JPH1036949A - Alloy for rare earth magnet and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably exhibit a high magnetic characteristics in which residual magnetization is high in an R-T-B alloy by controlling cooling conditions at the time of strip casting and reducing the volume ratio of R-enriched phases. SOLUTION: An alloy molten metal having a compsn. contg., by weight, 27 to 34% R (one or more kinds among rare earth elements including Y), 0.7 to 1.4% B, and the balance T (transition metals essentially consisting of Fe) is cast by a strip casting method, and the average cooling rate from the m.p. of this alloy to 1000 deg.C is regulated to >=300 deg.C/sec, and the average cooling rate from 800 to 600 deg.C is regulated to <=1.0 deg.C/sec. In this way, a strong permanent magnet in which the volume ratio V(%) of phases other than R-enriched phases is regulated to >=(138-1.6r) where (r) denotes the content of R}, the average particle diameter of the main R2 T14 B phases is regulated to 10 to 100μm, the distance between the R-enriched phases is regulated to 3 to 15μm, and the maximum magnetic force product (BH) MAX} is regulated to >=40MGOe class can easily be obtd.

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 and a method for producing the same.

[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.
Other ferromagnetic phase R ₂ T ₁₄ B phase responsible for the magnetism in the R-T-B magnet, such as Nd nonmagnetic high phase concentrations of rare earth elements (referred to as R-rich phase) exists, the following 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.

[0003] However, the volume ratio of the R ₂ T ₁₄ B phase, which is a ferromagnetic phase, must be increased as the magnet becomes higher in performance. In many cases, shortage occurs and sufficient characteristics cannot be obtained. 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, the grain boundary phase becomes Fe-rich as compared with a raw material alloy prepared by a normal one alloy method. Since the volume ratio of the grain boundary phase can be increased, the dispersibility of the R-rich phase during the production of the magnet is improved, and the magnetic properties are successfully improved. In addition, suppression of powder oxidation by using an amorphous alloy also functions very effectively (E. Otsuki, T. Otsukaand T. Imai, 11th International W
orkshop on Rare Earth magnets and theirApplication
s, vol. 1, p328 (1990)). In addition, there has been reported a study that succeeded in suppressing powder oxidation by using an alloy that supplies an R-rich phase with a high Co composition (M. Honshima and K. Ohashi, Journal)
of Materials Engineering and Performance P.218-22
2 vol.3 (2) April 1994).

[0006] The other is an alloy having a structure in which the microstructure is refined by solidifying the alloy of the final composition by a strip casting method at a cooling rate higher than that of a conventional die casting method, and an R-rich phase is finely dispersed. Is generated. Because the R-rich phase in the alloy is finely dispersed,
The dispersibility of the R-rich phase after pulverization and sintering has also been improved, and the magnetic properties have been successfully improved (JP-A-5-222488, JP-A-5-29-92).
5490). On the other hand, since the R ₂ T ₁₄ B phase is formed by a peritectic reaction between the primary crystal α-Fe and the liquid phase, when the R content decreases, α-Fe
Is easily generated. 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. Further, even when the R content of one alloy is relatively reduced by the two-alloy method and a structure mainly composed of the R ₂ T ₁₇ phase is generated, the production of α-Fe is suppressed by the strip casting method and the crushability is improved. Has 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).

[0007]

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.

[0008]

The present inventor has studied the relationship between the structure of the RTB-based alloy and the magnetic properties. As a result, by controlling the cooling conditions during strip casting, the volume fraction of the R-rich phase is controlled. By reducing
It has been found that the remanent magnetization increases. Alternatively,
By reducing the volume ratio of the R-rich phase by heat treatment after casting, it was found that when magnetized and evaluated, the residual magnetization increased. This fact was also confirmed when the main alloy of the two-alloy method was produced by the strip casting method.

Further, the present inventor has reported that the R-rich phase exists at the crystal grain boundaries in the RTB-based magnet alloy ingots, including the strip cast material, and the R-rich phase is required for uniform fine distribution of the R-rich phase. The difference between the R-rich phase and the crystal grain boundary does not always correspond to the conventional analysis result in which it is important to reduce the phase interval, that is, to reduce the crystal grain size. It has also been found that in order to obtain good magnetic properties, it is necessary that the crystal grain size is large and the interval between R-rich phases is small. By controlling the cooling condition of the ingot during casting, it has been found that it is possible to increase the crystal grain size while reducing the interval between R-rich phases.

