Method for manufacturing r-t-b based sintered magnet, and r-t-b based sintered magnet

Abstract

To provide an R-T-B based sintered magnet with excellent orientation and residual magnetic flux density (Br).SOLUTION: A method for manufacturing an R-T-B based sintered magnet includes the steps of: preparing an R-T-B based raw material powder; mixing the R-T-B based raw material powder and a lubricant to obtain a mixture; compacting the R-T-B based raw material powder in the mixture in a magnetic field to obtain a compact; and sintering the compact to obtain an R-T-B based sintered magnet. The lubricant contains a compound represented by the following formula (1) or (2). In the formula (1), R1 and R2 each independently represent a saturated or unsaturated hydrocarbon group. In the formula (2), R3 represents a saturated or unsaturated hydrocarbon group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing an RTB based sintered magnet, and to an RTB based sintered magnet. [Background technology]

[0002] RTB-based sintered magnets containing rare earth elements R, transition metal elements T, and boron B are widely used as magnets with excellent magnetic properties. In recent years, with the shift to electric vehicles, demand for high-performance magnets for use in automotive motors has increased. In the production of RTB-based sintered magnets, a raw material alloy is generally pulverized to obtain alloy powder. The alloy powder is then compacted by pressing in a magnetic field and heat-treated to produce a sintered magnet. A lubricant may also be used during the pulverization process.

[0003] For example, Patent Document 1 describes R2T 14 The RTB sintered magnet disclosed is a sintered body having a crystal grain as a main phase, which is made of a B compound (R is one or more elements selected from rare earth elements, and T is one or more elements selected from Fe or transition metal elements including Fe and Co), and which contains 10 to 220 ppm of P and / or S.

[0004] For example, Patent Document 2 discloses a lubricant containing a rare earth element for a metal powder to be compacted, which is represented by the general formula R1-CONH2 (where R1 is C n H 2n+1 where n represents the number of carbon atoms in R1), and wherein two or more fatty acid amides having a total carbon number (n+1) of 16 or less in the general formula account for 80 mass % or more of the lubricant for powder compaction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-210377 A [Patent Document 2] Patent Publication No. 2007-197826 Summary of the Invention [Problem to be solved by the invention]

[0006] It is desirable for an RTB sintered magnet to have both excellent orientation and excellent residual magnetic flux density (Br). Patent Document 2 leaves room for improvement in that the orientation decreases when the amount of lubricant added is reduced. The problem to be solved by the present invention is to provide a method for producing an RTB based sintered magnet that has excellent orientation and remanence (Br), and an RTB based sintered magnet produced by the method. [Means for solving the problem]

[0007] The present invention includes the following aspects. <1> A method for producing an RTB based sintered magnet, comprising the steps of: preparing an RTB based raw material powder; mixing the RTB based raw material powder and a lubricant to obtain a mixture; compacting the RTB based raw material powder in the mixture in a magnetic field to obtain a green body; and sintering the green body to obtain an RTB based sintered magnet, wherein the lubricant contains a compound represented by the following formula (1) or (2):

[0008] [ka]

[0009] In formula (1), R 1 ~R 2 each independently represents a saturated or unsaturated hydrocarbon group.

[0010] [ka]

[0011] In formula (2), R 3 represents a saturated or unsaturated hydrocarbon group. <2> In formula (1) and formula (2), R 1 ~R 3 wherein each of the hydrocarbon groups is independently a saturated hydrocarbon group. <1> 2. A method for producing the RTB based sintered magnet described in claim 1. <3> In formula (1) and formula (2), R 1 ~R 3 At least one selected from the group consisting of the hydrocarbon groups in <1> or <2> 2. A method for producing the RTB based sintered magnet described in claim 1. <4> In formula (1) and formula (2), R 1 ~R 3 wherein at least one selected from the group consisting of hydrocarbon groups contains at least one selected from the group consisting of nitrogen, oxygen, and halogen. <1> ~ <3> 1. A method for producing an RTB based sintered magnet according to any one of the above. <5> The amount of the lubricant added is 1.0 mass % or less based on the total amount of the RTB-based raw material powder. <1> ~ <4> 1. A method for producing an RTB based sintered magnet according to any one of the above. <6> An RTB sintered magnet having a sulfur content of 100 ppm or more and 1000 ppm or less, and a carbon content of 500 ppm or less. <7> The degree of orientation is 97.0% or more <6> The RTB sintered magnet according to claim 1. [Effects of the Invention]

[0012] The present invention provides a method for producing an RTB based sintered magnet that is excellent in degree of orientation and remanence (Br), and an RTB based sintered magnet produced by the method. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a graph showing the degrees of orientation in Examples 1 to 6 and Comparative Example 1. [Figure 2] 1 is a graph showing Br in Examples 1 to 6 and Comparative Example 1. [Figure 3] 1 is a graph showing the carbon and sulfur contents in Examples 1 to 6 and Comparative Example 1. [Figure 4]1 is a graph showing the degrees of orientation in Examples 1-1 to 1-3. [Figure 5] 1 is a graph showing Br in Examples 1-1 to 1-3. [Figure 6] 1 is a graph showing the carbon and sulfur contents in Examples 1-1 to 1-3. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail.

