Rare earth sintered magnet

Abstract

A rare-earth sintered magnet is provided, characterized in that it comprises R (R is one or more elements selected from rare earth elements, with Nd being essential), T (T is one or more elements selected from iron group elements, with Fe being essential), X (X is one or two elements selected from B and C, with B being essential), and M. 1 (M 1 The rare earth sintered magnet is selected from one or more of Al, Si, Cr, Mn, Cu, Zn, Ga, Ge, Mo, Sn, W, Pb, and Bi, with less than 0.1% O, less than 0.05% N, and less than 0.07% C, and has an average crystal grain size of less than 4.0 μm. Furthermore, when the orientation degree is set to Or [%] and the average crystal grain size is set to D [μm], it satisfies the relationship (1): 0.26×D+97≦Or≦0.26×D+99. Based on this rare earth sintered magnet, it is possible to obtain magnets with both high Br and high H content. cJ It has excellent magnetic properties.

Description

TECHNICAL FIELD

[0001] The present application relates to a rare earth sintered magnet having excellent magnetic properties with both high Br and high H cJ , and a manufacturing method thereof. BACKGROUND

[0002] The rare earth sintered magnet, as a functional material indispensable for energy saving and high functionality, has been expanding in the range of application and production volume year by year. Among the rare earth sintered magnets, in particular, the Nd-based sintered magnet (hereinafter referred to as "Nd magnet") has a high residual magnetic flux density (hereinafter referred to as "Br"), and is used for, for example, a drive motor for a hybrid vehicle, an electric vehicle, a motor for electric power steering, a motor for a compressor of an air conditioner, a voice coil motor (VCM) for a hard disk drive, and the like. Thus, in a variety of motors, the Nd magnet having a high Br is used, but, for example, in order to further downsize the motor, a higher Br is required for the Nd magnet.

[0003] On the other hand, at a high temperature, the coercive force (hereinafter referred to as "H cJ ") of the rare earth sintered magnet decreases, and thus irreversible thermal demagnetization occurs. Therefore, in particular, in the rare earth sintered magnet for a motor for an electric vehicle and the like, which is used for a vehicle, a high H cJ is required.

[0004] In the past, as a method of increasing the Br of the Nd magnet, there are a method in composition and a method in manufacturing process, and as the method in composition, there are known a method of reducing the content of R in order to increase the proportion of R2T 14 X phase in the Nd magnet, and a method of reducing the amount of an additive element that reduces the Br by being solid-solved in the R2T 14 X phase.

[0005] However, it is known that, by reducing the amount of R and other additive elements, the H cJ related to the heat resistance of the rare earth sintered magnet decreases. In particular, in the case of reducing the amount of R, in the sintering process of the Nd magnet in which densification is caused with the generation of a liquid phase, the sinterability thereof decreases, and there is also a risk that abnormal grain growth occurs. Therefore, in order to obtain a Nd magnet having higher properties, it is important to suppress the decrease in H cJ caused by reducing the amount of R and other additive elements, and to achieve a high Br. In this case, in order to suppress the decrease in H cJ or increase H cJ , it is generally known to add a heavy rare earth element such as Dy and Tb, but the decrease in Br caused by the addition thereof, and the fact that the heavy rare earth element such as Dy and Tb is also rare in resources and expensive, and thus this method is not necessarily preferable.

[0006] In addition, as the method in manufacturing process, there are known a method of increasing the proportion of R2T14 A method of increasing the amount of a lubricant (saturated fatty acid, ester thereof, etc.) added to a powder before molding, a method of adjusting the conditions by increasing the applied magnetic field during molding, etc., in order to increase the degree of orientation of the X phase.

[0007] However, it is known that in the case of increasing the amount of lubricant added to the powder before molding, although an increase in Br is obtained by an increase in the degree of orientation, in general, the Nd magnet obtained thereby has a large amount of C from the lubricant, and thus the H cJ decreases significantly. In addition, in order to increase the applied magnetic field during the X phase orientation, a large electromagnetic body for generating the magnetic field is required, and further, a large device is required, and the magnetic field space is reduced, and thus industrial efficiency cannot be achieved. 14

[0008] On the other hand, as a method of increasing the H cJ of an Nd magnet, a method of refining the crystal grain diameter is known. It is known that this is mainly a method of refining (refining) the crystal grain diameter after sintering by making the particle size of the micro powder fine when the raw alloy is micro-pulverized before molding, and within a certain particle diameter range, as the particle diameter is refined, the H cJ increases linearly.

[0009] However, in the case of performing refinement of a certain degree or more, the concentration of impurities (mainly oxygen and nitrogen) of the micro powder increases due to a decrease in the pulverization ability at the time of micro-pulverization, an increase in the reactivity of the micro powder, etc., and thus the H cJ of the Nd magnet decreases, or even if the H cJ increases, it is difficult to apply the grain boundary diffusion method described later. In order to improve this, a method of changing the pulverization gas at the time of micro-pulverization to an inert gas such as He or Ar has been proposed (Patent Document 1).

