JP3175841B2 - Manufacturing method of permanent magnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a permanent magnet,
The present invention relates to a method for producing an Fe—B based sintered magnet (R is at least one rare earth element including Y).

[0002]

2. Description of the Related Art R-Fe-B sintered magnets are used to reduce a powder alloy obtained by a reduction diffusion method or an alloy powder obtained by pulverizing an alloy obtained by a melting method to 1 to 20 μm. It is obtained by pulverizing, shaping the product while orienting it in a magnetic field, then sintering, and subjecting it to a heat treatment.

[0003] Such R-Fe-B-based sintered magnets have the advantage that raw materials are inexpensive and their magnetic properties are larger than those of conventional SmCo-based magnets, but they have the property of being extremely rust-resistant. . For this reason, when it becomes fine powder in the process, the surface area becomes large, and the fine powder is very easily oxidized and handling becomes difficult.

In order to improve such a point, R-Fe
In preparing the -B based sintered magnet, be handled in a non-oxidizing gas such as N ₂ is generally performed. However, the complete sealing of the process equipment is difficult to achieve, especially in the case of mass production, giving more or less opportunities for the fines and compacts to be exposed to oxygen and moisture in the air.

Until now, it has been considered that contact with oxygen or moisture in the air increases the amount of oxygen in the magnet and deteriorates the magnetic characteristics. From this viewpoint, it is considered that the amount of oxygen is regulated. A proposal has been made (JP-A-62-625).
03). It is also considered that the amount of oxygen varies depending on the degree of exposure to oxygen and moisture in the air, and that not only the magnetic properties but also the dimensions and strength of the magnet and the quality such as moisture resistance vary.

[0006]

However, when the molded body comes into contact with the air, especially moisture, after molding and before sintering, even if the amount of oxygen in the obtained sintered magnet is kept constant, The strength of the body and the strength of the sintered body are not sufficient, and the dimensions of these and the sintered body vary, sintering defects such as cracks and chips occur, and the moisture resistance and stability of the magnet Or lower.

[0007] The main object of the present invention is to facilitate the process control, to have a high strength of the compact and sintered body, to stabilize the strength and the size of the sintered body, and to prevent sintering defects such as cracks and chips. An object of the present invention is to provide a method for producing an R-Fe-B based sintered magnet which does not occur, exhibits good and stable molding or sinterability, has high moisture resistance and stability, and has stable quality.

[0008]

This and other objects are achieved by the present invention which is defined below as (1) and (2). (1) A raw material powder as a starting material is obtained, and the raw material powder is molded to obtain a molded body. The molded body is exposed to an atmosphere having a water content of 0.005 g / liter or more for 1 minute or more, and then sintered. ,
R (where R is at least one of the rare earth elements including Y
Seed), a method for producing a permanent magnet containing Fe and B, wherein the amount of RN in the starting material is regulated,
A method for producing a permanent magnet, wherein the N content of a starting material is adjusted to 10 to 40 ppm to enhance the strength of a compact. (2) The method for producing a permanent magnet according to the above (1), wherein the content of N in the permanent magnet is 10 to 250 ppm.

[0009]

[0010]

[0011]

According to the present invention, the amount of N in the R-Fe-B alloy as a raw material is restricted to 10 to 40 ppm. This is based on the finding that the amount of N in the raw material alloy has a large effect on the change over time of the powder during the process, the corrosion resistance of the magnet body, and the like.

In the R—Fe—B sintered magnet, the finer the particle size of the fine powder, the better the coercive force and magnetizing performance of the magnet.
If the fineness is too small, the degree of oxidation increases and the coercive force deteriorates. Therefore, an average particle size of about 2 to 5 μm is often used in consideration of both. However, when comparing the time-dependent changes in the amount of O ₂ during the process, it was found that N in the composition had a great effect even with the same particle size. Since the R-Fe-B based sintered magnet allows oxygen up to several thousand ppm, it seems that such a phenomenon has been overlooked in the past.
However, the greatest influence of N in the composition is that the properties of the powder and the green compact change every moment due to the moisture in the air, causing variations in the quality of the magnet.

[0013] N in the raw material alloy is provided by the raw material metal, particularly the rare earth metal. It is believed that N exists in the form of rare earth nitride RN. The rare earth nitride is stable even at high temperatures and remains after the melting step. When the alloy containing the remaining N is pulverized, the pulverization is usually performed in an atmosphere of N ₂ or a solvent, so that the nitride does not change or deteriorate.

However, once in contact with air after the pulverization, the nitride undergoes the following reaction to become a gas and diffuse into the air, pass through the rare earth hydroxide, and become a rare earth oxide in the powder or green compact. It is estimated that it will remain. RN + 3H ₂ O → NH ₃ ↑ + R (OH) ₃

This reaction is known as a chemical reaction of rare earths. However, several tens to several hundreds of ppm of nitride in the alloy cause the strength, sintering size and strength of the compact, and the reliability of the final product. It was unpredictable to get involved.

