JPH11297519A - Manufacturing method of rare earth magnet alloy and rare earth magnet alloy cast by centrifugal casting method - Google Patents

Abstract

(57) [Problem] When an ingot obtained by centrifugally casting an alloy for SmCo magnets is magnetized by powder metallurgy, the coercive force is improved, but the residual magnetization tends to deteriorate. This problem is solved by centrifugal casting to produce a magnet alloy having characteristics equivalent to those obtained by a box mold. SOLUTION: When centrifugal casting is performed while rotating a mold in which an annular weir 5 serving as a partition for forming two or more pool portions 10 is formed on the inner surface of a centrifugal casting mold 1, the main phase S
Sm ₁ Co ₅ exists in a network around m ₂ Co ₁₇ , and the average crystal grain size of the main phase Sm ₂ Co ₁₇ is 100 μm.
The above rare earth magnet alloy is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a raw material alloy for producing a rare earth magnet, and more particularly, to a method for casting a molten metal of an SmCo-based magnet alloy, in particular, a Sm ₂ Co _17- based magnet alloy, into a centrifugal casting mold. . Further, the present invention relates to an alloy which is cast by centrifugal casting and is in the form of an ingot or a crushed powder thereof, which is a raw material used for producing an Sm ₂ Co ₁₇ magnet.

[0002]

2. Description of the Related Art As a conventional method of casting an alloy for a rare earth magnet, a method of casting a molten alloy in a mold such as a box has been adopted. Particularly, the cooling condition desired at present is a direction in which the cooling rate is moderately increased. Therefore, in order to increase the cooling rate by a conventional casting method using a mold such as a box-shaped mold, Japanese Patent Publication No. 5-38051 is required. A method of winding a cooling pipe around a mold as proposed in Japanese Patent Application Laid-Open Publication No. H10-15083, or a method of setting a mold cavity narrow so as to reduce the thickness of an ingot is performed. In order to cast a large volume of molten metal to obtain a thin ingot, it is necessary to increase the area of the main surface by the thickness of the ingot. However, if a large amount of molten metal is poured into the pouring section of a mold with a narrow mold spacing, the molten metal will be deprived of heat by the mold and flow, so the cooling state will differ depending on the location of the ingot, and the structure will be partially different, resulting in segregation. Also easily occur.

In general, a box-type mold requires disassembly and assembling work for taking out an ingot for each mold. Further, the box-shaped mold is easily deformed by thermal strain, the cost required for repairing the mold is high, and the life is short. Furthermore, the larger the mold, the greater the deformation, the more difficult it is to reassemble, and the higher the frequency of troubles such as leakage of hot water. In particular, in the case of a water-cooled box-type mold, great care must be taken because leakage of hot water leads to a disaster such as steam explosion.

[0004] The centrifugal casting of alloys for rare earth magnets is disclosed in Japanese Patent Application Laid-Open No. Hei 9-111383 (Japanese Patent Application No. 7-29).
No. 3617). In this publication, a molten metal is deposited on a rotating cylindrical mold through a special tundish at a low average deposition rate, and is cast under conditions such that the next molten layer is stacked on a layer once solidified.
It is claimed that fine structure control with little segregation of Zr, which is an additive element of the -Co alloy, can be obtained and magnet properties can be improved. However, when a magnet was manufactured using the ingot cast under the conditions employed in this method as a raw material, it was confirmed that the coercive force was improved but the residual magnetization was rather deteriorated. As described above, the manufacturing conditions of centrifugal casting that can provide magnets having magnet properties equal to or higher than those of ingots obtained by conventional box casting have not been elucidated.

