METHOD FOR PRODUCING Sm-Fe-N-BASED MAGNETIC POWDER AND Sm-Fe-N-BASED 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 Sm-Fe-N-based magnetic powder.

Background Art

[0002] Sm2Fe 17 A substance obtained by introducing nitrogen into an intermetallic compound (a typical composition formula is Sm2Fe 17 N3) is known to be a ferromagnetic material exhibiting excellent hard magnetism. In this specification, a powder of a substance obtained by introducing nitrogen into an Sm-Fe-based alloy having a stoichiometric composition of Sm2Fe 17 or a composition around it, and being a ferromagnetic material is referred to as "Sm-Fe-N-based magnetic powder". Sm-Fe-N-based magnetic powder is useful as a material for bonded magnets.

[0003] As production techniques for Sm-Fe-N-based magnetic powder, methods using a solidification process such as an atomization method or a single-roll method, and methods using a reduction diffusion method using Ca or the like as a reducing agent are known.

[0004] For example, Patent Document 1 describes that spherical particles of an Sm2Fe 17 alloy were synthesized by a gas atomization method, and the obtained powder was nitrided in a tubular furnace to obtain an alloy powder having a composition of Sm2Fe 17 N3. The average particle diameter 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 in which magnetic powder having a composition obtained by adding an element such as Si to an Sm-Fe-based or Sm-Fe-C-based system was synthesized by an atomization method using gas spraying, gas-water spraying, and water spraying. The particle diameter is about 80 to 110 μm (paragraph 0019). By nitriding the obtained particles, an Sm-Fe-(C)-Si-N-based powder is obtained. The magnetic powder after nitriding has a maximum energy product (BH) max of 6 to 13 MGOe (48 to 103 kJ / m 3) Many are at such a level, and the maximum is 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 a single roll method is heat-treated at 750 °C, then nitrided at 450 °C for 2 hours, and then pulverized to obtain Sm-Fe-N-based magnetic powder with a particle size of 106 μm or less (Example 1). The maximum energy product (BH) max of the powder is 102 kJ / m 3 (Table 2).

[0007] Patent Document 4 discloses a technique for obtaining magnetic powder such as Sm-Fe-N-based by using a reduction-diffusion method using Ca and nitriding treatment, and adopting a process in which the reduction reaction is carried out in two steps, so as to obtain powder with an average particle size of 5 μm or less without using any pulverization process. Regarding the powder after the second reduction step, it is described that "after washing with water, weak acids such as acetic acid are used to thoroughly separate calcium." Nevertheless, 0.01 wt% of Ca remains in the powder obtained in the example (paragraphs 0034, 0037, 0047, 0050, 0060).

[0008] Patent Document 5 discloses a technique for obtaining Sm-Fe-N-based magnetic powder with a core-shell structure by using a method in which particles obtained by a reduction-diffusion method using Ca are subjected to hydrogen treatment and disintegration treatment and then nitriding treatment. The particle size of the Sm-Fe-N-based magnetic powder obtained in the example is D 50 which is 2.8 to 9.1 μm (paragraphs 0122, 0131, 0136, 0139, 0144, 0151, 0158, 0165, 0172), and the residual magnetization σ r is about 101 to 102 A·m 2 / kg (paragraphs 0123, 0133). Ca is contained in the particles, for example, in an amount of less than 0.01 mass% (paragraph 0114). It is said that Ca is not contained in the inner layer of the shell consisting of the outer layer and the inner layer, but "not containing Ca" as referred to in Patent Document 5 means that the Ca content is less than 1.0 atomic% (paragraph 0043).

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0010] In recent years, in order to cope with the higher performance of automotive motors and sensors, for bonded magnets using Sm-Fe-N-based magnetic powder, further improvement in magnetic properties has been expected. In particular, for improving the properties of anisotropic bonded magnets, it is advantageous to apply magnetic powder with the highest possible maximum energy product (BH). max The solidified metal obtained by a rapid solidification process such as the atomization method or the single-roll method generally has a polycrystalline structure composed of microcrystals. In magnetic powder derived from such fine polycrystalline solidified metal, it is not easy to achieve a high (BH). max Although the (BH) values of magnetic powder using Sm are shown in Patent Documents 2 and 3, further improvement in (BH) is desired to contribute to the improvement of the properties of anisotropic bonded magnets. max value is shown, but in order to contribute to the improvement of the properties of anisotropic bonded magnets, further improvement in (BH) max is desired.

[0011] On the one hand, the reduction diffusion method using a reducing agent such as Ca has a complicated process and a large environmental load such as the generation of alkaline drainage. In addition, in the Sm-Fe-N-based magnetic powder obtained by the process using the reduction diffusion method, the remaining reducing agent components such as Ca and other alkaline earth metals and alkali metals are inevitable. The alkaline earth metals and alkali metals remaining in the magnetic powder can easily gel the resin when using the powder as a material to produce a bonded magnet, which may be a factor in reducing the manufacturability of the bonded magnet.

