Producing method of rare earth magnet powder

Abstract

To provide a producing method of efficiently obtaining a rare earth magnet powder having high magnetic properties.SOLUTION: A producing method of a rare earth magnet powder of the present invention includes: a hydrogen crushing step of introducing hydrogen after heating a cast alloy to obtain a magnet raw material; a disproportionation step of causing a disproportionation reaction by absorbing hydrogen into the magnet raw material; and a recombination step of causing a recombination reaction by dehydrogenating the magnet raw material after the disproportionation step. The recombination step includes a controlled exhaust step of performing dehydrogenation in an atmosphere having a high hydrogen partial pressure, and a forced exhaust step of performing dehydrogenation in the atmosphere having a lower hydrogen partial pressure than the controlled exhaust step. In the producing method of the present invention, before the forced evacuation step, the magnet raw material after the controlled evacuation step is crushed or pulverized. As a result, polycrystallization in which a single crystal having different magnetization easy axis directions are connected to each other is suppressed, and magnetic characteristics (particularly, Br) of the magnet powder are improved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing rare earth magnet powder used in bonded magnets and the like. [Background technology]

[0002] Bonded magnets, which are made by solidifying rare earth magnetic powder with a binder resin, offer excellent shape flexibility and exhibit high magnetic properties, and are therefore widely used in a variety of electromagnetic devices, such as electrical appliances and automobiles, where energy savings and weight reduction are desired. To further expand the use of bonded magnets, there is a demand for improving the magnetic properties of rare earth magnetic powder, and various proposals have been made regarding hydrogen treatment that is carried out during the manufacturing process of rare earth magnetic powder. Relevant disclosures can be found in the following patent documents:

[0003] Hydrogen treatment mainly consists of a disproportionation reaction caused by hydrogen absorption (also called the "Hydrogenation-Disproportionation" or "HD reaction") and a recombination reaction caused by desorption (also called the "Desorption-Recombination" or "DR reaction"). The HD reaction and DR reaction are collectively referred to as "HDDR (reaction)," or the hydrogen treatment process is referred to as "HDDR (treatment)." Unless otherwise specified, HDDR as used in this specification also includes improved methods such as d-HDDR (dynamic-Hydrogenation-Disproportionation-Desorption-Recombination). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6760538 (WO2020 / 017529) [Patent Document 2] Patent No. 3452254 (JP 2002-93610) Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, a magnet raw material obtained by subjecting a cast alloy to hydrogen crushing is subjected to a high-temperature hydrogenation process to induce a forward transformation reaction (HD reaction), and then a controlled evacuation process and a forced evacuation process are carried out successively to induce a reverse transformation reaction (DR reaction). In other words, in Patent Document 1, the magnet raw material after hydrogen crushing is subjected to HDDR treatment all at once.

[0006] In Patent Document 2, a mixture of NdFeB-based hydride powder (NdFeBHx) and Dy-based diffusion powder (DyH2, DyCo, etc.) is subjected to a diffusion treatment (800°C x 10 -2 In this patent, an anisotropic magnet powder is produced by subjecting an NdFeB alloy to a low-temperature hydrogenation process (room temperature x 0.1 MPa x 1 hour), a high-temperature hydrogenation process (820°C x 0.03 MPa x 8 hours), and a first evacuation process (820°C x 1 kPa x 240 minutes) in succession.

[0007] However, Patent Document 2 did not undergo the hydrogen crushing process used in Patent Document 1, and the anisotropic magnet powder of Patent Document 2 contained many magnet particles that were a mixture of crystal grains with different easy axis directions of magnetization. As a result, the magnetic properties (particularly Br) of the anisotropic magnet powder of Patent Document 2 were not necessarily sufficient.

[0008] The present invention has been made under these circumstances, and an object of the present invention is to provide a new manufacturing method and the like that can efficiently obtain rare earth magnet powder with higher magnetic properties. [Means for solving the problem]

[0009] Through extensive research, the inventors discovered that cracks introduced into the grain boundaries of magnet alloys by the hydrogen crushing process before HDDR are repaired (welded) during the forced evacuation process that follows the controlled evacuation process, resulting in magnet particles composed of crystal grains with different easy axis directions. To prevent the accompanying degradation of magnetic properties, the inventors came up with the idea of ​​splitting the magnet alloy (magnet raw material) after the hydrogen crushing process along the cracks before the cracks are repaired, thereby obtaining single-crystal particles with a uniform easy axis direction. They then succeeded in obtaining rare earth magnet powder with higher magnetic properties by crushing or pulverizing the magnet raw material between the start of the disproportionation process and the start of the forced evacuation process.

