Evolution of magnetic properties and microstructure of high-silicon steel during hot dipping and diffusion annealing

Hot dipping and diffusion annealing is an alternative production process to obtain steel with high silicon contents while avoiding rolling problems. Surface alloying with Si and Al is achieved on a low-Si steel substrate (≈ 3%Si) by hot dipping in a hypereutectic Al-27%Si molten bath. To obtain a sufficient amount of Al and Si in solid solution over the thickness, a diffusion annealing treatment is performed after hot dipping. A diffusion annealing at 1250°C allows the homogenization of the composition obtaining a concentration of 6.3% Si and 4.5% Al over the thickness. The evolution of microstructure, crystallographic texture, and magnetic properties in each step of the process is reported. After dipping and annealing, the losses decreased proportionally with the total Si-Al concentration achieved during the process. Values as low as 0.6 W/kg at 50 Hz (1T) and 10 W/kg at 400 Hz (1T) have been obtained in the experimental materials with high Si + Al content and 0.35-mm thickness.