Processing and Microstructure of Grain Non-Oriented Electrical Steel Strips with Improved Magnetic Properties

The effects of annealing prior to cold rolling on the microstructure and magnetic properties of a low-C grain non-oriented (GNO) electrical steel strip have been investigated. It is shown that annealing of the hot-rolled strips in the intercritical region, Ac-1<T<Ac-3, causes rapid decarburization and development of large columnar ferrite grains. This microstructure leads, after cold-rolling and a fast annealing treatment at temperatures between 800 and 850 degrees C, to a polygonal ferrite gain microstructure with magnetic properties superior to those observed typically in the same steel in the industrial fully processed condition. The results are attributed to the {100}-fiber texture developed during the final annealing. Annealing at T<800 degrees C or T>850 degrees C results in formation of {111}-fiber texture components due to recristallization or transformation of deformed ferrite leading to a negative effect on the final magnetic properties. The results suggest that annealing prior to cold rolling offers an attractive alternative processing route for the manufacture of fully processed low-C, Si-Al GNO electrical steels strips.