JP2018056301A - Method for manufacturing r-t-b based sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an R-T-B based sintered magnet having high B, Hand H/Hwithout using RH.SOLUTION: Disclosed is a method for manufacturing an R-T-B based sintered magnet which includes R of 27.5-34.0 mass% (where R is at least one kind of rare earth elements, including at least one of Nd and Pr necessarily), B of 0.85-0.93 mass%, Ga of 0.2-0.7 mass%, Cu of 0.05-0.7 mass%, Al of 0.05-0.4 mass% and T of 61.5 mass% or more (where T represents Fe and Co, and the Fe accounts for 90% or more of T on a mass percentage basis), and satisfies the following expressions: (1)([T]-72.3[B]>0); and (2)(([T]-72.3[B])/55.85<13[Ga]/69.72). The method comprises: a step of preparing an R-T-B based alloy; a hydrogen pulverizing step of heating the alloy under a hydrogen pressurized atmosphere at 5-350°C for hydrogen embrittlement thereof and then, heating the resultant alloy at 750-850°C to perform a dehydrogenation treatment in a reduced-pressure atmosphere of 3000 Pa or less or an inert gas atmosphere; a fine pulverization step of pulverizing coarse powder of the alloy; a shaping step of shaping the resultant alloy powder into a compact; and a sintering step of sintering the compact.SELECTED DRAWING: None

Description

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

  An RTB-based sintered magnet (R is at least one of rare earth elements and always includes at least one of Nd and Pr) is known as the most powerful magnet among permanent magnets, and is a hard disk drive. Used in various motors such as voice coil motors (VCM), motors for electric vehicles (EV, HV, PHV, etc.), motors for industrial equipment, and home appliances.

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

The _RTB -based sintered magnet has irreversible thermal demagnetization because the coercive force H _cJ (hereinafter sometimes simply referred to as “H _cJ ”) decreases at high temperatures. Therefore, it is required to have a high H _cJ especially when used for an electric vehicle motor.

In the R-T-B based sintered magnet, a part of the light rare earth element RL (hereinafter sometimes simply referred to as “RL”) contained in R in the main phase R ₂ T ₁₄ B compound is 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, when RL in the R ₂ T ₁₄ B compound is replaced with RH, the H _{cJ of the RTB} -based sintered magnet is improved, while the residual magnetic flux density B _r (hereinafter simply referred to as “B _r ”). There is). In particular, Dy has a problem that its supply is not stable and its price fluctuates greatly because of its low resource abundance and limited production area. Therefore, in recent years, it has been demanded to improve _HcJ without using RH as much as possible (with the least amount used).

In Patent Document 1, the amount of B is limited to a specific range relatively smaller than that of an R-T-B alloy that has been generally used in the past, and at least one selected from Al, Ga, and Cu. By containing the metal element M, the 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 secured. It is described that an RTB-based rare earth sintered magnet having a high coercive force while suppressing the Dy content can be obtained.

International Publication No. 2013/008756

As described above, the R-T-B type sintered magnet is most often used for a motor, and by improving the magnetic characteristics of the R-T-B type sintered magnet, the output of the motor is improved or the motor is reduced in size. 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 limit demagnetizing field strength becomes small, which causes a problem of easy demagnetization. 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, generally, H _k , which is a parameter to be measured for obtaining the squareness ratio, is an I (magnetization strength) -H (magnetic field strength) curve. in the second quadrant, reading the H-axis of the position where I is the value of 0.9B _r are used. A value (H _k / H _cJ ) _obtained by dividing H _k by H _cJ of the demagnetization curve is defined as the squareness ratio.

However, the amount of B is smaller than that of a general RTB-based sintered magnet as described in Patent Document 1 (that is, more than the amount of B in 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 _{2 The} same as the stoichiometric ratio of the T ₁₄ B type compound (hereinafter, sometimes referred to as a general _RTB -based sintered magnet), the problem that H _k / H _cJ decreases 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 a heavy rare earth element RH (Dy). In many cases, it is in the 80% range, and it is difficult to say that the level is high. In addition, although the definition of the squareness ratio is not described in Patent Document 1, Japanese Patent Application Laid-Open No. 2007-119882, cited as a prior art document of Patent Document 1, describes that “magnetization is 90% of saturation magnetization. Since the value obtained by dividing the value of the external magnetic field to be% by iHc is expressed as%, the definition of the squareness ratio in Patent Document 1 seems to be the same. In other words, the definition of the squareness ratio in Patent Document 1 seems to be the same as the commonly used definition.

