JP2007197826A - Lubricant for compacting, composition for compacting and method for producing r-t-b based sintered magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the sticking of powder to a mold without adding a large quantity of lubricant upon compacting metal powder in a process controlled at a low oxygen concentration, and to reduce the content of residual carbon in a sintered compact as well. <P>SOLUTION: The method for producing an R-T-B based sintered magnet composed of a sintered compact with crystal grains consisting of an R<SB>2</SB>T<SB>14</SB>B compound as the main phase comprises: a stage where a composition for compacting composed of a mixture consisting of alloy powder including an R<SB>2</SB>T<SB>14</SB>B compound and a lubricant is subjected to compacting in a magnetic field, so as to obtain a compact; and a stage where the compact is sintered. The lubricant comprises two or more kinds of fatty acid amides expressed by general formula R<SB>1</SB>-CONH<SB>2</SB>(wherein, R<SB>1</SB>is represented by C<SB>n</SB>H<SB>2n+1</SB>, and (n) denotes carbon number in R<SB>1</SB>), and in which the total carbon number (n+1) is ≤16 in the general formula, and also, the ratio of the fatty acid amides in which the total carbon number (n+1) is ≤16 occupies ≥80 wt.%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In the present invention, R-T-B (R is one or more rare earth elements including Y (yttrium), T is one or more transition metal elements essential to Fe, Fe and Co, B relates to a lubricant suitable for producing a boron) -based sintered magnet, a molding composition containing the lubricant, and a method for producing an RTB-based sintered magnet.

Among rare earth sintered magnets, RTB-based sintered magnets are used in various electrical equipment because they have excellent magnetic properties and Nd, which is the main component, is abundant in resources and relatively inexpensive. ing.
Various studies have been made to improve the performance of RTB-based sintered magnets. To achieve higher performance, the amount of rare earth elements in the sintered body is reduced, and the main phase It is effective to increase the proportion of the R ₂ Fe ₁₄ B phase. However, rare earth elements are liquid phase components at the time of sintering, and are also grain boundary components after sintering. Therefore, unless a sufficient amount is ensured, sinterability and magnetic properties are deteriorated. Therefore, as the amount of rare earth elements is reduced, it is necessary to reduce the amount of impurities such as oxygen and carbon, particularly the amount of oxygen.

  The RTB-based sintered magnet is manufactured as follows. The raw material alloy is coarsely and finely pulverized to obtain a finely pulverized powder of several μm. The finely pulverized powder thus obtained is magnetically oriented in a static magnetic field, and press molding is performed while the magnetic field is applied. In this case, the pulverized powder alone does not improve the orientation due to the friction between the powders during molding or the friction between the powder and the mold wall surface, and the magnetic properties cannot be sufficiently improved. In addition, the mold wall surface and the surface of the molded body are likely to be scratched, peeled off, cracked, etc., which is undesirable in terms of quality and product yield. As a solution, a lubricant is added to the finely pulverized powder, and the lubricant is added to the surface of the magnet powder. It is done to coat. As a method of adding a lubricant to finely pulverized powder, a method of performing fine pulverization after adding a lubricant is known (Patent Document 1). As another method for preventing the finely pulverized powder from adhering to the mold, a method of applying a lubricant to the wall surface of the mold (die) is also known (Patent Document 2). As the lubricant, an organic material such as zinc stearate is usually used.

  The oxygen content of the sintered body can be reduced by controlling the oxygen concentration in the processes from pulverization to molding and sintering to a very low level, for example, 200 ppm or less. However, in the molding process controlled to a low oxygen concentration, there is a problem that the adhesion of the raw material powder to the mold becomes remarkable. That is, the raw material powder produced in a process controlled at a low oxygen concentration is very active and is more likely to adhere to the mold than before, and conventional methods of adding a lubricant are insufficient. It is possible to suppress adhesion of the mold by mixing a large amount of lubricant with the raw material powder, but a large amount of carbon derived from the lubricant remains in the sintered body, resulting in a decrease in sinterability and magnetic properties. I will invite you.

JP-A-7-240330 JP 2000-197997 A

  The present invention has been made on the basis of such a technical problem. When molding metal powder in a process controlled at a low oxygen concentration, the powder to the mold is added without adding a large amount of lubricant. The purpose is to prevent adhesion. Another object of the present invention is to provide a molding powder capable of reducing the amount of residual carbon in the sintered body.

Under such a purpose, the present inventors have used a general formula R ₁ -CONH ₂ (where R ₁ is represented by C _n H _{2n + 1} as a lubricant for a metal powder containing a rare earth element and pressed. n represents the number of carbon atoms in R ₁ ), and two or more types of fatty acid amides having a total carbon number (n + 1) of 16 or less in the above general formula occupy 80 wt% or more are controlled at a low oxygen concentration It has been found that in the step of forming the metal powder in the step, the adhesion of the powder to the mold can be prevented without adding a large amount of lubricant.

