JP2014209560A - Method for manufacturing rare earth-iron-boron based magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a RFeB based magnet which is high in magnetization properties.SOLUTION: A method for manufacturing a RFeB based magnet including, as a rare earth element R, a light rare earth element Rconsisting of at least one element of a group consisting of Nd and Pr comprises: a before-magnetization base material-preparation step in which a before-magnetization base material of the RFeB based magnet is prepared from powder of a raw material alloy of the RFeB based magnet having an average grain diameter of smaller than 5 μm; a grain boundary diffusion treatment step in which the before-magnetization base material is heated to a given temperature with a deposit left adhering to the surface of the before-magnetization base material, provided that the deposit includes a heavy rare earth element Rconsisting of at least one element of a group consisting of Tb, Dy and Ho; a precise processing step in which a precisely processed body is prepared by shaping, by means of machining, the before-magnetization base material into a finished product form; and a post-precise-processing heating step in which the precisely processed body is heated to a temperature of 200-900°C.

Description

The present invention relates to a method for producing an RFeB-based magnet whose main phase is R ₂ Fe ₁₄ B (R is a rare earth element), and in particular, the rare earth element R is at least one of the group consisting of Nd and Pr. The present invention relates to a method for producing an RFeB-based sintered magnet or hot plastic working magnet that is a light rare earth element _RL .

  RFeB magnets have a feature that many magnetic properties such as residual magnetic flux density are higher than those of conventional permanent magnets. For this reason, RFeB magnets are used in various products such as motors for hybrid and electric vehicles, motors for electric bicycles, industrial motors, voice coil motors such as hard disks, high-end speakers, headphones, and permanent magnet magnetic resonance diagnostic equipment. Is used.

Early RFeB-based magnets had the disadvantage of a relatively low coercive force H _cJ among various magnetic properties. As a method for improving this drawback, when R is a light rare earth element R _L , (1) a heavy rare earth element R _H which is at least one of the group consisting of Tb, Dy, and Ho in the alloy of the raw material increasing the magnetocrystalline anisotropy of the major phase by adding method, (2) two heavy rare-earth element R _H not containing a main phase alloy and the grain boundary phase alloy with the addition of heavy rare-earth element R _H in A method using a mixture of starting alloy powders as a raw material (two-alloy method), (3) R _L FeB-based sintered body or powder containing heavy rare earth element R _H on the surface of a hot plastic processed body A grain boundary diffusion method is known in which heavy rare earth elements _RH are introduced into the main phase particles through the grain boundaries of the sintered body by heating them after attaching them. Among these methods, in particular, the grain boundary diffusion method (3) retains _RH near the surface of the main phase particles that are greatly affected by the decrease in coercive force, and does not significantly affect the decrease in coercive force. Since heavy rare earth elements _RH are not introduced into the interior, the amount of expensive and rare heavy rare earth elements _RH can be suppressed as compared to other methods, and the residual magnetic flux accompanying the increase in heavy rare earth elements _RH. It is excellent in that the decrease in density _Br can be suppressed.

In addition to methods using heavy rare earth elements R _H , methods described in Patent Document 1 and Non-Patent Document 1 are known as methods for increasing the coercive force H _cJ . The method described in Patent Document 1 is to heat-treat at a predetermined temperature after producing a sintered body of an RFeB-based magnet, and the method described in Non-Patent Document 1 is to separate individual crystal grains constituting the RFeB-based magnet. It is to be miniaturized. In particular, grain refining method described in Non-Patent Document 1 is excellent in that it is possible to increase the coercive force H _cJ without decreasing the remanence B _r. This is believed to be due to the fact that single magnetic domains are more easily formed as the crystal grains become smaller. That is, when a magnetic field in the opposite direction to the magnetization of the entire magnet is applied, the magnetization is smoothly reversed by moving the domain wall when there are a plurality of magnetic domains in the crystal grains. The coercive force, which is an index against the magnetic field, becomes low. On the other hand, in the case of a single magnetic domain, since there is no domain wall, magnetization reversal hardly occurs and the coercive force is increased. Non-Patent Document 1, than the average particle diameter D _AVE of about 7.0μm NdFeB (R = Nd) based sintered magnet, and NdFeB sintered magnet D _AVE is about 1.8～1.9Myuemu, is D _AVE It is described that a hot plastic working magnet of about 2 μm has a higher coercive force. In order to reduce the individual crystal grains constituting the RFeB-based magnet, first, the particle size of the RFeB-based alloy powder as the raw material must be reduced.