[0015] It should be noted that the following embodiments are merely examples for explaining the present invention, and the present invention is not limited to the following embodiments. The present invention can be practiced by appropriately modifying it within the scope of its gist. In this embodiment, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in this embodiment in stages, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in an example. In this embodiment, a combination of two or more preferred aspects is a more preferred aspect. In this embodiment, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances unless otherwise specified.

[0016] <Manufacturing method for RTB sintered magnets> The method for producing an RTB based sintered magnet of this embodiment includes the steps of: preparing an RTB based raw material powder (also referred to herein as a preparation step); a step of mixing the RTB-based raw material powder and the lubricant to obtain a mixture (also referred to as a mixing step in this specification); a step of forming the RTB-based raw material powder in the mixture in a magnetic field to obtain a green body (also referred to as a forming step in this specification); a step of sintering the compact to obtain an RTB based sintered magnet (also referred to herein as a sintering step), The lubricant contains a compound represented by the following formula (1) or formula (2):

[0017] [ka]

[0018] In formula (1), R 1 ~R 2 each independently represents a saturated or unsaturated hydrocarbon group.

[0019] [ka]

[0020] In formula (2), R 3 represents a saturated or unsaturated hydrocarbon group.

[0021] The method for producing the RTB based sintered magnet of this embodiment can be a method for producing the RTB based sintered magnet of this embodiment. The method for producing an RTB sintered magnet according to this embodiment uses a compound represented by formula (1) or (2) as a lubricant. Mixing the RTB raw material powder with the lubricant reduces the kinetic friction between the RTB raw material powder particles during compaction. This is expected to improve the degree of orientation of the resulting RTB sintered magnet, resulting in a higher remanence (Br). The reason for this is unclear, but is presumed to be as follows. When the compound represented by formula (1) or (2) in this embodiment is used as a lubricant, sulfur in the lubricant bonds with the powder particles of the RTB-based raw material. As a result, the surfaces of the powder particles become covered with saturated or unsaturated hydrocarbon groups. Because a repulsive force occurs between the saturated or unsaturated hydrocarbon groups, aggregation between adjacent powder particles is suppressed, and the kinetic friction force between the powder particles is reduced. In general, the addition of a lubricant increases the amount of residual carbon, which can reduce the coercive force (Hcj) of an RTB sintered magnet. As a result of extensive research, the inventors have found that the method for producing an RTB based sintered magnet according to this embodiment can suppress the amount of residual carbon. The reason for this is unclear, but is presumed to be as follows. That is, when the compound represented by formula (1) or (2) in this embodiment is used as a lubricant, the sulfur in the lubricant bonds with the RTB raw material powder particles. When the RTB raw material powder is then compacted and sintered, the carbon contained in the lubricant decomposes, thereby significantly reducing the carbon content in the resulting RTB sintered magnet. As a result, an RTB based sintered magnet with a relatively reduced carbon content, such as the RTB based sintered magnet of this embodiment, can be obtained.

[0022] <Preparation process> The preparation step in this embodiment is a step of preparing a powder of an RTB-based raw material. The powder of the RTB-based raw material may be obtained by manufacturing, or a commercially available product may be used. When producing powder of RTB-based raw materials, there are no particular limitations on the production method. For example, the preparation step may include a step of obtaining a raw alloy and a step of pulverizing the raw alloy.

[0023] The preparation step may include a step of obtaining a raw alloy (also referred to herein as an alloy preparation step). The raw material alloy can be a metal (metal raw material) containing each of the elements that make up the RTB based sintered magnet. The starting alloy may be produced by strip casting, book molding, or centrifugal casting. The metal raw material may be, for example, a rare earth element (metal element), pure iron, ferroboron, or an alloy containing any of these. These metal raw materials are weighed out so as to roughly match the composition of the desired RTB based sintered magnet. One type of raw material alloy may be used, or multiple types of raw material alloys may be used. The raw alloy may be in the form of a number of particles, for example, flake particles, or an ingot.

[0024] The raw alloy contains a rare earth element R, a transition metal element T, and boron B. Specific examples, preferred aspects, and other details of the rare earth element R, the transition metal element T, and boron B are as described above. The raw alloy may also contain elements such as Al, Cu, Zr, Nb, Hf, and Co. Specific examples, preferred aspects, and other details of Al, Cu, Zr, Nb, Hf, and Co are as described above.

[0025] The preparation step may include a step of pulverizing the raw alloy to obtain a powder of the RTB raw material (also referred to as a pulverization step in this specification), whereby the powder of the RTB raw material can be obtained.

[0026] The pulverization step may include a coarse pulverization step and a fine pulverization step. That is, the pulverization step may be a coarse pulverization step, or may be a combination of a coarse pulverization step and a fine pulverization step. Furthermore, the powder of RTB raw material in this embodiment is a concept that includes the coarse powder of RTB raw material obtained by the coarse pulverization step, and the fine powder of RTB raw material obtained by the fine pulverization step.

