METHOD FOR MANUFACTURING HIGH-STRENGTH STEEL OF TENSILE STRENGTH OF 780 MPA CLASS HAVING EXCELLENT TOUGHNESS OF WELD HEAT AFFECTED ZONE

摘要

PROBLEM TO BE SOLVED: To provide a method for manufacturing high-strength steel of tensile strength of 780 MPa class having excellent toughness of a weld heat affected zone with unexperienced low alloy component and at high productivity.;SOLUTION: In themethod for manufacturing the high-strength steel of tensile strength of 780 MPa class having excellent toughness of the weld heat affected zone, a steel slab having the composition consisting of, by mass, ≥0.005% and 0.030% C, 0.05% Si, 1.0-2.5% Mn, 0.02-0.08% Nb, 0.001-0.10% Al, and 0.0001 to ≤0.01% N with the weld cracking parameter PCM being ≤0.25, and the balance Fe with inevitable impurities is heated to 1,020-1,300°C, and rolled so that the cumulative draft in the temperature range of ≤1,020°C and 920°C is 60%, and the cumulative draft below Ar₃ point is 30-95%, and cooled after the rolling.;COPYRIGHT: (C)2008,JPO&INPIT