PREVENTIVE METHOD FOR GRAIN BOUNDARY EMBRITTLEMENT AFTER STRESS RELIEF ANNEALING OF WELD HEAT AFFECTED ZONE

摘要

PURPOSE:To prevent effectively the grain boundary embrittlement of a weld heat affected zone after stress relief annealing in a low alloy steel by controlling the compsn. thereof in association with the content of P and Ceq and limiting the cooling conditions in the bond part after welding. CONSTITUTION:The steel is made of the compsn. contg. 0.004-0.40wt.% C, 0.10-0.30% Si, 0.50-3.00% Mn, contg. further =1 kinds among 0.05-6.00% Ni, 0.05-3.00% Cr, 0.05-1.00% Mo, 0.005-0.10% V, 0.01-1.00% Ti, 0.005-0.10% Nb, 0.0005-0.0030% B, 0.05-1.00% Cu and 0.010-0.100% Al and consisting of the balance Fe and inevitable impurities. Ceq is controlled to =0.43 Ceq when =0.015% P and to =0.45 Ceq when 0.015% P. Ceq is determined by the formula. The bond part after the end of welding of the steel sheet having such compsn. is cooled for =11 seconds in the temp. region from 800 deg.C to 500 deg.C. The grain boundary embrittlement of the heat affected zone after stress relief annealing is prevented by the above-mentioned compsn. and cooling control.