JP3452561B2 - Rare earth magnet and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an R—Fe—B rare earth magnet, an alloy powder for the magnet, and a method for producing the same.

[0002]

2. Description of the Related Art Sintered rare earth magnets are manufactured by pressing an alloy powder formed by crushing an alloy (raw material alloy) for rare earth magnets, followed by a sintering step and an aging heat treatment step. Currently, two types of rare earth sintered magnets are widely used in various fields: samarium / cobalt based magnets and rare earth / iron / boron based magnets. Among them, rare earth / iron / boron magnets (hereinafter referred to as “R—Fe—B magnets. R is a rare earth element including Y, Fe is iron, and B is boron).
Has the highest magnetic energy product among various permanent magnets and is relatively cheap in price, and is therefore actively used in various electronic devices. A part of Fe may be replaced with a transition metal element such as Co.

The powder of the raw material alloy for the R-Fe-B system rare earth magnet is produced by a method including a first pulverizing step for coarsely pulverizing the raw material alloy and a second pulverizing step for finely pulverizing the raw material alloy. Sometimes. In that case, in the first crushing step, the hydrogen storage phenomenon is utilized to embrittle the raw material alloy and coarsely crush it into a size of, for example, several hundred μm or less, and then in the second crushing step, the coarsely crushed alloy (coarse crushed (Powder) is finely pulverized by a jet mill device or the like into particles having an average particle size of about several μm.

There are roughly two types of methods for producing the raw material alloy itself. The first method is an ingot casting method in which a melt of a raw material alloy is put into a mold and cooled relatively slowly. The second method is to melt the alloy with a single roll, a twin roll,
It is a rapid cooling method typified by a strip casting method or a centrifugal casting method in which a solidified alloy thinner than an ingot alloy is produced by rapidly cooling the molten alloy by contacting it with a rotating disk or a rotating cylindrical mold.

In the case of such a quenching method, the cooling rate of the molten alloy is in the range of 10 ² ° C / sec or more and 2 × 10 ⁴ ° C / sec or less. The thickness of the quenched alloy produced by the quenching method is in the range of 0.03 mm or more and 10 mm or less.
The molten alloy solidifies from the contact surface of the cooling roll (roll contact surface), and crystals grow in columns from the roll contact surface in the thickness direction. As a result, the quenched alloy has R ₂ T ₁₄ B crystal phase having a minor axis size of 0.1 μm or more and 100 μm or less and a major axis size of 5 μm or more and 500 μm or less, and R ₂ T.
_{14 It} has a fine crystal structure containing an R-rich phase (phase in which the concentration of the rare earth element R is relatively high) dispersedly present in the grain boundaries of the ₁₄ B crystal phase. R-rich phase is rare earth element R
Is a non-magnetic phase having a relatively high concentration, and its thickness (corresponding to the width of the grain boundary) is 10 μm or less.

The quenched alloy is an alloy produced by the conventional ingot casting method (die casting method) (ingot alloy).
Compared with the above, since the structure is cooled in a relatively short time, the structure is made finer and the crystal grain size is smaller. Further, since the crystal grains are finely dispersed and the area of the grain boundary is wide, and the R-rich phase spreads thinly inside the grain boundary, the dispersibility of the R-rich phase is also excellent.

After such a quenched alloy is crushed by the above-mentioned method, the powder is compression-molded by a press machine to produce a molded body. By sintering this compact, an R-Fe-B based rare earth magnet can be obtained.

Conventionally, after obtaining a block-shaped sintered magnet larger than a finally required magnet product, the block-shaped sintered magnet is cut and / or processed to obtain a desired shape and Had a magnet with a size.

[0009]

Recently, a sintered magnet having a complicated shape (an irregular shape) such as a roof tile is required, and it is possible to manufacture a magnet having a shape close to that of a final product from the stage of powder molding. I need it. In order to produce a compact having such a complicated shape, it is necessary to reduce the pressure (pressing pressure) applied to the powder when the powder is compression-molded, as compared with the conventional pressure. Further, in the case of manufacturing an anisotropic magnet, the pressing pressure is lowered in order to improve the degree of magnetic field orientation of powder particles.

However, when the pressing pressure is lowered in this way, the density of the molded body (molding density or green density) is lowered, so that the strength of the molded body is lowered, and when the molded body is taken out from the die cavity of the press machine. In addition, cracks and chips of the molded body are likely to occur in various subsequent steps. In particular, since most R-Fe-B rare earth magnet alloy powders have an angular shape, they generally have poorer formability than other magnet material powders. Further, if the structure is fine, as in a strip cast alloy, the particle size distribution of the powder becomes sharp, so the amount of spring back (the amount of spring in the compact produced when the press pressure applied to the compact during press compression is released) The amount of expansion) becomes large, and the molded body is likely to be cracked or chipped. When the molded body is cracked or chipped as described above, the yield of non-defective products is reduced, which not only increases the manufacturing cost but also impairs the effective use of valuable material resources. Such a problem is that when finely pulverizing the R-Fe-B rare earth magnet alloy with a jet mill or the like, by removing relatively coarse powder particles with a classifying rotor or the like for the purpose of improving coercive force, the particle size distribution can be improved. It becomes remarkable when the particle size distribution on the larger particle size side is sharpened with respect to the peak. The decrease in compressibility due to such a particle size distribution becomes a particularly serious problem when the average particle size (FSSS particle size) of the powder is 4 μm or less.

The present invention has been made in view of the above points, and its main purpose is to provide R-Fe-B rare earth magnets capable of improving formability even under a relatively low press pressure. To provide an alloy powder.

[0012]

R-Fe-according to the present invention
The method for producing an alloy powder for a B-based rare earth magnet comprises the steps of preparing an R-Fe-B-based rare earth magnet alloy containing a chilled crystal structure in an amount of 2 to 20% by volume, and hydrogen-occluding the above-mentioned R-
A first pulverizing step of coarsely pulverizing the Fe-B rare earth magnet alloy, and the coarsely pulverized powder is further finely pulverized, and at least a part of the fine powder having a particle size of 1.0 μm or less is finely pulverized. A second pulverizing step of removing the fine powder having a particle diameter of 1.0 μm or less, thereby reducing the volume, and a step of coating the surface of the pulverized powder with a lubricant after the second pulverizing step.

