Manufacturing method of Sm-Fe-N magnetic powder and Sm-Fe-N magnetic powder

Abstract

To provide Sm-Fe-N-based magnetic powder which exhibits a high maximum energy product (BH)max and has less impurities and is effective for performance improvement and producibility improvement of a bonded magnet.SOLUTION: A method for producing Sm-Fe-N-based magnetic powder is provided, having: a heat treatment step of heating powder of Sm-Fe-based alloy which has a Sm / Fe molar ratio of 0.09 or more and 0.25 or less and is formed by a coagulation process by a gas atomization method to a temperature of 900°C or higher and 1200°C or lower thereby coarsening crystal grains of the powder; a pulverization step of pulverizing the powder of Sm-Fe-based alloy, whose crystal grains have been coarsened by the heat treatment step, thereby refining the powder grains by rupture including crystal transgranular fracture; and a nitriding step of heating and holding the powder of Sm-Fe-based alloy which has been refined by the pulverization step, in a non-oxidizing gas atmosphere containing nitrogen compound or nitrogen within a temperature range of 500°C or lower thereby introducing nitrogen into the powder grains.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for producing Sm-Fe-N based magnetic powder and to Sm-Fe-N based magnetic powder. [Background technology]

[0002] SmFe 17 A material in which nitrogen is introduced into an intermetallic compound (the typical composition formula is Sm2Fe 17 N3) is known to be a ferromagnetic material that exhibits excellent hard magnetic properties. 17 Powder of a substance in which nitrogen is introduced into an Sm-Fe alloy with a stoichiometric composition or a composition close to the stoichiometric composition, and which is a ferromagnetic material, is called "Sm-Fe-N magnetic powder." Sm-Fe-N magnetic powder is useful as a material for bonded magnets.

[0003] Known manufacturing techniques for Sm-Fe-N magnetic powder include methods that use solidification processes such as the atomization method and the single roll method, and methods that use a reduction diffusion method using Ca or other reducing agents.

[0004] For example, Patent Document 1 describes a method for producing SmFe 17 Spherical particles of the alloy were synthesized, and the resulting powder was nitrided in a tube furnace to produce SmFe 17 It is described that an alloy powder having a composition of N3 was obtained. The average particle size of the particles obtained by the gas atomization method is 110 μm (paragraph 0012) or 80 μm (paragraph 0014).

[0005] Patent Document 2 describes an example of the synthesis of magnetic powder having a composition in which elements such as Si are added to Sm-Fe or Sm-Fe-C systems using an atomization method involving gas atomization, gas-water atomization, and water atomization. The particle size is about 80 to 110 μm (paragraph 0019). The particles obtained are then subjected to a nitriding treatment to obtain Sm-Fe-(C)-Si-N powder. The magnetic powder after nitriding has a maximum energy product (BH) max 6-13 MGOe (48-103 kJ / m 3), with a maximum of 18.2 MGOe (145 kJ / m 3 ) (Table 5).

[0006] Patent Document 3 shows an example (Example 1) of obtaining Sm-Fe-N magnetic powder with a particle size of 106 μm or less by heat treating a thin plate-shaped quenched alloy obtained by the single roll method at 750°C, nitriding it at 450°C for 2 hours, and then pulverizing it. The maximum energy product (BH) of the powder is max is 102kJ / m 3 (Table 2).

[0007] Patent Document 4 discloses a technique for obtaining magnetic powder such as Sm-Fe-N powder by using a reduction diffusion method and nitriding treatment using Ca, and by adopting a process of performing the reduction reaction twice, thereby obtaining powder with an average particle size of 5 μm or less without using any pulverization process. It is described that the powder that has undergone the second reduction process is "washed with water and then thoroughly separated from the calcium using a weak acid such as acetic acid." Nevertheless, 0.01 wt% of Ca remains in the powder obtained in the examples (paragraphs 0034, 0037, 0047, 0050, 0060).

[0008] Patent Document 5 discloses a technique for obtaining Sm-Fe-N magnetic powder having a core-shell structure by subjecting particles obtained by a reduction diffusion method using Ca to hydrogen treatment, crushing treatment, and then nitriding treatment. The particle size of the Sm-Fe-N magnetic powder obtained in the examples is D 50 is 2.8 to 9.1 μm (paragraphs 0122, 0131, 0136, 0139, 0144, 0151, 0158, 0165, 0172), and the residual magnetization σ r 101~102Am 2 / kg (paragraphs 0123 and 0133). The particles contain Ca at, for example, less than 0.01 mass% (paragraph 0114). The inner layer of the shell consisting of an outer layer and an inner layer is said to contain no Ca, but in Patent Document 5, "containing no Ca" means that the Ca content is less than 1.0 atomic % (paragraph 0043). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 7-11307 [Patent Document 2] JP 2001-68315 A [Patent Document 3] JP 2002-246212 A [Patent Document 4] Japanese Patent Application Publication No. 11-310807 [Patent Document 5] JP 2022-177699 A Summary of the Invention [Problem to be solved by the invention]

[0010] In recent years, in order to meet the increasing demands for high performance automobile motors and sensors, bonded magnets using Sm-Fe-N magnetic powders are expected to have even better magnetic properties. In particular, the maximum energy product (BH) is essential for improving the properties of anisotropic bonded magnets. max It is advantageous to use magnetic powder with as high a BH as possible. The solidified metal obtained by rapid solidification processes such as the atomization method and the single roll method generally has a polycrystalline structure consisting of fine crystals. In magnetic powder derived from such fine polycrystalline solidified metal, a high BH max It is not easy to realize this. As described above, Patent Documents 2 and 3 disclose the (BH) of magnetic powder using Sm. max However, in order to contribute to improving the properties of anisotropic bonded magnets, (BH) max Further improvement is desired.

[0011] On the other hand, the reduction-diffusion method, which uses Ca as a reducing agent, is complicated and generates alkaline wastewater, which places a heavy burden on the environment. In addition, the Sm-Fe-N magnetic powder obtained by the reduction-diffusion method inevitably contains residual reducing agent components such as Ca and other alkaline earth metals and alkali metals. The alkaline earth metals and alkali metals remaining in the magnetic powder tend to gel the resin when the powder is used as a raw material to produce bonded magnets, which can reduce the manufacturability of the bonded magnets.

