JPH04348002A - Manufacture of permanent magnet powder - Google Patents

Abstract

PURPOSE:To provide a manufacturing method which enables easy manufacture of magnet powder of ultrafine crystal which can acquire coercive force of 6kOe or more and manufactures permanent magnet powder whose following handling is easy by obtaining a composition replacing R-T nitride. CONSTITUTION:Heating treatment in H2 gas alone or in a mixture air with inert gas (excepting N2 gas) and de-H2 treatment for heating and holding in specified atmosphere are performed for coarsely crushed powder which mainly consists of T, contains at least Pr or Nd as R and contains at least one kind of Ti, V, Cr, Mo and is formed to required composition. It is possible to form a powder body having aggregate structure of average crystal grain diameter of 0.05 to 0.5mum as it is coasely crushed powder of required average grain size, to enable extremely easy handling of powder in a following process and to acquire a magnet of high coercive force by magnetizing it by following nitrization treatment.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is for use in new R (rare earth elements)-T (iron group elements)-M-N system bonded magnets with high coercive force that can be used in various motors, actuators, etc. Regarding the manufacturing method of permanent magnet powder for sintered magnets, this coarsely pulverized powder is subjected to heat treatment in H2 gas alone or in a mixture with inert gas (excluding N2 gas), and decomposition by heating and holding in a predetermined atmosphere. A method for producing R-T-M-N-based permanent magnet powder that is easy to handle and has a high coercive force by performing H2 treatment to form a textured powder having a microcrystal grain size, and then nitriding the powder. Regarding.

0002

BACKGROUND OF THE INVENTION Magnet powders having an ultrafine structure obtained by ultra-quenching, mechanical alloying, etc. have been used as Nd--Fe--B permanent magnet powders.

[0003] Nd-Fe-B powder for permanent magnets has a low Curie point (Tc) of around 300°C and a large temperature coefficient of Br and iHc, so by increasing Tc by adding Co etc. Although it is possible to improve B
The temperature coefficient α of r was limited to about -0.08/deg at most.

[0004]Recently, R2Fe17 compounds have become nearly twice as high in absolute temperature by absorbing N2;
It is 160℃ higher than Tc of d-Fe-B system, and S
It has been reported that m2Fe17 nitride provides an anisotropic magnetic field that exceeds the anisotropy of R2Fe14B.

[0005]

[Problems to be Solved by the Invention] The Sm2Fe17 nitride does not have the iHc that is practically required in the normal manufacturing method.
It is not possible to produce magnet powder that yields 6 kOe or more, and the required ultrafine crystal magnet powder can only be obtained by special manufacturing methods such as mechanical alloying, which poses problems in mass production on an industrial scale. .

[0006] In addition, the nitriding reaction to obtain Sm2Fe17 nitride has a slow reaction rate, so unless the raw material powder is pulverized to 10 μm or less before the nitriding process, the N atoms will not diffuse into the interior of the powder. Moreover, the finely pulverized powder of 10 μm or less is difficult to handle in the subsequent process, and unless extreme care is taken, it may catch fire or easily oxidize, resulting in deterioration of properties and even corrosion.

[0007] Furthermore, Sm2Fe17 nitride has the problem of being relatively expensive because it contains a large amount of Sm, which is scarce in terms of resources, and there is a need for permanent magnet powder containing other elements that are abundant in terms of resources.

[0008] In order to obtain a permanent magnet having a composition that replaces the Sm2Fe17N23 system permanent magnet, the present invention is capable of easily producing ultrafine crystal powder for the magnet that can obtain a coercive force of 6 kOe or more, and that the subsequent powder is The purpose of this invention is to provide a new method for producing permanent magnet powder that is easy to handle.

[0009]

[Means for Solving the Problems] This invention provides R7-
9 at% (R: at least one rare earth element and Pr
or containing 50% or more of one or two types of Nd), T
76 to 87 at% (T: Fe or a part of Fe to 5
(substituted with 0% or less Co, Ni), M 3.5-17
at% (M: containing at least one of Ti, V, Cr, and Mo) is coarsely crushed to have an average particle size of 50 to 50
After making it into a coarsely pulverized powder consisting of a compound in which at least 80 vol% of 0 μm has a ThMn12 type crystal structure,
The coarsely pulverized powder is heated to 0.1 to 10 atm (normal temperature equivalent) of H2.
gas or an inert gas with an equal H2 partial pressure (
(excluding N2 gas) (however, the total pressure is 10 at at room temperature)
500°C or less), heated and held at 500 to 900°C for 30 minutes to 8 hours, and then heated to 500°C in a vacuum with a H2 partial pressure of 1 x 10-2 Torr or less or in a mixture with an inert gas excluding N2.
A deH2 treatment is performed by holding the temperature at ~900°C for 30 minutes to 8 hours to obtain a powder having a texture with an average crystal grain size of 0.05 to 0.5 μm, and then the powder is heated under a N2 pressure of 0.5 ~50
After being maintained at 350 to 550°C for 30 minutes to 6 hours in N2 gas of ATM, it was cooled to give R 7 to 9 at%, T
76-87 at%, M 3.5-17 at%, N
This is a method for producing permanent magnet powder, which is characterized by obtaining permanent magnet powder containing 0.8 to 8 at% and having a high coercive force.

