JP2010232357A - Method of manufacturing surface-modified rare earth based sintered magnet - Google Patents
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本発明は、湿度管理がなされていない輸送環境や保管環境などの湿度が変動する環境においても十分な耐食性を有するとともに、優れた磁気特性を有する希土類系焼結磁石の製造方法に関する。 The present invention relates to a method for producing a rare earth sintered magnet having sufficient corrosion resistance and excellent magnetic properties even in an environment where humidity varies, such as a transportation environment and a storage environment where humidity control is not performed.
Ｎｄ−Ｆｅ−Ｂ系焼結磁石に代表されるＲ−Ｆｅ−Ｂ系焼結磁石などの希土類系焼結磁石は、資源的に豊富で安価な材料が用いられ、かつ、高い磁気特性を有していることから今日様々な分野で使用されているが、反応性の高い希土類金属：Ｒを含むため、大気中で酸化腐食されやすいという特質を有する。従って、希土類系焼結磁石は、通常、その表面に金属被膜や樹脂被膜などの耐食性被膜を形成して実用に供されるが、ＩＰＭ（Ｉｎｔｅｒｉｏｒ Ｐｅｒｍａｎｅｎｔ Ｍａｇｎｅｔ）モータなどのように磁石が部品に埋め込まれて使用される態様の場合には、必ずしもこのような耐食性被膜を磁石の表面に形成することは必要とされない。しかしながら、磁石が製造されてから部品に埋め込まれるまでの期間における磁石の耐食性の確保は当然に必要となる。そこで、このような期間における希土類系焼結磁石の耐食性を確保するための方法として、酸化性雰囲気下で熱処理を行うことによって磁石の表面を改質する方法が提案されており、この方法は、上記の目的を達成できるに足る簡易耐食性向上技術として注目されている。 Rare earth-based sintered magnets such as R-Fe-B-based sintered magnets typified by Nd-Fe-B-based sintered magnets are made of resource-rich and inexpensive materials and have high magnetic properties. However, since it contains a highly reactive rare earth metal: R, it has the property of being easily oxidized and corroded in the atmosphere. Accordingly, rare earth-based sintered magnets are usually put to practical use by forming a corrosion-resistant coating such as a metal coating or a resin coating on the surface thereof, but the magnet is embedded in a component such as an IPM (Interior Permanent Magnet) motor. In the case of the embodiment to be used, it is not always necessary to form such a corrosion-resistant film on the surface of the magnet. However, it is of course necessary to ensure the corrosion resistance of the magnet during the period from when the magnet is manufactured to when it is embedded in the part. Therefore, as a method for ensuring the corrosion resistance of the rare earth-based sintered magnet in such a period, a method for modifying the surface of the magnet by performing a heat treatment in an oxidizing atmosphere has been proposed. It attracts attention as a simple anti-corrosion technology that can achieve the above object.
酸化熱処理による希土類系焼結磁石の表面改質を行うために必要な酸化性雰囲気は、酸素を利用して形成される場合（例えば特許文献１や特許文献２を参照のこと）の他、水蒸気を利用して形成される場合もある。例えば、特許文献３〜特許文献６には、水蒸気を単独で利用して、或いは、水蒸気に酸素を組み合わせて酸化性雰囲気を形成する方法が記載されている。 The oxidizing atmosphere necessary for surface modification of the rare earth sintered magnet by oxidative heat treatment is formed using oxygen (see, for example, Patent Document 1 and Patent Document 2), and water vapor. It may be formed using For example, Patent Documents 3 to 6 describe a method of forming an oxidizing atmosphere using water vapor alone or combining water vapor with oxygen.
希土類系焼結磁石が製造されてから部品に埋め込まれるまでの期間における磁石の腐食は、磁石が置かれる環境の良し悪しに左右される。特に湿度の変動は、磁石の表面に微細な結露を繰り返し生じさせ、磁石の腐食を早めてしまう。本発明者は、上記の特許文献に記載された簡易耐食性向上技術の有用性を検証した結果、いずれの技術を採用した場合も、湿度の変動が激しい環境においては必ずしも十分な耐食性が得られないこと、特許文献３〜特許文献６においては、水蒸気分圧は１０ｈＰａ（１０００Ｐａ）以上が好適とされているが、このような水蒸気分圧が高い雰囲気下で熱処理を行うと、磁石の表面で起こる酸化反応によって水素が副産物として大量に生成し、磁石が生成した水素を吸蔵して脆化することで磁気特性が低下してしまうことが判明した。
そこで本発明は、湿度が変動する環境においても十分な耐食性が酸化熱処理によって付与されているとともに、酸化熱処理による磁気特性の低下が抑制された希土類系焼結磁石の製造方法を提供することを目的とする。
Corrosion of the magnet in the period from when the rare earth sintered magnet is manufactured to when it is embedded in the part depends on the environment in which the magnet is placed. In particular, fluctuations in humidity repeatedly cause fine condensation on the surface of the magnet, which accelerates the corrosion of the magnet. As a result of verifying the usefulness of the simple corrosion resistance improvement technique described in the above-mentioned patent document, the present inventor does not always have sufficient corrosion resistance in an environment where the humidity fluctuates greatly even when any technique is adopted. In Patent Documents 3 to 6, the water vapor partial pressure is preferably 10 hPa (1000 Pa) or more. However, when heat treatment is performed in an atmosphere having such a high water vapor partial pressure, it occurs on the surface of the magnet. It has been clarified that magnetic properties are deteriorated when hydrogen is generated in large quantities as a by-product by the oxidation reaction, and the hydrogen generated by the magnet is occluded and embrittled.
Therefore, the present invention has an object to provide a method for producing a rare earth sintered magnet in which sufficient corrosion resistance is imparted by an oxidation heat treatment even in an environment where the humidity varies, and a decrease in magnetic properties due to the oxidation heat treatment is suppressed. And
本発明者は、上記の点に鑑みて鋭意研究を重ねた結果、酸素分圧と、特許文献３〜特許文献６において不適とされている１０ｈＰａ未満の水蒸気分圧を適切に制御した酸化性雰囲気下、磁石の酸素含有量に基づいて適切な温度管理の下に熱処理を行うことによって表面改質された希土類系焼結磁石は、湿度が変動する環境においても十分な耐食性を有すること、熱処理による磁気特性の低下が抑制されていることを見出した。 As a result of intensive studies in view of the above points, the inventor of the present invention appropriately controlled an oxygen partial pressure and a water vapor partial pressure of less than 10 hPa, which is inappropriate in Patent Documents 3 to 6. The rare earth-based sintered magnet surface-modified by performing heat treatment under appropriate temperature control based on the oxygen content of the magnet has sufficient corrosion resistance even in an environment where humidity varies, It has been found that the deterioration of magnetic properties is suppressed.
上記の知見に基づいて完成された本発明の表面改質された希土類系焼結磁石の製造方法は、請求項１記載の通り、希土類系焼結磁石が、２５質量％〜４０質量％の希土類元素：Ｒ、０．６質量％〜１．６質量％のＢ（但しその一部はＣによって置換されていてもよい）、０質量％〜１．０質量％のＡｌ、Ｓｉ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ，Ｚｒ、Ｎｂ、Ｍｏ、Ａｇ、Ｉｎ、Ｓｎ、Ｈｆ、Ｔａ、Ｗ、Ｐｂ、およびＢｉからなる群から選択される少なくとも１種の添加元素：Ｍ、残部は、その５０質量％以下がＣｏおよび／またはＮｉによって置換されていてもよいＦｅ、および不可避不純物からなる組成を有するものであり、酸素分圧が１×１０２Ｐａ〜１×１０５Ｐａで水蒸気分圧が０．１Ｐａ〜１０００Ｐａ（但し１０００Ｐａを除く）の雰囲気下、磁石の酸素含有量が０．０１質量％〜０．３質量％（但し０．３質量％を除く）の場合には４００℃〜６００℃で、磁石の酸素含有量が０．３質量％〜０．６質量％の場合には２００℃〜４００℃（但し４００℃を除く）で熱処理を行う工程を含んでなることを特徴とする。
また、請求項２記載の表面改質された希土類系焼結磁石の製造方法は、請求項１記載の表面改質された希土類系焼結磁石の製造方法において、酸素分圧と水蒸気分圧の比率（酸素分圧／水蒸気分圧）を１〜４００とすることを特徴とする。
また、請求項３記載の表面改質された希土類系焼結磁石の製造方法は、請求項１または２記載の表面改質された希土類系焼結磁石の製造方法において、常温から熱処理を行う温度までの昇温を、酸素分圧が１×１０２Ｐａ〜１×１０５Ｐａで水蒸気分圧が１×１０−３Ｐａ〜１００Ｐａの雰囲気下で行うことを特徴とする。
また、請求項４記載の表面改質された希土類系焼結磁石の製造方法は、請求項１乃至３のいずれかに記載の表面改質された希土類系焼結磁石の製造方法において、磁石表面に対して平面研削加工を行ってから熱処理を行うことを特徴とする。
また、請求項５記載の表面改質された希土類系焼結磁石の製造方法は、請求項４記載の表面改質された希土類系焼結磁石の製造方法において、番手が♯６０〜♯４００の粒度を有する砥石を用いて平面研削加工を行うことを特徴とする。
また、本発明の表面改質された希土類系焼結磁石は、請求項６記載の通り、請求項１記載の表面改質された希土類系焼結磁石の製造方法にて製造されてなることを特徴とする。
また、請求項７記載の表面改質された希土類系焼結磁石は、請求項６記載の表面改質された希土類系焼結磁石において、表面改質された部分が、磁石の内側から順に、Ｒ、Ｆｅ、Ｂおよび酸素を含む主層、少なくともＲ、Ｆｅおよび酸素を含む非晶質層、ヘマタイトを主体とする酸化鉄を構成成分として含む最表層の少なくとも３層を有する表面改質層からなることを特徴とする。
また、本発明の表面改質された希土類系焼結磁石は、請求項８記載の通り、希土類系焼結磁石が、２５質量％〜４０質量％の希土類元素：Ｒ、０．６質量％〜１．６質量％のＢ（但しその一部はＣによって置換されていてもよい）、０質量％〜１．０質量％のＡｌ、Ｓｉ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ，Ｚｒ、Ｎｂ、Ｍｏ、Ａｇ、Ｉｎ、Ｓｎ、Ｈｆ、Ｔａ、Ｗ、Ｐｂ、およびＢｉからなる群から選択される少なくとも１種の添加元素：Ｍ、残部は、その５０質量％以下がＣｏおよび／またはＮｉによって置換されていてもよいＦｅ、および不可避不純物からなる組成を有するもので、磁石の酸素含有量が０．０１質量％〜０．３質量％（但し０．３質量％を除く）であり、表面改質された部分が、磁石の内側から順に、Ｒ、Ｆｅ、Ｂおよび酸素を含む主層、少なくともＲ、Ｆｅおよび酸素を含む非晶質層、ヘマタイトを主体とする酸化鉄を構成成分として含む最表層の少なくとも３層を有する表面改質層からなることを特徴とする。
また、本発明の表面改質された希土類系焼結磁石は、請求項９記載の通り、希土類系焼結磁石が、２５質量％〜４０質量％の希土類元素：Ｒ、０．６質量％〜１．６質量％のＢ（但しその一部はＣによって置換されていてもよい）、０質量％〜１．０質量％のＡｌ、Ｓｉ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ，Ｚｒ、Ｎｂ、Ｍｏ、Ａｇ、Ｉｎ、Ｓｎ、Ｈｆ、Ｔａ、Ｗ、Ｐｂ、およびＢｉからなる群から選択される少なくとも１種の添加元素：Ｍ、残部は、その５０質量％以下がＣｏおよび／またはＮｉによって置換されていてもよいＦｅ、および不可避不純物からなる組成を有するもので、磁石の酸素含有量が０．３質量％〜０．６質量％であり、表面改質された部分が、磁石の内側から順に、Ｒ、Ｆｅ、Ｂおよび酸素を含む主層、少なくともＲ、Ｆｅおよび酸素を含む非晶質層、ヘマタイトを主体とする酸化鉄を構成成分として含む最表層の少なくとも３層を有する表面改質層からなることを特徴とする。
The manufacturing method of the surface-modified rare earth sintered magnet of the present invention completed based on the above knowledge is as described in claim 1, wherein the rare earth sintered magnet is 25 mass% to 40 mass% rare earth. Element: R, 0.6 mass% to 1.6 mass% B (some of which may be replaced by C), 0 mass% to 1.0 mass% Al, Si, Ti, V At least one additive element selected from the group consisting of Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi: M The remainder has a composition composed of Fe that may be substituted with Co and / or Ni by 50% by mass or less, and inevitable impurities, and has an oxygen partial pressure of 1 × 10 2 Pa to 1 × 10 5. The partial pressure of water vapor is 0.1 Pa to 1000 Pa (however, When the oxygen content of the magnet is 0.01 mass% to 0.3 mass% (excluding 0.3 mass%), the oxygen content of the magnet is 400 ° C to 600 ° C. When the amount is 0.3 mass% to 0.6 mass%, it includes a step of performing a heat treatment at 200 ° C. to 400 ° C. (excluding 400 ° C.).
