JP2006210376A - R-t-b-based sintered magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an R-T-B-based sintered magnet that obtains a high magnetization rate at a low magnetization magnetic field and has a fast rise in the magnetization rate until a magnetization rate of almost 100%, for example approximately 85%, is reached. <P>SOLUTION: The R-T-B-based sintered magnet is made of a sintered body having a main phase comprising R<SB>2</SB>T<SB>14</SB>B crystal grains (however, for example R is one type or at least two types of rare earth elements;T is one type or at least two types of transition metal elements with Fe or Fe and Co as requisites), the average grain diameter of the R<SB>2</SB>T<SB>14</SB>B crystal grains is 10 μm or smaller, and the presence ratio in the sintered body of the R<SB>2</SB>T<SB>14</SB>B crystal grains having a particle diameter of 15 μm or higher is 1-8%, and the amount of oxygen in the sintered body is 4,500-6,000 ppm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an R-T-B (wherein R is one or more rare earth elements, T is one or more transition metal elements in which Fe, Fe and Co are essential) based sintered magnets. In particular, the present invention relates to an RTB-based sintered magnet having high magnetization characteristics.

Among rare earth magnets, RTB-based sintered magnets are used in various electrical devices because they are excellent in magnetic properties and Nd as a main component is abundant and relatively inexpensive. .
Until now, research and development have been mainly conducted for improving the magnetic characteristics of the RTB-based sintered magnet, specifically, the residual magnetic flux density, the coercive force, or the maximum energy product. However, recently, research and development focusing on magnetizing characteristics have been carried out. The RTB-based sintered magnet requires a higher magnetizing magnetic field than the ferrite magnet. For example, when a ring-shaped RTB-based sintered magnet is used as a rotor of a motor, the ring-shaped RTB-based sintered magnet is incorporated after the RTB-based sintered magnet is incorporated into the motor. Magnetization may be performed using a motor coil wound around a magnet. When the motor is small, the coil wire diameter becomes thin to obtain a predetermined number of turns, and a large current cannot be passed. Therefore, sufficient attachment to the R-T-B system sintered magnet is possible. A magnetic field cannot be applied. Accordingly, the RTB-based sintered magnet used for the above-described applications is required to have as high a magnetization characteristic as possible with a low magnetization magnetic field.

For example, in Japanese Patent Laid-Open No. 2002-356701 (Patent Document 1), the average composition of the main phase is (LR _1-x HR _x ) ₂ T as an RTB-based sintered magnet having excellent magnetization characteristics. ₁₄ A (T is Fe or a mixture of Fe and at least one transition metal element other than Fe, A is boron or a mixture of boron and carbon, LR is at least one light rare earth element, and HR is heavy rare earth A rare earth alloy sintered body represented by at least one element, 0 <x <1, and having a composition represented by (LR _1-p HR _p ) ₂ T ₁₄ A (0 ≦ p <x) It includes crystal grains having a plurality of at least one of the first main phase and the second main phase having a composition represented by (LR _1-q HR _q ) ₂ T ₁₄ A (x <q ≦ 1). A rare earth alloy sintered body is disclosed.

Japanese Patent Laid-Open No. 2003-217918 (Patent Document 2) describes, for the purpose of improving the magnetizing characteristics, in weight%, R (R is at least one kind of rare earth element including Y, and Nd occupies R). Is 25-35%, B: 0.8-1.5%, M (Ti, Cr, Ga, Mn, Co, Ni, Cu, Zn, Nb, Al if necessary) At least one selected from the group consisting of 8% or less and the balance T (Fe or Fe and Co) and unavoidable impurities, and Fe phase having an Fe _A Co _1-A content of 80 at% or more is 0.01 to 300 μm. In a rare earth sintered magnet having a size and a crystal structure remaining in the sintered body, the magnetization rate Br (0.2 MA / m) / Br (2.0 MA / m) evaluated by the residual magnetic flux density is 59. % Or more, magnetization rate Φ (0.3M Discloses that /M)/fai(4.0MA/m) is 4% or more.

