JP4692783B2 - Manufacturing method of rare earth sintered magnet - Google Patents

Description

The present invention relates to a method for producing a rare earth sintered magnet such as an Nd ₂ Fe ₁₄ B-based magnet.

As a rare earth magnet having high performance, for example, an Nd ₂ Fe ₁₄ B-based magnet described in Japanese Patent No. 1431617 is known.

In order to improve the residual magnetic flux density of the Nd ₂ Fe ₁₄ B-based magnet, it is effective to reduce the oxygen content of the magnet. However, if the oxygen content is extremely reduced in the Nd ₂ Fe ₁₄ B-based sintered magnet, abnormal grain growth occurs during sintering, and the coercive force and squareness become low, and the overall magnet characteristics are good. There is a problem of not becoming. In addition, the rare-earth sintered magnet having the SmCo ₅ system composition also has a problem that abnormal grain growth occurs during sintering as the oxygen amount is reduced.

  In order to improve the coercive force of a rare earth sintered magnet, Japanese Patent Publication No. 4-26525 discloses that a rare earth oxide is added to an alloy composed of Nd, Fe and B, assuming that the rare earth oxide suppresses the crystal grain size of the sintered body. It is proposed to produce a permanent magnet by mixing, pulverizing, orienting, molding and sintering in a magnetic field. However, since the rare earth oxide is expensive, the cost of the magnet is increased. In addition, rare earth oxide powder is different from alloy powder in density, particle size, etc., and the amount added to the alloy powder is small, so it is difficult to disperse uniformly during mixing, and it takes a long time for mixing or is complicated. It is necessary to use expensive mixing equipment.

  In Japanese Patent Publication No. 7-107882, the coercive force is improved by controlling the oxygen content in the magnet so that the mass ratio is 3000 ppm or more.

Japanese Patent No. 1431617 Japanese Patent Publication No. 4-26525 Japanese Patent Publication No. 7-107882

  The inventors of the present invention produce a rare earth sintered magnet having a high residual magnetic flux density and a high coercive force by controlling the oxygen content in the rare earth sintered magnet without using an expensive rare earth oxide. An experiment was conducted. Generally, a rare earth sintered magnet is manufactured by coarsely pulverizing a raw material alloy, then finely pulverizing, and then performing molding and sintering. The inventors control the oxygen content in the sintered magnet by controlling the oxygen concentration in the atmosphere during pulverization to obtain a sintered magnet with good residual magnetic flux density and coercive force. An experiment was conducted.

  As a result, by eliminating oxygen in the atmosphere as much as possible during pulverization, the oxygen content of the sintered magnet can be less than 500 ppm, and as a result, a sintered magnet having a high residual magnetic flux density and a low coercive force can be obtained. did it. However, in this case, the range of manufacturing conditions became extremely narrow, and reproducibility was poor. On the other hand, by leaving a certain amount of oxygen in the atmosphere at the time of pulverization, the oxygen content of the sintered magnet could be about 4000 ppm. As a result, a sintered magnet having a high coercive force and a high squareness ratio could be obtained.

  However, in order to improve both the residual magnetic flux density and the coercive force, a sintered magnet was produced by changing the oxygen concentration in the grinding atmosphere in various ways. It has proved extremely difficult to control the oxygen content. Specifically, the relationship between the oxygen concentration in the pulverizing atmosphere and the oxygen content of the pulverized powder is not linear. For example, when the oxygen concentration in the atmosphere is lowered, When the oxygen content of the pulverized powder suddenly decreases when it becomes low, and when the oxygen concentration in the atmosphere is increased, the oxygen content of the pulverized powder becomes higher when the oxygen concentration becomes higher than the specified oxygen concentration. A tendency for the amount to increase rapidly was observed. In addition, the specific oxygen concentration varied depending on the particle size of the pulverized powder, the processing amount at the time of pulverization, and so on.

An object of the present invention is to stably and easily manufacture an Nd ₂ Fe ₁₄ B-based sintered magnet having a high residual magnetic flux density and a high coercive force.

