Method for producing sm-fe-n-based magnetic powder and sm-fe-n magnetic powder

Abstract

[Problem] To provide an Sm-Fe-N-based magnetic powder useful for improving the performance and manufacturability of bonded magnets, said powder exhibiting a high maximum energy product (BH)max and having few impurities. [Solution] This method for producing an Sm-Fe-N-based magnetic powder comprises: a heat treatment step in which a powder of Sm-Fe alloy, which has been formed in a solidification process according to a gas atomization method and of which the Sm / Fe molar ratio is between 0.09 and 0.25 inclusive, is heated to a temperature between 900°C and 1200°C inclusive to thereby coarsen the crystal grains of the particles of said powder; a crushing step in which the powder of the Sm-Fe alloy of which the crystal grains have been coarsened by the heat treatment step is crushed to thereby make the particles of said powder finer by fracture, which includes intragranular fracture; and a nitriding step in which the powder of the Sm-Fe alloy made finer by the crushing step is heated and held in an atmosphere of a non-oxidizing gas containing a nitrogen compound or nitrogen in a temperature range of 500°C or less to thereby introduce nitrogen into the particles of the powder.

Description

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

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

[0002] Sm ２ Fe １７ A material in which nitrogen is introduced into an intermetallic compound (the typical composition formula is Sm ２ Fe １７ N ３ ) is known to be a ferromagnetic material that exhibits excellent hard magnetic properties. ２ Fe １７ Powder of a substance in which nitrogen is introduced into an Sm—Fe alloy having a stoichiometric composition or a composition close to this, 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 techniques for producing Sm-Fe-N magnetic powder include methods that utilize solidification processes such as atomization and single roll methods, and methods that utilize a reduction diffusion method using Ca or the like as a reducing agent.

[0004] For example, Patent Document 1 discloses a method for producing Sm by gas atomization. ２ Fe １７ Spherical particles of the alloy were synthesized, and the resulting powder was nitrided in a tubular furnace to produce Sm ２ Fe １７ N ３ The average particle size of the particles obtained by gas atomization is 110 μm (paragraph 0012) or 80 μm (paragraph 0014).

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

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

[0007] Patent Document 4 discloses a technique for obtaining magnetic powders such as Sm-Fe-N powders using a reduction-diffusion method and nitriding treatment with Ca, which involves two separate reduction reactions to obtain powders with an average particle size of 5 μm or less without any pulverization process. It also describes how, after the second reduction process, the powder is "washed with water and then thoroughly separated using a weak acid such as acetic acid." Even so, 0.01 wt. % of Ca remains in the powders obtained in the examples (paragraphs 0034, 0037, 0047, 0050, and 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 and crushing treatment, followed by nitriding treatment. The particle diameter 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 is 101-102 Am ２ / kg (paragraphs 0123 and 0133). The particles contain, for example, less than 0.01 mass% of Ca (paragraph 0114). The inner layer of the shell consisting of an outer layer and an inner layer is said to be free of Ca, but "free of Ca" in Patent Document 5 means that the Ca content is less than 1.0 atomic % (paragraph 0043).

[0009] Japanese Patent Laid-Open No. 7-11307 Japanese Patent Laid-Open No. 2001-68315 Japanese Patent Laid-Open No. 2002-246212 Japanese Patent Laid-Open No. 11-310807 Japanese Patent Laid-Open No. 2022-177699

[0010] In recent years, in order to respond to the increasing performance of automobile motors and sensors, bonded magnets using Sm-Fe-N magnetic powder are expected to have even better magnetic properties. In particular, to improve the properties of anisotropic bonded magnets, the maximum energy product (BH) ｍａｘ It is advantageous to use magnetic powder with as high a BH as possible. Solidified metals obtained by rapid solidification processes such as atomization and single roll methods generally have a polycrystalline structure consisting of fine crystals. In magnetic powders derived from such fine polycrystalline solidified metals, a high BH is required. ｍａｘ It is not easy to realize the above. As described above, Patent Documents 2 and 3 disclose the (BH) of magnetic powder using Sm. ｍａｘ Although the value is shown, 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 or other reducing agents, is complex and has a significant environmental impact, such as producing alkaline wastewater. Furthermore, the Sm-Fe-N magnetic powder obtained through a process using 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 can easily cause resin to gel when the powder is used as a raw material to produce a bonded magnet, potentially reducing the manufacturability of the bonded magnet.

[0012] The present invention provides a high maximum energy product (BH). ｍａｘ The present invention aims 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.