JP-A-61-140108 JP 2007-266199 A International Publication WO2006 / 004014 Japanese Patent Laid-Open No. 11-329810

Hisashi Kobayashi and 4 others, “Role of interaction between magnetic domain structure and microstructure in the coercivity development mechanism of rare earth magnets”, IEEJ Technical Report. MAG, Magnetics Technical Association, The Institute of Electrical Engineers of Japan, 2012 December 6, MAG-12-140

In the RFeB magnet, the coercive force can be sufficiently increased by using both the grain boundary diffusion method and the crystal grain refining method. However, in order to use a magnet incorporated in an automobile motor or the like, it is necessary not only to increase the coercive force but also to increase the magnetization characteristics. The reason will be described below.
When manufacturing an RFeB-based sintered magnet, it is heated to a temperature (usually 1000 ° C. or higher) higher than the Curie temperature (about 310 ° C.) in the sintering process. Also, when manufacturing an RFeB-based hot plastic working magnet, plastic working is performed in a state heated to about 800 ° C. in order to form and to orient the crystal grains. Magnetization has disappeared as a whole in the sintered body and hot plastic processed body obtained through such a process involving heating. Therefore, in order to use these sintered bodies and hot plastic processed bodies as magnets, a process of magnetizing them must be performed by applying a magnetic field. Such a process is called “magnetization”.

The magnetization characteristic is indicated by the magnetization rate defined by the ratio of the residual magnetic flux density after the magnetization process to the residual magnetic flux density that should be obtained when the magnetic flux is completely magnetized. Although the magnetization rate depends on the strength of the magnetic field used during the magnetization process, in the present invention, the magnetization is performed when the magnetization process is performed using a magnetic field having a strength of 20 kOe ((20 × 10 ⁶ / 4π) A / m). Magnetic susceptibility is used as an index of magnetization characteristics. The reason is that the maximum magnetic field strength of the magnetizing device used by many manufacturers of products (for example, motors) using RFeB magnets (referred to as “product manufacturers” in this paragraph) is about 20 kOe. The problem with the magnetizing device used by the product manufacturer is that the magnetized RFeB magnet has strong magnetization and is difficult to handle. This is because magnetizing treatment is performed after purchasing hot plastic workpieces and incorporating them into the product.

  As a magnet, of course, the coercive property is important, but as mentioned above, magnetism is also an important property for practical use. The present inventor has discovered that the magnetization characteristics are lowered by performing the process for increasing the coercive force as described above while researching to improve both characteristics. The problem to be solved by the present invention is to provide an RFeB-based magnet that can be sufficiently magnetized even with a relatively weak magnetic field of about 20 kOe in a case where processing for increasing the coercive force is performed.

  According to the results of the above research conducted by the present inventors, the cause of the decrease in the magnetization characteristics when processing for increasing the coercive force is that the coercive force is high, that is, the characteristic that magnetization is difficult to reverse, When magnetizing, it is considered that there is a demerit that even if a magnetic field is applied so that the magnetization of the entire magnet is aligned in one direction, the magnetization direction of each crystal grain is hardly changed.

  Therefore, the present inventor performs high-coercivity and good magnetization characteristics by removing the cause of deterioration of the magnetization characteristics while performing grain refinement and grain boundary diffusion treatment in order to improve the coercivity. It was considered that an RFeB magnet could be obtained, and the present invention was achieved.

