JP2005288493A - Method and apparatus for producing alloy strip, and method for producing alloy powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently produce an alloy strip having good crushable property without bringing about the fusion and the coarseness of the structure. <P>SOLUTION: When the alloy strip is produced from molten alloy with a strip-cast method, after heating and holding the rapidly cooled cast alloy strip at a prescribed temperature, this strip is cooled to a room temperature. The heating and holding temperature is 300-800°C and the heating and holding time is 1-120 min. Then, the used apparatus is provided with a cooling-roll for rapidly casting the molten alloy and a heating chamber disposed near the cooling-roll and heating and holding the alloy strip rapidly cast, to a prescribed temperature. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and an apparatus for producing an alloy thin plate used as a raw material alloy in the production of a rare earth permanent magnet mainly composed of, for example, a rare earth element, a transition metal element, and boron. The present invention relates to a method for producing an alloy powder as a raw material alloy powder.

  In recent years, rare earth permanent magnets such as Nd—Fe—B sintered magnets have advantages such as excellent magnetic properties, Nd as a main component is abundant in resources, and is relatively inexpensive. The demand is increasing. Under these circumstances, research and development for improving the magnetic properties of Nd—Fe—B based sintered magnets, improvement of manufacturing methods for manufacturing high-quality rare earth permanent magnets, etc. have been promoted in various fields. Yes.

  As a method for producing rare earth permanent magnets, powder metallurgy is known and widely used since it can be produced at low cost. In the powder metallurgy method, first, a raw material alloy is coarsely pulverized and finely pulverized to obtain a raw material alloy fine powder having a particle size of about several μm. The raw material alloy fine powder thus obtained is magnetically oriented in a static magnetic field, and press molding is performed in a state where a magnetic field is applied. After molding in a magnetic field, the compact is sintered in a vacuum or in an inert gas atmosphere.

  By the way, in the production of the rare earth permanent magnet by powder metallurgy, it is necessary to cast an alloy as a raw material and pulverize it to produce a rare earth alloy powder. Usually, an ingot having a predetermined composition is cast into a mold. Then, a method of pulverizing is employed. However, this method has a problem in that coarsening of crystal grains, precipitation of αFe, segregation of components, and the like occur during the cooling process of the ingot, resulting in deterioration of pulverizability and magnetic properties of the sintered magnet.

  Therefore, a manufacturing method has been proposed in which a thin plate having a fine homogeneous structure is manufactured by a strip casting method in which a molten alloy is dropped onto a rotating roll and rapidly forged, and this is roughly pulverized and finely pulverized (for example, patents). Reference 1 etc.).

  However, the thin plate manufactured by the strip casting method has a problem that the surface layer portion is hardened particularly by the rapid cooling effect, and the pulverizability is extremely deteriorated. In addition, the fine R (rare earth element) rich phase in the thin plate is not a hydride that is stable against oxidation, and there is a problem that the oxidation proceeds during the pulverization process and the magnetic properties deteriorate.

In order to deal with the latter problem, a method has been proposed in which a thin plate alloy is made to absorb and collapse hydrogen to perform a dehydrogenation treatment (see, for example, Patent Document 2). On the other hand, for the former problem, a method of heat treatment at a temperature of about 800 to 1000 ° C. is proposed before hydrogen treatment in order to relax the hardening state of the surface layer portion of the thin plate alloy and improve the pulverization property. (For example, see Patent Document 3).
JP-A-63-317643 JP-A-6-349618 JP-A-8-264363

  However, the hydrogen treatment described in Patent Document 2 and the heat treatment described in Patent Document 3 both include heating and cooling steps, and thus there is a problem that the processing time is significantly increased. In addition, the heat treatment at a high temperature has a disadvantage that a liquid phase is generated and the thin plates are welded to each other after the heat treatment to make handling difficult. Furthermore, there is a problem that a step of pulverizing again becomes necessary and the structure of the thin plate becomes coarse.

  The present invention has been proposed in order to eliminate such drawbacks of the prior art. That is, the present invention aims to provide a method for producing an alloy thin plate that can be produced efficiently and in a short time without causing welding or coarsening of the structure, etc. Furthermore, it aims at providing a manufacturing apparatus. Another object of the present invention is to provide an efficient method for producing alloy powder by increasing the efficiency of production of the alloy sheet.

  In order to achieve the above object, the present inventors have made various studies over a long period of time. And as a result of earnestly examining the improvement of the pulverization property of the thin plate in particular, the alloy thin plate formed on the surface of the cooling roll is not cooled to room temperature as it is, but is cooled after being heated and held at a predetermined temperature. It has been found that a high alloy sheet can be obtained.

