The development of a multi-frequency electromagnetic instrument for monitoring the phase transformation of hot strip steel.

This paper describes the development of an instrument to analyze the phase transformations of hot strip steel using an electromagnetic sensor. The sensor exploits variations in the electrical conductivity and magnetic permeability of the steel to monitor microstructure evolution during processing. The sensor is an inductive device based on a H-shaped ferrite core, which is interrogated with a multi-frequency impedance analyzer (MFIA) containing a digital signal processor (DSP). An overview of the instrument and measurements from a range of carbon steels sample are presented. The results verify the ability of the instrument both to monitor the micro-structural changes and to reject variations in liftoff distance between the sensor and the hot strip