  In order to reduce residual carbon in the sintered body, it is preferable to use a fatty acid amide having a small number of carbon atoms. In the present invention, two or more types of fatty acid amides having a total carbon number (n + 1) of 14 or less in the general formula are used. It is recommended that two or more types of fatty acid amides having a total carbon number (n + 1) of 12 or less in the above general formula occupy 50 wt% or more.

The lubricant according to the present invention is usually used in the form of a solid, more specifically in the form of a powder, but can be used as a liquid lubricant by dissolving in a solvent. That is, the present invention is represented by the general formula R ₁ -CONH ₂ (wherein R ₁ is represented by C _n H _{2n + 1} and n represents the number of carbons in R ₁ ), and the total number of carbons in the general formula ( It can be assumed that a lubricant in which n + 1) is 16 or less and two or more fatty acid amides occupy 80 wt% or more is dissolved in a solvent.

The lubricant of the present invention is used as a composition mixed with metal powder to be subjected to pressure forming. That is, the present invention is a composition to be subjected to pressure molding, comprising a metal powder and a lubricant contained in a ratio of 0.05 to 0.25 wt% with respect to the metal powder. , R ₁ —CONH ₂ (where R ₁ is represented by C _n H _{2n + 1} and n is the number of carbons in R ₁ ), and the total number of carbons (n + 1) in the general formula is 16 A fatty acid amide containing two or more of the following fatty acid amides and having a total carbon number (n + 1) of 16 or less in the general formula occupies 80 wt% or more.

  As this metal powder, R-T-B (R is one or more of rare earth elements including Y (yttrium), T is one or more of transition metals which essentially require Fe, Fe and Co. Element, B is boron) Raw material powder of a sintered magnet. Since this raw material powder contains R, which is an active element, adhesion of the mold when the amount of oxygen is small becomes significant. When manufacturing an RTB-based sintered magnet, it is necessary to specify the amount of lubricant added in consideration of not only adhesion of the mold but also carbon residue derived from the lubricant. It is preferable that 0.08 to 0.2 wt% is contained with respect to the metal powder.

The method for producing an RTB-based sintered magnet using the lubricant according to the present invention includes an R ₂ T ₁₄ B compound (where R is one or more of rare earth elements including Y (yttrium), and T is Method for producing an RTB-based sintered magnet comprising a sintered body having crystal grains composed of Fe or Fe and Co as essential components and crystal grains composed of B or B) A step of pressing a molding composition comprising a mixture of an alloy powder containing an R ₂ T ₁₄ B compound and a lubricant in a magnetic field to obtain a molded body, and a step of sintering the molded body. The lubricant is represented by the general formula R ₁ -CONH ₂ (wherein R ₁ is represented by C _n H _{2n + 1} and n represents the number of carbons in R ₁ ), Including two or more fatty acid amides having 16 or less carbon atoms (n + 1), and the above general Total carbon number (n + 1) is 16 or less fatty acid amide is characterized in that account for more than 80 wt% in.

The alloy powder to be subjected to pressure forming is obtained by pulverizing the raw material alloy, but it is preferable to add the lubricant in the step of pulverizing the raw material alloy in order to increase the dispersion state. Here, when the raw material alloy is pulverized in a plurality of stages, the lubricant may be added at any stage of the pulverization. The present invention is particularly effective when manufacturing in a low oxygen atmosphere where the oxygen concentration in a series of atmospheres from the step of pulverizing the raw material alloy to the step of sintering the compact is 200 ppm or less. This is because if the oxygen concentration in the atmosphere in the molding in the magnetic field is low and the oxygen concentration in the atmosphere in the previous process is low, the alloy powder is very likely to adhere to the mold.
In molding in a magnetic field, by applying a liquid lubricant containing a lubricant as a solute to the wall surface of the mold to be used, the effect of preventing the adhesion of the mold can be exhibited more.

  As described above, according to the present invention, when metal powder is molded in a process controlled at a low oxygen concentration, it is possible to prevent the powder from adhering to the mold without adding a large amount of lubricant. it can. According to the present invention, the amount of residual carbon in the sintered body can be further reduced.

