WO2022172995A1 - 鉄－クロム－コバルト系合金磁石およびその製造方法 - Google Patents

鉄－クロム－コバルト系合金磁石およびその製造方法 Download PDF

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WO2022172995A1
WO2022172995A1 PCT/JP2022/005363 JP2022005363W WO2022172995A1 WO 2022172995 A1 WO2022172995 A1 WO 2022172995A1 JP 2022005363 W JP2022005363 W JP 2022005363W WO 2022172995 A1 WO2022172995 A1 WO 2022172995A1
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chromium
iron
cobalt alloy
alloy magnet
cobalt
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PCT/JP2022/005363
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English (en)
French (fr)
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岡本晋哉
大沼篤彦
岡村信之
桑原孝介
足達俊哉
佐藤正博
石井祟博
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日立金属株式会社
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Priority to JP2022580679A priority Critical patent/JP7524979B2/ja
Priority to US18/276,245 priority patent/US20240304365A1/en
Priority to CN202280013964.2A priority patent/CN116917517A/zh
Publication of WO2022172995A1 publication Critical patent/WO2022172995A1/ja

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    • C22C33/02—Making ferrous alloys by powder metallurgy
    • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
    • C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
    • C22C33/0285—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5% with Cr, Co, or Ni having a minimum content higher than 5%
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H—ELECTRICITY
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    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
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    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
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    • B22F2009/0824—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid with a specific atomising fluid
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    • C22C2202/02—Magnetic

Definitions

  • the present invention relates to an iron-chromium-cobalt alloy magnet capable of improving magnetic properties and a method for producing the same.
  • Magnetic materials are divided into hard magnetic materials and soft magnetic materials.
  • the hard magnetic material refers to a magnetic material that has a large coercive force and is difficult to demagnetize due to an external magnetic field.
  • metal magnets have the advantage that they are suitable for mass production of relatively small items and complicated shapes by adopting a manufacturing method based on sintering.
  • Examples of metal magnets having such advantages include magnets mainly composed of the three elements iron, chromium and cobalt (hereinafter referred to as iron-chromium-cobalt alloy magnets), iron, aluminum, nickel and cobalt magnets.
  • iron-chromium-cobalt alloy magnets iron-chromium-cobalt alloy magnets
  • iron-chromium-cobalt alloy magnets iron-chromium-cobalt alloy magnets
  • iron-chromium-cobalt alloy magnets iron-chromium-cobalt alloy magnets
  • iron-chromium-cobalt alloy magnets iron-chromium-cobalt alloy magnet
  • iron-chromium-cobalt alloy magnets Compared to alnico magnets, iron-chromium-cobalt alloy magnets have higher magnetic flux density and maximum energy product, so they have excellent magnetic performance, and because they contain less cobalt, they can reduce price fluctuation risk. In addition, like alnico magnets, iron-chromium-cobalt alloy magnets have a small temperature coefficient of residual magnetic flux density, so they have excellent temperature stability. There is an advantage that it is easy to apply to products. Iron-chromium-cobalt alloy magnets are used in stepping motors, relays, torque limiters, magnetic sensors and the like.
  • Patent Document 1 describes an iron-chromium-cobalt magnet alloy containing 17 to 45% Cr and 3 to 35% Co by weight, with the balance being Fe, containing 0.1 to 5% Si and 0.01 to 5% Si. % of Ti is disclosed. Since Ti has a strong affinity with N, in the iron-chromium-cobalt magnet alloy of Patent Document 1 to which Ti is added, N that enters from the outside during the manufacturing process is fixed outside the matrix as TiN by Ti. Therefore, since the influence of N can be removed without deteriorating the magnetic properties, it is possible to give good magnetic properties by casting, which cannot be obtained by adding Si alone.
  • Patent Document 2 discloses a technique for obtaining an iron-chromium-cobalt permanent magnet by discharge plasma sintering using an iron-chromium-cobalt alloy powder with an average particle size of 1.0 to 500 ⁇ m.
  • the discharge plasma sintering method is a method of applying an AC pulse current to a powder compact of raw material powder and performing sintering by utilizing an electric discharge occurring in the gaps between the powder particles. Since the discharge between powder particles is used, a dense sintered body can be obtained in a short time without applying high heat from the outside, even if a hard-to-sinter material such as metal or ceramic is used.
  • the discharge plasma sintering method for sintering the iron-chromium-cobalt alloy powder By using the discharge plasma sintering method for sintering the iron-chromium-cobalt alloy powder, the tendency of Ti to be concentrated in the precipitate phase is alleviated, the Ti content in the matrix phase is increased, and the crystal structure is improved. It is said that by stabilizing the iron-chromium-cobalt permanent magnet, high magnetic properties can be achieved.
  • iron-chromium-cobalt permanent magnets are required to have higher magnetic properties. Even with the iron-chromium-cobalt permanent magnets obtained by either technique of Patent Document 1 or Patent Document 2, it is becoming difficult to sufficiently satisfy the required magnetic properties.
  • the present invention solves the problems of the prior art, and aims to provide an iron-chromium-cobalt alloy magnet with improved magnetic properties, particularly the maximum energy product, and a method for producing the same.
  • the inventors of the present application suppress the formation of the precipitated phase containing titanium carbide and/or titanium nitride, or reduce the size of the precipitated phase. As a result of intensive studies considering the need to reduce the influence as much as possible, the present invention was achieved.
  • An iron-chromium-cobalt alloy magnet is an iron-chromium-cobalt alloy magnet, which contains titanium and has a number density of Ti-enriched phases having a maximum diameter of 3 ⁇ m or more in a cross section of 10000 ⁇ m 2 . It is characterized by an average of less than 1.0 pieces per square and a squareness ratio expressed by (BH) max /(B r ⁇ H cB ) of more than 0.72.
  • the content of titanium is preferably 0.10 to 0.60% by mass.
  • the defect rate in the cross section is 0.50% or less.
  • the defect rate is 0.05% or less.
  • the squareness ratio is preferably 0.80 or more.
  • the maximum energy product is preferably 51.0 kJ/m 3 or more.
  • a method for manufacturing an iron-chromium-cobalt alloy magnet according to the second invention of the present application is characterized in that the iron-chromium-cobalt alloy magnet is formed by an additive manufacturing method.
  • the second invention is characterized in that the energy density of the heat source irradiated during additive manufacturing is 35 J/mm 3 or more.
  • an iron-chromium-cobalt alloy magnet capable of improving magnetic properties, particularly the maximum energy product, and a method for producing the same.
  • the present invention relates to providing a magnetic alloy capable of suppressing the formation of coarse precipitates on the grain boundaries of the structure that constitutes the parent phase, and a method for producing the same.
  • the additive manufacturing method is based on the modeling principle of irradiating raw material powder with a high-energy-density heat source such as a laser or an electron beam for high-speed melting and rapid solidification.
  • a shaped body is produced directly from an iron-chromium-cobalt alloy powder by an additive manufacturing method without going through a melting/casting process, so that the grain boundaries of the structure that constitutes the matrix phase are formed.
  • Embodiments of the present invention will be described below. Regarding the manufacturing method of the alloy magnets in the examples, a method using a powder bed type additive manufacturing method is exemplified as a representative example of the additive manufacturing method. The manufacturing method is not limited to the embodiments shown below.
