JP2017139385A - Production method of rare-earth magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rare-earth magnet production method allowing for production of a rare-earth magnet with an excellent magnet characteristic even with an increased relative density.SOLUTION: The rare-earth magnet production method is provided that comprises: a preparation step of preparing a base powder composed of a rare earth-iron-based alloy including a rare earth element and an iron group element; a hydrogenation step of producing hydrogenated powder by applying a hydrogenation processing to the base powder at a temperature of disproportionation temperature or higher in an atmosphere including hydrogen; a granulation step of producing granulated powder obtained by consolidating powder particles of the hydrogenated powder by plastic deformation; a molding step of producing a molded article by applying pressure molding to the granulated powder; and a dehydrogenation step of applying a dehydrogenation processing to the molded article at a temperature of a re-coupling temperature or higher in the inert atmosphere or a reduced pressure atmosphere thereby producing a re-coupled material.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a rare earth magnet for producing a rare earth magnet used for a permanent magnet or the like.

Rare earth magnets are used in motors and generators. Conventional rare earth magnets are mainly sintered magnets obtained by sintering magnet powder, and bonded magnets obtained by solidifying magnet powder with a binder resin. Typically, there is a neodymium magnet using an Nd—Fe—B alloy having Nd ₂ Fe ₁₄ B as a main phase. In addition, Sm—Fe—N alloys containing Sm ₂ Fe ₁₇ N ₃ as a main phase have been studied as magnet powders for bonded magnets.

  As rare earth magnets other than sintered magnets and bonded magnets, there is a dust magnet described in Patent Document 1. The dust magnet is obtained by subjecting raw material powder made of Nd-Fe-B alloy, Sm-Fe alloy, etc. to hydrogenation (HD) to separate Fe-containing components, and to obtain the obtained hydrogenation. It is manufactured through a process in which powder is molded with a mold, and this molded body is subjected to a dehydrogenation (DR: Desorption-Recombination) treatment and recombined. In the Sm—Fe—N-based magnet, a nitriding step is further performed after the dehydrogenation treatment.

  Since the above-mentioned hydrogenated powder contains a component containing soft Fe, it is excellent in plastic deformability. If such a hydrogenated powder is used, a compact with a large relative density can be formed, and finally a dense dust magnet can be obtained.

JP 2011-241453 A

Rare earth magnets that are superior in magnet properties such as coercive force are desired.
Theoretically, the larger the ratio of the magnet component, the better the magnet characteristics. If hydrogenated powder is used as described above, a compact having a large relative density can be formed (Embodiments 1 and 2 of Patent Document 1), and a dust magnet having a large proportion of magnet components can be obtained. However, a compact magnet with a low density using a compact having a smaller relative density even if it is subjected to dehydrogenation or nitriding on a compact having a large relative density, particularly 80% or more, and even 90% or more. As a result, it was found that the magnetic properties such as coercive force could not be sufficiently improved. Further, when the molding pressure is increased (eg, more than 980 MPa (10 ton / cm ² )), although the relative density can be increased in a short time and the productivity is excellent, it is difficult to improve the magnet characteristics such as the coercive force. In some cases, the coercive force is lower than that of a dense dust magnet (see test examples described later).

  Accordingly, one object of the present invention is to provide a method for producing a rare earth magnet that can produce a rare earth magnet having excellent magnet characteristics even when the relative density is increased.

A method for producing a rare earth magnet according to an aspect of the present invention includes:
Preparing a raw material powder composed of a rare earth-iron alloy containing a rare earth element and an iron group element;
A hydrogenation step of producing a hydrogenated powder by subjecting the raw material powder to a hydrogenation treatment at a temperature equal to or higher than a disproportionation temperature in an atmosphere containing hydrogen;
A granulating step for producing a granulated powder obtained by hardening powder particles of the hydrogenated powder by plastic deformation;
A molding step of pressure-molding the granulated powder to produce a molded body;
A dehydrogenation step of producing a recombination material by subjecting the molded body to a dehydrogenation treatment at a temperature equal to or higher than a recombination temperature in an inert atmosphere or a reduced pressure atmosphere.

  The above-described method for producing a rare earth magnet can produce a rare earth magnet having excellent magnet characteristics even when the relative density is increased.

Sample No. produced in Test Example 1 It is the microscope picture which observed the cross section of the recombining material of 1-7 with the optical microscope. Sample No. produced in Test Example 1 It is the microscope picture which observed the cross section of the recombining material of 1-107 with the optical microscope.

[Description of Embodiment of the Present Invention]
When the present inventors performed dehydrogenation treatment or nitriding treatment on a molded article having a large relative density using the above-described hydrogenated powder, in particular, a molded article having a relative density of 80% or more, more preferably 90% or more, The reason why the magnetic properties such as coercive force cannot be improved sufficiently was investigated. As a result, in a compact with a large relative density, the hydrogenated powder is easily plastically deformed, so that the powder particles forming the surface of the compact rub against the mold to extend the pores on the surface of the compact. It has been found that the powder particles forming the inside of the body are deformed so as to crush each other, thereby easily closing the pores inside the molded body. It was found that as the molding pressure was increased, the problem of blocking the above-described pores was likely to occur. One of the reasons for plugging the pores may be that the hydrogenated powder is inferior in fluidity. If the hydrogenated powder in the mold sufficiently flows along with the compression operation of the hydrogenated powder by the mold, the pressing force of the mold punch can uniformly act on the hydrogenated powder in the mold. However, when it is difficult to flow, it is considered that the pressing force of the punch of the mold locally acts on the hydrogenated powder in the mold and is easily pressed nonuniformly, so that the pores inside the molded body are easily crushed ( (See FIG. 2 below). It is also conceivable that the spacing between the powder particles is locally narrowed due to uneven pressing. When the dehydrogenation process is performed in a state where the interval is narrow, it is considered that the pores are easily crushed even by the thermal contraction after the dehydrogenation process. Further, if the hydrogenated powder is difficult to flow, it is considered that the frictional force with the mold becomes large at the time of demolding and the pores on the surface of the molded body are easily crushed.

