R-Fe-B sintered magnets

Abstract

To achieve both high residual magnetic flux density and high coercive force, which are conventionally considered paradoxical characteristics, an R-Fe-B system sintered magnet is provided, characterized in that it has the following composition: containing R (R is one or more elements selected from rare earth elements, and Nd is essential), B, M (M is at least one of Si, Al, Mn, Ni, Co, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, and Bi), X (X is at least one of Ti, Zr, Hf, Nb, V, and Ta), and C, with the balance being Fe, O, and unavoidable impurities, and having R2Fe 14 A main phase of B and a grain boundary phase containing an R-C phase having a higher R concentration and a higher C concentration than the main phase, wherein the area ratio of the R-C phase in the magnet cross section exceeds 0 and is 0.5% or less.

Description

Technical Field

[0001] The present invention relates to an R-Fe-B based rare earth sintered magnet which suppresses a decrease in coercive force and improves residual magnetic flux density. Background Art

[0002] R-Fe-B sintered magnets (hereinafter sometimes referred to as Nd magnets) are essential functional materials for energy conservation and enhanced functionality, and their application range and production volume are expanding year by year. For example, they are used in drive motors for hybrid and electric vehicles, electric power steering motors, compressor motors for air conditioners, and voice coil motors (VCMs) for hard disk drives. The high remanent flux density (Br) of R-Fe-B sintered magnets is a major advantage in these various applications. For example, further miniaturization of motors requires further improvement of Br.

[0003] As a method for increasing the Br content of R-Fe-B system sintered magnets, it is conventionally known to increase the R2Fe 14 Methods to reduce the content of R by reducing the proportion of B phase, reducing the solid solution in R2Fe 14 A method of reducing the amount of Br by adding elements in the B phase.

[0004] However, it is known that the coercive force (hereinafter referred to as H) related to the heat resistance of the sintered magnet can be reduced by reducing the amount of R and other added elements. cJ ) is reduced. In particular, when the amount of R element is reduced, there is a risk that the sinterability of the R-Fe-B system sintered magnet will be reduced and abnormal grain growth will occur during the sintering process of the R-Fe-B system sintered magnet, which is densified due to the formation of a liquid phase. Therefore, in order to obtain a R-Fe-B system sintered magnet with higher characteristics, it is necessary to suppress the H caused by reducing the amount of R and other added elements. cJ To suppress H cJ In order to reduce or increase Br, it is generally known to add heavy rare earth elements such as Dy and Tb. However, since their addition leads to a decrease in Br and their resources are rare and expensive, methods related to reducing the use of heavy rare earth elements such as Dy and Tb have been proposed so far.

[0005] For example, International Publication No. 2013 / 191276 (Patent Document 1) proposes a sintered magnet in which the B content is reduced compared to the stoichiometric composition, 0.1 to 1.0 mass % of Ga is added, and the values ​​of [B] / ([Nd]+[Pr]) and ([Ga]+[C]) / [B] are adjusted to satisfy specific relationships among the amount ratios of B, Nd, Pr, C, and Ga. Thus, a high H content can be obtained even in a composition in which the amount of heavy rare earth elements such as Dy and Tb is reduced. cJ .

[0006] In addition, International Publication No. 2004 / 081954 (Patent Document 2) proposes that the content of B be adjusted to about the stoichiometric composition to suppress the R 1.1 The formation of Fe4B4 phase leads to the formation of sintered magnet with high Br. Furthermore, it is described that by containing 0.01 to 0.08 mass% of Ga, when B is lower than the stoichiometric composition, the formation of Fe4B4 phase leads to the formation of sintered magnet with high Br. cJ The reduction of R2Fe 17 Phase precipitation, so as to take into account both high Br and high H cJ .

[0007] In addition, Japanese Patent Application Laid-Open No. 2016-143828 (Patent Document 3) proposes that a structure having an R-Ga-C concentrated portion is formed to improve H by miniaturizing the particle size of the raw material powder. cJ Even when a large amount of lubricant is added to suppress the decrease in orientation, H cJ , get high H cJ .

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: International Publication No. 2013 / 191276

[0011] Patent Document 2: International Publication No. 2004 / 081954

[0012] Patent Document 3: Japanese Patent Application Laid-Open No. 2016-143828 Summary of the Invention

[0013] Problems to be solved by the invention

[0014] However, in the magnet described in Patent Document 1, by adding 0.1 mass % or more of Ga, the amount of heavy rare earth elements such as Dy and Tb is relatively reduced, thereby achieving R2Fe 14 The saturation magnetization of the B phase increases, while the addition of Ga increases the R2Fe 14 Since the saturation magnetization of the B phase decreases, a sufficient increase in Br cannot necessarily be achieved.

