JP2019009313A - Manufacturing method of rare-earth magnet, and rare-earth magnet - Google Patents

Abstract

To provide a manufacturing method of rare-earth magnet having high density and excellent in shape retention, and to provide a rare-earth magnet.SOLUTION: A manufacturing method of rare-earth magnet includes a preparation step of preparing a foil of Nd-Fe-B based alloy of 25 μm or less having a Nd-Fe-B phase as a main phase, a pulverization step of pulverizing foils of the Nd-Fe-B based alloy and obtaining flaky powder P thereof passed through the sieve mesh having an opening of two times or more of the thickness of the foils, a hydrogen treatment step of hydrogenating the Nd-Fe-B based alloy, a blending step of blending a solid lubricant to the powder of the Nd-Fe-B based alloy subjected to hydrogen treatment and obtaining mixed powder, a molding step of obtaining a hydrogenation compact by pressure molding the mixed powder, and a dehydrogenation step of obtaining a magnet molding having a Nd-Fe-N phase as a main phase, by performing dehydrogenation processing of the hydrogenation compact.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a rare earth magnet and a rare earth magnet.

As permanent magnets used in motors and generators, rare earth magnets containing rare earth elements and iron, and using rare earth-iron alloys with a rare earth-iron compound as the main phase are widely used. . As rare earth magnets, typically, Nd—Fe—B magnets (neodymium magnets) whose main phase is an Nd—Fe—B compound (eg, Nd ₂ Fe ₁₄ B phase), Sm—Fe—N Sm—Fe—N magnets having a main phase of a compound (eg, Sm ₂ Fe ₁₇ N ₃ phase) are known. As the rare earth magnets, the mainstream is a sintered magnet obtained by pressure-molding and sintering a rare earth-iron alloy magnetic powder, and a bonded magnet obtained by mixing a magnetic powder with a binder and then pressing and solidifying the binder. . Recently, a dust magnet in which magnetic powder of a rare earth-iron alloy is pressure-molded has been proposed (see, for example, Patent Document 1).

  Patent Document 1 discloses a method for producing a rare earth magnet. A raw material rare earth-iron alloy powder is subjected to a hydrogenation (HD) treatment, and then subjected to pressure molding, and the compact is dehydrogenated ( The manufacturing technology of the dust magnet which processes DR: Desorption-Recombination is described. According to the manufacturing technique described in this document, the formability can be improved by hydrogenating a rare earth-iron-based alloy, and a high-density powder compact (magnet) can be formed by pressure-forming the hydrogenated alloy powder. Molded body) can be obtained, and the density of the rare earth magnet can be increased.

JP2015-128118A

  There is a demand for further enhancement of performance of rare earth magnets, and development of rare earth magnets not only having excellent magnetic properties but also high density and excellent shape retention is desired.

  Since the bond magnet contains a resin as a binder, the relative density is lowered. For this reason, there is a problem that the proportion of the magnetic powder of the Sm—Fe—N alloy decreases, and the magnetic properties are reduced accordingly. Moreover, since the resin used as a binder has low thermal stability, the use temperature of the magnet may be limited.

On the other hand, the dust magnet does not require a binder, and the above problems of the bond magnet can be solved by applying the above-described dust magnet manufacturing technology. In the case of a Nd-Fe-B-based dust magnet, the Nd-Fe-B-based alloy powder as a raw material is subjected to a hydrogenation treatment, and the Nd-Fe-B-based compound (Nd-Fe-B Phase) is decomposed into three phases of NdH ₂ , Fe, and Fe ₂ B, thereby obtaining a mixed crystal structure in which these phases are mixed. Thus, by phase Nd-Fe-B phase and NdH ₂ phase compared to the soft Fe phase and Fe ₂ B phase and said Fe-containing material is present, have improved formability.

  However, in the prior art, depending on the raw material powder to be used, the moldability at the time of pressure molding may be insufficient, and the shape retention property that maintains the shape of the molded body may be low. Therefore, in some cases, it may be difficult to ensure sufficient shape retention strength of the rare earth magnet (powder magnet), and defects such as cracks may occur in the manufactured rare earth magnet.

  An object of the present disclosure is to provide a method of manufacturing a rare earth magnet that can increase density and improve shape retention. Another object of the present disclosure is to provide a rare earth magnet having high density and excellent shape retention.

A method for producing a rare earth magnet according to the present disclosure includes:
A preparatory step in which a molten alloy containing Nd, Fe and B is rapidly solidified to prepare a flake of an Nd—Fe—B alloy having a thickness of 25 μm or less with an Nd—Fe—B phase as a main phase;
Crushing the Nd-Fe-B-based alloy flakes to obtain a flaky Nd-Fe-B-based alloy powder that has passed through a mesh whose opening is twice or more the thickness of the flakes;
Hydrotreating the Nd-Fe-B alloy, and at least partially decomposing it into three phases of NdH ₂ , Fe, and Fe ₂ B by a disproportionation reaction;
A mixing step of obtaining a mixed powder by mixing a solid lubricant with the hydrogenated Nd-Fe-B alloy powder;
A molding step of pressing the mixed powder to obtain a hydrogenated molded body; and
A dehydrogenation step of dehydrogenating the hydrogenated molded body and recombining the phases decomposed by the hydrogenation treatment by a recombination reaction to obtain a magnet molded body having an Nd-Fe-N phase as a main phase. Prepare.

The rare earth magnet according to the present disclosure is
A rare earth magnet made of a powder compact including a powder of an Nd-Fe-B alloy,
The relative density is 83% or more,
In an arbitrary cross section, the total area of the fine powder region in which fine powder having a maximum diameter of 25 μm or less exists in the powder included in the observation visual field is 25% or more of the area of the observation visual field.

  The manufacturing method of the rare earth magnet can increase the density of the rare earth magnet and improve the shape retention. The rare earth magnet has a high density and excellent shape retention.

It is a figure for demonstrating the measuring method of the particle size of a powder in the rare earth magnet which concerns on embodiment of this invention. Sample No. It is a figure which shows the cross-sectional SEM observation image of 1-1. Sample No. It is a figure which shows the cross-sectional SEM observation image of 100. FIG. Sample No. It is a figure which shows the external appearance photograph of 1-1. Sample No. It is a figure which shows the external appearance photograph of 100. FIG.

