JP6798546B2 - Manufacturing method of RTB-based sintered magnet - Google Patents

Description

The present disclosure relates to a method for manufacturing an RTB-based sintered magnet.

R-TB based sintered magnets (R is at least one of rare earth elements and contains at least one of Nd and Pr, T is at least one of transition metal elements and always contains Fe) are R ₂ It is composed of a main phase composed of a compound having a T ₁₄ B type crystal structure and a grain boundary phase located at the grain boundary portion of this main phase, and is known as the highest performance magnet among permanent magnets. ..

Therefore, it is used in a wide variety of applications such as various motors such as voice coil motors (VCM) for hard disk drives, motors for electric vehicles (EV, HV, PHV), motors for industrial equipment, and home appliances.

As the applications are expanded in this way, for example, motors for electric vehicles may be exposed to high temperatures such as 100 ° C. to 160 ° C., and stable operation is required even at high temperatures.

However, the conventional _RTB -based sintered magnet has a _problem that the coercive force H _cJ (hereinafter, may be simply referred to as "H _cJ ") decreases at a high temperature and irreversible thermal demagnetization occurs. is there. When an _RTB -based sintered magnet is used in a motor for an electric vehicle, _HcJ may decrease due to use at a high temperature, and stable operation of the motor may not be obtained. Therefore, there is a _demand for _RTB -based sintered magnets having high H _cJ at room temperature and high H _cJ even at high temperatures.

Conventionally, a heavy rare earth element RH (mainly Dy) has been added to an RTB-based sintered magnet in order to improve _HcJ at room temperature, but the residual magnetic flux density _Br (hereinafter, simply referred to as “ _Br ”). There was a problem that (may be described) decreased. Further, Dy has a problem that the supply is unstable and the price may fluctuate greatly because the production area is limited. Therefore, there is a demand for a technique for improving _HcJ of _RTB -based sintered magnets without using heavy rare earth elements RH such as Dy as _much as possible.

As such a technique, for example, Patent Document 1 contains a metal element M which is one or more selected from Al, Ga and Cu while lowering the amount of B as compared with a normal RTB-based alloy. By allowing the R ₂ T ₁₇ phase to be generated, and by ensuring a sufficient volume ratio of the transition metal rich phase (RT-Ga phase) generated from the R ₂ T ₁₇ phase as a raw material, the content of Dy is contained. It is disclosed that an RTB-based sintered magnet having a high coercive force can be obtained while suppressing the amount.

International Publication No. 2013/0087756

However, although the _RTB -based sintered magnet described in Patent Document 1 has improved _HcJ , it is insufficient to satisfy recent demands.

Therefore, it is an object of the present invention to provide a method for manufacturing an _RTB -based sintered magnet having a high coercive force _HcJ .

Aspect 1 of the present invention is R: 28.5 to 33.0% by mass (R is at least one of rare earth elements and includes at least one of Nd and Pr), B: 0.850 to 0. It contains 910% by mass, Ga: 0.2 to 0.7% by mass, Cu: 0.05 to 0.50% by mass, Al: 0.05 to 0.50% by mass, and the balance is T (T is Fe and Co, and 90% by mass or more of T is Fe) and unavoidable impurities, which is a method for producing an RTB-based sintered magnet satisfying the following formula (1).

14 [B] /10.8 <[T] /55.85 (1)
([B] is the content of B indicated by mass%, and [T] is the content of T indicated by mass%)

A step of preparing an alloy powder in which the particle diameter D ₅₀ and the particle diameter D ₉₉ satisfy the following formulas (2) and (3), a molding step of molding the alloy powder to obtain a molded body, and firing of the molded body. This is a method for manufacturing an RTB-based sintered magnet, which includes a sintering step of connecting to obtain a sintered body and a heat treatment step of applying a heat treatment to the sintered body.

