Wear of Low Alloy Steels at Elevated Temperatures

Abstract

A pin on disc wear machine was used to study the wear behaviour of EN8 and EN31 low alloy steels at various loads and at disc temperatures ranging from room temperature to 500°C. Wear rate, frictional force and temperatures of the pin and disc were continuously monitored during each test. The wear debris and worn samples were examined using x-ray diffraction techniques for the identification of compounds produced by the wear process. Scanning electron microscopy of worn samples provided not only valuable topographical information but also a direct measurement of the thickness of surface oxide films. Auger electron spectroscopy was employed to study oxygen and iron concentration depth profiles on some selected worn pin surfaces. Under all loads and temperature conditions the mechanism which was prevalent in the wear process was mild oxidational wear. It was found that transitions occur in the wear rate versus load curves at certain critical loads, the magnitude of which increase with temperature. These transitions were found to be associated with change in surface oxide, lower wear rates being recorded when the predominant oxide was the spinel Fe304,. At disc temperatures above 300°C out of contact oxidation appears to be the most important wear limiting factor. A method was developed enabling contact temperature, numbers and size of contacts and critical oxide film thickness to be deduced from direct measurements of heat flow into the pin. Remarkable agreement was found between oxide thicknesses estimated from this method and measured values using a scanning electron microscope.