[0010] Based on the above newly discovered problem, we came up with the idea of ​​separating the series of controlled evacuation processes and forced evacuation processes that constituted the recombination process (DR), and we also succeeded in consolidating the forced evacuation process into post-processing. By further developing these results, we have completed the present invention, which will be described below.

[0011] <<Method for producing rare earth magnet powder>> (1) The present invention is a method for producing rare earth magnet powder, comprising: a hydrogen disintegration process in which a cast alloy containing a rare earth element (R), boron (B), and a transition element (TM) is heated in a treatment furnace, and then hydrogen is introduced into the treatment furnace to expose the cast alloy to a hydrogen atmosphere at a predetermined temperature to obtain a magnet raw material; a disproportionation process in which hydrogen is absorbed into the magnet raw material to cause a disproportionation reaction; and a recombination process in which hydrogen is removed from the magnet raw material after the disproportionation process to cause a recombination reaction, the recombination process comprising a controlled evacuation process in a controlled atmosphere having a predetermined hydrogen partial pressure, and a forced evacuation process in a dehydrogenation atmosphere having a lower hydrogen partial pressure than the controlled atmosphere, and further comprising a pulverization process in which the magnet raw material is disintegrated or pulverized between the start of the disproportionation process and the start of the forced evacuation process.

[0012] According to the manufacturing method of the present invention, rare earth magnet powder with higher magnetic properties than conventional ones can be obtained, although the details of the mechanism are not necessarily clear.

[0013] (2) If the controlled evacuation process and the forced evacuation process are separated, the forced evacuation process can be performed as a batch process, enabling efficient production of rare earth magnet powder. Furthermore, by separating the controlled evacuation process and the forced evacuation process, the forced evacuation process can be used for other processes (such as diffusion processes) and essentially omitted, thereby reducing the labor, time, energy, etc. involved in producing rare earth magnet powder.

[0014] Rare earth magnet powder, compounds, bonded magnets The present invention can also be understood as a rare earth magnetic powder obtained by the above-mentioned manufacturing method. It can also be understood as a bonded magnet made of the rare earth magnetic powder and a resin that solidifies the powder particles, or a compound used to manufacture the bonded magnet. The compound is made by first adhering a resin binder to the surface of the powder particles. The magnetic powder used in the bonded magnet or compound can also be a composite powder made up of a mixture of multiple types of magnetic powder with different average particle sizes, alloy compositions, etc.

[0015] "others" (1) The rare earth magnet powder according to the present invention may be either isotropic or anisotropic. Anisotropic magnet powder consists of magnet particles whose magnetic flux density (Br) in one direction (the easy axis of magnetization, or c-axis direction) is greater than the magnetic flux density in other directions. Isotropy and anisotropy can be distinguished by the degree of texture (DOT) obtained when a magnetic field is applied parallel ( / / ) and perpendicular (⊥) to the c-axis direction, i.e., [Br( / / )-Br(⊥)] / Br( / / ). A DOT value of 0 indicates isotropy, and a DOT value greater than 0 indicates anisotropy.

[0016] (2) In this specification, "R" is one or more of Nd, Pr, Tb, Ce, La, Sm, Dy, Y, etc. A typical example of R is Nd. TM is a transition metal element such as Nb, Ti, V, Cr, Ni, Zn, Ga, Zr, Mo, Sn, Hf, Ta, or W, as well as Group 8 to 10 elements (mainly Fe, Co, and Ni). A typical example of TM is Fe. B may be partially substituted with C. Cast alloys, magnet raw materials, or magnet powders may contain modifying elements that are effective in improving properties, or (unavoidable) impurities.