That is, the RFeB-based magnet manufacturing method according to the present invention, which has been made to solve the above-described problems, includes a light rare earth element _RL that is at least one of the group consisting of Nd and Pr as the rare earth element R. A method for producing a contained RFeB-based magnet,
An average particle size of less than 5 μm, a pre-magnetization base material preparation step for preparing a pre-magnetization base material of an RFeB-based magnet from a raw material alloy powder of an RFeB-based magnet,
Particles that are heated to a predetermined temperature in a state where a deposit containing a heavy rare earth element _RH , which is at least one of the group consisting of Tb, Dy, and Ho, is adhered to the surface of the base before magnetization. A field diffusion treatment process;
A precision processing step of producing a precision processed body by forming the base material before magnetization after the grain boundary diffusion treatment step into a shape of a final product by machining;
And a heating step after the fine processing for heating the precision processed body to a temperature of 200 to 900 ° C.

  Conventionally, when manufacturing RFeB-based sintered magnets and RFeB-based hot plastic working magnets, the coercive force is applied after sintering at a temperature of 1000 ° C or higher or hot plastic working at a temperature of about 800 ° C. In order to increase the temperature, a heat treatment called “aging treatment” is performed at a temperature lower than those temperatures (see, for example, Patent Document 2), and then machining (fine processing) is performed to form a final product shape. Magnetization processing is performed (or at the shipping destination after shipping at this stage). Conventionally, there has been a concern that heating after precision processing may cause problems such as the generation of scale on the surface and reduced dimensional accuracy depending on the temperature. No heat treatment was performed after processing. As a result of studying such a conventional manufacturing method, the present inventor has found that the decrease in magnetization characteristics is not only due to an increase in coercive force, but also due to the introduction of processing strain on the surface of the molded body by precision processing. I found out that it was happening. And this inventor can remove a process distortion by performing the heating process after precise processing heated to the temperature of 200-900 degreeC after precise processing, and can improve a magnetization characteristic by it. I found.

  If the heating temperature in the post-precision processing heating step is less than 200 ° C., the processing strain cannot be removed sufficiently. On the other hand, when the heating temperature exceeds 900 ° C., the main phase particles grow and the diameter increases, so that the coercive force decreases. Therefore, the heating temperature in the heating step after the fine processing is set to 200 to 900 ° C.

In the present invention, the average particle diameter of the raw material alloy powder of the RFeB magnet is determined by the median particle diameter measured by a laser type powder particle size distribution measuring apparatus.
In the present invention, the “substrate before magnetizing the RFeB-based magnet” is obtained by a sintering process or a hot plastic working process, and is a sintered body or hot plastic processed body having R ₂ Fe ₁₄ B as a main phase. This means that the magnetizing process has not yet been performed.
In the present invention, the treatment performed in the grain boundary diffusion treatment step is the same as the grain boundary diffusion treatment conventionally performed when producing an RFeB magnet. The predetermined temperature in the grain boundary diffusion treatment step is typically 800 to 1000 ° C., but is not limited to this temperature range, and may be any temperature used in conventional grain boundary diffusion treatment. Also applies.

  The magnetizing process is performed after the heating process after the fine processing.

  In the present invention, it is desirable that the heating temperature in the post-precision processing heating step is 400 ° C. to 560 ° C. Thereby, the heating in the heating step after the fine processing also serves as an aging treatment, that is, not only the magnetization characteristics but also the coercive force can be increased. Therefore, it is not necessary to perform an aging treatment separately, and the process can be simplified. In addition, when heat treatment is performed multiple times, a rare earth-rich phase with a higher rare earth element content than the main phase is formed on the surface of the main phase particles in the RFeB sintered magnet or RFeB hot plastic working magnet. Is peeled off from the surface of the main phase particles, thereby reducing the coercive force, whereas the aging treatment is performed by combining the heating in the heating step after fine processing with the aging treatment as described above. The heating corresponding to can be performed only once, and the reduction of the coercive force can be prevented.

