Nippon Steel Corporation

Nippon Steel Sumitomo Metal Corporation

Arcelor France

Arcelormittal

Arcelormittal France

Natsuko Sugiura

Naoki Yoshinaga

Yuji Yamaguchi

Manabu Takahashi

Tatsuo Yokoi

Kohichi Sano

Naoki Maruyama

Hiroshi Shuto

Masahiro Nakata

Mitsuru Yoshida

Masayuki Wakita

Makoto Uno

Ryoichi Nishiyama

Hiroyuki Kawata

Riki Okamoto

Kaoru Kawasaki

Akihiro Miyasaka

Koji Hanya

Nobuhiro Fujita

Tohru Yoshida

Eisaku Sakurada

Masahiro Fuda

Hironori Sato

Akinobu Murasato

Chisato Wakabayashi

Takehide Senuma

Akinobu Minami

Shunji Hiwatashi

Ryoichi Kanno

Nobuyoshi Uno

Kiyoyuki Fukui

Kunio Hayashi

Takamasa Suzuki

Masao Kurosaki

Shigeru Yonemura

Takuya Kuwayama

Ken Kimura

Takeshi Yasui

Takeshi Toyoda

Hiromasa Shoji

Yasuhiro Shinohara

Teruki Hayashida

Yuuki Kanzawa

Taihei Kaneto

Takaaki Nakamura

Tetsuya Hirashima

Mutsumi Sakakibara

Masaaki Sugiyama

Takehiro Nakamoto

Yohji Nakamura

A steel sheet has a specific chemical composition and has a structure represented by, by area ratio, ferrite: 5 to 60%, and bainite: 40 to 95%. When a region that is surrounded by a grain boundary having a misorientation of 15&#xb0; or more and has a circle-equivalent diameter of 0.3 &#x3bc;m or more is defined as a crystal grain, the proportion of crystal grains each having an intragranular misorientation of 5 to 14&#xb0; to all crystal grains is 20 to 100% by area ratio. A precipitate density of Ti(C,N) and Nb(C,N) each having a circle-equivalent diameter of 10 nm or less is 10precipitates/mmor more. A ratio (Hvs/Hvc) of a hardness at 20 &#x3bc;m in depth from a surface (Hvs) to a hardness of the center of a sheet thickness (Hvc) is 0.85 or more.

Steel sheet and plated steel sheet

A hot-rolled steel sheet includes a specific chemical composition, and includes a microstructure represented by, in vol %: retained austenite: 2% to 30%; ferrite: 20% to 85%; bainite: 10% to 60%; pearlite: 5% or less; and martensite: 10% or less. A proportion of grains having an intragranular misorientation of 5&#xb0; to 14&#xb0; in all grains is 5% to 50% by area ratio, the grain being defined as an area which is surrounded by a boundary having a misorientation of 15&#xb0; or more and has a circle-equivalent diameter of 0.3 &#x3bc;m or more.

Hot-rolled steel sheet

A hot rolled steel sheet is provided, which is excellent in collision characteristics, excellent in anisotropy of toughness, and high in strength. The hot rolled steel sheet is characterized by containing, by mass %, C: 0.10% to 0.50%, Si: 0.10% to 3.00%, Mn: 0.5% to 3.0%, P: 0.100% or less, S: 0.010% or less, Al: 1.00% or less, N: 0.010% or less and a balance of Fe and impurities, wherein a metal structure at position of &#xbc; thickness from surface in L-cross-section of the steel sheet comprises prior austenite grains of average value of aspect ratios of 2.0 or less, average grain size of 0.1 &#x3bc;m to 3.0 &#x3bc;m, and coefficient of variation of a standard deviation of grain size distribution/average grain size of 0.40 or more, and a texture with X-ray diffraction intensity ratio of {001}&#x3c;110&#x3e;orientation for random samples of 2.0 or more, and the steel sheet has tensile strength of 1180 MPa or more.

Hot rolled steel sheet and method for producing same

A steel sheet has a specific chemical composition and has a structure represented by, by area ratio, ferrite: 30 to 95%, and bainite: 5 to 70%. When a region that is surrounded by a grain boundary having a misorientation of 15&#xb0; or more and has a circle-equivalent diameter of 0.3 &#x3bc;m or more is defined as a crystal grain, the proportion of crystal grains each having an intragranular misorientation of 5 to 14&#xb0; to all crystal grains is 20 to 100% by area ratio. An average aspect ratio of ellipses equivalent to the crystal grains is 5 or less. An average distribution density of the total of Ti-based carbides and Nb-based carbides each having a grain size of 20 nm or more on ferrite grain boundaries is 10 carbides/&#x3bc;m or less.

