JP2010270382A - Method for producing magnet powder containing rare-earth element, transition metal and nitrogen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which can inexpensively and stably produce a magnet powder containing a rare-earth element, a transition metal and nitrogen, and having high characteristics, by a reduction and diffusion reaction. <P>SOLUTION: This production method includes: a first step of slurrying an iron oxide powder with a water medium, charging a predetermined amount of an oxide of a rare-earth element into the slurry to dissolve the oxide while adding a dilute acid of 1 mol/L or less into the slurry so that the pH value of the slurry is maintained in a range of 2-5, adding a salt of an alkali metal or an alkaline-earth metal to the slurry to adjust the pH so as to be higher than 7.0, and consequently producing a raw mixed powder which has a hydroxide of the rare-earth element precipitated on the surface of the iron oxide; a second step of subjecting the obtained raw mixed powder to hydrogen heat-treatment; a third step of adding a predetermined amount of an alkaline-earth metal which is a component of a reducing agent, to the mixed powder which has been subjected to the hydrogen heat-treatment, mixing them, heat-treating the mixture in an inert gas atmosphere, and then cooling the mixture in the same atmosphere to obtain a rare-earth-iron based mother alloy; a forth step of subsequently nitriding the mother alloy; and a fifth step of wet-treating the nitrided material to separate and remove a byproduct of the component of the reducing agent, and then pulverizing the obtained crude powder. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a rare earth-transition metal-nitrogen magnet powder, and more specifically, a reduction-diffusion reaction of wet-mixed raw material powder to suppress the generation of nuclei on the reverse axis and suppress grain growth due to heat generation. The present invention also relates to a method for producing a rare earth-transition metal-nitrogen magnet powder that can stably produce inexpensive and high-performance magnet powder.

Rare earth-transition metal-nitrogen-based magnets represented by Sm-Fe-N magnets are known as high-performance and inexpensive magnets, and this Sm-Fe-N-based magnet powder is Sm ₂ Fe ₁₇ N _x . If so, it is said that the maximum saturation magnetization is exhibited by being composed of a composition of x = 3 (see Non-Patent Document 1).
This rare earth-transition metal-nitrogen based magnet has been conventionally used in a melting method in which a rare earth-iron alloy is produced using a high frequency furnace, an arc furnace, etc. using Fe and Sm metal, Fe, Fe ₂ O ₃ , Sm ₂ O _3, etc. It is manufactured by nitriding a rare earth-iron master alloy obtained by a reduction diffusion method in which a rare earth-iron alloy is produced by mixing heat treatment with Ca and Ca. The rare earth-transition metal-nitrogen based magnet powder obtained in this way is pulverized until the average particle size becomes several μm to about 5 μm in the next step because the coercive force generation mechanism is a nucleation type. It is processed.

  Here, in the melting method, heat treatment for melting, pulverizing, and homogenizing the composition of the raw material powder at 1500 ° C. or higher is required (see Patent Document 3). However, in the dissolution method, the process is extremely complicated, and impurities are generated by oxidation because the process is once exposed to the atmosphere between the processes, and nitriding is performed after the wet process, but the surface is oxidized during the wet process. Therefore, nitriding cannot proceed uniformly, and there is a problem that the saturation magnetization, coercive force, and squareness of the magnetic characteristics are lowered, and as a result, the maximum energy product is lowered. In addition, because the rare earth metal required as a raw material is very expensive, it is considered to be disadvantageous in cost as compared with the reduction diffusion method in which an inexpensive rare earth oxide powder can be used as a raw material.

On the other hand, in the reduction diffusion method, an iron powder of several tens of μm is usually used as a starting material, and after mixing a rare earth metal or rare earth oxide and an alkaline earth metal, a reduction heat treatment is performed to produce a master alloy. Since mechanical pulverization to several μm after a typical nitriding treatment occurs, there is a problem in that protrusions on the fracture surface that can be the nucleus of the reverse axis and crystal distortion occur, and magnetic properties are degraded.
As a solution to this problem, there has been proposed a method for obtaining a magnet powder without pulverizing the master alloy by reducing the particle size of the powder as a starting material. When mixing is carried out dry, there is a problem that the influence of the particle size and specific gravity is large and the mixing tends to be non-uniform.

  In addition, a wet mixing method has been proposed as in Patent Document 2, but instead of being able to perform uniform mixing, a part of the rare earth oxide is dissolved and re-precipitated in water, so that a fine submicron rare earth hydroxide is obtained. In the subsequent hydrogen reduction heat treatment, rare earth iron composite oxides are generated, and a large thermite heat generation may occur during the reduction heat treatment with an alkaline earth metal to cause local grain growth. This is because fine iron oxides used for industrial use are generally produced by dissolution and precipitation of Fe with hydrochloric acid and neutralization with caustic soda, etc. When the rare earth oxide is dispersed, the rare earth oxide is slightly soluble in water but is more soluble in acid than that.

  Furthermore, a method for producing a co-precipitated hydroxide of Sm and Fe has been proposed as in Patent Document 3, but the rare earth salt used is expensive, and since the precipitate is a hydroxide, it is often used during hydrogen reduction heat treatment. Since the rare earth iron complex oxide is produced, the same phenomenon as described above occurs.

  As described above, the establishment of a method capable of producing rare earth-transition metal-nitrogen based magnet powders having excellent magnetic properties at low cost without causing the generation of reverse-axis nuclei and grain growth that degrade the magnetic properties is strong. It was desired.

Japanese Patent Laid-Open No. 11-310807 JP 2003-297660 A Japanese Patent No. 3698538

T.A. Iriyama IEEE TRANSATIONS ON MAGNETICS, VOL. 28, no. 5 (1992)

  In view of the above-mentioned problems of the prior art, the object of the present invention is to carry out a reduction diffusion reaction on the wet-mixed raw material powder to suppress the generation of nuclei on the reverse axis and to suppress the grain growth due to local heat generation, thereby reducing Another object of the present invention is to provide a method for producing a rare earth-transition metal-nitrogen magnet powder capable of stably producing high-performance magnet powder.

  In order to achieve high performance of rare earth-transition metal-nitrogen magnet powders, the present inventors have conducted extensive research to achieve the above-mentioned object, and have conducted extensive research to solve such conventional problems. The raw material powder is wet-mixed with an aqueous solvent and dilute acid under specific conditions, and the rare earth hydroxide is precipitated on the iron oxide surface during this wet mixing, so that a specific amount of rare earth iron composite oxide is produced during the reduction diffusion treatment. As a result, it was found that local heat generation was suppressed, and a rare earth-iron-based master alloy with very few coarse particles due to grain growth could be obtained, thereby achieving extremely excellent magnetic properties, and the present invention was completed. It came to do.

