NL8100435A - MAGNETIC ELEMENT FOR MAGNETICALLY OPERATED DEVICES, METHOD FOR THE MANUFACTURE THEREOF - Google Patents

Description

· "C VO 1371

Magnetic element for magnetically actuated devices, method for the manufacture thereof. :

The invention relates to magnetic elements for magnetically actuated devices and methods for their manufacture.

Magnetically actuated devices can be designed for 5 different purposes, e.g. electric switch, position reading, synchronization, flow measurement, and stirring.

Among such devices of particular interest are so-called circuitry such as e.g. described in LRMoskowitz's book, Permanent Magnet Design and Application Handbook, 10 Cahners Books, 1976, biz.211 - 220, in U.S. Patent 3,624,568, and in MRPinnel's article, "Magnetic Materials for Dry Reed Contacts" , IEE Trans. Mag., Vol. MAG-12, No.6, 1976, pp. 789-794. Tongue circuitry includes flexible metallic tongues made of the material having semi-hard magnetic properties, characterized by an essentially rectangular BH hysteresis loop and a high remanent induction 8 ^ ,; during operation, tongues bend elastically, making or breaking electrical contact in response to changes in the magnetic field.

Established alloys with semi-hard magnetic properties include Co-Fe-V alloys known as Vicalloy and Remen-dur, Co-Fe-Nb alloys known as Nibcolloy, and Co-Fe-Ni-Al-Ti alloys known as Vacozet. These alloys have adequate magnetic properties; however, they contain significant amounts of cobalt whose rising costs on world markets are a concern. In addition, high cobalt alloys tend to be brittle, i.e. lack sufficient cold formability to be formed, e.g. by cold drawing, rolling, bending or flattening.

8100435 * * - 2 -

Relevant to the invention are the following literature references: M. Hansen's book, Constitution of Binary Alloys, 2nd ed., McGraw-Hill, 1956, pp. 664-667; the bleach of R.M.Bozorth, Ferromagnetism, Van Nostrand, 1951, pp. 234 - 236 and pp. 418 - 419, 5 the article by M.J. Roberts, "Effect of Transformation Substructure on the Strength and Toughness of Fe-Mn Alloys", Met. Trans., Vol. 1, 1970, biz. 3267 - 3294, the article by F. M. Walters, Jr., "Transformations and Heterogeneity in the Binary Alloys of Iron and Manganese", Trans. American Soc. for Steel Treating, Vol. 21, 10 No. 10, 1933, biz.1002-1015, and the article by GMFedash, "Study of Coercivity of Cold-Worked and Annealed Iron Alloys", The Physics of Metals and Metallography, Vol. 4, No. 2 , 1957, pp. 50-55.

These literature locations involve phase transitions, mechanical properties and the co-reactivity of iron-rich Fe-Mn alloys. Semi-15 hard magnetic properties of Fe-Mn ternary and quaternary alloys are described by W. Jellinghaus, "Kaltverformter Manganstahl als neuer Magnetwerkstoff", Archiv fur dat Eisenhutten-Wesen, Vol. 15, No. 2, 1941, p. 99 - 102, by H. Kaneko et al., "Cold Worked Fe-Mn Semihard Magnet Alloy", Journal of the Japanese 20 Institute of Metals, Vol. 34, No. 4, 1970, pp. 441 - 445, and by K. Ogawa, "Semihard Magnetic Material of the Fe-Cu-Mn System", J. App. Phys., Vol. 44, No. 4, April 1973, pp. 1810-1812.

According to the invention, semi-hard magnetic properties are realized, in Fe-Mn alloys, preferably containing Fe and 25 Mn in a combined amount of at least 98% by weight and Mn in an amount of 3-25% by weight of this combined amount. . The retentive magnetic induction Br of alloys of the invention is typically greater than or equal to a value of B (Gauss) = 20,000-500 x (wt% Mn) (B (Tesla) = ^ -4 ** 30 (20,000 - 500 x (wt% Mn) x 10) and their squareness ratio Br / Bs is greater than 0.7 and typically greater than or equal to 0.95.

Alloys of the invention typically exhibit an anisatropic biphasic or multiphase microstructure, with particles 35 and granules being elongated with a length to width ratio of at least en t - 3 - preferably at least S and most preferably at least 30. The particle diameter or thickness is preferably less than 800 nm and preferably less than 200 nm.

Magnets made from such alloys can be formed by, e.g. cold drawing, rolling, bending or flattening and can be used in devices such as electric contact switches, hysteresis motors and other magnetically actuated devices.

