US2002696A

US2002696A - Magnetic material

Info

Publication number: US2002696A
Application number: US697576A
Authority: US
Inventors: George A Kelsall
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1933-11-11
Filing date: 1933-11-11
Publication date: 1935-05-28
Anticipated expiration: 1952-05-28

Description

May 28, 1935. G. A. KELSALL 2,602,696

MAGNETIC MTERIL Filed Nov. 11, 1933 4 Sheets-Sheet 2 l l l I l l loo zoo rEuPERA Tune "C -IOO | l l I l g d d o o o o' w 'n n N /N V E N TUR v,f1/71s ram/sd Q A KELSALL A TTORNQ/ May 28, 1935.

G. A, KELSALL MAGNETIC MATERIAL Filed Nov. 11, 1953 4 Sheets-Sheet 3 FIG. 4

l l 'l A' l 1 200 3DO 400 500 600 700 TEMP/53,4 ruRE "C WV/SNTOR G. A. KELSA'LL A TTORNEV May 28, 1935. G. A. KELsALL A2,002,696

. MAGNETIC MTRIAL Filed Nov. l1, 1933 4 Sheets-Sheet 4 4s la .w40 la Fe-zs k co zo 40 n.0 5.010

L .O03 .005 .0l

ATTORNEY Patented May 1935 UNITED lSTATES PATENT OFFICE.

MAGNETIC. MATERIAL 6eme A. Keleall, Belleville, N. l., einer tellen Telephone laboratories, Incorporated, New York, N. Yi., a corporation of New York Applleetlen November 11, 1933, serial No. 697,513 21 claims. j(cl. ris-21) This invention relates to ferromagnetic mate'-nk rials and particularly to methods of increasing the maximum permeability of these materials.

Thev permeability of certain magnetic alloys, such as iron-nickel alloys and iron-nickel-cobalt alloys having special magnetic properties similar to those disclosed in U. S. Patentsto G. W.

Elmen 1,586,883, June l, 1926; Elmen 1,768,237, June 24, 1930; Elmen 1,788,017, January 6, 1931; Elmen 1,715,646, June 4, 1929; and Elmen, 1,715,541, June 4, 1929, may be greatly increased by rapidly cooling these alloys through'the mag,- netic transformation temperature range.

However, when the magnetic bodies of these alloys are large or irregular in shape and crosssection, or both, it is very difiicult, if not impossible, to rapidly and uniformly cool them so that undue stresses and strains will not be set up in the bodies. These stresses and strains may reducethe permeabilityof the material more than the rapid cooling will increase it.

It is the object of this invention to secure a great increase in the maximum permeability of these alloys without rapidly cooling them and setting up stresses and strains 1n them. This is ftesting furnace for toroidal Cores published in 25 accomplished by slowly cooling the alloys in a magnetic field, the direction of which corresponds to the direction in which the high permeability is desired. l

A feature of the invention resides in the discovery that the permeability of the* material so treated in a, direction at right angles to the direction of the magnetic field applied during the heat treatment is from 0.1 to 0.01 the permeability in the direction of the magnetic fleld which is applied during the heat treatment. l

This invention may be more fully understood from the followingde'scriptions of several 'embodiments of the invention when read with reference to the attached drawings in which:

Fig. 1 illustrates one shape ofthe magnetic material used and the manner in which the mag:-

v netic fields are applied to it vduring the heat treatment;

Fig. 2 illustrates by means of curves the eifect of heat treating an iron-nickel alloy consisting .of 781/ nickel and 211/2% iron in accordance with this invention; e i Fig. 3 illustrates the' effect ofthe dierexlt values of field strength applied to the lsame alloy during heat treatment;

Fig. 4 illustrates by means of a. set of curvesthe leffect of various manners, temperatures and time durations of applying magnetic fields to the same alloy;

Fig. 5 shows several curves which illustrate the effect of variousmagnetic field strengths applied to an iron-nickel-cobalt alloy comprising 45% nickel, 30% iron and.25% cobalt during the heat treatment; and 5 Fig. 6 illustrates'the effect on the permeability of various heat treatments at 725 C. and 'of applying the magnetic field in different directions during the heat treatment of specimens of iron-nickel-cobalt comprising 45% nickel, 30% 10 iron and 25% cobalt.

