JPH09283313A - Sintered permanent magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve corrosion resistance by making the main phase crystal particle diameters of a magnet to be not more than a specified value in the R-Fe-B system sintered permanent magnet with rare earth and oxygen of the specified range amounts. SOLUTION: In the sintered permanent magnet, composition where R (R is one type or more than two types of rare earth elements containing Y) is 28.0-33.0%, B is 0.5-2.0%, O is 0.3-0.7% and a remaining part is Fe at a weight percentage is provided, and the sum of the areas of main phase crystal particles whose crystal particle diameters are not more than 10μm is not more than 10% against the total area of the magnetic main phase. In the sintered permanent magnet, a part of Fe is substituted for one type or more than two types among Nb 0.1-2.0%, Al 0.02-2.0%, Co 0.3-5.0%, Ga 0.01-0.5% and Cu 0.01-1.0 or the value of coercive force iHc is made to be not less than 13.0kOe. Thus, the R-Fe-B system sintered permanent magnet having superior corrosion resistance can be obtained without deteriorating a magnetic characteristic.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to improving the performance of R-Fe-B rare earth magnets.

[0002]

2. Description of the Related Art Among sintered rare earth permanent magnets, R-Fe-B (R
Is one or more of rare earth elements including Y). Sintered permanent magnets are attracting attention as high-performance magnets and are used in a wide range of fields. This R-Fe-B sintered permanent magnet basically consists of R2Fe14B phase (main phase), RFe7B6 phase (Brich phase), R85Fe15 phase (Rr
ich phase). Due to the existence of the Rrich phase compositionally rich in rare earth elements and such three-phase structure, the R-Fe-B system sintered permanent magnets are better than the Sm-Co system sintered permanent magnets. It is inferior in corrosion resistance and is one of the drawbacks from the beginning of the development of this permanent magnet to the present. R-Fe-B
Although there is no established theory about the corrosion mechanism of sintered sintered permanent magnets, there is a general view that the Rrich phase is the starting point of corrosion, and therefore it is also regarded as anodic corrosion using the Rrich phase as an anode. Certainly, by reducing the amount of rare earth elements in the R-Fe-B system sintered permanent magnet, the amount of Rrich phase inside the sintered body is reduced, and the phase morphology becomes finer. As a result, the corrosion resistance of the permanent magnet is improved. Therefore, reducing the amount of rare earth elements is one method of improving the corrosion resistance of the R-Fe-B system sintered permanent magnet.

Sintering type rare earth permanent magnets containing R-Fe-B system are powder metallurgy in which raw metal is melted and an ingot obtained by pouring in a mold is crushed, molded, sintered, heat treated and processed. It is generally manufactured by a conventional process. However, the alloy powder obtained by crushing the ingot is chemically very active because it contains a large amount of rare earth elements, and is oxidized in the atmosphere to increase the oxygen content. As a result, in the sintered body after sintering, a part of the rare earth element forms an oxide, and the magnetically effective rare earth element is reduced. Therefore, in order to achieve a practical level of magnetic characteristics, for example, iHc ≧ 13 kOe, it is necessary to increase the amount of rare earth elements in the R-Fe-B sintered permanent magnet, which is 31% by weight. The amount of rare earth element added exceeding the range is adopted in practical materials. Therefore, the corrosion resistance of the R-Fe-B system sintered permanent magnets to date has not been sufficient.

[0004]

The present invention has been described above.
It is intended to significantly improve the corrosion resistance of R-Fe-B sintered permanent magnets.

[0005]

[Means for Solving the Problems] The inventors of the present invention have conducted various studies to improve the corrosion resistance of R-Fe-B system sintered permanent magnets, and as a result, R-Fe of a specific range amount of rare earth and oxygen The present invention has been completed by finding that in a Fe-B sintered permanent magnet, the corrosion resistance is improved by setting the crystal grain size of the main phase of the magnet to a specific value or less.

Hereinafter, the present invention will be described specifically. The sintered permanent magnet according to the present invention has a weight percentage of R (R is one or more of rare earth elements including Y) 28.0 to 33.0%, B
It has a composition of 0.5 to 2.0%, O 0.3 to 0.7%, and the balance of Fe, and the total area of main phase crystal grains with a grain size of 10 μm or less is 80% or more with respect to the total area of the magnet main phase. The sum of the areas of the main phase crystal grains having a diameter of 13 μm or more is 10% or less. Further, in the sintered permanent magnet of the present invention, part of Fe is Nb 0.1
~ 2.0%, Al 0.02 ~ 2.0%, Co 0.3 ~ 5.0%, Ga 0.01 ~ 0.5
%, Cu 0.01 to 1.0%, and may be replaced by one kind or two or more kinds.

