Tailoring microstructures to achieve high strength–ductility with preserved soft magnetic properties in an Fe–Co–V alloy

Near-equiatomic Fe-Co soft-magnetic alloys offer a high saturation induction yet often exhibit a poor room-temperature ductility. To improve the mechanical performance, several heat-treatment schedules were applied to commercial 1J22 plate: isothermal holding at 600°C for 1 h (HT600) or 900°C for 2 h (HT900), as well as a two-step route of 900°C for 2 h followed by furnace cooling to 600°C (HTS600) or 750°C (HTS750)and holding for 1 h, focusing on the establishment of processing-microstructure-property relationships. The HT600 condition exhibited the best magnetic softness, with a saturation magnetic flux density of ∼2.25 T and the lowest coercivity of ∼27 Oe, while the two-step HTS600 treatment achieved the best strength-ductility balance, reaching an ultimate tensile strength of 1354 MPa with a total elongation of 19.6%. Aging at 750°C further increased the total elongation to 24.3%, with only a modest increase in coercivity. The enhanced strength-ductility synergy arises from the two-step schedule: solutionizing at 900°C homogenizes the matrix and reduces the initial microstructural heterogeneity and dissolves locally enriched V-rich regions, whereas subsequent aging relaxes residual stresses and promotes a dense network of low-angle grain boundaries (LAGBs) and nanoscale (Fe, Co)-V precipitates, which stabilize substructures and sustain dislocation storage. This combination raises the yield strength and delays strain localization, thereby increasing the total elongation. The trade-off between mechanical properties and magnetic softness is discussed, providing guidance for processing high-stress soft-magnetic components. • Heat treatment transforms lamellae to bands and forms V-rich precipitates. • Two-step annealing enhances strength-ductility; 900°C+750°C reaches ∼24% elongation. • 600°C single-step improves strength and magnetic softness simultaneously.