RTB-based permanent magnet and its manufacturing method, motor and automobile

Abstract

[Problem] To provide an R-T-B-based permanent magnet having a high residual magnetic flux density Br and a high coercivity Hcj. [Solution] An R-T-B-based permanent magnet which contains R that represents at least one rare earth element essentially including Tb or Dy, T that represents Fe or at least one iron-group element essentially including Fe and Co, and B that represents boron, and further contains Cu. The total content of R is 28.35 to 29.95% by mass, inclusive, the content of Cu is 0.05 to 0.40% by mass, inclusive, and the content of B is 0.93 to 1.00% by mass, inclusive. The distribution of the concentration of Tb or Dy decreases from the outside of the R-T-B-based permanent magnet toward the inside of the R-T-B-based permanent magnet.

Description

[Technical Field]

[0001] The present invention relates to an RTB permanent magnet, a method for manufacturing the same, a motor, and an automobile. [Background technology]

[0002] Rare earth permanent magnets with RTB-based compositions have excellent magnetic properties, and much research is being done to further improve these properties. Residual magnetic flux density (residual magnetization) Br and coercive force Hcj are generally used as indicators of magnetic properties. Magnets with high values ​​for these can be said to have excellent magnetic properties.

[0003] Patent Document 1 describes a rare earth permanent magnet in which a magnet body is immersed in a slurry in which fine powders containing various rare earth elements are dispersed in water or an organic solvent, and then heated to cause grain boundary diffusion.

[0004] Patent Document 2 describes an RTB-based permanent magnet in which Ga is used to improve the coercive force.

[0005] Patent Document 3 discloses a technique for reducing the carbon content and obtaining a high coercive force by not performing a dehydrogenation treatment during coarse pulverization. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2006 / 043348 [Patent Document 2] Japanese Patent Application Publication No. 2018-93202 [Patent Document 3] International Publication No. 2014 / 017249 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide an RTB permanent magnet with high residual magnetic flux density Br and high coercive force Hcj. [Means for solving the problem]

[0008] In order to achieve the above object, an RTB permanent magnet according to a first aspect of the present invention comprises: An RTB-based permanent magnet in which R is one or more rare earth elements, essentially Tb or Dy, T is one or more iron group elements, essentially Fe or Fe and Co, and B is boron, and further contains Cu, The total content of R is 28.35 mass% or more and 29.95 mass% or less, Cu content is 0.05 mass% or more and 0.40 mass% or less, The B content is 0.93 mass% or more and 1.00 mass% or less, the concentration distribution of Tb or Dy decreases from the outside toward the inside of the RTB permanent magnet, This is an RTB-based permanent magnet with a residual magnetic flux density of 1485 mT or more and a coercive force of 1800 kA / m or more.

[0009] The RTB permanent magnet according to the first aspect of the present invention has the above-described configuration, resulting in a magnet with high residual magnetic flux density and coercive force, specifically a magnet with a residual magnetic flux density of 1485 mT or more and a coercive force of 1800 kA / m or more.

[0010] R may be one or more rare earth elements, with Tb being essential.

[0011] The C content may be less than 750 ppm.

[0012] The N content may be less than 500 ppm.

[0013] The O content may be less than 650 ppm.

[0014] R may include a light rare earth element, and the total concentration of the light rare earth elements may be distributed so as to decrease from the outside to the inside of the RTB permanent magnet.

[0015] The Cu concentration may be distributed so that it decreases from the outside to the inside of the RTB permanent magnet.

[0016] The RTB permanent magnet may further contain Al, and the Al concentration may be distributed so as to decrease from the outside toward the inside of the RTB permanent magnet.

[0017] Co may be further contained, and the concentration of Co may be distributed so as to decrease from the outside to the inside of the RTB permanent magnet.

[0018] The RTB permanent magnet may further contain Ga, and the Ga concentration may be distributed so as to decrease from the outside toward the inside of the RTB permanent magnet.

[0019] The motor of the present invention has the above-mentioned RTB-based permanent magnet.

[0020] The automobile of the present invention has the motor described above.

[0021] An RTB permanent magnet according to a second aspect of the present invention is an RTB permanent magnet in which R is one or more rare earth elements essentially containing a light rare earth element, T is one or more iron group elements essentially containing Fe or Fe and Co, B is boron, and further contains Cu, The total content of light rare earth elements is 27.95% by mass or more and 29.55% by mass or less, Cu content is 0.05 mass% or more and 0.40 mass% or less, The B content is 0.93 mass% or more and 1.00 mass% or less, C content less than 750 ppm, N content less than 500 ppm, The RTB permanent magnet has an O content of less than 650 ppm.

[0022] Due to having the above configuration, the R-T-B-based permanent magnet according to the second aspect of the present invention becomes an R-T-B-based permanent magnet whose magnetic properties are greatly improved by grain boundary diffusion.

[0023] The manufacturing method of the R-T-B-based permanent magnet of the present invention includes a step of hydrogen storage in a raw material alloy and a step of dehydrogenating the hydrogen-stored raw material alloy, When dehydrogenating the hydrogen-stored raw material alloy, the dehydrogenation temperature is set to 50°C or higher and 200°C or lower, and the dehydrogenation time is set to 5 minutes or longer and 600 minutes or shorter.

[0024] The content of H in the coarsely pulverized powder obtained by dehydrogenating the hydrogen-stored raw material alloy may be 2100 ppm or more and 3100 ppm or less.

Brief Description of Drawings

[0025] [Figure 1] It is a schematic diagram of the R-T-B-based permanent magnet according to the present embodiment. [Figure 2] It is a SEM image of the R-T-B-based permanent magnet before grain boundary diffusion. [Figure 3] It is a SEM image of the R-T-B-based permanent magnet after grain boundary diffusion.

Modes for Carrying Out the Invention

[0026] Hereinafter, the present invention will be described based on the embodiments shown in the drawings.

[0027] <R-T-B-based permanent magnet> The R-T-B-based permanent magnet 1 according to the present embodiment has main phase particles composed of R2T 14 B crystals and grain boundaries. The grain boundaries may contain a secondary phase which is a part other than the main phase particles.

[0028] Furthermore, the main phase volume fraction of the RTB magnet is preferably 95.0% or higher. Having a main phase volume fraction within the above range facilitates improving magnetic properties. Specifically, the main phase volume fraction can be measured by cutting the RTB magnet after grain boundary diffusion and observing it using an SEM, and assuming that the area fraction of the main phase particles in the observation area is the same as the main phase volume fraction. For SEM observation, the observation area is set to a size that allows at least 200 main phase particles to be observed at a magnification of 1000 to 3000 times. Ten such observation areas are then set, and the main phase volume fraction in each observation area is measured and averaged, thereby measuring the main phase volume fraction in this embodiment.

