RU2596563C1 - Method for production of hard-magnetic material - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy and can be used in production of hard-magnetic material based on system of rare-earth metal-iron-cobalt-boron, which is used in making magnets for making navigation devices. Method involves loading iron and cobalt into a melting crucible and their melting in vacuum, introduction of alloying elements into melt, casting melt into mould and cooling casting. Working layer of melting crucible contains at least one oxides of magnesium, yttrium, hafnium, scandium or zirconium, After melting in vacuum boron is added to melt, then in vacuum adding into melt at least one rare-earth metal, selected from: praseodymium, gadolinium, neodymium, cerium, then in atmosphere of inert gas adding into melt at least one rare-earth metal, selected from: dysprosium, samarium.

EFFECT: invention enables to obtain a hard-magnetic material of system rare-earth metal-Fe-Co-B with stable chemical composition, uniform distribution of alloying elements throughout ingot and high purity on impurities of aluminium and oxygen.

7 cl, 2 ex, 4 tbl

Description

The invention relates to the field of metallurgy, in particular to the production of hard magnetic material based on the rare-earth metal-iron-cobalt-boron (REM-Fe-Co-B) system, which can be used for the manufacture of magnets.

To create navigation devices (gyroscopes, accelerometers, etc.), magnets made of hard magnetic materials are used. The possibilities of improving these materials in the main indicator - the temperature coefficient of induction (TCI) have been exhausted. An integrated system of alloying magnetically hard materials allows you to control the value of Br from T over a wider range, unlike the Silicon compound. Obtaining the required composition of the hard magnetic material of the REM-Fe-Co-B system is possible using the technology of smelting the starting material, which would provide the necessary completeness of assimilation in the REM melt at narrow doping intervals for the remaining elements (Co, Fe, B). Obtaining a hard magnetic material of the REM-Fe-Co-B system with a given composition is complicated by the multicomponent alloying system of this material and the significant REM content (over 30% by mass), which are active and have a high chemical affinity for oxygen. The stability of the magnetic properties of materials of the REM-Fe-Co-B system is strongly influenced by the impurity of the alloy obtained, for example, aluminum reduces the magnetization of the main phase and, most importantly, its temperature coefficient of induction, and oxygen reduces the coercive force and residual induction (Burzo E., Plugaru N. Magnetic properties of R2 Fe14-x Cux B compounds with R = Nd or Er // J. of Magn. And Magn. Mater. 1990. V. 86. P. 97-101; Hirosawa S., Hanaki A., Tomizawa H., Hamamura A. Current status of Nd-Fe-B permanent magnet materials // Physica B. 1990. V. 164. P. 117-123; Piskorsky V.P. Thermostable magnetically hard materials based on rare-earth inte metalloids with tetragonal structure. Thesis for the degree of Doctor of Science. 157-158, 2013. c) so to obtain a given magnetic material need technology allowing to reach the minimum content of impurities.

The prior art metallothermic method for producing an alloy based on transition and rare-earth elements (Patent RU 2210607 C1, C22C 28/00; publ. 08/20/2003). The method consists in forming the upper layer of the mixture from the oxide of the transition element and the reducing agent, mainly aluminum, the lower layer from rare earth elements, layer-by-layer loading of the mixture into the reaction volume, isolating the upper layer of the mixture from the lower layer. In this case, the metallothermal reduction and separation of the metal and slag phases is carried out only in the upper layer of the mixture, after phase separation, the insulation between the upper and lower layers is partially violated, and the slag phase is separated before the interaction of the metal phase with rare-earth elements and crystallization of the alloy. As rare earth elements, cerium, lanthanum, neodymium, praseodymium or their alloy are used. The upper layer of the charge may additionally contain a transition element, which is used as iron, nickel, cobalt, and the lower layer is a dopant in the form of calcium, aluminum, silicon, copper, boron. The disadvantage of this method is that since aluminum is used as a reducing agent, it will be present as an impurity in the obtained alloy, which is not allowed for alloys of the REM-Fe-Co-B system. Also, the authors of the patent do not provide the results of a gas analysis of the obtained alloys, but when using this method, there is the possibility of oxygen pollution. In addition, this method does not provide for intensive mixing of the melt, as in induction smelting, which can lead to an uneven distribution of alloying elements in the obtained ingot.

The prior art method for smelting magnetic alloys containing iron, cobalt, nickel, aluminum, copper and others in an induction furnace (Patent SU 1671720 A1, C22C 1/02; publ. 23.06.91). The method consists in melting a filling consisting of a ferroalloy containing Co and Ni, adding the remaining part of Fe, Co, Ni, deoxidizing the melt and introducing low-melting components (Al, Cu, FeS). The disadvantage of this method is that it is not suitable for smelting alloys containing rare earth elements. An alloy containing a significant amount of rare-earth metals melted by this method can have significant deviations from the specified composition, since the interaction of the active components of the rare-earth melt with traditional crucible materials (Al ₂ O ₃ and MgO) will occur. The order and environment for the introduction of rare-earth metals are also not provided, which will lead to uncontrolled evaporation of some rare-earth metals.

