JP4798357B2 - Manufacturing method of 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 producing a rare earth sintered magnet capable of efficiently removing a lubricant added to ensure formability and orientation during molding in a magnetic field. Is.

  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 organic substances such as fatty acids and hydrocarbons 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, this treatment is referred to as a lubricant removal treatment) ( For example, see Patent Document 1.)

  However, even if heat treatment is performed in a vacuum or an inert gas atmosphere, the lubricant cannot be sufficiently removed, and heat treatment must be performed for a long time in order to sufficiently remove the lubricant. 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, see 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. Accordingly, the present invention provides a method for producing a rare earth sintered magnet capable of obtaining a high magnetic property while efficiently removing a lubricant from a molded body and suppressing deformation and cracking after sintering. With the goal.

The present inventors have found that when the lubricant removal treatment is performed in an atmosphere containing hydrogen, it is preferable to perform the heat treatment at a temperature as high as possible in order to prevent cracks generated in the rare earth sintered magnet. However, it has also been found that when heat treatment is performed at a high temperature, organic substances contained in the lubricant remain in the molded body, and the residual carbon concentration in the final sintered body increases.
Accordingly, the present invention provides a method for producing a RTB (where R is one or more rare earth elements, T is Fe, Fe and Co) based sintered magnets, wherein The hydrogen treatment process in which hydrogen is exhausted by heating to a predetermined temperature after the occlusion is performed, and the alloy powder obtained in the hydrogen treatment process is further finely pulverized in a state where a lubricant containing an organic substance is added. A pulverizing step, a step of molding the pulverized powder obtained in the pulverizing step in a magnetic field, and a molded body obtained by molding in the magnetic field at least in a temperature range lower than the boiling point or decomposition temperature of the lubricant. Characterized in that it comprises a step of removing the lubricant by heat treatment under an atmosphere gas containing hydrogen (H ₂ ) in a part of the process, and a step of sintering the molded body from which the lubricant has been removed. To do.
By doing in this way, it can prevent that a lubricant decomposes | disassembles in heat processing, and can suppress the residue of the organic substance which comprises a lubricant.
In this case, in order to suppress the occurrence of cracks in the molded body, a lubricant having a boiling point or a decomposition temperature of 300 ° C. or higher is used, and the heat treatment is performed at a temperature as high as possible.
In order to enhance the effect of removing the lubricant , at least the heat treatment temperature is varied among the hydrogen concentration contained in the atmospheric gas and the heat treatment temperature in the step of removing the lubricant. In the case where the heat treatment temperature is changed, the temperature may be maintained in the temperature range in at least a part of the heat treatment.
After the step of removing the lubricant, it may further include a step of further removing the lubricant by heat-treating the molded body at a temperature higher than the above temperature range.

  As described above, according to the present invention, the lubricant can be efficiently removed, and even when the lubricant removal treatment is performed under an atmosphere gas containing hydrogen, the residual carbon amount is suppressed and the magnetic characteristics are improved. In addition, it is possible to suppress the occurrence of cracks in a sintered body such as a rare earth sintered magnet.

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 way has a large affinity with oxygen that deteriorates the magnetic properties of the Nd—Fe—B alloy, so that 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.

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. Examples of the lubricant include fatty acids or fatty acid derivatives such as stearic acid-based and oleic acid-based zinc stearate, calcium stearate, stearic acid amide, oleic acid amide, ethylenebisstearic acid amide, hexadecane, octadecane, eicosane, tetracosane. , Octacosane, dotriacontane, hexatriacontane, tetracontane, tetratetracontane, pentacontane and 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, the lubricant removal treatment for removing the lubricant is performed by heat treatment 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.

