JP2002332507A - Rare earth magnet and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the magnetic properties of a magnet by improving the properties of an alloy powder for a rare earth magnet. SOLUTION: The production method includes a first pulverizing stage where a raw material alloy for a rare earth magnet is coarsely pulverized and a second pulverizing stage where the raw material alloy is finely pulverized. In the first pulverizing stage, for raw material alloy is pulverized by using a hydrogen pulverizing method. In the second pulverizing stage, hyperfine powders easy to be oxidized (having a grain size of <=1.0 μm) are removed, and the piece ratio of the hyperfine powders is controlled to <=10% of the whole of the powders.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an R-Fe-B rare earth magnet and a method for producing an alloy powder for the magnet.

[0002]

2. Description of the Related Art Rare earth sintered magnets are produced by pressing an alloy powder formed by pulverizing an alloy for a rare earth magnet (raw material alloy), followed by a sintering step and an aging heat treatment step. At present, two types of rare earth sintered magnets, samarium / cobalt magnets and neodymium / iron / boron magnets, are widely used in various fields. Among them, neodymium / iron / boron magnets (hereinafter referred to as "R-Fe-B magnets").
R is a rare earth element and / or Y (yttrium), F
e is iron and B is boron) has the highest magnetic energy product among various magnets and is relatively inexpensive.
Actively used in various electronic devices. Note that a part of Fe may be replaced by a transition metal element such as Co, or a part of B may be replaced by C.

[0003] Powders of raw material alloys for R-Fe-B rare earth magnets are produced by a method including a first pulverizing step of roughly pulverizing the raw material alloy and a second pulverizing step of finely pulverizing the raw material alloy. . Usually, in the first pulverizing step, the raw material alloy is coarsely pulverized to a size of several hundred μm or less by a hydrogen pulverizer, and in the second pulverizing step, the coarsely pulverized alloy (coarse pulverized powder) is averaged by a jet mill pulverizer or the like. Finely pulverize to a size of about several μm.

[0004] 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 molten metal of a raw material alloy is put into a mold and cooled relatively slowly. The second method is to melt the alloy in a single roll, a twin roll,
This is a quenching method typified by a strip casting method or a centrifugal casting method in which a solidified alloy thinner than an ingot alloy is produced from a molten alloy by rapidly cooling by contacting with a rotating disk or a rotating cylindrical mold or the like.

[0005] In the case of this quenching method, the cooling rate of the molten alloy is in the range of 10 ² ° C / sec to 10 ⁴ ° C / sec. And the thickness of the quenched alloy produced by the quenching method is
It 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 from the roll contact surface in a columnar (needle) shape in the thickness direction. As a result, the rapidly solidified alloy has a minor axis size is 5μm or more longitudinal size 0.1μm or 100μm or less 500μm following R ₂ T ₁₄ B crystal phase, R ₂
It has a fine crystal structure containing an R-rich phase (a phase in which the concentration of the rare earth element R is relatively high) dispersed and present at the grain boundaries of the T ₁₄ B crystal phase. The R-rich phase is a non-magnetic phase in which the concentration of the rare-earth element R is relatively high, and its thickness (corresponding to the width of the grain boundary) is 10 μm or less.

[0006] The quenched alloy is an alloy (ingot alloy) produced by a conventional ingot casting method (die casting method).
As compared with the case of (1), since the cooling is performed in a relatively short time, the structure is refined and the crystal grain size is small. Further, since the crystal grains are finely dispersed and the area of the grain boundary is wide, and the R-rich phase is thinly spread in the grain boundary, the dispersibility of the R-rich phase is excellent.

[0007]

In the case where a rare earth alloy (particularly a quenched alloy) is temporarily absorbed with hydrogen gas and coarsely pulverized by a so-called hydrogen pulverization treatment (in this specification, such a pulverization method is referred to as a "hydrogen pulverization method". ), The R-rich phase located at the grain boundary reacts with hydrogen and expands, so that it tends to break from the R-rich phase portion (grain boundary portion). For this reason, an R-rich phase is likely to appear on the particle surface of the powder obtained by pulverizing the rare earth alloy with hydrogen. In the case of a quenched alloy, the R-rich phase is finely divided and has a high dispersibility, so that the R-rich phase is particularly easily exposed to the surface of the ground hydrogen powder.

According to an experiment conducted by the present inventor, when the coarsely pulverized powder in such a state is finely pulverized by a jet mill pulverizer or the like, R-rich ultrafine powder (fine powder having a particle diameter of 1 μm or less) is obtained.
Is generated. Since the R-rich ultrafine powder is much more easily oxidized than other powder particles (having a relatively large particle size) having a relatively low content of the rare earth element R,
If a sintered magnet is produced as it is without removing the rich fine powder from the powder, the oxidation reaction of the rare earth element remarkably proceeds during the manufacturing process up to the sintering process. As a result, the rare earth element R is consumed for bonding with oxygen, and the main phase R ₂ T ₁₄ B
The generation amount of the type crystal phase is reduced. This results in lowering the coercive force and residual magnetic flux density of the magnet and deteriorating the squareness of the demagnetization curve.

