Influence of oxide films on the wear of steels

Abstract

The effect of oxygen-free atmospheres (nitrogen and hydrogen) upon the wear of a hypoeutectoid, a eutectoid, and a hypereutectoid carbon steel was studied. It was found that when these steels were hardened and subsequently tempered at low temperatures, the rates of wear were comparatively low; the wearing surfaces were smooth and were covered by a thin oxide film and the abraded particles consisted of Fe2 3 and Fe 3 4. When these steels were tempered above certain temperatures, the rates of wear were extremely high; the worn surfaces were very rough and bright and the abraded particles were metallic iron. Microscopic examination showed that those steels which had rough, film-free worn surfaces had severely distorted structures adjacent to these surfaces. In the case of steels which showed only the filmed, worn surfaces, the structures adjacent to these surfaces were not greatly changed by the wear test and the worn surfaces themselves were smooth. The severely distorted structure was also observed in the case of certain steels which showed characteristics of both types of wear. Numerous cracks intersecting or approximately parallel to the worn surfaces were observed in the microexaminations of both types of surfaces. These tests indicated that a film of either ferric or ferroso-ferric oxide on the wearing surfaces of carbon steels results in a certain degree of protection against wear, probably by preventing actual metal-to-metal contact. When these films are absent, severe wear of a galling type takes place. Page