JPH0684677A - Production of permanent magnet - Google Patents

Abstract

PURPOSE:To produce a large permanent magnet having uniform magnetic characteristics and excellent mechanical characteristics. CONSTITUTION:A material containing a rare earth element mainly composed of praseodymium or neodymium, iron, and boron, as main constituents, is cast to produce an ingot for permanent magnet. A plurality of ingots are then laid side by side and subjected to hot machining to integrate the plurality of ingots and to bring about magnetic anisotropy thus producing a permanent magnet having uniform magnetic characteristics. In the production of the permanent magnet, cross-sectional area of molten metal injecting face of the ingot is set at 20cm<2> or less at the time of casting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a large permanent magnet from a plurality of ingots. More specifically, it is mainly composed of rare earth elements, iron and boron, and is magnetically uniform and has a high mechanical strength. The present invention relates to a method of manufacturing a permanent magnet.

[0002]

BACKGROUND OF THE INVENTION Permanent magnets have hitherto been used in various electric devices, but their applications have greatly expanded with the recent development of electronic technology.

Typical permanent magnets are alnico type,
Hard ferrite-based and samarium-cobalt-based alloys are known, but recently, rare earth elements-iron-boron-based alloys have been used as a permanent magnet having high magnetic properties without containing expensive samarium or cobalt. It has attracted attention and has been put to practical use in various applications.

Along with the increase in size and performance of industrial equipment, the permanent magnets used are also required to increase in size and performance.

As a method for producing a rare earth element-iron-boron permanent magnet, a rare earth element-iron-boron alloy is pressed while applying magnetism to magnetically anisotropically produce a permanent magnet. There is. However, in this method, there is a limit to the size of the magnet that can be obtained because the range of generation of the uniform magnetic field is limited, and the size is about 150 mm × 150 mm × 25 mm. Therefore, in order to manufacture a large magnet, a small magnet must be bonded with an adhesive such as an epoxy resin.

However, there are a number of problems with this method. Since the adhesive surface is magnetically neutral, it forms a magnetic valley, resulting in poor magnetic properties. Moreover, it is weak in bending strength and shear strength, and also weak in heat. The heat resistant temperature is about 200 ° C. In addition to that, mechanical precision is not obtained.

On the other hand, there is also a method in which a large ingot is made of a rare earth element-iron-boron system alloy and is anisotropically made by rolling to make a large permanent magnet.

In the method for producing such a large ingot, the cooling rate inside the cast ingot becomes small and the equiaxed crystal inside and the columnar crystal at the outer peripheral portion are macroscopically divided. Therefore, if it is left as it is, the magnetic characteristics after hot working will be high or low. Therefore, in order to obtain a magnet having uniform characteristics from the magnet, it is necessary to cut out the magnet, but this leads to a low yield and a high cost. In addition, since the high-characteristic portion is limited, it is not possible to make a high-performance and uniform large magnet.

Therefore, it is an object of the present invention to provide a method for producing a large permanent magnet which is magnetically uniform and mechanically excellent.

[0010]

In view of the above object, a keen study on a method of placing a plurality of ingots side by side and performing hot working to integrate the plurality of ingots and cause magnetic anisotropy As a result, the present inventor limits the volume fraction of columnar crystals in the ingot or the average particle diameter of the main phase particles to a specific range, or the pouring surface cross-sectional area or volume in the production of the ingot to a specific range. It was discovered that by limiting or limiting the average cooling rate after casting to a specific range, a large permanent magnet that is magnetically uniform and mechanically excellent can be produced. The present invention is based on the above findings.

That is, the first method of the present invention is to place a plurality of permanent magnet ingots having the same composition side by side,
A method for producing a magnetically uniform permanent magnet by integrating a plurality of the ingots and causing magnetic anisotropy by performing hot working, wherein the first method is the casting At the time of
It is characterized by being 20 cm ² or less. The second method is characterized in that the volume fraction of columnar crystals in the ingot is 40% or more. The third method is characterized in that the average cooling rate is 5 ° C./sec or more during the rapid cooling after the casting. The fourth method is to adjust the volume of the ingot to 0.1
It is characterized in that it is at least cm ³ . A fifth method is characterized in that the main phase particles in the ingot have an average particle size of 15 μm or less.

