MANUFACTURE OF HIGH STRENGTH STEEL OR LINE PIPE, EXCELLENT IN HIC RESISTANCE

摘要

PROBLEM TO BE SOLVED: To provide a method of manufacture of a high strength steel for line pipe, excellent in HIC resistance, capable of stably and inexpensively preventing the occurrence of HIC while having strength as high as X80 grade. ;SOLUTION: This steel can be manufactured by subjecting a steel slab, having a composition which contains, by weight, 0.02-0.08% C, 0.05-0.50% Si, 1.0-1.8% Mn, ≤0.010% P, ≤0.002% S, 0.005-0.05% Nb, 0.005-0.10% Ti, 0.01-0.07% Al, and 0.0005-0.0040% Ca and in which the carbon equivalent represented by (carbon equivalent)=C+Mn/6+(Cu+Ni)/15+(Cr+Mo+V)/5 is regulated to ≥0.32%, to heating and to rolling and then subjecting the resultant steel plate or a steel pipe, prepared by using the steel plate, to hardening treatment from ≥850°C at (5 to 40)°C/sec cooling rate.;COPYRIGHT: (C)1997,JPO