The method for producing a surface-modified rare earth-based sintered magnet according to claim 2 is the method for producing a surface-modified rare earth-based sintered magnet according to claim 1, wherein the oxygen partial pressure and the water vapor partial pressure are The ratio (oxygen partial pressure / water vapor partial pressure) is 1 to 400.
The method for producing a surface-modified rare earth-based sintered magnet according to claim 3 is the method for producing a surface-modified rare earth-based sintered magnet according to claim 1 or 2, wherein the temperature at which heat treatment is performed from room temperature. Is performed in an atmosphere having an oxygen partial pressure of 1 × 10 2 Pa to 1 × 10 5 Pa and a water vapor partial pressure of 1 × 10 −3 Pa to 100 Pa.
The method for producing a surface-modified rare earth-based sintered magnet according to claim 4 is the method for producing a surface-modified rare earth-based sintered magnet according to any one of claims 1 to 3, wherein: A heat treatment is performed after surface grinding is performed on the surface.
The method for producing a surface-modified rare earth-based sintered magnet according to claim 5 is the method for producing a surface-modified rare earth-based sintered magnet according to claim 4, wherein the number is # 60 to # 400. Surface grinding is performed using a grindstone having a grain size.
Moreover, the surface-modified rare earth-based sintered magnet of the present invention is manufactured by the method for manufacturing a surface-modified rare earth-based sintered magnet according to claim 1, as described in claim 6. Features.
The surface-modified rare earth-based sintered magnet according to claim 7 is the surface-modified rare earth-based sintered magnet according to claim 6, wherein the surface-modified portions are sequentially arranged from the inside of the magnet. From a surface modified layer having a main layer containing R, Fe, B and oxygen, an amorphous layer containing at least R, Fe and oxygen, and an outermost layer containing iron oxide mainly composed of hematite as a constituent component It is characterized by becoming.
Further, according to the surface-modified rare earth sintered magnet of the present invention, the rare earth sintered magnet is 25 mass% to 40 mass% rare earth element: R, 0.6 mass% to 1.6 mass% B (some of which may be replaced by C), 0 mass% to 1.0 mass% Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn , Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi, at least one additive element selected from the group consisting of M and the balance is 50% by mass or less. It has a composition consisting of Fe that may be substituted by Co and / or Ni, and unavoidable impurities, and the oxygen content of the magnet is 0.01 mass% to 0.3 mass% (however, 0.3 mass%) The surface-modified portions are R in order from the inside of the magnet. It consists of a surface modification layer having at least three layers of a main layer containing Fe, B and oxygen, an amorphous layer containing at least R, Fe and oxygen, and an outermost layer containing iron oxide mainly composed of hematite. It is characterized by.
The surface-modified rare earth-based sintered magnet of the present invention is the rare earth-based sintered magnet according to claim 9, wherein the rare earth-based sintered magnet is 25 mass% to 40 mass% of rare earth elements: R, 0.6 mass% to 1.6 mass% B (some of which may be replaced by C), 0 mass% to 1.0 mass% Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn , Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi, at least one additive element selected from the group consisting of M and the balance is 50% by mass or less. It has a composition comprising Fe that may be substituted by Co and / or Ni, and unavoidable impurities, and the oxygen content of the magnet is 0.3 mass% to 0.6 mass%, and the surface is modified. The main part contains R, Fe, B and oxygen in order from the inside of the magnet. Characterized in that it consists of at least R, amorphous layer containing Fe and oxygen, the surface modified layer comprising at least three layers of the outermost layer containing iron oxide consisting mainly of hematite as a constituent.
本発明によれば、湿度が変動する環境においても十分な耐食性が酸化熱処理によって付与されているとともに、酸化熱処理による磁気特性の低下が抑制された希土類系焼結磁石の製造方法を提供することができる。 According to the present invention, it is possible to provide a method for producing a rare earth-based sintered magnet in which sufficient corrosion resistance is imparted by an oxidation heat treatment even in an environment where the humidity varies, and a decrease in magnetic properties due to the oxidation heat treatment is suppressed. it can.
本発明の表面改質された希土類系焼結磁石の製造方法は、希土類系焼結磁石が、２５質量％〜４０質量％の希土類元素：Ｒ、０．６質量％〜１．６質量％のＢ（但しその一部はＣによって置換されていてもよい）、０質量％〜１．０質量％のＡｌ、Ｓｉ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ，Ｚｒ、Ｎｂ、Ｍｏ、Ａｇ、Ｉｎ、Ｓｎ、Ｈｆ、Ｔａ、Ｗ、Ｐｂ、およびＢｉからなる群から選択される少なくとも１種の添加元素：Ｍ、残部は、その５０質量％以下がＣｏおよび／またはＮｉによって置換されていてもよいＦｅ、および不可避不純物からなる組成を有するものであり、酸素分圧が１×１０２Ｐａ〜１×１０５Ｐａで水蒸気分圧が０．１Ｐａ〜１０００Ｐａ（但し１０００Ｐａを除く）の雰囲気下、磁石の酸素含有量が０．０１質量％〜０．３質量％（但し０．３質量％を除く）の場合には４００℃〜６００℃で、磁石の酸素含有量が０．３質量％〜０．６質量％の場合には２００℃〜４００℃（但し４００℃を除く）で熱処理を行う工程を含んでなることを特徴とするものである。酸素分圧と、１０ｈＰａ未満の水蒸気分圧を適切に制御した酸化性雰囲気下、磁石の酸素含有量が０．３質量％未満であるか０．３質量％以上であるかを指標にした適切な温度管理の下に熱処理を行うことで、優れた耐食性を発揮する表面改質を磁石に対して効果的に行うことができるとともに、過剰な水蒸気の存在によって引き起こされる水素の大量生成に伴う磁石の磁気特性の低下を抑制することができる。 In the method for producing a surface-modified rare earth sintered magnet according to the present invention, the rare earth sintered magnet comprises 25 mass% to 40 mass% of rare earth element: R, 0.6 mass% to 1.6 mass%. B (however, part thereof may be substituted by C), 0% by mass to 1.0% by mass of Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb , Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi, at least one additive element selected from the group consisting of: M, and the balance is 50% or less by Co and / or Ni It has a composition consisting of Fe that may be substituted, and inevitable impurities, and has an oxygen partial pressure of 1 × 10 2 Pa to 1 × 10 5 Pa and a water vapor partial pressure of 0.1 Pa to 1000 Pa (excluding 1000 Pa) ), The oxygen content of the magnet In the case of 0.01 mass% to 0.3 mass% (excluding 0.3 mass%), the temperature is 400 ° C. to 600 ° C., and the oxygen content of the magnet is 0.3 mass% to 0.6 mass% Is characterized by comprising a step of performing heat treatment at 200 ° C. to 400 ° C. (excluding 400 ° C.). Appropriately based on whether the oxygen content of the magnet is less than 0.3% by mass or more than 0.3% by mass in an oxidizing atmosphere in which the oxygen partial pressure and water vapor partial pressure of less than 10 hPa are appropriately controlled By performing heat treatment under proper temperature control, surface modification that exhibits excellent corrosion resistance can be effectively performed on the magnet, and magnets accompanying mass production of hydrogen caused by the presence of excess water vapor It is possible to suppress the deterioration of the magnetic characteristics of the.
希土類系焼結磁石の表面に対して所望する改質をより効果的かつ低コストに行うためには、酸素分圧は５×１０３Ｐａ〜５×１０４Ｐａが望ましく、１×１０４Ｐａ〜４×１０４Ｐａがより望ましい。水蒸気分圧は２５０Ｐａ〜９００Ｐａが望ましく、４００Ｐａ〜７００Ｐａがより望ましい。また、酸素分圧と水蒸気分圧の比率（酸素分圧／水蒸気分圧）は１〜４００が望ましく、５〜１００がより望ましい。処理室内の酸化性雰囲気は、例えば、これらの酸化性ガスを所定の分圧となるように個別に導入することによって形成してもよいし、これらの酸化性ガスが所定の分圧で含まれる露点を有する大気を導入することによって形成してもよい。また、処理室内には、窒素やアルゴンなどの不活性ガスを共存させてもよい。 In order to perform the desired modification on the surface of the rare earth sintered magnet more effectively and at low cost, the oxygen partial pressure is preferably 5 × 10 3 Pa to 5 × 10 4 Pa, and 1 × 10 4 Pa. -4 × 10 4 Pa is more desirable. The water vapor partial pressure is preferably 250 Pa to 900 Pa, and more preferably 400 Pa to 700 Pa. The ratio of oxygen partial pressure to water vapor partial pressure (oxygen partial pressure / water vapor partial pressure) is preferably 1 to 400, and more preferably 5 to 100. The oxidizing atmosphere in the processing chamber may be formed, for example, by individually introducing these oxidizing gases so as to have a predetermined partial pressure, or these oxidizing gases are included at a predetermined partial pressure. You may form by introduce | transducing the atmosphere which has a dew point. Further, an inert gas such as nitrogen or argon may coexist in the processing chamber.
