Jfe Steel Corporation

Minoru Suwa

Kenji Hayashi

Kaoru Sato

Yoshimasa Funakawa

Nobuyuki Ishikawa

Toyohisa Shinmiya

Shigeru Endo

Masao Yuga

Kunikazu Tomita

Takanobu Saito

Tsuyoshi Shiozaki

Hiroshi Nakata

Shigeki Kitsuya

Yusuke Terazawa

Eiji Maeda

Koichi Nakashima

A high-tensile steel plate has a chemical composition containing, by mass, specific amounts of C, Mn, Si, P, S, Al, Ni, B, N, one or more elements selected from Cr, Mo, V, Cu, Ti, and Ca as needed, Ceq&#x2264;0.80, and a center-segregation zone hardness index HCS satisfying 5.5[C]+15[P]+0.90[Mn]+0.12[Ni]+0.53[Mo]&#x2264;2.5. The hardness of a center-segregation zone satisfies HV/HV&#x2264;1.35+0.006/C&#x2212;t/750. A steel having the above-described chemical composition is subjected to hot rolling at a specific slab-heating temperature at a specific rolling reduction ratio, subsequently reheated, cooled at a cooling rate of 0.3&#xb0; C./s or more until the temperature of a central portion in a plate-thickness direction reaches 350&#xb0; C. or less, and tempered to a specific temperature range.

High-tensile steel plate giving welding heat-affected zone with excellent low-temperature toughness, and process for producing same

The present invention provides a high tensile strength steel plate having a chemical composition containing, in percent by mass, 0.03% to 0.12% of C, 0.01% to 0.30% of Si, 0.5% to 1.95% of Mn, 0.008% or less of P, 0.005% or less of S, 0.015% to 0.06% of Al, 0.011% to 0.05% of Nb, 0.005% to 0.02% of Ti, 0.001% to 0.006% of N, 0.0005% to 0.003% of Ca, optionally, one or two or more of Cr, Mo, V, Cu, and Ni, in which Ceq is 0.44 or less, Ti/N is 1.5 to 3.5, and parameter formulas composed of specific elements for controlling the sulfide morphology and the degree of center segregation in the steel are satisfied, and the balance being Fe and incidental impurities, in which the hardness of the center segregation area of the steel sheet is further specified.

High tensile strength steel plate having excellent weld heat-affected zone low-temperature toughness and method for producing same

A high strength steel plate containing 0.02 to 0.08% C, by mass, and has substantially a two phase microstructure of ferrite and bainite. The ferrite contains precipitates having a particle size of 30 nm or smaller grain size. The steel plate has a yield strength of 448 MPa or higher. A method for manufacturing the high strength steel plate which comprises hot rolling, accelerated cooling and reheating. The accelerated cooling is conducted down to a temperature of 300 to 600&#xb0; C. at a cooling rate of 5&#xb0; C./s or higher. The reheating is conducted up to a temperature of 550 to 700&#xb0; C. at a heating rate of 0.5&#xb0; C./s or higher.

Method for manufacturing high strength steel plate

A high-strength steel pipe having a strength of API X65 grade or higher consisting essentially of, by mass %, 0.02 to 0.08% of C, 0.01 to 0.5% of Si, 0.5 to 1.8% of Mn, 0.01% or less of P, 0.002% or less of S, 0.01 to 0.7% of Al, 0.005 to 0.04% of Ti, 0.05 to 0.50% Mo, at least one element selected from 0.005 to 0.05% of Nb and 0.005 to 0.10% of V, and the balance being Fe, in which the volume percentage of the ferritic phase is 90% or higher, and complex carbides containing Ti, Mo, and at least one element selected from the group consisting of Nb and V are precipitated in the ferritic phase. The high-strength steel pipe has excellent HIC resistance and good toughness of a heat-affected zone, and can be manufactured stably at a low cost.

High-strength steel pipe of API X65 grade or higher

High strength steel plate

Growing community of inventors

Tokyo, Japan

Minoru Suwa