  • the iron-chromium-cobalt alloy magnet of the present invention is an iron-chromium-cobalt alloy magnet composed of 17 to 45% Cr, 3 to 35% Co, and the balance being Fe and unavoidable impurities in mass ratio, and at least Ti is added to obtain a composition of 17 to 45% Cr, 3 to 35% Co, 0.1 to 0.6% Ti, and the balance being Fe and unavoidable impurities.
  • elements other than Ti can be contained in a composite manner. For example, Ti and Si are added in combination, and the mass ratio is 17 to 45% Cr, 3 to 35% Co, 0.1 to 0.6% Ti, 0.1 to 0.6% Si, and the balance is Fe and unavoidable
  • the composition may be composed of impurities.
  • a crucible is charged with raw materials obtained by weighing and mixing predetermined amounts of feed materials of each element so as to obtain a shaped body with the desired composition, high-frequency melting is performed, and the melted alloy is dropped from a nozzle under the crucible, and high pressure is applied.
  • a gas atomized powder is produced by atomizing with argon. This gas-atomized powder is classified to obtain an iron-chromium-cobalt alloy powder. This is used as raw material powder.
  • the beam diameter of the laser is preferably about 0.1 mm at the position of the raw material powder to be irradiated.
  • the laser output is preferably 200-400W.
  • the laser scanning speed is preferably 500-2500 mm/s.
  • the laser scanning pitch is preferably 0.05 to 0.15 mm.
  • the density of energy (heat source energy density: J/mm 3 ) applied by laser irradiation to melt the raw material powder at high speed is preferably 35 or more, more preferably 35 or more and 130 or less, and 50 or more and 110 or less. A range is more preferable, and a range of more than 60 and 95 or less is even more preferable.
  • the energy density E (J/mm 3 ) is expressed by the formula using laser output P (W), laser scanning speed v (mm/s), laser scanning pitch a (mm), and layer thickness d (mm) of the raw material powder layer. Obtained from (1).
  • the shaped body is subjected to solution treatment, heat treatment in a magnetic field, and aging treatment.
  • the solution treatment is performed at 700 to 1000 ° C. for 1 to 1.5 hours to make the structure ⁇ -phase
  • the heat treatment in the magnetic field is performed at 600 to 700 ° C. for 1 to 5 hours in a magnetic field of 150 to 300 kA / m.
  • the structure is phase-separated into the ⁇ 1 ferromagnetic phase and the ⁇ 2 paramagnetic phase at 600 to 700° C. for 0.5 to 3 hours. After that, cooling is performed at a rate of about 2 to 8°C/min.
  • the iron-chromium-cobalt alloy magnet according to the first invention of the present application manufactured by the above-described manufacturing method, wherein the number density of Ti-enriched phases having a maximum diameter of 3 ⁇ m or more in a cross section is 1.0 on average per 10000 ⁇ m 2 . It is possible to produce an iron-chromium-cobalt alloy magnet having a squareness ratio expressed by (BH) max /(B r ⁇ H cB ) exceeding 0.72.
  • a fine and uniform structure in which the number density of Ti-enriched phases with a maximum diameter of 3 ⁇ m or more is less than 1.0 per 10000 ⁇ m 2 on average is the residual magnetic flux density Br and maximum energy product (BH ) contributes to the improvement of magnetic properties such as max .
  • a high squareness ratio of more than 0.72 contributes to increasing (BH) max .
  • the reason why the iron-chromium-cobalt alloy magnet according to the present invention has a finer and more uniform structure than the iron-chromium-cobalt alloy magnet produced by conventional casting is that the and rapid heating and cooling inhibited the grain growth of the Ti-enriched phase, resulting in a finely dispersed structure.
  • the squareness ratio is a numerical value determined by (BH) max /(B r ⁇ H cB ).
  • Hk which is a parameter measured to obtain Hk/ HcJ
  • J magnetization strength
  • H magnetic field strength
  • H k is lower than that of Nd-Fe-B magnets and ferrite magnets, and H cJ and H cB are almost the same. This is because the squareness ratio defined as (BH) max /(B r ⁇ H cB ) is more suitable as an index of squareness.
  • Example 1 A raw material obtained by weighing and mixing predetermined amounts of feed materials of each element so as to obtain a shaped body with the desired composition is charged into a crucible, high-frequency melting is performed in a vacuum, and the alloy is melted from a nozzle with a diameter of 5 mm under the crucible. was dropped and sprayed with high-pressure argon to prepare gas-atomized powder. This gas-atomized powder was classified to obtain an iron-chromium-cobalt alloy powder of 10 to 60 ⁇ m. This was used as raw material powder.
  • the raw material powder supplied on the S45C base plate is melted at high speed by laser irradiation and rapidly cooled and solidified, and the width after removal of the processing allowance is 10 mm. , a length of 10 mm and a stacking height of 10 mm.
  • the additive manufacturing conditions were as follows. ⁇ One layer thickness of raw material powder layer / 40 ⁇ m ⁇ Laser beam diameter / about 0.1 mm ⁇ Laser output/200W ⁇ Laser scanning speed/800mm/s ⁇ Scan pitch/0.09mm ⁇ Energy density/69.4 J/mm 3
  • FIG. 1(a) A dot-like area with dark brightness in the image is a void (defect).
  • FIG. 1(b) is a diagrammatic representation of FIG. 1(a) to facilitate understanding of the voids.
  • the defect rate was defined as the ratio of the area of the region with the dark brightness to the area of the entire nine images, and the defect rate was calculated to be 0.01%. Table 1 shows the defect rate together with the additive manufacturing conditions.
  • Magnetic properties A BH tracer was used to evaluate the magnetic properties of the shaped bodies. Obtain the BH curve of each shaped body, and from the BH curve, residual magnetic flux density B r 1.39 [T], coercive force H cB 48.7 [kA / m], maximum energy product (BH) max 54 .4 [kJ/m 3 ] and squareness ratio 0.80. These magnetic properties were significantly superior to those of cast magnets.
  • the test piece used for the image analysis of the defect rate was used for magnetic property evaluation. Table 1 shows the magnetic properties.
  • Elemental analysis of the shaped bodies was performed using Energy-Dispersive X-ray Spectroscopy (EDS) associated with a Scanning Electron Microscope (SEM).
  • EDS Energy-Dispersive X-ray Spectroscopy
  • SEM Scanning Electron Microscope
  • a test piece used for analysis was prepared by cutting a part of the shaped body into small pieces, embedding them in resin, and polishing the cut surface of the embedded shaped body to a mirror finish.
  • the analysis was carried out using a scanning electron microscope with an acceleration voltage of 15 kV, a working distance from the objective lens to the observation surface of 10 mm, and an observation magnification of 1000 times.
  • Ten elements of Al, C, Co, Cr, Fe, Mn, N, O, Si and Ti were analyzed. Table 2 shows the results of elemental analysis.
  • the acquired SEM image and EDS surface analysis image are shown in FIG.
  • SEM image a columnar structure, which is often seen in a three-dimensional laminate-molded body obtained by subjecting metal raw material powder to high-speed melting and rapid solidification by laser irradiation, was observed.
  • EDS surface analysis image it was confirmed that Ti was finely and uniformly present (dispersed) throughout the tissue.
  • the number of Ti-enriched phases having a maximum diameter of 3 ⁇ m or more in the cross section was measured.
