JPH0774010A - Method for manufacturing permanent magnet powder - Google Patents

Abstract

(57) [Summary] [Purpose] To find a composition that replaces RT nitride,
Provided is a method for producing a permanent magnet powder, which can easily produce an ultrafine crystal powder for a magnet having the above coercive force and can easily handle the powder thereafter. [Structure] Coarse pulverized powder containing T as a main component and at least Pr or Nd as R and at least one of V and Mo and having a required structure is used as H ₂ gas alone or an inert gas (N ₂ (Excluding gas) and heat treatment in a mixture gas and H ₂ treatment for heating and holding in a predetermined atmosphere.
An average crystal grain size of 0.0
A powder having a texture of 5 to 0.5 μm can be formed, and handling of the powder in a later step becomes extremely easy. After that, nitriding is performed in a specific mixed gas of N ₂ and H _2. By magnetizing, the nitriding reaction is promoted and a high coercive force magnet is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel R (rare earth element) -T (iron group element) -MN system bond magnet having a high coercive force which can be used in various motors and actuators. The present invention relates to a method for producing a permanent magnet powder for a sintered magnet, in which a coarse pulverized powder of this system is subjected to heat treatment in a mixture of H ₂ gas alone or an inert gas (excluding N ₂ gas) and heating and holding in a predetermined atmosphere. R-T-M-N system that obtains low cost, excellent corrosion resistance, and high coercive force by performing a de-H ₂ treatment to obtain a textured powder having a fine crystal grain size and further performing a specific nitriding treatment. The present invention relates to a method for producing permanent magnet powder.

[0002]

2. Description of the Related Art As powders for Nd-Fe-B based permanent magnets, powders for magnets having an ultrafine structure obtained by a superquenching method, a mechanical alloying method, etc. have been used.
The Nd-Fe-B system permanent magnet powder has a Curie point (T
Since c) is as low as around 300 ° C. and the temperature coefficient of Br and iHc is large, it is possible to raise Tc by adding Co or the like to improve the temperature coefficient of Br, but the temperature coefficient α of Br is at most − The limit was about 0.08 / deg.

Recently, the R ₂ Fe ₁₇ compound has occluded N ₂ to increase Tc nearly twice as much as an absolute temperature, resulting in Nd-
160 ° C higher than Tc of Fe-B system, and further Sm ₂
It has been reported that the Fe ₁₇ nitride can provide an anisotropic magnetic field exceeding the anisotropy of R ₂ Fe ₁₄ B.

[0004]

The above-mentioned Sm ₂ Fe ₁₇ nitride cannot be used to produce a magnet powder capable of obtaining an iHc of 6 kOe or more, which is practically required, by a conventional production method. Since the powder for magnets can be obtained only by a special manufacturing method such as a mechanical alloying method, there is a problem in mass production on an industrial scale.

Further, since the reaction rate of the nitriding reaction for obtaining the Sm ₂ Fe ₁₇ nitride is slow, the raw material powder must be finely pulverized to 10 μm or less before the nitriding treatment so that N atoms can reach the inside of the powder. The above-mentioned finely pulverized powder of 10 μm or less that does not diffuse is difficult to handle in the subsequent step, and unless careful attention is paid, there is a problem that it is ignited or easily oxidized to deteriorate the characteristics and further corrode. . Further, since Sm ₂ Fe ₁₇ nitride contains a large amount of Sm, which is a small amount of resources, there is a problem that it becomes relatively expensive, and there is a demand for permanent magnet powders containing abundant resources of other elements.

Recently, many patent applications have been filed for powders for R-T-M-N type permanent magnets. For example, JP-A-4
No. 308062 and Japanese Unexamined Patent Publication No. 4-308063 propose powders for magnets having a ThMu ₁₂ type crystal structure, but an RTMN-based ingot is crushed by mechanical crushing. Therefore, a powder having ultrafine crystals cannot be obtained, and improvement in magnetic characteristics cannot be expected. Further, JP-A-3-153852 and JP-A-3-16102 propose a magnet powder having a two-phase separation type crystal structure, and the addition of an additive element is also performed in the step before the nitriding treatment.