JP 2002-356701 A JP 2003-217918 A

According to the technique disclosed in Patent Document 1, the magnetization characteristics can be improved without deteriorating the magnetic characteristics. However, a magnetizing magnetic field of about 0.8 MA / m (10 kOe) is necessary to obtain a magnetizing ratio of about 50%, and it is desirable to obtain a magnetizing ratio of about 50% with a lower magnetizing field. In addition, the magnetization rate Br (0.2 MA / m) / Br (2.0 MA / m) evaluated by the residual magnetic flux density in Patent Document 2 is 59% or more, and the magnetization rate Φ (0.3 MA / m) evaluated by the flux. When the value of m) / Φ (4.0 MA / m) is 4% or more, it cannot be said that the magnetization characteristics are good.
On the other hand, according to the study by the present inventors, the R-T-B type sintered magnet that can obtain a higher magnetization rate with a low magnetic field has a gentle magnetization characteristic curve that represents the fluctuation of the magnetization rate due to the magnetization magnetic field. It tends to show an inclination. That is, since the magnetization characteristic curve is gentle, a larger magnetizing magnetic field is required to reach a magnetization rate near 100%.
The present invention has been made on the basis of such a technical problem, and obtains a higher magnetization rate with a low magnetization magnetic field, and further increases the magnetization rate until reaching a magnetization rate of around 100%, for example, about 85%. An object of the present invention is to provide an R-T-B based sintered magnet having a quick rise of.

For this purpose, the present inventor examined a magnet made of a sintered body having a main phase composed of R ₂ T ₁₄ B crystal grains, and found that a relatively coarse R ₂ T _{14 in the} sintered body. By allowing a predetermined amount of B crystal grains to be present, an RTB-based sintered magnet having high magnetization characteristics was obtained.
That is, the RTB-based sintered magnet of the present invention has R ₂ T ₁₄ B crystal grains (where R is one or more of rare earth elements, and T is one of the essential elements Fe, Fe and Co). Or a sintered body having a main phase composed of two or more transition metal elements, the same shall apply hereinafter), the R ₂ T ₁₄ B crystal grains have an average grain size of 10 μm or less and a grain size of 15 μm or more. The R ₂ T ₁₄ B crystal grains having an existing ratio in the sintered body is 1 to 8%, and the oxygen content of the sintered body is 4500 to 6000 ppm.

  The RTB-based sintered magnet of the present invention has a total flux of f1 when an effective magnetic field of 400 kA / m (where effective magnetic field = applied magnetic field-demagnetizing field) is applied at a Pc (permeance coefficient) of 2. When the total flux when an effective magnetic field of 600 kA / m is applied is f2, and the total flux when an effective magnetic field of 2000 kA / m is applied is f3, the magnetization rate a (= f1 / f3 × 100) is 35% or more. In addition, it is possible to obtain an excellent magnetization characteristic that the magnetization rate b (= f2 / f3 × 100) is 85% or more.

  Conventionally, an RTB-based sintered magnet has a low residual magnetic flux density when trying to obtain a high coercive force, and conversely, when an attempt is made to obtain a high residual magnetic flux density, the coercive force is low. It is known to be lower. For example, adjusting the amount of heavy rare earth elements (typically Dy and / or Tb) contained as rare earth elements, specifically increasing the amount of heavy rare earth elements to obtain a high coercive force, When obtaining the magnetic flux density, the desired characteristics were obtained by reducing the amount of heavy rare earth elements. And it was conceptually known that the RTB-based sintered magnet with a low coercive force has low magnetization characteristics. However, no effective means for improving the magnetization characteristics has been found so far.

However, according to the present invention, even in a low coercive force type R-T-B sintered magnet having a coercive force (HcJ) of 1600 kA / m (20 kOe) or less, it is possible to improve the magnetization characteristics in a low magnetization field. There is an advantage that you can. This RTB-based sintered magnet can ensure the characteristic that the residual magnetic flux density (Br) is 1.3 T or more.
In the RTB-based sintered magnet of the present invention, the amount of oxygen in the sintered body is in the range of 4500 to 6000 ppm contributes to the excellent magnetization characteristics described above. Furthermore, it is preferable for the present invention that Zr, Nb, and Hf are dispersed in the sintered body.

  As an RTB-based sintered magnet, R: 25 to 35 wt%, B: 0.5 to 4 wt%, one or two of Al and Cu are 0.02 to 0.6 wt%, Zr, Nb It is preferable that one or two or more of Hf has a composition of 0.02 to 1.5 wt%, Co: 0.5 to 5 wt% or less, and the balance substantially consisting of Fe. A composition containing 0.01 to 0.2 wt% of one or two of these is preferred.