In general, when a Sm ₂ Co ₁₇ alloy ingot obtained by a conventional die casting is observed with a reflected electron beam image using, for example, a scanning electron microscope, it is found that Sm ₂ C
It can be clearly confirmed that the Sm ₁ Co ₅ phase exists in a network state around the o ₁₇ main phase. On the other hand, the Sm obtained by the centrifugal casting method described in Japanese Patent Application Laid-Open No.
_As shown in FIG. 8, the metal structure of the ₂ Co _17- based alloy ingot has a high cooling rate, so that the separation of both phases becomes fine and unclear. In addition, Sm ₂ determined by observation with a polarizing microscope
The crystal grain size of the Co ₁₇ main phase is also reduced to 100 μm or less.
When the alloy ingot having such a structure is pulverized, the ratio of the particles that are not single crystals, that is, the crystal grain boundaries are present in the pulverized particles is increased, so that the degree of orientation when the magnetic field is formed is reduced,
After all, it is considered that the residual magnetization was reduced even after the sintering heat treatment.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method for producing an alloy for a rare earth magnet, particularly an alloy for a SmCo-based magnet, which solves the above-mentioned problems. That is, rather than the moldability using a box mold or the like, which is inferior in workability as in the past, cost and safety are disadvantageous in terms of safety, centrifugal casting method, by devising the mold shape and pouring method, the box An object of the present invention is to provide a casting method capable of realizing substantially the same cooling conditions as when a mold is used, and a centrifugal casting alloy capable of producing a magnet having the same performance as a box-shaped casting alloy.
In the present invention, the alloy for a rare earth magnet is an alloy which is magnetized by a powder metallurgy process as it is. Also, Sm
In some cases, two or more alloy powders having different Sm contents in a Co-based magnet are mixed to obtain a raw material powder.
One or more alloys for producing alloy powders are also included in the alloy for rare earth magnets of the present invention.

[0007]

Means for Solving the Problems The present inventors have proposed SmCo
While analyzing the cooling conditions and the structure of ingots using a water-cooled box-shaped mold for alloys for magnets, when the structure of the centrifugal casting mold is modified, it is surprising that the cast structure fundamentally changes, It has been found that substantially the same casting structure is obtained as in the form casting. That is, the present invention relates to a centrifugal casting mold in which a mold having an annular weir serving as a partition for forming two or more pools is formed on the inner surface of a centrifugal casting mold while rotating the mold. A method for producing a rare earth magnet alloy, characterized in that a molten metal of the rare earth magnet alloy is poured into the well portion from a nozzle moving in a direction. Further, the present invention relates to an ingot or a crushed powder thereof used for producing an Sm ₂ Co ₁₇ based rare earth magnet, wherein Sm ₁ Co ₅ exists in a network around Sm ₂ Co _{17 as} a main phase, A rare earth magnet alloy cast by a centrifugal casting method, characterized in that the phase has an average crystal grain size of Sm ₂ Co ₁₇ of 100 μm or more. Hereinafter, the present invention will be described in detail.

In the present invention, as in the conventional method, first,
A pure metal, a mother alloy, or the like, which is a raw material of a rare earth element-containing alloy, is dissolved in a vacuum or an inert atmosphere such as argon gas. Next, when casting after melting, centrifugal casting is performed. At this time, the centrifugal casting equipment used is composed of a rotary drive mechanism and a cylindrical mold. In the present invention, solidification cooling conditions of the obtained alloy are important, and in order to make the same conditions as solidification cooling conditions in a normal thin ingot casting mold, an appropriate space in the rotation axis direction is provided on the inner surface of the cylindrical mold. And a plurality of annular weirs having a suitable height. Then, the molten metal for the rare earth magnet alloy is cast into a pool formed between adjacent weirs via a tundish and a nozzle provided on the tundish. When the molten metal has accumulated in the basin to an appropriate thickness, the position of the tundish is moved, and the molten metal is sequentially poured into the next basin.
The molten metal poured into each of the basins is solidified while being pressed against the wall surface of the basin by centrifugal force.

