JP4529180B2 - Rare earth permanent magnet - Google Patents

Description

  The present invention relates to a rare earth permanent magnet containing a rare earth element R.

  In recent years, rare earth permanent magnets such as Nd—Fe—B sintered magnets have advantages such as excellent magnetic properties, Nd as a main component is abundant in resources, and is relatively inexpensive. The demand is increasing. In addition, the performance and functionality of electronic devices are remarkably increased, and Nd—Fe—B based sintered magnets used in such devices are required to have better characteristics than ever.

  Under such circumstances, research and development for enhancing magnetic properties such as coercive force and saturation magnetic flux density of Nd—Fe—B based sintered magnets are actively being promoted in various fields. For example, in Patent Document 1, by adding 0.02 at% to 0.5 at% Cu to an R—Fe—B permanent magnet, the magnetic properties and sintering temperature range of the R—Fe—B permanent magnet are reduced. There are reports of improvement. Further, for example, in Patent Document 2, the coercive force and the maximum energy product are obtained by adding Al, Cu, Si to the R—Fe—B rare earth magnet and adding at least one of Cr, Mn, and Ni. There are reports of improvement.

  By the way, the magnetic characteristics of the RTB-based rare earth permanent magnet obtained by sintering may depend on the sintering temperature. On the other hand, on an industrial production scale, it is difficult to make the heating temperature uniform throughout the sintering furnace. Therefore, the R-T-B rare earth permanent magnet is required to obtain desired magnetic characteristics even when the sintering temperature varies. Here, the temperature range where desired magnetic characteristics can be obtained is referred to as a sintering temperature range.

  Various studies have also been made on techniques for improving the sintering temperature range. For example, in Patent Document 3, an RTB-based rare earth permanent magnet containing Co, Al, Cu, and Zr, Nb, or Hf is disclosed. It is proposed that the fine ZrB compound, NbB compound, or HfB compound be uniformly dispersed and precipitated to suppress the grain growth of the magnet alloy during the sintering process and improve the magnetic properties and the sintering temperature range. ing.

Furthermore, the present applicant has proposed an RTB-based rare earth permanent magnet containing 0.05 mass% to 0.2 mass% of Zr in Patent Document 4. According to the invention described in Patent Document 4, abnormal grain growth at the time of sintering can be suppressed by adding Zr, and therefore the reduction in the squareness ratio is suppressed even when a process such as oxygen content reduction is adopted. can do.
JP-A-1-219143 Japanese Unexamined Patent Publication No. 1-2220803 JP 2002-75717 A International Publication No. 2004/029995 Pamphlet

  However, in order to obtain high magnetic properties required for high performance magnets, specifically, high coercive force (Hcj) and residual magnetic flux density (Br), the inventions described in Patent Document 1 and Patent Document 2 That is not enough. In order to further improve the coercive force and the residual magnetic flux density of the R-T-B rare earth permanent magnet, it is effective to reduce the oxygen content in the alloy. There is an inconvenience that abnormal grain growth tends to occur during the setting process, and the squareness ratio decreases. This is because the oxide in the alloy suppresses the growth of crystal grains.

  Patent Document 4 is an improvement of the problem of the reduction in squareness ratio of Patent Document 1 and Patent Document 2. However, considering further enhancement of performance of applied products in the future, the magnetic characteristics of the magnet described in Patent Document 4 are not always satisfactory, and further improvement is strongly demanded.

Furthermore, according to Patent Document 3, although abnormal grain growth is improved and the sintering temperature range is expanded, as is apparent from Table 13, coarse particles of 100 μm or more still exist, and the abundance thereof is It has reached about 0.3% to several percent. If such an amount of coarse particles is present, usually the squareness ratio of the rare earth permanent magnet is significantly reduced. On the other hand, in the examples of Table 1 to Table 12 of Patent Document 3, the squareness ratio is a good result. However, in Patent Document 3, as a method for obtaining the squareness ratio, a high coercive force component is used. It is mentioned that “4 × (BH) max / (Br) ² ”, which is a method of obtaining that hardly reflects the squareness (bending of the demagnetization curve), is used. How to find the squareness ratio that more accurately reflects the squareness of the high coercive force component (for example, “
Hk / HcJ ")), the sample described in Patent Document 3 is estimated to show a value significantly lower than the values shown in Tables 1 to 12. In addition, although the addition of Tb is effective as a technique for obtaining even higher characteristics in rare earth permanent magnets, when the amount of oxygen in the alloy is reduced and Tb is added, abnormal grain growth is more likely to occur and the squareness ratio is reduced. It tends to be very large. Therefore, in the invention described in Patent Document 3, the effect of suppressing abnormal grain growth in the sintering process is still insufficient, and further improvement is desired.