  • Example 2 Iron-chromium was manufactured by the additive manufacturing method (laminate manufacturing method) in the same manner as in Example 1 except that the laser output was 350 W, the laser scanning speed was 1750 mm/s, the scanning pitch was 0.11 mm, and the energy density was 45.5 J/mm.
  • a modeled body made of a cobalt-based alloy was produced and heat-treated to obtain a laminate-molded magnet (iron-chromium-cobalt-based alloy magnet) made of an iron-chromium-cobalt-based hard magnetic material.
  • this laminate-molded magnet was subjected to measurement of the defect rate, evaluation of magnetic properties, elemental analysis, and acquisition of SEM images and EDS surface analysis images. The defect rate was 0.45%, which was expected to meet the level of reducing cracks and chips during processing.
  • Magnetic properties were a residual magnetic flux density of 1.37 [T], a coercive force of 47.8 [kA/m], a maximum energy product of 51.3 [kJ/m 3 ], and a squareness ratio of 0.78. These magnetic properties were significantly superior to those of cast magnets. From the obtained SEM image, it was confirmed that the alloy magnet had the same metal structure as that of the alloy magnet of Example 1. From the EDS surface analysis image, it was confirmed that Ti was finely and uniformly present (dispersed) throughout the tissue.
  • the number of Ti-enriched phases having a maximum diameter of 3 ⁇ m or more in the cross section was measured.
  • no Ti-enriched phase with a maximum diameter of 3 ⁇ m or more was observed in three fields of view of 90 ⁇ m ⁇ 120 ⁇ m (area of 10,800 ⁇ m 2 ), and the average number density of Ti-enriched phases was 0.0 per 10,000 ⁇ m 2 .
  • rice field. Ti is finely and uniformly present (dispersed) in the crystal grains without forming a concentrated phase containing hard and brittle Ti with a maximum diameter of 3 ⁇ m or more, and the defect rate is low. In addition to obtaining extremely superior magnetic properties, cracks and chips during processing are reduced, and an improvement in yield is expected.
  • Example 3 Iron-chromium was manufactured by the additive manufacturing method (laminate manufacturing method) in the same manner as in Example 1 except that the laser output was 350 W, the laser scanning speed was 2000 mm/s, the scanning pitch was 0.11 mm, and the energy density was 39.8 J/mm. - A modeled body made of a cobalt-based alloy was produced and heat-treated to obtain a laminate-molded magnet (iron-chromium-cobalt-based alloy magnet) made of an iron-chromium-cobalt-based hard magnetic material.
  • this laminate-molded magnet was subjected to measurement of the defect rate, evaluation of magnetic properties, elemental analysis, and acquisition of SEM images and EDS surface analysis images.
  • the defect rate was 0.82%.
  • Magnetic properties were a residual magnetic flux density of 1.35 [T], a coercive force of 47.6 [kA/m], a maximum energy product of 50.0 [kJ/m 3 ], and a squareness ratio of 0.78. These magnetic properties were significantly superior to those of cast magnets. From the obtained SEM image, it was confirmed that the metal structure was the same as that of Example 1. From the EDS surface analysis image, it was confirmed that Ti was finely and uniformly present (dispersed) throughout the tissue.
  • the number of Ti-enriched phases having a maximum diameter of 3 ⁇ m or more in the cross section was measured.
  • no Ti-enriched phase with a maximum diameter of 3 ⁇ m or more was observed in three fields of view of 90 ⁇ m ⁇ 120 ⁇ m (area of 10,800 ⁇ m 2 ), and the average number density of Ti-enriched phases was 0.0 per 10,000 ⁇ m 2 .
  • rice field. Ti-containing concentrated phases with a maximum diameter of 3 ⁇ m or more are not formed, Ti is present (dispersed) finely and uniformly in the crystal grains, and the defect rate is low. In addition to obtaining magnetic properties, cracking and chipping during processing are reduced, and an improvement in yield is expected.
  • Example 4 Iron-chromium-cobalt-based alloy was fabricated by additive manufacturing in the same manner as in Example 1 except that the laser output was 350 W, the laser scanning speed was 800 mm/s, the scanning pitch was 0.11 mm, and the energy density was 99.4 J/mm. A shaped body was produced and heat-treated to obtain a laminate-molded magnet (iron-chromium-cobalt alloy magnet) made of an iron-chromium-cobalt-based hard magnetic material.
  • the laser output was 350 W
  • the laser scanning speed was 800 mm/s
  • the scanning pitch was 0.11 mm
  • the energy density was 99.4 J/mm.
  • a shaped body was produced and heat-treated to obtain a laminate-molded magnet (iron-chromium-cobalt alloy magnet) made of an iron-chromium-cobalt-based hard magnetic material.
  • this laminate-molded magnet was subjected to measurement of the defect rate, evaluation of magnetic properties, elemental analysis, and acquisition of SEM images and EDS surface analysis images.
  • the defect rate is 0.02%, which sufficiently satisfies the level for reducing cracks and chips during processing.
  • Magnetic properties were a residual magnetic flux density of 1.40 [T], a coercive force of 48.5 [kA/m], a maximum energy product of 54.1 [kJ/m 3 ], and a squareness ratio of 0.80. These magnetic properties were significantly superior to those of cast magnets. From the obtained SEM image, it was confirmed that the metal structure was the same as that of Example 1. From the EDS surface analysis image, it was confirmed that Ti was finely and uniformly present (dispersed) throughout the tissue.
  • the number of Ti-enriched phases having a maximum diameter of 3 ⁇ m or more in the cross section was measured.
  • no Ti-enriched phase with a maximum diameter of 3 ⁇ m or more was observed in three fields of view of 90 ⁇ m ⁇ 120 ⁇ m (area of 10,800 ⁇ m 2 ), and the average number density of Ti-enriched phases was 0.0 per 10,000 ⁇ m 2 .
  • rice field. Ti is finely and uniformly present (dispersed) in the crystal grains without forming a concentrated phase containing hard and brittle Ti with a maximum diameter of 3 ⁇ m or more, and the defect rate is low. In addition to obtaining extremely superior magnetic properties, cracks and chips during processing are reduced, and an improvement in yield is expected.
  • a hard magnetic material (iron-chromium-cobalt alloy magnet) made of an iron-chromium-cobalt alloy was produced by casting. Specifically, raw material powder produced in the same manner as in Example 1 was melted in a melting furnace and then poured into a sand mold. After cooling, the hard magnetic material was removed from the sand mold, and rough processing was performed for the purpose of removing the sprue portion and burrs. After that, the same heat treatment (solution treatment, magnetic field heat treatment, aging treatment) as in Example 1 is performed to obtain a cast magnet (iron-chromium-cobalt alloy magnet) made of an iron-chromium-cobalt-based hard magnetic material. rice field.
  • this cast magnet was subjected to measurement of the defect rate, evaluation of magnetic properties, elemental analysis, and acquisition of SEM images and EDS surface analysis images.
  • the hard magnetic material produced by casting had a defect rate of 0.66%, and there was a possibility that it could not fully satisfy the level for reducing cracks and chips during processing.
  • the magnetic properties were a residual magnetic flux density of 1.35 [T], a coercive force of 49.5 [kA/m], a maximum energy product of 47.8 [kJ/m 3 ], and a squareness ratio of 0.72. These magnetic properties did not necessarily sufficiently satisfy the level of practical application as iron-chromium-cobalt permanent magnets.
