The effect of Cu and/or Nb addition on crystallization processes and soft magnetic properties for Fe-Si-B alloys has been investigated. For Fe-Si-B, Fe-Cu-Si-B, and Fe-Nb-Si-B alloys annealed at various temperatures, the effective permeabilities were very low and decreased considerably as they crystallized, while for Fe-Cu-Nb-Si-B alloy annealed at a temperature above Tx, a very good soft magnetic property was obtained. From DTA analysis of Fe-Cu-Nb-Si-B alloys, it became clear that the combined addition of Cu and Nb expanded largely the temperature range over 100°C where a single phase of α-Fe solid solution can exist. Above 580°C, the second crystalline phase such as Fe2 B and some unidentified phases other than the α-Fe phase precipitated, and soft magnetic properties deteriorated rapidly. It is concluded that the combined addition of Cu and Nb makes the α-Fe single phase stable in a broad temperature range, which is considered to be the necessary condition for the superior soft magnetic properties.