That is, the present invention relates to a raw material alloy for a permanent magnet and a raw material alloy 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. In the manufacturing method, by controlling the solidification rate,
Alternatively, by controlling the cooling rate after the solidification, the volume ratio of the R-rich phase, and further, the interval between the R-rich phases is optimized, and further, by controlling the crystal grain size of the R ₂ T ₁₄ B phase,
This causes an increase in remanent magnetization.

Before describing the structure of the present invention in detail, R ₂
Solidification of T ₁₄ B stoichiometry is somewhat R-rich than the composition common main phase alloy, with respect to tissue changes due to heat treatment Nd-
The Fe-B ternary system will be described 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 generated 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 becomes Nd ₂ F
remaining in the e ₁₄ B phase. Thereafter, the Nd ₂ Fe ₁₄ B phase is discharged from the liquid phase as the temperature decreases, and the liquid phase decreases in volume ratio and the composition also changes to the Nd-rich side.
Solidifies into three phases of Nd ₂ Fe ₁₄ B phase, Nd-rich phase and B-rich phase by a ternary eutectic reaction at ℃.

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

Next, the configuration of the present invention will be described in detail below. (1) Volume fraction of phases other than R-rich phase In the present invention, the volume fraction V (%) of phases other than the R-rich phase is 13
8-1.6 r or more (r is the R content in weight%). Here, the phase other than the R-rich phase, the main phase R ₂ T ₁₄ B phase, B-rich phase, other rare-earth than the main phase R ₂ T ₁₄ B phase of the R ₂ T ₁₇ phase etc. appearing by alloy composition The phases with low content are generically indicated. As described above, when the solidification rate is increased by the strip casting method or the like, the R-rich phase increases and the volume ratio of the R ₂ T ₁₄ B phase decreases as expected from the equilibrium diagram. The alloy of the present invention employs a strip casting method and further optimizes cooling conditions after casting to prevent the formation of α-Fe, reduce the volume fraction of the R-rich phase, and reduce the volume fraction of the main phase. At the same time, the structure is characterized by having a structure in which fine R-rich phases are distributed.

The present invention has focused on the point that the volume fraction of the R-rich phase of the raw material alloy contributes to the improvement of the residual magnetization of the magnet. As long as the sinterability does not decrease due to the lack of the R-rich phase, the residual magnetism of the magnet increases as the volume fraction of the R ₂ T ₁₄ B phase increases and the volume fraction of the R-rich phase decreases. Here, as the R content is lower, the R-rich phase decreases, and the volume fraction of the phase other than the R-rich phase mainly composed of the R ₂ T ₁₄ B phase increases. As a result of estimating the volume fraction of the main phase R ₂ T ₁₄ B phase from the equilibrium diagram and confirming it by experiments, the volume fraction V of the phase other than the R-rich phase, which brings about the effect of the present invention, is expressed by R in wt%. It has been found that the preferable range of V is V> (138-1.6r) because the residual magnetization increases and the preferable range of V becomes higher. Further, when r is relatively large, about 30 (wt%) or more, the volume ratio of the main phase R ₂ T ₁₄ B phase is set to V ′ (%) from the balance between the residual magnetization and the sinterability. It has been found that V 'is preferably (138-1.6r) <V'<95. In the two-alloy method, the amount of rare earth in the main phase alloy is generally 30 (wt.) Because it is used by mixing with a grain boundary phase alloy having a large amount of rare earth.
%) Or less. Even in that case, V ′> 91 is preferable. More preferably, V ′> 93. On the other hand, the grain boundary phase alloy has a larger rare earth content than the alloy described in this patent,
Since the organization differs greatly, it is not specified here.

[0015] Japanese Patent Laid-Open No. 7-1764, which was previously mentioned in the prior art,
According to FIG. 14, the decrease in the R-rich phase of the main phase alloy simply causes a decrease in the remanent magnetization due to the decrease in the sinterability. However, in the present invention, the volume ratio of the R-rich phase increases as the sinterability decreases. It has been confirmed that the remanence increases if the value does not decrease.

[0016] (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 10~100μm
It is characterized by being. When the crystal grain size of the main phase is 10 μm or less, the ratio of the powder particles having crystal grain boundaries in the milled particle size increases when the powder for magnetic field molding is finely pulverized to 3 to 5 μm. 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, when the thickness is 100 μm or more, the effect of the high cooling rate of the strip casting method is weakened, and adverse effects such as α-Fe precipitation are caused. More preferably, when r is relatively large, about 30 or more, 10 to 10
It is 50 μm, more preferably 15 to 35 μm. On the other hand, as the main alloy of the two alloy method in which r is relatively small,
Most preferably, it is 20 to 50 μm.