  As a result of intensive studies by the present inventors, flaky Nd—Fe—B alloy powder obtained by pulverizing Nd—Fe—B alloy flakes having a thickness of 25 μm or less obtained by rapid solidification. It was found that the magnetic properties can be improved by using as a raw material powder. This is because when an Nd—Fe—B alloy is made into a flake having a thickness of 25 μm or less by rapid solidification, an amorphous or nanocrystalline or amorphous and nanocrystalline mixed crystal structure is easily obtained. This is because the nano-sized fine crystal Nd—Fe—B system phase is generated and the fine crystal structure is formed.

  However, it has been found that the flaky Nd—Fe—B alloy powder is inferior in formability during pressure forming and has low shape retention. The reason is considered as follows. In the case of a flaky powder, the longitudinal direction of the powder is aligned in a direction perpendicular to the pressing direction at the time of pressure molding, and the powder tends to be laminated in the thickness direction. In such a laminated state, there are many interfaces where the surfaces of the powder are in surface contact, and the area of the interface becomes large. Therefore, since the contact resistance (friction) between the powder particles is large, the powder is difficult to flow during pressure molding. In addition, peeling is likely to occur at this interface, and cracks are likely to propagate along the interface starting from the peeling portion, leading to a decrease in shape retention strength, such as cracks being easily formed in a pressure-molded molded body. .

  The present inventor improves the shape retention by increasing the fluidity of the powder during pressure molding by mixing a solid lubricant with the hydrogenated flaky Nd-Fe-B alloy powder. It was found that a rare earth magnet having high density and excellent shape retention can be obtained. The present invention has been made based on the above findings. First, embodiments of the present invention will be listed and described.

[Description of Embodiment of the Present Invention]
(1) A method for producing a rare earth magnet according to an embodiment of the present invention includes:
A preparatory step in which a molten alloy containing Nd, Fe and B is rapidly solidified to prepare a flake of an Nd—Fe—B alloy having a thickness of 25 μm or less with an Nd—Fe—B phase as a main phase;
Crushing the Nd-Fe-B-based alloy flakes to obtain a flaky Nd-Fe-B-based alloy powder that has passed through a mesh whose opening is twice or more the thickness of the flakes;
Hydrotreating the Nd-Fe-B alloy, and at least partially decomposing it into three phases of NdH ₂ , Fe, and Fe ₂ B by a disproportionation reaction;
A mixing step of obtaining a mixed powder by mixing a solid lubricant with the hydrogenated Nd-Fe-B alloy powder;
A molding step of pressing the mixed powder to obtain a hydrogenated molded body; and
A dehydrogenation step of dehydrogenating the hydrogenated molded body, recombining the phases decomposed by the hydrogenation treatment by a recombination reaction, and obtaining a magnet molded body having an Nd-Fe-B phase as a main phase; Prepare.

  According to the method for producing a rare earth magnet, a Nd—Fe—B alloy (or a powder thereof) having a Nd—Fe—B phase as a main phase is subjected to a hydrogenation treatment, and the powder is subjected to pressure forming → dehydrogenation treatment. Thus, a magnet compact (rare earth magnet) of a high-density Nd—Fe—B alloy powder that does not contain a binder can be produced. In the method for producing a rare earth magnet, the fluidity of the powder at the time of pressure molding is improved by mixing a solid lubricant with the flaky Nd—Fe—B alloy powder subjected to the hydrogenation treatment. It is possible to improve the shape retention. Therefore, the density can be increased even if the pressure (surface pressure) in pressure molding is lowered. Therefore, the manufacturing method of the rare earth magnet can increase the density of the rare earth magnet and improve the shape retention. For example, the relative density can be 83% or more, and the shape retention strength and magnetic properties (particularly residual magnetization) can be improved by increasing the density of the rare earth magnet.

  The reason why the shape retention is improved is considered as follows. In the case of flaky Nd—Fe—B alloy powder, as described above, the longitudinal direction of the powder is aligned in the direction perpendicular to the pressing direction (lateral direction) during pressure forming, and the powder is in the thickness direction. It is easy to become the lamination state laminated | stacked on. Since this laminated portion is in contact with the flaky powder surfaces, they are not firmly bonded, so they are easy to peel off, and the molded product may be chipped or destroyed by impact during the manufacturing process. . In the manufacturing method of the rare earth magnet, the contact resistance between the powders is reduced by mixing the solid lubricant, so that the powder easily flows during the pressure molding. When the powder flows, not only the compressive force in the thickness direction but also the compressive force acts in the longitudinal direction due to collision of powders adjacent in the lateral direction. As a result, the powder is pulverized, the powder is finely divided, and many fine powder regions where fine powder exists are formed in the compact. The fine powder region is a region in which fine powders having a maximum diameter of 25 μm or less are densely gathered, the contact area between the powder particles is large, and the powder particles are tightly connected and aggregated, so that a molded body due to the progress of cracks, etc. It has the effect of suppressing chipping and destruction. By increasing such a fine powder region, it is possible to suppress the occurrence of peeling and cracking and to increase the shape retention strength.

  Further, in the method for producing a rare earth magnet, an Nd—Fe—B alloy flake having a thickness of 25 μm or less obtained by rapid solidification is used as a starting material. In this case, the structure of the Nd—Fe—B alloy as a starting material is likely to be amorphous or nanocrystalline, or a mixed crystal structure of amorphous and nanocrystalline, and when this is hydrogenated / dehydrogenated, A nano-sized fine crystalline Nd—Fe—B phase is generated, and a fine crystalline structure is formed. As a result, a rare earth magnet having excellent magnetic properties such as improved coercive force can be obtained. In addition, the Nd—Fe—B alloy flakes are pulverized to form Nd—Fe—B alloy powders whose meshes pass through a sieve having a size of at least twice the thickness of the flakes. The filling operation for filling the mold is easy to perform, and the packing density (bulk density) of the powder can be increased. This is because the Nd—Fe—B alloy powder is not excessively refined by passing the crushed Nd—Fe—B alloy flakes through a sieve having a mesh size of twice or more the thickness of the flakes, This is because the fluidity of the powder can be secured to some extent. The pulverization step may be performed before the molding step, and the order of the pulverization step and the hydrogenation step may be reversed. Therefore, the starting Nd—Fe—B alloy flakes may be pulverized, or the hydrogenated Nd—Fe—B alloy flakes may be pulverized first. That is, the pulverization process may be performed either before or after the hydrogenation process.