熱処理温度は、磁石の酸素含有量が０．３質量％以上の場合には２００℃〜４００℃（但し４００℃を除く）を採用するが、２５０℃〜３８０℃が望ましく、３００℃〜３７０℃がより望ましい。２００℃未満の温度で処理を行うと希土類系焼結磁石の表面に対して所望する改質が行い難くなる恐れがある一方、４００℃以上の温度で処理を行うと磁石の磁気特性に悪影響を及ぼす恐れや磁石表面の改質が過剰に行われてしまうことで形成された改質層が脱落したりする恐れがある。また、磁石の酸素含有量が０．３質量％未満の場合には４００℃〜６００℃を採用するが、４０５℃〜５５０℃が望ましく、４１０℃〜４８０℃がより望ましい。驚くべきことに、酸素含有量が０．３質量％未満の磁石に対し、酸素含有量が０．３質量％以上の磁石に対して採用する例えば３００℃〜４００℃（但し４００℃を除く）で熱処理を行うと、磁石の磁気特性に悪影響を及ぼす一方、４２０℃〜４８０℃で熱処理を行うと、磁石の磁気特性は向上する傾向にある。しかしながら６００℃を超える温度で処理を行うと磁石の磁気特性に悪影響を及ぼす恐れや磁石表面の改質が過剰に行われてしまうことで形成された改質層が脱落したりする恐れがある。なお、処理時間は１分〜３時間が望ましい。 The heat treatment temperature is 200 ° C. to 400 ° C. (except 400 ° C.) when the oxygen content of the magnet is 0.3% by mass or more, preferably 250 ° C. to 380 ° C., preferably 300 ° C. to 370 ° C. Is more desirable. If the treatment is performed at a temperature of less than 200 ° C., the surface of the rare earth sintered magnet may be difficult to be modified. On the other hand, if the treatment is performed at a temperature of 400 ° C. or more, the magnetic properties of the magnet will be adversely affected. There is a risk that the modified layer formed may fall off due to excessive influence or modification of the magnet surface. Further, when the oxygen content of the magnet is less than 0.3% by mass, 400 ° C. to 600 ° C. is adopted, but 405 ° C. to 550 ° C. is desirable, and 410 ° C. to 480 ° C. is more desirable. Surprisingly, for a magnet having an oxygen content of less than 0.3% by mass, it is employed for a magnet having an oxygen content of 0.3% by mass or more, for example, 300 ° C. to 400 ° C. (except 400 ° C.). When the heat treatment is carried out, the magnetic properties of the magnet are adversely affected. On the other hand, when the heat treatment is performed at 420 to 480 ° C., the magnetic properties of the magnet tend to be improved. However, if the treatment is performed at a temperature exceeding 600 ° C., the magnetic properties of the magnet may be adversely affected, and the modified layer formed due to excessive modification of the magnet surface may fall off. The processing time is preferably 1 minute to 3 hours.
常温（例えば１０℃〜３０℃）から熱処理温度までの昇温は、酸素分圧が１×１０２Ｐａ〜１×１０５Ｐａで水蒸気分圧が１×１０−３Ｐａ〜１００Ｐａの雰囲気下で行うことが望ましい。昇温工程を雰囲気制御せずに例えば大気中で行うと、昇温時に大気中に含まれる水分による酸化反応が磁石の表面で起こることで、水素の大量発生に伴う磁石の磁気特性の低下を招く恐れがある。また、大気中に含まれる水分の量は季節によって変動するので、年間を通して安定した品質の表面改質を磁石に対して行えない恐れがある。これに対し、上記の雰囲気は、適度の酸素と水蒸気を含んでいるので、昇温工程自体が磁石の表面改質に好ましい影響を与え、磁石に対する優れた耐食性の付与と磁気特性の低下の抑制に寄与する。常温から熱処理温度までの昇温速度は１００℃／時間〜１８００℃／時間が望ましく、昇温時間は２０分〜２時間が望ましい。磁石を熱処理温度まで昇温させた後は、すぐさま熱処理工程に移ってもよいし、昇温工程の雰囲気中で磁石をしばらく保持してから（例えば１分〜６０分）熱処理工程に移ってもよい。 The temperature rise from room temperature (for example, 10 ° C. to 30 ° C.) to the heat treatment temperature is performed in an atmosphere having an oxygen partial pressure of 1 × 10 2 Pa to 1 × 10 5 Pa and a water vapor partial pressure of 1 × 10 −3 Pa to 100 Pa. It is desirable to do. If the temperature raising step is performed in the air without controlling the atmosphere, for example, an oxidation reaction due to moisture contained in the air occurs at the time of temperature rising, and the magnetic characteristics of the magnet are reduced due to the large amount of hydrogen generated. There is a risk of inviting. In addition, since the amount of moisture contained in the atmosphere varies depending on the season, there is a risk that surface modification with stable quality throughout the year cannot be performed on the magnet. On the other hand, since the above atmosphere contains moderate oxygen and water vapor, the temperature raising process itself has a favorable effect on the surface modification of the magnet, and imparts excellent corrosion resistance to the magnet and suppresses deterioration of the magnetic properties. Contribute to. The rate of temperature increase from room temperature to the heat treatment temperature is preferably 100 ° C./hour to 1800 ° C./hour, and the temperature increase time is preferably 20 minutes to 2 hours. After the magnet is heated to the heat treatment temperature, it may be immediately transferred to the heat treatment step, or after the magnet is held for a while (for example, 1 to 60 minutes) in the atmosphere of the temperature increase step, the heat treatment step may be performed. Good.
熱処理を行った後の降温も、酸素分圧が１×１０２Ｐａ〜１×１０５Ｐａで水蒸気分圧が１×１０−３Ｐａ〜１００Ｐａの雰囲気下で行うことが望ましい。このような雰囲気中で降温することにより、工程中に磁石の表面が結露して腐食の原因となることを防ぐことができる。 The temperature lowering after the heat treatment is also desirably performed in an atmosphere having an oxygen partial pressure of 1 × 10 2 Pa to 1 × 10 5 Pa and a water vapor partial pressure of 1 × 10 −3 Pa to 100 Pa. By lowering the temperature in such an atmosphere, it is possible to prevent the surface of the magnet from condensing and causing corrosion during the process.
昇温工程、熱処理工程、降温工程は、磁石が収容された処理室内の環境を順次変化させることで行ってもよいし、処理室内をそれぞれの環境に制御した領域に分割し、各領域に磁石を順次移動させることで行ってもよい。 The temperature raising process, the heat treatment process, and the temperature lowering process may be performed by sequentially changing the environment in the processing chamber in which the magnet is accommodated, or the processing chamber is divided into regions controlled by the respective environments, and the magnet is divided into each region. You may carry out by moving sequentially.
図１（ａ）は、昇温工程、熱処理工程、降温工程を、内部がそれぞれの環境に制御された領域に分割され、各領域に磁石を順次移動させることで行うことができる連続処理炉の一例の概略図（側面図）である。図１（ａ）に示す連続処理炉においては、ベルトコンベアなどの移動手段によって磁石を図の左から右に移動させながら各処理を施す。矢印は図略の給気手段と排気手段によって形成される各領域における雰囲気ガスの流れである。昇温領域の入口および降温領域の出口は、例えばエアカーテンで区画され、昇温領域と熱処理領域の境界および熱処理領域と降温領域の境界は、例えば矢印の雰囲気ガスの流れにより区画される（これらの区画は機械的にシャッターで行われてもよい）。図１（ｂ）は、図１（ａ）に示す連続処理炉の内部を移動する磁石の温度変化を示す図である。このような連続処理炉を用いれば、大量の磁石に対して安定した品質の表面改質を連続的に行うことができる。 FIG. 1 (a) shows a continuous processing furnace in which the temperature raising process, the heat treatment process, and the temperature lowering process can be performed by dividing the interior into regions controlled by the respective environments and moving the magnets sequentially to each region. It is a schematic diagram (side view) of an example. In the continuous processing furnace shown in FIG. 1 (a), each processing is performed while moving the magnet from the left to the right in the drawing by moving means such as a belt conveyor. Arrows indicate the flow of the atmospheric gas in each region formed by an unillustrated air supply means and exhaust means. The inlet of the temperature rising region and the outlet of the temperature falling region are partitioned by, for example, an air curtain, and the boundary between the temperature rising region and the heat treatment region and the boundary between the heat treatment region and the temperature lowering region are partitioned by, for example, the flow of the atmospheric gas indicated by the arrows (these This may be done mechanically with a shutter). FIG.1 (b) is a figure which shows the temperature change of the magnet which moves the inside of the continuous processing furnace shown to Fig.1 (a). If such a continuous processing furnace is used, surface modification with stable quality can be continuously performed for a large number of magnets.
