JP3536943B2 - Alloy for rare earth magnet and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a raw material alloy used as a raw material for a magnet containing a rare earth element and a method for producing the raw material alloy.

[0002]

2. Description of the Related Art Recently, a rare-earth sintered magnet or a rare-earth bonded magnet utilizing the excellent magnetic properties of a rare-earth alloy has been attracting attention.
Magnets with further improved magnetic properties are being developed. In the R-Fe-B-based magnet, a ferromagnetic phase R ₂ F which is responsible for magnetism
In addition to the e ₁₄ B phase, there is a nonmagnetic phase having a high concentration of rare earth elements such as Nd (referred to as an R-rich phase), and plays an important role as follows. It has a low melting point and becomes a liquid phase at the time of sintering in the magnetizing step, which contributes to increasing the density of the magnet and thus improving the magnetization. Eliminates irregularities at grain boundaries, reduces nucleation sites in reverse magnetic domains, and increases coercive force. The R-rich phase is non-magnetic and magnetically insulates the main phase, thereby increasing the coercive force. Therefore, if there is an interface that is not covered by the R-rich phase due to a low volume ratio of the R-rich phase or a poor dispersion state, the squareness deteriorates due to a local decrease in coercive force at that portion, It is known that the magnetization is also reduced due to poor sintering, resulting in a reduction in the maximum magnetic energy product.

However, the volume ratio of the R ₂ Fe ₁₄ B phase, which is a ferromagnetic phase, needs to be increased as the magnet becomes higher in performance.
In many cases, a lack of a rich phase occurs, and sufficient characteristics cannot be obtained. In view of this, many studies have been reported on the prevention of property deterioration due to the lack of the R-rich phase in high-performance materials, and they are roughly divided into two groups.

One is to supply the main phase R ₂ Fe ₁₄ B phase and the R rich phase from different alloys, which is generally called a two-alloy method. After dispersing the R-rich phase by a method of finely pulverizing two kinds of alloys, each consisting essentially of a single phase of R ₂ Fe ₁₄ B phase and an alloy producing an R-rich phase, and mixing and molding and sintering at an appropriate ratio. Many improvements have been made to alloys that produce R-rich phases to improve. For example, when an amorphous alloy having a liquid phase composition at a sintering temperature is used, Fe is more effective than an R-rich phase.
Is high, so that a magnet having the same composition is
The mixing ratio with the alloy that forms the main phase can be made higher than when the rich phase is mixed, and as a result, the dispersibility of the R-rich phase generated during sintering becomes better, and the magnetic properties have been improved (E. Otsuki) , T.Otsuka and T.Imai, 11th Internatinal W
orkshopon Rare Earth magnets and their Application
s, vol.1, p328 (1990)).

[0005] The other is to form an alloy having a structure in which an R-rich phase is finely dispersed by solidifying at a higher cooling rate than a conventional die casting method by a strip casting method to make the structure finer. is there. Since the R-rich phase in the alloy is finely dispersed, the dispersibility of the R-rich phase after pulverization and sintering is also improved, and the magnetic properties have been successfully improved (Japanese Patent Application Laid-Open Nos. 5-222488 and 5-205). 295490).

[0006]

As described above, the two-alloy method and the strip casting method provided good dispersion of the R-rich phase and improved the magnetic properties.
These methods have the following problems.

First, the former two-alloy method has been reported to have extremely high characteristics. However, liquid super-quenching must be used to produce an amorphous alloy that generates an R-rich phase. Poor productivity leads to increased costs. There is also a report that uses a Co-based intermetallic compound in an R-rich phase-forming alloy to exhibit characteristics of 45MGOe or more without using liquid rapid quenching (Kusu, Minowa, Honjima, IEEJ Transactions A, 113, 12
No., P849-853, 1993). However, the R ₂ Fe ₁₄ B phase is α-
Since it is produced by peritectic reaction from Fe and the liquid phase, almost R
_In an alloy that produces a main phase that requires casting with a ₂ Fe ₁₄ B stoichiometric composition, the residual amount of α-Fe is extremely large. And
α-Fe significantly impairs the pulverizability, causes the composition to change during pulverization, and causes a decrease in magnetic properties and an increase in variation. Therefore, the alloy that generates the main phase is α-
Long-term homogenization treatment is required since Fe is extinguished and the R ₂ Fe ₁₄ B phase is required to be a single phase. Further, in the two-alloy method, two kinds of alloy powders must be separately ground and uniformly mixed, so that the productivity is remarkably worse and the cost increases compared to the conventional method of grinding one alloy of as cast. Because it cannot be avoided, it can be used only for extremely high-performance materials with high added value of about 45MGOe or more.