[0012] The present invention has a high maximum energy product (BH) max The objective of the present invention is to provide an Sm-Fe-N magnetic powder that exhibits excellent magnetic properties and has few impurities, and is useful for improving the performance and manufacturability of bonded magnets. [Means for solving the problem]

[0013] The use of gas atomization is an effective way to obtain powder of Sm-Fe alloys with an extremely small amount of Ca. In this specification, the term "gas atomized powder" refers to powder composed of particles that have not been subjected to any physical or chemical treatment (e.g., application of external force, magnetic force, heat treatment, surface treatment, etc.) after synthesis by gas atomization. Gas atomized powder particles are formed by rapid solidification, and are therefore polycrystalline particles composed of very fine crystal grains. Polycrystalline particles have a high maximum energy product (BH), maxIt is difficult to obtain a fine grain size. In addition, according to the inventors' research, when polycrystalline particles consisting of fine crystal grains are reduced in size by mechanical pulverization, many grain boundaries where cracks are likely to propagate exist, and therefore fracture at the grain boundaries proceeds preferentially, and each reduced particle is likely to become a particle consisting of a plurality of crystal grains with the grain boundaries remaining inside. In other words, it is very difficult to divide particles consisting of fine crystal grains into particles consisting of single crystal grains by pulverization. Therefore, the inventors have investigated an effective means for obtaining a powder containing many particles consisting of single crystal grains by using gas atomized powder as a raw material. As a result, it has been found that when gas atomized powder of Sm-Fe alloy is heat-treated at high temperature, the growth of fine crystal grains occurs, and the crystal grains can be coarsened to a size of, for example, about 3 to 15 μm in average crystal grain size in the circle equivalent diameter in the cross-sectional structure of the particles. It was found that when mechanically pulverizing Sm-Fe alloy powder composed of such coarse grains, the individual particles are broken by fracture at the grain boundaries (intergranular fracture) as well as within the grains (intragranular fracture), resulting in a fine Sm-Fe alloy powder with a high proportion of particles made up of single grains. In addition, the powder was nitrided to obtain Sm-Fe-N magnetic powder, which has a maximum energy product (BH) of max It was also confirmed that the above-mentioned effects were significantly improved. The present invention is based on such findings.

[0014] The above object can be achieved by the following invention. [1] A heat treatment process in which a powder of an Sm-Fe alloy having a Sm / Fe molar ratio of 0.09 to 0.25, formed during the solidification process by the gas atomization method, is heated to a temperature of 900°C to 1200°C to coarsen the crystal grains of the powder; a crushing step of crushing the powder of the Sm-Fe alloy, the crystal grains of which have become coarse by the heat treatment step, to thereby reduce the particles of the powder by fracture, including intragranular fracture; a nitriding step of introducing nitrogen into the particles of the Sm-Fe alloy powder refined by the pulverization step by heating and holding the powder at a temperature range of 500°C or less in a nitrogen compound or nitrogen-containing non-oxidizing gas atmosphere; A method for producing Sm-Fe-N based magnetic powder having the above structure. [2] The method for producing the Sm-Fe-N magnetic powder according to the above [1], wherein the powder of the Sm-Fe alloy to be pulverized in the pulverization step is subjected to a hydrogen treatment in which the powder is heated and held in a hydrogen atmosphere after the heat treatment step. [3] In the pulverization process, the cumulative 50% particle diameter D 50 The method for producing an Sm-Fe-N based magnetic powder according to the above [1] or [2], wherein a powder having a particle size of 0.5 μm or more and 5.0 μm or less is obtained. [4] The method for producing an Sm-Fe-N magnetic powder according to any one of the above [1] to [3], wherein in the pulverizing step, the Sm-Fe alloy powder is pulverized using a jet mill. [5] The method for producing an Sm-Fe-N magnetic powder according to any one of the above [1] to [4], wherein the non-oxidizing gas atmosphere in the nitriding step is a nitrogen gas atmosphere. [6] The Sm-Fe-N magnetic powder has a maximum energy product (BH) of max is 150kJ / m 3 The above is a method for producing an Sm-Fe-N magnetic powder according to any one of the above [1] to [5]. [7] The Sm-Fe-N magnetic powder is Th2Zn 17 The method for producing an Sm-Fe-N based magnetic powder according to any one of the above [1] to [6], which has a type crystal structure. [8] The method for producing a Sm-Fe-N magnetic powder according to any one of the above [1] to [7], wherein the Sm-Fe-N magnetic powder has an N / Fe molar ratio of 0.06 or more and 0.30 or less. [9] A powder consisting of particles mainly composed of Sm, Fe, and N, in which the molar ratio of Sm to Fe (Sm / Fe) is 0.09 to 0.25, and the Ca content in the powder is 0.005 mass% or less, and the cumulative 50% particle diameter D in the volume-based particle size distribution by the laser diffraction / scattering method is 50 is 0.5μm or more and 5.0μm or less, and the maximum energy product (BH) max is 150kJ / m 3 That is all for the Sm-Fe-N magnetic powder.

[10] Squareness ratio σ r / σ s The Sm-Fe-N magnetic powder according to the above [9], wherein the σ is 0.760 or more.

[11] Th2Zn 17 The Sm-Fe-N magnetic powder according to the above [9] or

[10] , having a type crystal structure.

[12] The Sm-Fe-N magnetic powder according to any one of the above [9] to

[11] , having a composition in which the molar ratio of N to Fe, N / Fe, is 0.06 or more and 0.30 or less. Effect of the Invention

[0015] According to the present invention, the maximum energy product (BH) can be achieved by a process that does not cause an environmental load due to alkaline waste liquid. max This Sm-Fe-N magnetic powder has an extremely low amount of Ca, which avoids the problem of Ca promoting gelation of resin when producing bonded magnets using resin, and is expected to improve productivity in processes such as magnetic field orientation. [Brief description of the drawings]

[0016] [Figure 1] An example of an IPF map taken by EBSD for the cross section of a particle obtained by heating Sm-Fe gas atomized powder at 700°C for 1 minute. [Diagram 2] An example of an IPF map taken by EBSD for the cross section of a particle obtained by heating Sm-Fe gas atomized powder at 1000°C for 1 minute. [Diagram 3]FIG. 2 is a diagram showing a schematic configuration of a gas atomizing device used in the examples and comparative examples. [Figure 4] FIG. 2 is a schematic diagram showing a cross-sectional structure near the bottom of a crucible of a gas atomizing device used in Examples and Comparative Examples. [Diagram 5] FIG. 13 is a diagram illustrating an IPF map by EBSD for the particle cross section of the Sm—Fe—N magnetic powder obtained in Example 2. [Figure 6] FIG. 2 is a diagram illustrating an IPF map by EBSD for a particle cross section of the Sm—Fe—N magnetic powder obtained in Comparative Example 1. [Figure 7] FIG. 2 is a diagram illustrating an X-ray diffraction pattern using Co-Kα radiation for the Sm-Fe-N magnetic powder obtained in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A typical manufacturing process for the Sm-Fe-N magnetic powder according to the present invention is "gas atomization -> heat treatment -> hydrogen treatment -> pulverization -> nitriding treatment."

