JP7572775B2 - Manufacturing method of RTB based sintered magnet - Google Patents

Description

This disclosure relates to a method for producing R-T-B based sintered magnets.

R-T-B system sintered magnets (R is a rare earth element containing at _least one selected from the group consisting of Nd, Pr and Ce, T is Fe or Fe and Co, and 90% or more by mass of _T is Fe) with an R 2 T 14 B type compound as the main phase are known as the highest performance magnets among permanent magnets, and are used in various motors for hybrid cars, electric cars and home appliances.

At high temperatures, R-T-B based sintered magnets lose their coercive force H _cJ (hereinafter sometimes simply referred to as "H _cJ "), causing irreversible thermal demagnetization. Therefore, when they are used in motors for hybrid and electric vehicles, in particular, they are required to maintain a high H _cJ even at high temperatures.

Conventionally, large amounts of heavy rare earth elements (mainly Dy) have been added to sintered R-T-B magnets to improve _HcJ , but this has the problem of reducing the remanence B _r (hereinafter sometimes simply referred to as "B _r "). For this reason, in recent years, a method has been adopted in which heavy rare earth elements are diffused from the surface to the interior of a sintered R-T-B magnet, concentrating the heavy rare earth elements in the outer periphery of the main phase crystal grains, thereby obtaining a high _HcJ while suppressing the reduction in B _r .

However, Dy has problems such as unstable supply and price fluctuations due to the limited production areas, etc. For this reason, there is a demand for technology that improves the _HcJ of R-T-B based sintered magnets while using as little heavy rare earth elements as possible, such as Dy (using as little as possible).

Patent Document 1 describes that by reducing the B content compared to normal R-T-B based alloys and adding one or more metal elements M selected from Al, Ga, and Cu to form an R ₂ T ₁₇ phase, and by sufficiently ensuring the volume fraction of a transition metal-rich phase (R ₆ T ₁₃ M) formed using the R ₂ T ₁₇ phase as a raw material, an R-T-B based sintered magnet with a high coercive force H _cJ can be obtained while suppressing the Dy content.

International Publication No. 2013/008756

There has been a demand for further improvements in the magnetic properties of sintered R-T-B magnets with a low Dy content, such as those described in Patent Document 1. An object of the present disclosure is to provide a method for producing a sintered R-T-B magnet that has high B _r and high H _cJ while keeping the Dy content low.

Aspect 1 of the present invention is
Contains at least R, B, Ga and T;
R: 27.0% by mass or more and 35.0% by mass or less, R is a rare earth element and includes at least one selected from the group consisting of Nd, Pr, and Ce;
B: 0.80% by mass or more and 0.93% by mass or less;
Ga: 0.15% by mass or more and 1.0% by mass or less;
preparing a sintered R-T-B based magnet material having T of 61.5 mass % or more and 70.0 mass % or less (T is Fe or Fe and Co, and 90 mass % or more of T is Fe) and satisfying the following formula (1);

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

and a heat treatment step of heat treating the sintered R-T-B based magnet material by holding the heat treatment temperature at 400° C. or higher and 600° C. or lower for a holding time of 10 seconds or higher and less than 30 minutes.

Aspect 2 of the present invention is
Aspect 2 is a method for producing a sintered RTB based magnet according to aspect 1, wherein the holding time in the heat treatment step is from 10 seconds to 10 minutes.

Aspect 3 of the present invention is
3. The method for producing a sintered RTB based magnet according to claim 1, wherein the holding time in the heat treatment step is from 10 seconds to 3 minutes.

The manufacturing method of the present disclosure can provide a method for producing a sintered RTB based magnet having high B _r and high H _cJ while keeping the Dy content low.

It is generally known that the H _cJ of an R-T-B based sintered magnet is improved by heat treatment after sintering. In order for H _cJ to reach its maximum value, it was thought that it was necessary to hold the heat treatment temperature at the optimum temperature for at least 1.5 to 3 hours. Therefore, in order to fully exhibit the magnetic properties (especially H _cJ ) of an R-T-B based sintered magnet, the heat treatment was usually performed with a holding time of 1.5 hours or more. In addition, there is a trade-off between B _r and H _cJ . Therefore, usually, if the holding time is short (e.g., 5 minutes), the value of B _r is high, but the value of H _cJ is significantly reduced. And, if the holding time is long (e.g., 3 hours), the value of H _cJ is high, and the value of B _r is reduced as H _cJ is improved.

