JP2004071949A

JP2004071949A - Manufacturing method of rare earth sintered magnet

Info

Publication number: JP2004071949A
Application number: JP2002231363A
Authority: JP
Inventors: Tetsuya Hidaka; 日高　徹也; Hironari Okada; 岡田　宏成; Kazuya Sakamoto; 坂元　一也
Original assignee: TDK Corp
Current assignee: TDK Corp
Priority date: 2002-08-08
Filing date: 2002-08-08
Publication date: 2004-03-04
Anticipated expiration: 2022-08-08
Also published as: JP4194021B2

Abstract

<P>PROBLEM TO BE SOLVED: To easily and stably manufacture an Nd<SB>2</SB>Fe<SB>14</SB>group sintered magnet having both a high residual magnetic flux density and a coercive force. <P>SOLUTION: The manufacturing method of the rare earth sintered magnet includes a raw material alloy manufacturing process for manufacturing a raw material alloy containing an R (R indicates at least a kind of rare earth elements); a pulverizing process for pulverizing the raw material alloy in one stage or multi-stages to obtain raw material powder; a forming process of forming the raw material powder to obtain a forming; and a sintering process of sintering the forming to obtain the sintered magnet. At least one kind of oxygen rich raw materials (raw material is referred to as the raw material alloy or its pulverized powder) that are manufactured to relatively contain much oxygen contents and one kind of oxygen poor raw materials whose oxygen contents are less than those of the oxygen rich raw materials by 300 ppm (mass ratio) or more are blended before the forming process. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、Ｎｄ_２Ｆｅ_１４Ｂ系磁石などの希土類焼結磁石を製造する方法に関する。
【０００２】
【従来の技術】
高性能を有する希土類磁石としては、例えば特許第１４３１６１７号公報に記載されているＮｄ_２Ｆｅ_１４Ｂ系磁石が知られている。
【０００３】
Ｎｄ_２Ｆｅ_１４Ｂ系磁石の残留磁束密度を向上させるためには、磁石の酸素含有量を少なくすることが有効である。しかし、Ｎｄ_２Ｆｅ_１４Ｂ系焼結磁石において酸素含有量を極端に少なくすると、焼結時に異常粒成長が生じて保磁力および角形性が低くなってしまい、総合的な磁石特性が良好とはならないという問題がある。また、ＳｍＣｏ_５系組成をもつ希土類焼結磁石においても、やはり酸素量低減に伴い、焼結時に異常粒成長が生じるという問題がある。
【０００４】
希土類焼結磁石の保磁力向上を図るために、特公平４−２６５２５号公報では、希土類酸化物が焼結体の結晶粒径を抑制するとして、Ｎｄ、ＦｅおよびＢからなる合金に希土類酸化物を混合して粉砕し、磁場中配向、成形および焼結して永久磁石を製造することを提案している。しかし、希土類酸化物は高価であるため、磁石のコストアップを招く。また、希土類酸化物粉末は、合金粉末と密度、粒径等が異なり、かつ合金粉末に対する添加量が少ないため、混合時に均一に分散することが難しく、混合に長時間を要したり、複雑で高価な混合装置を使用する必要がある。
【０００５】
また、特公平７−１０７８８２号公報では、磁石中の酸素含有量を質量比で３０００ｐｐｍ以上となるように制御することにより、保磁力を向上させている。
【０００６】
【発明が解決しようとする課題】
本発明の発明者らは、高価な希土類酸化物を使用することなく、希土類焼結磁石中の酸素含有量を制御することによって、残留磁束密度が高くかつ保磁力が高い希土類焼結磁石を製造する実験を行った。希土類焼結磁石は、一般に、原料合金を粗粉砕した後、微粉砕し、次いで、成形および焼結を行って製造される。発明者らは、粉砕時の雰囲気中の酸素濃度を制御することにより、焼結磁石中の酸素含有量を制御して、残留磁束密度および保磁力のいずれもが良好な焼結磁石を得ようとする実験を行った。
【０００７】
その結果、粉砕時に雰囲気中の酸素を極力排除することにより、焼結磁石の酸素含有量を５００ｐｐｍ未満とでき、その結果、残留磁束密度が高めで保磁力が低めの焼結磁石を得ることができた。ただし、この場合、製造条件の幅が著しく狭くなり、再現性に乏しかった。一方、粉砕時に雰囲気中の酸素をある程度残すことにより、焼結磁石の酸素含有量を４０００ｐｐｍ程度とでき、その結果、保磁力が高く、角形比の高い焼結磁石を得ることができた。
【０００８】
しかし、残留磁束密度および保磁力を共に向上させようとして、粉砕雰囲気中の酸素濃度を様々に変更して焼結磁石を作製したところ、残留磁束密度および保磁力が共に高くなるように磁石中の酸素含有量を制御することが、極めて困難であることがわかった。具体的には、粉砕雰囲気中の酸素濃度と粉砕粉の酸素含有量との関係が線形的とはならず、たとえば雰囲気中の酸素濃度を低くしていった場合には、特定の酸素濃度より低くなったときに粉砕粉の酸素含有量が急激に少なくなり、逆に、雰囲気中の酸素濃度を高くしていった場合には、特定の酸素濃度より高くなったときに粉砕粉の酸素含有量が急激に多くなる傾向が認められた。しかも、前記特定の酸素濃度は、粉砕粉の粒度や粉砕時の処理量などに依存して変動したため、再現性が低いこともわかった。
【０００９】
本発明は、残留磁束密度および保磁力が共に高いＮｄ_２Ｆｅ_１４Ｂ系焼結磁石を、安定して容易に製造することを目的とする。
【００１０】
【課題を解決するための手段】
このような目的は、下記（１）〜（１３）の本発明により達成される。
（１）　Ｒ（Ｒは、希土類元素の少なくとも１種）を含有する原料合金を製造する原料合金製造工程と、原料合金を１段階または多段階で粉砕して原料粉末を得る粉砕工程と、原料粉末を成形して成形体を得る成形工程と、成形体を焼結して焼結磁石を得る焼結工程とを有し、
原料合金またはその粉砕粉を原料と呼んだとき、
酸素含有量が相対的に多くなるように製造された原料である酸素リッチ原料の少なくとも１種と、酸素含有量が相対的に少なくなるように製造され、酸素リッチ原料より酸素含有量が３００ｐｐｍ（質量比）以上少ない原料である酸素プア原料の少なくとも１種とを、成形工程の前に混合する希土類焼結磁石の製造方法。
（２）　酸素リッチ原料の酸素含有量（質量比）が６００〜５０００ｐｐｍであり、酸素プア原料の酸素含有量（質量比）が３００〜２０００ｐｐｍである上記（１）の希土類焼結磁石の製造方法。
（３）　酸素リッチ原料と酸素プア原料との合計に対する酸素リッチ原料の比率が１０質量％以上９０質量％未満である上記（１）または（２）の希土類焼結磁石の製造方法。
（４）　酸素リッチ原料と酸素プア原料との合計に対する酸素リッチ原料の比率が１０〜６０質量％である上記（１）〜（３）のいずれかの希土類焼結磁石の製造方法。
（５）　酸素リッチ原料および酸素プア原料の少なくとも一方が、酸素含有量の相異なる２種以上の原料から構成され、その２種以上の原料間における酸素含有量の差の最大値が、酸素リッチ原料を構成する原料と酸素プア原料を構成する原料との間の酸素含有量の差の最小値よりも小さい上記（１）〜（４）のいずれかの希土類焼結磁石の製造方法。
（６）　酸素含有量（質量比）が５００〜４５００ｐｐｍである焼結磁石が製造される上記（１）〜（５）のいずれかの希土類焼結磁石の製造方法。
（７）　酸素リッチ原料と酸素プア原料との間の酸素含有量の相違が、これら両原料の製造工程の少なくとも一部において、雰囲気中の酸素濃度を相異なるものとすることにより実現されたものである上記（１）〜（６）のいずれかの希土類焼結磁石の製造方法。
（８）　酸素リッチ原料は、製造工程の少なくとも一部において、酸化性気体または水分を含む孔部を有する多孔性物質との接触または前記多孔性物質の近傍に配置されることにより、酸素含有量が制御されたものである上記（１）〜（７）のいずれかの希土類焼結磁石の製造方法。
（９）　粉砕工程において原料合金が多段階で粉砕され、
少なくとも１段階の粉砕を行った後に、酸素リッチ原料と酸素プア原料とを混合する上記（１）〜（８）のいずれかの希土類焼結磁石の製造方法。
（１０）　粉砕工程において原料合金が多段階で粉砕され、
多段階の粉砕の最終段階終了後に、酸素リッチ原料と酸素プア原料とを混合する上記（１）〜（８）のいずれかの希土類焼結磁石の製造方法。
（１１）　Ｒ、ＦｅおよびＢを含有する焼結磁石が製造される上記（１）〜（１０）のいずれかの希土類焼結磁石の製造方法。
（１２）　焼結磁石のＲ含有量が２８〜３２質量％である上記（１１）の希土類焼結磁石の製造方法。
（１３）　焼結磁石が、Ｒとして少なくともＳｍを含有し、さらにＣｏを含有する上記（１）〜（１０）のいずれかの希土類焼結磁石の製造方法。
【００１１】
【作用および効果】
残留磁束密度および保磁力が共に高い希土類焼結磁石を得ようとする場合、前述したように磁石の酸素含有量が特定の範囲内となるように制御することが有効である。しかし、前述したように、残留磁束密度および保磁力の一方だけが高くなる酸素含有量とすることは容易であるが、両者が共に高くなる酸素含有量を安定して実現することは困難である。
【００１２】
そこで本発明では、希土類焼結磁石を製造するに際し、酸素含有量が多くなるように製造された酸素リッチ原料と、酸素含有量が少なくなるように製造された酸素プア原料とを混合して用いる。本明細書において原料とは、急冷法や鋳造法により製造された原料合金またはその粉砕粉である。
【００１３】
前述したように、酸素プア原料は、酸素を極力排除した雰囲気を用いることにより容易に製造でき、酸素リッチ原料は、雰囲気中に酸素をある程度残留させることにより容易に製造できる。そして、焼結磁石の酸素含有量は、酸素プア原料と酸素リッチ原料との混合比を制御することにより、正確に制御できる。したがって本発明では、残留磁束密度および保磁力が共に高い希土類焼結磁石を、容易にかつ再現性よく製造することができる。しかも本発明では、均一な分散が困難で、かつ高価でもある希土類酸化物を使う必要がないため、安定して高性能が得られる希土類焼結磁石を低コストで製造できる。
【００１４】
さらに、本発明の製造方法を用いることにより、角形比の高い磁石が得られることがわかった。すなわち、従来の方法により単一の原料を用いて製造した焼結磁石と本発明により製造した焼結磁石とを比較したとき、酸素含有量が同等であっても本発明により製造した焼結磁石のほうが角形比が高くなる。
【００１５】
なお、本明細書において、角形比とはＨｋ／ＨｃＪを意味する。Ｈｋ／ＨｃＪにおけるＨｋは、磁気ヒステリシスループの第２象限において磁束密度が残留磁束密度の９０％になるときの外部磁界強度である。Ｈｋが低いと高い最大エネルギー積が得られない。Ｈｋ／ＨｃＪは、磁石性能の指標となるものであり、磁気ヒステリシスループの第２象限における角張りの度合いを表わす。ＨｃＪが同等であってもＨｋ／ＨｃＪが大きいほど磁石中のミクロ的な保磁力の分布がシャープとなるため、着磁が容易となり、かつ着磁ばらつきも少なくなり、また、最大エネルギー積が高くなる。そして、磁石使用時の外部からの減磁界や自己減磁界の変化に対する磁化の安定性が良好となり、磁石を含む磁気回路の性能が安定したものとなる。
【００１６】
本発明は、希土類元素Ｒとして少なくともＮｄおよび／またはＰｒを含有し、さらに、ＦｅおよびＢを含有する焼結磁石の製造に好適である。この組成系の磁石は、Ｎｄ_２Ｆｅ_１４ＢなどのＲ_２Ｆｅ_１４Ｂ金属間化合物からなる硬質磁性相を有し、Ｆｅの一部がＣｏで置換されうるものである。このうち特に、Ｒ含有量の比較的少ない磁石の製造に本発明は適する。磁石中の酸素はＲ酸化物として存在するものが多いと考えられる。Ｒ含有量の比較的少ない磁石は、元素Ｒの酸化に対するマージンが小さい。すなわち、Ｒ含有量が比較的多い場合と同等の酸素含有量であっても、元素Ｒの酸化率は高くなり、その結果、磁石特性発現のために必要なＲが不足し、磁石特性が低くなりやすい。製造が容易な原料粉末は、前述したように酸素含有量が比較的多いため、この原料粉末を単独で用いると、良好な磁石特性を得ることは難しい。
