| 摘要 |
PROBLEM TO BE SOLVED: To provide non-heat treated type high tensile strength steel having excellent weld zone toughness even in large heat input welding of >=200 kJ/cm heat input. SOLUTION: This steel contains, by weight, <=0.02% C, <=0.50% Si, 0.5 to 2.0% Mn, 0.005 to 0.10% Al, 0.010 to 0.10% Nb, 0.3 to 3.0% Ni, 0.0003 to 0.0040% B and <0.0050% N, and the ratio between the B content and the N content, i.e., B/N is also controlled to the range of 0.3 to 1.0. The steel may moreover contain one or >= two kinds among 0.05 to 0.70% Cu, 0.10 to 0.60% Cr, 0.10 to 0.50% Mo and 0.005 to 0.05% Ti and may further contain 0.0005 to 0.0100% Ca.
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