JP5906874B2 - Manufacturing method of RTB-based permanent magnet - Google Patents

Description

  The present invention relates to an RTB system permanent magnet having a porous structure manufactured by the HDDR method, and an RTB system manufactured by hot compressing the RTB system permanent magnet. The present invention relates to a method for manufacturing a high-density magnet.

R-T-B type permanent magnets typical as high performance permanent magnets (R is a rare earth element containing Nd and / or Pr of 50 atomic% or more, T is Fe, or Fe and Co) is a ternary tetragonal compound It has a structure containing the R ₂ T ₁₄ B phase as a main phase and exhibits excellent magnetic properties. In R-T-B permanent magnets, it is known that the coercive force is improved by reducing the crystal grain size of the R ₂ T ₁₄ B phase, which is the main phase. As a method for obtaining an RTB-based permanent magnet having an average crystal grain size of 1 μm or less, an HDDR (Hydrogenation-Disposition-Desorption-Recombination) processing method is known.

  “HDDR” means a process of sequentially performing hydrogenation and disproportionation, dehydrogenation and recombination. The known HDDR treatment is performed, for example, by holding an R-T-B alloy ingot or powder at a temperature of 500 ° C. to 1000 ° C. in a hydrogen atmosphere or a mixed atmosphere of a hydrogen gas and an inert gas. Alternatively, after hydrogen is occluded in the powder (hydrogen occlusion treatment), dehydrogenation treatment is performed at a temperature of 500 ° C. to 1000 ° C. until, for example, a vacuum atmosphere with a hydrogen pressure of 13 Pa or less, or an inert atmosphere with a hydrogen partial pressure of 13 Pa or less. And then cooled.

In the above treatment, the following reaction typically proceeds. That is, by the hydrogen storage treatment, hydrogenation and disproportionation reaction (both are referred to as “HD reaction”. Example of reaction formula: Nd ₂ Fe ₁₄ B + 2H ₂ → 2NdH ₂ + 12Fe + Fe ₂ B) progresses and is fine. An organization is formed. Next, dehydrogenation treatment causes dehydrogenation and recombination reaction (both are referred to as “DR reaction”. Example of reaction formula: 2NdH ₂ + 12Fe + Fe ₂ B → Nd ₂ Fe ₁₄ B + 2H ₂ ) An alloy containing the R ₂ Fe ₁₄ B phase is obtained.

  The RTB-based alloy powder produced by the HDDR process has a large coercive force and magnetic anisotropy. A method for producing an RTB-based alloy powder by HDDR processing is disclosed in, for example, Patent Document 1 and Patent Document 2. According to the HDDR treatment, a permanent magnet powder having a very fine crystal grain size of 0.1 μm to 1 μm can be obtained.

  Furthermore, in recent years, an R-T-B alloy powder finely pulverized to an average particle size of less than 10 μm is molded to produce a green compact, and a porous material produced by subjecting the green compact to HDDR treatment. A bulk magnet (hereinafter referred to as a porous magnet) has been developed and disclosed in Patent Document 3. Since this porous magnet is subjected to HDDR treatment on fine powder having an average particle size of less than 10 μm, the HDDR reaction can proceed in a short time, and as a result, the HDDR reaction can proceed uniformly. Therefore, the squareness of the demagnetization curve is excellent. In Patent Document 3, in the HDDR process, it is desirable to perform the temperature rising process for the HD reaction in a vacuum or an inert atmosphere in order to suppress a decrease in magnetic characteristics due to difficulty in controlling the reaction rate at the time of temperature rising. It is described.

  Patent Document 4 discloses that the permanent magnet powder obtained by the HDDR process can be bulked by a hot molding method such as hot pressing.

In Patent Document 5, when magnet powder is obtained by HDDR treatment, a hydrogen atmosphere of 30 kPa (0.3 atm) or more and 100 kPa (1.0 atm) or less is required before performing HD treatment on the RTB-based alloy powder. Below, it is disclosed to hold at temperatures below 600 ° C. According to this method, hydrogen is contained in the R ₂ T ₁₄ B phase at a temperature at which no HD reaction occurs to obtain R ₂ Fe ₁₄ BH _x (x represents the amount of hydrogen), and then 20 kPa (0.2 atm). ) The temperature is raised to the HD reaction temperature in a hydrogen atmosphere of 60 kPa (0.6 atm) or less and maintained in that state. At this time, by performing hydrogenation and disproportionation, a permanent magnet powder having a high degree of anisotropy after the subsequent DR reaction is obtained.

JP-A-1-132106 JP-A-2-4901 International Publication No. 2007/135981 JP-A-4-253304 JP 2001-76917 A

  According to the description of Patent Document 3, an anisotropic porous magnet is produced by subjecting the green compact molded while applying a magnetic field to HDDR treatment. However, it cannot be said that the degree of orientation is sufficiently large.

  The present invention has been made to solve the above-mentioned problems, and a main object of the present invention is an RTB-based permanent magnet having a higher degree of orientation and a residual magnetic flux density than conventional porous magnets. Is to provide.

The manufacturing method of the R-T-B system permanent magnet of the present invention is a R-T-B system alloy having a 50% volume center particle size of 1 μm or more and less than 10 μm and containing an R ₂ T ₁₄ B phase (R is Nd and / Or a rare earth element containing 50 atomic% or more of Pr, T is Fe, or Fe and Co), a step of molding the powder to produce a green compact, A first heat treatment step in which heat treatment is performed in a hydrogen atmosphere at a temperature of not less than 600 ° C. and not more than 600 ° C., and after the first heat treatment step, heat treatment is performed on the green compact in a hydrogen atmosphere at 650 ° C. to 1000 ° C. Including a second heat treatment step, and a third heat treatment step in which, after the second heat treatment step, the green compact is subjected to heat treatment in a vacuum of 650 ° C. or higher and 1000 ° C. or lower in an inert atmosphere. Start of the second heat treatment process from the end of the process The heating up performed in a vacuum or inert atmosphere.

  In a preferred embodiment, the hydrogen partial pressure in the hydrogen atmosphere in the first heat treatment step is 10 kPa or more and 500 kPa or less.

  In a preferred embodiment, the time from the end of the first heat treatment step to the start of the second heat treatment step is 60 minutes or less.

  In a preferred embodiment, the hydrogen partial pressure in the hydrogen atmosphere in the second heat treatment step is 20 kPa or more and 500 kPa or less.

  In a preferred embodiment, the temperature of the heat treatment in the second heat treatment step and the third heat treatment step is 950 ° C. or lower.

  In a preferred embodiment, the green compact is held in a molded container during the first heat treatment step, the second heat treatment step, and the third heat treatment step.

  An R-T-B system high-density magnet manufacturing method according to the present invention includes a step of preparing an R-T-B system permanent magnet manufactured by any one of the manufacturing methods described above, and the R by hot compression molding. A step of increasing the density of the TB permanent magnet.

  According to the present invention, a green compact obtained by molding an RTB-based alloy powder having a 50% volume center particle size of 1 μm or more and less than 10 μm is first heat-treated in a hydrogen atmosphere at 600 ° C. or less to obtain RT -Hydrogen is occluded in the rare earth-rich phase in the B-based alloy, and then the atmosphere is switched to a vacuum or an inert atmosphere to raise the temperature to the HD reaction temperature. By doing so, it is possible to suppress a decrease in the degree of orientation and squareness due to the reaction non-uniformity in the subsequent HDDR process, and to manufacture a magnet having excellent magnetic properties.

