Manufacturing method for rare-earth magnet powder

Abstract

Provided is a manufacturing method with which it possible to obtain a rare-earth magnet powder that has high magnetic characteristics while, inter alia, reducing rare Ga that runs the risk of unstable supply and conserving energy during the manufacturing process. The present invention is a manufacturing method for a rare-earth magnet powder, the method including: a hydrogen cracking step for introducing hydrogen into a treatment furnace after a casting alloy is heated in the treatment furnace, and obtaining a magnet raw material from the casting alloy that has been exposed to a hydrogen atmosphere of a prescribed temperature; a disproportionation step for causing a disproportionation reaction by causing the magnet raw material to absorb hydrogen; and a recombination step for causing a recombination reaction by dehydrogenating the magnet raw material that has undergone the disproportionation step. The casting alloy contains a rare-earth element (R), boron (B), a transition element (TM), and 0.02-0.3 at% of Cu with respect to the entire alloy, and has a Ga content of 0.1 at% or less. The hydrogen cracking step is performed in a hydrogen atmosphere of 300-525°C.

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 (Hydrogenation-Disproportionation, also simply referred to as the "HD reaction") and a recombination reaction due to dehydrogenation (Desorption-Recombination, also simply referred to as the "DR reaction"). The HD reaction and DR reaction are collectively referred to as the "HDDR reaction," and the hydrotreatment process is referred to 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] Patent No. 6760538 (WO2020 / 017529)

[0005] In Patent Document 1, a rare earth magnet powder with high magnetic properties is obtained by subjecting a cast alloy to a hydrogen crushing process and then subjecting the resulting magnet raw material to an HDDR process. However, in the example, a cast alloy containing 0.3 at% Ga is used.

[0006] Ga is a rare typical metal element, and its metal production is concentrated in certain countries, which creates geopolitical supply instability. For this reason, there is a demand to reduce the use of Ga in rare earth magnet powders.

[0007] The present invention has been made under these circumstances, and has as its object to provide a new manufacturing method that can reduce the amount of Ga while still obtaining rare earth magnet powder with high magnetic properties.

[0008] As a result of intensive research conducted by the inventors to solve this problem, they succeeded in obtaining rare earth magnet powder with high magnetic properties without substantially using Ga by subjecting a magnet raw material that had been previously subjected to hydrogen crushing treatment under specified conditions from a cast alloy containing Cu to HDDR (including d-HDDR).By further developing this result, they were able to complete the present invention, which will be described below.

[0009] <<Method for Producing Rare Earth Magnet Powder>> (1) The present invention is a method for producing rare earth magnet powder, comprising a hydrogen-crushing step of heating a cast alloy in a treatment furnace, introducing hydrogen into the treatment furnace, and obtaining a magnet raw material from the cast alloy exposed to a hydrogen atmosphere at a predetermined temperature; a disproportionation step of causing the magnet raw material to absorb hydrogen 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 cast alloy contains rare earth elements (R), boron (B), transition elements (TM), and Cu: 0.02 to 0.3 at% relative to the total, and has a Ga content of 0.1 at% or less, and the hydrogen-crushing step sets the hydrogen atmosphere at 300 to 525°C.

[0010] (2) According to the manufacturing method of the present invention, rare earth magnet powder with high magnetic properties can be efficiently obtained while reducing the use of Ga. The mechanism by which this effect is achieved will be described later.

[0011] In this specification, the state of the magnet raw material to be subjected to HDDR (lump, particulate, powder, etc.) does not matter. Hydro-crushed cast alloys are usually easily disintegrated and become coarse lump or particulate after only light crushing. The magnet raw material may be subjected to HDDR in its coarse state, or may be subjected to HDDR after being crushed into a finer state.

[0012] <Magnet Raw Material, Rare Earth Magnet Powder, Compound, Bonded Magnet> The present invention can also be understood as the above-mentioned magnet raw material (the powdered form is also called "raw material powder") or magnet powder. The present invention can also be understood as a bonded magnet made of rare earth magnet powder and a resin that solidifies the powder particles. Furthermore, the present invention can also be understood as a compound used to manufacture the bonded magnet. The compound is made by previously adhering a resin that acts as a 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 by mixing multiple types of powders with different average particle sizes, alloy compositions, etc.