[0027] The coarse pulverization step is a step in which the raw alloy is coarsely pulverized to obtain a coarse powder of the RTB raw material. The method for coarse pulverization is not particularly limited. For example, the raw alloy may be coarsely pulverized in an inert gas atmosphere using a stamp mill, a jaw crusher, a Braun mill, or the like. The coarse powder of the RTB-based raw material is a powder with an average particle size of about several hundred μm (for example, 100 μm to 950 μm). The average particle size is measured using a HELOS Particle Size Analyzer manufactured by Sympatec.

[0028] In order to improve the coarse pulverizability, it is preferable to occlude hydrogen and then pulverize the mixture. Alternatively, coarse pulverization can be performed by absorbing hydrogen and then releasing the hydrogen. Hydrogen absorption can be achieved by exposing the raw alloy to a hydrogen-containing atmosphere at room temperature. Since the hydrogen absorption reaction is an exothermic reaction, measures such as cooling the reaction vessel may be applied to prevent a decrease in the amount of absorbed hydrogen due to a rise in temperature. In the raw alloy in which hydrogen is absorbed, cracks occur, for example, along the grain boundaries.

[0029] After the hydrogen absorption is completed, the raw alloy in which the hydrogen absorption has been performed may be subjected to a dehydrogenation treatment in which the raw alloy is heated and maintained for the purpose of reducing the amount of hydrogen that becomes an impurity in the magnet. The temperature for heating and holding is preferably 200°C or higher, and more preferably 350°C or higher. The holding time can be adjusted as appropriate depending on the holding temperature, the thickness of the raw alloy, etc. The holding time is preferably 5 minutes or more, more preferably 30 minutes or more, and even more preferably 1 hour or more. The dehydrogenation treatment may be carried out in a vacuum or in an Ar gas flow. However, the dehydrogenation treatment is not necessarily required.

[0030] The fine pulverization step is a step in which the coarse powder of the RTB raw material is pulverized to obtain a fine powder of the RTB raw material, the fine powder having an average particle size of 3 μm to 5 μm. The method for finely pulverizing is not particularly limited, and examples thereof include a jet mill. Jet milling is a method in which high-pressure inert gas (such as nitrogen gas) is released from a narrow nozzle to generate a high-speed gas flow, which accelerates the coarse powder, causing it to collide with other particles and with a target or the wall of a container, thereby pulverizing the powder.

[0031] <Mixing process> The mixing step is a step in which the RTB raw material powder and the lubricant are mixed to obtain a mixture. The powder of the RTB-based raw material may be the coarse powder of the RTB-based raw material described above, or may be a fine powder, or may be both. The mixing method is not particularly limited, and for example, mixing may be performed using a conical mixer (Nauta mixer), a V-type mixer, or a stirring blade mixer.

[0032] The method for producing an RTB based sintered magnet of this embodiment may include the mixing step only once or multiple times. For example, the method for producing an RTB based sintered magnet of this embodiment may include a mixing step after the coarse pulverization step and before the fine pulverization step, or after the fine pulverization step and before the compacting step, or may include a mixing step in both steps. That is, the method for producing an RTB based sintered magnet of this embodiment is as follows: (1) The method may include, in this order, an alloy preparation step, a coarse pulverization step, a first mixing step of mixing a coarse powder of the RTB-based raw material and a lubricant to obtain a first mixture, a fine pulverization step, a second mixing step of mixing a fine powder of the RTB-based raw material and a lubricant to obtain a second mixture, a molding step, and a sintering step, (2) The method may include, in this order, an alloy preparation step, a coarse pulverization step, a first mixing step of mixing a coarse powder of the RTB-based raw material and a lubricant to obtain a first mixture, a fine pulverization step, a molding step, and a sintering step, (3) The method may include, in this order, an alloy preparation step, a coarse pulverization step, a fine pulverization step, a second mixing step of mixing a fine powder of the RTB-based raw material and a lubricant to obtain a second mixture, a molding step, and a sintering step. In the case of (2), a lubricant other than the compound represented by formula (1) or (2) may be added after the fine pulverization step and before the compacting step, and in the case of (3), a lubricant other than the compound represented by formula (1) or (2) may be added after the coarse pulverization step and before the fine pulverization step.

[0033] The amount of lubricant added is preferably 1.0 mass% or less, more preferably 0.8 mass% or less, even more preferably 0.5 mass% or less, particularly preferably 0.3 mass% or less, and even more preferably 0.1 mass% or less, based on the total amount of RTB raw material powder.

[0034] (lubricant) The lubricant contains a compound represented by the following formula (1) or (2): By using the compound represented by the following formula (1) or (2) as the lubricant, the resulting RTB based sintered magnet has excellent orientation and remanence (Br). The total content of the compounds represented by formula (1) and formula (2) is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the total amount of the lubricant. The total content of the compounds represented by formula (1) and formula (2) may be 100% by mass or less, or may be 99% by mass or less, based on the total amount of the lubricant.