【００１７】
これに対し本発明では、いずれも製造が容易な酸素リッチ原料および酸素プア原料を用いることで、酸素含有量の比較的少ない焼結磁石を容易に実現できる。Ｒ含有量の少ない磁石は残留磁束密度を高くできるため、本発明により、残留磁束密度、保磁力および角形比のいずれもが良好な焼結磁石を容易に実現できる。
【００１８】
ところで、特許第２５７１４０３号公報には、Ｆｅ−Ｂ−Ｒ系（ＲはＮｄ、Ｐｒ、Ｄｙ、Ｈｏ、Ｔｂの少なくとも１種）磁石用のＣａ還元粉末４０〜９５重量％と、上記Ｆｅ−Ｂ−Ｒ系磁石用の鋳塊粉砕粉末５〜６０重量％とを混合配合して、Ｒ：２７〜３７重量％、Ｂ：０．５〜５重量％、Ｆｅ：５８〜７２．５重量％を有する混合原料粉末中のＯ_２含有量を３５００ｐｐｍ以下に調整後、微粉砕、プレス成形、焼結することにより、希土類磁石を製造する方法が記載されている。
【００１９】
この方法で用いるＣａ還元粉末とは、希土類酸化物のうち少なくとも１種および鉄粉、ならびに、純ボロン粉、フェロボロン粉およびホウ素酸化物のうち少なくとも１種、または、上記構成元素の合金粉または混合酸化物を所要組成に配合した混合粉に、金属ＣａおよびＣａＣｌ_２を混合して、不活性ガス雰囲気中にて還元拡散を行って得られた反応生成物をスラリー化し、水処理したものである。Ｃａ還元粉末は、安価であるが、還元後、還元剤であるＣａ（還元後はＣａＯ）を除去する工程において水を使用するため、鋳塊粉砕粉末と比較して含有Ｏ_２量が多く、かつ含有Ｏ_２量の変動が大きいことから、得られる焼結磁石の組成に変動を生じやすく、磁石特性にばらつきが生じる。そのため、同公報では、Ｃａ還元粉末と鋳塊粉砕粉末との混合物を微粉砕し、成形して焼結することにより、焼結磁石中のＯ_２量を低減している。同公報には、Ｃａ還元粉末のＯ_２含有量は２０００〜５０００ｐｐｍが好ましく、鋳塊粉砕粉砕中のＯ_２含有量は５００〜２５００ｐｐｍが好ましいことが記載されており、含有酸素量は、実施例１において、鋳塊粉砕粉が１１００ｐｐｍ、Ｃａ還元粉が４０００ｐｐｍであり、実施例２において、鋳塊粉砕粉が１５００ｐｐｍ、Ｃａ還元粉が４３００ｐｐｍである。
【００２０】
酸素含有量の相異なる２種の粉末の混合物を成形して焼結し、希土類焼結磁石を得るという点で、本発明と特許第２５７１４０３号公報に記載された発明とは類似する。しかし、同公報では、Ｃａ還元粉と鋳塊粉砕粉とを混合した後、微粉砕している。同公報に記載されたＣａ還元粉は、一般に球状粒子であり、粉砕後も球状となりやすく、一方、鋳造や急冷法により製造した合金を粉砕すると、一般に不定形の粉砕粉が得られる。そのため、Ｃａ還元粉の粗粉と鋳塊粉砕粉の粗粉とを混合して同時に粉砕した場合、両者を同等の粒度とすることは困難である。そのため、混合粉末中においてＣａ還元粉の分散が不均一となりやすい。その結果、期待される磁石性能が得られなかったり、磁石性能にばらつきが生じたりしやすくなる。このような問題は、混合粉末中におけるＣａ還元粉の比率が低い場合に特に生じやすい。また、Ｃａ還元粉は球状であるため、スプリングバックが大きく、成形体の保型性が低くなるという問題もある。また、Ｃａ還元粉は、ＣａやＣｌなどの不純物を多く含むため、高特性磁石の原料には不向きである。
【００２１】
これに対し本発明では、Ｃａ還元粉ではなく、鋳造や急冷法などにより製造した合金を粉砕した合金粉末を用いるため、上記問題は生じない。
【００２２】
【発明の実施の形態】
本発明の製造方法は、Ｒ（Ｒは、希土類元素の少なくとも１種であり、本明細書において希土類元素とは、Ｙ、Ｓｃおよびランタノイドである）を含有する原料合金を製造する原料合金製造工程と、原料合金を１段階または多段階で粉砕して原料粉末を得る粉砕工程と、原料粉末を成形して成形体を得る成形工程と、成形体を焼結して焼結磁石を得る焼結工程とを有する。
【００２３】
本明細書では、原料合金またはその粉砕粉を原料と呼ぶ。本発明では、酸素含有量が相対的に多くなるように製造した酸素リッチ原料と、酸素含有量が相対的に少なくなるように製造した酸素プア原料とを用意する。酸素リッチ原料および酸素プア原料は、いずれも１種または２種以上の原料から構成される。ここで、２種以上の原料とは、組成が相異なる複数の原料を意味するほか、組成が同じで酸素含有量が相異なる複数の原料も意味する。なお、組成が相異なる原料は、製造条件が同じであっても酸素含有量は同じとはならないのが一般的である。
【００２４】
本発明では、酸素リッチ原料と酸素プア原料とを、成形工程の前に混合することを特徴とする。
【００２５】
酸素リッチ原料の酸素含有量（質量比）と酸素プア原料の酸素含有量（質量比）との差は、３００ｐｐｍ以上、好ましくは５００ｐｐｍ以上、より好ましくは１０００ｐｐｍ以上である。なお、本発明において、酸素リッチ原料および酸素プア原料の酸素含有量とは、これら両者を混合する直前における酸素含有量を意味する。前述したように、酸素含有量が比較的少ない原料および比較的多い原料は製造が容易であるが、酸素含有量がその中間である原料は安定して製造することが困難である。そのため、酸素リッチ原料と酸素プア原料との酸素含有量の差を、上記範囲を下回る程度に小さくしようとすると、原料の製造が容易になるという本発明の効果が得られにくくなる。なお、酸素リッチ原料および酸素プア原料の少なくとも一方が、酸素含有量の相異なる２種以上の原料から構成される場合における上記差とは、酸素リッチ原料のうち酸素含有量が最も少ないものと、酸素プア原料のうち酸素含有量が最も多いものとの差を意味する。
【００２６】
ただし、酸素リッチ原料と酸素プア原料との酸素含有量の差が著しく大きくなるように設定する場合、酸素プア原料の酸素含有量を著しく少なくする、および／または、酸素リッチ原料の酸素含有量を著しく多くする必要がある。酸素プア原料の酸素含有量を著しく少なくする場合、酸素プア原料の製造が困難となる。酸素リッチ原料の酸素含有量を著しく多くする場合、両原料中における酸素リッチ原料の比率をかなり低くする必要が生じ、その結果、両原料（粉末）の混合物中において酸素リッチ原料を均一に分散させることが困難となり、磁石特性の低下を招きやすい。このような理由から、酸素リッチ原料と酸素プア原料との酸素含有量の差は、４０００ｐｐｍ以下、特に３０００ｐｐｍ以下であることが好ましい。
【００２７】
酸素プア原料の酸素含有量（質量比）は、好ましくは３００〜２０００ｐｐｍ、より好ましくは４００〜１０００ｐｐｍ、さらに好ましくは４００〜９００ｐｐｍである。この範囲を下回る酸素含有量とすることは困難であり、また、酸素含有量が著しく少ない合金粉末は、活性度が高いため取り扱いが困難である。一方、本発明において酸素プア原料を用いるのは、前述したように、希土類焼結磁石に適した酸素含有量をもつ原料を安定して製造することが困難だからである。したがって、酸素含有量が上記範囲を上回る酸素プア原料が安定して製造できるのであれば、本発明を採用する意義が小さい。
【００２８】
酸素リッチ原料の酸素含有量（質量比）は、好ましくは６００〜５０００ｐｐｍ、より好ましくは１０００〜４０００ｐｐｍである。酸素含有量がこの範囲を下回る酸素リッチ原料が安定して製造できるのであれば、本発明を採用する意義が小さい。一方、酸素含有量がこの範囲を上回る合金粉末を製造しようとすると、合金粉末が急激に酸化する、すなわち燃えてしまうことがあるので、安定して製造することが困難である。本発明は、Ｎｄ_２Ｆｅ_１４Ｂ系磁石およびＳｍＣｏ_５系磁石の製造に好適であるが、Ｎｄ_２Ｆｅ_１４Ｂ系合金はＳｍＣｏ_５系合金に比べ酸化により特性が低下しやすいため、Ｎｄ_２Ｆｅ_１４Ｂ系の酸素リッチ原料の酸素含有量は、１２００〜３７００ｐｐｍであることがさらに好ましい。
【００２９】
なお、酸素プア原料の好ましい酸素含有量範囲と酸素リッチ原料の好ましい酸素含有量範囲とがオーバーラップしているのは、酸素プア原料において再現性よく容易に実現可能な酸素含有量が組成等によって異なり、かつ、酸素リッチ原料において再現性よく容易に実現できる酸素含有量が組成等によって異なるためである。
【００３０】
ところで、たとえば酸素プア原料を２種以上用いる場合において、これら２種以上の原料を製造する際に、製造工程における雰囲気中の酸素濃度が同じとなるように制御しても、酸素濃度の微小な差や原料組成の相違に起因して、それぞれの酸素含有量は相異なることが普通である。しかし、酸素プア原料として製造されたものは、酸素含有量のばらつきはあっても、酸素リッチ原料として製造されたものよりは酸素含有量が少なくなる。具体的には、酸素プア原料同士の間の酸素含有量の差（酸素プア原料が３種以上ある場合、この差は３以上存在するが、その場合はそのなかの最大値）は、酸素リッチ原料と酸素プア原料との間の酸素含有量の差（酸素プア原料が３種以上ある場合、この差は３以上存在するが、その場合はそのなかの最小値）よりも小さくなる。また、酸素プア原料として２種以上の原料を使用する場合も同様である。さらに、酸素プア原料および酸素リッチ原料をいずれも２種以上使用する場合も、同様である。
【００３１】
すなわち、酸素リッチ原料および酸素プア原料の少なくとも一方が、酸素含有量の相異なる２種以上の原料から構成される場合、その２種以上の原料間における酸素含有量の差（最大値）は、酸素リッチ原料と酸素プア原料との間の酸素含有量の差（最小値）よりも小さい。たとえば、２種以上の酸素リッチ原料からなるグループと、２種以上の酸素プア原料からなるグループとにおいて、同じグループに所属する原料同士の酸素含有量の差より、相異なるグループに所属する原料同士の酸素含有量の差のほうが大きい。
【００３２】
なお、通常、酸素リッチ原料および酸素プア原料はいずれも１種だけ用いれば本発明の効果は十分に実現する。ただし、後述する２合金法に本発明を適用する場合には、酸素リッチ原料および酸素プア原料の一方または両方、通常は一方だけを、酸素含有量の相異なる２種の原料から構成する。すなわち、本発明では、４種を超える原料を用いる必要はなく、通常は３種以下の原料を用いる。
【００３３】
酸素リッチ原料と酸素プア原料との合計に対する酸素リッチ原料の比率は、１０質量％以上９０質量％未満であることが好ましい。この比率が低すぎても高すぎても、酸素リッチ原料と酸素プア原料とを混合して用いることによる効果が十分に実現しなくなる。また、本発明により製造される焼結磁石の好ましいＲ含有量およびそれに対応する好ましい酸素含有量から考えて、両原料中において酸素リッチ原料の比率は、より好ましくは６０質量％以下、さらに好ましくは５０質量％未満、特に好ましくは２０〜４０質量％である。本発明では、磁石中のＲ含有量を比較的少なくすることが好ましいが、前述したように、Ｒ含有量の少ない磁石は酸素含有量が多くなると性能が著しく低下する。また、酸素リッチ原料は、酸素含有量を比較的多くするほうが製造が容易である。したがって、製造の容易な原料を用いて、Ｒ含有量の比較的少ない高性能な焼結磁石を得るためには、上記のように両原料中における酸素リッチ原料の比率をあまり多くしないことが好ましく、相対的に少なくすることがより好ましい。
【００３４】
なお、酸素含有量は、原料合金よりもその粉砕粉のほうが多くなり、また、粉砕を多段階で行う場合、粉砕が進むにつれて多くなる。また、酸素リッチ原料と酸素プア原料とを混合した後にさらに粉砕を行う場合において、両原料の組成およびサイズが著しく異ならなければ、混合時における両原料の酸素含有量の差は、その後の粉砕においてもほぼ維持され、大きくは変わらない。
【００３５】
酸素リッチ原料および酸素プア原料において、それぞれの酸素含有量および比率の具体的値は、得ようとする焼結磁石の酸素含有量に応じて決定すればよい。本発明により製造される焼結磁石の酸素含有量（質量比）は、好ましくは５００〜４５００ｐｐｍである。焼結磁石の酸素含有量が少なすぎると、高保磁力および高角形比が得られにくく、多すぎると、高残留磁束密度が得られにくい。Ｎｄ_２Ｆｅ_１４Ｂ系合金はＳｍＣｏ_５系合金に比べ酸化により磁石特性が低下しやすいため、Ｎｄ_２Ｆｅ_１４Ｂ系焼結磁石では、酸素含有量を好ましくは５００〜３０００ｐｐｍ、より好ましくは６００〜２５００ｐｐｍ、さらに好ましくは８００〜２４００ｐｐｍとすることが望ましい。
【００３６】
原料合金は、鋳造法または急冷法により製造される。急冷法では、合金溶湯を一方向または対向する二方向から冷却することにより固化し、たとえばストリップ状の急冷合金を得る。一方向から冷却する方法としては、単ロール法や回転ディスク法が好ましく、二方向から冷却する方法としては双ロール法が好ましい。
【００３７】
粉砕は、２段階以上で行うことが好ましい。通常、まず、急冷合金を水素ガスを吸蔵させて粗粉砕する水素吸蔵粉砕工程（第１の粗粉砕工程）を設ける。次いで、ディスクミル等により１０〜１００μｍ程度の粒径まで粉砕する第２の粗粉砕工程を設ける。次いで、ジェットミル等により０．５〜５μｍ程度の粒径まで粉砕する微粉砕工程を設ける。ただし、第２の粗粉砕工程は、省略してもよい。
【００３８】
酸素リッチ原料および酸素プア原料の酸素含有量を制御する手段としては、原料を製造する工程において雰囲気中の酸素濃度を制御する方法を用いることが好ましい。具体的には、原料合金製造の際、および／または、原料合金粉砕の際に、雰囲気中の酸素濃度を制御すればよい。