  The present invention has been proposed in view of such a conventional situation, is excellent in magnetic properties such as residual magnetic flux density and coercive force, can reliably suppress grain growth in the sintering process, and is sintered. An object of the present invention is to provide a rare-earth permanent magnet capable of expanding the sintering temperature range.

  In order to solve the above-mentioned problems, the rare earth permanent magnet according to the present invention has Tb: 0 to 10% by mass (excluding 0), R: 25% by mass to 35% by mass (R is selected from rare earth elements) And at least the Tb.), Co: 0 to 2% by mass, B: 0.5% to 4.5% by mass, one or more selected from Cu and Al : 0.02 mass% to 0.5 mass%, Zr: 0.03 mass% to 0.25 mass%, Zn: 0.02 mass% to 0.05 mass%, O: 0.03 mass% to 0 .2% by mass, Fe and inevitable impurities: characterized by having a composition comprising the balance.

  In the present invention, in a rare earth permanent magnet having a low oxygen content as described above, containing Tb as an essential element, and further containing appropriate amounts of Co, B, Cu, and Al, appropriate amounts of Zn and Zr are contained. Contains. In particular, by containing Tb as an essential element, the magnetic properties such as residual magnetic flux density and coercive force are improved, and the combined addition of Zn and Zr reliably suppresses abnormal grain growth during the sintering process, for example, Generation of coarse particles having a diameter of 100 μm or more is almost certainly suppressed. Moreover, the sintering temperature range is expanded by the combined addition of Zn and Zr.

  In addition, in the above-mentioned Patent Document 2, although it is described that the oxygen amount is preferably 6000 ppm or less and that the effect of increasing the coercive force can be obtained by adding Zr or Zn, the oxygen amount is 2000 ppm (= 0. (2% by mass), it is not recognized that abnormal grain growth occurs when it is extremely reduced as follows, and of course, it is not recognized at all that the abnormal grain growth is suppressed by the combined addition of Zn and Zr. . Further, in Patent Document 2, although Tb is described as the rare earth element R, a magnet that actually contains Tb has not been studied and is merely listed. That is, in Patent Document 2, it is completely unexpected to combine specific elements such as Tb, Zr, Zn, etc. and to reduce the amount of oxygen.

  Moreover, although the above-mentioned patent document 3 contains Zr in a rare earth magnet and has a low oxygen content, there is no idea that Tb is an essential element. When a composition containing Tb as an essential element is applied to a low oxygen content rare earth magnet not containing Zn but containing Zr, the reduction in squareness ratio (Hk / HcJ) and coercivity (HcJ) due to abnormal grain growth during the sintering process. ).

  Furthermore, although the rare earth permanent magnet described in Patent Document 4 contains Zr, it does not contain Zn. In order to further improve the magnetic characteristics of such a permanent magnet, for example, when Tb is used as an essential element, there arises a disadvantage that the square characteristics deteriorate.

  According to the present invention, a rare earth permanent magnet having a high coercive force and a residual magnetic flux density and reliably suppressing grain growth in the sintering process, for example, having an excellent squareness ratio and an expanded sintering temperature range is provided. can do.

Hereinafter, a rare earth permanent magnet to which the present invention is applied will be described in detail with reference to the drawings.
First, the chemical composition of the rare earth permanent magnet to which the present invention is applied will be described. Here, the chemical composition refers to the chemical composition in the rare earth permanent magnet after sintering.

In the rare earth permanent magnet of the present invention, the content of the rare earth element R is 35% by mass or less. If the rare earth element R exceeds 35% by mass, the volume ratio of the R ₂ T ₁₄ B phase, which is the main phase, decreases, and the residual magnetic flux density significantly decreases. Further, the rare earth element R reacts with oxygen, the amount of oxygen contained increases, and accordingly, the R-rich phase effective for generating the coercive force decreases, leading to a significant decrease in the coercive force. On the other hand, if the content of the rare earth element R is less than 25% by mass, the R ₂ T ₁₄ B phase, which is the main phase of the rare earth permanent magnet, is not sufficiently generated, and α-Fe having soft magnetism is precipitated and retained. The magnetic force is significantly reduced. For the above reasons, the rare earth element R content is set to 25 mass% to 35 mass%. Moreover, content of desirable rare earth elements R is 28 mass%-32 mass%. Further, the rare earth element R content is most preferably 30% by mass or less. By setting the content of the rare earth element R to 30% by mass or less, the volume ratio of the R ₂ T ₁₄ B phase that is the main phase is increased, and the residual magnetic flux density is greatly improved.

