WO2009125671A1

WO2009125671A1 - R-t-b-base alloy, process for producing r-t-b-base alloy, fines for r-t-b-base rare earth permanent magnet, r-t-b-base rare earth permanent magnet, and process for producing r-t-b-base rare earth permanent magnet

Info

Publication number: WO2009125671A1
Application number: PCT/JP2009/055939
Authority: WO
Inventors: 健一朗中島
Original assignee: 昭和電工株式会社
Priority date: 2008-04-10
Filing date: 2009-03-25
Publication date: 2009-10-15
Also published as: JP2009249729A

Abstract

Disclosed is an R-T-B-base alloy that is a raw material for a rare earth permanent magnet. In the R-T-B-base alloy, R represents at least one of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, T represents a transition metal containing not less than 80% by mass of Fe, and B contains not less than 50% by mass of B and contains not less than 0% by mass and less than 50% by mass of at least one of C and N. The R-T-B-base alloy is characterized in that the contents of R, T, and B are not less than 20% by mass and not more than 80% by mass, not less than 20% by mass and not more than 80% by mass, and not less than 0% by mass and not more than 1.5% by mass, respectively, R contains not less than 20% by mass of Dy, and diffraction peaks appear at 31.1 to 31.3° and 37.8 to 38.0° as measured by X-ray diffractometry (2θ/θ) using CuKα.

Description

RTB-based alloy and manufacturing method of RTB-based alloy, fine powder for RTB-based rare earth permanent magnet, RTB-based rare earth permanent magnet, RTB-based rare earth permanent magnet Manufacturing method

The present invention relates to an RTB-based alloy and a method for producing an RTB-based alloy, a fine powder for an RTB-based rare earth permanent magnet, an RTB-based rare earth permanent magnet, an RTB In particular, the present invention relates to an RTB-based alloy capable of producing an RTB-based rare earth permanent magnet excellent in coercive force and a fine powder for an RTB-based rare earth permanent magnet. is there.
This application claims priority based on Japanese Patent Application No. 2008-102600 filed in Japan on April 10, 2008, the contents of which are incorporated herein by reference.

RTB-based magnets are used for HD (hard disk), MRI (magnetic resonance imaging), various motors and the like because of their high characteristics. In recent years, in addition to the improvement in heat resistance of RTB-based magnets, the demand for energy saving has increased, so the ratio of motor applications including automobiles has increased.
An RTB-based magnet is generically called an Nd-Fe-B-based magnet or an RTB-based magnet because its main components are Nd, Fe, and B. R in the R—T—B system magnet is mainly obtained by substituting a part of Nd with other rare earth elements such as Pr, Dy, Tb, and T is a part of Fe other than Co, Ni, etc. Substituted with a transition metal. B is boron, and a part thereof can be substituted with C or N.

An RTB-based alloy serving as an RTB-based magnet is composed of a main phase composed of a R ₂ T ₁₄ B phase, which is a magnetic phase that contributes to the magnetization action, and a non-magnetic, rare-earth element-concentrated low melting point. An alloy in which an R-rich phase coexists. Since the RTB-based alloy is an active metal, it is generally melted or cast in a vacuum or an inert gas. In order to produce a sintered magnet from a cast RTB-based alloy ingot by powder metallurgy, the alloy ingot is pulverized to an average particle size of about 5 μm (d50: measured by a laser diffraction particle size distribution meter). After forming into an alloy powder, it is press-molded in a magnetic field, sintered at a high temperature of about 1,000 to 1,100 ° C in a sintering furnace, and then heat-treated and machined as necessary to further improve corrosion resistance. In order to achieve this, it is common to apply plating to obtain a sintered magnet.

In the RTB-based sintered magnet, the R-rich phase plays an important role as follows.
1) The melting point is low and it becomes a liquid phase at the time of sintering, which contributes to increasing the density of the magnet and thus improving the magnetization.
2) Eliminate grain boundary irregularities, reduce reverse domain nucleation sites and increase coercivity.
3) The main phase is magnetically insulated to increase the coercive force.
Therefore, if the dispersion state of the R-rich phase in the molded magnet is poor, local sintering failure and decrease in magnetism may occur. Therefore, it is important that the R-rich phase is uniformly dispersed in the molded magnet. Become. The distribution of the R-rich phase of the RTB-based sintered magnet is greatly influenced by the structure of the RTB-based alloy as a raw material.

