JP2006210377A - Rtb-based sintered magnet and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To unify the crystal organization of an RTB-based sintered magnet, by uniformizing the crystal organization of a raw material alloy manufactured by a strip casting method. <P>SOLUTION: In the R-T-B-based sintered magnet, a sintered body uses a crystal particle comprising an R<SB>2</SB>T<SB>14</SB>B compound (R is one type or two types of elements selected from among rare earth elements; T is one type or at least two types of elements selected from among transition metal elements containing Fe, or Fe and Co) as the main phase, P and/or S is contained in the sintered body by 10-220 ppm. P and/or S, contained in the sintered body, is preferably in the range of 50-200 ppm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an R-T-B based sintered magnet (R is one or more elements selected from rare earth elements, T is one or more elements selected from transition metal elements including Fe or Fe and Co, or In particular, the present invention relates to an RTB-based sintered magnet having improved magnetic properties by improving the grindability of the raw material alloy.

  The basic manufacturing process of the RTB-based sintered magnet includes production of a raw material alloy, pulverization of the obtained raw material alloy, shaping of the pulverized alloy powder in a magnetic field, sintering and aging treatment. In order to improve the magnetic properties of the RTB-based sintered magnet, various attempts have been made in each manufacturing process. For example, in order to reduce the amount of oxygen in the sintered body, the amount of oxygen in the atmosphere in the manufacturing process is reduced, or a plurality (typically two types) of raw material alloys are used. Among them, as described below, improvement of magnetic properties by improving the structure of the raw material master alloy has been studied.

Conventionally, a raw material master alloy has been produced by using an ingot method by die casting or a strip casting method in which a molten alloy is rapidly cooled using a cooling roll.
In the alloy produced by the ingot method, the production of α-Fe is unavoidable. As a result, the grinding efficiency of the alloy is remarkably lowered, and the finally obtained magnet characteristics are also low. In order to solve this problem, it is known that α-Fe disappears by solution treatment of an alloy obtained by the ingot method. However, by performing solution treatment, productivity is lowered and manufacturing cost is reduced. Was inviting a rise.

  On the other hand, in an alloy produced by a strip cast method (for example, JP-A-5-222488 (Patent Document 1), JP-A-5-295490 (Patent Document 2)) which is a kind of rapid solidification method, Almost no α-Fe is produced. Further, a relatively fine crystal structure can be obtained, in which the crystal grain size in the minor axis direction is 20 to 30 μm and the major axis direction is about 300 μm at the maximum.

JP-A-5-222488 Japanese Patent Laid-Open No. 5-295490

Although the raw material alloy produced by the strip cast method has a fine structure as described above, even if this raw material alloy is pulverized under certain conditions, the particle size distribution of the pulverized powder varies. The crystal structure of the R-T-B system sintered magnet obtained by molding and sintering the pulverized powder having a variation in particle size distribution in a magnetic field is also non-uniform, and the magnetic properties, particularly the coercive force, are reduced. There has been a problem of growing.
The present invention has been made on the basis of such a technical problem. By making the crystal structure of the raw material alloy produced by the strip casting method more uniform, the R-T-B system sintered magnet can be obtained. The purpose is to make the crystal structure uniform. This RTB-based sintered magnet is effective in improving the coercive force.

  In order to make the structure of the raw material alloy uniform by the strip casting method, the ribbon produced by the strip casting method needs to be cooled more uniformly. That is, if the thickness of the molten metal supplied to the roll is large, the cooling ability in the thickness direction is different, so that it is not easy to obtain uniform cooling, in other words, a uniform structure. In order to make the molten metal thinner and supply it to the roll, the viscosity of the molten alloy was considered important. That is, when the viscosity of the molten metal is low, the alloy supplied to the roll can be made thin, and as a result, a raw material alloy by strip casting having a uniform structure can be provided. For reducing the viscosity of the molten metal, P (phosphorus) and S (sulfur) are effective. However, if the amount of P and / or S is too large, the particle size of the pulverized powder becomes too fine. . According to the study by the present inventors, it is effective for achieving the object of the present invention that P and / or S is in the range of 10 to 220 ppm.

