JP4282016B2 - Manufacturing method of rare earth sintered magnet - Google Patents

Description

  The present invention relates to a raw material powder used when producing a rare earth sintered magnet typified by an Nd-Fe-B system, and in particular, by granulating the raw material powder, it can be applied to a mold during molding in a magnetic field. The present invention relates to a technology capable of improving the filling property to obtain high productivity and facilitating the reduction in size of the rare earth sintered magnet.

When manufacturing rare earth sintered magnets, magnetic properties such as saturation magnetic flux density and coercive force are ensured by refining the raw material powder used for sintering. However, the refinement of the raw material powder becomes a factor that hinders the dimensional accuracy and productivity of the compact.
The raw material powder forms a compact by pressure molding in a magnetic field. In the molding in the magnetic field, the raw powder particles are oriented by applying a static magnetic field or a pulse magnetic field. At the time of molding in this magnetic field, the finer the raw material powder, the worse the fluidity and the problem of filling into the mold. If the powder filling property is inferior, the powder cannot be sufficiently filled into the die, so the dimensional accuracy of the molded product cannot be obtained, or the filling of the die itself takes time and productivity. There is a problem of inhibiting. In particular, it is difficult to accurately and efficiently produce a molded body having a thin shape or a complicated shape.

Attempts have been made to granulate the raw material powder as one means for improving the fluidity of the raw material powder. For example, JP-A-8-107034 (Patent Document 1) and JP-A-8-88111 (Patent Document 2) propose to granulate by spray-drying a slurry in which a binder is added to a rare earth metal powder. Yes.
Japanese Patent Publication No. 7-6025 (Patent Document 3) proposes granulating a rare earth metal powder by applying a magnetic field.

JP-A-8-107034 JP-A-8-88111 Japanese Patent Publication No. 7-6025

According to Patent Documents 1 and 2, fluidity can be improved by producing granules. However, since the primary alloy particles are bound together by a binder such as PVA (polyvinyl alcohol), the binding force between the primary alloy particles is relatively strong. Even if the granules having such a strong binding force are subjected to molding in a magnetic field, it is not easy to orient each primary alloy particle. Therefore, the rare earth sintered magnet obtained has a low degree of orientation and magnetic properties, particularly a residual magnetic flux density (Br). Further, since carbon contained in the binder causes a decrease in magnetic characteristics, a step of removing the binder is necessary.
According to Patent Document 3, a magnetic field application process at the time of producing a pressurizing body and an AC magnetic field application process for improving magnetic properties after filling the granules with the granules are required. Moreover, since it is the granule which applied the magnetic field, we are anxious about the fall of the fluidity | liquidity by residual magnetization.
The present invention has been made on the basis of such a technical problem, and uses granules having excellent fluidity to improve the dimensional accuracy and productivity of the molded body and to greatly reduce the characteristics. An object of the present invention is to provide a method for producing a rare earth sintered magnet without any problems.

In order to solve the problems as described above, the present inventors have studied to produce granules without using a binder. As a result, it is possible to produce a granule by crushing the primary alloy particles by pressurizing and pre-molding the primary alloy particles without using a binder, and the granules are excellent in fluidity at the time of mold filling. It was confirmed that this granule produced only by the binding force of the primary alloy particles can be easily separated into primary alloy particles by a magnetic field applied at the time of molding in a magnetic field, and a good orientation state can be realized.
Accordingly, the present invention includes the steps of forming a first molded body raw material powder of a rare earth sintered magnet (primary alloy particles) directly pressure molded, the raw material powder by directly crushing the first molded body A step of producing a granule in which the particles are bonded together only by van der Waals force, a step of introducing the granule into a mold cavity, a magnetic field is applied to the granule, and a second molded body is formed by pressure molding. There is provided a method for producing a rare earth sintered magnet comprising a step of obtaining and a step of sintering a second compact.
At this time, in the step of putting the granules into the mold cavity, it is preferable to put the granules having a particle size of 0.07 to 0.6 mm into the mold cavity.
The granules produced in this manner are bound by solid components such as a binder having the other binding power, in which the particles constituting the granules are bound only by van der Waals force without using a binder or the like. Not. And in this invention, the granule is produced, without applying a magnetic field. Therefore, unlike a granule to which a magnetic field is applied, there is no decrease in fluidity due to residual magnetization, and a granule having a high fluidity such as an angle of repose of 50 ° or less and further 47 ° or less can be produced. As a result, it is possible to obtain a rare earth sintered magnet having a high magnetic property while realizing rapid introduction into the mold cavity. In order to obtain such granules, the raw material powder is preferably pressed at a pressure of 0.03 to 1.3 ton / cm ^{2 in} the step of forming the first molded body. Moreover, you may make it form the 1st molded object which has a molded object density of 3.8-4.35 g / cc.
In addition, a lubricant may be added to the raw material powder in the step of forming the first molded body.

