Nippon Steel Corporation

Nippon Steel Sumitomo Metal Corporation

Masaharu Kameda

Kohichi Sano

Hiroyuki Kawata

Kunio Hayashi

Akihiro Uenishi

Koutarou Hayashi

Jun Haga

Koji Hashimoto

Akio Saito

Naoki Maruyama

Riki Okamoto

Kaoru Kawasaki

Kazuhiko Honda

Yasuharu Sakuma

Atsushi Itami

Tetsuo Nishiyama

In a metal coated steel sheet, a chemical composition contains, in mass %, at least C: 0.03% to 0.70%, Si: 0.25% to 2.50%, Mn: 1.00% to 5.00%, P: 0.100% or less, S: 0.010% or less, sol. Al: 0.001% to 2.500, N: 0.020% or less, and a balance composed of iron and impurities, a metal structure contains greater than 5.0 vol % of retained austenite and greater than 5.0 vol % of tempered martensite, and satisfies a C content in the retained austenite being 0.85 mass % or more.

Metal coated steel sheet, manufacturing method of hot-dip galvanized steel sheet, and manufacturing method of alloyed galvannealed steel sheet

A hot dip galvanized steel sheet and hot dip galvannealed steel sheet improved in uniform ductility and local ductility, yield strength and tensile strength, and low temperature impact property, characterized by having a predetermined chemical composition, having a metal structure containing, by volume %, retained austenite: over 5.0% and tempered martensite: over 5.0%, having retained austenite containing C: 0.85 mass % or more, and having a ratio [C]/[P]of an amount of segregation of C (number of atoms/nm): [C]to an amount of segregation of P (number of atoms/nm): [P]at prior austenite grain boundaries of 4.0 or more.

Hot dip galvanized steel sheet and hot dip galvannealed steel sheet

A base material () included in a plated steel sheet () includes a structure, at a &#xbc; sheet thickness position, represented by, in volume fraction: tempered martensite: 3.0% or more; ferrite: 4.0% or more; and retained austenite: 5.0% or more. An average hardness of the tempered martensite in the base material () is 5 GPa to 10 GPa, and a part or all of the tempered martensite and the retained austenite in the base material form an M-A. A volume fraction of ferrite in a decarburized ferrite layer () included in the plated steel sheet () is 120% or more of the volume fraction of the ferrite in the base material () at the &#xbc; sheet thickness position, an average grain diameter of the ferrite in the decarburized ferrite layer () is 20 &#x3bc;m or less, a thickness of the decarburized ferrite layer () is 5 &#x3bc;m to 200 &#x3bc;m, a volume fraction of tempered martensite in the decarburized ferrite layer () is 1.0 volume% or more, a number density of the tempered martensite in the decarburized ferrite layer () is 0.01/&#x3bc;mor more, and an average hardness of the tempered martensite in the decarburized ferrite layer () is 8 GPa or less.

Plated steel sheet

A cold-rolled steel sheet includes a predetermined chemical composition, and includes a structure expressed by: an area fraction of ferrite: 95% or more; an area fraction of retained austenite and an area fraction of martensite: 1% to 3% in total; a product of the area fraction of retained austenite and a carbon concentration in retained austenite: 1 or more; a value of I(111)/{I(100)+I(110)} at a region where a depth from a surface is &#xbc; of a thickness of the cold-rolled steel sheet when intensity of a (hkl) plane is expressed by I(hkl): 2 or less.

Cold-rolled steel sheet, galvanized cold-rolled steel sheet and method of manufacturing the same

A strain aging hardening type steel sheet excellent in aging resistance, and manufacturing method thereof, said steel sheet comprises: in mass %, C: 0.0010 to 0.010%; Si: 0.005 to 1.0%; Mn: 0.08 to 1.0%; P: 0.003 to 0.10%; S: 0.0005 to 0.020%; Al: 0.010 to 0.10%; Cr: 0.005 to 0.20%; Mo: 0.005 to 0.20%; Ti: 0.002 to 0.10%; Nb: 0.002 to 0.10%; N: 0.001 to 0.005%; and a balance being composed of Fe and inevitable impurities, in which a ferrite fraction is 98% or more, an average grain diameter of ferrite is 5 to 30 &#x3bc;m, a minimum value of dislocation density in a portion having a &#xbd; thickness of a sheet thickness and a minimum value of dislocation density in a surface layer portion are each 5&#xd7;10/mor more, and an average dislocation density falls within a range of 5&#xd7;10to 1&#xd7;10/m.

Strain aging hardening steel sheet excellent in aging resistance, and manufacturing method thereof

Galvannealed steel sheet simultaneously able to achieve excellent workability and high strength and a method of production of the same are provided as an objective, in particular high strength galvannealed steel sheet excellent in workability, comprising high strength steel sheet containing, by mass %, C: 0.05 to 0.15%, Si: 0.3 to 2.0%, Mn: 1.0 to 2.8%, P: 0.03% or less, S: 0.02% or less, Al: 0.005 to 0.5%, and N: 0.0060% or less and a balance of Fe and unavoidable impurities, where, when % C, % Si, and % Mn respectively represent the C, Si, and Mn contents, (% Mn)/(% C)&#x2267;12 and (% Si)/(% C)&#x2267;4 being satisfied, on the surface of which having a galvannealed layer containing Al: 0.05 to 0.5 mass % and Fe: 5 to 15 mass % and a balance of Zn and unavoidable impurities, said steel sheet satisfying a relationship of tensile strength F (MPa) and elongation L (%) of L&#x2267;52&#x2212;0.035&#xd7;F.

High strength galvannealed steel sheet excellent in workability and a method of production of the same

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Tokyo, Japan

Masaharu Kameda