Additive Manufacturing of High-Silicon Steel Soft Magnetic Material

Licentiatavhandling, 2026

Soft magnetic materials play a critical role in electric motors and transformers, where high efficiency and low energy losses are essential. High-silicon steels (Fe-6.5 wt.% Si) offer superior soft magnetic properties but are difficult to process using conventional manufacturing due to their inherent brittleness. Powder bed fusion-laser beam (PBF‑LB) provides a promising alternative by enabling near‑net‑shape fabrication and microstructural control.

This thesis investigates the influence of PBF‑LB processing parameters, scan strategies, and heat treatments on the evolution of microstructure and the magnetic, mechanical, and electrical properties of high-silicon steel soft magnetic material. The first part of the thesis focuses on the influence of process parameters and heat treatment on the microstructure and multi-functional properties. A wide parameter space of laser power and scan speed was systematically explored to identify processing regimes associated with lack‑of‑fusion defects, keyhole‑induced porosity, and near‑full densification. Magnetic characterization revealed pronounced anisotropic behavior relative to the build orientation, while post‑processing annealing treatments significantly enhanced soft magnetic performance by reducing coercivity and promoting grain growth as well as microstructural homogenization. The second part of the thesis investigates the influence of laser scan rotation on melt pool behavior, grain structure, and multi-functional properties. Variations in scan rotation altered melt pool overlap and grain morphology, leading to pronounced differences in texture, magnetic anisotropy, hardness, and electrical resistivity. A 90° scan rotation promoted the formation of coarse, textured columnar grains and superior soft magnetic properties, whereas annealing consistently reduced coercivity and anisotropy across all scan strategies. The results demonstrate that careful control of both energy input and laser path design provides an effective route for tailoring the microstructure and coupled properties of additively manufactured high‑silicon steel, enabling site‑specific optimization for energy‑efficient electrical machine applications.