[0029] The RTB permanent magnet 1 according to this embodiment can have any shape.

[0030] The RTB permanent magnet 1 according to this embodiment contains a number of specific elements in specific ranges, thereby improving the remanence Br and coercivity Hcj. Specifically, Br is 1485 mT or more, and Hcj is 1800 kA / m or more.

[0031] Furthermore, the RTB permanent magnet 1 according to this embodiment has a distribution in which the concentration of Tb or Dy decreases from the outside to the inside of the RTB permanent magnet 1. In the following description, we will explain the case in which the concentration of Tb decreases from the outside to the inside, but the same applies if some or all of the Tb is replaced with Dy. However, including Tb is preferable to including Dy, as it is easier to improve Hcj.

[0032] Specifically, as shown in FIG. 1, when the rectangular parallelepiped RTB permanent magnet 1 according to this embodiment has a surface portion and a center portion, the Tb content in the surface portion can be 2% or more higher than the Tb content in the center portion, and can also be 5% or more, or 10% or more. The surface portion refers to the surface of the RTB permanent magnet 1. For example, POINTS C and C' in FIG. 1 (the centers of gravity of the opposing surfaces in FIG. 1) are surface portions. The center portion refers to the center of the RTB permanent magnet 1. For example, it refers to a portion halfway through the thickness of the RTB permanent magnet 1. For example, POINT M in FIG. 1 (the midpoint between POINTS C and C') is the center portion.

[0033] Furthermore, the RTB permanent magnet 1 according to this embodiment may contain one or more light rare earth elements as R, and the concentration of the one or more light rare earth elements may have a distribution in which it decreases from the outside to the inside of the RTB permanent magnet 1. The concentration of Cu may also have a distribution in which it decreases from the outside to the inside of the RTB permanent magnet 1.

[0034] There are no particular limitations on the method for generating the above-mentioned Tb concentration distribution, but the Tb concentration distribution can be generated within the magnet by the grain boundary diffusion of Tb, as described below. Furthermore, the concentration distribution of one or more light rare earth elements, Cu, Al, Co, and Ga, can be generated by including them in the diffusion material used when diffusing Tb into the grain boundaries. Details will be described later. There are no particular limitations on the type of light rare earth element. For example, Nd and / or Pr may be used, or Nd alone may be used.

[0035] R represents a rare earth element. Rare earth elements include Sc, Y, and lanthanoid elements, which belong to Group 3 of the long period periodic table. Lanthanoid elements include, for example, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Furthermore, the RTB permanent magnet according to this embodiment (the RTB permanent magnet after grain boundary diffusion, described below) contains Tb as R. As described above, some or all of this Tb may be substituted with Dy. Furthermore, it is preferable that R contains Nd.

[0036] Rare earth elements are generally classified into light rare earth elements and heavy rare earth elements, but the light rare earth elements in the RTB permanent magnet according to this embodiment are Sc, Y, La, Ce, Pr, Nd, Sm, and Eu, and the heavy rare earth elements are Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0037] T represents one or more iron group elements, of which Fe or Fe and Co are essential. The iron group elements are Fe, Co, and Ni.

[0038] B is boron.

[0039] The RTB permanent magnet according to this embodiment may further contain Cu, Al, Ga, Zr, O, C, and N.

[0040] The composition of the RTB permanent magnet according to this embodiment will be explained below, but unless otherwise specified, the parameter for the content of each element is the entire magnet.

[0041] The total content of R is 28.35% by mass or more and 29.95% by mass or less. If the total content of R is less than 28.35% by mass, Hcj decreases. If the total content of R is more than 29.95% by mass, Br decreases. Alternatively, the total content of R may be 28.75% by mass or more and 29.95% by mass or less.

[0042] When the total content of light rare earth elements is TRL, TRL may be 27.95 mass% or more and 29.55 mass% or less, or 28.35 mass% or more and 29.55 mass% or less. By having TRL within this range, Br and Hcj can be further improved.

[0043] The light rare earth elements may include at least Nd and / or Pr.

[0044] The alloy may also contain heavy rare earth elements in a total amount of 1.0 mass% or less. When the total content of heavy rare earth elements is 1.0 mass% or less, Br is easily maintained at a good level. The heavy rare earth element may be substantially Tb alone. In this case, the Tb content may be 0.20 mass% or more and 1.0 mass% or less, or 0.40 mass% or more and 0.65 mass% or less. When the Tb content is less than 0.20 mass%, Hcj is likely to decrease. When the Tb content exceeds 1.0 mass%, Br is likely to decrease.

[0045] In this embodiment, it is expected that Br will be high because the total content of R is relatively small. However, if the total content of R is small, the sinterability may decrease, and if sintering is not sufficient, Hcj will decrease significantly.

[0046] There is no particular limit to the Co content. It may be 0 mass % or more and 2.0 mass % or less. In other words, Co does not need to be contained. The Co content may be 0.5 mass % or more and 1.5 mass % or less. When the Co content is within the above range, Br tends to be high. Note that in this embodiment, sufficient corrosion resistance is easily ensured even when the Co content is low or when Co is not contained. This is because the total R content is relatively low.

[0047] There is no particular limitation on the Ni content, and Ni does not necessarily have to be contained. The Ni content may be, for example, 0.5 mass % or less.

[0048] The B content is 0.93% by mass or more and 1.00% by mass or less. It may be 0.93% by mass or more and 0.99% by mass or less, or 0.95% by mass or more and 0.98% by mass or less. If the B content is too low or too high, subphases tend to increase, making it difficult to increase Br. By keeping the B content within the above range, Br and Hcj can be further improved.

[0049] The Cu content is 0.05% by mass or more and 0.40% by mass or less. If the Cu content is less than 0.05% by mass, Br and Hcj decrease. If the Cu content exceeds 0.40% by mass, Br decreases. The Cu content may also be 0.06% by mass or more and 0.30% by mass or less, or 0.06% by mass or more and 0.20% by mass or less. By including 0.06% by mass or more of Cu, the variation in characteristics is reduced. In other words, manufacturing stability tends to be improved.

[0050] There are no particular restrictions on the Ga content. The Ga content may be 0% by mass or more and 0.05% by mass or less. In other words, Ga need not be included. The higher the Ga content, the more likely Br will decrease. This is because the higher the Ga content, the more likely the volume fraction of the main phase particles will decrease. Conventionally, magnets with low B contents and high Ga contents are known, but these magnets are more likely to have low Br than the RTB permanent magnet according to this embodiment.

