Abstract: In a steel sheet, a cleanliness of a metal structure is 0.08% or less, a which is an Mn segregation degree is 1.6 or less, and a difference ?Hv between a low strain formed portion that undergoes a plastic strain of 5% or less and a high strain formed portion that undergoes a plastic strain of 20% or higher in a hot forming in average hardness after the hot forming is 40 or less.

Abstract: A heat treated galvannealed steel material having excellent post-painting corrosion resistance and a high strength which is suitable for use as an automotive part and a method for its manufacture are provided. A galvannealed steel material having a galvannealed coating on at least one side thereof is heat treated by heating at least a portion thereof to a temperature range in which hardening is possible. The coating remaining on the surface of at least a part of the portion which underwent heat treatment has a coating weight of at least 20 g/m2 and at most 80 g/m2 per side and an Fe content of at least 15% and at most 35%, an ? phase is present in the coating, and the centerline average roughness Ra of the surface of the coating is at most 1.5 ?m.

Abstract: A steel material which is suitable for hot press working or hot three-dimensional bending and direct quench and which can be used to manufacture a high-strength formed article with sufficient quench hardening even by short time heating at a low temperature has a chemical composition comprising, in mass percent, C: 0.05-0.35%, Si: at most 0.5%, Mn: 0.5-2.5%, P: at most 0.03%, S: at most 0.01%, sol. Al: at most 0.1%, N: at most 0.01%, and optionally at least one element selected from the group consisting of B: 0.0001-0.005%, Ti: 0.01-0.1%, Cr: 0.18-0.5%, Nb: 0.03-0.1%, Ni: 0.18-1.0%, and Mo: 0.03-0.5% and has a steel structure in which the spheroidization ratio of carbides is 0.60-0.90.

Abstract: A side structure for an automobile body has an A-pillar having a first portion which has a closed cross section and which is connected to a side sill and extends upwards, and a second portion which has a closed cross section and which is continuous with the first portion and extends along a slope therefrom, and a roof rail side member which has a closed cross section and which is continuous with the A-pillar and is connected to a B-pillar. The side reinforcing member having a closed cross section and a shape which is bent three-dimensionally and which is constituted by a single member in the axial direction and has undergone high frequency quenching is disposed so a to extend at least inside the second portion and inside the roof rail side member to be positioned to the rear of the connection with the B-pillar.

Abstract: A high-strength cold-rolled steel sheet providing a product with a good surface condition after press forming, having excellent bake hardenability and anti room temperature aging property, and having a dual phase structure with a tensile strength of at least 340 MPa is provided. A high-strength cold-rolled steel sheet has a structure comprising a main phase which is a ferrite and a secondary phase which is a low temperature transformation product including a martensite and has a hardness distribution of the ferrite phase in an arbitrary cross section having a length of 10 mm in the widthwise 10 direction of the sheet which satisfies the relationship prescribed by (HV(max)?HV(ave))<0.5×(Hv(ave). HV(max) is the maximum Vickers hardness of ferrite grains in a region at a distance of from (?)t to (¼)t in the thickness direction from the surface when the thickness of the high-strength cold-rolled steel sheet is t, and Hv(ave) is the average Vickers hardness of ferrite grains in this region.

Abstract: A side structure for an automobile body has an A-pillar having a first portion which has a closed cross section and which is connected to a side sill and extends upwards, and a second portion which has a closed cross section and which is continuous with the first portion and extends along a slope therefrom, and a roof rail side member which has a closed cross section and which is continuous with the A-pillar and is connected to a B-pillar. The side reinforcing member having a closed cross section and a shape which is bent three-dimensionally and which is constituted by a single member in the axial direction and has undergone high frequency quenching is disposed so a to extend at least inside the second portion and inside the roof rail side member to be positioned to the rear of the connection with the B-pillar.

Abstract: A bent metal member has a body formed from a tubular metal material and has a shape which is bent two-dimensionally or three-dimensionally. The surface of the body has a Zn-based coating which contains an ? phase and which satisfies the following condition: coating weight: at most 90 g/m2 per side, Fe content: 8-35 mass %, and a surface roughness Ra prescribed by WS B 0601: at most 2.0 ?m. The bent metal member can have a closed cross section, an open cross section, or a shaped cross section.

