Applications of Impedance Plane and Magnetic Differential Permeability in Microstructural Characterization of AISI D2 Tool Steel

Abstract

Two nondestructive electromagnetic techniques, hysteresis loop and eddy current methodologies, have<br><br>been used to characterize the microstructural changes of D2 tool steel in the course of quench and<br><br>tempering treatments. To measure the retained austenite fraction in the quenched microstructure, six<br><br>specimens were austenitized in the range of 1000-1130 °C. Samples austenitized at 1080 °C were also<br><br>tempered in the range of 200-650 °C for characterization by eddy current and magnetic hysteresis loop<br><br>outputs.. Impedance point movement and maximum differential permeability were measured as a<br><br>function of austenitizing/tempering temperature to characterize the microstructural features. The study<br><br>showed that good correlations exist between microstructural variations detected by destructive methods<br><br>(hardness, XRD and microscopic observation) and outputs of the nondestructive techniques.