PLATE STEEL FOR HIGH-STRENGTH AND HIGH IMPACT STRENGTH OF STEEL PIPES AND METHOD FOR PRODUCTION OF PLATE STEEL Russian patent published in 2019 - IPC C22C38/58 C22C38/38 C22C38/16 C22C38/14 C21D8/02 

FIELD: metallurgy.

SUBSTANCE: steel has a chemical composition containing the following, wt. %: C: 0.03-0.08, Si: more than 0.05 and 0.50 or less, Mn: 1.5–2.5, P: 0.001–0.010, S: 0.0030 or less, Al: 0.01–0.08, Nb: 0.010–0.080, Ti: 0.005–0.025, N: 0.001–0.006, at least one of: Cu: 0.01–1.00, Ni: 0.01–1.00, Cr: 0.01–1.00, Mo: 0.01–1.00, V: 0.01–0.10 and B: 0.0005–0.0030, balance - Fe and unavoidable impurities. Steel has a microstructure in which the ferrite area share is 20–80 % in the position located in 1/2 thickness of the steel plate, and from 50 to 100 % of the amount of ferrite is deformed ferrite. In testing for breaking of falling load at temperature of -55 °C on surface of fracture of sample of steel plate there are cracks located in direction perpendicular to direction of development of crack when testing for rupture by falling weight, characterized by index of cracks (SI_-55 °C) of 0.10 mm^-1 or more, and ultimate tensile strength is 625 MPa or more.

EFFECT: invention relates to metallurgy, namely to plate steel for high-strength and high impact strength steel pipes.

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