Rare earth magnet and method for manufacturing the same

Abstract

To provide an R-T-B-based rare earth magnet with an excellent magnetic property.SOLUTION: The present invention relates to an R-T-B-based rare earth magnet in which R is a rare earth element, T is Fe and / or Co, and B is boron, the carbon arrangement in the R-T-B-based rare earth magnet being adjusted.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to rare earth magnets and methods for manufacturing the same. [Background technology]

[0002] In recent years, high-performance rare-earth magnets such as Sm-Co rare-earth magnets and RTB permanent magnets, such as Nd-Fe-B rare-earth magnets, have been put into practical use.

[0003] For example, Patent Document 1 contains R2T 14 An RTB-type permanent magnet having main phase particles made of a type B compound, wherein R is a rare earth element, T is an iron group element requiring Fe or Fe and Co, and B is boron, the average particle size of the main phase particles is 0.8 μm or more and 2.8 μm or less, and in addition to R, T, and B, it contains at least C and Ga, the content of B is 0.71 mass% or more and 0.86 mass% or less, the content of C is 0.13 mass% or more and 0.34 mass% or less, and the content of Ga is 0.40 mass% or more and 1.80 mass% or less, and the following formula (1) 0.14≦[C] / ([B]+[C])≦0.30 (1) Here, [B] is the B content expressed in atomic percent, and [C] is the C content expressed in atomic percent. A permanent magnet of the RTB type, characterized by satisfying the following conditions, is disclosed.

[0004] Patent Document 2 describes an RTB-type permanent magnet in which R is a rare earth element, T is Fe, or Fe and Co, and B is boron, and R2T 14A permanent magnet of the RTB type is disclosed, comprising a main phase particle consisting of a B crystal phase and grain boundaries formed between the main phase particles, wherein the grain boundaries contain an R-OC-N concentrated portion in which the concentrations of R, O, C, and N are all higher than in the main phase particles, the ROCN concentrated portion contains heavy rare earth elements, the ROCN concentrated portion has a core portion and a shell portion covering at least a part of the core portion, the concentration of heavy rare earth elements in the shell portion is higher than the concentration of heavy rare earth elements in the core portion, and the coverage rate of the shell portion over the core portion in the ROCN concentrated portion is 45% or more on average. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-157834 [Patent Document 2] Japanese Patent Publication No. 2019-160949 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to provide an RTB-type rare-earth magnet with excellent magnetic properties. [Means for solving the problem]

[0007] As a result of various investigations into means to solve the above-mentioned problems, the present inventors have found that by concentrating carbon (C), which is known to improve anisotropic magnetic fields, in the grain boundary phase and the shell portion of the main phase of an NdFeB-based rare earth magnet, the resulting NdFeB-based rare earth magnet has improved coercivity (heat resistance), thus completing the present invention.

[0008] In other words, the gist of this invention is as follows: (1) An RTB-type rare earth magnet in which R is a rare earth element, T is Fe and / or Co, and B is boron, The aforementioned RTB-type rare earth magnet is R2T 14 The system comprises a main phase having a type B crystal structure, and a grain boundary phase present around the main phase. The average particle size of the main phase is 1 μm or less. The main phase has a core portion and a shell portion surrounding the core portion. The total content ratio of cerium, lanthanum, gadolinium, yttrium, and scandium in the core portion relative to the total constituent elements of the core portion is higher than the total content ratio of cerium, lanthanum, gadolinium, yttrium, and scandium in the shell portion relative to the total constituent elements of the shell portion. The total content ratio of neodymium, praseodymium, terbium, dysprosium, and holmium relative to the total constituent elements of the shell portion is higher than the total content ratio of neodymium, praseodymium, terbium, dysprosium, and holmium relative to the total constituent elements of the core portion. The RTB-type rare earth magnet contains 0.50 atomic% to 1.1 atomic% of carbon relative to the total constituent elements of the RTB-type rare earth magnet. In the shell portion, when the content of carbon in atomic percent is [C] and the content of boron is [B] relative to the total constituent elements of the shell portion, [C] is 0.50 atomic percent to 1.1 atomic percent, and [C] / ([C]+[B]) is 0.10 to 0.18, and The carbon content in the grain boundary phase relative to the total constituent elements of the grain boundary phase is higher than the carbon content in the main phase relative to the total constituent elements of the main phase. RTB-type rare earth magnets. (2) The RTB-type rare earth magnet according to (1), wherein the carbon content in the shell portion relative to the total constituent elements of the shell portion is higher than the carbon content in the core portion relative to the total constituent elements of the core portion. (3) The RTB-type rare earth magnet according to (1) or (2), wherein the average particle size of the main phase is 0.1 μm to 1 μm. (4) A method for manufacturing an R-T-B rare earth magnet, where R is a rare earth element, T is Fe and / or Co, and B is boron, comprising: The method includes: Diffusing and infiltrating a modifier into a rare earth magnet precursor; and The rare earth magnet precursor contains, as rare earth elements, one or more elements selected from the group consisting of cerium, lanthanum, gadolinium, yttrium, and scandium; The R-T-B rare earth magnet has a main phase with a R2T 14 B-type crystal structure and a grain boundary phase existing around the main phase; The average particle size of the main phase is 1 μm or less; The modifier contains, based on the total constituent elements of the modifier, 60 atomic% to 80 atomic% of one or more elements selected from the group consisting of neodymium, praseodymium, terbium, dysprosium, and holmium, and 10 atomic% to 20 atomic% of carbon, and The modifier is diffused and infiltrated at 5.0 mol to 15.0 mol per 100 mol of the rare earth magnet precursor; The method.