However, as a result of intensive research by the present inventors, it was unexpectedly found that, in an R-T-B based sintered magnet containing Ga and having a B content less than the stoichiometric composition ratio of the R ₂ T ₁₄ B compound as described in Patent Document 1, the H _cJ can be improved by performing heat treatment for an extremely short holding time of less than 30 minutes. It was also found that as the holding time was increased, both B _r and H _cJ decreased. That is, in an R-T-B based sintered magnet containing Ga and having a B content less than the stoichiometric composition ratio of the R ₂ T ₁₄ B compound, it was found that both B _r and H _cJ showed maximum values or values close to maximum values when the holding time was less than 30 minutes (preferably 10 minutes or less, more preferably 3 minutes or less). Based on this finding, the present inventors have completed a method for producing an R-T-B based sintered magnet according to the present invention.

The manufacturing method according to the embodiment of the present invention will be described in detail below.
In the present invention, a material at a stage prior to completion of heat treatment under specific conditions (heat treatment at a temperature of 400°C or higher and 600°C or lower for a holding time of 10 seconds to less than 30 minutes) is referred to as an "RTB-based sintered magnet material" or simply as a "sintered magnet material." A material obtained after subjecting an R-T-B based sintered magnet material to heat treatment under the above-mentioned specific conditions is referred to as an "RTB-B based sintered magnet" or simply as a "sintered magnet." In other words, in this specification, the material before the heat treatment under the above-mentioned specific conditions and the material in the middle of said heat treatment are referred to as an "RTB-B based sintered magnet material."

<Method of manufacturing R-T-B based sintered magnet>
A method for producing a sintered RTB based magnet according to the present invention will now be described.
The method for producing a sintered R-T-B based magnet includes a step of preparing a sintered R-T-B based magnet material having a predetermined composition, and a heat treatment step of heat treating the sintered R-T-B based magnet material under specific conditions.
Each step will be described below.

(1) Step of Preparing Sintered RTB Based Magnet Material The sintered RTB based magnet material of the present disclosure contains at least R, B, Ga, and T, and the composition thereof satisfies the following requirements.

(R content: 27.0 mass% or more and 35.0 mass% or less)
R is a rare earth element, and includes at least one selected from the group consisting of Nd, Pr, and Ce. The content of R is 27.0 mass% or more and 35.0 mass% or less. If the content of R is less than 27.0 mass%, densification during sintering may be difficult, and if it exceeds 35.0 mass%, the main phase ratio may decrease and high B _r may not be obtained. The content of R is preferably 29.5 mass% or more and 33.0 mass% or less. If R is in such a range, higher B _r can be obtained.

(B content: 0.80 mass% or more and 0.93 mass% or less)
The content of B in the sintered magnet material is 0.80% by mass or more and 0.93% by mass or less, and satisfies the formula (1) described below. If the content of B is less than 0.80% by mass, the R ₂ T ₁₇ phase may be generated, and a high H _cJ may not be obtained, whereas if the content of B exceeds 0.93% by mass, the amount of the R-T-Ga phase generated may be too small to obtain a high H _cJ . The content of B is more preferably 0.88% by mass or more and 0.90% by mass or less, and a higher effect of improving H _cJ may be obtained.

(Ga content: 0.15 mass% or more and 1.0 mass% or less)
The Ga content is 0.15 mass% or more and 1.0 mass% or less. If the Ga content is less than 0.15 mass%, the amount of R-T-Ga phase produced is too small to eliminate the R ₂ T ₁₇ phase, and there is a risk that a high H _cJ cannot be obtained, and if the Ga content exceeds 1.0 mass%, unnecessary Ga is present, and there is a risk that the main phase ratio decreases and B _r decreases. Preferably, the Ga content is 0.2 mass% or more and 0.8 mass% or less, and more preferably 0.3 mass% or more and 0.6 mass% or less. A higher B _r and a higher H _cJ can be obtained.

(T content: 61.5% by mass or more and 70.0% by mass or less)
T is Fe or Fe and Co, and 90 mass % or more of T is Fe. By including Co, the corrosion resistance can be improved, but if the amount of Co substituted exceeds 10 mass % of T, If the content of T is less than 61.5 mass %, a high B _r may not be obtained. The content of T is 61.5 mass % or more and 70.0 mass % or less, and satisfies the above-mentioned formula (1). If it is less than 61.5% by mass, there is a risk of the _Br decreasing significantly.

