Research on improving durability of high-strength spheroidal graphite cast iron gears by nitriding heat treatment

Abstract

The vibration damping property of high-strength spheroidal graphite cast iron is higher than that of steel materials, and it is possible to reduce gear meshing vibration, which is effective in reducing noise in gear devices. This material is significantly stronger than conventional spheroidal graphite cast iron. However, the problem is that the fatigue strength is inferior at the as-cast material level compared to conventional railway gear materials. Gas nitriding can significantly improve the fatigue strength of cast iron. In this study, we report the results of material fatigue test and improvement of nitriding heat treatment property by adding alloying elements in order to determine the optimum gas nitriding treatment conditions for cast iron gears. Furthermore, we manufactured the nitriding gear for railway vehicles and this noise performance was evaluated by rotation test. The thermal strain of the gear due to the nitriding heat treatment is less than that of carburizing, and the noise is reduced by about 2 dB on average compared to the conventional material tooth grinding gear.