JPH09260171A - Manufacture of rare earth permanent magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent lowering of an yield due to a crack by having a cooling process by relaxing a stress due to a a difference in the thermal expansion coefficients between an alloy and a capsule after hot working. SOLUTION: A rare-earth alloy having R (R denotes at least one kind or more of rare earth elements including Y), Fe and B as basic components or rare earth alloy powder are encapsulated for being subjected to hot working. Then, after hot working, a cooling process for selaxing a stress due to a difference in thermal expansion between the alloy and the capsule is carried out. Here, the cooling process for relaxing a stress due to a difference in the thermal expansion coefficients of the alloy and the capsule is made to be a process of gradual cooling at a cooling speed of 0.01 to 2 deg.C/min. Further, it is to be process of cooling while applying a compression stress to a work material. Therefore, a large-sized magnet with a high mechanical strength can be stably produced.

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 wt% or less and a melting point of 600 ° C. or more, and the ingot is sealed and hot-worked. It is disclosed that 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 for producing a rare earth permanent magnet according to claim 1, wherein a rare earth alloy containing R (where R is at least one of rare earth elements including Y), Fe and B as basic components. Alternatively, a method of manufacturing a permanent magnet in which a rare earth alloy powder is put into a capsule and hot-worked is characterized by having a cooling step for relaxing stress caused by a difference in thermal expansion coefficient between the alloy and the capsule after hot-working.

In the method for manufacturing a rare earth permanent magnet according to a second aspect, the cooling step for relaxing the stress due to the difference in the coefficient of thermal expansion between the alloy and the capsule is gradually cooled at a cooling rate of 0.01 to 2 ° C./min. It is characterized by being a process.

In the method for manufacturing a rare earth permanent magnet according to a third aspect of the present invention, the cooling step of relaxing the stress due to the difference in the coefficient of thermal expansion between the alloy and the capsule is a step of cooling the processed material while applying compressive stress. Characterize.

In the method for producing a rare earth permanent magnet according to claim 4, (a) R (where R is at least one of rare earth elements including Y), an alloy containing Fe and B as basic components is melted and cast. And (b) charging and sealing the casting alloy in an iron-based metal capsule having an A ₃ transformation point,
(c) a step of hot working the capsule at a temperature not lower than the A ₃ transformation point of 800 to 1100 ° C., (d) then starting the hot working rolled material (capsule) to the A ₃ transformation of the iron-based metal capsule A step of gradually cooling from the temperature (T ₁ ) to the A ₃ transformation end temperature (T ₂ ) at a cooling rate of 0.05 to ₂ ° C./minute, and further cooling to room temperature.

It is characterized by comprising the above steps (a) to (d) and magnetically anisotropy of the alloy.

According to a fifth aspect of the present invention, there is provided a method for producing a rare earth permanent magnet, which comprises: (a) R (wherein R is at least one of rare earth elements including Y), Fe and B are alloys, and alloys having basic components are melted and cast. And (b) charging and sealing the casting alloy in an iron-based metal capsule having an A ₃ transformation point,
(c) a step of hot working the capsule at a temperature not lower than the A ₃ transformation point of 800 to 1100 ° C., (d) then starting the hot working rolled material (capsule) to the A ₃ transformation of the iron-based metal capsule A step of gradually cooling from a temperature (T ₁ ) to an A ₃ transformation end temperature (T ₂ ) at a cooling rate of 0.05 to ₂ ° C./minute, and further cooling to room temperature; Process of taking out heat treatment.

The method is characterized by comprising the steps (a) to (e) and magnetically anisotropy of the alloy.

The method for producing a rare earth permanent magnet according to claim 6 is: (a) R (where R is at least one or more of rare earth elements including Y), Fe and B are alloyed and cast as an alloy. And (b) charging and sealing the casting alloy in an iron-based metal capsule having an A ₃ transformation point,
(c) a step of hot working the capsule at a temperature not lower than the A ₃ transformation point of 800 to 1100 ° C., (d) then starting the hot working rolled material (capsule) to the A ₃ transformation of the iron-based metal capsule A step of gradually cooling from a temperature (T ₁ ) to an A ₃ transformation end temperature (T ₂ ) at a cooling rate of 0.05 to ₂ ° C./minute, and further cooling to room temperature; Step of taking out heat treatment, (f) Step of cutting and polishing into a desired shape.