3.8 μm ≤ D ₅₀ ≤ 5.5 μm (2)
D ₉₉ ≤ 10 μm (3)

Aspect 2 of the present invention is the method for manufacturing an RTB-based sintered magnet according to the first aspect, wherein B in the RTB-based sintered magnet is 0.870 to 0.910% by mass. is there

Aspect 3 of the present invention is the production of the RTB-based sintered magnet according to aspect 1 or 2, wherein the particle diameters D ₅₀ and D ₉₉ further satisfy the following formulas (4) and (5). The method.
3.8 μm ≤ D ₅₀ ≤ 4.5 μm (4)
D ₉₉ ≤ 9 μm (5)

According to the embodiment of the present invention, it is possible to provide a method capable of producing an _RTB -based sintered magnet having a high coercive force _HcJ .

FIG. 1 is a diagram showing the relationship between the improvement width ΔH _cJ of the coercive force and the amount of B in the embodiment.

The embodiments shown below exemplify a method for manufacturing an RTB-based sintered magnet for embodying the technical idea of the present invention, and the present invention is not limited to the following.

As a result of diligent studies, the present inventors have classified the RTB-based sintered magnets having a specific composition range as described in the embodiment of the present invention, particularly a very narrow specific range of B content. By adjusting the particle size distribution of the alloy powder by removing the fine powder having a relatively large particle size using a machine or the like, the _HcJ of the _RTB -based sintered magnet finally obtained can be significantly increased. I found that I could rise.

Even in the production of conventional RTB-based sintered magnets, it has been practiced to remove fine powder having a relatively large particle size. However, as shown in Examples described later, the improvement _range of _HcJ of the _RTB -based sintered magnet finally obtained is small outside the specific composition range of the present invention. Further, in order to remove the fine powder having a relatively large particle size, the crushing time must be lengthened, and the crushing efficiency is lowered, resulting in deterioration of mass production efficiency. That is, in the past, the improvement _range of H _cJ was too small to cause deterioration of mass production efficiency, so that it was not positively performed in actual mass production.

However, as will be described later, the present inventors have an RTB-based sintered magnet having a specific composition range (particularly, a B content of 0.850 to 0.910% by mass) according to an embodiment of the present invention. The average particle size D ₅₀ is 3.8 μm or more and 5.5 μm or less, and D ₉₉ is 10 μm or less (preferably, the average particle size D ₅₀ is 3.8 μm or more and 4.5 μm or less, and D ₉₉ is 9 μm or less. ), And the RTB-based sintered magnet obtained by molding, sintering, and heat-treating such alloy powder has mass production efficiency due to a long crushing time. It was found that the _HcJ is significantly improved so that it can be positively carried out even if it causes the deterioration of the above, and the present invention has been reached.
The manufacturing method according to the embodiment of the present invention will be described in detail below.

[RTB-based sintered magnet]
First, the RTB-based sintered magnet obtained by the manufacturing method according to the embodiment of the present invention will be described.

[Composition of RTB-based sintered magnet]
The composition of the RTB-based sintered magnet according to this embodiment is
R: 28.5 to 33.0% by mass (R is at least one rare earth element and contains at least one of Nd and Pr),
B: 0.850 to 0.910% by mass,
Ga: 0.2 to 0.7% by mass,
Cu: 0.05 to 0.50% by mass,
Al: contains 0.05 to 0.50% by mass,
The balance is T (T is Fe and Co, and 90% by mass or more of T is Fe) and unavoidable impurities, satisfying the following formula (1).

14 [B] /10.8 <[T] /55.85 (1)
([B] is the content of B represented by mass%, and [T] is the content of T represented by mass%.)

With the above composition, the amount of B is smaller than that of a general RT-B-based sintered magnet, and Ga and the like are contained, so that an RT-Ga phase is generated at the two-particle boundary. High H _cJ can be obtained. Here, the RT-Ga phase is typically an Nd ₆ Fe ₁₃ Ga compound. The R ₆ T ₁₃ Ga compound has a La ₆ Co ₁₁ Ga type ₃ crystal structure. Further, the R ₆ T ₁₃ Ga compound may be an R ₆ T _13-δ Ga _{1 + δ} compound (δ is typically 2 or less) depending on the state. For example, when the R-TB-based sintered magnet contains a relatively large amount of Cu and Al, it may be R ₆ T _13-δ (Ga _1-xy Cu _x Al _y ) _{1 + δ.} is there.
Each composition will be described in detail below.

