JPH09270347A - Method of producing rare earth bond magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a rare earth bond magnet by sealing an alloy containing R, Fe, and B as fundamental components in a capsule and performing hot working, in which cracking occurring during cooling operation is prevented and the yield is improved. SOLUTION: An iron base metal in which no A3 transformation occurs is capsuled. Specifically, the iron base material is one of a metal material in which the carbon content is 0.12% by weight or less, 13 to 30 atomic % of Cr is included, and the balance is iron; a metal material in which the carbon content is 0.12% by weight or less, 0.2 to 3 atomic % of at least one kind of Al, Ti, V, Sn, W, and Mo is included, and the balance is iron; and a metal material in which the carbon content is 0.12% by weight or less, 2 to 5 atomic % of at least one kind of Si, Ge, and Ga is included, and the balance is iron.

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 permanent magnet in which a rare earth alloy or a rare earth alloy powder containing a rare earth element, iron and B as basic components is encapsulated and hot worked.

[0002]

2. Description of the Related Art A permanent magnet is a material for generating a magnetic field without supplying electric energy from the outside, and it is suitable that it has a large coercive force and a high residual magnetic flux density, which is the opposite of a high magnetic permeability material. , It is one of the important electrical and electronic materials used in a wide range of fields from various household electric appliances to peripheral devices for large computers.

Among the permanent magnets currently in use, rare earth permanent magnets have been extensively researched and developed as permanent magnets having extremely high coercive force and energy product. And as a method for manufacturing this rare earth permanent magnet, Japanese Patent Publication No. 61-3
No. 4242, etc., a method using a sintering method, as in Japanese Patent Publication No. 4-20975, etc., a method in which a quenched thin piece is made into a magnet by a resin bonding method, and further, Japanese Patent Publication No. 4-202.
A method called a two-step hot pressing method such as Japanese Patent No. 42 has been known.

Further, by hot working an alloy containing a rare earth element, iron and B as the basic components as disclosed in JP-A-62-276803, the crystal grains are made finer and the crystal axes thereof are oriented in a specific direction. A method of obtaining a rare earth-iron-based permanent magnet excellent in magnetic properties and mechanical strength has also been known. In this method, as disclosed in Japanese Unexamined Patent Publication No. 1-171204, a method of covering the alloy with a metal capsule and performing hot working is disclosed as a method suitable for mass production without the need for atmosphere management during heating. .

The following method has been known as a method for producing a rare earth magnet in which this rare earth alloy is encapsulated and hot-worked.

(1) Japanese Unexamined Patent Publication (Kokai) No. 2-3901, page 2, lower right column, lines 7 to 16 shows a rare earth element including a step of hot working an ingot of an alloy containing a rare earth element, iron and boron as basic components. −
In the Fe-B magnet manufacturing method, the reaction between the magnet and the metal capsule is prevented by hot working after encapsulating the ingot in the metal capsule through a release agent (glass lubricant, BN, alumina, etc.). It is disclosed that it is possible to prevent the occurrence of cracks.

(2) JP-A-3-287723, page 2, upper left column, line 20 to lower left column, line 4 describes a step of hot working an ingot of an alloy containing a rare earth element, iron and boron as basic components. In the method for producing a rare earth-Fe-B based magnet containing, the ingot is surrounded by a metal material having a carbon content of 0.25% by weight or less and a melting point of 600 ° C or more, and sealed, and then hot working is performed, It is disclosed that the subsequent cooling at a cooling rate of less than 10 ° C./minute is effective in preventing cracking of the magnet.

[0008]

[Problems to be Solved by the Invention] (1) to (2) above
The conventional method for manufacturing a rare earth permanent magnet described above has the following drawbacks.

In the method of manufacturing a permanent magnet of (1), the reaction between the magnet and the capsule was prevented by a release agent / lubricant, so that fusion and integration of the two could be reduced on average. Even when the lubricant holding material is used, there is a drawback that the spread due to the processing of the lubricant is not uniform, and in some cases, the lubricant is cut off and fusion occurs to cause cracking of the magnet.