Advantages of the Invention

[0009] According to the present invention, an R-T-B rare earth magnet with excellent magnetic properties is provided.

Brief Description of the Drawings

[0010] [Figure 1] It is a graph showing the relationship between the C molar ratio in the modifier and the coercive force of the hot-worked magnet for Example 1 prepared with a diffusion infiltration amount of 10% by mass, and Comparative Examples 1 and 4. [Figure 2] It is a graph showing the relationship between the C molar ratio in the modifier and the coercive force of the hot-worked magnet for Example 2 prepared with a diffusion infiltration amount of 15% by mass, and Comparative Examples 2 and 5. [Figure 3] It is a graph showing the relationship between the C molar ratio in the modifier and the coercive force of the hot-worked magnet for Example 3 prepared with a diffusion infiltration amount of 20% by mass, and Comparative Examples 3 and 6. [Figure 4] It is an explanatory drawing schematically showing a cooling device used in the liquid quenching method.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, preferred embodiments of the present invention will be described in detail. In this specification, the features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. Note that the rare earth magnet and its manufacturing method of the present invention are not limited to the following embodiments, and can be implemented in various forms with modifications and improvements that can be made by those skilled in the art without departing from the gist of the present invention.

[0012] In the R-T-B-based rare earth magnet of the present invention, R is a rare earth element, and is, for example, one or more selected from the group consisting of cerium, lanthanum, yttrium, scandium, neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium. Further, T is an iron group element, and is iron, cobalt, or iron and cobalt (iron and / or cobalt), and here, the ratio of each element in the case of iron and cobalt is not limited. Furthermore, B is boron. Note that the R-T-B-based rare earth magnet of the present invention may contain one or more selected from the group consisting of additive elements known in the art, such as titanium, vanadium, copper, chromium, manganese, nickel, zirconium, niobium, molybdenum, hafnium, tantalum, tungsten, aluminum, gallium, silicon, bismuth, tin, etc., as long as the coercive force of the R-T-B-based rare earth magnet is not impaired.

[0013] In the RTB-based rare earth magnet of the present invention, the R content is typically 12 to 20 atoms relative to the total number of atoms in the RTB-based rare earth magnet. In one embodiment, the Nd content is typically 10 to 20 atoms relative to the total number of atoms in R, the Pr content is typically 1 to 10 atoms relative to the total number of atoms in R, the Ce content is typically 40 to 60 atoms relative to the total number of atoms in R, and the La content is typically 25 to 35 atoms relative to the total number of atoms in R. In the RTB-based rare earth magnet of the present invention, the T content is typically 60 to 83 atoms relative to the total number of atoms in the RTB-based rare earth magnet. In one embodiment, the Fe content is typically 60 to 70 atoms relative to the total number of atoms in the RTB-based rare earth magnet, and the Co content is typically 10 to 20 atoms relative to the total number of atoms in the RTB-based rare earth magnet. In the RTB-based rare earth magnet of the present invention, the content of B is typically 5 to 20 atoms relative to the total number of atoms in the RTB-based rare earth magnet. In the RTB-based rare earth magnet of the present invention, the content of the added elements is typically 0 to 2 atoms relative to the total number of atoms in the RTB-based rare earth magnet. In one embodiment, the content of Ga is typically 0 to 0.5 atoms relative to the total number of atoms in the RTB-based rare earth magnet, the content of Cu is typically 0 to 0.2 atoms relative to the total number of atoms in the RTB-based rare earth magnet, and the content of Al is typically 0 to 0.2 atoms relative to the total number of atoms in the RTB-based rare earth magnet. The content of each element in the RTB-based rare earth magnet may be calculated based on the amount of each element added during manufacturing, but it can also be measured by methods known in the art, such as X-ray fluorescence analysis (XRF) or inductively coupled plasma mass spectrometry (ICP-MS).