  The pores of the molded body described above are used as a discharge path for discharging hydrogen from the molded body during the dehydrogenation process, and as an introduction path for introducing nitrogen into the molded body during the nitriding process. If the pores inside the molded body or inside the molded body are blocked as described above, the gas passages such as hydrogen and nitrogen are not sufficiently provided, and hydrogen is discharged during dehydrogenation and nitrogen is introduced during nitriding. It becomes difficult. Since the atomic diameter of the nitrogen atom is larger than that of the hydrogen atom, it is difficult to introduce nitrogen. Dehydrogenation, recombination, and nitridation can be sufficiently performed by increasing the heating temperature of the dehydrogenation treatment or nitriding treatment or by increasing the treatment time. However, when dehydrogenation is performed at a high temperature for a long time, crystals of the recombined alloy grow. Since the coercive force is inversely proportional to the crystal size, having a coarse crystal structure lowers the magnet characteristics such as the coercive force even though the relative density is large and the ratio of the magnet component is large.

Then, when granulated powder was produced and fluidity | liquidity was improved, if it was set as specific granulated powder, the rare earth magnet which has a high coercive force according to high relative density was obtained.
The present invention is based on the above findings.
First, embodiments of the present invention will be listed and described.

(1) A method for producing a rare earth magnet according to an aspect of the present invention includes:
Preparing a raw material powder composed of a rare earth-iron alloy containing a rare earth element and an iron group element;
A hydrogenation step of producing a hydrogenated powder by subjecting the raw material powder to a hydrogenation treatment at a temperature equal to or higher than a disproportionation temperature in an atmosphere containing hydrogen;
A granulating step for producing a granulated powder obtained by hardening powder particles of the hydrogenated powder by plastic deformation;
A molding step of pressure-molding the granulated powder to produce a molded body;
A dehydrogenation step of producing a recombination material by subjecting the molded body to a dehydrogenation treatment at a temperature equal to or higher than a recombination temperature in an inert atmosphere or a reduced pressure atmosphere.

  The method for producing a rare earth magnet can produce a rare earth magnet having excellent magnet characteristics such as coercive force even when the relative density is increased using the hydrogenated powder for the following reasons.

The powder used for molding is a granulated powder hardened by plastic deformation between powder particles of hydrogenated powder, that is, a binderless granulated powder that does not use a binder such as an organic binder. Each particle (secondary particle) of the granulated powder is larger than the powder particle (primary particle) of the hydrogenated powder and has excellent fluidity. For example, the molding pressure is higher than 980 MPa, further high pressure such as 1470 MPa (15 ton / mm ² ) or more, and it is good even when producing a molded article having a large relative density, for example, a molded article having a relative density of 80% or more and further 90% or more. Can flow into.
And this molded object has a pore formed along the interface of granulated powder. Since each particle of the granulated powder is larger than the powder particle of the hydrogenated powder, the cross-sectional area of the pores is likely to be large, and it is difficult to be completely blocked even during molding or demolding. Therefore, this molded object can fully have the open pores which continue from the surface inside to the whole molded object. These open pores can be used as a hydrogen discharge path during dehydrogenation and a nitrogen introduction path during nitriding. Since these gas passages can be used, the ratio of magnet components (recombined alloys and nitrided alloys) can be increased by uniformly and sufficiently performing dehydrogenation and nitriding over the entire object to be treated. In addition, magnetic properties such as coercive force can be effectively improved.
In this way, if the molded body has sufficient gas passages such as hydrogen and nitrogen, dehydration can be performed without excessively increasing the temperature or excessively increasing the processing time during the dehydrogenation process or the nitriding process. Elemental recombination and nitridation can proceed. Therefore, the recombination material having a fine crystal structure can be obtained by suppressing the coarsening of the crystal of the recombination alloy due to the dehydrogenation treatment at a high temperature for a long time.
This is because, in the above rare earth magnet manufacturing method, by using the recombination material as a raw material, it is possible to have a coercive force according to the ratio of the magnet component.

  Moreover, it is because it does not cause the fall of the ratio of the magnet component by containing of a binder, and the fall of the magnet characteristic resulting from the binder residue by setting it as binderless granulated powder.

(2) As an example of the method for producing the rare earth magnet,
The granulation step includes
A rolling process for producing a rolled material by performing powder rolling using the hydrogenated powder;
And a classification step of pulverizing the rolled material to obtain the granulated powder having a predetermined size.

  The said form can mass-produce the binderless granulated powder of a desired magnitude | size easily. In the said form, the granulated powder which consists of a thin plate-shaped piece typically can be formed.

(3) As an example of the manufacturing method of the rare earth magnet which performs said powder rolling, the form which makes the aspect ratio of the said granulated powder 3 or less is mentioned.
The aspect ratio is the ratio of the maximum length to the thickness (substantially equal to the thickness of the rolled material) in each particle of the granulated powder that is plate-like, and the maximum length / thickness. The measuring method will be described later.

  The said form can manufacture the rare earth magnet which is excellent in magnet characteristics, such as a coercive force, for the following reasons. The granulated powder used in the above form can be said to be a plate-like piece having a relatively small maximum length. The molded body formed of such granulated powder has a sufficient number of interfaces of the granulated powder, and can sufficiently have the above-described gas passages formed along this interface. Each particle of the granulated powder has pores formed along the interface of the powder particles of the hydrogenated powder, and these pores can also be used for the above-described gas passage. The shortest distance of the gas passage provided for each particle of the granulated powder can be set to about the maximum length of each particle of the granulated powder. This is because the gas passage is sufficiently provided, so that even when the relative density is increased, the dehydrogenation process or the like can be performed without the conditions of high temperature and long time.

(4) As an example of the method for producing the rare earth magnet, there may be mentioned a form in which the relative density of the molded body is 90% or more.
The relative density of the molded body is the actual density of the molded body with respect to the true density of the molded body. Specifically, (density of molded body / true density of molded body) × 100 (%).
The density of the molded body can be obtained by, for example, the Archimedes method in an oil-impregnated state, or can be obtained by calculation by measuring the dimensions and mass if the shape is simple.
The true density of the compact is obtained, for example, by analyzing the composition ratio of the constituent phases of the hydrogenated alloy forming the compact, the composition of the constituent phases, and the crystal structure, or by measuring the hydrogenated alloy in the powder state by the pycnometer method, etc. It can be obtained by actual measurement.
In the method for producing a rare earth magnet according to the present invention, since granulation is performed without a binder, the region other than the hydrogenated alloy in the compact is substantially void, and the relative density of the compact is the volume ratio of the hydrogenated alloy. This value correlates with.