One of the applicants of the present invention is to manufacture an R-T-M-N-based permanent magnet powder which can easily produce an ultra-fine crystal powder for a magnet in advance, and can easily handle the powder thereafter and make a bond magnet. As a manufacturing method, an RT-M-N alloy ingot having a specific composition is roughly crushed to obtain a coarsely crushed powder having a specific average grain size having a specific crystal structure, and then hydrogen treatment under a specific condition, nitrogen After hydrogen treatment, the average crystal grain size is 0.05-
A method of nitriding in N ₂ gas under specific conditions after forming a powder having a texture of 0.5 μm is proposed (Japanese Patent Application No. 4-
No. 202935). However, in the above method, the nitriding speed is slow, and the temperature range in which the nitriding reaction occurs and the generated nitride become thermodynamically unstable and the decomposition temperature is close, so that the soft magnetic α-Fe phase is synthesized during synthesis. Was generated along with, and there was a risk that the magnetic characteristics would deteriorate.

The present invention is based on the previously proposed R-T-M-N.
After subjecting the coarsely pulverized alloy powder to hydrogen treatment and hydrogen nitriding treatment under specific conditions to obtain a powder having a texture with an average crystal grain size of 0.05 to 0.5 μm, in a N ₂ gas under specific conditions It is possible to solve the problems of the method of nitriding treatment with R, reduce the nitriding temperature, perform the nitriding reaction without promoting the decomposition, suppress the generation of α-Fe, and improve and improve the magnetic characteristics. It is an object of the present invention to provide a method for producing a -T-M-N based permanent magnet powder.

[0009]

DISCLOSURE OF THE INVENTION The inventors of the present invention have eliminated the drawbacks of the above method, lowered the nitriding temperature, and performed a nitriding reaction without promoting decomposition to suppress the formation of α-Fe, As a result of various studies on methods for improving and improving the magnetic properties, H atoms were first diffused into the powder having the texture by nitriding in a mixed gas of N ₂ and H ₂ under specific conditions, and crystallized. The present invention has been completed by finding that the lattice is expanded, and then N atoms diffuse while substituting H atoms, so that the nitriding rate can be improved and the nitriding temperature can be lowered.

The present invention provides R 7 at% to 9 at%
(R: at least one rare earth element and Pr or N
50% or more of 1 type or 2 types of d), T 76at
% To 89 at% (T: Fe or a part of Fe is 50%
Substituted with Co and Ni below), M 3.5 at% to 17
The ingot made of at% (containing at least one of M: Ti, V, Cr, and Mo) is roughly crushed to have an average particle size of 20 μm.
At least 80 vol% or more of 500 μm is ThMn ₁₂
After the coarsely pulverized powder made of a compound having a crystal structure is formed, the coarsely pulverized powder is converted into 0.1 atm to 10 atm (at room temperature) H ₂ gas or an inert gas (N ₂ gas) having an H ₂ partial pressure equal to that. (However, the total pressure is 10 atm or less at room temperature), 500 to 900 ° C for 30 minutes to 8
Heating and holding for an hour, and further holding at 500 ° C. to 900 ° C. for 30 minutes to 8 hours in a vacuum with a H ₂ partial pressure of 1 × 10 ⁻² Torr or less or in a gas mixture with an inert gas except N _{2 2}
And the average crystal grain size is 0.05 μm to 0.5 μm
To have a texture of 0.2 atm to 10 atm at room temperature and a H2 molar ratio of 1 to 9
40% in a mixed gas of N ₂ and H ₂ consisting of 5% and the balance N _2.
After being kept at 0 ° C to 600 ° C for 0.1 to 30 hours, it is cooled to R 7 at% to 9 at% and T 76 at% to 89a.
t%, M 3.5 at% to 17 at%, N 0.8 at
% To 20 at%, and a permanent magnet powder having a high coercive force is obtained.

