GB1587268A - Magnetic alloys - Google Patents

Description

(54) MAGNETIC ALLOYS (71) We, WESTERN ELECTRIC COMPANY, INCORPORATED of 222 Broadway, New York City, New York State, United States of America, a Corporation organised and existing under the laws of the State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention is concerned with hard magnetic materials, processes for shaping such materials, and devices utilizing materials so shaped. Shaping is accomplished by steps including working with at least some critical part of the working being conducted at low temperature, sometimes at room temperature. Magnetic properties are sufficient to permit use in many magnetically biased devices, such as, electroacoustic transducers, including receivers, loudspeakers, and the like.

The development history of hard magnetic materials is characterized as a continuing search for higher and higher values of coercivity, remanent magnetization, and energy product. This is evident from consideration of such devices as permanent magnet loudspeakers, where increased energy product results in improved bass response for given magnet size. In receivers too, engineering design considerations, such as air gap and volume, suggest increasing values of coercivity, as well as of energy product. The quest has been accelerated by recent design trends, all of which lead toward increasing miniaturization which, in turn, indicate larger energy product, as well as coercivity to accomplish a desired permanent bias for now reduced proportions.

From many standpoints, it is reasonable to characterize modern, permanent magnet materials as having coercivities of the order of at least 250 Oe. and remanent magnetizations of at least 7,000 Gauss, indicating a maximum energy product of at least one million Gauss-oersteds. For real operating devices, the energy product value of concern is that measured along an operating line (or load line) which depends upon design parameters, such as, circuit reluctance, etc.; and here a useful energy product may be somewhat less than the maximum value.

From the standpoint of processing, hard magnetic materials may be classified as belonging to either of two categories. Brittle alloys, are exemplified by the Alnico series (see R. M. Bozorth: Ferromagnetism, D. Van Nostrand, 1951). Such compositions, based on aluminum, nickel, and cobalt do not lend themselves to working, e.g., by rolling, or drawing. Thus piece parts of such alloys are most expeditiously or necessarily formed by casting or powder metallurgy. Ductile alloys, exemplified by the alloys: Cunife (cobalt, nickel, copper and iron), Cunico (cobalt, nickel, and copper) and Vicalloy (vanadium, cobalt and iron), can be worked readily at room temperature. Piece parts of such alloys are generally processed by operations such as flat rolling and wire drawing.

From a commercial standpoint, other fabrication approaches are sometimes indicated.

An example involves Remalloy, an alloy of iron, cobalt, and molybdenum--e.g., 20 weight percent molybdenum, 12 weight percent cobalt, and the remainder (to equal 100 weight percent) iron. Piece parts of Remalloy, which is in the brittle category, are produced by working which, however, requires temperatures exceeding 1,100 degrees C. This exemplary Remalloy composition, already reflecting a compromise between workability and maximization of magnetic characteristics, is notably used in telephone receivers. This alloy is typically formed into a rolled hot band of the order of 100 mils in thickness by a series of steps that include (1) casting of ingot; (2) hot rolling at 1200 degrees C to the desired thickness in a series of rolling operations; (3) stamping to desired configuration with the stamping operation necessarily carried out at elevated temperature; (4) solution heat treatment at 1200 degrees C; (5) grinding to final dimensions; and (6) finally, a terminal heat treatment near 700 degrees C to develop the permanent magnetic characteristics. Such a Remalloy piece part, designed, for example, in the telephone receiver, may have a coercivity of 300 Oe., a remanence of 9,000 Gauss, and a usable energy product of perhaps one million Gauss-oersteds.

Hot workable Remalloys, processable as described, are characterized by magnetic properties among the best obtainable for hot workable materials, at least for materials within an acceptable price range for mass production. For certain uses where piece parts are subject to shock, even hot workable Remalloys are unacceptable; and so, for example, even the handset receiver used as an example above, may not be constructed of Remalloy for certain uses, for example, for use in pay telephones where abuse may be expected.

The invention provides a cold formable magnetic alloy having a ternary chromium, cobalt, iron system wherein the alloy comprises 25-30 parts by weight chromium, 10-20 parts by weight cobalt and remainder iron with or without impurities to result in 100 parts by weight of these elements, and wherein the alloy further comprises at least 0.1 percent by weight based on the said 100 parts of at least one additional element selected from zirconium, molybdenum, aluminium, niobium, titanium, vanadium and manganese, the maximum weight percent of each of elements zirconium, niobium, manganese and titanium being 1, of aluminium being 1.5, and of each of molybdenum and vanadium being 3.

The invention also provides a method of producing a magnetic element comprising mechanically working stock material of a composition comprising a ternary chromium, cobalt, iron system comprising 25-30 parts by weight chromium, 10-20 parts by weight cobalt and remainder iron with or without impurities to result in 100 parts by weight of these elements, the stock material further comprising at least 0.1 weight percent based on the said 100 parts of at least one element selected from zirconium, molybdenum, vanadium, niobium, titanium, manganese and aluminium, the maximum weight percentage of each of elements manganese, zirconium, niobium and titanium being 1, of aluminium being 1.5 and of each of molybdenum and vanadium being 3, the method comprising the step of cold forming to result in deformation of the stock material which includes bending to produce a change in direction of at least 25 degrees with such bending having a radius of curvature of a magnitude which is linearly proportional to the extent of change in direction with such magnitude corresponding with a 25 degree change in direction being no greater than the thickness of the stock material and the radius corresponding with a 90 degree change in direction being no greater than four times the thickness of the said stock material.

