JP6623998B2 - Method for producing RTB based sintered magnet - Google Patents

Description

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

  RTB based sintered magnets (R is at least one of the rare earth elements and always includes at least one of Nd and Pr) are known as the most high-performance magnets among permanent magnets, and hard disk drives , Such as voice coil motors (VCM), electric vehicles (EV, HV, PHV, etc.), industrial motors, and home appliances.

The RTB-based sintered magnet is mainly composed of a main phase mainly composed of an R ₂ T ₁₄ B compound and a grain boundary phase located at a grain boundary portion of the main phase. The R ₂ T ₁₄ B compound as the main phase is a ferromagnetic material having a high saturation magnetization and an anisotropic magnetic field, and forms the basis of the properties of the RTB-based sintered magnet.

Since the coercive force _HcJ (hereinafter sometimes simply referred to as " _HcJ ") of the _RTB -based sintered magnet decreases at high temperatures, irreversible thermal demagnetization occurs. Therefore, particularly when used for an electric vehicle motor, it is required to have a high _HcJ .

In the RTB-based sintered magnet, a part of the light rare earth element RL (hereinafter may be simply referred to as “RL”) contained in R in the R ₂ T ₁₄ B compound as a main phase is replaced with a heavy rare earth element. RH (hereinafter simply is referred to as "RH") is known to H _cJ is enhanced when substituted by, H _cJ with increasing RH replacement amount is improved.

_However, substitution with RH to RL in R _{2 T 14} B compound, while improving _{H cJ} of the R-T-B-based sintered magnet, the remanence _{B r} (hereinafter, simply referred to as _{"B r"} is There is). In particular, Dy has a problem in that the supply is not stable due to the small amount of resources and the limited production area, and the price fluctuates greatly. Therefore, in recent years, it has been required to improve _HcJ without using RH as much as possible (using as little as possible).

Patent Document 1 discloses that a B content is limited to a specific range relatively smaller than that of a conventionally used RTB-based alloy, and that at least one kind selected from Al, Ga and Cu is used. By containing the metal element M, an R ₂ T ₁₇ phase is generated, and the volume ratio of the transition metal rich phase (R ₆ T ₁₃ M) generated using the R ₂ T ₁₇ phase as a raw material is sufficiently ensured. It is described that an RTB-based rare earth sintered magnet having high coercive force while suppressing the content of Dy can be obtained.

International Publication No. WO 2013/008756

As described above, motors are most commonly used for RTB-based sintered magnets. By improving the magnetic properties of RTB-based sintered magnets, the output of the motor can be improved or the size of the motor can be reduced. Can be achieved. Therefore, although the improvement of _{B r} and _{H cJ} is very effective, along with their characteristics squareness ratio _H k _{/ H cJ} (hereinafter, simply referred to as _"H k _{/ H cJ")} it must also be high. If H _k / H _cJ is low, the critical demagnetizing field strength becomes small, which causes a problem that demagnetization becomes easy. Therefore, while having a high _{B r} and high _{H cJ,} the development of the R-T-B sintered magnets are required to have a high _H k _{/ H cJ.}
In the field of RTB-based sintered magnets, Hk, which is a parameter measured for obtaining the squareness ratio, is generally _represented by an I (magnetization intensity) -H (magnetic field intensity) curve. in the second quadrant, reading the H-axis of the position where I is the value of 0.9B _r are used. Divided by the _{H cJ} of the demagnetization curve The _{H k (H k / H cJ} ) is defined as the shape factor.

However, the amount of B is smaller than that of a general RTB-based sintered magnet as described in Patent Document 1 (that is, the B amount is smaller than the B amount of the stoichiometric ratio of the R ₂ T ₁₄ B type compound). even less), and the sintered magnet of a composition with the addition of Ga or the like, high although B _r and can have a high H _cJ, general R-T-B based sintered magnet (that is, B amount is R H _k / H _cJ is lower than that of the ₂ T ₁₄ B type compound (similar to the stoichiometric ratio of the compound. Hereinafter, it may be referred to as a general _RTB -based sintered magnet). There was a point. For example, as shown in Tables 4 to 6 of Patent Document 1, the squareness ratio (indicated as Sq (squareness) in Patent Document 1) is around 90%, and particularly contains the heavy rare earth element RH (Dy). In many cases, it is in the range of 80%, which is hardly high. Although the definition of the squareness ratio is not described in Patent Document 1, Japanese Patent Application Laid-Open No. 2007-119882, which is cited as a prior art document of Patent Document 1, discloses that “magnetization is 90% of saturation magnetization. % Is the value obtained by dividing the value of the external magnetic field that becomes% by iHc, "and the definition of the squareness ratio in Patent Document 1 seems to be the same. That is, it is considered that the definition of the squareness ratio in Patent Document 1 is the same as the definition generally used above.