The content of T in the sintered magnet material and the content of B together satisfy the following formula (1).

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

By satisfying formula (1), the content of B becomes smaller than that of a general R-T-B based sintered magnet. A general R-T-B based sintered magnet has a composition in which [ _{T]/55.85 (atomic weight of Fe) is smaller than 14[B]/10.8 (atomic weight of B) ([T] is the content of T in mass%) so that the soft magnetic phase R 2 T 17 phase} is not generated in addition to the main phase R 2 T 14 B phase. Unlike a general R-T-B based sintered magnet, the R-T-B based sintered magnet of the present invention is specified by formula (1) so that [T]/55.85 is larger than 14[B]/10.8. Note that the main component of T in the R-T-B based sintered magnet of the present invention is Fe, so the atomic weight of Fe is used.

(Remainder)
In one preferred embodiment of the sintered magnet material, the balance is T and inevitable impurities. In other words, as long as T satisfies formula (1), T and inevitable impurities may constitute the balance.
The inevitable impurities may include Cr, Mn, Si, La, Ce, Sm, Ca, Mg, etc., which are usually contained in didymium alloys (Nd-Pr), electrolytic iron, ferroboron, etc. Furthermore, the inevitable impurities in the manufacturing process may include O (oxygen), N (nitrogen), C (carbon), etc.

In yet another preferred embodiment of the sintered magnet material, any other elements may be further included within the scope of achieving the object of the present invention. Examples of other elements that can be selectively included in this way are listed below.

(Cu: more than 0 mass%, 1.0 mass% or less)
By including an appropriate amount of Cu, the _HcJ can be further improved.
Cu may be contained in an amount of 1.0 mass% or less. The Cu content is preferably 0.05 to 0.50 mass%. When contained, _HcJ can be further improved.

(Al: more than 0 mass%, 1.0 mass% or less)
By including an appropriate amount of Al, _HcJ can be further improved.
Al may be contained in an amount of 1.0 mass% or less. The content of Al is preferably 0.05 to 0.50 mass%. When Al is contained in an amount of 0.50 mass% or less, H _cJ Generally, 0.05 mass % or more of Al may be contained as an unavoidable impurity in the manufacturing process, but the total amount of the unavoidable impurities and the amount intentionally added is 1. The Al content may be 0 mass % or less, and more preferably 0.05 mass % or more and 0.5 mass % or less.

(Other elements)
In addition to the above elements, the sintered magnet material may contain one or more other elements (elements added intentionally other than unavoidable impurities). For example, such elements may contain small amounts (about 0.1 mass% each) of Ag, Zn, In, Sn, Ti, Ge, Y, H, F, P, S, V, Ni, Mo, Hf, Ta, W, Nb, Zr, etc. Furthermore, the elements listed as the above-mentioned unavoidable impurities may be intentionally added. Such elements may be contained in a total amount of, for example, about 1.0 mass%. This amount is sufficient to obtain an R-T-B based sintered magnet with a high H _cJ .

The R-T-B based sintered magnet material having the above composition can be prepared by the following steps (i) to (iii). In other words, the process for preparing the sintered magnet material can include the following steps (i) to (iii). Note that steps (i) to (iii) are merely examples of how the sintered magnet material can be manufactured, and the present invention is not limited thereto.
Furthermore, the process of preparing the sintered magnet material may further include a high-temperature heating step (step (iv)) and a diffusion step (step (v)) in addition to steps (i) to (iii).

(i) Step of Preparing Alloy Powder Metals or alloys of the respective elements are prepared so as to obtain the above-mentioned composition, and these are subjected to strip casting or the like to produce alloy flakes.
The obtained alloy flakes are subjected to hydrogen pulverization to obtain a coarsely pulverized powder having a size of, for example, 1.0 mm or less. The coarsely pulverized powder is then finely pulverized by a jet mill or the like to obtain a finely pulverized powder (alloy powder) having a particle size D50 (a value (median diameter) obtained by a laser diffraction method using an airflow dispersion method) of, for example, 3 to 7 μm. Note that a known lubricant may be used as an auxiliary agent in the coarsely pulverized powder before the jet mill pulverization, and in the alloy powder during and after the jet mill pulverization.

