JP3135120B2 - Manufacturing method of warm-worked magnet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement in a method for producing a warm-worked magnet substantially consisting of a rare earth element R, a transition metal T, and boron B.

[Prior Art] A permanent magnet substantially consisting of a rare earth element R, a transition metal T and boron B (hereinafter referred to as an RTB-based permanent magnet).
Has a crystal magnetic anisotropy and the intermetallic compound is high saturation magnetization, represented by R ₂ T ₁₄ B having a tetragonal crystal structure, inexpensive and exhibit high permanent magnet properties than conventional rare earth cobalt magnets Attention is drawn from doing. This intermetallic compound has a square of 0.878 nm on one side at room temperature and a lattice constant of 1.218 nm in the C-axis direction perpendicular to the plane. However,
Industrial manufacturing methods of this type of magnet are roughly classified into a sintering method and a super-quenching method. The sintering method is a manufacturing method generally called a powder metallurgy method, in which a magnet fine powder having an average particle diameter of 2 to 4 μm obtained by pulverizing an ingot is molded while applying a magnetic field in a cold manner, and a desired shape is formed. This is a method of obtaining a dense permanent magnet by sintering at 1000 ° C. or higher after imparting magnetic anisotropy. On the other hand, the ultra-quenching method is to rapidly quench a molten alloy having a desired composition by a melt spinning method, a gas atomizing method, or the like,
In this method, the obtained powder or ribbon is densified by warm working at 600 to 1000 ° C. to impart anisotropy. Magnetic anisotropy is provided by aligning crystal axes in a desired direction by warm plastic working.

In the case of a sintered magnet, carbon powder or Ti, Zr,
An invention is known which contains a carbide-forming component powder such as Hf to form a metal carbide, thereby suppressing the growth of crystal grains during sintering and increasing the density (Japanese Patent Application Laid-Open No. 63-163).
No. 98105). This invention does not mention the lubricating action of carbon powder.

However, when trying to obtain a magnetically anisotropic sintered magnet, a complicated step of molding in a magnetic field is required, and the shape is restricted.

Therefore, quenching magnets that do not require molding in a magnetic field, especially R-
The TB melt is solidified by a super-quenching method, and the obtained ribbon or flake is pulverized and then hot-pressed (high-temperature treatment)
Then, a permanent magnet (hereinafter referred to as a warm-worked magnet) which has been subjected to plastic working in a warm state to impart magnetic anisotropy (hereinafter, referred to as a warm-worked magnet) has attracted attention (see Japanese Patent Application Laid-Open No. 60-100402). The ribbon or flake obtained by the rapid quenching method is composed of fine crystal grains. Therefore,
The thickness of the ribbon or flake obtained by the rapid quenching method is 30μm
Although it is in the form of an irregular plate having a length of about 500 μm or less and a sintered magnet (for example, JP-B-61-34242)
The average crystal grain size inside is as fine as 0.02 to 0.5 μm as compared with 1 to 90 μm of the magnet described in Japanese Unexamined Patent Application Publication No. 2000-209, and is essentially superior to the single-domain critical particle size (0.3 μm) of the magnet of this system. This is because characteristics can be obtained.

For warm-worked magnets, the close correlation between plastic flow and the state of magnetic alignment in the direction perpendicular to the direction is important. It is necessary to uniformly and sufficiently perform plastic flow on the entire workpiece to improve the degree of orientation related to magnetic properties. In addition, large cracks occur at the edges due to non-uniform deformation, for example, a bulge phenomenon (the edges are deformed into a barrel shape) of the workpiece in plastic working. This is a serious problem in practical use.

Here, most of the working force applied at the time of warm working is used for plastic work, but is partially wasted as friction work. This is also a cause of the bulge phenomenon.

Therefore, in order to improve the warm workability and obtain a hot-worked magnet without cracks, Japanese Patent Application Laid-Open No. 60-100402 discloses a lining using graphite as an external lubricant on the surface of a die used for warm upsetting. Examples are given. In this publication, there is no mention of the effect on the inside of the magnet body.

[Problem to be Solved by the Invention] In the above conventional invention, a thickness of 30 μ
The graphite applied to the dies hardly adheres to the flakes, which are about m in length and have a side length of 500 μm or less, even if some of the graphite adheres to the dies. The grains are not covered by the additives.

