JP3547016B2

JP3547016B2 - Rare earth bonded magnet and method of manufacturing the same

Info

Publication number: JP3547016B2
Application number: JP29477093A
Authority: JP
Inventors: 裕和金清; 哲広沢
Original assignee: Neomax Co Ltd
Current assignee: Hitachi Metals Ltd
Priority date: 1993-10-28
Filing date: 1993-10-28
Publication date: 2004-07-28
Anticipated expiration: 2019-07-28
Also published as: JPH07130514A

Description

【0001】
【産業上の利用分野】
この発明は、マグネットロール、スピーカー、磁気センサー用磁気回路、各種メーターおよびフォーカス用マグネットならびにモーターやアクチュエーターなどに最適な希土類ボンド磁石とその製造方法に係り、希土類元素の含有量が少ない特定組成の Fe-Cr-B-R-M(M=Al,Si,Pb)合金溶湯を回転ロールを用いた超急冷法、スプラット急冷法、ガスアトマイズ法あるいはこれらの併用法にてアモルファス組織とし、特定の熱処理にて体心正方晶Fe₃P型結晶構造を有する鉄を主成分とするホウ化物相とNd₂Fe₁₄B型結晶構造の構成相との微細結晶集合体からなる合金粉末を得、これを樹脂にて結合することにより、ハードフェライト磁石では得られなかった5kG以上の残留磁束密度Brを有するFe-B-R系ボンド磁石を得る希土類ボンド磁石とその製造方法に関する。
【０００２】
【従来の技術】
家電用ステッピングモーター、電装品用モーター、アクチュエーターなどに使用される永久磁石は主にハードフェライト磁石に限定されていたが、低温でのｉＨｃ低下に伴う低温減磁特性が有ること、セラミックス材質のために機械的強度が低くて割れ、欠けが発生し易いこと、複雑な形状が得難いことなどの問題があった。
【０００３】
今日、自動車は省資源のため車両の軽量化による燃費の向上が強く要求されており、自動車用電装品はより一層の小型、軽量化が求められている。
また、自動車用電装品以外の家電用モーターなどの用途においても、性能対重量比を最大にするための設計が検討されており、現在のモーター構造では磁石材料としてＢｒが５〜７ｋＧ程度のものが最適とされている。
すなわち、使用する磁石材料のＢｒが８ｋＧ以上の場合、現在のモーター構造では磁路となる回転子やステーターの鉄板の断面積を増大させる必要があり、重量の増大を招来するが、Ｂｒが５〜７ｋＧであれば性能対重量比を最大にすることができる。
【０００４】
従って、小型モーター用の磁石材料は磁気特性的には特に５ｋＧ以上の残留磁束密度Ｂｒが要求されているが、従来のハードフェライト磁石では得ることができない。
例えばＮｄ−Ｆｅ−Ｂ系ボンド磁石ではかかる磁気特性を満足するが、金属の分離精製や還元反応に多大の工程並びに大規模な設備を要するＮｄ等を１０〜１５ａｔ％含有しているため、ハードフェライト磁石に比較して著しく高価であり、現在のところ大量生産が可能で安価に提供できるＢｒが５〜７ｋＧ程度の磁石材料は、見出されていない。
【０００５】
【発明が解決しようとする課題】
一方、Ｎｄ−Ｆｅ−Ｂ系磁石において、最近、Ｎｄ₄Ｆｅ₇₇Ｂ₁₉（ａｔ％）近傍でＦｅ₃Ｂ型化合物を主相とする磁石材料が提案（Ｒ．Ｃｏｅｈｏｏｒｎ等、Ｊ．ｄｅＰｈｙｓ．，Ｃ８，１９８８，６６９〜６７０頁）された。この磁石材料はアモルファスリボンを熱処理することにより、準安定なＦｅ₃Ｂと準安定相のＮｄ₂Ｆｅ₁₄Ｂの結晶集合組織を有する磁石材料が得られるが、ｉＨｃが２〜３ｋＯｅ程度と低く、またこのｉＨｃを得るための熱処理条件が狭く限定され、工業生産上実用的でない。
【０００６】
このＦｅ₃Ｂ型化合物を主相とする磁石材料に添加元素を加えて多成分化し、性能向上を図った研究が発表されている。その１つは希土類元素にＮｄのほかにＤｙとＴｂを用いてｉＨｃの向上を図るものであるが、高価な元素を添加する問題のほか、添加希土類元素はその磁気モーメントがＮｄやＦｅの磁気モーメントと反平行して結合するため磁化が減少する問題がある（Ｒ．Ｃｏｅｈｏｏｒｎ、Ｊ．Ｍａｇｎ，Ｍａｇｎ，Ｍａｔ．、８３（１９９０）２２８〜２３０頁）。
【０００７】
他の研究（ＳｈｅｎＢａｏ−ｇｅｎら，Ｊ．Ｍａｇｎ，Ｍａｇｎ，Ｍａｔ．、８９（１９９１）３３５〜３４０頁）として、Ｆｅの一部をＣｏにて置換してキュリー温度を上昇させ、ｉＨｃの温度係数を改善するものであるが、Ｃｏの添加にともないＢｒを低下させる問題がある。
【０００８】
いずれにしてもＦｅ₃Ｂ型Ｎｄ−Ｆｅ−Ｂ系磁石は、超急冷法によりアモルファス化した後、熱処理してハード磁石材料化できるが、ｉＨｃが低く、かつ前記熱処理条件が狭く、安定した工業生産ができず、ハードフェライト磁石の代替えとして安価に提供することができない。
【０００９】
この発明は、Ｆｅ₃Ｂ型Ｆｅ−Ｂ−Ｒ系磁石（Ｒは希土類元素）に着目して、ｉＨｃを向上させ、安定した工業生産が可能な製造方法の確立と、６ｋＧ以上の残留磁束密度Ｂｒを有しハードフェライト磁石に匹敵するコストパフォーマンスを有し、安価に提供できるＦｅ₃Ｂ型Ｎｄ−Ｆｅ−Ｂ系ボンド磁石とその製造方法の提供を目的としている。
【００１０】
【課題を解決するための手段】
この発明は、Ｆｅ₃Ｂ型系Ｆｅ−Ｂ−Ｒ磁石のｉＨｃを向上させ、安定した工業生産が可能な製造方法を目的に種々検討した結果、希土類元素の含有量が少なく、ＣｒあるいはさらにＡｌ、Ｓｉ、Ｐｂの少なくとも１種を少量添加した鉄基の特定組成の合金溶湯を超急冷法等にてアモルファス組織となし、特定の昇温速度による熱処理にて微細結晶集合体を得ることにより、ハードフェライト磁石では得られなかった５ｋＧ以上の残留磁束密度Ｂｒを有するボンド磁石が得られることを知見し、この発明を完成した。