[0017] (3) Unless otherwise specified, "x to y" in this specification includes a lower limit value x and an upper limit value y. Any numerical value included in the various numerical values ​​or numerical ranges described in this specification may be used as a new lower limit or upper limit value to create a new range such as "a to b." For example, "x to y kPa" means x kPa to y kPa. This also applies to other units. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a flowchart showing a manufacturing process of magnet powder. [Figure 2] The SEM images show the magnet raw material (sample 11) after the controlled evacuation process and before the forced evacuation process, and the magnet raw material (sample 21) after the controlled evacuation process and then the forced evacuation process. [Figure 3] FIG. 1 is a schematic diagram illustrating the mechanism by which the forced evacuation process affects the grain boundary phase (cracks). DETAILED DESCRIPTION OF THE INVENTION

[0019] One or more components arbitrarily selected from this specification may be added to the components of the present invention described above. The content described in this specification applies not only to the manufacturing method of the present invention, but also to the magnet raw material, rare earth magnet powder, compound, bonded magnet, etc. as appropriate. A method-related component can also be a product-related component. Which embodiment is best depends on the target, required performance, etc.

[0020] Casting alloy (1) Alloy composition R2TM 14The theoretical composition of the tetragonal compound constituting the B1 type crystal (main phase) is, in atomic percentage, R: 11.8%, B: 5.9%, and TM: the remainder. If the cast alloy is richer in R than its theoretical composition, an R-rich grain boundary phase will be formed during hydrocrushing, and this grain boundary phase will facilitate separation into single crystals. For example, when the entire cast alloy is taken as 100%, it is preferable that the R content be 11-15% or 12-14%, and the B content be 5-9% or 6-8%. In this specification, unless otherwise specified, the component composition (chemical composition) is expressed in atomic percentage (at%), and will be expressed as "%" or only numerical values ​​as appropriate.

[0021] In addition to R, Tm, and B, the casting alloy may contain at least one of Ga, Nb, Cu, Al, Zr, Ti, V, Cr, Ni, Ta, W, Dy, Tb, Co, etc. (For example, Ga is 0.01 to 0.5 at% or 0.1 to 0.4 at%, Nb is 0.05 to 0.5 at% or 0.02 to 0.3 at%, Cu is 0.03 to 1 at%, 0.04 to 0.5 at%, or 0.04 to 0.20 at%, and Al is 0.1 to 3 at%, 0.3 to 2.7 at%, or 0.5 to 2.4 at%. These elements, along with R, contribute to the formation of grain boundary phases and can improve the coercivity (Hc) of the magnet powder. While insufficient amounts of these elements have little effect, excessive amounts can reduce the remanence (Br) of the magnet powder. The cast alloy may contain small amounts of modifying elements in addition to those elements.

[0022] (2) Casting The cast alloy may be an ingot alloy obtained by pouring a molten alloy of a desired composition into a mold and solidifying it, or a rapidly solidified alloy obtained by rapidly solidifying the molten alloy. Rapidly solidified alloys can be obtained, for example, by strip casting.

[0023] (3) Solution treatment (homogenization treatment) The cast alloy may be subjected to a solution treatment (step) before the hydrogen cracking treatment. Since the solidification of the ingot alloy is slow (the cooling rate is low), the soft magnetic α-Fe phase is likely to crystallize (remain). When the ingot alloy is subjected to the solution treatment, the α-Fe phase disappears, segregation and the like are eliminated, and a homogeneous structure with fine crystal grains grown (for example, grain size: 50 to 250 μm) is obtained.

[0024] Rapidly solidified alloys solidify faster (the cooling rate is higher) than ingot alloys, so the soft magnetic α-Fe phase hardly crystallizes (remains), or only a small amount of it crystallizes finely. Such rapidly solidified alloys have a relatively more homogeneous crystalline structure than ingot alloys. By subjecting rapidly solidified alloys to solution treatment, a structure with finely grown crystal grains (e.g., grain size: 50 to 250 μm) can be obtained. Both ingot alloys and rapidly solidified alloys have in common the fact that solution treatment can homogenize the metal structure of the cast alloy before hydrogen decomposition treatment. In this specification, solution treatment is also referred to as homogenization heat treatment.

[0025] The solution treatment is carried out, for example, by heating the cast alloy before the hydrogen cracking treatment in a treatment furnace (heating furnace) at 1050 to 1250°C or 1100 to 1200°C for a time of, for example, 3 to 50 hours or 10 to 40 hours, in an inert atmosphere (an inert gas atmosphere such as Ar or a vacuum atmosphere; the same applies below).

