Barkhausen noise in steels

Abstract

A survey of the methods of observing Barkhausen noise was made and a suitable system of measurement Identified for laboratory measurements to be carried out on steel samples. A coil system to measure the Barkhausen noise from samples was constructed. The noise was sampled and recorded to microcomputer by means of a transient recorder. The experimental parameters were selected to optimise the data. A Fast Fourier Transform was performed on the noise data by means of a library routine on a mainframe computer and the results plotted as the power spectra of the data. The recorded voltage profile of the noise was also plotted. The system was verified by use of grain oriented silicon iron samples. The power spectra and voltage profiles were plotted and, when compared with the results of other workers, were found to be favourable. Tests were performed on constructional steel samples. The power spectra and voltage profiles from the constructional steels were considered with the coercivity and remanence of the steels and a relationship sought. No simple general relationship was identified although empirical relationships were suggested for some of the data. A knowledge of the microstructure of the steel is required to explain some of the results. The power spectra and voltage profiles were assessed in terms of the hysteresis loop shape and influence of microstructure on the value of coercivity. It was found that these were the influencing factors in the Barkhausen noise. The effect of plastic deformation on power spectra was investigated. Results of an industrial investigation were reported.