NL7905311A - FE-CR-CO PERMANENT MAGNETIC ALLOY AND THE METHOD FOR OBTAINING THE ALLOY. - Google Patents

Description

1 Λ VO 7864 **

Western Electric Company, incorporated New York, United States of America.

Fe-Cr-Co permanent magnetic alloy and the method of obtaining the alloy.

The invention relates to Fe-Cr-Co magnetic materials.

Magnetic materials suitable for the use of relays, bells and electro-acoustic transducers such as loudspeakers and telephones have a high value of magnetic coercive force, remanence and energy product.

Among existing alloys with suitable magnetic properties are Al-Ni-Co-Fe and Cu-Ni-Fe alloys, which are drawers of a group of alloys believed to be a spinodal microstructure.

10 Recently, alloys containing Fe, Cr and Co have been investigated for their potential for the manufacture of permanent magnets. In particular, certain temperature Fe-Cr-Co alloys are described in the publication of H. Kaneko et al, "New Ductile Permanent Magnet of Fe-Cr-Co systems", AIP Conference Proceedings No. 5, 1972, p.

15 1088 and U.S. Patent 3,806,336. Quaternary alloys containing ferrite-forming elements, such as, for example, Ti, Al, Si, Nb, or Ta in addition to Fe, Cr, and Co, are described in U.S. Patents 3,954,519, 3,989,556, 3,982,972, and 4,075,437.

The use of ferrite-forming elements, such as e.g.

Ti, Al, Si, Nb or Ta in quaternary alloys have been advocated, in particular at higher Co levels * or in the presence of impurities such as, for example, C, N or O, to produce a previously fine-grained alpha phase structure by simplify low temperature heating.

The invention is an essentially temar Fe-Cr-Co magnetic alloy, the grain size of which is sufficiently small to result in at least three thousand grains per mm 2 and which has a coercive force in the range of 30Q-6QQ Oersted, a remanence in the range of 3000-13000 Gauss and a maximum magnetic energy product in the range of 1-6 MGOe.

7905311 * 2 "Γ *". The alloy consists in fibers of 25-29% Cr, 7-12% Co and the remainder Fe and can be produced in suitable form by, for example, a process involving solution liquor and solution at a temperature in the range of 650-1000 ° C to produce a fine grained, single phase alpha structure 5, followed by cold forming and aging. For example, magnets made from such alloys can be used in electro-acoustic transducers, such as loudspeakers and telephone receiver, in relays and in bells.

The invention will be described in more detail below with reference to the drawing, in which: Fig. 1 shows phase diagrams of Fe-Cr-Co alloy systems containing resp. 9 $ Co and 11 $ Co; Figure 2 is a micrograph showing 100 times the grain structure of a Fe-Cr-Co magnetization alloy containing 28% 15 Cr and 11% Co and dissolution annealed at 900 ° C; and Figure 3 shows a micrograph, magnifying 100 times, the grain structure of a Fe-Cr-Co magnetic alloy containing 28% Cr and 11% Co and dissolution annealed at 1300 ° C.

In accordance with the invention, it has been fabricated that Fe-Cr-Co 20 alloys containing Cr can be produced in a preferred range of 25-29 wt%, Co in a preferred range of 7-12 wt% and the remainder in Fe fibers, such as that at the same time they have a maximum energy product in the range of 1-6 MGOe and a grain size corresponding to at least 3000 grains per mm, whereby such a grain structure is particularly advantageous when the alloy has to be cold-formed. A narrower range for the Cr content may be preferred, and in the interest of optimizing the alloy's formability, an upper limit of 28% by weight and, in the interest of optimizing the magnetic properties, a lower limit of 26% by weight. . $ 30 Cr preferred.

