R-T-B series permanent magnet

Abstract

[Problem] To obtain an R-T-B based permanent magnet with improved magnetic characteristics, particularly residual magnetic flux density Br and coercive force Hcj. [Solution] An R-T-B based permanent magnet comprising R2T14B main phase crystal grains and a grain boundary. R represents one or more rare earth elements, T represents one or more iron group elements essentially including Fe or Fe and Co, and B represents boron. In a cross-section parallel to the alignment direction of the R-T-B based permanent magnet, the coverage of the R2T14B main phase crystal grains is 50.0% or more, and the area ratio of the R2T14B main phase crystal grains is 92.0% or more.

Description

Technical Field

[0001] The present invention relates to an R-T-B based permanent magnet.

Background Art

[0002] R-T-B based permanent magnets are known to have excellent magnetic properties. And the development of R-T-B based permanent magnets with further improved magnetic properties has been carried out.

[0003] Patent Document 1 describes a method for manufacturing an R-T-B based sintered magnet in which a heavy rare earth element RH is diffused.

[0004] Patent Document 2 describes a rare earth sintered magnet produced through processes such as laminating and processing a composite material of magnet particles and a binder after forming the composite material into a sheet.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the R-T-B based sintered magnet described in Patent Document 1 does not have a sufficiently high residual magnetic flux density. Also, when actually manufacturing the rare earth sintered magnet described in Patent Document 2, the temperature characteristics are not sufficient. Furthermore, the manufacturing process is complicated and the productivity is low.

[0007] Currently, there is a demand for providing an R-T-B based permanent magnet that has high magnetic properties both at room temperature and at high temperature and also has excellent temperature characteristics.

[0008] An object of the present invention is to provide an R-T-B-based permanent magnet having a high coercive force Hcj and a residual magnetic flux density Br at room temperature, and excellent coercive force Hcj and temperature characteristics at high temperatures.

Means for Solving the Problems

[0009] In order to achieve the above object, the R-T-B-based permanent magnet of the present invention is an R-T-B-based permanent magnet including R2T 14 main phase crystal particles and grain boundaries, wherein R is one or more rare earth elements, T is Fe or one or more iron group elements including Fe and Co as essential elements, and B is boron, in a cross section parallel to the orientation direction of the R-T-B-based permanent magnet, the coverage rate of the R2T 14 main phase crystal particles is 50.0% or more, and the area ratio of the R2T 14 main phase crystal particles is 92.0% or more.

[0010] Due to having the above characteristics, the R-T-B-based permanent magnet according to the present invention becomes an R-T-B-based permanent magnet having excellent magnetic properties in a wide temperature range.

[0011] The R-T-B-based permanent magnet may further contain C, and the content of C in the R-T-B-based permanent magnet may be 500 ppm or less.

[0012] The R-T-B-based permanent magnet may further contain O, and the content of O in the R-T-B-based permanent magnet may be less than 900 ppm.

[0013] The residual magnetic flux density of the R-T-B-based permanent magnet may be 14.0 kG or more.

[0014] The content of R in the R-T-B-based permanent magnet may be 27.5 mass% or more and 31.5 mass% or less.

Brief Description of the Drawings

[0015]

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Mode for Carrying Out the Invention

[0016] Hereinafter, the present invention will be described based on specific embodiments.

[0017] <R-T-B-based permanent magnet> The R-T-B-based permanent magnet according to this embodiment includes R2T 14 B main-phase crystal particles and grain boundaries.

[0018] R2T 14 The B main-phase crystal particles are main-phase particles composed of R2T 14 B crystals. And in a cross-section parallel to the orientation direction of the R-T-B-based permanent magnet, the area ratio of the R2T 14 B main-phase crystal particles in the R-T-B-based permanent magnet is 92.0% or more. Details of the calculation method of the area ratio will be described later.

[0019] The grain boundaries of the R-T-B-based permanent magnet according to this embodiment can be distinguished into two-particle grain boundaries existing between two main-phase crystal particles and grain boundary triple points existing between three or more main-phase crystal particles.

[0020] The R-T-B-based permanent magnet according to this embodiment has a coverage rate of R2T 14 B main-phase crystal particles of 50.0% or more in a cross-section parallel to the orientation direction of the R-T-B-based permanent magnet.

[0021] The R-T-B-based permanent magnet according to this embodiment has an area ratio of R2T 14 B main-phase crystal particles of 92.0% or more, and the coverage rate of R2T 14 B main-phase crystal particles of 50.0% or more, so that the volume ratio of R2T 14 B main-phase crystal particles in the R-T-B-based permanent magnet is large, and the R-T-B-based permanent magnet is likely to have thick two-particle grain boundaries. As a result, the absolute value of the temperature coefficient β of the coercive force of the R-T-B-based permanent magnet is likely to be small, the temperature characteristics of the coercive force are excellent, and an R-T-B-based permanent magnet with a high residual magnetic flux density can be obtained.

[0022] Note that β is calculated as β = (ΔHcj / Hcj(T1)) / ΔT, where the reference temperature is T1, the measurement temperature is T2, T2 - T1 is ΔT, Hcj at temperature T1 is Hcj(T1), Hcj at temperature T2 is Hcj(T2), and Hcj(T2) - Hcj(T1) = ΔHcj.

[0023] In particular, a large area ratio of R2T 14 B main-phase crystal particles tends to increase the residual magnetic flux density, and a high coverage rate of R2T 14 B main-phase crystal particles and thick two-particle grain boundaries tend to improve the temperature characteristics of the coercive force.

[0024] R2T 14 B main-phase crystal particles have a thermal expansion coefficient in the easy magnetization axis direction smaller than that in the hard magnetization axis direction. Therefore, at high temperatures, R2T 14 B main-phase crystal particles tend to thermally expand in the hard magnetization axis direction. And R2T 14The strain of the crystal lattice of the B main-phase crystal particles tends to increase. As a result, the anisotropic magnetic field decreases and the coercivity decreases at high temperatures compared to low temperatures. When the above coating rate is high and the two-particle grain boundary is thick, the strain of the above crystal lattice is likely to be relaxed. As a result, the decrease in the anisotropic magnetic field is suppressed, and the temperature characteristics of the coercivity are likely to be improved.

[0025] There is no particular limitation on the average thickness of the two-particle grain boundary, but it may be 5 nm or more and 50 nm or less, or may be 6 nm or more and 21 nm or less.

[0026] R is one or more rare earth elements, T is Fe or one or more iron group elements including Fe and Co as essential elements, and B is boron. The rare earth elements included as R refer to Sc, Y, and lanthanoid elements belonging to Group 3 of the long-period type periodic table. The rare earth element R is classified into a heavy rare earth element RH and a light rare earth element RL. RH refers to Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. RL refers to rare earth elements other than RH. The iron group elements refer to Fe, Co, Ni.