[0013] Others: (1) The rare earth magnet powder according to the present invention may be either an isotropic magnet powder or an anisotropic magnet powder with higher magnetic properties. 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.

[0014] (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. The casting alloy, magnet raw material, or magnet powder may contain modifying elements and (unavoidable) impurities that are effective in improving the properties.

[0015] (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." "x to y kPa" means x kPa to y kPa, and the same applies to other units.

[0016] Fig. 1 is a flowchart showing a manufacturing process of magnet powder (without diffusion treatment); Fig. 2 is a pattern diagram showing the hydrogen atmosphere of hydrogen crushing treatment; Fig. 3 is a scatter diagram showing the relationship between hydrogen crushing temperature and residual magnetic flux density (Br) of magnet powder; Fig. 4 is a flowchart showing a manufacturing process of magnet powder (with diffusion treatment); Fig. 5 is a scatter diagram showing the influence of the presence or absence of diffusion treatment on the relationship between hydrogen crushing temperature and Br of magnet powder.

[0017] 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 magnet raw materials, rare earth magnet powder, compounds, bonded magnets, etc., as appropriate, and even method-related components can be considered product-related components. Which embodiment is best depends on the target, required performance, etc.

[0018] <<Casting Alloy>> (1) Alloy Composition First, R ２ TM １４ B １ The theoretical composition of the tetragonal compound constituting the tetragonal crystal (main phase) is, in atomic percent (at%), R: 11.8 at%, B: 5.9 at%, and TM: the remainder. If the cast alloy is richer in R than the theoretical composition, it will be more likely to separate into R-rich grain boundary phases during hydrogen crushing. For example, when the entire cast alloy is taken as 100 at%, it is preferable that the R: be 11 to 15 at%, or even 12 to 14 at%, and the B: be 5 to 9 at%, or even 6 to 8 at%.

[0019] Next, the Ga content is, for example, 0.1 at% or less, 0.05 at% or less, or 0.01 at% or less, relative to the entire cast alloy (100 at%). Ga may not be contained except when it is an unavoidable impurity. In other words, the lower limit of the Ga content may be substantially 0 at%.

[0020] The Cu content is, for example, 0.02 to 0.3 at%, 0.03 to 0.2 at%, 0.04 to 0.15 at%, or 0.04 to 0.1 at%, based on the entire cast alloy. Furthermore, the Al content contained together with Cu is, for example, 0.3 to 2.5 at%, 0.4 to 2 at%, or 0.5 to 1 at%, based on the entire cast alloy. Cu and Al contribute to the formation of grain boundary phases together with R. Insufficient Cu or Al may result in an increase in cracks within crystal grains (main phases) and a decrease in the coercive force (Hc) of the magnet powder. Excessive Cu or Al may result in a decrease in the remanence (Br) of the magnet powder.

[0021] (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.

[0022] (3) Solution 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.

[0023] 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 crystallizes finely. Such rapidly solidified alloys have a relatively more homogeneous crystalline structure than ingot alloys. When rapidly solidified alloys are subjected to solution treatment, a structure in which fine crystal grains have grown (for example, grain size: 50 to 250 μm) is 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. Solution treatment is also referred to as homogenization heat treatment where appropriate.

[0024] 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, in an inert atmosphere (an inert gas atmosphere such as Ar, or a vacuum atmosphere).

[0025] (4) Dispersion Treatment The solution-treated cast alloy (ingot) may be further heated at a temperature lower than the solution treatment temperature but higher than the hydrogen crushing temperature (hydrogen crushing temperature) (this heat treatment is referred to as "R-rich dispersion treatment"). The temperature is, for example, 650 to 900°C, 650 to 800°C, or even 680 to 750°C. The heating time is, for example, 10 minutes to 10 hours or even 0.5 to 3 hours. The atmosphere is, for example, an inert atmosphere (an inert gas atmosphere (e.g., Ar) atmosphere or a vacuum atmosphere). The R-rich dispersion treatment promotes the dispersion (distribution) of rare earth elements (R) and the like at the grain boundaries of the cast alloy, resulting in each grain of the cast alloy being uniformly covered with an R-rich phase. When such a cast alloy is subjected to hydrogen crushing treatment, fracture (separation) at the grain boundaries of the cast alloy occurs more preferentially, making it easier to obtain a magnet raw material with reduced intragranular cracking.

