JPH02285603A - Hot-worked magnet and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain an R-T-B hot-worked magnet having no cracks and uniform orientation by facilitating the plastic processing conducted on an R-T-B hot- worked magnet by containing the specific value or less of carbon and oxygen respectively. CONSTITUTION:In a hot-worked magnet, having fine crystal grains of 0.02 to 1.0mum in average crystal grains of magnetic anisotropy, made of R-T-B alloy mainly composed of transition metal T and containing an yttrium-carrying rare-earth element R and boron B, the content of carbon is 0.8wt.% or less and the content of oxygen is 0.3wt.% or less. Also, thin bands or thin pieces are obtained by chill-solidifying the R-T-B molten metal, which is mainly com posed of transition metal T, containing thin yttrium-carrying rare-earth element R and boron B, and after magnetic powder has been obtained by crushing the above-mentioned material, hydrocarbon having the boiling point of 50 deg.C or higher is mixed to the above-mentioned magnetic powder when a hot- processed magnet is manufactured by giving magnetic anisotropy by conducting a hot-working process. for example, a molding operation is conducted by adding hexane of 0.05 to 2.0wt.%.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a permanent magnet consisting essentially of rare earth elements, transition metals, and boron, and is an improvement of a warm-worked magnet that imparts magnetic anisotropy through warm working. In particular, by adding an appropriate amount of additives, the workability is improved, there is no cracking, and the orientation is improved, resulting in good (2) permanent magnets having good feelability and a method for producing the same.

[Conventional technology]

Permanent magnets made essentially of rare earth elements, transition metals, and boron (hereinafter referred to as R-T-B permanent magnets) are attracting attention as they are inexpensive and have high magnetic properties. This is because the intermetallic compound represented by R2Tl4B, which has a tetragonal crystal structure, exhibits excellent magnetic properties. This intermetallic compound has a square side of 0.878 nm at room temperature, and a lattice constant of C=1.218 nm in the C-axis direction perpendicular to the surface.

However, this type of magnet is broadly divided into sintered magnets and ultra-quenched magnets. No matter which manufacturing method is used, it is necessary to mold it into a desired shape, and moldability is important. It has been conventional practice to use lubricants to improve moldability. Lubricant is an external lubricant that is applied to the die surface or the surface of the molded object to reduce the coefficient of friction between the molded object and the die surface, and the friction between the powder particles that make up the molded object. Internal lubricants are broadly classified into internal lubricants, which are powder, liquid, and solid lubricants added to reduce the coefficient.

In the case of sintered magnets, many inventions are known in which stearic acid is added as an internal lubricant (Japanese Patent Laid-Open No. 61-341
01, 61-119006, and 61-208809). Here, stearic acid is CH3 (CH2)
+ It is a saturated fatty acid with the molecular formula expressed as 6cOOH.

Note that carbon powder, Ti, and Zr are contained within the sintered magnet.

There is a known invention in which crystal grain growth during sintering is suppressed and density is increased by containing powder of a carbide-forming component such as Hf to form a metal carbide (Japanese Unexamined Patent Application Publication No. 1983-1992).
(See Publication No. 98105). Although this invention does not mention the lubricating effect of carbon powder, it is understood that the effect inherent in carbon having a lubricating effect is used during molding.

However, in order to obtain magnetic anisotropy in a sintered magnet, a tedious process of molding in a magnetic field is essential, and the formation is restricted.

In addition, since the manufacturing method of sintered magnets includes a pulverization process, it is unavoidable that oxygen intrudes from the atmosphere during the pulverization or subsequent forming and sintering processes.
000 to 8000 ppm of oxygen is contained as an impurity. This impurity oxygen combines with the rare earth components in the alloy and exists as a nonmagnetic oxide, so it lowers the saturation magnetic moment of the alloy and also acts as a nucleation site for reversal magnetic domains when a reversal magnetic field is excited in a permanent magnet. This causes a decrease in coercive force.