[0010] As another method of increasing the H cJ of an Nd magnet, a method of selectively aggregating a heavy rare earth element (Dy, Tb, etc.) in the grain boundary phase in the Nd magnet (hereinafter referred to as the “grain boundary diffusion method”) is known (Patent Documents 2 and 3). This method is a method of forming a structure in which the concentration of Dy and Tb is high only in a region close to the grain boundary of the main phase particles in the Nd magnet by performing heat treatment at a high temperature after a heavy rare earth element compound such as Dy or Tb is attached to the surface of the magnet by a coating method or the like, and thus a high H cJ increase effect can be obtained while suppressing a decrease in Br.

[0011] Prior Art Documents

[0012] Patent Documents

[0013] Patent Document 1: International Publication No. 2014 / 142137

[0014] ​Patent Literature 2: International Publication No. 2006 / 044348

[0015] Patent Literature 3: International Publication No. 2013 / 100010 SUMMARY

[0016] PROBLEMS TO BE SOLVED BY THE INVENTION

[0017] However, in the method described in Patent Literature 1, the grain boundary diffusion method described in Patent Literatures 1 and 2, and the like, the following problems exist.

[0018] That is, in the method in which the pulverizing gas at the time of the fine pulverization proposed in Patent Literature 1 is changed to an inert gas such as He or Ar, if the price difference from nitrogen gas is considered, industrial production is difficult. In addition, although the grain boundary diffusion method is very useful for high coercivity, in the case where the amount of an additive element, excess R, in the magnet is reduced in order to increase the Br of the Nd magnet, or in the case where the amount of an impurity element (carbon, oxygen, nitrogen) is increased due to the increase in the amount of a lubricant and the like, there is a problem that the H cJ increase effect is significantly reduced. In addition, since the H cJ increase effect amount is also limited, for applications requiring high heat resistance such as electric vehicles, it is necessary to increase the H cJ coercivity of the magnet raw material itself before the grain boundary diffusion method is performed.

[0019] The present application was completed in view of the above problems, and aims to provide a rare earth sintered magnet which realizes high Br and high H cJ by a method different from the implementation of the fine pulverization and the grain boundary diffusion at the time of the manufacture proposed in the past.

[0020] MEANS FOR SOLVING THE PROBLEMS

[0021] The present inventors conducted intensive studies focusing on the amount of impurities, the average crystal grain diameter, and the degree of orientation in the rare earth sintered magnet in order to achieve the above object, and as a result, found that in the case where the average crystal grain diameter of the rare earth sintered magnet is suppressed to 4.0 μm or less on the basis of reducing the amounts of O, N, and C, which are normally evaluated as impurities in the rare earth sintered magnet, and the degree of orientation satisfies a specific relationship with respect to the average crystal grain diameter, a rare earth sintered magnet having excellent magnetic properties with high Br and high H cJ is obtained, and completed the present application.

[0022] Therefore, the present application provides the following rare earth sintered magnet.

[0023] [1] A rare-earth sintered magnet comprising R (R is one or more elements selected from among rare-earth elements, with Nd being an essential element), T (T is one or more elements selected from among iron group elements, with Fe being an essential element), X (X is one or two elements selected from among B and C, with B being an essential element), M (M is one or more elements selected from among Al, Si, Cr, Mn, Cu, Zn, Ga, Ge, Mo, Sn, W, Pb, Bi) 1 (M 1 ) and containing 0.1 mass% or less of O, 0.05 mass% or less of N, and 0.07 mass% or less of C, wherein the average crystal grain diameter of the rare-earth sintered magnet is 4.0 μm or less, and, with respect to degree of orientation, when the degree of orientation is set as Or[%] and the average crystal grain diameter is set as D[μm], the following relational expression (1) is satisfied:

[0024] 0.26×D+97≦Or≦0.26×D+99···(1).

[0025] [2] The rare-earth sintered magnet according to [1], wherein, as a part of the R, an R element introduced to the sintered magnet after sintering by grain boundary diffusion is contained.

[0026] [3] The rare-earth sintered magnet according to [2], wherein the R element introduced by the grain boundary diffusion is one or more elements selected from among Dy, Tb, and Ho.

[0027] [4] The rare-earth sintered magnet according to any one of [1] to [3], wherein, when the atomic percentages of the R, T, and X are set as [R], [T], and [X] respectively, the following relational expression (2) is satisfied:

[0028] [T] / 14≦[X]≦[R] / 2···(2).

[0029] [5] The rare-earth sintered magnet according to any one of [1] to [3], further comprising M 2 (M 2 ) selected from among Ti, V, Zr, Nb, Hf, and Ta), wherein, when the atomic percentages of the R, T, X, and M 2 are set as [R], [T], [X], and [M 2 ] respectively, the following relational expression (3) is satisfied:

[0030] ([T] / 14)+([M 2 ]×2)≦[X]≦([R] / 2)+([M 2 ]×2)···(3).

