Method for producing rare-earth magnet powder

Abstract

Provided is a method for producing a rare-earth magnet powder having high magnetic properties. The present invention is a method for producing a rare-earth magnet powder, the method comprising: a disproportionation step for causing hydrogen to be absorbed into a magnet raw material comprising a cast alloy containing a rare earth element, a transition element, and B to cause a disproportionation reaction; and a recombination step for causing a recombination reaction by desorbing hydrogen from the magnet raw material after the disproportionation step. The cast alloy contains 0.02-0.4 at% of Cu and preferably further contains 0.02-1.5 at% of Al. The recombination step is preferably carried out through a controlled exhaust step for heating the magnet raw material after the disproportionation step in a hydrogen atmosphere having a hydrogen pressure of 1.5-3.5 kPa. Further improvement of the magnetic properties (especially coercive force) can be attained by performing a diffusion step for 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 the recombination step.

Description

Manufacturing method for rare earth magnet powder

[0001] The present invention relates to a method for producing rare earth magnet powder.

[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 need to improve the magnetic properties of rare earth magnetic powder. Because the magnetic properties of rare earth magnetic powder are significantly affected by the hydrogen treatment conditions used in the manufacturing process, various proposals have been made regarding hydrogen treatment, and relevant disclosures can be found in the following patent documents:

[0003] Hydrogenation (HDDR) mainly consists of a disproportionation reaction due to hydrogen absorption (Hydrogenation-Disproportionation, or "HD") and a recombination reaction due to desorption (Desorption-Recombination, or "DR"). In this specification, unless otherwise specified, the term "HDDR" is used to refer to improved versions such as dynamic-HDDR (d-HDDR).

[0004] JP 10-317003, WO 2011 / 070847, WO 2013 / 035628, JP 2014-177660, WO 2020 / 017529

[0005] Patent Document 1 describes that a Cu-containing NdFeB-based alloy ingot is subjected to a hydrogen absorption treatment (HD) and a dehydrogenation treatment (DR). According to Patent Document 1, a rare earth alloy powder with high magnetic properties (particularly coercive force Hcj) is obtained by dehydrogenation treatment under a hydrogen partial pressure of about 1 kPa (see

[0035] and Table 2 in Patent Document 1).

[0006] Patent Documents 2 to 5 do not describe hydrogen treatment of Cu-containing cast alloys (master alloys, raw alloys, alloy ingots, etc.). When dehydrogenation treatment (DR) is performed on Cu-free cast alloys, Patent Documents 2 and 3 describe a vacuum degree in the furnace of 3.2 kPa, while Patent Documents 4 and 5 describe a hydrogen partial pressure of 1 to 5 kPa. However, none of these patent documents provide a detailed study of the hydrogen partial pressure during dehydrogenation, and there is no specific description or suggestion regarding this point.

[0007] The present invention has been 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.

[0008] Through extensive research, the inventors have newly discovered that when hydrogen treatment (HDDR) is performed on a Cu-containing cast alloy to obtain rare earth magnet powder, there is a unique correlation between the hydrogen pressure (partial pressure) during the recombination reaction (dehydrogenation) and the magnetic properties of the rare earth magnet powder. Based on this finding, the inventors have completed 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 disproportionation step in which a magnet raw material made of a cast alloy containing rare earth elements, transition elements, and B is allowed to absorb hydrogen to cause a disproportionation reaction; and a recombination step in which hydrogen is removed from the magnet raw material after the disproportionation step to cause a recombination reaction, the cast alloy containing 0.02 to 0.4 at% Cu based on the total amount of the cast alloy, and the recombination step comprises a controlled evacuation step in which the magnet raw material after the disproportionation step is heated in a hydrogen atmosphere at a hydrogen pressure of 1.5 to 3.5 kPa.

