JP2024008327A - Method for producing rare earth magnet powder - Google Patents

Abstract

To provide a production method, capable of obtaining rare earth magnet powder having high magnetic characteristics.SOLUTION: The present invention relates to a method for producing rare earth magnet powder. The method includes: a disproportionation step of causing a disproportionation reaction through hydrogenation in a magnet raw material comprising a casting alloy in which a rare earth element and a transition element B are contained; and a recombination step of causing a recombination reaction through dehydrogenation from the magnet raw material after subjected to the disproportionation step. The casting alloy may include 0.02-0.4 at% of Cu, and further 0.02-1.5 at% of Al. The recombination step may performed by a controlled exhaust step of heating the magnet raw material after subjected to the disproportionation step, in a hydrogen atmosphere with a hydrogen pressure of 1.5-3.5 kPa. If a diffusion step of heating, in an inert atmosphere, a mixed raw material obtained by adding a diffusion raw material (Nd-Cu-Al) to the magnet raw material after subjected to the recombination step is performed, magnetic characteristics (especially coercive force) can be improved furthermore.SELECTED DRAWING: Figure 4B

Description

The present invention relates to a method for producing rare earth magnet powder, etc.

Bonded magnets, which are made by hardening rare earth magnet powder with binder resin, have excellent shape freedom and exhibit high magnetic properties, so they are often used in various electromagnetic devices such as electric appliances and automobiles that require energy savings and weight reduction. In order to further expand the use of bonded magnets, it is desired to improve the magnetic properties of rare earth magnet powder. Since the magnetic properties of rare earth magnet powder are greatly affected by the hydrogen treatment conditions performed during its manufacturing process, various proposals related to hydrogen treatment have been made, and related descriptions can be found in the following patent documents.

Hydrogen treatment (HDDR) mainly involves a disproportionation reaction by hydrogen absorption (referred to as "HD") and a recombination reaction by dehydrogenation (referred to as "DR"). Consisting of In this specification, unless otherwise specified, it is simply referred to as "HDDR" including its improved type, d-HDDR (dynamic-hydrogenation-disproportionation-desorption-recombination).

JP 10-317003 WO2011/070847 WO2013/035628 JP2014-177660 WO2020/017529

Patent Document 1 describes that a NdFeB-based alloy ingot containing Cu is subjected to hydrogen absorption treatment (HD) and dehydrogenation treatment (DR). According to Patent Document 1, rare earth alloy powder with high magnetic properties (especially coercive force Hcj) is obtained during dehydrogenation treatment at a hydrogen partial pressure of about 1 kPa (see [0035] of Patent Document 1, Table 2). ).

Patent Documents 2 to 5 do not mention that a cast alloy (mother alloy, raw material alloy, alloy ingot, etc.) containing Cu is subjected to hydrogen treatment. When performing dehydrogenation treatment (DR) on a cast alloy that does not contain Cu, Patent Documents 2 and 3 set the degree of vacuum in the furnace to 3.2 kPa, and Patent Documents 4 and 5 set the hydrogen partial pressure to 1 to 5 kPa. However, none of the patent documents provides a detailed study on the hydrogen partial pressure during dehydrogenation, and there is no specific description or suggestion regarding this point.

The present invention was made under these circumstances, and an object of the present invention is to provide a new manufacturing method etc. that can obtain rare earth magnet powder with high magnetic properties.

As a result of intensive research by the present inventor, we found that when hydrogen treating (HDDR) a cast alloy containing Cu to obtain rare earth magnet powder, the hydrogen pressure (partial pressure) during the recombination reaction (during dehydrogenation) and the rare earth magnet powder We have newly discovered that there is a unique correlation between the magnetic properties of Based on this result, the present invention described below has been completed.

《Method for producing rare earth magnet powder》
(1) The present invention includes a disproportionation process in which a magnet raw material made of a cast alloy containing rare earth elements, transition elements, and B is made to absorb hydrogen to cause a disproportionation reaction, and a magnet after the disproportionation process. The cast alloy includes a recombination step in which raw materials are dehydrogenated to cause a recombination reaction. The method for producing rare earth magnet powder includes a controlled exhaust step of heating the magnet raw material after the disproportionation step in a hydrogen atmosphere of 1.5 to 3.5 kPa.