  The present invention has been completed based on such findings. That is, the method for producing an alloy sheet according to the present invention is characterized in that when an alloy sheet is produced from molten alloy by a strip casting method, the rapidly cooled cast alloy sheet is heated and held at a predetermined temperature and then cooled to room temperature. To do. The method for producing an alloy powder according to the present invention is characterized in that the alloy thin plate produced as described above is pulverized by hydrogen storage and dehydrogenation to obtain an alloy powder.

  When manufacturing an alloy sheet from molten alloy by the strip casting method, the pulverizability is greatly improved by cooling the quenched alloy sheet after heating and holding it, instead of directly cooling it to room temperature. The reason for this is considered to be that through such a process, the alloy thin plate could be cooled to room temperature without forming a surface hardened layer.

  The apparatus for producing an alloy thin plate according to the present invention includes a cooling roll for quench casting the molten alloy, and a heating chamber for heating and holding the alloy thin plate disposed in the vicinity of the cooling roll and quenched and cast at a predetermined temperature. It is characterized by that.

  In the manufacturing apparatus having the above-described configuration, the alloy sheet that has been more rapidly cast by the cooling roll is immediately accommodated in a heating chamber disposed close to the alloy roll and heated and held. Therefore, an efficient production of the alloy thin plate having excellent pulverizability can be realized with an extremely simple structure.

  According to the present invention, it is possible to efficiently produce an alloy thin plate excellent in grindability, and further, an alloy powder without causing deterioration in handleability or characteristics, and as a result, for example, high as a final product. It is possible to provide a rare earth permanent magnet or the like having magnetic properties.

  Hereinafter, a method for manufacturing an alloy sheet to which the present invention is applied, a manufacturing apparatus, and a method for manufacturing an alloy powder will be described in detail with reference to the drawings.

  The production method of the present invention is intended for various alloy thin plates and alloy powders, and is particularly suitable for producing rare earth alloy thin plates and rare earth alloy powders that are raw materials for rare earth permanent magnets. First, the rare earth permanent magnet will be described.

The rare earth permanent magnet is mainly composed of a rare earth element, a transition metal element and boron, and the magnet composition may be arbitrarily selected according to the purpose. For example, R-T-B (one or more of R = Y-containing rare earth elements, T = one or more of transition metal elements essential to Fe or Fe and Co, B = boron) system In the case of a rare earth permanent magnet, in order to obtain a rare earth permanent magnet having excellent magnetic properties, the sintered magnet composition has a rare earth element R of 27.0 to 32.0% by weight and boron B of 0.5 to 0.5%. It is preferable that the blending composition is 2.0% by weight and the balance is substantially the transition metal element T (for example, Fe). When the amount of the rare earth element R is less than 27.0% by weight, α-Fe or the like that is soft magnetic precipitates, and the coercive force decreases. Conversely, when the rare earth element R exceeds 32.0% by weight, the amount of the R-rich phase increases and the corrosion resistance deteriorates, and the volume ratio of the R ₂ T ₁₄ B crystal grains as the main phase decreases. The residual magnetic flux density is reduced. Further, when boron B is less than 0.5% by weight, a high coercive force cannot be obtained. Conversely, if boron B exceeds 2.0% by weight, the residual magnetic flux density tends to decrease.

Here, the rare earth element R is a rare earth element including Y, that is, one selected from Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu, or 2 More than a seed. Among these, Nd and Pr are preferably Nd and Pr because the balance of magnetic properties is good and they are abundant and relatively inexpensive. Further, Dy ₂ Fe ₁₄ B and Tb ₂ Fe ₁₄ B compounds have a large anisotropic magnetic field, and adopting Dy or Tb as a substitution element for Nd is effective in improving the coercive force Hcj.

  Further, the rare earth permanent magnet may be an R-TBM type rare earth permanent magnet by adding the additive element M. In this case, examples of the additive element M include Al, Cr, Mn, Mg, Si, Cu, C, Nb, Sn, W, V, Zr, Ti, and Mo. One or two of these may be used. The above can be selected and added. For example, the addition of Nb, Zr, W or the like, which is a refractory metal, has an effect of suppressing crystal grain growth. Of course, it is needless to say that the composition of the rare earth permanent magnet is not limited to these compositions, and can be applied to all conventionally known compositions.