[0013] In order to obtain powder of Sm-Fe alloys with an extremely small amount of Ca, it is effective to employ a gas atomization method. In this specification, a powder composed of particles that have not been subjected to physical or chemical treatment (e.g., application of external force, application of magnetic force, heat treatment, surface treatment, etc.) after synthesis by the gas atomization method is called "gas atomized powder." The particles of gas atomized powder are formed by rapid solidification, and therefore become polycrystalline particles consisting of very fine crystal grains. When left as polycrystalline particles, they have a high maximum energy product (BH) ｍａｘ It is difficult to obtain a powder containing many single crystal grains. Furthermore, the inventors' research has revealed that when polycrystalline particles consisting of fine crystal grains are reduced in size by mechanical pulverization, fracture at the grain boundaries, which are prone to crack propagation, occurs preferentially, and each reduced particle tends to become a particle consisting of multiple crystal grains with the grain boundaries remaining inside. In other words, it is extremely difficult to break 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 single crystal grains using gas-atomized powder as a raw material. As a result, they have found that when gas-atomized powder of an Sm—Fe alloy is heat-treated at high temperatures, 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 equivalent circle diameter in the cross-sectional structure of the particles. It was found that when mechanically pulverizing a powder of Sm-Fe alloy composed of particles with coarse crystal grains, the individual particles are broken by fracture at the grain boundaries (intergranular fracture) as well as fracture within the grains (intragranular fracture), resulting in a fine powder of Sm-Fe alloy with a high proportion of particles consisting of single crystal grains. Furthermore, it was found that the Sm-Fe-N magnetic powder obtained by nitriding this powder has a maximum energy product (BH) ｍａｘ It was also confirmed that the above-mentioned effects were significantly improved. The present invention is based on this finding.

[0014] The above object can be achieved by the following invention: [1] A method for producing Sm—Fe—N magnetic powder, comprising: a heat treatment step in which Sm—Fe alloy powder, formed by a solidification process using a gas atomization method and having an Sm / Fe molar ratio of 0.09 to 0.25, is heated to a temperature of 900°C to 1200°C to coarsen the crystal grains of the powder particles; a crushing step in which the Sm—Fe alloy powder, the crystal grains of which have been coarsened by the heat treatment step, is crushed to refine the particles by fracture, including intragranular fracture; and a nitriding step in which the Sm—Fe alloy powder, the refined by the crushing step, is heated and maintained at a temperature of 500°C or less in a non-oxidizing gas atmosphere containing a nitrogen compound or nitrogen, to introduce nitrogen into the particles of the powder. [2] The method for producing an Sm—Fe—N based magnetic powder according to the above [1], wherein the Sm—Fe based alloy powder to be pulverized in the pulverization step is one that has been subjected to hydrogen treatment by heating and holding in a hydrogen atmosphere after the heat treatment step. ５０ [4] A method for producing an Sm-Fe-N magnetic powder according to any one of [1] to [3] above, wherein in the pulverizing step, powder of an Sm-Fe alloy is pulverized using a jet mill. [5] A method for producing an Sm-Fe-N magnetic powder according to any one of [1] to [4] above, 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): ｍａｘ is 150 kJ / m ３ [7] The method for producing the Sm-Fe-N based magnetic powder according to any one of the above [1] to [5]. ２ Zn １７[8] A method for producing an Sm-Fe-N magnetic powder according to any one of the above [1] to [6], wherein the Sm-Fe-N magnetic powder has a N / Fe molar ratio of 0.06 or more and 0.30 or less. [9] A powder consisting of particles containing Sm, Fe, and N as main components, having a composition in which the molar ratio of Sm to Fe, Sm / Fe, is 0.09 or more and 0.25 or less, and the Ca content in the powder is 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 is 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

[10] Squareness ratio σ ｒ / σ ｓ

[11] The Sm—Fe—N magnetic powder according to the above [9], wherein Th is 0.760 or more. ２ Zn １７

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

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

[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 Ca content, which avoids the problem of Ca promoting gelation of resin when using resin to produce bonded magnets, and is expected to improve productivity in processes such as magnetic field orientation.

[0016] FIG. 1 is a diagram illustrating an IPF map by EBSD of a cross section of a particle obtained by heating Sm—Fe-based gas atomized powder at 700°C for 1 minute. FIG. 2 is a diagram illustrating an IPF map by EBSD of a cross section of a particle obtained by heating Sm—Fe-based gas atomized powder at 1000°C for 1 minute. FIG. 3 is a diagram illustrating a configuration of a gas atomizing apparatus used in Examples and Comparative Examples. FIG. 4 is a diagram illustrating a cross-sectional structure near the bottom of the crucible of the gas atomizing apparatus used in Examples and Comparative Examples. FIG. 5 is a diagram illustrating an IPF map by EBSD of a particle cross section of the Sm—Fe—N-based magnetic powder obtained in Example 2. FIG. 6 is a diagram illustrating an IPF map by EBSD of a particle cross section of the Sm—Fe—N-based magnetic powder obtained in Comparative Example 1. FIG. 7 is a diagram illustrating an X-ray diffraction pattern using Co-Kα radiation for the Sm—Fe—N-based magnetic powder obtained in Example 1.