(ii) Compaction step: The obtained alloy powder is compacted in a magnetic field to obtain a compact. Compaction in a magnetic field may be performed by any known method including a dry compaction method in which dried alloy powder is inserted into a cavity of a die and compacted while a magnetic field is applied, and a wet compaction method in which a slurry in which the alloy powder is dispersed is poured into a cavity of a die and compacted while the dispersion medium of the slurry is discharged.

(iii) Sintering Step The compact obtained in the molding step is sintered to obtain a sintered R-T-B based magnet material. The compact can be sintered by a known method (for example, a sintering temperature of 1000°C to 1090°C and a sintering time of about 1 to 10 hours). In order to prevent oxidation due to the atmosphere during sintering, sintering is preferably carried out in a vacuum atmosphere or in an inert gas. The inert gas used is preferably an inert gas such as helium or argon.

(iv) High-temperature heating step The sintered magnet material obtained in the sintering step may be further subjected to a high-temperature heating step in which the material is heated at a relatively high temperature of 700° C. or higher and the sintering temperature or lower. By performing the high-temperature heating step, a sintered magnet having a higher _HcJ can be obtained. The heating time in the high-temperature heating step is preferably 1.5 hours or longer.

(v) Diffusion Step The sintered magnet material obtained in the sintering step or the sintered magnet material after the high-temperature heating step may be further subjected to a diffusion step. The diffusion step can be performed using a known diffusion source and diffusion method. For example, JP 2008-147634 A discloses a method in which a powder containing Dy, Tb, etc. is present on the surface of a sintered body (the surface of a sintered R-T-B magnet material) and heated at a temperature lower than the sintering temperature to diffuse Dy, Tb, etc. from the powder into the sintered body. In addition, WO2018/143230 discloses a method in which at least a part of an R-Ga alloy is brought into contact with at least a part of the surface of a sintered R-T-B magnet material, and a first heat treatment is performed at a temperature of 700°C or more and 950°C or less to diffuse R and Ga into the magnet.

After the sintering process (or after the high-temperature heating process and/or the diffusion process), the R-T-B sintered magnet material may be machined and then subjected to a heat treatment process.

(2) Heat Treatment Step The sintered magnet material obtained in the step of preparing the sintered magnet material is subjected to a heat treatment for the purpose of improving the magnetic properties. The heat treatment temperature is 400°C or more and 600°C or less. If the heat treatment temperature is less than 400°C or more than 600°C, the effect of improving _HcJ and _Br cannot be obtained. As a method for measuring the heat treatment temperature, it is preferable to measure the temperature by contacting a thermocouple with the R-T-B based sintered magnet material in the heat treatment furnace. Alternatively, simply, the temperature in the heat treatment furnace and the temperature of another R-T-B based sintered magnet material placed in the heat treatment furnace are simultaneously measured in advance using a thermocouple to investigate the correspondence between the temperature in the heat treatment furnace and the temperature of the R-T-B based sintered magnet material in the heat treatment furnace, and the temperature of the R-T-B based sintered magnet material in the heat treatment furnace can be read from the temperature in the heat treatment furnace based on the correspondence.

After the R-T-B based sintered magnet material reaches the heat treatment temperature, it is held at that heat treatment temperature for a period of 10 seconds or more and less than 30 minutes. The manufacturing method according to this embodiment is characterized in that this holding time is much shorter than conventional methods.

As described above, it has been known for some time that the H _cJ of the final R-T-B based sintered magnet can be improved by subjecting the sintered magnet material obtained by sintering to heat treatment. It was believed that in order to maximize the H _cJ of an R-T-B based sintered magnet, it was necessary to hold the magnet at the optimum heat treatment temperature for about 1.5 to 3 hours or more. It was also believed that B _r reached its maximum value with a holding time of about 10 seconds, and that as the holding time was further extended, it would decrease in line with the improvement of H _cJ . Because a short holding time results in a large decrease in H _cJ , heat treatment was conventionally performed with a holding time of 1.5 hours or more.

