Factors affecting grain growth of very thin silicon steel sheets

Very thin (less than 100 μm) grain oriented silicon steel sheets can be obtained by using a tertiary grain growth. This paper reports studies about factors affecting grain growth of very thin grain oriented silicon steel sheets. The effect of impurity was found to be large. In high-purity samples, secondary recrystallization began at higher temperature than that for low purity samples. In addition, an annealing time for completion of the tertiary recrystallization was a few minutes at 1323 K in the high-purity samples while it was several hours in the low-purity samples. The effect of a thickness annealing temperature and annealing atmosphere using the high-purity samples were investigated. The higher the annealing temperature is, the shorter becomes the induction period before the tertiary grain growth, and the larger the growth rate of tertiary grains. In the samples having thinner thickness, the growth rate of the tertiary grains becomes higher. By the annealing in a low vacuum or a hydrogen atmosphere, the growth rate of the tertiary grains decreased.