Nippon Steel Corporation

Nippon Steel Sumitomo Metal Corporation

Sumitomo Metal Industries, Inc.

Nobusato Kojima

Masaru Takahashi

Masahiro Nakata

Atsushi Tomizawa

Naoaki Shimada

Kazuo Hikida

Shinichiro Tabata

Mitsuru Yoshida

Masaharu Oka

Michitaka Yoshida

Tamotsu Toki

Kazuhito Imai

Kazuya Ishii

Toyomitsu Nakamura

Riki Okamoto

Hiroshi Takebayashi

Jun Haga

Yutaka Mikazuki

Yuuki Kanzawa

Eiji Isogai

Tetsuya Okada

Naomitsu Mizui

Yukihiro Yoshikawa

Yuta Dairokuno

Toshinobu Nishibata

Michihiro Nono

Akari Tamaki

Kohhei Kamiya

Takahiro Moriki

Kazuo Hikita

This steel sheet has a predetermined chemical composition and the steel sheet in which, at a ¼ depth position of a sheet thickness from a surface, an average grain size is 15.0 μm or less, a total grain boundary number density of solute C and solute B is 1.0 solute/nmor more and 12.0 solutes/nmor less, a total of pole densities of {211}<011> and {332}<113> in a thickness middle portion is 12.0 or less, and a tensile strength is 780 MPa or more is adopted.

Steel sheet, method for manufacturing same and plated steel sheet

A hot-rolled steel sheet has a predetermined chemical composition in which a microstructure includes 99% or more of martensite by volume fraction and a remainder in microstructure including residual austenite and ferrite, in a cross section parallel to a rolling direction, an average aspect ratio of prior austenite grains is less than 3.0, a proportion of sulfides having an aspect ratio of more than 3.0 among sulfides having an area of 1.0 μmor more is 1.0% or, less, in a thickness middle portion, and a pole density of {211}<011> orientation is 3.0 or less, and a tensile strength TS is 980 MPa or higher.

Hot rolled steel sheet and production method thereof

A hot-rolled steel sheet according to an aspect of the present invention has a predetermined chemical composition, in which, in a location at a depth of &#xbc; of a sheet thickness from a surface, an area ratio of ferrite is 10% to 55%, a total area ratio of bainite and martensite is 45% to 90%, a total area ratio of the ferrite, the bainite, and the martensite is 90% or more, an average crystal grain size is 12.0 &#x3bc;m or less, in a texture measured in a sheet thickness central portion, a maximum pole density of orientation groups of {100} &#x3c;011&#x3e;, {211} &#x3c;011&#x3e;, {311} &#x3c;011&#x3e;, {110} &#x3c;011&#x3e;, and {332} &#x3c;113&#x3e; is 8.0 or less, a total of pole densities of {211} &#x3c;011&#x3e; and {332} &#x3c;113&#x3e; is 10.0 or less, and a tensile strength is 950 MPa or more.

Hot-rolled steel sheet and method for manufacturing same

A steel sheet for a drawn can has a predetermined chemical composition and has a ferrite single-phase structure with a crystal grain size number of 11.0 or more, the sheet thickness is 0.15 to 0.50 mm, in an L direction of the steel sheet after an ageing treatment at 100&#xb0; C. for one hour, an yield strength YP is 220 to 290 MPa, a tensile strength TS is 330 to 390 MPa, a total elongation EL is 32% or more, an yield point elongation YP-EL is 0%, an average plastic strain ratio ris more than 1.35, and an in-plane anisotropy &#x394;r is &#x2212;0.30 to +0.15.

Cold rolled steel sheet for drawn can and method for manufacturing same

Provided is a galvannealed steel sheet having high strength and excellent deep drawability, and being further excellent in slab cracking resistance and secondary working embrittlement resistance. A base metal steel sheet of the galvannealed steel sheet has a chemical composition containing, in mass %: C: 0.0080% or less; Si: 0.7% or less; Mn: 1.0 to 2.5%; P: more than 0.030 to 0.048%; S: 0.025% or less; Al: 0.005 to 0.20%; N: 0.010% or less; Ti: 0.005 to 0.040%; Nb: 0.005 to 0.060%; and B: 0.0005 to 0.0030%, with the balance being Fe and impurities, satisfying Formula (1) to (4). A galvannealed layer contains 7 to 15 mass % of Fe.25&#xd7;P+4&#xd7;Si&#x2264;3.6&#x2003;&#x2003;(1)B&#x2212;X1&#x2265;0.0005&#x2003;&#x2003;(2)C&#x2212;(12/93)&#xd7;Nb&#x2212;X2&#x2265;&#x2212;0.0035&#x2003;&#x2003;(3)110&#xd7;Si+48&#xd7;Mn+550&#xd7;P&#x2265;120&#x2003;&#x2003;(4)