In addition, when carbon powder or carbide forming component powder such as Ti, Zr, Hf is added to the sintered magnet, the powder can be relatively easily dispersed among the individual magnetic powders by devising the powder shape and mixing method to be added. is expected. This is because in the case of a sintered magnet, the magnetic powder used is an alloy ingot (ingot).
This is considered to be due to a relatively spherical shape obtained by pulverizing the powder.

However, unlike sintered magnets manufactured by powder metallurgy, which are molded at room temperature, warm-worked magnets are usually upset at 600 to 850 ° C, so additives added between individual flakes Is thought to be fundamentally different,
No consideration has been given to this point in the conventional invention.

In addition, the conventional technique of applying an external lubricant to the die surface does not give a special working effect to the warm-worked magnet, but rather reduces the coefficient of friction between the die surface and the workpiece surface by the usual metal processing. Does not exhibit the effect more than that of the lubricant. In fact, it has not been reported that warm workability is remarkably improved, cracks are suppressed, and the orientation is improved to improve magnetic properties.

Accordingly, an object of the present invention is to provide a method for manufacturing a warm-worked magnet that can improve the warm-workability, increase the degree of orientation, suppress cracks, and improve the magnetic properties.

[Means for Solving the Problems] The method for manufacturing a warm-worked magnet having R ₂ T ₁₄ B as a main phase according to the present invention which has solved the above-mentioned problems includes an RTB-based alloy (R is a rare earth element containing yttrium). One or more of the elements,
Is a transition metal mainly composed of iron, and B is boron). The molten metal is rapidly quenched, and the obtained ribbon or flake is pulverized. Then, 0.001 to 5 weight of rare earth carbide is added to the obtained pulverized powder. %, And after mixing, the resulting mixed powder is formed into a high density, and then plastically deformed to impart magnetic anisotropy.

It is preferred that R is one or more of Nd, Ce, Pr, Tb, and Dy.

It has been believed in the common sense of conventional warm-worked magnets that the addition of additives that leave carbon, oxygen and the like is harmful to magnetic properties. However, the present inventors are not bound by the fixed concept, by adding an appropriate amount of a rare earth element carbide instead of adding carbon in units, it is possible to significantly improve both warm workability and magnetic properties. I found the effect.

The working temperature of the warm-worked magnet according to the present invention is suitably from 680 to 800 ° C. In other words, below 680 ° C, Nd required for plastic deformation
This is because a rich phase hardly occurs and many cracks occur. With the increase in the amount of rare earth carbide added, the warm working temperature shifts to a slightly higher temperature side, but up to 800 ° C., it is possible to easily work without significantly lowering the magnetic properties. When the temperature exceeds 800 ° C, the magnetic properties are significantly reduced due to the coarsening of crystal grains,
Many cracks also occur.

In the present invention, if the added amount of the rare earth carbide is less than 0.001% by weight, the residual carbon component during the high-temperature treatment is too small, and the effect of the present invention for improving both the degree of orientation of the crystal grains and the magnetic properties cannot be obtained. %, The magnetic properties are undesirably deteriorated. The warm-worked magnet according to the present invention to which a predetermined amount of rare earth carbide is added exhibits a unique grain boundary structure that cannot be obtained by simply adding carbon. Fig. 1 shows Nd carbide
FIG. 3 shows a schematic diagram of crystal grains of a warm-worked magnet to which 0.5 wt% is added. FIG. 2 shows the case where Nd carbide is not added. 1 and 2 are views as seen from the upsetting direction. It can be seen that the crystal grains of the warm-worked magnet according to the present invention are thin and uniformly deformed in the direction perpendicular to the upsetting direction, and that the crystal grain boundaries appear clearly when viewed from the upsetting direction. Concentration of carbides is observed at the crystal grain boundaries composed of the rare earth-rich (enriched) phase surrounding the main phase. Therefore, it is concluded that the added rare earth carbides contribute to the improvement of magnetic properties by enrichment at the crystal grain boundaries. Seem.

The carbon content of the warm-worked magnet according to the invention is 0.8% by weight
When the oxygen content exceeds 0.8% by weight, and when the oxygen content exceeds 0.8% by weight, the deformation resistance of the workpiece is remarkably increased, and the warm workability is deteriorated.