  Here, the rare earth element R is two or more selected from rare earth elements. Specifically, the rare earth element R is Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu. “The content of the rare earth element R is 25% by mass to 35% by mass” means that the total content of the rare earth elements such as Tb, Nd, Dy is 25% by mass to 35% by mass. It means that it is.

In the present invention, at least Tb is selected and used as the rare earth element R. Tb is an element effective for further improving the coercive force as compared with Dy generally used for rare earth permanent magnets. This is because the Tb ₂ T ₁₄ B phase exhibits a higher anisotropic magnetic field than, for example, the Dy ₂ T ₁₄ B phase. Content of Tb shall be 0-10 mass% (however, 0 is not included). When the Tb content is 0, improvement in magnetic properties cannot be expected. When the Tb content exceeds 10% by mass, the residual magnetic flux density is remarkably reduced. Desirable Tb content is 0.1 mass% to 6 mass%.

As the rare earth element R, it is preferable to select and use Nd and Dy in addition to the Tb. This is because Nd is abundant in resources and relatively inexpensive. Further, Dy has an advantage that the anisotropic magnetic field of the Dy ₂ T ₁₄ B phase is larger than the anisotropic magnetic field of the Nd ₂ T ₁₄ B phase, for example, and is effective in improving the coercive force. The Dy content is desirably 0.1% by mass to 8% by mass. It is desirable to determine the amount of Dy within the above range depending on which of the residual magnetic flux density and the coercive force is important. That is, when it is desired to obtain a high residual magnetic flux density, the Dy amount is 0.1% to 3.5% by mass, and when a high coercive force is desired, the Dy amount is 3.5% to 8% by mass. It is desirable to do.

  Moreover, the rare earth permanent magnet of the present invention can contain 0 to 2% by mass of Co. Co forms the same phase as Fe. However, when Co is contained in the rare earth permanent magnet of the present invention, it is effective in improving the Curie temperature and improving the corrosion resistance of the grain boundary phase. A more desirable Co content is 0 to 2% by mass (however, 0 is not included).

  Moreover, the rare earth permanent magnet of the present invention contains 0.5% by mass to 4.5% by mass of B. When the content of B is less than 0.5% by mass, a high coercive force cannot be obtained. However, when B exceeds 4.5 mass%, the residual magnetic flux density tends to decrease. Therefore, the upper limit of the B content is 4.5% by mass. Desirable content of B is 0.5 mass%-1.5 mass%.

  Moreover, the rare earth permanent magnet of this invention contains 0.02 mass%-0.5 mass% of 1 type or 2 types chosen from Cu and Al. By containing one or two of Al and Cu within this range, it is possible to increase the coercive force, corrosion resistance, and temperature characteristics of the obtained rare earth permanent magnet. In the case of adding Al, a desirable amount of Al is 0.03% by mass to 0.25% by mass. Moreover, when adding Cu, the quantity of desirable Cu is 0-0.15 mass% (however, 0 is not included).

  The rare earth permanent magnet of the present invention contains 0.03% by mass to 0.2% by mass of oxygen (O). If the amount of oxygen is large, the oxide phase, which is a nonmagnetic component, increases and the magnetic properties are degraded. Therefore, the upper limit of the oxygen amount is set to 0.2% by mass. However, if the oxygen amount in the rare earth permanent magnet is simply reduced, the oxide phase having the effect of suppressing crystal grain growth is reduced, and grain growth occurs easily in the process of obtaining a sufficient density increase during sintering. Therefore, in the present invention, as described later, a predetermined amount of Zn and Zr having an effect of suppressing abnormal growth of crystal grains during the sintering process is contained. If the oxygen content is too small, oversintering is likely to occur, and the squareness is lowered, so the lower limit of the amount of oxygen is 0.03% by mass. A more desirable amount of oxygen is 0.03% by mass to 0.1% by mass.