The present inventors have found that the corrosion resistance of the R-Fe-B system sintered permanent magnet having the above composition depends on the crystal grain size, and the crystal grain size of the main phase of the magnet is set to a specific value or less. It has been found that particularly excellent corrosion resistance is exhibited. There are various methods for defining and measuring the magnet crystal grain size, and although it is not unambiguous, the inventors of the present invention calculated the sum of the areas of the main phase crystal grains whose grain size is equal to or less than a certain dimension with respect to the total area of the magnet main phase. Similarly, the ratio of the ratio and the sum of the areas of the main phase crystal grains having a grain size equal to or larger than a certain dimension to the total area of the magnet main phase was used as a scale indicating the state of the magnet crystal grain size. The effects of the present invention will be described below using this scale. The measurement in calculating this ratio was performed by observing the crystal structure of the target R-Fe-B sintered permanent magnet with an OLYMPUS microscope (product name VANOX), and measuring this image by NIRECO. It was carried out by directly inserting it into an image processing device (trade name LUZEX2).

The present inventors have made the following evaluations on the relationship between the main phase crystal grain size and the corrosion resistance of the R-Fe-B system sintered permanent magnet having the composition shown in the claims. The results shown in are obtained. FIG. 1 shows the ratio of the sum of the areas of the main phase crystal grains having a grain size of 10 μm or less to the total area of the magnet main phase crystals, and the crystal grain size of the total area of the magnet main phase crystals.
It shows the relationship between the ratio of the sum of the areas of the crystal grains of the main phase of 13 μm or more and the elapsed time until the initiation of peeling of Ni plating in the accelerated corrosion resistance test. ○ indicates percentage by weight of Nd 22.8%, Pr 6.7%, Dy 2.0%, B 1.0%, Al 1.0
%, O 0.45%, C 0.08%, N 0.015%, balance Fe composition, □ indicates weight percentage of Nd 31.0%, Dy 1.0%, B
1.05%, Al 0.05%, Co 2.0%, Ga 0.09%, O 0.55%, C 0.
Sintered body with composition of 07%, N 0.008%, balance Fe, △ mark is Nd 23.0%, Pr 5.0%, Dy 4.5%, B1.1%, N in percentage by weight.
b 1.0%, Al 0.2%, Co 2.0%, Cu 0.08%, O 0.35%, C 0.0
A sintered body having a composition of 6%, N 0.030% and balance Fe is shown. In the acceleration test in this case, the magnet was processed into a size of 10 mm × 10 mm × 2 mm, the surface thereof was plated with Ni of 15 μm, and then the sample was left under the conditions of 2 atm, 120 ° C., and 100% humidity. FIG.
Therefore, the crystal grain size is 10μ with respect to the total area of the crystals of the main phase of the magnet.
When the sum of the areas of the main phase crystal grains of m or less is 80% or more and the sum of the areas of the main phase crystal grains of 13 μm or more of the crystal grain size is 10% or less, it has the composition shown in the claims. R-
It can be seen that the corrosion resistance of the Fe-B sintered permanent magnet is particularly excellent. Therefore, the size of the crystal grains of the main phase of the magnet is specified above.

Presuming the cause of this, in the permanent magnet sintered body in which relatively large main phase crystal grains are present, the voids between the main phase crystal grains, specifically, the grain boundary triple point is the cause. Nd, which is a seed part, is extremely susceptible to oxidation.
Although the rich phase exists, the volume of the void filled with the Ndrich phase becomes large. Factors that cause corrosion destruction, such as water in this accelerated test, are considered to be in a state in which the permeability of such factors is good and the destruction of grain boundaries is likely to occur in a chain reaction. The above shows that the corrosion resistance of the R-Fe-B system sintered permanent magnet having the composition shown in the claims depends on the crystal grain size of the main phase, and shows an example of the research results of the present inventors. It was explained by.

The method of controlling the crystal grain size of the main phase of the R-Fe-B system sintered permanent magnet having the composition of the claims to the above-specified range is not necessarily unique, and various methods or Although it can be achieved by a combination of these methods, our work involves considerable difficulty with conventional methods. Generally, in the production of R-Fe-B system sintered permanent magnets, raw material coarse powder is pulverized into fine powder, and the fine powder is molded in a magnetic field to obtain a compact, which is then sintered. A method of forming a sintered body is adopted. For example, when fine pulverization is performed using a jet mill, fine powder having a predetermined average particle size and particle size distribution can be obtained by controlling the gas pressure during pulverization, the coarse powder supply rate, and the like. In addition, the particle size distribution of the fine powder can be controlled by performing classification, if necessary. When molding and sintering the fine powder produced in this way, the crystal grains of the main phase of the R-Fe-B sintered permanent magnet can be selected by selecting an appropriate sintering temperature, time, and pattern. It is not always impossible to set the diameter within the specified range. However, it has been found that it is extremely difficult to manufacture a sintered body having a predetermined crystal grain size with good reproducibility because many conditions must be set and controlled.