Abstract: A steel material which is suitable for hot press working or hot three-dimensional bending and direct quench and which can be used to manufacture a high-strength formed article with sufficient quench hardening even by short time heating at a low temperature has a chemical composition comprising, in mass percent, C: 0.05-0.35%, Si: at most 0.5%, Mn: 0.5-2.5%, P: at most 0.03%, S: at most 0.01%, sol. Al: at most 0.1%, N: at most 0.01%, and optionally at least one element selected from the group consisting of B: 0.0001-0.005%, Ti: 0.01-0.1%, Cr: 0.18-0.5%, Nb: 0.03-0.1%, Ni: 0.18-1.0%, and Mo: 0.03-0.5% and has a steel structure in which the spheroidization ratio of carbides is 0.60-0.90.

Abstract: A method of manufacturing a bent metal member comprises supporting the outer surface of a tubular metal material having a Zn-Fe alloy coating layer at two locations spaced in the axial direction of the metal material. The metal material is fed in its axial direction and heated at a position between the two locations to a temperature range of at least the Ac3 point at a heating speed such that the rate of temperature increase is at least 3.0×102° C. per second, held so that the time for which the surface of the metal material is at a temperature of 8.0×102° C. or higher is at most 2 seconds, and then rapid cooled. A bending moment is imparted to the healed portion in two or three dimensions to manufacture a bent metal member having on its surface a Zn-based layer which contains an ?, phase.

Abstract: A front side member having a single body formed from a tubular body having a closed cross section has a front portion which extends in the fore and aft direction of a vehicle body, a sloping portion which is continuous with the front portion and slopes downwards along a dash panel, and a rear portion continuous with the sloping portion and extending along the bottom surface of a floor panel joined to the dash panel. A portion of the front portion is an unquenched portion which has not undergone quenching treatment and the remainder is a high frequency quenched portion which has undergone high frequency quenching. The sloping portion is a high frequency quenched portion. A portion of the rear portion is an unquenched portion which has not undergone quenching and the remainder other than that portion is a high frequency quenched portion which has undergone high frequency quenching.

Abstract: A front side member having a single body formed from a tubular body having a closed cross section has a front portion which extends in the fore and aft direction of a vehicle body, a sloping portion which is continuous with the front portion and slopes downwards along a dash panel, and a rear portion continuous with the sloping portion and extending along the bottom surface of a floor panel joined to the dash panel. A portion of the front portion is an unquenched portion which has not undergone quenching treatment and the remainder is a high frequency quenched portion which has undergone high frequency quenching. The sloping portion is a high frequency quenched portion. A portion of the rear portion is an unquenched portion which has not undergone quenching and the remainder other than that portion is a high frequency quenched portion which has undergone high frequency quenching.

Abstract: A strength member for an automobile body such as a side member or a pillar which has a bent portion which is bent two-dimensionally or three-dimensionally and which has an ultrahigh strength with a tensile strength exceeding 1100 MPa is provided. The strength member for an automobile body has a tubular body which has a closed cross section which does not have an outwardly-extending flange and which has a bent portion which is bent two-dimensionally or three-dimensionally, a portion to be cut or punched, and a portion to be welded.

Abstract: A bent metal member which is obtained by bending accompanied by heat treatment of a zinc-based coated metal material and which is suitable for use in components of automobiles due to having a high strength and excellent post-painting corrosion resistance is manufactured. The outer surface of a tubular metal material having on its surface a Zn—Fe alloy coating layer with a coating weight of 30-90 g/m2 per side, an Fe content of 8-20%, and a surface roughness Ra of at most 0.8 ?m is supported at two locations spaced in the axial direction of the metal material so that the material can move in its axial direction, the metal material is heated between the two locations to a temperature range of at least the Ac3 point at a heating speed such that the rate of temperature increase is at least 3.0×102° C. per second while feeding the metal material in its axial direction, holding so that the length of time for which the surface of the metal material is at 8.0×102° C.