On the other hand, the strip casting method also takes a long time for casting, and a molten metal containing a highly active rare earth element is held for a long time and supplied in small amounts. Therefore, the components are formed by the reaction of the molten metal with a crucible, a holding furnace or a tundish. Easy to fluctuate. Further, there is a problem that it is extremely difficult to maintain a constant temperature and maintain stable casting in a steady state, resulting in a low yield. In addition, there is a problem that a special and expensive casting facility is required, and an increase in cost is inevitable.

[0009]

SUMMARY OF THE INVENTION The present inventor has developed a method of producing an alloy which is less likely to cause deterioration in properties due to lack of R-rich phase and uneven distribution by a conventional die casting method without using special and expensive casting equipment. As a result, the inventors focused on a region (hereinafter referred to as a eutectic region) in which an R-rich portion existing as a liquid phase at the time of casting was solidified, which was conventionally simply referred to as a grain boundary phase or an R-rich phase. As a result, it was found that the morphology changes depending on the cooling rate at around 600-800 ° C at which the eutectic portion solidifies, and that the coercive force and the squareness of the magnet are related. Further, the inventors have found that the effect is further enhanced by controlling the dispersion state of the eutectic region and the crystal grain size of the main phase. The present invention has been made based on these findings.

That is, the present invention relates to a raw material alloy for a permanent magnet containing R (at least one of rare earth elements including Y), T (transition metal having Fe as an essential component) and B (boron) as basic components. Conventionally simply called a grain boundary phase or an R-rich phase, a region in which the R-rich portion present as a liquid phase to the end at the time of casting solidified, that is, by controlling the dispersion state of the eutectic region, substantially The object of the present invention is to solve the above problem by increasing the volume ratio of the usable R-rich phase and controlling the structure of the eutectic region and the crystal grain size of the main phase.

Next, the configuration of the present invention will be described in detail below. FIG. 1 and FIG. 2 are schematic diagrams of typical microstructures of the present invention and a conventional alloy. In the conventional alloy shown in FIG. 2, the main phase 1 is crystallized in a columnar shape, and a structure surrounded by a eutectic region 2 that solidifies last around the main phase 1 is exhibited. In addition, in the alloy of the present invention shown in FIG. 2 is slightly enlarged, and the size of the main phase 1 is larger in the alloy of the present invention in FIG.

(1) Distribution of eutectic region The eutectic region 2 is characterized in that it exists in the crystal grains of the main phase 1 in addition to the grain boundaries of the main phase R ₂ Fe ₁₄ B1. The portion rich in R (rare earth) existing as a liquid phase to the end is 6
Between 00 and 800 ° C., it finally transforms and solidifies into several solid phases by a eutectic reaction. For example, it is known that a liquid phase is transformed and solidified into three phases of a Nd metal phase, a Nd ₂ Fe ₁₄ B phase and a NdFe ₄ B ₄ phase by a eutectic reaction at 665 ° C. in a ternary system of Nd—Fe—B. I have. When other component elements are included, it is considered that the reaction temperature and the generated phase change. Originally, the Nd-rich phase refers to the Nd metal phase in the ternary system of Nd—Fe—B, but Nd ₂ formed by the eutectic reaction.
In some cases, the Fe ₁₄ B phase and the NdFe ₄ B ₄ phase are also treated as a collective term, and are often seen particularly when discussing the structure of the raw material alloy. The same applies when other component elements are included. Therefore, in the present invention, a region in which an R-rich portion which has been widely known as an R-rich phase or a grain boundary phase and which remains as a liquid phase at the time of casting and solidified is referred to as a eutectic region 2,
Expressed separately from the R-rich phase, which is the primary solid solution of R.
In the alloy of the present invention, the eutectic region 2 is present in the columnar crystal structure portion at the grain boundaries of the main phase R ₂ Fe ₁₄ B1 and also in the crystal grains mainly extending parallel to the major axis direction, and is equiaxed. Some tissue parts exist spherically.

