RTB series permanent magnets

Abstract

[Problem] To obtain an inexpensive rare earth magnet that includes Ce, the rare earth magnet having high residual magnetic flux density (Br), coercive force (HcJ), and squareness ratio (Hk / HcJ), and also having high corrosion resistance. [Solution] An R-T-B-based permanent magnet including: R (rare earth element); T (Fe and Co); B (boron); and one or more selected from Al, Cu, Ga, and Zr. R includes Ce. The total R content is 31.3-34.0 mass% (inclusive), the Co content is 1.85-3.00 mass% (inclusive), the B content is 0.80-0.90 mass% (inclusive), the Al content is 0.03-0.90 mass% (inclusive), the Cu content is 0-0.25 mass% (inclusive), the Ga content is 0-0.10 mass% (inclusive), the Zr content is 0-0.60 mass% (inclusive), and the Fe content is substantially the remainder. The Ce content relative to R is 15-25 mass% (inclusive).

Description

[Technical field]

[0001] The present invention relates to an RTB-based permanent magnet. [Background technology]

[0002] Patent Document 1 describes an RTB permanent magnet that contains Ce as R and that contains an RT phase within a predetermined range. Due to the above characteristics, it is possible to obtain an RTB permanent magnet with improved flexural strength. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-174323 A Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, among rare earth elements, Ce has a low cost, and therefore there is a demand for using Ce to obtain rare earth magnets with sufficient magnetic properties.

[0005] An object of the present invention is to provide a low-cost rare earth magnet that contains Ce, which has high residual magnetic flux density (Br), coercive force (HcJ) and squareness ratio (Hk / HcJ), as well as high corrosion resistance. [Means for solving the problem]

[0006] In order to achieve the above object, the RTB permanent magnet according to the present invention comprises: An RTB permanent magnet containing R (rare earth element), T (Fe and Co), B (boron), and at least one element selected from Al, Cu, Ga, and Zr, R contains Ce, The total content of R is 31.3 mass% or more and 34.0 mass% or less, The Co content is 1.85 mass% or more and 3.00 mass% or less, The B content is 0.80 mass% or more and 0.90 mass% or less, The Al content is 0.03 mass% or more and 0.90 mass% or less, Cu content is 0 mass% or more and 0.25 mass% or less, The Ga content is 0 mass% or more and 0.10 mass% or less, The Zr content is 0 mass% or more and 0.60 mass% or less, The content of Fe is substantially the remainder, The Ce content relative to R is 15 mass % or more and 25 mass % or less.

[0007] R2T 14 It may contain main phase grains made of a B compound and grain boundaries, and the grain boundaries may contain an RT phase.

[0008] The Ce content relative to R in the RT phase may be greater than that in the main phase grains.

[0009] The total content of heavy rare earth elements may be 0% by mass or more and 0.10% by mass or less.

[0010] The Co content may be 1.85 mass % or more and 2.09 mass % or less. [Brief description of the drawings]

[0011] [Figure 1] 1 is a SEM image of Example 1. [Diagram 2] 1 is a graph plotting the magnetic properties of each experimental example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described with reference to the following embodiments. The RTB permanent magnet of the present invention can be an RTB sintered magnet.

[0013] (composition) The composition of the RTB based sintered magnet will be described. R is a rare earth element. R contains cerium (Ce). When R contains Ce, the raw material cost is reduced. Furthermore, in order to suitably control the raw material cost of the RTB based sintered magnet and the magnetic properties of the RTB based sintered magnet, it is preferable that R contains one or more elements selected from neodymium (Nd) and praseodymium (Pr).

[0014] T is Fe and Co. B is boron.

[0015] Furthermore, the RTB sintered magnet contains at least one selected from aluminum (Al), copper (Cu), gallium (Ga) and Zr (zirconium), and may contain two or more.

[0016] The content of each element in the RTB based sintered magnet is described below. Note that unless otherwise specified, the content of each element shown below is the content when the entire RTB based sintered magnet is taken as 100 mass %.

