JP2011210850A - Method of manufacturing rare-earth sintered magnet, and the rare-earth sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a rare-earth sintered magnet which improves the grindability and the magnetic characteristics, and to provide a rare-earth sintered magnet.SOLUTION: A method of manufacturing a rare-earth sintered magnet, when a rare-earth sintered magnet having a main phase containing RTB (R represents one or more kinds of rare-earth element is manufactured, T represents one or more kinds of transition metal element containing Fe or Fe and Co, and B represents B or B and C) compound and a grain boundary phase containing lots of R; obtains the rare-earth sintered magnet by mixing an alloy powder of a first alloy containing RTB compound and an alloy powder of a second alloy containing HRTB compound (HR represents one or more kinds of a heavy rare-earth element), where a containing amount of HR is 25.0 mass% or more and 32.5 mass% or less, and a containing amount of B is 0.6 mass% or more and 1.4 mass% or less; and sinters the mixture. The rare-earth sintered magnet has a composition that R is 25.0 mass% or more and is less than 32.5 mass%, and B is 0.5 mass% or more and 1.5 mass% or less.

Description

  The present invention relates to a method for producing a rare earth sintered magnet and a rare earth sintered magnet, and more particularly, to a method for producing a rare earth sintered magnet and a rare earth sintered magnet having improved magnetic properties and improved crushability of the alloy powder of the second alloy. .

A rare earth permanent magnet having a composition of R-T-B (R represents a rare earth element, T represents one or more transition metal elements including Fe or Fe and Co, and B represents B or B and C), a major phase comprising R ₂ T ₁₄ B compound represented by the composition formula of R ₂ T ₁₄ B, have a tissue containing a grain boundary phase containing R-rich phase containing more R than R ₂ T ₁₄ B, It is a permanent magnet that exhibits excellent magnetic properties such as a high coercive force HcJ. R-Fe-B rare earth permanent magnets have high performance as high performance permanent magnets such as hard disk drive (Voice Coil Motor: VCM), electric cars and hybrid cars. Used for required motors.

For example, a first alloy containing the R ₂ T ₁₄ B compound as a main phase and a second alloy containing 25% by mass or more of the R ₂ T ₁₇ phase as a main phase are mixed, and a rare earth element such as Dy is mixed in the outer portion of the main phase. There has been proposed a method for efficiently producing a sintered magnet having a high coercive force HcJ by concentrating at a higher concentration than other parts (see, for example, Patent Document 1).

Japanese Patent No. 3765793

In the conventional permanent magnet such as the sintered magnet of Patent Document 1, since B is not contained in the second alloy, no R ₂ T ₁₄ B compound is generated in the second alloy, and the R-rich phase is not produced. And R ₂ T ₁₇ phase. When hydrogen was occluded in the mixed powder in which the first alloy and the second alloy were mixed, the R ₂ T ₁₄ B compound contained in the first alloy was difficult to occlude hydrogen and there was almost no volume expansion. On the other hand, the second alloy contained many phases such as R-rich phase and R ₂ T ₁₇ phase that have the property of easily absorbing hydrogen and expanding. After the second alloy occludes hydrogen, it is considered that there is almost no difference in expansion caused by the occlusion of hydrogen, so the second alloy has poor grindability and poor fine powder productivity.

  If the pulverizability of the second alloy is poor, when the first alloy and the second alloy are mixed and then pulverized to produce a rare earth sintered magnet, the deviation from the target composition tends to increase, and the target composition It was difficult to produce rare earth sintered magnets having a magnetic property, and there was a problem that the magnetic properties of the obtained rare earth sintered magnets deteriorated.

  This invention is made in view of the above, Comprising: It aims at providing the manufacturing method and rare earth sintered magnet of the rare earth sintered magnet which improved the magnetic characteristic.

In order to solve the above-mentioned problems and achieve the object, a method for producing a rare earth sintered magnet according to the present invention is based on R ₂ T ₁₄ B (R represents one or more rare earth elements, T represents Fe or Fe and A rare earth-firing having a main phase containing a compound including one or more transition metal elements including Co, wherein B represents B or B and C, and a grain boundary phase containing more R than the R ₂ T ₁₄ B compound. In producing the magnet, the alloy powder of the first alloy containing the R ₂ T ₁₄ B compound and inevitable impurities and the HR ₂ T ₁₄ B compound (HR represents one or more kinds of heavy rare earth elements) The alloy powder of the 2nd alloy whose content is 25.0 mass% or more and 32.5 mass% or less, and whose B content is 0.6 mass% or more and 1.4 mass% or less is mixed. Obtaining a mixture preparation step, molding the mixture and obtaining a molded body, and Sintering the molded body to obtain a sintered body, and R contained in the main phase and the grain boundary phase is 25% by mass or more and less than 32.5% by mass, and B is 0.5% by mass. % Or more and 1.5% by mass or less.