0010

[Operation] This invention provides an R-T-N permanent magnet,
As a result of various studies with the aim of manufacturing a powder for magnets made of ultrafine crystals that is easy to handle and has a coercive force of 6 kOe or more, we found that the R-T-N compound represented by Sm2Fe17N2 The R-T compound is about 0.3
It has been found that an R-T-N based permanent magnet powder having a high coercive force can be obtained by nitriding the powder having a microcrystalline texture with a single magnetic domain particle critical diameter of μm or so.

That is, the inventors conducted R-T in H2 gas.
When the alloy is heated, the R-T compound becomes RH2■3 and αFe
The same R-T as before is obtained by further decomposing H2
Furthermore, by controlling the temperature and holding time of heating in H2 gas and H2 removal treatment, the crystal grain size of the generated RT compound can be controlled, and by subsequent nitriding treatment, high storage stability can be achieved. It has been found that an R-T-N permanent magnet powder having an ultrafine structure that exhibits magnetic force can be obtained.

[0012] In addition to R2Fe17 compounds, rare earth compounds of iron group elements can also be used under specific H2 conditions as described above.
It has been found that ultrafine crystal texture can be obtained by heating in gas and H2 removal treatment, and that magnetic properties can be controlled by subsequent N2 diffusion treatment.

Furthermore, as a result of examining various compositions to replace RT nitride represented by Sm2Fe17N2■3, we found that T
An R-T-M nitride with a composition containing at least Pr or Nd as the main component and at least one of Ti, V, Cr, and Mo has an anisotropic magnetic field equivalent to that of the R-T nitride. We found that H under the above specific conditions can be obtained.
By performing heating in two gases and H2 removal treatment, a new R-T-M represented by NdFe11TiN0.1■1
-N-based permanent magnet powder can be made into a powder having a texture with an average grain size of 0.05 to 0.5 μm while remaining a coarsely pulverized powder with a required average grain size, and has a coercive force of 6 kOe or more. The present invention was completed based on the finding that not only can the powder be obtained, but also that handling of the powder in subsequent steps becomes extremely easy.

Reasons for limiting the powder composition In the powder composition of the present invention, the rare earth element R is Y, La
, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho,
Er, Tm, and Lu are included, and at least one of these includes one or two of Pr or Nd as 5 of R.
0% or more, and all of R may be Pr or Nd, or Pr and Nd. 50% or more of R
Or, one or two types of Nd are Pr or Nd.
This is because sufficient magnetization cannot be obtained if one or both of d is less than 50%, and the use of Pr or Nd has the effect of reducing raw material costs compared to Sm. R is 7
If it is less than at%, the coercive force decreases due to the precipitation of α-Fe,
Moreover, if it exceeds 9 at%, R2Fe17 phase etc. will precipitate and the coercive force will deteriorate, so it is set to 7 to 9 at%.

[0015] The iron group element T includes at least one of Fe, Co, and Ni, and it is important that Fe is contained in an amount of 50% or more of T. That is, if Fe in T is less than 50%, sufficient magnetization cannot be obtained, which is not preferable. In addition, Co is T5
It is particularly preferable to add less than 0% because the Curie temperature increases and the anisotropic magnetic field increases slightly. T is 76a
If it is less than t%, a compound with a low coercive force will appear and the coercive force will decrease, and if it exceeds 87 at%, the coercive force will decrease due to α-Fe precipitation, so it is set to 76 to 87 at%.

M, ie, at least one of Ti, V, Cr, and Mo, is RFe12 having a ThMn12 type structure.
-xMx It is an essential element that generates compounds, and 3.5a
If it is less than t% (x is less than 0.5), R2Fe17 phase or α-
Since Fe precipitates and the desired compound cannot be obtained, and if it exceeds 17 at% (x exceeds 2.0), the magnetization decreases significantly, so it is set to 3.5 to 17 at%.