[0017] The total R content is from 31.3 mass % to 34.0 mass % or less, based on 100 mass % of the entire RTB based sintered magnet. It may be from 32.0 mass % to 34.0 mass % or less. If the total R content is too low, HcJ decreases. If the total R content is too high, Br decreases.

[0018] The B content is 0.80% by mass or more and 0.90% by mass or less. It may be 0.80% by mass or more and 0.89% by mass or less, or 0.80% by mass or more and 0.86% by mass or less. If the B content is too low, Hk / HcJ decreases. If the B content is too high, HcJ decreases. If the B content is too low, Hk / HcJ decreases because the 2-17 phase, which is a different phase, is formed at the grain boundaries, decreasing Hk.

[0019] The Co content is 1.85% by mass or more and 3.00% by mass or less. It may be 1.85% by mass or more and 2.80% by mass or less, or 1.85% by mass or more and 2.40% by mass or less. The Co content may be 1.91% by mass or more, or 2.00% by mass or more. The Co content may be 1.85% by mass or more and 2.09% by mass or less, or 1.91% by mass or more and 2.09% by mass or less, or 1.91% by mass or more and 2.00% by mass or less. If the Co content is too low, the corrosion resistance decreases. If the Co content is too high, the HcJ decreases.

[0020] The Ga content is 0% by mass or more and 0.10% by mass or less. In other words, Ga may not be contained. The lower the Ga content, the easier it is to improve the magnetic properties and manufacturing stability. If the Ga content is too high, the magnetic properties, especially HcJ, decrease.

[0021] The Al content is 0.03% by mass or more and 0.90% by mass or less. It may be 0.30% by mass or more and 0.90% by mass or less. If the Al content is too low, HcJ decreases. If the Al content is too high, Br decreases.

[0022] The Cu content is 0% by mass or more and 0.25% by mass or less. In other words, Cu may not be contained. The Cu content may be 0% by mass or more and 0.10% by mass or less. If the Cu content is too high, the HcJ decreases.

[0023] The Zr content is 0% by mass or more and 0.60% by mass or less. That is, Zr need not be contained. It may be 0.40% by mass or more and 0.60% by mass or less. The lower the Zr content, the more likely abnormal grain growth occurs. And the occurrence of abnormal grain growth reduces Hk / HcJ. If the Zr content is too high, a heterogeneous phase, the 2-17 phase, is formed at the grain boundaries, reducing Hk / HcJ.

[0024] The Ce content relative to the total R content (TRE) (Ce / TRE) is 15% by mass or more and 25% by mass or less. It may be 16% by mass or more and 24% by mass or less. If Ce / TRE is too small, the raw material cost does not decrease sufficiently. This is because the advantage of Ce being less expensive than other rare earth elements is offset by the disadvantage of the manufacturing process becoming more complicated due to the increase in the number of raw metals containing rare earth elements. If Ce / TRE is too large, HcJ decreases.

[0025] The total content of the heavy rare earth elements contained as R may be 0% by mass or more and 0.10% by mass or less. The higher the content of the heavy rare earth elements, the easier it is to increase HcJ, but the higher the cost. Also, the higher the content of the heavy rare earth elements, the easier it is to decrease Br. Furthermore, the heavy rare earth elements are more likely to enter the RT phase 13 than the main phase 11 described below. As a result, the microstructure of the RTB sintered magnet does not easily exhibit suitable magnetic properties. The heavy rare earth elements are Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0026] It is also preferable that R does not substantially contain yttrium (Y) and lanthanum (La). Substantially free of Y and La means that the total content of Y relative to R and the total content of La relative to R is 0.5 mass% or less. If Y and La are substantially contained, the RT phase described below is unlikely to be formed, and the effect of improving HcJ due to the RT phase is unlikely to be obtained. Furthermore, if Y is contained, the anisotropic magnetic field of the main phase particles is likely to decrease. If La is contained, the anisotropic magnetic field of the main phase particles is likely to decrease.