[0027] Furthermore, the content of C in the R-T-B-based permanent magnet according to this embodiment may be 500 ppm or less. When the content of C is 500 ppm or less, the formation of the rare earth carbide phase at the grain boundary triple point is suppressed. And the two-particle grain boundary tends to become thick and the coating rate tends to be high. As a result, the temperature characteristics of the R-T-B-based permanent magnet are likely to be improved. There is no particular lower limit on the content of C in the R-T-B-based permanent magnet according to this embodiment. For example, it may be 50 ppm or more, or may be 80 ppm or more.

[0028] Furthermore, the content of O in the R-T-B based permanent magnet according to this embodiment may be less than 900 ppm. When the content of O is less than 900 ppm, the formation of the rare earth oxide phase at the grain boundary triple points is suppressed. Then, the two-particle grain boundary tends to become thick, and the coverage rate tends to become high. As a result, the temperature characteristics of the R-T-B based permanent magnet tend to be improved. Also, the rare earth oxide phase does not contribute to the improvement of the coercive force Hcj at all. Therefore, the higher the content of O, the more likely Hcj is to decrease. Note that there is no particular lower limit for the content of O. For example, it may be 200 ppm or more.

[0029] The R-T-B based permanent magnet according to this embodiment is R2T 14 There may be a case where an R-OCN phase is included in the grain boundary other than the R2T 14 B main phase crystal particles. The R-OCN phase is a phase in which the content of R, the content of O, the content of C, and the content of N are all higher than the content of each element in the R2T

[0030] B main phase crystal particles. And, in the R-T-B based permanent magnet according to this embodiment, the volume ratio of the R-OCN phase to the grain boundary may be 34.0% or less, may be 31.5% or less, or may be 29.9% or less. Also, the R-T-B based permanent magnet may not contain the R-OCN phase, but the volume ratio of the R-OCN phase may be 18.4% or more. 14 The R-OCN phase has a high melting point and is difficult to melt even during sintering. Therefore, especially when the area ratio of the R2T 14 B main phase crystal particles is large, the presence of the R-OCN phase suppresses the grain growth of the R2T 14 B main phase crystal particles, and the shape of the R2T 14 B main phase crystal particles becomes distorted. As a result, the two-particle grain boundary tends not to have a smooth shape. However, by reducing the volume ratio of the R-OCN phase, it becomes difficult to suppress the grain growth of the R2T 14 B main phase crystal particles, and the two-particle grain boundary tends to have a smooth shape. As a result, the generation of reverse magnetic domains can be suppressed, and even when the area ratio of the R2T

[0031] The R-T-B-based permanent magnet according to this embodiment is R2T 14 phase may be included in the grain boundaries other than the R2T 14 B main-phase crystal particles. The higher the content of O in the R-T-B-based permanent magnet, the easier it is for R other than the R2T 14 B main-phase crystal particles to combine with O, the easier it is for the R2O3 phase to be included, and the less likely it is for the R-OCN phase to be included. When the R-OCN phase decreases, the two-particle grain boundary tends to have a smooth shape, and the occurrence of reverse magnetic domains becomes less likely. However, when the R-OCN phase is small and the R2O3 phase is large, due to the remaining C caused by the decrease in the R-OCN phase, R2T 14 part of B in the B main-phase crystal particles is replaced by C. As a result, the temperature characteristics tend to deteriorate. Also, when the R2O3 phase increases, R2T

[0032] The R-T-B-based permanent magnet according to this embodiment is R2T 14 phase may be included in the grain boundaries other than the R2T 14 B main-phase crystal particles, in addition to the above-mentioned R-OCN phase and R2O3 phase, an R-rich phase may be included. Note that the R-rich phase in this embodiment has an R content higher than that in the R2T 14 B main-phase crystal particles and an O content less than that in the R2T

[0033] Hereinafter, the method for calculating the area ratio of the R2T 14 B main-phase crystal particles and the method for calculating the volume ratio of the R-OCN phase will be described.

[0034] The above area ratio is calculated from a backscattered electron image obtained, for example, using FE-SEM (field emission scanning electron microscope). When using FE-SEM, first, a sample for FE-SEM is prepared. Specifically, an R-T-B-based permanent magnet is embedded in an epoxy resin and polished so that a cross-section parallel to the orientation direction of the R-T-B-based permanent magnet can be observed. Specifically, after rough polishing by a normal method, finish polishing is performed. The finish polishing is performed so that the cross-section has a luster. Note that there is no particular limitation on the method of finish polishing. It is preferable to perform finish polishing by dry polishing without using a polishing liquid such as water. When using a polishing liquid such as water, appropriate analysis may not be possible due to corrosion of the grain boundary phase. Next, ion milling treatment is performed on the cross-section of the polished R-T-B-based permanent magnet to remove an oxide film, a nitride film, etc.

[0035] Next, the cross-section of the obtained R-T-B-based permanent magnet is observed with FE-SEM, and a backscattered electron image is obtained at a magnification of 1000 times or more and 3000 times or less and with a size of 50 μm square or more and 100 μm square or less. From the contrast of the backscattered electron image and the results of point analysis of EDS, it can be confirmed that the R-T-B-based permanent magnet is composed of main phase crystal particles (main phase) and other parts (grain boundaries), and the area ratio of each phase can be calculated. More specifically, by collating the results of point analysis by EDS (energy dispersive X-ray spectrometer) attached to FE-SEM with the contrast of the backscattered electron image, R2T 14 B main phase crystal particles (main phase), R-rich phase, R-OCN phase, R2O3 phase, R6T 13 Phases such as the M phase (grain boundary phase) can be classified. Note that M is one or more elements selected from Ga, Sn, Si, Cu, etc. From the measurement results by EDS, R2T 14 B main phase crystal particles and other phases are discriminated, and the area ratio of each phase can be calculated from the difference in contrast of each phase.

[0036] R2T 14 To calculate the area ratio of the R2T 14When binarized to form B main-phase crystal particles, the image shown in Fig. 2 is obtained. Grain boundaries are generally R2T 14 The content of rare-earth element R is higher than that of the B main-phase crystal particles. Here, the rare-earth element R is an element with a particularly large atomic number among the elements usually contained in the R-T-B system permanent magnet. It is known that the signal intensity of the backscattered electron image becomes stronger and appears brighter as the content of the element with a large atomic number increases. By collating the results of point analysis of EDS and the contrast of the backscattered electron image and extracting regions having a signal intensity above a predetermined level, R2T 14 The B main-phase crystal particles and the grain boundaries can be distinguished and binarized. Note that between two R2T 14 The two-particle grain boundaries formed between the B main-phase crystal particles are thin and thus hardly observed in Fig. 2. However, the area of the two-particle grain boundaries is so small as to be within the error range when viewed from the area of the entire grain boundaries. Therefore, in calculating the area ratio of the R2T 14 B main-phase crystal particles, the fact that no two-particle grain boundaries are observed in Fig. 2 does not pose a problem.

