Real time in-line measurements of phase transformation in structural steels

Zhou, Lei; WMG, Warwick University; United Kingdom

Davis, C.; University of Warwick; United Kingdom
Hall, R.; Tata Steel; United Kingdom
Kok, P.J.J.; Tata Steel; Netherlands
van den Berg, F.D.; Tata Steel; Netherlands
Yang, H.; Tata Steel; Netherlands
Zhou, L.; University of Warwick; United Kingdom

ID: ECNDT-0415-2018
Session: Modeling and data processing Electromagnetic Techniques 2
Room: J2
Date: 2018-06-12
Time: 11:50 - 12:10

EM sensors, such as EMspecTM, operating at a low applied magnetic field, are sensitive to the low field relative permeability of steel, which depends on the microstructure. EM sensors have recently been shown to be a viable method for in-line monitoring of phase transformation during steel processing with the benefit of being non-contact, having a short response time and not being influenced by steam or dust. The objective is to have a quantitative measurement of the phase fraction at high temperature to be used for in-situ feedback control of cooling to allow optimization of the microstructure formed. Models have been developed that relate the sensor signals to the magnetic and electrical properties of the steel, which are in turn related to the microstructure, in particular the phase balance.

In this paper, a cylindrical shaped EM sensor has been used to measure a range of steels, and hence microstructures, during heat treatment up to 800 °C. The electrical resistivity change with temperature is measured separately. The relative permeability values at temperature are determined by fitting the experimental values to a sensor output model developed using finite element software (COMSOL Multiphysics). Based on these permeability values, the ferrite fractions are predicted using previously developed microstructure-permeability models and compared with interrupted microstructure measurements. The relative permeability and electrical resistivity can then be used in EMspecTM sensor models to determine the sensor response to transformation.