STEEL MATERIALS EXCELLENT IN TOUGHNESS IN WELDHEAT-AFFECTED ZONE AND FATIGUE CHARACTERISTICS OF BASE MATERIAL, AND MANUFACTURING METHOD OF THE SAME

摘要

PURPOSE: A steel with improved toughness and a base material fatigue resistance, and a method for forming thereof are provided to improve HAZ toughness by adding oxide like ZR, REM, and Ca IN a steel material. CONSTITUTION: A steel with improved toughness comprises C 0.02~0.12 weight%, Si 0.5 weight%, Mn less than 1~2 weight%, Zr 0.0002~0.050 weight%, REM 0.0002~0.050 weight%, Ca 0.0005~0.010 weight%, Ti 0.005~0.02 weight%, N 0.0040~0.01 weight%, O 0.0005~0.010 weight%, P less than 0.02 weight%, S less than 0.015 weight%, Al less than 0.05 weight% and foreign matters. A steel material comprises oxide containing Zr, REM, and Ca. The steel material comprises ZrO2 5~50 weight%, REM oxide 10~50 weight% and CaO 5.0~50 weight%. An averaging gradient of the steel material is 170Hv or greater.