[0031] [6] The rare-earth sintered magnet according to [5], wherein the M2 It is less than 0.5 atomic percent.

[0032] Rare earth sintered magnets of any one of [7][1] to [6], wherein R is 12.5 atomic% to 16.0 atomic%, M 1 It ranges from 0.1 atomic percent to 2.0 atomic percent.

[0033] Invention Effects

[0034] According to the rare earth sintered magnet of the present invention, by adjusting the O, N, C content, average grain size, and orientation degree in the rare earth sintered magnet to a specific range, and optimizing the relationship between the average grain size and orientation degree, it is possible to obtain a magnet with both high Br and high H. cJ It has excellent magnetic properties. Detailed Implementation

[0035] As described above, the rare earth sintered magnet of the present invention comprises R (R is one or more elements selected from rare earth elements, with Nd being essential), T (T is one or more elements selected from iron group elements, with Fe being essential), X (X is one or two elements selected from B and C, with B being essential), M 1 (M 1 It is composed of one or more elements selected from Al, Si, Cr, Mn, Cu, Zn, Ga, Ge, Mo, Sn, W, Pb, and Bi, and contains O, C, N, and unavoidable impurities.

[0036] As described above, R is selected from one or more rare earth elements, with Nd being essential. There is no particular limitation on the content of R, but from the viewpoint of suppressing the crystallization and precipitation of α-Fe in the dissolved alloy and promoting normal densification during sintering, it is preferably 12.5 atomic% or more, more preferably 13.0 atomic% or more. Furthermore, from the viewpoint of obtaining high Br content, it is preferably 16.0 atomic% or less, more preferably 15.5 atomic% or less.

[0037] There is no particular limitation on the proportion of Nd in R, but it is preferably 60 atomic% or more of all R elements, and more preferably 75 atomic% or more. In addition, there are no particular restrictions on the R elements other than Nd, and it is preferable to include Pr, Dy, Tb, Ho, Ce, Y, etc.

[0038] As mentioned above, T is selected from one or more elements of the iron group, namely Fe, Co, and Ni, with Fe being essential. The content of T is as described above for R, X, and M. 1 O, C, N and M (described later) 2The remaining portion, excluding the rare earth magnet, is preferably 70 atomic% or more and 80 atomic% or less. It should be noted that the Fe content is preferably 70 atomic% or more and 85 atomic% or less of the total rare earth magnet, more preferably 75 atomic% or more and 80 atomic% or less.

[0039] As described above, X is selected from one or two of B and C, with B being essential. From the viewpoint of sufficiently forming the main phase to ensure sufficient Br, the content of X is preferably 5.0 atomic% or more, more preferably 5.5 atomic% or more. Furthermore, considering the effect of Nd1Fe4X4 phase precipitation on Br when the X content is too high, it is preferably 8.0 atomic% or less, more preferably 7.0 atomic% or less.

[0040] Here, without particular restriction, the contents of the above R, T and X, when their atomic percentages are set as [R], [T] and [X] respectively, preferably satisfy the following relationship (2).

[0041] [T] / 14≦[X]≦[R] / 2···(2)

[0042] That is, from R2T 14 The effect of the decrease in the X ratio on Br and the formation of R2T 17 The phase brought about by H cJ From the perspective of the influence of [T], the content of X is preferably [T] / 14 or higher. Furthermore, considering R... 1.1 The formation of X-rich phases such as Fe4B4 phase leads to R2T 14 The effect of the change in the X ratio on Br is preferably [R] / 2 or less.

[0043] As described above, the aforementioned M 1 It consists of one or more elements selected from Al, Si, Cr, Mn, Cu, Zn, Ga, Ge, Mo, Sn, W, Pb, and Bi. From the viewpoint of ensuring a sufficiently wide range of optimal temperatures in heat treatments used to ensure good productivity, and thus suppressing H... cJ Starting from the perspective of reduction, M 1 The content of Br is preferably 0.1 atomic% or more, more preferably 0.3 atomic% or more, and even more preferably 0.5 atomic% or more. In addition, from the viewpoint of obtaining high Br, it is preferably 2.0 atomic% or less, and more preferably 1.5 atomic% or less.

[0044] The O content is 0.1% by mass or less, preferably 0.08% by mass or less. When the O content exceeds 0.1% by mass, the magnetic properties, especially H... cJ The content of N is reduced. Furthermore, the N content is 0.05% by mass or less, preferably 0.03% by mass or less. When the N content exceeds 0.05% by mass, H...cJ decrease. Further, the content of C, including the case where C is contained as a part of the above-mentioned X element, is 0.07 mass% or less, preferably 0.05 mass% or less. When the content of C exceeds 0.07 mass%, H cJ decrease. Note that in the present application, the smaller the contents of these O, N, and C are, the better, but generally, these elements are unavoidable elements that are difficult to completely eliminate.