Further, if N is less than 0.8 at%, uniaxial anisotropy cannot be obtained, and if it exceeds 8 at%, the ThMn12 type structure becomes unstable, and the matrix becomes R2Fe17 phase or α-Fe17.
Since it is undesirable because it decomposes into

[0018] In this invention, the average particle size is 50 to 50
The reason why the coarsely ground powder is limited to a compound in which at least 80 vol% of 0 μm has a ThMn12 type crystal structure is that in this invention, the coarsely ground powder before heating in H2 gas under the above specific conditions is substantially ThMn12 type. The compound needs to have a structure, and is preferably a ThMn12 type compound having a volume ratio of 80% or more. That is, when the compositional alloy of the present invention is produced by a casting method, in addition to the ThMn12 type compound, α-Fe and Th
2Zn17 type coexists, and this coexistence ratio depends on manufacturing conditions such as ingot cooling conditions, but the coexistence ratio depends on the H of the subsequent process.
There is almost no change in heating in two gases, deH2 treatment, or nitriding treatment. When such α-Fe phase and Th2Zn17 type compound exist, the characteristics of the obtained magnetic powder, especially iH
c decreases, it is necessary that the ThMn12 type compound be present in the coarsely ground powder at 80 vol % or more. In order to obtain a coarsely pulverized powder having a ThMn12 type compound with a volume ratio of 80% or more, the as-cast ingot is heated to 900 to 1200°C.
The temperature can be selected as appropriate, such as by annealing at a temperature of 1 hour or more, or by controlling the cooling conditions of the mold when cooling the ingot in the ingot making process.

Reasons for limiting manufacturing conditions The present invention is characterized in that coarsely pulverized powder with a required particle size can be obtained as an aggregate of fine crystal structures without changing its size in appearance, and this point is different from conventional H2 This method is essentially different from the occlusion pulverization method. That is, ThMn12 type R-
When a TM compound is reacted with H2 gas at high temperature, RH2
(3) When the phase is separated into α-Fe, TM alloy phases, etc., and the H2 gas is further removed by degassing, a recrystallized structure of the ThMn12 type R-TM compound is obtained again. The starting material may be coarsely pulverized by a conventional mechanical pulverization method or gas atomization method, or by an H2 storage pulverization method, and in order to simplify the process, this coarse pulverization method using H2 storage and the method according to the present invention are used. It is also preferable to adopt a method in which heat treatment in H2 gas for ultrafine crystallization is combined and the treatment is performed continuously in the same apparatus. In this invention, the average particle size of the coarsely pulverized powder is limited to 50 to 500 μm because if it is less than 50 μm, there is a risk of magnetic deterioration due to oxidation of the powder.
This is because if it exceeds .mu.m, the nitriding treatment will take a long time, which is undesirable.

In the present invention, when heating H2 gas alone or in a mixture with an inert gas (excluding N2 gas), if the H2 partial pressure is less than 0.1 atm (converted to room temperature), the above-mentioned decomposition and formation may occur. If the pressure exceeds 10 atm, the processing equipment becomes too large, which is not preferable in terms of industrial production costs. Therefore, the H2 partial pressure is set to 0.1 to 10 atm. A more preferable range is 0.5 to 1.5 atm. Further, when using a mixture of an inert gas other than N2 gas and H2 gas at the above H2 partial pressure, the maximum pressure is set to 10 atm or less for the same reason.

[0021] The heat treatment temperature for H2 gas alone or in a mixture with inert gas (excluding N2 gas) is 500°C.
If it is less than RH2, the RT compound will only absorb H2,
3 and αFe, etc., and if the temperature exceeds 900°C, RH2■3 becomes unstable and the product grows grains, making it difficult to convert it into an RT compound with an ultrafine structure after H2 removal. Therefore, the temperature is set in the range of 500 to 900°C. Further, in order to sufficiently carry out the above-mentioned decomposition reaction, it is necessary to hold the heat treatment for 30 minutes to 8 hours.

[0022] In this invention, if the temperature of the H2 removal treatment of H2 gas is lower than 500°C, the decomposition of RH2■3 will not proceed and the desired ThMn12 type compound will not be obtained.
If the temperature exceeds .degree. C., a recrystallized structure of the ThMn12 type compound can be obtained, but the structure becomes coarse due to grain growth, and excellent high coercive force cannot be obtained. Further, in order to sufficiently carry out the above-mentioned decomposition reaction, it is necessary to hold the heat treatment for 30 minutes to 8 hours.

[0023] The H2 partial pressure during the H2 removal process is 1×10-2
If it exceeds Torr, the processing will take a long time and is not preferable, so it is set to 1×10 −2 Torr or less. If the H2 partial pressure is within this range, this treatment may be carried out in an inert gas other than N2 gas, which eliminates the need for vacuum container equipment that can withstand high pressure, which simplifies the equipment and is economical.