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 aims at providing the manufacturing method of.

The first aspect of the present invention is:
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 includes at least one of Nd and Pr),
B: 0.85 mass% or more, 0.93 mass% or less,
Ga: 0.20 mass% or more, 0.70 mass% or less,
Cu: 0.05 mass% or more, 0.70 mass% or less,
Al: 0.05 mass% or more, 0.40 mass% or less, and T: 61.5 mass% or more (T is Fe and Co, and 90% or more of T is Fe by mass ratio) ,
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 content of T expressed in mass%, [B] is the content of B expressed in mass%, and [Ga] is the content of Ga expressed in mass%)

An RTB-based alloy preparation step of preparing an RTB-based alloy;
The RTB-based alloy is heated to 5 ° C. or higher and 350 ° C. or lower in a hydrogen pressurized atmosphere and subjected to hydrogen embrittlement treatment, and then further 750 ° C. or higher and 850 ° C. in a reduced pressure atmosphere or inert gas atmosphere of 3000 Pa or lower. A hydrogen pulverization step of carrying out a dehydrogenation treatment to be heated to a temperature of ℃ or less to obtain an R-T-B system alloy crude powder;
A finely pulverizing step of 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;
Sintering step for obtaining a sintered body by sintering the molded body;
It is a manufacturing method of the RTB system sintered magnet containing this.

  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 at a temperature of 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 hydrogen pulverizing (coarse pulverizing) a raw material alloy, 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 storage process (also referred to as a hydrogen embrittlement process) in which a raw material alloy is roughly pulverized by heating in a hydrogen pressure atmosphere, and a dehydrogenation process in which the stored hydrogen is released by heating in a reduced pressure atmosphere. .
As will be described in detail later, as a result of intensive studies, the present inventors conducted hydrogen embrittlement treatment at a predetermined temperature in the hydrogen pulverization step, and then heated to a high temperature of 750 ° C. or higher and 850 ° C. or lower to perform dehydrogenation treatment. As a result, it was found that the _RTB -based sintered magnet finally obtained has high B _r , H _cJ and H _k / H _cJ .

The reason why an _RTB -based sintered magnet having high B _r , H _cJ and H _k / H _cJ can be obtained by the manufacturing method according to the embodiment of the present invention is still unclear. Based on the knowledge obtained so far, the mechanism considered by the present inventors will be described below. It should be noted that the following description of the 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 Ga or the like is added, the grain boundary is smaller than that of a general RTB-based sintered magnet. Fe is excessively present in the phase, and therefore there are many R-Fe phases (Nd ₂ Fe ₁₇ phase, etc.) and R-Fe-Ga (Nd ₆ Fe ₁₃ Ga phase, etc.) phases in the grain boundary phase. In such an RTB-based sintered magnet, when heated in a hydrogen atmosphere during the hydrogen embrittlement process in the hydrogen pulverization step, the R-Fe phase and the R-Fe-Ga phase present at the grain boundaries become R hydrides. And the 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 it has magnetism, which may deteriorate the magnetic properties of the sintered magnet. Are known. The present inventors have studied to improve the magnetic properties of the R-T-B system sintered magnet by reducing the amount of the α-Fe phase having such magnetism.

In the manufacturing method of the RTB-based sintered magnet, the dehydrogenation treatment is usually performed without heating to a temperature exceeding about 600 ° C. If the heating temperature for the dehydrogenation process is too high, hydrogen is released from the R hydride described above to form a simple R (metal R, for example, Nd), which is oxidized in the pulverization step, and causes deterioration in magnetic properties. It becomes. Therefore, dehydrogenation is performed at about 600 ° C. or less to suppress the generation of R that deteriorates such magnetic characteristics.
As a result of intensive studies, the inventors of the present invention have a B content lower 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 high temperature range exceeding 600 ° C. By performing dehydrogenation treatment, hydrogen is released from R hydride, and the magnetic properties of the sintered magnet finally obtained are greatly increased by actively generating R, which was previously thought to reduce the magnetic properties. I found that it can be improved.
That is, after storing the hydrogen, it is heated to a high temperature of 750 ° C. or higher and 850 ° C. or lower to perform dehydrogenation, thereby releasing hydrogen from the R hydride and actively generating R, whereby R and α− It is considered that the R-Fe phase is formed again by recombination with the Fe phase. 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-based sintered magnet]
First, the RTB system 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 as follows:
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 includes at least one of Nd and Pr),
B: 0.85 mass% or more, 0.93 mass% or less,
Ga: 0.20 mass% or more, 0.70 mass% or less,
Cu: 0.05 mass% or more, 0.70 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 by mass ratio is Fe), Expressions (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 content of T expressed in mass%, [B] is the content of B expressed in mass%, and [Ga] is the content of Ga expressed in mass%)