  In the rare earth permanent magnet described above, the oxygen content is preferably 2500 ppm or less. This is because when the oxygen content exceeds 2500 ppm, the amount of rare earth elements present as oxides increases, the magnetically effective rare earth elements to be present in the main phase and subphase decrease, and the coercive force decreases. The problem arises. Furthermore, the generated oxide is non-magnetic and causes a decrease in magnetization of the sintered body. The relationship between the amount of oxygen and the amount of oxide produced has a linear relationship according to the stoichiometric ratio of the compounds, but in order to satisfy the coercive force and magnetization required for high performance rare earth magnets in recent magnet applications. It is required to be 2500 ppm or less. In the present invention, the amount of oxygen contained in the raw material alloy powder is preferably 1000 ppm or less, particularly 400 ppm or less.

  Further, the rare earth permanent magnet preferably has a carbon (C) content of 1500 ppm or less and a nitrogen (N) content of 200 to 1500 ppm. When the carbon content exceeds 1500 ppm, carbon forms a carbide with a part of the rare earth element, and the magnetically effective rare earth element is reduced and the coercive force is lowered. Further, by setting the nitrogen amount in the above range, both excellent corrosion resistance and high magnetic properties can be achieved.

  The above-mentioned rare earth permanent magnet is manufactured by powder metallurgy and is made into a sintered body by sintering. Hereinafter, the example which applied the manufacturing method of the alloy thin plate of this invention and the manufacturing method of alloy powder to the manufacturing method by the powder metallurgy method of a rare earth permanent magnet is demonstrated.

  FIG. 1 shows an example of a process for producing a rare earth permanent magnet by powder metallurgy. This manufacturing process basically includes an alloying step 1, a coarse pulverizing step 2, a fine pulverizing step 3, a magnetic field forming step 4, a sintering step 5, an aging step 6, a processing step 7, and a surface treatment step 8. Consists of. In order to prevent oxidation, most of the steps after sintering are performed in a vacuum or in an inert gas atmosphere (in a nitrogen atmosphere, an Ar atmosphere, etc.).

  In the alloying step 1, a metal or alloy as a raw material is blended according to the magnet composition, dissolved in an inert gas, for example, Ar atmosphere, and cast into an alloy. In the present invention, a strip casting method (continuous casting method) is adopted in which molten high-temperature liquid metal (alloy molten metal) is supplied onto a rotating roll and the alloy thin plate is continuously cast.

  In the strip casting method, first, a raw metal (alloy) is melted in a melting furnace and supplied onto a rotating roll. As the raw material metal (alloy), pure rare earth elements, rare earth alloys, pure iron, ferroboron, and alloys thereof can be used.

  In a normal strip casting method, a molten alloy is supplied onto a rotating roll and quenched and then the obtained alloy thin plate is cooled to room temperature as it is. In the present invention, the rapidly cooled cast alloy sheet is not cooled directly to room temperature, but is once heated and held at a predetermined temperature in a heating chamber and then cooled to room temperature.

  The temperature to be held by heating is preferably 300 ° C to 800 ° C, more preferably 500 ° C to 750 ° C. If the temperature to hold by heating is less than 300 ° C., the pulverizability of the obtained alloy thin plate may not be sufficiently improved. On the other hand, when the temperature for heating and holding exceeds 800 ° C., a liquid phase appears, partial welding occurs, handling properties are lowered, and there is a possibility that inconveniences such as a long time for cooling occur. On the other hand, the heating and holding time is preferably 1 minute to 120 minutes. If the heat holding time is less than 1 minute, the pulverizability of the obtained alloy thin plate may not be sufficiently improved. On the other hand, if the heating and holding time is 120 minutes or longer, the treatment takes a long time, which is not preferable.

  In the heating and holding, any heating method may be used. For example, resistance heating or heating with hot air may be used. It is also effective to circulate an air current in order to heat the alloy thin plate uniformly.

  FIG. 2 shows an example of the manufacturing apparatus of the present invention. This manufacturing apparatus rotates a melting furnace 11 for melting a raw metal (alloy) to form a molten alloy, a rotating roll 12 as a cooling roll for rapidly casting the molten alloy, and a molten alloy in the melting furnace 11. The tundish 13 for supplying the roll 12 at a predetermined flow rate and the rotary roll 12 are arranged in proximity to each other, and are heated and held in the heating chamber 14 and the heating chamber 14 for heating and holding the alloy thin plate quenched and forged by the rotary roll 12. And a recovery container 15 for cooling the alloy thin plate to room temperature.

