JP4353430B2 - Method for removing lubricant and method for producing rare earth sintered magnet - Google Patents

Description

  The present invention relates to a method for producing a rare earth sintered magnet, and more particularly to a method for removing a lubricant capable of efficiently removing a lubricant added to ensure formability and orientation during molding in a magnetic field, and rare earth sintering. The present invention relates to a method for manufacturing a magnetized magnet.

  R-T-B system sintered magnet mainly composed of at least one kind of transition metal element (T) and boron (B), which essentially contains rare earth elements (R), Fe or Fe and Co, has a predetermined particle size. The alloy powder is formed in a magnetic field and then sintered. In order to obtain an RTB-based sintered magnet having high magnetic properties, it is required to improve the orientation of a molded body obtained by molding in a magnetic field. The alloy powder used for forming in a magnetic field is obtained by finely pulverizing to an average particle size of about 2 to 6 μm by, for example, a jet mill, and is required to have high pulverizability at this time. In order to meet these demands, it is conventionally known to add a lubricant containing an organic substance such as oleic acid amide before pulverization (see, for example, Patent Document 1 and Patent Document 2). It is known that the added lubricant is removed by heating the molded body at 100 to 500 ° C. in a vacuum or an inert gas atmosphere (hereinafter referred to as a lubricant removal treatment) (for example, patents). Reference 1).

  However, even if heat treatment is performed in a vacuum or an inert gas atmosphere, the lubricant cannot be sufficiently removed, or heat treatment for removal must be performed for a long time. If a large amount of lubricant remains in the molded body, it reacts with rare earth elements during sintering to form rare earth carbides, thereby reducing the magnetic properties. Or the shrinkage | contraction rate of a molded object becomes non-uniform | heterogenous, and a deformation | transformation may arise in a molded object and by extension, a sintered compact. In order to solve such a problem, it is effective to perform the lubricant removal treatment in an atmosphere containing hydrogen (for example, Patent Document 3).

Japanese Patent Laid-Open No. 7-240329 JP-A-8-111308 JP 2003-313602 A

  The present inventors experienced that a crack was generated in the rare earth sintered magnet when the lubricant removal treatment was performed in an atmosphere containing hydrogen. Therefore, the present invention provides a method for removing a lubricant and a method for producing a rare earth sintered magnet that can efficiently remove a lubricant from a molded body and suppress deformation and cracking after sintering. Objective.

The present inventors conducted various experiments in order to investigate the cause of cracks generated in the rare earth sintered magnet. As a result, the compact (RTB-based alloy) occludes hydrogen during the lubricant removal treatment. It was found that expansion was the cause of cracking. More specifically, as shown in the column of Examples described later, when the lubricant removal treatment is performed in an atmosphere containing hydrogen, the lattice volume of the R ₂ T ₁₄ B phase is expanded. In view of this, the present invention proposes to adopt a condition in which the molded body that is the object of the lubricant removal treatment does not occlude hydrogen in the lubricant removal treatment in an atmosphere containing hydrogen. Here, the occlusion amount of hydrogen depends on the temperature, and increases as the temperature decreases. As a general tendency, the molded body inevitably or intentionally occludes hydrogen, and this molded body occludes hydrogen in a low temperature region and discharges hydrogen in a high temperature region. The boundary between the occlusion and discharge of hydrogen during the lubricant removal process depends on the amount of hydrogen occluded in the molded body subjected to the lubricant removal process. That is, if the hydrogen occlusion amount of the molded body subjected to the lubricant removal treatment is equal to or greater than the hydrogen occlusion amount in the condition for performing the lubricant removal treatment, hydrogen is not newly occluded during the lubricant removal treatment. Therefore, the lattice does not expand and cracks do not occur. The method for removing a lubricant of the present invention based on the above knowledge is obtained by performing hydrogen storage on a lubricant containing an organic substance and a raw material alloy, wherein R is 25 to 37 wt%, B is A composition containing 0.5 to 4.5 wt% of R-T-B (R is one or more of rare earth elements, T is Fe or Fe and Co) based alloy powder is added in a magnetic field. A step of obtaining a molded body by pressure molding, a step of grasping the amount of hydrogen in the molded body, and a molded body in an atmosphere gas containing hydrogen (H ₂ ) and in a temperature range of 100 to 550 ° C. And a step of removing the lubricant by heat treatment while maintaining or reducing the amount of hydrogen.

