Manufacturing method for RTB sintered magnets

Abstract

To provide a novel manufacturing method of an R-T-B-based sintered magnet capable of improving pulverization efficiency.SOLUTION: A manufacturing method of an R-T-B-based sintered magnet includes the steps of: obtaining a fine powder by adding, mixing and pulverizing at least one kind of lubricant to a coarse pulverized powder of an alloy for R-T-B-based sintered magnet (R is at least one of rare earth elements and always contains at least one selected from among Nd, Pr and Ce, T is at least one of transition metal elements and always contains Fe, and B is boron); and creating a sintered body of the fine powder. The lubricant contains an alkyl amide amine type compound expressed by the following formula (1) (R1)CONH(R2)N(R3)2 (where R1 is an alkyl chain of which the carbon number is 17 or more and 21 or less and each of R2 and R3 is an alkyl chain of which the carbon number is 1 or more and 4 or less).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application relates to a method for producing an RTB based sintered magnet. [Background technology]

[0002] RTB sintered magnets (R is a rare earth element and must contain at least one selected from the group consisting of Nd, Pr, and Ce, T is at least one transition metal element and must contain Fe, and B is boron) are classified into RFe 14 It consists of a main phase of a compound with a B-type crystal structure, a grain boundary phase located at the grain boundaries of this main phase, and a compound phase formed by the influence of trace additive elements and impurities. RTB-based sintered magnets have a high residual magnetic flux density B r (Hereafter, simply "B r ") and high coercive force H cJ (Hereafter, simply "H cJ ") and is known as the highest performance magnet among permanent magnets.

[0003] For this reason, RTB sintered magnets are used in a variety of motors in the automotive sector, including electric vehicles (EVs, HVs, PHVs), renewable energy sectors such as wind power generation, home appliances, and industrial sectors. RTB sintered magnets are an essential material for making these motors smaller, lighter, more efficient, and more energy-efficient (improving energy efficiency). RTB sintered magnets are also used in the drive motors of electric vehicles, and the replacement of internal combustion engine vehicles with electric vehicles contributes to preventing global warming by reducing greenhouse gases such as carbon dioxide (reducing fuel and exhaust gases). In this way, RTB sintered magnets are making a significant contribution to the realization of a clean energy society.

[0004] Such an RTB based sintered magnet is manufactured, for example, through steps such as preparing an alloy powder, press-molding the alloy powder to produce a powder compact, and sintering the powder compact. The alloy powder is manufactured, for example, by the following method. First, an alloy is produced from a molten metal of various raw material metals by a method such as the ingot method or strip casting method. The obtained alloy is subjected to a pulverization process to obtain an alloy powder with a predetermined particle size distribution. This pulverization process usually includes a coarse pulverization process and a fine pulverization process, the former of which is carried out, for example, by utilizing the hydrogen embrittlement phenomenon, and the latter of which is carried out, for example, by using an airflow pulverizer (jet mill).

[0005] There is a demand for further improvements in performance and cost reduction for RTB sintered magnets. Techniques for improving performance include, for example, making the structure finer (reducing the size of the alloy powder) and reducing the oxygen content, while techniques for reducing cost include, for example, improving milling efficiency. Patent Document 1 describes a method for improving milling efficiency in which an alloy cast by strip casting is coarsely milled to obtain alloy powder, to which a specific lubricant is added and blended, and the resulting powder is then milled using a jet mill. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 9-17677 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, efforts have been made to further refine alloy powders in order to improve performance, but this has led to problems such as reduced productivity due to reduced pulverization efficiency. Therefore, there is a strong demand for improved pulverization efficiency in fine pulverization. Embodiments of the present disclosure provide a new method for producing RTB-based sintered magnets that can improve pulverization efficiency. [Means for solving the problem]

[0008] In a non-limiting exemplary embodiment, the method for producing an RTB based sintered magnet according to the present disclosure includes: Produced by the rapid cooling methodThe method includes the steps of adding at least one lubricant to a coarsely pulverized powder of an alloy for an RTB sintered magnet (R is at least one rare earth element and must include at least one selected from the group consisting of Nd, Pr, and Ce; T is at least one transition metal element and must include Fe; and B is boron), mixing the mixture, and pulverizing the mixture to obtain a fine powder; and preparing a sintered body from the fine powder, wherein the lubricant includes an alkylamidoamine-type compound represented by the following formula (1). (R 1 )CONH(R 2 )N(R 3 )2 formula (1) (R 1 is an alkyl chain having 17 to 21 carbon atoms, and R 2 and R 3 are alkyl chains with 1 to 4 carbon atoms.) In one embodiment, the alloy for an RTB based sintered magnet is produced by strip casting.