[0010] (2) The manufacturing method of the present invention produces rare earth magnet powder with high magnetic properties. The reason for this is not entirely clear, but it is currently thought to be as follows. In the manufacturing method of the present invention, a magnet raw material made of an R-TM-B based cast alloy (R: rare earth element, TM: transition element) containing Cu is subjected to a controlled evacuation process in which the hydrogen pressure (partial pressure) is kept within a specific range. This controlled evacuation process can prevent the crystal nuclei that will become the main phase from growing abnormally locally during the recombination process, resulting in non-uniform coarsening of crystal grains, or the coarsening of homogeneous crystal grains. This allows the main phase (R ２TM １４ It is believed that rare earth magnet particles with high magnetic properties, consisting of a metal structure in which crystal grains (B) are finely and uniformly distributed, were obtained.

[0011] <Rare Earth Magnetic Powder, Compound, Bonded Magnet> The present invention can be understood as a rare earth magnetic powder, a bonded magnet in which the rare earth magnetic powder is bound with a resin, and a compound used to manufacture the bonded magnet. The compound is made by first adhering a resin binder to the surface of the powder particles. The powder used in the bonded magnet or compound may also be a composite powder containing a powder other than the rare earth magnetic powder of the present invention.

[0012] Others (1) The cast alloy and magnet raw materials (including crushed raw materials) may be in any form or state, such as lumps, particles, or powder, and the particle size may be adjusted by classification or the like.

[0013] Regardless of particle shape, the size (particle size) of a particle is appropriately referred to as "particle diameter." In this specification, particle size is indicated by particle size. For example, particles with a particle size (d) of less than α (μm) (d<α) mean particles that pass through a sieve with a nominal mesh size α.

[0014] (2) The rare earth magnet powder may be either isotropic or anisotropic. Anisotropic magnet powder consists of magnet particles whose magnetic flux density (Br) in one direction (the easy axis of magnetization, c-axis direction) is greater than the magnetic flux density in other directions. Isotropy and anisotropy can be distinguished by the degree of texture (DOT), where a DOT value of 0 indicates isotropy, and a DOT value greater than 0 indicates anisotropy. DOT is calculated from the magnetic flux density Br( / / ) or Br(⊥) when a magnetic field parallel ( / / ) or perpendicular (⊥) to the c-axis direction is applied, as follows: DOT = [Br( / / ) - Br(⊥)] / Br( / / ).

[0015] (3) Rare earth elements (R) include Nd, Pr, Ce, La, etc., as well as Y, Sm, Tb, Dy, etc. 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 portion of the Nd may be substituted with Pr. A portion of the Fe may be substituted with Co, for example, at a substitution amount of 0.01 to 20.0 at%, or even 0.5 to 5.4 at%, relative to the entire cast alloy. A portion of the B may be substituted with C, for example, at a substitution amount of 0.05 to 1 at%, or even 0.1 to 0.6 at% or less, relative to the entire cast alloy.

[0016] In addition to (unavoidable) impurities, the cast alloy or rare earth magnet powder may contain modifier elements effective for improving properties, such as Al, Ti, V, Cr, Ni, Zn, Ga, Zr, Nb, Mo, Sn, Hf, Ta, W, Dy, Tb, and Co, which are effective for improving coercivity.

[0017] (4) 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." Furthermore, "x to y kPa" means x kPa to y kPa, and the same applies to other unit systems.

[0018] The following shows an example of a manufacturing process for rare earth magnet powder. The following shows an example of a hydrogen atmosphere setting pattern for HDDR. The magnetic properties of rare earth magnet powder (cast alloy A / no diffusion treatment) and DR pressure (P Ｈ２ The relationship between the magnetic properties of rare earth magnet powder (cast alloy A / diffusion treated) and DR pressure (P Ｈ２ The relationship between the magnetic properties of rare earth magnet powder (cast alloy B / no diffusion treatment) and DR pressure (P Ｈ２ ) shows the relationship between the magnetic properties of rare earth magnet powder (cast alloy C / no diffusion treatment) and DR pressure (P Ｈ２ ) shows the relationship between the magnetic properties of rare earth magnet powder (cast alloy C / diffusion treated) and DR pressure (P Ｈ２ The relationship between the magnetic properties of rare earth magnet powder (cast alloy D / no diffusion treatment) and DR pressure (P Ｈ２3 shows the magnetic curve for rare earth magnet powder (cast alloy C / diffusion treated).

