JP4244089B2

JP4244089B2 - Method for producing rare earth alloy powder for permanent magnet

Info

Publication number: JP4244089B2
Application number: JP29396599A
Authority: JP
Inventors: 浩之冨澤
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 1999-10-15
Filing date: 1999-10-15
Publication date: 2009-03-25
Anticipated expiration: 2019-10-15
Also published as: JP2001115220A

Description

【０００１】
【発明の属する技術分野】
この発明は、永久磁石用希土類系合金粉末の製造方法の改良に係り、特に、各種モータ、アクチュエータ等に適した希土類系ボンド磁石ならびに焼結磁石に用いられる永久磁石用希土類系合金粉末の製造方法に関する。
【０００２】
【従来の技術】
希土類系永久磁石用合金粉末の金属組織制御法として、HDDR(Hydrogenation‐Disproportionation‐Desorption‐Recombination)処理法と呼ばれるものがある。HDDR処理とは、水素化(Hydrogenation)、不均化(Disproportionation)、脱水素化(Desorption)、および再結合(Recombination)を順次実行するプロセスである。
【０００３】
このHDDR処理にて、永久磁石用の合金粉末を製造するには、R‐T‐(M)‐B系原料合金(RはYを含む希土類元素、TはFeまたはFeとCoとの混合物、Mは添加元素、BはボロンでCにて一部又は全量置換可能、R₂T₁₄B系化合物が主相となる)の鋳塊または粉末を、H₂ガス雰囲気またはH₂ガスと不活性ガスとの混合雰囲気中で温度500℃〜1000℃に保持し、それによって上記合金の鋳塊または粉末に水素を吸蔵させた後、H₂分圧13Pa以下の真空雰囲気またはH₂分圧13Pa以下の不活性ガス雰囲気になるまで、温度500℃〜1000℃で脱水素処理し、次いで冷却する。
【０００４】
HDDR処理法によって希土類系永久磁石用合金粉末を製造する方法は、例えば特開平1-132106号公報に開示されている。当該水素雰囲気での熱処理法で製造されたR‐T‐(M)‐B合金磁石粉末は大きな保磁力を有しており、組成および処理条件の選択によっては磁気的な異方性を有する。
【０００５】
このような性質を有するのは、金属組織が実質的に0.1〜1μmの非常に微細な結晶の集合体となるためである。より詳細には、上記HDDR処理によって得られる極微細結晶の粒径が正方晶R₂T₁₄B系化合物の単磁区臨界粒径に近いために高い保磁力を発揮し、しかも、極微細結晶粒が結晶方位をある程度、揃えて集合しているためである。
【０００６】
また、特開平2-4901号公報には、HDDR処理法に用いられ得る種々のヒートパターンが開示されている。この公報では、原料合金に対して水素雰囲気熱処理の前に均一化熱処理を行うことも提案されている。
【０００７】
R‐T‐(M)‐B系磁石では、用途に応じて種々の減磁耐力が要求され、その要求に見合う保磁力の値を得るために、磁石の組成そのものが調整される。一般に、保磁力HcJを高めると残留磁束密度Brが小さくなる。
【０００８】
保磁力の値を大きくするには、重希土類であるDyやTbをRの一部として加える方法が採られている。この方法は、同時に残留磁束密度を低下させる。前記HDDR処理法でも、Rの一部をDyやTbで置換すると、高い保磁力が得られることが知られており、保磁力の向上を狙って添加されることがある。
【０００９】
一方、HDDR処理法では、処理条件の適正化によってその磁気特性を改良しようとする研究が盛んに行われている。特開平5-163510号公報には、脱水素処理において、その反応が吸熱反応であるために温度低下が生じるが、この温度変化が50℃以内になるように制御する方法及び装置が示され、この温度変化制御によって優れた磁気特性が得られることを示している。
【００１０】
特開平5-166616号公報には、脱水素処理中に処理温度を徐々に下げることで、再結晶粒子の粒成長を防止し、高い保磁力が得られることが示されている。また、特開平7-90308号公報には、脱水素処理の真空度の変化率を、特に脱水素処理の初期段階において所定範囲に制御することで、優れた磁気特性を有する磁性粉末が得られることが示されている。
【００１１】
【発明が解決しようとする課題】
永久磁石の使用に当たって、その使用環境で減磁をしないことが材料選定の基準となる。減磁に対する対策は、温度上昇によって減磁する不可逆熱減磁も含め、保磁力を高めることが実用的であり、残留磁束密度を犠牲にしても高い保磁力の磁石が要求されるのはこのためである。
【００１２】
しかしながら、前記方法では、合金の組成から期待される保磁力が充分には得られておらず、そのため、目的の保磁力、減磁耐力を得るためには必要以上にDyやTbを添加したり、R量を増やしたりして磁化を低下させてしまう問題があった。また、重希土類であるDyやTbは高価な元素であり、これらの必要以上の使用はコスト上昇の要因になっていた。
【００１３】
この原因は、HDDR処理が、水素化・不均化反応、脱水素・再結合反応共に、固相-気相反応であり、その化学反応速度に関する解析が不充分なことによる。そのため、実操業では、処理量が変わるだけで磁気特性が変動するなどの問題点もあった。
【００１４】
この発明は、上述のHDDR処理における種々の問題点を鑑みてこれらを解消することを目的とし、各反応速度の影響等の解析に基づき、組成的に高価な重希土類元素を多量に用いることなく、残留磁化を低下させずに安定して高い保磁力が得られる永久磁石用希土類系合金粉末の製造方法の提供を目的としている。
【００１５】
【課題を解決するための手段】
発明者は、組成的に高価なDyやTbをできるだけ用いずに、大きな磁化を維持したまま、粉末状態で大きな保磁力を得ることが可能な処理方法を目的に鋭意検討した結果、HDDR処理における脱水素時の水素放出速度の変化が再結合反応速度の変化となって、結果的に磁性粉末の磁気特性に大きく影響することを見出し、その反応速度を制御することで高い保磁力が得られることを知見し、この発明を完成した。
【００１６】
すなわち、この発明は、R₂T₁₄B(BはCで一部又は全量置換可能)型化合物が50vol%以上を占める合金からなる鋳塊または粉末を、例えば、温度650〜950℃において水素分圧10〜1000kPaの雰囲気中に保持し、水素化・不均化反応を起こさせ、引き続き温度650〜1000℃において水素分圧100Pa以下に保持し、脱水素・再結合反応を起こさせて後、冷却する、永久磁石用希土類系合金粉末の製造方法において、脱水素・再結合反応の各反応速度を、雰囲気の制御、例えば圧力及び/又は温度制御により多段階に変化させることを特徴とする永久磁石用希土類系合金粉末の製造方法である。
【００１７】
また、この発明は、上記の脱水素・再結合反応において、
水素放出速度の調整で再結合反応速度を変え、被処理物中の水素濃度が所定の値に達するまでを第1段階、それ以後を第2段階とし、
第1段階の水素放出速度が0.1wt%/h〜5.0wt%/h、第2段階の水素放出速度が0.01wt%/h〜0.20wt%/hであって、かつ第2段階の水素放出速度を第1段階よりも小さな放出速度とすることを特徴とする。
【００１８】
さらに、この発明は、脱水素・再結合反応の第1段階は、反応開始から被処理物の水素濃度C_Hが次式の範囲に達するまでとし、第2段階は被処理物の水素濃度が最終的に100ppm以下に至る範囲とすることを特徴とする。但し、C_Hは合金中の水素濃度(wt%)、C_Rは合金中の希土類成分濃度(wt%)である。
0.000725×C_R≦C_H≦0.00750×C_R
【００１９】
【発明の実施の形態】
この発明は、HDDR処理法による永久磁石用希土類系合金粉末の製造方法において、脱水素・再結合反応の各反応速度を、例えば雰囲気の圧力や温度の制御にて多段階に変化させることにより、重希土類元素を多量に用いることなく、残留磁化を低下させずに安定して高い保磁力が得られるることを特徴としている。以下に好ましい実施条件を詳述する。
【００２０】
合金組成
この発明の対象とする合金組成は、R₂T₁₄B(BはCで一部又は全量置換可能)型化合物が50vol%以上を占める合金であり、また種々の添加元素Mを含有し得る。希土類元素Rは、Yを含むいずれの希土類元素を含有することも制限しないが、Rのうち少なくともNdまたはPrの一方、あるいはその両方を含む必要がある。また、Dy、Tb、Hoのうち、1種以上を含有することは、最終的に得られる磁石材料の保磁力を高める効果があり、好ましい。
【００２１】
Rの量は、10〜20at%が望ましく、より好ましくは11〜15at%である。R量が10at%未満では保磁力が低下し、20at%を越えると強磁性相の比率が低下し、磁化が小さくなる。
【００２２】
Tは、鉄属元素であり、Fe、Co、Niが該当する。CoをFeと置換して添加すると、キュリー点が上昇する効果以外に、HDDR処理における磁気的な異方性をより得やすくなり、高い磁化が得られる。Coの添加はTのうち50%まで可能で、50%を越えると磁化が低下するので好ましくない。Niは、小量の添加では異方性の向上に効果があるが、磁化を下げるのでTの5%以下の添加が望ましい。
【００２３】
Tの量は、67〜85at%が望ましく、67at%未満ではR₂T₁₄B相の比率が低下して磁化が小さくなり、85at%を越えると磁気的にソフトの相が生成し、保磁力が低下する。
【００２４】
Bは、その一部をCで置換することができ、また、全量Cで置換することも可能である。Bの量は、4〜10at%が良く、4at%未満では磁気的にソフトの相が生成して保磁力が低下し、10at%を越えるとR₂T₁₄B相の比率が低下して磁化が小さくなる。
【００２５】
必要に応じて添加する添加元素Mは、磁気的な異方性を高めたり、保磁力を高めることを目的に添加される。異方性向上に効果のある元素として、Ga、Zr、Hf等が良く知られており、保磁力を高める元素としてCu、Al等がある。このほか、Si、Ti、V、Cr、Mn、Zn、Ge、Nb、In、Sn、Ta、W、Pbなどを添加含有させることができる。
【００２６】
添加元素Mは、1種または2種以上を組み合わせて添加することが可能である。Mの添加量は、前記効果を目的として添加する場合、5at%以下にすることが望ましい。添加量が5at%を越えると、磁性に寄与しない相が増加して磁化が低下する。
【００２７】
水素化条件
水素化温度は、650℃未満であると、水素化・不均化反応が充分に進行せず、950℃を超える、後述の雰囲気水素分圧の範囲内では水素化・不均化反応が生じない条件となるため、水素化温度範囲は650〜950℃が望ましい。
【００２８】
水素化時の水素分圧は、10kPa未満では反応の進行が不充分で、高い保磁力を発現することができず、また1000kPaを超えると、装置に高い耐圧構造が要求され、またHDDR処理して得た合金粉末の磁気特性上のメリットが特に認められないことから、水素分圧範囲は10〜1000kPaが望ましい。
【００２９】
なお、高い磁気異方性を有する高磁化の合金粉末を得るには、さらに処理温度を750℃以上に限定し、昇温速度を10℃/min以上で700℃以上の温度域まで昇温することが好ましい。
【００３０】
脱水素条件と反応速度
HDDR処理時の雰囲気条件をの一例を図1に示す。水素化・不均化反応は、雰囲気の水素分圧が10〜1000kPaの条件で行う。通常、その終了時点で、雰囲気ガスを放出するか、Arガスを導入して雰囲気を大気圧に戻し、引き続きArガスを大気圧で流気して雰囲気の水素ガスを追い出す、Ar置換処理を行う。この時、雰囲気の水素分圧は徐々に低下するので、水素放出反応の最初期の反応は始まっている。
【００３１】
この発明において、水素放出速度にはAr置換時の水素放出反応を除外する。Ar置換処理は、引き続き行う水素放出処理の安全性を確保するためにも有用であり、大きな残留磁化を得るためには所定時間行うことが好ましい。なお、後続の工程も含め、Arに換えてHeやNe等の希ガスを使用することができる。ガス種は使用する装置や工程での至便性やコストなどで適宜選択するとよい。
【００３２】
Ar置換の処理時間は、短時間では大きな残留磁化が得られず、長すぎると保磁力が小さくなる。このAr置換処理の時間は、処理量、処理装置の内容積等で決定される。なお、等方性の磁粉を得る場合は、当該処理は必須ではない。
【００３３】
Ar置換処理に引き続き、脱水素・再結合反応工程を実施する。R水素化物の水素解離条件は、例えばNd水素化物の場合、温度650℃では水素分圧3Pa以下、温度800℃では水素分圧を100Pa以下、温度850℃では水素分圧を1000Pa以下であり、脱水素反応を進行させるには上記条件の実施が必要である。
【００３４】
この脱水素処理の具体的方法として、減圧Ar処理を行う。脱水素処理では、雰囲気の水素分圧が水素放出速度に効果的に作用するが、多量処理においては水素放出量が多大になるため、ボイル-シャルルの法則に則り、雰囲気の全ガス分子量を制御する必要がある。実処理では雰囲気置換が効率的に行われないとミクロな原料粉末表面近傍に水素濃度の高い領域が生じ、水素放出速度を低下させてしまう。
【００３５】
この現象を回避するには、減圧状態で充分な量の雰囲気ガスを流気する方法が簡単で効果的である。実際には、ロータリーポンプ等の雰囲気ガス排気手段で雰囲気ガスを排気しながら、Arガスを導入し、炉内の全圧を100Pa〜10kPaの範囲の一定値に維持する方法を用いる。この雰囲気下で、R水素化物から水素ガスが放出できる条件が維持される。
【００３６】
水素を放出させる脱水素処理法には、上記の減圧Ar処理以外に種々の方法を採用できる。例えば、特開平2-4901号公報などに示された真空排気による方法や、単に大気圧や加圧条件でArガス等を流気する方法、また、特開平5-156320号公報に示したような、密閉系で水素吸蔵合金を用いて系内の水素分圧を制御する方法等が挙げられる。
【００３７】
いずれの脱水素処理方法を採用する場合においても、脱水素処理の初期(第1)段階での水素放出速度が0.1wt%/h〜5.0wt%/hの範囲に調整できることが望ましい。水素放出速度が0.1wt%/h未満であると、水素放出に時間がかかりすぎて、得られる磁性粉末の保磁力が低下してしまうため、好ましくない。また、水素放出速度が5.0wt%/hを超えると、当該速度の実現のために例えば処理量を著しく少なくするなど、実操業上の困難が多いため、第1段階における水素放出速度は、0.1wt%/h〜5.0wt%/hの範囲が望ましい。
【００３８】
脱水素処理の多段化
従来の脱水素処理技術では、原料粉末中の残存水素量が100ppm以下となって実用的な保磁力が発現するまで脱水素・再結合反応処理を行うが、この発明では、さらに高い保磁力を得るためには以下の処理を行う。
【００３９】
脱水素処理、例えば減圧Ar処理により、原料粉末中の水素量C_Hが、下記式の範囲まで低下させた後、雰囲気の減圧排気を止め、大気圧に復圧してAr流気のみで徐々に水素放出させる。もちろん、この時の雰囲気制御方法も、大気圧のAr流気法に限定されない。
0.000725×C_R≦C_H≦0.00750×C_R
(但し、C_Hは合金中の水素濃度(wt%)、C_Rは合金中の希土類成分濃度(wt%)である。)
【００４０】
第2段階における水素放出速度は、0.2wt%/h以下であり、かつ第1段階よりも小さな速度とする。水素放出速度が0.2wt%/hを越えたり、また第1段階の水素放出速度よりも大きくすると、保磁力の向上効果が認められないため、好ましくない。また、水素放出速度が0.01wt%/h未満の場合は、処理に多大の時間を要する他、処理条件の設定が困難になるため、第2段階における水素放出速度は、0.01wt%/h〜0.2wt%/hの範囲が好ましい。
【００４１】
この発明によるHDDR処理における原料粉末中の水素量変化の一例を図2に示す。図中、実線がこの発明の処理例を示したものであり、破線で示したものが、第1段階の条件のままで脱水素・再結合反応工程を継続した場合における水素量の時間変化の一例である。
【００４２】
第1段階の脱水素・再結合反応終了時点での原料粉末中の水素量C_Hの適正値は、原料合金のR成分量の影響を受ける。C_H＞0.00750×C_Rの場合は、保磁力の向上効果がなく、また処理に多大な時間を要する。一方、C_H＜0.000725×C_Rの場合は、保磁力の向上効果がない。
【００４３】
なお、脱水素水素処理の第2段階では、反応速度が小さいので、水素残存量を例えば0.002wt%(20ppm)以下にするには多大な時間を要する。実用上、水素量が0.01wt%(100ppm)以下であれば磁粉の磁気特性にはほとんど変化は生じない。
【００４４】
より水素量を少なくするために、第2段階の脱水素・再結合反応が終了し、原料粉末の水素量が0.01wt%(100ppm)以下となった後に、再度雰囲気を減圧するなどして原料粉末の水素量を低下させてもよい。
【００４５】
さらに、水素量の調整を行う熱処理は、本工程の熱処理に引き続き行っても、一旦冷却した後、別途行ってもよい。いずれにしても、磁気特性にはほとんど影響はない。しかし、まだ明確にされていないが、水素量は磁粉の耐酸化性などの安定性には影響する可能性がある。
【００４６】
この発明において、水素量及び水素放出速度の評価には水素量の測定が不可欠であるが、処理中の原料粉末の水素量を連続的に監視し続けることは困難である。そこで、実際の処理前に予め同一条件の水素量評価用の処理を行い、予め処理時間と水素量の変化との関係を求めておくことにより、処理時間の管理でこの発明の工程を制御できる。
【００４７】
【実施例】
実施例1
27.5%Nd‐bal.Fe-9.5%Co-1.0%Ga-0.1%Zr-1.0%B(Wt%)の組成の鋳塊を、Ar中1100℃24時間の均質化処理を行い、さらに0.1MPa、10l/minの水素ガス流気中で400℃2時間の水素脆化処理を行い、冷却した後、目開き425μmのふるいで整粒して原料粉末とした。この原料粉末50gを、開口部寸法30×45mmのSUS310S製容器に充填し、インコネル製炉心管を有する管状熱処理炉に装填し、HDDR処理を行った。
【００４８】
HDDR処理条件は、0.1MPaの水素雰囲気中(5l/min流気)で840℃まで15℃/minで昇温し、その温度で2時間保持した後、温度を維持しながら10l/minのArガスで5分間、Ar置換を行い、引き続き同温度でArガスを20l/min導入しながらロータリーポンプにより炉内を真空排気し、炉内圧力を6kPaに所定時間維持する減圧Ar処理を行った。
【００４９】
所定時間経過後、炉温を維持したまま、真空排気を止め、雰囲気圧力を大気圧まで復圧し、10l/minのArを流気しながら所定時間処理した後、冷却した。その後、得られた磁性粉の磁気特性を測定した結果を表1に示す。
【００５０】
磁粉の組成から、この発明の特に好ましい範囲に該当する、減圧脱水素終了時点での水素量C_Hは、0.020wt%(200ppm)以上、0.206wt%(2060ppm)以下である。表中、*印で表示した条件は、上記の特に好ましい範囲外の実施例(1G1,1G3)である。なお、前記処理と同様の処理条件で減圧Ar処理まで行って冷却した原料粉末の不活性ガス抽出法で測定した水素分析値を、表1の処理中の減圧Ar処理後の水素量推定値として表中に併記する。
【００５１】
表1に明らかなごとく、減圧Ar処理法による脱水素処理で、原料粉末中の水素量が0.020〜0.206wt%となった時点で、Ar流気法による脱水素処理に切り替え、水素量が最終的に0.010wt%以下となったときに高い保磁力と大きな残留磁化が同時に得られたことが分かる。
【００５２】
【表１】