We have the claimed composition
As a result of searching for a method that is easy and suitable for mass production so that the crystal grain size of the main phase of the R-Fe-B sintered permanent magnet falls within the specified range, it was manufactured by the so-called strip casting method. An R-Fe-B system quenched ribbon-shaped alloy having a predetermined composition was heat-treated in a predetermined temperature range and pulverized to obtain a raw material coarse powder. Further, in crushing the ribbon-shaped alloy after the heat treatment, it is effective to naturally disintegrate by hydrogen absorption and then to perform dehydrogenation treatment in order to improve the fine pulverization performance. Figure 2 shows Nd 22.
7%, Pr 7.6%, Dy 1.5%, B 1.05%, Al 0.05%, O0.01%, N
This is a cross-sectional structure of a strip-shaped alloy produced by strip casting with a composition of 0.004%, C 0.007%, and the balance Fe.
(as cast). There is a dendrite-like fine structure. In the photograph, the phase observed in white corresponds to the main phase of the permanent magnet sintered body with a small amount of rare earth, and the phase observed in black corresponds to the Rrich phase of the sintered permanent magnet with a large amount of rare earth. It is a phase. Since this Rrich phase becomes the starting point of fracture during fine pulverization, when a strip-shaped alloy in which this Rrich phase is finely dispersed is used, a fine powder with a fine grain size is generated stochastically. It's easy to do. Therefore, it is possible to manufacture a sintered body having a particle size distribution within the scope of the claims with relative ease and with good reproducibility without strictly controlling many conditions during fine pulverization and sintering. However, this ribbon alloy
Directly crushing (as-quenched casting) as it is to obtain raw material coarse powder, even if this is finely pulverized, a good particle size distribution of fine powder cannot be obtained. The crystal grain size of the main phase cannot be obtained. The reason for this is that the surface of the ribbon-shaped alloy is hardened by quenching casting, and the pulverizability during fine pulverization is significantly deteriorated.

The present inventors have found that as a means for solving this problem, it is effective to heat-treat the ribbon-shaped alloy within a specific temperature range to remove the hardening of the ribbon-shaped alloy surface. The heat treatment temperature is set to 800 ° C to 1100 ° C. This is because if the heat treatment temperature is lower than 800 ° C., the curing removal is insufficient. Further, at a temperature higher than 1100 ° C., a reaction occurs between the ribbon-shaped alloys during the heat treatment, which makes it difficult to perform the treatment in the subsequent step. Needless to say, the heat treatment must be performed in an inert gas atmosphere or in a substantial vacuum because it is a ribbon-shaped alloy containing a large amount of active rare earth elements. In addition, as described above, it is more effective to make the strip-shaped alloy after heat treatment occlude hydrogen to spontaneously disintegrate, dehydrogenate, and then coarsely pulverize it so as to improve fine pulverizability. is there. This is because, in addition to the effect of removing the hardening of the surface of the ribbon alloy by heat treatment, the effect of embrittlement of the Rrich phase mainly inside the ribbon alloy by hydrogen is added.

In Table 1, the ribbon-shaped alloy is heat-treated under various conditions (1
Hr) or crushed into coarse powder, finely crushed under the same conditions, shaped and sintered, and shows the state of the main phase crystal grain size of the sintered body.

[0014]

[Table 1]

