Magnetic hysteresis and Barkhausen effect signal measurements offer realistic prospects for nondestructive evaluation of surface-modified magnetic materials, in particular for measurements of case depths of surface hardened ferrous components [1]. Recent systematic studies of induction-hardened steels with a range of case depths have shown a high degree of correlation between the depth profiles of hardness and magnetic properties including coercivity and Barkhausen signal [2]. In this study, we developed a model-based approach for determining case depths of surface hardened steels from hysteresis data. A magnetic hysteresis model was extended to simulate the observed two-stage magnetization reversal process which took place in the core and case regions of hardened samples under different applied fields. Case depths were estimated by modeling the hysteresis loop as a weighed sum of signals from the case and the core. The results were found to agree with the values measured from the hardness depth profiles.
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