In a preferred embodiment, the volume particle size distribution has a single peak, the average particle size (FSSS particle size) is 4 μm or less, and the particle size A indicating the peak value of the volume particle size distribution is set to a predetermined value. First particle size range up to particle size B (particle size A>
The total volume of the particles having the particle size included in the particle size B) is the second particle size range from the particle size A to the predetermined particle size C (particle size C).
> Particle size A, "Particle size C-Particle size A" = "Particle size A-Particle size B")
Make a powder that is larger than the total volume of the particles having the particle size contained in.

In a preferred embodiment, the volume particle size distribution has a single peak, the average particle size (FSSS particle size) is 4 μm or less, and the particle size D corresponding to the center of the full width at half maximum of the volume particle size distribution. , A powder smaller than the particle size A showing the peak value of the volume particle size distribution in the previous period is prepared.

In the second crushing step, it is preferable that the alloy is finely crushed using a high-speed stream of an inert gas.

In a preferred embodiment, the milling of the alloy is carried out using a jet mill device.

In a preferred embodiment, the fine pulverization of the alloy is carried out by using a pulverizer combined with a classifier,
The powder discharged from the pulverizer is classified by the classifier.

The raw material alloy for rare earth magnets is preferably one in which the raw material alloy melt is cooled at a cooling rate of 10 ² ° C / sec or more and 2 x 10 ⁴ ° C / sec or less.

Cooling of the raw material alloy melt is preferably performed by a strip casting method.

The method for producing an R-Fe-B rare earth magnet according to the present invention is an R-Fe-B produced by any one of the above methods for producing an alloy powder for an R-Fe-B rare earth magnet.
Of the alloy powder for rare earth magnets of the R-Fe-B system by uniaxial pressing.
The method includes the steps of forming at a pressure of 0 MPa or less to produce a powder compact, and sintering the powder compact to produce a sintered magnet.

The R-Fe-B system rare earth magnet alloy powder according to the present invention is obtained by pulverizing an R-Fe-B system rare earth magnet alloy containing 2 to 20% by volume of the chill crystal structure. Powder having a single peak in the volume particle size distribution, an average particle diameter (FSSS particle diameter) of 4 μm or less, and a predetermined particle diameter B from the particle diameter A showing the peak value of the volume particle diameter distribution. The total volume of particles having a particle size included in the first particle size range (particle size A> particle size B) up to the second particle size range from the particle size A to the predetermined particle size C (particle size C > Particle size A, “particle size C−particle size A” = “particle size A−particle size B”), which is larger than the total volume of particles having a particle size.

The R-Fe-B system rare earth magnet alloy powder according to the present invention is obtained by pulverizing the R-Fe-B system rare earth magnet alloy containing 2 to 20% by volume of the chill crystal structure. Powder having a single peak in the volume particle size distribution, an average particle size (FSSS particle size) of 4 μm or less, and the particle size D corresponding to the center of the full width at half maximum of the volume particle size distribution is It is smaller than the particle size A indicating the peak value of the volume particle size distribution.

The R-Fe-B rare earth magnet alloy powder of the present invention contains 2 to 20% by volume of the chill crystal structure in the R alloy.
-Fe-B based rare earth magnet alloy powder having an average particle size of 2 μm or more and 10 μm or less, and the volume of fine powder having a particle size of 1.0 μm or less is adjusted to 10% or less of the particle volume of the entire powder, The surface of the powder particles is coated with a lubricant.

[0024] The raw alloy molten metal is added at 10 ² ° C / sec or more 2 × 10 ⁴
It is preferably obtained by pulverizing an alloy cooled at a cooling rate of ° C / sec or less.

The R-Fe-B rare earth magnet according to the present invention is characterized by being produced from the above-mentioned R-Fe-B rare earth magnet alloy powder.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor examined how the structure of a rapidly solidified alloy produced by strip casting or the like affects the particle size distribution of powder.
Then, if the volume ratio of the chill crystal structure in the rapidly solidified alloy is controlled within the range of 2 to 20% by volume (volume%), a finely pulverized powder having an optimum particle size distribution for improving powder formability is obtained. The inventors have found that they can be obtained and arrived at the present invention.

Here, "chill crystal structure" means R-Fe-
It is a crystal phase formed in the vicinity of the roll surface at an early stage when the molten metal of the B-based rare earth alloy comes into contact with the surface of a cooling member such as a cooling roll of a quenching device and solidification is started. The structure of the chill crystal structure has a relatively isotropic (isotropic) and finer structure than the columnar structure (dendritic structure) formed after the initial stage of the cooling solidification process.

Conventionally, there has been a common general knowledge that it is preferable that the R—Fe—B rare earth alloy does not contain a chill crystal structure as much as possible. For example, JP-A-10-3171
No. 10 teaches that the chill crystal structure is regarded as a cause of generation of fine powder and the formation of such chill crystal structure should be suppressed, and then the roll surface contacting with the molten alloy in the rapid solidification process of the raw material alloy is performed. A technique for reducing thermal conductivity is disclosed.

However, according to the experiments of the present inventor,
It has been found that increasing the proportion of the chill crystal structure to 2% by volume or more of the entire quenched alloy causes the powder particle size distribution obtained after pulverization of the alloy to broaden appropriately, resulting in improved compressibility. It is considered that such an effect may be obtained by pulverizing an equiaxed chill crystal structure and including it in the pulverized powder.

Therefore, in the present invention, the raw alloy for rare earth magnets is coarsely pulverized by subjecting the quenched alloy in which the chill crystal structure accounts for 2 to 20% by volume of the whole to hydrogen treatment (first). After the crushing step), the raw material alloy is finely crushed (second crushing step). After that, by coating the surface of the powder particles with a lubricant, the degree of powder orientation in the magnetic field is improved while suppressing the oxidation of the powder particles by the atmosphere.