[0018] [Gas atomization] In the present invention, powder of Sm-Fe alloy solidified by gas atomization is used. Gas atomization is a powder formation technique in which gas is blown at high speed onto the molten metal discharged into a gas space, the molten metal is divided into fine liquid phase particles, and the liquid phase particles are rapidly cooled and solidified while flying in the gas space. As the metal raw material for generating the molten metal to be subjected to gas atomization, Sm-Fe master alloy, metal Sm, metal Fe, etc., which are melted in advance and have a known composition, can be used. Sm2Fe 17 The stoichiometric Sm / Fe molar ratio is 0.118. The composition of the molten metal is SmFe 17It is desirable to adjust the Sm / Fe molar ratio to a value relatively close to the stoichiometric composition, specifically, to a range of 0.09 to 0.25. Although the inclusion of metal elements other than Sm and Fe is permitted to the extent that it does not impair the required properties of the magnetic powder finally obtained, the total content of Sm and Fe in the molten metal is preferably 95.0 mass% or more, and more preferably 98.0 mass% or more. It is desirable to generate the molten metal in an inert gas atmosphere other than nitrogen or in a vacuum.

[0019] The molten metal, which is kept at a specified temperature and sufficiently homogenized, is discharged from the nozzle into the gas phase space, and cooling gas is forcefully sprayed onto the molten metal immediately after discharge. This causes the molten metal to turn into fine liquid phase particles, which fly through the gas phase space and solidify. The temperature of the molten metal at the time of discharge may be set within the range of 1400 to 1900°C. The particle size can be controlled by the atomization conditions, but if necessary, the gas atomized powder may be classified using a sieve or the like to adjust the particle size, and then sent to the post-processing. Considering that the gas atomized powder will be pulverized into fine particles with an average particle size of several μm or less in the post-processing, the particle size of the gas atomized powder should be determined based on the cumulative 50% particle size D in the volume-based particle size distribution determined by the laser diffraction and scattering method. 50 For example, the particle size of the gas atomized powder is preferably 70.0 μm or less, more preferably 50.0 μm or less, and even more preferably 25.0 μm or less. There is no particular lower limit to the particle size of the gas atomized powder, but the above D 50 At present, it is extremely difficult to industrially synthesize particles with a diameter of less than 5.0 μm. 50 It is sufficient to adjust the thickness to be in the range of 5.0 μm or more, and it may be controlled to be in the range of 10.0 μm or more.

[0020] In the gas atomization process, it is desirable that the pressurizing gas for discharging the molten metal, the injection gas sprayed onto the molten metal, and the atmospheric gas in the gas phase space in which the liquid particles fly are all inert gases other than nitrogen. If these gases contain nitrogen, the gas atomized powder will be incompletely nitrided, making it difficult to achieve highly uniform nitriding in the subsequent nitriding process.

[0021] [Heat treatment] The gas atomized powder of Sm-Fe alloy (hereinafter, sometimes referred to as "Sm-Fe gas atomized powder") is subjected to a high-temperature heat treatment to coarsen the crystal grains. Specifically, by heating to 900°C or higher, the crystal grains can be coarsened to a size in which the average crystal grain size in the equivalent circle diameter in the cross-sectional structure of the particles is, for example, about 3 to 15 μm. This coarsening of the crystal grains makes it easier to obtain fine Sm-Fe alloy powder with a high ratio of particles consisting of single crystal grains in the subsequent crushing process. Intragranular fracture is more likely to occur. It is more preferable to heat to 930°C or higher. Since excessive heating is uneconomical, the heating temperature is preferably set in the range of 1200°C or lower, and may be controlled to 1100°C or lower, or 1000°C or lower. The holding time in the temperature range of 900°C to 1200°C can be, for example, 10 seconds to 10 minutes, and may be set in the range of 30 seconds to 5 minutes. The heating atmosphere is preferably an inert gas atmosphere other than nitrogen, or a vacuum.

[0022] 1 and 2 show examples of IPF maps (inverse pole figure crystal orientation maps) by EBSD (electron backscatter diffraction) for the cross-sections of particles obtained by heating Sm-Fe gas atomized powder obtained by the same method as in Example 1 described later at 700°C and 1000°C, respectively. The atmosphere during heating in both cases was argon gas, and the heating retention time at each temperature was 1 minute. These IPF maps are monochromeized color images of IPF maps obtained by EBSD measurement for the sample surface on which the cross-sections of the particles appeared, which was prepared by ion milling after polishing the resin in which the powder particles were embedded. In the monochrome IPF map, each crystal grain is represented as a brightness difference based on the crystal orientation difference. Comparison between FIG. 1 and FIG. 2 shows that the coarsening of the crystal grains is further promoted by heating to a high temperature.

[0023] In Sm-Fe gas atomized powder, it is possible that a Sm-Fe metal phase with a TbCu7 type crystal structure may be generated depending on the conditions. The TbCu7 type Sm-Fe metal phase is Th2Zn17 Since the anisotropic magnetic field after nitriding is smaller than that of the TbCu7 type and it is difficult to obtain a high coercive force, it is desirable to have as little of the TbCu7 type Sm-Fe metal phase as possible. 17 Since the heat treatment changes the structure, it is also effective in homogenizing the structure.

[0024] [Hydrogen treatment] In order to facilitate intragranular fracture in the subsequent crushing process, it is effective to perform hydrogen treatment by heating in a hydrogen gas atmosphere before crushing. Hydrogen penetrates into the crystal grains of the Sm-Fe alloy by hydrogen treatment, and intragranular fracture becomes more likely to occur due to the phenomenon of so-called hydrogen embrittlement. Therefore, hydrogen treatment can be performed as necessary. The heating temperature for hydrogen treatment is preferably set in the range of 200°C to 600°C, and the holding time in that temperature range may be set in the range of, for example, 30 minutes to 600 minutes.

[0025] [Crush] When mechanically pulverizing the powder of Sm-Fe alloy with the grains coarsened by the above heat treatment, the individual particles are broken by the occurrence of fracture within the grains (intragranular fracture) in addition to fracture at the grain boundaries (intergranular fracture). When the powder particles are refined by such "fracture including intragranular fracture", fine Sm-Fe alloy powder with a high ratio of particles consisting of single grains can be obtained. For example, a wet ball mill can be cited as a suitable pulverizing means for the present invention. In this case, it is effective to make it easy to disperse the fine particles generated by fracture at the grain boundaries in the solvent by, for example, pouring a large amount of solvent into the container so that a small gas phase space remains, thereby reducing the chance of applying an external force to the fractured particles (excessive crushing chance). In addition, a jet mill can be cited as another suitable pulverizing means for the present invention. Jet mill pulverization has a maximum energy product (BH) max This is advantageous for improving the

[0026] From the viewpoint of dividing particles by fracture, including intragranular fracture, the particle size after crushing is determined as the cumulative 50% particle size D 50 It is preferable to adjust the particle diameter D to 5.0 μm or less, and more preferably to 3.0 μm or less. If the particle diameter is made too fine, the crystal lattice distortion increases due to the application of an excessive external force, which may adversely affect the magnetic properties. 50 It is preferable to carry out the pulverization so that the particle size becomes 0.5 μm or more, and it is also possible to carry out the pulverization so that the particle size becomes 1.0 μm or more.

