Method for producing r-t-b sintered magnet

Abstract

A method for producing an R-T-B sintered magnet includes: a step of preparing an additive alloy powder containing 33-69 mass% R1, 0.2-0.8 mass% B, 0.8-3.0 mass% Cu, 1.8-10 mass% Ga, and 15-60 mass% T; a step of preparing a main alloy powder containing 28.5-33.0 mass% R, 0.80-1.0 mass% B, 0.1-0.4 mass% Ga, and 64-70 mass% T; a step of preparing a mixed alloy powder; a step of supplying the mixed alloy powder to a jet mill device in which an inert gas is filled in a pulverizing chamber to pulverize the mixed alloy powder and obtain a fine powder; and a step of producing a sintered body of the fine powder. The Pr content of the additive alloy powder is greater than the Pr content of the main alloy powder, the inert gas is humidified, the oxygen content in the sintered magnet is 1000 ppm or more and 3000 ppm or less, and [T] / 55.85 > 14 x [B] / 10.8 is satisfied.

Description

Technical Field

[0001] This invention relates to a method for manufacturing R-T-B sintered magnets. Background Technology

[0002] R-T-B sintered magnets (where R is at least one of rare earth elements and must contain Nd, and T is at least one of transition metal elements and must contain Fe) are known to be the highest-performing permanent magnets. They are used in a wide variety of applications, such as voice coil motors (VCMs) for hard disk drives, motors for electric vehicles (EVs, HVs, PHVs), motors for industrial equipment, and various motors or household appliances.

[0003] R-T-B series sintered magnets are mainly composed of R2T 14 Compound B consists of a main phase and grain boundary phases (two-grain boundaries and / or multi-point boundaries) located in the grain boundary portion of the main phase. R2T is the main phase. 14 B compounds are strongly magnetic materials with high saturation magnetization and anisotropic magnetic fields, forming the basis for the characteristics of R-T-B sintered magnets.

[0004] R-T-B series sintered magnets can be manufactured, for example, through a process of preparing alloy powder, pressing the alloy powder into a powder mold to form a powder body, and sintering the powder mold. Alternatively, the alloy powder can be produced, for example, by the following method: First, an alloy is produced from molten metals of various raw materials using methods such as molding or strip casting. The resulting alloy is then subjected to a pulverizing process to obtain alloy powder with a specified particle size distribution. This pulverizing process typically includes a coarse pulverizing step and a fine pulverizing step; the former is performed, for example, using hydrogen embrittlement, and the latter, for example, using an air jet mill.

[0005] The coercivity H of such R-T-B sintered magnets cJ (Hereinafter sometimes abbreviated as "H") cJ The temperature decreases at high temperatures, leading to irreversible thermal demagnetization. Therefore, especially in applications like electric motors for electric vehicles, it is crucial to maintain high H values ​​even at high temperatures. cJ It needs to have a higher H at room temperature cJ .

[0006] In existing technologies, in order to improve H cJ A large amount of heavy rare earth elements (mainly Dy) were added to the R-T-B system sintered magnet, but a residual magnetic flux density B exists. r (Hereinafter sometimes abbreviated as "B") r The problem of B's ​​degradation has been addressed in recent years. Therefore, methods have been employed to diffuse heavy rare earth elements from the surface of R-T-B sintered magnets inwards, enriching these elements in the outer shell of the main phase grains, thereby suppressing the degradation of B.r The reduction and obtaining high H cJ The method.

[0007] However, heavy rare earth elements such as Dy are expensive and their prices fluctuate. Therefore, it is necessary to minimize the amount of heavy rare earth elements such as Dy used to improve the H of R-T-B sintered magnets. cJ The technology.

[0008] Patent document 1 describes a method that reduces the amount of boron (B) compared to conventional R-T-B alloys and contains one or more metallic elements (M) selected from Al, Ga, and Cu to form R2T alloys. 17 Phase, fully ensure that the R2T 17 The transition metal-rich phase (R6T) is generated from the phase as a raw material. 13 By adjusting the volume ratio of M), it is possible to obtain R-T-B rare earth sintered magnets with suppressed Dy content and high coercivity.

[0009] In addition, H is improved in ways other than those described in Patent Document 1. cJ High-performance enhancement methods include, for example, refining the microstructure and reducing oxygen content. In addition to high performance, R-T-B sintered magnets also require low cost. Methods for reducing cost include, for example, improving grinding efficiency.

[0010] Patent Document 2 discloses a method for improving grinding efficiency by using a humidified, inert gas stream with a dew point of -20°C to 0°C for jet milling. A similar method is described in Patent Document 3.

[0011] Existing technical documents

[0012] Patent documents

[0013] Patent Document 1: International Publication No. 2013 / 008756

[0014] Patent Document 2: Japanese Patent Application Publication No. 8-148317

[0015] Patent Document 3: Japanese Patent Application Publication No. 6-140220 Summary of the Invention

[0016] In the manufacture of R-T-B sintered magnets with reduced oxygen content, for example, oxygen content below 3000 ppm, high-purity nitrogen is used as an inert gas to prevent oxidation of powder particles during the pulverization process.

[0017] According to the inventors' research, it has been found that when using inert gases such as high-purity nitrogen for jet milling, it is sometimes impossible to achieve the high performance envisioned in a low-oxygen environment. Furthermore, when attempting to achieve high performance by refining the powder, refining sacrifices grinding efficiency. Regarding grinding efficiency, methods disclosed in Patent Documents 2 and 3 exist, but the configurations disclosed in Patent Documents 2 and 3 are designed to suppress reactivity, achieving high oxygen content exceeding 3000 ppm, which is not applicable when achieving high performance through low oxidation. The embodiments of the present invention provide a method for manufacturing R-T-B series magnets that, even by reducing the particle size of the fine powder, can suppress the deterioration of grinding efficiency during jet milling and reduce the content of heavy rare earth elements, obtaining high B... r and high H cJ .

[0018] In a non-limiting exemplary embodiment, the method for manufacturing an R-T-B sintered magnet of the present invention is a method for manufacturing an R-T-B sintered magnet (R is at least one of rare earth elements and must contain Nd, T is Fe or Fe and Co), comprising:

[0019] The process of preparing to add alloy powder, wherein the alloy powder contains R1 (R1 is at least one of the rare earth elements, and more than 50% by mass of all R1 is Pr) 33-69% by mass, B: 0.2-0.8% by mass, Cu: 0.8-3.0% by mass, Ga: 1.8-10% by mass, and T: 15-60% by mass.

