JP2004281873A

JP2004281873A - Method for manufacturing rare earth magnet

Info

Publication number: JP2004281873A
Application number: JP2003073677A
Authority: JP
Inventors: Shigeo Tanigawa; 茂穂谷川; Yuichi Ogawa; 雄一小川
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 2003-03-18
Filing date: 2003-03-18
Publication date: 2004-10-07

Abstract

<P>PROBLEM TO BE SOLVED: To realize micronization of R-Fe-B magnetic powder in which contamination of C or the like is reduced, to improve the high coercive force and mechanical strength and to obtain high coercive force by micronization even when the contents of inexpensive Dy and Tb are small as compared with conventional methods. <P>SOLUTION: Rare earth magnets are manufactured in process for pulverizing material powder for R-Fe-B rare earth magnets in oil by a wet method without using a pulverization medium, a process for obtaining compacts by wet molding in a magnetic field by using the oil and the pulverized magnetic powder, a process for deoiling the compacts, and a process for sintering the deoiled compacts. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、希土類永久磁石とくにＲ−Ｆｅ−Ｂ系希土類焼結磁石の製造方法に関する。
【０００２】
【従来の技術】
希土類永久磁石は、エネルギー変換材料として幅広い産業分野において利用されている。特にＲ−Ｆｅ−Ｂ系永久磁石は、最大エネルギー績で３０ＭＧＯｅ以上の磁気特性の磁石が工業的に大量に製造され、情報家電、産業用モータ、情報処理端末装置等のモータやアクチュエータ構成部材として利用されている。希土類永久磁石は、原料金属を溶解して得られたインゴットを粉砕、成形、焼結、熱処理、加工する工程により製造される。このプロセスは一般的に、粉末冶金プロセスと呼ばれている。
【０００３】
Ｒ−Ｆｅ−Ｂ系焼結磁石においても、工業的な製造プロセスとして粉末冶金法が採用されている。しかし、希土類合金粉末、特にＲ−Ｆｅ−Ｂ系合金微粉末は酸素に対する親和力が強く大気中において極めて容易に酸化し、磁気特性の劣化を招いてしまうという問題点がある。一方Ｒ−Ｆｅ−Ｂ系永久磁石の磁気特性は、この磁石の磁気特性が単磁区微粒子理論により導かれるために、焼結体の結晶粒径を微細にすればするほど磁気性能は基本的に向上する。焼結体の結晶粒径を微細にするためには、成形前の磁粉の粒径も微細にする必要があるが、微細にすればするほど磁粉の比表面積が増大し、酸化による磁気特性の劣化を招きやすいというジレンマが存在する。したがって、従来Ｒ−Ｆｅ−Ｂ系永久磁石粉末の製造方法としては、インゴットをあらかじめ数１０μｍまで粗粉砕した後、酸素を５００〜２０００ｐｐｍ含むアルゴンあるいは窒素ガスなどの弱酸化雰囲気中でジェットミル等の乾式粉砕機を用いて平均粒径３．５〜５μｍに粉砕しつつ、微粉の表面を微量の酸素により酸化させ安定化させることにより、粉砕後のハンドリングを大気中で行なうという手法が一般的に行なわれていた。この場合、得られる微粉の酸素量は４，０００ｐｐｍ以上となり、微粉表面の希土類酸化物は非磁性介在物として焼結体中に残存し磁気特性の低下が避けられない。