[0027] Fe is the substantial remainder of the components of the RTB sintered magnet. That Fe is the substantial remainder means that the elements contained other than the group consisting of R, B, Co, Ga, Al, Cu, and Zr are only Fe and unavoidable impurities. The content of the unavoidable impurities may be 0.5 mass% or less (including 0) in total with respect to the RTB sintered magnet.

[0028] In addition, when Cu is contained, the Cu content is preferably about 0.05 mass%, specifically, 0.02 mass% or more and 0.08 mass% or less. When the contents of other elements are within the above ranges and the Cu content is about 0.05%, the wettability of the R-rich phase during heat treatment is improved. As a result, the coverage of the main phase particles by the R-rich phase is increased, magnetic decoupling between the main phase particles is promoted, and HcJ is improved. However, when the amount of Cu added is too small or too large, the wettability and HcJ are reduced.

[0029] (fine structure) The RTB sintered magnet 1 will be described below with reference to Fig. 1. Fig. 1 is a backscattered electron image obtained by observing a cross section of Example 1, which will be described later, with a field emission scanning electron microscope (FE-SEM). A backscattered electron image obtained by observation with a FE-SEM may simply be called an SEM image.

[0030] When a cross section of an RTB sintered magnet 1 is observed with an SEM, main phase grains 11 and multiple types of grain boundary phases existing at the grain boundaries are visible, as shown in Figure 1. The multiple types of grain boundary phases each have a color shade according to their composition and a shape according to their crystal system.

[0031] For example, by using an energy dispersive X-ray spectrometer (EDS), an electron probe microanalyzer (EPMA), a transmission electron microscope (TEM), or other equipment attached to an FE-SEM to perform point analysis of each grain boundary phase and clarify the composition, it is possible to identify the type of grain boundary phase they are.

[0032] Furthermore, the crystal structure of each grain boundary phase may be confirmed by a transmission electron microscope (TEM). By confirming the crystal structure of each grain boundary phase by a TEM, each grain boundary phase can be more clearly identified.

[0033] As shown in the SEM image of FIG. 1, the RTB sintered magnet 1 includes main phase grains 11 and grain boundaries present between the main phase grains 11. The main phase grains 11 are 14 It consists of B compounds. R2T 14 Compound B is R2T14 It is a compound having a crystal structure made of B-type tetragonal crystals. The main phase particles 11 are black in the SEM image. There is no particular limit to the size of the main phase particles 11, but the circle equivalent diameter is generally 1.0 μm to 10.0 μm.

[0034] The grain boundaries include multi-grain boundaries, which are boundaries surrounded by three or more main phase grains, and two-grain boundaries, which are boundaries between two adjacent main phase grains.

[0035] The grain boundary includes at least two types of grain boundary phases. In Fig. 1, these include an RT phase 13 and an R-rich phase 15. When comparing the brightness of the main phase grains 11, the RT phase 13, and the R-rich phase 15 in an SEM image, the main phase grains 11 are the darkest and the R-rich phase 15 are the brightest.

[0036] In the RT phase 13, the content ratio of R and T is approximately 1:2 in terms of atomic ratio. Specifically, the content of R is 20.0 at% or more and 40.0 at% or less, and the content of T is 55.0 at% or more and 80.0 at% or less. The content of R may be 24.0 at% or more and 32.0 at% or less, and the content of T may be 61.0 at% or more and 75.0 at% or less. The content of elements other than R and T contained in the RT phase 13 is 10.0 at% or less in total. The content of elements other than R and T contained in the RT phase 13 may be 0.5 at% or more and 8.0 at% or less in total. The content of R, T and elements other than R and T is the content excluding oxygen (O), carbon (C) and nitrogen (N).

[0037] The R-rich phase 15 refers to a phase in which the R content is 40.0 at% or more and the T content is lower than that of the RT phase 13. The R content may be 47.0 at% or more. There is no particular upper limit to the R content, but the R content may be 68.0 at% or less. The T content may be 55.0 at% or less, or 50.0 at% or less. There is no particular lower limit to the T content, but the T content may be 31.0 at% or more. The R and T contents are the contents excluding O, C, and N.

