JP3267133B2 - Alloy for rare earth magnet, method for producing the same, and method for producing permanent magnet - 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 for a permanent magnet containing a rare earth element, a method for producing a raw material alloy, and a method for producing a permanent magnet using the alloy.

[0002]

2. Description of the Related Art The production of rare earth magnets has been increasing steadily with the miniaturization and high performance of electronic devices. Especially NdF
The production of eB-based materials continues to increase due to their superior properties over SmCo and superior raw materials, and among them, the need for magnets with further improved magnetic properties is increasing.
In the RTB-based magnet, in addition to the ferromagnetic phase R ₂ T ₁₄ B which is responsible for magnetism, there is a non-magnetic phase having a high concentration of rare earth elements such as Nd (referred to as an R-rich phase). Plays an important role. 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 the poor dispersion state of the R-rich phase, the rectangularity is deteriorated due to a local decrease in coercive force, and the magnetization is also reduced due to poor sintering. It is known that lowering results in lowering of the maximum magnetic energy product.

However, the volume ratio of the R ₂ T ₁₄ B phase, which is a ferromagnetic phase, needs to be increased as the performance of the magnet becomes higher.
Inevitably, the volume ratio of the R-rich phase is inevitably reduced, resulting in a partial R-rich phase shortage, often failing to obtain sufficient characteristics.
Therefore, many studies have been reported on methods for preventing deterioration of properties due to lack of R-rich phase in high-performance materials, and they are roughly divided into two groups.

One is to supply the main phase R ₂ T ₁₄ B phase and the R-rich phase from different alloys, which is generally called a two-alloy method. Although the two-alloy method is similar to the final magnet composition, there are some interesting results because the choice of the composition of the two alloys is wide, the composition of the alloy that supplies the R-rich phase, and the manufacturing method is high. Have been reported.

For example, when an amorphous alloy having a composition that becomes a liquid phase at a sintering temperature is used as a grain boundary phase alloy, a non-equilibrium state is brought about, so that the Fe content is lower than that of a normal R-rich phase composition. Since the amount is large, the mixing ratio with the alloy that generates the main phase can be increased as compared with the case of mixing the conventional R-rich phase alloy to produce a magnet having the same composition. The dispersibility was improved, and the magnetic properties were successfully improved. In addition, suppression of powder oxidation by using an amorphous alloy also functions very effectively (E.Otsuki, T.Ots
uka and T. Imai, 11th International Workshop on Rare
Earth magnetsand their Applications, vol.1, p328 (19
90)). In addition, a study has been reported that succeeded in suppressing powder oxidation by making the alloy supplying the R-rich phase a high Co composition (M. Honshima and K. Ohashi, Journal of Materials E
ngineering and Performance P218-222 vol3 (2) April
1994).

The other is to form an alloy having a structure in which the structure is refined by solidifying at a higher cooling rate than the conventional die casting method by a strip casting method, and an R-rich phase is finely dispersed. is there. R in the alloy
Since the rich phase is finely dispersed, the R
The dispersibility of the rich phase was also improved, and the magnetic properties were successfully improved (Japanese Patent Application Laid-Open Nos. 5-222488 and 5-295490). Further, since the composition of the high-performance material increases the volume ratio of the R ₂ T ₁₄ B phase,
It approaches the stoichiometric composition of ₂ T ₁₄ B. Since the R ₂ T ₁₄ B phase is generated by the peritectic reaction between the primary crystal α-Fe and the liquid phase, α-Fe is likely to be generated as the R content decreases. α-Fe causes deterioration of the pulverization efficiency during the production of the magnet, and if it remains on the magnet after sintering, the properties are reduced. Therefore, in the case of an ingot produced by a normal die casting method, it is necessary to eliminate α-Fe by a homogenizing heat treatment at a high temperature for a long time. However, if the solidification rate can be increased by the strip casting method and supercooled below the peritectic reaction temperature, α-Fe
Precipitation can be suppressed.

[0007] Recently, an alloy close to the stoichiometric composition of R ₂ T ₁₄ B used in the two-alloy method, that is, a main phase alloy, has been manufactured by a strip casting method, and the pulverizability at the time of magnet production and the magnetic properties have been successfully improved. Studies have been reported. For example, in a main phase alloy melted by a strip casting method, α-Fe generation is suppressed and the average crystal grain size is 3 to
As fine as 50 μm, the dispersion of the R-rich phase is good, the dispersion in the magnet after sintering is also good, a high coercive force is achieved, and the pulverizability and particle size distribution during magnet production are improved.
It has been reported that a grain boundary phase alloy is also effective in improving the pulverizability (Japanese Patent Application Laid-Open No. 7-176414). In addition, even when the R content of the grain boundary phase alloy is relatively small to form a structure mainly composed of the R ₂ T ₁₇ phase, suppression of α-Fe generation and improvement in pulverizability have been recognized. At this time, since the R content of the main phase alloy is larger than that of the previous example, it is considered that the amount of α-Fe generated is small even in the conventional casting method, but the dispersibility of the R rich phase is extremely low by the strip casting method. In addition, a good structure is formed, and the pulverizability and the particle size distribution are improved (Japanese Patent Application Laid-Open No. 7-45413).

