Kawasaki Steel Corporation

Jfe Steel Corporation

Toyota Jidosha Kabushiki Kaisha

Kei Sakata

Osamu Furukimi

Toshiyuki Kato

Kazuhiro Seto

Saiji Matsuoka

Takashi Obara

Yoshikazu Kawabata

Tetsuo Shimizu

Susumu Satoh

Kaneharu Okuda

Akio Tosaka

Masahiko Morita

Eiko Yasuhara

Kazunori Osawa

Tetsuya Mega

Susumu Masui

Akio Shinohara

Yoshitsugu Suzuki

Akio Sato

Chiaki Kato

Shunsuke Toyoda

Susumu Okada

Koichi Hashiguchi

Fusao Togashi

Masayuki Sakaguchi

Atsushi Ogino

Tomohiro Inoue

Hiroshi Takahashi

Koji Suzuki

Mitsuo Kimura

Hiroshi Kawaguchi

Yasuhide Ishiguro

Takatoshi Okabe

Yuji Hashimoto

Yoichi Tobiyama

Yoshio Yamazaki

Toshio Ichida

Shusaku Takagi

Nobusuke Kariya

Masatoshi Aratani

Motoaki Itadani

Kazuhito Kenmochi

Takashi Ono

Takaaki Hira

Hideo Kuguminato

Shigeru Umino

Yukio Miyata

Hiroyasu Yokoyama

Minoru Nishida

Masahito Tanaka

Shinobu Okano

Yasuo Nishida

Makio Gunji

Yoichi Tominaga

Kazuya Miura

Yuji Sugimoto

Hiroyuki Shirosawa

Tetsuro Sawaki

Yasue Koyama

Nobutaka Kurosawa

Muneyoshi Murakami

Tateo Higashino

Kouichi Kaneko

Hidetaka Kawabe

Masayoshi Ishida

Sinjiro Kaneko

Noriyuki Katayama

Tetsuo Mochida

Tomohisa Oonishi

Takashi Kobayashi

Yoshifumi Fujioka

Syusaku Takagi

Motoaki Egi

A method for manufacturing an electric resistance welded steel tube including: forming a steel tube material into an almost cylindrical open pipe, the steel tube material being a steel sheet wherein Ti and N satisfy (N/14)&#x3c;(Ti/47.9); forming an electric resistance welded steel tube by bonding ends of the open pipe to each other by induction resistance welding with heat input controlled so that the bond width is 30 to 65 &#x3bc;m; heating the electric resistance welded steel tube to a temperature equal to or higher than the Actransformation temperature; and diameter-reducing rolling the heated electric resistance welded steel tube with rolling reduction expressed by an outer diameter ratio greater than (1&#x2212;25/the bond width before diameter-reducing rolling (&#x3bc;m))&#xd7;100% such that the bond width is 25 &#x3bc;m or less.

Method for electric resistance welded steel tube

A method of efficiently manufacturing electric resistance welding pipes having excellent characterization of welded seams is provided, by which each lateral edge of a rounded strip immediately before electric resistance welding is securely shaped with desired tapering flexibly in response to change in strip thickness, so that welding quality may be kept to be excellent. A method of manufacturing electric resistance welding pipes, in which a strip is subjected to forming, then edges thereof are formed to substantially face each other, and then the edges are subjected to electric resistance welding to form a pipe, wherein an edge and an edge opposed thereto at one of an upper-surface side and a lower-surface side of the strip are shaped with tapering before the forming by means of cutting or shaving, or finpass forming.

Method of manufacturing electric resistance welding pipes having excellent characterization of welded seams

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.

Steel for structural part of automobile and method for producing the same

A seamless expandable oil country tubular article, which has a superior pipe expansion property in a expanding process at an expand ratio of more than about 30% although having a high strength such as a tensile strength (TS) of about 600 MPa or more, and a manufacturing method thereof, the seamless expandable oil country tubular goods being in an as-rolled state or being processed, optionally necessary, by inexpensive nonthermal-refining type heat treatment.

Seamless expandable oil country tubular goods and manufacturing method thereof

A steel pipe blank having a composition containing 0.5% or less C and 85% or more Fe in terms of mass percent is heated, and stretch-reducing is then performed so that the diameter decrease ratio is 15% or more and the rolling finishing temperature is (the Artransformation point&#x2212;10)&#xb0; C. or lower. Consequently, a structure in which the ratio of X-ray diffraction intensity obtained from the plane in which the &#x3c;100&#x3e; direction of crystal grains is preferentially oriented parallel to the circumference direction and the &#x3c;011&#x3e; direction of crystal grains is preferentially oriented parallel to the rolling direction of the steel pipe to that obtained for a three-dimensionally randomly oriented sample is 3.0 or more is formed, and the r-value is increased, thereby improving the magnetic properties of the steel pipe.