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) The interval between R-rich phases The interval between R-rich phases is 3 to 15 μm. When the interval between the R-rich phases is 15 μm or more, the dispersion state of the R-rich phase becomes worse, and the particle size of the magnetic field-forming powder is 3 to 3 μm.
When finely ground to 5 μm, the proportion of powder particles in which the R-rich phase is present decreases. Therefore, the dispersion state of the R-rich phase after the magnetic field molding is also deteriorated, resulting in a decrease in sinterability and a decrease in magnetization and coercive force after magnetization. In addition, the uneven distribution of the R-rich phase causes a partial decrease in coercive force and a decrease in squareness after magnetization. On the other hand, when the thickness is 3 μm or less, it corresponds to a case where the solidification speed is too high, and causes an adverse effect such as crystal grain refinement. More preferably, r is 30
When it is relatively large, such as at least about 3 to 10 μm, it is more preferably 3 to 8 μm. On the other hand, 5 to 12 μm is most preferable as the main phase alloy of the two-alloy method in which r is relatively small.

The R-rich phase can be observed by a reflection electron beam image of a scanning electron microscope (SEM) after polishing the alloy with emery paper and then buffing the surface using alumina, diamond or the like. Since the R-rich phase has a larger average atomic number than the main phase, it is observed brighter than the main phase in the reflected electron beam image. The interval between the R-rich phases can be calculated by, for example, observing the cross section of a strip, drawing a line parallel to the roll surface or the free surface, and dividing the length of the line by the number of R-rich phases crossed by the line. You can ask.

(4) Manufacturing method First, it is characterized by being manufactured by a strip casting method. In particular, after strip casting, the melting point is 1000
The average cooling rate to 300 ° C. is 300 ° C./sec or more,
The cooling rate at -600 ° C is set to 1.0 ° C / sec or less. According to the strip casting method,
It is possible to produce a flaky alloy without α-Fe,
Recently, the productivity has been improved with the improvement of the apparatus. It is considered that the influence of the crystal grain size and the presence / absence of α-Fe is the solidification rate and the cooling rate in a high-temperature region 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.

As a result of conducting a wide range of experiments, it was
It has been known that the average cooling rate to 00 ° C. should be 300 ° C./sec or more, more preferably 500 ° C./sec or more. At 300 ° C./sec or less, α-Fe is generated, and the interval between R-rich phases is wide, and a fine structure is not formed. The factor that most affects the cooling rate of the strip before it is released from the roll is the strip thickness. In order to set the average cooling rate from the melting point to 1000 ° C. at 300 ° C./sec or more, and to obtain a structure having an optimum crystal grain size and an interval between R-rich phases, the strip thickness is 0.15 to 0.6.
It is good to be 0 mm. More preferably, 0.20 to 0.2.
45 mm. When the thickness of the strip is 0.15 mm or less, the solidification rate becomes too fast, and the crystal grain size becomes smaller than a preferable range. Although accurate measurement of the cooling rate is difficult, it can be simply obtained as follows. The temperature of the strip immediately after leaving the roll is
It can be easily measured, and is about 700 to 800 ° C.
Then, after the molten metal is supplied to the roll,
The average cooling rate in the temperature range can be obtained by dividing by the time required for separation and temperature measurement. By this method, the average cooling rate from the melting point to 800 ° C. is determined.
In the ordinary solidification and cooling processes including this method, the cooling rate is higher in a higher temperature range. Therefore, the average cooling rate from the melting point to 800 ° C. is 30
If it can be confirmed that the temperature is 0 ° C./second or more, the melting point is 10
It can be said that the cooling rate at 00 ° C. is 300 ° C./sec or more. Although it is difficult to accurately define the upper limit of the cooling rate, it is considered that the cooling rate is preferably about 10 ⁴ ° C / sec or less.