It is to be understood that these descriptionsl as applied to specific alloys are to illustrate the principles and features of this invention so that it may be more clearly and fully understood but 15 that they are not to restrict, in any way, the scope of the invention as recited in the appended claims.

Referring now-to Figfl, l represents a furnace in which a core of magnetic material 2 is to be 20 heat treated. The furnace may be of any suit` able-construction and heated in any convenient o' manner. For example, a lfurnace similar to that disclosed by G. A. Kelsall in an article Magnetic the July 1929 number of the Journal of the Optical Society of America and Review of Scientific Instruments, volume 19, pages 47 to 49, wasv used to perform some of the heat treatments to be described. In the method shown in Fig. 1, yin- 30 sulated windings 1 are wound on core 2 in any convenient manner, preferably insulated with asbestos or other heat resisting insulation material.` Two wires are welded to opposite sides of the magnetic core 2 at 3 and l and are connected 35 to a source of electrical energy 6 through a switch f 5. When switch 5 is closed current will flow through both sides of the toroidal ring 2 of magnetic material and create a magnetic fleld within said material which will decrease from the surface 0 of said ring to the center and will be in a direction similarto that of the wire with which coils 1 are 4 wound.' A detailed description of the magnetic field created in this manner may be found in Principles of Electrical Engineering, by 'Iirnbiel and Bush, published by John Wiley and Sons, on pages :199 to 202 of the flrst edition. By connecting avscurce o f electrical energy; not shown,v

to terminals 8 of winding 1, an electromagnetic field will be created within the toroidal ring 2 of 5 Y magnetic material, the direction of which will be .around .the ring. Thus, the direction of these two fields will be substantially at right angles to eheh other in the magnetic material of ring 2. It is te be understood that these pwd fields/at right e tape wound to fo angles to each other may be obtained in any other suitable manner. 1f it is' desired winding I'may also be used to measure the permeability and other magnetic properties of the magnetic core 2 during the heat treatment. In

.In one experiment a. ring of .tape of an alloy consisting of 'ISI/,2% nickel and 211/2% iron which had been previously heated to above 900 C. and slowly cooled and then reheated to about 600 C. and rapidly cooled by being placed upona copper plate in accordance with the double heat treatment described in the above identified patents was heated from room temperature to above=600 C. in the manner illustrated by curve l yoi.' Fig. 2. The vtemperatures of the ri are plotted as the abscissas and the time as the ordinates. It should be noted that the time scale is on the right hand side ofthe curve sheet and starts at the top of the sheet. Curve 2 shows the corresponding permeability for ay eld strength of .085 gauss. This is approximately the magnetizing force for which this alloy *has maximum permeability after the Adouble heat treatment. As the temperature increases the permeability decreases to` a low value at a temperature slightly below 600 C. where the material becomes non-magnetic. now the ring were slowly' cooled at avrate vas illustrated by curve 3 in the absence of any magnetic i'leld the permeability on arrival at room temperature would have been about 20,000 as illustrated at point X on Fig.`2. When, however, the ring was cooled in a magnetic i'leld of .085 gauss the permeability followed curve l so that it is higher on arrival at room temperature than. after the double heat treatment; The

permeability then decreased as the material was cooled to a low temperature but again increased as illustrated by curve 6- as the temperature slowly rose alongcurve 5 to normal room temperature.

Itbshould be noted that the origin of the time scale has been shifted-and the scale reduced for the low temperature treatment as illustrated by curve 5. Curve 'l shows the relation between the permeability and the magnetizing force before the specimen was subjected to this heat treatment in a magnetic field, while curve 8 shows the samef'relation after the specimen has been heat treated in a magnetic field as described."

In addition it should be noted that since there The curve in Fig..3 shows the relation betweenthe maximum permeability of the material Y and `the strength of :the magnetic iield which is applied to it during the 'heat treatment.. .In -these ltests an alloy consisting of 'Zal/2% nickel and 2l1/% iron after having been mechanically.

