Abstract: A steel sheet including a chemical composition satisfying an equivalent carbon content of 0.60% or more and less than 0.85%, and a steel microstructure with an area fraction of ferrite: less than 40%, tempered martensite and bainite: 40% or more in total, retained austenite: 3% to 15%, and ferrite, tempered martensite, bainite, and retained austenite: 93% or more in total. A 90-degree bending at a curvature radius/thickness ratio of 4.2 in a rolling (L) direction with respect to an axis extending in a width (C) direction causes a change of 0.40 or more in (a grain size in a thickness direction)/(a grain size in a direction perpendicular to the thickness) of the tempered martensite in an L cross section in a 0- to 50-?m region from a surface of the steel sheet on a compression side. The steel sheet has a tensile strength of 980 MPa or more.

Abstract: A galvanized steel sheet including a steel sheet having a chemical composition with an equivalent carbon content Ceq of 0.60% or more and less than 0.85%, and a specified steel microstructure; and a galvanized layer on a surface of the steel sheet. The retained austenite has a solute C content of 0.6% or more by mass, and retained austenite grains with an aspect ratio of less than 2.0 constitute 50% or more of all retained austenite grains. In 90-degree bending at a curvature radius/thickness ratio of 4.2 in a rolling (L) direction with respect to an axis extending in a width (C) direction, an L cross section in a 0- to 50-µm region from a surface of the steel sheet on a compression side has a number density of voids of 1500 /mm2 or less, and the galvanized steel sheet has a tensile strength of 980 MPa or more.

Abstract: A galvanized steel sheet includes: a steel sheet having a chemical composition satisfying an equivalent carbon content Ceq of 0.35% or more and less than 0.60%, and a specified steel microstructure; and a galvanized layer on a surface of the steel sheet. The retained austenite has a solute C content of 0.6% or more by mass, and retained austenite grains with an aspect ratio of less than 2.0 constitute 50% or more of all retained austenite grains. In 90-degree bending at a curvature radius/thickness ratio of 4.2 in a rolling (L) direction with respect to an axis extending in a width (C) direction, an L cross section in a 0 to 50 ?m region from a surface of the steel sheet on a compression side has a number density of voids of 1000/mm2 or less, and the galvanized steel sheet has a tensile strength of 590 MPa or more.

Abstract: A steel sheet including a chemical composition satisfying an equivalent carbon content of 0.60% or more and less than 0.85%, and a steel microstructure with an area fraction of ferrite: less than 40%, tempered martensite and bainite: 40% or more in total, retained austenite: 3% to 15%, and ferrite, tempered martensite, bainite, and retained austenite: 93% or more in total. A 90-degree bending at a curvature radius/thickness ratio of 4.2 in a rolling (L) direction with respect to an axis extending in a width (C) direction causes a change of 0.40 or more in (a grain size in a thickness direction)/(a grain size in a direction perpendicular to the thickness) of the tempered martensite in an L cross section in a 0- to 50-?m region from a surface of the steel sheet on a compression side. The steel sheet has a tensile strength of 980 MPa or more.

Abstract: The high-strength hot-dip galvanized steel sheet, which includes a hot-dip galvanized coating layer on a surface of the steel sheet, has a component composition containing, in mass %, C: 0.07% to 0.20%, Si: 0.1% to 2.0%, Mn: 2.0% to 3.5%, P: 0.05% or less, S: 0.05% or less, and sol. Al: 0.005% to 0.1%, with the balance being Fe and incidental impurities; and has a steel microstructure containing, in area fraction, 60% or less of ferrite, 40% or more of tempered martensite, and 10% or less of fresh martensite and having a void number density of 1,500/mm2 or less in a bent portion in the VDA bending test.

Abstract: A strain state of a bending outside surface of a test specimen is photographed by use of a camera without falling out of focus during a bending test. A bending test facility for a metal sheet material for an automobile body includes a supporting member that supports two supported portions of a flat test specimen formed of the metal sheet material for an automobile body, a punch for performing a bending test in which an area between the two supported portions of the test specimen is pressed from an opposite side to the supporting member so that the test specimen is bent to be deformed, and a camera for photographing, from the side of the supporting member, a bending outside surface of the test specimen during the bending test using the punch, with relative positions of the punch and the camera during the bending test being fixed.