[0026] <<Hydrogen Crushing Treatment>> (1) Treatment Conditions By subjecting the above-described cast alloy to a hydrogen crushing treatment (step), a magnet raw material for HDDR can be obtained. The 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. Specifically, the cast alloy is first placed in a treatment furnace and heated to 300 to 525°C, 350 to 450°C, or even 375 to 425°C. Next, hydrogen is introduced into the heated treatment furnace.

[0027] The inside of the treatment furnace is preferably evacuated 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 in the treatment furnace may be low or high. In consideration of efficiency and safety, the hydrogen partial pressure is, for example, 1 kPa to 250 kPa, or even 5 kPa to 150 kPa.

[0028] The hydrogen cracking treatment is carried out for, for example, 0.3 to 5 hours, or even 0.6 to 3 hours, after the cast alloy (atmosphere) reaches the target temperature. Regardless of the atmosphere of the treatment furnace, the temperature of the cast alloy in the treatment furnace is appropriately referred to as the atmospheric temperature of the treatment furnace.

[0029] (2) Magnet Raw Material After the hydrogen crushing process, the cast alloy either disintegrates or is lightly crushed due to hydrogen absorption, becoming magnet raw material with a maximum length of several centimeters to several millimeters. Lumped magnet raw material is called "raw material lump." The raw material lump may be separately crushed and pulverized to a powder (raw material powder) with a particle size (maximum diameter) of approximately 100 μm to 1 mm, and then supplied to the next process (HDDR). While it is difficult to strictly distinguish between "crushing" and "pulverization," if we were to venture a term, "pulverization" would be when particles are intentionally refined by applying shear force, and "crushing" would be when lumps are broken down by applying a light impact, etc.

[0030] The magnet raw material supplied to HDDR may still have absorbed hydrogen, or may have been dehydrogenated. If the production of magnet raw material (hydrogen crushing treatment) and the production of magnet powder (HDDR treatment) are not performed consecutively, the hydrogen-absorbed magnet raw material is prevented from deteriorating before HDDR. Hydrogen release (dehydrogenation) from the magnet raw material may be performed while heating at the same temperature as during hydrogen absorption (hydrogen crushing treatment).

[0031] Because the hydrogen crushing process tends to result in a crushed or atomized state as a by-product, the cast alloy may be supplied directly to the HDDR without any special crushing (e.g., as raw material ingots). Of course, particle size adjustments such as light crushing, grinding, and classification may be performed before supplying the alloy to the HDDR, taking into consideration the specifications of the magnet powder, the manufacturing process (equipment), and the specifications of the bonded magnet. Particle size adjustments may be performed, for example, to a particle size of -212 μm or an average particle size of 30 to 200 μm. The average particle size is determined, for example, as follows: First, powder with a particle size of -212 μm is extracted by sieving. This powder is then sieved (classified) into sizes 0 to 53 μm, 53 to 75 μm, 75 to 106 μm, 106 to 150 μm, and 150 to 212 μm. The weight ratio (referred to as "weight frequency") of each classified powder (y to x: μm) to the whole is determined. For each classified powder, the product of the average particle size ((y + x) / 2: μm) and the weight frequency is determined. The sum of these products is taken as the "average particle size."

[0032] The notation according to the sieve classification method (see JIS Z 8801) is as follows: -x μm: powder that passes through a sieve with an opening of x (μm) (powder with a maximum particle size less than x μm); (+)y μm: powder that does not pass through a sieve with an opening of y (μm) (powder with a minimum particle size greater than y μm); y to x (μm): powder that passes through a sieve with an opening of x (μm) but does not pass through a sieve with an opening of y (μm).

[0033] Incidentally, when particle size measurement is performed using laser diffraction, the high-pressure gas sprayed onto the magnet raw material after hydrogen crushing further atomizes it, making it difficult to perform an appropriate measurement.