[0020] The process of preparing the main alloy powder, which contains R: 28.5-33.0% by mass, B: 0.80-1.0% by mass, Ga: 0.1-0.4% by mass, and T: 64-70% by mass;

[0021] The process of preparing mixed alloy powder, wherein the mixed alloy powder contains 1 to 16% by mass of the above-mentioned additive alloy powder and 84 to 99% by mass of the above-mentioned main alloy powder;

[0022] The process involves feeding the aforementioned mixed alloy powder into a jet mill filled with an inert gas into the grinding chamber, and grinding the mixed alloy powder to obtain micro-powder with an average particle size of 2.0 μm to 4.5 μm; and

[0023] The process for producing the sintered body of the above-mentioned micro-powder,

[0024] The Pr content of the above-mentioned added alloy powder is greater than the Pr content of the above-mentioned main alloy powder. The above-mentioned inert gas is humidified. The oxygen content of the above-mentioned R-T-B system sintered magnet is 1000ppm to 3000ppm. It contains R: 28.5% to 33.0% by mass, B: 0.85% to 0.91% by mass, Cu: 0.05% to 0.50% by mass, Ga: 0.3% to 0.7% by mass and T: 63% to 70% by mass (T is Fe or Fe and Co). When the content of T (by mass) is set as [T] and the content of B (by mass) is set as [B], [T] / 55.85 > 14 × [B] / 10.8.

[0025] In one embodiment, the R content of the R-T-B sintered magnet is 31% by mass or less.

[0026] In one embodiment, the aforementioned inert gas is nitrogen.

[0027] In one embodiment, the process of making the sintered body of the above-mentioned micro powder includes: the step of making a powder molded body from the above-mentioned micro powder by wet pressing in a magnetic field or pressing in a magnetic field in an inert gas atmosphere, and the step of sintering the above-mentioned powder molded body.

[0028] In one embodiment, the average particle size of the micro powder obtained in the process of obtaining the micro powder is 2.0 μm or more and 3.5 μm or less.

[0029] Invention Effects

[0030] According to embodiments of the present invention, it is possible to provide a method that can suppress the deterioration of grinding efficiency during jet milling even when reducing the particle size of the micro powder, and to reduce the content of heavy rare earth elements and obtain high B content. r and high H cJ The manufacturing method of R-T-B system magnets. Attached Figure Description

[0031] Figure 1 This is a schematic diagram illustrating an example of the configuration of the R-T-B system sintered magnetic alloy crushing system 1000 of this embodiment.

[0032] Symbol Explanation

[0033] 100: Jet mill device; 200: Cyclone collection device; 300: Bag filter device. Detailed Implementation

[0034] The inventors of this invention conducted research and found that in manufacturing R-T-B sintered magnets with reduced oxygen content, once the powder particles become smaller during the pulverization process, not only does the pulverization efficiency deteriorate, but the powder particles also become nitrided by inert gases (especially when dry nitrogen is used as the inert gas) during the pulverization process. Even if the pulverized particles are reduced, the expected improvement in magnetic properties cannot be achieved. The inventors of this invention further conducted research and found that by using a humidified inert gas, the deterioration of powder particles caused by inert gases can be reduced. This can be attributed to the formation of an oxide film on the surface of the powder particles, preventing inert gases (especially nitrogen) from being introduced into the powder particles, thereby suppressing the deterioration (nitriding) of powder particles caused by inert gases. In the prior art, it is known that when powder particles are reduced in size during the pulverization process, the pulverization efficiency deteriorates, and these deteriorations can be improved by using a humidified inert gas flow (e.g., Patent Document 2 or Patent Document 3). However, considering that powder particles are oxidized and their magnetic properties decrease when pulverized using a humidified inert gas stream, and that R-T-B sintered magnets with reduced oxygen content are manufactured to improve magnetic properties, it is not considered to actively use a humidified inert gas stream for pulverization in order to reduce the particle size (for example, the micropowder in Patent Document 2 has a high oxygen content of 4500 ppm and 4900 ppm, while Patent Document 3 does not disclose the oxygen content). However, based on the above-mentioned insight of reducing the degradation of powder particles caused by inert gases by using humidified inert gases, the inventors of the present invention have repeatedly conducted research and unexpectedly discovered that in the final R-T-B sintered magnets, when the powder particles are humidified and pulverized to reduce the oxygen content to a specific range, it is possible to simultaneously suppress the degradation (nitriding) of powder particles and the reduction of magnetic properties caused by oxidation due to humidification. Typically, in the processes following pulverization, the oxygen content of R-T-B sintered magnets increases primarily in the process of forming and sintering the micro-powder to create the sintered body. However, the increase in oxygen content in R-T-B sintered magnets is relatively small (e.g., 50 ppm to 300 ppm). Therefore, the oxygen content of R-T-B sintered magnets can be adjusted through the pulverization process. The inventors of this invention further investigated and found that when performing the humidified pulverization of a mixed alloy powder (consisting of a main alloy powder and additive alloy powder) according to this invention, compared to pulverization without humidification, the oxygen content can be increased. cJThat is, in this invention, by using additive alloy powder and main alloy powder with specific compositions, the composition of the R-T-B sintered magnet is made to be within a specific range. Furthermore, in the pulverization process of the R-T-B sintered magnet, humidified pulverization is performed to ensure that the oxygen content of the obtained R-T-B sintered magnet reaches a specific range (1000ppm to 3000ppm, preferably 1000ppm to 2500ppm), thereby reducing the particle size (average particle size of 2.0μm to 4.5μm, preferably 2.0μm to 3.5μm). This mitigates the decrease in magnetic properties caused by oxidation or nitriding during the pulverization process, suppresses the deterioration of pulverization efficiency during jet milling, and reduces the content of heavy rare earth elements, resulting in a high-B content. r and high H cJ R-T-B system sintered magnets.

