PLATE STEEL FOR MAIN PIPE AND MAIN PIPE Russian patent published in 2017 - IPC C22C38/14 C21D8/02 

FIELD: metallurgy.

SUBSTANCE: invention relates to plate steel of thickness of 25 mm or more for making the main pipe. Steel contains wt %: C 0.040-0.080, Si 0.05-0.40, Mn 1.60-2.00, P 0.020 or less, S 0.0025 or less, Mo 0.05-0.20, Ca 0.0011- 0.0050, Al 0.060 or less, Nb 0.010-0.030, Ti 0.008-0.020, N 0.0015-0.0060, O 0.0040 or less, the rest is Fe and unavoidable impurities. Ratio of Ca content to S content [Ca/S] is from 0.90 to 2.70, and ratio of Ti content to N content [Ti/N] is from 2.20 to 5.00. Value of carbon equivalent Ceq is from 0.380 to 0.480. In the position of 1/4 of sheet thickness, ferrite fraction (F1) is 20 to 60%, the rest is bainite, wherein ferrite average grain diameter is 2.0 to 15.0 mcm. In the position of 1/2 of sheet thickness, ferrite fraction (F2) is 5 to 60%, the rest is bainite or bainite and martensite, wherein ferrite average grain diameter is 5.0 to 20.0 mcm. Ratio (F1/F2) is from 1.00 to 5.00. Hardness in the position of 1/2 of sheet thickness is 400 Hv or less, and the length of MnS in the position of 1/2 of sheet thickness is 1.00 mm or less.

EFFECT: steel has high resistance to hydrogen cracking, strength and toughness.

4 cl, 1 dwg, 4 tbl