Manufacturing method null of the high intensity high tenacious seamless metal tubing where resistance SSC Characteristic

摘要

PURPOSE: To obtain a seamless steel tube excellent in SCC resistance and having high strength and high toughness by specially controlling steel components and hot rolling conditions, respectively. ;CONSTITUTION: A billet of a steel which has a composition consisting of, by weight, 0.03-0.35% C, 0.01-0.5% Si, 0.15-2.5% Mn, ≤0.020% P, ≤0.010% S, 0.005-0.1% each of Al, Ti, and Nb, ≤0.01% N, and the balance Fe and containing, if necessary, prescribed amounts of Cr, Mo, Ni, V, B and/or Ca, Co, and Cu is used. This billet is heated up to ≤1100°C and hot-pierced, and the resulting hollow tube stock is subjected, prior to former-stage and final-stage cross helical rollings, to cooling and to holding to and at a temp. between the Ar₃ point and 1100°C and then to forming with a reduction ratio of wall thickness cross section of 20-70% by means of respective cross helical rolling mills. After continuous hot rolling for shape straightening is done, the hollow tube stock whose temp. is dropped to a temp. between the Ar₃ point and 900°C is heated up to 900-950°C and hot-finish-rolled at ≥(Ar₃ point +50°C) finishing temp., and the resulting finished steel tube is quenched from a temp. not lower than the Ar, point to undergo hardening treatment and successively heated up to a temp. not higher than the Ac₁ point and cooled to undergo tempering treatment.;COPYRIGHT: (C)1994,JPO&Japio