The present invention (to minimize the amount) without using as much as possible RH, high _{B r} and high and having a _{H cJ,} R-T-B based sintered magnet having a high _H k _{/ H cJ} It is an object of the present invention to provide a method for producing the same.

According to a first aspect of the present invention,
R: 27.5% by mass or more and 34.0% by mass or less (R is at least one of rare earth elements and always contains at least one of Nd and Pr).
B: 0.85% by mass or more, 0.93% by mass or less,
Ga: 0.20% by mass or more and 0.70% by mass or less,
Cu: 0.05% by mass or more, 0.70% by mass or less,
Al: 0.05% by mass or more, 0.40% by mass or less, and T: 61.5% by mass or more (T is Fe and Co, and 90% or more of T in mass ratio is Fe) ,
A method for producing an RTB based sintered magnet satisfying the following formulas (1) and (2),
[T] -72.3 [B]> 0 (1)
([T] -72.3 [B]) / 55.85 <13 [Ga] /69.72 (2)
([T] is the T content in mass%, [B] is the B content in mass%, and [Ga] is the Ga content in mass%.)

An RTB-based alloy preparing step of preparing an RTB-based alloy;
The RTB-based alloy is heated to 5 ° C. or more and 350 ° C. or less in a hydrogen pressurized atmosphere to perform hydrogen embrittlement treatment, and then 750 ° C. or more to 850 ° C. in a reduced pressure atmosphere of 3000 Pa or less or an inert gas atmosphere. A hydrogen pulverizing step of performing a dehydrogenation treatment of heating to not more than 0 ° C. to obtain an RTB-based alloy coarse powder;
Pulverizing the RTB-based alloy coarse powder to obtain an RTB-based alloy powder;
A molding step of molding the RTB-based alloy powder to obtain a molded body;
A sintering step of sintering the molded body to obtain a sintered body,
This is a method for producing an RTB-based sintered magnet containing:

  A second aspect of the present invention is the method for producing an RTB-based sintered magnet according to the first aspect, wherein the dehydrogenation treatment is performed by heating to 780 ° C or higher and 820 ° C or lower.

The present invention, without using as much as possible RH, which has a high _{B r} and high _{H cJ,} it is possible to provide a manufacturing method of the R-T-B based sintered magnet having a high _H k _{/ H cJ.}

The RTB-based sintered magnet is usually obtained by subjecting a raw material alloy to hydrogen pulverization (coarse pulverization), further pulverizing the obtained coarse pulverized powder, and molding and sintering the obtained alloy powder. be able to. The hydrogen pulverization step includes a hydrogen occlusion treatment (also referred to as hydrogen embrittlement treatment) in which the raw material alloy is roughly pulverized by heating in a hydrogen pressurized atmosphere, and a dehydrogenation treatment in which the occluded hydrogen is released by heating in a reduced pressure atmosphere. .
As will be described in detail later, the present inventors have conducted intensive studies. As a result, in the hydrogen pulverization step, after performing hydrogen embrittlement treatment at a predetermined temperature, the hydrogen debris treatment is performed by heating to a high temperature of 750 ° C. or more and 850 ° C. or less. by performing, R-T-B based sintered magnet finally obtained has found high _{B r, that H cJ} and _H k _{/ H cJ} can be obtained.

The manufacturing method according to the embodiment of the present invention, a high _{B r,} there is also still questions about why the R-T-B based sintered magnet is obtained having a _{H cJ} and _H k _{/ H cJ.} The mechanism considered by the present inventors based on the knowledge obtained so far will be described below. It should be noted that the description of the following mechanism is not intended to limit the technical scope of the present invention.

In a sintered magnet having a composition in which the amount of B is smaller than that of a general RTB based sintered magnet and to which Ga or the like is added, the grain boundary is larger than that of a general RTB based sintered magnet. phase and Fe is present in excess in so that the grain boundary phase is present R-Fe phase _(Nd 2 _{Fe 17} phase etc.) and _{R-Fe-Ga (Nd 6} Fe 13 Ga equality) phase number. In such an RTB-based sintered magnet, when heated in a hydrogen atmosphere at the time of hydrogen embrittlement in the hydrogen grinding step, the R-Fe phase and the R-Fe-Ga phase present at the grain boundaries become R hydride. And an α-Fe phase. Since the α-Fe phase is a very stable phase, it remains without being taken into the main phase and the grain boundary phase even after sintering, and has magnetic properties, which may deteriorate the magnetic properties of the sintered magnet. Are known. The present inventors have studied to improve the magnetic characteristics of the RTB-based sintered magnet by reducing the amount of the α-Fe phase having such magnetism.

