Optimized rolling processes to balance magnetic and mechanical properties of high-strength non-oriented silicon steels

Abstract

A bottleneck in the development of high-strength non-oriented silicon steels for drive motors of new energy vehicles is the balance of strength and magnetic properties. This paper successfully tackled this problem through the optimization of thickness reduction for hot and cold rolling and the formation of coherent precipitates using a Cu-alloyed non-oriented silicon steel. More specifically, a thickness reduction of 96% in the course of hot rolling promoted the homogenization of microstructure during the following normalization treatment. Subsequently, a deformation degree of 80% during cold rolling ensured the inheritance of the uniform microstructure and inhibited the abnormal growth of recrystallized grains during annealing, thereby suppressing the iron loss to a value as low as 15.6 W/kg. At the meantime, this combined process promoted the inheritance of λ-fibers and the formation of {114}〈481〉 texture in the annealed sheet, improving the magnetic induction intensity B50 to 1.606 T. In addition, under the joint effect of a variety of strengthening mechanisms, the yield strength of this annealed sheet reached 668 MPa. A pronounced increase in strength, about 207 MPa, was derived from precipitation hardening by the great difference in the modulus between coherent Cu-rich clusters and the α-Fe matrix.