When B is not contained in the second alloy, an R-rich phase or a phase such as Dy ₂ Fe ₁₇ is formed in the second alloy. When hydrogen is stored in the second alloy, phases such as R-rich phase and Dy ₂ Fe ₁₇ included in the second alloy easily store hydrogen and easily expand. Therefore, even if hydrogen is occluded in the second alloy and the second alloy is formed only with a phase that easily absorbs hydrogen and expands, even if hydrogen is occluded in the second alloy, the phase of the second alloy The difference in expansion between them is small, and the alloy is less likely to crack. On the other hand, in the present invention, the second alloy contains HR and B, and a phase containing the HR ₂ T ₁₄ B compound is formed. Unlike the R-rich phase and Dy ₂ Fe ₁₇ phase, the HR ₂ T ₁₄ B compound hardly absorbs hydrogen and is a phase that is less likely to expand than the R-rich phase and Dy ₂ Fe ₁₇ phase. For this reason, when the R ₂ T ₁₄ B compound is included in the second alloy, cracks are generated in the second alloy when hydrogen is occluded as compared to the case where an R-rich phase or a phase such as Dy ₂ Fe ₁₇ is formed. It becomes easy to generate | occur | produce, the grindability of a 2nd alloy can be improved, and the productivity of the fine powder of a 2nd alloy can be improved. Since the second alloy is more likely to crack, the amount of fine powder of the second alloy is further increased, so that the composition deviation of the components contained in the rare earth sintered magnet obtained by mixing with the alloy powder of the first alloy is reduced. Therefore, the magnetic properties of the rare earth sintered magnet can be improved.

The rare earth sintered magnet according to the present invention is R ₂ T ₁₄ B (R represents one or more rare earth elements, T represents one or more transition metal elements including Fe or Fe and Co, and B represents B or An alloy powder of a first alloy containing a compound (representing B and C) and unavoidable impurities, and an HR ₂ T ₁₄ B compound (HR represents one or more heavy rare earth elements), and the HR content is 25.0 It is obtained by mixing and sintering the alloy powder of the second alloy having a B content of 0.6% by mass or more and 1.4% by mass or less. a major phase comprising R ₂ T ₁₄ B compound, wherein R ₂ T ₁₄ and a grain boundary phase containing a large amount of R than B compounds, R contained in the main phase and the grain boundary phase is more than 25 wt% 32 Less than 5% by mass, and B is 0.5% by mass or more and 1.5% by mass or less.

The present invention is a rare earth sintered magnet manufactured using the method for manufacturing a rare earth sintered magnet according to the present invention. The second alloy contains HR and B, and a phase containing an R ₂ T ₁₄ B compound is formed. The R ₂ T ₁₄ B compound is a phase that is less likely to expand due to occlusion of hydrogen than the R-rich phase or the phase such as Dy ₂ Fe ₁₇ . For this reason, when hydrogen is occluded in the second alloy, cracks are likely to occur in the second alloy, the pulverization property of the second alloy can be improved, and the productivity of the fine powder of the second alloy can be improved. Thereby, since the fine powder of the second alloy further increases, the composition deviation of the components contained in the rare earth sintered magnet obtained by mixing with the alloy powder of the first alloy can be reduced. It is possible to improve the magnetic characteristics.

  According to the present invention, it is possible to provide a method for producing a rare earth sintered magnet and a rare earth sintered magnet having improved crushability and improved magnetic properties.

FIG. 1 is a flowchart showing a method for manufacturing a rare earth sintered magnet according to an embodiment of the present invention. FIG. 2 is a diagram showing the relationship between the measured coercive force HcJ and the residual magnetic flux density Br.

  Hereinafter, embodiments (hereinafter referred to as embodiments) and examples of rare earth sintered magnets according to the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by the embodiment and the Example for implementing the following invention. In addition, constituent elements in the following embodiments and examples include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those in a so-called equivalent range. Furthermore, the constituent elements disclosed in the following embodiments and examples may be appropriately combined or may be appropriately selected and used.

