Modelling the electromagnetic response of two-phase steel microstructures

Multi-frequency electromagnetic sensors have the potential to provide the signals necessary for on-line processing control of two-phase steel microstructures. Experiments on model steel samples show that both air-cored and ferrite-cored sensors can measure the ferrite fraction from 0% to 100% by choosing appropriate parameters. The electromagnetic response of the two-phase microstructures was modelled using multi-scale numerical models. At the micro-scale, the effective permeability of the two-phase microstructure was modelled based on the actual microstructures of the model samples and simulated banded microstructures. It was found that currently available effective medium theories used in this study are not sufficient to describe the effective permeability over the whole range of ferrite fraction. The effective permeability was significantly affected by ferrite morphology and distribution. At the macro-scale, the sensor output was linked to the effective permeability using the real sensor and sample geometries. The modelled results show good agreement with measured results.