[0038] The inventors have discovered that for an RTB sintered magnet that uses Ce, a rare earth element that is low cost but has a lower HcJ compared to Nd and Pr, by setting the magnet composition within the above ranges, it is possible to obtain a magnet that has high Br, HcJ, Hk / HcJ and corrosion resistance.

[0039] The R-rich phase 15 promotes magnetic decoupling between the main phase particles 11 and between the main phase particles 11 and the RT phase 13. As a result, the inclusion of the R-rich phase 15 can improve HcJ. Furthermore, by setting the magnet composition within the above range, the wettability between the main phase particles 11 and the R-rich phase 15 during aging treatment is improved, and the coverage of the main phase particles 11 by the R-rich phase 15 is improved.

[0040] By setting the magnet composition within the above range, the RT phase 13 tends to have a higher Ce content relative to R than the main phase grains 11. This is because Ce is expelled from the main phase grains 11 when the RT phase 13 is formed. As a result, the main phase grains 11 have a higher content of R other than Ce, specifically Nd. This in turn increases the anisotropic magnetic field in the main phase grains 11. Furthermore, the RT phase 13 itself contributes to magnetic isolation as a thick soft magnetic grain boundary.

[0041] When the magnet composition is within the above range, it is possible to achieve both the effect of promoting magnetic isolation and the effect of expelling Ce from main phase grains 11. As a result, an RTB sintered magnet with high HcJ is obtained.

[0042] The area ratio of the RT phase 13 to the grain boundaries is not particularly limited, and may be, for example, 0.60 or more and 0.85 or less.

[0043] Although there is no particular limitation on the area ratio of the R-rich phase 15 to the grain boundary, it is preferable that the portion of the grain boundary other than the RT phase 13 is the R-rich phase 15. Specifically, it is preferable that the area ratio of the phase other than the R-rich phase 15 and the RT phase 13 to the grain boundary is 10.0% or less (including 0%).

[0044] There is no particular limit to the area of ​​the observation range of the SEM image for calculating the above area ratio, but the range should be large enough to calculate the above area ratio. For example, the area of ​​the observation range is 0.01 mm 2 It may be more than that.

[0045] (Manufacturing method) An example of a method for producing an RTB based sintered magnet will now be described. The method for producing an RTB based sintered magnet includes the following steps.

[0046] (a) Alloy preparation process for producing alloys (raw alloys) for RTB sintered magnets (b) A crushing process for crushing the raw alloy (c) A molding step for molding the obtained alloy powder. (d) Sintering process for sintering the green compact to obtain an RTB based sintered magnet (e) Aging treatment process for aging the RTB sintered magnet (f) Processing process for processing RTB sintered magnets (g) Grain boundary diffusion process in which heavy rare earth elements are diffused into the grain boundaries of RTB sintered magnets (h) Surface treatment process for RTB sintered magnets

[0047] [Alloy preparation process] An alloy for an RTB sintered magnet is prepared (alloy preparation step). In the following, strip casting will be described as an example of an alloy preparation method, but the alloy preparation method is not limited to strip casting.

[0048] Raw material metals corresponding to the composition of the RTB sintered magnet are prepared, and the prepared raw material metals are melted in a vacuum or in an inert gas atmosphere such as argon (Ar) gas. The melted raw material metals are then cast to produce a raw material alloy that will be the raw material for the RTB sintered magnet. Note that, although the following description will be of the one-alloy method, a two-alloy method in which two alloys, a first alloy and a second alloy, are mixed to produce raw material powder, may also be used.

[0049] There is no particular limit to the type of raw material metal. For example, rare earth metals, pure iron, pure cobalt, compounds such as ferroboron (FeB), and alloys such as rare earth alloys can be used. There is no particular limit to the casting method for casting the raw material metal. For example, ingot casting, strip casting, book molding, centrifugal casting, and the like can be used. If the obtained raw material alloy has solidification segregation, it may be subjected to homogenization treatment (solution treatment) as necessary.