The present invention also provides an R ₂ T ₁₄ B phase (where R is one or more elements selected from rare earth elements, and T is one or two elements selected from transition metal elements including Fe, Fe, and Co). It is desirable to apply to a raw material powder having a composition containing the above elements) and having an average particle size of 2.5 to 6 μm.

  According to the present invention, since a granule obtained by pressure-molding raw material powder and pulverizing the powder is used, there is no need to perform a binder removal process, and the rare earth sintered magnet is improved while improving the dimensional accuracy of the molded body. As well as improving the productivity, it contributes to the improvement of magnetic properties.

Hereinafter, the present invention will be described in detail based on embodiments.
In the present invention, after forming a preform by pressure-molding the powders, granules are obtained by crushing the preform. That is, granules are formed by binding primary alloy particles (raw material powders) only with van der Waals force without using a binder or the like having a binding function. The binding force of such granules is extremely weak compared to the binding force of a conventional binder such as PVA. Therefore, the granules obtained according to the present invention are easily disintegrated by the magnetic field applied during molding in a magnetic field and separated into primary alloy particles. Therefore, a high degree of orientation can be obtained. Up to now, the use of a binder has been considered as a premise for the production of granules, but it is highly valuable to find that high fluidity can be obtained even in granules formed without using a binder. Moreover, since the granules are collapsed by applying a magnetic field, they are suitable for rare earth sintered magnets that are molded in a magnetic field. In addition, it is possible to omit the binder removal process that is essential when the conventional granule technology is used, which also includes process advantages.

A method for producing a rare earth sintered magnet to which the above granulation technique is applied will be described below.
The raw material alloy can be produced by a strip casting method or other known melting methods in a vacuum or an inert gas, preferably in an Ar atmosphere. In the strip casting method, a molten metal obtained by melting a raw metal in a non-oxidizing atmosphere such as an Ar gas atmosphere is ejected onto the surface of a rotating roll. The melt rapidly cooled by the roll is rapidly solidified in the form of a thin plate or flakes (scales). This rapidly solidified alloy has a homogeneous structure with a crystal grain size of 1 to 50 μm. The raw material alloy can be obtained not only by the strip casting method but also by a melting method such as high frequency induction melting. In order to prevent segregation after dissolution, for example, it can be solidified by pouring into a water-cooled copper plate. An alloy obtained by the reduction diffusion method can also be used as a raw material alloy.
When obtaining an RTB-based sintered magnet, a so-called alloy using a R ₂ T ₁₄ B crystal grain (low R alloy) and an alloy containing more R than a low R alloy (high R alloy) is used. A mixing method can also be applied to the present invention.

  The raw material alloy is subjected to a grinding process. In the case of the mixing method, the low R alloy and the high R alloy are pulverized separately or together. The pulverization process includes a coarse pulverization process and a fine pulverization process. First, the raw material alloy is coarsely pulverized until the particle size becomes about several hundred μm. The coarse pulverization is desirably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill or the like. Prior to coarse pulverization, it is effective to perform pulverization by allowing hydrogen to be stored in the raw material alloy and then releasing it. The hydrogen releasing treatment is performed for the purpose of reducing hydrogen as an impurity as a rare earth sintered magnet. The heating and holding temperature for storing hydrogen is 200 ° C. or higher, preferably 350 ° C. or higher. The holding time varies depending on the relationship with the holding temperature, the thickness of the raw material alloy, etc., but is at least 30 minutes or longer, preferably 1 hour or longer. The hydrogen release treatment is performed in a vacuum or Ar gas flow. The hydrogen storage process and the hydrogen release process are not essential processes. This hydrogen pulverization can be regarded as coarse pulverization, and mechanical coarse pulverization can be omitted.

