Jfe Steel Corporation

Hitachi, Ltd.

Kawasaki Steel Corporation

Hitachi-ge Nuclear Energy, Ltd.

Other

Chugai Seiyaku Kabushiki Kaisha

Pioneer Electronic Corporation

Hitachi Plant Technologies, Ltd.

Hitachi Plant Engineering Construction Co., Ltd.

Thyssenkrupp Steel Ag

Thyssenkrupp Steel Europe Ag

Takeshi Yokota

Kazuhiro Seto

Hidekazu Minami

Yoshiyasu Kawasaki

Hiroshi Matsuda

Susumu Satoh

Shinjiro Kaneko

Kenji Araki

Nobutake Konishi

Yuji Tanaka

Akio Kobayashi

Takumi Ujiro

Reiko Sugihara

Yuka Miyamoto

Takako Yamashita

Yasushi Kato

Yoshimasa Funakawa

Koichi Nakagawa

Katsutoshi Takashima

Tsutomu Yatsuo

Kaneharu Okuda

Hideyuki Kimura

Yoshitaka Sugawara

Masahiro Okamura

Makoto Kobayashi

Takashi Kobayashi

Katsumi Yamada

Tatsuya Nakagaito

Yasushi Tanaka

Osamu Furukimi

Nobuyuki Nakamura

Shin Ishikawa

Atsushi Miyazaki

Kanji Kato

Takaaki Tanaka

Yuki Toji

Yusuke Fushiwaki

Toru Hoshi

Yoshihiro Hosoya

Toshiyuki Miyake

Kenji Kawamura

Hidetaka Kawabe

Hisanori Nonaka

Kazunori Tahara

Yoshie Obata

Hayato Saito

Yoshibumi Fukuda

Yoshiteru Shimizu

Fusao Togashi

Kenji Takao

Shotaro Terashima

Kenji Akagi

Yoichiro Matsui

Norimasa Hirata

Kensuke Morita

Misako Tochihara

Nobusuke Kariya

Satoshi Ueoka

Susumu Murakami

Masatoshi Takada

Kazuhide Ishii

Shogo Sato

Yasuhiro Mochizuki

Norito Watanabe

Lingling Yang

Yusuke Wada

Thomas Heller

Satoshi Kinoshiro

Seiji Futatsugi

Yukihiro Matsubara

Youichi Nishikawa

Satoshi Tsutsumi

Shigeru Takano

Shigetoshi Sakimura

Keijiro Shigeru

Brigitte Hammer

Katsumi Nakajima

Nobuo Nishiura

Shuji Kawamura

Kazuhiko Yamazaki

Toshihiko Makino

Hiroyuki Nagano

Keiji Ueda

Noriaki Moriyasu

Junya Tobata

Tetsuya Mega

Fusae Shiimori

Masami Iwasaki

Sadao Hasuno

Hiromi Yoshida

Osamu Kubo

Kouichi Nakagawa

Rolf Bode

Günter Stich

Yoichi Tominaga

Haruhiko Ishizuka

Yasuhiro Sakurai

Kazuki Nakazato

Ichiro Sugimoto

Masayuki Haramura

Provided are a high-strength hot-dip galvanized steel sheet that has a tensile strength of 1180 MPa or more and excellent ductility, stretch flangeability, bendability and LME resistance and can manufacture parts with high dimensional accuracy, and its manufacturing method. The high-strength steel sheet with a tensile strength of 1180 MPa or more has a chemical composition containing C, Si, Mn, P, S, Al and N, with [% Si], [% Mn], [% P], [% Mo] and [% Cr] satisfying a predetermined relationship and the balance being Fe and inevitable impurities, and a steel microstructure including ferrite, tempered martensite and bainite, and retained austenite, where the diffusible hydrogen amount in the steel sheet is 0.60 mass ppm or less, a thickness of softened surface layer is 5 μm or more and 150 μm or less, and a frequency of coincidence boundary in the steel sheet surface layer after a high-temperature tensile test is 0.45 or less.

High-strength steel sheet and method for manufacturing same

A high-strength steel sheet with a tensile strength of 1,180 MPa or more has a predetermined chemical composition and a steel microstructure in which the area fraction of ferrite is 5% or less, the area fraction of martensite is 2% to 10%, the area fraction of bainite is 5% to 37%, the area fraction of tempered martensite is 42% to 65%, the volume fraction of retained austenite is 3% to 15%, the average grain size of ferrite and bainite is 3 μm or less, in a region extending 50 μm from a surface of the steel sheet in a through-thickness direction, and the average grain size of prior austenite grains is 10 μm or less, the average grain size of the prior austenite grains in the through-thickness direction is 0.9 or less of the average grain size thereof in a rolling direction.

