JP2008127648A - Method for producing rare earth anisotropic magnet powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnet powder with a relatively low Co composition having high saturation magnetic flux density, high coercive force and satisfactory squareness without adopting complicated processes such as Dy diffusion treatment. <P>SOLUTION: The method comprises: a stage A where the fine powder of an (Nd, Pr)-Dy-Fe-Co-B based raw material alloy is prepared; a stage B where the fine powder is heated to occlude hydrogen in the fine powder in the temperature range of <500°C under the hydrogen pressure of 100 to 300 kPa, so as to introduce cracks into the grains, and further, temperature is raised in the temperature range of ≥500°C in a vacuum or an inert gas atmosphere, and thereafter, hydrogen is introduced therein at 750 to <1,000°C; a stage C where heat treatment is performed at 800 to <900°C under the hydrogen pressure of 100 to 300 kPa for 3 to <8 hr; a stage D where heat treatment is performed at 800 to <900°C under the hydrogen partial pressure of ≤10 kPa for 30 min to <8 hr; and a stage E where cooling is performed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a rare earth anisotropic magnet powder, and more particularly to a method for producing an Nd—Dy—Fe—Co—B based anisotropic magnet powder by the HDDR method.

R-Fe-B rare earth magnets (R is a rare earth element, Fe is iron, B is boron), which is a typical high performance permanent magnet, has a ternary tetragonal compound R ₂ Fe ₁₄ B phase as the main phase. It has a containing structure and exhibits excellent magnetic properties. The “rare earth element” in this specification is 17 elements including Sc (scandium), Y (yttrium), and lanthanoid.

  Such R—Fe—B rare earth magnets are roughly classified into sintered magnets and bonded magnets. The sintered magnet is manufactured by compressing and molding a fine powder (average particle size: several μm) of an R—Fe—B based magnet alloy with a press machine. In contrast, bond magnets are usually manufactured by compression molding or injection molding a mixture (compound) of R-Fe-B magnet alloy powder (average particle size: for example, about 100 μm) and a binding resin. Is done.

  In the case of a sintered magnet, since a powder having a relatively small particle size is used, each powder particle has magnetic anisotropy. For this reason, when performing compression molding of powder with a press device, an orientation magnetic field is applied to the powder, thereby producing a compact in which the powder particles are oriented in the direction of the magnetic field.

  The molded body thus obtained is usually sintered at a temperature of 1000 ° C. to 1200 ° C., and becomes a permanent magnet by heat treatment as necessary. As an atmosphere during sintering, a vacuum atmosphere or an inert atmosphere is mainly used in order to suppress oxidation of rare earth elements.

  On the other hand, in order to develop magnetic anisotropy in bonded magnets, the easy magnetization axes of the hard magnetic phase in the powder particles are aligned in one direction even if the average particle size of the powder particles used is relatively large. It is necessary to be. In order to obtain a coercive force necessary for practical use, it is necessary to reduce the crystal grains of the hard magnetic phase constituting the powder particles to about the single-domain critical particle size. Therefore, in order to produce an excellent anisotropic bonded magnet, it is necessary to obtain a rare earth alloy powder satisfying these conditions.

Currently, an HDDR (Hydrogenation-Deposition-Desorption-Recombination) treatment method is generally employed to produce rare earth alloy powders for anisotropic bonded magnets. “HDDR” means a process of sequentially performing hydrogenation and disproportionation, dehydrogenation and recombination. According to the known HDDR treatment, an R-Fe-B alloy ingot or powder is maintained at a temperature of 500 ° C. to 1000 ° C. in an H ₂ gas atmosphere or a mixed atmosphere of an H ₂ gas and an inert gas. It said after absorbing hydrogen into ingots or powder, such as H ₂ and dehydrogenation at a temperature 500 ° C. to 1000 ° C. up to a pressure 13Pa following vacuum atmosphere or H ₂ partial pressure 13Pa following inactive atmosphere by, then cooled It is characterized by doing.

In the above treatment, typically, the following reaction proceeds. That is, the hydrogenation and disproportionation reaction (both are collectively referred to as “HD reaction” by the heat treatment for causing hydrogen occlusion). An example of a reaction formula: Nd ₂ Fe ₁₄ B + 2H ₂ → 2NdH ₂ + 12Fe + Fe ₂ B) It progresses and a fine structure is formed. Next, by performing heat treatment for performing dehydrogenation treatment, dehydrogenation and disproportionation 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 ) occurs, and an alloy containing a fine R ₂ Fe ₁₄ B crystal phase is obtained.

The R—Fe—B alloy powder produced by the HDDR treatment has a relatively large coercive force and exhibits magnetic anisotropy. The reason for having such a property is that the metal structure is substantially as fine as 0.1 μm to 1 μm, and the structure after the HD reaction is changed to that of the starting material by appropriately selecting the reaction conditions and composition. This is because the orientation of the main phase (Nd ₂ Fe ₁₄ B type compound phase) is memorized (memory effect), and the subsequent DR treatment forms an aggregate of crystals with easy magnetization axes aligned in one direction. More specifically, since the grain size of the ultrafine crystal obtained by the HDDR treatment is close to the single domain critical grain size of the tetragonal R ₂ Fe ₁₄ B-based compound, a high coercive force is exhibited. An aggregate of very fine crystals of this tetragonal R ₂ Fe ₁₄ B compound is referred to as a “recrystallized texture”. For example, Patent Document 1 and Patent Document 2 disclose a method for producing an R—Fe—B alloy powder having a recombination texture by performing HDDR treatment.

  The HDDR process is known to greatly change the magnetic properties of the finally obtained magnet powder depending on the process conditions, and various processing methods are disclosed in known documents other than the above-mentioned patent documents.

  For example, Patent Document 3 discloses the following processing method.

That is, an R-T-B alloy cast iron having a specific composition range is pulverized to obtain a coarsely pulverized powder in which 80% by volume or more of an average particle size of 50 μm to 5000 μm is composed of a tetragonal structure Nd ₂ Fe ₁₄ B type compound. This coarsely pulverized powder is used as a raw material powder, and this is heated to a temperature range of 750 ° C. or higher in a vacuum or an inert gas, and then H ₂ gas of 10 kPa to 1000 kPa is introduced into the furnace. Thus, it is heated and held at a temperature of 750 ° C. to 900 ° C. for 30 minutes to 8 hours in H ₂ gas. At this time, a mixed structure of at least four phases of an R hydride phase, a TB compound phase, a T phase, and an Nd ₂ Fe ₁₄ B type compound phase is formed. Thereafter, a dehydrogenation treatment is further performed in an atmosphere having an H ₂ partial pressure of 10 kPa or less and maintained at a temperature of 700 ° C. to 900 ° C. for 5 minutes to 8 hours, followed by cooling.