[0008]

As described above, although the two-alloy method and the strip casting method, or a combination thereof, provided an excellent dispersion of the R-rich phase after sintering and improved the magnetic properties. However, the required characteristics have not yet been sufficiently satisfied. It is an object of the present invention to stably express high magnetic characteristics with high residual magnetization (Br) by further improving these conventional methods.

As a result of studying the relationship between the structure of the main phase alloy and the magnetic properties in the two-alloy method, the present inventors paid attention to the relationship between the volume ratio of the R ₂ T ₁₄ B phase and the remanent magnetization. For the main phase alloy of the two alloy method to supply the R ₂ T ₁₄ B phase as a main phase, generally close to the R ₂ T ₁₄ B stoichiometry, the compositionally R ₂
The alloy composition is such that the volume ratio of the T ₁₄ B phase can be increased. However, in such an alloy, α-Fe is liable to be generated during solidification cooling, and if it is manufactured by a strip casting method in order to avoid this, a structure close to the equilibrium state at a high temperature in the equilibrium diagram is carried over to room temperature. The rich phase increases and the volume ratio of the main phase decreases.

[0010]

The inventor of the present invention controlled the cooling conditions during strip casting to reduce the R value.
It has been found that by reducing the volume fraction of the rich phase and increasing the volume fraction of the R ₂ T ₁₄ B phase, the residual magnetization is increased. Alternatively, when ingots produced under the same conditions are used, R ₂ T
_{14 By} increasing the volume fraction of phase B,
When magnetized and evaluated, it was found that the residual magnetization increased. Further, the structure of an ingot of a Nd-based magnet alloy as a rare earth magnet alloy was examined in detail, and as a result of examining the effect of the structure on magnetic properties, a fact was found that was significantly different from conventional analysis results. In other words, Nd-based magnet alloy ingots including the conventional strip cast material
It has been considered that a d-rich phase exists and it is important to reduce the crystal grain size, that is, to reduce the interval between the Nd-rich phases, for uniform fine distribution of the Nd-rich phase. But,
The Nd-rich phase does not necessarily correspond to the crystal grain boundary. Further, they have found that in order to obtain good magnetic properties, it is necessary that the crystal grain size is large and the interval between Nd-rich phases is small. By controlling the cooling conditions of the ingot during casting, it has been found that it is possible to increase the crystal grain size while reducing the interval between Nd-rich phases. This applies not only to Nd but also to other rare earth magnets.

That is, the present invention provides a method of forming R (Y
In a method for producing a raw material alloy for a permanent magnet and a method for manufacturing a raw material alloy containing at least one of the rare earth elements containing T), T (transition metal having Fe as an essential component) and B as a basic component, R ₂ T ₁₄
Increasing the volume fraction of the R ₂ T ₁₄ B phase in the main phase alloy supplying the B phase by controlling the solidification rate or by heat treatment after the solidification, and further increasing the R ₂ T ₁₄ B phase crystal grain size and R richness By controlling the phase spacing, remnant magnetization is increased. Further, the grain boundary phase alloy is designed to reduce the volume fraction of the R ₂ T ₁₄ B phase in the alloy, thereby increasing the residual magnetization after magnetization.

Before describing the configuration of the present invention in detail, R
Regarding the solidification of a general main phase alloy that is slightly R-rich than the ₂ T ₁₄ B stoichiometric composition,
A description will be given of a d-Fe-B ternary system as an example. In the case of solidification using an ordinary mold, especially near the center in the thickness direction of the ingot where the cooling rate is slow, firstly, primary crystal α-Fe is generated, and the two phases coexist with the liquid phase. Next, an Nd ₂ Fe ₁₄ B phase is formed from α-Fe and the liquid phase by the peritectic reaction at 1155 ° C., but since the reaction rate is slower than the cooling rate, α
-Fe is left inside Nd ₂ Fe ₁₄ B phase. Thereafter, as the temperature decreases, the Nd ₂ Fe ₁₄ B phase is discharged from the liquid phase, the volume ratio of the liquid phase decreases, the composition also changes to the Nd-rich side, and finally the liquid phase becomes ternary eutectic at 665 ° C. Nd ₂ F
e ₁₄ B phase, Nd rich phase solidifies to three phases B-rich phase.

