| 摘要 |
PROBLEM TO BE SOLVED: To provide a technique of inexpensively producing high strength steel which has excellent fracture toughness (CTOD) in multi-layer welding of small to medium heat input. SOLUTION: The steel having excellent toughness in a welding heat affected zone has a composition substantially containing no Al, and containing, by mass, 0.03 to 0.09% C, 0.05 to 0.2% Si, 2.0 to 2.5% Mn, <=0.008% P, <=0.005% S, 0.005 to 0.02% Ti, 0.01 to 0.03% Nb, <=0.0035% O, and 0.003 to 0.006% N, and in which AGB-1 lies in the range of 0.39 to 0.47, and the balance iron with inevitable impurities; wherein, AGB-1 =C+1/24Si+1/6Mn+2Nb.
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