In a method of manufacturing an RTB based sintered magnet, the dehydrogenation treatment is usually performed without heating to a temperature exceeding about 600 ° C. If the heating temperature of the dehydrogenation treatment is too high, hydrogen is released from the above-mentioned R hydride to become a simple substance R (metal R, for example, Nd), and this R is oxidized in the pulverization step and deteriorates magnetic properties. It becomes. Therefore, the dehydrogenation treatment is performed at about 600 ° C. or less to suppress the generation of R that degrades such magnetic characteristics.
As a result of intensive studies, the present inventors have found that the amount of B is smaller than that of a general RTB-based sintered magnet, and in the case of a composition to which Ga or the like is added, in a specific temperature range of a high temperature exceeding 600 ° C. By performing dehydrogenation and releasing hydrogen from the R hydride to actively generate R, which was conventionally considered to lower magnetic properties, the magnetic properties of the finally obtained sintered magnet can be significantly increased. I found that it can be improved.
That is, by heating to a high temperature of 750 ° C. or more and 850 ° C. or less after desorbing hydrogen, hydrogen is released from the R hydride to generate R positively, so that the R and α- It is considered that the Fe phase is recombined to form the R-Fe phase again. Thus, it is possible to reduce the amount of alpha-Fe phase having magnetism, so that the finally obtained sintered magnet high B _r, H _cJ and H _{k /} H _cJ can be obtained.
Hereinafter, embodiments of the present invention will be described in detail.

[RTB sintered magnet]
First, an RTB-based sintered magnet obtained by the manufacturing method according to the embodiment of the present invention will be described.
The composition of the RTB-based sintered magnet according to the embodiment of the present invention is such that when the entire RTB-based sintered magnet is 100% by mass,
R: 27.5% by mass or more and 34.0% by mass or less (R is at least one of rare earth elements and always contains at least one of Nd and Pr).
B: 0.85% by mass or more, 0.93% by mass or less,
Ga: 0.20% by mass or more and 0.70% by mass or less,
Cu: 0.05% by mass or more, 0.70% by mass or less,
Al: 0.05% by mass or more, 0.40% by mass or less, and T: 61.5% by mass or more (T is Fe and Co, and 90% or more of T in mass ratio is Fe), Equations (1) and (2) are satisfied.

[T] -72.3 [B]> 0 (1)
([T] -72.3 [B]) / 55.85 <13 [Ga] /69.72 (2)
([T] is the T content in mass%, [B] is the B content in mass%, and [Ga] is the Ga content in mass%.)

With the above composition, the amount of B is made smaller than that of a general RTB-based sintered magnet, and Ga and the like are contained, so that an RT-Ga phase is generated at the two grain boundary, High _HcJ can be obtained. Here, the RTGA layer is typically a Nd ₆ Fe ₁₃ Ga compound. The R ₆ T ₁₃ Ga compound has a La ₆ Co ₁₁ Ga _3- type crystal structure. Further, the R ₆ T ₁₃ Ga compound may be an R ₆ T ₁₃ −δGa _{1 + δ} compound (δ is typically 2 or less) depending on the state. For example, Cu in R-T-B based sintered magnet, if the Al is contained relatively _large, it may have been the _{R 6 T 13-δ (Ga} 1-x-y Cu x Al y) 1 + δ is there.

  In another preferred embodiment of the present invention, the balance may be unavoidable impurities.

  Next, details of each element will be described.

(1) Rare earth element (R)
R in the RTB based sintered magnet according to the embodiment of the present invention is at least one kind of rare earth element and always includes at least one of Nd and Pr. R-T-B based sintered magnet according to an embodiment of the present invention it is possible to obtain a high B _r and high H _cJ also contain no heavy rare-earth element (RH), obtained higher H _cJ Even in this case, the amount of RH to be added can be reduced, and the RH content can be typically reduced to 5% by mass or less. However, this does not mean that the RH content of the RTB-based sintered magnet according to the embodiment of the present invention is limited to 5% by mass or less.
The content of R is 27.5% by mass or more and 34.0% by mass or less.
If R is less than 27.5% by mass, a liquid phase may not be sufficiently formed during the sintering process, and it may be difficult to sufficiently densify the RTB-based sintered body. 0 exceeds wt%, the main phase ratio can not be obtained a high B _r drops. R is, in order to obtain a higher _{B r} is preferably not more than 31.0 wt%.

(2) Boron (B)
The content of B is 0.85% by mass or more and 0.93% by mass or less.
If B is less than 0.85% by mass, the R ₂ T ₁₇ phase precipitates and high _HcJ cannot be obtained. Furthermore, it is impossible to main phase ratio to obtain a high B _r drops. If B exceeds 0.93% by mass, the amount of the generated RT-Ga phase may be too small to obtain a high _HcJ .