  After the coarse pulverization process, the process proceeds to the fine pulverization process. A jet mill is mainly used for fine pulverization, and a coarsely pulverized powder having a particle size of about several hundreds of μm has an average particle size of 2.5 to 6 μm, preferably 3 to 5 μm. The jet mill releases a high-pressure inert gas from a narrow nozzle to generate a high-speed gas flow, accelerates the coarsely pulverized powder with this high-speed gas flow, collides with the coarsely pulverized powder, and collides with the target or the container wall. It is a method of generating a collision and crushing.

  In the case of the mixing method, the timing of mixing the two kinds of alloys is not limited. However, when the low R alloy and the high R alloy are separately pulverized in the pulverization step, the pulverized low R alloy powder is used. And high R alloy powder in a nitrogen atmosphere. The mixing ratio of the low R alloy powder and the high R alloy powder may be about 80:20 to 97: 3 by weight. The mixing ratio when the low R alloy and the high R alloy are pulverized together is the same. In addition, fatty acids or fatty acid derivatives and hydrocarbons for the purpose of improving the lubrication and orientation during molding, such as zinc stearate, calcium stearate, aluminum stearate, stearamide, olein, which are stearic acid and oleic acid Acid amide, ethylenebisisostearic acid amide, hydrocarbon paraffin, naphthalene and the like can be added in an amount of about 0.01 to 0.3 wt% during pulverization.

The finely pulverized powder obtained above is granulated.
In the present invention, a finely pulverized powder is pressure-molded to form a preform (first molded body), and then the preform is crushed to produce granules.
For this purpose, finely pulverized powder is filled into a mold cavity, and this mold is press-molded at a predetermined press pressure with a press machine to obtain a preform.
At this time, the press pressure applied to form the preform is not particularly limited, but if the press pressure is too low, the strength of the granule itself becomes excessively weak and fragile, and as a result, the granule collapses and pulverizes. It becomes powder and fluidity decreases. Further, in the crushing step described later, the finely pulverized powder passes through the sieve, so that the yield of granules having a predetermined particle size range is reduced. On the other hand, if the pressing pressure is too high, the granules are not sufficiently collapsed during molding in a magnetic field, and the orientation is lowered, which causes a decrease in magnetic properties (particularly Br).
For this reason, it is preferable that the press pressure for forming the preform is 0.03 to 1.3 ton / cm ² , whereby the density of the preform is 3.8 to 4.35 g / cc. It is preferable to do this.

  Next, the preform is crushed with a crusher or a mortar to obtain a crushed material. And this crushed material is collect | recovered for the pulverized material of a predetermined | prescribed particle size range using two sieves (1st sieve and 2nd sieve) from which an opening dimension differs. That is, the crushed material that passes through the first sieve having a large mesh size and does not pass through the second sieve having a small mesh size is collected. Thereby, the obtained granule has a particle size smaller than the opening size of the first sieve and larger than the opening size of the second sieve. At this time, the particle size of the crushed material to be collected is preferably 0.07 to 0.6 mm.

  The granules thus obtained are bound to each other by only the binding force between the pulverized powders. At this time, the contact between the finely pulverized powders does not substantially contain a solid component such as a binder for binding the finely pulverized powders. However, when a lubricant is added to improve grindability and orientation during molding, the solid component of the lubricant is allowed to be present on the finely ground powder surface and contacts.

The granules are subjected to molding in a magnetic field.
The molding pressure in the magnetic field molding may be in the range of 0.3 to 3 ton / cm ² (30 to 300 MPa). The molding pressure may be constant from the beginning to the end of molding, may be gradually increased or gradually decreased, or may vary irregularly. The orientation becomes better as the molding pressure is lower, but if the molding pressure is too low, the strength of the molded body (second molded body) will be insufficient and handling will be problematic. Select the molding pressure. The final relative density of the molded body obtained by molding in a magnetic field is usually 50 to 60%.
The applied magnetic field may be about 12 to 20 kOe (960 to 1600 kA / m). By applying a magnetic field of this level, the granules are broken down and decomposed into primary alloy particles. The applied magnetic field is not limited to a static magnetic field, and may be a pulsed magnetic field. A static magnetic field and a pulsed magnetic field can also be used in combination.