[0035] <Manufacturing Method of R-T-B System Sintered Magnets>

[0036] The method for manufacturing the R-T-B sintered magnet of the present invention includes: (1) a step of preparing an alloy powder to be added; (2) a step of preparing a main alloy powder; (3) a step of preparing a mixed alloy powder; (4) a step of supplying the mixed alloy powder to a jet mill device filled with an inert gas in a grinding chamber, and grinding the mixed alloy powder to obtain micro-powder with an average particle size of 2.0 μm or more and 4.5 μm or less; and (5) a step of producing a sintered body of the micro-powder, wherein the inert gas is humidified. The average particle size (d50) can be determined by airflow dispersion laser diffraction.

[0037] <R-T-B series sintered magnets>

[0038] The oxygen content of the R-T-B sintered magnet of the present invention is 1000 ppm to 3000 ppm by mass. By keeping the oxygen content at 1000 ppm to 3000 ppm, it is possible to suppress the decrease in magnetic properties caused by the nitridation of powder particles due to inert gas or the decrease in magnetic properties caused by the oxidation of powder particles due to humidification when the humidification of inert gas is too weak in the above-mentioned (4) process of obtaining micro powder. In order to obtain higher magnetic properties, the oxygen content of the R-T-B sintered magnet is preferably 1000 ppm to 2500 ppm, more preferably 1000 ppm to 2000 ppm.

[0039] Furthermore, the R-T-B sintered magnet (sometimes simply referred to as "sintered magnet") involved in this invention contains R: 28.5-33.0% by mass, B: 0.85-0.91% by mass, Cu: 0.05-0.50% by mass, Ga: 0.3-0.7% by mass, and T: 63-70% by mass. When the content of T (by mass) is set as [T] and the content of B (by mass) is set as [B], the R-T-B sintered magnet satisfies [T] / 55.85 > 14 × [B] / 10.8.

[0040] With the above composition, the amount of boron (B) is reduced compared to that of typical R-T-B sintered magnets, and Ga is included. This results in the formation of R-T-Ga phases, particularly at multi-grain boundaries, and R-Cu-Ga phases, especially at two-grain boundaries, thus reducing the content of heavy rare earth elements and yielding magnets with high boron content. r and high H cJ R-T-B system sintered magnets. Here, R-T-Ga phase refers to magnets typically composed of Nd6Fe. 13 The phase composed of Ga compounds. R6T 13 Ga compounds have La6Co 11 Ga3-type crystal structure. Additionally, R6T... 13 Ga compounds sometimes become R6T depending on their state. 13－δ Ga 1+δ Compounds (δ typically below 2). For example, in R-T-B sintered magnets containing a large amount of Cu and Al, it sometimes becomes R6T. 13－δ (Ga 1－x－y Cu x Al y ) 1+δ In addition, the R-Cu-Ga phase is a phase in which a portion of the Ga in the R-Ga phase is replaced by Cu, containing R: 70% to 95% by mass, Ga: 5% to 30% by mass, and T(Fe): 20% to 20% by mass (including 0). For example, the compound R3(Ga,Cu)1 can be listed.

[0041] A detailed description of the components contained in R-T-B system sintered magnets is provided.

[0042] (R: 28.5–33.0% by mass)

[0043] R must be at least one of the rare earth elements and must contain Nd.

[0044] The content of R (R amount) is 28.5%–33.0% by mass. When the R amount is below 28.5% by mass, there is a risk of difficulty in densification during sintering; when it exceeds 33.0% by mass, the proportion of the main phase decreases, resulting in a failure to obtain high B content. r The risks.

[0045] The amount of R is preferably 31% by mass or less, more preferably 29% to 31% by mass. When R is in this range, higher B can be obtained. r .

[0046] (B: 0.85–0.91% by mass)

[0047] The boron content (B content) of the sintered magnet is 0.85–0.91% by mass. When the B content is below 0.85% by mass, R2T is formed. 17 However, high H cannot be obtained. cJ There is a risk that when the content exceeds 0.91% by mass, the amount of R-T-Ga phase generated may be too small to obtain high H. cJ The risks.

[0048] (Cu: 0.05–0.50% by mass)

[0049] The Cu content (Cu weight) of the sintered magnet is 0.05–0.50% by mass. When the Cu content is below 0.05% by mass, high H content cannot be obtained. cJ The risk is that when the content exceeds 0.50% by mass, there is a risk of sintering degradation, resulting in the inability to obtain high H. cJ The risks.

[0050] (Ga: 0.3–0.7% by mass)

[0051] The Ga content (Ga content) of the sintered magnet is 0.3–0.7% by mass. When the Ga content is less than 0.3% by mass, the amount of R-T-Ga phase formed is too small to achieve the desired R2T phase. 17 Phase disappearance prevents the attainment of high H cJ The risk is that when it exceeds 0.7% by mass, unwanted Ga will be present, leading to a decrease in the proportion of the main phase and thus affecting B. r Reduced risk.

[0052] (T: 63-70% by mass)

[0053] T represents Fe or a mixture of Fe and Co.

[0054] The content of T (T amount) is 63.0% to 70% by mass. When the T content is below 63.0% by mass or above 70% by mass, B is present. r The risk has been significantly reduced.

[0055] The content of B satisfies the following formula (1).

[0056] [T] / 55.85 > 14 × [B] / 10.8

[0057] By satisfying equation (1), the content of B is less than that of typical R-T-B sintered magnets. In typical R-T-B sintered magnets, in order to remove R2T as the main phase... 14 R2T, a soft magnetic phase, is not generated except in the B phase. 17 The phase becomes a composition where [T] / 55.85 (atomic weight of Fe) is less than 14 × [B] / 10.8 (atomic weight of B) ([T] is the Fe content expressed in mass %). In the R-T-B sintered magnet of the present invention, unlike general R-T-B sintered magnets, [T] / 55.85 is specified to be greater than 14 × [B] / 10.8 using formula (1). In the R-T-B sintered magnet of the present invention, the main component of T is Fe, therefore the atomic weight of Fe is used.

[0058] (Unavoidable impurities and other elements)

[0059] Furthermore, the R-T-B sintered magnets of the present invention may contain Cr, Mn, Si, La, Ce, Sm, Ca, Mg, etc., as unavoidable impurities commonly found in neodymium-praseodymium alloys (Nd-Pr), electrolytic iron, iron-boron alloys, etc. The total content of such elements may be, for example, about 2.0% by mass or less. At this level, it is possible to obtain magnets with high B content. r and high H cJ The R-T-B sintered magnet of the present invention. Furthermore, unavoidable impurities introduced during the manufacturing process include, for example, O (oxygen), N (nitrogen), and C (carbon). Additionally, the R-T-B sintered magnet of the present invention may also contain one or more other elements (intentionally added elements other than unavoidable impurities). For example, such elements may be contained in small amounts (each less than 0.2% by mass) of Ag, Zn, In, Sn, Ti, Ge, Y, H, F, P, S, V, Ni, Mo, Hf, Ta, W, Nb, Zr, etc.

