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BELL SYSTEM TECHNICAL JOURNAL 

 Heal-Trealmenl 



High permeability materials are annealed primarily to relieve the internal 

 strains introduced during fabrication. On the contrary permanent magnet 

 materials are heat-treated to introduce strains by precipitating a second 

 phase. Heat-treatments are decidedly characteristic of the materials and 

 their intended uses and are best discussed in detail in connection with them. 



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TIME IN HOURS 



Fig. 16 — Some common heat treatments for magnetic materials. 



Figure 16 shows some of the commonest treatments in the form of tempera- 

 ture-time curves. The purpose of these various heating and cooling cycles, 

 and typical materials subjected to them, may be listed as follows: 



(1) Relief of internal strains due to fabrication or phase-changes (furnace 

 cool). Magnetic iron. 



(2) Increase of internal strains by precipitation hardening (air quench 

 and bake). Alnico type of permanent magnets. 