【００３９】
また、多孔性物質の孔部内に酸化性気体または水分を含ませておき、この多孔性物質を原料合金またはその粉砕粉に接触させるかその近傍に配置することによっても、原料の酸素含有量を制御することが可能である。前記多孔性物質としては、たとえばスポンジや紙、織布、不織布を用いることができる。合金を多段階で粉砕する際には、前段の粉砕工程により得られた粉末を、次段の粉砕工程に気流によって輸送することが一般的であるが、この輸送に利用する配管の内壁に、多孔性物質を貼り付ければよい。なお、配管の内壁は一般に平滑であるが、粉末に対する多孔性物質の接触面積を大きくするために、配管の内壁の一部に凹凸を設け、そこに多孔性物質を貼り付けてもよい。また、粉末の混合装置内に多孔性物質を配置してもよい。その場合、混合装置の内壁に多孔性物質を貼り付けてもよく、スクリュー状、リボン状、パドル状などの混合羽根に、多孔性物質を貼り付けてもよい。なお、多孔性物質に酸化性気体を補充する方法は特に限定されず、たとえば、装置内部に取り付けた多孔性物質を取り外し、空気や酸素ガスにさらせばよい。ただし、配管内部に多孔性物質を貼り付けた状態で、装置の点検や清掃の際に配管内に空気を導入するだけでもよい。このとき導入する空気が、水蒸気を含む通常の空気であれば、同時に水分の補充も可能なので、多孔性物質を取り外して水に漬ける必要はない。
【００４０】
酸素含有量制御の具体的手順を、以下に例示する。
【００４１】
本発明では、たとえば、酸素リッチ原料の原料合金と、酸素プア原料の原料合金とを、それぞれ酸素含有量を制御して製造した後、両原料合金を混合して同時に粉砕してもよい。
【００４２】
また、たとえば、酸素含有量が同一である２つの原料合金（組成は同一であっても異なっていてもよい）を、相異なる酸素含有量となるように制御しながら独立して粗粉砕することにより、酸素リッチ原料の粗粉と酸素プア原料の粗粉とを作製し、次いで、両粗粉を混合した後、微粉砕してもよい。また、前記２つの原料合金を、独立して粗粉砕した後、独立して微粉砕することにより、酸素リッチ原料の微粉と酸素プア原料の微粉とを独立して作製し、次いで、両微粉を混合してもよい。この場合、相異なる酸素含有量とするための操作は、粗粉砕工程および微粉砕工程のいずれか一方だけで実施してもよく、両工程で実施してもよい。独立して粉砕した後に混合することにより、酸素リッチ原料と酸素プア原料との酸素含有量の差を大きくすることが容易となるので、磁石全体の酸素含有量の制御が容易になるとともに、酸素含有量の調整範囲が広がる。このような効果は、微粉砕後に混合する場合により高くなり、また、粗粉砕および微粉砕の両工程において、相異なる酸素含有量とするための操作を行う場合により高くなる。すなわち、このような効果を十分に得るためには、多段階の粉砕の最終段階終了後に、酸素リッチ原料と酸素プア原料とを混合することが好ましい。また、粗粉砕粉は粒径が大きいため、酸化されにくい。そのため、酸素含有量の特に多い粗粉砕粉（酸素リッチ原料）を得ようとする場合、粉砕時や粉末搬送時の雰囲気中の酸素濃度を高くする以外に、加熱が必要になったりするなど制御すべき項目が増え、生産上好ましくない。したがって、この点からも、多段階の粉砕の最終段階終了後に、酸素リッチ原料と酸素プア原料とを混合することが好ましい。
【００４３】
なお、前述したように、原料の酸素含有量を比較的多くすることおよび比較的少なくすることは容易であっても、その中間の酸素含有量をもつ原料を安定して製造することは困難である。これが、本発明がなされた背景である。したがって、酸素プア原料を製造する際に、合金鋳造工程、合金溶湯急冷工程、粉砕工程などにおける酸素濃度や酸素分圧の具体的値は特に限定されず、利用する製造装置に応じ、比較的少ない酸素含有量をもつ原料がその装置で安定して製造できるように製造条件を設定すればよい。酸素リッチ原料においても同様であり、利用する製造装置に応じ、比較的多い酸素含有量をもつ原料がその装置で安定して製造できるように製造条件を設定すればよい。
【００４４】
酸素リッチ原料と酸素プア原料とは、組成が同一であっても異なっていてもよい。また、酸素リッチ原料および／または酸素プア原料は、組成の相異なる２種以上の原料を含むものであってもよい。
【００４５】
組成の相異なる原料を用いる場合としては、いわゆる２合金法を用いる場合が挙げられる。２合金法は、組成の異なる２種の合金粉末を混合して焼結することにより、磁気特性や耐食性を向上させる方法である。２合金法に関して様々な提案がなされているが、いずれも主相とほぼ同じ組成（Ｒ_２Ｆｅ_１４Ｂ）の合金粉末に第二の合金の粉末を添加するものである。第二の合金としては、主相よりもＲ比率が高く融点の低いＲリッチ合金（特開平４−３３８６０７号公報、特開平５−１０５９１５号公報等）、Ｒの種類が主相とは異なるＲ_２Ｆｅ_１４Ｂ合金（特開昭６１−８１６０３号公報等）、Ｒの金属間化合物を含むもの（特開平５−２１２１９号公報等）などがある。また、特開平７−１７６４１４号公報には、主相用母合金の粉末と粒界相用母合金の粉末との混合物からなる成形体を焼結して磁石とする方法が開示されている。同公報において主相用母合金とは、実質的にＲ_２（Ｆｅ，Ｃｏ）_１４Ｂから構成される柱状結晶粒と、Ｒ_２（Ｆｅ，Ｃｏ）_１４ＢよりもＲの含有率が高いＲリッチ相を主体とする結晶粒界とを有するものであり、粒界相用母合金とは、Ｒを３２〜６０質量％含み、残部が実質的にＣｏ、またはＣｏおよびＦｅである結晶質合金である。同公報では前記混合物中における主相用母合金の比率を６０〜９５質量％としている。
【００４６】
本発明において２合金法を用いる場合、組成の相異なる２種の原料のうちの一方を酸素リッチ原料とし、他方を酸素プア原料としてもよい。ただし、両原料の混合比は、磁石の最終組成に応じて決定される（たとえば、主相とほぼ同じ組成の合金粉末は混合比が高くなる）ので、磁石中の酸素含有量を所望の値とするのが困難となることがある。このような問題を回避するために、組成の相異なる２種の原料の一方を、酸素リッチ原料と酸素プア原料とに分割してもよい。また、組成の相異なる２種の原料の両方を、いずれも酸素リッチ原料と酸素プア原料とに分割してもよい。
【００４７】
成形は、好ましくは磁場中で行う。この場合、磁場強度は８００ｋＡ／ｍ以上、成形圧力は１０〜５００ＭＰａ程度であることが好ましい。成形には、一軸加圧またはＣＩＰなどの等方加圧のいずれを用いてもよい。
【００４８】
得られた成形体を、焼結する。焼結条件は、磁石組成に応じて適宜決定すればよく、たとえばＮｄ_２Ｆｅ_１４Ｂ系組成およびＳｍＣｏ_５系組成では、１０００〜１２００℃で０．１〜１００時間焼結すればよい。焼結は、複数回行ってもよい。焼結は、非酸化性雰囲気、たとえば真空中またはＡｒガス等の不活性ガス雰囲気中で行うことが好ましい。また、加圧焼結（ホットプレス）を行ってもよい。
【００４９】
焼結後、保磁力を向上させるために時効処理を行うことが好ましい。たとえばＮｄ_２Ｆｅ_１４Ｂ系磁石では、好ましくは不活性ガス雰囲気中において、好ましくは５００℃以上焼結温度以下の温度、より好ましくは５００〜９５０℃の温度で、０．１〜１００時間時効処理を行うことが好ましい。なお、時効処理は、多段階の熱処理から構成してもよい。例えば２段の熱処理からなる時効処理では、１段目の熱処理を７００℃以上焼結温度未満の温度で０．１〜５０時間行い、２段目の熱処理を５００〜７００℃で０．１〜１００時間行うことが好ましい。一方、ＳｍＣｏ_５系磁石では、焼結工程の降温過程の一部において、降温速度を遅くして徐冷することにより、時効処理を行うことができる。
【００５０】
本発明により製造される希土類焼結磁石の組成は特に限定されないが、本発明はＮｄ_２Ｆｅ_１４Ｂ系焼結磁石の製造に特に好適である。
【００５１】
本発明が適用されるＮｄ_２Ｆｅ_１４Ｂ系焼結磁石は、Ｒとして少なくともＮｄおよび／またはＰｒを含有し、さらに、ＦｅおよびＢを含有するものが好ましく、Ｆｅの一部をＣｏで置換したものがより好ましい。各元素の含有量は、
Ｒ：２８〜３２質量％、
Ｂ：０．８〜１．２質量％、
残部：Ｆｅ
であることが好ましい。各元素の含有量をこのような範囲内とすることにより、良好な磁石特性が得られる。特に、
Ｒ：２８〜３１．５質量％、
Ｂ：０．９〜１．１質量％、
残部：Ｆｅ
とすれば、より高い残留磁束密度が得られる。
【００５２】
Ｒ含有量が少なくなるにつれて残留磁束密度は向上するが、Ｒ含有量が少なくなりすぎると、α−Ｆｅ相等の鉄に富む相が析出して粉砕に悪影響を与え、磁気特性も低下する。また、焼結が困難となって焼結密度が低くなってしまうので、残留磁束密度向上は頭打ちになってしまう。Ｒ含有量が多すぎると、高残留磁束密度が得られなくなる。元素Ｒには、Ｎｄおよび／またはＰｒが必ず含まれる。ＮｄとＰｒとの比率は特に限定されない。元素ＲとしてＮｄおよび／またはＰｒだけを用いてもよいが、これら以外の希土類元素、すなわちＹ、Ｓｃ、Ｌａ、Ｃｅ、Ｐｍ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、ＹｂおよびＬｕの少なくとも１種を用いてもよい。これらのうちでは、Ｄｙおよび／またはＴｂが好ましい。磁石特性を低下させないためには、ＮｄおよびＰｒの両者以外の元素の合計量は、元素Ｒ全体の３０質量％以下とすることが好ましい。なお、元素Ｒとして２種以上の元素を用いる場合、原料としてミッシュメタル等の混合物を用いることもできる。
【００５３】
Ｂ含有量が少なすぎると、菱面体組織となるため保磁力が低くなる。一方、Ｂ含有量が多すぎると、Ｂリッチな非磁性相が多くなるため残留磁束密度が低くなる。
【００５４】
残部は実質的にＦｅであるが、Ｆｅの一部をＣｏで置換してもよい。Ｃｏを添加することにより、保磁力の温度依存性および耐食性を改善することができ、残留磁束密度も向上できる。ただし、Ｃｏ含有量が多すぎると保磁力が低下するため、磁石中におけるＣｏの含有量は０．１〜１０質量％とすることが好ましい。
【００５５】
焼結磁石中には、上記各元素のほか、微量添加物ないし不可避的不純物として例えばＣｕ、Ｃ、Ｐ、Ｓ、Ａｌ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｂｉ、Ｎｂ、Ｔａ、Ｍｏ、Ｗ、Ｓｂ、Ｇｅ、Ｓｎ、Ｚｒ、Ｎｉ、Ｓｉ、Ｈｆ、Ｇａ、Ｚｎなどの少なくとも１種が含有されていてもよい。ただし、磁石特性低下を抑えるためには、これらの合計含有量を５質量％以下とすることが好ましい。
【００５６】
本発明は、Ｎｄ_２Ｆｅ_１４Ｂ系磁石のほか、Ｒとして少なくともＳｍを含有し、さらにＣｏを含有する焼結磁石の製造にも好適である。このような磁石としては、ＳｍＣｏ_５系立方晶磁性材料が好ましい。この系の磁石では、Ｓｍの一部を他の希土類元素で置換したり、Ｃｏの一部を他の遷移金属元素で置換してもよい。
【００５７】
本発明により製造される焼結磁石の用途は特に限定されず、例えばモータやスピーカなど各種機器に適用可能である。
【００５８】
【実施例】
実施例１
以下に示す組成の原料合金を、急冷法（ストリップキャスティング）により製造した。ただし、組成Ｄのものは鋳造法により製造した。なお、下記組成において、数値は質量百分率である。
【００５９】
組成Ａ：３０．０％Ｎｄ−１．０％Ｂ−０．５％Ｃｏ−０．２％Ａｌ−０．０５％Ｃｕ−Ｆｅ、
組成Ａ１：２９．３％Ｎｄ−１．１％Ｂ−０．２％Ａｌ−０．０５％Ｃｕ−Ｆｅ、
組成Ａ２：４０．５％Ｎｄ−５．０％Ｃｏ−０．２％Ａｌ−０．０５％Ｃｕ−Ｆｅ、
組成Ｂ：２８．９％Ｎｄ−２．０％Ｄｙ−１．０％Ｂ−０．５％Ｃｏ−０．３％Ａｌ−０．０８％Ｃｕ−Ｆｅ、
組成Ｃ：２４．３％Ｎｄ−７．１％Ｄｙ−１．０％Ｂ−１．０％Ｃｏ−０．５Ａｌ−０．０８％Ｃｕ−０．２％Ｓｎ−Ｆｅ、
組成Ｄ：３５．４％Ｓｍ−Ｃｏ
【００６０】
これらの原料合金を、水素吸蔵により粗粉砕した後、窒素ガス気流中で微粉砕することにより、表１〜表７にそれぞれ示す酸素プア原料（微粉）および酸素リッチ原料（微粉）を得た。これらの原料微粉の平均粒径は４．０〜５．５μｍ程度であった。なお、これらの原料微粉の酸素含有量は、粗粉砕および微粉砕における雰囲気中の酸素濃度を制御することにより制御した。具体的には、酸素プア原料微粉は酸素濃度５０ｐｐｍ以下の雰囲気中で、酸素リッチ原料微粉は酸素濃度０．３〜０．５％の雰囲気中でそれぞれ作製した。各表に示す原料微粉の酸素含有量は、不活性ガス融解法により測定した。この測定は、正確な結果を得るために非酸化雰囲気中で行った。
【００６１】
これらの原料微粉を表１〜表７にそれぞれ示す比率で混合し、１２００ｋＡ／ｍの磁場中で圧力１５０ＭＰａで成形した。得られた成形体を真空中において１０００〜１１００℃で４時間焼結した後、アルゴンガス雰囲気中において５００〜９００℃の温度範囲で１〜４時間の時効処理を、１段または多段で行い、焼結磁石サンプルを得た。ただし、組成Ｄの粉末を含む成形体については、水素雰囲気中において１１５０℃で焼結した。
【００６２】
これらの焼結磁石サンプルについて、密度ρ、磁気特性（残留磁束密度Ｂｒ、保磁力ＨｃＪ、角形比Ｈｋ／ＨｃＪ）をＢ−Ｈトレーサで測定した。また、サンプル断面を走査型電子顕微鏡により観察して、異常粒成長（ＡＧＧ：ａｂｎｏｒｍａｌ　ｇｒａｉｎｇｒｏｗｔｈ）の有無を調べた。また、サンプルの酸素含有量を、不活性ガス融解法により測定した。これらの結果を表１〜表７に示す。
【００６３】
【表１】