It is a figure which shows the hot press apparatus which can be used suitably by embodiment of this invention. It is a graph which shows the relationship between temperature T1 of a _1st heat treatment process, and residual magnetic flux density _Br . It is a graph which shows the relationship between temperature T1 of a _1st heat treatment process, and coercive force _HcJ . It is a graph which shows the relationship between temperature T1 of a _1st heat treatment process, and orientation degree ( _Br / _Jmax ). It is a graph showing the relationship between the temperatures T ₁ and squareness ratio of the first heat-treatment step (H _k / H _cJ). It is a graph which shows the relationship between temperature T1 of a _1st heat treatment process, and maximum energy product ((BH) _max ). In an embodiment of the present invention, it is a diagram showing an electron microscope image showing the fracture surface of the samples produced in T ₁ = 600 ℃. It is a graph which shows the demagnetization curve of an Example and a comparative example. It is a graph which shows the demagnetization curve of a porous magnet and a high-density magnet. It is a figure which shows the example of the shaping | molding container and press jig which can be used for preparation of a green compact.

  As a result of detailed investigations on the cause of the poor orientation degree of the porous magnet of Patent Document 3, the present inventors have found that in a green compact of an RTB-based alloy powder having a 50% volume center particle size of less than 10 μm. I came up with the need to consider the following points.

C-axis is an axis of easy magnetization of the R ₂ T ₁₄ B phase in the R-T-B magnet thus obtained magnetic anisotropy by HDDR treatment, the c-axis of the HDDR treatment before the R ₂ T ₁₄ B phase It is known that the directions are almost the same. Various considerations have been made on the mechanism for storing the orientation of the R ₂ T ₁₄ B phase. In the structure obtained after the HD treatment, there are typically RH ₂ phase, α-Fe phase, Fe ₂ B phase and the like. This structure is hereinafter referred to as “disproportionated structure”. In this organization, it is considered that there is a region where the direction of the c-axis of the R ₂ T ₁₄ B phase before HDDR processing is passed. This is considered to be the same for the porous magnet of Patent Document 3.

As described above, Patent Document 3 describes the reaction rate control at the time of temperature increase in the HDDR process in which an RTB-based alloy powder is molded to produce a green compact and applied to the green compact. It is described that it is desirable to perform the temperature raising step for the HD reaction in a vacuum or in an inert atmosphere in order to suppress a decrease in magnetic characteristics due to difficulty. However, when the green compact is heated in vacuum or in an inert atmosphere, it exists in the rare earth-rich phase (R ₂ T ₁₄ B phase grain boundary portion) in the R-T-B alloy powder, and R is 50 atoms. % Or more) (for example, in the Nd—Fe—B ternary system, the rare earth-rich phase dissolves at the eutectic temperature of 680 ° C.), a liquid phase is formed, and R ₂ T ₁₄ There is a possibility of dissolving a part of the B phase.

Thereafter, in the ordinary HD reaction in the prior art, both the R ₂ T ₁₄ B phase and the liquid phase react with hydrogen and decompose into RH ₂ phase, α-Fe phase, Fe ₂ B phase, etc. Form a chemical structure. At this time, the structure formed by the reaction between the component in which the R ₂ T ₁₄ B phase is dissolved at least during the temperature rise in the liquid phase and the hydrogen is aligned with the c-axis direction of the R ₂ T ₁₄ B phase by molding in a magnetic field. The c-axis direction of the R ₂ T ₁₄ B phase recombined by the subsequent DR reaction is the same as the c-axis direction of the R ₂ T ₁₄ B phase formed by magnetic field molding. The orientation may be irrelevant to the direction, and the degree of orientation as a whole may be lower than that before the HDDR process.

In addition, when the RH ₂ phase, α-Fe phase, and Fe ₂ B phase are decomposed and produced from any of the R ₂ T ₁₄ B phase and the liquid phase, the structure formed by the HD reaction becomes uneven. As a result, it is considered that the variation in coercive force increases and the squareness deteriorates.

Therefore, the present inventors have found that the deterioration of the degree of orientation and squareness caused by the HDDR treatment of the green compact of the R-T-B type alloy powder is caused by the fact that the liquid phase produced in the temperature rising process before the HD reaction is R _{2 The} main cause is to dissolve a part of the T ₁₄ B phase. If the formation of this liquid phase can be suppressed, the deterioration of the orientation degree and the squareness can be prevented. -Occurrence of hydrogen in the rare earth-rich phase in the TB-based alloy to form a rare earth hydride having a melting point higher than the HDDR processing temperature (RH _x : x represents the amount of hydrogen), thereby increasing the liquid in the temperature rising process. The R-T-B alloy green compact is hydrogenated under a hydrogen atmosphere of 600 ° C. or less, and heated to the HD processing temperature under the hydrogen atmosphere of the HD reaction. , HD reaction, then DR treatment, porous magnet I tried to make. However, contrary to expectation, the degree of orientation and squareness of the magnet obtained were deteriorated.

  The present inventors considered the cause of the deterioration of the degree of orientation and squareness of the porous magnet that had been subjected to the hydrogenation process at a temperature of 600 ° C. or less before the HD reaction, and was adopted in the manufacturing process of the porous magnet. In the compact of R-T-B type alloy powder having a 50% volume center particle size of less than 10 μm, the surface area of each particle of the powder in contact with hydrogen gas is an alloy powder particle for producing a conventional HDDR magnetic powder HD that occurs during temperature rise by performing the temperature raising process from the hydrogenation process at a low temperature of 600 ° C. or less to the HD process in the same hydrogen atmosphere as the HD process at least 100 times larger than (about 50 μm to 10 mm). The progress of the reaction is remarkable as compared with the conventional manufacturing process of HDDR magnetic powder, and this is considered to be one factor that causes deterioration of the degree of orientation contrary to the initial expectation.

  In view of the above, the present inventors have set the degree of orientation and squareness by setting the atmosphere of the temperature raising step to a vacuum or an inert atmosphere in order to suppress inappropriate HD reaction in the temperature raising step. The present inventors have found that an R-T-B type porous magnet having excellent resistance can be obtained, and have completed the present invention.

  Hereinafter, preferred embodiments of the method for producing an R-T-B permanent magnet according to the present invention will be described in detail.

<Raw material alloy>
First, an RTB-based alloy (raw material alloy) including an R ₂ T ₁₄ B phase that is a hard magnetic phase as a main phase is prepared. Here, “R” is a rare earth element and contains Nd and / or Pr by 50 atomic% or more. The rare earth element R in this specification may contain yttrium (Y). T is Fe or Fe and Co. This RTB-based alloy (raw material alloy) preferably contains 50% or more of the R ₂ T ₁₄ B phase by volume. Most of the rare earth element R contained in the raw material alloy constitutes the R ₂ T ₁₄ B phase and the rare earth rich phase, but a part constitutes R ₂ O ₃ and other phases.

