JP2012204581A - PRODUCTION METHOD OF SURFACE MODIFIED R-Fe-B BASED SINTERED MAGNET - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a surface modified R-Fe-B based sintered magnet having excellent corrosion resistance and excellent magnetic characteristics.SOLUTION: An atmosphere where the oxygen partial pressure is 1×10to 1×10Pa, the partial water vapor pressure is lower than 1000 Pa, and the ratio of the oxygen partial pressure and the partial water vapor pressure (oxygen partial pressure/partial water vapor pressure)is 1 to 20000 (where, excepting 1) is formed so that a positive pressure state is brought in the processing chamber by performing introduction of the atmospheric gas per 1 mof the volume in the processing chamber on conditions of 0.028 m/min or more as the oxygen flow rate, and 3 m/min or less as the total flow rate. Subsequently, an R-Fe-B based sintered magnet having an oxygen content of 0.1 mass% or less is heat treated at 230 to 260°C.

Description

  The present invention relates to a method for producing a surface-modified R—Fe—B based sintered magnet having excellent corrosion resistance and excellent magnetic properties.

R-Fe-B-based sintered magnets represented by Nd-Fe-B-based sintered magnets are widely used today because they use resource-rich and inexpensive materials and have high magnetic properties. Although it is used in various fields, since it contains a highly reactive rare earth element: R, it has the property of being easily oxidized and corroded in the atmosphere. Therefore, the R—Fe—B based sintered magnet is usually used for practical use by forming a corrosion-resistant coating such as a metal coating or a resin coating on the surface thereof. However, it can be used as a drive motor for a hybrid vehicle or an electric vehicle. In the case where the magnet is embedded in a part, such as an IPM (Interior Permanent Magnet) motor incorporated in a compressor of an air conditioner, etc., such a corrosion-resistant coating is not necessarily provided on the surface of the magnet. It is not required to form. However, it is of course necessary to ensure the corrosion resistance of the magnet during the period from when the magnet is manufactured to when it is embedded in the part.
As described above, as a method of imparting corrosion resistance to the R—Fe—B based sintered magnet, a method of forming a corrosion resistant coating such as a metal coating or a resin coating on the surface is representative, but in recent years, oxidation A method of modifying the surface of a magnet by performing heat treatment (oxidation heat treatment) on the magnet in a neutral atmosphere has attracted attention as a simple technique for improving corrosion resistance. For example, Patent Document 1 and Patent Document 2 describe a method of forming an oxidizing atmosphere using oxygen and performing a heat treatment, and Patent Documents 3 to 6 use water vapor alone, or A method is described in which oxygen is combined with water vapor to form an oxidizing atmosphere and heat treatment is performed. However, even if surface modification is performed on the magnet by these methods, the surface of the magnet is finely affected by fluctuations in temperature and humidity, such as in transportation and storage environments where temperature and humidity are not controlled. In an environment where repeated condensation occurs repeatedly, sufficient corrosion resistance is not necessarily obtained. In Patent Documents 3 to 6, the water vapor partial pressure is preferably 10 hPa (1000 Pa) or more. When heat treatment is performed in an atmosphere with a high water vapor partial pressure, a large amount of hydrogen is generated as a by-product due to an oxidation reaction that occurs on the surface of the magnet, and the magnetic properties are reduced by occlusion and embrittlement of the hydrogen generated by the magnet. This has been clarified by the study of the present inventors. Therefore, the present inventors, as a better surface modification method for R-Fe-B based sintered magnets, oxygen partial pressure and water vapor partial pressure of less than 10 hPa, which is inappropriate in Patent Documents 3 to 6. Is a heat treatment method in an oxidizing atmosphere appropriately controlled, specifically, an oxygen partial pressure of 1 × 10 ² Pa to 1 × 10 ⁵ Pa and a water vapor partial pressure of 0.1 Pa to 1000 Pa (excluding 1000 Pa) Patent Document 7 proposed a method of performing heat treatment at 200 ° C. to 600 ° C. in the atmosphere described above.
Furthermore, the present inventors perform heat treatment under appropriate temperature control according to the oxygen content of the magnet based on the surface modification method of the R—Fe—B based sintered magnet proposed in Patent Document 7. A surface modification method was proposed in Patent Document 8. In the surface modification method proposed by the present inventors in Patent Document 8, an appropriate heat treatment temperature for a magnet having an oxygen content of less than 0.3% by mass is set to 400 ° C. to 600 ° C. This is because when the heat treatment temperature is less than 400 ° C., deterioration of the magnetic properties is observed (particularly in the vicinity of 350 ° C.). It is confirmed with a 13 mass% magnet and a 0.24 mass% magnet.