以上の工程によって希土類系焼結磁石の表面に形成される改質層は、磁石の内側から順に、Ｒ、Ｆｅ、Ｂおよび酸素を含む主層、少なくともＲ、Ｆｅおよび酸素を含む非晶質層、ヘマタイト（α−Ｆｅ２Ｏ３）を主体とする酸化鉄を構成成分として含む最表層の少なくとも３層を有する。表面改質層中の主層は、その組成を表面改質されていない磁石（素材）の組成と比較すると、Ｆｅの含量が減少し、酸素の含量が増加しており、酸素の含量は例えば２．５質量％〜１５質量％である。表面改質層中の主層は、横方向に伸びる長さが０．５μｍ〜３０μｍで厚みが５０ｎｍ〜４００ｎｍのＲ濃化層を有する場合がある。このＲ濃化層は、磁石に存在した加工歪部分にＲが析出して形成されたものと推察され、脱粒などによる磁石の強度の低下を補強し、また、部品に埋め込む際の接着剤を介した部品との接着強度の向上に寄与すると考えられる。表面改質層中の最表層は、その構成成分として含まれる酸化鉄の９０質量％以上がヘマタイトであることが望ましい。より望ましくは９５質量％以上であり、さらに望ましくは９８質量％以上である。酸化鉄がヘマタイトを高比率で含有し、マグネタイト（Ｆｅ３Ｏ４）をできる限り含まないことが、磁石の表面改質を行うことによる優れた耐食性の付与に寄与する。酸素分圧と、１０ｈＰａ未満の水蒸気分圧を適切に制御した酸化性雰囲気下で熱処理を行うことで、表面改質層中の最表層を、ヘマタイトを高比率で含有する酸化鉄から構成されるようにすることができる。これとは対照的に、特許文献３〜特許文献６に記載されているような水蒸気分圧が高い雰囲気下で熱処理を行うと、表面改質層中の最表層を構成する酸化鉄はマグネタイトを高比率で含有するようになる。このことが、これらの特許文献に記載の方法では、湿度の変動が激しい環境において十分な耐食性を発揮する表面改質を磁石に対して行うことができない原因であると考えられる。なお、最表層に構成成分として含まれる酸化鉄中のヘマタイトの比率は例えばラマン分析法で磁石表面から分析することにより求めることができる。表面改質層中の主層と最表層の間に位置する非晶質層は、磁石に含まれるＲやＦｅが酸化反応によって酸化物に変換される際、安定な結晶形成がなされなかった部分であると考えられる。 The modified layer formed on the surface of the rare earth-based sintered magnet by the above steps is, in order from the inside of the magnet, a main layer containing R, Fe, B and oxygen, and an amorphous layer containing at least R, Fe and oxygen. And at least three outermost layers containing iron oxide mainly composed of hematite (α-Fe 2 O 3 ) as a constituent component. When the composition of the main layer in the surface-modified layer is compared with the composition of the magnet (material) that is not surface-modified, the Fe content is decreased and the oxygen content is increased. It is 2.5 mass%-15 mass%. The main layer in the surface modified layer may have an R-concentrated layer having a length extending in the lateral direction of 0.5 μm to 30 μm and a thickness of 50 nm to 400 nm. This R-concentrated layer is presumed to be formed by precipitation of R in the work strain part existing in the magnet, reinforcing the decrease in the strength of the magnet due to degranulation, etc. It is thought that it contributes to the improvement of the adhesive strength with the interposed parts. As for the outermost layer in the surface modified layer, it is desirable that 90% by mass or more of iron oxide contained as a constituent component is hematite. More preferably, it is 95 mass% or more, More preferably, it is 98 mass% or more. The fact that iron oxide contains hematite in a high ratio and does not contain magnetite (Fe 3 O 4 ) as much as possible contributes to imparting excellent corrosion resistance by performing surface modification of the magnet. By performing heat treatment in an oxidizing atmosphere in which the oxygen partial pressure and the water vapor partial pressure of less than 10 hPa are appropriately controlled, the outermost layer in the surface modified layer is composed of iron oxide containing hematite in a high ratio. Can be. In contrast, when heat treatment is performed in an atmosphere having a high water vapor partial pressure as described in Patent Documents 3 to 6, iron oxide constituting the outermost layer in the surface modified layer is magnetite. Contains at a high ratio. This is considered to be the reason why the methods described in these patent documents cannot perform surface modification that exhibits sufficient corrosion resistance in an environment where the humidity fluctuates greatly. The ratio of hematite in iron oxide contained as a constituent component in the outermost layer can be obtained by analyzing from the magnet surface by, for example, Raman analysis. The amorphous layer located between the main layer and the outermost layer in the surface modified layer is a portion where stable crystals were not formed when R or Fe contained in the magnet was converted into an oxide by an oxidation reaction. It is thought that.
なお、希土類系焼結磁石の表面に形成される表面改質層の厚みは０．５μｍ〜１０μｍが望ましい。厚みが薄すぎると十分な耐食性を発揮しない恐れがある一方、厚みが厚すぎると磁石の磁気特性に悪影響を及ぼす恐れがある。表面改質層中の主層の厚みは０．４μｍ〜９．９μｍが望ましく、１μｍ〜７μｍがより望ましい。非晶質層の厚みは１００ｎｍ以下であることが望ましく、７０ｎｍ以下がより望ましい（下限値は例えば１０ｎｍが望ましい）。最表層の厚みは１０ｎｍ〜３００ｎｍであることが望ましく、５０ｎｍ〜２００ｎｍがより望ましい。 The thickness of the surface modification layer formed on the surface of the rare earth sintered magnet is preferably 0.5 μm to 10 μm. If the thickness is too thin, sufficient corrosion resistance may not be exhibited. On the other hand, if the thickness is too thick, the magnetic properties of the magnet may be adversely affected. The thickness of the main layer in the surface modification layer is preferably 0.4 μm to 9.9 μm, and more preferably 1 μm to 7 μm. The thickness of the amorphous layer is preferably 100 nm or less, more preferably 70 nm or less (the lower limit is preferably 10 nm, for example). The thickness of the outermost layer is desirably 10 nm to 300 nm, and more desirably 50 nm to 200 nm.
また、酸化熱処理を行う前に磁石表面に対して平面研削加工を行ってもよい。かかる工程を付加することにより、磁石の表面組成が均一化され、これにより磁石の表面全体に均一な酸化熱処理を行うことが可能となり、最表層をヘマタイトによる表面被覆率が高い均一なものとすることができる。ヘマタイトによる表面被覆率は９０％以上が望ましく９５％以上がより望ましい。平面研削加工は、自体公知の平面研削盤や両頭研削盤を用いて行うことができる。使用する砥石は番手が♯６０〜♯４００の粒度を有するものが望ましい。番手が♯６０未満であると（粒度が粗すぎると）、磁石表面が必要以上に研削されてしまうことによって磁石の寸法精度に無視できない悪影響を及ぼす恐れがある一方、番手が♯４００を超えると（粒度が細かすぎると）、磁石の表面組成の均一化が不十分になる恐れがある。なお、砥石の回転数は６００ｒｐｍ〜２０００ｒｐｍが望ましく、研削盤への磁石の送り込み速度は０．１ｍ／分〜５ｍ／分が望ましい。平面研削加工は、磁石の寸法調整のための研削を別の方法で行った後に行ってもよいが、磁石の寸法調整のための研削を平面研削加工によって行うことで、磁石の寸法調整と磁石の表面組成の均一化を同時に達成することができる。 Further, surface grinding may be performed on the magnet surface before performing the oxidation heat treatment. By adding such a step, the surface composition of the magnet is made uniform, thereby making it possible to perform uniform oxidation heat treatment on the entire surface of the magnet, and making the outermost layer uniform with a high surface coverage by hematite. be able to. The surface coverage by hematite is desirably 90% or more, and more desirably 95% or more. The surface grinding can be performed using a known surface grinding machine or a double-head grinding machine. It is desirable that the grindstone used has a grain size of # 60 to # 400. If the count is less than # 60 (if the grain size is too coarse), the magnet surface may be ground more than necessary, which may adversely affect the dimensional accuracy of the magnet, while if the count exceeds # 400 (If the particle size is too fine), the surface composition of the magnet may become insufficiently uniform. The rotational speed of the grindstone is desirably 600 rpm to 2000 rpm, and the feeding speed of the magnet to the grinding machine is desirably 0.1 m / min to 5 m / min. The surface grinding process may be performed after the grinding for adjusting the size of the magnet is performed by another method. However, by performing the grinding for the dimension adjustment of the magnet by the surface grinding process, the size adjustment of the magnet and the magnet can be performed. The surface composition can be made uniform at the same time.
本発明が適用される希土類系焼結磁石としては、その組成に対応する合金から、例えば、下記の製造方法によって製造したＲ−Ｆｅ−Ｂ焼結磁石が挙げられる。なお、磁石の酸素含有量は、磁石の製造工程中の環境における酸素含有量に左右されるものである。磁石の製造は、基本的に酸素を遮断した状態で行われるが、酸素の遮断をより厳密に行うことで、磁石の酸素含有量をより少なくすることができる。
上記の合金は、原料合金の溶湯を例えばストリップキャスト法によって急冷して好適に作製され得る。以下、ストリップキャスト法による急冷凝固合金の作製を説明する。
まず、上記組成を有する原料合金をアルゴン雰囲気中において高周波溶解によって溶解し、原料合金の溶湯を形成する。次に、この溶湯を１３５０℃程度に保持した後、単ロール法によって急冷し、例えば厚さ約０．３ｍｍのフレーク状合金鋳塊を得る。こうして作製した合金鋳片を、次の水素粉砕処理前に例えば１〜１０ｍｍのフレーク状に粉砕する。なお、ストリップキャスト法による原料合金の製造方法は、例えば、米国特許第５、３８３、９７８号明細書に開示されている。
［粗粉砕工程］
上記のフレーク状に粗く粉砕された合金鋳片を水素炉の内部へ収容する。次に、水素炉の内部で水素脆化処理（以下、「水素粉砕処理」や単に「水素処理」と称する場合がある）工程を行う。水素粉砕処理後の粗粉砕粉合金粉末を水素炉から取り出す際、粗粉砕粉が大気と接触しないように、不活性雰囲気下で取り出し動作を実行することが好ましい。そうすれば、粗粉砕粉が酸化・発熱することが防止され、磁石の磁気特性の低下が抑制できるからである。
水素粉砕処理によって、希土類合金は、その平均粒径が５００μｍ以下の大きさにまで粉砕される。水素粉砕処理後、脆化した原料合金をより細かく解砕するとともに冷却することが好ましい。比較的高い温度状態のまま原料を取り出す場合は、冷却処理の時間を相対的に長くすればよい。
［微粉砕工程］
次に、粗粉砕粉に対してジェットミル粉砕装置を用いて微粉砕を実行する。本実施形態で使用するジェットミル粉砕装置にはサイクロン分級機が接続されている。ジェットミル粉砕装置は、粗粉砕工程で粗く粉砕された希土類合金（粗粉砕粉）の供給を受け、粉砕機内で粉砕する。粉砕機内で粉砕された粉末はサイクロン分級機を経て回収タンクに集められる。こうして、０．１〜２０μｍ程度（典型的には平均粒径３〜５μｍ）の微粉末を得ることができる。このような微粉砕に用いる粉砕装置は、ジェットミルに限定されず、アトライタやボールミルであってもよい。粉砕に際して、ステアリン酸亜鉛などの潤滑剤を粉砕助剤として用いてもよい。
［プレス成形］
本実施形態では、上記方法で作製された磁性粉末に対し、例えばロッキングミキサー内で潤滑剤を例えば０．３ｗｔ％添加・混合し、潤滑剤で合金粉末粒子の表面を被覆する。次に、上述の方法で作製した磁性粉末を公知のプレス装置を用いて配向磁界中で成形する。印加する磁界の強度は、例えば１．５〜１．７テスラ（Ｔ）である。また、成形圧力は、成形体のグリーン密度が例えば４〜４．５ｇ／ｃｍ３程度になるように設定される。
［焼結工程］
上記の粉末成形体に対して、６５０〜１０００℃の範囲内の温度で１０〜２４０分間保持する工程と、その後、上記の保持温度よりも高い温度（例えば、１０００〜１２００℃）で焼結を更に進める工程とを順次行うことが好ましい。焼結時、特に液相が生成されるとき（温度が６５０〜１０００℃の範囲内にあるとき）、粒界相中のＲリッチ相が融け始め、液相が形成される。その後、焼結が進行し、焼結磁石体が形成される。焼結工程の後、時効処理（４００℃〜７００℃）や寸法調整のための研削を行ってもよい。
The rare earth sintered magnet to which the present invention is applied includes, for example, an R—Fe—B sintered magnet manufactured from an alloy corresponding to the composition by the following manufacturing method. The oxygen content of the magnet depends on the oxygen content in the environment during the magnet manufacturing process. Manufacture of a magnet is basically performed in a state where oxygen is shut off, but the oxygen content of the magnet can be reduced by more strictly shutting off oxygen.