<Lubricant>
In the present invention, a fatty acid amide that is a compound represented by the general formula R ₁ —CONH ₂ is used as a lubricant. Here, R ₁ is represented by C _n H _{2n + 1} , and n represents the number of carbon atoms in R ₁ . In particular, the present invention is characterized in that 80% by weight or more of the added lubricant is occupied by two or more fatty acid amides having a total carbon number (n + 1) of 16 or less in the above general formula. Hereinafter, the total carbon number (n + 1) in the general formula is abbreviated as the total carbon number (n + 1).
The reason why the total carbon number (n + 1) is 16 or less is that when the total carbon number (n + 1) exceeds 16, the amount of carbon remaining after sintering (residual C amount) increases. Therefore, considering the amount of residual C, it is preferable to use a fatty acid amide having a total carbon number (n + 1) of 16 or less and a small total carbon number (n + 1). Here, the remaining part of the lubricant other than the general formula R ₁ —CONH ₂ added as the lubricant of the present invention may include a fatty acid amide represented by a formula other than the general formula R ₁ —CONH ₂ .

Even if it is a fatty acid amide having a total carbon number (n + 1) of 16 or less, one type is insufficient in preventing the powder from adhering to the mold. By using two or more types of fatty acid amides having a total carbon number (n + 1) of 16 or less as in the present invention, it is possible to prevent mold adhesion. Moreover, the amount of residual C can be reduced by using two or more fatty acid amides having a total carbon number (n + 1) of 16 or less.
In the present invention, the total amount of the lubricant is preferably occupied by a fatty acid amide having a total carbon number (n + 1) of 16 or less. However, if 80 wt% or more of the lubricant is occupied by a fatty acid amide having a total carbon number (n + 1) of 16 or less, the effects of the present invention can be obtained. Preferably, the fatty acid amide having a total carbon number (n + 1) of 14 or less is 70% or more of the lubricant addition amount, more preferably, the fatty acid amide having a total carbon number (n + 1) of 12 or less is 50% or more of the lubricant addition amount. And

  The lubricant of the present invention contains two or more fatty acid amides having different total carbon numbers (n + 1). Therefore, it is presumed that two or more fatty acid amides having different total carbon numbers (n + 1) can be sequentially released out of the system at the time of temperature increase in the sintering process. Therefore, when one type of fatty acid amide is used, it is understood that the release is facilitated as compared with the case where the fatty acid amide is released from the system at a predetermined temperature all at once. As a result, there is a high possibility that the amount of residual C in the sintered body is reduced. In addition, according to the lubricant of the present invention, since it contains two or more types of fatty acid amides having different total carbon numbers (n + 1), a rapid decomposition reaction does not occur, so carbonization and cracks in the sintered body It is understood that the generation of holes and vacancies can be suppressed.

  The names of fatty acid amides based on the number of carbon atoms are as follows. In the present invention, 80 wt% or more of the lubricant added is palmitic acid amide, pentadecylic acid amide, myristic acid having a total carbon number (n + 1) of 16 or less. Two or more fatty acid amides can be used among amides, lauric acid amides, capric acid amides, pelargonic acid amides, caprylic acid amides, enanthic acid amides, caproic acid amides, valeric acid amides, butyric acid amides, and the like. In addition, the name of the following fatty acid amide names in parentheses is a name based on IUPAC (International Union of Pure and Applied Chemistry).

Total carbon number (n + 1) 4: Butyramide (n-butanoic acid amide)
Total carbon number (n + 1) 5: Valeric acid amide (n-pentanoic acid amide)
Total carbon number (n + 1) 6: caproic acid amide (n-hexanoic acid amide)
Total carbon number (n + 1) 7: Enanthamide (n-heptanoic acid amide)
Total carbon number (n + 1) 8: caprylic acid amide (n-octanoic acid amide)
Total carbon number (n + 1) 9: Pelargonic acid amide (n-nonanoic acid amide)
Total carbon number (n + 1) 10: capric acid amide (n-decanoic acid amide)
Total carbon number (n + 1) 12: Lauric acid amide (n-dodecanoic acid amide)
Total carbon number (n + 1) 14: Myristic acid amide (n-tetradecanoic acid amide)
Total carbon number (n + 1) 15: pentadecylic acid amide (n-pentadecanoic acid amide)
Total carbon number (n + 1) 16: Palmitic acid amide (n-hexadecanoic acid amide)
Total carbon number (n + 1) 17: Margaric acid amide (n-heptadecanoic acid amide)
Total carbon number (n + 1) 18: stearamide (n-octadecanoamide)
Total carbon number (n + 1) 20: arachidic acid amide (n-icosanoic acid amide)
Total carbon number (n + 1) 22: behenic acid amide (n-docosanoic acid amide)
Total carbon number (n + 1) 24: lignoceric acid amide (n-tetracosanoic acid amide)
Total carbon number (n + 1) 26: serotic acid amide (n-hexacosanoic acid amide)
Total carbon number (n + 1) 28: Montanic acid amide (n-octacosanoic acid amide)
Total carbon number (n + 1) 30: Melicinamide (n-triacontanamid)

  The amount of lubricant added to the powder to be molded is preferably as large as possible from the viewpoint of avoiding adhesion of the mold. However, when manufacturing an RTB-based sintered magnet, it is preferable that the amount of lubricant added is as small as possible in consideration of magnetic properties and sinterability. Therefore, when manufacturing an R-T-B system sintered magnet, it is preferable to set it as 0.05-0.25 wt%. When manufacturing an R-T-B type sintered magnet, it is preferably 0.08 to 0.2 wt%, more preferably 0.1 to 0.18 wt%.