[0014] By being composed of the aforementioned elements, RTB-type rare earth magnets can possess high coercivity.

[0015] The RTB-type rare earth magnet of the present invention is R2T 14 The system comprises a main phase having a type B crystal structure, and a grain boundary phase surrounding the main phase, with R2T constituting the main phase. 14Crystals with a type B crystal structure are bonded together via grain boundary phases. In other words, the main phase is separated by the grain boundary phase, and therefore is also magnetically separated, suppressing magnetization reversal and allowing for higher coercivity compared to cases where the crystal is not separated by grain boundary phases.

[0016] The average particle size of the main phase is 1 μm or less, and in one embodiment, it is 0.1 μm to 0.5 μm.

[0017] Here, the "average particle size" is measured as follows: A certain region is defined in a scanning electron microscope image or a transmission electron microscope image, observed from a direction perpendicular to the easy magnetization axis. Multiple lines are drawn perpendicular to the easy magnetization axis for the main phase within this region, and the diameter (length) of the main phase is calculated from the distance between the points where the lines intersect within the particles of the main phase (section method). If the cross-section of the main phase is close to a circle, it is converted using the projected area equivalent diameter. If the cross-section of the main phase is close to a rectangle, it is converted using the cuboid approximation. The D50 value of the diameter (length) distribution (particle size distribution) obtained in this way is the average particle size.

[0018] By having the average particle size of the main phase fall within the aforementioned range, the coercivity of the rare earth magnet can be improved.

[0019] The main phase has a core portion and a shell portion surrounding the core portion.

[0020] The average particle size of the core portion of the main phase is typically 900 nm or less. The average thickness of the shell portion of the main phase is typically 50 nm or less, and in one embodiment, it is 20 nm to 30 nm. Note that the particle size of the core portion corresponds to the particle size of the main phase minus 2 × (shell thickness).

[0021] Here, the average thickness of the shell portion of the main phase can be measured as a compositionally modulated portion from the core portion by TEM-EDX analysis or the like.

[0022] In the main phase, the total content of cerium, lanthanum, gadolinium, yttrium, and scandium in the core relative to the total constituent elements of the core is higher than the total content of cerium, lanthanum, gadolinium, yttrium, and scandium in the shell relative to the total constituent elements of the shell. For example, the ratio (core:shell) of the total content of cerium, lanthanum, gadolinium, yttrium, and scandium in the core relative to the total constituent elements of the core (e.g., in terms of moles) to the total content of cerium, lanthanum, gadolinium, yttrium, and scandium in the shell relative to the total constituent elements of the shell (e.g., in terms of moles) is usually 1.1:1 to 10:1.

[0023] In the main phase, the total content of neodymium, praseodymium, terbium, dysprosium, and holmium in the shell portion relative to the total constituent elements of the shell portion is higher than the total content of neodymium, praseodymium, terbium, dysprosium, and holmium in the core portion relative to the total constituent elements of the core portion. For example, the ratio (shell portion:core portion) of the total content of neodymium, praseodymium, terbium, dysprosium, and holmium in the shell portion relative to the total constituent elements of the shell portion (e.g., ratio in terms of amount of substance (moles)) to the total content of neodymium, praseodymium, terbium, dysprosium, and holmium in the core portion relative to the total constituent elements of the core portion (e.g., ratio in terms of amount of substance (moles)) is usually 1.1:1 to 10:1.

[0024] Increasing the remanent magnetization and coercivity in the shell portion is more effective in increasing the overall remanent magnetization and coercivity of a rare-earth magnet than increasing the remanent magnetization and coercivity in the core portion. Remanent magnetization and coercivity increase as the content of neodymium, praseodymium, terbium, dysprosium, and holmium increases. Therefore, the diffusion and penetration of the modifier is advantageous in improving remanent magnetization and coercivity because cerium, lanthanum, gadolinium, yttrium, and scandium in the rare-earth magnet precursor are discharged from the shell portion to the grain boundary phase, and neodymium, praseodymium, terbium, dysprosium, and holmium in the modifier diffuse and penetrate from the grain boundary phase to the shell portion.