On the other hand, the alloy obtained by the conventional casting method has a structure structure in which the main phase R ₂ Fe ₁₄ B1 constituting the crystal grains is covered with the phase 3 having a high R content constituting the crystal grain boundary ( JP-A-5-295490), and the main phase R ₂ Fe ₁₄ B1 according to the present invention.
There is no description regarding the existence of the eutectic region 2 including the phase 3 having a large content of a plurality of Rs in the crystal grains of the above, and it can be said that the structure is completely different.

In the alloy of the present invention, the volume (D) of the region where the distance (D) between the eutectic regions 2 is less than half the size (W) in the minor axis direction of the main phase R ₂ Fe ₁₄ B crystal grains 1 The rate is 70% or more. Here, the interval (D) between the eutectic regions 2 may be either the eutectic regions at the crystal grain boundaries or the eutectic regions within the crystal grains. Alternatively, the distance may be between a crystal grain boundary and a eutectic region in the crystal grain. In other words, the distance between adjacent eutectic regions may be equal to or less than half the size of the main phase in the minor axis direction. It is more convenient that the eutectic region 2 is finely dispersed. Specifically, the distance (D) between the eutectic regions 2 is the size (W) of the main phase R ₂ Fe ₁₄ B crystal grains 1 in the minor axis direction. It is preferable that the volume ratio of a region which is equal to or less than half of the volume ratio is equal to or greater than 70%.

(2) Structure of Eutectic Region The phase in the minor axis direction of the phase having a smaller R content in the eutectic region is preferably 3 μm or less. FIG. 3 is a schematic diagram showing an enlarged structure in the eutectic region of the alloy according to the present invention.
The inside of the eutectic region 2 has a structure in which the phase 4 having a smaller R content than the surroundings is precipitated in a thin rod shape. The phase 4 having a smaller R content in the eutectic region 2 is the R ₂ Fe ₁₄ B phase and the RFe ₄ B ₄ phase described above, and different phases when other component elements are contained. May be present, but it can also be said to be a phase other than the surrounding phase 3 having a high R content. The minor axis size of phase 4 having a smaller R content is
Finely pulverized particle size to obtain powder for magnetic field molding in magnetizing process,
In other words, when the particle size is 3 to 5 μm or less, the pulverized powder containing the phase 4 always coexists with the phase 3 having a high R content. Therefore, the ratio of the powder containing the phase 3 having a high R content is increased, the dispersibility of the phase 3 having a high R content is improved, the densification at the time of sintering is promoted, and the heat treatment after the sintering is performed. The temperature dependency of the coercive force is improved, and a magnet having excellent magnetic properties can be manufactured.

When this alloy is finely pulverized, the ratio of the powder containing the phase 3 containing a large amount of R increases due to the refinement of the structure inside the eutectic region 2, and the dispersibility of the phase 3 containing a large amount of R is increased. Sinterability and magnetic properties can be improved. And, the dispersibility of the phase 3 having a large R content is further improved because the eutectic region 2 including the phase 3 having a large R content is finely dispersed in the alloy. That is, the eutectic region 2 and the main phase 1
The amount of the pulverized powder containing the phase 3 having a high R content at the time of fine pulverization increases in accordance with the expansion of the interface with Pb, so that the dispersibility of the phase 3 having a high R content is improved. Therefore, in order to enlarge the interface between the eutectic region 2 and the main phase 1 and enhance the dispersibility of the phase 3 having a high R content, a columnar crystal structure in which the eutectic region 2 is thin and long is preferable.

FIG. 4 is an enlarged schematic diagram showing the structure in the eutectic region of the alloy according to the conventional method. In the conventional alloy, the size of the phase 4 having a lower R content is larger than in the case of the present invention, and some have a flaky shape. Compared with the alloy according to the present invention, the minor axis direction of the phase 4 having a lower R content in the eutectic region 2 is larger than the finely pulverized particle size and includes the phase 3 having a higher R content. Due to the increase in the proportion of non-
, The dispersibility of the phase 3 having a large content of Ni and the magnetic properties are lowered. In order to refine the phase 4 having a smaller R content, it is effective to increase the cooling rate during the eutectic reaction for generating these phases, increase the nucleation frequency, and prevent coarsening of each generated phase. is there. Further, there is a possibility that miniaturization is promoted by a certain kind of additive element.

