Thin-gauge non-oriented silicon steel with balanced magnetic and mechanical properties processed by strip casting

Abstract

Thin-gauge non-oriented silicon steel with high strength was successfully processed using strip casting. Texture evolution and strengthening mechanism via nanoscale Cu-rich precipitates were studied to fundamentally understand the balanced combination of magnetic properties and mechanical properties. Coarse equiaxed grains with average size of ∼190 μm and relatively random texture were formed in the as-cast strip, which contributed to the inhomogeneous deformation, resulting in high density of shear bands. Exact Cube was retained from the initial Cube texture and new Goss was formed during the heavy rolling process in the 0.20 mm cold rolled sheet, which promoted relatively strong Cube and Goss texture after recrystallization annealing. The 0.20 mm annealed sheet exhibited high magnetic induction of 1.709 T, which corresponds to the high texture factor of 0.5. The total iron losses were significantly reduced with decrease in thickness, and the P1.5/50, P1.0/400, and P1.0/1000 in 0.20 mm sheet were as low as 2.63, 15.17 and 55.63 W/kg, respectively, which showed a good match between magnetic induction and iron loss. During the aging process, both the magnetic induction and total iron loss exhibited relatively good stability. With increase in aging time, the yield strength first rapidly increased and then slightly decreased. In 0.20 mm sheet, peak yield strength of ∼630 MPa was obtained on aging at 550 °C for 90–120 min. The key mechanism of precipitation strengthening was attributed to the difference in modulus and coherency strain associated with high density of nanoscale precipitates of ∼5 nm. The study revealed that the nanoscale Cu-rich precipitates can be adopted as effective approach to increase the yield strength over ∼100 MPa without deteriorating iron loss in thin-gauge non-oriented silicon steel by strip casting, which guaranteed the balance of magnetic properties and mechanical properties to meet the requirements of high-speed motor.