  In the apparatus for manufacturing an alloy thin plate having such a configuration, the raw material alloy is melted in the melting furnace 11 to form a molten alloy, and this molten alloy is supplied onto the rotary roll 12 via the tundish 13 and rapidly cast. The rapidly cooled cast alloy sheet is immediately accommodated in the heating chamber 14 and heated and held for a predetermined temperature and for a predetermined time. After this heating and holding, it is cooled to room temperature in the collection container 15. The recovery container 15 cools the recovered alloy thin plate by air cooling or water cooling.

  In the manufacturing apparatus, any heating mechanism such as resistance heating or hot air heating may be provided as the heating means of the heating chamber 14. Further, in order to make the temperature distribution in the heating chamber 14 uniform, an airflow circulation mechanism using an inert gas (in a nitrogen atmosphere, an Ar atmosphere, or the like) may be provided. When hot air heating using an inert gas (in a nitrogen atmosphere, Ar atmosphere, or the like) is employed as the heating mechanism, it is preferable because it also serves as an air flow circulation mechanism.

  Moreover, although the rotary roll 12 was made into the single roll in this example, it can also be made into a double roll. In the case of the present invention, it is preferable to avoid excessive cooling with the rotating roll 12, and it is preferable to stop the cooling to about the heating holding temperature in the heating chamber 14. Therefore, for example, it is preferable to suppress the supercooling by reducing the thermal conductivity of the rotary roll 12.

   Specifically, the thermal conductivity of the surface layer of the rotary roll 12 is made lower than the thermal conductivity of the internal substrate. In this case, the thermal conductivity of the surface layer is preferably 0.6 J / (cm · s · K) or less, and the thermal conductivity of the substrate is 1.4 J / (cm · s · K) or more. It is preferable. When the thermal conductivity is 0.6 J / (cm · s · K) or less, the grindability is further improved. The lower limit is not particularly limited, but if the thermal conductivity is less than 0.1 / (cm · s · K), the heat transfer is deteriorated, so that only the vicinity of the surface becomes high temperature and seizure may occur. . Therefore, more preferably, the thermal conductivity of the surface layer is 0.45 J / (cm · s · K) or less and 0.1 J / (cm · s · K) or more. Examples of the material for the surface layer satisfying such conditions include metals or alloys containing at least one selected from Cr, Ni, Co, Nb and V. In addition, it is preferable that the thickness of the said surface layer shall be 10 micrometers-100 micrometers.

  After manufacturing an alloy thin plate by the above, this is coarsely pulverized and pulverized to produce an alloy powder. First, in the coarse pulverization step 2, the previously cast raw alloy thin plate is pulverized until the particle size is about several hundred μm. As the pulverizing means, a stamp mill, a jaw crusher, a brown mill, or the like can be used. In order to improve the coarse pulverization property, it is effective to perform coarse pulverization after occlusion of hydrogen and embrittlement.

  After the aforementioned coarse pulverization step 2 is completed, a pulverization aid is usually added to the coarsely pulverized raw material alloy powder. As the grinding aid, for example, a fatty acid compound or the like can be used. Particularly, by using fatty acid amide as the grinding aid, a rare earth permanent magnet having good magnetic properties, particularly high orientation and high magnetization can be obtained. Can be obtained. The addition amount of the grinding aid is preferably 0.03 to 0.4% by weight. If the addition amount of the grinding aid is less than 0.03% by weight, the effect on the magnetic properties of the lubricant cannot be sufficiently obtained. If the addition amount is 0.4% by weight or less, the residual after sintering The amount of carbon can be effectively reduced, which is effective in improving the magnetic properties of the rare earth permanent magnet.

  After the coarse pulverization step 2, a fine pulverization step 3 is performed. The fine pulverization step 3 is performed using, for example, an airflow pulverizer. The conditions for fine pulverization may be appropriately set according to the airflow pulverizer to be used, and the raw material alloy powder is finely pulverized until the average particle size becomes about 1 to 10 μm, for example, 3 to 6 μm. A jet mill or the like is suitable as the airflow pulverizer. A jet mill opens a high-pressure inert gas (for example, nitrogen gas) from a narrow nozzle to generate a high-speed gas flow, accelerates powder particles by this high-speed gas flow, and collides powder particles with each other. Or, it is a method of crushing by generating a collision with a collision plate or a container wall. Jet mills are generally classified into jet mills that use fluidized beds, jet mills that use vortex flow, jet mills that use impingement plates, and the like. Among these jet mills, a jet mill using a fluidized bed and a jet mill using a vortex are preferable, and a jet mill using a fluidized bed is particularly preferable. For example, the specific gravity of the raw material alloy powder and the grinding aid are greatly different, but in the fluidized bed and in the vortex, the grinding and mixing are performed well regardless of the difference in specific gravity. It is because it does not become.