[0024] The average crystal grain size of the powder after H2 removal treatment is 0.
The reason why crystals are limited to 0.05 to 0.5 μm is that crystals smaller than 0.05 μm are practically difficult to form, and even if crystals smaller than 0.05 μm are obtained, there is no advantage in terms of properties.
This is because if it exceeds m, the single magnetic domain particle critical diameter becomes larger and the coercive force of the powder decreases, making it undesirable as a powder for permanent magnets.

The reason why the temperature during nitriding treatment was limited to 350 to 550°C is that nitriding does not proceed below 350°C.
This is because when the temperature exceeds 0° C., α-Fe and RN are generated and the R-T-M compound (RT12-xMx) is decomposed, leading to deterioration of the magnetic properties. The holding time during the nitriding treatment is set to 30 minutes to 6 hours, since sufficient nitriding will not proceed if it is less than 30 minutes, and decomposition will occur if it exceeds 6 hours, resulting in deterioration of the magnetic properties.

[0026] N2 pressure during nitriding treatment is 0.5 to 50at.
The reason why it is limited to m is that the nitriding reaction rate is slow below 0.5 atm, and when the pressure is increased, the reaction proceeds quickly.
This is because if it exceeds 50 atm, the processing equipment becomes too large, which is unfavorable in terms of industrial production costs.

[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 ~7 was annealed at 1100°C for 24 hours,
After making the ThMn12 type compound in the ingot to be 95 vol% or more, it was coarsely pulverized to an average particle size of 100 μm with a stamp mill in an Ar gas atmosphere, and then the coarsely pulverized powder was heated to a H2 partial pressure of 1.0 atm (converted to room temperature). After heating to 800°C in H2 gas and holding for 2 hours, the H2 partial pressure becomes 1 x 10-4 To
Perform H2 removal treatment at 800°C for 1 hour in an atmosphere of rr,
A powder having a texture with an average grain size shown in Table 1 was obtained. After that, 40 mL of N2 gas with a N2 partial pressure of 5.0 atm was
After nitriding at 0° C. for 2 hours, the powder was cooled to obtain R-T-M-N magnet powder having the properties shown in Table 1.

[0028] After mixing 2.0 wt% epoxy resin with R-T-M-N magnet powder,
．． Compression molding at a pressure of 0 ton/cm2 and further at a temperature of 1
A bonded magnet was produced by curing the resin at 50°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 powder as in 1, it was held in H2 gas with a H2 partial pressure of 2.0 atm (normal temperature equivalent) for 2 hours, and after exhausting excess H2 gas, it was heated to 80
De-H2 at 0℃, 2 hours, H2 partial pressure 1 x 10-4 Torr
After processing, a ground powder was obtained. Table 1 shows the average grain size at this time.
Shown below. Table 1 shows the properties of the R-T-M-N magnet powder after it was further subjected to the same nitriding treatment as in the example. Thereafter, a bonded magnet was produced under the same conditions as in the example, and its magnetic properties are shown in Table 2.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

Effects of the Invention: The R-T-M-N permanent magnet powder according to the present invention is obtained by mixing roughly pulverized R-T-M powder in a mixture of H2 gas alone or with an inert gas (excluding N2 gas). heat treatment and H2 removal treatment by heating and holding in a predetermined atmosphere, leaving the coarsely ground powder with the required average grain size, with an average crystal grain size of 0.
The powder can be made into a powder having a texture of 0.05 to 0.5 μm, making it extremely easy to handle the powder in the subsequent process, and then nitriding it to obtain a coercive force of 6 kOe or more as shown in the examples. It will be done.

Claims (1)

[Claims] Claim 1: R 7 to 9 at% (R: at least one rare earth element and one or two of Pr or Nd)
Contains 50% or more seeds), T 76-87 at% (T:
Replace Fe or part of Fe with 50% or less of Co, Ni), M 3.5 to 17 at% (M: Ti, V, C
Coarsely pulverize an ingot consisting of at least one of
After forming a coarsely pulverized powder consisting of a compound having a ThMn12 type crystal structure of 0.1 to 1 mol%, the coarsely pulverized powder is
0 atm (normal temperature equivalent) H2 gas or equivalent H
In an inert gas (excluding N2 gas) with a partial pressure of 2 (however, the total pressure is 10 atm or less at room temperature), 500 to 90
Heat and hold at 0℃ for 30 minutes to 8 hours, and further increase the H2 partial pressure to 1×
30 minutes at 500-900℃ at 10-2 Torr or less
After performing H2 removal treatment for 8 hours, the average crystal grain size was 0.
A powder having a texture of 0.05 to 0.5 μm is prepared, and then the powder is maintained at 350 to 550° C. for 30 minutes to 6 hours in N2 gas with a N2 pressure of 0.5 to 50 atm, and then cooled. A method for producing permanent magnet powder characterized by: