Optimization of soft magnetic properties in Super-Invar alloy FeNi₃₂Co₅ through heat treatment temperature control

Through systematic regulation of heat treatment temperatures, this study comprehensively investigates the effects of different thermal processing conditions on the soft magnetic properties, thermal expansion behavior, and microstructural evolution of a 0.3% Nb-containing FeNi₃₂Co₅ Super-Invar alloy. Experimental results demonstrate that the alloy subjected to 1 150 ℃ heat treatment exhibited the optimal overall performance. Post-treatment microstructural characterization revealed coordinated grain growth and optimized distribution of secondary phases, which synergistically enhanced the soft magnetic characteristics. Specifically, the magnetic permeability parameters showed significant improvements with μ0.4, μ_m, and Bs reaching 3.910 mH/m, 5.903 mH/m, and 1.279 T respectively, while residual induction (B_r) and coercivity (H_c) were reduced to 0.412 6 T and 13.71 A/m. Crucially, the alloy maintained its intrinsic low thermal expansion characteristics with a coefficient of thermal expansion (α) below 0.3×10^-6 /K. This optimized thermal-mechanical treatment protocol achieved remarkable enhancement in the comprehensive performance metrics of the super-invar alloy system, demonstrating exceptional balance between magnetic functionality and dimensional stability.