438 BELL SYSTEM TECHNICAL JOURNAL 



at the diagram will give you an appreciation of the completeness with 

 which the field was covered. 



In preparing these alloys we used the best commercial materials 

 available. These contained small amounts of impurities, some of 

 which afi^ect unfavorably the magnetic properties. It was considered 

 beyond the scope of this investigation, in which such a large number of 

 alloys were required, to attempt to remove these impurities completely 

 or even partially. Moreover we were especially interested in alloys 

 which could be reproduced on a commercial scale, without too great 

 cost due to refinements of raw materials or to methods of preparing 

 the alloys. 



Throughout the investigation we have followed a standard procedure 

 for preparing our samples. We have also followed a standard pro- 

 cedure for heat treating and in magnetic measurements. The result 

 is that we have accumulated a large mass of data over a number of 

 years, all of which may be significantly compared. 



The alloys were cast from Armco iron, electrolytic nickel, and a 

 very high grade of commercial cobalt containing only small amounts of 

 impurities. They were melted together in the desired proportions in 

 a silica crucible in a high frequency induction furnace. The metal 

 was cast into bars 18 in. long and ^ in. in diameter. The bars were 

 rolled or swaged into 3^ in. rods; then they were drawn into wire and 

 flattened and trimmed into }/^ in. by .006 in. tape. The material was 

 annealed several times in the reduction process, for the cold working 

 hardened the alloys rapidly and made them difficult to work. 



To prepare the tape for heat treatment and subsequent magnetic 

 measurements, about 30 ft. of it was wound spirally into a ring of 

 3 in. inside diameter, the ends being spot welded to the adjacent turns. 

 Care was taken to wind the rings loosely to prevent the turns from 

 sticking to each other during annealing. 



For convenient comparison of the magnetic properties of the alloys 

 with those of the metals from which the alloys were cast, sample 

 lots of the iron, nickel, and cobalt which we used in making the alloys, 

 were melted, cast, and prepared in the same manner as the alloy test 

 samples. 



In Fig. 2 the various steps through which the alloys had to pass 

 in the mechanical reduction to tape are shown. Between each step 

 in the reduction, as indicated by a sample, the alloy had to be annealed 

 to remove the mechanical hardness. A sample ring wound from the 

 finished tape, ready for heat treatment, is also shown in the figure. 



The next step in the process of preparing these alloys for magnetic 

 measurements is the heat treatment. Early experience with the 