  Patent Document 4 discloses the following processing method.

  That is, a rare earth magnet alloy raw material containing Co and Dy having a specific quantitative relationship is heated from room temperature to a predetermined temperature lower than 500 ° C. in a hydrogen gas atmosphere at a pressure of 1.2 to 5 atm. Thus, after the above rare earth magnet alloy raw material is subjected to hydrogen absorption treatment for absorbing hydrogen, the temperature is raised to a predetermined temperature within a range of 500 ° C. to 1000 ° C. in a hydrogen gas atmosphere at a pressure of 1.2 to 5 atm. Then, the rare earth magnet alloy raw material is further subjected to hydrogen absorption / decomposition treatment for absorbing and decomposing hydrogen. After performing the intermediate heat treatment in which the rare earth magnet alloy raw material is held in an inert gas atmosphere at a pressure of 1.2 to 10 atm at a predetermined temperature in the range of 500 to 1000 ° C., the rare earth magnet alloy raw material is heated to 500 to 1000 ° C. It is maintained in a hydrogen atmosphere having an absolute pressure of 5 to 100 Torr at a predetermined temperature within the range, or in a mixed gas atmosphere of hydrogen and an inert gas having a hydrogen partial pressure of 5 to 100 Torr. In this way, after performing heat treatment in hydrogen under reduced pressure while leaving a part of hydrogen in the rare earth magnet alloy, the rare earth magnet alloy raw material is maintained at a predetermined temperature of 500 to 1000 ° C. in a vacuum atmosphere of an ultimate pressure of 1 Torr or less. The hydrogen is forcibly released from the hydrogen, and a dehydrogenation treatment that promotes phase transformation is performed. Then, it cools and grind | pulverizes.

  Patent Document 5 discloses the following processing method.

That is, after HD treatment is performed on an R—Fe—B alloy in an atmosphere having a hydrogen partial pressure of 10 to 100 kPa and a temperature of 953 to 1133 K, HD is performed under a condition in which at least one of the hydrogen partial pressure and the temperature is increased. Process. According to Patent Document 5, such a treatment stabilizes the HD structure and makes it possible to stably obtain a powder having high magnetic properties. After the HDDR treatment or during the HDDR treatment, Dy, Tb, etc. It is described that the coercive force can be improved and the permanent demagnetization rate can be reduced by mixing and heat treating the materials.
JP-A-1-132106 JP-A-2-4901 JP-A-6-128610 Japanese Patent Laid-Open No. 2003-243211 WO2004 / 064085

  By using the HDDR method, an anisotropic magnet powder having a relatively high coercive force can be obtained and applied as a magnetic powder for an anisotropic bonded magnet. However, in the conventional method, it is difficult to obtain magnetic powder satisfying all of high saturation magnetic flux density, high coercive force, and good squareness at low cost.

For example, according to the method disclosed in Patent Document 3, it is worth noting that a high main phase orientation degree can be realized by leaving the Nd ₂ Fe ₁₄ B type compound phase after the HD treatment. not high. In the example shown in Patent Document 3, the coercive force (H _cJ ) obtained is 1 MA / at most even in a composition in which Dy or Tb, which is known as an additive element for increasing the coercive force, is added at 1.5 atomic%. m. The magnetic powder having such a coercive force cannot be used for applications requiring high heat resistance, for example, electrical applications. Patent Document 3 does not describe any specific technique or conditions for achieving a high coercive force exceeding 1.4 MA / m, for example.

Further, according to the method disclosed in Patent Document 4, it is necessary to set the composition containing Co and Dy at a high concentration so as to satisfy the condition of Co + 10Dy ≧ 23 atomic%. Increasing the Co and Dy concentrations increases the raw material cost and requires a relatively high hydrogen pressure. There also, in the method disclosed in Patent Document 4, when reducing Co concentration, reduces the degree of orientation of main phase after HDDR treatment, as a result, a problem of reduced saturation magnetic flux density B _r is actualized .

  According to the method disclosed in Patent Document 5, it is possible to promote the progress of the HDDR reaction by executing the HD process in two stages. However, Patent Document 5 describes nothing about the effect obtained by adding Dy to the starting alloy, and an increase in coercive force by utilizing Dy or the like is achieved by applying a heat diffusion treatment. Has been.

  The present invention has been made in view of the above problems. In an alloy composition with a relatively small amount of Co addition, a high saturation magnetic flux density, a high coercive force, and a good condition can be obtained without employing a complicated method such as Dy diffusion treatment. An object of the present invention is to provide an anisotropic magnet having excellent squareness.

  The method for producing a rare earth anisotropic magnet powder according to the present invention includes Nd and / or Pr of 10 atomic% to 20 atomic%, Dy of 0.3 atomic% to 2 atomic%, 1 atomic% to 10 atomic%. Of Co, 6 to 8 atomic% of B (partially substituted with C), and satisfies the relation of Co + 10Dy <23 atomic% (Nd, Pr) -Dy-Fe-Co- Step A for preparing a fine powder of a B-based raw material alloy, and heating the fine powder in a vacuum or an inert gas atmosphere at a temperature range of at least 500 ° C. to less than 750 ° C. After reaching a temperature of less than ℃, step B introducing hydrogen in a temperature range of 750 ° C or more and less than 1000 ° C, and after step B, at a temperature of 800 ° C or more and less than 900 ° C, a hydrogen pressure of 100 kPa or more and 300 kPa or less 3 o'clock Step C for performing heat treatment for less than 8 hours, Step D for performing heat treatment for 30 minutes to 8 hours at a temperature of 800 ° C. to less than 900 ° C. and a hydrogen partial pressure of 10 kPa or less after Step C, and Step D And the step E of cooling after.

  In a preferred embodiment, the raw material alloy further contains 0.01 atomic% or more and 1 atomic% or less of Ga.