[0045] Further, in the rare-earth sintered magnet of the present application, the average crystal grain diameter is made 4 μm or less, more preferably 3.5 μm or less. When the average crystal grain diameter exceeds 4 μm, it is difficult to obtain a high H cJ , the object of the present application cannot be achieved in some cases. Note that the measurement of the average crystal grain diameter can be performed, for example, by the following procedure. First, after polishing the cross section of the sintered magnet to be a mirror surface, the cross section is observed using a laser microscope after selectively etching the grain boundary phase by immersing in an etching solution such as Vilella etching solution (for example, a mixed solution of glycerin : nitric acid : hydrochloric acid = 3 : 1 : 2 in the mixing ratio) or the like. Next, based on the obtained observation image, the cross-sectional area of each particle is measured by image analysis, and the diameter of the equivalent circle is calculated. Then, based on the data of the area fraction occupied by each particle size, the average diameter is calculated. Note that the average diameter is preferably the average of a plurality of particles in images of a plurality of sites, and for example, although not particularly limited, the average diameter is preferably measured by a method of setting the average of a total of 2000 or more particles in images of 20 or more different sites, or the like.

[0046] Further, in the rare-earth sintered magnet of the present application, with respect to the degree of orientation, when the degree of orientation is set to Or [%] and the above-mentioned average crystal grain diameter is set to D [μm], it is adjusted so as to satisfy the following relational expression (1).

[0047] 0.26 x D + 97 ≦ Or ≦ 0.26 x D + 99... (1)

[0048] By satisfying such a relationship, a high Br and a high H cJ can be obtained. The reason for this is not necessarily clear, but it can be conjectured as follows. Generally, the refinement of the crystal grain diameter is performed by the refinement of the fine powder particle diameter before molding and sintering, but the finer the fine powder particle diameter is, the larger the surface area ratio of the fine powder is, and thus the frictional resistance between the fine powders increases, so the fine powders are difficult to orient during magnetic field molding. With respect to the amount of change, the experiments by the present inventors showed that the degree of orientation deteriorated by 0.26% with respect to the refinement of the crystal grain diameter to 1 μm with respect to a fine powder particle size of 4 μm or less. Further, it is known that a high Br cannot be achieved when the degree of orientation of the fine powder is low, and on the other hand, when the degree of orientation is too high, H cJdecrease. The present inventors have intensively studied them and found that when the degree of orientation is within the range of the above relational expression (1), high Br and high H cJ .

[0049] Here, the degree of orientation Or [ % ] is not particularly limited, and from the viewpoint of exploiting the potential of the starting material and obtaining good Br, it is preferably 96% or more, and further preferably 97% or more, and within the range satisfying the necessary conditions of the preferred degree of orientation and the above average crystal grain size of 4 μm or less, the above relational expression (1) is preferably satisfied. Note that the degree of orientation Or [ % ] can be measured by a known method such as electron beam backscattering diffraction (EBSD).

[0050] In the rare earth sintered magnet of the present application, as M 2 One or more elements selected from Ti, V, Zr, Nb, Hf, and Ta can be contained. By containing this M 2 , abnormal grain growth of the crystal grains during sintering can be suppressed, and an effect of preventing a decrease in Br can be obtained. This M 2 is not particularly limited, and is preferably 0.5 atomic% or less, more preferably 0.3 atomic% or less, and further preferably 0.2 atomic% or less. If the content of M 2 exceeds 0.5 atomic%, M 2 elements sometimes form M 2 phases, which decrease the ratio of R2T 14 phases, thereby causing a decrease in Br.

[0051] In the case where this M 2 element is contained, it is not particularly limited, and regarding the content of the above R, T, X, and this M 2 , in the case where these atomic percentages are respectively set to [R], [T], [X], and [M 2 ], the following relational expression (3) is preferably satisfied.

[0052] ([T] / 14) + ([M 2 ] x 2) ≦ [X] ≦ ([R] / 2) + ([M 2 ] x 2)...(3)

[0053] That is, from the viewpoint of the effect of the decrease in the ratio of R2T 14 phases on Br and the effect of the formation of R2T 17 phases on H cJ , the content of X when M 2 is contained is preferably ([T] / 14) + ([M 2 ] x 2) or more, and in consideration of the R 1.1R2T 14 The change in the ratio of the X phase has an effect on Br, and is preferably ([R] / 2) + ([M 2 ] x 2) or less.

[0054] The rare-earth sintered magnet of the present application, in addition to the above-mentioned elements, sometimes contains H, F, Mg, P, S, Cl, Ca, and the like as unavoidable impurities. In this case, the content of these unavoidable impurities is allowed to be 0.1 mass% or less as the total of the unavoidable impurities with respect to the total of the above-mentioned constituent elements of the magnet and the unavoidable impurities, but it is preferable that the content of these unavoidable impurities be small.

[0055] Next, a method for manufacturing the rare-earth sintered magnet of the present application will be described.

