The influence of steel microstructure and inclusion characteristics on the formation of premature bearing failures with microstructural alterations

The formation of premature cracking damage associated with local microstructural alterations, commonly referred to as “white etching cracks” (WECs) has led to unpredictable bearing failures in numerous industrial applications. WECs are known to occur in the field independent of material characteristics such as heat treatment, predominant microstructure and surface coatings, as well as lubricant characteristics such as additive packages and viscosity. However, WECs have proven difficult to recreate at a benchtop scale; to date, no benchtop test has been reported to recreate WECs using commercially available field lubricants. The present work intends to identify key differences between the microstructure of field bearings and the microstructure of benchtop samples, focusing on the characteristics of the inclusions contained in both steels. Synchrotron scale X-ray tomography revealed that AISI 52100 steel used in industrial scale field bearings contained a drastically different inclusion microstructure then the AISI 52100 steels used in standard benchtop test specimens. Additionally, the authors were able to form WECs in test samples manufactured out of the steel of a field bearing using fully formulated field lubricants; a finding which has not yet been reported in open literature.