  In a preferred embodiment, the average particle size of the fine powder is 30 μm or more and less than 300 μm.

  In a preferred embodiment, the particles constituting the fine powder have cracks accompanying hydrogen occlusion before performing Step B.

  In a preferred embodiment, the step B is a step B in which cracks are introduced into particles constituting the fine powder by occluding hydrogen in the fine powder in a hydrogen atmosphere at a pressure of 100 kPa or more and 300 kPa or less in a temperature range of less than 500 ° C. 'including.

  In a preferred embodiment, in Step B, the hydrogen partial pressure increase rate at the time of hydrogen introduction is set to 5 kPa / min or more and 100 kPa / min or less.

In a preferred embodiment, in Step C, three phases of R (R is Nd or Pr) hydride phase, TB (T is Fe or Co) compound phase, and T phase coexist and substantially Nd. _A structure free of ₂ Fe ₁₄ B-type crystal phase is formed in the fine powder.

The rare earth anisotropic magnet powder according to the present invention is a rare earth anisotropic magnet powder obtained by any one of the above-described production methods, and has magnet characteristics with a saturation magnetic flux density B _r ≧ 1T and a coercive force H _cJ ≧ 1600 kA / m. Indicates.

  According to the present invention, prior to starting the HD reaction, the conventional HDDR process in which the temperature is raised in hydrogen to raise the temperature to an appropriate temperature range in a vacuum or in an inert atmosphere and then introduce hydrogen is performed. The progress of the HD reaction is moderate compared to when it is performed. As a result, an anisotropic magnet satisfying a high saturation magnetic flux density, a high coercive force, and a good squareness can be obtained with a relatively low Co addition amount and without employing a complicated process such as Dy diffusion treatment.

  The present inventor sets the HD processing conditions appropriately without increasing the composition ratio of expensive additive elements such as Co and Dy, and substantially converts the structure after HD into an R hydride phase, TB. The present inventors have found that a high saturation magnetic flux density, a high coercive force, and a good squareness can be obtained by using a mixed structure in which three phases of a compound phase and a T phase coexist.

  FIG. 1 is a diagram showing an example of the relationship between HD temperature and pressure when the HD reaction time is fixed to a certain value. In FIG. 1, a solid line indicates an equilibrium line (hereinafter referred to as “HDDR equilibrium line”) between the HD reaction and DR reaction, and a dotted line indicates an HD reaction start line (hereinafter referred to as “HD start line”). .

In the region A on the higher temperature side than the HDDR equilibrium line and the region B on the lower temperature side than the HDDR equilibrium line and on the lower pressure side than the HD start line, the reaction reaction left side (Nd ₂ Fe ₁₄ B + 2H ₂ ) is stable. is there. On the other hand, in the region C on the lower temperature side than the HDDR equilibrium line and on the higher pressure side than the HD start line, the state of the right side of the HD reaction equation (2NdH ₂ + 12Fe + Fe ₂ B) is stable.

From the viewpoint of phase rule, in the case of the Nd—Fe—B ternary composition, the region where the four phases (NdH ₂ , Fe, Fe ₂ B, Nd ₂ Fe ₁₄ B) coexist thermodynamically is shown in FIG. As shown in the figure, it is indicated by a straight line (HDDR equilibrium line). On the other hand, in the quaternary composition containing an additive element such as Co as in the alloy employed in the present invention, for example, NdH ₂ , (Fe, Co), (Fe, Co) ₂ B, Nd ₂ (Fe, The region where the four phases of Co) ₁₄ B) coexist is indicated by a region having a width with respect to temperature and pressure. However, in any case, the following argument holds.

  Route (a) in FIG. 1 is an example of a pattern in which the temperature is increased after hydrogen is introduced. In this case, since the HD reaction, which is an exothermic reaction, proceeds rapidly during the temperature raising process, in order to optimize the reaction rate, it is necessary to add a large amount of Co as described in Patent Document 4. Therefore, as in the alloy employed in the present invention, when the Co composition ratio is low, the orientation degree of the main phase is lowered, and finally a magnet having high magnetic anisotropy cannot be obtained.

  As shown in route (b) of FIG. 1, the present inventor does not introduce hydrogen in the temperature rising process from room temperature until reaching 750 ° C., but introduces hydrogen after reaching a predetermined temperature of 750 ° C. or higher. As a result, it was found that a magnet having high magnetic anisotropy can be finally obtained even with a low Co composition ratio.

FIG. 2 is an enlarged view of region C in FIG. 1, and shows the retention temperature, hydrogen partial pressure, and magnet obtained during the HD reaction when the amount of Co and Dy added is within a certain range of values. 3 schematically shows a relationship of H _k (a demagnetizing field value at which the magnetization J is 90% of the residual magnetic flux density B _r ), which is one of the indices indicating the squareness of the magnetic field. In the figure, the value of most H _k data points indicated by "×" is low, the value of H _k of the other data points, "△" → "○" → are higher in the order of "◎".

In the region C2 surrounded by the dotted line in FIG. 2, it can be seen that a relatively high H _k magnet is obtained. It can also be seen that in the region C1 on the higher temperature side than the region C2, the value of H _k is drastically reduced as compared to the data points in the region C2.

  Since the HD reaction is an exothermic reaction, in region C1, the temperature rapidly increases due to locally generated thermal energy, and the probability of exceeding the temperature at which the reverse reaction (DR reaction) occurs is increased. When such a temperature rise occurs and the DR reaction is remarkably generated, the apparent speed of the HD reaction becomes extremely low, so that it takes a long time to complete the HD reaction.

  On the other hand, in the region C3 on the lower temperature side than the region C2, even if heat is generated by the HD reaction, the temperature does not reach the temperature at which the DR reaction occurs, so it is considered that only the HD reaction proceeds at an accelerated rate. As a result, even in the region C3, although not as much as the region C1, the characteristics are relatively low.

  In the region C2 where good characteristics are obtained with respect to the regions C1 and C3, the apparent reaction rate is relatively low, and the HD reaction proceeds uniformly in an appropriate time. Since such a region C2 is located within a specific narrow temperature range, in order to advance the HD reaction in the region C2, it is possible to introduce hydrogen after heating the magnetic powder to the specific temperature range. preferable.

