| 摘要 |
PURPOSE: To develop a case hardening steel having good hot ductility in hot forging immediately after carburizing treatment, in the compsn. of a case hardening steel, by compositely adding Mn and B and regulating the contents of Mn, B and S in specified ratios. CONSTITUTION: The compsn. of a case hardening steel is constituted of, by weight, 0.10 to 0.30% C, 0.05 to 0.50% Si, 0.45 to 2.00% Mn, 0.05 to 0.80% Cr, <0.10% S, <0.50% Mo, 0.0005 to 0.0050% B, 0.01 to 0.10% Ti, <0.0100% N, and the balance Fe. In particular, Mn and B as elements for improving the hot ductility of the steel as well as for improving its hardenability are contained by the amounts satisfying [%Mn]+10×[%B]>=6×[%S] in the relationship with S as an element for improving its machinability. The case hardening steel good in hot ductility so as to enable its application to a carburizing and forging method and moreover excellent in strength and toughness can be obtd.
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