  In the above embodiment, since the relative density is sufficiently large and the ratio of the magnet component can be increased, it is possible to manufacture a rare earth magnet that is superior in magnet characteristics such as coercive force.

[Details of the embodiment of the present invention]
Hereinafter, embodiments of the present invention will be described in detail.

[Rare earth magnet manufacturing method]
The manufacturing method of the rare earth magnet according to the embodiment manufactures a dust magnet through a process of forming a hydrogenated powder and then performing a dehydrogenation process to manufacture a recombined material. One feature of the method for producing a rare earth magnet of the embodiment is that the powder to be molded is not a hydrogenated powder, but is a specific granulated powder produced using the hydrogenated powder. When a compact is formed from a specific granulated powder, a rare earth magnet having a large relative density and excellent in magnetic properties such as coercive force and remanent magnetization can be produced.

  The outline of the method for producing a rare earth magnet of the embodiment is described. A preparation step for preparing raw material powder, a hydrogenation step for subjecting the raw material powder to a hydrogenation treatment, and the above-mentioned specific granulated powder is produced using the hydrogenated powder. A granulating step, a molding step for molding the granulated powder, and a dehydrogenation step for subjecting the compact to a dehydrogenation process. Hereinafter, each process will be described in detail.

(Preparation process)
In the preparation step, a raw material powder composed of a rare earth-iron alloy containing a rare earth element and an iron group element is prepared.

-Rare earth-iron-based alloy The rare earth element includes one or more elements selected from scandium (Sc), yttrium (Y), lanthanoids and actinoids. A rare earth magnet having excellent magnet characteristics when it contains at least one element selected from neodymium (Nd), samarium (Sm), praseodymium (Pr), cerium (Ce), dysprosium (Dy), and Y as the rare earth element Is preferable. When Nd or Sm is contained, a rare earth magnet having excellent magnet characteristics can be obtained.

The rare earth element content may be 10 mass% or more and less than 40 mass%. In the composition containing Nd, the content of Nd is 25% by mass or more (further 28% by mass or more) and 35% by mass or less. In the composition containing Sm, the Sm content is 24 mass% or more and 26.5 mass% or less. When the content of Nd or Sm is within the above range, a rare earth-iron alloy such as Nd ₂ Fe ₁₄ B or Sm ₂ Fe ₁₇ can be obtained as the stoichiometric composition.

  Examples of the iron group element include one or more elements selected from iron (Fe), cobalt (Co), and nickel (Ni). Specifically, a form in which Fe is a main component of the rare earth-iron alloy (more than 50% by mass), a form containing both Fe and Co, and the like can be given. In the form containing Fe and Co, the coercive force can be further improved.

  The composition containing Nd includes at least one element selected from boron (B), carbon (C), and nitrogen (N) in addition to the rare earth element and the iron group element described above. Examples of the content of B, C, and N include 0.1% by mass or more and 5.0% by mass or less, and further 0.5% by mass or more and 1.5% by mass or less.

The rare earth-iron-based alloy can further include one or more elements selected from a transition metal element, gallium (Ga), aluminum (Al), and silicon (Si). Examples of the transition metal element include copper (Cu), titanium (Ti), manganese (Mn), niobium (Nb), and the like. The content of these additive elements (the total content in the case of plural elements) is 0.1% by mass or more and 20% by mass or less, and further 0.1% by mass or more and 5% by mass or less. If these elements are contained, effects such as improvement in coercive force (eg, Ga) can be expected. These additive elements are present, for example, by being replaced with part of Fe.
In addition, rare earth-iron alloys allow the inclusion of inevitable impurities.

Specific examples of the rare earth-iron alloy include the following.
[Composition containing Nd]
Nd—Fe—B based alloy having Nd—Fe—B based compound (eg, Nd ₂ Fe ₁₄ B) as main phase, Nd—Fe—C based compound (eg, Nd ₂ Fe ₁₄ C) as main phase Nd-Fe-C-based alloys, Nd-Fe-Co-B-based alloys having Nd-Fe-Co-B-based compounds (eg, Nd ₂ (Fe ₁₃ Co ₁ ) B) as the main phase, Nd-Fe-Co Nd—Fe—Co—C based alloys having a main phase of a —C compound (eg, Nd ₂ (Fe ₁₃ Co ₁ ) C) [composition containing Sm]
Sm-Fe based alloys having Sm—Fe based compounds (eg, Sm ₂ Fe ₁₇ , Sm ₁ Ti ₁ Fe ₁₁ ) as the main phase

-Raw material powder The magnitude | size of the raw material powder comprised from the said rare earth-iron type alloy can be selected suitably. For example, the maximum diameter of the powder particles of the raw material powder can be 10 μm or more and 0.5 mm or less. If the maximum diameter is within this range, it is easy to perform a hydrogenation treatment or to form granulated powder. The smaller the maximum diameter is in the above range, the easier it is to perform the hydrogenation process in a shorter time, so the maximum diameter can be 0.4 mm or less, further 0.3 mm or less, and 0.15 mm (150 μm) or less. Since the larger the maximum diameter in the above range, the easier the handling and the better the workability, the maximum diameter can be set to 30 μm or more, further 40 μm or more, 50 μm or more.
The maximum diameter of the raw material powder can be adjusted by adjusting the powder production conditions or separately pulverizing. When the pulverization is performed in an inert gas atmosphere such as Ar or N ₂ , oxidation of the rare earth-iron alloy can be prevented.
The maximum diameter of the raw material powder is the length of the longest portion when the powder particles of the raw material powder are viewed in plan from an arbitrary direction.

  The shape of the raw material powder is not particularly limited. Various shapes such as a spherical shape, a rod shape, and a flake shape can be used.

  The manufacturing method of raw material powder can be selected according to a composition etc. Specific methods include a rapid solidification method, a reduction diffusion method, a melt casting method, a gas atomizing method, and the like. Examples of the rapid solidification method include a strip cast method and a melt span method.

