MAGNETIC MATERIALS IN RELATION TO STRUCTURE 



31 



structure and furnishes resistance to change in magnetic condition, a 

 property which is measured as coercive force. 



Permanent Magnet Steels 

 Many types of steel have been developed for magnet appUcations.^* 

 The most important commercial ones are carbon-manganese, 1 per cent 

 and higher chrome steels of which 3.5 chrome is typical, tungsten steel, 

 and 35 per cent cobalt steel. Typical magnetic characteristics and 

 required heat treatments are shown in Table I. 



TABLE I 

 The Properties of Permanent Magnet Steels 



The heat treatment for the permanent magnet steels consists of a 

 quench from a high temperature at which the carbon is in solution. 

 During the period of cooling in the quench, the supersaturated solution 

 precipitates the carbides. This is designated "quench hardening." 

 The quenching treatment varies with the type of steel, but in general, 

 quenching in either oil or water is used. In this connection, it is im- 

 portant that the austenite transformation occur during the quench, 

 since austenite is non-ferromagnetic and its presence will result in low 

 values of residual induction. 



The carbon-manganese and 1 per cent chrome steels are the least 

 expensive and enjoy a large use in low cost apparatus where space re- 

 quirements are liberal. Typical values for coercive force and residual 

 induction for these materials are 40-50 oersteds and 9000 to 9500 