  After the pulverizing step 3, in the forming step 4 in the magnetic field, the raw material alloy fine powder is formed in the magnetic field. Specifically, the raw material alloy fine powder obtained in the fine pulverization step 3 is filled in a mold in which an electromagnet is arranged, and is formed in a magnetic field with the crystal axis oriented by applying a magnetic field. The forming in the magnetic field may be either a vertical magnetic field forming in which the forming pressure and the magnetic field direction are parallel, or a horizontal magnetic field forming in which the forming pressure and the magnetic field direction are orthogonal to each other. Further, a pulse power source and an air-core coil can be employed as the magnetic field applying means. The forming in the magnetic field may be performed at a pressure of about 100 to 200 MPa in a magnetic field of 700 to 1300 kA / m, for example.

  Next, the molded body formed by the molding step in the magnetic field is sintered, but it is preferable to perform a debinding process in the debinding step prior to sintering. This binder removal process is a process for removing the lubricant added in the pulverization process and contained in the molded body, and by removing the binder, carbon remaining as a carbide, oxide, etc. after sintering. And the remaining amount of oxygen can be reduced.

  Next, in the sintering step 5, sintering is performed. That is, after forming the raw material alloy fine powder in a magnetic field, the formed body (pre-sintered body) subjected to the binder removal treatment 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, and the difference of a particle size and a particle size distribution, for example, what is necessary is just to sinter at 1000-1150 degreeC for about 5 hours. The heating method is arbitrary such as resistance heating and high frequency induction heating.

  After sintering, in the aging step 6, it is preferable to subject the obtained sintered body to an aging treatment. This aging treatment is an important step in controlling the coercive force Hcj of the obtained rare earth permanent magnet. For example, the aging treatment is performed in an inert gas atmosphere or in a vacuum. As the aging treatment, a two-stage aging treatment is preferable, and in the first aging treatment step, the temperature is maintained at a temperature of about 800 ° C. for 1 to 3 hours. Next, a first quenching step is provided for quenching to room temperature to 200 ° C. In the second stage aging treatment step, the temperature is maintained at about 550 ° C. for 1 to 3 hours. Next, a second quenching step for quenching to room temperature is provided. Since the coercive force Hcj is greatly increased by heat treatment at around 600 ° C., when aging treatment is performed in a single stage, it is preferable to perform aging treatment at around 600 ° C.

  After the aging step 6, a processing step 7 and a surface treatment step 8 are performed. The processing step 7 is a step of mechanically forming into a desired shape. The surface treatment step 8 is a step performed to suppress oxidation of the obtained rare earth permanent magnet. For example, a plating film or a resin film is formed on the surface of the rare earth permanent magnet.

  Next, specific examples of the present invention will be described based on experimental results.

<Experiment 1>
A metal or alloy as a raw material was blended so as to have a predetermined composition, and an alloy melted by high frequency melting in an alumina crucible was formed into an alloy thin plate having a thickness of 0.3 mm by strip casting. The alloy composition is Nd 25 wt%, Pr 5 wt%, Dy 1.5 wt%, B 1 wt%, Al 0.2 wt%, Zr 0.3 wt%, Co 1.5 wt%, and Fe balance.

  In producing the alloy thin plate, the molten alloy is melted at a high frequency, and then cast on a copper roll for strip casting, and then the obtained thin plate is dropped into a heating chamber maintained at 650 ° C. and heated for 30 minutes. Then, it was dropped into a water-cooled chamber and cooled.

  The obtained alloy thin plate was coarsely pulverized to 3 mm or less using a brown mill. Furthermore, alloy fine powder was produced using a jet mill. Table 1 shows a comparison of particle size distributions when the heat treatment is performed in the heating chamber (Example 1) and when the heat treatment is not performed (Comparative Example 1). Similarly, the particle size distribution is also shown in Table 1 for the case of using an alloy thin plate heated at 1000 ° C. after being directly cooled to room temperature without being heated in the heating chamber (Comparative Example 2).