(3) Gallium (Ga)
The content of Ga is 0.20% by mass or more and 0.70% by mass or less.
When the content of Ga is less than 0.20 wt%, and the amount of R-T-Ga phase is too _small, it is impossible to eliminate the R _{2 T 17} phase, it is impossible to obtain a high _{H cJ} There is fear. When the content of Ga is more than 0.70 wt%, will be unnecessary Ga is present, there is a possibility that B _r decreases to decrease the main phase proportion.

(4) Copper (Cu)
The content of Cu is 0.05% by mass or more and 0.70% by mass or less.
If the Cu content is less than 0.05% by mass, a high _HcJ cannot be obtained. The content of Cu is liable to decrease _{B r} exceeds 0.70 mass%.

(5) Aluminum (Al)
The content of Al is 0.05% by mass or more and 0.40% by mass or less. By containing Al, _HcJ can be improved. Al may be contained as an unavoidable impurity, or may be positively added and contained. The total content of the inevitable impurities and the positively added amount is 0.05% by mass to 0.40% by mass.

(6) Transition metal element (T)
T is Fe and Co, and 90% or more of T in mass ratio is Fe. Furthermore, as long as the effects of the present invention are not impaired, a small amount of a transition metal element such as V, Mo, Hf, Ta, or W may be contained.
T is less than 61.5 mass%, there is a possibility _{that B r} is greatly reduced. Therefore, the content of T is 61.5% by mass or more. If the proportion of Fe in T is less than 90% by mass, _Br may be reduced. Therefore, the proportion of the Co content in the T content is preferably 10% or less, more preferably 2.5% or less of the entire T content.

(7) Equation (1) and Equation (2)
The composition of the RTB-based sintered magnet material according to the embodiment of the present invention satisfies the expression (1), so that the B content is lower than that of a general RTB-based sintered magnet. ing. A general RTB-based sintered magnet has a [Fe] /55.847 (of Fe) so that an R ₂ T ₁₇ phase which is a soft magnetic phase is not precipitated in addition to an R ₂ T ₁₄ B phase which is a main phase. (Atomic weight) is smaller than [B] /10.811 (atomic weight of B) × 14 ([] means the content shown by mass% of the element described therein. , [Fe] means the content of Fe in mass%). The RTB-based sintered magnet according to the embodiment of the present invention is different from a general RTB-based sintered magnet in that [Fe] /55.847 (atomic weight of Fe) is [B] / A composition satisfying the expression (1) is set so as to be larger than 10.811 (atomic weight of B) × 14, and an RT—Ga phase is precipitated by containing Ga from surplus Fe. A composition satisfying the expression (2) is set so that ([T] -72.3B) /55.85 (atomic weight of Fe) is less than 13 Ga / 69.72 (atomic weight of Ga). Although T is Fe and Co, T in the embodiment of the present invention is based on the atomic weight of Fe since Fe is a main component (90% or more by mass ratio). Thereby, high _HcJ can be obtained without using a heavy rare earth element such as Dy as _much as possible.

[T] -72.3 [B]> 0 (1)
([T] -72.3 [B]) / 55.85 <13 [Ga] /69.72 (2)
([T] is the T content in mass%, [B] is the B content in mass%, and [Ga] is the Ga content in mass%.)

(8) Remainder As described above, in one preferred embodiment, the remnant may be an unavoidable impurity. For example, the effects of the embodiment of the present invention can be sufficiently achieved even if the dissolving raw materials such as the didymium alloy (Nd-Pr), electrolytic iron, and ferroboron contain unavoidable impurities which are usually unavoidable. Can be played. Such unavoidable impurities are, for example, La, Ce, Cr, Mn, Si, Sm, Ca and Mg. Furthermore, examples of unavoidable impurities during the manufacturing process include O (oxygen), N (nitrogen), and C (carbon).

  The composition of the RTB-based sintered magnet according to the embodiment of the present invention is not limited to the above-described elements. In another preferred embodiment, one or more optional elements other than the above-mentioned elements may be included. The following are examples of such optional elements.

(9) Niobium (Nb), zirconium (Zr)
The RTB-based sintered magnet may include at least one of Nb and Zr. By containing both or one of Nb and Zr, abnormal growth of crystal grains during sintering can be suppressed more reliably. However, the content of Nb and / or Zr is present unwanted Nb and Zr exceeds 0.1 mass% in total, there is a possibility that the main phase ratio is lowered B _r drops. Therefore, the total content of Nb and / or Zr is preferably 0.1% by mass or less.