In order to prevent oxidation of the R-rich finely pulverized powder, it is ideal to carry out all steps from the pulverization step to the sintering step in an inert atmosphere. It is extremely difficult to implement on a mass production scale.

On the other hand, the surface of the finely pulverized powder is intentionally covered with a thin oxide film by performing the finely pulverizing step in an inert atmosphere into which a trace amount of oxygen has been introduced. Methods of suppressing have been proposed.

However, even with such a technique, as long as the R-rich ultrafine powder is present in a certain proportion or more in the powder, the final magnet properties cannot be sufficiently improved or improved, and the maximum magnet properties cannot be stably obtained. It has been found by the inventor's experiments that it cannot be kept at the level.

The present invention has been made in view of the above points, and a main object thereof is to provide an R-Fe-B-based rare-earth magnet alloy powder capable of sufficiently improving and stabilizing magnet properties. It is in.

Another object of the present invention is to sufficiently improve and improve the final magnet properties and stably achieve the highest performance even when coarse grinding is performed by hydrogen grinding using a raw alloy containing an R-rich phase. Excellent R-Fe-B that can be kept at a level
An object of the present invention is to provide a method for producing an alloy powder for a rare earth magnet.

[0014]

According to the present invention, R-Fe-
A method for producing a B-based rare earth magnet alloy powder includes an R-Fe-B based rare earth element including a first pulverizing step of roughly pulverizing a rare earth magnet raw material alloy and a second pulverizing step of finely pulverizing the raw material alloy. A method for producing an alloy powder for a magnet, wherein the first pulverizing step includes a step of pulverizing the raw material alloy using a hydrogen pulverizing method, and wherein the second pulverizing step has a particle diameter of 1.0.
a step of removing at least a part of the fine powder having a particle diameter of 1.0 μm or less, thereby adjusting the number of the fine powder having a particle diameter of 1.0 μm or less to 10% or less of the total number of particles in the powder.

In a preferred embodiment, the particle size is 1.0 μm
The average concentration of the rare earth element contained in the following fine powder is higher than the average concentration of the rare earth element contained in the whole powder.

The method for producing an R-Fe-B rare earth magnet alloy powder according to the present invention comprises a first pulverizing step of roughly pulverizing a rare earth magnet raw material alloy produced by a quenching method, and a fine pulverization of the raw material alloy. R-Fe-
A method for producing a B-based rare earth magnet alloy powder, wherein the second pulverizing step removes at least a part of the powder in which the concentration of the rare earth element is higher than the average concentration of the rare earth element contained in the entire powder, And reducing the average concentration of oxygen contained in the powder in a form that combines with the rare earth element.

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

It is preferable that a predetermined amount of oxygen is introduced into the inert gas. In that case, it is preferable that the concentration of the oxygen is adjusted to 0.05% by volume or more and 3% by volume or less.

As the rare earth alloy, a plurality of kinds of rare earth alloys having different rare earth contents may be used.

In one embodiment, the first pulverizing step is performed separately for the plurality of rare earth alloys having different rare earth contents, and the second pulverizing step is performed for the plurality of rare earth alloys having different rare earth contents. Performed simultaneously on alloys.

In one embodiment, the first and second pulverizing steps are separately performed on a plurality of kinds of rare earth alloys having different rare earth contents, and after the second pulverizing step, the plurality of kinds of rare earth alloys are different. Mix powder.

The alloy can be finely pulverized using a jet mill pulverizer.

In a preferred embodiment, a classifier is connected to the subsequent stage of the jet mill pulverizer, and the powder discharged from the jet mill pulverizer is classified.

In a preferred embodiment, the material alloy for the rare earth magnet material alloy melt of 10 ² ° C. / sec 10 ⁴
It is cooled at a cooling rate of not more than ° C / sec.

Preferably, the cooling of the raw material alloy melt is performed by a strip casting method.

In a preferred embodiment, the average particle size of the powder obtained in the first pulverizing step is 200 to 100.
0 μm. In the case of a rapidly cooled alloy such as a strip cast, the average particle size of the powder is 500 μm or less.

The average particle size of the powder obtained in the second pulverizing step is preferably in the range of 2 μm to 10 μm.

Preferably, the method further comprises a step of adding a lubricant to the powder obtained in the second pulverizing step.

The method for producing an R—Fe—B rare earth magnet according to the present invention is directed to a method for producing an R—Fe—B rare earth magnet produced by any of the above methods for producing an alloy powder for an R—Fe—B rare earth magnet. A step of preparing an alloy powder;
Molding a B-based rare earth magnet alloy powder to produce a permanent magnet.

Another method for producing an R—Fe—B based rare earth magnet according to the present invention is a method for producing an R—Fe—B based rare earth magnet alloy powder according to any one of the above methods.
A step of preparing an alloy powder for an Fe-B-based rare-earth magnet; and a step of preparing a second R-Fe-B-based rare-earth magnet having a rare earth content different from that of the first alloy powder for an R-Fe-B-based rare earth magnet. Preparing an alloy powder, mixing the first and second alloy powders to form a mixed powder, forming the mixed powder to form a compact, and sintering the compact. And producing a permanent magnet.

