HOT-ROLLED PLATE STEEL AND METHOD OF ITS PRODUCTION Russian patent published in 2020 - IPC C22C38/14 C22C38/12 C22C38/58 C22C38/54 C22C38/50 C22C38/48 C22C38/38 C22C38/32 C22C38/28 C22C38/26 C21D8/02 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, particularly, to hot-rolled plate steel used for production of high-strength welded pipes for main pipelines. Steel has chemical composition containing, wt. %: C: from 0.04 to 0.08; Si: from 0.01 to 0.50; Mn: from 1.2 to 2.0; P: from 0.001 to 0.010; S: 0.0030 or less; Al: from 0.01 to 0.08; Nb: from 0.050 to 0.100; Ti: from 0.005 to 0.025; N: from 0.001 to 0.006; at least one element selected from Cu: from 0.01 to 1.00; Ni: from 0.01 to 1.00; Cr: from 0.01 to 1.00; Mo: from 0.01 to 1.00; V: from 0.01 to 0.10 and B: from 0.0005 to 0.0030; the balance is Fe and unavoidable impurities. In microstructure in position by 1/2 thickness of plate steel surface share concentration of martensite is less than 3 %, and the surface share concentration of bainitic ferrite is 95 % or more. Bainitic ferrite has an average grain diameter of 6.0 mcm or less. Number of Nb release in form of Nb carbonitride is 0.025 wt. % or more, and the amount of Nb release in the form of Nb carbonitride, having grain diameter of 20 nm or more, is 50 % or more of the total weight of Nb release in the form of Nb carbonitride.

EFFECT: obtaining high-strength and high-viscosity steel plate, having high absorbed energy during Charpy impact test at -40 °C.

4 cl, 5 tbl, 2 ex