[0026] (4) Distributed processing The cast alloy (ingredient) after the solution treatment may be further heat-treated (referred to as "(R-rich) dispersion treatment") at a temperature range lower than the temperature of the solution treatment but higher than the temperature of the hydrogen cracking treatment (step) (hydrogen cracking temperature). The temperature is, for example, 650 to 900°C, 665 to 800°C, or 680 to 750°C. The time is, for example, 10 minutes to 10 hours or 0.5 to 3 hours. The atmosphere is, for example, an inert atmosphere. The dispersion treatment promotes the dispersion (distribution) of rare earth elements (R) and the like to the grain boundaries of the cast alloy, and the crystal grains of the cast alloy can be uniformly covered with the R-rich phase. If the cast alloy after the dispersion treatment is subjected to the hydrogen cracking treatment described below, the introduction of cracks into the grain boundaries (phases) is promoted, making the cast alloy more susceptible to cracking along the grain boundaries.

[0027] <Hydrogen crushing treatment> The magnet raw material obtained by subjecting a cast alloy to a hydrogen crushing treatment (process) is subjected to HDDR. The hydrogen crushing treatment is preferably performed by first heating the cast alloy to a predetermined temperature and then exposing the cast alloy to a hydrogen atmosphere. For example, the cast alloy may be placed in a treatment furnace and heated to 300 to 550°C or 325 to 525°C, and then hydrogen may be introduced into the treatment furnace. The heating temperature may be adjusted depending on the component composition of the cast alloy.

[0028] The inside of the treatment furnace is evacuated, for example, before heating the cast alloy (before hydrogen is introduced). Only hydrogen gas may be introduced into the treatment furnace, or a mixture of hydrogen and an inert gas may be introduced. Gas may be introduced into the treatment furnace in a flow state. The hydrogen partial pressure is not critical, but is set to, for example, 1 kPa to 250 kPa or 10 kPa to 150 kPa, taking into consideration efficiency and safety.

[0029] The hydrogen cracking treatment is carried out for, for example, 0.3 to 5 hours or 0.6 to 3 hours after the cast alloy (atmosphere) reaches the target temperature. In this specification, the temperature of the cast alloy in the treatment furnace is also referred to as the atmosphere temperature, regardless of the atmosphere.

[0030] The magnet raw material that has been subjected to the hydrogen crushing process may be supplied to the HDDR in a state containing hydrogen without being dehydrogenated. This allows for efficient transfer to the HDDR. The magnet raw material may also be crushed or pulverized before the HDDR. The magnet raw material (lump, granular, or powder form) consisting of crystal grains with a uniform axis of easy magnetization can be supplied to the HDDR.

[0031] 《HDDR》 By applying HDDR to the magnet raw material after hydrogen crushing, fine R2TM 14 The resulting magnet powder is made up of polycrystalline bodies (magnet particles) consisting of aggregates of B1 type crystals (average crystal grain size: 0.05 to 1 μm). HDDR consists of a disproportionation process (HD) and a recombination process (DR).

[0032] (1) Disproportionation process (HD) The disproportionation process involves exposing the magnet raw material placed in a treatment furnace to a specified hydrogen atmosphere, causing a disproportionation reaction (forward transformation reaction) in the hydrogen-absorbed magnet raw material, which results in a three-phase decomposed structure (αFe phase, RH2 phase, and Fe2B phase).

[0033] The disproportionation step is carried out, for example, under a hydrogen partial pressure of 10 to 300 kPa or 15 to 50 kPa, at an atmospheric temperature of 600 to 900° C. or 730 to 880° C., for a treatment time of 1 to 6 hours or 2 to 5 hours.

[0034] During this process, the hydrogen partial pressure or the atmospheric temperature may be constant or may vary. For example, in the later stage when the reaction rate slows, at least one of the hydrogen partial pressure or the temperature may be increased to adjust the reaction rate and promote three-phase decomposition (structure stabilization process). The hydrogen atmosphere may be a mixed gas atmosphere of hydrogen and an inert gas (the same applies below).