(2) According to the manufacturing method of the present invention, rare earth magnet powder with high magnetic properties can be obtained. Although the reason for this is not necessarily certain, it is currently thought to be as follows. In the manufacturing method of the present invention, controlled exhaust gas with hydrogen pressure (partial pressure) within a specific range is applied to a magnet raw material made of an R-TM-B cast alloy containing Cu (R: rare earth element, TM: transition element). Process is applied. Due to this controlled evacuation process, during the recombination process, the crystal nuclei that become the main phase grow abnormally locally, causing uneven crystal grain coarsening, or homogeneous crystal grain coarsening. can be inhibited. It is believed that this resulted in rare earth magnet particles having high magnetic properties and having a metal structure in which crystal grains serving as the main phase (R ₂ TM ₁₄ B) were finely and uniformly distributed.

《Rare earth magnet powder, compound, bonded magnet》
The present invention can be understood as a rare earth magnet powder, a bonded magnet in which the rare earth magnet powder is bonded with a resin, and a compound used for manufacturing the bonded magnet. The compound is made by attaching a resin, which is a binder, to the surface of powder particles in advance. Note that the powder used for the bonded magnet or compound may be a composite powder in which powder other than the rare earth magnet powder according to the present invention is mixed.

"others"
(1) Casting alloys and magnet raw materials (including crushed raw materials) may be in the form of lumps, particles, powder, etc., regardless of form or state, and particle size may be adjusted by classification etc. .

Regardless of the shape of particles, the size (particle size) is appropriately referred to as "particle size." Further, in this specification, particle size is indexed by particle size. For example, particles having a particle size (d) of less than α (μm) (d<α) mean particles that pass through a sieve with a nominal opening (mesh size) α.

(2) The rare earth magnet powder may be an isotropic magnet powder or an anisotropic magnet powder. Anisotropic magnet powder consists of magnet particles in which the magnetic flux density (Br) in one direction (easy axis direction, c-axis direction) is larger than the magnetic flux density in the other direction. Isotropy and anisotropy can be distinguished by the degree of anisotropy (DOT: Degree of Texture); if the value of DOT is 0, it is isotropic, and if it is greater than 0, it is anisotropic. In addition, DOT is calculated from the magnetic flux density Br (//) or Br (⊥) when applying a magnetic field parallel (//) or perpendicular (⊥) to the c-axis direction, DOT = [Br (//) - Br (⊥)]/Br(//).

(3) Rare earth elements (R) include Y, Sm, Tb, Dy, etc. in addition to Nd, Pr, Ce, La, etc. Examples of transition elements (TM) include 3d transition elements (Sc to Ni) and 4d transition elements (Y to Ag). A typical example of R is Nd, and a typical example of TM is Fe. A part of the Nd may be replaced by Pr. In addition, a part of the Fe may be replaced by Co in an amount of, for example, 0.01 to 20.0 at%, or even 0.5 to 5.4 at%, based on the entire cast alloy. Further, a part of B may be replaced by C. The amount of substitution is, for example, 0.05 to 1 at%, more preferably 0.1 to 0.6 at%, based on the entire cast alloy.

In addition to (inevitable) impurities, the cast alloy or rare earth magnet powder may contain modifying elements effective for improving properties. Modifying elements include, for example, Al, Ti, V, Cr, Ni, Zn, Ga, Zr, Nb, Mo, Sn, Hf, Ta, W, Dy, Tb, Co, etc., which are effective in improving coercive force. .

(4) Unless otherwise specified, "x to y" as used herein includes a lower limit x and an upper limit y. A new range such as "a to b" can be established by setting any numerical value included in the various numerical values or numerical ranges described herein as a new lower limit or upper limit. Furthermore, "x~ykPa" means xkPa~ykPa, and the same applies to other unit systems.

The manufacturing process of rare earth magnet powder will be illustrated. An example of a hydrogen atmosphere setting pattern related to HDDR is illustrated. The relationship between the magnetic properties of rare earth magnet powder (casting alloy A/no diffusion treatment) and DR pressure (P _H2 ) is shown. The relationship between the magnetic properties of rare earth magnet powder (casting alloy A/with diffusion treatment) and DR pressure (P _H2 ) is shown. The relationship between the magnetic properties of rare earth magnet powder (cast alloy B/no diffusion treatment) and DR pressure (P _H2 ) is shown. The relationship between the magnetic properties of rare earth magnet powder (cast alloy C/no diffusion treatment) and DR pressure (P _H2 ) is shown. The relationship between the magnetic properties of rare earth magnet powder (cast alloy C/with diffusion treatment) and DR pressure (P _H2 ) is shown. The relationship between the magnetic properties of rare earth magnet powder (cast alloy D/no diffusion treatment) and DR pressure (P _H2 ) is shown. A magnetic curve related to rare earth magnet powder (cast alloy C/with diffusion treatment) is shown.

