| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing high tensile strength steel which has excellent toughness and weldability. SOLUTION: A steel slab or a cast slab having a composition containing, by mass, 0.005 to 0.045% C, <=0.6% Si, 0.6 to 2.0% Mn, <=0.02$ P, <=0.01% S, 0.01 to 0.1% Nb, 0.005 to 0.035% Ti, <=0.06% Al, <=0.006% N, and one or more kinds selected from 0.05 to 2.0% Cu, Ni in the range of 0.05 to 1.0% also by >=1/2 of the amount of Cu to be added, 0.05 to 1.0% Cr and 0.05 to 1.0% Mo, also satisfying Ceq: 0.28 to 0.45%, and PCM: 0.12 to 0.2%, and the balance iron with inevitable impurities is reheated to the temperature range of 1,000 to 1,300 deg.C. The slab is thereafter rolled at a cumulative draft of >=30% at <=1,000 deg.C so as to be finished at >=720 deg.C. After that, the steel is subjected to accelerated cooling from >=700 to <=300 deg.C. If required, specified amounts of V, Ta, Ca, rare eath metals and Mg are incorporated therein.
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