The R-Fe-B rare earth magnet alloy powder according to the present invention has an average particle size of 2 μm or more and 10 μm or less, and the number of fine particles of 1.0 μm or less is adjusted to 10% or less of the total number of particles in the powder. Have been.

In a preferred embodiment, the magnet powder of the present invention is obtained by pulverizing an alloy obtained by cooling a molten raw material alloy at a cooling rate of not less than 10 ² ° C / sec and not more than 10 ⁴ ° C / sec.

The R-Fe-B rare earth magnet according to the present invention is characterized in that it is produced from the above alloy powder for an R-Fe-B rare earth magnet.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION The inventor of the present application has proposed that if an R-rich ultrafine powder having a particle size of 1 μm or less is present in an R-Fe-B-based rare earth magnet alloy powder in a ratio exceeding a predetermined ratio, such a powder may be used. The present inventors have found that the magnetic properties of the permanent magnet produced by sintering the molded article of Example 1 are deteriorated, and have arrived at the present invention.

In the present invention, after the raw alloy for the rare-earth magnet is roughly pulverized (first pulverizing step), the raw alloy is finely pulverized (second pulverizing step). At least a part of the fine powder having a particle size of 1 μm or less is removed, whereby the ratio of the number of the R-rich ultrafine powder to the whole powder is adjusted to 10% or less. The concentration of the rare earth element R contained in the R-rich ultrafine powder is at least 38% by mass,
This is higher than the average concentration of the rare earth element R contained in the whole powder. For this reason, if such an ultrafine powder is partially removed, the concentration of the rare earth element R contained in the entire powder is reduced. The rare earth element R is indispensable for the R ₂ T ₁₄ B type crystal phase, which is the main phase responsible for hard magnetism, and it seems that a decrease in the concentration of the rare earth element R is not preferable.
The rare earth element R contained in the ultrafine powder to be removed is consumed for bonding with oxygen and does not sufficiently contribute to the formation of the R ₂ T ₁₄ B type crystal phase. For this reason, by removing the R-rich ultrafine powder, the amount of oxygen in the powder can be reduced as a result, so that the amount of the R ₂ T ₁₄ B type crystal phase contained in the sintered magnet increases rather, The magnetic properties will be improved.

According to the experiment of the present inventor, R-rich ultrafine powder is likely to be generated when a rapidly quenched alloy (for example, a strip cast alloy) is pulverized as described above. Also easy to be generated.
Therefore, in the following description, an embodiment of the present invention will be described by taking, as an example, a case where a crushed alloy is roughly pulverized by a hydrogen pulverization method and then a fine pulverization step is performed. In addition, when using a jet mill pulverizer that performs fine pulverization of an alloy using a high-speed air flow of an inert gas, if an airflow (centrifugal force) classifier is connected to the subsequent stage of the jet mill pulverizer, the alloy is carried by the airflow. R-rich ultra fine powder (particle size 1μm)
Can be efficiently removed. Therefore, in the following embodiment, an example in which the fine pulverization step is performed using a jet mill pulverizer will be described.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Raw Material Alloy] First, a raw material alloy for an R—Fe—B based magnet alloy having a desired composition having a desired composition is prepared by a known strip casting method and stored in a predetermined container. Specifically, first, Nd: 30.8 wt% (atomic%), P
r: 3.8 wt%, Dy: 0.8 wt%, B: 1.0 w
t%, Co: 0.9 wt%, Al: 0.23 wt%, C
u: An alloy having a composition of 0.10 wt%, the balance being Fe and unavoidable impurities is melted by high frequency melting to form a molten alloy. After maintaining this molten alloy at 1350 ° C,
The alloy melt is quenched by the single roll method to a thickness of about 0.3
mm flake-like alloy ingot was obtained. The quenching conditions at this time were as follows: a roll peripheral speed of about 1 m / sec, a cooling speed of 500 ° C./sec,
The temperature was supercooled to 200 ° C. The quenched alloy slab thus produced is pulverized into flakes having a size of 1 to 10 mm before the next pulverization with hydrogen. In addition, the manufacturing method of the raw material alloy by the strip casting method is described in, for example, US Pat. No. 5,383,383.
No. 978.

[First pulverizing step] A plurality of raw material packs (stainless steel) of raw material alloy slabs roughly pulverized into flakes
And mounted on a rack. Thereafter, 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 a hydrogen crushing step (first crushing step) is started. The hydrogen pulverization process is performed, for example, according to a temperature profile shown in FIG. In the example of FIG. 1, first, the evacuation process I is performed for 0.5 hour, 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, and the furnace is set to a hydrogen atmosphere. The hydrogen pressure at that time is preferably about 200 to 400 kPa.