【０００４】
このような、問題点を解決する手段として、特開昭６１−１１４５０５号公報においては、無酸素雰囲気中で粉砕した微粉をトルエンやアルコールなどの有機溶媒中で回収し、湿式成形し焼結する製造方法が提案されている。また特開昭６１−１１４５０５号公報をさらに改良した発明として、特許第２７３１３３７号公報においては、溶媒として鉱物油あるいは合成油を使用し、無酸素雰囲気中でジェットミル（乾式粉砕）した微粉を上記油中に回収しスラリーとする。あるいは、上記油を溶媒として湿式粉砕しスラリーとし、このスラリーを脱油しながら磁場中で湿式成形し、成形体を真空中１００〜５００℃で脱油処理を行ない、焼結する製造方法も開示されている。
【０００５】
しかし、これらの改良手段を用いても以下の理由により、３μｍ以下の微粉を用いて高い磁気特性を有する焼結磁石を得ることは出来なかった。すなわち、無酸素雰囲気中でジェットミルを行ない、微粉を油中に回収する手法においては、ジェットミルの粉砕能力では、Ｒ−Ｆｅ−Ｂ系磁石合金を、３μｍ以下に微粉砕することが極めて困難なため、この手法で得られる微粉の最小平均粒径は３μｍが限界である。一方、ボールミルや、振動ミルにおいては粉砕時間と粉砕メディアの形状を選択することにより、粉砕粒径を３μｍ以下にすることは可能である。しかしながら、この場合は、粉砕中の溶媒である油とＲ−Ｆｅ−Ｂ磁石粉末のメカノケミカル反応により、希土類カーバイト（ＲＣ_２）が粉末表面に生成される。メカノケミカル反応により、形成された希土類カーバイトは熱力学的に安定であるため、湿式成形後の真空中１００〜５００℃の処理で還元し脱Ｃを行なうことが出来ないため、焼結後の磁石中に非磁性介在物として残存するため、磁気特性の低下をもたらす。このメカノケミカル反応は、粉砕時間が長くなればなるほど、また磁石粉末の粒径が小さくなればなるほど比表面積が増大し、より磁気特性の低下をもたらすという問題点があった。また、従来のボールミルや振動ミルによる湿式粉砕を行なうと、粉砕メディアからのコンタミも避けられず、このコンタミも磁気特性の低下をもたらす要因となる。
【０００６】
【特許文献１】
特開昭６１−１１４５０５号（第２頁右上欄１８行目〜左下欄１０行目）
【特許文献２】
特許第２７３１３３７号公報（第３頁４欄４４行目〜第４頁５欄５行目）
【０００７】
【発明が解決しようとする課題】
本発明はかかる、従来技術の問題点を解消し従来困難であった、Ｃなどのコンタミの少ない、Ｒ−Ｆｅ−Ｂ磁石粉末の微粒化を実現し、高保磁力で、機械強度に優れるＲ−Ｆｅ−Ｂ焼結磁石を提供するものである。また従来回転機用の用途などでは、使用時の減磁界に十分耐えるように保磁力を高くしておく必要があり、そのためにＲ−Ｆｅ−Ｂ磁石のＲの一部をＤｙやＴｂで置換することが一般的に行なわれてきた。ＤｙやＴｂは希土類元素の中でもＮｄに比較し存在量が少なく、分離コストが高いため高価である。本発明の微粒化により、高保磁力が実現されるため、従来のＲ−Ｆｅ−Ｂ焼結磁石に比較し、ＤｙやＴｂ量を低減できるという、省資源面での効果もある。
【０００８】
【問題を解決するための手段】
本発明においては、粉砕手段としてメディアレスの湿式粉砕を用いることを特徴とする。すなわち、あらかじめ平均粒径１００μｍ以下に粗粉砕したＲ−Ｆｅ−Ｂ系磁石粉末を、鉱物油あるいは合成油中に投入し、このＲ−Ｆｅ−Ｂ磁石粉末を含む油をコンプレッサにより７０〜２００ＭＰａに加圧し、加圧した油を２流路に分岐した後、再度合流させ対向衝突させることにより、３μｍ以下の微粉砕を短時間に行なうことが可能であることを見出した。本発明による高圧対向衝突粉砕によると、従来のボールミルや振動ミルによる湿式粉砕と比較し短時間での粉砕が可能であり、メカノケミカル反応による希土類カーバイトの生成を防止できるばかりでなく、鋼球ボールやセラミックスボールなどの粉砕メディアを使用しないため、メディアからのコンタミがない。そのため焼結磁石の非磁性介在物を最小限に低減することが可能である。
【０００９】