[0027] The powder obtained by pulverization may be classified to remove coarse particles or, if necessary, excessively small fine particles, thereby optimizing the particle size distribution.

[0028] [Nitriding] Next, a nitriding treatment is carried out to obtain Sm-Fe-N magnetic powder. The nitriding treatment can be carried out by heating and holding the Sm-Fe alloy powder finely pulverized by the above-mentioned pulverization in a non-oxidizing gas atmosphere containing a nitrogen compound or nitrogen. If the heating temperature is too high, Sm2Fe 17 Sm2Fe with nitrogen atoms inserted into the crystal 17The structure based on N3 becomes unstable, making nitriding difficult. The heating temperature for nitriding is preferably 500°C or less. If the temperature is too low, it takes a long time for nitriding to proceed, which is disadvantageous in diffusing nitrogen atoms uniformly to the inside of the particles. It is effective to set the heating temperature to 300°C or more. As the atmospheric gas for nitriding, it is practical to use a reducing atmosphere consisting of a mixture of ammonia (NH3) and hydrogen (H2). For example, the mixture ratio of ammonia and hydrogen, NH3:H2, can be in the range of 10:90 to 60:40. Other atmospheric gases used for nitriding include a mixture of hydrogen, ammonia, and nitrogen (N2), a mixture of hydrogen, ammonia, and argon (Ar), ammonia only, a mixture of ammonia and nitrogen, a mixture of ammonia and argon, nitrogen gas, and a mixture of nitrogen and hydrogen, and these are used to create a non-oxidizing atmosphere. For example, a non-oxidizing atmosphere consisting of nitrogen gas (i.e., a "nitrogen gas atmosphere") has a saturation magnetization σ s and maximum energy product (BH) max The optimum time for the nitriding treatment varies somewhat depending on the average particle size of the powder, the composition of the atmospheric gas, and the temperature, but the optimum time can usually be found within the range of 15 to 240 minutes.

[0029] The nitrogen atom is Th2Zn 17 The SmFe type crystal structure 17 It is believed that nitrogen occupies an interstitial position in the crystal lattice, and the nitrogen is still in the Th2Zn 17 The crystal structure is maintained. Sm2Fe 17 When nitrogen atoms are introduced into the Sm-Fe-N system, the crystal magnetic anisotropy changes from in-plane to uniaxial and the Curie point rises, making it a practical magnet material. The typical composition of Sm-Fe-N magnetic powder with excellent magnetic properties is Sm2Fe 17 The Sm / Fe molar ratio, which means the molar ratio of Sm to Fe, and the N / Fe molar ratio, which means the molar ratio of N to Fe, are Sm2Fe 17 It is believed that the closer the composition is to the stoichiometric composition of N3, the more advantageous it is in terms of magnetic properties, but it also exhibits hard magnetism in the composition range around that. 17The stoichiometric Sm / Fe molar ratio of N3 is 0.118, and the N / Fe molar ratio is 0.176. In the present invention, in order to stably obtain an effective coercive force as a material for bonded magnets in a temperature range including room temperature, it is preferable that the Sm / Fe molar ratio is in the range of 0.09 to 0.25. The Sm / Fe molar ratio reflects the composition of the gas atomized powder. In addition, when the Sm-Fe alloy powder is subjected to nitriding treatment under the above-mentioned conditions, Sm2Fe 17 Nitrogen is introduced into the crystals, and Sm-Fe-N magnetic powder with an N / Fe molar ratio in the range of 0.06 to 0.30 is obtained, which exhibits excellent magnetic properties. 17 Although it is possible to obtain Sm-Fe-N magnetic powder with a composition close to N3, in order to obtain Sm-Fe-N magnetic powder with a more uniform nitrogen distribution, the present invention performs nitriding treatment on the Sm-Fe alloy powder finely pulverized by pulverization. After nitriding treatment, classification may be performed to adjust the particle size distribution to an appropriate size according to the application.

[0030] As described above, a powder consisting of particles mainly composed of Sm, Fe, and N has a composition in which the molar ratio of Sm to Fe, Sm / Fe, is 0.09 to 0.25 and the Ca content in the powder is 0.005 mass% or less, and the cumulative 50% particle diameter D 50 is 0.5μm or more and 5.0μm or less, and the maximum energy product (BH) max is 150kJ / m 3 Thus, the Sm-Fe-N magnetic powder can be obtained.

[0031] "Particles mainly composed of Sm, Fe, and N" refers to particles in which the top three elements, Sm, Fe, and N, occupy the top three positions in the order of the elements contained in the particles in terms of the mass percentage. If the Ca content is 0.005% by mass or less, the problem of Ca promoting gelation of the resin is considered to be almost solved in the general process of producing a bonded magnet using a resin. It is more preferable that the Ca content is 0.002% by mass or less. By strictly controlling the inclusion of impurity elements according to the above-mentioned manufacturing process, it is possible to obtain Sm-Fe-N magnetic powder with a Ca content of less than 0.001% by mass. Note that the composition ranges of "Ca content of 0.005% by mass or less," "Ca content of 0.002% by mass or less," and "Ca content of less than 0.001% by mass" include the case where the Ca content is 0% by mass.

[0032] Maximum Energy Product (BH) max is 150kJ / m 3 The Sm-Fe-N magnetic powder described above is extremely useful as a material for anisotropic bonded magnets, which require excellent magnetic properties. By adjusting the manufacturing conditions in the above-mentioned manufacturing process, (BH) max is 200kJ / m 3 It is also possible to obtain Sm-Fe-N magnetic powder having the above properties. (BH) max There is no particular upper limit, but it is usually set to 350 kJ / m 3 The saturation magnetization σ s is 140Am 2 / kg or more, and the residual magnetization σ r is 115Am 2 / kg or more. r / σ s is 0.760 or more, high (BH) max It is effective to realize the above, and it is more effective to have a coercive force of 0.790 or more. c is preferably 700 kA / m or more. EXAMPLES

[0033] In the following examples, elemental analysis, powder particle size distribution measurement, powder magnetic measurement, and X-ray diffraction measurement were performed by the following methods.

[0034] (Elemental analysis) The analytical sample was dissolved and diluted with hydrochloric acid in a glove box filled with argon (Ar) gas to prepare a sample solution for analysis. This solution was analyzed using an ICP emission spectrometer (Agilent Technologies, Agilent 720).

