JP2016044352A - Method for producing powder for magnet, and method for producing rare earth magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing powder for a magnet capable of producing powder for a magnet excellent in magnetic properties at high productivity, and a method for producing a rare earth magnet.SOLUTION: Provided is a method for producing powder 1 for a magnet comprising: a preparation step where rare earth-iron based alloy powder 10 composed of a plurality of rare earth-iron based alloy particles 11 is prepared; a surface nitriding step where the rare earth-iron based alloy powder is heat-treated in a nitrogen element-containing atmosphere to form nitrided powder 20 having a nitrogen holding region 21 where the respective rare earth-iron based alloy particles are intruded into the vicinity of the surface thereof; and a magnetic field treatment step where the nitrided powder is applied with a fixed magnetic field in a nitrogen element-free atmosphere and is heat-treated to diffuse the nitrogen in the nitrogen holding region into the rare earth-iron based alloy particles, thus powder 1 for a magnet composed of rare earth-iron-nitrogen based alloy particles substantially uniformly nitrided over the whole of the rare earth-iron based alloy particles is formed. In the magnetic field treatment step, heat treatment temperature is 280 to 430°C and magnetic field strength is 2 to 12T.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a magnet powder used in a rare earth magnet and a method for producing a rare earth magnet. In particular, the present invention relates to a method for producing a magnet powder capable of producing a magnet powder having excellent magnetic properties with high productivity, and a method for producing a rare earth magnet capable of producing a rare earth magnet excellent in magnetic properties with high productivity.

Rare earth magnets using R-Fe alloys, whose main phase is a rare earth-iron (R-Fe) compound containing rare earth elements (R) and iron (Fe), for applications such as motors and generators Is widely used. As a typical rare earth magnet, an Nd ₂ Fe ₁₄ B magnet (neodymium magnet) using an Nd ₂ Fe ₁₄ B alloy whose main phase is an Nd ₂ Fe ₁₄ B compound as a raw material can be mentioned. Except neodymium _magnets, Sm 2 the _Sm 2 _{Fe 17} alloy as a main phase of _{Fe 17} compound as a raw material, _Sm 2 _Fe 17 _{N 3} magnet practical use as a main phase of which _Sm 2 _Fe 17 _{N 3} compound nitride Has been.

  As a kind of rare earth magnet, compression molding is performed on R-Fe alloy magnetic powder, and a sintered magnet obtained by sintering this, or binder resin is mixed with R-Fe alloy magnetic powder, and then compression molding to solidify. Bonded magnets are the mainstream. Recently, a dust magnet has been developed in which magnetic powder of an R—Fe-based alloy is compression-molded (see Patent Document 1).

  Patent Document 1 discloses that R-Fe-based alloy powder is hydrogenated at a hydrogen disproportionation temperature or higher (HD) (Hydrogenation-Disproportionation) ⇒ Compression molding ⇒ Dehydrogenation (Recombination-Recombination) at a temperature higher than the recombination temperature ⇒ It is described that nitriding is performed at a nitriding temperature or higher and a nitrogen disproportionation temperature or lower. The nitriding treatment is performed by applying a magnetic field of 3.5 T or more to the R—Fe based alloy material, so that N atoms can be easily arranged at ideal positions in the crystal lattice, and R—Fe— having an ideal atomic ratio. It is described that a rare earth magnet that can form an N-based alloy material and has excellent magnetic properties can be obtained.

JP 2012-241280 A

  By performing nitriding in a magnetic field, there is a certain effect in improving the magnetic properties of the R—Fe—N alloy material. However, this nitriding treatment is performed stably and the R—Fe—N alloy has good productivity. It is desired to produce a material. When nitriding is performed in a magnetic field, especially when coarse alloy powder particles are used, the nitriding state may vary from the surface to the inside of the R—Fe-based alloy material. Therefore, it is desired to perform nitriding treatment substantially uniformly over the entire R—Fe alloy material to produce an R—Fe—N alloy material with high productivity.

  This invention is made | formed in view of the said situation, and one of the objectives of this invention is to provide the manufacturing method of the powder for magnets which can manufacture the powder for magnets excellent in a magnetic characteristic with sufficient productivity. Another object of the present invention is to provide a method for producing a rare earth magnet capable of producing a rare earth magnet having excellent magnetic properties with high productivity.

  The manufacturing method of the powder for magnets which concerns on 1 aspect of this invention comprises a preparatory process, a surface nitriding process, and a magnetic field heat treatment process. The preparation step is a step of preparing a rare earth-iron alloy powder composed of a plurality of rare earth-iron alloy particles containing a rare earth element. In the surface nitriding step, the rare earth-iron-based alloy powder is heat-treated at a temperature not lower than the nitriding temperature of the rare-earth-iron-based alloy and not higher than the nitrogen disproportionation temperature in an atmosphere containing nitrogen element. In this step, each of the particles forms a nitride powder having a nitrogen holding region where nitrogen penetrates in the vicinity of the surface thereof. In the magnetic field heat treatment step, the nitride powder is heat-treated in a nitrogen-free atmosphere by applying a constant magnetic field to diffuse the nitrogen in the nitrogen holding region to the inside of the rare earth-iron alloy particles, This is a step of forming a magnet powder composed of rare earth-iron-nitrogen alloy particles nitrided substantially uniformly over the entire rare earth-iron alloy particles.

