region and the second region to a distance of 100 μm toward the first region side and a region from the boundary to a distance of 100 μm toward the second region side is defined as a third region, When the vickers hardness is measured at 15 μm intervals along a virtual straight line extending from the central portion of the first region toward the second region side with a load of 10gf, the average vickers hardness Hv Ave at a measurement portion corresponding to the first region on the virtual straight line and the lowest vickers hardness Hv Min at a measurement portion corresponding to the third region on the virtual straight line satisfy Hv Ave -Hv Min +≤100 Hv.
2. 2. The frame member according to claim 1, wherein the frame member has a cross-sectional area in which a ratio h1/w of a height h1 of the first steel plate member along a plate thickness direction of a portion of the first steel plate member where the spot-welded portion is formed to a width w of the frame member along a direction perpendicular to the plate thickness direction of the portion of the first steel plate member where the spot-welded portion is formed in a cross-section perpendicular to a longitudinal direction of the frame member is 0.6 or less.
3. 3. The skeletal member according to claim 2, wherein a cross-sectional area of the ratio h1/w of 0.6 or less is present at 50% or more of the entire length of the skeletal member in the longitudinal direction.

Description

Skeleton member Technical Field The present invention relates to a skeleton member that can exhibit excellent energy absorption performance commensurate with an increase in strength by suppressing breakage derived from spot welded portions at the time of collision. The present application claims priority based on 22 nd month 2021 in japanese patent application No. 2021-072691, the contents of which are incorporated herein by reference. Background In the automotive industry, development of a vehicle body structure capable of reducing impact at the time of collision is advancing. For example, a structure is employed in which a plurality of steel plates are formed into a predetermined shape by press forming or the like, and then the steel plates are closed and sectioned by spot welding. In such a structure, it is important to ensure strength such that the spot welded portion is not easily broken even when the member is deformed by input at the time of collision, and the closed cross section of the member can be maintained. In general, the steel sheet is strengthened to thereby increase the absorption energy per unit mass of the skeleton member at the time of collision. Therefore, a steel sheet having high strength is often used as a means for reducing the weight of an automobile body. On the other hand, it is known that the strength of the spot welded portion is lowered due to the increase in the strength of the steel sheet. Therefore, when a high-strength steel sheet is used to form a closed cross section by spot welding, it is necessary to prevent the spot welding portion from breaking when a collision input is applied to the member. This is because if a fracture occurs due to the spot welded portion, the closed cross section cannot be maintained, and energy absorption performance commensurate with the increase in strength cannot be obtained. In view of such actual conditions, a framework member has been proposed for the purpose of obtaining energy absorption performance commensurate with the enhancement of strength. For example, patent document 1 discloses an automobile skeleton member including a first steel sheet, a second steel sheet, and a first weld metal portion, wherein the minimum vickers hardness of a region within 4mm around the first weld metal portion of the second steel sheet is 80% or more of the hardness of the outside of the region of the second steel sheet. Prior art literature Patent literature Patent document 1 International publication No. 2020/090916 Disclosure of Invention Problems to be solved by the invention According to the technique of patent document 1, it is considered that the improvement of the strength of the entire member including the welded portion and the improvement of the impact absorbing property can be achieved at the same time. However, the problem to be solved by patent document 1 is to suppress the decrease in hardness due to HAZ softening, but the cause of the decrease in joining strength when the steel sheet is made high-strength is not limited to the decrease in hardness due to HAZ softening, and even if the technique of patent document 1 is adopted, there is a possibility that the desired energy absorption performance cannot be exhibited due to breakage originating from the spot welded portion depending on the steel material used, and there is room for further improvement in energy absorption performance. The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a skeleton member that can exhibit excellent energy absorption performance commensurate with high strength by suppressing breakage at a spot-welded portion at the time of collision. Means for solving the problems In order to solve the above problems, the present invention adopts the following configuration. (1) A first aspect of the present invention is a skeleton member joined by spot welding a first steel sheet member and a second steel sheet member at spot welding portions, the skeleton member having a cross-sectional area in which a cross-section perpendicular to a longitudinal direction of the skeleton member is a closed cross-section, the first steel sheet member having a tensile strength of 1900MPa or more, the spot welding portions having a molten metal portion formed by the spot welding and a heat-affected portion adjacent to an outer side of the molten metal portion, wherein, in the cross-section perpendicular to the longitudinal direction including a center point of the molten metal portion, an area corresponding to the molten metal portion is defined as a first area, an area corresponding to the heat-affected portion is defined as a second area, A region consisting of a region from the boundary between the first region and the second region to a distance of 100 [ mu ] m toward the first region side and a region from the boundary to a distance of 100 [ mu ] m toward the second region side is defined as a third region, and