MAGNETIC ALLOYS 



123 



TABLE II 

 Magnetic Constants for Alloys Discussed in This Paper 



Material 



"Armco" iron 



4% silicon-steel 



78.5 permalloy, 



quenched 



45 permalloy 



3.8-78.5 Cr-permalloy . . 

 3.8-78.5 Mo-permalloy. 

 45-25 perminvar, 



baked 



7-45-25 Mo-perminvar, 



baked 



Permendur 



{B-II)ii = oc 



22,000 

 20,000 



10,700 



16,000 



8,000 



8,500 



15,500 



10,300 

 24,000 



11 

 50 



16 



45 

 65 



55 



19 



80 

 6 



Here no and ^m are the initial and maximum permeabilities, respectively; I^//=co 

 is the hysteresis loss in ergs per cubic centimeter per cycle for saturation value of 

 flux density; Br is the residual induction in gausses; H^ is the coercive force in oersteds; 

 {B — H)f{=co is the saturation value of the intrinsic induction in gausses; p is the 

 resistivity in microhms-centimeter. 



the alloys containing between 70 and 80 per cent nickel ; for example, 

 78.5 permalloy with a standard anneal has its initial permeability 

 reduced to 1,200. If the alloy is baked for several hundred hours this 

 permeability can be reduced still further to about 500. There is a 

 very rapid decrease in the coercive force as the nickel increases above 

 27 per cent, and the lowest values are reached in the region between 

 70 and 80 per cent nickel. The resistivity increases rapidly just below 

 the permalloy region, and reaches maximum at about 31 per cent 

 nickel. It should be noted that the large changes in the coercive 

 force and the resistivity are at the lower end of the permalloy region, 

 while the highest permeabilities are developed in the alloys containing 

 between 75 and 80 per cent nickel. 



45-Permalloy 



One of the alloys developed for commercial use is 45-permalloy. 

 This attains a saturation flux density as high as any of the permalloys. 

 At 40 oersteds the flux density is 16,000 gausses, substantially the same 

 as for "Armco" iron, and considerably higher than for ordinary silicon 

 steel (Fig. 4). The initial and maximum permeabilities (under 

 standard practice of heat-treating) are 2,700 and 23,000, respectively 

 (Fig. 5 and Table II). For cores requiring flux densities between 8,000 

 and 12,000 gausses this alloy is specially useful. The resistivity of 

 the alloy is 45 microhms-centimeter, which is high enough to make it 

 superior for use in cores in a.-c. circuits. The higher permeability at 



