JP4650218B2 - Method for producing rare earth magnet powder - Google Patents

Description

  The present invention relates to a method for producing a rare earth magnet powder using the HDDR method.

R-Fe-B rare earth magnets that are typical high performance permanent magnets (R is a rare earth element including Y, Fe is iron, and B is boron) is an R ₂ Fe ₁₄ B phase that is a ternary tetragonal compound. It has a structure that contains it as a main phase and exhibits excellent magnetic properties. Such R—Fe—B rare earth magnets are roughly classified into sintered magnets and bonded magnets. The sintered magnet is manufactured by compressing and molding a fine powder (average particle diameter: several μm) of an R—Fe—B based magnet alloy with a press machine. On the other hand, bond magnets are usually manufactured by compression molding or injection molding a mixture (compound) of R-Fe-B magnet alloy powder (particle size: about 100 μm, for example) and a binding resin. Is done.

  In the case of a sintered magnet, since a powder having a relatively small particle size is used, each powder particle has magnetic anisotropy. For this reason, when compressing powder with a press device, an orientation magnetic field is applied to the powder, whereby a compact in which the powder particles are oriented in the direction of the magnetic field can be produced.

On the other hand, in a bonded magnet, in order to develop magnetic anisotropy, the easy magnetization axis (c-axis in the case of R ₂ Fe ₁₄ B phase) of the hard magnetic phase in the powder particles used is oriented in one direction. It is necessary to be. In order to obtain a coercive force necessary for practical use, it is necessary to reduce the crystal grains of the hard magnetic phase constituting the powder particles to about the single-domain critical particle size. Therefore, in order to produce an excellent anisotropic bonded magnet, it is necessary to obtain a rare earth alloy powder satisfying these conditions.

Currently, HDDR (Hydrogenation-Disproportionation-Desorption-Recombination) treatment is generally employed to produce rare earth alloy powders for anisotropic bonded magnets. “HDDR” means a process of sequentially executing hydrogenation and disproportionation, desorption and recombination. According to the known HDDR treatment, the ingot or powder of the R—Fe—B alloy is maintained at a temperature of 500 ° C. to 1000 ° C. in an H ₂ gas atmosphere or a mixed atmosphere of an H ₂ gas and an inert gas, thereby , after absorbing hydrogen in the ingot or powder, for example dehydrogenation treatment at 500 ° C. to 1000 ° C. until the following inactive atmosphere H ₂ partial pressure 13Pa following vacuum atmosphere or H ₂ partial pressure 13Pa, then The alloy magnet powder is obtained by cooling.

The R—Fe—B alloy powder produced by the HDDR treatment exhibits a large coercive force and has magnetic anisotropy. The reason for having such a property is that the metal structure is a very fine structure of 0.1 to 1 μm, and an aggregate of crystals having easy magnetization axes aligned in one direction. More specifically, since the grain size of the ultrafine crystal obtained by the HDDR treatment is close to the single domain critical grain size of the tetragonal R ₂ Fe ₁₄ B-based compound, a high coercive force is exhibited. An aggregate of very fine crystals of this tetragonal R ₂ Fe ₁₄ B-based compound is referred to as “recrystallized texture”. A method for producing an R—Fe—B alloy powder having a recrystallized texture by performing the HDDR process is disclosed in, for example, Patent Documents 1 to 6.

Anisotropic bonded magnets produced using magnetic powder produced by HDDR processing (hereinafter referred to as “HDDR powder”) are applied to various products because of their high energy product and shape flexibility. Is expected
Japanese Patent Publication No. 6-82575 Japanese Patent Publication No. 7-68561 JP 2000-96102 A JP 2002-93610 A JP-A-2005-97711 Japanese Patent Laid-Open No. 2005-15918

  A normal HDDR powder has insufficient heat resistance, and has problems such as irreversible heat demagnetization in a temperature environment of 80 ° C. or more and large deterioration of magnetic flux over time. Conventionally, in order to solve this problem, it has been proposed to add Dy or Al, which contributes to improving the coercive force, to the starting alloy. However, when Dy or Al is contained in the starting alloy, there is a problem that the progress of the HDDR reaction is hindered, the degree of orientation of the main phase after the HDDR treatment is lowered, and the magnetization is significantly reduced.