[0009] In one embodiment, the alkylamidoamine-type compound is behenamidopropyldimethylamine.

[0010] In one embodiment, the amount of the lubricant added to the coarsely pulverized powder is 0.02% by mass or more and 0.3% by mass or less.

[0011] In one embodiment, the lubricant is dissolved in a solvent to prepare a solvent solution, and the solvent solution is added to and mixed with the coarsely pulverized powder. [Effects of the Invention]

[0012] According to the embodiments of the present disclosure, it is possible to provide a new method for producing an RTB based sintered magnet that can improve pulverization efficiency. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing a schematic configuration example of an RTB sintered magnet alloy crushing system 1000 according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] In the fine pulverization of RTB sintered magnets, Patent Document 1 proposes using a fine, homogeneous alloy obtained by strip casting and then adding a lubricant to the coarsely pulverized alloy powder, thereby improving pulverization efficiency, corrosion resistance, and magnetic properties. In this way, the combination of the refinement of the alloy structure achieved by switching from the ingot method to the strip casting method and the lubricant's effects has led to improvements in pulverization efficiency, corrosion resistance, and magnetic properties. To produce even higher-performance RTB sintered magnets, it has become common to use a high-purity inert gas (e.g., nitrogen, argon, or helium) with a purity of 99.5% or higher as the pulverization gas. However, it has been found that conditions with little or no oxygen or moisture in the pulverization gas can significantly increase the aggregation of pulverized powder particles and adhesion to the inside of the pulverizer, reducing the probability of collisions between powder particles and impairing fluidity within the pulverization chamber, slowing the progress of pulverization and resulting in a significant decrease in pulverization efficiency. This phenomenon is difficult to resolve simply by increasing the amount of stearic acid added as a lubricant. Furthermore, if an attempt is made to solve this problem by adding stearic acid alone, it would be necessary to add an excessive amount of stearic acid, which would result in an increase in the amount of residual C due to the addition of stearic acid, which could have a negative impact on the magnetic properties.

[0015] Based on these findings, as a result of repeated studies, the inventors have found that by adding a lubricant (a lubricant containing a surfactant coupling agent) containing an alkylamide amine type compound represented by the following formula (1) to the coarse pulverized powder and performing pulverization, the pulverization efficiency can be significantly improved. This is because a lubricating surface with a surfactant effect containing an alkylamide amine type compound is formed on the surface of the powder particles during the pulverization process, suppressing the reaction between the powder particles and an inert gas (e.g., nitrogen gas) and impurities (such as moisture and carbon dioxide) in the gas, suppressing the aggregation of the powder particles during pulverization, improving the collision probability between the powders, and preventing the energy of the pulverization gas from being used for disintegrating the aggregation, and being efficiently used for pulverization. (R 1 )CONH(R 2 )N(R 3 )2 Formula (1) (R 1 is an alkyl chain having 17 or more and 21 or less carbon atoms, and R 2 and R 3 are each an alkyl chain having 1 or more and 4 or less carbon atoms.)

[0016] <Method for Manufacturing R-T-B Sintered Magnet> Hereinafter, embodiments of the method for manufacturing an R-T-B sintered magnet according to the present disclosure will be described.

[0017] The present disclosure is a method for manufacturing an R-T-B sintered magnet. Here, R is at least one of rare earth elements, and necessarily includes at least one selected from the group consisting of Nd, Pr, and Ce, and T is at least one transition metal element and necessarily includes Fe.

[0018] This method for manufacturing an R-T-B sintered magnet includes (1) A step of adding and mixing at least one lubricant to the coarse pulverized powder of the alloy for the R-T-B sintered magnet and performing pulverization to obtain fine powder, and (2) A step of producing a sintered body of the fine powder.

[0019] First, the following shows a preferable composition of the R-T-B sintered magnet. R is a rare earth element and must contain at least one element selected from the group consisting of Nd, Pr, and Ce. Preferably, a combination of rare earth elements represented by Nd-Dy, Nd-Tb, Nd-Dy-Tb, Nd-Pr-Dy, Nd-Pr-Tb, Nd-Pr-Dy-Tb, Nd-Ce-Dy, Nd-Ce-Tb, Nd-Ce-Dy-Tb, Nd-Pr-Ce-Dy, Nd-Pr-Ce-Tb, or Nd-Pr-Ce-Dy-Tb is used.