One or more components arbitrarily selected from the present 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 rare earth magnet powder, compounds, bonded magnets, etc., and even a method-related component can be a product-related component. Which embodiment is best depends on the object, required performance, etc.

《Rare earth magnet powder》
(1) Rare earth magnet powder (simply referred to as "magnet powder") consists of magnet particles, which include fine R ₂ TM ₁₄ B ₁ type crystals (main phase), which are tetragonal compounds, and the surroundings of the crystal grains. It consists of a grain boundary phase surrounding the grain boundary phase. The stoichiometric composition of the tetragonal compound constituting the main phase is R: 11.8 at%, B: 5.9 at%, and the balance is TM. Considering the grain boundary phase, for example, the rare earth element (R) is 12 to 18 at%, 12.5 to 16.5 at%, and further 13 to 15 at%, and B is It contains 5.5 to 8 at% and further 6 to 7 at%. The remainder other than R and B is mainly a transition metal element (TM), but may also contain typical metal elements (Al, etc.), typical nonmetal elements (C, O, etc.), impurities, and the like.

(2) R is, for example, Nd, Pr, Dy, Tb, etc. In addition to Cu, the magnet particles include at least one of Al, Si, Ti, V, Cr, Ni, Zn, Ga, Zr, Nb, Mo, Mn, Sn, Hf, Ta, W, Dy, Tb, Co, etc. May include.
For example, Cu is 0.02 to 2 at%, 0.05 to 1 at%, and even 0.1 to 0.5 at%, and Al is 0.02 to 3.5 at%, 0.2 to 2.5at% and 0.4 to 1.5at%, 0.05 to 0.7at% for Nb and Zr, 0.1 to 0.5at% and further 0.15 to 0.3at%, and 0 for Ga. The content may be 0.4 at% or less (0.01 to 0.4 at%), 0.35 at% or less, and further 0.25 at% or less.

"Production method"
(1) Casting alloy The casting alloy may be an ingot alloy obtained by pouring a molten R-TM-B alloy into a mold and solidifying it, or a rapidly solidified alloy obtained by rapidly cooling and solidifying the molten metal. The rapidly solidified alloy can be obtained, for example, by strip casting (SC).

The composition of the cast alloy is adjusted by taking into account not only the composition of the magnet powder but also the composition and amount of the diffusion raw material when it is subjected to diffusion treatment. For example, the casting alloy has R of 11.5 to 15 at%, 12 to 14 at%, further 12.2 to 13.5 at%, B of 5.5 to 8 at%, and further 6 to 7 at%, assuming that the entire casting alloy is 100 at%. %include. The remainder of the cast alloy is a transition element (eg, Fe) or a modifying element (eg, Cu, Al, Nb, Zr, etc.).

The casting alloy according to the present invention contains at least Cu. Cu is contained in, for example, 0.02 to 0.4 at%, 0.03 to 0.25 at%, 0.05 to 0.2 at%, and further 0.07 to 0.15 at%, based on the entire cast alloy. . If Cu is too small, the coercive force will not improve much even if the hydrogen pressure is adjusted in the controlled exhaust process. If Cu becomes too large, the coercive force of the magnet powder may decrease.

The casting alloy may contain Al in addition to Cu. Al is contained in the entire cast alloy, for example, 0.02 to 1.5 at%, 0.2 to 1.2 at%, and further 0.5 to 0.9 at%. If the amount of Al is too small, the effect of improving the coercive force will be poor, and if it is too large, it will cause a decrease in the residual magnetic flux density.

The casting alloy may include at least one of Nb and Zr. Nb and Zr are contained in a total of, for example, 0.05 to 0.7 at%, 0.1 to 0.5 at%, and further 0.15 to 0.3 at%, based on the entire cast alloy. If the amount of either element is too small, the effect of improving magnetic anisotropy will be poor, and if it is too large, the residual magnetic flux density of the magnet powder may decrease.