Abstract: An object of the present invention is to provide a collision performance evaluation test method and apparatus that achieve a part collision test that satisfactorily reproduces the state of an actual automobile body collision, allow the test to be performed in a high-speed region, and increase the economic rationality of the test. A motion control mechanism formed of a translation control mechanism or a rotation control mechanism is provided in at least one of a support jig that supports one end portion of an automobile body part and a support jig that supports the other end portion of the automobile body part. The motion control mechanism includes a fixed member fixed to a motion restriction member in the support jig and a movable member so connected to the fixed member as to be movable and fixed to the one end portion or the other end portion of the automobile body part.

Abstract: A translation control and rotation control mechanism support jig for supporting a front end portion of an automobile body part includes a pair of support members, a rotary box having an L-shaped plate, a rotary shaft pin, a compression pin, and a connection plate. The translation control mechanism includes a support plate, a slide guide, an automobile body part securing disk, a translation plate, and a compression pin. Energy-absorbing members are disposed in an arcuate guide groove on a side surface of the rotary box and a linear guide groove arranged on the support plate or the translation plate. A collision punch collides at a test speed with the L-shaped plate of the rotary box. The compression pin deforms the energy-absorbing members to apply torque opposite to a rotation direction and a reaction force in an opposite direction to a translation direction.

Abstract: A collision resistance performance of a structural member is effectively improved while suppressing an unnecessary increase in mass of the structural member. The structural member includes a hollow member and a tension member. The hollow member forms a closed cross-sectional shape by a top sheet portion, a pair of sidewall portions each continuous to each side of the top sheet portion in a width direction, and a bottom sheet portion arranged to face the top sheet portion. The tension member is formed by a metal sheet extending along the width direction of the top sheet portion and being thinner than the sheet thickness of the hollow member, and connects inner surfaces of the pair of sidewall portions facing each other to each other to restrain the distance between the pair of sidewall portions from increasing.

Abstract: The high-strength hot-dip galvanized steel sheet, which includes a hot-dip galvanized coating layer on a surface of the steel sheet, has a component composition containing, in mass %, C: 0.07% to 0.20%, Si: 0.1% to 2.0%, Mn: 2.0% to 3.5%, P: 0.05% or less, S: 0.05% or less, and sol. Al: 0.005% to 0.1%, with the balance being Fe and incidental impurities; and has a steel microstructure containing, in area fraction, 60% or less of ferrite, 40% or more of tempered martensite, and 10% or less of fresh martensite and having a void number density of 1,500/mm2 or less in a bent portion in the VDA bending test.

Abstract: An object of the present invention is to provide a collision performance evaluation test method and apparatus that achieve a part collision test that satisfactorily reproduces the state of an actual automobile body collision, allow the test to be performed in a high-speed region, and increase the economic rationality of the test. A motion control mechanism formed of a translation control mechanism or a rotation control mechanism is provided in at least one of a support jig that supports one end portion of an automobile body part and a support jig that supports the other end portion of the automobile body part. The motion control mechanism includes a fixed member fixed to a motion restriction member in the support jig and a movable member so connected to the fixed member as to be movable and fixed to the one end portion or the other end portion of the automobile body part.

Abstract: A collision performance evaluation test with few variations in test results with high accuracy in which a complicated phenomenon that actually occurs can be reproduced in a simple manner by considering the history of deformation in both the press forming and a collision. A collision performance evaluation test method for a metal sheet material for an automobile body is characterized in that a press working apparatus first forms a flat test specimen made of a metal sheet material to be tested into a V shape by primary bending, a bending test apparatus then deforms, by secondary bending, the test specimen formed by the primary bending in a direction intersecting with the primary bending direction, and a bending load and a bending stroke for the test specimen during the secondary bending deformation are recorded and evaluated.