(3) Grain Size of Main Phase The size of R ₂ Fe ₁₄ B crystal grains as the main phase in the major axis direction is 5
The volume ratio of a region having a size of 0 μm or more and a size of 10 μm or more in the minor axis direction is 70% or more. In the microstructure shown in FIG. 1 cut along the solidification direction,
When the crystal grain size of the main phase 1 is about the size of finely pulverized particles for obtaining a magnetic field forming powder, that is, about 3 to 5 μm or less, two or more main phases having different orientations exist in one pulverized powder. And the orientation decreases. Therefore, the larger the crystal grain size of the main phase 1 is, the better, and the size (L) in the long axis direction is 50.
It is preferable that the volume ratio of crystal grains having a size (W) of at least 10 μm in the minor axis direction is 70% or more.
More preferably, the size (L) in the long axis direction is 100 μm
As described above, the size (W) in the short axis direction is preferably 20 μm or more.
Each crystal grain of the main phase can be easily identified by polishing the alloy with emery paper and then observing the surface buffed with alumina, diamond or the like with a polarizing microscope. In the polarization microscope, the incident polarized light is reflected by the rotation of the polarization plane corresponding to the magnetization direction of the surface of the ferromagnetic material due to the magnetic Kerr effect, so that the difference in the polarization plane reflected from each crystal grain is observed as light and dark. FIG. 5 is a polarization micrograph of the alloy of the present invention, showing the grain boundaries of the main phase R ₂ Fe ₁₄ B. The difference in the crystal direction of each crystal grain becomes light and dark, and can be clearly identified. Further, a eutectic region observed as a black streak exists not only in the main phase crystal grain boundaries but also in the main phase R ₂ Fe ₁₄ B crystal grains substantially parallel to the major axis direction. The fine stripes in the main phase crystal grains correspond to the magnetic domains.

(4) Manufacturing Method The method of manufacturing the alloy according to the present invention is characterized in that a temperature range from 800 ° C. to 600 ° C. is cooled at a cooling rate of 5 ° C./sec or more during casting. The cooling rate is increased in the temperature range in which the eutectic region 2 is generated, that is, in the temperature range in which the R (rare earth) -rich portion existing as a liquid phase to the end solidifies, and the nucleation frequency is increased while the coarseness of each generated phase is increased. Prevention of the formation makes the phase 4 having a smaller R content in the eutectic region 2 finer. Depending on the composition, the solidification temperature fluctuates somewhat,
Specifically, it is preferable to cool the temperature range from 800 ° C. to 600 ° C. at a cooling rate of 5 ° C./sec or more, and a more preferable cooling rate is 10 ° C./sec or more. Such conditions are:
Without using a special casting method such as a strip casting method, for example, a conventional casting method can also be achieved by sufficiently increasing the mold ratio (mold ratio).

The mold ratio is a value obtained by dividing the heat capacity of the mold by the heat capacity of the alloy to be cast, and the weight ratio can be easily compared, and more simply, the ratio of the thickness of each side plate can be sufficiently compared. For example, since iron and copper, which are typical mold materials, have almost the same heat capacity per unit volume, it is possible to make a comparison including the difference in the material when discussing the ratio of the side plate thickness. An increase in the mold ratio suppresses a rise in the temperature of the mold. Therefore, it is possible to increase the cooling rate at 800 ° C. or lower, where the cooling efficiency of the ingot has been particularly reduced due to the rise in the temperature of the mold. The mold ratio can be increased by increasing the thickness of the side plate or increasing the thickness of the ingot. It is also effective to have a more efficient water cooling mechanism to quickly remove the heat transferred from the molten metal and prevent the mold temperature from rising,
Combining both enables more efficient cooling. In addition, it is effective to reduce the thickness of the ingot by centrifugal casting or the like.

In the present invention, the cooling rate at 800 ° C. or more and 600 ° C. or less is not particularly specified, but at 800 ° C. or more, the crystal size of the main phase R ₂ Fe ₁₄ B phase 1 and the dispersibility of the eutectic region 2 are affected. It is well known to do. General R-Fe
In the -B-based magnet composition, primary α-Fe is generated from the liquid phase,
Or generating a R ₂ Fe ₁₄ B phase 1 by the peritectic reaction from which the liquid phase, or if the solidification speed is high is subcooled to below peritectic reaction temperature liquid phase from the R ₂ Fe ₁₄ B phase 1 Generate directly. Therefore, the cooling rate until the peritectic reaction is completed has a particularly large effect on the macroscopic alloy structure, and the higher the cooling rate, the finer the macrostructure. Due to this effect, the strip casting method suppresses the production of α-Fe, and successfully disperses the phase 3 having a good R content. However, due to the refinement of the R ₂ Fe ₁₄ B phase crystal grains 1, the probability that two or more R ₂ Fe ₁₄ B phases 1 having different orientations are present in the pulverized powder after pulverization is increased, and the decrease in orientation is reduced. Therefore, it is necessary to appropriately control the cooling rate. In the alloy of the present invention, it is necessary to appropriately increase the cooling rate at 800 ° C. or higher, particularly until the peritectic reaction is completed, so that the size (W) in the minor axis direction of the main phase does not become less than 10 μm. It is effective to improve the dispersibility of the phase 3 having a high R content by improving the dispersibility of the eutectic region 2.