  That is, according to the first invention of the present invention, iron oxide powder having an average particle diameter of 2 μm or less, which is a magnet raw material, is slurried with an aqueous solvent, and then the pH value of this slurry is maintained in the range of 2 to 5. As described above, a predetermined amount of rare earth oxide is added and dissolved while adding 1 mol / L or less of dilute acid, and then an alkali metal salt or an alkaline earth metal salt is added so that the pH exceeds 7.0. The first step of producing the raw material mixed powder in which the rare earth hydroxide is precipitated on the iron oxide surface, the second step of subjecting the obtained raw material mixed powder to the hydrogen heat treatment, and the reduction to the hydrogen-heat treated mixed powder A predetermined amount of an alkaline earth metal is added as an agent component, mixed, heat-treated at a temperature of 900 to 1300 ° C. in an inert gas atmosphere, and then cooled in the same atmosphere to form a rare earth-iron-based master alloy. A third step to obtain, Subsequently, a fourth step of nitriding by introducing a mixed gas containing at least ammonia and hydrogen into the obtained rare earth-iron based master alloy and performing a heat treatment at a predetermined temperature in this air stream, then obtained. A process for producing a rare earth-transition metal-nitrogen magnet powder comprising a fifth step of wet-treating the resulting nitrided product, separating and removing the by-products of the reducing agent component, and then crushing the resulting coarse powder. Provided.

According to a second aspect of the present invention, there is provided a rare earth-transition metal-nitrogen magnet powder characterized in that, in the first step, the diluted acid is either hydrochloric acid or nitric acid in the first step. A manufacturing method is provided.
According to the third invention of the present invention, in the first invention, in the first step, the alkali metal salt or alkaline earth metal salt in the first step is a hydroxide or an oxide that exhibits alkalinity in water. There is provided a method for producing rare earth-transition metal-nitrogen magnet powders, characterized in that the rare earth-transition metal-nitrogen magnet powder is characterized in that it is an oxide, a nitride or a composite compound thereof.
According to a fourth aspect of the present invention, there is provided a rare earth-transition metal-nitrogen magnet powder characterized in that, in the first step, the drying temperature of the mixed powder is 300 ° C. or lower in the first step. A manufacturing method is provided.
According to a fifth aspect of the present invention, in the first aspect, the rare earth characterized in that, in the second step, the mixed powder is subjected to a hydrogen heat treatment at 500 to 800 ° C. for 1 to 8 hours. A method for producing a transition metal-nitrogen magnet powder is provided.
According to the sixth invention of the present invention, in the first invention, in the third step, the amount of the alkaline earth metal added is the amount of oxygen in the raw material powder that has not been reduced up to the second step. Provided is a method for producing a rare earth-transition metal-nitrogen magnet powder, characterized in that when the amount necessary for reduction is 1 equivalent, it is 1.1-3.0 equivalents.
Further, according to the seventh invention of the present invention, in the first invention, in the third step, the reaction gas after the reduction-diffusion reaction is continued with the atmosphere gas being an inert gas. There is provided a method for producing a rare earth-transition metal-nitrogen magnet powder characterized by cooling to 300 ° C. or lower.
According to the eighth invention of the present invention, in the first invention, in the fifth process, the powder obtained by wet treatment and pulverization accumulates primary particles having a major axis particle diameter exceeding 4 μm. Provided is a method for producing rare earth-transition metal-nitrogen magnet powder, characterized in that the percentage is less than 5%.
Furthermore, according to the ninth invention of the present invention, in the first invention, the rare earth-transition metal-nitrogen based magnet powder contains Sm as a rare earth, and the content thereof is 23.2 to the whole magnet powder. A method for producing a rare earth-transition metal-nitrogen magnet powder characterized by being 23.6% by weight is provided.

According to the method for producing a rare earth-transition metal-nitrogen magnet powder of the present invention, in the raw material powder mixing step, an aqueous solvent is used to disperse iron oxide powder as a magnetic raw material in water, and the pH of this slurry is 2 to 2. A predetermined amount of rare earth oxide powder is added and dissolved while adding a specific concentration of dilute acid so as to be maintained in the range of 5, and then the alkali metal salt or alkaline earth metal salt is added to make the slurry alkaline. In order to produce a raw material mixed powder in which a rare earth hydroxide is precipitated on the iron oxide surface, the abundance of SmFeO ₃ produced by hydrogen reduction based on this raw material mixed powder is greatly increased to 30 wt% to 40 wt% By making the following, uniform generation of heat after reduction diffusion treatment in the next step and local grain growth are suppressed, and generation of nuclei and crystals on the reverse axis due to reduction of crushing strength in the next step Distortion can be prevented.
Furthermore, in the next reduction diffusion treatment process, local heat generation is suppressed, and the generation of coarse particles of rare earth-iron master alloy is suppressed. As a result, the generation of reverse axis nuclei and crystal distortion due to the reduction of crushing strength. Prevention becomes possible.
In addition, when the rare earth-iron mother alloy is subjected to nitriding / wet treatment in the next step, the particle surface is oxidized by controlling the atmosphere and temperature from the end of the reduction diffusion treatment to the start of the nitriding treatment. Therefore, high-performance rare earth-transition metal-nitrogen magnet powder can be produced because the nitriding treatment can be performed without reducing the nitriding efficiency.
In addition, since the rare earth-iron-based master alloy is not nitrided after the wet treatment, but is wet-treated after the nitridation treatment, the nonmagnetic phase can be reduced, and the iron oxyhydroxide adheres around the main phase during the wet treatment and is nitrided. Occasionally, the iron oxyhydroxide does not precipitate as α-Fe, so a rare earth-transition metal-nitrogen magnet with a low α-Fe ratio and a high saturation magnetization, coercive force and good demagnetization curve squareness A powder can be obtained. As a result, the manufacturing cost is also low, and its industrial value is extremely high.

  Hereinafter, the method for producing the rare earth-transition metal-nitrogen magnet powder of the present invention will be described in detail.

In the production method of the present invention, an iron oxide powder having an average particle size of 2 μm or less, which is a magnet raw material, is slurried with an aqueous solvent, and then 1 mol / mol so that the pH value of the slurry is maintained in the range of 2 to 5. Rare earth water is added by adding a predetermined amount of rare earth oxide while adding dilute acid of L or less, and then adding an alkali metal salt or alkaline earth metal salt so that the pH exceeds 7.0. The first step of producing a raw material mixed powder in which oxides are deposited on the iron oxide surface, the second step of subjecting the obtained raw material mixed powder to a hydrogen heat treatment, and the alkaline earth as a reducing agent component in the hydrogen heat treated mixed powder A third step of adding a predetermined amount of metal, mixing, heat-treating at a temperature of 900 to 1300 ° C. in an inert gas atmosphere, and then cooling in that atmosphere to obtain a rare earth-iron-based master alloy; Continuously obtained A fourth step of nitriding by introducing a mixed gas containing at least ammonia and hydrogen into the earth-iron-based master alloy and heat-treating it at a predetermined temperature in this air stream; Is produced by a wet process, and a by-product of the reducing agent component is separated and removed. Thereafter, the obtained coarse powder is crushed, and then a rare earth-transition metal-nitrogen magnet powder production method comprising a fifth step.
Below, it demonstrates in detail in order of each process.