[Method of Manufacturing RTB Based Sintered Magnet]
A method for manufacturing an RTB-based sintered magnet having the above-described composition will be described. The method of manufacturing the RTB based sintered magnet includes an RTB based alloy preparing step, a hydrogen pulverizing step, a fine pulverizing step, a forming step, a sintering step, and a heat treatment step. The manufacturing method according to the embodiment of the present invention is particularly characterized in the hydrogen grinding step. In the hydrogen pulverization step, R and α-Fe phase are heated by heating to a high temperature of 750 ° C. or more and 850 ° C. or less to release hydrogen from R hydride and to actively generate R. Are recombined to form an R-Fe phase. Thus, it is possible to reduce the amount of alpha-Fe phase having magnetism, so that it is possible to improve the H _cJ and H _{k /} H _cJ of the finally sintered magnet obtained.
Hereinafter, each step will be described.

(1) RTB-based alloy preparation step A metal or an alloy (melting raw material) of each element is prepared so that the composition of the finally obtained RTB-based sintered magnet falls within the above-described composition range. Then, a flake-shaped raw material alloy (RTB-based alloy) is produced by an ingot method by die casting, a strip casting method of rapidly cooling the molten alloy using a cooling roll, or the like.

(2) Hydrogen crushing process resulting R-T-B alloy to hydrogen pulverization, the particle diameter _{D 50} is obtained 100μm or 300μm or less coarse pulverized powder (R-T-B type alloy coarse powder). The particle diameter D ₅₀ is the volume center value obtained by the laser diffraction method by air flow dispersion method (volume-based median diameter). Specifically, the RTB-based alloy is heated to 5 ° C. or more and 350 ° C. or less in a hydrogen pressurized atmosphere to perform a hydrogen embrittlement treatment (also referred to as a hydrogen occlusion treatment). A dehydrogenation treatment is performed by heating to 750 ° C. or higher and 850 ° C. or lower in the following reduced pressure atmosphere or inert gas atmosphere to obtain an RTB-based alloy coarse powder. Hereinafter, the hydrogen embrittlement treatment and the dehydrogenation treatment according to the present embodiment will be described.
The heating temperature in the hydrogen pulverizing step can be confirmed by attaching a thermocouple to the RTB-based alloy and the coarsely pulverized powder.

(2-1) Hydrogen embrittlement treatment (hydrogen pressurized atmosphere)
After charging the RTB-based alloy into the furnace, the furnace is heated to a vacuum and then hydrogen is introduced to make a hydrogen pressurized atmosphere. If the absolute pressure of hydrogen during the hydrogen embrittlement treatment is too low, there is a possibility that the RTB-based alloy may not be able to occlude hydrogen sufficiently. Therefore, it is preferable to introduce hydrogen so that the absolute pressure of hydrogen becomes 150 kPa or more.

(Hydrogen embrittlement temperature: 5 ° C or higher and 350 ° C or lower)
If the heating temperature during the hydrogen embrittlement treatment is too high, it may not be possible to occlude hydrogen satisfactorily, and the magnetic properties of the finally obtained RTB-based sintered magnet deteriorate. Therefore, the heating temperature during the hydrogen embrittlement treatment is 350 ° C. or lower, and preferably 300 ° C. or lower.
On the other hand, if the heating temperature at the time of the hydrogen embrittlement treatment is too low, hydrogen cannot be sufficiently absorbed. Therefore, the heating temperature during the hydrogen embrittlement treatment is 5 ° C. or higher, preferably 20 ° C. or higher.

(2-2) Dehydrogenation treatment After the hydrogen embrittlement treatment, dehydrogenation (that is, release of hydrogen from the coarsely pulverized powder) is performed by heating the coarsely pulverized powder storing hydrogen in a reduced pressure atmosphere. In the manufacturing method according to the embodiment of the present invention, by controlling the heating temperature in the dehydrogenation process in the range temperatures higher than 750 ℃ 850 ° C. or less, the finally obtained sintered magnet high B _r, H _cJ and H _k / _HcJ is obtained. More specifically, by performing the dehydrogenation treatment at a high temperature of 750 ° C. or more and 850 ° C. or less, not only hydrogen is released from the main phase but also hydrogen is released from the R hydride present in the grain boundary phase, and R Can be generated, and the amount of the magnetic α-Fe phase can be reduced by recombining R and the α-Fe phase present in the grain boundary phase to generate an R-Fe phase. as a result, sintered magnet finally obtained high _{B r, H cJ} and _H k _{/ H cJ} can be obtained.