【００５３】
実施例2
29.5%Nd‐bal.Fe‐15.0%Co-0.3%Ga-0.1%Zr-1.0%B(Wt%)の組成のインゴットを、Ar中1100℃24時間の均質化処理を行い、さらに0.1MPa、10l/minの水素ガス流気中で400℃2時間の水素脆化処理を行い、冷却した後、目開き425μmのふるいで整粒して原料粉末とした。この原料粉末200gを、開口部寸法80×200mmのSUS310S製容器に充填し、インコネル製炉心管を有する管状熱処理炉に装填し、HDDR処理を行った。
【００５４】
処理条件は、0.1MPaの水素雰囲気中(5l/min流気)で820℃まで15℃/minで昇温し、その温度で2時間保持した後、温度を維持しながら10l/minのArガスで5分間Ar置換を行い、引き続き同温度でArガスを導入しながらロータリーポンプにより炉内を真空排気し、Ar導入量と排気弁の開度を調節して所定の炉内圧力を所定時間維持する減圧Ar処理を行った。
【００５５】
所定時間経過後、炉温を維持したまま、真空排気を止め、雰囲気圧力を大気圧まで復圧し、10l/minのArを流気しつつ6.0ks処理した後、冷却した。その後、得られた磁粉の磁気特性を測定し、その結果を表2に示す。
【００５６】
磁粉の組成から、この発明の特に好ましい範囲に該当する、減圧脱水素終了時点での水素量C_Hは、0.021wt%(210ppm)以上、0.221wt%(2210ppm)以下である。表中、*印で表示した条件は、上記の特に好ましい範囲外の実施例(2G2)である。なお、前記処理と同様の処理条件で減圧Ar処理まで行って冷却した原料粉末の水素分析値を、表2の処理中の減圧Ar処理後の水素量推定値として表中に併記する。
【００５７】
表2から明らかなように、第1段階の脱水素処理における水素放出速度が0.1〜5.0wt%/hの範囲で保磁力の向上効果が認められることが分かる。
【００５８】
【表２】