[0034] (3) Mechanism: Hydrogen crushing is performed to minimize the occurrence of cracks in the crystal grains (single crystal grains) of a cast alloy. When a cast alloy heated to a predetermined temperature is exposed to a hydrogen atmosphere, hydrogen hardly penetrates into the crystal grains but preferentially penetrates into the grain boundary phase (R-rich phase / Nd-rich phase) between the crystal grains (grain boundaries). The grain boundary phase expands in volume due to hydrogen penetration, separating the crystal grains. In this way, hydrogen crushing of a cast alloy produces a magnet raw material consisting of crystal grains with almost no cracks. It is believed that HDDR of this magnet raw material produces a magnet powder with high magnetic properties. Note that the magnet raw material obtained by hydrogen crushing of a cast alloy may be particles consisting of individual crystal grains (single crystal particles) or an aggregate of such crystal grains (polycrystalline particles). Typically, magnet raw materials (raw material blocks, etc.) are composed of polycrystalline particles.

[0035] <HDDR> By applying HDDR to the magnet raw material (raw material powder / raw material lump) obtained after the hydrogen crushing process, 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 is roughly divided into a disproportionation process (HD) and a recombination process (DR).

[0036] (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 in the hydrogen-absorbed magnet raw material. The magnet raw material that has undergone the disproportionation reaction (forward transformation reaction) is decomposed into a three-phase structure (α-Fe phase, RH phase, ２ phase, Fe ２ Phase B).

[0037] The disproportionation step is carried out, for example, at a hydrogen partial pressure of 10 to 300 kPa, further 20 to 60 kPa, an atmospheric temperature of 600 to 900° C., further 750 to 860° C., and a treatment time of 1 to 5 hours, further 2 to 4 hours.

[0038] During this process, the hydrogen partial pressure or the atmospheric temperature does not need to be constant. For example, at the end of the reaction 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).

[0039] (2) Recombination Process (DR) The recombination process is a process in which hydrogen is removed from the magnet raw material after the disproportionation process, and a recombination reaction occurs in the magnet raw material. The recombination reaction (reverse transformation reaction) of the three-phase decomposed structure results in RH ２ The hydrogen is removed from the Fe phase. ２ Fine R formed by transferring the crystal orientation of the B phase ２ TM １４ B １ type crystal or its hydride (RFeBH Ｘ ) is obtained.

[0040] The recombination step is performed, for example, under conditions of a hydrogen partial pressure of 1 kPa or less, an atmospheric temperature of 600 to 900° C., and a treatment time of 1 to 5 hours.

[0041] This process may be performed by combining a controlled evacuation process and a forced evacuation process as follows. In the controlled evacuation process, the magnet raw material after the disproportionation process is held in a hydrogen atmosphere at a hydrogen partial pressure of 0.7 to 6 kPa and a temperature of 750 to 850°C. Because the controlled evacuation process is performed under a relatively high hydrogen partial pressure, the recombination reaction proceeds slowly. If the controlled evacuation process is performed at approximately the same temperature as the disproportionation process, the process can be transitioned by simply changing the hydrogen partial pressure.

[0042] The forced evacuation step is carried out, for example, at 750 to 850° C. in a vacuum atmosphere of 1 Pa or less. The forced evacuation step removes hydrogen remaining in the magnet raw material, completing the dehydrogenation.

[0043] The forced evacuation step and the controlled evacuation step may be performed consecutively, or the forced evacuation step may be performed after the controlled evacuation step. Ｘ ) may be batch-processed. After the forced evacuation step, the cooling is preferably rapid cooling to prevent the growth of crystal grains.

[0044] (3) Diffusion Treatment The magnet raw material (magnet powder) may be further subjected to a diffusion treatment to increase the coercive force. ２ TM １４ B １ This is done by adding a diffusion material that forms a nonmagnetic phase on the surface or grain boundary of the type crystal to the magnet raw material, and then heating and mixing them in a vacuum or inert gas atmosphere. The diffusion material may be added at any stage before the forced evacuation process, and the diffusion process may also be performed in a subsequent process. The diffusion material may be, for example, a heavy rare earth element (Dy, Tb, etc.), an alloy or compound thereof (e.g., fluoride), or an alloy or compound of a light rare earth element (e.g., Cu alloy, Cu-Al alloy).

