Relationship between surface oxide layer and transient traction characteristics for two steel rollers under unlubricated and water lubricated conditions

This paper describes the relationship between transient variation in the traction coefficient of a twin-disc of pearlitic carbon steel and variation in the surface oxide layer on a twin roller under unlubricated and water lubricated conditions, in order to investigate the cause of the transient variation of traction coefficient in rail/wheel contacts. This was measured by using auger Electron Spectroscopy (AES) with sputter etching by argon ions, laser Raman scattering spectroscopy (LRSS) and Fourier transform infrared spectroscopy (FT-IR) for the analysis of oxide and hydro-oxide composition. It can be seen that hard a-Fe2O3 in the thin oxide layer causes an abrupt increase in the traction coefficient under both dry and wet conditions. Soft Fe3O4 in the oxide layer may suppress the increase in the traction coefficient. Tribochemical reaction between the surface material and water prevent the mechanical mixing on the surface.