  Moreover, the rare earth permanent magnet of the present invention may contain C. Content of C is 0.03 mass%-0.1 mass%. If the amount of C is less than 0.03% by mass, oversintering is likely to occur, and the squareness may be deteriorated. If the amount of C exceeds 0.1% by mass, both sinterability and squareness may be reduced.

  The rare earth permanent magnet of the present invention may contain N. Content of N is 0.02 mass%-0.05 mass%. If the amount of N is less than 0.02% by mass, oversintering is likely to occur, and the squareness may be lowered. If the amount of N exceeds 0.05% by mass, both sinterability and squareness may be reduced.

  Furthermore, the rare earth permanent magnet of the present invention has a great feature in that each contains an appropriate amount of Zn and Zr in addition to the aforementioned composition. By using appropriate amounts of Zn and Zr in combination, abnormal grain growth during sintering is suppressed, and good squareness is obtained. In addition, the sintering temperature range of the rare earth permanent magnet can be expanded. Zr is known as an element that can suppress abnormal grain growth during sintering. However, even when Zr is added alone to a rare earth permanent magnet having a composition that requires Tb, sufficient effects are obtained. It is not possible. In addition, the coercive force is reduced. In addition, when Zn is added alone to the above-described composition requiring Tb, the effect of suppressing abnormal grain growth is insufficient as in the case of Zr alone, and the squareness ratio is greatly reduced. That is, the effect of the present invention is exhibited by adding Zn and Zr in combination.

  The combined addition of appropriate amounts of Zn and Zr is very effective when the amount of rare earth element R contained in the alloy is reduced. When the content of the rare earth element R is, for example, 30% by mass or less, the residual magnetic flux density (Br) can be greatly improved. However, since the liquid phase component at the time of sintering is reduced, the sinterability is reduced. Grain growth becomes difficult. As a countermeasure, if the sintering temperature is raised in order to increase the density of the sintered body, there is a disadvantage that abnormal grain growth tends to occur. The combined addition of appropriate amounts of Zn and Zr is very effective in suppressing abnormal grain growth when the amount of the rare earth element R is 30% by mass or less. By adding Zn and Zr in combination, the advantage of reducing the amount of rare earth element R (the effect of improving the residual magnetic flux density) is ensured while suppressing abnormal grain growth caused by reducing the amount of rare earth element R. Can get to.

  The appropriate content of Zn is 0.02 mass% to 0.05 mass%. When reducing the oxygen content in order to improve the magnetic properties of rare earth permanent magnets, Zn exhibits the effect of suppressing abnormal growth of crystal grains during the sintering process, making the structure of the sintered body uniform and fine. To do. Therefore, the addition of Zn becomes significant when the oxygen content in the rare earth permanent magnet is low. Further, an appropriate amount of Zn expands the sintering temperature range of the rare earth permanent magnet. When the amount of Zn is too small, the effect of suppressing abnormal growth of crystal grains in the sintering process becomes insufficient, and the squareness ratio of the rare earth permanent magnet tends to deteriorate. In addition, the improvement effect of the sintering temperature range tends to be insufficient. Therefore, the lower limit of the amount of Zn is 0.02% by mass. Conversely, when the amount of Zn becomes excessive, the residual magnetic flux density and coercive force of the rare earth permanent magnet tend to decrease. Therefore, the upper limit of the amount of Zn is set to 0.05 mass%. A more desirable amount of Zn is 0.02% by mass to 0.04% by mass.

  An appropriate content of Zr is 0.03% by mass to 0.25% by mass. When reducing the oxygen content in order to improve the magnetic properties of rare earth permanent magnets, Zr exhibits the effect of suppressing abnormal growth of crystal grains during the sintering process, making the structure of the sintered body uniform and fine. To do. Therefore, the addition of Zr becomes remarkable when the oxygen content in the rare earth permanent magnet is low. Further, an appropriate amount of Zr expands the sintering temperature range of the rare earth permanent magnet. When the amount of Zr is too small, the effect of suppressing abnormal growth of crystal grains in the sintering process becomes insufficient, and the squareness ratio of the rare earth permanent magnet tends to deteriorate. In addition, the improvement effect of the sintering temperature range tends to be insufficient. Therefore, the lower limit of the amount of Zr is 0.03% by mass. Conversely, when the amount of Zr is excessive, the residual magnetic flux density and coercive force of the rare earth permanent magnet tend to decrease. Therefore, the upper limit of the amount of Zr is 0.25% by mass.

