KR102696554B1 - Manufacturing Method Of Anisotropic Rare Earth Bulk Magnet - Google Patents

Abstract

The present invention relates to a method for manufacturing an anisotropic rare earth bulk magnet, comprising the steps of: preparing an amorphous magnetic powder including Re-Fe-B (Re is at least one rare earth element including Nd); sintering the amorphous magnetic powder under pressure to manufacture an isotropic bulk magnet; applying a slurry containing a solid powder of one of graphite, BN, and B2O3-SiO2 and alcohol to a surface of the isotropic bulk magnet and the inner surface of a hot deformation mold; loading the isotropic bulk magnet to which the slurry has been applied onto the inner surface of the hot deformation mold to which the slurry has been applied, and hot-deforming it at 650 to 800°C in a vacuum or inert gas atmosphere to manufacture an anisotropic bulk magnet.

Description

{Manufacturing Method Of Anisotropic Rare Earth Bulk Magnet}

The present invention relates to a method for manufacturing an anisotropic rare-earth bulk magnet, and more particularly, to a method for manufacturing an anisotropic rare-earth bulk magnet having a low difference in magnetic properties between a location where deformation is concentrated and a location where deformation is relatively less after a hot forming process is performed during the manufacturing of the anisotropic rare-earth bulk magnet.

The demand for Nd-Fe-B magnets is increasing due to the spread of automobiles that respond to home appliances and the environment. The main applications of these magnets are places where heat resistance is required. In order to increase the heat resistance of Nd-Fe-B magnets, the coercivity must be improved, and generally, some of the Nd is replaced with Dy or Tb.

Most rare earth raw materials depend on China, making it difficult to increase prices and secure a stable supply. In particular, Dy and Tb have small reserves compared to Nd, so the price increase is serious. Therefore, much research is being conducted to reduce Dy.

Anisotropic rare earth bulk magnets are manufactured as Nd-Fe-B type magnets by hot forming. These magnets are manufactured by a different process from sintered magnets, and are effective materials for reducing Dy because they are easy to obtain high coercivity in microcrystals. They are materials with Dy-free potential for automotive use.

Nd-Fe-B hot-formed magnets are called MQ3 magnets. These magnets are manufactured through a different process from sintered magnets. Sintered magnets are manufactured by slip casting Nd-Fe-B raw alloys, and then crushing and fine-grinding them into micro-level single crystal particles. These particles are compressed and sintered in an inert atmosphere by aligning the crystals in a specific direction in a magnetic field, and then densifying them to near theoretical density. Then, they are processed into the final shape through cutting and polishing.

Anisotropic rare earth bulk magnets use thin plate-shaped Nd-Fe-B powders manufactured by rapid cooling using rollers as raw materials. This powder is a nanoparticle with a crystal grain size of about 20 nm. The average size of one powder is about 150 μm, and countless crystals exist in one powder.

Anisotropic rare earth bulk magnets are magnetically isotropic because the crystal orientation of the raw powder is random. After the raw powder is pre-formed at room temperature, it is hot pressed to obtain a high-density isotropic magnet. Then, hot forming is performed to produce anisotropic rare earth bulk magnets.

The characteristic of this manufacturing method is that the randomly oriented Nd-Fe-B crystal group is oriented so that the stress direction and the c-axis direction of the crystal are aligned during the hot forming process, thereby manufacturing it to have anisotropy.

In general, the finer the crystal grains of a magnetic material, the higher the coercive force and the better the heat resistance. Anisotropic rare earth bulk magnets are advantageous in obtaining high heat resistance because they have fine crystal grains.

Anisotropic rare earth bulk magnets have a problem in that there is a difference in magnetic properties between locations where deformation is concentrated and locations where deformation is relatively less after a hot forming process using a mold is performed.

Hot-formed anisotropic rare-earth bulk magnets have a high residual flux density due to the addition of crystal strain throughout the entire magnetization, which is oriented along the c-axis, the easy magnetization direction.

However, as strain is added to the crystal of an anisotropic rare-earth bulk magnet, the crystal grains grow, and as the crystal grains grow, the grain boundary phase that contributes to the magnetic separation between crystals decreases, resulting in a decrease in coercivity.