(Reduced pressure atmosphere of 3000 Pa or less or inert gas atmosphere)
The dehydrogenation treatment is performed in a reduced pressure atmosphere of 3000 Pa or less or an inert gas atmosphere. By performing the treatment in such a reduced pressure atmosphere or an inert gas atmosphere, hydrogen can be efficiently extracted from the coarsely pulverized powder after the hydrogen embrittlement treatment. The inert gas atmosphere includes an argon gas atmosphere. Other than the argon gas, for example, helium gas is used.
When the dehydrogenation treatment is performed, the pressure in the furnace increases with the release of hydrogen from the coarsely pulverized powder after the hydrogen embrittlement treatment, and exceeds 3000 Pa. Thereafter, when the release of hydrogen from the coarsely pulverized powder is completed, the pressure in the furnace gradually decreases, and is finally maintained at 3000 Pa or less again. In this specification, "implementing the dehydrogenation treatment in a reduced-pressure atmosphere of 3000 Pa or less" means that the furnace pressure at the start of heating in the dehydrogenation treatment is 3000 Pa or less, and the furnace pressure during the dehydrogenation treatment is It means that the pressure in the furnace has become 3000 Pa or less after the temperature has risen and then decreased again.

(Dehydrogenation temperature: 750 ° C to 850 ° C)
When the temperature of the dehydrogenation treatment is less than 750 ° C., _B r of the finally sintered magnet _obtained, is _{H cJ} and _H k _{/ H cJ} decreases. It is considered that if the temperature is lower than 750 ° C., hydrogen cannot be released from the R hydride, so that the α-Fe phase having magnetism cannot be reduced. Therefore, the heating temperature at the time of the dehydrogenation treatment is 750 ° C or higher, preferably 780 ° C or higher.
On the other hand, if the temperature of the dehydrogenation treatment is too high, grain growth of the coarsely pulverized powder occurs and the magnetic properties of the finally obtained RTB-based sintered magnet deteriorate. Therefore, the dehydrogenation treatment is performed at 850 ° C. or lower, preferably at 820 ° C. or lower.

(3) a milling step resulting crude pulverized powder (R-T-B based alloy coarse powder), finely pulverized by a jet mill in an inert gas such as nitrogen, than the particle size D ₅₀ of the coarsely pulverized powder obtaining a finely pulverized powder (R-T-B-based alloy powder) having an even smaller particle size _{D 50.} Finely pulverized powder having a particle size D _{50 (volume} center value obtained by measurement by the air flow distributed Laser diffraction (volume basis median diameter)) is, 3Myuemu～5myuemu is preferred. As the alloy powder, one kind of alloy powder (single alloy powder) may be used, or a so-called two-alloy method of obtaining an alloy powder (mixed alloy powder) by mixing two or more kinds of alloy powder may be used. An alloy powder may be produced using a known method or the like so as to have the composition of the embodiment of the present invention.
Note that a known lubricant may be added as an auxiliary agent to the coarsely pulverized powder before the jet mill pulverization, the alloy powder during the jet mill pulverization and after the jet mill pulverization.

(4) Forming Step The obtained alloy powder is formed in a magnetic field to obtain a formed body. In the magnetic field molding, dry alloy powder is inserted into the cavity of the mold, and a dry molding method of molding while applying a magnetic field, a slurry in which the alloy powder is dispersed in the cavity of the mold is injected, Any known magnetic field molding method may be used, including a wet molding method in which the slurry is discharged while the dispersion medium is discharged. The direction of the magnetic field applied during molding may be a direction orthogonal to the pressing direction (so-called perpendicular magnetic field forming method) or a direction parallel to the pressing direction (so-called parallel magnetic field forming method).

(5) Sintering step A sintered body (sintered magnet) is obtained by sintering the compact. A known method can be used for sintering the compact. Note that sintering is preferably performed in a vacuum atmosphere or an atmosphere gas in order to prevent oxidation due to an atmosphere during sintering. As the atmosphere gas, it is preferable to use an inert gas such as helium or argon.

(6) Heat treatment step It is preferable to perform a heat treatment on the obtained sintered magnet for the purpose of improving magnetic properties. Known conditions such as a heat treatment temperature and a heat treatment time can be used. For example, heat treatment (one-step heat treatment) at only a relatively low temperature (400 ° C. or more and 600 ° C. or less) may be performed, or heat treatment at a relatively high temperature (700 ° C. or more and a sintering temperature or less (eg, 1050 ° C. or less)). After that, heat treatment (two-step heat treatment) may be performed at a relatively low temperature (400 ° C. or more and 600 ° C. or less). Preferred conditions are a heat treatment at 730 ° C. or more and 1020 ° C. or less for about 5 minutes to 500 minutes, and after cooling (after cooling to room temperature or after cooling to 440 ° C. or more and 550 ° C. or less), Heat treatment for about 1 minute to about 500 minutes. The heat treatment is preferably performed in a vacuum atmosphere or an inert gas (such as helium or argon).

  The obtained sintered magnet may be subjected to machining such as grinding for the purpose of obtaining a final product shape. In that case, the heat treatment may be performed before or after machining. Further, the obtained sintered magnet may be subjected to a surface treatment. The surface treatment may be a known surface treatment, for example, a surface treatment such as Al vapor deposition, electric Ni plating, and resin paint.

