HIGH TENSION STEEL SHEET EXCELLENT IN TOUGHNESS OF WELD HEAT-AFFECTED ZONE AND CONTROL OF FATIGUE CRACK GROWTH

摘要

PURPOSE: A high tension steel sheet having excellent toughness of weld heat-affected zone and controlling fatigue crack growth is provided to secure the toughness balance and improve the toughness of the weld heat-affected zone by obtaining the bainite block size. CONSTITUTION: The high tension steel sheet having excellent toughness of weld heat-affected zone and controlling fatigue crack growth includes C 0.02~0.05%, Si 0.20% below, Mn 0.5~2.0%, Al 0.01~0.07%, Cr 0.6~ 1.5%, Ti 0.010~0.040%, B 0.0010~0.0050%, N 0.0040~0.0080%, Ca 50% or less, and 0.1~2.4% of sum of Cu and Ni. The content(mass %) of C, Si, Mn, Cr, Cu, Ni and Mo is C, Si, Mn, Cr, Cu, Ni and Mo. The BP value(mass %) is 414 C + 78 Si + 31 Mn + 79 Cr - 14 Cu - 26 Ni + 218 Mo. The BP value is in the range of 900~190 (mass %). The Nb content of the steel plate is less than 0.005%. The steel plate includes Mo less than 0.4%. The Nb content of the steel plate is less than 0.005%. The yield stress of the steel plate is over 480MPa and the tensile strength of the steel plate is over 590MPa.