[0025] The RTB-based rare earth magnet of the present invention contains 0.50 atomic% to 1.1 atomic% of carbon, and in one embodiment, 0.6 atomic% to 0.9 atomic% of carbon, relative to the total constituent elements of the RTB-based rare earth magnet. The carbon content can be measured, for example, by combustion-infrared absorption spectroscopy in an oxygen stream or STEM-EDX analysis.

[0026] In the RTB-type rare earth magnet of the present invention, when the content of carbon in atomic percent is [C]' and the content of boron in atomic percent is [B]', the ratio [C]' / ([C]'+[B]') is typically 0.05 to 0.18, and in one embodiment 0.09 to 0.16. Here, [B]' is not limited as long as it is within the above ratio, but is typically 5.0 atomic percent to 6.0 atomic percent, and in one embodiment 5.3 atomic percent to 5.6 atomic percent.

[0027] By including carbon within the aforementioned range in RTB-type rare-earth magnets, the anisotropic magnetic field of the rare-earth magnet can be improved. By improving the anisotropic magnetic field, the coercivity of the entire magnet can be improved.

[0028] In the RTB-type rare earth magnet of the present invention, in the shell portion, when the content of carbon is [C] and the content of boron is [B] in atomic percent relative to the total constituent elements of the shell portion, [C] is 0.50 atomic percent to 1.1 atomic percent, and in one embodiment, 0.6 atomic percent to 0.9 atomic percent, and [C] / ([C]+[B]) is 0.10 to 0.18, and in one embodiment, 0.12 to 0.16. Here, [B] is not limited as long as it is within the above ratio, but is usually 4.7 atomic percent to 6.0 atomic percent, and in one embodiment, 4.8 atomic percent to 5.3 atomic percent. The carbon and boron content in the shell portion can be measured, for example, by electron probe microanalyzer (EPMA) or energy dispersive X-ray spectroscopy (EDX).

[0029] By ensuring that the carbon and boron content ratios of the shell portion of the main phase fall within the aforementioned range, it is possible to improve the anisotropic magnetic field while maintaining the saturation magnetization of the rare-earth magnet.

[0030] The RTB-type rare earth magnet of the present invention is typically processed into any shape for use. The shape of the RTB-type rare earth magnet of the present invention is not particularly limited. The shape of the RTB-type rare earth magnet of the present invention can be any shape, such as a rectangular parallelepiped, a hexahedron, a flat plate, a columnar shape such as a rectangular prism, or a cylindrical shape with a C-shaped cross-section.

[0031] Furthermore, the RTB-type rare earth magnets of the present invention include both magnet products in which the magnet has been magnetized after processing and magnet products in which the magnet has not been magnetized.

[0032] Because the RTB-based rare earth magnet of the present invention has the above-described configuration and composition, the RTB-based rare earth magnet of the present invention can have high coercivity.

[0033] The RTB-type rare earth magnet of the present invention can be manufactured using known techniques in the art, except that a rare earth magnet precursor and a modifier are prepared to have the configuration and composition of the RTB-type rare earth magnet of the present invention, and the modifier is diffused and permeated into the grain boundary during grain boundary diffusion.

[0034] The R-T-B rare earth magnet of the present invention can be manufactured, for example, as follows. First, a rare earth magnet precursor is prepared by melt preparation, melt cooling, sintering, and optionally anisotropy imparting, which will be described below. (Melt preparation) Prepare a melt adjusted to the composition of the R-T-B rare earth magnet of the present invention. For elements that may be depleted in subsequent processes, the depletion may be anticipated.

[0035] (Melt cooling) Subsequently, the melt having the above-described composition is rapidly quenched. "Rapid quenching" generally means cooling at 5×10 5 °C / second or more, in one embodiment 1×10 6 °C / second or more, in one embodiment 5×10 6 °C / second or more, and generally 5×10 7 °C / second or less, in one embodiment 1×10 7 °C / second or less. When the melt having the above-described composition is rapidly quenched, a magnetic thin strip or magnetic thin sheet having a nanocrystallized main phase can be obtained.