The permanent magnet manufacturing method (2) improves the drawbacks of the manufacturing method (1) and defines the cooling rate after hot working. Even in this case, cracking of the magnet occurs. Is not completely prevented, and large cracks that divide the magnet material into two occur at a frequency of 10 to 20%, and shallow small cracks still occur on the magnet surface layer to remove the cracks. However, there is a drawback that the yield is reduced.

The present invention has the above-mentioned drawbacks of the prior art, (1)
The object of the present invention is to solve the disadvantage of yield loss due to cracking in the permanent magnet manufacturing method of (2), and the purpose thereof is to use a casting / hot working method that is excellent in mechanical strength and capable of producing a large magnet. An object of the present invention is to provide a high-performance and low-cost manufacturing method for a permanent magnet, which prevents yield reduction due to cracking in an R-Fe-B based permanent magnet.

[0012]

A method of manufacturing a rare earth permanent magnet according to claim 1 is a rare earth alloy containing R (where R is at least one of rare earth elements including Y), Fe and B as basic components, or In a method for producing a permanent magnet in which a rare earth alloy powder is put in a capsule and hot-worked, the capsule is made of a material having a coefficient of thermal expansion close to that of the alloy.

The method for manufacturing a rare earth permanent magnet according to a second aspect is characterized in that the capsule is made of an iron-based metal having a body-centered cubic structure at a temperature at which hot working is performed.

According to a third aspect of the present invention, in the method for producing a rare earth permanent magnet, the capsules are cooled by A after hot working.
3 Characterized by being composed of an iron-based metal that does not cause transformation.

In the method for producing a rare earth permanent magnet according to claim 4, the metal material in which the capsule has a carbon content of 0.12% by weight or less, contains 13 to 30 atom% of Cr, and the balance is iron. It is characterized by being composed of.

According to a fifth aspect of the present invention, in the method for producing a rare earth permanent magnet, the first-stage capsule has a carbon content of 0.12% by weight or less, and at least P, Al, Ti, V, Sn, W, Mo. It is characterized in that it contains 0.2 to 3 atomic% of one kind and the balance is made of a metal material which is iron.

According to a sixth aspect of the present invention, in the method for producing a rare earth permanent magnet, the capsule has a carbon content of 0.12% by weight or less and contains at least one of Si, Ge, and Ga.
.About.5 atomic%, and the balance is composed of a metallic material which is iron.

According to a seventh aspect of the present invention, in the method for producing a rare earth permanent magnet, the first capsule has a multi-layered structure, and at least one of the capsules has a carbon content of 0.12% by weight or less and a Cr content of 13 to 30. Atomic% or P, A
At least one of l, Ti, V, Sn, W and Mo is contained in an amount of 0.2 to 3 atomic%, or at least one of Si, Ge and Ga is contained in an amount of 2 to 5 atomic%, and the balance is iron. It is characterized by being made of a metal material.

In the method for producing a rare earth permanent magnet according to claim 8, the capsule in the first stage has a multiple structure, and the capsule in contact with the innermost alloy has a carbon content of 0.12% by weight.
It is the following and 13 to 30 atomic% of Cr, or P, A
It is composed of a metal material containing 0.2 to 3 atomic% of at least one of l, Ti, V, Sn, W and Mo, or 2 to 5 atomic% of Si, Ge and Ga, and the balance being iron. And has a layer of a heat resistant release material on the outer side thereof.

Here, the A3 transformation point refers to the transformation point and transformation temperature range of iron and iron-based alloys α iron (body centered cubic lattice) ⇔ γ iron (face centered cubic lattice), for example, in hypoeutectoid steel. In such a case, it refers to a continuous transformation temperature range of the transformation from γ iron to α iron during cooling and the transformation from γ iron to α iron + cementite.

[0021]

Preferred conditions for the rare earth permanent alloy or rare earth alloy powder according to the present invention will be described below.

As rare earth elements, Y, La, Ce, P
r, Nd, Sm, Eu, Gd, Tb, Dy, Ho, E
r, Tm, Yb, and Lu are listed as candidates, and of these, one kind or a combination of two or more kinds is used. Since the highest magnetic characteristics are obtained with Pr, practically, Pr,
Pr-Nd, Ce-Pr-Nd alloy or the like is used.