[0012]

The method of the present invention for producing a permanent magnet will be described in detail below. In the method of the present invention, excellent magnetic properties, large mechanical strength, praseodymium-iron-boron-based permanent magnet, or neodymium-iron-boron-based permanent magnet can be produced, but in the following description For the sake of simplicity, the production of a permanent magnet having Pr ₂ Fe ₁₄ B as a ferromagnetic main phase will be described as an example. However, the present invention is not limited to this.

FIG. 1 is a flow chart showing the steps of manufacturing a permanent magnet using the method of the present invention.

First, the raw materials are mixed in step (a). In this type of permanent magnet, the phase (main phase) that exhibits magnetic characteristics is
It consists of Pr ₂ Fe ₁₄ B. In the method of the present invention, the raw materials are basically mixed so as to match this composition, but in practice, the addition amounts of praseodymium, iron, and boron are set to Pr ₂ Fe ₁₄ in consideration of the ease of pressure molding. It is preferable to adjust appropriately from the composition of B.

Further, in the present invention, other elements may be blended for the purpose of improving the magnetic properties of the finally obtained magnet.

For example, a transition metal element such as Co, Cu, Nb or V can be added. These transition metal elements are
Co can replace up to 50 atom% of Fe, and
Can be compounded so as to replace up to 3 atom%.

It is also possible to add elements of Group 3B of the periodic table such as Al and Ga. These Group 3B elements can be mixed so as to replace up to 1.5 atom% of B.

When a raw material mixture containing the above elements is obtained,
Next, in step (b), this is heated and melt mixed.
This melt mixing must be performed in an inert gas atmosphere for the purpose of preventing oxidation. Specifically, the raw material mixture is
_It is placed in a crucible such as ₂ O ₃ and vacuumed once, and then an inert gas such as high-purity argon gas is introduced and heated and melted.

In the present invention, the heat-melted raw material mixture is used for casting to produce an ingot. Here, the finally obtained magnet has excellent magnetic properties,
The conditions for achieving excellent mechanical strength are (1) the cross-sectional area of the ingot pouring surface, (2) the volume fraction of columnar crystals in the ingot, (3) the average cooling rate after ingot casting, The volume of the ingot (4) and the average particle diameter of the main phase particles in the ingot (5) are preferably as follows. However, it is not necessary to satisfy all the conditions in (1) to (5), and when one condition is prioritized, the ranges in other conditions may change with a certain width.

(1) Ingot pouring surface cross-sectional area Once the raw material mixture is heated and melted to a uniform state,
As (c), the melt is poured into a mold. As a mold,
It is preferable to use a material made of Cu-Be, pure Cu, stainless steel or the like. In order for the obtained magnet to have characteristics of 25 MGOe or more, casting is performed with the cross-sectional area of the pouring surface being 20 cm ² or less. It is particularly preferably 0.5 to 16 cm ² . here,
The cross-sectional area of the pouring surface in the mold is defined by the cross-sectional area of the pouring surface (A) = V / h, where V is the volume of the casting ingot and h is the average height of the casting ingot. . At this time, the cross section of the cast ingot is preferably a rectangle whose shortest side is in the range of 0.4 to 4 cm.

(2) Volume of columnar crystals in ingot
The volume fraction of the columnar crystals in the rate of the ingot is 40% or more. If the volume fraction of columnar crystals is less than 40%, the volume fraction of equiaxed crystals will increase, and there will be a magnetic difference in height inside the magnet obtained after hot working. Can't get The volume fraction of columnar crystals is 40 to 10
Magnet obtained if the 0% (BH) _{ma x} is equal to or greater than 25 MGOe. In order to adjust the volume fraction to the above range, the temperature of the mold is set to 200 ° C. or lower in the step (c). Mold temperature is 20
Above 0 ° C, the volume fraction of columnar crystals formed in the ingot becomes less than 40%.