【００６４】
【表２】

【００６５】
【表３】

【００６６】
【表４】

【００６７】
【表５】

【００６８】
【表６】

【００６９】
【表７】

【００７０】
表１〜表５から、酸素リッチ原料と酸素プア原料とを混合して用いることにより、残留磁束密度、保磁力および角形比がいずれも高い焼結磁石が得られることがわかる。また、酸素リッチ原料と酸素プアとの合計に対する酸素リッチ原料の比率が６０質量％以下、特に５０質量％未満であれば、より良好な磁石特性が得られることがわかる。
【００７１】
表６に示される磁石は、２合金法により製造したものである。表６に示す原料微粉において、組成Ａ１は磁石の主相に近い組成であり、組成Ａ２は磁石の粒界相に近い組成である。そして、組成Ａ１の微粉と組成Ａ２の微粉とを質量比でＡ１：Ａ２＝９：１となるように混合して製造した磁石の組成は、組成Ａの微粉だけを用いて製造した磁石の組成とほぼ同じとなる。表６において、酸素リッチ原料は微粉Ｒ６であり、酸素プア原料は微粉Ｐ６−１および微粉Ｐ６−２である。表６から、２合金法を用いた場合でも、本発明の効果が実現することがわかる。
【００７２】
表７において、サンプルＮｏ．７０１は、酸素リッチ微粉と酸素プア微粉とを用いて製造され、サンプルＮｏ．７０２は、原料微粉を１種だけ用いて製造されたものである。サンプルＮｏ．７０２に用いた原料微粉Ｓの酸素含有量は、サンプルＮｏ．７０２の酸素含有量がサンプルＮｏ．７０１とほぼ同じとなるように設定してある。
【００７３】
表７から、組成がほぼ同じであっても、本発明を適用することにより角形比が向上することが明らかである。
【００７４】
実施例２
実施例１と同様にして粗粉砕まで行うことにより酸素リッチ原料（粗粉）と酸素プア原料（粗粉）とを製造し、これらの粗粉を混合した後、微粉砕した。ただし、表９に示す酸素リッチ粗粉Ｒ９を製造するに際しては、酸素含有量を多くするために、加熱も併用した。微粉砕の際の雰囲気中の酸素濃度は、５０ｐｐｍ以下とした。このほかは実施例１と同様にして、焼結磁石サンプルを作製した。これらのサンプルについて実施例１と同様な測定を行った。結果を表８および表９に示す。
【００７５】
【表８】