本発明で粉砕粒径を３μｍ以下と規定した理由は、３μｍ以上の粉砕は従来の特許２７３１３３７号に開示されているように、乾式ジェットミル粉砕と湿式成形により、非磁性介在物の比較的少ない焼結磁石がえられるため、本発明による効果が小さいためである。本発明の対向衝突粉砕により得られた、Ｒ−Ｆｅ−Ｂ磁石合金を含むスラリーは、脱油しながら磁場中で湿式成形することにより成形体とし、１００〜７００℃の温度域で脱油後、真空中１０００〜１２００℃で焼結し、ほぼ真密度に近い焼結磁石が得られる。脱油雰囲気は、真空中でも水素中でも良いが、焼結体中の残留Ｃをより少なくするためには、水素雰囲気がより好ましい。また脱油は１００〜７００℃の温度域を５℃／ｍｉｎ以下の昇温速度で加熱することにより可能であるが、場合によっては昇温過程の特定温度で定温保持することは、残留Ｃ低減に有効である。定温保持する温度は、使用する鉱物油あるいは合成油の沸点直上が好ましい。この様にして得られた、燒結磁石が従来磁石に比較し高保磁力あるいは，同一保磁力で比較すると高Ｂｒで低Ｄｙ（Ｔｂ）省資源効果が大きい。また本発明による焼結磁石は、組織がち密で機械強度に優れるという付随的効果もあり高速回転機用磁石として適する。
【００１０】
本発明に用いる合金粉末について記載する。単に％と記してあるのは質量％を意味するものとする。
本発明に用いる合金粉末はＲ_２Ｆｅ_１４Ｂ系金属間化合物（ＲはＹを含む希土類元素の少なくとも１種であり、ＴはＦｅ又はＦｅ及びＣｏである）を主相とするものであり、主要成分のＲ、Ｔ及びＢの総計を１００％として、Ｒ：２５．０〜３２．５％、Ｂ：０．５〜２％、残部Ｆｅからなる組成が選択される。
Ｒとして（Ｎｄ、Ｄｙ）、（Ｐｒ、Ｄｙ）、又は（Ｎｄ、Ｐｒ、Ｄｙ）の組合せが実用性が高い。又Ｒ量は２５〜３２．５％が好ましく、さらには２７．０〜３１．０％が好ましい。Ｄｙの一部をＴｂで置換しても良い。Ｂ量は０．５〜２％が好ましく、０．８〜１．２％がより好ましい。Ｂ量が０．５％未満では実用に耐えるｉＨｃを得られず、２％超ではＢｒ、（ＢＨ）ｍａｘが大きく低下する。Ｂの一部がＣで置換可能な事は公知であり、本発明にも適用可能である。
表面磁束密度や耐食性を向上するために、Ｎｂ、Ａｌ、Ｃｏ、Ｇａ及びＣｕの群から選択される少なくとも１種の元素を適量含有することが好ましい。
Ｎｂの含有量は０．１〜２％が好ましい。Ｎｂの含有により焼結過程でＮｂのほう化物が生成し、結晶粒の異常粒成長が抑制できる。Ｎｂ含有量が０．１％未満では添加効果が認められず、２％超ではＮｂのほう化物の生成量が多くなりＢｒの低下が顕著になる。
Ａｌの含有量は０．０２〜２％が好ましい。Ａｌ含有量が０．０２％未満ではＨｃｊや耐食性の向上効果を得られず、２％超ではＢｒ、（ＢＨ）ｍａｘが顕著に低下する。
Ｃｏ含有量は０．３〜５％が好ましい。Ｃｏ含有量が０．３％未満ではキュリー点や耐食性を向上する効果が得られず、５％超ではＢｒ、Ｈｃｊが共に大きく低下する。
Ｇａ含有量は０．０１〜０．５％が好ましい。Ｇａ含有量が０．０１％未満ではＨｃｊの向上効果を得られず、０．５％超ではＢｒ、（ＢＨ）ｍａｘの低下が顕著になる。
Ｃｕ含有量は０．０１〜１％が好ましい。Ｃｕ含有量が０．０１％未満では耐食性やＨｃｊを向上する効果を得られず、１％超ではＢｒの低下が顕著になる。
Ｃｕ及びＣｏが前記特定量範囲で共に含有されるとき、第２次熱処理の許容温度幅が広がる効果を得られ好ましい。
【００１１】
以下本発明の効果を実施例により説明する。
本発明に用いたメディアレスの湿式粉砕装置の要部を図１に示す。湿式粉砕装置１０は垂直方向に備えられた主管１と、その主管１の下部に備えられた衝突室が備えられている。また、この衝突室の側面には流入口３ａおよび３ｂが対向して設けられ、その流入口を介して衝突室の側部には流入管８ａおよび８ｂが備えられている。図示はしないがこの主管１の上方と流入管は循環可能なように連結されており、その途中にはこの循環機関内の被粉砕物および循環流体に高圧をかけるための駆動手段が備えられている。
まず、駆動手段により流入管８ａおよび８ｂ内の被粉砕物および循環流体が流入口３ａおよび３ｂを介して衝突室に高圧で射出される。図中４ａおよび４ｂの矢印はその流れ方向である。被粉砕物である磁粉６が高速で対向する流入口から入り、衝突室２内でぶつかり合い、その衝撃により磁粉が粉砕されて微粉砕粉７となる。衝突室内に注入された被粉砕物および循環流体は主管１を通って上方に運ばれ、上方で二つに分流されて再度流入管８ａ，ｂに流れこみ、磁粉が所望の寸法になるまでこのサイクルが繰り返される。
【００１２】
（実施例１）
質量％でＮｄ３１％−Ｆｅｂａｌ−Ｂ０．９５％−Ａｌ０．３％（不可避不純物含む）からなる、インゴットを溶製した。本インゴットを図２の湿式粉砕装置にて平均粒径４５μｍに粗粉砕した。この粗粉を表１に示す３つの条件で微粉砕した。得られた微粉の平均粒径、酸素量、炭素量を表２に示す。
【００１３】
【表１】