[0056] The process for manufacturing the rare-earth sintered magnet of the present application is basically the same as the general powder metallurgy method, and is not particularly limited, and generally includes: a melting process of melting raw materials so as to obtain a raw alloy having a prescribed composition; a pulverization process of pulverizing the raw alloy so as to prepare alloy fine powder; a molding process of performing powder molding on the alloy fine powder in a magnetic field application to obtain a molded body; and a heat treatment process of performing heat treatment on the molded body to obtain a sintered body.

[0057] First, in the melting process, a metal or an alloy that becomes a raw material of each element is weighed so as to become a prescribed composition. After being weighed to the prescribed composition, the raw materials are melted, for example, by high-frequency melting, and are cooled to manufacture a raw alloy. The casting of the raw alloy is generally performed by a melting casting method in which it is cast into a flat mold or a book mold, or a thin strip continuous casting method. In addition, the present application can also be applied to a so-called two-alloy method in which an alloy close to the composition of the R2Fe 14 B compound as a main phase and an R-rich alloy that becomes a liquid phase aid at the sintering temperature are weighed and mixed after being coarsely pulverized. However, the alloy close to the main phase composition easily crystallizes an α-Fe phase depending on the cooling speed at the time of casting and the alloy composition, and thus, in order to homogenize the structure and eliminate the α-Fe phase, it is preferable to perform a homogenization treatment at 700 to 1200°C for one hour or more in a vacuum or an Ar atmosphere as necessary. It should be noted that, in the case where the alloy close to the main phase composition is manufactured using a thin strip continuous casting method, the homogenization can also be omitted. As for the R-rich alloy that becomes a liquid phase aid, in addition to the above-mentioned casting method, a so-called liquid quenching method can also be applied.

[0058] The pulverization process can be, for example, a process including a coarse pulverization process and a fine pulverization process. In the coarse pulverization process, for example, a jaw crusher, a Brown pulverizer, a pin mill, or hydrogen pulverization can be used. In this case, in the present application, hydrogen pulverization is preferably used from the viewpoint of achieving a reduction in the amounts of O, N, and C and obtaining excellent magnetic properties. In particular, in the case where the alloy is produced by thin strip casting, hydrogen pulverization is preferably used, and coarse powder of 0.05 mm to 3 mm, particularly 0.05 mm to 1.5 mm, can generally be obtained.

[0059] In the above fine pulverization process, a method of pulverizing the coarse powder using, for example, a jet mill using a non-oxidizing gas such as N2, He, Ar, or the like can be used. In the present application, in the fine pulverization process, the coarse powder is fine pulverized to preferably 0.2 μm to 15 μm, more preferably 0.5 μm to 10 μm. O and N of the rare earth sintered magnet are mainly mixed in the fine pulverization process, and thus, in order to adjust the contents of O and N in the rare earth sintered magnet, the atmosphere of the jet mill needs to be controlled. The adjustment of the O content in the rare earth sintered magnet is performed by controlling the amount of O and the dew point in the atmosphere of the jet mill, and the amount of O in the atmosphere at the time of pulverization is preferably 1 ppm or less, and the dew point is preferably -60°C or lower.

[0060] In addition, the N content in the rare earth sintered magnet can be adjusted, for example, by (A) a method of fine pulverization using a jet mill using He or Ar gas, (B) a method of fine pulverization in which hydrogen is introduced in a jet mill using N2 gas, or (C) a method of fine pulverization using a jet mill using N2 gas containing hydrogen. In this case, in the methods of (B) or (C), by introducing hydrogen or using coarse powder containing hydrogen, hydrogen is preferentially adsorbed to the active surface generated by pulverization, and the adsorption of nitrogen is hindered, and thus, the amount of N in the rare earth sintered magnet can be reduced.

[0061] Here, in the process of one or both of the coarse pulverization and the fine pulverization of the raw material alloy, in order to improve the orientation of the powder in the molding in a magnetic field as the next process, for example, a lubricant composed of a saturated fatty acid or an ester thereof can be appropriately added. At this time, generally, increasing the amount of the lubricant added is effective for improving the orientation, but C from the lubricant forms a large amount of R-CON phase in the rare earth sintered magnet, and thus, H cJSignificant reduction in the dilemma. Therefore, in the case where an increase in orientation is desired, it is preferable to use a lubricant extender of a micro powder obtained by micronizing a coarse powder containing hydrogen using the method of (C) described above. It is considered that in a rare earth sintered magnet produced from this micro powder, at the time of heat treatment, when hydrogen contained in the interior is released, by this hydrogen, the lubricant chemisorbed to the surface of the micro powder is decomposed by a carbonyl reduction reaction or the like, and further decomposed into a lower alcohol having high volatility by a cleavage reaction based on hydrogen gas, and by the action of dissociation, the C content remaining in the rare earth sintered magnet can be reduced.