Alloys of the invention can be prepared, for example, by melt casting the Fe, Cr, Co elements forming their components and their alloys in a melting pot or furnace such as an induction furnace. On the other hand, a metal body having a composition within the specified range may be prepared by 790 53 1 1 i 3 powder metallurgy. The preparation of an alloy and, in particular, the preparation by casting from a melt requires some care to protect against the inclusion of excessive amounts of impurities, which may arise from raw materials, from the furnace or from the atmosphere above the melt. If this is taken care of, and if particular care is taken to minimize the presence of impurities such as nitrogen, for example, the addition of ferrite-forming elements can be omitted. To minimize oxidation or excessive nitrogen entrapment, it is desirable to prepare a melt with slag protection, in a vacuum or in an inert atmosphere, such as, for example, an argon atmosphere. The levels of specific impurities are preferably kept below 0.05 wt. # C, 0.05 wt. # IT, 0.2 wt.% Si, 0.5 wt. # Mg, 0.1 wt. # Ti, 0.5 wt. # Ca, 0.1 wt. # Al, 0.5 wt. # Mn, 0.05 wt. # ST and 0.5 wt. # 0.

In particular, the treatment of the alloy after casting is as follows. The alloy is soaked at a temperature, the alloy being in a two-phase, alpha plus gamma state for a period of 1 - 1 hour, with temperatures in the range of 1100 - 1300 ° C generally being suitable for this purpose. More specific preferred limits for such a temperature corresponding to alloys containing cw% Co and 11 wt% Co, respectively, can be obtained from Figure 1. The alloy is then hot-worked in such a two-phase state, eg, by hot rolling, forging or extrusion to break up the mold as cast and, if desired, the alloy can be cold-formed. To develop a uniform fine grain structure, the alloy is then solution-annealed at a temperature at which the alloy is in a substantially one-phase alpha state and generally located in the range of 650-1000 ° C C. Preferred upper limits for the heating temperature for specific alloys can be conveniently obtained by an approximate linear interpolation between the following values: 9502C for one alloy containing 25 wt. # Cr and 7 wt. # Co. 375 for an alloy containing 25 wt. . # Cr and 12 wt. # Co, 11QGcC for an alloy containing 29 wt. # Cr and 7 wt. # Co and 975 ° C for 7905311 '<rks'.

an alloy containing 29% by weight of Cr and 12% by weight of Co and further, in the interest of minimizing grain growth, should not exceed 100 ° C. For the sake of improved kinetics, lower limits of 800 ° C are preferred, and terville of minimizing the gamma-5 phase, preferred upper limits are obtained by approximate linear interpolation between the respective "values of 925 ° C, 850 ° C, 1075 ° C and 950 ° C and also on the further condition that the heating temperature does not exceed 1000 ° C.

When the alloy is cold worked, solution annealing to substantially recrystallize and homogenize the alloy can take from 10 minutes to 2 hours depending on the heating temperature and the size of the rod. More specifically, the time required is in the range of 30-90 minutes. Solution annealing can be carried out in air or, with a view to minimizing surface classification, with the exclusion of oxygen.

The solution annealing is terminated by rapid quenching by, e.g., water or quenching in saline, or in the case of thin strips by quenching in air, so that preferably a cooling rate of 1000 ° C / minute occurs throughout the alloy. At this point, the alloy is at or near room temperature, i.e., a temperature which does not exceed 100 ° C and has an essentially uniform fine grain size, which does not exceed 70 microns.

O

(corresponding to at least 3000 grains per nmr). Such a grain structure is shown in Figure 2 and can be compared to the coarse structure obtained by heating at a high temperature, as shown in Figure 3.

At a temperature not exceeding 100 ° C, the alloy can then be cold formed by, for example, bending, wire drawing, deep drawing or forging. The fine-grained structure offers particular advantages if the alloy is to be cold-formed by wire drawing, deep drawing or bending, i.e. by a technique that causes at least a local tensile deformation. Due to the uniformly fine grain structure of the alloy, which has been heated and quenched, drawing can take place to a degree corresponding to a substantial cross-sectional reduction of at least 50%. Likewise, 7905311 5 * * * bending can result in a change of direction of at least 30 °, the resulting radius of curvature being such that it does not exceed a value proportional to the change of direction which is equal for a change of direction of 30 ° is the thickness of the bent portion, and for a direction change of 90 ° is equal to h times the thickness of the bent portion.

The above-described treatment typically includes a step of keeping the alloy at a temperature corresponding to an essentially single phase alpha state. The other treatment so characterized can be effected, for example, by hot processing with a final temperature in an essentially single phase alpha region, cooling and molding. In addition, the molding can be performed in steps with intermediate additional solution annealing and quenching. Additional treatment steps, such as machining by drilling, turning or framing before or after shaping, are not excluded.