[0035] (Particle size distribution measurement of powder) The particle size distribution of the powder was measured using a laser diffraction particle size distribution analyzer (Sympatec, Helos / Rodos). The cumulative 50% particle diameter D 50 asked for.

[0036] (Magnetic measurement of powder) The magnetic properties of the powder were measured using a VSM (PPMS DynaCool, manufactured by Quantum Design) in the following manner. 10 mg of the sample powder and 10 mg of low molecular weight polyethylene powder (Hiwax 100P, manufactured by Mitsui Chemicals, Inc.) were filled into a dedicated aluminum cell, heated to 170°C in a magnetic field of 1.59 MA / m to melt the polyethylene and orient the magnetic particles, and then cooled to room temperature to measure the saturation magnetization σ s , residual magnetization σ r , coercive force H c , maximum energy product (BH) max The measurement conditions were: maximum applied magnetic field 7.16MA / m, sweep speed 12kA / m·sec, time constant 1sec, amplitude 2mm, and frequency 40kHz. From the above measurement results, the squareness ratio σ r / σ s was calculated.

[0037] (X-ray diffraction measurement) The X-ray diffraction patterns of the powder samples were measured using Co-Kα radiation at a tube voltage of 45 kV and a tube current of 40 mA.

[0038] [Example 1] (Synthesis of Sm-Fe powder by gas atomization method) FIG. 3 shows a schematic diagram of the gas atomizing device used in this example. There are two independent spaces, an upper space and an lower space, in the chamber, which can be evacuated by a vacuum exhaust device 10, and these spaces can be turned into gas-phase spaces having a predetermined gas atmosphere by introducing gas from atmospheric gas supply sources 11a and 11b. The upper space contains a crucible 1, in which raw materials are melted by induction heating with a high-frequency coil 4 to form a molten metal 5. A molten metal discharge nozzle member 2 is attached to the bottom of the crucible 1 for discharging the molten metal 5 into the gas-phase space below. The molten metal flow path is blocked by pressing a stopper 3 against the molten metal discharge nozzle member 2 until the molten metal 5 is discharged. After the molten metal 5 is sufficiently homogenized and a predetermined temperature is obtained, the stopper 3 is raised while gas is supplied at a predetermined pressure from the gas supply device 13 for discharging the molten metal to the surface of the molten metal in the crucible 1, and the molten metal 5 is discharged from the tip of the nozzle member 2 for discharging the molten metal to the gas space at the bottom. The gas space at the bottom is equipped with a gas injection nozzle 6 for blowing gas onto the discharged molten metal 5. Before the start of discharging, the gas supply device 12 starts to supply gas to the gas injection nozzle 6, and the gas is injected from the gas injection nozzle 6 at high pressure. By applying a strong jet of the injected gas to the molten metal 5, fine particles of the molten metal 5 are formed, and the fine particles are rapidly cooled and solidified. The solidified metal particles 7 are deposited at the bottom of the gas space at the bottom.

[0039] FIG. 4 shows a schematic diagram of an example of a cross-sectional structure near the bottom of the crucible of a gas atomizing device. The molten metal discharge nozzle member 2 attached to the bottom of the crucible 1 has a discharge port 21, which is an opening at the tip of the nozzle, and a stopper abutment surface 22. The stopper 3 is movable in the vertical direction and has the function of blocking the nozzle flow path by abutting against the stopper abutment surface 22 of the molten metal discharge nozzle member 2, and opening the nozzle flow path by moving away from the stopper abutment surface 22 when the molten metal is discharged. In this example, the entire crucible 1 is made of boron nitride (BN), the entire molten metal discharge nozzle member 2 is made of boron nitride (BN), and at least the entire part of the stopper 3 to be immersed in the molten metal 5 is made of yttrium oxide (Y2O3). The nozzle inner diameter of the molten metal discharge nozzle member 2 is 3.0 mm.

[0040] As the raw material, a pre-melted Sm-Fe alloy was used. As a result of elemental analysis, the Sm / Fe molar ratio of this raw material alloy was 0.16, and the Ca content in the raw material was 0.002 mass%. 996.7 g of this raw material was placed in a crucible and melted by high-frequency induction heating in an Ar atmosphere. After the raw material alloy was completely melted, 27 minutes after the start of heating, the entire amount of 1637°C molten metal was discharged from the nozzle into the lower gas phase space. The maximum supply pressure of the molten metal discharge gas was 65 kPa in terms of the pressure difference with the atmospheric gas pressure. Ar was used as the injection gas. The lower gas phase space was also in an Ar atmosphere. The generated powder was collected, and excessively small particles were removed using a sieve with a mesh size of 16 μm in a glove box under a nitrogen atmosphere. In this way, gas atomized powder was obtained.

[0041] Elemental analysis of the gas atomized powder revealed that the Sm / Fe molar ratio was 0.16, which was equivalent to that of the raw alloy. The Ca content was less than 0.001% (below the measurement limit). In addition, the cumulative 50% particle diameter D 50 was 22.8 μm. The obtained Sm-Fe gas atomized powder was used to carry out the following steps.

[0042] (Heat treatment) The heat treatment furnace used was an electrically heated tubular furnace connected to a glove box filled with argon (Ar) gas. The Sm-Fe gas-atomized powder was placed in a sealed container filled with argon gas, transferred to the glove box, and loaded into the tubular furnace without being exposed to the atmosphere. The tubular furnace was heated from room temperature to 950°C at a rate of 150°C / min while flowing argon gas, and then held at 950°C for 1 minute, and then cooled to 50°C or less while flowing argon gas to obtain a heat-treated powder.

[0043] (Hydrogen processing) The obtained heat-treated powder was transferred to another tubular furnace, and the temperature was raised to 300°C at a rate of 10°C / min while flowing hydrogen (H2) gas, and then held at 300°C for 180 minutes. Next, the temperature was cooled to below 50°C while still flowing hydrogen gas, and the inside of the furnace was replaced with argon gas. In this way, hydrogen-treated powder was obtained.

[0044] (Crushing) The obtained hydrogen-treated powder was placed in an airtight container filled with argon gas and transferred from the tubular furnace to another glove box filled with argon gas. Grinding was carried out in the glove box to which it was transferred. A 50 mL glass bottle with a screw cap was used as a mill pot, and a grinding experiment simulating a wet ball mill was carried out as follows. 1.0 g of hydrogen-treated powder, 75 g of stainless steel balls with a diameter of 2.5 mm, and 38 mL of acetonitrile as a solvent were placed in the glass bottle. A rotary mixer (As One Corporation Mix Rotor Variable, 3-roller type, model number VMR-3R) was used to place the glass bottle containing the hydrogen-treated powder between two rollers, and grinding was carried out at a rotation speed of 110 rpm and an operating time of 8 hours. After grinding, the contents of the glass bottle were passed through a sieve to remove the stainless steel balls, and the slurry that had passed through the sieve was left to stand, the supernatant liquid was discarded, and the remaining slurry was vacuum-dried to obtain a ground powder. The above operations from grinding to drying were carried out in a glove box under an argon gas atmosphere.