[Embodiment]
<Rare earth sintered magnet>
The rare earth sintered magnet is a sintered body formed using an R-T-B alloy. The rare earth sintered magnet has a crystal grain composition of R ₂ T ₁₄ B (R represents one or more rare earth elements including Nd, T represents one or more transition metal elements including Fe or Fe and Co, B represents B or B and C), and has a main phase containing an R ₂ T ₁₄ B compound represented by a composition formula, and a grain boundary phase containing more R than the R ₂ T ₁₄ B compound.

  R represents one or more rare earth elements. Rare earth elements refer to Sc, Y, and lanthanoid elements belonging to Group 3 of the long-period periodic table. Lanthanoid elements include, for example, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and the like. The rare earth elements are classified into light rare earth elements and heavy rare earth elements. The heavy rare earth elements are Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and the light rare earth elements are other rare earth elements. From the viewpoint of manufacturing cost and magnetic properties, R preferably contains Nd.

  T represents one or more transition metal elements including Fe or Fe and Co. T may be Fe alone or a part of Fe may be substituted with Co. When a part of Fe is replaced with Co, the temperature characteristics can be improved without deteriorating the magnetic characteristics. Further, the Co content is desirably suppressed to 20% by mass or less of the Fe content. This is because if a part of Fe is replaced with Co so that the Co content is larger than 20 mass% of the Fe content, the magnetic properties may be deteriorated. Moreover, it is because a rare earth sintered magnet becomes expensive. In addition to Fe and Co, T includes at least one element such as Al, Ga, Si, Ti, V, Cr, Mn, Ni, Cu, Zr, Nb, Mo, Hf, Ta, and W. Further, it may be included.

The alloy powder of the second alloy according to the present embodiment includes an HR ₂ T ₁₄ B compound (HR represents one or more kinds of heavy rare earth elements), and the HR amount is 25 mass% or more and 32.5 mass% or less, B The amount is 0.6 mass% or more and 1.4 mass% or less. When the amount of HR exceeds 32.5% by mass, fine crystal grains cannot be obtained and the magnetic properties are deteriorated. On the other hand, when the amount of HR is less than 25% by mass, the amount of Fe single phase, which is a soft magnetic phase, is increased, and the grindability and magnetic properties are deteriorated.

In the alloy powder of the second alloy according to this embodiment, when the amount of B exceeds 1.4% by mass, a different phase precipitates in addition to the HR ₂ T ₁₄ B compound (HR represents one or more types of heavy rare earth elements). , Reduce grindability. On the other hand, when the amount of B is less than 0.6% by mass, the amount of the HR ₂ T ₁₄ B compound is not sufficient, and the effect of improving grindability cannot be obtained. When B is not contained in the alloy powder of the second alloy and no HR ₂ T ₁₄ B compound is present, an R-rich phase or a phase such as Dy ₂ Fe ₁₇ is formed in the alloy powder of the second alloy. When the second alloy is occluded and pulverized, phases such as R-rich phase and Dy ₂ Fe ₁₇ contained in the second alloy easily absorb hydrogen and easily expand. Therefore, in the case where the second alloy is formed only with a phase that easily absorbs hydrogen and expands, the difference in expansion between the phases of the second alloy is small even if hydrogen is stored in the second alloy. Cracks are unlikely to occur. On the other hand, the second alloy of the present embodiment includes HR and B, and a phase including the HR ₂ T ₁₄ B compound is formed in the second alloy. Unlike the R-rich phase and Dy ₂ Fe ₁₇ phase, the HR ₂ T ₁₄ B compound hardly absorbs hydrogen and is a phase that is less likely to expand than the R-rich phase and Dy ₂ Fe ₁₇ phase. For this reason, when manufacturing the rare earth sintered magnet according to the present embodiment, when the second alloy contains the R ₂ T ₁₄ B compound, a phase such as an R rich phase or Dy ₂ Fe ₁₇ is formed. When hydrogen is occluded in comparison with this, the difference in expansion between phases contained in the second alloy becomes large, so that cracks are likely to occur in the alloy powder of the second alloy. Thereby, the grindability of the second alloy can be improved, and the productivity of the fine powder of the second alloy can be improved. Since the fineness of the second alloy is further increased by improving the pulverization property of the second alloy, the deviation of the composition of the components contained in the rare earth sintered magnet obtained by mixing with the alloy powder of the first alloy is The magnetic properties of the rare earth sintered magnet according to the present embodiment are improved.

