Nippon Steel Corporation

Nippon Steel Sumitomo Metal Corporation

Tatsuo Yokoi

Hiroshi Shuto

Natsuko Sugiura

Riki Okamoto

Nobuhiro Fujita

Eisaku Sakurada

Kazuaki Nakano

Teruki Hayashida

Takeshi Yamamoto

Hiroshi Abe

Masafumi Azuma

Osamu Yoshida

Mitsuru Yoshida

Osamu Kawano

Akifumi Sakakibara

Tetsuya Yamada

Jun Ando

Takeshi Toyoda

Daisuke Maeda

Hiroyuki Okada

Akihiro Uenishi

Shigeru Yonemura

Daisuke Ito

Naoki Maruyama

Takuya Hara

Manabu Takahashi

Jun Takahashi

Yuri Toda

Shinichiro Watanabe

Toshimitsu Aso

Masanori Minagawa

Kensuke Nagai

Yuuki Kanzawa

Masayuki Wakita

Kazuya Ootsuka

Atsushi Itami

Nobuo Yoshikawa

Mutsumi Sakakibara

Kiyoyuki Fukui

Shinya Saitoh

Atsushi Seto

Masahiro Ohara

Yasuharu Sakuma

Yukiko Yamaguchi

Junji Haji

Yuzo Takahashi

Hiroyuki Tanahashi

Takaaki Nakamura

Kohsaku Ushioda

Shunichi Kobayashi

Genichi Shigesato

Shinsuke Kai

Yukiko Kobayashi

Shiro Fujii

Shinichi Araki

Hideto Kawano

Fuminori Tasaki

Takehiro Nakamoto

Makoto Tezuka

Satoshi Horioka

Ryohta Niiya

Yasuhiro Miyatani

Kouichi Tsuchihashi

A hot-rolled steel sheet has, as a chemical composition, by mass %: C: 0.01% to 0.30%; Si: 0.01% to 3.00%; Mn: 0.20% to 3.00%; P: 0.030% or less; S: 0.030% or less; Al: 0.001% to 2.000%; N: 0.0100% or less; and Ni: 0.02% to 0.50%, in which among measurement points at which elemental analysis is performed at a measurement pitch of 1 μm using an EPMA in a region of 250 μm×250 μm on a surface, the percentage of measurement points having a Ni content of 0.5 mass % or more is 10% to 70%.

Hot-rolled steel sheet and method for manufacturing same

In a hot-rolled steel sheet, a microstructure contains, in area ratio, at a location at ¼ a sheet thickness, a total amount of 90% or more of one or more of martensite and tempered martensite and a total amount of 10% or less of one or more of ferrite, bainite, and pearlite, at a location of 200 μm from the surface, a total amount of 70% or more and less than 90% of one or more of martensite and tempered martensite and a total amount of more than 10% and 30% or less of one or more of ferrite, bainite, and pearlite.

Hot-rolled steel sheet

This hot-rolled steel sheet has a predetermined chemical composition, and in a case where the thickness is denoted by t, the metallographic structure at a t/4 position from the surface contains one or both of tempered martensite and lower bainite at a volume percentage of 90% or more, the tensile strength is 980 MPa or more, and the average Ni concentration on the surface is 7.0% or more.

A high-strength hot-rolled steel sheet: having a predetermined chemical composition; having a mean dislocation density of from 1×10to 1×10m, and containing at least bainitic ferrite, in which a total area ratio of the bainitic ferrite and ferrite is 70% or more and less than 90%, and in which a total area ratio of martensite and retained austenite is 5% or more and 30% or less, in which, in ferrite crystal grains and in bainitic ferrite crystal grains, a mean number density of TiC precipitates is from 1×10to 5×10[precipitates/cm], in which an amount of Ti present as a TiC precipitate precipitated in a matrix not on dislocations is 30 mass % or more of a total amount of Ti in the steel sheet, and in which a tensile strength is 850 MPa or more.