【００５９】
実施例3
実施例2で用いた原料粉末100gを、開口部寸法60×100mmのSUS310S製容器に充填し、インコネル製炉心管を有する管状熱処理炉に装填し、HDDR処理を行った。処理条件は、0.1MPaの水素雰囲気中(5l/min流気)で820℃まで15℃/minで昇温し、その温度で2時間保持した後、温度を維持しながら10l/minのArガスで5分間、Ar置換を行い、引き続き同温度でArガスを導入しながらロータリーポンプにより炉内を真空排気し、Ar導入量と排気弁の開度を調節して所定の炉内圧力を所定時間維持する減圧Ar処理を行った。
【００６０】
所定時間経過後、炉温を維持したまま、真空排気を止め、雰囲気圧力を大気圧まで復圧し、10l/minのArを流気しつつ6.0ks処理した後、冷却した。この時得られた磁粉の磁気特性を表3に示す。なお、前記処理と同様の処理条件で減圧Ar処理まで行って冷却した原料粉末の水素分析値を、表3の処理中の減圧Ar処理後の水素量推定値として表中に併記する。
【００６１】
表3から明らかなように、第2段階の脱水素処理における水素放出速度が、雰囲気全圧を制御することで調節可能であり、0.01〜0.20wt%/hの範囲で、かつ第1段階の脱水素処理における水素放出速度よりも小さい値であれば、特に保磁力の向上効果が認められることが分かる。
【００６２】
【表３】