Therefore, a quenched magnet that does not require forming in a magnetic field, especially an R-
T-B molten metal is solidified by an ultra-quenching method to obtain ribbons or flakes, which are pulverized and hot-pressed (high-temperature treatment), and then warm-plastically worked to give magnetic anisotropy to permanent magnets (hereinafter referred to as "
"warm-processed magnets") are attracting attention (Japanese Unexamined Patent Application Publication No. 1989-1999)
(Refer to Publication No.-100402). The ribbon or flake obtained by the ultra-quenching method further consists of countless fine crystal grains inside.

Therefore, although the ribbon or flake obtained by the ultra-quenching method has an irregular plate-like shape with a thickness of about 30 μm and a side length of 500 μm or less, the crystal grains contained inside the ribbon or flake are similar to those of a sintered magnet (e.g. (See Special Publication No. 61-34242) No. 1~
This is also because it is finer at 0.02 to 0.5 μm compared to 90 μm, and is close to the critical dimension of 0.3 μm of a single magnetic domain in this type of magnet, resulting in essentially excellent magnetic properties.

In warm-worked magnets, a close correlation between plastic flow and perpendicular magnetic alignment is important.

It is necessary to uniformly and sufficiently apply plastic flow to the entire workpiece in order to improve the degree of orientation related to magnetic properties. Also,
Non-uniform deformation is caused by the bulge phenomenon (
The edge is deformed into a barrel shape. ) causes large racks at the edges.

This is a major problem when trying to obtain a magnet as a product.

Here, most of the working force applied during warm working is used for plastic work, but a portion is wasted as friction work.

This also causes the aforementioned bulge phenomenon.

Therefore, in order to improve the workability during warm working and obtain a crack-free warm worked magnet, Japanese Patent Application Laid-Open No. 60100402 discloses that the surface of the die used for warm upsetting is lined with graphite as an external lubricant. Examples are given. In this case, there is no mention of the effect on the inside of the magnet.

[Problem to be solved by the invention]

In the conventional invention described above, the thin strip obtained by the ultra-quenching method or the irregular plate-shaped flake with a thickness of about 30 μm and a side length of 500 μm or less contains a portion of the graphite coated on the die. Even if it does adhere, it does not adhere to most of the thin pieces, much less the countless fine crystal grains inside are not covered with the additive.

In addition, carbon powder or Ti, Zr + H
When adding a carbide-forming component powder such as f, it is expected that it will be relatively easily dispersed between individual magnetic powders by devising the shape of the powder to be added and the mixing method. The same applies to stearate.

This is thought to be because the magnetic powder used in the case of sintered magnets is obtained by crushing an alloy ingot and has a relatively spherical shape.

However, unlike sintered magnets made by powder metallurgy, which are formed at room temperature, warm processing is usually done at temperatures of 600 to 850°C.
Since the upsetting process is carried out at a warm temperature, it is thought that the role of the additives added between the individual flakes is fundamentally different, but this point has not been considered in the conventional inventions.

Furthermore, the conventional technique of applying external lubricant to the die surface is
It does not exhibit the effects peculiar to warm-processed magnets,
It does not exhibit any more effect than a lubricant used in ordinary metal processing, which slightly lowers the coefficient of friction between the die surface and the workpiece surface.

In fact, it has not been reported that this improves workability without significant cracking or improves uniform orientation.

Therefore, the present invention aims to provide R-TM-B warm-worked magnets that are free from cracks by facilitating plastic working, and that also have uniform orientation and good magnetic properties. purpose.

[Means to solve the problem]

The present invention first focuses on an R-T-B containing a transition metal T as a main component, a rare earth element R including yttrium, and boron B.
In the method for manufacturing a warm-worked magnet, in which a molten metal of the alloy is ultra-rapidly solidified to obtain a ribbon or flake, and the magnetic powder is obtained by pulverization, magnetic anisotropy is imparted by warm working. This is a method for producing a warm-processed magnet, characterized by mixing a hydrocarbon having a boiling point of 50° C. or higher with powder.

Conventional wisdom regarding warm-processed magnets has been that adding additives that leave carbon, oxygen, etc. after processing is harmful to the magnetic properties.

However, the inventors of the present invention, thinking outside the box, believe that by adding an appropriate amount of a specific hydrocarbon, rather than adding carbon or oxygen alone, both formability and magnetic properties can be significantly improved. This is what we found to be effective.