1. First Step: Preparation of Raw Material Powder First, iron oxide and rare earth oxide powder to be used as a magnet raw material are mixed.

In addition to Fe ₂ O ₃ , FeO or Fe ₃ O ₄ can also be used as the iron oxide powder as a magnet raw material. The particle diameter is required to be 2 μm or less as an average particle diameter (D50 value) by laser diffraction particle size distribution measurement, and more preferably 1 μm or less. This is because when the average particle diameter exceeds 2 μm, the rare earth-iron mother alloy produced later becomes larger than the particle diameter, so that large particles are easily formed and the coercive force is reduced. This is because a shortage occurs.
The rare earth oxide powder is not particularly limited, but at least one element selected from Sm, Gd, Tb and Ce is preferable. Those containing Sm are particularly preferable because the effects of the present invention can be remarkably exhibited. When Sm is contained, in order to obtain a high coercive force, it is desirable that Sm be 60% by weight or more, preferably 90% by weight or more of the entire rare earth element in order to obtain a high coercive force. The particle diameter of the rare earth oxide powder is preferably smaller than the particle diameter of the iron oxide powder so as to facilitate diffusion in the solid phase and prevent non-uniform diffusion.

The raw material powder can be mixed by the following procedure. First, iron oxide powder and pure water are put into a stainless steel container to make a slurry, and the pH is maintained in the range of 2 to 5 using 1 mol / L or less of dilute acid. A dilute acid is added so that the pH is maintained in a range of 2 to 5 while the rare earth oxide is added thereto, and all of the charged rare earth oxide is dissolved in the slurry.
The diluted acid used at this time is preferably hydrochloric acid or nitric acid. Also, if the acid concentration exceeds 1 mol / L, it becomes an acidic bath with a high concentration locally before being dispersed, so that part of the iron oxide also dissolves, resulting in a deviation in the composition ratio. The iron oxide that determines the diameter and shape melts, so that the powder properties change greatly and the shape cannot be controlled.
Further, it is preferable to maintain the pH at 2 to 5, but this is because if the pH is too low, a large amount of alkali salt is required for neutralization and it is difficult to precipitate on the iron oxide surface, and the pH is too high. This is because the rare earth oxide is difficult to dissolve and the pH is difficult to control because it is close to the inflection point. Next, in order to precipitate the rare earth salt again in the slurry in which the rare earth salt is dissolved, an alkali metal salt or an alkaline earth metal salt is used, the pH is shifted to alkaline, and then washing, splashing, filtering, and drying are performed.
The alkali metal salt used at this time is preferably a hydroxide, oxide, nitride, or composite compound of at least one of Li, Na, and K at low cost. As for alkaline earth metals, hydroxides, oxides, nitrides, or composite compounds of at least one of Mg and Ca are preferable because they are inexpensive. The powder obtained by the above procedure is a particle in which rare earth hydroxide is precipitated on the surface of the iron oxide powder.

Thereafter, the wet-mixed slurry is filtered by a filtration method such as vacuum filtration, filter press, or centrifugal separation, and dried to obtain a processed product according to the first step.
Also, the drying may be performed by a normal drying method. For example, the drying can be performed using a method such as stationary drying, fluidized drying, airflow drying, stirring drying, vacuum drying, and vibration drying. The drying temperature is preferably 300 ° C. or lower in order to prevent formation of complex oxide.

2. Second step: Hydrogen heat treatment of the obtained raw material mixed powder The second step in the present invention is a step of heat-treating the raw material mixed powder obtained in the first step in a hydrogen stream to reduce only iron oxide. It is.

  Since this heat treatment is to reduce only iron oxide, the temperature range is 500 to 800 ° C, preferably 500 to 700 ° C. Below 500 ° C, the reduction is insufficient and iron oxide tends to remain, and the crystal after reduction is unstable, so that it may be oxidized immediately upon contact with the atmosphere and return to iron oxide again. If the temperature exceeds ℃, the reduction will occur, but the particle size of the starting material will increase due to grain growth due to the high temperature, and the coercive force of the final product will decrease when the rare earth-iron master alloy is obtained in the next step. The particle diameter may become coarse up to. The heat treatment is performed for 1 to 8 hours, preferably 2 to 6 hours.

  Further, the powder obtained at this time contains iron rare earth composite oxide in addition to iron powder and rare earth oxide, and the abundance ratio of this iron rare earth composite oxide is 30% by weight or more and 40% by weight or less. preferable. Within this range, thermite heat generation that occurs in the subsequent reduction diffusion is uniform throughout, local heat generation does not occur, and a powder unfavorable for the broad squareness of the particle size distribution cannot be formed. Until now, as in Patent Document 2, a part of the rare earth oxide is dissolved and reprecipitated in water to become a fine submicron rare earth hydroxide, and a rare earth iron composite oxide is formed during the subsequent hydrogen reduction heat treatment. Therefore, it is said that a large thermite heat generation occurs during the reduction heat treatment with an alkaline earth metal to cause local grain growth. In the present invention, in spite of the fact that a large amount of 30-40% by weight iron rare earth composite oxide is produced in the second step, a magnet powder having excellent magnetic properties is finally obtained. The large amount of the generated iron rare earth composite oxide is uniformly distributed without being unevenly distributed. Therefore, it is considered that uniform thermite heat generation may occur in the reduction diffusion.

3. Third step: Reduction diffusion treatment Next, a predetermined amount of alkaline earth metal is added to and mixed with the powder obtained in the second step, and heat treatment is performed at a predetermined temperature in an inert gas atmosphere. A rare earth-iron master alloy having a Th ₂ Zn ₁₇ type crystal structure is produced by a reduction diffusion method that is cooled as it is.
In the reduction diffusion method of the present invention, as described above, a mixture of a rare earth oxide powder, another metal powder, and a reducing agent such as Ca is heated in an inert gas atmosphere at, for example, 900 to 1300 ° C., and then a reaction product is generated. The product is wet-treated to remove reducing agent components such as CaO and residual Ca, which are by-produced, to directly obtain an alloy powder.