  The composition ratio of the rare earth element R is desirably 12 atom% or more and 30 atom% or less, and more desirably 13 atom% or more and 18 atom% or less of the entire raw material alloy. Moreover, the coercive force can be improved by setting a part of R to Dy and / or Tb. Further, it is more preferable that the composition ratio of the rare earth element R is 15 atomic% or less because it is easy to remove from the mold after hot pressing.

  The composition ratio of B is preferably 3 atomic percent or more and 15 atomic percent or less, more preferably 5 atomic percent or more and 8 atomic percent or less, and further preferably 5.5 atomic percent or more and 7.5 atomic percent or less. A part of B may be substituted with C, but the amount of substitution is preferably 10 atomic% or less with respect to the amount of B before substitution.

  “T” occupies the remainder and is Fe or Co substituted for Fe and part of Fe. The amount of substitution is desirably 50 atomic% or less of the entire T. Further, the total amount of Co with respect to the entire raw material alloy is preferably 20 atomic% or less, and more preferably 5 atomic% or less from the viewpoint of cost and the like. High magnetic properties can be obtained even when Co is not contained at all, but more stable magnetic properties can be obtained when Co of 0.5 atomic% or more is contained.

  In order to obtain effects such as improvement of magnetic characteristics, elements such as Al, Ti, V, Cr, Ga, Nb, Mo, In, Sn, Hf, Ta, W, Cu, Si, Zr, and Ni may be added as appropriate. Good. However, since an increase in the amount of addition causes a decrease in saturation magnetization in particular, the total amount is preferably 10 atomic% or less. The raw material alloy may contain inevitable impurities.

  The raw material alloy is preferably produced by a strip casting method that can reduce the amount of α-Fe phase that adversely affects magnetic properties, but can also be produced by a book mold method, a centrifugal casting method, an atomizing method, or the like. it can. For the purpose of homogenizing the structure of the raw material alloy, heat treatment may be performed on the raw material alloy before pulverization. Such heat treatment can be performed in a vacuum or inert atmosphere, typically at a temperature of 1000 ° C. or higher.

<Crushing>
Next, the raw material powder is produced by pulverizing the raw material alloy by a known method. In this embodiment, first, a raw material alloy is coarsely pulverized using a mechanical crushing method such as a jaw crusher or a hydrogen occlusion pulverizing method to produce a coarsely pulverized powder having a size of about 50 μm to 1000 μm. The coarsely pulverized powder is finely pulverized by a jet mill or the like to produce a raw material powder typically having a 50% volume center particle size of 1 μm or more and less than 10 μm. The 50% volume center particle size (D ₅₀ ) can be measured by a gas flow dispersion type laser diffraction method.

  From the viewpoint of handling, the 50% volume center particle size of the raw material powder is preferably 1 μm or more. This is because when the 50% volume center particle size is less than 1 μm, the raw material powder easily reacts with oxygen in the air atmosphere, increasing the risk of heat generation and ignition due to oxidation. In order to make handling easier, it is preferable to set the 50% volume center particle size to 3 μm or more. From the viewpoint of improving the mechanical strength of the molded body, the preferable upper limit of the 50% volume center particle size is 9 μm, and the more preferable upper limit is 8 μm.

<Green compact>
Next, the raw material alloy powder is molded to produce a green compact. The step of molding the green compact is preferably performed in a magnetic field of 0.4 MA / m to 16 MA / m (static magnetic field, pulsed magnetic field, etc.) by applying a pressure of 10 MPa to 200 MPa. Molding can be performed by a known powder press apparatus. Compact density (compact density) when removed from the powder press device is 3.5g / cm ³ ~5.2g / cm ³ order.

Further, the molding may be performed by filling a raw material alloy powder in a container as shown in FIG. 10 or JP-A-7-153612, and then applying a pressure of 0.05 MPa to 10 MPa to produce a green compact. Good. In this case, the HDDR process is performed with the green compact in the container. By forming in a container, handling becomes easy even when the green compact density is low. By reducing the density of the green compact, internal stress generated by volume expansion accompanying hydrogen occlusion can be relieved in the green compact in subsequent HDDR processing, so that the occurrence of cracks can be suppressed. Compact density in this case is about ^{3.0g / cm 3 ~4.0g / cm 3} .

  You may perform said shaping | molding process, without applying a magnetic field. When magnetic field orientation is not performed, an isotropic porous magnet is finally obtained. However, in order to obtain higher magnetic characteristics, it is desirable to execute a molding process while performing magnetic field orientation and finally obtain an anisotropic porous magnet.

  It is desirable to perform the raw material alloy pulverization step and the green compact molding step while suppressing oxidation of the raw material powder. In order to suppress the oxidation of the raw material powder, it is desirable to carry out each process and the handling between the processes in an inert atmosphere in which the amount of oxygen is suppressed as much as possible. The amount of oxygen in the green compact before the DR treatment is preferably suppressed to 1% by mass or less, and more preferably to 0.6% by mass or less.

<HDDR processing>
Next, the HDDR process is performed on the green compact obtained by the molding step. In the present embodiment, the HDDR process includes three steps of a first heat treatment step, a second heat treatment step, and a third heat treatment step.

The first heat treatment step is a step of subjecting the green compact molded using the raw material powder to a heat treatment at a temperature of 250 ° C. or higher and 600 ° C. or lower in a hydrogen atmosphere. In the first heat treatment step, but does not occur HD reaction R ₂ T ₁₄ B phase, hydrogen is occluded between the crystal lattice of the R ₂ T ₁₄ B phase. Further, the rare earth-rich phase existing between the crystal grains of the R ₂ T ₁₄ B phase is hydrogenated and exists mainly as a hydride of R. The hydrogenated rare earth-rich phase exists mainly as a rare earth hydride RH _x , and its melting point is higher than the heat treatment temperature in the second heat treatment step (HD step). Therefore, by performing the first heat treatment step, the liquid phase is generated before the second heat treatment step, the R ₂ T ₁₄ B phase is dissolved, and the magnetic properties, particularly the degree of orientation and the squareness are deteriorated. Suppress.

In the first heat treatment step, hydrogen is occluded between the crystal lattice of the R ₂ T ₁₄ B phase, that the volume of the R ₂ T ₁₄ B phase expands approximately 2%, the lattice constant determined from X-ray powder diffraction measurement Confirmed from. Therefore, depending on the size and shape of the green compact, there is a possibility that the green compact may crack due to internal stress caused by volume expansion. In order to suppress this crack, for example, the HDDR process may be performed using a restraining jig that suppresses the volume expansion of the green compact, such as a container hermetically sealed to allow hydrogen to pass through.

The heat treatment temperature of the first heat treatment step, the thus occurred HD reaction R ₂ T ₁₄ B phase, because the degree of orientation deteriorates the difficulty of reaction rate control, the temperature at which HD reaction R ₂ T ₁₄ B phase will occur You need to do the following:

When the hydrogen absorption behavior was investigated while raising the green compact of the RTB-based alloy powder in a hydrogen atmosphere of 100 kPa, it was confirmed that hydrogen was rapidly absorbed at 610 ° C to 700 ° C. Therefore, when the constituent phase was investigated by X-ray diffraction measurement after hydrogenating the green compact of the RTB-based alloy powder at 700 ° C., the R ₂ T ₁₄ B phase was disproportionated and the RH _x phase It was confirmed that it was decomposed into an α-Fe phase and an Fe ₂ B phase. Therefore, this hydrogen absorption is considered to be due to the HD reaction of the R ₂ T ₁₄ B phase. Further, when the constituent phase was investigated by X-ray diffraction measurement after hydrogenating the green compact of the RTB-based alloy powder at 600 ° C. lower than the reaction temperature, the HD reaction of the R ₂ T ₁₄ B phase was It was confirmed that the rare earth-rich phase was mainly the RH _x phase. Therefore, the heat treatment temperature in the first heat treatment step for converting the rare earth-rich phase to the rare earth hydride RH _x that is a high melting point compound without disproportionating the R ₂ T ₁₄ B phase is 600 ° C. or less.

