JPH0897020A - Manufacture of rare earth-iron-nitrogen permanent magnet - Google Patents

Abstract

PURPOSE: To suppress the deposition of αFe and to enhance magnetic characteristics by limiting the nitriding temperature, gas pressure, hydrogen concentration and grain diameter in the nitrification using the mixed gas of nitrogen and hydrogen. CONSTITUTION: In the manufacture of a rare earth-iron-nitrogen magnet which is obtained by nitridizing the alloy indicated by Ke2 TM17 (Re indicates rate-earth metal mainly composed of Sm, TM indicates one or more kinds of transition metals mainly composed of Fe) by the mixed gas of nitrogen and hydrogen, the grain diameter of Re2 TM17 alloy powder to be nitrided is 75μm or smaller, the mixture ratio of hydrogen against nitrogen of the mixture gas to be used is 5 to 30%, Re2 TM17 alloy powder is heated up to 350 to 430 deg.C in the mixture gas pressure of 20atm or higher and nitrided in the rare earth-iron-nitrogen permanent magnet manufacturing method. As a result, an anisotropic rare-earth magnet, having high magnetic characteristics, can be produced at low cost.

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 rare earth-iron-nitrogen permanent magnet which is a raw material powder for a rare earth bonded magnet, and more particularly to a method for nitriding a rare earth-iron alloy.

[0002]

2. Description of the Related Art Recently, it has been known that rare earth-iron based permanent magnets produce excellent magnetic properties by containing nitrogen in their alloys. The nitriding method is mainly disclosed in JP-A-2-
Mixed gas of ammonia and hydrogen as seen in Japanese Patent No. 57663, high-pressure pure nitrogen gas as seen in Japanese Patent Laid-Open No. 4-325652, and nitrogen as seen in Examples of Japanese Laid-Open Patent Publication No. 5-275219. It is performed by a solid phase-gas phase reaction such as a mixed gas of hydrogen.

[0003]

However, when a mixed gas of ammonia and hydrogen is used, nitriding can be performed relatively quickly, but the unit cost of the gas itself is high and the amount of use is large, so the production cost is high and Since hydrogen is used at a concentration, there is a problem in safety. Further, when high-pressure pure nitrogen gas is used, the above problems are cleared, but there are problems such as long reaction time and easy generation of αFe due to oxidation due to residual oxygen or moisture on the powder surface or in the electric furnace. there were. As another nitriding method, a mixed gas of nitrogen and hydrogen is used, but in this method, when the reaction system is at normal pressure, the rare earth-iron-based alloy is decomposed by nitrogen gas,
Since the reducing power of hydrogen is weak, the alloy is oxidized to generate αFe, and when the hydrogen concentration is increased to increase the reducing power, nitrogen is not sufficiently introduced, which causes problems.

Therefore, the present invention has been made in view of the above problems.
Even if a mixed gas of nitrogen and hydrogen is used, the temperature and pressure at which oxides and decomposition products are not produced, and by limiting the hydrogen concentration and the particle size of the alloy powder that can sufficiently introduce nitrogen even if hydrogen is mixed, It is an object of the present invention to provide a manufacturing method by which an anisotropic rare earth magnet having high magnetic properties can be obtained.

[0005]

In order to achieve the above object, in the present invention, a solution of a raw material alloy represented by the chemical formula Re ₂ TM ₁₇ (Re is a rare earth metal, TM is a transition metal) is coarsely crushed. Then, nitriding is performed by applying a mixed gas in which the ratio of high-purity hydrogen is 5% to 30% with respect to high-purity nitrogen between 350 ° C. and 430 ° C., and high pressure of 20 atm or higher. In addition, at this time, a step of nitriding the Re ₂ TM ₁₇ alloy powder to 75 μm or less and then nitriding or selecting after nitriding is included.

Here, the nitriding temperature is limited to 350 ° C. or higher and 430 ° C. or lower, because when nitriding is performed at a temperature of 430 ° C. or higher, α in the rare earth-iron alloy due to oxidation due to residual oxygen.
This is because precipitation of Fe increases and nitrogen is not sufficiently introduced at 350 ° C or lower. Further, the mixed gas pressure in the nitriding reaction was set to a high pressure of 20 atm or more because the rare earth-iron alloy of the raw material powder reacts with nitrogen, and the rare earth nitride and αFe
This is to prevent decomposition into hydrogen and to effectively use the reducing power of hydrogen. Further, the hydrogen concentration is limited to 5% or more and 30% or less because if 30% or more of hydrogen is present in the furnace, an unnitrided phase remains inside the particles even if it is nitrided at a high temperature for a long time to deteriorate the magnetic properties. This is because if it is 5% or less, the reducing power is insufficient and αFe is generated. Therefore, only when nitriding is performed within the range of the above conditions, a magnet having good magnetic characteristics can be obtained with a particle size of 75 μm or less (desirably 53 μm or less).

[0007]

EXAMPLES The present invention will be described in detail below with reference to examples.

Purity 99.9% Sm and purity 99.9%
Fe metal was melt-mixed in a high-frequency melting furnace in an argon atmosphere so that the weight ratio was 24.5: 75.5, and then the molten metal was poured into a mold and cooled. Further, by annealing at 1250 ° C. for 3 hours in an electric furnace in an argon atmosphere, a Sm ₂ Fe ₁₇ system alloy was obtained. The obtained alloy is subjected to solution treatment at 1250 ° C. for 30 hours in an argon atmosphere, and after cooling, has a particle size of 106 μm with a jaw crusher.
The powder was pulverized to obtain Sm ₂ Fe ₁₇ based alloy powder as a raw material powder.