  The method for producing a rare earth magnet according to one aspect of the present invention includes a preparation step, a hydrogenation step, a forming step, a dehydrogenation step, a surface nitriding step, and a magnetic field heat treatment step. The preparation step is a step of preparing a rare earth-iron alloy powder composed of a plurality of rare earth-iron alloy particles containing a rare earth element. The hydrogenation step is a step of forming the hydrogenated powder by heat-treating the rare earth-iron-based alloy powder in an atmosphere containing hydrogen element at a temperature equal to or higher than the hydrogen disproportionation temperature of the rare-earth-iron-based alloy. . The forming step is a step of compression-molding the hydrogenated powder to form a hydrogenated powder molded body. The dehydrogenation step is a step of forming the dehydrogenated powder compact by heat-treating the hydrogenated powder compact in an inert atmosphere or a reduced pressure atmosphere at a temperature equal to or higher than the recombination temperature of the hydrogenated powder compact. is there. In the surface nitriding step, the dehydrogenated powder compact is heat-treated at a temperature not lower than the nitriding temperature of the dehydrogenated powder compact and not higher than the nitrogen disproportionation temperature in an atmosphere containing nitrogen element. This is a step of forming a nitrided powder molded body in which each of the dehydrogenated powder molded body particles to be formed has a nitrogen holding region where nitrogen has penetrated in the vicinity of the surface thereof. In the magnetic field heat treatment step, the nitride powder compact is heat-treated in a nitrogen-free atmosphere by applying a constant magnetic field, and nitrogen in the nitrogen holding region is spread over the entire dehydrogenated powder compact particles. This is a step of forming a magnet material that is substantially uniformly nitrided.

  The method for producing a magnet powder can produce a magnet powder having excellent magnetic properties with high productivity. In addition, the method for producing a rare earth magnet can produce a rare earth magnet having excellent magnetic properties with high productivity.

It is process explanatory drawing which shows typically an example of the manufacturing process of the powder for magnets of Embodiment 1. FIG. It is process explanatory drawing which shows an example of the manufacturing process of the rare earth magnet of Embodiment 2 typically.

[Description of Embodiment of the Present Invention]
The R—Fe—N based alloy material is obtained by nitrogen entering from the surface of the R—Fe based alloy material and diffusing nitrogen toward the inside. However, since the diffusion rate is slower than the nitrogen penetration rate, the difference between the nitrogen penetration rate and the diffusion rate is based on the idea that the nitriding state varies from the surface to the inside of the R-Fe alloy material. Even if there is, there has been studied a configuration capable of obtaining an R—Fe—N based alloy material that is substantially uniformly distributed in the entire nitriding state, and has completed the present invention. The contents of the embodiments of the present invention will be listed and described below.

  (1) The manufacturing method of the powder for magnets which concerns on embodiment is equipped with a preparatory process, a surface nitridation process, and a magnetic field heat treatment process. The preparation step is a step of preparing a rare earth-iron alloy powder composed of a plurality of rare earth-iron alloy particles containing a rare earth element. In the surface nitriding step, the rare earth-iron-based alloy powder is heat-treated at a temperature not lower than the nitriding temperature of the rare-earth-iron-based alloy and not higher than the nitrogen disproportionation temperature in an atmosphere containing nitrogen element. In this step, each of the particles forms a nitride powder having a nitrogen holding region where nitrogen penetrates in the vicinity of the surface thereof. In the magnetic field heat treatment step, the nitride powder is heat-treated in a nitrogen-free atmosphere by applying a constant magnetic field to diffuse the nitrogen in the nitrogen holding region to the inside of the rare earth-iron alloy particles, This is a step of forming a magnet powder composed of rare earth-iron-nitrogen alloy particles nitrided substantially uniformly over the entire rare earth-iron alloy particles.

  When forming rare earth-iron alloy powder by nitriding to form magnet powder (rare earth-iron-nitrogen alloy powder), nitriding treatment is performed by performing two steps: surface nitriding process ⇒ magnetic field heat treatment process. This can be carried out stably, and the magnet powder can be produced with high productivity. Nitrogen treatment is divided into two steps: a surface nitriding process that mainly penetrates into the surface of nitrogen particles and a magnetic field heat treatment process that mainly diffuses nitrogen into the particles. Even if there is a difference in the diffusion rate, nitriding can be performed substantially uniformly over the entire particle. Since the diffusion rate of nitrogen can be increased by applying a magnetic field in the magnetic field heat treatment step, the magnet powder can be produced with high productivity.

  (2) As a manufacturing method of the powder for magnets of embodiment, it is mentioned that the magnetic field strength in the above-mentioned magnetic field heat treatment process is 2T or more and 12T or less.

By applying a specific magnetic field to the nitride powder, the crystal lattice of the crystals constituting the rare earth-iron alloy particles is distorted by the magnetostrictive effect. Specifically, between the iron atoms constituting the crystal lattice and the iron atoms is stretched in the direction in which the magnetic field is applied. When the magnetic field strength is 2T or more, it is easy to stretch between iron atoms and iron atoms in a specific direction (typically, the orientation direction) in the crystal lattice, and nitrogen is stretched between the stretched iron atoms and iron atoms. , And it becomes easy to perform nitriding substantially uniformly over the entire particle. On the other hand, when the magnetic field strength exceeds 12T, it is preferentially spent on the reaction between the constituent material of the particles (eg, Sm ₂ Fe ₁₇ ) and nitrogen rather than promoting the penetration of nitrogen into the particles, and excessive nitriding To do. Excessive nitridation may cause α-Fe to be formed and deteriorate the magnetic properties. However, when the magnetic field strength is 12 T or less, excessive nitridation on the surface side of each particle can be suppressed, and the magnet powder has excellent magnetic properties. Can be manufactured.

  (3) As a manufacturing method of the powder for magnets of embodiment, it is mentioned that the heat processing temperature in the said magnetic field heat processing process is 280 degreeC or more and 430 degrees C or less.

When the heat treatment temperature is 280 ° C. or higher, the nitrogen in the nitrogen holding region of each rare earth-iron-based alloy particle can be easily diffused inside, and nitriding can be performed substantially uniformly over the entire particle. On the other hand, when the heat treatment temperature is 430 ° C. or lower, the reaction between the constituent material of the particles (for example, Sm ₂ Fe _{17 and the} like) and nitrogen can be suppressed, and excessive nitridation on the surface side of each particle can be suppressed. Can be produced.

  (4) As a manufacturing method of the powder for magnets of embodiment, the heat processing time in the said magnetic field heat processing process is 1 hour or more and 10 hours or less.