[0011]

The present invention relates to an RTN-based permanent magnet,
As a result of various studies aimed at a method for producing a powder for a magnet, which is made of ultrafine crystals that can easily handle the powder and has a coercive force of 6 kOe or more, R- typified by Sm ₂ Fe ₁₇ N _{2 3}
The TN compound is about 0.3 μm from the RT compound, which is the base.
After making into a powder having a microcrystalline texture of about the critical diameter of single magnetic domain particles, nitriding treatment under a specific condition in a mixed gas of N ₂ and H ₂ is carried out, and an RTN permanent magnet having a high coercive force is obtained. It was found that a powder for magnets can be obtained. That is, when the inventors heat the RT alloy in H ₂ gas, the RT compound is decomposed into RH _{2 3} and α-Fe and the same RT compound as before is obtained by de-H ₂ treatment. Is produced, and at that time, the crystal grain size of the RT compound produced can be controlled by controlling the temperature and holding time of heating in H ₂ gas and de-H ₂ treatment, and then by nitriding treatment. It has been found that an R-T-N based permanent magnet powder having an ultrafine structure exhibiting high coercive force can be obtained.

Further, not only the R ₂ Fe ₁₇ compound but also the rare earth compound of the iron group element is subjected to heating in H ₂ gas under a specific condition and de-H ₂ treatment as described above to obtain a texture of ultrafine crystals. And the subsequent N ₂ diffusion treatment with a mixed gas of N ₂ and H _{2 under} specific conditions lowers the nitriding temperature and performs the nitriding reaction without proceeding the decomposition,
It has been found that the magnet characteristics can be controlled by suppressing the generation of α-Fe.

Further, as a result of various studies on the composition of the RT nitride typified by Sm ₂ Fe ₁₇ N _{2 (3)} , the main component is T and at least Pr or Nd is contained as R,
And R-T- having a composition containing at least one of V and Mo
It was found that M nitride can obtain an anisotropic magnetic field equivalent to that of R-T nitride, and by performing heating in H ₂ gas and de-H ₂ treatment under the above specific conditions, a novel NdFe ₁₀ V ₂ N
_The powder for RTN-M-N permanent magnets represented by _{0.1 1} is a powder having a texture with an average crystal grain size of 0.05 to 0.5 μm as it is as a coarsely pulverized powder having a required average grain size. It was found that not only the coercive force of 6 kOe or more can be obtained, but also the handling of the powder in the subsequent step becomes extremely easy, and the present invention was completed.

Reasons for Limiting Powder Composition In the powder composition of the present invention, the rare earth elements R are Y and L.
a, Ce, Pr, Nd, Sm, Gd, Tb, Dy, H
o, Er, Tm, and Lu are included, and at least one or more of these are R or 1 or 2 of Pr or Nd.
Content of 50% or more, and all of R is Pr or N
It may be d or Pr and Nd. The reason why 50% or more of R is one or two kinds of Pr or Nd is that one or two kinds of Pr or Nd cannot obtain sufficient magnetization when less than 50%. When used, it has an effect of reducing the raw material cost as compared with Sm. R
Is less than 7 at%, the coercive force is lowered by the precipitation of α-Fe, and if it exceeds 9 at%, the R ₂ Fe ₁₇ phase and the like are precipitated and the coercive force is deteriorated.

It is important that the iron group element T contains at least one of Fe, Co and Ni, and contains Fe in an amount of 50% or more of T. That is, when Fe in T is less than 50%, sufficient magnetization cannot be obtained, which is not preferable. Note that Co is 5 of T
It is particularly preferable to add less than 0% because the Curie temperature rises and the anisotropic magnetic field increases slightly. T is 76a
If it is less than t%, a compound having a low coercive force appears to lower the coercive force, and if it exceeds 89 at%, the coercive force due to α-Fe precipitation is lowered, so the content is set to 76 to 89 at%.

