Microstructural Characterization of Quenched AISI D2 Tool Steel Using Magnetic/Electromagnetic Nondestructive Techniques

In the past decade, nondestructive electromagnetic techniques have been extensively used for the characterization of materials. In this paper, the relation between the microstructural/mechanical characteristics of D2 tool steel with magnetic and electrical properties and eddy current (EC) test outputs has been established. Quenched samples obtained from different austenitizing temperatures (from 1000°C to 1130°C) were used to investigate the effect of retained austenite, martensite, and carbides phase fraction as well as prior austenite grain size, on the electromagnetic properties such as electrical resistivity and magnetic saturation. Variations of induced voltage in the pickup coil and location of impedance point in the impedance plane as a function of austenitizing temperature were interpreted by considering the changes in magnetic saturation and electrical resistivity and their effects on the EC outputs. This paper indicated that there is a good correlation between the EC parameters and retained austenite.