Based on the above findings, the present inventors have limited the heat treatment temperature in hydrogen to a specific range, so that the structure after the HD treatment does not become a four-phase coexistence state including the Nd ₂ Fe ₁₄ B type crystal phase. In both cases, it has been found that a relatively high magnetic anisotropy can be maintained after HDDR treatment, and a higher coercive force can be obtained than in the case of a four-phase coexistence state.

In the present specification, “substantially coexisting with three phases” mainly means an R hydride phase (eg, NdH ₂ type crystal phase), a T phase (eg, α-Fe type crystal phase), T— This is a state composed of three kinds of crystal phases of B phase (for example, Fe ₂ B type crystal phase) and substantially does not contain Nd ₂ Fe ₁₄ B type crystal phase. In addition, “a state that does not substantially contain the Nd ₂ Fe ₁₄ B-type crystal phase” means that the Nd ₂ Fe ₁₄ B-type crystal phase cannot be identified from a diffraction peak observed by a general-purpose powder X-ray diffraction method. Point to.

In the region C3, as a result of the complete progress of the HD reaction, the structure after the HD reaction becomes a three-phase coexistence state, but a high saturation magnetic flux density _Br cannot be obtained. This is presumed to be because the HD reaction proceeds rapidly in the region C3, and the structure after the HD reaction does not memorize the orientation of the main phase. Even in the region C2, when the HD treatment time is 3 hours or less, the HD reaction does not proceed sufficiently, and the structure after the HD reaction coexists in four phases.

In region C1, it takes a longer time than the time required to complete the HD reaction in region C2 in order to allow the HD reaction to proceed completely. Therefore, typically, HD processing for 8 hours or more is not performed. And the structure | tissue after reaction becomes 4 phase coexistence. In this case, since the reaction proceeds slowly, the reaction proceeds uniformly and a high saturation magnetic flux density _Br is obtained. However, if the DR reaction is advanced from such a state, a high coercive force cannot be obtained. This is considered to be because the organization after HDDR processing is not a post-HD organization that is optimized.

On the other hand, when the reaction proceeds in the region C2, the reaction proceeds uniformly and completely, and the structure after the HD reaction coexists in three phases, and a high saturation magnetic flux density B _r and a high coercive force H _cJ are obtained. The HD processing time at that time requires a relatively long time of 3 to 8 hours.

  The position of the region C2 shown in FIG. 2 shifts in the drawing depending on the concentrations of Co and Dy contained in the alloy. Hereinafter, the conditions for making the structure after the HD reaction coexist in the three phases in the region C2 in the composition having a low Co and Dy concentration employed in the present invention will be described.

<Alloy composition>
The starting alloy in the production method of the present invention contains 10 to 20 atomic% Nd and / or Pr, 0.3 to 2 atomic% Dy, 1 to 10 atomic% Co, 6 to 8 atomic% B (partially And may be substituted with C), and has a low Co and low Dy composition satisfying the relational expression of Co + 10 Dy <23 atomic%.

  Nd and / or Pr preferably has a total sum of 10 atomic% or more and less than 20 atomic%. If it is less than 10 atomic%, it is difficult to obtain a high coercive force even if 2 atomic% of Dy, which is the maximum amount of the above composition, is added, and if it exceeds 20 atomic%, it causes a decrease in magnetization. At the same time, a problem arises in the corrosion resistance of the magnetic powder obtained. A more preferable Nd and / or Pr content is 10.5 atomic% or more and less than 14 atomic%.

  In addition, if Pr is excessive, problems may occur in terms of corrosion resistance and thermal demagnetization at high temperatures. Therefore, the ratio of Pr to the total of Nd and Pr is preferably 10% or less, and more preferably 5% or less. Preferably, 3% or less is more preferable.

Dy is used in the present invention to develop a high coercive force. When the added amount of Dy is less than 0.3 atomic%, it becomes difficult to obtain, for example, a high coercive force (H _cJ ). On the other hand, when 2% or more of Dy is added, it is difficult to advance the HD reaction in the present invention, and the hydrogen pressure needs to be set high. However, increasing the hydrogen pressure promotes non-uniformity of the temperature distribution in the furnace during processing, and may cause problems in mass production. Therefore, the amount of Dy added is preferably 0.3 atomic percent or more and 2 atomic percent or less, and more preferably 0.5 atomic percent or more and 1.5 atomic percent or less.

  In addition to Nd, Pr, and Dy, a rare earth element may be contained. The lower limit of the sum of the rare earth elements is preferably 12 atomic%. This is because it is difficult to obtain a high coercive force when the sum of the rare earth elements is 12 atomic% or less. Further, the upper limit of the sum of the rare earth elements is preferably 22 atomic%, more preferably 15 atomic%, and still more preferably 14 atomic%. This is because if the total sum of the rare earth elements is large, the magnetization is lowered and a problem arises in the corrosion resistance of the obtained magnetic powder.

Including _Td in addition to Nd, Pr, and Dy is effective from the viewpoint of improving the coercive force H _cJ . However, Tb is a very expensive element, and its content is preferably 1 atomic% or less.

Co works effectively to cause the HDDR reaction to proceed appropriately and to obtain a high coercive force even when added in a small amount. The amount of Co is preferably 1 atom% or more and 10 atom% or less. The amount of Co is less than 1%, whereas it is difficult to achieve both high saturation magnetic flux density B _r and the coercive force H _cJ, the Co exceeds 10 atomic%, with respect to Dy added weight in the present invention, It becomes difficult to advance the HD reaction, and the hydrogen pressure needs to be set high. However, as described above, increasing the hydrogen pressure promotes nonuniformity of the temperature distribution in the furnace during processing, and may cause a problem in mass production.

In the present invention, the total amount of Co and Dy is preferably Co + 10Dy <23 atomic%. When Co + 10Dy is 23 atomic% or more, by HDDR treatment according to the invention, the progress of the HD reaction becomes extremely slow, not only affects the productivity, to achieve both high saturation magnetic flux density B _r and the coercive force H _cJ This is because it becomes extremely difficult. More preferably, it is preferable to satisfy Co + 10Dy ≦ 20 atomic%.