Such an object is achieved by the present inventions (1) to (9) below.
(1) A raw material alloy manufacturing process for manufacturing a raw material alloy containing R (R is at least one rare earth element), Fe and B by a casting method or a rapid cooling method, and pulverizing the raw material alloy in one or more stages Pulverizing step for obtaining raw material powder, molding step for forming raw material powder to obtain a molded body, sintering the molded body, R: 28 to 32% by mass, B: 0.8 to 1.2% by mass, Balance: having a sintering step of obtaining a sintered magnet made of Fe,
When the pulverized powder obtained by pulverizing the raw material alloy is called the raw material,
Manufactured with a relatively high oxygen content, and at least one oxygen-rich raw material that is a raw material having an oxygen content of 1200 to 5000 ppm (mass ratio);
Manufactured so that the oxygen content is relatively low, the oxygen content is 300 to 1000 ppm (mass ratio), the oxygen content is less than 1000 ppm (mass ratio) than the oxygen-rich raw material, and the oxygen content is further reduced A method for producing a rare earth sintered magnet, wherein at least one oxygen poor raw material that is different from an oxygen-rich raw material in composition removed is mixed before the forming step.
(2) The method for producing a rare earth sintered magnet according to (1), wherein the ratio of the oxygen-rich material to the total of the oxygen-rich material and the oxygen poor material is 10% by mass or more and less than 90% by mass.
(3) The method for producing a rare earth sintered magnet according to (1) or (2), wherein the ratio of the oxygen-rich material to the total of the oxygen-rich material and the oxygen poor material is 10 to 60% by mass.
(4) At least one of the oxygen-rich raw material and the oxygen poor raw material is composed of two or more kinds of raw materials having different oxygen contents, and the maximum value of the difference in oxygen content between the two or more kinds of raw materials is oxygen rich. The method for producing a rare earth sintered magnet according to any one of the above (1) to (3), which is smaller than the minimum value of the difference in oxygen content between the raw material constituting the raw material and the raw material constituting the oxygen poor raw material.
(5) The method for producing a rare earth sintered magnet according to any one of (1) to (4) above, wherein a sintered magnet having an oxygen content (mass ratio) of 500 to 4500 ppm is produced.
(6) The difference in oxygen content between the oxygen-rich raw material and the oxygen poor raw material is realized by making the oxygen concentration in the atmosphere different in at least a part of the manufacturing process of both raw materials. The method for producing a rare earth sintered magnet according to any one of (1) to (5) above.
(7) The oxygen-rich raw material is placed in contact with or in the vicinity of the porous material having pores containing an oxidizing gas or moisture in at least a part of the production process. The method for producing a rare earth sintered magnet according to any one of the above (1) to (6), wherein is controlled.
(8) The raw material alloy is pulverized in multiple stages in the pulverization process,
The method for producing a rare earth sintered magnet according to any one of (1) to (7), wherein the oxygen-rich raw material and the oxygen poor raw material are mixed after at least one stage of pulverization.
(9) The raw material alloy is pulverized in multiple stages in the pulverization process,
The method for producing a rare earth sintered magnet according to any one of the above (1) to (7), wherein the oxygen-rich raw material and the oxygen poor raw material are mixed after the final stage of the multistage grinding.

  When obtaining a rare earth sintered magnet having both a high residual magnetic flux density and a high coercive force, it is effective to control the oxygen content of the magnet within a specific range as described above. However, as described above, it is easy to achieve an oxygen content in which only one of the residual magnetic flux density and the coercive force is high, but it is difficult to stably realize an oxygen content in which both are high. .

  Therefore, in the present invention, when manufacturing a rare earth sintered magnet, an oxygen-rich raw material manufactured to increase the oxygen content and an oxygen poor raw material manufactured to reduce the oxygen content are mixed and used. . In this specification, the raw material is a pulverized powder obtained by pulverizing a raw material alloy produced by a rapid cooling method or a casting method.

  As described above, the oxygen poor raw material can be easily manufactured by using an atmosphere in which oxygen is excluded as much as possible, and the oxygen rich raw material can be easily manufactured by leaving oxygen to some extent in the atmosphere. The oxygen content of the sintered magnet can be accurately controlled by controlling the mixing ratio of the oxygen poor raw material and the oxygen rich raw material. Therefore, in the present invention, a rare earth sintered magnet having a high residual magnetic flux density and a high coercive force can be manufactured easily and with good reproducibility. Moreover, in the present invention, it is not necessary to use a rare earth oxide that is difficult to disperse uniformly and is expensive, and thus a rare earth sintered magnet that can stably obtain high performance can be manufactured at a low cost.

  Furthermore, it has been found that a magnet having a high squareness ratio can be obtained by using the manufacturing method of the present invention. That is, when a sintered magnet manufactured using a single raw material by a conventional method is compared with a sintered magnet manufactured according to the present invention, a sintered magnet manufactured according to the present invention even if the oxygen content is equivalent. The squareness ratio is higher.

  In this specification, the squareness ratio means Hk / HcJ. Hk in Hk / HcJ is the external magnetic field strength when the magnetic flux density is 90% of the residual magnetic flux density in the second quadrant of the magnetic hysteresis loop. If Hk is low, a high maximum energy product cannot be obtained. Hk / HcJ serves as an index of magnet performance and represents the degree of angularity in the second quadrant of the magnetic hysteresis loop. Even if HcJ is the same, the larger the Hk / HcJ, the sharper the distribution of the microscopic coercive force in the magnet, so that the magnetization becomes easier and the variation in magnetization is reduced, and the maximum energy product is higher. Become. And the stability of the magnetization with respect to the change of the demagnetizing field or the self-demagnetizing field from the outside when using the magnet becomes good, and the performance of the magnetic circuit including the magnet becomes stable.

The present invention is suitable for producing a sintered magnet containing at least Nd and / or Pr as the rare earth element R, and further containing Fe and B. The magnet of this composition system has a hard magnetic phase made of an R ₂ Fe ₁₄ B intermetallic compound such as Nd ₂ Fe ₁₄ B, and a part of Fe can be substituted with Co. Among these, the present invention is particularly suitable for producing a magnet having a relatively small R content. It is considered that oxygen in the magnet is often present as R oxide. A magnet having a relatively small R content has a small margin for the oxidation of the element R. That is, even if the oxygen content is the same as when the R content is relatively high, the oxidation rate of the element R is high, and as a result, the R required for the manifestation of the magnet characteristics is insufficient and the magnet characteristics are low. Prone. Since the raw material powder that is easy to manufacture has a relatively high oxygen content as described above, it is difficult to obtain good magnet characteristics when this raw material powder is used alone.