Furthermore, it is preferable to select a casting condition that keeps almost all of the casting metal immediately after casting completely filling the basin portion in a liquid phase state. This is basically performed by selecting casting conditions such as the thickness of the ingot, the shape of the mold (specifically, the ratio of the mold), and the casting speed (specifically, the speed of pouring the molten metal). The adjustment is performed by appropriately selecting a mold material, a mold cooling method, a mold diameter, a rotation speed (centrifugal acceleration), an inert atmosphere, and the like, which are factors that give the following. If the melting scale is small, the molten metal can be easily maintained in “almost liquid state” by the time casting of the molten metal in the cavity is completed, and solidification can be started after the flow of the molten metal is calmed down. It is known that the thickness of the ingot at that time is desirably in the range of 15 to 70 mm. According to the present invention described above, the heat is taken away from the mold only on one side, and therefore, by casting into an ingot having a thickness almost half that of the box-shaped mold, the conventional small-scale melting is performed. The solidification and cooling can be carried out under substantially the same conditions as in the casting in the box-shaped mold at the time.

In the present invention, the structure of the obtained ingot is important, and the outer shape of the ingot itself does not matter. The shape of the mold is determined as follows. That is, the required total area of the mold is determined by the molten casting amount and the thickness of the ingot, and the inner diameter and the length in the major axis direction of the mold can be determined mainly from workability such as ease of taking out the ingot after casting. Here, the inner diameter of the mold is desirably 300 mm or more, and is desirably 400 mm or more in consideration of improvement in workability. The length of the mold is preferably three times or less, more preferably two times or less, the diameter of the mold in consideration of the ease of taking out the ingot after casting.

The mold ratio that determines the preferred casting conditions in the present invention is represented by M weight / A weight in FIG. M is a mold fragment in a portion off the weir, A is an ingot fragment having the same bottom area as M, and the mold diameter is sufficiently large and the curvature can be ignored with respect to the ingot thickness.
M weight = mold thickness × bottom area of M part × mold density,
Weight of A = ingot thickness × bottom area of M part × ingot density. Therefore, the mold ratio is M weight / A weight =
(Bottom mold thickness x mold density) / (ingot thickness x ingot density). The mold ratio is preferably in the range of 1 to 10. If the mold ratio is less than 1, cooling will be too slow,
In particular, it takes a long time to lower the temperature to a temperature at which oxidation does not pose a problem even when taken out of the chamber, and productivity cannot be improved. On the other hand, if it exceeds 10, the cooling becomes too fast, the mold weight becomes heavy, the mold and the rotary drive become expensive, and it is not economical. More preferably, the mold ratio is in the range of 1 to 5.

The interval between the weirs is 30 mm or more and 30
0 mm or less is desirable. When this interval is 30 mm or less, heat transfer in the axial direction as well as in the circumferential direction becomes so large that it cannot be ignored. On the other hand, if the distance between the weirs is 300 mm or more, the distance over which the molten metal flows in the longitudinal direction of the mold becomes large, and solidification tends to start before the molten metal is sufficiently accumulated in the pool, so that a conventional box-shaped mold is used. It becomes difficult to realize cooling conditions. The interval between the weirs is more desirably 50 mm or more and 200 mm or less. When the alloy composition is the same, the height of the weir provided in the circumferential direction and serving as a partition for the molten metal can be determined using a half of the optimum mold cavity gap conventionally cast by the box mold as a guide. The specific numerical value is in the range of 5 mm to 50 mm, and more preferably, is selected in the range of 8 mm to 35 mm.

It is desirable that the molten metal discharged from the nozzle at the time of casting be cast such that the average molten metal deposition rate in each molten metal pool is 0.1 cm / sec or more. Here, the average molten metal deposition rate refers to a numerical value obtained by dividing the molten metal pouring amount (volume) per unit time by the bottom area of each pool.
On the upper limit side of the weir interval range described in [0012], there is a tendency that solidification considerably progresses before pouring into the pool is finished. To counteract this tendency, it is advantageous to control the average melt deposition rate as described above.