[0037] When calculating the volume ratio of the R-OCN phase in the grain boundaries, first, the area ratio of the grain boundary phase is calculated using Fig. 2, which is a FE-SEM image obtained by binarizing the backscattered electron image of the R-T-B system permanent magnet shown in Fig. 1. Next, the type of each grain boundary phase is identified by collating the results of point analysis of EDS and the contrast of the backscattered electron image. Figs. 3 to 5 are FE-SEM images binarized such that the white portions are R6T 13 the M phase, the R-OCN phase, and the R-rich phase, respectively. Here, by dividing the area ratio of the R-OCN phase by the area ratio of the grain boundary phase, the area ratio of the R-OCN phase in the grain boundaries can be calculated. In the present embodiment, the volume ratio of the R-OCN phase in the grain boundaries is calculated on the assumption that the area ratio and the volume ratio of the R-OCN phase in the grain boundaries are equal.

[0038] Hereinafter, a method for calculating the coverage rate of the R2T 14 B main-phase crystal particles will be described.

[0039] The above area ratio is calculated from a backscattered electron image obtained using an FE-SEM (field emission scanning electron microscope). Therefore, first, a sample for FE-SEM is prepared. The method for preparing the sample is the same as the above R2T 14 as in the method for preparing the sample in the method for calculating the area ratio of the B main phase crystal particles.

[0040] The cross-section of the obtained R-T-B-based permanent magnet is observed with an FE-SEM, and a backscattered electron image with a magnification of 5000 times or more and 10000 times or less, a size of 10 μm square or more and 20 μm square or less, and a resolution of 1280 pixel × 960 pixel is obtained. Next, the white part of the backscattered electron image is binarized so that it becomes the R2T 14 B main phase crystal particles. For example, when binarizing the white part of the backscattered electron image shown in FIG. 6 so that it becomes the R2T 14 B main phase crystal particles, the image shown in FIG. 7 is obtained. Next, the contour of the R2T 14 B main phase crystal particles is extracted from FIG. 7. Specifically, the part where the white part (R2T 14 B main phase crystal particles) in FIG. 7 is in contact with the black part (heterophase) in FIG. 7 is extracted. The actually extracted result is shown in FIG. 8. The total length of the white part (the contour of the R2T 14 B main phase crystal particles in contact with the heterophase) in FIG. 8 is defined as A total .

[0041] Next, for FIG. 8, particle boundaries, which are parts where the R2T 14 B main phase crystal particles are in contact with each other, are manually added. The result of the addition is shown in FIG. 9. The length of the added particle boundaries is defined as B total . The coverage rate is calculated as A total / (A total +B total ). Note that the R2T 14 B main phase crystal particles that are cut off in the backscattered electron image are excluded from the calculation for calculating the coverage rate.

[0042] Generally, the length at which the exchange coupling between the R2T 14 B main phase crystal particles is broken is about 3 nm. On the other hand, in the backscattered electron image obtained by FE-SEM, a region with a width of generally 20 nm or more is the R2T 14It can be recognized as a part having a contrast different from that of the B main-phase crystal particles. And in FIG. 8, R2T that contacts a grain boundary having a width of generally 20 nm or more 14 The contour of the B main-phase crystal particles is extracted.

[0043] Hereinafter, a method for calculating the average thickness of the two-particle grain boundary will be described.

[0044] When calculating the average thickness of the two-particle grain boundary, the above-mentioned R2T 14 The area ratio of the B main-phase crystal particles and R2T 14 Different from the coverage rate of the B main-phase crystal particles, a high-resolution transmission electron microscope (HR-TEM) is used. There is no particular limitation on the magnification of the HR-TEM image, and it may be appropriately set according to the thickness of the two-particle grain boundary. For example, the magnification is set to 500,000 times or more and 2,000,000 times or less. Next, at least 20 two-particle grain boundaries for measuring the thickness are determined from the HR-TEM image. Then, the boundary between the two-particle grain boundary and the grain boundary triple point connected to the two-particle grain boundary is determined.

[0045] It is not necessary to accurately determine the boundary, and it may be visually determined from the HR-TEM image. This is because the difference in the position of the boundary has a small effect on the finally obtained average thickness of the two-particle grain boundary and is within the error range. In addition, the reason why the difference in the position of the boundary has a small effect on the finally obtained average thickness of the two-particle grain boundary is that even if the position of the boundary is slightly different, the vicinity of the grain boundary triple point where the two-particle grain boundary becomes thick will not be the location for measuring the thickness of the two-particle grain boundary.

[0046] Next, the space between adjacent boundaries is divided into four equal parts, and three equally divided lines are drawn. The positions of these three equally divided lines are used as the measurement locations for the thickness of the two-particle grain boundary. That is, for one two-particle grain boundary, the thickness is measured at three locations. This measurement is performed for at least 20 two-particle grain boundaries, and the average thickness of the two-particle grain boundary is obtained by averaging the obtained thicknesses of the two-particle grain boundaries. Then, the average thickness can be regarded as the average thickness of the two-particle grain boundary in the entire R-T-B system permanent magnet.

[0047] The magnet composition of the R-T-B type permanent magnet will be described below. Although there is no particular limitation on the content of R, it may be 25.0 mass% or more and 35.0 mass% or less, may be 27.5 mass% or more and 32.0 mass% or less, may be 27.5 mass% or more and 31.5 mass% or less, or may be 28.0 mass% or more and 31.5 mass% or less. When the content of R is more than a predetermined amount, R2T contained in the R-T-B type permanent magnet 14 The generation of the R2T 14 B main phase crystal particles is likely to be sufficiently carried out, the precipitation of soft magnetic α-Fe and the like is suppressed, and the decrease in magnetic properties is likely to be suppressed. When the content of R is less than a predetermined amount, R2T

[0048] There is no particular limitation on the type of R, but it preferably contains at least RL. There is no particular limitation on the type of RL, but RL may contain at least Nd or Pr, or RL may contain Nd. When RH is included, there is no particular limitation on the type of RH. RH may contain at least Dy or Tb. RH may contain Tb. When RH is included, Hcj is likely to improve, but Br and the temperature characteristic (ΔHcj / ΔT) are likely to decrease.

