Microstructure evolution and strengthening mechanism in thin-gauge non-oriented silicon steel with high strength

• Thin-gauge non-oriented silicon steels with high strength were processed with different strengthening mechanism. • Strong {100} texture was retained during hot rolling and final annealing in composite strengthened steel. • High magnetic induction B 50 of 1.724 T and extremely low iron loss P 1.0/1000 of 51.415 W/kg were achieved in composite strengthened steel. • Precipitation strengthening from nano Cu-rich precipitates significantly improved yield strength by modulus strengthening. • The highest yield strength of 627.3 MPa was obtained in composite strengthened steel where Orowan bypassing mechanism dominated. Solid solution strengthening with Ni, precipitation strengthening with Cu and composite strengthening with Ni and Cu high-strength non-oriented silicon steels were processed and the effect of strengthening methods on microstructure, texture and properties of thin-gauge non-oriented silicon steel was comparatively studied. Coarse recrystallized grains with strong {221}<221> and weak Goss texture were formed in the hot rolled sheet of solution strengthened non-oriented silicon steel, leading to obvious shear deformation during rolling and optimized recrystallization texture. While coarse grains with γ-fiber orientation were formed in the center layers of hot rolled sheet in precipitation strengthened steel, and strong γ-fiber texture was gradually accumulated as well as relatively fine recrystallization grain. In composite strengthened steel, strong λ-fiber texture was retained in the hot rolled sheet and beneficial Goss texture and λ-fiber texture were formed after final annealing. The optimum magnetic induction B 50 was as high as 1.794 T in solution strengthened steel due to the texture improvement, while 1.698 T in precipitation strengthened steel. The lowest high-frequency iron loss was obtained in composite strengthened steel, with P 1.0/400 and P 1.0/1000 of 13.61 and 51.415 W/kg respectively. The solution strengthening from Ni contributed to limited increase in strength, while the precipitation strengthening from nano Cu-rich precipitates significantly improved the yield strength. The highest yield strength of 627.3 MPa was achieved in the composite strengthened steel under peak aging where Orowan bypassing mechanism dominated. The present study underscores that the composite strengthening with Ni + Cu addition can achieve good balance between magnetic properties and mechanical properties of thin-gauge high-strength non-oriented silicon steel to meet the requirement of high-speed motor.