【００１１】
この発明は、
組成式を Fe _100-x-y-z-w Cr_xB_yR_zM_w (但しRはPrまたはNdの1種または2種、MはAl、SiまたはPbの1種または2種以上)と表し、組成範囲を限定する記号x、y、z、wが下記値を満足し、体心正方晶Fe₃P型結晶構造を有する鉄を主成分とするホウ化物相とNd₂Fe₁₄B型結晶構造を有する構成相とが同一粉末粒子中に共存し、各構成相の平均結晶粒径が5nm〜100nmの範囲内のとき、実用的に必要な4kOe以上の固有保持力を発現し、平均粒径が3μm〜500μmである粉末を樹脂にて結合して所要形状に成型固化することにより、室温付近で準安定な結晶構造相が分解することなく、ボンド磁石として利用可能な形態として提供できる。
0.01≦x≦5at%
16≦y≦22at%
3≦z≦5.5at%
0.1≦w≦3at%
【００１２】
また、この発明は、
(1)組成式を Fe _100-x-y-z-wCr_xB_yR_zM_w (但しRはPrまたはNdの1種または2種、MはAl、SiまたPbの1種または2種以上)と表し、組成範囲を限定する記号x、y、z、wが上述の値を満足する合金溶湯を回転ロールを用いた超急冷法、スプラット急冷法、ガスアトマイズ法あるいはこれらを組み合せて急冷し、 90%以上をアモルファス組織となし、
(2)さらに熱処理の際に、Fe₃P型結晶構造を有する鉄を主成分とするホウ化物相が析出する温度からの昇温速度を1℃/分〜15℃/分で昇温して600℃〜750℃で10秒間〜6時間保持する熱処理を施し、
(3)Fe₃P型結晶構造を有する鉄を主成分とするホウ化物相と、Nd₂Fe₁₄B型結晶構造を有す構成相とが同一粉末粒子中に共存し、各構成相の平均結晶粒径が5nm〜100nmの範囲にある微結晶集合体を得たのち、
(4)平均粒径3μm〜500μmに粉砕して得られた磁石合金粉末を樹脂にて結合したことを特徴とする希土類ボンド磁石の製造方法である。
【００１３】
組成の限定理由
希土類元素ＲはＰｒまたはＮｄの１種また２種以上を特定量含有のときのみ、高い磁気特性が得られ、他の希土類、例えばＣｅ、ＬａではｉＨｃが２ｋＯｅ以上の特性が得られず、またＳｍ以降の中希土類元素、重希土類元素は磁気特性の劣化を招来するとともに磁石を高価格にするため好ましくない。
Ｒは、３ａｔ％未満では４ｋＯｅ以上のｉＨｃが得られず、また５．５ａｔ％を超えるとＦｅ₃Ｂ相が生成せず、硬磁性を示さない準安定相のＲ₂Ｆｅ₂₃Ｂ₃相が折出しｉＨｃは著しく低下するので好ましくないため、３〜５．５ａｔ％の範囲とする。
【００１４】
Ｂは、１６ａｔ％未満および２２ａｔ％を超えると４ｋＯｅ以上のｉＨｃが得られないため、１６〜２２ａｔ％の範囲とする。
【００１５】
Ｃｒは、ｉＨｃの向上に有効であるが、０．０１ａｔ％未満ではかかる効果が得られず、５ａｔ％を超えるとＢｒが低下し、６ｋＧ以上のＢｒが得られないため、０．０１〜５ａｔ％の範囲とする。
【００１６】
Ａｌ、Ｓｉ、Ｐｂは減磁曲線の角型性を改善し、磁気特性のＢｒ、（ＢＨ）ｍａｘを増大させる効果を有し、かかる効果を得るには少なくとも０．１ａｔ％以上の添加が必要であるが、３ａｔ％を超えるとかえって角型性を劣化させ、（ＢＨ）ｍａｘも低下するため、０．１〜３ａｔ％の範囲とする。
【００１７】
Ｆｅは、上述の元素の含有残余を占める。
【００１８】
粉末の構成相の限定理由
この発明によるボンド磁石構成する合金粉末は、１．６Ｔという高い飽和磁化を持つ体心正方晶Ｆｅ₃Ｐ型結晶構造を有する鉄を主成分とするホウ化物相を主相とすることを特徴としている。このホウ化物相は特定の範囲で準安定的に空間群Ｐ₄／ｎｍｎのＮｄ₂Ｆｅ₁₄Ｂ型結晶構造を有する強磁性相と共存できる。
これらのホウ化物相と強磁性相が共存することが高い磁束密度と十分なｉＨｃを得るためには必須であり、同一組成であっても、例えば鋳造法などではその製法に起因して、Ｃ１６型結晶構造を有するＦｅ₂Ｂ相と体心正方晶のα−Ｆｅ相とが主相となると、高い磁化が得られるが、各相の結晶粒径が数μｍから数十μｍと大きいため、ｉＨｃは１ｋＯｅ以下に劣化して磁石として使用できなくなり、好ましくない。
【００１９】
結晶粒径、粉末粒径の限定理由
この発明のボンド磁石を構成する合金粉末中に共存する体心正方晶Ｆｅ₃Ｐ型結晶構造を有する鉄を主成分とするホウ化物相とＮｄ₂Ｆｅ₁₄Ｂ型結晶構造は、いずれも強磁性相であるが、前者相は単独では磁気的に軟質であり、後者相が共存することがｉＨｃを発現するのに不可欠である。
しかし、単に両相が共存するだけでは不十分であり、両者の平均結晶粒径が５ｎｍ〜１００ｎｍの範囲にないと、減磁曲線の第２象限の角形性が悪化して、永久磁石としては動作点において十分な磁束を取り出すことができないため、平均結晶粒径は５ｎｍ〜１００ｎｍに限定する。
複雑形状や薄肉形状の磁石が得られるボンド磁石としての特徴を生かし、高精度の成型を行うには、粉末の粒径は十分小さいことが必要であるが、アトマイズで得られる粒径が１００μｍを越える合金粉末は急冷時に十分粉末内部まで冷却されず大部分がα−Ｆｅ相となるため、熱処理を施してもＦｅ₃Ｂ並びにＮｄ₂Ｆｅ₁₄Ｂ相が析出せずに、硬磁性材料となり得ない。
また、３μｍ未満の粒径では、比表面積増大に伴い多量の樹脂を使用する必要があり、充填密度が低下して好ましくないため、粉末粒径を３μｍ〜５００μｍに限定する。
【００２０】
この発明によるボンド磁石は等方性磁石であり、以下に示す圧縮成型、射出成型、押し出し成型、圧延成型、樹脂含浸法など公知のいずれの製造方法であってもよい。
圧縮成型の場合は、磁性粉末に熱硬化性樹脂、カップリング剤、滑剤等を添加混練したのち、圧縮成型して加熱樹脂を硬化して得られる。
射出成型、押し出し成型、圧延成型の場合は、磁性粉末に熱可塑性樹脂、カップリング剤、滑剤等を添加混練したのち、射出成型、押し出し成型、圧延成型のいずれかの方法にて成型して得られる。