【００７６】
【表９】

【００７７】
表８および表９から、酸素リッチ原料と酸素プア原料とを粗粉砕後かつ微粉砕前に混合した場合でも、本発明の効果が得られることがわかる。
【００７８】
実施例３
組成Ｅ：２８．２％Ｎｄ−１．０％Ｂ−０．２％Ｃｏ−０．０５％Ａｌ−０．０５％Ｃｕ−Ｆｅ
の原料合金を用いたほかは実施例２と同様にして、焼結磁石サンプルを作製した。これらのサンプルについて実施例１と同様な測定を行った。結果を表１０に示す。
【００７９】
【表１０】

【００８０】
本実施例で用いた組成Ｅは、Ｒ含有量が少ないため、元素Ｒの酸化に対するマージンが小さい。そのため、酸素量に関連して特性が敏感に変化する。このような低Ｒ組成に対して本発明を適用する場合、酸素リッチ原料の比率を比較的低くすることにより、特に４０質量％以下とすることにより、特に良好な性能が得られることがわかる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to Nd₂Fe₁₄The present invention relates to a method for manufacturing a rare earth sintered magnet such as a B-based magnet.
[0002]
[Prior art]
As a rare earth magnet having high performance, for example, Nd described in Japanese Patent No. 1431617 is used.₂Fe₁₄B-based magnets are known.
[0003]
Nd₂Fe₁₄In order to improve the residual magnetic flux density of the B-based magnet, it is effective to reduce the oxygen content of the magnet. However, Nd₂Fe₁₄If the oxygen content in the B-based sintered magnet is extremely reduced, abnormal grain growth occurs during sintering, and the coercive force and the squareness are reduced, resulting in a problem that the overall magnet properties are not good. Also, SmCo₅Even rare earth sintered magnets having a system composition have the problem that abnormal grain growth occurs during sintering as the amount of oxygen is reduced.
[0004]
In order to improve the coercive force of a rare earth sintered magnet, Japanese Patent Publication No. 4-26525 discloses that rare earth oxides suppress the crystal grain size of a sintered body and rare earth oxides are added to an alloy composed of Nd, Fe and B. Are mixed, ground, and oriented in a magnetic field, molded and sintered to produce a permanent magnet. However, since rare earth oxides are expensive, the cost of the magnet is increased. In addition, the rare earth oxide powder is different from the alloy powder in density, particle size, etc., and has a small amount added to the alloy powder, so that it is difficult to uniformly disperse the powder during mixing, and it takes a long time to mix, It is necessary to use expensive mixing equipment.
[0005]
In Japanese Patent Publication No. 7-107882, the coercive force is improved by controlling the oxygen content in the magnet to be 3000 ppm or more by mass ratio.
[0006]
[Problems to be solved by the invention]
The inventors of the present invention produce a rare earth sintered magnet having a high residual magnetic flux density and a high coercive force by controlling the oxygen content in the rare earth sintered magnet without using an expensive rare earth oxide. An experiment was performed. Rare earth sintered magnets are generally manufactured by coarsely pulverizing a raw material alloy, finely pulverizing, then molding and sintering. By controlling the oxygen concentration in the atmosphere at the time of pulverization, the inventors will control the oxygen content in the sintered magnet to obtain a sintered magnet having both good residual magnetic flux density and good coercive force. An experiment was conducted.
[0007]
As a result, oxygen content in the atmosphere can be reduced to less than 500 ppm by eliminating oxygen in the atmosphere as much as possible during pulverization. As a result, a sintered magnet having a high residual magnetic flux density and a low coercive force can be obtained. did it. However, in this case, the range of the manufacturing conditions was extremely narrow, and the reproducibility was poor. On the other hand, by leaving some oxygen in the atmosphere during the pulverization, the oxygen content of the sintered magnet can be set to about 4000 ppm, and as a result, a sintered magnet having a high coercive force and a high squareness ratio can be obtained.
[0008]
However, in order to improve both the residual magnetic flux density and the coercive force, when the sintered magnet was manufactured by changing the oxygen concentration in the pulverizing atmosphere in various ways, it was found that the residual magnetic flux density and the coercive force in the magnet were both increased. Controlling the oxygen content has proven to be extremely difficult. Specifically, the relationship between the oxygen concentration in the crushing atmosphere and the oxygen content of the crushed powder is not linear. For example, when the oxygen concentration in the atmosphere is reduced, When the oxygen content of the pulverized powder suddenly decreases when the oxygen content decreases, and when the oxygen concentration in the atmosphere increases, the oxygen content of the pulverized powder increases when the oxygen content exceeds a specific oxygen concentration. There was a tendency for the amount to increase rapidly. In addition, since the specific oxygen concentration fluctuated depending on the particle size of the pulverized powder and the amount of processing at the time of pulverization, it was also found that reproducibility was low.
[0009]
The present invention provides Nd with high residual magnetic flux density and high coercive force.₂Fe₁₄An object is to stably and easily manufacture a B-based sintered magnet.
[0010]
[Means for Solving the Problems]
Such an object is achieved by the following (1) to (13) of the present invention.
(1) a raw material alloy manufacturing step of manufacturing a raw material alloy containing R (R is at least one of rare earth elements), a pulverizing step of pulverizing the raw material alloy in one or multiple steps to obtain a raw material powder, Having a molding step of molding a powder to obtain a molded body, and a sintering step of sintering the molded body to obtain a sintered magnet,
When the raw material alloy or its pulverized powder is called raw material,
At least one oxygen-rich raw material, which is a raw material manufactured to have a relatively high oxygen content, and is manufactured so as to have a relatively low oxygen content, and has an oxygen content of 300 ppm more than the oxygen-rich raw material ( (Ratio by mass) A method for producing a rare earth sintered magnet in which at least one kind of oxygen poor raw material which is a raw material less than or equal to the mass ratio is mixed before the forming step.
(2) The method for producing a rare earth sintered magnet according to (1) above, wherein the oxygen content (mass ratio) of the oxygen-rich raw material is 600 to 5000 ppm and the oxygen content (mass ratio) of the oxygen poor raw material is 300 to 2000 ppm. .
(3) The method for producing a rare earth sintered magnet according to the above (1) or (2), wherein the ratio of the oxygen-rich raw material to the total of the oxygen-rich raw material and the oxygen poor raw material is 10% by mass or more and less than 90% by mass.
(4) The method for producing a rare earth sintered magnet according to any one of the above (1) to (3), wherein the ratio of the oxygen-rich raw material to the total of the oxygen-rich raw material and the oxygen poor raw material is 10 to 60% by mass.
(5) At least one of the oxygen-rich raw material and the oxygen poor raw material is composed of two or more raw materials having different oxygen contents, and the maximum value of the difference in oxygen content between the two or more raw materials is the oxygen-rich raw material. The method for producing a rare earth sintered magnet according to any one of the above (1) to (4), which is smaller than a minimum value of a difference in oxygen content between a raw material constituting a raw material and a raw material constituting an oxygen poor raw material.
(6) The method for producing a rare earth sintered magnet according to any one of the above (1) to (5), wherein a sintered magnet having an oxygen content (mass ratio) of 500 to 4500 ppm is produced.
(7) The difference in oxygen content between the oxygen-rich raw material and the oxygen-poor raw material is realized by making the oxygen concentration in the atmosphere different in at least a part of the manufacturing process of both raw materials. The method for producing a rare earth sintered magnet according to any one of the above (1) to (6).
(8) The oxygen-rich raw material is brought into contact with a porous substance having pores containing an oxidizing gas or moisture or is placed near the porous substance in at least a part of the production process, so that the oxygen content is increased. The method for producing a rare earth sintered magnet according to any one of the above (1) to (7), wherein
(9) In the pulverization process, the raw material alloy is pulverized in multiple stages,
The method for producing a rare earth sintered magnet according to any one of the above (1) to (8), wherein the oxygen-rich raw material and the oxygen poor raw material are mixed after at least one stage of pulverization.
(10) In the pulverizing step, the raw material alloy is pulverized in multiple stages,
The method for producing a rare earth sintered magnet according to any one of (1) to (8), wherein the oxygen-rich raw material and the oxygen-poor raw material are mixed after the final stage of the multi-stage pulverization.
(11) The method for producing a rare earth sintered magnet according to any one of the above (1) to (10), wherein a sintered magnet containing R, Fe and B is produced.
(12) The method for producing a rare earth sintered magnet according to (11) above, wherein the R content of the sintered magnet is 28 to 32% by mass.
(13) The method for producing a rare earth sintered magnet according to any one of the above (1) to (10), wherein the sintered magnet contains at least Sm as R and further contains Co.
[0011]
[Action and effect]
In order to obtain a rare earth sintered magnet having both high residual magnetic flux density and high coercive force, it is effective to control the magnet so that the oxygen content is within a specific range as described above. However, as described above, it is easy to set the oxygen content such that only one of the residual magnetic flux density and the coercive force is increased, but it is difficult to stably realize the oxygen content in which both are increased. .
[0012]
Therefore, in the present invention, when manufacturing a rare earth sintered magnet, an oxygen-rich raw material manufactured to have a high oxygen content and an oxygen poor raw material manufactured to have a low oxygen content are mixed and used. . In this specification, the raw material is a raw material alloy produced by a quenching method or a casting method or a pulverized powder thereof.
[0013]
As described above, the oxygen poor raw material can be easily manufactured by using an atmosphere from which oxygen is eliminated as much as possible, and the oxygen-rich raw material can be easily manufactured by leaving oxygen to some extent in the atmosphere. The oxygen content of the sintered magnet can be accurately controlled by controlling the mixing ratio between the oxygen poor raw material and the oxygen-rich raw material. Therefore, in the present invention, a rare earth sintered magnet having both high residual magnetic flux density and high coercive force can be easily and reproducibly manufactured. In addition, according to the present invention, it is not necessary to use a rare earth oxide which is difficult to disperse uniformly and is expensive, so that a rare earth sintered magnet with stable and high performance can be manufactured at low cost.
[0014]
Furthermore, it was found that a magnet having a high squareness ratio can be obtained by using the manufacturing method of the present invention. That is, when a sintered magnet manufactured using a single raw material by a conventional method and a sintered magnet manufactured according to the present invention are compared, the sintered magnet manufactured according to the present invention has the same oxygen content even when the oxygen content is the same. Has a higher squareness ratio.
[0015]
In addition, in this specification, squareness means Hk / HcJ. Hk in Hk / HcJ is the external magnetic field strength when the magnetic flux density becomes 90% of the residual magnetic flux density in the second quadrant of the magnetic hysteresis loop. If Hk is low, a high maximum energy product cannot be obtained. Hk / HcJ is an index of the magnet performance, and indicates the degree of squareness in the second quadrant of the magnetic hysteresis loop. Even if HcJ is the same, the larger the Hk / HcJ, the sharper the distribution of the microscopic coercive force in the magnet, so that the magnetization becomes easier and the magnetization variation becomes smaller, and the maximum energy product becomes higher. Become. Further, the stability of the magnetization against changes in the external demagnetizing field and the self-demagnetizing field when the magnet is used is improved, and the performance of the magnetic circuit including the magnet is stabilized.
[0016]
The present invention is suitable for producing a sintered magnet containing at least Nd and / or Pr as the rare earth element R and further containing Fe and B. The magnet of this composition system is Nd₂Fe₁₄R such as B₂Fe₁₄It has a hard magnetic phase composed of a B intermetallic compound and can partially replace Fe with Co. Among them, the present invention is particularly suitable for producing a magnet having a relatively low R content. It is considered that oxygen in the magnet often exists as an R oxide. A magnet having a relatively low R content has a small margin for oxidation of the element R. That is, even if the oxygen content is the same as that of the case where the R content is relatively large, the oxidation rate of the element R is high, and as a result, R required for developing the magnet properties is insufficient, and the magnet properties are low. Prone. As described above, since the raw material powder which is easy to produce has a relatively high oxygen content, it is difficult to obtain good magnet properties if this raw material powder is used alone.
[0017]
In contrast, in the present invention, a sintered magnet having a relatively low oxygen content can be easily realized by using an oxygen-rich raw material and an oxygen poor raw material, both of which are easily manufactured. Since a magnet having a small R content can increase the residual magnetic flux density, the present invention can easily realize a sintered magnet having good residual magnetic flux density, coercive force and squareness ratio.
[0018]
By the way, Japanese Patent No. 2571403 discloses that Fe-B-R (R is at least one of Nd, Pr, Dy, Ho, and Tb) 40 to 95% by weight of a Ca reduced powder for a magnet and the Fe-B -5 to 60% by weight of ingot pulverized powder for R-based magnets is mixed and mixed to obtain R: 27 to 37% by weight, B: 0.5 to 5% by weight, and Fe: 58 to 72.5% by weight. O in the mixed raw material powder having₂A method for producing a rare-earth magnet by adjusting the content to 3500 ppm or less, finely pulverizing, press-forming, and sintering is described.
[0019]