It is characterized by comprising the above steps (a) to (f) and magnetically anisotropy of the alloy.

In the method for producing a rare earth permanent magnet according to claim 7, in the cooling step of the step (d), (T ₁ +5
The temperature range from 0) ℃ to (T ₂ -50) ℃ is 0.05 ~
Gradually cool at a cooling rate of 1 ° C./min, then (T ₂ −50) ° C.
To 250 ° C. is characterized by slow cooling at a cooling rate of 0.01 to 2 ° C./min.

In the method for producing a rare earth permanent magnet according to claim 8, the casting alloy in the step (a) is R14 to 19 atom%,
B4 to 6 atomic%, Cu 0.1 to 2 atomic%, the balance iron and impurities inevitable in production, and the iron-based metal capsule of the step (b) has an A ₃ transformation point of 600 to 90 during cooling.
It is characterized by being a general-purpose steel with a temperature of 0 ° C.

The method for producing a rare earth permanent magnet according to claim 9 is characterized in that, when the casting alloy in the step (b) is charged into the iron-based metal capsule, a release agent is interposed between the alloy and the capsule. And

Here, the A ₃ transformation point refers to the transformation point and transformation temperature range of iron and iron-based alloy α iron (body centered cubic lattice) ⇔ γ iron (face centered cubic lattice), for example, cooling from high temperature. In the case of hypoeutectoid steel, it refers to the continuous transformation temperature range of the transformation from γ iron to α iron and the transformation from γ iron to α iron + cementite.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The preferred composition of 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 cracking easily occurs during processing, and the yield decreases. 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 atomic%, 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.

Cu, Ag, Au, and Ga have the effects of improving hot workability and coercive force and squareness, so addition is effective, but a nonmagnetic phase is formed, so the addition amount is 6 atomic% or less. Is preferred. 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 and the like may be further contained, and the coercive force may be improved by adding a small amount so as not to reduce the residual magnetic flux density.

The above-described alloy containing the rare earth elements, iron and B as the 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 and casting, the alloy ingot may be cast so that the macrostructure of the ingot is columnar and the main phase has a mean 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 such a high temperature 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. And the ductility and strength that can respond to the deformation of the alloy in hot working are required, such as iron-based alloys, copper-based alloys,
A metal capsule such as a nickel alloy is used. Many of these metal capsules exhibit monotonic thermal expansion in the temperature range above room temperature.

Further, since the liquid phase at this high temperature is rich in rare earths and has high reactivity, an iron-based metal capsule which produces a relatively gentle reaction with the liquid phase to form an alloy layer or a compound layer is desirable. JIS G 3101 rolled steel for general structure, JIS G 3131 hot rolled mild steel plate and strip, JIS G 3141
Cold rolled steel sheet and strip, carbon steel for machine construction steel of JIS G 4051, hot rolled stainless steel sheet and strip of JIS G 4304, a cold JIS G 4305 rolled stainless steel plate and A ₃ transformation of the steel strip or the like Iron-based metal capsules with dots can be used. These iron-based metal capsules have an A ₃ transformation point at the time of cooling to 600 to 900 ° C., and regarding the thermal expansion at the time of temperature rise, α iron (body centered cubic lattice) → γ iron (face centered cubic lattice) ) A ₃
Although it contracts at the transformation point, it exhibits monotonic expansion in other temperature regions above room temperature.

The thickness of the metal capsule is preferably 20% or more with respect to the size of the alloy charged therein. For example, a rectangular parallelepiped capsule having an outer shape of width W1 × length L1 × height H1 has width W2 × length L2 × height H2.
When the alloy is charged, the capsule thickness in the width direction Tw =
The capsule thickness is set so that (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 multiple alloy ingots are charged, the sum of the thickness of the encapsulant in the width direction, the length direction, and the height direction toward the outside of a certain alloy ingot satisfies the above-mentioned capsule thickness condition. It only has to meet. If the capsule is thinner than this thickness, the capsule may be broken during hot working to cause a large crack.

These capsules are preferably made by hollowing out the metal lumps of the above-mentioned material in terms of strength, but those obtained by encapsulating a plate material by welding can also be used. It is also possible to create capsules by multiple capsules.