樹脂含浸法においては、磁性粉末を圧縮成型後、必要に応じて熱処理した後、熱硬化性樹脂を含浸させ、加熱して樹脂を硬化させて得る。また、磁性粉末を圧縮成型後、必要に応じて熱処理した後、熱可塑性樹脂を含浸させて得る。
【００２１】
この発明において、ボンド磁石中の磁性粉末の重量比は、前記製法により異なるが、７０〜９９．５ｗｔ％であり、残部０．５〜３０ｗｔ％が樹脂その他である。圧縮成型の場合、磁性粉末の重量比は９５〜９９．５ｗｔ％、射出成型の場合、磁性粉末の充填率は９０〜９５ｗｔ％、樹脂含浸法の場合、磁性粉末の重量比は９６〜９９．５ｗｔ％が好ましい。
この発明における合成樹脂は、熱硬化性、熱可塑性のいずれの性質を有するものも利用できるが、熱的に安定な樹脂が好ましく、例えば、ポリアミド、ポリイミド、フェノール樹脂、弗素樹脂、けい素樹脂、エポキシ樹脂などを適宜選定できる。
【００２２】
製造条件の限定理由
この発明において、上述の特定組成の合金溶湯を超急冷法にてアモルファスとなし、Ｆｅ₃Ｐ型結晶構造を有する鉄を主成分とするホウ化物相が析出する温度付近からの昇温速度を１℃／分〜１５℃／分で昇温して６００℃〜７５０℃で１０秒間〜６時間保持する熱処理を施すことにより、熱力学的には準安定相であるＦｅ₃Ｐ型結晶構造を持つＦｅ₃Ｂ相と、Ｎｄ₂Ｆｅ₁₄Ｂ型結晶構造を有する強磁性相が共存し、各構成相の平均結晶粒径が５ｎｍ〜１００ｎｍの範囲にある微結晶集合体を得ることが最も重要であり、合金溶湯の超急冷処理には公知の回転ロールを用いた超急冷法を採用できるが、実質的に９０％以上のアモルファスが得られれば、回転ロールを用いた超急冷法の他にもスプラット急冷法、ガスアトマイズ法あるいはこれらを組み合わせた急冷方法を採用してもよい。
例えば、Ｃｕ製ロールを用いる場合は、そのロール表面周速度が１０〜５０ｍ／秒の範囲が好適な組織が得られるため好ましい。すなわち周速度が１０ｍ／秒未満ではアモルファスとならずα−Ｆｅ相の析出量が増大して好ましくなく、ロール表面周速度が５０ｍ／秒を超えると、急冷された合金が連続的なリボンとして生成せず、合金片が飛散し、装置から合金を回収する際の回収率や回収能率が低下して好ましくない。ただし、少量のα−Ｆｅ相が急冷薄帯中に存在しても特性を著しく低下させるものでなく許容される。
【００２３】
この発明において、上述の特定組成の合金溶湯を超急冷法にて実質的に９０％以上をアモルファスとなした後、磁気特性が最高となる熱処理は組成に依存するが、熱処理温度が６００℃未満ではＮｄ₂Ｆｅ₁₄Ｂ相が析出せず、４ｋＯｅ以上のｉＨｃが得られず、また７５０℃を超えると熱平衡相であるα−Ｆｅ相とＦｅ₂ＢまたはＮｄ_1.1Ｆｅ₄Ｂ₄相が生成してｉＨｃが発現しないため、熱処理温度は６００〜７５０℃以下に限定する。
熱処理雰囲気はＡｒガスなどの不活性ガス雰囲気もしくは１０^-3Ｔｏｒｒ以上の真空中が好ましい。
熱処理時間は短くてもよいが、１０秒未満では十分なミクロ組織の生成が行われず、ｉＨｃ及び減磁曲線の角型性が劣化し、また６時間を超えると４ｋＯｅ以上のｉＨｃが得られないので、熱処理保持時間を１０秒〜６時間に限定する。
【００２４】
この発明において重要な特徴として、熱処理に際してＦｅ₃Ｐ型結晶構造を有する鉄を主成分とするホウ化物相が析出する温度からの昇温速度であり、１℃／分未満の昇温速度では、昇温中にＮｄ₂Ｆｅ₁₄Ｂ相とＦｅ₃Ｂ相の結晶粒径が大きく成長しすぎてｉＨｃが劣化し、４ｋＯｅ以上のｉＨｃが得られない。
また、１５℃／分を超える昇温速度では、６００℃を通過してから生成するＮｄ₂Ｆｅ₁₄Ｂ相の析出が十分に行われず、α−Ｆｅ相の析出量が増大して、磁化曲線の第２象限にＢｒ点近傍に磁化の低下のある減磁曲線となり、（ＢＨ）ｍａｘが劣化するため好ましくない。ただし、少量のα−Ｆｅ相の存在は許容できる。
なお、熱処理に際してＦｅ₃Ｐ型結晶構造を有する鉄を主成分とするホウ化物相が析出する温度未満まではその昇温速度は任意であり、急速加熱などを適用して処理能率を高めることができる。
【００２５】
結晶構造
この発明による希土類磁石並びに希土類磁石合金粉末の結晶相は、Ｆｅ₃Ｐ型結晶構造を有する鉄を主成分とするホウ化物を主相とし、Ｎｄ₂Ｆｅ₁₄Ｂ型結晶構造を有する強磁性相を有し、平均結晶粒径が５ｎｍ〜１００ｎｍの微細結晶集合体からなることを特徴としている。
この発明において、磁石合金の平均結晶粒径が１００ｎｍを超えると、減磁曲線の角型性が著しく劣化し、Ｂｒ≧６ｋＧ、（ＢＨ）ｍａｘ≧７ＭＧＯｅの磁気特性を得ることができない。また、平均結晶粒径は細かいほど好ましいが、５ｎｍ未満の平均結晶粒径を得ることは工業生産上困難であるため、下限を５ｎｍとする。
【0026】
【作用】
この発明は、希土類元素の含有量が少ない特定組成の Fe-Cr-B-R-M合金溶湯(R は Nd 、 Pr の 1 種もしくは 2 種、MはAl、Si、Pbの1種もしくは2種以上)を前述の超急冷法にて 90%以上をアモルファス組織となし、得られたリボン、フレーク、球状粉末をFe₃B析出温度以上から1〜15℃/分の昇温速度で昇温した後、600〜750℃で10秒〜6時間保持する熱処理を施すことにより、熱力学的には、準安定相であるFe₃P型結晶構造をもつFe₃B相とNd₂Fe₁₄B型結晶構造を有する強磁性相が共存し、各構造相の平均結晶粒径が5nm〜100nmの範囲にある微結晶集合体を得る。この際、Crを加えることでCrの一部が硬磁性相であるNd₂Fe₁₄B相のFe原子と置換することでNd₂Fe₁₄B相の異方性定数が向上すること、残部のCrがiHcを低減する軟磁性相であるα-Feとの間に非磁性の金属間化合物を作ることにより、Crを含有しない組成より高いiHcが発現する。
さらにCrと同時にAl、Si、Pbを1種あるいは2種以上含有することにより、Cr含有時のBr、減磁曲線の角形の劣化を改善することができ、iHc≧4kG、Br≧6kG、(BH)max≧6MGOeの磁気特性を有するボンド磁石を得ることができる。
【００２７】
【実施例】
実施例１
