Local Hardening Evaluation of Carbon Steels by Using Frequency Sweeping Excitation and Spectrogram Method

This paper presents our proposed frequency sweeping excitation and spectrogram method (FSES method) by a magnetic sensor for non-destructive testing of hardened low carbon steels. This method can evaluate the magnetic properties of low carbon steels which were changed after induction heating treatment. It was examined by our proposed method that the degrees of yield strength of low carbon steels were varied depending on hardened conditions. Moreover, it was made clear that the maximum magnetic field strength, H-max, derived from the measured B-H loops was very sensitive to the hardening if the surface of the samples were flat.