[0060] The oxygen content of R-T-B sintered magnets is in the range of 1000ppm to 3000ppm (preferably 1000ppm to 2500ppm). This suppresses both nitriding of powder particles and oxidation caused by humidification, resulting in high magnetic properties. The oxygen content of R-T-B sintered magnets can be adjusted through the pulverization process described later.

[0061] The R-T-B sintered magnet of the present invention contains R, B, Cu, and Ga within the aforementioned range, with the remainder being Fe and unavoidable impurities. That is, it is possible to produce an R-T-B sintered magnet containing only B, R, Cu, Ga, Fe, and unavoidable impurities, without any other intentionally added elements.

[0062] (1) Preparation for adding alloy powder

[0063] In this process, additive alloy powder is prepared for manufacturing sintered magnets.

[0064] The alloy powder with the specified composition, described later, can be manufactured using the same methods as those used in the manufacture of known R-T-B sintered magnets. For example, sheet-like alloy castings can be produced by a casting method using a mold or a strip casting method using a cooling roller to rapidly cool the molten alloy. The resulting sheet-like alloy castings are then hydrogen-milled to produce coarsely ground powder (alloy powder) with a size of, for example, 1.0 mm or less.

[0065] The composition of the added alloy powder includes R1: 33-69% by mass, B: 0.2-0.8% by mass, Cu: 0.8-3.0% by mass, Ga: 1.8-10% by mass, and T: 15-60% by mass.

[0066] The following explains the reasons for the limitations on the elements contained in the added alloy powder.

[0067] (R1: 33–69% by mass)

[0068] R1 is at least one of the rare earth elements, and more than 50% by mass of all R1 is Pr.

[0069] By making Pr more than 50% by mass of all R1, grain boundaries containing Pr can be easily formed in the grain boundaries of the obtained R-T-B sintered magnet, thus obtaining high magnetic properties.

[0070] The content of R1 in the added alloy powder (R1 amount) is 33-69% by mass. When the R1 amount is less than 33% by mass, relative to R2T... 14 In stoichiometric composition B, the amount of R1 is relatively too small, thus posing a risk of difficulty in forming the R-Ga and R-Ga-Cu phases. When the amount of R1 exceeds 69% by mass, the excessive amount of R1 may lead to R1 oxidation, resulting in reduced magnetic properties or the risk of fire, posing a risk of becoming a production problem.

[0071] The preferred R1 content is 40-60% by mass. The Pr content of the added alloy powder is set to be greater than the Pr content of the main alloy powder.

[0072] (B: 0.2–0.8% by mass)

[0073] The content of boron (B content) in the added alloy powder is 0.2–0.8% by mass. B reacts with R and T to form R₂T as the main phase. 14 The essential element for type B compounds. When the amount of B is less than 0.2% by mass, R2T 14 The amount of type B compounds formed is small, and R2T is generated when added to alloy powder. 17Phase. Therefore, the H of the final sintered magnet is cJ When the boron content exceeds 0.8% by mass, it is necessary to reduce the boron content in the main alloy powder, which leads to the formation of R2T in the main alloy powder. 17 The phase, H, exists in the final sintered magnet. cJ Reduced risk.

[0074] The preferred amount of B is 0.2% to 0.7% by mass.

[0075] (Cu: 0.8–3.0% by mass)

[0076] The Cu content (Cu weight) of the added alloy powder is 0.8–3.0% by mass. When the Cu content is less than 0.8% by mass, the Cu content of the final sintered magnet is insufficient, resulting in the presence of H. cJ Reduced risk. When the Cu content exceeds 3.0% by mass, the sinterability of the mixed alloy powder containing additive alloy powder and main alloy powder deteriorates, resulting in H in the sintered magnet. cJ Reduced risk.

[0077] The Cu content is preferably 1.5–2.6% by mass.

[0078] (Ga: 1.8–10% by mass)

[0079] The Ga content in the added alloy powder is 1.8–10% by mass. When the Ga content is less than 1.8% by mass, the Ga content in the main alloy powder must be increased, resulting in the formation of the R-T-Ga phase in the main alloy powder, which contains H in the final sintered magnet. cJ Reduced risk. When the content exceeds 10% by mass, an R-T-Ga phase is formed in the added alloy powder, resulting in H in the final sintered magnet. cJ Reduced risk.

[0080] The preferred Ga content is 3-8% by mass.

[0081] (T: 15-60% by mass)

[0082] T represents Fe or a mixture of Fe and Co.

[0083] The content of T in the added alloy powder is 15-60% by mass. It reacts with R and T to form R2T as the main phase. 14 Elements essential for type B compounds. When the amount of T is less than 15% by mass, R2T 14 The amount of type B compound formed is small, therefore, the final sintered magnet has low H content. cJ When the nitrogen (T) content exceeds 60% by mass, it is necessary to reduce the T content in the main alloy powder, which leads to the formation of R2T in the main alloy powder. 17 The phase, H, exists in the final sintered magnet. cJReduced risk.

[0084] The preferred T content is 20-50% by mass.

[0085] (Unavoidable impurities and other elements)

[0086] As unavoidable impurities, alloy powder may contain Cr, Mn, Si, La, Ce, Sm, Ca, Mg, etc. Additionally, the elements listed above as unavoidable impurities may be intentionally added. The total content of such elements may be, for example, less than 1.0% by mass. At this level, it is possible to obtain sufficiently high H... cJ The R-T-B sintered magnet of the present invention. Furthermore, unavoidable impurities introduced during the manufacturing process include, for example, O (oxygen), N (nitrogen), and C (carbon). Additionally, the R-T-B sintered magnet of the present invention may contain one or more other elements (intentionally added elements other than unavoidable impurities). For example, such elements may be contained in small amounts (approximately 0.1% by mass or less each) of Ag, Zn, In, Sn, Ti, Ge, Y, H, F, P, S, V, Ni, Mo, Hf, Ta, W, Nb, Zr, etc.