[0015] Furthermore, the technology described in Patent Document 2 does indeed achieve good magnetic properties in the case of an R-Fe-B system sintered magnet with an oxygen concentration of approximately 0.4 mass %. However, the relationship between the oxygen concentration in the sintered magnet and the magnetic properties is not fully described. Below this oxygen concentration, especially below 0.2 mass %, the property behavior changes significantly, and it is not necessarily possible to achieve high Br and high H. cJTaking both into account.

[0016] Furthermore, in the technology described in Patent Document 3, since a relatively large amount of Ga of 0.42 to 1.5 mass % is contained, R2Fe 14 The saturation magnetization of the B phase decreases, making it difficult to obtain high Br. In addition, since the formation of the R-Ga-C concentrated portion requires a holding step at 500 to 700°C for a predetermined time in the normal sintering process, this is disadvantageous in terms of productivity.

[0017] The present invention has been made in view of the above problems and aims to provide an R-Fe-B system sintered magnet having high Br and stable H by adjusting and optimizing the content ratio of the constituent elements and the structure of the R-Fe-B system sintered magnet. cJ .

[0018] Means for solving problems

[0019] In order to achieve the above object, the present inventors have made a study on an R-Fe-B based sintered magnet containing R (R is one or more elements selected from rare earth elements, with Nd being an essential element), B, M (M is one or more elements selected from Si, Al, Mn, Ni, Co, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, and Bi), X (one or more elements selected from Ti, Zr, Hf, Nb, V, and Ta), C, O, and Fe. 14 The magnet structure of the main phase and grain boundary phase of the B intermetallic compound was studied intensively. As a result, it was found that high Br and stable H can be obtained by having the following specified structure morphology composed of the main phase and grain boundary phase. cJ , completed the present invention.

[0020] That is, the present invention provides the following R-Fe-B system sintered magnet.

[0021] [1] R-Fe-B system sintered magnet having the following composition: containing 12.5 to 14.5 atomic % of R (R is one or more elements selected from rare earth elements, with Nd being an essential element), 5.0 to 6.5 atomic % of B, 0.15 to 5.0 atomic % of M (M is one or more elements selected from Si, Al, Mn, Ni, Co, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi), 0.02 to 0.5 atomic % of X (X is one or more elements selected from Ti, Zr, Hf, Nb, V, Ta), 0.1 to 1.6 atomic % of C, and the balance being Fe, O and unavoidable impurities, containing R2Fe 14B intermetallic compound main phase and grain boundary phase, characterized in that the grain boundary phase contains an RC phase with higher R concentration and C concentration than the main phase, and the area ratio of the RC phase in the cross section of the R-Fe-B system sintered magnet exceeds 0 and is not more than 0.5%.

[0022] [2] The R-Fe-B sintered magnet of [1], wherein the content of the R is 12.8 to 14.0 atomic %.

[0023] [3] The R-Fe-B sintered magnet of [1] or [2], wherein the O content is 0.1 to 0.8 atomic %.

[0024] [4] The R-Fe-B system sintered magnet according to any one of [1] to [3], wherein the C content is 0.2 to 1.0 atomic %.

[0025] [5] The R-Fe-B based sintered magnet according to any one of [1] to [4], wherein the B content is 5.2 to 5.9 atomic %.

[0026] [6] The R-Fe-B system sintered magnet according to any one of [1] to [5], wherein Ga is contained in an amount exceeding 0 and not more than 0.1 atomic % as a part of the M element.

[0027] [7] The R-Fe-B sintered magnet according to any one of [1] to [6], wherein the C concentration of the RC phase is higher than that of the main phase by 20 atomic % or more.

[0028] Effects of the Invention

[0029] According to the R-Fe-B system sintered magnet of the present invention, by adjusting the 14 The microstructure of the main phase and grain boundary phase composed of B intermetallic compounds can achieve the balance of high Br and high H, which were previously contradictory characteristics. cJ . DETAILED DESCRIPTION

[0030] As described above, the R-Fe-B system sintered magnet of the present invention has the following composition: it contains 12.5 to 14.5 atomic % of R (R is one or more elements selected from rare earth elements, with Nd being an essential element), 5.0 to 6.5 atomic % of B, 0.15 to 5.0 atomic % of M (M is one or more elements selected from Si, Al, Mn, Ni, Co, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, and Bi), 0.02 to 0.5 atomic % of X (X is one or more elements selected from Ti, Zr, Hf, Nb, V, and Ta), 0.1 to 1.6 atomic % of C, and the balance is Fe, O, and inevitable impurities.