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

Means for Solving the Problems

[0013] In order to obtain a powder of an Sm-Fe alloy with an extremely small amount of Ca present, it is effective to adopt the gas atomization method. In this specification, a powder composed of particles that have not been subjected to physical or chemical treatment (such as applying external force, magnetic force, heat treatment, surface treatment, etc.) after being synthesized by the gas atomization method is called "gas atomized powder". Since the particles of the gas atomized powder are formed by rapid solidification, they become polycrystalline particles composed of very fine crystal grains. As polycrystalline particles, they have a high maximum energy product (BH) maxIt is difficult to obtain. Also, according to the research of the inventors, when polycrystalline particles composed of fine crystal grains are made into small particles by mechanical grinding, since there are many grain boundaries where cracks are likely to propagate, fracture at the grain boundaries preferentially proceeds, and it has been found that the small-sized individual particles tend to be particles composed of a plurality of crystal grains with grain boundaries remaining inside. That is, it is very difficult to break particles composed of fine crystal grains into particles composed of a single crystal grain by grinding. Therefore, the inventors have advanced the study on an effective means capable of obtaining a powder containing many particles composed of a single crystal grain using gas atomized powder as a raw material. As a result, it has been found that when the gas atomized powder of the Sm-Fe alloy is heat-treated at a high temperature, growth of the fine crystal grains occurs, and the crystal grains can be coarsened to a size such that the average crystal grain size in terms of the equivalent circle diameter in the cross-sectional structure of the particles is, for example, about 3 to 15 μm. And when mechanical grinding is performed on the powder of the Sm-Fe alloy composed of particles with coarsened crystal grains like this, each particle is broken by the occurrence of fracture within the crystal grains (intragranular fracture) in addition to fracture at the grain boundaries (intergranular fracture), and as a result, it has been found that a fine powder of the Sm-Fe alloy with a high proportion of particles composed of a single crystal grain can be obtained. Also, it has been confirmed that the maximum energy product (BH) max is remarkably improved in the Sm-Fe-N magnetic powder obtained by nitriding the powder. The present invention is based on such findings.

[0014] The above object is achieved by the following invention. [1] A heat treatment step of coarsening the crystal grains of the particles of a powder of a Sm-Fe alloy having a Sm / Fe molar ratio of 0.09 or more and 0.25 or less formed in the solidification process by the gas atomization method by heating the powder to a temperature of 900°C or more and 1200°C or less, A grinding step of refining the particles of the powder of the Sm-Fe alloy with coarsened crystal grains by the heat treatment step by breaking the particles by fracture including intragranular fracture, A nitriding step of introducing nitrogen into the particles of the powder by heating and holding the powder of the Sm-Fe alloy refined by the above-mentioned pulverization step in a temperature range of 500 °C or lower in an atmosphere of a nitrogen compound or a non-oxidizing gas containing nitrogen, A method for producing an Sm-Fe-N-based magnetic powder having . [2] The method for producing an Sm-Fe-N-based magnetic powder according to [1] above, wherein the powder of the Sm-Fe alloy to be pulverized in the pulverization step is subjected to a hydrogen treatment of heating and holding 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 50 The method for producing an Sm-Fe-N-based magnetic powder according to [1] or [2] above, 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-based magnetic powder according to any one of [1] to [3] above, wherein in the pulverization step, the powder of the Sm-Fe alloy is pulverized using a jet mill. [5] The method for producing an Sm-Fe-N-based 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 maximum energy product (BH) of the Sm-Fe-N-based magnetic powder max is 150 kJ / m 3 or more. The method for producing an Sm-Fe-N-based magnetic powder according to any one of [1] to [5] above. [7] The Sm-Fe-N-based magnetic powder has a Th2Zn 17 type crystal structure. The method for producing an Sm-Fe-N-based magnetic powder according to any one of [1] to [6] above. [8] The Sm-Fe-N-based magnetic powder has an N / Fe molar ratio of 0.06 or more and 0.30 or less. The method for producing an Sm-Fe-N-based magnetic powder according to any one of [1] to [7] above. [9]A powder composed of particles mainly containing Sm, Fe, and N, having a composition in which the molar ratio Sm / Fe of Sm to 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 by the laser diffraction / scattering method 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 or more, Sm-Fe-N-based magnetic powder.

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

[11] Th2Zn 17 having a type crystal structure, the Sm-Fe-N-based magnetic powder according to the above [9] or

[10] .

[12] Having a composition in which the molar ratio N / Fe of N to Fe is 0.06 or more and 0.30 or less, the Sm-Fe-N-based magnetic powder according to any one of the above [9] to

[11] . [Advantages of the Invention]

[0015] According to the present invention, a Sm-Fe-N-based magnetic powder having a high maximum energy product (BH) can be obtained by a process that does not cause an environmental load due to alkaline waste liquid. Since the amount of Ca present in this Sm-Fe-N-based magnetic powder is extremely low, the problem of promoting gelation of the resin by Ca is avoided when producing a bonded magnet using the resin, and an improvement in productivity can be expected, for example, in a magnetic field orientation process. max [Brief Description of the Drawings]

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

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

[0018] [Gas Atomization] In the present invention, powders of Sm-Fe alloys solidified by the gas atomization method are used. The gas atomization method is a powder formation method in which a metal melt discharged into a gas phase space is divided into fine liquid phase particles by spraying a gas at high speed onto the metal melt, and the liquid phase particles are rapidly solidified during flight in the gas phase space. As the metal raw material for generating the metal melt 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. The stoichiometric Sm / Fe molar ratio of Sm2Fe 17 is 0.118. The composition of the metal melt is Sm2Fe 17It is desirable to adjust it to a value relatively close to the stoichiometric composition, specifically, in the range where the Sm / Fe molar ratio is 0.09 or more and 0.25 or less. Although the incorporation of metal elements other than Sm and Fe can be tolerated as long as it does not inhibit the required characteristics of the finally obtained magnetic powder, 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 maintained at a predetermined temperature and sufficiently homogenized is discharged from the nozzle into the gas phase space, and a cooling gas is vigorously sprayed onto the molten metal immediately after discharge. As a result, the molten metal becomes fine liquid-phase particles and flies through the gas phase space and solidifies. The molten metal temperature 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, classification may be performed using a sieve or the like, and the gas atomized powder with adjusted particle size may be supplied to the subsequent process. Considering that it is 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 the cumulative 50% particle size D in the volume-based particle size distribution by the laser diffraction / scattering method. 50 For example, it 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 limitation on the lower limit of the particle size of the gas atomized powder, but since it is currently very difficult to industrially synthesize particles with D 50 less than 5.0 μm, it may be adjusted within the range where D 50 is 5.0 μm or more, and it may be controlled within the range of 10.0 μm or more.