(3) Rapid cooling is performed as the average cooling rate step (d) after ingot casting . The rapid cooling can be performed by bringing the cooling medium into contact with the side surface of the mold. By this quenching, fine crystal nuclei (which become the nuclei of columnar crystals formed in the material in the heat treatment described later) consisting of the ferromagnetic main phase are formed in the material. Average cooling rate is 5 ℃ /
It is preferably not less than sec, especially 5 to 200 ° C./sec. If it is less than 5 ° C / sec, the obtained magnet cannot have characteristics of 25MGOe or more. Further, at 200 ° C./sec, the upper limit value of 35 MGOe is reached, so it is not preferable in terms of cost to set the cooling rate higher than that. The average cooling rate can be calculated by measuring the cooling curve with a thermocouple.

(4) Volume of Ingot Once the ingot is obtained by the step (d), it is released from the mold (step
(e)) and machine to the required size (cross-sectional area: 0.2 to 20 cm ² ) by mechanical cutting and polishing. Volume of each cast ingot and 0.1 cm ³ or more, particularly preferably in the 0.1 ~1000cm ^3. If you use an ingot of this size,
The finally obtained magnet will have characteristics of 25 MGOe or more. When an ingot larger than 1000 cm ³ is used, the volume fraction of equiaxed crystals increases when cast. It should be noted that each ingot does not necessarily have to have the same volume as long as it has a volume within the above-mentioned range, and the volume may be slightly different depending on the position. If necessary, degreasing is performed using acetone or the like. Repeating steps (a) to (e), considering the size of the finally obtained magnet,
Make the required number of ingots.

[0024] (5) a heat treatment for a plurality of ingots obtained in an average particle size above the main phase particles in the ingot (step (f)
)I do. By this heat treatment, α-Fe in the ingot
Disappears and the main phase (Pr ₂ Fe ₁₄ B), which is a ferromagnetic phase, crystallizes out. The heat treatment must be performed in a vacuum of 5.0 × 10 ^-4 Torr or less or in an inert gas. The average particle size of the main phase particles in the ingot is 15 μm or less, and particularly preferably 1 to 15 μm. According to the research conducted by the present inventors, if the average particle size is within the above range, the finally obtained permanent magnet (BH)
_{The max} is 25 MGOe or more, and the 4-point bending strength is 20 kgf / mm ² or more. In order to obtain such a magnet, the heat treatment time is preferably about 1 to 10 hours, and the heat treatment temperature is preferably 600 to 1100 ° C. In addition, the particle diameter in the present invention is measured by a direct intersection method.

In the above conditions (1) to (5), other conditions that can change when one condition is prioritized are shown below. (1) When the cross-sectional area of the pouring surface is 0.5 to 20 cm ² , (a) the volume fraction of columnar crystals is preferably 80 to 100%. (b) The average cooling rate is preferably 10 to 200 ° C./sec. (c) The volume of the ingot is preferably 0.5 to 500 cm ³ . (d) The average particle size of the main phase particles is preferably 1 to 10 μm. (2) When the volume fraction of columnar crystals is 40 to 100%, (a) the cross-sectional area of the pouring surface is preferably 1 to 20 cm ² . (b) The average cooling rate is preferably 5 to 200 ° C./sec. (c) The volume of the ingot is preferably 0.1 to 1000 cm ³ . (d) The average particle size of the main phase particles is preferably 3 to 15 μm. (3) When the average cooling rate is 5 to 200 ° C./sec, (a) the cross-sectional area of the pouring surface is preferably 1 to 20 cm ² . (b) The volume fraction of columnar crystals is preferably 80 to 100%. (c) The volume of the ingot is preferably 0.5 to 1000 cm ³ . (d) The average particle size of the main phase particles is preferably 1 to 10 μm. (4) When the volume of the ingot is 0.1 to 1000 cm ³ , (a) the cross-sectional area of the pouring surface is preferably 0.5 to 20 cm ² . (b) The volume fraction of columnar crystals is preferably 80 to 100%. (c) The average cooling rate is preferably 5 to 100 ° C./sec. (b) The average particle size of the main phase particles is preferably 1 to 15 μm. (5) When the average particle size of the main phase particles is 15 μm or less, (a) the cross-sectional area of the pouring surface is preferably 1 to 20 cm ² . (b) The volume fraction of columnar crystals is preferably 80 to 100%. (c) The average cooling rate is preferably 10 to 200 ° C./sec. (d) The volume of the ingot is preferably 0.5 to 1000 cm ³ .