However, as a result of intensive research by the present inventors, it was found that in an R-T-B based sintered magnet material containing Ga and having a B content less than the stoichiometric composition ratio of the R ₂ T ₁₄ B compound, an R-T-B based sintered magnet with high B _r and high H _cJ can be obtained by setting the holding time during heat treatment to a very short time. It was found that in an R-T-B based sintered magnet material having the composition specified in this embodiment, the holding time at which the H _cJ of the R-T-B based sintered magnet is maximized exists in a range of 10 seconds or more and less than 30 minutes. Therefore, in this embodiment, the holding time during heat treatment is set to 10 seconds or more and less than 30 minutes.
The holding time is preferably from 10 seconds to 25 minutes, more preferably from 10 seconds to 10 minutes, even more preferably from 10 seconds to 5 minutes, and even more preferably from 10 seconds to 3 minutes. A sintered R-T-B based magnet having a higher _HcJ can be produced.

During the heat treatment process, it is preferable to perform the heat treatment in a vacuum atmosphere or an inert gas atmosphere to suppress oxidation due to oxygen in the atmosphere. Examples of the inert gas that can be used include helium and argon.

The obtained sintered magnet may be subjected to machining such as grinding in order to obtain the final product shape. In this case, the heat treatment may be performed before or after the machining. Furthermore, the obtained sintered magnet may be subjected to a surface treatment. The surface treatment may be a known surface treatment, such as Al vapor deposition, Ni electric plating, or resin paint.

The R-T-B based sintered magnet obtained in this manner has high _HcJ and B _r . The composition of the R-T-B based sintered magnet is substantially the same as that of the above-mentioned R-T-B based sintered magnet material.

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

Experimental Example 1

Each element was weighed so that the composition of the R-T-B based sintered magnet would be approximately the composition of No. 1 to No. 3 in Table 1 (for No. 2, the composition after diffusion would be approximately the composition of No. 2), and cast by strip casting to prepare a quenched alloy. The quenched alloy obtained was hydrogen embrittled in a pressurized hydrogen atmosphere, and then heated to 550°C in a vacuum and cooled to obtain a dehydrogenation treatment, to obtain a coarsely pulverized powder. Next, 0.04 mass% of zinc stearate was added to the obtained coarsely pulverized powder as a lubricant relative to 100 mass% of the coarsely pulverized powder, mixed, and then dry-pulverized in a nitrogen gas flow using an airflow pulverizer (jet mill device) to obtain a finely pulverized powder (alloy powder) with a particle size D ₅₀ (median diameter) of 4 μm.

The obtained alloy powder was mixed with a dispersion medium to prepare a slurry. Normal dodecane was used as the solvent, and methyl caprylate was mixed as the lubricant. The concentration of the slurry was 70% by mass of alloy powder, 30% by mass of dispersion medium, and 0.16% by mass of lubricant relative to 100% by mass of alloy powder. The slurry was molded in a magnetic field to obtain a compact. The magnetic field during molding was a static magnetic field of 0.8 MA/m, and the pressure was 5 MPa. The molding device used was a so-called perpendicular magnetic field molding device (horizontal magnetic field molding device), in which the magnetic field application direction and pressure direction are perpendicular to each other.

The obtained compacts were sintered in a vacuum at 1000°C to 1090°C (a temperature at which sufficient densification by sintering occurs for each sample) for 4 hours, cooled to room temperature, and then subjected to a high-temperature heat treatment in a vacuum at 800°C for 2 hours, after which they were rapidly cooled to room temperature to obtain sintered R-T-B magnet materials (Nos. 1' to 3'). The densities of the obtained sintered R-T-B magnet materials were 7.5 Mg/ ^m3 or more.

Next, the R-T-B sintered magnet material No. 2' was subjected to a diffusion treatment. First, a diffusion alloy was prepared. The raw materials of each element were weighed so that the composition of the diffusion alloy was approximately Pr: 80 mass%, Tb: 10 mass%, Ga: 5 mass%, and Cu: 5 mass%, and the raw materials were melted and a ribbon or flake-shaped alloy was produced by a single roll super-quenching method (melt spinning method). The obtained alloy was crushed in an argon atmosphere using a mortar and then passed through a sieve with a mesh size of 425 μm to prepare a diffusion alloy (PrTbGaCu alloy). The components of the obtained diffusion alloy were measured using high-frequency inductively coupled plasma optical emission spectroscopy (ICP-OES), and the composition was almost as intended (Pr: 80 mass%, Tb: 10 mass%, Ga: 5 mass%, Cu: 5 mass%). Next, No. The diffusion alloy was sprayed onto the surface (entire surface) of the R-T-B based sintered magnet material No. 2'. The amount sprayed was 3.3 mass% relative to 100 mass% of the R-T-B based sintered magnet material. After that, a diffusion process was performed in which the material was heated at 900°C for 3 hours in reduced pressure argon controlled at 50 Pa. In this way, an R-T-B based sintered magnet material (No. 2'') that had been subjected to the diffusion process was prepared.