High-strength steel sheet and method for manufacturing the same

A high-strength steel sheet comprises: a chemical composition containing C, Si, Mn, P, S, Al, N, Mo, Cr, Ca, and Sb with a balance consisting of Fe and inevitable impurities, wherein [% Si], [% Mn], [% P], [% Mo], and [% Cr] satisfy a predetermined relationship; a steel microstructure that contains ferrite, hard phase, and retained austenite and in which a carbon concentration in the retained austenite is 0.55% or more and 1.10% or less, an amount of diffusible hydrogen in the steel sheet is 0.80 mass ppm or less, a surface layer softening thickness is 5 μm or more and 150 μm or less, and a corresponding grain boundary frequency in a surface layer of the steel sheet after a high-temperature tensile test is 0.45 or less; and a tensile strength of 980 MPa or more.

High-strength steel sheet and method for producing same

A steel sheet according to the present invention has a specific chemical composition and a steel microstructure including, in terms of area fraction, ferrite: 40% or more and 70% or less, a total of bainite and tempered martensite: 5% or more and 30% or less, retained austenite: 4% or more and 18% or less, fresh martensite: 8% or more and 35% or less, and the remainder: 5% or less. Cementite particles are present in the retained austenite, a ratio of an area fraction of the cementite particles in the retained austenite to an area fraction of the retained austenite is 5% or more and 25% or less, and the steel sheet has a tensile strength of 780 MPa or more and less than 980 MPa.

Steel sheet, member, and methods for manufacturing the same

A high-strength cold rolled steel sheet has a specific composition and a steel structure that is, by volume %, 10%-70% ferrite, 1%-10% retained austenite, 10%-60% bainite, and 2%-50% martensite, the average crystal grain size of the ferrite being no more than 6.0 μm, the average crystal grain size of the retained austenite being no more than 4.0 μm, the average crystal grain size of the bainite being no more than 6.0 μm, and the average crystal grain size of the martensite being no more than 4.0 μm. The concentration ratio of the average concentration of Si to a depth of 10 μm from the surface of the high-strength cold-rolled steel sheet to the average concentration of Si throughout the high-strength cold-rolled steel sheet is, by mass ratio, greater than 1.00 but less than 1.30.

High-strength cold-rolled steel sheet and production method for same

The high-strength thin steel sheet has a chemical composition containing C, Si, Mn, P, S, Al, and N, with the balance being Fe and inevitable impurities, and a complex structure containing ferrite, tempered martensite, and bainite, where a volume fraction of a total of tempered martensite and bainite containing five or more carbides with a particle size of 0.1 μm or more and 1.0 μm or less in a grain with respect to a total of the tempered martensite and the bainite is 85% or more, and C mass % and Mn mass % in a region of 20 μm or less in a thickness direction from a surface of the steel sheet are each 20% or less with respect to C mass % and Mn mass % in a region of 100 μm or more and 200 μm or less from the surface of the steel sheet.

High-strength thin steel sheet and method for manufacturing same

A steel sheet and a member excellent in cold workability, hardenability, and post-quenching surface layer hardness, and methods for manufacturing the steel sheet and the member. The steel sheet has a specified chemical composition and a microstructure containing ferrite and carbides, a ratio of the volume of ferrite and carbides to the volume of the entire microstructure is 90% or more, a ratio of the volume of proeutectoid ferrite to the volume of the entire microstructure is 20% or more and 80% or less, a Mn concentration in the carbides is 0.10 mass % or more and 0.50 mass % or less, and a ratio of the number of carbides with particle diameters of 1 μm or more to the total number of carbides is 30% or more and 60% or less.

Steel sheet and member, and methods for manufacturing same

A high-strength hot rolled steel sheet and a method for manufacturing the high-strength hot rolled steel sheet are disclosed. The high-strength hot rolled steel sheet includes a specific chemical composition, and a steel structure in which a lower bainite phase and/or a tempered martensite phase at 90% or more in terms of a total area fraction is contained as a dominant phase, an average grain size of the dominant phase is 10.0 μm or less, and an amount of Fe in Fe-based precipitates is 0.70% or less in mass %, in which an arithmetic average roughness (Ra) of a surface is 2.50 μm or less, and a tensile strength TS is 1180 MPa or more.

High-strength hot rolled steel sheet and method for manufacturing same

A high-strength steel sheet having a tensile strength of 1,180 MPa or more, and specified chemical composition. The steel sheet includes a steel structure in which an area fraction of martensite having a carbon concentration of more than 0.7×[% C] and less than 1.5×[% C] is 55% or more, an area fraction of tempered martensite having a carbon concentration of 0.7×[% C] or less is 5% or more and 40% or less, a ratio of a carbon concentration in retained austenite to a volume fraction of retained austenite is 0.05 or more and 0.40 or less, and the martensite and the tempered martensite each have an average grain size of 5.3 μm or less, where [% C] represents the content, by mass %, of compositional element C in steel.