  In contrast, in the present invention, a sintered magnet having a relatively small oxygen content can be easily realized by using an oxygen-rich material and an oxygen poor material, both of which are easy to manufacture. Since a magnet having a small R content can increase the residual magnetic flux density, a sintered magnet having good residual magnetic flux density, coercive force and squareness ratio can be easily realized by the present invention.

Incidentally, in Japanese Patent No. 2571403, Ca-reduced powder for Fe-B-R system (R is at least one of Nd, Pr, Dy, Ho, Tb) magnets, 40 to 95% by weight, and Fe-B -Mixing and blending 5 to 60 wt% of ingot pulverized powder for R magnet, R: 27 to 37 wt%, B: 0.5 to 5 wt%, Fe: 58 to 72.5 wt% It describes a method for producing a rare earth magnet by adjusting the O ₂ content in a mixed raw material powder to 3500 ppm or less, followed by pulverization, press molding, and sintering.

The Ca-reduced powder used in this method is at least one of rare earth oxides and iron powder, and at least one of pure boron powder, ferroboron powder and boron oxide, or alloy powder or mixed of the above constituent elements This is a mixture obtained by mixing metal Ca and CaCl ₂ in a mixed powder in which an oxide is blended in a required composition, and performing a reduction diffusion in an inert gas atmosphere to make a slurry and water-treat it. . Although Ca reduced powder is inexpensive, since water is used in the process of removing Ca, which is a reducing agent after reduction (CaO after reduction), the amount of O ₂ contained is large compared to the ingot pulverized powder, and since the variation of the content amount of O ₂ is large, prone to variations in the composition of the sintered magnet obtained, variation in the magnetic properties. Therefore, in this publication, the amount of O ₂ in the sintered magnet is reduced by pulverizing, molding and sintering a mixture of Ca reduced powder and ingot pulverized powder. The same publication describes that the O ₂ content of the Ca reduced powder is preferably 2000 to 5000 ppm, and the O ₂ content during ingot crushing is preferably 500 to 2500 ppm. The ingot pulverized powder is 1100 ppm and the Ca reduced powder is 4000 ppm. In Example 2, the ingot pulverized powder is 1500 ppm and the Ca reduced powder is 4300 ppm.

  The present invention is similar to the invention described in Japanese Patent No. 2571403 in that a mixture of two kinds of powders having different oxygen contents is molded and sintered to obtain a rare earth sintered magnet. However, in this publication, the Ca reduced powder and the ingot pulverized powder are mixed and then finely pulverized. The Ca reduced powder described in the publication is generally spherical particles and tends to be spherical after pulverization. On the other hand, when an alloy produced by casting or a rapid cooling method is pulverized, generally irregular pulverized powder is obtained. Therefore, when the coarse powder of Ca reduced powder and the coarse powder of the ingot pulverized powder are mixed and pulverized at the same time, it is difficult to make them both equal particle sizes. Therefore, dispersion of Ca reduced powder tends to be non-uniform in the mixed powder. As a result, the expected magnet performance cannot be obtained or the magnet performance tends to vary. Such a problem is particularly likely to occur when the ratio of Ca reduced powder in the mixed powder is low. Moreover, since Ca reduction | restoration powder is spherical, there exists a problem that a spring back is large and the shape retention of a molded object becomes low. Further, Ca-reduced powder is not suitable as a raw material for high-performance magnets because it contains many impurities such as Ca and Cl.

  On the other hand, in the present invention, since the alloy powder obtained by pulverizing an alloy produced by casting or a rapid cooling method is used instead of the Ca reduced powder, the above problem does not occur.

  The production method of the present invention is a raw material alloy production process for producing a raw material alloy containing R (R is at least one kind of rare earth element, and in this specification, the rare earth element is Y, Sc and a lanthanoid). A pulverization process for pulverizing the raw material alloy in one stage or in multiple stages to obtain a raw material powder, a molding process for molding the raw material powder to obtain a compact, and sintering to obtain a sintered magnet by sintering the compact Process.

  In this specification, the pulverized powder obtained by pulverizing the raw material alloy is referred to as a raw material. In this invention, the oxygen rich raw material manufactured so that oxygen content may become relatively large, and the oxygen poor raw material manufactured so that oxygen content may become relatively small are prepared. Both the oxygen-rich material and the oxygen poor material are composed of one or more materials. Here, two or more kinds of raw materials mean a plurality of raw materials having different compositions, and also means a plurality of raw materials having the same composition and different oxygen contents. In general, raw materials having different compositions do not have the same oxygen content even if the production conditions are the same.

  In the present invention, the oxygen-rich material and the oxygen poor material are mixed before the molding step.

  The difference between the oxygen content (mass ratio) of the oxygen-rich material and the oxygen content (mass ratio) of the oxygen poor material is 1000 ppm or more. In the present invention, the oxygen content of the oxygen-rich material and the oxygen poor material means the oxygen content immediately before mixing them. As described above, a raw material having a relatively low oxygen content and a raw material having a relatively high oxygen content are easy to manufacture, but a raw material having an intermediate oxygen content is difficult to manufacture stably. Therefore, if the difference in oxygen content between the oxygen-rich raw material and the oxygen poor raw material is reduced to an extent below the above range, it is difficult to obtain the effect of the present invention that the raw material is easily manufactured. Note that the difference in the case where at least one of the oxygen-rich material and the oxygen-poor material is composed of two or more materials having different oxygen contents is the one having the smallest oxygen content among the oxygen-rich materials, It means the difference from the oxygen poor raw material with the highest oxygen content.

