| 摘要 |
Steel for forming a gear by carburizing and quenching consisting essentially of: 0.1 to 0.35 wt. % C, 0.5 to 2.5 wt. % Si, 0.2 to 2.5 wt. % Mn, 0.01 to 2.5 wt. % Cr, 0.01 to 0.7 wt. % Mo, and the balance being Fe and inevitable impurities. The steel has an Ac3 point parameter (Ac3) and an ideal critical diameter (DI), the Ac3 point parameter being in a range of 850 DEG to 960 DEG C., the ideal critical diameter (DI) being in a range of 30 to 250 mm, and the Ac3 point parameter (Ac3) and the ideal critical diameter (DI) being defined by the following equations.Ac3=920-203 2ROOT +E,rad C+EE +44.7 Si+31.5xMo-30xMn-11xCrDI=7.95 2ROOT +E,rad C+EE (1+0.70xSi) (1+3.3xMn)(1+2.16xCr) (1+3.0xMo)The steel has a non-carburized portion after carburizing and quenching, an internal structure of the non-carburized portion comprising a dual phase of martensite and ferrite, said ferrite having an area percentage of 10 to 70% in the dual phase.
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