Therefore, the composition of the rare earth permanent magnet of the present invention is expressed as follows.
Tb: 0 to 10% by mass (excluding 0)
R: 25% by mass to 35% by mass (R is at least two selected from rare earth elements and contains at least the Tb)
Co: 0 to 2% by mass
B: 0.5% by mass to 4.5% by mass
One or more selected from Cu and Al: 0.02% by mass to 0.5% by mass
Zr: 0.03 mass% to 0.25 mass%
Zn: 0.02 mass% to 0.05 mass%
O: 0.03 mass% to 0.2 mass%
Fe and inevitable impurities: balance

The desirable composition of the rare earth permanent magnet of the present invention is expressed as follows.
Tb: 0.1% by mass to 6% by mass
R: 28% by mass to 32% by mass (R is at least two selected from rare earth elements and contains at least the Tb)
Co: 0 to 2% by mass (excluding 0)
B: 0.5% by mass to 1.5% by mass
Cu: 0 to 0.15 mass% (however, 0 is not included)
Al: 0.03 mass% to 0.25 mass%
Zr: 0.03 mass% to 0.25 mass%
Zn: 0.02 mass% to 0.04 mass%
O: 0.03 mass% to 0.1 mass%
Fe and inevitable impurities: balance

Next, the suitable manufacturing method of the rare earth permanent magnet of this invention is demonstrated.
In the present embodiment, a powder of a main phase alloy mainly composed of R ₂ T ₁₄ B (T is Fe, Co or Fe) phase, and a grain boundary mainly composed of R and T but not B A method for producing a rare earth permanent magnet according to the present invention using a phase alloy powder will be described.

  First, a main phase alloy and a grain boundary phase alloy are obtained by strip casting the raw metal in a vacuum or an inert gas, preferably in an Ar atmosphere. As the raw material metal, rare earth metals or rare earth alloys, pure iron, ferroboron, and alloys thereof can be used. The obtained raw material alloy is subjected to a solution treatment as necessary when there is solidification segregation. The conditions may be maintained in a region of 700 ° C. to 1500 ° C. for 1 hour or more under vacuum or Ar atmosphere.

  Although the rare earth permanent magnet of the present invention contains Zn as an essential component, Zn is preferably supplied from a grain boundary phase alloy. More preferably, Zn, Cu and Co are supplied from the grain boundary phase alloy. Moreover, although the rare earth permanent magnet of this invention contains Zr as an essential component, it is preferable that Zr is supplied from a main phase system alloy. Specifically, the main phase alloy can contain Zr, Al and the like in addition to the rare earth element R and the transition metal elements T and B. The main phase alloy is, for example, Nd-Dy-B-Al. -Zr-Fe alloy. In addition, the grain boundary phase-based alloy can be an alloy containing Zn, Cu, Co, etc. as well as containing R and T as a main component. The grain boundary phase alloy is, for example, a Tb—Cu—Co—Al—Fe alloy or a Tb—Cu—Co—Al—Zn—Fe alloy.

  After the main phase alloy and the grain boundary phase alloy are produced, each of these master alloys is ground separately or together. The pulverization process includes a coarse pulverization process and a fine pulverization process. First, each mother alloy is coarsely pulverized until the particle size becomes about several hundred μm. The coarse pulverization is desirably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill or the like. Moreover, each alloy can be coarsely pulverized by performing coarse pulverization after occluding hydrogen or releasing hydrogen after occluding hydrogen.

  After the coarse pulverization process, the process proceeds to the fine pulverization process. In the fine pulverization, a jet mill is mainly used, and a coarsely pulverized powder having a particle size of about several hundreds of μm is pulverized until the average particle size becomes 3 to 5 μm. The jet mill opens a high-pressure inert gas (for example, nitrogen gas) from a narrow nozzle to generate a high-speed gas flow, and the high-speed gas flow accelerates the coarsely pulverized powder. Or it is the method of generating and colliding with a container wall. As a result, a main phase alloy powder and a grain boundary phase alloy powder are obtained.