  In the present invention, the alloy powder can be obtained by subjecting the raw material alloy to hydrogen storage. Although alloy powder can be obtained by pulverizing (hydrogen pulverizing) by storing hydrogen, the present invention can be applied to such hydrogen-pulverized alloy powder. The hydrogen-pulverized alloy powder contains a predetermined amount of hydrogen, and this hydrogen may be an adverse effect for obtaining the desired properties. In that case, a hydrogen discharge process is performed after storing the hydrogen, and the present invention can be applied also in that case. Since the alloy powder contains a large amount of hydrogen in the state where the hydrogen is occluded, there are almost no examples of occlusion of hydrogen during the process of removing the lubricant. On the other hand, when the hydrogen discharge process is performed, the amount of hydrogen is reduced, and therefore, the amount of hydrogen may increase due to occlusion of hydrogen in the lubricant removal process. The present invention avoids this increase in the amount of hydrogen.

In the present invention, atmosphere gas heating in the lubricant removal treatment preferably contains an inert gas.

The present invention is preferably applied to a rare earth sintered magnet. Therefore, R-T-B containing R of 25 to 37 wt% and B of 0.5 to 4.5 wt% (R is one or two of rare earth elements). More than seeds, T is Fe or Fe and Co). Oxygen is occluded by hydrogen treatment process in which hydrogen is occluded in a raw material alloy and heated to a predetermined temperature to discharge hydrogen. A fine pulverization step for further finely pulverizing the lubricant as a constituent element, a step of forming the pulverized powder obtained in the fine pulverization step in a magnetic field, a step of grasping the hydrogen content of the molded body, The molded body obtained by molding in a magnetic field is heated and held in a temperature range of 100 to 550 ° C. under an atmosphere gas containing hydrogen (H ₂ ) to maintain or reduce the amount of hydrogen in the molded body while maintaining the lubricant. The step of removing and the molded body from which the lubricant has been removed are sintered. Method for producing a rare earth sintered magnet characterized by comprising the steps, is provided.

  As described above, according to the present invention, the occurrence of cracks in a sintered body such as a rare earth sintered magnet can be suppressed even when the lubricant removal treatment is performed under an atmosphere gas containing hydrogen. In addition, according to the present invention, since the lubricant removal treatment is performed under an atmosphere gas containing hydrogen, the lubricant can be efficiently removed and deformation of the sintered body can be reduced.

Hereinafter, embodiments of the present invention will be described in detail by taking a method for producing a rare earth sintered magnet as an example.
Rare earth sintered magnets are usually produced through the basic steps of producing a raw material alloy, grinding the raw material alloy, forming the pulverized powder in a magnetic field, and sintering the compact. Hereinafter, the manufacturing method will be described in the order of steps including the lubricant removal treatment step which is a characteristic part of the present invention.

  The raw material alloy can be produced by a strip casting method or other known melting methods in a vacuum or an inert gas, preferably in an Ar atmosphere. In the strip casting method, a molten metal obtained by melting a raw metal in a non-oxidizing atmosphere such as an Ar gas atmosphere is ejected onto the surface of a rotating roll. The melt rapidly cooled by the roll is rapidly solidified in the form of a thin plate or flakes (scales). This rapidly solidified alloy has a homogeneous structure with a crystal grain size of 1 to 50 μm. The raw material alloy can be obtained not only by the strip casting method but also by a melting method such as high frequency induction melting.

  The raw material alloy is subjected to a grinding process. The pulverization process includes a coarse pulverization process and a fine pulverization process. First, the raw material alloy is coarsely pulverized until the particle size becomes about several hundred μm. The coarse pulverization is preferably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill or the like. Prior to coarse pulverization, it is effective to perform pulverization by storing the hydrogen in the raw material alloy and then discharging it. This hydrogen pulverization can be regarded as coarse pulverization, and mechanical coarse pulverization can be omitted. In this case, for example, the raw material alloy obtained by the strip casting method is subjected to hydrogen pulverization in a state of being cut into a size of several mm to several tens mm.

