| 摘要 |
PROBLEM TO BE SOLVED: To provide a method of manufacture of a high tensile strength steel having >=570 N/mm<2> tensile strength, -50 deg.C vTrs, -10 deg.C vTre at a joint, and >=2%εZc. SOLUTION: A slab, having a steel composition which consists of, by weight, 0.04-0.10% C, 0.05-0.40% Si, 1.00-2.0% Mn, <=0.025% P, <=0.010% S, <=0.050% Al, 0.030-0.060% Ti, 0.01-0.10% Nb, 0.002-0.005% N, and the balance Fe with inevitable impurities and in which Ti/N is regulated to 6.0-20.0, is used. This slab is heated to 1050-1250 deg.C, finish-rolled at a temp. not lower than the Ar3 point, and successively water-cooled at >=5 deg.C/sec cooling rate down to <=550 deg.C.
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