In the embodiment of the present invention, the “Nd—Fe—B” phase is an Nd—Fe—B-based compound that contains Nd, Fe, and B as main components and exhibits hard magnetism, specifically, Nd _2. Fe ₁₄ B phase may be mentioned. Examples of the Nd—Fe—B alloy include an Nd ₂ Fe ₁₄ B alloy. Here, “main component” means that the total content of each constituent element occupies 90 atomic% or more of the total.

  (2) As one form of the manufacturing method of the said rare earth magnet, it is mentioned that the said solid lubricant is a zinc stearate.

The solid lubricant to be used is not particularly limited as long as it does not greatly affect the magnetic properties of the magnet and improves the fluidity of the Nd—Fe—B alloy powder during pressure forming. Thus, it is preferable that the particles overlap each other with a weak binding force and have a cleavage property. Examples of the solid lubricant include stearic acid, at least one metal stearate selected from stearic acid, zinc stearate, calcium stearate, magnesium stearate, lithium stearate and barium stearate, molybdenum disulfide (MoS ₂ ). , Tungsten disulfide (WS ₂ ), hexagonal boron nitride (hBN), and the like. With such a solid lubricant, the Nd—Fe—B alloy is applied when a compressive force is applied by interposing the solid lubricant between the surfaces of the Nd—Fe—B alloy powder during pressure forming. When the powder slides (slides), the powder easily flows. Among them, zinc stearate has good adhesion to the Nd—Fe—B alloy powder, is easy to improve the fluidity of the powder even in a small amount, and is advantageous from the viewpoint of availability.

  (3) As one form of the manufacturing method of the said rare earth magnet, it is mentioned that the addition amount of the said solid lubricant shall be 0.001 mass% or more and 0.1 mass% or less.

  By making the addition amount of the solid lubricant 0.001% by mass or more, the fluidity of the Nd—Fe—B alloy powder at the time of pressure forming can be effectively enhanced. By setting the addition amount of the solid lubricant to 0.1% by mass or less, it is possible to suppress a decrease in density due to the solid lubricant and a decrease in magnetic properties due to generation of residues during the dehydrogenation process.

  (4) As one form of the manufacturing method of the said rare earth magnet, it is mentioned that the pressure of the said pressure molding shall be 1470 Mpa or less.

In the rare earth magnet manufacturing method, by mixing a solid lubricant, the fluidity of the Nd-Fe-B alloy powder at the time of pressure forming is increased, so that the density can be increased even if the pressure of the pressure forming is low. Is possible. For example, even if the pressure of pressure molding is 1470 MPa (15 ton / cm ² ) or less, the molded body can be densified and the relative density can be 80% or more. Therefore, compared with the case where a solid lubricant is not mixed, the pressure of pressure molding can be lowered, and cost reduction and productivity improvement can be realized. Further, by setting the pressure of pressure molding to 1470 MPa or less, it is possible to reduce the punching pressure when the molded body is extracted from the mold after pressure molding, or to reduce the cost of the press device used for pressure molding. it can.

(5) A rare earth magnet according to an embodiment of the present invention includes:
A rare earth magnet made of a powder compact including a powder of an Nd-Fe-B alloy,
The relative density is 83% or more,
In an arbitrary cross section, the total area of the fine powder region in which fine powder having a maximum diameter of 25 μm or less exists in the powder included in the observation visual field is 25% or more of the area of the observation visual field.

  According to the rare earth magnet, since the relative density is 83% or more, the residual magnetism is high in density and high. The ratio of the total area of the fine powder region to the cross section of the molded product when the total area of the fine powder region where the fine powder having the maximum diameter of 25 μm or less exists is 25% or more of the area of the observation visual field in the observation visual field of any cross section Is large, and the proportion of the fine powder region in the entire compact is large. In the fine powder region, fine powder gathers densely, the contact area between the powder particles is large, and the powder particles are tightly connected and agglomerated, which suppresses the occurrence of chipping and breakage of the molded product due to the progress of cracks, etc. Is done. Therefore, the occurrence of peeling and cracking can be suppressed, and the shape retention strength is high. Therefore, the rare earth magnet has a high density and excellent shape retention.

The “fine powder region” is a region where a fine powder having a maximum diameter of 25 μm or less exists among Nd—Fe—B alloy powders included in an observation field of an arbitrary cross section. This refers to the region of a group of particles in which particles are closely gathered. The size of the observation field is set so as to include at least 1000 or more (preferably 3000 or more) Nd—Fe—B alloy powders, for example, 300 μm × 300 μm (area: 90000 μm ² ) or more and 1000 μm × 1000 μm (area) : 1000000 μm ² = 1 mm ² ) or less. As shown in FIG. 1, the particle diameter of the Nd—Fe—B alloy powder is determined by specifying the contour of the powder P, drawing a minimum circumscribed rectangle R circumscribing the contour, and setting the short side length to the minimum diameter. a, the length of the long side is the maximum diameter b. The minimum circumscribed rectangle R is obtained by obtaining a pair of parallel lines having a minimum distance (corresponding to the minimum diameter) between the parallel lines when the outline of the powder P is sandwiched between the pair of parallel lines. When the outline of the powder is sandwiched between the parallel lines, a pair of parallel lines having the maximum distance (corresponding to the maximum diameter) between the parallel lines can be obtained, and can be obtained as a rectangle surrounded by these two parallel lines. . The “total area of the fine powder region” is the total area of the individual fine powder regions obtained by specifying the contours of the fine powder particles having a maximum diameter of 25 μm or less forming the fine powder region. It means that the larger the total area of the fine powder region in the observation field of view of any cross section (that is, the larger the area ratio of the fine powder region in the observation visual field), the larger the proportion of the fine powder region in the entire molded body.

  The relative density of the rare earth magnet is, for example, preferably 85% or more, and more preferably 87% or more, whereby the shape retention strength and magnetic properties can be further improved.

[Details of the embodiment of the present invention]
A method for producing a rare earth magnet according to an embodiment of the present invention and a specific example of the rare earth magnet will be described below. In addition, this invention is not limited to these illustrations, is shown by the claim, and is intended that all the changes within the meaning and range equivalent to the claim are included.

<Rare earth magnet manufacturing method>
The manufacturing method of the rare earth magnet according to the embodiment of the present invention includes the following steps.
(A) A preparation step of preparing a starting Nd—Fe—B alloy flake.
(B) A crushing step of crushing Nd—Fe—B alloy flakes.
(C) A hydrogenation process for hydrotreating an Nd—Fe—B alloy.
(D) A mixing step of mixing a solid lubricant with the hydrogenated Nd—Fe—B alloy powder.
(E) A molding step of pressure-molding the mixed powder mixed with the solid lubricant.
(F) A dehydrogenation step of dehydrogenating the pressure-molded compact.
Below, each process is demonstrated in detail.