【００６３】
【発明の効果】
この発明は、HDDR処理法における脱水素工程において、原料粉末の水素量が0.2wt%(2000ppm)〜0.050wt%(500ppm)に達するまで大きな水素放出反応速度で、0.010wt%(100ppm)以下に達するまでを小さな反応速度で処理を進行させることにより、組成に重希土類を多く含有しなくとも、また残留磁化を低下させることなく、高い保磁力を有した永久磁石用希土類系合金粉末を製造することができる。
【図面の簡単な説明】
【図１】この発明によるHDDR処理工程を示すヒートパターン図である。
【図２】 HDDR処理工程における時間と原料粉末の水素量との関係を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a method for producing a rare earth alloy powder for permanent magnets, and more particularly, a method for producing a rare earth alloy powder for permanent magnets used in sintered magnets and rare earth bond magnets suitable for various motors and actuators. About.
[0002]
[Prior art]
There is a method called HDRD (Hydrogenation-Disproportionation-Desorption-Recombination) as a method for controlling the microstructure of rare earth-based permanent magnet alloy powders. The HDDR process is a process for sequentially executing hydrogenation, disproportionation, desorption, and recombination.
[0003]
In order to produce alloy powder for permanent magnets by this HDDR treatment, R-T- (M) -B-based raw material alloy (R is a rare earth element including Y, T is Fe or a mixture of Fe and Co, (M is an additive element, B is boron, part or all of which can be replaced by C, R ₂ T ₁₄ B compound is the main phase) Ingot or powder is inert with H ₂ gas atmosphere or H ₂ gas in a mixed atmosphere of a gas maintained at a temperature 500 ° C. to 1000 ° C., whereby after absorbing hydrogen in ingot or powder of the alloy, H ₂ partial pressure 13Pa or less following a vacuum atmosphere or H ₂ partial pressure 13Pa Until an inert gas atmosphere is obtained, it is dehydrogenated at a temperature of 500 ° C. to 1000 ° C. and then cooled.
[0004]
A method for producing a rare earth-based permanent magnet alloy powder by the HDDR treatment method is disclosed in, for example, Japanese Patent Laid-Open No. 1-132106. The RT- (M) -B alloy magnet powder produced by the heat treatment in the hydrogen atmosphere has a large coercive force, and has magnetic anisotropy depending on the selection of composition and processing conditions.
[0005]
The reason for having such a property is that the metal structure becomes an aggregate of very fine crystals of substantially 0.1 to 1 μm. More specifically, since the grain size of the ultrafine crystal obtained by the above-mentioned HDDR treatment is close to the single domain critical grain size of the tetragonal R ₂ T ₁₄ B compound, it exhibits a high coercive force, and the ultrafine crystal grain This is because the crystal orientations are aligned to some extent.
[0006]
Japanese Patent Laid-Open No. 2-4901 discloses various heat patterns that can be used in the HDRR processing method. In this publication, it is also proposed to perform a uniform heat treatment on the raw material alloy before the heat treatment in the hydrogen atmosphere.
[0007]
In RT- (M) -B magnets, various demagnetization proof strengths are required depending on the application, and the magnet composition itself is adjusted to obtain coercive force values that meet the requirements. Generally, when the coercive force HcJ is increased, the residual magnetic flux density Br is decreased.
[0008]
In order to increase the coercive force, a method of adding heavy rare earths Dy and Tb as a part of R is employed. This method simultaneously reduces the residual magnetic flux density. Even in the aforementioned HDDR processing method, it is known that a part of R is replaced with Dy or Tb, a high coercive force can be obtained, and it may be added to improve the coercive force.
[0009]
On the other hand, in the HDRR processing method, researches are being actively conducted to improve the magnetic properties by optimizing the processing conditions. Japanese Patent Laid-Open No. 5-135510 discloses a method and an apparatus for controlling the temperature change to be within 50 ° C. in the dehydrogenation process because the reaction is an endothermic reaction. It shows that excellent magnetic characteristics can be obtained by this temperature change control.
[0010]
Japanese Patent Application Laid-Open No. 5-166616 shows that by gradually lowering the treatment temperature during the dehydrogenation treatment, grain growth of recrystallized particles can be prevented and a high coercive force can be obtained. Japanese Patent Application Laid-Open No. 7-90308 discloses that a magnetic powder having excellent magnetic properties can be obtained by controlling the rate of change in the degree of vacuum in the dehydrogenation process within a predetermined range, particularly in the initial stage of the dehydrogenation process. It has been shown.
[0011]
[Problems to be solved by the invention]
When using permanent magnets, the standard for material selection is not to demagnetize in the usage environment. As countermeasures against demagnetization, it is practical to increase the coercive force, including irreversible thermal demagnetization, which is demagnetized due to temperature rise, and this is the reason why high coercivity magnets are required even at the expense of residual magnetic flux density. Because.
[0012]
However, in the above method, the coercive force expected from the composition of the alloy has not been sufficiently obtained. Therefore, in order to obtain the desired coercive force and demagnetization resistance, Dy or Tb is added more than necessary. There is a problem that the magnetization is lowered by increasing the R amount. Moreover, Dy and Tb, which are heavy rare earth elements, are expensive elements, and their use more than necessary has been a factor in increasing costs.
[0013]
This is because the HDDR treatment is a solid-gas phase reaction for both hydrogenation / disproportionation reaction and dehydrogenation / recombination reaction, and the chemical reaction rate is insufficiently analyzed. For this reason, in actual operation, there is a problem that the magnetic characteristics fluctuate only by changing the processing amount.
[0014]
The present invention aims to eliminate these problems in view of the various problems in the above-mentioned HDDR processing, and based on the analysis of the influence of each reaction rate, etc., without using a large amount of compositionally expensive heavy rare earth elements An object of the present invention is to provide a method for producing a rare earth alloy powder for a permanent magnet that can stably obtain a high coercive force without lowering the residual magnetization.
[0015]
[Means for Solving the Problems]
The inventor has intensively studied for the purpose of a processing method capable of obtaining a large coercive force in a powder state while maintaining a large magnetization without using compositionally expensive Dy and Tb as much as possible. It was found that the change in the hydrogen release rate during dehydrogenation changed the recombination reaction rate, resulting in a large influence on the magnetic properties of the magnetic powder, and a high coercive force was obtained by controlling the reaction rate. As a result, the present invention was completed.
[0016]
That is, the present invention relates to an ingot or powder made of an alloy in which R ₂ T ₁₄ B (B can be partially or wholly replaced by C) type compound accounts for 50 vol% or more, for example, at a temperature of 650 to 950 ° C. After maintaining in an atmosphere with a pressure of 10 to 1000 kPa to cause hydrogenation / disproportionation reaction, and subsequently maintaining a hydrogen partial pressure of 100 Pa or less at a temperature of 650 to 1000 ° C., causing dehydrogenation / recombination reaction, In the method for producing a rare earth alloy powder for permanent magnet to be cooled, each reaction rate of dehydrogenation / recombination reaction is changed in multiple stages by controlling the atmosphere, for example, pressure and / or temperature control. This is a method for producing a rare earth alloy powder for a magnet.
[0017]
Further, the present invention provides the above dehydrogenation / recombination reaction,
By changing the recombination reaction rate by adjusting the hydrogen release rate, the first stage until the hydrogen concentration in the workpiece reaches a predetermined value, the second stage thereafter,
The first stage hydrogen release rate is 0.1 wt% / h to 5.0 wt% / h, the second stage hydrogen release rate is 0.01 wt% / h to 0.20 wt% / h, and the second stage hydrogen release is The release rate is smaller than that of the first stage.
[0018]
Further, according to the present invention, the first stage of the dehydrogenation / recombination reaction is from the start of the reaction until the hydrogen concentration C _H of the workpiece reaches the range of the following formula, and the second stage is the hydrogen concentration of the workpiece to be treated. It is characterized in that the range finally reaches 100 ppm or less. However, C _H is the hydrogen concentration (wt%) in the alloy, and C _R is the rare earth component concentration (wt%) in the alloy.
0.000725 × C _R ≦ C _H ≦ 0.00750 × C _R
[0019]
DETAILED DESCRIPTION OF THE INVENTION
This invention is a method for producing a rare earth alloy powder for permanent magnets by the HDDR treatment method, and by changing each reaction rate of the dehydrogenation / recombination reaction in multiple stages by controlling the pressure and temperature of the atmosphere, for example, It is characterized in that a high coercive force can be obtained stably without reducing residual magnetization without using a large amount of heavy rare earth elements. The preferred implementation conditions are described in detail below.
[0020]
Alloy composition The alloy composition of the present invention is an alloy in which R ₂ T ₁₄ B (B can be partially or wholly replaced by C) type compound accounts for 50 vol% or more, and contains various additive elements M. obtain. The rare earth element R is not limited to containing any rare earth element including Y, but it is necessary to include at least one of Nd and Pr or both of R. In addition, it is preferable that one or more of Dy, Tb, and Ho are contained because of the effect of increasing the coercive force of the finally obtained magnet material.
[0021]
The amount of R is desirably 10 to 20 at%, more preferably 11 to 15 at%. If the amount of R is less than 10 at%, the coercive force decreases, and if it exceeds 20 at%, the ratio of the ferromagnetic phase decreases and the magnetization decreases.
[0022]
T is an iron group element and corresponds to Fe, Co, and Ni. When Co is substituted for Fe and added, in addition to the effect of increasing the Curie point, it becomes easier to obtain magnetic anisotropy in the HDDR process, and high magnetization can be obtained. Co can be added up to 50% of T, and if it exceeds 50%, the magnetization decreases, which is not preferable. Ni is effective in improving anisotropy when added in a small amount, but it is desirable to add 5% or less of T because it lowers the magnetization.
[0023]
The amount of T is preferably 67 to 85 at%. If it is less than 67 at%, the ratio of the R ₂ T ₁₄ B phase decreases and the magnetization decreases, and if it exceeds 85 at%, a magnetically soft phase is generated and the coercive force is generated. Decreases.
[0024]
A part of B can be substituted with C, or the entire amount can be substituted with C. The amount of B is preferably 4 to 10 at%, and if it is less than 4 at%, a magnetically soft phase is generated and the coercive force is lowered, and if it exceeds 10 at%, the ratio of the R ₂ T ₁₄ B phase is lowered and magnetized. Becomes smaller.
[0025]
The additive element M added as necessary is added for the purpose of increasing the magnetic anisotropy or increasing the coercive force. Ga, Zr, Hf, and the like are well known as elements that are effective in improving anisotropy, and Cu, Al, and the like are elements that increase the coercive force. In addition, Si, Ti, V, Cr, Mn, Zn, Ge, Nb, In, Sn, Ta, W, Pb, and the like can be added and contained.
[0026]
The additive element M can be added alone or in combination of two or more. The amount of M added is desirably 5 at% or less when added for the purpose described above. When the addition amount exceeds 5 at%, phases that do not contribute to magnetism increase and magnetization decreases.
[0027]
