Nippon Steel Corporation

Nippon Steel & Sumitomo Metal Corporation

Sumitomo Metal Industries, Inc.

Toyomitsu Nakamura

Naoki Maruyama

Masahiro Nakata

Hiroyuki Kawata

Satoshi Uchida

Yuji Yamaguchi

Kohei Ueda

Takeshi Yasui

Ryosuke Komami

Hayato Arai

Kengo Takeda

Jun Maki

Atsushi Tomizawa

Naoaki Shimada

Soshi Fujita

Nobusato Kojima

Kunio Hayashi

Akihiro Uenishi

Takuya Mitsunobu

Hiroshi Takebayashi

Kazuya Ishii

Tamotsu Toki

Kazuhito Imai

Yasunobu Miyazaki

Yuya Suzuki

Seiji Furusako

Kenichiro Matsumura

Chisato Yoshinaga

Masahiro Matsuba

Masaaki Uranaka

Yasuhiro Nakashima

To more reliably suppress LME and blowhole formation while maintaining excellent corrosion resistance. A plated steel sheet according to the present invention, includes: a steel sheet as a base material; a plating layer located on at least part of a surface of the steel sheet; and an oxide layer located on a surface of the plating layer, where a chemical composition of the plating layer is made up of prescribed components, and Zn and impurities as the balance, and when a position at a depth of 5 nm from an uppermost surface of the oxide layer is observed by X-ray photoelectron spectroscopy (XPS), a value of an intensity ratio ([Al—O]+[Mg—O])/[Zn—O]) calculated from intensity of peaks respectively attributed to an Al—O bond, an Mg—O bond, and a Zn—O bond is 5.0 or more.

Plated steel sheet

An Al plated electric resistance welded steel pipe for hardening use suppressing the formation of scale to the inside of the plating layer while performing hot forming and an Al plated hollow member using that Al plated electric resistance welded steel pipe, wherein the Al plated electric resistance welded steel pipe for hardening use is comprised of a base material made of a tubular steel plate and having a predetermined chemical composition and an electric resistance welded zone provided at a seam portion of the steel plate and extending in a longitudinal direction of the steel plate, the base material is further provided with an intermetallic compound layer positioned on the surface of the steel plate and including an Al—Fe—Si-based intermetallic compound and an Al plating layer positioned on the surface of the intermetallic compound layer and containing Al and Si, and 70×X/D≤Y/t≤30 is satisfied, wherein X (μm) is a thickness of the intermetallic compound layer, Y (μm) is a thickness of the Al plating layer, t (mm) is a pipe thickness of the steel pipe, and D (mm) is an outside diameter of the steel pipe.

Al plated welded pipe for hardening use and al plated hollow member and method for producing same

Provided is a steel sheet having a predetermined chemical composition and structure wherein (Fe, Mn)B precipitates having a circle equivalent diameter of 50 to 300 nm are present in a number density of 1/500 μmor more in a surface layer region down to a depth of 100 μm from the surface in the sheet thickness direction. Further, provided is a method for producing a steel sheet comprising continuously casting a molten steel having a predetermined chemical composition to form a steel slab, wherein the continuously casting includes introducing more than 10 ppm and less than 100 ppm of oxygen into the surface layer of the steel slab, hot rolling including finish rolling the steel slab, wherein a completion temperature of the finish rolling is 650 to 950° C., coiling the obtained hot rolled steel sheet at a coiling temperature of 400 to 700° C., and cold rolling the hot rolled steel sheet, then annealing it.

Steel sheet and method for producing same

An Al plated electric resistance welded steel pipe for hardening use suppressing the formation of scale to the inside of the plating layer while performing hot forming and an Al plated hollow member using that Al plated electric resistance welded steel pipe, wherein the Al plated electric resistance welded steel pipe for hardening use is comprised of a base material made of a tubular steel plate and having a predetermined chemical composition and an electric resistance welded zone provided at a seam portion of the steel plate and extending in a longitudinal direction of the steel plate, the base material is further provided with an intermetallic compound layer positioned on the surface of the steel plate and including an Al&#x2014;Fe&#x2014;Si-based intermetallic compound and an Al plating layer positioned on the surface of the intermetallic compound layer and containing Al and Si, and 70&#xd7;X/D&#x2264;Y/t&#x2264;30 is satisfied, wherein X (&#x3bc;m) is a thickness of the intermetallic compound layer, Y (&#x3bc;m) is a thickness of the Al plating layer, t (mm) is a pipe thickness of the steel pipe, and D (mm) is an outside diameter of the steel pipe.

Al plated welded pipe for hardening use and Al plated hollow member and method for producing same

A manufacturing method of a steel sheet includes: a step of performing continuous casting of molten steel having a Si content of 0.4 mass % to 3.0 mass % to obtain a slab; a step of performing hot rolling of the slab to obtain a hot-rolled steel sheet; a step of performing cold rolling of the hot-rolled steel sheet to obtain a cold-rolled steel sheet; a step of performing cold-rolled sheet annealing of the cold-rolled steel sheet; a step of performing pickling after the cold-rolled sheet annealing; a step of performing water washing after the pickling; and a step of performing drying after the water washing. A dew point is set to &#x2212;35&#xb0; C. or lower in the cold-rolled sheet annealing, an electrical conductivity of a rinse water to be used in the water washing is set to 5.0 mS/m or less, a water-washing time is set to 15 seconds or less in the water washing, and the drying is started within 60 seconds from an end of the water washing.