(Preparation process)
The preparation step is a step of preparing a flake of an Nd—Fe—B alloy having a thickness of 25 μm or less by quenching and solidifying a molten alloy containing Nd, Fe and B, using the Nd—Fe—B phase as a main phase. is there. A typical example of the Nd—Fe—B alloy is an Nd ₂ Fe ₁₄ B alloy having a Nd ₂ Fe ₁₄ B phase as a main phase. The Nd—Fe—B alloy (Nd—Fe—B phase) may contain surplus Fe, for example, surplus in a range of 1% or more and 30% or less of Fe in terms of atomic ratio than the stoichiometric composition. To contain. The Nd—Fe—B alloy includes, for example, Co, Ga, Cu, Al, Zr, Nb, Ta, Hf, Ti, Si, Ca, Sm, Pr, Y, Ce, Dy, You may contain Tb, N, C, etc.

  The Nd—Fe—B based alloy is obtained by rapidly solidifying a molten alloy blended so as to have a predetermined composition to form a flaky shape (including a ribbon shape). By forming a Nd—Fe—B alloy flake with a thickness of 25 μm or less by rapid solidification, the cooling rate is high and the structure of the Nd—Fe—B alloy is amorphous or nanocrystalline, or amorphous and nanocrystalline. It tends to be a crystalline mixed crystal structure. When an Nd—Fe—B alloy having such a structure is used as a starting material, the structure of a magnet compact to be described later can be a fine crystal structure, and magnetic characteristics (particularly coercive force) can be improved. The width and length of the Nd—Fe—B alloy flakes are not particularly limited, but the width is 10 times or more of the thickness and the length is 100 times or more of the thickness. For example, the width is 1 ˜2 mm, length is 5 cm or more.

  The Nd—Fe—B alloy flakes can be prepared by, for example, rapid solidification by a melt span method. The melt span method is a method in which a molten alloy is jetted onto a cooled metal roll and rapidly cooled, and an alloy flake is obtained. In the melt span method, the cooling rate can be controlled by changing the peripheral speed of the roll. Specifically, the higher the peripheral speed of the roll, the thinner the alloy and the faster the cooling rate. The peripheral speed of the roll is preferably 30 m / second or more, more preferably 35 m / second or more and 40 m / second or more. Generally, when the peripheral speed of the roll is 35 m / sec or more, the thickness of the alloy flake is about 10 to 20 μm. The upper limit of the peripheral speed of the roll is, for example, 100 m / second or less from the viewpoint of manufacturing. Moreover, since it becomes difficult to obtain a homogeneous structure when the thickness of the alloy flake becomes too thick, the thickness of the alloy flake is preferably 10 μm or more and 20 μm or less.

(Crushing process)
The pulverization step is a step of pulverizing a thin piece of Nd-Fe-B alloy to obtain a flaky Nd-Fe-B alloy powder that has passed through a sieve whose opening is twice or more the thickness of the thin piece. is there. By pulverizing the Nd—Fe—B alloy flakes into powder, it becomes easy to perform a filling operation of filling the mold with the powder in a subsequent molding step. By passing the crushed Nd-Fe-B alloy flakes through a sieve having a mesh size of twice or more the thickness of the flakes, the powder is not excessively refined and fluidity can be secured to some extent. The packing density (bulk density) can be increased. Moreover, since powder is not refined | miniaturized excessively, it is easy to suppress the oxidation of powder.

The pulverization is preferably performed so that the particle diameter (maximum length) of the Nd—Fe—B alloy powder is, for example, 300 μm or less, further 200 μm or less, and particularly 106 μm or less. However, when the particle size (maximum length) of the powder is 25 μm or less, the fluidity of the powder is reduced and the influence of oxidation becomes large. Therefore, the particle size is preferably more than 25 μm. The atmosphere for pulverization is preferably an inert atmosphere in order to suppress oxidation of the powder, and the oxygen concentration in the atmosphere is preferably 5% by volume or less, and more preferably 1% by volume or less. The inert atmosphere, for example, include an inert gas atmosphere such as Ar or N _2.

  For example, the mesh opening is preferably 3 times or more the thickness of the flakes, and a specific numerical range is 45 μm or more and 355 μm or less, and further 106 μm or less. By setting the mesh opening to 355 μm or less, coarse particles can be removed and the bulk density of the powder can be increased.

(Hydrogenation process)
The hydrogenation process is a process in which an Nd—Fe—B alloy is hydrotreated and at least a part thereof is decomposed into three phases of NdH ₂ , Fe, and Fe ₂ B by a disproportionation reaction. By this step, the Nd—Fe—B phase undergoes phase decomposition, and a hydrogenated alloy having a mixed crystal structure including the NdH ₂ phase, the Fe phase, and the Fe ₂ B phase is obtained. In the hydrogenation treatment, for example, 40% by volume or more, and 50% by volume or more of the Nd—Fe—B based alloy (Nd—Fe—B phase) are phase decomposed, and the hydrogenated Nd—Fe—B based alloy is obtained. For example, the structure separated into three phases of NdH ₂ phase, Fe phase, and Fe ₂ B phase may be 40% by volume or more, and further 50% by volume or more. In the hydrogenation treatment, heat treatment is performed in a hydrogen-containing atmosphere at a temperature higher than the temperature at which the hydrogen disproportionation reaction of the Nd—Fe—B alloy (Nd—Fe—B phase) occurs. The temperature at which the hydrogen disproportionation reaction starts can be defined as follows. In a sealed container filled with hydrogen at an internal pressure of 0.8 to 1.0 atm (81.0 to 101.3 kPa) at room temperature (25 ° C.), the sample of the Nd—Fe—B alloy was put and heated. Go. The internal pressure when reaching 400 ° C. is defined as P _H2 (400 ° C.) [atmospheric pressure], and the minimum internal pressure in the temperature range of 400 to 900 ° C. is defined as P _H2 (MIN) [atmospheric pressure]. When the difference between P _H2 (400 ° C.) and P _H2 (MIN) is ΔP _H2 [atmospheric pressure], 400 when the internal pressure is {P _H2 (400 ° C.) − ΔP _H2 × 0.1} or less. It can be defined at a temperature in the range of ~ 900 ° C. When there are two or more applicable temperatures, the lowest temperature is set. At this time, it is preferable to set the weight of the sample so that P _H2 (MIN) is 0.5 atm (50.6 kPa) or less. The heat treatment temperature of the hydrogenation treatment may be, for example, more than 550 ° C. and 1100 ° C. or less, 650 ° C. or more and 950 ° C. or less, and 700 ° C. or more and 900 ° C. or less. As the heat treatment temperature of the hydrogenation treatment is higher, the phase decomposition of the Nd—Fe—B phase proceeds, but if it is too high, the structure may be coarsened. If the heat treatment temperature of the hydrogenation treatment is lower than the temperature indicating P _H2 (MIN), only a part of the Nd—Fe—B phase is likely to undergo phase decomposition. The temperature at which the disproportionation reaction of the Nd—Fe—B alloy (v phase) peaks depends on the composition, but is about 700 ° C. When only a part of the phase is decomposed, for example, over 550 ° C. and 700 ° C. Less than 575 ° C. or more and 675 ° C. or less.