[0049] There is no particular limitation on the content of B in the R-T-B type permanent magnet according to this embodiment, but it may be 0.50 mass% or more and 1.50 mass% or less, may be 0.90 mass% or more and 1.05 mass% or less, or may be 0.92 mass% or more and 0.98 mass% or less. When the content of B is within a predetermined range, R2T 14 The area ratio of the B main phase crystal particles is likely to be increased, and Hcj and Br tend to improve.

[0050] T may be Fe alone, or a part of Fe may be substituted with Co. There is no particular limitation on the content of Fe in the R-T-B-based permanent magnet according to this embodiment, but it may be substantially the remainder when the following inevitable impurities are removed in the R-T-B-based permanent magnet. The content of Co is preferably 0 mass% or more and 4.00 mass% or less, and preferably 0.50 mass% or more and 3.00 mass% or less.

[0051] There is no particular limitation on the content of N in the R-T-B-based permanent magnet according to this embodiment. When the content of N is small, specifically 300 ppm or less, even if the content of C is large, R2T 14 It becomes easier to keep the area ratio and coverage rate of the R2T14B main phase crystal particles within a predetermined range.

[0052] There is no particular limitation on the content of H in the R-T-B-based permanent magnet according to this embodiment. It may be 100 ppm or less, or may be 50 ppm or less. When the content of H is large, cracks are likely to occur in the R-T-B-based permanent magnet.

[0053] When the R-T-B-based permanent magnet according to this embodiment is an R-T-B-based sintered magnet, setting the content of H to 50 ppm or less makes it easier to perform sintering sufficiently and easier to improve Br. Also, if an attempt is made to manufacture an R-T-B-based sintered magnet with an H content exceeding 100 ppm, the cost will increase. Also, it becomes difficult for the R-T-B-based sintered magnet to be sufficiently densified, and the residual magnetic flux density is likely to decrease.

[0054] Also, when the R-T-B-based permanent magnet contains H, H may be contained between the crystal lattices. The more H contained between the crystal lattices, the more the crystal lattice is distorted. Due to the distortion of the crystal lattice, the absolute value of the temperature coefficient β of the coercive force of the R-T-B-based permanent magnet tends to increase, and the temperature characteristics tend to deteriorate. Setting the content of H to 50 ppm or less makes it easier to suppress the distortion of the crystal lattice and easier to improve the temperature characteristics. There is no particular lower limit on the content of H in the R-T-B-based permanent magnet according to this embodiment, and it may be below the detection limit. The detection limit is generally 5 ppm.

[0055] The R-T-B based permanent magnet according to this embodiment may contain Ga, Cu, Al, and / or Zr as metal elements other than R, T, and B. There are no particular restrictions on the content of each element.

[0056] The content of Ga may be 0 mass% or more and 1.00 mass% or less, and may also be 0 mass% or more and 0.20 mass% or less. The content of Cu may be 0.01 mass% or more and 1.00 mass% or less, and may also be 0.10 mass% or more and 0.20 mass% or less. The content of Al may be 0.03 mass% or more and 0.60 mass% or less. The content of Zr may be 0.05 mass% or more and 0.60 mass% or less. In particular, when the content of Ga is below a predetermined amount, R2T 14 It becomes easier to keep the area ratio of the R2TB main-phase crystal particles and the volume ratio of the R-OCN phase at the grain boundaries within a predetermined range, and the Br of the R-T-B based permanent magnet tends to improve.

[0057] In addition, the R-T-B based permanent magnet may contain inevitable impurities such as Mn, Ca, Cl, S, F, etc. as elements other than the above, in a total amount of 0.001 mass% or more and 1.0 mass% or less.

[0058] R2T 14 There are no particular restrictions on the particle size of the R2TB main-phase crystal particles. Usually, it is 10 μm or less. R2T 14 The smaller the particle size of the R2TB main-phase crystal particles, the easier it is for the Hcj of the R-T-B based permanent magnet to improve. However, R2T 14 The smaller the particle size of the R2TB main-phase crystal particles, the more R2T 14 The R2TB main-phase crystal particles are more likely to combine with oxygen in the atmosphere, and the O content of the R-T-B based permanent magnet is likely to increase.

[0059] In addition, the R-T-B based permanent magnet according to this embodiment is R2T 14 The content of C in the R2TB main-phase crystal particles may be 300 ppm or less.

[0060] The R-T-B-based permanent magnet contains at least a trace amount of C. Part of the C contained in the R-T-B-based permanent magnet replaces part of the B in the R2T 14 B main-phase crystal particles. That is, in the R2T 14 B main-phase crystal particles of the R-T-B-based permanent magnet, part of the B is replaced by C.

[0061] The inventors of the present invention have found that when part of the B in the R2T 14 B main-phase crystal particles is replaced by C, the Curie point of the R-T-B-based permanent magnet decreases. And the inventors of the present invention have found that by reducing the amount of C replacing part of the B in the R2T 14 B main-phase crystal particles, it becomes easier to increase the Curie point of the R-T-B-based permanent magnet. Specifically, the inventors of the present invention have found that by reducing the C content in the R2T 14 B main-phase crystal particles to 300 ppm or less, it becomes easier to increase the Curie point of the R-T-B-based permanent magnet. Note that there is no particular lower limit for the C content in the R2T 14 B main-phase crystal particles. For example, it may be 10 ppm or more, or may be 20 ppm or more.

[0062] And the inventors of the present invention have found that by increasing the Curie point of the R-T-B-based permanent magnet, the absolute value of the temperature coefficient (β) of Hcj of the R-T-B-based permanent magnet tends to become smaller. That is, it has been found that the temperature characteristics of the R-T-B-based permanent magnet are likely to be improved. Furthermore, it has been found that Hcj is likely to be improved.

[0063] Also, the R-T-B-based permanent magnet according to the present embodiment may have an orientation degree (Br / Js) obtained by dividing the magnetic flux density (Br) in the orientation direction by the saturation magnetic flux density (Js) of 94% or more. By having a high orientation degree, the temperature characteristics are likely to be improved, and furthermore, it becomes easier to obtain a sufficient magnetic flux density.

[0064] Also, the crystal orientation degree measured by the Lotgering method may be 66% or more.

[0065] The following describes a method for measuring the degree of crystal orientation by the Lotgering method in this embodiment.