Next, the R-T-B based sintered magnet materials No. 1', 2'' and 3' were subjected to heat treatment under the conditions shown in Table 2 to obtain R-T-B based sintered magnets. The heat treatment temperature was measured by contacting a thermocouple with the R-T-B based sintered magnet material in the heat treatment furnace.

The components of the obtained R-T-B based sintered magnet are shown in Table 1. The components in Table 1 were measured using inductively coupled plasma optical emission spectroscopy (ICP-OES). Table 1 also shows the sufficiency of formula (1). Here, "○" means that formula (1) is satisfied, and "×" means that formula (1) is not satisfied. Table 2 also shows the B _r and H _cJ values of the obtained R-T-B based sintered magnet. These B _r and H _cJ values were measured by machining the R-T-B based sintered magnet to a sample of 7 mm × 7 mm × 7 mm using a BH tracer.

In Table 2, values that were judged to have high magnetic properties were underlined. Specifically, when B _r was 1.40 (T) or more and H _cJ was 1500 (kA/m), both the B _r value and the H _cJ value were underlined. When either B _r or H _cJ did not meet the above criteria, neither value was underlined.

From the comparison of the five sintered magnets No. 1, the five sintered magnets No. 2, the two sintered magnets No. 4, the two sintered magnets No. 5, and the two sintered magnets No. 6 in Table 2, it can be seen that by setting the holding time in the heat treatment within the range of the present invention, both B _r and H _cJ show maximum values or values close to the maximum values obtained for that composition. In contrast, for No. 3, whose composition of the R-T-B based sintered magnet is outside the composition range of the present invention (the B content and formula (1) are outside the range), the H _cJ is significantly reduced at the holding time of the present invention (5 minutes). On the other hand, for No. 3, which has the same composition, when the holding time is extended (180 minutes), H _cJ improves, but B _r decreases with the improvement in H _cJ . Furthermore, as shown in Table 2, in order to obtain a higher B _r and a higher H _cJ , the holding time in the heat treatment is preferably 10 minutes or less, more preferably 5 minutes or less, and even more preferably 3 minutes or less.

Claims (5)

Contains at least R, B, Ga and T;
R: 27.0% by mass or more and 35.0% by mass or less, R is a rare earth element and includes at least one selected from the group consisting of Nd, Pr, and Ce;
B: 0.80% by mass or more and 0.93% by mass or less;
Ga: 0.15% by mass or more and 1.0% by mass or less;
preparing a sintered R-T-B based magnet material having T of 61.5 mass % or more and 70.0 mass % or less (T is Fe or Fe and Co, and 90 mass % or more of T is Fe) and satisfying the following formula (1);

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

and a heat treatment step of heat treating the sintered R-T-B based magnet material at a heat treatment temperature of 400°C or higher and 600°C or lower for a holding time of 3 minutes or higher and less than 30 minutes. The method for producing an R-T-B based sintered magnet according to claim 1, wherein the holding time in the heat treatment step is 3 minutes or more and 10 minutes or less. The step of preparing the R-T-B based sintered magnet material includes:
Providing an alloy powder having the composition of claim 1;
a compacting step of compacting the alloy powder in a magnetic field to obtain a compact;
3. The method for producing a sintered R-T-B based magnet according to claim 1, further comprising the step of sintering the compact to obtain a sintered magnet material. The step of preparing the R-T-B based sintered magnet material further includes the steps of:
The method for producing a sintered R-T-B based magnet according to claim 3, further comprising a high-temperature heating step of heating the sintered magnet material obtained in the step of obtaining the sintered magnet material at a temperature of 700° C. or higher and lower than a sintering temperature. The step of preparing the R-T-B based sintered magnet material further includes the steps of:
The method for producing a sintered R-T-B based magnet according to claim 4, further comprising a diffusion step of subjecting the sintered magnet material after the high-temperature heating step to a diffusion treatment.