Comparative study on microstructure and texture evolution of low silicon non-oriented electrical steels along one-stage and two-stage cold rolling processes

Fe-0.9% Si-0.3% Al non-oriented electrical steels were fabricated by two-stage cold rolling process including hot rolling, first cold rolling, intermediate batch annealing, second cold rolling and final annealing, in which the first cold rolling reduction varied from 15% to 54%. One-stage cold rolling process with hot band normalization was also investigated for comparison. The findings revealed that, in two-stage cold rolling process, the final recrystallization texture and magnetic properties heavily relied on the rolling reduction schedule. As the first rolling reduction increased, the core loss increased and the magnetic induction decreased owing to the enhanced gamma-fiber ((111)//ND) texture in the final annealed sheets. Relatively lower first cold rolling reduction (15%) was beneficial to generate coarse grains during intermediate annealing and led to large grains with weakened gamma-fiber and enhanced Goss textures in final sheets. By contrast, relatively higher first cold rolling reduction (30% and 54%) caused small grains by promoting the occurrence of recrystallization during intermediate annealing and resulted in small grains with stronger gamma-fiber texture after final annealing. The hot band normalization in one -stage cold rolling process could also effectively improve the grain size prior to cold rolling, though MnS pre-cipitate and sharp gamma-fiber recrystallization texture were promoted in the final sheets due to the high normali-zation temperature and much higher cold rolling reduction, respectively. Therefore, two-stage cold rolling process was propitious to reduce gamma-fiber recrystallization texture and MnS precipitate compared with one-stage cold rolling process. The appropriate rolling reduction schedule (15%+75.6%) and suitable intermediate annealing process (750 degrees C for 1.5 h) were propitious to produce high-performance non-oriented silicon steel with lowest core loss and highest magnetic induction.

Automated summary

Non-oriented electrical steels with Fe-0.9% Si-0.3% Al composition were produced using a two-stage cold rolling process. The final recrystallization texture and magnetic properties were heavily influenced by the rolling reduction schedule. Different levels of first cold rolling reduction resulted in variations in grain size and texture in the final annealed sheets. Compared to a one-stage cold rolling process, the two-stage process showed reduced gamma-fiber recrystallization texture and MnS precipitate. The optimal rolling reduction schedule and intermediate annealing process resulted in non-oriented silicon steel with the lowest core loss and highest magnetic induction.