In the present invention, it is preferable because it is possible to obtain a magnetic powder to achieve both high saturation magnetic flux density B _r and a high coercive force H _cJ easy addition of Ga of 1 atomic% or less than 0.01 atomic%. If Ga is less than 0.01%, the effect of Ga addition is not observed. On the other hand, Ga is an expensive element. If the addition amount exceeds 1 atomic%, not only will the cost increase, but the progress of the HD reaction will be extremely slow, and it will be difficult to obtain high magnetic properties. Become. In addition, as for Ga addition amount, 0.1 atomic% or more and 0.7 atomic% or less are more preferable.

  In the present invention, in addition to Co, Dy, Ga, etc., Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Zr, Nb, Mo, In, Sn, Ta, W, Bi, etc. These elements may be added as appropriate. However, if the total addition amount of these elements exceeds 5 atomic%, the magnetic properties are deteriorated. Therefore, the total addition amount is preferably adjusted to 5 atomic% or less.

<Starting alloy>
The starting alloy is obtained, for example, by a known alloy production method such as a book mold method, a centrifugal casting method, a strip casting method, an atomizing method, or a diffusion reduction method. The starting alloy produced by these methods may be subjected to homogenization heat treatment for the purpose of eliminating macro segregation, coarsening of crystal grains, reduction of α-Fe phase, and the like. As the homogenization heat treatment, for example, a treatment is performed at 1000 to 1200 ° C. for 1 to 48 hours in an inert gas atmosphere other than nitrogen. By this heat treatment, diffusion of elements in the R-T-B alloy ingot occurs, and the components are homogenized. The R-T-B alloy ingot is mainly composed of a main phase of R ₂ Fe ₁₄ B phase, R-rich phase, and B-rich phase, but in addition to R ₂ Fe ₁₄ B phase, α- There are often ferromagnetic phases such as Fe phase and R ₂ Fe ₁₇ phase. Therefore, the heat treatment diffuses the α-Fe phase, the R ₂ Fe ₁₇ phase, and the like in the RTB-based alloy ingot, and extinguishes these phases as much as possible, so that the ferromagnetic phase substantially becomes the R ₂ Fe ₁₄ B phase. It is preferable to make the structure consisting of only. By such a homogenization treatment, the average crystal grain size of the R ₂ Fe ₁₄ B phase is coarsened to about 100 μm or more. The coarsening of the average crystal grain size is preferable because the HDDR-treated magnetic powder has a large magnetic anisotropy.

  The reason why nitrogen is not used as the inert gas atmosphere is that nitrogen reacts with the RTB-based alloy. If the temperature is lower than 1000 ° C., it takes too much time for the element diffusion in the R—T—B alloy to increase the manufacturing cost, and another phase is formed, which is not preferable. On the other hand, when the heat treatment temperature exceeds 1200 ° C., melting of the alloy occurs, which is not preferable. A more preferable heat treatment temperature range is appropriately set in the range of 1100 ° C. to 1150 ° C. according to the alloy composition and the like. When the heat treatment time is less than 1 hour, the element diffusion becomes insufficient, but conversely, it is not meaningful to perform the treatment for a long time exceeding 48 hours.

<Crushing>
Next, the starting alloy powder is prepared by pulverizing the starting alloy by a known method. The pulverization can be performed using, for example, a mechanical pulverization method such as a jaw crusher or a hydrogen storage / disintegration method.

In the case of the hydrogen storage / collapse method, the alloy may be embrittled by storing the above starting alloy in a hydrogen atmosphere of 0.05 to 1.0 MPa for 5 minutes to 10 hours to store hydrogen in the alloy. When the starting alloy occludes hydrogen, it spontaneously collapses and cracks occur. In such hydrogen pulverization, an R-T-B system ingot is put in a pressure vessel, H ₂ gas having a purity of 99.9% or more is introduced to 50 to 1000 kPa, and then the state is maintained for 5 minutes to 10 hours. This can be done by holding. In this way, a raw material powder having a particle size of 1000 μm or less is obtained. The mechanical pulverization performed after hydrogen pulverization can be performed using a pulverizer such as a feather mill, a ball mill, or a power mill.

The coarsely pulverized powder thus obtained is composed of particles having a substantially single crystal orientation, and the magnetization easy axes are aligned in one direction in each particle. As a result, the rare earth alloy powder for permanent magnets obtained by the HDDR process can exhibit anisotropy. In the starting alloy used in this embodiment, the Nd ₂ Fe ₁₄ B type compound phase having crystal orientations aligned in the same direction has a size of 20 μm or more. This is important in finally obtaining high magnetic characteristics, particularly high saturation magnetic flux density _Br .

When the average particle size of the starting alloy powder in the present embodiment is less than 30 μm, diffusion aggregation between particles constituting the powder is excessively generated by the HDDR process, so that the crushing after the HDDR process becomes difficult, resulting in high magnetic properties. It becomes difficult to obtain magnetic powder having anisotropy. On the other hand, when the average grain size exceeds 300 μm, it is difficult to obtain an alloy structure composed of only Nd ₂ Fe ₁₄ B type compound phases having crystal orientations aligned in the same direction and having no α-Fe phase. as, it is difficult to obtain a magnetic powder to achieve both high saturation magnetic flux density B _r and coercivity H _cJ. For these reasons, the average particle size of the starting alloy powder is preferably 30 to 300 μm, and more preferably 50 to 150 μm.

  One of the features of the present invention is that the HDDR process reaction proceeds relatively slowly. For this reason, a difference occurs in the degree of progress of the reaction for each particle size, and as a result, the magnetic properties of the entire magnetic powder may be deteriorated. When hydrogen pulverization is employed as the pulverization method, cracks are introduced into the particles, so that the difference in the degree of progress of the HDDR reaction due to the difference in particle size can be reduced. The introduction of such cracks can also be achieved by exposing the powder to a hydrogen atmosphere of 500 ° C. or lower during the HDDR process described later.

  FIG. 3A shows a SEM photograph of the magnetic particle before the HDDR process in which cracks are introduced in this way. Since the HDDR magnetic powder has a different shape from the surface of the particle after processing, whether such cracks were introduced before the HDDR processing is the same as that of the particle surface by observing the shape of the crystal grains in the cracked part by SEM. It can be determined by confirming whether it is in the form of

  FIG. 3B shows the result of cross-sectional observation of the magnetic powder immediately after heating in hydrogen for a short time and immediately cooling the situation in which the HD reaction proceeds through such cracks.