[0087] The alloy powder added can be within the composition range of the alloy powders mentioned above, and multiple alloy powders can be prepared. When the mixed alloy powder is taken as 100% by mass, the total of the various alloy powders reaches 1-16% by mass.

[0088] (2) Process of preparing main alloy powder

[0089] In this process, the main alloy powder used to manufacture sintered magnets is prepared.

[0090] The main alloy powder can be manufactured using the same methods as the added alloy powder. For example, sheet-like alloy castings can be produced by casting using a mold or by strip casting using a cooling roller to quench the molten alloy. The resulting sheet-like alloy castings are then hydrogen-milled to produce coarsely ground powder (main alloy powder) with a size of, for example, 1.0 mm or less.

[0091] The composition of the main alloy powder is prepared with the contents of R, B, Ga, and T within the following ranges.

[0092] R: 28.5–33.0% by mass, B: 0.80–1.00% by mass, Ga: 0.1–0.4% by mass, T: 64–70% by mass

[0093] The following explains the reasons for the limitations on the elements contained in the main alloy powder.

[0094] (R: 28.5–33.0% by mass)

[0095] R must be at least one of the rare earth elements and must contain Nd.

[0096] The content of R (R amount) in the main alloy powder is 28.5%–33.0% by mass. When the R amount is less than 28.5% by mass, H is present. cJ Reduced risk. When R exceeds 33.0% by mass, B is present. r Reduced risk.

[0097] (B: 0.80–1.00% by mass)

[0098] The boron content (B mass) of the main alloy powder is 0.80–1.10% by mass. B reacts with R and T to form R2T as the main phase. 14 The essential element for type B compounds. When the amount of B is less than 0.80% by mass, R2T 14 Type B compounds are formed in small quantities and readily generate R2T when added to alloy powders. 17 Phase. Therefore, the H phase exists in the final sintered magnet. cJ Reduced risk. When the amount of B exceeds 1.10% by mass, it is necessary to reduce the amount of B in the added alloy powder, which leads to the formation of R2T in the added alloy powder. 17 The phase, H, exists in the final sintered magnet. cJ Reduced risk.

[0099] (Ga: 0.1–0.4% by mass)

[0100] The Ga content (Ga amount) of the main alloy powder is 0.1–0.4% by mass. When the Ga content is less than 0.1% by mass, the formation of R-Ga and R-Ga-Cu phases is too small, resulting in the presence of H. cJ Reduced risk. When the Ga content exceeds 0.4% by mass, an R-T-Ga phase is formed in the main alloy powder, resulting in H in the final sintered magnet. cJ Reduced risk.

[0101] (T: 64-70% by mass)

[0102] T represents Fe or a mixture of Fe and Co.

[0103] The nitrogen (T) content (T weight) of the main alloy powder is 64–70% by mass. When the T weight is below 64% by mass, hydrogen (H) is present. cJ The risk of a sharp decrease. When the T content exceeds 70% by mass, there is a risk of R2T formation. 17 Phase, H cJ Reduced risk.

[0104] When the total amount of T is set to 100% by mass, for example, 0-10% by mass of T can be replaced by Co. That is, 90-100% by mass of the total amount of T is Fe and 0-10% by mass is Co.

[0105] (Unavoidable impurities and other elements)

[0106] The main alloy powder may contain Cr, Mn, Si, La, Ce, Sm, Ca, Mg, etc., as unavoidable impurities. Additionally, the elements listed above as unavoidable impurities may be intentionally added. The total content of such elements may be, for example, less than 2.0% by mass. At this level, it is possible to obtain sufficiently high H... cJ The R-T-B sintered magnet of the present invention. Furthermore, unavoidable impurities introduced during the manufacturing process include, for example, O (oxygen), N (nitrogen), and C (carbon). Additionally, the R-T-B sintered magnet of the present invention may contain one or more other elements (intentionally added elements other than unavoidable impurities). For example, such elements may be contained in small amounts (approximately 0.2% by mass or less each) of Ag, Zn, In, Sn, Ti, Ge, Y, H, F, P, S, V, Ni, Mo, Hf, Ta, W, Nb, Zr, etc.

[0107] The main alloy powder only needs to be within the composition range of the main alloy powder mentioned above, and multiple main alloy powders can be prepared. In this case, when the mixed alloy powder is taken as 100% by mass, the total of the multiple main alloy powders reaches 84-99% by mass.

[0108] (3) The process of preparing mixed alloy powder

[0109] Mix the additive alloy powder with the main alloy powder to prepare the mixed alloy powder. When the mixed alloy powder is set to 100% by mass, mix 1-16% by mass of the additive alloy powder with 84-99% by mass of the main alloy powder.

[0110] When the amount of alloy powder added is less than 1% by mass, the amount of alloy powder added is too small and cannot suppress the formation of the R-T-Ga phase, resulting in the presence of H. cJ Reduced risk. When the amount of alloy powder added exceeds 16% by mass, B is present. r Reduced risk. Regarding the mixed alloy powder, the additive alloy powder is mixed with the main alloy powder using a known device such as a V-type mixer. Then, the mixed alloy powder is fed into a jet mill for pulverization to obtain micro powder with an average particle size of 2.0 μm to 4.5 μm.

[0111] (4) A process of feeding mixed alloy powder into a jet mill filled with inert gas to pulverize the mixed alloy powder to obtain micro powder with an average particle size of 2.0 μm to 4.5 μm.

[0112] <Grinding System>

[0113] First, refer to Figure 1 The following example illustrates the pulverizing system used in the manufacturing method of the R-T-B sintered magnet of the present invention. Figure 1 This is a schematic diagram illustrating an example of the configuration of the pulverizing system 1000 in this embodiment. In this example, the R-T-B sintered magnet alloy pulverizing system 1000 includes a jet mill 100, a cyclone collection device 200, and a bag filter device 300.

[0114] The jet mill 100 receives the material to be pulverized from a raw material tank (not shown) via a raw material feed pipe 34. The material to be pulverized in this invention is a mixed alloy powder, for example, with an average particle size of 10 μm to 500 μm. The average particle size (d50) in this invention can be determined using airflow dispersion laser diffraction (refer to JIS Z 8825: 2013 revised edition). That is, in this specification, the average particle size refers to the particle size (median particle size) that represents the cumulative particle size distribution (volume basis) from the smallest particle size side that reaches 50%.