[0062] In the above molding step, a magnetic field of 400 to 1600 kA / m is applied while the alloy powder is oriented in the direction of the easy magnetization axis, and the powder is compacted using a compression molding machine. At this time, the molded body density is preferably 2.8 to 4.2 g / cm 3 . That is, from the viewpoint of ensuring the strength of the molded body and obtaining good workability, the molded body density is preferably 2.8 g / cm 3 or more, and 4.2 g / cm 3 or less. Above all, in order to improve the strength of the molded body after molding, a binder such as PVA or a fatty acid can also be added. On the other hand, from the viewpoint of obtaining sufficient molded body strength while suppressing the disordering of the orientation of the particles at the time of pressing and obtaining a preferable Br, the molded body density is preferably 4.2 g / cm 3 or less. Above all, in order to suppress oxidation of the alloy micro powder, it is preferable to perform molding in a non-oxidizing gas atmosphere such as nitrogen or Ar gas.

[0063] In the above heat treatment step, the molded body obtained in the molding step is sintered in a non-oxidizing gas atmosphere such as Ar gas or in a high vacuum. In the case where a coarse powder containing hydrogen is used by the method of (C) described above, in order to suppress the decrease in the temperature of the molded body accompanying the release of hydrogen gas (endothermic reaction) in the molded body, and the generation of cracks due to the temperature difference, it is preferable to perform baking after holding at 200 to 600°C for 5 minutes to 10 hours in a non-oxidizing gas atmosphere or a low vacuum gas atmosphere. The sintering is generally preferably performed by holding at a temperature in the range of 950°C to 1200°C for 0.5 to 10 hours. Subsequently, in order to improve the H cJ , the obtained sintered body can be subjected to heat treatment at a temperature lower than the sintering temperature. As for the heat treatment after sintering, two-stage heat treatment of high-temperature heat treatment and low-temperature heat treatment can be performed, or only low-temperature heat treatment can be performed. As for the high-temperature heat treatment, it is preferable to perform heat treatment on the sintered body at a temperature of 600 to 950°C, and as for the low-temperature heat treatment, it is preferable to perform heat treatment at a temperature of 400 to 600°C.

[0064] Thus, the rare-earth sintered magnet of the present application can be obtained. The average crystal grain size of the rare-earth sintered magnet can be easily measured by observation with a laser microscope, as described above. Specifically, for example, after polishing and mirror finishing the magnet, the surface can be etched with an etching solution such as Nital etching solution or Vilella etching solution, and the average crystal grain size can be determined from the reflected electron image of the surface by image analysis. In addition, as described above, the degree of orientation of the obtained rare-earth sintered magnet can be measured by electron beam backscattering diffraction (EBSD).

[0065] In addition, after the obtained rare-earth sintered magnet is polished to a prescribed shape, a so-called grain boundary diffusion treatment can be performed, that is, heat treatment is performed in the presence of a diffusion source of one or two or more of oxides of R 1 , fluorides of R 2 , oxyfluorides of R 3 , hydroxides of R 4 , carbonates of R 5 , alkaline carbonates of R 6 , elemental metals or alloys of R 7 (R 1 to R 7 are one or more selected from rare-earth elements) on the surface of the above-described rare-earth sintered magnet. The method of fixing the above-described diffusion source to the surface of the magnet can employ dip coating in which the sintered magnet is dipped in a slurry containing the diffusion source in powder form, thereby applying the slurry and drying, screen printing, or dry film formation methods such as sputtering, PLD, and the like. The temperature of the grain boundary diffusion heat treatment is lower than the sintering temperature, and is preferably 700°C or higher. The time is not particularly limited, and is preferably 5 minutes to 80 hours, and more preferably 10 minutes to 50 hours, from the viewpoint of obtaining a good microstructure and magnetic properties of the sintered magnet. By the grain boundary diffusion treatment, the above-described R 1 to R 7 contained in the powder are diffused into the magnet, and further increase of H cJ can be achieved. Note that the rare-earth elements introduced by the grain boundary diffusion are R 1 to R 7 as described above for the sake of convenience of explanation, but are included in the above-described R components in the rare-earth sintered magnet of the present application after the grain boundary diffusion. In addition, although not particularly limited, as the above-described diffusion source containing R 1 to R 7 , a metal, compound, or intermetallic compound containing HR (HR is one or more selected from Dy, Tb, and Ho) is preferably used, and thus further increase of H cJ can be more effectively achieved.

[0066] It should be noted that the rare earth sintered magnet of the present application can satisfy the above-mentioned element composition and the above-mentioned relational expression (1), and it is preferable to further satisfy the above-mentioned relational expression (2) or (3), and as the above-mentioned R element, it is not necessarily required to contain R introduced by the above-mentioned grain boundary diffusion, but since a more excellent H CJ , the present application can more excellently achieve the object of giving consideration to both high Br and high H CJ , and thus it is preferable to contain R introduced by the above-mentioned grain boundary diffusion. In this case, the above-mentioned R 1 ~ R 7 , and it is known that the R concentration shows a characteristic concentration distribution in the thus obtained magnet. Specifically, it is known that the concentration (RE) of the above-mentioned R element at the surface of the magnet to which the diffusion source is given and the concentration (RC) of the above-mentioned R at the center portion of the magnet are in the relationship of RE > RC.

