Nippon Steel Corporation

Nippon Steel & Sumitomo Metal Corporation

Toyota Jidosha Kabushiki Kaisha

Toyota Jidosha Kogyo Kabushiki Kaisha

Aisin Takaoka Co., Ltd.

Sumitomo Metal Corporation

Kunio Hayashi

Nobuhiro Fujita

Hiroyuki Kawata

Akihiro Uenishi

Riki Okamoto

Kohichi Sano

Yuri Toda

Eisaku Sakurada

Takafumi Yokoyama

Kazuaki Nakano

Yuji Yamaguchi

Toshimasa Tomokiyo

Satoshi Uchida

Katsuya Nakano

Genki Abukawa

Toshimitsu Aso

Hiroshi Yoshida

Toshio Ogawa

Manabu Takahashi

Masahiro Nakata

Kengo Takeda

Masafumi Azuma

Koichi Goto

Kaoru Kawasaki

Koutarou Hayashi

Yasunobu Miyazaki

Jun Haga

Yoshihiro Suwa

Tetsuo Kishimoto

Masaharu Kameda

Yoshisada Wada

Hiroyuki Okada

Kazuo Hikida

Yuya Suzuki

Shinya Saitoh

Shunji Hiwatashi

Takahiro Iwase

Hiroyuki Tanahashi

Shigemi Shioya

Hitoshi Tanino

Chisato Yoshinaga

Kazuhiko Tsuda

Naoki Matsutani

Ryozo Wada

Masashi Fukuda

Yasushi Hayashida

Koichi Sato

Takeshi Yamamoto

Noriyuki Suzuki

Shinichi Suzuki

Hiroyuki Tanaka

Masayuki Abe

Jun Maki

Natsuko Sugiura

Fuminori Watanabe

Hironori Sato

Masanori Yasuyama

Seiji Furusako

Takayuki Nozaki

Chisato Wakabayashi

Kazuhisa Kusumi

Naoki Inoue

Yusuke Kondo

Toyomitsu Nakamura

Nobuo Fukuma

Shohei Yabu

Yuzo Takahashi

Kimimasa Murayama

Kazuki Shiokawa

Shuhei Noro

Mutsumi Sakakibara

Yukiko Kobayashi

Sho Matsui

Shinya Nakajima

Tatsuya Obuchi

Masahiro Oogami

Toshiyuki Kanda

Hisayasu Hasegawa

Yoshihiro Tokudome

Marina Mori

Takuma Kawanaka

Provided are a steel sheet having a predetermined chemical composition and having the following steel structure, and a method of manufacturing the steel sheet. (1) In area ratio %, ferrite: 0 to 5%, martensite: 90 to 100%, a ratio of tempered martensite to total martensite: 80 to 100%, and retained austenite: 0.5 to 6.0% are contained. (2) The number density of inclusions satisfying the maximum diameter≥3 μm is 40 inclusions/mmor less. (3) When the number density of the inclusions satisfying the maximum diameter≥3 μm in each section is calculated, the number density in the section where the number density of inclusions is in the top 10% is 80 inclusions/mmor less. (4) Formula (A) is satisfied.γ≥0.1  (A) Vγ: Initial retained austenite, Vγ′: Retained austenite after deep cooling at −196° C. (5) The tensile strength is 1470 MPa or more.

Steel sheet

Provided are a hot dip galvanized steel sheet comprising a base steel sheet wherein the base steel sheet has a predetermined chemical composition, and contains ferrite: 50% or less, retained austenite: 30% or less, tempered martensite: 5% or more, fresh martensite: 10% or less, and pearlite and cementite in total: 5% or less, remaining structures consist of bainite, and a number ratio of tempered martensite with a Mn concentration profile satisfying [Mn]/[Mn]>1.2 and [Mn]/[Mn]<2.0 ([Mn] is the Mn content in the base steel sheet, [Mn]is the average Mn concentration in the tempered martensite, and [Mn]is the Mn concentration at the interfaces of different phases of the tempered martensite and ferrite phase and bainite phase) is 0.2 or more with respect to the total number of tempered martensite, and a method for producing the same.

