| 摘要 |
PROBLEM TO BE SOLVED: To provide high strength steel for welding structures which has excel lent base metal toughness and HAZ(heat affected zone) toughness, and to pro vide a production method therefor. SOLUTION: The high strength steel for welding structures having excellent base metal toughness and HAZ toughness has a composition containing by mass, 0.01 to 0.2% C, 0.02 to 0.5% Si, 0.3 to 2% Mn, <=0.03% P, 0.0001 to 0.03% S, 0.0005 to 0.05% Al and 0.003 to 0.05% Ti, and further containing one or more kinds selected from 0.0001 to 0.01% Mg, 0.0001 to 0.01% Ca and 0.0001 to 0.05% rare earth metals, and the balance iron with inevitable impurities, and also containing one or more kinds selected from Mg, Ca and rare earth metals and one or both of O and S, and in which grains having a grain size of 0.005 to 0.5μm are dispersed, there being >=10,000 pieces per square mm.
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