[0045] However, the Cu (and also Al) contained in the casting alloy of the present invention contributes significantly to the formation of grain boundary phases that increase coercivity. This makes it possible to obtain high-coercivity magnet powder without diffusion treatment (i.e., even with non-diffusion treatment). This is thought to be because Cu hardly forms a solid solution in the crystal grains (main phase).

[0046] The manufacturing method of the present invention makes it possible to reduce the temperature and time required for the hydrogen cracking process compared to conventional methods, and to eliminate the need for a diffusion process. In other words, the manufacturing method of the present invention makes it possible to obtain magnet powder with high magnetic properties while saving energy.

[0047] <<Applications>> The rare earth magnet powder of the present invention can be used for a variety of purposes, with a typical example being bonded magnets. Bonded magnets are primarily composed of rare earth magnet powder and a binder resin. The binder resin may be a thermosetting resin or a thermoplastic resin. Bonded magnets may also 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. The magnet powder used for bonded magnets has, for example, a particle size of -212 μm and an average particle size of 30 to 200 μm.

[0048] Samples (magnet powders) were produced by varying the component composition of the cast alloy and the conditions of the hydrogen crushing treatment, and their magnetic properties were evaluated. The present invention will be explained in more detail based on these examples.

[0049] [First Example] <<Production of Sample>> As shown in Fig. 1A, a solution-treated cast alloy was subjected to hydrogen crushing treatment and HDDR. Specifically, the procedure is as follows.

[0050] (1) Cast Alloys First, ingots with the following composition (Alloys A to D) were prepared. The ingots were obtained by melting in a high-frequency melting furnace. The composition is expressed as the atomic percentage (at%) of the entire alloy, with the remainder being Fe(TM). In this example, unless otherwise specified, the numerical values ​​indicating the composition are in at%. Alloy A: Nd １２．７ FeB ６．４ Nb ０．２ Cu ０．１ Alloy B: Nd １２．７ FeB ６．４ Nb ０．２ Cu ０．１ Al ０．７ Alloy C: Nd １２．７ FeB ６．４ Nb ０．２ Al ０．７ Alloy D: Nd １２．７ FeB ６．４ Nb ０．２ Ga ０．３

[0051] (2) Solution Treatment The ingot was heated in an Ar gas atmosphere at 1140°C for 20 hours to be homogenized.

[0052] (3) Hydrogen crushing treatment The treatment furnace containing the ingot after the solution treatment was evacuated to a vacuum (10 -２ While maintaining the vacuum, the ingot in the treatment furnace was heated over one hour as shown in FIG. 1B until the desired atmospheric temperature was reached within the treatment furnace. The atmospheric temperature was varied between room temperature (RT) and 600°C. The atmospheric temperature within the treatment furnace was measured using a thermocouple in contact with the ingot.

[0053] After the ambient temperature reached the target temperature, hydrogen was introduced into the treatment furnace. Then, as shown in Figure 1B, the hydrogen partial pressure in the treatment furnace was kept constant (98 kPa) and maintained for 1 hour. The hydrogen partial pressure was measured using a pressure gauge installed in the treatment furnace.

[0054] Thereafter, the atmospheric temperature was lowered to room temperature while maintaining the hydrogen partial pressure. Further, the hydrogen in the processing furnace was replaced with an inert gas (Ar at atmospheric pressure), and the magnet raw material was removed from the furnace in the Ar atmosphere.

[0055] Light crushing was applied to the magnet raw material in an atmosphere temperature of RT to 500°C. Since it was difficult to powder the magnet raw material in an atmosphere temperature of 600°C by light crushing alone, mechanical crushing was also applied. Crushing and classification were carried out in an inert gas atmosphere.

[0056] Incidentally, as described in Patent Publication WO2020 / 017529, furnace cooling after the hydrocracking treatment may be performed after hydrogen evacuation (Ar replacement). Note that the entire contents of this patent publication, including but not limited to furnace cooling, are incorporated into this specification as appropriate within the scope of the present invention.

[0057] (4) HDDR Treatment Each raw material powder was subjected to HDDR treatment. First, the raw material powder (15 g) in the treatment furnace after evacuation was exposed to a high-temperature hydrogen atmosphere to cause a disproportionation reaction (forward transformation reaction) (disproportionation step / HD step). In this step, the hydrogen partial pressure in the treatment furnace was kept at 25 kPa, and the atmosphere temperature was increased to 780°C for 2 hours, after which the atmosphere temperature was further increased to 840°C for 2 hours (structure stabilization step).