[0051] There are no particular restrictions on the Al content. The Al content may be 0% by mass or more and 0.30% by mass or less. In other words, Al may not be contained. The Al content may be 0.06% by mass or more and 0.30% by mass or less.

[0052] There are no particular restrictions on the Zr content. It may be 0% by mass or more and 0.40% by mass or less. In other words, Zr need not be contained. The Zr content may be 0.05% by mass or more and 0.40% by mass or less, or 0.10% by mass or more and 0.25% by mass or less. When the Zr content is within the above range, Br and Hcj tend to be high. The lower the Zr content, the more likely Hcj is to decrease. The higher the Zr content, the more likely Br is to decrease.

[0053] There are no particular restrictions on the C content. It may be 1000 ppm or less, 790 ppm or less, or 750 ppm or less. By keeping the C content within the above range, it becomes easier to improve Br and Hcj. C may not be included, but producing an RTB permanent magnet with a low C content places a heavy burden on the process and increases costs. The C content may be 250 ppm or more, or 450 ppm or more.

[0054] There are no particular restrictions on the N content. It may be 900 ppm or less, 540 ppm or less, or 500 ppm or less. By keeping the N content within the above range, it becomes easier to improve Br and Hcj. N does not have to be contained, but producing an RTB permanent magnet with a low N content places a heavy burden on the process and increases costs. The N content may be 150 ppm or more, or 210 ppm or more.

[0055] There are no particular restrictions on the O content. It may be 1000 ppm or less, 700 ppm or less, or 650 ppm or less. By keeping the O content within the above range, it becomes easier to improve Br and Hcj. O need not be included, but producing an RTB permanent magnet with a low O content places a heavy burden on the process and increases costs. The O content may be 350 ppm or more, or 590 ppm or more.

[0056] There are no particular restrictions on the Fe content. Fe may be the substantial remainder of the RTB permanent magnet. "Fe being the substantial remainder of the RTB permanent magnet" means that the total content of elements other than Fe and the above elements, i.e., the total content of elements other than R, Fe, Co, Ni, Cu, Al, Ga, Zr, O, C, and N, is 5% by mass or less. The total content of elements other than Fe and the above elements may be 1% by mass or less, or even 0.1% by mass or less.

[0057] The various components contained in the RTB permanent magnet according to this embodiment can be measured using conventionally known methods. The amounts of various elements are measured, for example, by X-ray fluorescence analysis and inductively coupled plasma atomic emission spectrometry (ICP analysis). The O content is measured, for example, by inert gas fusion-non-dispersive infrared absorption spectrometry. The C content is measured, for example, by oxygen flow combustion-infrared absorption spectrometry. The N content is measured, for example, by inert gas fusion-thermal conductivity spectrometry.

[0058] The RTB permanent magnet according to this embodiment includes a plurality of main phase particles and grain boundaries. The main phase particles may be core-shell particles each consisting of a core and a shell covering the core. At least the shell may contain a heavy rare earth element, and Tb may also be present.

[0059] By having a heavy rare earth element present in the shell portion, the magnetic properties of the RTB-based permanent magnet can be efficiently improved.

[0060] In this embodiment, the shell is defined as the portion where the ratio of heavy rare earth elements to light rare earth elements (heavy rare earth elements / light rare earth elements (molar ratio)) is at least twice the ratio in the center (core) of the main phase particle.

[0061] The thickness of the shell is not particularly limited, but may be 100 nm or less, or may be 50 nm or less. The particle size of the main phase particles is not particularly limited, but may be 2.5 μm or more and 6.0 μm or less.

[0062] The main phase particles can be made into the above-mentioned core-shell particles by any method. For example, there is a method using grain boundary diffusion, which will be described later. The heavy rare earth element diffuses through the grain boundaries and replaces the rare earth element R on the surface of the main phase particle, forming a shell with a high ratio of heavy rare earth element, resulting in the above-mentioned core-shell particle.

[0063] The method for producing an RTB permanent magnet will be described in detail below, but the method for producing an RTB permanent magnet is not limited to this, and other known methods may also be used.

[0064] [Raw powder preparation process] The raw material powder can be prepared by a known method. In this embodiment, a one-alloy method using a single alloy will be described, but a so-called two-alloy method in which a first alloy and a second alloy having different compositions are mixed to prepare the raw material powder may also be used.

[0065] First, a raw material alloy for the RTB permanent magnet is prepared (alloy preparation step). In the alloy preparation step, raw material metals corresponding to the composition of the RTB permanent magnet according to this embodiment are melted by a known method, and then cast to produce a raw material alloy having the desired composition.

[0066] Examples of raw material metals that can be used include rare earth metals or rare earth alloys, pure iron, ferroboron, metals such as Co and Cu, and alloys or compounds thereof. Any casting method can be used to cast raw material alloys from raw material metals. Strip casting can also be used to obtain RTB permanent magnets with high magnetic properties.

[0067] After the raw alloy is prepared, it is pulverized (pulverization step). Hereinafter, the pulverization step will be described as being carried out in two stages: a coarse pulverization step in which the alloy is pulverized to particle sizes of several hundred μm to several mm, and a fine pulverization step in which the alloy is pulverized to particle sizes of several μm.

[0068] In the coarse pulverization step, the material is coarsely pulverized until the particle size is approximately several hundred μm to several mm. This produces a coarsely pulverized powder. In this embodiment, the coarse pulverization is performed by hydrogen absorption pulverization. Hydrogen absorption pulverization is a process in which the raw material alloy is pulverized by absorbing hydrogen and then dehydrogenating it.

[0069] Then, during the dehydrogenation treatment after hydrogen absorption, the dehydrogenation conditions are set to a lower temperature and shorter time than conventional conditions. As a result, dehydrogenation is not performed sufficiently, and hydrogen (H) is intentionally left in the coarsely pulverized powder. Specifically, the dehydrogenation temperature is set to 50°C or higher and 200°C or lower, and the dehydrogenation time is set to 5 minutes or higher and 600 minutes or lower. The dehydrogenation time is preferably 5 minutes or higher and 120 minutes or lower, and more preferably 5 minutes or higher and 30 minutes or lower.

[0070] When the total R content is relatively low, as in this embodiment, the O, C, and N contents in the final magnet tend to be low. O, C, and N often bond with R other than that in the main phase particles and are incorporated into the magnet. When the total R content is low, the amount of R that bonds with O, C, and N is reduced, and the O, C, and N contents also tend to be low.

[0071] Here, by intentionally leaving H in the coarsely pulverized powder, R and H bond together. As a result, the amount of R bonding to O, C, and N is further reduced, and the contents of O, C, and N also tend to be further reduced. There is no particular restriction on the content of H contained in the coarsely pulverized powder, but it is preferably 2100 ppm or more and 3100 ppm or less.