[0035] [ka]

[0036] In formula (1), R 1 ~R 2 each independently represents a saturated or unsaturated hydrocarbon group.

[0037] [ka]

[0038] In formula (2), R 3 represents a saturated or unsaturated hydrocarbon group.

[0039] In this embodiment, the hydrocarbon group refers to a group containing carbon and hydrogen, and may contain atoms other than carbon and hydrogen.

[0040] In formula (1), R 1 ~R 2 The hydrocarbon groups in the formula (I) are each preferably a saturated hydrocarbon group. Examples of the saturated hydrocarbon group include an alkyl group. In formula (2), R 3 The hydrocarbon group in is preferably a saturated hydrocarbon group from the viewpoint of excellent friction-reducing effect. The saturated hydrocarbon group includes an alkyl group. In formula (1), R 1 ~R 2 The hydrocarbon groups in each independently preferably have 1 to 20 carbon atoms, more preferably 2 to 15 carbon atoms, and even more preferably 2 to 10 carbon atoms. In formula (2), R 3 The hydrocarbon group in the formula (I) preferably has 1 to 20 carbon atoms, more preferably 2 to 15 carbon atoms, and even more preferably 2 to 12 carbon atoms.

[0041] In formula (1), R 1 ~R 2 At least one selected from the group consisting of hydrocarbon groups in the above formula (I) preferably contains a branch. In formula (2), R 3 The hydrocarbon group in the formula (I) preferably contains a branch. In formula (1) and formula (2), R 1 ~R 3 By including a branch in the hydrocarbon group in the formula (1), aggregation of the powder particles to which the lubricant is adsorbed is suppressed, improving lubrication performance. This reduces the friction of the powder, lowering the dynamic friction coefficient of the powder and enabling the production of a highly oriented sintered magnet. Since the friction of the powder is easily reduced, R 1 and R 2 In order to reduce the friction of the powder, it is preferable that both R 1 ~R3 Preferably, each of the hydrocarbon groups in the formula (I) independently contains two or more branches, and more preferably contains three branches.

[0042] In formula (1), R 1 ~R 2 At least one selected from the group consisting of hydrocarbon groups in the formula (I) preferably contains at least one selected from the group consisting of nitrogen, oxygen, and halogen, more preferably contains at least one selected from the group consisting of nitrogen and oxygen, and even more preferably contains oxygen. In formula (2), R 3 The hydrocarbon group in the formula (I) preferably contains at least one selected from the group consisting of nitrogen, oxygen and halogen, and more preferably contains at least one selected from the group consisting of nitrogen and oxygen. When the same atom is located at the end of the hydrocarbon group, the repulsive force acting between the powder particles becomes large, so it is more preferable that at least one selected from the group consisting of nitrogen, oxygen, and halogen is contained in a position other than the end of the hydrocarbon group. In the formula (2), examples of the halogen include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0043] In formula (2), R 3 The hydrocarbon group in the formula (I) preferably contains a ring structure. Examples of the ring structure include a 3- to 10-membered ring, preferably a 4- to 8-membered ring, and more preferably a 5- to 7-membered ring. The ring structure may be a fused ring or a hetero ring. Examples of the heteroatom in the hetero ring include nitrogen, oxygen, and halogen, with nitrogen and oxygen being preferred. Examples of the ring structure include a benzene ring, an aryl ring, a pyrrole ring, a pyridine ring, and a furan ring.

[0044] Specific examples of the compound represented by formula (1) include the following compounds.

[0045] [ka]

[0046] Specific examples of the compound represented by formula (2) include the following compounds.

[0047] [ka]

[0048] <Forming process> The compacting step is a step in which the powder of the RTB-based raw material in the mixture is compacted in a magnetic field to obtain a compact. In the molding step, a mold may be used to produce a molded body from the powder of the RTB-based raw material. The mold may be made of at least one material selected from the group consisting of resin, metal, and ceramic. The pressure exerted by the mold on the alloy powder may be 0.049 MPa or more and 20 MPa or less.

[0049] The compacting step and the orientation step may be performed simultaneously. In the orientation step, a magnetic field is applied to the compact held in the mold. That is, by applying a magnetic field to the compact in the mold, the alloy powder constituting the compact is oriented along the magnetic field. The magnetic field may be a static magnetic field or a pulsed magnetic field. When the compacting and orienting steps are performed simultaneously, the alloy powder is compressed in the die while a magnetic field is applied to the alloy powder in the die. As a result, a compact is obtained containing RTB raw material powder oriented along the magnetic field. The RTB raw material powder contains the lubricant of this embodiment, reducing friction between powder particles. As a result, the density of the compact increases, the RTB raw material powder is more likely to be oriented along the magnetic field, and the remanence of the RTB sintered magnet increases. In this case, the pressure exerted by the mold on the powder may be 0.049 MPa or more and 20 MPa or less. The strength of the magnetic field applied to the RTB-based raw material powder in the mold may be 796 kA / m or more and 5173 kA / m or less. The magnetic field may be a static magnetic field or a pulsed magnetic field. After the compacting and orienting steps, the compact may be demagnetized.

