Determination of the rolling direction of electrolytic zinc-coated steel plate by Barkhausen emission

An electrolytic zinc-coated steel plate is inspected by the Barkhausen emission (BE) measurement. In the fabrication of steel plates, the rolling process is always employed. Such a rolling process would greatly alter the microstructure as well as the grain orientation of the steel plate; it turns out that the defect density will have various distribution inside the steel and the grains will be elongated in the rolling direction. Due to the fact that BE measurement is sensitive to the microstructure of steel, we have obtained different BE profiles when the magnetizing field is applied in different directions, during the BE measurements. When the magnetizing field is perpendicular to the rolling direction, a two peak BE profile is obtained; between the large initial peak and the small final peak there exists a central dip. This indicates that the magnetization process involves the domain nucleaion, wall motion and annihilation. On the other hand, when the magnetizing field is applied along the rolling direction, the BE profile contains only one peak, which implies the magnetization process is largely due to domain wall motion.