US2084133A

US2084133A - Method of producing magnetic materials

Info

Publication number: US2084133A
Application number: US701254A
Authority: US
Inventors: Alfred L Dixon; John V Davis
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1933-12-07
Filing date: 1933-12-07
Publication date: 1937-06-15
Anticipated expiration: 1954-06-15

Description

. A. L. DIXON El AL METHOD OF PRODUCING MAGNETIC MATERIALS June 15, 1937.

Filed Dec. 7, 1933 FIG. /4 /5 Patented June 15, 1937 PATENT OFFICE METHOD oF PnoDUcmG MAGNETIC MATERIALS Alfred L. Dixon, Hollywood, Ill., and John V.

Davis, Daphne, Ala., assgnors to Western Electric Company, Incorporated, New York, N. Y., a' corporation of New York Application December 7, 1933, Serial No. 701,254

8 Claims.

This invention relates to methods of proy ducing magnetic materials.

Objects of the invention are to provide magnetic materials of high permeability and practical and effective methods of producing such materials. A

In accordance with one embodiment of the invention, a ferromagnetic material is heattreated in a reducing atmosphere and during the heat-treatment a magnetic field is applied to the material whereby the permeability of the material is greatly increased.

' Other objects and advantages will appear from the following detailed description taken in conjunction with the accompanying drawing, in which Fig. 1 is a sectional view of a device which may be used inpracticing the invention.

Fig. 2 is a plan view of the device shown in Fig. l; and

Fig. 3 is a modied form of device of the type shown in Fig. 1.

In practicing the invention a piece of ferromagnetic material, as, for' instance, a piece of 5 iron of any suitable shape, such as 'a ring, bar

or vthe like, is placed in a fur-nace having a reducing atmosphere, such ashydrogen, and heated to slightly below the melting point of the iron, as, for instance, a temperature of 2700 F., and 30 the material is maintained at this temperature for a period of about A24 hours. It appears that y the hydrogen combines with some of the impurities in the iron, such asv sulphur, oxygen, nitrogen, carbon, etc., producing volatile compounds 35 which are expelled from the iron and thus tends to purify the iron. rDuring this period the iron is in the gamma phase and it appears that the gamma crystals of the material are greatly increased in size. The period of 24 hours during 40 which the material is maintained at this high temperature is not critical, although the best results lare obtained by treating the material for approximately this period.' The material is then cooled and it has been found that the rate of cooling is not critical, although the best results are obtained by cooling the material at a slow rate by allowing it to cool in the furnace. When the material is cooled and passes through the A3 transformation point, at a temperature of about 1652 F., it passes into theealpha phase accompanied by a change in crystal structure. It appears that during this change certain strains are set up in the material which impair the magnetic properties of the material. kThe 55 material is therefore again heated to abtemperatu're just slightly below the A3 transformation point as, for instance, a temperature of 1620 F.. in the case of iron, and maintained at this tern- Y perature for a period of about 2 hours. This second heat-treatment is also preferably carried out in a hydrogen atmosphere and during this treatment the'material is subjected to the influence of a magnetic eld for the purpose of increasingthe permeability of the material. It has been found that iron which is heat-treated as described above, without the application of .a magnetic eld during the treating process, has a maximum permeability in the neighborhood of 50,000; whereas, the same material when subjected to the inuence of a magnetic field during the heat-treatment has a maximum permeability of 100,000 to 150,000. In some cases permeabilities as high as 228,000 have been obtained by this process.

Referring now to the drawing, Figs. 1 and 2 show a device for applying a magnetic field to magnetic materials in ring form.V This devicev consists of upper and lower plates 5 and 6 which have annular cut-out portions 1 and 8 which form an annular cavity or tunnel 9 when the plates are superposed. The plates 5 and 6 are provided with conducting inserts Il and l2. Inserts l2 are provided with a bore at their upper ends and the inserts Il are provided with projections I3 which t into the bores ofthe inserts l2 to make a conducting connection between the inserts in the upper and lower plates. The outer ends of the pins Il and I2 are connected by conductors I4 in such-a manner as to provide a helical winding around the material in the annular cavity 9. The plates 5 and 6 are preferably made of a refractory material to withstand the high temperatures in the furnace and are preferably provided with apertures l5 to provide access of the hydrogen in the furnace to -the material in the device. 'I'he material to be treated may be placed in the-furnace in the device described at the beginning of the heattreating operation and leads I6 of the device may be connected to a source of current to provide a magnetic eld vfor `the material during the heat treatment. It is not essential that the magnetic field be maintained during the en- -tire heat-treatment and excellent results have been obtained 'by applying the magnetic iield only during the second heat-treatment, while the material is being heated for Several hours slightly below the A3 transformation point. Preferably, however, the magnetic eld is applied during the entire second heat-treatment, that is, while the material is being heated to a point slightly below the A3 transformation point until it is cooled. y

