The effect of microstructure and applied stress on magnetic Barkhausen emission in induction hardened steel

The influence of elastic deformation on the emission of magnetic Barkhausen noise (MBN) was investigated for induction-hardened low alloy steel with two different treatments: a standard temper (ST) and an over temper (OT) heat treatment. The rectified MBN profiles were found to be reversible with respect to loading and unloading, i.e., a profile that was changed by application of stress was recovered when the stress was removed. Characteristics of the profiles (peak height V _p, peak position I _p and half-width W _p) were recorded as a function of applied stressσ. Plots of V _p versus σ were S-shaped, with V _p reaching a maximum on the tensile side of the graph and a minimum on the compression side. In a more restricted stress range, between −500 and 1,000 MPa, V _p was an approximately a linear function of σ. The OT specimens showed greater sensitivity to stress than the ST specimens. Another difference was that the OT specimens produced an MBN profile with two overlapping peaks when under compression. The other profile characteristics showed a relationship with stress that ran counter to that of V _p, i.e., where V _p increased with increasing stress, I _p and W _p decreased. The observations are discussed in the light of established models of Barkhausen noise.