The Ca reduced powder used in this method is at least one of rare earth oxides and iron powder, and at least one of pure boron powder, ferroboron powder and boron oxide, or an alloy powder or a mixture of the above constituent elements. Metal Ca and CaCl are added to the mixed powder in which the oxide is blended to the required composition.₂Are mixed and subjected to reductive diffusion in an inert gas atmosphere to obtain a reaction product, which is slurried and treated with water. Although the Ca reduced powder is inexpensive, water is used in the step of removing the reducing agent Ca (CaO after the reduction) after the reduction, so that the content of the reduced O powder is smaller than that of the ingot pulverized powder.₂Large amount and containing O₂Due to the large variation in the amount, the composition of the obtained sintered magnet tends to fluctuate, and the magnet characteristics vary. Therefore, in the same publication, a mixture of reduced Ca powder and crushed ingot powder is finely pulverized, molded and sintered to obtain O 2 in a sintered magnet.₂The amount has been reduced. The same publication states that O powder of Ca reduced powder₂The content is preferably 2000 to 5000 ppm, and O₂It is described that the content is preferably 500 to 2500 ppm, and the content of oxygen is 1100 ppm for ingot pulverized powder and 4000 ppm for Ca reduced powder in Example 1, and in Example 2, the ingot pulverized powder is 1500 ppm, Ca reduced powder is 4300 ppm.
[0020]
The present invention is similar to the invention described in Japanese Patent No. 2571403 in that a mixture of two kinds of powders having different oxygen contents is molded and sintered to obtain a rare earth sintered magnet. However, in this publication, the reduced Ca powder and the ingot pulverized powder are mixed and then finely pulverized. The Ca-reduced powder described in the publication is generally spherical particles and tends to be spherical even after pulverization. On the other hand, when an alloy produced by casting or quenching is pulverized, an amorphous pulverized powder is generally obtained. Therefore, when the coarse powder of the Ca-reduced powder and the coarse powder of the ingot pulverized powder are mixed and pulverized at the same time, it is difficult to make both particles the same particle size. Therefore, the dispersion of the reduced Ca powder in the mixed powder tends to be uneven. As a result, the expected magnet performance cannot be obtained or the magnet performance tends to vary. Such a problem tends to occur particularly when the ratio of the Ca reduced powder in the mixed powder is low. Further, since the Ca reduced powder is spherical, there is a problem that the springback is large and the shape retention of the molded body is lowered. Further, the Ca reduced powder contains many impurities such as Ca and Cl, and thus is not suitable as a raw material for high-performance magnets.
[0021]
On the other hand, in the present invention, the above problem does not occur because an alloy powder obtained by pulverizing an alloy produced by casting or quenching is used instead of Ca reduced powder.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
The production method of the present invention is a raw alloy production step for producing a raw alloy containing R (R is at least one kind of rare earth element, and in this specification, the rare earth elements are Y, Sc and lanthanoid). And a pulverizing step of pulverizing the raw material alloy in one or more stages to obtain a raw material powder, a forming step of forming the raw material powder to obtain a compact, and a sintering of the compact to obtain a sintered magnet And a process.
[0023]
In this specification, a raw material alloy or its pulverized powder is referred to as a raw material. In the present invention, an oxygen-rich raw material manufactured to have a relatively high oxygen content and an oxygen poor raw material manufactured to have a relatively low oxygen content are prepared. Each of the oxygen-rich raw material and the oxygen-poor raw material is composed of one or two or more raw materials. Here, the two or more kinds of raw materials mean a plurality of raw materials having different compositions and also a plurality of raw materials having the same composition and different oxygen contents. Note that raw materials having different compositions generally do not have the same oxygen content even under the same production conditions.
[0024]
The present invention is characterized in that the oxygen-rich raw material and the oxygen-poor raw material are mixed before the forming step.
[0025]
The difference between the oxygen content (mass ratio) of the oxygen-rich raw material and the oxygen content (mass ratio) of the oxygen poor raw material is 300 ppm or more, preferably 500 ppm or more, more preferably 1000 ppm or more. In the present invention, the oxygen content of the oxygen-rich raw material and the oxygen-poor raw material means the oxygen content immediately before mixing both of them. As described above, a raw material having a relatively low oxygen content and a raw material having a relatively high oxygen content are easy to produce, but a raw material having an intermediate oxygen content is difficult to produce stably. Therefore, if the difference between the oxygen content of the oxygen-rich raw material and the oxygen content of the oxygen-poor raw material is reduced below the above range, the effect of the present invention that the production of the raw material is facilitated becomes difficult to obtain. Note that the difference in the case where at least one of the oxygen-rich raw material and the oxygen poor raw material is composed of two or more raw materials having different oxygen contents means that the oxygen-rich raw material has the lowest oxygen content, It means the difference from the oxygen poor raw material having the highest oxygen content.
[0026]
However, when the difference in oxygen content between the oxygen-rich raw material and the oxygen-poor raw material is set to be significantly large, the oxygen content of the oxygen-poor raw material is significantly reduced and / or the oxygen content of the oxygen-rich raw material is reduced. Need to be significantly higher. When the oxygen content of the oxygen poor raw material is significantly reduced, it becomes difficult to produce the oxygen poor raw material. When the oxygen content of the oxygen-rich raw material is significantly increased, the ratio of the oxygen-rich raw material in both raw materials needs to be considerably reduced. As a result, the oxygen-rich raw material is uniformly dispersed in the mixture of both raw materials (powder). This makes it difficult to reduce the magnet properties. For this reason, the difference in oxygen content between the oxygen-rich raw material and the oxygen-poor raw material is preferably 4000 ppm or less, particularly preferably 3000 ppm or less.
[0027]
The oxygen content (mass ratio) of the oxygen poor raw material is preferably 300 to 2000 ppm, more preferably 400 to 1000 ppm, and further preferably 400 to 900 ppm. It is difficult to reduce the oxygen content below this range, and alloy powders with extremely low oxygen content are difficult to handle due to high activity. On the other hand, the reason why the oxygen poor raw material is used in the present invention is that, as described above, it is difficult to stably produce a raw material having an oxygen content suitable for a rare earth sintered magnet. Therefore, if the oxygen poor raw material having an oxygen content exceeding the above range can be produced stably, the significance of adopting the present invention is small.
[0028]
The oxygen content (mass ratio) of the oxygen-rich raw material is preferably from 600 to 5,000 ppm, more preferably from 1,000 to 4,000 ppm. If the oxygen-rich raw material having an oxygen content below this range can be produced stably, the significance of adopting the present invention is small. On the other hand, if an attempt is made to produce an alloy powder having an oxygen content exceeding this range, the alloy powder may be rapidly oxidized, that is, burnt, so that it is difficult to produce it stably. The present invention relates to Nd₂Fe₁₄B-based magnet and SmCo₅Nd is suitable for the production of₂Fe₁₄B-based alloy is SmCo₅Since the characteristics are easily degraded by oxidation compared to the base alloy, Nd₂Fe₁₄The oxygen content of the B-based oxygen-rich raw material is more preferably 1200 to 3700 ppm.
[0029]
Note that the preferable oxygen content range of the oxygen poor raw material and the preferable oxygen content range of the oxygen-rich raw material overlap because the oxygen content that can be easily realized with good reproducibility in the oxygen poor raw material depends on the composition and the like. This is because the oxygen content differs and the oxygen content that can be easily realized with good reproducibility in the oxygen-rich raw material differs depending on the composition and the like.
[0030]
By the way, for example, when two or more types of oxygen poor raw materials are used, even when the two or more types of raw materials are manufactured so that the oxygen concentration in the atmosphere in the manufacturing process is controlled to be the same, even if the oxygen concentration is very small. Usually, the oxygen contents are different from each other due to the difference or the difference in the raw material composition. However, those manufactured as oxygen-poor raw materials have less oxygen content than those manufactured as oxygen-rich raw materials, even though the oxygen content varies. Specifically, the difference in the oxygen content between the oxygen-poor raw materials (when there are three or more oxygen-poor raw materials, the difference is three or more, but in that case, the maximum value is the oxygen-rich raw material) The difference in oxygen content between the raw material and the oxygen-poor raw material (when there are three or more oxygen-poor raw materials, the difference is three or more, in which case the minimum value is smaller). The same applies when two or more kinds of raw materials are used as the oxygen poor raw materials. Further, the same applies to the case where two or more oxygen poor raw materials and two or more oxygen rich raw materials are used.
[0031]
That is, when at least one of the oxygen-rich raw material and the oxygen poor raw material is composed of two or more types of raw materials having different oxygen contents, the difference (maximum value) of the oxygen content between the two or more types of raw materials is as follows. It is smaller than the difference (minimum value) of the oxygen content between the oxygen-rich raw material and the oxygen-poor raw material. For example, in a group consisting of two or more oxygen-rich raw materials and a group consisting of two or more oxygen poor raw materials, the raw materials belonging to different groups are determined by the difference in oxygen content between the raw materials belonging to the same group. Are larger in oxygen content.
[0032]
In general, the effect of the present invention can be sufficiently realized by using only one of the oxygen-rich raw material and the oxygen-poor raw material. However, when the present invention is applied to the two-alloy method described below, one or both, usually only one, of the oxygen-rich raw material and the oxygen-poor raw material are constituted by two types of raw materials having different oxygen contents. That is, in the present invention, it is not necessary to use more than four types of raw materials, and usually three or less types of raw materials are used.
[0033]
The ratio of the oxygen-rich raw material to the total of the oxygen-rich raw material and the oxygen poor raw material is preferably 10% by mass or more and less than 90% by mass. If the ratio is too low or too high, the effect obtained by mixing and using the oxygen-rich raw material and the oxygen-poor raw material cannot be sufficiently realized. Further, in view of the preferable R content of the sintered magnet produced according to the present invention and the preferable oxygen content corresponding thereto, the ratio of the oxygen-rich raw material in both raw materials is more preferably 60% by mass or less, and still more preferably. It is less than 50% by mass, particularly preferably 20 to 40% by mass. In the present invention, it is preferable that the R content in the magnet is relatively small. However, as described above, the performance of a magnet having a low R content is significantly reduced as the oxygen content increases. The production of an oxygen-rich raw material is easier when the oxygen content is relatively high. Therefore, in order to obtain a high-performance sintered magnet having a relatively small R content using a raw material that is easy to manufacture, it is preferable that the ratio of the oxygen-rich raw material in both raw materials is not so large as described above. It is more preferable to make the number relatively small.
[0034]
The oxygen content of the pulverized powder is larger than that of the raw material alloy, and when the pulverization is performed in multiple stages, the oxygen content increases as the pulverization proceeds. Further, in the case of further pulverizing after mixing the oxygen-rich raw material and the oxygen poor raw material, if the composition and size of both raw materials are not significantly different, the difference between the oxygen contents of both raw materials at the time of mixing will be reduced in subsequent pulverization. Is almost maintained and does not change much.
[0035]
In the oxygen-rich raw material and the oxygen-poor raw material, specific values of the respective oxygen contents and ratios may be determined according to the oxygen content of the sintered magnet to be obtained. The oxygen content (mass ratio) of the sintered magnet manufactured according to the present invention is preferably 500 to 4500 ppm. If the oxygen content of the sintered magnet is too small, it is difficult to obtain a high coercive force and a high squareness ratio, and if it is too large, it is difficult to obtain a high residual magnetic flux density. Nd₂Fe₁₄B-based alloy is SmCo₅Since the magnet properties are easily degraded by oxidation compared to the base alloy, Nd₂Fe₁₄In the B-based sintered magnet, the oxygen content is preferably 500 to 3000 ppm, more preferably 600 to 2500 ppm, and further preferably 800 to 2400 ppm.
[0036]
The raw material alloy is manufactured by a casting method or a quenching method. In the quenching method, the molten alloy is solidified by cooling from one direction or two opposing directions to obtain a quenched alloy in a strip shape, for example. As a method of cooling from one direction, a single roll method or a rotating disk method is preferable, and as a method of cooling from two directions, a twin roll method is preferable.
[0037]
The pulverization is preferably performed in two or more stages. Usually, first, a hydrogen storage and pulverization step (first coarse pulverization step) of storing a hydrogen gas and roughly pulverizing the quenched alloy is provided. Next, there is provided a second coarse pulverizing step of pulverizing to a particle size of about 10 to 100 μm by a disk mill or the like. Next, a fine pulverizing step of pulverizing the particles to a particle size of about 0.5 to 5 μm by a jet mill or the like is provided. However, the second coarse grinding step may be omitted.
[0038]
As a means for controlling the oxygen content of the oxygen-rich raw material and the oxygen-poor raw material, it is preferable to use a method of controlling the oxygen concentration in the atmosphere in the process of manufacturing the raw material. Specifically, the concentration of oxygen in the atmosphere may be controlled during the production of the raw material alloy and / or the pulverization of the raw material alloy.
[0039]