  In order to improve the reaction rate of hydrogenation of the rare earth-rich phase, the heat treatment temperature is 250 ° C. or higher and desirably 400 ° C. or higher. Moreover, in order to fully advance hydrogenation, you may hold | maintain for a predetermined time, after heating up to the predetermined temperature of 600 degrees C or less, and it is desirable that the holding time is 120 minutes or less. Even if the heat treatment is carried out for more than 120 minutes, no further effect is seen and the productivity is deteriorated.

  Moreover, the hydrogen partial pressure of the atmosphere in the first heat treatment step is 10 kPa or more. Moreover, if it is 50 kPa or more, since hydrogenation of a rare earth rich phase will fully advance, it is preferable. In addition, when the hydrogen partial pressure exceeds 500 kPa, a special apparatus is required for the treatment, and therefore, it is preferably 500 kPa or less. A more preferable hydrogen partial pressure is 150 kPa or less. When the hydrogen partial pressure exceeds 150 kPa, hydrogen occlusion occurs abruptly, and the green compact may crack due to volume expansion accompanying hydrogen occlusion.

Next, the atmosphere is switched to a vacuum (1.3 Pa or less) or an inert atmosphere, and the temperature is raised to the heat treatment temperature of the second heat treatment step. If hydrogen gas is present in the temperature-raising atmosphere, the hydrogenation and disproportionation reactions of the R ₂ T ₁₄ B phase will proceed, making it difficult to control the reaction rate and possibly resulting in a decrease in magnetic properties. However, in the production of conventional HDDR magnetic powder (the average particle diameter of the raw material alloy powder is 50 μm to 10 mm) such as Patent Document 5, there is only one region that is disproportionated by the HD reaction caused by the presence of hydrogen gas. Under a suitable heating rate, even if a certain amount of hydrogen is present, only a very small area of the surface is hydrogenated and disproportionated during the heating, and the degree of orientation after HDDR treatment. The impact on is not so obvious. On the other hand, in the production method of the present invention, a fine powder having a 50% volume center particle size of less than 10 μm is targeted, the surface area is more than 100 times larger than that of the conventional HDDR magnetic powder, and hydrogen exists in the atmosphere during temperature rise. The progress of the HD reaction caused by this is remarkable as compared with the production of conventional HDDR magnetic powder, and as a result, a decrease in the degree of orientation after the HDDR treatment becomes obvious. In the present specification, an inert gas means a gas that does not react with rare earth elements such as argon and / or helium. If the temperature raising step is performed in a nitrogen atmosphere, the RTB-based alloy powder may be nitrided, which is not preferable.

On the other hand, if the temperature raising time is too long, dehydrogenation reaction of the RH _x phase once generated by the first heat treatment process occurs, and as a result, a liquid phase is generated and reacted with the main phase R ₂ T ₁₄ B phase. In addition, since the degree of orientation and squareness of the obtained magnet may be deteriorated, the temperature raising time (time from the end of the first heat treatment step to the start of the second heat treatment step) is 60 minutes or less. It is desirable to set it to 30 minutes or less, more desirably 10 minutes or less. In consideration of the time required for the replacement of the atmospheric gas, the temperature increase capability of the apparatus, etc., the temperature increase time is usually 1 minute or more.

Next, the second heat treatment step to be performed is a step of obtaining a disproportionated structure by HD reaction of the R ₂ T ₁₄ B phase in a hydrogen atmosphere. At this time, the magnetic anisotropy of the finally obtained magnet can be increased by appropriately controlling the temperature and the hydrogen partial pressure in the second heat treatment step.

The temperature of the second heat treatment step is 650 ° C. or higher and 1000 ° C. or lower. Below 650 ° C., it takes too much time to complete disproportionation. Further, when the temperature exceeds 1000 ° C., the disproportionated structure becomes coarse, and the texture of the R ₂ T ₁₄ B phase obtained by the subsequent third heat treatment step becomes coarse, resulting in a decrease in magnetic properties, particularly coercive force. From the viewpoint of suppressing grain growth, the temperature of the second treatment step is preferably set to 950 ° C. or lower, and more preferably set to 900 ° C. or lower.

The hydrogen partial pressure in the second heat treatment step is desirably 20 kPa or more. When the hydrogen partial pressure is less than 20 kPa, it takes too much time for the disproportionation of the R ₂ T ₁₄ B phase to proceed sufficiently, which may lead to a decrease in productivity. In addition, when the hydrogen partial pressure exceeds 500 kPa, a special apparatus is required for the treatment, and therefore, it is preferably 500 kPa or less. A more preferable hydrogen partial pressure is 150 kPa or less. When the hydrogen partial pressure exceeds 150 kPa, hydrogen occlusion occurs abruptly, and the green compact may crack due to volume expansion accompanying hydrogen occlusion.

The time required for the second heat treatment step is desirably 10 minutes or more and 5 hours or less. If it is less than 10 minutes, disproportionation of the R ₂ T ₁₄ B phase may not proceed sufficiently. Further, when the time exceeds 5 hours, the disproportionated structure becomes coarse, and the recombination structure after the third heat treatment step becomes coarse, which may cause a decrease in magnetic properties, particularly coercive force. More desirably, it is 15 minutes or more and 2 hours or less.

Next, in the third heat treatment step to be performed, the dehydration reaction of the RH _x phase is caused by holding at 650 ° C. or more and 1000 ° C. or less in a vacuum (1.3 Pa or less) or an inert atmosphere, and the R ₂ T ₁₄ B phase is regenerated. It is produced by a binding reaction. In addition, the process of a dehydrogenation reaction can also be controlled by changing the atmosphere of a 3rd heat treatment process in steps. For example, after controlling the absolute pressure or hydrogen partial pressure in an atmosphere of 1 kPa to 20 kPa for a time of 5 minutes or more and 5 hours or less, H _cJ is controlled by maintaining the vacuum at 650 ° C. or more and 1000 ° C. or less in an inert atmosphere. be able to.

The R ₂ T ₁₄ B phase generated in the third heat treatment step typically forms a texture having an average crystal grain size of 0.1 μm or more and 1.0 μm or less. In addition, a dehydrogenation reaction from RH _x not used for recombination occurs, and a liquid phase rich in R is generated. In this liquid phase, the R′-M compound remaining at the time of HD treatment is dissolved, and enters the crystal grain boundary of the R ₂ T ₁₄ B phase. As a result, a nonmagnetic grain boundary phase (rare earth rich phase) is formed, and the individual R ₂ T ₁₄ B phases are magnetically isolated, so that a coercive force is developed. Further, a part of the M element diffuses into the R ₂ T ₁₄ B phase, thereby improving the coercive force. At this time, a sintering reaction also occurs at the same time, resulting in a porous permanent magnet. From the viewpoint of suppressing grain growth, the temperature of the third treatment step is preferably set to 950 ° C. or lower, and may be set to 900 ° C. or lower.