[Patent Document 1] Japanese Patent Publication No. 2018-505540 [Patent Document 2] Korean Patent Publication No. 10-2022-0115773

In order to solve the problems of the prior art, the present invention provides a method for manufacturing an anisotropic rare-earth bulk magnet having a low difference in magnetic properties between a location where deformation is concentrated and a location where deformation is relatively less after a hot forming process is performed during the manufacturing of the anisotropic rare-earth bulk magnet.

In order to achieve the above-mentioned object, the method for manufacturing an anisotropic rare earth bulk magnet according to the present invention is characterized by comprising the steps of: preparing an amorphous magnetic powder containing Re-Fe-B; sintering the amorphous magnetic powder under pressure to manufacture an isotropic bulk magnet; performing surface treatment by infiltrating one of Carbon, Boron, and Nitrogen into the inner surface of a hot deformation mold; and loading the isotropic bulk magnet into the inner surface of the surface-treated hot deformation mold and performing hot deformation at 650 to 800°C in a vacuum or inert gas atmosphere to manufacture an anisotropic bulk magnet.

The method for manufacturing an anisotropic rare earth bulk magnet according to the present invention comprises the steps of: preparing a fine-grained magnetic powder containing Re-Fe-B; sintering the amorphous magnetic powder under pressure to manufacture an isotropic bulk magnet; applying a slurry containing a solid powder of one of graphite, BN, and B2O3-SiO2 and alcohol to the surface of the isotropic bulk magnet and the inner surface of a hot deformation mold; loading the isotropic bulk magnet to which the slurry has been applied onto the inner surface of the hot deformation mold to which the slurry has been applied, and hot-deforming it at 650 to 800°C in a vacuum or inert gas atmosphere to manufacture the anisotropic bulk magnet.

A slurry of one of graphite, BN, and B2O3-SiO2 is applied to the surface of the hot mold at a rate of 0.1 to 0.3 g/cm2 using a spray or brush.

Above The isotropic bulk magnet surface is characterized by applying 0.15 to 2 wt% of a slurry of one of graphite, BN, and B2O3-SiO2 to 100 wt% of the isotropic bulk magnet using a spray or brush.

After applying the BN slurry above, heat at 80 to 150°C for 10 to 30 minutes.

The above B2O3-SiO2 is mixed in alcohol to form a slurry and applied.

According to the method for manufacturing a rare earth permanent magnet according to the present invention, when manufacturing an anisotropic rare earth bulk magnet, after a hot deformation process is performed, the difference in magnetic characteristics between a location where deformation is concentrated and a location where deformation is relatively less is small, so that the quality is equalized.

Figure 1 is a manufacturing process flow chart of the present invention.
Figure 2 is a schematic diagram of the manufacturing process of the present invention.

Hereinafter, the present invention will be described in more detail. Hereinafter, “upper”, “lower”, “front”, “rear” and other directional terms are defined based on the state illustrated in the drawings.

[Manufacturing method]

(1) Rare earth alloy raw material powder preparation stage

The amorphous magnetic powder can be manufactured by a method of manufacturing an amorphous powder by rapidly cooling an alloy ingot containing Re-Fe-B, and specifically, the amorphous magnetic powder can be manufactured using a method such as melt spinning, a gas injection method, a water injection method, a high-energy mill, etc., and in particular, examples of melt spinning are as follows, but are not limited thereto.

The raw material powder using melt spinning of the present invention may be manufactured by the steps of preparing an amorphous magnetic powder, including: a step of preparing an ingot containing Re-Fe-B; a step of melt spinning the ingot to manufacture it into a ribbon; and a step of pulverizing the ribbon to manufacture it into a powder shape.

The ingot containing the above Re-Fe-B can be prepared by melting and mixing the raw material metal bulks constituting the corresponding composition. That is, Nd, Ce, Fe, and B can be melted and mixed to produce an ingot. In this process, other rare earth metals and/or non-rare earth metals can be added, and the contents of other Nd, Ce, Fe, and B and the rare earth metals and/or non-rare earth metals can be adjusted according to the purpose and needs of the magnet being manufactured.

Specifically, the Re is at least one of rare earth elements including Nd, and the rare earth elements are Ce, Sc, Y, La, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. In addition to the elements listed above, a non-rare earth metal may be further included depending on the purpose, and for example, the non-rare earth metal may be a metal element such as Ga, Co, Al, Cu, Nb, Ti, Si, Zr, Ta, V, Mo, Mn, Zn, Ni, Cr, Pb, Sn, In, Mg, Ag, Ge, and may be included in an amount of about 10 at% or less.