  Patent Documents 3 to 5 disclose that a rare earth compound is mixed and heated with an alloy powder before, during, or after HDDR treatment. Since the concentration is increased on the surface of the powder particles, there is a problem that the corrosion resistance is greatly reduced. In addition, before and after the HDDR process, a heat treatment for diffusing the rare earth compound is required, and productivity is reduced.

  Patent Document 6 discloses that the powder particle surface after HDDR is coated with Al and heated, but this method also requires an additional heat treatment step as in the above method. Decreases. Also, if the HDDR powder particle surface is insufficiently coated with Al, the magnetic properties may deteriorate during the heat treatment due to the influence of adsorbed moisture and the like.

  The present invention has been made to solve the above problems, and a main object thereof is to provide a method for producing HDDR powder having excellent magnetic properties and corrosion resistance.

  The method for producing a rare earth-based magnet powder according to the present invention comprises a step (A) of preparing an alloy powder having an R—Fe—B phase, and a non-rare earth layer substantially free of rare earth metal elements on the surface of the alloy powder. The alloy powder is subjected to hydrogenation / disproportionation treatment by performing a heat treatment at a temperature of 750 ° C. or higher and lower than 900 ° C. in a hydrogen-containing atmosphere (B). The temperature is raised to 750 ° C. or more and less than 900 ° C. between step (C), step (D) for performing dehydrogenation / recombination treatment on the alloy powder, and step (A) and step (C). Step (E).

  In a preferred embodiment, in the step (B), a layer of a single metal, alloy, and / or compound of a non-rare earth metal element is formed as the non-rare earth layer.

  In a preferred embodiment, the atmosphere during the temperature raising process in the step (E) contains hydrogen.

  In a preferred embodiment, the temperature increase in the step (E) is started after forming the non-rare earth layer in the step (B).

  In a preferred embodiment, the temperature increase in the step (E) starts before forming the non-rare earth layer in the step (B), and the non-rare earth layer is made of a material that dissolves during the temperature increase. ing.

  In a preferred embodiment, the powder of the alloy in the step (A) includes non-rare earth powder particles composed of a single metal of a non-rare earth metal, an alloy, and / or a compound, and at least a part of the non-rare earth powder particles includes: The non-rare earth layer is formed by dissolving in the temperature raising process of the step (E).

  In a preferred embodiment, the non-rare earth powder particles are formed of a material having a melting point of 700 ° C. or lower.

  In a preferred embodiment, the material includes at least one of aluminum and gallium.

  In a preferred embodiment, the non-rare earth powder particles have a 50% center particle size of 0.5 μm or more and 20 μm or less.

  In a preferred embodiment, the alloy having the R—Fe—B phase has a composition satisfying a relationship of 10 atomic% ≦ R ≦ 14 atomic%, 5 atomic% ≦ B ≦ 10 atomic%.

  The method for producing an anisotropic magnet according to the present invention includes a step of preparing a rare earth magnet powder produced by the method for producing a rare earth magnet powder described above, and molding the rare earth magnet powder in an orientation magnetic field. The process of including.

In the present invention, when the HDDR process is performed, all or part of the surface of the R—Fe—B alloy powder particles is covered with a non-rare earth layer, and this non-rare earth layer functions as a barrier against hydrogen. . In general, it has been reported that when the reaction rate of the hydrogenation reaction becomes excessively high, the degree of crystal orientation of the main phase (R ₂ Fe ₁₄ B phase) after HDDR treatment decreases. Can reduce the rate of arrival of hydrogen to the surface of the R-Fe-B alloy powder particles. As a result, since the speed of the hydrogenation reaction is controlled within an appropriate range, it is considered that the degree of orientation of the main phase (R ₂ Fe ₁₄ B phase) after HDDR treatment is improved. Further, even after the HDDR treatment, the non-rare earth layer on the surface of the powder particles suppresses the contact between the use environment atmosphere such as a high temperature atmosphere in the atmosphere and the rare earth alloy, so that the corrosion resistance and oxidation resistance are improved.

  In addition, by performing the temperature rising process for HDDR processing in a hydrogen atmosphere, it is possible to suppress a decrease in magnetic characteristics due to adsorbed moisture.

  In the present invention, a non-rare earth layer substantially free of rare earth metal elements is formed on the whole or a part of the surface of the alloy powder before the HDDR treatment is performed on the alloy powder having the R—Fe—B phase. .