Next, the molded body is sintered in a vacuum or an inert gas atmosphere. Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, the difference of an average particle diameter, and a particle size distribution, what is necessary is just to sinter at 1000-1200 degreeC for about 1 to 10 hours.
After sintering, the obtained sintered body can be subjected to an aging treatment. This process is an important process for controlling the coercive force. In the case where the aging treatment is performed in two stages, holding for a predetermined time at around 800 ° C. and around 600 ° C. is effective. When the heat treatment at around 800 ° C. is performed after sintering, the coercive force increases, which is particularly effective in the mixing method. In addition, since the coercive force is greatly increased by the heat treatment at around 600 ° C., the aging treatment at around 600 ° C. is preferably performed when the aging treatment is performed in one stage.

Next, a rare earth sintered magnet to which the present invention is applied will be described.
The present invention is particularly preferably applied to an RTB-based sintered magnet. This RTB-based sintered magnet contains 25 to 37 wt% of a rare earth element (R). Here, R in the present invention has a concept including Y, and therefore 1 of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. It is selected from species or two or more species. If the amount of R is less than 25 wt%, the R ₂ T ₁₄ B phase, which is the main phase of the R-T-B system sintered magnet, is not sufficiently generated, and α-Fe having soft magnetism is precipitated and retained. The magnetic force is significantly reduced. On the other hand, when R exceeds 37 wt%, the volume ratio of the R ₂ T ₁₄ B phase, which is the main phase, decreases, and the residual magnetic flux density decreases. Further, R reacts with oxygen, the amount of oxygen contained increases, and accordingly, the R-rich phase effective for the generation of coercive force decreases, leading to a decrease in coercive force. Therefore, the amount of R is set to 25 to 37 wt%. A desirable amount of R is 28 to 35 wt%, and a more desirable amount of R is 29 to 33 wt%.

Further, the RTB-based sintered magnet to which the present invention is applied contains 0.5 to 4.5 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. On the other hand, when B exceeds 4.5 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit of B is set to 4.5 wt%. A desirable amount of B is 0.5 to 1.5 wt%, and a more desirable amount of B is 0.8 to 1.2 wt%.
The RTB-based sintered magnet to which the present invention is applied has a Co content of 2.0 wt% or less (not including 0), preferably 0.1 to 1.0 wt%, more preferably 0.3 to 0. .7 wt% can be contained. Co forms the same phase as Fe, but is effective in improving the Curie temperature and improving the corrosion resistance of the grain boundary phase.

Moreover, the RTB-based sintered magnet to which the present invention is applied can contain one or two of Al and Cu in a range of 0.02 to 0.5 wt%. By including one or two of Al and Cu in this range, it is possible to increase the coercive force, increase the corrosion resistance, and improve the temperature characteristics of the obtained RTB-based sintered magnet. In the case of adding Al, the desirable amount of Al is 0.03 to 0.3 wt%, and the more desirable amount of Al is 0.05 to 0.25 wt%. Further, in the case of adding Cu, the desirable amount of Cu is 0.15 wt% or less (not including 0), and the more desirable amount of Cu is 0.03 to 0.12 wt%.
The RTB-based sintered magnet to which the present invention is applied allows the inclusion of other elements. For example, elements such as Zr, Ti, Bi, Sn, Ga, Nb, Ta, Si, V, Ag, and Ge can be appropriately contained. On the other hand, it is desirable to reduce impurity elements such as oxygen, nitrogen, and carbon as much as possible. In particular, the amount of oxygen that impairs magnetic properties is preferably 5000 ppm or less, more preferably 3000 ppm or less. This is because when the amount of oxygen is large, the rare-earth oxide phase, which is a nonmagnetic component, increases and the magnetic properties are deteriorated.

Although it is desirable to apply the present invention to an RTB-based sintered magnet, the present invention can also be applied to other rare earth sintered magnets. For example, the present invention can be applied to an R—Co based sintered magnet.
The R—Co based sintered magnet contains R, one or more elements selected from Fe, Ni, Mn, and Cr, and Co. In this case, it preferably further contains Cu or one or more elements selected from Nb, Zr, Ta, Hf, Ti and V, and particularly preferably from Cu and Nb, Zr, Ta, Hf, Ti and V. Containing one or more selected elements. Among these, in particular, an intermetallic compound of Sm and Co, preferably an Sm ₂ Co ₁₇ intermetallic compound, is the main phase, and a subphase mainly composed of SmCo ₅ exists at the grain boundary. The specific composition may be appropriately selected according to the production method, required magnetic characteristics, and the like. For example, R: 20 to 30 wt%, particularly about 22 to 28 wt%, Fe, Ni, Mn, and Cr Above: about 1 to 35 wt%, one or more of Nb, Zr, Ta, Hf, Ti and V: 0 to 6 wt%, especially about 0.5 to 4 wt%, Cu: 0 to 10 wt%, especially 1 to 10 wt% To the extent, Co: the balance composition is desirable.
The R-T-B sintered magnet and the R-Co sintered magnet have been described above, but the present invention does not prevent application to other rare earth sintered magnets.