[0050] <Sintering process> The sintering step is a step in which the compact is sintered to obtain an RTB based sintered magnet. In the sintering step, the compact is sintered in a sintering furnace to obtain a sintered body. The atmosphere inside the sintering furnace may be a vacuum or an inert gas. The inert gas may be, for example, Ar. The conditions for the sintering step may be appropriately set depending on the composition of the desired RTB-based sintered magnet, the method for pulverizing the raw alloy, the average particle size of the alloy powder, and the like. The sintering temperature may be, for example, 900°C or higher and 1200°C or lower. The sintering time may be 1 hour or higher and 20 hours or lower. A portion of the lubricant contained in the compact volatilizes at high temperatures, while the remainder is reduced by hydrogen in the compact and released from the compact. This reduces the amount of residual carbon in the resulting sintered body. In this embodiment, the carbon in the lubricant is decomposed and volatilized by sintering, significantly reducing the amount of carbon remaining in the sintered body.

[0051] In the aging treatment step, the sintered body may be further heated. The aging treatment step improves the magnetic properties of the sintered body. The atmosphere in the aging treatment step may be a vacuum or an inert gas. The inert gas may be, for example, Ar. In the aging treatment step, the sintered body may be heated at about 600°C for 1 to 3 hours. A multi-stage aging treatment step may be performed. For example, in the first aging treatment, the sintered body may be heated at 700 to 900°C for 1 to 3 hours, and in the second aging treatment following the first aging treatment, the sintered body may be heated at 500 to 700°C for 1 to 3 hours. The aging treatment step may be performed consecutively to the sintering step.

[0052] The sintered body may be rapidly cooled by a cooling step following the aging treatment step. The sintered body may be rapidly cooled in an inert gas. The inert gas may be, for example, Ar. The cooling rate of the sintered body may be, for example, 5°C / min or more and 100°C / min or less.

[0053] In the processing step, the size and shape of the sintered body may be adjusted by cutting, polishing, etc. The sintered body obtained by the above method may or may not contain a heavy rare earth element. Regardless of whether or not the sintered body contains a heavy rare earth element, the following diffusion step may be carried out. However, the diffusion step is not essential.

[0054] When manufacturing an RTB-based sintered magnet containing a heavy rare earth element, a diffusion step is preferably carried out. The heavy rare earth element may be, for example, at least one of Tb and Dy. In the diffusion step, the heavy rare earth element or a compound thereof may be attached to the surface of the sintered body, and then the sintered body may be heated. For example, the heavy rare earth element may be attached to the surface of the sintered body. The sintered body may be heated in vapor containing the heavy rare earth element. In the diffusion step, the heavy rare earth element diffuses from the surface to the interior of the sintered body, and further the heavy rare earth element is transported through the grain boundaries to the R2T 14 It diffuses to the surface of the grains of the phase having crystal grains made of B compounds.

[0055] A paint containing a heavy rare earth element may be applied to the surface of the sintered compact. The composition of the paint is not limited as long as the paint contains a heavy rare earth element. The paint may be, for example, a simple heavy rare earth element, an alloy containing a heavy rare earth element, or a compound containing a heavy rare earth element. The compound containing a heavy rare earth element may be a hydride, a fluoride, or an oxide. The solvent (dispersion medium) contained in the paint may be a solvent other than water. For example, the solvent may be an organic solvent such as an alcohol, an aldehyde, or a ketone. The concentration of the heavy rare earth element in the paint is not limited.

[0056] The diffusion temperature in the diffusion step may be 800°C or higher and 950°C or lower. The diffusion time may be 1 hour or higher and 50 hours or lower. When the diffusion temperature and time are within the above ranges, the concentration distribution of the heavy rare earth element is easily controlled, and the production cost of the RTB based sintered magnet is reduced. The diffusion step may also serve as the above-mentioned aging treatment step.

[0057] After the diffusion step, the RTB based sintered magnet may be further subjected to a heat treatment. The heat treatment temperature after the diffusion step may be 450°C or higher and 600°C or lower. The heat treatment time may be 1 hour or higher and 10 hours or lower. The heat treatment after the diffusion step tends to improve the magnetic properties (particularly the coercive force) of the finally obtained RTB based sintered magnet.

[0058] After the diffusion step, the size and shape of the sintered body may be adjusted by cutting, polishing, or the like.

[0059] A passive layer may be formed on the surface of the sintered body by oxidation or chemical treatment of the surface of the sintered body. The surface of the sintered body may also be covered with a resin film. The formation of the passive layer or resin film further improves the corrosion resistance of the RTB based sintered magnet.

[0060] <RTB sintered magnet> The RTB based sintered magnet of this embodiment has a sulfur content of 100 ppm or more and 1000 ppm or less, and a carbon content of 500 ppm or less. The RTB based sintered magnet of this embodiment has the above-mentioned structure and is therefore excellent in degree of orientation and residual magnetic flux density (Br). The carbon contained in the RTB based sintered magnet of this embodiment is a carbon residue generated during the manufacturing process, and the amount of carbon contained in the RTB based sintered magnet of this embodiment is relatively small. The RTB sintered magnet of this embodiment has excellent orientation and remanence (Br) due to a combination of the carbon content being kept within a relatively small range and the sulfur content being within the above-mentioned range. In this specification, "ppm" means ppm by mass.

