METHOD OF MANUFACTURING HIGH-TENSION STEEL OF 600MPA IN TENSION STRENTH HAVING LOW YIELD RATE

PURPOSE: A method of manufacturing a high-tension steel of 600MPa in tension strength is provided to be excellent in toughness of a portion influenced by welding heat and to have low yield rate of material. CONSTITUTION: A steel slab consists of, by weight %: at least one from 0.05-0.10% of C, 0.1-0.5% of Si, 1.0-1.6% of Mn, 0.01-0.08% of Al, 0.005-0.025% of Ti, 0.0003-0.003% of B, 0.002-0.010% of N, not more than 0.5% of Cu, not more than 1.0% of Ni, not more than 0.5% of Cr, not more than 0.5% of Mo, not more than 0.1% of Nb and not more than 0.1% of V. The steel slab also contains Fe and incidental impurities. The steel slab is hot-rolled and quenched. The steel slab is heated again and tempered to manufacture a high-tension steel of 600MPa.