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

Abstract

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 γ-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 γ-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 γ-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 precipitate and sharp γ-fiber recrystallization texture were promoted in the final sheets due to the high normalization temperature and much higher cold rolling reduction, respectively. Therefore, two-stage cold rolling process was propitious to reduce γ-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 °C for 1.5 h) were propitious to produce high-performance non-oriented silicon steel with lowest core loss and highest magnetic induction.