  What is necessary is just to set the time of a hydrogenation process suitably, for example to set it as 30 minutes or more and 180 minutes or less. If the hydrogenation time is too short, the Nd—Fe—B phase may not be sufficiently decomposed. On the other hand, if the time for the hydrogenation treatment is too long, the phase decomposition of the Nd—Fe—B phase may proceed excessively or the structure may become coarse. The ratio of phase decomposition of the Nd—Fe—B phase can also be changed by changing the time of the hydrotreatment.

Examples of the hydrogen-containing atmosphere in the hydrogenation treatment include a H ₂ gas atmosphere or a mixed gas atmosphere of H ₂ gas and an inert gas such as Ar or N ₂ . The atmospheric pressure (hydrogen partial pressure) of the hydrogen-containing atmosphere is, for example, 20.2 kPa (0.2 atm) or more and 1013 kPa (10 atm) or less.

When a part of the Nd—Fe—B alloy (Nd—Fe—B phase) is phase-decomposed by lowering the heat treatment temperature of the hydrogenation treatment, undecomposed Nd—Fe—B remains, so NdH It becomes a mixed crystal structure including _two phases, Fe phase and Fe ₂ B phase and undecomposed Nd—Fe—B phase. In this case, since the heat treatment temperature is low, grain growth is suppressed, and the phase-decomposed structure is further refined as compared with the case where the entire Nd—Fe—B phase is phase-decomposed. Therefore, the structure recombined by the dehydrogenation process can be further refined in the subsequent dehydrogenation process.

  Furthermore, when the Nd—Fe—B alloy contains excessive Fe, an excessive Fe phase is precipitated during the dehydrogenation process, and a nanocomposite mixed crystal structure of the Nd—Fe—B phase and the Fe phase is formed. May be. In this case, in the hydrogenation process, if only a part of the Nd—Fe—B alloy is phase decomposed and the structure is refined, the formation of a coarse Fe phase is suppressed during the dehydrogenation process, and the Fe phase is reduced. Since it is refined, a finer nanocomposite mixed crystal structure tends to be formed. For example, the average crystal grain size of the Fe phase when the entire Nd—Fe—B based alloy is phase decomposed is about 300 nm, whereas when the Nd—Fe—B based alloy is partially decomposed, The average crystal grain size of the Fe phase can be 200 nm or less, and further 100 nm or less.

  When a part of the Nd—Fe—B alloy is phase decomposed by the hydrogenation treatment, the hydrogenated Nd—Fe—B alloy has an undecomposed Nd—Fe—B phase of 20% by volume to 60% by volume. It is preferable to contain, thereby ensuring both formability and miniaturization of the structure. As the proportion of the Nd—Fe—B phase is smaller, the proportion of the Fe phase generated by the phase decomposition of the Nd—Fe—B phase is increased, so that the moldability is improved. There is a tendency to become coarse. On the contrary, as the proportion of the Nd—Fe—B phase increases, the proportion of the undecomposed Nd—Fe—B phase increases and the proportion of the Fe phase decreases, so that the moldability decreases. Can be suppressed, and a fine structure tends to be formed. By setting the content ratio (volume ratio) of the Nd—Fe—B phase to 20% by volume or more and 60% by volume or less, it is easy to refine the structure while ensuring sufficient moldability. As for the volume ratio of a Nd-Fe-B phase, 35 volume% or more and 50 volume% or less are more preferable.

The volume ratio of the Nd—Fe—B phase in the Nd—Fe—B based alloy after the hydrogenation treatment can be determined as follows. By observing the structure of the alloy cross section with a scanning electron microscope (SEM) and analyzing the composition with an energy dispersive X-ray analyzer (EDX), Nd—Fe—B phase, NdH ₂ phase, Fe phase, Fe in the field of view ₂ Separate and extract phase B. And the area ratio of the Nd-Fe-B phase which occupies for a visual field can be calculated | required, and the area ratio can be calculated | required considering that it is a volume ratio. For analysis of the composition, other than EDX, an appropriate analyzer can be used.

  The order of the pulverization step and the hydrogenation step described above may be interchanged. After pulverizing the starting Nd—Fe—B alloy flakes, the Nd—Fe—B alloy powder may be hydrotreated, or after the Nd—Fe—B alloy flakes are hydrotreated, May be pulverized to obtain Nd—Fe—B alloy powder.

(Mixing process)
The mixing step is a step of obtaining a mixed powder by mixing a solid lubricant with hydrogenated Nd—Fe—B alloy powder. The solid lubricant is not particularly limited as long as it does not greatly affect the magnetic properties of the magnet and can improve the fluidity of the Nd—Fe—B alloy powder during pressure forming in the subsequent forming step. However, it is preferable that it is a powder form which has cleavage property. Examples of the solid lubricant include stearic acid, at least one metal stearate selected from zinc stearate, calcium stearate, magnesium stearate, lithium stearate, and barium stearate, MoS ₂ , WS ₂ , hBN. Etc. are available. Among them, zinc stearate has good adhesion to the Nd—Fe—B alloy powder, is easy to improve the fluidity of the powder even in a small amount, and is preferable from the viewpoint of availability.