However, when the solidification rate is increased by a strip casting method or the like, the molten alloy can be supercooled to a temperature below the peritectic reaction temperature, as mentioned above.
-Fe generation is suppressed, and the Nd ₂ Fe ₁₄ B phase can be directly generated from the liquid phase. In addition, since the subsequent cooling is fast and solidifies before the Nd ₂ Fe ₁₄ B phase is sufficiently generated from the liquid phase, the volume ratio of the Nd ₂ Fe ₁₄ B phase is smaller than expected in the equilibrium diagram, and the The concentration of Nd in the Nd-rich phase corresponding to the liquid phase in the region is low, and the volume fraction of the Nd-rich phase increases. The Nd-Fe-B ternary system has been described above as an example. However, it is known that even if the reaction system is expanded to a general RTB system, the reaction temperature and the like are slightly changed, although they are slightly different. .

Next, the configuration of the present invention will be described in detail below. Unless otherwise specified, the following description is all about the main phase alloy. (1) Volume Ratio of Main Phase The volume ratio of the main phase and the R ₂ T ₁₄ B phase is 93% or more. The main phase-based alloy of the two-alloy method is the main phase R ₂ T
_In order to supply the ₁₄ B phase, the alloy composition is generally close to the R ₂ T ₁₄ B stoichiometric composition, and the composition is such that the volume ratio of the R ₂ T ₁₄ B phase can be increased. However, such alloys tend to form α-Fe during solidification and cooling, and since they are conventionally manufactured by a quenching method, they have a non-equilibrium structure, so that the R-rich phase increases and the volume ratio of the main phase increases. Is decreasing. The alloy of the present invention employs a strip casting method and further optimizes cooling conditions after forging to prevent the formation of α-Fe and to reduce the volume ratio of non-magnetic phases such as the R-rich phase to reduce the main phase. Is characterized by having a structure in which a fine R-rich phase is distributed at the same time as increasing the volume ratio.

Another method for producing a main phase alloy is as follows.
Α-Fe produced by ingot manufactured by ordinary casting method
A method of performing a heat treatment in order to erase the data can be given. However, in the case of a normal ingot, heat treatment at a high temperature for a long time is required to eliminate α-Fe, and the volume ratio of the main phase increases, but the R-rich phase becomes coarse and the sinterability deteriorates. There are drawbacks. There is also a disadvantage that the coercive force after the magnet is formed is reduced.

The present invention has focused on the point that the volume fraction of the R ₂ T ₁₄ B phase of the raw material alloy contributes to the improvement of the residual magnetization of the magnet. As for the main phase alloy, as the volume fraction of the R ₂ T ₁₄ B phase increases, the residual magnetization of the magnet increases. To take advantage of its strengths,
The volume ratio of the R ₂ T ₁₄ B phase is preferably 93% or more. It is more preferably at least 95%. Because earlier reduction of R-rich phase Hei 7-176414 In the main phase alloy covered in the prior art is directed to result in reduced sinterability and a decrease in residual magnetization, the volume of the R ₂ T ₁₄ B phase Although the rate increase is limited, there is no such phenomenon observed in the experimental results by the present inventors probably because the dispersion state of the R-rich phase is different as described in the next section.

[0017] (2) Average crystal grain diameter in the short axis direction of the R ₂ T ₁₄ B phase with an average grain size R ₂ T ₁₄ B phase is 20 to 100
μm, and the interval between R-rich phases is 15 μm or less. When the crystal grain size of the main phase is 20 μm or less, the ratio of powder particles having crystal grain boundaries in the milled particle size when the powder for magnetic field molding is finely pulverized to 3 to 5 μm increases. Therefore, such powder particles have two or more main phases having different orientations, which lowers the orientation and lowers the residual magnetization. Therefore, the larger the average crystal grain size, the better. On the other hand, above 100 μm, the effect of the high cooling rate of the strip casting method diminishes,
It causes adverse effects such as α-Fe precipitation.

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 a polarization microscope, the polarization of the incident 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.

(3) Manufacturing method of main phase alloy Firstly, it is characterized by being manufactured by a strip casting method. Especially after strip casting, 800-600 ° C
The cooling rate at 10 ° C./sec or less, preferably 5 ° C./sec or less. According to the strip casting method, a flaky alloy free of α-Fe can be produced, and recently, the apparatus has been improved and the productivity has been improved. In the strip casting method, since the cooling rate is as fast as several hundreds to several thousand degrees Celsius / second, as described above, a structure having a fine crystal grain size and a higher volume fraction of the R-rich phase than expected in the equilibrium diagram is obtained. As a result, such tissues have heretofore been accepted as preferred. However, in the present invention, in order to increase the volume fraction of the main phase, the cooling rate at 800 to 600 ° C. is set to 10 ° C./sec or less, preferably 5 ° C./sec or less to promote the generation of the R ₂ T ₁₄ B phase from the liquid phase. It was decided to.