  In the HDDR treatment in the present invention, the alloy powder is subjected to a heat treatment at a temperature of 750 ° C. or higher and lower than 900 ° C. to perform a hydrogenation / disproportionation treatment on the alloy powder. This is performed by dehydrogenating and recombining the powder. In the present invention, the surface of the individual particles of the alloy powder is covered with a non-rare earth layer during the hydrogenation / disproportionation treatment, so that excessive hydrogen supply is not performed, and finally excellent magnet characteristics are exhibited. The hydrogenation / disproportionation process proceeds.

  The non-rare earth layer needs to be formed from a material that does not degrade the magnet properties even if it reacts with the alloy powder during HDDR processing. According to the study of the present inventors, when formed from a material containing non-rare earth metal such as Al, Ti, V, Cr, Ga, Nb, Mo, In, Sn, Hf, Ta, W, and / or Cu. It was found that an excellent effect was exhibited. The form of the non-rare earth metal element is not limited to a single metal, and may be an alloy of these non-rare earth metals or a compound in which other elements are combined.

  The non-rare earth layer can be deposited on the surface of the powder particles by various methods before starting the HDDR process, but when formed from a material having a sufficiently low melting point, the powder of such material is used as the starting alloy powder. And dissolved in the temperature rising process for HDDR treatment. When such dissolution occurs, the non-rare earth layer in the liquid phase covers the powder particle surface and functions as a barrier for hydrogen supply.

  Hereinafter, embodiments of a method for producing a rare earth magnet powder according to the present invention will be described.

<Starting alloy>
First, an alloy having an R—Fe—B phase obtained by pulverizing a cast alloy is prepared. Specifically, an R-T-B alloy (starting alloy) ingot is prepared. Here, R is a rare earth element containing 50 atomic% or more of Nd and / or Pr. T is selected from one or more of Fe, Co and Ni, is a transition metal element containing 50 atomic% or more of Fe, and B is boron. This RTB-based alloy contains Nd ₂ Fe ₁₄ B-type compound phase in a volume ratio of 50% or more.

  The composition ratio of R is preferably 10 to 20 atomic% of the whole alloy, more preferably 11 to 15 atomic%, and further preferably 12 to 14 atomic%. In order to improve the coercive force, it is effective to include Dy or Tb in a part of R. However, when the concentration of Dy and / or Tb is increased, the progress of the HDDR reaction is inhibited. Therefore, the amount of substitution is preferably 30 atomic% or less of the total R.

  The content of B is preferably 4 to 15 atomic%, and more preferably 5 to 9 atomic%. A part of B may be substituted with C (carbon). In that case, it is preferable to set the total amount of (B + C) to 4 to 15 atomic%.

  T occupies the remainder. In order to obtain effects such as improvement of magnetic properties, elements such as Al, Ti, V, Cr, Ga, Nb, Mo, In, Sn, Hf, Ta, W, and / or Cu may be added as appropriate. However, since an increase in the amount of addition causes a decrease in magnetization in particular, the total amount is preferably 10 atomic% or less.

The starting alloy is obtained by a known alloy production method such as a book mold method, a centrifugal casting method, a strip casting method, an atomizing method, or a diffusion reduction method. The starting alloy produced by these methods may be subjected to homogenization heat treatment for the purpose of eliminating macro segregation, coarsening of crystal grains, reduction of α-Fe phase, and the like. The homogenization heat treatment is preferably performed, for example, at 1000 to 1200 ° C. for 1 to 48 hours in an inert gas atmosphere other than nitrogen. By this heat treatment, diffusion of elements in the R-T-B alloy ingot occurs, and the components are homogenized. More specifically, the R-T-B type alloy ingot is mainly composed of an R ₂ Fe ₁₄ B phase and an R-rich phase which are main phases, but in addition to the R ₂ Fe ₁₄ B phase, α-Fe There are often ferromagnetic phases such as the phase and the R ₂ Fe ₁₇ phase. Therefore, by heat treatment, the α-Fe phase, R ₂ Fe ₁₇ phase, etc. in the RTB-based alloy ingot are diffused and extinguished as much as possible, and the ferromagnetic phase substantially consists of only the R ₂ Fe ₁₄ B phase. Make it an organization. By such a homogenization treatment, the average crystal grain size of the R ₂ Fe ₁₄ B phase is coarsened to about 100 μm or more. The coarsening of the average crystal grain size is preferable because the HDDR-treated magnetic powder has a large magnetic anisotropy.