In the present invention, one fountain is usually poured from one nozzle. It is desirable to move the nozzle so that the pouring position can be poured into the next pool. Specifically, the tundish is moved in the axial direction of the mold in order to move the position of the pouring nozzle provided on the tundish above the plurality of wells. At that time, it is more preferable than the continuous movement that the nozzle stops once above the basin, then moves over the weir, and stops again above the next basin. Here, in order to make the thickness of each ingot in the longitudinal direction uniform and to prevent the molten metal from overflowing over the entire circumference of the weir, the notch is formed so that the molten metal flows into the adjacent pool at the top of the weir. Can also be provided. If a notch is provided in the partition weir,
The height from the bottom of the pool to the bottom of the notch is the same as the height of the weir described above.

When the molten casting amount is large, for example, as shown in FIG.
By providing the nozzles 7 at the locations, it is possible to simultaneously cast from two locations into the pools located below each. By using such a casting device, it is possible to increase the amount of molten metal per unit time from the crucible, and to prevent the temperature of the molten metal from dropping on the fixed tundish 3 and the movable tundish 2, thereby enabling stable casting. Also, the residual metal on the tundish 2 can be reduced,
It is also possible to increase the yield. Further, by doing so, the moving distance of the fixed tundish 3 can be reduced to half as compared with the case where the number of nozzles is one, and the restriction on the space of the vacuum chamber 2 can be reduced. That is, the necessity of enlarging the chamber for storing the movable tundish 2 in the chamber is eliminated, and the equipment can be economical.
In addition, the number of the nozzles 7 is set within a range where the average deposition rate in each of the pools can be maintained at 0.1 cm / s or more by increasing the pouring rate per unit time from the crucible.
It is also possible to provide three or more at equal intervals.

In practice, the rotation speed of the mold must be such that the acceleration of the centrifugal force is at least 1 G so that the molten metal does not fall when it reaches the upper part of the mold. Further increasing the centrifugal force avoids the so-called "raining phenomenon" in which the molten metal falls in a rainy manner due to insufficient acceleration of the molten metal. The effect can be reduced. For this reason, the rotation speed of the mold is preferably set to be 3 G or more. In centrifugal casting using a mold provided with a weir, shrinkage after casting does not allow a sufficient gap between the ingot and the mold so that the ingot cannot be taken out, but the SmCo-based magnet alloy remains brittle and remains in the mold. The ingot in the state can be easily taken out by crushing it with a hammer or the like.

Next, the structure of the cast alloy for a rare earth magnet according to the present invention will be described. The structure of the alloy according to the present invention is basically the same as that of the box-type mold casting alloy although it is a centrifugal casting alloy. Specifically, first, 50-
A reticulated (network) structure is observed with a SEM (reflection electron beam) microscope of about 1000 times. In this organization Sm
_This is a structure in which the SmCo ₅ phase is distributed in a network around the ₂ Co ₁₇ crystal phase. On the other hand, the alloy obtained by the conventional centrifugal casting method disclosed in Japanese Patent Application Laid-Open No. Hei 9-111383 has a fine casting structure and a small crystal grain size of the main phase Sm ₂ Co ₁₇ phase. In other words, since the ratio of particles in which the grain boundaries exist in the pulverized particles increases,
It is considered that the degree of orientation when the magnetic field was formed was lowered, and eventually, the residual magnetization was lowered even after the sintering heat treatment. On the other hand, the crushed powder of the ingot having the structure of the present invention has a moderately large crystal grain size, and thus can avoid the above-mentioned disadvantages. The crystal grain size of the cast alloy is measured by a polarizing microscope. The grain size of the cast alloy of the present invention is generally 120 to 3 mm.
It is in the range of 00 μm, and is coarser than the conventional centrifugally cast alloy. The alloy composition of the Sm ₂ Co ₁₇ based magnet of the present invention is a general one, and is expressed by weight percentage of Sm 24
~ 27%, Fe10 ~ 22%, Cu4.5 ~ 9%, Zr
1.5 to 3.5%, with Co remaining, can be preferably used. Further, various elements that partially substitute these components may be used. For example, C to substitute for Sm
e, such as Ti, Nb, and Hf, which substitute for Zr.

