SAE International Fatigue Performance Improvements of Wheel Bearing Rolling Elements 2017-01-2524

Wheel bearings are safety-critical automotive components. For this application, the steel rolling elements are subjected to fatigue failure and therefore play a key role in overall bearing fatigue life performance. This performance is influenced by metallurgical, mechanical, and physical properties obtained by precise manufacturing process parameters. These properties are continuously analyzed and are evolving at all bearing manufacturing companies. Last year, the Precision Bearing Components (PBC) Group of NN Inc., a global supplier of steel rolling elements for wheel bearings, developed a non-conventional heat treatment process for 100Cr6 (SAE 52100) rolling element steel for improved fatigue performance. The results of wheel bearing rolling contact fatigue (RCF) tests showed the importance of rolling element dimensional stability. As retained austenite transformed to the martensite phase, rolling element volume increase occurred, leading to fatigue failure. The fatigue life of rolling elements is directly proportional to their dimensional stability. As a result of the experimental tests, a project was initiated with the goal of increasing the dimensional stability of rolling elements, thereby enhancing RCF performance. The use of another conventional steel alloy not typically applied in automotive wheel bearing applications was the proposed solution. The goal of this new application package of rolling elements is to improve fatigue performance: in particular, sub-surface fatigue, as well as increased resistance to wear and stability at higher operating temperatures. A subsequent evolution of the project will be to develop a non-conventional alloy grade for greater rolling element dimensional stability, resulting in an expected expansion of fatigue performance.