In the present invention, in order to broaden the powder particle size distribution by increasing the ratio of the chill crystal structure, it is essential to embrittle the alloy by absorbing hydrogen before the pulverization step. it is conceivable that. The chill crystal structure includes a main phase composed of an R ₂ Fe ₁₄ B type tetragonal compound and an R-rich phase, and has a composition similar to that of the portion other than the chill crystal structure, but has a fine structure and R It is considered that the rich phase is finely embedded in the main phase, and when hydrogen storage treatment is performed, the rich phase expands and collapses from the R rich phase, so that it is likely to be more finely pulverized than other structures. Therefore, when only the mechanical pulverization treatment is performed without performing the hydrogen treatment, the final powder particle size distribution is not appropriate and the compacting density cannot be sufficiently improved.

Further, there is a possibility that a large number of ultrafine powders having a particle size of 1 μm or less will be formed only by performing such hydrogen treatment and fine pulverization, increasing the oxygen concentration of the sintered body and increasing the coercive force. Lower. In order to avoid this, in the present invention, at least a part of the ultrafine powder (particle size 1.0 μm or less) is removed during the pulverization step, and the volume of the ultrafine powder having a particle size of 1.0 μm or less is set to the particle volume of the entire powder. The amount will be adjusted to 10% or less.

Embodiments of the present invention will be described below with reference to the drawings.

[Raw Material Alloy] First, using the single roll type strip caster (quenching device) shown in FIG. 1, a raw material alloy of an alloy for R—Fe—B magnets having a desired composition is prepared. The quenching apparatus shown in FIG. 1 has a quenching chamber 1 capable of having a vacuum state or a decompressed state in an inert gas atmosphere inside. A melting furnace 3 for forming the molten metal 2, a cooling roll 5 for rapidly cooling and solidifying the alloy molten metal 2 supplied from the melting furnace 3, and a chute (tanning) for guiding the molten alloy 3 from the melting furnace 3 to the cooling roll 5. A dish 4 and a recovery container 8 for recovering the ribbon-shaped alloy 7 which solidifies and is separated from the cooling roll 5 are provided.

The melting furnace 3 can supply the melt 2 produced by melting the alloy raw material to the chute 4 at a substantially constant supply amount. This supply amount can be arbitrarily adjusted by controlling the operation of tilting the melting furnace 3.

The outer peripheral surface of the cooling roll 5 is made of a material having good thermal conductivity such as copper, and has a diameter of 3 mm, for example.
It has a dimension of 0 cm to 100 cm and a width of 15 cm to 100 cm. The cooling roll 5 is cooled by passing water inside the roll. The cooling roll 5 can be rotated at a predetermined rotation speed by a drive device (not shown). By controlling this rotation speed, the peripheral speed of the cooling roll 5 can be arbitrarily adjusted. The cooling rate by this quenching device is, for example, 10 ² ° C / sec to 2 × 10 ⁴ ° C / sec by selecting the rotation speed of the cooling roll 5 or the like.
It can be controlled in the range of seconds.

The tip of the chute 4 is arranged at a position having a certain angle θ with respect to the line connecting the top of the cooling roll 5 and the center of the roll. The molten alloy 2 supplied onto the chute 4 is cooled by the cooling roll 5 from the tip of the chute 4.
Is supplied to.

The chute 4 is made of ceramics or the like, and temporarily stores the molten alloy 2 continuously supplied from the melting furnace 3 at a predetermined flow rate so that the flow velocity is delayed and the flow of the molten alloy 2 is prevented. Can be rectified. If a damming plate (not shown) capable of selectively damaging the flow of the molten alloy surface 2 in the molten alloy 2 supplied to the chute 4 is provided, the rectifying effect can be further improved.

By using the chute 4, it is possible to supply the molten alloy 2 in a state where the cooling roll 5 is spread in a substantially uniform thickness over a certain width in the cylinder length direction (axial direction). In addition to the above functions, the chute 4 also has a function of adjusting the temperature of the molten alloy 2 immediately before reaching the cooling roll 5. The temperature of the molten alloy 2 on the chute 4 is preferably 100 ° C. or more higher than the liquidus temperature. This is because if the temperature of the molten alloy 2 is too low, the primary crystals that adversely affect the alloy properties after quenching may locally nucleate and remain after solidification. The molten metal retention temperature on the chute 4 can be controlled by adjusting the molten metal temperature at the time of pouring from the melting furnace 3 into the chute 4, the heat capacity of the chute 3 itself, and the like, if necessary, a chute heating facility (not shown). ) May be provided.

Using the above quenching apparatus, specifically, for example, Nd: 30.8 wt% (mass%), Pr: 3.8 w
t%, Dy: 0.8 wt%, B: 1.0 wt%, Co:
0.9 wt%, Al: 0.23 wt%, Cu: 0.10.
An alloy having a composition of wt%, balance Fe and unavoidable impurities is melted to form a molten alloy. This alloy melt 13
After holding at 50 ° C., the molten alloy was brought into contact with the surface of a cooling roll to quench it, and a flaky alloy ingot having a thickness of about 0.1 to 5 mm was obtained. The rapid cooling conditions at this time were a roll peripheral speed of about 1 to 3 m / sec and a cooling rate of 10 ² to 2 × 10 ⁴ ° C./sec. In the present embodiment, in order to intentionally increase the volume ratio of the chill crystal structure, the atmosphere pressure in the quenching chamber is lowered so that the molten alloy can efficiently remove heat from the roll contact surface, whereby the molten metal and the cooling roll are Enhances the adhesion between the two. Even if the amount of tapped water is reduced, the cooling rate is improved, so that the volume ratio of the chill crystal structure can be increased.

The quenched alloy slab thus produced is crushed into flakes having a size of 1 to 10 mm before the subsequent hydrogen crushing. The method for producing a raw material alloy by the strip casting method is also disclosed in, for example, US Pat. No. 5,383,978.

[First Grinding Step] A plurality of raw material packs (for example, made of stainless steel) are filled with the raw material alloy slabs roughly crushed into flakes and mounted on a rack. After this,
The rack on which the raw material pack is mounted is inserted into the hydrogen furnace. Next, the lid of the hydrogen furnace is closed, and the hydrogen embrittlement treatment (hereinafter sometimes referred to as “hydrogen pulverization treatment”) process is started. The hydrogen pulverization process is executed according to the temperature profile shown in FIG. 2, for example. In the example of FIG. 2, the vacuum evacuation process I is first performed for 0.5 hours, and then the hydrogen storage process II is performed for 2.5 hours.
Run for hours. In the hydrogen storage process II, hydrogen gas is supplied into the furnace to create a hydrogen atmosphere in the furnace. The hydrogen pressure at that time is preferably about 200 to 400 kPa.