Hydrogenation conditions If the hydrogenation temperature is less than 650 ° C, the hydrogenation / disproportionation reaction does not proceed sufficiently and exceeds 950 ° C. Since the reaction does not occur, the hydrogenation temperature range is preferably 650 to 950 ° C.
[0028]
If the hydrogen partial pressure during hydrogenation is less than 10 kPa, the progress of the reaction is insufficient and high coercive force cannot be exhibited. If the hydrogen partial pressure exceeds 1000 kPa, a high pressure resistance structure is required for the device, and the HDDR treatment is performed. Since the merit on the magnetic properties of the alloy powder obtained in this way is not particularly recognized, the hydrogen partial pressure range is preferably 10 to 1000 kPa.
[0029]
In order to obtain a highly magnetized alloy powder having high magnetic anisotropy, the treatment temperature is further limited to 750 ° C. or higher, and the temperature is raised to a temperature range of 700 ° C. or higher at a rate of temperature increase of 10 ° C./min or higher. It is preferable.
[0030]
Dehydrogenation conditions and reaction rate
Figure 1 shows an example of atmospheric conditions during HDDR processing. The hydrogenation / disproportionation reaction is carried out under conditions where the hydrogen partial pressure of the atmosphere is 10 to 1000 kPa. Usually, at the end of the process, the atmospheric gas is released or Ar gas is introduced to return the atmosphere to atmospheric pressure, and then Ar gas is flowed at atmospheric pressure to expel the hydrogen gas in the atmosphere and perform Ar replacement treatment. . At this time, since the hydrogen partial pressure in the atmosphere gradually decreases, the initial reaction of the hydrogen releasing reaction has started.
[0031]
In this invention, the hydrogen release rate excludes the hydrogen release reaction during Ar substitution. The Ar substitution treatment is useful for ensuring the safety of the subsequent hydrogen release treatment, and is preferably performed for a predetermined time in order to obtain a large residual magnetization. Including the subsequent steps, a rare gas such as He or Ne can be used instead of Ar. The gas type may be appropriately selected depending on the convenience and cost in the apparatus and process to be used.
[0032]
When the Ar replacement treatment time is short, large remanent magnetization cannot be obtained, and if it is too long, the coercive force becomes small. The Ar replacement processing time is determined by the processing amount, the internal volume of the processing apparatus, and the like. In addition, when obtaining isotropic magnetic powder, the said process is not essential.
[0033]
Following the Ar replacement treatment, a dehydrogenation / recombination reaction step is performed. For example, in the case of Nd hydride, the hydrogen dissociation condition of R hydride is a hydrogen partial pressure of 3 Pa or less at a temperature of 650 ° C., a hydrogen partial pressure of 100 Pa or less at a temperature of 800 ° C., and a hydrogen partial pressure of 1000 Pa or less at a temperature of 850 ° C. In order to proceed with the dehydrogenation reaction, it is necessary to carry out the above conditions.
[0034]
As a specific method of this dehydrogenation treatment, a reduced pressure Ar treatment is performed. In the dehydrogenation process, the hydrogen partial pressure of the atmosphere effectively affects the hydrogen release rate, but in the case of a large amount of process, the hydrogen release amount becomes large, so the total gas molecular weight of the atmosphere is controlled according to Boyle-Charles' law. There is a need to. In the actual process, if the atmosphere replacement is not efficiently performed, a region with a high hydrogen concentration is generated near the surface of the micro raw material powder, and the hydrogen release rate is reduced.
[0035]
In order to avoid this phenomenon, a method of flowing a sufficient amount of atmospheric gas in a reduced pressure state is simple and effective. Actually, Ar gas is introduced while the atmospheric gas is exhausted by an atmospheric gas exhaust means such as a rotary pump, and the total pressure in the furnace is maintained at a constant value in the range of 100 Pa to 10 kPa. Under this atmosphere, the conditions under which hydrogen gas can be released from the R hydride are maintained.
[0036]
Various methods other than the above-described reduced pressure Ar treatment can be adopted as the dehydrogenation treatment method for releasing hydrogen. For example, a method by vacuum evacuation shown in Japanese Patent Laid-Open No. 2-4901, a method of simply flowing Ar gas or the like under atmospheric pressure or a pressurized condition, or a method shown in Japanese Patent Laid-Open No. 5-156320 Moreover, a method of controlling the hydrogen partial pressure in the system using a hydrogen storage alloy in a closed system can be used.
[0037]
In any case of adopting any dehydrogenation method, it is desirable that the hydrogen release rate in the initial (first) stage of the dehydrogenation process can be adjusted in a range of 0.1 wt% / h to 5.0 wt% / h. If the hydrogen release rate is less than 0.1 wt% / h, it takes too much time for hydrogen release, and the coercive force of the resulting magnetic powder decreases, which is not preferable. In addition, when the hydrogen release rate exceeds 5.0 wt% / h, there are many actual operational difficulties such as significantly reducing the amount of treatment for realizing the rate, so the hydrogen release rate in the first stage is 0.1 The range of wt% / h to 5.0wt% / h is desirable.
[0038]
Multi-stage dehydrogenation In conventional dehydrogenation technology, dehydrogenation and recombination reaction treatment is performed until the residual hydrogen content in the raw material powder is 100 ppm or less and a practical coercive force is developed. In order to obtain a higher coercive force, the following processing is performed.
[0039]
Dehydrogenation treatment, for example by vacuum Ar treatment, hydrogen content C _H in the raw material powder, after being lowered to the range of the following formula, stop the evacuation of the atmosphere, and gradually only Ar Nagareki by applying restored to the atmospheric pressure Release hydrogen. Of course, the atmosphere control method at this time is not limited to the Ar flow method at atmospheric pressure.
0.000725 × C _R ≦ C _H ≦ 0.00750 × C _R
(However, the C _H hydrogen concentration (wt% in the alloy), C _R is a rare earth component concentration in the alloy (wt%).)
[0040]
The hydrogen release rate in the second stage is 0.2 wt% / h or less and is smaller than that in the first stage. If the hydrogen release rate exceeds 0.2 wt% / h or is larger than the first-stage hydrogen release rate, the effect of improving the coercive force is not recognized, which is not preferable. In addition, when the hydrogen release rate is less than 0.01 wt% / h, it takes a lot of time for processing, and it becomes difficult to set the processing conditions, so the hydrogen release rate in the second stage is 0.01 wt% / h ~ A range of 0.2 wt% / h is preferred.
[0041]
An example of the change in the amount of hydrogen in the raw powder in the HDDR process according to the present invention is shown in FIG. In the figure, the solid line shows a processing example of the present invention, and the broken line shows the time change of the hydrogen amount when the dehydrogenation / recombination reaction process is continued under the conditions of the first stage. It is an example.
[0042]
Proper value of the hydrogen content C _H of the raw material powder in the dehydrogenation-recombination reaction completion time of the first stage, affected by the R component amount of the raw material alloy. For C _H> 0.00750 × C _R, no effect of improving the coercive force, also takes much time to process. On the other hand, in the case of C _H <0.000725 × C _R, there is no effect of improving the coercive force.
[0043]
In the second stage of the dehydrogenation treatment, since the reaction rate is low, it takes a long time to reduce the amount of remaining hydrogen to 0.002 wt% (20 ppm) or less, for example. In practical use, if the hydrogen content is 0.01 wt% (100 ppm) or less, the magnetic properties of the magnetic powder hardly change.
[0044]
In order to reduce the amount of hydrogen, after the dehydrogenation / recombination reaction in the second stage is completed and the amount of hydrogen in the raw material powder becomes 0.01 wt% (100 ppm) or less, the raw material is decompressed again, etc. The amount of hydrogen in the powder may be reduced.
[0045]
Further, the heat treatment for adjusting the amount of hydrogen may be performed subsequently to the heat treatment in this step or may be performed separately after being cooled. In any case, the magnetic properties are hardly affected. However, although not clarified yet, the amount of hydrogen may affect the stability of the magnetic powder, such as the oxidation resistance.
[0046]
In the present invention, measurement of the hydrogen amount is indispensable for evaluating the hydrogen amount and the hydrogen release rate, but it is difficult to continuously monitor the hydrogen amount of the raw material powder being processed. Therefore, by performing the process for evaluating the hydrogen amount under the same conditions in advance before the actual process and obtaining the relationship between the process time and the change in the hydrogen amount in advance, the process of the present invention can be controlled by managing the process time. .
[0047]
【Example】
Example 1
An ingot with a composition of 27.5% Nd-bal.Fe-9.5% Co-1.0% Ga-0.1% Zr-1.0% B (Wt%) was homogenized in Ar at 1100 ° C for 24 hours, and further 0.1 MPa Then, hydrogen embrittlement treatment was performed at 400 ° C. for 2 hours in a 10 l / min hydrogen gas stream, cooled, and then sized with a sieve having an opening of 425 μm to obtain a raw material powder. 50 g of this raw material powder was filled into a SUS310S container having an opening size of 30 × 45 mm, and loaded into a tubular heat treatment furnace having an Inconel furnace core tube, and subjected to HDDR treatment.
[0048]
The HDDR treatment conditions were as follows: in a hydrogen atmosphere of 0.1 MPa (5 l / min flow), the temperature was raised to 840 ° C at 15 ° C / min, held at that temperature for 2 hours, and then maintained at 10 l / min Ar while maintaining the temperature. The gas was purged with Ar for 5 minutes, and then the inside of the furnace was evacuated by a rotary pump while introducing Ar gas at the same temperature at 20 l / min, and the reduced pressure Ar treatment was performed to maintain the furnace pressure at 6 kPa for a predetermined time.
[0049]
After a predetermined time, the vacuum exhaust was stopped while the furnace temperature was maintained, the atmospheric pressure was restored to atmospheric pressure, the treatment was performed for a predetermined time while flowing 10 l / min Ar, and then cooled. Thereafter, the results of measuring the magnetic properties of the obtained magnetic powder are shown in Table 1.
[0050]
The composition of the magnetic powder, corresponding to a particularly preferred range of the present invention, hydrogen content C _H at reduced dehydrogenation end is, 0.020 wt% (200 ppm) or more and less 0.206wt% (2060ppm). The conditions indicated by * in the table are Examples (1G1, 1G3) outside the above-mentioned particularly preferable range. The hydrogen analysis value measured by the inert gas extraction method of the raw material powder cooled to the reduced pressure Ar treatment under the same treatment conditions as the above treatment is the estimated hydrogen amount after the reduced pressure Ar treatment during the treatment in Table 1. It is written together in the table.
[0051]
As is clear from Table 1, when the amount of hydrogen in the raw material powder was 0.020 to 0.206 wt% in the dehydrogenation treatment using the reduced pressure Ar treatment method, switching to the dehydrogenation treatment using the Ar flow method was performed. It can be seen that a high coercive force and a large remanent magnetization were obtained at the same time when it was 0.010 wt% or less.
[0052]
[Table 1]

