| 摘要 |
PURPOSE:To produce a high tensile steel having excellent low-temp. toughness after linear and spotty reheating by subjecting a low-C steel slab having a specific compsn. consisting of C, Si, Mn, S, Al, Ti, N, and Fe to hot rolling and cooling under specific conditions. CONSTITUTION:The steel slab which contains 0.01-0.08wt.% C, 0.05-0.50% Si, 0.80-2.0% Mn, <=0.030% S, 0.010-0.060% Al, 0.005-0.020% Ti, 0.0020-0.0080% N, contains further, >=1 kinds among <=0.70% Cu, <=2.0% Ni, <=0.50% Cr, <=0.50% Mo, 0.01-0.10% V, 0.005-0.030% Nb, and 0.005-0.030% Ca at need, consists of the balance Fe and unavoildable impurities and has <=0.36% carbon equiv. is heated to 950-1,150 deg.C. The steel is then subjected to hot rolling at <=50% cumulative draft at <=850 deg.C and Ar3 point + or - 40 deg.C rolling finish temp. The hot rolled sheet is subjected to accelerated cooling down to a 600-300 deg.C range at >=2 deg.C/sec cooling rate.
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