  When the main phase alloy and the grain boundary phase alloy are separately ground in the fine grinding step, the finely ground main phase alloy powder and the grain boundary phase alloy powder are mixed in a nitrogen atmosphere. The mixing ratio of the main phase alloy powder and the grain boundary phase alloy powder may be about 80:20 to 97: 3 by weight. Similarly, the mixing ratio when the main phase alloy and the grain boundary phase alloy are pulverized together may be about 80:20 to 97: 3 by weight. By adding about 0.01% by mass to 0.3% by mass of an additive such as zinc stearate at the time of fine pulverization, fine powder having high orientation can be obtained at the time of molding.

Next, a mixed powder composed of a main phase alloy powder and a grain boundary phase alloy powder is filled in a mold held by an electromagnet and molded in a magnetic field with its crystal axis oriented by applying a magnetic field. The magnetic field molding, in a magnetic field of 12KOe～17kOe, may be performed from 0.7t / cm ² 1.5t / cm ² at a pressure of about.

  After molding in a magnetic field, the compact is sintered in a vacuum or an inert gas atmosphere. Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, a particle size, and a particle size distribution difference, what is necessary is just to sinter at 1000 to 1100 degreeC for about 1 to 5 hours.

  After sintering, the obtained sintered body can be subjected to an aging treatment. The aging treatment is important for controlling the coercive force. In the case where the aging treatment is performed in two stages, it is effective to hold for a predetermined time in the vicinity of 800 ° C. and 600 ° C. When the heat treatment in the vicinity of 800 ° C. is performed after sintering, the coercive force increases, which is particularly effective in the mixing method. In addition, since the coercive force is greatly increased by heat treatment at around 600 ° C., when the aging treatment is performed in one stage, the aging treatment at around 600 ° C. is preferably performed. As described above, the rare earth permanent magnet of the present invention can be obtained.

  In the rare earth permanent magnet of the present invention, the oxygen content is set to 0.03% by mass to 0.2% by mass for the purpose of obtaining high magnetic properties. This oxygen content is controlled by the atmosphere in each manufacturing process, It is adjusted by controlling the amount of oxygen contained in the raw material. In particular, to suppress the atmosphere of each step from hydrogen pulverization treatment to sintering to a low oxygen concentration of less than 100 ppm is to adjust the oxygen content within the range of 0.03% by mass to 0.2% by mass. It is valid.

  Further, the amount of C contained in the rare earth permanent magnet is adjusted by the type and amount of the grinding aid used in the production process. Further, the amount of N contained in the rare earth permanent magnet is adjusted by the type and amount of the raw material alloy, the pulverizing conditions when the raw material alloy is pulverized in a nitrogen atmosphere, and the like.

  In the rare earth permanent magnet of the present invention obtained as described above, high residual magnetic flux density and retention can be obtained by making the contents of Tb, rare earth elements R, Co, B, Cu, Al, O, Zn and Zr appropriate. While realizing the magnetic force, the abnormal grain growth in the sintering process is reliably suppressed, and the generation of coarse particles of, for example, 100 μm or more can be reliably suppressed. Furthermore, in the rare earth permanent magnet of the present invention, there is no generation of finer coarse particles of 50 μm or more and less than 100 μm, and abnormal grain growth is reliably prevented.

  Hereinafter, specific examples to which the present invention is applied will be described based on experimental results. In addition, this invention is not limited to description of a following example.

(1) Raw material alloys Four types of alloys shown in Table 1 were produced by strip casting.

(2) Hydrogen pulverization step After occluding hydrogen at room temperature, hydrogen pulverization treatment was performed in which dehydrogenation was performed in an Ar atmosphere at 600 ° C for 1 hour.
In this example, in order to set the sintered body oxygen content to 0.03% by mass to 0.2% by mass, each from hydrogen treatment (recovery after pulverization treatment) to sintering (put into a sintering furnace) The atmosphere of the process is suppressed to an oxygen concentration of less than 100 ppm. Hereinafter, this is referred to as a low oxygen process.

(3) Grinding step A grinding aid was mixed before fine grinding. In addition, although the coarse pulverization process may be performed after the hydrogen pulverization process, it is omitted in this embodiment. The grinding aid is not particularly limited, but in this example, zinc stearate was mixed in an amount of 0.05% to 0.1%. The mixing of the grinding aid may be performed for about 5 minutes to 30 minutes using, for example, a Nauter mixer.
Thereafter, fine pulverization is performed using an airflow pulverizer. In this experiment, fine pulverization was performed using a jet mill. Using an airflow pulverizer, fine pulverization was performed until the alloy powder had an average particle size of about 3 μm to 6 μm. In this experiment, pulverized powder having an average particle size of 4 μm was prepared.
Of course, both the mixing step and the fine pulverization step of the pulverization aid were performed by a low oxygen process.