The temperature of the third heat treatment step is 650 ° C. or higher and 1000 ° C. or lower. Below 650 ° C., it takes too much time to complete dehydrogenation. Further, when the temperature exceeds 1000 ° C., the recombined R ₂ T ₁₄
Since the B phase grows crystal grains, the magnetic properties, particularly the coercive force, are reduced. The time required for the third heat treatment step is preferably 5 minutes or more and 10 hours or less, and more preferably 10 minutes or more and 2 hours or less.

<Porous magnet>
By the HDDR treatment, a porous magnet having a density of 3.5 g / cm ³ or more and 7.0 g / cm ³ or less is obtained. In this porous magnet, the easy magnetization axis of the powder particles is oriented in a predetermined direction before the second heat treatment step, so that the fine Nd ₂ Fe ₁₄ B type crystal phase in the texture formed by the HDDR process is obtained. Can be oriented in a predetermined direction throughout the magnet.

In this porous magnet, there is a void having a major axis of about 10 μm communicating with the three-dimensional network between the powder particles bonded to each other in the HDDR processing step. The individual powder particles constituting the green compact are combined with the adjacent powder particles by the HDDR process to form a three-dimensional structure exhibiting rigidity, and fine Nd ₂ Fe ₁₄ B in each powder particle. A texture of the type crystal phase is formed.

The density of the R-T-B type porous magnet of the present invention is 3.5 g / cm ³ or more and 7.0 g / cm ³ or less, but the particles are bonded to each other even when there are gaps between the powder particles. Demonstrate sufficient mechanical strength and excellent magnetic properties.

  In this embodiment, since the HDDR process is performed on the green compact after the molding process, the powder molding is not performed after the HDDR process. For this reason, it does not occur after HDDR processing that the magnetic powder is crushed by pressurization for molding, and high magnetic characteristics can be obtained compared to a bonded magnet that compresses HDDR powder.

<Hot compression molding of porous magnet>
The porous magnet obtained by the above method can be used as a bulk permanent magnet as it is, but it is further densified by using hot compression molding such as a hot press method, and the average crystal A high-density magnet having a texture of R ₂ T ₁₄ B phase with a particle size of 0.1 μm or more and 1 μm or less can be obtained.

  An example of a specific embodiment will be shown below for densification by hot compression molding. Hot compression on the porous magnet can be performed using a known hot compression technique. For example, hot compression molding such as hot pressing, SPS (spark plasma sintering), HIP, and hot rolling can be performed. Especially, the hot press and SPS which are easy to obtain a desired shape can be used suitably. Hereinafter, a procedure for performing hot pressing will be described.

  In the present embodiment, a hot press apparatus having the configuration shown in FIG. 1 is used. This apparatus includes a die (die) 27 having an opening in the center, an upper punch 28a and a lower punch 28b for pressurizing a porous magnet, and drive units 30a and 30b for raising and lowering these punches 28a and 28b. I have.

  A porous magnet (indicated by reference numeral “10” in FIG. 1) produced by the method described above is loaded into the mold 27 shown in FIG. At this time, it is desirable to perform loading so that the orientation direction and the pressing direction coincide. The mold 27 and the punches 28a and 28b are formed of a material that can withstand the heating temperature and the applied pressure in the atmosphere gas to be used. As such a material, carbon or cemented carbide such as tungsten carbide is desirable. In addition, the anisotropy can be increased by setting the outer dimension of the porous magnet 10 to be smaller than the opening dimension of the mold 27. Next, the mold 27 loaded with the porous magnet 10 is set in a hot press apparatus. The hot press apparatus preferably includes a chamber 26 that can be controlled to a vacuum (1.3 Pa or less) or an inert atmosphere. In the chamber 26, for example, a heating device such as a carbon heater by resistance heating and a cylinder for pressurizing and compressing the porous magnet are provided.

  After filling the chamber 26 with a vacuum or an inert atmosphere, the mold 27 is heated by a heating device, and the temperature of the porous magnet 10 loaded in the mold 27 is increased to 600 ° C. to 900 ° C. The porous magnet 10 is pressurized with a pressure P of 294 MPa. It is desirable that the pressurization to the porous magnet 10 is started after the temperature of the mold 27 reaches a set level. If the mold temperature is not sufficiently high, the porous magnet may be cracked during pressurization, or the degree of orientation of the resulting high-density magnet may deteriorate. While maintaining the pressure at 600 ° C. to 900 ° C. for 10 minutes or more while cooling, it is cooled. After the magnet, which has been densified by heat compression, is cooled to a low temperature (about 100 ° C. or less) that does not oxidize due to contact with the atmosphere, the magnet of this embodiment is taken out of the chamber. Thus, the RTB-based high density magnet of the present embodiment can be obtained from the porous magnet.

  The density of the magnet thus obtained reaches 90% or more of the true density. In addition, according to the present embodiment, in the final crystal phase texture, the crystal grains in which the ratio b / a of the shortest particle diameter a to the longest particle diameter b of each crystal grain is less than 2 are 50 of the total crystal grains. It exists by volume% or more. In this respect, the magnet of the present embodiment is greatly different from the conventional anisotropic bulk magnet by hot plastic working described in, for example, Japanese Patent Laid-Open No. 02-39503. In such a crystal structure of a magnet, flat crystal grains in which the ratio b / a between the shortest particle diameter a and the longest particle diameter b exceeds 2 are dominant.

(Experimental example 1)
As a raw material alloy powder, an alloy powder having the composition shown in Table 1 below was prepared, and a porous magnet was manufactured by the manufacturing method of the above-described embodiment. Hereinafter, a method for producing a porous magnet in this experimental example will be described.

  First, a rapidly solidified alloy having the composition shown in Table 1 was produced by strip casting. The obtained rapidly solidified alloy was coarsely pulverized into a powder having a particle size of 425 μm or less by the hydrogen occlusion / disintegration method, and then the coarse powder was finely pulverized using a jet mill to obtain a 50% volume center particle size of 4.2 to 4.5 μm. A fine powder was obtained. The 50% volume center particle size was measured by an air flow dispersion type laser diffraction particle size distribution measuring device (manufactured by Sympatec, HEROS / RODOS, hereinafter all 50% volume center particle sizes in this example were measured with the same device). .

Next, this powder was filled in a die of a press machine, and a green compact was produced by applying a pressure of 76 MPa in a direction parallel to the magnetic field in a magnetic field of 0.64 MA / m. The density of the green compact was calculated to be 4.2 to 4.5 g / cm ³ based on the size and weight.

Next, HDDR processing was performed on the green compact. Specifically, the green compact is heated to a temperature T ₁ = 200, 250, 300, 400, 600, 700 (° C.) at a heating rate of 14 ° C./min in a hydrogen gas of 100 kPa for 30 minutes. The first heat treatment step was performed. Then, after switching the atmosphere to 100 kPa argon flow, the temperature was raised to 840 ° C. at a rate of 14 ° C./min, and then the atmosphere was switched to 100 kPa hydrogen flow, and then maintained at 840 ° C. for 2 hours. The second heat treatment step was performed. Then, it hold | maintained for 1 hour in the argon air pressure-reduced to 5.3 kPa with 840 degreeC, and performed the 3rd heat treatment process. Next, the sample was cooled to room temperature in a 100 kPa argon stream to prepare a sample.

