Magnetic Properties and Strengthening Mechanism of Cu-Bearing Non-Oriented Silicon Steel

The effects of Cu content on the microstructure, texture, precipitates, and magnetic and mechanical properties of 0.20 mm-thick non-oriented silicon steel (3.0% Si-0.8% Al-0.5% Mn) were systematically investigated using optical microscopy, X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. The strengthening mechanisms of Cu-bearing high-strength non-oriented silicon steel were further elucidated. Increasing Cu content inhibited grain growth and suppressed the development of the α*-fiber texture in annealed sheets, while promoting the formation of γ-fiber texture. As a result, the P1.0/400 and B50 values deteriorated. The P1.0/400 and B50 values of 1.47% Cu non-oriented silicon steel were 13.930 W/kg and 1.614 T, respectively. However, due to the solid solution strengthening effect of 0.5% Cu and partial precipitation strengthening, the Rp0.2 increased by 43 MPa. After aging treatment at 550 °C for 20 min, the P1.0/400 values of the aged sheets slightly increased, while the B50 values remained almost unchanged. In the aged sheets containing 1.0–1.5% Cu, clustered Cu-rich precipitates with average sizes of 2.71 nm and 13.28 nm were observed. The crystal structure of these precipitates transitioned from the metastable B2-Cu to the stable FCC-Cu. These precipitates enhanced the Rp0.2 of the non-oriented electrical steel to 241 MPa and 269 MPa through cutting and bypass mechanisms, respectively. A high-strength non-oriented silicon steel with balanced magnetic and mechanical properties was developed for driving motors of new energy vehicles by utilizing nanoscale Cu-rich precipitates formed through aging treatment. The optimized steel exhibits a yield strength of 708 MPa, a magnetic induction B50 of 1.639 T, and high-frequency iron loss P1.0/400 of 14.77 W/kg.