[0035] (2) Recombination process (DR) The recombination process is a process in which hydrogen is removed from the magnet raw material after the disproportionation process, causing a recombination reaction (reverse transformation reaction) in the three-phase decomposed structure described above. This process is divided into a controlled evacuation process, which is carried out in a controlled atmosphere with a predetermined hydrogen partial pressure, and a forced evacuation process, which is carried out in a dehydrogenation atmosphere with a lower hydrogen partial pressure than the controlled atmosphere.

[0036] During the controlled evacuation process, hydrogen is slowly removed from the RH2 phase, resulting in the formation of fine R2TM, which is a crystal orientation transfer of the Fe2B phase. 14 B1-type crystal hydride (RFeBH X The controlled evacuation step is performed by exposing the magnet raw material to a controlled atmosphere with a hydrogen partial pressure of 0.5 to 6 kPa or 1 to 5 kPa and a temperature of 750 to 890°C or 800 to 880°C. The treatment time is, for example, 0.5 to 3 hours or 1 to 2.5 hours.

[0037] The forced evacuation step is performed by exposing the magnet raw material that has been subjected to the controlled evacuation step to a dehydrogenation atmosphere at, for example, 550 to 880°C, 650 to 865°C, or 750 to 850°C. The dehydrogenation atmosphere has a hydrogen partial pressure of, for example, 100 Pa or less, 50 Pa or less, 25 Pa or less, 10 Pa or less, or 1 Pa or less. The treatment time is, for example, 0.2 to 3 hours or 0.3 to 1 hour. Incidentally, the dehydrogenation atmosphere is ... X Any atmosphere capable of removing hydrogen from the atmosphere (volume) can be used. Therefore, the dehydrogenation atmosphere may be a vacuum atmosphere or a mixed gas atmosphere in which the hydrogen partial pressure is equal to or less than a predetermined value. The mixed gas atmosphere may be an atmosphere of an inert gas flow. Note that the hydrogen partial pressure referred to in this specification is the absolute pressure of hydrogen relative to the total atmosphere (volume).

[0038] The forced evacuation process almost completely removes hydrogen remaining in the magnet raw materials, and the dehydrogenation is completed in the recombination process. Because the forced evacuation process according to the present invention is not performed consecutively with the controlled evacuation process, there is a great degree of freedom in setting and selecting the temperature range, timing, processing method, etc.

[0039] Diffusion processing The magnet raw material may be further subjected to a diffusion treatment. The diffusion treatment (step) is carried out, for example, by heating a mixed raw material obtained by adding a diffusion material to the magnet raw material in an inert atmosphere. 14 A non-magnetic phase (R-rich phase) is formed on the surface or at the grain boundaries of the B1 type crystals, improving the coercive force of the magnetic powder.

[0040] If the magnet raw material is subjected to a diffusion treatment in a dehydrogenation atmosphere after the controlled evacuation process (before the forced evacuation process), the forced evacuation process is essentially performed during the diffusion process, eliminating the need for a separate forced evacuation process after the diffusion process. In other words, the forced evacuation process can be omitted. The diffusion process is performed, for example, in a dehydrogenation atmosphere at 700-880°C or 750-840°C for 0.3-2 hours or 0.5-1 hour. Cooling after each heat treatment is preferably rapid cooling to prevent grain growth. The dehydrogenation atmosphere referred to here is the same as the dehydrogenation atmosphere in the forced evacuation process described above. That is, the hydrogen partial pressure in the atmosphere is, for example, 100 Pa or less, 50 Pa or less, 25 Pa or less, 10 Pa or less, or 1 Pa or less.

[0041] The diffusion raw material is, for example, an alloy or compound containing at least R and Cu and / or Al. R may be a light rare earth element (such as Nd) or a heavy rare earth element (such as Dy or Tb). In addition to an R-Cu(Al) alloy (compound), a hydride or fluoride of R may also be used as the diffusion raw material.

[0042] When the casting alloy of the present invention already contains Cu and / or Nd-rich phase-forming elements such as Al and Ga, the coercivity of the magnet powder can be improved without a diffusion treatment (i.e., even without a diffusion treatment).Even in such cases, the above-mentioned diffusion treatment may be further carried out.