After the heat treatment, a plurality of these ingots are lined up and put in a frame (step (g)). Frame is mild steel (S35C)
It is preferable to use a material made of a metal material whose composition can be modified as described above. The thickness of the frame is preferably 1 to 4 mm. If the thickness is less than 1 mm, it tends to be damaged during deformation, while if it exceeds 4 mm, it becomes difficult to deform.

Next, in the step (h), hot working is performed on the plurality of ingots arranged side by side in the frame to make them magnetically anisotropic and diffusion bonded. This hot working is preferably carried out under the following conditions: (a) working temperature, (b) strain rate, (c) working rate, and (d) average working pressure. However, it is not necessary to satisfy all the conditions in (a) to (d), and when one condition is prioritized, the ranges under the other conditions may change with a certain width. When a pressure is applied to the ingot in one direction under these conditions, the ingot easily plastically deforms. During this plastic deformation, each component element diffuses, and the dividing surface of the ingot, or if there is a crack in the ingot, the interface of the crack joins. As a result, magnetic anisotropy is achieved in a completely bonded state without magnetic drop at the bonded interface.

(B) Working temperature Hot working is preferably carried out within a temperature range of 800 to 1140 ° C. Α-Fe precipitates at temperatures higher than 1140 ° C,
The (BH) _max of the resulting magnet is below 25 MGOe. Also, if hot working is performed at a temperature lower than 800 ° C, the mechanical strength is reduced. Specifically, the 4-point bending strength is 20 kgf / mm ² or less.

(B) Strain rate The strain rate in hot working is preferably 0.0001 to ¹ sec ^-1 . In order for the finally obtained magnet to obtain a coercive force of 10 kOe or more, the strain rate must be 0.0001 sec ^-1 or more. To obtain a 4-point bending strength of 20 kgf / mm ² or more, the strain rate must be It must be less than 1 sec ^-1 . Distortion speed is 1 sec ^-1
If it exceeds, diffusion of each component element does not proceed sufficiently,
This is because a uniform member cannot be obtained and sufficient strength cannot be obtained. Here, as shown schematically in FIG. 2, when the object (ingot) having the height L is pressed in one direction to have the height L ′, the strain rate is ΔL = L−L ′, and the strain rate is Speed (S) = (ΔL / L) / time required for processing (se
c), the dimension is [sec ^-1 ].
Is. Therefore, for example, the strain rate S when an object having a height of 40 mm is processed to a height of 10 mm in 20 minutes is S = (30/40) /20×60=6.25×10 ⁻⁴ / sec.

(C) Working Rate The working rate in hot working is preferably 30% or more. If the processing rate is lower than 30%, the anisotropy under plastic deformation does not proceed sufficiently, so the residual magnetic flux density, which is a guide for the anisotropy, does not improve, and the (BH) _max value is
This is because it is not possible to obtain the characteristics of 25 MGOe or more. If the processing rate is 10% or less, the diffusion under plastic deformation does not proceed sufficiently, resulting in a significant decrease in strength and 20 kgf / mm
You cannot get more than ² strengths. Here, the processing rate is ΔL when an object (ingot) having a height L is pressed in one direction to a height L ′, as schematically shown in FIG.
= L−L ′, the processing rate (P) = (ΔL / L) × 100.

(D) Average working pressure The average working pressure in hot working is 5 to 50,000 kg.
/ cm ² is preferable. When hot working is performed at an average working pressure outside that range, the (BH) _{max of the} resulting magnet
The value cannot get the characteristic more than 25MGOe.

The hot working is performed in a vacuum of 2 × 10 ^-3 Torr or less or in an inert gas such as argon gas in order to prevent the material from being oxidized.