The upper limit temperature of the heat treatment for the lubricant removing treatment is preferably set so as to be lower than the boiling point or decomposition temperature of the lubricant. This is because if the heat treatment temperature is too higher than the boiling point and decomposition temperature of the lubricant, the organic matter constituting the lubricant remains in the molded body without being removed. Therefore, the upper limit temperature of the heat treatment is preferably 5 ° C. lower than the lower of the boiling point or the decomposition temperature of the lubricant. The upper limit temperature of the preferred heat treatment is a temperature 10 ° C. lower than the lower temperature of the boiling point or decomposition temperature of the lubricant, and the more preferred lower limit temperature of the heat treatment is the lower of the boiling point or decomposition temperature of the lubricant. The temperature is 20 ° C. lower than By doing in this way, it becomes possible to suppress the residual organic substance in the molded body and to suppress the amount of residual carbon.
The heat treatment is preferably held in a temperature range where the lower limit is at least 100 ° C. This is because if it is less than 100 ° C., the effect of removing the lubricant cannot be obtained sufficiently. A preferable lower limit temperature of the heat treatment is 150 ° C., and a more preferable lower limit temperature of the heat treatment is 200 ° C.
Moreover, it is preferable to set the temperature of the heat treatment as high as possible within the above temperature range. This is because the higher the heating temperature, the lower the amount of hydrogen contained in the molded body, and the less likely the cracks are generated in the sintered body. Therefore, the lower limit temperature of the heat treatment is preferably set within 50 ° C., more preferably within 30 ° C., whichever is lower of the boiling point or the decomposition temperature of the lubricant. Further, for the same reason, it is preferable to use a lubricant having a high boiling point or decomposition temperature. Among them, hexadecane (boiling point or decomposition temperature: 287 ° C.), octadecane (same: 317 ° C.), eicosane are used. (Same as 344 ° C), tetracosane (same as 392 ° C), octacosane (same as 430 ° C), dotriacontane (same as 468 ° C), hexatriacontane (same as 497 ° C), tetracontane (same as 523 ° C) ), Tetratetracontane (same: 548 ° C.), pentacontane (same: 568 ° C.) and the like are preferable.
Here, holding in the temperature range as described above 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. Just do it. Therefore, various forms are included, such as a form in which the temperature is continuously raised from the lower limit to the upper limit of the set temperature range, and a form in which the temperature is raised stepwise in the set temperature range.

  During the lubricant removal process, the hydrogen concentration is preferably maintained at 95% or more, but it is also effective to vary the hydrogen concentration. For example, the hydrogen concentration can be made less than 1% and then 95% or more, and conversely, the hydrogen concentration can be made 95% or more and then less than 1%. Further, such a hydrogen concentration fluctuation operation may be repeated a plurality of times. When the hydrogen concentration is less than 1%, it may be replaced with an inert gas as described above or evacuated. By performing such an operation, the lubricant can be removed together with hydrogen, and the removal efficiency can be increased.

Also, during the lubricant removal process, the temperature is varied within the above temperature range . Further, such temperature fluctuation operation may be repeated a plurality of times. By performing such an operation, the lubricant can be removed together with hydrogen, and the removal efficiency can be increased.

  If the holding time of the heat treatment for the lubricant removing process 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 7 hours.

  Thereafter, as shown in FIG. 1, it is preferable to perform the second heat treatment in order to further enhance the effect of the lubricant removal treatment. In the second heat treatment, it is preferable that the atmospheric gas is mainly an inert gas or is evacuated and maintained in a temperature range of 600 to 650 ° C. Thereby, further removal of the lubricant in the molded body and hydride of the R component (rare earth component) can be effectively removed. Here, the preferable temperature of the second heat treatment is 610 to 640 ° C, and the more preferable temperature of the heat treatment is 620 to 630 ° C.

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 of the sintering temperature rising process for removing 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. 2 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. 3, or as shown in FIG. The temperature may be raised stepwise.

The present invention is applied to an RTB-based sintered magnet represented by RTB (R is one or more rare earth elements, and T is Fe or Fe and Co) .
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.

  The R-T-B system sintered magnet has been described above. However, those skilled in the art can apply the present invention to other rare earth sintered magnets, and other sintered bodies other than magnets. It is clear from the above description or the description of the following examples.

The following two types of raw material alloys were produced by strip casting.
Alloy (1) 28.0 wt% Nd-0.2 wt% Al-1.0 wt% B-0.2 wt% Zr-bal. Fe
Alloy (2) 32.0 wt% Nd-10.0 wt% Co-1.0 wt% Cu-0.2 wt% Al-bal. Fe

  Next, after each of the obtained alloys (1) and (2) was occluded with hydrogen at room temperature, a dehydrogenation treatment was performed in an Ar atmosphere at 600 ° C. for 1 hour to obtain a coarsely pulverized powder.

  The above coarsely pulverized powder was finely pulverized by an airflow type jet mill using high-pressure nitrogen gas to obtain finely pulverized powder having an average particle size of 3 to 6 μm. When finely pulverizing with a jet mill, oleic acid amide, ethylenebisstearic acid amide, hexadecane, eicosane, tetracosane, octacosane, dotriacontane, hexatriacontane, tetracontane, tetratetracontane, pentacon Tan was added at 0.15 wt%.

  The fine powders of the obtained alloys (1) and (2) were mixed with the desired final composition: 28.4 wt% Nd-1.0 wt% Co-0.1 wt% Cu-0.2 wt% Al-1.0 wt% B -0.2 wt% Zr-bal. It mix | blended and mixed so that it might become Fe.