In the present invention, the iron powder obtained in the second step and the rare earth oxide, or the mixed powder containing the rare earth iron composite oxide and the alkaline earth metal reducing agent are put into a reaction vessel, and heat treatment is performed. To do. As a result, the rare earth oxide and other oxide raw materials are reduced, and the reduced rare earth element and other metal elements are diffused into the iron powder, so that the rare earth-iron base having a Th ₂ Zn ₁₇ type crystal structure is obtained. An alloy is formed.
Here, it is necessary to uniformly mix the powder charged into the reaction vessel so as not to be separated depending on the powder characteristics. As a mixing method, for example, a ribbon blender, a tumbler, an S-shaped blender, a V-shaped blender, a Nauter mixer, a Henschel mixer, a high speed mixer, a ball mill, a vibration mill, an attritor and the like can be used.
The alkaline earth metal as the reducing agent is preferably granular metallic calcium or metallic magnesium classified into an opening of 4.00 mm or less in terms of handling safety and cost. The addition amount of the alkaline earth metal is 1.1 to 3.0 equivalents when the amount necessary for reducing the amount of oxygen in the raw material powder not reduced until the second step is 1 equivalent, It is preferable that it is 1.3-2.0 equivalent. If it is this range, raw material powder can fully be reduced.
In addition to the raw material powder and the reducing agent, it is also effective to mix an additive that promotes the decay of the reaction product later in the wet processing step of the fifth step. As the disintegration accelerator, salts or oxides of alkaline earth metals such as calcium chloride can be used, and they are uniformly mixed simultaneously with the raw material powder. Here, as the inert gas, one or more selected from argon and helium are used.

  In the present invention, in the reduction diffusion in the third step, it is important that the heat treatment temperature is in the range of 900 to 1180 ° C. If the temperature is lower than 900 ° C., the rare earth element does not diffuse uniformly with respect to the iron powder, the coercive force and the squareness of the finally obtained rare earth-transition metal-nitrogen magnet powder are reduced, and the time required for the diffusion is very large. And the productivity decreases. If the temperature exceeds 1180 ° C, the rare earth-iron-based master alloy produced undergoes grain growth, making uniform nitriding difficult, and the finally obtained magnet powder has saturation magnetization, squareness and coercive force. May decrease. Further, the amount of evaporation of Sm, which is an expensive rare earth metal, is very large, and an excessive amount is required, resulting in high costs. At 900-1180 ° C., such a phenomenon does not occur, and secondary particles obtained in a state where the primary particles are small and sintered in a grape shape are weakly sintered. There is also an advantage that crystal distortion is less likely to occur.

Here, the product obtained by the reduction diffusion reaction, for example, when metallic calcium is used as the reducing agent, rare earth-iron master alloy having a Th ₂ Zn ₁₇ type crystal structure and calcium oxide, unreacted surplus It is a massive mixture of metallic calcium. Furthermore, when granular metal calcium is mixed with the raw material powder and subjected to a reduction diffusion reaction, a porous massive mixture that can be easily processed in the next step is obtained.
In the present invention, the reaction product after the reduction-diffusion reaction is continuously changed to 300 ° C. or less, preferably 50 to 280 ° C., more preferably 100 to 250 without changing the atmospheric gas as an inert gas. Cool to ° C.
If the temperature after cooling exceeds 300 ° C, the nitridation reaction with the reaction product proceeds rapidly during nitriding, which may increase the α-Fe phase. It is desirable to cool to a lower temperature. That is, at temperatures exceeding 300 ° C., the reaction product is active, so that the alloy is rapidly nitrided, and the intermetallic compound having a Th ₂ Zn ₁₇ type crystal structure is decomposed into an Fe-rich phase and SmN. It is guessed.

After cooling, the reaction product, which is a porous massive mixture, is not wet-treated, and the atmosphere gas is changed from an inert gas to a mixed gas containing at least ammonia and hydrogen, and the process proceeds to the next nitriding step.
If the reaction product is exposed to the atmosphere at this time, the active rare earth-iron master alloy powder in the reaction product is oxidized and the reactivity is lost. It is important to bring it into the nitriding process so that it is not exposed to (oxygen).

4). Fourth step: nitriding treatment In the nitriding step, first, after cooling in the final stage of the third step, the inert gas of the atmospheric gas is discharged, and then a mixed gas containing at least ammonia and hydrogen is introduced into the atmosphere. After the gas is completely replaced, the temperature is raised and the reaction product is heat-treated at a predetermined temperature.

The nitriding gas needs to contain at least ammonia and hydrogen, and argon, nitrogen, helium, etc. can be mixed to control the reaction.
The ratio of ammonia to the total airflow pressure (ammonia partial pressure) is 0.2 to 0.6, preferably 0.3 to 0.5. Within this range, the nitridation of the rare earth-iron master alloy is sufficiently advanced without taking a long time, and the nitrogen in the rare earth-iron master alloy necessary for obtaining the satisfactory saturation magnetization and coercive force of the magnet powder. The amount can be 3.3 to 3.7% by weight.

It is important to supply a mixed gas stream containing ammonia and hydrogen at a nitriding temperature of 350 to 500 ° C., preferably 400 to 480 ° C., and to subject the rare earth-iron base alloy to a nitriding heat treatment. When the heat treatment temperature is lower than 350 ° C., it takes a long time to introduce 3.3 to 3.7% by weight of nitrogen into the rare earth-iron master alloy in the reaction product. . On the other hand, when the temperature exceeds 500 ° C., for example, when the rare earth is samarium, the Sm ₂ Fe ₁₇ phase, which is the main phase, is decomposed to produce α-Fe, so that the finally obtained rare earth-transition metal-nitrogen based magnet This is not preferable because the squareness of the demagnetization curve of the powder is lowered. From the cooling temperature to the nitriding temperature, it is desirable to raise the temperature relatively rapidly at a rate of 4 to 10 ° C. per minute in order to increase production efficiency.
The retention time for the nitriding treatment is 100 to 300 minutes, preferably 140 to 250 minutes, although it depends on the nitriding temperature. If it is less than 100 minutes, nitriding becomes insufficient, while if it exceeds 300 minutes, nitriding proceeds excessively, which is not preferable.

In the present invention, following the nitriding treatment, the alloy powder can be further heat-treated in an inert gas such as hydrogen gas, nitrogen gas, argon gas, helium gas or the like. The alloy powder may be heat treated in two or more stages. It is particularly preferable to perform heat treatment with nitrogen gas and / or argon gas after heat treatment with hydrogen gas.
Thereby, the nitrogen distribution in the individual crystal cells constituting the magnet powder can be made more uniform, and the squareness can be improved. The holding time of the heat treatment is 30 to 200 minutes, preferably 60 to 250 minutes.

