| 摘要 |
PROBLEM TO BE SOLVED: To provide an annealing-omission-type steel for high-strength bolt, having high weatherability in an environment where salt, particularly of >=0.05 mdd, comes flying, having <=HRB 85 hardness after hot rolling, and also having >=980 MPa tensile strength after quench-and-temper treatment. SOLUTION: The steel has a composition containing, by weight, 0.15-0.3% C, <=0.15% Si, 0.3-0.6% Mn, <=0.01% P, <=0.01% S, 0.01-0.05% Al, 0.002-0.01% N, 1-2% Ni, 0.1-0.3% Mo, 0.01-0.05% Ti, and 0.0003-0.005% B.
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