When the heat treatment time is 1 hour or longer, it is easy to diffuse nitrogen in the nitrogen holding region of each rare earth-iron-based alloy particle to the inside, and nitriding can be performed uniformly over the entire particle. On the other hand, when the heat treatment time is 10 hours or less, the reaction between the constituent material of the particles (for example, Sm ₂ Fe _{17 and the} like) and nitrogen can be suppressed, and excessive nitridation on the surface side of each particle can be suppressed. Can be produced.

  (5) As a manufacturing method of the powder for magnets of embodiment, it is mentioned that the average particle diameter of the said rare earth-iron-type alloy particle is 30 micrometers or more and 300 micrometers or less.

  When the average particle diameter of the rare earth-iron-based alloy particles is 30 μm or more, the specific surface area can be made smaller than that of the fine particles to easily suppress the oxidation of the powder, and the handling in an oxidizing atmosphere can be facilitated. Further, when the alloy powder is compression-molded, a powder compact can be easily formed, and a high-density rare earth magnet can be manufactured. On the other hand, when the average particle diameter of the rare earth-iron-based alloy particles is 300 μm or less, nitrogen easily diffuses into the crystal grains in the magnetic field heat treatment step. In particular, uniform nitriding over the entire alloy particles can be performed efficiently in a short time.

  (6) The method for producing a rare earth magnet of the embodiment includes a preparation step, a hydrogenation step, a forming step, a dehydrogenation step, a surface nitriding step, and a magnetic field heat treatment step. The preparation step is a step of preparing a rare earth-iron alloy powder composed of a plurality of rare earth-iron alloy particles containing a rare earth element. The hydrogenation step is a step of forming the hydrogenated powder by heat-treating the rare earth-iron-based alloy powder in an atmosphere containing hydrogen element at a temperature equal to or higher than the hydrogen disproportionation temperature of the rare-earth-iron-based alloy. . The forming step is a step of compression-molding the hydrogenated powder to form a hydrogenated powder molded body. The dehydrogenation step is a step of forming the dehydrogenated powder compact by heat-treating the hydrogenated powder compact in an inert atmosphere or a reduced pressure atmosphere at a temperature equal to or higher than the recombination temperature of the hydrogenated powder compact. is there. In the surface nitriding step, the dehydrogenated powder compact is heat-treated at a temperature not lower than the nitriding temperature of the dehydrogenated powder compact and not higher than the nitrogen disproportionation temperature in an atmosphere containing nitrogen element. This is a step of forming a nitride powder molded body having a nitrogen holding region in which nitrogen penetrates in the vicinity of the surface of each powder molded body particle constituting. In the magnetic field heat treatment step, the nitride powder compact is heat-treated in a nitrogen-free atmosphere by applying a constant magnetic field, and nitrogen in the nitrogen holding region is spread over the entire dehydrogenated powder compact particles. This is a step of forming a magnet material that is substantially uniformly nitrided.

  According to the above configuration, in forming the nitrided magnet material, the nitriding process can be stably performed by performing the two-step process of the surface nitriding process → the magnetic field heat treatment process, and the magnet material can be produced with high productivity. Can be manufactured.

[Details of the embodiment of the present invention]
Details of the embodiment of the present invention will be described below. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to the claim are included.

<Embodiment 1>
[Method for producing magnet powder]
The method for producing a magnet powder is a method for producing a magnet powder for use in a rare earth magnet, and includes a preparation step, a surface nitriding step, and a magnetic field heat treatment step. Hereafter, each process is demonstrated in detail based on FIG.

(Preparation process)
The preparation step is a step of preparing a rare earth-iron alloy powder 10 composed of a plurality of rare earth-iron alloy particles 11 containing a rare earth element as an additive element (see the left diagram in FIG. 1). The rare earth-iron alloy powder 10 may be selected from the constituent elements of the rare earth-iron alloy so as to have a desired composition.

  The rare earth element contained as the additive element is at least one element selected from Sc, Y, lanthanoids and actinoids. In particular, when at least one element selected from Sm, Nd, Pr, Ce, Dy, Tb and Y is included, it is preferable in terms of magnetic properties. In particular, it is preferable to contain Sm or Nd as an essential element from the viewpoint of raw material cost and magnetic properties. The rare earth element may be a single element or a combination of a plurality of elements. The combination of a plurality of elements refers to, for example, replacing a part of a rare earth element with another rare earth element. The rare earth element content is more than 0% by mass, preferably 5% by mass or more, more preferably 15% by mass or more, and preferably less than 25% by mass.

  Iron (Fe) contained as an additive element is a form of only Fe (pure iron) or a part of Fe is replaced with at least one element selected from Co, Ga, Cu, Al, Si and Nb, The form which consists of Fe and the said substitution element etc. are mentioned. By replacing part of Fe with the above element, the magnetic properties and corrosion resistance of the rare earth magnet can be improved. Further, a part of Fe may be substituted with at least one element selected from Ti, Mn, Ni and the like. The total content of iron and the above substitution elements is 80% by mass or more. When the content is 80% by mass or more, hard rare earth elements are relatively reduced, and the alloy powder is easily compression-molded. On the other hand, when the total content of iron and the above-described substitutional elements is 95% by mass or less, rare earth elements are relatively increased, and the magnetic properties are excellent. More preferably, the total content of iron and the above substitution elements is 85% by mass or more and 95% by mass or less.

  The size of the rare earth-iron alloy particles is relatively coarse with an average particle size of 30 μm to 300 μm. Since the average particle size of the rare earth-iron-based alloy particles is 30 μm or more, the specific surface area can be made smaller than that of the fine particles to easily suppress the oxidation of the powder, and the handling in an oxidizing atmosphere can be facilitated. Further, when the alloy powder is compression-molded, a high-density powder compact can be easily formed, and a high-density rare earth magnet can be produced. On the other hand, the size of the rare earth-iron-based alloy particles is such that the average particle size is 300 μm or less, so that nitrogen can be diffused into the crystal grains in the magnetic field heat treatment step described later. In particular, uniform nitriding over the entire alloy particles can be performed efficiently in a short time. More preferably, the average particle size of the rare earth-iron-based alloy particles is 35 μm or more and 280 μm or less, and further 50 μm or more and 200 μm or less.

