Microstructural Stability and Bearing Performance

Predicting rolling performance and dimensional stability of rolling bearings under all combinations of load and temperature becomes a real challenge in the material science discipline, even knowing the differences in bearing performance for different steel alloys and applied heat treatments. The consistently maintained high level of steel cleanliness in present day bearing manufacturing, based on modern steel making technology, is not the only decisive parameter minimizing the probability for spalling fatigue. A second highly important factor is the micro-plastic behavior of the steel under conditions of repetitive cyclic stressing. The steel's elastic response, acquired during running-in, will deteriorate after some time, increasing the probability for crack initiation at and around weak points in the steel matrix and crack propagation away from there leading to fatigue failure. Aspects of shakedown and materials decay are thus related to the probability for bearing failure to occur in combination with steel cleanliness. The ability to maintain an elastic response during cyclic stressing is determined on one hand by the combined effects of applied stress level, running temperature and number of revolutions, and on the other by the selected steel alloy, the applied heat treatment and the work hardening response during running-in. Examples are discussed of observed microstructural stability and superb bearing performance under extreme conditions.