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

In the cooling process IV, when the atmosphere temperature in the furnace is relatively high (for example, when the temperature exceeds 100 ° C.), an inert gas at room temperature is supplied to the inside of the hydrogen furnace for cooling. Thereafter, at the stage when the temperature of the raw material alloy is lowered to a relatively low level (for example, when the temperature is 100 ° C. or lower), an inert gas cooled to a temperature lower than normal temperature (for example, room temperature minus about 10 ° C.) is introduced into the hydrogen furnace 10. Supply is preferable from the viewpoint of cooling efficiency. The supply amount of argon gas is 10 ~
It may be about 100 m ³ / min.

When the temperature of the raw material alloy is reduced to about 20 to 25 ° C., an inert gas at substantially normal temperature (a temperature lower than room temperature but a difference from room temperature within 5 ° C.) is blown into the hydrogen furnace. It is preferable to wait until the temperature of the raw material reaches the normal temperature level. By doing so, when the lid of the hydrogen furnace is opened, a situation in which dew condensation occurs inside the furnace can be avoided. If moisture is present inside the furnace due to condensation,
Since the water freezes and evaporates in the evacuation step, it is difficult to increase the degree of vacuum, and the time required for the evacuation step I is undesirably increased.

When the coarsely pulverized alloy powder after hydrogen pulverization is taken out of the hydrogen furnace, it is preferable to carry out the taking out operation under an inert atmosphere so that the coarsely pulverized powder does not come into contact with the atmosphere.
This prevents the coarsely pulverized powder from oxidizing and generating heat, thereby improving the magnetic properties of the magnet. Next, the coarsely pulverized raw material alloy is filled into a plurality of raw material packs and mounted on a rack.

The rare earth alloy is reduced to 0.1 m by hydrogen pulverization.
m to several mm, and the average particle size is 2
It becomes 00-1000 micrometers. After the hydrogen pulverization, it is preferable that the embrittled raw material alloy is further finely pulverized and cooled by a cooling device such as a rotary cooler. In the case where the raw material is taken out in a relatively high temperature state, the time of the cooling process using a rotary cooler or the like may be made relatively long.

[Second Pulverization Step] Next, the coarsely pulverized powder produced in the first pulverization step is finely pulverized using a jet mill pulverizer. A cyclone classifier suitable for removing fine powder is connected to the jet mill pulverizer used in the present embodiment.

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

The illustrated jet mill pulverizer 10 comprises:
Rare earth alloy coarsely pulverized in the first pulverization step (object to be pulverized)
Feeder 12 for supplying the raw material, a pulverizer 14 for pulverizing the material to be pulverized input from the material inputter 12, and a cyclone classifier for classifying the powder obtained by pulverizing the material to be pulverized by the pulverizer 14. And a collection tank 18 for collecting powder having a predetermined particle size distribution classified by the cyclone classifier 16.
And

The raw material input device 12 includes a raw material tank 20 for storing the material to be ground, a motor 22 for controlling the supply amount of the material to be ground from the raw material tank 20, and a spiral feeder ( Screw feeder) 2
And 4.

The crusher 14 has a vertically long, substantially cylindrical crusher main body 26, and a lower part of the crusher main body 26 is provided with a nozzle for ejecting an inert gas (eg, nitrogen) at a high speed. A plurality of nozzle ports 28 are provided. To the side of the crusher main body 26, a raw material input pipe 30 for charging an object to be crushed into the crusher main body 26 is connected.

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

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

The crusher 14 has a plurality of legs 4 serving as support portions.
2 is provided. A base 44 is provided 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 42 of the crusher 14 is used.
A weight detector 4 such as a load cell is
6 are provided. Based on the output from the weight detector 46, the control unit 48 controls the number of rotations of the motor 22, and thereby can control the amount of the material to be ground.

The cyclone classifier 16 comprises a classifier body 64
An exhaust pipe 66 is inserted into the classifier main body 64 from above. On the side of the classifier body 64,
Inlet 68 for introducing the powder classified by the classification rotor 36
Is provided, and the inlet 68 is connected to the connection pipe 40 by a flexible pipe 70. Classifier body 64
An outlet 72 is provided at a lower portion of the container, 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, rubber, or the like, or may be made to have flexibility by forming a highly rigid material into a bellows shape or a coil shape. preferable. Such flexible pipes 34 and 7
If 0 is used, the weight change of the raw material tank 20, the feeder 24, the classifier main body 64, and the collection tank 18 is reduced by
Is not transmitted to the leg portion 42 of the main body. Therefore, if the weight is detected by the weight detector 46 provided on the leg 42, the weight of the material to be ground remaining in the crusher 14 and the change amount thereof can be accurately detected, and the crushed material supplied to the crusher 14 can be detected. The quantity of things can be controlled accurately.

Next, a pulverizing method using the above jet mill pulverizing apparatus 10 will be described.

First, the material to be ground 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 supply device 24. At this time, by controlling the number of revolutions of the motor 22, the supply amount of the crushed material can be adjusted. The material to be crushed supplied from the supply device 24 is once blocked by the valve 32. Here, the pair of upper valve 32a and lower valve 32b perform opening and closing operations alternately. 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 manner, the pressure in the crusher 14 can be prevented from leaking to the material input device 12 side. As a result, the object to be ground 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 charging pipe 30 and introduced into the crusher 14. The valve 32 is driven at a high speed by a sequence circuit (not shown) different from the control circuit 48, and the material to be ground is continuously supplied into the mill 14.

