38 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



Table I — Soft IVIagnetic Materials 



Material 



Magnetic iron 



Sheet 



Rod 



Mild steel 



Cast iron 



1% silicon iron. . . 

 2}-^% silicon iron. 

 4% silicon iron . . 



H2 anneal iron 



Sheet 



Rod 



45 permalloy . . 



7,000 

 4,500 

 15,000 

 78 permalloy 50,000 



Magnetization 



Min. 



4,300* 

 4,300* 

 2,200 



Max. 



12,000 

 8,000 

 7,500 



(Nominal: 600) 



4,000 

 4,000 

 5,000 



15,000 

 12,000 

 12,000 



15,000 

 8,000 

 60,000 

 250,000 \ 10,000 



(gauss ' ) 



Min. 



15,500 

 15,500 

 14,000 



16,200 

 16,200 

 16,000 



(B" = 10,000) 



14,700 

 14,000 

 13,500 



15,500 

 15,500 

 14,000 



15,600 

 15,000 

 15,000 



16,500 

 16,500 

 15,000 

 10,400 



Nickel (Nominal: 600) (B" = 6,000) 



Demagnetization 



Br 



(gauss) 



Min. 



10,500 

 10,500 



,000 

 ,000 

 ,000 



14,000 

 12,000 

 8,000 

 5,000 



Max. 



15,000 

 12,000 

 15,000 



He 



(oersteds) 



Min. Max. 



0.5 

 0.5 



0.8 



14,500 

 12,000 

 12,000 



0.4 

 0.4 

 0.3 



15,000 

 14,000 

 12,000 

 7,500 



0.5 

 0.7 

 0.1 

 0.02 



1.4* 

 1.4* 

 2.5 



1.4 

 1.4 

 1.1 



0.9 

 1.0 

 0.4 

 0.1 



Resistivity 



Microhms 



cm"' 



* After aging, //,nax for magnetic iron may be as low as 3000, and H^ as high as 2.5. 

 t B,v/: Density for^ = 1000. B": Saturation density. 



applications in which release performance is important. Aging also re- 

 duces the permeability. In materials other than magnetic iron, the aging 

 effect is relatively minor. 



Because it is cheap and easily fabricated, magnetic iron has been the 

 most commonl}^ used magnetic material in Bell System relaj^s and 

 switching electromagnets. Other materials, particularly 45 permalloj^, 

 have been used in special applications where the improvement in per- 

 formance, as in higher sensitivity or faster release, warranted the in- 

 creased cost. The superiority of the permalloys in these respects is offset 

 for heavy duty applications by the lower level of flux attainable with a 

 given core cross-section, as measured b}^ 5.U . 



The silicon steels are comparable with magnetic iron in cost, and 

 similar in magnetic properties, except for slightly smaller values of B^ . 

 They are, however, superior in their relative freedom from aging, and 

 in their higher resistivity. These advantages are offset, in the case of the 

 4 per cent material, by its hardness and brittleness. All the silicon steels 

 are used in sheet form for the construction of transformers and electrical 

 machines. The 1 per cent and 2}-^ per cent materials are available in rod 

 and bar form, and have working properties intermediate between those 

 of magnetic iron and 4 per cent silicon iron. Because of its advantages in 

 aging and resistivity, 1 per cent silicon iron has been used in preference 