[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 an Sm—Fe alloy solidified by gas atomization is used. Gas atomization is a powder formation technique in which a gas is blown at high speed onto a molten metal discharged into a gas space, breaking the molten metal 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, a pre-melted Sm—Fe based master alloy, metallic Sm, metallic Fe, etc., whose composition is known, can be used. Sm ２ Fe １７ The stoichiometric Sm / Fe molar ratio is 0.118. The composition of the molten metal is Sm ２ Fe １７ It 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. While the inclusion of metal elements other than Sm and Fe is permissible to the extent that the required properties of the magnetic powder finally obtained are not impaired, 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 excluding nitrogen or in a vacuum.

[0019] The molten metal, which has been maintained at a predetermined temperature and made sufficiently uniform, 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 a subsequent process. Considering that the gas atomized powder will be pulverized into fine particles with an average particle size of several μm or less in the subsequent process, the particle size of the gas atomized powder is determined based on the cumulative 50% particle diameter D in the volume-based particle size distribution determined by the laser diffraction / 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. ５０ At present, it is extremely difficult to industrially synthesize particles having a particle diameter of less than 5.0 μm. ５０ It is sufficient to adjust the thickness to a range of 5.0 μm or more, and it may be controlled to a 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 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] Gas-atomized powder of Sm—Fe alloy (hereinafter, sometimes referred to as "Sm—Fe gas-atomized powder") is subjected to 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 such that the average crystal grain size in the equivalent circle diameter of the cross-sectional structure of the particles is, for example, approximately 3 to 15 μm. This coarsening of the crystal grains facilitates the production of fine Sm—Fe alloy powder with a high proportion of particles consisting of single crystal grains in the subsequent milling process. Intragranular fracture is more likely to occur. Heating to 930°C or higher is more preferable. 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, or may be set to 30 seconds to 5 minutes. The heating atmosphere is preferably an inert gas atmosphere other than nitrogen, or a vacuum.

[0022] Figures 1 and 2 show examples of IPF maps (inverse pole figure crystal orientation maps) obtained by electron backscatter diffraction (EBSD) on the cross sections of particles obtained by heating Sm—Fe-based gas-atomized powder obtained by a method similar to that described in Example 1 below at 700°C and 1000°C, respectively. The heating atmosphere was argon gas, and the heating time at each temperature was 1 minute. These IPF maps are monochrome versions of color images obtained by EBSD measurement of the surface of a sample, on which the cross sections of the particles were revealed, prepared by ion milling after polishing the resin in which the powder particles were embedded. In the monochrome IPF maps, individual crystal grains are represented as brightness differences based on crystal orientation differences. Comparing Figures 1 and 2 reveals that heating to high temperatures further promotes coarsening of the crystal grains.

[0023] In Sm-Fe gas atomized powder, TbCu can be obtained depending on the conditions. ７ It is also possible that a Sm-Fe based metal phase with a TbCu type crystal structure is formed. ７ The Sm-Fe metal phase is ２ Zn １７Since the anisotropic magnetic field after nitriding is smaller than that of the mold, it is difficult to obtain a high coercive force. ７ It is desirable that the amount of the Sm—Fe-based metal phase present in the TbCu alloy be as small as possible. ７ The crystalline phase of the type is Th ２ Zn １７ Since the material changes shape, the heat treatment is also effective in homogenizing the structure.

[0024] [Hydrogen Treatment] To facilitate the occurrence of intragranular fracture in the subsequent milling process, it is effective to perform hydrogen treatment by heating in a hydrogen gas atmosphere before milling. Hydrogen treatment causes hydrogen to penetrate into the crystal grains of the Sm—Fe alloy, making intragranular fracture more likely to occur due to the so-called hydrogen embrittlement phenomenon. Therefore, hydrogen treatment can be performed as needed. 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] [Pulverization] When mechanical pulverization is performed on Sm—Fe alloy powder whose crystal grains have become coarse by the heat treatment described above, individual particles are fractured by fracture at the grain boundaries (intergranular fracture) as well as fracture within the grains (transgranular fracture). When the powder particles are refined by such "fracture including transgranular fracture," a fine Sm—Fe alloy powder with a high proportion of particles consisting of single crystal grains can be obtained. A wet ball mill, for example, can be used as a suitable pulverization method for the present invention. In this case, it is effective to add a large amount of solvent to the container, for example, leaving a small amount of gas phase space, so that the fine particles generated by fracture at the grain boundaries are easily dispersed in the solvent, thereby reducing the opportunity for external force to be applied to the fractured particles (the opportunity for excessive pulverization). Another suitable pulverization method for the present invention can be used is a jet mill. Jet mill pulverization achieves the maximum energy product (BH) ｍａｘ This is advantageous for improving the