The material to be pulverized introduced into the pulverizer 14 is wound up in the pulverizer 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 airflow. Then, the objects to be ground are finely ground by mutual collision.

The finely pulverized powder particles are guided to the classifying rotor 36 by the rising airflow,
6 and the coarse powder will be ground again.
On the other hand, the powder pulverized to a predetermined particle size or less is
0, it is introduced into the classifier body 64 of the cyclone classifier 16 from the inlet 68 via the flexible pipe 70. In the classifier main body 64, relatively large powder particles having a predetermined particle size or more are deposited in the recovery tank 18 provided at the lower portion, and the ultrafine powder is discharged to the outside from the exhaust pipe 66 together with the inert gas stream. . In the present embodiment, the ultrafine powder is removed through the exhaust pipe 66, whereby the ultrafine powder occupying the powder collected in the collection tank 18 (particle diameter: 1.0 μm)
m) is adjusted to 10% or less. When the R-rich ultrafine powder is removed in this manner, the amount of the rare earth element R in the sintered magnet consumed for bonding with oxygen can be reduced, and the magnet properties can be improved.

As described above, in the present embodiment, the cyclone classifier 16 with blow-up is used as a classifier connected to the subsequent stage of the jet mill pulverizer (pulverizer 14). According to such a cyclone classifier 16, the ultrafine powder having a particle size equal to or smaller than a predetermined value is inverted and rises without being collected in the collection tank 18, 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 can be determined, for example, by referring to “Powder Technology Pocket Book”
The parameters can be controlled by appropriately defining the parameters of each part of the cyclone as described on pages 92 to 96, and adjusting the pressure of the inert gas stream.

FIG. 3 shows an example of the particle size distribution of the powder obtained through the second pulverizing step. According to the present embodiment, it is possible to obtain an alloy powder having an average particle size of about 4.0 μm, for example, and the number of ultrafine powder having a particle size of 1.0 μm or less is 10% or less of the total number of powders. it can. The preferred average particle size range of the finely pulverized powder used for manufacturing the sintered magnet is 2 μm or more and 10 μm or less. In the example of FIG. 3, since the metal structure of the raw material alloy (strip cast alloy) used was fine, a very sharp particle size distribution was obtained as compared with the conventional ingot alloy powder. In this embodiment, the particle size is 5 μ
The number of powders of m or more was 13% or less of the total number of powders. By reducing large powder particles having a particle size of 5 μm or more, the magnetic properties of the finally obtained sintered magnet can be improved. The “particle size” in the present specification is defined as the size of a particle measured by the Fisher Sub-Siever Sizer (FSSS) method.

In order to suppress oxidation in the pulverizing step as much as possible, it is preferable to suppress the amount of oxygen in the high-speed gas stream (inert gas) used in the pulverization to as low as about 0.02 to 5% by volume. . A pulverization method for controlling the oxygen concentration in the high-speed airflow gas is described in Japanese Patent Publication No. 6-6728. More preferably, the amount of oxygen in the inert gas is adjusted in the range of 0.05 to 3% by volume.

As described above, by controlling the concentration of oxygen contained in the atmosphere at the time of pulverization, the oxygen content (weight) of the alloy powder after pulverization is adjusted to 6,000 p.
pm or less. If the amount of oxygen in the rare earth alloy powder exceeds 6,000 ppm and becomes too large, the proportion of the nonmagnetic oxide in the sintered magnet increases, and the magnetic properties of the final sintered magnet deteriorate. It is. As described above, by covering the surface of the finely pulverized powder with the oxide layer, press molding in the air becomes possible.

In this embodiment, since the R-rich ultrafine powder is appropriately removed, the oxygen concentration in the inert gas atmosphere during the fine pulverization is adjusted so that the oxygen concentration of the powder is 6,000 ppm. The following can be controlled, but if the R-rich ultrafine powder is not removed,
If the number ratio of ultrafine powder exceeds 10% of the total, no matter how the oxygen concentration in the inert gas atmosphere is reduced, the oxygen concentration in the finally obtained powder will exceed 6,000 ppm. become.

By removing the R-rich ultrafine powder having a particle size of 1 μm or less as described above, the fluidity of the powder finally obtained through the second pulverization step is improved, BH is used to make the size of crystal grains uniform.
The squareness of the demagnetization curve is excellent, and an effect of realizing a high coercive force can also be obtained.