5). Fifth Step: Wet Treatment / Crushing In this step, the treated product after nitriding is wet treated, and a by-product of a reducing agent component contained therein (when calcium is used as a reducing agent, calcium oxide) And calcium nitride) are separated and removed from the rare earth-transition metal-nitrogen magnet coarse powder, and then pulverized.

In the present invention, as described above, the wet treatment is performed on the magnet powder after completion of nitridation. When the reaction product is wet-treated before nitriding, the surface of the rare earth-iron-based master alloy is treated in this wet treatment process. This is because the degree of nitridation is varied by being oxidized.
In addition, if the treatment product is left in the atmosphere for a long time after nitriding, oxides of reducing agent components such as calcium are generated and difficult to remove, or the surface of the magnet powder is oxidized, resulting in non-uniform nitriding and the main phase. Since the squareness decreases due to the decrease in the ratio and the generation of nucleation of nucleation, it is preferable to proceed the process as soon as possible.

In the wet treatment, first, the product obtained in the fourth step is put into water, decantation-water injection-decantation is repeated, and the hydroxide (Ca (OH) ₂ generated from the byproduct of the reducing agent. Etc.) a lot. Further, if necessary, acid cleaning is performed using acetic acid and / or hydrochloric acid in order to remove residual hydroxide (Ca (OH) _{2 and the} like). The hydrogen ion concentration of the aqueous solution at this time is preferably in the range of pH 4-7. A rare-earth-transition metal-nitrogen-based magnet may be present around the main phase due to the influence of rare earth metal (Sm) added excessively during reduction diffusion. In order to obtain good magnet characteristics as a coarse powder, when the rare earth is samarium, pickling is preferably performed so that the amount of Sm is 23.2 to 23.6% by weight with respect to the total amount of the magnet powder.
After completion of the acid cleaning treatment, for example, washing with water, dehydrating with an organic solvent such as alcohol or acetone, and drying in an inert gas atmosphere or vacuum to obtain a rare earth-transition metal-nitrogen magnet coarse powder. Can do.

  The obtained rare earth-transition metal-nitrogen based magnet coarse powder is composed of two kinds of secondary particles obtained by collecting a large number of particles having a small particle diameter and sintered in a grape shape, and single primary particles. Yes. Such a magnetic coarse powder is put together with a solvent into a pulverizer such as a bead mill or a medium stirring mill, and then pulverized to such an extent that the sintered portion of the rare earth-transition metal-nitrogen based magnetic coarse powder composed of secondary particles is removed, and then filtered. ,dry.

In order to crush the rare earth-transition metal-nitrogen based magnet coarse powder in the present invention, a pulverizer is used. The pulverizer is not particularly limited as long as it is widely used in various chemical industries that handle solids and can pulverize various materials to a desired degree. Among these, a medium stirring mill or a bead mill, which is excellent in that it is easy to make the composition and particle size of the powder uniform, is preferable. It is preferable to use a wet pulverization method using these, but it is important to avoid pulverization that is strong enough to break the primary particles.
As a solvent used for crushing, isopropyl alcohol, ethanol, toluene, methanol, hexane, or the like can be used, and isopropyl alcohol is particularly preferable. After pulverization, the rare earth-transition metal-nitrogen based magnet powder of the present invention can be obtained by finally filtering and drying using a filter having a predetermined opening.

6). Obtained Magnet Powder The rare earth-transition metal-nitrogen based magnet powder obtained by the production method of the present invention has a specific particle shape and particle size distribution, and exhibits excellent magnetic properties.
The rare earth-transition metal-nitrogen based magnet powder of the present invention has a particle surface shape and a cross section observed with a scanning electron microscope (SEM: Carl Zeiss, ULTRA55), and an average particle diameter is a laser diffraction particle size distribution manufactured by Sympatec. When measured with a measuring apparatus, the proportion of primary particles having a major axis particle diameter exceeding 4 μm is 5% or less in terms of the cumulative number percentage. The proportion of primary particles having a major axis particle diameter exceeding 4 μm is more preferably 3% or less in terms of cumulative number percentage. When primary particles whose major axis particle diameter exceeds 4 μm are increased, it is observed that particles causing nitriding deficiency exist when the cross section is confirmed. The present invention is characterized in that there are few large particles that also cause a decrease in saturation magnetization, squareness, and coercive force.
The magnetic properties of the magnet powder are measured according to Japan Bond Magnet Industry Association, Bond Magnet Test Method Guidebook, BM-2002, BM-2005. Specifically, a rare earth-transition metal-nitrogen magnet powder is oriented in stearic acid by applying an orientation magnetic field of 1600 A / m, and the sample is magnetized with a magnetic field of 4000 kA / m and measured. When the specific gravity of the magnet alloy powder is 7.67 g / cm ³ and measurement is performed using a vibrating sample magnetometer having a maximum magnetic field of 1200 kA / m without demagnetizing correction, the saturation magnetization: 4πIm (T) is 1.40. As described above, the coercive force: iHc (kA / m) is 870 or more, and the squareness: Hk (kA / m) is 410 or more. By optimizing the manufacturing conditions, the saturation magnetization: 4πIm (T) is 1.45 or more, the coercive force: iHc (kA / m) is 890 or more, and the squareness: Hk (kA / m) is , 420 or more. Hk represents the squareness of the demagnetization curve, and is the magnitude of the demagnetizing field when the magnetization 4πI takes 90% of the residual magnetization 4πIr in the second quadrant.
In order to obtain good magnet characteristics as the rare earth-transition metal-nitrogen based magnet powder, the rare earth content after the wet treatment in the fifth step is preferably maintained as it is after pulverization. In the case of samarium, the amount of Sm is preferably 23.2 to 23.6% by weight based on the total amount of the magnet powder.

  EXAMPLES Next, although this invention is further demonstrated using an Example and a comparative example, this invention is not limited at all by these Examples. The ratio of components in the heat treated hydrogen product obtained by the present invention, the exothermic behavior during reduction diffusion, and the particle shape and particle size distribution and magnetic properties of the obtained rare earth-transition metal-nitrogen based magnet powder were measured by the following methods. evaluated.

(1) Component ratio of hydrogen heat-treated product Using a powder X-ray diffractometer by XRD, the compounds are identified based on the measured data, and Rietveld analysis is used to determine the semi-quantitative values for the abundance ratio of these compounds. By calculating, the existence ratio of each compound component was determined.
(2) Exothermic behavior During reduction diffusion with Ca metal, an R thermocouple was set in the reaction vessel, and the magnitude of the exothermic reaction (heat generation amount) and the maximum exothermic temperature were measured and determined.
(3) Particle shape The particle surface shape and cross section of the rare earth-transition metal-nitrogen magnet powder obtained by wet treatment and pulverization treatment were observed with a scanning electron microscope (SEM: Carl Zeiss, ULTRA55).
(4) Particle size distribution The average particle size was measured by a laser diffraction particle size distribution measuring device manufactured by Sympatec: Heros Rhodes. The major axis diameter of the primary particles can be obtained by enlarging the photograph taken at 1000 times the primary particle size from the SEM image, measuring the length with a ruler with a minimum memory of 1 mm, and calculating the cumulative number percentage of particles. Asked.

(5) Magnetic properties The magnetic properties of the magnet powder are rare earths in stearic acid by applying an orientation magnetic field of 1600 A / m according to Japan Bond Magnet Industry Association, Bond Magnet Test Method Guidebook, BM-2002, BM-2005. -A sample was prepared by orienting transition metal-nitrogen based magnet powder, and measurement was performed by magnetizing with a magnetic field of 4000 kA / m.
The specific gravity of the magnet powder was 7.67 g / cm ^3, and a vibration sample type magnetometer with a maximum magnetic field of 1200 kA / m without demagnetizing correction was used. Saturation magnetization: 4πIm (T), coercivity: iHc (kA / m), squareness: Hk (kA / m) was measured. Hk represents the squareness of the demagnetization curve, and is the magnitude of the demagnetizing field when the magnetization 4πI takes 90% of the residual magnetization 4πIr in the second quadrant.
(6) Powder composition About the powder composition of the magnet powder, Sm, N, and O were analyzed by the following analysis method.
Sm: ICP emission spectroscopic analysis N: inert gas-impulse heating-melting-thermal conductivity method (LECO method)
O: Inert gas-impulse heating-melting-infrared absorption method (LECO method)

Example 1
As the magnet raw material powder, 100.0 g of iron oxide Fe ₂ O ₃ powder (manufactured by High-Purity Chemical Co., Ltd.) with an average particle size adjusted to 1.2 μm and 96% of the powder having a particle size of 0.1-10 μm 31.8 g of occupied samarium oxide Sm ₂ O ₃ powder (Kanto Chemical) was weighed, and then iron oxide weighed in a 1 L plastic container was dispersed in 200 g of pure water to form a slurry. At this time, since the pH was 7.2, 0.5 mol / L dilute hydrochloric acid was dropped into the stirring slurry, and the whole amount of samarium oxide was gradually added while controlling the pH to be 2. After the addition, the mixture was stirred for about 1 hour until all the samarium oxide was dissolved, and then calcium oxide was added until pH = 8.
Thereafter, the slurry was discharged from the plastic container, washed with water, sprayed, filtered, and then dried at a setting of 100 ° C. for 24 hours in a stationary vacuum dryer.
100.0 g of the dried mixed powder was flowed in a box-type atmosphere furnace with 25 ml / (min · g) of hydrogen, heated to 600 ° C. at a heating rate of 5 ° C./min and held for 4 hours, then cooled to room temperature, The inside was replaced with air, and the hydrogen reduction product was recovered.
A part of the hydrogen reduction product at this time was identified by XRD, and the abundance ratio was calculated as a semi-quantitative value by Rietveld analysis. The abundance ratio at this time was α-Fe: Sm ₂ O ₃ : SmFeO ₃ = 57.8: 3.8: 38.4 (% by weight).
3.6 g of metal calcium particles (made by Wako Pure Chemical Industries) having a particle size of 4 mesh (Tyler mesh) or less were mixed with 16 g of this hydrogen reduction product with a conditioning mixer (MX-201: made by Sinky) for 30 seconds.
This was inserted into a stainless steel reaction vessel, and the inside of the vessel was evacuated with a rotary pump and replaced with Ar gas. Then, the temperature was raised to 950 ° C. while flowing Ar gas, held for 8 hours, and then Ar gas in the furnace to 250 ° C. Cooled while circulating. Next, the Ar gas is switched to an ammonia-hydrogen mixed gas with an ammonia partial pressure of 0.33, the temperature is raised, held at 450 ° C. for 200 minutes, then switched to hydrogen gas at the same temperature and held for 30 minutes, It switched to nitrogen gas, hold | maintained for 30 minutes, and cooled.
The taken porous mass reaction product was immediately poured into pure water, and collapsed to obtain a slurry. From this slurry, the Ca (OH) ₂ suspension was separated by decantation, and the operation of stirring pure water for 1 minute after water injection and then decanting was repeated 5 times to obtain an alloy powder slurry.
While stirring the obtained alloy powder slurry, dilute acetic acid was added dropwise, and the pH was maintained at pH 5.0 for 7 minutes. The alloy powder is filtered, washed with water several times with ethanol, and vacuum-dried at 35 ° C., thereby forming Sm—Fe—N magnets composed of primary particles and grape-like secondary particles sintered together. A powder was obtained.
The powder composition was Sm: 23.4% by weight, N: 3.35% by weight, O: 0.12% by weight, and the balance Fe.
This alloy powder was crushed in ethanol using a vibration mill (multi-mill: manufactured by Narumi Giken) in ethanol at SUJ2 balls 5/32 inches, vibration frequency 30 Hz, for 30 minutes, and vacuum dried at room temperature.
The magnetic properties of the obtained magnet powder and the magnetic properties of the alloy powder were applied with an orientation magnetic field of 1600 A / m in accordance with Japan Bond Magnet Industry Association, Bond Magnet Test Method Guidebook, BM-2002, BM-2005. A sample was prepared by orienting rare earth-iron-nitrogen magnet powder in stearic acid, and magnetized with a magnetic field of 4000 kA / m. The specific gravity of the magnet alloy powder was 7.67 g / cm ^3, and a saturation sample: 4πIm (T) and coercive force: iHc (kA) using a vibrating sample magnetometer with a maximum magnetic field of 1200 kA / m without correcting the demagnetizing field. / M), squareness: Hk (kA / m) was measured.
The X-ray density of the powder calculated from the analytical composition and the lattice constant of the Th ₂ Zn ₁₇ type crystal structure was 7.67 g / cm ³ , and the saturation magnetization (4πIm) was converted with this value. iHc is the coercive force. Hk represents the squareness of the demagnetization curve, and is the magnitude of the demagnetizing field when the magnetization 4πI takes 90% of 4πIr in the second quadrant. The results are shown in Table 1, and high magnetic properties were obtained.
Furthermore, as a result of calculating the abundance ratio of primary particles exceeding the major axis diameter of 4 μm from the pulverized magnet powder by the cumulative number percentage, it was 2.0%.