Subsequently, a dehydrogenation process III is performed for 5.0 hours under a reduced pressure of about 0 to 3 Pa, and then a cooling process IV of the raw material alloy is performed for 5.0 hours while supplying argon gas into the furnace. .

In the cooling step IV, when the atmospheric temperature in the furnace is relatively high (for example, when it exceeds 100 ° C.), an inert gas at room temperature is supplied to the inside of the hydrogen furnace for cooling. After that, when the raw material alloy temperature has dropped to a relatively low level (for example, 100 ° C. or lower), an inert gas cooled to a temperature lower than room temperature (for example, room temperature minus 10 ° C.) is introduced into the hydrogen furnace 10. Supplying is preferable from the viewpoint of cooling efficiency. The supply amount of argon gas is 10 to 10.
It may be about 100 Nm ³ / min.

When the temperature of the raw material alloy is lowered to about 20 to 25 ° C., an inert gas at about room temperature (a temperature lower than room temperature but within a range of 5 ° C. or less) is blown into the hydrogen furnace. However, it is preferable to wait until the temperature of the raw material reaches the room temperature level. By doing so, when the lid of the hydrogen furnace is opened, it is possible to avoid the situation where dew condensation occurs inside the furnace. If moisture is present inside the furnace due to condensation,
Since the water content is frozen and vaporized in the evacuation step, it is difficult to increase the degree of vacuum, and the time required for the evacuation step I becomes longer, which is not preferable.

When the roughly crushed alloy powder after hydrogen crushing is taken out from the hydrogen furnace, it is preferable to carry out the taking out operation in an inert atmosphere so that the roughly crushed powder does not come into contact with the atmosphere.
This is because the coarsely pulverized powder is prevented from oxidizing and generating heat, and the magnetic characteristics of the magnet are improved. Next, the roughly crushed raw material alloy is filled in a plurality of raw material packs and mounted on a rack.

By the hydrogen treatment, the rare earth alloy is crushed to a size of, for example, about 0.1 mm to several mm, and the average particle size becomes 500 μm or less. After pulverizing with hydrogen, it is preferable that the embrittled raw material alloy is finely pulverized and cooled by a cooling device such as a rotary cooler. When the raw material is taken out in a relatively high temperature state, the time for the cooling process by the rotary cooler or the like may be relatively long.

A large amount of rare earth elements such as Nd is exposed on the surface of the coarsely pulverized powder produced by hydrogen pulverization, and it is in a state of being very easily oxidized. Before the next fine grinding step, zinc stearate is added as a grinding aid in an amount of about 0.04 wt%.

[Second crushing step] Next, the coarsely crushed powder produced in the first crushing step is finely crushed using a jet mill. In this embodiment, a cyclone classifier suitable for removing ultrafine powder is connected to the crusher.

Hereinafter, the fine pulverization step (second pulverization step) performed using the jet mill device will be described in detail with reference to FIG.

The illustrated jet mill apparatus 10 includes a first
The raw material charging machine 12 for supplying the rare earth alloy (material to be crushed) roughly crushed in the crushing process, the crusher 14 for crushing the crushed material charged from the raw material charging machine 12, and the crusher 14 for crushing the crushed material. A cyclone classifier 16 for classifying the powder obtained by crushing and a recovery tank 18 for collecting the powder having a predetermined particle size distribution classified by the cyclone classifier 16 are provided.

The raw material charging machine 12 includes a raw material tank 20 for containing the material to be crushed, a motor 22 for controlling the supply amount of the material to be crushed from the raw material tank 20, and a spiral feeder ( Screw feeder) 2
4 and.

The crusher 14 has a vertically elongated substantially cylindrical crusher main body 26, and a nozzle for ejecting an inert gas (for example, nitrogen) at a high speed is attached to the lower portion of the crusher main body 26. A plurality of nozzle openings 28 are provided. A raw material charging pipe 30 for charging an object to be crushed into the crusher body 26 is connected to a side portion of the crusher body 26.

The raw material feeding pipe 30 is provided with a valve 32 for temporarily holding the material to be crushed and for confining the pressure inside the crusher 14. The valve 32 is a pair of an upper valve 32a and a lower valve 32b. And have. The feeder 24 and the raw material feeding pipe 30 are flexible pipes 3.
4 are connected.

The crusher 14 includes a classification rotor 36 provided inside the crusher body 26, a motor 38 provided outside the crusher body 26, and a connecting pipe provided above the crusher body 26. 40 and 40. Motor 38
Drives the classification rotor 36, and the connection pipe 40 discharges the powder classified by the classification rotor 36 to the outside of the crusher 14.

The crusher 14 has a plurality of leg portions 4 serving as supporting portions.
Equipped with 2. A base 44 is arranged near the outer periphery of the crusher 14, and the crusher 14 is mounted on the base 44 by the legs 42. In the present embodiment, the leg portion 42 of the crusher 14
Between the base and the base 44, a weight detector 4 such as a load cell is provided.
6 is provided. Based on the output from the weight detector 46, the control unit 48 can control the rotation speed of the motor 22 and thereby control the input amount of the crushed object.

The cyclone classifier 16 includes a classifier body 64.
The exhaust pipe 66 is inserted into the classifier body 64 from above. On the side of the classifier body 64,
Introducing port 68 for introducing the powder classified by the classifying rotor 36
And the introduction port 68 is connected to the connection pipe 40 by a flexible pipe 70. Classifier body 64
An outlet 72 is provided in the lower part of the, and a recovery tank 18 for a desired finely pulverized powder is connected to the outlet 72.

The flexible pipes 34 and 70 may be made of resin or rubber or the like, or may be made flexible by forming a material having high rigidity into a bellows shape or a coil shape. preferable. When such flexible pipes 34 and 70 are used, the weight change of the raw material tank 20, the feeder 24, the classifier main body 64, and the recovery tank 18 causes the crusher 1 to change in weight.
4 is not transmitted to the leg portion 42. Therefore, if the weight detector 46 provided in the leg portion 42 detects the weight, it is possible to accurately detect the weight of the object to be ground accumulated in the crusher 14 and the amount of change thereof, and the object to be crushed to be supplied into the crusher 14 can be accurately detected. The amount of material can be controlled accurately.