The alloy formed is eventually subjected to an aging bond to develop a magnetic cure. Such aging treatment can follow any of a number of schemes, such as described, for example, in U.S. Patent No. U.075-3720 which allow the production of magnets with a magnetic retention of 8000-13000 Gauss, a magnetic coercive force of 300 -600 Oersted and a magnetic energy product of 1-6 mega Gauss-Oersted. Consequently, such alloys after magnetization in a magnetic field can serve as magnets in relays, bells and electro-acoustic transducers, such as loudspeakers and telephone receivers.

In the following examples, the phase structure and grain size were determined by X-ray diffraction analysis, hardness measurements and metallographic analysis of the microstructure after solution annealing and quenching, but before cold forming. The average grain size 30 was in the range 25 micron, as shown in Table I. In ta.

bubble I are also shown the magnetic remanence B, coercive force H, and energy product (BH), which were determined after the aging of the alloys.

Example I

An alloy bar containing 26.3 wt% Cr, 9 wt% 7905311 W '6 *.

Co and the res.t poured into fibers Fe from a melt. The bar dimensions sail: a thickness of 31.8 mm, a width of 127 mm and a length of 30h, 3 mm. The cast rod is heated to a temperature of 1250 ° C, hotest to a 6, mm mm plate and cooled with more water. Portions of the sheet were cold rolled at room temperature to 2.5 mm thick and 15.9 mm wide strips. The strips were heated at 900 ° C for 30 minutes and cooled with more water. The strips then heated again to 630 ° C, held at this temperature for 1 hour, cooled at a fiber constant rate of 15 C / hour to a temperature of 555 ° C, at 5 ° C for 3 hours. C and kept at 525 ° C for hours.

Example II

Strips of an alloy containing 27.7% Cr, 10.9% Co and the Fe test Fe were prepared by casting, hot pouring, quenching, solution annealing, cooling and rolling, as described in Example I. The strips were then reheated to Ö35 ° C, held at this temperature for 3 minutes, cooled at constant rate from 15 ° C / hour in vesicles, held at 5 ° C ° C for 3 hours and left at Kept at 525 ° C.

Example III

Strips of an alloy, containing 27.3% by weight,% Cr, 7.2 gav.% Co and the remainder in fiber Fe., Were prepared as described in Example 1. The strips were further heated to o20 ° C, at kept at this temperature for 1 hour, cooled at a constant rate in veins from 15 ° C / hour to 555 ° C, and held at 555 ° C for 2 hours, during. 3 hours at 5 ° C and for 16 hours at 525 ° C.

Example IV

Strips of an alloy containing 26.8% $ Cr, 10.6% by weight Co and the remainder in fiber iron were prepared as described in Example I. The strips sail softly and bendable and could easily , bent at 90 ° in any direction over a super-sharp edge with a radius of curvature of 0.08 mm or drawn, resulting in a surface reduction of 99% · The strips were aged by the alloy for 30 minutes at a temperature of 680 ° C te. Eouden, cool quickly with a first rate of 1 ^ 0 ° C / hour to 615 ° C and then 7905311 7 s. * • m cool with exponentially decreasing rates of 2Q-2 ° C / hour to a temperature of 525 ° C.

Example 7

Bars with a diameter of 17.8 mm of an alloy, containing 27.9% w / v Cr, 10.7% by weight of Co and the remainder Fe were prepared by casting, hot working, solution annealing and quenching. The bars were cold drawn to 1.78 mm diameter wire (with a cross-sectional area 99% reduced), solution annealed at 930 ° C for 30 minutes and cooled to room temperature. Aging heat treatment was carried out by holding the drawn wire at 700 ° C for 30 minutes, cooling to 615 ° C at a rate of 30 ° C / hour in a 1000 Oersted magnetic field and cooling to a temperature of 1 + 80 ° C with exponentially decreasing speeds of 20-2 ° C / hour.

15 TABLE I

granular 3r Hc (BH)

Cr Co size max

Example% wt.% .Mu.m 0 0th MGOe. .

