JP4976626B2 - Sintered alloy material, method for producing the same, and mechanical structural member using the same - Google Patents
Sintered alloy material, method for producing the same, and mechanical structural member using the same Download PDFInfo
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【０００１】
【発明の属する技術分野】
本発明は焼結合金材料およびその製造方法に関する。より詳細には、Ｍｏ2ＮｉＢ2型複硼化物を主体とする焼結合金において、焼結合金の表面に窒化物又は窒化物と酸化物を形成させることにより、耐磨耗性、耐食性、離型性を大幅に向上させた焼結合金材料、その製造方法、およびその焼結合金を用いた機械構造部材に関する。
【０００２】
【従来の技術】
樹脂などの射出成形機や溶融金属鋳造装置などの機械構造部材、特に耐磨耗性が要求される用途に用いられる部材としてはシリンダー、スクリュー、プランジャー、成形金型などがある。これらの部材としては、セラミックスや工具鋼に各種の表面処理を施したものが使用されている。サイアロン、アルミナなどのセラミックスの中でも、特にサイアロンは従来のセラミックスに比べて強度、靱性、および耐磨耗性に優れており、各種のエンジニアリング用部品に適用されている。しかしながら、工具鋼やＳＫＤ６１をはじめとする熱間工具鋼などよりも強度に劣り、ダイカストマシンのスリーブなどに適用した場合、割れなどの問題があった。
【０００３】
また、近年は構成部材に対する要求が厳しくなってきており、これらの工具鋼や熱間工具鋼に各種の窒化処理を施したものが用いられるようになっている。窒化処理の中でもＰＶＤやＣＶＤなどによるＴｉＮ、ＣｒＮなどのコーティングは耐食性や耐磨耗性の向上には有効であるが、母材に対するコーティング皮膜の密着性に乏しく、ヒートクラックなどの欠陥が発生しやすい。これらの欠陥は部材を短寿命化し、その部材を装填した機械装置の生産性を低下させる要因となる。
【０００４】
そのため、溶融アルミニウム等の溶融金属に対する耐食性に優れているのみならず、セラミックス材料よりも優れた耐熱衝撃性を有する材料として、Ｎｉ基の結合相を有する３元系複硼化物が提案（例えば特開平２−２９９７４０号公報、特開平５−３２０８１６号公報）されている。しかしながら、Ｎｉ基の結合相は高温における強度などの高温特性には優れているものの、溶融金属に対しては浸食されたり相手材と凝着するなど、耐食性が十分でなく、長時間使用した場合の部材の耐久性に問題があった。
【０００５】
また、特開平５−１４８５８８号公報や特開平９−２１７１６７号公報は、鋼、鋳鉄、およびステンレス鋼表面に酸化物皮膜を設けることにより、部材の耐食性の改善を図ることを開示している。しかし、形成された酸化物皮膜は非常に薄く、硬度も低いために、耐摩耗性強度が必要となるプランジャー、スリーブには適用不可能であるばかりでなく、母材との密着性に乏しいことによる、酸化物皮膜の剥離等による溶融金属中への混入といった問題の生じる恐れがある。
【０００６】
【発明が解決しようとする課題】
本発明においては、溶融樹脂や溶融金属に対する耐食性、および耐摩耗性を改善するとともに、優れた離型性をも有し、さらに優れた耐薬品性も有するＭｏ2ＮｉＢ2型複硼化物を主体とする焼結合金材料、その製造方法、およびその焼結合金材料を用いた機械構造部材を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明の焼結合金材料は、Ｍｏ２ＮｉＢ２型複硼化物とＮｉ基結合相からなる焼結合金の最表面に窒化物皮膜、又は該窒化物皮膜上にさらに酸化物皮膜を形成してなり、前記窒化物皮膜がＭｏ、Ｃｒ、Ｎｉ、Ｂの金属元素と窒素を主体とする（Ｎｉ，Ｍｏ，Ｃｒ，Ｂ）ｍＮｎ型の複合窒化物からなる皮膜であることを特徴とする焼結合金材料である。前記窒化物皮膜の厚さは、０．５〜２０μｍであること、及び前記酸化物皮膜の厚さは０．５〜２０μｍであることが望ましい。