[0020] In the gas atomization process, the pressurizing gas for discharging the molten metal, the injection gas sprayed onto the molten metal, and the atmosphere gas in the gas phase space through which the liquid-phase particles fly are all desirably inert gases excluding nitrogen. If nitrogen is contained in these gases, the gas atomized powder will be incompletely nitrided, making it difficult to achieve highly uniform nitridation by the nitridation treatment in the subsequent process.

[0021] [Heat treatment] By subjecting the gas atomized powder of the Sm-Fe alloy (hereinafter sometimes referred to as "Sm-Fe gas atomized powder") to heat treatment at a high temperature, the coarsening of crystal grains is achieved. 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 terms of the equivalent circle diameter in the cross-sectional structure of the particles is, for example, about 3 to 15 μm. By this coarsening of the crystal grains, in the subsequent pulverization process, it becomes easier to obtain a fine powder of the Sm-Fe alloy in which the proportion of particles composed of a single crystal grain is large. Grain boundary fracture is likely to occur. It is more preferable to heat to 930 °C or higher. Since excessive temperature increase is uneconomical, the heating temperature is preferably set in the range of 1200 °C or lower, and may be controlled in the range of 1100 °C or lower, or 1000 °C or lower. The holding time in the temperature range of 900 °C or higher and 1200 °C or lower can be, for example, 10 seconds or more and 10 minutes or less, and may be set in the range of 30 seconds or more and 5 minutes or less. The heating atmosphere is desirably an inert gas atmosphere excluding nitrogen, or a vacuum.

[0022] In FIGS. 1 and 2, IPF maps (inverse pole figure crystal orientation maps) obtained by EBSD (electron backscatter diffraction method) for the cross-sections of the particles obtained by heating the Sm-Fe gas atomized powder obtained in the same manner as in Example 1 described later at 700 °C and 1000 °C, respectively, are illustrated. In both cases, the atmosphere during heating is argon gas, and the heating holding time at each temperature is 1 minute. These IPF maps are obtained by monochromatizing the color images of the IPF maps obtained by EBSD measurement for the sample surface on which the cross-section of the particles appears, which is prepared by ion milling after polishing the resin embedding the powder particles. In the monochromatized IPF maps, individual crystal grains are represented as brightness differences based on the crystal orientation difference. From the comparison between FIG. 1 and FIG. 2, it can be seen that the coarsening of the crystal grains progresses more by heating at a high temperature.

[0023] In the Sm-Fe gas atomized powder, it is also conceivable that a Sm-Fe metal phase with a TbCu7-type crystal structure is formed depending on the conditions. The Sm-Fe metal phase of the TbCu7 type is Th2Zn17 Since the anisotropic magnetic field after nitriding treatment is smaller than that of the [type] and it is difficult to obtain a high coercive force, it is desirable that the abundance of the TbCu7-type Sm-Fe-based metal phase be as small as possible. By raising the temperature to the above temperature range, the TbCu7-type crystal phase changes to the Th2Zn 17 type, so the heat treatment is also effective for homogenizing the structure.

[0024] [Hydrogen treatment] In order to easily cause intragranular fracture during pulverization in a later process, it is effective to perform hydrogen treatment by heating in a hydrogen gas atmosphere before pulverization. Hydrogen penetrates into the crystal grains of the Sm-Fe-based alloy by hydrogen treatment, and intragranular fracture is likely to occur due to the so-called phenomenon of hydrogen embrittlement. Therefore, hydrogen treatment can be performed as needed. The heating temperature of the hydrogen treatment is preferably set in the range of 200°C or higher and 600°C or lower, and the holding time in that temperature range may be set, for example, in the range of 30 minutes or longer and 600 minutes or shorter.

[0025] [Pulverization] When mechanical pulverization is performed on the powder of the Sm-Fe-based alloy whose crystal grains have been coarsened by the above heat treatment, each particle breaks by causing fracture within the crystal grains (intragranular fracture) in addition to fracture at the crystal grain boundaries (intergranular fracture). When the powder particles are refined by such "fracture including intragranular fracture", a fine powder of the Sm-Fe-based alloy with a high proportion of particles composed of a single crystal grain can be obtained. As a pulverization means suitable for the present invention, for example, a wet ball mill can be mentioned. In this case, by introducing a large amount of solvent into the container so that, for example, a slight gas phase space remains, the fine particles generated by fracture at the crystal grain boundaries are easily dispersed in the solvent, and it is effective to reduce the opportunity for applying an external force (excessive pulverization opportunity) to the fractured particles. Also, as another pulverization means suitable for the present invention, a jet mill can be mentioned. Jet mill pulverization is advantageous for improving the maximum energy product (BH) max of.