<Method of adding lubricant>
The method for adding the lubricant to the molding powder is not limited, but it is preferable to obtain a lubricant addition effect that the molding powder and the solid lubricant are uniformly dispersed. For this purpose, it is preferable to add a lubricant to the molding powder and then perform pulverization or mixing treatment. For example, if there is a step of pulverizing the raw material alloy in the process of obtaining the molding powder, it is preferable to add a lubricant in the pulverization step. The fatty acid amide used as the lubricant of the present invention is a solid substance and is usually added in the form of particles to the molding powder, but it can also be dissolved in a solvent and added.

  Further, the lubricant of the present invention dissolved in the solvent can be added to the molding powder and applied to the wall surface of the molding die, thereby contributing to prevention of the molding powder from adhering to the molding die. it can. In the case of applying to the mold wall surface, a liquid lubricant obtained by dissolving the lubricant according to the present invention in ethanol or other solvent may be prepared, and this liquid lubricant may be applied to the mold wall surface. The concentration of the lubricant in the liquid lubricant is not particularly limited, but the effect of the present invention can be enjoyed if the concentration is about 5 to 50 wt%.

<Target material>
The material of the molding powder to which the lubricant of the present invention is added is not limited. Widely includes metal powders that are feared to adhere to the mold in pressure molding using the mold. However, since adhesion to the mold is likely to occur when the molding powder is active, the effect of reducing the adhesion of the mold can be achieved by applying the present invention to metal powder and metal powder containing rare earth elements. Can be remarkably enjoyed. Further, in the case of a metal powder containing rare earth elements, the lower the amount of oxygen, the more active the surface, and mold adhesion tends to occur. Therefore, the present invention is effective for a molding powder produced with an oxygen concentration in a series of atmospheres from the step of pulverizing the raw material alloy to the step of pulverizing at 200 ppm or less. Also, the lubricant added to the molding powder has a function of improving the slippage between particles constituting the molding powder in addition to the function of preventing adhesion of the mold. It is preferable to apply to the powder to be produced. As such a powder, there is the above-described RTB-based sintered magnet. In addition, there is a giant magnetostrictive material that contains a rare earth element and is subjected to molding in a magnetic field, and it is preferable to add the lubricant of the present invention to the molding powder.

<Molding atmosphere>
The molding powder containing the lubricant according to the present invention is effective when molding is performed in a low oxygen atmosphere. This is because molding in a low oxygen atmosphere tends to cause the molding powder to adhere to the mold. Molding in a low oxygen atmosphere is performed for the purpose of reducing the amount of oxygen in the sintered body to be finally obtained. Specifically, in order to produce an RTB-based sintered magnet having an oxygen amount of 2000 ppm or less, each step from pulverization of raw material alloy to sintering, oxygen concentration between the steps is preferably 200 ppm or less, preferably Is 150 ppm, more preferably 100 ppm or less. In contrast to molding in such a low oxygen atmosphere, the lubricant of the present invention is effective in preventing adhesion of the molding powder to the mold.

Hereinafter, a method for producing an RTB-based sintered magnet using the lubricant of the present invention will be described.
<Chemical composition>
First, the desirable chemical composition of the RTB-based sintered magnet will be described. The chemical composition here refers to the chemical composition after sintering.
The RTB-based sintered magnet to which the present invention is applied contains 25 to 37 wt% of a rare earth element (R).
Here, R has a concept including Y (yttrium). Therefore, R in the present invention is selected from one or more of Y (yttrium), La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. . If the amount of R is less than 25 wt%, the R ₂ T ₁₄ B phase, which is the main phase of the RTB-based sintered magnet, is not sufficiently generated, and α-Fe having soft magnetism is precipitated and retained. The magnetic force is significantly reduced. On the other hand, when R exceeds 37 wt%, the volume ratio of the R ₂ T ₁₄ B phase, which is the main phase, decreases, and the residual magnetic flux density decreases. Further, R reacts with oxygen, the amount of oxygen contained increases, and accordingly, the R-rich phase effective for the generation of coercive force decreases, leading to a decrease in coercive force. Therefore, the amount of R is set to 25 to 37 wt%. A desirable amount of R is 28 to 35 wt%, and a more desirable amount of R is 29 to 33 wt%.