【００１４】
【表２】

【００１５】
表１の微粉を含むスラリーを１Ｔの磁界を印加し、湿式成形し２０×２０×１０ｍｍの成形体を成形した。この成形体を、１００〜７００℃の温度まで水素を５Ｌ／ｍｉｎで流しながら３℃／ｍｉｎにて昇温し脱油を行なった。その後７００℃で炉内を真空にし、５０℃／ｍｉｎで１０６０℃まで昇温し、１０６０℃で２時間定温保持し、室温まで冷却した。得られた焼結体を６５０℃で２時間Ａｒ雰囲気中で熱処理し、１００℃以下に急冷したのち、磁気特性を測定した。結果を表３に示す。
【００１６】
【表３】

【００１７】
（実施例２）
質量％でＮｄ２７％‐Ｄｙ５％−Ｆｅｂａｌ−Ｃｏ１％−Ｂ１．０％−Ａｌ０．２％（不可避不純物含む）からなるインゴットを溶製し、インゴットを平均粒径４５μｍに粗粉砕後、図２に記載の湿式粉砕装置により平均粒径２．２μｍの微粉を得た、粉砕時の粗粉を含む鉱物油の吐出圧力を１００ＭＰとした。
得られた、微粉を実施例１と同様に湿式磁場中成形し、２０×２０×１０ｍｍの成形体を得た。この成形体を表４に示す条件で脱油および焼結を行ない、実施例１と同様の条件で熱処理した。熱処理後の、磁気特性と不純物酸素量，炭素量を表５に示す。
【００１８】
【表４】

【００１９】
【表５】

【００２０】
（実施例３）
質量比で、Ｎｄ（３１−Ｘ）％−ＤｙＸ％−Ｆｅ_ｂａｌ−Ｂ０．９５％−Ａｌ０．１％（不可避不純物含む）からなるインゴットを溶製し、実施例２と同様の方法で、湿式粉砕し平均粒径で２．１〜２．７μｍの微粉を得た。この微分を湿式成形し２０×２０×１０ｍｍの成形体を成形した。この成形体を１００〜７００℃の温度まで水素を５Ｌ／ｍｉｎで流しながら３℃／ｍｉｎにて昇温し脱油を行なった。その後７００℃で炉内を真空にし、５０℃／ｍｉｎで１０６０℃まで昇温し、１０６０℃で２時間定温保持し、室温まで冷却した。得られた焼結体を６２０℃で２時間熱処理し１００℃以下に急冷した。熱処理後の磁気特性と、焼結体中の不純物酸素量と炭素量を表６に示す。
また、比較として前記のインゴットを比較例２に記載したボールミルにより２４時間湿式粉砕した。それ以外は実施例３と同様の方法で焼結体を製造した。実施例３およびこの比較例のＤｙ量と保磁力の関係を図１に示す。
【００２１】
【表６】

