JPH06302411A - Manufacture of permanent magnet - Google Patents

Abstract

PURPOSE:To acquire magnetic characteristic which is higher than conventional one in an R-Fe-B-Ag permanent magnet by casting/hot working method. CONSTITUTION:After hot working is performed at a temperature of 500 deg.C or higher for an R, Fe, B, Ag-based alloy ingot whose 10 to 20% consists of R, 4 to 8% consists of B, 4% or less (exceptng 0) consists of Ag and a remainder thereof consists of Fe and impurities which are inevitable in manufacturing, it is thermally treated at a temperature range of 800 t0 1100 deg.C. Thereby, high characteristic, especially high coercive force can be acquired. Furthermore, Fe is partially displaced with Co of 50% or less.

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 containing R (where R is at least one kind of rare earth element containing Y), Fe, B and Ag as raw material basic components.

[0002]

2. Description of the Related Art As one of methods for manufacturing an R-Fe-B system permanent magnet, a manufacturing method has been proposed in which a cast ingot is hot-worked to be anisotropic.

Japanese Patent Laid-Open No. 64-704 discloses R, Fe, B,
After melting and casting an alloy containing Cu as a basic component, the cast ingot is subjected to hot working at a temperature of 500 ° C or higher to refine the crystal grains and to orient the crystal axis (axis of easy magnetization) in a specific direction. At least, a rare earth-iron-based permanent magnet is disclosed which is characterized by magnetically anisotropy of the cast alloy. Japanese Unexamined Patent Publication No. 2-250922 discloses a manufacturing method capable of achieving high characteristics by hot rolling a cast ingot and then performing a two-step heat treatment from high temperature to low temperature.

As a conventional technique using Ag as an additive element, Japanese Patent Laid-Open No. 2-3206 can be cited. In this patent, 8 to 30% R, 2 to 28% B, and 6% or less M (where M is at least 1 of Cu, Ag, Au, and Zn).
A manufacturing method is disclosed in which an ingot composed of seeds is hot-worked and then heat-treated at 250 ° C. or higher. As the effect of adding Ag, the effect of lowering the melting point during hot working and improving the degree of orientation is shown.

[0005]

By adding Ag to the R-Fe-B type alloy, the melting point of the grain boundary phase during hot working is certainly lowered. However, as a result of a detailed investigation by the present inventors, even an alloy in the composition range shown in the above-mentioned JP-A No. 2-3206, does not necessarily improve the degree of orientation depending on the composition, In some cases, the magnetic properties remained low.

Further, also in the heat treatment temperature, there is a problem that the coercive force remains at a very low value unless the temperature range is properly selected.

The present invention solves the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a high-performance and low-cost rare earth permanent magnet and a manufacturing method thereof.

[0008]

The method of manufacturing a permanent magnet according to the present invention uses 10 to 20% R in terms of atomic percentage (where R is Y).
At least one of rare earth elements including) 4 to 8% of B,
4% or less (excluding 0) Ag and the balance Fe
And other alloys containing inevitable impurities,
After melting and casting, the cast ingot is hot-worked at a temperature of 500 ° C. or higher, and then heat-treated at a temperature range of 800 to 1100 ° C.

Further, it is characterized in that 50 atomic% or less of Fe is replaced with Co.

[0010]

First, the reasons for limiting the alloy composition range of the present invention will be described. R is preferably 10 to 20%. If the addition amount is less than 10%, the main phase R
Other ₂ Fe ₁₄ B phase, in remaining magnets tissue of alpha-Fe is a soft phase, with the formation of R ₂ Fe _{1 7} phase lowers the coercive force occurs, the liquid in the hot working temperature The degree of orientation is not increased due to the decrease in the phase amount, and the magnetic properties are insufficient. On the contrary, when R is more than 20%, the hydrostatic stress due to the liquid increases with the excess amount of the liquid phase, which hinders the uniaxial orientation of the main phase crystal grains.

When the amount of B is less than 4%, the amount of main phase is not sufficient, so that the magnetic potential is low, and R ₂ Fe
A soft magnetic phase such as the _17th phase is likely to appear, resulting in a decrease in coercive force. If the addition amount is more than 8%, the crystal grain size in the cast ingot becomes coarse and the hot workability is remarkably reduced.