It can be seen from Table 1 that a sintered body having the proportion of the main phase grain size shown in the claims is obtained by heat treating the ribbon alloy at a temperature of 800 ° C. or higher and using it. Moreover, as described above, the effectiveness of the hydrogen treatment is also clear. At the same time, from Table 1, the state of the grain size of the main phase in the heat treatment at 700 ° C. is almost the same level as that in the as-quenched casting. It can be seen that the heat treatment temperature of 700 ° C is insufficient for removing the surface hardening of the ribbon alloy. At the same time, the present inventors have found that heat treatment of the ribbon-shaped alloy at a temperature of 800 ° C. or higher brings about an effect of improving Br in the magnetic properties. The results are also shown in Table 1. From Table 1, B of the permanent magnet sintered body made of ribbon-shaped alloy in the state of rapid casting and heat treatment at 700 ° C
Although r is 12.8 to 12.9 KG, Br rapidly increases to 13.1 KG when using a ribbon alloy heat treated at 800 ℃ and 900 ℃. At a heat treatment temperature of 1000 ° C, the resulting Br
Is slightly increased to 13.2KG. At the heat treatment temperatures of 1100 ℃ and 1200 ℃, the increase of Br reaches saturation, which is the same as 13.2KG. Among the thin alloys shown in Table 1, a metallographic photograph of the thin alloy after rapid cooling casting is shown in FIG. 2, and a metallographic photograph of the thin alloy subjected to heat treatment at 1000 ° C. after rapid casting is shown in FIG. . FIG.
Comparing FIG. 3, it can be seen that the heat treatment causes coarsening of both the white structure corresponding to the main phase and the black structure corresponding to the Rrich phase in the thin alloy. From these facts, the inventors of the present invention have found that when a fine alloy is produced by using a thin alloy that has been as-quenched and cast, the structure composed of a phase corresponding to the main phase and the Rrich phase is fine. , Among the fine powders, there are stochastically many that remain in the polycrystalline state,
Inducing deterioration of orientation when molding fine powder in a magnetic field,
It is considered that Br of the permanent magnet sintered body is lowered. At the heat treatment temperature of 700 ° C., the growth of the structure is insufficient and the orientation cannot be improved. Although the internal structure of the thin alloy is coarsened as the heat treatment temperature is increased, it is considered that the probability of generation of fine powder in a polycrystalline state is reduced and Br is improved. As far as it can be judged, it is considered that the effect is remarkable at the heat treatment temperature of 800 ° C. As the heat treatment temperature of the thin alloy further increases, the Br of the obtained sintered body increases, but it tends to be saturated at the heat treatment temperature of 1000 ° C. or higher. This is because when the structure inside the thin alloy is coarsened to some extent, and fine powder in a polycrystalline state has reached a state in which almost no stochastically occurs, even if the heat treatment temperature is further raised to promote coarsening of the structure, It can be understood that this is not reflected as an improvement in Br of the obtained sintered body.

As described above in detail, the rapidly cast ribbon-shaped alloy having a predetermined composition by the strip casting method is heat-treated in a specific temperature range, or is subjected to a hydrogen storage treatment to spontaneously disintegrate and is crushed. By crushing into coarse powder, the pulverizability at the time of fine pulverization is improved, and the permanent magnet sintered body produced using this is excellent in corrosion resistance. However, not only that, but also those having high magnetic characteristics. In addition, 800 to 1 of thin strip alloy
The heat treatment time at 100 ° C. needs to be at least 15 minutes or longer, preferably 30 minutes or longer.

The reasons for limiting the composition of the R-Fe-B system sintered permanent magnet of the present invention will be described below. The amount of rare earth element is 28.0 to 33.0% by weight. Amount of rare earth elements 31.0
%, The amount of Rrich phase inside the sintered body increases,
In addition, the morphology becomes coarse and the corrosion resistance deteriorates. On the other hand, if the amount of rare earth element is less than 28.0%, the amount of liquid phase required for densification of the sintered body is insufficient and the density of the sintered body decreases, and at the same time, among the magnetic properties, the residual magnetic flux density Br and the coercive force are reduced. iHc decreases together.
Therefore, the amount of rare earth elements is 28.0 to 33.0%. Moreover, by setting the amount of the rare earth element to 31.0% or more, a sintered body having a high sintered body density can be easily obtained. The amount of O is 0.3 to 0.7% by weight. The amount of O
If it exceeds 0.7%, a part of the rare earth element forms an oxide, and the magnetically effective rare earth element decreases, resulting in a coercive force iH.
c decreases. On the other hand, it is difficult to reduce the O content in the final sintered body to less than 0.3% due to the oxidation in the fine pulverization process.
The amount is 0.3-0.7%.

The amount of C is preferably 0.15% or less by weight. When the amount of C is more than 0.15%, a part of the rare earth element forms a carbide, the magnetically effective rare earth element is reduced, and the coercive force iHc is lowered. The C content is more preferably 0.12% or less, further preferably 0.10% or less. On the other hand, the level of C content of the ingot produced by melting is 0.008% at maximum, and it is difficult to keep the C content of the final sintered body below this value.
It is preferably 0.01 to 0.15%. The amount of N is preferably 0.002 to 0.04% by weight. The amount of N
If it exceeds 0.04%, a part of the rare earth element forms a nitride, the magnetically effective rare earth element is reduced, and the coercive force iHc is lowered. Further, it is difficult to set the N content of the final sintered body to less than 0.002% because some nitriding is involved in the process of fine pulverization. Therefore, the N content is preferably 0.002 to 0.04%.

