Jfe Steel Corporation

Toyota Jidosha Kabushiki Kaisha

Shunsuke Toyoda

Sota Goto

Takatoshi Okabe

Akio Sato

Taro Kizu

Kazuhiko Yamazaki

Tomohiro Inoue

Kei Sakata

Yuji Hashimoto

Yoshikazu Kawabata

Hiroshi Nakata

Akihide Matsumoto

Noriaki Moriyasu

Akimasa Kido

Tetsushi Tadani

Atsushi Yonemoto

Takashi Kobayashi

Koji Suzuki

Hiroshi Kawaguchi

Takaaki Tanaka

Masatoshi Aratani

Yuka Miyamoto

Kinya Nakagawa

Yutaka Matsui

Osamu Sonobe

Shuji Kawamura

Kenichi Iwazaki

Yasuhiro Sakurai

Hiromichi Hori

Makio Gunji

Ichiro Sugimoto

Sumio Kaiho

Tetsuro Sawaki

Yukihiko Okazaki

Kentaro Irisa

Satoru Yabumoto

Motoharu Egi

Kouichi Kaneko

There are provided a high-strength hot-rolled steel sheet having a tensile strength of 980 MPa or more and a production method therefor. The high-strength hot-rolled steel sheet has a predetermined component composition and a microstructure containing 75.0% or more by area and less than 97.0% by area of a primary phase composed of an upper bainite phase, the primary phase having an average grain size of 12.0 &#x3bc;m or less, and more than 3.0% by area and 25.0% or less by area of a secondary phase that is a structure composed of one or two of a lower bainite phase and/or a tempered martensite phase, and a martensite phase, in which the number density of grains of the secondary phase having an equivalent circular diameter of 0.5 &#x3bc;m or more is 150,000 grains/mmor less, and the steel sheet has an arithmetic mean surface roughness of 2.00 &#x3bc;m or less.

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

A high-strength hot-rolled steel sheet that has excellent punching workability and hole expandability, and a method for manufacturing the same. The hot-rolled steel sheet has a tensile strength of 980 MPa or more. The hot-rolled steel sheet has a chemical composition containing C, Si, Mn, P, S, Al, N, Ti, Cr, and B, and has a microstructure including a bainite phase having an area ratio of 85% or more as a main phase, and a martensite phase or martensite-austenite constituent having an area ratio of 15% or less as a second phase, the balance being a ferrite phase. The second phase has an average grain diameter of 3.0 &#x3bc;m or less, prior-austenite grains have an average aspect ratio of 1.3 or more and 5.0 or less, and recrystallized prior-austenite grains have an area ratio of 15% or less relative to non-recrystallized prior-austenite grains.

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

There is provided an electric resistance welded steel tube having a yield strength of 896 MPa or more, and excellent low-cycle fatigue resistance, for coiled tubing without performing whole-tube quenching treatment and reheating-tempering treatment after performing electric resistance welding and a method for manufacturing the same. The steel tube includes, by mass %, C, Si, Mn, P, S, Al, Cr, Cu, Ni, Mo, Nb, V, Ti, and N at a specific content. The steel tube has a microstructure that contains 2% to 10% retained austenite and 20% or less martensite on a volume fraction basis, and the remainder being bainite. The yield strength is set to 896 MPa or more and the uniform elongation is set to 9.0% or more.

Electric resistance welded steel tube for coiled tubing and method for manufacturing the same

Provided are a high-carbon hot-rolled steel sheet with excellent formability and hardenability and a method for manufacturing the same. The high-carbon hot-rolled steel sheet has a composition containing, on a mass basis, C: 0.10% to 0.33%, Si: 0.15% to 0.35%, Mn: 0.5% to 0.9%, P: 0.03% or less, S: 0.010% or less, sol. Al: 0.10% or less, N: 0.0065% or less, and Cr: 0.90% to 1.5%, the remainder being Fe and inevitable impurities, has a microstructure containing ferrite and cementite, a cementite density being 0.25 grains/&#x3bc;mor less, and has a hardness of 110 HV to 160 HV and a total elongation of 40% or more.