[0045] (nitriding) The powder obtained after pulverization as described above was transferred to an electrically heated tubular furnace under an argon gas atmosphere, and then a mixed gas of 35% by volume of ammonia (NH3) gas and 65% by volume of hydrogen (H2) gas was flowed into the tubular furnace to replace the gas in the tubular furnace. Then, while flowing the mixed gas, the temperature was raised to 430°C at a rate of 5°C / min, and the temperature was held at 430°C for 30 minutes to perform nitriding treatment. Next, the gas flowing in the tubular furnace was changed to hydrogen (H2) gas and the temperature was held at 430°C for another 120 minutes, and then the gas flowing in the tubular furnace was changed to argon gas and the temperature was held at 430°C for 90 minutes. Then, the heating was stopped, and the temperature was cooled to near room temperature while flowing argon gas, to obtain a nitrided powder.

[0046] Next, the obtained nitrided powder was transferred from the tubular furnace into a glove box filled with argon gas, and then placed in a 20 mL screw-capped glass bottle, to which 15 mL of heptane was added as a solvent. Next, the glass bottle was placed in an ultrasonic disperser (UH-150 model, manufactured by SMT Corporation) and operated for 100 minutes under output conditions of 20 kHz, 0.3 seconds transmission, and 0.7 seconds off. Next, the supernatant in the glass bottle was removed, and the remaining heptane was removed by vacuum drying to obtain the Sm-Fe-N magnetic powder according to Example 1.

[0047] The cumulative 50% particle diameter D in the volumetric particle size distribution of the obtained Sm-Fe-N magnetic powder by laser diffraction and scattering method was 50 The saturation magnetization σ of this Sm-Fe-N magnetic powder was 1.46 μm. s is 143Am 2 / kg, residual magnetization σ r is 117Am 2 / kg, squareness ratio σ r / σ s is 0.818, coercive force H c is 716kA / m, maximum energy product (BH) max is 162kJ / m 3 The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit). The above results are shown in Table 1 together with the production conditions (the same applies to the following examples).

[0048] [Example 2] A Sm-Fe-N magnetic powder was obtained in the same manner as in Example 1, except that the operation time of the rotary mixer in the pulverization in Example 1 was changed from 8 hours to 10 hours. Here, the hydrogen-treated powder to be subjected to pulverization was taken from the powder obtained in Example 1 and used (the same applies to the following Examples 3 and 4). The cumulative 50% particle diameter D in the volumetric particle size distribution of the obtained Sm-Fe-N magnetic powder by laser diffraction and scattering method was 50 The saturation magnetization of this Sm-Fe-N magnetic powder was σ s is 155Am 2 / kg, residual magnetization σ r is 131Am 2 / kg, squareness ratio σ r / σ s is 0.845, coercive force H c is 780kA / m, maximum energy product (BH) max is 210kJ / m 3 The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0049] [Example 3] An Sm-Fe-N magnetic powder was obtained in the same manner as in Example 1, except that the operation time of the rotary mixer in the pulverization in Example 1 was changed from 8 hours to 12 hours. The cumulative 50% particle diameter D in the volumetric particle size distribution of the obtained Sm-Fe-N magnetic powder by laser diffraction and scattering method was 50 The saturation magnetization of this Sm-Fe-N magnetic powder was σ s is 146Am 2 / kg, residual magnetization σ r is 126Am 2 / kg, squareness ratio σ r / σ s is 0.863, coercive force H c is 812kA / m, maximum energy product (BH) max is 209kJ / m 3The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0050] [Example 4] An Sm-Fe-N magnetic powder was obtained in the same manner as in Example 1, except that the operation time of the rotary mixer in the pulverization in Example 1 was changed from 8 hours to 14 hours. The cumulative 50% particle diameter D in the volumetric particle size distribution of the obtained Sm-Fe-N magnetic powder by laser diffraction and scattering method was 50 The saturation magnetization of this Sm-Fe-N magnetic powder was σ s is 141Am 2 / kg, residual magnetization σ r is 119Am 2 / kg, squareness ratio σ r / σ s is 0.844, coercivity H c is 875kA / m, maximum energy product (BH) max is 189kJ / m 3 The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0051] [Example 5] An Sm-Fe-N magnetic powder was obtained in the same manner as in Example 1, except that the holding time in the heat treatment in Example 1 was changed from 1 minute to 120 minutes, the operating time of the rotary mixer in the grinding was changed from 8 hours to 2 hours, and the holding temperature in the nitriding treatment was set to 420°C. The cumulative 50% particle diameter D in the volumetric particle size distribution of the obtained Sm-Fe-N magnetic powder by laser diffraction and scattering method was 50 The saturation magnetization of this Sm-Fe-N magnetic powder was σ s is 138Am 2 / kg, residual magnetization σ r is 120Am 2 / kg, squareness ratio σ r / σ s is 0.870, coercive force H c is 770kA / m, maximum energy product (BH) max is 211kJ / m3 The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0052] In addition, EBSD observation of the heat-treated powder obtained in this example confirmed that the crystal grain size was 3 μm or more and that fracture, including intragranular fracture, occurred during grinding (the same applies to the following Examples 6 to 10).

[0053] [Example 6] A Sm-Fe-N magnetic powder was obtained in the same manner as in Example 1, except that the holding time in the heat treatment in Example 1 was changed from 1 minute to 120 minutes, that the pulverization was performed using a jet mill as described below, and that the nitriding treatment was performed under the conditions of nitrogen gas replacement as described below.

[0054] (Crushing) The jet mill used was a Nano Grinding Mill, model NJ-50, manufactured by Sunrex Industries Co., Ltd. The operating conditions were a grinding pressure of 1 MPa, and processing was performed in one pass. (nitriding) The ground powder obtained as described above was transferred to an electrically heated tubular furnace under an argon gas atmosphere, and then nitrogen gas (100% by volume N2) was flowed into the tubular furnace to replace the gas in the tubular furnace. Then, while flowing the nitrogen gas, the temperature was raised to 460°C at a rate of 5°C / min, and the temperature was maintained at 460°C for 360 minutes to perform a nitriding treatment. The subsequent treatment was carried out in the same manner as in Example 1 to obtain a Sm-Fe-N based magnetic powder.