【００２２】
【発明の効果】
本発明にしたがって、希土類磁石の粉末をメディアレス高圧湿式粉砕で３μｍ以下微粉末を出発原料として、脱油焼結行なうことにより従来より高保磁力あるいは、従来材と同一保磁力においては低Ｄｙ，低Ｔｂの焼結磁石が得られる。
また本発明による焼結磁石は焼結体組織が微細で機械強度にも優れるという効果もある。
【図面の簡単な説明】
【図１】本発明と比較例でのＤｙ量と保磁力の関係を示す図である。
【図２】本発明に用いた湿式粉砕装置の要部断面図である。
【符号の説明】
１主管、２衝突室、３流入口、６磁石粗粉、７磁石微粉、
８流入管、１０湿式粉砕装置（要部）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a rare earth permanent magnet, particularly an R—Fe—B based rare earth sintered magnet.
[0002]
[Prior art]
Rare earth permanent magnets are used in a wide range of industrial fields as energy conversion materials. In particular, R-Fe-B permanent magnets are manufactured in large quantities industrially with magnets having a magnetic characteristic of 30 MGOe or more in maximum energy performance, and are used as motor and actuator components for information home appliances, industrial motors, information processing terminal devices, and the like. It's being used. The rare-earth permanent magnet is manufactured by a process of pulverizing, forming, sintering, heat-treating, and processing an ingot obtained by melting a raw metal. This process is commonly called a powder metallurgy process.
[0003]
Powder metallurgy is also used as an industrial manufacturing process for R-Fe-B based sintered magnets. However, rare earth alloy powders, particularly R-Fe-B based alloy fine powders have a problem that they have a strong affinity for oxygen and are very easily oxidized in the air, leading to deterioration of magnetic properties. On the other hand, the magnetic properties of the R—Fe—B permanent magnet are basically based on the single domain fine particle theory. improves. In order to reduce the crystal grain size of the sintered body, it is necessary to reduce the particle size of the magnetic powder before molding. However, the finer the particle size, the larger the specific surface area of the magnetic powder, and the better the magnetic properties due to oxidation. There is a dilemma that degradation is likely to occur. Therefore, conventionally, as a method for producing an R-Fe-B-based permanent magnet powder, an ingot is coarsely pulverized to several tens of μm in advance, and then a jet mill or the like is used in a weakly oxidizing atmosphere such as argon or nitrogen gas containing 500 to 2000 ppm of oxygen. In general, a method is used in which the surface of the fine powder is oxidized and stabilized with a small amount of oxygen while being pulverized to an average particle size of 3.5 to 5 μm using a dry pulverizer, and handling after pulverization is performed in the atmosphere. Was being done. In this case, the oxygen content of the obtained fine powder becomes 4,000 ppm or more, and the rare earth oxide on the surface of the fine powder remains in the sintered body as a nonmagnetic inclusion, and a decrease in magnetic properties is inevitable.
[0004]
As means for solving such a problem, Japanese Patent Application Laid-Open No. 61-114505 discloses a method in which fine powder pulverized in an oxygen-free atmosphere is recovered in an organic solvent such as toluene or alcohol, and wet-molded and sintered. Manufacturing methods have been proposed. As a further improved invention of Japanese Patent Application Laid-Open No. 61-114505, Japanese Patent No. 2731337 discloses a method of using a mineral oil or a synthetic oil as a solvent and jet milling (dry grinding) in an oxygen-free atmosphere the fine powder described above. Collect in oil to make slurry. Alternatively, a production method is disclosed in which a slurry is formed by wet grinding using the above oil as a solvent, and the slurry is wet-molded in a magnetic field while deoiling, and the molded body is subjected to a deoiling treatment at 100 to 500 ° C. in a vacuum and sintered. Have been.
[0005]
However, even with these improvement means, it was not possible to obtain a sintered magnet having high magnetic properties using fine powder of 3 μm or less for the following reasons. That is, in the method of performing a jet mill in an oxygen-free atmosphere and collecting fine powder in oil, it is extremely difficult to finely pulverize the R-Fe-B-based magnetic alloy to 3 μm or less with the pulverizing ability of the jet mill. Therefore, the minimum average particle size of the fine powder obtained by this method is limited to 3 μm. On the other hand, in a ball mill or a vibration mill, the pulverized particle size can be reduced to 3 μm or less by selecting the pulverization time and the shape of the pulverization medium. However, in this case, a rare-earth carbide (RC ₂ ) is generated on the powder surface by a mechanochemical reaction between the oil as the solvent during the pulverization and the R-Fe-B magnet powder. Since the rare earth carbide formed by the mechanochemical reaction is thermodynamically stable, it cannot be reduced and de-C-treated by a treatment at 100 to 500 ° C. in a vacuum after wet molding. Since it remains as a non-magnetic inclusion in the magnet, the magnetic properties are degraded. This mechanochemical reaction has a problem that the longer the grinding time and the smaller the particle size of the magnet powder, the larger the specific surface area, and the more the magnetic properties are reduced. In addition, when wet grinding is performed using a conventional ball mill or vibration mill, contamination from the grinding media is inevitable, and this contamination also causes a reduction in magnetic characteristics.
[0006]
[Patent Document 1]
JP 61-114505 A (page 2, upper right column, line 18 to lower left column, line 10)
[Patent Document 2]
Japanese Patent No. 2731337 (page 3, column 4, line 44 to page 4, column 5, line 5)
[0007]
[Problems to be solved by the invention]
The present invention solves the problems of the prior art and realizes the atomization of R-Fe-B magnet powder with little contamination such as C, which has been difficult in the past, and achieves a high coercive force and excellent mechanical strength. An object is to provide an Fe-B sintered magnet. Also, in applications such as conventional rotating machines, it is necessary to increase the coercive force so as to sufficiently withstand the demagnetizing field during use. Therefore, a part of R of the R-Fe-B magnet is replaced with Dy or Tb. Has been commonly done. Among rare earth elements, Dy and Tb are less expensive than Nd and are expensive because of high separation cost. Since a high coercive force is realized by the atomization of the present invention, the amount of Dy and Tb can be reduced as compared with the conventional R-Fe-B sintered magnet, and there is also an effect on resource saving.
