CN111696777A - Method for producing R-T-B sintered magnet - Google Patents

Abstract

The present invention provides a method for producing an R-T-B based sintered magnet with reduced RH content and high H _cJ and high H _k . The method for producing an R-T-B based sintered magnet of the present invention is characterized in that the R-T-B based sintered magnet contains R: 28.5 mass % or more and 33.0 mass % or less (R is at least one of rare earth elements, At least one of Nd and Pr), B: 0.85 mass % or more and 0.91 mass % or less, Ga: 0.2 mass % or more and 1.0 mass % or less, Cu: 0.05 mass % or more and 0.50 mass % or less, T: 61.5 mass % or more 70.0 mass % or less, and satisfy the relationship of 14[B]/10.8<[T]/55.85 ([B] is the content of B expressed in mass %, and [T] is the content of T expressed in mass %); The method for producing an R-T-B based sintered magnet includes a step of producing a quenched alloy having a thickness of 0.4 mm or less by supplying a raw material alloy melt to a rotating cooling roll at a temperature of 1520°C or more and 1650°C or less for quenching.

Description

Manufacturing method of R-T-B based sintered magnet

technical field

The present invention relates to a method for manufacturing an R-T-B based sintered magnet.

Background technique

R-T-B based sintered magnet (R is at least one of rare earth elements, contains at least one of Nd and Pr, T is Fe or Fe and Co, and 90% by mass or more of T is Fe) mainly contains R The main phase of the ₂ T ₁₄ B compound and the grain boundary phase located in the grain boundary portion of the main phase are known to have the highest performance among permanent magnets.

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

With the expansion of such applications, for example, when it is used in an electric motor for an electric vehicle, it is sometimes exposed to a high temperature such as 100° C. to 160° C., and it is required to be able to operate stably even at a high temperature.

However, the conventional R-T-B based sintered magnet has a problem that the coercive force H _cJ (hereinafter abbreviated as "H _cJ ") decreases at high temperature, and irreversible thermal demagnetization occurs. When an R-T-B-based sintered magnet is used in an electric vehicle motor, there is a concern that the motor may not operate stably due to a decrease in H _cJ due to use at a high temperature. Therefore, there is a need for an R-T-B based sintered magnet which has high H _cJ at room temperature and also has high H _cJ at high temperature.

In order to increase the H _cJ at room temperature, the heavy rare earth element RH (mainly Dy) has been added to the _R -T-B sintered magnet, but there is a residual magnetic flux density Br (hereinafter sometimes abbreviated as " _Br ") lowering problem. In addition, due to the limited production area of Dy, there are problems that supply is unstable and prices fluctuate greatly. Therefore, a technique for increasing the H _cJ of an R-T-B based sintered magnet without using a heavy rare-earth element RH such as Dy as much as possible is required.

As such a technique, for example, Patent Document 1 discloses a technique in which the content of B is reduced compared with that of a general R-T-B based sintered magnet, and one or more kinds selected from the group consisting of Al, Ga, and Cu are included. The metal element M is used to generate the R ₂ T ₁₇ phase, and the volume ratio of the transition metal-rich phase (R-T-Ga phase) generated using the R ₂ T ₁₇ phase as a raw material can be sufficiently ensured, thereby suppressing the content of Dy and obtaining R-T-B sintered magnet with high coercivity.

In addition, as described above, the most widely used application of R-T-B sintered magnets is electric motors. Especially in applications such as electric vehicles for electric vehicles, it is very effective to increase H _cJ in order to ensure high temperature stability. However, these characteristics are accompanied by , the squareness ratio H _k /H _cJ (hereinafter sometimes simply referred to as “H _k /H _cJ ”) also needs to be improved. If H _k /H _cJ is low, there is a problem of easy demagnetization. Therefore, there is a need for an R-T-B based sintered magnet having high H _k /H _cJ as well as high H _cJ . In addition, in the field of R-T-B based sintered magnets, in general, the parameter Hk measured to obtain H _k /H _cJ is used as J (magnetization strength)−H (magnetic field strength) ) in the second quadrant of the curve, the read value of the H-axis when J reaches a position where J reaches a value of 0.9×J _r (J _r is the residual magnetization, J _r =B _r ). A value obtained by dividing this Hk by _HcJ of the demagnetization curve ( _Hk / _HcJ = _Hk (kA/m)/ _HcJ (kA/m)×100(%)) is defined as a squareness ratio.