[0036] The rapid quenching method is not limited as long as the melt can be rapidly quenched at the above-described speed. As the rapid quenching method, typically, the liquid quenching method can be applied. Alternatively, the cooling roll of the strip casting method may be rapidly quenched by rotating at high speed. Hereinafter, the liquid quenching method will be briefly described using the drawings.

[0037] FIG. 4 is an explanatory diagram schematically showing a cooling device used for the liquid quenching method.

[0038] The liquid quenching device 50 includes an injection nozzle 51, a heater 52, and a cooling roll 53. The injection nozzle 51 is installed facing the outer surface of the cooling roll 53. Molten metal is injected from the injection nozzle 51 onto the outer surface of the cooling roll 53, which rotates at high speed, and the molten metal is cooled to obtain a magnetic strip 54. Depending on the rotation speed of the cooling roll and / or the injection conditions, a magnetic flake 55 can be obtained. In the liquid quenching device 50, since the molten metal is injected directly from the injection nozzle 51 onto the outer surface of the cooling roll 53, the molten metal can be cooled very rapidly.

[0039] Molten metal may be supplied to the injection nozzle 51, or raw materials for the molten metal may be charged into the injection nozzle 51 and melted by the heater 52.

[0040] The cooling roll 53 is made of a highly thermally conductive material such as copper or chromium, and its surface is plated with chromium or the like to prevent erosion from high-temperature molten metal. The cooling roll 53 can be rotated at a predetermined rotational speed in the direction of the arrow by a drive device (not shown).

[0041] To rapidly cool the molten metal at the above-mentioned speed, the peripheral speed of the cooling roll 53 may be, for example, typically 15 m / sec to 30 m / sec. When rapidly cooling the molten metal using the liquid quenching method, an inert gas atmosphere is preferred to prevent oxidation of the molten metal, etc. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0042] The temperature of the molten metal when it is sprayed from the injection nozzle 51 onto the outer surface of the cooling roll 53 may be, for example, 1350°C or higher in one embodiment, 1400°C or higher in one embodiment, 1450°C or higher, and 1600°C or lower in one embodiment, 1550°C or lower in one embodiment, and 1500°C or lower in one embodiment.

[0043] (sintering) Furthermore, the magnetic strip or flake is sintered to obtain a sintered body (rare earth magnet precursor). Well-known sintering methods and conditions can be applied. Pressure sintering is used as the sintering method. Compared to the generally known non-pressure sintering, pressure sintering allows for sintering of the magnetic strip or flake at a relatively low temperature and in a short time by applying pressure. Therefore, pressure sintering is typically applied to the sintering of magnetic strips or flakes having a nanocrystalline main phase. This allows for obtaining a sintered body without coarsening the nanocrystalline main phase.

[0044] The sintering conditions can be appropriately determined to prevent the main phase from becoming coarse and to obtain a good sintered body density. The sintering conditions in pressure sintering are described below.

[0045] The pressurized sintering temperature may be, for example, 470°C or higher in one embodiment, 500°C or higher in one embodiment, 550°C or higher in one embodiment, 600°C or higher in one embodiment, and 750°C or lower in one embodiment, 700°C or lower in one embodiment, 670°C or lower in one embodiment, and 650°C or lower in one embodiment. The pressurized sintering pressure may be, for example, 50 MPa or higher in one embodiment, 100 MPa or higher in one embodiment, 150 MPa or higher in one embodiment, 200 MPa or higher in one embodiment, 350 MPa or higher in one embodiment, and 600 MPa or lower in one embodiment, 500 MPa or lower in one embodiment, 450 MPa or lower in one embodiment, and 400 MPa or lower in one embodiment. The pressurized sintering time may be, for example, 0.5 minutes or more in one embodiment, 1 minute or more in one embodiment, 5 minutes or more in one embodiment, 10 minutes or more in one embodiment, 15 minutes or more in one embodiment, 30 minutes or more in one embodiment, and 60 minutes or more in one embodiment, and 150 minutes or less in one embodiment, 120 minutes or less in one embodiment, and 90 minutes or less in one embodiment. After the pressure sintering is complete, it is preferable to remove the sintered body from the sintering mold and then cool the sintered body rapidly. This suppresses the formation of phases other than the desired phase. The cooling rate may be, for example, usually 10°C / min or more, 30°C / min or more in one embodiment, 50°C / min or more in one embodiment, and usually 1000°C / min or less, 800°C / min or less in one embodiment, 600°C / min or less in one embodiment, 400°C / min or less in one embodiment, 200°C / min or less in one embodiment, 100°C / min or less in one embodiment, 80°C / min or less in one embodiment, and 70°C / min or less in one embodiment. To suppress oxidation of the magnetic strip or magnetic flake during pressure sintering, an inert gas atmosphere is preferred for the pressure sintering atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0046] (Anisotropy conferred) Furthermore, to improve the remanent magnetization of the obtained rare-earth magnet precursor, an optional anisotropy induction process may be applied. Well-known methods can be used for anisotropy induction. When the main phase is nanocrystalline, hot plastic deformation of the sintered body is typical. The hot plastic deformation process will be described below.