(R: 28.5 to 33.0% by mass)
R is at least one of the rare earth elements and contains at least one of Nd and Pr. The content of R is 28.5 to 33.0% by mass. R is may become difficult to densification during sintering is less than 28.5% by mass may main phase proportion exceeds 33.0% by weight can not be obtained a high B _r drops .. The content of R is preferably 29.5 to 32.5% by mass. If R is in such a range, a higher _Br can be obtained.

(B: 0.850 to 0.910% by mass)
The content of B is 0.850 to 0.910% by mass. In the embodiment of the present invention, particularly when the content of B is in such a narrow range, the particle sizes D ₅₀ and D ₉₉ of the alloy powder are predetermined as defined in the embodiment of the present invention in the step of obtaining the alloy powder described later. By managing the range so as to be within the range, the _HcJ of the finally obtained _RTB -based sintered magnet can be significantly improved. If the content of B is less than 0.850% by mass and exceeds 0.910% by mass, a high _HcJ improving effect cannot be obtained. Preferably, the content of B is 0.870 to 0.910% by mass. A higher H _cJ improving effect can be obtained.

Further, the content of B satisfies the following formula (1).

14 [B] /10.8 <[T] /55.85 (1)

By satisfying the formula (1), the content of B becomes smaller than that of a general RTB-based sintered magnet. Typical R-T-B based sintered magnet, the main phase _R 2 _{T 14} in addition to B phase as _R 2 _{T 17} phase is not generated corresponding to the soft magnetic phase, [T] /55.85 ( The atomic weight of Fe) is less than 14 [B] / 10.8 (atomic weight of B) ([T] is the content of T in mass%). The RTB-based sintered magnet of the embodiment of the present invention is different from a general RTB-based sintered magnet, and [T] /55.85 is higher than 14 [B] /10.8. It is specified by the formula (1) so that the number increases. Since the main component of T in the RTB-based sintered magnet of the embodiment of the present invention is Fe, the atomic weight of Fe was used.

(Ga: 0.2 to 0.7% by mass)
The content of Ga is 0.2 to 0.7% by mass. If Ga is less than 0.2% by mass, the amount of R-T-Ga phase produced is too small, and the R ₂ T ₁₇ phase cannot be eliminated, and a high H _cJ may not be obtained. It will be present unnecessary Ga exceeds 0.7 weight%, there is a possibility that B _r decreases to decrease the main phase proportion.

(Cu: 0.05 to 0.50% by mass)
The content of Cu is 0.05 to 0.50% by mass. If Cu is less than 0.05% by mass, high H _cJ may not be obtained, and if it exceeds 0.50% by mass, sinterability may deteriorate and high H _cJ may not be obtained.

(Al: 0.05 to 0.50% by mass)
The Al content is 0.05 to 0.50% by mass. _HcJ can be improved by containing Al. Al is usually contained in an amount of 0.05% by mass or more as an unavoidable impurity in the manufacturing process, but even if it is contained in an amount of 0.5% by mass or less in total of the amount contained in the unavoidable impurity and the amount intentionally added. Good.

(Remaining: T and unavoidable impurities)
The rest are T and unavoidable impurities. Here, T is Fe and Co, and 90% by mass or more of T is Fe. Corrosion resistance can be improved by containing Co, but if the substitution amount of Co exceeds 10% by mass of Fe, high _Br may not be obtained.
Further, the RTB-based sintered magnet according to the embodiment of the present invention has Cr, Mn, Si, La, Ce as unavoidable impurities usually contained in didymium alloy (Nd-Pr), electrolytic iron, ferrobolon and the like. , Sm, Ca, Mg and the like can be contained. Further, O (oxygen), N (nitrogen), C (carbon) and the like can be exemplified as unavoidable impurities in the manufacturing process. Further, a small amount (about 0.1% by mass) of V, Ni, Mo, Hf, Ta, W, Nb, Zr and the like may be contained.

The details of the method for manufacturing the RTB-based sintered magnet according to the embodiment of the present invention will be described below.

[Manufacturing method of RTB-based sintered magnet]
A method for manufacturing an RTB-based sintered magnet having the above-mentioned composition will be described. The method for producing an RTB-based sintered magnet includes a step of obtaining an alloy powder, a molding step, a sintering step, and a heat treatment step.
Hereinafter, each step will be described.