[0066] To measure the degree of crystal orientation of an R-T-B-based permanent magnet, first, the magnetic pole surface of the R-T-B-based permanent magnet is mirror-polished. Then, X-ray diffraction measurement is performed on the mirror-polished surface. And based on the diffraction peaks obtained by the X-ray diffraction measurement, the degree of orientation is calculated. In the Lotgering method, the crystal orientation degree fc can be calculated by the following formula based on the X-ray diffraction intensity I(00l) of the (00l) reflection component and the X-ray diffraction intensity I(hkl) of the (hkl) reflection component

[0067] When calculating the degree of crystal orientation by the Lotgering method, only the component of the reflection in the orientation direction among the diffraction peaks, that is, the component of the (00l) reflection, is integrated on the numerator side of the following formula. Also, all diffraction peaks are integrated on the denominator side of the following formula. Therefore, the calculated degree of crystal orientation is a considerably small value compared to the actual degree of crystal orientation. In order to calculate the degree of crystal orientation closer to the actual situation, it is preferable to perform vector correction on the diffraction peaks. However, in this embodiment, vector correction is not performed.

[0068]

Equation

[0069] <Manufacturing method of R-T-B-based permanent magnet> Next, the manufacturing method of the R-T-B-based permanent magnet according to this embodiment will be described. Hereinafter, as an example of the manufacturing method of the R-T-B-based permanent magnet, the manufacturing method of the R-T-B-based permanent magnet produced by the powder metallurgy method will be described.

[0070] The manufacturing method of the R-T-B-based permanent magnet according to this embodiment includes a molding step of molding raw material powder to obtain a molded body, a hydrogen decarburization step of reducing the content of C contained in the molded body and reducing the volume ratio of the grain boundary, a sintering step of sintering the decarburized molded body to obtain a sintered body, and an aging treatment step of holding the sintered body at a temperature lower than the sintering temperature for a certain period of time.

[0071] Hereinafter, the manufacturing method of the R-T-B type permanent magnet will be described in detail. For matters not specifically noted, known methods may be used.

[0072] [Raw Material Powder Preparation Process] The raw material powder can be produced by known methods. In this embodiment, an R-T-B type permanent magnet is manufactured by a single alloy method using one type of raw material alloy mainly composed of the R2T 14 B phase, but it may also be manufactured by a two alloy method using two types of raw material alloys.

[0073] First, raw material metals corresponding to the composition of the raw material alloy according to this embodiment are prepared, and the raw material alloy corresponding to this embodiment is produced from the raw material metals. There is no particular limitation on the method for producing the raw material alloy. For example, the raw material alloy can be produced by the strip casting method.

[0074] After producing the raw material alloy, the produced raw material alloy is pulverized (pulverization process). The pulverization process may be carried out in two stages or one stage. There is no particular limitation on the pulverization method. For example, it is carried out by a method using various pulverizers. For example, the pulverization process is carried out in two stages: a coarse pulverization process and a fine pulverization process. In the coarse pulverization process, for example, hydrogen pulverization treatment can be performed. Specifically, after hydrogen is occluded in the raw material alloy at room temperature, dehydrogenation can be carried out at 400°C or higher and 650°C or lower for 0.5 hours or more and 2 hours or less in an Ar gas atmosphere. In the fine pulverization process, after adding lubricants such as isobutylamide and methyl carbamate as pulverization aids to the powder after coarse pulverization, it can be carried out using, for example, a jet mill, a wet attritor, etc. There is no particular limitation on the particle size of the obtained fine pulverized powder (raw material powder). For example, the fine pulverization can be carried out so that the fine pulverized powder (raw material powder) has a particle size (D50) of 1 μm or more and 10 μm or less. Note that from hydrogen occlusion pulverization to the sintering process, it was always carried out in a low oxygen atmosphere with an oxygen concentration of less than 230 ppm.

[0075] In addition, in order to reduce the carbon content ratio in the raw material powder, the amount of carbon contained in the raw material alloy and the addition amount of the lubricant used as the pulverization aid may be reduced. However, the carbon content ratio in the raw material powder is preferably not reduced and is added in a certain amount. By adding a certain amount of the lubricant, it becomes easier to improve Br / Js and the crystal orientation degree in the molding process described later, and it becomes easier to improve the temperature characteristics. Furthermore, it is for the purpose of easily reducing the O content of the finally obtained R-T-B based permanent magnet. Specifically, it is preferable to add the lubricant in an amount of 0.05% by mass or more and 0.20% by mass or less.

[0076] [Molding process] In the molding process, the finely pulverized powder (raw material powder) obtained by the pulverization process is molded into a predetermined shape. The molding method is not particularly limited, but in this embodiment, the finely pulverized powder (raw material powder) is filled into a mold and pressurized in a magnetic field. By pressurizing in a magnetic field, R2T 14 The B main phase crystal particles are oriented in the magnetic field direction.

[0077] The pressurization during molding is preferably performed at 30 MPa or more and 300 MPa or less. The applied magnetic field is preferably 950 kA / m or more and 1600 kA / m or less. The applied magnetic field is not limited to a static magnetic field and can also be a pulsed magnetic field. Also, a static magnetic field and a pulsed magnetic field can be used in combination. The shape of the molded body obtained by molding the finely pulverized powder (raw material powder) is not particularly limited, and can be an arbitrary shape according to the desired shape of the R-T-B based permanent magnet, such as a rectangular parallelepiped, a flat plate shape, a columnar shape, etc.

[0078] [Hydrogen decarburization process] In this embodiment, after the above molding process, a hydrogen decarburization treatment may be performed to reduce the C content of the obtained molded body and reduce the volume ratio of the grain boundaries. Note that the C contained in the molded body at the stage after the molding process mainly comes from the lubricant. By performing the hydrogen decarburization treatment, the lubricant can be decomposed by hydrogen, and the lubricant can be removed from the molded body. As a result, even if a certain amount of the lubricant is added, C can be removed. Furthermore, hydrogen has a high permeation power into substances. As a result, especially R2T14 The carbon content contained in the B main-phase crystal particles decreases. As a result, it becomes easier to reduce the volume ratio of the grain boundaries of the finally obtained R-T-B-based permanent magnet, and R2T 14 It becomes easier to control the area ratio of the B main-phase crystal particles to 92.0% or more.

[0079] The hydrogen decarburization treatment is performed by heat-treating the compact in a hydrogen atmosphere or a hydrogen-inert gas (e.g., Ar gas) mixed atmosphere. The content ratio of hydrogen gas in the atmosphere may be 5% or more 100% or less. The atmospheric pressure may be atmospheric pressure (101 kPa) or a pressure lower than atmospheric pressure. Specifically, the atmospheric pressure may be 5 kPa or more and 101 kPa or less. There is no particular limitation on the heat treatment time. It may be 1 hour or more and 30 hours or less. There is no particular limitation on the heat treatment temperature. It may be 150°C or more and 600°C or less.