[0047] (hot plastic working) The sintered body obtained by pressure sintering is subjected to hot plastic deformation. This makes it possible to impart anisotropy to the rare earth magnet of this disclosure. The conditions for hot plastic deformation can be appropriately determined so as to impart anisotropy to the sintered body while avoiding coarsening of the main phase.

[0048] The hot plastic working temperature may be, for example, 700°C or higher in one embodiment, 750°C or higher in one embodiment, 770°C or higher in one embodiment, 790°C or higher in one embodiment, and 850°C or lower in one embodiment, 830°C or lower in one embodiment, and 800°C or lower in one embodiment. The hot plastic working pressure may be, for example, 50 MPa or higher in one embodiment, 100 MPa or higher in one embodiment, 200 MPa or higher in one embodiment, 500 MPa or higher in one embodiment, 700 MPa or higher in one embodiment, and 900 MPa or higher in one embodiment, and 3000 MPa or lower in one embodiment, 2500 MPa or lower in one embodiment, 2000 MPa or lower in one embodiment, 1500 MPa or lower in one embodiment, and 1000 MPa or lower in one embodiment. The reduction ratio may be, for example, 10% or higher in one embodiment, 30% or higher in one embodiment, 50% or higher in one embodiment, and 60% or higher in one embodiment, and 80% or lower in one embodiment, 75% or lower in one embodiment, 70% or lower in one embodiment, and 65% or lower in one embodiment. The strain rate during hot plastic deformation may be, for example, typically 0.01 / s or more, 0.1 / s or more in one embodiment, 1.0 / s or more in one embodiment, 3.0 / s or more in one embodiment, and typically 15.0 / s or less, 10.0 / s or less in one embodiment, and 5.0 / s or less in one embodiment.

[0049] After the completion of hot plastic deformation, it is preferable to cool the sintered body rapidly. This helps to avoid coarsening of the main phase and suppress the formation of harmful phases that adversely affect magnetism. The cooling rate may be, for example, usually 10°C / min or more, 30°C / min or more in one embodiment, 50°C / min or more in one embodiment, and usually 1000°C / min or less, 800°C / min or less in one embodiment, 600°C / min or less in one embodiment, 400°C / min or less in one embodiment, 300°C / min or less in one embodiment, 200°C / min or less in one embodiment, 100°C / min or less in one embodiment, and 70°C / min or less in one embodiment. In order to suppress oxidation of the sintered body during hot plastic deformation, an inert gas atmosphere is preferred for the hot plastic deformation atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0050] Next, rare earth magnets are manufactured by diffusing and permeating the obtained rare earth magnet precursor with a modifying agent, as described below. (Diffusion and penetration) A modifying agent is diffused and permeated into the rare earth magnet precursor obtained by pressure sintering and, optionally, anisotropy. This advantageously improves the coercivity of the rare earth magnet of the present invention, particularly its coercivity at high temperatures.

[0051] The diffusion and permeation of the modifier involves preparing the modifier and then diffusing and permeating it into the rare earth magnet precursor. The modifier contains 60 to 90 percent (65 to 85 percent in one embodiment) of one or more elements selected from the group consisting of neodymium, praseodymium, terbium, dysprosium, and holmium, and 5 to 25 percent (10 to 20 percent in one embodiment) of carbon, relative to the total constituent elements of the modifier.

[0052] Methods for preparing the modifier include, for example, obtaining thin strips and / or flakes from molten metal having the composition of the modifier using methods such as liquid quenching or strip casting. In these methods, the molten metal is ultra-rapidly cooled or rapidly cooled, resulting in less segregation in the modifier, which is preferable. Another method for preparing the modifier is to cast molten metal having the composition of the modifier into a mold such as a book mold. This method allows for the relatively simple acquisition of a large amount of modifier. To reduce segregation of the modifier, it is preferable that the book mold be made of a material with high thermal conductivity. It is also preferable to homogenize the cast material through heat treatment to suppress segregation. Furthermore, another method for preparing the modifier involves charging the raw materials of the modifier into a container, arc melting the raw materials in the container, and cooling the molten material to obtain an ingot. In this method, the modifier can be obtained relatively easily even when the melting point of the raw materials is high. From the viewpoint of reducing segregation of the modifier, it is preferable to homogenize the ingot through heat treatment.