Next, the chemical composition of the rare earth sintered magnet according to this embodiment will be described. The R content in the present invention is preferably 25% by mass or more and less than 32.5% by mass, and if the R content is less than 25% by mass, it becomes the main phase of the R-T-B system sintered magnet. The formation of R ₂ T ₁₄ B compound is not sufficient. For this reason, there exists a possibility that alpha-Fe etc. which have soft magnetism may precipitate, and a magnetic characteristic may fall. The amount of R is more preferably 27% by mass or more and 32% by mass or less.

  The content of B is preferably 0.5% by mass or more and 1.5% by mass or less. When the B content is less than 0.5% by mass, the coercive force decreases. On the other hand, if the B content exceeds 1.5% by mass, the residual magnetic flux density tends to decrease. Therefore, the more preferable amount of B is 0.5% by mass or more and 1.3% by mass or less, and the more preferable amount of B is 0.8% by mass or more and 1.2% by mass or less.

  The rare earth sintered magnet according to the present embodiment is obtained by being molded into a desired predetermined shape by, for example, press molding. The shape of the rare earth sintered magnet is not particularly limited, and may be changed according to the shape of the rare earth sintered magnet, for example, a flat plate shape, a columnar shape, a cross-sectional shape such as a ring shape, etc. it can.

  The rare earth sintered magnet according to the present embodiment uses a rare earth sintered magnet made of an R-T-B alloy, but the present embodiment is not limited to this. For example, an R-T-B rare earth alloy powder and a resin binder are kneaded to prepare a rare earth bonded magnet compound (composition), and the resulting rare earth bonded magnet compound is molded into a predetermined shape. It may be used as a rare earth sintered magnet.

In the rare earth sintered magnet according to the present embodiment, the second alloy powder used for manufacturing the magnet contains the R ₂ T ₁₄ B compound, so that the pulverizability of the alloy powder of the second alloy is improved, and the second alloy powder of the second alloy Improve the productivity of fine powder. Compared with the case where the second alloy powder not containing the R ₂ T ₁₄ B compound is used, the fine powder of the alloy powder of the second alloy further increases, so that the rare earth sintering obtained by mixing with the alloy powder of the first alloy The composition deviation of the components contained in the magnet can be reduced, and the magnetic properties can be improved.

<Method for producing rare earth sintered magnet>
A method for manufacturing a rare earth sintered magnet according to the present embodiment having the above-described configuration will be described with reference to the drawings. In the present embodiment, the first alloy powder contains an R ₂ Fe ₁₄ B compound and inevitable impurities. The second alloy powder contains an HR ₂ T ₁₄ B compound. A method for producing a rare earth sintered magnet according to the present invention using the first alloy powder and the second alloy powder will be described. FIG. 1 is a flowchart showing a method for manufacturing a rare earth sintered magnet according to an embodiment of the present invention. As shown in FIG. 1, the manufacturing method of the rare earth sintered magnet according to the present embodiment includes the following steps.
(A) Alloy preparation process for preparing the first alloy and the second alloy (step S11)
(B) Crushing step of crushing the first alloy and the second alloy (Step S12)
(C) Mixing step of mixing the first alloy powder and the second alloy powder (step S13)
(D) Molding process for molding the mixed powder mixture (step S14)
(E) Sintering step of sintering the compact (step S15)
(F) Aging treatment step of aging the sintered body (step S16)
(G) Cooling process for cooling the sintered body (step S17)

<Alloy preparation step: Step S11>
The alloy preparation step (step S11) is a step of preparing the first alloy and the second alloy. In the alloy preparation step (step S11), the raw material metal is cast in an inert gas atmosphere of an inert gas such as vacuum or Ar gas to obtain a first alloy and a second alloy. In the present embodiment, the second alloy includes the HR ₂ T ₁₄ B compound, the HR content is 25.0 mass% to 32.5 mass%, and the B content is 0.6 mass% to 1 Adjust to 4 mass% or less. As the raw material metal, rare earth metals or rare earth alloys, pure iron, ferroboron, and alloys thereof can be used. Casting methods for casting the raw metal include, for example, an ingot casting method, a strip casting method, a book mold method, and a centrifugal casting method. The obtained raw material alloy is subjected to a homogenization treatment as necessary when there is solidification segregation. When homogenizing the raw material alloy, it is carried out by holding at a temperature of 700 ° C. or higher and 1500 ° C. or lower for 1 hour or longer in a vacuum or an inert gas atmosphere. As a result, the rare earth magnet alloy is homogenized by removing a small amount of the heterogeneous phase incorporated into the main phase, the R-rich phase, and the R ₂ T ₁₇ phase. After the first alloy and the second alloy are produced, the process proceeds to the pulverization step (step S12).