[0055] The cumulative 50% particle diameter D in the volumetric particle size distribution of the obtained Sm-Fe-N magnetic powder by laser diffraction and scattering method was 50 The saturation magnetization of this Sm-Fe-N magnetic powder was σ s is 147Am 2 / kg, residual magnetization σ r is 133Am 2 / kg, squareness ratio σ r / σ s is 0.905, coercive force Hc is 768kA / m, maximum energy product (BH) max is 251kJ / m 3 The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0056] [Example 7] In the synthesis of Sm-Fe powder by gas atomization, a Sm-Fe alloy with a Sm / Fe molar ratio of 0.14 was used as the raw material to obtain gas atomized powder. Elemental analysis of the obtained gas atomized powder revealed that the Sm / Fe molar ratio was 0.14, which was equivalent to that of the raw material alloy. The Ca content was less than 0.001% (below the measurement limit). In addition, the cumulative 50% particle diameter D 50 was 25.9 μm. An Sm-Fe-N magnetic powder was obtained in the same manner as in Example 1, except that the Sm-Fe gas atomized powder obtained in this manner was used, the operating time of the rotary mixer in the grinding process was 4 hours, and the holding temperature in the nitriding process was 420°C.

[0057] The cumulative 50% particle diameter D in the volumetric particle size distribution of the obtained Sm-Fe-N magnetic powder by laser diffraction and scattering method was 50 The saturation magnetization σ of this Sm-Fe-N magnetic powder was 1.41 μm. s is 153Am 2 / kg, residual magnetization σ r is 129Am 2 / kg, squareness ratio σ r / σ s is 0.843, coercive force H c is 724kA / m, maximum energy product (BH) max is 219kJ / m 3 The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0058] [Example 8] An Sm-Fe-N magnetic powder was obtained in the same manner as in Example 7, except that the operation time of the rotary mixer in the pulverization in Example 7 was changed from 4 hours to 6 hours. The cumulative 50% particle diameter D in the volumetric particle size distribution of the obtained Sm-Fe-N magnetic powder by laser diffraction and scattering method was 50 The saturation magnetization of this Sm-Fe-N magnetic powder was σ s is 153Am 2 / kg, residual magnetization σ r is 121Am 2 / kg, squareness ratio σ r / σ s is 0.791, coercivity H c is 817kA / m, maximum energy product (BH) max is 188kJ / m 3 The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0059] [Example 9] In Example 1, the temperature of the heat treatment was changed from 950°C to 900°C, the time from 1 minute to 10 minutes, hydrogen treatment was not performed, a vibration mill was used for pulverization as described below, and the holding temperature in the nitriding treatment was changed from 430°C to 400°C, except for the above, Sm-Fe-N magnetic powder was obtained in the same manner as in Example 1.

[0060] (Crushing) In a glove box filled with nitrogen gas, 200g of Sm-Fe-N coarse powder, 4500g of chrome steel balls with a diameter of 1.6mm, and 2.1g of ethanol were placed in a 1.2L stainless steel pot using a vibration mill (YAMP-2SND, manufactured by Euras Techno Co., Ltd.) and sealed. The pot was then ground for 2.8 hours under conditions of amplitude of ±2.5mm and frequency of 29.1Hz. The ground sample was separated from the balls in the glove box filled with nitrogen gas. The resulting powder was subjected to the above-mentioned nitriding treatment to obtain Sm-Fe-N magnetic powder.

[0061] The cumulative 50% particle diameter D in the volumetric particle size distribution of the obtained Sm-Fe-N magnetic powder by laser diffraction and scattering method was 50 The saturation magnetization σ of this Sm-Fe-N magnetic powder was 1.61 μm. s is 140Am 2 / kg, residual magnetization σ r is 117Am 2 / kg, squareness ratio σ r / σ s is 0.836, coercive force H c is 692kA / m, maximum energy product (BH) max is 181kJ / m 3 The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0062] [Example 10] An Sm-Fe-N magnetic powder was obtained in the same manner as in Example 9, except that the nitriding treatment was carried out in a nitrogen gas atmosphere as follows.

[0063] (nitriding) The ground powder was transferred to an electrically heated tubular furnace under an argon gas atmosphere, and then nitrogen gas (100% by volume N2) was flowed into the tubular furnace to replace the gas in the furnace. Then, while flowing the nitrogen gas, the temperature was raised to 460°C at a rate of 5°C / min, and the nitriding treatment was performed by holding at 460°C for 60 minutes. The subsequent processing is the same as in the first embodiment.

[0064] The cumulative 50% particle diameter D in the volumetric particle size distribution of the obtained Sm-Fe-N magnetic powder by laser diffraction and scattering method was 50 The saturation magnetization of this Sm-Fe-N magnetic powder was σ s is 142Am 2 / kg, residual magnetization σ r is 119Am 2 / kg, squareness ratio σ r / σ s is 0.838, coercive force H c is 764kA / m, maximum energy product (BH) max is 191kJ / m3 The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0065] [Comparative Example 1] The Sm-Fe gas atomized powder obtained in Example 1 was used to carry out the following steps.

[0066] (Heat treatment) Heat treatment was performed in the same manner as in Example 1, except that the heating conditions were as follows: while flowing argon gas in a tubular furnace, the temperature was raised from room temperature to 850°C at a rate of 150°C / min, then the temperature was held at 850°C for 1 minute, and then the temperature was cooled to 50°C or less while flowing argon gas, to obtain a heat-treated powder.

[0067] (nitriding) After the heat treatment was completed and the temperature was confirmed to be below 50°C, the flow gas flowing in the tubular furnace was changed from argon gas to a mixed gas of 35% by volume of ammonia (NH3) gas and 65% by volume of hydrogen (H2) gas, and the gas in the tubular furnace was replaced. Then, while flowing the mixed gas, the temperature was raised to 420°C at a rate of 5°C / min, and the temperature was held at 420°C for 60 minutes to perform nitriding treatment. Next, the gas flowing in the tubular furnace was changed to hydrogen (H2) gas and held at 420°C for another 60 minutes, and then the gas flowing in the tubular furnace was changed to argon gas and held at 420°C for 60 minutes. Then, the heating was stopped and the temperature was cooled to near room temperature while flowing argon gas, and nitrided powder was obtained. The cooled powder was transferred from the tubular furnace to a glove box filled with argon gas. Elemental analysis of the nitrided powder revealed that the Sm / Fe molar ratio was 0.15 and the N / Fe molar ratio was 0.19.

[0068] (Crushing) The obtained nitrided powder was placed in an airtight container filled with argon gas and transferred from the tubular furnace to another glove box filled with argon gas. The powder was pulverized in the glove box. The pulverization method was the same as that of Example 1, except that the pulverization target was the nitrided powder described above and the operation time of the rotary mixer was changed from 8 hours to 22 hours in the pulverization method of the hydrogen-treated powder of Example 1. In this manner, the Sm-Fe-N magnetic powder according to Comparative Example 1 was obtained.