[0031] As described above, the element R constituting the sintered magnet of the present invention is one or more elements selected from rare earth elements, with Nd being an essential element. Preferred rare earth elements other than Nd include Pr, La, Ce, Gd, Dy, Tb, and Ho, with Pr, Dy, and Tb being particularly preferred, and Pr being particularly preferred. Within R, the ratio of Nd, an essential component, is preferably 60 atomic % or greater, and particularly preferably 70 atomic % or greater, of the total R content.

[0032] As mentioned above, the R content is 12.5 to 14.5 atomic %, preferably 12.8 to 14.0 atomic %. If the R content is less than 12.5 atomic %, α-Fe crystals will form in the raw material alloy, and even homogenization will make it difficult to eliminate the α-Fe. As a result, the H content of the R-Fe-B system sintered magnet will be reduced. cJ , the squareness is greatly reduced. In addition, even when the raw material alloy is produced by the strip casting method, in which α-Fe crystallization is difficult to occur, α-Fe crystallization will occur, so the H of the R-Fe-B system sintered magnet is cJ , squareness is greatly reduced. In addition, the amount of liquid phase mainly composed of R components, which has the effect of promoting densification during the sintering process, is reduced, so the sintering property is reduced and the densification of the R-Fe-B system sintered magnet is insufficient. On the other hand, when the R content exceeds 14.5 atomic%, there is no problem in production, but the R2Fe in the sintered magnet is 14 The ratio of B phase decreases and Br decreases.

[0033] As described above, the sintered magnet of the present invention contains 5.0 to 6.5 atomic % of boron (B). A more preferred content is 5.2 to 5.9 atomic %, and even more preferably 5.3 to 5.7 atomic %. In the present invention, the content of B is consistent with the content of C and X described below, and plays a decisive role in obtaining a stable H cJ The main reason for the required oxygen concentration range is that if the B content is less than 5.0 atomic %, the R2Fe 14 The ratio of B phase becomes lower, Br is greatly reduced, and due to the formation of R2Fe 17 phase, so H cJ On the other hand, if the B content exceeds 6.5 atomic %, a B-rich phase is formed, and the R2Fe 14 The ratio of the B phase decreases, resulting in a decrease in Br.

[0034] As described above, the sintered magnet of the present invention contains one or more elements selected from Si, Al, Mn, Ni, Co, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, and Bi as the M element. As described above, the M content is 0.15 to 5.0 atomic %, preferably 0.3 to 4.0 atomic %, and more preferably 0.5 to 3.0 atomic %. If the M content is less than 0.15 atomic %, it is difficult to obtain sufficient H. cJ On the other hand, when the content of M exceeds 5.0 atomic %, there is a possibility that Br may be reduced. In addition, although there is no particular limitation, it is particularly preferred that M elements contain Co, Cu, Al, and Ga.

[0035] The above-mentioned Co content may affect the Curie temperature, corrosion resistance, H cJ , it can be set by considering the balance of these characteristics. For example, from the viewpoint of obtaining the effect of improving the Curie temperature and corrosion resistance caused by the inclusion of Co, it is preferably 0.1 atomic % or more, more preferably 0.5 atomic % or more. In addition, from the viewpoint of stably obtaining high H cJ From the viewpoint of Co, the content of Co is preferably 3.5 atomic % or less, more preferably 2.0 atomic % or less.

[0036] The Cu content may affect the optimum temperature range in the low-temperature heat treatment for magnet production, the sinterability during sintering, and the resulting magnetic properties (Br, H cJ ), it can be set by taking into account the balance of these characteristics. For example, from the perspective of obtaining the optimal temperature range in the low-temperature heat treatment after sintering that is appropriately performed to ensure good mass productivity, it is preferably 0.05 atomic % or more, and more preferably 0.1 atomic % or more. In addition, from the perspective of obtaining good sintering properties and high magnetic properties (Br, H cJ ), it is preferably 0.5 atomic % or less, and more preferably 0.3 atomic % or less.

[0037] The above Al and Ga contents may affect the magnetic properties (Br, H cJ ), as long as we consider the cJ For example, from obtaining sufficient H cJ From the perspective of obtaining high Br, the Al content is preferably 0.05 atomic % or more, and from the perspective of obtaining high Br, it is preferably 1.0 atomic % or less, and more preferably 0.5 atomic % or less. cJ From the viewpoint of the balance between the Ga and the Ga, the Ga content is preferably more than 0 atomic % and 0.1 atomic % or less, and more preferably 0.05 to 0.1 atomic %.