  The present disclosure will be described in more detail with reference to experimental examples, but the present disclosure is not limited thereto.

(1) Experimental example 1
Each element was weighed and cast by a strip casting method so that the RTB-based sintered magnet had a composition shown in Table 1 to prepare a plurality of flake-like RTB-based alloys. The obtained RTB-based alloy was pulverized with hydrogen. Hydrogen pulverization is performed by first charging the RTB-based alloy in a hydrogen furnace and then evacuating, heating at a hydrogen embrittlement temperature shown in Table 2, and introducing hydrogen until the absolute pressure becomes 295 kPa. Hydrogen embrittlement treatment was performed. Next, a dehydrogenation treatment was performed by heating at a dehydrogenation treatment temperature shown in Table 2 in a vacuum (specifically, a reduced-pressure atmosphere of 100 Pa or less), followed by cooling to obtain an RTB-based alloy coarse powder. Where the R-T-B alloy coarse powder particle size D ₅₀ of the measured by a laser diffraction method by air flow dispersion method, was 200 [mu] m. 0.04% by mass of zinc stearate is added as a lubricant to 100% by mass of the coarse powder as a lubricant to the RTB-based alloy coarse powder, and the mixture is then mixed with an air-flow crusher (jet mill device). Then, dry pulverization was performed in a nitrogen stream to obtain an RTB-based alloy powder. Where it said R-T-B alloy powder particle size D ₅₀ of the measured by a laser diffraction method by air flow dispersion method, was 4.5 [mu] m.

  Zinc stearate was added as a lubricant to the RTB-based alloy powder in an amount of 0.05% by mass with respect to 100% by mass of the finely pulverized powder. Note that a so-called right-angle magnetic field forming apparatus (transverse magnetic field forming apparatus) in which the magnetic field application direction and the pressing direction are orthogonal to each other was used as the forming apparatus.

The obtained molded body was sintered in a vacuum at 1000 ° C. or higher and 1040 ° C. or lower (a temperature at which densification by sintering was sufficiently selected for each sample) for 4 hours and then rapidly cooled to obtain a sintered body. The density of the obtained sintered body was 7.5 Mg / m ³ or more. The obtained sintered body is kept in a vacuum at 900 ° C. for 2 hours, cooled to room temperature, and then kept in a vacuum at 500 ° C. for 2 hours, and then subjected to a heat treatment of cooling to room temperature to obtain an RTB-based material. Sintered magnets (Nos. 1 to 12) were obtained. No. of the obtained RTB based sintered magnet. Table 1 shows the results of the components. In addition, each component (other than O, N, and C) in Table 1 was measured using high frequency inductively coupled plasma emission spectroscopy (ICP-OES). The O (oxygen) content is measured by a gas melting and infrared absorption method, the N (nitrogen) content is measured by a gas melting and heat conduction method, and the C (carbon) content is measured by a combustion and infrared absorption method. And measured. The same applies to Tables 3 and 5 below. In addition, No. Nos. 2 to 12 are also Nos. When the components of the RTB-based sintered magnet were measured in the same manner as in No. 1, no. 1 (Table 1). Further, the equations (1) and (2) according to the embodiment of the present invention are calculated, respectively, and “○” indicates that the equations (1) and (2) are satisfied, and “×” indicates that the equations (1) and (2) are not satisfied. , Was described. Hereinafter, the same applies to Tables 3 and 5. The heat-treated RTB-based sintered magnets (Sample Nos. 1 to 12) were each machined to prepare samples having a length of 7 mm, a width of 7 mm, and a thickness of 7 mm, and the magnetic properties of each sample were measured by a BH tracer. The properties were measured. Table 2 shows the measurement results. In H _k / H _cJ (square ratio), H _k is 0.9 × J _r (J _r is in the second quadrant of the I (magnetization magnitude) -H (magnetic field strength) curve). This is the value of H at the position where the value of the residual magnetization, _Jr = _Br ) (the same applies hereinafter).

As shown in Tables 1 and 2, Example No. 1 satisfies the chemical composition and the hydrogen crushing conditions (hydrogen embrittlement temperature and dehydrogenation temperature) specified in the present invention. Nos. 3 to 7 and Nos. 9 to 11, high magnetic properties such as Br ≧ 1.348T, H _cJ ≧ 1396 kA / m, and H _k / H _cJ ≧ 0.943 were obtained. On the other hand, in Comparative Example No. in which the dehydrogenation treatment temperature in the hydrogen grinding step was out of the range specified in the present invention. 1, 2 and No. Comparative Example No. 8 in which the hydrogen embrittlement treatment temperature in the hydrogen grinding step was outside the range specified in the present invention. In No. 12, high magnetic properties such as Br ≧ 1.348T, H _cJ ≧ 1396 kA / m and H _k / H _cJ ≧ 0.943 were not obtained. In addition, the dehydrogenation temperature in the hydrogen grinding step was 780 ° C or higher and 820 ° C or lower. In Nos. 4 to 6, Br ≧ 1.411T, H _cJ ≧ 1432 kA / m and H _k / H _cJ ≧ 0.951, and higher magnetic properties are obtained.

