JP4706900B2 - Rare earth permanent magnet manufacturing method - Google Patents

Description

The present invention relates to a method for producing a rare earth permanent magnet containing rare earth 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 is 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.
JP-A-1-219143 Japanese Unexamined Patent Publication No. 1-2220803 JP 2002-75717 A

  However, in order to obtain the high magnetic characteristics required for high-performance magnets, specifically, high coercive force (Hcj) and residual magnetic flux density (Br), Patent Document 1 and Patent Document 2 (Japanese Patent Laid-Open No. Hei 1). The invention described in 220803) is still insufficient. 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.

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 set to 0. It has reached about 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 contrary, in the examples of Table 1 to Table 12 of Patent Document 3, the squareness ratio is a good result. As a cause of this, in Patent Document 3, as a method for obtaining the squareness ratio, a high coercive force component is obtained. 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 employed. If the sample described in Patent Document 3 is evaluated by a method of obtaining a squareness ratio that more accurately reflects the squareness on the high coercive force side (for example, “Hck / HcJ”), the values shown in Tables 1 to 12 are obtained. Is estimated to be significantly lower. 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-described problems, a method for producing a rare earth permanent magnet according to the present invention includes a hydrogen pulverization step, a pulverization step, a forming step in a magnetic field, and a firing step. R ₂ T ₁₄ B (R is a rare earth element) 1 or 2 or more, and T is Fe, or Co and Fe.) A rare earth permanent magnet manufacturing method mainly comprising: a forming step in a magnetic field by dry forming, and a hydrogen pulverizing step The atmosphere of each step from the firing step to the firing step is suppressed to a low oxygen concentration of less than 100 ppm, R: 28 mass% to 33 mass%, Co: 0 to 2 mass% (however, 0 is not included), B: 0.5 % By mass to 1.5% by mass, Cu: 0 to 0.15% by mass (excluding 0), Al: 0.03% by mass to 0.25% by mass, Ga: 0.05% by mass to 0% .15 mass%, O: 0.03 mass% to 0.1 mass%, C: 0.03 Mass% to 0.1 mass%, N: 0.02 mass% to 0.05 mass%, Fe and inevitable impurities: A rare earth permanent magnet having a composition composed of the balance and having no particles having a particle size of 50 μm or more is obtained. It is characterized by that.

  In the rare earth permanent magnet of the present invention, excellent magnetic properties such as residual magnetic flux density and coercive force are realized by reducing the oxygen content in the alloy. In such a rare earth permanent magnet having a low oxygen content, by adding an appropriate amount of Ga, the growth of grain growth in the sintering process is suppressed, and the sintering temperature range is expanded.

  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 Ga, the oxygen amount is 2000 ppm (= 0.2 mass%). It does not recognize that abnormal grain growth occurs when it is extremely reduced as follows, and of course, Ga does not recognize at all that Ga suppresses abnormal grain growth. Further, in Patent Document 2, although there is a description of Ga, no actual examination has been made, and it is merely a list. That is, the effect of Ga addition is unclear.

  In addition, Ga in Patent Document 3 is merely treated as an impurity, and is only listed together with many other elements such as La and Ce. That is, Patent Document 3 does not recognize that Ga has an effect of suppressing abnormal grain growth. Moreover, the permanent magnet described in Patent Document 3 contains an element selected from Zr, Nb, and Hf as an essential component.

  In contrast, the present invention is premised on a composition that does not contain Zr, Nb, and Hf. By reducing the amount of oxygen with this composition, the residual magnetic flux density and the coercive force are improved, and an anomaly associated with the reduction in the amount of oxygen. The problem of grain growth is to be solved by positive addition of Ga. That is, the present invention realizes a remarkable effect of suppressing abnormal grain growth that cannot be expected from Patent Document 2 and Patent Document 3 by combining reduction of oxygen amount and addition of Ga. Generation of coarse particles of 100 μm or more is almost certainly suppressed.

  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.

The rare earth permanent magnet to which the present invention is applied contains 25% by mass to 35% by mass of the rare earth element R. Here, the rare earth element R is one or more 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. When the content of the rare earth element R is less than 25% by mass, the R ₂ T ₁₄ B ₁ phase that is the main phase of the rare earth permanent magnet is not sufficiently generated, and α-Fe or the like having soft magnetism is precipitated. Is significantly reduced. On the other hand, when the rare earth element R exceeds 35 mass%, the volume ratio of the R ₂ T ₁₄ B ₁ phase that is the main phase is lowered, and the residual magnetic flux density is lowered. 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 decrease in coercive force. For the above reasons, the rare earth element R content is 25 mass% to 35 mass%, and the more desirable rare earth element R content is 28 mass% to 33 mass%.