[0038] As described above, the sintered magnet of the present invention contains one or more elements selected from Ti, Zr, Hf, Nb, V, and Ta as the X element. The inclusion of these elements can suppress abnormal grain growth during sintering through the formation of an XB phase. While not particularly limited, it is preferred that Zr be included as the at least one X element.

[0039] The X content is 0.02 to 0.5 atomic %, preferably 0.05 to 0.3 atomic %, and more preferably 0.07 to 0.2 atomic %. If the X content is less than 0.02 atomic %, the effect of suppressing abnormal grain growth of grains during sintering cannot be obtained. On the other hand, if the X content exceeds 0.5 atomic %, the XB phase is formed, and thus the XB phase used to form R2Fe 14 The amount of B in the B phase is reduced, possibly due to R2Fe 14 The reduction of B ratio leads to the reduction of Br, which in turn forms R2Fe 17 phase, which results in a large H cJ reduce.

[0040] As mentioned above, the carbon (C) content of the sintered magnet of the present invention is 0.1 to 1.6 atomic%, preferably 0.2 to 1.0 atomic%. C is derived from the raw materials and the lubricant added to improve the orientation of the powder during molding in a magnetic field. Therefore, it is difficult to obtain an R-Fe-B system sintered magnet with a C content of less than 0.1 atomic%. On the other hand, when the C content exceeds 1.6 atomic%, a large amount of RC phase exists in the sintered magnet, so H cJ Significantly reduced.

[0041] The sintered magnet of the present invention contains the aforementioned R, B, M, X, and C, and further contains Fe and O as the balance. The O content is not particularly limited, but is preferably 0.1 to 0.8 atomic percent, more preferably 0.2 to 0.5 atomic percent. By adjusting the O content in this manner, it is believed that the phases defined by the RC phase, described later, are favorably precipitated.

[0042] In addition, the sintered magnet of the present invention may contain H, N, F, Mg, P, S, Cl, Ca and other elements as inevitable impurities in addition to the above elements. In this case, the total amount of the inevitable impurities may be allowed to be less than 0.1% by mass relative to the total amount of the constituent elements of the magnet and the inevitable impurities. However, the amount of these inevitable impurities is preferably as small as possible. In addition, among these inevitable impurities, the amount of H cJ From the viewpoint of nitrogen content, it is particularly preferred that the nitrogen content be 0.5 atomic % or less.

[0043] The sintered magnet of the present invention comprises R2Fe as a main phase and is composed of the above-mentioned element composition. 14B intermetallic compound and grain boundary phase, and further, in the grain boundary phase, there is an RC phase with a higher R and C concentration than the main phase, and the area ratio of the RC phase in the cross section of the sintered magnet is greater than 0 and less than 0.5%. By having such a structure, it is possible to achieve both high Br and stable H cJ The reason is not necessarily clear, but it can be inferred as follows.

[0044] That is, it is known that R2Fe 14 A portion of B in the B intermetallic compound can be replaced by C, but C usually forms an ROC phase as an impurity phase at the grain boundary triple point and hardly contributes to the formation of the main phase. On the other hand, when attempting to obtain a high Br by reducing the R content as in the present invention, it is necessary to reduce the content of O as an impurity in order to promote liquid phase sintering. It is believed that under such a low oxygen content condition, the amount of ROC phase formed is reduced, and a portion of C can form R2Fe 14 C or RC phase. On the other hand, it is known that the melting point of the compound with R and C as main elements is higher than the sintering temperature of R-Fe-B system sintered magnet, but it is found that the content of RC phase contained in the sintered magnet structure depends on the C concentration contained in the raw material. In other words, the formation of RC phase requires more than R2Fe 14 The sintering temperature of the B sintered magnet is high, and it is believed that the RC phase is mainly formed during the preparation stage of the raw material alloy by high-frequency melting. In addition, the C consumed by the high-melting-point RC phase does not contribute to the formation of the main phase, but instead consumes R to form H. cJ Based on this consideration, the inventors have optimized the amount of RC phase contained in the R-Fe-B system sintered magnet by reducing the amount of C contained in the alloy raw materials as much as possible, thereby achieving high Br and high H cJ Taking both into account.

[0045] Here, the "area ratio of the RC phase in the cross section of the sintered magnet" mentioned above can be measured by measuring the area ratio of the RC phase in a specified area of ​​any cross section of the sintered magnet. In this case, "any cross section" can be a cross section obtained by cutting any part of the sintered magnet, which means that the above area ratio can be achieved even if the cross section is cut from any part of the sintered magnet. In addition, the size of the "specified area" in the cross section is appropriately set according to the measurement equipment, etc. In order to reliably understand the state of the entire magnet, it is preferably set to an area of ​​15000μm. 2 More than 30000 μm 2 In addition, it is also preferred to measure in multiple areas and use the average value as the above-mentioned area ratio. In this case, it is preferred to set the total area of ​​the multiple areas provided for measurement as the above-mentioned preferred area.