A steel sheet has a specific chemical composition and has a structure represented by, by area ratio, ferrite: 0 to 30%, and bainite: 70 to 100%. When a region that is surrounded by a grain boundary having a misorientation of 15&#xb0; or more and has a circle-equivalent diameter of 0.3 &#x3bc;m or more is defined as a crystal grain, the proportion of crystal grains each having an intragranular misorientation of 5 to 14&#xb0; to all crystal grains is 20 to 100% by area ratio. A grain boundary number density of solid-solution C or a grain boundary number density of the total of solid-solution C and solid-solution B is 1 piece/nmor more and 4.5 pieces/nmor less. An average grain size of cementite precipitated at grain boundaries is 2 &#x3bc;m or less.

A hot press-formed part according to an aspect of the present invention contains a predetermined chemical composition; in which a microstructure in a thickness &#xbc; portion includes, by unit vol %, tempered martensite: 20% to 90%, bainite: 5% to 75%, and residual austenite: 5% to 25%, and ferrite is limited to 10% or less; and a pole density of an orientation {211}&#x3c;011&#x3e; in the thickness &#xbc; portion is 3.0 or higher.

Hot press-formed part

A hot-rolled steel sheet includes a predetermined chemical composition, and a structure which include, by area ratio, ferrite and bainite in a range of 80% to 98% in total, and martensite in a range of 2% to 10%, in which in the structure, in a case where a boundary having an orientation difference of equal to or greater than 15&#xb0; is defined as a grain boundary, and an area which is surrounded by the grain boundary, and has an equivalent circle diameter of equal to or greater than 0.3 &#x3bc;m is defined as a grain, the ratio of the grains having an intragranular orientation difference in a range of 5&#xb0; to 14&#xb0; is, by area ratio, in a range of 10% to 60%.

A steel sheet having a specific chemical composition and structure represented by, by area ratio, ferrite: 5 to 95%, and bainite: 5 to 95%. The proportion of crystal grains having an intragranular misorientation of 5 to 14&#xb0; to all crystal grains is 20 to 100% by area ratio. Hard crystal grains A in which precipitates or clusters with a maximum diameter of 8 nm or less are dispersed in the crystal grains with a number density of 1&#xd7;10to 1&#xd7;10pieces/cm. Soft crystal grains B in which precipitates or clusters with a maximum diameter of 8 nm or less are dispersed in the crystal grains with a number density of 1&#xd7;10pieces/cmor less are contained. The volume % of the hard crystal grains A/(the volume % of the hard crystal grains A+the volume % of the soft crystal grains B) is 0.1 to 0.9.

A hot-rolled steel sheet includes a predetermined chemical composition, and a structure which includes, by area ratio, a ferrite in a range of 5% to 60% and a bainite in a range of 30% to 95%, in which in the structure, in a case where a boundary having an orientation difference of equal to or greater than 15&#xb0; is defined as a grain boundary, and an area which is surrounded by the grain boundary and has an equivalent circle diameter of equal to or greater than 0.3 &#x3bc;m is defined as a grain, the ratio of the grains having an intragranular orientation difference in a range of 5&#xb0; to 14&#xb0; is, by area ratio, in a range of 20% to 100%.

A surface-treated steel sheet for fuel tanks, including a Zn&#x2014;Ni alloy plating layer on one surface or both surfaces of a steel sheet; and a trivalent chromate covering layer or a chromate-free covering layer on the Zn&#x2014;Ni alloy plating layer, wherein, in a surface outermost layer of the trivalent chromate covering layer or the chromate-free covering layer, concavities, of which a depth from an arithmetic average height of a cross-sectional curve of the surface outermost layer is more than or equal to 0.1 &#x3bc;m, exist in a proportion of 50 to 1000 concavities/mm2 and at an area ratio of 20 to 80% to a surface area of the steel sheet.