[0050] [Crushing process] After the raw alloy is prepared, the raw alloy is pulverized (pulverization step). The pulverization step may be performed in two stages, a coarse pulverization step in which the alloy is pulverized to a particle size of several hundred μm to several mm, and a fine pulverization step in which the alloy is pulverized to a particle size of several μm, or may be performed in a single stage, the fine pulverization step alone.

[0051] (Coarse grinding process) The raw alloy is coarsely pulverized until the particle size is about several hundred μm to several mm (coarse pulverization step). This produces a coarsely pulverized powder of the raw alloy. The coarse pulverization can be performed, for example, by absorbing hydrogen into the raw alloy, then releasing hydrogen based on the difference in the amount of hydrogen absorbed between different phases, and dehydrogenating the alloy to cause self-destructive pulverization (hydrogen absorption pulverization). There are no particular limitations on the dehydrogenation conditions, but the dehydrogenation can be performed, for example, at 300 to 650°C in an Ar flow or in a vacuum.

[0052] The method of coarse pulverization is not limited to the above-mentioned hydrogen absorption pulverization. For example, coarse pulverization may be performed in an inert gas atmosphere using a coarse pulverizer such as a stamp mill, a jaw crusher, or a Braun mill.

[0053] In order to obtain an RTB-based sintered magnet with high magnetic properties, it is preferable that the atmosphere in each step from the coarse pulverization step to the sintering step described below be an atmosphere with a low oxygen concentration. The oxygen concentration is adjusted by controlling the atmosphere in each manufacturing step. If the oxygen concentration in each manufacturing step is high, the rare earth elements in the alloy powder obtained by pulverizing the raw alloy will be oxidized to produce R oxides. The R oxides are not reduced during sintering and will precipitate in the form of R oxides at the grain boundaries as they are. As a result, the coercive force HcJ of the obtained RTB-based sintered magnet is likely to decrease. For this reason, for example, it is preferable that each step (fine pulverization step, molding step) be performed in an atmosphere with an oxygen concentration of 100 ppm or less.

[0054] (Fine grinding process) After the raw alloy is coarsely pulverized, the obtained coarsely pulverized powder of the raw alloy is finely pulverized until the average particle size is about several μm (fine pulverization step). In this way, finely pulverized powder of the raw alloy can be obtained. There is no particular restriction on the D50 of the particles contained in the finely pulverized powder. For example, the D50 may be 1.0 μm or more and 10.0 μm or less.

[0055] Fine pulverization is performed by further pulverizing the coarsely pulverized powder using a fine pulverizer such as an airflow pulverizer (jet mill) while appropriately adjusting conditions such as pulverization time. Jet mills are described below. A jet mill is a fine pulverizer that releases high-pressure inert gas (e.g., He gas, N2 gas, Ar gas) from a narrow nozzle to generate a high-speed gas flow, and accelerates the coarsely pulverized powder of the raw alloy by this high-speed gas flow, causing collisions between the coarsely pulverized powder of the raw alloy and with a target or a container wall, thereby pulverizing the powder.

[0056] When the coarsely pulverized powder of the raw alloy is pulverized, a lubricant such as an organic lubricant or a solid lubricant may be added. Examples of the organic lubricant include oleic acid amide, lauric acid amide, and zinc stearate. Examples of the solid lubricant include graphite. By adding the lubricant, it is possible to obtain a pulverized powder that is likely to be oriented when a magnetic field is applied in the molding process. Either the organic lubricant or the solid lubricant may be used alone, or both may be used in combination.