Another problem that arises in the casting of RTB-based alloys is the formation of α-Fe in the cast alloy. α-Fe has deformability and remains in the pulverizer without being pulverized, so it not only lowers the pulverization efficiency when pulverizing the alloy, but also affects the composition variation and particle size distribution before and after pulverization. Effect. Furthermore, if α-Fe remains in the magnet after sintering, the magnetic properties of the magnet will be reduced.
For this reason, conventional alloys have been subjected to homogenization treatment for a long time at a high temperature as necessary to eliminate α-Fe. However, since α-Fe exists as peritectic nuclei, long-term solid phase diffusion is required for its erasure. When the rare earth content is 33% or less in an ingot with a thickness of several centimeters, α-Fe is erased. Was virtually impossible.

In order to solve the problem of α-Fe formation in this RTB-based alloy, a strip cast method (hereinafter referred to as “SC method”) for casting an alloy ingot at a higher cooling rate was developed. It is practically used. The SC method is a method in which the alloy is rapidly solidified by casting a thin piece of about 0.1 to 1 mm by pouring a molten metal onto a copper roll whose inside is water-cooled. In the SC method, since the molten metal is supercooled to a temperature below the formation temperature of the main phase R ₂ T ₁₄ B phase, it is possible to generate the R ₂ T ₁₄ B phase directly from the molten alloy, thereby suppressing the precipitation of α-Fe. can do. Furthermore, since the crystal structure of the alloy is refined by performing the SC method, an alloy having a structure in which the R-rich phase is finely dispersed can be generated. The R-rich phase reacts with hydrogen in a hydrogen atmosphere and expands into a brittle hydride. When this property is used, fine cracks are introduced in accordance with the degree of dispersion of the R-rich phase. When finely pulverized after this hydrogenation step, the alloy is broken by the large number of fine cracks generated by hydrogenation, so that the pulverizability becomes very good. In this way, the alloy cast by the SC method has a fine dispersion of the R-rich phase inside, so the dispersibility of the R-rich phase in the magnet after pulverization and sintering is also good, and the magnetic properties of the magnet (See, for example, Patent Document 1).

Also, the alloy flakes cast by the SC method are excellent in the homogeneity of the structure. The homogeneity of the structure can be compared with the crystal grain size and the dispersion state of the R-rich phase. In alloy flakes produced by the SC method, chill crystals may occur on the casting roll side of the alloy flakes (hereinafter referred to as the “mold surface side”), but as a whole, it is moderately fine and homogeneous that is brought about by rapid solidification. Can get a good organization.
As described above, the RTB-based alloy cast by the SC method is excellent in producing a sintered magnet because the R-rich phase is finely dispersed and the production of α-Fe is suppressed. Has an organization.

In addition, in order to obtain an RTB-based sintered magnet having a higher coercive force, the RTB-based alloy to which Dy is added is sintered using a two-alloy method to obtain the sintered magnet after sintering. A method is known in which a large amount of Dy is present in the vicinity of the grain boundary of the RTB-based sintered magnet obtained. As the two-alloy method, for example, an alloy having a low Dy concentration is prepared as a main phase RTB alloy, and an alloy having a high Dy concentration is prepared as a grain boundary phase RTB alloy. There is known a method in which two types of alloys, a phase system RTB alloy and a grain boundary phase system RTB alloy, are mixed and molded and sintered at a predetermined ratio. In the case of an RTB-based sintered magnet to which Dy is added using the two-alloy method, compared with the RTB-based sintered magnet having the same composition prepared using the one-alloy method, the coercive force The magnetic characteristics such as the above are excellent (see, for example, Patent Document 2).
Japanese Patent No. 3449166 JP-A-5-21219

