JP3846835B2 - R-T-B sintered permanent magnet - Google Patents

Description

【０００１】
【発明の属する技術分野】
本発明は高い保磁力、残留磁束密度及び最大エネルギー積を有するR-T-B系焼結型永久磁石に関する。
【０００２】
【従来の技術及び発明が解決しようとする課題】
R-T-B系焼結型永久磁石（RはYを含む少なくとも一種の希土類元素であり、TはFe又はFeとCoである。）は、最大エネルギー積でほぼ40MGOeのものが量産されている。R-T-B系焼結型永久磁石の合金組成を調整する手段として、シングル法とブレンド法とがある。
【０００３】
シングル法は、溶解/鋳造段階でR-T-B系焼結型永久磁石の主成分組成に調整したインゴットを用いて、粉砕、磁界中成形、焼結及び熱処理を行いR-T-B系焼結型永久磁石を製造する方法であり、得られたR-T-B系焼結型永久磁石は所望の機械加工及び表面処理を施して実用に供される。
【０００４】
ブレンド法は、組成の異なる２種以上のR-T-B系焼結型永久磁石用合金粉末を最終的に所望のR-T-B系焼結型永久磁石の主成分組成になる配合比で混合した後、必要に応じて粉砕を行い、以後磁界中成形、焼結、熱処理及び表面処理を行いR-T-B系焼結型永久磁石を製造する方法である。
【０００５】
上記シングル法によれば、保磁力iHcを高めるのは比較的容易であるが、残留磁束密度Br及び最大エネルギー積(BH)maxが低くなり、高いBr及び高い(BH)maxが要求される用途には適さないという問題がある。
【０００６】
また従来のブレンド法の適用例として、R含有量の高いR-T系合金とR含有量の低いR-T-B系合金とを配合してなるR-T-B系焼結型永久磁石（特開平7-122413号）や、Ga，C，ＯがRリッチ相及びその周辺に偏析しているR-T-B系焼結型永久磁石（特開平9-232121号）が提案されているが、高いBr及び高い(BH)maxの用途に好適にするに改良の余地がある。特に磁気特性への影響が大きい主相結晶粒の重希土類元素の最適な濃度分布及びその制御方法については、何も解明されていない。
【０００７】
従って本発明の目的は、高いBr及び高い(BH)maxが要求される用途に好適な高性能のR-T-B系焼結型永久磁石を提供することである。
【０００８】
【課題を解決するための手段】
上記目的に鑑み鋭意研究の結果、本発明者らは、重量百分率でR 28〜33％、B0.5〜２％、０〜0.6％のM₁、残部実質的にT及び不可避的不純物からなる組成（RはYを含む少なくとも一種の希土類元素であって、Dy，Tb及びHoからなる群から選ばれた少なくとも一種の重希土類元素を必ず含み、M₁はNb，Mo，W，V，Ta，Cr，Ti，Zr及びHfからなる群から選ばれた少なくとも一種の元素であり、TはFe又はFeとCoである。）を有し、前記重希土類元素の濃度（EPMAの測定強度により表される）が結晶粒界相より高い第一のR₂T₁₄B型主相結晶粒と、前記重希土類元素の濃度（EPMAの測定強度により表される）が結晶粒界相より低い第二のR₂T₁₄B型主相結晶粒と、前記重希土類元素の濃度（ EPMA の測定強度により表される）が結晶粒界相とほぼ等しい第三の R ₂ T ₁₄ B 型主相結晶粒とを含有する組織を有し、結晶組織の断面写真における R ₂ T ₁₄ B 型主相結晶粒の総個数を 100 ％として前記第一の R ₂ T ₁₄ B 型主相結晶粒の個数の比率が 1 〜 35 ％であり、前記第二の R ₂ T ₁₄ B 型主相結晶粒の個数の比率が 3 〜 55 ％であり、前記第三の R ₂ T ₁₄ B 型主相結晶粒の個数の比率が 96 〜 10 ％であり、２種類以上の合金粉末を混合して得られ、第一の合金粉末中における前記重希土類元素の含有量が10重量％超40重量％以下であり、第二の合金粉末中における前記重希土類元素の含有量が０〜３重量％であるR-T-B系焼結型永久磁石が、高いBr及び高い(BH)maxを示すことを見出し本発明に想到した。
【００１０】
本発明の好ましい別の実施例によるR-T-B系焼結型永久磁石は、重量百分率でR: 28〜33％、B: 0.5〜２％、M₁: 0.01〜0.6％（M₁はNb，Mo，W，V，Ta，Cr，Ti，Zr及びHfからなる群から選ばれた少なくとも一種の元素である。）、M₂: 0.01〜0.3％（M₂はAl，Ga及びCuからなる群から選ばれた少なくとも一種の元素である。）、残部実質的にT及び不可避的不純物からなる組成を有する。
【００１１】
本発明のさらに好ましい実施例によるR-T-B系焼結型永久磁石は、重量百分率でRが31％を超えて33％以下であり、かつ不可避的不純物として0.6％以下の酸素、0.15％以下の炭素、0.03％以下の窒素、及び0.3％以下のCaを含有する組成を有する。
【００１２】
本発明のさらに好ましい実施例によるR-T-B系焼結型永久磁石は、重量百分率でRが28〜31％であり、かつ不可避的不純物として0.25％以下の酸素、0.15％以下の炭素、0.15％以下の窒素、及び0.3％以下のCaを含有する組成を有する。
【００１３】
本発明のR-T-B系焼結型永久磁石は、例えば希土類元素の全量は同じで、重希土類元素（ Dy ， Tb 及び Ho ）の含有量が異なる以外は組成が実質的に同じ２種類以上の合金粉末を混合し、磁界中成形、焼結及び熱処理を行い、次いで必要に応じて機械加工、仕上げ加工（バレル加工等）、及び表面処理（Niめっき等）を行なうことより得られる。２種類以上の合金粉末を混合して R-T-B 系焼結型永久磁石を製造する場合、第一の合金粉末における重希土類元素の含有量を 10 重量％超 40 重量％以下とし、第二の合金粉末における重希土類元素の含有量を０〜３重量％とする。前記２種類以上の合金粉末の組成及びR-T-B系焼結型永久磁石の最終組成に応じて、最適の焼結条件を選択し、もって焼結体組織内での重希土類元素（Dy等）の拡散状態を厳密に制御するのが重要である。その結果、R₂T₁₄B型主相結晶粒（ほぼ中心部）及び結晶粒界相における重希土類元素（Dy等）の濃度分布に関して、重希土類元素（Dy等）の濃度が結晶粒界相より高いR₂T₁₄B型主相結晶粒と、重希土類元素（Dy等）の濃度が結晶粒界相より低いR₂T₁₄B型主相結晶粒とを含有する結晶組織が得られる。
【００１４】
このような焼結体組織を有するR-T-B系焼結型永久磁石は、シングル法によるR-T-B系焼結型永久磁石に比べて保磁力iHcはやや低いが、格段に高いBr及び(BH)maxを有する。これと重希土類元素（Dy等）の濃度分布との相関はまだ十分に明確になっていないが、重希土類元素（Dy等）濃度が結晶粒界相より高いR₂T₁₄B型主相結晶粒が高いBrの実現に寄与し、重希土類元素（Dy等）濃度が結晶粒界相より低いR₂T₁₄B型主相結晶粒がシングル法に近い高いiHcの実現に寄与しているものと推定される。
【００１５】
【発明の実施の形態】
[1] R-T-B系焼結型永久磁石
(A)組成
(a)主成分本発明のR-T-B系焼結型永久磁石の組成は、重量百分率でR 28〜33％、B 0.5〜２％、０〜 0.6 ％の M ₁ 、及びTからなる主成分と不可避的不純物とからなる（ R は Y を含む少なくとも一種の希土類元素であって、 Dy ， Tb 及び Ho からなる群から選ばれた少なくとも一種の重希土類元素を必ず含み、 M ₁ は Nb ， Mo ， W ， V ， Ta ， Cr ， Ti ， Zr 及び Hf からなる群から選ばれた少なくとも一種の元素であり、 T は Fe 又は Fe と Co である。）。その他に、主成分として0.01〜0.3重量％のM₂（Al，Ga及びCuからなる群から選ばれた少なくとも一種の元素）を含有するのが好ましい。
【００１６】
(1) R元素
R元素はYを含む少なくとも一種の希土類元素であって、Dy，Tb及びHoからなる群から選ばれた少なくとも一種の重希土類元素を必ず含む。重希土類元素以外の希土類元素（Yを含む）としては、Nd、Pr、La、Sm、Ce、Eu、Gd、Er、Tm、Yb、Lu及びYが挙げられる。希土類元素Rとして、ミッシュメタルやジジムのように二種以上の希土類元素の混合物を用いてもよい。
【００１７】
Rの含有量は28〜33重量％である。Rの含有量が28重量％未満であると、実用に耐える高いiHcが得られず、また33重量％を超えるとBrの低下が顕著になる。
【００１８】
重希土類元素の含有量は、0.2〜15重量％の範囲内であるのが好ましい。重希土類元素の含有量が0.2重量％未満であると、結晶組織中の重希土類元素の分布による磁気特性の向上効果が不十分である。また重希土類元素の含有量が15重量％を超えると、R-T-B系焼結型永久磁石のBr及び(BH)maxは大きく低下する。より好ましい重希土類元素の含有量は0.5〜13重量％である。
【００１９】
(2) B
Bの含有量は0.5〜２重量％である。Bの含有量が0.5重量％未満であると、実用に耐える高いiHcを得るのが困難であり、また２重量％を超えるとBrの低下が顕著になる。
【００２０】
(3) T元素
T元素はFe単独又はFe＋Coである。Coの添加により焼結型永久磁石の耐食性が改善されるとともに、キュリー点が上昇して永久磁石としての耐熱性が向上する。しかしCoの含有量が５重量％を超えるとR-T-B系焼結型永久磁石の磁気特性に有害なFe−Co相が形成され、BrとiHcがともに低下する。従ってCo含有量は５重量％以下とする。一方、Co含有量が0.5重量％未満では耐食性の改善効果や耐熱性の向上効果が不十分である。従ってCoを添加する場合、Co含有量を0.5〜５重量％とするのが好ましい。
【００２１】
(4) M₁元素
M₁はNb，Mo，W，V，Ta，Cr，Ti，Zr及びHfからなる群から選ばれた少なくとも一種の高融点金属元素である。M₁元素の存在により、焼結過程において重希土類元素（Dy等）の拡散によって生じる主相結晶粒の過度の成長が抑えられ、シングル法に近い高いiHcを安定して得ることができる。しかし、M₁元素を過剰に添加すると、逆に主相結晶粒の正常な粒成長が阻害され、Brの低下を招く。よって、M₁元素の含有量の上限は0.6重量％である。一方、M₁元素の含有量が0.01重量％未満では十分な添加効果が認められない。従って、M₁元素の含有量は0.01〜0.6重量％であるのが好ましい。
【００２２】
(5) M₂元素
M₂はAl，Ga及びCuからなる群から選ばれた少なくとも一種の元素である。
【００２３】
Alの微量添加によってR-T-B系焼結型永久磁石のiHc及び耐食性が改善される。しかしAl含有量が0.3重量％を超えるとBrが大きく低下するのでAl含有量は0.3重量％以下とする。一方、Al含有量が0.01重量％未満ではiHcや耐食性の改善効果が不十分である。
【００２４】
Gaの微量添加によりR-T-B系焼結型永久磁石のiHcが顕著に向上する。しかしAlと同様に、0.3重量％を超えるとBrが大幅に低下するのでGa含有量は0.3重量％以下とする。また0.01重量％未満ではiHcの意味ある向上効果が認められない。
【００２５】
Cuの微量添加は焼結体の耐食性の改善とiHcの向上に有効である。しかしAl及びGaと同様、Cu含有量が0.3重量％を超えるとR-T-B系焼結型永久磁石のBrが大幅に低下し、また0.01％未満では耐食性の改善及びiHcの向上効果が不十分である。
【００２６】
以上の通り、M₂元素の含有量は、Al，Ga又はCuのいずれも0.01〜0.3重量％とする。
【００２７】
(b) 不可避的不純物
不可避的不純物としては、酸素、炭素、窒素、カルシウム等が挙げられる。Caは重希土類元素の含有量が異なる二種類以上のR-T-B系合金を還元拡散法（希土類元素の酸化物粉末を還元剤（Ca）で還元し、続いて他の主成分金属との相互拡散により合金粉末を得る方法）により作製した場合に、不可避的不純物として混入する。
【００２８】
酸素の含有量は0.6 重量％以下であるのが好ましく、炭素の含有量は0.15重量％以下であるのが好ましく、窒素の含有量は0.03重量％以下であるのが好ましく、カルシウムの含有量は0.3 重量％以下であるのが好ましい。各不可避的不純物の含有量が上記上限を超えると、R-T-B 系焼結型永久磁石の磁気特性は低下する。より好ましい不可避的不純物の含有量としては、酸素が0.25重量％以下であり、炭素が0.15重量％以下であり、窒素が0.15重量％以下である。特に好ましい不可避的不純物の含有量は、酸素が0.05〜0.25重量％であり、炭素が0.01〜0.03％であり、窒素が0.02〜0.15％である。
【００２９】
このような不可避的不純物量を有するR-T-B系焼結型永久磁石の組成の具体例としては、以下のものが挙げられる。
【００３０】
(i) 重量百分率でRが31％を超えて33％以下であり、酸素が0.6％以下であり、炭素が0.15％以下であり、窒素が0.03％以下であり、Caが0.3％以下である組成。例えば乾式成形法の採用により、酸素を0.25〜0.6％、炭素を0.01〜0.15％、窒素を0.005〜0.03％にすることができる。
【００３１】
(ii) 重量百分率でRが28〜31％であり、酸素が0.25％以下であり、炭素が0.15％以下であり、窒素が0.15％以下であり、Caが0.3％以下である組成。例えば湿式成形法の採用により、酸素を0.05〜0.25重量％、炭素を0.01〜0.15％、窒素を0.02〜0.15％にすることができる。
【００３２】
(B) 組織
本発明のR-T-B系焼結型永久磁石の結晶組織はR₂T₁₄B型主相結晶粒と結晶粒界相を有し、前記R₂T₁₄B型主相結晶粒は少なくとも、(i)重希土類元素の濃度が結晶粒界相より高い第一のR₂T₁₄B型主相結晶粒と、 (ii)重希土類元素の濃度が結晶粒界相より低い第二のR₂T₁₄B型主相結晶粒とを含有する。前記R₂T₁₄B型主相結晶粒はさらに (iii) 重希土類元素の濃度が結晶粒界相とほぼ等しい第三の主相結晶粒を含有しても良い。ここでR₂T₁₄B型主相結晶粒における重希土類元素の濃度はR₂T₁₄B型主相結晶粒のほぼ中心部（芯部）において測定したものであり、R₂T₁₄B型主相結晶粒の芯部とは結晶粒界から1.0μｍ以上入り込んだ領域をいう。重希土類元素としてはDyが好ましいが、Tb及び／又はHo、又はそれらとDyとの混合物であっても良い。
【００３３】
撮影した結晶組織の断面写真においてR₂T₁₄B型主相結晶粒の総個数を100％として、第一のR₂T₁₄B型主相結晶粒の個数の比率は1〜35％であり、第二のR₂T₁₄B型主相結晶粒の個数の比率は3〜55％であり、第三のR₂T₁₄B型主相結晶粒の個数の比率は96〜10％であるのが好ましい。第一〜第三のR₂T₁₄B型主相結晶粒の個数の比率が上記範囲外であると、R-T-B系焼結型永久磁石は高い保磁力iHc、残留磁束密度Br及び最大エネルギー積(BH)maxを有するのが困難である。より好ましくは、第一のR₂T₁₄B型主相結晶粒の個数の比率が3〜30％であり、第二のR₂T₁₄B型主相結晶粒の個数の比率が10〜45％であり、第三のR₂T₁₄B型主相結晶粒の個数の比率が87〜25％である。
【００３４】
[2] 製造方法
上記組織を有する本発明のR-T-B系焼結型永久磁石を製造するには、例えばDy等の重希土類元素の含有量が異なる２種類以上のR-T-B系合金粉末を混合するいわゆるブレンド法を採用する。この場合、各R-T-B系合金粉末の組成は、R元素の合計量が各合金粉末で同じになるようにする。例えばNd＋Dyの場合、後述の実施例１に示すように、一方の合金粉末を29.0%Nd＋1.0%Dyとし、他方の合金粉末を15.0%Nd＋15.0%Dyとする。R元素以外の元素については、各合金粉末が実質的に同じであるのが好ましいが、M₁及び／又はM₂の含有量に若干の差があっても良い。
【００３５】
例えば二種類の合金粉末を混合する場合、両者のR元素の合計量を同じにするとともに、第一の合金粉末中における重希土類元素の含有量を10 重量％超 40 重量％以下とし、第二の合金粉末中における重希土類元素の含有量を０〜３重量％とする。この場合、第二の合金粉末／第一の合金粉末の配合比を重量で70／30〜95／5とするのが好ましく、80／20〜90／10とするのがより好ましい。これは、第一の合金粉末と第二の合金粉末との間の重希土類元素の含有量の差が大きくなるほど、第一の合金粉末と第二の合金粉末との間の微粉砕性（微粉の粒径分布）の差異が大きくなり、最終的に得られるR-T-B系焼結型永久磁石の主相結晶粒の粒径分布が幅広くなり、磁化の強さ（4πI）-磁界の強さ（H）の関係を示す減磁曲線の角形性及び(BH)maxの劣化を招来するからである。
【００３６】
R-T-B系合金粉末の微粉砕は、不活性ガスを媒体とするジェットミル等の乾式粉砕法又はボールミル等の湿式粉砕法により行うことができる。高い磁気特性を得るために、実質的に酸素を含有しない（濃度: 体積比で1000ppm 以下）不活性ガス雰囲気中でジェットミル微粉砕後、大気に触れないようにして不活性ガス雰囲気中から微粉を直接鉱油、合成油、植物油又はそれらの混合油中に回収し、混合物（スラリー）にするのが好ましい。微粉を大気から遮断することにより、酸化及び水分の吸着を抑制することができる。鉱油、合成油又は植物油として、脱油性及び成形性の観点から、分留点が350℃以下のものが好ましく、動粘度は室温において10cSt以下のものがよく、５cSt以下のものがより好ましい。
【００３７】
本発明の永久磁石を製造するために配合する２種以上のR-T-B系焼結型永久磁石用合金として、日本国特許第2,665,590号、日本国特許第2,745,042号等に例示されている薄板状合金（ストリップキャスト合金）を使用してもよい。この薄板状合金（ストリップキャスト合金）は、本発明の要件を満たす組成を有する合金溶湯を単ロール法、双ロール法又は回転ディスク法等の溶湯急冷法により急冷、凝固してなり、ほぼ柱状結晶の均質な組織を有し、かつ前記柱状結晶の短軸方向の平均結晶粒径が３〜20μｍである。高いBr及び(BH)maxを得るためには、薄板状合金を不活性ガス（Aｒ等）雰囲気中で900〜1200℃×１〜10時間加熱後室温まで冷却する均質化熱処理を行った後、粉砕するのが好ましい。
【００３８】
混合物（スラリー）を用いて、所望の成形装置により磁界中で湿式成形することにより成形体を得る。酸化による磁気特性の劣化を抑えるために、成形直後から焼結炉に入れるまでの間、油中又は不活性ガス雰囲気中に保持するのが望ましい。成形は乾式法により行なっても良い。乾式成形法の場合、不活性ガス雰囲気中で乾燥微粉の混合物を磁場中でプレス成形する。
【００３９】
湿式成形体の焼結に際し、常温から焼結温度まで急激に昇温すると、成形体中に残留した鉱油、合成油又は植物油が希土類元素と反応して希土類炭化物を生成し、得られる焼結磁石の磁気特性の劣化を招く。この対策として、温度100〜500℃、真空度10^-1 Torr以下で30分以上保持する脱油処理を施すのが望ましい。脱油処理により成形体中に残留する鉱油、合成油又は植物油を十分に除去することができる。なお加熱温度は100〜500℃の温度範囲であれば一定である必要はない。また10^-1 Torr以下の真空度で室温から500℃まで昇温する間、昇温速度を10℃／分以下、好ましくは５℃／分以下としても、ほぼ同等の脱油効果を得ることができる。
【００４０】
成形体を不活性ガス雰囲気中で約1000〜1200℃の温度で焼結することにより、R-T-B系焼結型永久磁石を製造する。得られたR-T-B系焼結型永久磁石に所望の機械加工及び表面処理を施す。表面処理としては、Niめっきや電着エポキシ樹脂コーティング等が挙げられる。
【００４１】
【実施例】
本発明を以下の実施例によりさらに詳細に説明するが、本発明はそれらに限定されるものではない。
【００４２】
実施例１
表１の主成分組成を有する溶製合金A及び溶製合金Bをそれぞれ不活性ガス雰囲気中で粗粉砕し、篩分することにより粒径500μｍ以下の粗粉を得た。合金Aの粗粉87.9kgと合金Bの粗粉12.1kgとをV型混合機に投入して混合し、100kgの混合粗粉を得た。混合粗粉の組成を分析したところ、重量百分率で主成分は、Nd27.3％、Dy2.7％，B1.0％，Nb0.2％，Al0.1％，Co1.0％，Cu0.1％，残部Feであり、この混合粗粉に含有される不純物は、0.15重量％のO，0.01重量％のN，及び0.02重量％のCであった。
【００４３】
【表１】