In order to suppress the excessive reaction between the liquid phase and the iron-based metal capsule, it is effective to interpose a release material between the alloy and the capsule. As the release agent, BN, alumina, silica or the like can be used. .

Further, it is not preferable to leave oxygen, water, etc., which cause oxidation of the alloy during hot working, in the capsule, and in particular, a plurality of alloy ingots are fused during hot working to form an integral magnet. In such a case and when the alloy powder is hot-worked, it is desirable to degas the inside of the capsule to a vacuum of about 10 ⁻³ torr to encapsulate the alloy.

The temperature at which hot working is carried out 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. Further, the upper limit is preferably set to 1100 ° C. or less in order to avoid a decrease in iHc due to abrupt coarsening of the main phase grains (R ₂ Fe ₁₄ B grains). The processing temperature for the iron-based metal capsules described above, A ₃ being hot working is desirably in the form of a time A ₃ becomes lower than the transformation point temperature γ iron phases than is the way transformation.

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 carry out 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 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 above special roll 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 one-way 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.

Next, regarding the behavior of the rare earth alloy and the capsule during the cooling after the hot working is finished, as described above, the rare earth alloy uniformly contracts to the solidification point of its grain boundary phase (liquid phase), and there, It shows a change that reduces the shrinkage rate and turns to expansion at temperatures below the Curie point. This state is shown in FIG. 1, for example. As for the capsule, a general metal capsule such as a copper alloy shrinks uniformly to room temperature at a shrinkage ratio substantially similar to that before solidification of the grain boundary phase of the rare earth alloy. Therefore, the stress due to the difference in the coefficient of thermal expansion between the metal capsule and the rare earth alloy is generated near the solidification point of the grain boundary phase of the rare earth alloy.

When the capsule is an iron-based metal having an A ₃ transformation point during cooling in the range of 900 to 600 ° C., it expands once at the A ₃ transformation point during cooling and then contracts uniformly. This shows a change as shown in FIG. 2, for example. Therefore, the stress due to the difference in thermal expansion between the iron-based metal capsule having such an A ₃ transformation point and the rare earth alloy is generated near the A ₃ transformation point of the capsule.

In both the general metal capsules such as the copper alloy and the iron-based metal capsules having the A ₃ transformation point, the cooling step for relaxing the stress due to the difference in the coefficient of thermal expansion between the alloy and the capsules after hot working is A slow cooling step at a cooling rate of 0.01 to 2 ° C./min, or a step of cooling the processed material while applying compressive stress can be employed.

In the latter case, for example, the above stress relaxation can be achieved by holding the forging die at the same position after the hot forging is finished and cooling it in the compressed state.

Regarding the cooling conditions in the former case of slow cooling, if a rapid cooling such as a cooling rate of 10 ° C./min or more is performed, a large crack such that the magnet is divided into two is surely generated and stress relaxation. I can't do it. Further, at a cooling rate of about 5 ° C./min, large cracks can be considerably prevented, but since they occur with a probability of 10 to 20%, they cannot be said to be sufficient stress relaxation. At a cooling rate of 2 ° C./min or less, the stress relaxation effect is exerted, and a large crack such that the magnet is divided into two can be prevented by almost 100%. However, from the viewpoint of productivity, cooling that is too slow is not preferable, and a cooling rate of 0.01 ° C./min or more is desired.

[0052] Particularly in the case of using the iron-based metal capsule with A ₃ transformation point, as cooling conditions for relieving the stress due to the difference in thermal expansion in the vicinity of A ₃ transformation point of the capsule, it is the stress generation start point It is preferable to gradually cool from the A ₃ transformation start temperature (T ₁ ) to the A ₃ transformation end temperature (T ₂ ) which is the end point of the stress expansion region at a cooling rate of 0.05 to ₂ ° C./min. Here, the lower limit of the cooling rate is as high as 0.05 ° C., because at a cooling rate lower than this, the reaction between the capsule and the magnet alloy proceeds too much, and cracking due to the reaction and fusion easily occurs. Then, in order to further reduce the probability of occurrence of cracks, the above-mentioned slow cooling region is expanded, and (T ₁ +50) ° C. to (T ₂
The temperature range up to −50) ° C. is gradually cooled at a cooling rate of 0.05 to 1 ° C./min, and then the temperature range from (T ₂ −50) ° C. to 250 ° C. is 0.01 to 2 ° C./min. It is desirable to gradually cool at a cooling rate. Here, at 250 ° C. or lower, new stress does not increase due to the difference in thermal expansion between the alloy and the capsule, and the tensile strength of the alloy is large.