[0046] As described above, the area ratio of the RC phase in one region of the arbitrary cross section is more than 0 and is 0.5% or less. In order to obtain sufficient H more reliably, cJ , preferably 0.01% or more and 0.3% or less, more preferably 0.01% or more and 0.27% or less. When the area ratio of the RC phase is 0, that is, when the RC phase does not exist, it is difficult to achieve both high Br and stable H cJ On the other hand, when the area ratio is 0.5% or more, the amount of R required for the formation of the grain boundary phase is insufficient due to the formation of the RC phase, and H cJ , the squareness is reduced.

[0047] The above-mentioned area ratio can be confirmed by observing the structure of the cross section of the sintered magnet using a SEM (scanning electron microscope: Scanning Electron Microscope). In this case, the analysis of the composition can be performed by EDS (energy dispersive X-ray spectrometry) attached to the SEM device. Generally, wet mechanical grinding is sometimes used to perform pre-treatment of the cross section when observing the metal surface, but in the present invention, in order to remove the effects of oxidation on the outermost surface, FIB-SEM (focused ion beam scanning electron microscope: Focused Ion Beam-Scanning Electron Microscope) can also be used for surface processing, and observation and composition analysis can be performed directly without exposure to the atmosphere. In addition, the above-mentioned area ratio can be calculated by taking the obtained electron image into image analysis software and comparing the contrast and composition information.

[0048] Furthermore, the RC phase contained in the grain boundary phase may contain small amounts of O, Fe, Cu, and other elements other than R and C, but is essentially composed of R and C. As described above, it is a phase with higher R and C concentrations than the main phase. The R concentration is not particularly limited but is between 30 atomic % and 50 atomic %, preferably between 35 atomic % and 45 atomic %. Furthermore, the C concentration is preferably higher than that of the main phase by 10 atomic %, more preferably by 20 atomic %. By adjusting the R and C concentrations of the RC phase in this manner, the RC phase is formed in an optimal state, enabling more reliable and effective achievement of the objectives of the present invention.

[0049] Next, a method for producing the R-Fe-B system sintered magnet of the present invention will be described below.

[0050] The various steps in manufacturing the R-Fe-B system sintered magnet of the present invention are basically the same as those of the conventional powder metallurgy method and are not particularly limited. They generally include a melting step of melting the raw materials to obtain a raw material alloy, a pulverizing step of pulverizing the raw material alloy having a specified composition to prepare alloy fine powder, a molding step of compacting the alloy fine powder under application of a magnetic field to obtain a molded body, and a heat treatment step of heat-treating the molded body to obtain a sintered body.

[0051] First, in the melting step, the metals or alloys serving as the raw materials for each element are weighed to form the composition specified in the present invention. For example, the raw materials are melted by high-frequency melting and then cooled to produce a raw material alloy. In this case, the raw material metals or alloys should be low in carbon content so that the carbon concentration of the raw material alloy obtained after the melting step is 0.03% by mass or less. High-purity raw materials are more preferably used to achieve a carbon concentration of 0.01% by mass or less. Casting of the raw material alloy is generally performed using a melt casting method or strip casting method, where the raw material alloy is poured into a flat mold or book mold.

[0052] In addition, R2Fe 14 The so-called two-alloy method, in which an alloy with a B compound composition close to that of the main phase and an R-rich alloy that becomes a liquid phase auxiliary at the sintering temperature are weighed and mixed after coarse grinding, can also be applied to the present invention. However, the alloy close to the main phase composition depends on the cooling rate and alloy composition during casting. The α-Fe phase is easy to crystallize. Therefore, in order to make the structure uniform and eliminate the α-Fe phase, it is preferred to carry out a homogenization treatment at 700-1200°C for more than 1 hour in a vacuum or Ar atmosphere as needed. It should be noted that when an alloy close to the main phase composition is produced by a strip casting method, homogenization can also be omitted. For the R-rich alloy that becomes a liquid phase auxiliary, in addition to the above-mentioned casting method, the so-called liquid rapid cooling method can also be used.