【００４４】
前記混合粗粉を酸素濃度が10ppm以下（体積比）の窒素ガス雰囲気中でジェットミル粉砕し、平均粒径4.0μｍの微粉とした。微粉を窒素ガス雰囲気中で大気と非接触状態で直接鉱油（出光興産（株）製、商品名：出光スーパーゾルPA-30）中に回収し、微粉スラリーを得た。この微粉スラリーを用いて磁界強度10kOe及び成形圧1.0ton/cm²の条件で湿式圧縮成形し、得られた成形体を約５×10^-1 Torrの真空中で200℃で１時間加熱して脱油後、引き続き約３×10^-5 Torrで1050〜1100℃の温度範囲で各々２時間焼結し、室温まで冷却して焼結体を得た。
【００４５】
各焼結体に不活性ガス雰囲気中で900℃×２時間と500℃×１時間の熱処理を各１回施した後、室温まで冷却してR-T-B系焼結型永久磁石を得た。20℃において磁気特性を測定したところ、図１に示す結果を得た。図１から明らかなように、焼結温度を1070〜1110℃とした場合に永久磁石として好ましい磁気特性が得られた。特に焼結温度を1090℃とした場合に13.8kGのBr，18kOeのiHc及び45.9MGOe の(BH)maxが得られ、焼結温度を1100℃とした場合に13.8kGのBr，17.9kOeのiHc，45.7MGOe の(BH)maxが得られ、Br及び(BH)maxが高かった。
【００４６】
前記焼結磁石のうち代表的な焼結磁石の組成を分析したところ、重量百分率で主成分はNd: 27.3％、Dy: 2.7％，B: 1.0％，Nb: 0.2％，Al: 0.1％，Co: 1.0％，Cu: 0.1％，残部: Feであり、不可避的不純物は、0.17％のO，0.05％のN，及び0.07％のCであった。
【００４７】
前記焼結磁石のうち代表的な焼結磁石の断面組織を後述の実施例７と同様にして観察し、主相結晶粒（R₂T₁₄B）内（ほぼ中心部）及び結晶粒界相における重希土類元素(Dy)の濃度を測定した。その結果、R₂T₁₄B型主相結晶粒が、重希土類元素(Dy)の濃度が結晶粒界相より高い第一の主相結晶粒と、重希土類元素(Dy)の濃度が結晶粒界相より低い第二の主相結晶粒と、重希土類元素(Dy)の濃度が結晶粒界相とほぼ等しい第三の主相結晶粒とから構成されていることが分かった。
【００４８】
比較例１
表２の主成分組成を有する溶製合金Cを用いた以外は実施例１と同様にして粗粉砕した。この粗粉の組成（重量％）を分析したところ、主成分はNd: 27.3％、Dy: 2.7％，B: 1.0％，Nb: 0.2％，Al: 0.1％，Co: 1.0％，Cu: 0.1％，残部: Feであり、不純物はＯ: 0.13％，N: 0.008％，C: 0.02％であった。
【００４９】
【表２】

【００５０】
この粗粉を用いて実施例１と同様にして微粉砕（平均粒径4.1μｍ）、スラリー化、磁界中成形、脱油、焼結及び熱処理を行い、シングル法による比較例の焼結型永久磁石を得た。この焼結型永久磁石の組成（重量％）を分析したところ、主成分は、Nd: 27.3％、Dy: 2.7％，B: 1.0％，Nb: 0.2％，Al: 0.1％，Co: 1.0％，Cu: 0.1％，残部: Feであり、不純物は、O: 0.15％，N: 0.04％，C: 0.06％であった。
【００５１】
20℃において磁気特性を測定した結果を図１に示す。図１より、iHcのレベルは19kOe前後と高いが、Brは13.3kG以下、(BH)maxは42.5MGOe以下であり、実施例１のBr及び(BH)maxに比べて低いことが分かる。またこの比較例の焼結磁石の断面組織には、重希土類元素Dyの濃度が結晶粒界相より高い主相結晶粒は観察されなかった。
【００５２】
実施例２
表３の主成分組成を有する溶製合金D及び溶製合金Eをそれぞれ用いた以外は実施例１と同様にして粗粉砕した。合金Dの粗粉94kgと合金Eの粗粉６kgとをV型混合機に投入して混合し、100kgの混合粗粉とした。混合粗粉の組成を分析したところ、重量百分率で主成分はNd: 22.4％，Pr: 8.9％，Dy: 1.2％，B: 1.0％，Al: 0.1％，Ga: 0.15％，残部: Feであり、不純物はO: 0.14％，N: 0.01％，C: 0.01％であった。
【００５３】
【表３】

【００５４】
混合粗粉を酸素濃度が500ppm（体積比）以下の窒素ガス雰囲気中でジェットミル粉砕し、平均粒径4.1μｍの微粉とした。この微粉を用いて磁界強度10kOe、成形圧1.5ton/cm²の条件で乾式圧縮成形した。得られた成形体を約３×10^-5 Torrの真空中、1040〜1110℃の温度範囲で各々２時間焼結した後、室温まで冷却して焼結体を得た。
【００５５】
各焼結体に不活性ガス雰囲気中で900℃×３時間と550℃×１時間の熱処理を各１回施した後、室温まで冷却してR-T-B系焼結型永久磁石を得た。20℃で磁気特性を測定したところ、図２に示す結果を得た。図２から、焼結温度を1050〜1100℃とした場合に永久磁石として好ましい磁気特性が得られることが分かった。特に焼結温度が1070℃の場合に13.4kGのBr，16.3kOeのiHc，及び43.2MGOeの(BH)maxが得られ、また焼結温度が1080℃の場合に13.4kGのBr，15.1kOeのiHc，及び43.3MGOeの(BH)maxが得られ、Br及び(BH)maxが高かった。
【００５６】
前記焼結磁石のうち代表的な焼結磁石の組成を分析したところ、重量百分率で主成分はNd: 22.4％，Pr: 8.9％，Dy: 1.2％，B: 1.0％，Al: 0.1％，Ga: 0.15％，残部: Feであり、不純物はO:0.45％，N:0.02％，C:0.07％であった。
【００５７】
前記焼結磁石のうち代表的な焼結磁石の断面組織を後述の実施例７と同様にして主相結晶粒（R₂T₁₄B）内（ほぼ中心部）及び結晶粒界相における重希土類元素(Dy)の濃度を測定した。その結果、R₂T₁₄B型主相結晶粒が、重希土類元素(Dy)の濃度が結晶粒界相より高い第一のR₂T₁₄B型主相結晶粒と、重希土類元素(Dy)の濃度が結晶粒界相より低い第二のR₂T₁₄B型主相結晶粒と、重希土類元素(Dy)の濃度が結晶粒界相とほぼ等しい第三のR₂T₁₄B型主相結晶粒とから構成されていることが分かった。
【００５８】
比較例２
表４の主成分組成を有する溶製合金Fを用いた以外は実施例１と同様にして粗粉砕した。粗粉の組成を分析したところ、重量百分率で主成分は、Nd: 22.4％，Pr: 8.9％，Dy: 1.2％，B: 1.0％，Al: 0.1％，Ga: 0.15％，残部: Feであり、不純物はO: 0.14％，N: 0.01％，C: 0.02％であった。
【００５９】
【表４】

【００６０】
この粗粉を用いて実施例２と同様にして微粉砕（平均粒径4.0μｍ）、磁界中成形、焼結及び熱処理を行い、シングル法による比較例の焼結型永久磁石を得た。この磁石の成分を分析したところ、重量百分率で主成分はNd: 22.4％，Pr: 8.9％，Dy: 1.2％，B: 1.0％，Al: 0.1％，Ga: 0.15％，残部: Feであり、不純物はO: 0.43％，N: 0.03％，C: 0.06％であった。
【００６１】
20℃で磁気特性を測定した結果を図２に示す。図２から明らかなように、iHcのレベルは実施例２に比べてやや高いが、Brは12.9kG以下で、(BH)maxは40.1MGOe以下と低かった。またこの比較例の焼結磁石の断面組織には、重希土類元素（Dy）の濃度が結晶粒界相より高い主相結晶粒は観察されなかった。
【００６２】
実施例３
表５の主成分組成を有する溶製合金G及び溶製合金Hを用いた以外は実施例１と同様にして粗粉砕した。次に合金Gの粗粉81.8kgと合金Hの粗粉18.2kgとをV型混合機に投入して混合し、100kgの混合粗粉を得た。混合粗粉の組成を分析したところ、重量百分率で主成分はNd: 19.14％，Pr: 5.34％，Dy: 6.00％，B: 0.97％，Nb: 0.29％，Al: 0.10％，Co: 2.00％，Ga: 0.08％，Cu: 0.10％，残部: Feであり、不純物O: 0.14％，N: 0.01％，C: 0.02％であった。
【００６３】
【表５】

【００６４】
この混合粗粉を用いて実施例１と同様にして微粉砕（平均粒径4.2μｍ）、スラリー化、磁界中圧縮成形を行った。得られた成形体を約５×10^-1 Torrの真空中で200℃で１時間加熱して脱油し、次いで約２×10^-5 Torrの真空中、1060〜1130℃の温度範囲内の各温度で２時間焼結後、室温まで冷却した。得られた各焼結体に不活性ガス雰囲気中で900℃×２時間と500℃×１時間の熱処理を各１回施した後、室温まで冷却してR-T-B系焼結型永久磁石を得た。20℃において磁気特性を測定した結果を図３に示す。図３から明らかなように、焼結温度を1070〜1120℃とした場合に永久磁石として好ましい磁気特性が得られた。特に焼結温度を1100℃とした場合に12.7kGのBr，25.5kOeのiHc及び38.8MGOeの(BH)maxが得られ、1110℃とした場合に12.7kGのBr，25.3kOeのiHc及び38.6MGOeの(BH)maxが得られ、Br及び(BH)maxが高かった。
【００６５】
前記永久磁石のうち代表的な永久磁石の組成を分析したところ、重量百分率で主成分はNd: 19.14％，Pr: 5.34％，Dy: 6.00％，B: 0.97％，Nb: 0.29％，Al: 0.10％，Co: 2.00％，Ga: 0.08％，Cu: 0.10％，残部Feであり、不純物はO:0.16％，N:0.05％，C:0.07％であった。
【００６６】
焼結温度1100℃及び1110℃の条件で作製した前記永久磁石の断面組織について、後述の実施例７と同様にして主相結晶粒（R₂T₁₄B）内（ほぼ中心部）及び結晶粒界相における重希土類元素(Dy)の濃度を測定した。その結果、R₂T₁₄B型主相結晶粒が、重希土類元素(Dy)の濃度が結晶粒界相より高い第一の主相結晶粒と、重希土類元素(Dy)の濃度が結晶粒界相より低い第二の主相結晶粒と、重希土類元素(Dy)の濃度が結晶粒界相とほぼ等しい第三の主相結晶粒とから構成されていることが分かった。
【００６７】
比較例３
表６の主成分組成を有する溶製合金Ｉを用いた以外は実施例１と同様にして粗粉を得た。この粗粉の組成を分析したところ、重量百分率で主成分は、Nd: 19.14％，Pr: 5.34％，Dy: 6.00％，B: 0.97％，Nb: 0.29％，Al: 0.10％，Co: 2.00％，Ga: 0.08％，Cu: 0.10％，残部: Feであり、不純物はO: 0.12％，N: 0.01％，C: 0.01％であった。
【００６８】
【表６】

【００６９】
この粗粉を用いた以外は実施例１と同様にして微粉砕（平均粒径4.2μｍ）、スラリー化及び磁界中成形を行った。得られた成形体に対し、実施例３と同条件で脱油、焼結及び熱処理を行い、シングル法による比較例の焼結型永久磁石を得た。この磁石の組成を分析したところ、重量百分率で主成分は、Nd: 19.14％，Pr: 5.34％，Dy: 6.00％，B: 0.97％，Nb: 0.29％，Al: 0.10％，Co: 2.00％，Ga: 0.08％，Cu: 0.10％，残部: Feであり、不純物はO: 0.14％，N: 0.04％，C: 0.06％であった。
【００７０】
20℃で磁気特性を測定した結果を図３に示す。図３から明らかなように、iHcのレベルは25kOe前後と高いが、Brは12.2kG以下、(BH)maxは35.7MGOe以下であり、実施例３に比べて低かった。またこの比較例の焼結磁石の断面組織において、重希土類元素（Dy）の濃度が結晶粒界相より高い主相結晶粒は観察されなかった。
【００７１】
比較例４
表７の主成分組成を有する溶製合金J及び溶製合金Kをそれぞれ用いた以外は実施例１と同様にして粗粉砕した。合金Jの粗粉81.8kgと合金Kの粗粉18.2kgとをV型混合機に投入して混合し、100kgの混合粗粉とした。混合粗粉の組成を分析したところ、重量百分率で主成分は、Nd: 19.14％，Pr: 5.34％，Dy: 6.00％，B: 0.97％，Nb: 0.65％，Al: 0.10％，Co: 2.00％，Ga: 0.08％，Cu: 0.10％，残部: Feであり、不純物はO: 0.15％，N: 0.02％，C: 0.02％であった。
【００７２】
【表７】

【００７３】
この粗粉を用いた以外は実施例１と同様にして微粉砕（平均粒径4.1μｍ）、スラリー化及び磁界中成形を行った。得られた成形体を約５×10^-1 Torrの真空中で200℃で１時間加熱して脱油し、次いで約２×10^-5 Torrの真空中で1060〜1130℃の温度範囲内の各温度で２時間焼結後、室温まで冷却した。得られた各焼結体に不活性ガス雰囲気中で900℃×２時間と500℃×１時間の熱処理を各１回施した後、室温まで冷却して、ブレンド法による比較例の焼結型永久磁石を得た。20℃において磁気特性を測定した結果を図３に示す。図３から明らかなように、焼結温度が1100℃の場合に12.1kGのBr、25.4kOeのiHc及び35.1MGOeの(BH)maxが得られ、焼結温度が1110℃の場合に12.1kGのBr、25.2kOeのiHc及び35.0MGOeの(BH)maxが得られ、Br及び(BH)maxは低かった。
【００７４】
この比較例の焼結磁石の組成を分析したところ、重量百分率で主成分は、Nd: 19.14％，Pr: 5.34％，Dy: 6.00％，B: 0.97％，Nb: 0.65％，Al: 0.10％，Co: 2.00％，Ga: 0.08％，Cu: 0.10％，残部: Feであり、不純物はO:0.17％，N:0.06％，C:0.06％であった。この比較例の焼結磁石のBr及び(BH)maxが低いのは、Nb含有量が0.65％と高いので、主相結晶粒の焼結時の正常な粒成長が抑制されたためであると考えられる。
【００７５】
実施例４
表８の主成分組成を有する溶製合金L及び溶製合金Mをそれぞれ用いた以外は実施例１と同様にして粗粉砕した。合金Lの粗粉90.0kgと合金Hの粗粉10.0kgとをV型混合機に投入して混合し、100kgの混合粗粉とした。混合粗粉の組成を分析したところ、重量百分率で主成分は、Nd: 22.83％，Pr: 6.37％，Dy: 1.30％，B: 1.05％，Mo:0.13％，Al:0.10％，残部Feであり、不純物はO:0.15％，N:0.01％，C:0.02％であった。
【００７６】
【表８】

【００７７】
この混合粗粉を用いた以外は実施例１と同様にして、微粉砕（平均粒径4.0μｍ）、スラリー化及び磁界中成形を行った。得られた成形体を約５×10^-1 Torrの真空中で200℃で１時間加熱して脱油し、引き続き約２×10^-5 Torrの真空中で1050〜1100℃の温度範囲内の各温度で２時間焼結後室温まで冷却した。得られた各焼結体に不活性ガス雰囲気中で900℃×２時間と550℃×１時間の熱処理を各１回施した後、室温まで冷却してR-T-B系焼結型永久磁石を得た。20℃で磁気特性を測定した結果、焼結温度が1060〜1090℃の場合に永久磁石として好ましい磁気特性が得られた。特に焼結温度が1070℃の場合に13.9kGのBr、15.5kOeのiHc及び46.5MGOeの(BH)maxが得られ、焼結温度が1080℃の場合に14.0kGのBr、15.3kOeのiHc及び47.2MGOeの(BH)maxが得られ、Br及び(BH)maxが高かった。
【００７８】
前記永久磁石のうち代表的な永久磁石の組成を分析したところ、重量百分率で主成分組成がNd: 22.83％，Pr: 6.37％，Dy: 1.30％，B: 1.05％，Mo: 0.13％，Al: 0.10％，残部: Feであり、不純物はO: 0.18％，N: 0.06％，C: 0.08％であった。
【００７９】
焼結温度1070℃、1080℃の条件で作製した前記永久磁石の断面組織について、後述の実施例７と同様にして主相結晶粒（R₂T₁₄B）内（ほぼ中心部）及び結晶粒界相における重希土類元素(Dy)の濃度を測定した。その結果、R₂T₁₄B型主相結晶粒が、重希土類元素(Dy)の濃度が結晶粒界相より高い第一の主相結晶粒と、重希土類元素(Dy)の濃度が結晶粒界相より低い第二の主相結晶粒と、重希土類元素(Dy)の濃度が結晶粒界相とほぼ等しい第三の主相結晶粒とから構成されていることが分かった。
【００８０】
実施例５
表９の主成分組成を有する溶製合金N及び溶製合金Oをそれぞれ用いた以外は実施例１と同様にして粗粉砕した。合金Nの粗粉80.0kgと合金Oの粗粉20.0kgとをV型混合機に投入して混合し、100kgの粗粉とした。混合粗粉の組成を分析したところ、重量百分率で主成分は、Nd: 26.2％，Dy: 5.8％，B: 0.95％，Nb: 0.20％，Al: 0.1％，Co: 2.5％、Cu: 0.15％，Ga: 0.15％，残部: Feであり、不純物はO: 0.15％，N: 0.02％，C: 0.02％であった。
【００８１】
【表９】

【００８２】
混合粗粉を酸素濃度が500ppm以下（体積比）の窒素ガス雰囲気中でジェットミル粉砕し、平均粒径4.2μｍの微粉とした。この微粉を磁界強度10kOe、成形圧1.5ton/cm²の条件で乾式圧縮成形した。得られた成形体を約３×10^-5 Torrの真空中で、1040〜1100℃の温度範囲内の各温度で２時間焼結後室温まで冷却した。
【００８３】
得られた各焼結体に不活性ガス雰囲気中で900℃×３時間と480℃×１時間の熱処理を各１回施した後、室温まで冷却してR-T-B系焼結型永久磁石を得た。20℃で磁気特性を測定したところ、焼結温度を1050〜1090℃とした場合に永久磁石として好ましい磁気特性が得られた。特に焼結温度が1070℃の時に12.5kGのBr，24.5kOeのiHc及び37.5MGOeの(BH)maxが得られ、焼結温度が1080℃の時に12.5kGのBr，24.2kOeのiHc及び37.4MGOeの(BH)maxが得られ、Br及び(BH)maxが高かった。前記永久磁石を分析したところ、重量百分率で主成分は、Nd: 26.2％，Dy: 5.8％，B: 0.95％，Nb: 0.20％，Al: 0.1％，Co: 2.5％、Cu: 0.15％，Ga: 0.15％，残部: Feであり、不純物はO: 0.38％，N: 0.03％，C: 0.05％であった。
【００８４】
焼結温度が1070℃、1080℃の前記焼結磁石の断面組織について、後述の実施例７と同様にして主相結晶粒（R₂T₁₄B）内（ほぼ中心部）及び結晶粒界相における重希土類元素(Dy)の濃度を測定した。その結果、R₂T₁₄B型主相結晶粒が、重希土類元素(Dy)の濃度が結晶粒界相より高い第一の主相結晶粒と、重希土類元素(Dy)の濃度が結晶粒界相より低い第二の主相結晶粒と、重希土類元素(Dy)の濃度が結晶粒界相とほぼ等しい第三の主相結晶粒とから構成されていることが分かった。
【００８５】
実施例６
表10の主成分組成を有する溶製合金P及び溶製合金Qをぞれぞれ用いた以外は実施例１と同様にして粗粉砕した。合金Pの粗粉90.0kgと合金Qの粗粉10.0kgとをV型混合機に投入して混合し、100kgの混合粗粉とした。混合粗粉の組成を分析したところ、重量百分率で主成分は、Nd: 20.6％，Pr: 8.8％，Dy: 2.6％，B: 1.06％，W: 0.18％，Al: 0.05％，Ga: 0.17％，残部: Feであり、不純物はO: 0.15％，N: 0.01％，C: 0.01％であった。
【００８６】
【表１０】

【００８７】
混合粗粉を酸素濃度が500ppm以下（体積比）の窒素ガス雰囲気中でジェットミル粉砕し、平均粒径4.2μｍの微粉とした。この微粉を磁界強度10kOe、成形圧1.5ton/cm²の条件で乾式圧縮成形した。得られた成形体を約３×10^-5 Torrの真空中で、1040〜1100℃の温度範囲内の各温度で２時間焼結後、室温まで冷却した。
【００８８】
得られた各焼結体に不活性ガス雰囲気中で900℃×３時間と550℃×１時間の熱処理を各１回施した後室温まで冷却し、R-T-B系焼結型永久磁石を得た。20℃で磁気特性を測定したところ、焼結温度を1050〜1090℃とした場合に永久磁石として好ましい磁気特性が得られた。特に焼結温度が1070℃のときに13.2kGのBr、19.5kOeのiHc及び41.8MGOeの(BH)maxが得られ、焼結温度が1080℃のときに13.2kGのBr、19.3kOeのiHc及び41.7MGOeの(BH)maxが得られ、Br及び(BH)maxが高かった。
【００８９】
前記永久磁石のうち代表的な永久磁石の組成を分析したところ、重量百分率でNd: 20.6％，Pr: 8.8％，Dy: 2.6％，B: 1.06％，W: 0.18％，Al: 0.05％，Ga: 0.17％，残部: Feであり、不純物はO: 0.50％，N: 0.02％，C: 0.06％であった。
【００９０】
焼結温度1070℃及び1080℃の条件で作製した前記永久磁石の断面組織について、後述の実施例７と同様にして主相結晶粒（R₂T₁₄B）内（ほぼ中心部）及び結晶粒界相における重希土類元素(Dy)の濃度を測定した。その結果、R₂T₁₄B型主相結晶粒が、重希土類元素(Dy)の濃度が結晶粒界相より高い第一の主相結晶粒と、重希土類元素(Dy)の濃度が結晶粒界相より低い第二の主相結晶粒と、重希土類元素(Dy)の濃度が結晶粒界相とほぼ等しい第三の主相結晶粒とから構成されていることが分かった。
【００９１】
実施例７
表11の主成分組成を有する溶製合金R及び溶製合金Sを各々用いた以外は実施例１と同様にして粗粉砕した。合金Rの粗粉90.0kgと合金Sの粗粉10.0kgとをV型混合機に投入して混合し、100kgの混合粗粉とした。混合粗粉の組成を分析したところ、重量百分率で主成分は、Nd: 21.38％，Pr: 7.12％，Dy: 1.50％，B: 1.03％，Al: 0.08％，Co: 2.00％，Ga: 0.08％，Cu: 0.1％，残部: Feであり、O: 0.14％，N: 0.02％，C: 0.02％であった。
【００９２】
【表１１】