【０００８】
そして、前記酸化物皮膜はＭｏ、Ｃｒ、Ｎｉ、Ｂの金属元素と酸素を主体とする（Ｎｉ，Ｍｏ，Ｃｒ，Ｂ）ｘＯｙ型の複合酸化物からなる皮膜であることが望ましい。
【０００９】
前記焼結合金の組成としては、３〜７．５％のＢ、２１〜７９．９％のＭｏ、２〜３５％のＣｒ、残部が１０％以上のＮｉおよび不可避的不純物からなる組成が採用できる。あるいは、前記焼結合金の前記全組成に対して、０．１〜８％のＭｎを含有すること、前記焼結合金に含有されるＭｏ含有量の一部を、全組成に対して０．１〜３０％のＷで置換してなること、前記焼結合金に含有されるＭｏ含有量の一部を、全組成に対して０．１〜１０％のＮｂで置換してなること、前記焼結合金に含有されるＭｏ含有量の一部を、全組成に対してＷおよびＮｂの両者の合計で０．２〜３０％置換してなること、前記焼結合金に含有されるＮｂ含有量の一部又は全部をＺｒ、Ｔｉ、Ｔａ、Ｈｆのいずれか１種又は２種以上と置換してなること、前記焼結合金に含有されるＮｉ含有量の一部を、全組成に対してＦｅおよび／又はＣｏのいずれか一方又は両者の合計で０．１〜２０％置換してなること、焼結合金に含有されるＣｒ含有量の一部を、全組成に対して０．１〜２５％のＶで置換してなることの何れかの組成も採用することができる。
【００１０】
また本発明の焼結合金材料の製造方法は、上記のいずれかの焼結合金を窒素雰囲気あるいは窒素を含む還元性雰囲気中で加熱してその表面に窒化物皮膜を形成させる、
又は上記のいずれかの焼結合金を大気中あるいは酸素を含む雰囲気中で加熱してその表面に酸化物皮膜を形成させた後、窒素を含む還元性雰囲気中で加熱し、酸化物皮膜を還元して窒化物皮膜を形成させる、又は
上記のいずれかの焼結合金を大気中あるいは酸素を含む雰囲気中で加熱してその表面に酸化物皮膜を形成させた後、窒素雰囲気中で加熱し、酸化皮膜の下層に窒化物皮膜を形成させることを特徴とするものである。前記窒素を含む還元性雰囲気又は窒素雰囲気の圧力が０．１０３〜１ＭＰａであることが望ましい。
【００１１】
さらに本発明の機械構造部材は、上記のいずれかの焼結合金材料の製造方法を用いて作成した焼結合金材料を部材とすることを特徴とする機械構造部材であり、
機械構造部材が射出成形機用部材、又は溶融金属鋳造装置用部材であることを特徴とする。
【００１２】
【発明の実施の形態】
本発明は、Ｍｏ２ＮｉＢ２型複硼化物を主体とする焼結合金の最表面に窒化物皮膜、又は上層の酸化物皮膜と下層の窒化物皮膜の２層皮膜を形成することにより、溶融樹脂や溶融金属に対して優れた耐磨耗性、耐食性、離型性を付与するものである。
本発明の機械構造部材の母材となる焼結合金において、Ｂ、Ｍｏ、Ｃｒの含有量を一定範囲内に限定することにより、複硼化物とＮｉ基の結合相との２相組織の焼結合金となり、優れた耐磨耗性、耐食性が得られるばかりでなく、上記の窒化物皮膜又は窒化物皮膜と酸化物皮膜からなる表面処理層を緻密かつ安定に形成させることにより、溶融樹脂や溶融金属に対する優れた離型性をも付与することができる。
また、母材中にＭｎを含有させることにより、母材の機械的特性、表面処理層の耐食性および自己修復性が向上し、さらにＷを含有させることにより母材の機械的特性、表面処理層の耐食性および耐摩耗性が向上する。またさらに、Ｎｂ、Ｚｒ、Ｔｉ、Ｔａ、Ｈｆを含有させることにより、表面処理層の耐食性および耐摩耗性が向上し、Ｆｅおよび／又はＣｏを含有させることにより母材の耐熱衝撃性および高温強度が向上する。
以下に本発明を詳細に説明する。
【００１３】
本発明者らは本発明に至るまでに、Ｍｏ2ＮｉＢ2型複硼化物を主体とする焼結合金が、溶融樹脂や溶融金属が使用される腐食雰囲気や高温度領域などの環境下で耐えられるだけの十分な耐食性および耐磨耗性を有していることを見出していた。しかしながら、近年、樹脂を高性能化するためにガラス繊維やフェライト粒子などの各種フィラーが多量に添加され、機械構造部材のさらなる耐磨耗性の向上が必要とされていた。また、溶融金属に対しては、長時間溶融金属と接触した場合、Ｎｉ基の結合相が溶融金属と反応し、耐食性、離型（剥離）性の改善が必要であることが判明した。そこで種々検討した結果、Ｍｏ2ＮｉＢ2型複硼化物を主体とする焼結合金の表面に、緻密かつ安定な窒化物皮膜又は窒化物皮膜と酸化物皮膜からなる表面処理層を形成させることにより、母材の強度を維持させたまま、表面硬度を上昇させ、長期間使用しても溶融金属および溶融樹脂に対する耐食性、離型性、耐磨耗性が大幅に向上することを見出した。