<Crushing step: Step S12>
The crushing step (step S12) is a step of crushing each of the first alloy and the second alloy. In the pulverization step (step S12), after the first alloy and the second alloy are produced, the first alloy and the second alloy are separately pulverized. Although the first alloy and the second alloy may be pulverized together, it is preferable to pulverize them separately in order to reduce the composition deviation. The pulverization step (step S12) includes a coarse pulverization step (step S12-1) for pulverizing until the particle size becomes several hundred μm to several mm, and a fine pulverization step (for pulverizing until the particle size becomes about several μm (step S12-1). Step S12-2).

(Coarse grinding step: Step S12-1)
In the coarse pulverization step (step S12-1), the first alloy and the second alloy are coarsely pulverized until the particle diameter is about several hundred μm or more and several mm or less. Thereby, coarsely pulverized powders of the first alloy and the second alloy are obtained. In the coarse pulverization, the first alloy and the second alloy are coarsely pulverized by allowing the first alloy and the second alloy to absorb hydrogen and then releasing the hydrogen and performing dehydrogenation. The R-rich phase contained in the second alloy and the phase such as Dy ₂ Fe ₁₇ are easy to occlude and expand hydrogen, but the HR ₂ T ₁₄ B compound contained in the coarsely pulverized powder of the second alloy contains the R-rich phase and Unlike a phase such as Dy ₂ Fe ₁₇ , it hardly absorbs hydrogen and is a phase that hardly expands compared to a phase such as an R-rich phase or Dy ₂ Fe ₁₇ . When the second alloy contains the R ₂ T ₁₄ B compound, the volume expansion difference between the R-rich phase and the phase such as Dy ₂ Fe ₁₇ becomes large, so that the second alloy is likely to crack, The grindability of the alloy is improved and the productivity of the fine powder of the second alloy is improved.

  Further, when coarse pulverization is performed, a stamp mill, a jaw crusher, a brown mill, etc. may be used, and it may be performed in an inert gas atmosphere. However, in order to obtain the effects of the present invention sufficiently, Coarse grinding by hydrogen storage and release is desirable.

  In order to obtain high magnetic properties, it is preferable that the atmosphere of each step from the pulverization step (step S12) to the sintering step (step S15) be a low oxygen concentration. The oxygen content is adjusted by controlling the atmosphere in each manufacturing process, controlling the amount of oxygen contained in the raw material, and the like. When the oxygen content of the sintered body obtained in the sintering step (step S15) described later is 5000 ppm or less, the oxygen concentration in each step is 3000 ppm or less, and the oxygen content of the sintered body is 3000 ppm or less. In this case, the oxygen concentration in each step is preferably 100 ppm or less.

  After roughly pulverizing the first alloy and the second alloy, the process proceeds to the fine pulverization step (step S12-2).

(Fine grinding process: Step S12-2)
In the fine pulverization step (step S12-2), the coarsely pulverized powders of the first alloy and the second alloy are finely pulverized until the particle diameter becomes about several μm. Thus, finely pulverized powders of the first alloy and the second alloy are obtained. In the fine pulverization, a jet mill is mainly used, and the coarsely pulverized powders of the first alloy and the second alloy are pulverized until the average particle size becomes about several μm. A jet mill opens a high-pressure inert gas (for example, N ₂ gas) from a narrow nozzle to generate a high-speed gas flow, and the high-speed gas flow accelerates coarsely pulverized powders of the first alloy and the second alloy. In this method, the coarsely pulverized powders of the first alloy and the second alloy are collided with each other and collided with the target or the container wall.

  When the coarsely pulverized powders of the first alloy and the second alloy are finely pulverized, a finely pulverized powder with high orientation can be obtained at the time of molding by adding a grinding aid such as zinc stearate and oleic acid amide.

  After making the first alloy powder and the second alloy powder, the process proceeds to the mixing step (step S13).