The oxygen content of the raw material can also be reduced by including an oxidizing gas or moisture in the pores of the porous material and contacting the porous material with the raw material alloy or its pulverized powder or disposing the porous material in the vicinity thereof. It is possible to control. As the porous substance, for example, sponge, paper, woven fabric, or nonwoven fabric can be used. When the alloy is pulverized in multiple stages, the powder obtained in the previous pulverization step is generally transported by airflow to the next pulverization step, but on the inner wall of a pipe used for this transport, What is necessary is just to stick a porous substance. The inner wall of the pipe is generally smooth. However, in order to increase the contact area of the porous substance with the powder, irregularities may be provided on a part of the inner wall of the pipe, and the porous substance may be attached thereto. Further, a porous substance may be arranged in a powder mixing device. In this case, a porous substance may be attached to the inner wall of the mixing device, or the porous substance may be attached to a screw-shaped, ribbon-shaped, or paddle-shaped mixing blade. The method for replenishing the porous substance with the oxidizing gas is not particularly limited. For example, the porous substance attached inside the apparatus may be removed and exposed to air or oxygen gas. However, it is only necessary to introduce air into the pipe when checking and cleaning the apparatus with the porous substance adhered inside the pipe. If the air to be introduced at this time is ordinary air containing water vapor, it is possible to replenish the water at the same time, and it is not necessary to remove the porous substance and soak it in water.
[0040]
A specific procedure for controlling the oxygen content will be exemplified below.
[0041]
In the present invention, for example, a raw material alloy of an oxygen-rich raw material and a raw material alloy of an oxygen poor raw material may be manufactured by controlling the oxygen content, and then both raw material alloys may be mixed and pulverized at the same time.
[0042]
Further, for example, two raw alloys having the same oxygen content (the compositions may be the same or different) are independently coarsely pulverized while being controlled so as to have different oxygen contents. Thus, a coarse powder of the oxygen-rich raw material and a coarse powder of the oxygen-poor raw material may be prepared, and then both coarse powders may be mixed and then finely pulverized. In addition, the two raw material alloys are independently coarsely pulverized and then finely pulverized independently, thereby independently producing a fine powder of an oxygen-rich raw material and a fine powder of an oxygen poor raw material. You may mix. In this case, the operation for obtaining different oxygen contents may be performed in only one of the coarse grinding step and the fine grinding step, or may be performed in both steps. Mixing after independent pulverization makes it easy to increase the difference in oxygen content between the oxygen-rich raw material and the oxygen-poor raw material. The adjustment range of the content is widened. Such an effect is higher when mixing is performed after pulverization, and is higher when operations for obtaining different oxygen contents are performed in both the coarse pulverization and the fine pulverization. That is, in order to sufficiently obtain such an effect, it is preferable to mix the oxygen-rich raw material and the oxygen-poor raw material after the final stage of the multi-stage pulverization. Further, the coarsely pulverized powder has a large particle size, and therefore is not easily oxidized. Therefore, when attempting to obtain coarse pulverized powder (oxygen-rich raw material) having a particularly high oxygen content, in addition to increasing the oxygen concentration in the atmosphere during pulverization or powder transportation, control such as heating is required. The number of items to be increased increases, which is not preferable in production. Therefore, from this point as well, it is preferable to mix the oxygen-rich raw material and the oxygen-poor raw material after the final stage of the multi-stage pulverization.
[0043]
As described above, although it is easy to relatively increase and decrease the oxygen content of the raw material, it is difficult to stably produce a raw material having an intermediate oxygen content. is there. This is the background on which the present invention was made. Therefore, when manufacturing the oxygen poor raw material, the specific values of the oxygen concentration and the oxygen partial pressure in the alloy casting step, the molten alloy quenching step, the pulverizing step, etc. are not particularly limited, and are relatively small depending on the manufacturing apparatus to be used. The production conditions may be set so that a raw material having an oxygen content can be produced stably by the apparatus. The same applies to oxygen-rich raw materials, and the production conditions may be set so that a raw material having a relatively high oxygen content can be stably produced by the equipment according to the production equipment to be used.
[0044]
The composition of the oxygen-rich raw material and the oxygen-poor raw material may be the same or different. Further, the oxygen-rich raw material and / or the oxygen poor raw material may include two or more raw materials having different compositions.
[0045]
As a case where raw materials having different compositions are used, there is a case where a so-called two-alloy method is used. The two-alloy method is a method of improving magnetic properties and corrosion resistance by mixing and sintering two kinds of alloy powders having different compositions. Various proposals have been made regarding the two-alloy method, but all have almost the same composition (R₂Fe₁₄The second alloy powder is added to the alloy powder of B). Examples of the second alloy include R-rich alloys having a higher R ratio and a lower melting point than the main phase (JP-A-4-338607, JP-A-5-105915, etc.), and R having a different type of R from the main phase.₂Fe₁₄B alloys (JP-A-61-81603, etc.) and those containing an R intermetallic compound (JP-A-5-21219, etc.) are exemplified. Also, Japanese Patent Application Laid-Open No. 7-176414 discloses a method of sintering a compact formed of a mixture of a main phase master alloy powder and a grain boundary phase master alloy powder to form a magnet. In this publication, the main phase master alloy is substantially R₂(Fe, Co)₁₄A columnar crystal grain composed of B;₂(Fe, Co)₁₄And a crystal grain boundary mainly composed of an R-rich phase having a higher R content than B. The master alloy for a grain boundary phase contains 32 to 60% by mass of R, and the balance is substantially Co. Or a crystalline alloy of Co and Fe. In this publication, the ratio of the main phase master alloy in the mixture is set to 60 to 95% by mass.
[0046]
When the two-alloy method is used in the present invention, one of two kinds of raw materials having different compositions may be used as an oxygen-rich raw material and the other may be used as an oxygen poor raw material. However, the mixing ratio of the two raw materials is determined according to the final composition of the magnet (for example, an alloy powder having substantially the same composition as the main phase has a high mixing ratio), so that the oxygen content in the magnet is set to a desired value. May be difficult to do. In order to avoid such a problem, one of the two types of raw materials having different compositions may be divided into an oxygen-rich raw material and an oxygen poor raw material. Further, both of the two types of raw materials having different compositions may be divided into an oxygen-rich raw material and an oxygen poor raw material.
[0047]
The shaping is preferably performed in a magnetic field. In this case, the magnetic field strength is preferably 800 kA / m or more, and the molding pressure is preferably about 10 to 500 MPa. For molding, either uniaxial pressing or isostatic pressing such as CIP may be used.
[0048]
The obtained molded body is sintered. The sintering conditions may be appropriately determined according to the magnet composition.₂Fe₁₄B-based composition and SmCo₅In the system composition, sintering may be performed at 1000 to 1200 ° C. for 0.1 to 100 hours. Sintering may be performed multiple times. The sintering is preferably performed in a non-oxidizing atmosphere, for example, in a vacuum or an inert gas atmosphere such as Ar gas. Further, pressure sintering (hot pressing) may be performed.
[0049]
After sintering, it is preferable to perform aging treatment in order to improve coercive force. For example, Nd₂Fe₁₄The B-based magnet is preferably subjected to aging treatment in an inert gas atmosphere, preferably at a temperature of 500 ° C. or more and a sintering temperature or less, more preferably at a temperature of 500 to 950 ° C. for 0.1 to 100 hours. . Note that the aging treatment may be constituted by a multi-step heat treatment. For example, in the aging treatment including the two-stage heat treatment, the first-stage heat treatment is performed at a temperature of 700 ° C. or more and less than the sintering temperature for 0.1 to 50 hours, and the second-stage heat treatment is performed at 500 to 700 ° C. for 0.1 to 50 hours. It is preferably performed for 100 hours. On the other hand, SmCo₅In the system magnet, an aging treatment can be performed by slowing down the cooling rate and slowing down the cooling in a part of the cooling process in the sintering process.
[0050]
Although the composition of the rare earth sintered magnet produced by the present invention is not particularly limited, the present invention₂Fe₁₄It is particularly suitable for manufacturing a B-based sintered magnet.
[0051]
Nd to which the present invention is applied₂Fe₁₄The B-based sintered magnet preferably contains at least Nd and / or Pr as R, and further contains Fe and B, and more preferably replaces part of Fe with Co. The content of each element is
R: 28 to 32% by mass,
B: 0.8 to 1.2% by mass,
The balance: Fe
It is preferable that By setting the content of each element within such a range, good magnet properties can be obtained. In particular,
R: 28 to 31.5% by mass,
B: 0.9 to 1.1% by mass;
The balance: Fe
Then, a higher residual magnetic flux density can be obtained.
[0052]
As the R content decreases, the residual magnetic flux density improves. However, when the R content is too low, an iron-rich phase such as an α-Fe phase precipitates, adversely affects the pulverization, and deteriorates the magnetic properties. In addition, since sintering becomes difficult and the sintering density decreases, the improvement of the residual magnetic flux density reaches a peak. If the R content is too large, a high residual magnetic flux density cannot be obtained. The element R always contains Nd and / or Pr. The ratio between Nd and Pr is not particularly limited. As the element R, only Nd and / or Pr may be used, but other rare earth elements, that is, Y, Sc, La, Ce, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb And at least one of Lu and Lu. Of these, Dy and / or Tb are preferred. In order not to deteriorate the magnet properties, the total amount of elements other than both Nd and Pr is preferably set to 30% by mass or less of the entire element R. When two or more elements are used as the element R, a mixture such as misch metal can be used as a raw material.
[0053]
If the B content is too small, a rhombohedral structure results and the coercive force decreases. On the other hand, if the B content is too large, the B-rich non-magnetic phase increases, so that the residual magnetic flux density decreases.
[0054]
The balance is substantially Fe, but a part of Fe may be replaced by Co. By adding Co, the temperature dependency of the coercive force and the corrosion resistance can be improved, and the residual magnetic flux density can also be improved. However, if the Co content is too large, the coercive force decreases, so the Co content in the magnet is preferably 0.1 to 10% by mass.
[0055]
In the sintered magnet, in addition to the above-mentioned elements, trace additives or inevitable impurities such as Cu, C, P, S, Al, Ti, V, Cr, Mn, Bi, Nb, Ta, Mo, W, At least one of Sb, Ge, Sn, Zr, Ni, Si, Hf, Ga, Zn and the like may be contained. However, in order to suppress the deterioration of the magnet properties, it is preferable that the total content thereof is 5% by mass or less.
[0056]
The present invention relates to Nd₂Fe₁₄In addition to the B-based magnet, it is also suitable for manufacturing a sintered magnet containing at least Sm as R and further containing Co. Such magnets include SmCo₅A cubic magnetic material is preferred. In this type of magnet, a part of Sm may be replaced with another rare earth element, or a part of Co may be replaced with another transition metal element.
[0057]
The use of the sintered magnet manufactured by the present invention is not particularly limited, and can be applied to various devices such as a motor and a speaker.
[0058]
【Example】
Example 1
Raw material alloys having the following compositions were produced by a rapid cooling method (strip casting). However, the composition D was manufactured by a casting method. In the following compositions, numerical values are percentages by mass.
[0059]
Composition A: 30.0% Nd-1.0% B-0.5% Co-0.2% Al-0.05% Cu-Fe,
Composition A1: 29.3% Nd-1.1% B-0.2% Al-0.05% Cu-Fe;
Composition A2: 40.5% Nd-5.0% Co-0.2% Al-0.05% Cu-Fe,
Composition B: 28.9% Nd-2.0% Dy-1.0% B-0.5% Co-0.3% Al-0.08% Cu-Fe,
Composition C: 24.3% Nd-7.1% Dy-1.0% B-1.0% Co-0.5Al-0.08% Cu-0.2% Sn-Fe;
Composition D: 35.4% Sm-Co
[0060]
These raw material alloys were roughly pulverized by hydrogen absorption and then finely pulverized in a nitrogen gas stream to obtain oxygen poor raw materials (fine powders) and oxygen-rich raw materials (fine powders) shown in Tables 1 to 7, respectively. The average particle size of these raw material powders was about 4.0 to 5.5 μm. In addition, the oxygen content of these raw material fine powders was controlled by controlling the oxygen concentration in the atmosphere in the coarse pulverization and the fine pulverization. Specifically, the oxygen-poor raw material fine powder was prepared in an atmosphere having an oxygen concentration of 50 ppm or less, and the oxygen-rich raw material fine powder was prepared in an atmosphere having an oxygen concentration of 0.3 to 0.5%. The oxygen content of the raw material fine powder shown in each table was measured by an inert gas melting method. This measurement was performed in a non-oxidizing atmosphere to obtain accurate results.
[0061]
These raw material powders were mixed at the ratios shown in Tables 1 to 7 and molded at a pressure of 150 MPa in a magnetic field of 1200 kA / m. After sintering the obtained molded body in a vacuum at 1000 to 1100 ° C. for 4 hours, aging treatment is performed in an argon gas atmosphere at a temperature range of 500 to 900 ° C. for 1 to 4 hours in one or more stages, A sintered magnet sample was obtained. However, the compact containing the powder of the composition D was sintered at 1150 ° C. in a hydrogen atmosphere.
[0062]
For these sintered magnet samples, the density ρ and the magnetic properties (residual magnetic flux density Br, coercive force HcJ, squareness ratio Hk / HcJ) were measured with a BH tracer. In addition, the cross section of the sample was observed with a scanning electron microscope to check for abnormal grain growth (AGG). Further, the oxygen content of the sample was measured by an inert gas melting method. Tables 1 to 7 show these results.
[0063]
[Table 1]

