Multi-frequency electromagnetic sensor measurement of ferrite/austenite phase fraction-Experiment and theory

摘要

A multi-frequency electromagnetic sensor was used to measure the impedance and inductance of samples containing varying fractions of ferromagnetic phase over a range of frequencies (100 Hz to 1 MHz). The impedance values are approximately linearly related to ferrite fraction for random microstructures up to about 40 percent ferrite, at which point the ferrite increasingly forms connected pathways and the impedance signal does not increase significantly. The zero cross-point frequency was found to distinguish between samples with higher (>40 percent) ferrite percentages and can be related to the effective relative permeability of the sample.