`worked to its final form, which in this case is a a ring, is heated to a -high temperature above 900 C., preferably say l000 to 1100 C., and then slowly cooled to relieve `internal stresses and strains within the material..

It was then reheated to above the non-magnetic temperature of the material and themagnetic 70%.cld of the varius values applied and then the 'naterial was slowly. cooled while in this magnetic iild. If-it is desired or convenient, this heat treatmentv may be madei continuously with the same results by first heating the material. to a 16- .,high temperature above say 900"y C. andthen slowly cooling it in a magnetic iield which may be applied at'any temperature above the nonmagnetic temperature of the material. However, since it is dilcult to apply the magnetic field at the higher temperatures the double treatment yis preferred. 'i

As illustrated in the following Table I showing nal values of initial permeability (au). and maximumpermeability (am) either an alternating. or a direct current eld may be employed during the heat treatment as there appears to be very little difference between thesetwo dierent types of magnetic fields insofar as they eiect the maximum permeability= of the specimen. An alloy consisting of 781/2% nickel and 211/2% iron was used to secure the data recorded in this table.

Effective values of alternating current magnetiz- Aing force used 'during cooling are given.

Table I F Magnetizing force in oersteds "m used on cooling from 600 C.

3150 14300 0 2700 46500 l0 A.C. 2100 64100 .20 A.C. 2800 81750 .40 A.C. 2400 95300 80 A.C. 3700 100500 1. 47 A.C. 4000 100600 2. 96 AFC. 3000 98500 l0. 35. A.C. 2900 100500 2. 96 D.C. f 2400 98200 1.00 D.-C.

zooo 68900 .2o D.C.

The curves'of Fig. 4 show the eect'of various .manners of cooling from diierent temperatures when an alloy consisting of 'w1/2% nickel and 2l1/%"iron is heattreated in a magnetic iield.

In order to 'simplify the description of these curves the first portion of the heat treatment which is slowly cooling the material from a high temperature of y.say 100`0 tp 1100 C: to room temperature'to remove the stresses and strains due to the mechanic working of the specimen will be omitted, but i is to be understood that this treatment is to precede all the heat treatments described and represented by the various curves in this ligure. Of course, as pointed out before, the two heat treatments may be combined if it is desired by slowly cooling from the high temperature. to a temperature at which the special treatmentis applied.

Point I shows the maximum permeability of a double heat treated specimemof an alloy of 781/ nickel and 2l1/2% iron as disclosed in the above mentioned patents in which the specimen was rst slowly cooled. from a temperature labove 900 C., say'l000 to 1100 C., to room temperature and then reheated to 600 C. and rapidly cooled to room temperature by being placed upon Aa copper plate.

Point 2 represents the maximum permeability of the samaspecimen asrepresented by point I after the specimen has been heated and maintained at 400 C. for one hour. This shows that fthis treatment reduces the maximum permeability of the specimen by about one-third.

Curve 3 was obtained in the following manner.

A specimen slowly cooled from 1100 C. in the form of a ring of tape of an alloy of HB1/2% nickel and 211/2%v iron was heated to above.

600 C. and then slowly cooledto 575 C. A magmax um permeability was then measured and which gave point 2l. vIn a similar manner other points were obtained by heating the ring above 600 IC. and then slowlyeooling it to a lower temperature, hereinafter called the indicated temperature, at which time a magneticl field is applied and the ring further slowly cooled to room temperature whilein this magnetic field. Then the maximum permeability was measured and curve 3 plotted and drawn. The cooling rate for the points on this curve was such that it required forty-five minutes to cool the ring from 600 C. to 200 C. While it is not necessary to employ the same ring for all the points on -a curve it is desirable to do so since it the variations between the different rings. It is necessary that the stress and Ystrains have been removed by slowly. cooling the specimens from a high temperature and that other previous heat treatments and magnetic effects have been cancelled by heating the material above its nonmagnetic temperature.