[0072] In sintered magnets manufactured by conventional compression molding, if dehydrogenation is not carried out sufficiently at this stage, the powder after pulverization is prone to oxidation, and the final magnetic properties tend to deteriorate. However, by keeping the total R content relatively low, oxidation of the powder after pulverization is suppressed even without sufficient dehydrogenation, and excellent magnetic properties are obtained after grain boundary diffusion.

[0073] Although dehydrogenation is not necessary, magnets with even better magnetic properties are more likely to be obtained if dehydrogenation is performed at a low temperature for a short time. Furthermore, if dehydrogenation is not performed, the hydrogen content after coarse pulverization will be too high, making cracks more likely to occur during sintering.

[0074] Furthermore, by controlling the nitrogen gas concentration in the atmosphere during dehydrogenation, it is possible to further control the N content in the RTB permanent magnet. Furthermore, by controlling the oxygen gas concentration in the atmosphere during dehydrogenation, it is possible to further control the O content in the RTB permanent magnet. Specifically, it is preferable to keep the nitrogen gas concentration in the atmosphere at 50 ppm or less, and it is preferable to keep the oxygen gas concentration at 50 ppm or less.

[0075] Furthermore, by keeping the oxygen gas concentration in the atmosphere from the crushing process to the sintering process at 100 ppm or less, the O content in the RTB permanent magnet can be reduced.

[0076] Next, the obtained coarsely pulverized powder is finely pulverized until the average particle size is about several μm (fine pulverization step). This results in a finely pulverized powder (raw material powder). The average particle size of the finely pulverized powder may be 2 μm or more and 5 μm or less. In addition, the amount of nitrogen contained in the RTB permanent magnet can be controlled by controlling the nitrogen gas concentration in the atmosphere during the fine pulverization step.

[0077] The fine pulverization can be carried out by any method, for example, by using various fine pulverizers.

[0078] When the coarsely pulverized powder is finely pulverized, various grinding aids such as lauric acid amide and oleic acid amide can be added to obtain a finely pulverized powder with high orientation during molding. Furthermore, by changing the amount of grinding aid added, the carbon content of the RTB permanent magnet can be controlled.

[0079] [Molding process] In the compacting step, the finely pulverized powder is compacted into the desired shape. Compacting may be performed by any method. In this embodiment, the finely pulverized powder is filled into a mold and pressed in a magnetic field. The resulting compact has main phase particles oriented in a specific direction, resulting in an RTB permanent magnet with a higher remanence Br.

[0080] The pressure applied during molding can be 20 MPa to 300 MPa. The magnetic field applied can be 950 kA / m or more, and can also be 950 kA / m to 1600 kA / m. The magnetic field applied is not limited to a static magnetic field, but can also be a pulsed magnetic field. Furthermore, a static magnetic field and a pulsed magnetic field can also be used in combination.

[0081] As a molding method, in addition to the dry molding in which the finely pulverized powder is molded as is as described above, wet molding in which a slurry in which the finely pulverized powder is dispersed in a solvent such as oil can also be applied.

[0082] The shape of the compact obtained by compacting the finely pulverized powder can be any shape. The density of the compact at this stage is 4.0 Mg / m 3 ~4.3Mg / m 3 It can be said that:

[0083] [Sintering process] The sintering process is a process in which the compact is sintered in a vacuum or in an inert gas atmosphere to obtain a sintered body. The sintering temperature needs to be adjusted depending on various conditions, such as the composition, the pulverization method, the particle size and particle size distribution, etc., but the compact is fired, for example, by heating it in a vacuum or in the presence of an inert gas at 1000°C to 1200°C for 1 hour to 20 hours. This results in a high-density sintered body. In this embodiment, a minimum of 7.45 Mg / m 3 The density of the sintered body is 7.50 Mg / m 3 It may be more than that.

[0084] [Aging treatment process] The aging treatment step is a step in which the sintered body is heat-treated at a temperature lower than the sintering temperature. There are no particular restrictions on whether or not aging treatment is performed, and there are no particular restrictions on the number of times aging treatment is performed, and it is performed appropriately depending on the desired magnetic properties. In addition, the grain boundary diffusion step described below may also serve as the aging treatment step. The RTB-based permanent magnet according to this embodiment is subjected to two aging treatments.

[0085] The first aging step is referred to as the first aging step, the second aging step is referred to as the second aging step, the aging temperature of the first aging step is referred to as T1, and the aging temperature of the second aging step is referred to as T2.

[0086] There are no particular limitations on the temperature T1 and aging time in the primary aging step, but they can be set at 700° C. or higher and 900° C. or lower for 1 hour to 10 hours.

[0087] There are no particular limitations on the temperature T2 and aging time in the second aging step, but they can be set at 500° C. or higher and 700° C. or lower for 1 hour to 10 hours.

[0088] Such an aging treatment can improve the magnetic properties, particularly Hcj, of the finally obtained RTB permanent magnet.

[0089] The RTB permanent magnet obtained at this stage has poorer magnetic properties than RTB permanent magnets that are not subjected to the conventional grain boundary diffusion process. However, when Tb is diffused into the grain boundaries using the grain boundary diffusion process described below, Hcj increases significantly. Furthermore, the RTB permanent magnet after Tb grain boundary diffusion has better magnetic properties than the conventional RTB permanent magnet after Tb grain boundary diffusion.

[0090] There are no particular limitations on the composition of the RTB permanent magnet obtained at this stage. For example, R is one or more rare earth elements, essentially including a light rare earth element; T is one or more iron group elements, essentially including Fe or Fe and Co; B is boron; and the RTB permanent magnet may further contain Cu; The total content of light rare earth elements is 27.95% by mass or more and 29.55% by mass or less, Cu content is 0.05 mass% or more and 0.40 mass% or less, The B content is 0.93 mass% or more and 1.00 mass% or less, C content less than 750 ppm, N content less than 500 ppm, The O content may be less than 650 ppm.

[0091] In this embodiment, the R content in the magnet before grain boundary diffusion is relatively low. This allows the composition of the entire magnet to be R2T 14 As a result, R2T 14 There is little R other than in the B main phase particles. Furthermore, the contents of O, C, and N are also relatively low. This makes it difficult for R and O, R and C, and R and N to bond together. In other words, it is difficult for subphases other than the main phase particles to form. In addition, the proportion of active rare earth elements increases, so sufficient sinterability is achieved even with a relatively low R content.

