Formation and wear mechanism of tribo-oxides and the regime of oxidational wear of steel

A pin-on-disc configuration was employed for studying the formation and wear mechanism of tribo-oxides on sliding contact surfaces of some steels. The sliding speed was set at values from 0.6 to 8 m/s and the nominal pressure was set at values from 0.55 to 8.86 MPa. Three wear mechanisms were found from the micrographic results. When rubbing pairs were subjected to small nominal pressure and sliding speed, the wear loss was mainly due to adhesive and abrasive mechanisms. When the nominal pressure was increased to over 4.4 MPa and the sliding speed was greater than 3 m/s, the wear loss was mainly due to plastic extrusion of material from the pin and the wear became severe. In between these two extremes, the wear mechanism fell in the regime of oxidational wear. In which, the tribo-oxides mainly formed in the plastic zones just underneath the adhesive junctions of the contact surfaces. Once an oxide had formed, the growth of its size was insignificant. The temperature distribution and the nominal contact temperature of the stationary pin were calculated with a simplified mathematical analysis in a steady-state condition of natural heat transfer. The real contact temperature could only be approximated with an average value, because the real contact area was only an integrated value of all small areas of contact junctions at which the temperatures were different.