[0053]
Example 2
An ingot having a composition of 29.5% Nd-bal.Fe-15.0% Co-0.3% Ga-0.1% Zr-1.0% B (Wt%) was subjected to homogenization treatment at 1100 ° C. for 24 hours in Ar, and further 0.1 MPa, Hydrogen embrittlement treatment was performed at 400 ° C. for 2 hours in a 10 l / min hydrogen gas stream, and after cooling, the mixture was sized with a sieve having an opening of 425 μm to obtain a raw material powder. 200 g of this raw material powder was filled into a SUS310S container having an opening size of 80 × 200 mm, and loaded into a tubular heat treatment furnace having an Inconel furnace core tube, and subjected to HDDR treatment.
[0054]
The treatment conditions were as follows: in a 0.1 MPa hydrogen atmosphere (5 l / min flow), the temperature was raised to 820 ° C. at 15 ° C./min, held at that temperature for 2 hours, and then maintained at that temperature for 10 l / min Ar gas. 5 minutes, and then, while introducing Ar gas at the same temperature, evacuate the furnace with a rotary pump and adjust the Ar introduction amount and the opening of the exhaust valve to maintain the specified furnace pressure for a specified time. The reduced pressure Ar treatment was performed.
[0055]
After a predetermined period of time, while maintaining the furnace temperature, evacuation was stopped, the atmospheric pressure was restored to atmospheric pressure, and after 6.0 k treatment with flowing 10 l / min Ar, it was cooled. Thereafter, the magnetic properties of the obtained magnetic powder were measured, and the results are shown in Table 2.
[0056]
The composition of the magnetic powder, corresponding to a particularly preferred range of the present invention, hydrogen content C _H at reduced dehydrogenation end is, 0.021wt% (210ppm) or more and less 0.221wt% (2210ppm). In the table, the conditions indicated by * are examples (2G2) outside the above-mentioned particularly preferable range. The hydrogen analysis value of the raw material powder cooled to the reduced pressure Ar treatment under the same treatment conditions as in the above treatment is also shown in the table as the estimated hydrogen amount after the reduced pressure Ar treatment during the treatment of Table 2.
[0057]
As is clear from Table 2, it can be seen that the coercive force improving effect is observed when the hydrogen release rate in the first-stage dehydrogenation treatment is in the range of 0.1 to 5.0 wt% / h.
[0058]
[Table 2]