Suitable hydrocarbons in the present invention refer to aliphatic, carbocyclic, and heterocyclic hydrocarbons having a boiling point of 50°C or higher, more preferably 150°C or higher. Aliphatic hydrocarbons include hexane, heptane, octane, nonane,
Paraffinic hydrocarbons such as decane, undecane, dodecane, tridecane, tetratecane, pentadecane, and eicosane; cycloparaffinic hydrocarbons such as cyclohexane, cyclohebutane, and cyclooctane; and olefins such as thiramethylethylene, heptene, octene, and nonene. These include hydrocarbons, acetylene hydrocarbons such as 1-hexyne, heptyne, octyne, nonine, and decine, and aromatic hydrocarbons such as benzene, toluene, xylene, anthracene, and naphthalene.

Although the mechanism of the effect of the hydrocarbon additive in the present invention as a lubricant and the effect of improving magnetic properties is not necessarily clear, it is believed that these hydrocarbons dissociate hydrogen atoms during the heating process before warm plastic working. It is presumed that active free radicals generated by this are involved. These free radicals are thought to easily react with the rare earth-rich grain boundary phase or main phase even at low temperatures below 600°C, improving mechanical properties during upsetting and significantly improving magnetic properties. It will be done. If a compound with a boiling point of 50° C. or lower is used as an additive compound, the effect of the addition will not be observed because it evaporates and escapes during mixing or in the early stage of the temperature raising process.

The processing temperature of the warm processed magnet of the present invention is about 630 to about 820.
A temperature within the range of ℃ is appropriate. In other words, below 600°C,
This is because, regardless of the presence or absence of additives, the Nd-rich phase necessary for plastic deformation is difficult to generate, and as a result, many cracks occur. Although the processing temperature shifts to a slightly higher temperature side by increasing the amount of additive added, processing can be easily performed up to 850°C without significantly deteriorating the magnetic properties. 85
If the temperature exceeds 0°C, the magnetic properties will deteriorate significantly due to coarsening of the crystal grains, and many cracks will occur.

The additive compound in the present invention is mainly composed of hydrocarbons, and the bond chains begin to break away at about 250°C.

Therefore, during warm processing at about 630 to about 820°C, the bond chain is broken and the hydrogen atoms are volatilized as molecular hydrogen H2. At this time, it is presumed that the radical carbon atoms with disconnected bond chains are active and have extremely high reactivity with the surface of the R-T-B-based magnetic powder, which is the reason for the remarkable effects of the present invention. be done.

This is because it exhibits a more remarkable effect than simply mixing carbon powder or introducing an appropriate amount of oxygen.

In the present invention, if the additive amount is less than 0.01 wt%, the residual carbon component during high-temperature treatment is too small and the effect of the present invention of improving both crystal grain orientation and magnetic properties cannot be obtained, and 2 wt% If it exceeds this value, the magnetic properties will deteriorate, which is undesirable.

It is most preferable when the additive is a liquid because it uniformly wets the entire surface of the magnetic powder, but even powdered additives can be mixed relatively uniformly if a little care is taken.

As a result of the present invention, the main component is a transition metal T,
An RT, -B alloy containing a rare earth element R containing yttrium and boron B, which has fine crystal grains with an average crystal grain size of 0.02 to 0.5 μm and has magnetic anisotropy. In a warm worked magnet, the carbon content of grain boundaries is 0.
The warm-processed magnet is characterized in that the oxygen content is 8% by weight or less and the oxygen content is 0.8% by weight or less.

In the present invention, when the carbon content exceeds 0.8% by weight, the magnetic properties deteriorate, and similarly, when the oxygen content exceeds 0.3% by weight, the deformation resistance of the workpiece increases significantly and the workability deteriorates. Undesirable.

The alloy according to the present invention has a transition metal as a main component, and contains a rare earth element R including yttrium and boron B. The composition range is based on the warm worked magnet known in Japanese Patent Application Laid-Open No. 60-100402. However, in the present invention, the transition metals are mainly composed of iron, with some of them being Co, Ni, Ru, Rh, and Pd.

It refers not only to transition metals in the narrow sense of Os Ir and Pt, but also to transition metals in a broader sense, including all elements with atomic numbers of 21 to 29.39 to 47.72 to 79.89 or higher.

