Effect of rolling reduction on microstructure, texture and magnetic properties of twin-roll casting non-oriented 6.5 wt% Si electrical steel

Abstract

In this study, an as-cast strip of non-oriented 6.5 wt% Si electrical steel with an equiaxed structure was fabricated by twin-roll strip casting and then treated by hot and warm rolling with different reductions, and annealing. The results showed that the as-cast microstructure was gradually pancaked and then underwent dynamic and static recrystallization as the hot rolling reduction exceeded 52%. The subsequent warm rolling brought about shear bands in part of the deformed grains. The texture evolution in the multiple rolling routes basically conformed to the classical gain-orientation rotating paths. The {001}∼{118} 〈110〉, {223} 〈110〉 and {111} 〈110〉 texture components were intensified after warm rolling. A decreased hot rolling reduction accompanied by an increased warm rolling reduction raised the number of shear bands in the warm rolled sheets and decreased the annealing grain size. An improper combination of hot and warm rolling reductions tended to make the γ nuclei gain the superiority in number through grain-boundary or shear-band nucleation, leading to the prevalence of the γ annealing texture. By comparison, an alternative rolling regime adopting moderate hot (∼50%) and warm rolling (∼70%) reductions promoted the oriented nucleation of λ, {114} 〈48¯1〉 and many other non-γ nuclei in shear bands of the {223} 〈110〉 deformed grains which had already acquired a high volume fraction in the warm rolled sheet. Consequently, mixed λ, α* and γ annealing textures were formed, giving rise to enhanced magnetic properties. The combined oriented nucleation and oriented growth mechanism was responsible for the overall evolutions of the annealing textures.