Magnetic characterization of surface-hardened steel

By the analysis of measured magnetization curves and hysteresis loops, the differential permeability and saturation magnetization of the rods were extracted. It was found that differential permeability increases with increasing case depth at a certain strength of the applied field (1350-1450 A/m) for both hardening mechanisms, but only significantly for induction-hardened rods. Saturation magnetization Ms was evaluated using the 'law of approach' and was observed to decrease as the depth of case hardening increases, for both induction-hardened and carburized steel rods. The observed behavior is described adequately by a simple model in which Ms for the rod is represented as a volume-weighted sum of saturation magnetization values in the core and in the surface layer.