(Hydrogenation process)
In the hydrogenation step, the above-mentioned raw material powder is subjected to hydrogenation treatment at a temperature equal to or higher than the disproportionation temperature in an atmosphere containing hydrogen to produce hydrogenated powder.

The hydrogenated powder is composed of a hydrogenated alloy having a structure in which a rare earth-iron-based alloy is phase-decomposed into a phase of a rare earth element hydrogen compound and a phase of an iron-containing material containing iron. Examples of the rare earth element hydrogen compound include NdH ₂ and SmH ₂ . Examples of the iron-containing material include pure iron (Fe). When the raw material powder has the above-described composition containing Nd, typically, pure iron and an iron compound such as Fe ₂ B or Fe ₂ C are included. Since the hydrogenated alloy has a pure iron phase that is softer than the rare earth-iron-based alloy before phase decomposition and softer than the phase of the rare earth element hydrogen compound, it is excellent in plastic deformability. When such hydrogenated powder is pressurized in the granulation process or the molding process, the powder particles can be bonded together by plastic deformation.

  When the hydrogenated alloy has a structure composed of a rare earth element hydrogen compound phase of 10 volume% or more and less than 40 volume% and the iron-containing material phase containing iron, the iron-containing material phase is the main component. Since it is (60 volume% or more and 90 volume% or less), it is excellent in plastic deformability and a moldability, and is preferable.

Examples of the conditions for the hydrogenation treatment include the following.
(Atmosphere) H ₂ gas atmosphere, mixed gas atmosphere of H ₂ gas and inert gas such as Ar or N ₂ (Temperature) Above the hydrogen disproportionation temperature of the rare earth-iron alloy used for the hydrogenation treatment, Below the temperature at which the iron-based alloy does not melt and fix Depending on the composition, for example, 600 ° C. or higher and 1100 ° C. or lower (holding time) 30 minutes or longer and 300 minutes or shorter

  The shape and size of the hydrogenated powder substantially maintain the shape and size of the raw material powder. Therefore, the shape and size of the raw material powder may be adjusted so that the hydrogenated powder has a desired shape and size.

  A known technique can be appropriately referred to for the steps until the hydrogenated powder is produced.

(Granulation process)
In the granulation step, using the above-described hydrogenated powder excellent in plastic deformability, a granulated powder is produced by solidifying the powder particles of the hydrogenated powder by plastic deformation.

  That is, a binderless granulated powder that does not use a binder is prepared. By forming a molded body from the granulated powder, a decrease in the relative density of the molded body due to the binder content does not substantially occur, and a molded body having a sufficiently large relative density can be manufactured. For example, a molded body having a relative density of 80% or more and further 90% or more can be produced. Moreover, the process of removing a binder is also unnecessary.

-Powder rolling method In order to produce the binderless granulated powder, it is possible to collect hydrogenated powder and perform plastic working. In particular, powder rolling can be suitably used. If powder rolling is used, a strip composed of a hydrogenated alloy can be easily manufactured continuously, and a long strip can also be manufactured. If the obtained (long) strip is appropriately pulverized and then classified, a powder larger than the hydrogenated powder can be easily produced, and this powder can be used as a granulated powder. From the above points, powder rolling can easily mass-produce binderless granulated powder. Therefore, the granulation step includes a rolling step of performing powder rolling using hydrogenated powder to produce a rolled material, and a classification step of pulverizing the rolled material to obtain a granulated powder of a predetermined size. be able to.

..Rolling process Powder rolling is a process in which the axes of a pair of rolling rolls are arranged parallel to each other, and powder is supplied between the rolling rolls in a state where a predetermined pressure is applied in a direction to narrow the interval between the rolling rolls. Thus, this is a plastic working method capable of producing a strip or a strip (having a relatively short length) in which powder particles are bonded by plastic deformation. A commercially available apparatus can be used for powder rolling. Although the powder rolling atmosphere can be selected as appropriate, an inert atmosphere is preferable because oxidation of the hydrogenated powder and the rolled material can be prevented.

  It is preferable to lower the relative density of the rolled material produced by powder rolling (the density of the rolled material / the true density of the rolled material) to some extent. Specifically, the relative density is 35% or more and 75% or less. When the relative density is 35% or more, a rolled material having sufficient strength that powder particles can be sufficiently bonded to each other to produce a rolled material and can maintain a granulated state during pulverization can be obtained. By pulverizing and classifying the rolled material, a granulated powder having a desired size can be obtained. When the relative density is 75% or less, the powder particles are excessively crushed, the increase in hardness due to work hardening can be reduced, and a granulated powder having excellent moldability can be easily obtained. Considering strength, moldability, and the like, the relative density can be 40% or more and 70% or less, and further 45% or more and 65% or less. The rolling conditions (such as applied pressure during rolling) may be adjusted so that the relative density satisfies the above range. This rolled material typically has a direction in which a plurality of powder particles of hydrogenated powder are stacked in the thickness direction of the rolled material and intersects the thickness direction of the rolled material (for example, the direction of the rolled material in the orthogonal direction). (Longitudinal direction) each powder particle has a structure extended by plastic deformation. The relative density of the rolled material can be measured in the same manner as the above-described method for measuring the relative density of the formed body.

  Although the thickness of a rolling material is based also on the magnitude | size of hydrogenation powder, about 100 micrometers or more and 2000 micrometers or less are mentioned, for example. If the thickness is about 100 μm or more, it is easy to produce a granulated powder that is sufficiently larger than the hydrogenated powder. In addition, the thinner the rolled material, the more easily the powder particles are crushed and work hardened. However, if the thickness is about 100 μm or more, the amount of plastic deformation of the powder particles is not excessively increased, and hydrogen The softness of the powdered powder can be maintained, and it is easy to obtain a granulated powder excellent in moldability. The thickness can be further set to 200 μm or more and 300 μm or more. If the said thickness is about 2000 micrometers or less, it will be easy to bite a powder between rolling rolls, and it is excellent in the productivity of a rolling material. The said thickness can be 1000 micrometers or less, 800 micrometers, and 600 micrometers or less.

..Classification process In the above-mentioned powder rolling, a long rolled material can be produced to some extent. Since it is difficult to mold in the molding process as long as it is long, it is pulverized so as to be easily molded and classified into a predetermined size. For the pulverization, a known pulverization apparatus such as a jet mill, a ball mill, a hammer mill, a brown mill, a pin mill, a disk mill, or a jaw crusher can be used.