<Mixing step: Step S13>
The mixing step (step S13) is a step of mixing the first alloy powder and the second alloy powder. In the mixing step (step S13), the first alloy powder and the second alloy powder are mixed in a low oxygen atmosphere. Thereby, mixed powder is obtained. The low oxygen atmosphere is formed as an inert gas atmosphere such as an N ₂ gas or Ar gas atmosphere. The mixing ratio of the first alloy powder and the second alloy powder is preferably 80:20 or more and 97: 3 or less in mass ratio, more preferably 90:10 or more and 97: 3 or less in mass ratio, and still more preferably. Is about 95 to 5 in mass ratio.

  Further, in the pulverization step (step S12), the mixing ratio when the first alloy and the second alloy are pulverized together is the same as in the case where the first alloy and the second alloy are separately pulverized. The mixing ratio of the second alloy powder is preferably 80 to 20 or more and 97 to 3 or less in terms of mass ratio, more preferably 90 to 10 or more and 97 to 3 or less in mass ratio, and even more preferably 95 in mass ratio. About five.

  After mixing the first alloy powder and the second alloy powder, the process proceeds to the forming step (step S14).

<Molding process: Step S14>
The forming step (step S14) is a step of forming the mixed powder. In the forming step (step S14), the mixed powder of the first alloy powder and the second alloy powder is filled in a mold held by an electromagnet and formed in a magnetic field with its crystal axis oriented by applying a magnetic field. . Thereby, a molded object is obtained. Since the obtained molded body is oriented in a specific direction, a rare earth sintered magnet having stronger magnetic anisotropy can be obtained. The magnetic field molding, in a magnetic field above 1.2Tesla, it is preferably performed from 0.7ton / cm ² at a pressure of 1.5 ton / cm ² before and after. The magnetic field to be applied is not limited to a static magnetic field, and may be a pulsed magnetic field. A static magnetic field and a pulsed magnetic field can also be used in combination.

  The molded body is formed into a desired predetermined shape by, for example, press molding. The shape of the molded body obtained by molding the mixed powder is not particularly limited. Depending on the shape of the mold to be used, the shape of the rare earth sintered magnet, for example, a flat plate shape, a column shape, a cross-sectional shape is a ring shape, etc. It can be changed accordingly.

  Further, when the mixed powder of the first alloy powder and the second alloy powder is formed into a predetermined shape, a formed body obtained by forming by applying a magnetic field may be oriented in a certain direction. Thereby, since the rare earth sintered magnet is oriented in a specific direction, an anisotropic rare earth sintered magnet having stronger magnetism can be obtained.

  After forming the mixed powder, the process proceeds to the sintering step (step S15).

<Sintering process: Step S15>
A sintering process (step S15) is a process of sintering a molded object. After shaping in a magnetic field, the resulting shaped body is sintered in a vacuum or an inert gas atmosphere. The sintering temperature needs to be adjusted according to various conditions such as composition, pulverization method, difference in particle size and particle size distribution, and for example, sintering is performed at 1000 ° C. to 1200 ° C. for 1 hour to 10 hours. Thereby, a sintered compact is obtained. After sintering the molded body, the process proceeds to an aging treatment step (step S16).

<Aging process: Step S16>
The aging treatment step (step S16) is a step of aging treatment of the sintered body. In the aging treatment step (step S16), after calcination, the sinter is subjected to aging treatment by, for example, holding the obtained sintered body at a temperature lower than that during firing. The aging treatment is, for example, two-stage heating in which the temperature is 700 ° C. to 900 ° C. for 1 hour to 3 hours, and further 500 ° C. to 700 ° C. for 1 hour to 3 hours, or the temperature near 600 ° C. The treatment conditions are appropriately adjusted according to the number of times of aging treatment such as one-step heating for 3 hours. Such an aging treatment can improve the magnetic properties of the sintered body.

<Cooling process: Step S17>
In the cooling step (step S17), after the aging treatment is performed on the sintered body, the sintered body is rapidly cooled while being pressurized with Ar gas. Thereby, the rare earth sintered magnet which concerns on this embodiment can be obtained. The cooling rate is not particularly limited, and is preferably 30 ° C./min or more. After cooling, polishing and chamfering are performed, the rare earth sintered magnet is cut into a desired size, and the surface is smoothed to obtain a rare earth sintered magnet having a predetermined shape. Further, the rare earth sintered magnet may be subjected to a surface treatment such as Ni plating on the surface of the rare earth sintered magnet to improve the corrosion resistance.