[0020] Among R, Dy and Tb have particularly high coercive force H cJ This is effective in improving the properties. In addition to the above elements, other rare earth elements such as La may also be contained. The R content of the RTB sintered magnet is, for example, 27% by mass or more and 35% by mass or less. Preferably, the R content of the RTB sintered magnet is 32% by mass or less (more preferably 27% by mass or more and 31% by mass or less, and even more preferably 29% by mass or more and 31% by mass or less). This allows for better magnetic properties to be obtained.

[0021] T contains iron (including when T consists essentially of iron), and up to 50% by mass of iron may be replaced with cobalt (Co) (including when T consists essentially of iron and cobalt). Co is effective in improving temperature characteristics and corrosion resistance, and the alloy powder may contain up to 10% by mass of Co. The content of T may account for the remainder of R and B, or R, B, and M, which will be described later.

[0022] The content of B may be a known content, and for example, a preferred range is 0.85 mass % to 1.2 mass %. If it is less than 0.85 mass %, high H cJ However, if the B content exceeds 1.2 mass%, the Br content may decrease. The B content is more preferably 1.0 mass% or less, and even more preferably 0.98 mass% or less. Note that a portion of B can be substituted with C (carbon).

[0023] In addition to the above elements, H cJTo improve the properties, an M element can be added. The M element is one or more elements selected from the group consisting of Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, and W. The total amount of the M element added is preferably 5.0 mass% or less. If it exceeds 5.0 mass%, Br may decrease. Inevitable impurities are also acceptable.

[0024] Furthermore, the R2T, which is the main phase of the RTB based sintered magnet of the present disclosure, 14 The average crystal grain size of the B phase is preferably 2.0 μm or more and 7.0 μm or less, more preferably 3.0 μm or more and 5.0 μm or less, and even more preferably 3.0 μm or more and 4.0 μm or less. Higher magnetic properties can be obtained. The average crystal grain size can be determined, for example, by the number-average equivalent circle diameter of crystal grains (5,000 or more) evaluated by EBSD (Electron Backscatter Diffraction). Next, a method for producing the RTB based sintered magnet of the present disclosure will be described.

[0025] <(1) Example of a process in which at least one lubricant is added to coarsely pulverized powder of an alloy for an RTB sintered magnet, the mixture is then pulverized to obtain a fine powder> The process of adding at least one lubricant to a coarsely pulverized powder of an alloy for an RTB sintered magnet, mixing the mixture, and pulverizing the mixture to obtain a fine powder includes the steps of preparing an alloy for an RTB sintered magnet, coarsely pulverizing the alloy by, for example, a hydrogen pulverization method to obtain a coarsely pulverized powder, and supplying the coarsely pulverized powder to, for example, a jet mill device to pulverize the coarsely pulverized powder to obtain a fine powder.

[0026] Here is an example of a method for producing an alloy for an RTB sintered magnet. An alloy ingot can be obtained by ingot casting, in which a metal or alloy previously prepared to have the composition described above is melted and poured into a mold. Alternatively, alloy flakes can be produced by a rapid cooling method, such as strip casting or centrifugal casting, in which the molten metal is brought into contact with a single roll, twin rolls, rotating disk, or rotating cylindrical mold, and quenched to produce a solidified alloy that is thinner than the alloy produced by the ingot method.

[0027] In embodiments of the present disclosure, materials produced by either the ingot method or the quenching method can be used, but production by a quenching method such as strip casting is preferred. The thickness of quenched alloys produced by the quenching method is typically in the range of 0.03 mm to 1 mm and is plate-shaped. The molten alloy begins to solidify from the surface that contacts the chill roll (the roll contact surface), and crystals grow columnarly from the roll contact surface in the thickness direction. Compared to alloys (ingot alloys) produced by conventional ingot casting (mold casting), quenched alloys have a refined structure and small crystal grain size due to the shorter cooling time. Because the R-rich phase is finely distributed within the grain boundaries, the quenching method provides excellent dispersibility of the R-rich phase. Therefore, fracture at the grain boundaries is more likely to occur when using hydrogen pulverization. By hydrogen pulverizing the quenched alloy, the size of the hydrogen pulverized powder (coarsely pulverized powder) can be reduced to, for example, 1.0 mm or less. At least one lubricant is added to the coarsely pulverized powder obtained in this manner, and then the resulting powder is finely pulverized, for example, using a jet mill.