The prior art method for smelting magnetic alloys containing iron, cobalt, nickel, aluminum, copper and thallium in an induction furnace (Patent RU 2001140 C1, C22C 1/02; publ. 15.10.93). The method consists in melting the filling, consisting of the waste from previous melts, overheating the melt to a temperature of 1500-1550 ° C and holding to reduce the content of non-metallic inclusions and improve the quality of permanent magnets. The disadvantage of this method is that it is not suitable for smelting alloys containing rare earth elements, since their melts when overheated are characterized by high activity and can interact with traditional crucible materials (Al ₂ O ₃ and MgO), which leads not only to contamination of the alloy with impurities , but can also contribute to damage to the crucible and the penetration of the melt to the turns of the inductor. Some rare-earth metals exhibit increased values of vapor elasticity and, when overheated, intensively evaporate from the surface of the melt, so the content of rare-earth metals in the resulting alloy can be very different from the set value. In addition, this method involves obtaining an alloy from waste and is not suitable for smelting alloys from the starting components.

The closest analogue of the proposed method is a method of smelting hard alloys in an induction furnace (Patent SU 901322 A1, C22C 1/02; publ. 30.01.82). The method consists in melting the filling, consisting of Fe, Co, Ni, Cu, introducing the waste from the previous heats and other components (Nb, C, Al, Ti, and S) after melting the main filling, bringing the melt to a predetermined composition, followed by casting.

The disadvantage of this method is that it is not suitable for smelting alloys containing rare earth elements, because an alloy containing a significant amount of rare-earth metals melted by this method may have significant deviations from a given composition. This is because:

- uncontrolled evaporation of rare-earth metals from the surface of the melt will occur due to non-compliance with the order and environment of introduction of rare-earth metals;

- there will be an interaction of the active components of the melt with traditional crucible materials (Al ₂ O ₃ and MgO), which can lead to destruction of the crucible and penetration of the melt to the turns of the inductor.

Another disadvantage of the known method is that due to the interaction of the melt with the crucible material (Al ₂ O ₃ ), the alloy will be contaminated with impurities that are unacceptable in alloys of the REM-Fe-Co-B system, such as oxygen and aluminum.

The technical result of the claimed method is to obtain a hard magnetic material of the REM-Fe-Co-B system with a stable chemical composition, a uniform distribution of alloying elements throughout the volume of the material and high purity in aluminum and oxygen impurities. This will ensure the stability of the phase composition, increase the amount of the main magnetic phase and, accordingly, improve the properties of magnets made of hard magnetic material obtained by the proposed method.

The technical result is achieved by a method of producing a hard magnetic material based on the rare-earth metal-iron-cobalt-boron system in a vacuum induction furnace, including loading iron and cobalt into a melting crucible and melting them in a vacuum, introducing alloying elements into the melt, casting the melt into a mold (for example, metal (cast iron or steel) or graphite) and casting cooling, characterized in that the working layer of the melting crucible contains at least one of the oxides of magnesium, yttrium, hafnium, scandium or c rconium, introducing into the melt of boron, introducing into the melt in vacuum at least one rare-earth metal selected from the group: praseodymium, gadolinium, neodymium, cerium, introducing at least one rare-earth metal into the melt in an atmosphere of inert gas (e.g. argon), selected from the group: dysprosium, samarium.

The castings are cooled in a closed furnace in an inert atmosphere for at least 6 hours to prevent oxidation of the hot ingot in the atmosphere.

In the process of vacuum melting, oxygen is degassed.

Stable assimilation of rare-earth metals is achieved by observing the order of introducing rare-earth metals into smelting and maintaining various rare-earth metals in a vacuum or argon atmosphere, which is due to different values of the vapor pressure of these elements.

The material of the working layer of the crucible should not have aluminum oxide in its composition, since Aluminum is a harmful impurity in alloys based on the REM-Fe-Co-B system.

Preferably, boron is administered as a Fe-B ligature.

Preferably, the introduction of at least one rare earth metal is carried out in an inert gas atmosphere at a pressure of from 10 to 30 kPa.

It was found that smelting of hard magnetic material of the REM-Fe-Co-B system by this method provides the production of ingots with a stable chemical composition, uniform distribution of alloying elements over the entire volume of the ingot and high purity of impurities. A stable chemical composition is achieved by observing the order of introducing REM into the smelting and maintaining various REM groups in a vacuum or argon atmosphere, which is due to different values of the vapor pressure of these elements. A uniform distribution of alloying elements in the ingot is achieved due to intensive induction mixing of the melt during vacuum induction melting, and high purity by impurities is achieved by minimizing the interaction of the melt with the crucible material through the use of inert ceramics. In the magnetic solid material melted by this method, the phase composition is stable and the amount of the main magnetic phase is increased, which makes it possible to increase the properties of magnets made from it.