[0053] The pulverization step can be a multi-stage process including, for example, a coarse pulverization step and a fine pulverization step. In the coarse pulverization step, for example, a jaw crusher, Brownian mill, pin mill, or hydrogenation pulverization is used. In the case of alloys produced by strip casting, hydrogenation pulverization is generally applied to obtain a coarse powder that has been coarsely pulverized to, for example, 0.05 to 3 mm, particularly 0.05 to 1.5 mm. In the fine pulverization step, the coarse powder obtained in the coarse pulverization step is finely pulverized to, for example, 0.2 to 30 μm, particularly 0.5 to 20 μm, using a method such as jet milling. It should be noted that, in either or both of the coarse pulverization and fine pulverization steps of the raw alloy, additives such as lubricants can be added as needed to adjust the carbon content to a predetermined range. In this case, the lubricant is not particularly limited and can include fatty acids, including stearic acid, alcohols, esters, and metal soaps. In addition to the lubricant, hydrocarbons such as carbon black, paraffin wax, and polyvinyl alcohol can also be added as a carbon source. The raw material alloy coarse pulverization step and fine pulverization step are preferably performed in a gas atmosphere such as nitrogen or Ar gas, and the oxygen concentration in the gas atmosphere can be controlled so that the O content falls within a predetermined range.

[0054] In the above molding process, a magnetic field of 400 to 1600 kA / m is applied to orient the alloy powder in the direction of the easy magnetization axis while compacting the powder using a compression molding machine. At this time, the density of the compact is preferably 2.8 to 4.2 g / cm 3 From the perspective of ensuring the strength of the molded body and obtaining good handling properties, the density of the molded body is preferably 2.8 g / cm 3 On the other hand, from the viewpoint of obtaining a sufficient molded body strength while ensuring good orientation of particles during pressurization to obtain a suitable Br, the molded body density is preferably 4.2 g / cm 3 In order to suppress oxidation of the alloy fine powder, it is preferable to perform the molding in a gas atmosphere such as nitrogen or Ar.

[0055] In the heat treatment step, the molded body obtained in the molding step is sintered in a high vacuum or non-oxidizing atmosphere such as Ar gas. Generally, sintering is preferably performed by maintaining the temperature within the range of 950°C to 1200°C for 0.5 to 5 hours. Cooling at the end of sintering can be performed by any of a variety of methods, including gas quenching (cooling rate: 20°C / minute or higher), controlled cooling (cooling rate: 1 to 20°C / minute), or furnace cooling. The resulting R-Fe-B sintered magnets exhibit similar magnetic properties.

[0056] There is no particular limitation on the heat treatment for sintering. cJ, heat treatment can be carried out at a temperature lower than the above-mentioned sintering temperature. The post-sintering heat treatment can be a two-stage heat treatment of high-temperature heat treatment and low-temperature heat treatment, or only a low-temperature heat treatment can be carried out. In the high-temperature heat treatment in the post-sintering heat treatment, the sintered body is preferably heat treated at a temperature of 600 to 950°C, and in the low-temperature heat treatment, it is preferably heat treated at a temperature of 400 to 600°C. The cooling at this time can also be carried out by any method of gas rapid cooling (cooling rate: 20°C / min or more), controlled cooling (cooling rate: 1 to 20°C / min), or furnace cooling. Regardless of which cooling method is used, an R-Fe-B system sintered magnet with the same magnetic properties can be obtained.

[0057] In addition, the obtained R-Fe-B system sintered magnet can be ground into a predetermined shape, and the surface of the magnet can be coated or coated with a material containing a material selected from R 1 Oxide, R 2 Fluoride, R 3 Fluoride oxide, R 4 The hydroxide, R 5 Carbonate, R 6 Alkaline carbonate, R 7 One or more of the elemental metals or alloys (R 1 ~R 7 After preparing a slurry of powders of at least one rare earth element (which may be the same or different) and allowing the powders to be present on the surface of the sintered magnet, heat treatment is performed. This treatment is the so-called grain boundary diffusion method. The temperature of the grain boundary diffusion heat treatment is preferably a temperature lower than the sintering temperature and above 350°C. The time is not particularly limited. From the perspective of obtaining a good structure and magnetic properties of the sintered magnet, it is preferably 5 minutes to 80 hours, and more preferably 10 minutes to 50 hours. By this grain boundary diffusion treatment, the R 1 ~R 7 Diffusion in the magnet to achieve H cJ It should be noted that, for the sake of convenience, the rare earth element introduced by the grain boundary diffusion is set as R 1 ~R 7 , but after grain boundary diffusion, they are all included in the above-mentioned R component in the magnet of the present invention.

[0058] Example

[0059] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples.