  Moreover, the RTB-based sintered magnet contains 0.5 to 4.5 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. On the other hand, when B exceeds 4.5 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit is 4.5 wt%. A desirable amount of B is 0.5 to 1.5 wt%, and a more desirable amount of B is 0.8 to 1.2 wt%.

  The RTB-based sintered magnet contains Co of 4.0 wt% or less (excluding 0), desirably 0.1 to 2.0 wt%, and more desirably 0.3 to 1.0 wt%. be able to. Co forms the same phase as Fe, but is effective in improving the Curie temperature and improving the corrosion resistance of the grain boundary phase.

  The RTB-based sintered magnet to which the present invention is applied can contain one or two of Al and Cu in a range of 0.02 to 0.5 wt%. By including one or two of Al and Cu in this range, it is possible to increase the coercive force, increase the corrosion resistance, and improve the temperature characteristics of the obtained RTB-based sintered magnet. In the case of adding Al, the desirable amount of Al is 0.03 to 0.3 wt%, and the more desirable amount of Al is 0.05 to 0.25 wt%. Further, in the case of adding Cu, the desirable amount of Cu is 0.15 wt% or less (not including 0), and the more desirable amount of Cu is 0.03 to 0.12 wt%.

  In addition, the RTB-based sintered magnet allows the inclusion of other elements. For example, elements such as Zr, Ti, Bi, Sn, Ga, Nb, Ta, Si, V, Ag, and Ge can be appropriately contained.

  The RTB-based sintered magnet to which the present invention is applied preferably has an oxygen content of 2000 ppm or less. When the amount of oxygen is large, the oxide phase, which is a nonmagnetic component, increases and the magnetic properties are deteriorated. Therefore, the amount of oxygen contained in the sintered body is 2000 ppm or less, preferably 1500 ppm or less, more preferably 1000 ppm or less.

<Manufacturing method>
Hereinafter, the manufacturing method of the RTB system sintered magnet of the present invention is explained.
The raw material alloy can be produced by a strip casting method or other known melting methods in a vacuum or an inert gas, preferably an argon atmosphere. In the strip casting method, a molten metal obtained by melting a raw material metal in a non-oxidizing atmosphere such as an argon gas atmosphere is jetted onto the surface of a rotating roll. The melt rapidly cooled by the roll is rapidly solidified in the form of a thin plate or flakes (scales). This rapidly solidified alloy has a homogeneous structure with a crystal grain size of 1 to 50 μm. The raw material alloy can be obtained not only by the strip casting method but also by a melting method such as high frequency induction melting. In addition, when the obtained alloy has solidification segregation, solution treatment is performed as necessary. The conditions may be maintained at a temperature of 700 to 1500 ° C. for 1 hour or more in a vacuum or an argon atmosphere.

When obtaining an RTB-based sintered magnet, an alloy mainly composed of the R ₂ T ₁₄ B phase (main phase alloy) and an alloy not containing R ₂ T ₁₄ B (grain boundary phase alloy) are used. The so-called mixing method used can also be applied to the present invention.

The raw material alloy is subjected to a grinding process. In the case of a mixing method, each alloy is ground separately or together. The pulverization process is generally divided into a coarse pulverization process and a fine pulverization process.
First, in the coarse pulverization, the raw material alloy is pulverized until the particle diameter is about several hundred μm. The coarse pulverization is desirably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill or the like. In order to improve the coarse pulverization property, it is effective to perform coarse pulverization after occlusion of hydrogen. Further, after hydrogen storage, hydrogen can be released and further coarse pulverization can be performed.
After the coarse pulverization process, the process proceeds to the fine pulverization process. The coarsely pulverized powder having a particle size of about several hundred μm is finely pulverized until the average particle size becomes 3 to 8 μm. A jet mill can be used for fine pulverization.

At this time, a lubricant is added to the raw material alloy powder in the fine grinding step. The lubricant is preferably added to the raw material alloy powder before the start of the fine pulverization process. However, the lubricant may be added during the pulverization process or after the fine pulverization process. In this way, a molding composition containing finely pulverized powder and a lubricant is obtained.
Next, this molding composition is molded in a magnetic field. The molding in the magnetic field may be performed at a pressure of about 0.3 to 3.0 ton / cm ² (30 to 300 MPa) in a magnetic field of 12.0 to 20.0 kOe (955 to 1600 kA / m).

