Deteriorating effect of manganese on magnetic properties of Fe-Cr-Co permanent magnet alloys

Effect of manganese on magnetic properties of an Fe-24Cr-12Co-1.5Si alloy (weight fraction) has been systematically studied by electron microscopy and magnetic measurements, in order to estimate the availability of certain grades of ferro-chromium as raw material for manufacturing Fe-Cr-Co magnet alloys. It has been found that manganese deteriorates magnetic properties of the Fe-Cr-Co alloys. As the Mn content of the alloy exceeds 0.2%, the degraded magnetic properties become very difficult to recover by heat treatments. The reasons are attributed to, as evidenced from transmission electron microscopy, (1) much inferior enlongation and alignment of the spinodal phase in Mn containing alloys, (2) the possible existence between the spinodally decomposed α1and α2phases a third phase which degrades the squareness of the B-H loops, (3) the gamma stabilizing effect of Mn. Trials to compensate for the Mn effect by adding sulfur are not pronounced. It is concluded that ferro-chromium or any other raw materials for manufacturing Fe-Cr-Co permanent magnets should be free from manganese.