HIGH TENSILE STRENGTH STEEL PLATE EXCELLENT IN TOUGHNESS OF PARENT METAL AND LARGE HEAT-INPUT WELD HEAT AFFECTED ZONE AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To obtain a high tensile strength steel plate improved in the toughness of the parent material and large heat-input weld heat affected zone by specifying each content of C, Ti, B, total Nb and insoluble Nb and specifying Ceq (IIW) value and pseudo-polygonal ferrite. ;SOLUTION: A high tensile strength steel plate having a compsn. composed of, by mass, 0.05 to 0.10% C, 0.005 to 0.025% Ti, 0.0003 to 0.0020% B, 0.005 to 0.025% total Nb and insoluble Nb: the total Nb content × $0.8, in which the content of N is the one satisfying the inequality of -0.00≤×≤0 (X= N-0.293×Ti-1.296×B-0.151×Nb), Ceq (IIW) expressed by Ceq (IIW)=C+Mn/6+(Cu+Ni)/15+(Cr+Mo+V)/5 is regulated to 0.30 to 0.38%, and the area ratio of pseudo-polygonal ferrite (αq) is regulated to ≤5% is prepd. In this way, the high tensile strength steel plate having ≥460 N/mm² yield strength and ≥570 N/mm² tensile strength and satisfyinq ≥46JυE_-40 (average) and υE_-40(minimum) in the parent metal can be obtd.;COPYRIGHT: (C)1999,JPO