HAZ characteristic at the time of full house thermal welding is superior, being the steel sheet which after the 590N/mm2 class steel sheet and its production methodological null hot rolling where for the welding structure

摘要

PROBLEM TO BE SOLVED: To secure toughness in an HAZ(heat-affected zone) by subjecting a steel slab of specific composition to hot rolling and to accelerated cooling under respectively specified conditions. ;SOLUTION: A steel slab, having a composition which consists of, by mass, 0.10-0.16% C, ≤0.40% Si, 1.00-1.80% Mn, ≤0.025% P, ≤0.012% S, 0.005-0.020% Ti, 0.010-0.080% Al, 0.0020-0.0080% N, and the balance Fe with inevitable impurities and in which Ceq, represented by Ceq=C+Si/24+Mn/6+Ni/40+Cr/5+Mo/4+V/14, is regulated to 0.37-0.40%, is hot-rolled at ≥850°C rolling temp. Subsequently, cooling is performed from a temp. not lower than the Ar₁ point down to ≤500°C at (6 to 14)°C/sec cooling rate, by which a steel plate, in which toughness in the whole region of HAZ after large heat input welding of ≥30kj/mm amount of weld heat input is regulated to ≥47J by 0°C Charpy absorption energy, is prepared. By this method, the 590N/mm² class steel plate for welded structure, excellent in toughness in HAZ at the time of large heat input welding and having ≤80% yield ratio, can be obtained.;COPYRIGHT: (C)1998,JPO