Nippon Steel Corporation

Nippon Steel & Sumitomo Metal Corporation

Sony Corporation

Atsushi Itami

Yasuharu Sakuma

Kazuo Koyama

Nobuhiko Matsuzu

Tatsuo Yokoi

Naoki Yoshinaga

Shunji Hiwatashi

Akio Saito

Naoki Maruyama

Takeshi Kubota

Masafumi Azuma

Kaoru Kawasaki

Kazuhiko Honda

Hiroaki Kato

Satoru Tanaka

Atsushi Seto

Teruo Takeuchi

Hiroshi Katoh

Hiroyuki Tanahashi

Tetsuo Nishiyama

Kohsaku Ushioda

Masaharu Kameda

Yujiro Miyauchi

Shiro Fujii

Chohachi Sato

Taketoshi Taira

Makoto Tezuka

Takahito Watanabe

Shunji c/o Nippon Steel Corporation Hiwatashi

Naoki c/o Nippon Steel Corporation Yoshinaga

Yasuharu c/o Nippon Steel Corporation Sakuma

A hot rolled steel sheet consisting of, in mass %, C: 0.05% to 0.15%, Si: 0% to 0.2%, Al: 0.5% to 3.0%, Mn: 1.2% to 2.5%, P: 0.1% or less, S: 0.01% or less, N: 0.007% or less, Ti: 0.03% to 0.10%, Nb: 0.008% to 0.06%, V: 0% to 0.12%, one or more of Cr, Cu, Ni, and Mo: 0% to 2.0% in total, B: 0% to 0.005%, one or more of Ca, Mg, La, and Ce: 0% to 0.01% in total, total amount of Si and Al: 0.8&#xd7;(Mn&#x2212;1)% or more, total amount of Ti and Nb: 0.04% to 0.14%, and the balance: Fe and impurities. In a structure of steel, a total area ratio of martensite and retained austenite is 3% to 20%, an area ratio of ferrite is 50% to 96%, and an area ratio of pearlite is 3% or less. In a superficial layer part, the thickness in a sheet thickness direction of a region in which a network-like oxide is present is less than 0.5 &#x3bc;m, and a maximum tensile strength is 720 MPa or more.

Hot rolled steel sheet and method for manufacturing the same

High yield ratio high-strength hot rolled thin steel sheet superior in weldability and ductility comprising, by mass %, C: over 0.030 to less than 0.10%, Si: 0.30 to 0.80%, Mn: 1.7 to 3.2%, P: 0.001 to 0.02%, S: 0.0001 to 0.006%, Al: 0.060% or less, N: 0.0001 to 0.0070%, containing further Ti: 0.01 to 0.055%, Nb: 0.012 to 0.055%, Mo: 0.07 to 0.55%, B: 0.0005 to 0.0040%, and simultaneously satisfying 1.1&#x2266;14&#xd7;Ti(%)+20&#xd7;Nb(%)+3&#xd7;Mo(%)+300&#xd7;B(%)&#x2266;3.7, the balance comprised of iron and unavoidable impurities, and having a yield ratio of 0.64 to less than 0.92, a TS&#xd7;Elof 3320 or more, an YR&#xd7;TS&#xd7;Elof 2320 or more, and a maximum tensile strength (TS) of 780 MPa or more.

High yield ratio and high-strength thin steel sheet superior in weldability and ductility, high-yield ratio high-strength hot-dip galvanized thin steel sheet, high-yield ratio high-strength hot-dip galvannealed thin steel sheet, and methods of production of same

High yield ratio high-strength thin steel sheet superior in weldability and ductility characterized by: being comprised of steel containing, by mass %, C: over 0.030 to less than 0.10%, Si: 0.30 to 0.80%, Mn: 1.7 to 3.2%, P: 0.001 to 0.02%, S: 0.0001 to 0.006%, Al: 0.060% or less, N: 0.0001 to 0.0070%, containing further Ti: 0.01 to 0.055%, Nb: 0.012 to 0.055%, Mo: 0.07 to 0.55%, B: 0.0005 to 0.0040%, and simultaneously satisfying 1.1 &#x2266;14&#xd7;Ti(%)+20&#xd7;Nb(%)+3&#xd7;Mo(%)+300&#xd7;B(%)&#x2266;3.7, the balance comprised or iron and unavoidable impurities, and having a yield ratio of 0.64 to less than 0.92, a TS&#xd7;E1of 3320 or more, an YR&#xd7;TS&#xd7;ELof 2320 or more, and a maximum tensile strength (TS) of 780 MPa or more.

