Effect of Surface Modification by Selective Oxidation on the Microstructure and Core Loss in Fe–3Si–5.5Cr Soft Magnetic Composite

This study investigated the impact of selective oxidation on the core loss of soft magnetic composites. The Fe–3Si–5.5Cr powders were annealed in an atmosphere where Fe was reduced, and Cr and Si were selectively oxidized, forming an insulation oxide layer on the powder surface. To examine the core loss changes due to the insulation coating formed by selective oxidation, the toroidal core samples were fabricated using powders with and without selective oxidation. The core losses of the toroidal core samples fabricated by the selectively oxidized powders were reduced, and as the selective oxidation time increased, the core loss was further reduced. To analyze the cause of the reduction in core loss, the total core loss was separated into the hysteresis, eddy current, and anomalous losses based on the variable separation method. The three losses were reduced in the toroidal core samples fabricated by the selectively oxidized powder. These results confirmed that selective oxidation could form a uniform and dense insulation coating on the Fe–Si–Cr powder, effectively reducing the core loss.