Jfe Steel Corporation

Yamazaki Mazak Corporation

Ryo Nagao

Nobuyuki Ishikawa

Hideyuki Kimura

Kazukuni Hase

Shusaku Ota

Shinichi Kakihara

Youji Tamura

Takeshi Yasui

A steel plate for high-strength and high-toughness steel pipes has a chemical composition containing, by mass %, C: 0.03% or more and 0.08% or less, Si: more than 0.05% and 0.50% or less, Mn: 1.5% or more and 2.5% or less, P: 0.001% or more and 0.010% or less, S: 0.0030% or less, Al: 0.01% or more and 0.08% or less, Nb: 0.010% or more and 0.080% or less, Ti: 0.005% or more and 0.025% or less, and N: 0.001% or more and 0.006% or less, and further containing, by mass %, at least one selected from Cu: 0.01% or more and 1.00% or less, Ni: 0.01% or more and 1.00% or less, Cr: 0.01% or more and 1.00% or less, Mo: 0.01% or more and 1.00% or less, V: 0.01% or more and 0.10% or less, and B: 0.0005% or more and 0.0030% or less, with the balance being Fe and inevitable impurities. The steel plate has a microstructure in which an area fraction of ferrite at a &#xbd; position of a thickness of the steel plate is 20% or more and 80% or less and deformed ferrite constitutes 50% or more and 100% or less of the ferrite.

Steel plate for high-strength and high-toughness steel pipes and method for producing steel plate

A high strength/highstrength, high toughness steel sheet having tensile strength, Charpy impact absorption energy, and ductile fracture rate are equal to or greater than specified values comprises, in mass %, 0.03-0.08% of C, 0.01-0.50% of Si, 1.5-2.5% of Mn, 0.001-0.010% of P, 0.0030% or less of S, 0.01-0.08% of Al, 0.010-0.080% of Nb, 0.005-0.025% of Ti, 0.001-0.006% of N, at least one substance selected from among 0.01-1.00% of Cu, 0.01-1.00% of Ni, 0.01-1.00% of Cr, 0.01-1.00% of Mo, 0.01-0.10% of V, and 0.0005-0.0030% of B, and a remainder of Fe and unavoidable impurities. At a position at &#xbd; the sheet thickness, the area ratio of island-like martensite is less than 3%, the area ratio of bainite is 90% or more, and the average particle size of cementite within the bainite is 0.5 &#x3bc;m or less.

High-strength, high-toughness steel plate, and method for producing the same

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Tokyo, Japan

Ryo Nagao