Enhancement of Soft Magnetic Properties in FeCo-2V Steels via Optimization of Annealing Temperature

Electric vehicles are a key component in carbon neutrality policies, and electrical steels used in EV motors must exhibit high magnetic flux density and low core loss. The Fe-Co alloy is known for its high saturation magnetization; however, its brittleness limits its practical applications. The Fe-Co alloy overcame brittleness by adding vanadium, which expands the two-phase coexistence region of the ordered body-centered cubic structure (α phase) and face-centered cubic structure (γ phase). As a result, the α phase with good soft magnetic properties has a stable structure at room temperature. In this study, steel with thicknesses of 0.2 mm and 0.15 mm were heat-treated based on the differential scanning calorimetry (DSC) results to form the α phase, and their structural and magnetic properties were subsequently analyzed. 0.2 mm steel heat-treated at 775 ℃ had low coercivity (50.58 A/m) and a high magnetic flux density of 5000 A/m (2.14 T). 0.15 mm steel heat-treated at 850 ℃ had low coercivity (60.18 A/m) and a high magnetic flux density of 5000 A/m (2.22 T). The increase of coercivity observed at 900 ℃ is attributed to V-rich phases formed at grain boundaries, which likely act as pinning sites. The hysteresis loss of 0.15 mm steels in a DC environment had the lowest value at 800 ℃, while under an AC environment, it had a minimum of 750 to 850 ℃.