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

There is provided a hot-rolled steel sheet suitable for manufacturing an electric resistance welded steel tube, having workability necessary for roll forming and high yield strength, for coiled tubing without performing whole-tube quenching treatment and reheating-tempering treatment after electric resistance welding. The steel sheet includes, by mass %, C, Si, Mn, P, S, Al, Cr, Cu, Ni, Mo, Nb, V, Ti, and N contained at a specific content. The steel sheet has a microstructure containing 3% to 20% martensite and 10% or less retained austenite on a volume fraction basis, the remainder being bainite. The yield strength is set to 600 MPa or more, the tensile strength is set to 950 MPa or more, and the uniform elongation is set to 7.0% or more.

Hot-rolled steel sheet for coiled tubing

A steel member, a hot-rolled steel sheet to be used as a material thereof, and production methods therefor are provided. A steel member contains 0.010% to 0.120% Ti, in which 0.005% or more of Ti is precipitated as a precipitate having a particle size of 20 nm or less in the microstructure. A hot-rolled steel sheet for the steel member contains 0.010% to 0.120% Ti, in which 0.005% or more of Ti is present as dissolved Ti in the microstructure. A method for producing the steel member includes subjecting a hot-rolled steel sheet to forming processing and then performing heat treatment including heating to a temperature of higher than 550&#xb0; C. and 1,050&#xb0; C. or lower and then cooling at an average cooling rate of 10&#xb0; C./s or more in the temperature range of 550&#xb0; C. to 400&#xb0; C.

Steel member and production method therefor

Provided is a high-strength hot-rolled coated steel sheet with excellent formability, A high-strength hot-rolled coated steel sheet has a constituent composition containing, in a mass percent, C: 0.03% to 0.15%, Si: 0.4% or less, Mn: 1.2% to 1.9%, Ti: 0.05% to 0.25%, B: 0.0005% to 0.0050%, P: 0.03% or less, S: 0.005% or less, Al: 0.005% to 0.4%, and N: 0.01% or less, the balance being Fe and incidental impurities. The total area fraction of one or more of ferrite and tempered bainite is 90% or more. The steel sheet has a structure in which the volume fraction of Ti carbides having particle sizes of 20 nm or less is 0.05 vol % or more.

High-strength hot-rolled coated steel sheet

A high strength steel sheet having high strength such as a tensile strength of 780 MPa or more and having excellent blanking workability and stretch flangeability and a manufacturing method therefor are provided. A high strength steel sheet comprises: a chemical composition containing, in mass %, C: 0.05% to 0.30%, Si: 0.6% to 2.0%, Mn: 1.3% to 3.0%, P: 0.10% or less, S: 0.030% or less, Al: 2.0% or less, N: 0.010% or less, and one or more of Ti, Nb, and V: 0.01% to 1.0% each, with a balance being Fe and incidental impurities; a ferrite microstructure of 50% or more in area ratio; an amount of precipitated Fe of 0.04 mass % or more; and a precipitate with a particle size of less than 20 nm, wherein C* and C*satisfy specific conditions.

High strength steel sheet and manufacturing method therefor

A resistance welded steel pipe is provided. A hot-rolled steel sheet having a composition containing, in mass %, C: 0.025 to 0.168%, Si: 0.10 to 0.30%, Mn: 0.60 to 1.90%, and one or at least two selected from Ca, Nb, V, and Ti such that Pcm is 0.20 or less is subjected to continuous cold roll forming to obtain a pipe-shaped body. Tapered grooves are formed in the steel sheet such that the ratio of the tapered portions to the wall thickness of the steel sheet is 10 to 80%. Then end surfaces of the pipe-shaped body are butted against each other and subjected to electric resistance welding. Ultrasonic waves are transmitted toward the electric resistance weld surface such that a beam width is within the range of 0.1 to 4.0 mm, and the reflected waves are used for ultrasonic flaw detection using an ultrasonic flaw detector.

Electric resistance welded steel pipe and manufacturing method therefor

This disclosure provides a predetermined composition, where a conversion value C* of total carbon contents in Ti, Nb and V precipitates whose grain sizes are less than 20 nm is 0.010 mass % to 0.100 mass %, Fe content in Fe precipitates is 0.03 mass % to 0.50 mass %, and an average grain size of ferrite grains whose grain sizes are top 5 % large in ferrite grain size distribution of rolling direction cross section is (4000/TS)&#x3bc;m or less, the TS indicating tensile strength in unit of MPa.