[0060] [Example 1]

[0061] Raw materials were weighed to give the composition of Alloy A shown in Table 1. The alloy was melted in an Ar gas atmosphere using a high-frequency induction furnace. The molten alloy was then cooled on water-cooled copper rollers using a strip casting method to produce alloy ribbons. The amount of carbon in the alloy can be adjusted based on the amount of carbon in the raw materials, for example, by adjusting the amount of carbon in the electrolytically produced Nd metal or by adding carbon black. The resulting alloy ribbons were then coarsely pulverized by hydrogenation to obtain a coarse powder. 0.1% by mass of stearic acid was then added to the resulting coarse powder as a lubricant and mixed.

[0062] The mixture of the coarse powder and lubricant was finely pulverized using a jet mill in a nitrogen stream to an average particle size of approximately 3.5 μm. The oxygen concentration within the jet mill system was set to 0 ppm. The fine powder was then placed in a mold equipped with an electromagnet in a nitrogen atmosphere and oriented in a 15 kOe (1.19 MA / m) magnetic field while being pressed and molded perpendicularly to the magnetic field.

[0063] The resulting molded body was sintered at 1050°C for 3 hours in a vacuum, cooled to below 200°C, and then subjected to high-temperature heat treatment at 900°C for 2 hours and low-temperature heat treatment at 500°C for 3 hours to obtain a sintered body. The composition of the resulting sintered body is shown in Table 2. Metal elements were analyzed by ICP analysis, C by combustion infrared absorption, and O by inert gas fusion infrared absorption.

[0064] [Comparative Example 1]

[0065] Raw materials were weighed to give the composition of Alloy C shown in Table 1, and alloy ribbons were produced in the same manner as in Example 1. The resulting alloy ribbons were then coarsely pulverized by hydrogenation to obtain a coarse powder. The resulting coarse powder was then finely pulverized using a jet mill in a nitrogen stream without adding a lubricant to an average particle size of approximately 3.5 μm. Subsequently, the alloys were molded and heat-treated in the same manner as in Example 1 to obtain a sintered body, and the composition was analyzed in the same manner as in Example 1. The results are shown in Table 2.

[0066] [Example 2]

[0067] Raw materials were weighed to give the composition of Alloy B shown in Table 1, and alloy ribbons were produced in the same manner as in Example 1. The resulting alloy ribbons were then coarsely pulverized by hydrogenation to obtain a coarse powder. 0.05% by mass of stearic acid was then added to the resulting coarse powder as a lubricant and mixed. Subsequently, pulverization, molding, and heat treatment were performed in the same manner as in Example 1 to obtain a sintered body, and the composition was analyzed in the same manner as in Example 1. The results are shown in Table 2.

[0068] [Comparative Example 2]

[0069] Alloy ribbons were prepared, hydrogenated and pulverized, and a lubricant was mixed with the coarse powder in the same manner as in Example 1. The coarse powder and lubricant mixture was then pulverized using a jet mill in a nitrogen stream to produce a fine powder with an average particle size of approximately 3.5 μm. The oxygen concentration within the jet mill system was appropriately adjusted to increase the oxygen content compared to the powder in Example 1. The resulting fine powder was then molded and heat-treated using the same methods as in Example 1 to produce a sintered body. The composition was then analyzed in the same manner as in Example 1. The results are shown in Table 2.

[0070] The center of each sintered body obtained in Examples 1 and 2 and Comparative Examples 1 and 2 was cut into a rectangular parallelepiped shape with a size of 18 mm × 15 mm × 12 mm to obtain a sintered magnet. The magnetic properties (Br, H cJ ), and the results are recorded in Table 2.

[0071] In addition, the structure of each of the above-mentioned sintered magnets was observed using a focused ion beam scanning electron microscope (FIB-SEM) (Scios; manufactured by FEI Corporation) and a scanning transmission electron microscope (STEM) (JEM-ARM200F; manufactured by JEOL) to calculate the area ratio of the RC phase contained in the grain boundary phase. The analysis results are recorded in Table 2. The analysis method first cuts the surface part of the cross section of each sample obtained by FIB, and then obtains a reflected electron image and a secondary electron image of an area of ​​69×46μm square. In this area, the composition analysis of each phase with the same contrast in each image is performed by energy dispersive X-ray analysis (EDS), and each phase is identified. Furthermore, the obtained electron image is taken into the image analysis software, the contrast is compared with the previously obtained composition information, and the area fraction of the RC phase is calculated. It should be noted that after the surface processing using FIB, a series of observations and composition analyses are performed directly without exposure to the atmosphere. Regarding the results of the tissue observation, the results of the 5 measurement locations are taken as the average value. In addition, Table 3 shows the analysis values ​​of the RC phase in Example 1 as a representative.

