Microstructural Development of Electrical Steels under Si and Al Diffusion

The effect of Si and Al diffusion from a coating in the microstructure of electrical steels have been investigated for three different processing routes. In general the final texture is not affected by the diffusion of Si or Al from the coating whereas the grain size and mor- phology can be affected if the silicon content of the substrate is low enough to allow phase transformation. The gamma to alpha phase transformation caused by the diffusion of Si and Al determines the grain size and morphology resulting in columnar grain growth. The evolu- tion of the microstructures during the diffusion annealing for the production of high Si steels shows some common features with the microstructure evolution during the grain growth in conventional low silicon (Si < 3 wt.%) electrical steels.