| 摘要 |
PROBLEM TO BE SOLVED: To obtain a steel in which the necessity of extreme reduction in the amounts of C, N, and Al is obviated and which is easily capable of stable and mass production and has desired base-material characteristics and weld cracking resistance by incorporating respectively specified percentages of elements and specifying the relation between Al content and O content. SOLUTION: The B-added high tensile strength steel excellent in toughness in weld heat-affected zone has a composition which consists of, by weight, 0.05-0.15% C, <=0.3% Si, 0.5-3.5% Mn, <=0.03% P, <=0.01% S, 0.3-2.5% Ni, <=0.005% Ti, 0.0003-0.0025% B, 0.002-0.06% Al, <=0.004% N, <=0.004% O, one or more kinds among 0.2-0.8% Cu, 0.2-1.0% Cr, 0.2-1.0% Mo, 0.005-0.1% V, and 0.005-0.1% Nb, and the balance Fe and in which the relation between Al content and O content satisfies inequality Al/O>=1.12. The tensile strength of this high tensile strength steel is >=80 kgf/m2.
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