The RTB-based sintered magnet according to the present invention may contain 0.5 to 12 wt% heavy rare earth element as R. The heavy rare earth element preferably contains Dy and / or Tb.
In addition, the RTB-based sintered magnet according to the present invention can be used for various types of magnets, but the effect can be remarkably exhibited when used for magnets that are multipolarly magnetized. .
In order for the RTB-based sintered magnet according to the present invention to have high magnetic properties, it is preferable to regulate the amount of nitrogen in the sintered body to 20 to 600 ppm and the amount of carbon to 1500 ppm or less.

  According to the present invention, the magnetization rate in a magnetization field as low as about 400 kA / m (5.1 kOe) is improved, and the magnetization rate in a magnetization field of 600 kA / m (7.6 kOe) or more is also improved. An RTB-based sintered magnet is provided. Such an RTB-based sintered magnet having excellent magnetization characteristics can reduce the width of the neutral zone when used in a multipolar magnetized magnet. A motor using such a ring magnet can maintain high rotational performance. In addition, a magnet with a high magnetization rate has a high cost and high magnetic properties as a material, but there are cases where a total flux actually generated is larger than a magnet with a low magnetization rate. Therefore, the present invention can realize a predetermined total flux with a low-cost magnet. Alternatively, the size of the magnet can be reduced.

Hereinafter, the RTB-based sintered magnet and the manufacturing method thereof according to the present invention will be described in detail.
<Sintered body structure>
As is well known, the RTB-based sintered magnet according to the present invention has R ₂ T ₁₄ B crystal grains (R is one or more rare earth elements, and T is Fe or Fe and Co. A main phase composed of one or more transition metal elements as a main component. In addition to this main phase, a grain boundary phase is included. This grain boundary phase has a larger R content than the main phase.
In addition, the RTB-based sintered magnet of the present invention has 1 to 8 R ₂ T ₁₄ B crystal grains (hereinafter sometimes simply referred to as crystal grains) having a grain size of 15 μm or more in the sintered body. % Is important. As will be described in a first example to be described later, the magnetization rate cannot be improved if the sintered body has less than 1% of crystal grains having a grain size of 15 μm or more. Further, when the crystal grains having a grain size of 15 μm or more exist in the sintered body in excess of 8%, a high magnetization can be obtained, but the coercive force is significantly lowered. Therefore, in the present invention, 1 to 8%, preferably 2 to 7%, more preferably 3 to 6% of crystal grains having a grain size of 15 μm or more are present.

In the present invention, the reason why excellent magnetization characteristics can be obtained by the presence of relatively coarse crystal grains having a grain size of 15 μm or more is not clear. However, it can be understood that such a coarse crystal grain is easier to rotate the magnetic domain, and the rotation of the magnetic domain of the coarse grain induces the rotation of the magnetic domain of the surrounding fine grains, so that the magnetization characteristics are improved.
This invention does not ask | require the method of obtaining the sintered compact in which the crystal grain which has a particle size of 15 micrometers or more exists 1-8%. It is possible to obtain a sintered body in which 1 to 8% of crystal grains having a particle size of 15 μm or more exist by manipulating the particle size distribution and sintering conditions of the finely pulverized powder subjected to molding in a magnetic field. is there.

In the RTB-based sintered magnet of the present invention, the average particle size of the R ₂ T ₁₄ B crystal grains is 10 μm or less. This is because when the average particle size exceeds 10 μm, the coercive force is significantly reduced. However, in the present invention, since crystal grains having a grain size of 15 μm or more are intentionally present, it is advantageous to set a larger average grain size within a range of 10 μm or less. Therefore, in this invention, it is preferable to make the average particle diameter of a crystal grain into the range of 6-9 micrometers.

<Magnetic properties>
In the present invention, when Pc (permeance coefficient) is 2, an effective magnetic field of 400 kA / m (however, effective magnetic field = applied magnetic field-demagnetizing field) is applied, the total flux is f1, and an effective magnetic field of 600 kA / m is applied. If the total flux when f2 and an effective magnetic field of 2000 kA / m are applied is f3, the magnetization a (= f1 / f3 × 100) is 35% or more and the magnetization b (= f2 / f) f3 × 100) is 85% or more. Further, the RTB-based sintered magnet of the present invention has a magnetization rate c (= f4 / f3 × 100) of 95% or more when the total flux when an effective magnetic field of 790 kA / m is applied is f4. The magnetization rate is extremely high. Note that Pc in the present invention is determined based on FIG. 5-4 on page 146 of “sintered magnet” by Yoshio Tsuji and Kenji Ohashi (Morikita Publishing). The magnetization rate was measured as follows. A magnet to be evaluated was sandwiched between pole pieces to form a closed magnetic circuit, and then an electric current was passed through the electromagnet for magnetization. In this case, the applied magnetic field = effective magnetic field. After magnetization, the total flux was measured with a flux meter.