[0008]
[Means to solve the problem]
The present invention is characterized in that medialess wet pulverization is used as pulverization means. That is, an R-Fe-B magnet powder coarsely pulverized in advance to an average particle diameter of 100 μm or less is put into a mineral oil or a synthetic oil, and the oil containing the R-Fe-B magnet powder is reduced to 70 to 200 MPa by a compressor. It has been found that, after pressurized and pressurized oil is branched into two flow paths, they are joined again and collided against each other, so that the fine pulverization of 3 μm or less can be performed in a short time. According to the high-pressure counter-impact grinding according to the present invention, grinding can be performed in a shorter time than conventional wet grinding using a ball mill or a vibration mill, and not only can rare metal carbide be prevented from being generated by a mechanochemical reaction, but also steel balls can be prevented. Since no grinding media such as balls and ceramic balls are used, there is no contamination from the media. Therefore, it is possible to minimize non-magnetic inclusions in the sintered magnet.
[0009]
The reason that the pulverized particle size is specified to be 3 μm or less in the present invention is that the pulverization of 3 μm or more is relatively small in non-magnetic inclusions by dry jet mill pulverization and wet molding, as disclosed in the conventional Patent No. 2731337. This is because the effect of the present invention is small because a sintered magnet is obtained. The slurry containing the R-Fe-B magnet alloy obtained by the opposed collision pulverization of the present invention is formed into a compact by wet molding in a magnetic field while deoiling, and after deoiling in a temperature range of 100 to 700 ° C. Sintered at 1000 to 1200 ° C. in a vacuum to obtain a sintered magnet having almost a true density. The deoiling atmosphere may be a vacuum or hydrogen, but a hydrogen atmosphere is more preferable in order to further reduce residual C in the sintered body. Deoiling can be performed by heating a temperature range of 100 to 700 ° C. at a temperature rising rate of 5 ° C./min or less, but in some cases, maintaining a constant temperature at a specific temperature in the temperature rising process reduces residual C. It is effective for The temperature for maintaining the constant temperature is preferably just above the boiling point of the mineral oil or synthetic oil used. The sintered magnet thus obtained has a high Br and a low Dy (Tb) resource saving effect when compared with a conventional magnet with a higher coercive force or with the same coercive force. Further, the sintered magnet according to the present invention has an ancillary effect of having a dense structure and excellent mechanical strength, and is suitable as a magnet for a high-speed rotating machine.
[0010]
The alloy powder used in the present invention will be described. The expression “%” simply means “% by mass”.
The alloy powder used in the present invention has a main phase of R ₂ Fe ₁₄ B-based intermetallic compound (R is at least one kind of rare earth element including Y, and T is Fe or Fe and Co), Assuming that the total of R, T and B of the main components is 100%, a composition comprising R: 25.0 to 32.5%, B: 0.5 to 2%, and the balance Fe is selected.
A combination of (Nd, Dy), (Pr, Dy), or (Nd, Pr, Dy) as R has high practicality. Further, the R amount is preferably from 25 to 32.5%, more preferably from 27.0 to 31.0%. Part of Dy may be replaced with Tb. B content is preferably 0.5 to 2%, more preferably 0.8 to 1.2%. If the amount of B is less than 0.5%, iHc that can withstand practical use cannot be obtained. If the amount of B exceeds 2%, Br and (BH) max are greatly reduced. It is known that a part of B can be replaced by C, and is applicable to the present invention.
In order to improve the surface magnetic flux density and corrosion resistance, it is preferable to contain an appropriate amount of at least one element selected from the group consisting of Nb, Al, Co, Ga and Cu.
The content of Nb is preferably 0.1 to 2%. By containing Nb, a boride of Nb is generated during the sintering process, and abnormal grain growth of crystal grains can be suppressed. When the Nb content is less than 0.1%, the effect of addition is not observed. When the Nb content is more than 2%, the amount of Nb boride generated increases and the reduction of Br becomes remarkable.
The content of Al is preferably 0.02 to 2%. If the Al content is less than 0.02%, the effect of improving Hcj and corrosion resistance cannot be obtained, and if it exceeds 2%, Br and (BH) max are significantly reduced.
The Co content is preferably from 0.3 to 5%. If the Co content is less than 0.3%, the effect of improving the Curie point and corrosion resistance cannot be obtained, and if it exceeds 5%, both Br and Hcj are greatly reduced.
The Ga content is preferably 0.01 to 0.5%. If the Ga content is less than 0.01%, the effect of improving Hcj cannot be obtained, and if it exceeds 0.5%, the reduction of Br and (BH) max becomes remarkable.
The Cu content is preferably 0.01 to 1%. If the Cu content is less than 0.01%, the effect of improving the corrosion resistance and Hcj cannot be obtained, and if it exceeds 1%, the reduction of Br becomes remarkable.
When both Cu and Co are contained in the specific amount range, the effect that the allowable temperature range of the second heat treatment is expanded is preferably obtained.
[0011]
Hereinafter, the effects of the present invention will be described with reference to examples.
FIG. 1 shows a main part of a media-less wet pulverizer used in the present invention. The wet crushing apparatus 10 includes a main pipe 1 provided in a vertical direction and a collision chamber provided below the main pipe 1.