(Example) This Sm ₂ Fe ₁₇ alloy powder was heated to 400 ° C. in an electric furnace at a purity of 99 at 50 atm.
9999% nitrogen gas 90%, and purity 99.9999
After nitriding for 100 hours in a mixed gas containing 10% of hydrogen gas, the mixture was cooled to room temperature. This 106
32 μm or less, 32-53 μm,
3 to 75 μm, 75 to 106 μm, 5 of 106 μm or more
Classified into stages.

(Comparative Example 1) Sm ₂ Fe used in Examples
Nitriding was performed under the same conditions as in the example except that the raw material powder of the ₁₇ series alloy powder was used, the purity of 99.9999% and the nitrogen gas of 100% were used instead of the mixed gas. Obtained 106μ
m or less nitride powder 32 μm or less, 32-53 μm, 5
3 to 75 μm, 75 to 106 μm, 5 of 106 μm or more
Classified into stages.

Comparative Example 2 Sm ₂ Fe used in the examples
Purity 99.9999% using the raw material powder of ₁₇ series alloy powder
Nitrogen gas was used under the same conditions as in Example and Comparative Example 1 except that a mixed gas of 50% nitrogen gas and 50% hydrogen gas was used. The obtained nitriding powder of 106 μm or less is 32 μm or less, 32-53 μm, 53-75 μm, 75
It was classified into 5 stages of ˜106 μm and 106 μm or more.

The state of nitriding and precipitation of αFe was analyzed by an X-ray diffractometer for the nitride powders obtained in Examples and Comparative Examples 1 and 2. The analysis result of the nitride powder obtained in the example is shown in FIG.
The results of Comparative Example 1 are shown in FIG. 2, and the results of Comparative Example 3 are shown in FIG.
As can be seen from FIG. 2, in Comparative Example 1 where nitriding was performed with 0% hydrogen, αFe was often precipitated due to oxidation, and in Comparative Example 2 where nitriding was performed with 50% hydrogen, Sm ₂ Fe ₁₇ which is an unnitrided layer was observed in FIG. You can see it remains. In the embodiment of the present invention shown in FIG. 1, almost no αFe or Sm ₂ Fe ₁₇ was observed, and neither the unnitrided layer nor the decomposition due to oxidation occurred. In addition, 32-53 μm, 53-, obtained in Examples, Comparative Examples 1 and 2,
The nitrogen and oxygen contents of 75 μm and 75 to 106 μm nitride powder were analyzed by a nitrogen / oxygen analyzer. As a rare earth-iron-nitrogen based magnet, it is desirable that the content of nitrogen is large and the content of oxygen is as small as possible. The results are shown in Table 1. The nitride powder obtained according to the present invention had a smaller amount of oxygen than Comparative Example 1 and a larger amount of nitrogen than Comparative Example 2, and the examples of the present invention satisfied both values.

[0013]

[Table 1]

32-53 μm, 53-75 μm, 75-106 μm obtained in Examples, Comparative Example 1 and Comparative Example 2
Each of the nitriding powders of No. 1 was finely pulverized with a jet mill to an average particle size of 3 μm or less. 3 wt% of epoxy resin in the obtained fine powder
Mix and outline 4m at 10t / cm ² in 20kOe magnetic field.
An anisotropic rare earth magnet was manufactured by molding into a size of m × 4 mm × 2 mm and curing at 150 ° C. for 2 hours. The manufactured magnet was used to measure the residual magnetism (B
r), coercive force (iHc), and maximum energy product (B
H) magnetic properties such as max were measured. The results are shown in Table 2.
Shown in. In the examples of the present invention, the magnetic properties such as (BH) max were significantly higher than those of the comparative examples especially at 75 μm or less.

[0015]

[Table 2]

[0016]

As described above, according to the present invention, the nitriding temperature, the gas pressure, the hydrogen concentration, and the particle size in the nitriding with the mixed gas of nitrogen and hydrogen are limited, so that the conventional high-pressure pure nitrogen gas is used. While maintaining the same amount of nitrogen as a magnet, the precipitation of αFe can be further suppressed, resulting in significantly improved magnetic properties, which is safer and cheaper to manufacture than a magnet manufactured using a mixed gas of ammonia and hydrogen. can do.

[Brief description of drawings]

FIG. 1 is a graph showing a result of analyzing a nitride powder nitrided in an example of the present invention with an X-ray diffractometer.

FIG. 2 is a graph showing a result of analysis of a nitride powder nitrided in Comparative Example 1 with an X-ray diffractometer.

FIG. 3 is a graph showing a result of analyzing the nitride powder nitrided in Comparative Example 2 with an X-ray diffractometer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C22C 38/00 303 D H01F 1/04 (72) Inventor Hiroshi Ikeda 6-1, Honmachi, Tanashi, Tokyo No. 12 Citizen Watch Co., Ltd. Tanashi Factory

Claims (1)

[Claims] 1. An alloy represented by Re ₂ TM ₁₇ (wherein Re is a rare earth metal mainly composed of Sm and TM is one or more transition metals mainly composed of Fe) is nitrided with a mixed gas of nitrogen and hydrogen. In the method for producing the obtained rare earth-iron-nitrogen based magnet, the particle size of the Re ₂ TM ₁₇ alloy powder to be nitrided is 75 μm or less, and the mixed gas used has a hydrogen to nitrogen mixing ratio of 5% to 30%. Yes, the Re ₂ TM ₁₇ alloy powder
Within the mixed gas pressure of 0 atm or higher, 350 ° C to 43 ° C.
Rare earths characterized by heating to a temperature of 0 ° C and nitriding
Method for manufacturing iron-nitrogen permanent magnet.