The above-mentioned alloy can be suitably produced by rapidly cooling a molten raw material alloy by, for example, a strip casting method. Hereinafter, preparation of a rapidly solidified alloy by a strip casting method will be described.
First, a raw material alloy having the above composition is melted by high-frequency melting in an argon atmosphere to form a molten raw material alloy. Next, after holding this molten metal at about 1350 ° C., it is rapidly cooled by a single roll method to obtain, for example, a flake-shaped alloy ingot having a thickness of about 0.3 mm. The alloy slab thus produced is pulverized into, for example, 1 to 10 mm flakes before the next hydrogen pulverization treatment. In addition, the manufacturing method of the raw material alloy by a strip cast method is disclosed by US Patent 5,383,978 specification, for example.
[Coarse grinding process]
The alloy slab coarsely crushed into flakes is accommodated in the hydrogen furnace. Next, a hydrogen embrittlement treatment process (hereinafter sometimes referred to as “hydrogen pulverization treatment” or simply “hydrogen treatment”) is performed inside the hydrogen furnace. When the coarsely pulverized powder alloy powder after the hydrogen pulverization treatment is taken out from the hydrogen furnace, the takeout operation is preferably performed in an inert atmosphere so that the coarsely pulverized powder does not come into contact with the atmosphere. By doing so, it is possible to prevent the coarsely pulverized powder from oxidizing and generating heat, and to suppress the deterioration of the magnetic properties of the magnet.
By the hydrogen pulverization treatment, the rare earth alloy is pulverized to an average particle size of 500 μm or less. After the hydrogen pulverization treatment, the embrittled raw material alloy is preferably crushed more finely and cooled. When the raw material is taken out in a relatively high temperature state, the cooling process time may be relatively long.
[Fine grinding process]
Next, the coarsely pulverized powder is finely pulverized using a jet mill pulverizer. A cyclone classifier is connected to the jet mill crusher used in the present embodiment. The jet mill pulverizer is supplied with the rare earth alloy (coarse pulverized powder) coarsely pulverized in the coarse pulverization step, and pulverizes in the pulverizer. The powder pulverized in the pulverizer is collected in a collection tank through a cyclone classifier. In this way, a fine powder of about 0.1 to 20 μm (typically an average particle size of 3 to 5 μm) can be obtained. The pulverizer used for such fine pulverization is not limited to a jet mill, and may be an attritor or a ball mill. In grinding, a lubricant such as zinc stearate may be used as a grinding aid.
[Press molding]
In this embodiment, for example, 0.3 wt% of a lubricant is added to and mixed with the magnetic powder produced by the above method in a rocking mixer, and the surface of the alloy powder particles is coated with the lubricant. Next, the magnetic powder produced by the above-described method is molded in an orientation magnetic field using a known press machine. The intensity of the applied magnetic field is, for example, 1.5 to 1.7 Tesla (T). The molding pressure is set so that the green density of the molded body is, for example, about 4 to 4.5 g / cm 3 .
[Sintering process]
With respect to said powder molded body, the step of holding at a temperature in the range of 650 to 1000 ° C. for 10 to 240 minutes, and then sintering at a temperature higher than the above holding temperature (for example, 1000 to 1200 ° C.). It is preferable to sequentially perform the further steps. During sintering, particularly when a liquid phase is generated (when the temperature is in the range of 650 to 1000 ° C.), the R-rich phase in the grain boundary phase begins to melt and a liquid phase is formed. Then, sintering progresses and a sintered magnet body is formed. After the sintering step, aging treatment (400 ° C. to 700 ° C.) and grinding for dimension adjustment may be performed.
以下、本発明を実施例によってさらに詳細に説明するが、本発明はこれに限定して解釈されるものではない。 EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is limited to this and is not interpreted.
（実施例１）磁石の酸素含有量が０．３質量％未満の希土類系焼結磁石（その１）
Ｎｄ：１７．４、Ｐｒ：５．４、Ｄｙ：７．６、Ｂ：１．００、Ｃｏ：０．９、Ａｌ：０．２、Ｇａ：０．０５、Ｃｕ：０．１、残部：Ｆｅ（単位は質量％）の組成を有する厚さ０．２〜０．３ｍｍの合金薄片をストリップキャスト法により作製した。
次に、この合金薄片を容器に充填し、水素処理装置内に収容した。そして、水素処理装置内を圧力５００ｋＰａの水素ガスで満たすことにより、室温で合金薄片に水素吸蔵させた後、放出させた。このような水素処理を行うことにより、合金薄片を脆化し、大きさ約０．１５〜０．２ｍｍの不定形粉末を作製した。
上記の水素処理により作製した粗粉砕粉末に対し粉砕助剤として０．０４ｗｔ％のステアリン酸亜鉛を添加し混合した後、ジェットミル装置による粉砕工程を行うことにより、平均粉末粒径が約３μｍの微粉末を作製した。
こうして作製した微粉末をプレス装置により成形し、粉末成形体を作製した。具体的には、印加磁界中で粉末粒子を磁界配向した状態で圧縮し、プレス成形を行った。その後、成形体をプレス装置から抜き出し、真空炉により１０５０℃で４時間の焼結工程を行い、焼結体ブロックを得た。この焼結体ブロックの酸素含有量を酸素・窒素分析装置（ＥＭＧＡ−６２０Ｗ：ＨＯＲＩＢＡ社製）で測定したところ、０．２４質量％であった（熱処理を行うまでこの酸素含有量を維持）。
得られた焼結体ブロックの表面に対し、平面研削盤（大昌精機社製）を用いて平面研削加工を行い（砥石の番手：♯１００、砥石の回転数：１５００ｒｐｍ、研削盤への磁石の送り込み速度：０．６ｍ／分）、厚さ６ｍｍ×縦７ｍｍ×横７ｍｍに寸法調整した焼結磁石（以下、「磁石体試験片」と称する）を得た。
磁石体試験片をアルコール洗浄した後、真空中にて５００℃で２．５時間の時効処理を行った。この磁石体試験片の磁気特性を磁気測定装置（ＴＰＭ−２−１０：東英工業社製、以下同じ）を用いて測定した結果、固有保磁力は２３５３ｋＡ／ｍであった。
次に、時効処理を行った磁石体試験片に対し、露点０℃の大気（酸素分圧２００００Ｐａ，水蒸気分圧６００Ｐａ，酸素分圧／水蒸気分圧＝３３．３）の雰囲気下、４１０℃で２時間の熱処理を行うことで、表面改質された磁石体試験片を得た。なお、磁石体試験片の室温から熱処理温度までの昇温は、露点−４０℃の大気（酸素分圧２００００Ｐａ，水蒸気分圧１２．９Ｐａ）の雰囲気下、約９００℃／時間の昇温速度で行った（昇温時間は２５分）。また、熱処理後の降温も、同様の雰囲気下で行った。この磁石体試験片を樹脂埋め研磨後、イオンビーム断面加工装置（ＳＭ０９０１０：日本電子社製）を用いて試料作製し、電界放出型走査電子顕微鏡（Ｓ−４３００：日立ハイテクノロジー社製）を用いて断面観察を行った結果を図２に示す。図２から明らかなように、この観察ポイントでは、磁石体試験片の表面に形成された改質層の厚みは約４．７μｍであること、この改質層は複数の層からなり、少なくとも主層と、厚みが約１４０ｎｍの最表層が存在することがわかった。さらに、改質層中には、厚みが約１００ｎｍで長さが約５μｍのＲからなる層状構造（Ｒの組成が８５質量％以上のＲ濃化層）が水平方向（磁石体の表面と略平行方向）に形成されていることが確認できた。改質層中の主層の組成と素材（磁石体試験片）の組成をエネルギー分散型Ｘ線分析装置（Ｇｅｎｅｓｉｓ２０００：ＥＤＡＸ社製）を用いて分析した結果を表１に示す。表１から明らかなように、改質層中の主層は素材に比較してＦｅの含量が少ない反面、酸素の含量が非常に多いことがわかった。さらに、表面改質された磁石体試験片の表面付近の断面観察を、透過型電子顕微鏡（ＨＦ２１００：日立ハイテクノロジー社製）を用いて行った結果、選択した観察ポイントでは、主層と厚みが約１６０ｎｍの最表層の間には、厚みが約６０ｎｍの層が存在することがわかった。また、この層は非晶質であることがわかった（電子線回折分析による）。改質層中の非晶質層と最表層の組成を、エネルギー分散型Ｘ線分析装置（ＥＤＸ：ＮＯＲＡＮ社製）を用いて分析した結果、改質層中の最表層はＲがほとんど存在しない酸化鉄から構成されること、非晶質層はＲとＦｅの複合酸化物から構成されることがわかった。また、表面改質された磁石体試験片の改質層中の最表層を、表面からＸ線回折装置（ＲＩＮＴ２４００：Ｒｉｇａｋｕ社製）を用いて分析した結果を図３に示す。図３から明らかなように、改質層中の最表層はヘマタイトを主体とする層であることがわかった（図中の◆：ヘマタイトのピーク）。このヘマタイトを主体とする最表層は、熱処理によって素材の主相（Ｒ２Ｆｅ１４Ｂ）の一部が分解されたことでＦｅが主相から流出するとともに酸化して形成されたものであると推測された。さらに、表面改質された磁石体試験片の改質層中の最表層を、表面からラマン分光分析装置（Ｈｏｌｏ Ｌａｂ ５０００Ｒ：ＫＡＩＳＥＲ ＯＰＴＩＣＡＬ ＳＹＳＴＥＭ社製）を用いて分析した結果、最表層に構成成分として含まれる酸化鉄のすべて（１００質量％）がヘマタイトであること、ヘマタイトによる表面被覆率は９５．７％であることがわかった。また、この表面改質された磁石体試験片の磁気特性を磁気測定装置を用いて測定した結果、固有保磁力は２３５４ｋＡ／ｍであり、酸化熱処理による磁気特性の劣化は認められなかった。
(Example 1) Rare earth sintered magnet having an oxygen content of less than 0.3% by mass (No. 1)
Nd: 17.4, Pr: 5.4, Dy: 7.6, B: 1.00, Co: 0.9, Al: 0.2, Ga: 0.05, Cu: 0.1, balance: An alloy flake having a composition of Fe (unit: mass%) and having a thickness of 0.2 to 0.3 mm was produced by strip casting.