  In the pre-magnetization base material preparation step, the powder is filled by filling the powder in the mold without compressing the raw alloy powder and applying a magnetic field to the powder in the mold. It is desirable to produce the base before magnetization (sintered body of RFeB magnet) by orienting and heating the powder in the mold to a predetermined sintering temperature. A method for producing a sintered body of an RFeB-based magnet without performing compression molding on the raw material alloy powder in this way is called a PLP (Pressless process) method. Details of the PLP method are described in Patent Document 3. According to the PLP method, since it is not necessary to use a press machine, it is possible to reduce the space to be in an inert gas atmosphere in order to prevent the raw alloy powder from being oxidized. Therefore, the PLP method can easily handle a powder with a small average particle size of less than 5 μm and contributes to an improvement in coercive force. In addition, the PLP method contributes to increasing the residual magnetic flux density because the powder particles are easily rotated by the torque generated by the magnetic field during orientation by not applying pressure to the powder.

  According to the present invention, by removing the processing strain of the RFeB-based sintered magnet or RFeB-based hot plastic working magnet, the RFeB-based magnet that has been processed to increase the coercive force can be used with a relatively weak magnetic field of about 20 kOe. It becomes possible to magnetize.

The flowchart which shows the outline of one Embodiment of the manufacturing method of the RFeB type magnet which concerns on this invention. The graph which shows the magnetization rate measured about the RFeB type magnet manufactured by one Example of the manufacturing method of the RFeB type magnet which concerns on this invention, and the RFeB type magnet of the comparative example. The graph which shows the magnetization rate measured about the RFeB type magnet manufactured by the other Example of the manufacturing method of the RFeB type magnet which concerns on this invention, and the RFeB type magnet of the comparative example. The graph which shows the magnetization rate measured about the RFeB type magnet of the present Example and comparative example manufactured from the raw material alloy from which a particle size differs. The graph which shows the result of the X-ray-diffraction measurement (wavelength of X-ray ≒ 0.179nm) performed about the RFeB type | system | group magnet of a present Example and a comparative example. The figure which expanded 2 (theta) = 72 degree vicinity of the graph of FIG.

1 to 6, an embodiment of a method for manufacturing an RFeB magnet according to the present invention will be described.
In this embodiment, as shown in FIG. 1, (1) pre-magnetization base material preparation step, (2) grain boundary diffusion treatment step, (3) fine processing step, (4) post-fine processing heating step, (5 ) RFeB magnets are manufactured by performing each step in the order of the magnetizing step. Hereinafter, each process will be described in detail.

(1) Substrate preparation step before magnetization In this step, the steps performed before magnetization in the conventional manufacturing method for RFeB sintered magnets and RFeB hot plastic working magnets can be used as they are. For producing the base material before magnetizing the RFeB-based sintered magnet, both the conventional press method and the above PLP method can be used, but it is desirable to use the PLP method for the above-mentioned reasons. For example, the method described in Patent Document 4 can be used to prepare the base material before magnetizing the RFeB hot plastic working magnet. In addition, since the base material before magnetization is heated to a temperature higher than the Curie temperature (about 310 ° C.) of the RFeB magnet at the time of production, no residual magnetization is generated.

  In the pressing method, a RFeB-based alloy powder as a raw material is filled in a mold, and then a pressure is applied by a press to produce a molded body having a shape close to the final product. The alloy powder is oriented by applying a magnetic field to the alloy powder before or simultaneously with the molding by the press. Then, a base material before magnetization is obtained by heating a molded object to predetermined sintering temperature (1000-1100 degreeC).

  In the PLP method, an RFeB-based alloy powder is filled in a mold having a shape close to the final product, and then the alloy powder is oriented by applying a magnetic field without applying pressure, and the pressure is applied while the alloy powder remains in the mold. By heating to the sintering temperature without applying, a base material before magnetization is obtained. In this PLP method, since molding using a press machine is not performed, work in an oxygen-free atmosphere becomes easy, so alloy powder having a smaller particle diameter than the case of the press method can be handled easily. Thereby, the coercive force can be increased. Moreover, the base material before magnetization can be obtained even at a sintering temperature of 900 to 1000 ° C., which is lower than that of the pressing method.