Example 1

According to the proposed method was carried out smelting of hard magnetic material composition (% wt.): Fe (ocH.) - (11.00-13.00) Pr- (14.5-17.0) Dy- (2.20-4.20 ) Gd- (24.30-25.30) Co- (0.50-1.50) B.

For smelting, a vacuum induction furnace with a crucible was used, the working layer of which consisted of a mixture of magnesium and yttrium oxides. Iron and cobalt were introduced into the filling, melting of the filling was carried out in vacuum, after the degassing of the melt, boron was placed in the form of an iron-boron ligature, then praseodymium and gadolinium were introduced in vacuum in several portions, then argon was introduced into the furnace chamber, after which dysprosium was introduced into the melt . The casting was carried out in a steel pipe, the ingot was cooled in an argon atmosphere for 6 hours.

The results of chemical analysis from samples taken by the height of the casting are presented in table 1.

Table 1 shows that in the alloy smelted by the proposed method, the content of alloying elements is stable, practically do not differ in different parts of the ingot and is much closer to the calculated composition than in the alloy smelted by the prototype method. The content of aluminum and oxygen in the alloy smelted by the proposed method is 5 times lower than in the alloy smelted by the prototype method.

From the obtained ingots, samples were taken from which magnets were made. The manufacturing process of magnets included standard technological stages: mechanical crushing, grinding, pressing in a magnetic field, sintering in vacuum, homogenization, machining (cutting, grinding) and magnetization. The properties of magnets made from the obtained alloy are presented in table 2.

Table 2 shows that the proposed method allows to increase the value of tension at the operating point by 11% and coercive force by 21% compared with the prototype method.

Example 2

According to the proposed method, the alloy composition was smelted (% wt.): Fe (ocH.) - (14.50-16.50) Pr- (8.5-10.5) Dy- (5.50-6.50) Sm- (24.50-25.50) Co- (0.50-1.50) B.

For smelting, a vacuum induction furnace with a crucible was used, the working layer of which consisted of yttrium oxide. Iron and cobalt were introduced into the filling, melting of the filling was carried out in vacuum, after the degassing of the melt, boron was introduced in the form of an iron-boron ligature, then praseodymium was placed in vacuum in several portions, then argon was introduced into the furnace chamber, after which dysprosium and samarium were introduced into the melt . The casting was carried out in a steel pipe, the ingot was cooled in an argon atmosphere for 7 hours.

The results of chemical analysis from samples taken by the height of the casting are presented in table 3.

From table 3 it is seen that in the hard magnetic material melted by the proposed method, the content of alloying elements is stable, practically does not differ in different parts of the ingot and is much closer to the calculated composition than in the alloy smelted by the prototype method. The aluminum content in the hard magnetic material smelted by the proposed method is 7.5 times lower than in the alloy smelted by the prototype method, and the oxygen content is 4 times lower.

From the obtained ingots, samples were taken from which magnets were made. The manufacturing process of magnets included standard technological stages: mechanical crushing, grinding, pressing in a magnetic field, sintering in vacuum, homogenization, machining (cutting, grinding) and magnetization. The properties of magnets made from the obtained alloy are presented in table 4.

Table 2 shows that the proposed method allows to increase the value of tension at the operating point by 8% and coercive force by 20% compared with the prototype method.

The proposed method allows to obtain solid magnetic material ingots based on the REM-Fe-Co-B system with a stable chemical composition, uniform distribution of alloying elements throughout the entire volume of the ingot, and high purity of aluminum and oxygen impurities.

The use of the invention allows to obtain materials with increased magnetic properties, which allows to increase the accuracy of navigation devices made from them.

Claims (7)

1. A method of producing a hard magnetic material based on the rare-earth metal-iron-cobalt-boron boron system in a vacuum induction furnace, comprising loading iron and cobalt into a melting crucible and melting them in a vacuum, introducing alloying elements into the melt, casting the melt into the mold and cooling the casting, characterized in that the working layer of the melting crucible contains at least one of the oxides of magnesium, yttrium, hafnium, scandium or zirconium, after melting in vacuum, boron is introduced into the melt, then at least less is introduced into the melt in the melt it least one rare earth metal selected from the group consisting of praseodymium, gadolinium, neodymium and cerium, and then in an inert gas is introduced into the melt of at least one rare earth metal selected from the group consisting of dysprosium and samarium. 2. The method according to p. 1, characterized in that the boron is introduced into the melt in the form of a ligature iron-boron. 3. The method according to p. 1, characterized in that at least one rare-earth metal is introduced in an inert gas atmosphere at a pressure of from 10 to 30 kPa. 4. The method according to p. 1, characterized in that argon is used as an inert gas. 5. The method according to p. 1, characterized in that the casting of the melt is carried out in a metal form. 6. The method according to p. 1, characterized in that the casting of the melt is carried out in graphite form. 7. The method according to p. 1, characterized in that the cooling of the casting is carried out in an inert atmosphere for at least 6 hours.