As described above, Ag improves the hot workability by lowering the melting point of the liquid phase during hot working. Further, the grain size of the main phase in the cast structure can be reduced, which greatly contributes to the improvement of magnetic properties. However, if the added amount exceeds 4%, the residual magnetic flux density is reduced due to the decrease of the magnetic phase, and the coercive force is also reduced. Therefore, the added amount is preferably 4% or less.

Co is an element effective in increasing the Curie point in the R-Fe-B system magnet, and basically replaces the Fe site in the main phase, but since the anisotropic magnetic field becomes small, it is added. The coercive force decreases as the amount increases. Therefore, it is desirable that the added amount be 50 atomic% or less.

Next, the manufacturing method will be described.

In the method for producing a magnet of the present invention by the casting / hot working method, first, the hot working of the cast ingot is preferably performed at the recrystallization temperature of the main phase or more in order to secure sufficient workability, 500 ° C for the alloy of the present invention
It is desirable to set the above.

Next, heat treatment conditions after hot working will be described. The above-mentioned Japanese Patent Application No. 2-250922 discloses a manufacturing method capable of achieving high characteristics by hot rolling a cast ingot and then performing a two-step heat treatment from a high temperature to a low temperature. However, such a two-step heat treatment causes C as an additional element.
As a result of the experiments conducted by the present inventors, it was revealed that the coercive force was lowered when Ag was added, although it is true when u is selected.

More specifically, it was revealed that a high coercive force can be obtained by performing a heat treatment at 800 to 1100 ° C. after hot working, and a coercive force is lowered when a subsequent low temperature heat treatment is performed. In other words, in the case of adding Ag, a high coercive force can be obtained by performing only one heat treatment after hot working. It is not yet clear exactly why such a difference in heat treatability occurs between Cu and Ag. However, looking at the magnet structures of both heat treated at 1000 ° C., in the structure with Cu added, the main phase grains grow and the main phases become a state of diffusion bonding, and the separation between the grains is very poor. . Therefore, it is considered that the Cu-added magnet has a tendency that the magnetic flux density increases after the high temperature heat treatment, but the coercive force decreases.
On the other hand, in the case of the Ag-added magnet, which was also heat-treated at 1000 ° C., homogenization of the entire structure was achieved, but grain growth of the main phase did not occur unlike the Cu-added magnet, and The phases are separated well. It is considered that such a difference in phenomenon is caused by various properties such as wettability between the main phase and the liquid phase depending on the additive element.

When the heat treatment is performed at a temperature lower than 800 ° C., α-Fe which is a soft magnetic phase existing in the main phase grains is used.
Does not disappear completely due to diffusion, which adversely affects the magnetic properties. Further, the coercive force is lowered due to the change of the state of the grain boundary phase. On the contrary, at a temperature higher than 1100 ° C, the main phase crystal grains are abruptly coarsened and the magnetic properties are deteriorated, so that it is necessary to set the temperature range to 800 to 1100 ° C.

The cooling rate after the heat treatment in the temperature range of 800 to 1100 ° C. is preferably to prevent the decrease of the coercive force by shortening the time for passing through the region of 800 ° C. or less as described above. It is desirable to

Next, examples of the present invention will be described.

[0021]

【Example】

(Example 1) After melting and casting an alloy having the composition shown in Table 1,
A sample was cut out from the ingot and subjected to hot pressing at a strain rate of 1 × 10 ^-2 s ^{-1 in} an argon atmosphere at 950 ° C with a final working ratio of 80%. The pressing direction during hot pressing was perpendicular to the columnar crystal structure development direction. Pressed sample 1000 ℃ × 12 in argon atmosphere
After heat treatment for h, remove it from the heating furnace and remove it by 2.8 barr.
Pressure cooling was performed in argon. At this time, the cooling rate was about 20 ° C./min, indicating a sufficient rapid cooling. The magnetic characteristics obtained as a result are shown in Table 2. As is clear from the table, high magnetic properties can be obtained in the samples whose alloy composition is in the composition range of the present invention.

[0022]

[Table 1]

[0023]

[Table 2]

(Example 2) Pr _15.5 Fe _78.5-x B _5.0 A
FIG. 1 shows the relationship between the addition amount (x) of Ag and the coercive force and energy product of a sample obtained by hot pressing and heat treating an ingot having an alloy composition of g _{x under} the same conditions as in Example 1. As is clear from the figure, it is possible to obtain a high coercive force and a high energy product when the added amount is 4 atomic% or less (excluding 0).

