Effect of solute carbon present during cold rolling and annealing on the magnetic properties of electrical steels

Abstract
Fully processed (FP) electrical steels benefit from vacuum degassing thanks to the improved cleanliness and the superfluity of decarburisation during annealing. On the other hand, it is known from research on deep drawing steels [1], that lowering the carbon content by vacuum degassing significantly increases the intensity of (magnetically unfavourable) [111]-grains in the final product. In this paper. it is shown for three FP-steels with Si-contents between 0 and 1.8 wt % that a higher amount of solute carbon (C,) present during cold rolling and annealing results in an increase of the magnetic polarisation measured in the rolling direction. The polarisation in the transverse direction is almost independent of C, and so are the eddy current and hysteresis loss. The observations can be explained by the fact that solute carbon promotes a higher intensity of magnetically favourable Goss grains and in a lover intensity of [111]-grains. The current study implies that in non-degassed steels, carbon can be used to improve the magnetic polarisation, provided coiling after hot rolling retains sufficient carbon in solution. For degassed steels, this work shows that there is no reason to reduce the C-content below the 30 ppm for prevention of magnetic ageing.