The amount of the rare earth element is suitably 12 to 25 atomic%, and if it is less than 12 atomic%, the amount of the R-rich phase is small and it is easily cracked during processing and the yield is lowered. Also 25
If it exceeds atomic%, the amount of non-magnetic phase increases and the magnetic properties are significantly deteriorated. In order for the rare earth magnet to have high magnetic properties and excellent mechanical strength, the amount of rare earth element should be 14
It is desired to be -19 atom%.

Fe is preferably 65 to 85 atom%, and 6
If it is less than 5 atomic%, the amount of the non-magnetic phase increases too much and the performance deteriorates. On the other hand, when it exceeds 85 atomic%, the amount of the rare earth element decreases, and the problem described in the explanation of the rare earth element appears.

B is preferably 2 to 8 atomic%, and 2 atomic%
If it is less than the above, a high coercive force cannot be expected because it becomes a rhombohedral R-Fe system. On the other hand, if it exceeds 8 atom%, it is difficult to obtain fine R ₂ Fe ₁₄ B grains, and the hot workability is deteriorated, and it becomes impossible to obtain a high coercive force. In order for the rare earth magnet to have high magnetic properties and excellent mechanical strength, the amount of B should be 4 to
It is desired to be 6 atomic%.

Further, Co is effective for raising the Curie temperature, and if it is replaced within 50% with respect to Fe, it can be replaced without significantly impairing the coercive force.

Addition of Cu, Ag, Au, and Ga is effective in enhancing hot workability and improving coercive force and squareness, but since the nonmagnetic phase is formed, its addition amount is preferably 6 atomic% or less. . Of these, Cu has the highest effect, and in order for the rare earth magnet to obtain high magnetic characteristics and excellent mechanical strength, Cu is preferably 0.1 to 2 atomic%.

Further, in addition to the above, Al, Si, etc. may be further contained, and the coercive force may be improved by adding a small amount such that the residual magnetic flux density is not lowered.

The above-described alloy containing the rare earth elements, iron and B as its basic components exhibits the following thermal expansion behavior when the temperature is raised. First, this alloy, whose main phase is a ferromagnetic material, contracts from room temperature to a Curie temperature of about 300 ° C., and expands at the Curie temperature or higher. And 450 ° C to 700
Some of the grain boundary phases have melting points within the temperature range of ℃, and from that temperature, the expansion rate changes due to the appearance of the liquid phase. And above this melting point, it almost monotonically expands.

For the preparation of the above rare earth alloy or rare earth alloy powder, any of the currently known manufacturing methods can be adopted,
For example, creating an alloy ingot by arc melting on a water-cooled copper hearth, making an alloy ingot by high-frequency melting and then casting in a mold of iron, copper, etc., making quenched alloy ribbons and flakes by the melt-span method, from rare earth compounds Methods such as alloy powder preparation by reduction / diffusion method and alloy powder preparation by mechanical alloying method using a ball mill can be adopted. The alloy ingots (1) and (2) may be mechanically pulverized into powder, or may be pulverized into powder by hydrogen embrittlement. Further, it is desired that the production of these rare earth alloys and rare earth alloy powders is carried out in an inert atmosphere of Ar, nitrogen or the like in order to prevent the alloy from being oxidized.

When an alloy ingot is prepared by melting / casting, the ingot may be cast so that the macrostructure of the ingot is columnar and the main phase has an average grain size of 1 to 50 μm. Preferably, for that purpose, a mold having a large volume or a water cooling mechanism so that the cooling capacity of the mold is sufficiently large is used.

Next, in the production method of the present invention, the rare earth alloy ingot or the rare earth alloy powder is encapsulated, and the hot working thereof produces a liquid phase in the alloy at a high temperature such that it becomes a so-called semi-molten state. Since this is performed, a material having a melting point sufficiently higher than this processing temperature is used as the capsule. Since the liquid phase is rich in rare earths and highly reactive, an iron-based metal capsule that produces a relatively slow reaction with the liquid phase to form an alloy layer or a compound layer is desirable.

Iron-based metals are generally A at 700 to 950 ° C.
3 has a transformation point and
Iron (body centered cubic lattice) → γ iron (face centered cubic lattice) contracts at the A3 transformation point. Therefore, during cooling, it expands once at the A3 transformation point and then contracts uniformly,
The stress caused by the difference in thermal expansion between the iron-based metal capsule and the rare earth alloy causes cracking.