However, in recent years, even higher performance RTB-based rare earth permanent magnets have been demanded, and it has been required to further improve the magnetic properties such as coercive force of RTB-based rare earth permanent magnets.
In order to improve the coercive force of the RTB-based rare earth permanent magnet, a method of increasing the Dy concentration in the RTB-based alloy can be considered. As the Dy concentration in the RTB-based alloy is increased, the rare earth permanent magnet obtained after sintering is more likely to concentrate in the grain boundary phase, and a rare earth permanent magnet having a higher coercive force is more likely to be obtained. . However, the higher the Dy concentration in the RTB-based alloy, the lower the pulverizability of the RTB-based alloy. Therefore, the grain boundary phase of the rare earth permanent magnet obtained using this alloy is reduced. In some cases, Dy cannot be uniformly distributed, and variation becomes large, and a certain quality cannot be obtained. In particular, when a plurality of RTB-based alloys are mixed and used for the production of a rare earth permanent magnet, there is a problem because the uniformity of the grain boundary phase of the obtained rare earth permanent magnet is lowered.
For this reason, in the prior art, the Dy concentration must be lowered at the expense of the effect of improving the coercive force by increasing the Dy concentration in the RTB-based alloy. The Dy concentration therein was in the range of 3% to 15% by mass.

The present invention has been made in view of the above circumstances, and has an excellent magnetic property in which the Dy concentration in the RTB-based alloy is high and the grindability of the RTB-based alloy is not reduced. An object of the present invention is to provide an RTB-based alloy as a raw material for a rare earth-based permanent magnet having characteristics.
Also, a method for producing the RTB-based alloy, fine powder for RTB-based rare earth permanent magnets and RTB-based rare earth permanent magnets prepared from the RTB-based alloy, RTB An object of the present invention is to provide a method for producing a TB-based rare earth permanent magnet.

The present inventors investigated the relationship between the RTB-based alloy used as a rare earth permanent magnet and the magnetic properties of the rare earth permanent magnet obtained using the alloy. Then, when producing a rare earth permanent magnet using an RTB-based alloy containing Dy, the present inventors used X-ray diffraction (2θ / θ) by CuKα as an RTB-based alloy. Even when the Dy concentration in the RTB-based alloy is increased, RT-T- is used by using a material having a diffraction peak at 31.1 to 31.3 ° and 37.8 to 38.0 °. It was found that a B-based alloy can be easily pulverized, a region having a high Dy concentration is uniformly formed in the grain boundary phase, and a rare earth-based permanent magnet having excellent coercive force and excellent magnetic properties can be obtained. Invented.

That is, the present invention provides the following inventions.
(1) RTB system which is a raw material used for rare earth permanent magnets (where R is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, At least one of Er, Tm, Yb, and Lu, T is a transition metal containing 80 mass% or more of Fe, B contains 50 mass% or more of B, and 0 mass of at least one of C and N %) And less than 50% by mass.) An alloy in which R is 20% by mass to 80% by mass, T is 20% by mass to 80% by mass, and B is 0% by mass to 1.5% by mass. The R contains 20% by mass or more of Dy, and X-ray diffraction (2θ / θ) by CuKα shows diffraction peaks at 31.1 to 31.3 ° and 37.8 to 38.0 °. An RTB-based alloy characterized by appearing.

(2) The RTB-based alloy according to (1), which is a flake having an average thickness of 0.1 to 2 mm manufactured by a strip casting method.
(3) The RTB-based alloy according to (1), which has an average thickness of 5 to 50 mm manufactured by a centrifugal casting method.
(4) The RTB-based alloy according to (1), which has an average thickness of 10 to 50 mm manufactured by a book mold method.

