Influence of subsurface non-metallic inclusions on rolling contact fatigue behavior in bearing steels - Experimental and numerical investigations

The early failures in rolling bearings made of 100Cr6 (SAE 52100) steel have been observed in various industrial applications, which are associated with high maintenance and downtime costs. The damage is usually characterized in the form of axial cracks or volumetric breakouts on the running surface of the bearing components. Metallographic examinations revealed areas below the raceway that do not react to etching with alcoholic nitric acid and therefore appear visually white. These areas are referred to as "white etching areas" or "WEA" for short. Cracks that lead to bearing damage along these WEA are accordingly referred to as "white etching cracks" (WEC). This subsurface damage initiated from non-metallic inclusions has been identified as the dominant initiation mechanism in the formation of butterflies. This study presents a comprehensive analysis of the intricate mechanisms governing the formation of butterflies in SAE 52100 bearing steel, utilizing multiscale finite element modeling and detailed microstructural investigations. The research offers valuable insights into the role of nonmetallic inclusions, such as MnS, in butterfly formation, emphasizing that MnS influences butterfly formation through its size, orientation, and interactions with the inclusion-matrix interface. Moreover, it classifies butterflies into propagating and non-propagating types based on their interactions with the inclusion-matrix interface, revealing that non-propagating butterflies can coexist within the steel without causing bearing failure under specific conditions. In contrast, propagating butterflies, which lead to WEA formation, are unequivocally linked with bearing failure.