[0018]

[Action] Industrially used SmCo magnet alloys include:
Since Fe, Cu, Zr, etc. are added, and various crystal phases are present, and the crystal phases existing between a high temperature region and a low temperature region also change, the structure of the alloy obtained, the crushability, depending on the casting conditions. And other physical properties such as magnetism change slightly. Therefore, the particle size distribution after pulverization in the pulverization step for magnet production, the degree of orientation at the time of magnetic field molding, and the like are not always good under the casting conditions that simply prevent segregation of Zr. In consideration of such points, in the present invention, in addition to the use of centrifugal casting, the structure of the mold is modified, and in some cases, the casting conditions of the molten metal are further defined, which is the same as that of the conventional box mold. It is possible to create cooling conditions. Furthermore, the adoption of centrifugal casting makes it possible to solve various problems, such as deformation, leakage of hot water, poor durability, poor workability, and various problems of the conventional box mold. Hereinafter, the present invention will be described with reference to examples.

[0019]

EXAMPLE 1 An apparatus was prepared by combining a vacuum induction melting furnace and a centrifugal casting apparatus as shown in FIG. In FIG. 2, 1 is a mold, 2 is a moving tundish, 3 is a fixed tundish, 4 is a melting crucible, 5 is a weir, and 7 is two nozzles. The inner diameter of the steel mold used was 450 mmφ, and as shown in the sectional view of the mold in FIG.
mm, the height of the weir was 20 mm, and the height (h) from the bottom of the pool to the bottom of the notch was 15 mm. The mold 1 is driven and rotated by a rotation mechanism 6 (FIG. 2). The molten metal 41 was poured from the melting crucible 4 through the fixed tundish 3 and the movable tundish 2 to the pool 10 of the mold 1 from the nozzle 7 to form an ingot on the inner surface of the mold. When the molten metal is cast to a predetermined thickness in the basin section 10, the moving tundish 2 is sequentially moved so that the nozzle 7 is positioned above the adjacent basin section 10. Using an alumina melting crucible 4 of FIG. 2, in an argon gas atmosphere, the composition of the ingot after casting was Sm 25 wt%, Fe 16 wt%, C
The raw materials are blended in consideration of the dissolution yield of each element so as to have a composition of u5 wt%, Zr3 wt%, and the balance Co, and 70 kg
Was produced and then cast in the manner described above. The average melt deposition rate was 0.23 to 0.29 cm / s, and the thickness of the ingot was in the range of 15 mm to 18 mm.
The template ratio was 1.8.

FIG. 5 shows a backscattered electron beam image of the cross section of the ingot in the thickness direction by SEM. The Sm ₂ Co ₁₇ alloy ingot has a structure in which mainly a 2-17 phase (a phase which looks blacker in the reflected electron beam image) is surrounded by a 1-5 phase (a phase which looks whiter in the reflected electron beam image) in a net-like manner. ing. This structure is equivalent to the structure of an ingot cast in a conventional box mold, as described later. In addition, as a result of examining the crystal grain size of Sm ₂ Co ₁₇ by observation with a polarizing microscope,
It was found to be in the range of 270 μm, which was also equivalent to the ingot structure when cast into a conventional box mold. The obtained ingot was pulverized, and a sintered magnet was prepared by a conventional method, and the magnetic properties were evaluated. As shown in Table 1, the results are magnetic properties equivalent to those of a sintered magnet produced by pulverizing an ingot cast in a conventional box mold, and sufficient properties expected from the composition can be obtained. Was. Furthermore, as a result of repeating the casting 100 times using the same mold, no deformation or erosion of the mold was observed, and it was confirmed that the durability of the mold was extremely excellent. Further, since there is no need to perform operations such as disassembly of the mold for assembling the mold and removing the ingot, the workability has been significantly improved.