[0022]

The present invention relates to a raw material alloy for a permanent magnet containing R (rare earth element), which has been conventionally called simply a grain boundary phase or an R-rich phase. By controlling the distribution of the solidified region (eutectic region), the volume fraction of the R-rich phase that can be substantially used is increased, and the crystal grain size of the main phase and the dispersion state of the eutectic region Is to provide an alloy suitable as a raw material for a high-performance R—Fe—B based sintered magnet. In particular, the main phase R ₂ Fe _{14 has been}
The present invention focuses on the solidification cooling rate from 800 ° C. to 600 ° C. after the formation of the B phase, and provides an excellent alloy for sintered magnets without using complicated processes and equipment.

[0023]

The present invention will be described in more detail with reference to the following examples. (Example 1) As shown in Table 1, the composition of the alloy ingot was as follows: Nd: 29.0% by weight, Dy: 3.4% by weight, B:
1.0% by weight, Al: 0.35% by weight, the balance being iron neodymium alloy, metal dysprosium, ferroboron, aluminum and iron, and using an alumina crucible in an argon gas atmosphere. And melted in a high-frequency melting furnace and cast into a copper box mold. At this time, the temperature change during solidification of the alloy was measured with a thermocouple installed in the mold,
As shown in Table 1, the cooling rate at 600 ° C. was an average of 17 ° C. /
Seconds. The mold ratio was 20, and the thickness of the obtained ingot was 5 mm. The macrostructure of the cross section is columnar except for the chill crystal part near the mold, and after further polishing, the structure of the cross section was observed with a polarizing microscope. As a result, the main phase Nd ₂ Fe ₁₄ B phase of the columnar crystal was obtained. The particle size is about 200 to 1000 μm in the major axis direction and 20 to 100 μm in the minor axis direction.
m, and the volume ratio of the columnar crystal portion to the entire ingot was 85%. Further, as a result of observation with a reflection electron microscope, the eutectic region is elongated in the major axis direction of the main phase Nd ₂ Fe ₁₄ B phase, the interval is about 10 to 30 μm,
The minor axis of the phase having a smaller R content precipitated in the eutectic region was about 1 μm.

Next, the obtained alloy ingot was pulverized in a nitrogen gas to a size of 35 mesh or less by a brown mill, and further pulverized to 4 μm in a nitrogen gas by a jet mill.
Until finely ground. Next, the obtained fine powder was 10 KOe,
Magnetic field molding under the condition of 1 tonf / cm ² and 10 × 10 ×
After obtaining a molded body of 10 mm, it was sintered at 1060 ° C. for 2 hours in vacuum, and further subjected to aging treatment at 620 ° C. for 1 hour in vacuum. Table 1 shows the magnetic properties of the obtained sintered magnet. The maximum magnetic energy product was 39.8 MGOe, and the coercive force was 20.0 kOe.

Example 2 The same composition as in Example 1 was melted in the same manner as in Example 1 and cast into a water-cooled copper box mold. At this time, the temperature change during solidification was measured in the same manner as in Example 1, and the cooling rate at 800 ° C. to 600 ° C. was 1 on average.
2 ° C./sec. Water cooling of the mold was conducted by flowing water into a copper tube brazed to the outer periphery of the mold. The mold ratio was 10, and the thickness of the obtained ingot was 5 mm. The macrostructure of the cross section was columnar except for the chill crystal part near the mold. After further polishing, the structure was observed in the same manner as in Example 1. As a result, the main phase Nd ₂ Fe ₁₄ B phase of the columnar crystal part was observed. Has an average particle size of about 200 to 1000 μm in the major axis direction and about 20 to 100 μm in the minor axis direction. The volume ratio of the columnar crystal portion to the entire ingot was 83%. The eutectic region is the same as that of the ingot produced in Example 1 but the main phase Nd ₂
The Fe ₁₄ B phase is elongated in the major axis direction, and its interval is 10
４０40 μm, and the minor axis of the phase having a lower R content precipitated in the eutectic region was about 2 μm. Next, a sintered magnet was manufactured from the obtained ingot in the same manner as in Example 1, and the maximum energy product was 38.8 MGO.
e, the coercive force was 19.3 kOe.