The influence of the crystal grain size and the presence or absence of α-Fe is considered to be the solidification rate or the cooling rate in a high temperature range near the peritectic temperature. In order to increase the crystal grain size, it is desirable that the cooling rate be low, while it is desirable that the cooling rate be high in order to prevent the formation of α-Fe. Further, the interval between the R-rich phases depends on the cooling rate in these high-temperature areas and the cooling rate in a lower temperature area closer to the eutectic temperature area, and the higher the cooling rate, the smaller and finer the distribution. Become. As described above, in order to obtain an optimal structure, there are optimal cooling conditions. After conducting extensive experiments,
Average cooling rate from melting point to 800 ° C is 300-100
It was known that 0 ° C./sec should be used. At 300 ° C./second or less, α-Fe is generated, and the interval between R-rich phases is wide.
Does not have a fine structure. On the other hand, at a temperature of 1000 ° C./sec or more, the crystal grain size becomes 20 μm or less, and cooling on the rolls becomes strong, and the temperature drops to 600 ° C. or less at the time of falling. The factor that has the greatest effect on the cooling rate of the strip before leaving the roll is the strip thickness. The average cooling rate from the melting point to 800 ° C. is 300 ° C./sec to 1000 ° C./sec,
In order to obtain a structure having an optimum crystal grain size and an interval between R-rich phases, the strip thickness is preferably set to 0.2 to 0.6 mm. More preferably, it is 0.225 to 0.4 mm.

In the present invention, the temperature at the time of dropping from the roll is set to 700 ° C. or more, and a process capable of appropriately keeping the temperature after that makes it possible to control the cooling rate at 800 to 600 ° C.

In the present invention, in order to increase the volume fraction of the main phase, 8
A step of setting the cooling rate at 00 to 600 ° C. to 10 ° C./sec or less, preferably 5 ° C./sec or less to promote the formation of the R ₂ T ₁₄ B phase from the liquid phase, or heat-treating at 800 to 600 ° C. after casting cooling. Having a process. When the cooling rate at 800 to 600 ° C. exceeds 10 ° C./sec, the R ₂ T ₁₄
The B phase solidifies before it is not sufficiently formed, and as a result, the volume ratio of the non-magnetic phase such as the R-rich phase is large, and the R ₂ T
_Since the volume ratio of the ₁₄ B phase is small, it falls outside the gist of the present invention.

As a second method for obtaining the alloy for the main phase of the present invention, the same effect can be obtained by heat-treating at 800 to 600 ° C. after casting and cooling by a strip casting method. Since this heat treatment is performed at a lower temperature and a shorter time than the homogenization heat treatment for the purpose of eliminating α-Fe,
There are few adverse effects in terms of equipment and production efficiency. Since the cast piece is thin, the heat treatment time usually needs to be 1 hour or more, and need not exceed 3 hours. Heat treatment atmosphere to prevent oxidation,
It is necessary to use a vacuum or an inert atmosphere. It is preferable that the cooling after the heat treatment is gradually cooled to about 600 ° C.

(4) Structure of Grain Boundary Phase Alloy The volume ratio of the R ₂ T ₁₄ B phase is 30% or less. In the two-alloy method in which the present invention is employed, since the main phase alloy has an R ₂ T ₁₄ B phase of 93% or more by volume, most of the R-rich phase of the magnet is supplied from the grain boundary phase alloy. It will be. At this time, if the composition of the magnet is fixed, the mixing ratio with the main phase alloy can be adjusted by the composition of the grain boundary phase alloy or the amount of the R ₂ T ₁₄ B phase contained in the structure. According to the present inventor, here, R ₂ in the grain boundary phase alloy is
It was found that the smaller the volume fraction of the T ₁₄ B phase, the higher the residual magnetization of the magnet. Therefore, the smaller the volume fraction of the R ₂ T ₁₄ B phase, the better, and preferably 30% or less. It is more preferably at most 20%, further preferably at most 10%. As an example of a preferable alloy composition for obtaining such a structure, R: 46%, B: 0.5%, Co: 2
0%, Cu: 0.7%, Al: 0.3%, Fe: near the balance.

[0025]

According to the present invention, 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 as basic components by a two-alloy method. In the method for producing an alloy for a raw material, the volume fraction of the R ₂ T ₁₄ B phase in the main phase alloy supplying the R ₂ T ₁₄ B phase is determined by the solidification rate,
Or increased by heat treatment after solidification, and R ₂
By controlling the crystal grain size of the T ₁₄ B phase, and further reducing the volume fraction of the R ₂ T ₁₄ B phase in the grain boundary phase alloy, the remanent magnetization after the formation of the sintered magnet was increased. . Here, the reason why the volume fraction of the R ₂ T ₁₄ B phase in each alloy affects the residual magnetization of the magnet will be considered. From the above experimental results by the present inventors, it was estimated that the ratio of other phases coexisting in the fine powder composed of the R ₂ T ₁₄ B phase after the pulverization of the main phase alloy affects the degree of orientation of the magnet. That is,
When the amount of the non-magnetic phase in the fine powder containing the R ₂ T ₁₄ B phase increases, the magnetization of the fine powder as a whole decreases, and the torque of the magnetic field orientation decreases. However, there is no change in the particle size itself, and there is no change in the torque to be shifted from the orientation direction received by the press. As a result, the ratio of powder shifted from the orientation direction increases, and the orientation ratio after magnetization decreases. It can be assumed that Meanwhile The grain boundary phase alloy the volume ratio of the R ₂ T ₁₄ B phase increases, increasing the probability that during individual fines include R ₂ T ₁₄ B phase, also R ₂ T ₁₄ B phase included in the fines Also increases. Such a powder has a poor degree of orientation and a large R ₂ T ₁₄ B phase in the middle, so that it does not disappear during sintering, but rather increases as a growth nucleus and may become coarse. It may cause disturbance.