After this hot working, the obtained magnet material is cooled at a cooling rate of 2 ° C./sec (step (i)) to obtain a desired permanent magnet member. In addition, in order to use it for various purposes, the permanent magnet member is machined into a predetermined shape (process
(j)) It is necessary to cut out.

As described above, the magnet member according to the present invention can be used as a large magnet in which all parts are magnetically uniform.

Example 1 As a starting material, electrolytic iron having a purity of 99.9% or more, purity 99.0%
Using the above praseodymium, crystal boron having a purity of 99.0% or more, pure copper having a purity of 99.5% or more, and gallium having a purity of 99.5% or more, the composition is Pr ₁₉ Fe ₇₄ B ₅ Cu _1.5 Ga _0.5 , and the total amount is 140 g. And mixed.

The above mixture was placed in an alumina crucible, the atmosphere was once set to a vacuum of 2 × 10 ^-4 Torr or less, and then high frequency heating was performed under an argon gas pressure of 26 cmHg. 1500 ° C
And held for 5 minutes to obtain a melt.

Next, the obtained melt was kept at 1400 ° C.,
This was poured into a pure copper mold shown in FIG. At this time,
The mold temperature is 25 ° C and the cross-sectional area of the pouring surface is 2.9 cm.
^{It was 2} (1.7 cm x 1.7 cm). Immediately after this casting, the side surface of the mold was rapidly cooled at an average cooling rate of 20 ° C / sec. After that, let it cool and ingot from the mold (16.5mm × 16.5mm × 43
mm) was taken out.

The obtained ingot was degreased and washed with acetone, and then machined and polished to 16 mm × 16 mm × 40.
The size is mm. When the macrostructure of the cross section of the ingot was visually observed, it was confirmed that columnar crystals were developed in the entire area. The volume fraction of columnar crystals was 100%. In the same manner, three ingots were produced to make a total of four ingots.

Next, these ingots were treated with 1 × 10 ^-4 Torr.
Heat treatment was performed in the following vacuum. In this heat treatment, (1) the temperature was raised from room temperature to 850 ° C over 30 minutes, (2) the temperature was maintained at 850 ° C for 8 hours, and then (3) cooled down to 500 ° C over 1 hour.
The average particle size of the main phase particles of the obtained ingot was 9 μm.

As shown in FIG. 4, four ingots each have a size of 3 mm.
It was inserted into the frame 2 made of thick mild steel material (S35C).

Next, the ingot inserted into the frame is set to 2 × 10.
Under a vacuum of ^-3 Torr or less, and at a temperature of 1090 ° C, pressure was applied in the direction of the arrow in Fig. 2 with an average processing pressure of 500 kg / cm ² . At this time, the ingot was compressed from a height of 40 mm to a height of 10 mm over 20 minutes. That is, the processing rate of the height of the ingot was 75%, and the strain rate was 6.25 × 10 ⁻⁴ / sec.

After cooling, the resulting magnet member was 16 mm × 10 mm ×
It was cut into a size of 64 mm, and the magnetic properties and mechanical strength were measured by the following methods.

Measuring Method (1) Measurement of Magnetic Properties As shown in FIG. 5, the magnet member was divided into three parts in the longitudinal direction and eight parts in the lateral direction to obtain 24 samples a1 to h3.
The size of each sample was 4 mm x 4 mm x 8 mm. The residual magnetic flux density B _r , the coercive force _i H _c , and the maximum energy product (BH) _max at 22 ° C. were measured for each sample using a measuring device (VSM) manufactured by Toei Industry Co., Ltd. (BH) _max average,
And the standard deviation was calculated.

(2) Measurement of Mechanical Strength A total of 10 samples of 3 mm × 4 mm × 36 mm were cut out from the above-mentioned magnet member in the longitudinal direction, and 4 samples were obtained for each sample.
A point bending test was conducted. With respect to the test results, a 4-point bending strength average value and a 4-point bending strength standard deviation were calculated.

The measurement results of the magnetic properties of this sample are shown in Table 1.
Table 3 shows the results of calculating the average value and standard deviation of the values measured for magnetic properties and mechanical strength.