Manufacturing method of steel sheet

A steel sheet having a chemical composition of the base metal including, in mass %, C: 0.17 to 0.40%, Si: 0.10 to 2.50%, Mn: 1.00 to 10.00%, P: 0.001 to 0.03%, S: 0.0001 to 0.02%, Al: 0.001 to 2.50%, N: 0.0001 to 0.010%, O: 0.0001 to 0.010%, Ti: 0 to 0.10%, Nb: 0 to 0.10%, V: 0 to 0.10%, B: 0 to 0.010%, Cr: 0 to 2.00%, Ni: 0 to 2.00%, Cu: 0 to 2.00%, Mo: 0 to 2.00%, Ca: 0 to 0.50%, Mg: 0 to 0.50%, REM: 0 to 0.50%, the balance: Fe and impurities, wherein the steel sheet has an internal oxidized layer in which at least one part of a crystal grain boundary is covered by oxides, and in which a grain boundary coverage ratio of oxides is 60% or more in a region from the surface of the base metal to a depth of 5.0 &#x3bc;m.

Steel sheet, hot-dip galvanized steel sheet and galvannealed steel sheet

A hot-dip galvanized steel sheet includes a base steel sheet and a hot-dip galvanized layer formed on at least one surface of the base steel sheet, in which the hot-dip galvanized layer includes Fe in a content of more than 0% to 5% or less, Al in a content of more than 0% to 1.0% or less, and columnar grains formed by a &#x3b6; phase on the surface of the steel sheet, further, 20% or more of the entire interface between the hot-dip galvanized layer and the base steel sheet is coated with the &#x3b6; phase, and a ratio of an interface formed between &#x3b6; grains in which coarse oxides are present among grains and the base steel sheet with respect to the entire interface between the &#x3b6; phase and the base steel sheet in the hot-dip galvanized layer is 50% or less, the base steel sheet has predetermined chemical components and a refined layer in direct contact with the interface between the base steel sheet and the hot-dip galvanized layer, an average thickness of the refined layer is 0.1 to 5.0 &#x3bc;m, an average grain size of ferrite in the refined layer is 0.1 to 3.0 &#x3bc;m, one or two or more of oxides of Si and Mn are contained in the refined layer, and a maximum size of the oxide is 0.01 to 0.4 &#x3bc;m, and a volume fraction of residual austenite in a range of &#x215b; thickness to &#x215c; thickness centered at a position of &#xbc; thickness from the surface of the base steel sheet is 1% or more.

Hot-dip galvanized steel sheet

A hot-dip galvanized steel sheet includes a base steel sheet and a hot-dip galvanized layer formed on at least one surface of the base steel sheet, in which the hot-dip galvanized layer includes Fe in a content of more than 0% to 5% or less, Al in a content of more than 0% to 1.0% or less, and columnar grains formed by a &#x3b6; phase on the surface of the steel sheet, further, 20% or more of the entire interface between the hot-dip galvanized layer and the base steel sheet is coated with the &#x3b6; phase, and a ratio of an interface formed between &#x3b6; grains in which coarse oxides are present among &#x3b6; grains and the base steel sheet with respect to the entire interface between the &#x3b6; phase and the base steel sheet in the hot-dip galvanized layer is 50% or less, the base steel sheet has predetermined chemical components and a refined layer in direct contact with the interface between the base steel sheet and the hot-dip galvanized layer, an average thickness of the refined layer is 0.1 to 5.0 &#x3bc;m, an average grain size of ferrite in the refined layer is 0.1 to 3.0 &#x3bc;m, one or two or more of oxides of Si and Mn are contained in the refined layer, and a maximum size of the oxide is 0.01 to 0.4 &#x3bc;m.

A hot-dip galvanized steel sheet wherein the hot-dip galvanized steel sheet comprises a base steel sheet and a hot-dip galvanized layer, a ferrite phase is, by volume fraction, 40% or more and 97% or less in a range of &#x215b; thickness to &#x215c; thickness centered at a position of &#xbc; thickness from the surface of the base steel sheet, a hard structure is 3% or more in total, wherein the hot-dip galvanized steel sheet has the hot-dip galvanized layer in which Fe is 5.0% or less and Al is 1.0% or less, and columnar grains formed of a &#x3b6; phase is 20% or more in an entire interface between the plated layer and the base steel sheet on the surface of the base steel sheet in which a ratio of a volume fraction of the hard structure in a surface layer range of 20 &#x3bc;m depth in a steel sheet direction from an interface between the hot-dip galvanized layer and the base steel sheet is 0.10 times or more to 0.90 times or less of a volume fraction of the hard structure in the range of &#x215b; thickness to &#x215c; thickness, and wherein the hot-dip galvanized steel sheet has a refined layer at the side of the interface in the base steel sheet, and wherein an average thickness of the refined layer, an average grain size of ferrite in the refined layer and a maximum size of the oxide included in the refined layer are defined respectively.

A hot-dip galvanized steel sheet having a base steel sheet and a hot-dip galvanized layer, a ferrite phase is, by volume fraction, 50% or less in a range of &#x215b; thickness to &#x215c; thickness centered at a position of &#xbc; thickness from the surface of the base steel sheet, a hard structure is 50% or more, wherein the hot-dip galvanized steel sheet has the hot-dip galvanized layer in which Fe is 5.0% or less and Al is 1.0% or less, and columnar grains formed of a &#x3b6; phase is 20% or more in an entire interface between the plated layer and the base steel sheet. On the surface of the base steel sheet, a volume fraction of a residual austenite is 3% or less.

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 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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Kisarazu, Japan

Toyomitsu Nakamura