[0067] Examples

[0068] Hereinafter, examples, comparative examples will be shown, and the present application will be more specifically described, but the present application is not limited to the following examples.

[0069] [Examples 1 to 3]

[0070] Nd metal, Pr metal, Dy metal, boron-iron alloy, electrolytic Co, Al metal, Cu metal, Ga metal, Si metal, zirconium metal, and electrolytic iron (all of the metals are 99% or more in purity) were weighed and mixed so as to become a prescribed ratio, melted, and cast by a thin strip continuous casting method to obtain a thin sheet-shaped raw material alloy having a thickness of 0.2 to 0.4 mm. The obtained thin sheet-shaped raw material alloy was hydrogen embrittled under a hydrogen pressurized atmosphere, whereby a coarse pulverized powder was obtained. Next, after stearic acid as a lubricant was added and mixed in the obtained coarse pulverized powder at a ratio of 100 mass% of the coarse pulverized powder as shown in Table 1, a jet mill (jet mill device) was used to perform dry pulverization in a nitrogen stream, whereby a micro-pulverized powder (alloy powder) having a pulverization particle diameter (D 50 ) shown in Table 1 was obtained. It should be noted that the pulverization particle diameter (D 50 ) is a volume-based median particle diameter obtained by a laser diffraction method using an air flow dispersion method.

[0071] The micro-pulverized powder was filled into a mold of a molding device in a non-active gas atmosphere, and orientation was performed in a magnetic field of 15 kOe (1.19 MA / m), and at the same time, press molding was performed in a direction perpendicular to the magnetic field. The molding density at this time was 3.0 to 4.0 g / cm 3The obtained molded body was kept at 600°C for 2 hours under an Ar atmosphere, and then sintered at 1040°C or higher and 1080°C or lower (for each sample, a temperature at which sufficient densification due to sintering occurred was selected) for 5 hours in a vacuum, to obtain a Nd magnet raw material. The density of the obtained Nd magnet raw material was 7.5 g / cm3 3 The above.

[0072] For the sintered magnet structure, observation with a laser microscope was performed, and the average crystal grain size was measured. In addition, the degree of orientation of the crystal structure in the magnet was measured by EBSD measurement. The results are shown in Table 1. In addition, for the obtained Nd magnet raw material, metal component analysis was performed using high-frequency inductively coupled plasma emission spectrometry (ICP-OES), and oxygen, carbon, and nitrogen analysis was performed by infrared absorption gas analysis. The results are shown in Table 2. Note that the values described in Table 2 are mass%. In addition, the Nd magnet raw material was processed into a cuboid shape having dimensions of 15 mm x 7 mm x 12 mm, and a sample was prepared, and Br, H cJ The results are shown in Table 3.

[0073] After the Nd magnet raw material was processed into a cuboid shape having dimensions of 20 mm x 20 mm x 2.2 mm, the Nd magnet raw material was immersed in a slurry of terbium oxide particles having an average particle diameter of 0.5 μm mixed with ethanol at a mass fraction of 50%, the slurry was coated, and dried, to form a coating film of terbium oxide on the surface of the Nd magnet raw material. Next, the Nd magnet raw material on which the coating film was formed was heated at 950°C for 5 hours in a vacuum, and high-temperature heat treatment was performed in which cooling was performed at a cooling rate of 20°C / min to 200°C, to diffuse terbium grain boundaries. Next, low-temperature heat treatment was performed in which heating was performed at 450°C for 2 hours, and cooling was performed at a cooling rate of 20°C / min to 200°C, to obtain a Nd sintered magnet. The center portion of the obtained Nd sintered magnet was cut into a cuboid shape having dimensions of 6 mm x 6 mm x 2 mm, and H cJ The results are shown in Table 3. Note that in Table 3, elements that satisfy the prescribed elements of the present application are indicated as O, and elements that do not satisfy the prescribed elements are indicated as X.

[0074] [Comparative Example 1]

[0075] A flaky raw alloy was produced in the same manner as in Example 1. After the alloy was hydrogen embrittled under a hydrogen pressurized atmosphere, dehydrogenation treatment of the alloy was performed by heating treatment at 400°C for 4 hours. The obtained coarse crushed powder was subjected to the same steps as in Example 1, that is, pulverization, molding, sintering, and diffusion treatment, and the pulverized particle diameter, crystal grain size, degree of orientation, composition, Br and H cJ before grain boundary diffusion treatment, and H after grain boundary diffusion treatment were measured in the same manner as in Example 1.cJ The results are shown in Tables 1 to 3.

