METHOD FOR MANUFACTURING QUENCHED AND TEMPERED STEEL WITH SUPERIOR TENSILE STRENGTH OF AROUND 600MPa AND IMPROVED TOUGHNESS IN WELDED PART

摘要

PURPOSE: Provided is a method for manufacturing quenched and tempered steel with superior tensile strength of around 600MPa and improved toughness in welded part. CONSTITUTION: The quenched and tempered steel is manufactured by (i) hot rolling of a steel slab comprising C 0.06-0.12wt.%, Si 0.1-0.5wt.%, Mn 1.0-1.6wt.%, Al 0.01-0.08wt.%, Ti 0.005-0.02wt.%, B 0.0003-0.003wt.%, N 0.002-0.008wt.% and two or more metals selected from Cu 0.5wt.% or less, Ni 1.0wt.% or less, Cr 0.5wt.% or less, Mo 0.5wt.% or less, Nb 0.1wt.% or less, V 0.1wt.% or less, Ti/N 1.5-2.5, a balance of Fe and other unavoidable impurities wherein carbon equivalent(Ceq) is 0.32-0.38wt.%; (ii) reheating the slab at a temperature range of Ac3 and 950deg.C followed by water-cooling; (iii) tempering at a temperature range of 500deg.C to Ac1.