Next, a crushing method by the above jet mill device 10 will be described.

First, the material to be crushed is put into the raw material tank 20. The material to be crushed in the raw material tank 20 is supplied to the crusher 14 by the feeder 24. At this time, by controlling the rotation speed of the motor 22, the supply amount of the crushed material can be adjusted. The material to be crushed supplied from the feeder 24 is once blocked by the valve 32. Here, the pair of upper valve 32a and lower valve 32b are alternately opened and closed. That is, when the upper valve 32a is open, the lower valve 32b is closed, and when the upper valve 32a is closed, the lower valve 32b is open. By alternately opening and closing the pair of valves 32a and 32b in this way, the pressure in the crusher 14 can be prevented from leaking to the raw material charging machine 12 side. As a result, the pulverized material is supplied between the pair of upper valve 32a and lower valve 32b when the upper valve 32a is opened. Then, when the lower valve 32b is opened next time, it is guided to the raw material feeding pipe 30 and introduced into the crusher 14. The valve 32 is driven at high speed by a sequence circuit (not shown) different from the control circuit 48, and the material to be crushed is continuously supplied into the crusher 14.

The object to be crushed introduced into the crusher 14 is wound up into the crusher 14 by the high-speed injection of the inert gas from the nozzle port 28, and swirls in the apparatus together with the high-speed air stream. Then, the crushed objects are finely crushed by mutual collision.

The powder particles thus finely pulverized are carried by the ascending air current to the classification rotor 36, and the classification rotor 3
The coarse powder is pulverized again after being classified in 6.
On the other hand, the powder crushed to a predetermined particle size or less is connected to the connection pipe 4
0, it is introduced into the classifier body 64 of the cyclone classifier 16 from the inlet 68 via the flexible pipe 70. By using the classification rotor 36, it is possible to efficiently remove powder particles having a particle size larger than the particle size showing the peak of the particle size distribution. If a large amount of coarse powder particles having a particle size of more than 10 μm are present in the finally obtained powder,
Since the coercive force of the sintered magnet decreases, the classification rotor 3
It is preferable to use 6 to reduce powder particles having a particle size of more than 10 μm. In the present embodiment, in the finally obtained powder, the particle volume of particles having a particle size of more than 10 μm is adjusted to 10% or less of the particle volume of the entire powder.

In the main body 16 of the classifier, a recovery tank 1 in which relatively large powder particles having a predetermined particle size or more are installed in the lower portion.
8, the ultrafine powder is discharged to the outside through the exhaust pipe 66 together with the inert gas flow. In this embodiment,
The ultrafine powder is removed through the exhaust pipe 66, whereby the ultrafine powder (particle size:
Volume ratio (1.0 μm or less). In a preferred embodiment, the volume ratio of ultrafine powder (particle size: 1.0 μm or less) is adjusted to 10% or less.

When the R-rich ultrafine powder is removed in this way, the amount of the rare earth element R in the sintered magnet consumed for bonding with oxygen can be reduced and the magnet characteristics can be improved.

As described above, in this embodiment, the cyclone classifier 16 with blow-up is used as the classifier connected to the subsequent stage of the jet mill device (crusher 14).
According to the cyclone classifier 16 as described above, the ultrafine powder having a predetermined particle size or less is not collected in the recovery tank 18 but rises in reverse and is discharged from the pipe 66 to the outside of the apparatus.

The particle size of the fine powder removed from the pipe 66 to the outside of the apparatus is, for example, “Powder Technology Pocketbook” of the Industrial Research Group.
It can be controlled by appropriately defining the parameters of each part of the cyclone as described on pages 92 to 96 of the above and adjusting the pressure of the inert gas stream.

According to this embodiment, the average particle size (FSSS
Particle size) is, for example, 4.0 μm or less, and the volume of the ultrafine powder having a particle size of 1.0 μm or less is 10% of the volume of the entire powder.
% Alloy powder can be obtained.

In order to suppress the oxidization in the pulverization process as much as possible, the oxygen content in the high-speed gas stream (inert gas) used during the fine pulverization is, for example, 1000 to 20000.
It is preferable to keep the volume within the range of about 50 ppm,
It is more preferable to keep it as low as about 00 to 10,000 volume ppm. A fine pulverization method for controlling the oxygen concentration in the high-speed gas stream is described in Japanese Patent Publication No. 6-6728.

By controlling the concentration of oxygen contained in the atmosphere during fine pulverization as described above, the oxygen content of the alloy powder after fine pulverization is 6000 mass p of the total.
It is preferably adjusted to pm or less. If the oxygen content in the rare earth alloy powder exceeds 6000 mass ppm and becomes too large, the proportion of the non-magnetic oxide in the sintered magnet increases and the final magnetic properties of the sintered magnet deteriorate. Because it will be.

In this embodiment, since the R-rich ultrafine powder is properly removed, the oxygen concentration of the powder is adjusted to 6000 mass ppm by adjusting the oxygen concentration in the inert gas atmosphere during the fine pulverization. It is possible to control below, but if the volume ratio of the ultrafine powder exceeds 10% of the whole without removing the R-rich ultrafine powder, how is the oxygen concentration in the inert gas atmosphere? The oxygen concentration in the powder finally obtained is 6000 mass pp
It will exceed m. However, when the powder is molded in the air atmosphere, it is preferable that the powder contains 3500 mass ppm or more of oxygen in order to suppress oxidation and heat generation of the molded body.

According to the present embodiment, since the rapidly solidified alloy contains a chill crystal structure, after the crushing process, the average particle size is small, but the particle size distribution becomes broad on the finer side than the peak size. Thus, finely pulverized powder having excellent press moldability can be obtained.

In the present embodiment, the second milling process was executed using the jet mill device 10 having the structure shown in FIG. 3, but the present invention is not limited to this, and the jet mill having another structure is used. A device, or other type of fine grinding device (eg, an attritor or ball mill grinder) may be used. Further, as a classifier for removing ultrafine powder, a centrifugal classifier such as a Fatongelen classifier or a micro separator may be used in addition to the cyclone classifier.