  As the base material before magnetization, an RFeB-based sintered body or a hot plastic processed body may be used as it is, but when the rare earth element R is a light rare earth element such as Nd or Pr, the above-mentioned grain boundary diffusion is used. The coercive force can be increased by using a sintered body or a hot plastic processed body that has been treated by the method.

(2) Grain boundary diffusion treatment process Also in the grain boundary diffusion treatment process, the conventional grain boundary diffusion treatment can be used as it is. Specifically, an adhering material containing one or more of Tb, Dy, and Ho (heavy rare earth element R _H ) is attached to the surface of the base material before magnetization and heated to a predetermined temperature. . The deposit may be a single element (metal) of heavy rare earth element _RH , or may be an alloy or compound with another element. In addition, as the deposit, various forms such as powder, powder mixed with grease or liquid, and foil can be used. The predetermined temperature is typically 800 to 1000 ° C. as described above, but is not limited to this temperature range.

(3) Precision processing step Although each of the above methods (press method and PLP method which are sintering methods, and hot plastic processing) can obtain a pre-magnetization base material having a shape close to the final product, It does not meet the accuracy dimensions required for the final product and does not have an accurate shape. In addition, a shape deviation also occurs due to the remaining deposits adhered to the surface of the substrate before magnetization for the grain boundary diffusion treatment. Therefore, the base material before magnetization that has undergone the grain boundary diffusion treatment step is formed into a final product shape by machining. For machining, a simple cutting method can be used, but it is desirable to perform cutting in order to form a machined surface with higher accuracy. Alternatively, only the surface that requires high-precision processing may be cut and the other surfaces may be formed by cutting. For example, in a plate-like magnet, only the front and back surfaces of the plate may be processed with high precision by cutting, and the four side surfaces may be cut.
Before this fine processing step, an aging treatment for heating the pre-magnetization substrate may be performed, but at this stage, it is preferable to perform only the post-fine processing heating step described below without performing the aging treatment. desirable.

(4) Heating step after fine processing Next, the fine processed body obtained by the above-described fine processing step is heated (heating step after fine processing). Thereby, the process distortion which arose during the precision process can be removed. As described above, the heating temperature is 200 to 900 ° C, and preferably 400 to 560 ° C. The heating time is not particularly limited, but if it is less than 10 minutes, the processing strain cannot be sufficiently removed, and even if heating is performed for more than 24 hours, the effect of removing the processing strain is not obtained any more. Therefore, the heating time is desirably 10 minutes to 24 hours.

  In this embodiment, it is desirable not to perform the aging treatment before the fine processing step, and to heat to 400 ° C. to 560 ° C. in the heating step after the fine processing. Thereby, removal of a process distortion and an aging treatment can be performed simultaneously. This not only simplifies the manufacturing process, but also has the effect of preventing overaging and improving coercivity.

  In order to prevent the finely processed body from being oxidized, it is desirable to perform the heating process after the fine processing in a vacuum or an inert gas atmosphere.

(5) Magnetization process The fine processed body is magnetized by applying a magnetic field in one direction to the fine processed body that has undergone the heating process after the fine processing. Thereby, the RFeB system sintered magnet or the RFeB system hot plastic working magnet is completed. In this embodiment, since the magnetization characteristics are improved by heating after precision processing, the magnetic field applied during magnetization may be about 20 kOe as usual. Of course, in order to further increase the magnetization rate, the magnetic field may be magnetized with a magnetic field stronger than 20 kOe. Further, the manufacturer of the RFeB-based magnet may perform the magnetizing step without performing the magnetizing step, and the manufacturer of the product (such as a motor) using the RFeB-based magnet may perform the magnetizing step.