  However, when the oxygen content difference between the oxygen-rich raw material and the oxygen-poor raw material is set to be extremely large, the oxygen content of the oxygen-poor raw material is remarkably reduced and / or the oxygen content of the oxygen-rich raw material is reduced. There is a need to significantly increase. When the oxygen content of the oxygen poor raw material is significantly reduced, it becomes difficult to produce the oxygen poor raw material. When the oxygen content of the oxygen-rich raw material is remarkably increased, the ratio of the oxygen-rich raw material in both raw materials needs to be considerably reduced. As a result, the oxygen-rich raw material is uniformly dispersed in the mixture of both raw materials (powder). It becomes difficult to cause deterioration of magnet characteristics. For these reasons, the difference in oxygen content between the oxygen-rich material and the oxygen poor material is preferably 4000 ppm or less, particularly preferably 3000 ppm or less.

  The oxygen content (mass ratio) of the oxygen poor raw material is 300 to 1000 ppm, more preferably 400 to 1000 ppm, and still more preferably 400 to 900 ppm. It is difficult to make the oxygen content below this range, and the alloy powder having a remarkably low oxygen content is difficult to handle because of its high activity. On the other hand, the reason why the oxygen poor raw material is used in the present invention is that, as described above, it is difficult to stably produce a raw material having an oxygen content suitable for a rare earth sintered magnet. Therefore, if the oxygen poor raw material whose oxygen content exceeds the above range can be stably produced, the significance of adopting the present invention is small.

The oxygen content (mass ratio) of the oxygen-rich raw material is 1200 to 5000 ppm, more preferably 1200 to 4000 ppm. If an oxygen-rich raw material having an oxygen content below this range can be produced stably, the significance of adopting the present invention is small. On the other hand, if an alloy powder having an oxygen content exceeding this range is to be produced, the alloy powder may be rapidly oxidized, that is, burned, and thus it is difficult to produce it stably. The present invention is suitable for the production of Nd ₂ Fe ₁₄ B-based magnets, but Nd ₂ Fe ₁₄ B-based alloys are more susceptible to degradation by oxidation than SmCo _5- based alloys, and therefore Nd ₂ Fe ₁₄ B-based oxygen. The oxygen content of the rich raw material is more preferably 1200 to 3700 ppm.

  By the way, for example, when two or more oxygen poor raw materials are used, even when these two or more raw materials are manufactured, even if the oxygen concentration in the atmosphere in the manufacturing process is controlled to be the same, the oxygen concentration is very small. Due to differences and differences in raw material composition, the oxygen content is usually different. However, those produced as an oxygen poor raw material have a lower oxygen content than those produced as an oxygen rich raw material, even though the oxygen content varies. Specifically, the difference in oxygen content between oxygen poor raw materials (when there are three or more oxygen poor raw materials, this difference is three or more, in which case the maximum value among them) is oxygen rich. It is smaller than the difference in oxygen content between the raw material and the oxygen poor raw material (if there are three or more oxygen poor raw materials, this difference is three or more, but in that case, the minimum value in that case). The same applies when two or more raw materials are used as the oxygen poor raw material. Furthermore, the same applies when two or more oxygen poor raw materials and oxygen rich raw materials are used.

  That is, when at least one of the oxygen-rich raw material and the oxygen poor raw material is composed of two or more raw materials having different oxygen contents, the difference (maximum value) in oxygen content between the two or more raw materials is It is smaller than the difference (minimum value) of the oxygen content between the oxygen-rich material and the oxygen poor material. For example, in a group consisting of two or more oxygen-rich raw materials and a group consisting of two or more oxygen-poor raw materials, due to the difference in oxygen content between the raw materials belonging to the same group, the raw materials belonging to different groups The difference in oxygen content is greater.

  In general, the effects of the present invention can be realized sufficiently if only one oxygen-rich material and one oxygen-poor material are used. However, when the present invention is applied to the two-alloy method described later, one or both of the oxygen-rich raw material and the oxygen poor raw material, usually only one, is constituted by two raw materials having different oxygen contents. That is, in the present invention, it is not necessary to use more than four kinds of raw materials, and usually three or less kinds of raw materials are used.

  The ratio of the oxygen-rich material to the total of the oxygen-rich material and the oxygen poor material is preferably 10% by mass or more and less than 90% by mass. If this ratio is too low or too high, the effect of using a mixture of the oxygen-rich material and the oxygen poor material will not be sufficiently realized. Further, considering the preferable R content of the sintered magnet produced according to the present invention and the corresponding preferable oxygen content, the ratio of the oxygen-rich raw material in both raw materials is more preferably 60% by mass or less, and still more preferably It is less than 50% by mass, particularly preferably 20 to 40% by mass. In the present invention, it is preferable to relatively reduce the R content in the magnet. However, as described above, the performance of a magnet having a small R content is significantly reduced when the oxygen content is increased. Further, the oxygen-rich raw material is easier to manufacture when the oxygen content is relatively increased. Therefore, in order to obtain a high-performance sintered magnet having a relatively small R content using raw materials that are easy to manufacture, it is preferable not to increase the ratio of oxygen-rich raw materials in both raw materials as described above. More preferably, it is relatively less.