  The raw material alloy inevitably contains hydrogen as an impurity. Therefore, even if a mechanical pulverization method is employed as the coarse pulverization, the coarsely pulverized powder contains about 10 to 30 ppm of hydrogen. On the other hand, when hydrogen pulverization is applied as the coarse pulverization, the coarsely pulverized powder contains about 3500 to 5000 ppm of hydrogen. If the purpose is only crushing, it is sufficient to store only hydrogen. However, the coarsely pulverized powder in a state in which a large amount of hydrogen is occluded in this manner has a large affinity with oxygen that deteriorates the magnetic properties of the Nd—Fe—B alloy, and thus, conventionally, after hydrogen occlusion The hydrogen was discharged. However, considering the pulverization property in the subsequent fine pulverization, it is preferable that the coarsely pulverized powder contains hydrogen. Therefore, even if hydrogen is discharged, it is preferable to leave about 1000 to 2000 ppm of hydrogen. In addition, if the amount of hydrogen is about this level, it can be reduced to a level that does not cause a problem for the rare earth sintered magnet in the subsequent lubricant removal processing step or sintering step.

  In the subsequent pulverization process and forming process in a magnetic field, the amount of hydrogen in the RTB-based alloy does not basically increase. As described above, in the present invention in which the lubricant removal treatment process is performed in an atmosphere containing hydrogen, if the amount of hydrogen in the molded object that is the subject of the lubricant removal treatment is small, the rare earth sintered magnet is cracked by occlusion of hydrogen. Occurs. Therefore, it is preferable for the present invention to secure a certain amount of hydrogen in the state of the coarsely pulverized powder after the coarsely pulverized step. When hydrogen pulverization is applied as coarse pulverization, there is an option not to discharge hydrogen. Even when hydrogen is discharged, there is an option to limit the discharge amount. On the other hand, when mechanical pulverization is applied as coarse pulverization, the amount of hydrogen can be increased by performing pulverization in an atmosphere containing hydrogen or exposing the coarsely pulverized powder to an atmosphere containing hydrogen. The specific amount of hydrogen is appropriately changed depending on the temperature in the lubricant removal treatment process.

After the coarse pulverization process, the process proceeds to the fine pulverization process. A jet mill is mainly used for the fine pulverization, and the coarsely pulverized powder having a particle size of about several hundreds of μm has an average particle size of 2.5 to 6 μm, preferably 3 to 5 μm. The jet mill releases a high-pressure inert gas from a narrow nozzle to generate a high-speed gas flow, accelerates the coarsely pulverized powder with this high-speed gas flow, collides with the coarsely pulverized powder, and collides with the target or the container wall. It is a method of generating a collision and crushing.
By adding about 0.01 to 0.5 wt% of a lubricant containing an organic substance before and after pulverization or both, fine powder with high orientation can be obtained at the time of molding in the next magnetic field. In addition, when a lubricant is added before fine pulverization, fine powder having a desired particle diameter can be efficiently produced in the fine pulverization step. As this lubricant, fatty acid or a derivative of fatty acid, for example, stearic acid-based or oleic acid-based zinc stearate, calcium stearate, stearamide, oleamide, or the like can be used.

The fine powder obtained as described above is subjected to molding in a magnetic field. The forming in the magnetic field may be performed at a pressure of about 50 to 200 MPa (0.5 to ² ton / cm ² ) in a magnetic field of 800 to 1360 kA / m (10 to 17 kOe). The applied magnetic field is not limited to a static magnetic field, and a pulsed magnetic field can be used. Furthermore, the direction of the magnetic field to be applied may be either a direction parallel to the pressing direction or a direction orthogonal to the pressing direction.