Curve 4 shows the maximum permeability Lfl another specimen after it was heated to 600 C. and then slowly cooled to the indicated temperature at which time the magnetic field was applied, and their the specimen was maintained at this temperature in the magnetic field for one hour after which time it was slowly cooled in the magnetic field Vto room temperature in such a manner that the specimen would have been cooled'from 600 C. to 200 C. in forty-five minutes. It should be noted that when the specimen was cooled to some temperature below 400 before the magnetic field was applied, the permeability is the same for both vtreatments rep- \resented by

curves

3 and 4 as illustrated by the portion V lll of these curvesand is of a comparatively low value. This is probably due to the fact that the cooling rate of these specimens from 600 to some temperature below- 400 C. was the same.' This fact also indicates that some phenomenon takes place between the temperatures of-600`and 400 C. for this particular alloy which greatly influences the maximum magnetic permeability ofthe specimen. This temperature region from a temperature near yor :above the magnetic transformation temperature `to a lower temperature of approximately 400 C. will be called the magnetic' transformation temperature region in what 'follows hereinafter.

The heat treatment which produced the resultant maximum permeability as shown by curve 5 was as follows: The slowly cooled specimen was placed in a hot furnace at the temperature indicated and allowed to remain there for fifteen minutes.' This provided adequate time to allow the specimen to acquire the temperature of the furnace. A magnetic field was then applied to the specimen which was then slowly cooled in such a manner that it would require one hour and thirty-five minutes to cool it from 600 C. to 200 C.

To secure the maximum permeability as shown by curve 6 the specimenl was placed in the furnace at the indicated temperature and allowed to remain there for fifteen minutes. The magnetic field was applied at the same time the specimen was introduced into the furnace so that the field was acting upon the specimen during the eliminates heating of the specimen. The specimen was then allowed to slowly cool in the magnetic field at the same rate which was used in obtaining curve 5.'

For curve 'l a specimen was raised to 600 C. and then slowly cooled. On arriving at the indicated temperature the magnetic field was applied to the specimen and it was maintained at this temperature in the magnetic field for five hours and then slowly cooled to room tempera- 'ture ata cooling rate such that it required one hour and thirty-five minutes to cool the specimen from 600 to' 200. The permeability of the specimen as treated for

curves

5, 6 and 'l approaches the same value when the magnetic field is applied at 375 C. or below and, as illustrated by the'pol'- tion Il of these curves, is of a lower value than that of curve I0. This is due to the slower cooling rate which is about half that employed when the specimen was treated for

curves

3 and 4 so thaty it required twice as long to cool the specimen in this case as it did for

curves

3 and 4.

For obtaining curve 8 several specimens from the same lot of material of an alloy of 'lill/2% nickel and 211/2% iron were used. rIhey were all.

slowly cooled from a high temperature to remove..

the stresses and strains due to working. They.

were then reheated to above 600 C. where a magvnetic field was applied and then they were slowly cooled. Each rspecimen'was cooled to a different temperature and maintained at these respective temperatures in the magnetic field for ve hours after which time they were slowly cooled to room temperature. would require thirty-one minutes to' cool the specimens from 600 C. to 200 .C. The permeabilities were then measured and plotted as a function of the temperature at which `the specimens remained for five hours.

Curve 9 shows the result of maintaining the specimens as heat treated for curve 8 at 400 C. for one hour. This shows a much less decrease 'I'he cooling ratewas such that it in permeability by baking for one hour at 400 C.

While lnot in a magnetic field than that shown by the ordinary double heat treated specimen as illustrated by the difference between points I and.2. Thus the permeability of the specimen heat treated in a magnetic field as for example in accordance with heat treatment for curve 8 is believed to be much more stable and permanent and less subject to change with time and temperature thanit is forthe ordinary double heat treatment now in use.