The alloys are magnetic and processing may result in remanent magnetization of 7,000 Gauss and higher, coercivity of 300 Oe. and higher, and maximum and typically usable energy products of two million and one million gauss-oersteds, respectively.

While additional functions may be served, it is considered that the elements modifying the ternary system are believed to perform at least one function in common, i.e., suppression of the low temperature sigma phase. The alloys are consequently largely ferritic (alpha phase). Minimization of the amount of sigma phase reduces brittleness.

Preferred compositions provide for supprcssion of the gamma phase, as well as the sigma phase. While presence of this phase may have some embrittling effect, its significance is largely concerned with dilution of magnetic moment. Introduction of zirconium has the effect of suppressing both unwanted phases sigma and gamma. Desired processability consistent with the economy are realized by introduction of zirconium together with at least one of the elements aluminum, niobium, and titanium.

Such added elements perform a most important first function. They render alloys of the class described ductile so that piece parts such as cupped rings can be successfully stamped at room temperature. Preferred compositions of the invention are so processable without need for protective environment so, for example, an exemplary composition containing both aluminum and zirconium is processable as described at temperatures which need not exceed 900 degrees C with all processing steps being carried out in air.

Materials of the invention are characteristically processed by (1) formation of a massive ingot; (2) sequential hot rollings at temperatures of 1200 degrees C and below to a thickness of perhaps 200 mils; (3) water quenching; (4) cold rolling to fifty percent thickness reduction; (5) solution heat treatment, perhaps at 900 degrees C, for periods of fifteen minutes to ninety minutes, to produce a fine-grained, recrystallized single phase body (if the solution temperature is excessive, e.g. greater than 1100 degrees C, the structure is recrystallized single-phase but coarse-grained; if the solution temperature is too low, e.g.

less than 850 degrees C, the part may fail to recrystallize and also contains a precipitate phase, the so-called sigma phase. Either condition renders the part sufficiently brittle that stamping e.g. into cupped rings -- cannot be done successfully at room temperature); (6) rapid quenching (e.g., in iced brine); (7) room temperature forming, as by stamping (it is important that this most critical step may be carried out at room temperature), (8) as an optional step, where desired, in contrast to the grinding required for final shaping of usual comparable prior art magnetic materials, material of the invention may be machined to final configuration; (9) heat treatment (aging) of the final piece part to produce desired magnetic properties. Heat treatment parameters are dependent upon the precise composition. Typically, temperatures of 550-625 degrees C are utilized followed by cooling rates in the range of 10-25 degrees C per hour for total times of the order of six hours. As in terminal heat-treatment of some prior art materials, the effect is a precipitation hardening which in the present case may be characterized as a spinodal transformation. Products using the invention are characterized by inclusion of one or more parts fabricated of compositions herein processed as described. An example is the cupped ring of the telephone receiver of the typical handset.

As a variation in processing, steps (2) to (5) may be combined and modified so that the ingot is hot rolled starting at temperatures of 1200 degrees C sequentially to the final thickness (perhaps 100 mils), ending up with the final rolling temperature at the solution heat treatment temperature (perhaps 900 degrees C for series A (quinary compositions) and 1050 degrees C for series B (quaternary compositions)). In this way, the cold rolling step is eliminated.

The materials described are characterized by retention of the described magnetic properties through a series of working steps, the final one of which may be performed at low temperature--even at room temperature--and the final one of which may be carried out on a material which can be stamped at room temperature. However, even though materials of the invention are characterized by such unusual properties, economic or other considerations may dictate use in processes or inclusion in products which do not take full advantage of all such properties, for example, simple tapes or other forms which do not require stamping but which may benefit by improved magnetic properties or economic advantages as compared with competitive prior art materials.

A specific example of a magnetic alloy, embodying the invention will now be described with reference to the accompanying drawings, in which: Figure 1 on coordinates of remanent magnetization, BR in gauss, on the ordinate, and coercivity Hc, in oersteds, on the abscissa, is a plot of the second quadrant of hysteresis loops of a variety of materials, some of prior art, as well as a variety of compositions in accordance with the invention; and Figure 2 is a cross-sectional view of a telephone receiver containing an element of cupped ring configuration of a composition herein.

The plot of Figure 1 familiar to design engineers working with magnetic materials includes three bands each defined between maximum and minimum hysteresis loop bounds with such variation in properties within bands resulting from a variety of diverse parameter variations--e.g., composition, heat treatment, degree of working, etc. Band 1, defined as lying between maximum loop bound 2 and minimum loop bound 3, includes a reasonably illustrative range of values which result in compositions of the invention as processed (with a permitted final room temperature forming step). Band 4, bounded between loops 5 and 6, includes reasonably characteristic magnetic properties for hot-worked (as distinguishable from cast) Remalloy compositions. Band 7, included primarily for reference purposes, bounded by loops 8 and 9, is representative of that range of Alnico alloys of coercivity, remanent magnetization, and energy product values comparable with compositions of the invention. The Alnico series is characterized by increasing coercivity and generally also energy product with successive members of the series so that Alnico 5, 4, etc., show lessening values of such parameters.