  • the acquired SEM image and EDS surface analysis image are shown in FIG. From the SEM image, it was observed that precipitates were spotted at grain boundaries, and precipitates having a maximum diameter of about 5 ⁇ m and a shape close to a square were observed in the metal structure. From the EDS surface analysis image, it was confirmed that these precipitates were Ti-enriched phases formed by uneven distribution of Ti. Since C and N are also detected in the Ti-enriched phase, it was confirmed that the Ti-enriched phase mainly contains titanium in the form of titanium carbides such as TiC and titanium nitrides such as TiN.
  • the number of Ti-enriched phases having a maximum diameter of 3 ⁇ m or more in the cross section was measured from the EDS surface analysis image.
  • four Ti-enriched phases with a maximum diameter of 3 ⁇ m or more were confirmed in measurements at three locations in a field of view of 90 ⁇ m ⁇ 120 ⁇ m (area of 10,800 ⁇ m 2 ), and the average number density of the Ti-enriched phases was 1.23 per 10,000 ⁇ m 2 . there were.
  • the Ti concentration present in the metallographic structure including the Ti-enriched phase in the entire field of view is 1.07 mass%
  • the Ti concentration in the center of the Ti-enriched phase (#001) is 87.88 mass%.
  • the Ti concentration in the center (#002) of the parent phase was 0.14 mass%. The reason why the Ti concentration in the raw material is 0.55 mass% and the Ti concentration in the metal structure of the entire field of view is as high as 1.07% is due to the nonuniform existence of the Ti-enriched phase it is conceivable that.
  • iron-chromium-cobalt-based hard magnetic material iron-chromium-cobalt-based alloy magnet
  • iron-chromium-cobalt-based alloy magnet having a metallographic structure in which such a Ti-enriched phase with a large maximum diameter exists, cracks and chipping occur starting from defects during processing. Therefore, if casting is used for the manufacture of magnet products, no improvement in yield can be expected.
  • Iron-chromium was manufactured by the additive manufacturing method (laminate manufacturing method) in the same manner as in Example 1 except that the laser output was 250 W, the laser scanning speed was 1750 mm/s, the scanning pitch was 0.11 mm , and the energy density was 32.5 J/mm.
  • a modeled body made of a cobalt-based alloy was produced and heat-treated to obtain a laminate-molded magnet (iron-chromium-cobalt-based alloy magnet) made of an iron-chromium-cobalt-based hard magnetic material.
  • this laminate-molded magnet was subjected to measurement of the defect rate, evaluation of magnetic properties, elemental analysis, and acquisition of SEM images and EDS surface analysis images. The defect rate was 1.93%, and there was a possibility that the standard for reducing cracks and chips during processing could not be fully satisfied.
  • the magnetic properties were a residual magnetic flux density of 1.25 [T], a coercive force of 47.4 [kA/m], a maximum energy product of 39.5 [kJ/m 3 ], and a squareness ratio of 0.67. These magnetic properties are not necessarily sufficient for practical use as iron-chromium-cobalt alloy magnets. It was confirmed from the acquired SEM image that the metal structure was the same as in Example 1 except for the defect rate. From the EDS surface analysis image, it was confirmed that Ti was finely and uniformly present (dispersed) throughout the tissue. Next, the number of Ti-enriched phases having a maximum diameter of 3 ⁇ m or more in the cross section was measured.