[0028] A pulverization system for performing fine pulverization according to the present disclosure will be described with reference to Fig. 1. Fig. 1 is a diagram schematically illustrating a configuration example of a pulverization system 1000 according to this embodiment. In this example, the RTB sintered magnet alloy pulverization system 1000 includes a jet mill device 100, a cyclone collection device 200, and a bag filter device 300.

[0029] The jet mill device 100 receives a supply of material to be pulverized from a raw material tank (not shown) containing coarsely pulverized powder to which a lubricant has been added via a raw material input pipe 34. The addition of the lubricant will be described in detail later. The material to be pulverized is a coarsely pulverized powder of an alloy for an RTB-based sintered magnet, with an average particle size of 10 μm or more and 500 μm or less.

[0030] The raw material input pipe 34 is provided with multiple valves, which are opened and closed to maintain an appropriate internal pressure in the jet mill device 100. The material to be pulverized introduced into the jet mill device 100 is finely pulverized by the high-speed injection of inert gas from the nozzle pipe 36, which causes the material to collide with each other and with collision plates installed to efficiently advance the pulverization.

[0031] Powder of alloys for RTB sintered magnets is active and easily oxidized. For this reason, the gas used in the jet mill device 100 is preferably a dry (high-purity) inert gas such as nitrogen, argon, or helium with a dew point of -60°C or below, in order to avoid the risk of heat generation and fire and to reduce the oxygen content as an impurity, thereby improving the performance of the magnet.

[0032] The powder particles (fine powder) finely pulverized inside the jet mill apparatus 100 are carried by the ascending air current and guided from the upper outlet to the inlet pipe 20 of the cyclone collector 200. Insufficiently pulverized coarse particles are separated by a classifying rotor installed to classify the coarse particles, remaining inside the jet mill apparatus 100 and undergoing further pulverization by collision. The coarse particles may be classified using a classifying rotor or by centrifugal separation using a swirling flow. Thus, the material to be pulverized (coarsely pulverized powder) introduced into the jet mill apparatus 100 is pulverized into fine powder with an average particle size (median diameter: d50) of, for example, 2.0 μm to 6.0 μm before being transferred to the cyclone collector 200. The average particle size of the fine powder is preferably 2.0 μm to 6.0 μm, more preferably 2.5 μm to 4.5 μm, and even more preferably 2.5 μm to 3.5 μm. The final RTB sintered magnet can have higher magnetic properties.

[0033] The cyclone collector 200 is used to separate the powder from the airflow carrying it. Specifically, coarsely pulverized powder of an alloy for an RTB-based sintered magnet is pulverized in a jet mill in a preceding stage, and the fine powder produced by the pulverization is supplied to the cyclone collector 200 through an inlet pipe 20 together with the gas used in the pulverization. A mixture of an inert gas (pulverization gas) and the pulverized fine powder forms a high-velocity airflow and is sent to the cyclone collector 200. The cyclone collector 200 is used to separate the pulverization gas from the fine powder. The fine powder separated from the pulverization gas is collected in a powder collector 50 via an outlet 40. The pulverization gas is supplied to a bag filter device 300 via an outlet pipe 30. The bag filter device 300 collects very small particles, and clean gas is released to the outside through an exhaust port 32. It is also possible to use only a bag filter for such solid-gas separation without using the cyclone collector 200, but this would have a significant impact on the environment and safety, such as the dispersion of fine powder into the atmosphere due to filter damage.Fine particles may also be separated from the gas separated by the cyclone collector by using a bag filter in combination.

[0034] In the method for producing an RTB-based sintered magnet of the present disclosure, at least one lubricant is added to and mixed with the coarsely pulverized powder, and then the mixture is pulverized using the pulverization system described above to obtain a fine powder. A distinctive feature of the present disclosure is that the lubricant contains an alkylamidoamine-type compound represented by the following formula (1): (R 1 )CONH(R 2 )N(R 3 )2 formula (1) (R 1 is an alkyl chain having 17 to 21 carbon atoms, and R 2 and R 3 are alkyl chains with 1 to 4 carbon atoms.) This can improve the crushing efficiency.

[0035] The lubricant may contain a small amount of other known lubricating ingredients such as zinc stearate, but to more reliably obtain high milling efficiency, it is preferable that 50% by mass or more of the lubricant is an alkylamidoamine-type compound, more preferably 80% by mass or more of the lubricant is an alkylamidoamine-type compound, even more preferably 90% by mass or more of the lubricant is an alkylamidoamine-type compound, and most preferably the lubricant is an alkylamidoamine-type compound (excluding unavoidable impurities). Furthermore, the alkylamidoamine-type compound contained in the lubricant is preferably behenamidopropyldimethylamine, which is an alkylamidoamine-type compound satisfying the above formula (1). This makes it possible to more reliably improve milling efficiency.