Figure 2, a cross-sectional view of a typical receiver as found in a telephone handset, consists of cupped ring member 10 of a composition herein which provides a permanent DC biasing magnetic field. Remaining elements include an aluminum diaphragm 11, a vanadium permendur (2% vanadium, 49% cobalt, 49% iron) armature 12, a permalloy (45% nickel, 55% iron) pole piece 13, a non-magnetic nickel-chromium alloy diaphragm seat 14, and a copper wound coil 15. When an AC signal energizes the coil, the resultant magnetic field is superimposed onto the DC field created by the biasing magnet at the gap between armature 12 and pole piece 13. This causes the armature and diaphragm to vibrate.

For a detailed description see E. E. Mott and R. C. Miner: "The Ring Armature Telephone Receiver", Bell System Technical Journal, Vol. 30, 1951, p. 110.

Magnetism is a very old art. Terminology, while familiar to the worker in the field, may not have a concise meaning--may vary somewhat depending on the time of usage and the particular specialty involved. For convenience, terminology used in this description is briefly defined.

Energy product, BH, is the product of the magnetization B in Gauss and demagnetizing field H in Oersteds along the demagnetization curve, i.e., the second quadrant of the hysteresis loop.

Maximum energy product, (BH)rn.jx, is the highest value of the product of B and H.

Effective energy product, (BH)eff, is the product of B and H as measured under the operating conditions of a particular device of concern. This product is often shown as the second quadrant intercept of the hysteresis loop and a "load line"--i.e., that line initiating at the origin and extending outwardly whose slope depends on the length and cross-sectional areas of the air gap and of the permanent magnet, hence the magnetic parameters characterized in the environment in which the material is utilized. For devices such as the U-type telephone receiver, such load lines initiate at the origin of the hysteresis loop and extend to include a point in the vicinity of B = 4000 G and H = -250 Oe. For this case, then, (BH)eff = 4000 x 250 = 1 million G-Oe.

Working is a procedure whereby preliminary shaping is brought about through mechanical deformation. Typical metallurgical procedures falling within this category are swaging, drawing, flat rolling, roll flattening, extruding. Where reference is made to the degree of working, the degree of reduction of the most altered dimension is intended--e.g., 25 percent deformation by flat rolling implies a reduction in thickness of 25 percent.

Reaystallization implies a crystalline regrowth generally occurring during a high temperature heat treatment of cold worked material, resulting in a change in crystal morphology from the condition produced during proceding deformation. Complete recrystallization is desirable for maximum ultimate forming but is not necessary to every inventive process herein--only that degree of recrystallization needed to permit the desired deformation is required. In fact, recrystallization carried out at excessive temperatures or prolonged times results in large grain growth and consequent deterioraton of subsequent formability. A fine-grained recrystallized structure is generally most desirable for forming.

Forming is the final working which results in the final part configuration. It may consist of one or more steps as, for example, a deep drawing step, followed by a stamping step. It is to be distinguished from the initial deformation from the ingot which, in many instances, takes the form of a flat rolling or wire-drawing procedure. The deformation incurred in forming is generally more severe and complex as compared with rolling or wire drawing; material which is rolled successfully could fail in forming. Forming, or stamping, in accordance with the invention, is a low temperature operation permissibly conducted at room temperature.

In specific instances it involves the forming of cupped rings for telephone receiver use from 100 mil. thick blanks. An acceptable test for such formability would be a satisfactory bend to a 90-degree angle around a tool with radius equal to the thickness of the strip. Note that while a significant aspect of the invention involves the ability to carry out forming at room temperature, high temperature forming is not precluded.

Two classes of compositions are contemplated: Series (A) which are generally preferred taking account of both formability and economy and Series (B) compositions which are not necessarily optimum, but are found amenable to contemplated forming to result in desired mechanical configuration, as well as magnetic properties.

Both Series (A) and Series (B) compositions are based on mixtures of the three elements 25-30 and prefcrably 26-28 parts by weight chromium, 10-20 and preferably 15-20 parts by weight cobalt, remainder iron to result in 100 parts by eight of these three elements. Series (B) compositions contain at least ().l weight percent based on the recited 100 parts of at least one additional element of the group zirconium, molybdenum, niobium, vanadium, titanium and aluminium. Series (A) compositions necessarily contain zirconium in the same minimal amount together with at least one of the elements aluminium, niobium and titanium. Experimental indications dictate the minimum of 0.1 percent as the smallest practical addition resulting in significant measurable improvement. In general, a maximum of 1.0 percent of each included additional element is indicated (again, regardless of series) so that Series (A) compositions could on this basis contain as much as 4 percent of such additional elements. It has been found that somewhat greater amounts of aluminum--up to 1.5 percent on the same basis and of molybdenum and vanadium - up to 3 percent - may generally be tolerated but that titanium may, under extreme processing conditions, result in observable change in grain morphology so that a preferred maximum of 0.5 percent is indicated for this element.

Extreme processing here defined as cold formability to result in bend of a radius of curvature approximating that of the thickness of the stock material, as well as retention of magnetic properties, is best assured by a peferred compositional range containing at least 0.5 percent by weight of zirconium. Receiver cups of particular consequence from the inventive standpoint are formed from 100 mil stock material.