High-strength thin steel sheet and method for manufacturing the same

By using, as a raw material, a thick hot-rolled steel sheet having a chemical composition containing, by mass %, C: 0.02% or more and 0.10% or less, Si: 0.05% or more and 0.30% or less, Mn: 0.80% or more and 2.00% or less, and Nb: 0.010% or more and 0.100% or less and satisfying the condition that a carbon equivalent Ceq is 0.25% or more and 0.50% or less, a microstructure including a bainitic ferrite phase and/or a bainite phase, a high strength of 52 ksi or more in terms of yield strength and a high toughness of &#x2212;45&#xb0; C. or lower in terms of fracture transition temperature vTrs, and satisfying the condition that the ratio of the average crystal grain size of the coarsest-grain portion to the average crystal grain size of the finest-grain portion is 2.0 or less in every portion in the wall thickness direction is obtained.

Heavy wall electric resistance welded steel pipe for line pipe and method for manufacturing the same

Electric resistance welded steel pipes or steel tubes with a tensile property TS of not less than 434 MPa which have electric resistance welded parts exhibiting both excellent HIC resistance and excellent low-temperature toughness, and methods for manufacturing such steel pipes or steel tubes.

Electric resistance welded steel pipe or steel tube having excellent HIC resistance and low-temperature toughness in electric resistance welded part, and method for manufacturing the same

A high-strength thick-walled electric resistance welded steel pipe has excellent low-temperature toughness and excellent HIC resistance and a yield strength of 400 MPa or more. The steel has a chemical composition consisting of C: 0.025% to 0.084%, Si: 0.10% to 0.30%, Mn: 0.70% to 1.80%, controlled amounts of P, S, Al, N, and O, Nb: 0.001% to 0.065%, V: 0.001% to 0.065%, Ti: 0.001% to 0.033%, and Ca: 0.0001% to 0.0035% on a mass percent basis and the remainder being Fe and incidental impurities, and satisfies Pcm of 0.20 or less.

High-strength thick-walled electric resistance welded steel pipe having excellent low-temperature toughness and method of manufacturing the same

A high strength electric resistance welded steel pipe has a yield strength of 450 MPa or more and excellent resistance to softening for a long period in an intermediate temperature range and a method of manufacturing the steel pipe are provided. The steel pipe has a chemical composition containing, by mass%, C: 0.026% or more and 0.084% or less, Si: 0.10% or more and 0.30% or less, Mn: 0.70% or more and 1.90% or less, Al: 0.01% or more and 0.10% or less, Nb: 0.001% or more and 0.070% or less, V: 0.001% or more and 0.065% or less, Ti: 0.001% or more and 0.033% or less, Ca: 0.0001% or more and 0.0035% or less, in which the condition that Pcm is 0.20 or less is satisfied.

High-strength electric-resistance-welded steel pipe of excellent long-term softening resistance in intermediate temperature ranges

A steel having excellent formability, fatigue endurance after quenching, low temperature toughness, resistance for hydrogen embrittlement, and corrosion fatigue endurance. A method includes heating a steel slab at 1160&#xb0; C. to 1320&#xb0; C., hot-finish-rolling the steel slab at a finisher delivery temperature of 750&#xb0; C. to 980&#xb0; C., and then coiling the hot-rolled steel at a coiling temperature of 560&#xb0; C. to 740&#xb0; C. after slow cooling for a time of 2 seconds or more to produce a hot-rolled steel strip having a structure in which the ferrite grain diameter df corresponding to a circle is 1.1 &#x3bc;m to less than 1.2 &#x3bc;m and the ferrite volume fraction Vf is 30% to 98%, the steel slab containing 0.18 to 0.29% of C, 0.06 to 0.45% of Si, 0.91 to 1.85% of Mn, 0.019% or less of P, 0.0029% or less of S, 0.015 to 0.075% of sol. Al, 0.0049% or less of N, 0.0049% or less of O, 0.0001 to 0.0029% of B, 0.001 to 0.019% of Nb, 0.001 to 0.029% of Ti, 0.001 to 0.195% of Cr, and 0.001 to 0.195% of Mo so that the carbon equivalent Ceq satisfies a value of 0.4 to less than 0.58, and the total x of multiplying factors including that for B according to Grossmann satisfies a value of 1.2 to less than 1.7.

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Tokyo, Japan

Shunsuke Toyoda