[0069] The cumulative 50% particle diameter D in the volumetric particle size distribution of the obtained Sm-Fe-N magnetic powder by laser diffraction and scattering method was 50 The saturation magnetization of this Sm-Fe-N magnetic powder was σ s is 146Am 2 / kg, residual magnetization σ r is 109Am 2 / kg, squareness ratio σ r / σ s is 0.747, coercivity H c is 629kA / m, maximum energy product (BH) max is 95kJ / m 3 The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0070] [Table 1]

[0071] In each example, a high maximum energy product (BH) max This is believed to be because the crystal grains that were coarsened by heat treatment were crushed to cause grain boundary and intragranular fracture, ultimately resulting in an Sm-Fe-N magnetic powder with a high proportion of particles consisting of single crystal grains. In contrast, the Sm-Fe-N magnetic powder obtained in Comparative Example 1 had a maximum energy product (BH) of maxThis is thought to be because, although the grain boundaries are destroyed by pulverization, the grains are too small to be completely monodispersed, and as a result, a Sm-Fe-N magnetic powder containing many particles made up of multiple crystal grains was obtained.

[0072] FIG. 5 illustrates an IPF map (inverse pole figure crystal orientation map) by EBSD (electron backscatter diffraction) for the particles of the Sm-Fe-N magnetic powder obtained in Example 2. FIG. 6 illustrates an IPF map (inverse pole figure crystal orientation map) by EBSD (electron backscatter diffraction) for the particles of the Sm-Fe-N magnetic powder obtained in Comparative Example 1. These IPF maps are monochromeized color images of IPF maps obtained by EBSD measurement of the sample surface on which the cross section of the particles appears, which is prepared by ion milling after polishing the resin in which the powder particles are embedded. In the monochrome IPF map, each crystal grain is represented as a brightness difference based on the crystal orientation difference. The Sm-Fe-N magnetic powder according to the present invention (FIG. 5) has a higher ratio of particles consisting of a single crystal grain than the Sm-Fe-N magnetic powder of the comparative example (FIG. 6).

[0073] FIG. 7 shows an example of an X-ray diffraction pattern by Co-Kα radiation for the Sm-Fe-N magnetic powder obtained in Example 1. 17 SmFe with the type crystal structure 17 The theoretical peak positions and peak heights for Th2Zn and N3 are also shown. 17 It can be seen that the Sm-Fe-N magnetic powders obtained in Examples 2 to 4 have a Th2Zn type crystal structure. 17 It was confirmed that the compound had a type crystalline structure.

[0074] From the results of Examples 9 and 10, it can be seen that the saturation magnetization and maximum energy product were improved by changing the non-oxidizing gas atmosphere of the nitriding treatment from a mixed gas atmosphere of ammonia gas and hydrogen gas to a nitrogen gas atmosphere. Also, a particularly high maximum energy product was obtained in Example 6, and it can be seen that jet mill pulverization is advantageous in improving the maximum energy product. [Explanation of symbols]

[0075] 1 crucible 2 Molten metal discharge nozzle parts 3 Stopper 4 High frequency coil 5 Molten metal 6 Gas injection nozzle 7 Solidified metal particles 10 Vacuum exhaust device 11a, 11b Atmospheric gas supply source 12 Injection gas supply device 13 Gas supply device for discharging molten metal 21 Discharge port 22 Stopper contact surface

Claims

1. a heat treatment process for coarsening the crystal grains of the powder particles by heating the powder of the Sm-Fe alloy having a Sm / Fe molar ratio of 0.09 or more and 0.25 or less, which is formed in the solidification process by the gas atomization method, to a temperature of 900° C. or more and 1200° C. or less; a crushing step of crushing the powder of the Sm—Fe alloy, the crystal grains of which have become coarse by the heat treatment step, to thereby reduce the particles of the powder by fracture, including intragranular fracture; a nitriding step of introducing nitrogen into the particles of the Sm—Fe alloy powder refined by the pulverization step by heating and holding the powder at a temperature range of 500° C. or less in a nitrogen compound or nitrogen-containing non-oxidizing gas atmosphere; The method for producing Sm-Fe-N based magnetic powder having the above structure.

2. 2. The method for producing Sm-Fe-N magnetic powder according to claim 1, wherein the powder of Sm-Fe alloy subjected to pulverization in the pulverization step is subjected to hydrogen treatment in which the powder is heated and held in a hydrogen atmosphere after the heat treatment step.

3. In the pulverization step, the cumulative 50% particle diameter D in the volume-based particle size distribution by the laser diffraction / scattering method is ５０ 3. The method for producing Sm-Fe-N based magnetic powder according to claim 1, wherein the powder has a particle size of 0.5 μm or more and 5.0 μm or less.

4. 3. The method for producing Sm-Fe-N based magnetic powder according to claim 1, wherein in the pulverizing step, the Sm-Fe based alloy powder is pulverized using a jet mill.

5. 3. The method for producing Sm-Fe-N based magnetic powder according to claim 1, wherein the non-oxidizing gas atmosphere in the nitriding step is a nitrogen gas atmosphere.

6. The Sm-Fe-N magnetic powder has a maximum energy product (BH) of ｍａｘ is 150 kJ / m ３ The method for producing the Sm-Fe-N magnetic powder according to claim 1 or 2.

7. The Sm-Fe-N magnetic powder is Th ２ Zinc １７ 3. The method for producing an Sm-Fe-N magnetic powder according to claim 1, which has a type crystal structure.

8. 3. The method for producing Sm-Fe-N based magnetic powder according to claim 1, wherein the Sm-Fe-N based magnetic powder has an N / Fe molar ratio of 0.06 or more and 0.30 or less.

9. A powder composed of particles mainly composed of Sm, Fe, and N, the molar ratio of Sm to Fe being 0.09 or more and 0.25 or less, and the Ca content in the powder being 0.005 mass% or less, and the cumulative 50% particle diameter D in a volume-based particle size distribution measured by a laser diffraction / scattering method being 0.005 mass% or less. ５０ is 0.5 μm or more and 5.0 μm or less, and the maximum energy product (BH) ｍａｘ is 150 kJ / m ３ This is the Sm-Fe-N magnetic powder.

10. Squareness ratio σ ｒ / σ ｓ The Sm-Fe-N magnetic powder according to claim 9, wherein the Sm-Fe-N magnetic powder has a refractive index of 0.760 or more.

11. Th ２ Zinc １７ The Sm-Fe-N magnetic powder according to claim 9, having a type crystal structure.

12. 10. The Sm-Fe-N magnetic powder according to claim 9, having a composition in which the molar ratio of N to Fe, N / Fe, is 0.06 or more and 0.30 or less.

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