Magnetic nondestructive characterization of case depth in surface-hardened steel components

The magnetic hysteresis properties and Barkhausen effect signals in a series of induction hardened steel rods were studied through measurements and model simulations, with the objective of developing the measurement techniques for nondestructive evaluation of case depth. It was inferred from the measured hysteresis loop that magnetization reversal proceeded in two stages which took place in the core and the case of the hardened rods. The case depths of the samples were estimated by considering the hysteresis loops as a weighed sum of signals from the case and the core. The results were in good agreement with the nominal case depths determined from the hardness depth profiles.