(5) A method for producing an RTB-based alloy according to any one of (1) to (4),
A method for producing an RTB-based alloy comprising casting a molten alloy and solidifying it, followed by heat treatment at a temperature of 1,100 to 1,300 ° C. for 5 minutes to 120 hours.
(6) The RTB system alloy produced by the method for producing the RTB system alloy according to any one of (1) to (4) or the RTB system alloy according to (5) A fine powder for RTB-based rare earth permanent magnets, characterized by being made from an alloy.
(7) An RTB-based rare earth permanent magnet produced using the fine powder for RTB-based rare earth permanent magnet according to (6).
(8) The RTB-based alloy according to any one of (1) to (4) or the RTB-based alloy produced by the method for producing the RTB-based alloy according to (5) An RTB system rare earth permanent comprising: a step of mixing an alloy with at least one other alloy for a rare earth permanent magnet; and a step of forming and sintering the mixed alloy. Magnet manufacturing method.

In the RTB-based alloy of the present invention, the R is 20% by mass to 80% by mass, the T is 20% by mass to 80% by mass, and the B is 0% by mass to 1.5% by mass. And R contains 20% by mass or more of Dy, and X-ray diffraction (2θ / θ) by CuKα shows diffraction peaks at 31.1 to 31.3 ° and 37.8 to 38.0 °. Therefore, it can be easily pulverized, a region having a high Dy concentration is formed uniformly in the grain boundary phase, and a rare earth permanent magnet having a high coercive force and excellent magnetic characteristics can be realized.
Further, in the method for producing an RTB-based alloy of the present invention, a molten alloy is cast and solidified, and then heat treatment is performed at a temperature of 1,100 to 1,300 ° C. for 5 minutes to 120 hours. The R is 20% by mass to 80% by mass, the T is 20% by mass to 80% by mass, the B is 0% by mass to 1.5% by mass, and the R is 20% by mass or more. In addition, the RTB-based alloy of the present invention in which diffraction peaks appear at 31.1 to 31.3 ° and 37.8 to 38.0 ° by X-ray diffraction (2θ / θ) by CuKα is obtained.

FIG. 1 is a photograph showing an example of an RTB-based alloy of the present invention, and a backscattered electron image when a cross section of a thin piece of the RTB-based alloy is observed with a scanning electron microscope (SEM). It is. FIG. 2 is a schematic front view showing a configuration of an alloy manufacturing apparatus according to an embodiment of the present invention. FIG. 3 is an X-ray diffraction diagram of fine powder for RTB-based rare earth permanent magnets. FIG. 4 is a diagram showing the Dy concentration contained in the powder left in the pulverizer after the fine powder for RTB system rare earth permanent magnets was produced.

Explanation of symbols

1 ... crucible, 2 ... tundish, 3 ... cooling roll, 4 ... container, 5 ... cast alloy flake.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a photograph showing an example of an RTB-based alloy of the present invention, and a backscattered electron image when a cross section of a thin piece of the RTB-based alloy is observed with a scanning electron microscope (SEM). It is. In FIG. 1, the left side is the mold surface side.
The RTB-based alloy shown in FIG. 1 is a raw material used for a rare earth-based permanent magnet, and is manufactured by the SC method. In FIG. 1, a white part is a part (R rich layer) where the concentration of rare earth elements is higher than the surroundings, and a black part is a part (phase) containing a lot of iron.

In the RTB-based alloy shown in FIG. 1, R is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. It is at least one kind, T is a transition metal containing 80 mass% or more of Fe, B contains 50 mass% or more of B, and at least one of C and N contains 0 mass% or more and less than 50 mass%. Further, the RTB-based alloy shown in FIG. 1 has an R of 20% by mass to 80% by mass, T of 20% by mass to 80% by mass, and B of 0% by mass to 1.5% by mass. It is included in the range.

In addition, the RTB-based alloy shown in FIG. 1 includes Dy containing R of 20% by mass or more.
As the Dy concentration contained in the RTB-based alloy is higher, the rare earth permanent magnet obtained after sintering is more likely to concentrate in the grain boundary phase, and a rare earth permanent magnet having a higher coercive force is more likely to be obtained. Become. If the Dy contained in the RTB-based alloy is less than 20% by mass, the coercive force of a rare earth permanent magnet produced using this may not be improved effectively.