[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 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.

[0020] <Rare Earth Magnet Powder> (1) Rare earth magnet powder (simply referred to as "magnet powder") is made of magnet particles, and the magnet particles are fine R, which is a tetragonal compound. ２ TM １４ B １ The magnet consists of a tetragonal crystal (main phase) and a grain boundary phase surrounding the crystal grains. The stoichiometric composition of the tetragonal compound constituting the main phase is 11.8 at% R, 5.9 at% B, and the remainder TM. Considering the grain boundary phase, the rare earth elements (R) are contained in an amount of, for example, 12 to 18 at%, 12.5 to 16.5 at%, or even 13 to 15 at%, and B is contained in an amount of 5.5 to 8 at%, or even 6 to 7 at%, relative to the entire magnet particle (100 at%). The remainder other than R and B is mainly transition metal elements (TM), but may also contain typical metal elements (e.g., Al), typical nonmetal elements (e.g., C, O), impurities, etc.

[0021] (2) R is, for example, Nd, Pr, Dy, Tb, etc. The magnet particles may contain at least one of Al, Si, Ti, V, Cr, Ni, Zn, Ga, Zr, Nb, Mo, Mn, Sn, Hf, Ta, W, Dy, Tb, Co, etc. in addition to Cu. With respect to the entire magnet particle, for example, Cu may be contained at 0.02 to 2 at%, 0.05 to 1 at%, or even 0.1 to 0.5 at%, Al at 0.02 to 3.5 at%, 0.2 to 2.5 at%, or even 0.4 to 1.5 at%, Nb or Zr at 0.05 to 0.7 at%, 0.1 to 0.5 at%, or even 0.15 to 0.3 at%, and Ga at 0.4 at% or less (0.01 to 0.4 at%), 0.35 at% or less, or even 0.25 at% or less.

[0022] <<Production Method>> (1) Cast Alloy The cast 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 solidifying the molten alloy. Rapidly solidified alloys can be obtained, for example, by strip casting (SC).

[0023] The composition of the cast alloy is adjusted taking into consideration not only the composition of the magnet powder, but also the composition and amount of the diffusion raw material if a diffusion process is performed. The cast alloy contains, for example, 11.5 to 15 at%, 12 to 14 at%, or even 12.2 to 13.5 at% of R and 5.5 to 8 at%, or even 6 to 7 at% of B, assuming the entire alloy to be 100 at%. The remainder of the cast alloy is a transition element (e.g., Fe) or a modifier element (e.g., Cu, Al, Nb, Zr, etc.).

[0024] The casting alloy according to the present invention contains at least Cu. The Cu content is, for example, 0.02 to 0.4 at%, 0.03 to 0.25 at%, 0.05 to 0.2 at%, or even 0.07 to 0.15 at%, based on the total amount of the casting alloy. If the Cu content is too low, the coercivity will not improve significantly even if the hydrogen pressure is adjusted in the controlled evacuation process. If the Cu content is too high, the coercivity of the magnet powder may decrease.

[0025] The casting alloy may contain Al in addition to Cu. The Al content is, for example, 0.02 to 1.5 at%, 0.2 to 1.2 at%, or even 0.5 to 0.9 at% of the entire casting alloy. If the Al content is too low, the effect of improving the coercive force will be poor, and if the Al content is too high, it will cause a decrease in the residual magnetic flux density.

[0026] The cast alloy may contain at least one of Nb and Zr. The total content of Nb and Zr relative to the entire cast alloy is, for example, 0.05 to 0.7 at%, 0.1 to 0.5 at%, or even 0.15 to 0.3 at%. If either element is too little, the effect of improving magnetic anisotropy will be poor, and if it is too much, the remanence of the magnet powder may decrease.

[0027] (2) Homogenization Treatment Homogenization treatment (solution treatment) is intended to homogenize the metal structure of the cast alloy and eliminate the segregation of the soft magnetic α-Fe phase.

[0028] The homogenization treatment is performed, for example, by heating the cast alloy at 1000 to 1200°C, or 1050 to 1150°C. The treatment time is, for example, 3 to 50 hours, or 10 to 40 hours. The heating atmosphere is, for example, an inert atmosphere (an inert gas (Ar, etc.) atmosphere, a vacuum atmosphere, etc.).