  The addition amount of the solid lubricant is, for example, 0.001% by mass or more and 0.1% by mass or less. Here, the “addition amount” is the mass ratio of the solid lubricant to the Nd—Fe—B alloy powder. By making the addition amount of the solid lubricant 0.001% by mass or more, the fluidity of the Nd—Fe—B alloy powder at the time of pressure forming can be effectively enhanced. The density fall by a solid lubricant can be suppressed because the addition amount of a solid lubricant shall be 0.1 mass% or less. The addition amount of the solid lubricant is more preferably 0.01% by mass or more and 0.05% by mass or less.

(Molding process)
The forming step is a step of obtaining a hydrogenated molded body by pressure-molding the mixed powder. Specifically, the mixed powder is filled in a mold and pressure-molded using a press device. The pressure applied during the pressure molding include be, for example, 980MPa (10ton / cm ²⁾ or more 1960MPa (20ton / cm ²⁾ or less. The higher the pressure of pressure molding, the higher the density of the hydrogenated molded body. The relative density of the hydrogenated article is, for example, 83% or more, preferably 85% or more, and more preferably 87% or more. By increasing the density, the shape retention strength and magnetic properties (particularly residual magnetization) can be improved. The upper limit of the relative density of the molded body is, for example, 95% or less from the viewpoint of manufacturing. Here, “relative density” means the actual density (percentage of [actual density of the molded body / true density of the molded body] relative to the true density). The true density is the density of the Nd—Fe—B alloy used as a starting material.

  In the case of flaky Nd-Fe-B alloy powder, the laminated state in which the longitudinal direction of the powder is aligned in the direction perpendicular to the pressing direction (lateral direction) during pressing and the powder is stacked in the thickness direction In such a laminated state, the powder does not easily flow during pressure molding (see FIG. 3 described later). In the present embodiment, by mixing the solid lubricant with the Nd—Fe—B alloy powder in the mixing step described above, the fluidity of the powder is improved, and the powder is easy to flow during pressure molding. Therefore, when the powder flows, not the compressive force in the thickness direction on the flaky powder, but the compressive force acts in the longitudinal direction, causing the powder to be crushed and the powder to be finely granulated and molded Many fine powder regions where fine powder having a maximum diameter of 25 μm or less exists in the body are formed (see FIG. 2 described later). Thereby, generation | occurrence | production of peeling and a crack can be suppressed and the shape-retaining property of a molded object can be improved.

  As the pressure of the pressure molding is increased, the fine powder region is easily formed and the fine powder region is increased, so that the total area of the fine powder region is increased in the cross section of the molded body. The greater the proportion of the fine powder region in the entire molded body, that is, the greater the ratio of the total area of the fine powder region in the cross section of the molded body, the higher the effect of suppressing the occurrence of peeling and cracking. The total area of the fine powder region is preferably 25% or more, more preferably 30% or more, of the area of the observation field in the observation field of the cross section of an arbitrary molded body. On the other hand, the fine powder region is a region in which fine powder particles are gathered and includes fine voids. Therefore, if the fine powder region is excessively increased, the porosity may increase and the magnetization may be lowered. The upper limit of the area ratio of the fine powder region in the observation view of the cross section of the molded body is not particularly limited, but from the viewpoint of manufacturing, and further from the viewpoint of increasing the magnetic properties by reducing the voids due to the fine region, for example, 80% or less, Furthermore, it is 70% or less. There may be a flaky powder having a maximum length (maximum diameter) of more than 25 μm in the molded body. In this case, the total area of the flaky powder in the observation field of any cross section of the molded body For example, it is 50% or more of the remaining area obtained by subtracting the total area of the fine powder region from the area. The “flaky powder” as used herein is a powder having a maximum diameter of more than 25 μm among Nd—Fe—B alloy powders included in the observation field of view, and is represented by a ratio between the maximum diameter and the minimum diameter. The aspect ratio (maximum diameter / minimum diameter) is 3 or more and the minimum diameter is 25 μm or less.

  In general, the higher the pressure of pressure molding, the greater the density of the molded body tends to increase due to local stress concentration in the mold, and the density of the molded body tends to be uneven. In the present embodiment, by mixing the solid lubricant, the fluidity of the powder at the time of pressure molding is increased, and the powder flows at the time of pressure molding, so that it is difficult for roughness to occur inside the molded body. The body density can be made uniform and densified. On the other hand, by increasing the fluidity of the powder at the time of pressure molding, it is possible to increase the density even if the pressure of pressure molding is lowered, compared with the case where no solid lubricant is mixed, pressure molding. The pressure can be lowered. For example, even if the pressure of pressure molding is 1470 MPa or less, the density can be increased, and the relative density of the molded body can be 83% or more. By lowering the pressure of pressure molding, it is possible to reduce the punching pressure when the molded body is pulled out from the mold after pressure molding, or to reduce the cost of the press device.

(Dehydrogenation process)
The dehydrogenation step is a step of obtaining a magnet molded body having a Nd-Fe-B phase as a main phase by dehydrogenating the hydrogenated molded body and recombining phases decomposed by the hydrogenation treatment by a recombination reaction. . By this step, the NdH ₂ phase, the Fe phase, and the Fe ₂ B phase are recombined to generate a nano-sized fine Nd—Fe—B phase, and the Nd—Fe—B phase (typically Nd ₂ A magnet compact (rare earth dust magnet) having a nanocrystalline structure containing (Fe ₁₄ B phase) is obtained. In the dehydrogenation treatment, heat treatment is performed in an inert atmosphere or a reduced-pressure atmosphere at a temperature at which a recombination reaction of NdH ₂ , Fe, and Fe ₂ B phase-decomposed by the hydrogenation treatment occurs. The heat treatment temperature of the dehydrogenation treatment is preferably a temperature condition such that NdH ₂ is not detected (substantially does not exist) at the center of the dehydrogenation molded body (the part farthest from the outer surface of the molded body). It is mentioned that it is 1000 degrees C or less. The recombination reaction proceeds as the heat treatment temperature for the dehydrogenation process is increased. However, if the temperature is too high, the structure may become coarse. The heat treatment temperature for the dehydrogenation treatment is more preferably 650 ° C. or higher and 800 ° C. or lower.

  What is necessary is just to set the time of a dehydrogenation process suitably, for example to set it as 30 minutes or more and 180 minutes or less. If the dehydrogenation time is too short, the recombination reaction may not sufficiently proceed to the inside of the molded body. On the other hand, if the dehydrogenation time is too long, the structure may become coarse.