表１のＮｏ．１〜５の組成となるように、純度９９．５％以上のＦｅ、Ｃｒ、Ｂ、Ｎｄ、Ｐｒ、Ａｌ、Ｓｉの金属を用いて、総量が３０ｇｒとなるように秤量し、底部に直径０．８ｍｍのオリフィスを有する石英るつぼ内に投入し、圧力５６ｃｍＨｇのＡｒ雰囲気中で高周波加熱により溶解し、溶解温度を１４００℃にした後、湯面をＡｒガスにより加圧して室温にてロール周速度２０ｍ／秒にて高速回転するＣｕ製ロールの外周面に０．７ｍｍの高さから溶湯を噴出させて、幅２〜３ｍｍ、厚み３０〜４０μｍの超急冷薄帯を作製した。
得られた超急冷薄帯をＣｕＫαの特性Ｘ線によりアモルファスであることを確認した。
【００２８】
この超急冷薄帯をＡｒガス中で５９０℃まで急速加熱した後、５９０℃以上を表１に示す昇温速度で昇温し、表１に示す熱処理温度で７分間保持し、その後室温まで冷却して薄帯を取り出し、幅２〜３ｍｍ、厚み３０〜４０μｍ、長さ３〜５ｍｍの試料を作製し、ＶＳＭを用いて磁気特性を測定した。測定結果を表２に示す。
なお、試料の測定結果は、正方晶と斜方晶が混在するＦｅ₃Ｂ相が主相で、Ｎｄ₂Ｆｅ₁₄Ｂ相とα−Ｆｅ相が混在する多相組織であり、平均結晶粒径はいずれも１００ｎｍ以下であった。なお、Ｃｒはこれらの各相でＦｅの一部を置換するが、Ａｌ、Ｓｉ、Ｐｂについては添加量が少ない上、超微細結晶であるため分析不能であった。
この薄帯を粉砕して、粒径が５〜１２０μｍにわたって分布する平均粒径６０μｍの粉末を得たのち、粉末９８ｗｔ％に対してエポキシ樹脂を２ｗｔ％の割合で混合したのち、６ｔｏｎ／ｃｍ²の圧力で圧縮成型し、１５０℃で硬化処理してボンド磁石を得た。
このボンド磁石の密度は６．０ｇｒ／ｃｍ³であり、磁石特性を表２に示す。
【００２９】
比較例
表１のＮｏ．６の組成となるように純度９９．５％以上のＦｅ、Ｂ、Ｎｄを用いて実施例１と同条件で超急冷薄帯を作製した。
得られた薄帯を実施例１と同一条件の熱処理を施し、冷却後に実施例１と同条件で粉砕して、平均粒径６０μｍの粉末を得たのち、実施例１と同一条件にてボンド磁石を作成した。
得られたボンド磁石の磁石特性を表２に示す
【００３０】
【表１】

【００３１】
【表２】

【0032】
【発明の効果】
この発明は、希土類元素の含有量が少ない特定組成の Fe-Cr-B-R-M合金溶湯(R は Nd 、 Pr の 1 種もしくは 2 種、MはAl、Si、Pbの1種もしくは2種以上)を前述の超急冷法にて 90%以上をアモルファス組織となし、得られたリボン、フレーク、球状粉末を得、これに特定条件の熱処理を施すことにより、熱力学的には準安定相であるFe₃P型結晶構造をもつFe₃B相とNd₂Fe₁₄B型結晶構造を有する強磁性相が共存し、各構成相の平均結晶粒径が5nm〜100nmの範囲にある微結晶集合体を得る。この際、Crを加えることでCrの一部が硬磁性相であるNd₂Fe₁₄B相のFe原子と置換することでNd₂Fe₁₄B相の異方性定数が向上すること、残部のCrがiHcを低減する軟磁性相であるα-Feとの間に非磁性の金属間化合物を作ることにより、Crを含有しない組成より高いiHcが発現する。
さらにCrと同時にAl、Si、Pbを1種あるいは2種以上含有することにより、Cr含有時のBr、減磁曲線の角形の劣化が改善されることにより、iHc≧4kG、Br≧6kG、(BH)max≧6MGOeの磁気特性を有するボンド磁石を得ることができる。
また、この発明は、希土類元素の含有量が少なく、製造方法が簡単で大量生産に適しているため、5kG以上の残留磁束密度Brを有し、ハードフェライト磁石を超える磁気的性能を有するボンド磁石を提供できる。[0001]
[Industrial applications]
The present invention, a magnet roll, a speaker, a magnetic circuit for magnetic sensors, relates to various meters and focusing magnet and motors and the like optimal rare earth bonded magnet and a method of manufacturing the actuator, Fe having a specific composition containing a small amount of rare earth elements -Cr-BRM (M = Al, Si, Pb) alloy melt is made to have an amorphous structure by a super-quenching method using a rotating roll, a splat quenching method, a gas atomizing method, or a combination of these methods. Alloy powder consisting of a fine crystal aggregate of a boride phase mainly composed of iron having a crystalline Fe ₃ P type crystal structure and a constituent phase of a Nd ₂ Fe ₁₄ B type crystal structure, which is bonded with a resin The present invention relates to a rare earth bonded magnet for obtaining an Fe-BR based bonded magnet having a residual magnetic flux density Br of 5 kG or more, which cannot be obtained with a hard ferrite magnet, and a method for manufacturing the same.
