Nippon Steel Corporation

Nippon Steel Sumitomo Metal Corporation

Genichi Shigesato

Masafumi Azuma

Naoki Maruyama

Hiroyuki Kawata

Yoshiyuki Ushigami

Takashi Doi

Akihiro Uenishi

Yuri Toda

Daisuke Maeda

Hiroyasu Fujii

Kenichi Yamamoto

Shuichi Nakamura

Tatsuo Yokoi

Naoki Yoshinaga

Kenichi Murakami

Eisaku Sakurada

Satoshi Hirose

Yoshihiro Suwa

Kazuyuki Kashima

Masaaki Sugiyama

When a zone surrounded by a grain boundary that is measured to be 5.0&#xb0; or more by an EBSD analysis is assumed to be a grain, and when a K value is a value obtained by multiplying an average value of Image Qualities in a grain by 10, a Y value is an average crystal misorientation (&#xb0;) in the grain, a metallic phase 1 is a metallic phase the K value of which is less than 4.000, a metallic phase 2 is a metallic phase the K value of which is 4.000 or more and the Y value of which is 0.5 to 1.0, a metallic phase 3 is a metallic phase the K value of which is 4.000 or more and the Y value of which is less than 0.5, and a metallic phase 4 is a metallic phase that falls under none of metallic phases 1 to 3, there is provided a steel sheet that has a predetermined chemical composition and includes a microstructure including, in area percent, a metallic phase 1: 1.0% or more and less than 35.0%, a metallic phase 2: 30.0% or more and 80.0% or less, a metallic phase 3: 5.0% or more and 50.0% or less, and a metallic phase 4: 5.0% or less. The steel sheet has a strength as high as 590 MPa or more (further, 780 MPa or more) in terms of tensile strength and has an excellent hole-expansion property.

Steel sheet and plated steel sheet

A steel sheet according to an aspect of the present invention has predetermined chemical composition, in which a structure at a thickness &#xbc; portion includes, in terms of volume ratios, tempered martensite: 30% to 70% and one or both of ferrite and bainite: a total of 20% to 70%, in the structure at the thickness &#xbc; portion, a volume ratio of residual austenite is less than 10%, a volume ratio of fresh martensite is 10% or less, a volume ratio of pearlite is 10% or less, and a total volume ratio of the residual austenite, the fresh martensite, and the pearlite is 15% or less, a number density of iron-based carbides having a major axis of 5 nm or more in the tempered martensite at the thickness &#xbc; portion is 5&#xd7;10particles/mmor more, a ratio of the number of &#x3b5;-type carbides in the number of the iron-based carbides having the major axis of 5 nm or more at the thickness &#xbc; portion is 20% or more, and a tensile strength is 780 MPa or higher.

Steel sheet, hot-dip galvanized steel sheet, galvanized steel sheet, and manufacturing methods therefor

A steel sheet according to an aspect of the present invention has predetermined chemical composition, in which a structure at a thickness &#xbc; portion includes, in terms of volume ratios, tempered martensite: 70% or more and one or both of ferrite and bainite: a total of less than 20%, in the structure at the thickness &#xbc; portion, a volume ratio of residual austenite is less than 10%, a volume ratio of fresh martensite is 10% or less, a volume ratio of pearlite is 10% or less, and a total volume ratio of the residual austenite, the fresh martensite, and the pearlite is 15% or less, a number density of iron-based carbides having a major axis of 5 nm or more in the tempered martensite at the thickness &#xbc; portion is 5&#xd7;10particles/mmor more, a ratio of the number of &#x3b5;-type carbides in the number of the iron-based carbides having the major axis of 5 nm or more at the thickness &#xbc; portion is 20% or more, and a tensile strength is 780 MPa or higher.

Steel sheet, hot-dip galvanized steel sheet, galvannealed steel sheet, and manufacturing methods therefor

A hot-rolled steel sheet includes a specified chemical composition and includes a steel structure represented by an area ratio of ferrite being 5% to 50%, an area ratio of bainite composed of an aggregate of bainitic ferrite whose grain average misorientation is 0.4&#xb0; to 3&#xb0; being 50% to 90%, and a total area ratio of martensite, pearlite, and retained austenite being 5% or less.

Hot-rolled steel sheet

A high-strength steel sheet includes, by mass %, C: 0.03% to 0.30%, Si: 0.08% to 2.1%, Mn: 0.5% to 4.0%, P: 0.05% or less, S: 0.0001% to 0.1%, N: 0.01% or less, acid-soluble Al: more than 0.004% and less than or equal to 2.0%, acid-soluble Ti: 0.0001% to 0.20%, at least one selected from Ce and La: 0.001% to 0.04% in total, and a balance of iron and inevitable impurities, in which [Ce], [La], [acid-soluble Al], and [S] satisfy 0.02&#x2266;([Ce]+[La])/[acid-soluble Al]&#x3c;0.25, and 0.4&#x2266;([Ce]+[La])/[S]&#x2266;50 in a case in which the mass percentages of Ce, La, acid-soluble Al, and S are defined to be [Ce], [La], [acid-soluble Al], and [S], respectively, and a microstructure includes 1% to 50% of martensite in terms of an area ratio.

High-strength steel sheet and method for producing same

The present invention provides a grain-oriented silicon steel sheet excellent in adhesiveness to tension-creating insulating coating films formed on the grain-oriented silicon steel sheet produced by removing inorganic mineral films composed of forsterite and so on with pickling or the like or by deliberately preventing the formation thereof, characterized by: having, at the interface between each of the tension-creating insulating coating films and the steel sheet, an external oxidation type membranous oxide film of 2 to 500 nm in average thickness mainly composed of amorphous silica and/or a mixed oxide film consisting of an external oxidation type membranous oxide film of 2 to 500 nm in average thickness mainly composed of amorphous silica and particulate oxides mainly composed of amorphous silica: and satisfying any one or more of the specified requirements.

Grain-oriented silicon steel sheet excellent in adhesiveness to tension-creating insulating coating films and method for producing the same

Growing community of inventors

Tokyo, Japan

Genichi Shigesato