That is, the RTB-based sintered magnet of the present invention is an R ₂ T ₁₄ B compound (where R is one or more elements selected from rare earth elements, T is a transition metal containing Fe, Fe, and Co). 1 or 2 or more elements selected from elements) as a main phase, and the sintered body contains 10 to 220 ppm of P and / or S. Yes.
In the RTB-based sintered magnet of the present invention, P and / or S contained in the sintered body is preferably 50 to 200 ppm.
In the RTB-based sintered magnet of the present invention, the sintered body is R: 25 to 35 wt%, B: 0.5 to 4 wt%, and one or two of Al and Cu are 0.02 to 0.02 wt%. It is preferable that the composition be 0.6 wt%, Co: 0.5 to 4 wt% or less, and the balance substantially consisting of Fe.

  The above-mentioned RTB-based sintered magnet of the present invention is a step of pulverizing a raw material alloy produced by strip casting a molten alloy having a P and / or S content of 10 to 220 ppm to a powder having a predetermined particle size. And it can manufacture by passing through the process of shape | molding the obtained powder in a magnetic field, and producing a molded object, and the process of sintering this molded object.

  According to the present invention, by making the amount of P and / or S contained in the raw material alloy by strip casting 50 to 200 ppm, the structure of the raw material alloy is made uniform, and as a result, finely pulverized which is the object of forming in a magnetic field. By making the particle size of the powder fine and sharp, it is possible to improve the magnetic properties, particularly the coercive force, of the obtained RTB-based sintered magnet.

The RTB-based sintered magnet according to the present invention is composed of a sintered body whose main phase is crystal grains made of an R ₂ T ₁₄ B compound. Here, R has a concept including Y, and one or two selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, and Y More than a seed element. In R, since Nd is abundant in resources and relatively inexpensive, it is preferable that the main component as R is Nd. The inclusion of heavy rare earth elements (one or more of Dy, Tb, Gd, Ho, Er, Tm and Y) is effective in improving the coercive force because it increases the anisotropic magnetic field. . Therefore, a heavy rare earth element can also be contained in the RTB-based sintered magnet of the present invention. It is preferable to use Dy and / or Tb as the heavy rare earth element.

  The RTB-based sintered magnet according to the present invention has a grain boundary phase in addition to the main phase. This grain boundary phase has several phases such as a phase called an Nd-rich phase because the amount of Nd is richer than that of the main phase, and a phase called a B-rich phase because B is rich.

  The RTB-based sintered magnet of the present invention having the above main phase and grain boundary phase has a P and / or S content of 10 to 220 ppm. In the present invention, P and / or S has an effect of making the structure of the raw material alloy obtained by reducing the viscosity of the molten metal uniform and fine. Therefore, the particle size of the finely pulverized powder obtained by the subsequent fine pulverization is small, and the particle size distribution is sharp. As a result, the magnetic properties of the RTB-based sintered magnet obtained using this finely pulverized powder, particularly the coercive force, is increased, and variations in the coercive force of the RTB-based sintered magnet are suppressed. be able to.

  Here, if the viscosity of a molten metal falls, the thickness of an alloy can be made thin. When the molten metal touches the rotating roll, the temperature decreases from the contact surface with the roll, and crystals grow in a columnar shape. When the alloy in contact with the roll is thick, it takes time for cooling, and crystals grow in the horizontal direction on the side opposite to the contact surface with the roll. For this reason, the pillar is formed in a shape that increases in thickness as it is separated from the roll, that is, in a trumpet shape. In this case, it is understood that the problem that the particle size of the pulverized powder does not become uniform and the particle size becomes large arises.

  In the present invention, if the content of P and / or S is less than 10 ppm, the effect of lowering the viscosity of the molten metal is not sufficiently exhibited, so that the effect of improving the coercive force cannot be obtained. However, if the content of P and / or S is too large, the structure of the raw material alloy becomes too fine, and the particle size after pulverization becomes corresponding to it. As a result, the orientation during molding in a magnetic field becomes insufficient, and there is a concern about residual magnetic flux density degradation. Therefore, this invention makes content of P and / or S 10-220 ppm. The preferable content of P and / or S is 50 to 200 ppm, and the more preferable content is 50 to 180 ppm.

The RTB-based sintered magnet in the present invention is R: 25 to 35 wt%, B: 0.5 to 4 wt%, one or two of Al and Cu: 0.02 to 0.6 wt%, Zr And one or two of Nb and Hf: 2 wt% or less, Co: 4 wt% or less, and the balance being preferably substantially composed of Fe. Hereinafter, each element will be mentioned.
The RTB-based sintered magnet according to the present invention contains 25 to 35 wt% of R.
Here, as described above, R has a concept including Y, and is selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, and Y. Or one or more elements. When the amount of R is less than 25 wt%, the generation of R ₂ T ₁₄ B crystal grains that are the main phase of the R-T-B sintered magnet is not sufficient. For this reason, α-Fe or the like having soft magnetism is precipitated, and the coercive force is remarkably lowered. On the other hand, when the amount of R exceeds 35 wt%, the volume ratio of R ₂ T ₁₄ B crystal grains constituting the main phase is lowered, and the residual magnetic flux density is lowered. On the other hand, when the amount of R exceeds 35 wt%, R reacts with oxygen, and the amount of oxygen contained increases, and as a result, the R-rich phase effective for the generation of coercive force decreases and the coercive force decreases. Therefore, the amount of R is set to 25 to 35 wt%. A preferable amount of R is 26 to 33 wt%, and a more preferable amount of R is 27 to 32 wt%.

  When heavy rare earth elements are included, R is 25 to 35 wt% including heavy rare earth elements. In this range, the amount of heavy rare earth element is preferably 0.1 to 8 wt%. The amount of the heavy rare earth element is preferably determined within the above range depending on which of the residual magnetic flux density and the coercive force is important. In other words, when it is desired to obtain a high residual magnetic flux density, the amount of heavy rare earth element is set to 0.1 to 3.5 wt%, and when it is desired to obtain a high coercive force, the amount of heavy rare earth element is set to 3.5 to 8 wt%. Is preferred.

  The RTB-based sintered magnet according to the present invention contains 0.5 to 4% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. However, when B exceeds 4 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit is 4 wt%. A preferable amount of B is 0.5 to 1.5 wt%, and a more preferable amount of B is 0.8 to 1.2 wt%.

  The RTB-based sintered magnet according to the present invention can contain one or two of Al and Cu in the range of 0.02 to 0.6 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, a preferable amount of Al is 0.03 to 0.3 wt%, and a more preferable amount of Al is 0.05 to 0.25 wt%. When Cu is added, the amount of Cu is 0.01 to 0.3 wt%, preferably 0.02 to 0.2 wt%, and more preferably Cu is 0.03 to 0.15 wt%.

  The RTB-based sintered magnet according to the present invention contains 0.01 to 2 wt% of one or two of Zr, Nb, and Hf. When reducing the oxygen content in order to improve the magnetic properties of the RTB-based sintered magnet, Zr, Nb, and Hf exhibit the effect of suppressing abnormal growth of crystal grains during the sintering process, Make the structure of the sintered body uniform and fine. Therefore, the effect of Zr, Nb, and Hf becomes remarkable when the amount of oxygen is low. A preferable amount of one or two of Zr, Nb, and Hf is 0.05 to 1.5 wt%, and a more preferable amount is 0.1 to 0.5 wt%.

  The RTB-based sintered magnet of the present invention can contain 4 wt% or less of Co. Co is effective in improving the Curie temperature and the corrosion resistance. Moreover, it has the effect that the aging treatment temperature range from which a high coercive force is obtained is expanded by adding together with Cu. However, excessive addition causes a decrease in coercive force and increases the cost. A preferable Co content is 0.2 to 3 wt%, and a more preferable Co content is 0.2 to 1.5 wt%.

  The RTB-based sintered magnet of the present invention has an oxygen content of 3000 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, in the present invention, the amount of oxygen contained in the sintered body is 3000 ppm or less, preferably 2000 ppm or less, and more preferably 1000 ppm or less. However, if the oxygen amount is simply reduced, the oxide phase having the effect of suppressing grain growth is insufficient, and abnormal grain growth easily occurs in the process of obtaining a sufficient density increase during sintering. Therefore, in the present invention, in the case of such a low oxygen content, one or more of Zr, Nb and Hf exhibiting an effect of suppressing abnormal growth of main phase crystal grains during the sintering process. Is preferably contained in the RTB-based sintered magnet in a predetermined amount.

Next, the preferable form of the manufacturing method of the RTB system sintered magnet by this invention is demonstrated.
A raw material alloy can be obtained by strip casting the raw metal in a vacuum or an inert gas, preferably in an Ar atmosphere. As a raw material metal for obtaining a raw material alloy, a rare earth metal or a rare earth alloy, pure iron, ferroboron, or an alloy thereof can be used. At this time, it is necessary to select the raw metal so that the content of P and / or S of the obtained RTB-based sintered magnet is 10 to 220 ppm. Since P and / or S is an element contained as an impurity in a raw metal, for example, pure iron, the RTB-based sintered magnet of the present invention is obtained by selecting the impurity level of the raw metal. Can do. The content of P and / or S of the present invention can be obtained by appropriately adding P and / or S without selecting the impurity level of the raw metal. In short, what is necessary is just to contain the quantity of P and / or S required as a molten metal.

  After the raw material alloys are produced, these raw material alloys are pulverized. The pulverization process includes a coarse pulverization process and a fine pulverization process. First, each mother alloy is coarsely pulverized until the particle size becomes about several hundred μm. The coarse pulverization is preferably 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 absorption, coarse pulverization can be performed by releasing hydrogen. In order to obtain high magnetic properties, it is preferable to suppress the atmosphere in each step from pulverization (recovery after pulverization) to sintering (put into a sintering furnace) to an oxygen concentration of less than 100 ppm. By doing so, the amount of oxygen contained in the sintered body can be controlled to 3000 ppm or less.

  Hydrogen storage can be performed by exposing the raw material alloy to a hydrogen-containing atmosphere at room temperature. Since the hydrogen occlusion reaction is an exothermic reaction, means such as cooling the reaction vessel may be applied to prevent the amount of occluded hydrogen from decreasing as the temperature rises. In the raw material alloy stored with hydrogen, cracks occur, for example, along grain boundaries.

  After the hydrogen storage is completed, a dehydrogenation process is performed in which the raw material alloy that has been subjected to hydrogen storage is heated and held. This treatment is performed for the purpose of reducing hydrogen as an impurity as a magnet. The heating and holding temperature is 200 ° C. or higher, preferably 350 ° C. or higher. The holding time varies depending on the relationship with the holding temperature, the thickness of the raw material alloy, etc., but is at least 30 minutes or more, preferably 1 hour or more. The dehydrogenation process is performed in a vacuum or Ar gas flow. Note that the dehydrogenation process is not an essential process.

  After the coarse pulverization process, the process proceeds to the fine pulverization process. In the fine pulverization, a jet mill is mainly used, and a coarsely pulverized powder having a particle diameter of about several hundreds of micrometers is pulverized until the average particle diameter becomes 3 to 5 μm. The jet mill opens a high-pressure inert gas (for example, nitrogen gas) from a narrow nozzle to generate a high-speed gas flow, and the high-speed gas flow accelerates the coarsely pulverized powder. Or it is the method of generating and colliding with a container wall. By adding about 0.01 to 0.3 wt% of additives such as zinc stearate at the time of fine pulverization, fine powder having high orientation can be obtained at the time of molding.

Next, the finely pulverized alloy powder is formed in a magnetic field with its crystal axis oriented by applying a magnetic field. The molding pressure in the magnetic field molding may be in the range of 0.3 to 3 ton / cm ² (30 to 300 MPa). The molding pressure may be constant from the beginning to the end of molding, may be gradually increased or gradually decreased, or may vary irregularly. The lower the molding pressure is, the better the orientation is. However, if the molding pressure is too low, the strength of the molded body is insufficient and handling problems occur. Therefore, the molding pressure is selected from the above range in consideration of this point. The final relative density of the molded body obtained by molding in a magnetic field is usually 50 to 60%. The applied magnetic field may be about 12 to 20 kOe (960 to 1600 kA / m). Further, the applied magnetic field is not limited to a static magnetic field, and may be a pulsed magnetic field. A static magnetic field and a pulsed magnetic field can also be used in combination.