M, that is, at least one of V and Mo is an essential element that forms an RFe _12-x M _x compound having a ThMn ₁₂ type structure, and is less than 3.5 at% (x is less than 0.5). The R ₂ Fe ₁₇ phase and α-Fe are precipitated, whereby the desired compound cannot be obtained, and when the content exceeds 17 at% (x exceeds 2.0), the magnetization remarkably decreases, so that 3.5 to 17 at %.

When N is less than 0.8 at%, uniaxial anisotropy cannot be obtained, and when it exceeds 20 at%, the ThMn ₁₂ type structure becomes unstable, and the parent phase becomes R ₂ Fe ₁₇ phase or α-Fe. Since it is not preferable because it decomposes, it is set to 0.8 to 20 at%.

In the present invention, the average particle size is 20-50.
The reason why the coarsely pulverized powder consisting of the compound having a ThMn ₁₂ type crystal structure of at least 80 vol% of 0 μm is limited in the present invention is that the coarsely pulverized powder before heating in H ₂ gas under the above specific conditions is substantially It is necessary that the compound has a ThMn ₁₂ type structure, and a volume ratio of Th is 80% or more.
A Mn ₁₂ type compound is desirable. That is, when the composition alloy of the present invention is produced by the casting method, in addition to the ThMn ₁₂ type compound, α-Fe and Th ₂ Zn ₁₇ are contained in the ingot.
And coexist type, the coexistence ratio depends on the production conditions such as the ingot cooling conditions, coexistence ratio of H ₂ gas heating subsequent step, hardly changes depending removing H ₂ treatment or nitriding treatment. When such α-Fe phase and Th ₂ Zn ₁₇ type compound are present, the properties of the obtained magnet powder, particularly iHc, are deteriorated, so that 80Mn of the ThMn ₁₂ type compound is contained in the coarsely pulverized powder.
It is necessary that 1% or more is present. In order to obtain a coarsely pulverized powder having a volume ratio of 80% or more of the ThMn ₁₂ type compound, the as-cast ingot is heated to a temperature of 900 to 1200 ° C.
It can be appropriately selected by annealing for 50 to 50 hours, or by controlling the cooling condition of the mold when cooling the ingot in the ingot making process.

Reasons for limiting production conditions The present invention is characterized in that a coarsely pulverized powder having a required particle size does not change its size in appearance, and an aggregate having a fine crystal structure can be obtained. ₂ Essentially different from the occlusion crushing method. That is, ThMn ₁₂ type RT
When the -M compound is reacted with H ₂ gas at high temperature, R
When phase separation into H _{2 ₃ 3} , α-Fe, T-M alloy phase, and the like, and further removal of H ₂ gas by degassing, a recrystallized structure of the ThMn ₁₂ -type R-T-M compound is obtained again. The method of coarsely pulverized starting materials other conventional mechanical grinding method or a gas atomization method may be coarsely pulverized with H ₂ occlusion pulverization method, in order to simplify the process and the coarse grinding method according to the H ₂ storage this It is also preferable to employ a method in which heat treatment in H ₂ gas for ultrafine crystallization according to the present invention is combined, and the treatment is continuously performed in the same apparatus. In the present invention, the reason why the average particle size of the coarsely pulverized powder is limited to 20 to 500 μm is that if the particle size is less than 20 μm, there is a risk of magnetic deterioration due to oxidation of the powder.
This is because if it exceeds μm, it takes a long time for the nitriding treatment, which is not preferable.

In the present invention, when H ₂ gas is heated alone or in a mixed gas with an inert gas (excluding N ₂ gas), the above decomposition occurs when the H ₂ partial pressure is less than 0.1 atm (normal temperature conversion). A sufficient effect of generation cannot be obtained, and if it exceeds 10 atm, the processing equipment becomes too large, which is not preferable in terms of industrial production cost. Therefore, the H ₂ partial pressure is set to 0.1 to 10 atm. A more preferable range is 0.5 to 1.5 atm. Also, when a mixture of an inert gas other than N ₂ gas and H ₂ gas is used at the H ₂ partial pressure, the maximum pressure is 10 atm or less for the same reason.