prior art literature

Patent Literature

Patent Document 1: International Patent Publication No. 2013/008756

SUMMARY OF THE INVENTION

The problem to be solved by the invention

In the R-T-B-based rare earth magnet described in Patent Document 1, although the content of Dy can be reduced and high H _cJ can be obtained, it is different from the general R-T-B-based sintered magnet (the amount of B is more than that of R _{2 )} . Compared with the stoichiometric ratio of the T ₁₄ B type compound), there is a problem that H _k /H _cJ decreases. Specifically, in a general R-T-B based sintered magnet, H _k is a value of 90% or more of H _cJ (that is, H _k /H _cJ is 90% or more). On the other hand, the R-T-B-based rare earth magnet described in Patent Document 1 has a high H _cJ , and the value of H _k is higher than that of a general R-T-B-based sintered magnet, but is higher than that of a general R-T-B-based sintered magnet. - Compared with the TB-based sintered magnet, the value of H _k is relatively lower than the value of H _cJ , and there is a problem that H _k /H _cJ may be less than 90%.

To this end, the present invention provides a method for producing an RT-B based sintered magnet with a reduced RH content and high H _cJ and high H _k .

Technical solutions for solving problems

The manufacturing method of the R-T-B-based sintered magnet of the present invention is characterized in that, in the exemplary embodiment, the manufactured R-T-B-based sintered magnet contains:

R: 28.5 mass % or more and 33.0 mass % or less (R is at least one of rare earth elements, and contains at least one of Nd and Pr);

B: 0.85 mass % or more and 0.91 mass % or less;

Ga: 0.2 mass % or more and 1.0 mass % or less;

Cu: 0.05 mass % or more and 0.50 mass % or less;

T: 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),

The R-T-B sintered magnet satisfies the following formula (1):

14[B]/10.8＜[T]/55.85(1)

(wherein, [B] is the content of B expressed in mass %, and [T] is the content of T expressed in mass %)

The manufacturing method of the R-T-B sintered magnet includes:

A step of producing a quenched alloy with a thickness of 0.4 mm or less by supplying the molten material of the raw material alloy to a rotating cooling roll at a temperature of 1520°C or more and 1650°C or less for quenching;

The process of making alloy powder from the above alloy;

The forming process of forming the above-mentioned alloy powder to obtain a formed body;

a sintering step of sintering the above-mentioned molded body to obtain a sintered body; and

A heat treatment step of subjecting the sintered body to heat treatment.

In one embodiment, in the step of producing the quenched alloy, the amount of the molten metal supplied to the cooling roll per unit time and the rotational speed of the cooling roll are adjusted to produce quenching with a thickness of 0.15 mm or more and 0.35 mm or less. alloy.

In one embodiment, the molten metal of the raw material alloy is supplied to a rotating cooling roll at a temperature of 1550° C. or higher and 1600° C. or lower, and quenched.

In one embodiment, in the step of producing the quenched alloy, a copper roll having a diameter in the range of 200 to 400 mm is used as the cooling roll, and the amount of the molten metal supplied to the cooling roll per unit time is set to Within the range of 50-250 g/sec, the rotational peripheral speed of the said cooling roll shall be within the range of 500-2000 mm/sec.

Invention effect

According to an embodiment of the present invention, it is possible to provide a method for producing an R-T-B based sintered magnet having a reduced RH content and having high H _cJ and high H _k .

Description of drawings

FIG. 1 is a schematic diagram showing a configuration example of a thin strip continuous casting apparatus 100 used in the embodiment of the present invention.

Symbol Description

10: cooling roll; 20: crucible; 22: high frequency coil; 24: melt of raw material alloy; 30: rotating disk; 40: quenched alloy

Detailed ways

The embodiment shown below is an example of a manufacturing method of an R-T-B based sintered magnet in order to embody the technical idea of the present invention, and the present invention is not limited to the following.

As described in Patent Document 1, by making the amount of B less than that of a general R-T-B based sintered magnet (less than the amount of B in the stoichiometric ratio of the R ₂ T ₁₄ B-type compound) and adding Ga or the like to generate a rich The transition metal phase (R-T-Ga phase) can increase H _cJ .

However, as a result of intensive research, the inventors of the present invention found that the microstructure of the quenched alloy formed from the melt of the raw material alloy cannot be sufficiently uniformly refined by the conventional strip casting method, and the improvement of H _k is insufficient. Happening. The inventors have tried methods such as changing the composition of the raw material alloy, adding trace elements, etc., but no sufficient effect has been obtained. However, it has been found that R-T-B sintering with high H _cJ and high H _k can be obtained by increasing the temperature of the alloy melt before quenching to a temperature higher than the conventional value, for example, by about 50° C. or more. magnet. This is considered to be due to the realization of a uniformly refined tissue structure after quenching. In addition, it has been found that such an effect is effective when the amount of B is lower than that of a normal R-T-B-based alloy and Ga is added.

Hereinafter, the manufacturing method according to the embodiment of the present invention will be described in detail.

[R-T-B sintered magnet]

First, the R-T-B based sintered magnet obtained by the production method according to the embodiment of the present invention will be described.

[Composition of R-T-B sintered magnet]

The composition of the R-T-B based sintered magnet according to this embodiment includes:

R: 28.5 mass % or more and 33.0 mass % or less (R is at least one of rare earth elements, and contains at least one of Nd and Pr);

B: 0.85 mass % or more and 0.91 mass % or less;

Ga: 0.2 mass % or more and 1.0 mass % or less;

Cu: 0.05 mass % or more and 0.50 mass % or less;

T: 61.5 mass % or more and 70.0 mass % or less,

And satisfy 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 %)

By having the above-mentioned composition, the amount of B is less than that of a general R-T-B based sintered magnet, and Ga and the like are contained, so that the R-T-Ga phase can be formed in the two-grain boundary, and the H _cJ is high. Here, the R-T-Ga phase refers to a compound represented by Nd ₆ Fe ₁₃ Ga. The R ₆ T ₁₃ Ga compound has a La ₆ Co ₁₁ Ga ₃ type crystal structure. In addition, the R ₆ T ₁₃ Ga compound may become an R ₆ T _13-δ Ga _1+δ compound (δ is typically 2 or less) in some states. For example, when a large amount of Cu and Al are contained in the R-T-B based sintered magnet, it may become R ₆ T _13-δ (Ga _1-x-y Cu _x A _y ) _1+δ .

Hereinafter, each composition will be described in detail.

(R: 28.5 to 33.0 mass %)

R is at least one of rare earth elements, and contains at least one of Nd and Pr. Content of R is 28.5-33.0 mass %. When _R is less than 28.5 mass %, densification at the time of sintering may become difficult, and when it exceeds 33.0 mass %, the main phase ratio may decrease and high Br may not be obtained. The content of R is preferably 29.5 to 32.5 mass %. As long as R is within such a range, a higher B _r can be obtained.

(B: 0.85 to 0.91 mass %)

The content of B is 0.85 to 0.91 mass %. When B is less than 0.85 mass %, the R ₂ T ₁₇ phase may be formed and high H _cJ may not be obtained. If B exceeds 0.91 mass %, the amount of R-T-Ga phase formed may be too small and high H _cJ may not be obtained. . A part of B can be replaced by C.

The content of B satisfies the following formula (1):

14[B]/10.8＜[T]/55.85 (1)

By satisfying the formula (1), the content of B is smaller than that in a general R-T-B based sintered magnet. In a general R-T-B sintered magnet, the ratio of [T]/55.85 (atomic weight of Fe) is less than the ratio of [T]/55.85 (atomic weight of Fe) so that the R ₂ T ₁₇ phase of the soft magnetic phase is not formed in addition to the R ₂ T ₁₄ B phase as the main phase. The composition of 14 [B]/10.8 (atomic weight of B) ([T] is the content of T in mass %). The R-T-B-based sintered magnet of the present invention is different from a general R-T-B-based sintered magnet in that [T]/55.85 is more than 14[B]/10.8 as defined by the formula (1). In addition, since the main component of T in the R-T-B based sintered magnet of this invention is Fe, the atomic weight of Fe is used.

(Ga: 0.2 to 1.0 mass %)

The content of Ga is 0.2 to 1.0 mass %. When Ga is less than 0.2 mass %, the amount of the R-T-Ga phase produced is too small, the R ₂ T ₁₇ phase cannot be eliminated, and there is a possibility that high H _cJ cannot be obtained, and when it exceeds 1.0 mass %, excess is generated. With Ga, there is a possibility that the ratio of the main phase decreases and _Br decreases.

(Cu: 0.05 to 0.50 mass %)

The content of Cu is 0.05 to 0.50 mass %. When Cu is less than 0.05 mass %, high H _cJ may not be obtained, and if Cu exceeds 0.50 mass %, sinterability may be deteriorated and high H _cJ may not be obtained.

(Al: 0.0 to 0.50 mass %)

The content of Al is 0.0 to 0.50 mass %. H _cJ can be increased by containing Al. Al is usually contained as an unavoidable impurity in the production process, for example, at 0.02 mass % or more, but may be contained in a total of 0.50 mass % or less of the amount contained as an unavoidable impurity and the amount added intentionally.

(T: 61.5% by mass to 70.0% by mass)

Among T, T is Fe or Fe and Co, and 90 mass % or more of T is Fe. Corrosion resistance can be improved by containing Co, but when the substitution amount of Co exceeds 10 mass % of Fe, there is a possibility that high _Br cannot be obtained. The content of T is 61.5 mass % or more and 70.0 mass % or less, and the above formula (1) is satisfied. When content of T is less than 61.5 mass %, there exists a possibility that _Br will fall significantly. Preferably T is the remainder.

The R-T-B based sintered magnet of the present invention may further contain Cr, Mn, Si, La, and Ce as unavoidable impurities generally contained in neodymium-praseodymium alloy (Nd-Pr), electrolytic iron, iron-boron alloy, and the like. , Sm, Ca, Mg, etc. Moreover, O (oxygen), N (nitrogen), C (carbon), etc. can be illustrated as an unavoidable impurity in a manufacturing process. In addition, the R-T-B based sintered magnet of the present invention may contain one or more other elements (elements intentionally added other than unavoidable impurities). For example, a small amount (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. In addition, the above-mentioned elements listed as unavoidable impurities may be intentionally added. Such elements can be contained, for example, in a total amount of about 1.0% by mass. At this level, there is a sufficient possibility to obtain an R-T-B based sintered magnet having high H _cJ and high H _k .

The R-T-B based sintered magnet having the above-described composition according to the present embodiment is produced by the following production method including the steps of: a step of producing a quenched alloy; a step of producing an alloy powder from the above-mentioned alloy; A molding process of molding the above alloy powder to obtain a molded body; a sintering process of sintering the molded body to obtain a sintered body; and a heat treatment process of subjecting the sintered body to heat treatment.

Next, the manufacturing method of the R-T-B based sintered magnet which concerns on embodiment of this invention is demonstrated in detail.

1. The process of making the quenched alloy

In the embodiment of the present invention, a quenched alloy is produced by weighing and preparing raw materials so that the composition of the above-mentioned R-T-B based sintered magnet may be obtained. Quench alloys are produced by strip casting. The strip casting method is a casting method in which a molten alloy is quenched using a cooling roll. Compared with mold casting in which the cooling rate is relatively low, in the quenched solidified alloy obtained by the strip casting method, the crystal structure becomes uniform and fine. In addition, the quenched alloy may be produced by crushing the quenched solidified alloy obtained by the strip casting method.

FIG. 1 is a schematic diagram showing a configuration example of a thin strip continuous casting apparatus 100 used in the present embodiment. The apparatus 100 shown in the figure includes a cooling roll 10 that is rotated at a predetermined peripheral speed by a motor (not shown), and a crucible 20 that is supported so as to be capable of tilting. The cooling roll 10 is preferably a cooling roll made of copper having excellent thermal conductivity. It is preferable to use a copper roll as a cooling roll. The copper roll refers to a cooling roll mainly composed of copper having excellent thermal conductivity. The crucible 20 is provided with a high-frequency coil 22 for melting the raw material alloy. The solid raw material alloy thrown into the crucible 20 is heated and melted by induction heating by the high-frequency current flowing through the high-frequency coil 22 . The melt 24 of the molten raw material alloy is kept at a predetermined temperature inside the crucible 20 .

In the present embodiment, the temperature of the raw material alloy melt (alloy melt) 24 is adjusted to be in the range of 1520°C or higher and 1650°C or lower, which is higher than the conventional temperature (typically 1450°C). After that, the molten alloy 24 at the temperature is supplied from the crucible 20 to the cooling roll 10 . In the example of FIG. 1 , the molten alloy 24 is supplied to the cooling roll 10 through the rotating disk 30 . The temperature of the molten metal is the temperature in the crucible (preferably measured in the vicinity of the bottom surface in the crucible). It should be noted that the temperature of the molten alloy 24 can be measured with an accuracy of within ±0.005°C of error by, for example, a B thermocouple. The alloy melt 24 in contact with the surface of the rotating cooling roll 10 is rapidly deheated and solidified into a thin strip extending in the direction of the rotational peripheral speed of the cooling roll 10 , whereby the quenched alloy 40 is produced. The thickness of the thin strip-shaped quenched alloy 40 can be adjusted by adjusting the amount (supply rate) of the molten alloy 24 supplied to the cooling roll 10 per unit time and the rotational speed of the cooling roll 10 . Since the cooling rate of the quenched alloy 40 varies depending on the thickness of the quenched alloy 40 , the thickness of the quenched alloy 40 is an important factor as an index of the cooling rate. In the present embodiment, the quenched alloy 40 having a thickness of 0.4 mm or less is produced.

In the embodiment of the present invention, it was found that α-Fe can be suppressed by setting the temperature of the alloy melt 24 to 1520° C. or more and 1650° C. or less, and controlling the strip casting conditions so that the thickness of the quenched alloy 40 becomes 0.4 mm or less. and the formation of the R ₂ T ₁₇ phase, resulting in high H _k . The temperature of the molten alloy 24 is preferably a temperature of 1550° C. or higher and 1600° C. or lower from the viewpoint that such effects can be remarkably achieved.

In a preferred embodiment, in the step of producing the quenched alloy, the amount of molten metal supplied to the cooling roll per unit time and the rotational speed of the cooling roll are adjusted to produce a quenched alloy with a thickness of 0.15 mm or more and 0.35 mm or less. When a quenched alloy having such a thickness range is formed, the cooling rate is increased, so that the formation of the R ₂ T ₁₇ phase can be further suppressed.

In addition, the thickness in the quenched alloy of the present invention refers to an average value obtained by arbitrarily extracting 100 quenched alloys (cast pieces produced by the strip casting method) and measuring the thickness direction.

In a preferred embodiment, in the step of producing the quenched alloy, a copper roll having a diameter in the range of 200 to 400 mm is used as a cooling roll. Then, the amount of the molten metal supplied to the cooling roll per unit time was set to be in the range of 50 to 250 g/sec, and the rotational speed of the cooling roll was set to be in the range of 500 to 2000 mm/sec.

After the quenched alloy is obtained in this way, a step of producing an alloy powder from the quenched alloy, a molding step of molding the alloy powder to obtain a molded body, a sintering step of sintering the molded body to obtain a sintered body, and a heat treatment step of subjecting the sintered body to heat treatment are sequentially performed. . Hereinafter, these steps will be described.

2. The process of making alloy powder

Next, the raw material alloy is roughly pulverized by, for example, hydrogen pulverization, etc., to prepare a roughly pulverized powder having an average particle size of 1.0 mm or less. Then, the coarsely pulverized powder is finely pulverized by a jet mill or the like in an inert gas to obtain a finely pulverized powder (raw material alloy powder) having, for example, a particle size D50 of 3 to 5 μm. As an auxiliary agent, a known lubricant can be added to the coarsely pulverized powder before the jet mill pulverization, the alloy powder during the jet mill pulverization, and the jet mill pulverization.

3. Forming process

Using the obtained raw material alloy powder, it was molded in a magnetic field to obtain a molded body. Forming in a magnetic field can use any known forming methods in a magnetic field, including: inserting dry alloy powder into the cavity of a metal mold, and applying a magnetic field while forming a dry molding method; while injecting slurry into the cavity of the metal mold Wet molding method, etc.

4. Sintering process

The molded body is sintered to obtain a sintered body (sintered magnet). The sintering of the molded body can use a known method. In addition, in order to prevent oxidation by the atmosphere at the time of sintering, it is preferable to perform sintering in a vacuum atmosphere or an inert gas. As the inert gas, inert gases such as helium and argon are preferably used.

5. Heat treatment process

For the purpose of improving the magnetic properties, the sintered magnet is preferably subjected to heat treatment. Known conditions can be used for the heat treatment temperature, heat treatment time, and the like. For example, heat treatment (one-stage heat treatment) may be performed only at a relatively low temperature (400°C or more and 600°C or less), or after heat treatment at a relatively high temperature (700°C or more and below the sintering temperature (for example, 1050°C or less)), Heat treatment (two-stage heat treatment) is performed at a relatively low temperature (400°C or more and 600°C or less). Preferable conditions include 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), and further at 440°C or more and 550°C or less. The heat treatment is performed for about 5 minutes to 500 minutes. The heat treatment is preferably performed in a vacuum atmosphere or an inert gas (helium, argon, etc.).