Furthermore, as previously announced by the present inventors, the addition of Ga has the effect of significantly improving the coercive force in warm-worked magnets, so it is effective to add Ga as necessary. Furthermore, addition of known additive elements according to the purpose does not deviate from the effects of the present invention.

The rare earth elements R are also mainly composed of Nd and Pr, and as is known,
It goes without saying that partial substitution with Ce, sydim, etc. can be used for the purpose of cost reduction, and partial substitution with Dy, Tb, etc. can be used for the purpose of improving temperature characteristics.

In the present invention, the average grain size is fine, which is a characteristic of warm worked magnets. It is difficult to stably obtain ultrafine crystals of less than 0.02 μm industrially with current technology, and 1
．． If it exceeds 0 μm, the coercive force decreases, which is not preferable.

Here, the average crystal grain size is measured by a cutting method in a micrograph. In other words, when a straight line is arbitrarily drawn on a photograph, the line segment length divided by the number of crystal grains that cut the line segment is the grain size, and the average value obtained for at least 20 points is the average grain size. .

What should be noted here is that warm-processed magnets have a flat shape in a plane perpendicular to the C-axis of the crystal, and when cutting along a plane that includes the C-axis, the direction is the thickness direction of the flat plate. Therefore, the above-mentioned average grain size refers to that on a plane perpendicular to the C-axis.

Furthermore, the key to the magnetism of the RTB permanent magnet according to the present invention is the RTB intermetallic compound, which is a tetragonal crystal. This crystal has lattice constants at room temperature a = 0.878℃m, c
= 1.218 near the fin. Furthermore, warm-worked magnets actively utilize the unique property of a mixture of these crystals to generate magnetic anisotropy in a direction perpendicular to that direction under the action of plastic flow.

Therefore, the addition of the specific additive according to the present invention significantly improves the orientation of crystal grains due to the lubricating effect, thereby providing good magnetic properties.

Here, 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 was measured using a diffractometer, and then the X-ray diffraction intensity of each diffraction surface of the sample cut from the anisotropic warm-processed magnet was measured. The intensity is normalized by the intensity of the isotropic sample. Next, the normalized values are plotted with respect to the angle that each diffraction plane makes with the zero plane, approximated by a Gaussian distribution, and the crystal orientation can be evaluated based on the dispersion.

The present invention can bring about a remarkable improvement in the degree of orientation in which the angular dispersion of the crystal orientation from the C axis of the crystal is less than 30° on the magnet surface. In conventional warm-processed magnets, 30
Since the temperature was more than 100°C, the magnetic orientation was not aligned and sufficient orientation could not be obtained, resulting in insufficient magnetic properties.

The warm-worked magnet of the present invention is obtained by warm plastic working, and plastic working such as extrusion, swaging, rolling, spinning, and upsetting is used as a means for that purpose. Upsetting is particularly effective in imparting anisotropy. This is because the stress distribution and strain rate can be selected to obtain an excellent warm-worked magnet.

A feature of the warm-worked magnet to which the specific compound according to the present invention is added as an additive is that the deformation is uniform and, as a result, the strain distribution within the cross section is uniform. In conventional warm-processed magnets, the strain distribution is non-uniform, and as a result, many cracks occur and the magnets cannot be used as is as actual products. The method for measuring strain distribution is
Based on linear stress measurement method, hardness distribution measurement method, etc.

In addition, in the warm-worked magnet according to the present invention, carbon, oxygen, or what appears to be carbides or oxides caused by additives can be seen under a microscope at the grain boundaries of crystal grains due to the addition of additives.
A characteristic of B-series warm-processed magnets is that the grain boundary width is extremely narrow.
In addition, it is susceptible to oxidation and deterioration during processing, making analysis difficult and uncertain at present.

Furthermore, conventional warm-worked magnets had the disadvantage that plastic flow was difficult to occur on the end surface of the sample and the degree of crystal orientation was low; however, with the present invention, plastic flow during warm working is significantly reduced. In order to improve this, it is possible to obtain an angular dispersion of the crystal orientation from the C axis of the crystal by X-ray measurement of 30° or less on the magnet surface.