Hot dip galvanized steel sheet and method for producing same

Provided are a hot dip galvanized steel sheet comprising a base steel sheet wherein the base steel sheet has a predetermined composition and contains ferrite: 0% to 50%, retained austenite: 0% to 30%, tempered martensite: 5% or more, fresh martensite: 0% to 10%, and pearlite and cementite in total: 0% to 5%, remaining structures consist of bainite, when defining a region having a hardness of 90% or less of the hardness at a position of ¼ thickness to the base steel sheet side from an interface of the base steel sheet and a hot dip galvanized layer as a 'soft layer', there is a soft layer having a thickness of 10 μm or more at the base steel sheet side from the interface, the soft layer contains tempered martensite, and an increase rate in a thickness direction of an area % of tempered martensite from the interface to the inside of the base steel sheet inside the soft layer is 5.0%/μm or less, and a method for producing the same.

A hot-rolled steel sheet includes, as chemical composition, C, Si, Mn, and sol.Al. In the hot-rolled steel sheet, an average of pole densities in crystal orientation group consisting of {110}<110> to {110}<001> in surface region is 0.5 to 3.0, a standard deviation of the pole densities in the crystal orientation group is 0.2 to 2.0, and the tensile strength is 780 to 1370 MPa.

Hot-rolled steel sheet

A hot dip galvanized steel sheet includes a base steel sheet and a hot dip galvanized layer on at least one surface of the base metal steel sheet, wherein the base steel sheet has a predetermined chemical composition, and contains, by volume fraction, ferrite: 0% to 50%, retained austenite: 0% to 30%, tempered martensite: 5% or more, fresh martensite: 0% to 10%, and pearlite and cementite in total: 0% to 5%, when there are remaining structures, the remaining structures consist of bainite, a concentration of B atoms at prior austenite grain boundaries is 2.0 atm % or more, and an average effective crystal grain size is 7.0 μm or less, and a method for producing the same.

A zinc-plated steel sheet includes a steel sheet having a predetermined chemical composition and a zinc-plated layer. In the steel sheet, steel microstructures in a range of ⅛ thickness to ⅜ thickness, having the center at ¼ thickness from a steel sheet surface, include, by vol %, ferrite: 0% to 10%, bainite: 0% to 30%, tempered martensite: 50% or more, fresh martensite: 0% to 10%, retained austenite: more than 10% and 30% or less, and pearlite: 0% to 5%. In the zinc-plated steel sheet, the amount of hydrogen emitted when the steel sheet is heated to 200° C. from room temperature after removal of the zinc-plated layer is 0.40 ppm or less per mass of the steel sheet, the tensile strength is 1470 MPa or more, and no cracking occurs in a U-shape bending test where a stress equivalent to 1000 MPa is applied for 24 hours.

Zinc-plated steel sheet and manufacturing method thereof

Provided are a hot dip galvanized steel sheet comprising a base steel sheet and a hot dip galvanized layer on at least one surface of the base metal steel sheet, wherein the base steel sheet has a predetermined chemical composition and contains, by volume fraction, ferrite: 0% to 50%, retained austenite: 6% to 30%, bainite: 5% or more, tempered martensite: 5% or more, fresh martensite: 0% to 10%, and pearlite and cementite in total: 0% to 5%, a number density of tempered martensite with a circle equivalent diameter of 5.0 &#x3bc;m or more is 20/1000 &#x3bc;mor less, and an area ratio of fresh martensite with a circle equivalent diameter of 2.0 &#x3bc;m or more after imparting 5% plastic strain is 10% or less, and a method for producing the same.

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 zinc-plated steel sheet of an aspect of the present invention includes a steel sheet having a predetermined chemical composition and a zinc-plated layer. In the steel sheet, steel microstructures in a range of &#x215b; thickness to &#x215c; thickness, having the center at &#xbc; thickness from a steel sheet surface, include, by vol %, ferrite: 0% to 10%, bainite: 0% to 20%, tempered martensite: 70% or more, fresh martensite: 0% to 10%, retained austenite: 0% to 10%, and pearlite: 0% to 5%. In the zinc-plated steel sheet, the amount of hydrogen emitted when the steel sheet is heated to 200&#xb0; C. from a room temperature after removal of the zinc-plated layer is 0.40 ppm or less per mass of the steel sheet, the tensile strength is 1470 MPa or more, and no cracking occurs in a U-shape bending test where a stress equivalent to 1000 MPa is applied for 24 hours.