The curves in Figs. 5 and 6 show the permeabilities of' an iron-nickel-cobalt alloy comprising 45% nickel, 30% 'iron and 25% cobalt as treated in accordance with this invention. 4It should be noted that the curves of Fig'. 6 are plottedon logarithmic scales so that the range in value of the permeability is greater than it appears from these curves. Curve l in Fig. 5 shows the effect of various field strengths used 4during cooling upon initial-permeability of the sample as it was taken from the heat treating furnace at room temperature. For curve 2 thc sample has been demagnetized. Curve 3 shows the maximum permeability of the sample as it came from the furnace for various magnetic-field strengths used during the heat treatment and for cobalt in I tiie ferm of a solid ring after it has been heated to 1100 C. and maintained at this temperature for one hour and then slowly cooled. In curve 2 the specimen was then heated to 725, which is 5 slightly above the non-magnetictemperature of fteen minutes and slowly cooled with the cross f magneticiield applied during cooling by sending an electrical current through the specimen as illustrated in Fig. 1. It is to be noted that .this

somewhat increases the permeability atflow magnetizing forces but that the permeability still remains `fairly` constant to rather high .values of H. 55% i For curve 4 the specimen was heated to 725 C.. which is slightly above the non-magnetic temperature for this alloy, for fteen minutes after it had previously been slowly cooled from 1100 C. A direct'current magnetic eld of 24'gauss was then applied and the spcimen slowly cooled. Thisfeld was applied circumferentially in the same direction-in which the permeability was measured. For curve 5 the specimen was again heated,` after cooling from 1100 Cf, to '725 C. for ten minutes and then rapidly cooledv by dropping it into water with no magnetic force applied. For curve 6 the specimen was similarly treated excepting that it was quenched in oil instead of water. For curye 1 two layers of 3 mil metallic tape were wrapped about the specimen in order to prevent too rapid a cooling oif the surface so that excessive strains would not be set up within the specimen.

l From these curves it is evident that this ma terial behaved similar to the iron-nickel alloy consisting of 781/2 nickel and 21,1/2 iron in that 40 vrapidly cooling it through the magnetic transformation temperature region, in this case from between approximately 725 and 400 C., produces a marked increase'in the maximum permeability of the specimen; and, also, that applyinga magnetic rfield while 'slowly -cooling the specimen throughA this temperature region very greatly increases the maximum permeability of the ma-f terial. In. addition, from curves 3 and I, it' is quite evident that there is a diiIei-.encein the maximum permeability of more than 60 to 1, .and

for certain values of eld strength there is al difference of more than meability in the direc ion which coincides with the direction ofthe magnetic fleldemployed dur- `ing the heat treatment andthe permeability at right angles to that direction. By the use ofsuch a material having these pro rties it is quite evident' that the stray magne ic iiux surrounding magnetic'cores can Joe reduced since the ux'would tend to follow the direction o'i. the magnetic`eld applied during the heat treatment. A further falvantage'of the iron-nickel@- cobalt alloys as `heat treated in a magneticeld is that the 'maximum permeability occurs for relatively ,high values of ux densities so that for a range of flux density from 12,000 to 14,500

Jthe permeability is higher than that for any other substance known today.

In later tests it was found unnecessary in some cases to heat alloys of iron,v nilzel, and cobalt to over 900"` C. and slowly cool themto remove internal stresses and strains. It was found that a temperature as low as 700 C. was suilcient to remove the internal strains.' This isespecially true if it ismaintained at this temperature for 0 to 1 between the per- Table II H iii' bei-stede .7.. Material a., p used en 'mpem e cooling ture o.

Nickel zio i281 0 400 1320 26.5 450 11000 o y Y, 500 11410 0.05 500 ggz, pickel 1 30 1200` 'o u 625 iron l 6 625 18.5% hlekei 1000 25800 500 3.8% chromium. 7000 27950 6.0 600 17.7% iron.

Y113.5% nickel 0850 16000l 0 s 480 3.8% molybdenum... 9650 52900 6 4 480 17.7% iron 50% iron. 2 600 I 3980 50% cubain--. ,K 540 6150 21 1025 Armco l 160 l 6950 vIron 100 8600 25 800 Siiieen sieei 340 5820 0 810 300 8080 30 A. c. 810 24o 1880 30 D. C. 8x0

l For regular double treatment. l Alter vacuum annealing at l000. j After vacuum annealing at 925. 1'