In the R-Fe-B system sintered permanent magnet of the present invention, a part of Fe can be replaced by one kind or two or more kinds of Nb, Al, Co, Ga and Cu. Is the substitution amount of each element (here, the weight percentage with respect to the total composition of the permanent magnet after substitution)
The reason for the limitation will be explained. The substitution amount of Nb is set to 0.1 to 2.0%. The addition of Nb produces Nb boride during the sintering process, which suppresses abnormal grain growth. When the Nb substitution amount is less than 0.1%, the effect of suppressing abnormal grain growth of crystal grains becomes insufficient. On the other hand, the substitution amount of Nb is 2.0
%, The amount of Nb boride produced increases, and the residual magnetic flux density Br decreases. The substitution amount of Al is 0.02 to 2.0%. The addition of Al has the effect of increasing the coercive force iHc. Al
When the substitution amount of is less than 0.02%, the effect of improving the coercive force is small. When the substitution amount exceeds 2.0%, the residual magnetic flux density B
r decreases sharply. The substitution amount of Co is 0.3 to 5.0%. The addition of Co brings about the improvement of the Curie point, that is, the temperature coefficient of the saturation magnetization. When the substitution amount of Co is less than 0.3%, the effect of improving the temperature coefficient is small. The substitution amount of Co is 5.
When it exceeds 0%, the residual magnetic flux density Br and the coercive force iHc both decrease sharply. The substitution amount of Ga is 0.01 to 0.5%. Addition of a small amount of Ga improves the coercive force iHc, but the substitution amount is 0.0
If it is less than 1%, the effect of addition is small. On the other hand, Ga
When the amount of substitution of is greater than 0.5%, the residual magnetic flux density Br is significantly reduced and the coercive force iHc is also reduced. The substitution amount of Cu is 0.01 to 1.0%. Addition of a small amount of Cu improves the coercive force iHc, but if the amount of substitution exceeds 1.0%, the effect of addition becomes saturated. If the added amount is less than 0.01%, the effect of improving the coercive force iHc is small.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be specifically described with reference to Examples, but the contents of the present invention are not limited thereto. (Example 1) Nd 23.5%, Pr 7.0%, Dy 1.5% by weight percentage,
A strip-shaped alloy with a thickness of 0.2 to 0.5 mm having a composition of B 1.05%, Al 0.10%, O 0.03%, C 0.005%, N 0.004% and the balance Fe was prepared by the strip casting method. This ribbon-shaped alloy was heated in an Ar gas atmosphere at 1000 ° C. for 2 hours. Next, using a hydrogen furnace, this ribbon-shaped alloy was allowed to occlude hydrogen at room temperature in a hydrogen gas atmosphere and naturally collapsed. Then, while the vacuum in the furnace was evacuated, the ribbon-shaped alloy was heated to 550 ° C., and was held at that temperature for 1 hour for dehydrogenation treatment. The collapsed alloy was mechanically crushed in a nitrogen gas atmosphere to obtain a raw material coarse powder of 32 mesh or less. Analysis of the composition of this raw material coarse powder revealed that Nd 23.5%, Pr 7.0%, Dy 1.5%, B 1.05%, Al 0.10
%, O 0.14%, C 0.02%, N 0.007%, balance Fe were obtained. After charging 50 kg of this raw material coarse powder into a jet mill, the inside of the jet mill was replaced with N2 gas, and the oxygen concentration in the N2 gas was set to 0.100 vol% as an oxygen analyzer value. Then, the crushing pressure was 7.0 kg / cm 2 and the raw material coarse powder was supplied at a rate of 10 kg / Hr. The average particle size of the fine powder was 4.3 μm. The fine powder was molded in a mold cavity at a molding pressure of 0.8 ton / cm2 while applying an orientation magnetic field of 12 kOe. The application direction of the orientation magnetic field is perpendicular to the molding direction. Molded body is 4.0 × 10-4 torr
Under the above conditions, the temperature was raised to 1100 ° C at a rate of 15 ° C / min, and the temperature was maintained for 2 hours for sintering. When the composition of the sintered body was analyzed, Nd 23.5%, Pr 7.0%, Dy 1.5%, B 1.05%, A
The analytical values were 0.10%, O 0.55%, C 0.07%, N 0.012% and balance Fe. The sum of the area of the main phase crystal grains with a grain size of 10 μm or less to the total area of the magnet main phase crystals of this sintered body is
94%, the sum of the areas of the main phase crystal grains with a grain size of 13 μm or more is
3%. 900 ° C x 2 in this sintered body in Ar gas atmosphere
Heat treatment for 1 hour and 550 ° C. × 1 hour each. When the magnetic properties were measured after machining, good values as shown in Table 2 were obtained. In order to evaluate the corrosion resistance of this permanent magnet, after processing the magnet to a certain size of 10 mm × 10 mm × 2 mm, 1
Ni plating of 0 μm was applied. The sample was then placed at 2 atmospheres and 120
After leaving it in the condition of ℃ and 100% humidity, the degree of peeling of the Ni plating with time was examined. As shown in Table 2, no abnormalities were found in the Ni plating even after 2000 hours, indicating good corrosion resistance.