[Addition of Lubricant] To the powder of the raw material alloy produced by the above method, a liquid lubricant or binder containing fatty acid ester as a main component is added. For example, it is preferable to add and mix 0.15 to 5.0 wt% of the lubricant in an inert atmosphere by using a device such as a rocking mixer. Examples of the fatty acid ester include methyl caproate, methyl caprylate, and methyl laurate. The important point is that the lubricant can be volatilized and removed in a later step. Further, when the lubricant itself is in a solid form which is difficult to mix uniformly with the alloy powder, it may be diluted with a solvent before use. As the solvent, a petroleum solvent represented by isoparaffin, a naphthene solvent, or the like can be used. The timing of adding the lubricant is arbitrary, and may be before pulverization, during pulverization, or after pulverization. The liquid lubricant covers the surface of the powder particles and exerts an antioxidant effect on the particles. Further, the liquid lubricant reduces the friction between the powder particles by making the density of the molded body uniform during pressing,
It not only improves the compressibility but also exerts the function of suppressing the disorder of orientation. When a solid lubricant such as zinc stearate is used, it can be added before pulverization and mixed during pulverization. This mixing may be performed with a rocking mixer after fine grinding.

[Press Molding] Next, using a known press machine, the magnetic powder manufactured by the above-described method is molded in an orientation magnetic field. In this embodiment, in order to enhance the orientation in the magnetic field, the pressing pressure is 5 to 100 MPa, preferably 15 to
Adjust within the range of 40 MPa. After the press molding is completed, the powder compact is pushed up by the lower punch and taken out of the press machine.

According to this embodiment, since the powder formability is improved, the amount of springback immediately after the breathing is reduced, and a powder compact can be obtained in which cracking and chipping are less likely to occur. Further, by lowering the pressing pressure, it is possible to manufacture a molded product having a high degree of orientation and a complicated shape with a high yield. As described above, according to the present embodiment, compared with the conventional example in which the block-shaped sintered magnet is manufactured and then the magnet having a desired shape is obtained by processing, the working time required for all steps is reduced, and the polishing process is performed. It is possible to reduce the consumption of material due to.

Next, the compact is placed on a sintering base plate made of, for example, a molybdenum material, and is mounted on the sintering case together with the base plate. The sintering case carrying the sintered body is transferred into a sintering furnace and undergoes a known sintering process in the furnace. The molded body is transformed into a sintered body through a sintering process.
Then, if necessary, an aging heat treatment, a polishing process for the surface of the sintered body, or a protective film deposition process is performed.

In the case of the present embodiment, since there are few R-rich ultrafine powders that are easily oxidized in the powder to be molded, heat generation and ignition due to oxidation are less likely to occur immediately after press molding. By removing the R-rich ultrafine powder, not only the magnetic characteristics but also the safety can be improved.

[Example and Comparative Example] In this example, 30.
When cooling and solidifying the melt of the alloy containing 8 wt% Nd, 1.2 wt% Dy, 1.0 wt% B, 0.3 wt% Al, and Fe (residual), by adjusting the amount of tapping , Chill crystal structure ratio in the quenched alloy is 0 to 25% by volume
Was changed within the range.

FIG. 4 is a micrograph showing a cross-sectional structure structure of a rapidly solidified alloy in which a chill crystal structure is not formed, and FIG. 5 is a rapidly solidified alloy in which a chill crystal structure is formed in a volume ratio of about 10%. It is a microscope picture which shows a cross-section structure structure.

In FIGS. 4 and 5, the lower end of the quenched alloy corresponds to the surface in contact with the roll surface. In the quenched alloy of FIG. 4, the columnar crystal structure occupies the entire cross section, whereas in the quenched alloy of FIG. 5, columnar crystals are present within a region of several tens of μm from the surface in contact with the roll surface. Chill crystal structures having different fine structures are formed.

The volume ratio (chill crystal structure ratio) of the chill crystal structure in the quenched alloy is measured from the area ratio of the chill crystal structure observed in the cross section of the quenched alloy. In the micrograph of the cross section of the quenched alloy, whether or not it has a chill crystal structure is determined by the presence or absence of a columnar structure. That is, in the region near the roll contact surface of the quenched alloy, a portion having no columnar structure and having a size of 5 μm or less is specified as a chill crystal structure.

The above-mentioned quenched alloy was crushed by the crushing method described above to obtain an average particle size (FSSS particle size) of 2.8 to 4.0.
A finely pulverized powder of about μm was prepared. FIG. 6 shows a particle size distribution of a finely pulverized powder (Example) produced from a comparative example having a chill crystal structure ratio of 0 vol% and a rapidly solidified alloy having a chill crystal structure ratio of 10 vol%. The particle size distribution is measured by a particle size distribution analyzer manufactured by Sympatec (product number HELOS Particle Size Analyz
er) was used. This particle size distribution measuring device utilizes the fact that the amount of transmitted light decreases when a laser beam scanned at high speed is blocked by particles, and the particle size is directly measured from the time required for the laser beam to pass through the particles. You can ask.

In the graph of FIG. 6, the volume ratio of particles having a particle size within the particle size range of 0.5 to 1.5 μm or less is plotted as the volume particle size distribution when the particle size is 1 μm. Further, the volume ratio of particles having a particle diameter included in the particle diameter range of 1.5 to 2.5 is plotted as the volume particle diameter distribution in the particle diameter of 2 μm. Similarly, the volume ratio of particles having a particle diameter within the particle diameter range of (N−0.5) to (N + 0.5) is plotted as the volume particle size distribution in the particle diameter of N μm. There is. In this specification, such a particle size distribution is referred to as a “volume particle size distribution”.

The following can be seen from FIG.

Both the volume particle size distribution of the present example and the volume particle size distribution of the comparative example have a single peak, but when the chill crystal structure is included, the particle size distribution is smaller than that in the case where it does not. It is broad.

In this embodiment, the particle size A showing the peak value of the volume particle size distribution is 4 μm, and the first particle size range from this particle size A to the predetermined particle size B (particle size A> particle size) The total volume of the particles having the particle size included in B) is the total of the particles having the particle size included in the second particle size range from the particle size A to the predetermined particle size C (particle size C> particle size A). Greater than volume. However, the width of the second particle size range (particle size C-particle size A) is assumed to be equal to the width of the first particle size range (particle size A-particle size B).