After molding in a magnetic field, the compact is sintered in a vacuum or an inert gas atmosphere. Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, a difference of a particle size and a particle size distribution, what is necessary is just to sinter at 1000-1150 degreeC for about 1 to 5 hours.
After sintering, the obtained sintered body can be subjected to an aging treatment. This step is an important step in controlling the coercive force. In the case where the aging treatment is performed in two stages, holding for a predetermined time at around 800 ° C. and around 600 ° C. is effective. When the heat treatment at around 800 ° C. is performed after sintering, the coercive force increases, which is particularly effective in the mixing method. In addition, since the coercive force is greatly increased by the heat treatment at around 600 ° C., the aging treatment at around 600 ° C. is preferably performed when the aging treatment is performed in one stage.

The R-T-B sintered magnet has been described above, but the application of the present invention is not limited to this. For example, the present invention can also be applied to a giant magnetostrictive material made of a sintered body having a composition represented by RT _y (y represents 1 <y <4).
Here, R represents one or more rare earth elements including Y (yttrium). Among these, R is particularly preferably a rare earth metal such as Nd, Pr, Sm, Tb, Dy, and Ho, more preferably Tb and Dy, and these can be used in combination. T represents one or more transition metals. Among these, as T, transition metals such as Fe, Co, Ni, Mn, Cr, and Mo are particularly desirable, Fe, Co, and Ni are more desirable, and these can be used in combination.

Hereinafter, the present invention will be described based on examples relating to an RTB-based sintered magnet.
A raw material alloy was produced by high frequency melting in an Ar atmosphere. In this example, R-T is obtained by a mixing method using an alloy mainly composed of R ₂ T ₁₄ B phase (main phase alloy) and an alloy not containing R ₂ T ₁₄ B (grain boundary phase alloy). A B-type sintered magnet was produced.
The composition of the main phase alloy is shown below.
Nd: 26 wt%, Dy: 4 wt%, Al: 0.2 wt%, B: 1.1 wt%, Zr: 0.2 wt%, balance: Fe and inevitable impurities The composition of the grain boundary phase alloy is shown below.
Dy: 32 wt%, Co: 10 wt%, Cu: 1 wt%, Al: 0.2 wt%, balance: Fe and inevitable impurities

  The raw material alloy produced as described above was mixed in a weight ratio of main phase alloy: grain boundary phase alloy = 90: 10, occluded hydrogen at room temperature, and then dehydrated at 600 ° C. for 1 hour in an Ar atmosphere. Hydrogen pulverization treatment was performed. In order to obtain an RTB-based sintered magnet with high magnetic properties, in this example, sintering (sintering) from hydrogen pulverization (recovery after pulverization) was performed in order to suppress the sintered body oxygen content to 2000 ppm or less. The atmosphere of each step until the furnace is charged) is suppressed to an oxygen concentration of less than 100 ppm. Hereinafter, this series of steps is referred to as a low oxygen process.

Next, the raw material alloy that had been subjected to the hydrogen pulverization treatment was finely pulverized. Normally, two-stage pulverization by coarse pulverization and fine pulverization is performed after the hydrogen pulverization treatment. However, since it is difficult to perform the coarse pulverization process by a low oxygen process, the coarse pulverization process is omitted in this embodiment. .
However, a lubricant was added and mixed before pulverization. As the lubricant, various fatty acid amides having different total carbon numbers (n + 1) were added at a ratio (wt%) shown in Table 1 and mixed. The addition amount was 0.15 wt% with respect to the raw material alloy. As described above, the fatty acid amide is represented by the general formula R ₁ -CONH ₂ (where R ₁ is represented by C _n H _{2n + 1} , and n represents the number of carbon atoms in R ₁ ). The mixing may be performed for about 5 to 30 minutes using, for example, a Nauta mixer.
After the addition and mixing of the lubricant, pulverization was performed using a jet mill until the raw material alloy became a molding powder having an average particle size of about 3 to 6 μm. In this example, pulverized powder having an average particle diameter of 4 μm was produced.

The obtained finely pulverized powder (molding composition) was charged with 1 g of finely pulverized powder into a mold having a diameter of 10 mm, and molded at a pressure of 1.5 ton / cm ² . The adhesion of finely pulverized powder was confirmed. The results are shown in Table 2. The mark in the table is “◯” when there is no adhesion to the wall surface, and “x” when there is adhesion.

The obtained finely pulverized powder was molded in a magnetic field. Specifically, it was molded at a pressure of 1.2 ton / cm ^{2 in} a magnetic field of 15 kOe to obtain a molded body. The molded body was sintered at 1090 ° C. for 4 hours in a vacuum and then rapidly cooled. Next, the obtained sintered body was subjected to a two-stage aging treatment of 800 ° C. × 1 hour and 550 ° C. × 1 hour (both in an Ar atmosphere).
The amount of C remaining in the obtained sintered body and magnetic characteristics (residual magnetic flux density (Br), coercive force (HcJ)) were measured, and the results are shown in Table 2. Table 2 shows the type (number) of substances having a total carbon number (n + 1) of 16 or less and the ratio (wt%) of the substances having a total carbon number (n + 1) of 16 or less in the lubricant. .