  The reason why nitrogen is not used as the inert gas atmosphere is that nitrogen reacts with the RTB-based alloy. If the temperature is lower than 1000 ° C., it takes too much time for the element diffusion in the R—T—B alloy to increase the manufacturing cost, and another phase is formed, which is not preferable. On the other hand, when the heat treatment temperature exceeds 1200 ° C., melting of the alloy occurs, which is not preferable. A more preferable heat treatment temperature range is appropriately set in the range of 1100 ° C. to 1150 ° C. according to the alloy composition and the like. In addition, when the heat treatment time is less than 1 hour, element diffusion becomes insufficient, but conversely, it is not meaningful to perform the treatment for a long time exceeding 48 hours.

Next, the starting alloy powder is prepared by pulverizing the starting alloy by a known method. The pulverization can be performed using a mechanical pulverization method such as a jaw crusher or a hydrogen storage / disintegration method. The average particle size of the starting alloy powder in this embodiment is preferably 10 to 500 μm, and more preferably 30 to 150 μm. In the case of the hydrogen storage / collapse method, the alloy may be embrittled by storing the above starting alloy in a hydrogen atmosphere of 0.05 to 1.0 MPa for 5 minutes to 10 hours to cause the alloy to store hydrogen. When the starting alloy occludes hydrogen, it spontaneously collapses and cracks occur. In such hydrogen pulverization, an R-T-B system ingot is put in a pressure vessel, H ₂ gas having a purity of 99.9% or more is introduced to 50 to 1000 kPa, and then the state is maintained for 5 minutes to 10 hours. This can be done by holding. In this way, a raw material powder having a particle size of 1000 μm or less is obtained. The mechanical pulverization performed after hydrogen pulverization can be performed using a pulverizer such as a feather mill, a ball mill, or a power mill.

The coarsely pulverized powder thus obtained is composed of particles having a substantially single crystal orientation, and the magnetization easy axes are aligned in one direction in each particle. As a result, the rare earth alloy powder for permanent magnets obtained by the HDDR process can exhibit anisotropy. In the starting alloy used in this embodiment, the Nd ₂ Fe ₁₄ B type compound phase having crystal orientations aligned in the same direction has a size of 20 μm or more. This is important in finally obtaining high magnetic properties, particularly saturation magnetic flux density Br.

<Coating non-rare earth metal powder on starting alloy powder>
Next, a step of coating the surface of the individual powder particles of the alloy powder with a non-rare earth layer is performed. The non-rare earth layer is formed from a single metal, alloy, and / or compound of a non-rare earth metal. The formation of the non-rare earth layer may be performed before the HDDR process is started, or may be performed during the temperature rising process for the HDDR process, as will be described later.

  When the powder particles are coated with the non-rare earth layer before the start of the HDDR process, a known thin film forming method can be employed. However, since the starting alloy powder contains an active rare earth element (R), it is desirable to employ a vapor deposition method such as a sputtering method or an ion plating method. The film forming conditions vary depending on the film forming method and the material to be formed, but the average thickness of the layer deposited on the surface of each powder particle is preferably set to 1 μm or less. This is because if the thickness of the non-rare earth layer exceeds 1 μm, the progress of the HDDR reaction is hindered excessively. When the thickness of the non-rare earth layer is less than 0.01 μm, the effect of the present invention cannot be sufficiently obtained. For this reason, the thickness of the non-rare earth layer is preferably 0.01 μm or more and 1 μm or less, and more preferably 0.05 μm or more and 0.5 μm or less.

  Next, a method for forming a non-rare earth layer using a temperature raising process for HDDR processing will be described.

  First, the above-mentioned starting alloy powder is prepared, and non-rare earth powder is mixed therewith. As the non-rare earth powder, a metal single metal, alloy and / or compound powder can be used. The average particle size of the non-rare earth powder is preferably from 0.1 to 20 μm, more preferably from 0.5 to 10 μm.

