PURPOSE:To manufacture a high tensile steel with superior toughness at low temp. and superior weldability by heating and rolling a steel contg. adequate amounts of B and Ti under specified conditions and by carrying out accelerated cooling. CONSTITUTION:A steel slab contg. 0.02-0.12% C, 0.03-0.60% Si, 1.0-2.5% Mn, 0.005-0.01% sol.Al, 0.01-0.10% Nb, 0.0003-0.003% B, 0.005-0.08% Ti and =0.008% each of N and S as impurities or further contg. a specified small amount of one or more among Ni, Cu, Mo, V, Cr, Ca and a rare earth element is heated to 1,050-1,250 deg.C and rolled at a temp. in a temp. range where austenite is recrystallized and =50% total draft. It is further rolled at Ar3-Ar3+ 150 deg.C and =50% total draft and immediately quenched to =600 deg.C at =2 deg.C/sec cooling rate.
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