The molded body obtained as described above contains the lubricant described above. As described above, since this lubricant reacts with Nd, which is a rare earth element, the amount of the rare earth element is insufficient as an R—Fe—B based sintered magnet, thereby deteriorating magnetic properties. In addition, when a large amount of lubricant is contained, shrinkage during sintering becomes non-uniform in the sintered body and there is a risk of deformation after sintering.
Therefore, in the present invention, a lubricant removal process for removing the lubricant is performed under an atmosphere gas containing hydrogen (H ₂ ). When the lubricant removal treatment is performed on the molded body under an atmosphere gas containing hydrogen, the amount of carbon remaining in the molded body can be rapidly reduced compared to the lubricant removal treatment in a vacuum or an inert gas atmosphere. it can.

In the present invention, the lubricant removal treatment, which is a heat treatment for removing the lubricant, is performed in an atmosphere gas containing hydrogen. However, when the partial pressure P (H ₂ ) is lowered, the effect of removing the lubricant is reduced. Conversely, if the hydrogen partial pressure P (H ₂ ) becomes too high, depending on the amount of hydrogen in the molded body, the molded body occludes hydrogen unless the lubricant removal temperature is high. Accordingly, P (H ₂ ) is preferably in the range of 3 to 100 kPa. Further preferred P (H ₂ ) is 10 to 95 kPa, and more preferred P (H ₂ ) is 25 to 90 kPa.
This atmospheric gas preferably contains an inert gas in addition to hydrogen (H ₂ ). This inert gas functions as a carrier gas for H ₂ . Ar gas or N ₂ gas can be used as the inert gas.

Heat treatment for the lubricant removal treatment, that holds the temperature range of 100 to 550 ° C.. This is because the effect of removing the lubricant cannot be sufficiently obtained when the temperature is lower than 100 ° C., and the effect is saturated when the temperature exceeds 550 ° C. Here, holding in the temperature range of 100 to 550 ° C. is not limited to holding the molded body at a constant temperature in the temperature range, and the molded body is heated to any temperature in the temperature range for a predetermined time. It only has to be. Therefore, various forms, such as a form in which the temperature is continuously increased over 100 to 550 ° C. and a form in which the temperature is raised stepwise in the range of 100 to 550 ° C., are included. A preferable heat treatment temperature is 150 to 450 ° C., and a more preferable heat treatment temperature is 200 to 400 ° C.

Here, it is necessary to pay attention to the heating temperature in the lubricant removal treatment because it is necessary to determine the heating temperature in consideration of the amount of hydrogen contained in the molded body (or finely pulverized powder constituting the molded body). is there. This is because if the molded body occludes hydrogen in the lubricant removing process, cracks may occur in the rare earth sintered magnet. Whether or not the molded body occludes hydrogen is affected by the temperature of the atmosphere and the hydrogen partial pressure. That is, when the molded body contains hydrogen only in an amount less than the hydrogen storage amount under the conditions, the molded body occludes hydrogen. On the contrary, when the molded body contains an amount of hydrogen that exceeds the hydrogen storage amount under the above conditions, the molded body does not occlude hydrogen. Therefore, the amount of hydrogen contained in the molded body should be grasped, and the lubricant removal process should be performed at a temperature at which the hydrogen occlusion amount under the condition of the lubrication removal process is less than the amount of hydrogen contained in the molded body.
Some cracks are observed by visually observing the appearance at the stage of the molded body, but may not be observed from the appearance at the stage of the molded body. In this case, cracks may be observed on the surface of the sintered body through sintering.

  If the holding time of the heat treatment is short, the effect of removing the lubricant is insufficient, while if the holding time is too long, the effect of removing the lubricant is saturated. Therefore, the heat treatment holding time is preferably 0.5 to 10 hours, and more preferably 1 to 3 hours.

The molded body that has been subjected to the above lubricant removal treatment is subjected to sintering. Sintering is performed in a vacuum or an inert gas atmosphere, preferably in a vacuum. Sintering conditions need to be adjusted according to various conditions such as composition, pulverization method, difference in average particle size and particle size distribution, etc., but a dense sintered body can be maintained at a temperature of 1000 to 1100 ° C. for about 1 to 10 hours. Can be obtained.
After sintering, the obtained sintered body can be subjected to an aging treatment. This process is an important process for controlling the coercive force. When the aging treatment is performed in two stages, holding for a predetermined time at 750 to 950 ° C. and 500 to 700 ° C. is effective. Further, since the coercive force is greatly increased by heat treatment at 500 to 700 ° C., the aging treatment at 500 to 700 ° C. is preferably performed when the aging treatment is performed in one stage.