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Abstract

本発明は、磁気特性、特に最大エネルギー積の向上を図った鉄－クロム－コバルト系合金磁石、およびその製造方法を提供することを目的とする。　鉄－クロム－コバルト系合金磁石であって、チタンを含み、断面における最大径３μｍ以上のＴｉ濃化相の個数密度が１００００μｍ２当たり平均１．０個未満であり、（ＢＨ）ｍａｘ／（Ｂｒ×ＨｃＢ)で表される角型比が０．７２超である鉄－クロム－コバルト系合金磁石。

Description

鉄－クロム－コバルト系合金磁石およびその製造方法
　本発明は、磁気特性を向上することのできる鉄－クロム－コバルト系合金磁石およびその製造方法に関するものである。
　磁性材料は、硬質磁性材料と軟質磁性材料に区分される。そのうち、硬質磁性材料とは保磁力が大きく、外部磁場に対して減磁しにくい磁性材料を指し、代表的なものとして、フェライト磁石、ＮｄＦｅＢ系磁石、ＳｍＣｏ系磁石、金属磁石などがある。中でも、金属磁石は焼結による製造方法を採用することにより、比較的小物や複雑な形状の量産に向いているという利点を有している。そのような利点を有する金属磁石の例としては、鉄、クロムおよびコバルトの３元素を主成分とした磁石（以下、鉄－クロム－コバルト系合金磁石と称す）や、鉄、アルミニウム、ニッケル、コバルトを主成分とした磁石（以下、アルニコ磁石と称す）がある。
　鉄－クロム－コバルト系合金磁石は、アルニコ磁石に比べ、高い磁束密度と最大エネルギー積を持つため、磁気性能に優れ、さらにコバルト含有量が少ないため、価格変動リスクを低減できる。また、鉄－クロム－コバルト系合金磁石は、アルニコ磁石と同様、残留磁束密度の温度係数が小さいため、温度安定性に優れるほか、原料にレアアースを使用していないため、調達安定性に優れ、製品適用し易いメリットがある。なお、鉄－クロム－コバルト系合金磁石は、ステッピングモーターやリレー、トルクリミッター、磁気センサー等に利用されている。
　特許文献１は、重量比で１７～４５％Ｃｒ、３～３５％Ｃｏを含み、残部Ｆｅからなる鉄－クロム－コバルト系磁石合金において、０．１～５％のＳｉと０．０１～５％のＴｉを複合的に添加含有せしめた鉄－クロム－コバルト系磁石合金を開示する。ＴｉはＮとの親和力が強いので、Ｔｉを添加した特許文献１の鉄－クロム－コバルト系磁石合金においては、製造過程で外部から侵入してくるＮはＴｉによって、ＴｉＮとしてマトリックス外に固定されるので磁気特性を劣化させずにＮの影響を取り除くことができることから、Ｓｉ単独添加では得られない良好な磁気特性を鋳造で与えることを可能にする、としている。
　特許文献２は、平均粒径が１．０～５００μｍの鉄－クロム－コバルト合金粉末を用い、放電プラズマ焼結法により鉄－クロム－コバルト永久磁石を得る技術を開示する。放電プラズマ焼結法は、原料粉末の圧紛体に交流パルス電流を印加して、粉末粒子間の空隙で起こる放電を利用して焼結を行う方法である。粉末粒子間の放電を利用することから、外部から高熱を加えることなく、金属、セラミックスの難焼結性材料を用いても、短時間で緻密な焼結体を得ることができる。放電プラズマ焼結法を鉄－クロム－コバルト合金粉末の焼結に用いることで、Ｔｉが析出相中に濃縮される傾向が緩和されて母相中へのＴｉ含有量が増加し、結晶構造が安定することで鉄－クロム－コバルト永久磁石の高磁気特性化が可能となる、としている。
特公昭５８－９８２７号 特開２００５－１５０３５５号
　近年、機器の小型化、高出力化、高精度化等の要求の高まりに伴い、鉄－クロム－コバルト永久磁石については、より高い磁気特性が求められるようになっている。特許文献１および特許文献２の何れの技術によって得られる鉄－クロム－コバルト永久磁石をもってしても、求められる磁気特性を十分に満足することは困難になりつつある。
　そこで、本発明は従来技術の問題を解決するものであり、磁気特性、特に最大エネルギー積の向上を図った鉄－クロム－コバルト系合金磁石、およびその製造方法を提供することを目的とする。
　本願の発明者は上記課題を解決し磁気特性を向上するためには、チタン炭化物および／またはチタン窒化物を含む析出相の生成を抑制するか、析出相の大きさを小さくして析出相の影響をできるだけ低減する必要があると考え鋭意検討した結果、本発明に至った。
　本願第１の発明に係る鉄－クロム－コバルト系合金磁石は、鉄－クロム－コバルト系合金磁石であって、チタンを含み、断面における最大径３μｍ以上のＴｉ濃化相の個数密度が１００００μｍ２当たり平均１．０個未満であり、（ＢＨ）ｍａｘ／（Ｂｒ×ＨｃＢ）で表される角型比が０．７２超であることを特徴とする。
　第１の発明において、前記チタンの含有量が質量比で０．１０～０．６０％であることが好ましい。
　第１の発明において、断面における欠陥率が０．５０％以下であることが好ましい。
　第１の発明において、前記欠陥率が０．０５％以下であることが更に好ましい。
　第１の発明において、前記角形比が０．８０以上であることが好ましい。
　第１の発明において、最大エネルギー積が５１．０ｋＪ／ｍ３以上であることが好ましい。
　また、本願第２の発明に係る鉄－クロム－コバルト系合金磁石の製造方法は、前記鉄－クロム－コバルト系合金磁石を付加製造法で形成することを特徴とする。
　第２の発明において、付加製造する際に照射する熱源のエネルギー密度が３５Ｊ／ｍｍ３以上であることを特徴とする。
　本発明により、磁気特性、特に最大エネルギー積を向上することのできる鉄－クロム－コバルト系合金磁石、およびその製造方法を提供することができる。
実施例１で欠陥率を測定した際に取得した画像（ａ）と、画像（ａ）の模式図（ｂ）である。 実施例１で得られた造形磁石および比較例１で得られた鋳造磁石のＳＥＭ像およびＴｉの分布を示すＥＤＳ面分析像である。
　本発明は、母相を構成する組織の結晶粒界への粗大な析出物の形成を抑制することのできる磁石合金、およびその製造方法を提供することに関する。付加製造法（Ａｄｄｉｔｉｖｅ　Ｍａｎｕｆａｃｔｕｒｉｎｇ）は原料粉末にレーザや電子ビーム等の高エネルギー密度の熱源を照射して高速溶融・急冷凝固させることを造形原理とする。本発明によれば、溶解・鋳造工程を経ることなく、付加製造法によって鉄－クロム－コバルト系合金粉末から直接、造形体を作製することにより、母相を構成する組織の結晶粒界への粗大な析出物の形成が抑制され、磁気特性の向上した鉄－クロム－コバルト系合金磁石、およびその製造方法を提供することができる。その結果、合金磁石の製造方法として付加製造法を採用することで、所望の部品形状に近いニアネットシェイプにすることができるだけでなく、最終的な仕上げ加工においても、粗大な析出物を起点とする割れや欠けの低減に寄与し得るため、磁石製品の歩留まりを向上することができるという効果も期待される。