(2) Homogenization treatment Homogenization treatment (solution treatment) makes the metal structure of the cast alloy uniform and eliminates the segregation of the soft magnetic αFe phase.

The homogenization treatment is performed, for example, by heating the cast alloy at 1000 to 1200°C, or further at 1050 to 1150°C. The treatment time is, for example, 3 to 50 hours, or even 10 to 40 hours. The heating atmosphere is, for example, an inert atmosphere (an inert gas (Ar, etc.) atmosphere, a vacuum atmosphere, etc.).

(3) Dispersion treatment The dispersion treatment promotes the uniform formation of an R-rich (for example, Nd-rich) grain boundary phase. When the cast alloy subjected to the dispersion treatment is subjected to high-temperature hydrogen cracking treatment, fracture (separation) occurs preferentially at the grain boundaries, and the generation of cracks within the main phase grains can be suppressed.

The dispersion treatment is performed by heating at a temperature higher than that of high-temperature hydrogen cracking (and lower than that of homogenization treatment), for example, 650 to 900°C, 650 to 800°C, or further 680 to 750°C. The treatment time is, for example, 10 minutes to 10 hours, and further 0.5 to 3 hours. The heating atmosphere is, for example, an inert atmosphere.

(4) Hydrogen cracking Hydrogen cracking (step) may be performed in which the cast alloy before HDDR (before the disproportionation process) is exposed in advance to a hydrogen atmosphere. In other words, the disproportionation step may be performed on the magnet raw material obtained by exposing the cast alloy to a hydrogen atmosphere below the temperature that causes the disproportionation reaction.

Hydrogen cracking treatment can be carried out in a low temperature range (e.g. room temperature to 300°C or even room temperature to 100°C) or in a high temperature range (e.g. 350 to 585°C, 400 to 575°C or even 425 to 550°C). It may also be high-temperature hydrogen cracking performed at

The hydrogen partial pressure is, for example, 1 kPa to 250 kPa, and further 5 kPa to 150 kPa. The processing time (the elapsed time after the ambient temperature reaches the target temperature) is, for example, 0.1 to 10 hours, and further 0.5 to 5 hours. In high-temperature hydrogen cracking, hydrogen is preferably introduced into the processing furnace after the cast alloy (atmosphere) reaches a predetermined temperature.

By the way, when high-temperature hydrogen cracking (process/treatment) is performed, hydrogen hardly penetrates into the grains, but mainly enters the grain boundary phase (R-rich phase/Nd-rich phase), causing volume expansion of the grain boundary phase. Cracks occur preferentially between crystal grains. As a result, the cast alloy is separated between crystal grains, and a magnet raw material (crushed raw material) consisting of main phase grains with few cracks and cracks is obtained. The effects, mechanism, etc. of such hydrogen cracking are detailed in WO2020/017529. The written content (full text) shall be incorporated into this application as appropriate.

(5) Classification A cast alloy that has absorbed hydrogen through hydrogen disintegration may collapse on its own or become granular through light disintegration. The cast alloy may be made into a powder by further crushing or pulverization, or the particle size may be adjusted by classification. HDDR is preferably performed on the magnet raw material from which at least coarse particles have been removed.

(6) HDDR
By HDDR, a magnet powder consisting of a polycrystalline body (magnet particles) in which fine R ₂ TM ₁₄ B type ₁ crystals (average grain size: 0.05 to 2 μm) are aggregated is obtained. HDDR can be roughly divided into a disproportionation process (HD) and a recombination process (DR).

In the disproportionation process, the magnet raw material placed in the processing furnace is exposed to a predetermined hydrogen atmosphere. The magnet raw material that has absorbed hydrogen in this step undergoes a disproportionation reaction (forward transformation reaction) and becomes a three-phase decomposed structure (αTM phase, RH ₂ phase, TM ₂ B phase).

The disproportionation step is performed, for example, at a hydrogen partial pressure of 10 to 150 kPa, further 15 to 50 kPa, an ambient temperature of 600 to 900°C, further 750 to 860°C, and a treatment time of 1 to 5 hours. Note that the hydrogen atmosphere referred to in this specification may be a mixed gas atmosphere of hydrogen and an inert gas.