(Example 2)
Under the conditions of Example 1, when the hydrogen heat treatment was performed in the same manner as in Example 1 except that the time to wait until samarium oxide was dissolved was changed to about 5 hours by changing from pH = 2 to 5, The abundance ratio of α-Fe: Sm ₂ O ₃ : SmFeO ₃ = 60.0: 9.3: 30.7 (% by weight). Thereafter, reduction diffusion, nitriding treatment, and wet treatment were performed to obtain Sm—Fe—N crude powder. Grape-like secondary particles in which the primary particles and the primary particles were sintered were observed in the obtained powder.
The powder composition was Sm: 23.3 wt%, N: 3.31 wt%, O: 0.15 wt%, and the balance Fe. In the same manner as in Example 1, after crushing and sampling, magnetic characteristics were obtained. The results are shown in Table 1, and high magnetic properties were obtained. Further, the proportion of primary particles having a major axis diameter exceeding 4 μm was calculated from the pulverized magnet powder by the cumulative number percentage, which was 4.2%.

(Example 3)
Under the conditions of Example 1, hydrogen heat treatment was performed in the same manner as in Example 1 except that dilute hydrochloric acid was changed to dilute nitric acid. The abundance ratio at this time was α-Fe: Sm ₂ O ₃ : SmFeO ₃ = It was 57.8: 3.9: 38.3 (% by weight). Thereafter, reduction diffusion, nitriding treatment, and wet treatment were performed to obtain Sm—Fe—N crude powder. Grape-like secondary particles in which the primary particles and the primary particles were sintered were observed in the obtained powder.
The powder composition was Sm: 23.5 wt%, N: 3.36 wt%, O: 0.14 wt%, and the balance Fe. In the same manner as in Example 1, after crushing and sampling, magnetic characteristics were obtained. The results are shown in Table 1, and high magnetic properties were obtained.
Furthermore, as a result of calculating the abundance ratio of primary particles having a major axis diameter exceeding 4 μm from the pulverized magnet powder by the cumulative number percentage, it was 2.3%.

Example 4
Under the same conditions as in Example 1, except that the calcium oxide for neutralizing the slurry was changed to sodium hydroxide (Kanto Chemical) and hydrogen reduction was performed, the abundance ratio at this time was α —Fe: Sm ₂ O ₃ : SmFeO ₃ = 57.8: 3.9: 38.3 (% by weight). Thereafter, reduction diffusion, nitriding treatment, and wet treatment were performed to obtain Sm—Fe—N crude powder. Grape-like secondary particles in which the primary particles and the primary particles were sintered were observed in the obtained powder.
The powder composition was Sm: 23.2% by weight, N: 3.33% by weight, O: 0.14% by weight, and the balance Fe. In the same manner as in Example 1, after crushing and sampling, magnetic characteristics were obtained. The results are shown in Table 1, and high magnetic properties were obtained.
Furthermore, as a result of calculating the abundance ratio of primary particles having a major axis diameter exceeding 4 μm from the pulverized magnet powder by the cumulative number percentage, it was 2.6%.

(Comparative Example 1)
As the magnet raw material powder under the conditions of Example 1, 100.0 g of iron oxide Fe ₂ O ₃ powder (Wako Pure Chemical Industries) with an average particle diameter adjusted to 0.7 μm and a powder having a particle diameter of 0.1 to 10 μm as a whole 31.8 g of samarium oxide Sm ₂ O ₃ powder (Kanto Chemical) accounting for 96% of the total was then weighed, and then iron oxide weighed in a 1 L plastic container was dispersed in 200 g of pure water to make a slurry. At this time, although the pH was 2.3, samarium oxide was further added thereto, followed by stirring (pH at the end of the charging = 8.2), filtration, and drying. Thereafter, when hydrogen reduction was performed in the same manner as in Example 1, the abundance ratio at this time was as follows: α-Fe: Sm ₂ O ₃ : SmFeO ₃ = 64.3: 20.1: 15.6 (% by weight) Met. Thereafter, reduction diffusion, nitriding treatment, and wet treatment were performed to obtain Sm—Fe—N crude powder. The resulting powder was observed to have primary particles and grape-like secondary particles, and large primary particles, which were sintered together. The powder composition was Sm: 23.3 wt%, N: 3.31 wt%, O: 0.16 wt%, and the balance Fe. In the same manner as in Example 1, after crushing and sampling, magnetic characteristics were obtained. The results are shown in Table 1.
Furthermore, as a result of calculating the abundance ratio of primary particles having a major axis diameter exceeding 4 μm from the pulverized magnet powder by the cumulative number percentage, it was 9.3%.

(Comparative Example 2)
When hydrogen reduction was performed in the same manner except that wet mixing was not performed during initial powder mixing under the conditions of Example 1 and the dry mixing was performed using a Julia mixer manufactured by Deoksugaku Kosakusho, the abundance ratio at this time was α-Fe : Sm ₂ O ₃ : SmFeO ₃ = 67.4: 28.1: 4.5 (% by weight). Thereafter, reduction diffusion, nitriding treatment, and wet treatment were performed to obtain Sm—Fe—N crude powder. Grape-like secondary particles in which the primary particles and the primary particles were sintered were observed in the obtained powder.
The powder composition was Sm 23.4% by weight, N 3.36% by weight, O 0.14% by weight and the balance Fe. In the same manner as in Example 1, after crushing and sampling, magnetic characteristics were obtained. The results are shown in Table 1.
Furthermore, the proportion of primary particles having a major axis diameter exceeding 4 μm was calculated from the pulverized magnet powder by the cumulative number percentage, and the result was 3.4%.

(Comparative Example 3)
When hydrogen reduction was performed in the same manner as in Example 1 except that a large amount of dilute hydrochloric acid was added and the pH was changed from 2 to 1, hydrogen reduction was performed. The abundance ratio at this time was α-Fe: Sm. ₂ O ₃ : SmFeO ₃ = 62.7: 16.3: 21.0 (% by weight). Thereafter, reduction diffusion, nitriding treatment, and wet treatment were performed to obtain Sm—Fe—N crude powder. Grape-like secondary particles in which the primary particles and the primary particles were sintered were observed in the obtained powder.
The powder composition was Sm: 23.3 wt%, N: 3.31 wt%, O: 0.16 wt%, and the balance Fe. In the same manner as in Example 1, after crushing and sampling, magnetic characteristics were obtained. The results are shown in Table 1.
Furthermore, as a result of calculating the abundance ratio of primary particles having a major axis diameter exceeding 4 μm from the pulverized magnet powder by the cumulative number percentage, it was 6.7%.