[0092] In this embodiment, the proportion of main phase particles in the magnet before grain boundary diffusion is large, while the proportion of subphases other than the main phase particles is small. Furthermore, the proportion of grain boundaries is small. Figure 2 shows an SEM image of the magnet before grain boundary diffusion, observed using an SEM. Compared to conventional RTB permanent magnets, the grain boundary triple junctions are small, and the two-particle grain boundary phase in particular is significantly thin. Furthermore, there are also locations where the main phase particles appear to be directly connected to each other without the two-particle grain boundary phase in between. Specifically, the average thickness of the two-particle grain boundary phase may be 5 nm or less, or even 2 nm or less. Furthermore, at this point, the Hcj is significantly lower than that of conventional magnets before grain boundary diffusion.

[0093] However, if the magnet before grain boundary diffusion is subjected to grain boundary diffusion using a diffusion material containing Tb, as described below, Hcj is significantly improved. Furthermore, because the proportion of subphases is small, it is easy to obtain a magnet with a high Br.

[0094] This is because the diffusion material diffuses sufficiently even when the two-particle grain boundary phase is thin. The diffusion of the diffusion material is sufficient because the proportion of subphases and the size of the grain boundary triple junctions are small, reducing segregation of the diffusion material to the subphases and the grain boundary triple junctions, and because the proportion of active rare earth elements is high, as described above. Furthermore, the relatively low total R content suppresses dissolution of the main phase particles due to grain boundary diffusion. As a result, the thickness of the Tb-containing shell in the main phase particles with a core-shell structure after grain boundary diffusion becomes thin. This increases the Tb concentration in the shell. Therefore, the improvement in Hcj due to Tb diffusion is large, resulting in a significant improvement in Hcj.

[0095] A method for diffusing Tb into the grain boundaries of the resulting sintered body that is an RTB permanent magnet will now be described.

[0096] [Processing process (before grain boundary diffusion)] Before grain boundary diffusion, a step may be included in which the RTB permanent magnet according to this embodiment is processed into a desired shape, as necessary. Processing methods include, for example, shaping such as cutting and grinding, and chamfering such as barrel polishing.

[0097] [Grain boundary diffusion process] Grain boundary diffusion can be achieved by applying a diffusion material containing a heavy rare earth element metal, a compound or alloy containing a heavy rare earth element, or the like to the surface of the RTB permanent magnet by coating or vapor deposition, followed by heat treatment. In this embodiment, the heavy rare earth element is Tb. Grain boundary diffusion of the heavy rare earth element can further improve the Hcj of the final RTB permanent magnet. Tb is preferred as the heavy rare earth element to be diffused through grain boundaries in the sintered compact. Using Tb makes it possible to obtain a higher Hcj.

[0098] In the embodiment described below, a paint containing Tb as a diffusing material is prepared and applied to the surface of an RTB-based permanent magnet.

[0099] The form of the paint is arbitrary. The compound containing Tb and the solvent or dispersion medium to be used are also arbitrary. The concentration of Tb in the paint is also arbitrary. An example of a method for preparing the paint will be described below.

[0100] First, a source metal for the diffusing material is prepared. Tb is prepared as the source metal for the diffusing material. The source metal for the diffusing material may be Tb alone, or multiple types of source metals for the diffusing material containing Tb may be prepared. Source metals for the diffusing material other than Tb may include, for example, light rare earth elements (e.g., Nd, Pr), Cu, Co, Fe, Al, Ga, and Dy, or Nd, Cu, Co, and Pr. In particular, Nd and Cu may be used together with Tb as the diffusing material. Next, the source metal for the diffusing material is melted by high-frequency induction heating, and the resulting molten metal is quenched with a roll to produce a quenched ribbon, which is a source alloy for the diffusing material. The obtained quenched ribbon is coarsely pulverized using a stamp mill in an Ar-substituted glove box. The coarsely pulverized source alloy for the diffusing material is then sealed in a sealed container substituted with an Ar atmosphere and pulverized to obtain a diffusing material powder with an average particle size of 5 to 20 μm. Next, a gradual oxidation treatment is performed. Specifically, air is gradually introduced into the sealed container, which is in an Ar atmosphere. The reason for the gradual oxidation treatment is that there is a risk of the powder catching fire if suddenly exposed to air.

[0101] Here, it is more preferable that the diffusing material contains at least one selected from Nd, Cu, Co, Pr, Al, and Ga in addition to Tb, rather than Tb alone. The diffusing material may contain at least one selected from Nd, Cu, Co, and Pr in addition to Tb. The Tb content in the diffusing material is not particularly limited. For example, it may be 50 parts by mass or more, assuming that the total diffusing material is 100 parts by mass. The melting point of Tb alone is 1356°C. In contrast, an alloy containing at least one selected from Nd, Cu, Co, Pr, Al, and Ga in addition to Tb has a lower melting point. For example, the melting point of a Tb-Nd-Cu alloy varies depending on the content ratio of each element, but can be set to 890°C or below. In other words, when the diffusing material contains at least one selected from Nd, Cu, Co, Pr, Al, and Ga in addition to Tb, grain boundary diffusion can be performed at low temperatures. Furthermore, Nd, Cu, Co, Pr, Al, and Ga are all components that form a two-particle grain boundary phase. Because the two-particle grain boundary phase is very thin before grain boundary diffusion, the components that form the two-particle grain boundary phase can diffuse efficiently. Because the two-particle grain boundary phase of the RTB permanent magnet according to this embodiment is very thin before grain boundary diffusion, the content of the components that form the two-particle grain boundary phase is low. Therefore, when the diffusing agent contains components that form the two-particle grain boundary phase in addition to Tb, the concentration gradient caused by the difference in concentration between the components that form the two-particle grain boundary phase in the diffusing agent and the components that form the two-particle grain boundary phase in the two-particle grain boundary phase becomes large. The concentration gradient of the components that form the two-particle grain boundary phase then serves as a driving force for the rapid diffusion of the components that form the two-particle grain boundary phase. As a result, because the two-particle grain boundary phase is very thin before grain boundary diffusion, it is believed that the components that form the two-particle grain boundary phase can diffuse efficiently. Furthermore, the RTB permanent magnet according to this embodiment can have a higher main phase volume fraction after grain boundary diffusion than conventional RTB permanent magnets. As a result, Hcj can be significantly improved while maintaining a high Br.

[0102] Furthermore, if grain boundary diffusion can be performed at low temperatures, the dissolution of main phase particles that occurs during heat treatment in the grain boundary diffusion process can be reduced. As a result, the thickness of the shell containing the diffusing material in the main phase particles with a core-shell structure after grain boundary diffusion is reduced. As a result, the Tb concentration in the shell can be increased, significantly improving Hcj.

[0103] Next, a binder resin and alcohol are added to the obtained diffusion material powder, and the resulting mixture is made into a paint in a ball mill to prepare a coating material for application.