The preparation of alloys according to the invention can take place by treatment of initial deformation, aging, deformation and final aging. The aging steps are preferably conducted at temperatures where an alloy is in a two-phase or multiphase state. The second deformation stage is preferably a uniaxial deformation stage.

Fig. 1 shows phases as a function of the temperature and manganese contents of Fe-Mn alloys;

Fig. 2 shows magnetic properties of a Fe-ΘΜη alloy as a function of a first aging temperature;

Fig. 3 shows magnetic properties of a Fe-8Mn blank-20 ring as a function of cross-sectional area reduction by wire drawing;

Fig. 4 shows magnetic properties of an Fe-12Mn alloy as a function of cross-sectional area reduction by wire drawing; Fig. 5 shows a reed switch construction comprising Fe-Mn reeds.

According to the invention it has been realized that Fe-Mn alloys, preferably comprising Fe and Mn in a combined amount of at least 38 wt.% And Mn in an amount of 3-25 wt.% Of this combined amount, can be obtained with desired semi-hard magnetic properties. Such semi-hard magnetic properties are suitably defined by a remanent magnetic induction Br of more than 7,000 gauss (0.7 T] and a rectangular ratio Sr / Bs of more than 0.7. Alloys with such properties are suitable for use in 8100435 * * - 4 - magnetically actuated devices suitably characterized by containing a component the position of which depends on the strength, direction, or presence of a magnetic field and further by comprising means such as an electrical contact to read the position of such a component Alloys of the invention may contain small amounts of additives such as Cr to obtain better corrosion resistance, or Co to obtain better magnetic properties, however excessive amounts of Cr 10 may harmful to the magnetic properties.

Other elements such as Ni, Si, Al, Cu, Mo, V, Ti, Nb, Zr, Ta, Hf and W may be present as impurities in individual amounts, preferably less than 0.2% by weight, and in a combined amount preferably less than 1% by weight. Also, elements such as C, N, S, P, B, H, and 0 are preferably kept below 0.1 wt% individually and below 0.5 wt% in combination.

Keeping impurities to a minimum is in the interest of maintaining the malleability of the alloy to develop an anisotropic structure and molding to the desired shape. Too large amounts of the mentioned elements can also lead to poorer magnetic properties.

Magnetic alloys according to the invention have an anisotropic multiphase grain and microstructure in which the particles and grains have a length to width ratio of preferably at least 8 and most preferably at least 30. The length-width ratio can be suitably defined as the length-diameter ratio when the deformation is uni-axial, e.g., by wire drawing, and as the length-thickness ratio, when the deformation is planar, e.g. by rolling. The particle size is preferably less than 800 nm and most preferably less than 200 nm. The submicron structure can conveniently be determined by e.g. electron microscopy.

The remanent magnetic induction B ^ of alloys according to the invention is almost linearly dependent on the Mn content of the alloys. In particular, the remanent magnetic induction Br of alloys of the invention is equal to 81 00 43 5 - 5 - * * or greater than a value that can be approximately expressed by the formula B (gauss) = 20,000 - 500 x (wt% Mn] (B (Tesla) = Γ. Γ ^ "20,000-500 x (wt% Mn) _J x 10). The rectangular ratio B / B of alloys of the invention is typically greater X s 5. then or equal to 0.95 and the magnetic coercivity is in the range 1 - 500 Oersted (79.6 - 397Θ9 A / m].

Alloys according to the invention can e.g. are prepared by pouring from a melt of the constituent elements Fe and Mn into a crucible or oven, e.g. an induction furnace on the other hand, a metallic body having a composition in the specified range can be prepared by powder metallurgical methods.

The preparation of an alloy and in particular the preparation by casting from a melt requires care to guard against the incorporation of excessive amounts of impurities which may be from raw materials, from the furnace or from the atmosphere above the melt. In order to minimize oxidation or excessive nitrogen uptake, it is desirable that a slag protection melt be prepared in a vacuum or in an inert atmosphere.

Castings of an alloy according to the invention can typically be processed by hot working, cold working and solution annealing to pursue homogenization, grain refinement, molding, or the development of desired mechanical properties.

Processing to obtain a desired anisotropic structure, such as elongated grains and crystallographic texture, can be carried out by various combinations of subsequent treatment steps. A particularly efficient processing sequence can be specified for reference by reference to Figure 1 and includes processing at temperatures associated with a two-phase region in the phase diagram by (1) an initial plastic deformation, (2) an initial aging, which leads to an essentially two-phase decomposition, (3) a plastic deformation, and (4) a final aging.