[0080] When performing the hydrogen decarburization treatment, it is important to perform the hydrogen decarburization treatment after the forming step and before the sintering step described later. When the hydrogen decarburization treatment is carried out before the forming step, Br / Js and the crystal orientation degree decrease, and the residual magnetic flux density decreases. When the hydrogen decarburization treatment is carried out after the sintering step, the sintered body may expand due to hydrogen absorption and crack. Also, the carbon contained in the compact is further incorporated into the R2T 14 B main-phase crystal particles and grain boundaries. The carbon incorporated into the R2T 14 B main-phase crystal particles and grain boundaries cannot be sufficiently removed even by performing the hydrogen decarburization treatment.

[0081] The hydrogen deoxidation treatment and the sintering described later may be carried out continuously. Specifically, sintering may be carried out by changing the atmosphere gas, temperature, etc. while the compact is placed in the furnace where the hydrogen decarburization treatment has been carried out.

[0082] [Sintering step] The sintering process is a process of sintering a compact in a vacuum or an inert gas atmosphere to obtain a sintered body. The sintering temperature needs to be adjusted according to various conditions such as composition, grinding method, differences in particle size and particle size distribution. For the compact, for example, heating is performed in a vacuum or in the presence of an inert gas at 1000 °C or higher and 1200 °C or lower for 1 hour or longer and 10 hours or shorter to perform sintering. Thereby, a high-density sintered body (permanent magnet) can be obtained.

[0083] [Aging treatment process] The aging treatment process is carried out by heating the sintered body (permanent magnet) after the sintering process in a vacuum or an inert gas atmosphere at a temperature lower than the sintering temperature. There are no particular restrictions on the temperature and time of the aging treatment. For example, it can be carried out at 450 °C or higher and 900 °C or lower for 0.2 hours or longer and 3 hours or shorter. Note that this aging treatment process may be omitted.

[0084] Also, the aging treatment process may be carried out in one stage or in two stages. When carried out in two stages, for example, the first stage may be at 700 °C or higher and 900 °C or lower for 0.2 hours or longer and 3 hours or shorter, and the second stage may be at 450 °C or higher and 700 °C or lower for 0.2 hours or longer and 3 hours or shorter. Also, the first stage and the second stage may be carried out continuously, or after the first stage, it may be cooled to near room temperature once and then reheated to carry out the second stage.

[0085] [Diffusion treatment process] A diffusion treatment may be performed on the obtained permanent magnet to diffuse a heavy rare earth element from the outside of the permanent magnet to the inside of the permanent magnet. There are no particular restrictions on the method of the diffusion treatment. For example, a coating diffusion method in which a powder or foil containing a heavy rare earth element is adhered to the permanent magnet and heat treatment is performed, or a gas phase diffusion method in which heat treatment is performed on the permanent magnet in an atmosphere in which a heavy rare earth element is evaporated may be used.

[0086] In addition, the material may be prevented from coming into contact with nitrogen in all processes from coarse grinding to sintering. An atmosphere with a nitrogen concentration of 200 ppm or less using high-purity Ar gas may be used in all processes from coarse grinding to sintering. In this case, the nitrogen content in the finally obtained R-T-B-based permanent magnet can be reduced. As a result, even without performing the above hydrogen decarburization treatment, R2T 14 The area ratio of the main phase crystal particles of B and the volume ratio of the R-OCN phase can be within a predetermined range.

[0087] As described above, the preferred embodiments of the R-T-B-based permanent magnet of the present invention have been described. However, the R-T-B-based permanent magnet of the present invention is not limited to the above embodiments. The R-T-B-based permanent magnet of the present invention can be variously modified and variously combined without departing from the gist thereof.

[0088] Furthermore, the R-T-B-based permanent magnet according to the present embodiment may be cut and divided to obtain two or more R-T-B-based permanent magnets.

[0089] There is no particular limitation on the use of the R-T-B-based permanent magnet according to the present embodiment. Specifically, the R-T-B-based permanent magnet according to the present embodiment is suitably used for applications such as motors, compressors, magnetic sensors, and speakers.

[0090] Also, two or more R-T-B-based permanent magnets may be combined and used as needed. There is no particular limitation on the bonding method. For example, there are a method of mechanically bonding and a method of bonding with a resin mold.

[0091] By combining two or more R-T-B-based permanent magnets, a large R-T-B-based permanent magnet can be easily manufactured. The magnet obtained by combining two or more R-T-B-based permanent magnets is preferably used for applications where a particularly large R-T-B-based permanent magnet is required, such as IPM motors, wind turbines, and large motors.

Examples

[0092] Next, the present invention will be described in more detail based on specific examples, but the present invention is not limited to the following examples.

[0093] (Experimental Example 1) As raw material metals, Nd, Pr, electrolytic iron, and low-carbon ferroboron alloy were prepared. Further, Ga, Al, Cu, Co, and Zr were prepared in the form of pure metals or alloys with Fe.

[0094] Using the strip casting method, raw material alloys were produced from the above raw material metals. Specifically, alloys A to H were produced with the compositions shown in Table 1 as raw material alloys. Also, the alloy thickness of the raw material alloy was set to 0.2 mm to 0.6 mm.

[0095] [Table 1]

[0096] Next, hydrogen gas was flowed through the raw material alloy at room temperature for 1 hour to absorb hydrogen. Then, the atmosphere was switched to Ar gas, and dehydrogenation treatment was performed at 450 °C for 1 hour to hydrogen pulverize the raw material alloy. Further, after cooling, a powder with a particle size of 400 μm or less was obtained using a sieve.

[0097] Next, a lubricant in the amount shown in Table 2 by mass ratio was added to the powder of the raw material alloy after hydrogen pulverization as a pulverization aid and mixed. Isobutylamide was used as the lubricant. Note that the contents of C and O in the magnet composition were controlled by controlling the addition amount of the lubricant.

[0098] Next, using a collision plate type jet mill device, fine pulverization was performed in a nitrogen stream to obtain fine powders (raw material powders) each having an average particle size of about 4 μm. The average particle size is D50 measured by a laser diffraction type particle size distribution meter.

[0099] In addition, the content of O in the magnet composition was controlled by changing the content of oxygen in the atmosphere during pulverization. In Example 4, which had the highest O content among the examples, the oxygen content in the atmosphere during pulverization was 200 ppm. Also, in Comparative Example 3, which had the highest O content among the comparative examples, the oxygen content in the atmosphere during pulverization was 900 ppm.

[0100] Note that as inevitable impurities, etc., Si, Ca, La, Ce, Cr, etc. may be detected. Si may mainly be mixed in from the ferroboron raw material and the crucible during alloy melting. Ca, La, Ce may be mixed in from the rare earth raw materials. Also, Cr may be mixed in from electrolytic iron.