The obtained sintered magnet may be subjected to mechanical processing such as grinding for the purpose of forming the final product shape or the like. In this case, the heat treatment may be performed before machining or after machining. In addition, a surface treatment may be applied to the obtained sintered magnet. The surface treatment may be a known surface treatment, and for example, surface treatment such as Al vapor deposition, Ni electroplating, resin paint, and the like can be performed.

Example

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

[Example 1]

(The process of producing a quenched alloy)

Each element was weighed so that the composition of the R-T-B based sintered magnet might be approximately the composition of No. 1 to No. 23 in Table 1, and cast by the strip casting method to produce a quenched alloy. The process of producing the quenched alloy used the strip casting apparatus 100 shown in FIG. 1 . In addition, the cooling roll 10 in the thin strip continuous casting apparatus 100 is a copper roll with a diameter of 240 mm, and the gate width of the crucible 20 is 40 mm. In addition, at this time, a quenched alloy was produced under the production conditions of A to F shown in Table 2. Table 2 shows the melt temperature of the raw material alloy, the supply speed of the melt, and the peripheral speed of the roll. Note that, for No. 1 to No. 23, the conditions of A and C were used as the conditions for producing the quenched alloy, and for No. 12, the conditions of B and D to F were used as the conditions for the production of the quenched alloy. In addition, the thicknesses of the quenched alloys produced under the conditions of A to F were measured respectively (100 sheets of the quenched alloys having the compositions of No. 1 to No. 23 were arbitrarily extracted, and the average thickness was measured), and the results were shown as in Table 2. It should be noted that the thickness of the quenched alloy shown in Table 2 may vary depending on the conditions of A to F, but it is almost between the compositions (No. 1 to No. 23) of the R-T-B based sintered magnet. Since no difference is seen, only the thickness of the quenched alloy is described according to the conditions of A to F. In addition, the melt temperature of the raw material alloy was measured with a B thermocouple in the vicinity of the bottom surface in the crucible.

(Step of producing alloy powder from the above alloy)

The obtained quenched alloy was subjected to hydrogen embrittlement in a hydrogen pressurized atmosphere, and then subjected to a dehydrogenation treatment of heating to 550C in a vacuum and cooling to obtain a coarsely pulverized powder. Next, 0.04 mass % of zinc stearate was added as a lubricant to the obtained coarsely pulverized powder with respect to 100 mass % of the coarsely pulverized powder, and after mixing, it was carried out in a nitrogen stream using a jet mill (jet mill). Dry crushing was performed to obtain a fine crushed powder (alloy powder) having a particle size D50 (median diameter) of 4 μm.

(Molding process of molding alloy powder to obtain a molded body)

The obtained alloy powder is mixed with a dispersion medium to prepare a slurry. As a solvent, n-dodecane was used, and methyl octanoate was mixed as a lubricant. The concentration of the slurry was 70% by mass of the alloy powder, 30% by mass of the dispersion medium, and 0.16% by mass of the lubricant relative to 100% by mass of the alloy powder. The above slurry is molded in a magnetic field to obtain a molded body. The magnetic field at the time of molding was a static magnetic field of 0.8 MA/m, and the pressing force was 5 MPa. In addition, the shaping|molding apparatus used the so-called right-angle magnetic field shaping|molding apparatus (transverse magnetic field shaping|molding apparatus) in which the magnetic field application direction and the pressing direction were orthogonal.

(Sintering step of sintering the molded body to obtain a sintered body)

The obtained molded body was sintered in a vacuum at 1000° C. or more and 1050° C. or less (a temperature at which densification can be sufficiently generated by sintering was selected for each sample) for 4 hours, and then quenched to obtain a sintered body. The density of the obtained sintered body was 7.5Mg/m ³ or more.

(Heat treatment step of applying heat treatment to the sintered body)

The obtained sintered body was kept in a vacuum at 800°C for 2 hours, then rapidly cooled to room temperature, then kept in a vacuum at 430°C for 2 hours, cooled to room temperature, and heat-treated to obtain an R-T-B sintered body magnet.

The components of the obtained R-T-B based sintered magnet are shown in Table 1. In addition, each component (other than O, N, and C) in Table 1 can be measured using the high frequency inductively coupled plasma optical emission spectrometry (ICP-OES). In addition, the O (oxygen) content was measured using a gas analyzer using a gas melting-infrared absorption method, the N (nitrogen) content was measured using a gas analyzer using a gas melting-thermal conductivity method, and the C (carbon) content was using Measurement was performed using a gas analyzer using a combustion-infrared absorption method.