[0026] From the viewpoint of dividing particles by fractures including intragranular fractures, the particle size after pulverization is determined as the cumulative 50% particle size D in the volume-based particle size distribution by laser diffraction / scattering method. ５０It is preferable to adjust the particle size D to 5.0 μm or less, and more preferably to 3.0 μm or less. If the particle size is made too small, the application of an excessive external force may increase the crystal lattice distortion, which may adversely affect the magnetic properties. ５０ It is desirable to carry out pulverization so that the particle size is 0.5 μm or more, and pulverization may be carried out so that the particle size is 1.0 μm or more.

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

[0028] [Nitriding Treatment] Next, 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 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, Sm ２ Fe １７ Sm crystal with nitrogen atoms inserted ２ Fe １７ N ３ The structure based on this becomes unstable, making nitriding difficult. The heating temperature for nitriding is preferably 500°C or lower. If the temperature is too low, it takes a long time for nitriding to proceed, which is disadvantageous in terms of diffusing nitrogen atoms uniformly into the interior of the particles. It is effective to set the heating temperature to 300°C or higher. The atmospheric gas for nitriding is ammonia (NH ３ ) and hydrogen (H ２ For example, a reducing atmosphere consisting of a mixture of ammonia and hydrogen in a ratio of NH ３ : H ２ The ratio can be in the range of 10:90 to 60:40. Other atmospheric gases used in the nitriding treatment include hydrogen, ammonia, and nitrogen (N ２ Examples of suitable non-oxidizing atmospheres include a mixture of hydrogen, ammonia, and argon (Ar), ammonia alone, a mixture of ammonia and nitrogen, a mixture of ammonia and argon, nitrogen gas, and a mixture of nitrogen and hydrogen. These can be used to form 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 ｓand maximum energy product (BH) ｍａｘ The optimum time for 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 in the range of 15 to 240 minutes.

[0029] Nitrogen atoms are Th ２ Zn １７ Sm type crystal structure ２ Fe １７ It is thought that nitrogen occupies an interstitial position in the crystal lattice, and even after the introduction of nitrogen, ２ Zn １７ The crystal structure is maintained. ２ Fe １７ When nitrogen atoms are introduced into the powder, the crystal magnetic anisotropy changes from in-plane to uniaxial, and the Curie point rises, making it possible to make it into a practical magnetic material. A typical composition of Sm-Fe-N magnetic powder with excellent magnetic properties is Sm ２ Fe １７ N ３ 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 ２ Fe １７ N ３ It is believed that the closer the composition is to the stoichiometric composition, the more advantageous it is in terms of magnetic properties, but hard magnetism is also exhibited in the composition range around this. ２ Fe １７ N ３ The stoichiometric Sm / Fe molar ratio 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 a bonded magnet 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. Furthermore, when the Sm-Fe alloy powder is nitrided under the above conditions, Sm ２ Fe １７ Nitrogen is introduced into the crystals, and Sm-Fe-N magnetic powder having an N / Fe molar ratio in the range of 0.06 to 0.30 is obtained, which exhibits excellent magnetic properties. ２ Fe １７ N ３However, in order to obtain a Sm—Fe—N magnetic powder having a more uniform nitrogen distribution, the present invention performs a nitriding treatment on the Sm—Fe alloy powder that has been pulverized by nitriding. After the nitriding treatment, classification may be performed to adjust the particle size distribution to an appropriate value depending on the application.

[0030] As described above, a powder consisting of particles mainly composed of Sm, Fe, and N is obtained, the powder having a composition in which the molar ratio of Sm to Fe, Sm / Fe, is 0.09 or more and 0.25 or less, 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 measured by a laser diffraction / scattering method is 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 As described above, an Sm--Fe--N magnetic powder can be obtained.

[0031] "Particles primarily composed of Sm, Fe, and N" refers to particles in which the three elements Sm, Fe, and N occupy the top three positions in a ranking of the elements contained in the particles in order of their mass percentage content. A Ca content of 0.005% by mass or less is believed to virtually eliminate the problem of Ca promoting resin gelation in the general process of producing bonded magnets using resin. A Ca content of 0.002% by mass or less is more preferable. By strictly controlling the inclusion of impurity elements according to the manufacturing process described above, Sm-Fe-N magnetic powders with a Ca content of less than 0.001% by mass can be obtained. 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 cases where the Ca content is 0% by mass.

