THICK-WALLED STEEL PIPE FOR OIL WELLS AND METHOD FOR MANUFACTURE THEREOF

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FIELD : metallurgy. SUBSTANCE : invention relates to the field of metallurgy, namely to a thick-walled steel pipe for oil wells, having a wall thickness of 40 mm or more. In the method, a steel pipe is made having the following chemical composition, wt.% : C : from 0.40 to 0.65, Si : from 0.05 to 0.50, Mn : from 0.10 to 1.0, P : 0.020 or less, S : 0.0020 or less, dissolved Al : from 0.005 to 0.10, Cr : more than 0.40 to 2.0, Mo : more than 1.15 to 5.0, Cu : 0.50 or less, Ni : 0.50 or less, N : 0.007 or less, O : 0.005 or less, V : from 0 to 0.25, Nb : from 0 to 0.10, Ti : from 0 to 0.05, Zr : from 0 to 0.10, W : from 0 to 1.5, B : from 0 to 0.005, Ca : from 0 to 0.003, Mg : from 0 to 0.003, rare earth metal : from 0 to 0.003, Fe and impurities – the rest. Further, the amount of carbide having an equivalent diameter of 100 nm or more and containing 20 wt.% or more of Mo is 2 or less per 100 mcm2. Said steel pipe is hardened once or repeatedly, moreover, the temperature of at least one hardening operation is from 925 °C to 1, 100 °C, it is followed by tempering at a temperature of from 650 °C to Ac1 with a hold time of 15 to 120 minutes. EFFECT : pipe has a limit of plastic deformation of 827 MPa or more, the difference between the maximum value and the minimum value of the limit of plastic deformation in the direction of the wall thickness of 45 MPa or less, and high resistance to sulfide cracking under stress. 2 cl, 6 dwg, 5 tbl