In order to prevent the occurrence of such cracks, it is advisable to use a metal capsule having a coefficient of thermal expansion close to that of a rare earth alloy and not undergoing A3 transformation during cooling. In particular, iron except high alloy steel and general structural steel have a stable body-centered cubic structure at low temperatures, so if the capsule has a body-centered cubic structure at the rolling temperature, phase transformation does not occur during cooling. , Desirable as a material for metal capsules.

The iron-based alloy containing 13 to 30 atomic% of Cr is
It is generally called ferritic stainless steel and has a body-centered cubic structure over the entire temperature range. Therefore, it is excellent as a capsule material because A3 transformation does not occur. Carbon is A
3 In order to lower the transformation temperature, it must be 0.12% by weight or less.

P, Al, Ti, V, Sn, W and Mo are so-called α phase stabilizing elements and have a function of shifting the A3 transformation temperature to a high temperature. The optimum addition amount depends on the rolling temperature, but it is necessary to increase the addition amount as the rolling temperature increases. For example, the addition of about 0.2 atomic% of the above elements raises the A3 transformation temperature to 910 ° C. or higher. Therefore, when the rolling temperature is 900 ° C., A3 transformation does not occur during cooling. Further, when the rolling temperature is as high as about 1100 ° C., the addition of 1.5 to 2 atomic% of the above elements stabilizes the α phase up to the melting point, so that the A3 transformation does not occur during cooling. The effect does not change even if the amount added exceeds 3 atomic%.

Si, Ge and Ga are also α-stabilizing elements,
It has the function of shifting the A3 transformation temperature to a high temperature. Also in this case, the optimum addition amount depends on the rolling temperature, but it is necessary to increase the addition amount as the rolling temperature increases. The addition amount of 2 atomic% or more is effective, and even if the addition amount is 5 atomic% or more, the effect is not changed and the workability may be deteriorated.

FIG. 1 compares the thermal expansion of Pr ₁₇ Fe ₇₇ B ₅ Cu ₁ alloy, low carbon steel SS41 and ferritic stainless steel SUS430. When SS41 is cooled, the A3 transformation start temperature (T1) is about 800 ° C and the A3 transformation end temperature (T2) is about 700 ° C. Since SUS430 does not undergo A3 transformation, there is no rapid change in thermal expansion. Also,
2 (a), iron, P, Al, Ti, V, Sn, W, M
In which 1 atomic% of o is added, Si and G are shown in FIG.
2 shows the thermal expansion of the one containing 2 atomic% of e and Ga. The A3 transformation temperature is shifted to a high temperature due to the added elements.

It is preferable that the capsule has a multi-layered structure for the purpose of ensuring strength and vacuum sealing, but at least one of the capsules is made of the above-mentioned material, which has an effect of suppressing the influence of A3 transformation. . All of the multiple capsules may be made of the above materials. FIG.
Fig. 3 shows a schematic view of a cross section (a plane perpendicular to the length direction of the rolled material) of a rolling capsule having a triple structure. Here, they are called the first capsule, the second capsule, and the third capsule from the inside.

In the case where the peeling layer provided at the capsule interface relaxes the strain and suppresses the occurrence of cracks, at least the innermost capsule in contact with the rare earth alloy is A3 during cooling as described above.
It must be made of a material that does not undergo transformation. When the capsule is removed, the outer capsule is separated by the release layer and can be easily separated, but the inner capsule is bonded to the rare earth alloy. The thickness is 2mm to make it easier to remove
It is desirable that: As a material for forming the release layer, Al ₂ O ₃ , MgO, S, which is stable at a high temperature of 1000 ° C. or higher,
Those containing ceramic powder such as i0 ₂ and BN are preferable. There are various methods for applying the release material, but the simplest method is to apply the ceramic fine powder to a solvent and apply it to the capsule surface by spraying or brushing.