[0043] Crushing, grinding, and classification (1) Breaking process The magnet raw material should be crushed or pulverized after the start of the disproportionation process and before the start of the forced evacuation process (or before the diffusion process). This makes it possible to utilize the cracks introduced into the grain boundaries during the hydrogen crushing process, making it easier to obtain magnet particles consisting of fine crystal grains with aligned axes of easy magnetization.

[0044] The crushing and pulverization should be carried out in an atmosphere and at a temperature that will not cause dehydrogenation from the magnet raw material after the controlled evacuation step, for example, in an inert atmosphere in the warm to cold range (for example, about 250 to 10°C or 50 to 15°C).

[0045] It is difficult to strictly distinguish between "crushing" and "pulverization," but for example, "pulverization" is when particles are intentionally made finer by applying shear force, while "crushing" is when lumps are broken down by applying a light impact, etc.

[0046] (2) Classification process The magnet raw material after the forced evacuation process or the diffusion treatment may be crushed or pulverized, and then the particle size may be adjusted by classification. For example, the magnet powder is sieved (see JIS Z 8801) to a particle size of -212 μm.

[0047] 《Application》 Rare earth magnet powder is used, for example, in bonded magnets. Bonded magnets are primarily made of rare earth magnet powder and a binder resin. The binder resin may be a thermosetting resin or a thermoplastic resin. Bonded magnets may be compression molded or injection molded. Bonded magnets using rare earth anisotropic magnet powder can exhibit high magnetic properties when molded in an aligning magnetic field. [Example]

[0048] Samples (magnet powder) were produced with different times for the forced evacuation process, and their magnetic properties were evaluated. The present invention will be described in more detail based on these examples.

[0049] <<Sample Preparation>> The treatments shown in Figure 1 were carried out in order to produce the samples shown in Table 1. The details are as follows:

[0050] [Samples 10 and 11] (1) Casting alloy Ingots having the following composition (Alloys A and B) were prepared. The ingots were obtained by melting in a high-frequency melting furnace. The composition is the atomic ratio relative to the total alloy, with the remainder being Fe(TM). Unless otherwise specified, the composition is expressed in "%" or numerical values ​​only. Alloy A: Nd 12.7 FeB 6.4 Nb 0.2 Ga 0.3 Alloy B: Nd12.7 FeB 6.4 Nb 0.2 Cu 0.07 Al 1.1

[0051] (2) Solution treatment process The ingot was subjected to solution treatment (homogenization treatment) by heating at 1140°C for 20 hours in an Ar gas atmosphere.

[0052] (3) Dispersion process The ingot after the solution treatment was subjected to an (R(Nd) rich) dispersion treatment by heating the magnet raw material at 700°C for 1 hour in a treatment furnace with a vacuum atmosphere (10 Pa or less). (4) Hydrocracking process The ingots after the dispersion treatment were subjected to a hydrogen crushing treatment. In the hydrogen crushing treatment, the treatment furnace in which the ingots were placed was evacuated (10 Pa or less) and the treatment furnace was heated to the desired temperature over one hour. Hydrogen was then introduced into the treatment furnace. The hydrogen partial pressure in the treatment furnace was kept at 100 kPa (constant) and maintained for one hour. The cast alloy (ingredient) after the hydrogen crushing treatment is referred to as the magnet raw material. The temperature in the treatment furnace was measured using a thermocouple in contact with the ingot, and was 500°C for Alloy A (containing Ga) and 450°C for Alloy B (containing CuAl). The hydrogen partial pressure was measured using a pressure gauge installed in the treatment furnace.

[0053] The hydrocracking treatment was carried out with reference to the description in Patent Publication WO2020 / 017529. The entire contents of the patent publication, including the hydrocracking treatment, are incorporated herein by reference, unless they are contrary to the spirit of the present invention.

[0054] (5) Disproportionation process (HD process) The magnet raw material (12.5 g) after the hydrogen crushing process was further treated in the same treatment furnace without cooling. Alloy A (containing Ga) was exposed to a high-temperature hydrogen atmosphere (780°C x 30 kPa x 0.5 hours: high-temperature hydrogenation process), and then to a higher-temperature hydrogen atmosphere (840°C x 30 kPa x 1 hour: structure stabilization process). Alloy B (containing CuAl) was exposed to a high-temperature hydrogen atmosphere (780°C x 25 kPa x 2 hours: high-temperature hydrogenation process), and then to a higher-temperature hydrogen atmosphere (840°C x 25 kPa x 2 hours: structure stabilization process). In this way, a disproportionation reaction (forward transformation reaction) occurred in the magnet raw material.