[0032] Maximum energy product (BH) ｍａｘ is 150 kJ / 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 200 kJ / m ３It is also possible to obtain the above Sm-Fe-N magnetic powder. (BH) ｍａｘ There is no particular upper limit to the amount of oxidative stress, but it is usually 350 kJ / m ３ It can be adjusted within the following range: 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 coercive force H ｃ is preferably 700 kA / m or more.

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

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

[0035] (Measurement of particle size distribution of powder) The particle size distribution of the powder was measured using a laser diffraction particle size distribution analyzer (Helos / Rodos, manufactured by Sympatec). In the obtained particle size distribution based on volume by the laser diffraction / scattering method, 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) by the following method: 10 mg of 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 a maximum applied magnetic field of 7.16 MA / m, a sweep rate of 12 kA / m·sec, a time constant of 1 sec, an amplitude of 2 mm, and a frequency of 40 kHz. ｒ / σ ｓ was calculated.

[0037] (X-ray Diffraction Measurement) The X-ray diffraction pattern of the powder sample was measured using Co-Kα rays at a tube voltage of 45 kV and a tube current of 40 mA.

[0038] Example 1 (Synthesis of Sm—Fe-based powder by gas atomization) Figure 3 shows a schematic diagram of the gas atomization apparatus used in this example. A chamber contains two independent upper and lower spaces that can be evacuated using a vacuum exhaust device 10. These spaces can be converted into gas-phase spaces with 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 using 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 lower gas-phase space. A stopper 3 is pressed against the molten metal discharge nozzle member 2 to block the molten metal flow path until the molten metal 5 is discharged. After the molten metal 5 has been sufficiently homogenized and attained a predetermined temperature, gas is supplied at a predetermined pressure from the molten metal discharge gas supply device 13 to the surface of the molten metal in the crucible 1. The stopper 3 is then raised, and the molten metal 5 is discharged from the tip of the molten metal discharge nozzle member 2 into the lower gas phase space. The lower gas phase space is equipped with a gas injection nozzle 6 for spraying gas onto the discharged molten metal 5. Prior to discharge, gas is supplied from the gas supply device 12 to the gas injection nozzle 6, and the gas is injected from the gas injection nozzle 6 at high pressure. By impinging the strong jet of injected gas on 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 lower gas phase space.

[0039] 4 shows a schematic diagram of an example of the 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 flow path of the nozzle by abutting against the stopper abutment surface 22 of the molten metal discharge nozzle member 2, and opening the flow path of the nozzle 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 portion of the stopper 3 that is immersed in the molten metal 5 is made of yttrium oxide (Y ２ O ３ The inner diameter of the molten metal discharge nozzle member 2 was 3.0 mm.

[0040] A pre-melted Sm-Fe alloy was used as the raw material. Elemental analysis revealed that the Sm / Fe molar ratio of this raw material alloy was 0.16, and the Ca content of 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 molten, 27 minutes after the start of heating, the entire amount of 1637°C molten metal was ejected from the nozzle into the lower gas phase space. The maximum supply pressure of the molten metal ejection gas was 65 kPa, calculated as the differential pressure with the atmospheric gas pressure. Ar was used as the injection gas. The lower gas phase space was also an Ar atmosphere. The resulting powder was collected and sieved through a 16 μm mesh sieve in a nitrogen-atmosphere glove box to remove excessively small particles. 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 material alloy. The Ca content was less than 0.001% (below the measurement limit). Furthermore, the cumulative 50% particle diameter D ５０ The particle size was 22.8 μm. The obtained Sm—Fe gas atomized powder was used to carry out the following steps.

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

[0043] (Hydrogen Treatment) The obtained heat-treated powder was transferred to another tubular furnace and heated with hydrogen (H ２ While flowing hydrogen gas, the temperature was raised to 300°C at a rate of 10°C / min, and then held at 300°C for 180 minutes. Next, while continuing to flow hydrogen gas, the temperature was cooled to 50°C or less, and the atmosphere inside 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. Crushing was carried out in this glove box. A 50 mL screw-capped glass bottle was used as a mill pot, and a crushing experiment simulating a wet ball mill was carried out as follows. 1.0 g of hydrogen-treated powder, 75 g of 2.5 mm diameter stainless steel balls, and 38 mL of acetonitrile as a solvent were placed in the glass bottle. A rotary mixer (As One Corporation, Mix Rotor Variable, three-roller type, model VMR-3R) was used. The glass bottle containing the hydrogen-treated powder was placed between two rollers and crushed at 110 rpm for 8 hours. After crushing, the contents of the glass bottle were sieved to remove the stainless steel balls. The sieved slurry was then allowed to settle, the supernatant liquid was discarded, and the remaining slurry was vacuum-dried to obtain a crushed powder. The above operations from grinding to drying were carried out in a glove box under an argon gas atmosphere.

