Em sensor array system and performance evaluation for in-line measurement of phase transformation in steel

In a hot strip mill (HSM), the evolution of phase transformation in steel during the dynamic cooling process on a runout table has a significant effect on the microstructure and mechanical properties of hot-rolled materials and further processing in the subsequent processing steps. An electromagnetic (EM) sensor array system, EMSpec® (ElectroMagnetic Spectroscopy), has been developed for in-line measurement of steel phase transformation. The first industrialised system has been installed on the run-out table (ROT) of HSM #2 at Tata Steel in the Netherlands for industrial trials. The EMSpec system consists of multiple sensor nodes located at different positions on the run-out table. Each sensor node measures the impedance spectrum, from which the amount of transformed phase fraction is determined based on a measurement model. All of the sensor nodes are calibrated for the delivery of proper sensor signals, such that progressively increasing phase transformation of the steel strip travelling from one node to the next can be correctly measured. Besides the sensing principle and system calibration, this paper presents in-line measurement results, which are interpreted and compared with phase transformation predictions from a physical thermodynamic and kinetic phase transformation model