A steel sheet includes a predetermined chemical composition and a metal structure represented by, in area fraction, ferrite: 50% to 95%, granular bainite: 5% to 48%, martensite: 2% to 30%, and upper bainite, lower bainite, tempered martensite, retained austenite, and pearlite: 5% or less in total.

A blank material is formed from a steel sheet, a first quenching of the blank material is performed, and a second quenching of the blank material is performed after the first quenching. When the first quenching is performed, the blank material is heated to a first temperature of not lower than (Ac3 point&#x2014;50)&#xb0; C. nor higher than 1200&#xb0; C. at an average heating rate of 2&#xb0; C./sec or more, and the blank material is cooled from the first temperature to a second temperature of 250&#xb0; C. or lower. When the second quenching is performed, the blank material is heated from the second temperature to a third temperature of not lower than (Ac3 point&#x2014;50)&#xb0; C. nor higher than 1200&#xb0; C. at an average heating rate of 2&#xb0; C./sec or more, and the blank material is cooled from the third temperature to a fourth temperature of 250&#xb0; C. or lower. Forming of the blank material is performed in the first quenching or the second quenching or both of the above.

Hot stamped part and manufacturing method thereof

A steel sheet has a predetermined chemical composition and a metal structure represented by, in area fraction, polygonal ferrite: 40% or less, martensite: 20% or less, bainitic ferrite: 50% to 95%, and retained austenite: 5% to 50%. In area fraction, 80% or more of the bainitic ferrite is composed of bainitic ferrite grains that have an aspect ratio of 0.1 to 1.0 and have a dislocation density of 8&#xd7;10(cm/cm) or less in a region surrounded by a grain boundary with a misorientation angle of 15&#xb0; or more. In area fraction, 80% or more of the retained austenite is composed of retained austenite grains that have an aspect ratio of 0.1 to 1.0, have a major axis length of 1.0 &#x3bc;m to 28.0 &#x3bc;m, and have a minor axis length of 0.1 &#x3bc;m to 2.8 &#x3bc;m.

A steel sheet includes a predetermined chemical composition and a metal structure represented by, in area fraction, ferrite: 50% to 95%, granular bainite: 5% to 48%, tempered martensite: 2% to 30%, upper bainite, lower bainite, fresh martensite, retained austenite, and pearlite: 5% or less in total, and the product of the area fraction of the tempered martensite and a Vickers hardness of the tempered martensite: 800 to 10500.

High strength steel sheet having a tensile strength of 800 MPa or more comprising a middle part in sheet thickness and a soft surface layer arranged at one side or both sides of the middle part in sheet thickness, wherein each soft surface layer has a thickness of more than 10 &#x3bc;M and 30% or less of the sheet thickness, the soft surface layer has an average Vickers hardness of more than 0.60 time and 0.90 time or less the average Vickers hardness of the sheet thickness 1/2 position, and the soft surface layer has a nano-hardness standard deviation of 0.8 or less is provided.

High strength steel sheet

A high-strength hot-dip galvanized steel sheet contains predetermined amounts of C, Si, Mn, P, S, N, O, sol. Al, Ti, and B, 0.1 to 1.5 mass % of Cr+2&#xd7;Mo, and a balance in a form of Fe and inevitable impurities. A steel structure includes, in area %, ferrite: 1 to 50%, martensite: 20 to 70%, residual austenite: 0 to 5%, pearlite: 0 to 5%, MA and cementite having 0.2 &#x3bc;m or more grain size: 0 to 5% in total, and a balance in a form of bainite. A number density of MA or cementite having 0.2 &#x3bc;m or more grain size and isolated in ferrite or bainite grains is 100 pcs/1000 &#x3bc;mor less, and an average hardness of martensite is in a range from 330 to 500 Hv.

High strength hot-dip galvanized steel sheet and production method therefor

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Tokyo, Japan

Kunio Hayashi