Compositions of the invention in common with many other magnetic compositions may be affected by environmental constituents. A prevalent effect is nitrogen embrittlement which, in severe cases, may significantly impair formability, particularly at lower temperatures and may also impair magnetic properties even where insufficiently severe to significantly impair formability. Nitrogen susceptibility is substantially avoided by use of preferred compositions herein. So that, for example, the use of certain additives or additive additions permit the entire processing sequence to be carried out in air. Zirconium, titanium and aluminum are particularly effective agents for removing nitrogen. In operations which are carried out in the presence of nitrogen, amounts of additives greater than the minima prescribed by the present invention may be necessary, since formation of nitrides effectively removes combined material. Minimum additions of 0.2% rather than 0.1% at least for one of the elements Zr, Ti or Al satisfies this need.

The additive materials indicated are those required for workability. Certain other additives may be included intentionally for purposes that are well known; for example, manganese may be included in amount of up to one part by weight to bind sulphur which otherwise results in embrittlement. Silicon, again in minor amount, may be added as a flux.

It is no requirement that compositions herein be chemically pure. Unintentional impurities may be tolerated depending on intended use in amount which does not impair or significantly impair grain structure or magnetic prdperties. An additional limitation on impurities has to do with the impairment of processing under conditions indicated.

Generally, commercial grade ingredients are acceptable.

Typical processing steps together with parameter ranges are set forth. Certain optional steps sometimes indicated, sometimes otherwise known to those skilled in the art, are permitted. Certain other variations may be tolerated where maximized processability and magnetic properties are not required.

A suitable processing outline is first set forth: 1. An ingot is formed by conventional processing. For commercial fabrication, ingots are typically 100 pounds or more. Typically, the ingot is formed by melting in an induction furnace. Adequate mixing results from the induced currents inherent to the melting process. Substitution of other heating means may require mechanical stirring. Vacuum or neutral atmosphere is preferred. If processing is carried out in air, adjustment in composition as discussed hereinbefore may be needed.

2. Hot working, as indicated, may be carried out initially at temperatures above about 1200 degrees C but ending at temperatures below about 1100 degrees C. A general purpose served during this hot working is homogenization and recrystallization of the cast structure so as to eliminate the coarse "coring"--i.e., dendritic structure characteristically resulting during casting. For alloys of the present invention and the intended final room temperature formability, however, it is vital that the hot working step be carried out within specified temperature limits. If the hot working temperature is too low, recrystallization may not occur or may be incomplete. In addition, a second low temperature phase, known in the literature as sigma phase, may appear. If the hot working temperature is too high, excessive growth of the recrystallized grain may occur and the likelihood of atmosphere contamination is increased. All these conditions contribute to brittleness in subsequent cold working operations. For best results temperature at the end of the hot working operation should not be above 1200 degrees C nor below 900 degrees C for a zirconium-aluminum alloy nor below 1050 degrees C for a niobium-titanium-zirconium alloy. All limits expressed, as well as understood, assume typical processing. Generally, times of the order of up to about one half hour and reductions of some dimension df at least fifty percent are contemplated.

Decreasing either time or dimensional reduction permits some decrease in minimum permitted temperature for a given state of recrystallization. It is convenient, for many purposes, to carry out this step by hot rolling, since the resulting product is in appropriate configuration for subsequent processing to the shapes contemplated for many of the purposes set forth. Other hot working procedures, such as swaging, extruding, heading, drawing, are suitably substituted from the standpoint of recrystallization. There is, of course, no requirement that any such working take place in but a single pass but, in fact, it is to be expected that this procedural step will involve a number of sequential passes.

3. Quenching: The hot worked body must be reduced from its final elevated temperature to at least 400 degrees C at a cooling rate of at least 100 degrees C per second.

This is easily accomplished by simple water quenching using conventional facilities.

4. Cold working: The purpose of cold working is to produce a fine grained structure upon subsequent solution heat treatment (Step 5) which, in turn, permits the low temperature forming of Step 7. Regardless of the working procedure utilized, i.e., swaging, drawing, rolling, etc., a range of from 30-70 percent is generally desirable for formability as contemplated. Outside this range, an intermediate product may still be sufficiently deformable to meet a particular device need. So, for example, for the extreme case in which Step 7 does not involve stamping at all but might result, for example, in a simple tape, this cold working may be carried out over the broader range of from 30 percent to 90 percent or greater. The lower limit of about 30 percent is indicated by virtue of the fact that lesser dimension reduction does not result in sufficiently uniform deformation of the product so that the grain structure becomes inhomogeneous after the solution heat treatment.

5. Solution heat treatment: This is a simple heating into the temperature regime whereby '.' .;ingle phase structure, known in the literature as alpha, exists. This treatment, for preferred compositions herein, may be carried out in a normal air atmosphere, and generally requires sufficient time to raise the innermost portion of the worked body to minimum temperature and to maintain it for an additional period of perhaps 10-15 minutes.