The warm-worked magnet according to the present invention contains a transition metal T as a main component and a rare earth element R containing yttrium and boron B as essential components. The composition range conforms to that of a warm-worked magnet known in JP-A-60-100402. However, in the present invention, the transition metal T is mainly composed of iron, and is partially Co, Ni, Ru, Rh, Pd, Os, I
r, not only transition metals in the narrow sense of Pt, but also atomic numbers 21 to 29, 39
A transition metal in a broad sense including all elements of 〜47,72 to 79,89 or more.

In addition, since the addition of Ga has an effect of remarkably improving the coercive force in a warm-worked magnet as already announced by the present inventors, it is effective to add Ga as needed. Furthermore, addition of a known additive element according to the purpose does not depart from the effects of the present invention.

It is needless to say that the rare earth element R is mainly composed of Nd and Pr, and can be partially substituted with Ce, Sidium or the like for cost reduction, and partially substituted with Dy or Tb for the purpose of improving temperature characteristics.

The average grain size of the warm-worked magnet according to the present invention is minute as a feature of the magnet by the ultra-quenching method. Average grain size is 0.
It is difficult with current technology to obtain a warm-worked magnet of less than 02 μm in an industrially stable manner, and the average crystal grain size is 0.5 μm.
If it exceeds m, the coercive force is undesirably reduced. The average crystal grain size is measured by a cutting method in a micrograph. That is, the value obtained by dividing the length of the line segment by the number of crystal grains that cut the line segment when a straight line is arbitrarily drawn in the micrograph is defined as the crystal grain size, and the average value obtained for at least 20 or more crystal grains is averaged. The crystal grain size is used. It should be noted here that the warm-worked magnet according to the present invention has a flat shape in a plane perpendicular to the C-axis of the crystal grain, and when cut along a plane including the C-axis, the thickness is in the thickness direction of the flat plate. Therefore, the above-mentioned average crystal grain size refers to a measured value on a plane perpendicular to the C axis.

In addition, the key to the magnetic expression of the warm-worked magnet according to the present invention is R ₂ T ₁₄ B
It is a tetragonal crystal of a type intermetallic compound. At room temperature, one side of the tetragonal crystal is 0.878 nm, and the lattice constant in the C-axis direction perpendicular to the plane is around 1.218 nm. Further, the warm-worked magnet positively utilizes the unique property that an aggregate of these crystal grains generates magnetic anisotropy in a direction perpendicular to the plastic flow direction. In the warm-worked magnet according to the present invention, the rare-earth carbide acts as an internal lubricant, so that the warm-workability is improved, and the working ratio can be higher than that of the conventional warm-worked magnet. Therefore, in the warm-worked magnet according to the present invention, the crystal grains are greatly deformed, and the average crystal grain size (c) in the direction perpendicular to the C axis of the crystal axis in the aggregate of oriented crystal grains and the average crystal grain in the C axis direction The ratio c / a to the diameter (a) can be 2 or more. According to experiments by the present inventors, if the c / a value is 2 or more, a magnetic flux density of 8 kG or more can be obtained, so that industrial applicability is high.

Further, the addition of the rare earth carbide in the present invention causes the carbide to concentrate at the crystal grain boundaries, and the degree of orientation of the crystal grains is remarkably improved due to the lubrication effect by the concentration during warm working, so that the magnetic properties can be improved. The degree of orientation can be measured by X-ray diffraction. That is, first, the X-ray diffraction intensity of each diffraction surface of an isotropic sample is measured by a diffractometer, and then the X-ray diffraction intensity of each diffraction surface of a sample cut out from a warmed anisotropic magnet is measured. Then, the measured X-ray diffraction intensity is normalized by the X-ray diffraction intensity of the isotropic sample. Next, the normalized value is plotted with respect to the angle between each diffraction plane and the C plane, approximated by a Gaussian distribution, and the crystal orientation can be evaluated based on the degree of dispersion. The warm-worked magnet according to the present invention has a good degree of orientation with an angular dispersion value of less than 30 °. The conventional warm-worked magnet has an angular dispersion value of 30 ° or more, and has a low degree of orientation (magnetic properties).

In the present invention, warm plastic working is essentially performed. Extrusion, swaging, rolling, spinning, upsetting or the like is used as a means of warm plastic working. In particular, upsetting is effective in providing anisotropy. This is because the stress distribution and the strain rate can be selected so as to obtain a warm-worked magnet having excellent properties. When the present invention is applied, plastic deformation during warm working becomes more uniform than before, so that strain distribution in an arbitrary cross section can be made more uniform than before. Conventional warm-worked magnets have a non-uniform strain distribution and many cracks cannot be put to practical use. In particular, cracks in the peripheral bulge portion are required to be cut in a post-process, thereby reducing industrial applicability. The strain distribution is measured by an X-ray stress measurement method, a hardness distribution measurement method, or the like.