  Here, regarding the magnetization characteristics, as described above, it is ideal that the magnetic field has a larger magnetization rate in a low magnetic field and that the magnetization rate rises steeply. However, conventionally, a low coercive force type R-T-B type sintered magnet having a coercive force (HcJ) of 1600 kA / m or less has not been easy to satisfy both. However, according to the present invention, the magnetization a (= f1 / f3 × 100) is 35% or more, the magnetization b (= f2 / f3 × 100) is 85% or more, and the magnetization c (= f4 / f3). The present invention provides an RTB-based sintered magnet having a high magnetization rate in an unprecedented low magnetic field of × 100) of 95% or more and a rapid rise in magnetization rate.

Next, a preferable chemical composition of the RTB-based sintered magnet of the present invention will be described. This chemical composition is that of the main phase and the whole grain boundary phase.
The RTB-based sintered magnet of the present invention preferably contains 25 to 35 wt% of R. When the amount of R is less than 25 wt%, the generation of R ₂ T ₁₄ B crystal grains that are the main phase of the R-T-B sintered magnet is not sufficient. For this reason, α-Fe or the like having soft magnetism is precipitated, and the coercive force is remarkably lowered. On the other hand, when the amount of R exceeds 35 wt%, the volume ratio of R ₂ T ₁₄ B crystal grains constituting the main phase is lowered, and the residual magnetic flux density is lowered. On the other hand, when the amount of R exceeds 35 wt%, R reacts with oxygen, and the amount of oxygen contained increases, and as a result, the R-rich phase effective for the generation of coercive force decreases and the coercive force decreases. Therefore, the amount of R is set to 25 to 35 wt%. A desirable amount of R is 26 to 33 wt%, and a more desirable amount of R is 27 to 32 wt%.

  When Dy and / or Tb is included as R, the sum of Dy and / or Tb and other R is set to 25 to 35 wt%. And in this range, it is preferable that the quantity of Dy and / or Tb shall be 0.1-8 wt%. The amount of Dy and / or Tb is desirably determined 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 amount of Dy and / or Tb is set to 0.1 to 3.5 wt%. When a high coercive force is desired to be obtained, the amount of Dy and / or Tb is set to 3.5. It is desirable to set it to -8 wt%.

  The RTB-based sintered magnet of the present invention contains 0.5 to 4 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. However, when B exceeds 4 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit is 4 wt%. A desirable amount of B is 0.5 to 1.5 wt%, and a more desirable amount of B is 0.8 to 1.2 wt%.

  The RTB-based sintered magnet of the present invention uses Co as an essential element, but the amount is preferably 0.5 to 5 wt%. Co is effective in improving the Curie temperature and the corrosion resistance. In order to obtain this effect, it is preferably 0.5 wt% or more. Moreover, it has the effect that the aging treatment temperature range from which a high coercive force is obtained is expanded by adding together with Cu. However, excessive addition causes a decrease in coercive force and increases the cost, so the upper limit is made 5 wt%. The desirable Co content is 0.5-3 wt%, and the more desirable Co content is 0.8-2.5 wt%.

  The RTB-based sintered magnet of the present invention can contain one or two of Al and Cu in the range of 0.02 to 0.6 wt%. By including one or two of Al and Cu in this range, it is possible to increase the coercive force, increase the corrosion resistance, and improve the temperature characteristics of the obtained RTB-based sintered magnet. In the case of adding Al, a desirable amount of Al is 0.03 to 0.3 wt%, and a more desirable amount of Al is 0.05 to 0.25 wt%. When Cu is added, the amount of Cu is 0.3 wt% or less (excluding 0), desirably 0.2 wt% or less (excluding 0), and the more desirable amount of Cu is 0 0.03 to 0.15 wt%. One or two kinds of Al and Cu do not adversely affect the effect of the present invention even if they are contained in either the main phase or the grain boundary phase.