[0058] Next, a controlled evacuation process (840°C x 2.5 kPa x 1.5 hours) was performed to continuously evacuate hydrogen from the treatment furnace, followed by a forced evacuation process (840°C x 10 -２ The raw material powder was subjected to a hydrogen pressure of 1.0 kPa x 0.5 hours to induce a recombination reaction (reverse transformation reaction) in the raw material powder after the HD process (recombination process / DR process). After this, Ar gas was introduced into the processing furnace to rapidly cool the processed material (cooling process). This processed material was lightly crushed in Ar gas and classified (sieved) to -212 μm to obtain magnet powder. Note that for Alloy D, the hydrogen pressure in the controlled evacuation process was set to 1.0 kPa.

[0059] <<Measurement>> The produced magnet powder 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 magnetized magnet powder were measured using a vibrating sample magnetometer (VSM).

[0060] The relationship between the residual magnetic flux density (Br) and the hydrogen decomposition temperature for each magnet powder having a different alloy composition is shown in FIG.

[0061] 2, the magnetic powders made of Alloy A and Alloy B, which contain Cu, exhibited high magnetic properties equal to or greater than those of Alloy D, which does not contain Cu but contains Ga. In addition, the magnetic powders made of Alloy A and Alloy B, which do not contain Cu, exhibited lower magnetic properties than the magnetic powders made of Alloy A and Alloy B.

[0062] (2) Hydrogen Crushing Temperature Furthermore, as can be seen from Figure 2, the magnetic properties of the magnet powders made from Alloy A and Alloy B were significantly improved when the hydrogen crushing temperature was set to 300 to 525°C, 325 to 500°C, or 375 to 475°C. These temperature ranges were shifted significantly lower than the temperature range in which the magnetic properties of the magnet powder made from Alloy D, which contains Ga, peaked. Incidentally, the temperature range in which the magnetic properties peaked shifted lower in the following order: Alloy D (Cu-free / Ga-containing) → Alloy C (Cu-free / Al-containing) → Alloy A (Cu-containing) → Alloy B (Cu and Al-containing).

[0063] Furthermore, in this example, the processing time for hydrogen decomposition was significantly reduced from the conventional 5 hours (see WO2020 / 017529) to approximately 1 hour, but the magnetic powders made from alloys A and B exhibited higher magnetic properties than the magnetic powder made from the conventional alloy D containing Ga.

[0064] (3) Non-Diffusion Treatment In this example, no diffusion treatment to increase coercivity was performed after HDDR, but the magnet powders made from Alloy A and Alloy B exhibited sufficiently high coercivity. For example, when Alloy A was used at a hydrogen-crushing temperature of 450°C, the magnet powder's coercivity (Hc) was 1057 kA / m (Br: 1.42 T), and when Alloy B was used at a hydrogen-crushing temperature of 400°C, the magnet powder's Hc was 1266 kA / m (Br: 1.40 T). Incidentally, when Alloy C was used at a hydrogen-crushing temperature of 450°C, the magnet powder's Hc was 557 kA / m (Br: 1.37 T). Furthermore, when Alloy D was used at a hydrogen-crushing temperature of 500°C, the magnet powder's Hc was 1238 kA / m (Br: 1.40 T).

[0065] [Second Example] (1) Diffusion Treatment As shown in Figure 3, a diffusion treatment was further carried out after the above-mentioned HDDR treatment. Specifically, the mixed raw material, which was made by adding a diffusion raw material to the magnet powder made of alloy B after HDDR, was further heated in a vacuum atmosphere (800°C x 1 hour) (diffusion step). The diffusion raw material contained Nd ５１ Cu １５ Al ３４ The proportion of the diffusion material to the total mixed material was 2 mass %.

[0066] (2) Magnetic Properties The magnetic properties of the diffusion-treated magnet powder were measured using the method described above. The relationship between Br and the hydrogen-crushing temperature is shown in Figure 4. For reference, Figure 4 also shows the relationship between Br and the hydrogen-crushing temperature for the magnet powder (first example / Alloy B) before the diffusion treatment.