[0026]

The present invention will be described in more detail with reference to the following examples. (Example 1) An iron neodymium alloy, ferroboron, and a main phase alloy were composed so that the composition was 28.0% by weight of Nd, 1.0% by weight of B, 0.3% by weight of Al, and the balance of iron. Aluminum and iron were mixed and melted in an argon crucible using an alumina crucible in a high-frequency melting furnace, and a strip having a thickness of about 0.35 mm was produced by a strip casting method. At this time, the high-temperature strip detached from the casting roll was kept in a box made of a heat insulating material having a large heat retaining effect for 1 hour, and then placed in a box having a water-cooled structure and rapidly cooled to room temperature. As a result of measuring the temperature change of the strip in the insulated box with a thermocouple installed in the box,
The temperature when dropped into the heat insulating box was 750 ° C. Then, 10 minutes passed until the temperature reached 600 ° C. Therefore, even if the time required for cooling from 800 ° C. to 750 ° C. is ignored, the average cooling rate from 800 to 600 ° C. is 0.33 ° C. per second, which is actually lower than this. on the other hand,
The cooling rate from the melting point to 800 ° C. was 400 ° C. or more per second, based on the time required to drop to the heat insulating box. The result of observing the cross-sectional structure of the obtained strip with a polarizing microscope is shown in FIG. In the figure, one main phase crystal grain is precipitated in a polygonal shape. The average crystal grain size of the main phase Nd ₂ Fe ₁₄ B phase was about 35 μm. FIG. 2 shows the result of observation with a reflection electron microscope. The R-rich phase was granular and scattered linearly in the crystal grain boundaries and the main phase grains, and the spacing was finely dispersed at about 8 μm. In addition, a slight amount of the B-rich phase was confirmed at the crystal grain boundaries. As a result of measuring the volume ratio of the main phase Nd ₂ Fe ₁₄ B phase using an image processing apparatus, it was found to be 94%.

On the other hand, the grain boundary phase alloy has a composition of Nd: 3
8.0% by weight, Dy: 8.0% by weight, B: 0.5% by weight, Co: 20% by weight, Cu: 0.67% by weight, Al:
0.3% by weight, iron neodymium alloy so that the balance is iron,
Metal dysprosium, ferroboron, cobalt, copper,
Mixing aluminum and iron, in argon gas atmosphere,
Using an alumina crucible, melting was performed in a high-frequency melting furnace, and an ingot having a thickness of about 10 mm was produced by centrifugal casting. The cross section of the tissue was observed with a reflection electron microscope and X
From the RD measurement, a slight amount of the Nd ₂ Fe ₁₄ B phase was confirmed, but the volume ratio was 10% or less. Next, 85% by weight of the main phase alloy and 15% by weight of the grain boundary phase alloy were mixed, hydrogen was absorbed at room temperature, and hydrogen was released at 600 ° C. This mixed powder was roughly pulverized with a brown mill to obtain an alloy powder having a particle size of 0.5 mm or less, and then finely pulverized with a jet mill.
A magnet powder having an average particle size of 5 μm was obtained. The obtained fine powder was molded at a pressure of 1.5 ton / cm ^{2 in} a magnetic field of 15 kOe. The obtained molded body is heated at 1060 ° C. in vacuum for 4 hours.
After sintering for 1 hour, the first stage heat treatment is performed at 850 ° C. for 1 hour,
The second heat treatment was performed at 520 ° C. for 1 hour. Table 1 shows the magnetic properties of the obtained magnet. Table 1 shows that the residual magnetism (B
r) is improved by about 5%, and accordingly, a maximum magnetic impulse · (BH) _{MAX of} 45MGOe class is achieved.