Further, if stress is concentrated on a part of the capsule due to local cooling of the part of the capsule or temperature unevenness generated during hot working, cracking will occur.
It is preferable that the capsules are placed in a furnace or brought into contact with a metal mass that serves as a heat bath to increase the temperature uniformity of the capsules or to gradually cool the capsules while the uniformity is increased.

In this way, if the capsule is removed from the material to be processed cooled to room temperature by a method such as gas fusing or saw blade cutting, and the magnet alloy is taken out, it can be used as a magnet. 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. 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, when the desired shape is small, a large number of magnets can be cut out from the hot-worked magnet alloy by cutting with a diamond wheel, grinding with a grindstone, cutting by wire electric discharge machining, or the like.

The present invention will be described below based on examples.

Example 1 Using an induction heating furnace in an argon atmosphere, an alloy having a composition of Pr _17.2 Fe ₇₇ B _5.2 Cu _0.6 was melted in an alumina crucible and poured into a water-cooled copper mold at 1550 ° C. for casting. I got 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 × 500 mm in width × 240 mm in height, and had a macrostructure in which columnar crystals were developed in the thickness direction. The average grain size of this columnar crystal structure was 15 μm.

Φ10 mm × 20 mm from this ingot
After cutting out a cylindrical sample of 1025 ° C. × 1 h, after heating from room temperature to 1000 ° C. (heating rate 1 ° C. /
Min) was measured. The result is shown in FIG.

Next, a sample having a width (thickness) of 17 mm, a length of 130 mm, and a height of 60 mm was cut out from this cast ingot. Five sample ingots of this size are arranged side by side in the width direction into one block, which is inserted into the first capsule formed into a square pipe by welding SS400 steel with a thickness of 3 mm to insert the width direction (side surface) and height direction (upper and lower surfaces) of the ingot. ). The same capsule material was also spot-welded in the length direction (front and back) to complete the first capsule. And the outer shape is made of SS400 steel (width of carbon: 0.16, width: 230 mm, length: 230 mm, height: 120 mm).
wt%, silicon 0.20 wt%, manganese 0.75 wt
%) In a second capsule. There is a hole with a diameter of 1.5 mm on one surface of the second capsule in the length direction.
The capsule was vacuum-sealed by sealing by electron beam welding in a vacuum chamber of 10 ⁻⁴ torr.

Also, from this second capsule, φ10 mm
Cylinder sample of × 20mm is cut out and 100
During temperature increase and decrease to 0 ° C (temperature increase and decrease rate 1 ° C /
Min) was measured. The result is shown in FIG. From this figure, it is understood that the A ₃ transformation start temperature (T ₁ ) is 800 ° C. and the A ₃ transformation end temperature (T ₂ ) is 700 ° C. when the capsule is cooled.

As a hot working method, a rolling method is adopted, the capsule is heated at 1025 ° C. for 90 minutes, and a rolling machine with a φ450 roll is used to make 120 → 110 → 95 → 80 → 7.
Rolling was performed 5 times with a pass schedule of 0 → 60 mm, and the total workability was set to 50%. At this time, the so-called reverse rolling is performed twice, and at 1025 ° C. for 15 times between the fourth and fourth rolling.
Intermediate heating for 1 minute was performed.

After the rolling, the surface of the rolled material was cooled to about 950 to 980 ° C., but it was immediately put into a furnace at 950 ° C., and the temperature range of 950 to 400 ° C. was cooled in various types shown in Table 1. Cooled at a rate of 0.1 to 400 ℃ to room temperature
Cooled at ° C / min. Some rolled material was air cooled on bricks without being placed in a 950 ° C furnace. The cooling rate in this case is about 20 from 950 ℃ to 600 ℃.
℃ / 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 and the surface roughness of the rolled surface were measured. At this time, when the capsule was cut, the magnet / capsule was already separated. Further, a 10 mm square sample was cut out, and the magnetic characteristics were measured using a DC self-recording magnetometer (BH tracer) after pulse magnetization of 40 kOe without heat treatment.