Hereinafter, an example in which an RFeB magnet was actually produced using the method of the present invention will be shown.
(a) Production method of RFeB magnet of this example
(a-1) Pre-magnetization base material preparation step In this example, a sintered body prepared by the PLP method was used as the pre-magnetization base material. Specifically, the base material before magnetization was produced by the following method.
First, Nd: 26.6 wt%, Pr: 4.7 wt%, Fe: 65.5 wt%, Co: 1.9 wt%, B: 1.0 wt%, Al: 0.2 wt%, Cu: 0.1 wt% by strip casting method A raw material alloy piece was prepared, and the raw material alloy piece was hydrogen crushed and then finely pulverized using a jet mill. As a result, raw material alloy powders having an average particle diameter of (i) 3 μm and (ii) 4 μm were produced. Hereinafter, the powder of (i) is referred to as “3 μm powder”, and the powder of (ii) is referred to as “4 μm powder”.

  Each of the obtained raw material alloy powders was filled into a mold having a rectangular parallelepiped with an inside of 89 mm × 62 mm × 6.5 mm, and then the raw material alloy powder was oriented by a 5.5 T magnetic field without compression molding. Thereafter, the raw material alloy powder was heated to 1010 ° C. while being put in the mold (without applying pressure) to obtain a plate-like RFeB-based sintered body. Subsequently, the pre-magnetization base material is obtained by processing the RFeB-based sintered body to a size of approximately 72 mm x 50 mm and a thickness of approximately 2.3 mm (this process is not a precision process). It was. Hereinafter, the pre-magnetization base material prepared from 3 μm powder is referred to as “3 μm base material”, and the pre-magnetization base material prepared from 4 μm powder is referred to as “4 μm base material”.

(a-2) Grain boundary diffusion treatment step After the powder containing the Tb-Ni-Al alloy was adhered to the surface of the substrate before magnetization, the grain boundary diffusion treatment was performed by heating to 875 ° C.

  Some 3 μm base materials and 4 μm base materials were subjected to an aging treatment by heating to 520 ° C. before performing the next precision processing step.

(a-3) Precise processing step After cutting the front and back two plate surfaces in each base material, by cutting in the thickness direction with a wire cutter, the side surfaces (four surfaces) are formed. A precision processed body having a surface size of 6.0 mm × 6.0 mm and a thickness of 2.0 mm was obtained.

(a-4) Heating step after fine processing The obtained fine processed body was heated to any temperature within a range of 200 to 520 ° C. in an Ar gas atmosphere. In the finely processed body obtained from the 3 μm base material not subjected to the aging treatment, the heating temperature in the heating step after the fine processing was set to 520 ° C. (hereinafter referred to as “Example 1”). In addition, the precision processed body obtained from the aging-treated 3 μm base material was heated after precision processing at four different temperatures of 500 ° C., 400 ° C., 300 ° C. and 200 ° C. (hereinafter referred to as “Examples”). 2 ”(500 ° C.),“ Example 3 ”(400 ° C.),“ Example 4 ”(300 ° C.), and“ Example 5 ”(200 ° C.)). The precision processed body obtained from the 4 μm base material was heated after precision processing at 500 ° C. (hereinafter referred to as “Example 6”). In this embodiment, the heating temperature is within the above temperature range, but in the present invention, the heating temperature may be up to about 900 ° C.

(a-5) Magnetization (application of magnetic field) Steps were performed with a magnetic field within a range of 50 kOe or less, using an air-core coil on a sample consisting of two precision workpieces stacked together. Specifically, a set of samples was magnetized with each magnetic field in order from the smallest applied magnetic field, and the magnetic flux was obtained using a flux meter each time the magnetization was completed. Here, the sample when the applied magnetic field is 50 kOe is considered to be completely magnetized, and “(magnetic flux at each applied magnetic field) / (magnetic flux when the applied magnetic field is 50 kOe) × 100” is defined as the magnetization rate in the magnetic field. Asked. The magnetic flux was measured using a flux meter manufactured by Electron Magnetic Industry Co., Ltd.