In addition, the RTB-based alloy shown in FIG. 1 has characteristic diffraction peaks of 31.1 to 31.3 ° and 37.8 to 38.0 ° in X-ray diffraction (2θ / θ) by CuKα. It is what appears. In the RTB-based alloy shown in FIG. 1, diffraction peaks appear at 31.1 to 31.3 ° and 37.8 to 38.0 ° in X-ray diffraction (2θ / θ) by CuKα. Therefore, even if the RTB-based alloy contains 20% by mass or more of Dy, excellent grindability can be obtained. Therefore, the fine powder for rare earth permanent magnets made of the fine powder of the RTB system alloy can be easily prepared using the RTB system alloy shown in FIG. 1, and the obtained fine powder for the rare earth permanent magnet can be used. By producing a rare earth permanent magnet, it is possible to produce a rare earth permanent magnet in which a region having a high Dy concentration is uniformly formed in the grain boundary phase.

In order to produce the RTB-based rare earth permanent magnet of the present invention shown in FIG. 1, first, an RTB-based alloy is cast.
In this embodiment, the case where a cast alloy flake is produced by the SC method using the casting apparatus shown in FIG. 2 will be described as an example. The casting apparatus shown in FIG. 2 casts molten alloy by the SC method. In the casting apparatus shown in FIG. 2, reference numeral 1 is a crucible for supplying molten alloy to the dundish 2, reference numeral 2 is a dundish for supplying molten alloy to the cooling roll 3, and reference numeral 3 represents the molten alloy. A cooling roll having a diameter of about 60 to 80 mm for rapidly cooling and casting and solidifying the cast alloy flakes 5. Reference numeral 4 denotes a container for accommodating the cast alloy flakes 5 cast by the cooling roll 3.

The molten alloy is prepared in a high-frequency melting furnace (not shown). The temperature of the molten alloy is adjusted in the range of 1,300 ° C. to 1,500 ° C., although it depends on the alloy components. The prepared molten alloy is supplied from the crucible 1 to the cooling roll 3 through the tundish 2 as shown in FIG. The supply speed of the molten alloy and the number of rotations of the cooling roll 3 are controlled according to the thickness of the cast alloy. The number of rotations of the cooling roll 3 is, for example, about 0.5 to 3 m / s in terms of peripheral speed. The cast alloy flakes 5 solidified on the cooling roll 3 are separated from the cooling roll 3 on the opposite side of the tundish 2. The separated cast alloy flakes 5 are dropped and supplied to the container 4.
The average thickness of the cast alloy flakes 5 thus obtained is preferably in the range of 0.1 to 2 mm. When the average thickness is in the range of 0.1 to 2 mm, a fine alloy structure can be obtained, so that excellent grindability can be exhibited.

Next, the RTB-based alloy cast alloy flake 5 thus obtained is heat-treated at a temperature of 1,100 to 1,300 ° C. for 5 minutes to 120 hours. The heat treatment here can be performed by a method of holding at a temperature of 1,100 to 1,300 ° C. for 5 minutes to 120 hours when the molten alloy is cooled immediately after casting and solidifying. The heat treatment here is a method in which the molten alloy is immediately cooled to 200 ° C. or less immediately after the molten alloy is solidified, again heated to a temperature of 1,100 to 1,300 ° C. in a heating furnace, and held for 5 minutes to 120 hours. May be performed.

When the temperature of the heat treatment is less than 1,100 ° C. or when the heat treatment time is less than 5 minutes, 31.1 to 31.3 ° and 37.8 to 38.0 ° by powder X-ray diffraction measurement using CuKα. And a characteristic diffraction peak does not appear, and there is a possibility that sufficient grindability may not be obtained. Further, when the heat treatment temperature exceeds 1,300 ° C. or when the heat treatment time exceeds 120 hours, the structure becomes coarse, which is not preferable.

Thereafter, the cast alloy flakes 5 subjected to heat treatment are mixed at a predetermined ratio with another at least one rare earth permanent magnet cast alloy flakes obtained by different components and / or different production methods, and mixed flakes. Is done.
Thereafter, hydrogen cracking is performed by allowing the mixed flakes to store hydrogen at room temperature. At this time, since the volume of the cast alloy flake 5 of the present embodiment that has been heat-treated expands by occlusion of hydrogen, a large number of cracks (cracks) are easily generated inside the alloy and hydrogen is crushed. . Therefore, the cast alloy flakes 5 can be easily pulverized by hydrogen crushing the cast alloy flakes 5 subjected to the heat treatment. The mixed flakes thus crushed by hydrogen are pulverized to an average particle size d50 = 4 to 5 μm using a pulverizer such as a jet mill to obtain fine powder for a rare earth permanent magnet.

Thereafter, the RTB-based rare earth permanent magnet fine powder thus obtained is press-molded using, for example, a transverse magnetic field molding machine and baked at 1,050 to 1,100 ° C. in a vacuum. By bonding, an RTB-based rare earth permanent magnet can be obtained.

In the RTB-based alloy of this embodiment, R is 20% by mass to 80% by mass, T is 20% by mass to 80% by mass, and B is 0% by mass to 1.5% by mass. Since R contains Dy of 20% by mass or more and X-ray diffraction (2θ / θ) by CuKα shows diffraction peaks at 31.1 to 31.3 ° and 37.8 to 38.0 °, A region having a high Dy concentration is formed uniformly in the grain boundary phase, and a rare earth permanent magnet having a high coercive force and excellent magnetic characteristics can be realized.

More specifically, the RTB-based alloy of this embodiment has diffraction peaks at 31.1 to 31.3 ° and 37.8 to 38.0 ° in X-ray diffraction (2θ / θ) by CuKα. Therefore, even if R contains 20% by mass or more of Dy, excellent grindability can be obtained. Therefore, by using the RTB-based alloy of the present embodiment, it is possible to easily create a fine powder for a rare-earth permanent magnet composed of the fine powder of the RTB-based alloy of the present embodiment. By producing a rare earth permanent magnet using fine powder for magnets, a rare earth permanent magnet in which a region having a high Dy concentration is uniformly formed in the grain boundary phase can be produced. The rare earth permanent magnets thus obtained have a constant quality and excellent magnetic properties with high coercive force because composition fluctuations are suppressed.

In addition, in the manufacturing method of the RTB-based alloy of the present embodiment, the molten alloy is cast and solidified, and then heat treatment is performed at a temperature of 1,100 to 1,300 ° C. for 5 minutes to 120 hours. , R contains 20% by mass or more of Dy, and X-ray diffraction (2θ / θ) by CuKα shows unique diffraction peaks at 31.1 to 31.3 ° and 37.8 to 38.0 °. Thus, the RTB-based alloy of this embodiment having a high coercive force can be obtained.

Further, the method for producing a rare earth permanent magnet of the present embodiment includes a step of mixing the RTB-based alloy of the present embodiment with at least one other alloy for a rare earth permanent magnet, and the mixed alloy. The magnetic properties such as coercive force are further improved by appropriately changing the characteristics and mixing ratio of another rare earth permanent magnet alloy to be mixed. be able to.

In the above-described example, the case where the RTB-based alloy is manufactured using the SC method has been described. However, the RTB-based alloy according to the present invention is manufactured using the SC method. It is not limited. For example, a molten alloy may be cast using a centrifugal casting method, a book mold method, or the like as a method for producing an RTB-based alloy.
When the centrifugal casting method is used, for example, it is preferable to manufacture one having an average thickness of 5 to 50 mm. When the average thickness is in the range of 5 to 50 mm, the structure is larger than that produced by the SC method, but a predetermined pulverization characteristic can be exhibited by the subsequent heat treatment. Further, when the book mold method is used, it is preferable to manufacture a product having an average thickness of 10 to 50 mm. When the average thickness is in the range of 10 to 50 mm, predetermined grinding characteristics can be exhibited by heat treatment.

Further, in the above-described example, the cast alloy flakes which are the RTB-based alloy of the present invention and another cast alloy for at least one rare earth permanent magnet obtained by different components and / or different production methods are used. The flakes were mixed at a predetermined ratio to obtain mixed flakes, and the mixed flakes were finely pulverized into fine powders for rare earth permanent magnets. The present invention is not limited to this example.
For example, the mixing of the RTB-based alloy of the present invention with at least one other rare earth permanent magnet alloy can be performed in the state of a cast alloy flake, as shown in the above example. However, you may carry out in the state of the fine powder for rare earth permanent magnets formed by pulverizing the cast alloy flakes.
Further, the RTB-based alloy of the present invention can be used alone as a raw material for rare earth permanent magnet fine powder or rare earth permanent magnet without being mixed with another rare earth permanent magnet alloy.

"Example"
Weighed the raw materials blended so as to be Dy 35%, B 0.0%, Al 0.5%, Cu 10% and the balance Fe by mass ratio, using an alumina crucible, and in a high pressure atmosphere of argon gas at 1 atm. An alloy melt was prepared by melting in a melting furnace. Next, this molten alloy was supplied to the casting apparatus shown in FIG. 2 and cast by the SC method. The peripheral speed of the cooling roll 3 at the time of casting was 1.0 m / s. The average thickness of the cast alloy flakes 5 of the obtained RTB-based alloy was 0.3 mm.
Next, the cast alloy flakes 5 thus obtained were heat-treated in argon at a temperature of 1,200 ° C. for 12 hours using a heating furnace to obtain a cast alloy flake A1 of the example.

FIG. 3 shows an X-ray diffraction pattern of the powder of the cast alloy flake A1 of the example thus obtained.
Note that the powder X-ray diffraction (2θ / θ) measurement shown in FIG. 3 was performed with CuKα rays at a scanning speed of 2 ° / sec. As shown by arrows in FIG. 3, in the examples, characteristic diffraction peaks appeared at diffraction angles of 31.2 and 37.9 °.

Next, a cast alloy flake M was produced as another alloy for a rare earth permanent magnet. That is, the raw materials blended so that the mass ratio is Nd 32%, B 1.0%, Al 0.2%, and the balance Fe are weighed, and the cast alloy flake M is produced under the same conditions as when the cast alloy flake A is produced. did.

Then, the cast alloy flake A1 and the cast alloy flake M are mixed at a mass ratio of 5:95, subjected to a hydrogen storage treatment in hydrogen at 2 atm at room temperature, and then heated to 500 ° C. in a vacuum to remain. Hydrogen was extracted, 0.07% by mass of zinc stearate was added, and finely pulverized using a jet mill in a nitrogen stream. The average particle size of the alloy powder of the example obtained after fine pulverization (fine powder for RTB rare earth permanent magnet) by laser diffraction measurement was 5.0 μm.

"Comparative example"
A cast alloy flake A2 of a comparative example was obtained in the same manner as the production method of the cast alloy flake A1 in Example 1 except that the heat treatment was not performed.
For the powder of the cast alloy flake A2 of the comparative example thus obtained, X-ray diffraction measurement was performed in the same manner as the powder of the cast alloy flake A1 of Example 1. The result is shown in FIG. As shown in FIG. 3, in the comparative example, the specific diffraction peaks at the diffraction angles of 31.2 and 37.9 ° appearing in the example were not observed.

Next, as another alloy for a rare earth permanent magnet, a cast alloy flake M similar to that of the example is used, and the cast alloy flake A2 of the comparative example and the cast alloy flake M are mixed at the same ratio as in the example. In the same manner as in Example 1, it was subjected to hydrogen storage treatment and pulverized. The average particle size of the alloy powder of the comparative example (RTB-based rare earth permanent magnet fine powder) obtained after pulverization was 5.0 μm as measured by laser diffraction.

Subsequently, after the alloy powders of Examples and Comparative Examples obtained by fine pulverization were manufactured, the content of Dy with respect to all the elements contained in the alloy powder left in the pulverizer was examined. The result is shown in FIG.
The higher the Dy concentration shown in FIG. 4, the more powder of cast alloy flakes (RTB-based alloy) that remains in the pulverizer without being pulverized. As shown in FIG. 4, in the comparative example, it is about 1.5%, and the Dy concentration is higher than that of the example that is about 0.6%, and there are many powders remaining in the pulverizer. I understand. Therefore, in an Example, it turns out that crushability is improved compared with the comparative example.