The above-mentioned rolling is 5 times for one cooling condition.
From the number of 10 rolled, the crack occurrence rate of the magnet taken out as a crack index (number of cracked rolled material / total number of rolled) and surface roughness Rmax (reference length 25 mm, rolled material in the center of the rolled material width direction) The average of 3 points in the length direction) was evaluated. As a result, the maximum energy product (B
H) max (hereinafter referred to as (BH) max) is shown in Table 1. The crack here is a large crack that divides the magnet in two.

[0066]

[Table 1]

From this, it can be seen that by setting the cooling rate in the temperature range of 950 ° C. to 400 ° C. to 0.05 to 2 ° C./min, the occurrence of cracks can be made as low as less than 10% and the yield can be improved. .

Example 2 The same capsule (ingot-loaded) used in Example 1 was hot-rolled under the same conditions as in Example 1.

The rolled material after rolling is the same as in Example 1
The surface was cold at 0-980 ℃, but soon 950
It was air cooled on the bricks to the temperatures shown in Table 2 without being placed in a 0 ° C oven. Next, after being put in a furnace at 950 ° C. and held for 15 minutes, the temperature range of 950 ° C. to 400 ° C. is changed to 0.3 ° C.
The cooling rate was 400 rpm to room temperature at 0.1 ° C./min.

The magnet was taken out from the rolled material cooled to room temperature and the cracking condition and the surface roughness of the rolled surface were measured. At this time, when the capsule was cut, the magnet / capsule was already separated.

The above rolling is carried out by 5 times for one air cooling condition.
The number of rollings equal to or more than the number of rollings and the cracking index of the taken out magnet (number of cracked rolled material / total number of rolled) and surface roughness Rmax (reference length 25 mm, length of rolled material in the center of width direction of rolled material) The average of 3 points in the vertical direction) was evaluated. Table 2 shows the results. The crack here is a large crack that divides the magnet in two.

[0072]

[Table 2]

From the A ₃ transformation start temperature (T ₁ )
It can be seen that the gradual cooling from a temperature higher than ℃ has a higher stress relaxation effect, prevents the occurrence of cracks, and improves the yield.

Example 3 Using an induction heating furnace in an argon atmosphere, an alloy having a composition of Nd ₁₆ Fe _77.5 B ₆ Al _0.5 was melted in an alumina crucible and poured into an iron mold at 1600 ° C. to cast an ingot. Got At this time, raw materials of rare earth, iron, and aluminum having a purity of 99.9% were used, and ferroboron was used as boron. The size of the cast ingot was 10 mm thick × 50 mm wide × 100 mm high. When this ingot is crushed into a suitable size and put in a quartz tube and melted by high frequency heating in an argon atmosphere, an argon pressure of 40 kP is applied from a small nozzle of the quartz tube.
a with a diameter of 200 mm directly below this nozzle
Then, it was rapidly solidified on a copper wheel rotating at a high speed of 3000 rpm to obtain a quenched thin piece. In this X-ray diffraction pattern, this quenched thin piece showed an amorphous broad diffraction intensity pattern from the diffraction peak due to the crystal.

Next, 480 g of this quenched thin piece was put into a capsule made of S10C steel having an outer diameter of 75 mm × height of 80 mm and an internal volume of 40 mm in diameter × 50 mm of height, which was made by welding. Φ on one surface in the height direction of this capsule
The capsule was vacuum-sealed by having a hole of 1.5 mm and sealing by electron beam welding in a vacuum chamber of 1.5 × 10 ⁻⁴ torr.

As a hot working method, a hot pressing method is adopted, and this capsule is heated at 1000 ° C. for 70 minutes to obtain 250
The upper and lower punches heated to 0 ° C. were pressed at a pressing speed of 10 mm / s to a height of 32 mm.