  Note that the oxygen content is higher in the pulverized powder than in the raw material alloy, and when the pulverization is performed in multiple stages, the oxygen content increases as the pulverization proceeds. In addition, in the case of further pulverizing after mixing the oxygen-rich raw material and the oxygen poor raw material, if the composition and size of both raw materials are not significantly different, the difference in oxygen content of both raw materials at the time of mixing Is almost maintained and does not change greatly.

In the oxygen-rich raw material and the oxygen poor raw material, the specific values of the oxygen content and the ratio may be determined according to the oxygen content of the sintered magnet to be obtained. The oxygen content (mass ratio) of the sintered magnet produced according to the present invention is preferably 500 to 4500 ppm. When the oxygen content of the sintered magnet is too small, it is difficult to obtain a high coercive force and a high squareness ratio, and when it is too large, it is difficult to obtain a high residual magnetic flux density. Since Nd ₂ Fe ₁₄ B-based alloys are more susceptible to deterioration in magnet properties due to oxidation than SmCo ₅ -based alloys, the Nd ₂ Fe ₁₄ B-based sintered magnet preferably has an oxygen content of 500 to 3000 ppm, more preferably 600 to It is desirable to set it to 2500 ppm, more preferably 800 to 2400 ppm.

  The raw material alloy is manufactured by a casting method or a rapid cooling method. In the rapid cooling method, the molten alloy is solidified by cooling from one direction or two opposite directions to obtain, for example, a strip-like quenched alloy. As a method of cooling from one direction, a single roll method or a rotating disk method is preferable, and as a method of cooling from two directions, a twin roll method is preferable.

  The pulverization is preferably performed in two or more stages. Usually, first, a hydrogen storage and pulverization step (first coarse pulverization step) is performed in which a rapidly cooled alloy is occluded with hydrogen gas and coarsely pulverized. Next, a second coarse pulverization step is performed in which the particles are pulverized to a particle size of about 10 to 100 μm by a disk mill or the like. Next, a fine pulverization step is performed in which the particles are pulverized to a particle size of about 0.5 to 5 μm by a jet mill or the like. However, the second coarse pulverization step may be omitted.

  As a means for controlling the oxygen content of the oxygen-rich raw material and the oxygen poor raw material, it is preferable to use a method of controlling the oxygen concentration in the atmosphere in the step of producing the raw material. Specifically, the oxygen concentration in the atmosphere may be controlled during the production of the raw material alloy and / or during the pulverization of the raw material alloy.

  The oxygen content of the raw material can also be reduced by placing an oxidizing gas or moisture in the pores of the porous material and placing the porous material in contact with or close to the raw material alloy or pulverized powder thereof. It is possible to control. As the porous material, for example, sponge, paper, woven fabric, and non-woven fabric can be used. When the alloy is pulverized in multiple stages, the powder obtained in the previous pulverization process is generally transported by airflow to the subsequent pulverization process, but on the inner wall of the piping used for this transportation, What is necessary is just to stick a porous substance. In addition, although the inner wall of piping is generally smooth, in order to enlarge the contact area of the porous substance with respect to powder, an unevenness | corrugation may be provided in a part of inner wall of piping, and a porous substance may be affixed there. Further, a porous substance may be disposed in the powder mixing apparatus. In that case, a porous material may be affixed to the inner wall of the mixing device, or a porous material may be affixed to mixing blades such as a screw shape, a ribbon shape, and a paddle shape. The method for replenishing the porous material with the oxidizing gas is not particularly limited. For example, the porous material attached to the inside of the apparatus may be removed and exposed to air or oxygen gas. However, it is also possible to simply introduce air into the pipe at the time of inspection and cleaning of the apparatus with the porous material stuck inside the pipe. If the air introduced at this time is normal air containing water vapor, it is possible to replenish moisture at the same time, so there is no need to remove the porous material and soak it in water.

  Specific procedures for controlling the oxygen content are exemplified below.

  In the present invention, for example, a raw material alloy of an oxygen-rich raw material and a raw material alloy of an oxygen poor raw material may be produced by controlling the oxygen content, respectively, and then both raw material alloys may be mixed and pulverized simultaneously.

  In addition, for example, two raw material alloys having the same oxygen content (compositions may be the same or different) are independently coarsely pulverized while being controlled to have different oxygen contents. Thus, the coarse powder of the oxygen-rich raw material and the coarse powder of the oxygen poor raw material may be produced, and then both coarse powders may be mixed and then finely pulverized. In addition, the two raw material alloys are independently coarsely pulverized and then independently finely pulverized to independently produce the fine powder of the oxygen-rich raw material and the fine powder of the oxygen poor raw material. You may mix. In this case, the operation for obtaining different oxygen contents may be performed in either one of the coarse pulverization step and the fine pulverization step, or may be performed in both steps. By independently mixing after pulverization, it becomes easy to increase the difference in oxygen content between the oxygen-rich raw material and the oxygen poor raw material. The range of content adjustment is expanded. Such an effect becomes higher when mixing after fine pulverization, and becomes higher when operations for different oxygen contents are performed in both the coarse pulverization and fine pulverization steps. That is, in order to sufficiently obtain such an effect, it is preferable to mix the oxygen-rich raw material and the oxygen poor raw material after completion of the final stage of the multistage pulverization. Moreover, since the coarsely pulverized powder has a large particle size, it is difficult to be oxidized. Therefore, when trying to obtain a coarsely pulverized powder (oxygen-rich raw material) with a particularly high oxygen content, control such as heating is required in addition to increasing the oxygen concentration in the atmosphere during pulverization and powder conveyance. The number of items to be increased is undesirable in production. Therefore, also from this point, it is preferable to mix the oxygen-rich raw material and the oxygen poor raw material after completion of the final stage of the multistage grinding.