  In order to control the HDDR reaction by coating the surface of the powder particles with a non-rare earth layer, a material that melts at a temperature (for example, 750 ° C. or less) lower than the temperature of the HDDR process (750 ° C. or more and less than 900 ° C.) is used. It is preferable to form a rare earth powder. Specifically, non-rare earth metals such as Al, Sn, Zn, and Ga can be used. Among these metals, Al or Ga is particularly preferable because it exhibits an effect of improving the coercive force HcJ by diffusion into the magnetic powder particles. Since Ga has a melting point near room temperature, it may melt in the process of mixing with the starting alloy powder and coat the individual particle surfaces of the starting alloy powder. However, it goes without saying that the effect of the present invention is exhibited even in this case.

  The 50% center particle size of the non-rare earth powder is preferably 0.5 μm or more and 20 μm or less. When the 50% average particle size is less than 0.5 μm, handling becomes difficult due to problems such as ignition. On the other hand, if the 50% average particle diameter exceeds 20 μm, uniform mixing with the starting alloy powder becomes difficult, and the effects of the present invention may not be obtained. A more preferable range is 1 μm or more and 10 μm or less.

<HDDR processing>
As described above, the HDDR process is divided into a hydrogenation / disproportionation process (HD process) and a dehydrogenation / recombination process (DR process). The hydrogenation / disproportionation treatment and dehydrogenation / recombination treatment can be performed in the same apparatus, but can also be performed using different apparatuses. The HDDR process can be completed by continuously or discontinuously performing the hydrogenation / disproportionation process and the dehydrogenation / recombination process.

The hydrogenation / disproportionation treatment is performed at 750 ° C. to 950 ° C. in H ₂ gas, or H ₂ gas and inert gas (Ar, He, etc.). The hydrogen partial pressure during the hydrogenation / disproportionation treatment can be optimized as appropriate depending on the composition of the starting alloy powder, but is usually set in the range of 10 kPa to 500 kPa. The time required for the hydrogenation / disproportionation treatment is usually 10 minutes to 10 hours, and is typically set within a range of 20 minutes to 5 hours. The atmosphere at the time of temperature rise is not particularly limited, but the temperature is preferably raised at a hydrogen partial pressure of 50 kPa or more.

  According to the present embodiment, at least when the hydrogenation / disproportionation treatment is performed, the powder particle surface is coated with the non-rare earth layer, so that the hydrogenation / disproportionation reaction proceeds at an appropriate rate. become.

  If the particle surface of the starting alloy powder is covered with the non-rare earth layer before starting the HDDR processing step or at a relatively early stage of the temperature rising process for the HDDR processing, the rare earth element (R ) And the adsorbed moisture can also be suppressed. If the non-rare earth layer does not exist, the rare earth element (R) in the starting alloy powder reacts with the adsorbed moisture, and there is a possibility that the magnetic properties will eventually deteriorate. In order to further suppress the reaction with adsorbed moisture during the temperature raising process, it is preferable to raise the temperature in a reducing atmosphere containing hydrogen.

  After hydrogenation / disproportionation treatment, dehydrogenation / recombination treatment is performed. The atmosphere during the dehydrogenation / recombination treatment may be an inert atmosphere (Ar, He, etc.) or a vacuum. As for the atmosphere control (atmosphere gas type, pressure, temperature, time) in the dehydrogenation / recombination treatment, a known method may be adopted as appropriate, but the treatment temperature is usually 750 to 900 ° C., and the treatment time is 10 5 hours from minutes. Needless to say, the atmosphere can be controlled stepwise (for example, the hydrogen partial pressure can be lowered stepwise or the reduced pressure can be lowered stepwise).

  After the dehydrogenation / recombination process is completed, the cooling step is executed to obtain the alloy magnet powder according to the present embodiment. In the cooling step, the reduced pressure state may be maintained as it is, but in order to increase the cooling efficiency, the vacuum exhaust is stopped, the argon gas is supplied into the furnace, and the furnace pressure is returned to the atmospheric pressure. Further, in order to achieve a higher cooling rate, pressurization may be performed with argon gas or helium gas. Thereafter, the powder after the HDDR process is taken out of the hydrogen treatment apparatus.

