Surface hardening is commonly applied to improve wear and fatigue properties of industrial parts. From practical point of view, determining the depth of hardened layer is important in quality control process which is traditionally performed by the time-consuming and costly destructive method of micro-hardness testing. Eddy current test is a non-destructive technique which can be performed rapidly. Since the electromagnetic responses are sensitive to chemical composition and the microstructure of the materials under investigation, it can be used to determine the depth of the hardened layer in steels and cast iron parts due to the difference in magnetic properties of the hardened layer in comparison with the core of the specimens. In the present study, identical rods of ductile cast iron were case hardened using induction hardening technique and by plotting hardness profile, case depths were determined. In order to investigate the applicability of the eddy current technique, relation between case depth and eddy current outputs (primary and secondary voltages as well as normalized impedance) were studied. High correlation coefficients of these relations indicate an acceptable level of accuracy in comparison with the destructive method.

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