[0029] (3) Dispersion Treatment Dispersion treatment promotes the uniform formation of R-rich (e.g., Nd-rich) grain boundary phases. When the cast alloy after dispersion treatment is subjected to high-temperature hydrogen crushing treatment, fracture (separation) occurs preferentially at the grain boundaries, and the occurrence of cracks within the main phase grains can be suppressed.

[0030] The dispersion treatment is carried out by heating at a temperature higher than that of high-temperature hydrocracking (and lower than that of homogenization treatment), for example, 650 to 900°C, 650 to 800°C, or 680 to 750°C. The treatment time is, for example, 10 minutes to 10 hours, or 0.5 to 3 hours. The heating atmosphere is, for example, an inert atmosphere.

[0031] (4) Hydrogen cracking (a process) may be performed in which the cast alloy before HDDR (before the disproportionation process) is exposed to a hydrogen atmosphere in advance. In other words, the disproportionation process may be performed on a magnet raw material obtained by exposing the cast alloy to a hydrogen atmosphere at a temperature lower than the temperature at which the disproportionation reaction occurs.

[0032] The hydrocracking treatment may be low-temperature hydrocracking carried out in a low temperature range (e.g., room temperature to 300°C, or room temperature to 100°C), or high-temperature hydrocracking carried out in a high temperature range (e.g., 350 to 585°C, 400 to 575°C, or 425 to 550°C).

[0033] The hydrogen partial pressure is, for example, 1 kPa to 250 kPa, or further 5 kPa to 150 kPa. The treatment time (the time elapsed after the atmospheric temperature reaches the target temperature) is, for example, 0.1 to 10 hours, or further 0.5 to 5 hours. In high-temperature hydrogen cracking, it is advisable to introduce hydrogen into the treatment furnace after the cast alloy (atmosphere) reaches a predetermined temperature.

[0034] Incidentally, when high-temperature hydrogen cracking (process / treatment) is performed, hydrogen penetrates mainly into the grain boundary phase (R-rich phase / Nd-rich phase) with almost no penetration into the crystal grains, and cracks preferentially form between the crystal grains due to the volume expansion of the grain boundary phase. As a result, the cast alloy is separated between the crystal grains, and a magnet raw material (crushed raw material) consisting of main phase grains with few cracks or breaks is obtained. The effects and mechanisms of such hydrogen cracking are described in detail in WO 2020 / 017529, the entire contents of which are incorporated herein by reference.

[0035] (5) Classification The cast alloy that has absorbed hydrogen through hydrogen cracking may disintegrate on its own or may be lightly crushed into particles. The cast alloy may be further crushed or pulverized into powder, or the particle size may be adjusted by classification. It is recommended that HDDR be performed on the magnet raw material from which at least coarse particles have been removed.

[0036] (6) HDDR HDDR allows for 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 2 μm). HDDR is roughly divided into a disproportionation process (HD) and a recombination process (DR).

[0037] In the disproportionation process, the magnet raw material placed in a treatment furnace is exposed to a predetermined hydrogen atmosphere. The magnet raw material absorbs hydrogen in this process, causing a disproportionation reaction (forward transformation reaction) to form a three-phase decomposed structure (αTM phase, RH ２ Ai, TM ２ Phase B).

[0038] The disproportionation step is performed, for example, at a hydrogen partial pressure of 10 to 150 kPa, or even 15 to 50 kPa, an atmospheric temperature of 600 to 900° C., or even 750 to 860° C., and a treatment time of 1 to 5 hours. Note that the hydrogen atmosphere referred to in this specification may also be a mixed gas atmosphere of hydrogen and an inert gas.

[0039] During the disproportionation step, the hydrogen partial pressure or the atmospheric temperature does not have to be constant throughout. For example, at the end of the step when the reaction rate is decreasing, at least one of the pressure (hydrogen partial pressure) and the temperature may be increased to adjust the reaction rate and promote three-phase decomposition (structure stabilization step).