[0104] Next, a coating material is applied to the sintered body before grain boundary diffusion, but an etching treatment may be performed on the sintered body before grain boundary diffusion before coating. Next, the coating material is applied to the sintered body after the etching treatment. There is no particular limit to the number of surfaces to be coated. For example, the coating material may be applied to the entire surface of the sintered body, or to only two opposing surfaces of the sintered body.

[0105] The diffusion treatment temperature in the grain boundary diffusion step according to this embodiment may be 650° C. to 930° C. The diffusion treatment time may be 5 hours to 24 hours. The grain boundary diffusion step may also serve as the above-mentioned aging treatment step.

[0106] By using the above-mentioned diffusion treatment temperature and time, it is possible to keep production costs low and to easily obtain a favorable Tb concentration distribution. Furthermore, when a metal element other than Tb (e.g., a light rare earth element (e.g., Nd, Pr), Cu, Co, Fe, Al, Ga, or Dy) is used as the diffusing agent, it is also possible to easily obtain a favorable concentration distribution of that metal element. Then, by performing a grain boundary diffusion process on the magnet shown in FIG. 2, the magnet shown in FIG. 3 can be obtained. It can be seen that the two-particle grain boundary phase, which was very thin in FIG. 2, has become thicker in FIG. 3.

[0107] Furthermore, after grain boundary diffusion, a further heat treatment may be carried out. In this case, the heat treatment temperature may be 480°C to 680°C. The heat treatment time may be 0.5 to 3 hours. Such a heat treatment can improve the magnetic properties, particularly the Hcj, of the final RTB permanent magnet.

[0108] [Processing process (after grain boundary diffusion)] After the grain boundary diffusion step, the RTB permanent magnet may be subjected to various types of processing. There are no particular restrictions on the type of processing that may be performed. For example, shape processing such as cutting or grinding, or surface processing such as chamfering using barrel polishing may be performed.

[0109] The RTB permanent magnet according to this embodiment obtained by the above method can be magnetized to become an RTB permanent magnet product.

[0110] The RTB permanent magnet according to this embodiment obtained in this manner has the desired properties: specifically, high residual magnetic flux density Br and coercive force Hcj, as well as excellent corrosion resistance and manufacturing stability.

[0111] The RTB permanent magnet according to this embodiment is suitable for use in motors, generators, etc. It is also suitable for use in automobiles equipped with such motors.

[0112] The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention. [Example]

[0113] The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

[0114] (Experimental Example 1) (Production of RTB sintered magnets) The raw materials used were Nd, Pr, electrolytic iron, and low-carbon ferroboron alloy. Additionally, Al, Ga, Cu, Co, and Zr were prepared in the form of pure metals or alloys with Fe.

[0115] Using the above raw materials, raw alloys were produced by strip casting, so that the final magnet composition after grain boundary diffusion, described below, would be the composition of each sample shown in Table 1. The content of each component shown in Table 1 represents the content relative to the total mass of the magnet. The Fe content is listed as the balance (bal.) meaning that this is the balance excluding impurities not listed in the table. Each magnet may contain impurities not listed in the table to a degree that does not affect the magnetic properties, specifically, a total of 5 mass% or less. The alloy thickness of the raw alloy was 0.2 mm to 0.4 mm.

[0116] Next, hydrogen gas was flowed through the raw alloy at room temperature for one hour to absorb hydrogen. The atmosphere was then switched to Ar gas, and dehydrogenation was performed at the dehydrogenation temperature and for the dehydrogenation time listed in Tables 1 and 2. The raw alloy was then hydrogen-absorbed and crushed (coarsely crushed) to obtain coarsely crushed powder. The nitrogen and oxygen gas concentrations in the atmosphere were controlled for each sample so that the final RTB-based sintered magnet would have the O and N content listed in Table 1. For each example and comparative example, the nitrogen and oxygen gas concentrations were adjusted to approximately 50 ppm or less. After cooling, the mixture was sieved to obtain powder with a particle size of 425 μm or less. Note that a low-oxygen atmosphere with an oxygen concentration of less than 100 ppm was maintained throughout the hydrogen-absorption and crushing steps until the sintering step described below. The hydrogen content of the cooled coarsely crushed powder was measured using an inert gas non-dispersive infrared absorption method. The results are shown in Tables 1 and 2.

[0117] Next, oleic acid amide was added as a grinding aid to the raw alloy powder after hydrogen absorption grinding and sieving, and mixed so that the C content in the final RTB permanent magnet would be the content shown in Table 1.

[0118] The mixture was then pulverized using a collision plate type jet mill to obtain fine powder having an average particle size of 3.9 μm to 4.2 μm, where the average particle size is the average particle size D50 measured using a laser diffraction type particle size distribution analyzer.

[0119] The obtained fine powder was compacted in a magnetic field to produce a compact. The applied magnetic field was a static magnetic field of 1200 kA / m. The applied pressure during compaction was 98 MPa. The magnetic field application direction and the pressure direction were perpendicular to each other. When the density of the compacts was measured at this point, the density of all the compacts was 4.10 Mg / m 3 ~4.25Mg / m 3 was within the range.

[0120] Next, the compact was sintered to obtain a sintered body. The sintering conditions were changed as appropriate depending on the composition, etc., but the temperature was kept within the range of 1040°C to 1100°C for 5 hours. The sintering atmosphere was a vacuum. The sintered density was 7.45 Mg / m 3 ~7.55Mg / m 3 Thereafter, the specimens were subjected to a first aging treatment in an Ar atmosphere at atmospheric pressure at a first aging temperature of 900°C for 2 hours, and then to a second aging treatment at a second aging temperature of 550°C for 2 hours.

[0121] Thereafter, the sintered body after the aging treatment was vertically machined to a size of 12 mm x 12 mm x 4.5 mm (thickness in the direction of easy magnetization 4.5 mm) to prepare a sintered body before grain boundary diffusion, which will be described later.

[0122] A coating material containing Tb as a diffusing material was prepared separately from the sintered body before grain boundary diffusion. In Experimental Example 1, first, Tb alone was prepared as the raw material metal of the diffusing material. Next, the raw material metal of the diffusing material was melted by high-frequency induction heating, and the resulting molten metal was rapidly cooled with a roll at a temperature of 1370°C to produce a quenched ribbon of the diffusing material raw material alloy (diffusing material raw material alloy 1). The obtained quenched ribbon was coarsely pulverized using a stainless steel stamp mill in an Ar atmosphere. The coarsely pulverized diffusing material raw material alloy was then sealed together with stainless steel media in a sealed container substituted with an Ar atmosphere and pulverized using a ball mill to obtain a diffusing material powder with an average particle size of 10 to 20 μm. Next, a gradual oxidation treatment was performed. Specifically, air was gradually introduced into the sealed container in an Ar atmosphere glove box. The gradual oxidation treatment was performed because there was a risk of fire if the powder was suddenly exposed to air.