In the present embodiment, the second pulverizing step is performed using the jet mill pulverizing apparatus 10 having the configuration shown in FIG. 2, but the present invention is not limited to this, and the jet pulverizing apparatus having another configuration is used. A mill pulverizer or another type of pulverizer (attritor or ball mill) may be used. Further, as a classifier for removing the 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] In the present embodiment, for example, 0.3% by weight of a lubricant is added to and mixed with the finely pulverized powder produced by the above method in a rocking mixer. Cover the surface. As the lubricant, a fatty acid ester diluted with a petroleum solvent can be used. In this embodiment, methyl caproate is used as the fatty acid ester, and isoparaffin is used as the petroleum solvent. The weight ratio between methyl caproate and isoparaffin is, for example, 1: 9. Such a liquid lubricant covers the surface of the powder particles, exhibits an effect of preventing the particles from being oxidized, and also has a function of improving the orientation at the time of pressing and the powder moldability (the density of the molded body becomes uniform, and Eliminating defects such as cracks).

The type of the lubricant is not limited to the above. As the fatty acid ester, other than methyl caproate, for example, methyl caprylate, methyl laurate (methyl laurate) and the like may be used. 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 for example, may be before, during, or after the fine pulverization by the jet mill pulverizer. Instead of the liquid lubricant or together with the liquid lubricant, a solid (dry) lubricant such as zinc stearate may be used.

By coating the surface of the finely pulverized powder with the lubricant as described above, the oxidation of the powder can be suppressed.

[Press molding] Using a known press machine,
The magnetic powder produced by the above method is molded in an orientation magnetic field. After the press molding is completed, the powder compact is pushed up by the lower punch and taken out of the press device.

Next, the compact is mounted on a sintering base plate made of, for example, a molybdenum material, and is mounted together with the base plate in a sintering case. The sintering case on which the sintered body is mounted is transferred into a sintering furnace, and undergoes a known sintering process in the furnace. The formed body undergoes a sintering process and changes into a sintered body.
Thereafter, aging heat treatment, polishing of the surface of the sintered body, and deposition of a protective film are performed as necessary.

In the case of the present embodiment, since there is little R-rich ultrafine powder which is easily oxidized in the powder to be molded, heat and ignition due to oxidation are less likely to occur even immediately after press molding. By removing the R-rich ultrafine powder, not only the improvement of the magnetic properties but also the improvement of the safety can be realized.

[Examples and Comparative Examples] In this example, when the fine pulverization step (second pulverization step) is performed using the jet mill pulverizer connected to the cyclone classifier described above, the pulverization in the cyclone classifier is performed. By adjusting the gas pressure, the amount of ultrafine powder contained in the recovered powder was changed. A gas containing 1% by volume of oxygen and 99% by volume of nitrogen was used as a pulverizing atmosphere gas of the jet mill.

Sample No. For 1 to 8, the particle size is 1 μm
The ratio (number ratio), magnetic characteristics, and oxygen content of the following ultrafine powder in the whole powder were evaluated. Table 1 shows the results.

[0075]

[Table 1]

Here, the sample No. Sample Nos. 1 to 6 are examples of the present invention. 7 and 8 are comparative examples. The preparation conditions for each sample are as follows.

First, the powder produced by the method described in the above embodiment was pressed into a 15 mm × 20 mm × 10
A compact having a size of mm was produced. Press pressure is 9
8 MPa. When pressing, the thickness of the compact is 15m
An orientation magnetic field (1.0 MA / m) oriented in the direction of m was applied. After pressing, the compact was sintered in an argon atmosphere. The sintering temperature was 1,100 ° C., and the sintering time was 2 hours. After the aging treatment, the sintered density, the coercive force iHc of the sintered magnet,
And the residual magnetic flux density Br were measured. The oxygen content in Table 1 was determined by measuring the oxygen content in the finely pulverized alloy powder.

As can be seen from Table 1, as the number ratio of ultrafine powder having a particle size of 1 μm or less increases, the amount of oxygen increases and the sintering density tends to decrease. Particle size 1μ
If the number ratio of ultrafine powders of m or less further exceeds 10.0%, the oxygen content becomes 6,000 pp by weight.
m and the sintering density was below 7.4 g / cm ³ . In this case, the coercive force iHc of the sintered magnet and the residual magnetic flux density B
r was also deteriorated.

On the other hand, if the number ratio of the ultrafine powder having a particle size of 1 μm or less is set to 10.0% or less, the coercive force iHc becomes 900 k
Excellent magnetic properties of A / m or more and residual magnetic flux density Br of 1.35 T or more could be obtained. In particular, when the number ratio of the ultrafine powder having a particle diameter of 1 μm or less is 5.0% or less, the coercive force iHc is 990 kA / m or more, and the residual magnetic flux density Br is 1.
Superior characteristics of 4T or more could be realized. Furthermore, when the number ratio of the ultrafine powder having a particle size of 1 μm or less is 3.0% or less, the most excellent magnetic properties are achieved.

As described above, if the proportion of the R-rich ultrafine powder in the rare earth alloy powder is reduced, the amount of oxygen in the pulverized powder can be reduced, and the density of the sintered body can be sufficiently improved. In addition, the magnet characteristics can be greatly improved.

Since the rare earth alloy powder particles used in the present invention are ferromagnetic, they tend to aggregate by magnetic force to form secondary particles. For this reason, when the conventional particle size distribution measuring method is used, there is a possibility that an accurate measurement result cannot be obtained. In this example, the particle size distribution was measured as follows.