  As described above, even if it is easy to relatively increase and decrease the oxygen content of the raw material, it is difficult to stably manufacture a raw material having an intermediate oxygen content. is there. This is the background behind the present invention. Therefore, when manufacturing the oxygen poor raw material, the specific values of the oxygen concentration and the oxygen partial pressure in the alloy casting process, the molten alloy quenching process, the pulverization process, etc. are not particularly limited, and are relatively small depending on the manufacturing apparatus to be used. Manufacturing conditions may be set so that a raw material having an oxygen content can be stably manufactured by the apparatus. The same applies to the oxygen-rich raw material, and the production conditions may be set so that a raw material having a relatively high oxygen content can be stably produced by the device depending on the production device to be used.

  The oxygen-rich raw material and the oxygen poor raw material have different compositions excluding the oxygen content. Further, the oxygen-rich material and / or the oxygen poor material may contain two or more materials having different compositions.

As a case where raw materials having different compositions are used, there is a case where a so-called two-alloy method is used. The two alloy method is a method of improving magnetic properties and corrosion resistance by mixing and sintering two kinds of alloy powders having different compositions. Various proposals have been made regarding the two-alloy method, but all of them add the powder of the second alloy to the alloy powder having the same composition (R ₂ Fe ₁₄ B) as the main phase. As the second alloy, an R-rich alloy having a higher R ratio and a lower melting point than the main phase (JP-A-4-338607, JP-A-5-105915, etc.), the type of R is different from the main phase R ₂ Fe ₁₄ B alloys (Japanese Patent Laid-Open No. 61-81603, etc.) and those containing an R intermetallic compound (Japanese Patent Laid-Open No. 5-21219, etc.). Japanese Laid-Open Patent Publication No. 7-176414 discloses a method of sintering a compact made of a mixture of a main phase mother alloy powder and a grain boundary phase mother alloy powder to obtain a magnet. The main-phase master alloy in the publication, is substantially more _R 2 (Fe, _{Co) 14} and the columnar crystal grains composed of _{B, R 2 (Fe, Co} ) 14 content of R than B R A grain boundary mainly composed of a rich phase, and a master alloy for grain boundary phase contains 32 to 60% by mass of R, and the balance is substantially Co or Co and Fe. It is. In the publication, the ratio of the main phase master alloy in the mixture is set to 60 to 95% by mass.

  In the case of using the two-alloy method in the present invention, one of two raw materials having different compositions may be an oxygen-rich raw material and the other may be an oxygen poor raw material. However, the mixing ratio of both raw materials is determined according to the final composition of the magnet (for example, the mixing ratio of the alloy powder having almost the same composition as the main phase is high), so the oxygen content in the magnet is set to a desired value. It may be difficult. In order to avoid such a problem, one of two kinds of raw materials having different compositions may be divided into an oxygen-rich raw material and an oxygen poor raw material. Further, both of two kinds of raw materials having different compositions may be divided into an oxygen-rich raw material and an oxygen poor raw material.

  Molding is preferably performed in a magnetic field. In this case, the magnetic field strength is preferably 800 kA / m or more, and the molding pressure is preferably about 10 to 500 MPa. For molding, either uniaxial pressing or isotropic pressing such as CIP may be used.

The obtained molded body is sintered. The sintering conditions may be appropriately determined according to the magnet composition. For example, in the case of an Nd ₂ Fe ₁₄ B-based composition, the sintering may be performed at 1000 to 1200 ° C. for 0.1 to 100 hours. Sintering may be performed a plurality of times. Sintering is preferably performed in a non-oxidizing atmosphere, for example, in a vacuum or an inert gas atmosphere such as Ar gas. Further, pressure sintering (hot pressing) may be performed.

After sintering, it is preferable to perform an aging treatment in order to improve the coercive force. For example, in an Nd ₂ Fe ₁₄ B-based magnet, an aging treatment is preferably performed in an inert gas atmosphere at a temperature of preferably 500 ° C. or higher and a sintering temperature or lower, more preferably 500 to 950 ° C. for 0.1 to 100 hours. It is preferable to carry out. In addition, you may comprise an aging treatment from multistep heat processing. For example, in the aging treatment including two-stage heat treatment, the first-stage heat treatment is performed at a temperature of 700 ° C. or higher and lower than the sintering temperature for 0.1 to 50 hours, and the second-stage heat treatment is performed at 500 to 700 ° C. for 0.1 to 50 hours. It is preferable to carry out for 100 hours.

The present invention is particularly suitable for the production of Nd ₂ Fe ₁₄ B-based sintered magnets.

The Nd ₂ Fe ₁₄ B-based sintered magnet to which the present invention is applied contains at least Nd and / or Pr as R, and further preferably contains Fe and B, and a part of Fe is substituted with Co. Those are more preferred. The content of each element is
R: 28-32% by mass,
B: 0.8-1.2% by mass,
The rest: Fe
It is. By setting the content of each element within such a range, good magnet characteristics can be obtained. In particular,
R: 28-31.5 mass%,
B: 0.9 to 1.1% by mass,
The rest: Fe
If so, a higher residual magnetic flux density can be obtained.

