| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel for screws with high strength, which improves the adverse effect of increased impurity elements such as P and S, and further has combination of strength required for bolts (800 N/mm<2> or more) and adequate tapping properties. SOLUTION: The steel comprises, by wt.%, 0.05-0.20% C, 0.20% or less Si, 0.5-2.0% Mn, 0.015-0.040% P, 0.040% or less S, 0.010-0.080% Al, 0.010% or less N, 2.0% or less Cr, 0.0005-0.0050% B, and the balance iron with unavoidable impurities. The manufacturing method is characterized by forming and then carburizing the screw.
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