[0053] A typical method of diffusion and penetration involves bringing a modifying material into contact with a rare-earth magnet precursor to obtain a contact body, and then heating this contact body to diffuse and penetrate the molten modifying material into the interior of the rare-earth magnet precursor. The molten modifying material diffuses and penetrates through the grain boundary phase. The molten modifying material then solidifies within the grain boundary phase, magnetically separating the main phases and advantageously improving coercivity, especially coercivity at high temperatures.

[0054] The form of the contacting body is not particularly limited as long as the modifying material is in contact with the rare earth magnet precursor. Examples of the form of the contacting body include contacting the rare earth magnet precursor with a thin strip and / or flake of the modifying material obtained by liquid quenching and / or strip casting. Other examples of the form of the contacting body include contacting the rare earth magnet precursor with a powder of the modifying material obtained by pulverizing a thin strip and / or flake, book mold material, or arc melting and solidification material obtained by liquid quenching and / or strip casting.

[0055] The diffusion and penetration conditions are not particularly limited, as long as they allow the modifying agent to diffuse and penetrate into the interior of the rare-earth magnet precursor, without causing the main phase to coarseen, and without suppressing the formation of harmful phases that adversely affect magnetism.

[0056] The diffusion and penetration temperature may be, for example, 550°C or higher in one embodiment, 600°C or higher in one embodiment, 650°C or higher in one embodiment, and 750°C or lower in one embodiment, 740°C or lower in one embodiment, 730°C or lower in one embodiment, 720°C or lower in one embodiment, 710°C or lower in one embodiment, and 700°C or lower in one embodiment. The diffusion and penetration time may be 30 minutes or more in one embodiment, 60 minutes or more in one embodiment, 90 minutes or more in one embodiment, and 120 minutes or more in one embodiment, and 300 minutes or less in one embodiment, 240 minutes or less in one embodiment, 210 minutes or less in one embodiment, 180 minutes or less in one embodiment, 165 minutes or less in one embodiment, and 150 minutes or less in one embodiment. After the diffusion and penetration of the modifier, it is preferable to cool the sintered body rapidly. This can suppress the generation of harmful phases that adversely affect magnetism. The cooling rate may be, for example, typically 10°C / min or more, 30°C / min or more in one embodiment, 50°C / min or more in one embodiment, and typically 1000°C / min or less, 800°C / min or less in one embodiment, 600°C / min or less in one embodiment, 400°C / min or less in one embodiment, 300°C / min or less in one embodiment, 200°C / min or less in one embodiment, 100°C / min or less in one embodiment, and 70°C / min or less in one embodiment. In order to suppress the oxidation of the rare earth magnet precursor during diffusion and permeation, an inert gas atmosphere is preferred for the diffusion and permeation atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0057] For the diffusion and penetration of the modifier, 1.0 mole to 15.0 moles, or in one embodiment 5.0 moles to 12.0 moles, of the modifier is brought into contact with 100 moles of rare earth magnet precursor.

[0058] Since the modifier is diffused and permeated under conditions that prevent the main phase of the rare-earth magnet precursor from becoming coarsened, the average particle size of the main phase before the diffusion and permeation of the modifier is substantially within the same size range as the average particle size of the main phase after the diffusion and permeation of the modifier. The average particle size and crystal structure of the main phase are as described above.

[0059] During the diffusion and permeation of the modifier, an inert gas atmosphere is preferred in order to suppress oxidation of the rare earth magnet precursor and the modifier. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0060] (Transformation) In addition to what has been described above, the rare earth magnet of the present invention can be modified in various ways within the scope of the claims. [Examples]

[0061] The following describes some embodiments of the present invention, but the present invention is not intended to be limited to those shown in these embodiments.

[0062] Based on the above description of the method for manufacturing rare earth magnets, rare earth magnets were manufactured as follows. 1. Method for manufacturing hot-worked magnets Liquid quenched thin strips with the compositions shown in Table 1 below were prepared, and sintered bodies were produced by sintering them at 600°C and 200 MPa for 10 minutes. Next, the fabricated sintered body was subjected to hot plastic deformation at 730°C, a reduction ratio of 70%, and a strain rate of 0.03 / s to produce a hot-worked magnet (rare-earth magnet precursor).