The total volume of particles having a particle size within the predetermined range of particle size corresponds to the area of the region between the curve showing the particle size distribution and the two straight lines defining the particle size range. Figure 6
FIG. 7A is a graph showing only the curve of the example in FIG. As shown in FIG. 7A, for example, the particle size is 2 μm.
The total volume of particles having a particle size in the range of m to 4 μm corresponds to the area of the region X. Further, the total volume of particles having a particle size in the range of 4 μm or more and 6 μm or less corresponds to the area of the region Y. Figure 7
As can be seen from (a), the area of the region X is larger than the area of the region Y.

On the other hand, in FIG. 7B, the total volume of particles having a particle size in the range of 2 μm to 4 μm corresponds to the area of the region X ′. Also, the particle size is 4 μm
The total volume of the particles having a particle size included in the range of the particle size of 6 μm or less corresponds to the area of the region Y ′. As can be seen from FIG. 7B, the area of the region X ′ is smaller than the area of the region Y ′.

As can be seen from FIG. 7A, in the example, the particle size D corresponding to the center of the full width at half maximum of the volume particle size distribution is smaller than the particle size A showing the peak value of the volume particle size distribution. ing. On the other hand, in the comparative example, FIG.
As can be seen, the particle size D corresponding to the center of the full width at half maximum of the volume particle size distribution is the particle size A showing the peak value of the volume particle size distribution.
Is bigger than

The average particle size of the examples (FSSS particle size)
Was 3.2 μm, and the average particle size (FSSS particle size) of the comparative example was 3.5 μm. As described above, when the average particle size of the powder is small, the fluidity is extremely deteriorated if it is in the situation, but according to the present invention, the particle size distribution width on the side where the particle size is relatively small is widened, Compressibility does not easily deteriorate. Further, according to the present invention, since the particle size distribution width on the side where the particle size is relatively large is narrowed, the average particle size is small, and by making the crystal grain size of the sintered body sufficiently small,
The effect of improving the coercive force can be obtained.

Next, 0.3 wt% of these powders
% Methyl caproate diluted with a petroleum-based solvent was added, mixed, and then press-molded by a mold pressing device to prepare a powder compact having a size of 25 mm × 20 mm × 20 mm. Breath pressure is about 30
It was set to MPa. At the time of pressing, an orientation magnetic field (1200 kA / m) perpendicular to the uniaxial compression direction was applied.
After pressing, the molded body was sintered in an argon atmosphere. The sintering temperature was 1060 ° C. and the sintering time was 5 hours. After the aging treatment, the residual magnetic flux density B _r , the coercive force H _cj , and the maximum energy product (BH) _max of the sintered magnet were measured. The results are shown in Table 1.
Shown in. Table 1 shows the molding density and the above magnetic properties for each chill crystal structure ratio.

[0092]

[Table 1]

As can be seen from Table 1, the chill crystal structure ratio is 2
%, A molding density of 4.3 g / cm ³ or more is obtained, and the compressibility is good. On the other hand, as the chill crystal structure ratio increases, the coercive force tends to decrease. This is because the chill crystal structure is easily oxidized, and an increase in the chill crystal structure ratio increases the amount of unnecessary oxide in the rare earth magnet.

From the above, it is understood that the chill crystal structure ratio is preferably 2% or more and 20% or less in volume ratio. In addition, when importance is placed on the improvement of the molding density, the chill crystal structure ratio is preferably more than 5%. On the other hand, when it is strongly required to avoid a decrease in coercive force, the chill crystal structure ratio is preferably 15% or less, more preferably 10% or less.

Although the present invention has been described with respect to the quenched alloy produced by the strip casting method, the scope of application of the present invention is not limited to this. The effect of the present invention can be exhibited even when using an alloy produced by a quenching method including a centrifugal casting method.

[Alloy composition] As the rare earth element R, specifically, Pr, Nd, Sm, Gd, Tb, Dy, Ho, E
At least one element of r, Tm, and Lu can be used. In order to obtain sufficient magnetization, it is preferable that 50 at% or more of the rare earth element R be occupied by either or both of Pr and Nd.

If the rare earth element R is less than 8 at%, α-
The coercive force may decrease due to the precipitation of the Fe phase.
Further, when the rare earth element R exceeds 18 at%, a large amount of R-rich second phase is precipitated in addition to the intended tetragonal Nd2Fe14B type compound, and the magnetization may decrease. Therefore, the rare earth element R is preferably in the range of 8 to 18 at% of the whole.

As a transition metal element substituting for Fe, Co
Besides, Ni, V, Cr, Mn, Cu, Zr, Mb, M
A transition metal element such as o can be preferably used. The proportion of Fe in the entire transition metal element is preferably 50 at% or more. This is because when the ratio of Fe is less than 50 at%, the saturation magnetization itself of the Nd2Fe14B type compound decreases.

B and / or C are tetragonal Nd2Fe
It is essential for stably precipitating the 14B type crystal structure. If the added amount of B and / or C is less than 3 at%, R
Since the 2T17 phase is precipitated, the coercive force is reduced and the squareness of the demagnetization curve is significantly impaired. Also, B and / or C
If the addition amount of Al exceeds 20 at%, the second phase with small magnetization will be precipitated.

In order to further enhance the magnetic anisotropy of the powder, another additive element M may be added. As the additive element M, Al, Ti, V, Cr, Ni, Ga, Zr, N
At least one element selected from the group consisting of b, Mo, In, Sn, Hf, Ta and W is preferably used. Such an additional element M may not be added at all. When adding, it is preferable that the addition amount be 3 at% or less. This is because if the addition amount exceeds 3 at%, not the ferromagnetism but the second phase is precipitated and the magnetization is lowered. The additive element M is not necessary to obtain magnetically isotropic magnetic powder, but Al, Cu, Ga, etc. may be added to enhance the intrinsic coercive force.

[0101]

EFFECTS OF THE INVENTION According to the alloy powder for R-Fe-B rare earth magnets of the present invention, a quenched alloy containing an appropriate amount of chill crystal structure is pulverized after being embrittled by hydrogen absorption, A powder with a high particle size distribution of the compact is obtained. As a result, according to the present invention, it is possible to mass-produce a compact having a high degree of magnetic field orientation and a complicated shape with a high yield under a relatively low press pressure.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a single roll type strip caster that is preferably used in an embodiment of the present invention.

