Influence of the particle shape on microstructure and magnetic properties of iron powder cores

The coercive force of an iron powder core decreases with an increase in the circularity of raw iron powder. Microstructural observation reveals that the crystal grain size of the iron powder core is reduced through recrystallization during the stress relief annealing after the powder compaction. An analysis of the work hardening behavior through the compaction process shows that a rounder particle shape leads to a smaller particle deformation, resulting in a reduction of the crystal grain refinement through recrystallization. A grain boundary pinning model well describes the reduction of coercive force with the increase in the eventual grain size.