  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 120 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 atmospheric gas containing 95% or more of hydrogen for 6 hours after reaching the predetermined temperature shown in Table 1. A vacuum was applied until a predetermined temperature was reached.
Then, it heat-processed at 600-650 degreeC in the vacuum for 3 hours.
In addition, for those using oleic acid amide as a lubricant, for comparison purposes, a material that was not subjected to heat treatment (second heat treatment) at 600 to 650 ° C. for 3 hours in this vacuum was also prepared (Examples). 1-3, 1-4).

Further, the molded body after removing the lubricant was subjected to sintering and aging treatment to obtain a sintered body. Sintering was carried out in vacuum at 1030 to 1090 ° C. for 4 hours, and the aging treatment was a two-stage aging treatment in which Ar was held at 900 ° C. for 1 hour and then held at 530 ° C. for 1 hour.
For comparison, a sintered body obtained by sintering and aging the molded body without preparing the lubricant was prepared.

About the obtained sintered compact, the amount of residual carbon and the residual magnetic flux density Br were measured. Moreover, the crack generation state of the obtained sintered compact was confirmed visually.
The results are shown in Table 1.

As shown in Table 1, it can be seen that in any lubricant, the lower the heat treatment temperature in the lubricant removal treatment, the lower the residual carbon amount and the higher the residual magnetic flux density Br. In particular, when the heat treatment is performed at a temperature lower than the boiling point or decomposition temperature of the lubricant used, the amount of residual carbon is particularly reduced.
On the other hand, the crack generation rate tends to increase if the heat treatment temperature is too low.
Accordingly, it can be said that the heat treatment for removing the lubricant is preferably performed at a temperature lower than the boiling point or decomposition temperature of the lubricant to be used and as high as possible.

  In addition, when compared with each type of lubricant, the higher the boiling point or decomposition temperature, the lower the temperature of the above-mentioned heat treatment conditions, that is, the boiling point or decomposition temperature of the lubricant, and the higher the temperature possible. Example 4-1 (heating temperature 300 ° C.) in the case of using eicosane, which is a lubricant having a low occurrence rate, particularly a boiling point or decomposition temperature exceeding 300 ° C., and Example 5-1 in the case of using tetraconsane. 5-2 (heating temperature 375 ° C., 300 ° C.), Example 6-1 using octacosan (heating temperature 400 ° C.), Example 7-1 using dotriacontane (heating temperature 450 ° C.) In Example 8-1 (heating temperature 450 ° C.) when hexatriacontane is used, the residual carbon amount is 550 ppm or less and the residual magnetic flux density Br is 15 kG or more. Similarly, in the case of tetracontane, tetratetracontane or pentacontane whose boiling point or decomposition temperature exceeds 500 ° C., a low crack generation rate and a high residual magnetic flux density Br can be obtained, but the residual carbon amount tends to increase slightly. I understand.

  Furthermore, when Examples 1-1, 1-3, 1-4, and Comparative Example 1-1 in the case of using oleic acid amide are compared, the amount of residual carbon is reduced by performing heat treatment for lubricant treatment. It can be seen that the residual magnetic flux density Br can be improved and the residual carbon amount is further reduced by performing both the heat treatment for the lubricant treatment and the second heat treatment.

Subsequently, the effect of changing the hydrogen concentration in the heat treatment for removing the lubricant was examined.
For this reason, the molded object was formed in the process similar to the above. At this time, the lubricant used in the pulverizing step was oleic acid amide and octadecane, and 0.15 wt% was mixed respectively.
In the subsequent heat treatment for removing the lubricant, after reaching the predetermined temperature shown in Table 2, the concentration of hydrogen gas was set as shown in Table 2 and heating was performed for a total of 6 hours. At this time, for comparison, heat treatment was also performed in vacuum without using hydrogen gas.

