Crack growth and microstructural changes in AISI 52100: white etching cracks (WEC) and fine granular area (FGA)

Abstract

The service life of rolling element bearings can usually be predicted with good accuracy. However, the damage phenomenon „white etching cracks” (WEC) can lead to premature and unforeseeable failures. The formation of zones with strongly decreased grain sizes at the crack faces is a characteristic of this type of failure. An earlier study showed that it is possible to reproduce this type of failure by multiaxial fatigue experiments with superposed cyclic compression and torsion. The present study shows the analysis of the stress state of those multiaxial fatigue tests with stress-based critical plane criteria. Using the critical plane results as a basis for a fracture mechanical analysis, a correlation is found between the crack length, the associated plastic zone size, and the extent of the transformed microstructure. This correlation is very similar to our results of the study of fine granular areas (FGA), a very high cycle fatigue phenomenon in bearing steels. It is argued that a plasticity-driven mechanism similar to the one proposed for FGA formation is responsible for WEC formation, too. Additional factors that are often cited as promoting WEC formation could explain the shift from very high cycle fatigue in the case of FGA to the early failures due to WEC.