  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 particle size, and a particle size distribution difference, what is necessary is just to sinter at 1000-1200 degreeC for about 1 to 10 hours. After sintering, the obtained sintered body can be subjected to an aging treatment. The aging treatment is important for controlling the coercive force. In the case where the aging treatment is performed in two stages, it is effective to maintain a predetermined time in the vicinity of 800 to 900 ° C. and in the vicinity of 600 to 700 ° C.

A high purity Fe raw material was prepared. 26.5 wt% Nd-5.9 wt% Dy-0.25 wt% Al-0.5 wt% Co-0.07 wt% Cu-1 wt% B-bal. A raw material alloy having a composition of Fe was produced. At this time, P (phosphorus) and S (sulfur) were appropriately added to produce raw material alloys having different amounts of P and S.
Next, after hydrogen was occluded in the raw material alloy at room temperature, hydrogen pulverization treatment was performed in which dehydrogenation was performed at 600 ° C. for 1 hour in an Ar atmosphere. The alloy that has been subjected to hydrogen pulverization treatment was mixed with 0.05 to 0.1 wt% of a lubricant that contributes to improvement of pulverization and orientation during molding. The lubricant may be mixed for about 5 to 30 minutes using, for example, a Nauta mixer. Thereafter, pulverization was performed under certain conditions to obtain a pulverized powder having an average particle size of 4 to 5 μm. The fine pulverization was performed with a jet mill. All the composition samples were pulverized under the same conditions. Table 1 shows the particle size of the pulverized powder measured by a laser diffraction particle size distribution analyzer.

The resulting finely pulverized powder was molded in a magnetic field. Molding in a magnetic field was performed at a pressure of 1.4 ton / cm ^{2 in} a magnetic field of 15 kOe. The obtained molded body was heated to 1080 ° C. in a vacuum and held for 4 hours for sintering. Next, the obtained sintered body was subjected to a two-stage aging treatment of 800 ° C. × 1 hour and 560 ° C. × 1 hour (both in an Ar atmosphere). After the sintered body was polished into a predetermined shape, the magnetic properties were measured. The results are shown in Table 1.
Next, the contents of P and S in the sintered body were measured by fluorescent X-ray analysis. The measured results are shown in Table 1.

1 shows the relationship between the P and S contents and D50, FIG. 2 shows the relation between the P and S contents and the coercive force (iHc), and FIG. 3 shows the P and S contents and the residual magnetic flux density. The relationship of (Br) is shown. The following can be said from Table 1 and FIGS.
As the P and S contents increase, the particle size of the finely pulverized powder decreases. Further, it can be seen that when the contents of P and S are increased, the difference of D90-D10 becomes small, and the particle size distribution becomes narrow and sharp. Furthermore, the coercive force (iHc) increases as the P and S contents increase. On the other hand, the residual magnetic flux density (Br) was constant or slightly increased as the contents of P and S increased, and decreased when exceeding 220 ppm.

It is a graph which shows the relationship between content of P and S, and D50. It is a graph which shows the relationship between content of P and S, and a coercive force (iHc). It is a graph which shows the relationship between content of P and S, and residual magnetic flux density (Br).

Claims (4)

From R ₂ T ₁₄ B compound (R is one or more elements selected from rare earth elements, T is one or more elements selected from transition metal elements including Fe or Fe and Co) A sintered body having a crystal grain as a main phase,
An RTB-based sintered magnet containing 10 to 220 ppm of P and / or S in the sintered body.   The RTB-based sintered magnet according to claim 1, wherein P and / or S contained in the sintered body is 50 to 200 ppm.   The sintered body is R: 25 to 35 wt%, B: 0.5 to 4 wt%, one or two of Al and Cu, 0.02 to 0.6 wt%, Co: 0.5 to 4 wt% or less The RTB-based sintered magnet according to claim 1, wherein the balance is substantially composed of Fe. From R ₂ T ₁₄ B compound (R is one or more elements selected from rare earth elements, T is one or more elements selected from transition metal elements including Fe or Fe and Co) A method for producing an RTB-based sintered magnet comprising a sintered body having crystal grains as a main phase,
A step of pulverizing the raw material alloy produced by strip casting the molten alloy having a P and / or S content of 10 to 220 ppm to a powder having a predetermined particle size;
Forming the powder in a magnetic field to produce a molded body;
Sintering the molded body;
The manufacturing method of the RTB system sintered magnet characterized by including these.

Images