The thickness of the metal capsule (total thickness of each capsule in the case of multiple capsules) is preferably 20% or more with respect to the size of the rare earth alloy charged therein. For example, the outer shape is width W1 x length L1 x height H
When a rare earth alloy having a width W2, a length L2, and a height H2 is charged into the rectangular parallelepiped capsule of No. 1, the capsule thickness T in the width direction is T.
The capsule thickness is set so that w = (W1−W2) / 2 is larger than 0.2 × W2. Further, the capsule thickness in the length direction Tl = (L1-L2) / 2 and the capsule thickness in the height direction Th = (H1-H2) / 2 are also larger than 0.2 × L2 and 0.2 × H2, respectively. Is set as follows. When a plurality of rare earth alloy ingots are charged, the sum of the thicknesses of the encapsulant in the width direction, the length direction, and the height direction toward the outside with respect to a certain rare earth alloy ingot is the capsule thickness described above. It only has to meet the conditions. If the capsule is thinner than this thickness, the capsule may be broken during hot working to cause a large crack.

It is preferable that these capsules are made by hollowing out the metal lumps of the above-mentioned material in terms of strength, but it is also possible to use those obtained by encapsulating plate materials by welding. It is also possible to create capsules by multiple capsules.

Further, it is not preferable to leave oxygen, water, etc. which cause the oxidation of the rare earth alloy during the hot working in the capsule, and in particular, a plurality of rare earth alloy ingots are fused and integrated during the hot working. If you want to make a magnet, or if you heat work rare earth alloy powder,
It is desirable to evacuate to a vacuum of about 0 ^-3 torr and encapsulate the rare earth alloy.

The temperature for carrying out hot working is preferably 800 ° C. or higher in order to obtain a sufficient orientation of the main phase grains and to prevent large cracks during rolling. The upper limit is preferably 1100 ° C. in order to avoid a decrease in iHc due to abrupt coarsening of the main phase grains (R ₂ Fe ₁₄ B grains).

As the hot working method, rolling, pressing, forging, extrusion or the like can be adopted, and the working conditions are such that the strain rate is 10 ⁻⁴ to 10 ² / s, and the total working ratio (sheet thickness reduction rate). Is preferably 50% or more in order to improve the orientation of crystal grains, that is, the residual magnetic flux density.

When the working method is hot rolling, it is desirable to perform the rolling while restraining the metal capsule from the width direction in order to improve the magnetic properties of the magnet and prevent cracking of the magnet during rolling. . For this purpose, for example, grooved male and female rolls or hole type rolls may be used, but most simply, the ratio W / H of the width W and the height H to the rolling direction of the capsule to be rolled is set to 1.0 or more. If this is done, the rare earth alloy in the capsule will be constrained by the capsule skin from both sides in the width direction, and the same effect as when using the special roll described above can be obtained, so this method can be adopted.

In the case of hot rolling, after heating once, it is not reheated during multiple passes (one heat / multipass).
It may be either a method to reheat to the middle of the multi-pass and to stabilize the processing temperature (multi-heat / multi-pass), but in the case of a large material to be rolled that exceeds 50 kg, its large heat capacity Therefore, the adverse effect due to the temperature drop during processing is reduced, and the one-heat / multi-pass method is desirable because the high productivity can be utilized.

Further, in the above multi-pass rolling, both a unidirectional rolling system in which the material to be rolled is always guided from one direction to the rolling apparatus and a so-called reverse rolling system in which the rolling material is alternately reciprocated for each pass can be considered. Although it can be adopted, the reverse rolling method is superior in terms of the uniformity of the magnetic characteristics of the rolled magnet in the rolling length direction. Further, it is preferable for improving the magnetic properties that there is a pass with a large workability of 15% or more in the pass schedule of multiple passes.

Further, when cooling after hot working, a part of the capsule is locally cooled, temperature irregularities generated during hot working, and cracks easily occur due to thermal stress due to A3 transformation, so that the furnace is cracked. It is desirable that the capsules are gradually cooled after the temperature uniformity of the capsules is increased or after the capsules are heated or brought into contact with a metal mass that becomes a hot bath. In the present invention, since the influence of the A3 transformation is eliminated by changing the material of the capsule, slow cooling is not always necessary, but slow cooling is more preferable to prevent cracking.

In this way, the material can be used as a magnet by removing the capsule from the material cooled to room temperature by a method such as gas fusing or saw blade cutting and taking out the rare earth alloy. However, if a further heat treatment is performed, a larger coercive force can be obtained. Therefore, it is desirable to perform the heat treatment in an inert atmosphere according to the required coercive force.