Abstract: A high-strength cold-rolled steel sheet providing a product with a good surface condition after press forming, having excellent bake hardenability and anti room temperature aging property, and having a dual phase structure with a tensile strength of at least 340 MPa is provided. A high-strength cold-rolled steel sheet has a structure comprising a main phase which is a ferrite and a secondary phase which is a low temperature transformation product including a martensite and has a hardness distribution of the ferrite phase in an arbitrary cross section having a length of 10 mm in the widthwise direction of the sheet which satisfies the relationship prescribed by (Hv(max)?Hv(ave))<0.5×(Hv(ave). Hv(max) is the maximum Vickers hardness of ferrite grains in a region at a distance of from (?)t to (¼)t in the thickness direction from the surface when the thickness of the high-strength cold-rolled steel sheet is t, and Hv(ave) is the average Vickers hardness of ferrite grains in this region.

Abstract: A heat treated galvannealed steel material having excellent post-painting corrosion resistance and a high strength which is suitable for use as an automotive part and a method for its manufacture are provided. A galvannealed steel material having a galvannealed coating on at least one side thereof is heat treated by heating at least a portion thereof to a temperature range in which hardening is possible. The coating remaining on the surface of at least a part of the portion which underwent heat treatment has a coating weight of at least 20 g/m2 and at most 80 g/m2 per side and an Fe content of at least 15% and at most 35%, an ? phase is present in the coating, and the centerline average roughness Ra of the surface of the coating is at most 1.5 ?m.

Abstract: A strength member for an automobile body such as a side member or a pillar which has a bent portion which is bent two-dimensionally or three-dimensionally and which has an ultrahigh strength with a tensile strength exceeding 1100 MPa is provided. The strength member for an automobile body has a tubular body which has a closed cross section which does not have an outwardly-extending flange and which has a bent portion which is bent two-dimensionally or three-dimensionally, a portion to be cut or punched, and a portion to be welded.

Abstract: Hot press forming of a steel material is made possible by coating the surface of the steel material with a plated layer of zinc or a zinc alloy and forming thereon a barrier layer which prevents the vaporization of zinc even when heated to 700-1000° C. Corrosion resistance can also be guaranteed without requiring post treatment, and hot press forming of high tensile steel sheet and stainless steel sheet is made possible. The barrier layer is formed by forming an upper plated layer, by surface oxidation, by contact with an oxidizing agent, by contact with Zn and an oxidizing agent, by anodic electrolysis, by cathodic electrolysis, or by coating with a ZnO sol.

Abstract: A high-strength cold-rolled steel sheet providing a product with a good surface condition after press forming, having excellent bake hardenability and anti room temperature aging property, and having a dual phase structure with a tensile strength of at least 340 MPa is provided. A high-strength cold-rolled steel sheet has a structure comprising a main phase which is a ferrite and a secondary phase which is a low temperature transformation product including a martensite and has a hardness distribution of the ferrite phase in an arbitrary cross section having a length of 10 mm in the widthwise direction of the sheet which satisfies the relationship prescribed by (Hv(max)?Hv(ave))<0.5×(Hv(ave). Hv(max) is the maximum Vickers hardness of ferrite grains in a region at a distance of from (?)t to (¼)t in the thickness direction from the surface when the thickness of the high-strength cold-rolled steel sheet is t, and Hv(ave) is the average Vickers hardness of ferrite grains in this region.

Abstract: Hot press forming of a steel material is made possible by coating the surface of the steel material with a plated layer of zinc or a zinc alloy and forming thereon a barrier layer which prevents the vaporization of zinc even when heated to 700-1000° C. Corrosion resistance can also be guaranteed without requiring post treatment, and hot press forming of high tensile steel sheet and stainless steel sheet is made possible. The barrier layer is formed by forming an upper plated layer, by surface oxidation, by contact with an oxidizing agent, by contact with Zn and an oxidizing agent, by anodic electrolysis, by cathodic electrolysis, or by coating with a ZnO sol.

Abstract: Hot press forming of a steel material is made possible by coating the surface of the steel material with a plated layer of zinc or a zinc alloy and forming thereon a barrier layer which prevents the vaporization of zinc even when heated to 700-1000° C. Corrosion resistance can also be guaranteed without requiring post treatment, and hot press forming of high tensile steel sheet and stainless steel sheet is made possible. The barrier layer is formed by forming an upper plated layer, by surface oxidation, by contact with an oxidizing agent, by contact with Zn and an oxidizing agent, by anodic electrolysis, by cathodic electrolysis, or by coating with a ZnO sol.