  Since Nd is abundant in resources and relatively inexpensive, it is desirable that the main component as the rare earth element R is Nd. Dy has a large anisotropic magnetic field and is effective in improving the coercive force. Therefore, it is desirable that Nd and Dy are selected as the rare earth element R, and the total of Nd and Dy is 25 mass% to 35 mass%. And in this range, it is desirable to make Dy 0.1 mass%-8 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 is greatly characterized in that it contains 0.05 mass% to 0.25 mass% of Ga. When reducing the oxygen content to improve the magnetic properties of rare earth permanent magnets, Ga exerts 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 Ga has a remarkable effect when the oxygen content in the rare earth permanent magnet is low. Further, an appropriate amount of Ga increases the sintering temperature range of the rare earth permanent magnet. When the amount of Ga 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 Ga is set to 0.05 mass%. Conversely, when the amount of Ga 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 Ga is 0.25% by mass. Furthermore, the desirable amount of Ga is 0.05 mass% to 0.15 mass%.

  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 above, a predetermined amount of Ga having an effect of suppressing abnormal growth of crystal grains in 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.

Therefore, the composition of the rare earth permanent magnet of the present invention is expressed as follows.
R: 25% by mass to 35% by mass
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
Ga: 0.05 mass% to 0.25 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.
R: 28% by mass to 33% by mass
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%
Ga: 0.05 mass% to 0.15 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 rare earth permanent according to the present invention is produced using an alloy mainly composed of R ₂ T ₁₄ B phase (low R alloy) and an alloy containing a higher amount of rare earth element R than a low R alloy (high R alloy). A method for manufacturing the magnet will be described.

  First, a low R alloy and a high R 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 in a vacuum or Ar atmosphere.

  The rare earth permanent magnet of the present invention contains Ga as an essential component, and this Ga is preferably supplied from a high R alloy. More preferably, Ga, Cu and Co are supplied from a high R alloy. Specifically, the low R alloy can contain Al or the like in addition to the rare earth element R and the transition metal elements T and B. The low R alloy is, for example, an Nd—Dy—B—Al—Fe alloy. It is. The high R alloy is, for example, a Dy—Cu—Co—Al—Fe alloy or a Dy—Cu—Co—Al—Ga—Fe alloy.

  After the low R and high R alloys are made, 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 diameter of about several hundreds of micrometers is pulverized until the average particle diameter 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. Thereby, a low R alloy powder and a high R alloy powder are obtained.

  When the low R alloy and the high R alloy are separately pulverized in the fine pulverization step, the finely pulverized low R alloy powder and high R alloy powder are mixed in a nitrogen atmosphere. The mixing ratio of the low R alloy powder and the high R alloy powder may be about 80:20 to 97: 3 by weight. Similarly, the mixing ratio when the low R alloy and the high R 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 during pulverization, a fine powder having high orientation can be obtained during molding.

Next, the mixed powder composed of the low R alloy powder and the high R 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 near 600 ° C., when aging treatment is performed in one stage, it is preferable to perform aging treatment near 600 ° C. 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, a high residual magnetic flux density and a coercive force are realized by setting the oxygen content to 0.03% by mass to 0.2% by mass. By making it within a specific composition range containing Ga, the effect of suppressing abnormal grain growth in the sintering process is remarkably exhibited. For example, coarse particles of 100 μm or more are not present. Furthermore, in the rare earth permanent magnet of the present invention, there is no generation of slightly fine 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 Three types of alloys shown in Table 1 were produced by a strip casting method.

(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 prepared and mixed so as to have a desired composition (particularly, Ga amount). 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, and subjected to hydrogen pulverization treatment, and then finely pulverized to a mean particle size of 4 μm by a jet mill. Table 2 also shows the types of raw material alloys used. Thereafter, after molding in a magnetic field, sintering was performed at 1050 ° 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. Hk 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 hysteresis loop. The results are also shown in Table 2.