[0059]
Example 3
100 g of the raw material powder used in Example 2 was filled into a SUS310S container having an opening size of 60 × 100 mm, and loaded into a tubular heat treatment furnace having an Inconel furnace core tube, and subjected to HDDR treatment. The treatment conditions were as follows: in a 0.1 MPa hydrogen atmosphere (5 l / min flow), the temperature was raised to 820 ° C. at 15 ° C./min, held at that temperature for 2 hours, and then maintained at that temperature for 10 l / min Ar gas. For 5 minutes at the same temperature, and then evacuating the furnace with a rotary pump while introducing Ar gas at the same temperature, adjusting the Ar introduction amount and the opening of the exhaust valve, and adjusting the pressure in the furnace for a predetermined time A reduced pressure Ar treatment was performed.
[0060]
After a predetermined period of time, while maintaining the furnace temperature, evacuation was stopped, the atmospheric pressure was restored to atmospheric pressure, and after 6.0 k treatment with flowing 10 l / min Ar, it was cooled. Table 3 shows the magnetic properties of the magnetic powder obtained at this time. The hydrogen analysis values of the raw material powder cooled to the reduced pressure Ar treatment under the same treatment conditions as in the above treatment are also shown in the table as the estimated hydrogen amount after the reduced pressure Ar treatment during the treatment shown in Table 3.
[0061]
As is clear from Table 3, the hydrogen release rate in the second stage dehydrogenation process can be adjusted by controlling the total atmospheric pressure, in the range of 0.01 to 0.20 wt% / h, and in the first stage. It can be seen that the effect of improving the coercive force is particularly recognized if the value is smaller than the hydrogen release rate in the dehydrogenation treatment.
[0062]
[Table 3]

