Microstructure and magnetic properties of Fe-Cr-Co alloys

The microstructures of an Fe-31wt%Cr-23wt%Co ductile permanent magnet alloy after isothermal aging, thermomagnetic treatment, and step aging have been characterized by transmission electron microscopy and by measurement of the Curie temperature. Isothermal aging itself produces the undesirable microstructure. Aging at 600°C develops the magnetic chromium-rich phase. Aging at 600°C produces a nonmagnetic chromium-rich phase dispersed within the iron-rich phase. The effect of thermomagnetic treatment on the microstructure of the alloy is discussed in comparison with that of Alnico alloys. Step aging produces the deskable microstructure, viz., the elongated ferromagnetic phase imbedded in the paramagnetic phase.