[0026] From the perspective of fragmenting particles by fracture including intragranular fracture, the particle size after pulverization is adjusted so that the cumulative 50% particle size D 50 in the volume-based particle size distribution by the laser diffraction / scattering method is 5.0 μm or less, and more preferably adjusted to 3.0 μm or less. If excessive refinement is attempted, crystal lattice strain may increase due to the application of excessive external force, which may have an adverse effect on magnetic properties. Usually, the above particle size D 50 is desirably pulverized in the range of 0.5 μm or more, and may be pulverized in the range of 1.0 μm or more.

[0027] Note that the particle size distribution may be optimized by classifying the powder obtained by pulverization and excluding coarse particles or, if necessary, unduly fine particles.

[0028] [Nitriding treatment] Next, a nitriding treatment is performed to obtain an Sm-Fe-N-based magnetic powder. The nitriding treatment can be carried out by heating and holding the powder of the Sm-Fe-based alloy refined by the above pulverization in an atmosphere of a nitrogen compound or a non-oxidizing gas containing nitrogen. If the heating temperature is too high, nitrogen atoms will penetrate into the Sm2Fe 17 crystal to form Sm2Fe 17Since the structure based on N3 becomes unstable, nitridation becomes difficult. It is desirable that the heating temperature for the nitridation treatment be 500 °C or lower. If the temperature is too low, it takes a long time for nitridation to proceed, which is disadvantageous for uniformly diffusing nitrogen atoms into the interior of the particles. A heating temperature of 300 °C or higher is effective. As the atmosphere gas for the nitridation treatment, a reducing atmosphere composed of a mixed gas of ammonia (NH3) and hydrogen (H2) is practical. For example, the mixing ratio of ammonia to hydrogen, NH3:H2, can be in the range of 10:90 to 60:40. In addition, examples of the atmosphere gas used for the nitridation treatment include a mixed gas of hydrogen, ammonia, and nitrogen (N2), a mixed gas of hydrogen, ammonia, and argon (Ar), ammonia alone, a mixed gas of ammonia and nitrogen, a mixed gas of ammonia and argon, nitrogen gas, and a mixed gas of nitrogen and hydrogen. These are used to create a non-oxidizing atmosphere. For example, a non-oxidizing atmosphere composed of nitrogen gas (i.e., "nitrogen gas atmosphere") is effective for improving the saturation magnetization σ s and the maximum energy product (BH) max . The optimum time for the nitridation treatment varies somewhat depending on the average particle size of the powder, the composition of the atmosphere gas, and the temperature. Usually, the optimum time can be found in the range of 15 to 240 minutes.

[0029] It is considered that nitrogen atoms enter the interstitial positions of the crystal lattice of the Th2Zn 17 type crystal structure of Sm2Fe 17 , and the Th2Zn 17 type crystal structure is maintained even after nitrogen is introduced. When nitrogen atoms are introduced into Sm2Fe 17 , the crystal magnetic anisotropy changes from in-plane type to uniaxial type and the Curie point rises, making it possible to obtain a practical magnet material. A typical composition of Sm-Fe-N-based magnetic powder excellent in magnetic properties is Sm2Fe 17 N3. It is considered that the closer the Sm / Fe molar ratio, which represents the molar ratio of Sm to Fe, and the N / Fe molar ratio, which represents the molar ratio of N to Fe, are to the stoichiometric composition of Sm2Fe 17 N3, the more advantageous it is in terms of magnetic properties. However, hard magnetism is also exhibited in the surrounding composition range. Sm2Fe 17The stoichiometric Sm / Fe molar ratio of N3 is 0.118, and the N / Fe molar ratio is 0.176. In the present invention, considering that a coercive force effective as a material for bonded magnets can be stably obtained in a temperature range including room temperature, the Sm / Fe molar ratio is preferably in the range of 0.09 or more and 0.25 or less. The Sm / Fe molar ratio reflects the composition of the gas atomized powder. Further, when the powder of the Sm-Fe-based alloy is nitrided under the above conditions, nitrogen is introduced into the Sm2Fe 17 crystal, and an Sm-Fe-N-based magnetic powder having an N / Fe molar ratio in the range of 0.06 or more and 0.30 or less is obtained, which exhibits excellent magnetic properties. Even if the nitriding treatment is performed before the above-mentioned pulverization, an Sm-Fe-N-based magnetic powder having a composition close to Sm2Fe 17 N3 can be obtained. However, from the viewpoint of obtaining an Sm-Fe-N-based magnetic powder having a more uniform nitrogen distribution, in the present invention, the powder of the Sm-Fe-based alloy refined by pulverization is nitrided. Classification may be performed after the nitriding treatment to adjust to an appropriate particle size distribution according to the application.

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

[0031] The "particles mainly composed of Sm, Fe, and N" refer to particles in which the top three elements in the order of the content of elements contained in the particles in terms of mass ratio are occupied by the three elements of Sm, Fe, and N. If the Ca content is 0.005% by mass or less, in the general process of manufacturing bonded magnets using resin, the problem of promoting gelation of the resin by Ca is considered to be almost eliminated. The Ca content is more preferably 0.002% by mass or less. If the mixing of impurity elements is strictly controlled according to the above-described manufacturing process, Sm-Fe-N-based magnetic powder 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", or "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 150 kJ / m 3 or more. The Sm-Fe-N-based magnetic powder is extremely useful as a material for anisotropic bonded magnets that require excellent magnetic properties. By adjusting the manufacturing conditions in the above-described manufacturing process, (BH) max can also be obtained to be 200 kJ / m 3 or more. The upper limit of (BH) max is not particularly limited, but it may usually be adjusted within the range of 350 kJ / m 3 or less. The saturation magnetization σ s is preferably 140 A·m 2 / kg or more, and the remanent magnetization σ r is preferably 115 A·m 2 / kg or more. The squareness ratio σ r / σ s is 0.760 or more, which is effective in realizing a high (BH) max , and more effective when it is 0.790 or more. The coercive force H c is preferably 700 kA / m or more.