[0115] In addition, the average particle size (d50) in the embodiments of the present invention represents the d50 measured using the particle size distribution measuring device "HELOS & RODOS" manufactured by Sympatec under the conditions of dispersion pressure: 4 bar, measurement range: R2, and calculation mode: HRLD.

[0116] The raw material feed pipe 34 is equipped with multiple valves, which are used to maintain the internal pressure of the jet mill 100. The material to be pulverized, introduced into the jet mill 100, is subjected to high-speed jets of inert gas from the nozzle pipe 36, which collide with impact plates designed to facilitate efficient pulverization and mutual impact of the material. The nozzle pipe 36 is connected to a humidification pipe to incorporate moisture into the inert gas.

[0117] The powder of R-T-B series sintered magnet alloys is reactive and easily oxidized. Therefore, to avoid the risk of overheating and fire, and to reduce the oxygen content as an impurity to achieve high magnet performance, dry (high-purity) inert gases such as nitrogen, argon, and helium with a dew point below -60°C are typically used as the gas used in the jet mill apparatus 100. However, in the embodiments of the present invention, the milling is performed in a humidified state in which moisture is intentionally introduced into such inert gases. Details regarding this will be explained later.

[0118] The finely pulverized powder particles (micropowder) inside the jet mill 100 are introduced into the inlet pipe 20 of the cyclone collector 200 from the upper outlet by an upward airflow. Insufficiently pulverized coarse particles are separated by a classifying rotor, which is configured to classify coarse particles with a median particle size (d50) or larger, and remain inside the jet mill 100 for further pulverization using impact. The classification of these coarse particles can be achieved using a classifying rotor or centrifugal separation utilizing a rotating airflow. Thus, the material (mixed powder) fed into the jet mill 100 is pulverized into micropowder with an average particle size (median particle size: d50) of 2.0 μm to 4.5 μm, and then moved to the cyclone collector 200.

[0119] Cyclone trap 200 is used to separate powder from the gas stream carrying the powder. Specifically, the mixed alloy powder (coarsely ground powder) is pulverized in a jet mill in the upstream section. The resulting fine powder, along with the gas used in the pulverization process, is supplied to the cyclone trap 200 through inlet pipe 20. The inert gas (pulverizing gas) and the mixture of pulverized fine powder form a high-speed gas stream, which is sent to the cyclone trap 200. The cyclone trap 200 is used to separate the pulverizing gas from the fine powder. The fine powder separated from the pulverizing gas is recovered in powder collector 50 through outlet 40. The pulverizing gas is supplied to bag filter device 300 through outlet pipe 30. Very small particles are recovered in bag filter device 300, and clean gas is discharged to the outside through exhaust port 32. Alternatively, a bag filter can be used instead of the cyclone trap 200 for such solid-gas separation, but the atmospheric dispersion of fine powder due to filter breakage has significant environmental and safety impacts. Furthermore, a bag filter can be used to separate the particles from the gas after it has been separated by the cyclone trap.

[0120] One feature of this invention is that the R-T-B sintered magnet is humidified and pulverized in a manner that achieves an oxygen content in the range of 1000 ppm to 3000 ppm. This suppresses both nitriding of the powder particles caused by pulverization and oxidation caused by humidification, resulting in high magnetic properties. As described above, the increase in oxygen content of the R-T-B sintered magnet due to subsequent pulverization processes (primarily the process of producing the sintered body of the aforementioned micro-powder) is generally small (e.g., 50 ppm to 300 ppm). Therefore, the oxygen content of the R-T-B sintered magnet can be adjusted through the pulverization process.

[0121] Specifically, the humidified inert gas in step (2) can be obtained, for example, by giving the inert gas a moisture content of 0.5g to 6.0g relative to 1kg of mixed alloy powder (coarsely ground powder).

[0122] The dew point in the pulverizing chamber and the amount of mixed alloy powder supplied to the jet mill also depend on the pulverizing time and the size of the jet mill. However, in a preferred embodiment, the aforementioned inert gas is humidified such that the dew point during pulverization reaches a level of -65°C to -30°C. In a further preferred embodiment, the rate at which the mixed alloy powder is supplied to the jet mill is 35 kg / h to 180 kg / h.

[0123] Examples of inert gases include nitrogen, argon, helium, and mixtures thereof. Nitrogen is preferred because it is readily available in high purity at low cost. Therefore, in a preferred embodiment, nitrogen is used as the inert gas. However, research by the inventors of this invention has revealed that when jet milling is performed using an inert gas composed of nitrogen, the magnetic properties of the resulting microparticles begin to decrease due to nitriding when the average particle size reaches 4.5 μm or less. Particularly when the average particle size reaches 3.5 μm or less, the decrease in magnetic properties due to nitriding sometimes becomes more significant. However, according to an embodiment of the invention, milling is performed in a properly regulated humidified atmosphere, thus both nitriding suppression and oxidation suppression can be achieved even when nitrogen is used as the inert gas. This can be attributed to the fact that even though the inert gas in the milling chamber is primarily nitrogen, by humidifying it with a specific regulated amount of water, the active surfaces of the particles exposed by micro-milling are thinly oxidized before nitriding. Furthermore, the increase in oxygen content of the R-T-B sintered magnet caused by the subsequent micronization process (mainly the process of producing the sintered body of the aforementioned micronized powder) is preferably 50 ppm to 300 ppm, more preferably 50 ppm to 200 ppm. To achieve this, as described later, the resulting molded body is sintered by wet pressing in a magnetic field or pressing in a magnetic field in an inert gas atmosphere. The average particle size of the micronized powder in the process of obtaining the micronized powder is more preferably 2.0 μm to 3.5 μm. By reducing the average particle size, the magnet properties can be improved.

[0124] (5) Process for preparing sintered bodies of micro powder

[0125] In a preferred embodiment, the process of producing a sintered body of micro-powder includes the steps of pressing the micro-powder in a magnetic field to form a powder molded body and sintering the powder molded body. When pressing in a magnetic field, from the viewpoint of suppressing oxidation, it is preferable to form the powder molded body by pressing in an inert gas atmosphere or by wet pressing. In particular, wet pressing, in which the surface of the particles constituting the powder molded body is coated with a dispersant such as an oil, suppresses contact with oxygen or water vapor in the atmosphere. Therefore, it is possible to prevent or suppress the oxidation of the particles by the atmosphere before, during, or after the pressing process.

