STEEL FOR A STRUCTURE HAVING EXCELLENT LOW TEMPERATURE TOUGHNETSS, TENSILE STRENGTH AND LOW YIELD RATIO, OF HEAT AFFECTED ZONE AND MANUFACTURING METHOD FOR THE SAME

摘要

A high intensity resistance yield ratio structural steel and a manufacturing method thereof are provided to have the low temperature toughness and intensity of the steel material by controlling a shape and kind of organization and a component system. A manufacturing method of a high intensity resistance yield ratio structural steel comprises: a step of heating steel slab of the composition satisfying a condition, that a formula(Ti+0.2Nb)/N is over than 2.5 and less than 5.5, at 900~1300°C; a step of rough rolling the steel slab with reduction rate more than 50%; a step of performing the finishing rolling to make the reduction rate at Ar3 to Ae3 over 60% even though the rolling is completed at Ar3 to Ae3; and a step of cooling at higher than 10°C/sec and stopping cooling at a temperature of less than 450°C. The steel slab includes one or more than two kind groups selected from the groups consisting of Cr 0.05~1.0 weight%; Ni 0.01~2.0 weight%; or Cu 0.01~10 weight%. The Cr is added in order to increase the intensity. The Ni is added in order to improve the intensity and toughness of the base material. The Cu minimizes the toughness degradation of the base material and is added in order to increase the intensity.