[0061] (Sulfur content) In this embodiment, the sulfur content is 100 ppm or more and 1000 ppm or less. When the sulfur content is 100 ppm or more and 1000 ppm or less, the degree of orientation and residual magnetic flux density are excellent. From the above viewpoint, the sulfur content is preferably 130 ppm or more, more preferably 160 ppm or more, and even more preferably 200 ppm or more. From the above viewpoint, the sulfur content is preferably 900 ppm or less, more preferably 700 ppm or less, and even more preferably 500 ppm or less.

[0062] (Carbon content) In this embodiment, the carbon content is 500 ppm or less. By keeping the carbon content at 500 ppm or less, the degree of orientation and residual magnetic flux density are excellent. From the above viewpoint, the carbon content is preferably 450 ppm or less, more preferably 400 ppm or less, and even more preferably 380 ppm or less. The carbon content may be 0 or more than 0, and is preferably 10 ppm or more, more preferably 50 ppm or more, and even more preferably 100 ppm or more. The sulfur and carbon contents are measured by an infrared absorption method using an EMIA-920V manufactured by Horiba Ltd.

[0063] The RTB based sintered magnet of this embodiment contains a rare earth element R, a transition metal element T, and boron B. The rare earth element R may be at least one selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Only one rare earth element R may be used, or two or more rare earth elements R may be used. The transition metal element T may be at least one selected from the group consisting of Fe, Co, Ni, Mn, Cr, and Mo, and is preferably at least one selected from the group consisting of Fe, Co, and Ni. Only one type of transition metal element T may be used, or two or more types may be used.

[0064] In the RTB sintered magnet of this embodiment, the R content is preferably 25 to 35 mass %, more preferably 26 to 33 mass %, and even more preferably 27 to 32 mass %, from the viewpoint of excellent residual magnetic flux density and coercive force. In order to achieve excellent residual magnetic flux density and coercive force, the RTB based sintered magnet of this embodiment preferably has a B content of 0.5 to 4 mass %, more preferably 0.5 to 1.5 mass %, and even more preferably 0.8 to 1.2 mass %.

[0065] The RTB based sintered magnet of this embodiment may contain at least one of Al and Cu. By including at least one of Al and Cu, the resulting RTB based sintered magnet can have higher coercive force, higher corrosion resistance, and improved temperature characteristics. When Al is added, the Al content is preferably 0.03 to 0.3 mass %, and more preferably 0.04 to 0.25 mass %. When Cu is added, the Cu content is preferably 0.01 to 0.3 mass %, more preferably 0.02 to 0.2 mass %, and even more preferably 0.03 to 0.15 mass %.

[0066] The RTB based sintered magnet of this embodiment may contain at least one element selected from the group consisting of Zr, Nb, and Hf. By including at least one selected from the group consisting of Zr, Nb and Hf, the structure of the resulting sintered body can be made uniform and fine. When at least one selected from the group consisting of Zr, Nb and Hf is contained, the total content of Zr, Nb and Hf is preferably 0.01 to 2 mass%, more preferably 0.0 The content is 5 to 1.5% by mass, and more preferably 0.1 to 0.5% by mass.

[0067] The RTB based sintered magnet of this embodiment may contain Co. By including Co, the Curie temperature and corrosion resistance can be improved. When the RTB based sintered magnetic material of this embodiment contains Co, the Co content is preferably 4 mass % or less, more preferably 0.2 to 3 mass %, and even more preferably 0.2 to 1.5 mass %.

[0068] The RTB sintered magnet of this embodiment may have a composition consisting essentially of R: 25 to 35 mass%, B: 0.5 to 4 mass%, Al and Cu: 0.02 to 0.6 mass%, Zr, Nb, and Hf: 2 mass% or less in total, Co: 4 mass% or less, and the remainder being Fe.

[0069] The RTB based sintered magnet of this embodiment is 14 The magnetic material may contain main phase particles having crystal grains made of a B compound. The average particle size of the main phase particles may be 0.5 μm or more and 20 μm or less, and preferably 1 μm or more and 10 μm or less. When the average particle size of the main phase particles is in this range, the coercive force tends to be high.

[0070] The RTB sintered magnet of this embodiment may have a grain boundary phase sandwiched between two or more main phase particles. The R content in the grain boundary phase may be greater than the R content in the main phase particles. The sulfur content in the grain boundary phase may be greater than the sulfur content in the main phase particles. In the mixing step of this embodiment, when the RTB raw material powder and lubricant are mixed, sulfur contained in the lubricant is adsorbed to the surface of the RTB raw material powder. Because the RTB raw material powder forms the main phase particles, the RTB sintered magnet produced according to the production method of this embodiment tends to have a greater sulfur content in the grain boundary phase than the sulfur content in the main phase particles.