The temperature at which the heat treatment is carried out is preferably 450 ° C. or higher in order to obtain the effect of increasing the coercive force. However, at 1100 ° C. or higher, the main phase grains are abruptly coarsened and iHc is reduced, so avoiding this The proper heat treatment temperature should be 450 to 1100 ° C. Furthermore, first 75
Heat treatment at a high temperature of 0 to 1100 ° C, and then 450 to 7
A two-step heat treatment in which a low-temperature heat treatment at 50 ° C. is performed, or a multi-step heat treatment in which it is repeated is more preferable because it is effective in improving coercive force and squareness.

Finally, if the desired shape is small, a large number of magnets can be cut out from the hot-worked rare earth alloy by cutting with a diamond wheel, grinding with a grindstone, cutting by wire electric discharge machining, or the like.

Example 1 Using an induction heating furnace in an argon atmosphere, a rare earth alloy having a composition of Pr _17.2 Fe ₇₇ B _5.2 Cu _0.6 was melted and cast in a copper mold to obtain an ingot. At this time, raw materials of rare earth, iron, and copper were used with a purity of 99.9%, and boron was ferroboron. The size of the cast ingot was 20 mm in thickness × 250 mm in width × 250 mm in height, and had a macrostructure in which columnar crystals developed in the thickness direction. The average grain size of this columnar crystal structure was 15 μm. 18 mm wide x 20 mm ingot
A rolled billet was produced by cutting into 0 mm × height 40 mm and polishing. If this is put in three, the width is 54 mm and the width is 80
It was enclosed in a capsule of mm × length 250 mm × height 80 mm. As the capsule, several materials as shown in Table 1 were used.

This capsule was preheated at 1025 ° C. for 90 minutes, and was rolled using a rolling mill with a diameter of 300 mm to obtain 80 → 65 →
Rolling was performed 5 times with a pass schedule of 50 → 40 → 30 → 20 mm, and the total workability was set to 75%. At this time, the rolling is so-called reverse rolling, and after the second and fourth rolling, 10
Intermediate heating was performed at 25 ° C for 15 minutes.

The rolled material is air-cooled on bricks, and the cooling rate is about 20 ° C / about from 950 ° C to 600 ° C.
Min, about 12 ℃ / from 600 ℃ to 300 ℃
Min, and 8 ° C / min from 300 ° C to around 100 ° C. The magnet was taken out from the rolled material cooled to room temperature and the cracking condition was measured. About one type of capsule material 5
Tens of rollings were performed from the book, and the crack occurrence rate (number of cracked rolled materials / total number of rollings) of the taken out magnet was evaluated.
Table 1 shows the results. The crack here is a large crack in which the magnet is completely separated.

[0056]

[Table 1]

It can be seen from Table 1 that the use of capsules containing the above elements added to iron reduces cracking and improves yield.

Further, this magnetic alloy was heat-treated at 1025 ° C. for 20 hours and subsequently at 500 ° C. for 6 hours, and then the magnetic characteristics and mechanical strength were measured. The result (BH)
25-28 MGOe max, bending strength 32-35 kg
/ Mm ² .

[Example 2] As in Example 1, the ingot was encapsulated in an iron capsule containing Cr, Ti, and Si and hot-rolled. The capsule shape and rolling conditions were set in the same manner as in Example 1, but the amounts of Cr, Ti, and Si added were changed as shown in Table 2 to compare the cracks of the magnets. Table 2 shows the results. The crack here is a large crack that separates the magnet.

[0060]

[Table 2]

From this, Cr is 13% or more and Ti is 0.2
%, And Si is added at 2% or more, it can be seen that there is an effect of preventing cracking.

Example 3 Using an induction heating furnace in an argon atmosphere, a rare earth alloy having a composition of Nd ₁₇ Fe _77.2 B _5.2 Cu _0.6 was melted and cast in a copper mold to obtain an ingot. At this time, raw materials of rare earth, iron, and copper were used with a purity of 99.9%, and boron was ferroboron. The size of the cast ingot was 20 mm in thickness × 250 mm in width × 250 mm in height, and had a macrostructure in which columnar crystals developed in the thickness direction. The average grain size of this columnar crystal structure was 15 μm. 18 mm wide x 20 mm ingot
A rolled billet was produced by cutting into 0 mm × height 40 mm and polishing. If this is put in three, the width is 54 mm and the thickness is 2
It was enclosed in a first capsule having a size of 80 mm, which was then enclosed in a second capsule having a width of 80 mm, a length of 250 mm, and a height of 80 mm.
For the first capsule and the second capsule, several materials as shown in Table 1 were used.