In the method for producing a rare earth sintered magnet to which the present invention is applied, the lubricant removal treatment can be performed independently of the sintering. In the present invention, the lubricant removal treatment can also be performed in the temperature rising process of sintering. The latter form is shown in FIG. As shown in FIG. 1, the atmosphere in the sintering furnace may be an atmosphere gas containing H ₂ in a predetermined temperature range (100 to 500 ° C.) in the temperature raising process of sintering in order to remove the lubricant. After a predetermined time has elapsed, the atmospheric gas is discharged from the sintering furnace, and the inside of the sintering furnace is depressurized to a predetermined degree of vacuum. While maintaining this degree of vacuum, the temperature is raised to the sintering temperature and held for a predetermined time. FIG. 1 shows an example in which the lubricant removal is maintained at a constant temperature. However, as described above, the temperature may be continuously increased as shown in FIG. 2, or as shown in FIG. The temperature may be raised stepwise.

FIG. 4 is a diagram showing changes in the amount of hydrogen in the production process. In FIG. 4, the present invention I shows a mode in which hydrogen is not discharged after storing hydrogen, and the present invention II shows a mode in which hydrogen is discharged after storing hydrogen. Moreover, in FIG. 4, the comparative example has shown the form which discharges | emits hydrogen after hydrogen storage. The amount of hydrogen after hydrogen discharge is different between the present invention II and the comparative example. Compared to the present invention II, the comparative example discharges more hydrogen and the amount of hydrogen after hydrogen discharge is small.
In FIG. 4, the present invention I maintains the amount of hydrogen after hydrogen storage until the lubricant is removed. As described above, the lubricant removal treatment is performed in an atmosphere gas containing hydrogen. However, since the amount of hydrogen in the compact (finely pulverized powder) is high, hydrogen is discharged during the lubricant removal treatment.
In FIG. 4, the present invention II discharges hydrogen after occlusion of hydrogen, so that the amount of hydrogen is reduced to a predetermined amount. Invention II can be divided into two forms according to the amount of hydrogen after hydrogen discharge.
One is a form (invention II-a) in which the amount of hydrogen is reduced in the lubricant removal treatment step. The other is a form in which the amount of hydrogen is maintained in the lubricant removal treatment process (present invention II-b). In any form, hydrogen is not occluded even if the lubricant removal treatment is performed in an atmosphere gas containing hydrogen thereafter, so that the amount of hydrogen after hydrogen discharge is maintained before sintering.
In FIG. 4, the comparative example discharges hydrogen after storing hydrogen. The amount of hydrogen at this time is lower than that of the present invention (I, II) as described above. This amount of hydrogen is maintained in the process of fine pulverization and molding in a magnetic field, but the amount of hydrogen increases because the compact (fine pulverized powder) occludes hydrogen in the lubricant removal step. Therefore, a crack occurs in the molded body.

The present invention is R-T-B (R is one or more rare earth elements, T is Fe or Fe and Co) that apply for R-T-B based sintered magnets represented by.
The RTB-based sintered magnet contains 25 to 37 wt% of rare earth element (R). Here, R has a concept including Y. Therefore, one or two of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Selected from more than species. If the amount of R is less than 25 wt%, the R ₂ T ₁₄ B phase, which is the main phase of the RTB-based sintered magnet, is not sufficiently generated, and α-Fe having soft magnetism is precipitated and retained. The magnetic force is significantly reduced. On the other hand, when R exceeds 37 wt%, the volume ratio of the R ₂ T ₁₄ B phase, which is the main phase, decreases, and the residual magnetic flux density decreases. Further, R reacts with oxygen, the amount of oxygen contained increases, and accordingly, the R-rich phase effective for the generation of coercive force decreases, leading to a decrease in coercive force. Therefore, the amount of R is set to 25 to 37 wt%. A preferable amount of R is 28 to 35 wt%.

