HIGH-STRENGTH STEEL SHEET HAVING EXCELLENT FRACTURE RESISTANCE PERFORMANCE AND HIC RESISTANCE PERFORMANCE

摘要

A high-strength steel sheet having improved HIC resistance and fracture resistance even when it is thick has a chemical composition comprising, in mass %, C: 0.02 - 0.07%, Si: 0.05 - 0.50%, Mn: 1.10 - 1.60%, P: at most 0.015%, S: at most 0.0030%, Nb: 0.005 - 0.030%, Ti: 0.005 - 0.020%, Al: 0.005 - 0.060%, Ca: 0.0005 - 0.0060%, N: 0.0015 - 0.0070%, at least one of Cu, Ni, Cr, and Mo in a total of greater than 0.1 % to less than 1.5%, and a remainder of Fe and impurities and a steel structure composed of at least 10% by area of bainite and a remainder of ferrite and pearlite. The degree of segregation is less than 1.6 for Nb and less than 1.4 for Mn in the central portion of the thickness of the steel sheet.