  As the R content decreases, the residual magnetic flux density improves. However, if the R content decreases too much, an iron-rich phase such as the α-Fe phase precipitates, adversely affects the pulverization, and the magnetic properties also deteriorate. Moreover, since sintering becomes difficult and the sintering density becomes low, the improvement of the residual magnetic flux density has reached its peak. If the R content is too large, a high residual magnetic flux density cannot be obtained. The element R necessarily contains Nd and / or Pr. The ratio between Nd and Pr is not particularly limited. Only Nd and / or Pr may be used as the element R, but other rare earth elements, that is, Y, Sc, La, Ce, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb And at least one of Lu may be used. Of these, Dy and / or Tb are preferred. In order not to deteriorate the magnet characteristics, the total amount of elements other than both Nd and Pr is preferably 30% by mass or less of the entire element R. In addition, when using 2 or more types of elements as the element R, mixtures, such as a misch metal, can also be used as a raw material.

  If the B content is too small, the rhombohedral structure is formed, and the coercive force is lowered. On the other hand, if the B content is too large, the B-rich non-magnetic phase increases and the residual magnetic flux density decreases.

  The balance is substantially Fe, but a part of Fe may be substituted with Co. By adding Co, the temperature dependency of the coercive force and the corrosion resistance can be improved, and the residual magnetic flux density can also be improved. However, since the coercive force decreases when the Co content is too large, the Co content in the magnet is preferably 0.1 to 10% by mass.

  In the sintered magnet, in addition to the above-mentioned elements, trace additives or unavoidable impurities such as Cu, C, P, S, Al, Ti, V, Cr, Mn, Bi, Nb, Ta, Mo, W, At least one of Sb, Ge, Sn, Zr, Ni, Si, Hf, Ga, Zn and the like may be contained. However, in order to suppress deterioration in magnet characteristics, the total content of these is preferably 5% by mass or less.

  The use of the sintered magnet manufactured by this invention is not specifically limited, For example, it can apply to various apparatuses, such as a motor and a speaker.

Example 1
A raw material alloy having the following composition was manufactured by a rapid cooling method (strip casting). However, the thing of the composition D was manufactured by the casting method. In addition, in the following composition, a numerical value is a mass percentage.

Composition A: 30.0% Nd-1.0% B-0.5% Co-0.2% Al-0.05% Cu-Fe,
Composition A1: 29.3% Nd-1.1% B-0.2% Al-0.05% Cu-Fe,
Composition A2: 40.5% Nd-5.0% Co-0.2% Al-0.05% Cu-Fe,
Composition B: 28.9% Nd-2.0% Dy-1.0% B-0.5% Co-0.3% Al-0.08% Cu-Fe,
Composition C: 24.3% Nd-7.1% Dy-1.0% B-1.0% Co-0.5Al-0.08% Cu-0.2% Sn-Fe,
Composition D: 35.4% Sm-Co

  These raw material alloys were coarsely pulverized by hydrogen storage, and then finely pulverized in a nitrogen gas stream to obtain oxygen poor raw materials (fine powder) and oxygen-rich raw materials (fine powder) shown in Tables 1 to 7, respectively. The average particle size of these raw material fine powders was about 4.0 to 5.5 μm. The oxygen content of these raw material fine powders was controlled by controlling the oxygen concentration in the atmosphere during coarse pulverization and fine pulverization. Specifically, the oxygen poor raw material fine powder was produced in an atmosphere having an oxygen concentration of 50 ppm or less, and the oxygen rich raw material fine powder was produced in an atmosphere having an oxygen concentration of 0.3 to 0.5%. The oxygen content of the raw material fine powder shown in each table was measured by an inert gas melting method. This measurement was performed in a non-oxidizing atmosphere to obtain accurate results.

  These raw material fine powders were mixed at the ratios shown in Tables 1 to 7, respectively, and molded at a pressure of 150 MPa in a magnetic field of 1200 kA / m. After the obtained molded body was sintered at 1000 to 1100 ° C. in vacuum for 4 hours, an aging treatment for 1 to 4 hours was performed in a temperature range of 500 to 900 ° C. in an argon gas atmosphere in one or more stages, A sintered magnet sample was obtained. However, the compact including the powder of composition D was sintered at 1150 ° C. in a hydrogen atmosphere.

  About these sintered magnet samples, density ρ and magnetic properties (residual magnetic flux density Br, coercive force HcJ, squareness ratio Hk / HcJ) were measured with a BH tracer. Moreover, the sample cross section was observed with the scanning electron microscope, and the presence or absence of abnormal grain growth (AGG: abnormal grain growth) was investigated. Moreover, the oxygen content of the sample was measured by an inert gas melting method. These results are shown in Tables 1-7. In Tables 1 to 7, Tables 1 to 4 and Table 7 are reference examples.

  From Table 1 to Table 5, it is understood that a sintered magnet having a high residual magnetic flux density, coercive force and squareness ratio can be obtained by using a mixture of an oxygen-rich raw material and an oxygen poor raw material. It can also be seen that better magnet properties can be obtained when the ratio of the oxygen-rich material to the total of the oxygen-rich material and the oxygen poor material is 60% by mass or less, particularly less than 50% by mass.