(1) Step of obtaining alloy powder In this step, it has the same composition as the above-mentioned RTB-based sintered magnet, the particle size D ₅₀ is 3.8 μm or more and 5.5 μm or less, and the particle size D An alloy powder having ₉₉ of 10 μm or less is obtained. By using an alloy powder adjusted so that the particle sizes D ₅₀ and D ₉₉ are in such a range and the composition of the RTB-based sintered magnet according to the present embodiment is obtained, it is finally obtained. The _RTB -based sintered magnet to be used can have a high coercive force _HcJ .

Such an alloy powder can be obtained, for example, as follows.
A metal or alloy (dissolved raw material) of each element is prepared so as to have the composition of the RTB-based sintered magnet described above, and a flake-shaped raw material alloy is produced by a strip casting method or the like. Next, an alloy powder is produced from the flake-shaped raw material alloy. The obtained flake-shaped raw material alloy is hydrogen-pulverized to obtain, for example, a coarsely pulverized powder of 1.0 mm or less. Next, the coarsely pulverized powder is finely pulverized in an inert gas by a jet mill or the like, and the finely pulverized powder having a large particle size is removed by using a classifier, and the particle size D ₅₀ is 3.8 μm or more and 5.5 μm or less. A finely pulverized powder (alloy powder) having a particle size D ₉₉ of 10 μm or less is obtained. By producing an RT-B-based sintered magnet having the above-mentioned composition using an alloy powder having such a particle size distribution, an RT-B-based sintered magnet having a high coercive force _HcJ can be obtained. be able to. It is more preferable that the alloy powder has a particle size D ₅₀ of 3.8 μm or more and 4.5 μm or less and a D ₉₉ of 9 μm or less. _Within such a range, the _HcJ of the finally obtained _RTB -based sintered magnet can be further improved.

As the alloy powder, one kind of alloy powder (single alloy powder) may be used, or an alloy powder (mixed alloy powder) may be obtained by mixing two or more kinds of alloy powders, or a so-called two-alloy method may be used. Often, an alloy powder may be prepared using a known method or the like so as to have the composition of the embodiment of the present invention. A known lubricant may be added as an auxiliary agent to the coarsely pulverized powder before jet mill pulverization, and the alloy powder during and after jet mill pulverization.

As described above, the alloy powder according to this embodiment has particle sizes D ₅₀ and D ₉₉ in a specific range, but the particle sizes D ₅₀ and D ₉₉ are determined by the air flow dispersion laser diffraction method (JIS Z 8825: 2013). It can be measured by (according to the revised version). That is, in the present specification, D ₅₀ means a particle size (median diameter) at which the integrated particle size distribution (volume basis) from the small particle size side is 50%, and D ₉₉ means an integrated particle size distribution from the small particle size side. It means a particle size having a particle size distribution (volume basis) of 99%.
Note that D ₅₀ and D ₉₉ in the embodiment of the present invention have a dispersion pressure of 4 bar in the particle size distribution measuring device "HELOS &RODOS" manufactured by Symboltec.
Measurement range: R2
Calculation mode: HRLD
It shows D ₅₀ and D ₉₉ measured under the condition of.

(2) Molding step Molding is performed in a magnetic field using the obtained alloy powder to obtain a molded product. Molding in a magnetic field is a dry molding method in which a dry alloy powder is inserted into a cavity of a mold and molded while applying a magnetic field, and a slurry in which the alloy powder is dispersed is injected into the cavity of the mold. Any known in-magnetic field molding method may be used, including a wet molding method of molding while discharging the dispersion medium of the slurry.

(3) Sintering step A sintered body (sintered magnet) is obtained by sintering the molded body. A known method can be used for sintering the molded product. In addition, in order to prevent oxidation due to the atmosphere at the time of sintering, it is preferable to perform sintering in a vacuum atmosphere or an atmospheric gas. As the atmospheric gas, it is preferable to use an inert gas such as helium or argon.

