| 摘要 |
PROBLEM TO BE SOLVED: To produce a steel material having good toughness at a good yield even in a large input welded heat affected part. SOLUTION: When a cast slab having the composition by mass% of 0.01-0.18% C, 0.02-0.60% Si, 0.60-2.00% Mn, <=0.030% P, <=0.015% S, 0.005-0.100% Al, 0.007-0.030% Ti, 0.0040-0.0100% N and the balance Fe with inevitable impurities, is cooled, regarding a cooling time t15/11 (second) from 1500 deg.C to 1100 deg.C averaged over the whole thickness of the cast slab and a Ti/N ratio, the relations in the following formula (1) is satisfied. 22600/(t15/11 )<1.25> <=Ti/ N<=1818000/(t15/11 )<1.7> ...(1).
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