When the density was calculated from the size and weight of the prepared sample, it was 5.4 to 6.2 g / cm ³ .

The prepared sample was magnetized with a pulse magnetic field of 3.2 MA / m, and then the magnetic properties were measured with a BH tracer (device name: MTR-1412 (manufactured by Metron Engineering Co., Ltd.)). 2 shows temperature T ₁ and residual magnetic flux density B _r , FIG. 3 shows T ₁ and coercive force H _cJ , FIG. 4 shows T ₁ and orientation (B _r / J _max ), and FIG. 5 shows T ₁ and squareness ratio ( H _k / H _cJ ), FIG. 6 shows the relationship between T ₁ and the maximum energy product ((BH) _max ). Note that J _max is the maximum measured value of the magnetization of the sample when an external magnetic field is applied up to 1.6 MA / m in the magnetization direction of the magnetized sample. The larger the _Br / J _max , the better the degree of orientation. ing. H _k is the value of the external magnetic field when the magnetization is B _r × 0.9, and the greater the H _k / H _cJ , the better the squareness of the demagnetization curve.

  2 to 6 also show the result without the first heat treatment step as a comparative example. The sample without the first heat treatment step was heated up to 840 ° C./min in a 100 kPa argon flow at 14 ° C./min, and then the atmosphere was switched to a 100 kPa hydrogen flow and held at 840 ° C. for 2 hours. A second heat treatment step was performed, and then the atmosphere was maintained at 840 ° C. for 1 hour in a 100 kPa argon flow to perform a third heat treatment step, and then cooled to room temperature in a 100 kPa argon flow.

As is clear from FIGS. 4 and 5, the sample having T ₁ of 250 ° C. or more and 600 ° C. or less is superior in orientation degree and squareness compared to the sample without the first heat treatment step, and T ₁ is 400. Samples manufactured at a temperature of from 600 ° C. to 600 ° C. are particularly excellent in the degree of orientation and squareness. In the sample prepared at T ₁ of 700 ° C., the hydrogenation / disproportionation reaction of the R ₂ T ₁₄ B phase proceeds in the process of raising the temperature up to 700 ° C. in a hydrogen stream. Both sexes show small values.

FIG. 7 is an SEM photograph showing a fracture surface of a sample prepared for Alloy A3 under the condition of T ₁ = 600 ° C. The pores present in the sample as seen in FIG. 7 are voids that exist between the powder particles that are bonded to each other in the HDDR processing step, and communicate with each other in a three-dimensional network. The individual powder particles constituting the green compact are combined with adjacent powder particles by the HDDR process to form a three-dimensional structure exhibiting rigidity, and within each powder particle, fine R ₂ T ₁₄ B-phase texture is formed.

Further, as an example of the demagnetization curve of the manufactured sample, FIG. 8 shows a demagnetization curve of the sample manufactured for A2 at T ₁ = 600 ° C. in the above manufacturing method. As a comparative example, a demagnetization curve of a sample without the first heat treatment step manufactured by the above manufacturing method is also shown. As is clear from FIG. 8, the demagnetization curve of the sample of the comparative example has very poor squareness, but a magnet having excellent squareness of the demagnetization curve is produced by performing the first heat treatment step of the present invention. can do.

(Experimental example 2)
The green compacts of the alloys A2 and A5 were produced by the same method as described in Experimental Example 1. Next, HDDR processing was performed on the green compact. Specifically, the green compact was heated to 600 ° C. at a heating rate of 14 ° C./min in a hydrogen gas of 100 kPa and held for 30 minutes to perform the first heat treatment step. Then, after switching the atmosphere to the atmosphere gas flow shown in Table 2 (Argon gas flow with a total pressure of 100 kPa, or a hydrogen / argon mixed gas flow with a total pressure of 100 kPa and a hydrogen partial pressure of 50 kPa), 840 The temperature was raised to 14 ° C. at a rate of 14 ° C./min. Next, after the atmosphere was switched to a hydrogen flow with a total pressure of 100 kPa, the second heat treatment step was performed while maintaining 840 ° C. for 2 hours. In addition, in the case where the atmosphere from the end of the first heat treatment step to the start of the second heat treatment step is performed with a hydrogen / argon mixed gas flow with a hydrogen partial pressure of 50 kPa, the sample in which the second heat treatment step is performed as it is Also made. Then, it hold | maintained for 1 hour in the argon air pressure-reduced to 5.3 kPa with 840 degreeC, and performed the 3rd heat treatment process. Next, the sample was cooled to room temperature in a 100 kPa argon stream to prepare a sample.

The prepared sample was magnetized with a pulse magnetic field of 3.2 MA / m, and then the magnetic properties were measured with a BH tracer (device name: MTR-1412 (manufactured by Metron Engineering Co., Ltd.)). Table 2 shows the density calculated from the measurement results and the dimensions and weights of the prepared samples. As can be seen from Table 2, good magnetic properties are obtained when the hydrogen partial pressure P ₂ of the gas flowing from the end of the first heat treatment step to the start of the second heat treatment step is 0 kPa, but when P ₂ is 50 kPa, Degree of orientation and squareness deteriorate. This is presumably because part of the HD reaction occurred during the temperature increase from the end of the first heat treatment step to the start of the second heat treatment step.

  Here, P2 is the hydrogen partial pressure of gas flowing from the end of the first heat treatment step to the start of the second heat treatment step, and P3 is the hydrogen partial pressure in the second heat treatment step.

[Reference example]
In addition, as a reference example, the influence of the atmosphere from the end of the first heat treatment process to the start of the second heat treatment process was investigated for the coarsely pulverized raw material alloy powder used in the conventional HDDR magnetic powder manufacturing process. .

  The alloy shown in Table 3 as a raw material alloy was produced by centrifugal casting, and the same HDDR treatment as in Experimental Example 2 was performed on the powder coarsely pulverized to a particle size of 300 μm or less by the hydrogen storage / disintegration method.

  The HDDR-treated powder was put into a cylindrical holder and fixed with paraffin while being oriented in a magnetic field of 800 kA / m. The obtained sample was magnetized with a pulse magnetic field of 4.8 MA / m, and the magnetic properties were measured with a vibrating sample magnetometer (VSM: device name VSM5 (manufactured by Toei Kogyo Co., Ltd.)). Note that demagnetizing field correction is not performed. Table 4 shows the measurement results.

B _r and J _max in the table, the true density of the samples was determined by calculation as being 7.6 g / cm ^3. Note that J _max is a value obtained by correcting the measured value of the magnetization of the sample when an external magnetic field is applied up to 1.6 MA / m in the magnetization direction of the magnetized sample in consideration of the mirror image effect in the VSM measurement. .

  As can be seen from Table 4, for the powder coarsely pulverized to a particle size of 300 μm or less, the hydrogen partial pressure during the temperature increase from the end of the first heat treatment step to the start of the second heat treatment step is either 0 kPa or 50 kPa. However, the degree of orientation of the raw material alloy is different from the tendency of the example of the present invention in which the 50% volume center particle diameter is less than 10 μm. This is because, as described above, the RTB-based alloy powder of the present invention has a small 50% volume center particle size of less than 10 μm, which increases the surface area, resulting in the influence of the HD reaction that occurs during temperature rise. It is thought that was manifested.