  It can be seen that hydrogenation and disproportionation proceed from the cracks of the magnetic powder. Without such cracks, the hydrogenation / disproportionation reaction takes place substantially only from the particle surface, which promotes the reaction non-uniformity and consequently makes it difficult to obtain high magnetic properties.

<HDDR processing>
FIG. 4 is a graph schematically showing an example of temporal changes in the HDDR process temperature and hydrogen partial pressure. Hereinafter, the HDDR process in the present embodiment will be described with reference to FIG.

  As described above, the HDDR process is divided into a hydrogenation / disproportionation process (HD process) and a dehydrogenation / recombination process (DR process). The hydrogenation / disproportionation treatment and dehydrogenation / recombination treatment can be performed in the same apparatus, but can also be performed using different apparatuses. The HDDR process can be completed by performing the hydrogenation / disproportionation process and the dehydrogenation / recombination process continuously or discontinuously.

  The atmosphere at the time of temperature rise for HD processing (step B in FIG. 4) is configured in vacuum or with an inert gas such as argon or helium in a temperature range of at least 500 ° C. and less than 750 ° C. When hydrogen is present at a temperature of 500 ° C. or higher and lower than 750 ° C., the HD reaction proceeds, and high magnetic anisotropy cannot be obtained with a composition having a low Co concentration. Moreover, since the presence of hydrogen deteriorates the temperature distribution in the furnace and causes variations in magnetic properties during mass production, it is preferable that the atmosphere does not substantially contain hydrogen at temperatures of 500 ° C. or higher.

  In addition, by introducing hydrogen temporarily in the temperature range of less than 500 ° C. during the temperature raising process, cracks may be introduced into the magnetic powder, and the difference in HDDR reaction progress due to the difference in particle size may be alleviated. It is preferable to switch the atmosphere to inert gas or argon gas before reaching 500 ° C. after the crack is introduced, and then raise the temperature to 500 ° C. or higher.

After the temperature is raised to 750 ° C. or higher and lower than 1000 ° C., hydrogen is introduced. The temperature at which hydrogen is introduced can be set to an appropriate level depending on the alloy composition. In the alloy composition employed in the present invention, when hydrogen is introduced at less than 750 ° C., the magnetic anisotropy of the finally obtained magnetic powder is lowered, and a high saturation magnetic flux density _Br cannot be obtained. On the other hand, when hydrogen is introduced at a temperature of 1000 ° C. or higher, the progress of the HD reaction becomes extremely slow.

  At the time of introducing hydrogen, it is preferable to set the rate of increase of the hydrogen partial pressure to 5 kPa / min or more and 100 kPa / min or less. In the alloy composition employed in the present invention, if the rate of increase in hydrogen partial pressure is less than 5 kPa / min, only an increase in processing time is brought about and no effect is obtained. On the other hand, when the hydrogen partial pressure increase rate exceeds 100 kPa / min, the initial HD reaction becomes excessive. In addition, when hydrogen at room temperature is introduced, the temperature in the furnace temporarily decreases, and as a result, it becomes difficult to obtain magnetic powder having high magnetic anisotropy.

  In addition, if it is 750 degreeC or more, you may introduce hydrogen, raising temperature. The temperature at which the hydrogen partial pressure is 100 kPa or higher is preferably 800 ° C. or higher. When hydrogen is introduced while maintaining the temperature at a predetermined level, the hydrogen introduction temperature is preferably set to 800 ° C. or higher.

  After the introduction of hydrogen, heat treatment is performed at a temperature of 800 ° C. or higher and lower than 900 ° C. and a hydrogen pressure of 100 kPa or higher and 300 kPa or lower for 3 hours or more and less than 8 hours (step C in FIG. 4). By this treatment, a hydrogenation / disproportionation reaction (HD reaction) proceeds. In the alloy composition employed in the present invention, when the temperature of this heat treatment is less than 800 ° C., it is difficult to obtain high magnetic anisotropy. On the other hand, when the temperature exceeds 900 ° C., the progress of the HD reaction is remarkably slow, and good magnetic properties cannot be obtained.

  If the hydrogen pressure becomes too high, the temperature distribution in the furnace will be deteriorated, so the upper limit is preferably 300 kPa or less, more preferably 200 kPa or less, and even more preferably 150 kPa or less.

  In the alloy composition employed in the present invention, when the treatment time for hydrogenation / disproportionation is 3 hours or less, the HD reaction does not proceed sufficiently, and it is difficult to obtain a high coercive force. In addition, since the treatment for 8 hours or more becomes a problem from the viewpoint of productivity, the treatment time is 3 hours or more and 8 hours or less.

  After performing hydrogenation / disproportionation treatment, dehydrogenation / recombination treatment is performed (step D in FIG. 4). The atmosphere during the dehydrogenation / recombination treatment may be set to an inert gas (Ar, He, etc.) or a vacuum.

  The atmosphere control in the dehydrogenation / recombination process (control of atmospheric gas type, pressure, temperature, time) may be realized by appropriately adopting a known method, but the process temperature is 800 ° C. to 900 ° C. The hydrogen partial pressure is preferably set to 10 kPa or less and the treatment time is set to 30 minutes to 8 hours.

  The atmosphere may be controlled in stages. That is, the hydrogen partial pressure may be lowered stepwise, or the atmospheric pressure during pressure reduction may be lowered stepwise.

  After the dehydrogenation / recombination process is completed, the cooling step (step E in FIG. 4) is executed, and the alloy magnet powder according to the present embodiment can be obtained. In the cooling step, the reduced pressure state may be maintained as it is, but in order to increase the cooling efficiency, the vacuum exhaust is stopped, the argon gas is supplied into the furnace, and the furnace pressure is returned to the atmospheric pressure. Further, in order to achieve a higher cooling rate, it may be pressurized with argon gas or helium gas, or it is useful to utilize a cooling device such as a heat exchanger. Thereafter, the powder after the HDDR process is taken out of the hydrogen treatment apparatus.

The alloy magnet powder thus obtained has a recombination texture of tetragonal R ₂ Fe ₁₄ B type compound as a result of HDDR treatment, and the average crystal grain size of this recombination texture is about 0.1 to 0.1 It is in the range up to about 0.8 μm. Since this size is close to the size of the single magnetic domain particles, each powder particle having a recombination texture can exhibit a high coercive force. In addition, since the crystal orientation of the recombination texture is aligned, the easy axis of magnetization is also aligned, and as a result, the powder particles having the recombination texture exhibit high magnetic anisotropy. It will be.