[0123] A coating material was prepared by adding a binder resin (butyral fine powder) and alcohol to the prepared diffusion material powder. Specifically, 2 parts by mass of binder resin and 100 parts by mass of alcohol were added to 100 parts by mass of diffusion material powder and mixed to obtain a mixture. Next, the obtained mixture was placed in a cylindrical resin container with a lid in an Ar atmosphere, the lid was closed, and the container was placed on a ball mill stand and rotated to form a coating material. The rotation time was 24 hours, and the rotation speed was 120 rpm.

[0124] Next, a coating material was applied to the sintered body before grain boundary diffusion. First, an etching treatment was performed on the sintered body before grain boundary diffusion. For the etching treatment, the sintered body before grain boundary diffusion was immersed in a mixed solution of nitric acid and ethanol (100% by mass ethanol and 3% by mass nitric acid) for 3 minutes, followed by immersion in ethanol for 1 minute. This process was repeated twice. Next, the coating material was uniformly applied to two 12 mm x 12 mm surfaces of the sintered body after the etching treatment. The coating material was also applied so that the final magnet composition would be the composition of each sample shown in Table 1.

[0125] After the coating material was applied and dried, a diffusion treatment was carried out at 950°C for 10 hours in a flow of Ar at atmospheric pressure, followed by a heat treatment at 550°C for 2 hours. The surface of the sample was then scraped off by 0.1 mm on each side to obtain the RTB sintered magnets shown in Tables 1 and 2. Note that TRL is the total content of light rare earth elements (Nd and Pr), and TRE is the total content of rare earth elements (Nd, Pr, and Tb).

[0126] The average composition of each of the resulting RTB-based sintered magnets was measured. Each sample was pulverized using a stamp mill and then subjected to analysis. The amounts of various elements were measured using X-ray fluorescence analysis. The boron (B) content was measured using ICP analysis. The oxygen content was measured using inert gas fusion / non-dispersive infrared absorption spectroscopy, the carbon content was measured using oxygen flow combustion / infrared absorption spectroscopy, and the nitrogen content was measured using inert gas fusion / thermal conductivity spectroscopy. The results are shown in Table 1.

[0127] The magnetic properties of the resulting sintered body before grain boundary diffusion and the RTB sintered magnet after grain boundary diffusion were evaluated using a BH tracer. The magnetic properties were evaluated after magnetization using a pulsed magnetic field of 4000 kA / m. Because the sintered magnets were thin, two sintered magnets were stacked on top of each other for evaluation. The results are shown in Table 2. The magnetic properties of the RTB sintered magnets after grain boundary diffusion were rated as good if they satisfied Br ≥ 1485 mT and Hcj ≥ 1800 kA / m, and even better if they satisfied Br ≥ 1500 mT and Hcj ≥ 1850 kA / m. Table 2 also lists the difference in Hcj before and after grain boundary diffusion.

[0128] The main phase volume fraction of the RTB magnet after grain boundary diffusion was also measured. Specifically, the RTB magnet after grain boundary diffusion was cut and observed using an SEM. For SEM observation, an observation area was set large enough to observe at least 200 main phase particles at a magnification of 2500x. The main phase volume fraction was then measured assuming that the area fraction of the main phase particles in the observation area was the same as the main phase volume fraction. Furthermore, a total of 10 observation areas were set in different locations, and the main phase volume fraction was measured and averaged for each observation area. The results are shown in Table 2.

[0129] [Table 1]

[0130] [Table 2]

[0131] As can be seen from Table 1, all of the Examples of Samples 1 to 3, in which the dehydrogenation temperature and dehydrogenation time were set so as to increase the hydrogen content after coarse pulverization, had good magnetic properties. In particular, Sample 2, which had a low N content, and Sample 3, which had a low C content, both had even better magnetic properties. In contrast, all of the Comparative Examples of Samples 4 to 6, in which the dehydrogenation temperature and dehydrogenation time were set so as to decrease the hydrogen content after coarse pulverization, had poor magnetic properties.

[0132] The Tb concentration distribution of all the RTB-based sintered magnets of the examples and comparative examples was analyzed using an electron probe microanalyzer (EPMA), and it was confirmed that the Tb concentration distribution decreased from the outside to the inside.

[0133] (Experimental Example 2) Experimental Example 2 was carried out in the same manner as Experimental Example 1 except for the following points. The results are shown in Tables 3 and 4. Note that in Experimental Example 1, Table 1 should be read as Table 3, and Table 2 should be read as Table 4.

[0134] In Experimental Example 2, the coating material used was changed from that used in Experimental Example 1. In Experimental Example 2, Tb, Nd, and Cu were each prepared individually as the raw material metals for the diffusing material. Next, the raw material metals for each diffusing material were weighed out so that the mass ratio of Tb:Nd:Cu was 68.8:15.6:15.6. The weighed raw material metals for each diffusing material were then melted in an arc melting furnace and cast, a process repeated three times. The resulting alloy was melted using high-frequency induction heating, and the resulting molten metal was cooled to a temperature of 1300°C using a roll to produce a quenched ribbon of the diffusing material raw material alloy (diffusing material raw material alloy 2). The subsequent steps were the same as in Experimental Example 1, and the coating material for Experimental Example 2 was produced.

[0135] For grain boundary diffusion, the coating material was applied and dried, followed by a diffusion treatment at 900°C for 10 hours while flowing Ar at atmospheric pressure, followed by a heat treatment at 550°C for 2 hours.

[0136] [Table 3]

[0137] [Table 4]

[0138] As shown in Tables 3 and 4, all of the Examples had good magnetic properties. In contrast, Sample No. 19, which had too little total rare earth element content; Sample Nos. 22 and 43, which had too much total rare earth element content; Sample No. 24, which had too little Cu content; Sample No. 27, which had too much Cu content; Sample Nos. 28 and 29, which had too little B content; and Sample No. 39, which had high Ga and C contents, all had low Br and / or Hcj. Furthermore, when the total rare earth element content was too high, when the Cu content was too high, when the B content was too low, and when the Ga and C contents were high, the main phase volume fraction after grain boundary diffusion was small, and the difference in Hcj before and after grain boundary diffusion was also small. The comparative examples of Sample Nos. 40 and 41, in which the dehydrogenation temperature and dehydrogenation time were set to reduce the hydrogen content after coarse grinding, all had poor magnetic properties. Furthermore, cracks occurred during sintering in samples 42 and 43, which were not subjected to dehydrogenation treatment. This is thought to be due to the fact that the hydrogen content after coarse crushing was too high.