Japanese Patent No. 2844269 JP 2002-57052 A JP 2006-156853 A JP 2006-210864 A JP 2007-103523 A JP 2007-207936 A International Publication No. 2009/041639 JP 2010-232357 A

With the recent development of R-Fe-B sintered magnet technology, a technology for producing a magnet having an oxygen content of 0.1% by mass or less has been established. The inventors of the present invention performed surface modification on a magnet having such an extremely low oxygen content at a heat treatment temperature of 400 ° C. or higher recommended in Patent Document 8, and particularly when the heat treatment is performed at around 350 ° C. Although it was possible to avoid the deterioration of the magnetic properties as expected, it was unexpectedly found that the magnetic properties were slightly deteriorated.
Therefore, an object of the present invention is to provide a method for producing a surface-modified R—Fe—B sintered magnet having excellent corrosion resistance and excellent magnetic properties.

  As a result of intensive studies in view of the above points, the present inventors have determined that an R-Fe-B sintered magnet having an oxygen content of 0.1% by mass or less has a predetermined oxidizing atmosphere. Performing heat treatment in a specific temperature range below 300 ° C with proper formation is effective for efficiently forming the desired modified layer on the surface without causing deterioration of magnetic properties. I found out.

The manufacturing method of the surface-modified R—Fe—B sintered magnet of the present invention completed based on the above findings has an oxygen partial pressure of 1 × 10 ³ Pa to 1 × as described in claim 1. An atmosphere having a water vapor partial pressure of less than 1000 Pa at 10 ⁵ Pa and an oxygen partial pressure to water vapor partial pressure ratio (oxygen partial pressure / water vapor partial pressure) of 1 to 20000 (excluding 1) is 0.028 m 3 ^/ min or more the introduction of the atmospheric gas per volume 1 m ³ as an oxygen flow, and formed as the processing by making the entire flow 3m 3 ^/ min under the following conditions chamber is a positive pressure state The heat treatment is performed at 230 ° C. to 260 ° C. for an R—Fe—B based sintered magnet having an oxygen content of 0.1% by mass or less.
Moreover, the surface-modified R—Fe—B based sintered magnet of the present invention is manufactured by the manufacturing method according to claim 1 as described in claim 2.

  ADVANTAGE OF THE INVENTION According to this invention, while having the outstanding corrosion resistance, the manufacturing method of the surface-modified R-Fe-B type sintered magnet which has the outstanding magnetic characteristic can be provided.

It is the schematic (side view) of an example of the continuous processing furnace which can be suitably employ | adopted for the manufacturing method of the surface-modified R-Fe-B type sintered magnet of this invention. It is a graph which shows the influence which heat processing has on the intrinsic coercive force of the R-Fe-B system sintered magnet whose oxygen content in reference example 1 is 0.1 mass% or less.

The method for producing a surface-modified R—Fe—B sintered magnet of the present invention has an oxygen partial pressure of 1 × 10 ³ Pa to 1 × 10 ⁵ Pa, a water vapor partial pressure of less than 1000 Pa, and oxygen An atmosphere having a ratio of partial pressure to water vapor partial pressure (oxygen partial pressure / water vapor partial pressure) of 1 to 20000 (excluding 1) is 0.028 m with the introduction of atmospheric gas per volume of 1 m ^{3 in the} processing chamber as an oxygen flow rate. R-Fe- having an oxygen content of 0.1% by mass or less, formed so as to be in a positive pressure state in the processing chamber by performing under conditions of ³ / min or more and a total flow rate of 3m ³ / min or less. A heat treatment is performed at 230 ° C. to 260 ° C. for the B-based sintered magnet. A predetermined oxidizing atmosphere is formed by introducing atmospheric gas under predetermined conditions so that the processing chamber is in a positive pressure state, and the heat treatment temperature is appropriately controlled without causing deterioration of magnetic characteristics. Moreover, the desired surface modification can be performed on a magnet having an oxygen content of 0.1% by mass or less without taking too much time for the treatment.