[0028]

[Table 1]

Comparative Example 1 A strip of a main phase alloy having a thickness of about 0.35 mm was produced by the strip casting method in the same manner as in Example 1 so as to have the same composition as in Example 1. At this time, the high-temperature strip detached from the casting roll was directly placed in a box having a water-cooled structure and rapidly cooled to room temperature. As a result of measuring the temperature change of the strip in the box with a thermocouple installed in the box, the temperature when dropped into the box was 750 ° C. Thereafter, the time required to reach 600 ° C. was 15 seconds. On the other hand, 800 ° C
Since the time required for cooling from to 750 ° C. is shorter than the time required for the strip to fall into the box, it is at most about 2 seconds. Therefore, even if it is added, 800
The average cooling rate of ~ 600 ° C is 12 ° C per second, which is actually higher. On the other hand, the cooling rate from the melting point to 800 ° C. is the same as that in Example 1. As a result of observing the structure of the cross section with a polarizing microscope, the average crystal grain size of the main phase Nd ₂ Fe ₁₄ B phase was about 35 μm. FIG. 3 shows the results of observation with a reflection electron microscope. As shown in FIG. 3, the R-rich phase was present in the form of streaks in the crystal grain boundaries and the main phase grains, and the interval between them was about 3 μm, and the dispersion was insufficient. Others
The B-rich phase became black spots at the crystal grain boundaries, and the amount was slightly confirmed. As a result of measuring the volume ratio of the main phase Nd ₂ Fe ₁₄ B phase using an image processing apparatus, it was found to be 82%. Next, using this main phase alloy and the grain boundary phase alloy produced in Example 1, a sintered magnet was produced in the same manner as in Example 1, and the magnetic properties are shown in Table 1.

(Comparative Example 2) Strips of the main phase alloy were produced by strip casting in the same manner as in Example 1 so as to have the same composition as in Example 1. At this time, since the pouring speed was reduced, the thickness of the strip was about 0.2.
2 mm. The strip separated from the roll was kept in a box made of a heat insulating material for one hour as in Example 1, and then placed in a box having a water-cooled structure and rapidly cooled to room temperature. As a result of measuring the temperature change of the strip in the insulated box with the thermocouple installed in the box, the temperature when dropped into the insulated box was 6
80 ° C. Thereafter, the time required to reach 600 ° C. was 7 minutes. Therefore, 800 to 600
The average cooling rate in ° C. is below 0.48 ° C. per second. on the other hand,
The cooling rate from the melting point to 800 ° C. was 500 ° C. or more per second. FIG. 4 shows the result of observing the structure of the cross section with a polarizing microscope. The average crystal grain size of the main phase Nd ₂ Fe ₁₄ B phase was about 18 μm, which was smaller than that of Example 1. Further, as a result of observation with a reflection electron microscope, the R-rich phase was scattered in the form of grains of about several μm in the crystal grain boundaries and the main phase grains, and the interval between them was about 6 μm. In addition, a slight amount of the B-rich phase was confirmed at the crystal grain boundaries. The volume ratio of the main phase Nd ₂ Fe ₁₄ B phase was measured using an image processing apparatus, and was found to be 90%. Next, using this main phase alloy and the grain boundary phase alloy produced in Example 1, a sintered magnet was produced in the same manner as in Example 1, and the magnetic properties are shown in Table 1.

(Comparative Example 3) A 25 m-thick steel mold having a water cooling mechanism was used to obtain the same composition as in Example 1.
m of main phase ingots were prepared. As a result of observing the structure of the cross section with a polarizing microscope, the average crystal grain size of the main phase Nd ₂ Fe ₁₄ B phase was about 150 μm. However, as a result of observation with a reflection electron microscope, a large amount of α-F
No magnet was made because e was present.

Example 2 A strip of the main phase alloy prepared in Comparative Example 1 was heat-treated at 700 ° C. for 2 hours in an argon atmosphere, and gas was rapidly cooled to room temperature. As a result of observing the structure of the cross section with a polarizing microscope, the average crystal grain size of the main phase Nd ₂ Fe ₁₄ B phase was about 35 μm. Further, as a result of observation with a reflection electron microscope, the R-rich phase was scattered in the form of grains in the crystal grain boundaries and the main phase grains, and the interval between them was about 10 μm. In addition, a slight amount of the B-rich phase was confirmed at the crystal grain boundaries. As a result of measuring the volume ratio of the main phase Nd ₂ Fe ₁₄ B phase using an image processing apparatus, it was found to be 95%. Next, using this main phase alloy and the grain boundary phase alloy produced in Example 1, a sintered magnet was produced in the same manner as in Example 1, and the magnetic properties are shown in Table 1.

Comparative Example 4 The main phase alloy strip prepared in Comparative Example 1 was heat-treated at 900 ° C. for 2 hours in an argon atmosphere, and gas was rapidly cooled to room temperature. As a result of observing the structure of the cross section with a polarizing microscope, the average crystal grain size of the main phase Nd ₂ Fe ₁₄ B phase was about 35 μm. As a result of observation with a reflection electron microscope, it was found that the R-rich phase was scattered in the form of grains in the crystal grain boundaries and the main phase grains, and the interval between them was about 16 μm. In addition, a slight amount of the B-rich phase was confirmed at the crystal grain boundaries. As a result of measuring the volume ratio of the main phase Nd ₂ Fe ₁₄ B phase using an image processing apparatus, it was found to be 89%. Next, using this main phase alloy and the grain boundary phase alloy produced in Example 1, a sintered magnet was produced in the same manner as in Example 1, and the magnetic properties are shown in Table 1.