The initial plastic deformation preferably takes place in an amount corresponding to at least 50% reduction of 8100435 * * - - 6 - the surface and can take place at temperatures in the range of -196 ° C (the temperature of liquid nitrogen) to 600 ° C. Such deformation can serve a variety of purposes and in particular can promote the transformation of undesired non-magnetic gamma or epsilon phases into a magnetic alpha-primary phase, especially for alloys with a high Mn content . Also, the initial plastic deformation can improve the kinetics of the initial biphasic alpha plus gamma decomposition and promote the formation of a uniform, fine scale, isotropic biphasic structure. At this point, the particle size can typically be in the range of 300 to 1000 nm. The initial deformation can be uniaxial, e.g. by bar rolling, extrusion, wire drawing, or swaging, on the other hand, deformation can take place by methods such as cross-rolling or cold rolling. When the deformation is performed at a temperature above room temperature, the alloy can then be cooled with air or quenched with water.

The heat treatment after the initial deformation is preferably performed at temperatures associated with an alpha plus 20 gamma two phase state of the alloy. Temperatures in the range of 400-600 ° C are particularly suitable in accordance with Fig. 2.

The duration of such a heat treatment is preferably at least 30 minutes. Subsequent cooling to a temperature near or below room temperature can lead to partial or complete transformation of the gamma phase to the alpha primary phase or epsilon phase.

The isotropic granules and fine shell structure obtained in the two-phase decomposition are then deformed, preferably uniaxially such as by wire drawing, rod drawing, stamping or extruding. Compared to stamping, wire drawing has been found to lead to superior magnetic properties. deformation by eg rolling is not excluded The deformation can be carried out at room temperature or any temperature in a range from -196 to 600 ° C. The amount of deformation preferably corresponds to a surface reduction of at least 80% and most preferably 81 00 43 5 * 7 - 7 - at least 35%, an adequate ductility for such deformation being ensured by the presence of impurities and in particular of elements from groups 4B and 5B of the Periodic System such as Ti, Zr, Hf, V, Nb and Limit Ta After deformation, the saturation magnetization B of the alloy is typically greater than or equal to a value of 8S (gauss) = 20,000 - 500 x Cwt% Mn) CB (Tesla) = / 20,000 - 500 x (wt%

7-4 S

Mn) ^ / x 10 Ί.

The final magnetic properties improve as the amount of deformation is increased; this is illustrated in Figure 3 for a Fe-Mn alloy containing 8 wt% Mn and in Figure 4 for a Fe-Mn alloy containing 12 wt% Mn. The calculated aspect ratio shown in Figures 3 and 4 is defined as the grain length divided by the grain diameter. The alloys of the invention remain very ductile even after strong deformation such as e.g. cold wire drawing to a surface reduction of 35%. Such deformed alloys can be further formed by e.g. bend or flatten without risk of splitting or cracking. Bending can give a direction change from 20 to 30 ° with a bend radius equal to or greater than the thickness.

For bending over larger angles, the safe bending radius can increase linearly to a value four times the thickness for a direction change of 90 °. Flattening can change the width-to-thickness ratio by at least a factor of 2.

High formability in the wire-drawn condition is of particular importance in the manufacture of devices such as reed switches, an example of which is shown in Figure 5. Fig. 5 shows tongues 1 and 2 made of a Fe-Mn alloy extending through a glass envelope 3 contained within magnetic coils 4 and 5. The formability is improved by the presence of impurities and in particular elements of groups 4B and 5B of the Periodic Table such as Ti, Zr,

Keep Hf, V, Nb and Ta to a minimum.

After the plastic deformation of a multiphase structure, a final temperature treatment at low temperature 8100435 »-» - a - within an alpha plus gamma two phase region is performed. Typical aging temperatures are in the range of 350-500 ° C depending on the manganese content, and the aging time is preferably in the range of 10 minutes to 4 hours. The final aging ring improves the B / B rectangular ratio of the B-H loop, which can be attributed to one or more metallurgical effects such as e.g. reducing the internal stress caused by the deformation. The rectangular ratio can also be improved by partial or total reverse martensitic transformation of an Mn rich phase formed during the initial isothermal decomposition in an alpha plus gamma region and then partially or completely transformed into the magnetic alpha primary phase in the course of the final deformation. Furthermore, a better rectangularity ratio may result from the presence of non-magnetic or weakly magnetic gamma or epsilon phases which can act as a desired barrier to demagnetization, or from the formation of a thin layer of non-magnetic or weakly magnetic gamma phase with higher Mn content along the grain boundaries of the elongated biphasic structure. The rate of cooling to room temperature after the discharge or aging heat treatments is not critical; one can cool with air or quench with water.