  When the rolled material is pulverized, a plate-like piece having a thickness substantially equal to the thickness of the rolled material is typically obtained. Of these plate-like pieces, at least the small powder below the hydrogenated powder is removed, and when the larger powder than the hydrogenated powder is extracted to form a granulated powder, the granulated powder having excellent fluidity can be used for molding. . When the granulated powder is large to some extent, the gas passage formed along the interface of the granulated powder is not easily crushed during molding or demolding, and the gas passage is easily maintained. From this, it is preferable to extract the plate-like piece having a maximum length of about 1 or more times its thickness, for example. On the other hand, if the granulated powder is too large, the shortest distance of the gas passage provided in each particle of the granulated powder becomes long, and it is necessary to perform dehydrogenation treatment or nitriding treatment under conditions of high temperature and long time. As a result, the crystal characteristics become coarse, and as a result, the magnet characteristics may be deteriorated. From this, it is preferable to extract the plate-shaped piece having a maximum length of, for example, less than about 4 times its thickness.

  More specifically, the aspect ratio, which is the ratio of the maximum length of each particle of the granulated powder to the thickness of each particle of the granulated powder, is preferably 1 or more and 3 or less. The larger the aspect ratio in this range, the easier it is to secure the gas passage formed along the interface of the granulated powder as described above, and the aspect ratio can be 1.2 or more, and more preferably 1.5 or more. . The smaller the aspect ratio in this range, the easier it is to shorten the gas passage provided in each particle of the granulated powder as described above, and the aspect ratio can be 2.8 or less, and further 2.5 or less. A plate-like piece having an aspect ratio that satisfies the above range may be extracted. A known classifier or the like can be used for this extraction.

  Typically, the extracted plate-like piece substantially maintains the structure of the rolled material described above, and a plurality of powder particles of hydrogenated powder are laminated in the thickness direction of the plate-like piece, and the plate-like piece Each powder particle extends in a plastically deformed direction in a direction intersecting the thickness direction of the piece (eg, orthogonal direction).

Other methods As another method, a preforming step for producing a sparse preform with a relatively low relative density as described above using hydrogenated powder, and pulverizing the preform to a predetermined size And a classification step for obtaining the granulated powder. For forming the preform, general uniaxial press molding, isostatic pressing, or the like can be used. In the classification step, the preform is crushed so as to be a plate-like piece as in the case of using the powder rolling method described above, and the ratio of the maximum length of the plate-like piece to the thickness of this plate-like piece is 1 or more. Extracting a plate-shaped piece satisfying 3 or less is mentioned.

(Molding process)
In the molding step, the granulated powder is pressure-molded to produce a molded body having a predetermined shape and size.

  The relative density of the molded body produced in the molding process is substantially maintained by the recombination material after the dehydrogenation treatment and the nitride material after the nitriding treatment. Therefore, the higher the relative density of this molded body, the larger the ratio of the magnet component, and the more rare earth magnets having excellent magnet characteristics such as high coercive force can be produced. In consideration of improvement in magnet characteristics, the relative density of the compact is preferably 80% or more, more preferably 82% or more, 84% or more, and particularly preferably 90% or more. Since granulated powder is excellent in fluidity | liquidity, the relative density of a molded object can be 91% or more, and also 92% or more. On the other hand, the molded body needs to have a certain amount of pores used for the above-described gas passage so that the dehydrogenation process and the nitriding process can be performed satisfactorily. Therefore, the relative density of the molded body is preferably 97% or less, more preferably 95% or less.

As the molding pressure is increased, a molded article having a large relative density can be molded in a short time, and the productivity is excellent. Since the granulated powder used for molding is excellent in fluidity as described above, even if the molding pressure is increased, it is difficult to block pores formed along the interface of the granulated powder, and the above-described gas passage is sufficiently provided. A molded body can be formed. For example, the molding pressure is, 980MPa (10ton / cm ^2), greater than can be further 1176MPa (12ton / cm ²⁾ or more, 1470MPa (15ton / cm ²⁾ or more.

  When the molding is performed in a low oxygen atmosphere having an oxygen concentration of 5% by volume or less, and further 1% by volume or less, oxidation of the granulated powder can be suppressed. The low oxygen atmosphere can be an inert gas atmosphere such as Ar, a reduced pressure atmosphere (eg, a vacuum atmosphere of 10 Pa or less), and the like.

  For molding, a mold having a desired shape may be used. The mold typically includes a die having a through-hole and a pair of die that forms a molding space together with the inner peripheral surface of the die and inserts into the through-hole to compress and compress powder (here, granulated powder). A thing provided with an up-and-down punch is mentioned. When a lubricant is applied to the inner surface of the mold, the friction between the granulated powder or molded body and the mold can be reduced, and the blockage of pores due to sliding with the mold can be reduced.

  When using what was produced using the above-mentioned powder rolling as granulated powder, the part similar to the structure of granulated powder may be included in at least one part of a molded object. Specifically, it has a structure in which powder particles of a plurality of hydrogenated powders are stacked and each powder particle extends in a plastically deformed direction in a direction intersecting the stacking direction (eg, orthogonal direction).

(Dehydrogenation process)
In the dehydrogenation step, a recombination material is produced by subjecting a molded body produced using the above-mentioned specific granulated powder to a dehydrogenation treatment at a temperature equal to or higher than the recombination temperature in an inert atmosphere or a reduced pressure atmosphere. .

  The recombination material is obtained by recombining a hydrogenated alloy phase-decomposed into a rare earth element hydrogen compound phase and an iron-containing material phase by the above-mentioned hydrogenation treatment, and the same rare earth-iron as the raw material powder. It is formed of a rare earth-iron alloy having a main compound as a main phase.

Examples of the dehydrogenation conditions include the following.
(Atmosphere) Non-hydrogen atmosphere Specifically, an inert gas atmosphere such as Ar or N ₂ or a reduced-pressure atmosphere (eg, a vacuum atmosphere whose pressure is lower than the standard atmospheric pressure)
(Temperature) Recombination temperature of the hydrogenated alloy or higher Depending on the composition, for example, 600 ° C. or higher and 1000 ° C. or lower (holding time) of 10 minutes or longer and 600 minutes or shorter. When the atmosphere is 10 Pa or less, and further 1 Pa or less, the rare earth element hydrogen compound hardly remains. Moreover, if it is said temperature range, the growth of the crystal | crystallization of a recombination alloy can be suppressed and it can be set as a fine crystal structure.