Comparative Example 5 The main phase alloy had the composition of Nd:
28.0% by weight, B: 1.0% by weight, Al: 0.3% by weight, iron-neodymium alloy, ferroboron, aluminum, and iron are blended so that the balance is iron, and strip casting is performed in the same manner as in Example 1. The method produced a strip having a thickness of about 0.35 mm. The strip separated from the roll was kept in a box made of a heat insulating material for one hour as in Example 1, and then placed in a box having a water-cooled structure and rapidly cooled to room temperature. As a result of measuring the temperature change of the strip in the insulated box with a thermocouple installed in the box, the temperature when dropped into the insulated box was 740 ° C. Thereafter, the time required to reach 600 ° C. was 10 minutes. Therefore, 800-
The average cooling rate at 600 ° C. is below 0.33 ° C. per second.
On the other hand, the cooling rate from the melting point to 800 ° C. was 400 ° C. or more per second due to the time required to fall into the heat insulating box. As a result of observing the cross-sectional structure of the obtained strip with a polarizing microscope, the average crystal grain size of the main phase Nd ₂ Fe ₁₄ B phase was about 3
It was 7 μm. Further, as a result of observation with a reflection electron microscope, the R-rich phase was scattered in the form of grains in the crystal grain boundaries and the main phase grains, and the interval between them was about 8 μm. In addition, a slight amount of the B-rich phase was confirmed at the crystal grain boundaries. Main phase Nd ₂ Fe ₁₄ B
As a result of measuring the volume ratio of the phase using an image processing apparatus, 93
%Met.

On the other hand, the grain boundary phase alloy has a composition of Nd: 3
8.0% by weight, Dy: 8.0% by weight, B: 1.0% by weight, Co: 20% by weight, Cu: 0.67% by weight, Al:
An ingot having a thickness of about 10 mm was produced by a centrifugal casting method in the same manner as in Example 1 so that 0.3% by weight and the balance were iron. An R ₂ T ₁₄ B phase was confirmed in the cross section by reflection electron microscopy and XRD measurement, and the volume ratio was measured using an image processing apparatus. As a result, it was 35%. Next, 85% by weight of the main phase-based alloy and 15% by weight of the grain boundary phase-based alloy produced here
To produce a sintered magnet in the same manner as in Example 1,
Table 1 shows the magnetic properties. The composition after magnetization in this comparative example is the same as the other examples and comparative examples. In this comparative example, although the main phase alloy was in accordance with the present invention, the desired magnetic properties could not be obtained because the grain boundary phase alloy was inappropriate.

Comparative Example 6 The composition of the main phase alloy was Nd:
26.0% by weight, B: 1.09% by weight, Al: 0.3% by weight, iron-neodymium alloy, ferroboron, aluminum and iron are blended so that the balance is iron, and strip casting is performed in the same manner as in Example 1. By method, thickness about 0.35mm
Produced strips. The strip separated from the roll was kept in a box made of a heat insulating material for one hour as in Example 1, and then placed in a box having a water-cooled structure and rapidly cooled to room temperature. As a result of measuring the temperature change of the strip in the heat insulating box with a thermocouple installed in the box, the temperature when dropped into the heat insulating box was 780 ° C. Thereafter, the time required to reach 600 ° C. was 11 minutes. Therefore, 800
The average cooling rate of ~ 600 ° C is below 0.3 ° C per second.
On the other hand, the cooling rate from the melting point to 800 ° C. was 400 ° C. or more per second due to the time required to fall into the heat insulating box. As a result of observing the cross-sectional structure of the obtained strip with a polarizing microscope, the average crystal grain size of the main phase Nd ₂ Fe ₁₄ B phase was about 2 μm.
It was 3 μm. As a result of observation with a reflection electron microscope, α-Fe was present in the main phase grains, and the R-rich phase was scattered in the form of grains in the crystal grain boundaries and the main phase grains, with an interval of about 5 μm. Met. In addition, a slight amount of the B-rich phase was confirmed at the crystal grain boundaries. Since this alloy was clearly inferior in pulverizability as compared with the main phase alloy in which the magnet was manufactured in the other Examples and Comparative Examples, no magnet was manufactured.

(Comparative Example 7) The composition of the main phase alloy was Nd:
31.0 wt%, B: 1.09 wt%, Al: 0.3 wt%, iron-neodymium alloy, ferroboron, aluminum, and iron are blended so that the balance is iron, and strip casting is performed in the same manner as in Example 1. By method, thickness about 0.37mm
Produced strips. The strip separated from the roll was kept in a box made of a heat insulating material for one hour as in Example 1, and then placed in a box having a water-cooled structure and rapidly cooled to room temperature. As a result of measuring the temperature change of the strip in the insulated box with a thermocouple installed in the box, the temperature when dropped into the insulated box was 750 ° C. Thereafter, the time required to reach 600 ° C. was 10 minutes. Therefore, 800
The average cooling rate of ~ 600 ° C is below 0.33 ° C per second. On the other hand, the cooling rate from the melting point to 800 ° C. was 400 ° C. or more per second due to the time required to fall into the heat insulating box. As a result of observing the cross-sectional structure of the obtained strip with a polarizing microscope, the average crystal grain size of the main phase Nd ₂ Fe ₁₄ B phase was about 35 μm. Further, as a result of observation with a reflection electron microscope, the R-rich phase was scattered in the form of grains in the crystal grain boundaries and the main phase grains, and the interval between them was about 9 μm. In addition, a slight amount of the B-rich phase was confirmed at the crystal grain boundaries. Main phase Nd ₂ Fe ₁₄
As a result of measuring the volume ratio of the B phase using an image processing apparatus, 9
It was 0%.