Examples

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

[0034] (Elemental analysis) In a glove box filled with argon (Ar) gas, the analysis sample was heated and dissolved with hydrochloric acid, diluted, and a sample solution for analysis was prepared. This solution was analyzed using an ICP emission spectroscopic analyzer (manufactured by Agilent Technologies, Agilent 720).

[0035] (Measurement of the particle size distribution of the powder) The particle size distribution of the powder was measured using a laser diffraction particle size distribution analyzer (manufactured by Sympatec, Helos / Rodos). In the volume-based particle size distribution obtained by the laser diffraction / scattering method, the cumulative 50% particle diameter D 50 was determined.

[0036] (Magnetic measurement of the powder) The magnetic properties of the powder were measured by the following method using a VSM (manufactured by Quantum Design, PPMS DynaCool). 10 mg of the sample powder and 10 mg of low molecular weight polyethylene powder (manufactured by Mitsui Chemicals, Inc., Hi-Wax 100P) 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 , the remanent magnetization σ r , the coercive force H c , and the 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·s, a time constant of 1 s, an amplitude of 2 mm, and a frequency of 40 kHz. Also, from the above measurement results, the squareness ratio σ r / σ s was calculated.

[0037] (X-ray diffraction measurement) For the powder sample, an X-ray diffraction pattern 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 method) Figure 3 schematically shows the configuration of the gas atomization apparatus used in this example. Inside the chamber, there are two independent upper and lower spaces that can be evacuated by a vacuum evacuation device 10, and these spaces can be made into gas phase spaces having predetermined gas atmospheres by introducing gas from atmosphere gas supply sources 11a and 11b, respectively. In the upper space, there is a crucible 1, and the raw material is melted by induction heating by a high-frequency coil 4 therein to form a molten metal 5. At the bottom of the crucible 1, a molten metal discharge nozzle member 2 for discharging the molten metal 5 into the lower gas phase space is attached. Until the molten metal 5 is discharged, the molten metal flow path is blocked by pressing a stopper 3 against the molten metal discharge nozzle member 2. After the molten metal 5 is sufficiently homogenized and a molten metal at a predetermined temperature is obtained, the stopper 3 is pulled up in a state where gas at a predetermined pressure is supplied from a molten metal discharge gas supply device 13 to the surface of the molten metal in the crucible 1, and the molten metal 5 is discharged from the tip of the molten metal discharge nozzle member 2 into the lower gas phase space. In the lower gas phase space, a gas injection nozzle 6 for spraying gas onto the discharged molten metal 5 is provided. Before the start of discharge, the supply of gas from a gas supply device 12 to the gas injection nozzle 6 is started, and the gas is sprayed from the gas injection nozzle 6 at a high pressure. By applying the strong jet of this injection gas to the molten metal |5, fine particles of the molten metal 5 are formed and the fine particles are rapidly solidified. The solidified metal particles 7 accumulate at the bottom of the lower gas phase space.

[0039] Fig. 4 schematically shows an example of the cross-sectional structure near the bottom of the crucible of the gas atomization device. The molten metal discharge nozzle member 2 attached to the bottom of the crucible 1 has a discharge port 21 which is the opening at the tip of the nozzle and a stopper contact surface 22. The stopper 3 is a movable type that moves in the vertical direction, and by contacting the stopper contact surface 22 of the molten metal discharge nozzle member 2, it closes the flow path of the nozzle, and has the function of opening the flow path of the nozzle by separating from the stopper contact surface 22 during the discharge of the molten metal. 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 that is immersed in the molten metal 5 is made of yttrium oxide (Y2O3). The nozzle inner diameter of the molten metal discharge nozzle member 2 was set to 3.0 mm.

[0040] As a 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 put into a crucible and melted by high-frequency induction heating in an Ar atmosphere. After the raw material alloy was completely melted, when the elapsed time from the start of heating was 27 minutes, the total amount of the molten metal at 1637 °C was discharged from the nozzle into the lower gas phase space. The maximum supply pressure of the gas for discharging the molten metal was 65 kPa in terms of the differential pressure from the atmospheric gas pressure. Ar was used as the injection gas. Also, the lower gas phase space was also an Ar atmosphere. The generated powder was collected, and undersized particles were removed by a sieve with an opening of 16 μm in a glove box under a nitrogen atmosphere. Thus, gas atomized powder was obtained.

[0041] As a result of elemental analysis of the gas atomized powder, the Sm / Fe molar ratio was 0.16, which was equivalent to the raw material alloy. The Ca content was less than 0.001% (below the measurement limit). Also, the cumulative 50% particle diameter D 50 in the volume-based particle size distribution of the gas atomized powder by the laser diffraction / scattering method was 22.8 μm. Using the obtained Sm-Fe-based gas atomized powder, the following steps were carried out.