Example 3 The same composition as in Example 1 was melted in the same manner as in Example 1 and cast into a water-cooled iron box mold. At this time, the temperature change during solidification was measured in the same manner as in Example 1, and the cooling rate at 800 ° C. to 600 ° C. was 8 on average.
° C / sec. Water cooling of the mold was performed by flowing water through a hole having a diameter of 20 mm provided at the center in the thickness direction of the mold side plate. The mold ratio was 20, and the thickness of the obtained ingot was 10
mm. The macrostructure of the cross section was columnar except for the chill crystal part near the mold.
As a result of observing the structure in the same manner as in the above, the main phase Nd
The average particle size of the ₂ Fe ₁₄ B phase is 300 to 1500 μm in the major axis direction.
m, 30 to 150 μm in the minor axis direction. The volume ratio of the columnar crystal portion to the entire ingot was 92%. Further, the eutectic region is elongated in the major axis direction of the main phase Nd ₂ Fe ₁₄ B phase similarly to the ingot produced in Example 1, and its interval is about 10 to 50 μm, which precipitates in the eutectic region. The minor axis of the phase having a lower R content was about 2 μm. Next, a sintered magnet was manufactured from the obtained ingot in the same manner as in Example 1, and the maximum energy product was 38.
5MGOe, coercive force was 19.1 kOe.

Example 4 The same composition as in Example 1 was melted by the same method as in Example 1, and the inner diameter of the mold was 500 m.
Casting was performed using a centrifugal casting machine with a length of 1000 mm. At this time, the rotation speed of the mold was set to 1 so that the centrifugal force was 10 G.
At 89 rpm, an argon gas was supplied into the mold after the completion of the supply of the molten metal to cool the ingot. Here, temperature measurement during solidification was not performed. The thickness of the obtained alloy ingot was 2-3 mm, and the macrostructure of the cross section was columnar except for the chill crystal part near the mold.
Then, as a result of observing the structure in the same manner as in Example 1, the average grain size of the main phase Nd ₂ Fe ₁₄ B phase in the columnar crystal part was 3 in the major axis direction.
It was 00 to 1000 μm and 30 to 100 μm in the minor axis direction. The volume ratio of the columnar crystals to the entire ingot is 98.
%Met. Further, the eutectic region is elongated in the major axis direction of the main phase Nd ₂ Fe ₁₄ B phase similarly to the ingot produced in Example 1, and its interval is about 10 to 30 μm, which precipitates in the eutectic region. The minor axis of the phase having a lower R content is 1
It was about μm. Next, a sintered magnet was prepared from the obtained ingot in the same manner as in Example 1, and the maximum energy product was 39.5 MGOe and the coercive force was 19.5 kOe.

(Comparative Example) The same composition as in Example 1 was melted in the same manner as in Example 1 and cast into a water-cooled iron box mold. At this time, the temperature change during solidification was measured in the same manner as in Example 1, and the temperature was changed from 800 ° C. to 6 ° C.
The cooling rate at 00 ° C. averaged 1 ° C./sec. The water cooling of the mold was performed in the same manner as in Example 2, and the mold ratio was 5%.
And the thickness of the obtained ingot was 20 mm. The macrostructure of the cross section was almost columnar, but a chill crystal structure was present near the mold, and an equiaxed crystal structure was present in the center of the ingot. After further polishing, the structure was observed in the same manner as in Example 1. As a result, the main phase Nd ₂ Fe ₁₄ B in the columnar crystal part was observed.
The average particle size of the phase was about 300 to 1500 μm in the major axis direction and about 30 to 200 μm in the minor axis direction. The volume ratio of the columnar crystal portion to the entire ingot was 80%. Also,
The eutectic region exists mainly in the grain boundary part of the main phase Nd ₂ Fe ₁₄ B phase, and particularly in the equiaxed crystal region, the eutectic region is coarsened to about 50 μm at the grain boundary triple point. Further, the minor axis of the phase having a smaller R content precipitated in the eutectic region was 5 μm or more. Next, a sintered magnet was manufactured from the obtained ingot in the same manner as in Example 1, and the maximum energy product was 35.2 MGO.
e, the coercive force was 15.5 kOe.