According to one embodiment of the present invention, the ingot can be manufactured into a ribbon by melt spinning at a wheel speed of 25 m/s to 50 m/s, 35 m/s to 50 m/s, or 35 m/s to 40 m/s. The wheel speed can be adjusted depending on the composition of the ingot, and for example, when the Ce content increases, melt spinning can be performed at a higher wheel speed. When the ingot is manufactured by melt spinning at a wheel speed within the above range, an amorphous ribbon can be manufactured, and when the ribbon is pulverized, a powder having excellent amorphousness can be provided.

Next, the ribbon may be pulverized to form a powder. The pulverization may be performed by a method used in the relevant technical field.

The average diameter of the above amorphous magnetic powder may be 50 μm or more, 100 μm or more, or 200 μm or more, and is not limited to the above range. However, if the diameter of the powder is too small, oxidation may easily occur as the surface area increases, so it is preferable to use an amorphous magnetic powder having a diameter within the above range.

(2) Pressure sintering stage

Next, the amorphous magnetic powder is subjected to pressure sintering to manufacture an isotropic bulk magnet. The pressure sintering may be performed by putting the amorphous magnetic powder into a mold and applying pressure, and the molded body thus manufactured may be an isotropic bulk magnet, and crystal grains may be formed during the pressure sintering process.

The above-mentioned pressure sintering is not particularly limited in its method as long as sintering can be performed, but may be performed by any one method selected from the group consisting of hot press sintering, hot isostatic pressing sintering, discharge plasma sintering, and microwave sintering, for example. The above-mentioned pressure sintering process is a step for densely binding magnetic powder, and can be said to be a step for bulking the magnet.

The above-mentioned pressure sintering can be performed, for example, using a hot press device, and specifically, a device can be used that inserts powder into a mold in a chamber, heats the powder to a specific temperature in a vacuum or inert gas atmosphere, and then applies pressure to the powder to sinter it.

The above pressure sintering may be performed at a temperature of 500° C. to 900° C., 600° C. to 800° C., 500° C. to 700° C., or 600° C. to 700° C. When the pressure sintering is performed within the above temperature range, the outer surface of the amorphous magnetic powder can be appropriately melted and sintered, and small-sized crystal grains can be formed inside.

The above-mentioned pressure sintering may be performed at a pressure of 50 MPa to 1000 MPa, 100 MPa to 500 MPa, 200 MPa to 500 MPa, or 100 MPa to 300 MPa. When the pressure sintering is performed within the above-mentioned pressure range, the outer surface of the amorphous magnetic powder can be appropriately melted and sintered, and small-sized crystal grains can be formed inside.

(3) Lubricant coating/application step for isotropic bulk magnets and hot deformation molds

In order to suppress the deterioration of coercivity as a result of the grain growth caused by the addition of deformation to the crystals generated by the hot deformation pressure applied to the hot deformation mold by inserting the above-mentioned pressurized isotropic bulk magnet, and the grain boundary phase contributing to the magnetic separation between crystals is reduced according to the grain growth, a lubricant is applied to the surface of the pressurized isotropic bulk magnet and the inside of the hot deformation mold so that the magnetization can be fluidly deformed.

The inner surface of a hot deformation mold is surface treated by infiltrating it with one of Carbon, Boron, or Nitrogen.

The carburizing depth for carbon penetration is 500 to 1200 μm, the boron penetration depth is 10 to 50 μm, and the nitrogen penetration depth is 50 to 300 μm.

Another embodiment applies one of graphite, BN, and B2O3-SiO2 to the surface of a pressurized isotropic bulk magnet and the inner surface of a hot deformation mold.

On the surface of the above hot deformation mold, a slurry of one of graphite, BN, and B2O3-SiO2 is applied at 0.1 to 0.3 g/cm2 by spraying or brushing, and on the surface of the isotropic bulk magnet, a slurry of one of graphite, BN, and B2O3-SiO2 is applied at 0.15 to 2 wt% by spraying or brushing to 100 wt% of the isotropic bulk magnet.

When applying the slurry of the above BN, heat at 80 to 150°C for 10 to 30 minutes, and apply the B2O3-SiO2 by mixing it in alcohol to form a slurry.

The above B2O3-SiO2 is mixed with alcohol to produce a slurry by mixing B2O3 and SiO2 in a ratio of 8:2, placing it in a crucible and heating it in the air to about 800℃ to melt the mixture, and using hand grinding or a pulverizer to make the material remaining inside the crucible into powder, which is then mixed with alcohol to produce a slurry.