The satisfaction of the formula (1) is shown in Table 1. Among them, "○" means that the formula (1) is satisfied, and "x" means that the formula (1) is not satisfied.

After the heat treatment, the R-T-B based sintered magnets (No. 1 to No. 23) were respectively machined to produce samples with a length of 7 mm, a width of 7 mm, and a thickness of 7 mm, and measured at room temperature with a B-H tracer. The magnetic properties ( _{Br, HcJ , Hk} , _Hk / _HcJ ) of each sample under the temperature (20°C±10°C).

The measurement results are shown in Tables 3 and 4. It should be noted that in Hk/H _cJ (square ratio), H _k is the I (magnetization size)-H (magnetic field strength) curve In the second quadrant, I reaches 0.9×J _r (J _r is the residual Magnetization, the value of H at the location of the value of J _r = _Br ). In addition, Table 3 shows the difference of H _k of the A condition and the C condition of the same composition of the R-T-B based sintered magnet (same No.).

[Table 1]

No. Nd Pr Dy Tb B Co Al Cu Ga Nb Zr Fe O N C Formula 1) 1 24.3 8.2 0.0 0.0 0.87 0.1 0.1 0.1 0.60 0.0 0.0 64.9 0.4 0.0 0.1 ○ 2 24.3 8.0 0.0 0.1 0.85 0.5 0.1 0.1 0.70 0.0 0.0 64.6 0.4 0.0 0.1 ○ 3 23.6 7.8 0.0 0.0 0.90 0.5 0.1 0.2 0.50 0.0 0.0 66.1 0.1 0.1 0.1 ○ 4 31.5 0.0 0.0 0.0 0.90 0.9 0.1 0.1 0.50 0.0 0.0 65.6 0.1 0.1 0.1 ○ 5 23.6 7.8 0.0 0.0 0.90 0.5 0.1 0.3 0.50 0.0 0.0 65.9 0.1 0.1 0.1 ○ 6 23.6 7.7 0.0 0.0 0.90 0.9 0.4 0.1 0.40 0.0 0.0 65.7 0.1 0.1 0.1 ○ 7 23.6 7.7 0.0 0.0 0.88 0.5 0.1 0.2 0.48 0.0 0.0 66.2 0.1 0.1 0.1 ○ 8 23.1 7.7 0.0 0.0 0.89 0.5 0.1 0.1 0.50 0.0 0.0 66.7 0.1 0.1 0.1 ○ 9 23.0 7.7 0.0 0.0 0.91 0.5 0.1 0.1 0.47 0.0 0.0 66.8 0.1 0.1 0.1 ○ 10 22.7 7.4 0.0 0.1 0.91 0.2 0.1 0.2 0.24 0.0 0.0 67.7 0.1 0.1 0.1 ○ 11 22.4 7.2 0.0 0.3 0.91 0.9 0.1 0.1 0.40 0.1 0.1 67.1 0.1 0.1 0.1 ○ 12 22.5 7.5 0.0 0.0 0.88 0.2 0.1 0.2 0.50 0.0 0.1 67.8 0.1 0.1 0.1 ○ 13 24.3 8.2 0.0 0.0 0.94 0.5 0.1 0.1 0.70 0.0 0.0 64.4 0.4 0.0 0.1 × 14 23.7 7.7 0.0 0.0 0.92 0.5 0.1 0.1 0.51 0.0 0.0 66.0 0.1 0.1 0.1 × 15 23.7 7.7 0.0 0.0 0.91 0.5 0.2 0.2 0.51 0.0 0.1 65.6 0.1 0.1 0.1 × 16 23.4 7.9 0.0 0.0 0.83 0.5 0.1 0.1 0.40 0.0 0.0 66.4 0.1 0.1 0.1 ○ 17 23.4 7.4 0.0 0.0 0.95 0.5 0.1 0.2 0.49 0.0 0.0 66.6 0.1 0.1 0.1 × 18 23.1 7.7 0.0 0.0 0.91 0.5 0.1 0.1 0.10 0.0 0.0 67.0 0.1 0.1 0.1 ○ 19 23.1 7.6 0.0 0.0 0.84 0.9 0.1 0.1 0.48 0.0 0.0 66.4 0.1 0.1 0.1 ○ 20 23.1 7.6 0.0 0.0 0.93 0.1 0.1 0.1 0.50 0.0 0.0 67.0 0.1 0.1 0.1 × twenty one 23.1 7.6 0.0 0.0 0.92 0.5 0.1 0.1 0.47 0.0 0.0 66.8 0.1 0.1 0.1 ○ twenty two 23.1 7.6 0.0 0.0 0.94 0.5 0.1 0.1 0.47 0.0 0.0 66.8 0.1 0.1 0.1 × twenty three 22.7 7.4 0.0 0.0 0.91 0.5 0.1 0.1 0.14 0.0 0.0 67.7 0.1 0.1 0.1 ○