[0126] In the case of wet pressing in a magnetic field, a slurry containing a dispersion medium mixed in micro powder is prepared and supplied to the mold cavity of the mold in the wet pressing device, and pressed and formed in a magnetic field.

[0127] • Dispersion medium

[0128] A dispersion medium is a liquid that can disperse alloy powder within it to obtain a slurry.

[0129] Mineral oil or synthetic oil can be cited as a preferred dispersion medium used in this invention. The type of mineral oil or synthetic oil is not specific, but when the kinematic viscosity at room temperature exceeds 10 cSt, the increased viscosity strengthens the bonding force between alloy powders, which can sometimes adversely affect the orientation of the alloy powders during wet molding in a magnetic field. Therefore, the kinematic viscosity of the mineral oil or synthetic oil at room temperature is preferably below 10 cSt. Furthermore, when the fractionation temperature of the mineral oil or synthetic oil exceeds 400°C, degreasing after obtaining the molded body becomes difficult, resulting in increased residual carbon content in the sintered body and a decrease in magnetic properties. Therefore, the fractionation temperature of the mineral oil or synthetic oil is preferably below 400°C. Alternatively, vegetable oil can also be used as a dispersion medium. Vegetable oil refers to oil extracted from plants, and the type of plant is not limited to a specific plant.

[0130] • Preparation of slurry

[0131] The obtained alloy powder is mixed with a dispersion medium to obtain a slurry.

[0132] The mixing ratio of alloy powder and dispersion medium is not particularly limited, but the concentration of alloy powder in the slurry, by mass ratio, is preferably 70% or more. This is because in the range of 20–600 cm⁻¹… 3 The slurry is efficient at supplying alloy powder into the mold cavity at a flow rate of [flow rate] / second, resulting in excellent magnetic properties. The concentration of alloy powder in the slurry is preferably 90% or less by mass ratio. The method of mixing the alloy powder and the dispersion medium is not particularly limited. The alloy powder and dispersion medium can be prepared separately, weighed in predetermined amounts, and mixed. Alternatively, when dry-milling the mixed alloy powder to obtain micropowder using a jet mill or similar device, a container filled with the dispersion medium can be placed at the alloy powder outlet of the jet mill or similar milling apparatus. The micropowder obtained from the milling can be directly recycled into the dispersion medium within the container to obtain a slurry. In this case, it is preferable to also create an atmosphere composed of nitrogen and / or argon within the container, directly recycling the obtained alloy powder into the dispersion medium without contacting the atmosphere to form a slurry. By molding the slurry obtained in this way using a known wet pressing apparatus, a molded body with a predetermined size and shape can be obtained. This molded body is then sintered to obtain a sintered body.

[0133] ·Sintering process

[0134] Next, the molded body is sintered to obtain a rare earth sintered magnet (sintered body).

[0135] The sintering of the molded body is preferably carried out at 0.13 Pa (10). －3 Torr) or less, more preferably 0.07 Pa (5.0 × 10⁻⁶ Pa). －4 The process is carried out at pressures below Torr and temperatures ranging from 1000°C to 1150°C. To prevent oxidation caused by sintering, residual gases in the atmosphere can be replaced with inert gases such as helium or argon. It is preferable to heat-treat the resulting sintered body. Heat treatment improves magnetic properties. Known conditions can be used for heat treatment, including temperature and time. The resulting rare-earth sintered magnet is then subjected to grinding, surface treatment, and magnetization processes as needed, resulting in the final rare-earth sintered magnet.

[0136] The invention will be described in more detail through embodiments, but the invention is not limited to these embodiments.

[0137] Experimental Example 1

[0138] Alloys were fabricated by strip casting, approximating the composition of R-T-B sintered magnets as shown in Samples No. 1 and 2 of Table 1 (excluding O, C, and N). The resulting alloys were coarsely pulverized using a hydrogen pulverization method to obtain coarse powder. The average particle size of the coarse powder was measured. The average particle size ranged from 200 μm to 400 μm. In this invention, the average particle size refers to the particle size (median particle size) that represents the 50% cumulative particle size distribution (volume basis) from the smallest particle size side. The average particle size (d50) was measured using a Sympatec particle size distribution measuring device, "HELOS & RODOS," under the conditions of a dispersion pressure of 4 bar, a measurement range of R2, and a measurement mode of HRLD.

[0139] Next, additive alloys and main alloys were prepared by strip casting, with compositions approximately corresponding to No. a in Table 2 and No. A to C in Table 3. The obtained alloys were coarsely pulverized using hydrogen pulverization to obtain additive alloy powder and main alloy powder. The average particle size of the obtained alloy powders ranged from 200 μm to 400 μm. The composition of the obtained alloy powders was determined. Each component was measured by ICP-N (Inductively Coupled Propagation) spectrophotometry. The measurement results are shown in Tables 2 and 3. Next, the additive alloy powder and main alloy powder were mixed separately in a V-type mixer under the mixing conditions specified in Table 4. No. 3 in Table 4 is a mixture of additive alloy powder No. a and main alloy powder No. A, containing 5% by mass of additive alloy powder (95% by mass of main alloy powder). Nos. 4 to 7 are also described in the same manner.