　以下、本発明の実施形態を説明する。実施例における合金磁石の製造方法について、付加製造法の代表例としてパウダーベッド方式の積層造形法を用いる方法を例示するが、指向性エネルギー堆積方式等を用いても良く、本発明の合金磁石の製造方法は以下に示す実施形態に限定されるものではない。
［原料粉末］
　本発明の鉄－クロム－コバルト系合金磁石は、質量比で１７～４５％Ｃｒ、３～３５％Ｃｏ、残部はＦｅおよび不可避不純物からなる鉄－クロム－コバルト系合金磁石に対して、少なくともＴｉを添加せしめて、質量比で１７～４５％Ｃｒ、３～３５％Ｃｏ、０．１～０．６％Ｔｉ、残部はＦｅおよび不可避不純物からなる組成とすることが好ましい。更にＴｉ以外の元素を複合的に含有することもできる。例えばＴｉとＳｉを複合添加して、質量比で１７～４５％Ｃｒ、３～３５％Ｃｏ、０．１～０．６％Ｔｉ、０．１～０．６％Ｓｉ、残部はＦｅおよび不可避不純物からなる組成としても良い。目的とする組成の造形体が得られるように各元素の供給材料を所定量計量し混合してなる原材料をるつぼに装填し、高周波溶解し、るつぼ下のノズルから溶融した合金を落下させ、高圧アルゴンで噴霧してガスアトマイズ粉を作製する。このガスアトマイズ粉を分級して鉄－クロム－コバルト系合金粉末を得る。これを原料粉末とする。
［造形体］
　パウダーベッド方式の３次元積層造形機を用い、ベースプレート上に供給した原料粉末をレーザ照射により高速溶融・急冷凝固させて造形体を作製し、ベースプレートから切り離す。得られた造形体が本発明の鉄－クロム－コバルト系合金磁石である。積層造形条件は原料粉末の粒径や組成、造形体の大きさ・形状・特性、生産効率等を考慮して適宜定められるが、本発明の合金磁石については、次の範囲から選択することができる。積層造形する際の原料粉末層の一層厚さは２０～８０μｍとすることが好ましい。レーザのビーム径は照射する原料粉末の位置で約０．１ｍｍとすることが好ましい。レーザ出力は２００～４００Ｗとすることが好ましい。レーザ走査速度は５００～２５００ｍｍ／ｓとすることが好ましい。レーザ走査ピッチは０．０５～０．１５ｍｍとすることが好ましい。原料粉末を高速溶融させるためにレーザ照射によって投入するエネルギーの密度（熱源のエネルギー密度：Ｊ／ｍｍ３）は３５以上が好ましく、３５以上、１３０以下の範囲がより好ましく、５０以上、１１０以下の範囲が更に好ましく、６０超、９５以下の範囲が更に好ましい。エネルギー密度が小さ過ぎると、磁気特性、特に角型比の低下や欠陥率の上昇を来たし、鉄－クロム－コバルト系合金磁石として実用に供することが困難になる。エネルギー密度が大き過ぎるとレーザ照射位置を中心とする広範囲の原料粉末が溶融し、造形体の形状を維持することが困難になる。エネルギー密度Ｅ（Ｊ／ｍｍ３）はレーザ出力Ｐ（Ｗ）、レーザ走査速度ｖ（ｍｍ／ｓ）、レーザ走査ピッチａ（ｍｍ）、原料粉末層の一層厚さｄ（ｍｍ）を用いて式（１）から求めた。
Figure JPOXMLDOC01-appb-M000001
［熱処理］
　造形後には、造形体の溶体化処理、磁場中での熱処理、時効処理を行う。具体的には、溶体化処理では７００～１０００℃、１～１．５時間で組織をα相とし、磁場中での熱処理は１５０～３００ｋＡ／ｍの磁界中、６００～７００℃、１～５時間とし、時効処理では６００～７００℃、０．５～３時間で組織をα１強磁性相とα２常磁性相とに相分離させる。その後、２～８℃／分程度で冷却を行う。
　上述の製造方法により本願第１の発明に係る鉄－クロム－コバルト系合金磁石であって、チタンを含み、断面における最大径３μｍ以上のＴｉ濃化相の個数密度が１００００μｍ２当たり平均１．０個未満であり、（ＢＨ）ｍａｘ／（Ｂｒ×ＨｃＢ）で表される角型比が０．７２超である鉄－クロム－コバルト系合金磁石を製造することができる。最大径３μｍ以上のＴｉ濃化相の個数密度が１００００μｍ２当たり平均１．０個未満となる微細、均一な組織は、鉄－クロム－コバルト系合金磁石の残留磁束密度Ｂｒおよび最大エネルギー積（ＢＨ）ｍａｘ等の磁気特性の向上に寄与する。０．７２超の高い角型比は（ＢＨ）ｍａｘを高めることに寄与する。本発明に係る鉄－クロム－コバルト系合金磁石において従来の鋳造で作製された鉄－クロム－コバルト系合金磁石と比較して微細かつ均一な組織が得られた理由としては、所定の粒径以下の合金粉末を使用し、かつ、急速に加熱、冷却することによって、Ｔｉ濃化相の粒成長が抑制されて微細に分散した組織が得られたことが考えられる。
　本発明において角型比は、（ＢＨ）ｍａｘ／（Ｂｒ×ＨｃＢ）により求めた数値である。一般に、Ｈｋ／ＨｃＪを求めるために測定するパラメータであるＨｋは、Ｊ（磁化の強さ）－Ｈ（磁界の強さ）曲線の第２象限において、Ｊが０．９×Ｊｒ（Ｊｒは残留磁化、Ｊｒ＝Ｂｒ）の値になる位置のＨ軸の読み値が用いられている。このＨｋを減磁曲線のＨｃＪで除した値（Ｈｋ／ＨｃＪ）が角形比として定義される。しかし、鉄－クロム－コバルト系磁石合金については、ＨｋがＮｄ－Ｆｅ－Ｂ磁石やフェライト磁石に比べて低く、またＨｃＪとＨｃＢとがほぼ同値になることからＪ－Ｈカーブの概念を持っておらず、角型性を表す指標として（ＢＨ）ｍａｘ／（Ｂｒ×ＨｃＢ）と定義された角型比がより適しているためである。
［実施例１］
　目的とする組成の造形体が得られるように各元素の供給材料を所定量計量し混合してなる原材料をるつぼに装填し、真空中で高周波溶解し、るつぼ下の直径５ｍｍノズルから溶融した合金を落下させ、高圧アルゴンで噴霧してガスアトマイズ粉を作製した。このガスアトマイズ粉を分級して１０～６０μｍの鉄－クロム－コバルト系合金粉末を得た。これを原料粉末とした。
　パウダーベッド方式の３次元積層造形機（ＥＯＳ社製ＥＯＳ－Ｍ２９０）を用い、Ｓ４５Ｃ製ベースプレート上に供給した原料粉末をレーザ照射による高速溶融・急冷凝固させて、加工代除去後の寸法で幅１０ｍｍ、長さ１０ｍｍ、積層高さ１０ｍｍの造形体を作製した。積層造形条件は次の通りとした。
・原料粉末層の一層厚さ／４０μｍ
・レーザビーム径／約０．１ｍｍ
・レーザ出力／２００Ｗ
・レーザ走査速度／８００ｍｍ／ｓ
・走査ピッチ／０．０９ｍｍ
・エネルギー密度／６９．４Ｊ／ｍｍ３
　造形体の熱処理として、先ず、溶体化処理９００℃、１．３時間、次いで、２６０ｋＡ／ｍの磁界中、６２０℃、２．５時間、更に、時効処理６５０℃、１．２時間を施した。その後、５℃／分程度で冷却した。かかる熱処理を経て、鉄－クロム－コバルト系合金磁石（積層造形磁石）を得た。
［欠陥率］
　熱処理後の造形体の幅中央で切断、研磨した後、その切断面の中央付近をマイクロスコープ（光学顕微鏡）で観察して析出物の欠陥率を測定した。具体的には、先ず、マイクロスコープの５００倍のレンズを用い、切断面の中央付近を視野中心とする所定の範囲を９分割（３×３）し、それぞれの範囲を撮影した画像を１枚の画像として取得した。取得画像を図１（ａ）に示す。画像における輝度の暗い点状の領域が空隙（欠陥）である。空隙を分かりやすくするために図１（ａ）を模式化した図を図１（ｂ）に示す。９枚の画像全体の面積に占める輝度が暗い領域の面積の割合を欠陥率と定義し、算出したところ欠陥率０．０１％であった。表１に積層造形条件とともに欠陥率を示す。
［磁気特性］
　造形体の磁気特性評価はＢ－Ｈトレーサーを用いて行った。各造形体のＢ－Ｈ曲線を求め、Ｂ－Ｈ曲線より、残留磁束密度Ｂｒ１．３９［Ｔ］、保磁力ＨｃＢ４８．７［ｋＡ／ｍ］、最大エネルギー積（ＢＨ）ｍａｘ５４．４［ｋＪ／ｍ３］、角型比０．８０であった。この磁気特性は、鋳造磁石のそれよりも極めて優れたものであった。なお、磁気特性評価には、欠陥率の画像解析に用いた試験片を使用した。表１に磁気特性を示す。
［元素分析］