[Table 2]

[table 3]

[Table 4]

As shown in Table 3, the C conditions of Nos. 1 to 12 (values indicated by bold lines and underlines) satisfying the conditions of the present invention yielded R-TB-based sintered magnets having high H _cJ and high H _k . On the other hand, even with the same magnet compositions (No. 1 to 12), in the condition A in which the melt temperature of the raw material alloy is outside the range of the present invention, H _k is lowered, so H _k /H _cJ is also lowered. . As shown in Table 3, by adopting the conditions of the present invention, the difference in H _k reached 80 kA/m or more, and the H _k was greatly improved. In addition, none of Nos. 13 to 23 having a magnet composition deviating from the present invention obtained high H _cJ (conditions of A and C). In addition, as shown by the difference of H _k in Table 3, in Nos. 13 to 23, compared between Condition A and Condition C, almost no improvement in H _k was observed. This shows that H _k is improved in the composition range of the R-T-B based sintered magnet of the present invention.

In addition, as shown in Tables 3 and 4, the melt temperature of the raw material alloy is preferably 1550°C (condition C) to 1640°C (condition E), and more preferably 1550°C (condition C) to 1600°C (condition D). Furthermore, as shown in Table 4, even in the range of the melt temperature of the raw material alloy of the present invention, under the condition (Condition F) in which the thickness of the quenched alloy deviates, H _cJ and H _k are greatly reduced .

Industrial Availability

The method for producing an R-T-B-based sintered magnet of the present invention can provide an R-T-B-based sintered magnet that can operate stably even at high temperatures. Such R-T-B-based sintered magnets can be used in a variety of motors such as voice coil motors (VCM) for hard disk drives, motors for electric vehicles (EV, HV, PHV), and motors for industrial equipment, and home appliances. the use of.

Claims (4)

1. A method for producing an R-T-B sintered magnet, comprising:

the R-T-B sintered magnet comprises:

r: 28.5 to 33.0 mass%, wherein R is at least 1 of rare earth elements and contains at least 1 of Nd and Pr;

b: 0.85 mass% or more and 0.91 mass% or less;

ga: 0.2 to 1.0 mass%;

cu: 0.05 to 0.50 mass%;

t: 61.5 to 70.0 mass%, wherein T is Fe or Fe and Co, and at least 90 mass% of T is Fe,

the R-T-B sintered magnet satisfies the following formula (1):

14[B]/10.8＜[T]/55.85(1)

wherein [ B ] is the content of B in mass%, and [ T ] is the content of T in mass%;

the method for producing the R-T-B sintered magnet comprises:

supplying the molten raw alloy to a rotating cooling roll at a temperature of 1520 ℃ to 1650 ℃ to quench the molten raw alloy, thereby producing a quenched alloy having a thickness of 0.4mm or less;

a step of preparing alloy powder from the alloy;

a molding step of molding the alloy powder to obtain a molded body;

a sintering step of sintering the molded body to obtain a sintered body; and

and a heat treatment step of performing heat treatment on the sintered body.

2. The method of manufacturing an R-T-B sintered magnet according to claim 1, wherein:

in the step of producing the quenching alloy, the amount of the melt supplied to the chill roll per unit time and the rotational speed of the chill roll are adjusted to produce the quenching alloy having a thickness of 0.15mm to 0.35 mm.

3. The method of manufacturing an R-T-B sintered magnet according to claim 1 or 2, wherein:

the molten metal of the raw material alloy is rapidly cooled by supplying the molten metal to a rotating cooling roll at a temperature of 1550 ℃ to 1600 ℃.

4. The method of manufacturing an R-T-B sintered magnet according to claim 2, wherein:

in the step of producing the quenching alloy, a copper roll having a diameter in the range of 200 to 400mm is used as the cooling roll, the amount of the melt supplied to the cooling roll per unit time is in the range of 50 to 250 g/sec, and the rotational speed of the cooling roll is in the range of 500 to 2000 mm/sec.

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