Mehmet Ozan Özel

Quantitative image analysis of white etching areas in SAE52100 bearing steel

SAE 52100 bearing steel is a common steel grade for several types of bearings used in various applications such as automotive and wind turbines. It consists of a bainitic or martensitic matrix with 0.1 to 5 μm dia. spherical carbides. This material suffers from an unexpected failure mechanism where the bearing abruptly fails as early as 10% of its expected fatigue life [1]. The failure is associated with the formation of white etching areas (WEA) and white etching cracks (WEC) (named after their appearance after Nital etching) within the first millimeter below the contact surface. Different theories exist to explain these microstructural changes: hydrogen induced, carbide dissolution, initiation at inclusions, etc. To better understand the role of the operating conditions (loading, frequency, temperature, type of lubricants, etc.) on the WEA formation, a project was started with the aims of (1) reproducing bearing failures seen in the field within a laboratory-controlled environment, (2) correlating the observed microstructure to the operating conditions and ultimately (3) explaining the failure mechanism.