When the heat treatment temperature of H ₂ gas alone or in a mixture with an inert gas (excluding N ₂ gas) is less than 500 ° C., the RT compound only occludes H ₂ and RH _{2 3} is not decomposed into α-Fe, etc., and if it exceeds 900 ° C, RH _{2 3} becomes unstable and the product grows into grains and dehydrogenates.
After _2, it becomes difficult to R-T compounds with a ultra fine structure, in the range of 500 to 900 ° C.. Also,
The heat treatment holding time is required to be 30 minutes to 8 hours in order to sufficiently carry out the above decomposition reaction.

In the present invention, when the temperature of the H ₂ gas removal H ₂ treatment is less than 500 ° C., decomposition of RH _{2 3} does not proceed, and the desired ThMn ₁₂ type compound cannot be obtained. A recrystallized structure of the ThMn ₁₂ type compound can be obtained, but a coarse structure is formed due to grain growth, and an excellent high coercive force cannot be obtained. Therefore, the range is set to 500 to 900 ° C. In addition, the heat treatment holding time is required to be 30 minutes to 8 hours in order to sufficiently carry out the above decomposition reaction.

The H ₂ partial pressure during de H ₂ treatment, 1 × 10 ^-2 To
If it exceeds rr, it takes a long time to process, which is not preferable.
It should be 1 × 10 ^-2 Torr or less. If the H ₂ partial pressure is within this range, this treatment may be performed in an inert gas other than N ₂ gas, which eliminates the need for vacuum container equipment that withstands high atmospheric pressure, and simplifies the equipment, making it economical. is there.

The average crystal grain size of the powder after the H ₂ removal treatment is 0.
The reason for limiting the thickness to 05 to 0.5 μm is that it is practically difficult to generate it when it is less than 0.05 μm, and even if crystals of less than 0.05 μm are obtained, there is no advantage in terms of characteristics,
This is because if it exceeds m, it becomes larger than the critical diameter of the single domain particle, and the coercive force of the powder decreases, which is not preferable as a powder for permanent magnet.

In the present invention, the reason why the mixed gas of N ₂ and H _{2 under} specific conditions is used in the nitriding treatment is that H atoms first diffuse into the powder to expand the crystal lattice, and then N atoms are added. This is because the nitriding rate is improved because it diffuses while substituting with H atoms, the nitriding temperature is lowered, the decomposition reaction of the main phase and the precipitation of the α-Fe phase are suppressed, and the magnetic properties are improved. The reason why the pressure range of the mixed gas of N ₂ and H ₂ at the time of nitriding treatment is limited to 0.2 to 10 atm at room temperature is as follows.
Slow nitriding reaction rate is less than 0.2 atm, the reaction and increase the pressure proceeds rapidly, too large processing facility exceeds 10 atm, it is not preferable because that lead to increase in production costs, also, the H ₂ If the molar ratio is less than 1%, the effect of improving the nitriding rate cannot be obtained, which is not preferable, and if it exceeds 95%, the substitution of N atoms with H atoms does not occur, and the diffusion of N atoms does not proceed, which is not preferable.

The reason for limiting the temperature during the nitriding treatment to 4000 to 600 ° C. is that nitriding does not proceed below 400 ° C.
When the temperature exceeds 00 ° C, α-Fe and RN are formed to form R-T-M.
This is because the compound (RT _12-x M _x ) decomposes and causes deterioration of magnet characteristics. If the holding time during the nitriding treatment is less than 0.1 hours, sufficient nitriding does not proceed, and if it exceeds 30 hours, decomposition occurs and the magnet characteristics are deteriorated. Therefore, the holding time is set to 0.1 hours to 30 hours.