A high-carbon hot-rolled steel sheet has a composition containing, on a percent by mass basis, C: 0.10% or more and less than 0.20%, Si: 0.5% or less, Mn: 0.25% to 0.65%, P: 0.03% or less, S: 0.010% or less, sol. Al: 0.10% or less, N: 0.0065% or less, Cr: 0.05% to 0.50%, and B: 0.0005% to 0.005%, the balance being Fe and incidental impurities, the high-carbon hot-rolled steel sheet having a microstructure containing ferrite and cementite, in which the percentage of the number of cementite grains having an equivalent circular diameter of 0.1 &#x3bc;m or less is 12% or less based on the total number of cementite grains, the amount of Cr dissolved in the steel sheet is 0.03% to 0.50%, and the high-carbon hot-rolled steel sheet has a hardness of 73 or less in terms of HRB and a total elongation of 37% or more.

High-carbon hot-rolled steel sheet and method for producing the same

Provided are a hot-rolled steel sheet for coiled tubing and a method for manufacturing the steel sheet. The steel sheet has a yield strength of 480 MPa or more, a tensile strength of 600 MPa or more, a yield-strength difference (&#x394;YS) of 100 MPa or more, where the yield-strength difference is defined as a difference in yield strength between before and after a prestrain-heat treatment performed for simulation of a tube-making process and a stress-relief annealing heat treatment which are currently implemented, and a yield strength of 620 MPa or more after the prestrain-heat treatment.

Hot-rolled steel sheet for coiled tubing and method for manufacturing the same

A hot-rolled steel plate has a predetermined chemical composition and a microstructure. In the microstructure, in a plate thickness 1/2 position, an area fraction of martensite is less than 3%, an area fraction of bainitic ferrite is 95% or greater, the bainitic ferrite has an average grain diameter of 6.0 &#x3bc;m or less, an amount of Nb precipitated as Nb carbonitride is 0.025 mass % or greater, and an amount of Nb precipitated as Nb carbonitride having a grain diameter of 20 nm or greater constitutes 50% or greater of a total mass of the Nb precipitated as Nb carbonitride. The hot-rolled steel plate has a tensile strength of 640 MPa or greater, a yield ratio of 85% or less, a Charpy impact absorbed energy at &#x2212;40&#xb0; C. of 300 J or greater, and a percent ductile fracture (SA value) of 85% or greater as determined by a DWTT test at &#x2212;40&#xb0; C.

Hot-rolled steel plate and method for manufacturing same

A high-carbon cold rolled steel sheet having a specified chemical composition, and a method for manufacturing the same. The method includes forming a hot rolled steel sheet, performing cooling at an average cooling rate of 30&#xb0; C./s or more and 70&#xb0; C./s or less through a temperature range of a finish rolling end temperature to 660&#xb0; C., coiling a hot rolled steel sheet at a temperature of 500&#xb0; C. or more and 660&#xb0; C. or less, and, optionally, pickling the coiled hot rolled steel sheet, and then performing a first box-annealing of holding at an annealing temperature in a temperature range of 650 to 720&#xb0; C., then performing cold rolling at a rolling reduction ratio of 20 to 50%, and then performing a second box-annealing of holding at an annealing temperature in a temperature range of 650 to 720&#xb0; C.

High-carbon cold rolled steel sheet and method for manufacturing same

A high strength steel sheet having a high Young's modulus, the steel sheet having a chemical composition including, by mass %, C: 0.060% or more and 0.150% or less, Si: 0.50% or more and 2.20% or less, Mn: 1.00% or more and 3.00% or less, and one or both of Ti: 0.001% or more and 0.200% or less and Nb: 0.001% or more and 0.200% or less, in which the contents of C, N, S, Ti, and Nb satisfy the equation 500&#x2264;C*&#x2264;1300. The steel sheet has a microstructure including ferrite in an amount of 20% or more and martensite in an amount of 5% or more, in terms of area ratio, such that the average grain size of the ferrite is 20.0 &#x3bc;m or less and the inverse intensity ratio of &#x3b3;-fiber for &#x3b1;-fiber is 1.00 or more in the ferrite and the martensite.

High strength steel sheet having high Young's modulus and method for manufacturing the same

A steel sheet has a microstructure that contains ferrite in an area ratio of 20% or more, martensite in an area ratio of 5% or more, and tempered martensite in an area ratio of 5% or more. The ferrite has a mean grain size of 20.0 &#x3bc;m or less. An inverse intensity ratio of &#x3b3;-fiber to &#x3b1;-fiber in the ferrite is 1.00 or more and an inverse intensity ratio of &#x3b3;-fiber to &#x3b1;-fiber in the martensite and the tempered martensite is 1.00 or more.

High-strength steel sheet and production method therefor

Growing community of inventors

Tokyo, Japan

Takeshi Yokota