FACTORS AFFECTING MAGNETIC QUALITY 



267 



(3) Purification by contact with hydrogen or other gases. SiUcon-iron 

 (cold rolled), hydrogen- treated iron, Supermalloy. 

 There are also special treatments, such as those used for "double-treated" 

 permalloy, "magnetically annealed" permalloy, and perminvar. 



Occasionally it is necessary to homogenize a material by maintaining the 



lO^x 32 



400 I 

 O 



-^^ 



900 9 



600 (/I 



500 S', 



1 23456789 to 



PER CENT SILICON IN IRON 



Fig. 17 — Variation of some properties of iron-silicon alloys with composition: B,, satura- 

 tion intrinsic induction; 0, magnetic transformation point; p, electrical resistivity; /xm, 

 maximum permeability as determined by Miss M. Goertz. 



temperature just below the freezing point for many hours. Heat-treatments 

 also may affect grain size and crystal orientation. 



Furnaces for heat-treating have various designs that will not be considered 

 here. A modern improvement has been the use of globar (silicon carbide) 

 heatmg elements that permit treatment at 1300 to 1350°C in an atmosphere 

 of hydrogen or air. 