Inflow ports

3a and 3b are provided opposite to the side surface of the collision chamber, and inflow pipes 8a and 8b are provided on the sides of the collision chamber via the flow ports. Although not shown, the upper part of the main pipe 1 and the inflow pipe are connected so as to be able to circulate, and a driving means for applying high pressure to the material to be pulverized and the circulating fluid in the circulating engine is provided in the middle thereof. I have.
First, the objects to be ground and the circulating fluid in the inflow pipes 8a and 8b are injected at high pressure into the collision chamber through the

inflow ports

3a and 3b by the driving means. Arrows 4a and 4b in the figure indicate the flow direction. The magnetic powder 6 to be pulverized enters from the inflow port facing at high speed and collides in the collision chamber 2, and the magnetic powder is pulverized by the impact to become the finely pulverized powder 7. The material to be ground and the circulating fluid injected into the collision chamber are conveyed upward through the main pipe 1, are divided into two parts at the upper part, and flow again into the inflow pipes 8a and 8b, until the magnetic particles have a desired size. The cycle repeats.
[0012]
(Example 1)
An ingot consisting of 31% by mass of Nd 31% -Febal-B 0.95% -Al 0.3% (including unavoidable impurities) was melted. This ingot was coarsely pulverized to a mean particle size of 45 μm by the wet pulverizer of FIG. This coarse powder was pulverized under the three conditions shown in Table 1. Table 2 shows the average particle size, oxygen content, and carbon content of the obtained fine powder.
[0013]
[Table 1]

[0014]
[Table 2]

[0015]
A slurry containing the fine powder of Table 1 was applied with a magnetic field of 1 T and wet-molded to form a molded body of 20 × 20 × 10 mm. The molded body was deoiled by heating at a rate of 3 ° C./min while flowing hydrogen at a rate of 5 L / min to a temperature of 100 to 700 ° C. Thereafter, the inside of the furnace was evacuated at 700 ° C., the temperature was raised to 1060 ° C. at 50 ° C./min, kept at a constant temperature of 1060 ° C. for 2 hours, and cooled to room temperature. The obtained sintered body was heat-treated at 650 ° C. for 2 hours in an Ar atmosphere, rapidly cooled to 100 ° C. or lower, and then its magnetic properties were measured. Table 3 shows the results.
[0016]
[Table 3]