Galvannealed steel sheet and production method thereof

A heat-treated steel material is provided having strength of 2.000 GPa or more. The heat-treated steel material includes a chemical composition represented by, in mass %: C: 0.05% to 0.30%; Si: 0.50% to 5.00%; Mn: 2.0% to 10.0%; Cr: 0.01% to 1.00%; Ti: 0.010% to 0.100%; B: 0.0020% to 0.0100%; P: 0.050% or less; S: 0.0500% or less; N: 0.0100% or less; Ni: 0% to 2.0%; each of Cu, Mo, and V: 0% to 1.0%; each of Al and Nb: 0% to 1.00%; and the balance: Fe and impurities. '4612&#xd7;[C]+51&#xd7;[Si]+102&#xd7;[Mn]+605&#x3e;2000' is satisfied. The heat-treated steel material includes a microstructure in which 90 volume % or more is formed of martensite, and a dislocation density in the martensite is equal to or more than 1.2&#xd7;10m.

Heat-treated steel material and method of manufacturing the same

A heat-treated steel material is provided having strength of 1.800 GPa or more. The heat-treated steel material includes a chemical composition represented by, in mass %: C: 0.05% to 0.30%; Mn: 2.0% to 10.0%; Cr: 0.01% to 1.00%; Ti: 0.010% to 0.100%; B: 0.0010% to 0.0100%; Si: 0.08% or less; P: 0.050% or less; S: 0.0500% or less; N: 0.0100% or less; Ni: 0% to 2.0%; each of Cu, Mo, and V: 0% to 1.0%; each of Al and Nb: 0% to 1.00%; and the balance: Fe and impurities. '4612&#xd7;[C]+102&#xd7;[Mn]+605&#x2265;1800' is satisfied where [C] denotes a C content and [Mn] denotes a Mn content. The heat-treated steel material includes a microstructure in which 90 volume % or more is formed of martensite, and a dislocation density in the martensite is equal to or more than 9.0&#xd7;10m.

The present invention provides a method of manufacturing a press-formed product. The method includes: a first process of preparing a material that is long in a first direction, and when viewed in a cross-section perpendicular to the first direction, the cross-section is a hollow cross-section that is long in a second direction perpendicular to the first direction; and a second process of bending the material in a direction intersecting the second direction when viewed from the first direction, by pressing the material along the second direction.

Method of manufacturing press-formed product, and press-formed product

A heat-treated steel material includes: a chemical composition expressed by, in mass %: C: 0.16% to 0.38%; Mn: 0.6% to 1.5%; Cr: 0.4% to 2.0%; Ti: 0.01% to 0.10%; B: 0.001% to 0.010%; Si: 0.20% or less; P: 0.05% or less; S: 0.05% or less; N: 0.01% or less; Ni: 0% to 2.0%; Cu: 0% to 1.0%; Mo: 0% to 1.0%; V: 0% to 1.0%; Al: 0% to 1.0%; Nb: 0% to 1.0%; REM: 0% to 0.1%; and the balance: Fe and impurities; and a structure expressed by: retained austenite: 1.5 volume % or less; and the balance: martensite.

A high-strength hot-formed steel sheet member exhibiting both a consistent hardness and delayed-fracture resistance, and is characterized in that: the high-strength hot-formed steel sheet member has a prescribed chemical composition; the degree of Mn segregation &#x3b1; (=[maximum Mn concentration (mass %) at the sheet center in the thickness direction]/[average Mn concentration (mass %) at a depth of &#xbc; of the total thickness of the sheet from the surface]) is less than or equal to 1.6; the steel purity value as defined in JIS G 0555 (2003) is less than or equal to 0.08%; the average grain size for prior &#x3b3; grains is less than or equal to 10 &#x3bc;m; and the number density of the residual carbides is less than or equal to 4&#xd7;10particles/mm.

High-strength hot-formed steel sheet member

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/mand at most 80 g/mper side and an Fe content of at least 15% and at most 35%, an &#x3b7; phase is present in the coating, and the centerline average roughness Ra of the surface of the coating is at most 1.5 &#x3bc;m.

Heat treated galvannealed steel material and a method for its manufacture

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.

Heat-treated steel material, method for producing same, and base steel material for same

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.

Strength member for an automobile body, front side member, and side structure for an automobile body

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&#x2212;HV)&#x3c;0.5&#xd7;(Hv. HVis the maximum Vickers hardness of ferrite grains in a region at a distance of from (&#x215b;)t to (&#xbc;)t in the thickness direction from the surface when the thickness of the high-strength cold-rolled steel sheet is t, and Hvis the average Vickers hardness of ferrite grains in this region.

High-strength cold-rolled steel sheet and high-strength plated steel sheet

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 Acpoint at a heating speed such that the rate of temperature increase is at least 3.0&#xd7;10&#xb0; C. per second, held so that the time for which the surface of the metal material is at a temperature of 8.0&#xd7;10&#xb0; 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 &#x3b7;, phase.

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Tokyo, Japan

Nobusato Kojima