US1987468A - Magnetic material and method of treatment - Google Patents

Description

Jan. 8, 1935.

o. DAHLV ET AL 1,987,468

MAGNETIC MATERIAL AND METHOD OF TREATMENT Filed Aug. 11. 1 933 3 Sheets-Sheet 1.

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1933, Serial No. 684,742

In Germany September 1, 1932 10 Claims.

This invention relates to magnetic cores of the type in which compact alloy material is made to acquire through a certain cold rolling a stability of permeability such as was hitherto believed to cores. We now show that certain elements added to iron-nickel alloys lead to magnetic materials which'possess a high stability of permeability and at the same time a sufficiently small hysteresis both obtained by one and the same working process, that is, a cold working which is favorable to stability.

The technical value of these materials is clear from the fact that the expression w/uo given as quality factor (quality figure for use as loading coil core) may be reducedto values around 6 to 2.

, The further detailed investigation of those alloys, in particular of the materials containing copper, has shown that the characteristics depend to a great extent not only on the composition and the nature of the cold working up but also on the thermal preliminary treatment.

The whole process for producing the stablematerial consists in the' following working processes: (1) Fusing, casting and the bringing of the cast billet through forging, hot and cold rolling to the penultimate thickness; (2) annealing of the tapes, strips or wires brought to the penultimate thickness at temperatures which are well characterized by increased solubility of the material added, cooling down at a certain rate, e. g. by quenching in water, in the air or by slow cooling in the furnace; in the case of more rapid cooling eventually repeated annealing at a moderate temperature of about 350 to 600 C.; (3) bringing the material to the final thickness by cold working, whereby in order to obtain the required stability and hysteresis the amount of working should generally cause a reduction in thickness of more than 50%; in a given case annealing of the material, whether in tape form or after the preparation of the core, at temperatures up to 200 0., in order to eliminate strains or relieve aging processes dependent on time.

A primary feature of the present invention consists in the use of the second process of the treatment.

The importance of this in causing the characteristics concerned is to be found in the processes of change or the special solub lity conditions which prevail beforehand. The a'.-so1utely stable was aimed at without regard to the value of the initial permeability. This state can be reached by a suitably chosen speed of cooling, e. g. air cooling in the case of high content of added element especially copper percentage alloys, slow cooling in the case of slightly alloyed materials or, however, by annealing the rapidly cooled alloys at a low temperature of about 350'to 600 C. It is seen that the procedure varies according to the composition of the alloy, and according .to what characteristics are desired. In' practice the process used may be accomplished very well with existing annealing apparatus. Rapid cooling with subsequent annealing must be termed the simplest method and it can be carried out reliably.

The efiect of the heat treatment described can be seen from the accompanying figures. All alloys of which the characteristic values are plotted there are tested in the cold rolled state reduction in thickness).

Figs. 1 to12, inclusive, are graphs illustrative of various properties of the materials with varying compositions and with varying treatments as will be hereinafter explained.

Figs. 1, 2, 3 and 4 give the characterizing magnetic constants for the ternary materials formed from the base-alloy of 36 parts nickel and 64 iron by the addition of increasing quantities of copper, i. e. hysteresis, initial permeability the expression l: w/uo and, Fig. 4 to the instability s. The annealing temperature amounted in all cases to 1000' C., the duration of the annealing always amounted to an hour. After the annealing and cooling the alloys were cold formed until there was a reduction in thickness of 90%.

For example, it can be seen from the curves that such an alloy with 11% copper for which as great an initial permeability as possible was required for tolerable values of the hysteresis, has to be cooled in water; because the alloys cooled in the furnace certainly possess a somewhat higher initial permeability but not a tolerable hysteresis. If in the case of the same alloy it is a matter of obtaining the smallest possible value 01 the quality factor.

i Ho cooling in air will be chosen. An alloy with less than about 8% copper will be' cooled suitably in the furnace in order to obtain a' favorable value of ho.

Each of the Figures 5, 6, 7 and 8, shows how the characteristics of hysteresis, the initial permeability, the expression ho, and the instability s of three alloys with 9, 11 and 13% copper (base alloy 40% nickel, iron) can be changed if the alloys heated to 1000 C. in hydrogen and cooled in water are annealed for an hour, before they are subjected to a 90% reduction in thickness by cold working.