[0140] The coarsely crushed powders of samples No.1 and No.2 and the mixed alloy powders of No.3 to No.7 were respectively put into... Figure 1 The powder was pulverized using a jet mill 100 to obtain fine powder. The pulverization conditions are shown in Table 5. In Table 5, No. 2, an inert gas was supplied with 1.4 g of water relative to 1 kg of coarsely pulverized powder for humidification pulverization, and the amount of coarsely pulverized powder supplied to the jet mill was 64.1 kg / h. Nos. 1 and 3 to 7 are also described in the same manner (Nos. 1 and 3 were pulverized without humidification). In this embodiment, nitrogen was used as the inert gas. The average particle size of the obtained fine powder is shown in Table 5. The fine powder was impregnated in a nitrogen atmosphere with mineral oil having a fractionation temperature of 250°C and a kinematic viscosity of 2 cSt at room temperature to prepare a slurry. The slurry concentration was 85% by mass. The obtained slurry was molded in a magnetic field (wet molding) to obtain a molded body. The molding apparatus used was a so-called right-angle magnetic field molding apparatus (transverse magnetic field molding apparatus) in which the direction of magnetic field application was orthogonal to the direction of pressure. The resulting molded body was sintered in a vacuum at 1040℃ (the selected temperature for sufficient densification by sintering) for 4 hours to obtain a sintered body. The density of the sintered body was 7.5 Mg / m³. 3 The above is a summary. Furthermore, the sintered body was subjected to a heat treatment process of holding at 800°C for 2 hours, cooling to room temperature, and then holding at 500°C for 2 hours before cooling to room temperature to obtain a sintered body (R-T-B system sintered magnet). The composition of the obtained sintered magnet was determined. The contents of Nd, Pr, Tb, B, Co, Al, Cu, Ga, and Zr were determined using ICP-N2 spectroscopy. Furthermore, O (oxygen content) was determined using a gas analyzer employing gas melting-infrared absorption, N (nitrogen content) was determined using a gas analyzer employing gas melting-thermal conductivity, and C (carbon content) was determined using a gas analyzer employing combustion-infrared absorption. The results are shown in Tables 1 and 6. It was confirmed that all R-T-B system sintered magnets No. 1 to 7 met the requirement of [T] / 55.85 > 14 × [B] / 10.8 of this invention. The sintered magnets were machined to produce samples with a length of 7 mm, a width of 7 mm, and a thickness of 7 mm. The biomass (B) of each sample was measured using a B-H analyzer. r and H cJ The measurement results are shown in Table 7.

[0141] [Table 1]

[0142]

[0143] [Table 2]

[0144]

[0145] [Table 3]

[0146]

[0147] [Table 4]

[0148]

[0149] [Table 5]

[0150]

[0151] [Table 6]

[0152]

[0153] [Table 7]

[0154]

[0155] As shown in Tables 1 (R-T-B sintered magnets prepared from single alloy powders) and 6 (R-T-B sintered magnets prepared from mixed alloy powders containing additive alloy powders and main alloy powders), Nos. 1 to 7 have almost identical compositions except for C, O, and N, and the average particle size (3.4 μm) of the micropowders obtained by jet milling is also the same. As shown in Table 3, the examples of the present invention (Nos. 4 to 6) all exhibited higher magnetic properties than Nos. 1 and No. 3, which were not subjected to humidified milling. It has always been believed that if the composition and particle size are basically the same, the magnetic properties decrease with increasing oxygen content. However, as shown in Nos. 3 and Nos. 4 to 6, the magnetic properties actually improve when the oxygen content is within the range of the R-T-B sintered magnets of the present invention. Furthermore, even when humidified milling is performed, the magnetic properties decrease when the oxygen content deviates from the range of the R-T-B sintered magnets of the present invention, as shown in No. 7. Furthermore, comparing No. 1 and 2 (magnets prepared from single alloy powders in a humidified and undried manner) with No. 3 and 4 (magnets prepared from the mixed alloy powders of the present invention in a humidified and undried manner), No. 4 has a higher B value compared to No. 3. r and H cJ Further improvements can be made. It is evident that by humidifying and pulverizing the mixed alloy powder containing additive alloy powder and main alloy powder according to the present invention, the magnetic properties can be further improved.

[0156] Industrial availability

[0157] The manufacturing method of the R-T-B sintered magnet of the present invention can be used as a permanent magnet in a variety of applications, such as voice coil motors (VCMs) for hard disk drives, motors for electric vehicles (EVs, HVs, PHVs), motors for industrial equipment, and household appliances.

Claims

1. A method for manufacturing an R-T-B system sintered magnet, wherein, R is at least one of rare earth elements and must contain Nd, T is Fe or Fe and Co, and the manufacturing method is characterized by comprising: The process of preparing to add alloy powder, which contains... R1: 33–69% by mass B: 0.2–0.8% by mass Cu: 0.8–3.0% by mass Ga: 1.8–10% by mass T: 15-60% by mass Among them, R1 is at least one of the rare earth elements, and more than 50% by mass of all R1 is Pr; The process of preparing the main alloy powder, which contains... R: 28.5–33.0% by mass B: 0.80–1.0% by mass Ga: 0.1–0.4% by mass T: 64-70% by mass; The process of preparing a mixed alloy powder, wherein the mixed alloy powder contains 1-16% by mass of the additive alloy powder and 84-99% by mass of the main alloy powder; The mixed alloy powder is fed into a jet mill containing an inert gas in the grinding chamber, and the mixed alloy powder is ground to obtain micro-powder with an average particle size of 2.0 μm to 4.5 μm; and The process of preparing the sintered body of the micro powder, The added alloy powder has a higher Pr content than the main alloy powder. The inert gas is humidified. The oxygen content of the R-T-B sintered magnet is between 1000 ppm and 3000 ppm. The R-T-B sintered magnet contains... R: ≥28.5% by mass, ≤33.0% by mass B: 0.85% by mass or more, 0.91% by mass or less Cu: ≥0.05% by mass and ≤0.50% by mass Ga: ≥0.3% by mass and ≤0.7% by mass T: 63% by mass or more but less than 70% by mass, where T is Fe or a mixture of Fe and Co. When the content of T in mass% is set as [T] and the content of B in mass% is set as [B], the condition [T] / 55.85 > 14 × [B] / 10.8 is satisfied.

2. The method for manufacturing an R-T-B sintered magnet as described in claim 1, characterized in that, The R content of the R-T-B sintered magnet is less than 31% by mass.

3. The method for manufacturing an R-T-B system sintered magnet as described in claim 1 or 2, characterized in that, The inert gas is nitrogen.

4. The method for manufacturing an R-T-B system sintered magnet as described in claim 1, characterized in that, The process of preparing the sintered body of the micro powder includes: The steps of preparing powder-shaped articles from the micro-powder by wet pressing in a magnetic field or pressing in a magnetic field in an inert gas atmosphere; and The step of sintering the powder molded body.

5. The method for manufacturing an R-T-B sintered magnet as described in claim 1, characterized in that, The average particle size of the micro powder obtained in the process of obtaining the micro powder is 2.0 μm or more and 3.5 μm or less.

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