With the above composition, the amount of B is smaller than that of a general RTB-based sintered magnet, and Ga and the like are contained. Therefore, an RT-Ga phase is generated at the two-grain grain boundary, High H _cJ can be obtained. Here, the R—T—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 ₃ type crystal structure. Moreover, 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, Cu in R-T-B based sintered magnet, if the Al is contained relatively _large, 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 inevitable 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 added can be reduced, and the content of RH can be typically 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.
Content of R is 27.5 mass% or more and 34.0 mass% or less.
If R is less than 27.5% by mass, a liquid phase is not sufficiently generated in the sintering process, and it may be difficult to sufficiently densify the R-T-B system 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)
Content of B is 0.85 mass% or more and 0.93 mass% or less.
If B is less than 0.85% by mass, the R ₂ T ₁₇ phase precipitates and high H _cJ cannot be obtained. Furthermore, it is impossible to main phase ratio to obtain a high B _r drops. If B exceeds 0.93 mass%, the amount of RT-Ga phase produced is so small that high _HcJ may not be obtained.

(3) Gallium (Ga)
The Ga content is 0.20% by mass or more and 0.70% by mass or less.
If the Ga content is less than 0.20% by mass, the amount of R—T—Ga phase produced is too small to eliminate the R ₂ T ₁₇ phase, and high H _cJ cannot be obtained. There is a 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 Cu content is 0.05% by mass or more and 0.70% by mass or less.
When the Cu content is less than 0.05% by mass, high _HcJ cannot be obtained. The content of Cu is liable to decrease _{B r} exceeds 0.70 mass%.

(5) Aluminum (Al)
The Al content 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 inevitable impurity, or may be positively added and contained. The total amount of unavoidable impurities and positively added amount is 0.05% by mass or more and 0.40% by mass or less.

(6) Transition metal element (T)
T is Fe and Co, and 90% or more of T is Fe by mass ratio. Furthermore, as long as the effects of the present invention are not impaired, a small amount of transition metal elements such as V, Mo, Hf, Ta, and 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. When the ratio of Fe in T is less than 90% by mass, _Br may be lowered. Therefore, the ratio 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) Formula (1) and Formula (2)
The composition of the RTB-based sintered magnet material in the embodiment of the present invention is such that the B content is lower than that of a general RTB-based sintered magnet by satisfying the formula (1). ing. A general R-T-B system sintered magnet has [Fe] /55.847 (Fe) so that the R ₂ T ₁₇ phase, which is the soft magnetic phase, does not precipitate in addition to the R ₂ T ₁₄ B phase, which is the main phase. (Atom weight) has a composition smaller than [B] /10.811 (B atomic weight) × 14 ([] means the content expressed by mass% of the element described therein. For example, [Fe] means the Fe content expressed 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 (the atomic weight of Fe) is [B] / So that the composition satisfies the formula (1) so as to be larger than 10.8111 (atomic weight of B) × 14, and the R—T—Ga phase is precipitated by containing Ga from the remaining Fe, The composition satisfies the formula (2) so that ([T] -72.3B) /55.85 (the atomic weight of Fe) is less than 13Ga / 69.72 (the atomic weight of Ga). Although T is Fe and Co, T in the embodiment of the present invention uses the atomic weight of Fe since Fe is a main component (mass ratio of 90% or more). Thereby, high _HcJ can be obtained without using heavy rare earth elements 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 content of T expressed in mass%, [B] is the content of B expressed in mass%, and [Ga] is the content of Ga expressed in mass%)

(8) Remainder As described above, in a preferred embodiment, the remainder may be an inevitable impurity. For example, the effects of the embodiments of the present invention are sufficiently obtained even if unavoidable impurities due to impurities inevitably contained in dissolved raw materials such as didymium alloy (Nd—Pr), electrolytic iron and ferroboron are contained. Can be played. Such inevitable impurities are, for example, La, Ce, Cr, Mn, Si, Sm, Ca and Mg. Furthermore, O (oxygen), N (nitrogen), C (carbon), etc. can be illustrated as an inevitable impurity in a manufacturing process.

