The present paper investigates the potential of using eddy current technique as a reliable nondestructive tool to detect microstructural changes during the different stages of tempering treatment in AISID2 tool steel. Five stages occur in tempering of the steel: precipitation of ɛ carbides, formation of cementite, retained austenite decomposition,secondary hardening effect and spheroidization o fcarbides.These stages were characterized by destructive methods,including dilatometry, differential scanning calori- metry, X-ray diffraction,scanning electron microscopic observations,and hardness measurements.The microstructural changes alter the electrical resistivity/magnetics aturation,which, in turn, influence the eddy currentsignals.Two EC parameters,induced voltage sensed by pickup coil and impedance point detected by excitation coil,were evaluated as a function of tempering temperature to characterize the microstructural features, nondestructively. The study revealed that a good correlation exists between the EC parameters and the microstructural changes.

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