By to define the oxygen partial pressure in the step of performing a heat treatment with ^{1 × 10 3 Pa~1 × 10 5} Pa is the oxygen partial pressure is less than 1 × ¹⁰ 3 Pa, the oxygen content in the atmosphere is too low When the surface modification of the magnet takes too much time or when the magnet is disposed on the holding member and heat treatment is performed, the portion of the magnet that is in contact with the holding member is not sufficiently surface modified, This is because there is a risk that sufficient corrosion resistance and stability will not be imparted, or that contact marks with the holding member may remain in the portion. On the other hand, even if the oxygen partial pressure is made higher than 1 × 10 ⁵ Pa, the improvement of the surface modification effect of the magnet by increasing the oxygen partial pressure is not recognized so much, which may only increase the cost. Because there is. In order to perform the desired modification on the surface of the magnet more effectively and at low cost, the oxygen partial pressure is preferably 1 × 10 ³ Pa to 5 × 10 ⁴ Pa, and 1 × 10 ⁴ Pa to ³ × 10. ⁴ Pa is more desirable. The water vapor partial pressure is defined as less than 1000 Pa. If the water vapor partial pressure is 1000 Pa or more, the amount of water vapor in the atmosphere is excessive, and the surface of the magnet is modified to a stable one that exhibits excellent corrosion resistance. Because there is a fear that it cannot be done. In order to perform the desired modification on the surface of the magnet more effectively and at low cost, the water vapor partial pressure is desirably 700 Pa or less, and more desirably 45 Pa or less. The lower limit of the water vapor partial pressure is not particularly limited, but is usually 1 Pa. The ratio between the oxygen partial pressure and the water vapor partial pressure is defined as 1 to 20000 (excluding 1) because when the ratio is 1 or less, the amount of water vapor with respect to the amount of oxygen in the atmosphere is too large. This is because the surface may not be modified to a stable one that exhibits excellent corrosion resistance. On the other hand, an atmosphere in which the ratio is greater than 20000 is a special environment and is not practical. In order to perform the desired modification on the surface of the magnet more effectively and at a low cost, the ratio is preferably 10 to 10,000, more preferably 300 to 5000, and further preferably 450 to 4000.

The atmosphere in the processing chamber may be formed by individually introducing oxygen or water vapor as an atmospheric gas so as to have a predetermined partial pressure, or an atmosphere having a dew point that includes these at a predetermined partial pressure is introduced. However, in any case, in the present invention, the atmosphere in the processing chamber is 0.028 m ³ / introduction of atmospheric gas per volume of 1 m ^{3 in the} processing chamber. It is formed so as to be in a positive pressure state in the processing chamber by performing it under the condition of not less than 3 minutes and not more than 3 m ³ / minute as a whole flow rate (having a dew point in which oxygen or water vapor is contained at a predetermined partial pressure as atmospheric gas) When the atmosphere is used, the oxygen flow rate is naturally controlled if the atmospheric flow rate is controlled as the total flow rate). By forming the atmosphere in the processing chamber in this way, even if the heat treatment temperature is as low as 230 ° C. to 260 ° C., the processing layer does not take too much time, and the modified layer is efficiently formed on the surface of the magnet. Can be formed. If the flow rate of oxygen introduced into the processing chamber is too small, it may take too much time for processing, whereas if the total flow rate is too high, the temperature distribution in the processing chamber will vary, resulting in a uniform distribution of all magnets in the processing chamber. There is a possibility that surface modification cannot be performed. Note that an inert gas such as nitrogen gas or argon gas may coexist in the processing chamber.

  The temperature of the heat treatment is defined as 230 ° C. to 260 ° C. If the temperature is lower than 230 ° C., there is a risk of causing a non-negligible magnetic particle detachment because a modified layer having a sufficient thickness cannot be formed on the surface of the magnet. On the other hand, if the temperature is higher than 260 ° C., the magnetic characteristics may be deteriorated. The heat treatment time is preferably 1 minute to 3 hours, more preferably 15 minutes to 2.5 hours. If the time is too short, it may be difficult to perform the desired modification on the surface of the magnet. On the other hand, even if the time is longer than necessary, energy is consumed and the cost is increased.

In addition, it is desirable to perform the process of raising the temperature of the magnet from room temperature to the temperature at which heat treatment is performed in an atmosphere having an oxygen partial pressure of 1 × 10 ³ Pa to 1 × 10 ⁵ Pa and a water vapor partial pressure of 1 Pa to 100 Pa. By raising the temperature in such an atmosphere, moisture that is naturally adsorbed on the surface of the magnet is desorbed at an early stage, so that the moisture present on the surface of the magnet is It is possible to avoid adverse effects as much as possible. The average heating rate may be, for example, 100 ° C./hour to 2000 ° C./hour. In the present invention, “normal temperature” refers to the temperature (for example, room temperature) of the environment in which the R—Fe—B sintered magnet subjected to surface modification is placed at the start of temperature rise, and is illustrative. Means a temperature defined as 5 ° C. to 35 ° C. in JIS Z 8703 of the Japanese Industrial Standard.