Table 1 Part of residual magnetic flux density coercive force maximum energy product in magnet B _r ⁽¹⁾ _i H _c ⁽²⁾ (BH) _max ⁽³⁾ a1 12.8 11.2 34.2 a2 12.8 12.0 35.0 a3 12.7 11.3 34.9 b1 12.5 11.4 31.4 b2 12.6 11.7 33.0 b3 12.6 11.5 33.0 c1 12.4 11.5 32.0 c2 12.4 11.8 31.0 c3 12.3 11.6 31.4 d1 12.1 11.5 31.1 d2 12.2 11.9 30.4 d3 12.1 11.7 31.4 e1 12.2 11.5 31.2 31.2 11.5 30.2 10.9 30.2 12.3 12.2 30.4 f3 12.3 11.7 31.4 g1 12.5 11.4 32.0 g2 12.4 12.7 33.0 g3 12.7 11.7 32.0 h1 12.6 11.9 34.0 h2 12.8 12.4 34.9 h3 12.8 12.0 34.0

Table 1 Note (1): The unit is kG. Note (2): The unit is kOe. Note (3): The unit is MGOe.

Comparative Example 1 As a starting material, electrolytic iron having a purity of 99.9% or more, purity 99.0%
Using the above praseodymium, crystal boron with a purity of 99.0% or more, pure copper with a purity of 99.5% or more, and gallium with a purity of 99.5% or more, the composition is Pr ₁₉ Fe ₇₄ B ₅ Cu _1.5 Ga _0.5 , and the total amount is 560 g. And mixed.

The above mixture was placed in an alumina crucible, the atmosphere was once set to a vacuum of 2 × 10 ^-4 Torr or less, and then high frequency heating was performed under an argon gas pressure of 26 cmHg. 1500 ° C
And held for 5 minutes to obtain a melt.

Next, the obtained melt was kept at 1400 ° C.,
This was poured into a pure copper mold shown in FIG. At this time,
The mold temperature is 220 ℃, the cross-sectional area of the pouring surface is 11.0 cm ²
(1.7 cm x 6.5 cm). Immediately after this casting, 3
The side surface of the mold was rapidly cooled at an average cooling rate of ° C / sec. Then, let it cool and ingot from the mold (16.5 mm × 64.5 mm × 43
mm) was taken out.

The obtained ingot was degreased and washed with acetone, and then machined and polished to 16 mm × 64 mm × 40
The size is mm. When the macrostructure of the cross section of the ingot was visually observed, as shown in FIG. 7, it was confirmed that equiaxed crystals 4 were developed in the central part and columnar crystals 3 were developed in the peripheral part. The volume fraction of columnar crystals was 35%.

Next, this ingot was heat-treated in a vacuum of 1 × 10 ^-4 Torr or less. In this heat treatment, (1) the temperature was raised from room temperature to 850 ° C over 30 minutes, (2) the temperature was maintained at 850 ° C for 8 hours, and then (3) cooled down to 500 ° C over 1 hour. The average particle size of the main phase particles of the obtained ingot was 9 μm.

This ingot was inserted into a frame 2 made of 3 mm thick mild steel material (S35C) as shown in FIG.

Next, the ingot inserted into the frame is set to 2 × 10.
^In a vacuum of ^-3 Torr or less and at a temperature of 1090 ° C, the pressure was increased in the direction of the arrow in Fig. 8 with an average processing pressure of 500 kg / cm ² .
At this time, it took 10 minutes to move the ingot from the height of 40 mm to 10
Compressed to a height of mm. That is, the processing rate of the height of the ingot was 75%, and the strain rate was 6.25 × 10 ⁻⁴ / sec.

After cooling, the obtained magnet member was subjected to 16 mm × 10 mm ×
It was cut out into a size of 64 mm, and the magnetic properties and mechanical strength were measured by the same method as in Example 1. The results of measuring the magnetic properties are shown in Table 2, and the results of calculating the average value and standard deviation of the measured values of the magnetic properties and mechanical strength are shown in Table 3.