[0057] [Molding process] The finely pulverized powder is molded into a desired shape (molding process). In the molding process, the finely pulverized powder is filled into a die placed in a magnetic field and pressurized to mold the finely pulverized powder into a green body. At this time, molding is performed while applying a magnetic field, so that the crystal axes of the finely pulverized powder can be oriented in a specific direction. Since the obtained green body is oriented in a specific direction, an RTB-based sintered magnet having stronger anisotropy can be obtained. A molding aid may be added during molding. There is no particular restriction on the type of molding aid. The above-mentioned lubricants may also be used.

[0058] The pressure during pressurization may be, for example, 30 MPa or more and 300 MPa or less. The applied magnetic field may be, for example, 1.0 T or more and 5.0 T or less. The applied magnetic field is not limited to a static magnetic field, and may be a pulsed magnetic field. Moreover, a static magnetic field and a pulsed magnetic field may be used in combination.

[0059] 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.

[0060] The shape of the green body obtained by compacting the finely pulverized powder is not particularly limited, and can be, for example, a rectangular parallelepiped, plate-like, columnar, ring-like, C-shaped, or any other shape that corresponds to the desired shape of the RTB-based sintered magnet.

[0061] [Sintering process] The obtained green body is sintered in a vacuum or inert gas atmosphere to obtain an RTB-based sintered magnet (sintering step). 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. The sintering temperature is not particularly limited, but may be, for example, 950°C or higher and 1100°C or lower. The sintering time is not particularly limited, but may be, for example, 2 hours or higher and 10 hours or lower. The atmosphere during sintering is not particularly limited. For example, an inert gas atmosphere or a vacuum atmosphere of less than 100 Pa may be used.

[0062] The higher the sintering temperature, the more easily sintering proceeds and the more easily Br and HcJ improve. However, the higher the sintering temperature, the more easily abnormal grain growth occurs. If abnormal grain growth occurs, Hk / HcJ is more likely to decrease. The lower the sintering temperature, the more difficult it is for sintering to proceed sufficiently and the more difficult it is for Br and HcJ to improve. However, the lower the sintering temperature, the more difficult it is for abnormal grain growth to occur and the more difficult it is for Hk / HcJ to decrease.

[0063] [Aging treatment process] After sintering the compact, the RTB based sintered magnet is subjected to an ageing treatment (ageing treatment step). After sintering, the obtained RTB based sintered magnet is subjected to an ageing treatment at a temperature lower than that during sintering.

[0064] In the aging treatment, the aging temperature may be 400° C. or more and 650° C. or less, and the aging time may be 10 minutes or more and 300 minutes or less.

[0065] The atmosphere during the aging treatment is not particularly limited. For example, an inert gas atmosphere (e.g., He gas, Ar gas) at a pressure equal to or higher than atmospheric pressure may be used. The aging treatment step may be performed after the processing step described below.

[0066] [Processing process] The obtained RTB based sintered magnet may be processed into a desired shape as required (processing step). Examples of processing methods include shaping such as cutting and grinding, and chamfering such as barrel polishing.

[0067] [Grain boundary diffusion process] A heavy rare earth element may be further diffused into the grain boundaries of the processed RTB based sintered magnet (grain boundary diffusion step). There are no particular limitations on the method of grain boundary diffusion. For example, it may be carried out by attaching a compound containing a heavy rare earth element to the surface of the RTB based sintered magnet by coating or vapor deposition, etc., and then carrying out a heat treatment. It may also be carried out by carrying out a heat treatment on the RTB based sintered magnet in an atmosphere containing vapor of the heavy rare earth element. Grain boundary diffusion can further improve the HcJ of the RTB based sintered magnet.

[0068] [Surface treatment process] The RTB sintered magnet obtained by the above steps may be subjected to a surface treatment such as plating, resin coating, oxidation treatment, chemical conversion treatment, etc. (surface treatment step), which can further improve the corrosion resistance.

[0069] In the above manufacturing method, the processing step, the grain boundary diffusion step, and the surface treatment step are performed, but these steps do not necessarily have to be performed.

[0070] The RTB based sintered magnet obtained in the above manner is an RTB based sintered magnet that contains Ce but has good Br, HcJ, Hk / HcJ and corrosion resistance.