I 26.8 9 Λ 30 10010 380 1.55 20 II 27.7 10.9 25 9 750 1 + 00 1.72 III 27.3 7.2 U0 9 280 300 1.10 17 26.8 10.6 L + o 10010 370 1.76 7 27.9 10.7 30 12750 570 5.03 7905311

Claims (6)

1. Object, Containing a Fe-Cr- * Co magae .- * · tic alloy body, with the Bet Characteristic, that the alloy Consists of Tilt 25-2% T Preferably 26-28 wt% Cr, 7- 12% by weight of Co and the remainder, with the exception of 5, a small amount of unintentional impurities, essentially Fe o 'and with at least 3000 grains, with mm', a 'coercive leakage rate In the region of 300-600 Oersted, a remanence in the Bet area of 8000 .- ^ 30.00. Gauss and a magnetic energy product in the Bet region of 1-6 MGOe., Article according to claim 1, characterized in that at least the following of the unintentional impurities are limited to at least 0.05 wt% C, 0.05 wt% N, 0.2 wt% Si, 0.5 wt.% Mg, 0.1 wt.% Ti, 0.5 wt.% Ca, 0.1 wt.% Al, 0.5 wt.% Mn, 0.05 wt.% S 0.05 wt% 0. A method of producing the article according to: claim 1 or 2, comprising treating a Fe ~ Cr-Co alloy body with steps comprising cold forming and aging, characterized by subjecting an alloy consisting of 25—29 wt.% Cr, 7-12 wt.% Co and the rest, except for the small amount of unintentional impurities Fe, to the following Treatment: 20 (1) exposing the body to a heating temperature selected to obtain an average grain size in an alloy? gene which does not exceed 70 micrometers, which heating temperature does not exceed 1000 ° C and which is located in the region of (a) 650-950 ° C when the alloy is 25 wt% Cr contains and 7 wt% Co, 25 (b) 650-875 ° C when the alloy contains 25 wt% Cr and 12 wt% Co, (c) 650-1100 ° C when the alloy 29 wt% Cr and Contains 7 wt% Co, (d) 650-795 ° C when the alloy Contains 29 wt% Cr and 12 wt% Co, and (e) in a range whose limits are obtained by approximate linear interpolation at intermediate levels * s of Cr-en Co, 30 (2) The shaping of the body into a desired shape at a temperature not exceeding 100 ° C, either by wire drawing or deep drawing to an extent corresponding to a reduction of the cross-sectional area of at least 50% or by deep drawing or bending, resulting in a change of direction of at least 30 °, the resulting radius of curvature being such that it does not exceed a value 7905 311 ¢. * ". which is proportional to the change of direction, and which for a change of direction of 30 ° is equal to the thickness of Set tolerated part and" for a change of direction of 90 ° is equal to: four times the thickness. of the bent part, and 5 (3) aging of the alloy Method according to claim 3, just Set characterized in that the heating temperature is preferably in the range of 80.0-2.25 ° C, 80.0-850 ° C, 800-1075 ° C and 800-950 ° C, for the alloy compositions according to (a), (b), (c) and (d). A method according to claim 3 or k, characterized by performing step (1) in at least one of the following ways: (a) solution annealing or (b) hot working ending at the heating temperature. 6. Method according to claim 3, or characterized by additional treatment of the. Before step (1). alloy in at least one of the following ways: (a) soaking the alloy at a temperature in Set range of 1100-1300 ° C; or (b) after soaking the additional hot working of the alloy at a temperature in the range of 110 ° -1300 ° C; or (c) after hot working the extra cold working of the body. A method according to claim 3, k, 5 or characterized by forming phasing of the additional intermediate solution solution and quenching. 25 δ. Method according to any one of claims 3-7S, characterized by carrying out the treatment by cooling a) at an essentially constant speed or (b). cool down with a first fast average speed, followed by cool down with a second slower average speed. Method according to any one of the preceding claims, characterized by performing the aging in the presence of a magnetic field. jQ. rterrwi, according to any one of the preceding claims, characterized by additional machining of the body already after step (1} _ and before star (2) 3p sn / cf (b} _ after step (2). and before step (3) .. 7905311