MAGNETIC ALLOYS OF IRON, NICKEL, AND COBALT 439 



nickel-iron alloys indicated the need for a variety of such treatments, 

 but of course it was impossible to apply to every alloy such a complete 

 variety of heat treatments, that all of the combinations of heat treat- 

 ment and composition could be known. Our procedure was to apply 

 three types of heat treatment. 



A number of rings of a given composition were packed in a nichrome 

 pot. The pot was placed in an electrical resistance furnace, the 

 temperature of the furnace raised to between 900° and 1,000° C. and 

 held at that temperature for one hour. The current was then turned 



Fig. 2 — Cast alloy bar and intermediate stages of samples in reduction to tape. 

 Also ring from tape ready for heat treatment. 



ofif and the pot cooled with the furnace. Ten hours were required 

 for the furnace to cool to the temperature of the room. Between 

 700° C. and 400° C. the rate of cooling was approximately 1.5° C. per 

 minute. 



At least two rings of each composition were always annealed 

 together. One of these rings received no further heat treatment. 

 The second ring was heated for 15 minutes in a furnace held at 600° C, 

 then removed and cooled rapidly on a copper plate in the air. With 

 this cooling the rate was approximately 20° C. per second. In some 

 cases a third annealed ring was heated 24 hours at 425° C. 



In the discussions and in the figures, the rings which received the 

 first heat treatment only are referred to as "annealed," those reheated 

 to 600° C. and rapidly cooled as "air quenched," and those held for a 

 long time at 425° C. as "baked." The magnetic measurements were 

 made on these rings. 



The magnetic induction, or flux density, was determined for a 

 large number of magnetizing forces, beginning at a few thousandths 

 of a gauss and increasing in uniform steps up to 100 gauss. Magnetiza- 

 tion curves were plotted from these measurements. The induction 

 was also determined for each composition at a magnetizing force of 

 1,500 gauss. 



The permeabilities were computed from the induction measurements, 