Next, this alloy flake was filled in a container and accommodated in a hydrogen treatment apparatus. Then, the hydrogen treatment apparatus was filled with hydrogen gas at a pressure of 500 kPa, so that hydrogen was occluded in the alloy flakes at room temperature and then released. By performing such a hydrogen treatment, the alloy flakes were embrittled to produce an amorphous powder having a size of about 0.15 to 0.2 mm.
After adding 0.04 wt% zinc stearate as a grinding aid to the coarsely pulverized powder produced by the above hydrogen treatment and mixing, an average powder particle size of about 3 μm is obtained by performing a pulverization step with a jet mill device. A fine powder was prepared.
The fine powder thus produced was molded by a press apparatus to produce a powder compact. Specifically, the powder particles were compressed in a magnetic field-oriented state in an applied magnetic field and pressed. Thereafter, the molded body was extracted from the press apparatus, and a sintering process was performed at 1050 ° C. for 4 hours in a vacuum furnace to obtain a sintered body block. It was 0.24 mass% when the oxygen content of this sintered compact block was measured with the oxygen and nitrogen analyzer (EMGA-620W: product made by HORIBA) (this oxygen content is maintained until it heat-processes).
The surface of the obtained sintered body block is subjected to surface grinding using a surface grinding machine (manufactured by Daisho Seiki Co., Ltd.) (grinding wheel count: # 100, grinding wheel rotation speed: 1500 rpm, magnet to grinding machine) A sintered magnet (hereinafter referred to as “magnet body test piece”) whose dimensions were adjusted to a thickness of 6 mm × length 7 mm × width 7 mm was obtained.
The magnet specimen was washed with alcohol and then subjected to an aging treatment at 500 ° C. for 2.5 hours in a vacuum. As a result of measuring the magnetic characteristics of the magnet specimen using a magnetometer (TPM-2-10: manufactured by Toei Kogyo Co., Ltd., the same shall apply hereinafter), the intrinsic coercive force was 2353 kA / m.
Next, with respect to the magnet body test piece subjected to the aging treatment, at 410 ° C. in an atmosphere of dew point 0 ° C. in the atmosphere (oxygen partial pressure 20000 Pa, water vapor partial pressure 600 Pa, oxygen partial pressure / water vapor partial pressure = 33.3). By performing heat treatment for 2 hours, a surface-modified magnet body test piece was obtained. The temperature of the magnet specimen from room temperature to the heat treatment temperature is about 900 ° C./hour in an atmosphere with a dew point of −40 ° C. (oxygen partial pressure 20000 Pa, water vapor partial pressure 12.9 Pa). (The temperature rising time was 25 minutes). Further, the temperature drop after the heat treatment was performed in the same atmosphere. After this magnet body test piece is resin-filled and polished, a sample is prepared using an ion beam cross-section processing apparatus (SM09010: manufactured by JEOL Ltd.), and a field emission scanning electron microscope (S-4300: manufactured by Hitachi High-Technologies Corporation) is used. The results of cross-sectional observation are shown in FIG. As is clear from FIG. 2, at this observation point, the thickness of the modified layer formed on the surface of the magnet test piece is about 4.7 μm, and this modified layer is composed of a plurality of layers, at least the main layer. It was found that there was a layer and an outermost layer having a thickness of about 140 nm. Further, in the modified layer, a layered structure composed of R having a thickness of about 100 nm and a length of about 5 μm (an R-concentrated layer having an R composition of 85% by mass or more) extends in the horizontal direction (approximately the same as the surface of the magnet body). It was confirmed that the film was formed in a parallel direction. Table 1 shows the results of analyzing the composition of the main layer in the modified layer and the composition of the material (magnet body test piece) using an energy dispersive X-ray analyzer (Genesis 2000: manufactured by EDAX). As is clear from Table 1, it was found that the main layer in the modified layer had a very high oxygen content while the Fe content was lower than that of the raw material. Furthermore, as a result of performing cross-sectional observation near the surface of the surface-modified magnetic body test piece using a transmission electron microscope (HF2100: manufactured by Hitachi High-Technology Corporation), the main layer and thickness are selected at the selected observation point. It was found that there was a layer having a thickness of about 60 nm between the outermost layers of about 160 nm. This layer was found to be amorphous (by electron diffraction analysis). As a result of analyzing the composition of the amorphous layer and the outermost layer in the modified layer using an energy dispersive X-ray analyzer (EDX: manufactured by NORAN), there is almost no R in the outermost layer in the modified layer. It was found that it was composed of iron oxide, and the amorphous layer was composed of a composite oxide of R and Fe. Moreover, the result of having analyzed the outermost layer in the modified layer of the surface-modified magnet test piece from the surface using an X-ray diffractometer (RINT2400: manufactured by Rigaku) is shown in FIG. As is apparent from FIG. 3, it was found that the outermost layer in the modified layer was a layer mainly composed of hematite (♦ in the figure: peak of hematite). The outermost layer mainly composed of hematite is formed by oxidizing part of the main phase (R 2 Fe 14 B) of the raw material by heat treatment, so that Fe flows out of the main phase and is oxidized. Was guessed. Furthermore, as a result of analyzing the outermost layer in the modified layer of the surface-modified magnetic body test piece from the surface using a Raman spectroscopic analyzer (manufactured by Holo Lab 5000R: KAISER OPTICAL SYSTEM), a constituent component is formed on the outermost layer. It was found that all (100% by mass) of the iron oxide contained as hematite was hematite and the surface coverage by hematite was 95.7%. Further, as a result of measuring the magnetic characteristics of the surface-modified magnetic body specimen using a magnetometer, the intrinsic coercive force was 2354 kA / m, and no deterioration of the magnetic characteristics due to the oxidation heat treatment was observed.
（実施例２）磁石の酸素含有量が０．３質量％未満の希土類系焼結磁石（その２）
実施例１と同じ方法で得た焼結体ブロック（酸素含有量は０．２４質量％：測定方法は実施例１と同じ、熱処理を行うまでこの酸素含有量を維持）に対し、実施例１と同じ条件で時効処理を行った後、実施例１と同じ条件で平面研削加工を行い、厚さ６ｍｍ×縦７ｍｍ×横７ｍｍに寸法調整した焼結磁石（以下、「磁石体試験片」と称する）を得た。この磁石体試験片の磁気特性を、アルコール洗浄した後、磁気測定装置を用いて測定した結果、固有保磁力は２３０９ｋＡ／ｍであった。この磁石体試験片をアルコール洗浄した後、熱処理温度を４２０℃とし、熱処理時間を３０分とすること以外は実施例１と同じ条件で熱処理を行うことで、表面改質された磁石体試験片を得た。この磁石体試験片について実施例１と同様の評価を行ったところ、磁石体試験片の表面に形成された改質層は、厚みが約１．９μｍであり、その構成は実施例１で得た表面改質された磁石体試験片における改質層と同様であることがわかった（最表層の厚み：約４０ｎｍ）。この表面改質された磁石体試験片の磁気特性を磁気測定装置を用いて測定した結果、固有保持力は２３１１ｋＡ／ｍであり、酸化熱処理による磁気特性の劣化は認められなかった。
(Example 2) Rare earth sintered magnet having an oxygen content of less than 0.3% by mass (No. 2)
In contrast to the sintered body block obtained by the same method as in Example 1 (oxygen content is 0.24% by mass: the measurement method is the same as in Example 1, this oxygen content is maintained until heat treatment is performed). After performing the aging treatment under the same conditions as in Example 1, a surface grinding process was performed under the same conditions as in Example 1, and the sintered magnets (hereinafter referred to as “magnet body specimens”) adjusted in dimensions to a thickness of 6 mm × length of 7 mm × width of 7 mm Obtained). As a result of measuring the magnetic properties of this magnet body test piece with alcohol after washing with alcohol, the intrinsic coercive force was 2309 kA / m. This magnet body test piece was subjected to alcohol cleaning, and then subjected to a heat treatment under the same conditions as in Example 1 except that the heat treatment temperature was 420 ° C. and the heat treatment time was 30 minutes. Got. When this magnet body test piece was evaluated in the same manner as in Example 1, the modified layer formed on the surface of the magnet body test piece had a thickness of about 1.9 μm, and the configuration was obtained in Example 1. It was found that this was the same as the modified layer in the surface-modified magnetic body specimen (the thickness of the outermost layer: about 40 nm). As a result of measuring the magnetic properties of the surface-modified magnetic body specimen using a magnetometer, the intrinsic coercive force was 2311 kA / m, and no deterioration of the magnetic properties due to oxidation heat treatment was observed.
（実施例３）磁石の酸素含有量が０．３質量％未満の希土類系焼結磁石（その３）
Ｎｄ：１６．４、Ｐｒ：４．７、Ｄｙ：９．４、Ｂ：１．００、Ｃｏ：２．０、Ａｌ：０．１５、Ｇａ：０．０７、Ｃｕ：０．１、残部：Ｆｅ（単位は質量％）の組成を有する厚さ０．２〜０．３ｍｍの合金薄片をストリップキャスト法により作製した。
次に、この合金薄片を容器に充填し、水素処理装置内に収容した。そして、水素処理装置内を圧力５００ｋＰａの水素ガスで満たすことにより、室温で合金薄片に水素吸蔵させた後、放出させた。このような水素処理を行うことにより、合金薄片を脆化し、大きさ約０．１５〜０．２ｍｍの不定形粉末を作製した。
上記の水素処理により作製した粗粉砕粉末に対し粉砕助剤として０．０４ｗｔ％のステアリン酸亜鉛を添加し混合した後、ジェットミル装置による粉砕工程を行うことにより、平均粉末粒径が約３μｍの微粉末を作製し、酸化防止のために鉱物油中に回収した。
こうして作製した微粉末をプレス装置により成形し、粉末成形体を作製した。具体的には、印加磁界中で粉末粒子を磁界配向した状態で圧縮し、プレス成形を行った。その後、成形体をプレス装置から抜き出し、真空炉により２００℃で２時間の脱脂工程と１０５０℃で４時間の焼結工程を行い、焼結体ブロックを得た。この焼結体ブロックの酸素含有量を実施例１と同じ方法で測定したところ、０．１３質量％であった（熱処理を行うまでこの酸素含有量を維持）。
得られた焼結体ブロックに対し、真空中にて４８０℃で８時間の時効処理を行った後、実施例１と同じ条件で平面研削加工を行い、厚さ６ｍｍ×縦７ｍｍ×横７ｍｍに寸法調整した焼結磁石（以下、「磁石体試験片」と称する）を得た。この磁石体試験片の磁気特性を、アルコール洗浄した後、磁気測定装置を用いて測定した結果、固有保磁力は２４０３ｋＡ／ｍであった。
次に、この磁石体試験片をアルコール洗浄した後、熱処理温度を４２０℃とし、熱処理時間を３０分とすること以外は実施例１と同じ条件で熱処理を行うことで、表面改質された磁石体試験片を得た。この磁石体試験片について実施例１と同様の評価を行ったところ、磁石体試験片の表面に形成された改質層は、厚みが約２．１μｍであり、その構成は実施例１で得た表面改質された磁石体試験片における改質層と同様であることがわかった（最表層の厚み：約６５ｎｍ）。この表面改質された磁石体試験片の磁気特性を磁気測定装置を用いて測定した結果、固有保磁力は２４１１ｋＡ／ｍであり、酸化熱処理による磁気特性の劣化は認められなかった。
(Example 3) Rare earth sintered magnet having an oxygen content of less than 0.3% by mass (No. 3)
Nd: 16.4, Pr: 4.7, Dy: 9.4, B: 1.00, Co: 2.0, Al: 0.15, Ga: 0.07, Cu: 0.1, balance: An alloy flake having a composition of Fe (unit: mass%) and having a thickness of 0.2 to 0.3 mm was produced by strip casting.