Further, the RTB-based sintered magnet to which the present invention is applied contains 0.5 to 4.5 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. On the other hand, when B exceeds 4.5 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit of B is set to 4.5 wt%. A preferable amount of B is 0.5 to 1.5 wt%, and a more preferable amount of B is 0.8 to 1.2 wt%.
The RTB-based sintered magnet to which the present invention is applied can contain Co of 5.0 wt% or less (excluding 0), preferably 0.1 to 3.0 wt%. Co forms the same phase as Fe, but is effective in improving the Curie temperature and the corrosion resistance of the grain boundary phase.

  The RTB-based sintered magnet to which the present invention is applied allows the inclusion of other elements. For example, elements such as Al, Cu, Zr, Ti, Bi, Sn, Ga, Nb, Ta, Si, V, Ag, and Ge can be appropriately contained. On the other hand, it is preferable to reduce impurity elements such as oxygen, nitrogen, and carbon as much as possible. In particular, the amount of oxygen that impairs magnetic properties is preferably 8000 ppm or less, more preferably 5000 ppm or less. This is because when the amount of oxygen is large, the rare-earth oxide phase, which is a nonmagnetic component, increases and the magnetic properties are deteriorated.

  An alloy having a composition of 30 wt% Nd-2 wt% Dy-0.2 wt% Al-0.5 wt% Co-0.1 wt% Cu-1 wt% B-bal.Fe was produced by strip casting. The obtained strip cast alloy was occluded with hydrogen at room temperature, and then coarsely pulverized powder was obtained by hydrogen treatment in which hydrogen was discharged at a temperature of 200 ° C or 600 ° C. A coarsely pulverized powder that does not discharge hydrogen after occlusion of hydrogen was also prepared. The above coarsely pulverized powder was finely pulverized by a jet mill to obtain a finely pulverized powder having an average particle size of 4.5 μm. When finely pulverizing with a jet mill, 0.1 wt% of oleic acid amide was added.

  The obtained finely pulverized powder was molded in a magnetic field under the conditions of an applied magnetic field of 1200 kA / m and a molding pressure of 100 MPa to obtain a molded body having a size of 70 × 10 × 50 mm. In addition, the orientation direction (magnetic field application direction) of this molded body is a direction of 70 mm. Lubricant removal treatment was performed in a state where 18 of the above molded bodies were placed on a tray having a size of 180 mm × 180 mm × 180 mm. In addition, the molded object was mounted in the tray so that the surface of 10 mm x 50 mm might become a bottom face.

The condition for the lubricant removal treatment is to hold in an atmosphere gas containing hydrogen at 120 ° C., 280 ° C., 320 ° C. and 500 ° C. for 1 hour. This atmosphere gas is a mixed gas of hydrogen (H ₂ ) and Ar, and the hydrogen partial pressure P (H ₂ ) is 50 kPa, and the argon partial pressure P (Ar) is 50 kPa.
For molded body subjected to lubricant removal treatment, the amount of hydrogen was measured lattice volume of the R ₂ Fe ₁₄ B phase by XRD (X Ray Diffraction) with measuring the carbon amount. The results are shown in Tables 1 to 3 and FIGS.

As shown in Table 1 and FIG. 5, the hydrogen content of the molded product in the hydrogen occluded state (before removing the lubricant) is about 4200 ppm, but the hydrogen content of the molded product is 3400 ppm by discharging hydrogen at 200 ° C. Further, by performing hydrogen discharge at 600 ° C., the hydrogen content of the compact is reduced to about 1600 ppm. Thus, the higher the hydrogen discharge temperature, the smaller the amount of hydrogen that the molded body can contain. This suggests that the amount of hydrogen contained in the molded body decreases as the lubricant removal temperature increases. However, as is apparent from Table 1 and FIG. 5, this suggestion applies when hydrogen is not discharged, but when hydrogen is discharged at 600 ° C., hydrogen removal is performed by removing the lubricant at 120 ° C. The amount has increased considerably. This is because the hydrogen amount of 1600 ppm of the molded body that had been discharged with hydrogen at 600 ° C. was lower than the hydrogen occlusion amount under the conditions of P (H ₂ ): 50 kPa and P (Ar): 50 kPa, 120 ° C. It is understood that. When hydrogen is discharged at 200 ° C., the hydrogen content of the molded body after hydrogen discharge is P (H ₂ ): 50 kPa and P (Ar): 50 kPa atmosphere gas, hydrogen storage amount under the conditions of 120 ° C. Is almost equivalent.