[0101] The obtained fine powder was formed in a magnetic field to produce a formed body. The applied magnetic field at this time was a static magnetic field of 1200 kA / m. Also, the pressure during forming was 120 MPa. Note that the magnetic field application direction and the pressure application direction were made orthogonal. When the density of the formed body at this point was measured, the density of all the formed bodies was 4.10 Mg / m 3 above 4.25 Mg / m 3 within the following range.

[0102] Next, except for Comparative Examples 2, 5 to 7 Examples and Comparative Examples the formed body was subjected to a hydrogen decarburization treatment. The atmosphere during the hydrogen decarburization treatment was a hydrogen atmosphere (atmospheric pressure, hydrogen partial pressure 101 kPa) except for Example 6, and Example 6 was a hydrogen-Ar mixed atmosphere (atmospheric pressure, hydrogen partial pressure 50 kPa, Ar partial pressure 51 kPa). The heat treatment temperature (hydrogen treatment temperature) is shown in Table 2. The heat treatment time was 1 to 48 hours. Note that by controlling the conditions of the hydrogen decarburization treatment, the content of C and H in the magnet composition was controlled.

[0103] Next, the formed body was sintered to obtain a permanent magnet. The sintering conditions were holding at 1060 °C for 4 hours. The sintering atmosphere was vacuum. At this time, the sintered density was 7.50 Mg / m 3 above 7.55 Mg / m 3It was within the following range. Then, in an argon atmosphere under atmospheric pressure, a first aging treatment was performed at a first aging temperature T1 = 900 °C for 1 hour, and further, a second aging treatment was performed at a second aging temperature T2 = 500 °C for 1 hour.

[0104] The compositions (contents of Nd, Pr, Al, Cu, Zr, Ga, Co, and Fe) of the R-T-B-based permanent magnets of each example and comparative example obtained by the above steps were measured by fluorescent X-ray analysis. The content of B was measured by high-frequency inductively coupled plasma (ICP) emission spectrometry. As a result, it was confirmed that the composition of the R-T-B-based permanent magnet, for example, the content of R was substantially the same as the composition of the raw material alloy and had the composition shown in Table 1.

[0105] For the R-T-B-based permanent magnets of each example and comparative example, the contents of C, O, and H were measured. First, the surface layer portion of the R-T-B-based permanent magnet was shaved with a grinder. Next, the obtained R-T-B-based permanent magnet was pulverized to a size of about 1 mm with a stamp mill. Next, a measurement sample was randomly collected from the pulverized R-T-B-based permanent magnet. The contents of O and H were measured by inert gas fusion-non-dispersive infrared absorption method. The content of C was measured by combustion-infrared absorption method in an oxygen stream. The above measurements were performed 5 times, and the averaged results were taken as the contents of C, O, and H in the R-T-B-based permanent magnet. The results are shown in Tables 2 and 3. Samples in which the content of H is described as N.D. are samples in which the content of H was below the measurement limit, and samples in which the content of H was generally 5 ppm or less.

[0106] For the R-T-B-based permanent magnets of each example and comparative example, R2T 14 The content of C in the B main phase crystal particles was measured by a three-dimensional atom probe microscope (3DAP).

[0107] First, an electron microscope image of the polished cross-section of each sample was obtained. The polished cross-section was a cross-section parallel to the orientation direction of the R-T-B-based permanent magnet. Next, in the obtained electron microscope image, R2T 14 B main phase crystal particles were selected. The R2T to be selected14 The B main-phase crystal particles were R2T with a particle diameter approximately the same as the average particle diameter. 14 The B main-phase crystal particles were used.

[0108] Next, a sampling location was set, which was the location where the needle-shaped sample was to be cut out. Hereinafter, the method for setting the sampling location will be described. FIG. 10 is a schematic diagram of an electron microscope image including the selected R2T 14 B main-phase crystal particle 1. And an example of the sampling location 3 is shown in FIG. 10. The sampling location 3 includes the vicinity of the center of the selected R2T 14 B main-phase crystal particle 1 and is set at a location that does not include the end 1a of the selected R2T 14 B main-phase crystal particle 1. The vicinity of the center of the selected R2T 14 B main-phase crystal particle 1 specifically refers to a portion where the distance from the incenter of the selected R2T 14 B main-phase crystal particle 1 is 100 nm or less. Also, the sampling location 3 is made to have a length in the longitudinal direction of 500 nm or more. Note that there is no particular limitation on the magnitude of the angle formed between the longitudinal direction of the sampling location 3 and the orientation axis of the selected R2T 14 B main-phase crystal particle 1. For example, the longitudinal direction of the sampling location 3 may be parallel to the orientation axis or perpendicular to the orientation axis.

[0109] Next, a needle-shaped sample was sampled from the sampling location 3. Specifically, a needle-shaped sample was cut out from the sampling location 3. Also, the needle-shaped sample was cut out so that the length in the longitudinal direction of the needle-shaped sample was 500 nm or more. The above-described cutting out of the needle-shaped sample was performed for five different R2T 14 B main-phase crystal particles 1. Then, three-dimensional atom probe measurements were continuously performed for at least 500 nm on the five needle-shaped samples, and the C content of each needle-shaped sample was measured. And the average value thereof was taken as the C content of the R2T 14 B main-phase crystal particles contained in the R-T-B-based permanent magnet. Note that the cutting out of the needle-shaped sample was performed so as not to include heterogeneous portions within the R2T 14 B main-phase crystal particles. The results are shown in Tables 2 and 3.

[0110] For the R-T-B based permanent magnets of each example and comparative example, magnetic properties and the orientation degree (Br / Js) obtained by dividing the residual magnetic flux density in the orientation direction by the saturation magnetic flux density were calculated. First, the surface of the R-T-B based permanent magnet was ground to a cubic shape of 10.0 mm × 10.0 mm × 10.0 mm. Next, for the ground R-T-B based permanent magnet, the coercive force Hcj, residual magnetic flux density Br, and saturation magnetic flux density Js were measured at room temperature (23 °C) using a BH tracer, and Br / Js was calculated. Further, at 160 °C, the coercive force Hcj was measured using a BH tracer, and the temperature coefficient β of the coercive force was calculated. The results are shown in Tables 2 and 3. Note that a case where Br / Js is 94% or more was regarded as good. A case where Hcj at room temperature is 15.0 kOe or more was regarded as good. A case where Br at room temperature is 14.0 kG or more was regarded as good. A case where Hcj at 160 °C is 5.0 kOe or more was regarded as good. A case where the absolute value of the temperature coefficient β of the coercive force is less than 0.50% / °C was regarded as good.

[0111] For the R-T-B based permanent magnets of each example and comparative example, R2T 14 The area ratio of the R2T

[0112] For the R-T-B based permanent magnets of each example and comparative example, the crystal orientation degree was measured by the Lotgering method.

