Excellent magnetic properties obtained in planar flow casting Fe-6.5 %Si steel via low strain cold-rolling and annealing

Abstract

Planar flow casting (PFC) has been applied to prepare Fe-6.5wt. %Si ultra-thin ribbons with a strong 〈001〉 fiber texture. However, critical issues such as fine grain size and large surface roughness are vital to overcome. In this study, low strain cold-rolling and subsequent annealing are applied to planar flow casting Fe-6.5 %Si ribbons. Cold-rolling reduces surface roughness and introduces heterogeneous deformation in the ribbons. Recrystallization occurs preferentially in high deformed areas during annealing. Recrystallizing grains grow significantly by consuming neighboring deformed grains with fine size and 〈001〉 orientation, leading to greatly reduced iron loss. Thus, the ribbon annealed at 1000 ℃ exhibits the best combination of magnetic properties with B8 of 1.29 T and P2/5000 of 6.95 W/kg. The kinetics of recrystallization and grain growth are described along with the calculations of activation energies, which suggests the cold-rolled ribbon has a faster growth rate than the undeformed one. Two mechanisms, namely strain-induced boundary migration (SIBM) and thermo-induced boundary migration (TIBM), are used to explain the grain growth. SIBM is dominant at low temperatures while TIBM is dominant at high temperatures. This work presents a strategy to tailor the microstructures and properties of PFC-prepared alloys with fine grain.