  Further, except that the sintering temperature was changed to 1030 ° C. or 1070 ° 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 in Table 2 (1050 ° 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 1050 ° C. in Table 3. In Table 3, No. 1-No. No. 21 has an oxygen content in the range of 0.03% by mass to 0.2% by mass. 22-No. No. 24 has an oxygen content exceeding 0.2% by mass.

  In Table 3, the rare earth permanent magnet having an oxygen amount in the range of 0.03% by mass to 0.2% by mass represents the relationship between the Ga addition amount and the residual magnetic flux density (Br) at each sintering temperature. The graph is shown in FIG. Similarly, a graph showing the relationship between the Ga addition amount and the coercive force (HcJ) at each sintering temperature is shown in FIG. Similarly, the graph showing the relationship between the Ga addition amount and the squareness ratio (Hk / HcJ) at each sintering temperature is shown in FIG.

  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, looking at FIG. 1 (c) and Table 3, when the Ga addition amount is less than 0.03% by mass, particularly when the sintering temperature is 1070 ° C., the squareness ratio (Hk / HcJ) is reduced. It shows a remarkable trend. When the sintering temperature range in which the squareness ratio (Hk / HcJ) of 90% or more is obtained is defined as the sintering temperature range, rare earth permanent magnets (No. 1 to No. 3) to which no Ga is added are sintered. The temperature range is 0. Similarly, when 0.03% by mass of Ga is added (No. 4 to No. 6), the sintering temperature width is zero.

  On the other hand, in the case of 0.08% by mass addition of Ga (No. 7 to No. 9) and 0.13% by mass addition of Ga (No. 10 to No. 12), the squareness ratio at 1030 ° C. and 1050 ° C. (Hk / HcJ) exceeds 90%, and the sintering temperature width is 20 ° C. Furthermore, in the rare earth permanent magnet (No. 13 to No. 18) to which Ga is added in an amount of 0.16 mass to 0.24 mass%, the squareness ratio (Hk / HcJ) exceeds 90% at all sintering temperatures. . That is, the sintering temperature range is further widened to 40 ° C.

  On the other hand, when 0.28% by mass of Ga is added (No. 19 to No. 21), the coercive force (HcJ) decreases as shown in Table 3 and FIG. Is recognized.

  When the oxygen amount exceeds 0.2 mass% (No. 22 to No. 24), the sintering temperature range is wide, but the coercive force (HcJ) is low.

  Furthermore, no. 1-No. 24 sintered bodies were cut, and the number of coarse particles of 50 μm or more and less than 100 μm and coarse particles of 100 μm or more present in an area having a cross section of 10 mm × 10 mm was examined using a scanning electron microscope (SEM). The results are also shown in Table 3. No decrease was observed in Br and HcJ, and in the sample having a squareness ratio of 90% or more, coarse particles of 50 μm or more were not present.

It is a graph showing the relationship between Ga addition amount and magnetic characteristics about the rare earth permanent magnet whose oxygen amount exists in the range of 0.03 mass%-0.2 mass%, (a) is Ga in each sintering temperature. A graph showing the relationship between the addition amount and the residual magnetic flux density (Br), (b) is a graph showing the relationship between the Ga addition amount and the coercive force (HcJ) at each sintering temperature, and (c) is each sintering. It is a graph showing the relationship between Ga addition amount in temperature, and squareness ratio (Hk / HcJ).

Claims (1)

R having hydrogen crushing step, crushing step, forming step in magnetic field, and firing step ₂ T ₁₄ A method for producing a rare earth permanent magnet mainly comprising B (R is one or more rare earth elements and T is Fe, or Co and Fe),
The molding step in the magnetic field is performed by dry molding,
The atmosphere of each step from the hydrogen pulverization step to the firing step is suppressed to a low oxygen concentration of less than 100 ppm,
R: 28 mass% to 33 mass%, Co: 0 to 2 mass% (however, 0 is not included), B: 0.5 mass% to 1.5 mass%, Cu: 0 to 0.15 mass% ( However, 0 is not included.), Al: 0.03% by mass to 0.25% by mass, Ga: 0.05% by mass to 0.15% by mass, O: 0.03% by mass to 0.1% by mass, C: 0.03% by mass to 0.1% by mass, N: 0.02% by mass to 0.05% by mass, Fe and inevitable impurities: having a composition composed of the remainder, and particles having a particle size of 50 μm or more do not exist A method for producing a rare earth permanent magnet, comprising obtaining a rare earth permanent magnet.

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