The material to be processed after pressing is 940 to 975.
Although the surface was cooled to about 0 ° C, under the condition 1 after processing, the press die was not removed and compression was continued at about 1 mm / h for about 1 mm / h until the sample surface was cooled to 150 ° C. The cooling rate of this condition 1 sample was about 20 ° C./min on average from about 950 ° C. to 150 ° C. After processing, the sample of Condition 2 was immediately put in a furnace at 950 ° C. and cooled in a temperature range of 950 ° C. to 600 ° C. at a cooling rate of 0.5 ° C./min. Cooled at / min. After processing, the sample under condition 3 is 950 ° C.
It was air cooled on bricks without being placed in the furnace. In this case, the cooling rate is about 20 ° C / min from 950 ° C to about 600 ° C, about 16 ° C / min from about 600 ° C to about 300 ° C, and 10 ° C / min from about 300 ° C to about 100 ° C. Met.

The magnet was taken out from the capsule cooled to room temperature by wire electric discharge machining and the cracking condition was observed.
At this time, when the capsule was cut, some fusion was observed between the magnet and the capsule, but most were separated. 10m again
Cut out an m-square sample, 1000 ° C x 5h and 650
After heat treatment at ℃ × 2h, pulse magnetization of 40kOe was performed, and the magnetic characteristics were measured using a BH tracer.

In the above hot press, five or more pieces were processed under one condition, and as a crack index, the crack occurrence rate of the magnet taken out (the number of cracked rolled materials / total rolled number).
Was evaluated. Table 3 shows the results and (BH) max as magnetic properties. The crack here is a large crack that divides the magnet in two.

[0080]

[Table 3]

Example 4 An alloy having the composition shown in Table 4 was melted and cast in the same manner as in Example 1 to have a thickness of 15 mm ×
A cast ingot having a width of 100 mm and a height of 100 mm was obtained. The structure of this ingot was columnar crystals, and the average grain size was 12 to 20 μm.

From this, width (thickness) 13 mm × length 60 m
A m × 38 mm ingot sample was cut out, and BN was applied as a release material on the surface of the ingot sample, and the width was 19 mm and the length was 6 mm.
It was put in a capsule made of 8 mm × 46 mm high SPCC steel by welding, and 1.5 × 10 ⁻⁴ as in Example 1.
The capsule was vacuum sealed by sealing one of the lids by electron beam welding in a torr vacuum chamber. Furthermore, this capsule is arranged in 3 rows horizontally, 2 rows in front and back, totaling 6 capsules,
It was enclosed in an S45C capsule having a width of 98 mm, a length of 160 mm, and a height of 78 mm.

Next, these are heated at 1000 ° C. for 80 minutes, and the height is increased to 78 →
The total workability was set to 76% by 6-pass reverse rolling for reducing 67 → 56 → 46 → 36 → 27 → 19 mm. At this time, 2 out of 6 rollings, 2 after 4 passes, 100
Intermediate heating was performed at 0 ° C for 15 minutes.

After the completion of rolling, the surface of these rolled materials was 8
It was placed in a furnace at 950 ° C without cooling to below 50 ° C. After being heated for 20 minutes, the rolled material is cooled from 950 ° C. to 600 ° C. at 1 ° C./min, from 600 ° C. to 400 ° C. at 0.5 ° C./min, and from 400 ° C. to room temperature at 0.
Cooled at 1 ° C / min.

The magnet was taken out from the rolled material cooled to room temperature and the cracking condition and the surface roughness of the rolled surface were measured. At this time, when the capsule was cut, the magnet / capsule was already separated.

Table 4 shows the number of cracks in the magnet taken out (a large crack dividing the magnet in two) as a crack index at this time.
The surface roughness Rmax (reference length: 25 mm, average of three points in the lengthwise direction of the rolled material at the center in the widthwise direction of the rolled material) was between 500 and 600 μm for these six types of rolled material.

Further, a sample of 6 × 6 × 40 mm long in the rolling direction was prepared from the rolled magnet taken out without cracks by cutting with a diamond wheel and grinding with a grindstone.
The bending strength by point bending was evaluated. The results are also shown in Table 4. 3-point bending condition is span 30mm, load point R
= 2 mm, crosshead speed = 1 mm / min.

For comparison, a sample of the same shape was cut out from a magnet prepared by a sintering method from the alloy composition Nd ₁₄ Fe ₇₉ B ₇ .
When the bending strength by the same 3-point bending was evaluated, it was 24.6k.
gf / mm ₂ .