　造形体の元素分析は、走査型電子顕微鏡（ＳＥＭ：Ｓｃａｎｎｉｎｇ　Ｅｌｅｃｔｒｏｎ　Ｍｉｃｒｏｓｃｏｐｅ）に付随するエネルギー分散型Ｘ線分析分光法（ＥＤＳ：Ｅｎｅｒｇｙ－Ｄｉｓｐｅｒｓｉｖｅ　Ｘ－ｒａｙ　Ｓｐｅｃｔｒｏｓｃｏｐｙ）を用いて行った。分析に用いた試験片は、造形体の一部を小片に切断して樹脂に包埋したのち、包埋した造形体の切断面を鏡面まで研磨仕上げして作製した。分析は走査型電子顕微鏡における加速電圧を１５ｋＶ、対物レンズから観察表面までの作動距離を１０ｍｍとし、観察倍率は１０００倍で行った。分析元素は、Ａｌ、Ｃ、Ｃｏ、Ｃｒ、Ｆｅ、Ｍｎ、Ｎ、Ｏ、Ｓｉ、Ｔｉの１０種類とした。表２に元素分析の結果を示す。
［ＳＥＭ像、ＥＤＳ面分析像（Ｔｉ）］
　上記の走査型電子顕微鏡を用いて実施例１で得られた造形体（積層造形磁石）のＳＥＭ像およびＴｉの分布を示すＥＤＳ面分析像を同視野において取得した。用いた試験片は、造形体の一部を小片に切断して樹脂に包埋したのち、包埋した造形体の切断面を鏡面まで研磨仕上げして作製した。分析は走査型電子顕微鏡における加速電圧を１０ｋＶ、対物レンズから観察表面までの作動距離を１０ｍｍとし、観察倍率は１０００倍で行った。
　取得したＳＥＭ像およびＥＤＳ面分析像を図２に示す。ＳＥＭ像から、金属原料粉末をレーザ照射によって高速溶融・急冷凝固させてなる３次元積層造形体において、しばしばみられる柱状組織が観察された。ＥＤＳ面分析像からＴｉが組織全体に亘って微細かつ均一に存在（分散）することを確認した。次いで、断面における最大径３μｍ以上のＴｉ濃化相の個数を測定した。その結果、最大径３μｍ以上のＴｉ濃化相は９０μｍ×１２０μｍ（面積１０８００μｍ２）の視野３箇所の測定において確認されず、Ｔｉ濃化相の個数密度は１００００μｍ２当たり平均０．０個であった。硬質で脆性的なＴｉを含有した最大径３μｍ以上の濃化相が形成されずに結晶粒中にＴｉが微細かつ均一に存在（分散）しており、また欠陥率が低いことから、鋳造磁石よりも極めて優れた磁気特性が得られることに加えて、加工時の割れや欠けが低減し、歩留まりの向上が見込まれる。
［実施例２］
　レーザ出力３５０Ｗ、レーザ走査速度１７５０ｍｍ／ｓ、走査ピッチ０．１１ｍｍ、エネルギー密度４５．５Ｊ／ｍｍ３としたことを除いて実施例１と同様にして付加製造法（積層造形法）により鉄－クロム－コバルト系合金からなる造形体を作製し、熱処理して鉄－クロム－コバルト系硬質磁性材料からなる積層造形磁石（鉄－クロム－コバルト系合金磁石）を得た。この積層造形磁石について実施例１と同様に欠陥率の測定、磁気特性の評価、元素分析、およびＳＥＭ像・ＥＤＳ面分析像取得を実施した。欠陥率は０．４５％、であり、加工時の割れや欠けを低減できる水準を満たすことが期待されるものであった。
　磁気特性は、残留磁束密度１．３７［Ｔ］、保磁力４７．８［ｋＡ／ｍ］、最大エネルギー積５１．３［ｋＪ／ｍ３］、角型比０．７８であった。この磁気特性は、鋳造磁石のそれよりも極めて優れたものであった。取得したＳＥＭ像から実施例１の合金磁石と同様の金属組織であることが確認できた。ＥＤＳ面分析像からＴｉが組織全体に亘って微細かつ均一に存在（分散）することを確認した。
　次いで、断面における最大径３μｍ以上のＴｉ濃化相の個数を測定した。その結果、最大径３μｍ以上のＴｉ濃化相は９０μｍ×１２０μｍ（面積１０８００μｍ２）の視野３箇所の測定において確認されず、Ｔｉ濃化相の個数密度は１００００μｍ２当たり平均０．０個であった。硬質で脆性的なＴｉを含有した最大径３μｍ以上の濃化相が形成されずに結晶粒中にＴｉが微細かつ均一に存在（分散）しており、また欠陥率が低いことから、鋳造磁石よりも極めて優れた磁気特性が得られることに加えて、加工時の割れや欠けが低減し、歩留まりの向上が見込まれる。
［実施例３］
　レーザ出力３５０Ｗ、レーザ走査速度２０００ｍｍ／ｓ、走査ピッチ０．１１ｍｍ、エネルギー密度３９．８Ｊ／ｍｍ３としたことを除いて実施例１と同様にして付加製造法（積層造形法）により鉄－クロム－コバルト系合金からなる造形体を作製し、熱処理して鉄－クロム－コバルト系硬質磁性材料からなる積層造形磁石（鉄－クロム－コバルト系合金磁石）を得た。
　この積層造形磁石について実施例１と同様に欠陥率の測定、磁気特性の評価、元素分析、およびＳＥＭ像・ＥＤＳ面分析像取得を実施した。欠陥率は０．８２％、であった。磁気特性は、残留磁束密度１．３５［Ｔ］、保磁力４７．６［ｋＡ／ｍ］、最大エネルギー積５０．０［ｋＪ／ｍ３］、角型比０．７８であった。この磁気特性は、鋳造磁石のそれよりも極めて優れたものであった。取得したＳＥＭ像から実施例１と同様の金属組織であることが確認できた。ＥＤＳ面分析像からＴｉが組織全体に亘って微細かつ均一に存在（分散）することを確認した。
　次いで、断面における最大径３μｍ以上のＴｉ濃化相の個数を測定した。その結果、最大径３μｍ以上のＴｉ濃化相は９０μｍ×１２０μｍ（面積１０８００μｍ２）の視野３箇所の測定において確認されず、Ｔｉ濃化相の個数密度は１００００μｍ２当たり平均０．０個であった。Ｔｉを含有した最大径３μｍ以上の濃化相が形成されずに結晶粒中にＴｉが微細かつ均一に存在（分散）しており、また欠陥率が低いことから、鋳造磁石よりも極めて優れた磁気特性が得られることに加えて、加工時の割れや欠けが低減し、歩留まりの向上が見込まれる。
［実施例４］
　レーザ出力３５０Ｗ、レーザ走査速度８００ｍｍ／ｓ、走査ピッチ０．１１ｍｍ、エネルギー密度９９．４Ｊ／ｍｍ３としたことを除いて実施例１と同様にして積層造形法により鉄－クロム－コバルト系合金からなる造形体を作製し、熱処理して鉄－クロム－コバルト系硬質磁性材料からなる積層造形磁石（鉄－クロム－コバルト系合金磁石）を得た。
　この積層造形磁石について実施例１と同様に欠陥率の測定、磁気特性の評価、元素分析、およびＳＥＭ像・ＥＤＳ面分析像取得を実施した。欠陥率は０．０２％であり、加工時の割れや欠けを低減できる水準を十分に満たすことができる。磁気特性は、残留磁束密度１．４０［Ｔ］、保磁力４８．５［ｋＡ／ｍ］、最大エネルギー積５４．１［ｋＪ／ｍ３］、角型比０．８０であった。この磁気特性は、鋳造磁石のそれよりも極めて優れたものであった。取得したＳＥＭ像から実施例１と同様の金属組織であることが確認できた。ＥＤＳ面分析像からＴｉが組織全体に亘って微細かつ均一に存在（分散）することを確認した。
　次いで、断面における最大径３μｍ以上のＴｉ濃化相の個数を測定した。その結果、最大径３μｍ以上のＴｉ濃化相は９０μｍ×１２０μｍ（面積１０８００μｍ２）の視野３箇所の測定において確認されず、Ｔｉ濃化相の個数密度は１００００μｍ２当たり平均０．０個であった。硬質で脆性的なＴｉを含有した最大径３μｍ以上の濃化相が形成されずに結晶粒中にＴｉが微細かつ均一に存在（分散）しており、また欠陥率が低いことから、鋳造磁石よりも極めて優れた磁気特性が得られることに加えて、加工時の割れや欠けが低減し、歩留まりの向上が見込まれる。
［比較例１］
　本比較例では、鋳造によって鉄－クロム－コバルト系合金からなる硬質磁性材料（鉄－クロム－コバルト系合金磁石）を作製した。具体的には、実施例１と同様に作製した原料粉末を溶解炉で溶解したのち、砂型に流し込んで作製した。冷却後、砂型から硬質磁性材料を取り出し、湯口部分の除去およびバリの除去が必要な状態であったため、それを目的とした粗加工を行った。その後、実施例１と同様の熱処理（溶体化処理、磁場中熱処理、時効処理）を行って、鉄－クロム－コバルト系硬質磁性材料からなる鋳造磁石（鉄－クロム－コバルト系合金磁石）を得た。
