JPH07120576B2 - Cast rare earth-method for manufacturing iron-based permanent magnets - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rare earth-low permanent magnet.

[Outline of Invention]

The present invention does not crush and sinter the cast ingot,
On the other hand, after being cast by the solidification method so that the cast macrostructure has only columnar crystals, it is magnetically hardened only by heat treatment, and it is magnetically anisotropy by hot working. -To obtain an iron-based permanent magnet.

[Conventional technology]

Conventionally, the following three methods have been reported for producing R-Fe-B magnets.

(1) Sintering method based on powder metallurgy (Reference 1).

(2) A quenching ribbon manufacturing apparatus used for producing an amorphous alloy is used to make a quenching thin piece with a thickness of about 30 μm, and the thin piece is made into a magnet by a resin bonding method (Reference 2).

(3) A method of mechanically orienting the same thin piece used in the method of (2) by a two-step hot press method (reference document 2).

Reference 1 M. Sagawa, S. Fujimura, N. Togawa H. Yamamot
o and Y.Matsuura; J.Appl.Phys, Vol.55 (6), 15Maroh1
984, P2083 References 2. RWLee; Appl.Phys, Lett, Vol.46 (8), 15
April1985, P790 The above-mentioned prior art will be explained along with the literature. First, in the sintering method (1), an alloy ingot is produced by melting and casting, and is crushed into magnet powder having a particle size of about 3 μm. Magnet powder is kneaded with a binder that serves as a molding aid,
It is press-molded in a magnetic field to form a molded body. The compact is sintered in argon at a temperature around 1100 ° C for 1 hour,
Then it is rapidly cooled to room temperature. After sintering, heat treatment at a temperature of around 600 ° C further improves the holding power.

(2) First, R- at the optimum rotation speed of the quenching ribbon manufacturing apparatus.
Create a quenched ribbon of Fe-B alloy. The obtained ribbon has a thickness of 30μ
It is in the shape of a ribbon of m, and is a collection of polycrystals with a diameter of 1000Å or less. The ribbon is brittle and easy to crack, and the crystal grains are isotropically distributed, so it is also magnetically isotropic.This ribbon has a proper grain size, and if it is kneaded with a resin and pressed, it will be 7 tons. A pressure of about / cm ² enables filling of about 85% by volume.

In the manufacturing method of (3), first, a ribbon-shaped quenched ribbon or a strip of ribbon is placed at about 700 in a vacuum or in an inert atmosphere.
Place in Graphite or other heat-resistant press mold preheated at ℃. When the ribbon reaches the desired temperature-axial pressure is applied. The temperature and time are not specified,
T = 725 ± 250 ° C, pressure is P
About 1.4 ton / cm ² is suitable. At this stage the magnets are generally isotropic although they are slightly oriented in the pressing direction. The next hot press is carried out in a mold with a large area. Most commonly, it presses at 700 to 0.7 ton for a few seconds. Then, the sample becomes 1/2 of the initial thickness, the easy axis of magnetization is oriented parallel to the pressing direction, and the alloy becomes anisotropic. These steps are performed by the two-step hot press method (tw
This method, which is called an o-stage hot-press procedure, can produce a dense and anisotropic R-Fe-B magnet. In addition, the crystal grain of the ribbon ribbon made by the first melt spinning method should be made smaller than the grain size when it shows the maximum holding power, and the coarsening of the crystal grain will occur during hot pressing later, which is optimum. The particle size of.

[Problems to be solved by the invention]

In the above-mentioned conventional techniques, R-Fe-B magnets can be produced for the time being, but the production methods using these techniques have the following drawbacks. In the sintering method of (1), it is essential to make the alloy into a powder, but since the R-Fe-B alloy is very active with respect to oxygen, if powdered, excessive oxidation will occur, resulting in sintering. The oxygen concentration in the body is inevitably high. Also, when molding the powder, it must be used with a molding aid, such as zinc stearate, which is also removed during the sintering process, but a few tens of carbons in the magnet body. Remains in the form of. This carbon significantly deteriorates the magnetic performance of R-Fe-B. The green body is the green body after press molding by adding a molding aid. It is very fragile and difficult to handle. Therefore, it takes a great deal of time to neatly put them side by side in the sintering furnace, which is a big drawback. Due to these drawbacks, it is generally said that the production of R-Fe-B system sintered magnets requires not only expensive equipment, but also poor production efficiency and high magnet production costs. I will end up. Therefore,
It is hard to say that this is a manufacturing method that can bring out the low cost of raw materials for R-Fe-B magnets.

The manufacturing methods (2) and (3) use a vacuum melt spinning device. This device is currently very unproductive,
Moreover, it is expensive. In (2), since it is isotropic in principle, it is a low energy product, and since the squareness of the hysteresis loop is not good, it is disadvantageous in terms of temperature characteristics and use. The method (3) is a unique method in which the hot press is used in two steps, but it cannot be denied that it will be very inefficient when actually considering mass production.

The method for producing an R-Fe-B magnet according to the present invention solves these drawbacks, and an object thereof is to provide a high-performance magnet at low cost.

[Means for solving problems]

The manufacturing method of the permanent magnet of the present invention is R8 in atomic percentage.
~ 25% (where R is at least 1 of rare earth elements including Y)
Seed), a step of melting an alloy containing B2 to 8% and the balance of iron as a main component, a step of obtaining a cast ingot by casting using a unidirectional solidification method, and a heat treatment of the cast ingot at 500 ° C. or higher after casting. And a magnetic hardening step.

As described above, the sintering method and the quenching method, which are the existing methods for manufacturing rare earth-iron permanent magnets, respectively, have major drawbacks such as difficulty in powder management by pulverization and poor productivity. In order to remedy these drawbacks, the present inventors have started research on an alloy capable of obtaining a holding force in the bulk state, and it is possible to obtain the holding force in the bulk state in the above composition. Yes, at this time, if the casting structure is a unidirectionally solidified structure without disorder, it is easy to obtain holding force,
In addition, since the anisotropy of the solidified structure can be used, a more uniform high-performance permanent magnet can be obtained than when using a normal solidified structure, and if continuous casting is applied to this, productivity can be significantly increased. Inventing that it is possible to make it anisotropic by hot working. In this method, since it is not necessary to crush the cast ingot, it is not necessary to perform the strict atmosphere control as in the sintering method, and the equipment cost is greatly reduced.
Furthermore, the anisotropic type by hot working can be done in one step instead of two steps like the quenching method, and since it can be processed as a bulk, it can be used not only for pressing but also for rolling, stamping, extrusion, drawing, etc.・ Productivity will increase significantly. For research on the same system, refer to Reference 3 Hiroaki Miho et al.
There is a lecture in the end of 60, lecture number (544), but this research not only differs from the present invention in the composition range, but also does not mention any performance change due to macrostructure and it is a book on performance. Greatly inferior to the invention. Further, in the case of the present system, the secondary processing for obtaining the desired shape is very easy to perform even in the cold state because the bending strength and the compressive strength are larger than those of the conventional samarium-cobalt rare earth magnet.

As the composition of the conventional R-Fe-B magnet is represented in reference 1, R ₁₅ Fe ₇₇ B ₈ has been the optimum composition. This composition shifts to the side rich in both R and B elements compared to the composition R _11.7 Fe _32.4 B _{5.9 in} which the main phase R ₂ Fe ₁₄ B compound of the R-Fe-B system magnet is expressed in atomic percentage. This is explained from the point that not only the main phase but also a non-magnetic phase called R-rich phase / B-rich phase is necessary to obtain coercive force.
On the contrary, in the composition according to the present invention, on the contrary, a peak value is present when the composition shifts to the side with less B. In this composition range, since the holding power is drastically reduced by the sintering method, much attention has not been given so far. However, according to the casting method, a high coercive force can be obtained only in this composition range, and a sufficient coercive force cannot be obtained on the usual B-rich side. It is considered that this is due to some change in the holding force mechanism.

On the other hand, the solidification method is used for permanent magnet materials, including Alnico magnets, rare earth magnet-based cerium-cobalt-copper-iron-based cast magnets (reference 4. GYCHIN et al., IEEE Uransacti
ons or Maghetics, Vol.MAG-8, No.1, March1972P29), and one of the inventors of the present invention in 1981, on the other hand, did not solidify, but the effect of the columnar crystal structure was confirmed by the resin-bonded samarium cobalt magnet. (Reference 5, T. Shimoda et al., Proceedings of the fifth intern.
ational Workshop on Rare Earth-Cobalt Permanent M
agnets, 1981P595). Also in the present invention, obtaining a solidified structure on the other hand in a cast state is an important point for making a high-performance magnet. That is, in the present magnet, the process of obtaining the coercive force by heat treatment is due to diffusion, and like the samarium-cobalt in Reference 5, the unidirectionally solidified structure is easier to obtain the coercive force than the isocrystal. Furthermore, this system magnet has the property that the easy axis of magnetization is oriented in the plane perpendicular to the unidirectionally solidified tissue,
If this is utilized, it will become an in-plane anisotropic magnet. Generally, the biggest problem with cast magnets is how to make them anisotropic. Alcohol magnets employ means such as controlled cooling in a magnetic field, but this system allows mechanical orientation by hot working. That is, the easy axis of magnetization is oriented in the direction of deformation. In the columnar crystal structure cast in a normal die instead of unidirectional solidification, not only the magnetic properties deteriorate due to the disorder of the structure, but also the difference in the development direction of the columnar crystal structure occurs in the peripheral part and the central part of the mold wall. However, it is difficult to achieve uniform orientation even by hot working. However, in the case of unidirectional solidification, orientation variation is unlikely to occur, and orientation can be easily performed. The orientation direction is not limited to vertical and horizontal directions, but radial orientation is also possible by using a device such as rotary swaging that applies deformation pressure from multiple directions or a ring-shaped extruder that reduces the ring thickness.

Hereinafter, the reason for the composition limit of the permanent magnet according to the present invention will be described. As rare earths, Y, La, Ce, Pr, Nd, Sm, Er, Gd, Tb, Dy, H
o, Eu, Tm, Yb, and Lu are listed as candidates, and one or more of these may be used in combination. The highest magnetic properties are obtained with Pr. Therefore, in practice, Pr, Pr
-Nd alloy, Ce-Pr-Nd alloy, etc. are used. Further, a small amount of additional elements, such as heavy rare earth elements Dy, Tb, etc., Al, Mo, Si, etc., are effective for improving the coercive force. The main phase of the R-Fe-B magnet is
R ₂ Fe ₁₄ B. Therefore, when R is less than 8 atomic%. Since the above compound is no longer formed and a cubic crystal structure having the same structure as α-iron is formed, high magnetic properties cannot be obtained. On the other hand, R is 25 atom%
If it exceeds, the amount of non-magnetic Rrich phase increases and the magnetic properties deteriorate significantly. Therefore, the range of R is appropriately 8 to 25 atomic%.

B is an essential element for forming the R ₂ Fe ₁₄ B phase, and 2
If it is less than atomic%, a rhombohedral R-Fe system is obtained, so high holding power cannot be expected. However, when 8 atom% or more is added as in the case of a magnet produced by the conventional sintering method, the holding force in the cast state cannot be obtained, on the contrary. Therefore, the amount of B is preferably in the range of 2 to 8 atomic%.

Example 1 An example of a manufacturing process diagram according to the present invention is shown in FIG. First, an alloy having a desired composition is melted in an induction furnace, continuously unidirectionally solidified using a heating mold, and subsequently hot worked in a temperature range of 500 ° or more to impart anisotropy, Next, annealing is performed in the temperature range of 500 ° C to 1050 ° C to magnetically elevate, and then the final shape is finished by cutting and grinding. In this example, the composition shown in Table 1 was melted, a size of 20 mm × 10 mm was used as a heating mold, and a size of 10 mm × 10 mm was finished by hot forging at 800 ° C., and hot working was performed at 800 ° C. Annealing was performed in a belt furnace at 1000 ° C for 24 hours.

The results obtained are shown in Table 2.

[Example 2] Using the composition Pr ₁₅ Fe ₈₁ B ₄ having the highest function obtained in Example 1,
A tubular sample with an outer diameter of 30 mm and an inner diameter of 10 mm was made by the continuous one-way solidification method, and this was made into a rotary swaging machine shown in Fig. 2, which was radially oriented at about 900 ° C using the rotary swaging machine shown in Fig. 2. Then, after being processed to have an outer diameter of 20 mm and an inner diameter of 10 mm, heat treatment was performed at 1000 ° C. × 24 H in a belt furnace. Performance measurement is about 1/8 from the finished sample
Table 3 shows the results of VSM after cutting out and performing demagnetizing field correction.