In the strip casting method, the cooling rate is as fast as several hundreds to several thousands ° C./sec.
Microstructures are obtained in which the volume fraction of the R-rich phase is higher than expected in the equilibrium diagram, and such microstructures have heretofore been accepted as preferred. However, in the present invention, in order to increase the volume ratio of the phase other than the R-rich phase, the cooling rate at 800 to 600 ° C. is set to 1.0 ° C./sec or less, preferably 0.75 ° C./sec.
It was decided to promote the formation of the R ₂ T ₁₄ B phase from the liquid phase by setting the time to less than seconds. When the cooling rate at 800 to 600 ° C. exceeds 1.0 ° C./sec, the R ₂ T ₁₄ B phase solidifies from the liquid R rich phase before it is not sufficiently formed, and as a result, the R rich phase Is out of the gist of the present invention because the volume ratio of Further, by controlling the cooling rate, an effect of appropriately increasing the interval between the R-rich phases is also provided.

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 thereafter is provided, so that the cooling rate at 800 to 600 ° C. can be controlled.

As another method for obtaining the alloy of the present invention, the same effect can be obtained by heat-treating at 800 to 600 ° C. after casting and cooling by strip casting. 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 is little harm in terms of equipment and production efficiency. Since the cast piece is thin, the heat treatment time usually needs to be 10 minutes or more, and need not exceed 3 hours. The heat treatment atmosphere needs to be a vacuum or an inert atmosphere in order to prevent oxidation. It is preferable that the cooling after the heat treatment is gradually cooled to about 600 ° C.

Recently, several inventions relating to strip cast materials have been reported. One is to produce a desired structure also at a specific cooling rate (JP-A-8-269643). It is 2 × 10 ³ ℃
/ Sec ~ 7 × 10 ³ ℃ / sec.
After cooling to 00 to 1000 ° C and removing the rolls, the slab was cooled to a temperature below the solidus temperature of the alloy at 50 to 2 × 10 ³ ° C / min.
Cool at the next cooling rate, average short axis crystal grain size 3 ~ 15μm
The R ₂ T ₁₄ B phase and the R-rich phase of 5 μm or less form a micro-dispersed structure, reduce the degree of orientation, prevent pulverization at the time of pulverization during magnetization, and prevent oxidation of the powder. The characteristics have been successfully improved.

On the other hand, in the present invention, the cooling rate at the time of casting is defined separately for a high temperature range and a low temperature range, thereby producing a desired structure and improving the magnetic properties. However, the alloy structure of the present invention has an average crystal grain size of the R ₂ T ₁₄ B phase of 10 to 100 μm,
It is different from 3 to 15 μm of JP-A-8-269643. In the present invention, the interval between the R-rich phases is also 3 to 15 μm.
In contrast, Japanese Patent Application Laid-Open No. Hei 8-269643 mentions only the size. Japanese Unexamined Patent Publication No. Hei 8-269643 states that if the secondary cooling rate corresponding to a low temperature range is low, crystal grains grow, which causes a decrease in iHc of the sintered magnet. The preferable secondary cooling rate is 50 ° C./min to 2 × 10 ³ ° C./mi.
n, and the upper limit of the cooling rate is also set from the viewpoint of mass productivity, and is not specified from the characteristics.
On the other hand, in the present invention, the cooling rate of each of the high-temperature region and the low-temperature region is controlled so that the crystal grain size of the R ₂ T ₁₄ B phase is large, the spacing of the R-rich phase is small, and the volume ratio is small. Yes,
For example, the cooling rate in the low temperature range from 800 to 600 ° C. is from 50 ° C./min to 2 × 10 ³ ° C./min in JP-A-8-269643.
(0.83 ~ 33.3 ° C / sec)
It is 1.0 ° C./sec or less, preferably 0.75 ° C./sec or less, and mentions the effectiveness of heat treatment after casting, which is completely different.

The other is to heat-treat the thin plate obtained by the strip casting method at 800 to 1100 ° C. to remove the hardening of the surface layer portion, accelerate the disintegration of the alloy in the hydrogen absorbing process in the next step, and promote the miniaturization. (JP-A-8-264363). However, there is no stipulation on the alloy structure, and the preferable range of the heat treatment is different from 600 to 800 ° C. of the present invention.

[0028]

According to the present invention, R (at least one of rare earth elements including Y), T (transition metal having Fe as an essential component) and B
In a method for producing a raw material alloy for a permanent magnet and a raw material alloy having a basic component of, the volume ratio of a phase other than the R-rich phase in the alloy is increased by a solidification rate or a heat treatment after the solidification, By controlling the crystal grain size of the R ₂ T ₁₄ B phase,
By controlling the interval of the rich phase, the residual magnetization after the conversion to the sintered magnet was increased.

