Method for manufacturing rare-earth magnet powder

Abstract

Provided is a manufacturing method by which a rare-earth magnet powder having high magnetic properties can be efficiently obtained. This method for manufacturing a rare-earth magnet powder comprises: a hydrogen decrepitation step for obtaining a magnet raw material by introducing hydrogen after heating a cast alloy; a disproportionation step for causing a disproportionation reaction by allowing the magnet raw material to absorb hydrogen; and a recombination step for causing a recombination reaction by desorbing hydrogen from the magnet raw material after the disproportionation step. The recombination step includes: a controlled exhaust step for performing hydrogen desorption in an atmosphere having a large hydrogen partial pressure; and a forced exhaust step for performing hydrogen desorption in an atmosphere having a hydrogen partial pressure smaller than that of the controlled exhaust step. In the manufacturing method of the present invention, the magnet raw material after the controlled exhaust step is disintegrated or pulverized prior to the forced exhaust step. In this way, polycrystallization involving the connection of single crystals having different easy axis directions is suppressed, thereby improving the magnetic properties (particularly Br) of the magnet powder.

Description

Manufacturing method for rare earth magnet powder

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

[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 due to hydrogen absorption (also called the "Hydrogenation-Disproportionation" or "HD reaction") and a recombination reaction due to 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 itself as "HDDR (treatment)." Unless otherwise specified, HDDR as used in this specification also includes improved versions such as d-HDDR (dynamic-Hydrogenation-Disproportionation-Desorption-Recombination).

[0004] Japanese Patent No. 6760538 (WO2020 / 017529) Japanese Patent No. 3452254 (JP 2002-93610)

[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, NdFeB-based hydride powder (NdFeBHx) and Dy-based diffusion powder (DyH ２ , DyCo, etc.) and then subjected to diffusion treatment (800°C x 10 -２In this patent, the NdFeB alloy is subjected 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, in Patent Document 2, the hydrogen crushing process as in Patent Document 1 was not carried out, and the anisotropic magnet powder in Patent Document 2 contained many magnet particles in which crystal grains with different directions of the easy axis of magnetization were mixed together. For this reason, the magnetic properties (particularly Br) of the anisotropic magnet powder in 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.

[0009] Through extensive research, the inventors discovered that cracks introduced into the grain boundaries of a magnet alloy 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 resulting degradation of magnetic properties, they 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-mentioned 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-treatment. 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 step of heating a cast alloy containing a rare earth element (R), boron (B), and a transition element (TM) in a treatment furnace, and then introducing hydrogen 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 step of causing hydrogen to be absorbed by the magnet raw material to cause a disproportionation reaction; and a recombination step of dehydrogenating the magnet raw material after the disproportionation step to cause a recombination reaction, wherein the recombination step comprises 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 lower hydrogen partial pressure than the controlled atmosphere, and further comprising a pulverization step of crushing or pulverizing the magnet raw material between the start of the disproportionation step and the start of the forced evacuation step.

[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) When 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 man-hours, time, energy, etc. involved in the production of rare earth magnet powder.

[0014] <Rare Earth Magnetic Powder, Compound, Bonded Magnet> The present invention can also be understood as a rare earth magnetic powder obtained by the manufacturing method described above. 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 formed by first adhering a resin binder to the surface of the powder particles. The magnetic powder used in the bonded magnet or compound can be a composite powder made by mixing 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 is composed 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 anisotropy (DOT) obtained when a magnetic field is applied parallel ( / / ) and perpendicular (⊥) to the c-axis direction, where DOT = [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 or (unavoidable) impurities that are effective in improving characteristics.

[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.

[0018] Fig. 1 is a flowchart showing a manufacturing process of magnet powder; Fig. 2 is an SEM image of a magnet raw material (sample 11) after a controlled evacuation process and before a forced evacuation process, and a magnet raw material (sample 21) that has been subjected to a forced evacuation process subsequent to a controlled evacuation process; Fig. 3 is a schematic diagram illustrating the mechanism by which a forced evacuation process affects grain boundary phases (cracks);