[0002]
[Prior art]
Permanent magnets used in stepping motors for home appliances, motors for electrical components, actuators, etc. were mainly limited to hard ferrite magnets, but due to their low-temperature demagnetization properties associated with low iHc at low temperatures, and ceramic materials In addition, there are problems that the mechanical strength is low, cracks and chips are easily generated, and it is difficult to obtain a complicated shape.
[0003]
2. Description of the Related Art Today, automobiles are strongly required to improve fuel efficiency by reducing the weight of vehicles in order to save resources, and electric components for automobiles are required to be further reduced in size and weight.
In addition, designs for maximizing the performance-to-weight ratio are also being studied for applications such as electric motors for home appliances other than automotive electrical components, and the current motor structure has a magnet material of about 5-7 kG Br. Is optimal.
That is, when Br of the magnet material to be used is 8 kG or more, it is necessary to increase the cross-sectional area of the iron plate of the rotor or the stator which becomes the magnetic path in the current motor structure, which leads to an increase in weight. At ~ 7 kG, the performance to weight ratio can be maximized.
[0004]
Accordingly, a magnetic material for a small motor is required to have a residual magnetic flux density Br of at least 5 kG in terms of magnetic properties, but cannot be obtained with a conventional hard ferrite magnet.
For example, an Nd—Fe—B-based bonded magnet satisfies such magnetic properties, but contains 10 to 15 at% of Nd or the like that requires a large number of steps and large-scale facilities for metal separation and purification or reduction reaction. Magnet materials with a Br of about 5 to 7 kG, which are significantly more expensive than ferrite magnets, can be mass-produced, and can be provided at low cost, have not been found.
[0005]
[Problems to be solved by the invention]
On the other hand, among Nd-Fe-B-based magnets, recently, a magnet material having a Fe ₃ B-type compound as a main phase in the vicinity of Nd ₄ Fe ₇₇ B ₁₉ (at%) has been proposed (R. Coehorn et al., J. de Phys. , C8, 1988, pp. 669-670). This magnet material can be obtained by heat-treating an amorphous ribbon to obtain a magnet material having a crystal texture of metastable Fe ₃ B and a metastable phase of Nd ₂ Fe ₁₄ B. However, iHc is as low as about 2 to 3 kOe. Also, the heat treatment conditions for obtaining this iHc are narrow and limited, and are not practical for industrial production.
[0006]
A study has been published in which a magnetic material having the Fe ₃ B-type compound as a main phase is added with an additive element to form a multi-component to improve performance. One of them is to improve iHc by using Dy and Tb in addition to Nd as a rare earth element. However, in addition to the problem of adding an expensive element, the rare earth element has a magnetic moment of Nd or Fe. There is a problem that magnetization is reduced due to coupling in antiparallel with the moment (R. Coehorn, J. Magn, Magn, Mat., 83 (1990) pp. 228-230).
[0007]
In another study (Shen Bao-gen et al., J. Magn, Magn, Mat., 89 (1991) pp. 335-340), the Curie temperature was increased by substituting a part of Fe with Co to increase the temperature of iHc. Although the coefficient is improved, there is a problem that Br is reduced with the addition of Co.
[0008]
Fe ₃ B type Nd-Fe-B based magnet Anyway, after amorphous by rapid quenching, can be hard magnet material by being heat-treated, iHc is low and narrow the heat treatment conditions, stable industrial It cannot be produced and cannot be provided at low cost as a substitute for hard ferrite magnets.
[0009]
The present invention focuses on a Fe ₃ B type Fe—BR based magnet (R is a rare earth element), establishes a manufacturing method capable of improving iHc and achieving stable industrial production, and a residual magnetic flux density of 6 kG or more. has a cost performance comparable to hard ferrite magnets have a br, are intended to provide a Fe ₃ B type Nd-Fe-B based bonded magnet and a manufacturing method thereof can be provided at low cost.
[0010]
[Means for Solving the Problems]
As a result of various studies for the purpose of improving the iHc of the Fe ₃ B type Fe—BR magnet and achieving a stable industrial production, the present invention has found that the content of rare earth elements is small and that Cr or Al , A small amount of at least one of Si and Pb is added to a molten iron having a specific composition of an iron base to form an amorphous structure by a rapid quenching method or the like, and to obtain a fine crystal aggregate by heat treatment at a specific temperature increasing rate. The inventors have found that a bonded magnet having a residual magnetic flux density Br of 5 kG or more, which cannot be obtained with a hard ferrite magnet, can be obtained, and completed the present invention.
[0011]
The present invention
The composition formula is _expressed as Fe _100-xyzw Cr _x B _y R _z M _w (where R is one or two of Pr or Nd , M is one or two or more of Al, Si or Pb), and the composition range is A configuration in which the limiting symbols x, y, z, and w satisfy the following values, and have a boride phase mainly composed of iron having a body-centered tetragonal Fe ₃ P-type crystal structure and an Nd ₂ Fe ₁₄ B-type crystal structure Phase and coexist in the same powder particles, and when the average crystal grain size of each constituent phase is in the range of 5 nm to 100 nm, a practically necessary intrinsic coercive force of 4 kOe or more is exhibited, and the average grain size is 3 μm or more. By bonding the powder of 500 μm with a resin and molding and solidifying it into a required shape, a metastable crystal structure phase can be provided in a form usable as a bonded magnet without decomposition at around room temperature.