(Example 2) Nd 19.5% by weight percentage, Pr 6.5
%, Dy 5.5%, B 1.0%, Nb 0.5%, Al 0.2%, Co 2.0%, Ga
A strip-shaped alloy having a composition of 0.1%, O 0.02%, C 0.005%, N 0.003% and the balance Fe and a thickness of 0.2 to 0.4 mm was prepared by a strip casting method. This ribbon-shaped alloy was heated at 1100 ° C. for 1 hour in an Ar gas atmosphere. Next, using a hydrogen furnace, this ribbon-shaped alloy was allowed to occlude hydrogen at room temperature in a hydrogen gas atmosphere and naturally collapsed. Then, while the vacuum in the furnace was evacuated, the ribbon-shaped alloy was heated to 550 ° C., and was held at that temperature for 1 hour for dehydrogenation treatment. The collapsed alloy was mechanically crushed in a nitrogen gas atmosphere to obtain a raw material coarse powder of 32 mesh or less. When the composition of this raw material coarse powder was analyzed, Nd 19.5%,
Pr 6.5%, Dy 5.5%, B 1.0%, Nb 0.5%, Al 0.2%, Co 2.0
%, Ga 0.10%, O 0.12%, C 0.02%, N 0.007%, balance Fe were obtained. After charging 50kg of this raw material coarse powder into the jet mill, the inside of the jet mill was replaced with N2 gas,
The oxygen concentration in the gas was set to 0.15% as an oxygen analyzer value. Then, the crushing was performed under the conditions of a crushing pressure of 8.0 kg / cm 2 and a raw material coarse powder supply rate of 12 kg / Hr. The average particle size of the fine powder was 4.6 μm. This fine powder was molded in a mold cavity at a molding pressure of 1.5 ton / cm2 while applying an orientation magnetic field of 8 kOe. The application direction of the orientation magnetic field is perpendicular to the molding direction. Molded body is 5.0 × 10-
Under the conditions of 4 torr, the temperature was raised to 1080 ° C. at a heating rate of 15 ° C./min, and the temperature was maintained for 3 hours for sintering. When the composition of the sintered body was analyzed, Nd 19.5%, Pr 6.5%, Dy 5.5%, B 1.
0%, Nb 0.5%, Al 0.2%, Co 2.0%, Ga 0.10%, O 0.48%,
The analytical values were C 0.06%, N 0.008%, and the balance Fe. The crystal grain size of this sintered body is based on the total area of the magnet main phase crystals.
The sum of the areas of the main phase crystal grains of 10 μm or less is 90%, and the crystal grain size is
The sum of the areas of the main phase crystal grains of 13 μm or more was 6%. This sintered body was heat-treated once at 900 ° C. × 2 hours and 600 ° C. × 1 hour each in an Ar gas atmosphere. When the magnetic properties were measured after machining, good values as shown in Table 2 were obtained. In order to evaluate the corrosion resistance of this permanent magnet, a magnet of 10 mm × 10 mm ×
After processing to a constant size of 2 mm, its surface was plated with 10 μm of Ni. Next, this sample was left under the conditions of 2 atm, 120 ° C., and 100% humidity, and the degree of peeling of Ni plating with time was examined. As shown in Table 2, after 2000 hours
No abnormalities were found in the Ni plating, indicating good corrosion resistance.
A photograph of the metal structure of the obtained permanent magnet is shown in FIG.
It can be seen that the structure is fine and uniform as compared with the metal structure photograph of FIG.