  The composition of the RTB-based sintered magnet according to the embodiment of the present invention is not limited to the elements described above. In another preferred embodiment, one or more arbitrary elements other than the elements described above may be included. Examples of such elements that may optionally be included are given below.

(9) Niobium (Nb), zirconium (Zr)
The RTB-based sintered magnet may include at least one of Nb and Zr. By containing both Nb and / or Zr, abnormal growth of crystal grains during sintering can be more reliably suppressed. However, the content of Nb and / or Zr is present unwanted Nb and Zr exceeds 0.1 mass% in total, there is a concern 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 for producing RTB-based sintered magnet]
The manufacturing method of the RTB system sintered magnet which has the composition mentioned above is explained. The manufacturing method of the RTB-based sintered magnet includes an RTB-based alloy preparation step, a hydrogen pulverization step, a fine pulverization 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 pulverization step. In the hydrogen pulverization step, by dehydrogenating by heating to a high temperature of 750 ° C. or higher and 850 ° C. or lower, hydrogen is released from the R hydride and R is actively generated, so that the R and α-Fe phases Can be recombined to regenerate the 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) R-T-B system alloy preparation step Prepare a metal or alloy (melting raw material) of each element so that the composition of the finally obtained R-T-B system sintered magnet is in the composition range described above. A flaky raw material alloy (RTB-based alloy) is produced by an ingot method by die casting, a strip cast method in which a molten alloy is rapidly cooled 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 hydrogen embrittlement treatment (also referred to as hydrogen storage treatment), and then 3000 Pa. In the following reduced pressure atmosphere or inert gas atmosphere, a dehydrogenation treatment is performed by heating to 750 ° C. or higher and 850 ° C. or lower to obtain an RTB-based alloy coarse powder. Below, the hydrogen embrittlement process and dehydrogenation process which concern on this embodiment are demonstrated.
The heating temperature in the hydrogen pulverization 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 the RTB-based alloy is charged into the furnace, it is heated in a vacuum, and then hydrogen is introduced to form a hydrogen pressurized atmosphere. If the absolute pressure of hydrogen during the hydrogen embrittlement treatment is too low, there is a possibility that hydrogen cannot be fully occluded in the RTB-based alloy. Therefore, it is preferable to introduce hydrogen so that the absolute pressure of hydrogen is 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, hydrogen may not be occluded sufficiently, and the magnetic properties of the finally obtained R-T-B system sintered magnet will deteriorate. Therefore, the heating temperature at the time of hydrogen embrittlement is 350 ° C. or lower, preferably 300 ° C. or lower.
On the other hand, if the heating temperature at the time of hydrogen embrittlement is too low, hydrogen cannot be sufficiently occluded. Therefore, the heating temperature during the hydrogen embrittlement treatment is 5 ° C. or higher, preferably 20 ° C. or higher.

(2-2) Dehydrogenation treatment After hydrogen embrittlement treatment, dehydrogenation (that is, release of hydrogen from the coarsely pulverized powder) is performed by heating the coarsely pulverized powder occluded with hydrogen in a reduced-pressure atmosphere. In the manufacturing method according to the embodiment of the present invention, the sintered magnet finally obtained has a high B _r , H _cJ, and H by controlling the heating temperature during the dehydrogenation process to a range of 750 ° C. or higher and 850 ° C. or lower. _k / H _cJ is obtained. More specifically, by performing the dehydrogenation treatment at a high temperature of 750 ° C. or higher and 850 ° C. or lower, not only hydrogen is released from the main phase, but hydrogen is also released from R hydride present in the grain boundary phase to generate R The amount of magnetic α-Fe phase can be reduced by recombining R and the α-Fe phase present in the grain boundary phase to form the R-Fe phase. As a result, the sintered magnet finally obtained is considered to have high B _r , H _cJ and H _k / H _cJ .

(Reduced pressure atmosphere or inert gas atmosphere of 3000 Pa or less)
The dehydrogenation treatment is performed in a reduced pressure atmosphere or an inert gas atmosphere of 3000 Pa or less. By performing 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. An inert gas atmosphere includes an argon gas atmosphere. For example, helium gas is used other than argon gas.
When dehydrogenation is performed, the pressure in the furnace rises and exceeds 3000 Pa with the release of hydrogen from the coarsely pulverized powder after the hydrogen embrittlement. 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, “perform 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 inside the furnace is 3000 Pa or less after rising and decreasing again.