The step of lowering the temperature of the magnet after the heat treatment is also preferably performed in an atmosphere having an oxygen partial pressure of 1 × 10 ³ Pa to 1 × 10 ⁵ Pa and a water vapor partial pressure of 1 Pa to 100 Pa. By lowering the temperature in such an atmosphere, it is possible to prevent the surface of the magnet from condensing and causing corrosion during the process.

  In the temperature raising process, heat treatment process, and temperature lowering process for the magnet, for example, the magnet is housed in a heat resistant container made of a material such as SUS, Ti, Mo, Nb, etc., which can control the atmosphere by circulating an atmosphere gas inside. In addition, the heat-resistant container containing the magnet can be accommodated in a processing chamber of a batch-type heat treatment furnace while controlling the atmosphere inside the heat-resistant container. Moreover, it can also carry out using the batch-type heat processing furnace which can change the environment in the process chamber in which the magnet was accommodated into the environment for performing each process sequentially. Furthermore, the processing chamber can be divided into regions controlled to an environment suitable for each process, and magnets can be moved sequentially to the respective regions.

  FIG. 1 shows a continuous process in which a temperature raising process, a heat treatment process, and a temperature lowering process for a magnet are divided into areas whose interiors are controlled in an environment suitable for each process, and the magnet is sequentially moved to each area. It is the schematic (side view) of an example of a processing furnace. In the continuous processing furnace shown in FIG. 1, each processing is performed while moving the magnet from the left to the right in the drawing by moving means such as a belt conveyor. Arrows indicate the flow of the atmospheric gas in each region formed by an unillustrated air supply means and exhaust means. The inlet of the temperature rising region and the outlet of the temperature falling region are partitioned by, for example, an air curtain, and the boundary between the temperature rising region and the heat treatment region and the boundary between the heat treatment region and the temperature lowering region are partitioned by, for example, the flow of the atmospheric gas indicated by the arrows (these This may be done mechanically with a shutter). If such a continuous processing furnace is used, surface modification with stable quality can be continuously performed for a large number of magnets.

  Even if the modified layer formed on the surface of the R—Fe—B based sintered magnet by the above process is very thin with a thickness of 1 μm or less (nanometer order), sufficient corrosion resistance is exhibited.

Examples of the R—Fe—B based sintered magnet to which the present invention is applied include those manufactured by the following manufacturing method.
An alloy including 25% by mass to 40% by mass of rare earth element R, 0.6% by mass to 1.6% by mass of B (boron), and the balance Fe and inevitable impurities is prepared. Here, R may contain a heavy rare earth element RH. Further, a part of B may be substituted by C (carbon), and a part of Fe (50% by mass or less) may be substituted by another transition metal element (for example, Co or Ni). Good. This alloy is suitable for a variety of purposes, including Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and About 0.01% by mass to 1.0% by mass of at least one additive element M selected from the group consisting of Bi may be contained.
The above-mentioned alloy can be suitably produced by rapidly cooling a molten raw material alloy by, for example, a strip casting method. Hereinafter, preparation of a rapidly solidified alloy by a strip casting method will be described.
First, a raw material alloy having the above composition is melted by high-frequency melting in an argon atmosphere to form a molten raw material alloy. Next, after holding this molten metal at about 1350 ° C., it is rapidly cooled by a single roll method to obtain, for example, a flake-shaped alloy ingot having a thickness of about 0.3 mm. The alloy slab thus produced is pulverized into, for example, 1 to 10 mm flakes before the next hydrogen pulverization treatment. In addition, the manufacturing method of the raw material alloy by a strip cast method is disclosed by US Patent 5,383,978 specification, for example.
[Coarse grinding process]
The alloy slab coarsely crushed into flakes is accommodated in the hydrogen furnace. Next, a hydrogen embrittlement treatment process (hereinafter sometimes referred to as “hydrogen pulverization treatment” or simply “hydrogen treatment”) is performed inside the hydrogen furnace. When the coarsely pulverized powder after the hydrogen pulverization treatment is taken out from the hydrogen furnace, the takeout operation is preferably performed in an inert atmosphere so that the coarsely pulverized powder does not come into contact with the atmosphere. By doing so, it is possible to prevent the coarsely pulverized powder from oxidizing and generating heat, and to suppress the deterioration of the magnetic properties of the magnet.
By the hydrogen pulverization treatment, the rare earth alloy is pulverized to a size of about 0.1 mm to several mm, and the average particle size becomes 500 μm or less. After the hydrogen pulverization treatment, the embrittled raw material alloy is preferably crushed more finely and cooled. When the raw material is taken out in a relatively high temperature state, the cooling process time may be relatively long.
[Fine grinding process]
Next, the coarsely pulverized powder is finely pulverized using a jet mill pulverizer. A cyclone classifier is connected to the jet mill crusher used in the present embodiment. The jet mill pulverizer is supplied with the rare earth alloy (coarse pulverized powder) coarsely pulverized in the coarse pulverization step, and pulverizes in the pulverizer. The powder pulverized in the pulverizer is collected in a collection tank through a cyclone classifier. Thus, a fine powder of about 0.1 to 20 μm can be obtained. The pulverizer used for such fine pulverization is not limited to a jet mill, and may be an attritor or a ball mill. In grinding, a lubricant such as zinc stearate may be used as a grinding aid.
[Press molding]
In the present embodiment, for example, 0.3% by mass of a lubricant is added to and mixed with the finely pulverized powder produced by the above method in a rocking mixer, and the surface of the finely pulverized powder particles is coated with the lubricant. Next, the finely pulverized powder produced by the above-described method is molded in an orientation magnetic field using a known press apparatus. The intensity of the applied magnetic field is, for example, 1.0 to 1.7 Tesla (T). The molding pressure is set so that the green density of the molded body is, for example, about 4 to 4.5 g / cm ³ .
[Sintering process]
It carries out for 10 to 240 minutes with respect to said powder molded object at the temperature within the range of 1000-1200 degreeC, for example. Even if the step of holding at a temperature in the range of 650 to 1000 ° C. for 10 to 240 minutes and the step of further promoting the sintering at a temperature higher than the above holding temperature (for example, 1000 to 1200 ° C.) are sequentially performed. Good. During sintering, particularly when a liquid phase is generated (when the temperature is in the range of 650 to 1000 ° C.), the R-rich phase in the grain boundary phase begins to melt and a liquid phase is formed. Then, sintering progresses and a sintered magnet body is formed. After the sintering step, aging treatment (400 ° C. to 700 ° C.) and grinding for dimension adjustment may be performed.