Example 2 Using an apparatus similar to that used in Example 1, an alloy ingot having the same composition was melted on a larger scale. That is, the dissolution amount was 140 kg. Accordingly, the inner diameter of the mold is 900
mm, but the cross-sectional shape of the pool was the same as in Example 1. The average molten metal deposition rate is 0.30 to 0.41 cm /
s, and the thickness of the ingot was in the range of 15 mm to 19 mm. S of the cross section in the thickness direction of the obtained ingot
FIG. 6 shows a reflected electron beam image photograph by EM. Despite the dissolution scale being enlarged, the same structure as that of Example 1 shown in FIG. 5 was obtained by controlling the solidification and cooling conditions to be the same. Also, the crystal grain size of Sm ₂ Co ₁₇ is 135 to
It was within the range of 280 μm, which was almost the same as in Example 1. The obtained ingot was pulverized, and a sintered magnet was prepared by a conventional method, and the magnetic properties were evaluated. As a result, as shown in Table 1, sufficient magnetic properties expected from the composition could be obtained. In addition, as a result of performing casting repeatedly 50 times using the same mold, no deformation, erosion, etc. of the mold was observed despite the expansion of the melting scale, and it was confirmed that the durability was extremely excellent. . Further, since there is no need to perform operations such as disassembly of the mold for assembling the mold and removing the ingot, the workability has been significantly improved.

Comparative Example 1 A copper plate having a thickness of 15 mm was assembled into a box shape with bolts to produce a mold. The dimensions of the mold cavity are 22 mm gap,
The length was 740 mm and the depth was 520 mm. Further, a water-cooled jacket was attached to the back of the mold. 70k compounded so that the composition of the alloy ingot would be the same as in Example 1.
g of raw material was melted in an alumina crucible in an argon atmosphere in a high-frequency melting furnace. Subsequently, the molten metal was cast into an ingot. FIG. 7 shows a backscattered electron beam image photograph by SEM of a cross section in the thickness direction of the obtained ingot. The crystal grain size of Sm ₂ Co ₁₇ determined by observation with a polarizing microscope is 150 to 290 μm
Was within the range. The obtained ingot was crushed to produce a sintered magnet by a conventional method, and the magnetic properties were evaluated. As a result, as shown in Table 1, sufficient magnetic properties expected from the composition could be obtained. However, the deformation of the mold becomes noticeable even after casting about 10 times, and the gap at the center of the mold when repeating the casting 30 times is 18 mm larger than the gap at the start of use due to deformation. Since there was concern about the risk of molten metal leaking out of the gap between the peripheral fixing parts, it was necessary to repair the mold by press straightening. Also, assembling and disassembling operations of the mold are required, and the positions of the bolt holes are displaced due to the deformation, so that it is difficult to assemble, and it takes extra time and the workability is poor.

Comparative Example 2 The same dissolution as in Comparative Example 1 was carried out by increasing the amount of dissolution to 140 kg. As the dissolution scale increased, the mold cavity had a gap of 22 mm, a length of 1400 mm, and a depth of 560 mm. The crystal grain size of Sm ₂ Co ₁₇ determined by observation with a polarizing microscope was in the range of 75 to 320 μm, and the variation depending on the location of the ingot was extremely large. The obtained ingot was pulverized, and a sintered magnet was prepared by a conventional method, and the magnetic properties were evaluated. As a result, as shown in Table 1, both the remanent magnetization and the coercive force were lower than expected from the composition, and the characteristics were insufficient. In addition, the deformation was remarkable only after repeated use five times, and the gap at the center of the mold was 24 mm larger than the gap at the start of use, so that the mold had to be repaired by press straightening.

