Recently, characterization of properties of materials has been the focus of intense investigation. Magnetic response of steels parts to an applied field, using non-destructive Eddy Current method, is sensitive to microstructure of the part. By calibrating this correlation any change in microstructure such as grain size or any specific phase percentage could be detected which can be used for quality control of heat treated parts in mass production. To investigate the ability of the method for separation of different microstructures, cylinders of steel (CK45 ) have been subject to different heat treatment cycles including normalizing, annealing ,quenching and quenching &full tempering. To study and evaluate the effect of grain size, various grain sizes produced in samples of CK20 steel. Determining the optimum frequency, eddy current testing was applied for all samples and the response to electro-magnetic field such as primary and secondary voltages and normalized impedance has been established and correlation coefficient (R2) has been calculated. The study shows Eddy Current method could be successfully used to distinguish and separate undesired parts during mass production heat treating. The results indicate that a good relationship can be established between grain size and normalized impedance (R2=0.96). Besides, to separate different microstructures (CK45), best correlation appeared to be for normalized impedance with the applied frequency of 200Hz.

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