<Crushing and grinding>
After the dehydrogenation / recombination treatment is completed, the material cooled to room temperature may form a weak aggregate. In such a case, crushing may be performed by a known method. Further, the particle size may be adjusted by pulverization according to the final purpose. As the pulverization method, a known pulverization technique can be used, but it is preferable to perform pulverization in an inert gas atmosphere such as Ar in order to suppress oxidation of the magnet powder during pulverization.

<Application of magnet powder>
The obtained magnet powder can be used for production of a bonded magnet or a hot-formed magnet after performing a known surface treatment as necessary. When manufacturing a bonded magnet, it is mainly formed by compression molding, injection molding, extrusion molding or the like. A film may be formed on the obtained bonded magnet by a method such as resin coating or plating for the purpose of imparting further corrosion resistance and oxidation resistance.

(Example 1)
The alloy having the composition shown in Table 1 was prepared by melting and casting by the method described in the above embodiment. This alloy may contain a small amount of inevitable impurities not listed in Table 1.

  The above alloy was subjected to a homogenization heat treatment of 1110 ° C. × 20 hours. Subsequently, the alloy was stored in a pressurized hydrogen atmosphere with an absolute pressure of 250 kPa for 2 hours, so that hydrogen was occluded in the alloy, and then evacuated to remove hydrogen as much as possible. Thereafter, the raw material alloy fine powder was obtained by crushing with a mesh having an opening of 500 μm.

  As a result of evaluating the average particle size of the fine powder of the obtained raw material alloy using a standard sieve of JIS Z8801, the average particle size of any alloy was in the range of 50 μm to 150 μm. As a result of observing each fine powder with a scanning electron microscope, it was confirmed that cracks associated with hydrogen occlusion occurred in the particles constituting the fine powder.

  The HDDR process was performed on the obtained alloy powder under the conditions shown in Tables 2 and 3. The powder after the HDDR treatment was crushed with a mesh having an opening of 500 μm to obtain a sample of magnet powder.

The magnetic properties of the obtained magnet powder were measured with a vibrating sample magnetometer (VSM: device name VSM-5SC-10HF (manufactured by Toei Kogyo Co., Ltd.)). Table 3 shows the results of VSM measurement for the obtained samples. FIG. 5 is a graph showing the magnetic properties (B _r , H _cJ ) shown in Table 3.

In the sample for VSM measurement, the obtained magnetic powder was put into a cylindrical holder, fixed with paraffin while being oriented in a magnetic field of 800 kA / m, and then applied with a pulse magnetic field of 3.2 MA / m or more. A magnetized one was used. Also, for any sample, it was calculated value of the saturation magnetic flux density B _r a density of 7.60 g / cm ^3.

Magnetic particles according to an embodiment of the present invention, as compared with the magnetic powder of the comparative example, it was confirmed that can achieve both a relatively high saturation magnetic flux density B _r and coercivity H _cJ. Specifically, while maintaining the saturation magnetic flux density B _r of more than 1T, it was confirmed that the coercivity H _cJ can be at least 1400kA / m. Further, depending on conditions, it was possible to achieve a higher saturation magnetic flux density B _r and 1600 kA / m or more the coercive force H _cJ 1T.

Further, in order to confirm the presence or absence of the Nd ₂ Fe ₁₄ B type crystal phase after HD treatment, HD treatment (up to Step C) was performed on the fine powder produced by the same method as in Example 1 under the conditions shown in Table 2. A cooled sample was prepared without performing the DR treatment (step D). The obtained sample was analyzed with a powder X-ray diffractometer (RINT2000 manufactured by Rigaku). Measurement was performed using CuKα rays as X-rays, an X-ray generation tube voltage of 50 kV, and a tube current of 180 mA. As a result, Experiment No. For samples prepared under the same conditions as 1 to 10 and C1 and C5, there are diffraction peaks corresponding to three types of crystal phases: NdH ₂ type crystal phase, α-Fe type crystal phase, and Fe ₂ B type crystal phase. confirmed. However, the diffraction peak corresponding to the Nd ₂ Fe ₁₄ B type crystal phase was equal to or lower than the noise level and was not clearly identified. For samples prepared under the same conditions as in Experiments C2 to C4, four crystal phases of NdH ₂ type crystal phase, α-Fe type crystal phase, Fe ₂ B type crystal phase, and Nd ₂ Fe ₁₄ B type crystal phase were used. A diffraction peak corresponding to was confirmed.

(Example 2)
Melting and casting were performed in the same manner as in Example 1 to produce an alloy having the composition shown in Table 4 (including inevitable impurities).

  The alloy is subjected to a homogenization heat treatment at 1110 ° C. for 20 hours, followed by mechanically pulverizing the alloy using a stamp mill, and classifying with a JIS Z8801 sieve to obtain a raw material having an average particle diameter of 250 μm. An alloy fine powder was obtained.

  After the obtained raw material alloy powder was put into an HDDR processing furnace, hydrogen was occluded in the fine powder in a pressurized hydrogen atmosphere at a temperature of 150 ° C. and an absolute pressure of 250 kPa, and the inside of the furnace was replaced with Ar. Thereafter, the temperature was continuously raised, and HDDR treatment was performed under the conditions shown in Table 5, and then the treated powder was crushed with a mesh having an opening of 500 μm to obtain a magnet powder sample.

  The magnetic properties of the obtained magnet powder were measured with a vibrating sample magnetometer (VSM: device name VSM-5SC-10HF (manufactured by Toei Kogyo Co., Ltd.)). Table 6 shows the measurement results.

In the sample for VSM measurement, the obtained magnetic powder was put into a cylindrical holder, fixed with paraffin while being oriented in a magnetic field of 800 kA / m, and then applied with a pulse magnetic field of 3.2 MA / m or more. A magnetized one was used. Also, for any sample, it was calculated value of the saturation magnetic flux density B _r a density of 7.60 g / cm ^3.