[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 R ２ TM １４ B １ The theoretical composition of the tetragonal compound constituting the crystalline structure (main phase) is, in atomic percentages, 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, making it easier to separate into single crystals at the grain boundary phase. 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, the Ga content is 0.01 to 0.5 at% or 0.1 to 0.4 at%, the Nb content is 0.05 to 0.5 at% or 0.02 to 0.3 at%, the Cu content is 0.03 to 1 at%, 0.04 to 0.5 at%, or 0.04 to 0.20 at%, and the Al content 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 coercive force (Hc) of the magnet powder. While insufficient amounts of these elements are ineffective, 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 solution treatment (step) before the hydrogen cracking treatment. Since the ingot alloy solidifies slowly (the cooling rate is low), the soft magnetic α-Fe phase is likely to crystallize (remain). When the ingot alloy is subjected to 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 (have a higher cooling rate) than ingot alloys, so the soft magnetic α-Fe phase hardly crystallizes (remains), or only a small amount crystallizes. 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 performed, 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. The atmosphere is, for example, an inert atmosphere (an inert gas atmosphere such as Ar or a vacuum atmosphere; the same applies hereinafter).

[0026] (4) Dispersion Treatment 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 the cast alloy to hydrogen crushing treatment (step) is subjected to HDDR. Hydrogen crushing treatment is preferably performed by heating the cast alloy to a predetermined temperature in advance 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). Hydrogen gas alone 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 preferably 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 ambient 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 be crushed or pulverized before the HDDR. The magnet raw material (lump, granular, or powder form) made up 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 R ２ TM １４ B １ The resulting magnet powder is made up of polycrystalline bodies (magnet particles) consisting of aggregates of 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) In ​​the disproportionation process, the magnet raw material placed in a treatment furnace is exposed to a predetermined hydrogen atmosphere to cause a disproportionation reaction (forward transformation reaction) in the hydrogen-absorbed magnet raw material. As a result, the magnet raw material is decomposed into a three-phase structure (α-Fe phase, RH phase, ２ phase, Fe ２ Phase B).

[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 carried out in a controlled atmosphere having a predetermined hydrogen partial pressure, and a forced evacuation process carried out in a dehydrogenation atmosphere having a lower hydrogen partial pressure than the controlled atmosphere.

[0036] The controlled evacuation process reduces RH ２As hydrogen is slowly removed from the Fe phase, ２ Fine R formed by transferring the crystal orientation of the B phase ２ TM １４ B １ hydride of type crystal (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 a temperature range where the hydride (RFeBH 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 inert gas flow. Note that the hydrogen partial pressure referred to in this specification is the absolute pressure of hydrogen relative to the entire atmosphere (volume).

[0038] The forced evacuation process almost completely removes hydrogen remaining in the magnet raw material, completing the dehydrogenation process 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 Treatment>> 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 raw material to the magnet raw material in an inert atmosphere. By the diffusion treatment, R ２ TM １４ B １ A non-magnetic phase (R-rich phase) is formed on the surface or grain boundary of the type crystal, improving the coercive force of the magnet 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 elements that form a Nd-rich phase, such as Al and Ga, the coercivity of the magnetic powder can be improved without a diffusion treatment (i.e., a non-diffusion treatment).Even in such cases, the above-mentioned diffusion treatment may be further carried out.

[0043] <<Crushing, Pulverization, and Classification>> (1) Pulverization 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 are preferably carried out in an atmosphere and at a temperature that does 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 Step After the forced evacuation step or the diffusion treatment, the magnet raw material may be crushed or pulverized, and then its 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] <<Applications>> 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.

[0048] Samples (magnet powder) were prepared 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] <<Production of Samples>> The treatments shown in Fig. 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) Cast alloys 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: Nd １２．７ FeB ６．４ Nb ０．２ Cu ０．０７ Al １．１

[0051] (2) Solution Treatment Step The ingot was heated in an Ar gas atmosphere at 1140°C for 20 hours to perform solution treatment (homogenization treatment).

