PRODUCTION OF TEMPERED HIGH-TENSILE STEEL HAVING EXCELLENT LOW-TEMPERATURE TOUGHNESS AND WELDABILITY WITH LARGE HEAT INPUT

摘要

PURPOSE:To obtain a tempered high-tensile steel having excellent low-temp. toughness and weldability with large heat input by subjecting a low-alloy steel slab consisting of the specific compsn. contg. a slight amt. of Nb and Ti to cryogeonic heating then to controlled rolling followed by hardening and tempering under specific conditions. CONSTITUTION:A steel contg. 0.02-0.15wt% C, 0.02-0.80% Si, 0.60-2.50% Mn, 0.005-0.060% SolAl, 0.005-0.020% Nb, 0.005-0.15% Ti, =0.006% N and if necessary, a specific amt. of Cu, Ni, V, B, REM and Ca is melted. The steel slab of such compsn. is heated to 900-1,000 deg.C and is rolled down to =50% cumulative draft. The rolling is finished in an Ar3-40 deg.C range. The rolled steel is immediately quickly cooled down to =200 deg.C at =2-60 deg.C/S and is tempered at a temp. of the Ac1 point or below. The tempered high-tensile steel having excellent low-temp. toughness, base metal strength and joint strength is obtd. by the above-mentioned method.