Effect of time of a two-step annealing on the microstructure and magnetic properties of non-oriented electrical steels

In the present work, columnar microstructures were developed in the hot-rolled material by a two-step thermal treatment consisting of two stages: the first one conducted at 1150 degrees C for different times (10, 20, and 30 min), followed by a second stage conducted at 850 degrees C for 9 h. Samples were then processed by cold rolling and a final thirty-minute annealing conducted at 850, 900, and 950 degrees C. The results show that, although a duplex microstructure consisting of small equiaxed grains and large columnar grains was obtained prior to cold rolling, there was an improvement in the magnetic behavior of the final products compared to those properties obtained in samples processed without modification. The improvement was related to grain size increase and carbides reduction caused by the two-step thermal treatment.