[0071] The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention. For example, the permanent magnet according to the present invention may be manufactured by hot working.

[0072] The RTB permanent magnet of the present invention can be used in applications for which RTB permanent magnets are generally used, such as in rotating machines for automobiles. EXAMPLES

[0073] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0074] (Alloy preparation process) As the raw alloy, raw metals containing the specified elements were prepared, each of which had a purity of 99.9%: Nd, Pr, Ce, Fe, Co, FeB, Al, Cu, Zr, and Ga.

[0075] Next, these raw material metals were weighed so as to finally obtain RTB sintered magnets having the compositions shown in Tables 1 to 8, and thin plate-shaped raw material alloys were prepared by strip casting. In Tables 1 to 8, R other than Ce is Nd and Pr, with a mass ratio of Nd:Pr=8:2. The balance is essentially Fe only.

[0076] (Crushing process) The raw alloy obtained in the alloy preparation step was pulverized to obtain alloy powder. The pulverization was carried out in two stages: coarse pulverization and fine pulverization. The coarse pulverization was carried out by hydrogen absorption pulverization. After the raw alloy was allowed to absorb hydrogen at 600°C, it was dehydrogenated at 600°C for 3 hours in an Ar flow or in a vacuum. The coarse pulverization produced alloy powder with a particle size of several hundred μm to several mm.

[0077] The fine pulverization was carried out by adding 0.1 parts by mass of oleic acid amide as a lubricant to 100 parts by mass of the alloy powder obtained by the coarse pulverization, mixing, and then performing the fine pulverization in a high-pressure nitrogen gas atmosphere using a jet mill until the D50 of the alloy powder became about 3.5 μm.

[0078] (molding process) The mixed powder obtained in the pulverization process was molded in a magnetic field to obtain a compact. The mixed powder was filled into a die placed between electromagnets, and then pressed and molded while applying a magnetic field from the electromagnets. Specifically, the mixed powder was compacted at a pressure of 110 MPa in a magnetic field of 2.2 T. The direction in which the magnetic field was applied was perpendicular to the pressing direction.

[0079] (Sintering process) The obtained molded body was sintered to obtain a sintered body. Unless otherwise specified, the sintering temperature was 1000° C. and the sintering time was 8 hours. The sintering atmosphere was a vacuum atmosphere.

[0080] In Example 28a, the sintering temperature was set to 980° C., and in Examples 28b and 28c, the sintering temperature was set to 990° C. to obtain sintered bodies.

[0081] (Aging process) The resulting sintered body was subjected to aging treatment to obtain an RTB-based sintered magnet. The aging treatment was performed at a temperature of 600° C. for one hour in an Ar atmosphere.

[0082] (evaluation) It was confirmed by composition analysis using X-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry (ICP method), and gas analysis that the compositions of the RTB sintered magnets finally obtained in each of the Examples and Comparative Examples were as shown in Tables 1 to 9.

[0083] The magnetic properties of the RTB sintered magnets of each of the examples and comparative examples were measured using a BH tracer. Specifically, Br, HcJ, and Hk / HcJ were measured at room temperature. The results are shown in Tables 1 to 9. Br was rated as good when it was 1220 mT or more. HcJ was rated as good when it exceeded 1445 kA / m, and even better when it was 1450 kA / m or more. Hk / HcJ was evaluated as whether it was 95% or more. In Tables 1 to 9, 95% or more was rated as acceptable, and less than 95% was rated as unacceptable.

[0084] A corrosion resistance test was conducted on the RTB sintered magnets of each of the examples and comparative examples. The corrosion resistance test was conducted by a PCT test (Pressure Cooker Test) under saturated vapor pressure. Specifically, the RTB sintered magnets were placed in an environment of 2 atm and 100% RH for 1000 hours, and the change in mass was measured before and after the test. The mass loss per surface area of ​​the RTB sintered magnet was 3 mg / cm. 2 In Tables 1 to 9, it was evaluated whether the average particle size was 3 mg / cm or less. 2 If the density is less than 3mg / cm 2 Anything above this is not acceptable.