The rare earth-iron-based alloy powder may be, for example, a molten metal casting ingot made of a desired rare earth-iron-based alloy (for example, Sm ₂ Fe ₁₇ , Sm ₁ Fe ₁₁ Ti ₁ ) or a foil obtained by a rapid solidification method. It can manufacture by grind | pulverizing by. Examples of the pulverizer include a jaw crusher, a jet mill, and a ball mill. The rare earth-iron alloy powder can also be produced by utilizing an atomizing method such as a gas atomizing method, or by further pulverizing a powder produced by the atomizing method. When the gas atomization method is used, a powder containing substantially no oxygen (oxygen concentration: 500 mass ppm or less) can be obtained by forming the powder in a non-oxidizing atmosphere. A known production method can be used for the production of the rare earth-iron alloy powder. By appropriately changing the pulverization conditions and the production conditions, the particle size distribution and particle shape of the magnet powder can be adjusted. For example, when the atomizing method is used, it is easy to produce a powder having a high sphericity and excellent filling properties at the time of molding. Each particle constituting the rare earth-iron-based alloy powder may be a polycrystal or a single crystal. The particles made of a polycrystal can be appropriately heat treated to form particles made of a single crystal.

  As the rare earth-iron-based alloy powder, one subjected to hydrogenation → dehydrogenation can be used. First, the rare earth-iron-based alloy powder is subjected to a hydrogenation treatment to be separated into a rare earth element hydrogen compound and iron (or iron and an iron compound). The rare earth-iron-based alloy that has been subjected to the hydrogenation process changes to a structure in which a phase of a rare earth element hydrogen compound and a phase of an iron-containing material (including pure iron) containing iron are mixed. Next, the rare earth-iron-based alloy powder subjected to the hydrogenation treatment is subjected to a dehydrogenation treatment, whereby the rare-earth-iron-based alloying can be completely caused and a rare earth magnet having excellent magnetic properties can be obtained. The conditions for the hydrogenation treatment and dehydrogenation treatment will be described in detail in Embodiment 2.

(Surface nitriding process)
In the surface nitriding step, the rare earth-iron alloy powder 10 prepared in the above preparatory step is heat treated at a temperature not lower than the nitriding temperature of the rare earth-iron alloy and not higher than the nitrogen disproportionation temperature in an atmosphere containing nitrogen element. This is a step of forming the powder 20 (see the middle diagram of FIG. 1). The nitrided powder 20 has a nitrogen holding region 21 in which each rare earth-iron-based alloy particle 11 has nitrogen penetrated in the vicinity of the surface by the heat treatment.

The atmosphere containing nitrogen element may be a single atmosphere of only nitrogen (N ₂ ), an ammonia (NH ₃ ) atmosphere, or a mixed gas of a gas containing a nitrogen element such as nitrogen (N ₂ ) or ammonia and an inert gas such as Ar. An atmosphere or a mixed gas atmosphere of a gas containing nitrogen and hydrogen (H ₂ ) can be given. In particular, since the atmosphere containing hydrogen gas is a reducing atmosphere, oxidation and excessive nitriding of the generated nitride can be prevented, which is preferable.

The heat treatment temperature is equal to or higher than the temperature at which the rare earth-iron alloy reacts with the nitrogen element (nitriding temperature), the nitrogen disproportionation temperature (the temperature at which the iron-containing material and the rare earth element are separated and independently reacted with the nitrogen element) ) The following. The nitriding temperature and the nitrogen disproportionation temperature vary depending on the composition of the rare earth-iron alloy. For example, when the rare earth-iron alloy is Sm ₂ Fe ₁₇ , Sm ₁ Fe ₁₁ Ti ₁ , the temperature during the heat treatment is 200 ° C. or higher and 550 ° C. or lower. The heat treatment temperature is more preferably 300 ° C. or more and 500 ° C. or less, and further 320 ° C. or more and 400 ° C. or less. The holding time during the heat treatment is 10 minutes to 600 minutes, more preferably 20 minutes to 550 minutes, and further 40 minutes to 480 minutes.

  The nitrided powder 20 obtained by the surface nitriding step includes a nitrogen holding region 21 formed from the surface of each rare earth-iron-based alloy particle 11 toward the inside as shown in the middle diagram of FIG. And an internal region 22 following the region 21. The nitrogen holding region 21 is a region where nitrogen has entered from the surface of each particle 11. The internal region 22 is a region where nitrogen does not exist or the amount of nitrogen is insufficient compared to the nitrogen holding region 21 (the nitrogen holding region 21 holds excessive nitrogen (excess nitridation)). Usually, when heat treatment is performed in an atmosphere containing nitrogen element, a gradient of nitrogen potential is generated from the surface to the inside of each particle, and the existence state of nitrogen changes from the surface to the inside. That is, nitriding tends to proceed on the surface side of each particle, and nitriding becomes difficult as it goes inward.

(Magnetic heat treatment process)
The magnetic field heat treatment step is a step of forming the magnet powder 1 by heat-treating the nitride powder 20 obtained in the surface nitriding step by applying a certain magnetic field in an atmosphere not containing nitrogen element (FIG. 1). (See the right figure). In the magnet powder 1, the nitrogen in the nitrogen holding region 21 of each rare earth-iron-based alloy particle 11 is diffused to the inner region 22 by the heat treatment, and is nitrided substantially uniformly over the entire particle 11. It is composed of rare earth-iron-nitrogen alloy particles 31.

The atmosphere containing no nitrogen element may be a vacuum atmosphere having a degree of vacuum of 10 ⁻² Pa or less. More preferable vacuum degree of the vacuum atmosphere is 5 × 10 ⁻³ Pa or less, and further 1 × 10 ⁻³ Pa or less. By performing the heat treatment in a vacuum atmosphere that does not contain a nitrogen element, it is possible to further suppress the penetration of nitrogen into each rare earth-iron-based alloy particle and to suppress the excessive nitridation of the surface of each particle.