(Dehydrogenation temperature: 750 ° C or higher and 850 ° C or lower)
If the temperature of the dehydrogenation treatment is lower than 750 ° C., B _r , H _cJ and H _k / H _{cJ of} the finally obtained sintered magnet are lowered. If it is lower than 750 ° C., it is considered that hydrogen cannot be released from the R hydride, and therefore the magnetic α-Fe phase cannot be reduced. Therefore, the heating temperature at the time of dehydrogenation 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 R-T-B system sintered magnet finally obtained deteriorate. Therefore, the dehydrogenation treatment is performed at 850 ° C. or lower, preferably 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.} The particle size D ₅₀ of the finely pulverized powder (volume median value (volume-based median diameter) obtained by measurement by airflow dispersion type laser diffraction method) is preferably 3 μm to 5 μm. As the alloy powder, one kind of alloy powder (single alloy powder) may be used, or a so-called two alloy method may be used in which an alloy powder (mixed alloy powder) is obtained by mixing two or more kinds of alloy powder. The alloy powder may be produced by using a known method or the like so as to obtain 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.

(4) Forming step The obtained alloy powder is formed in a magnetic field to obtain a formed body. In the magnetic field molding, a dry alloy method in which a dry alloy powder is inserted into a mold cavity and molded while applying a magnetic field, a slurry in which the alloy powder is dispersed is injected into the mold cavity, Any known forming method in a magnetic field may be used, including a wet forming method of forming while discharging the slurry dispersion medium. 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 process A sintered compact (sintered magnet) is obtained by sintering a molded object. A known method can be used for sintering the molded body. In addition, in order to prevent the oxidation by the atmosphere at the time of sintering, it is preferable to perform sintering in a vacuum atmosphere or atmospheric gas. The atmosphere gas is preferably an inert gas such as helium or argon.

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

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

  The present disclosure will be described in more detail by 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, and a plurality of flaky RTB-based alloys were prepared. The obtained RTB-based alloy was hydrogen crushed. In the hydrogen pulverization, the R-T-B alloy is first charged in a hydrogen furnace and then evacuated, heated at the hydrogen embrittlement treatment temperature shown in Table 2, and hydrogen is introduced until the absolute pressure becomes 295 kPa, Hydrogen embrittlement treatment was performed. Next, the dehydrogenation process which heats at the dehydrogenation process temperature of Table 2 was implemented in the vacuum (specifically reduced pressure atmosphere of 100 Pa or less), it cooled, and the RTB system alloy coarse powder was obtained. 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. After adding 0.04% by mass of zinc stearate as a lubricant to 100% by mass of the coarse powder to the RTB-based alloy coarse powder and mixing the mixture, an airflow pulverizer (jet mill device) is used. 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.

  To the RTB-based alloy powder, zinc stearate as a lubricant was added in an amount of 0.05% by mass with respect to 100% by mass of finely pulverized powder, mixed, and then molded in a magnetic field to obtain a molded body. In addition, what was called a perpendicular magnetic field shaping | molding apparatus (transverse magnetic field shaping | molding apparatus) with which the magnetic field application direction and the pressurization direction orthogonally crossed was used for the shaping | molding apparatus.

The obtained molded body was sintered in 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 was held in vacuum at 900 ° C. for 2 hours, then cooled to room temperature, then held in vacuum at 500 ° C. for 2 hours, and then subjected to a heat treatment to cool to room temperature. Sintered magnets (No. 1 to 12) were obtained. No. of the obtained R-T-B system sintered magnet. The component results of 1 are shown in Table 1. In addition, each component (except O, N, and C) in Table 1 was measured using a high frequency inductively coupled plasma optical emission spectroscopy (ICP-OES). The O (oxygen) content is a gas melting-infrared absorption method, the N (nitrogen) content is a gas melting-thermal conduction method, and the C (carbon) content is a gas analysis device by a combustion-infrared absorption method. Measured using. The same applies to Tables 3 and 5 below. No. No. 2 to 12 In the same manner as in No. 1, the components of the RTB-based sintered magnet were measured. 1 (Table 1). Further, the equations (1) and (2) according to the embodiment of the present invention are calculated, respectively, and “○” is satisfied when the equations (1) and (2) are satisfied, and “×” is not satisfied. , Described. The same applies to Tables 3 and 5 below. Each of the R-T-B sintered magnets after heat treatment (sample Nos. 1 to 12) is machined to prepare samples having a length of 7 mm, a width of 7 mm, and a thickness of 7 mm, and each sample is magnetized by a BH tracer. Characteristics were measured. The measurement results are shown in Table 2. Note that, in H _k / H _cJ (square ratio), H _k is in the second quadrant of the I (magnetization magnitude) -H (magnetic field strength) curve, and I is 0.9 × J _r (J _r is This is the value of H at the position where the value of residual magnetization, J _r = B _r ) (hereinafter the same).