　この鋳造磁石について実施例１と同様に欠陥率の測定、磁気特性の評価、元素分析、およびＳＥＭ像・ＥＤＳ面分析像取得を実施した。鋳造により作製した硬質磁性材料は、欠陥率０．６６％であり、加工時の割れや欠けを低減できる水準を十分に満たすことができないおそれがあった。また、磁気特性は、残留磁束密度１．３５［Ｔ］、保磁力４９．５［ｋＡ／ｍ］、最大エネルギー積４７．８［ｋＪ／ｍ３］、角型比０．７２であった。この磁気特性は鉄－クロム－コバルト系永久磁石として実用に供しうる水準を必ずしも十分に満たすものではなかった。
　取得したＳＥＭ像およびＥＤＳ面分析像を図２に示す。ＳＥＭ像から、結晶粒界に点々と析出物が認められるとともに、金属組織内には最大径約５μｍの四角形に近い形状の析出物が観察された。これらの析出物はＥＤＳ面分析像から、Ｔｉの偏在によって形成されたＴｉ濃化相であることが確認された。Ｔｉ濃化相からはＣやＮも検出されていることから、Ｔｉ濃化相は主にＴｉＣ等のチタン炭化物やＴｉＮ等のチタン窒化物の形でチタンを含むことが確認された。
　次いで、ＥＤＳ面分析像から断面における最大径３μｍ以上のＴｉ濃化相の個数を測定した。その結果、最大径３μｍ以上のＴｉ濃化相は９０μｍ×１２０μｍ（面積１０８００μｍ２）の視野３箇所の測定において４個確認され、Ｔｉ濃化相の個数密度は１００００μｍ２当たり平均１．２３個であった。視野全体のＴｉ濃化相を含む金属組織に存在するＴｉ濃度は１．０７ｍａｓｓ％であり、Ｔｉ濃化相の中央（＃００１）におけるＴｉ濃度は８７．８８ｍａｓｓ％であり、Ｔｉ濃化相以外の母相の中央（＃００２）におけるＴｉ濃度は０．１４ｍａｓｓ％であった。原材料中のＴｉ濃度が０．５５ｍａｓｓ％であるのに対し視野全体の金属組織に存在するＴｉ濃度が１．０７％と高くなったのは、Ｔｉ濃化相が不均一に存在することによるものと考えられる。
　このような最大径の大きなＴｉ濃化相が存在する金属組織を持つ鉄－クロム－コバルト系硬質磁性材料（鉄－クロム－コバルト系合金磁石）の場合、加工時に、欠陥を起点として割れや欠けが発生し易いため、磁石製品の製造に鋳造を用いた場合には歩留まりの向上を期待できない。
［比較例２］
　レーザ出力２５０Ｗ、レーザ走査速度１７５０ｍｍ／ｓ、走査ピッチ０．１１ｍｍ、エネルギー密度３２．５Ｊ／ｍｍ３としたことを除いて実施例１と同様にして付加製造法（積層造形法）により鉄－クロム－コバルト系合金からなる造形体を作製し、熱処理して鉄－クロム－コバルト系硬質磁性材料からなる積層造形磁石（鉄－クロム－コバルト系合金磁石）を得た。この積層造形磁石について実施例１と同様に欠陥率の測定、磁気特性の評価、元素分析、およびＳＥＭ像・ＥＤＳ面分析像取得を実施した。欠陥率は１．９３％であり、加工時の割れや欠けを低減できる水準を十分に満たすことができないおそれがあった。
　また、磁気特性は、残留磁束密度１．２５［Ｔ］、保磁力４７．４［ｋＡ／ｍ］、最大エネルギー積３９．５［ｋＪ／ｍ３］、角型比０．６７であった。この磁気特性は鉄－クロム－コバルト系合金磁石として実用に供するには必ずしも十分ではなかった。取得したＳＥＭ像から欠陥率を除き実施例１と同様の金属組織であることが確認できた。ＥＤＳ面分析像からＴｉが組織全体に亘って微細かつ均一に存在（分散）することを確認した。次いで、断面における最大径３μｍ以上のＴｉ濃化相の個数を測定した。その結果、最大径３μｍ以上のＴｉ濃化相は９０μｍ×１２０μｍ（面積１０８００μｍ２）の視野３箇所の測定において確認されず、Ｔｉ濃化相の個数密度は１００００μｍ２当たり平均０．０個であった。
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
  

Claims (8)

  1. 　鉄－クロム－コバルト系合金磁石であって、
    チタンを含み、
    　断面における最大径３μｍ以上のＴｉ濃化相の個数密度が１００００μｍ２当たり平均１．０個未満であり、
    　（ＢＨ）ｍａｘ／（Ｂｒ×ＨｃＢ）で表される角型比が０．７２超であることを特徴とする鉄－クロム－コバルト系合金磁石。
  2. 　前記チタンの含有量が質量比で０．１０～０．６０％である請求項１に記載の鉄－クロム－コバルト系合金磁石。
  3. 　断面における欠陥率が０．５０％以下である請求項１または２に記載の鉄－クロム－コバルト系合金磁石。
  4. 　前記欠陥率が０．０５％以下である請求項３に記載の鉄－クロム－コバルト系合金磁石。
  5. 　前記角形比が０．８０以上である請求項１～４のいずれか一項に記載の鉄－クロム－コバルト系合金磁石。
  6. 　最大エネルギー積が５１．０ｋＪ／ｍ３以上である請求項１～５のいずれか一項に記載の鉄－クロム－コバルト系合金磁石。
  7. 　請求項１～６に記載の鉄－クロム－コバルト系合金磁石を付加製造法で形成することを特徴とする鉄－クロム－コバルト系合金磁石の製造方法。
  8. 　前記付加製造法において照射する熱源のエネルギー密度が３５Ｊ／ｍｍ３以上である請求項７に記載の鉄－クロム－コバルト系合金磁石の製造方法。
     
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JPS5394216A (en) * 1977-01-31 1978-08-18 Mitsubishi Metal Corp Manufacture of spinodal decomposition type fe-cr-co magnetic material
JPS5573854A (en) * 1978-11-30 1980-06-03 Mitsubishi Steel Mfg Co Ltd Fe-cr-co type magnet alloy
JP2005150355A (ja) * 2003-11-14 2005-06-09 Nec Tokin Corp 鉄−クロム−コバルト永久磁石及びその製造方法
CN101298648A (zh) * 2008-05-29 2008-11-05 天津冶金集团天材科技发展有限公司 复合钼、钛元素的铁铬钴永磁合金及其变形加工工艺
WO2017138191A1 (ja) * 2016-02-09 2017-08-17 株式会社日立製作所 合金部材、該合金部材の製造方法、および該合金部材を用いた製造物
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Publication number Priority date Publication date Assignee Title
JPS5394216A (en) * 1977-01-31 1978-08-18 Mitsubishi Metal Corp Manufacture of spinodal decomposition type fe-cr-co magnetic material
JPS5573854A (en) * 1978-11-30 1980-06-03 Mitsubishi Steel Mfg Co Ltd Fe-cr-co type magnet alloy
JP2005150355A (ja) * 2003-11-14 2005-06-09 Nec Tokin Corp 鉄−クロム−コバルト永久磁石及びその製造方法
CN101298648A (zh) * 2008-05-29 2008-11-05 天津冶金集团天材科技发展有限公司 复合钼、钛元素的铁铬钴永磁合金及其变形加工工艺
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