Next, this alloy flake was filled in a container and accommodated in a hydrogen treatment apparatus. Then, the hydrogen treatment apparatus was filled with hydrogen gas at a pressure of 500 kPa, so that hydrogen was occluded in the alloy flakes at room temperature and then released. By performing such a hydrogen treatment, the alloy flakes were embrittled to produce an amorphous powder having a size of about 0.15 to 0.2 mm.
After adding 0.04 wt% zinc stearate as a grinding aid to the coarsely pulverized powder produced by the above hydrogen treatment and mixing, an average powder particle size of about 3 μm is obtained by performing a pulverization process with a jet mill device. A fine powder was made and recovered in mineral oil to prevent oxidation.
The fine powder thus produced was molded by a press apparatus to produce a powder compact. Specifically, the powder particles were compressed in a magnetic field-oriented state in an applied magnetic field and pressed. Thereafter, the molded body was extracted from the press apparatus, and a degreasing process at 200 ° C. for 2 hours and a sintering process at 1050 ° C. for 4 hours were performed in a vacuum furnace to obtain a sintered body block. When the oxygen content of the sintered body block was measured by the same method as in Example 1, it was 0.13% by mass (maintaining this oxygen content until heat treatment was performed).
The obtained sintered body block was subjected to an aging treatment at 480 ° C. for 8 hours in a vacuum, and then surface grinding was performed under the same conditions as in Example 1 to obtain a thickness of 6 mm × length of 7 mm × width of 7 mm. A sintered magnet having a dimension adjusted (hereinafter referred to as “magnet specimen”) was obtained. As a result of measuring the magnetic characteristics of this magnet body test piece with alcohol after washing with alcohol, the intrinsic coercive force was 2403 kA / m.
Next, after the magnet body test piece was washed with alcohol, the surface-modified magnet was subjected to heat treatment under the same conditions as in Example 1 except that the heat treatment temperature was 420 ° C. and the heat treatment time was 30 minutes. A body specimen was obtained. When this magnet body test piece was evaluated in the same manner as in Example 1, the modified layer formed on the surface of the magnet body test piece had a thickness of about 2.1 μm, and the configuration was obtained in Example 1. It was found that this was the same as the modified layer in the surface-modified magnetic body specimen (the thickness of the outermost layer: about 65 nm). As a result of measuring the magnetic properties of the surface-modified magnetic body specimen using a magnetometer, the intrinsic coercive force was 2411 kA / m, and no deterioration of the magnetic properties due to oxidation heat treatment was observed.
（比較例１）磁石の酸素含有量が０．３質量％未満の希土類系焼結磁石
実施例１と同じ方法で得た焼結体ブロック（酸素含有量は０．２４質量％：測定方法は実施例１と同じ、熱処理を行うまでこの酸素含有量を維持）に対し、実施例１と同じ条件で平面研削加工を行い、厚さ６ｍｍ×縦７ｍｍ×横７ｍｍに寸法調整した焼結磁石（以下、「磁石体試験片」と称する）を得た。この磁石体試験片をアルコール洗浄した後、実施例１と同じ条件で時効処理を行った。この磁石体試験片の磁気特性を磁気測定装置を用いて測定した結果、固有保磁力は２３５３ｋＡ／ｍであった。次に、時効処理を行った磁石体試験片に対し、熱処理温度を３６０℃とすること以外は実施例１と同じ条件で熱処理を行うことで、表面改質された磁石体試験片を得た。この磁石体試験片について実施例１と同様の評価を行ったところ、磁石体試験片の表面に形成された改質層は、厚みが約２．２μｍであり、その構成は実施例１で得た表面改質された磁石体試験片における改質層と同様であることがわかった（最表層の厚み：約７０ｎｍ）。しかしながら、この表面改質された磁石体試験片の磁気特性を磁気測定装置を用いて測定した結果、固有保磁力は２２３５ｋＡ／ｍであり、酸化熱処理による磁気特性の大幅な劣化が認められた。
Comparative Example 1 Rare Earth Sintered Magnet with Magnet Oxygen Content of Less than 0.3% by Mass Sintered body block obtained by the same method as Example 1 (oxygen content is 0.24% by mass: measurement method is As in Example 1, this oxygen content is maintained until heat treatment is performed, and surface grinding is performed under the same conditions as in Example 1, and a sintered magnet (size 6 mm × length 7 mm × width 7 mm) is adjusted ( Hereinafter, referred to as “magnet specimen”. After this magnet body test piece was washed with alcohol, an aging treatment was performed under the same conditions as in Example 1. As a result of measuring the magnetic properties of this magnet body test piece using a magnetometer, the intrinsic coercive force was 2353 kA / m. Next, the magnet body test piece subjected to the aging treatment was subjected to heat treatment under the same conditions as in Example 1 except that the heat treatment temperature was set to 360 ° C., thereby obtaining a surface-modified magnet body test piece. . When this magnet body test piece was evaluated in the same manner as in Example 1, the modified layer formed on the surface of the magnet body test piece had a thickness of about 2.2 μm, and the configuration was obtained in Example 1. It was found that this was the same as the modified layer in the surface-modified magnetic body specimen (thickness of the outermost layer: about 70 nm). However, as a result of measuring the magnetic properties of the surface-modified magnetic body test piece using a magnetometer, the intrinsic coercive force was 2235 kA / m, and a significant deterioration of the magnetic properties due to oxidation heat treatment was recognized.
乾燥・湿潤サイクル試験による評価：
ＪＩＳ Ｈ８５０２−１９９９に基づく中性塩水噴霧サイクル試験方法を参考にし、塩水噴霧を除いた乾燥と湿潤だけのサイクル試験（サイクル数：３）を、実施例１〜実施例３、比較例１でそれぞれ得た表面改質された磁石体試験片に対して行い、試験後のレイティングナンバ評価（ＪＩＳ Ｈ８５０２−１９９９に基づく腐食欠陥評価）を実施した。結果を表２に示す。また、表２には、実施例１と同じ方法で得た時効処理を行った磁石体試験片（熱処理前のもの）の評価結果をあわせて示す（参考例）。
Evaluation by dry / wet cycle test:
With reference to the neutral salt spray cycle test method based on JIS H8502-1999, a cycle test (cycle number: 3) only for drying and wetting without salt spray was performed in Examples 1 to 3 and Comparative Example 1, respectively. It performed with respect to the obtained magnetic body test piece by which surface modification was carried out, and the rating number evaluation (corrosion defect evaluation based on JISH8502-1999) after the test was implemented. The results are shown in Table 2. Table 2 also shows the evaluation results of magnet body test pieces (before heat treatment) subjected to the aging treatment obtained by the same method as in Example 1 (reference example).
表２から明らかなように、実施例１〜実施例３の本発明の方法によって表面改質を行った磁石体試験片は、上述した通り、優れた磁気特性を有するとともに、乾燥・湿潤サイクル試験後も十分な耐食性を有していた。一方、比較例１の方法によって表面改質を行った磁石体試験片は、乾燥・湿潤サイクル試験後も十分な耐食性を有していたが、上述した通り、酸化熱処理による磁気特性の大幅な劣化が認められた。以上の結果には、酸化熱処理を行う前に磁石表面に対して平面研削加工を行ったことで、磁石の表面組成が均一化され、これにより磁石の表面全体に均一な酸化熱処理を行うことが可能となり、優れた耐食性を発揮する、少なくとも酸素の含量が素材よりも多い主層と、ＲとＦｅの複合酸化物から構成される非晶質層と、安定なヘマタイトを主体とする酸化鉄を構成成分とする最表層を有する構成からなる改質層が、磁石の表面全体にわたって形成されたことが寄与していると考えられた。また、改質層中に確認されたＲからなる層状構造は、熱処理によって素材の主相の一部が分解されたことで主相から流出したＲや、熱処理によって液相化した粒界成分が、素材と改質層の熱膨張率の違いにより改質層中に僅かに発生したクラック部分に供給されて形成されたものであると推測されたが、このＲからなる層状構造も、改質層の耐食性に寄与していることが考えられた。 As is apparent from Table 2, the magnet body test piece subjected to surface modification by the method of the present invention in Examples 1 to 3 has excellent magnetic properties as described above, and also has a dry / wet cycle test. Later, it had sufficient corrosion resistance. On the other hand, the magnet body test piece subjected to surface modification by the method of Comparative Example 1 had sufficient corrosion resistance even after the dry / wet cycle test, but as described above, the magnetic properties were greatly deteriorated by the oxidation heat treatment. Was recognized. The above results show that the surface composition of the magnet is made uniform by performing surface grinding on the surface of the magnet before performing the oxidation heat treatment, thereby performing a uniform oxidation heat treatment on the entire surface of the magnet. A main layer having at least oxygen content higher than that of the material, an amorphous layer composed of a composite oxide of R and Fe, and iron oxide mainly composed of stable hematite. It was thought that it contributed that the modified layer which consists of the structure which has the outermost layer as a structural component was formed over the whole surface of the magnet. In addition, the layered structure composed of R confirmed in the modified layer has R flowing out of the main phase due to the decomposition of part of the main phase of the material by heat treatment, and the grain boundary component that has become liquid phase by heat treatment. , It was speculated that it was formed by being supplied to the crack part slightly generated in the modified layer due to the difference in thermal expansion coefficient between the raw material and the modified layer. It was thought that it contributed to the corrosion resistance of the layer.