(b) Characteristics of RFeB-based magnets obtained in this example For the samples of Examples 1 to 6, the measurement results of the coercive force and the magnetization rate when the applied magnetic field is 20 kOe are shown in It shows in Table 1 together with conditions. Table 1 also shows the manufacturing conditions and the measurement results of the magnetization rate and the coercive force for samples of Comparative Examples 1 to 3 described later. Examples 1 to 6 show the coercive force before and after heating after precision processing. The coercive force was measured using a pulse coil excitation type JH [BH] tracer (manufactured by Toei Kogyo Co., Ltd.) on a sample obtained by stacking two precision processed bodies into one set.

Hereinafter, the measurement results in Table 1 will be described.
(b-1) Comparison by presence / absence of heating process after fine processing For the sample of Example 1 and two samples (Comparative Examples 1 and 2) that have not been subjected to the heating process after fine processing as described below, the magnetization rate is calculated. Compare the measured results. Here, the sample of Comparative Example 1 is a 3 μm base material that has been subjected to an aging treatment at 520 ° C. before the fine processing step, and the sample of Comparative Example 2 is a 3 μm base material that has not been subjected to an aging treatment. Both Example 1 and Comparative Example 1 were heated at 520 ° C., but the heating was performed after the precision processing step (Example 1) or before the precision processing step (Comparative Example 1). ) Is different.

  The measurement results are shown in the graph of FIG. From this graph, it is possible to make the magnetization rate higher in Example 1 than in Comparative Example 1 and Comparative Example 2 when compared with a magnetic field of the same strength, and magnetize with a weaker magnetic field when compared with the same magnetization rate. You can see that For example, in Example 1, when a magnetic field having a strength of 20 kOe obtained with a normal magnetizing apparatus is applied, a magnetization rate of 98% or more is obtained, whereas in Comparative Example 1 and Comparative Example 2, both are obtained. When the strength of the magnetic field is 20 kOe, the magnetization rate is 95% or less, and in order to obtain a magnetization rate of 98% or more, a strong magnetic field of 30 kOe or more is required.

(b-2) Difference in heating temperature in the heating process after the fine processing The results of measuring the magnetization rate of the samples of Examples 2 to 5 having different heating temperatures in the heating process after the fine processing are compared using the graph of FIG. To do. FIG. 3 also shows the magnetization rate of the sample of Comparative Example 1. In any of Examples 2 to 5, when compared with a magnetic field having the same strength as in Comparative Example 1, the magnetization rate could be increased, and when compared with the same magnetization rate, magnetization could be performed with a weaker magnetic field. In particular, in Examples 2 and 3, a high magnetization rate of 98% or more was obtained when the magnetic field strength was 20 kOe. Further, in Example 5 where the heating temperature was 200 ° C., although not as much as in Examples 2 to 4, an improvement in the magnetic permeability was observed as compared with Comparative Example 1.

(b-3) Comparison by raw material alloy powder particle size Next, Example 2 (particle size 3 μm) and Example 6 in which the heating temperature in the heating step after fine processing is equal (500 ° C.) and the particle size of the raw material alloy is different The results of measuring the magnetization rate for (particle size 4 μm) are compared using the graph of FIG. In addition to this graph, the magnetic susceptibility of a sample of a 4 μm base material (Comparative Example 3) that was subjected to aging treatment before Comparative Example 1 and the precision processing step and not subjected to heat treatment in the precision processing step was measured. Results are also shown. When Example 6 and Example 2 are compared, the magnetization rate in each magnetic field is higher in Example 6 in which the particle diameter of the raw material alloy is larger. This is considered to be due to the fact that in Example 6, the particle diameter of the RFeB-based sintered magnet finally obtained is larger due to the larger particle diameter of the raw material alloy. In addition, the magnetization rate of Example 2 is higher than that of Comparative Example 1, and the magnetization rate of Example 6 is higher than that of Comparative Example 3. By the method of the present invention, the magnetization rate does not depend on the particle size. It was confirmed that the magnetization rate was improved.