'I'his table shows that those alloys which respond to rapid` cooling through the magnetic transformation temperature region also exhibit a marked increase in maximum permeability' when slowly cooled in a magneticy eld through its magnetic transformation temperature region. By treating magnetic alloys in accordance with this invention the permeability in many cases ex-\ ceeds that which may be obtained by the usual double heat treatment and in addition the alloy seems toi-be .more stable magnetically. -Further K' more, 'this method may be applied' to all types of magnetic bodies, of various shapes and cross- '.sections. It is, moreover, impossible to rapidly and iformly, cool some large or irregularly yshaped magnetic sections of either solid or laminated constructions so as to secure aggreat increase in the' maximum permeability. .This is due tothe fact that th rapid cooling cannot be uniformly controlledthroughout the section so that various portions of the section which may be of different shapesand crosssections will be cooled at lconsiderably different rates. This may develop large stresses and strains within the section which may reduce the permeability morethan theurapid cooling increasesit. For example, a large'cylin drical casting of* an alloy of '781/2%"nickel and 211/2 iron was double heat treated by quenching and the maximum 0f permeability obtained-was about 9000 while-by heat treating `it in a magnetic eld in accordance `with this invention by slowly coollng'it 'from 600 C. in the magnetic eld, a maximum permeability of 111,000 was obtained. In addition, the permealiility for high values of induction of alloys having high saturation values of induction when heat` treated in a magnetic -eld in accordance with this invention is yin excess of the permeabilities at these high values of induction of any magnetic'material known today.

It should also be noted that while no figures have been'given relating to the hysteresis, magnetic alloys reated in accordance with this invention have the hysteresis loss reduced in a manner similar to the reduction secured by the double heat treatment in which the alloy is rapidly cooled through the magnetic transformation temperature. This method of heat treatment possesses the further advantage of tending to reduce stray magnetic fiux leakages from cores heat treated in this manner since the permeability -v thereto.

structures and other types of magnetic apparatus `of the stray magnetic fiux.

inthe desired direction may be made many times greater thana the permeability at right `angles This would be an advantage in relay in which it is desired to re uce or limit the value This treatment'also producesmore uniform permeability throughout -the cross-section of specimens.

What is claimed is: l

1. A method of increasing the magnetic permeability of irregularly shaped made of magnetic alloys, the permeability of which is increased -by rapidly cooling.) them through the magnetic transformation temperature region, characterized in that said magnetic bodies are slowly cooled through the magnetic transformation region in a magnetic field directed in the direction in which the high permeability is desired.

2. A method of increasing the magnetic permeability of ferro-magnetic materials, the permeability of which is increased by rapidly cooling them through the magnetic transformation temperature region, which comprises cooling the material in a magnetic field from a temperature above the magnetic transformation temperature region ofthe material.

3. A method of increasing the vmaximum magnetic permeability ofmagnetic bodies of irregular shapes and cross-sections of magnetic alloys, the maximum permeability of which is 4increased by rapidly cooling them through the regions of the magnetic transformation temperatures which comprises slowly cooling the bodies from a high temperature and then reheating and slowly cooling the bodies in a magnetic eld from a temperature below themen-magnetic temperature of the material.

4. A methodpf increasing the permeability of magnetic bodies of large cross-sections,- the permeability of `which is increased by rapidly cooling the magnetic material of said bodies through' the region of the magnetic transformation temperatures which comprises slowly cooling the bodies from a high temperature through the magnetic transformation temperature region while subjected to amagnetic field.

5. A Vmethod of heat treating magnetic alloy which comprises slowly cooling thealloy from a temperature above 900 C., reheating it to a temperature above non-magnetic temperature and cooling it through the magnetic transformation temperature region in a magnetic field.

6. lA method of heat treating magnetic alloy which comprises heating the alloy to a temperature above 900 C., slowly cooling the alloy to a temperature above non-magnetic temperatures of the alloy, applying a magnetic field tothe alloy and cooling the alloy through the magnetictransformation temperature region in vsaid magnetic field.

'1. A method of heatjtreating magnetic. alloy which comprises slowly cooling the alloy from a temperature above 900 C., reheating it to a temmagnetic bodies within the magnetic transformation temperature -perature region but which is below thev nonmagnetic temperature of the alloy, in a magnetic field and slowly coolingthe alloy in said magnetic field.