Surface-treated steel sheet for fuel tanks

A hot-rolled steel sheet includes a chemical composition represented by, in mass %, C: 0.010% to 0.100%, Si: 0.30% or less, Cr: 0.05% to 1.00%, Nb: 0.003% to 0.050%, Ti: 0.003% to 0.200% and others, wherein a proportion of grains having an intragranular misorientation of 5&#xb0; to 14&#xb0; in all grains is 20% or more by area ratio, the grain being defined as an area which is surrounded by a boundary having a misorientation of 15&#xb0; or more and has a circle-equivalent diameter of 0.3 &#x3bc;m or more.

There is provided a steel sheet with strain induced transformation type composite structure having a predetermined chemical composition in which a microstructure at the &#xbc; thickness of the steel sheet includes, by area ratio, 50% to 85% of a polygonal ferrite, 3% to 10% of a residual austenite, 5% to 47% of bainite and 1% or less of a fresh martensite and a tempered martensite in total and satisfies the equation of 0.01&#x3c;Ex.C/fsd&#x2264;0.015, the microstructure includes 1&#xd7;10pieces/cmor more of precipitates containing TiC, an average grain diameter of the residual austenite 1.0 &#x3bc;m to 5.0 &#x3bc;m at an equivalent circle diameter, an average of closest distances of the austenite is 3.0 &#x3bc;m to 10.0 &#x3bc;m, and an average diameter of the precipitates is 3 nm or less.

Steel sheet with strain induced transformation type composite structure and method of manufacturing same

A hot-rolled steel sheet for a tailored rolled blank is provided that has high tensile strength and is excellent in cold formability. The hot-rolled steel sheet has: a chemical composition that contains, in mass %, C, Si, Mn, P, S, Al, N and Ti, with the balance being Fe and impurities, and that satisfies Formula (1); and a microstructure containing, in terms of area ratio, 20% or more of bainite, wherein 50% or more in terms of area ratio of the balance is ferrite. In the interior of the hot-rolled steel sheet an average value of pole densities of an orientation group {100}&#x3c;011&#x3e; to {223}&#x3c;110&#x3e; is 4 or less, and a pole density of a {332}&#x3c;113&#x3e; crystal orientation is 4.8 or less. In an outer layer of the hot-rolled steel sheet, a pole density of a {110}&#x3c;001&#x3e; crystal orientation is 2.5 or more. Furthermore, among Ti carbo-nitrides in the hot-rolled steel sheet, the number density of fine Ti carbo-nitrides having a particle diameter of 10 nm or less is 1.0&#xd7;10per cmor less, and a bake hardening amount is 15 MPa or more,[Ti]&#x2212;48/14&#xd7;[N]&#x2212;48/32&#xd7;[S]&#x2265;0&#x2003;&#x2003;(1).

Hot-rolled steel sheet for tailored rolled blank and tailored rolled blank

A heat-rolled steel plate has a chemical composition that contains, in mass %, C, Si, Mn, P, S, Al, N and Ti, and that satisfies Formula (1); and a microstructure containing bainite and ferrite. In the interior of the steel plate an average value of pole densities of an orientation group {100}&#x3c;011&#x3e; to {223}&#x3c;110&#x3e; is 4 or less, and a pole density of a {332}&#x3c;113&#x3e; crystal orientation is 4.8 or less. In an outer layer of the steel plate, a pole density of a {110}&#x3c;001&#x3e; crystal orientation is 2.5 or more. Furthermore, among Ti carbo-nitrides in the steel plate, the number density of fine Ti carbo-nitrides having a particle diameter of 10 nm or less is 1.0&#xd7;10per cmor less, and a bake hardening amount is 15 MPa or more.[Ti]&#x2212;48/14&#xd7;[N]&#x2212;48/32&#xd7;[S]&#x2265;0&#x2003;&#x2003;(1)

Heat-rolled steel plate for tailored rolled blank, tailored rolled blank, and methods for producing these

The present invention provides a high-strength steel sheet excellent in shape fixability. The high-strength steel sheet contains C, Si, Mn, P, S, Al, N, and O with predetermined contents, in which a retained austenite phase of 5 to 20% in volume fraction is contained, an amount of solid-solution C contained in the retained austenite phase is 0.80 to 1.00% in mass %, Wis 1.10 times or more W, Wis 1.10 times or more W, and when a frequency distribution is measured with respect to a sum of a ratio between Wand Wand a ratio between Wand W, a mode value of the frequency distribution is 1.95 to 2.05, and a kurtosis is 2.00 or more.

High-strength steel sheet and high-strength galvanized steel sheet excellent in shape fixability, and manufacturing method thereof

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Tokyo, Japan

Natsuko Sugiura