[0071] The RTB based sintered magnet of this embodiment preferably has a degree of orientation of 97.0% or more. When the degree of orientation is in this range, the remanence (Br) of the RTB based sintered magnet tends to be high. The RTB based sintered magnet of this embodiment has a degree of orientation of more preferably 97.4% or more, even more preferably 97.7% or more, and particularly preferably 97.9% or more.

[0072] In this embodiment, the degree of orientation is measured by the Lotgering method. Specifically, first, the magnetic pole face of the RTB sintered magnet is mirror-polished. Then, X-ray diffraction measurement is performed on the mirror-polished surface. The intensity of the diffraction peak obtained by the measurement is then substituted into the following mathematical formula 1 to calculate the degree of orientation (unit: %). I(00l) in the following mathematical formula 1 is the diffraction intensity of the X-ray reflected from the (00l) plane of the RTB sintered magnet. I(hkl) in the following mathematical formula 1 is the diffraction intensity of the X-ray reflected from the (hkl) plane of the RTB sintered magnet.

[0073]

number

[0074] The shape of the RTB based sintered magnet is not limited, and may be, for example, a rectangular parallelepiped, a cube, a rectangle (plate), a polygonal prism, an arc segment, a fan, an annular sector, a sphere, a disk, a cylinder, a tube, a ring, or a capsule. The cross-sectional shape of the RTB based sintered magnet may be, for example, a polygon, a circular arc (circular chord), a bow, an arch, a C-shape, or a circle. RTB based sintered magnets may be applied to motors, generators, actuators, etc. For example, RTB based sintered magnets are used in a variety of fields, such as hybrid vehicles, electric vehicles, hard disk drives, magnetic resonance imaging devices (MRI), smartphones, digital cameras, flat-screen TVs, scanners, air conditioners, heat pumps, refrigerators, vacuum cleaners, washer-dryers, elevators, and wind power generators. [Example]

[0075] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0076] Example 1 A flake-shaped raw alloy was produced by strip casting. The raw alloy consisted of Nd, Pr, Al, Cu, Zr, B, and Fe. The contents of each element in the raw alloy were as follows: Nd content: 28.40 mass% Pr content: 0.07 mass% Al content: 0.05 mass% Cu content: 0.05% by mass Zr content: 0.20 mass% B content: 0.972 mass% Fe content: balance (remainder)

[0077] Next, the raw alloy was coarsely pulverized. In the coarse pulverization process, hydrogen was absorbed into the raw alloy at room temperature and 100 kPa for 3 hours. After hydrogen absorption, the raw alloy was heated in an Ar atmosphere at 100°C and 100 kPa for 5 hours to dehydrogenate the raw alloy. The raw alloy was pulverized by the above hydrogen absorption pulverization, and a coarse powder was obtained. The average particle size of the coarse powder obtained by the coarse pulverization process was 500 μm.

[0078] In the subsequent fine pulverization process, the alloy powder was further pulverized using a jet mill until the average particle size of the alloy powder reached 3 μm. The airflow in the jet mill was N2 gas. The oxygen concentration in the airflow was 50 ppm or less.

[0079] After the coarse pulverization step and before the fine pulverization step, and after the fine pulverization step and before the compaction step, the coarse powder and the fine powder were mixed with the lubricant at room temperature for 10 minutes to obtain mixtures. The lubricant and each powder were mixed in a V-type mixer. The types and amounts of lubricants added are shown in Table 1. The amounts of lubricants added are total amounts. The details of each lubricant are as follows:

[0080] Lubricant A1: Diethyl disulfide The structural formula is shown below.

[0081] [ka]

[0082] Lubricant A2: Dicyclohexyl disulfide The structural formula is shown below.

[0083] [ka]

[0084] Lubricant A3: Dibenzyl disulfide The structural formula is shown below.

[0085] [ka]

[0086] Lubricant A4: Bis(2,2-diethoxyethyl) disulfide The structural formula is shown below.

[0087] [ka]

[0088] Lubricant A5: 2-methyl-2-propanesulfonic acid The structural formula is shown below.

[0089] [ka]

[0090] Lubricant A6: 3-Cyclohexylaminopropanesulfonic acid The structural formula is shown below.

[0091] [ka]

[0092] Lubricant A7: Zinc stearate The structural formula is shown below.

[0093] [ka]

[0094] Next, the alloy powder in the mixture was pressed in a die while a magnetic field was applied to produce a compact. In other words, the compacting and orientation processes were carried out simultaneously. The pressure exerted by the die on the alloy powder was 1.37 MPa. The strength of the magnetic field applied to the alloy powder in the die was 1193 kA / m.

[0095] In the sintering process, the compact was heated in a vacuum to obtain a sintered body. In the sintering process, the compact was heated at 1030°C for 4 hours. After the sintering process, the sintered body was rapidly cooled.