（実施例４）磁石の酸素含有量が０．３質量％以上の希土類系焼結磁石
Ｎｄ：１８．６、Ｐｒ：５．５、Ｄｙ：７．１、Ｂ：１．００、Ｃｏ：０．９、Ａｌ：０．２、Ｃｕ：０．１、残部：Ｆｅ（単位は質量％）の組成を有する厚さ０．２〜０．３ｍｍの合金薄片をストリップキャスト法により作製した。
次に、この合金薄片を容器に充填し、水素処理装置内に収容した。そして、水素処理装置内を圧力５００ｋＰａの水素ガスで満たすことにより、室温で合金薄片に水素吸蔵させた後、放出させた。このような水素処理を行うことにより、合金薄片を脆化し、大きさ約０．１５〜０．２ｍｍの不定形粉末を作製した。
上記の水素処理により作製した粗粉砕粉末に対し粉砕助剤として０．０４ｗｔ％のステアリン酸亜鉛を添加し混合した後、ジェットミル装置による粉砕工程を行うことにより、平均粉末粒径が約３μｍの微粉末を作製した。
こうして作製した微粉末をプレス装置により成形し、粉末成形体を作製した。具体的には、印加磁界中で粉末粒子を磁界配向した状態で圧縮し、プレス成形を行った。その後、成形体をプレス装置から抜き出し、真空炉により１０５０℃で４時間の焼結工程を行い、焼結体ブロックを得た。この焼結体ブロックの酸素含有量を実施例１と同じ方法で測定したところ、０．４３質量％であった（熱処理を行うまでこの酸素含有量を維持）。
得られた焼結体ブロックの表面に対し、実施例１と同じ条件で平面研削加工を行い、厚さ６ｍｍ×縦７ｍｍ×横７ｍｍに寸法調整した焼結磁石（以下、「磁石体試験片」と称する）を得た。この磁石体試験片をアルコール洗浄した後、実施例１と同じ条件で時効処理を行った。この磁石体試験片の磁気特性を実施例１と同様にして測定した結果、固有保磁力は２１３６ｋＡ／ｍであった。次に、時効処理を行った磁石体試験片に対し、熱処理温度を３６０℃とすること以外は実施例１と同じ条件で熱処理を行うことで、表面改質された磁石体試験片を得た。この磁石体試験片について実施例１と同様の評価を行ったところ、磁石体試験片の表面に形成された改質層は、厚みが約２．０μｍであり、その構成は実施例１で得た表面改質された磁石体試験片における改質層と同様であることがわかった（最表層の厚み：約９０ｎｍ）。この表面改質された磁石体試験片の磁気特性を実施例１と同様にして測定した結果、固有保磁力は２１３０ｋＡ／ｍであり、酸化熱処理による磁気特性の劣化はほとんど認められなかった。
(Example 4) Rare earth sintered magnet having an oxygen content of 0.3% by mass or more Nd: 18.6, Pr: 5.5, Dy: 7.1, B: 1.00, Co: 0 .9, Al: 0.2, Cu: 0.1, balance: Fe (unit: mass%), and a 0.2 to 0.3 mm thick alloy flake was prepared by strip casting.
Next, this alloy flake was filled in a container and accommodated in a hydrogen treatment apparatus. Then, the hydrogen treatment apparatus was filled with hydrogen gas at a pressure of 500 kPa, so that hydrogen was occluded in the alloy flakes at room temperature and then released. By performing such a hydrogen treatment, the alloy flakes were embrittled to produce an amorphous powder having a size of about 0.15 to 0.2 mm.
After adding 0.04 wt% zinc stearate as a grinding aid to the coarsely pulverized powder produced by the above hydrogen treatment and mixing, an average powder particle size of about 3 μm is obtained by performing a pulverization step with a jet mill device. A fine powder was prepared.
The fine powder thus produced was molded by a press apparatus to produce a powder compact. Specifically, the powder particles were compressed in a magnetic field-oriented state in an applied magnetic field and pressed. Thereafter, the molded body was extracted from the press apparatus, and a sintering process was performed at 1050 ° C. for 4 hours in a vacuum furnace to obtain a sintered body block. When the oxygen content of this sintered body block was measured by the same method as in Example 1, it was 0.43% by mass (this oxygen content was maintained until heat treatment was performed).
The surface of the obtained sintered block was subjected to surface grinding under the same conditions as in Example 1, and the sintered magnet (hereinafter referred to as “magnet test piece”) whose dimensions were adjusted to a thickness of 6 mm × length of 7 mm × width of 7 mm. Called). After this magnet body test piece was washed with alcohol, an aging treatment was performed under the same conditions as in Example 1. As a result of measuring the magnetic properties of this magnet body test piece in the same manner as in Example 1, the intrinsic coercive force was 2136 kA / m. Next, the magnet body test piece subjected to the aging treatment was subjected to heat treatment under the same conditions as in Example 1 except that the heat treatment temperature was set to 360 ° C., thereby obtaining a surface-modified magnet body test piece. . When this magnet body test piece was evaluated in the same manner as in Example 1, the modified layer formed on the surface of the magnet body test piece had a thickness of about 2.0 μm, and the configuration was obtained in Example 1. It was found that this was the same as the modified layer in the surface-modified magnetic body specimen (the thickness of the outermost layer: about 90 nm). As a result of measuring the magnetic properties of the surface-modified magnetic body test piece in the same manner as in Example 1, the intrinsic coercive force was 2130 kA / m, and almost no deterioration of the magnetic properties due to the oxidation heat treatment was observed.
（参考例１）磁石の酸素含有量と熱処理が及ぼす磁気特性への影響との関係の検討
実施例１と同じ方法で得た時効処理を行った磁石体試験片（以下、「磁石体試験片１」と称する）と、実施例４と同じ方法で得た時効処理を行った磁石体試験片（以下、「磁石体試験片２」と称する）のそれぞれについて、２４０℃〜４６０℃の範囲の任意の温度において真空中で２時間の熱処理を行った後の磁気特性を磁気測定装置（ＴＰＭ−２−１０：東英工業社製）を用いて測定し、熱処理を行う前の磁気特性と比較することで、熱処理が及ぼす磁気特性への影響を調べた。結果を図４に示す。なお、図４の縦軸は固有保持力の劣化率であり、下記の数式で求めたものである。
固有保磁力劣化率（％）＝（（Ａ−Ｂ）／Ａ）×１００
Ａ：熱処理前の固有保磁力，Ｂ：熱処理後の固有保磁力
図４から明らかなように、磁石体試験片１と磁石体試験片２とでは、熱処理が及ぼす磁気特性への影響が温度によって全く異なり、磁石体試験片１の磁気特性に悪影響を与えない温度範囲（４００℃以上）での熱処理によって磁石体試験片２の磁気特性は劣化するのに対し、磁石体試験片２の磁気特性に悪影響を与えない温度範囲（４００℃未満）での熱処理によって磁石体試験片１の磁気特性は劣化することがわかった。この知見を元にさらに詳細な検討を行った結果、磁石の酸素含有量が０．３質量％未満の場合において磁石体試験片１と同様の熱処理温度に依存した磁気特性の変化を示すことが判明したことから、磁石の酸素含有量が０．３質量％未満であるか０．３質量％以上であるかを指標に、熱処理の温度を４００℃以上にするか４００℃未満にするかを決定することで、磁気特性に悪影響を与えることなく熱処理が行えることがわかった。
(Reference Example 1) Examination of the relationship between the oxygen content of a magnet and the effect on the magnetic properties of heat treatment A magnet test piece (hereinafter referred to as “magnet test piece”) subjected to aging treatment obtained by the same method as in Example 1. 1 ”) and each of the magnet specimens (hereinafter referred to as“ magnet specimen 2 ”) subjected to the aging treatment obtained by the same method as in Example 4 in the range of 240 ° C. to 460 ° C. The magnetic properties after heat treatment for 2 hours in vacuum at an arbitrary temperature are measured using a magnetometer (TPM-2-10: manufactured by Toei Kogyo Co., Ltd.) and compared with the magnetic properties before heat treatment. The effect of heat treatment on the magnetic properties was investigated. The results are shown in FIG. In addition, the vertical axis | shaft of FIG. 4 is a deterioration rate of intrinsic | native holding force, and was calculated | required with the following numerical formula.
Inherent coercive force deterioration rate (%) = ((A−B) / A) × 100
A: Intrinsic coercive force before heat treatment, B: Intrinsic coercivity after heat treatment As is apparent from FIG. 4, the magnetic body test piece 1 and the magnetic body test piece 2 affect the magnetic properties of the heat treatment depending on the temperature. The magnetic properties of the magnet specimen 2 are deteriorated by heat treatment in a temperature range (400 ° C. or higher) that does not adversely affect the magnetic characteristics of the magnet specimen 1, whereas the magnetic characteristics of the magnet specimen 2 are deteriorated. It was found that the magnetic properties of the magnet specimen 1 deteriorated by heat treatment in a temperature range (less than 400 ° C.) that does not adversely affect As a result of further detailed examination based on this knowledge, when the oxygen content of the magnet is less than 0.3% by mass, the magnetic property change depending on the heat treatment temperature similar to that of the magnet specimen 1 is shown. From the fact that the oxygen content of the magnet is less than 0.3% by mass or more than 0.3% by mass, it is determined whether the heat treatment temperature is 400 ° C. or more or less than 400 ° C. By deciding, it was found that heat treatment can be performed without adversely affecting the magnetic properties.
本発明は、湿度が変動する環境においても十分な耐食性が酸化熱処理によって付与されているとともに、酸化熱処理による磁気特性の低下が抑制された希土類系焼結磁石の製造方法を提供することができる点において産業上の利用可能性を有する。
The present invention can provide a method for producing a rare earth-based sintered magnet in which sufficient corrosion resistance is imparted by an oxidation heat treatment even in an environment where the humidity varies, and a decrease in magnetic properties due to the oxidation heat treatment is suppressed. Has industrial applicability.
Claims (9)
A rare earth-based sintered magnet having a surface modified, wherein the rare-earth sintered magnet is 25% to 40% by mass of rare earth element: R, 0.6% to 1.6% by mass of B (provided that Some may be substituted by C), 0% by mass to 1.0% by mass of Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag , In, Sn, Hf, Ta, W, Pb, and Bi, at least one additive element selected from the group consisting of M and M, and the balance is 50% by mass or less substituted with Co and / or Ni The oxygen content of the magnet is 0.3% by mass to 0.6% by mass, and the surface-modified portions are in order from the inner side of the magnet to R. , Fe, B and a main layer containing oxygen, at least R, Fe and Amorphous layer containing oxygen, the outermost layer of the surface-modified rare earth metal-based sintered magnet, comprising the surface-modified layer comprising at least three layers including an iron oxide mainly composed of hematite as a constituent.
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| JP2012204486A (en) * | 2011-03-24 | 2012-10-22 | Hitachi Metals Ltd | SURFACE-MODIFIED R-Fe-B BASED SINTERED MAGNET AND PRODUCTION METHOD THEREFOR |
| JP5900335B2 (en) * | 2010-06-30 | 2016-04-06 | 日立金属株式会社 | Method for producing surface-modified rare earth sintered magnet |
| JP2020043151A (en) * | 2018-09-06 | 2020-03-19 | 大同特殊鋼株式会社 | Rare-earth sinter magnet and manufacturing method therefor |
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