Furthermore, the present invention has the effect of significantly improving the workability not only of warm-processed magnets but also of consolidated magnets obtained by simply pressing thin pieces obtained by ultra-quenching.

Alternatively, the permanent magnet according to the present invention can be crushed into magnetic powder and kneaded with a binder such as a resin or a low melting point metal to form a bonded magnet.

Hereinafter, the present invention will be specifically explained with reference to Examples [Example] (Example 1) Nd (FeolzCOo, +Bo, o7Gao,
An alloy having the following compositions was produced by arc melting. This alloy was injected onto a single roll rotating at a circumferential speed of 30 m/sec in an Ar atmosphere to produce irregular flake-like flakes with a thickness of about 30 μm. As a result of X-ray diffraction, it was found to be a mixture of amorphous and crystalline materials. Then,
Hexane, which belongs to paraffinic hydrocarbons, is added and mixed in stages to magnetic powder obtained by pulverizing flakes to a size of 500 μm or less, and a mixture without additives is processed under a molding pressure of 6 tons/cn! A molded body having a density of 5.7 g/cc, a diameter of 28 mm, and a height of 47 mm was produced by molding without applying a magnetic field.

The obtained molded body was hot pressed at 740°C and 2 tons/c+J, and the density was 7.4 g/cc and the diameter was 3.
A molded body having a thickness of 0++n and a height of 30 mm was obtained. Next, the densified compact was further upset at 740°C so that the compression ratio (the value obtained by dividing the height before upsetting, 30 m1 by the height after upsetting, 7.5**) was 4. The magnetic anisotropy was imparted by warm working. After measuring the magnetic properties of the obtained magnetically anisotropic warm-processed magnet, the carbon content and oxygen concentration remaining in the magnet were analyzed.

FIG. 3 shows the residual carbon content, oxygen concentration, and magnetic properties for each amount of hexane input.

Figure 1 shows that the residual carbon content increases directly with the amount of hexane added, and furthermore, the residual carbon content increases by only a small amount of O compared to the case without additives.
It can be seen that the addition of 0,004 wt % hexane significantly improves the magnetic properties. The magnetic properties are particularly improved for 4πIr, and (BH) max is 8 MGO compared to the case without additives.
e also improves.

When the input amount was 3 ivt%, workability deteriorated, and as a result of upsetting, many cracks were generated at the edges, and the magnetic properties, particularly the coercive force, also decreased.

(Example 2) Using the same warm processing method as in Example 1, the upsetting processing temperature was changed to 5 degrees: 600°C, 680°C, 740°C, and 850°C.
Upsetting was performed at each hexane input amount under each temperature. The relationship between deformation resistance (compressive nominal stress) and strain was calculated from the recording paper during processing, and the results are summarized in Table 1.

Here, if the number of cracks on the peripheral edge of the warm-processed magnet exceeds 14 after processing to a compression ratio of 4, it is marked with an "X", and for other magnets, the strain is 0.3 (compression ratio of approximately 1.43 ) was taken as the nominal stress (ton/c♂).

At a processing temperature of 600°C, many cracks occurred in all cases, and some of them even buckled. On the other hand, even at 850°C, the stress increased significantly and many cracks occurred.

Therefore, the warm working according to the present invention is about 630° to about 820°.
C is preferred.

The overall trend was that the optimal warm working temperature shifted toward higher temperatures as the amount of hexane input increased. The warm-processed magnets surrounded by large frames in Table 1 are those that have been molded to a compression ratio of 4 and have extremely good workability, with cracks occurring at the periphery of the final warm-processed magnets of 4 or less.

(Hereafter, margin) Table 1 Processability was also improved.

* indicates a comparative example.

(Hereinafter, blank spaces) (Example 3) Using toluene, which belongs to aromatic hydrocarbons, as an additive, the results of processing in exactly the same experimental method as in Example 1 were shown in the second example.
Shown in the table. The residual carbon component showed the same linear trend as hexane. The magnetic properties also showed values almost corresponding to the residual carbon component when hexane was added, (Example 4) Nd (Feo, oJo, 07ca0.01)5.
An alloy having the composition No. 7 was produced by arc melting. This alloy was injected onto a single roll rotating at a circumferential speed of 30 m/sec in a measuring atmosphere to produce irregular flake-like flakes with a thickness of about 30 μm.

