PRODUCTION OF 60 KILO CLASS NON-HEAT-TREATED HIGH TENSILE STRENGTH STEEL EXCELLENT IN WELDABILITY AND TOUGHNESS AFTER STRAIN AGING

摘要

PROBLEM TO BE SOLVED: To provide a method for producing 60 kilo class non-heat-treated steel excellent in weldability and toughness after strain aging and having low temp. toughness even after cold working such as bending. ;SOLUTION: Steel contg., by weight, 0.04 to 0.09% C, 0.1 to 0.5% Si, 1.2 to 1.8% Mn, 0.01 to 0.05% Nb, 0.002 to 0.070% sol. Al and 0.001 to 0.004% N and also satisfying P cm≤0.20% and Ceq (WES) ≤0.42% is subjected to rolling satisfying ld/hm≥1.0 in a recrystallization temp. region for one or more passes, is successively subjected to rolling at 10 to 60% cumulative draft in a unrecrystallization temp. region and is thereafter cooled from ≥Ar3 at the cooling rate of ≥2°C/sec to 300 to 600°C, where Pcm=C+Mn/20+Si/30+Cu/20+ Ni/60+Cr/20+Mo/15+V/10+5B, and Ceq (WES)=C+Mn/6+Si/24+Ni/40+Cr/5+Mo/4+V/14.;COPYRIGHT: (C)2001,JPO