On the other hand, the grain boundary phase alloy has a composition of Nd: 2
1.0% by weight, Dy: 8.0% by weight, B: 0.5% by weight, Co: 20% by weight, Cu: 0.67% by weight, Al:
An ingot having a thickness of about 10 mm was produced by a centrifugal casting method in the same manner as in Example 1 so that 0.3% by weight and the balance were iron. An R ₂ T ₁₄ B phase of the cross section was confirmed by reflection electron microscope observation and XRD measurement, and the volume ratio was measured by an image processing apparatus to be 45%. Next, 85% by weight of the main phase-based alloy and 15% by weight of the grain boundary phase-based alloy produced here
To produce a sintered magnet in the same manner as in Example 1,
Table 1 shows the magnetic properties. The composition after magnetization in this comparative example is the same as the other examples and comparative examples.

[0039]

According to the present invention, the maximum magnetic impulse · (BH)
It is possible to easily obtain a strong permanent magnet having a _MAX of 45MGOe class.

[Brief description of the drawings]

FIG. 1 is a polarizing microscope structure photograph showing a crystal grain size of a main phase alloy of Example 1 (magnification: 200 times).

FIG. 2 is a reflection electron microscopic structure photograph showing a dispersion state of an R-rich phase in the alloy for a main phase of Example 1 (250 magnification).
Times).

FIG. 3 is a micrograph of the structure of the alloy for a main phase of Comparative Example 1 showing a dispersion state of an R-rich phase by a reflection electron microscope (250 magnification).
Times).

FIG. 4 is a polarizing microscopic structure photograph showing a crystal grain size of a main phase alloy of Comparative Example 2 (magnification: 200 times).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H01F 1/053 H01F 41/02 G 41/02 1/04 H (56) References JP-A-7-18366 (JP, A) JP-A-2-149650 (JP, A) JP-A-5-222488 (JP, A) JP-A-5-295490 (JP, A) JP-A-7-45413 (JP, A) (58) (Int.Cl. ⁷ , DB name) C22C 38/00 303 B22D 11/06 360 B22F 1/00 C22C 33/02 H01F 1/053 H01F 41/02

Claims (4)

(57) [Claims] 1. R (at least one of rare earth elements including Y) is 27 to 30 wt%, and B is 1.0 to 1.3 wt%.
%, And the balance is composed of T (transition metal having Fe as an essential component), the volume fraction of the R ₂ T ₁₄ B phase is 93% or more, the average crystal grain size is 20 to 100 μm, and the interval between the R-rich phases. Is 1
An alloy for a rare-earth magnet for use in a two-alloy method, wherein the R-rich phase is 5 μm or less, and the R-rich phase is scattered in a crystal grain boundary and a main phase grain. 2. R (at least one of the rare earth elements including Y) is 27 to 30 wt% and B is 1.0 to 1.3 wt%.
An alloy melt having a composition consisting of T (transition metal containing Fe as essential) is cast by strip casting, and the average cooling rate from the melting point of the alloy to 800 ° C. is 30%.
The method for producing an alloy for a rare earth magnet according to claim 1, wherein the alloy is used for a two-alloy method, wherein the temperature is set to 0 ° C / sec or more and the average cooling rate between 800 to 600 ° C is set to 10 ° C / sec or less. 3. R (at least one of the rare earth elements including Y) is 27 to 30 wt%, and B is 1.0 to 1.3 wt%.
After casting a molten alloy having a composition consisting of T (transition metal essentially including Fe) by a strip casting method, a vacuum or an inert atmosphere at a temperature of 800 to 600 ° C.
2. The method for producing an alloy for a rare earth magnet according to claim 1, wherein the alloy is heated in air for 1 hour to 3 hours . 4. The alloy 70 for a rare earth magnet according to claim 1,
And R (at least one of rare earth elements including Y), B and T (transition metal having Fe as an essential component), and the volume fraction of R ₂ T ₁₄ B phase is 30
% Or less of 5 to 30 parts by weight of the rare earth alloy, so that the composition is R: 28 to 32 wt%, B: 0.9 to 1 wt%, and the balance is T (transition metal containing Fe as an essential component). And pulverizing in an inert atmosphere, followed by magnetic field shaping.