High-strength hot-rolled steel sheet

This hot-rolled steel sheet has a predetermined chemical composition, in which in a case where the thickness is denoted by t, a metallographic structure at a t/4 position from the surface includes, by area fraction, 77.0% to 97.0% of bainite or tempered martensite, 0% to 5.0% of ferrite, 0% to 5.0% of pearlite, 3.0% or more of residual austenite, and 0% to 10.0% of martensite, in the metallographic structure, the average grain size excluding the residual austenite is 7.0 &#x3bc;m or less, the average number density of iron-based carbides having a diameter of 20 nm or more is 1.0&#xd7;10carbides/mmor more, a tensile strength is 980 MPa or more, and an average Ni concentration on the surface is 7.0% or more.

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.

There is provided a hot-rolled steel sheet in which a composition contains: in mass %, C: 0.01% to 0.2%; Si: 2.5% or less; Mn: 4.0% or less; P: 0.10% or less; S: 0.03% or less; Al: 0.001% to 2.0%; N: 0.01% or less; O: 0.01% or less; Ti: 0.01 to 0.30%; and the balance being composed of iron and impurities and a structure is composed of by volume fraction, 90% or more of tempered martensite with an average aspect ratio of 2 or less, or 90% or more in total of both tempered martensite and lower bainite.

Hot-rolled steel sheet and manufacturing method thereof

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 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 hot rolled steel sheet having a chemical composition consisting of, in mass %, C: 0.020-0.180%, Si: 0.05-1.70%, Mn: 0.50-2.50%, Al: 0.010-1.000%, N: 0.0060%, P&#x2264;0.050%, S&#x2264;0.005%, Ti: 0-0.150%, Nb: 0-0.100%, V: 0-0.300%, Cu: 0-2.00%, Ni: 0-2.00%, Cr: 0-2.00%, Mo: 0-1.00%, B: 0-0.0100%, Mg: 0-0.0100%, Ca: 0-0.0100%, REM: 0-0.1000%, Zr: 0-1.000%, Co: 0-1.000%, Zn: 0-1.000%, W: 0-1.000%, the balance: Fe and impurities, wherein a metal microstructure includes, in area %, at a position &#xbc; W or &#xbe; W from an end face of the steel sheet and &#xbc; t or &#xbe; t from a surface, martensite: more than 2%-10%, retained austenite &#x3c;2%, bainite 40%, pearlite 2%, the balance: ferrite, an average circle-equivalent diameter of a metallic phase constituted of martensite/retained austenite is 1.0-5.0 &#x3bc;m, an average of minimum distances between adjacent metallic phases is 3 &#x3bc;m or more, and a standard deviation of nano hardness is 2.0 GPa or less.

Hot rolled steel sheet

A hot rolled steel sheet including a chemical composition consisting of, in mass %, C: 0.07-0.22%, Si: 1.00-3.20%, Mn: 0.80-2.20%, Al: 0.010-1.000%, N&#x2264;0.0060%, P&#x2264;0.050%, S&#x2264;0.005%, Ti: 0-0.150%, Nb: 0-0.100%, V: 0-0.300%, Cu: 0-2.00%, Ni: 0-2.00%, Cr: 0-2.00%, Mo: 0-1.00%, B: 0-0.0100%, Mg: 0-0.0100%, Ca: 0-0.0100%, REM: 0-0.1000%, Zr: 0-1.000%, Co: 0-1.000%, Zn: 0-1.000%, W: 0-1.000%, Sn: 0-0.050%, the balance: Fe and impurities, wherein a metal microstructure includes, in area %, at a position &#xbc; W or &#xbe; W from an end face of the steel sheet and &#xbc; t or &#xbe; t from a surface, retained austenite: more than 2%-10%, martensite &#x2264;2%, bainite: 10-70%, pearlite &#x2264;2%, the balance: ferrite, an average circle-equivalent diameter of a metallic phase constituted of retained austenite/martensite is 1.0 to 5.0 &#x3bc;m, an average of minimum distances between adjacent metallic phases is 3 &#x3bc;m or more, and a standard deviation of nano hardness is 2.5 GPa or less.

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 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

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Tokyo, Japan

Tatsuo Yokoi