[0052] (3) Dispersion Process: The ingot after the solution treatment was heated to 700°C for 1 hour in a treatment furnace under a vacuum atmosphere (10 Pa or less) to form a magnet raw material (R(Nd)-rich) dispersion process. (4) Hydrogen Crushing Process: The ingot after the dispersion process was subjected to hydrogen crushing. In the hydrogen crushing process, the treatment furnace containing the ingot was evacuated to a vacuum atmosphere (10 Pa or less) and the treatment furnace was heated to the desired temperature over 1 hour. Hydrogen was then introduced into the treatment furnace. The hydrogen partial pressure in the treatment furnace was maintained at 100 kPa (constant) and held for 1 hour. The cast alloy (ingot) after the hydrogen crushing process 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 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 Evacuation Step Following the disproportionation step, the magnet raw material in the treatment furnace was 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 material after the disproportionation step (recombination step / DR step). Hydrogen remained in the magnet raw material 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) Pulverization Step The magnet raw material after the controlled evacuation step was rapidly cooled to room temperature (cooling step). This magnet raw material was further pulverized in an inert gas (nitrogen gas) using a disk mill (pulverization step).

[0057] (8) Forced Evacuation Step The pulverized magnet raw material was returned to the processing furnace and heated in a vacuum atmosphere (dehydrogen atmosphere) (800° C.×1 Pa or less×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 treatment. The diffusion treatment was carried out by adding a diffusion material to the magnet material after the controlled evacuation process (before the forced evacuation process), and then heating the mixed raw material in a vacuum atmosphere (dehydrogen atmosphere) (800°C × 1 Pa or less × 1 hour) (diffusion process).

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

[0061] [Samples 20 to 22] For samples 20 and 21, a forced evacuation step was performed following a controlled evacuation step, and then pulverization was performed. The other steps were the same as for samples 10 and 11. Naturally, the forced evacuation step was not performed after pulverization.

[0062] Sample 22 was subjected to a controlled evacuation step followed by a forced evacuation step, and then a diffusion step, in the same manner as Sample 12.

[0063] [Samples 30-32] For Samples 30-32, the magnet raw material was crushed and pulverized even after the hydrogen crushing process (before the disproportionation process). That is, for Samples 30-32, 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 20-22.

[0064] <<Measurement>> The magnet powder of each sample was packed into a capsule, and after magnetic field orientation (1193 kA / m) in molten paraffin (approximately 80°C) 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 FIG.

[0066] <Evaluation> (1) As can be seen from Figure 2, the magnet raw material (Sample 11 / left side of Figure 2) after the controlled evacuation process (before the forced evacuation process) clearly had grain boundaries (cracks) introduced by the hydrogen crushing process, and it was confirmed that the magnet raw material was mainly composed of single crystals with an aligned 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 a controlled evacuation process, the grain boundaries (cracks) partially disappeared, and polycrystallization was observed in which single crystals with different easy axis directions were connected. It is thought that when high-temperature dehydrogenation was performed in the forced evacuation process following the controlled evacuation process, 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 to 12 and Samples 20 to 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 magnetic powder with high magnetic properties can be obtained by performing crushing or pulverization after the hydrogen crushing process and before the forced evacuation process. It was also found that if the hydrogen crushing process and the controlled evacuation process are performed continuously, as in Samples 10-12, magnetic powder with high magnetic properties can be obtained regardless of whether or not a diffusion process is performed, while omitting crushing or pulverization after the hydrogen crushing 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]

Claims

1. A method for manufacturing rare earth magnet powder, comprising: a hydrogen crushing step of introducing hydrogen into a treatment furnace after heating a cast alloy containing rare earth elements (R), boron (B), and transition elements (TM) in the treatment furnace, and exposing the cast alloy to a hydrogen atmosphere at a predetermined temperature 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 dehydrogenating the magnet raw material after the disproportionation step to cause a recombination reaction. The recombination step includes a controlled exhaust step performed in a controlled atmosphere having a predetermined hydrogen partial pressure, and a forced exhaust step performed in a dehydrogenation atmosphere having a lower hydrogen partial pressure than the controlled atmosphere. The method further includes a pulverizing step of pulverizing or crushing the magnet raw material between the start of the disproportionation step and the start of the forced exhaust step.

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

3. The method for manufacturing 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 exhaust step.

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

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

7. The method for manufacturing rare earth magnet powder according to any one of claims 1 to 4, further comprising a crushing step of further crushing the magnet raw material after the forced exhaust step.

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

9. The method for manufacturing rare earth magnet powder according to claim 1 or 8, wherein the cast alloy contains Cu: 0.02 to 1 at% and / or Al: 0.1 to 3 at% with respect to the whole.

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

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