  The surface-modified R—Fe—B sintered magnet produced by the production method of the present invention has excellent corrosion resistance imparted by an oxidation heat treatment, and a decrease in coercive force when the temperature is lowered after the heat treatment is suppressed. Therefore, for example, it is suitable for use in an IPM motor that is used as a drive motor for a hybrid vehicle or an electric vehicle, or incorporated in a compressor of an air conditioner. In addition, what is necessary is just to pass through the process of embedding a magnet in the inside of a rotor, when manufacturing an IPM motor using the surface-modified R-Fe-B system sintered magnet manufactured by the manufacturing method of this invention.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is limited to this and is not interpreted.

(Production Example 1)
Nd: 18.6, Pr: 5.5, Dy: 7.1, B: 0.98, Co: 0.9, Cu: 0.1, Al: 0.2, Ga: 0.1, balance: An alloy flake having a composition of Fe (unit: mass%) and having a thickness of 0.2 mm to 0.3 mm was prepared by strip casting.
Next, this alloy flake was filled in a container and accommodated in a hydrogen treatment apparatus. Then, the hydrogen treatment apparatus was filled with hydrogen gas at a pressure of 500 kPa, so that hydrogen was occluded in the alloy flakes at room temperature and then released. By performing such hydrogen treatment, the alloy flakes were embrittled and coarsely pulverized powder having a size of about 0.15 mm to 0.2 mm was produced.
After adding 0.04% by mass of zinc stearate as a grinding aid to the coarsely pulverized powder produced by the hydrogen treatment described above, the powder particle size is about 3 μm by performing a pulverization step with a jet mill device. A fine powder was prepared.
The fine powder thus produced was molded by a press apparatus to produce a powder compact. Specifically, the powder particles were compressed in a magnetic field-oriented state in an applied magnetic field and pressed. Thereafter, the molded body was extracted from the press apparatus, and a sintering process was performed at 1050 ° C. for 4 hours in a vacuum furnace to obtain a sintered body block. It was 0.08 mass% when the oxygen content of this sintered compact block was measured with the oxygen and nitrogen analyzer (EMGA-620W: product made by HORIBA) (this oxygen content is maintained until it heat-processes).
The obtained sintered body block was subjected to an aging treatment at 490 ° C. for 2.5 hours in a vacuum, and then the surface was ground to adjust the dimensions, and the thickness was 6 mm × length 7 mm × width 7 mm. An R—Fe—B sintered magnet (hereinafter referred to as “magnet test piece 1”) was obtained.