【００９３】
混合粗粉を酸素濃度が10ppm以下（体積比）の窒素ガス雰囲気中でジェットミル粉砕し、平均粒径4.2μｍの微粉とした。得られた微粉を窒素ガス雰囲気中で、大気に触れさせずに直接鉱油（出光興産（株）製、商品名：出光スーパーゾルPA-30）中に回収した。得られたスラリーを磁界強度10kOe、成形圧1.0ton/cm²で圧縮成形した。得られた成形体を約５×10^-1 Torrの真空中で200℃で１時間加熱して脱油し、約３×10^-5 Torrの真空中で1040〜1100℃の温度範囲内の各温度で２時間焼結後、室温まで冷却した。
【００９４】
各焼結体に不活性ガス雰囲気中で900℃×２時間と480℃×１時間の熱処理を各１回施した後、室温まで冷却してR-T-B系焼結型永久磁石を作製した。20℃で磁気特性を測定したところ、焼結温度が1060〜1090℃の場合に永久磁石として好ましい磁気特性が得られた。特に焼結温度が1070℃の場合に13.9kGのBr，15kOeのiHc及び46.5MGOeの(BH)maxが得られ、焼結温度が1080℃の場合に14.0kGのBr，14.8kOeのiHc及び47.2MGOeの(BH)maxが得られ、Br及び(BH)maxが高かった。
【００９５】
前記焼結磁石のうち代表的な焼結磁石を分析したところ、重量百分率で主成分は、Nd: 21.38％，Pr: 7.12％、Dy: 1.50％，B: 1.03％，Al: 0.08％，Co: 2.00％，Ga: 0.08％，Cu: 0.1％，残部: Feであり、不純物はO: 0.16％，N: 0.06％，C: 0.06％であった。
【００９６】
前記焼結磁石のうち代表的な焼結磁石の断面組織を、EPMA（Electron Probe Micro-Analyzer；JEOL製、型式JXA-8800）を用いて、下記の条件で分析した。
加速電圧: 15kV、
試料吸収電流: 約４×10^-8A、
１分析点当たりのX線取り込み時間（計数時間）: 10msec、
分析点数: 縦（X）方向及び横（Y）方向がともに400点、
X及びY方向の各分析点の間隔: 0.12μｍ、
面分析のエリア: 0.12μｍ×400点＝48μｍの矩形範囲、
【００９７】
上記条件でビームを最小スポットに絞り照射することにより、Dy，Nd及びPrの濃度分布を測定した。Dy，Nd及びPrの分析に用いた分光結晶は高感度型ふっ化リチウム（LiF）であった。本実施例のR-T-B系焼結型永久磁石の結晶組織を図４に概略的に示す。結晶組織はR₂T₁₄B型主相結晶粒1と結晶粒界相2とを有し、結晶粒界相の３重点2'は黒い領域で示す。また図４の結晶組織におけるDyの濃度分布を図５に示し、Ndの濃度分布を図６(a)に示し、Prの濃度分布を図６(b)に示す。図５、図６(a),(b)から明らかなように、結晶粒界相ではNd，Dy，Prの分布は実質的に３重点で認められたが、これは３重点のみにNd，Dy，Prが分布しているわけではなく、３重点以外では結晶粒界相が非常に薄いので、Nd，Dy，Prの分布量が非常に少ないからである。
【００９８】
図４において、結晶粒界相の３重点を形成しているのはR（Nd，Dy，Pr）リッチ相である。図６(a)及び(b)からNd及びPrはほぼ同位置に存在することが分かる。また図５、図６(a),(b)から、DyはNd及びPrとほぼ同じ結晶粒界相の領域にも存在するが、結晶粒界から1.0μｍ以上離れたR₂T₁₄B型主相結晶粒内の部分（芯部）でも高濃度に存在することがあることが分かった。
【００９９】
これらの観察結果から、結晶粒界相から主相結晶粒内の中心部に至るDy濃度分布に関し、３種類のDy濃度分布のパターンがあることが分かった。第一のパターンでは、結晶粒界相より主相結晶粒内の芯部の方がDy濃度が高い。第二のパターンでは、結晶粒界相のDy濃度が高く主相結晶粒内の芯部のDy濃度が低い。第三のパターンでは、結晶粒界相から主相結晶粒の中心部に至るDy濃度分布がほぼ均一である。図５において、結晶粒界相より主相結晶粒内の芯部の方がDy濃度が高い第一の主相結晶粒は６個であり、結晶粒界相よりDy濃度が低い第二の主相結晶粒は15個であり、結晶粒界相とほぼ等しいDy濃度を有する第三の主相結晶粒は19個であった。なお図５、図６(a),(b)においてDy，Nd及び Prの濃度分布を評価する際に、顕微鏡観察用試料の作成時に形成されたボイドの影響を考慮した。また図４、図５及び図６(a),(b)は断面組織の一例にすぎず、Dyの濃度分布を決定するには多数の視野における断面組織から求めたデータを平均する必要がある。このように本発明のR-T-B系焼結型永久磁石は、主相結晶粒及び結晶粒界相において特徴的なDy濃度分布を有する。
【０１００】
前記永久磁石のうち代表的なものの主相結晶粒の粒径分布を図７に示す。図７の横軸は主相結晶粒の粒径範囲を示し、例えば「９〜10μｍ」は主相結晶粒の粒径範囲が「９μｍ以上10μｍ未満」であることを意味する。主相結晶粒の粒径は、光学顕微鏡（型式UFX-II，株式会社ニコン製）を用いて、永久磁石の任意の断面の写真（倍率1000倍）を撮影し、この断面写真をプラネトロン社製の画像処理ソフト（Image Pro. Plus (DOS/V))により画像処理した。画像処理で測定した任意の各主相結晶粒の面積をS_iとして、さらに各主相結晶粒の断面形状を円と仮定し、各主相結晶粒径d_iを（４×S_i÷π）^1/2と定義した。縦軸の分布率（％）は、測定した視野における主相結晶粒の総数Tに対する各粒径範囲内にある主相結晶粒の個数T_Nの比率〔（T_N／T）×100％〕を示す。
【０１０１】
図７から明らかなように、本発明の永久磁石では、粒径２μｍ未満の主相結晶粒の分布率が０％であり、かつ16μｍ以上の主相結晶粒の分布率が5.8％であった。さらに検討した結果、粒径２μｍ未満の主相結晶粒の分布率が５％未満でかつ16μｍ以上の主相結晶粒の分布率が10％以下であれば永久磁石として好ましい磁気特性を実現できることが分かった。さらに粒径２μｍ未満の主相結晶粒の分布率が３％以下でかつ16μｍ以上の主相結晶粒の分布率が８％以下であるのがより好ましく、粒径２μｍ未満の主相結晶粒の分布率が０％でかつ16μｍ以上の主相結晶粒の分布率が６％以下であるのが特に好ましいことが分かった。なお前記主相粒径分布はNb含有量が0.01〜0.6％の場合でも実現可能である。
【０１０２】
比較例５
表12の主成分組成を有する溶製合金Tを用いた以外は実施例７と同様にして粗粉砕した。粗粉の組成を分析したところ、重量百分率で主成分は、Nd: 21.38％，Pr: 7.12％，Dy: 1.50％，B: 1.03％，Nb: 0.70％，Al: 0.08％，Co: 2.00％，Ga: 0.08％，Cu: 0.1％，残部: Feであり、不純物はO: 0.15％，N: 0.01％，C: 0.02％であった。
【０１０３】
【表１２】