  From FIG. 5, it can be said that if the hydrogen content of the compact is 3500 ppm or more, the hydrogen content of the compact does not increase regardless of the temperature of the lubricant removal treatment.

Next, regarding the lattice volume of the R ₂ Fe ₁₄ B phase in Table 2 and FIG. 6, it can be seen that the same tendency as the hydrogen amount behavior in Table 1 and FIG. 5 is shown. It can be seen that when the hydrogen discharge is performed at 600 ° C., the lattice volume is increased by performing the lubricant removing process at 120 ° C. This increase in the lattice volume can be regarded as a cause of the occurrence of cracks in the rare earth sintered magnet.
Further, as shown in FIGS. 5 and 6, when hydrogen is not discharged, there is no possibility of cracking due to hydrogen occlusion in the lubricant removal process even if the lubricant removal temperature is not regulated.

  When hydrogen is discharged, it is necessary to determine the temperature of hydrogen discharge in consideration of the amount of hydrogen after hydrogen discharge. Specifically, a lubricant removal temperature-hydrogen amount curve as shown in FIG. 5 is obtained in advance, and the lubricant removal process is performed under conditions where the hydrogen amount does not increase, in other words, under conditions where the hydrogen amount is maintained or decreased. Just do it. For example, when hydrogen is discharged at 200 ° C., an increase in the amount of hydrogen can be avoided even if the lubricant removal treatment is performed at any temperature of 120 ° C. or higher. However, when hydrogen is discharged at a temperature exceeding 200 ° C., the amount of hydrogen is increased in the lubricant removal treatment at 120 ° C., and the possibility of occurrence of cracks increases. In comparison, if the temperature of hydrogen discharge is high, the temperature of the lubricant removal process must be increased, and if the temperature of hydrogen discharge is low, the temperature of the lubricant removal process can be decreased. According to FIG. 5, even when hydrogen is discharged at 600 ° C., an increase in the amount of hydrogen can be prevented by performing the lubricant removal treatment at 400 ° C. or higher. In terms of the greatest common divisor, if the lubricant removal treatment is performed at the temperature of hydrogen discharge, hydrogen is not occluded during the lubricant removal process.

  Next, as shown in Table 3 and FIG. 7, it can be seen that the higher the lubricant removal temperature, the lower the carbon content of the molded body and the more the lubricant is removed. However, when the lubricant removal temperature is as high as 500 ° C., the effect of reducing the carbon content of the compact is reduced. This is presumably because carbon is in a form that is not removed by reaction with rare earth. A large amount of carbon adversely affects magnetic properties and increases the risk of deformation during sintering. Therefore, from the viewpoint of the effect of removing the lubricant, the lubricant removal temperature is preferably 500 ° C. or lower.

  Further, the molded body after removing the lubricant was subjected to sintering and aging treatment to obtain a sintered body. Sintering was performed under the condition of holding at 1030 ° C. for 4 hours in vacuum, and the aging treatment was a two-stage aging treatment of holding at 900 ° C. for 1 hour in an Ar atmosphere and then holding at 530 ° C. for 1 hour. The resulting sintered body was measured for the occurrence of cracks and the amount of deformation. The results are shown in Tables 4 and 5. In addition, the crack was confirmed visually. As for the amount of deformation, the bulging value of the intermediate part in the width of 40 mm of the obtained sintered body was measured as shown in FIG. 8, and the maximum value among the 18 sintered bodies was defined as the amount of deformation. However, the amount of deformation was not measured for the sintered body in which the crack occurred (indicated as “unmeasureable” in Table 5).

