Hardness profile plotting using multi-frequency multi-output electromagnetic sensor

Induction hardening technique was used to produce different case depths on nine AISI 1045 steel rods. Determining the optimum frequency for each depth below the surface, relations between eddy current outputs (primary and secondary voltages and normalized impedance) and hardness at each specific depth were investigated. Finally, the hardness values for each depth with the optimum eddy current output were determined and hardness profiles were plotted nondestructively. Comparisons were made with destructive hardness results.