【０１０４】
この粗粉を用いて実施例７と同様にして、微粉砕（平均粒径4.1μｍ）、スラリー化、磁界中成形、脱油、焼結及び熱処理を行い、シングル法による比較例の焼結型永久磁石を得た。この焼結磁石の組成を分析したところ、重量百分率で主成分は、Nd: 21.38％,Pr:7.12％，Dy: 1.50％，B: 1.03％，Nb: 0.70％，Al: 0.08％，Co: 2.00％，Ga: 0.08％，Cu: 0.1％，残部: Feであり、不純物はO: 0.17％，N:0.05％，C: 0.07％であった。
【０１０５】
20℃において磁気特性を測定した結果、iHcのレベルは16kOe前後と高いが、Brは13.5kG以下、(BH)max44.0MGOe以下であり、実施例７に比べて低かった。
【０１０６】
図８はこの焼結磁石の断面組織を概略的に示す。結晶組織中の３はボイドを示し、その他の番号は図４と同じである。図８より、結晶粒界相から主相結晶粒の中心部までほぼ均一なDy濃度分布と、結晶粒界相のDy濃度が高く主相結晶粒内のほぼ中心部のDy濃度が低い分布の２パターンが存在することが確認された。結晶粒界相とほぼ同じDy濃度分布を有する主相結晶粒は31個であり、結晶粒界相よりDy濃度が低い主相結晶粒は15個であった。しかし結晶粒界相より主相結晶粒内のほぼ中心部のDy濃度が高い分布は観察されなかった。
【０１０７】
この比較例の焼結磁石の主相結晶粒径分布を実施例７と同様にして評価した結果を図９に示す。図９から明らかなように、この焼結磁石では粒径１μｍ以上２μｍ未満の主相結晶粒の分布率が12.5％であり、かつ図７の分布に比べて全体的に小粒径側に主相結晶粒径分布が大きくシフトしていて、主相結晶粒が十分粒成長していない。このため実施例７に比べてBr及び(BH)maxが低いと判断される。
【０１０８】
上記実施例では重希土類元素がDyの場合を記載したが、Tb又はHoの場合も、Dyの場合とほぼ同様に、芯部において結晶粒界相よりTb又はHoの濃度が高い主相結晶粒を有し、上記実施例と同様に高いBr及び(BH)maxを有するR-T-B系焼結型永久磁石を得ることができる。
【０１０９】
上記実施例では、同じR含有量でかつR元素を構成するDy，Nd等の比率のみが異なる以外は他の主成分が一致する２種のR-T-B系合金粉末、又は同じR含有量でかつR元素を構成するDy，Nd等の比率及びFeの一部を高融点金属元素（Nb等）で置換した以外は他の主成分が一致する２種のR-T-B系合金粉末を用いて混合することにより、特徴あるDy濃度分布を有する主相結晶粒を有し、かつ高いBr及び(BH)maxの用途に好適な主相結晶粒径分布を有するR-T-B系焼結型永久磁石を安定に得ることができた。本発明では前記R-T-B系合金粉末として、３種以上のR-T-B系合金粉末を用いてもよい。またこれらR-T-B系合金粉末の混合は微粉段階で行ってもよい。
【０１１０】
上記実施例のR-T-B系焼結型永久磁石に各種の表面処理（Niめっき及び／又は電着エポキシ樹脂コーティング等）を施こせば、各種の用途（ボイスコイルモータ又はCDピックアップ等のアクチュエータ、あるいは回転機等）に好適に用いることができる。
【０１１１】
【発明の効果】
以上詳述したとおり、本発明のR-T-B系焼結型永久磁石は、R₂T₁₄B型主相結晶粒が、重希土類元素（Dy等）濃度が結晶粒界相より高い第一のR₂T₁₄B型主相結晶粒と、重希土類元素（Dy等）濃度が結晶粒界相より低い第二のR₂T₁₄B型主相結晶粒と、重希土類元素（Dy等）濃度が結晶粒界相とほぼ等しい第三のR₂T₁₄B型主相結晶粒とから構成されているので、シングル法により得られたR-T-B系焼結型永久磁石と同程度に高いiHcを有するとともに、より高いBr及び(BH)maxを有する。したがって本発明のR-T-B系焼結型永久磁石は、高いBr及び高い(BH)maxが要求される用途に好適に用いることができる。
【図面の簡単な説明】
【図１】実施例１及び比較例１のR-T-B系焼結型永久磁石について、焼結温度と磁気特性（Br，iHc）との関係を示すグラフである。
【図２】実施例２及び比較例２のR-T-B系焼結型永久磁石について、焼結温度と磁気特性（Br，iHc）との関係を示すグラフである。
【図３】実施例３及び比較例３，４のR-T-B系焼結型永久磁石について、焼結温度と磁気特性（Br，iHc）との関係を示すグラフである。
【図４】実施例７のR-T-B系焼結型永久磁石の結晶組織を示す概略図である。
【図５】実施例７のR-T-B系焼結型永久磁石の結晶組織におけるDyの濃度分布を示すEPMA写真である。
【図６】実施例７のR-T-B系焼結型永久磁石の結晶組織における重希土類元素の濃度分布を示し、(a)は結晶組織におけるNdの濃度分布を示すEPMA写真であり、(d)は結晶組織におけるPrの濃度分布を示すEPMA写真である。
【図７】実施例７のR-T-B系焼結型永久磁石における主相結晶粒の粒径分布を示すグラフである。
【図８】比較例５のR-T-B系焼結型永久磁石の結晶組織を示す概略図である。
【図９】比較例５のR-T-B系焼結型永久磁石における主相結晶粒の粒径分布を示すグラフである。
【符号の説明】
１・・・R₂T₁₄B型主相結晶粒
２・・・結晶粒界相
2'・・・三重点
３・・・ボイド[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an R-T-B sintered permanent magnet having a high coercive force, a residual magnetic flux density and a maximum energy product.
[0002]
[Prior art and problems to be solved by the invention]
R-T-B sintered permanent magnets (R is at least one rare earth element including Y, and T is Fe or Fe and Co) are mass-produced with a maximum energy product of approximately 40 MGOe. There are a single method and a blend method as means for adjusting the alloy composition of the R-T-B sintered permanent magnet.
[0003]
The single method uses an ingot adjusted to the main component composition of the RTB sintered permanent magnet at the melting / casting stage to produce an RTB sintered permanent magnet by grinding, molding in a magnetic field, sintering and heat treatment. The obtained RTB sintered permanent magnet is subjected to desired machining and surface treatment and is put to practical use.
[0004]
The blending method involves mixing two or more types of RTB-based sintered permanent magnet alloy powders with different compositions at a blending ratio that will ultimately result in the main component composition of the desired RTB-based sintered permanent magnet. The RTB-based sintered permanent magnet is manufactured by performing pulverization and thereafter performing molding in a magnetic field, sintering, heat treatment and surface treatment.
[0005]
According to the single method, it is relatively easy to increase the coercive force iHc, but the residual magnetic flux density Br and the maximum energy product (BH) max are low, and a high Br and high (BH) max are required. There is a problem that it is not suitable.
[0006]
As an application example of the conventional blending method, an RTB-based sintered permanent magnet (Japanese Patent Laid-Open No. 7-12213) formed by blending an RT-based alloy with a high R content and an RTB-based alloy with a low R content, RTB sintered permanent magnets (JP-A-9-232121) in which Ga, C, and O are segregated in the R-rich phase and its surroundings have been proposed, but for high Br and high (BH) max applications. There is room for improvement to make it suitable. In particular, nothing has been elucidated about the optimum concentration distribution of heavy rare earth elements in the main phase crystal grains having a large influence on the magnetic properties and the control method thereof.
[0007]
Accordingly, an object of the present invention is to provide a high-performance R-T-B sintered permanent magnet suitable for applications requiring high Br and high (BH) max.
[0008]
[Means for Solving the Problems]
  As a result of diligent research in view of the above object, the present inventors have found that R 28-33%, B 0.5-2%, 0-0.6% M in weight percentage.₁A composition consisting essentially of the balance T and inevitable impurities (R is at least one rare earth element including Y, and necessarily includes at least one heavy rare earth element selected from the group consisting of Dy, Tb and Ho; M₁Is at least one element selected from the group consisting of Nb, Mo, W, V, Ta, Cr, Ti, Zr and Hf, and T is Fe or Fe and Co. And the concentration of the heavy rare earth element (expressed by the measured strength of EPMA) is higher than the grain boundary phase.₂T₁₄B-type main phase grains and a second R in which the concentration of the heavy rare earth element (expressed by the measured strength of EPMA) is lower than the grain boundary phase₂T₁₄B-type main phase grains and, The concentration of the heavy rare earth element ( EPMA Is represented by the measured intensity of R ₂ T ₁₄ B Type main phase grainsContaining tissueIn the cross-sectional picture of the crystal structure R ₂ T ₁₄ B The total number of main phase grains 100 % As the first R ₂ T ₁₄ B The ratio of the number of type main phase grains 1 ~ 35 % And said second R ₂ T ₁₄ B The ratio of the number of type main phase grains Three ~ 55 % And the third R ₂ T ₁₄ B The ratio of the number of type main phase grains 96 ~ Ten %It is obtained by mixing two or more kinds of alloy powders, and the content of the heavy rare earth element in the first alloy powder is more than 10% by weight and not more than 40% by weight, and the heavy rare earth element in the second alloy powder The present inventors have found that RTB-based sintered permanent magnets having a content of 0 to 3 wt% exhibit high Br and high (BH) max, and have arrived at the present invention.
[0010]
According to another preferred embodiment of the present invention, the R-T-B sintered permanent magnet has a weight percentage of R: 28-33%, B: 0.5-2%, M₁: 0.01-0.6% (M₁Is at least one element selected from the group consisting of Nb, Mo, W, V, Ta, Cr, Ti, Zr and Hf. ), M₂: 0.01-0.3% (M₂Is at least one element selected from the group consisting of Al, Ga and Cu. ), And the balance is substantially composed of T and inevitable impurities.
[0011]
An RTB sintered permanent magnet according to a further preferred embodiment of the present invention has a weight percentage of R exceeding 31% and 33% or less, and 0.6% or less oxygen, 0.15% or less carbon as unavoidable impurities, It has a composition containing 0.03% or less of nitrogen and 0.3% or less of Ca.
[0012]
An RTB sintered permanent magnet according to a further preferred embodiment of the present invention has an R of 28 to 31% by weight and 0.25% or less oxygen, 0.15% or less carbon, and 0.15% or less as unavoidable impurities. It has a composition containing nitrogen and 0.3% or less of Ca.
[0013]
  The R-T-B sintered permanent magnet of the present invention has, for example, the same total amount of rare earth elements and heavy rare earth elements.( Dy , Tb as well as Ho ) ContentTwo or more types of alloy powders with substantially the same composition except for the difference are mixed and subjected to forming, sintering and heat treatment in a magnetic field, followed by machining, finishing (barrel processing, etc.) and surface treatment as necessary. It can be obtained by performing (Ni plating, etc.).Mix two or more kinds of alloy powder RTB When producing sintered sintered permanent magnets, the content of heavy rare earth elements in the first alloy powder Ten More than% by weight 40 The content of heavy rare earth elements in the second alloy powder is 0 to 3% by weight.Said2Select the optimum sintering conditions according to the composition of the alloy powder of more than one kind and the final composition of the RTB sintered permanent magnet, so that the diffusion state of heavy rare earth elements (Dy etc.) in the sintered body structure It is important to strictly control. As a result, R₂T₁₄Regarding the concentration distribution of heavy rare earth elements (Dy, etc.) in the B-type main phase grains (substantially in the center) and the grain boundary phase, the concentration of heavy rare earth elements (Dy, etc.) is higher than that of the grain boundary phase.₂T₁₄B-type main phase grains and R whose concentration of heavy rare earth elements (Dy, etc.) is lower than the grain boundary phase₂T₁₄A crystal structure containing B-type main phase grains is obtained.
[0014]
An RTB sintered permanent magnet having such a sintered body structure has a slightly lower coercive force iHc than an RTB sintered permanent magnet by a single method, but has a significantly higher Br and (BH) max. . The correlation between this and the concentration distribution of heavy rare earth elements (Dy, etc.) is not yet clear enough, but the concentration of heavy rare earth elements (Dy, etc.) is higher than the grain boundary phase.₂T₁₄B-type main phase grains contribute to the realization of high Br, and the concentration of heavy rare earth elements (Dy, etc.) is lower than the grain boundary phase.₂T₁₄B-type main phase grains are presumed to contribute to the realization of high iHc, which is close to the single method.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
[1] R-T-B sintered permanent magnet
(A) Composition
(a) Main component The composition of the R-T-B sintered permanent magnet of the present invention is as follows: R 28-33%, B 0.5-2%,0 0.6 %of M ₁ ,And a main component consisting of T and inevitable impurities( R Is Y At least one rare earth element containing Dy , Tb as well as Ho Necessarily containing at least one heavy rare earth element selected from the group consisting of M ₁ Is Nb , Mo , W , V , Ta , Cr , Ti , Zr as well as Hf At least one element selected from the group consisting of: T Is Fe Or Fe When Co It is. ). In addition, 0.01 to 0.3% by weight of M as the main component₂(At least one element selected from the group consisting of Al, Ga and Cu) is preferably contained.
[0016]
(1) R element
The R element is at least one kind of rare earth element including Y and necessarily contains at least one kind of heavy rare earth element selected from the group consisting of Dy, Tb and Ho. Examples of rare earth elements (including Y) other than heavy rare earth elements include Nd, Pr, La, Sm, Ce, Eu, Gd, Er, Tm, Yb, Lu, and Y. As the rare earth element R, a mixture of two or more rare earth elements such as misch metal or didymium may be used.
[0017]
The content of R is 28 to 33% by weight. When the R content is less than 28% by weight, high iHc that can withstand practical use cannot be obtained, and when it exceeds 33% by weight, the decrease in Br becomes significant.
[0018]
The content of heavy rare earth elements is preferably in the range of 0.2 to 15% by weight. If the content of heavy rare earth element is less than 0.2% by weight, the effect of improving magnetic properties due to the distribution of heavy rare earth element in the crystal structure is insufficient. On the other hand, when the content of heavy rare earth elements exceeds 15% by weight, Br and (BH) max of the R—T—B based sintered permanent magnet are greatly reduced. A more preferable heavy rare earth element content is 0.5 to 13% by weight.
[0019]
(2) B
The content of B is 0.5 to 2% by weight. If the B content is less than 0.5% by weight, it is difficult to obtain high iHc that can withstand practical use, and if it exceeds 2% by weight, the reduction in Br becomes significant.
[0020]
(3) T element
The T element is Fe alone or Fe + Co. The addition of Co improves the corrosion resistance of the sintered permanent magnet and raises the Curie point to improve the heat resistance of the permanent magnet. However, if the Co content exceeds 5% by weight, an Fe—Co phase harmful to the magnetic properties of the R—T—B sintered permanent magnet is formed, and both Br and iHc decrease. Therefore, the Co content is 5% by weight or less. On the other hand, if the Co content is less than 0.5% by weight, the effect of improving the corrosion resistance and the effect of improving the heat resistance are insufficient. Therefore, when adding Co, it is preferable to make Co content into 0.5 to 5 weight%.
[0021]
(4) M₁element
M₁Is at least one refractory metal element selected from the group consisting of Nb, Mo, W, V, Ta, Cr, Ti, Zr and Hf. M₁Due to the presence of elements, excessive growth of main phase crystal grains caused by diffusion of heavy rare earth elements (Dy, etc.) during the sintering process can be suppressed, and high iHc close to the single method can be stably obtained. But M₁If an element is added excessively, the normal grain growth of the main phase grains is hindered, leading to a decrease in Br. Therefore, M₁The upper limit of the element content is 0.6% by weight. Meanwhile, M₁When the element content is less than 0.01% by weight, a sufficient addition effect is not observed. Therefore, M₁The element content is preferably 0.01 to 0.6% by weight.
[0022]
(5) M₂element
M₂Is at least one element selected from the group consisting of Al, Ga and Cu.
[0023]
The addition of a small amount of Al improves the iHc and corrosion resistance of the R-T-B sintered permanent magnet. However, when the Al content exceeds 0.3% by weight, the Br content is greatly reduced, so the Al content is 0.3% by weight or less. On the other hand, if the Al content is less than 0.01% by weight, the effect of improving iHc and corrosion resistance is insufficient.
[0024]
By adding a small amount of Ga, iHc of the R-T-B sintered permanent magnet is remarkably improved. However, as with Al, when the content exceeds 0.3% by weight, Br decreases significantly, so the Ga content is set to 0.3% by weight or less. If it is less than 0.01% by weight, a significant improvement effect of iHc is not recognized.
[0025]
Adding a small amount of Cu is effective for improving the corrosion resistance of the sintered body and improving iHc. However, as with Al and Ga, if the Cu content exceeds 0.3% by weight, the Br of the RTB sintered permanent magnet will be significantly reduced. If it is less than 0.01%, the corrosion resistance and iHc will not be improved sufficiently. .
[0026]
As above, M₂The element content is 0.01 to 0.3% by weight for any of Al, Ga and Cu.
[0027]
(b) Inevitable impurities
Inevitable impurities include oxygen, carbon, nitrogen, calcium and the like. Ca is a reduction diffusion method for two or more types of RTB alloys with different heavy rare earth element contents (reducing rare earth element oxide powder with a reducing agent (Ca), followed by mutual diffusion with other main component metals) When produced by the method of obtaining alloy powder, it is mixed as an inevitable impurity.
[0028]
The oxygen content is preferably 0.6% by weight or less, the carbon content is preferably 0.15% by weight or less, and the nitrogen content is0.03The content is preferably not more than wt%, and the calcium content is preferably not more than 0.3 wt%. If the content of each unavoidable impurity exceeds the above upper limit, the magnetic properties of the R-T-B sintered permanent magnet will deteriorate. More preferable contents of inevitable impurities include oxygen of 0.25% by weight or less, carbon of 0.15% by weight or less, and nitrogen0.15% By weight or less. Particularly preferable inevitable impurity contents are 0.05 to 0.25% by weight of oxygen, 0.01 to 0.03% of carbon, and 0.02 to 0.15% of nitrogen.
[0029]
Specific examples of the composition of the R—T—B based sintered permanent magnet having such an inevitable impurity amount include the following.
[0030]
(i) By weight percentage, R exceeds 31% and is 33% or less, oxygen is 0.6% or less, carbon is 0.15% or less, nitrogen is 0.03% or less, and Ca is 0.3% or less. composition. For example, by adopting a dry molding method, oxygen can be 0.25 to 0.6%, carbon 0.01 to 0.15%, and nitrogen 0.005 to 0.03%.
[0031]
(ii) A composition in which R is 28 to 31% by weight, oxygen is 0.25% or less, carbon is 0.15% or less, nitrogen is 0.15% or less, and Ca is 0.3% or less. For example, by employing a wet molding method, oxygen can be 0.05 to 0.25% by weight, carbon 0.01 to 0.15%, and nitrogen 0.02 to 0.15%.
[0032]
(B) Organization
The crystal structure of the R-T-B sintered permanent magnet of the present invention is R₂T₁₄B-type main phase grains and grain boundary phase, R₂T₁₄The B-type main phase grains are at least (i) the first R in which the concentration of heavy rare earth elements is higher than the grain boundary phase₂T₁₄B-type main phase grains and (ii) a second R in which the concentration of heavy rare earth elements is lower than the grain boundary phase₂T₁₄Contains B-type main phase crystal grains. R₂T₁₄The B-type main phase crystal grains may further include (iii) a third main phase crystal grain in which the concentration of the heavy rare earth element is substantially equal to the grain boundary phase. Where R₂T₁₄The concentration of heavy rare earth elements in the B-type main phase grains is R₂T₁₄Measured at approximately the center (core) of the B-type main phase grains, R₂T₁₄The core of the B-type main phase crystal grains refers to a region that enters 1.0 μm or more from the crystal grain boundary. The heavy rare earth element is preferably Dy, but may be Tb and / or Ho, or a mixture thereof with Dy.
[0033]
R in the cross-sectional photograph of the crystal structure taken₂T₁₄The total number of B-type main phase grains is 100%, and the first R₂T₁₄The ratio of the number of B-type main phase grains is 1 to 35%, and the second R₂T₁₄The ratio of the number of B-type main phase grains is 3 to 55%, and the third R₂T₁₄The ratio of the number of B-type main phase crystal grains is preferably 96 to 10%. 1st to 3rd R₂T₁₄If the ratio of the number of B-type main phase grains is outside the above range, it is difficult for the RTB sintered permanent magnet to have a high coercive force iHc, residual magnetic flux density Br, and maximum energy product (BH) max. . More preferably, the first R₂T₁₄The ratio of the number of B-type main phase grains is 3 to 30%, and the second R₂T₁₄The ratio of the number of B-type main phase grains is 10 to 45%, and the third R₂T₁₄The ratio of the number of B-type main phase grains is 87 to 25%.
[0034]
[2] Manufacturing method
In order to manufacture the R-T-B system sintered permanent magnet of the present invention having the above structure, a so-called blending method is used in which two or more types of R-T-B system alloy powders having different contents of heavy rare earth elements such as Dy are mixed. In this case, the composition of each R-T-B alloy powder is set so that the total amount of R element is the same for each alloy powder. For example, in the case of Nd + Dy, as shown in Example 1 described later, one alloy powder is 29.0% Nd + 1.0% Dy, and the other alloy powder is 15.0% Nd + 15.0% Dy. For elements other than R element, it is preferable that each alloy powder is substantially the same, but M₁And / or M₂There may be a slight difference in the content of.
[0035]
  For example, when two types of alloy powders are mixed, the total amount of both R elements is the same, and the content of heavy rare earth elements in the first alloy powder isTen More than% by weight 40 % By weightAnd the content of heavy rare earth elements in the second alloy powder0 to 3% by weightAnd in this case,secondAlloy powder /firstThe mixing ratio of the alloy powder is preferably 70/30 to 95/5 by weight, and more preferably 80/20 to 90/10. This is because the greater the difference in the content of heavy rare earth elements between the first alloy powder and the second alloy powder, the finer the grindability (fine powder) between the first alloy powder and the second alloy powder. The particle size distribution of the main phase crystal grains of the finally obtained RTB sintered permanent magnet becomes wider, and the strength of magnetization (4πI)-strength of magnetic field (H This is because the squareness of the demagnetization curve showing the relationship (2) and the deterioration of (BH) max are caused.
[0036]
The fine pulverization of the R-T-B alloy powder can be performed by a dry pulverization method such as a jet mill using an inert gas as a medium or a wet pulverization method such as a ball mill. In order to obtain high magnetic properties, it contains virtually no oxygen (concentration: 1000 ppm by volume or less). After finely pulverizing in an inert gas atmosphere, finely pulverize from the inert gas atmosphere without touching the atmosphere. Is directly recovered in mineral oil, synthetic oil, vegetable oil, or a mixed oil thereof to form a mixture (slurry). By blocking the fine powder from the atmosphere, oxidation and moisture adsorption can be suppressed. As the mineral oil, synthetic oil or vegetable oil, from the viewpoint of deoiling property and moldability, those having a fractional point of 350 ° C. or less are preferable, and those having a kinematic viscosity of 10 cSt or less at room temperature are preferable, and those of 5 cSt or less are more preferable.
[0037]
As an alloy for two or more kinds of RTB sintered permanent magnets blended for producing the permanent magnet of the present invention, a thin plate-like alloy exemplified in Japanese Patent No. 2,665,590, Japanese Patent No. 2,745,042 and the like ( Strip cast alloys) may be used. This thin plate alloy (strip cast alloy) is obtained by rapidly cooling and solidifying a molten alloy having a composition satisfying the requirements of the present invention by a molten metal quenching method such as a single roll method, a twin roll method or a rotating disk method. And the average crystal grain size in the minor axis direction of the columnar crystals is 3 to 20 μm. In order to obtain high Br and (BH) max, after performing a homogenization heat treatment in which the thin plate-like alloy is heated in an inert gas (Ar, etc.) atmosphere at 900 to 1200 ° C. for 1 to 10 hours and then cooled to room temperature, It is preferable to grind.
[0038]
Using the mixture (slurry), a molded body is obtained by wet molding in a magnetic field using a desired molding apparatus. In order to suppress the deterioration of the magnetic properties due to oxidation, it is desirable to keep it in oil or an inert gas atmosphere immediately after molding until it is put into the sintering furnace. Molding may be performed by a dry method. In the case of the dry molding method, a dry fine powder mixture is press-molded in a magnetic field in an inert gas atmosphere.
[0039]
When a wet molded body is sintered, the mineral magnet, synthetic oil or vegetable oil remaining in the molded body reacts with the rare earth element when the temperature is rapidly raised from room temperature to the sintering temperature, thereby producing a rare earth carbide, and a sintered magnet obtained. Causes deterioration of the magnetic properties. As a countermeasure, the temperature is 100 to 500 ° C and the vacuum is 10^-1It is desirable to perform a deoiling treatment that is held for 30 minutes or less at Torr or less. The mineral oil, synthetic oil or vegetable oil remaining in the molded body can be sufficiently removed by the deoiling treatment. The heating temperature need not be constant as long as it is in the temperature range of 100 to 500 ° C. Also 10^-1While raising the temperature from room temperature to 500 ° C. at a vacuum level of Torr or less, a substantially equivalent deoiling effect can be obtained even if the rate of temperature rise is 10 ° C./min or less, preferably 5 ° C./min or less.
[0040]
An R-T-B sintered permanent magnet is produced by sintering the compact in an inert gas atmosphere at a temperature of about 1000 to 1200 ° C. The obtained R-T-B system sintered permanent magnet is subjected to desired machining and surface treatment. Examples of the surface treatment include Ni plating and electrodeposition epoxy resin coating.
[0041]
【Example】
The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
[0042]
Example 1
The melted alloy A and the melted alloy B having the main component composition shown in Table 1 were each roughly pulverized in an inert gas atmosphere and sieved to obtain a coarse powder having a particle size of 500 μm or less. 87.9 kg of coarse powder of alloy A and 12.1 kg of coarse powder of alloy B were put into a V-type mixer and mixed to obtain 100 kg of mixed coarse powder. When the composition of the mixed coarse powder was analyzed, the main components were Nd27.3%, Dy2.7%, B1.0%, Nb0.2%, Al0.1%, Co1.0%, Cu0.1 by weight percentage. The impurities contained in this mixed coarse powder were 0.15 wt% O, 0.01 wt% N, and 0.02 wt% C.
[0043]
[Table 1]

