FACTORS AFFECTING MAGNETIC QUALITY 



261 



high-frequency and resistance-wound furnaces. In commercial furnaces Rohn 

 has used hydrogen and vacuum alternately before pouring, for purification 

 in the melt, in low-frequency induction furnaces having capacities of several 

 tons. 



Just before casting a melt of a high-permeability alloy such as iron nickel, 

 a deoxidizer may be added, e.g. aluminum, magnesium, calcium or silicon, 

 in an amount averaging around 0.1 per cent. The efficacy of a deoxidizer is 

 measured by its heat of formation, and this is given for the common ele- 



- 240 



V) 



m 200 



160 



uj 80 

 < 



600 800 1000 1200 1400 1600 



TEMPERATURE IN DEGREES CENTIGRADE 



Fig. 12 — Solubility of some gases in iron and nickel at various temperatures. Sieverts. 



ments in Table II, taken from Sachs and Van Horn.^ Also several tenths of a 

 per cent of manganese may be put in to counteract the sulfur so that the 

 material may be more readily worked; the manganese sulfide so formed col- 

 lects into small globular masses which do not interfere seriously with the 

 magnetic or mechanical properties of most materials. 



Ordinarily a quantity of gas is dissolved in molten metal, and this is likely 

 to separate during solidification and cause unsound ingots. The solubilities 

 of some gases in iron and nickel have been determined by Sieverts^ and 

 others and are given in Fig. 12, adapted from the compilation by Dushman.® 

 The characteristic decrease of solubility during freezing is apparent. Most 



* G. Sachs and K. R. Van Horn, Practical Metallurgy, Am. See. Metals, Cleveland 

 (1940). 



6 A. Sieverts, Zeits.f. Metallkimde 21, 37-46 (1929). 



^S. Dushman, Vacuum Technique, Wiley, New York (1949). 