As shown in Table 2, Examples 1 to 5 in which two or more types of lubricants having a total carbon number (n + 1) of 16 or less and 80% by weight or more of all the lubricants are free from mold adhesion and baked. The amount of C remaining in the body is also low. For this reason, the magnetic properties, particularly the coercive force (HcJ) are also high.
On the other hand, although two or more types of lubricants having a total carbon number (n + 1) of 16 or less are included, Comparative Examples 1 and 2 having less than 80 wt% of the total lubricants are accompanied by die adhesion and remain. The amount of C is also a high value. Furthermore, in Comparative Example 3 consisting only of a lubricant having a total carbon number (n + 1) exceeding 16, die adhesion occurs and the amount of remaining C is higher than those of Comparative Examples 1 and 2. Further, a lubricant having a total carbon number (n + 1) of 16 or less occupies 80% wt or more (100 wt%), but Comparative Example 4 in which only one type is included is the amount of C remaining, and the magnetic characteristics are Examples 1 to 5 However, mold adhesion occurred.

  The same study as described above was performed by using the lubricant of Example 1 and changing the addition amount of the lubricant to 0.03, 0.1, 0.15, 0.2, and 0.3 wt%. The results are shown in Table 3. Table 3 also shows the results of Example 1 (added amount: 0.15 wt%).

As shown in Table 3, if the addition amount of the lubricant is small, there is no effect in preventing the adhesion of the mold. Conversely, if the amount of lubricant added is large, the effect of preventing the adhesion of the mold can be obtained, but the amount of C remaining in the sintered body increases and the magnetic properties (coercivity (HcJ)) deteriorate. From the above results, when producing an RTB-based sintered magnet, the amount of lubricant added is preferably in the range of 0.05 to 0.25 wt%, and more preferably 0.1 to 0. It can be seen that the content is more preferably 2 wt%.
The amount of lubricant used in Comparative Example 1 was increased and the same study as described above was conducted. Although the adhesion of the mold could be prevented by increasing the amount of lubricant added, it remained in the sintered body. The amount of C to be increased increased, and the magnetic properties (coercive force (HcJ)) significantly decreased.

Next, the lubricant used in Example 1 was dissolved in ethanol to prepare a liquid lubricant. The amount of the lubricant of Example 1 dissolved in the liquid lubricant is 10 wt%. After applying this liquid lubricant to the mold wall surface, pressure molding was performed in the same manner as described above to confirm the presence or absence of the mold adhesion.
Further, after applying the liquid lubricant to the mold wall surface formed in the magnetic field, the molding in the magnetic field was performed in the same manner as described above, and the obtained molded body was sintered and aged in the same manner as described above. About the obtained sintered compact, the residual C amount and magnetic characteristics (residual magnetic flux density (Br), coercive force (HcJ)) were measured. The results are shown in Table 4. Note that the lubricant used in Example 1 was also added to the finely pulverized powder in an amount shown in Table 4.

  As shown in Table 4, by applying the liquid lubricant to the mold wall surface, the adhesion of the mold can be prevented even if the amount of the lubricant added to the finely pulverized powder is reduced. When considering only prevention of mold adhesion, it is preferable to apply a liquid lubricant to the mold. However, unless a lubricant is added to the finely pulverized powder, the orientation of the magnet powder in the molding in the magnetic field becomes insufficient, and the magnetic properties (residual magnetic flux density (Br)) are lowered.

Next, a main phase alloy and a grain boundary phase alloy having the following composition were prepared as raw material alloys.
Main phase alloy: Nd: 22 wt%, Pr: 6 wt%, Dy: 2 wt%, Al: 0.2 wt%, Cu: 0.01 wt%, B: 1.1 wt%, balance: Fe and inevitable impurities Grain boundary phase Alloy: Nd: 40 wt%, Co: 5 wt%, Cu: 1 wt%, Al: 0.2 wt%, balance: Fe and inevitable impurities Oxygen during pulverization using the above main phase alloy and grain boundary phase alloy Except for adjusting the concentration as shown in Table 5, sintering and two-stage aging treatment were performed in the same procedure and conditions as in Example 1. The oxygen concentration at the time of fine pulverization was adjusted by adjusting the oxygen concentration contained in the inert gas that forms a high-speed air flow in the jet mill. Further, except for the fine pulverization treatment, the atmosphere of each step from the hydrogen pulverization treatment (recovery after the pulverization treatment) to the sintering (put into the sintering furnace) was suppressed to an oxygen concentration of less than 100 ppm.
The adhesion of finely pulverized powder to the mold wall surface during molding in a magnetic field was confirmed, and the oxygen content and magnetic properties of the sintered body were evaluated. The results are also shown in Table 5. Note that the amount of C remaining in the obtained sintered body was 700 ppm or less.

