Effect of gas oxynitrocarburising on properties of medium carbon railway axle steel

Abstract

In order to investigate the effect of the gas oxynitrocarburising on the properties of the medium carbon railway axle steel, the steel was gas oxynitrocarburised at five different temperatures for 2 h by applying a low temperature gas multielement penetrating system. The results show that the compound layer composed of γ′-Fe₄N and ϵ-Fe_2–3N and the oxide layer consisting of Fe₃O₄ and Fe₂O₃ are formed on the surface after treatment. The thickness of the compound layer increases with increasing temperature; however, the case depth decreases when the temperature is above the temper temperature of the origin material. The increase in treatment temperature resulted in an increase in the surface roughness. The properties of wear and corrosion resistance are improved, and the fatigue limit of the specimen treated at the optimum temperature, which is 570°C, improves largely compared to that of the untreated one and the one treated by microshot peening.

Keywords:

• Oxynitrocarburising
• Microhardness
• Wear
• Corrosion
• Fatigue

This work was supported by the National Natural Science Foundation of China (grant no. 50671086), National Basic Research Program of China (grant no. 2007CB714705), State Key Laboratory Independent Research of China (grant no. 2009TPL_T04) and Fundamental Research Funds for the Central Universities (grant no. SWJTU09CX060).