Fatigue properties of oxynitrocarburized medium carbon railway axle steel in very high cycle regime

The medium carbon railway axle steel was oxynitrocarburized and the 109 cycles fatigue tests were carried out by rotary bending fatigue machine to investigate the fatigue properties in the very high cycle fatigue (VHCF) regime. The results show that for the treated specimens the cracks initiate from the surface oxide layer and it has the fatigue limit which is improved by 120% compared to that of the untreated specimens; however, when the oxide layer is removed, the crack initiation sites shift from compound layer on the surface to the diffusion layer at subsurface in VHCF regime and the fatigue strength improves slightly.