[0044]
The mixed coarse powder was crushed by a jet mill in a nitrogen gas atmosphere having an oxygen concentration of 10 ppm or less (volume ratio) to obtain a fine powder having an average particle diameter of 4.0 μm. The fine powder was directly recovered in mineral oil (made by Idemitsu Kosan Co., Ltd., trade name: Idemitsu Supersol PA-30) in a nitrogen gas atmosphere in a non-contact state with the atmosphere to obtain a fine powder slurry. Using this fine powder slurry, magnetic field strength 10kOe and molding pressure 1.0ton / cm²Wet compression molding under the conditions of^-1After deoiling by heating at 200 ° C in Torr vacuum for 1 hour, continue to about 3 x 10^-FiveSintering was performed at Torr in the temperature range of 1050 to 1100 ° C. for 2 hours, and cooled to room temperature to obtain a sintered body.
[0045]
Each sintered body was subjected to a heat treatment of 900 ° C. × 2 hours and 500 ° C. × 1 hour once in an inert gas atmosphere, and then cooled to room temperature to obtain an R-T-B system sintered permanent magnet. When the magnetic properties were measured at 20 ° C., the results shown in FIG. 1 were obtained. As is apparent from FIG. 1, when the sintering temperature is set to 1070 to 1110 ° C., preferable magnetic characteristics as a permanent magnet were obtained. In particular, 13.8kG Br, 18kOe iHc and 45.9MGOe (BH) max were obtained when the sintering temperature was 1090 ° C, and 13.8kG Br, 17.9kOe iHc when the sintering temperature was 1100 ° C. 45.7MGOe (BH) max was obtained, and Br and (BH) max were high.
[0046]
The composition of typical sintered magnets among the sintered magnets was analyzed. The main components were Nd: 27.3%, Dy: 2.7%, B: 1.0%, Nb: 0.2%, Al: 0.1% in weight percentage. Co: 1.0%, Cu: 0.1%, balance: Fe, inevitable impurities were 0.17% O, 0.05% N, and 0.07% C.
[0047]
Among the sintered magnets, the cross-sectional structure of a representative sintered magnet was observed in the same manner as in Example 7 described later, and main phase crystal grains (R₂T₁₄B) The concentration of heavy rare earth element (Dy) in the inside (substantially in the center) and in the grain boundary phase was measured. As a result, R₂T₁₄A B-type main phase crystal grain has a first main phase crystal grain in which the concentration of heavy rare earth element (Dy) is higher than the grain boundary phase, and a second main phase crystal grain in which the concentration of heavy rare earth element (Dy) is lower than the grain boundary phase. It was found that it was composed of main phase crystal grains and third main phase crystal grains in which the concentration of heavy rare earth element (Dy) was almost equal to the grain boundary phase.
[0048]
Comparative Example 1
Coarse pulverization was performed in the same manner as in Example 1 except that the melted alloy C having the main component composition shown in Table 2 was used. When the composition (% by weight) of this coarse powder was analyzed, the main components were Nd: 27.3%, Dy: 2.7%, B: 1.0%, Nb: 0.2%, Al: 0.1%, Co: 1.0%, Cu: 0.1 %, Balance: Fe, impurities were O: 0.13%, N: 0.008%, C: 0.02%.
[0049]
[Table 2]

[0050]
Using this coarse powder, fine pulverization (average particle size 4.1 μm), slurrying, forming in a magnetic field, deoiling, sintering and heat treatment were performed in the same manner as in Example 1, and a sintered type permanent of a comparative example by a single method. A magnet was obtained. The composition (weight%) of this sintered permanent magnet was analyzed. The main components were Nd: 27.3%, Dy: 2.7%, B: 1.0%, Nb: 0.2%, Al: 0.1%, Co: 1.0% Cu: 0.1%, balance: Fe, and impurities were O: 0.15%, N: 0.04%, C: 0.06%.
[0051]
The results of measuring the magnetic properties at 20 ° C. are shown in FIG. As can be seen from FIG. 1, the iHc level is as high as about 19 kOe, but Br is 13.3 kG or less and (BH) max is 42.5 MGOe or less, which is lower than Br and (BH) max in Example 1. In the cross-sectional structure of the sintered magnet of this comparative example, main phase grains having a heavy rare earth element Dy concentration higher than the grain boundary phase were not observed.
[0052]
Example 2
Coarse pulverization was carried out in the same manner as in Example 1 except that the molten alloy D and molten alloy E having the main component composition shown in Table 3 were used. 94 kg of coarse powder of alloy D and 6 kg of coarse powder of alloy E were put into a V-type mixer and mixed to obtain 100 kg of mixed coarse powder. When the composition of the mixed coarse powder was analyzed, the main components were Nd: 22.4%, Pr: 8.9%, Dy: 1.2%, B: 1.0%, Al: 0.1%, Ga: 0.15%, the balance: Fe. The impurities were O: 0.14%, N: 0.01%, and C: 0.01%.
[0053]
[Table 3]

[0054]
The mixed coarse powder was pulverized by jet mill in a nitrogen gas atmosphere having an oxygen concentration of 500 ppm (volume ratio) or less to obtain a fine powder having an average particle size of 4.1 μm. Using this fine powder, magnetic field strength 10kOe, molding pressure 1.5ton / cm²Dry compression molding was performed under the conditions of: The resulting compact is about 3 × 10^-FiveAfter sintering for 2 hours in a temperature range of 1040 to 1110 ° C. in a Torr vacuum, the sintered body was obtained by cooling to room temperature.
[0055]
Each sintered body was subjected to heat treatment at 900 ° C. × 3 hours and 550 ° C. × 1 hour once in an inert gas atmosphere, and then cooled to room temperature to obtain an R-T-B sintered permanent magnet. When the magnetic properties were measured at 20 ° C., the results shown in FIG. 2 were obtained. From FIG. 2, it was found that when the sintering temperature was set to 1050 to 1100 ° C., magnetic characteristics preferable as a permanent magnet were obtained. In particular, when the sintering temperature is 1070 ° C, 13.4kG Br, 16.3kOe iHc, and 43.2MGOe (BH) max are obtained, and when the sintering temperature is 1080 ° C, 13.4kG Br, 15.1kOe (BH) max of iHc and 43.3MGOe was obtained, and Br and (BH) max were high.
[0056]
The composition of typical sintered magnets among the sintered magnets was analyzed. The main components in weight percentage were Nd: 22.4%, Pr: 8.9%, Dy: 1.2%, B: 1.0%, Al: 0.1%, Ga: 0.15%, balance: Fe, impurities were O: 0.45%, N: 0.02%, C: 0.07%.
[0057]
Among the sintered magnets, the cross-sectional structure of a typical sintered magnet is the same as in Example 7 described later, and main phase crystal grains (R₂T₁₄B) The concentration of heavy rare earth element (Dy) in the inside (substantially in the center) and in the grain boundary phase was measured. As a result, R₂T₁₄B-type main phase grains are the first R in which the concentration of heavy rare earth elements (Dy) is higher than the grain boundary phase.₂T₁₄B-type main phase grains and a second R in which the concentration of heavy rare earth elements (Dy) is lower than the grain boundary phase₂T₁₄B-type main phase grains and a third R in which the concentration of heavy rare earth elements (Dy) is almost equal to the grain boundary phase₂T₁₄It was found to be composed of B-type main phase grains.
[0058]
Comparative Example 2
Coarse pulverization was performed in the same manner as in Example 1 except that the melted alloy F having the main component composition shown in Table 4 was used. When the composition of the coarse powder was analyzed, the main components by weight percentage were Nd: 22.4%, Pr: 8.9%, Dy: 1.2%, B: 1.0%, Al: 0.1%, Ga: 0.15%, the balance: Fe The impurities were O: 0.14%, N: 0.01%, C: 0.02%.
[0059]
[Table 4]

[0060]
Using this coarse powder, fine pulverization (average particle size: 4.0 μm), molding in a magnetic field, sintering and heat treatment were performed in the same manner as in Example 2 to obtain a sintered permanent magnet of a comparative example by a single method. When the components of this magnet were analyzed, the main components were Nd: 22.4%, Pr: 8.9%, Dy: 1.2%, B: 1.0%, Al: 0.1%, Ga: 0.15%, and the balance: Fe. The impurities were O: 0.43%, N: 0.03%, C: 0.06%.
[0061]
The results of measuring the magnetic properties at 20 ° C. are shown in FIG. As is clear from FIG. 2, the iHc level was slightly higher than that in Example 2, but Br was 12.9 kG or less and (BH) max was 40.1 MGOe or less. In the cross-sectional structure of the sintered magnet of this comparative example, main phase crystal grains having a heavy rare earth element (Dy) concentration higher than the grain boundary phase were not observed.
[0062]
Example 3
Coarse pulverization was carried out in the same manner as in Example 1 except that the molten alloy G and molten alloy H having the main component composition shown in Table 5 were used. Next, 81.8 kg of the coarse powder of alloy G and 18.2 kg of the coarse powder of alloy H were put into a V-type mixer and mixed to obtain 100 kg of mixed coarse powder. When the composition of the mixed coarse powder was analyzed, the main components were Nd: 19.14%, Pr: 5.34%, Dy: 6.00%, B: 0.97%, Nb: 0.29%, Al: 0.10%, Co: 2.00%. , Ga: 0.08%, Cu: 0.10%, balance: Fe, impurities O: 0.14%, N: 0.01%, C: 0.02%.
[0063]
[Table 5]

[0064]
Using this mixed coarse powder, fine pulverization (average particle size: 4.2 μm), slurrying, and compression molding in a magnetic field were performed in the same manner as in Example 1. The resulting molded body is about 5 × 10^-1Deoil by heating at 200 ° C in Torr vacuum for 1 hour, then about 2 x 10^-FiveAfter sintering for 2 hours at each temperature within the temperature range of 1060 to 1130 ° C. in a vacuum of Torr, it was cooled to room temperature. Each obtained sintered body was heat-treated at 900 ° C. × 2 hours and 500 ° C. × 1 hour once in an inert gas atmosphere, and then cooled to room temperature to obtain an RTB sintered permanent magnet. . The results of measuring the magnetic properties at 20 ° C. are shown in FIG. As is apparent from FIG. 3, when the sintering temperature is 1070 to 1120 ° C., favorable magnetic characteristics as a permanent magnet are obtained. In particular, 12.7 kG Br, 25.5 kOe iHc and 38.8 MGOe (BH) max were obtained when the sintering temperature was 1100 ° C., and 12.7 kG Br, 25.3 kOe iHc and 38.6 MGOe when 1110 ° C. (BH) max was obtained, and Br and (BH) max were high.
[0065]
The composition of typical permanent magnets among the permanent magnets was analyzed. The main components were Nd: 19.14%, Pr: 5.34%, Dy: 6.00%, B: 0.97%, Nb: 0.29%, Al: 0.10%, Co: 2.00%, Ga: 0.08%, Cu: 0.10%, balance Fe, and impurities were O: 0.16%, N: 0.05%, C: 0.07%.
[0066]
About the cross-sectional structure of the permanent magnet produced under the conditions of sintering temperatures of 1100 ° C. and 1110 ° C., the main phase crystal grains (R₂T₁₄B) The concentration of heavy rare earth element (Dy) in the inside (substantially in the center) and in the grain boundary phase was measured. As a result, R₂T₁₄A B-type main phase crystal grain has a first main phase crystal grain in which the concentration of heavy rare earth element (Dy) is higher than the grain boundary phase, and a second main phase crystal grain in which the concentration of heavy rare earth element (Dy) is lower than the grain boundary phase. It was found that it was composed of main phase crystal grains and third main phase crystal grains in which the concentration of heavy rare earth element (Dy) was almost equal to the grain boundary phase.
[0067]
Comparative Example 3
A coarse powder was obtained in the same manner as in Example 1 except that the melted alloy I having the main component composition shown in Table 6 was used. When the composition of this coarse powder was analyzed, the main components by weight percentage were Nd: 19.14%, Pr: 5.34%, Dy: 6.00%, B: 0.97%, Nb: 0.29%, Al: 0.10%, Co: 2.00 %, Ga: 0.08%, Cu: 0.10%, balance: Fe, and impurities were O: 0.12%, N: 0.01%, C: 0.01%.
[0068]
[Table 6]

[0069]
Except for using this coarse powder, fine pulverization (average particle size: 4.2 μm), slurrying and molding in a magnetic field were performed in the same manner as in Example 1. The obtained compact was deoiled, sintered and heat treated under the same conditions as in Example 3 to obtain a sintered permanent magnet of a comparative example by a single method. When the composition of this magnet was analyzed, the main components in weight percentage were Nd: 19.14%, Pr: 5.34%, Dy: 6.00%, B: 0.97%, Nb: 0.29%, Al: 0.10%, Co: 2.00% , Ga: 0.08%, Cu: 0.10%, balance: Fe, impurities were O: 0.14%, N: 0.04%, C: 0.06%.
[0070]
The result of measuring the magnetic properties at 20 ° C. is shown in FIG. As is clear from FIG. 3, the iHc level was as high as around 25 kOe, but Br was 12.2 kG or less, and (BH) max was 35.7 MGOe or less, which was lower than that in Example 3. Further, in the cross-sectional structure of the sintered magnet of this comparative example, main phase crystal grains having a heavy rare earth element (Dy) concentration higher than the grain boundary phase were not observed.
[0071]
Comparative Example 4
Coarse pulverization was carried out in the same manner as in Example 1 except that melted alloy J and melted alloy K having the main component compositions shown in Table 7 were used. 81.8 kg of the coarse powder of alloy J and 18.2 kg of the coarse powder of alloy K were put into a V-type mixer and mixed to obtain 100 kg of mixed coarse powder. When the composition of the mixed coarse powder was analyzed, the main components by weight percentage were Nd: 19.14%, Pr: 5.34%, Dy: 6.00%, B: 0.97%, Nb: 0.65%, Al: 0.10%, Co: 2.00 %, Ga: 0.08%, Cu: 0.10%, balance: Fe, and impurities were O: 0.15%, N: 0.02%, C: 0.02%.
[0072]
[Table 7]