(4) Heat Treatment Step It is preferable to heat-treat the obtained sintered magnet for the purpose of improving the magnetic characteristics. Known conditions can be used for the heat treatment temperature, heat treatment time, and the like. For example, heat treatment (one-step heat treatment) may be performed only at a relatively low temperature (400 ° C. or higher and 600 ° C. or lower), or heat treatment may be performed at a relatively high temperature (700 ° C. or higher and sintering temperature or lower (for example, 1050 ° C. or lower)). After that, heat treatment (two-stage heat treatment) may be performed at a relatively low temperature (400 ° C. or higher and 600 ° C. or lower). Preferred conditions are heat treatment at 730 ° C. or higher and 1020 ° C. or lower for about 5 to 500 minutes, after cooling (after cooling to room temperature or cooling to 440 ° C. or higher and 550 ° C. or lower), and further at 440 ° C. or higher and 550 ° C. or lower. Heat treatment may be performed for about 1 to 500 minutes. The heat treatment atmosphere is preferably a vacuum atmosphere or an inert gas (helium, argon, etc.).

The obtained sintered magnet may be machined by grinding or the like for the purpose of forming the final product shape. In that case, the heat treatment may be performed before or after machining. Further, the obtained sintered magnet may be surface-treated. The surface treatment may be a known surface treatment, and for example, surface treatment such as Al vapor deposition, nickel plating, or resin coating can be performed.

The present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

・ Example 1
Sample No. in Table 1 Each element was weighed so as to have the composition of the RTB-based sintered magnet shown in 1-27, and an alloy was prepared by a strip casting method. Each of the obtained alloys was coarsely pulverized by a hydrogen pulverization method to obtain a coarsely pulverized powder. The coarsely pulverized powder was finely pulverized by a jet mill under any of the conditions A to C described below (however, only sample No. 13 was pulverized under condition C).

(Condition A)
Under condition A, the amount of raw material supplied to the jet mill was 200 g / min, and the number of revolutions of the classification rotor was 4500 rpm for fine pulverization. The crushing time was about 10 minutes. Condition A is a normal pulverization condition, and the target values are particle size D ₅₀ : 4 μm and particle size D ₉₉ : 12 μm. The D ₅₀ and the D ₉₉ have a particle size and a small particle size distribution in which the integrated particle size distribution (volume basis) from the small particle size side is 50% in the particle size distribution obtained by the laser diffraction method by the air flow dispersion method, respectively. The particle size is such that the integrated particle size distribution (volume basis) from the diameter side is 99%. Further, D ₅₀ and D ₉₉ were measured by using a particle size distribution measuring device “HELOS & RODOS” manufactured by Symbolec under the conditions of dispersion pressure: 4 bar, measurement range: R2, and calculation mode: HRLD.

(Condition B)
In condition B, the amount of raw material supplied to the jet mill was set to 50 g / min, the classifying rotor rotation speed was set to 5500 rpm, and fine pulverization was performed. The crushing time was about 40 minutes. Condition B is performed to obtain the particle size (D ₅₀ and D ₉₉ ) of the embodiment of the present invention, and the target values are the particle size D ₅₀ : 4 μm and the particle size D ₉₉ : 9.5 μm. Under condition C, the amount of raw material supplied to the jet mill was 50 g / min, and the number of revolutions of the classification rotor was 6000 rpm for fine pulverization. The crushing time was about 40 minutes.

(Condition C)
Condition C is performed in order to obtain preferable particle sizes (D ₅₀ and D ₉₉ ) of the embodiment of the present invention, and the target values are particle size D ₅₀ : 4 μm and particle size D ₉₉ : 8.5 μm.

Tables 2 and 3 show the measured values of the particle sizes (D ₅₀ and D ₉₉ ) of the finely pulverized powder obtained by pulverizing under each condition. In "Condition A" in Table 2, the sample No. The measured values of the particle diameters of the finely pulverized powder obtained by finely pulverizing 1 to 27 under the condition A are shown. “Condition B” in Table 2 shows the sample No. The measured values of the particle diameters of the finely pulverized powder obtained by finely pulverizing 1 to 27 under the condition B are shown. “Condition A” in Table 3 shows the sample No. The actually measured value of the particle diameter obtained by finely pulverizing No. 13 under the condition A is shown. “Condition C” in Table 3 shows the sample No. The actually measured value of the particle diameter obtained by finely pulverizing No. 13 under the condition C is shown.