Subsequently, among the alloy powders of the examples obtained by fine pulverization, a powder of 10 to 30 minutes from the start of pulverization was formed in a 100% nitrogen atmosphere using a molding machine in a transverse magnetic field, and a molding pressure of 0.8 t / cm ^2. The product was obtained by press molding. Then, the obtained molded body was heated from room temperature in a vacuum of 1.33 × 10 ⁻⁵ hPa and kept at 500 ° C. and 800 ° C. for one hour to remove zinc stearate and residual hydrogen. Then, it heated up to 1050 degreeC which is sintering temperature, was hold | maintained for 3 hours, and the magnet of five Examples was produced.

And the magnetic characteristic of the obtained magnet was measured with the BH curve tracer. The results are shown in Table 1.
In Table 1, “SR” is squareness, “BHmax” is the maximum energy product, “Br” is the residual magnetic flux density, and “Hcj” is the coercive force.

Further, five comparative example magnets were produced in the same manner as the example magnets, except that the alloy powders of the comparative examples obtained by fine pulverization were used instead of the alloy powders of the examples.
And the magnetic characteristic of the obtained magnet was measured like the magnet of an Example. The results are shown in Table 2.

From Table 1 and Table 2, it was confirmed that the magnets of the examples had sufficiently large Hcj, and SR, BHmax, and Br were large and excellent in magnetic characteristics as compared with the magnets of the comparative examples.
Further, in the magnet of the comparative example, the composition of the magnets of the example and the comparative example and the composition of the designed target magnet were investigated in order to investigate the cause of the SR, BHmax and Br being smaller than those of the magnet of the example. And compared. The results are shown in Table 3. In addition, the numerical value shown in Table 3 shows weight%.

From Table 3, it was found that in the comparative example, the Dy component was higher than the target composition, and Dy was excessively contained in the powder at the later stage of pulverization. This is presumably because the cast alloy flake A2 of the comparative example was hard to be crushed and was excessively discharged in the later stage of pulverization.

Claims

RTB system, which is a raw material used for rare earth permanent magnets (where R is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm) , Yb, and Lu, T is a transition metal containing 80 mass% or more of Fe, B contains 50 mass% or more of B, and at least one of C and N is 0 mass% or more of 50 mass%. Including less than mass%) alloy,
The R is 20% by mass to 80% by mass, the T is 20% by mass to 80% by mass, the B is 0% by mass to 1.5% by mass,
The R contains 20% by mass or more of Dy, and X-ray diffraction (2θ / θ) by CuKα shows diffraction peaks at 31.1 to 31.3 ° and 37.8 to 38.0 °. An RTB-based alloy characterized by
2. The RTB-based alloy according to claim 1, wherein the RTB-based alloy is a thin piece having an average thickness of 0.1 to 2 mm manufactured by a strip casting method.
2. The RTB-based alloy according to claim 1, which has an average thickness of 5 to 50 mm manufactured by a centrifugal casting method.
The RTB-based alloy according to claim 1, which has an average thickness of 10 to 50 mm manufactured by a book mold method.
A method for producing an RTB-based alloy according to claim 1,
A method for producing an RTB-based alloy comprising casting a molten alloy and solidifying it, followed by heat treatment at a temperature of 1,100 to 1,300 ° C. for 5 minutes to 120 hours.
An RTB-based alloy according to claim 1 or an RTB-based alloy manufactured by the method for manufacturing an RTB-based alloy according to claim 5 is used. Fine powder for RTB rare earth permanent magnets.
7. An RTB-based rare earth permanent magnet produced using the fine powder for RTB-based rare earth permanent magnet according to claim 6.
An RTB-based alloy according to claim 1 or an RTB-based alloy produced by the method for producing an RTB-based alloy according to claim 5 and at least one other rare earth Mixing the alloy for the permanent magnet;
And a method of manufacturing an RTB rare earth permanent magnet, comprising: forming and sintering a mixed alloy.