(3) Hot deformation stage

After applying a lubricant to an isotropic bulk magnet and a hot deformation mold, the isotropic bulk magnet is hot deformed to produce an anisotropic bulk magnet. Through the hot deformation process, the crystal grains included in the isotropic bulk magnet can be aligned, and through this anisotropy, an anisotropic bulk magnet can be produced.

The above hot deformation may be performed at a temperature of 500° C. to 900° C., 600° C. to 800° C., 500° C. to 800° C., or 600° C. to 800° C. in a vacuum or inert gas atmosphere. When the hot deformation is performed within the above temperature range, the crystal grains of the isotropic bulk magnet can be efficiently aligned, and thus the magnetic properties of the anisotropic bulk magnet can be improved.

The above hot deformation may be performed at a pressure of 20 MPa to 1000 MPa, 100 MPa to 500 MPa, 200 MPa to 500 MPa, or 100 MPa to 300 MPa. When the hot deformation is performed within the above temperature range, the crystal grains of the isotropic bulk magnet can be efficiently aligned, and thus the magnetic properties of the anisotropic bulk magnet can be improved.

The above hot deformation may be performed so that the strain ratio is 2 to 4.

ε = h0/h (Equation 1)

In the above equation 1, ε represents the strain, h0 is the initial height of the sample, and h is the height of the sample after deformation.

When the strain satisfies a value within the above range, the residual magnetic flux density can be increased by grain anisotropy. Specifically, during the pressurized sintering and hot deformation processes, the internal grains can grow into a plate-like shape, and the plate-like shape can correspond to a shape that is elongated in a direction perpendicular to the direction in which magnetization is easy. The melting point of the grain boundary phase is lower than the process temperature, so that the grain boundary phase exists in a liquid phase during the process. When the sample is pressurized at this time, the internal grains rotate, and the direction in which magnetization is easy of each grain is aligned horizontally to the pressing direction, so that crystallographic anisotropy can occur.

The above hot deformation may be performed so that the deformation rate expressed by Equation 2 below is 0.001/s to 1.0/s.

ν = ε/t (Equation 2)

The above ν is the strain rate, the above ε is the strain, and the above t is time.

The above transformation rate may vary depending on the composition of the amorphous magnetic powder, the process temperature, and the purpose and needs of the magnet being manufactured.

Hereinafter, the present invention will be described in detail by way of examples in order to specifically explain the present invention. However, the examples according to the present invention may be modified in various different forms, and the scope of the present invention is not construed as being limited to the examples described below. The examples in this specification are provided to more completely explain the present invention to a person having average knowledge in the art.

The permanent magnet material used in this test was an alloy with a composition of 13.6Nd-72.6Fe-6.6B-0.6Ga-6.6Co (at%). The permanent magnet material used in this test was an alloy ingot with a composition of 13.6Nd-72.6Fe-6.6B-0.6Ga-6.6Co (at%). An isotropic flake powder with a size of 150–200 μm containing fine crystal grains with a grain size of 30–80 nm was manufactured by heating and melting it at high temperature using the melt-spinning method.
The Nd-Fe-B rapid solidification magnetic powder manufactured above was subjected to a pressure sintering process at 600°C or higher to manufacture an isotropic hot-pressed magnet having a certain density or higher.
When manufacturing the above isotropic hot-pressed magnet, it was performed at a high temperature of 600°C or higher, so it was performed in a vacuum atmosphere to prevent oxidation of the magnetic powder.
Specifically, magnetic powder was uniformly charged into a 9×9 mold, the mold was heated to 600°C, a hot pressing process was performed in which 200 MPa of pressure was applied vertically, and the pressure was removed at 700°C and the resulting hot-pressed magnet was cooled to manufacture a hot-pressed magnet. At this time, the density of the hot-pressed magnet thus manufactured was 7.5 g/cc or higher, which is sufficient to reach the theoretical density, and the microstructure formed an isotropic structure with no orientation of crystal grains constituting the magnet.
In order to improve the magnetic properties by converting the manufactured isotropic pressure-sintered magnet into anisotropic one, a hot deformation process was performed as follows. The pressure-sintered magnet was loaded into a 36×9 mold, which had been respectively subjected to carburizing, nitriding, and boronizing treatments (Examples 1-1 to 1-3), and the magnet was heated in a vacuum or inert gas atmosphere to reach approximately 750°C. Then, hot deformation was performed by moving the punch at a constant speed for 60 seconds so that the height of the magnet was reduced by 75% to fill the inside of the mold.
When manufacturing an anisotropic hot-deformed magnet under the above conditions, the differences in pressure and magnetic properties according to the surface condition of the mold are shown in Table 1.
Changes in magnetic properties according to hot deformation pressure and coating on hot deformation mold Surface coating conditions Hot deformation pressure (MPa) Magnetic properties Br(kG) Hcj(kOe) (BH)max(MGOe) Comparative Example 1 Not 680 11.63 13.80 34.45 Example 1-1 C 530 12.31 14.22 38.26 Example 1-2 B 582 12.26 14.17 37.95 Example 1-3 N 593 12.23 14.25 37.77
As can be seen in Table 1, it can be seen that the magnetic properties of Examples 1-1 to 1-3, which were coated on the hot deformation mold, are all improved compared to Comparative Example 1, which was not coated on the hot deformation mold. This is because when deformation is added to the crystal of the anisotropic rare earth bulk magnet, the crystal grains grow, and as the crystal grains grow, the grain boundary phase, which contributes to the magnetic separation between crystals, decreases, resulting in a decrease in the coercivity as in Comparative Example 1. However, it is judged that the magnetic properties of Examples 1-1 to 1-3, which were hot deformation molded by forming a coating layer having lubricating performance, increased the coercivity because friction was reduced during deformation.