[0113] For the permanent magnets of each example and comparative example, the magnetic pole surfaces were mirror polished. Then, X-ray diffraction measurement of the mirror polished surfaces was performed, and the crystal orientation degree was calculated by the Lotgering method based on the obtained diffraction peaks. Vector correction was not performed. The results are shown in Tables 2 and 3.

[0114]

Table 2

[0115]

Table 3

[0116] In Examples 1 to 7 where 0.12% by mass of a lubricant was added as a pulverization aid and a hydrogen decarburization treatment was performed, the area ratio of the main-phase crystal particles was 92.0% or more and the coverage rate was 50.0% or more in all cases. As a result, both the magnetic properties at room temperature and the magnetic properties at 160°C were excellent, and the temperature characteristics were also good.

[0117] In Example 8, the content of R is 31.4% by mass, which is large compared with Examples 1 to 7. In Example 9, the content of R is 27.5% by mass, which is small compared with Examples 1 to 7. However, in both cases, the area ratio of the main-phase crystal particles and the coverage rate were within a predetermined range, and good characteristics were obtained. In particular, even when the content of R is small and sintering is difficult, if the area ratio of the main-phase crystal particles and the coverage rate are within a predetermined range, it becomes difficult for R to exist at grain boundaries such as grain boundary triple points, and it was confirmed that the density of the R-T-B-based sintered magnet was maintained sufficiently high.

[0118] On the other hand, Comparative Example 1, which was carried out in the same manner as each Example except that the heat treatment temperature during the hydrogen decarburization treatment was low, and Comparative Example 2, which was carried out in the same manner as each Example except that the hydrogen decarburization treatment was not performed, had a coverage rate that was too low. As a result, the temperature characteristics deteriorated. Furthermore, the coercive force also decreased. Also, in Comparative Example 5 in which the content of B was decreased and the content of Ga was increased from Comparative Example 2, the area ratio of the R2T 14 B main-phase crystal particles became too small. As a result, Br at room temperature decreased.

[0119] In Comparative Example 3 in which the content of O in the R-T-B-based permanent magnet was increased, the coverage rate decreased, Hcj at room temperature decreased, and the temperature characteristics also decreased.

[0120] In Comparative Example 4 in which the alloy composition was relatively high in the content of R, the area ratio of the R2T 14 B main-phase crystal particles decreased, and Br at room temperature decreased.

[0121] In Comparative Example 6 where the addition amount of the lubricant was reduced and the hydrogen decarburization treatment was not performed, the coating rate decreased. As a result, the crystal orientation degree decreased, Br at room temperature decreased, and the temperature characteristics also decreased.

[0122] In Comparative Example 7 where the content of R in the R-T-B-based permanent magnet was reduced and the hydrogen decarburization treatment was not performed, the coating rate decreased. As a result, the sintered body had a low density, and Br, Hcj, and the temperature characteristics decreased particularly significantly.

[0123] In Comparative Example 8 where the content of O in the R-T-B-based permanent magnet was increased and the content of R was reduced, the coating rate decreased, and the area ratio of the R2T 14 B main phase crystal particles became too small. As a result, the sintered body had a low density, and Br, Hcj, and the temperature characteristics decreased particularly significantly.

[0124] (Experimental Example 2) In Experimental Example 2, different from Experimental Example 1, the material was prevented from coming into contact with nitrogen in all processes from coarse pulverization to sintering. Specifically, nitrogen gas was not used in all the above processes, and instead, high-purity argon gas was used. Further, in Experimental Example 2, different from Experimental Example 1, the hydrogen decarburization treatment was not performed. Except for the above points, it was the same as Example 1 of Experimental Example 1. The results are shown in Tables 4 and 5. The content of N was measured by the inert gas fusion - thermal conductivity method, different from the contents of O and H.

[0125]

Table 4

[0126]

Table 5

[0127] In Example 10, compared with each example of Experimental Example 1, the content of C increased and the content of N decreased. Example 10 has R2T 14The area ratio of the B main-phase crystal particles and the coverage rate were within a predetermined range, and good characteristics were obtained. Therefore, even when the content of C is high without performing the hydrogen decarburization treatment, R2T 14 It was confirmed that good characteristics can be obtained if an R-T-B-based permanent magnet in which the area ratio of the B main-phase crystal particles and the coverage rate are within a predetermined range can be obtained.

[0128] In addition, it was confirmed that the N content in Examples 2 to 9 was 450 to 650 ppm, the same as the N content in Example 1.

Claims

1. R 2 T 14 An R-T-B-based permanent magnet containing R-T-B main-phase crystal particles and grain boundaries, R is one or more rare earth elements, T is Fe or one or more iron group elements essentially including Fe and Co, B is boron, the content of B is 0.92% by mass or more and 0.98% by mass or less, In a cross-section parallel to the orientation direction of the R-T-B-based permanent magnet, the coverage rate of the R 2 T 14 coated rate of the B main-phase crystal particles is 50.0% or more, and the area ratio of the R 2 T 14 B main-phase crystal particles is 92.0% or more, the remanent magnetic flux density of the R-T-B based permanent magnet is 14.2 kG or more, and the coercive force at room temperature is 15.2 kOe or more. The R-T-B based permanent magnet is characterized by these.

2. the R-T-B based permanent magnet further contains C, The above-mentioned R 2 T 14 The R-T-B permanent magnet according to claim 1, wherein the content of C in the main phase crystal particles of B is 300 ppm or less.

3. the R-T-B based permanent magnet further contains O, The R-T-B based permanent magnet according to Claim 1 or 2, wherein the content of O in the R-T-B based permanent magnet is less than 900 ppm.

4. the grain boundary contains an R-OCN phase, The R-T-B based permanent magnet according to any one of Claims 1 to 3, wherein the volume ratio of the R-OCN phase in the grain boundary is 34.0% or less.

5. the R-T-B based permanent magnet further contains C, The R-T-B based permanent magnet according to any one of Claims 1 to 4, wherein the content of C in the R-T-B based permanent magnet is 500 ppm or less.

6. the R-T-B based permanent magnet further contains H, The R-T-B based permanent magnet according to any one of Claims 1 to 5, wherein the content of H in the whole R-T-B based permanent magnet is 50 ppm or less.

7. The R-T-B based permanent magnet according to any one of Claims 1 to 6, wherein the orientation degree obtained by dividing the remanent magnetic flux density in the orientation direction of the R-T-B based permanent magnet by the saturation magnetic flux density is 94% or more.

8. The R-T-B based permanent magnet according to any one of Claims 1 to 7, wherein the content of R in the R-T-B based permanent magnet is 27.5% by mass or more and 31.5% by mass or less.

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