HIGH TENSILE STRENGTH STEEL FOR WELDING STRUCTURE EXCELLENT IN FATIGUE STRENGTH AND TOUGHNESS AT WELD HEAT-AFFECTED ZONE

摘要

PURPOSE: To develop high tensile strength steel for welding structure improved in the fatigue strength of the weld zone and excellent in the toughness of the weld heat- affected zone by regulating the amounts of Si and Cu in steel for welding structure having a specified compsn. into optimum ones and regulating the structure of the weld heat-affected zone. ;CONSTITUTION: This steel for welding structure is one having a compsn. contg., by weight, 0.04 to 0.12% C, 0.3 to 0.6% Si, 0.8 to 2.O% Mn, ≤0.02% P, ≤0.01% S, 0.5 to 1.2% Cu, 0.02 to 0.06% Al, 0.005 to 0.04% Ti, 0.002 to 0.008% N and 0.0005 to O.002% B or furthermore contg. 0.1 to 2.0% Ni or 0.005 to 0.O6% Nb independently or doubly. The high tensile strength steel for welding structure in which, fatigue strength is improved by regulating the area ratio of islanded martensite in the weld heat-affected zone (HAZ) into ≥10% by the addition of a suitable amt. of Si, the deterioration in HAZ toughness is suppressed by regulating the area ratio of boundary pro-eutectoid ferrite into ≤1% by the optimum addition of Cu and excellent in HAZ fatigue strength and toughness are imparted by regulating the area ratio of the upper bainite into ≥80% can be produced.;COPYRIGHT: (C)1994,JPO&Japio