As described above, the obtained rare earth sintered magnet according to the present embodiment is manufactured using the second alloy containing the HR ₂ T ₁₄ B compound. When the second alloy contains the HR ₂ T ₁₄ B compound, when the second alloy occludes hydrogen, cracks occur in the second alloy by utilizing the difference in expansion between the phases contained in the second alloy. Therefore, the pulverizability of the second alloy is improved, and when the mixed powder with the first alloy is finely pulverized, a homogeneous second alloy powder with little composition deviation can be obtained. As a result, the rare earth sintered magnet according to the present embodiment can reduce the amount of deviation from the intended predetermined composition, and can improve the magnetic characteristics. Therefore, if the method for producing a rare earth sintered magnet according to the embodiment of the present invention is used, a rare earth sintered magnet having high magnetic properties can be produced more efficiently.

  The amount of C contained in the rare earth sintered magnet is adjusted by the type and amount of grinding aid used in the production process. Further, the amount of N contained in the rare earth sintered magnet is adjusted by the type and amount of the raw material alloy, the pulverizing conditions when the raw material alloy is pulverized in a nitrogen atmosphere, and the like.

  In the pulverization of the first alloy and the second alloy, hydrogen is occluded in the first alloy and the second alloy, and then the hydrogen is released and coarsely pulverized. However, this embodiment is limited to this. is not. For example, the first alloy powder and the second alloy powder may be obtained by pulverizing the first alloy and the second alloy by using a so-called hydrocracking and dehydrogenation recombination (HDDR) method. . In the HDDR method, a raw material (starting alloy) is heated in hydrogen to hydrogenate and decompose the raw material (HD), and then dehydrogenate and recombine (DR) to produce crystals. This is a method for making the size fine.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not restrict | limited to this. The present invention can be variously modified and variously combined without departing from the gist of the present invention, and can be similarly applied to components other than permanent magnets.

  The content of the present invention will be described in detail below using examples and comparative examples, but the present invention is not limited to the following examples.

<Example 1>
A first alloy and a second alloy having the composition shown in Table 1 were produced by the strip casting method, and blended in the mixing ratio shown in Table 1.

The mixed alloy consisting of the first alloy and the second alloy is subjected to hydrogen storage treatment at room temperature and then dehydrogenated in an inert gas atmosphere at 600 ° C. for 1 hour to coarsely pulverize the first alloy and the second alloy. did. In the process from coarse pulverization to sintering, the oxygen concentration was 4000 ppm or less. 0.1 wt% of oleic acid amide was added to the coarsely pulverized mixed alloy as a pulverization aid, and finely pulverized with a jet mill to obtain an alloy powder having an average particle size of about 4.0 μm. The obtained alloy powder was molded in a magnetic field with an applied magnetic field of 1.5 Tesla and a molding pressure of 1.2 ton / cm ² to obtain a molded body. The obtained molded body was fired by holding at 1030 ° C. for 4 hours in a vacuum to obtain a sintered body. Thereafter, the sintered body was subjected to an aging treatment in an inert gas atmosphere to perform a heat treatment. The aging treatment was performed in two stages. After holding at 850 ° C. for 1 hour, it was held at 540 ° C. for 2 hours. The cooling rate in the temperature lowering process (1040 to 800 ° C.) up to the first stage of the aging treatment after sintering in an inert gas atmosphere was 50 ° C./min. The cooling rate of the temperature lowering process (800 to 550 ° C.) from the first stage to the second stage of the aging treatment was set to 50 ° C./min. Thereby, a rare earth sintered magnet was obtained.

<Examples 2 to 4 and Comparative Examples 1 to 4>
Examples 2 to 4 and Comparative Examples 1 to 4 are the same as Example 1 except that the first alloy and the second alloy having different composition ratios of the first alloy and the second alloy used in Example 1 were used. In the same manner, a rare earth sintered magnet was obtained. Table 1 shows the composition ratio and blending ratio of the first alloy and the second alloy and the composition ratio of the rare earth sintered magnet.

[Crush recovery efficiency]
The input mass charged into the pulverizer and the discharge mass discharged after being pulverized by the pulverizer were calculated to determine the pulverization recovery efficiency.