[0096] After quenching, the sintered body was subjected to a first aging treatment followed by a second aging treatment. In both the first and second aging treatments, the sintered body was heated in Ar gas. In the first aging treatment, the sintered body was heated at 900°C for 1 hour. In the second aging treatment, the sintered body was heated at 530°C for 1 hour. By the above method, the RTB based sintered magnet of Example 1 was produced.

[0097] (Examples 2 to 6, Comparative Example 1) In Examples 2 to 6 and Comparative Example 1, RTB based sintered magnets were produced in the same manner as in Example 1, except that the type and amount of lubricant was changed as shown in Table 1.

[0098] <Evaluation> [Measurement of residual magnetic flux density (Br)] The remanence (Br) of the RTB sintered magnet was measured at room temperature (23°C) using a BH tracer. A remanence of 1350 mT or higher is considered excellent.

[0099] [Method for measuring the degree of orientation] The degree of orientation of the RTB sintered magnet was measured by the Lotgering method. Specifically, first, the magnetic pole surface of the RTB sintered magnet was mirror-polished. Then, X-ray diffraction measurements were performed on the mirror-polished surface. The intensity of the diffraction peak obtained by the measurement was then substituted into the following mathematical formula 1 to calculate the degree of orientation (unit: %). I(00l) in the following mathematical formula 1 is the diffraction intensity of the X-ray reflected from the (00l) plane of the RTB sintered magnet. I(hkl) in the following mathematical formula 1 is the diffraction intensity of the X-ray reflected from the (hkl) plane of the RTB sintered magnet. Note that, in order to calculate a crystal orientation that is more realistic, it is preferable to perform vector correction on the diffraction peak, and therefore, in this example, the degree of orientation was calculated after performing vector correction. A degree of orientation of 97% or more is considered excellent.

[0100]

number

[0101] [Measurement of sulfur and carbon content] The sulfur and carbon contents in the RTB-based sintered magnets were measured by infrared absorption spectroscopy.

[0102] [Table 1]

[0103] As shown in Table 1, the RTB based sintered magnets of the examples, which had a sulfur content of 100 ppm or more and 1000 ppm or less and a carbon content of 500 ppm or less, were excellent in degree of orientation and residual magnetic flux density. On the other hand, the RTB based sintered magnet of Comparative Example 1, which contained no sulfur and had a carbon content of over 500 ppm, was inferior in degree of orientation and remanence. Graphs showing the orientation degree, Br, carbon and sulfur contents in Examples 1 to 6 and Comparative Example 1 are shown in FIGS. 1, 2 and 3, respectively.

[0104] (Examples 1-1 to 1-3) In Examples 1-1 to 1-3, RTB based sintered magnets were produced in the same manner as in Example 4, except that the amount of lubricant was changed as shown in Table 2. The resulting RTB based sintered magnets were measured for remanence (Br), degree of orientation, and sulfur and carbon contents. Graphs showing the degree of orientation, Br, carbon and sulfur contents in Examples 1-1 to 1-3 are shown in FIGS. 4, 5 and 6, respectively.

[0105] [Table 2]

[0106] As shown in Table 2, in the examples where the amount of lubricant added was 0.05% by mass to 0.50% by mass, RTB based sintered magnets were produced with a sulfur content of 100 ppm to 1000 ppm and a carbon content of 500 ppm or less. The resulting RTB based sintered magnets had excellent orientation and remanence.

Claims

1. A step of preparing a powder of an R-T-B based raw material; a step of mixing the R-T-B-based raw material powder and a lubricant to obtain a mixture; a step of compacting the R-T-B-based raw material powder in the mixture in a magnetic field to obtain a compact; and a step of sintering the compact to obtain a sintered R-T-B based magnet. The method for producing an RTB based sintered magnet, wherein the lubricant contains a compound represented by the following formula (1) or (2): 【Chemical 1】 In formula (1), R 1 ~R 2 each independently represents a saturated or unsaturated hydrocarbon group. 【Chemistry 2】 In formula (2), R 3 represents a saturated or unsaturated hydrocarbon group.

2. In formula (1) and formula (2), R 1 ~R 3 2. The method for producing a sintered RTB based magnet according to claim 1, wherein each of the hydrocarbon groups is independently a saturated hydrocarbon group.

3. In formula (1) and formula (2), R 1 ~R 3 2. The method for producing a sintered RTB based magnet according to claim 1, wherein at least one selected from the group consisting of the hydrocarbon groups in the formula (I) contains a branch.

4. In formula (1) and formula (2), R 1 ~R 3 2. The method for producing a sintered R-T-B based magnet according to claim 1, wherein the at least one selected from the group consisting of hydrocarbon groups contains at least one selected from the group consisting of nitrogen, oxygen, and halogen.

5. 2. The method for producing a sintered RTB based magnet according to claim 1, wherein the amount of the lubricant added is 1.0 mass % or less based on the total amount of the RTB based raw material powder.

6. The sulfur content is 100 ppm or more and 1000 ppm or less, An RTB-based sintered magnet having a carbon content of 500 ppm or less.

7. 7. The RTB based sintered magnet according to claim 6, which has a degree of orientation of 97.0% or more.

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