Among the advantages of Fe-Mn semi-hard alloys of the invention are: (1) a high magnetic rectangular ratio as desired in switchgear and other magnetically actuated devices; (2) the abundant presence and low cost of constituent elements iron and manganese; (3) ease of processing and forming due to high formability; (4) a low magnetostriction such as 30 can be specified by a saturation magnetostriction coefficient of not more than 5 x 10 and preferably not more than * 6 2 x 10 such as e.g. may be desirable to prevent sticking of tongue contacts; (5) the simplicity of the binary composition, making it easy to adhere to magnet tolerances such as e.g. 35 to meet a nominal coercivity; and CS] the ease of coating with contact metal such as gold.

The magnetic properties realized in the following alloys according to the invention are shown in the table. Example I

A Fe-SMn alloy was hot rolled, cold rolled, cold formed into a 0.53 cm diameter rod, annealed at 900 ° C for 1 hour, and air cooled. The sample was cold worked (surface reduction 90%) to a wire with a diameter of 0.17 cm and an initial aging treatment given at 10 500 ° C for 3.5 hours, resulting in a two-phase alpha plus gamma

decomposition and recrystallization was obtained. The decomposed isotropic grain size was uniformly fine and the average grain size was less than 1 µm in diameter. The manster was then drawn [surface reduction 95% 3 to a wire with a diameter of 0.038 cm, given a final aging heat treatment at 450 ° C

for 3 hours, and air cooled. The magnetostriction of this 6 sample was found to be approximately 1.3 x 10.

Example II

• A 0.17 cm diameter wire sample of a Fe-8Mn 20 alloy was prepared and cold worked as in Example I, subjected to an initial aging heat treatment at 550 ° C for 3.5 hours, whereby an alpha plus gamma two phase decomposition wire drawn (surface reduction 95%], a final aging heat treatment given at 400 ° C for 40 minutes, and air cooled.

Example III

A Fe-7.5Mn alloy sample was prepared and processed as in Example I.

Example IV

A Fe-12Mn alloy sample was hot rolled, cold rolled, cold formed into a 0.53 cm diameter rod, annealed at 930 ° C for 1 hour and cooled with water. The sample was further cold-drawn (surface reduction 90%) to a wire with a diameter of 0.17 cm and subjected to an initial aging heat treatment at 550 ° C for 3.5 hours, using a 2 - 8100435 V * - 10 - phases alpha plus gamma decomposition and recrystallization were caused. The isotropically granulated, submicronfine biphasic structure was then drawn (surface reduction 95%] to a wire with a diameter of 0.038 cm, given a final aging heat treatment at 450 ° C for 40 minutes, and cooled with air.

Example V

A Fe-12Mn alloy sample was prepared as in Example IV except that final aging was carried out at 400 ° C for 40 minutes.

Example VI

A Fe-12Mn alloy sample was prepared as in Example IV, except that the initial aging was conducted at 50 ° C for 3.5 hours and the final aging was performed at 450 ° C for 10 minutes. The magnetic energy product of this sample was found to be about 0.96 MGOe C7641.6T (A / m)).

Example VII

A Fe-12Mn alloy sample was prepared as in Example 20 IV, except that the initial aging for 16

hours at 450 ° C and final aging at 450 ° C for 40 minutes. The magnetic energy product of this sample was found to be about 1.05 MGOe (8358T (A / m)). Example VIII

An Fe-12Mn alloy sample was prepared according to Example VII, except that the degree of final wire drawing resulted in a 90% surface reduction.

Table

Magnetic properties of rectangular loop, high 3Q retentivity, Fe-Mn semi-hard magnet alloys

Example 8 - B / B H

rrsc (gauss) (Tesla) (oersted) (A / m) I 17200 1.72 0.94 28 2228.8 II 17300 1.73 0.90 26 2069.6 35 III 18100 1.81 0.96 25 1990 , 0 81 00 43 5 'i * - 11 -

Table C continued IV 15200 1.52 0.997 57 5333.2V 16700 1.67 0.968 63 5014.8 VI 15400 1.54 0.992 87 6925.2 5 VII 15300 1.53 0.989 85 6766.0 VIII 15800 1.58 0.954 60 4776.0