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

[0043] (Hydrogen treatment) The obtained heat-treated powder was transferred into another tubular furnace, and while flowing hydrogen (H2) 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, after cooling to 50 °C or below while flowing hydrogen gas, the inside of the furnace was replaced with argon gas. In this way, hydrogen-treated powder was obtained.

[0044] (Grinding) The obtained hydrogen-treated powder was put into an airtight container filled with argon gas and transferred from the tubular furnace into another glove box filled with argon gas. Grinding was performed in this glove box at the transfer destination. As the mill pot, a glass bottle with a screw cap and a capacity of 50 mL was used, and a grinding experiment imitating a wet ball mill was conducted 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 put into the above glass bottle. Using a rotary mixer (Mix Rotator Variable, manufactured by AS ONE Corporation, 3-roller type, model number VMR-3R), the above glass bottle containing the hydrogen-treated powder was placed between two rollers, and grinding treatment was performed at a rotation speed of 110 rpm and an operation time of 8 hours. After the grinding treatment, the contents in the glass bottle were passed through a sieve to remove the stainless steel balls, and then the slurry passing through the sieve was allowed to stand. After that, the supernatant was discarded, and the remaining slurry was vacuum dried to obtain the ground powder. The 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 a tubular furnace with an electric heating system under an argon gas atmosphere. After that, a mixed gas composed of 35% by volume of ammonia (NH3) gas and 65% by volume of hydrogen (H2) gas was passed through the tubular furnace to displace the gas in the tubular furnace. Then, while flowing the above-mentioned 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 a nitriding treatment. Next, the gas flowing through the tubular furnace was changed to hydrogen (H2) gas and held at 430 °C for another 120 minutes. Then, the gas flowing through the tubular furnace was changed to argon gas and held at 430 °C for 90 minutes. After that, the heating was stopped and cooled to a temperature near room temperature while flowing argon gas to obtain nitrided powder.

[0046] Next, the obtained nitrided powder was transferred into a glove box filled with argon gas from the tubular furnace, and then put into a glass bottle with a screw cap having a volume of 20 mL, and 15 mL of heptane was added as a solvent. Next, this glass bottle was placed in an ultrasonic disperser (manufactured by SMT Co., Ltd., UH-150 type) and operated for 100 minutes under a cycle of output conditions of 20 kHz, transmitting for 0.3 seconds, and pausing for 0.7 seconds. Then, the supernatant in the glass bottle was removed, and the remaining heptane was removed by vacuum drying to obtain the Sm-Fe-N-based magnetic powder according to Example 1.

[0047] The cumulative 50% particle diameter D in the volume-based particle size distribution of the obtained Sm-Fe-N-based magnetic powder by the laser diffraction / scattering method 50 was 1.46 μm. Also, the saturation magnetization σ of this Sm-Fe-N-based magnetic powder s was 143 A·m 2 / kg, the remanent magnetization σ r was 117 A·m 2 / kg, the squareness ratio σ r / σ s was 0.818, the coercive force H c was 716 kA / m, and the maximum energy product (BH) max was 162 kJ / m 3 . Also, the Ca content of this Sm-Fe-N-based magnetic powder was less than 0.001% (below the measurement limit). The above results are shown in Table 1 together with the manufacturing conditions (the same applies to 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 to be subjected to pulverization was taken from the powder obtained in Example 1 and used (the same applies to Examples 3 and 4 below). The cumulative 50% particle diameter D in the volume-based 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 1.39 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 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 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 in the volume-based 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 1.37 μm. 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 3It was. Also, the Ca content of this Sm-Fe-N-based magnetic powder was less than 0.001% (below the measurement limit).

[0050] [Example 4] An Sm-Fe-N-based magnetic powder was obtained in the same manner as in Example 1, except that the operating time of the rotary mixer in the pulverization of Example 1 was changed from 8 hours to 14 hours. The cumulative 50% particle diameter D in the volume-based particle size distribution of the obtained Sm-Fe-N-based magnetic powder by the laser diffraction / scattering method 50 was 1.21 μm. Also, the saturation magnetization σ of this Sm-Fe-N-based magnetic powder s was 141 A·m 2 / kg, the remanent magnetization σ r was 119 A·m 2 / kg, the squareness ratio σ r / σ s was 0.844, the coercive force H c was 875 kA / m, and the maximum energy product (BH) max was 189 kJ / m 3 It was. Also, the Ca content of this Sm-Fe-N-based magnetic powder was less than 0.001% (below the measurement limit).

[0051] [Example 5] An Sm-Fe-N-based magnetic powder was obtained in the same manner as in Example 1, except that the holding time in the heat treatment of 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 in the volume-based particle size distribution of the obtained Sm-Fe-N-based magnetic powder by the laser diffraction / scattering method 50 was 1.77 μm. Also, the saturation magnetization σ of this Sm-Fe-N-based magnetic powder s was 138 A·m 2 / kg, the remanent magnetization σ r was 120 A·m 2 / kg, the squareness ratio σ r / σ s was 0.870, the coercive force H c was 770 kA / m, and the maximum energy product (BH) max was 211 kJ / m3 It was. Also, the Ca content of this Sm-Fe-N-based magnetic powder was less than 0.001% (below the measurement limit).

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

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

[0054] (Pulverization) As the jet mill device, a nano-grinding mill, model NJ-50, manufactured by Sanrex Corporation was used. The operating conditions were a pulverization pressure of 1 MPa, and the treatment was performed in one pass. (Nitriding treatment) The pulverized powder obtained as described above was transferred into a tubular furnace with an electric heating system 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 above nitrogen gas, the temperature was raised to 460 °C at a rate of 5 °C / min and held at 460 °C for 360 minutes to perform nitriding treatment. Subsequent treatment was carried out in the same manner as in Example 1 to obtain an Sm-Fe-N-based magnetic powder.