Next, magnetic powder obtained by pulverizing the flakes to a size of 500μ or less, to which 0.5 wt% of cyclohexane was added (invention), and one without additive (comparative example) were each molded with a mold at a molding pressure of 6 tons/- to give a density of 57 g. /cc, diameter 28 cranes, height 47+u
A molded body was produced. The obtained molded body was hot-pressed at 720° C. to make it dense, and then warm-worked by upsetting to give a compression ratio of 4.0 to impart magnetic anisotropy.

The magnetic properties of the obtained magnetically anisotropic warm-processed magnet and the degree of crystal orientation of samples cut from each part of the magnet were measured using X-rays, and the distribution of the dispersion of crystal orientation from the crystal C axis in the depth direction and radial direction was compared. did. The magnetic properties are shown in Table 3, the crystal orientation distribution is shown in FIG. 4, and a comparative example is shown in FIG. 4 and 5 show cross-sectional views taken along a plane including the upsetting direction of the warm worked magnet.

The cones in FIGS. 2 and 3 conceptually illustrate the angular dispersion of crystal orientation, and the numerical values written beside them are angular dispersion values. That is, it is a statistical dispersion of the angle of deviation of the orientation direction from the C axis. Here, if the angular dispersion is 18 degrees, for example, 18 degrees with respect to the C axis of the tetragonal crystal.
It shows that all the crystals in the sample exist within a solid angle of degrees, and the smaller this number is, the higher the degree of crystal orientation is.

As is clear from Table 3, Figures 2 and 3, the addition of cyclohexane significantly improves the fluidity during plastic working, and improves the degree of crystal orientation, thereby significantly improving magnetic properties. Recognize.

Table 3 (Example 5) Next, in the same manner as in Example 1 except for the additives, when Q, 5iyt% of compounds consisting of various hydrocarbons were added (BH
) max is shown in Table 4. It can be seen that this also has the effect of improving magnetic properties. In all cases, the carbon content was 0.6 wt% or less, the oxygen content was 0.3 wt% or less, and there were few cracks.

(Hereinafter, blank spaces) [Effects of the Invention] According to the present invention, it is possible to obtain a warm-worked magnet in which both formability and magnetic properties, which were conventionally insufficient, are significantly improved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the amount of additive added, carbon content, oxygen content, and magnetic properties in one embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the amount of additive added, carbon content, oxygen content, and magnetic properties. FIG. 3 is a diagram showing the distribution of the degree of crystal orientation with respect to the crystal C axis in a cross section of the warm worked magnet according to the present invention.

Claims (4)

[Claims] (1) An R-T-B alloy whose main component is a transition metal T, a rare earth element R including yttrium, and boron B, and has an average crystal grain size of 0.02 to 0.02 or more with magnetic anisotropy.
A warm worked magnet having fine crystal grains of 1.0 μm, characterized in that the carbon content is 0.8% by weight or less and the oxygen content is 0.3% by weight or less. . (2) An R-T-B alloy containing transition metal T as a main component, rare earth element R including yttrium, and boron B, and having an average crystal grain size of 0.02 to 1 with magnetic anisotropy.
．． A warm-worked magnet having fine crystal grains of 0 μm, characterized in that the residual strain distribution is substantially uniform. (3) An R-T-B alloy containing transition metal T as a main component, rare earth element R including yttrium, and boron B, and having an average crystal grain size of 0.02 to 1 with magnetic anisotropy.
．． A warm-worked magnet having fine crystal grains of 0 μm, characterized in that the angular dispersion of the crystal orientation from the C-axis of the crystal as determined by X-ray measurement is less than 30 degrees on the magnet surface. (4) A molten R-T-B alloy containing transition metal T as a main component, rare earth element R including yttrium, and boron B is ultra-rapidly solidified to obtain a ribbon or flake, which is crushed to make it magnetic. A method for producing a warm-worked magnet in which magnetic anisotropy is imparted by warm working after obtaining a powder, characterized in that a hydrocarbon having a boiling point of 50° C. or higher is mixed with the magnetic powder. manufacturing method.