[0089]

[Table 4]

Example 5 By the same method as in Example 1, an ingot of the same composition and the same size was obtained. Next, from this cast ingot, width (thickness) 17.5 mm x length 250 m
An ingot sample of m × high 225 mm was cut out and used as a billet. 6 billets are arranged in the thickness direction, and SS
400 steel sheet (carbon content 0.06wt%, silicon 0.01w)
t%, manganese 0.24 wt%) to cover six capsules. This capsule formation is performed by welding each edge of the steel plate, and the welding check is performed by measuring the leakage value of the capsule with a helium leak detector and measuring 1 × 10 5.
It was confirmed to be _-8 torr / l / s or less. The capsule was provided with a hole for evacuation, kept at 2 × 10 ₋₄ torr or less for 1 hour in a vacuum chamber, and then sealed with an electron beam for vacuum sealing. The outside of the capsule is further made of SS400 steel (carbon content of 0.
15wt%, silicon 0.27wt%, manganese 1.55w
(t%) capsules, each edge was welded, and triple capsules were prepared. The outermost shape is 1000 mm x 400 mm x 1
It was 700 mm. The size of the capsule is a = 105m
m, h1 = 3.2 mm, c1 = 111.4 mm, h2 =
28.0 mm, c2 = 812.4 mm, h3 = 56.3
mm. Rolling is performed by heating at 1000 ° C. for 8 hours, 400 → 345 → 290 → 235 → 185 → 145.
The pass schedule was 120 → 100 mm (working rate: 75%). The diameter of the rolling roll is φ1200 mm. The peripheral speed is 45 m / min. Reheating on the way between each pass was not performed. After rolling, the surface of the rolled material is 840 ℃
It was cold to 1,200 ℃, heated to 1100 ℃
mm x length 6500 mm x thickness 240 mm SS400
Using four steel sheets, two rolled sheets were sandwiched between the upper and lower sheets, and immediately placed in a slow cooling box (an iron box with fire bricks stuck inside) to gradually cool to 200 ° C. At this time, a thermocouple was sandwiched between the rolled material and the SS400 steel plate, and the temperature change of the surface of the rolled material during slow cooling was measured. The annealing curve is shown in FIG. After this, the rolled material was reheated to 910 ° C and then
A cooling rate of approximately 0.5 ° C / min up to around 00 ° C
In the range of 00 to 600 ° C, the cooling rate is approximately 0.2 ° C / min, in the range of 600 to 400 ° C, the cooling rate is 0.1 to 0.2 ° C / min, and in the temperature range of 400 ° C to 200 ° C. 0.
It can be seen that the film was gradually cooled at a cooling rate of 03 to 0.1 ° C./min. It was cooled at about 0.05 ° C / min from 200 ° C to room temperature.

In the rolled material cooled to room temperature, the capsule was removed by gas fusing and saw blade cutting, and the magnet was taken out. As a result of observing the cut surface of the capsule at the time of cutting, the upper and lower plates of the first capsule were not easily discerned, and separation of the second and third capsules was partially observed, but there was no vacancy and no breakage. There was no place where it was difficult to take out the magnet due to fusion between the magnet and the capsule, and the magnet could be taken out soundly.

[0092]

By adopting the manufacturing method of the present invention,
The following effects can be obtained.

(1) Large magnets having high mechanical strength, which cannot be obtained by the sintering method, can be stably produced.

(2) Compared with the case of the conventional hot working method,
Most of the magnets can be prevented from cracking, and the magnet surface can be prevented from being uneven, which can significantly improve the yield and reduce the cost.

(3) Further, since it is packed in a capsule and can be processed in the atmosphere, the production efficiency is high and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a thermal expansion curve of an alloy ingot used in Example 1 of the present invention.

FIG. 2 is an encapsulant used in Example 1 of the present invention (SS4
(00 steel) thermal expansion curve.

FIG. 3 is a schematic cross-sectional view of multiple capsules according to a fifth embodiment of the present invention.

FIG. 4 is a cooling curve on the surface of a rolled material according to Example 5 of the present invention.