Typically, depending upon ingot size, the entire solution heat treatment processing may require heating for a period of from 30 minutes to 90 minutes. The maximum is dictated by diffusion of and reaction with nitrogen. Nitrogen attack, minimized for preferred compositions of the invention, is found to cause some embrittlement with attendant processing difficulty at that level. Worked bodies at this stage are perhaps 100 mils in thickness and may be in the form of a loosely wound coil or other configuration which minimizes thermal lag. It follows that the cross-section of the as-worked body subjected to this step may have a thickness as great as one inch without need for exceeding the critical 90 minute limit (a cross-sectional thickness far in excess of that ordinarily produced by the preceding cold working step and, in fact, greater than thicknesses expedient for the following quenching step).

6. Quenching: This process is designed to retain the high temperature "alpha" phase.

The kinetics of the transformation suggest a cooling rate which is appreciably greater than that of Step 3. While no requirement, it has been found expedient to quench in iced brine at least to a temperature of 400 degrees C. For typical dimensions at this stage, this amounts to a cooling rate in excess of 1,000 degrees C/second. Slower rates, particularly for fine dimensioned bodies, are adequate for complete retention of the high temperature phase.

Under certain circumstances where forming does not require large distortion, existence of a multiphase body after quenching is permitted; and, in fact, under certain circumstances, the quenching may be eliminated altogether. Even in such instances, however, a solution treatment and a quench will eventually be required to develop the magnetic properties characteristic of the invention compositions.

7. Forming: It has been stated that a significant characteristic of the alloys at this stage is permitted forming at room temperature. Formability is desirable for all but the simplest configurations and is necessary. for example, for the cupped ring for the receiver shown in Figure 2. It may be accomplished in any of several procedures, for example, the ring configuration of Figure 2 is produced by progressive die stamping or by compound die stamping. In accordance with the progressive stamping procedure, a flat configuration is changed to a cupped configuration in perhaps four steps--all carried out cold and without need for intermediate treatment. This is a commercially significant aspect of the invention.

Simpler configurations which may or may not require the same degree of formability can utilize any of a variety of classical techniques--e.g., heading.

It has been indicated that magnetic elements may be formed by stamping to result in cup shapes evidencing curvature about a radius approximately equal to the thickness to produce a 90 degree bend. Since the permitted radius of curvature becomes larger for greater chang magnetic characteristics consits of holding the specimens at temperature typically between 600-640 degrees C for a period from about 10 minutes up to about 2 hours. It is usual to ramp to a lower temperature to perhaps within the range of from 500 to 525 degrees C and to hold from 1-4 hours.

Operation within the exemplary conditions set forth results in useful magnetic properties in any of the alloys discussed. Processing specification to result in properties tailored to a particular end use is expedited by a consideration of the responsible mechanism. The mechanism is one which may be broadly described as precipitation hardening (although the specific precipitation mechanism may take the form of a spinodal decomposition). It is well known that coercivity, dependent upon domain wall reversal, is, in turn, related to size and spacing of precipitant. The usual technique, once relevant conditions have been identified, involves high temperature treatment during which precipitation (or decomposition) is initiated, generally followed by cooling under conditions such that precipitation (or decomposition) is controlled to produce desired "hardness'. Phase boundaries and kinetics play their traditional role and best conditions are empirically determined. Appropriate magnetic properties for a variety of end uses have been experimentally produced with various heat treatment schedules usually involving high temperature treatment at the said range of 600 - 640 degrees C but sometimes cooling directly to room temperature-sometimes holding at an intermediate temperature--at a variety of cooling rates.

In general, useful results obtain by holding at an elevated temperature for a period of at least ten minutes. Where slow cooling is carried out, rates no faster than about 50 degrees C/hour are generally indicated, since much faster rates essentially fix the conditions produced during the high temperature treatment. While variations are possible--indeed, are indicated in at least one specific example--cooling is usually carried to a temperature no lower than about 500 degrees C. Further controlled cooling at economically feasible rates have little effect due to severely reduced kinetics at lower temperatures. It has, however, been found useful to maintain a temperature, for example, at 500 degrees C for periods of an hour or more and such a schedule is an example of a permitted alternative approach.

It is unnecessary to subject material under treatment to an external magnetic field during aging. The use of such external magnetic fields, however, is not precluded and may be useful for certain configurations.

Procedures as carried out in the numerical order set forth constitute preferred embodiment steps. It has been indicated that variations are permitted--indeed are sometimes indicated by economics; so, for example, the quenching of Step 6 may be eliminated altogether. For many purposes, the processing steps may be restricted to Steps 1, 2, and 6 to 8. Such a process may be adequate where forming requirements (Step 7) are not stringent and, in certain instances, may even suffice for the 90 degree forming described. For such an optional process involving severe forming, however, it is important that hot working (Step 2) terminate at a temperature prescribed for the solution heat treatment of now omitted Step 5. The aim here is to develop a fine-grained, recrystallized single-phase structure which is necessary for room temperature formability (Step 7). Hot working (Step 2), under these circumstances should terminate with a temperature of about 900 degrees C for the zirconium-aluminum alloy and about 1050 degrees C for niobium-titanium-zirconium alloy.

The broad processing limits set forth above are usefully applied to any of the included alloys of the invention. Compositional examples, all based on the same ternary composition but with various amount and kind of additional elements, were processed into final receiver cup rings (detail 10 of Figure 2). The following Table sets forth four such compositions indicating minimum and maximum solution heat treatment temperatures permitting required forming.