  The RTB-based sintered magnet of the present invention can contain 0.02 to 1.5 wt% of one or more of Zr, Nb, and Hf. When reducing the oxygen content in order to improve the magnetic properties of the RTB-based sintered magnet, Zr, Nb and Hf exhibit the effect of suppressing abnormal growth of crystal grains during the sintering process, Make the structure of the sintered body uniform and fine. Therefore, Zr, Nb, and Hf have a remarkable effect when the amount of oxygen is low. A desirable amount of one or more of Zr, Nb and Hf is 0.05 to 1.3 wt%, and a more desirable amount is 0.08 to 1.0 wt%.

  The RTB-based sintered magnet of the present invention allows the inclusion of other elements. For example, it is effective to contain one or two of Bi and Ga in order to improve the coercive force. One or two of Bi and Ga are preferably contained in the range of 0.01 to 0.2 wt%. A more preferable range of one or two of Bi and Ga is 0.03 to 0.15 wt%, and a more preferable range is 0.05 to 0.12 wt%. Even if Bi and Ga are contained in either the main phase or the grain boundary phase, they do not adversely affect the effects of the present invention.

  The RTB-based sintered magnet of the present invention preferably has an oxygen content of 4500 to 6000 ppm. When the amount of oxygen is large, the oxide phase, which is a nonmagnetic component, increases and the magnetic properties are deteriorated. On the other hand, when the amount of oxygen is lowered, the amount of the oxide phase having the function of suppressing the growth of crystal grains during the sintering process is reduced. As described above, the present invention expects the effect of improving the magnetization characteristics by generating relatively coarse crystal grains, and the amount of oxygen contained in the sintered body in consideration of the increase in the oxide phase. Is 4500 to 6000 ppm.

<Multipolar magnetized magnet>
The present invention is preferably applied to a magnet subjected to multipolar magnetization.
The magnets magnetized with multiple poles include radial or polar anisotropic ring magnets used for motors, rectangular parallelepiped magnets used for driving pickups of devices such as CDs and DVDs, and VCM (Voice Coil Motors). ) Fan-shaped magnet. These multipolar magnets have a plurality of N · S polarities.
When the RTB-based sintered magnet of the present invention is applied to the above multipolar magnetized magnet, the width of the neutral zone can be reduced. Therefore, the total flux amount is increased. For example, if used for a motor, the characteristics of the motor can be improved. Here, the neutral zone refers to a region that is not magnetized by either N or S at the boundary where the polarity (N · S) is reversed when the magnet is magnetized. In particular, in a small-sized magnet or a magnet having a large number of poles, the ratio of the neutral zone increases. Therefore, the width of the neutral zone can be narrowed by using the R-T-B sintered magnet having excellent magnetization characteristics according to the present invention for multipolar magnetization, and thus the characteristics of the motor in which the magnet is used can be reduced. Can be improved.

<Manufacturing method>
Next, the suitable manufacturing method of the RTB system sintered magnet by this invention is demonstrated.
In this embodiment mode, a method of manufacturing using a single raw material alloy is described. However, the RTB-based sintered magnet according to the present invention can be manufactured by a mixing method using an alloy mainly composed of R ₂ T ₁₄ B crystal grains and an alloy containing more R than this alloy. Needless to say.

First, a raw material alloy having a predetermined composition is obtained by strip casting in a vacuum or an inert gas, preferably in an Ar atmosphere.
After the raw material alloy is produced, the raw material alloy is pulverized. The pulverization process includes a coarse pulverization process and a fine pulverization process. First, the raw material alloys are coarsely pulverized until each particle size becomes about several hundred μm. The coarse pulverization is preferably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill or the like. In order to improve the coarse pulverization property, it is effective to perform coarse pulverization after occlusion of hydrogen. Moreover, hydrogen occlusion itself can also be positioned as coarse pulverization.
After the coarse pulverization process, the process proceeds to the fine pulverization process. For pulverization, a jet mill is mainly used. 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. By adding about 0.01 to 0.3 wt% of a grinding aid such as zinc stearate at the time of fine grinding, a fine powder with high orientation can be obtained at the time of molding.

Next, the fine powder is molded in a magnetic field with its crystal axis oriented by applying a magnetic field. The forming in the magnetic field may be performed at a pressure of about 0.3 to 3.0 ton / cm ² (30 to 300 MPa) in a magnetic field of about 12 to 20 kOe (960 to 1600 kA / m). The applied magnetic field may be a pulsed magnetic field in addition to the static magnetic field.

