Extrusion wear and transition of wear mechanisms of steel

A pin-on-disc configuration was used for studying the wear mechanisms of steel tested in conditions commonly known as oxidational wear regime. The results show that when the nominal contact pressures on the sliding pairs made of medium carbon steel pin/die steel disc and die steel pin/die steel disc at a sliding velocity of 4 m/s were larger than 5.5 and 7.7 MPa, respectively, severe wear would happen to the pairs. By observing the edge of the contact interface during a test, we found that thin layers of debris were extruded out from the contact in the direction perpendicular to that of sliding. At the same time, flakes of debris were extruded from the contact in the sliding direction. Some of them piled up at the periphery of the pin, the rest formed sparks. The wear surfaces were usually flat but without significantly thick oxide films on them. The results also indicate that the tested pairs always required high shear forces to initiate an extrusion wear mechanism. Such phenomena are different from those resulting from oxidational, adhesive and abrasive wear mechanisms. The mechanism of this kind is now termed as extrusion wear.