  As shown in Table 5, in any case, occurrence of mold adhesion was not observed. However, as the oxygen concentration during pulverization increased, the amount of oxygen in the sintered body increased. Furthermore, the magnetic characteristics of the sintered body showed no difference in residual magnetic flux density (Br), but the coercive force (HcJ) tended to decrease as the oxygen concentration during pulverization increased. This decrease in coercive force (HcJ) is thought to be due to an increase in the amount of oxygen in the sintered body. In this experiment, the oxygen concentration during fine pulverization, which is easy to adjust, was adjusted. However, the oxygen concentration in the atmosphere of each process that can increase the amount of oxygen in the sintered body is low, specifically 200 ppm. The following is effective in obtaining a high coercive force (HcJ).

Claims (10)

A lubricant for a metal powder containing rare earth elements and press-molded,
It is represented by the general formula R ₁ —CONH ₂ (wherein R ₁ is represented by C _n H _{2n + 1} and n represents the carbon number in R ₁ ), and the total carbon number (n + 1) in the general formula is 16 or less. A powder molding lubricant characterized by comprising two or more fatty acid amides and occupying 80 wt% or more.   2. The powder molding lubricant according to claim 1, wherein the lubricant comprises two or more fatty acid amides having a total carbon number (n + 1) of 14 or less in the general formula and occupies 70 wt% or more.   2. The powder molding lubricant according to claim 1, wherein two or more types of fatty acid amides having a total carbon number (n + 1) of 12 or less in the general formula occupy 50 wt% or more. It is represented by the general formula R ₁ —CONH ₂ (wherein R ₁ is represented by C _n H _{2n + 1} and n represents the carbon number in R ₁ ), and the total carbon number (n + 1) in the general formula is 16 or less. The powder molding lubricant according to any one of claims 1 to 3, wherein two or more types of the fatty acid amide and the lubricant occupying 80 wt% or more are dissolved in a solvent. A composition that is subjected to pressure molding,
Metal powder,
A lubricant contained in a ratio of 0.05 to 0.25 wt% with respect to the metal powder,
The lubricant is represented by the general formula R ₁ —CONH ₂ (where R ₁ is represented by C _n H _{2n + 1} , and n represents the number of carbons in R ₁ ), and the total number of carbons in the general formula ( A molding composition characterized in that n + 1) contains two or more fatty acid amides having 16 or less, and the fatty acid amide having 16 or less carbon atoms (n + 1) in the general formula occupies 80 wt% or more.   The metal powder is R-T-B (R is one or more rare earth elements including Y (yttrium), and T is one or more transition metal elements essential to Fe, Fe and Co. The molding composition according to claim 5, wherein B is a raw material powder of a boron) -based sintered magnet.   The molding composition according to claim 6, wherein the lubricant is contained in an amount of 0.08 to 0.2 wt% with respect to the metal powder. R ₂ T ₁₄ B compound (R is one or more of rare earth elements including Y (yttrium), T is one or more transition metal elements in which Fe or Fe and Co are essential, and B is boron And a method for producing an RTB-based sintered magnet made of a sintered body having a crystal grain as a main phase,
A step of pressure-molding a molding composition comprising a mixture of an alloy powder containing the R ₂ T ₁₄ B compound and a lubricant in a magnetic field to obtain a molded body;
Sintering the molded body;
With
The lubricant is represented by the general formula R ₁ -CONH ₂ (where R ₁ is represented by C _n H _{2n + 1} , and n represents the number of carbons in R ₁ ), and the number of carbons in the general formula (n + 1) ) Includes two or more fatty acid amides having 16 or less, and the fatty acid amide having 16 or less carbon atoms (n + 1) in the general formula occupies 80 wt% or more. Production method. The alloy powder is obtained by pulverizing a raw material alloy, and the lubricant is added in the step of pulverizing the raw material alloy,
The production of an RTB-based sintered magnet according to claim 8, wherein an oxygen amount in an atmosphere from a step of pulverizing the raw material alloy to a step of sintering the compact is 200 ppm or less. Method.   10. The RTB-based sintered magnet according to claim 8, wherein a liquid lubricant containing the lubricant as a solute is applied to a wall surface of a mold that performs pressure molding in the magnetic field. Production method.