[0040] The recombination process removes hydrogen from the magnet raw material after the disproportionation process. This process causes a recombination reaction (reverse transformation reaction) in the dehydrogenated magnet raw material (three-phase decomposed structure), resulting in RH ２ As hydrogen is removed from the phase, TM ２ Fine R where the crystal orientation of B phase is transferred ２ TM １４ B １ Hydride of type crystal (RTMBH Ｘ )

[0041] The recombination step (controlled evacuation step) is performed, for example, at a hydrogen partial pressure of 1.5 to 3.5 kPa, 1.8 to 3.2 kPa, or even 2 to 3 kPa, an atmospheric temperature of 600 to 900°C or even 750 to 860°C, and a treatment time of 0.5 to 5 hours or even 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.

[0042] After the recombination step (controlled evacuation step), the inside of the processing furnace is evacuated to a vacuum atmosphere (1 Pa or less, or even 0.1 Pa or less), whereby hydrogen remaining in the magnet raw material is removed and dehydrogenation is completed (forced evacuation step). This step is performed, for example, at an atmospheric temperature of 600 to 900°C, or even 750 to 860°C, for a processing time of 0.1 to 5 hours, or even 0.3 to 1 hour. Cooling after the forced evacuation step is preferably rapid cooling to suppress grain growth.

[0043] 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 only the hydrogen partial pressure may be changed. The controlled evacuation step and the forced evacuation step may be performed continuously or discontinuously. For example, the controlled evacuation step may be followed by a cooling step to cool the magnet raw material, and the forced evacuation step may be performed batchwise.

[0044] (7) Diffusion Treatment Diffusion treatment may be performed after HDDR. The diffusion treatment (diffusion step) is performed by, for example, heating a mixed raw material obtained by adding a diffusion raw material to the magnet raw material after HDDR (recombination step). ２ TM １４ B １A non-magnetic phase is formed on the surface or grain boundary of the type crystal, which can improve the coercive force of the magnet particles. Note that the diffusion treatment is preferably carried out in an inert atmosphere (an inert gas atmosphere, a vacuum atmosphere, etc.).

[0045] Examples of diffusion raw materials include alloys and compounds of light rare earth elements, heavy rare earth elements (Dy, Tb, etc.) or alloys and compounds (e.g., fluorides) of these elements, etc. If a light rare earth element (e.g., Nd)-Cu-(Al) alloy or compound is used, the use of rare heavy rare earth elements can be avoided.

[0046] <<Applications>> Rare earth magnet powder can be used for a variety of applications. A typical example is a bonded magnet. A bonded magnet is primarily made of rare earth magnet powder and a binder resin. The binder resin can be either a thermosetting resin or a thermoplastic resin. Bonded magnets can also be compression molded or injection molded. Bonded magnets using rare earth anisotropic magnet powder are preferably molded in an aligning magnetic field.

[0047] Rare earth magnet powders (samples) were produced using different casting alloy compositions and manufacturing conditions, and their magnetic properties were evaluated. The present invention will be described in detail based on these examples.

[0048] <<Sample Production>> Rare earth magnet powders belonging to the sample group shown in Table 1 were produced according to the steps shown in Figures 1A and 1B (collectively referred to as "Figure 1"). Specifically, the steps are as follows.

[0049] (1) Casting Several types of cast alloys A to D shown in Table 1 were prepared by arc melting. The component compositions shown in Table 1 are blend compositions relative to the entire cast alloy, and are shown as atomic ratios relative to the entire alloy (remainder: Fe).

[0050] (2) Homogenization Treatment After evacuation, an inert atmosphere (P Ａｒ Each cast alloy was heated at 1140°C for 20 hours in a treatment furnace (pressure: 35 kPa).

[0051] Unless otherwise specified, the atmosphere, temperature, and pressure referred to in this example are as follows. The atmosphere is the atmosphere inside the treatment furnace containing the workpiece (cast alloy, magnet raw material). The temperature (T) was measured using a thermocouple in contact with the workpiece (cast alloy, magnet raw material). The pressure (P) was measured using a pressure gauge, measuring the internal pressure of the treatment furnace (near the workpiece).