As for the temperature of heat processing, 280 degreeC or more and 430 degrees C or less are mentioned. When the heat treatment temperature is 280 ° C. or more, nitrogen in the nitrogen holding region of each rare earth-iron alloy particle can be diffused to the inner region, and nitridation can be performed substantially uniformly over the entire particle. be able to. On the other hand, when the heat treatment temperature is 430 ° C. or lower, the reaction between the constituent material of the particles (such as Sm ₂ Fe ₁₇ ) and nitrogen can be suppressed, and excessive nitridation on the surface side of each particle can be suppressed. When excessive nitriding is performed, α-Fe is formed and the magnetic properties are deteriorated. More preferable heat treatment temperature is 300 ° C. or more and 400 ° C. or less, and further 320 ° C. or more and 380 ° C. or less.

The heat treatment time is 1 hour or more and 10 hours or less. When the heat treatment time is 1 hour or more, nitrogen in the nitrogen holding region of each rare earth-iron alloy particle can be diffused to the inner region, and nitridation can be performed substantially uniformly over the entire particle. be able to. On the other hand, when the heat treatment time is 10 hours or less, the reaction between the constituent material of the particles (such as Sm ₂ Fe ₁₇ ) and nitrogen can be suppressed, and excessive nitridation on the surface side of each particle can be suppressed. More preferable heat treatment time is 1.5 hours or more and 8 hours or less, and further 3 hours or more and 6 hours or less.

In the magnetic field heat treatment step, the heat treatment is performed in a state where a constant magnetic field is applied to the nitride powder. The magnetic field strength is a strong magnetic field of 2T or more and 12T or less. When the magnetic field strength is 2T or more, the crystal lattice of the crystals constituting each rare earth-iron alloy particle can be extended in one direction, and the nitrogen in the nitrogen holding region of each particle can be diffused to the internal region. The nitridation can be performed substantially uniformly over the entire particle. The larger the magnetic field strength, the easier the crystal lattice is stretched in one direction, the easier it is for nitrogen atoms to penetrate between the stretched iron atoms and the iron atoms, and nitridation is performed substantially uniformly over the entire particle. On the other hand, when the magnetic field strength is 12 T or less, the reaction between the constituent material of the particles (Sm ₂ Fe _{17 and the} like) and nitrogen can be suppressed, and excessive nitridation on the surface side of each particle can be suppressed. More preferable magnetic field strength is 3T or more and 10T or less, and further 4T or more and 7T or less. Such a strong magnetic field can be stably formed by using, for example, a high-temperature superconducting magnet.

  As shown in the right diagram of FIG. 1, the magnet powder 1 obtained by the magnetic field heat treatment step is a rare earth-iron-nitrogen alloy in which each rare earth-iron alloy particle 11 is uniformly nitrided throughout. It is composed of particles 31. In the first embodiment, when nitriding the rare earth-iron-based alloy powder, first, heat treatment is performed in an atmosphere containing nitrogen element to form a region where nitrogen enters from the surface of each particle, and then nitrogen element is introduced. By performing a heat treatment in an atmosphere that does not contain and diffusing the nitrogen into the interior of each particle, nitriding can be performed substantially uniformly over the entire particle. When diffusing nitrogen, by applying a magnetic field, the diffusion rate of nitrogen can be increased, and magnet powder can be manufactured with high productivity.

  The magnet powder can be suitably used for rare earth magnets. The rare earth magnet can be obtained by compression-molding or injection-molding a mixture of the magnet powder and the binder resin to form a magnet material, and appropriately magnetizing the magnet material.

<Embodiment 2>
[Production method of rare earth magnet]
The method for manufacturing a rare earth magnet includes a preparation step, a hydrogenation step, a forming step, a dehydrogenation step, a surface nitridation step, and a magnetic field heat treatment step. Hereinafter, each step will be described in detail with reference to FIG.

(Preparation process)
The preparation step is a step of preparing a rare earth-iron alloy powder 10 composed of a plurality of rare earth-iron alloy particles 11 containing a rare earth element as an additive element (see the upper left diagram in FIG. 2). The rare earth-iron-based alloy powder 10 to be prepared is the same as in the first embodiment.

(Hydrogenation process)
In the hydrogenation step, the rare earth-iron alloy powder 10 prepared in the above preparation step is heat-treated at a temperature equal to or higher than the hydrogen disproportionation temperature of the rare earth-iron alloy in an atmosphere containing hydrogen element, and the hydrogenated powder 120 is obtained. (See the upper middle diagram of FIG. 2).

Atmosphere containing hydrogen elements, hydrogen and a single atmosphere (H ₂₎ only, a mixed atmosphere of inert gas and the like, such as hydrogen (H ₂₎ and Ar and N _2. The temperature during the heat treatment is set to a temperature at which the disproportionation reaction of the rare earth-iron alloy proceeds, that is, the disproportionation temperature or higher. The disproportionation reaction is a reaction in which a rare earth element hydrogen compound and Fe (or Fe and Fe compound) are separated by preferential hydrogenation of the rare earth element, and the lower limit temperature at which this reaction occurs is defined as the disproportionation temperature. Call. The disproportionation temperature varies depending on the composition of the rare earth-iron alloy and the type of rare earth element. For example, when the rare earth-iron-based alloy is Sm ₂ Fe ₁₇ , Sm ₁ Fe ₁₁ Ti ₁ , the temperature may be 600 ° C. or higher. When the temperature during the heat treatment is in the vicinity of the disproportionation temperature, a layered form is obtained in which the phase of the rare earth element hydrogen compound and the phase of the iron-containing material have a multilayer structure. When the temperature is increased to a disproportionation temperature + 100 ° C. or more, as shown in FIG. 2, a phase 121 of an iron-containing material is used as a parent phase, and a phase 122 of a granular rare earth element hydrogen compound is dispersed in the parent phase. An existing dispersion form is obtained. The higher the temperature during heat treatment, the more the matrix of the iron-containing material progresses, and a powder with excellent moldability can be obtained. However, if the temperature is too high, problems such as melting and fixing of the powder occur, and subsequent dehydrogenation Since recombination becomes difficult, 1100 degrees C or less is preferable. When the rare earth-iron-based alloy is Sm ₂ Fe ₁₇ , Sm ₁ Fe ₁₁ Ti ₁ , if the temperature during the heat treatment is made relatively low at 700 ° C. or more and 900 ° C. or less, it becomes a powder with a fine structure and has a high coercive force. A magnet is easily obtained. Examples of the holding time during the heat treatment include 0.5 hours or more and 5 hours or less. Known heat disproportionation conditions can be applied to this heat treatment. In addition to a general heating furnace, an oscillating furnace such as a rotary kiln furnace can be used for the heat treatment. When a rocking furnace is used, even if a relatively large material such as a cast ingot is used, it is pulverized by embrittlement as the hydrogenation proceeds, and becomes powder.