0.01 ≦ x ≦ 5at%
16 ≦ y ≦ 22at%
3 ≦ z ≦ 5.5at%
0.1 ≦ w ≦ 3at%
[0012]
In addition, the present invention
(1) The composition formula is represented as Fe _100-xyzw Cr _x B _y R _z M _w (where R is one or two of Pr or Nd , M is one or more of Al, Si or Pb), symbol x limiting the composition range, y, z, w super quenching method using a rotating roll molten alloy satisfying the above-mentioned values, splat quenching method, and quenched in conjunction gas atomizing method or these, more than 90% With and without amorphous structure
(2) Further during heat treatment, Fe ₃ P type crystalline structure raised at 1 ° C. / minute to 15 ° C. / min heating rate of temperature or et al boride phase composed mainly of iron is precipitated with And heat-treated at 600 ° C to 750 ° C for 10 seconds to 6 hours.
(3) A boride phase mainly composed of iron having a Fe ₃ P type crystal structure and a component phase having an Nd ₂ Fe ₁₄ B type crystal structure coexist in the same powder particle, and the average of each component phase After obtaining a microcrystalline aggregate having a crystal grain size in the range of 5 nm to 100 nm,
(4) A method for producing a rare earth bonded magnet, characterized in that a magnet alloy powder obtained by pulverization to an average particle size of 3 μm to 500 μm is bonded with a resin.
[0013]
Reasons for limitation of composition High magnetic properties can be obtained only when the rare earth element R contains one or more of Pr or Nd in a specific amount, and other rare earth elements such as Ce and La have iHc of 2 kOe or more. However, medium rare earth elements and heavy rare earth elements after Sm are not preferable because they cause deterioration of magnetic properties and increase the cost of magnets.
If R is less than 3 at%, iHc of 4 kOe or more cannot be obtained, and if it exceeds 5.5 at%, no Fe ₃ B phase is formed and a metastable phase R ₂ Fe ₂₃ B ₃ that does not show hard magnetism is formed. The unfolded iHc is unpreferably because it significantly decreases, so the range is 3 to 5.5 at%.
[0014]
B is in the range of 16 to 22 at% because iHc of 4 kOe or more cannot be obtained if B is less than 16 at% or exceeds 22 at%.
[0015]
Although Cr is effective in improving iHc, such an effect cannot be obtained at less than 0.01 at%, and Br decreases at more than 5 at%, and Br of 6 kG or more cannot be obtained. % Range.
[0016]
Al, Si, and Pb have the effect of improving the squareness of the demagnetization curve and increasing the Br and (BH) max of the magnetic properties. To obtain such an effect, addition of at least 0.1 at% or more is necessary. However, if it exceeds 3 at%, the squareness is rather deteriorated, and (BH) max also decreases. Therefore, the range is 0.1 to 3 at%.
[0017]
Fe accounts for the residual content of the above-mentioned elements.
[0018]
Reasons for Limiting Constituent Phase of Powder The alloy powder constituting the bonded magnet according to the present invention mainly comprises a boride phase mainly composed of iron having a body-centered tetragonal Fe ₃ P type crystal structure having a high saturation magnetization of 1.6 T. It is characterized by a phase. This boride phase can be metastable in a specific range and coexist with a ferromagnetic phase having an Nd ₂ Fe ₁₄ B type crystal structure of a space group P ₄ / nmn.
The coexistence of the boride phase and the ferromagnetic phase is essential for obtaining a high magnetic flux density and sufficient iHc. Even if the composition is the same, for example, in a casting method or the like, C16 When the Fe ₂ B phase having the type crystal structure and the body-centered tetragonal α-Fe phase are the main phases, high magnetization is obtained, but since the crystal grain size of each phase is as large as several μm to several tens μm, iHc deteriorates to 1 kOe or less and cannot be used as a magnet, which is not preferable.
[0019]
Reasons for limiting crystal grain size and powder grain size A boride phase containing iron as a main component having a body-centered tetragonal Fe ₃ P type crystal structure and Nd ₂ Fe ₁₄ coexisting in the alloy powder constituting the bonded magnet of the present invention Each of the B-type crystal structures is a ferromagnetic phase, but the former phase is magnetically soft by itself, and the coexistence of the latter phase is essential for expressing iHc.
However, simply coexisting both phases is not sufficient, and if the average crystal grain size of both is not in the range of 5 nm to 100 nm, the squareness of the second quadrant of the demagnetization curve deteriorates, and as a permanent magnet, Since sufficient magnetic flux cannot be extracted at the operating point, the average crystal grain size is limited to 5 nm to 100 nm.
In order to make the most of the characteristics of bonded magnets, which can produce magnets with complex shapes and thin shapes, and to perform high-precision molding, the particle size of the powder needs to be sufficiently small, but the particle size obtained by atomization must be 100 μm. Since the alloy powder exceeding the temperature is not sufficiently cooled to the inside of the powder during quenching and is mostly in the α-Fe phase, the Fe ₃ B and Nd ₂ Fe ₁₄ B phases do not precipitate even after heat treatment, and the alloy powder can be a hard magnetic material. Absent.
If the particle diameter is less than 3 μm, a large amount of resin must be used as the specific surface area increases, and the packing density decreases, which is not preferable. Therefore, the powder particle diameter is limited to 3 μm to 500 μm.
[0020]
The bonded magnet according to the present invention is an isotropic magnet, and may be any known manufacturing method such as compression molding, injection molding, extrusion molding, rolling molding, and resin impregnation described below.
In the case of compression molding, a thermosetting resin, a coupling agent, a lubricant, and the like are added to the magnetic powder, kneaded, and then compression-molded to cure the heated resin.
In the case of injection molding, extrusion molding, and rolling molding, a thermoplastic resin, a coupling agent, a lubricant, etc. are added and kneaded to the magnetic powder, and then molded by any of injection molding, extrusion molding, and rolling molding. Can be
In the resin impregnation method, a magnetic powder is obtained by compression molding, heat-treating as necessary, then impregnating with a thermosetting resin, and heating to cure the resin. Further, the magnetic powder is obtained by compression molding, heat-treating as necessary, and then impregnating with a thermoplastic resin.
[0021]
In the present invention, the weight ratio of the magnetic powder in the bonded magnet varies depending on the manufacturing method, but is 70 to 99.5 wt%, and the remaining 0.5 to 30 wt% is resin or the like. In the case of compression molding, the weight ratio of the magnetic powder is 95 to 99.5 wt%. In the case of injection molding, the filling ratio of the magnetic powder is 90 to 95 wt%. In the case of the resin impregnation method, the weight ratio of the magnetic powder is 96 to 99. 5 wt% is preferred.