Also, using these fine powders, press molding at a magnetic field of 12 kOe, 1.5 t / cm ³ , then sintering at 1090 ° C. for 3 hours, holding at 850 ° C. for 1 hour, and further aging at 570 ° C. for 1 hour Processed. Magnetic properties [residual magnetic flux density Br, coercive force iHc] were measured for the magnets obtained using each alloy fine powder (Example 1 and Comparative Examples 1 and 2). Magnet characteristics [residual magnetic flux density Br, coercive force iHc,] were measured using a BH tracer. The results are also shown in Table 1.

  As is apparent from Table 1, by performing heating and holding in the heating chamber, the pulverizability of the alloy thin plate is improved, and both the particle size distribution and the average particle size are good. Moreover, it turns out that the magnet which has a high magnetic characteristic can be obtained by using the alloy fine powder produced in this way.

<Experiment 2>
In this experiment, a copper roll with Cr plating was used as a cooling roll, and the others were made in the same manner as in Experiment 1 to produce an alloy thin plate, alloy fine powder, and magnet. Table 2 shows a comparison of the particle size distribution between the case where the heat treatment is performed in the heating chamber (Example 2) and the case where the heat treatment is not performed (Comparative Example 3), and the magnetic characteristics of the produced magnet. The thermal conductivity of Cr plating is 0.43 J / (cm · s · K), the thickness is 6 μm, and the thermal conductivity of the copper roll as the substrate is 1.5 J / (cm · s · K). Met.

  As is apparent from Table 2, by using a roll having a low thermal conductivity, the grindability is further improved, and both the particle size distribution and the average particle size are good. Moreover, the magnet which has a high magnetic characteristic can be obtained by using the alloy fine powder produced in this way.

It is a flowchart which shows an example of the manufacturing process of a rare earth permanent magnet. It is a figure which shows typically an example of the manufacturing apparatus of an alloy thin plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Alloying process, 2 Coarse grinding process, 3 Fine grinding process, 4 Magnetic field forming process, 5 Sintering process, 6 Aging process, 7 Processing process, 8 Surface treatment process, 11 Melting furnace, 12 Rotary roll, 13 Tundish , 14 Heating chamber, 15 Recovery container

Claims (15)

  A method for producing an alloy thin plate, comprising: heating and holding a rapidly cast alloy thin plate at a predetermined temperature when producing the alloy thin plate from molten alloy by a strip casting method, and then cooling to a room temperature.   The method for producing an alloy thin plate according to claim 1, wherein the temperature to be heated and held is 300 ° C to 800 ° C and the time is 1 minute to 120 minutes.   The method for producing an alloy thin plate according to claim 1 or 2, wherein heating and holding are performed by hot air.   4. The method for producing an alloy sheet according to claim 1, wherein the alloy sheet is a rare earth alloy sheet.   5. The method for producing an alloy thin plate according to claim 4, wherein the rare earth alloy thin plate is a rare earth alloy thin plate for a rare earth permanent magnet.   6. The method for producing an alloy thin plate according to claim 5, wherein the rare earth alloy thin plate is an NdFeB-based alloy thin plate.   An apparatus for producing an alloy thin plate, comprising: a cooling roll for rapidly casting a molten alloy; and a heating chamber for heating and holding the alloy thin plate disposed in the vicinity of the cooling roll and quenched and cast at a predetermined temperature.   The apparatus for producing an alloy thin plate according to claim 7, wherein the heating chamber is provided with a heating mechanism by hot air.   The apparatus for producing an alloy thin plate according to claim 7, wherein an airflow circulation mechanism is provided in the heating chamber.   The apparatus for producing an alloy thin plate according to any one of claims 7 to 9, wherein the thermal conductivity of the surface layer of the cooling roll is lower than the thermal conductivity of the substrate.   The surface layer has a thermal conductivity of 0.6 J / (cm · s · K) or less, and the substrate has a thermal conductivity of 1.4 J / (cm · s · K) or more. The apparatus for producing an alloy thin plate according to claim 10.   The apparatus for producing an alloy thin plate according to claim 11, wherein the thermal conductivity of the surface layer is 0.45 J / (cm · s · K) or less and 0.1 J / (cm · s · K) or more. .   The apparatus for producing an alloy thin plate according to any one of claims 10 to 12, wherein the surface layer has a thickness of 10 µm to 100 µm.    The said surface layer consists of a metal or alloy containing at least 1 sort (s) selected from Cr, Ni, Co, Nb, and V, The manufacture of the alloy thin plate of any one of Claims 10 thru | or 13 characterized by the above-mentioned. apparatus.   A method for producing an alloy powder, characterized in that the alloy thin plate produced by the production method according to claim 1 is pulverized by hydrogen storage and dehydrogenation to obtain an alloy powder.

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