Investigating eddy current response to Microstructural changes to Determine Case Depth of Induction Hardened Parts

Abstract

The ability to characterize hardness profile in induction hardened steel part is important from quality inspection point of view. Traditional destructive methods such as plotting hardness profile are generally time-consuming. Besides, the tests can not provide 100% quality control in a mass production line. Eddy current response of steel is sensitive to changes in microstructure of the material under investigation. So, the non-destructive method can be used in determining the depth of the hardened layer in steel parts due to the change in the microstructure from the surface to the core of the hardened part. In the present study, induction hardening technique was used to produce different case hardened depths in identical rods of CK45 carbon steel. Plotting hardness profile, effective and total case depths were determined. In order to investigate the applicability of the eddy current technique, relation between effective and total case depth and eddy current outputs (such as primary and secondary voltages and normalized impedance) were studied. High correlation coefficients of these relations indicate an acceptable level of accuracy in comparison with destructive method. © RILEM 2013.