[0085] [Table 1]

[0086] [Table 2]

[0087] [Table 3]

[0088] [Table 4]

[0089] [Table 5]

[0090] [Table 6]

[0091] [Table 7]

[0092] [Table 8]

[0093] [Table 9]

[0094] As can be seen from Tables 1 to 9, in the examples whose compositions were within the above ranges, Br, HcJ, Hk / HcJ and corrosion resistance were all good. In contrast, in the comparative examples whose compositions were outside the above ranges, one or more of Br, HcJ, Hk / HcJ and corrosion resistance were not good.

[0095] In particular, Comparative Example 4 in Table 3, which contained too little B, showed a decrease in Hk / HcJ due to the formation of heterogeneous phases, particularly the 2-17 phase. Comparative Example 10 in Table 7, which contained too little Co, showed a decrease in corrosion resistance. Comparative Example 13 in Table 8, which contained too much Zr, showed a decrease in Hk / HcJ due to the formation of heterogeneous phases, particularly the 2-17 phase.

[0096] Example 28c and Reference Example 1 in Table 8 are experimental examples in which sintered bodies were produced under the same conditions except for the sintering temperature.

[0097] Example 28c is an example in which the Zr content is reduced and the sintering temperature is lowered at the same time compared to Example 28 etc. Example 28c is an example in which an appropriate sintering temperature was selected according to the composition, so that abnormal grain growth did not occur and Hk / HcJ was good.

[0098] In contrast, Reference Example 1 is a reference example in which the Zr content was reduced compared to Example 28 etc., but the sintering temperature was not reduced at the same time. In Reference Example 1, abnormal grain growth occurred and Hk / HcJ decreased because an appropriate sintering temperature was not selected according to the composition.

[0099] Figure 2 is a graph plotting all of the examples and all of the comparative examples in which Br or HcJ was not good, with HcJ on the horizontal axis and Br on the vertical axis. Figure 2 also shows that in order to achieve Br of 1220 mT or more, HcJ greater than 1445 kA / m, and other good properties, the magnet composition must be within a specific range.

[0100] In addition, the microstructure of all examples was confirmed and R2T 14 It was confirmed that the specimen contains main phase particles made of a B compound and grain boundaries, that an RT phase is contained in the grain boundaries, and that the RT phase has a higher Ce content relative to R than the main phase particles. [Explanation of symbols]

[0101] 1. RTB-based sintered magnet 11...Main phase particles 13...RT phase 15 R-rich phase

Claims

1. An R-T-B system permanent magnet containing R (rare earth element), T (Fe and Co), B (boron), and at least one element selected from Al, Cu, Ga, and Zr, R includes Ce; The total content of R is 31.3 mass% or more and 34.0 mass% or less, The Co content is 1.85 mass% or more and 3.00 mass% or less, The B content is 0.80 mass% or more and 0.90 mass% or less, The Al content is 0.03 mass% or more and 0.90 mass% or less, The Cu content is 0 mass% or more and 0.25 mass% or less, The Ga content is 0 mass% or more and 0.10 mass% or less, The Zr content is 0 mass% or more and 0.60 mass% or less, The content of Fe is the substantial remainder, An R-T-B system permanent magnet in which the Ce content relative to R is 15 mass % or more and 25 mass % or less.

2. R 2 T 14 2. An RTB system permanent magnet according to claim 1, comprising main phase grains made of a B compound and grain boundaries, the grain boundaries including an R-T phase.

3. 3. The R-T-B system permanent magnet according to claim 2, wherein the content of Ce relative to R in the R-T phase is greater than that in the main phase grains.

4. 4. The R-T-B system permanent magnet according to claim 1, wherein the total content of heavy rare earth elements is from 0% by mass to 0.10% by mass.

5. 5. The R-T-B system permanent magnet according to claim 1, wherein the Co content is from 1.85 mass % to 2.09 mass %.

Images