A study has been made of the relation between wear characteristics of annealed mild steel and the worn surface layer. Unlubricated sliding wear tests were performed at sliding speed 0.5∼5 m/sec under a contact pressure of 13 kg/cm² in air, using a pin-on-ring machine.
The results obtained are as follows:
(1) When the sliding surface was covered with thick oxide powder, the wear rate markedly decreased. It was, however, observed that much of the oxide powder happened to be imbedded in the surface layer, so that the upper substrate could easily be torn off by friction force.
(2) The area near the sliding surface was severely deformed and showed considerably high hardness values due to work hardening or phase transformation.
(3) Although the average temperature of the sliding surface was low, viz. about 80∼180°C, the FeO oxide or a transformed phase was produced by friction heat at the real contact area (the flash temperature). Depending on the sliding speed, in particular, the transformed phase was in the form of a patch or comparatively uniform layer.
(4) The residual stress in the surface layer was exceedingly compressive at a low sliding speed, but it decreased or occasionally changed to tensile with increasing sliding speed. Therefore, no clear relation between the residual stress and the wear rate existed.