To the obtained finely pulverized powder (alloy powder), 0.05 part by mass of zinc stearate was added as a lubricant to 100 parts by mass of the finely pulverized powder, mixed, and then molded in a magnetic field to obtain a molded product. .. As the molding apparatus, a so-called right-angle magnetic field forming apparatus (transverse magnetic field forming apparatus) in which the magnetic field application direction and the pressurizing direction are orthogonal to each other was used. The obtained molded product was sintered in vacuum at 1030 to 1070 ° C. for 4 hours to obtain an RTB-based sintered magnet. The density of the sintered magnet was 7.5 Mg / m ³ or more. Further, the sintered RTB-based sintered magnet was subjected to a heat treatment of holding at 800 ° C. for 2 hours and then rapidly cooling to room temperature, then holding at 500 ° C. for 2 hours and then cooling to room temperature.

In order to determine the components of the obtained sintered magnet, the contents of Nd, Pr, Tb, B, Co, Al, Cu, Ga, Nb, Zr and Fe were measured by ICP emission spectroscopy. Furthermore, O (oxygen amount) was measured using a gas melting-infrared absorption method, N (nitrogen amount) was measured using a gas melting-heat conduction method, and C (carbon amount) was measured using a combustion-infrared absorption method. .. The results are shown in Table 1.

By machining the sintered magnet after the heat treatment, vertical 7 mm, transverse 7 mm, to prepare a sample having a thickness of 7 mm, were measured properties of each sample _{(B r} and _{H cJ)} by B-H tracer. The measurement results are shown in Tables 2 and 3.
The "example of the present invention" described in the remarks column of Tables 2 and 3 means that the example satisfies the requirements specified in the embodiment of the present invention.

“Condition A” in Table 2 includes the sample No. in Table 1. The characteristic values of the sintered magnet obtained by finely pulverizing an alloy having a composition of 1 to 27 under condition A, sintering the obtained finely pulverized powder, and heat-treating it are shown. “Condition B” in Table 2 includes the sample No. in Table 1. Alloy was milled in condition B the having a composition of 1 to 27, sintering the finely pulverized powder obtained, the characteristic values of the sintered magnet obtained by heat treatment (the value of B _r and H _cJ) is shown ing. Further, in “Condition B-Condition A” in Table 2, the improvement width (ΔH _cJ ) of H _cJ of the sintered magnet by changing the condition of pulverization from the condition A to the condition B is shown. That is, ΔH _cJ in Table 2 is the difference in H _{cJ in} the _RTB -based sintered magnet obtained by producing the finely pulverized powder under condition A or condition B (R obtained by using condition B). minus the value of H _cJ of R-T-B based sintered magnet obtained by using the condition a from the value of H _cJ of -T-B based sintered magnet) is.

“Condition A” in Table 3 includes the sample No. in Table 1. The characteristic values of the sintered magnet obtained by finely pulverizing the alloy having the composition of 13 under the condition A, sintering the obtained finely pulverized powder, and heat-treating it are shown. “Condition C” in Table 3 includes the sample No. in Table 1. The characteristic values of the sintered magnet obtained by finely pulverizing the alloy having the composition of 13 under the condition C, sintering the obtained finely pulverized powder, and heat-treating it are shown. “Condition C-Condition A” in Table 3 _shows the improvement width (ΔH _cJ ) of H _cJ of the sintered magnet by changing the pulverization condition from the condition A to the condition C. That is, ΔH _cJ in Table 3 is the difference in H _{cJ in} the _RTB -based sintered magnet obtained by producing the finely pulverized powder under condition A or C (R obtained by using condition C). minus the value of H _cJ of R-T-B based sintered magnet obtained by using the condition a from the value of H _cJ of -T-B based sintered magnet) is.