After placing the powder sample in a beaker together with ethyl alcohol, an ultrasonic dispersion treatment is performed. After removing the supernatant of the beaker, the powder sample is kneaded with a binder in a mortar to prepare a paste sample. Next, the paste sample is stretched on a slide glass free from scratches and stains to prepare a sample cell having a kneaded film having a uniform thickness. afterwards,
Before the agglomeration of the powder particles proceeds in the kneading film, the sample cell is quickly set in the particle size distribution measuring device. The particle size distribution measuring device used irradiates a sample cell with a laser beam emitted from a laser light source and scans the sample cell at high speed. A change in the intensity of the laser beam transmitted through the sample cell is detected, and the particle size distribution of the particles dispersed in the sample cell is measured based on the detected change. Such a particle size distribution measurement can be performed using, for example, a particle size distribution measuring device (product number GALAI CIS-1) manufactured by GALAI. This particle size distribution measurement device uses the fact that the amount of transmitted light decreases when a laser beam scanned at high speed is blocked by particles, and directly calculates the particle size from the time required for the laser beam to pass through the particles. Can be sought.

Although the present invention has been described with reference to a quenched alloy produced by the strip casting method, the scope of the present invention is not limited to this. Even when an alloy produced by the ingot method is used, an R-rich ultrafine powder is formed, so that the effects of the present invention are exhibited.

In the above description, a raw material alloy having one kind of composition is used, and the first and second pulverizing steps are performed on the raw material alloy. However, the present invention is not limited to this. As the object to be pulverized, a plurality of types of rare earth alloys having different production methods and rare earth contents may be used. That is, the present invention can also be applied to a “two-alloy method” in which two kinds of rare-earth alloy powders having different compositions are mixed, molded and sintered. In the case of the two-alloy method, specifically, after the first pulverizing step is separately performed on two kinds of rare-earth alloys having different rare-earth contents, the coarsely pulverized powder obtained by this is mixed and mixed powder is obtained. On the other hand, the second pulverizing step may be performed. Or. The first and second pulverization steps are separately performed on a plurality of types of rare earth alloys having different rare earth contents,
After the pulverized powder is finally obtained, the pulverized powder may be mixed and used. Further, the present invention may be applied to one of the two types of alloys, and two types of finely pulverized powders obtained by applying the conventional method may be used as a mixture for the other type.

The composition of the powder slightly changes during the pulverizing step. For this reason, in order to adjust the composition of the mixed powder to a target value with high accuracy by appropriately blending a plurality of types of powders having different compositions, the composition of the powder is measured after all the pulverization steps are completed, and the measurement is performed. It is preferable to determine the compounding ratio based on the value. In this case, for example, a plurality of types of powders can be blended in a step of applying a lubricant to the powders.

[0086]

According to the R-Fe-B-based rare earth magnet alloy powder of the present invention, since the abundance ratio of the oxidation-reactive powder component having a particle size of 1 μm or less is reduced, the oxidation of the rare earth element R is reduced. Thus, the deterioration of the magnet properties caused by the above can be sufficiently prevented, whereby the properties of the high performance rare earth magnet can be greatly improved, and the safety during the magnet manufacturing process can be improved.

The present invention has a particularly remarkable effect when using a quenched alloy (for example, a strip cast alloy) in which an R-rich ultrafine powder is easily generated or when a hydrogen grinding step is performed.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of a temperature profile of a hydrogen pulverization process performed in a coarse pulverization step in the present invention.

FIG. 2 is a cross-sectional view showing a configuration of a jet mill pulverizing apparatus suitably used for performing a fine pulverizing step in the present invention.

FIG. 3 is a graph showing a particle size distribution of an alloy powder for a rare earth magnet according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Jet mill crusher 12 Material input machine 14 Crusher 16 Cyclone classifier 18 Recovery tank 20 Material tank 22 Motor 24 Feeder (screw feeder) 26 Crusher main body 28 Nozzle port 30 Material input pipe 32 Valve 32a Upper valve 32b Lower valve 34 Flexible Pipe 36 Classification Rotor 38 Motor 40 Connection Pipe 42 Leg 44 Base 46 Weight Detector 48 Controller 64 Classifier Body 66 Exhaust Pipe 68 Inlet 70 Flexible Pipe

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shuhei Okumura 2-15-17 Egawa, Shimamoto-cho, Mishima-gun, Osaka Prefecture F-term in Sumitomo Special Metals Co., Ltd. Yamazaki Works (reference) 4K017 AA02 BA08 CA06 CA07 DA04 EA03 EA11 FA01 5E040 AA04 CA01 HB00 NN01

Claims (21)