[0036] The amount of lubricant added to the coarsely pulverized powder is preferably 0.02% by mass or more and 0.3% by mass or less. By adding 0.02% by mass or more and 0.3% by mass or less of the lubricant to the coarsely pulverized powder, it is possible to improve pulverization efficiency while suppressing an increase in the C (carbon) content in the fine powder after pulverization, and to suppress a deterioration in the magnetic properties of the final RTB-based sintered magnet. More preferably, the amount of lubricant added to the coarsely pulverized powder is 0.02% by mass or more and 0.15% by mass or less.

[0037] Preferably, the lubricant is dissolved in a solvent to prepare a solvent liquid containing the lubricant, and the solvent liquid is added and mixed with the coarsely pulverized powder. This further improves the pulverization efficiency. The solvent liquid consists of the lubricant and a liquid component that dissolves the lubricant. Examples of the dissolving solvent (liquid component) include xylene, alcohol, and isoparaffin. Fatty acid esters may also be used as the solvent. A solvent with a low boiling point poses safety issues, including handling, such as ignition, while a solvent with a high boiling point may not volatilize sufficiently or may increase residual carbon, affecting magnetic properties. Therefore, a solvent with a boiling point or initial boiling point of 60 to 200°C is preferred. The amount of the solvent liquid added to the coarsely pulverized powder is preferably 0.05% by mass or more but 1.50% by mass or less. The liquid component is preferably added in an amount 3 to 7 times the amount of the lubricant. Fine pulverization may be performed immediately after addition and mixing, or, if desired, the liquid component can be easily volatilized by leaving it in an inert gas such as nitrogen, argon, or helium. Because alkylamidoamine-type compounds are often granular or waxy, it is difficult to add them uniformly and homogeneously to coarsely pulverized powders. Therefore, as disclosed herein, by melting or gelling a lubricant consisting of an alkylamidoamine-type compound in a solvent beforehand, it becomes easier to add it uniformly and homogeneously to the coarsely pulverized powders. Furthermore, the use of a solvent containing a lubricating component such as a fatty acid ester can also improve the pulverization efficiency.

[0038] <(2) Example of a process for producing a sintered body of fine powder> In a preferred embodiment, the step of producing a sintered body of the fine powder includes the steps of producing a powder compact from the fine powder by pressing in a magnetic field, and sintering the powder compact.

[0039] A process of producing a powder compact from the fine powder by pressing in a magnetic field. When pressing in a magnetic field, it is preferable to form a powder compact by pressing in an inert gas atmosphere or wet pressing from the viewpoint of suppressing oxidation. Pressing can be performed using a known pressing device. This compact is then sintered to obtain a sintered body.

[0040] -Sintering process of powder compacts The compact is preferably sintered at a pressure of 0.13 Pa (10 -3 Torr) or less, preferably 0.07 Pa (5.0 × 10 -4 The sintering process is carried out at a temperature between 1000°C and 1150°C under a pressure of 1000 Torr or less. To prevent oxidation during sintering, residual gas in the atmosphere can be replaced with an inert gas such as helium or argon. The resulting sintered body is preferably subjected to heat treatment, which can improve its magnetic properties. Known conditions can be used for the heat treatment, such as the heat treatment temperature and time. The rare earth sintered magnet body thus obtained is then subjected to grinding and polishing, surface treatment, and magnetization, as necessary, to produce the final rare earth sintered magnet.

[0041] In a preferred embodiment, the method for producing an RTB-based sintered magnet according to the present disclosure further comprises a diffusion step of diffusing a heavy rare-earth element RH (RH being at least one of Tb, Dy, and Ho) from the surface of the sintered body to the interior thereof. Diffusing the heavy rare-earth element RH from the surface to the interior of the sintered body can efficiently increase the coercive force. [Example]

[0042] The present disclosure will be explained in more detail by way of examples, but the present disclosure is not limited thereto.

