New Steels Now in Use for Automotive Rolling Element Bearings

With the development of clean steels, the influence of retained austenite on the rolling contact fatigue (RCF) life has changed. Under clean oil lubrication, the favorable influence of retained austenite disappeared. Utilizing this phenomenon, a long life material for high temperature was developed with the use of the element Si which improves the heat resistance of steel. With the continuous casting becoming common steel making process, alloying elements should better be minimized because they cause segregation. From this point of view, a medium carbon through hardening steel which has competing RCF life with SUJ2 was developed. Under debris contaminated lubrication, retained austenite has ever favorable effect on RCF life. For these reason, surface modification is important. Long life bearings under debris contaminated lubrication were developed by carbonitriding a through hardening steel or a carburizing steel, respectively.