(Experimental example 3)
The green compacts of the alloys A2 and A5 were produced by the same method as described in Experimental Example 1. Next, HDDR processing was performed on the green compact. Specifically, the green compact has a total pressure of 100 kPa and a hydrogen partial pressure of P ₁ = 0, 10, 20, 50, 100 kPa. The first heat treatment step was performed by raising the temperature at a temperature rise rate of and holding for 30 minutes.

  Thereafter, the atmosphere was switched to an argon gas flow of 100 kPa, and the temperature was increased to 840 ° C. at a temperature increase rate of 14 ° C./min. Next, after switching the atmosphere to a hydrogen gas flow of 100 kPa, the second heat treatment step was performed while maintaining 840 ° C. for 2 hours. Then, it hold | maintained for 1 hour in the argon air pressure-reduced to 5.3 kPa with 840 degreeC, and performed the 3rd heat treatment process. Next, the sample was cooled to room temperature in a 100 kPa argon stream to prepare a sample.

The prepared sample was magnetized with a pulse magnetic field of 3.2 MA / m, and then the magnetic properties were measured with a BH tracer (device name: MTR-1412 (manufactured by Metron Engineering Co., Ltd.)). Table 5 shows the measurement results. As can be seen from Table 5, good magnetic properties can be obtained when the hydrogen partial pressure P ₁ of the gas flowing in the first heat treatment step is 10 kPa or more.

(Experimental example 4)
A rapidly solidified alloy having the composition shown in Table 6 was produced by strip casting. The obtained rapidly solidified alloy was coarsely pulverized into a powder having a particle size of 425 μm or less by the hydrogen occlusion / disintegration method, and then the coarse powder was finely pulverized using a jet mill to obtain a 50% volume center particle size of 4.2 to 4.5 μm. A fine powder was obtained.

Next, this powder was filled in a mold of a press machine, and a pressure of 72 MPa was applied in a direction perpendicular to the magnetic field in a magnetic field of 1.2 MA / m to produce a green compact. The density of the green compact was 4.0 to 4.2 g / cm ³ when calculated based on dimensions and weight.

  Next, HDDR processing was performed on the green compact. Specifically, the green compact was heated to 600 ° C. at a heating rate of 14 ° C./min in a hydrogen gas of 100 kPa and held for 30 minutes to perform the first heat treatment step. Then, after switching the atmosphere to 100 kPa argon flow, the temperature was increased to 860 ° C. at a rate of 14 ° C./min, and then the atmosphere was switched to 100 kPa hydrogen flow, and then maintained at 860 ° C. for 2 hours. The second heat treatment step was performed. Then, it hold | maintained for 1 hour in the argon air pressure-reduced to 5.3 kPa with 860 degreeC, and performed the 3rd heat treatment process. Next, the sample was cooled to room temperature in a 100 kPa argon stream to prepare a sample.

  Moreover, the sample of the result without a 1st heat treatment process was also produced as a comparative example. The sample without the first heat treatment step was heated up to 840 ° C./min in a 100 kPa argon flow at 14 ° C./min, and then the atmosphere was switched to a 100 kPa hydrogen flow and held at 840 ° C. for 2 hours. A second heat treatment step was performed, and then the atmosphere was maintained at 840 ° C. for 1 hour in a 100 kPa argon flow to perform a third heat treatment step, and then cooled to room temperature in a 100 kPa argon flow.

  The prepared sample was magnetized with a pulse magnetic field of 3.2 MA / m, and then the magnetic properties were measured with a BH tracer (device name: MTR-1412 (manufactured by Metron Engineering Co., Ltd.)). Table 7 shows the measurement results.

  As can be seen from Table 7, the degree of orientation and squareness were improved by introducing the first heat treatment step.

(Experimental example 5)
By heating the porous magnet of the Example of A6 composition prepared in Experimental Example 4 to 800 ° C. in a cemented carbide mold and performing hot compression treatment (hot pressing) for 30 minutes at a pressure of 50 MPa. A high density magnet having a density of 7.58 g / cm ³ was obtained.

  The prepared sample was magnetized with a pulse magnetic field of 3.2 MA / m, and then the magnetic properties were measured with a BH tracer (device name: MTR-1412 (manufactured by Metron Engineering Co., Ltd.)). The obtained results are shown in FIG. As can be seen from the figure, good magnetic properties were obtained for both the porous magnet and the high-density magnet. It was also confirmed that the squareness of the demagnetization curve was improved while the coercive force hardly changed by hot pressing.

(Experimental example 6)
First, an alloy A10 having the composition shown in Table 6 was produced by a centrifugal casting method. The obtained alloy A was subjected to homogenization heat treatment at 1110 ° C. for 480 minutes in an argon reduced pressure atmosphere of 4.2 kPa. Thereafter, the powder was coarsely pulverized to a particle size of 425 μm or less by the hydrogen storage / disintegration method, and then the coarse powder was finely pulverized using a jet mill to obtain a fine powder having a 50% volume center particle size of 5.1 μm. Next, this fine powder was filled in a die of a press machine, and a green compact was produced by applying a pressure of 32 MPa in a direction perpendicular to the magnetic field in a magnetic field of 1.2 MA / m. The density of the green compact was 4.2 g / cm ³ when calculated based on dimensions and weight.

Next, the above-mentioned HDDR process was performed on the green compact. Specifically, the green compact was heated to a temperature T ₁ = 600 ° C. at a temperature increase rate of 14 ° C./min in a 100 kPa hydrogen stream and held for 30 minutes to perform the first heat treatment step. Then, after switching the atmosphere to a 100 kPa argon flow, the temperature was increased to 860 ° C. at a rate of 14 ° C./min, and then the atmosphere was switched to a 100 kPa hydrogen flow, and then maintained at 860 ° C. for 120 minutes. The second heat treatment step was performed. Then, it hold | maintained for 60 minutes in the argon air pressure-reduced to 5.3 kPa with 860 degreeC, and performed the 3rd heat treatment process. Next, the sample was cooled to room temperature in a 100 kPa argon stream to prepare a sample.

When the density was calculated from the size and weight of the prepared sample, it was 5.67 g / cm ³ .

  The prepared sample was magnetized with a pulse magnetic field of 3.2 MA / m, and then the magnetic properties were measured with a BH tracer (device name: MTR-1412 (manufactured by Metron Engineering Co., Ltd.)). The results are shown in Table 8.

Further, the sample after HDDR treatment was heated to 800 ° C. in a cemented carbide metal mold and subjected to hot compression treatment (hot pressing) for 20 minutes at a pressure of 50 MPa, whereby a density of 7.57 g / cm ³ was obtained. A high density magnet was obtained. After magnetizing the produced high-density magnet with a pulse magnetic field of 3.2 MA / m, the magnetic properties were measured with a BH tracer (device name: MTR-1412 (Metron Giken Co., Ltd.)). The results are shown in Table 8. As can be seen from Table 8, all the samples have good magnetic properties, and particularly better magnetic properties are obtained by hot pressing than after HDDR treatment.

