Effects of slab reheating temperature and hot rolling process on microstructure, texture and magnetic properties of 0.4% Si non-oriented electrical steel

Abstract

The effect of different slab reheating temperatures (1150 °C and 1000 °C), thicknesses of hot rolled sheet (2.8 mm, 2.3 mm and 2.0 mm) and coiling temperatures (630 °C and 750 °C) on microstructure, texture and magnetic properties of 0.4 wt% Si non-oriented electrical steel was comparatively studied in detail. This work focused on the effect of ultra-low temperature slab reheating and ultra-thin gauge hot rolling on magnetic properties. It was found that with the thinning of hot-rolled sheet thickness, the final grain size increased and iron loss decreased regardless of slab reheating temperature and coiling temperature. Lowering slab reheating temperature or increasing coiling temperature could further reduce iron loss. However, their effect on magnetic induction was relatively complex. When coiling at low temperature of 630 °C after hot rolling, decreasing thickness of hot rolled sheet did not always improve magnetic induction, but also depended on the reheating temperature. Because the low coiling temperature could not eliminate severely deformed grains in hot rolled sheets, which obviously deteriorated magnetic induction. To eliminate the deformed grains, coiling temperature was increased from 630 °C to 750 °C, and the microstructures were fully equiaxed grains. Both thinning hot-rolled sheet thickness and lowering slab reheating temperature promoted the development of shear bands during cold rolling, thus resulting in weakening γ-fiber (<111>//ND) texture and strengthening λ-fiber (<100 >//ND) in final sheets. As a result, the magnetic induction was significantly increased. Furthermore, the recrystallization behavior of different cold rolled microstructures during annealing was investigated using a quasi-in-situ electron backscattered diffraction (EBSD) technique.