. The Bell System technical journal . there is a rapid drop in permeability until 500° C. isreached. With further increase in temperature the permeability risesvery rapidly to a sharp peak at about 530° C. and then decreases, thealloy becoming non-magnetic at 590° C. With decreasing temperaturethe alloy again becomes magnetic at about the same temperature, at 456 BELL SYSTEM TECHNICAL JOURNAL which the magnetism disappeared and the curve for decreasing temper-ature is the same as for increasing temperature over a short 500° C. the curve for decreasing temperature does not follow itsor
. The Bell System technical journal . there is a rapid drop in permeability until 500° C. isreached. With further increase in temperature the permeability risesvery rapidly to a sharp peak at about 530° C. and then decreases, thealloy becoming non-magnetic at 590° C. With decreasing temperaturethe alloy again becomes magnetic at about the same temperature, at 456 BELL SYSTEM TECHNICAL JOURNAL which the magnetism disappeared and the curve for decreasing temper-ature is the same as for increasing temperature over a short 500° C. the curve for decreasing temperature does not follow itsoriginal path but continues to drop until the temperature reachesabout 425° C. From that point on until room temperature is reachedthe return curve is nearly horizontal. At room temperature the permeability is only 2,000, a drop of 5,000from its value at the beginning of the run. With the alloy in thiscondition, if a second cycle is run, the permeability both for increasing 140000, 120000 100000 10000 80000 z ^ 60 0001 40000 20000. 20 40 60 80 100 120 140 COOLING RATE —DEG. CENT. PER SEC. 180 Fig. 17—Initial (mo) and maximum _(/xmax) permeabilities for permalloy fordifferent rates of air quenching from 600° C. and decreasing temperature will be substantially the same as the onein the figure for decreasing temperature. By heating the sample to600° C. and air quenching, the magnetic properties at the beginningof the test are restored. The connection between the permeability of this composition andthe heat treatment in the temperature range below 600° C. is alsoillustrated by a series of tests in which annealed rings were air quenchedfrom temperatures below 600° C. The rings were placed in a furnaceand heated at 600° for 15 minutes. The temperature was thendecreased slowly to 550° C. and held until the alloys had reached aconstant condition. One of the samples was then taken out of thefurnace and air quenched. The temperature of the furnace was then MAGNETIC ALLO
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