(Production Example 2)
Nd: 16.2, Pr: 4.5, Dy: 9.1, B: 0.93, Co: 2.0, Cu: 0.1, Al: 0.15, Ga: 0.07, balance: An alloy flake having a composition of Fe (unit: mass%) having a thickness of 0.2 mm to 0.3 mm was produced by strip casting, and a sintered body block was obtained in the same manner as in Production Example 1. The oxygen content of the sintered body block was 0.06% by mass (this oxygen content was maintained until heat treatment was performed). An R—Fe—B sintered magnet (hereinafter referred to as “magnet body test piece 2”) having a thickness of 6 mm × length of 7 mm × width of 7 mm was obtained in the same manner as in Production Example 1 from the obtained sintered body block.

Example 1
After magnet body test piece 1 obtained in Production Example 1 was ultrasonically washed, surface modification was performed using a continuous processing furnace having the configuration shown in FIG. The heat treatment step was performed at 240 ° C. for 120 minutes in an atmosphere having an dew point of 0 ° C. (oxygen partial pressure 20000 Pa, water vapor partial pressure 600 Pa, oxygen partial pressure / water vapor partial pressure = 33.3). The formation of the atmosphere in the heat treatment region (corresponding to the treatment chamber in the present invention: volume 0.64 m ³ ) is achieved by introducing air with a dew point of 0 ° C. into the heat treatment region at a flow rate of 0.12 m ³ / min. (The oxygen flow rate per volume of 1 m ³ is 0.037 m ³ / min and the total flow rate is 0.188 m ³ / min. The oxygen flow rate is 1/5 of the atmospheric flow rate that is the total flow rate. Conversion: Atmospheric flow rate is controlled by an area-type flow meter. In addition, the temperature increasing step from the normal temperature of the magnet body test piece 1 (meaning 25 ° C. in the present embodiment; the same applies hereinafter) to the temperature (240 ° C.) for performing the heat treatment, and the temperature lowering step after performing the heat treatment step, It was performed in an atmosphere of dew point −40 ° C. (oxygen partial pressure 20000 Pa, water vapor partial pressure 19 Pa, oxygen partial pressure / water vapor partial pressure = 1052). The thickness of the modified layer formed on the surface of the magnet body test piece 1 was on the order of nanometers (less than 1 μm). The thickness of the modified layer is such that after the surface-modified magnet body test piece 1 is resin-filled and polished, a sample is prepared using an ion beam cross-section processing apparatus (SM09010: manufactured by JEOL Ltd.), and field emission scanning electrons are used. It measured by observing a cross section using a microscope (S-4300: Hitachi High-Technology Co., Ltd.) (hereinafter the same).

(Example 2)
Magnet body test piece in the same manner as in Example 1 except that the heat treatment step was performed in an atmosphere with a dew point of −40 ° C. (oxygen partial pressure 20000 Pa, water vapor partial pressure 19 Pa, oxygen partial pressure / water vapor partial pressure = 1052). 1 surface modification was performed. The thickness of the modified layer formed on the surface of the magnet body test piece 1 was on the order of nanometers (less than 1 μm).

(Example 3)
Surface modification of the magnet test piece 2 was performed in the same manner as in Example 2 except that the magnet test piece 2 obtained in Production Example 2 was used. The thickness of the modified layer formed on the surface of the magnet test piece 2 was on the order of nanometers (less than 1 μm).

Example 4
Using a batch-type heat treatment furnace having a volume of 0.0034 m ^{3 in} the processing chamber, the atmosphere in the processing chamber is formed by introducing air with a dew point of −40 ° C. into the processing chamber at a flow rate of 0.003 m ³ / min. It was performed in a positive pressure state (the oxygen flow rate per volume of 1 m ³ was 0.176 m ³ / min and the total flow rate was 0.882 m ³ / min), and the heat treatment step was performed at 260 ° C. for 60 minutes. Except for the above, surface modification of the magnet body test piece 2 was performed in the same manner as in Example 3. The thickness of the modified layer formed on the surface of the magnet test piece 2 was on the order of nanometers (less than 1 μm).

(Example 5)
The surface modification of the magnet body test piece 2 was performed in the same manner as in Example 4 except that air having a dew point of 0 ° C. was used. The thickness of the modified layer formed on the surface of the magnet test piece 2 was on the order of nanometers (less than 1 μm).