[0055] The cumulative 50% particle diameter D in the volume-based particle size distribution of the obtained Sm-Fe-N-based magnetic powder by laser diffraction / scattering method 50 was 1.77 μm. Also, the saturation magnetization σ of this Sm-Fe-N-based magnetic powder <atag s was 147 A·m 2 / kg, the remanent magnetization σ r was 133 A·m 2 / kg, the squareness ratio σ r / σ s was 0.905, and the coercive force Hc was 768 kA / m, and the maximum energy product (BH) max was 251 kJ / m 3 . Also, the Ca content of this Sm-Fe-N-based magnetic powder was less than 0.001% (below the measurement limit).

[0056] [Example 7] In the synthesis of Sm-Fe-based powder by the gas atomization method, gas atomized powder was obtained using a Sm-Fe alloy with a Sm / Fe molar ratio of 0.14 as the raw material. As a result of elemental analysis of the obtained gas atomized powder, 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). Also, the cumulative 50% particle diameter D in the volume-based particle size distribution of the gas atomized powder by the laser diffraction / scattering method 50 was 25.9 μm. A Sm-Fe-N-based magnetic powder was obtained in the same manner as in Example 1, except that the Sm-Fe-based gas atomized powder thus obtained was used, the operating time of the rotary mixer in pulverization was 4 hours, and the holding temperature in 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-based magnetic powder by the laser diffraction / scattering method 50 was 1.41 μm. Also, the saturation magnetization σ of this Sm-Fe-N-based magnetic powder s was 153 A·m 2 / kg, the remanent magnetization σ r was 129 A·m 2 / kg, the squareness ratio σ r / σ s was 0.843, the coercive force H c was 724 kA / m, and the maximum energy product (BH) max was 219 kJ / m 3 . Also, the Ca content of this Sm-Fe-N-based magnetic powder was less than 0.001% (below the measurement limit).

[0058] [Example 8] An Sm-Fe-N-based magnetic powder was obtained in the same manner as in Example 7, except that the operating 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 in the volume-based particle size distribution of the obtained Sm-Fe-N-based magnetic powder by the laser diffraction / scattering method 50 was 1.17 μm. Also, the saturation magnetization σ of this Sm-Fe-N-based magnetic powder s was 153 A·m 2 / kg, the remanent magnetization σ r was 121 A·m 2 / kg, the squareness ratio σ r / σ s was 0.791, the coercive force H c was 817 kA / m, and the maximum energy product (BH) max was 188 kJ / m 3 . Also, the Ca content of this Sm-Fe-N-based magnetic powder was less than 0.001% (below the measurement limit).

[0059] [Example 9] In Example 1, an Sm-Fe-N-based 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 was changed from 1 minute to 10 minutes, hydrogen treatment was not performed, a vibration mill was used in the pulverization as shown below, and the holding temperature in the nitriding treatment was changed from 430 °C to 400 °C.

[0060] (Pulverization) In a glove box filled with nitrogen gas, using a vibration mill (manufactured by Eurastech Co., Ltd., YAMP-2SND), 200 g of Sm-Fe-N-based coarse powder, 4500 g of chromium steel balls with a diameter of 1.6 mm, and 2.1 g of ethanol were put into a 1.2 L stainless steel pot and sealed. Then, a pulverization treatment was performed for 2.8 hours under the conditions of an amplitude of ±2.5 mm and a vibration frequency of 29.1 Hz. After pulverization, the sample was separated from the balls in a glove box filled with nitrogen gas. The obtained powder was subjected to the above nitriding treatment to obtain an Sm-Fe-N-based magnetic powder.

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

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

[0063] (Nitriding treatment) After transferring the pulverized powder into a tubular furnace with an electric heating system under an argon gas atmosphere, nitrogen gas (100 vol% N2) was passed through the tubular furnace to replace the gas in the tubular furnace. Then, while flowing the above-mentioned nitrogen gas, the temperature was raised to 460 °C at a rate of 5 °C / min and held at 460 °C for 60 minutes to perform the nitriding treatment. The subsequent treatment was the same as in Example 1.

[0064] The cumulative 50% particle size D in the volume-based particle size distribution of the obtained Sm-Fe-N magnetic powder by the laser diffraction / scattering method 50 was 1.64 μm. Also, the saturation magnetization σ of this Sm-Fe-N magnetic powder s was 142 A·m 2 / kg, the remanent magnetization σ r was 119 A·m 2 / kg, the aspect ratio σ r / σ s was 0.838, the coercive force H c was 764 kA / m, and the maximum energy product (BH) max was 191 kJ / m3 It was. Also, the Ca content of this Sm-Fe-N-based magnetic powder was less than 0.001% (below the measurement limit).