[0027]

[Example] Example No. 1 shown in Table 1 obtained by melting in a high frequency melting furnace 1
An ingot having a composition of ~ 4 is annealed at 1100 ° C for 24 hours,
After adjusting the ThMn ₁₂ type compound in the ingot to 95 vol% or more, after coarsely pulverizing in an Ar gas atmosphere with a stamp mill to an average particle size of 100 μm, this coarsely pulverized powder has a H ₂ partial pressure of 1.0 atm (normal temperature). After being heated to 800 ° C. in H ₂ gas (converted) and kept for 2 hours, the H ₂ partial pressure is 1 × 10 ⁻⁴ Torr.
In the atmosphere shown in Table 1, deoxidized H ₂ treatment was performed at 800 ° C. for 1 hour.
A powder having a texture of the average crystal grain size shown in was obtained. Then, the powder was converted to room temperature at 1 atm and H ₂ molar ratio was 5
0%, temperature shown in Table 2 in a mixed gas of N ₂ and H ₂ the balance being N _2, and cooled after the nitriding treatment time, the resulting powder was mixed 2.0 wt% of epoxy resin Later,
A bond magnet was produced by compression-molding in a magnetic field of 10 kOe at a pressure of 3.0 ton / cm ² and further curing the resin at a temperature of 150 ° C. for 1 hour. Table 2 shows the magnetic properties of the obtained bonded magnet.

Comparative Example Composition No. 1 in Table 1 Using the same coarsely pulverized powders as those in Nos. 1 and 3, H ₂ treatment and de-H ₂ treatment under the same conditions as in the example, and nitriding treatment at a temperature and time shown in Table 2 in 1 atm N ₂ gas at room temperature. After that, it was cooled, and thereafter, a bonded magnet was produced under the same conditions as in the example, and its magnetic characteristics are shown in Table 2.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

The R-T-M-N system permanent magnet powder according to the present invention comprises the R-T-M system coarsely pulverized powder mixed with H ₂ gas alone or with an inert gas (excluding N ₂ gas). A powder having a texture with an average crystal grain size of 0.05 to 0.5 μm is obtained by performing a heat treatment in air and a H ₂ removal treatment in which it is heated and held in a predetermined atmosphere, and is a coarsely pulverized powder having a required average grain size. It is possible to do so, and the handling of the powder in the subsequent step becomes extremely easy, and after that, a specific nitriding treatment is performed to accelerate the nitriding reaction, and a coercive force of 6 kOe or more is obtained as is clear from the examples.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Hirosawa 2-15-17 Egawa, Shimamoto-cho, Mishima-gun, Osaka Prefecture Sumitomo Special Metals Co., Ltd. Yamazaki Works (72) Inventor Toshiro Tomita 4 Kitahama, Chuo-ku, Osaka-shi, Osaka 5-53, Sumitomo Metal Industries, Ltd. (72) Inventor, Kazutoshi Kuriyama 4-53-3, Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries, Ltd.

Claims (1)

[Claims] 1. R 7 at% to 9 at% (R: at least one kind of rare earth element and containing 50% or more of one or two kinds of Pr or Nd), T 76 at% to 89 at%
(T: Fe or a part of Fe is 50% or less of Co, N
i), M 3.5 at% to 17 at% (M:
At least one of V and Mo) is roughly crushed to have an average particle size of 20 μm to 500 μm of at least 8
After the coarsely pulverized powder of which 0 vol% or more is composed of a compound having a ThMn ₁₂ type crystal structure is prepared,
500 in tm to 10 atm (converted to room temperature) of H ₂ gas or an inert gas (except N ₂ gas) having H ₂ partial pressure equal to it (however, the total pressure is 10 atm or less converted to room temperature)
° C. to 900 ° C. in heated for 30 minutes to 8 hours, more H ₂
A powder having a texture with an average crystal grain size of 0.05 μm to 0.5 μm, which has been subjected to a de-H ₂ treatment of maintaining the pressure at 500 ° C. to 900 ° C. for 30 minutes to 8 hours at a partial pressure of 1 × 10 ⁻² Torr or less. Then, the powder is 0.2 atm to 10 at room temperature.
The molar ratio of atm and H ₂ is 1 to 95%, and the balance is N ₂ and N _2.
0.1 to 3 at 400 ° C to 600 ° C in a mixed gas of ₂ and H _2.
A method for producing permanent magnet powder, which comprises holding for 0 hour and then cooling.