(Nitriding process)
Depending on the composition of the recombination material, the recombination material can be subjected to nitriding treatment in a nitrogen-containing atmosphere at a temperature equal to or higher than the nitriding temperature of the recombination material. For example, when the recombination material is composed of an Sm—Fe based alloy, the Sm—Fe based alloy can be changed to an Sm—Fe—N based alloy by the nitriding treatment. In this case, the method for producing a rare earth magnet includes a nitriding step in which the recombination material is subjected to the nitriding treatment to produce a nitride material.

Examples of the nitriding conditions include the following.
(Atmosphere) The nitrogen-containing atmosphere is an atmosphere containing a nitrogen element and an atmosphere containing at least one of nitrogen (N ₂ ) and ammonia (NH ₃ ).
Specifically, NH ₃ gas atmosphere, mixed gas atmosphere of NH ₃ gas and H ₂ gas, N ₂ gas atmosphere, mixed gas atmosphere of N ₂ gas and H ₂ gas (temperature) 200 ° C. or more and 550 ° C. or less, Preferably it is 300 degreeC or more and 450 degrees C or less (holding time) 10 minutes or more and 1000 minutes or less, Preferably it is 30 minutes or more and 800 minutes or less

(effect)
In the method for producing a rare earth magnet of the embodiment, a specific granulated powder is produced with a hydrogenated powder, and this granulated powder is molded. Therefore, even if the relative density of the molded body is increased, particularly 90% or more, A molded body having sufficient open pores that serve as gas passages during dehydrogenation or nitriding can be produced. With such a molded body, dehydrogenation treatment and nitriding treatment can be performed without high temperature and long time conditions, and the crystals of the recombined alloy can be maintained finely. Therefore, the method for producing a rare earth magnet of the embodiment can produce a rare earth magnet having a large relative density and excellent magnet characteristics such as coercive force. This effect will be specifically described in test examples described later.

[Rare earth magnet]
A rare earth magnet can be obtained by magnetizing the recombination material or the nitride material. This rare earth magnet is mainly composed of a rare earth-iron alloy. The specific composition of the rare earth-iron-based alloy forming the rare earth magnet is the same as that of the above-mentioned raw rare earth-iron-based alloy in the composition containing Nd, and the composition containing Sm is the Sm-Fe-N-based alloy. (Example of main phase, Sm ₂ Fe ₁₇ N ₃ ), Sm—Ti—Fe—N alloy (example of main phase, Sm ₁ Ti ₁ Fe ₁₁ N ₂ ), Sm—Mn—Fe—N alloy, etc. Can be mentioned. The above-mentioned recombination material and the above-mentioned nitride material are manufactured using the above-mentioned molded body having a large relative density, in particular, a molded body having a relative density of 90% or more, so that a high coercive force according to the ratio of the magnet component is obtained. It has a high remanent magnetization and is a rare earth magnet with excellent magnet characteristics.

[Test Example 1]
As rare earth magnets, dust magnets were produced under various production conditions, and the magnet characteristics were examined.

≪Sample preparation≫
In this test, a dust magnet (sample No. 1-1 to No. 1-7, No. 1-101 to No. 1-107) composed of an Nd—Fe—Co—B alloy, and Sm— The dust magnets (samples No. 1-11 to No. 1-14, No. 1-111 to No. 1-114) made of Fe—N alloy are prepared.

The manufacturing process of the magnet material before magnetization is as follows.
In a granulation process in a sample having a granulation process, powder rolling is performed to produce a rolled material, and the rolled material is pulverized into plate-like pieces and classified to extract a predetermined size. .
[Nd system]
(Sample No. 1-1 to No. 1-7, with powder rolling / classification)
Preparation process-> hydrogenation process-> granulation process-> molding process-> dehydrogenation process (sample No. 1-101-No. 1-107, no powder rolling / classification)
Preparation process → Hydrogenation process → Molding process → Dehydrogenation process (Sm system)
(Sample No. 1-11 to No. 1-14, with powder rolling / classification)
Preparation process-> hydrogenation process-> granulation process-> molding process-> dehydrogenation process-> nitriding process (sample No. 1-111-No. 1-114, no powder rolling / classification)
Preparation process → Hydrogenation process → Molding process → Dehydrogenation process → Nitriding process

[Nd system]
By strip casting, 30.5% by mass Nd-5.0% by mass Co-1.0% by mass B-the balance is made of Fe and inevitable impurities, and a 300 μm thick ribbon is produced. Smash. This thin ribbon is composed of an Nd—Fe—Co—B alloy having Nd ₂ (Fe ₁₃ Co ₁ ) B as a main phase. The coarse pulverization is performed using a commercially available pulverizer under an inert atmosphere. Here, the crushed flakes are classified by an appropriate sieve. Then, among the flakes, those having a maximum diameter of 106 μm or more and 355 μm or less are extracted and used as raw material powder.

(Hydrogenation process)
The raw material powder is subjected to a hydrogenation treatment to produce a hydrogenated powder. The conditions for the hydrogenation treatment are a hydrogen atmosphere and 850 ° C. × 150 minutes.

(Granulation process)
Sample No. with a granulation step. 1-1-No. For 1-7, a commercial powder rolling mill is used to produce a rolled material having a relative density of 40% to 55% and a thickness of 350 μm. Here, the rolling material which satisfy | fills said relative density is produced by making an applied pressure into 5 tons and rolling speed into 0.5 m / min.