A raw material alloy having a composition of 26.6 wt% Nd-5.8 wt% Dy-0.25 wt% Al-0.53 wt% Co-0.07 wt% Cu-1.0 wt% B-Fe is produced by strip casting. did.
Next, after hydrogen was occluded in the raw material alloy at room temperature, hydrogen pulverization treatment was performed in which dehydrogenation was performed at 600 ° C. for 1 hour in an Ar atmosphere.
The alloy that has been subjected to the hydrogen pulverization treatment was mixed with 0.05 to 0.1% of a lubricant that contributes to improvement in pulverization and orientation during molding. The lubricant may be mixed for about 5 to 30 minutes using, for example, a Nauter mixer. Thereafter, a finely pulverized powder having an average particle size of 5.0 μm was obtained using a jet mill.

The above finely pulverized powder was pressure-molded with a press machine at the press pressure shown in Table 1 to obtain a preform.
The preform was crushed in a mortar to obtain a crushed material, and then the granulated material was produced as follows using the obtained crushed material. A 36-mesh sieve (first sieve) and an 83-mesh sieve (second sieve) were arranged in the vertical direction at a predetermined interval. In addition, the 1st sieve is located on the upper side. After placing the obtained crushed material on the first sieve, both the first sieve and the second sieve were vibrated for a predetermined time. After completion of the vibration, the granules remaining on the second sieve were collected. This granule has a particle size of 180 to 425 μm based on the opening size of the first sieve and the second sieve. In addition, the external appearance SEM image of the produced granule is shown in FIG. FIG. 1 also shows an appearance SEM image of the finely pulverized powder before granulation.

About the obtained granule, the angle of repose was measured based on the following method. The results are also shown in Table 1.
Angle of repose measurement: Granules were dropped little by little through a sieve from a certain height on a 60 mmφ circular table. The granule supply was stopped just before the granule pile collapsed. The bottom angle of the pile of granules formed on the round table was measured. The circular table was rotated by 120 °, the angles were measured at a total of three locations, and the average was taken as the angle of repose.
In addition, for comparison, the finely pulverized powder remains as it is without being granulated (Comparative Example 1), the granule obtained by spray-drying a slurry containing polystyrene as a binder (Comparative Example 2), and a magnetic field applied to the finely pulverized powder. The angle of repose was measured in the same manner for the granules produced by applying No. 1 (Comparative Example 3), and the results are shown in Table 1.

The resulting granules were then molded in a magnetic field. Specifically, molding was performed at a pressure of 1.4 t / cm ^{2 in} a magnetic field of 15 kOe to obtain a molded body. The obtained molded body was heated to 1080 ° C. in vacuum and Ar atmosphere and held for 4 hours for sintering. Next, the obtained sintered body was subjected to a two-stage aging treatment of 800 ° C. × 1 hour and 560 ° C. × 1 hour (both in an Ar atmosphere).

The results of measuring the magnetic properties of the obtained sintered magnet are shown in Table 1.
For comparison, the finely pulverized powder of Comparative Example 1 was obtained by spray-drying a slurry containing polystyrene as a binder, a sintered magnet obtained by subjecting the finely pulverized powder to molding, sintering and aging treatment in the same manner as above. Sintered magnet (Comparative Example 2) obtained by subjecting granules to molding, sintering and aging treatment in a magnetic field in the same manner as above, and granules produced by applying a magnetic field to finely pulverized powder. The magnetic characteristics of the sintered magnet (Comparative Example 3) obtained by performing the intermediate molding, sintering and aging treatment were measured in the same manner, and the results are shown in Table 1.