  Each particle constituting the hydrogenated powder obtained by the heat treatment has an iron-containing main component and a content of 60% by volume or more. When the content of the iron-containing material is 60% by volume or more, the hard rare earth element hydrogen compound is relatively reduced, and the iron-containing material is easily deformed during compression molding. On the other hand, when the content of the iron-containing material is 75% by volume or less, rare earth elements are relatively increased, and the magnetic properties are excellent. The content of the iron-containing material is more preferably 63% by volume to 72% by volume, and further 65% by volume to 70% by volume. The content of the rare earth element hydrogen compound is more than 0% by volume, preferably 10% by volume or more, preferably 40% by volume or less, and more preferably less than 30% by volume.

(Molding process)
The forming step is a step in which the hydrogenated powder 120 obtained by the hydrogenation step is compression-molded to obtain a hydrogenated powder molded body 130 (see the upper right diagram in FIG. 2). By compressing and molding the hydrogenated powder 120, a high-density hydrogenated powder compact 130 is obtained. Molding pressure at the time of compression molding, and be, for example, 294MPa (3ton / cm ²⁾ or more 1960MPa (20ton / cm ²⁾ or less. A more preferable molding pressure is 588 MPa (6 ton / cm ² ) or more and 1470 MPa (15 ton / cm ² ) or less. In addition, the relative density of the hydrogenated powder molded body 130 is, for example, about 80% to 95%, particularly 88% or more. The higher the relative density of the hydrogenated powder molded body 130, the higher the density of the hydrogenated powder molded body 130 (magnet material 160), which is preferable in that a rare earth magnet having a high magnetic phase content can be obtained. Here, “relative density” means the actual density (percentage of [actual density of powder compact / true density of alloy]) with respect to the true density of the rare earth-iron alloy constituting the hydrogenated powder compact 130. To do. In addition, by appropriately heating the molding die during compression molding, the deformation of the powder can be promoted, and a high-density hydrogenated powder compact 130 can be easily obtained.

(Dehydrogenation process)
In the dehydrogenation step, the hydrogenated powder molded body 130 obtained by the molding step is heat-treated at a temperature equal to or higher than the recombination temperature of the hydrogenated powder molded body 130 in an inert atmosphere or a reduced pressure atmosphere. This is a step of forming the molded body 140 (see the middle left diagram and the right diagram in FIG. 2).

The atmosphere for the dehydrogenation treatment is a non-hydrogen atmosphere so that each hydrogen can be efficiently removed without reacting with the hydrogenated powder. The non-hydrogen atmosphere includes an inert atmosphere or a reduced pressure atmosphere. For example, an inert gas atmosphere such as Ar or N ₂ or a vacuum atmosphere having a vacuum degree of 10 Pa or less can be used. The vacuum degree of a more preferable vacuum atmosphere is 1 Pa or less, and further 0.1 Pa or less. In particular, when dehydrogenation is performed in a reduced-pressure atmosphere (vacuum atmosphere), the recombination reaction further proceeds and the rare earth element hydrogen compound hardly remains. The temperature of the heat treatment during the dehydrogenation treatment is set to be equal to or higher than the recombination temperature of the hydrogenated powder molded body 130 (the temperature at which the separated iron-containing material and rare earth element combine). Although the recombination temperature varies depending on the composition of the particles constituting the hydrogenated powder molded body 130, it is typically 600 ° C or higher and 1000 ° C or lower, more preferably 650 ° C or higher and 850 ° C or lower, and further 700 ° C or higher and 800 ° C or lower. And so on. The heat treatment time for the dehydrogenation treatment is, for example, from 10 minutes to 10 hours, more preferably from 30 minutes to 5 hours, and further from 1 hour to 3 hours. The relative density of the dehydrogenated powder molded body 140 is substantially equal to the relative density of the hydrogenated powder molded body 130 although it varies somewhat depending on the temperature and time of the heat treatment.

(Surface nitriding process)
In the surface nitriding step, the dehydrogenated powder molded body 140 obtained by the above dehydrogenation treatment is subjected to heat treatment at a temperature not lower than the nitriding temperature of the dehydrogenated powder molded body 140 and not higher than the nitrogen disproportionation temperature in an atmosphere containing nitrogen element. This is a step of forming the nitride powder molded body 150 (see the second and third diagrams from the left in the middle of FIG. 2). The nitride powder molded body 150 includes a nitrogen holding region 151 in which nitrogen enters each of the dehydrogenated powder molded body particles constituting the dehydrogenated powder molded body 140 and an inner region 152 following the nitrogen holding region 151. Have The nitrogen holding region 151 is in a state where a larger amount of nitrogen has entered than the inner region 152. The heat treatment conditions in the surface nitriding step are the same as those in the first embodiment.

(Magnetic heat treatment process)
The magnetic field heat treatment step is a step of forming the magnet material 160 by applying a certain magnetic field to the nitride powder molded body 150 obtained in the surface nitridation step in a nitrogen-free atmosphere and applying a heat treatment (see FIG. (See the second figure from the middle right of Fig. 2 and the right figure). In the magnet material 160, nitrogen in the nitrogen holding region 151 of each dehydrogenated powder compact particle is diffused to the inner region 152, and is substantially uniformly nitrided over the entire particle. The heat treatment conditions in the magnetic field heat treatment step are the same as in the first embodiment.

  A rare earth magnet 170 is obtained by appropriately magnetizing the magnet material 160 (see the lower diagram of FIG. 2). The rare earth magnet 170 obtained by using the magnet material 160 of Embodiment 2 has excellent magnetic properties because the magnet material 160 is substantially uniformly nitrided throughout.