Here, the volume fraction of the R-rich phase in each alloy is
The factors affecting the residual magnetization of the magnet will be discussed.
When the volume fraction of the R-rich phase is large, the R-rich phase exists in a large amount in a non-equilibrium state. When performing the hydrogen crushing generally employed in the magnet manufacturing process, the R-rich phase preferentially absorbs hydrogen and becomes embrittled. Generation and propagation path. Therefore, as a result, it can be estimated that the volume ratio and the distribution state of the R-rich phase affect the shape and particle size distribution of the finely pulverized powder, and consequently affect the degree of orientation during magnetic field molding. Actually, it has been confirmed that when the interval between the R-rich phases is about 3 μm or less, the shape of the powder tends to be square.

[0030]

【Example】

(Example 1) Alloy composition: Nd: 30.7% by weight, B:
1.00% by weight, Co: 2.00% by weight, Al: 0.3
0% by weight, Cu: 0.10% by weight, the balance being iron neodymium alloy, metal dysprosium, ferroboron, cobalt, aluminum, copper, iron, and alumina crucible in an argon gas atmosphere. Melted in a high-frequency melting furnace using the strip casting method
A strip approximately 0.33 mm thick was produced. On this occasion,
The high-temperature strip detached from the casting roll was kept for 1 hour in a box made of a heat insulating material having a large heat-retaining effect, 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 710 ° C. After that, eight minutes had elapsed until the temperature reached 600 ° C. Therefore, from 800 ° C. to 710
Ignoring the time required for cooling to
The average cooling rate at 0 ° C. is 0.56 ° C. per second, which is actually lower. On the other hand, the cooling rate from the melting point to 800 ° C. is 4 times per second more than the time required to fall into the insulating box.
It was 00 ° C or higher. The temperature of the strip on the roll was measured with a radiation thermometer.
The cooling rate to 1000C was found to be 1000C or more per second. 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 R ₂ Fe ₁₄ B phase was about 28 μm.
m. Further, as a result of observing the reflected electron beam image of the scanning electron microscope, it was found that the R-rich phase was present in the form of streaks or partial grains in the crystal grain boundaries and the main phase grains, and the distance between them was approximately 5%.
μm. In addition, a small amount of a phase having a relatively low rare earth content, which is considered to be a B-rich phase, was present. The volume ratio V of the phase other than the R-rich phase and the volume ratio V ′ of the main phase R ₂ Fe ₁₄ B phase were measured using an image processing apparatus.
1%.

Next, hydrogen was absorbed into the alloy at room temperature,
Hydrogen was released at 00 ° C. This mixed powder was roughly pulverized by a brown mill to obtain an alloy powder having a particle diameter of 0.5 mm or less, and then finely pulverized by a jet mill to obtain a magnet powder having an average particle diameter of 3.5 μm. The obtained fine powder was molded at a pressure of 1.5 ton / cm ^{2 in} a magnetic field of 15 kOe. After sintering the obtained molded body in vacuum at 1050 ° C. for 4 hours, the first heat treatment is performed at 850 ° C. for 1 hour, and the second heat treatment is performed at 52
Performed at 0 ° C. for 1 hour. Table 1 shows the magnetic properties of the obtained magnets.
Shown in

Comparative Example 1 An alloy strip having a thickness of about 0.33 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 710 ° C. Thereafter, the time required to reach 600 ° C. was 15 seconds. On the other hand, from 800 ° C to 7
The time required for cooling at 10 ° C. is shorter than the time required for the strip to fall into the box, and is at most about 2 seconds. Therefore, even if it is added,
The average cooling rate at 0 ° 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 R ₂ Fe ₁₄ B phase was about 28 μm. Further, as a result of observing the reflected electron beam image of the scanning electron microscope, it was found that the R-rich phase was present in the form of streaks or partial grains in the crystal grain boundaries and the main phase grains, and the interval between them was about 2 μm. . The volume ratio V of the phase other than the R-rich phase and the volume ratio V ′ of the main phase R ₂ Fe ₁₄ B phase were measured using an image processing apparatus, and as a result, both were 87%. Next, using this alloy, a sintered magnet was produced in the same manner as in Example 1, and the magnetic properties are shown in Table 1.