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

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

[0067] (Nitriding treatment) After confirming that the temperature had reached 50°C or lower after the heat treatment, the flow gas flowing into the tubular furnace was changed from argon gas to a mixed gas composed of 35 vol% ammonia (NH3) gas and 65 vol% hydrogen (H2) gas, and the gas in the tubular furnace was replaced. Then, while flowing the above mixed gas, the temperature was raised to 420°C at a rate of 5°C / min, held at 420°C for 60 minutes for nitriding treatment. Next, the gas flowing into the tubular furnace was changed to hydrogen (H2) gas and held at 420°C for another 60 minutes, and then the gas flowing into the tubular furnace was changed to argon gas and held at 420°C for 60 minutes. Then, heating was stopped and cooled to a temperature near room temperature while flowing argon gas to obtain nitriding-treated powder. The powder after cooling was transferred into a glove box filled with argon gas from the tubular furnace. As a result of elemental analysis of the nitriding-treated powder, the Sm / Fe molar ratio was 0.15 and the N / Fe molar ratio was 0.19.

[0068] (Grinding) The obtained nitrided powder was placed in an airtight container filled with argon gas and transferred from a tubular furnace into another glove box filled with argon gas. Crushing was performed in this glove box at the transfer destination. The method of crushing was the same as that in Example 1 for the hydrogen-treated powder, except that the object to be crushed was the above-mentioned nitrided powder and the operation time of the rotary mixer was changed from 8 hours to 22 hours. In this way, the Sm-Fe-N-based 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-based magnetic powder by the laser diffraction / scattering method 50 was 1.53 μm. Also, the saturation magnetization σ of this Sm-Fe-N-based magnetic powder s was 146 A·m 2 / kg, the remanent magnetization σ r was 109 A·m 2 / kg, the squareness ratio σ r / σ s was 0.747, the coercive force H c was 629 kA / m, and the maximum energy product (BH) max was 95 kJ / m 3 . Also, the Ca content of this Sm-Fe-N-based magnetic powder was less than 0.001% (below the measurement limit).

[0070]

Table 1

[0071] In each example, an Sm-Fe-N-based magnetic powder exhibiting a high maximum energy product (BH) max was obtained. This is presumably because by causing grain boundary fracture and intragranular fracture by crushing the coarsened crystal grains by heat treatment, an Sm-Fe-N-based magnetic powder with a high proportion of particles composed of single crystal grains was finally obtained. On the other hand, the Sm-Fe-N-based magnetic powder obtained in Comparative Example 1 had a maximum energy product (BH) maxwas lower than that of the above-described example. This is presumably because although the pulverization progresses with grain boundary fracture to refine the particles, the crystal grains are small and thus cannot be completely monodispersed, resulting in a Sm-Fe-N-based magnetic powder containing many particles composed of a plurality of crystal grains.

[0072] Fig. 5 illustrates an IPF map (inverse pole figure crystal orientation map) obtained by EBSD (electron backscatter diffraction method) for the particles of the Sm-Fe-N-based magnetic powder obtained in Example 2. Fig. 6 also illustrates an IPF map (inverse pole figure crystal orientation map) obtained by EBSD (electron backscatter diffraction method) for the particles of the Sm-Fe-N-based magnetic powder obtained in Comparative Example 1. These IPF maps are the black-and-white displays of the color images of the IPF maps obtained by EBSD measurement for the surface of the sample on which the cross-section of the particles appears, which was prepared by ion milling after polishing the resin embedding the powder particles. In the black-and-white IPF map, individual crystal grains are represented as luminance differences based on the crystal orientation difference. The Sm-Fe-N-based magnetic powder according to the present invention (Fig. 5) has a higher proportion of particles composed of a single crystal grain than the Sm-Fe-N-based magnetic powder of the comparative example (Fig. 6).

[0073] Fig. 7 illustrates an X-ray diffraction pattern using Co-Kα rays for the Sm-Fe-N-based magnetic powder obtained in Example 1. In the figure, the theoretical peak positions and peak heights for Sm2Fe 17 N3 having a Th2Zn 17 type crystal structure are appended. It can be seen that the Sm-Fe-N-based magnetic powder obtained in Example 1 has a Th2Zn 17 type crystal structure. Similarly, it was confirmed that the Sm-Fe-N-based magnetic powders obtained in Examples 2 to 4 also have a Th2Zn 17 type crystal structure.

[0074] From the results of Examples 9 and 10, it can be seen that the saturation magnetization and the 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, in Example 6, a particularly high maximum energy product was obtained, indicating that jet mill pulverization is advantageous for improving the maximum energy product.

Explanation of Signs

[0075] 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 atmosphere gas supply source 12 gas supply device for injection 13 gas supply device for discharging molten metal 21 discharge port 22 stopper contact surface

Claims

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

2. The method for producing an Sm—Fe—N-based magnetic powder according to claim 1, wherein the powder of the Sm—Fe-based alloy to be pulverized in the pulverization step is subjected to a hydrogen treatment of heating and holding in a hydrogen atmosphere after the heat treatment step.

3. In the pulverization step, a powder having a cumulative 50% particle diameter D in the volume-based particle size distribution by the laser diffraction / scattering method ５０ is 0.5 μm or more and 5.0 μm or less, and the method for producing an Sm—Fe—N-based magnetic powder according to claim 1 or 2.

4. The method for producing an Sm—Fe—N-based magnetic powder according to claim 1 or 2, wherein in the pulverization step, the powder of the Sm—Fe-based alloy is pulverized using a jet mill.

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

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

8. The method for producing an 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 composed of particles mainly containing Sm, Fe, and N, having a composition in which the molar ratio Sm / Fe of Sm to 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 by the laser diffraction / scattering method 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 or more, an Sm-Fe-N-based magnetic powder.

10. Aspect ratio σ ｒ / σ ｓ The Sm—Fe—N-based magnetic powder according to claim 9, wherein is 0.760 or more.

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

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

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