TABLE (All compositions 28 Cr, 15 Co, remainder Fe additionally contain 0.5 weight percent Mn and 0.2 weight percent Si.) Percentages of Solution Temperature, Degrees C Added Elements Minimum Maximum 1% Nb-1% Al 950 1100 3% V-0.5% Ti 1000 1100 1% V-1% Nb 1000 1100 3% Mo-t% Nb 1100 1150 8. Examples Example numbers 1 to 6 illustrate the use of a variety of compositions in accordance with the invention. In each instance, the specimen is capable of being formed into cupped rings suitable for use in a telephone receiver as depicted in Figure 2. Examples 4 and 5 actually include this forming step.

Example 1: The alloy produced is of the composition 15 parts cobalt, 26-1/2 parts chromium, 58-1/2 parts iron--all by weight--together with 0.25% zirconium, 1.0% aluminum, and 0.5% manganese--all weight percent based on 100 parts of ternary.

Amounts of initial materials all introduced as the elements totaled 200 pounds. The ingot was produced by vacuum induction melting. Analysis revealed a content of approximately 0.25% silicon as an unintentional inclusion. Other impurities totaled an amount less than 1.0 percent. After stripping the mold and permitting the ingot to reach room temperature in air, it was reheated to 1200 degrees C and was hot rolled in about 20 passes to result in a thickness of 200 mils. During rolling, the temperature fell to approximately 1100 degrees C.

The rolled body was water quenched in tap water. Cold rolling on a reversing mill with about four passes resulted in a thickness reduction of about 100 mils. Material was then reheated in air to a solution temperature of 900 degrees C for 30 minutes and then iced brine-quenched. The quenched body was aged in air at a temperature of 620 degrees C and was maintained at such temperature for 30 minutes and was then ramped at a rate of 25 degrees C per hour to a final temperature of 525 degrees C, was held at such temperature for 4 hours and was then permitted to air cool to room temperature. Magnetic properties were: Hc = 450 Oe., BR = 8300 Gauss, BHCff = 1.6 x 106 Gauss-Oersteds.

Example 2: The procedure of Example 1 was followed, however, to produce the following composition: 15 parts cobalt, 26-1/2 parts chromium 58-1/2 parts iron, 1 percent niobium, 0.25 percent titanium, 0.25 percent zirconium, and 0.5 percent manganese.

Silicon content and other impurities were the same as in Example 1. Solution temperature was 1050 degrees C in lieu of 900 degrees C. Magnetic aging followed the following schedule: 625 degrees C for 20 minutes, ramped at a rate of 16 degrees C per hour to 540 degrees C, held at such temperature for 4 hours and was air cooled to room temperature.

Magnetic properties were: Hc = 480 Oe., BR = 8700 G, BHeff = 1.7 x 106 Gauss-Oersteds.

Example3: Ingot of alloy of Example 1 was reheated to 1200 degrees C and was hot rolled directly to 100 mils thickness at which time the temperature was about 900 degrees C.

The rolled body was water quenched in tap water. Samples were reheated to 620 degrees C and immediately ramped at a rate of 11 degrees C per hour to 505 degrees C, held at such temperature for 6 hours and then permitted to air cool to room temperature. Magnetic properties were: Hc = 510 Oe, BR = 6800 G. BHeff = 1.35 x 106 Gauss-Oersteds.

Example 4: The alloy of Example 1 was processed in the manner of Example 1 to 100 mils, was iced brine-quenched, and was stamped to yield cupped rings prescribed for U-type telephone receivers. The stamped body was aged at 620 degrees C for 10 minutes and was then cooled to 520 degrees C at a rate of 25 degrees C per hour. After aging at this temperature for one hour, the temperature was lowered to 510 degrees C and held for four additional hours and then permitted to air cool to room temperature. The cupped ring was fabricated into a telephone receiver and the standard flux test read 6900 maxwells.

Example 5: The alloys of Example 2 were processed in the manner of Example 2 to 100 mils and in the iced brine-quenched condition were stamped to yield cupped rings prescribed for U-tvpe telephone receivers. The stamped body was aged at 625 degrees C for 10 minutes and the temperature was then lowered at a rate of 25 degrees C per hour to 525 degrees C. After aging at this temperature for one hour, the cupped ring was allowed to air cool to room temperature. The cupped ring was fabricated into a telephone receiver and the standard flux test read 7300 maxwells.

Example 6: The procedure of Example 1 was followed, however, to produce the following composition: 15 parts Co, 27 parts Cr, 58 parts iron, 1 percent Nb, 3 percent Mo, and 0.5 percent Mn. Silicon content was the same as in Example 1. A solution temperature of 1100 degrees C was found appropriate. Magnetic aging followed the schedule: 615 degrees C for 50 minutes, followed by a ramp at 16 degrees C per hour to 540 degrees C, held at said temperature for 7 hours and air cooled to room temperature. Magnetic properties were Hc = 500 Oersteds BR = 8400 Gauss, BHeff = 1.75 x 106 Gauss-Oersteds.

