White etching crack (WEC) failure is distinct to classical fatigue and driven by the composition of lubricants under special loading conditions; for example, slippage and electricity. The white etching area (WEA) within WEC contains carbon supersaturated ferrite (bcc-iron) and carbides, with a size of a few nanometers. This article presents investigations supporting the hypothesis that WEC processes start within a failure-free period by successive accumulation of a structural distortion. This can be measured by acoustic emission. Failure statistics show a steep ascent in the Weibull diagram (ß values beyond 1) leading to the assumption that WEC processes start unsuspicious, as one would see as a failure-free period, but imply a hidden subsurface accumulation of material defects. It is suggested and supported by the evidence presented within this article that WEC is neither related to the presence of nonmetallic inclusions nor related to other impurities in the steel. Instead, the failure is a sequence and accumulation of plastic deformations in the microstructure. Within the SAE 52100 material as discussed in this article, this accumulation is located in the microstructure around cementite, seen in a turn of hard magnetization toward soft magnetization proven by Barkhausen noise measurements. This decay is caused by the plastic deformation of such domains. Distortions in the vicinity of a cementite first would lead to carbon supersaturation by diffusion processes and later to a plastic deformation of the carbides. In the end, the complete distorted region will release the accumulated energy by downsizing the microstructure toward WEC.

Rolling bearings are one of the most widely used components in industrial machinery. If suitably mounted, loaded, lubricated and isolated from contamination, rolling contact fatigue (RCF) is believed to be the most probable mode of failure resulting in subsurface originated failures. Over the past several decades many researchers have studied the failure and microstructural alterations in bearings such as dark etching regions and white etching bands and how operating conditions such as pressure, temperature and running time impact them during RCF. This paper aims to provide an overview of such alterations, their properties, formation mechanisms and impact on bearing failure.

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White etching cracks (WECs), or white structure flaking, is a failure phenomenon that has been reported as emerging in rolling bearing parts for more than the past two decades. This failure mode appears only if, in addition to the normal Hertzian load, a so-called additional load is applied. WECs can occur regardless of the bearing type and size and in both oil- and grease-lubricated bearings. By modifying the testing conditions of an FE8 type test rig, it is possible to alter the failure mechanism from classical wear failures to WEC formations. This allows for easy, fast, and reproducible testing of materials and heat treatment variants to check their WEC formation propensity. This paper explains the methodology of testing on a FE8 test rig, the subsequent failure analysis, and the testing results. The tested components are produced from a wide range of commonly used bearing materials that in these tests are through hardened variants of low and high alloyed steels, case carburized steel with high retained austenite content, and inductive hardened quenched and tempered steel. In addition to the spread in the base materials with different contents of carbon and alloying elements, the variations in materials and heat treatments offer the possibility of significantly varying the content of retained austenite and the residual stress distribution. The results show that all the tested low alloyed materials fail with the WEC mechanism, whereas a significant increase in lifetime can be observed in terms of inductive hardened quenched and tempered steel. Only the nitrogen alloyed stainless steel Cronidur 30 demonstrates an outstanding performance without WEC formation.

The rings of rolling bearings are either through hardened with a martensitic or bainitic structure or case hardened. They differ in cleanliness, structure and residual stresses. The over-rolling fatigue resistance mirrors these differences. Typical results are given for over-rolling conditions causing classical fatigue, surface-initiated failure or failure by white etching cracking. This paper is part of a Themed Issue on Recent developments in bearing steels.