[0063] 2. Penetration treatment The obtained hot-worked magnets were subjected to a penetration treatment with the modifying materials shown in Table 1 below, at a diffusion penetration rate of 10%, 15%, or 20% by mass relative to the total mass of the hot-worked magnets, at 700°C for 165 minutes. Furthermore, an optimized heat treatment was performed at 500°C for 60 minutes to produce rare-earth magnets.

[0064] [Table 1]

[0065] 3.Analysis The magnetic properties of the obtained rare-earth magnets were evaluated using a vibrating magnetometer (VSM). Further TEM observation was performed, and the component concentrations in the grain boundary phase and the shell were measured using STEM-EDX. The results are shown in Table 2 and Figures 1-3.

[0066] [Table 2]

[0067] Table 2 and Figures 1-3 show that, in rare earth magnets, by incorporating 0.50 atomic% to 1.1 atomic% of carbon, and adjusting the carbon content [C] and boron content [B] in atomic percent relative to the total constituent elements of the shell in the main phase, it was found that the magnetic properties of the rare earth magnet can be improved regardless of the difference in diffusion and penetration amounts by adjusting [C] to 0.50 atomic% to 1.1 atomic%, adjusting [C] / ([C]+[B]) to 0.10 to 0.18, and making the carbon content in the grain boundary phase higher than the carbon content in the main phase.

Claims

1. An R-T-B type rare earth magnet in which R is a rare earth element, T is Fe and / or Co, and B is boron, The aforementioned R-T-B rare earth magnet is R ２ T １４ The material comprises a main phase having a type B crystal structure, and a grain boundary phase present around the main phase. The average particle size of the main phase is 1 μm or less. The main phase has a core portion and a shell portion surrounding the core portion. The total content ratio of cerium, lanthanum, gadolinium, yttrium, and scandium in the core portion relative to the total constituent elements of the core portion is higher than the total content ratio of cerium, lanthanum, gadolinium, yttrium, and scandium in the shell portion relative to the total constituent elements of the shell portion. The total content ratio of neodymium, praseodymium, terbium, dysprosium, and holmium relative to the total constituent elements of the shell portion is higher than the total content ratio of neodymium, praseodymium, terbium, dysprosium, and holmium relative to the total constituent elements of the core portion. The R-T-B rare earth magnet contains 0.50 atomic% to 1.1 atomic% of carbon relative to the total constituent elements of the R-T-B rare earth magnet. In the shell portion, when the content of carbon in atomic percent is [C] and the content of boron is [B] relative to the total constituent elements of the shell portion, [C] is 0.50 atomic percent to 1.1 atomic percent, and [C] / ([C] + [B]) is 0.10 to 0.18, and The carbon content in the grain boundary phase relative to the total constituent elements of the grain boundary phase is higher than the carbon content in the main phase relative to the total constituent elements of the main phase. RTB rare earth magnet.

2. The R-T-B type rare earth magnet according to claim 1, wherein the carbon content in the shell portion relative to the total constituent elements of the shell portion is higher than the carbon content in the core portion relative to the total constituent elements of the core portion.

3. The R-T-B type rare earth magnet according to claim 1 or 2, wherein the average particle size of the main phase is 0.1 μm to 1 μm.

4. A method for manufacturing an R-T-B type rare earth magnet, wherein R is a rare earth element, T is Fe and / or Co, and B is boron, The method described above is Diffusing and permeating a modifying agent into a rare earth magnet precursor, Includes, The rare earth magnet precursor contains one or more elements selected from the group consisting of cerium, lanthanum, gadolinium, yttrium, and scandium as rare earth elements. The aforementioned R-T-B rare earth magnet is R ２ T １４ The material comprises a main phase having a type B crystal structure, and a grain boundary phase present around the main phase. The average particle size of the main phase is 1 μm or less. The modifier contains, with respect to the total constituent elements of the modifier, 60 to 80 atomic percent of one or more elements selected from the group consisting of neodymium, praseodymium, terbium, dysprosium, and holmium, and 10 to 20 atomic percent of carbon, and The aforementioned modifying agent is diffused and permeated at a concentration of 5.0 moles to 15.0 moles per 10 The aforementioned method.

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