As an inert atmosphere at the time of dehydrogenation, for example, an inert gas atmosphere such as Ar or N ₂ can be used. As a reduced pressure atmosphere, for example, a vacuum atmosphere having a degree of vacuum 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 easily proceeds, and the NdH ₂ phase hardly remains. When the density of the molded body is high or the size of the molded body is large, when the pressure is rapidly reduced to 10 Pa or less during dehydrogenation in a vacuum atmosphere, the reaction proceeds only on the surface layer of the molded body and shrinks so that voids are formed. There is a possibility of blocking and hindering hydrogen release from the inside of the molded body. Therefore, it is preferable to control the degree of vacuum when the dehydrogenation process is performed in a vacuum atmosphere. For example, the temperature is raised to a dehydrogenation temperature in a hydrogen-containing atmosphere of 20 to 101 kPa, and then depressurized, and finally, for example, the pressure is reduced to 10 Pa or less through a hydrogen-containing atmosphere having a degree of vacuum of about 0.1 to 20 kPa. It is done.

The structure of the magnet compact after the dehydrogenation process becomes a nanocrystal structure containing a nano-sized Nd—Fe—B phase. In addition, as described above, when the Nd—Fe—B alloy as the starting material contains excessive Fe, a nanocomposite mixed crystal structure of the Nd—Fe—B phase and the Fe phase may be formed. . For example, when the starting material is an Nd ₂ Fe ₁₄ B alloy containing excess Fe, a nanocomposite mixed crystal structure of an Nd ₂ Fe ₁₄ B phase and an Fe phase is formed.

{Function and effect}
The manufacturing method of the rare earth magnet according to the above-described embodiment has the following effects.
(1) Pressurized Nd—Fe—B alloy powder subjected to hydrogenation → Dehydrogenation treatment to form a magnet compact of a high density Nd—Fe—B alloy powder containing no binder (rare earth magnet) Can be manufactured.
(2) By mixing a solid lubricant with the Nd—Fe—B alloy powder, the fluidity of the powder during pressure molding can be increased, and the shape retention of the compact can be improved.

{Use of rare earth magnet manufacturing method}
The method for producing a rare earth magnet according to the embodiment can be suitably used for producing a rare earth dust magnet.

<Rare earth magnet>
The rare earth magnet according to the embodiment of the present invention can be manufactured by the above-described method for manufacturing a rare earth magnet, and includes a powder molded body (magnet molded body) containing a powder of an Nd—Fe—B alloy. One of the features of the rare earth magnet of the embodiment is that the relative density is 83% or more. Another feature is that the total area of the fine powder region where fine powder having a maximum diameter of 25 μm or less is 25% or more of the area of the observation visual field in the observation visual field of an arbitrary cross section. Hereinafter, the configuration of the rare earth magnet will be described in detail.

(Relative density)
When the relative density is 83% or more, the density is high, the residual magnetization is high, and the magnetic properties are excellent. Preferably, the relative density is 85% or more, and further 87% or more.

(Fine powder area)
The fine powder region is a region where a fine powder having a maximum diameter of 25 μm or less exists in an Nd—Fe—B-based alloy powder included in an observation field in an arbitrary cross section. Here, 10 or more fine powder regions exist. This refers to the area of a group of particles in which fine powder particles are closely gathered. And the total area of this fine powder area | region is 25% or more of the area of an observation visual field. In the fine powder region, fine powder gathers densely, the contact area between the powder particles is large, and the powder particles are firmly bonded to each other, so that peeling does not easily occur and the progress of cracks is suppressed. When the area ratio of the fine powder region in the observation visual field is 25% or more, the area ratio of the fine powder region in the cross section of the compact is large, and the proportion of the fine powder region in the entire compact is large. Therefore, the occurrence of peeling and cracking can be suppressed, and the shape retention strength is improved. The larger the area ratio of the fine powder region in the observation field, the higher the effect of suppressing the occurrence of peeling and cracking. The area ratio of the fine powder area is preferably 30% or more, and more preferably 35% or more. Although the upper limit of the area ratio of a fine powder area | region is not specifically limited, From a viewpoint on manufacture, it is 80% or less, for example, and also 70% or less.

  Further, the rare earth magnet of the present embodiment has a flaky Nd—Fe—B alloy powder having a maximum length (maximum diameter) of more than 25 μm in addition to a fine region in an observation field of an arbitrary cross section. Is mentioned. In this case, the total area of the flaky powder is, for example, 50% or more of the remaining area obtained by subtracting the total area of the fine powder region from the area of the observation field.

{Function and effect}
The rare earth magnet according to the embodiment described above has the following effects.
(1) Since it does not contain a binder and the relative density is 83% or more, the Nd—Fe—B alloy accounts for a large proportion, and the performance close to the original magnetic properties of the Nd—Fe—B alloy Can be demonstrated.
(2) In the observation field of an arbitrary cross section, the area ratio of the fine powder region is 25% or more, so that the occurrence of peeling and cracking can be suppressed, and the shape retention is excellent.

{Applications of rare earth magnets}
The rare earth magnet according to the embodiment can be suitably used as a permanent magnet used in various electric devices such as a motor and a generator.

[Test Example 1]
A molten alloy containing 30% by mass of Nd and 1% by mass of B and the balance being Fe and inevitable impurities (30% by mass Nd-1% by mass B-bal.Fe) is rapidly solidified by a melt span method. Nd—Fe—B alloy flakes as starting materials were prepared. Here, the peripheral speed of the roll was set to 40 m / sec, and the thickness of the Nd—Fe—B alloy flakes was controlled to be about 15 μm. The Nd—Fe—B alloy flakes were pulverized in a mortar in an inert atmosphere and passed through a sieve having a sieve mesh opening of 106 μm to obtain an Nd—Fe—B alloy powder that passed through the sieve mesh.

The Nd—Fe—B alloy powder was hydrogenated by heat treatment at 850 ° C. for 150 minutes in an H ₂ gas atmosphere (atmospheric pressure). This hydrogenated Nd—Fe—B alloy powder was mixed with 0.01% by mass of zinc stearate as a solid lubricant to obtain a mixed powder.

The mixed powder was filled in a mold and pressure-molded (uniaxial press) at 1370 MPa (14 ton / cm ² ) to obtain a cylindrical hydrogenated molded body having a diameter of 10 mm and a height of 8 mm. Here, the pressure molding was performed at room temperature, and a lubricant (myristic acid) was applied to the inner wall surface of the mold.