Conversion factors -4 1 gauss = 1 x 10 Tesla 1 oersted = 79.6 A / m

10 1 MGOe - X 106] t x 10'4T) (79.6 A / m) J

8100435

Claims (16)

1. Magnetic element, particularly useful for use in magnetically actuated devices, comprising a metallic alloy body with a magnetic rectangular strength ratio of more than 0.7 and a remanent magnetic induction of more than 7000 gauss (0, 7 T), characterized in that an amount of at least 98% by weight of the alloy consists of Fe and Mn, Mn constituting 3-25% by weight of said amount. 2. Element according to claim 1, characterized in that an amount of at least 99% by weight of the alloy consists of Fe and Mn. Element according to claim 1 or 2, characterized in that the presence in the alloy of one or more elements of a first series Ni, Si, Al, Cu, Mo, V, Ti, Nb, Zr, Ta, Hf and W is limited to less than 0.2% by weight individually and to less than a total of 15% by weight of any combination of five or more of these elements, and the presence of one or more elements from a second range C, N, S, P, B, H and 0 is limited to less than 0.1% by weight individually and to less than a total of 0.5% by weight of any combination of five or more of these elements of the second series. Element according to one or more of claims 1 to 3, characterized in that the alloy has an anisotropic biphasic or multiphase microstructure and an anisotropic granular structure, the aspect ratio of the particles in the microstructure being greater than or equal. is 8, preferably greater than or equal to 25. Element according to one or more of Claims 1 to 4, characterized in that the alloy has a microstructure in which the particle diameter is less than or equal to 800 nm, preferably less than or equal to 200 nm. Element according to one or more of claims 1 to 5, characterized in that the alloy has a magnetostriction coefficient less than or equal to 5 x 10, preferably less than or equal to 8100435 - 13 - 2 x 10 ®. 7. Element according to one or more of claims 1-6, characterized in that the alloy has a remanent magnetic induction B of greater than or equal to a value, which depends on the weight percentage Mn contained in said quantity of change, which value is approximately defined by the formula B Cgauss) = 20,000 - 500 x (wt,% Mn) (B CTesla) a Γ ^ X * £ 20,000 - 500 x Cwt.% Mn) jT x 10 Ί and wherein the alloy has a rectangular ratio greater than or equal to 0.95. Element according to one or more of claims 1 to 7, characterized in that at least a part of the surface of the body is coated with gold. 9. A method of manufacturing a magnetic element, comprising a metallic alloy body having a magnetic rectangular ratio of more than 0.7 and a remanent magnetic induction of more than 7000 gauss CO, 7 Tesla) comprising the following steps: Cl) manufacturing a body consisting essentially of an alloy comprising an amount of at least 98 wt.% Fe and 20 Mn, Mn constituting 3-25 wt.% of this amount , C2) plastically deforming this body in an amount corresponding to a surface reduction greater than or equal to 50%, C3) aging this body at a temperature corresponding to an essentially two phase state of the alloy; C4) plastically deforming this body in an amount corresponding to a surface reduction greater than or equal to 80%, and (5) aging this body at a temperature corresponding to an essentially two-phase state of the alloy. 30 Method according to claim 9, characterized in that step (2) is carried out by plastic deformation at a temperature in the range from -196 to 600 ° C. Method according to claim 9 or 10, characterized in that step (2) is performed by plastic deformation at a temperature above room temperature, followed by cooling of the body. 8100435 - 14 - Method according to one or more of claims 9-11, characterized in that step (3) is carried out by aging at a temperature in a range of 400-600 ° C for at least 30 minutes. Method according to one or more of claims 9 to 12, characterized in that step (4) is carried out by plastic deformation at a temperature in the range of -196 to 600 ° C. Method according to one or more of claims 9-13, characterized in that step (4) is performed by plastic deformation in an amount corresponding to a surface reduction of at least 95%. Method according to one or more of claims 9-14, characterized in that step C5J is carried out by aging at a temperature in a range of 350-500 ° C for at least 15 minutes. Process according to one or more of claims 9 to 15, characterized in that the presence in the alloy of one or more elements from a first group Ni, Si, Al, Cu, Mo, V, Ti, Nb, Zr , Ta, Hf and W is limited to less than 0.2 wt% individual and 20 to less than a total of 1.0 wt% of any combination of five or more of these elements, and the presence of one or more elements from a second group C, N, S, P, B, H and 0 are limited to less than 0.1 wt% individually and to less than a total of 0.5 wt% of any combination of five or more of these elements from the second group. 8 1 0 0 43 5