WHAT WE CLAIM IS: 1. A cold formable magnetic alloy having a ternary chromium, cobalt, iron system wherein the alloy comprises 25-30 parts by weight chromium, 10-20 parts by weight cobalt and remainder iron with or without impurities to result in 100 parts by weight of these elements, and wherein the alloy further comprises at least 0.1 percent by weight based on the said 100 parts of at least one additional element selected from zirconium, molybdenum, aluminium, niobium. titanium, vanadium and manganese, the maximum weight percentage of each of elements zirconium, niobium. manganese and titanium being 1, of aluminium

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (30)

**WARNING** start of CLMS field may overlap end of DESC **. 8. Examples Example numbers 1 to 6 illustrate the use of a variety of compositions in accordance with the invention. In each instance, the specimen is capable of being formed into cupped rings suitable for use in a telephone receiver as depicted in Figure 2. Examples 4 and 5 actually include this forming step. Example 1: The alloy produced is of the composition 15 parts cobalt, 26-1/2 parts chromium, 58-1/2 parts iron--all by weight--together with 0.25% zirconium, 1.0% aluminum, and 0.5% manganese--all weight percent based on 100 parts of ternary. Amounts of initial materials all introduced as the elements totaled 200 pounds. The ingot was produced by vacuum induction melting. Analysis revealed a content of approximately 0.25% silicon as an unintentional inclusion. Other impurities totaled an amount less than 1.0 percent. After stripping the mold and permitting the ingot to reach room temperature in air, it was reheated to 1200 degrees C and was hot rolled in about 20 passes to result in a thickness of 200 mils. During rolling, the temperature fell to approximately 1100 degrees C. The rolled body was water quenched in tap water. Cold rolling on a reversing mill with about four passes resulted in a thickness reduction of about 100 mils. Material was then reheated in air to a solution temperature of 900 degrees C for 30 minutes and then iced brine-quenched. The quenched body was aged in air at a temperature of 620 degrees C and was maintained at such temperature for 30 minutes and was then ramped at a rate of 25 degrees C per hour to a final temperature of 525 degrees C, was held at such temperature for 4 hours and was then permitted to air cool to room temperature. Magnetic properties were: Hc = 450 Oe., BR = 8300 Gauss, BHCff = 1.6 x 106 Gauss-Oersteds. Example 2: The procedure of Example 1 was followed, however, to produce the following composition: 15 parts cobalt, 26-1/2 parts chromium 58-1/2 parts iron, 1 percent niobium, 0.25 percent titanium, 0.25 percent zirconium, and 0.5 percent manganese. Silicon content and other impurities were the same as in Example 1. Solution temperature was 1050 degrees C in lieu of 900 degrees C. Magnetic aging followed the following schedule: 625 degrees C for 20 minutes, ramped at a rate of 16 degrees C per hour to 540 degrees C, held at such temperature for 4 hours and was air cooled to room temperature. Magnetic properties were: Hc = 480 Oe., BR = 8700 G, BHeff = 1.7 x 106 Gauss-Oersteds. Example3: Ingot of alloy of Example 1 was reheated to 1200 degrees C and was hot rolled directly to 100 mils thickness at which time the temperature was about 900 degrees C. The rolled body was water quenched in tap water. Samples were reheated to 620 degrees C and immediately ramped at a rate of 11 degrees C per hour to 505 degrees C, held at such temperature for 6 hours and then permitted to air cool to room temperature. Magnetic properties were: Hc = 510 Oe, BR = 6800 G. BHeff = 1.35 x 106 Gauss-Oersteds. Example 4: The alloy of Example 1 was processed in the manner of Example 1 to 100 mils, was iced brine-quenched, and was stamped to yield cupped rings prescribed for U-type telephone receivers. The stamped body was aged at 620 degrees C for 10 minutes and was then cooled to 520 degrees C at a rate of 25 degrees C per hour. After aging at this temperature for one hour, the temperature was lowered to 510 degrees C and held for four additional hours and then permitted to air cool to room temperature. The cupped ring was fabricated into a telephone receiver and the standard flux test read 6900 maxwells. Example 5: The alloys of Example 2 were processed in the manner of Example 2 to 100 mils and in the iced brine-quenched condition were stamped to yield cupped rings prescribed for U-tvpe telephone receivers. The stamped body was aged at 625 degrees C for 10 minutes and the temperature was then lowered at a rate of 25 degrees C per hour to 525 degrees C. After aging at this temperature for one hour, the cupped ring was allowed to air cool to room temperature. The cupped ring was fabricated into a telephone receiver and the standard flux test read 7300 maxwells. Example 6: The procedure of Example 1 was followed, however, to produce the following composition: 15 parts Co, 27 parts Cr, 58 parts iron, 1 percent Nb, 3 percent Mo, and 0.5 percent Mn. Silicon content was the same as in Example 1. A solution temperature of 1100 degrees C was found appropriate. Magnetic aging followed the schedule: 615 degrees C for 50 minutes, followed by a ramp at 16 degrees C per hour to 540 degrees C, held at said temperature for 7 hours and air cooled to room temperature. Magnetic properties were Hc = 500 Oersteds BR = 8400 Gauss, BHeff = 1.75 x 106 Gauss-Oersteds. WHAT WE CLAIM IS:

1. A cold formable magnetic alloy having a ternary chromium, cobalt, iron system wherein the alloy comprises 25-30 parts by weight chromium, 10-20 parts by weight cobalt and remainder iron with or without impurities to result in 100 parts by weight of these elements, and wherein the alloy further comprises at least 0.1 percent by weight based on the said 100 parts of at least one additional element selected from zirconium, molybdenum, aluminium, niobium. titanium, vanadium and manganese, the maximum weight percentage of each of elements zirconium, niobium. manganese and titanium being 1, of aluminium

being 1.5, and of each of molybdenum and vanadium being 3.