Example 3 An alloy ingot having the composition No. 1 in Table 1 was hot-pressed under the same conditions as in Example 1, and then in an argon atmosphere at 500 to 1200 ° C.
Heat treatment was performed for 12 hours at each temperature, and then cooling was performed under the same conditions as in Example 1. The relationship between the coercive force obtained at this time and the heat treatment temperature is shown in FIG.

As can be seen from the figure, the heat treatment temperature is 800 to 1
It becomes possible to obtain a high coercive force by carrying out in the temperature range of 100 ° C.

Example 4 Alloys having the compositions shown in Table 1 were
Melts using a high frequency induction melting furnace in an argon atmosphere,
Then, it was cast in a water-cooled copper mold to obtain an ingot with a wall thickness of 20 mm. In the cast structure, a structure in which columnar crystals developed in the thickness direction of the ingot was formed.

Next, the cast ingot thus obtained was cut into a predetermined size, put in a sheath made of low carbon steel (SS41), deaerated and sealed. After heating and holding this in an atmospheric furnace at 950 ° C, hot rolling with a working rate of 30% was performed 4 times in air so that the rolling direction was perpendicular to the columnar crystal development direction, and finally working The degree is 76%.
Further, during this hot rolling, the easy axis of magnetization of the main phase (R ₂ Fe ₁₄ B phase) was oriented so as to be parallel to the pushing direction of the alloy.

Table 3 shows the magnetic characteristics of each of the obtained rolled materials after the same heat treatment (1000 ° C. × 12 hours) and cooling as in Example 1.

[0030]

[Table 3]

Also in the magnet produced by the casting / hot rolling method as described above, a rare earth permanent magnet having good magnetic properties can be obtained when the alloy composition is within the composition range of the present invention.

Example 5 An ingot having the alloy composition shown in No. 1 of Table 1 was hot-rolled under the same conditions as in Example 4. About the obtained rolled material sample in Ar atmosphere
After performing heat treatment for 12 hours at each temperature of 500 to 1200 ° C., it was taken out of the heating furnace and pressure cooled in an argon atmosphere of 2.8 barr. The relationship between the coercive force and the heat treatment temperature at this time is shown in FIG.

As is clear from the figure, a high coercive force can be obtained by performing the heat treatment after hot rolling in the temperature range of 800 to 1100 ° C.

Example 6 Ingots having the alloy compositions shown in Nos. 1 to 5 in Table 1 were hot-rolled under the same conditions as in Example 4, and the obtained rolled material sample was heated to 1000 in an Ar atmosphere. The heat treatment was performed at ℃ × 12h. Regarding the cooling after this heat treatment, the magnetic properties obtained were measured for two types of samples, a sample cooled under pressure in an argon atmosphere of 2.8 barr and a sample cooled in a heating furnace. The results are shown in Table 4.
The cooling rate for argon pressure cooling is approximately 20 ° C / m.
In the case of furnace cooling, the cooling rate was about 3 ° C / min.

[0035]

[Table 4]

As is apparent from the table, high magnetic characteristics can be obtained by sufficiently increasing the cooling rate after the heat treatment.

[0037]

As described above, according to the present invention, R, Fe,
An alloy ingot with B and Ag in the proper composition range as the basic components of the raw material is hot-worked at a temperature of 500 ° C or higher, and further 800
By taking the manufacturing method of heat treatment at ~ 1100 ° C,
The advantages of the casting / hot working method that the magnetic properties superior to the conventional ones can be obtained and the process can be shortened and a high-performance magnet can be obtained at low cost are further promoted.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of added Ag and magnetic properties.

FIG. 2 is a diagram showing the relationship between coercive force and heat treatment temperature in a hot press magnet.

FIG. 3 is a diagram showing the relationship between coercive force and heat treatment temperature in a rolled magnet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Akioka 3-3-5 Yamato, Suwa, Nagano Seiko Epson Corporation

Claims (2)

[Claims] 1. Atomic percentage of 10 to 20% R (where R is at least one rare earth element including Y), 4 to 8%
B, 4% or less (excluding 0) of Ag, and the balance Fe and other alloys unavoidable in manufacturing, after melting and casting, the cast ingot is hot worked at a temperature of 500 ° C or higher. And a heat treatment in the temperature range of 800 to 1100 ° C. 2. The method for producing a permanent magnet according to claim 1, wherein 50 atomic% or less of Fe is replaced with Co.