  The magnets shown in Table 6 are manufactured by the two alloy method. In the raw material fine powder shown in Table 6, composition A1 is a composition close to the main phase of the magnet, and composition A2 is a composition close to the grain boundary phase of the magnet. And the composition of the magnet manufactured by mixing the fine powder of the composition A1 and the fine powder of the composition A2 so that the mass ratio is A1: A2 = 9: 1 is the composition of the magnet manufactured using only the fine powder of the composition A. Is almost the same. In Table 6, the oxygen-rich raw material is fine powder R6, and the oxygen poor raw material is fine powder P6-1 and fine powder P6-2. From Table 6, it can be seen that the effect of the present invention is realized even when the two-alloy method is used.

  In Table 7, sample no. 701 is manufactured using oxygen-rich fine powder and oxygen poor fine powder. 702 is manufactured using only one kind of raw material fine powder. Sample No. The oxygen content of the raw material fine powder S used in 702 is the sample No. The oxygen content of 702 is sample no. It is set to be almost the same as 701.

  From Table 7, it is clear that the squareness ratio is improved by applying the present invention even when the compositions are substantially the same.

Reference example 1
Oxygen-rich raw material (coarse powder) and oxygen poor raw material (coarse powder) were produced by carrying out until coarse pulverization in the same manner as in Example 1, and these coarse powders were mixed and then finely pulverized. However, in producing the oxygen-rich coarse powder R9 shown in Table 9, heating was also used in order to increase the oxygen content. The oxygen concentration in the atmosphere during pulverization was set to 50 ppm or less. Other than this, a sintered magnet sample was produced in the same manner as in Example 1. These samples were measured in the same manner as in Example 1. The results are shown in Table 8 and Table 9.

  From Tables 8 and 9, it can be seen that the effects of the present invention can be obtained even when the oxygen-rich raw material and the oxygen poor raw material are mixed after coarse pulverization and before fine pulverization.

Reference example 2
Composition E: 28.2% Nd-1.0% B-0.2% Co-0.05% Al-0.05% Cu-Fe
A sintered magnet sample was prepared in the same manner as in Reference Example 1 except that the above raw material alloy was used. These samples were measured in the same manner as in Example 1. The results are shown in Table 10.

  Since the composition E used in this reference example has a small R content, the margin for the oxidation of the element R is small. Therefore, the characteristics change sensitively in relation to the amount of oxygen. When the present invention is applied to such a low R composition, it can be seen that particularly good performance can be obtained by making the ratio of the oxygen-rich raw material relatively low, in particular, 40% by mass or less.

Claims (9)

A raw material alloy production process for producing a raw material alloy containing R (R is at least one rare earth element), Fe and B by a casting method or a rapid cooling method, and a raw material powder obtained by pulverizing the raw material alloy in one stage or multiple stages A pulverizing step to obtain a green body, a forming step to form a raw material powder to obtain a green body, and sintering the green body to obtain R: 28 to 32% by mass, B: 0.8 to 1.2% by mass, and the balance: Fe A sintering step of obtaining a sintered magnet consisting of
When the pulverized powder obtained by pulverizing the raw material alloy is called the raw material,
Manufactured with a relatively high oxygen content, and at least one oxygen-rich raw material that is a raw material having an oxygen content of 1200 to 5000 ppm (mass ratio);
Manufactured so that the oxygen content is relatively low, the oxygen content is 300 to 1000 ppm (mass ratio), the oxygen content is less than 1000 ppm (mass ratio) than the oxygen-rich raw material, and the oxygen content is further reduced A method for producing a rare earth sintered magnet, wherein at least one oxygen poor raw material that is different from an oxygen-rich raw material in composition removed is mixed before the forming step.   The method for producing a rare earth sintered magnet according to claim 1, wherein the ratio of the oxygen-rich material to the total of the oxygen-rich material and the oxygen poor material is 10% by mass or more and less than 90% by mass.   The method for producing a rare earth sintered magnet according to claim 1 or 2, wherein the ratio of the oxygen-rich material to the total of the oxygen-rich material and the oxygen poor material is 10 to 60% by mass.   At least one of the oxygen-rich raw material and the oxygen poor raw material is composed of two or more raw materials having different oxygen contents, and the maximum value of the difference in oxygen content between the two or more raw materials constitutes the oxygen-rich raw material The method for producing a rare earth sintered magnet according to any one of claims 1 to 3, which is smaller than a minimum value of a difference in oxygen content between a raw material to be formed and a raw material constituting the oxygen poor raw material.   The method for producing a rare earth sintered magnet according to any one of claims 1 to 4, wherein a sintered magnet having an oxygen content (mass ratio) of 500 to 4500 ppm is produced.   The difference in oxygen content between the oxygen-rich raw material and the oxygen poor raw material is realized by making the oxygen concentration in the atmosphere different in at least a part of the manufacturing process of both raw materials. Item 6. A method for producing a rare earth sintered magnet according to any one of Items 1 to 5.   In at least a part of the production process, the oxygen-rich raw material is placed in contact with or in the vicinity of the porous material having pores containing an oxidizing gas or moisture, thereby controlling the oxygen content. The method for producing a rare earth sintered magnet according to claim 1. In the pulverization process, the raw material alloy is pulverized in multiple stages,
The method for producing a rare earth sintered magnet according to any one of claims 1 to 7, wherein the oxygen-rich raw material and the oxygen poor raw material are mixed after at least one stage of pulverization. In the pulverization process, the raw material alloy is pulverized in multiple stages,
The method for producing a rare earth sintered magnet according to any one of claims 1 to 7, wherein the oxygen-rich raw material and the oxygen poor raw material are mixed after the final stage of the multistage grinding.