| 摘要 |
There is provided a Pb-free free cutting steel is formed of 0.03 to 0.30 wt % of carbon (C), 0.01 to 0.30 wt % of silicon (Si), 0.2 to 2.0 wt % of manganese (Mn), 0.02 to 0.10 wt % of phosphorus, 0.06 to 0.45 wt % of sulfur (S), 0.04 to 0.20 wt % of bismuth (Bi), 0.04 to 0.20 wt % of tin (Sn), 0.001 to 0.015 wt % of boron (B), 0.001 to 0.010 wt % of nitrogen (N), 0.002 to 0.025 wt % of total oxygen (T[O]), and residual Fe, and unavoidable impurities, wherein S, Bi, S, B, and N satisfy a certain relationship. The steel has excellent machinability no less than conventional free cutting steel including Pb, while being eco-friendly. Also, the steel has excellent hot ductility capable of reducing occurrence of defects on a surface, thereby improving hot rolling workability.
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