STEEL FOR LINE PIPE WITH SUPERIOR HYDROGEN SULFIDE CRACKING RESISTANCE AND ITS MANUFACTURE

摘要

PURPOSE:To obtain steel products for a line pipe with high strength, high toughness and superior hydrogen sulfide cracking resistance by primarily rolling a slab having a specified relation among the contents of the principal components, followed by heat treatment and final rolling. CONSTITUTION:A continuously cast slab or a bloomed slab consisting of =0.05% C, =0.50% Si, 1.0-2.0% Mn, 0.20-0.80% Cu, =1.0% Cr, =1.0% Ni, =0.05% Mo, a specified amount each of P, S, Al, N and Ca, 0.01-0.15% V, 0.0005-- 0.0050% B, one or more among a specified amount each of Nb, Ti and Zr, and the balance Fe and satisfying the relation of the equation is manufactured. The slab is primarily rolled at 1,100-1,350 deg.C and 5-70% reduction ratio and held at the temp. for 1-100hr. After the heat treatment, final rolling to a prescribed plate thickness is carried out to obtain steel products maintaining strength, toughness and weldability necessary for a line pipe and having superior cracking resistance in wet H2S environment.