Maximum Magnetic Permeability Research Articles

Manufacture of pure iron powder by the electrolysis of fused salts

A new method is described for preparing pure iron powder from pig iron and iron sponge by the electrolysis of fused salts at a temperature of 850–900°C. The article deals with the main variables and technical and economic parameters of the process, composition of the resulting iron powder, relative density of compacts produced at various compaction pressures, apparent density of the powder, and maximum magnetic permeability of Dynamaxalloys prepared on the base of pure iron obtained by the authors and on the base of other grades of iron.

Effect of heat treatment and nitriding on the magnetic properties of austenitic steels

1. A change of the normalizing temperature of steel A from 1070 to 1150°C and also an additional aging for 8 hrs at 800°C have practically no effect on the magnetic susceptibility of this steel. 2. Nitriding changes considerably the magnetic permeability of the steels in question. The nitrided case of both austenitic steels is ferromagnetic, this being due to the formation of nitrides, the depletion of austenite in alloy elements and its decomposition. 3. Nitriding results in a higher magnetic permeability of steel A (three-fold) compared with steel B. 4. An increasing depth of the nitrided case results in an increasing maximum magnetic permeability. An increase of the relative nitriding depth on steel A from 23 to 48.5% results in a doubling of the permeability. An equivalent change from 50% to 93.65% in steel B results in a jump of permeability from 3.7 to 19.8 gauss/oersted. 5. The results of this study indicate that it is possible to determine the depth of a nitrided case on a variety of austenitic steels by electromagnetic methods.

Permeability Changes in Ferromagnetic Materials Heat Treated in Magnetic Fields

Very high maximum magnetic permeability has been obtained in certain ferromagnetic alloys by slowly cooling them in a magnetic field. In permalloy with 78.5 percent nickel it has thus been raised above 140,000 that is, to the same order as is obtainable by rapid cooling without an applied field. In perminvar with 45 percent nickel, 30 percent iron and 25 percent cobalt this magnetic heat treatment is also found to be effective. It is also shown that the maximum permeability is highest if the testing field is in the same direction as that of the field applied during cooling. In directions at right angles to this, the maximum permeability is decreased. The ratio of the two permeabilities in one instance was over 14 for permalloy, and in another instance nearly 70 for perminvar.