Modeling and experimental study of a multi-frequency electromagnetic sensor system for rail decarburisation measurement

This paper presents a modeling and experimental study using a multi-frequency electromagnetic (EM) sensor system, for non-destructive evaluation of rail decarburisation. The EM sensor is configured with a H-shaped ferrite core, which was excited with a multi-frequency waveform over the range of approximately 1-100 kHz. Finite-element (FE) simulation was carried out to establish the link between the EM sensor output and the level of decarburization. Rail samples with different levels of decarburisation, due to different bloom reheat times prior to rolling were tested in the laboratory. It was found that the zero-crossing frequency of the EM sensor response is linearly proportional to the decarburisation level by FE simulation, theoretic analysis and experiment. This finding is helpful in understanding the response of the EM sensor to rail decarburisation and could lead to a non-contact, non destructive method for use during rail manufacturing. In addition, on-site measurement (tests carried out in the Rail & Section Mill at Tata Steel) was taken on a 110 m long rail product, with the results indicating that the EM sensor response correctly follows the expected decarburisation profile along the rail length.