FIG. 2 is a graph showing an example of a temperature profile of hydrogen pulverization processing executed in the coarse pulverization step in the present invention.

FIG. 3 is a cross-sectional view showing a configuration of a jet mill device preferably used for performing a fine pulverization step in the present invention.

FIG. 4 is a micrograph showing a cross-sectional structure structure of a rapidly solidified alloy in which a chill crystal structure is not formed.

FIG. 5 is a micrograph showing a structure of a cross-sectional structure of a rapidly solidified alloy in which a chill crystal structure is formed.

FIG. 6 is a graph showing the particle size distribution of the alloy powder for rare earth magnets according to the present invention.

FIG. 7A is a graph showing a particle size distribution of an example of the present invention, and FIG. 7B is a graph showing a particle size distribution of a comparative example.

[Explanation of symbols]

1 quenching room 2 molten alloy 3 melting furnace 4 shoots (tundish) 5 cooling rolls 7 Rapid solidification alloy 8 collection containers 10 Jet mill equipment 12 Raw material feeder 14 crusher 16 cyclone classifier 18 Recovery tank 20 Raw material tank 22 motor 24 feeder (screw feeder) 26 Crusher body 28 nozzle mouth 30 Raw material input pipe 32 valves 32a Upper valve 32b lower valve 34 Flexible pipe 36 classification rotor 38 motor 40 connection pipe 42 legs 44 base 46 Weight detector 48 control unit 64 classifier body 66 Exhaust pipe 68 Inlet 70 Flexible pipe 72 Exit

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP 2000-219943 (JP, A) JP 3-167803 (JP, A) JP 11-54351 (JP, A) JP 8-88112 (JP, A) JP 9-134836 (JP, A) JP 2000-12316 (JP, A) JP 6-6728 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01F 1/00-1/117 B22F 1/00-8/00 B22F 9/04 C22C 38/00 303

Claims (10)

(57) [Claims] 1. A step of preparing an R-Fe-B based rare earth magnet alloy containing a chill crystal structure in an amount of 2 to 20% by volume of the whole, and a step of preparing the R-Fe-B based rare earth magnet alloy by hydrogen absorption. A first pulverizing step of performing coarse pulverization, and further further finely pulverizing the coarsely pulverized powder, and removing at least a part of fine powder having a particle size of 1.0 μm or less from the finely pulverized powder, whereby the particle size of 1 A second pulverizing step of reducing the volume of fine powder of 0.0 μm or less; and a step of coating the surface of the pulverized powder with a lubricant after the second pulverizing step , the first pulverizing step and the second pulverizing step. By volume particle size
Distribution has a single peak, average particle size (FSSS particle size)
Is 4 μm or less and shows the peak value of the volume particle size distribution.
The first particle size range from the particle size A to the predetermined particle size B (particle size A
> The total volume of particles having a particle size included in the particle size B) is
The second particle size range from the particle size A to the predetermined particle size C (particle size
C> particle size A, “particle size C−particle size A” = “particle size A−particle size
B ”) larger than the total volume of particles having a particle size
Hear, and the particle size D corresponding to the center of the full width at half maximum of the volume particle size distribution
Is smaller than the particle size A indicating the peak value of the volume particle size distribution.
A method for producing an R-Fe-B-based alloy powder for a rare earth magnet , which comprises producing a powder. 2. The method for producing an alloy powder for R-Fe-B rare earth magnets according to claim 1 , wherein in the second pulverizing step, the alloy is finely pulverized by using a high-speed stream of an inert gas. 3. The method for producing an alloy powder for R—Fe—B based rare earth magnets according to claim 2 , wherein the fine pulverization of the alloy is carried out by using a jet mill device. 4. The R-Fe-B according to claim 3, wherein the fine pulverization of the alloy is performed by using a pulverizer combined with a classifier, and the powder discharged from the pulverizer is classified by the classifier.
Of manufacturing alloy powder for rare earth magnets. 5. A material alloy for the rare earth magnet, claim 1, wherein the raw material molten alloy is one that has been cooled at 10 ² ° C. / sec 2 × 10 ⁴ ℃ / sec cooling rate
4. The method for producing an alloy powder for R-Fe-B rare earth magnets according to any one of 4 above. 6. The method for producing an R—Fe—B based rare earth magnet alloy powder according to claim 5 , wherein the raw material alloy melt is cooled by a strip casting method. 7. The R-F according to any one of claims 1 to 6.
a step of preparing an R-Fe-B based rare earth magnet alloy powder prepared by the method for producing an e-B based rare earth magnet alloy powder; and a step of uniaxially pressing the R-Fe-B based rare earth magnet alloy powder A method for producing an R-Fe-B rare earth magnet, comprising: a step of forming a powder compact by molding at a pressure of 100 MPa or less; and a step of sintering the powder compact to produce a sintered magnet. 8. A powder obtained by crushing an R-Fe-B based rare earth magnet alloy containing a chilled crystal structure in an amount of 2 to 20% by volume, and having a single volume particle size distribution peak. And has an average particle size (FSS
S particle size) is 4 μm or less, and the particle size included in the first particle size range (particle size A> particle size B) from the particle size A showing the peak value of the volume particle size distribution to the predetermined particle size B is The total volume of the particles has a second particle size range from the particle size A to a predetermined particle size C (particle size C> particle size A, “particle size C
-Particle size A "=" particle size A-particle size B ") is larger than the total volume of particles having a particle size , and the average particle size (F
SSS particle size) is 4 μm or less,
The particle diameter D corresponding to the center of the full width at half maximum is
An R-Fe-B based rare earth magnet alloy powder having a particle size smaller than the peak value A. 9. The molten alloy material is 10 ² ° C./sec or more 2 × 1
The R according to claim 8 , which is obtained by crushing an alloy cooled at a cooling rate of 0 ⁴ ° C / sec or less.
-Fe-B type rare earth magnet alloy powder. 10. The R-Fe- according to claim 8 or 9.
An R-Fe-B rare earth magnet, which is produced from an alloy powder for a B rare earth magnet.