Effect of Cu addition on microstructure, texture and magnetic properties of 6.5 wt% Si electrical steel

The effect of Cu addition in the range of 0 - 1.0 wt% on the magnetic induction and iron loss of 6.5 wt% Si electrical steel is investigated. The microstructure and texture of the steels are also analysed to reveal the mechanisms by which their magnetic properties after annealing are affected by Cu addition. Cu addition up to 0.7 wt% is found to increase magnetic induction B50 although the increase is very small due to the formation of eta-fiber texture. The iron loss of 6.5 wt% Si electrical steel decreases with increasing Cu addition to up to 0.5 wt%, but increases with further Cu addition. When Cu addition is increased to 0.7 wt%, the iron loss for this steel becomes higher than for that without Cu addition. Microstructural analysis suggests that Cu addition of up to 0.5 wt% can promote the recrystallization during annealing and increase the recrystallized grain size, leading to a decrease in iron loss. With further increase in Cu addition, especially beyond 0.7 wt%, large numbers of fine epsilon-Cu precipitates form in the microstructure during warm-rolling, which inhibit grain growth during annealing. This is the main reason for the observed increase in iron loss when Cu addition is over 0.5 wt% Cu. The Cu addition range for achieving the optimum magnetic properties for 6.5 wt% Si electrical steel is 0.3 - 0.5 wt%.