During the disproportionation step, the hydrogen partial pressure or the ambient temperature may not be constant throughout. For example, at the end of the process when the reaction rate decreases, at least one of pressure (hydrogen partial pressure) or temperature may be increased to adjust the reaction rate and promote three-phase decomposition (structure stabilization step).

In the recombination step, the magnet raw material after the disproportionation step is dehydrogenated. Through this process, the dehydrogenated magnet raw material (three-phase decomposed structure) caused a recombination reaction (reverse transformation reaction), and hydrogen was removed from the RH ₂ phase and the crystal orientation of the TM ₂ B phase was transferred. A fine R ₂ TM ₁₄ B ₁ type crystal hydride (RTMBH _x ) is formed.

In the recombination process (controlled exhaust process), for example, hydrogen partial pressure: 1.5 to 3.5 kPa, 1.8 to 3.2 kPa, further 2 to 3 kPa, ambient temperature: 600 to 900°C, furthermore 750 to 860°C. , treatment time: 0.5 to 5 hours, further 1 to 3 hours. This step proceeds slowly because the hydrogen partial pressure is relatively high. Furthermore, by setting the hydrogen partial pressure within a specific range, the magnetic properties (coercive force) of the magnet powder can be improved.

When the inside of the processing furnace is made into a vacuum atmosphere (1 Pa or less, or even 0.1 Pa or less) after the recombination process (controlled exhaust process), the hydrogen remaining in the magnet raw material is removed and dehydrogenation is completed (forced exhaust process). . This step is carried out, for example, at an ambient temperature of 600 to 900°C, preferably 750 to 860°C, and a processing time of 0.1 to 5 hours, further 0.3 to 1 hour. The cooling after the forced evacuation process is preferably rapid cooling in order to suppress the growth of crystal grains.

From the start of the disproportionation step to the end of the recombination step (including the forced evacuation step), the temperature may be maintained at approximately the same level and the hydrogen partial pressure may be changed only. The controlled evacuation process and the forced evacuation process may be performed continuously or discontinuously. For example, a cooling process for cooling the magnet raw material may be performed after the controlled exhaust process, and the forced exhaust process may be batch processed.

(7) Diffusion processing Diffusion processing may be performed after HDDR. The diffusion treatment (diffusion process) is performed, for example, by heating a mixed raw material obtained by adding a diffusion raw material to the magnet raw material after HDDR (recombination process). As a result, a nonmagnetic phase is formed on the surface or grain boundaries of the R ₂ TM ₁₄ B ₁ type crystal, and the coercive force of the magnet particles can be improved. Note that the diffusion treatment is preferably performed in an inert atmosphere (an inert gas atmosphere, a vacuum atmosphere, etc.).

Examples of the diffusion raw material include alloys and compounds of light rare earth elements, heavy rare earth elements (Dy, Tb, etc.), and alloys and compounds thereof (for example, fluorides). By using a light rare earth element (such as Nd)-Cu-(Al) based alloy or compound, it is possible to avoid the use of rare heavy rare earth elements.

《Application》
Rare earth magnet powder can be used for various purposes. A typical example is a bonded magnet. Bonded magnets mainly consist of rare earth magnet powder and binder resin. The binder resin may be a thermosetting resin or a thermoplastic resin. Further, the bonded magnet may be compression molded or injection molded. A bonded magnet using rare earth anisotropic magnet powder is preferably molded in an orienting magnetic field.

We produced rare earth magnet powders (samples) with different cast alloy compositions and production conditions, and evaluated their magnetic properties. The present invention will be specifically explained based on such examples.

《Sample production》
Rare earth magnet powder belonging to the sample group shown in Table 1 was manufactured according to the steps shown in FIGS. 1A and 1B (both are collectively referred to as "FIG. 1"). Specifically, it is as follows.

(1) Casting A plurality of types of casting alloys A to D shown in Table 1 were prepared by an arc melting method. The component compositions shown in Table 1 are the compounding compositions for each cast alloy as a whole, and are expressed in atomic ratios (remainder: Fe) to the whole.

(2) Homogenization Treatment Each cast alloy was heated at 1140° C. for 20 hours in a processing furnace in an inert atmosphere (P _Ar : 35 kPa) into which Ar was introduced after evacuation.