Example 3 Nd 25.8%, Pr 5.5 by weight percentage
%, Dy 1.2%, B 1.05%, Al 0.08%, Co 2.0%, Ga 0.09%, C
A strip alloy having a composition of 0.1%, O 0.03%, C 0.005%, N 0.005% and the balance Fe and having a thickness of 0.1 to 0.5 mm was prepared by the strip casting method. This ribbon-shaped alloy was heated at 900 ° C. for 2 hours in an Ar gas atmosphere. Next, using a hydrogen furnace, this ribbon-shaped alloy was allowed to occlude hydrogen at room temperature in a hydrogen gas atmosphere and naturally collapsed. Then, while the vacuum in the furnace was evacuated, the ribbon-shaped alloy was heated to 550 ° C., and was held at that temperature for 1 hour for dehydrogenation treatment. The collapsed alloy was mechanically crushed in a nitrogen gas atmosphere to obtain a raw material coarse powder of 32 mesh or less. When the composition of this raw material coarse powder was analyzed, Nd 25.8%,
Pr 5.5%, Dy 1.2%, B 1.05%, Al 0.08%, Ga 0.09%, Cu
The analytical values were 0.1%, O 0.14%, C 0.03%, N 0.009% and balance Fe. After charging 50 kg of this raw material coarse powder into a jet mill, the inside of the jet mill was replaced with Ar gas, and the oxygen concentration in Ar gas was adjusted to 0.050 vol% as an oxygen analyzer value. Then
Crushing was performed under the conditions of a crushing pressure of 7.5 kg / cm2 and a raw material coarse powder supply rate of 9 kg / Hr. The average particle size of the fine powder was 4.7 μm. This raw material slurry was wet-molded in the mold cavity at a molding pressure of 0.6 ton / cm 2 while applying an orienting magnetic field of 8 kOe. The application direction of the orientation magnetic field is perpendicular to the molding direction. The molded body is 4.
110 at a heating rate of 15 ° C / min under the condition of 0 × 10-4 torr
The temperature was raised to 0 ° C., and the temperature was maintained for 2 hours for sintering.
When the composition of the sintered body was analyzed, Nd 25.8%, Pr 5.5%, D
y 1.2%, B 1.05%, Al 0.08%, Ga 0.09%, Cu 0.1%, O 0.3
The analytical values were 5%, C 0.07%, N 0.025% and balance Fe.
In this sintered body, the sum of the areas of the main phase crystal grains with a grain size of 10 μm or less to the total area of the magnet main phase crystals is 88%, and the sum of the areas of the main phase grains with a grain size of 13 μm or more is It was 7%. This sintered body was heated at 900 ° C for 2 hours and 580 in Ar gas atmosphere.
Heat treatment was performed once at each temperature of 1 ° C for 1 hour. When the magnetic properties were measured after machining, good values as shown in Table 2 were obtained. In order to evaluate the corrosion resistance of this permanent magnet, we
After processing to a certain size of mm × 10 mm × 2 mm, 10 μm on the surface
Ni plating was applied. Next, this sample was left under the conditions of 2 atm, 120 ° C., and 100% humidity, and the degree of peeling of Ni plating with time was examined. As shown in Table 2, no abnormalities were found in the Ni plating even after 2000 hours, indicating good corrosion resistance.

Comparative Example 1 The ribbon-shaped alloy produced in Example 1 was directly placed in a hydrogen furnace without heat treatment and allowed to occlude hydrogen in a hydrogen gas atmosphere at room temperature to spontaneously disintegrate. Then, dehydrogenation treatment and mechanical crushing were performed under the same conditions as in Example 1 to obtain raw material coarse powder of 32 mesh or less. When the composition of this raw material coarse powder was analyzed, Nd 23.5%, Pr
7.0%, Dy1.5%, B 1.05%, Al 0.10%, O 0.11%, C 0.02
%, N 0.006%, balance Fe were obtained. This raw material coarse powder was finely pulverized under the same conditions as in Example 1. The average particle size of the obtained fine powder was 4.6 μm, which was coarser than that in the case of Example 1. Subsequent steps such as molding, sintering, heat treatment, and evaluation of corrosion resistance were also performed under the same conditions as in Example 1. When the composition of the sintered body was analyzed, Nd 23.5%, Pr 7.0%, Dy 1.5%, B
1.05%, Al 0.10%, O 0.51%, C 0.06%, N 0.015%, balance F
An analytical value of e was obtained. In this sintered body, the sum of the areas of the main phase crystal grains with a grain size of 10 μm or less and the total area of the main phase grains with a grain size of 13 μm or more is 77% of the total area of the magnet main phase crystals. It was 14%. When the magnetic properties of this permanent magnet were evaluated, as shown in Table 2, both Br and iHc were slightly lower than those of Example 1. Also, as shown in Table 2, the corrosion resistance of this permanent magnet was found to be at a level where practically no problem was observed, with no abnormality observed in the Ni plating even after 1000 hours had passed, but after 1500 hours had passed. It was found that a slight peeling of the Ni plating occurred, which was inferior in corrosion resistance as compared with the sintered body produced in Example 1.