[0055] (6) Controlled exhaust process Following the disproportionation process, the magnet raw materials in the treatment furnace were exposed to a controlled atmosphere with a reduced hydrogen partial pressure (Alloy A (containing Ga): 840°C x 1.0 kPa x 1.5 hours, Alloy B (containing CuAl): 840°C x 2.5 kPa x 1.5 hours). This caused a recombination reaction (reverse transformation reaction) to occur in the magnet raw materials after the disproportionation process (recombination process / DR process). Hydrogen remained in the magnet raw materials at this stage, and it is believed that at least a portion of the grain boundary phase was in a NdHx (hydride) state.

[0056] (7) De-pulverization process The magnet raw material after the controlled evacuation step was rapidly cooled to room temperature (cooling step), and this magnet raw material was further pulverized in an inert gas (nitrogen gas) using a disc mill (pulverization step).

[0057] (8) Forced exhaust process The pulverized magnet raw material was returned to the processing furnace and heated in a vacuum atmosphere (dehydrogen atmosphere) (800°C x 1 Pa or less x 1 hour).

[0058] (9) Crushing The magnet raw material after the forced evacuation step was lightly crushed (crushing step) and then sieved to -212 μm (crushing step). In this way, magnet powder of Sample 10 or Sample 11 shown in Table 1 was obtained.

[0059] [Sample 12] Sample 12 was also produced, which had been subjected to a diffusion process. The diffusion process was carried out by adding a diffusion material to the magnet raw material after the controlled evacuation process (before the forced evacuation process), and then heating the mixed raw material (800°C x 1 Pa or less x 1 hour) in a vacuum atmosphere (dehydrogen atmosphere) (diffusion process).

[0060] The diffusion material is NdCu 15 Al 34 Alloy powder (<45 μm) was used. The diffusion material was added at 2 mass% of the total mixed material. The diffusion process was carried out in a vacuum atmosphere (dehydrogen atmosphere), so the forced evacuation process was omitted.

[0061] [Samples 20-22] For samples 20 and 21, a forced evacuation process was carried out after the controlled evacuation process, and then pulverization was carried out. The other procedures were the same as for samples 10 and 11. Naturally, no forced evacuation process was carried out after pulverization.

[0062] Sample 22 was subjected to a controlled evacuation step followed by a forced evacuation step, and then a diffusion step. The rest of the procedure was the same as for Sample 12.

[0063] [Samples 30-32] For Samples 30 to 32, the magnet raw material was crushed and pulverized even after the hydrogen crushing process (before the disproportionation process). In other words, for Samples 30 to 32, the magnet raw material was crushed and pulverized after the hydrogen crushing process, and then successively subjected to the disproportionation process, controlled evacuation process, and forced evacuation process, after which it was further crushed and sieved. The rest of the samples were the same as Samples 20 to 22.

[0064] "measurement" The magnet powder of each sample was packed into a capsule and subjected to magnetic field orientation (1193 kA / m) in molten paraffin (approximately 80°C), after which it was magnetized (3580 kA / m). The magnetic properties of the magnet powder after magnetization were measured using a pulse BH tracer (manufactured by OP Electronics Co., Ltd.). The magnetic properties of each sample (residual magnetic flux density: Br, coercive force: iHc, maximum energy product: BHmax) are also shown in Table 1.

[0065] "observation" The magnet raw material (powder particles) of Samples 11 and 21 was observed with a field emission scanning electron microscope (FE-SEM) before and after the forced evacuation process. The SEM images are shown in Figure 2.

[0066] "evaluation" (1) As can be seen in Figure 2, the magnet raw material (Sample 11 / left side of Figure 2) after the controlled evacuation process (before the forced evacuation process) clearly shows grain boundaries (cracks) introduced by the hydrogen crushing process, and it was confirmed that the material is mainly composed of single crystals with a uniform axis of easy magnetization.