[0139] The RTB-based sintered magnets of all examples and comparative examples were analyzed for Tb, Nd, and Cu concentration distributions using an electron probe microanalyzer (EPMA).The results confirmed that the Tb, Nd, and Cu concentration distributions all decreased from the outside to the inside.

[0140] (Experimental Example 3) Experimental Example 3 was carried out in the same manner as Experimental Example 2, except for the following points. The results are shown in Tables 6 to 9. Note that in Experimental Example 2, Table 3 should be read as Tables 6 and 8, and Table 4 should be read as Tables 7 and 9, respectively. TRE is the total content of rare earth elements (Nd, Pr, Tb, and Dy).

[0141] In Experimental Example 3, first, the heavy rare earth elements, light rare earth elements, and metallic elements shown in Table 5 were each prepared singly as the raw material metals for the diffusion materials. Next, the raw material metals for each diffusion material were weighed out to achieve the mass ratios shown in Table 5. The weighed raw material metals for each diffusion material were then melted in an arc melting furnace and cast, a process repeated three times. The resulting alloys were melted using high-frequency induction heating, and the resulting molten metal at a temperature of 1300°C was quenched with a roll to produce quenched ribbons of the diffusion material raw material alloys (diffusion material raw material alloys 3 to 12). The subsequent steps were the same as in Experimental Example 2, and the coating material for Experimental Example 3 was produced.

[0142] [Table 5]

[0143] In Experimental Example 3, the coating material was applied so that the total amount of heavy rare earth elements attached to the sintered body before grain boundary diffusion was 0.6 parts by mass per 100 parts by mass of the sintered body before grain boundary diffusion.

[0144] The magnetic properties of the RTB sintered magnet after grain boundary diffusion of Tb were rated as "good" if they satisfied Br ≥ 1485mT and Hcj ≥ 1800kA / m, and "even better" if they satisfied Br ≥ 1500mT and Hcj ≥ 1850kA / m. The magnetic properties of the RTB sintered magnet after grain boundary diffusion of Dy were rated as "good" if they satisfied Br ≥ 1485mT and Hcj ≥ 1400kA / m.

[0145] [Table 6]

[0146] [Table 7]

[0147] [Table 8]

[0148] [Table 9]

[0149] Tables 6 and 7 show examples and comparative examples in which Tb was diffused. Sample numbers 44 to 50, 52, and 53, in which the dehydrogenation temperature and dehydrogenation time were set so that the hydrogen content after coarse pulverization was sufficiently high, all had good magnetic properties. In contrast, sample numbers 54 to 60, 62, and 63, in which Tb was diffused in the same way as sample numbers 44 to 50, 52, and 53, but the dehydrogenation temperature and dehydrogenation time were set so that the hydrogen content after coarse pulverization was low, all had poor magnetic properties.

[0150] Tables 8 and 9 show examples and comparative examples in which Dy was diffused. Sample No. 51, in which the dehydrogenation temperature and dehydrogenation time were set so that the hydrogen content after coarse grinding was sufficiently high, had good magnetic properties. In contrast, sample No. 61, in which Dy was diffused in the same way as sample No. 51 but the dehydrogenation temperature and dehydrogenation time were set so that the hydrogen content after coarse grinding was low, resulted in poor magnetic properties.

[0151] For all of the RTB-based sintered magnets in the examples and comparative examples, the concentration distribution of elements contained in the raw material alloy of the diffusion material was analyzed using an electron probe microanalyzer (EPMA). As a result, it was confirmed that the concentration distribution of all metal elements contained in the raw material alloy of the diffusion material decreased from the outside to the inside. [Explanation of symbols]

[0152] 1...RTB permanent magnet

Claims

1. An R-T-B system permanent magnet in which R is one or more rare earth elements essentially containing Tb or Dy, T is one or more iron group elements essentially containing Fe or Fe and Co, and B is boron, and further contains Cu, the total content of R is 28.35 mass% or more and 29.95 mass% or less; The Cu content is 0.05 mass% or more and 0.40 mass% or less, The B content is 0.93 mass% or more and 1.00 mass% or less, C content is 790 ppm or less, N content of 540 ppm or less, The O content is 700 ppm or less, the concentration distribution of Tb or Dy decreases from the outside toward the inside of the R-T-B system permanent magnet, An RTB-based permanent magnet having a residual magnetic flux density of 1485 mT or more and a coercive force of 1800 kA / m or more.

2. 2. The RTB system permanent magnet according to claim 1, wherein R is one or more rare earth elements, with Tb being essential.

3. 3. The RTB system permanent magnet according to claim 1, wherein the C content is less than 750 ppm.

4. 4. The RTB system permanent magnet according to claim 1, wherein the N content is less than 500 ppm.

5. 5. The RTB system permanent magnet according to claim 1, wherein the O content is less than 650 ppm.

6. The R-T-B system permanent magnet according to any one of claims 1 to 5, wherein R contains one or more light rare earth elements, and the concentration distribution of the one or more light rare earth elements decreases from the outside toward the inside of the R-T-B system permanent magnet.

7. 7. The RTB system permanent magnet according to claim 1, wherein the Cu concentration distribution decreases from the outside to the inside of the RTB system permanent magnet.

8. 7. The RTB system permanent magnet according to claim 1, further comprising Al, wherein the concentration of Al is distributed so as to decrease from the outside toward the inside of the RTB system permanent magnet.

9. 7. The R-T-B system permanent magnet according to claim 1, further comprising Co, wherein the concentration of Co decreases from the outside toward the inside of the R-T-B system permanent magnet.

10. 7. The R-T-B system permanent magnet according to claim 1, further comprising Ga, wherein the Ga concentration distribution decreases from the outside toward the inside of the R-T-B system permanent magnet.

11. A motor having the RTB system permanent magnet according to any one of claims 1 to 10.

12. A motor vehicle comprising the motor of claim 11.

13. A method for producing an RTB based permanent magnet, comprising: The method includes a step of absorbing hydrogen into a raw alloy and a step of dehydrogenating the hydrogen-absorbing raw alloy, The method for producing an RTB-based permanent magnet comprises dehydrogenating the hydrogen-absorbed raw alloy at a dehydrogenation temperature of 50°C or higher and 200°C or lower for a dehydrogenation time of 5 minutes or higher and 600 minutes or lower.

14. 14. The method for producing an RTB system permanent magnet according to claim 13, wherein the coarsely pulverized powder obtained by dehydrogenating the hydrogen-absorbing raw alloy has an H content of 2100 ppm or more and 3100 ppm or less.

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