  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 1000-1100 degreeC for about 1 to 5 hours. You may perform the process which removes the grinding | pulverization adjuvant, gas, etc. which are contained in the molded object before a sintering process. After sintering, the obtained sintered body can be subjected to an aging treatment. This process is an important process for controlling the coercive force. In the case where the aging treatment is performed in two stages, holding for a predetermined time at around 800 ° C. and around 500 ° C. is effective. When the heat treatment at around 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 the heat treatment at around 500 ° C., when the aging treatment is performed in one stage, the aging treatment at around 500 ° C. is preferably performed.

Hereinafter, the present invention will be described based on specific examples.
<First embodiment>
Raw material alloys having the composition (wt%) shown in Table 1 were produced by the strip casting method.
The obtained raw material alloy was occluded with hydrogen at room temperature and then subjected to hydrogen pulverization treatment in which dehydrogenation was performed at 600 ° C. for 1 hour in an Ar atmosphere.
In order to obtain high magnetic properties, oxygen in each step from hydrogen crushing (recovered after crushing) to sintering (put into the sintering furnace) is controlled in this experiment to control the oxygen content of the sintered body to 4500-6000 ppm. The concentration is controlled in the range of 200 to 500 ppm.

  0.1% of stearic acid was added as a grinding aid to the hydrogen-pulverized alloy and finely pulverized with a jet mill to obtain five types of fine powders. The five fine powders were obtained by changing the pulverization time by a jet mill.

The obtained fine powder was subjected to pressure molding in a magnetic field of 1320 kA / m (16.5 kOe) to obtain a molded body. The density of the molded body is 4.2 Mg / m ³ .
The obtained molded body was sintered in vacuum at 1040 ° C. for 4 hours and then rapidly cooled. Next, the obtained sintered body was subjected to a two-stage aging treatment of 800 ° C. × 1 hour and 530 ° C. × 2.5 hours (both in an Ar atmosphere).

  The magnetic properties of the obtained RTB-based sintered magnet were measured with a BH tracer, and the average crystal grain size of the sintered body, the ratio of crystal grains having a grain size of 15 μm or more, density, oxygen content, The amount of nitrogen and the amount of carbon were measured. The results are shown in Table 2. In Table 2, d is the average crystal grain size of the sintered body, A1 is the ratio of crystal grains having a grain size of 15 μm or larger (rough grain ratio), ρ is the density of the sintered body, Br is the residual magnetic flux density, and HcJ is the retention rate. Showing magnetic force. The average crystal grain size d of the sintered body was determined by observing the polished surface of the sintered body with a simple polarizing microscope (BX60M manufactured by Olympus Optical Co., Ltd.), and using the image processing apparatus (IP-1000 manufactured by Asahi Kasei Kogyo Co., Ltd.). ). Since the area of each crystal grain is obtained by this evaluation, it is converted to the equivalent circle diameter to obtain the crystal grain size. The particle size of 15 μm, which is a reference for obtaining the coarse particle ratio A1, is obtained by determining the area ratio of coarse particles having a major axis of 15 μm or more from a fractured surface photograph of a sintered body structure of 480 μm × 540 μm observed with a simple polarizing microscope. A value obtained by averaging the area ratio of coarse particles in the visual field was used.

As shown in Table 2, sample no. It can be seen that all the R-T-B sintered magnets except 5 have a residual magnetic flux density (Br) of 1.3 T or more and a coercive force (HcJ) of 1300 kA / m or more.
Further, it can be seen that the oxygen content of the R-T-B system sintered magnet is in the range of 5300-5700 ppm, the nitrogen content is 100 ppm or less, the carbon content is 800 ppm or less, and the nitrogen content and the carbon content are low.

  Next, sample No. The magnetizability (Pc = 2) was measured for 1 to 5 RTB-based sintered magnets. The results are shown in Table 3. As shown in Table 3, the RTB-based sintered magnet of Sample 1 having the smallest coarse grain ratio A1 of 0.83% can obtain only a magnetization rate of less than 35% with a magnetizing magnetic field of 400 kA / m. I understand that there is no. On the other hand, it can be seen that when the coarse grain ratio A1 increases, the magnetization rate improves. However, as shown in Table 2, when the coarse particle ratio A1 reaches 8.66%, the decrease in coercive force (HcJ) cannot be ignored.