<Test example>
Test example 1
Various magnet powders containing rare earth elements were prepared, and the obtained magnet powders were compression molded to examine the magnetic properties of the magnet powders. The magnet powder was prepared according to the following preparation process ⇒ surface nitriding process ⇒ magnetic field heat treatment process.

Sm ₂ Fe ₁₇ alloy powder containing 24% by mass of Sm was prepared. Table 1 shows the average particle diameter of the particles constituting the Sm ₂ Fe ₁₇ alloy powder. This Sm ₂ Fe ₁₇ alloy powder was heat-treated at 320 ° C. for 3 hours in a mixed gas atmosphere of NH ₃ : H ₂ = 1: 3 to form a nitrided powder. This nitrided powder is subjected to a heat treatment under the heat treatment conditions (temperature, time) shown in Table 1 in a vacuum atmosphere with a degree of vacuum of 1 × 10 ⁻³ Pa and a magnetic field (T) shown in Table 1 is applied. Powders (Sample Nos. 1 to 7, 101 to 106) were prepared.

  The prepared sample No. The magnet powders 1 to 7 and 101 to 106 are mixed with a binder resin to form a mixture, and the magnetic powder is analyzed by crystal phase analysis by X-ray diffraction using this mixture to check the composition (appearance phase). It was. The results are shown in Table 2.

  Further, the nitridation state of each particle constituting the magnet powder was observed by EPMA (Electron Probe Micro Analyzer: X-ray microanalyzer). The results are shown in Table 2.

Each sample was magnetized with a pulse magnetic field of 3.98 MA / m (≈49.9 kOe), and then the coercive force (kOe =) was measured with a vibrating sample magnetometer (VSM-5SC-5HF type, manufactured by Toei Industry Co., Ltd.). (10 ³ / 4π) kA / m) and remanent magnetization (emu / g = A · m ² / kg) were measured. The results are shown in Table 2.

Sample No. As shown in Fig. 8, a magnet material was prepared by the following preparation process ⇒ hydrogenation process ⇒ molding process ⇒ dehydrogenation process ⇒ surface nitridation process ⇒ magnetic field heat treatment process. First, an Sm ₂ Fe ₁₇ alloy powder containing 24% by mass of Sm was prepared. The average particle diameter of the particles constituting the Sm ₂ Fe ₁₇ alloy powder was 150 μm. Next, a hydrogenated powder was formed by subjecting the Sm ₂ Fe ₁₇ alloy powder to a hydrogenation treatment by performing a heat treatment at 700 ° C. for 2 hours in a hydrogen atmosphere. The hydrogenated powder was filled in a mold and compression molded to form a hydrogenated powder molded body. The surface pressure during this compression molding was 980 MPa (10 ton / cm ² ). The relative density of the obtained hydrogenated powder molded body was 85%. Subsequently, the hydrogenated powder compact is subjected to heat treatment at 750 ° C. for 1.5 hours in a vacuum atmosphere of 3 × 10 ⁻⁵ Pa to form a dehydrogenated powder compact. did. The relative density of the obtained dehydrogenated powder molded body was 87%. This dehydrogenated powder compact was heat-treated at 320 ° C. for 3 hours in a mixed gas atmosphere of NH ₃ : H ₂ = 1: 3 to form a nitride powder compact. The relative density of the obtained nitrided powder molded body was 85%. This nitrided powder compact was heat-treated at 320 ° C. for 5 hours in a vacuum atmosphere with a vacuum degree of 1 × 10 ⁻³ Pa and a magnetic field with a magnetic field strength of 5 T was applied to produce a magnet material. Sample No. The production conditions of 8 are also shown in Table 1.

The prepared sample No. As for the magnet material No. 8, the powder constituting the magnet material was subjected to crystal phase analysis by X-ray diffraction, and the constituent composition (appearing phase) was examined. The results are shown in Table 2. Further, after magnetizing the obtained magnet material with a pulse magnetic field of 3.97 MA / m (≈49.8 kOe), a coercive force (kOe) is measured by an AC B-H magnet material evaluation device (manufactured by Toei Industry Co., Ltd.). = (10 ³ / 4π) kA / m) and remanent magnetization (T). The results are also shown in Table 2.

As shown in Table 2, in nitriding the Sm ₂ Fe ₁₇ alloy powder, a surface nitridation step that mainly penetrates into the surface of nitrogen particles and a magnetic field heat treatment that mainly diffuses nitrogen into the particles Sample No. 2 was divided into two steps and the magnetic field heat treatment step was performed under specific conditions. In Nos. 1 to 8, Sm ₂ Fe ₁₇ N ₃ was present uniformly throughout the entire particle. It can be seen that both the coercive force and the remanent magnetization are high due to the presence of Sm ₂ Fe ₁₇ N ₃ uniformly throughout the entire particle.

Even if nitriding was divided into two steps, the sample No. in which no magnetic field was applied in the magnetic field heat treatment step was used. In 103, unreacted Sm ₂ Fe ₁₇ was present, and the magnetic properties were low. This is considered to be because nitrogen could not be diffused to the inside because no magnetic field was applied. In the magnetic field heat treatment step, the sample No. In 104, α-Fe and a-Sm (amorphous Sm) existed in addition to Sm—Fe—N alloys having different amounts of nitrogen, resulting in unevenness in the amount of nitrogen and low magnetic properties. This is probably because the magnetic field strength was too high, so that nitrogen could be diffused into the interior, but the surface side was excessively nitrided with the diffusion of nitrogen. In addition, even if nitriding is divided into two steps, the sample No. 1 in which the heat treatment temperature is lowered and the heat treatment time is lengthened in the magnetic field heat treatment step. In No. 105, nitriding did not occur and the magnetic characteristics were low. On the other hand, in the magnetic field heat treatment step, Sample No. In 106, α-Fe and a-Sm (amorphous Sm) existed in addition to the Sm—Fe—N alloys having different amounts of nitrogen, resulting in unevenness in the amount of nitrogen and poor magnetic properties. That is, it is considered that when heat treatment is performed by applying a magnetic field, nitrogen can be uniformly diffused over the entire particle by setting a specific heat treatment temperature and heat treatment time. Furthermore, sample No. 1 in which the average particle size of each particle is too small. In Sample 101, α-Fe and a-Sm (amorphous Sm) are present in addition to Sm—Fe—N alloys having different nitrogen contents, and the amount of nitrogen is uneven and the average particle size is too large. . In 102, nitrogen could not be diffused to the inside, and both had low magnetic properties.