[0064]
[Table 2]

[0065]
[Table 3]

[0066]
[Table 4]

[0067]
[Table 5]

[0068]
[Table 6]

[0069]
[Table 7]

[0070]
From Tables 1 to 5, it can be seen that by using a mixture of the oxygen-rich raw material and the oxygen-poor raw material, a sintered magnet having a high residual magnetic flux density, a high coercive force and a high squareness can be obtained. Further, it can be seen that better magnet properties can be obtained when the ratio of the oxygen-rich raw material to the total of the oxygen-rich raw material and the oxygen poor is 60% by mass or less, particularly less than 50% by mass.
[0071]
The magnets shown in Table 6 were manufactured by a two-alloy method. In the raw material fine powder shown in Table 6, composition A1 is a composition close to the main phase of the magnet, and composition A2 is a composition close to the grain boundary phase of the magnet. The composition of the magnet produced by mixing the fine powder of the composition A1 and the fine powder of the composition A2 in a mass ratio of A1: A2 = 9: 1 is the composition of the magnet produced using only the fine powder of the composition A. Is almost the same as In Table 6, the oxygen-rich raw material is fine powder R6, and the oxygen poor raw material is fine powder P6-1 and fine powder P6-2. Table 6 shows that the effect of the present invention is realized even when the two-alloy method is used.
[0072]
In Table 7, sample no. Sample No. 701 is manufactured using oxygen-rich fine powder and oxygen poor fine powder. 702 is manufactured using only one kind of raw material fine powder. Sample No. The oxygen content of the raw material fine powder S used in Sample No. The oxygen content of Sample No. 701 is set to be almost the same.
[0073]
From Table 7, it is clear that even when the compositions are almost the same, the squareness ratio is improved by applying the present invention.
[0074]
Example 2
An oxygen-rich raw material (coarse powder) and an oxygen-poor raw material (coarse powder) were produced by performing up to coarse pulverization in the same manner as in Example 1, and these coarse powders were mixed and finely pulverized. However, in producing the oxygen-rich coarse powder R9 shown in Table 9, heating was also used in order to increase the oxygen content. The oxygen concentration in the atmosphere during the pulverization was set to 50 ppm or less. Except for this, a sintered magnet sample was prepared in the same manner as in Example 1. The same measurement as in Example 1 was performed on these samples. The results are shown in Tables 8 and 9.
[0075]
[Table 8]

[0076]
[Table 9]

[0077]
Tables 8 and 9 show that the effects of the present invention can be obtained even when the oxygen-rich raw material and the oxygen poor raw material are mixed after coarse pulverization and before fine pulverization.
[0078]
Example 3
Composition E: 28.2% Nd-1.0% B-0.2% Co-0.05% Al-0.05% Cu-Fe
A sintered magnet sample was produced in the same manner as in Example 2 except that the raw material alloy was used. The same measurement as in Example 1 was performed on these samples. Table 10 shows the results.
[0079]
[Table 10]

[0080]
The composition E used in this example has a small R content, and thus has a small margin for oxidation of the element R. Therefore, the characteristics change sensitively in relation to the amount of oxygen. When the present invention is applied to such a low R composition, it can be seen that particularly good performance can be obtained by making the ratio of the oxygen-rich raw material relatively low, particularly 40 mass% or less.

Claims

A raw material alloy manufacturing process for manufacturing a raw material alloy containing R (R is at least one rare earth element), a crushing process for crushing the raw material alloy in one or more stages to obtain a raw material powder, and forming the raw material powder And a sintering step of sintering the molded body to obtain a sintered magnet,
When the raw material alloy or its pulverized powder is called raw material,
At least one oxygen-rich raw material, which is a raw material manufactured to have a relatively high oxygen content, and is manufactured so as to have a relatively low oxygen content, and has an oxygen content of 300 ppm more than the oxygen-rich raw material ( (Ratio by mass) A method for producing a rare earth sintered magnet in which at least one kind of oxygen poor raw material which is a raw material less than or equal to a mass ratio is mixed before the forming step.

The method for producing a rare earth sintered magnet according to claim 1, wherein the oxygen content (mass ratio) of the oxygen-rich raw material is 600 to 5000 ppm, and the oxygen content (mass ratio) of the oxygen poor raw material is 300 to 2000 ppm.

3. The method for producing a rare earth sintered magnet according to claim 1, wherein a ratio of the oxygen-rich raw material to the total of the oxygen-rich raw material and the oxygen poor raw material is 10% by mass or more and less than 90% by mass.

The method for producing a rare-earth sintered magnet according to any one of claims 1 to 3, wherein a ratio of the oxygen-rich raw material to the total of the oxygen-rich raw material and the oxygen-poor raw material is 10 to 60% by mass.

At least one of the oxygen-rich raw material and the oxygen poor raw material is composed of two or more raw materials having different oxygen contents, and the maximum value of the difference in oxygen content between the two or more raw materials constitutes the oxygen-rich raw material. The method for producing a rare-earth sintered magnet according to any one of claims 1 to 4, wherein the difference between the oxygen content and the material constituting the oxygen-poor material is smaller than a minimum value of the difference.

The method for producing a rare-earth sintered magnet according to any one of claims 1 to 5, wherein a sintered magnet having an oxygen content (mass ratio) of 500 to 4500 ppm is produced.

The difference in oxygen content between the oxygen-rich raw material and the oxygen-poor raw material is realized by making the oxygen concentration in the atmosphere different in at least a part of the production process of these raw materials. Item 7. The method for producing a rare earth sintered magnet according to any one of Items 1 to 6.

In at least a part of the production process, the oxygen-rich raw material is controlled in oxygen content by being brought into contact with a porous substance having pores containing an oxidizing gas or moisture or being arranged near the porous substance. The method for producing a rare earth sintered magnet according to any one of claims 1 to 7, wherein

In the pulverization process, the raw material alloy is pulverized in multiple stages,
The method for producing a rare earth sintered magnet according to any one of claims 1 to 8, wherein the oxygen-rich raw material and the oxygen poor raw material are mixed after at least one stage of pulverization.

In the pulverization process, the raw material alloy is pulverized in multiple stages,
The method for producing a rare-earth sintered magnet according to any one of claims 1 to 8, wherein the oxygen-rich raw material and the oxygen-poor raw material are mixed after the final stage of the multi-stage pulverization.

The method for producing a rare earth sintered magnet according to claim 1, wherein a sintered magnet containing R, Fe, and B is produced.

The method for producing a rare earth sintered magnet according to claim 11, wherein the R content of the sintered magnet is 28 to 32% by mass.

The method for producing a rare earth sintered magnet according to any one of claims 1 to 10, wherein the sintered magnet contains at least Sm as R and further contains Co.