Steel pipe with good magnetic properties and method of producing the same

A high-tensile strength welded steel tube has excellent formability and torsional fatigue endurance after being formed into cross-sectional shape and then stress-relief annealed. A steel material used has a composition which contains C, Si, Al, 1.01% to 1.99% Mn, 0.041% to 0.150% Ti, 0.017% to 0.150% Nb, P, S, N, and O such that the sum of the content of Ti and that of Nb is 0.08% or more, the content of each of C, Si, and Al being within an appropriate range, the content of each of P, S, N, and O being adjusted to a predetermined value or less.

High-tensile strength welded steel tube for structural parts of automobiles and method of producing the same

The present invention relates to a high strength hot rolled steel sheet consisting of 0.04 to 0.15% C, 1.5% or less Si, 0.5 to 1.6% Mn, 0.04% or less P, 0.005% or less S, 0.04% or less Al, 0.03 to 0.15% Ti, 0.03 to 0.5% Mo, by mass, and balance of Fe and inevitable impurities, and having a microstructure consisting of ferrite containing precipitates, second phase of bainite and/or martensite, and other phase, wherein the percentage of the ferrite containing precipitates is 40 to 95%, and the percentage of the other phase is 5% or less. For example, the high strength hot rolled steel sheet having a thickness of 1.4 mm shows a tensile strength of 780 MPa or higher, an elongation of 22% or higher elongation, and a hole expansion ratio of 60% or higher, thus the steel sheet is suitable for reinforcing members automobile cabin and crash worthiness members of automobile.

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

This disclosure proposes a high-strength hot rolled steel sheet having excellent anti-die-galling property and anti-fatigue property, in which the steel sheet has a composition including C: not less than 0.02 mass % but not more than 0.2 mass %, Si: not less than 0.2 mass % but not more than 1.2 mass %, Mn: not less than 1.0 mass % but not more than 3.0 mass %, Mo: not less than 0.1 mass % but not more than 1.0 mass %, Al: not less than 0.01 mass % but not more than 0.1 mass %, P: not more than 0.03 mass % S: not more than 0.01 mass % and the remainder being substantially Fe and inevitable impurities, and has a steel microstructure containing not less than 55 vol % of ferrite and not less than 10 vol % but not more than 40 vol % of martensite provided that a total of both is not less than 95 vol %, and a ratio ds/dc of an average crystal grain size ds of the ferrite in a surface layer portion of the steel sheet to an average crystal grain size dc of the ferrite in a center portion of the steel sheet is 0.3&#x3c;ds/dc&#x2266;1.0 and a surface roughness is not more than 1.5 &#x3bc;m as an arithmetic mean roughness Ra, as well as a method of producing the same.

High tensile hot-rolled steel sheet excellent in resistance to scuff on mold and in fatigue characteristics

The present invention provides a steel sheet having a chemical composition comprising 0.15% or less C, 2.0% or less Si, 3.0% or less Mn, P, S, A1 and N in adjusted amounts, from 0.5 to 3.0% Cu, or one or more of Cr, Mo and W in a total amount of 2.0% or less, and having a composite structure comprising ferrite and martensite having an area ratio of 2% or more. The steel sheet is in the form of a high-strength hot-rolled steel sheet, a high-strength cold-rolled steel sheet, or a hot-dip galvanized steel sheet. There is thus available a steel sheet excellent in press-formability and in strain age hardening property as represented by a &#x394;TS of 80 MPa or more.

Hot-dip galvanized hot-rolled and cold-rolled steel sheets excellent in strain age hardening property

According to the invention, a high-strength hot rolled steel sheet having an excellent shape fixability as hot-rolled and an excellent fatigue durability after the forming, excellent weldability and phosphatability and a tensile strength of not less than 590 MPa level can be obtained by comprising C: not less than 0.02 mass % but not more than 0.2 mass %, Si: not less than 0.5 mass % but not more than 2.0 mass %, Mn: not less than 1.0 mass % but not more than 3.0 mass %, Al: not less than 0.01 mass % but not more than 0.1 mass %, N: not less than 0.002 mass % but not more than 0.006 mass %, P: not more than 0.03 mass %, S: not more than 0.01 mass % and solid-soluted (C+N): not less than 0.0010 mass % and the reminder being Fe and inevitable impurities, and having a steel structure that a primary phase is ferrite and a secondary phase is martensite phase of 5-30 % at a volume ratio and a total of both is not less than 95 % as a volume ratio, and further having an average crystal grain size of ferrite of not more than 8 &#x3bc;m.

