Non-Contact Evaluation of Hardened Steel Samples using Inductive Spectroscopy

When the metal undergoes the process of cold work and temperature treatment, the magnetic properties of the metal changes. The determination of metal hardness is vital in these processes. Thus, the need for non-destructive metallic material hardness analyzers is increasing.In this paper, we propose to design, test and evaluate an inductive sensor system, which can analyze the hardness level of metallic materials in relation to the lift-off between metal surface and coil sensor. In this work, we have used an eddy current inductive sensor, which can differentiate between unhardened and hardened metal surface on the basis of magnetic properties like ‘permeability’. The eddy current sensor was designed and tested with an impedance analyzer in the frequency range of 4 kHz to 4 MHz over the metallic surface and the inductance results were compared to the Dodd and Deeds model simulation on MATLAB. The system evaluation shows the different permeability values for unhardened and hardened metal surfaces thus, Dodd and Deeds model together with non-contact inductive sensor system design can be used for analysing hardness level of ferromagnetic materials.