Abstract
The influence of ferritic steel samples with different case-depths on the distortion behaviour of magnetic excitation voltage has been investigated. The systematic changes in the height and position of the peak and the trough on the ((dVE/dt) vs. VT) profile (distortion analysis of the magnetic excitation, DAME profile) reflect the difference in the magnetization process and hence the effect of distortion of VE in samples with different case-depths. This study shows the potential of this simple DAME method for evaluation of ferromagnetic steel components.
Highlights
The depth of surface hardening, known as “case-depth”, is normally determined from the hardness-depth profile obtained by the destructive method of hardness measurements in the cross-section of a surface hardened sample
The distortion analysis of magnetic excitation (DAME) profile in other half of magnetisation cycles is symmetrical, but is on the negative side of axis, which is not shown here for better clarity
The distortion behaviour depends on the microstructural condition of the sample supporting the influence of variation in rate of change of permeability associated with magnetisation process in ferromagnetic samples with different surface hardened case-depth
Summary
The depth of surface hardening, known as “case-depth”, is normally determined from the hardness-depth profile obtained by the destructive method of hardness measurements in the cross-section of a surface hardened sample. The low frequency MBN technique has been shown to reveal systematic changes in the two-peak MBN profile caused by the magnetisation process of softer and harder microstructural regions in different ranges of magnetic field strength [6]. It can clearly detect variations in case-depth less than ~1 mm. This study [9] does not clearly support the fact that the detected MBN signals are subjected to limitation of skin-depth due to electromagnetic attenuation similar to eddy current method These NDE techniques are relatively cumbersome for application on components. The MBN technique requires meticulous optimisation of maximum applied magnetic field strength and sensitivity and frequency response of MBN pick-up coil for maximising the MBN profile for appropriate detection of different case-depths [10]
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