As a result, as shown in Table 2, when oleic acid amide is used as the lubricant, the residual carbon amount can be reduced and the residual magnetic flux density Br can be improved by allowing hydrogen gas to exist in the atmosphere during the heat treatment. (Examples 20-1, 20-2, Comparative examples 20-1, 20-2). Moreover, from the comparison between Example 20-1 and Example 1-1, it can be confirmed that, as the hydrogen concentration is higher, the residual carbon amount is significantly reduced.
Further, as in Example 20-3 to Example 20-10, the residual carbon amount can be reduced and the residual magnetic flux density Br can be improved by changing the hydrogen concentration. At this time, from the comparison between Example 20-3 and Example 20-5, Example 20-4 and Example 20-6, the hydrogen gas concentration was changed from the low hydrogen gas concentration state to the high state state. The effect of reducing the residual carbon amount and improving the residual magnetic flux density Br becomes more remarkable when the state is shifted from the high state to the low state. This seems to be because the lubricant component escapes together with the hydrogen gas that escapes from the compact when the hydrogen gas concentration shifts from a high state to a low state.
This tendency is the same also in Example 20-7 to Example 20-10 in which the change of the hydrogen gas concentration was performed a plurality of times, and the effect becomes more remarkable due to the plurality of variations.
Moreover, also in Examples 21-1 to 21-10 using octadecane as a lubricant, the same tendency as in the case of using oleic amide can be confirmed, and furthermore, the case of using octadecane rather than oleic amide. However, it can be seen that more excellent characteristics can be obtained with respect to the residual carbon amount, the residual magnetic flux density Br, and the crack generation rate. In particular, the amount of residual carbon is greatly reduced as compared with the case of using oleic amide, and it can be confirmed that it is preferable to increase the heat treatment temperature for removing the lubricant as much as possible.

Next, the effect of changing the temperature in the heat treatment for removing the lubricant was examined.
For this reason, the molded object was formed in the process similar to the above. At this time, the lubricant used in the pulverizing step was oleic acid amide and octadecane, and 0.15 wt% was mixed respectively.
In the subsequent heat treatment for removing the lubricant, the temperature conditions shown in Table 3 were satisfied. At this time, the concentration of hydrogen gas was as shown in Table 3, and heating was performed for a total of 6 hours.

As a result, as shown in Table 3, it can be seen that even when the temperature is changed during the heat treatment, the crack generation rate, the residual carbon amount, and the residual magnetic flux density Br change as in the case where the hydrogen gas concentration is changed. .
This seems to be because the lubricant component escapes together with the hydrogen gas that escapes from the molded body by changing the heat treatment temperature.
Then, in the initial stage of the heat treatment, after maintaining the temperature below the boiling point or decomposition temperature of the lubricant to be used, the temperature is changed (Example 30-1 to Example 30-3). Examples 30-7 to 10), in particular, the effect of reducing the amount of residual carbon can be confirmed. In addition, as in Example 30-3 to Example 30-10, the boiling point or decomposition temperature of the lubricant during at least a part of the heat treatment even when the temperature is equal to or higher than the boiling point or decomposition temperature of the lubricant during the heat treatment. By maintaining the temperature below, the effect of reducing the amount of residual carbon can be secured. However, in that case as well, it is preferable to make the average temperature during the heat treatment as low as possible, and it can be seen that the effect of reducing the amount of residual carbon can be ensured.
Moreover, also in Examples 31-1 to 31-13 using octadecane as a lubricant, the same tendency as in the case of using oleic amide can be confirmed, and further, the case of using octadecane rather than oleic amide. However, it can be seen that more excellent characteristics can be obtained with respect to the residual carbon amount, the residual magnetic flux density Br, and the crack generation rate. In particular, the amount of residual carbon is greatly reduced as compared with the case of using oleic amide, and it can be confirmed that it is preferable to increase the heat treatment temperature for removing the lubricant as much as possible.

It is a figure which shows one form of a lubricant removal process. 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.

Claims (2)

R-T-B (R is one or more of rare earth elements, T is Fe or Fe and Co), a method for producing a sintered magnet,
A hydrogen treatment process in which hydrogen is stored in a raw material alloy having a predetermined composition and then heated to a predetermined temperature and discharged;
A fine pulverization step in which the alloy powder obtained in the hydrogen treatment step is further finely pulverized in a state where a lubricant having a boiling point or a decomposition temperature of 300 ° C. or more is added with an organic substance as a component;
Forming the pulverized powder obtained in the fine pulverization step in a magnetic field;
By heat-treating a molded body obtained by molding in a magnetic field in an atmosphere gas containing hydrogen (H ₂ ) in at least a part of the process in a temperature range lower than the boiling point or decomposition temperature of the lubricant. Removing the lubricant;
Sintering the molded body from which the lubricant has been removed, and
The method for producing a rare earth sintered magnet , wherein in the step of removing the lubricant , at least the heat treatment temperature is varied among the hydrogen concentration contained in the atmospheric gas and the heat treatment temperature. 2. The method according to claim 1 , further comprising a step of further removing the lubricant by heat-treating the molded body at a temperature higher than the temperature range after the step of removing the lubricant. Manufacturing method of rare earth sintered magnet .

Images