Magnet Steels and Permanent Magnets — Relationships 

 Among Their Magnetic Properties* 



By K. L. SCOTT 



Introduction 



A GENERAL study of the magnetic properties of magnet steels and 

 permanent magnets embraces a number of related problems. Of 

 chief interest to the designer of magnets is the problem of determin- 

 ing the relationship between the open-circuit remanence of a permanent 

 magnet and the various factors which determine its value. These 

 factors include the magnetic characteristics or properties of the steel, 

 as displayed by its hysteresis loop, and the shape and dimensions of the 

 magnet. Of interest to the manufacturer of magnet steel are the 

 questions of how chemical composition, melting practise, and rolling 

 practise affect the magnetic and mechanical properties of the steel. 

 The manufacturer of magnets is interested in the effect of the necessary 

 manufacturing operations, such as heating for hot forming and an- 

 nealing to increase machinability, upon the flux obtainable in the 

 finished magnet; on the tendency of the steel to warp and crack upon 

 quenching; and on the proper hardening treatment to use. 



These interests overlap, of course, and include many special sub- 

 jects, among which may be listed the manner in which various in- 

 fluences may affect the state of magnetization of a magnet, the correla- 

 tion of the microstructure and mechanical properties of a magnet steel 

 with its magnetic properties, the determination of a suitable criterion 

 of magnetic quality, the development of accurate and convenient test- 

 ing equipment, and various other matters of greater or less importance. 



It is the purpose of this paper to present data relating to some of the 

 above topics, which have been collected by the writer during the course 

 of several years connection with the manufacture of permanent mag- 

 nets, both in the laboratory and in the shop. 



Symbols and Notations 



The following symbols and notations will be used. See Fig. 1. 



All values of B are intrinsic or ferric induction. 



Bmax = The value of magnetic induction corresponding to the tip of 



a given hysteresis loop, in gauss. 



* Presented before A. I. E. E. in New York City, Jan. 26, 1932. Published in 

 abridged form in Elec. Engg., May, 1932. 



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