Relationship of Melting Practice, Inclusion Type, and Size with Fatigue Resistance of Bearing Steels

The evaluation of numerous steelmaking practices and the consequences of process modifications have been assessed by both fatigue tests and analysis of the inclusions at the origin of fracture. Increasing the average size of oxides causes the fatigue properties to deteriorate; the harmful influence of large globular Al2O3-CaO inclusions was confirmed, and the role of other types such as titanium nitrides, alumina, and certain sulfides was clarified. General criteria of total oxygen or total titanium content are not related to the fatigue performance of steels manufactured by different steelmaking processes and practices; within an individual practice, however, they may serve as useful indicators of fatigue life. The poor correlation between standard cleanliness ratings and fatigue performances has been explained. The application of these results to qualification procedures and quality-control methods are discussed. Currently, the best quality assurance can be obtained through the qualification of the steelmaking practice by fatigue tests and a strict control over the reliability of the process by measurements of the critical parameters.