[0045] (Nitriding Treatment) The pulverized powder obtained as described above was transferred into an electrically heated tubular furnace under an argon gas atmosphere, and then ammonia (NH３ ) gas 35% by volume, hydrogen (H ２ A mixed gas containing 65% by volume of hydrogen (H ) gas was then flowed to replace the gas inside the tubular furnace. Thereafter, while flowing the mixed gas, the temperature was raised to 430°C at a rate of 5°C / min and held at 430°C for 30 minutes to perform nitriding treatment. Next, the gas flowing in the tubular furnace was changed to hydrogen (H ). ２ The gas flowing through the tubular furnace was then changed to argon gas, and the temperature was maintained at 430°C for another 120 minutes. After that, the gas flowing through the tubular furnace was changed to argon gas, and the temperature was maintained at 430°C for 90 minutes. After that, heating was stopped, and the material was cooled to a temperature near room temperature while flowing argon gas, to obtain 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 glass bottle with a screw cap, and 15 mL of heptane was added as a solvent. Next, this 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 on, 0.7 seconds off. Next, the supernatant liquid in the glass bottle was removed, and the remaining heptane was removed by vacuum drying, thereby obtaining the Sm—Fe—N-based magnetic powder of Example 1.

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

[0048] [Example 2] Sm-Fe-N magnetic powder was obtained in the same manner as in Example 1, except that the operating time of the rotary mixer in the pulverization in Example 1 was changed from 8 hours to 10 hours. Here, the hydrogen-treated powder obtained in Example 1 was used as the powder to be pulverized (the same applies to Examples 3 and 4 below). The cumulative 50% particle diameter D of the obtained Sm-Fe-N magnetic powder in the volume-based particle size distribution measured by laser diffraction / scattering method was ５０ The saturation magnetization σ of this Sm—Fe—N magnetic powder was 1.39 μm. 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 210 kJ / m ３ The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0049] [Example 3] Sm-Fe-N magnetic powder was obtained in the same manner as in Example 1, except that the operating 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 of the obtained Sm-Fe-N magnetic powder in the volume-based particle size distribution by laser diffraction / scattering method was ５０ The saturation magnetization σ of this Sm—Fe—N magnetic powder was 1.37 μm. ｓ is 146 Am 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 209 kJ / m ３ The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0050] [Example 4] Sm-Fe-N magnetic powder was obtained in the same manner as in Example 1, except that the operating 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 of the obtained Sm-Fe-N magnetic powder in the volume-based particle size distribution by laser diffraction / scattering method was ５０ The saturation magnetization σ of this Sm—Fe—N magnetic powder was 1.21 μm. ｓ is 141 Am ２ / kg, residual magnetization σ ｒ is 119Am ２ / kg, squareness ratio σ ｒ / σ ｓ is 0.844, coercive force H ｃ is 875kA / m, maximum energy product (BH) ｍａｘ is 189 kJ / m ３ The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0051] [Example 5] 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 pulverization 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 ５０ The saturation magnetization σ of this Sm—Fe—N magnetic powder was 1.77 μm. ｓ is 138 Am 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 211 kJ / m ３ The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0052] Furthermore, 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 Examples 6 to 10 below).

[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 substitution as described below.

[0054] (Pulverization) A nano grinding mill, model NJ-50, manufactured by Sunrex Industries Co., Ltd. was used as the jet mill. The operating conditions were a pulverization pressure of 1 MPa, and processing was performed in one pass. (Nitriding) The pulverized powder obtained as described above was transferred into an electrically heated tubular furnace under an argon gas atmosphere, and then nitrogen gas (100% by volume N ２ ) was flowed to replace the gas inside the tubular furnace. Thereafter, 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 nitriding treatment. The subsequent treatment was carried out in the same manner as in Example 1, and a Sm—Fe—N magnetic powder was obtained.

[0055] The cumulative 50% particle diameter D in the volume-based particle size distribution of the obtained Sm—Fe—N magnetic powder by laser diffraction / scattering method was ５０ The saturation magnetization σ of this Sm—Fe—N magnetic powder was 1.77 μm. ｓ is 147 Am ２ / kg, residual magnetization σ ｒ is 133Am ２ / kg, squareness ratio σ ｒ / σ ｓ is 0.905, coercive force H ｃ is 768kA / m, maximum energy product (BH) ｍａｘ is 251 kJ / 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-based powder by gas atomization, a Sm-Fe alloy with a Sm / Fe molar ratio of 0.14 was used as a 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). Furthermore, the cumulative 50% particle diameter D in the volume-based particle size distribution of the gas atomized powder measured by laser diffraction / scattering method was ５０ The particle size was 25.9 μm. A 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 pulverization was 4 hours, and the holding temperature in the nitriding treatment was 420° C.

