Characterization of Structural Materials Using AC Permeability

Magnetic properties derived from major hysteresis loops are sensitive to the microstructures of iron-based steels and have therefore been used for nondestructive evaluation of degradation in ferromagnetic materials contained in structural components. A permeability obtained from an ac small field excitation may be a more useful parameter than one obtained from a major hysteresis loop from the viewpoints of electricity consumption and realtime measurement. In this paper, the relation between the ac permeability calculated from impedance measurements of coil elements and the ductile-brittle transition temperature (DBTT) and Vickers hardness of S15C steels is clarified. The possibility of nondestructive evaluation (NDE) using ac permeability measurements is also discussed.