(Comparative Example 4)
Under the same conditions as in Example 2, except that dilute hydrochloric acid was used in a small amount and the pH was changed from 5 to 6, hydrogen reduction was performed. The abundance ratio at this time was α-Fe: Sm ₂ O _3. : SmFeO ₃ = 65.8: 23.9: 10.3 (% by weight). Thereafter, reduction diffusion, nitriding treatment, and wet treatment were performed to obtain Sm—Fe—N crude powder. Grape-like secondary particles in which the primary particles and the primary particles were sintered were observed in the obtained powder.
The powder composition was Sm: 23.2% by weight, N: 3.32% by weight, O: 0.13% by weight, and the balance Fe. In the same manner as in Example 1, after crushing and sampling, magnetic characteristics were obtained. The results are shown in Table 1.
Further, the proportion of primary particles having a major axis diameter exceeding 4 μm was calculated from the pulverized magnet powder by the cumulative number percentage, which was 10.3%.

"Evaluation"
From the results shown in Table 1, in Examples 1 to 3, since the pH value of the slurry in which iron oxide is dispersed in water is in the range of 2 to 5, the amount of SmFeO ₃ produced is 30% by weight, which is larger than usual. As a result, it is possible to obtain a powder having a low presence ratio of coarse particles and excellent magnetic properties.
In Comparative Example 1, the rare earth oxide is changed directly into an acidic slurry in which iron oxide powder is dispersed in water. However, although SmFeO ₃ is produced, the increase in the amount of coarse particles and the overall magnetic properties are improved. Decline was confirmed. This is an acidic slurry having a pH of 2.3 when iron oxide is dispersed in pure water. When Sm ₂ O ₃ is added and dispersed therein, the pH exceeds neutral and is alkaline (pH = 8). However, Sm ₂ O ₃ does not dissolve in the whole amount but is present in the slurry as a mixture of microcrystalline samarium hydroxide and undissolved samarium oxide. When this is reduced with hydrogen, SmFeO ₃ is produced, but most of it is from microcrystalline samarium hydroxide. As a result, the amount of SmFeO ₃ produced is as low as 15.6%, and the uniformity of thermite heat generation is lost. It can be said that the grain size distribution was broadened due to rapid grain growth, causing a decrease in magnetic properties.
In Comparative Example 2, treatment by dry mixing was performed, but SmFeO ₃ was present due to the influence of moisture slightly because it was performed in an air atmosphere at this time, but the proportion of coarse particles was close to that of the Example. This is because SmFeO ₃ is hardly present unlike the example, so that thermite heat generation is very small and local grain growth is difficult to occur. However, since the mixing effect by dry mixing is insufficient and the distance between Sm and Fe is far, the presence of unreacted Sm fine powder or uniform diffusion is not performed and the composition of the product varies in a microscopic view. Therefore, it is considered that the magnetic characteristics were adversely affected.
In Comparative Examples 3 and 4, the pH outside the range of the present invention was carried out. However, when the pH was controlled to 1, hydroxylation of the iron oxide to the particle surface was carried out because a large amount of calcium oxide was added when finally making it alkaline. It shows a tendency to inhibit the precipitation of samarium, and many independent particles of samarium hydroxide are observed. For this reason, SmFeO ₃ tends to decrease as compared with the control of pH = 2, there are many coarse particles, and the magnetic properties tend to deteriorate. In addition, when the pH is controlled to 6, the dissolution of Sm ₂ O ₃ hardly progresses, and it is very difficult to control the pH because it is near the inflection point. However, the amount of SmFeO ₃ produced tends to increase in Comparative Example 1. For this reason, since the amount of SmFeO ₃ is not so much as in Comparative Example 1, the uniformity is further lost, and conversely, the number of coarse particles is large and the magnetic characteristics are also low.

Claims (9)

  Slurry iron oxide powder with an average particle size of 2 μm or less as a magnet raw material with an aqueous solvent, and then add 1 mol / L or less of dilute acid so that the pH value of this slurry is maintained in the range of 2 to 5 Then, a predetermined amount of the rare earth oxide is added and dissolved, and then the alkali metal salt or alkaline earth metal salt is added so that the pH exceeds 7.0, whereby the rare earth hydroxide is applied to the iron oxide surface. A first step of producing the precipitated raw material mixed powder, a second step of subjecting the obtained raw material mixed powder to a hydrogen heat treatment, a predetermined amount of alkaline earth metal as a reducing agent component is added to the hydrogen-heat treated mixed powder, A third step of mixing and heat-treating in an inert gas atmosphere at a temperature of 900 to 1300 ° C. and then cooling in the same atmosphere to obtain a rare earth-iron based master alloy, followed by the obtained rare earth- For ferrous mother alloys A fourth step of introducing a mixed gas containing at least ammonia and hydrogen and performing a nitriding treatment by heat-treating at a predetermined temperature in the air stream, then wet-treating the obtained nitriding product, and reducing agent A method for producing a rare earth-transition metal-nitrogen magnet powder comprising a fifth step of separating and removing component by-products and then crushing the obtained coarse powder.   2. The method for producing a rare earth-transition metal-nitrogen magnet powder according to claim 1, wherein in the first step, the dilute acid is either hydrochloric acid or nitric acid.   2. The rare earth according to claim 1, wherein in the first step, the alkali metal salt or alkaline earth metal salt is a hydroxide, oxide, nitride or a composite compound thereof exhibiting alkalinity in water. -Method for producing transition metal-nitrogen based magnet powder.   The method for producing a rare earth-transition metal-nitrogen based magnet powder according to claim 1, wherein the drying temperature of the mixed powder is 300 ° C. or lower in the first step.   2. The method for producing a rare earth-transition metal-nitrogen based magnet powder according to claim 1, wherein the mixed powder is subjected to hydrogen heat treatment at 500 to 800 ° C. for 1 to 8 hours in the second step.   In the third step, when the amount of alkaline earth metal added is 1 equivalent to the amount required to reduce the amount of oxygen in the raw material powder not reduced until the second step, 1.1 to The method for producing a rare earth-transition metal-nitrogen based magnet powder according to claim 1, wherein the equivalent is 3.0 equivalents.   3. The rare earth element according to claim 1, wherein in the third step, the reaction product after the reduction-diffusion reaction is further cooled to 300 ° C. or lower with the atmosphere gas kept as an inert gas. A method for producing a transition metal-nitrogen magnet powder.   The powder obtained by the wet treatment and pulverization in the fifth step is characterized in that primary particles having a major axis particle diameter exceeding 4 μm are less than 5% in cumulative number percentage. A method for producing a rare earth-transition metal-nitrogen based magnet powder.   The rare earth-transition metal-nitrogen based magnet powder contains Sm as a rare earth, and its content is 23.2 to 23.6 wt% with respect to the whole magnet powder. -Method for producing transition metal-nitrogen based magnet powder.