The present invention has the effect of remarkably improving the compressibility of not only warm-worked magnets but also compacted magnets obtained by simply hot pressing flakes or the like obtained by ultra-quenching.
In the case of hot pressing, the warm working method used in the present invention,
Although it is an isotropic deformation that does not generate plastic flow in a specific direction as in the upsetting work, compressibility is improved by adding a predetermined amount of rare earth carbide, and magnetic properties can be improved.

Also, the warm-worked magnet according to the present invention is pulverized into magnetic powder,
It can be kneaded with a binder such as a resin or a low melting point metal to form a bonded magnet. Compared to a sintered magnet having an average crystal grain size of about 1 to 90 μm, the average crystal grain size of the warm-worked magnet according to the present invention is 0.02 to 0.5 μm, which is one to two orders of magnitude smaller, and the deterioration of the magnetic properties due to grinding is reduced. This is because there is not substantially.

[Examples] Hereinafter, the present invention will be specifically described with reference to Examples.

(Example _{1) Nd (Fe 0.12 Co 0.1} B 0.07 Ga 0.01) 5.4 comprising the alloy of the composition to arc melting, and then injection to about 30μm on a single roll peripheral speed in an Ar atmosphere is rotated at 30 m / sec Amorphous flake-like flakes having a thickness were prepared. As a result of X-ray diffraction, it was found that the mixture was an amorphous and crystalline mixture. Next, a magnetic field was applied at a molding pressure of 6 tons / cm ² to each of the magnetic powder obtained by pulverizing the flake-shaped flakes to 500 μm or less and adding and mixing Nd carbide to the obtained magnetic powder at a molding pressure of 6 tons / cm ^2. Without using the specified mold, the density is 5.7g / cc, diameter 28mm, height
A 47 mm molded body was produced.

The obtained molded body was hot-pressed at 740 ° C. and 2 ton / cm ² to obtain a hot-pressed body having a high density of 7.4 g / cc, a diameter of 30 mm and a height of 30 mm. Next, the hot pressed body is further
Compression ratio at 0 ° C (30mm height before upsetting, 7.5% height after upsetting)
The magnetic anisotropy was imparted by warm working by upsetting so that the value (value divided by mm) was 4. After measuring the magnetic properties of the obtained warm-worked magnet, the carbon content and oxygen content remaining in the magnet were analyzed.

FIG. 3 shows the residual carbon content, the oxygen content, and the magnetic properties with respect to the respective Nd carbide input amounts. From Fig. 3, Nd
It can be seen that the residual carbon content increases linearly with the amount of carbide added, and that the magnetic properties are significantly improved by the addition of only 0.01 wt% of Nd carbide as compared to the case where no carbide is added. Among the magnetic properties, 4πlr is particularly improved, and (BH) max
Improves 8MGOe compared to the case where no additive is added.

(Example 2) By the same warm working method as in Example 1, the upsetting working temperature was changed to five stages of 600 ° C, 680 ° C, 740 ° C, 800 ° C, and 850 ° C. Upsetting was performed for each Nd carbide charge. The relationship between deformation resistance (compressive nominal stress) and strain was calculated from the recording paper during warm working, and the results are summarized in Table 1. Here, after processing to a compression ratio of 4, the number of occurrences of cracks in the peripheral portion of the warm-worked magnet exceeding 14 is marked with a cross, and for the other, the strain is 0.3 (compression ratio of about 1.4).
The nominal stress (ton / cm ² ) at the time of 3) was used. At the hot working temperature of 600 ° C, many cracks occurred and some of them buckled. On the other hand, even at 850 ° C, the stress increased remarkably and many cracks occurred. Therefore, the warm working temperature according to the present invention is preferably 680 to 800 ° C.

As a general trend, the optimal warming temperature shifted to the higher temperature side with the amount of Nd carbide input. The warm-worked magnets surrounded by the thick frames in Table 1 exhibited good workability in which the number of cracks at the peripheral portion of the final warm-worked magnet processed to the compression ratio was 4 or less.