(Example 6)
The atmosphere in the processing chamber was formed by introducing an atmosphere having a dew point of 0 ° C. at a flow rate of 0.01 m ³ / min into the processing chamber so that the processing chamber was in a positive pressure state (oxygen per 1 m ^{3 of} volume). The flow rate was 0.588 m ³ / min and the total flow rate was 2.94 m ³ / min), and the surface modification of the magnet specimen 2 was performed in the same manner as in Example 5 except that the heat treatment process was performed at 230 ° C. for 180 minutes. went. The thickness of the modified layer formed on the surface of the magnet test piece 2 was on the order of nanometers (less than 1 μm).

(Comparative Example 1)
The atmosphere was formed in the heat treatment region by introducing an atmosphere with a dew point of 0 ° C. at a flow rate of 0.07 m ³ / min into the heat treatment region so that the heat treatment region was in a positive pressure state (volume 1 m ^3). The oxygen flow rate per unit is 0.022 m ³ / min and the total flow rate is 0.109 m ³ / min), and the surface of the magnet specimen 1 is the same as in Example 1 except that the heat treatment process is performed at 400 ° C. for 20 minutes. Modification was performed. The thickness of the modified layer formed on the surface of the magnet body test piece 1 was on the order of nanometers (less than 1 μm).

(Comparative Example 2)
The surface modification of the magnet body test piece 1 was performed in the same manner as in Example 1 except that the heat treatment step was performed at 400 ° C. for 20 minutes. The thickness of the modified layer formed on the surface of the magnet body test piece 1 was on the order of nanometers (less than 1 μm).

(Comparative Example 3)
Surface modification of the magnet body test piece 2 was performed in the same manner as in Example 5 except that the heat treatment step was performed at 265 ° C. for 60 minutes. The thickness of the modified layer formed on the surface of the magnet test piece 2 was on the order of nanometers (less than 1 μm).

(Comparative Example 4)
The surface modification of the magnet body test piece 2 was performed in the same manner as in Example 3 except that the heat treatment step was performed at 220 ° C. for 240 minutes. The thickness of the modified layer formed on the surface of the magnet test piece 2 was on the order of nanometers (less than 1 μm).

(Comparative Example 5)
The atmosphere in the processing chamber was formed by introducing an atmosphere having a dew point of 0 ° C. at a flow rate of 0.015 m ³ / min into the processing chamber so that the processing chamber was in a positive pressure state (oxygen flow rate per volume of 1 m ³ Was modified by the same method as in Example 6 except that 0.882 m ³ / min and the total flow rate was 4.41 m ³ / min). The thickness of the modified layer formed on the surface of the magnet test piece 2 was on the order of nanometers (less than 1 μm).

(Comparative Example 6)
The atmosphere in the processing chamber was formed by introducing an atmosphere having a dew point of 0 ° C. at a flow rate of 0.0004 m ³ / min into the processing chamber so that the processing chamber was in a positive pressure state (oxygen flow rate per 1 m ^{3 of} volume) Was modified by the same method as in Example 6 except that 0.023 m ³ / min and the overall flow rate was 0.118 m ³ / min). The thickness of the modified layer formed on the surface of the magnet test piece 2 was on the order of nanometers (less than 1 μm).

(Evaluation of magnetic properties)
The intrinsic coercivity of the magnet body test piece subjected to the surface modification in each of Examples 1 to 6 and Comparative Examples 1 to 6 is the intrinsic coercivity of the magnet body test piece before the surface modification. In comparison, the intrinsic coercivity deterioration rate was calculated by the following formula. Table 1 shows the heat treatment conditions of Examples 1 to 6 and Comparative Examples 1 to 6, and Table 2 shows the calculated intrinsic coercivity deterioration rates. The intrinsic coercive force was measured using a magnetometer (SK-130: manufactured by Metron Giken).
Inherent coercive force deterioration rate (%) = ((A−B) / A) × 100
A: Intrinsic coercivity of the magnet specimen before surface modification (average value of 20)
B: Intrinsic coercive force (average value of 20 pieces) of the magnet specimen after surface modification

(Corrosion resistance evaluation)
Corrosion resistance under high-temperature and high-humidity conditions of temperature: 60 ° C. × relative humidity: 90% for the magnet body test pieces subjected to surface modification in each of Examples 1 to 6 and Comparative Examples 1 to 6. The test was conducted for 24 hours, and the presence or absence of surface rusting after the test was examined by appearance observation. Table 2 shows the number of magnet body test pieces in which surface rusting was recognized among the 30 magnet body test pieces used in the test. Further, after performing a pressure cooker test under the conditions of temperature: 125 ° C. × relative humidity: 85% × pressure: 2 atm for 96 hours, the magnetic particles that have been shed by the tape are removed, and the weight of the magnet specimen before and after the test. Is shown in Table 2 (average value of 10 samples subjected to the test). Table 2 also shows the results of the corrosion resistance evaluation performed on the magnet test piece 1 in the same manner.