The performance of this example is the average of eight samples. By rotary swaging as shown in the table,
Performance of about 80% was obtained.

[Example 3] Alloy ingots having the compositions shown in Table 4 were produced by continuous one-side solidification in the same manner as in Examples 1 and 2. At this time, use a heating mold with an outer diameter of 40 mm and an inner diameter of 30 mm and a length of 200 mm.
The sample was cut out and then sealed with a 1 mm thick ss material, an Al-added iron bar was set inside the tube, and the cross section was processed by extrusion in three stages from a diameter of 42 to a diameter of 25 at 950 ° C. And as heat treatment, at 1000 ℃ for 20 hours
It was carried out at 500 ° C. for 5 hours. Next, the iron bar in the center is BN on the surface.
Since it can be easily removed by applying as a release agent, the ss material on the tube surface is polished and removed. The porcelain performance in the radial direction of the thus obtained pipe-shaped magnet (outer diameter 24.5, inner diameter 18.5) was measured using a VSM with a 2.5 mm square sample cut in that direction. The results are shown in Table 5 (average of 8 samples). This shows that high-performance radical anisotropy with (BH) max of 25 MGOe was obtained.

Example 4 Composition of Pr _17.2 Fe ₇₇ B _5.2 Cu _0.6 (composition 1) and Pr _16.3 Fe
Two alloys having a composition of _76.3 B _5.2 Cu _1.5 MO _0.7 (composition 2) were melted in an induction furnace and then cast by the following three methods.

A. Casting on an alumina vibration mold with an outer diameter of 30 mm and an inner diameter of 10 mm B. Casting on an iron mold with an outer diameter of 30 mm and an inner diameter of 10 mm C. Casting on an alumina mold with an outer diameter of 30 mm and an inner diameter of 10 mm, and then again through an induction heating zone from the bottom Unidirectional solidification was performed.

In either composition 1 or 2, the ingot structure of A was an equiaxed crystal structure, and the ingot structure of B was a columnar crystal structure developed in the radial direction. The structure of the C ingot was a columnar crystal structure developed in the axial direction of the cylinder. Next, samples of these two compositions and six casting diameters of six diameters were processed into a 20 mm outer diameter and 8 mm inner diameter at 975% using a 100 mm long swaging machine. After processing, 12 hours at 1025 ℃ and then 550
Heat treatment was performed at 4 ° C. for 4 hours. The radial magnetic characteristics of the pipe-shaped magnet obtained in this way were cut out in 3 m
It was evaluated by measuring the m-square sample with VSM. The results are shown in Table 6.

The results are shown in Table 6.

〔The invention's effect〕

As described above, according to the present invention, it is possible to obtain the holding force in the bulk state in the composition range where the holding force iHc cannot be obtained by the conventional sintering method, and the manufacturing process can be significantly simplified. it can. Also, since radial anisotropic magnets with (BH) max of 25MGOe or more can be manufactured in a simple process, high performance of OA and FA motors can be expressed at low cost.

[Brief description of drawings]

 FIG. 1 is a manufacturing process drawing of the R—Fe—B system magnet of the present invention. FIG. 2 is a diagram of a rotary swaging machine.

Claims (4)

[Claims] 1. A step of melting R8 to 25% (provided that R is at least one rare earth element containing Y), B2 to 8% and the balance of iron as a main component in atomic percentage, and one direction. A step of obtaining a cast ingot by casting using a solidification method, and a step of magnetically hardening the cast ingot by heat treatment at 500 ° C. or higher after casting. Production method. 2. The method for producing a rare earth-iron-based permanent magnet according to claim 1, wherein unidirectional solidification is performed by using a continuous casting method. 3. A step of melting R8 to 25% (provided that R is at least one rare earth element containing Y), B2 to 8%, and the balance of iron as a main component in atomic percentage, and one direction. A step of casting using a solidification method to obtain a cast ingot, and after casting, hot-working the cast ingot at 500 ° C. or higher to orient the crystal axes of the crystal grains in a specific direction to make it magnetically anisotropic. And a step of magnetically hardening by heat-treating at a temperature of 500 ° C. or higher, a method for producing a cast rare earth-iron-based permanent magnet. 4. The method for producing a rare earth-iron-based permanent magnet according to claim 3, characterized in that the solid is unidirectionally solidified by a continuous casting method.