(2) Experimental example 2
The RTB-based sintered magnet is approximately No. 3 in Table 3. No. 13 of Experimental Example 1 except that each element was weighed so that the compositions shown in FIGS. Under the same conditions as in Example 6, an RTB-based sintered magnet was produced. Table 3 shows the component results of the obtained RTB-based sintered magnets (Nos. 13 to 22).

  The obtained RTB-based sintered magnets (Sample Nos. 13 to 22) were machined in the same manner as in Experimental Example 1, and the magnetic properties of each sample were measured in the same manner as in Experimental Example 1. Table 4 shows the measurement results.

As shown in Table 4, the composition of Example No. satisfying the chemical composition and the hydrogen pulverization conditions (hydrogen embrittlement temperature and dehydrogenation temperature) specified in the present invention. 22, high magnetic properties of Br ≧ 1.348T and _{H cJ} ≧ _1396kA / m and _H k _{/ H cJ} ≧ 0.943 is obtained. On the other hand, in Comparative Example No. out of the composition range specified in the present invention. 13 (the amount of B and the formula (1) are out of the range); 14 (Expression (1) is out of range); No. 15 (Expression (2) is out of range); No. 16 (B content and formula (2) are out of range), 17 (Ga content is out of range); Nos. 18 and 19 (Cu content is out of range); No. 20 (Al content is out of range), 21 (B amount and the formula (1) is out of range) _{is, Br ≧ 1.348T, H cJ ≧} 1396kA / m, and _H k _{/ H cJ} ≧ high magnetic properties of 0.943 is not obtained.

(3) Experimental example 3
The RTB-based sintered magnet is approximately No. 3 in Table 3. No. 23 of Experimental Example 1 except that each element was weighed so that the compositions shown in FIGS. Under the same conditions as in Example 6, an RTB-based sintered magnet was produced. Table 5 shows the results of the components of the obtained RTB-based sintered magnets (Nos. 23 and 24).

  The obtained RTB-based sintered magnets (Sample Nos. 23 and 24) were machined in the same manner as in Experimental Example 1, and the magnetic properties of each sample were measured as in Experimental Example 1. Table 6 shows the measurement results.

No. 23 and 24 contain the heavy rare earth element RH (containing 3.11% by mass of Dy), and have substantially the same composition except for the B content. As shown in Table 6, the sample No. No. 24 is a comparative example. 23 in comparison with (B amount and the formula (1) is out of range), high _{H cJ} and high _H k _{/ H cJ} can be obtained.

Claims (2)

R: 27.5% by mass or more and 34.0% by mass or less (R is at least one of rare earth elements and always contains at least one of Nd and Pr).
B: 0.85% by mass or more, 0.93% by mass or less,
Ga: 0.20% by mass or more and 0.70% by mass or less,
Cu: 0.05% by mass or more, 0.70% by mass or less,
Al: 0.05% by mass or more, 0.40% by mass or less, and T: 61.5% by mass or more (T is Fe and Co, and 90% or more of T in mass ratio is Fe),
A method for producing an RTB based sintered magnet satisfying the following formulas (1) and (2),
[T] -72.3 [B]> 0 (1)
([T] -72.3 [B]) / 55.85 <13 [Ga] /69.72 (2)
([T] is the T content in mass%, [B] is the B content in mass%, and [Ga] is the Ga content in mass%.)

An RTB-based alloy preparing step of preparing an RTB-based alloy;
The RTB-based alloy is heated to 5 ° C. or more and 350 ° C. or less in a hydrogen pressurized atmosphere to perform hydrogen embrittlement treatment, and then 750 ° C. or more to 850 ° C. in a reduced pressure atmosphere of 3000 Pa or less or an inert gas atmosphere. A hydrogen pulverizing step of performing a dehydrogenation treatment of heating to not more than 0 ° C. to obtain an RTB-based alloy coarse powder;
Pulverizing the RTB-based alloy coarse powder to obtain an RTB-based alloy powder;
A molding step of molding the RTB-based alloy powder to obtain a molded body;
A sintering step of sintering the molded body to obtain a sintered body,
A method for producing an RTB-based sintered magnet, comprising:   The method for producing an RTB-based sintered magnet according to claim 1, wherein the dehydrogenation treatment is performed by heating to 780C to 820C.