As shown in Table 4, generation of cracks was not confirmed in the sintered body obtained without discharging hydrogen and the sintered body obtained after discharging hydrogen at 200 ° C. In contrast, in the sintered body obtained by discharging hydrogen at 600 ° C., cracks occurred in all the sintered bodies when the lubricant removal temperatures were 120 ° C. and 280 ° C. However, when the lubricant removal temperature was 320 ° C., the frequency of occurrence of cracks was low, and when the lubricant removal temperature was 500 ° C., no cracks were generated.
Considering the above results and Table 1 and FIG. 5, it can be seen that if the lubricant removal treatment is performed under the condition that the amount of hydrogen is increased, the possibility of occurrence of cracks after sintering increases.

  As shown in Table 5, it can be seen that the deformation of the sintered body can be suppressed by performing the lubricant removal treatment. However, the removal amount of the lubricant at 500 ° C. with a high carbon content in the molded body was larger than that in the lubricant removal treatment at a temperature lower than that. This is proportional to the amount of carbon remaining in the molded body, and it is assumed that the carbon remaining in the molded body is the cause of deformation of the sintered body.

  Magnetic properties of some of the obtained sintered bodies were measured. The results are shown in Table 6. It was confirmed that the coercive force (HcJ) can be improved by performing the lubricant removal treatment.

  Except that hydrogen was discharged at 300 ° C., a compact was obtained in the same manner as in Example 1 until forming in a magnetic field. The resulting molded body was subjected to a lubricant removal treatment at 400 ° C. for 1 hour in an atmosphere gas composed of hydrogen and Ar shown in Table 7. The amount of hydrogen and carbon after the lubricant removal treatment were measured. The results are shown in Table 7.

  The molded body after the lubricant removal treatment was sintered and aged in the same manner as in Example 1 to obtain a sintered body. About the obtained sintered compact, the crack generation situation and the amount of deformation were measured similarly to Example 1, and the magnetic characteristics were also measured. The results are also shown in Table 7.

It is a figure which shows one form which performs the lubricant removal process of this invention in the temperature rising process of sintering. It is a figure which shows the other form which performs the lubricant removal process of this invention in the temperature rising process of sintering. It is a figure which shows the other form which performs the lubricant removal process of this invention in the temperature rising process of sintering. It is a figure which shows transition of the hydrogen amount in a manufacture process. It is a graph which shows the relationship between lubricant removal temperature and the amount of hydrogen. It is a graph which shows the relationship between lubricant removal temperature and lattice volume. It is a graph which shows the relationship between lubricant removal temperature and carbon content. It is a figure which shows the measuring method of deformation.

Claims (4)

A step of pressure-molding a composition containing a lubricant containing an organic substance and an alloy powder having a predetermined composition in a magnetic field to obtain a molded body;
Grasping the amount of hydrogen in the molded body;
Removing said lubricant said molded body under the atmospheric gas containing hydrogen (H _2), and in the temperature range of 100 to 550 ° C., by heating maintained or reduced, while the hydrogen content of the green body Including the steps of:
The alloy powder is obtained by subjecting a raw material alloy to hydrogen storage, and R-T-B (R is a rare earth element) containing 25 to 37 wt% R and 0.5 to 4.5 wt% B. 1 or 2 or more, T is Fe or Fe and Co) based alloy powder. The alloy powder, the method of removing the lubricant of claim 1, wherein is obtained by performing further hydrogen discharge treatment after hydrogen occlusion. The atmospheric gas, the method of removing the lubricant according to claim 1 or 2, characterized in that it comprises an inert gas. R-T-B (R is one or more of rare earth elements, T is Fe or Fe and Co) based material alloy containing 25 to 37 wt% R and 0.5 to 4.5 wt% B A hydrogen treatment process in which hydrogen is exhausted by heating to a predetermined temperature after occluding hydrogen;
A finely pulverizing step of further finely pulverizing the alloy powder obtained in the hydrogen treatment step with a lubricant containing an organic substance as a component;
Forming the pulverized powder obtained in the fine pulverization step in a magnetic field;
Grasping the amount of hydrogen in the molded body;
The molded body obtained in the magnetic field molding under an atmosphere gas containing hydrogen (H _2), and heated and maintained at a temperature range of 100 to 550 ° C., maintaining or reducing the hydrogen content of the forming body Removing the lubricant while
Sintering the molded body from which the lubricant has been removed;
A method for producing a rare earth sintered magnet.

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