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Production of energy saving high silicon electrical steel by hot dip coating and diffusion annealing (DIFFANSTEEL)


Technical parameters have been determined to allow coating of steels with an Al-Si alloy by hot dipping and subsequent diffusion annealing to give gradient or through thickness silicon contents in excess of the base material composition. Enhanced Si and Al contents resulting from these treatments should give the steel enhanced electrical and magnetic properties.
Pickling techniques have been developed to remove the highly corrosion resistant Al and Si layers which result from diffusion annealing of hot dipped electrical steels. Different regimes are required depending upon whether intermediate cold rolling has been carried out to reduce the strip and coating thickness. The techniques are only applicable to pickling of these high Al content coatings in preference to the base strip and as such have limited use outside the project or any successor.
The use of an intermediate cold rolling step between hot dipping with Al-Si and diffusion annealing, to produce a near final thickness strip with increased Si content. The surface finish after dipping is also improved. Advantages result in the: - Magnetic properties - Flatter strip - Reduced coating thickness and increased uniformity therefore more consistent properties ad easier pickling. - Removal of need for cold rolling to final thickness in the potentially brittle high Si state post diffusion annealing.