As the synthetic resin in the present invention, any of thermosetting and thermoplastic properties can be used, but a thermally stable resin is preferable.For example, polyamide, polyimide, phenol resin, fluorine resin, silicon resin, An epoxy resin or the like can be appropriately selected.
[0022]
Reasons for Limiting Manufacturing Conditions In the present invention, the molten alloy having the above-mentioned specific composition is made amorphous by a super-quenching method, and a temperature around a temperature at which a boride phase mainly composed of iron having a Fe ₃ P type crystal structure is precipitated. By performing a heat treatment at a heating rate of 1 ° C./min to 15 ° C./min and holding at 600 ° C. to 750 ° C. for 10 seconds to 6 hours, Fe ₃ P which is a metastable phase thermodynamically An Fe ₃ B phase having a type crystal structure and a ferromagnetic phase having an Nd ₂ Fe ₁₄ B type crystal structure coexist, and a microcrystal aggregate having an average crystal grain size of each constituent phase in the range of 5 nm to 100 nm is obtained. The most important thing is that the super-quenching process using a known rotating roll can be adopted for the ultra-quenching treatment of the molten alloy. However, if 90% or more of the amorphous material can be obtained, the ultra-quenching using the rotating roll is effective. Splat quenching method, gas at It is method or may be employed quenching method combining these.
For example, when a Cu roll is used, it is preferable that the roll surface peripheral speed is in the range of 10 to 50 m / sec because a suitable structure is obtained. That is, when the peripheral speed is less than 10 m / sec, the amorphous material is not formed and the amount of precipitation of the α-Fe phase is increased, and when the roll surface peripheral speed exceeds 50 m / sec, a quenched alloy is formed as a continuous ribbon. Without this, the alloy pieces are scattered, and the recovery rate and recovery efficiency when recovering the alloy from the apparatus are undesirably reduced. However, even if a small amount of the α-Fe phase is present in the quenched ribbon, the characteristics are not remarkably deteriorated but are acceptable.
[0023]
In the present invention, the heat treatment at which the magnetic properties are maximized after the melt of the alloy having the specific composition described above is made substantially 90% or more amorphous by the ultra-quenching method depends on the composition, but the heat treatment temperature is lower than 600 ° C. In this case, the Nd ₂ Fe ₁₄ B phase does not precipitate, iHc of 4 kOe or more cannot be obtained, and when the temperature exceeds 750 ° C., the α-Fe phase which is a thermal equilibrium phase and the Fe ₂ B or Nd _1.1 Fe ₄ B ₄ phase are formed. Therefore, the heat treatment temperature is limited to 600 to 750 ° C. or less because iHc does not appear.
The heat treatment atmosphere is preferably an inert gas atmosphere such as an Ar gas or a vacuum of 10 ^-3 Torr or more.
Although the heat treatment time may be short, if it is less than 10 seconds, a sufficient microstructure is not formed, iHc and the squareness of the demagnetization curve are deteriorated, and if more than 6 hours, iHc of 4 kOe or more cannot be obtained. Therefore, the heat treatment holding time is limited to 10 seconds to 6 hours.
[0024]
An important feature of the present invention is that the rate of temperature rise from the temperature at which a boride phase mainly composed of iron having an Fe ₃ P type crystal structure precipitates during heat treatment, and at a rate of less than 1 ° C./minute, During the temperature increase, the crystal grain size of the Nd ₂ Fe ₁₄ B phase and the Fe ₃ B phase grows too large to deteriorate iHc, and iHc of 4 kOe or more cannot be obtained.
At a heating rate exceeding 15 ° C./min, the Nd ₂ Fe ₁₄ B phase generated after passing 600 ° C. is not sufficiently precipitated, and the amount of α-Fe phase increases, resulting in a magnetization curve. In the second quadrant, a demagnetization curve having a decrease in magnetization near the Br point is obtained, which is not preferable because (BH) max deteriorates. However, the presence of a small amount of the α-Fe phase is acceptable.
The rate of temperature rise is arbitrary up to a temperature at which a boride phase mainly composed of iron having an Fe ₃ P-type crystal structure is precipitated during heat treatment, and the treatment efficiency can be increased by applying rapid heating or the like. it can.
[0025]
Crystal structure The crystal phase of the rare earth magnet and the rare earth magnet alloy powder according to the present invention is mainly composed of a boride mainly composed of iron having an Fe ₃ P type crystal structure and a ferromagnetic having an Nd ₂ Fe ₁₄ B type crystal structure. It is characterized by having a phase and comprising a fine crystal aggregate having an average crystal grain size of 5 nm to 100 nm.
In the present invention, if the average crystal grain size of the magnet alloy exceeds 100 nm, the squareness of the demagnetization curve is remarkably deteriorated, and the magnetic properties of Br ≧ 6 kG and (BH) max ≧ 7MGOe cannot be obtained. Although the average crystal grain size is preferably as small as possible, it is difficult to obtain an average crystal grain size of less than 5 nm in industrial production, so the lower limit is set to 5 nm.
[0026]
[Action]
The present invention (the R Nd, 1 kind or two kinds of Pr, M is Al, Si, 1 kind or 2 or more kinds of Pb) Fe -Cr-BRM alloy melt having a specific composition containing a small amount of rare earth elements to above without the hand 90% amorphous tissue in rapid quenching, resulting ribbons, flakes, after the spherical powder was heated at a heating rate of 1 to 15 ° C. / min from Fe ₃ B precipitation temperature above 600 By performing a heat treatment at 750 ° C. for 10 seconds to 6 hours, thermodynamically, a Fe ₃ B phase having a Fe ₃ P type crystal structure and a Nd ₂ Fe ₁₄ B type crystal structure, which are metastable phases, are obtained. The ferromagnetic phase has a coexistence, and a microcrystalline aggregate having an average crystal grain size of each structural phase in the range of 5 nm to 100 nm is obtained. At this time, by adding Cr, a part of Cr is replaced with Fe atoms of Nd ₂ Fe ₁₄ B phase which is a hard magnetic phase, thereby improving the anisotropy constant of Nd ₂ Fe ₁₄ B phase, By forming a nonmagnetic intermetallic compound between Cr and α-Fe, which is a soft magnetic phase that reduces iHc, iHc that is higher than the Cr-free composition is developed.
Further, by containing one or more of Al, Si, and Pb simultaneously with Cr, Br when Cr is contained, the deterioration of the square shape of the demagnetization curve can be improved, iHc ≧ 4 kG, Br ≧ 6 kG, ( BH) A bonded magnet having magnetic properties of max ≧ 6MGOe can be obtained.
