MAGNETIC ALLOYS OF IRON, NICKEL, AND COBALT 457 



dropped another step and the process of stabilization and air quenching 

 repeated for the next ring. This was repeated for a number of 

 temperatures until there was substantially no change between two 

 rings quenched from successive temperatures. Another series of 

 annealed rings was slowly heated in successive steps to the same 

 temperatures, stabilized, and then air quenched. 



F" 



13000r 



12000- 

 11000- 

 10000- 

 9000- 

 8000- 

 7000- 

 6000- 

 5000- 

 4000- 

 3000- 

 2000- 

 1000- 



"0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 

 DEGREES C. 



Fig. 18 — Temperature-permeability curve for 78.5 permalloy: 

 magnetizing force .003 gauss. 



A comparison of the initial permeabilities of these rings showed 

 that each ring attained a definite permeability, characteristic of the 

 temperature from which it was air quenched whether it reached that 

 point from a lower or a higher temperature, provided it was stabilized 

 before air quenching. The air quenched rings stabilized between 

 500° and 400° C. showed the greatest change in permeability. The 

 time required for stabilization at the higher temperatures was very 

 short, only a few minutes being required in the neighborhood of 

 500° C, but it increased progressively as the temperature was lowered, 

 and in the lower end of the range several days were required for the 

 alloy to reach a constant condition. 