This capsule was preheated at 1025 ° C. for 90 minutes, and was rolled 80 → 70 → by using a rolling mill of φ300.
Rolling was performed 6 times with a pass schedule of 60 → 50 → 40 → 30 → 20 mm, and the total workability was set to 75%. At this time, rolling was so-called reverse rolling three times, and intermediate heating was performed at 1025 ° C. for 15 minutes before the fifth rolling.

The rolled material is air-cooled on the brick, and the cooling rate is about 20 ° C./about from 950 ° C. to 600 ° C.
Min, about 12 ℃ / from 600 ℃ to 300 ℃
Min, and 8 ° C / min from 300 ° C to around 100 ° C. The magnet was taken out from the rolled material cooled to room temperature and the cracking condition was measured. Five to ten pieces of one type of capsule were rolled, and the crack occurrence rate (number of cracked rolled materials / total number of rolled pieces) of the taken-out magnet was evaluated. Table 1 shows the results. The crack here is a large crack in which the magnet is completely separated.

[0065]

[Table 3]

In the case of multiple capsules, at least one of them is made of the material of the present invention, which has the effect of suppressing the occurrence of cracks.

[Embodiment 4] Same thickness as in Embodiment 3 20 mm
× width 250 mm × height 250 mm ingot width 18
A length of 200 mm and a height of 200 mm were cut and polished to prepare a rolled billet. Put the 3 pieces together to make a width of 54 mm, and then enclose it in a first capsule with a thickness of 2 mm.
It was placed in a second capsule of mm × length 250 mm × height 250 mm and sealed. 3 in the width direction and 2 in the length direction
6 pieces in total, width 240 x length 500 x height 25
It was set to 0 mm, and it was placed in a third capsule having a width of 400 mm, a length of 600 mm, and a height of 350 mm, and sealed by welding. As the materials of the first capsule, the second capsule, and the third capsule, those shown in Table 4 were used.

This capsule was preheated at 1025 ° C. for 3 hours, and was rolled 10 times using a rolling machine with a roll diameter of φ900 to a height of 90 mm. The total workability is 75%. At this time, intermediate heating was not performed. Rolled material is air-cooled, approximately 95
It took about 5 hours to cool from 0 ° C to around 100 ° C. The magnet was taken out from the cooled rolled material, and the cracking condition (number of cracked rolled materials / total number of rolling) was measured. The crack here is a large crack in which the magnet is completely separated. The results are shown in Table 4.

[0069]

[Table 4]

It can be seen that the capsule material of the present invention which does not undergo the A3 transformation has less cracks as the volume of the entire capsule is increased.

[Embodiment 5] Same thickness as in Embodiment 3 20 mm
× width 250 mm × height 250 mm ingot width 18
A length of 200 mm and a height of 200 mm were cut and polished to prepare a rolled billet. Put these into a first capsule with a width of 54 mm, a thickness of 2 mm, and a ceramic powder applied as a release material on the outer surface, and put this into a second capsule of width 80 mm × length 250 mm × height 250 mm. It was put and sealed. 6 pieces in total, 3 pieces in the width direction and 2 pieces in the length direction, are arranged to make a width 240 x length 500 x height 250 mm, and put in a third capsule of width 400 x length 600 x height 350 mm and welded. Sealed by. 1st capsule, 2nd
As the materials and ceramics of the capsules and the third capsule, those shown in Table 5 were used.

This capsule was preheated at 1025 ° C. for 3 hours, and was rolled 10 times to obtain a height of 90 mm by using a rolling machine having a roll diameter of φ900. The total workability is 75%. At this time, intermediate heating was not performed. Rolled material is air-cooled, approximately 95
It took about 5 hours to cool from 0 ° C to around 100 ° C. Although the second capsule and the third capsule were integrated, they were easily removed because they were separated from the first capsule by a ceramic layer. Although the first capsule was bonded to the rare earth alloy, it was thinned to about 0.5 to 2 mm by rolling and could be easily peeled from the surface of the rare earth alloy. In this way, the capsules were removed, and the cracking condition (number of rolled materials with cracking / total number of rolling) was evaluated. The crack here is a large crack in which the magnet is completely separated.
The results are shown in Table 5.