[0029]

[Table 1]

[0030]

According to the present invention, it is possible to manufacture a raw material alloy that is optimal as a raw material for a high-performance rare earth magnet without using complicated processes and equipment, which is extremely useful.

Example 5 The ingot produced in Comparative Example 2 was divided into pieces having a diameter of 5 mm or less,
After heat treatment at 1 ° C. for 1 hour, argon gas was directly blown and cooled. When the temperature change of the sample surface at that time was measured, the cooling rate at 800 ° C. to 600 ° C. was 1 on average.
It was 0 ° C./sec. Macrostructure of the alloy, particle size of the main phase,
Although the dispersion state of the eutectic region did not change, the minor axis of the phase having a smaller R content precipitated in the eutectic region was about 3 μm. Next, a sintered magnet was manufactured from the obtained sample in the same manner as in Example 1, and the maximum energy product was 37.
5MGOe, coercive force was 18.0 kOe.

Comparative Example 4 The ingot produced in Comparative Example 2 was kept at 900 ° C. in an argon atmosphere while maintaining a thickness of 20 mm.
After the heat treatment for 1 hour, argon gas was directly blown and cooled. When the temperature change of the sample at that time was measured, the cooling rate at 800 ° C. to 600 ° C. was 3 ° C./sec on average. There is no change in the macrostructure of the ingot, the grain size of the main phase, and the dispersion state of the eutectic region.
The particle size of the phase having a lower content of 5 μm is the same as before the heat treatment.
That was all. Next, a sintered magnet was prepared from the obtained sample in the same manner as in Example 1, and the maximum energy product was 3
4.9 MGOe, coercive force was 15.1 kOe.

Comparative Example 5 The ingot produced in Comparative Example 2 was kept at 600 ° C. in an argon atmosphere at a thickness of 20 mm.
After the heat treatment for 1 hour, argon gas was directly blown and cooled. The macrostructure of the ingot, the particle size of the main phase, and the dispersion state of the eutectic region were not changed, and the particle size of the phase containing less R precipitated in the eutectic region was 5 μm or more as before the heat treatment. Was. Next, a sintered magnet was produced from the obtained sample in the same manner as in Example 1, and the maximum energy product was 35.1 MGOe and the coercive force was 15.3 kOe.

[0034]

[Table 1]

[0035]

According to the present invention, it is possible to manufacture a raw material alloy that is optimal as a raw material for a high-performance rare earth magnet without using complicated processes and equipment, which is extremely useful.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a microstructure of an alloy according to the present invention.

FIG. 2 is a diagram schematically showing a microstructure of a conventional alloy.

FIG. 3 is an enlarged schematic view showing the structure of the eutectic region of the alloy according to the present invention.

FIG. 4 is an enlarged schematic diagram showing the structure of a eutectic region of a conventional alloy.

FIG. 5 is a polarizing microscope photograph showing a crystallization state of a main phase and a eutectic region of the alloy of the present invention.

[Explanation of symbols]

1 R ₂ Fe ₁₄ B columnar crystal 2 Eutectic region 3 Phase with higher R content 4 Phase with lower R content

Continuation of the front page (72) Inventor Hiroshi Hasegawa 1505 Shimokagemori, Chichibu City, Saitama Prefecture Showa Denko KK Chichibu Laboratory (56) References JP-A-5-295490 (JP, A) JP-A-5-222488 ( JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00

Claims (1)

(57) [Claims] 1. A method according to claim 1, wherein R (at least one of the rare earth elements including Y), T (transition metal having Fe as an essential element) and B are basic components, and R ₂ Fe ₁₄ B columnar crystals as main phases and R ₂ Fe ₁₄
A eutectic region having a higher R content than B, and the eutectic region is crystallized in the R ₂ Fe ₁₄ B columnar crystal and in the R ₂ Fe ₁₄ B columnar crystal grain boundary, and R ₂ Fe ₁₄ B The size of the columnar crystal in the long axis direction is 1
The eutectic region is elongated in the major axis direction of the columnar crystal, and the interval between the eutectic regions is the size of the R ₂ Fe ₁₄ B columnar crystal in the minor axis direction. An alloy for a rare earth magnet, wherein a volume ratio of a crystallization region which is equal to or less than half of the thickness is 70% or more.