[0017]
(Example 2)
An ingot composed of 27% by mass of Nd 27% -Dy 5% -Febal-Co 1% -B 1.0% -Al 0.2% (including unavoidable impurities) was melted, and the ingot was coarsely pulverized to an average particle size of 45 μm. Fine powder having an average particle size of 2.2 μm was obtained by the wet grinding apparatus described above, and the discharge pressure of mineral oil containing coarse powder during grinding was 100 MPa.
The obtained fine powder was molded in a wet magnetic field in the same manner as in Example 1 to obtain a molded body of 20 × 20 × 10 mm. This compact was subjected to deoiling and sintering under the conditions shown in Table 4, and was heat-treated under the same conditions as in Example 1. Table 5 shows the magnetic properties and the amounts of impurity oxygen and carbon after the heat treatment.
[0018]
[Table 4]

[0019]
[Table 5]

[0020]
(Example 3)
A mass _{ratio, Nd (31-X)%} - DyX% -Fe bal -B0.95% -Al0.1% was melted ingots consisting of (unavoidable including impurities), in the same manner as in Example 2, wet It was pulverized to obtain a fine powder having an average particle size of 2.1 to 2.7 μm. This derivative was subjected to wet molding to form a molded body of 20 × 20 × 10 mm. The molded body was deoiled by heating at a rate of 3 ° C./min while flowing hydrogen at a rate of 5 L / min to a temperature of 100 to 700 ° C. Thereafter, the inside of the furnace was evacuated at 700 ° C., the temperature was raised to 1060 ° C. at 50 ° C./min, kept at a constant temperature of 1060 ° C. for 2 hours, and cooled to room temperature. The obtained sintered body was heat-treated at 620 ° C. for 2 hours and rapidly cooled to 100 ° C. or less. Table 6 shows the magnetic properties after the heat treatment and the amounts of impurity oxygen and carbon in the sintered body.
For comparison, the above-mentioned ingot was wet-pulverized by a ball mill described in Comparative Example 2 for 24 hours. Otherwise, a sintered body was manufactured in the same manner as in Example 3. FIG. 1 shows the relationship between the Dy amount and the coercive force of Example 3 and this comparative example.
[0021]
[Table 6]

[0022]
【The invention's effect】
According to the present invention, the rare earth magnet powder is subjected to deoiling and sintering using a fine powder having a particle size of 3 μm or less as a starting material by medialess high-pressure wet pulverization. A sintered magnet of Tb is obtained.
Further, the sintered magnet according to the present invention has an effect that the sintered body structure is fine and the mechanical strength is excellent.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between a Dy amount and a coercive force in the present invention and a comparative example.
FIG. 2 is a sectional view of a main part of a wet pulverizer used in the present invention.
[Explanation of symbols]
1 main pipe, 2 collision chambers, 3 inlets, 6 magnet coarse powder, 7 magnet fine powder,
8 Inflow pipe, 10 wet crusher (main part)

Claims

A step of wet-pulverizing the raw material powder for the R-Fe-B-based rare earth magnet in oil without using a pulverizing medium; and a step of obtaining a compact by wet molding in a magnetic field using the oil and the pulverized magnetic powder. And a step of deoiling the compact and sintering the deoiled compact.

The method for producing a rare earth magnet according to claim 1, wherein the wet pulverization is to reduce the raw material powder to 3 µm or less.

The wet pulverization is characterized in that the oil containing the raw material powder is pressurized to 70 to 200 MPa, the pressurized oil is branched again into a plurality of flow paths and then joined again, and the raw material powder in the oil is subjected to opposing collision. The method for producing a rare earth magnet according to claim 1.

4. The method according to claim 1, wherein the deoiling step is to heat the molded body in a hydrogen atmosphere at a temperature range of 100 to 700 [deg.] C. at a rate of 5 [deg.] C./min or less. A method for producing a rare earth magnet according to any one of the above.

The method for producing a rare earth permanent magnet according to any one of claims 1 to 4, wherein the compact is held at a temperature of 100 to 700 ° C in hydrogen for 1 hour or more.