As shown in Table 1, while the angle of repose of the finely pulverized powder of Comparative Example 1 is 60 °, in the granules produced by pressure molding, the angle of repose is set to 50 ° or less to improve the fluidity. be able to. Granules produced by applying a magnetic field to finely pulverized powder of Comparative Example 3 have an angle of repose of 54 °. This granule is considered to have a magnetic field remaining in the granule due to the magnetic field applied at the time of granule production, thereby reducing the fluidity of the granule. On the other hand, granules produced by pressure molding have high fluidity. In particular, in Examples 2 to 10 in which the press pressure is 0.05 ton / cm ² or more and the preform density is 3.85 g / cc or more, the angle of repose is 49 ° or less, and the press pressure is 0.45 ton / cm ² or more. In Examples 5 to 10 in which the preform density was 4.15 g / cc or more, the angle of repose was 47 ° or less, indicating higher fluidity.
In addition, the sintered magnet obtained from the granules produced by pressure molding has significantly higher magnetic properties than Comparative Example 2 in which the sintered magnet is produced from granules using a binder such as PVA, In Examples 1 to 8 in which the press pressure is 1.2 ton / cm ² or less and the preform density is 4.35 g / cc or less, a sintered magnet obtained by molding a finely pulverized powder in a magnetic field (Comparative Example 1) It can be seen that the magnetic properties are the same as those of a sintered magnet (Comparative Example 3) obtained from granules produced by applying a magnetic field. As can be seen from Comparative Example 2, when a sintered magnet is produced from granules using a binder such as PVA, the magnetic characteristics are significantly reduced unless the binder is removed, and the magnetic process is simplified while the manufacturing process is simplified. The effect of the present invention capable of obtaining the above is remarkable.

  An advantage of using granules with good fluidity is the ease of powder filling into a narrow-mouth mold. A feeder test was conducted to confirm this. An apparatus called a feeder is used to supply powder to a mold in a normal mass production process. This feeder is a box that reciprocates horizontally on a mold, and a supply hole is formed in the lower part of the box. A certain amount of powder is stored in the box, and when this box reciprocates, the powder falls from the supply hole at the bottom of the box into the mold. The more fluid the powder, the more powder falls with a certain number of reciprocating motions. Therefore, a 3 mm × 20 mm gap was provided in the mold cavity, and on this, the granules produced by pressure molding were reciprocated. The speed of reciprocating motion was 0.4 m / s, and the weight of the powder dropped into the gap after 5 reciprocations was measured. This five reciprocations were set as one measurement object, and 15 measurements were repeated. For comparison, the same measurement was performed on the finely pulverized powder (Comparative Example 1) that was not granulated. The measurement results are shown in FIG. 2, and it was confirmed that the filling properties into the mold cavity can be improved by using the granules.

It is a SEM image which shows the granule appearance produced in the Example. It is a graph which shows the result of the feeder test performed in the Example.

Claims (7)

A step of pressure-molding the raw powder of the rare earth sintered magnet as it is to form a first molded body,
A step of producing said first granules the raw material powder together were sintered wearing only van der Waals forces moldings as by crushing,
Introducing the granules into a mold cavity;
Applying a magnetic field to the granule and obtaining a second molded body by pressure molding;
Sintering the second molded body;
A method for producing a rare earth sintered magnet.   The method for producing a rare earth sintered magnet according to claim 1, wherein, in the step of producing the granules, the granules having an angle of repose of 50 ° or less are produced.   3. The rare earth firing according to claim 1, wherein in the step of introducing the granules into the mold cavity, the granules having a particle size of 0.07 to 0.6 mm are introduced into the mold cavity. A manufacturing method of a magnet. 4. The rare earth sintering according to claim 1, wherein in the step of forming the first molded body, the raw material powder is pressurized at a pressure of 0.03 to 1.3 ton / cm ^2. Magnet manufacturing method.   5. The method according to claim 1, wherein in the step of forming the first molded body, the first molded body having a molded body density of 3.8 to 4.35 g / cc is formed. A method for producing a rare earth sintered magnet according to claim 1.   The method for producing a rare earth sintered magnet according to any one of claims 1 to 5, wherein a lubricant is added to the raw material powder in the step of forming the first molded body. The raw material powder is R ₂ T ₁₄ B phase (R is one or more elements selected from rare earth elements, T is one or two elements selected from transition metal elements including Fe, Fe and Co) 7. The method for producing a rare earth sintered magnet according to claim 1, wherein the rare earth sintered magnet has a composition containing the above elements) and has an average particle diameter of 2.5 to 6 μm.

Images