(Experimental example 7)
Alloy A6 powder was prepared in the same manner as described in Experimental Example 4. Next, a forming container 2 and a pressing jig 3 as shown in FIG. 10 were prepared. The molded container 2 in this experimental example is made of nonmagnetic stainless steel. The produced powder 1 was filled into a rectangular shaped container 2 having an inner dimension of 12 mm × 20 mm and a height of 20 mm. Next, the release surface of the molded container 2 was covered with a square push rod (press jig) 3 slightly smaller than the inner dimension of the molded container 2. While applying a magnetic field of 1.2 MA / m in the direction perpendicular to the press direction (20 mm direction), the push rod 3 was pressed by hand. At this time, a pressure of about 0.1 MPa was applied to mold the powder 1 in the molding container 2 to produce a green compact. The density of the green compact was approximately 3.5 g / cm ³ .

Thereafter, the push rod 3 was removed from the forming container 2 and the entire forming container 2 was subjected to HDDR processing. Specifically, the green compact was heated to 600 ° C. at a rate of 14 ° C./min in a 100 kPa hydrogen flow. Then, the first heat treatment step was performed, the atmosphere was switched to an argon flow of 100 kPa without maintaining at 600 ° C., and the temperature was increased to 860 ° C. at a temperature increase rate of 14 ° C./min. Next, after the atmosphere was switched to a hydrogen flow of 100 kPa, the second heat treatment step was performed while maintaining 860 ° C. for 2 hours. Next, it kept at 860 degreeC in 100 kPa argon stream for 1 hour, and after performing the 3rd heat treatment process, it cooled to room temperature and produced the porous magnet. The density of the produced porous magnet was about 4.3 g / cm ³ .

  As described above, the “green compact” in the present specification includes a powder in a state where the mechanical strength is insufficient by itself due to low density due to low-pressure compression, and the powder cannot be self-supported. In addition, the shaping | molding container 2 is not limited to the container which has the shape shown in figure. The filling container disclosed in JP-A-7-153612 and a modified example thereof can also be used as a forming container in the green compact forming process and / or HDDR processing step.

Next, the porous magnet was heated to 800 ° C. in a cemented carbide metal mold and subjected to hot compression treatment (hot pressing) for 15 minutes at the pressure shown in Table 9, resulting in a density of 7.54. A high density magnet of ˜7.58 g / cm ³ was produced.

  The prepared sample was magnetized with a pulse magnetic field of 3.2 MA / m, and then the magnetic properties were measured with a BH tracer (device name: MTR-1412 (manufactured by Metron Engineering Co., Ltd.)). Table 9 shows the obtained results. As can be seen from Table 9, good magnetic properties can be obtained even when molding is performed using a molded container and HDDR treatment is performed on the entire molded container.

(Experimental example 8)
First, the raw material alloy powder of the raw material alloy A6 produced in Experimental Example 4 is filled in a die of a press machine, and a pressure of 32 MPa is applied in a direction perpendicular to the magnetic field in a 1.2 MA / m magnetic field. Was made. The density of the green compact was 4.3 g / cm ³ when calculated based on the dimensions and weight.

Next, the above-mentioned HDDR process was performed on the green compact. Specifically, the green compact was heated to a temperature T ₁ = 600 ° C. at a temperature increase rate of 14 ° C./min in a 100 kPa hydrogen stream and held for 30 minutes to perform the first heat treatment step. Then, after switching the atmosphere to a 100 kPa argon flow, the temperature was increased to 860 ° C. at a rate of 14 ° C./min, and then the atmosphere was switched to a 100 kPa hydrogen flow, and then maintained at 860 ° C. for 120 minutes. The second heat treatment step was performed. Thereafter, while maintaining the temperature at 860 ° C., as shown in Table 10, the hydrogen partial pressure in the furnace was maintained for 60 minutes while adjusting the pressure to 2.0 to 10.0 kPa, and then the argon flow reduced to 5.3 kPa while maintaining the temperature at 860 ° C. Holding in the air for 60 minutes, a third heat treatment step was performed. Then, it cooled to room temperature in 100 kPa argon flow, and the sample was produced.

When the density was calculated from the size and weight of the prepared sample, it was 5.7 to 6.0 g / cm ³ .

The prepared sample was magnetized with a pulse magnetic field of 3.2 MA / m, and then the magnetic properties were measured with a BH tracer (device name: MTR-1412 (manufactured by Metron Engineering Co., Ltd.)). The results are shown in Table 11. As can be seen from Table 11, all the samples have good magnetic properties. In particular, it can be seen that high H _cJ is obtained when treatment is performed at a hydrogen partial pressure of 2 kPa to 6 kPa in the first stage of the third heat treatment step as in the conditions S2 to S5.

  Since the magnet produced by this invention has a high degree of orientation and a residual magnetic flux density compared with the conventional porous magnet, it is used suitably for various uses as which these characteristics are calculated | required.

10 Porous magnet 27 Mold (die)
28a Upper punch 28b Lower punch 30a Driving unit 30b Driving unit 26 Chamber

Claims (7)

An RTB-based alloy having a 50% volume center particle size of 1 μm or more and less than 10 μm and containing an R ₂ T ₁₄ B phase (R is a rare earth element containing 50 atomic% or more of Nd and / or Pr, T is Fe, Or preparing a powder of Fe and Co);
Forming a green compact by molding the powder;
A first heat treatment step of heat treating the green compact in a hydrogen atmosphere at a temperature of 250 ° C. or higher and 600 ° C. or lower;
After the first heat treatment step, a second heat treatment step of performing heat treatment on the green compact in a hydrogen atmosphere at 650 ° C. or higher and 1000 ° C. or lower;
After the second heat treatment step, a third heat treatment step of performing heat treatment on the green compact in a vacuum of 650 ° C. or higher and 1000 ° C. or lower or an inert atmosphere;
Including
The manufacturing method of the RTB type | system | group permanent magnet which performs temperature rising from the time of completion | finish of said 1st heat processing process to the time of the start of said 2nd heat processing process in a vacuum or inert atmosphere.   The manufacturing method of the RTB system permanent magnet according to claim 1 whose hydrogen partial pressure of hydrogen atmosphere in said 1st heat treatment process is 10 kPa or more and 500 kPa or less.   The manufacturing method of the RTB type | system | group permanent magnet of Claim 1 which makes time from the completion | finish of said 1st heat treatment process to the start of said 2nd heat treatment process 60 minutes or less.   The manufacturing method of the RTB system permanent magnet according to claim 1 whose hydrogen partial pressure of hydrogen atmosphere in said 2nd heat treatment process is 20 kPa or more and 500 kPa or less.   The manufacturing method of the RTB type | system | group permanent magnet in any one of Claim 1 to 4 whose temperature of the heat processing in said 2nd heat treatment process and said 3rd heat treatment process is 950 degrees C or less.   5. The RT according to claim 1, wherein the green compact is held in a molded container during the first heat treatment step, the second heat treatment step, and the third heat treatment step. -Manufacturing method of B type permanent magnet. Preparing an RTB-based permanent magnet manufactured by the manufacturing method according to claim 1;
Increasing the density of the R-T-B permanent magnet by hot compression molding;
The manufacturing method of the RTB type | system | group high density magnet containing this.