(4) Blending step In order to perform the experiment efficiently, several types of finely pulverized powders may be mixed and mixed so as to have a desired composition. In this case, the mixing may be performed for about 5 to 30 minutes using, for example, a Nauter mixer.
Although it is desirable to perform the orientation step by a low oxygen process, when the amount of oxygen in the sintered body is slightly increased, the amount of oxygen in the forming fine powder is adjusted in this step. For example, a fine powder having the same composition and average particle diameter is prepared and left in an oxygen-containing atmosphere of 100 ppm or more for several minutes to several hours, whereby a fine powder of several thousand ppm can be obtained. The amount of oxygen is adjusted by mixing these two types of fine powders in a low oxygen process.

(5) Molding step The obtained fine powder is molded in a magnetic field. Specifically, a fine powder is filled in a mold held by an electromagnet, and molding is performed in a magnetic field in a state where the crystal axis is oriented by applying a magnetic field. The magnetic field molding, in a magnetic field of ^{12kOe~17kOe, 0.7t / cm 2 ~1.5t /} cm 2 may be carried out at a pressure of about. In this experiment, molding was performed in a magnetic field of 15 kOe at a pressure of 1.2 t / cm ² to obtain a molded body. This step was also performed by a low oxygen process.

(6) Sintering / aging process This compact was sintered in a vacuum at 1010 ° C to 1150 ° C for 4 hours and then rapidly cooled. Next, the obtained sintered body was subjected to a two-stage aging treatment at 800 ° C. for 1 hour and 550 ° C. for 2.5 hours (both in an Ar atmosphere).

  An alloy having the composition shown in Table 1 was blended so as to have the final composition shown in Table 2. At this time, the total content of the rare earth element R in the rare earth permanent magnet was 29.7% by mass, and the Tb content was adjusted to 1.4% by mass. After blending, hydrogen pulverization treatment was performed, and then fine pulverization was performed with a jet mill so that the average particle size became 4 μm. Table 2 also shows the types of raw material alloys used. Thereafter, after molding in a magnetic field, sintering was performed at 1090 ° C., and the obtained sintered body was subjected to two-stage aging treatment.

  About the obtained rare earth permanent magnet, residual magnetic flux density (Br), coercive force (HcJ), and squareness ratio (Hk / HcJ) were measured with a BH tracer. The results are also shown in Table 2. Hk is the magnetic field strength when the magnetization in the second quadrant of the magnetic hysteresis loop (4πI-H curve) is 90% of the residual magnetic flux density Br. The squareness ratio Hk / HcJ is particularly related to the effect of an external magnetic field and demagnetization due to a temperature rise, and is a value that serves as an index of magnet characteristics during actual use. Further, when Hk / HcJ is low, the magnetic field strength required for magnetization increases. Furthermore, a permanent magnet having a low Hk / HcJ has a problem in the loop shape in the second quadrant of the magnetic hysteresis loop, and the design conditions of the system to which the magnet is applied become severe.

  No. 1-No. 24 sintered bodies were cut, and the number of coarse particles having a major axis of 50 μm or more and less than 100 μm and coarse particles of 100 μm or more present in a region having a cross section of 10 mm × 10 mm was examined using a scanning electron microscope (SEM). It was. The results are also shown in Table 3.

  Further, except that the sintering temperature was changed to 1070 ° C. or 1110 ° C., a rare earth permanent magnet was produced in the same manner, and the magnetic properties were evaluated. The results are shown in Table 3 together with the results of Table 2 (1090 ° C.). That is, Table 2 is an extract of rare earth permanent magnets (No. 2, 5, 8, 11, 14, 17, 20, 23) whose sintering temperature is 1090 ° C. in Table 3.

  Among magnetic properties, the squareness ratio (Hk / HcJ) tends to decrease most rapidly due to abnormal grain growth. That is, the squareness ratio (Hk / HcJ) is an index that can grasp the tendency of abnormal grain growth. Here, from Table 3, No. 1 containing Zn alone was added. 1-No. No. 3 has a squareness ratio of less than 90%. When the sintering temperature range in which a squareness ratio (Hk / HcJ) of 90% or more is obtained is defined as a sintering temperature range, rare earth permanent magnets (No. 1 to No. 3) added with Zn alone are sintered. The temperature range is zero. No. 1-No. No. 3 contains coarse particles having a particle size of 50 μm or more. Many were confirmed in FIG. Therefore, no. 1-No. In No. 3, there is a significant decrease in squareness characteristics.

