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The development of a long life rolling element bearing for use under severe conditions is fundamental and important technology from an economic and environmental standpoint. Previously, NTJ2 was developed as a semi-heat resistant long life bearing steel, using silicon as an alloying element to enhance its heat resistance and life. It is thought, though, that the demand for a bearing material that can withstand higher temperatures and have a longer life than NTJ2 will be needed in the future. Thus, a new heat resistant, long life material called STJ2 was developed optimizing the alloying elements in the silicon-alloyed bearing steel. The new steel has good dimensional stability to 250°C, long life and is very resistant to surface damage.

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.