[0052] The atmosphere (gas) was changed after the processing furnace was evacuated. The vacuum atmosphere (Vac) was set to 10 Pa or less. The hydrogen atmosphere was set by introducing only hydrogen into the processing furnace after the evacuation (10 Pa or less), and the internal pressure of the processing furnace was set to the hydrogen pressure (P Ｈ２ ) (same below).

[0053] (3) Hydrogen Crushing Treatment The cast alloy after the homogenization treatment was subjected to either high-temperature hydrogen crushing or low-temperature hydrogen crushing, which will be described later.

[0054] (3-1) High-temperature hydrogen crushing Before high-temperature hydrogen crushing, the homogenized cast alloy was gradually heated to 700°C in a vacuum atmosphere and held there for 1 hour (dispersion treatment). The dispersed cast alloy was then held in a hydrogen atmosphere (100 kPa x 450°C) for 1 hour (high-temperature hydrogen crushing). Hydrogen was introduced into the treatment furnace after the dispersion treatment, after the temperature inside the vacuum-state treatment furnace (cast alloy) reached the predetermined temperature (450°C). The dispersion treatment and high-temperature hydrogen crushing were carried out continuously while the material to be treated was still inside the treatment furnace (without being taken out into the atmosphere, etc.).

[0055] P Ｈ２ The inside of the treatment furnace was cooled to room temperature while maintaining the above temperature. The hydrogen in the treatment furnace was replaced with Ar gas (atmospheric pressure), and the cast alloy was then removed from the treatment furnace and lightly crushed. In this way, a magnet raw material in a substantially powder form was obtained.

[0056] (3-2) Low-Temperature Hydrogen Crushing Low-temperature hydrogen crushing was carried out by holding the cast alloy after the homogenization treatment in a hydrogen atmosphere (100 kPa x room temperature) for 1 hour.

[0057] After the hydrogen in the treatment furnace was replaced with Ar gas (atmospheric pressure), the cast alloy was taken out of the treatment furnace and lightly crushed to obtain a substantially powdery magnet raw material.

[0058] (4) Classification The magnet raw material was classified by sieving to remove coarse particles. "<α" means that the raw material consisted of particles that passed through a test sieve (JIS Z 8801) with a nominal mesh size of α (μm). In this example, crushing (pulverization), classification, and transportation between processes were all carried out in an inert atmosphere (Ar) (in a glove box).

[0059] (5) Hydrogen pressure in the HDDR processing furnace (P Ｈ２ The pressure (V) and temperature (T) were controlled as shown in FIG. 1B, and the classified magnet raw material (12 g) was subjected to the following hydrogen treatment (HDDR).

[0060] First, a high-temperature hydrogenation step (25 kPa x 800°C x 2 hours) was performed to cause a disproportionation reaction (forward transformation reaction) in the magnet raw material (disproportionation step: HD).

[0061] Next, a controlled evacuation step was carried out for 1.5 hours, in which hydrogen was continuously evacuated while the inside of the processing furnace was kept at a constant hydrogen atmosphere (x kPa × 800°C: x = 0 to 4). Thereafter, a forced evacuation step was carried out for 0.5 hours, in which the inside of the processing furnace was kept at a vacuum atmosphere (0 kPa × 800°C).

[0062] The hydrogen pressure during the controlled evacuation step (DR pressure) was set to 0 kPa, 1 kPa, 2 kPa, 3 kPa, or 4 kPa. Ｈ２ = 0 kPa means that the inside of the treatment furnace was a vacuum atmosphere (1 Pa or less). In this way, a recombination reaction (reverse transformation reaction) was caused in the magnet raw materials (recombination step: DR).

[0063] After the treatment furnace was cooled to near room temperature while the inside of the treatment furnace was kept in a vacuum state, the HDDR-treated material was lightly crushed in an inert atmosphere (Ar) to obtain magnet powder (without diffusion treatment), a part of which was subjected to the diffusion treatment in the next step.

[0064] (6) Diffusion Treatment The mixed raw material, which was made by adding the diffusion raw material to the magnet powder after HDDR, was 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 %.