[0043] Example 1 An alloy for an RTB sintered magnet was produced by strip casting, so that the composition of the RTB sintered magnet was 22.7 mass% Nd, 7.5 mass% Pr, 0.07 mass% Tb, 0.95 mass% B, 2.0 mass% Co, 0.4 mass% Al, 0.1 mass% Cu, 0.3 mass% Ga, 0.5 mass% Zr, and the remainder Fe. The resulting alloy was coarsely pulverized by hydrogen pulverization to obtain a coarsely pulverized powder. The average particle size of the coarsely pulverized powder was measured. The average particle size was in the range of 200 μm to 400 μm.

[0044] Lubricants were added to the coarsely pulverized powder under the conditions shown in Table 1. The lubricants used were A: an alkylamidoamine-type compound (specifically, behenamidopropyldimethylamine), and B: zinc stearate. No. 1 in Table 1 uses zinc stearate as the lubricant, and the amount of lubricant added to the coarsely pulverized powder is 0.04% by mass. Nos. 2, 4, and 5 are examples in which the type or amount of lubricant added was varied. Nos. 3, 6, and 7 in Table 1 are examples in which a lubricant was dissolved in a solvent to prepare a solvent solution containing the lubricant, and the solvent solution was added to the coarsely pulverized powder and mixed. Isoparaffin was used as the liquid solvent component. No. 3 in Table 1 uses behenamidopropyldimethylamine as the lubricant, and the lubricant was dissolved in isoparaffin to prepare a solvent solution containing the lubricant. The amount of the solvent solution added to the coarsely pulverized powder is 0.24% by mass (0.04% by mass of lubricant, 0.2% by mass of the liquid solvent component). Nos. 6 and 7 are also examples in which the lubricant was dissolved in a solvent.

[0045] The coarsely pulverized powder to which a lubricant had been added was fed into the jet mill apparatus 100 shown in FIG. 1 and pulverized under the conditions shown in Table 1 to obtain a fine powder. In this example, nitrogen gas was used as the inert gas. The average particle size (median diameter: d50) and pulverization efficiency of the obtained finely pulverized powder are shown in Table 1.

[0046] [Table 1]

[0047] As shown in Table 1, when comparing samples with the same lubricant content (Nos. 1 to 3 and 4 to 6), the present invention examples, which satisfy the conditions of the present disclosure, achieve higher milling efficiency than the comparative examples. Furthermore, the present invention examples (Nos. 3 and 6), in which a lubricant was dissolved in a solvent to prepare a lubricant-containing solvent solution and then added to the coarsely pulverized powder, achieve higher milling efficiency. Although No. 7, which contains 0.15% by mass of lubricant, achieves high milling efficiency, the difference in milling efficiency is small compared to No. 6. Increasing the amount of lubricant increases the carbon content in the fine powder after milling, potentially degrading the magnetic properties of the final RTB-based sintered magnet. Therefore, from the perspective of magnetic properties, it is best to reduce the amount of lubricant added. Therefore, the amount of lubricant added to the coarsely pulverized powder is preferably 0.02% by mass or more and 0.3% by mass or less, and more preferably 0.02% by mass or more and 0.15% by mass or less. [Explanation of symbols]

[0048] 100···Jet mill equipment, 200···Cyclone collection equipment, 300···Bag filter equipment

Claims

1. A process of adding at least one lubricant to a coarsely pulverized powder of an R-T-B based sintered magnet alloy (R is at least one rare earth element and must include at least one element selected from the group consisting of Nd, Pr, and Ce, T is at least one transition metal element and must include Fe, and B is boron) produced by a rapid cooling method, mixing the mixture, and pulverizing the mixture to obtain a fine powder; and preparing a sintered body of the fine powder, The lubricant contains an alkylamidoamine compound represented by the following formula (1): A method for producing an RTB based sintered magnet. (R1)CONH(R2)N(R3)2 Formula (1) (R1 is an alkyl chain having 17 to 21 carbon atoms, and R2 and R3 are each an alkyl chain having 1 to 4 carbon atoms.)

2. A method for manufacturing an R-T-B based sintered magnet as described in claim 1, wherein the alloy for the R-T-B based sintered magnet is manufactured by a strip casting method.

3. 3. The method for producing a sintered RTB based magnet according to claim 1, wherein the alkylamidoamine compound is behenamidopropyldimethylamine.

4. 4. The method for producing a sintered RTB based magnet according to claim 1, wherein the amount of the lubricant added to the coarsely pulverized powder is 0.02% by mass or more and 0.3% by mass or less.

5. 5. The method for producing an RTB based sintered magnet according to claim 1, wherein the lubricant is dissolved in a solvent to prepare a solvent liquid, and the solvent liquid is added to and mixed with the coarsely pulverized powder.

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