Unless otherwise specified, the atmosphere, temperature, and pressure used in this example are as follows. The atmosphere is the atmosphere inside the processing furnace containing the objects to be processed (casting alloy, magnet raw material). The temperature (T) was measured with a thermocouple brought into contact with the object to be treated (casting alloy, magnet raw material). The pressure (P) was determined by measuring the internal pressure of the processing furnace (near the object to be processed) using a pressure gauge.

The atmosphere (gas) was changed after the processing furnace was evacuated. The vacuum atmosphere (Vac) was set to 10 Pa or less. For the hydrogen atmosphere, only hydrogen was introduced into the processing furnace after evacuation (10 Pa or less), and the internal pressure of the processing furnace was set to the hydrogen pressure ( _PH2 ) (the same applies below).

(3) Hydrogen cracking treatment The cast alloy after the homogenization treatment was subjected to either high-temperature hydrogen cracking or low-temperature hydrogen cracking, which will be described later.

(3-1) High-temperature hydrogen cracking Before high-temperature hydrogen cracking, the cast alloy after the homogenization treatment was gently raised to 700° C. in a vacuum atmosphere and then held for 1 hour (dispersion treatment). The cast alloy after this dispersion treatment was held in a hydrogen atmosphere (100 kPa x 450°C) for 1 hour (high temperature hydrogen cracking). Hydrogen was introduced into the processing furnace after the dispersion treatment after the inside of the processing furnace (cast alloy) in a vacuum state reached a predetermined temperature (450° C.). The dispersion treatment and high-temperature hydrogen cracking were performed continuously while the material to be treated was kept in the treatment furnace (without being taken out into the atmosphere, etc.).

The inside of the processing furnace was cooled to room temperature while maintaining P _H2 . After replacing the hydrogen in the processing furnace with Ar gas (atmospheric pressure), the cast alloy taken out from the processing furnace was lightly crushed. In this way, a substantially powdery magnet raw material was obtained.

(3-2) Low-temperature hydrogen cracking Low-temperature hydrogen cracking was performed by holding the cast alloy after homogenization in a hydrogen atmosphere (100 kPa x room temperature) for 1 hour.

After replacing the hydrogen in the processing furnace with Ar gas (atmospheric pressure), the cast alloy was taken out of the processing furnace and lightly crushed. In this way, a substantially powdery magnet raw material was obtained.

(4) Classification The magnet raw material was classified by sieving to remove coarse particles. "<α" means that the particles are made of particles that have passed through a test sieve (JIS Z 8801) with a nominal opening α (μm). In this example, crushing (pulverization), classification, transportation between processes, etc. were all performed in an inert atmosphere (Ar) (inside a glove box).

(5) HDDR
The hydrogen pressure (P _H2 ) and temperature (T) in the processing furnace were controlled as shown in FIG. 1B, and the classified magnet raw material (12 g) was subjected to the following hydrogen treatment (HDDR).

First, a disproportionation reaction (forward transformation reaction) was caused in the magnet raw material by a high temperature hydrogenation process (25 kPa x 800°C x 2 hours) (disproportionation process: HD).

Next, a controlled exhaust process was performed for 1.5 hours to maintain a constant hydrogen atmosphere (xkPa×800° C.: x=0 to 4) in the processing furnace while continuously exhausting hydrogen. Thereafter, a forced evacuation process was performed for 0.5 hours to create a vacuum atmosphere (0 kPa x 800°C) in the processing furnace.

The hydrogen pressure (DR pressure) during the controlled exhaust process was set to either 0 kPa, 1 kPa, 2 kPa, 3 kPa, or 4 kPa. P _H2 =0 kPa means that the inside of the processing furnace is in a vacuum atmosphere (1 Pa or less). In this way, a recombination reaction (reverse transformation reaction) was caused in the magnet raw material (recombination step: DR).

After cooling the processing furnace to around room temperature while keeping the inside of the processing furnace in a vacuum state, the HDDR processed material was lightly crushed in an inert atmosphere (Ar) to obtain magnet powder (without diffusion treatment). A part of it was used for the next step of diffusion treatment.

(6) Diffusion treatment A mixed raw material obtained by adding a diffusion raw material to the magnet powder after HDDR was heated (800° C. for 1 hour) in a vacuum atmosphere (diffusion step). An alloy powder (<45 μm) having an atomic ratio of Nd ₅₁ Cu ₁₅ Al ₃₄ was used as the diffusion raw material. The ratio of the diffusion raw material to the entire mixed raw material was 2% by mass.