[Claims] 1. A method for producing an R—Fe—B-based rare earth magnet alloy powder, comprising: a first pulverizing step of coarsely pulverizing a raw alloy for a rare earth magnet; and a second pulverizing step of pulverizing the raw material alloy. Wherein the first pulverizing step includes a step of pulverizing the raw material alloy using a hydrogen pulverizing method, and the second pulverizing step removes at least a part of fine powder having a particle size of 1.0 μm or less. A method for producing an alloy powder for R-Fe-B-based rare earth magnets, comprising the step of adjusting the number of fine powder having a particle size of 1.0 μm or less to 10% or less of the total number of particles. 2. The R- according to claim 1, wherein the average concentration of the rare earth element contained in the fine powder having a particle size of 1.0 μm or less is higher than the average concentration of the rare earth element contained in the whole powder.
A method for producing an Fe-B-based rare earth magnet alloy powder. 3. An R—Fe—B-based rare earth magnet for an R—Fe—B rare earth magnet, comprising: a first pulverizing step of roughly pulverizing a raw alloy for a rare earth magnet produced by a quenching method; and a second pulverizing step of pulverizing the raw material alloy. A method for producing an alloy powder, wherein the second pulverizing step removes at least a part of the powder in which the concentration of the rare earth element is higher than the average concentration of the rare earth element contained in the entire powder, thereby bonding with the rare earth element. A method for producing an alloy powder for R-Fe-B-based rare earth magnets, the method including a step of reducing the average concentration of oxygen contained in the powder in such a form. 4. The alloy for an R—Fe—B rare earth magnet according to claim 1, wherein in the second pulverizing step, the alloy is finely pulverized by using a high-speed gas stream of an inert gas. Powder manufacturing method. 5. The method of claim 4, wherein a predetermined amount of oxygen is introduced into the inert gas. 6. The oxygen concentration is not less than 0.05% by volume.
The R-Fe according to claim 5, which is adjusted to not more than% by volume.
A method for producing an alloy powder for a B-based rare earth magnet. 7. The method according to claim 1, wherein a plurality of kinds of rare earth alloys having different rare earth contents are used as the rare earth alloy. 8. The first pulverizing step is separately performed on a plurality of types of rare earth alloys having different rare earth contents, and the second pulverizing step is performed on a plurality of types of rare earth alloys having different rare earth contents. The method for producing an alloy powder for an R-Fe-B-based rare earth magnet according to claim 7, which is carried out simultaneously. 9. The first and second pulverizing steps are separately performed on a plurality of kinds of rare earth alloys having different rare earth contents. After the second pulverizing step, powders of the plurality of kinds of rare earth alloys are mixed. The method for producing an alloy powder for an R-Fe-B-based rare earth magnet according to claim 7, which is mixed. 10. The method according to claim 9, wherein the fine pulverization of the alloy is performed using a jet mill pulverizer. 11. The production of an alloy powder for an R—Fe—B-based rare earth magnet according to claim 10, wherein a classifier is connected to the subsequent stage of the jet mill pulverizer to classify the powder discharged from the jet mill pulverizer. Method. 12. The RF according to claim 1, wherein the raw material alloy for a rare earth magnet is obtained by cooling a molten material alloy at a cooling rate of 10 ² ° C / sec or more and 10 ⁴ ° C / sec or less.
A method for producing an eB-based rare earth magnet alloy powder. 13. The R-Fe- according to claim 12, wherein the cooling of the raw material alloy melt is performed by a strip casting method.
A method for producing a B-based rare earth magnet alloy powder. 14. The powder obtained by the first pulverizing step has an average particle size of 500 μm or less.
The method for producing an alloy powder for an R-Fe-B-based rare earth magnet according to the above. 15. The R-Fe- according to claim 1, wherein the average particle diameter of the powder obtained in the second pulverization step is in a range of 2 μm or more and 10 μm or less.
A method for producing a B-based rare earth magnet alloy powder. 16. The method according to claim 1, further comprising a step of adding a lubricant to the powder obtained in the second grinding step.
Or the method for producing an alloy powder for an R-Fe-B-based rare earth magnet according to 3 above. 17. A step of preparing an R—Fe—B-based rare earth magnet alloy powder produced by the production method according to claim 1; and molding the R—Fe—B-based rare earth magnet alloy powder. And a step of producing a permanent magnet. 18. A step of preparing a first R-Fe-B-based rare earth magnet alloy powder produced by the production method according to claim 1 or 3, and the first R-Fe-B-based rare earth element A step of preparing a second R-Fe-B-based rare earth magnet alloy powder having a rare earth content different from that of the magnet alloy powder; and forming a mixed powder by mixing the first and second alloy powders. A method for producing an R-Fe-B-based rare earth magnet, comprising: a step of molding the mixed powder to produce a molded body; and sintering the molded body to produce a permanent magnet. 19. An R-Fe-B-based rare earth magnet alloy powder having an average particle diameter of 2 μm or more and 10 μm or less, and wherein the number of fine powders of 1.0 μm or less is adjusted to 10% or less of the total number of particles. . 20. A raw material alloy melt is heated to 10 ² ° C./sec or more and 10 ⁴
The R-Fe-B-based rare-earth magnet alloy powder according to claim 19, which is obtained by pulverizing an alloy cooled at a cooling rate of not more than ° C / sec. 21. The RF according to claim 19 or 20.
An R-Fe-B-based rare-earth magnet produced from an alloy powder for an e-B-based rare-earth magnet.