[0057] The cumulative 50% particle diameter D in the volume-based particle size distribution of the obtained Sm—Fe—N magnetic powder by laser diffraction / scattering method was ５０ The saturation magnetization σ of this Sm—Fe—N magnetic powder was 1.41 μm. ｓ is 153 Am 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 219 kJ / m ３ The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0058] [Example 8] 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 of Example 7 was changed from 4 hours to 6 hours. The cumulative 50% particle diameter D of the obtained Sm-Fe-N magnetic powder in the volume-based particle size distribution by laser diffraction / scattering method was ５０ The saturation magnetization σ of this Sm—Fe—N magnetic powder was 1.17 μm. ｓ is 153 Am ２ / kg, residual magnetization σ ｒ is 121Am ２ / kg, squareness ratio σ ｒ / σ ｓ is 0.791, coercive force H ｃ is 817kA / m, maximum energy product (BH) ｍａｘ is 188 kJ / m ３ The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0059] [Example 9] A Sm-Fe-N magnetic powder was obtained in the same manner as in Example 1, except that the heat treatment temperature 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 for nitriding treatment was changed from 430°C to 400°C.

[0060] (Pulverization) In a glove box filled with nitrogen gas, a vibration mill (YAMP-2SND, manufactured by Uras Techno Co., Ltd.) was used. 200 g of Sm—Fe—N coarse powder, 4,500 g of 1.6 mm diameter chromium steel balls, and 2.1 g of ethanol were placed in a 1.2 L stainless steel pot and sealed. Pulverization was carried out for 2.8 hours under conditions of an amplitude of ±2.5 mm and a vibration frequency of 29.1 Hz. The pulverized sample was separated from the balls in the glove box filled with nitrogen gas. The obtained 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 volume-based particle size distribution of the obtained Sm—Fe—N magnetic powder by laser diffraction / 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 117 Am ２ / kg, squareness ratio σ ｒ / σ ｓ is 0.836, coercive force H ｃ is 692kA / m, maximum energy product (BH) ｍａｘ is 181 kJ / m ３ The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0062] Example 10 A 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 Treatment) The pulverized powder was transferred into an electrically heated tubular furnace under an argon gas atmosphere, and then nitrogen gas (100% by volume N ２ ) was flowed to replace the gas inside the tubular furnace. Thereafter, 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 60 minutes to perform nitriding treatment. The subsequent treatment was the same as in Example 1.

[0064] The cumulative 50% particle diameter D in the volume-based particle size distribution of the obtained Sm—Fe—N magnetic powder by laser diffraction / scattering method was ５０ The saturation magnetization σ of this Sm—Fe—N magnetic powder was 1.64 μm. ｓ is 142 Am 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 191 kJ / m ３ The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0065] Comparative Example 1 Using the Sm—Fe gas atomized powder obtained in Example 1, the following steps were carried out.

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

[0067] (Nitriding Treatment) After the heat treatment is completed and it is confirmed that the temperature has dropped to 50° C. or less, the flow gas flowing in the tubular furnace is changed from argon gas to ammonia (NH ３) gas 35% by volume, hydrogen (H ２ The gas in the tubular furnace was replaced with a mixed gas containing 65% by volume of hydrogen (H ). Then, while the mixed gas was being flowed, the temperature was raised to 420°C at a rate of 5°C / min and held at 420°C for 60 minutes to perform nitriding treatment. Next, the gas flowing in the tubular furnace was changed to hydrogen (H ). ２ The gas flowing through the tubular furnace was changed to argon gas and the temperature was maintained at 420°C for another 60 minutes. The heating was then stopped and the mixture was cooled to near room temperature while argon gas was being flowed, yielding nitrided powder. The cooled powder was transferred from the tubular furnace into 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] (Pulverization) 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. Pulverization was carried out in this 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 operating time of the rotary mixer was changed from 8 hours to 22 hours. In this way, a Sm—Fe—N magnetic powder according to Comparative Example 1 was obtained.

[0069] The cumulative 50% particle diameter D in the volume-based particle size distribution of the obtained Sm—Fe—N magnetic powder by laser diffraction / scattering method was ５０ The saturation magnetization σ of this Sm—Fe—N magnetic powder was 1.53 μm. ｓ is 146 Am ２ / kg, residual magnetization σ ｒ is 109Am ２ / kg, squareness ratio σ ｒ / σ ｓ is 0.747, coercive force H ｃ is 629kA / m, maximum energy product (BH) ｍａｘ is 95 kJ / m ３ The Ca content of this Sm-Fe-N magnetic powder was less than 0.001% (below the measurement limit).