(b-4) Coercive force In each of Examples 1 to 6, a high coercive force of 23.6 to 25.6 kOe was obtained. In addition, the coercive force does not change before and after heating after precision processing. Thus, in this example, the magnetization rate could be improved while maintaining a high coercive force by heating after fine processing.

(b-5) X-ray diffraction measurement For the samples of Example 1 and Comparative Example 2, the results of X-ray diffraction measurement (2θ scan) are shown in FIG. 5 and one of the obtained peaks (2θ FIG. 6 shows an enlarged view of a region around = 72 °. The X-ray used for the measurement is a Co—Kα ray. Co-K [alpha rays, X-rays produced when electrons transition to K-shell from the L shell of Co atoms, by degeneration of L shell is melted, the Co-K [alpha ₁ line wavelength is 0.1789nm occurs in a state in which the wavelength is called Co-K [alpha ₂ line is 0.1793Nm, X-ray of the two wavelengths are mixed. As shown in FIG. 6, in Example 1, the peak tops are separated while the two peaks of the Co—Kα ₁ line and the Co—Kα ₂ line overlap, but in Comparative Example 2, the peak tops are separated. I can't. Further, the full width at half maximum of the peak is 0.36 ° in Example 1, whereas it is 0.66 ° which is wider in Example 2 than in Example 1. These results indicate that Example 1 has fewer crystal structure defects and distortions in the individual microcrystals constituting the RFeB magnet than Comparative Example 2. The data of this X-ray diffraction measurement supports that the processing distortion can be removed as described above by the heating step after fine processing performed by the method of the present invention.

  In the above examples, raw material alloy powders having an average particle diameter of 3 μm and 4 μm were used, but the present invention is not limited to these average particle diameters. If the average particle size is less than 5 μm, even if it is less than 3 μm or more than 4 μm, an RFeB-based magnet base material having a high coercive force can be obtained. RFeB magnets having both high coercive force and high magnetization characteristics can be obtained by performing post-precision heating similar to the above.

Claims (6)

A method for producing an RFeB-based magnet containing a light rare earth element _RL that is at least one of the group consisting of Nd and Pr as the rare earth element R,
An average particle size of less than 5 μm, a pre-magnetization base material preparation step for preparing a pre-magnetization base material of an RFeB-based magnet from a raw material alloy powder of an RFeB-based magnet,
Particles that are heated to a predetermined temperature in a state where a deposit containing a heavy rare earth element _RH , which is at least one of the group consisting of Tb, Dy, and Ho, is adhered to the surface of the base before magnetization. A field diffusion treatment process;
A precision processing step of producing a precision processed body by forming the base material before magnetization after the grain boundary diffusion treatment step into a shape of a final product by machining;
A method for producing an RFeB-based magnet, comprising performing a heating step after fine processing for heating the fine processed body to a temperature of 200 to 900 ° C.   The method for producing an RFeB-based magnet according to claim 1, wherein the finely processed body is heated to 400 ° C to 560 ° C in the heating step after the fine processing.   The method for producing an RFeB magnet according to claim 1 or 2, wherein the heating step after the fine processing is performed in a vacuum or an inert gas atmosphere.   The RFeB magnet manufacturing method according to claim 1, wherein cutting is performed in the precision machining step.   In the pre-magnetization base material preparation step, the powder is filled by filling the powder in the mold without compressing the raw alloy powder and applying a magnetic field to the powder in the mold. The RFeB magnet according to any one of claims 1 to 4, wherein the pre-magnetization base material is produced by orienting and heating the powder in the mold to a predetermined sintering temperature. Manufacturing method.   The method for producing an RFeB magnet according to claim 5, wherein the sintering temperature is 900 ° C or higher and 1000 ° C or lower.

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