[Explanation of symbols]

 2: Alloy 31: First capsule upper and lower plates 32: Second capsule upper and lower plates 33: Third capsule upper and lower plates 4: Arrow showing rolling direction 5: Arrow showing rolling direction

Claims (9)

[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, or a rare earth alloy powder or a rare earth alloy powder is encapsulated and hot worked. A method for producing a rare earth permanent magnet, which comprises a cooling step for relaxing stress caused by a difference in thermal expansion coefficient between an alloy and a capsule after hot working. 2. The cooling step for relaxing the stress due to the difference in coefficient of thermal expansion between the alloy and the capsule is a step of gradually cooling at a cooling rate of 0.01 to 2 ° C./min. A method for producing the described rare earth permanent magnet. 3. The rare earth permanent magnet according to claim 1, wherein the cooling step for relaxing the stress due to the difference in thermal expansion coefficient between the alloy and the capsule is a step for cooling the processed material while applying compressive stress. Manufacturing method. 4. (a) a step of melting and casting R (where R is at least one of rare earth elements including Y), Fe and B as a basic component, and (b) casting the cast alloy with A A step of charging and sealing in an iron-based metal capsule having ₃ transformation points, (c) a step of hot working the capsule at a temperature of A ₃ transformation point of 800 to 1100 ° C. or higher, (d) a hot working step The rolled material (capsule) is gradually cooled from the A ₃ transformation start temperature (T ₁ ) to the A ₃ transformation end temperature (T ₂ ) of the iron-based metal capsule at a cooling rate of 0.05 to ₂ ° C./min. And a step of further cooling to room temperature. Above (a)-(d)
3. The method for producing a rare earth permanent magnet according to claim 2, wherein the alloy is magnetically anisotropicized. 5. (a) a step of melting and casting R (where R is at least one of rare earth elements including Y), Fe and B as basic components, and (b) casting the cast alloy with A A step of charging and sealing in an iron-based metal capsule having ₃ transformation points, (c) a step of hot working the capsule at a temperature of A ₃ transformation point of 800 to 1100 ° C. or higher, (d) a hot working step The rolled material (capsule) is gradually cooled from the A ₃ transformation start temperature (T ₁ ) to the A ₃ transformation end temperature (T ₂ ) of the iron-based metal capsule at a cooling rate of 0.05 to ₂ ° C./min. A step of further cooling to room temperature, and (e) a step of removing the cast alloy from the metal capsule and subjecting it to heat treatment. The method for producing a rare earth permanent magnet according to claim 2, comprising the steps (a) to (e) and magnetically anisotropy of the alloy. 6. (a) a step of melting and casting R (where R is at least one or more of rare earth elements including Y), Fe and B as basic components, and (b) the cast alloy is A A step of charging and sealing in an iron-based metal capsule having ₃ transformation points, (c) a step of hot working the capsule at a temperature of A ₃ transformation point of 800 to 1100 ° C. or higher, (d) a hot working step The rolled material (capsule) is gradually cooled from the A ₃ transformation start temperature (T ₁ ) to the A ₃ transformation end temperature (T ₂ ) of the iron-based metal capsule at a cooling rate of 0.05 to ₂ ° C./min. A step of further cooling to room temperature, (e) a step of taking out the cast alloy from the metal capsule and subjecting it to heat treatment, and (f) a step of cutting and polishing into a desired shape. the above
3. The method for producing a rare earth permanent magnet according to claim 2, which comprises steps (a) to (f) and magnetically anisotropies the alloy. 7. In the cooling step of the step (d),
The temperature range from (T ₁ +50) ° C. to (T ₂ −50) ° C. is gradually cooled at a cooling rate of 0.05 to 1 ° C./min, and then (T ₂
Temperature range from -50) ℃ to 250 ℃ is 0.01-2 ℃
5. Slow cooling at a cooling rate of 1 / min.
7. The method for producing a rare earth permanent magnet according to any one of 6 above. 8. The casting alloy of the step (a) is R14 to 1
9 atom%, B4 to 6 atom%, Cu 0.1 to 2 atom%, balance iron and impurities unavoidable in production. Further, the iron-based metal capsule of the step (b) has an A ₃ transformation point of 6 when cooled.
It is general-purpose steel having a temperature of 00 to 900 ° C, and the method for manufacturing a rare earth permanent magnet according to any one of claims 4 to 7. 9. A release agent is interposed between the alloy and the capsule when the cast alloy in the step (b) is charged into the iron-based metal capsule. A method for producing the described rare earth permanent magnet.