[0070]

[0071] In each embodiment, a high maximum energy product (BH) ｍａｘ This is thought 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) ｍａｘ This is thought to be because, although the particles are refined by grain boundary destruction during pulverization, the crystal grains are too small to be completely monodispersed, and as a result, an Sm—Fe—N magnetic powder containing many particles consisting of multiple crystal grains was obtained.

[0072] FIG. 5 illustrates an IPF map (inverse pole figure crystal orientation map) obtained 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) obtained by EBSD (electron backscatter diffraction) for the particles of the Sm—Fe—N magnetic powder obtained in Comparative Example 1. These IPF maps are monochrome versions of color images of IPF maps obtained by EBSD measurement of a sample surface where the cross section of the particles was revealed, prepared by ion milling after polishing the resin in which the powder particles were embedded. In the monochrome IPF map, individual crystal grains are represented as brightness differences based on crystal orientation differences. The Sm—Fe—N magnetic powder according to the present invention ( FIG. 5 ) has a higher proportion of particles consisting of single crystal grains 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 using Co-Kα radiation for the Sm—Fe—N magnetic powder obtained in Example 1. ２ Zn １７ Sm having a type crystal structure ２ Fe １７ N ３ The theoretical peak positions and peak heights for the Sm-Fe-N magnetic powder obtained in Example 1 were Th ２ Zn １７It can be seen that the Sm—Fe—N magnetic powders obtained in Examples 2 to 4 also have a Th type crystal structure. ２ Zn １７ It was confirmed that the compound had a type crystalline structure.

[0074] The results of Examples 9 and 10 show that the saturation magnetization and maximum energy product were improved by changing the non-oxidizing gas atmosphere for the nitriding treatment from a mixed gas atmosphere of ammonia gas and hydrogen gas to a nitrogen gas atmosphere. Furthermore, a particularly high maximum energy product was obtained in Example 6, which shows that jet mill pulverization is advantageous for improving the maximum energy product.

[0075] REFERENCE SIGNS LIST 1 crucible 2 molten metal discharge nozzle member 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 molten metal discharge gas supply device 21 discharge port 22 stopper contact surface

Claims

1. A method for producing Sm-Fe-N magnetic powder, comprising: a heat treatment step in which Sm-Fe alloy powder, formed during the solidification process by gas atomization and having an Sm / Fe molar ratio of 0.09 to 0.25, is heated to a temperature of 900°C to 1200°C to coarsen the crystal grains of the powder particles; a crushing step in which the Sm-Fe alloy powder, the crystal grains of which have been coarsened by the heat treatment step, is crushed to refine the powder particles by fracture, including intragranular fracture; and a nitriding step in which the Sm-Fe alloy powder, which has been crushed to refine the powder particles by heating and maintaining it at a temperature of 500°C or less in an atmosphere of a nitrogen compound or a non-oxidizing gas containing nitrogen, to introduce nitrogen into the powder particles.

2. A method for producing Sm-Fe-N magnetic powder as described in claim 1, wherein the Sm-Fe alloy powder 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 determined by the laser diffraction / scattering method 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. A method for producing Sm-Fe-N based magnetic powder according to claim 1 or 2, wherein in the pulverizing step, the Sm-Fe based alloy powder is pulverized using a jet mill.

5. The method for producing Sm-Fe-N magnetic powder according to claim 1 or 2, 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) ｍａｘ is 150 kJ / m ３ The method for producing Sm-Fe-N based magnetic powder according to claim 1 or 2, wherein the above-mentioned 7. The Sm-Fe-N magnetic powder is made of Th ２ Zn １７ 3. The method for producing Sm-Fe-N magnetic powder according to claim 1, wherein the powder has a crystalline structure.

8. A method for producing Sm-Fe-N based magnetic powder according to claim 1 or 2, 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 consisting of particles mainly composed of Sm, Fe, and N, in which the molar ratio of Sm to Fe (Sm / Fe) is 0.09 or more and 0.25 or less, 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 measured by the laser diffraction / scattering method is 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 The above is the Sm-Fe-N magnetic powder.

10. Rectangularity σ ｒ / σ ｓ 10. The Sm—Fe—N magnetic powder according to claim 9, wherein the value of σ is 0.760 or more.

11. Th ２ Zn １７ 10. The Sm—Fe—N magnetic powder according to claim 9, having a type crystal structure.

12. 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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