As an illustration of a specific vexample of a method embodying the invention, a ring of magnetic iron may be heated in a hydrogen atmosphere to 2700 F. for 24 hours and then cooled in the furnace. 'I'he material is then placed in a fixture such as shown in Fig. 1 and the material is again placed in the furnace and raised to a temperature of approximately 1620 F. and maintained at this temperature for approximately two hours. I'he fixture has twelve turns thereon and an alternating current of 60 cycles per minute and of 6 amperes is passed through the winding during the second heat treating operation. Due to the fact that the eddy currents set up in the material by an alternating current prevent effective penetration of the magnetic eld when high frequencies are used, a low frequency i'ield, preferably of 60 'cycles per minute, is applied.

In some cases a field strength of approximately 6 oersteds has been applied to the material with excellent results. It has been found that irnproved results may be had with various intensities of the magnetic eld. Magnetic fields as low as l oersted, as well as magnetic fields as high as 15 oersteds,` improve the magnetic properties o f the material.

Fig. 13 illustrates a device which may be used for treating magnetic material in bar shape and comprises a tube I1 in which the material may be inserted, having av winding IB thereon for subjecting the material to a magnetic eld.

After the iirst heat-treatment of the material, the material may be distorted or worked into any suitable shape desired. The distorting or working of the material will, of course. produce strains in the material which will ailect its magnetic properties. These strains, however, are removed in the second heat-treatment when the material is treated at a. temperature slightly below the A3 transformation point, and, therefore, material which has been worked after the first heattreatment may'. be subjected to the second heattreatment in the same manner as material which has not been worked after the first heat-treatment.

, It will be understood that the nature and embodiments of the invention herein described are merely illustrative and that many changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A method of producing magnetic iron which comprises treating the iron at a temperature of the order of 1600 F. and subjecting the iron to a varying magnetic iield at substantially said temperature during the heat-treatment and maintaining said temperature and the application of said magnetic iield for a period sufcient ito materially increase the permeability of the ron.

2. A method of producing magnetic iron which comprises treating the iron in a reducing atmosphere at a temperature of the order of 2700" F.,

cooling the iron, treating the iron at a temperature of the order of 1600 F. and subjecting the iron to a varying magnetic field during the second heat-treatment.

3. A method of producing magnetic iron which comprises heating the iron to a temperature 'of the order of 2700 F., maintaining said temperature for substantially twenty-four hours, cooling the iron, reheating the iron to a ltemperature of the order of 1620 F., maintaining said temperature for substantially two hours, subjecting the iron to the'iniiuence of a magnetic iield during the second heat-treatment, and cooling the iron at a rate to provide an annealed product.

4. A method of producing magnetic iron which j comprises heating the iron to a temperature of the order of 2700 F., maintaining said temperature for substantially twenty-four hours, cooling the iron, working the ir'on, reheating the iron to a temperature of the order'of 1620 F., maintaining said temperature for substantially two hours, subjecting the iron to the iniiuence of a magnetic field during the second heat-treatment, and cooling the iron at a rate to providev an annealed product.

5. A method of producing ferro-magnetic material which comprises heating the material at a high temperature but below its melting point in a reducing atmosphere, maintaining this tem- `perature for a substantial period, cooling the material, reheating the material to a temperature below the A3 transformation point, maintaining the material at this temperature for a substantial period, and applying a magnetic iield to the material during the second heat-treatment.

6. A method of producing ferro-magnetic material which comprises heating the material to a temperature slightly below the A3 transformation point and substantially above the A2 transformation point and applying a magnetic ield to the material during vthe heating operation, and maintaining substantially said temperature and the application of the magnetic field for a period to materially'increase the permeability of the iron.

' 7. A method of producing ferro-magnetic material which comprises heating the material to a temperature slightly below the A3 transformation point and substantially above the A2 transformation point and applying a varying magnetic field to the material during the heating operation and maintaining the material in said temperature range and applying said magnetic iield for a period suiiicient to materially increase the permeability of the material.

8. A method of producing magnetic iron which comprises heating'the iron to a temperature of the order of 1620 F., maintaining lsaid temperature for a period sufficient to materially increase the permeability of the iron, subjecting the iron to the influence of a magnetic ileld during the heat treatment, and cooling the iron at a rate to provide an annealed product.

ALFRED` L. DIXON. JOHN' V. DAVI.