(Summary)
As is apparent from Table 1, when the processing chamber has a predetermined oxidizing atmosphere, by appropriately adjusting the flow rate of the atmosphere used as the introduced atmosphere gas (in this embodiment, the atmospheric flow rate is the total flow rate of the present invention). The oxygen flow rate is naturally determined), and by making the inside of the processing chamber an appropriate positive pressure state, the heat treatment at 230 ° C. to 260 ° C. has improved the corrosion resistance without causing deterioration of the magnetic properties. The quality layer could be efficiently formed on the surface of the magnet specimen (Example 1 to Example 6). On the other hand, in the heat treatment at 400 ° C., the deterioration of the magnetic characteristics exceeding 3% was observed because the heat treatment temperature was too high (Comparative Example 1). Further, even if the oxygen flow rate was appropriately adjusted by appropriately adjusting the atmospheric flow rate introduced into the processing chamber, the result was the same (Comparative Example 2). Even if the air flow rate introduced into the processing chamber is properly adjusted, 1% deterioration in magnetic properties is observed at a heat treatment temperature of 265 ° C. (Comparative Example 3), and magnetic particle degranulation is observed at a heat treatment temperature of 220 ° C. (Comparative Example 4). Even if the heat treatment temperature is adjusted appropriately, if too much air flow is introduced into the processing chamber, uniform surface modification cannot be performed on all magnets in the processing chamber due to variations in temperature distribution in the processing chamber. In some magnets, non-negligible magnetic particle shedding was observed, resulting in an increase in weight loss (Comparative Example 5). Moreover, the result was the same even if there was too little oxygen flow rate because there was too little atmospheric flow rate introduce | transduced in a processing chamber (comparative example 6).

(Reference Example 1)
Each of the magnet body test piece 1 obtained in Production Example 1 and the magnet body test piece 2 obtained in Production Example 2 was subjected to heat treatment for 2 hours in vacuum at a temperature in the range of 240 ° C. to 440 ° C. The coercive force is measured using a magnetometer (TPM-2-10: manufactured by Toei Kogyo Co., Ltd.), and compared with the intrinsic coercive force before heat treatment, the oxygen content is 0.1% by mass or less. The effect of heat treatment on the intrinsic coercivity of the magnet was investigated. The results are shown in FIG. Note that the vertical axis in FIG. 2 represents the deterioration rate of the intrinsic coercive force, which is obtained by the following mathematical formula.
Inherent coercive force deterioration rate (%) = ((A−B) / A) × 100
A: Intrinsic coercive force before heat treatment, B: Intrinsic coercivity after heat treatment As is clear from FIG. 2, both the magnet specimen 1 and the magnet specimen 2 are particularly prominent when heat treatment is performed at around 350 ° C. The deterioration of the intrinsic coercive force is recognized as described in Patent Document 8 as a phenomenon observed in a magnet having an oxygen content of less than 0.3% by mass, but the oxygen content is 0.1% by mass or less. When the magnet was subjected to a heat treatment at 400 ° C. or higher recommended in Patent Document 8, deterioration of the intrinsic coercive force of 2% to 3% was recognized. Therefore, it was confirmed that heat treatment at 400 ° C. or higher should not be adopted for magnets having an oxygen content of 0.1 mass% or less.

  INDUSTRIAL APPLICABILITY The present invention has industrial applicability in that it can provide a method for producing a surface-modified R-Fe-B sintered magnet having excellent corrosion resistance and excellent magnetic properties. .

Claims (2)

A method for producing a surface-modified R—Fe—B sintered magnet having an oxygen partial pressure of 1 × 10 ³ Pa to 1 × 10 ⁵ Pa, a water vapor partial pressure of less than 1000 Pa, and an oxygen content 0.028m atmosphere of the ratio of pressure and water vapor partial pressure (oxygen partial pressure / water vapor partial pressure) is 1 to 20,000 (excluding proviso 1), the introduction of the atmospheric gas per volume 1 m ³ of the processing chamber as the oxygen flow rate ³ R-Fe-B having an oxygen content of 0.1% by mass or less and an oxygen content of 0.1% by mass or less and an overall flow rate of 3 m ³ / min or less. A manufacturing method characterized by performing heat treatment on a sintered system magnet at 230 ° C. to 260 ° C.   A surface-modified R-Fe-B sintered magnet produced by the production method according to claim 1.