2. An alloy as claimed in claim 1, wherein the alloy comprises at least 0.1 weight percent zirconium and at least 0.1 weight percent of at least one of aluminium, niobium, and titanium,

3. An alloy as claimed in claim 2, wherein the alloy comprises 0.2 weight percent zirconium and 0.2 weight percent of at least one of the elements aluminium, niobium and titanium.

4. An alloy as claimed in claim 1, 2 or 3, wherein silicon is present as an impurity in an amount up to 0.25 weight percent, other impurities when present being up to a maximum total content of 1 weight percent.

5. An alloy as claimed in claim 1 or claim 2, wherein the titanium is present in an amount up to 0.5 weight percent.

6. An alloy as claimed in any one of claims 1-5, wherein the chromium is present in an amount of 26-28 parts by weight, and the cobalt is present in an amount of from 15-20 parts by weight.

7. A method of producing a magnetic element comprising mechanically working stock material of a composition comprising a ternary chromium, cobalt, iron system comprising 25-30 parts by weight chromium, 10-20 parts by weight cobalt and remainder iron with or without impurities to result in 100 parts by weight of these elements, the stock material further comprising at least 0.1 weight percent based on the said 100 parts of at least one element selected from zirconium, molybdenum, vanadium, niobium, titanium, manganese and aluminium, the maximum weight percentage of each of elements manganese, zirconium, niobium and titanium being 1, of aluminium being 1.5 and of each of molybdenum and vanadium being 3, the method comprising the step of cold forming to result in deformation of the stock material which includes bending to produce a change in direction of at least 25 degrees with such bending having a radius of curvature of a magnitude which is linearly proportional to the extent of change in direction with such magnitude corresponding with a 25 degree change in direction being no greater than the thickness of the stock material and the radius corresponding with a 90 degree change in direction being no greater than four times the thickness of the said stock material.

8. A method as claimed in claim 7, wherein the magnitude is equal to the thickness of the stock material.

9. A method as claimed in any one of claims 7 or 8, wherein the working involves cupping the stock to produce a bend having a continuous curve.

10. A method as claimed in any one of claims 7 to 9, wherein the working is followed by magnetic aging including heating to increase magnetic coercivity.

11. A method as claimed in claim 10 wherein the heating includes maintaining at an elevated temperature of at least 6000C for a period of at least 10 minutes.

12. A method as claimed in claim 10, wherein the heating includes maintaining at an elevated temperature of from 600-640"C for 10 minutes to 2 hours.

13. A method as claimed in claim 11 or 12, wherein the magnetic aging includes cooling at a maximum rate of 50"C per hour down to a temperature of no greater than 500"C.

14. A method as claimed in claim 7, wherein a first working step is conducted at an initial temperature above 1200 degrees C.

15. A method as claimed in claim 14, wherein the first working step is succeeded by a first quenching at a rate of at least 100 degrees C per second to a temperature at least as low as 400 degrees C.

16. A method as claimed in claim 15, wherein the first quenching is followed by cold working to result in a reduction in a dimension of at least 30 percent.

17. A method as claimed in claim 16, wherein the cold working is succeeded by a solution heat treatment producing substantially single phase material.

18. A method as claimed in claim 17, wherein the solution heat treatment is a complete recrystallization treatment.

19. A method as claimed in claim 18, wherein the said solution heat treatment continues for from 30 minutes to 90 minutes.

20. A method as claimed in claim 16, wherein the working is preceded by second quenching to substantially retain the crystallographic conditions prior to the second quenching.

21. A method as claimed in claim 20, wherein the said second quenching is preceding by solution heat treatment so that the crystallographic conditions prior to quenching correspond with a substantially pure alpha phase.

22. A method as claimed in any one of claims 7-21, wherein the said composition includes zirconium in amount of at least 0.1 weight percent based on the said 100 parts by weight.

23. A method as claimed in claim 21, wherein the composition contains at least 0.1 weight percent aluminium based on the said 100 parts by weight.

24. A method as claimed in claim 22, wherein the composition contains at least 0.1 percent niobium and at least 0.1 percent titanium based on the said 100 parts by weight.

25. A method as claimed in claim 7, wherein the composition contains at least 0.2 weight percent of at least one of the said elements.

26. A method as claimed in claim 7, or any one of claims 22-25, wherein the method comprises melting the said composition in a nitrogen-containing atmosphere.

27. A method as claimed in claim 26, wherein the said atmosphere is air.

28. A method of producing a magnetic element substantially as hereinbefore described with reference to any one of examples 1-6.

29. A cold formable magnetic alloy substantially as hereinbefore described with reference to any one of examples 1-6.

30. A transducer containing a magnetic alloy produced according to the method of any one of claims 7-28.