The permanent magnet material used in this test is an alloy ingot having a composition of 13.6Nd-72.6Fe-6.6B-0.6Ga-6.6Co (at%), which was heated and melted at a high temperature and an isotropic flake powder having a size of 150 to 200 μm containing fine crystal grains having a grain size of 30 to 80 nm was manufactured by the melt-spinning method.

The Nd-Fe-B rapid solidification magnetic powder manufactured above was subjected to a pressure sintering process at 600°C or higher to manufacture an isotropic hot-pressed magnet having a certain density or higher.

When manufacturing the above isotropic hot-pressed magnet, it was performed at a high temperature of 600°C or higher, so it was performed in a vacuum atmosphere to prevent oxidation of the magnetic powder.

Specifically, magnetic powder was uniformly charged into a 9×9 mold, the mold was heated to 600°C, a hot pressing process was performed in which 200 MPa of pressure was applied vertically, and the pressure was removed at 700°C and the resulting hot-pressed magnet was cooled to manufacture a hot-pressed magnet. At this time, the density of the hot-pressed magnet thus manufactured was 7.5 g/cc or higher, which is sufficient to reach the theoretical density, and the microstructure formed an isotropic structure with no orientation of crystal grains constituting the magnet.

In order to improve the magnetic properties by converting the above-mentioned isotropic pressure-sintered magnet into anisotropic one, a hot deformation process was performed in a vacuum or inert gas atmosphere as follows.

Example 2-1: Boron Nitride (BN) was applied at 0.2 g/cm2 to the surface of a hot deformation mold with a size of 36×9 using a brush, and 0.15 to 2 wt% of Boron Nitride (BN) was applied to the surface of a pressure-sintered magnet with 100 wt% of isotropic bulk magnet, and then placed inside the mold. Boron Nitride was applied using a brush, and heated at a temperature of 100 degrees for 20 minutes, after which hot deformation was performed.

Example 2-2: B2O3 and SiO2 were mixed in a ratio of 8:2 on the surface of a hot deformation mold of 36×9 size, and then alcohol was mixed to form a slurry. After manufacturing, apply 0.2 g/cm2 of slurry to the mold surface, A slurry containing the above B2O3-SiO2 and alcohol was applied at 0.15 to 2 wt% to 100 wt% of an isotropic bulk magnet on the surface of a pressurized sintered magnet, then placed inside a mold and hot deformation was performed.

Examples 2 to 3 were conducted by spraying 0.5 g/cm2 of graphite onto the surface of a 36×9 hot deformation mold, and then applying 0.15 to 2 wt% of graphite to 100 wt% of isotropic bulk magnet onto the surface of a pressure-sintered magnet, placing the magnet inside the mold, and performing hot deformation.