The diffusion-treated material was taken out from the processing furnace, which was cooled to around room temperature in a vacuum state, and was lightly crushed in the atmosphere to obtain magnet powder (diffusion-treated). This magnet powder has Nd: 13.3 at%, B: 6.3 at%, and Nb: 0.2 at% with respect to the whole (100 at%). When casting alloy A was used, Cu: 0.3 at%, Al: 0.5 at%, when casting alloy B was used, Cu: 0.2 at%, Al: 1.2 at%, casting alloy C was used. When it was, Cu: 0.3 at% and Al: 1.2 at%.

"measurement"
The magnetic properties of the magnet powder were measured using a vibrating sample magnetometer (VSM). The measurement was carried out by filling a capsule with magnetic powder, oriented in a magnetic field (1193 kA/m) in molten paraffin (approximately 80° C.), and then magnetized (3580 kA/m). At this time, the density of each magnet powder was assumed to be 7.5 g/cm ³ .

FIG. 2A shows the relationship between DR pressure and coercive force (iHc) for sample groups (AL0, AH0) that were not subjected to diffusion treatment using cast alloy A. FIG. 2B shows the relationship between DR pressure and iHc for the sample groups (AL1, AH1) that were subjected to diffusion treatment using casting alloy A. FIG. 2A and FIG. 2B are collectively referred to as "FIG. 2."

FIG. 3 shows the relationship between DR pressure and iHc for sample groups (BL0, BH0) that were not subjected to diffusion treatment using casting alloy B.

FIG. 4A shows the relationship between DR pressure and iHc for sample groups (CL0, CH0) that were not subjected to diffusion treatment using cast alloy C. FIG. 4B shows the relationship between DR pressure and iHc for sample groups (CL1, CH1) that were subjected to diffusion treatment using cast alloy C. FIG. 4A and FIG. 4B are collectively referred to as "FIG. 4." FIG. 5 shows the relationship between DR pressure and iHc for the sample group (DL0) that was not subjected to diffusion treatment using casting alloy D.

For reference, the magnetization curves of each magnet powder in the sample group (CH1) at a DR pressure of 1 kPa or 2 kPa are collectively shown in FIG. 6.

"evaluation"
As is clear from FIGS. 2 to 5, when Cu was included in the cast alloy, the magnetic properties changed significantly due to the DR pressure. Specifically, when the DR pressure (P _H2 ) was set to around 2 to 3 kPa (for example, 1.5 to 3.5 kPa), the coercive force (iHc) increased to a peak. This tendency appeared regardless of the hydrogen cracking temperature or the presence or absence of diffusion treatment.

Even when a cast alloy containing Al in addition to Cu was used, as is clear from the comparison between Figures 2 and 4, iHc was improved at its peak by setting the DR pressure to 1.5 to 3.5 kPa. . Further diffusion treatment yielded magnet powder with even higher iHc. This tendency was observed regardless of the hydrogen cracking temperature or the presence or absence of diffusion treatment. In this case, as can be seen from the comparison between FIG. 4A and FIG. 5, the iHc was larger than that of the magnet powder using rare Ga (a coercive force improving element).

From the above, it was found that according to the manufacturing method of the present invention, rare earth magnet powder with high magnetic properties can be obtained without using rare elements.

Claims (6)

a disproportionation step in which a magnet raw material made of a cast alloy containing a rare earth element, a transition element, and B is made 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 cast alloy contains 0.02 to 0.4 at% of Cu based on the whole,
The recombination step includes a controlled exhaust step of heating the magnet raw material after the disproportionation step in a hydrogen atmosphere with a hydrogen pressure of 1.5 to 3.5 kPa. The method for producing rare earth magnet powder according to claim 1, wherein the casting alloy further contains 0.02 to 1.5 at% Al. The method for producing rare earth magnet powder according to claim 1 or 2, wherein the cast alloy further contains a total of 0.05 to 0.7 at% of Nb and/or Zr. 2. The method for producing rare earth magnet powder according to claim 1, wherein the disproportionation step is performed on a magnet raw material obtained by exposing the cast alloy to a hydrogen atmosphere at a temperature below the temperature at which the disproportionation reaction occurs. 5. 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. 6. The method for producing rare earth magnet powder according to claim 5, wherein the diffusion raw material is made of an alloy or compound containing at least Nd and Cu.

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