[0067] On the other hand, in the magnet raw material (Sample 21 / right side of Figure 2) that underwent a forced evacuation process following the controlled evacuation process, the grain boundaries (cracks) partially disappeared, and polycrystallization was observed, in which single crystals with different easy axis directions were connected. When high-temperature dehydrogenation was performed in the forced evacuation process following the controlled evacuation process, it is thought that the Nd-rich phase (Nd alloy phase) at the grain boundaries melted, repairing the cracks at the grain boundaries. This state is shown schematically in Figure 3.

[0068] (2) As can be seen from a comparison of Samples 10-12 and Samples 20-22 shown in Table 1, the magnetic properties (especially Br) were improved by separating the controlled evacuation process from the forced evacuation process and performing crushing or pulverization before the forced evacuation process.

[0069] Furthermore, Samples 10-12 and Samples 30-32 both had improved magnetic properties compared to Samples 20-22. It was found that if crushing or pulverization is performed after the hydrogen decomposition process and before the forced evacuation process, magnet powder with high magnetic properties can be obtained. It was also found that if the hydrogen decomposition process and the controlled evacuation process are performed continuously, as in Samples 10-12, magnet powder with high magnetic properties can be obtained regardless of whether or not a diffusion process is performed, while omitting the crushing or pulverization after the hydrogen decomposition process (before the disproportionation process). This makes it possible to separate the forced evacuation process and perform batch processing, or to combine the forced evacuation process with the diffusion process, thereby improving the efficiency of the manufacturing process (energy savings, reduction in process time, etc.).

[0070] From the above, it was confirmed that the manufacturing method of the present invention can efficiently obtain rare earth magnet powder with high magnetic properties.

[0071] [Table 1]

Claims

1. a hydrogen crushing step in which a cast alloy containing rare earth elements (R), boron (B), and transition elements (TM) is heated in a treatment furnace, and then hydrogen is introduced into the treatment furnace to expose the cast alloy to a hydrogen atmosphere at a predetermined temperature, thereby obtaining a magnet raw material; a disproportionation step of causing the magnet raw material to absorb hydrogen to cause a disproportionation reaction; a recombination step of dehydrogenating the magnet raw material after the disproportionation step to cause a recombination reaction, the recombination step includes a controlled evacuation step performed in a controlled atmosphere having a predetermined hydrogen partial pressure, and a forced evacuation step performed in a dehydrogenation atmosphere having a hydrogen partial pressure lower than that of the controlled atmosphere; The method for producing rare earth magnet powder further comprises a pulverizing step of crushing or pulverizing the magnet raw material after the start of the disproportionation step and before the start of the forced evacuation step.

2. The method for producing rare earth magnet powder according to claim 1 , wherein the pulverizing step is performed on the magnet raw material after the controlled evacuation step.

3. The method for producing rare earth magnet powder according to claim 2, further comprising a diffusion step of heating a mixed raw material obtained by adding a diffusion raw material to the magnet raw material after the controlled evacuation step.

4. 4. The method for producing rare earth magnet powder according to claim 3, wherein the diffusion step is performed in a dehydrogenated atmosphere and also serves as the forced evacuation step.

5. 2. The method for producing rare earth magnet powder according to claim 1, wherein the hydrogen atmosphere in the hydrogen crushing step has a hydrogen partial pressure of 1 kPa to 250 kPa and a temperature of 300 to 550°C.

6. The controlled atmosphere has a hydrogen partial pressure of 0.5 to 6 kPa and a temperature of 750 to 880°C, The method for producing rare earth magnet powder according to any one of claims 1 to 5, wherein the dehydrogenation atmosphere has a hydrogen partial pressure of 100 Pa or less and a temperature of 550 to 880°C.

7. 5. The method for producing rare earth magnet powder according to claim 1, further comprising a crushing step of crushing the magnet raw material after the forced evacuation step.

8. 4. The method for producing rare earth magnet powder according to claim 3, wherein the diffusion raw material is an alloy or compound containing at least R and Cu and / or Al.

9. 9. The method for producing rare earth magnet powder according to claim 1, wherein the casting alloy contains, based on the total amount of the alloy, 0.02 to 1 at % of Cu and / or 0.1 to 3 at % of Al.

10. The method for producing rare earth magnet powder according to claim 1, wherein the cast alloy is subjected to a solution treatment before the hydrogen decomposition step.

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