Hot deformation was performed by heating a mold with a pressurized sintering magnet inserted in it in an inert gas atmosphere until it reached approximately 750°C, then moving the punch at a constant speed for 60 seconds to reduce the height of the magnet by 75% and fill the inside of the mold.

When manufacturing an anisotropic hot-deformed magnet under the above conditions, the difference in pressure and magnetic properties according to the surface condition of the pressure-sintered magnet and the mold is shown in Table 2.

Changes in magnetic properties according to hot deformation pressure and coating on the surface and mold of a pressurized sintered magnet Surface coating conditions Hot deformation pressure (MPa) Magnetic properties Br(kG) Hcj(kOe) (BH)max(MGOe) Comparative Example 2 Not 682 11.63 13.80 34.45 Example 2-1 BN 638 12.12 14.31 37.09 Example 2-2 B2O3
-SiO2 624 12.25 14.18 37.89 Example 2-3 black smoke 583 12.31 14.01 38.26

As can be seen in Table 2, the magnetic properties of Examples 2-1 to 2-3, in which the hot deformation mold was coated, are all improved compared to Comparative Example 2, in which the surface of the hot deformation mold and the pressure-sintering magnet were not coated.

This is because when deformation is added to the crystal of an anisotropic rare-earth bulk magnet, the crystal grains grow, and as the crystal grains grow, the grain boundary phase that contributes to the magnetic separation between crystals decreases, resulting in a decrease in the coercivity as in Comparative Example 2. However, it is judged that the magnetic properties of Examples 2-1 to 2-3, in which a coating layer having lubricating properties was formed on a hot deformation mold and hot deformation was performed, increased the coercivity because friction was reduced during deformation.

Example 3 is the result of a test to compare the magnetic properties according to the location at the center and end of hot deformation using a specimen manufactured using the same manufacturing method as Example 2 and Comparative Example 2.

Comparison of magnetic properties at the center of hot deformation and the location with the highest residual flux density Surface coating conditions Psalm Central 1 Psalm 2 Difference in magnetic properties |1/2| Br(kG) Hcj(kOe) Br(kG) Hcj(kOe) Br(kG) Hcj(kOe) Comparative Example 3 Not 11.43 14.21 12.33 13.58 0.9 0.63 Example 3-1 BN 11.93 14.52 12.75 13.94 0.82 0.58 Example 3-2 B2O3
-SiO2 12.09 14.33 12.58 13.87 0.49 0.46 Example 3-3 Graphite 12.28 14.52 12.65 14.20 0.37 0.32

Looking at the results shown in Table 3, Comparative Example 3 had an absolute difference of 0.9 kG in the residual flux density (Br (kG)) and a difference of 0.63 kOe in the coercive force (Hcj (kOe)) in the center and end of the hot deformation, whereas Examples 3-1 to 3-3 had an absolute difference of 0.82, 0.49, and 0.7 kG in the residual flux density (Br (kG)) and a difference of 0.58, 046, and 032 kOe in the coercive force (Hcj (kOe)).

As a result, it was found that coating the surface of the hot deformation mold and the pressure-sintering magnet reduced the difference in magnetic properties between the center and end of the hot deformation.

This has the effect of equalizing quality by reducing the difference in magnetic characteristics between a location where deformation is concentrated and a location where deformation is relatively less concentrated after the hot deformation process is performed during the manufacturing of anisotropic rare earth bulk magnets.

The present invention is not limited to the form of the above-described embodiment, and it is possible to appropriately change it without departing from the gist of the present invention.

Claims (4)

delete A step of preparing an amorphous magnetic powder containing Re-Fe-B (Re is at least one rare earth element including Nd);
A step of manufacturing an isotropic bulk magnet by pressurizing and sintering the above amorphous magnetic powder;
A step of applying a slurry containing a solid powder of one of graphite, BN, and B2O3-SiO2 and alcohol to the surface of the above isotropic bulk magnet and the inner surface of a hot deformation mold;
A method for manufacturing an anisotropic rare earth bulk magnet, characterized by comprising the steps of: loading an isotropic bulk magnet coated with the above slurry into the inner surface of a hot deformation mold coated with the above slurry, and hot-deforming it at 650 to 800°C in a vacuum or inert gas atmosphere to manufacture an anisotropic bulk magnet. delete In the second paragraph,
A method for manufacturing an anisotropic rare earth bulk magnet, characterized in that the above-mentioned coating step comprises heating at 80 to 150° C. for 10 to 30 minutes after coating the BN slurry.