The obtained rolled material is a continuous strip having a certain length (eg, a length of less than 50 cm). The rolled material is pulverized using a commercially available pulverizer and then classified under the following conditions.
<Classification condition α> More than about 1 times the mesh thickness (355 μm) of the rolled material, less than about 2 times the mesh thickness (710 μm) of the rolled material, 350 μm in thickness, maximum extracted by this classification condition A plate-like piece having a length of more than 355 μm and less than 710 μm is used as granulated powder.
<Classification condition β> More than about 1 times the mesh thickness of rolled material (355 μm) and less than about 3 times the mesh thickness of rolled material (1180 μm) Thickness 350 μm extracted by this classification condition, maximum A plate-like piece having a length of more than 355 μm and less than 1180 μm is used as granulated powder.
<Classification condition γ> More than about 1 times the mesh thickness of rolled material (355 μm) and less than about 5 times the thickness of rolled material (1700 μm) Thickness 350 μm extracted by this classification condition, maximum A plate-like piece having a length of more than 355 μm and less than 1700 μm is used as granulated powder.
Table 1 shows the aspect ratio of the prepared granulated powder. As for the aspect ratio, the aspect ratio = (maximum length / thickness) is obtained for each particle of 100 or more granulated powders, and the average value is 100 or more.

(Molding process)
The above-mentioned granulated powder or non-granulated hydrogenated powder is pressure-molded with a mold to produce a compact. Here, the size Satoshi selected molding pressure from ^{980MPa~1961MPa (10ton / cm 2 ~20ton /} cm 2), is formed with a diameter 10mm, a height of 10mm cylindrical. Table 1 shows the molding pressure (ton / cm ² ). Here, a lubricant is applied in the mold.

Table 1 shows the relative density of the produced cylindrical molded body. The relative density (%) of the molded body is (density of molded body / true density of molded body) × 100. The density of the molded body is calculated from the size (diameter, height, mm) and mass (g) of the molded body. The calculated value is shown in Table 1 as the molding density (g / cm ³ ). The compact is X-ray diffracted, and the true density of the compact is determined from the constituent phase of the hydrogenated alloy and the atomic constituent ratio. NdH ₂ (true density = 5.96 g / cm ³ ), α-FeCo alloy (7.93 g / cm ³ ), Fe ₂ B (7.31 g / cm ³ ), and atomic composition ratio = NdH ₂ : FeCo: Fe ₂ B = 2: 12: 1, the true density of the compact is calculated to be 7.10 g / cm ³ .

(Dehydrogenation process)
The produced cylindrical shaped body is subjected to dehydrogenation treatment to produce a recombination material (an example of a magnet material). The conditions for the dehydrogenation treatment are a vacuum atmosphere and 850 ° C. × 250 minutes. When the relative density of the obtained recombined material was measured in the same manner as the molded body, the relative density of the molded body was substantially maintained.

[Sm system]
By reductive diffusion, a spherical powder having an average particle size of 50 μm is prepared with 24.5 mass% Sm—the balance being Fe and inevitable impurities. The average particle size is determined by obtaining a volume-based particle size distribution using a commercially available laser diffraction particle size distribution measuring device, and the particle size value is 50% cumulative from the small diameter side. This powder is composed of an Sm—Fe based alloy having Sm ₂ Fe ₁₇ as a main phase.

(Hydrogenation process)
The raw material powder is subjected to a hydrogenation treatment to produce a hydrogenated powder. The conditions for the hydrogenation treatment are a hydrogen atmosphere and 850 ° C. × 150 minutes.

(Granulation process)
Sample No. with a granulation step. 1-11-No. For sample No. 1-14, sample no. Similarly to 1-1 etc., a commercially available powder rolling machine is used to produce a rolled material having a relative density of 40% to 55% and a thickness of 250 μm. Here, the rolling material which satisfy | fills said relative density is produced by making an applied pressure into 5 tons and rolling speed into 1 m / min.

Sample No. Similar to 1-1, etc., the rolled material is pulverized using a commercially available pulverizer and then classified under the following conditions.
<Classification condition χ> More than about 1 times as large as the thickness of rolled material (250 μm) and less than about twice as large as the thickness of rolled material (500 μm) Max. A plate-like piece having a length of more than 250 μm and less than 500 μm is used as granulated powder.
<Classification condition ψ> A mesh (250 μm) or more that is about 1 times the thickness of the rolled material, and a mesh (850 μm) or less that is about 3 times the thickness of the rolled material. A plate-like piece having a length of more than 250 μm and less than 850 μm is used as granulated powder.
<Classification condition ω> More than about 1 times as large as the thickness of the rolled material (250 μm), and less than about 5 times as large as the thickness of the rolled material (1400 μm). A plate-like piece having a length of more than 250 μm and less than 1400 μm is used as granulated powder.
Table 1 shows the aspect ratio of the prepared granulated powder. The aspect ratio is the sample number. Obtained in the same manner as 1-1.

(Molding process)
Sample No. In the same manner as in 1-1, the above-mentioned granulated powder or non-granulated hydrogenated powder is pressure-molded with a mold to produce a cylindrical molded body having a diameter of 10 mm and a height of 10 mm. The molding pressure (ton / cm ² ) is shown in Table 1.

Table 1 shows the relative density and molding density of the produced cylindrical molded body. The relative density (%) and the molding density (g / cm ³ ) of the molded body are the same as those of Sample No. Obtained in the same manner as 1-1. The true density of the compact is calculated to be 7.32 g / cm ³ .

(Dehydrogenation process)
The produced cylindrical shaped body is subjected to dehydrogenation treatment to produce a recombining material. The dehydrogenation conditions are a vacuum atmosphere and 750 ° C. × 250 minutes.

(Nitriding process)
The produced recombination material is subjected to nitriding treatment to produce a nitride material (an example of a magnet material). The nitriding conditions are a mixed gas atmosphere of NH ₃ gas and H ₂ gas (a mixture ratio of ammonia gas and hydrogen gas is 1: 1 by volume), and 400 ° C. × 720 minutes. When the relative density of the obtained nitride material was measured in the same manner as the molded body, the relative density of the molded body was substantially maintained.

≪Evaluation of magnetic properties≫
Each sample magnet material is magnetized by applying a pulse magnetic field having a magnetic field strength of 4777 kA / m and a magnetic flux density of 5T. A commercially available magnetizing device (manufactured by Nippon Electromagnetic Instrument Co., Ltd., high voltage capacitor SR type) is used for magnetization. For each magnetized sample, the BH curve is measured using a BH tracer (DCBH tracer manufactured by Riken Denshi Co., Ltd.) to determine the residual magnetization and coercive force. Table 1 shows the remanent magnetization (T) and the coercive force (kA / m).