Further, the following problems can be cited as contributing factors that have confused such a problem and that the influence has not been regarded as a problem during the nitride process. That is, in the analysis of nitrides, it is difficult to quantify the trace amount of N discussed here unless the sample is measured in an inert gas so as not to come into contact with the air. In addition, nitrides are being reduced due to more or less exposure to air during the manufacturing process. Furthermore, since N ₂ gas is used during the process to prevent oxidation, there is adsorption N to the powder. These adsorbed N _2, unlike N of the nitride, do not adversely affect the process or the product. Further, since the amount of the nitride is small, even if the above reaction occurs, the amount of generated ammonia is small and it is difficult to detect ammonia. From these facts, although the amount of N in the product was a problem, the adverse effect of the nitride during the process was not considered to be a problem in the past.
Is present to some extent, and when it comes into contact with air, the generation of ammonia can be confirmed as an ammonia odor.

Incidentally, as for N in the magnet, as described in the above-mentioned publication, a proposal has been made to regulate the amount of N in the product. However, this is due to magnetic properties,
As in the present invention, there has been no attempt to improve the moisture resistance and stability of the powder and the magnet body obtained by suppressing N as a nitride in the raw material to a very small amount.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The permanent magnet of the present invention comprises R, Fe and B.
R (R is at least one of rare earth elements including Y) 27 to 38, Fe 51 to 72, B
It is preferable that the content of nitrogen is 0.5 to 4.5, furthermore, it is composed of unavoidable impurities and the content of nitrogen is 10 to 250 ppm.

When the R content decreases, an iron-rich phase precipitates and the coercive force decreases. When the R content increases, the residual magnetic flux density decreases. As the B content decreases, the coercive force decreases. When the B content increases, the residual magnetic flux density decreases. In addition, 3 of Fe
0% by weight or less may be replaced by Co. Further, Al,
Cr, Mn, Mg, Si, Cu, C, Nb, Sn, W,
Addition elements such as V, Zr, Ti, and Mo can improve the coercive force by adding a small amount, but if the addition element is more than 6% by weight, the residual magnetic flux density decreases.

When the content of nitrogen is 10 to 250 ppm, it is possible to prevent the R-Fe-B permanent magnet from improving the moisture resistance, particularly preventing rusting due to the improvement in the moisture resistance caused by the magnet body itself. . The oxygen content is 6000 ppm or less,
In particular, it is preferably 2500 to 4500 ppm.
The permanent magnet in the present invention has a main phase having a substantially tetragonal crystal structure. The particle size of this main phase is 1 to 100 μm
It is preferred that it is about. And usually, the volume ratio is 1
It contains about 50% of a non-magnetic phase.

As a method for controlling the nitrogen level in the magnet, a raw material having a low nitrogen content is used. That is, the amount of N in the raw material is restricted to 10 to 40 ppm.

The raw material used may be a powder alloy obtained by a reduction diffusion method. Such powder is 1
It is obtained with a particle size of about 0 to 500 μm.

Alternatively, an alloy having a desired composition may be cast to obtain an ingot, and the obtained ingot may be roughly pulverized to a particle size of about 10 to 500 μm by a stamp mill, a hydrogen absorbing pulverization method, or the like.

In these, the amount of N in the alloy, the coarsely pulverized powder, or the finely pulverized powder described later is regulated. The oxygen content in the alloy is 50 to 2000 ppm or less, especially 50 to 2000 ppm.
Preferably, it is 500 ppm. The measurement of the amount of N and O may be performed by a method of melting in an inert gas and detecting the thermal conductivity. Next, these are finely pulverized by a jet mill, a ball mill or the like to a particle size of about 0.5 to 5 μm, especially about 12 to 5 μm. At this time, it is preferable that the jet mill is performed in an N ₂ atmosphere, and the ball mill is performed in a solvent such as acetone, alcohol, and toluene.

The obtained powder is formed preferably in a magnetic field. In this case, the magnetic field strength is preferably 10 kOe or more, and the molding pressure is preferably about 0.5 to ³ t / cm ² .

Next, the molded body is heated at 1000 to 1200 ° C.
And quenched for 0.5-5 hours. The sintering atmosphere is preferably an inert gas atmosphere such as Ar gas or a vacuum. After that, aging treatment is preferably performed at 500 to 900 ° C. for 1 to 5 hours in an inert gas atmosphere or vacuum.