[0065] The diffusion-treated material was removed from the treatment furnace, which had been cooled to near room temperature while still in a vacuum state, and lightly crushed in the air to obtain magnetic powder (diffusion-treated). This magnetic powder had a total composition (100 at%) of 13.3 at% Nd, 6.3 at% B, and 0.2 at% Nb. When cast alloy A was used, the composition was 0.3 at% Cu and 0.5 at% Al. When cast alloy B was used, the composition was 0.2 at% Cu and 1.2 at% Al. When cast alloy C was used, the composition was 0.3 at% Cu and 1.2 at% Al.

[0066] <<Measurement>> The magnetic properties of the magnet powders were measured using a vibrating sample magnetometer (VSM). The measurements were carried out by filling the magnet powders into capsules, orienting them in a magnetic field (1193 kA / m) in molten paraffin (approximately 80°C), and then magnetizing them (3580 kA / m). The density of each magnet powder was 7.5 g / cm. ３ It was assumed that:

[0067] The relationship between DR pressure and coercive force (iHc) for the sample group (AL0, AH0) that was not subjected to diffusion treatment using cast alloy A is shown in Figure 2A. The relationship between DR pressure and iHc for the sample group (AL1, AH1) that was subjected to diffusion treatment using cast alloy A is shown in Figure 2B. Figures 2A and 2B are collectively referred to as "Figure 2."

[0068] The relationship between the DR pressure and iHc for the sample group (BL0, BH0) that was made of cast alloy B and was not subjected to diffusion treatment is shown in FIG.

[0069] The relationship between DR pressure and iHc for the sample group (CL0, CH0) that was not diffused using cast alloy C is shown in Figure 4A. The relationship between DR pressure and iHc for the sample group (CL1, CH1) that was diffused using cast alloy C is shown in Figure 4B. Figures 4A and 4B are collectively referred to as "Figure 4." The relationship between DR pressure and iHc for the sample group (DL0) that was not diffused using cast alloy D is shown in Figure 5.

[0070] For reference, the magnetization curves of the magnetic powders in sample group (CH1) when the DR pressure was 1 kPa or 2 kPa are shown together in FIG.

[0071] <Evaluation> As is clear from Figures 2 to 5, when the casting alloy contained Cu, the magnetic properties changed significantly depending on the DR pressure. Ｈ２ When the pressure 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 was observed regardless of the hydrogen cracking temperature or whether or not a diffusion treatment was performed.

[0072] Even when using a casting alloy containing Al in addition to Cu, as is clear from a comparison of Figures 2 and 4, iHc peaked when the DR pressure was set to 1.5 to 3.5 kPa. Furthermore, when a diffusion treatment was performed, magnetic powder with even higher iHc was obtained. This tendency was observed regardless of the hydrogen crushing temperature or whether or not a diffusion treatment was performed. In this case, as can be seen from a comparison of Figures 4A and 5, iHc was higher than that of magnetic powder using rare Ga (a coercivity-enhancing element).

[0073] From the above, it has been found that the manufacturing method of the present invention can produce rare earth magnet powder with high magnetic properties without the need to use rare elements.

[0074]

Claims

1. A method for manufacturing rare earth magnet powder, comprising: a disproportionation step of causing a disproportionation reaction by absorbing hydrogen into a magnet raw material made of a cast alloy containing a rare earth element, a transition element, and B; and a recombination step of dehydrogenating the magnet raw material after the disproportionation step to cause a recombination reaction, wherein the cast alloy contains 0.02 to 0.4 at% of Cu with respect to the whole, and 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.

2. The method for manufacturing rare earth magnet powder according to claim 1, wherein the cast alloy further contains 0.02 to 1.5 at% of Al.

3. The method for manufacturing 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.

4. The method for manufacturing 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 lower than the temperature at which the disproportionation reaction occurs.

5. The method for manufacturing rare earth magnet powder according to claim 1 or 4, 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 manufacturing rare earth magnet powder according to claim 5, wherein the diffusion raw material is composed of an alloy or a compound containing at least Nd and Cu.

Images