8. A method of heat treating magnetic alloys which comprises slowly cooling the alloy from a temperature above 900 C. to a temperature below non-magnetic temperature but within magnetic transformation temperature range, applying a magnetic field to the alloy and cooling the alloy in said magnetic field.

9. A method of heat treating magnetic alloys which comprises slowly cooling the alloys from al temperature above 900 C., reheating it to a temperature within the magnetic transformation temperature region, applying the magnetic field to said alloy, maintaining said alloy at said temperature in'said'ma'gnetic field for a time and cooling said alloy in said magnetic field.

10. A method of heat 'treating magnetic alloys which comprises slowly cooling the alloys from above 900 C. to -a temperature within the magnetic transformation temperature region, apply. ing a magnetic field to said alloy and maintaining said alloy in` said magnetic field for a specified time and then' cooling the alloy in said magnetic field.

11. A method of increasing the maximum permeabilityof large magnetic bodies of alloys comprising nickel and iron which comprises slowly cooling the. alloy from a temperature above 900 C., reheating the bodies to a temperature within the magnetic transformation temperature region and cooling said alloy in a magnetic field.

12. A method o f increasing the maximum permeability of alloys comprising nickel and iron which comprises'slowly cooling the alloy from a temperature'above 900 C., reheating the alloy in 'a magnetic field to a temperature within the magnetic transformation region, maintaining thel meability of large magnetic bodies of irregular cross-sections of magnetic alloys comprising nickel and'iron which comprises the alloy from'a temperature above 900 C.V to a temperature within the magnetic transformation temperature region of said. alloy, applying a magnetic field to said magnetic bodies and cooling said magnetic sections in said magnetic field.

14. A method of heat treating magnetic bodies of large and irregular cross-sections of magnetic alloys comprising nickel and iron which comprises cooling said magnetic sections from a temperature above 900 C. to a temperature within the magnetic transformation temperature region, applying a magnetic field to said bodies, maintaining said bodies at said temperature in the magnetic field for a time, and slowly cooling the bodies in said magnetic fleld.

15. A method ofV heat treating' large magnetic bodies of magnetic alloys comprising iron, nickel and cobalt which comprises slowly cooling said bodies from a temperature above 9009 C., reheating it to a temperature within the magnetic transformation temperature region and cooling it in a magnetic field.

16. A method of increasing the maximum perf meability of largeirregularly shaped magnetic bodies of magnetic alloys comprising nickel, iron and cobalt, which comprises slowly cooling the alloy from a temperature above 900 C.,Yreheat slowly cooling y a temperature above 900 C. to room temperature, reheating said alloy in -a magnetic eld in a direction in which the high permeability is desired to a temperature'withln the magnetic transformation temperature region vof said alloy, and slowly cooling saidK alloy in said magne'tic field. y

18. A method of reducing magnetic leakage .from the cores of electromagnetic apparatus by heat treating said cores to secure a high permeability in the direction of the desired `iiux and a low permeability in' the direction of the leakage ux, which comprises slowly cooling said cores from a temperature above 900 C. to room temperature, reheating said cores in a magnetic eld/to a temperature within the magnetic transformation temperature region in a magnetic eldi and slowly cooling Bald cores to room tempera-l 5 ture in said magnetic iield.

19. A method of liron, nickel, and ing said alloy yabo cooling said alloy ure, applying a magnetic eld to said treating magnetic alloy o i' cobalt which comprises heatve/its non-magnetic temperain said eld.

20. A method of increasing the permeability qof large irregularly shaped magnetic sections of -ialloys comprising comprises heating iron, nickel, and cobalt which saidsections to above 725 1" C., applying a magnetic eld; and cooling said sections in saidm agnetic eld.

21. Amagnetic material having a permeability to magnetic fields directed in jthe material which is over meability of the'material one direction in five times 'the per- 20 to magnetic iields directed in other directions in the naterial. A

e'GEoRGE a. KELsAU...

alloy, andv10 l