Table 2 Part of residual magnetic flux density coercive force maximum energy product in magnet B _r ⁽¹⁾ _i H _c ⁽²⁾ (BH) _max ⁽³⁾ a1 10.8 13.1 27.7 a2 10.9 13.0 28.0 a3 10.8 13.0 27.8 b1 10.4 14.0 25.0 b2 10.3 13.9 25.1 b3 10.7 13.6 25.3 c1 9.8 13.7 24.0 c2 9.5 13.5 22.0 c3 9.7 13.9 23.0 d1 9.5 13.8 20.0 d2 9.2 13.4 17.5 d3 9.4 13.0 20.0 e1 9.5 13.8 20.0 e2 9.6 13.4 20.0 10.0 20.0 20.0 e3 9.7 13.8 22.0 f3 9.8 13.3 23.0 g1 10.1 12.7 24.0 g2 10.2 13.6 24.1 g3 10.0 12.8 24.0 h1 10.8 13.9 28.0 h2 10.9 13.6 28.0 h3 10.8 12.7 27.1

Table 2 Note (1): The unit is kG. Note (2): The unit is kOe. Note (3): The unit is MGOe.

[0058]

Table 3 Note (1): The unit is MGOe. Note (2): The unit is kgf / mm ² .

As is clear from Table 3, in the first embodiment,
Compared to Comparative Example 1 using a magnet manufactured by the conventional method (B
H) The average value of _max is improved by 36%, and (BH)
_In the standard deviation of _max , the variation became about half.
Further, as can be seen from the four-point bending strength average value and standard deviation, the magnet of the present invention is comparable in strength to the magnet manufactured by the conventional method.

Example 2 A raw material mixture obtained in the same manner as in Example 1 was cast while changing the cross-sectional area of the pouring surface of the ingot from 3 cm ² to 30 cm ² . Example 1 was applied to the obtained cast ingot.
Hot working was performed in the same manner as in 1. to obtain a permanent magnet.

The maximum energy product of the obtained permanent magnet was measured in the same manner as in Example 1. FIG. 9 shows the relationship between the cross-sectional area of the pouring surface of the ingot and the maximum energy product.

Example 3 With respect to the raw material mixture obtained in the same manner as in Example 1, the temperature of the mold was changed from 25 ° C to 400 ° C so that the volume fraction of columnar crystals in the ingot changed from 5% to 100%. The casting was performed by changing to. The relationship between the template and the volume fraction of columnar crystals is shown in FIG. The obtained cast ingot was hot worked in the same manner as in Example 1 to obtain a permanent magnet.

The maximum energy product of the obtained permanent magnet was measured in the same manner as in Example 1. Fig. 11 shows the relationship between the volume fraction of columnar crystals and the maximum energy product.

Example 4 An ingot cast in the same manner as in Example 1 was rapidly cooled after casting by changing the average cooling rate from 0.3 ° C / sec to 200 ° C / sec. The obtained cast ingot was hot worked in the same manner as in Example 1 to obtain a permanent magnet.

The maximum energy product of the obtained permanent magnet was measured in the same manner as in Example 1. Figure 12 shows the relationship between the average cooling rate of the ingot and the maximum energy product.

Example 5 The raw material mixture obtained in the same manner as in Example 1 was cast by changing the volume of the ingot from 0.01 cm ³ to 1000 cm ³ . The obtained cast ingot was hot worked in the same manner as in Example 1 to obtain a permanent magnet.

The maximum energy product of the obtained permanent magnet was measured in the same manner as in Example 1. Figure 13 shows the relationship between the ingot volume and the maximum energy product.

Example 6 The treatment temperature was changed from 600 ° C. to 1150 ° C. for the ingot obtained in the same manner as in Example 1 so that the average particle size of the main phase particles in the ingot changed from 5 μm to 23 μm. Heat treatment was performed. Then, hot working was performed in the same manner as in Example 1 to obtain a permanent magnet.

The maximum energy product and the 4-point bending strength of the obtained permanent magnet were measured in the same manner as in Example 1. Figure 14 shows the relationship between ingot volume and maximum energy product. Figure 14 shows the relationship between ingot volume and four-point bending strength.
Shown in 15.