The alloy magnet powder thus obtained has a recombination texture of tetragonal R ₂ Fe ₁₄ B type compound as a result of HDDR treatment, and the average crystal grain size (primary particle diameter) of this recombination texture is In the range of about 0.1 to about 0.5 μm. Since this size is close to the size of the single magnetic domain particles, each powder particle having a recombination texture can exhibit a high coercive force. In addition, since the crystal orientation of the recombination texture is aligned, the easy axis of magnetization is also aligned, and as a result, the powder particles having the recombination texture exhibit high magnetic anisotropy. It will be.

<Crushing and grinding>
After the dehydrogenation / recombination process is completed, the material cooled to room temperature may be a weak aggregate. In this case, crushing may be performed by a known method. Further, the particle size may be adjusted by pulverization according to the final purpose. As the pulverization method, a known pulverization technique can be used, but it is preferable to perform pulverization in an inert gas atmosphere such as Ar in order to suppress oxidation of the magnet powder during pulverization.

<Application of magnet powder>
The obtained magnet powder is subjected to a surface treatment by a known method, if necessary, and then used for manufacturing a bonded magnet or a hot-formed magnet. When manufacturing a bonded magnet, it is mainly formed by compression molding, injection molding, extrusion molding or the like. Since the non-rare earth layer functions as an oxidation-resistant film, the magnet powder produced by the present invention is suitable for application to injection molding and extrusion molding in which kneading and molding need to be performed at a relatively high temperature. A film may be formed on the obtained bonded magnet by a method such as resin coating or plating for the purpose of imparting further corrosion resistance and oxidation resistance.

[Example 1]
Alloys having the compositions (A to F) shown in Table 1 were prepared by a known casting method and annealed in an Ar atmosphere at 1100 ° C. for 24 hours. The obtained cast iron was pulverized in an Ar atmosphere in which the oxygen concentration was limited to 0.5% or less to produce a powder having an average particle size of 150 μm.

As a result of evaluating the obtained powder with an X-ray diffractometer, all the alloys had an Nd ₂ Fe ₁₄ B type crystal phase. Hereinafter, this powder is referred to as “starting alloy powder”.

  In addition, the unit of the numerical value in Table 1 is the mass%.

  A metal layer (non-rare earth layer) shown in Table 2 below was formed on the surface of the starting alloy powder. The metal layer was formed by a high frequency sputtering method, and the thickness of the formed metal layer was set to about 0.1 μm. Sputtering conditions were optimized for individual metals. However, in order to cover a wide range (if possible, the entire surface) of the powder particle surface, powder agitation and film formation were repeated.

  The starting alloy powder having a metal film formed on the surface in this manner was put into a tubular furnace, heated to 840 ° C. in a hydrogen gas flow of 100 kPa (atmospheric pressure), and then kept at 840 ° C. for 3 hours to prevent hydrogenation / non-hydrogenation. Leveled. The heating rate was 13 ° C./min. Then, it hold | maintained in 840 degreeC * 1 hour in Ar air pressure-reduced to 5 kPa, and dehydrogenation and the recombination reaction were produced. Then, it cooled to room temperature in atmospheric pressure Ar flow. Thus, after completing the HDDR process, the obtained HDDR powder was crushed to obtain samples of Examples 1 to 5.

The magnetic properties of the obtained magnet powder were measured with a vibrating sample magnetometer (VSM: device name VSM5 (manufactured by Toei Kogyo Co., Ltd.)). In the sample for VSM measurement, the obtained magnetic powder was put into a cylindrical holder, fixed with paraffin while being oriented in a magnetic field of 800 kA / m, and then applied with a pulse magnetic field of 3.2 MA / m or more. A magnetized one was used. For all samples, the density was 7.60 g / cm ³ and the values of Br and (BH) _max were calculated. The results are shown in Table 2.

  The same HDDR treatment and evaluation were performed on the starting alloy powder not subjected to metal coating (Comparative Examples 1 and 2). As shown in Table 2, it can be seen that when the metal coating is formed on the surface of the starting alloy powder particles, the magnetic properties after HDDR treatment are improved.

[Example 2]
Al powder having a 50% center particle size of about 3 μm was mixed in the proportion shown in Table 3 with the starting raw material powder (composition shown in Table 1) obtained in the same manner as in Example 1. The average particle size of the powder was evaluated with a laser diffraction flow rate distribution measuring device.