[0073]
Except for using this coarse powder, fine pulverization (average particle size 4.1 μm), slurrying and molding in a magnetic field were carried out in the same manner as in Example 1. The resulting molded body is about 5 × 10^-1Deoil by heating at 200 ° C in Torr vacuum for 1 hour, then about 2 x 10^-FiveAfter sintering for 2 hours at each temperature within a temperature range of 1060 to 1130 ° C. in a Torr vacuum, it was cooled to room temperature. Each of the obtained sintered bodies was subjected to heat treatment at 900 ° C. × 2 hours and 500 ° C. × 1 hour once in an inert gas atmosphere, and then cooled to room temperature. A permanent magnet was obtained. The results of measuring the magnetic properties at 20 ° C. are shown in FIG. As is apparent from FIG. 3, when the sintering temperature is 1100 ° C., 12.1 kG Br, 25.4 kOe iHc and 35.1 MGOe (BH) max are obtained, and when the sintering temperature is 1110 ° C., 12.1 kG Br, 25.2 kOe iHc and 35.0 MGOe (BH) max were obtained, and Br and (BH) max were low.
[0074]
When the composition of the sintered magnet of this comparative example was analyzed, the main components in weight percentage were Nd: 19.14%, Pr: 5.34%, Dy: 6.00%, B: 0.97%, Nb: 0.65%, Al: 0.10% Co: 2.00%, Ga: 0.08%, Cu: 0.10%, balance: Fe, impurities were O: 0.17%, N: 0.06%, C: 0.06%. The reason why the Br and (BH) max of the sintered magnet of this comparative example is low is considered to be that normal grain growth during sintering of the main phase crystal grains was suppressed because the Nb content was as high as 0.65%. It is done.
[0075]
Example 4
Coarse pulverization was performed in the same manner as in Example 1 except that the molten alloy L and the molten alloy M having the main component composition shown in Table 8 were used. 90.0 kg of the coarse powder of alloy L and 10.0 kg of the coarse powder of alloy H were put into a V-type mixer and mixed to obtain 100 kg of mixed coarse powder. When the composition of the mixed coarse powder was analyzed, the main components by weight percentage were Nd: 22.83%, Pr: 6.37%, Dy: 1.30%, B: 1.05%, Mo: 0.13%, Al: 0.10%, and the balance Fe The impurities were O: 0.15%, N: 0.01%, C: 0.02%.
[0076]
[Table 8]

[0077]
Except that this mixed coarse powder was used, fine pulverization (average particle size: 4.0 μm), slurrying and molding in a magnetic field were performed in the same manner as in Example 1. The resulting molded body is about 5 × 10^-1Deoil by heating at 200 ° C for 1 hour in a vacuum of Torr, then about 2 x 10^-FiveAfter sintering for 2 hours at each temperature within the temperature range of 1050 to 1100 ° C. in a vacuum of Torr, it was cooled to room temperature. Each of the obtained sintered bodies was subjected to a heat treatment of 900 ° C. × 2 hours and 550 ° C. × 1 hour once in an inert gas atmosphere, and then cooled to room temperature to obtain an RTB sintered permanent magnet. . As a result of measuring the magnetic properties at 20 ° C., magnetic properties preferable as a permanent magnet were obtained when the sintering temperature was 1060 to 90 ° C. Especially when the sintering temperature is 1070 ° C, 13.9kG Br, 15.5kOe iHc and 46.5MGOe (BH) max are obtained, and when the sintering temperature is 1080 ° C, 14.0kG Br, 15.3kOe iHc and 47.2MGOe (BH) max was obtained, and Br and (BH) max were high.
[0078]
The composition of typical permanent magnets among the permanent magnets was analyzed. The main component composition was Nd: 22.83%, Pr: 6.37%, Dy: 1.30%, B: 1.05%, Mo: 0.13%, Al. : 0.10%, balance: Fe, impurities were O: 0.18%, N: 0.06%, C: 0.08%.
[0079]
About the cross-sectional structure of the permanent magnet produced under the conditions of sintering temperatures of 1070 ° C. and 1080 ° C., the main phase crystal grains (R₂T₁₄B) The concentration of heavy rare earth element (Dy) in the inside (substantially in the center) and in the grain boundary phase was measured. As a result, R₂T₁₄A B-type main phase crystal grain has a first main phase crystal grain in which the concentration of heavy rare earth element (Dy) is higher than the grain boundary phase, and a second main phase crystal grain in which the concentration of heavy rare earth element (Dy) is lower than the grain boundary phase. It was found that it was composed of main phase crystal grains and third main phase crystal grains in which the concentration of heavy rare earth element (Dy) was almost equal to the grain boundary phase.
[0080]
Example 5
Coarse pulverization was carried out in the same manner as in Example 1 except that the molten alloy N and molten alloy O having the main component composition shown in Table 9 were used. The alloy N coarse powder 80.0 kg and the alloy O coarse powder 20.0 kg were put into a V-type mixer and mixed to obtain 100 kg coarse powder. When the composition of the mixed coarse powder was analyzed, the main components by weight percentage were Nd: 26.2%, Dy: 5.8%, B: 0.95%, Nb: 0.20%, Al: 0.1%, Co: 2.5%, Cu: 0.15 %, Ga: 0.15%, balance: Fe, impurities were O: 0.15%, N: 0.02%, C: 0.02%.
[0081]
[Table 9]

[0082]
The mixed coarse powder was crushed by a jet mill in a nitrogen gas atmosphere having an oxygen concentration of 500 ppm or less (volume ratio) to obtain a fine powder having an average particle diameter of 4.2 μm. This fine powder is magnetic field strength 10kOe, molding pressure 1.5ton / cm²Dry compression molding was performed under the conditions of: The resulting compact is about 3 × 10^-FiveIn the Torr vacuum, sintering was performed at each temperature within a temperature range of 1040 to 1100 ° C. for 2 hours and then cooled to room temperature.
[0083]
Each obtained sintered body was subjected to heat treatment of 900 ° C. × 3 hours and 480 ° C. × 1 hour once in an inert gas atmosphere, and then cooled to room temperature to obtain an RTB sintered permanent magnet. . When the magnetic properties were measured at 20 ° C., favorable magnetic properties as a permanent magnet were obtained when the sintering temperature was 1050 to 90 ° C. In particular, 12.5kG Br, 24.5kOe iHc and 37.5MGOe (BH) max were obtained when the sintering temperature was 1070 ° C, and 12.5kG Br, 24.2kOe iHc and 37.4MGOe when the sintering temperature was 1080 ° C. (BH) max was obtained, and Br and (BH) max were high. When the permanent magnet was analyzed, the main components in weight percentage were Nd: 26.2%, Dy: 5.8%, B: 0.95%, Nb: 0.20%, Al: 0.1%, Co: 2.5%, Cu: 0.15%, Ga: 0.15%, balance: Fe, impurities were O: 0.38%, N: 0.03%, C: 0.05%.
[0084]
With respect to the cross-sectional structure of the sintered magnet having a sintering temperature of 1070 ° C. and 1080 ° C., the main phase crystal grains (R₂T₁₄B) The concentration of heavy rare earth element (Dy) in the inside (substantially in the center) and in the grain boundary phase was measured. As a result, R₂T₁₄A B-type main phase crystal grain has a first main phase crystal grain in which the concentration of heavy rare earth element (Dy) is higher than the grain boundary phase, and a second main phase crystal grain in which the concentration of heavy rare earth element (Dy) is lower than the grain boundary phase. It was found that it was composed of main phase crystal grains and third main phase crystal grains in which the concentration of heavy rare earth element (Dy) was almost equal to the grain boundary phase.
[0085]
Example 6
Coarse pulverization was performed in the same manner as in Example 1 except that the molten alloy P and the molten alloy Q having the main component composition shown in Table 10 were used. 90.0 kg of the coarse powder of alloy P and 10.0 kg of the coarse powder of alloy Q were put into a V-type mixer and mixed to obtain 100 kg of mixed coarse powder. When the composition of the mixed coarse powder was analyzed, the main components by weight percentage were Nd: 20.6%, Pr: 8.8%, Dy: 2.6%, B: 1.06%, W: 0.18%, Al: 0.05%, Ga: 0.17 %, Balance: Fe, impurities were O: 0.15%, N: 0.01%, C: 0.01%.
[0086]
[Table 10]

[0087]
The mixed coarse powder was crushed by a jet mill in a nitrogen gas atmosphere having an oxygen concentration of 500 ppm or less (volume ratio) to obtain a fine powder having an average particle diameter of 4.2 μm. This fine powder is magnetic field strength 10kOe, molding pressure 1.5ton / cm²Dry compression molding was performed under the conditions of: The resulting compact is about 3 × 10^-FiveAfter sintering for 2 hours at each temperature within a temperature range of 1040 to 1100 ° C. in a vacuum of Torr, it was cooled to room temperature.
[0088]
Each of the obtained sintered bodies was subjected to a heat treatment of 900 ° C. × 3 hours and 550 ° C. × 1 hour once in an inert gas atmosphere, and then cooled to room temperature to obtain an R-T-B sintered permanent magnet. When the magnetic properties were measured at 20 ° C., favorable magnetic properties as a permanent magnet were obtained when the sintering temperature was 1050 to 90 ° C. Especially when the sintering temperature is 1070 ° C, 13.2 kG Br, 19.5 kOe iHc and 41.8 MGOe (BH) max are obtained, and when the sintering temperature is 1080 ° C, 13.2 kG Br, 19.3 kOe iHc and (BH) max of 41.7MGOe was obtained, and Br and (BH) max were high.
[0089]
The composition of typical permanent magnets among the permanent magnets was analyzed. The weight percentage was Nd: 20.6%, Pr: 8.8%, Dy: 2.6%, B: 1.06%, W: 0.18%, Al: 0.05%, Ga: 0.17%, balance: Fe, impurities were O: 0.50%, N: 0.02%, C: 0.06%.
[0090]
About the cross-sectional structure of the permanent magnet produced under conditions of sintering temperatures of 1070 ° C. and 1080 ° C., the main phase crystal grains (R₂T₁₄B) The concentration of heavy rare earth element (Dy) in the inside (substantially in the center) and in the grain boundary phase was measured. As a result, R₂T₁₄A B-type main phase crystal grain has a first main phase crystal grain in which the concentration of heavy rare earth element (Dy) is higher than the grain boundary phase, and a second main phase crystal grain in which the concentration of heavy rare earth element (Dy) is lower than the grain boundary phase. It was found that it was composed of main phase crystal grains and third main phase crystal grains in which the concentration of heavy rare earth element (Dy) was almost equal to the grain boundary phase.
[0091]
Example 7
Coarse pulverization was carried out in the same manner as in Example 1 except that the molten alloy R and molten alloy S having the main component composition shown in Table 11 were used. 90.0 kg of alloy R coarse powder and 10.0 kg of alloy S coarse powder were put into a V-type mixer and mixed to obtain 100 kg of mixed coarse powder. When the composition of the mixed coarse powder was analyzed, the main components by weight percentage were Nd: 21.38%, Pr: 7.12%, Dy: 1.50%, B: 1.03%, Al: 0.08%, Co: 2.00%, Ga: 0.08 %, Cu: 0.1%, balance: Fe, O: 0.14%, N: 0.02%, C: 0.02%.
[0092]
[Table 11]