[0071]

As described in detail above, according to the method of the present invention, each component element diffuses at the joining interface between adjacent cast ingots, and a plurality of ingots are joined well. This makes it possible to produce a permanent magnet that is magnetically uniform and mechanically excellent.

According to the method of the present invention, a large-sized and high-performance permanent magnet, which has been impossible in the past, can be produced. Therefore, the permanent magnet according to the present invention can be widely used industrially.

[Brief description of drawings]

FIG. 1 is a flowchart showing a process of producing a permanent magnet.

FIG. 2 is a schematic view showing a state in which an ingot is pressure-formed in one direction in hot working.

FIG. 3 is a diagram showing a mold for casting an ingot in an example.

FIG. 4 is a diagram showing a state in which an ingot has entered a frame.

FIG. 5 is a diagram showing boundary lines of samples a1 to h3 in the obtained magnet.

FIG. 6 is a view showing a mold for casting an ingot in a comparative example.

FIG. 7 is a macrostructure diagram of a cross section of an ingot in a comparative example.

FIG. 8 is a diagram showing a state in which an ingot has entered a frame in a comparative example.

FIG. 9 is a graph showing changes in the maximum energy product with changes in the cross-sectional area of the pouring surface in Example 2.

FIG. 10 is a graph showing changes in the volume fraction of columnar crystals with changes in the temperature of the mold in Example 3.

FIG. 11 is a graph showing changes in the maximum energy product with changes in the volume fraction of columnar crystals in Example 3.

FIG. 12 is a graph showing changes in maximum energy product with changes in average cooling rate in Example 4.

FIG. 13 is a graph showing a change in maximum energy product with a change in casting ingot in Example 5.

FIG. 14 is a graph showing a change in maximum energy product with a change in average particle diameter in Example 6.

FIG. 15 is a graph showing changes in 4-point bending strength with changes in average particle diameter in Example 6.

[Explanation of symbols]

 1 Press type 2 Frame 3 Columnar crystal 4 Equiaxed crystal

Claims (5)

[Claims] 1. An ingot of a permanent magnet having a rare earth element mainly composed of praseodymium or neodymium, iron, and boron as main components and having the same composition is produced by casting, and a plurality of the ingots are placed side by side and heated. A method for producing a magnetically uniform permanent magnet by causing a plurality of the ingots to be integrated and magnetically anisotropy by subjecting the ingot to a hot-melting surface of the ingot during the casting. The method is characterized in that the cross-sectional area of is less than 20 cm ² . 2. An ingot of a permanent magnet having a rare earth element mainly composed of praseodymium or neodymium, iron, and boron as main components and having the same composition is produced by casting, and a plurality of the ingots are placed side by side and heated. A method for producing a magnetically uniform permanent magnet by integrating a plurality of the ingots by performing hot working and producing a magnetically uniform permanent magnet, wherein the volume fraction of columnar crystals in the ingot is Is 40% or more. 3. An ingot of a permanent magnet having a rare earth element mainly composed of praseodymium or neodymium, iron, and boron as main components and having the same composition is produced by casting, and a plurality of the ingots are placed side by side and heated. It is a method for producing a magnetically uniform permanent magnet by unifying a plurality of the ingots by performing hot working and producing a magnetically uniform permanent magnet. A method characterized in that the temperature is 5 ° C./sec or more. 4. An ingot of a permanent magnet having a rare earth element mainly composed of praseodymium or neodymium, iron, and boron as main components and having the same composition is produced by casting, and a plurality of the ingots are placed side by side and heated. A method for producing a magnetically uniform permanent magnet by unifying a plurality of the ingots and magnetically anisotropy by performing hot working.
A method characterized in that it is 0.1 cm ³ or more. 5. An ingot of a permanent magnet having a rare earth element mainly composed of praseodymium or neodymium, iron and boron as main components and having the same composition is produced by casting, and a plurality of the ingots are placed side by side and heat-treated. By subjecting the plurality of ingots to a magnetic anisotropy together with hot working, a method of producing a magnetically uniform permanent magnet, wherein the average grain size of the main phase particles in the ingot is A method in which the diameter is 15 μm or less.