High tensile hot rolled steel sheet excellent in shape freezing property and endurance fatigue characteristics after forming

A high tensile strength hot-rolled steel sheet having superior strain aging hardenability, which has high formability and stable quality characteristics, and in which satisfactory strength is obtained when the steel sheet is formed into automotive components, thus enabling the reduction in weight of automobile bodies is provided. Specifically, a method for producing a high tensile strength hot-rolled steel sheet having superior strain aging hardenability with a BH of 80 MPa or more, a &#x394;TS of 40 MPa or more, and a tensile strength of 440 MPa or more includes the steps of heating a steel slab to 1,000&#xb0; C. or more, the steel slab containing, in percent by mass 0.15% or less of C, 2.0% or less of Si, 3.0% or less of Mn, 0.08% or less of P, 0.02% or less of S, 0.02% or less of Al, 0.0050% to 0.0250% of N, and optionally 0.1% or less in total of at least one of more than 0.02% to 0.1% of Nb and more than 0.02% to 0.1% of V, the ratio N (mass %)/Al (mass %) being 0.3 or more, rough-rolling the steel slab to form a sheet bar; finish-rolling the sheet bar at a finishing temperature of 800&#xb0; C. or more; cooling at a cooling rate of 20&#xb0; C. to 40&#xb0; C./s or more within 0.5 second after the finish-rolling; and coiling at a temperature of 650&#xb0; C. to 450&#xb0; C. or less.

High tensile hot-rolled steel sheet having excellent strain aging hardening properties and method for producing the same

A steel sheet composition contains appropriate amounts of C, Si, Mn, P, S, Al and N and 0.5 to 3.0% Cu. A composite structure of the steel sheet has a ferrite phase or a ferrite phase and a tempered martensite phase as a primary phase, and a secondary phase containing retained austenite in a volume ratio of not less than 1%. In place of the Cu, at least one of Mo, Cr, and W may be contained in a total amount of not more than 2.0%. This composition is useful in production of a high-ductility hot-rolled steel sheet, a high-ductility cold-rolled steel sheet and a high-ductility hot-dip galvanized steel sheet having excellent press formability and excellent stain age hardenability as represented by a &Dgr;TS of not less than 80 MPa, in which the tensile strength increases remarkably through a heat treatment at a relatively low temperature after press forming.

High-ductility steel sheet excellent in press formability and strain age hardenability, and method for manufacturing the same

The present invention provides a steel sheet having a chemical composition comprising 0.15% or less C, 2.0% or less Si, 3.0% or less Mn, P, S, Al and N in adjusted amounts, from 0.5 to 3.0% Cu, or one or more of Cr, Mo and W in a total amount of 2.0% or less, and having a composite structure comprising ferrite and martensite having an area ratio of 2% or more. The steel sheet is in the form of a high-strength hot-rolled steel sheet, a high-strength cold-rolled steel sheet, or a hot-dip galvanized steel sheet. There is thus available a steel sheet excellent in press-formability and in strain age hardening property as represented by a &Dgr;TS of 80 MPa or more.

Methods of manufacturing hot-dip galvanized hot-rolled and cold-rolled steel sheets excellent in strain age hardening property

The present invention provides a high tensile cold-rolled steel sheet having superior ductility, strain age-hardening characteristics, and crash resistance properties, and also provides a manufacturing method therefor. As a particular means, a thin cold-rolled steel sheet containing 0.05% to 0.30% of C, 0.4% to 2.0% of Si, 0.7% to 3.0% of Mn, 0.08% or less of P, 0.02% or less of Al, and 0.0050% to 0.0250% of N on a mass % basis is manufactured in which N/Al is 0.3 or more. This thin cold-rolled steel sheet is heated to a temperature between (an Ac transformation point) and (an Ac transformation point&plus;50&deg; C.), is cooled at a cooling rate of 5 to 150&deg; C./second in the range of at least 600 to 500&deg; C., and is held in the temperature range of 350 to 500&deg; C. This steel sheet has superior ductility, strain age-hardening characteristics having a &Dgr;TS of 50 MPa or more, and crash resistance properties.

High tensile cold-rolled steel sheet excellent in ductility and in strain aging hardening properties, and method for producing the same

Hot rolled steel plate and cold rolled steel plate being excellent in strain aging hardening characteristics

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Chiba, Japan

Kei Sakata