[0027]
【Example】
Example 1
No. 1 in Table 1. Using Fe, Cr, B, Nd, Pr, Al, and Si metals having a purity of 99.5% or more so as to have a composition of 1 to 5, the weight is weighed so that the total amount is 30 gr. It was put into a quartz crucible having a 0.8 mm orifice, melted by high frequency heating in an Ar atmosphere at a pressure of 56 cmHg, and the melting temperature was set to 1400 ° C. A super-quenched ribbon having a width of 2 to 3 mm and a thickness of 30 to 40 μm was produced by ejecting a molten metal from a height of 0.7 mm onto the outer peripheral surface of a Cu roll rotating at a high speed of 20 m / sec.
The obtained ultra-quenched ribbon was confirmed to be amorphous by characteristic X-ray of CuKα.
[0028]
After rapidly heating the ultra-quenched ribbon to 590 ° C. in Ar gas, the temperature is raised to 590 ° C. or more at a temperature rising rate shown in Table 1, held at the heat treatment temperature shown in Table 1 for 7 minutes, and then cooled to room temperature. Then, the ribbon was taken out, a sample having a width of 2 to 3 mm, a thickness of 30 to 40 μm, and a length of 3 to 5 mm was prepared, and the magnetic characteristics were measured using a VSM. Table 2 shows the measurement results.
The measurement results of the sample show that the main phase is a Fe ₃ B phase in which tetragonal and orthorhombic are mixed, and a multiphase structure in which Nd ₂ Fe ₁₄ B and α-Fe are mixed. Were all 100 nm or less. Although Cr replaces part of Fe in each of these phases, it was impossible to analyze Al, Si, and Pb because of their small addition amounts and ultrafine crystals.
This ribbon is pulverized to obtain a powder having an average particle size of 60 μm distributed over a particle size of 5 to 120 μm. After mixing 98% by weight of the powder with 2% by weight of the epoxy resin, 6 ton / cm ^2. , And cured at 150 ° C. to obtain a bonded magnet.
The density of this bonded magnet was 6.0 gr / cm ³ , and the magnet properties are shown in Table 2.
[0029]
No. of Comparative Example Table 1. A super-quenched ribbon was produced under the same conditions as in Example 1 using Fe, B, and Nd having a purity of 99.5% or more so as to obtain a composition of No. 6.
The obtained ribbon was subjected to a heat treatment under the same conditions as in Example 1, and after cooling, pulverized under the same conditions as in Example 1 to obtain a powder having an average particle diameter of 60 μm, and then bonded under the same conditions as in Example 1. Created a magnet.
Table 2 shows the magnet properties of the obtained bonded magnet.
[Table 1]

[0031]
[Table 2]

[0032]
【The invention's effect】
The present invention (the R Nd, 1 kind or two kinds of Pr, M is Al, Si, 1 kind or 2 or more kinds of Pb) Fe -Cr-BRM alloy melt having a specific composition containing a small amount of rare earth elements to the aforementioned rapid quenching without the hand 90% amorphous structure, resulting resulting ribbons, flakes, spherical powder, followed by heat treatment of the specific conditions in which, in the thermodynamically metastable phase Fe _An Fe ₃ B phase having a 3P type crystal structure and a ferromagnetic phase having a Nd ₂ Fe ₁₄ B type crystal structure coexist, and a fine crystal aggregate having an average crystal grain size of each constituent phase in a range of 5 nm to 100 nm is formed. obtain. At this time, by adding Cr, a part of Cr is replaced with Fe atoms of Nd ₂ Fe ₁₄ B phase which is a hard magnetic phase, thereby improving the anisotropy constant of Nd ₂ Fe ₁₄ B phase, By forming a nonmagnetic intermetallic compound between Cr and α-Fe, which is a soft magnetic phase that reduces iHc, iHc that is higher than the Cr-free composition is developed.
Further, by containing one or more of Al, Si, and Pb simultaneously with Cr, Br when Cr is contained, the deterioration of the square shape of the demagnetization curve is improved, so that iHc ≧ 4 kG, Br ≧ 6 kG, ( BH) A bonded magnet having magnetic properties of max ≧ 6MGOe can be obtained.
Further, the present invention provides a bonded magnet having a residual magnetic flux density Br of 5 kG or more and a magnetic performance exceeding that of a hard ferrite magnet because the content of rare earth elements is small, the manufacturing method is simple and suitable for mass production. Can be provided.

Claims

The composition formula is _expressed as Fe _100-xyzw Cr _x B _y R _z M _w (where R is one or two of Pr or Nd, M is one or more of Al, Si or Pb), and the composition range is The limiting symbols x, y, z, and w satisfy the following values, and have a boride phase mainly composed of iron having a body-centered tetragonal Fe ₃ P-type crystal structure and an Nd ₂ Fe ₁₄ B-type crystal structure The constituent phases coexist in the same powder particles, the average crystal grain size of each constituent phase is in the range of 5 nm to 100 nm, and the powder having an average particle size of 3 μm to 500 μm is bonded with a resin. Rare earth bonded magnet.
0.01 ≦ x ≦ 5at%
16 ≦ y ≦ 22at%
3 ≦ z ≦ 5.5at%
0.1 ≦ w ≦ 3at%

The composition formula is _expressed as Fe _100-xyzw Cr _x B _y R _z M _w (where R is one or two of Pr or Nd , M is one or two or more of Al, Si or Pb), and the composition range is Super-quenching method using rotating rolls, splat quenching method, gas atomizing method or a combination of these methods is used to quench the molten alloy whose limiting symbols x, y, z, and w satisfy the following values , and 90% or more has no amorphous structure further during heat treatment, and raising the temperature of the Fe ₃ P type heating rate of temperature or et al boride phase is precipitated mainly composed of iron having a crystal structure at 1 ° C. / minute to 15 ° C. / min A heat treatment of holding at 600 ° C. to 750 ° C. for 10 seconds to 6 hours is performed, and a boride phase mainly containing iron having a Fe ₃ P type crystal structure and a constituent phase having an Nd ₂ Fe ₁₄ B type crystal structure Are present in the same powder particles, and the average crystal grain size of each constituent phase is 5 nm to 100 nm. A method for producing a rare earth bonded magnet, comprising:
0.01 ≦ x ≦ 5at%
16 ≦ y ≦ 22at%
3 ≦ z ≦ 5.5at%
0.1 ≦ w ≦ 3at%