[0093]
The mixed coarse powder was crushed by a jet mill in a nitrogen gas atmosphere having an oxygen concentration of 10 ppm or less (volume ratio) to obtain a fine powder having an average particle diameter of 4.2 μm. The obtained fine powder was directly recovered in mineral oil (made by Idemitsu Kosan Co., Ltd., trade name: Idemitsu Supersol PA-30) in a nitrogen gas atmosphere without being exposed to the air. The resulting slurry has a magnetic field strength of 10 kOe and a molding pressure of 1.0 ton / cm.²And compression molded. The resulting molded body is about 5 × 10^-1Deoil by heating at 200 ° C for 1 hour in Torr vacuum, about 3 x 10^-FiveAfter sintering for 2 hours at each temperature within a temperature range of 1040 to 1100 ° C. in a vacuum of Torr, it was cooled to room temperature.
[0094]
Each sintered body was subjected to a heat treatment of 900 ° C. × 2 hours and 480 ° C. × 1 hour once in an inert gas atmosphere, and then cooled to room temperature to produce an R-T-B sintered permanent magnet. When the magnetic properties were measured at 20 ° C., favorable magnetic properties as a permanent magnet were obtained when the sintering temperature was 1060 to 90 ° C. In particular, when the sintering temperature is 1070 ° C., 13.9 kG Br, 15 kOe iHc and 46.5 MGOe (BH) max are obtained, and when the sintering temperature is 1080 ° C., 14.0 kG Br, 14.8 kOe iHc and 47.2 MGOe (BH) max was obtained, and Br and (BH) max were high.
[0095]
When the representative sintered magnets among the above sintered magnets were analyzed, the main components in weight percentage were Nd: 21.38%, Pr: 7.12%, Dy: 1.50%, B: 1.03%, Al: 0.08%, Co : 2.00%, Ga: 0.08%, Cu: 0.1%, balance: Fe, impurities were O: 0.16%, N: 0.06%, C: 0.06%.
[0096]
A cross-sectional structure of a typical sintered magnet among the sintered magnets was analyzed using EPMA (Electron Probe Micro-Analyzer; JEOL, model JXA-8800) under the following conditions.
Accelerating voltage: 15kV,
Sample absorption current: approx. 4 × 10^-8A,
X-ray acquisition time per one analysis point (counting time): 10msec,
Analysis points: 400 in both the vertical (X) and horizontal (Y) directions
Interval between analysis points in X and Y direction: 0.12μm,
Surface analysis area: 0.12μm x 400 points = 48μm rectangular area,
[0097]
The concentration distribution of Dy, Nd and Pr was measured by irradiating the minimum spot with the beam under the above conditions. The spectroscopic crystal used for the analysis of Dy, Nd and Pr was highly sensitive lithium fluoride (LiF). The crystal structure of the R—T—B system sintered permanent magnet of this example is schematically shown in FIG. Crystal structure is R₂T₁₄It has a B-type main phase crystal grain 1 and a grain boundary phase 2, and the triple point 2 'of the grain boundary phase is shown by a black region. FIG. 5 shows the Dy concentration distribution in the crystal structure of FIG. 4, FIG. 6 (a) shows the Nd concentration distribution, and FIG. 6 (b) shows the Pr concentration distribution. As is clear from FIGS. 5 and 6 (a) and 6 (b), the distribution of Nd, Dy, and Pr was substantially observed at the triple boundary in the grain boundary phase. This is because Dy and Pr are not distributed, and since the grain boundary phase is very thin except for the triple point, the distribution amount of Nd, Dy, and Pr is very small.
[0098]
In FIG. 4, it is the R (Nd, Dy, Pr) rich phase that forms the triple point of the grain boundary phase. 6A and 6B that Nd and Pr exist at substantially the same position. 5 and 6 (a) and 6 (b), Dy is also present in the region of the grain boundary phase almost the same as Nd and Pr, but R separated by 1.0 μm or more from the grain boundary.₂T₁₄It was found that the portion (core portion) in the B-type main phase crystal grains may exist at a high concentration.
[0099]
From these observation results, it was found that there are three types of Dy concentration distribution patterns with respect to the Dy concentration distribution from the grain boundary phase to the central portion in the main phase crystal grains. In the first pattern, the core portion in the main phase crystal grain has a higher Dy concentration than the grain boundary phase. In the second pattern, the Dy concentration in the grain boundary phase is high, and the Dy concentration in the core portion in the main phase crystal grains is low. In the third pattern, the Dy concentration distribution from the grain boundary phase to the center of the main phase crystal grain is almost uniform. In FIG. 5, the number of the first main phase crystal grains having a higher Dy concentration in the core portion in the main phase crystal grain than the crystal grain boundary phase is six, and the second main main crystal grain having a Dy concentration lower than the grain boundary phase. There were 15 phase grains, and 19 third main phase grains having a Dy concentration almost equal to the grain boundary phase. In evaluating the concentration distribution of Dy, Nd, and Pr in FIGS. 5 and 6 (a) and 6 (b), the influence of voids formed during the preparation of the sample for microscopic observation was considered. 4, 5, and 6 (a) and 6 (b) are merely examples of the cross-sectional structure, and it is necessary to average the data obtained from the cross-sectional structures in many fields of view in order to determine the Dy concentration distribution. . Thus, the R-T-B sintered permanent magnet of the present invention has a characteristic Dy concentration distribution in the main phase crystal grains and the grain boundary phase.
[0100]
The particle size distribution of the main phase crystal grains of a typical permanent magnet is shown in FIG. The horizontal axis of FIG. 7 shows the grain size range of the main phase crystal grains. For example, “9 to 10 μm” means that the grain size range of the main phase crystal grains is “9 μm or more and less than 10 μm”. As for the grain size of the main phase crystal grains, an optical microscope (model UFX-II, manufactured by Nikon Corporation) was used to take a photograph of an arbitrary cross section of the permanent magnet (1000 times magnification), and this cross section photograph was manufactured by Planetron. Image processing software (Image Pro. Plus (DOS / V)). The area of each main phase crystal grain measured by image processing is S_iFurther, assuming that the cross-sectional shape of each main phase crystal grain is a circle, each main phase crystal grain size d_i(4xS_i÷ π)^1/2It was defined as The distribution rate (%) on the vertical axis indicates the number T of main phase grains in each grain size range with respect to the total number T of main phase grains in the measured field of view._NRatio [(T_N/ T) × 100%].
[0101]
As is apparent from FIG. 7, in the permanent magnet of the present invention, the distribution ratio of main phase crystal grains having a particle size of less than 2 μm was 0%, and the distribution ratio of main phase crystal grains having a particle diameter of 16 μm or more was 5.8%. . As a result of further investigation, if the distribution ratio of the main phase crystal grains having a particle size of less than 2 μm is less than 5% and the distribution ratio of the main phase crystal grains having a particle diameter of 16 μm or more is 10% or less, a preferable magnetic characteristic as a permanent magnet can be realized. I understood. Further, it is more preferable that the distribution ratio of the main phase grains having a grain size of less than 2 μm is 3% or less and the distribution ratio of the main phase grains having a grain size of 16 μm or more is 8% or less. It was found that the distribution rate of the main phase crystal grains having a distribution rate of 0% and 16 μm or more is particularly preferably 6% or less. The main phase particle size distribution can be realized even when the Nb content is 0.01 to 0.6%.
[0102]
Comparative Example 5
Coarse pulverization was carried out in the same manner as in Example 7 except that melted alloy T having the main component composition shown in Table 12 was used. When the composition of the coarse powder was analyzed, the main components by weight percentage were Nd: 21.38%, Pr: 7.12%, Dy: 1.50%, B: 1.03%, Nb: 0.70%, Al: 0.08%, Co: 2.00% , Ga: 0.08%, Cu: 0.1%, balance: Fe, impurities were O: 0.15%, N: 0.01%, C: 0.02%.
[0103]
[Table 12]

[0104]
Using this coarse powder, in the same manner as in Example 7, fine pulverization (average particle size 4.1 μm), slurrying, molding in a magnetic field, deoiling, sintering and heat treatment were performed. A permanent magnet was obtained. When the composition of this sintered magnet was analyzed, the main components in weight percentage were Nd: 21.38%, Pr: 7.12%, Dy: 1.50%, B: 1.03%, Nb: 0.70%, Al: 0.08%, Co: 2.00%, Ga: 0.08%, Cu: 0.1%, balance: Fe, impurities were O: 0.17%, N: 0.05%, C: 0.07%.
[0105]
As a result of measuring the magnetic properties at 20 ° C., the iHc level was as high as about 16 kOe, but Br was 13.5 kG or less and (BH) max 44.0 MGOe or less, which was lower than that in Example 7.
[0106]
FIG. 8 schematically shows the cross-sectional structure of this sintered magnet. 3 in the crystal structure indicates a void, and the other numbers are the same as those in FIG. From FIG. 8, it can be seen that there is a substantially uniform Dy concentration distribution from the grain boundary phase to the center portion of the main phase crystal grain, and a distribution in which the Dy concentration in the grain boundary phase is high and the Dy concentration in the center portion in the main phase crystal grain is low. Two patterns were confirmed to exist. There were 31 main phase grains having the same Dy concentration distribution as the grain boundary phase, and 15 main phase grains having a lower Dy concentration than the grain boundary phase. However, a distribution in which the Dy concentration in the central part of the main phase grains was higher than that in the grain boundary phase was not observed.
[0107]
The results of evaluating the main phase crystal grain size distribution of the sintered magnet of this comparative example in the same manner as in Example 7 are shown in FIG. As is clear from FIG. 9, in this sintered magnet, the distribution ratio of the main phase crystal grains having a grain size of 1 μm or more and less than 2 μm is 12.5%, and the overall distribution is mainly on the small grain size side compared to the distribution of FIG. The phase crystal grain size distribution is greatly shifted, and the main phase crystal grains are not sufficiently grown. For this reason, it is determined that Br and (BH) max are lower than those in Example 7.
[0108]
In the above examples, the case where the heavy rare earth element is Dy is described, but in the case of Tb or Ho, the main phase crystal grains having a higher concentration of Tb or Ho than the grain boundary phase in the core, as in the case of Dy. Thus, an RTB sintered permanent magnet having high Br and (BH) max can be obtained as in the above embodiment.
[0109]
In the above embodiment, two RTB alloy powders having the same R content and other main components are identical except that only the ratio of Dy, Nd, etc. constituting the R element is different, or the same R content and R By mixing two RTB-based alloy powders with the same main component except that the elements such as Dy, Nd, etc. and part of Fe are replaced with refractory metal elements (Nb, etc.) It is possible to stably obtain an RTB sintered permanent magnet having main phase crystal grains having a characteristic Dy concentration distribution and having a main phase crystal grain size distribution suitable for high Br and (BH) max applications. did it. In the present invention, three or more R-T-B alloy powders may be used as the R-T-B alloy powder. Further, the mixing of these R—T—B alloy powders may be performed at the fine powder stage.
[0110]
If various surface treatments (Ni plating and / or electrodeposition epoxy resin coating, etc.) are applied to the RTB sintered permanent magnets of the above embodiment, various applications (actuators such as voice coil motors or CD pickups, or rotation) Machine).
[0111]
【The invention's effect】
As detailed above, the R-T-B system sintered permanent magnet of the present invention is R₂T₁₄The first R in which the B-type main phase grains have a higher concentration of heavy rare earth elements (Dy, etc.) than the grain boundary phase₂T₁₄B-type main phase grains and the second R in which the concentration of heavy rare earth elements (Dy, etc.) is lower than the grain boundary phase₂T₁₄B-type main phase grains and a third R in which the concentration of heavy rare earth elements (Dy, etc.) is almost equal to the grain boundary phase₂T₁₄Since it is composed of B-type main phase crystal grains, it has iHc as high as that of the R-T-B system sintered permanent magnet obtained by the single method, and has higher Br and (BH) max. Therefore, the R-T-B system sintered permanent magnet of the present invention can be suitably used for applications requiring high Br and high (BH) max.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between sintering temperature and magnetic properties (Br, iHc) for R-T-B sintered permanent magnets of Example 1 and Comparative Example 1.
FIG. 2 is a graph showing the relationship between the sintering temperature and the magnetic properties (Br, iHc) for the R-T-B sintered permanent magnets of Example 2 and Comparative Example 2.
FIG. 3 is a graph showing the relationship between sintering temperature and magnetic properties (Br, iHc) for the R-T-B sintered permanent magnets of Example 3 and Comparative Examples 3 and 4.
4 is a schematic view showing a crystal structure of an R—T—B based sintered permanent magnet of Example 7. FIG.
5 is an EPMA photograph showing the Dy concentration distribution in the crystal structure of the R—T—B system sintered permanent magnet of Example 7. FIG.
FIG. 6 shows the concentration distribution of heavy rare earth elements in the crystal structure of the RTB sintered permanent magnet of Example 7, (a) is an EPMA photograph showing the concentration distribution of Nd in the crystal structure, (d) is It is an EPMA photograph showing the concentration distribution of Pr in the crystal structure.
7 is a graph showing the particle size distribution of main phase crystal grains in the R—T—B system sintered permanent magnet of Example 7. FIG.
8 is a schematic view showing a crystal structure of an R—T—B based sintered permanent magnet of Comparative Example 5. FIG.
9 is a graph showing the particle size distribution of main phase crystal grains in the R—T—B system sintered permanent magnet of Comparative Example 5. FIG.
[Explanation of symbols]
1 ... R₂T₁₄B-type main phase grains
2 ... Grain boundary phase
2 '・ ・ ・ Triple point
3. Void

Claims (5)

重量百分率でR:28〜33％、B:0.5〜２％、０〜0.6％のM₁、及び残部実質的にT及び不可避的不純物からなる組成を有するR-T-B系焼結型永久磁石（RはYを含む少なくとも一種の希土類元素であって、Dy，Tb及びHoからなる群から選ばれた少なくとも一種の重希土類元素を必ず含み、M₁はNb，Mo，W，V，Ta，Cr，Ti，Zr及びHfからなる群から選ばれた少なくとも一種の元素であり、TはFe又はFeとCoである。）であって、前記重希土類元素の濃度（EPMAの測定強度により表される）が結晶粒界相より高い第一のR₂T₁₄B型主相結晶粒と、前記重希土類元素の濃度（EPMAの測定強度により表される）が結晶粒界相より低い第二のR₂T₁₄B型主相結晶粒と、前記重希土類元素の濃度（ EPMA の測定強度により表される）が結晶粒界相とほぼ等しい第三の R ₂ T ₁₄ B 型主相結晶粒とを含有する組織を有し、結晶組織の断面写真における R ₂ T ₁₄ B 型主相結晶粒の総個数を 100 ％として前記第一の R ₂ T ₁₄ B 型主相結晶粒の個数の比率が 1 〜 35 ％であり、前記第二の R ₂ T ₁₄ B 型主相結晶粒の個数の比率が 3 〜 55 ％であり、前記第三の R ₂ T ₁₄ B 型主相結晶粒の個数の比率が 96 〜 10 ％であり、２種類以上の合金粉末を混合して得られ、第一の合金粉末中における前記重希土類元素の含有量が10重量％超40重量％以下であり、第二の合金粉末中における前記重希土類元素の含有量が０〜３重量％であることを特徴とするR-T-B系焼結型永久磁石。R in weight percent: 28~33%, B: 0.5~2% , 0~0.6% of M _1, and the RTB sintered permanent magnet (R having the composition balance consisting substantially T and inevitable impurities At least one kind of rare earth element including Y, and at least one kind of heavy rare earth element selected from the group consisting of Dy, Tb and Ho is necessarily included, and M ₁ is Nb, Mo, W, V, Ta, Cr, Ti , Zr and Hf, and T is Fe or Fe and Co.), and the concentration of the heavy rare earth element (expressed by the measured intensity of EPMA) is and higher than the grain boundary phase first R ₂ T ₁₄ B-type main-phase crystal grains, wherein the heavy rare earth element concentration (represented by the measured intensity of the EPMA) is a second lower than the crystal grain boundary phase R ₂ T ₁₄ containing the B-type main-phase crystal grains, and the heavy concentration of rare earth elements (represented by the measured intensity of the EPMA) is substantially equal to the third R ₂ T ₁₄ B-type main-phase crystal grains and grain boundary phase Tissue has a ratio of 1 to the first R ₂ T ₁₄ B-type main-phase crystal grain number of the total number of R ₂ T ₁₄ B-type main-phase crystal grain in the cross section photograph of the crystal structure as a 100% 35 %, the ratio of the number of the second R ₂ T ₁₄ B type main phase crystal grains is 3 to 55 %, and the ratio of the number of the third R ₂ T ₁₄ B type main phase crystal grains is 96 to 10 %, obtained by mixing two or more kinds of alloy powder, the content of the heavy rare earth element in the first alloy powder is more than 10 % by weight and 40% by weight or less, and the second alloy An RTB sintered permanent magnet, wherein the content of the heavy rare earth element in the powder is 0 to 3% by weight. 請求項１に記載のR-T-B系焼結型永久磁石において、前記第一の合金粉末中のR元素の合計量と前記第二の合金粉末中のR元素の合計量とが実質的に同じであることを特徴とするR-T-B系焼結型永久磁石。  2. The RTB sintered permanent magnet according to claim 1, wherein the total amount of R element in the first alloy powder and the total amount of R element in the second alloy powder are substantially the same. RTB sintered permanent magnet characterized by the above. 請求項１又は２に記載のR-T-B系焼結型永久磁石において、重量百分率で0.01〜0.3％のM₂（ただしM₂はAl，Ga及びCuからなる群から選ばれた少なくとも一種の元素である。）を含有することを特徴とするR-T-B系焼結型永久磁石。3. The RTB sintered permanent magnet according to claim 1, wherein 0.01 to 0.3% by weight of M ₂ (where M ₂ is at least one element selected from the group consisting of Al, Ga and Cu). RTB-based sintered permanent magnet characterized by containing. 請求項１〜３のいずれかに記載のR-T-B系焼結型永久磁石において、重量百分率でRが31％を超えて33％以下であり、前記不可避的不純物として、重量百分率で0.6％以下の酸素、0.15％以下の炭素、0.03％以下の窒素、及び0.3％以下のCaを含有することを特徴とするR-T-B系焼結型永久磁石。  The RTB sintered permanent magnet according to any one of claims 1 to 3, wherein R in weight percentage is more than 31% and not more than 33%, and the unavoidable impurity is oxygen not more than 0.6% in weight percentage. RTB-based sintered permanent magnets containing 0.15% or less carbon, 0.03% or less nitrogen, and 0.3% or less Ca. 請求項１〜３のいずれかに記載のR-T-B系焼結型永久磁石において、重量百分率でRが28〜31％であり、前記不可避的不純物として、重量百分率で0.25％以下の酸素、0.15％以下の炭素、0.15％以下の窒素、及び0.3％以下のCaを含有することを特徴とするR-T-B系焼結型永久磁石。  The RTB sintered permanent magnet according to any one of claims 1 to 3, wherein R is 28 to 31% by weight percentage, and the unavoidable impurities include oxygen of 0.25% or less by weight percentage and 0.15% or less. RTB-based sintered permanent magnet, characterized by containing carbon of 0.15% or less, and 0.3% or less of Ca.

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