  As shown in Table 1, it can be seen that the relative density can be increased as the molding pressure is increased. One reason for this is that the hydrogenated powder is excellent in plastic deformability. However, sample no. 1-101-No. 1-103, no. 1-111, no. As can be seen from 1-112, when the relative density is increased by molding the hydrogenated powder as it is, the coercive force and the residual magnetization tend to decrease despite the increase in the relative density.

In contrast, sample No. using a specific granulated powder. 1-1-No. 1-6 (hereinafter sometimes referred to as Nd-based granulated sample), No. 1-6. 1-11-No. 1-14 (hereinafter, sometimes referred to as Sm-based granulated sample), although the molding pressure was increased to produce a molded body (finally a rare earth magnet) having a relative density of 80% or more. Sample No. of the same composition not granulated. 1-101-No. 1-103, no. 1-111, no. It can be seen that the coercive force is high and the saturation magnetization is also high compared to 1-112 (hereinafter sometimes referred to as a comparative sample group).
Quantitatively, the Nd-based granulated sample satisfies a coercive force of 1114 kA / m (≈14 kOe) or higher and a saturation magnetization of 0.65 T or higher when the relative density is as high as 80% or higher. In particular, a sample having a relative density of 88% or more has a higher saturation magnetization, 0.70 T or more, and is excellent in magnet characteristics.
When the relative density is as high as 80% or more, the Sm-based granulated sample satisfies a coercive force of 796 kA / m (≈10 kOe) or more and a saturation magnetization of 0.57 T or more. In particular, a sample having a relative density of 90% or more has a higher saturation magnetization of 0.60 T or more, and is excellent in magnet characteristics.

  From this test, it can be said that when the granulated powder is produced by performing powder rolling, it is preferable to use the granulated powder whose aspect ratio satisfies a specific range. Specifically, Nd-based granulated sample No. 1-1-No. 1-6 and No. 1 1-104-No. Comparison with 1-106, Sm granulation sample No. 1-11-No. 1-14 and No.1. 1-113, no. In comparison with 1-114, the Nd-based granulated sample has an aspect ratio of less than 4.5, the Sm-based granulated sample has an aspect ratio of less than 4.3, and preferably any sample is 3 or less. It can be seen that it is easy to produce a rare earth magnet having high coercive force and saturation magnetization.

Sample No. 1-7, No. 1 Sample Nos. 1 to 107 each had a molding pressure of 15 ton / cm ² . In this sample, the dehydrogenation conditions were changed to 825 ° C. × 6 hours for 1-2 and 1-102. 1 and 2 are cross-sections of a cylindrical recombination material obtained by performing dehydrogenation treatment, cut along a plane orthogonal to the axial direction at an intermediate position in the axial direction. It is the observation image which observed the surface) with the optical microscope. FIG. The photomicrograph of 1-7, FIG. It is a micrograph of 1-107. 1 and 2, the circular portion is a recombination material, and a plurality of black particles dispersed inside the recombination material are pores.

  As shown in FIG. 1, sample No. using a specific granulated powder. As for 1-7, it turns out that a comparatively big black grain exists uniformly and the pore exists uniformly over the whole region of a cross section. On the other hand, sample No. which does not use specific granulated powder. 1-107 shows that although relatively large black particles exist on the surface layer side in the cross section, there are few black particles in the center, and the pores are blocked. Without using specific granulated powder, if the molding pressure is increased to increase the relative density, the pores are crushed from the surface side toward the central part, and the amount of hydrogen is reduced during the dehydrogenation process. It is thought that it was difficult to do.

  Therefore, even if the relative density is increased, the Nd-based granulated sample using specific granulated powder has pores uniformly throughout the molded body. It can be considered that the dehydrogenation treatment can be satisfactorily performed by being used for the passage, and that it has a high coercive force and a high saturation magnetization according to a high relative density. In addition, by using a specific granulated powder, it is possible to form a molded body having pores of a size that is difficult to be blocked by pressure compression in the molding process, at the time of demolding, or at the time of heat treatment such as a dehydrogenation process. It can be said. The same applies to the Sm-based granulated powder sample.

  From the above, when producing a compacted magnet with a large relative density, by using granulated powder obtained by hardening powder particles of hydrogenated powder by plastic deformation by powder rolling or the like, magnet characteristics such as coercive force can be obtained. It has been shown that excellent rare earth magnets can be produced.

  The present invention is not limited to these exemplifications, but is defined by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims. For example, the raw material powder manufacturing method, composition, size, conditions of hydrogenation treatment / dehydration treatment / nitriding treatment, granulated powder size, molding conditions (molding pressure, etc.), relative density of the compact, The granulation method can be changed as appropriate.

  The method for producing a rare earth magnet of the present invention can be used for producing a rare earth magnet used for a permanent magnet or the like. The manufactured rare earth magnet can be used as a permanent magnet, for example, a permanent magnet used in various motors, particularly in a high-speed motor provided in a hybrid vehicle or a hard disk drive.

Claims (4)

Preparing a raw material powder composed of a rare earth-iron alloy containing a rare earth element and an iron group element;
A hydrogenation step of producing a hydrogenated powder by subjecting the raw material powder to a hydrogenation treatment at a temperature equal to or higher than a disproportionation temperature in an atmosphere containing hydrogen;
A granulating step for producing a granulated powder obtained by hardening powder particles of the hydrogenated powder by plastic deformation;
A molding step of pressure-molding the granulated powder to produce a molded body;
A method for producing a rare earth magnet comprising: a dehydrogenation step of producing a recombination material by subjecting the molded body to a dehydrogenation treatment at a temperature equal to or higher than a recombination temperature in an inert atmosphere or a reduced pressure atmosphere. The granulation step includes
A rolling process for producing a rolled material by performing powder rolling using the hydrogenated powder;
A method for producing a rare earth magnet according to claim 1, further comprising a classification step of pulverizing the rolled material to obtain the granulated powder having a predetermined size.   The method for producing a rare earth magnet according to claim 2, wherein the granulated powder has an aspect ratio of 3 or less.   The method for producing a rare earth magnet according to any one of claims 1 to 3, wherein a relative density of the compact is 90% or more.