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Progress in the steel making process has improved the rolling contact fatigue life of bearing steels. Based on identical tests, conducted periodically over the past 20 years, improvements in the rolling contact fatigue life of through hardening bearing steels and various carburizing steels are described. Improvements in steel quality may alter the influence of various factors on rolling contact fatigue life, and because of this it is necessary for them to be re-examined. Based on recent test data, the influence of factors such as oxygen content, alloying elements, fibre orientation, steel making procedure and heat treatment factors such as microstructure and cooling speed during quenching on rolling contact fatigue life are described.

Rolling contact fatigue lives of various steels used for medium- and large-sized bearings were investigated, using Φ60×ι90 specimen. Through hardened steels and induction hardened steels have nearly the same life, while carburized steels have lives about 3 times as long as that of through hardened steels. Since rolling contact fatigue life is affected by the cleanliness most significantly, it is most important to use clean steels for good bearing life. The influence of chemical compositions upon rolling contact fatigue life varied with cooling speed during quenching of the specimen. Using a steel which has excessively high hardenability for a small-sized bearing leads to a poor rolling contact fatigue life. For a medium or large-sized bearing we have to use a steel which has high hardenability necessary for the thickness of the bearing, but it seems unnecessary to pay close attention to the steel type.