Kawasaki Steel Corporation

Jfe Steel Corporation

Kazunori Osawa

Shinjiro Kaneko

Osamu Furukimi

Susumu Satoh

Chikara Kami

Kei Sakata

Kaneharu Okuda

Akio Tosaka

Hideo Abe

Takashi Ishikawa

Takuya Yamazaki

Yoshitsugu Suzuki

Takashi Obara

Toshiyuki Kato

Keiji Nishimura

Akio Shinohara

Yoichi Tobiyama

Masahiko Morita

Chiaki Kato

Hideo Kuguminato

Minoru Nishida

The present invention presents a high tensile strength cold rolled steel sheet having excellent formability, impact resistance and strain age hardening characteristics, and the production thereof. As a specific means, a slab having a composition which contains, by mass %, 0.15% or less of C, 0.02% or less of Al, and 0.0050 to 0.0250% of N at N/Al of 0.3 or higher, and has N in a solid solution state at 0.0010% or more, is first hot rolled at the finish rolling delivery-side temperature of 800&#xb0; C. or above, and is subsequently coiled at the coiling temperature of 750&#xb0; C. or below to prepare a hot rolled plate. Then, after cold rolling, the hot rolled plate is continuously cooled at a temperature from the recrystallization temperature to 900&#xb0; C. at a holding time of 10 to 120 seconds, and is cooled by primary cooling in which the hot rolled plate is cooled to 500&#xb0; C. or below at a cooling rate of 10 to 300&#xb0; C./s, and furthermore if necessary, by secondary cooling in which a residence time is 300 seconds or less in a temperature range of the primary cooling stopping temperature or below and 350&#xb0; C. or higher. Provided is a steel sheet containing a ferritic phase having an average crystal grain size of 10 &#x3bc;m or less at an area ratio of 50% or more, and if necessary, a martensitic phase at an area ratio of 3% or more as a second phase.

High tensile strength cold rolled steel sheet having excellent strain age hardening characteristics and the production thereof

The present invention presents a high tensile strength cold rolled steel sheet having excellent formability, impact resistance and strain age hardening characteristics, and the production thereof. As a specific means, a slab having a composition which contains, by mass %, 0.15% or less of C, 0.02% or less of Al, and 0.0050 to 0.0250% of N at N/Al of 0.3 or higher, and has N in a solid solution state at 0.0010% or more, is first hot rolled at the finish rolling delivery-side temperature of 800&deg; C. or above, and is subsequently coiled at the coiling temperature of 750&deg; C. or below to prepare a hot rolled plate. Then, after cold rolling, the hot rolled plate is continuously cooled at a temperature from the recrystallization temperature to 900&deg; C. at a holding time of 10 to 120 seconds, and is cooled by primary cooling in which the hot rolled plate is cooled to 500&deg; C. or below at a cooling rate of 10 to 300&deg; C./s, and furthermore if necessary, by secondary cooling in which a residence time is 300 seconds or less in a temperature range of the primary cooling stopping temperature or below and 350&deg; C. or higher. Provided is a steel sheet containing a ferritic phase having an average crystal grain size of 10 &mgr;m or less at an area ratio of 50% or more, and if necessary, a martensitic phase at an area ratio of 3% or more as a second phase.

High tensile cold-rolled steel sheet having excellent strain aging hardening properties

Method for producing hot-dip galvanized steel sheet having high strength and also being excellent in formability and galvanizing property

The present invention provides a high strength thin excellent workability and galvanizability, having a composition comprising from 0.01 to 0.20 wt. % C, up to 1.0 wt. % Si, from 1.0 to 3.0 wt. % Mn, up to 0.10 wt. % P, up to 0.05 wt. % S, up to 0.10 wt. % Al, up to 0.010 wt. % N, up to 1.0 wt. % Cr, from 0.001 to 1.00 wt. % Mo, and the balance Fe and incidental impurities, wherein a band structure comprising a secondary phase has a thickness satisfying the relation Tb/T&lE;0.005 (where, Tb: average thickness of the band structure in the thickness direction of steel sheet; T: steel sheet thickness), and a manufacturing method thereof, and a manufacturing method of a high strength hot-dip galvanized steel sheet or a high strength galvannealed steel sheet applying hot-dip galvanizing or further galvannealing, and giving an excellent workability, a high tensile strength, and excellent galvanizability, coating adhesion and corrosion resistance.

High strength thin steel sheet, high strength alloyed hot-dip zinc-coated steel sheet, and method for producing them

Cold rolled steel sheet with excellent deep drawability and excellent anti-aging properties, and manufacturing method. The cold rolled steel sheet comprises about C: above 0.015 to 0.150 wt %, Si: 1.0 wt % or less, Mn: 0.01 to 1.50 wt %, P: 0.10 wt % or less, S: 0.003 to 0.050 wt %, Al: 0.001 to below 0.010 wt %, N: 0.0001 to 0.0050 wt %, Ti: 0.001 wt % or more and Ti(wt %)/[1.5.times.S(wt %)+3.4.times.N(wt %)].ltoreq.about 1.0 and B: about 0.0001 to 0.0050 wt %, during annealing, grain growth is improved; Ti is added to form a nitride and a sulfide to avoid precipitation of fine TiC; B is added to precipitate Boron precipitates (Fe.sub.2 B, Fex(C,B)y) in a cooling the hot rolled steel sheet and in cooling step during annealing after cold rolling; a spherical cementite is precipitated and grown in which the Boron series precipitate is a precipitation site.

Cold rolled steel sheet and method of making

A steel sheet for porcelain enameling having improved press formability and enameling properties comprises particular amounts of C, Mn, B, Cu, Al, O, N, and P or further Ti and Nb and the balance being Fe and inevitable impurities and is produced by hot rolling a slab of steel having a chemical composition as mentioned above as a starting material, cold rolling the resulting hot rolled sheet at a reduction of not less than 70%, and then subjecting the resulting cold rolled sheet to a continuous annealing at a heating temperature of not lower than 800.degree. C. but not higher than A.sub.c3 transformation point.

Steel sheets for procelain enameling and method of producing the same

Method of producing steel sheets for porcelain enameling having improved

Method of producing steel sheets for porcelain enameling and the same

Disclosed herein is a method of manufacturing a base steel sheet, which method comprises combined steps of: not rolling a steel slab containing not more than 0.0070% by weight of C (hereinafter referred to briefly as '%'), not more than 0.1% of Si, not more than 0.5% of Mn, 0.010 to 0.080% of Al, not more than 0.0050% of N, not more than 0.030% of S provided that the ratio of Mn/S is not less than 10, and not more than 0.030% of P while the hot rolling being terminated at a finish temperature of not less than 800.degree. C.; cold rolling thus obtained hot rolled steel sheet in an ordinary manner; continuously annealing the cold rolled steel sheet in which heating is done up to a temperature from a recrystallization temperature to 800.degree. C., followed by cooling; and then temper rolling the annealing steel sheet at a reduction of not less than 7% by using two or more stand rolling mill, whereby the thus obtained base sheet, to be surface-treated may be utilized for a tinplate or a tin free steel in which no stretcher strain is formed even after baking treatment.

Production of a base steel sheet to be surface-treated which is to

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Okayama, Japan

Kazunori Osawa