Study of subsurface initiation mechanism for white etching crack formation

The present paper describes a novel way to detect early stages in the gradual transformation of SAE 52100 bearing steel material to white etching cracks (WEC). The underlying transformation is recorded and investigated by a complementary use of Barkhausen noise measurements, ultrasonic measurements and scanning electron microscopy. While ultrasonic measurements can only be used to detect cracks in a failed component, the recently improved Barkhausen noise measurement technique can be used to detect possible early stages of microstructural transformation. A cross section from a region without ultrasonic signal but with a Barkhausen signal has been investigated by the use of scanning electron microscopes in order to reveal possible pre-stages of WEC formation. These findings support that WEC are locally initiated in subsurface regions. Within those modified regions, carbides start to dissolve in consequence of deformation accumulation, which has been identified as an early state of WEA microstructure formation. This paper is part of a Themed Issue on Recent developments in bearing steels.