[0076] [Comparative Examples 2, 3]

[0077] The magnets were produced in the same manner as in Example 1. At this time, the addition amount of the lubricant (stearic acid) and the pulverization particle diameter were changed as shown in Table 1. In the same manner as in Example 1, the pulverization particle diameter, the crystal grain diameter, the degree of orientation, the composition, Br and H cJ before the grain boundary diffusion treatment, and H cJ after the grain boundary diffusion treatment were measured. The results are shown in Tables 1 to 3.

[0078] [Table 1]

[0079]

[0080] [Table 2]

[0081] Nd Pr Fe Co Cu Al Zr Si Ga B O N C Example 1 24.1 6.5 66.3 0.5 0.2 0.1 0.2 0.1 0.8 1 0.08 0.02 0.05 Example 2 24.2 6.5 66.2 0.5 0.2 0.1 0.2 0.1 0.8 1 0.08 0.03 0.05 Example 3 24.3 6.5 66.1 0.5 0.2 0.1 0.2 0.1 0.8 1 0.08 0.03 0.05 Comparative Example 1 24.1 6.5 66.3 0.5 0.2 0.1 0.2 0.1 0.8 1 0.15 0.06 0.13 Comparative Example 2 24.3 6.6 66.1 0.5 0.2 0.1 0.2 0.1 0.8 1 0.06 0.04 0.03 Comparative Example 3 24.3 6.6 66.1 0.5 0.2 0.1 0.2 0.1 0.8 1 0.06 0.03 0.04

[0082] (wt%)

[0083] [Table 3]

[0084]

[0085] As shown in Table 3, the magnets of Examples 1 to 3, which satisfy the conditions of the content of oxygen, nitrogen and carbon and the above-described relational expression (1) of the present application, all obtained high Br, H cJ , H cJ after the grain boundary diffusion. On the other hand, as shown in Table 2, the magnet of Comparative Example 1 had a high content of oxygen, nitrogen and carbon, and thus had a small H cJ after sintering, and in addition, the H cJ increasing effect by the grain boundary diffusion treatment was also small, and a sufficient H cJ coercive force was not obtained. In addition, the magnet of Comparative Example 2 did not satisfy the above-described relational expression (1), and the addition amount of the lubricant was small, and thus the degree of orientation of the magnet was low, and a sufficient Br was not obtained. Furthermore, the magnet of Comparative Example 3 had a large crystal grain diameter, and the H cJ of the magnet before the grain boundary diffusion treatment was low, and thus although the H cJ increasing effect by the grain boundary diffusion treatment was large, the H cJ was poor compared to Examples 1 to 3.

[0086] As described above, the H cJ of the rare earth sintered magnet related to the present application obtained in Examples 1 to 3 after the grain boundary diffusion exceeded 27 kOe, and could be used for uses requiring high heat resistance such as electric automobiles and the like. In addition, a characteristic in which the Br also exceeded 13.7 kG was obtained, and miniaturization of, for example, a motor and the like could be achieved.

Claims

1. Rare earth sintered magnets contain R, T, X, and M elements. 1 Rare earth sintered magnets, wherein R is one or more elements selected from rare earth elements, with Nd as an essential element; T is one or more elements selected from iron group elements, with Fe as an essential element; X is one or two elements selected from B and C, with B as an essential element; M 1 The element is selected from one or more elements chosen from Al, Si, Cr, Mn, Cu, Zn, Ga, Ge, Mo, Sn, W, Pb, and Bi, characterized in that... Containing less than 0.1% by mass of O, less than 0.05% by mass of N, and less than 0.07% by mass of C, the average crystal grain size of this rare earth sintered magnet is more than 2.8 μm and less than 3.6 μm, and, for the degree of orientation, when the degree of orientation is set to Or [%] and the average crystal grain size is set to D [μm], the following relationship (1) is satisfied: 0.26×D+97≤Or≤0.26×D+99 ···(1) When the atomic percentages of R, T, and X are set as [R], [T], and [X] respectively, the following relationship (2) is satisfied: [T] / 14≤[X]≤[R] / 2···(2).

2. The rare earth sintered magnet according to claim 1, wherein, As part of R, it includes R elements introduced into the sintered magnet through grain boundary diffusion.

3. The rare earth sintered magnet according to claim 2, wherein, The R element introduced through grain boundary diffusion is selected from one or more elements selected from Dy, Tb and Ho.

4. The rare earth sintered magnet according to any one of claims 1 to 3, wherein, It also contains M 2 M 2 The elements are selected from one or more of Ti, V, Zr, Nb, Hf, and Ta, and the R, T, X, and M are... 2 The atomic percentages are set as [R], [T], [X], [M], respectively. 2 In the case of ], the following relation (3) is satisfied: ([T] / 14)+([M 2 ]×2)≤[X]≤([R] / 2)+([M 2 ]×2) ···(3)。 5. The rare earth sintered magnet according to claim 4, wherein, The M 2 It is less than 0.5% atomic percentage.

6. The rare earth sintered magnet according to any one of claims 1 to 3, wherein, R is 12.5 atomic% to 16.0 atomic%, M 1 It ranges from 0.1 atomic% to 2.0 atomic%.

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