Effect of annealing time on microstructure and properties of high-strength non-oriented silicon steel with Nb addition

To meet the requirements for high-quality non-oriented silicon steel used in drive motors for new energy vehicles, Nb addition was employed to inhibit recrystallization based on the dislocation strengthening mechanism to produce high-strength non-oriented silicon steel with the thickness of 0.35 and 0.2 mm. The effects of annealing time at 760 °C on the comprehensive properties of non-oriented silicon steel were systematically investigated. It was found that about 92 % of Nb was dissolved in the matrix, which played a major role in inhibiting recrystallization, and the remaining Nb formed Nb (C, N) distributed in the grains and grain boundaries. As the annealing time increased, the magnetic properties were improved, while the mechanical properties declined. The 0.35 mm non-oriented silicon steel produced by single-stage cold rolling achieved optimal performance after annealing for 120 s: the yield strength was 604 MPa (the contribution of dislocation strengthening was about 147 MPa), the iron loss P 1.0/400 and magnetic induction B 50 were 32.78 W/kg and 1.643 T, respectively. Besides, the 0.20 mm non-oriented silicon steel produced by two-stage cold rolling after annealing for 100 s exhibited excellent properties, with the yield strength of 598 MPa (the contribution of dislocation strengthening was about 228 MPa), the P 1.0/400 of 30.26 W/kg, and the B 50 of 1.674 T. The addition of Nb to inhibit recrystallization expands the process window for industrial continuous annealing at the available temperature, and matching the appropriate annealing time can meet the requirements of producing high-strength non-oriented silicon steel.