High-yield-ratio and high-strength thin steel sheet superior in weldability and ductility, high-yield-ratio high-strength hot-dip galvanized thin steel sheet, high-yield ratio high-strength hot-dip galvannealed thin steel sheet, and methods of production of same

Galvannealed steel sheet simultaneously able to achieve excellent workability and high strength and a method of production of the same are provided as an objective, in particular high strength galvannealed steel sheet excellent in workability, comprising high strength steel sheet containing, by mass %, C: 0.05 to 0.15%, Si: 0.3 to 2.0%, Mn: 1.0 to 2.8%, P: 0.03% or less, S: 0.02% or less, Al: 0.005 to 0.5%, and N: 0.0060% or less and a balance of Fe and unavoidable impurities, where, when % C, % Si, and % Mn respectively represent the C, Si, and Mn contents, (% Mn)/(% C)&#x2267;12 and (% Si)/(% C)&#x2267;4 being satisfied, on the surface of which having a galvannealed layer containing Al: 0.05 to 0.5 mass % and Fe: 5 to 15 mass % and a balance of Zn and unavoidable impurities, said steel sheet satisfying a relationship of tensile strength F (MPa) and elongation L (%) of L&#x2267;52&#x2212;0.035&#xd7;F.

High strength galvannealed steel sheet excellent in workability and a method of production of the same

Provided are a high strength cold rolled steel sheet and a high strength plated steel sheet possessing improved geomagnetic shielding properties, that is, having a high relative permeability in a d.c. magnetic field around 0.3 Oe, a process for producing the same, and an explosion-proof band or an outer magnetic shielding material, for television cathode-ray tubes, using the steel sheet. An ultra low carbon steel, which has a carbon content of not more than 0.0060% and has been subjected to solid solution strengthening utilizing silicon and magnesium without relying upon precipitation strengthening, is deoxidized with silicon so that aluminum is substantially absent in the steel. Alternatively, when the ultra low carbon steel is deoxidized with aluminum, boron is added to inhibit the precipitation of AlN. Next, the deoxidized steel is finish rolled at 750 to 980.degree. C., cold rolled with a reduction ratio of 60 to 90%, and then annealed in the temperature range of 750.degree. C. to the Ac.sub.3 point in a continuous annealing equipment or an in-line annealing type continuous galvanizing equipment to bring the ferrite grain diameter in the metallographic structure to 10 to 200 .mu.m.

High-strength cold rolled steel sheet and high-strength plated steel

Ultra low carbon, cold rolled steel sheet and galvanized steel sheet

A process for producing a cold-rolled high strength steel sheet having an excellent formability and conversion-treatability, comprising the steps of: heating to a temperature of 1150.degree. C. or lower, a steel slab comprising; 0.005 wt % or less of C, 0.5-1.5 wt % of Si, 0.1-0.5 wt % of Mn, 0.003-0.05 wt % and at least 3.4.times.N wt % of Ti, 0.003-0.05 wt % and at least 7.8.times.C wt % of Nb, 0.01-0.1 wt % of Al, 0.05-0.15 wt % of P, 0.010 wt % or less of S, 0.005 wt % or less of N, 0.0001-0.0050 wt % of B, the balance consisting of Fe and unavoidable impurities; hot-rolling the steel slab with a finishing rolling temperature of the A.sub.r3 point of the steel or higher to obtain a hot-rolled steel sheet; cooling the hot-rolled steel sheet at a cooling rate of 10.degree. C./sec or more in the stage between said finishing rolling and the following coiling step, with the provision that said cooling is started not later than 2 sec after the hot-rolling is finished and is continued for a duration of at least 3 sec; coiling the steel sheet at a temperature of 650.degree. C. or higher; cold-rolling the steel sheet at a usual rolling draft; and continuous-annealing the cold-rolled steel sheet at a heat-cycle of holding for 1 sec or longer at a temperature of 930.degree. C. or lower to complete the recrystallization of the cold-rolled steel sheet.

Process for producing cold-rolled high strength steel sheet having

A hot-rolled steel sheet suitable for enamelling on one side is disclosed. The steel consists essentially of 0.0050-0.07 wt % C, 0.05-1.5 wt % Mn, 0.03 0.15 wt % P, 0.03-0.1 wt % Al, 0.003-0.010 wt % N, provided that the N content is the sum of at least 0.002 wt % of free nitrogen not bound to Al and the content of nitrogen in other states, the nitrogen content as defined above satisfying the condition of Al/N.gtoreq.10 on the basis of weight percents and the balance being Fe and incidental impurities.

One-sided enamelable hot-rolled steel sheet and process for producing

An r value of a hot-rolled steel sheet is enhanced by: a specific composition consisting of not more than 0.015 wt % of C, from 1.0 to 2.5 wt % of Mn, from 0.005 to 0.10 wt % of Al, from 0.01 to 0.06 wt % of Nb, from 0.01 to 0.1 wt % of Ti; and, controlled rolling, characterized by in the rough rolling, imparting, in a temperature range of from 980.degree. to 1100.degree. C., a heavy reduction of not less than 20% per pass to the steel sheet; completing a finishing rolling at from Ar.sub.3 to 930.degree. C. and maintaining a total reduction at a temperature of not more than Ar.sub.3 +150.degree. C. to not less than 90%; and, coiling at a temperature of from 600.degree. to 800.degree. C.

Process for producing hot-rolled steel sheet having high r value

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Tokyo, Japan

Atsushi Itami