(Comparative Example 2) Same composition as in Example 2
An R-Fe-B alloy ingot was prepared. The compositional analysis value of this alloy is Nd 19.5%, Pr 6.5%, Dy 5.5%, B by weight percentage.
1.0%, Nb 0.5%, Al 0.2%, Co 2.0%, Ga 0.1%, O 0.01
%, C 0.004%, N 0.002%, and the balance Fe. Precipitation of α-Fe was found in the structure of the alloy, so in order to erase it, the alloy ingot was heated at 1100 ° C in an argon gas atmosphere.
A liquefaction process was performed for 6 hours. Next, the alloy ingot was put into a hydrogen furnace and allowed to occlude hydrogen at room temperature to spontaneously collapse.
The alloy after natural disintegration was subjected to dehydrogenation treatment and mechanical crushing under the same conditions as in Example 2 to obtain raw material coarse powder of 32 mesh or less. When the composition of this raw material coarse powder was analyzed, Nd 19.
5%, Pr 6.5%, Dy 5.5%, B 1.0%, Nb 0.5%, Al 0.2%, Co
2.0%, Ga 0.1%, O 0.09%, C 0.02%, N 0.006%, balance Fe
I got the analysis value. This raw material coarse powder was finely pulverized under the same conditions as in Example 2. The average particle size of the obtained fine powder is 5.1μ
m, which is coarser than that of the first embodiment. Molding, sintering,
Subsequent steps such as heat treatment and evaluation of corrosion resistance were also performed under the same conditions as in Example 2. When the composition of the sintered body was analyzed, Nd 19.5%, Pr 6.5%, Dy 5.5%, B 1.0%, Nb 0.5%, A
l 0.2%, Co 2.0%, Ga 0.10%, O 0.42%, C 0.06%, N 0.0
The analytical values were 07% and the balance Fe. In this sintered body, the total area of the main phase crystal grains with a grain size of 10 μm or less is 65%, and the total area of the main phase crystal grains with a grain size of 13 μm or more is 65% of the total area of the magnet main phase crystals. It was 19%. A photograph of the metal structure is shown in FIG. When the magnetic characteristics of this permanent magnet were evaluated,
As shown in Table 2, it was a good value almost equivalent to the value of Example 2. Further, as shown in Table 2, the corrosion resistance of this permanent magnet was found to be at a level where practically no problem was observed, with no abnormality observed in the Ni plating even after 700 hours had passed.
After a lapse of 00 hours, a slight peeling occurred on a part of the Ni plating, and it was found that the corrosion resistance was inferior to that of the permanent magnet manufactured in Example 2.

[0025]

[Table 2]

According to the present invention, an R-Fe-B system sintered permanent magnet having excellent corrosion resistance can be obtained without deteriorating the magnetic properties.

[Brief description of drawings]

Fig. 1 The crystal grain size is 10 with respect to the total area of the magnet main phase crystals.
The ratio of the sum of the areas of the main phase crystal grains of μm or less, the ratio of the sum of the areas of the crystal grains of the main phase with a crystal grain size of 13 μm or more to the total area of the magnet main phase crystals, and the corrosion resistance accelerated test FIG. 5 is a diagram showing a relationship with a lapse of time until peeling of Ni plating starts.

FIG. 2 is a metallographic photograph of a cross section of a ribbon-shaped alloy produced by a strip casting method.

FIG. 3 is a photograph of a metallographic structure of a cross section of a strip-shaped alloy produced by the strip casting method after heat treatment at 1000 ° C.

[Fig. 4] The crystal grain size with respect to the total area of the main phase of the magnet is 10 μm.
The sum of the areas of the following main phase crystal grains is 90%, and the crystal grain size is 13μ.
3 is a photograph of a metal structure of a sintered permanent magnet having a sum of areas of main phase crystal grains of m or more being 6%.

FIG. 5: Crystal grain size is 10 μm with respect to the total area of the magnet main phase
The sum of the areas of the following main phase crystal grains is 65%, and the crystal grain size is 13μ.
3 is a photograph of a metallographic structure of a sintered permanent magnet having a sum of areas of main phase crystal grains of m or more of 19%.

Claims (3)

[Claims] 1. R by weight percentage (R is one or more of rare earth elements including Y) 28.0 to 33.0%, B 0.5 to 2.0%, O
It has a composition of 0.3 to 0.7% and the balance Fe, and the total area of the main phase crystal grains with a grain size of 10 μm or less is 80% or more and the grain size of 13 μm or more with respect to the total area of the magnet main phase crystal grains. A sintered permanent magnet characterized in that the sum of the areas of the main phase crystal grains is 10% or less. 2. A part of Fe is Nb 0.1 to 2.0%, Al 0.02 to 2.0
%, Co 0.3 to 5.0%, Ga 0.01 to 0.5%, and Cu 0.01 to 1.0%. The sintered permanent magnet according to claim 1, which is substituted with one or more. 3. The sintered permanent magnet according to claim 1, wherein the value of coercive force iHc is 13.0 kOe or more.