Example 3 An alloy having a composition of Nd (Fe _0.83 B _0.07 Ga _0.01 ) _5.7 was melted by arc, and then injected on a single roll rotating at a peripheral speed of 30 m / sec in an Ar atmosphere to obtain a thickness of about 30 μm. An amorphous flake-like flake was prepared.

Next, a magnetic powder obtained by pulverizing the flake to 500 μm or less and adding 0.5 wt% of Nd carbide (the present invention)
And a sample to which no additive was added (Comparative Example) were each molded at a molding pressure of 6 ton / cm ² using a predetermined mold to produce a molded body having a density of 5.7 g / cc, a diameter of 28 mm and a height of 47 mm. The obtained compact was hot-pressed at 720 ° C. and densified, and then warm-worked by upsetting to give a compression ratio of 4, thereby imparting magnetic anisotropy.

The magnetic properties of the obtained warm-worked magnet and the degree of crystal orientation of the sample cut from each part of the magnet are measured by X-ray diffraction, and the distribution of the crystal orientation from the C axis of the crystal in the depth direction and the radial direction are compared. did. Table 3 shows the magnetic properties, FIG. 4 shows the crystal orientation distribution of the device according to the present invention, and FIG. 5 shows the crystal orientation distribution of the comparative example. FIG. 4 and FIG. 5 are views showing the crystal orientation in a cross section cut along a plane including the upsetting direction of the warm-worked magnet.

The cones in FIGS. 4 and 5 conceptually show the angular dispersion of the orientation of the crystal, and the numerical values described besides are the angular dispersion values. That is, it is a statistical dispersion of the angle of the deviation from the C axis in the alignment direction. Here, when the angular dispersion value is, for example, 18 degrees, it indicates that the C axis of all the crystal grains in the sample exists within the solid angle of 18 degrees, and the smaller the numerical value, the higher the degree of crystal orientation. Is shown.

As is clear from Table 3, FIG. 4 and FIG. 5, the addition of Nd carbide significantly improves the fluidity during plastic working, improves the degree of crystal orientation, and significantly improves the magnetic properties. Understand.

(Example 5) In the same manner as in Example 1, the addition amount of Nd carbide was set to 1.0 wt.
%, And the compression ratio was changed stepwise, and the relationship between the crystal grain size and the magnetic characteristics at that time was examined. The strain rate during processing is 0.00
1 (1 / second).

As a result, when the c / a value was 2 or more, the residual magnetic flux density became 8 kG or more. The compression ratio is a value obtained by dividing the height h ₀ of the sample before the upsetting by the height h of the sample after the upsetting.
The compression ratio 1 indicates a state before starting the warm working.

ADVANTAGE OF THE INVENTION According to this invention, the dispersion | variation of the residual magnetic flux density in one warm working magnet can be suppressed to 5% or less.

Although the above embodiment has been described with reference to the case of a warm-worked magnet, the effects of the present invention are also applicable to a compacted magnet.

[Effects of the Invention] According to the present invention, it is possible to provide a method for manufacturing a warm-worked magnet in which warm workability is improved, the degree of orientation is increased, cracks are suppressed, and magnetic properties are improved.

[Brief description of the drawings]

FIG. 1 is a schematic view of a micrograph of a metal structure of a warm-worked magnet according to the present invention, FIG. 2 is a schematic view of a micrograph of a conventional warm-worked magnet, and FIG. FIG. 4 is a diagram showing the relationship between the added amount of Nd carbide and the oxygen content, carbon content and magnetic properties in one embodiment of the warm-worked magnet, and FIG. 4 shows the degree of crystal orientation in the cross section of the warm-worked magnet according to the present invention. FIG. 5 is a diagram showing a distribution of the degree of crystal orientation in a cross section of the warm-worked magnet of the comparative example.

Claims (2)

(57) [Claims] 1. A molten metal of an RTB-based alloy (R is one or more rare earth elements including yttrium, T is a transition metal mainly composed of iron, and B is boron). Is rapidly quenched, and the obtained ribbon or flake is pulverized. Then, 0.001 to 5% by weight of rare earth carbide is added to and mixed with the obtained pulverized powder, and then the obtained mixed powder is molded and densified. And a method of producing a warm-worked magnet having R ₂ T ₁₄ B as a main phase, wherein magnetic deformation is imparted by plastic deformation. 2. The method according to claim 1, wherein R is one or more of Nd, Ce, Pr, Tb, and Dy.