| 摘要 |
PROBLEM TO BE SOLVED: To produce a steel having good HAZ toughness even in large heat input welding in which the amt. of heat to be inputted to welding exceeds 20 kJ/mm. SOLUTION: This steel has chemical components contg., by mass, 0.03 to 0.2% C, <=0.4% Si, 0.5 to 2% Mn, <=0.015% P, <=0.006% S, 0.01 to 0.01% Al, 0.007 to 0.02% Ti, >0.001 to 0.006% Mg, 0.001 to 0.004% O and 0.0025 to 0.006% N, and the balance Fe with inevitable impurities. In the steel, TiN of 0.01 to <0.5μm including the oxides of Mg and Al is present by >=10,000 pieces/mm2, and the average value of the content of Mg in the oxides of 0.5 to 5μm size is >=15%.
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