The hydrogenated compact was heat-treated at 800 ° C. for 150 minutes in a vacuum atmosphere (the degree of vacuum was 10 Pa or less) to obtain a magnet compact. About the obtained magnet compact, the cross-section was observed with a SEM-EDX apparatus and the composition was analyzed. As a result, it was composed of a powder compact of an Nd—Fe—B alloy, and a nanocrystal of Nd ₂ Fe ₁₄ B phase. Had an organization. This magnet compact is referred to as Sample No. 1-1.

  Sample No. The cross section of the 1-1 magnet molded body was observed with an SEM. Here, the cross section observed with the SEM was a vertical cross section passing through the central axis of the compact (a cross section parallel to the pressurizing direction during pressure molding). Sample No. A cross-sectional SEM observation image of 1-1 is shown in FIG. In FIG. 2, the vertical direction is the height direction of the molded body, and coincides with the pressing direction (the same applies to FIG. 3 described later). Moreover, in FIG. 2, a black part is a space | gap and a whitish flaky part is Nd-Fe-B type alloy powder (particle | grains) (FIG. 3 mentioned later is also the same).

  For comparison, Sample No. 4 was used except that the solid lubricant (zinc stearate) was not mixed with the Nd—Fe—B alloy powder. In the same manner as in 1-1, after performing pressure molding at the same pressure, a magnet molded body was obtained by dehydrogenation treatment. This magnet compact is referred to as Sample No. 100. Sample No. Similar to 1-1, the cross section of the magnet compact was observed with an SEM. Sample No. 100 cross-sectional SEM observation images are shown in FIG.

  The following evaluation was performed about the magnet molded object of each produced sample.

(Relative density)
The relative density of each molded body was evaluated. The relative density was obtained by measuring the volume and mass of the molded body to determine the actual density, and as a percentage of [actual density of the molded body / true density of the molded body]. The true density was the density of the starting Nd—Fe—B alloy (here, 7.6 g / cm ³ ). The results are shown in Table 1.

(Area ratio of fine area)
About each molded object, the area ratio of the fine area | region was evaluated. The area ratio of the fine regions was evaluated as follows. Within the observation field of the cross-sectional SEM observation image (see FIG. 2 and FIG. 3), the outline of the fine powder particles having a maximum diameter of 25 μm or less is extracted by image processing to obtain fine powder regions, and the area of each fine powder region Was measured and the total area was calculated. And the ratio of the total area of the fine powder area | region with respect to the area of an observation visual field was computed, and the ratio of the total area of the fine powder area | region occupied in an observation visual field was calculated | required. The results are shown in Table 1.

  2 and 3, the area surrounded by the solid line in the figure indicates the fine powder area. In 1-1, there are 10 fine powder regions in the observation field of view, whereas sample no. In 100, there were six fine powder regions.

(Appearance evaluation)
The appearance of each molded body was visually observed and evaluated for the presence or absence of peeling or cracking. The results are shown in Table 1. In Table 1, the case where peeling and a crack were not confirmed was set to A, and the case where peeling and a crack were confirmed was set to B. 4 and FIG. 1-1 and Sample No. 100 is a photograph of the appearance of each molded body of Sample No. 100. In 1-1, there is no conspicuous defect such as a crack. In 100, defects such as cracks (portions surrounded by broken lines in FIG. 5) were recognized.

(Magnetic properties)
The magnetic properties of each compact were evaluated. Specifically, after applying a pulsed magnetic field of 4777 kA / m (5T) using a magnetizing device (high voltage capacitor SR type manufactured by Nippon Electron Seiki Co., Ltd.), a BH tracer (RIKEN) The BH curve was measured using a DCBH tracer manufactured by Denki Co., Ltd., and the remanent magnetization and coercive force were determined. The results are shown in Table 1.

  From the results shown in Table 1, Sample No. mixed with a solid lubricant was used. 1-1 has a relative density of 83% or more, has a high density, and can achieve high density. Sample No. 1-1 is Sample No. which is not mixed with a solid lubricant. It can be seen that the residual magnetization and coercive force are equal to or greater than 100 and have excellent magnetic properties.

  Sample No. 1-1, the area ratio of the fine powder region satisfies 25% or more. It can be seen that the occurrence of peeling and cracking is suppressed as compared with 100, and the shape retention is excellent.

  Sample No. 1-1 and Sample No. For each of the 100 compacts, the area ratio of the flaky powder was evaluated. Specifically, within the observation field of the cross-sectional SEM observation image (see FIGS. 2 and 3), a flaky powder having a maximum diameter of 25 μm or more is extracted by image processing to measure individual areas, and the observation field The ratio of the total area of the flaky powder occupying was calculated. As a result, the area ratio of the flaky powder was determined as Sample No. 1-1, it was 62.2%. 100 was 89.0%.

P Nd-Fe-B alloy powder R Minimum circumscribed rectangle a Minimum diameter b Maximum diameter

Claims (5)

A preparatory step in which a molten alloy containing Nd, Fe and B is rapidly solidified to prepare a flake of an Nd—Fe—B alloy having a thickness of 25 μm or less with an Nd—Fe—B phase as a main phase;
Crushing the Nd-Fe-B-based alloy flakes to obtain a flaky Nd-Fe-B-based alloy powder that has passed through a mesh whose opening is twice or more the thickness of the flakes;
Hydrotreating the Nd-Fe-B alloy, and at least partially decomposing it into three phases of NdH ₂ , Fe, and Fe ₂ B by a disproportionation reaction;
A mixing step of obtaining a mixed powder by mixing a solid lubricant with the hydrogenated Nd-Fe-B alloy powder;
A molding step of pressing the mixed powder to obtain a hydrogenated molded body; and
A dehydrogenation step of dehydrogenating the hydrogenated molded body and recombining the phases decomposed by the hydrogenation treatment by a recombination reaction to obtain a magnet molded body having an Nd-Fe-N phase as a main phase. A method for producing a rare earth magnet.   The method for producing a rare earth magnet according to claim 1, wherein the solid lubricant is zinc stearate.   The method for producing a rare earth magnet according to claim 1 or 2, wherein the solid lubricant is added in an amount of 0.001 mass% to 0.1 mass%.   The method for producing a rare earth magnet according to any one of claims 1 to 3, wherein a pressure of the pressure molding is 1470 MPa or less. A rare earth magnet made of a powder compact including a powder of an Nd-Fe-B alloy,
The relative density is 83% or more,
A rare earth magnet having a total area of a fine powder region in which a fine powder having a maximum diameter of 25 μm or less exists in the observation field in an arbitrary cross section is 25% or more of the area of the observation field.