Monitoring of grinding burn via Barkhausen noise emission in case-hardened steel in large-bearing production

This paper deals with monitoring of thermally induced damage during grinding in case-hardened surfaces via magnetic Barkhausen noise (MBN) combined with other non-destructive techniques: positron annihilation spectroscopy (PAS) and X-ray diffraction (XRD). This study discusses the possible ways in which MBN signals could be calibrated as a function of microstructure expressed in terms of the heat-affected zone (HAZ) thickness, dislocation density, microhardness profile, or carbide distribution. It was found that MBN envelopes exhibit two peaks due to remarkable inhomogeneity of the carbide distribution. Resistance of carbides against elevated temperatures induced by grinding heat is employed in order to suggest the threshold MBN. It is concluded that, in the real production of large bearings for wind power stations, the MBN technique should be calibrated with respect to microstructural transformations rather than residual stress state.