As shown in Table 2, the sample No. For any of the sintered magnets 1 to 27, the particle size D ₅₀ and the particle size D ₉₉ of the finely pulverized powder (alloy powder) used are adjusted to the particle size of the embodiment of the present invention (fine pulverized powder produced under condition B). by, as compared to a regular particle size (prepared under the conditions a), H _cJ without loss of B _r is improved ([Delta] H _cJ is greater than 0). However, the sample No. which does not satisfy the composition of the embodiment of the present invention. In the comparative examples of _{15 to 26} , the improvement width (ΔH _cJ ) of H _cJ of the sintered magnet was 36 to 57 kA / m, which was not sufficient. On the other hand, in the composition range of the embodiment of the present invention (Sample Nos. 1 to 14 and 27), ΔH _cJ is 87 to ₁₀₁ kA / m, which is about 1.5 to 2.5 times that of the comparative example. Improved. Thus, by satisfying the composition of an embodiment of the present invention, a high B _r and high H _cJ are achieved. As described above, by changing from condition A (normal particle size) to condition B (particle size of the embodiment of the present invention), the pulverization time becomes as long as 10 to 40 minutes. Therefore, if the composition of the embodiment of the present invention is not satisfied, the improvement _range of _HcJ is small, and therefore the pulverization is not performed at the particle size of the embodiment of the present invention. However, in the composition range of the embodiment of the present invention, _HcJ is significantly improved, so that it is sufficiently worthwhile even if the pulverization time is long.

Here, FIG. 1 shows the relationship between the amount of B shown in Table 1 and the improvement width ΔH _cJ of the coercive force shown in Tables 2 and 3. In FIG. 1, the vertical axis shows ΔH _cJ of the examples of the present invention and the comparative example, and the horizontal axis shows the amount of B. The square plot (■) in FIG. 1 is an example of the present invention, and the triangular plot (▲) is a comparative example. As shown in FIG. 1, it can be seen that a high ΔH _cJ is obtained in an extremely narrow range where the amount of B is 0.850 to 0.910% by mass. Further, when the amount of B is 0.870 to 0.910% by mass, a higher ΔH _cJ (90 kA / m or more) is obtained.

Further, as shown in Table 3, the particle size D ₅₀ and the particle size D ₉₉ in the finely pulverized powder (alloy powder) are in the preferable range (3.8 μm ≦ D ₅₀ ≦ 4.5 μm and D ₉₉ ≦) of the embodiment of the present invention. If it is 9 .mu.m), without loss of _{B r} is [Delta] H _cJ and 173kA / m, even higher _{B r} and high _{H cJ} are achieved.

This application is accompanied by a priority claim based on Japanese Patent Application No. 2016-054153, which has a filing date of March 17, 2016. Japanese Patent Application No. 2016-054153 is incorporated herein by reference.

Claims (3)

R: 28.5 to 33.0% by mass (R is at least one rare earth element and contains at least one of Nd and Pr),
B: 0.870 to 0.899 % by mass,
Ga: 0.2 to 0.7% by mass,
Cu: 0.1 to 0.3 % by mass,
Al: contains 0.05 to 0.50% by mass,
A method for producing an RTB-based sintered magnet in which the balance is T (T is Fe and Co, and 90% by mass or more of T is Fe) and unavoidable impurities, and the following formula (1) is satisfied. And

14 [B] /10.8 <[T] /55.85 (1)
([B] is the content of B indicated by mass%, and [T] is the content of T indicated by mass%)

A step of preparing an alloy powder in which the particle size D ₅₀ and the particle size D ₉₉ satisfy the following formulas (2) and (3), and
3.8 μm ≤ D ₅₀ ≤ 5.5 μm (2)
D ₉₉ ≤ 10 μm (3)
A molding process of molding the alloy powder to obtain a molded product,
A sintering step of sintering the molded body to obtain a sintered body,
A heat treatment step of heat-treating the sintered body and
A method for producing an RTB-based sintered magnet, which comprises. The Cu in the R-T-B based sintered magnet Ru 0.2 to 0.3% by mass, the production method of the R-T-B based sintered magnet according to claim 1. The method for producing an RTB-based sintered magnet according to claim 1 or 2, wherein the particle size D ₅₀ and the particle size D ₉₉ further satisfy the following formulas (4) and (5).
3.8 μm ≤ D ₅₀ ≤ 4.5 μm (4)
D ₉₉ ≤ 9 μm (5)

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