[0063]
【The invention's effect】
In the dehydrogenation process in the HDDR treatment method, the present invention reduces the hydrogen content of the raw material powder to 0.010 wt% (100 ppm) or less at a large hydrogen release reaction rate until the amount of hydrogen in the raw material powder reaches 0.2 wt% (2000 ppm) to 0.050 wt% (500 ppm). The rare earth alloy powder for permanent magnets having a high coercive force is produced without increasing the amount of heavy rare earths in the composition and reducing the residual magnetization by proceeding with the treatment at a low reaction rate until it reaches the target. be able to.
[Brief description of the drawings]
FIG. 1 is a heat pattern diagram showing an HDRR process according to the present invention.
FIG. 2 is a graph showing the relationship between the time in the HDDR treatment process and the amount of hydrogen in the raw material powder.

Claims

R ₂ T ₁₄ B (B can be partly or wholly replaced by C) Rare earths that ingot, disproportionate, dehydrogenate, recombine ingots or powders made of an alloy whose compound is 50 vol% or more In the method for producing an alloy powder, the first stage hydrogen release rate in dehydrogenation is 0.1 wt% / h to 5.0 wt% / h, and the second stage hydrogen release rate is 0.01 wt% / h-0. A method for producing a rare earth alloy powder for permanent magnets in which the recombination reaction rate is changed in multiple stages by setting the hydrogen release rate in the second stage to a release rate smaller than that in the first stage at 20 wt% / h .

Dehydrogenation, the method of producing the rare-earth alloy powder for a permanent magnet according to claim 1 that is regulated by the total pressure of the atmosphere by an inert gas Nagareki during, and / or evacuation.

The first step in the dehydrogenation is from the start of the reaction until the hydrogen concentration C _H of the workpiece reaches the range of the following expression, the second stage, to the hydrogen concentration C _H is equal to or less than 0.01 wt% The method for producing a rare earth alloy powder for a permanent magnet according to claim 1 , wherein the range is a range.
0.000725 × C _R ≦ C _H ≦ 0.00750 × C _R
However, C _H is the hydrogen concentration (wt%) in the alloy, and C _R is the rare earth component concentration (wt%) in the alloy.