Comparative Example 3 A centrifugal casting apparatus as shown in FIG. 4 described in Japanese Patent Application Laid-Open No. Hei 9-111383 (Japanese Patent Application No. 7-293617) was prepared. The inner diameter of the steel cylindrical rotary mold used is 500 mmφ
And the mold thickness is 30 mm. 70 kg of a raw material blended so that the composition of the alloy ingot was the same as in Example 1 was melted in an argon gas atmosphere using an alumina melting crucible, and then the average melt deposition rate was reduced using the above-described apparatus. Casting was performed at 0.02 cm / s. In this casting method, the molten metal is simultaneously poured over the entire surface in the mold via the reciprocating tundish 21 having a plurality of nozzles, so that the average molten metal deposition rate can be controlled to be small. Therefore, the solidification of the poured molten metal was completed during one rotation of the mold, and an ingot was formed while the next molten metal solidified and laminated on the solidified layer. The thickness of the obtained ingot was in the range of 7 mm to 10 mm. FIG. 8 shows the backscattered electron image structure of the ingot in a cross section in the thickness direction by SEM. From this figure, it can be seen that the casting structure is very fine and corresponds to a high cooling rate. The obtained ingot was pulverized, and a sintered magnet was prepared by a conventional method, and the magnetic properties were evaluated. As a result, as shown in Table 1, the coercive force was increased, but the residual magnetization was low, and the characteristics were insufficient.

[0025]

Table 1 BriHc (BH) max Crystal grain size Mold durability (kG) (kOe) (MGOe) μm and workability Example 1 10.89 16.33 28.83 140-270 ◎ Example 2 10.84 16.20 28.75 135-280 ◎ Comparison Example 1 10.82 16.12 28.59 150-290 △ Comparative Example 2 10.30 15.23 26.89 75-320 × Comparative Example 3 10.28 17.25 27.06 50-95 ◎ Mold durability and workability: ◎ Highest, ○ good, △ poor, × worst

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a mold ratio.

FIG. 2 is a centrifugal casting apparatus used in an embodiment of the present invention.

FIG. 3 is a sectional view of a mold.

FIG. 4 is a conceptual diagram of a centrifugal mold casting apparatus of Comparative Example 3.

FIG. 5 is an SEM of a cross section in the thickness direction of the ingot of Example 1.
FIG.

FIG. 6 is an SEM of a cross section in the thickness direction of the ingot of Example 2.
FIG.

FIG. 7 is an SEM of a cross section in the thickness direction of the ingot of Comparative Example 1.
FIG.

FIG. 8 is an SEM of a cross section in the thickness direction of the ingot of Comparative Example 3.
FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Moving tundish 3 Fixed tundish 4 Melting crucible 5 Weir 6 Rotation drive mechanism 7 Nozzle 10 Hot water pool 21 Reciprocating tundish 41 Melt

Claims (4)

[Claims] 1. A centrifugal casting mold, wherein a mold having an annular weir serving as a partition for forming two or more pools is formed on the inner surface of a centrifugal casting mold while rotating above the pool, while rotating in a rotational direction of the mold. A molten metal of the alloy for a rare earth magnet is sequentially poured into the basin from a nozzle that moves to a second position. 2. The method for producing an alloy for a rare earth magnet according to claim 1, wherein the molten metal is poured at an average molten metal deposition rate of 0.1 cm / sec or more in the pool. 3. While rotating a centrifugal casting mold provided with a cutout having a depth equal to or less than 1/2 of the height of the weir in the transverse direction of the upper part of the annular weir, the nozzle is moved above a plurality of pools. The method for producing a rare earth magnet alloy according to claim 1, wherein the alloy is moved and the molten metal is caused to flow through the notch into the adjacent pool. 4. An ingot or a crushed powder thereof used for producing a Sm ₂ Co ₁₇ based rare earth magnet, wherein Sm ₁ Co ₅ is present in a network around Sm ₂ Co _{17 as} a main phase. A rare earth magnet alloy cast by a centrifugal casting method, wherein the average crystal grain size of the phase Sm ₂ Co ₁₇ is 100 μm or more.