[0067] As can be seen from Figure 4, if the component composition of the cast alloy is the same, the hydrogen cracking temperature (near 400°C) at which the Br of the magnet powder peaks remains almost unchanged before and after the diffusion treatment. When the hydrogen cracking temperature is 400°C, the diffusion treatment reduces the Br from 1.40 T to 1.36 T, but increases the Hc from 1266 kA / m to 1476 kA / m. This is presumably because the diffusion treatment sufficiently forms a non-magnetic grain boundary phase between the fine crystals that make up the magnetic particles.

[0068] The first example demonstrated that magnetic powder with sufficient magnetic properties can be obtained without performing a diffusion treatment (in other words, while still conserving resources and energy). When magnetic powder with a higher Hc is desired depending on the specifications (application), a diffusion treatment may be performed as in this example.

[0069] [Third Example] Magnet powder made of Alloy A was also subjected to a diffusion treatment in the same manner as in the second example. As a result, the hydrogen cracking temperature (around 450°C) at which Br peaked showed almost no change before and after the diffusion treatment. When the hydrogen cracking temperature was 450°C, the diffusion treatment reduced Br from 1.42 T to 1.36 T, but increased Hc from 1057 kA / m to 1302 kA / m.

[0070] From a comparison of the above-described examples, regardless of whether or not a diffusion treatment in which a diffusion raw material (NdCuAl) was further added after HDDR was performed, the Hc of the magnet powder made of alloy B (NdFeBCuAl alloy) which further contained Al was greater than that of the magnet powder made of alloy A (NdFeBCu alloy).

[0071] Furthermore, when the above-mentioned diffusion treatment was further performed in addition to the hydrogen cracking treatment and HDDR treatment, the Hc of Alloy B was greater than that of Alloy A. Although the reason for this is unclear, it is presumed that Alloy B, which contains Al, exhibits higher fluidity during the diffusion treatment in the grain boundary phase at the fine grain boundaries formed after the HDDR treatment (before the diffusion treatment) than Alloy A, which does not contain Al. In other words, it is thought that Al contributed to improving the fluidity of the Nd-rich phase generated at the fine grain boundaries not only during the hydrogen cracking treatment but also during the diffusion treatment.

[0072] From the above, it has been confirmed that the present invention makes it possible to obtain rare earth magnet powder with high magnetic properties while reducing the use of rare Ga, which is at risk of supply instability. It has also been confirmed that the present invention makes it possible to efficiently produce magnet powder and reduce energy consumption in the production process by reducing the temperature and time involved in the hydrogen crushing process and omitting the diffusion process.

Claims

1. A hydrogen crushing step of introducing hydrogen into a processing furnace after heating a cast alloy in the processing furnace to expose the cast alloy to a hydrogen atmosphere at a predetermined temperature to obtain a magnet raw material from the cast alloy; 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, wherein the cast alloy contains a rare earth element (R), boron (B), a transition element (TM), and Cu: 0.02 to 0.3 at% with respect to the whole thereof and has a Ga content of 0.1 at% or less, and the hydrogen crushing step is a method for producing rare earth magnet powder in which the hydrogen atmosphere is set to 300 to 525°C.

2. The method for producing rare earth magnet powder according to claim 1, wherein the cast alloy further contains Al: 0.3 to 2.5 at% with respect to the whole thereof.

3. The method for producing rare earth magnet powder according to claim 1 or 2, wherein the hydrogen crushing step sets the hydrogen partial pressure of the hydrogen atmosphere to 1 kPa to 250 kPa.

4. The method for producing rare earth magnet powder according to claim 1 or 2, wherein the cast alloy is subjected to a solution treatment before the hydrogen crushing step.

5. The method for producing rare earth magnet powder according to claim 1 or 2, wherein the cast alloy contains R: 11 to 15 at% and B: 5 to 9 at% with respect to the whole thereof.

6. The method for producing rare earth magnet powder according to claim 1, 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 recombination step.

7. The method for producing rare earth magnet powder according to claim 6, wherein the diffusion raw material is composed of an alloy or compound containing at least R and Cu.

8. The method for producing rare earth magnet powder according to claim 7, wherein the diffusion raw material further contains Al.

Images