[0072] [Table 1]

[0073]

[0074] [Table 2]

[0075]

[0076] As shown in Tables 1 and 2, the sintered magnets of Examples 1 and 2, in which the area ratio of the RC phase is greater than 0 and less than 0.5%, have a greater Br and H cJAs for Comparative Example 1, it is known that no lubricant was added when making the sintered magnet, so the orientation during molding was reduced and Br became a low value. However, in the R-Fe-B system sintered magnet, the lower the orientation, the lower the H cJ The more it increases, specifically, to about -4×10 -4 The ratio of T / (kA / m) changes. If this is taken into consideration, the C contained in the sintered magnet is entirely derived from H in Comparative Example 1 of the raw material alloy. cJ The H of Example 2, in which the amount of lubricant added was 0.05 wt%, was lower by 50 kA / m or more than that expected under the same degree of orientation as in Example 1, and it can be confirmed that it was significantly degraded compared to Example 1. cJ With the reduction of H considering the orientation cJ The difference is less than 50kA / m, and good H cJ On the other hand, the HcJ of Comparative Example 2, which has a higher O concentration than a C concentration in the sintered magnet and does not contain an RC phase, is significantly lower than that of Example 1.

[0077] [Table 3]

[0078]

[0079] As shown in Table 3, the RC phase contained in Example 1 and the R2Fe as the main phase were analyzed by EDS. 14 Phase B. The RC phase had higher R and C concentrations than the main phase. Furthermore, as shown in Table 3, the C concentration in the RC phase was at least 20 atomic % higher than that in the main phase. Since the C content in the RC phase includes contaminants from the sample surface, assuming the main phase also has the same level of contaminants, the increase in C from the main phase is considered to be C contained in the RC phase.

[0080] [Examples 3 and 4]

[0081] Raw materials were weighed to give the composition of Alloy A shown in Table 1, and alloy ribbons were prepared in the same manner as in Example 1. The prepared alloy ribbons were then coarsely pulverized by hydrogenation to obtain a coarse powder. The resulting coarse powder was then finely pulverized using a jet mill in a nitrogen stream without adding a lubricant to an average particle size of approximately 3.5 μm. 0.1 wt% of the carbon source shown in Table 4 was then added. The resulting alloy ribbons were then molded and heat-treated in the same manner as in Example 1 to obtain a sintered body. The composition was analyzed in the same manner as in Example 1. The results are shown in Table 4.

[0082] [Table 4]

[0083]

[0084] As shown in Table 4, when a C source different from the lubricant is added, the area ratio of the RC phase contained in the magnet can be set to greater than 0 and less than 0.5%, and the area ratio can be the same as that of Example 1 in which the same amount of lubricant is added. In addition, although these magnetic properties decrease with the deterioration of orientation, H cJ As the orientation deteriorates, it increases and is about 80 kA / m higher than that in Example 1. cJ -4×10 -4 T / (kA / m) relationship assumed H cJ , even when a C source other than stearic acid is used as a lubricant, good magnetic properties can be obtained.

Claims

1. An R-Fe-B based sintered magnet having a composition comprising 12.5-14.5 atomic % of R, 5.0-6.5 atomic % of B, 0.15-5.0 atomic % of M, 0.02-0.5 atomic % of X, 0.1-1.6 atomic % of C, 0.2-0.5 atomic % of O, with the balance being Fe and unavoidable impurities, wherein R is at least one element selected from the group consisting of rare earth elements, with Nd being essential; M is at least one element selected from the group consisting of Si, Al, Mn, Ni, Co, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, and Bi; and X is at least one element selected from the group consisting of Ti, Zr, Hf, Nb, V, and Ta. Contains R2Fe 14 B main phase and grain boundary phase of intermetallic compound, It is characterized in that The grain boundary phase includes an RC phase having a higher R concentration and a higher C concentration than the main phase, and an area ratio of the RC phase in a cross section of the R—Fe—B system sintered magnet exceeds 0 and is 0.5% or less.

2. The R-Fe-B system sintered magnet according to claim 1, wherein The content of R is 12.8 to 14.0 atomic %.

3. The R-Fe-B system sintered magnet according to claim 1 or 2, wherein: The C content is 0.2 to 1.0 atomic %.

4. The R-Fe-B system sintered magnet according to claim 1 or 2, wherein: The content of B is 5.2 to 5.9 atomic %.

5. The R-Fe-B system sintered magnet according to claim 1 or 2, wherein As a part of the M element, Ga is contained in an amount exceeding 0 and not more than 0.1 atomic %.

6. The R-Fe-B system sintered magnet according to claim 1 or 2, wherein: The C concentration of the RC phase is higher than that of the main phase by 20 atomic % or more.

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