  The starting alloy powder mixed with the Al powder was put into a tubular furnace and heated to 840 ° C. at a heating rate of 13 ° C./min in a 100 kPa (atmospheric pressure) hydrogen stream. Then, it hold | maintained at 840 degreeC for 3 hours, and performed hydrogenation and disproportionation processing. Thereafter, dehydrogenation / recombination treatment was performed by maintaining at 840 ° C. for 1 hour in an Ar flow reduced to 5 kPa. After cooling to room temperature in an atmospheric pressure Ar flow, it was crushed to obtain samples of Examples 6 to 9.

  When the obtained sample was observed with a scanning electron microscope (SEM), it was confirmed that Al covered a part of each particle surface of the magnetic powder. This Al is a mixture of Al powder mixed with the starting alloy powder, which is melted in the temperature rising process for HDDR treatment and finally solidified.

  The magnetic properties of the obtained magnet powder were measured in the same manner as in Example 1 using a vibrating sample magnetometer (VSM: device name VSM5 (manufactured by Toei Kogyo Co., Ltd.)). The evaluation results are shown in Table 3.

  As can be seen from Table 3, the magnetic properties were improved by subjecting the starting alloy powder mixed with Al powder to HDDR. Also in this example, it is considered that the Al layer present on the surface of the alloy powder functioned as a barrier against hydrogen during the HDDR process.

  In addition, the same process was performed using the starting alloys C-F which mix | blended and cast the same quantity of Al as the quantity of Al which said Example contains in a raw material alloy (reference examples 1-4). As a result, the coercive force HcJ was improved with an increase in the Al content, but no significant improvement in the residual magnetic flux density Br was observed. On the other hand, in the Example of this invention, both the coercive force HcJ and the residual magnetic flux density Br improved.

  The method for producing rare earth magnet powder of the present invention is used for producing HDDR powder having excellent magnetic properties and corrosion resistance.

Claims (10)

Preparing an alloy powder having an R-Fe-B phase (A);
After the step (A), a step (B) of forming a non-rare earth layer formed of a single metal, an alloy, and / or a compound of a non-rare earth metal on the whole or a part of the surface of the alloy powder;
After the step (B), performing a hydrogenation / disproportionation treatment on the alloy powder by performing a heat treatment at a temperature of 750 ° C. or more and less than 900 ° C. in an atmosphere containing hydrogen;
After the step (C), a step (D) of performing dehydrogenation / recombination treatment on the alloy powder;
A step (E) of raising the temperature to between 750 ° C. and less than 900 ° C. between step (A) and step (C);
A method for producing a rare earth magnet powder, comprising: The method for producing a rare earth-based magnet powder according to claim 1, wherein the atmosphere in the temperature raising process of the step (E) contains hydrogen. The method for producing a rare earth magnet powder according to claim 1 or 2 , wherein the temperature increase in the step (E) is started after the non-rare earth layer in the step (B) is formed. The temperature rise in the step (E) is started before forming the non-rare earth layer in the step (B), and the non-rare earth layer is made of a material that dissolves during the temperature rise. 3. A method for producing a rare earth magnet powder according to 1 or 2 . The alloy powder in the step (A) includes non-rare earth powder particles made of a single metal, alloy, and / or compound of a non-rare earth metal, and at least a part of the non-rare earth powder particles includes the step (E). The method for producing a rare earth-based magnet powder according to claim 4 , wherein the non-rare earth layer is formed by melting in the temperature rising process. The method for producing a rare earth magnet powder according to claim 5 , wherein the non-rare earth powder particles are formed of a material having a melting point of 700 ° C. or less. The method for producing a rare earth magnet powder according to claim 6 , wherein the material contains at least one of aluminum and gallium. The method for producing a rare earth based magnet powder according to any one of claims 5 to 7 , wherein the non-rare earth powder particles have a 50% center particle size of 0.5 µm or more and 20 µm or less. Alloys having the R-Fe-B phase is 10 atomic% ≦ R ≦ 14 atomic%, has a composition which satisfies the 5 atomic% ≦ B ≦ 10 atomic% of relationship, one of claims 1 8 A method for producing the rare earth magnet powder according to claim 1. Preparing a rare earth magnet powder produced by the production method of rare earth magnet powder according to any one of claims 1 to 9,
Forming the rare earth magnet powder in an orientation magnetic field;
A method for producing an anisotropic magnet including