Example 2 An alloy strip having a thickness of about 0.33 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. The strip separated from the roll was deposited so as to spread thinly in a box made of the same heat insulating material as in Example 1. After maintaining for one hour in that state, the resultant was put into 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 710 ° C. afterwards,
The time required to reach 600 ° C. was 4 minutes and 10 seconds. Therefore, the average cooling rate at 800 to 600 ° C is 0.80 ° C or less per second. 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 R ₂ Fe ₁₄ B phase was about 28 μm. In addition, as a result of observing the reflected electron beam image of the scanning electron microscope, the R-rich phase is present in the form of streaks or partly grains in the crystal grain boundaries and main phase grains,
The interval was about 4 μm. In addition, a small amount of a phase having a relatively low rare earth content, which is considered to be a B-rich phase, was present. The volume ratio V of the phase other than the R-rich phase and the volume ratio V ′ of the main phase R ₂ Fe ₁₄ B phase were measured using an image processing apparatus, and as a result, they were 91% and 90%, respectively. Next, using this alloy, 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 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, since the pouring speed was reduced, the thickness of the strip was about 0.1.
3 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
30 ° C. Thereafter, the time required to reach 600 ° C. was 3 minutes. Therefore, 800 to 600
The average cooling rate in ° C. is below 1.1 ° C. per second. On the other hand, the cooling rate from the melting point to 800 ° C. was 500 ° C. or more per second. As a result of observing the structure of the cross section with a polarizing microscope,
The average crystal grain size of the main phase R ₂ Fe ₁₄ B phase was about 12 μm.
Further, as a result of observing the reflected electron beam image of the scanning electron microscope, it was found that the R-rich phase was present in the form of streaks or partial grains in the crystal grain boundaries and the main phase grains, and the interval between them was about 4 μm. . The volume ratio V of the phase other than the R-rich phase and the volume ratio V ′ of the main phase R ₂ Fe ₁₄ B phase were measured using an image processing apparatus, and as a result, were 91% and 90%, respectively.

(Comparative Example 3) Using an iron mold having a water cooling mechanism and a thickness of 25 m so as to have the same composition as in Example 1,
m ingots were produced. As a result of observing the structure of the cross section with a polarizing microscope, the average crystal grain size of the main phase R ₂ Fe ₁₄ B phase was about 150 μm. However, as a result of observing the reflected electron beam image of the scanning electron microscope, a large amount of α-
Since Fe was present, no magnet was made.

Example 3 Nd and Dy were used as alloy compositions.
Are 30.8% by weight and 1.2% by weight, respectively, and the other components and contents are the same composition as in Example 1 by strip casting under the same conditions as in Example 1. An alloy strip of about 0.33 mm was produced, and a sintered magnet was produced in the same manner as in Example 1. Table 1 also shows the cooling rate, alloy structure and characteristics of the sintered magnet at this time.

(Example 4) In the two-alloy method, the composition of the main phase alloy was 28.0% by weight of Nd, 1.09% by weight of B, 0.3% by weight of Al, and the balance iron. Thus, a strip having a thickness of about 0.35 mm was produced by the strip casting method in the same manner as in Example 1. Table 1 shows the cooling rate and alloy structure at this time. On the other hand, the grain boundary phase alloy has a composition of 38.0% by weight of Nd, 10.0% by weight of Dy, and B:
0.5% by weight, Co: 20% by weight, Cu: 0.67% by weight, Al: 0.3% by weight, iron neodymium alloy, metal dysprosium, ferroboron, cobalt, copper Aluminum and iron were mixed and melted in a high frequency melting furnace using an alumina crucible in an argon gas atmosphere, and an ingot having a thickness of about 10 mm was produced by centrifugal casting. Next, 85% by weight of the main phase alloy and 15% by weight of the grain boundary phase alloy were mixed, and hydrogen was absorbed at room temperature.
Hydrogen was released at ° C. This mixed powder was roughly pulverized by a brown mill to obtain an alloy powder having a particle diameter of 0.5 mm or less, and then finely pulverized by a jet mill to obtain a magnet powder having an average particle diameter of 3.5 μm. The obtained fine powder was molded at a pressure of 1.5 ton / cm ^{2 in} a magnetic field of 15 kOe. After sintering the obtained molded body in vacuum at 1050 ° C. for 4 hours, the first-stage heat treatment was performed at 850 ° C. for 1 hour, and the second-stage heat treatment was performed at 520 ° C. for 1 hour. Table 1 also shows the magnetic properties of the obtained magnet.