[Amount of heavy rare earth element in alloy powder]
The composition of the alloy powder was measured using a fluorescent X-ray analyzer (XRF) before and after grinding. The amount of heavy rare earth element contained in the alloy powder was calculated from the analyzed composition result. From the measurement results, the compositional deviation of the composition of the heavy rare earth element contained in the alloy powder before and after grinding was calculated from the amount of the heavy rare earth element contained in the alloy powder before and after grinding.

[Magnetic properties]
As magnetic characteristics, residual magnetic flux density Br and coercive force HcJ were measured. The obtained rare earth sintered magnet was measured for magnetic properties using a BH tracer, and the average crystal grain size of the sintered body was determined. Table 3 shows the measurement results. The relationship between the measured coercive force HcJ and the residual magnetic flux density Br is shown in FIG.

[Average crystal grain size]
For the average crystal grain size, the area of each crystal grain was determined by image analysis from a polarizing microscope image of the cross section of the sintered body, and the average value of the equivalent circle diameter was used. Table 3 shows the measurement results.

  As shown in Table 2, in each of Examples 1 to 4, the pulverization recovery efficiency is 93.0% or more, and the deviation of the composition of heavy rare earth elements contained in the alloy powder before and after pulverization is 0.1 or less. Met. On the other hand, in Comparative Examples 1 to 4, the pulverization recovery efficiency was 90.0% or less, and the deviation of the composition of heavy rare earth elements contained in the mixed powder before and after pulverization was 0.10 or more. . Therefore, if the grain boundary phase alloy of the rare earth sintered magnet according to the present invention is used, the pulverization and recovery efficiency of heavy rare earth elements is hardly lowered, and the composition of the heavy rare earth elements contained in the mixed powder before and after pulverization is shifted. It was confirmed that the number was also reduced.

  Further, as shown in Table 3, in Examples 1 to 4, the residual magnetic flux density Br was 1310 mT or less, and the coercive force HcJ was 1860 kA / m or more. On the other hand, in Comparative Examples 1 to 4, the residual magnetic flux density Br was 1310 mT or more and the coercive force HcJ was almost 1830 kA / m or less. Therefore, it was confirmed that the magnetic properties can be improved as compared with the conventional case when the grain boundary phase alloy of the rare earth sintered magnet according to the present invention is used.

  Therefore, according to the rare earth sintered magnet according to the present embodiment, it has been found that the pulverization can be improved and the composition deviation of the alloy powder can be reduced, so that the magnetic characteristics can be improved.

  As described above, the method for producing a rare earth sintered magnet and the rare earth sintered magnet according to the present invention can be suitably used as a permanent magnet because it improves pulverizability and magnetic characteristics.

Claims (2)

R ₂ T ₁₄ B (R represents one or more rare earth elements, T represents one or more transition metal elements including Fe or Fe and Co, and B represents B or B and C). In manufacturing a rare earth sintered magnet having a phase and a grain boundary phase containing more R than the R ₂ T ₁₄ B compound,
The alloy powder of the first alloy containing the R ₂ T ₁₄ B compound and inevitable impurities, and the HR ₂ T ₁₄ B compound (HR represents one or more kinds of heavy rare earth elements), and the HR content is 25.0 mass % To 32.5% by mass and a mixture production step of mixing a second alloy alloy powder having a B content of 0.6% by mass to 1.4% by mass to obtain a mixture;
A molding step of molding the mixture to obtain a molded body,
Sintering the molded body to obtain a sintered body,
Including
Rare earth sintering characterized in that R contained in the main phase and the grain boundary phase has a composition of 25% by mass or more and less than 32.5% by mass, and B is 0.5% by mass or more and 1.5% by mass or less. Magnet manufacturing method. R ₂ T ₁₄ B (R represents one or more rare earth elements, T represents one or more transition metal elements including Fe or Fe and Co, and B represents B or B and C) and inevitable impurities And an HR ₂ T ₁₄ B compound (HR represents one or more heavy rare earth elements), and the HR content is 25.0% by mass or more and 32.5% by mass or less. Yes, obtained by mixing and sintering the alloy powder of the second alloy having a B content of 0.6 mass% or more and 1.4 mass% or less,
Comprises a main phase containing R ₂ T ₁₄ B compound, and a grain boundary phase containing a large amount of R than the R ₂ T ₁₄ B compound,
Rare earth sintering characterized in that R contained in the main phase and the grain boundary phase has a composition of 25% by mass or more and less than 32.5% by mass, and B is 0.5% by mass or more and 1.5% by mass or less. magnet.

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