(Example 3)
Next, the influence of the atmosphere at the time of temperature rise on the HD processing time dependence of the magnetic characteristics was evaluated. Here, an experiment was conducted in the case of Dy = 1.2 atomic% and Co = 5 atomic% (alloy F in Table 1). FIG. 6 shows the measurement results. 6 (a) is the saturation magnetic flux density B _r HD processing time (t _HD) graph showing the dependence, and FIG. 6 (b) is a graph showing the coercivity H _cJ HD processing time (t _HD) dependent FIG. 6C is a graph showing the dependency of the index H _k indicating the squareness on the HD processing time (t _HD ). In the HDDR process of raising the temperature in hydrogen, the time after the holding temperature (840 ° C.) is reached is the HD process time (t _HD ).

As shown in FIG. 6A, in the comparative example (indicated by “in H ₂ ” in the graph) in which the atmosphere at the time of temperature rise is hydrogen, the saturation magnetic flux density _Br is 0. It is less than 9T and decreases as the HD processing time becomes longer. On the other hand, in the embodiment of the present invention (indicated by “in Ar” in the graph), the saturation magnetic flux density _Br gradually decreases as the processing time increases, but its absolute value is high, and the processing is performed for 6 hours. Later, it was found that 1T or more could be maintained.

On the other hand, as shown in FIG. 6B, it can be seen that the coercive force H _cJ increases as the HD processing time increases in both the example and the comparative example. In an embodiment of the present invention, in order to obtain a coercive force H _cJ equivalent coercivity H _cJ of the comparative example, there is a need for a long time kept isothermally for about two hours. In the comparative example, it is suggested that the HD reaction is proceeding slowly in this example even when the HD reaction proceeds within the heating time (1 hour) in hydrogen.

As shown in FIG. 6C, the longer the processing time, the lower the H _k of the comparative example, while the H _{k of} this example gradually increases until the processing time reaches 5 hours. It can be seen that it improves, but then decreases. FIG. 7 shows a demagnetization curve of the magnetic powder of the sample (HD treatment condition: 840 ° C., 5 hours) in which the highest squareness H _k was obtained among the samples subjected to each of the above treatments. In this sample, excellent magnetic properties of B _r = 1.09 T, H _cJ = 1723 kA / m, (BH) _max = 216 kJ / m ³ , and H _k = 719 kA / m were obtained.

  According to the present invention, since the progress of the HD reaction becomes gentle compared to the HDDR process in which the temperature is increased in hydrogen, an anisotropic magnet having a high coercive force and improved irreversible demagnetization is obtained. Can be used.

It is a figure which shows an example of the relationship between HD temperature and pressure when the time of HD reaction is fixed to a certain value. FIG. 2 is an enlarged view of region C in FIG. 1, and schematically shows the relationship between the holding temperature and pressure during HD reaction and the squareness ratio H _k of the obtained magnet when the added amounts of Co and Dy are constant values. It shows. (A) is a SEM photograph of magnetic powder particles before the HDDR treatment in which cracks are introduced, and (b) is a SEM photograph of magnetic powder immediately cooled after being heated in hydrogen for a short time. It is a graph which shows typically an example of the time change of the temperature of a HDDR process, and hydrogen partial pressure. ₄ is a graph showing magnetic characteristics (B _r , H _cJ ) shown in Table 3. (A) is a graph showing the HD processing time (t _HD) dependence of the saturation magnetic flux density B _r, (b) is a graph indicating the coercivity H _cJ HD processing time (t _HD) dependent , (C) is a graph showing the HD processing time (t _HD ) dependence of the index H _k indicating the squareness. It is a graph which shows the demagnetization curve obtained in the Example of this invention.

Claims (8)

10 atomic% or more and 20 atomic% or less Nd and / or Pr, 0.3 atomic% or more and 2 atomic% or less Dy, 1 atomic% or more and 10 atomic% or less Co, 6 atomic% or more and 8 atomic% or less B ( Preparing a fine powder of a (Nd, Pr) -Dy-Fe-Co-B-based raw material alloy satisfying the relational expression of Co + 10Dy <23 atomic%, which may be partially substituted with C;
The fine powder is heated in a vacuum or an inert gas atmosphere at least in a temperature range of 500 ° C. or higher and lower than 750 ° C., reaches a temperature of 750 ° C. or higher and lower than 1000 ° C., and then reaches 750 ° C. or higher and 1000 ° C. or higher. Step B for introducing hydrogen in a temperature range of less than
After Step B, Step C is performed at a temperature of 800 ° C. or more and less than 900 ° C. and a hydrogen pressure of 100 kPa or more and 300 kPa or less for 3 hours or more and less than 8 hours;
After step C, a step D of performing heat treatment for 30 minutes to 8 hours at a temperature of 800 ° C. or higher and lower than 900 ° C. and a hydrogen partial pressure of 10 kPa or lower;
Step E for cooling after Step D;
A method for producing a rare earth anisotropic magnet powder.   The method for producing a rare earth anisotropic magnet powder according to claim 1, wherein the raw material alloy further contains 0.01 atomic% or more and 1 atomic% or less of Ga.   The method for producing a rare earth anisotropic magnet powder according to claim 1, wherein an average particle size of the fine powder is 30 μm or more and less than 300 μm.   The method for producing a rare earth anisotropic magnet powder according to any one of claims 1 to 3, wherein the particles constituting the fine powder have cracks accompanying hydrogen storage before performing Step B.   The step B includes a step B ′ of introducing cracks into particles constituting the fine powder by occluding hydrogen in the fine powder in a hydrogen atmosphere at a pressure of 100 kPa or more and 300 kPa or less in a temperature range of less than 500 ° C., Item 4. A method for producing a rare earth anisotropic magnet powder according to any one of Items 1 to 3.   The method for producing a rare earth anisotropic magnet powder according to any one of claims 1 to 5, wherein in step B, the hydrogen partial pressure increase rate at the time of hydrogen introduction is set to 5 kPa / min to 100 kPa / min. In Step C, three phases of R (R is Nd or Pr) hydride phase, TB (T is Fe or Co) compound phase, and T phase coexist, and substantially Nd ₂ Fe ₁₄ B type The method for producing a rare earth anisotropic magnet powder according to any one of claims 1 to 6, wherein a structure containing no crystal phase is formed in the fine powder. A rare-earth anisotropic magnet powder obtained by the production method according to any one of claims 1 to 7, the saturation magnetic flux density B _r ≧ 1T, rare earth shows the magnetic characteristics of a coercive force H _cJ ≧ 1600kA / m different Isotropic magnet powder.