  From the above, by setting the coarse grain ratio A1 (abundance ratio of crystal grains of 15 μm or more) of the sintered body to 1 to 8%, it is possible to obtain a magnetization rate of 35% or more with a low magnetization field of 400 kA / m. In addition, it is possible to obtain a magnetization rate of 85% or more with a magnetizing magnetic field of 600 kA / m, and more than 95% with a magnetizing magnetic field of 790 kA / m. As described above, the RTB-based sintered magnet according to the present invention has a rapid rise in magnetization rate.

<Second embodiment>
Four types were performed in the same manner as in the first example except that the oxygen content of the final sintered body was varied by controlling the oxygen content of the pulverized gas (nitrogen) in the jet mill when producing the fine powder. R-T-B rare earth permanent magnets (Sample Nos. 6 to 9) were obtained. About the obtained RTB-based sintered magnet, the magnetic properties and the like were measured in the same manner as in the first example. The results are shown in Table 4. The symbols in Table 4 are the same as those in Table 2.
As shown in Table 4, it can be seen that the lower the amount of oxygen (O ₂ ), the larger the average crystal grain size d and coarse grain ratio A1 of the sintered body. When the coarse particle ratio A1 is thus large, as shown in the first embodiment, an improvement in the magnetization rate cannot be expected. Further, when the oxygen amount exceeds the range of the present invention, both the residual magnetic flux density (Br) and the coercive force (HcJ) are lowered. From the above, in the present invention, the amount of oxygen is set to 4500 to 6000 ppm.

  Next, the magnetization rate (Pc = 0.5, 1.0, 2.0) was measured for the above sintered body. The results are shown in Table 5. The magnetization rate tends to decrease as Pc decreases. In a magnetized magnetic field of 400 kA / m, the magnetization rate of Pc = 0.5 is 29% or more, and the magnetization rate of Pc = 1.0 is 35% or more, indicating a high magnetization rate in a low magnetic field. Further, it can be seen that in a magnetization field of 790 kA / m, the magnetization rate of Pc = 0.5 is 85% or more, and the magnetization rate of Pc = 1.0 is 95% or more.

Claims (5)

R ₂ T ₁₄ B crystal grains (wherein R is one or more rare earth elements, T is one or more transition metal elements essential for Fe, Fe and Co, and the same shall apply hereinafter). It consists of a sintered body with a main phase,
The R ₂ T ₁₄ B crystal grains have an average grain size of 10 μm or less, and the abundance ratio of the R ₂ T ₁₄ B crystal grains having a grain size of 15 μm or more in the sintered body is 1 to 8%;
An RTB-based sintered magnet, wherein the sintered body has an oxygen content of 4500 to 6000 ppm.   When Pc (permeance coefficient) is 2, the total flux when an effective magnetic field of 400 kA / m (however, effective magnetic field = applied magnetic field−demagnetizing field) is applied is f1, and the total flux when an effective magnetic field of 600 kA / m is applied F2 and a total flux when an effective magnetic field of 2000 kA / m is applied is f3, the magnetization a (= f1 / f3 × 100) is 35% or more and the magnetization b (= f2 / f3 × 100) The RTB-based sintered magnet according to claim 1, wherein the ratio is 85% or more. _{3. The} RTB-based sintered magnet according to claim 1, wherein an average particle diameter of the R ₂ T ₁₄ B crystal grains is 6 to 9 μm.   The sintered body is R: 25 to 35 wt%, B: 0.5 to 4 wt%, one or two of Al and Cu, 0.02 to 0.6 wt%, one of Zr, Nb and Hf, or The R according to any one of claims 1 to 3, which has a composition of 0.02 to 1.5 wt%, Co: 0.5 to 5 wt% or less, and the balance substantially consisting of Fe. -TB sintered magnet.   The sintered body is R: 25 to 35 wt%, B: 0.5 to 4 wt%, one or two of Al and Cu, 0.02 to 0.6 wt%, one of Zr, Nb and Hf, or Two or more kinds are composed of 0.02 to 1.5 wt%, one or two kinds of Bi and Ga are 0.01 to 0.2 wt%, Co: 0.5 to 5 wt% or less, and the balance is substantially composed of Fe. The RTB-based sintered magnet according to any one of claims 1 to 3, wherein: