Abstract: This job was focused on the annealing technique of large-size nanocrystalline core with height of 50 mm, to meet the low core loss requirement of large-size nanocrystalline core used in large-capacity high-frequency transformer. Two typical nanocrystalline alloys, Fe_73.5Cu₁Nb₃Si_15.5B₇ and Fe_73.5Cu₁Nb₃Si_13.5B₉ ribbons (hereinafter referred to as B₇ and B₉) with the width of 50 mm, were selected to investigate the influence of annealing temperatures (330~600℃) on their soft magnetic properties and core losses. The experimental results were demonstrated that B₇ and B₉ alloys probably started to crystallize as early as annealed at 420 ℃, which is much lower temperature than the widely-held at 500 ℃. The two alloys were obtained the lowest core losses by being annealed at 550℃ and 580℃, respectively. However, they showed the highest permeability and the lowest coercivity when annealed at 500℃ and 550℃, respectively. The core losses of B₇ alloy was continued to reduce through by transversal field annealing, and the lowest value of P_cm(0.5T/20k) was 7.3W/kg, which is the lowest as far as we know. According to the measured data, the core losses of nanocrystalline magnetic core can be described by $ {P}_{{\rm{cm}}}=0.5{f}^{1.42}{{B}_{{\rm{m}}}}^{2.27} $ in fractional method, and has been confirmed by experimental results.

Key words: nanocrystalline alloy, core loss, annealing temperature, large-capacity high-frequency transformer, fractional method