[0073]

[Table 5]

It can be seen that at least the first capsule is made of a material that does not undergo A3 transformation, and by applying a release material to the outer surface of the first capsule, the cracking occurrence rate becomes extremely low.

[0075]

As described above, according to the present invention, in the method of manufacturing a rare earth permanent magnet in which a rare earth alloy is encapsulated and hot worked, the difference in the coefficient of thermal expansion that causes cracking during cooling is small. Or, the stress generated by the difference in thermal expansion is relaxed, and there is an effect that the generation of cracks is suppressed and the yield is improved. Further, there is an effect that fine cracks and residual stress inside the magnet are eliminated, the property that the original mechanical strength is high is further improved, and the reliability is improved.

[0076]

[Brief description of drawings]

FIG. 1 is a graph showing the coefficient of thermal expansion of a rare earth alloy and an iron-based metal for capsules.

FIG. 2 (a) is a graph showing the coefficient of thermal expansion of iron added with P, Al, Ti, V, Sn, W, and Mo. (B) A graph showing the coefficient of thermal expansion of iron added with Si, Ge, and Ga.

FIG. 3 is a schematic cross-sectional view of a multiple capsule for explaining the embodiment of the present invention.

[Explanation of symbols]

 1. Rare earth alloy 2. First capsule 3. Second capsule 4. 3rd capsule

Claims (8)

[Claims] 1. A method for producing a permanent magnet, wherein R (where R is at least one of rare earth elements including Y), Fe and B as a basic component, a rare earth alloy or a rare earth alloy powder is encapsulated and hot worked. 2. A method for manufacturing a rare earth permanent magnet, characterized in that the capsule is made of a material having a coefficient of thermal expansion close to that of an alloy. 2. The method for producing a rare earth permanent magnet according to claim 1, wherein the capsule is made of an iron-based metal having a body-centered cubic structure at a temperature at which hot working is performed. 3. The method for producing a rare earth permanent magnet according to claim 1, wherein the capsule is made of an iron-based metal that does not undergo A3 transformation in the cooling process after hot working. 4. The first-stage capsule has a carbon content of 0.12.
2. The method for producing a rare earth permanent magnet according to claim 1, wherein the content is 13 wt% or less by weight, 13 to 30 at% Cr, and the balance is iron. 5. The previous capsule has a carbon content of 0.12.
If it is less than wt%, P, Al, Ti, V, Sn, W,
The method for producing a rare earth permanent magnet according to claim 1, wherein at least one of Mo is contained in an amount of 0.2 to 3 atomic%, and the balance is made of a metal material which is iron. 6. The first-stage capsule has a carbon content of 0.12.
2. The rare earth permanent magnet according to claim 1, wherein the rare earth permanent magnet is at most 1 wt% and contains 2 to 5 atom% of at least one of Si, Ge and Ga, and the balance is iron. Manufacturing method. 7. The pre-capsule has a multi-layered structure, at least one of which has a carbon content of 0.1.
2 wt% or less, 13 to 30 atomic% of Cr, or 0.2 to 3 atomic% of at least one of P, Al, Ti, V, Sn, W and Mo, or Si, Ge, Ga 2. The method for producing a rare earth permanent magnet according to claim 1, wherein at least one of them is contained in an amount of 2 to 5 atom%, and the balance is made of a metal material which is iron. 8. The former capsule has a multi-layered structure, and the capsule in contact with the innermost alloy has a carbon content of 0.
12 wt% or less, 13 to 30 atomic% of Cr, or 0.2 to 3 atomic% of at least one of P, Al, Ti, V, Sn, W and Mo, or Si, Ge, Ga.
2. The rare earth according to claim 1, characterized in that at least one of them is contained in an amount of 2 to 5 atomic%, and the balance is made of a metal material which is iron, and a heat-resistant release material layer is provided on the outside thereof. Manufacturing method of permanent magnet.