  Based on the above results, the nitriding treatment is divided into two steps: a surface nitriding step that mainly penetrates into the surface of nitrogen particles, and a magnetic field heat treatment step that mainly diffuses nitrogen into the particles. It can be seen that in the heat treatment step, it is preferable to apply a specific magnetic field to a specific heat treatment temperature and heat treatment time.

Test example 2
Sample No. produced in Test Example 1 Yield was obtained for 8 magnet materials. For comparison, a magnet material was prepared by a conventional procedure of preparation step ⇒ hydrogenation step ⇒ molding step ⇒ dehydrogenation step ⇒ nitridation step (sample No. 201). Yield was calculated for 201 magnet materials. Sample No. According to the manufacturing method of the magnet material of No. 201, sample No. 1 was that a 5T magnetic field was applied during the heat treatment in the dehydrogenation process, and that the heat treatment was performed in the nitriding process with a 5T magnetic field applied in a nitrogen atmosphere. 8 is the main difference from the manufacturing method of the magnet material of No. 8, and other manufacturing conditions are as follows. It is the same as 8. About both produced samples, coercive force and residual magnetization were measured by the measuring method mentioned above. Yield was defined as a non-defective product when the coercive force and residual magnetization both satisfy the specified values, and a defective product when the coercive force and residual magnetization did not satisfy the specified value. As a result, the sample No. produced by the conventional manufacturing method was obtained. No. 201 is 65%, and the sample No. produced by the manufacturing method of the present embodiment is used. 8 was 95%. That is, it can be seen that the manufacturing method of the present embodiment can manufacture a magnet material having excellent magnetic characteristics with higher productivity than the conventional method.

  The manufacturing method of the magnet powder of the present invention and the manufacturing method of the rare earth magnet of the present invention can be applied to various motors, in particular, permanent magnets used in high-speed motors included in hybrid vehicles (HEV) and hard disk drives (HDD). It can utilize suitably for manufacture of a raw material and a raw material.

DESCRIPTION OF SYMBOLS 1 Magnet powder 10 Rare earth-iron system alloy powder 11 Rare earth-iron system alloy particle 20 Nitride powder 21 Nitrogen retention area 22 Inner area 31 Rare earth-iron-nitrogen system alloy particle 120 Hydrogenated powder 121 Phase of iron inclusion 122 Rare earth element Phase of hydrogen compound 130 Hydrogenated powder compact 140 Dehydrogenated powder compact 150 Nitrided powder compact 151 Nitrogen retention area 152 Internal area 160 Magnet material 170 Rare earth magnet

Claims (6)

A preparation step of preparing a rare earth-iron alloy powder composed of a plurality of rare earth-iron alloy particles containing a rare earth element;
The rare earth-iron-based alloy powder is heat-treated in an atmosphere containing nitrogen element at a temperature not lower than the nitriding temperature of the rare-earth-iron-based alloy and not higher than the nitrogen disproportionation temperature. A surface nitriding step for forming a nitrided powder having a nitrogen holding region in which nitrogen penetrates in the vicinity of the surface;
The nitride powder is heat-treated in a nitrogen-free atmosphere by applying a constant magnetic field to diffuse the nitrogen in the nitrogen holding region to the inside of the rare earth-iron alloy particles, the rare earth-iron system A magnetic powder manufacturing method comprising: a magnetic field heat treatment step of forming a magnetic powder composed of rare earth-iron-nitrogen based alloy particles nitrided substantially uniformly over the entire alloy particles.   The method for producing a magnet powder according to claim 1, wherein the magnetic field strength in the magnetic field heat treatment step is 2T or more and 12T or less.   The method for producing a magnet powder according to claim 1 or 2, wherein a heat treatment temperature in the magnetic field heat treatment step is 280 ° C or higher and 430 ° C or lower.   The method for manufacturing a magnet powder according to any one of claims 1 to 3, wherein a heat treatment time in the magnetic field heat treatment step is 1 hour or more and 10 hours or less.   The method for producing a magnet powder according to any one of claims 1 to 4, wherein the rare earth-iron-based alloy particles have an average particle size of 30 µm or more and 300 µm or less. A preparation step of preparing a rare earth-iron alloy powder composed of a plurality of rare earth-iron alloy particles containing a rare earth element;
A hydrogenation step of heat-treating the rare earth-iron alloy powder in a hydrogen element-containing atmosphere at a temperature equal to or higher than the hydrogen disproportionation temperature of the rare earth-iron alloy to form a hydrogenated powder;
Compression molding the hydrogenated powder to form a hydrogenated powder molded body,
A dehydrogenation step of forming a dehydrogenated powder molded body by heat-treating the hydrogenated powder molded body at a temperature equal to or higher than a recombination temperature of the hydrogenated powder molded body in an inert atmosphere or a reduced pressure atmosphere;
The dehydrogenated powder forming the dehydrogenated powder compact by heat-treating the dehydrogenated powder compact in a nitrogen element-containing atmosphere at a temperature not lower than the nitriding temperature of the dehydrogenated powder compact and not higher than the nitrogen disproportionation temperature. A surface nitridation step in which each of the molded body particles forms a nitrided powder molded body having a nitrogen holding region in which nitrogen penetrates in the vicinity of the surface;
The nitride powder compact is heat-treated in a nitrogen-free atmosphere by applying a constant magnetic field so that nitrogen in the nitrogen holding region is substantially uniform over the entire dehydrogenated powder compact particles. A method for producing a rare earth magnet comprising a magnetic field heat treatment step for forming a nitrided magnet material.

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