In such a case, before sintering, the compact is 0.005 g / liter or more, usually 0.007 g / liter.
It is exposed to an atmosphere containing 1 to 0.02 g / liter of water for 1 minute or more, usually about 3 minutes to 5 hours. Prior to molding, it is preferable to perform each step in an atmosphere of an inert gas such as N ₂ or Ar, and doing so does not require much labor in the step management. On the other hand, storing the compact completely in an inert gas atmosphere after molding and before sintering is almost impossible to implement on a merchandise storage system in mass production, and the compact is exposed to the above moisture atmosphere. There is an extremely large advantage in mass production in that it is acceptable.

In the present invention, since the amount of N in the raw material powder is regulated to 10 to 40 ppm as described above, the reaction between the RN compound and water can be neglected, and the above-mentioned molding or sintering properties and the like can be reduced. It improves the stability or the corrosion resistance and stability of the magnet.

[0029]

The present invention will be described below with reference to examples. Example 1 An alloy ingot having a composition of 30Nd3Dy65.8Fe1.2B at a weight percentage of 30 Nd3Dy65.8Fe1.2B was produced by a melting method in an Ar gas atmosphere. The N content of the ingot was changed as shown in Table 1 below by changing the starting materials. Using these ingots, magnetization was carried out through ordinary sintering processes of crushing, coarse grinding, fine grinding, molding in a magnetic field, sintering, and heat treatment.

In this case, the coarse pulverization was performed by a hydrogen storage method, and the coarse pulverized powder had an average particle diameter of 30 μm. In addition, fine pulverization is performed using N ₂
Average particle size of finely pulverized powder is 3μ by jet mill in air stream
m. This powder is 1.5 ton / cm in a magnetic field of 10 kOe.
Pressing at a pressure of ² and molding in a magnetic field. In the process from crushing to molding, contact with air is blocked, and after molding,
C. and an atmosphere of 0.01 g / liter of water (20.degree. C., relative humidity 60%) for 3 minutes.

Thereafter, the molded body is placed in an Ar atmosphere at 1100.
Sintering at 300 ° C. for 3 hours, and after quenching, it is
Aging treatment was performed at 0 ° C. for 3 hours to obtain a magnet having a diameter of 11 mm × 4 mm.

Table 1 shows the strength of the compact after moisture contact and the strength of the sintered compact (average value of five samples). In this case, the measurement of the strength of the molded body was performed in N ₂ . Table 1 shows the results of measuring the amounts of N and O in the sintered body by gas analysis. Gas analysis was performed by a method of melting in an inert gas and detecting thermal conductivity. Table 1 shows that the moisture atmosphere is 0.
The strength of the molded body when it is changed to 003 g / liter (20 ° C., 17% relative humidity) is also described.

[0033]

[Table 1]

From the results shown in Table 1, the effect of the present invention is clear. When the N content in the raw material was 400 ppm or more, the smell of ammonia could be confirmed after contact with water.

Example 2 31.5 Nd1.5 Dy65.8 Fe1.
An alloy powder having a composition of 2B was obtained by a reduction diffusion method. On this occasion,
The nitrogen content of the alloy powder was changed as shown in Table 2. This was finely pulverized by an Ar + N ₂ jet airflow pulverization method, and further molded in a magnetic field as in Example 1. After this, 25
° C, moisture atmosphere of 0.008 g / liter (relative humidity 3
5%) for 3 hours, followed by sintering as in Example 1.
It was magnetized through a heat treatment process. Table 2 shows the strength of the compact.

[0036]

[Table 2] From the results shown in Table 2, the effect of the present invention is clear.

Example 3 The magnet produced in Example 1 was subjected to electrolytic Ni plating at 10 μm. Next, Table 3 shows the results of a humidity resistance test conducted at 85 ° C. and a relative humidity of 85% for 500 hours.

[0038]

[Table 3] From the results shown in Table 3, the effect of the present invention is clear.

[0039]

According to the present invention, since the contact between the compact and the moisture is allowed, the process control becomes easy. In addition, the time-dependent change of the pulverized powder due to moisture in the air is reduced, and stable production can be performed. And the strength of the compact at the time of compacting is improved, and there is no deterioration with time of the strength, and a product free from chips and cracks can be obtained. Then, the moisture resistance of the magnet body is improved, and a highly reliable product is obtained.

Claims (2)

(57) [Claims] 1. A raw material powder as a starting material is obtained, the raw material powder is molded to obtain a molded body, and the molded body is exposed to an atmosphere having a water content of 0.005 g / liter or more for 1 minute or more, and then sintered. And R (where R is at least one rare earth element containing Y), a permanent magnet containing Fe and B, wherein the amount of RN in the starting material is regulated, A method for producing a permanent magnet, comprising increasing the strength of a molded body by making the N content of Nb to 10 to 40 ppm. 2. The N content in a permanent magnet is 10 to 250.
The method for producing a permanent magnet according to claim 1, wherein the amount is ppm.