Bearing steels with grinding burns studied by Barkhausen noise and advanced microscopy techniques – Role of carbides stability in steel performance

Magnetic Barkhausen noise (MBN) signal is very sensitive to microstructure and stresses of the sample. However, many details of the link between microstructure and MBN signal still remain to be understood. Here, advanced microscopy techniques together with X-ray diffraction method were used for characterization of the industrially-relevant steel structures and the results were linked to the MBN signal outcomes. This study deals with thermal burn during grinding cycles of two different roll-bearing steels, case-carburised (CC) steel and 100Cr6 bearing steel, with different carbide structures. Thermal stability of steels is analysed with many different characterization and visualisation methods to link the structural features affecting the observed magnetic Barkhausen noise signal changes. Due to the different manufacturing operations and compositions of the studied steels, the carbide structure and produced magnetic domain structure, were observed to vary in addition to their different MBN behaviour against thermal burn. Larger and more stable carbides in 100Cr6 bearing steel were noticed to tolerate better the thermal load whereas case-carburised steel underwent more changes in the microstructure and also in the MBN. The work explores the role of structure on carbide stability and discusses the correlation between Barkhausen noise signals and key factors, such as dislocation density, retained austenite fraction, residual stress state, domain wall thickness, and particularly carbide size.