The figures show, for example, that an alloy with 9% copper acquires by annealing for an hour after the quenching, the best results are obtained at about 500 to 600 C. and moreover for the alloys with 11 and 13% copper the best annealing temperatures can be gathered easily from the appropriate curves; diiferent annealing temperatures may be chosen according to the characteristic which is the most important for the purpose in view.

Whereas in the figures just described the influence of the annealing temperature is determined for a constant duration of heating of one hour, in Figs. 9, 10, 11 and 12 the effect of the duration of annealing on hysteresis, initial permeability, the expression and the instability s for two different annealing temperatures. It is seen, for example,-that by heating for about two hours to 450 C. practically the same eifect is produced with regard to the value as by heating for an hour at 550 C. Further it is seen for this example of an alloy with 11% copper (base alloy 40% nickel, 60% iron) that by heating for two hours at 550C. the value is still reduced, whilst the stability does not change very much. These curves relate to alloys which are annealed for two hours in hydrogen to a temperature of 1000 C. and cooled in water, before being subjected to the heat treatment shown in the figures, then cooled in air and worked up in the cold toa 90% reduction in in the cases where the base alloys are composed of 36% nickel and 64% iron or 40% nickel and 60% iron. It should be pointed out expressly that the same or similar results exist for series of alloys with a nickel content of the base alloy of about 30-70%. Thus the rule is valid which states that the effect of the annealing treatment is noticeable for a copper content which is the smaller, the smaller the'nickel content of the alloys. With higher nickel contents, e. g. nickel, the limiting concentration is about 17 copper.

What is claimed is:

1. In methods of processing magnetic materials, the final steps which comprise annealing the material at a temperature above 700 C.,'

to a temperature above 700 C., quenching the material, reheating it to a moderate temperature of between about 300 C. and 600 C., cooling the material to room temperature, and then cold working it into its final form.

3. In the process of preparing magnetic material, the steps which comprise annealing the material at a temperature above 700 C. quenching it and reheating it to a moderate temperature of between about 350 C. and 600 C., cooling the material, cold working it into its final form, and then aging the material by heating it to a temperature not to exceed about 200 C.

4. Methods of processing alloys comprising approximately 36 parts of nickel, 64 parts of iron,

and 1 to 9 parts of copper, which includes the steps of annealing the material at a temperature above 700 C., rapidly cooling the material to room temperature, and cold working it into its final form with a reduction in area of at least 50%. v

5. In the processes of preparing alloys comprising approximately 36 parts of nickel, 64 parts of iron, and 9 to 15 parts of copper, the steps which comprise heating the alloy to a temperature above 700 C., quenching the material and reheating it to a temperature 01' between approximately 350 C. and 600 0., cooling the material to room temperature, cold working it into its final form with 'a reduction of cross-sectional area of at least 50%, andiinally aging the material by heating it to a temperature not to exceed 200 C.

6. In the process of producing magnetic material from alloys comprising approximately 30 to nickel, and 1 to 17% copper, the final steps of annealing the material at a temperature above 700 0., cooling it to room temperature,

and cold working the material into its final form, with a corresponding reduction in cross- 1 sectional area of at least 50%.

7. An article of manufacture comprising a magnetic alloy comprising approximately 36 parts of nickel, approximately 64 parts of iron, and approximately 1 to9 parts of copper which has been annealed at a temperature above about 700 C., rapidly cooled and then cold worked into final form with a reduction in cross-sectional area of at least 50%.

8. An article of manufacture comprising a magnetic alloy comprising approximately 36 parts of nickel, approximately 64 parts of iron,

and approximately 9 to 15 parts of copper which has been annealed, quenched and cold worked into final form.

9. A magnetic material comprising approxi- 5 mately 36 parts nickel, approximately 64 parts temperature, and then cold worked into final form.

10. A magnetic material comprising an alloy which comprises 30% to 70% nickel and 1% to 17% copper which has been annealed, rapidly cooled and then cold worked into final form.

OTI'O DAHL. JOACHIM PFAFFENBERGER.

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