  In addition, no. 4-No. In No. 6, No. 6 with a sintering temperature of 1090 ° C. In the magnets obtained by sintering at 1070 ° C. and 1110 ° C., coarse particles due to abnormal grain growth were confirmed, and a reduction in the squareness ratio was observed. That is, the sintering temperature range when Zr is used alone is very narrow.

  Furthermore, although both Zn and Zr are contained, the Zn content is 0.01% by mass. 7-No. In No. 9, it can be seen from the results of Table 3 that the effect of suppressing abnormal grain growth during sintering is insufficient. Moreover, the sintering temperature range was not enlarged and was narrow.

  On the other hand, while using Zn and Zr together, No. 1 with these contents as appropriate amounts. 10-No. No. 21 shows a high squareness ratio exceeding 90% at any sintering temperature. Also, no coarse particles having a particle size of 50 μm or more were observed.

  When the Zn content is 0.06% by mass (No. 22 to No. 24), although the sintering temperature range is wide, the coercive force (HcJ) is less than 25 kOe at all sintering temperatures, and the coercive force (HcJ ) Is significantly reduced.

  Therefore, from the above results, it was confirmed that the optimum content of Zn used in combination with Zr in the rare earth permanent magnet of the present invention is 0.02 mass% to 0.05 mass%.

Claims (9)

  Tb: 0 to 10% by mass (however, 0 is not included), R: 25% by mass to 35% by mass (R is at least two selected from rare earth elements and contains at least the Tb), Co: 0 to 2 mass%, B: 0.5 mass% to 4.5 mass%, one or more selected from Cu and Al: 0.02 mass% to 0.5 mass%, Zr: 0.03 It has a composition comprising mass% to 0.25 mass%, Zn: 0.02 mass% to 0.05 mass%, O: 0.03 mass% to 0.2 mass%, Fe and inevitable impurities: the balance. Features rare earth permanent magnets.   Tb: 0.1% by mass to 6% by mass, R: 28% by mass to 32% by mass (R is at least two selected from rare earth elements and contains at least the Tb), Co: 0-2% by mass % (Excluding 0), B: 0.5 mass% to 1.5 mass%, Cu: 0 to 0.15 mass% (however, 0 is not included), Al: 0.03 mass% to 0.25% by mass, Zr: 0.03% by mass to 0.25% by mass, Zn: 0.02% by mass to 0.04% by mass, O: 0.03% by mass to 0.1% by mass, Fe and The rare earth permanent magnet according to claim 1, wherein the rare earth permanent magnet has a composition composed of inevitable impurities: the balance.   The rare earth permanent magnet according to claim 1 or 2, wherein C: 0.03 mass% to 0.1 mass%.   The rare earth permanent magnet according to claim 1 or 2, wherein N: 0.02 mass% to 0.05 mass%.   The rare earth permanent magnet according to any one of claims 1 to 4, wherein particles having a particle size of 100 µm or more are not present.   6. The rare earth permanent magnet according to claim 5, wherein there are no particles having a particle size of 50 μm or more and less than 100 μm. A powder of a main phase alloy mainly composed of an R ₂ T ₁₄ B (T is Fe, Co or Fe) phase, and a powder of an intergranular phase alloy mainly composed of R and T but not containing B The rare earth permanent magnet according to any one of claims 1 to 6, wherein the Zn is supplied from the grain boundary phase alloy after being formed and sintered. A powder of a main phase alloy mainly composed of an R ₂ T ₁₄ B (T is Fe, Co or Fe) phase, and a powder of an intergranular phase alloy mainly composed of R and T but not containing B 7. The rare earth permanent magnet according to claim 1, wherein the Zn, Co, and Cu are supplied from the grain boundary phase alloy after being formed and sintered. A powder of a main phase alloy mainly composed of an R ₂ T ₁₄ B (T is Fe, Co or Fe) phase, and a powder of an intergranular phase alloy mainly composed of R and T but not containing B 9. The rare earth permanent magnet according to claim 1, wherein the Zr is supplied from the main phase alloy after being formed and sintered.