As shown in Tables 1 and 2, No. 1 is an example that satisfies the chemical component composition and hydrogen grinding conditions (hydrogen embrittlement treatment temperature and dehydrogenation treatment temperature) defined in the present invention. 3-7 and no. Nos. 9 to 11 have high magnetic properties of Br ≧ 1.348T, H _cJ ≧ 1396 kA / m, and H _k / H _cJ ≧ 0.943. On the other hand, Comparative Example No. in which the dehydrogenation temperature in the hydrogen pulverization step is outside the range defined in the present invention. 1, 2 and no. 8 and Comparative Example No. in which the hydrogen embrittlement temperature in the hydrogen pulverization step is outside the range defined in the present invention. No. 12, high magnetic properties of 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 pulverization step is 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 characteristics are obtained.

(2) Experimental example 2
The R-T-B system sintered magnet is approximately No. 1 in Table 3. No. of Experimental Example 1 except that each element was weighed so as to have the composition shown in FIGS. An RTB-based sintered magnet was produced under the same conditions as in No. 6. 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 each machined in the same manner as in Experimental Example 1, and the magnetic characteristics 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, Example No. satisfying the chemical component composition and hydrogen grinding conditions (hydrogen embrittlement treatment temperature and dehydrogenation treatment temperature) defined in the present invention. No. 22 has high magnetic characteristics of Br ≧ 1.348T, H _cJ ≧ 1396 kA / m, and H _k / H _cJ ≧ 0.943. On the other hand, Comparative Example No. deviating from the composition range defined in the present invention. 13 (B amount and formula (1) are out of range), No. 14 (Formula (1) is out of range), No. 14 15 (equation (2) is out of range), No. 15 16 (B amount and formula (2) are out of range), No. 17 (Ga amount out of range), No. 18 and 19 (Cu amount out of range), No. 20 (Al amount out of range), No. No. 21 (the amount of B and formula (1) are out of range) does not provide high magnetic properties of Br ≧ 1.348T, H _cJ ≧ 1396 kA / m, and H _k / H _cJ ≧ 0.943.

(3) Experimental example 3
The R-T-B system sintered magnet is approximately No. 1 in Table 3. No. of Experimental Example 1 except that each element was weighed so as to have the composition shown in FIGS. An RTB-based sintered magnet was produced under the same conditions as in No. 6. Table 5 shows the results of the components of the obtained RTB-based sintered magnet (No. 23 and 24).

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

No. 23 and 24 contain heavy rare earth elements RH (containing 3.11% by mass of Dy), and have almost the same composition except for the content of B. As shown in Table 6, the example No. No. 24 is a comparative example. High H _cJ and high H _k / H _cJ are obtained compared to 23 (B amount and formula (1) are out of range).

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 includes at least one of Nd and Pr),
B: 0.85 mass% or more, 0.93 mass% or less,
Ga: 0.20 mass% or more, 0.70 mass% or less,
Cu: 0.05 mass% or more, 0.70 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 by 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 content of T expressed in mass%, [B] is the content of B expressed in mass%, and [Ga] is the content of Ga expressed in mass%)

An RTB-based alloy preparation step of preparing an RTB-based alloy;
The RTB-based alloy is heated to 5 ° C. or higher and 350 ° C. or lower in a hydrogen pressurized atmosphere and subjected to hydrogen embrittlement treatment, and then further 750 ° C. or higher and 850 ° C. in a reduced pressure atmosphere or inert gas atmosphere of 3000 Pa or lower. A hydrogen pulverization step of carrying out a dehydrogenation treatment to be heated to a temperature of ℃ or less to obtain an R-T-B system alloy crude powder;
A finely pulverizing step of 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;
Sintering step for obtaining a sintered body by sintering the molded body;
The manufacturing method of the RTB type | system | group sintered magnet containing this.   The said dehydrogenation process is a manufacturing method of the RTB type | system | group sintered magnet of Claim 1 heated to 780 degreeC or more and 820 degrees C or less.