Comparative Example 4 A main phase alloy strip having a thickness of about 0.35 mm was produced by a strip casting method in the same manner as in Example 4 so as to have the same composition as in Example 4. 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. Table 1 shows the cooling rate and alloy structure at this time. Next, using this main phase alloy and the grain boundary phase alloy produced in Example 4, a sintered magnet was produced in the same manner as in Example 4, and the magnetic properties are also shown in Table 1.

[0039]

[Table 1]

[0040]

According to the present invention, the maximum magnetic impulse ((BH)
MAX) can easily obtain a strong permanent magnet of 40 MGOe class or more.

[Brief description of the drawings]

FIG. 1 is a polarizing microscope micrograph (200 × magnification) showing the crystal grain size of the alloy of Example 1.

FIG. 2 is a photomicrograph (200 × magnification) of a microstructure of a reflection electron microscope showing a dispersion state of an R-rich phase of the alloy of Example 1.

FIG. 3 is a micrograph (200-fold magnification) of a structure of an alloy of Comparative Example 1 showing an R-rich phase in a dispersed state by a reflection electron microscope.

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

Claims (7)

[Claims] 1. R (at least one of rare earth elements including Y) is 27 to 34 wt%, and B is 0.7 to 1.4 wt%.
%, And the balance is composed of T (T is a transition metal that essentially requires Fe), and the volume fraction V (%) of phases other than the R-rich phase
Is (138-1.6r) or more (where r is the R content)
An alloy for rare earth magnets, characterized in that the average crystal grain size of the R ₂ T ₁₄ B phase is 10 to 100 μm and the interval between R-rich phases is 3 to 15 μm. 2. An alloy composition comprising 28 to 33 wt% of R (at least one of rare earth elements including Y) and 0.95 of B
T1.1 wt%, the balance being composed of T (transition metal with Fe indispensable), and the volume fraction V ′ (%) of the R ₂ T ₁₄ B phase
138-1.6r <V ′ <95, the average crystal grain size of the R ₂ T ₁₄ B phase is 10 to 50 μm, and the distance between the R-rich phases is 3
The alloy for a rare-earth magnet according to claim 1, wherein the thickness is from 10 to 10 m. 3. The alloy composition is such that R (at least one of rare earth elements including Y) is 30 to 32 wt% and B is 0.95 wt%.
And a balance of T (transition metal containing Fe as an essential component), and a volume fraction V ′ of the R ₂ T ₁₄ B phase.
(%) Is 138-1.6r <V ′ <95, and R ₂ T ₁₄ B
The rare earth magnet alloy according to claim 1, wherein the average crystal grain size of the phase is 15 to 35 µm, and the interval between the R-rich phases is 3 to 8 µm. 4. An alloy composition in which R (at least one of the rare earth elements including Y) is 27 to 30 wt% and B is 0.7 to 0.7 wt%.
It has a composition of 1.4 wt%, the balance being T (transition metal which essentially requires Fe), and the volume fraction V ′ (%) of the R ₂ T ₁₄ B phase.
Is 91 or more, and the average crystal grain size of the R ₂ T ₁₄ B phase is 15 to 1
2. The alloy for a rare earth magnet according to claim 1, wherein the interval between the R-rich phase and the R-rich phase is 3 μm to 15 μm. 3. 5. An alloy composition comprising 28 to 29.5 wt% of R (at least one of rare earth elements including Y) and B of 1.
1 to 1.3 wt%, the balance being composed of T (transition metal having Fe as an essential component), and the volume fraction V ′ of the R ₂ T ₁₄ B phase.
(%) Is 93 or more, and the average crystal grain size of the R ₂ T ₁₄ B phase is 2
The alloy for a rare-earth magnet according to claim 1, wherein the R-rich phase has an interval of 0 to 50 m and 5 to 12 m. 6. R (at least one of rare earth elements including Y) is 27 to 34 wt% and B is 0.7 to 1.4 wt%.
%, And the balance is cast by a strip casting method and has an average cooling rate from the melting point of the alloy to 1000 ° C. of 300 ° C./second or more. A method for producing an alloy for a rare earth magnet, wherein an average cooling rate between 800 ° C. and 600 ° C. is 1.0 ° C./sec or less. 7. An average cooling rate from the melting point to 1000 ° C. is 500 ° C./sec or more, and an average cooling rate between 800 ° C. and 600 ° C. is 0.75 ° C./sec or less. 3. The method for producing an alloy for a rare earth magnet according to claim 1.