【００１４】
これは、窒化物皮膜が母材の主要構成元素であるＭｏ、Ｃｒ、Ｎｉ、Ｂの金属元素と窒素を主体として構成される（Ｎｉ，Ｍｏ，Ｃｒ，Ｂ）ｍＮｎ型の複合窒化物からなる安定かつ緻密な皮膜であり、さらに酸化物皮膜も、母材の主要構成元素であるＭｏ、Ｃｒ、Ｎｉ、Ｂの金属元素と窒素を主体として構成される（Ｎｉ，Ｍｏ，Ｃｒ，Ｂ）ｘＯｙ型の複合酸化物からなる安定かつ緻密な皮膜であり、これらの表面処理層が保護膜を構成して溶融金属に対する耐食性や耐磨耗性を大幅に改善向上させるためである。さらに、窒化物皮膜を形成させる前に予め酸化物皮膜を形成させておき、この酸化物皮膜を還元しながら窒化することにより、先に生成した酸化物層によって窒化が促進され、窒化物皮膜をより厚く製膜することができる。
【００１５】
本発明の焼結合金は上記４元素に加えて、選択的にＭｎ、Ｗ、Ｎｂ、Ｚｒ、Ｔｉ、Ｔａ、Ｈｆ、Ｆｅ、Ｃｏ、Ｖが添加される場合もあり、この場合は合金表面に形成される窒化物皮膜や酸化物皮膜は、Ｍｏ、Ｃｒ、Ｎｉ、Ｂに加えて上記の選択的に添加される元素および窒素又は酸素から構成される。窒化物や酸化物にＭｏ、Ｃｒ、Ｎｉ、Ｂが含有されない場合は、表面処理層の結合力が弱く、かつ、母材との密着性が低下するために亀裂や剥離を生じやすく、耐摩耗性も十分でない。
複合窒化物としては、具体的には（Ni、Cr）2Mo3N、 CrN、Cr2N、MoN、Mo2N、BNなどが挙げられる。また複合酸化物としては、具体的には（Ｎｉ，Ｍｏ，Ｃｒ，Ｂ）2Ｏ3、（Ｎｉ，Ｍｏ，Ｃｒ，Ｂ）3Ｏ4、（Ｎｉ，Ｍｏ，Ｃｒ，Ｂ）Ｏ、（Ｎｉ，Ｍｏ，Ｃｒ，Ｂ）Ｏ3、（Ｎｉ，Ｍｏ，Ｃｒ，Ｂ）Ｏ2.7 〜 2.9、（Ｎｉ，Ｍｏ，Ｃｒ，Ｂ）Ｏ2などが挙げられる。
【００１６】
上記の複合窒化物や複合酸化物は、Ｍｏ2ＮｉＢ2型の複硼化物が窒化又は酸化されることにより得られるため、母材としては合金組成が主にＭｏ、Ｃｒ、Ｎｉ、ＢからなるＭｏ2ＮｉＢ2型複硼化物を主体とする焼結合金である必要がある。
この焼結合金において、Ｂは焼結合金の母材の硬質相となる複硼化物および表面処理層を形成するために必要不可欠な元素である。また、Ｂを含有した表面処理層は母材との密着性を向上させる効果を示す。Ｂ量が３％未満であると硬質相の割合が３５％を下回り、母材の機械的特性が劣る。一方、７．５％を超えると硬質相の割合が９５％を上回り、強度および耐熱衝撃性が低下する。よって、Ｂ含有量は３〜７．５％に限定する。
【００１７】
ＭｏはＢと同様に複硼化物および表面処理層を形成するために不可欠な元素である。母材においては、一部は焼結合金の結合相中に固溶し、母材の機械的強度を向上させる。しかし、適正量（７９．９％）を超えて含有させるとＭ6Ｃ型炭化物などの金属間化合物を形成して母材の強度が低下する。一方、含有量が２１％未満であると、Ｎｉ2ＢなどのＮｉ硼化物が形成するために母材の強度が低下する。よってＭｏ含有量は２１〜７９．９％に限定する。
【００１８】
Ｃｒは複硼化物中のＮｉと置換固溶し、複硼化物の結晶構造を正方晶に安定化させる効果を有する。また、Ｎｉ結合相中にも固溶し、焼結合金の耐食性、耐摩耗性、高温特性、および機械的特性を大幅に向上させる。しかし、３５％を超えて含有させるとＣｒ5Ｂ3などの硼化物を形成し、母材の強度が低下する。一方、２％未満になると表面処理層のＣｒ量が不十分となり、溶融金属や溶融樹脂に対する耐食性の低下を生じる。よって、Ｃｒ含有量は２〜３５％に限定する。
【００１９】
Ｍｎは母材の複硼化物の粒成長を抑制し、合金組織を微細化させることにより、機械的特性を著しく向上させる。また、Ｍｎの添加により、焼結時に型くずれの少ない良好な形状の焼結体が得られ、ニヤネット化が図られる効果を示す。さらにＭｎは酸素との親和力が強いため、表面処理層の厚膜化をもたらし、部材の耐久性を高める。含有量が０．１％未満では特性改善の効果が認められず、８％を超えて含有させると母材の機械的特性が低下する。よってＭｎの含有量は全組成に対して０．１〜８％に限定する。
【００２０】
ＷはＭｏと置換させることが可能な元素であり、母材の強度を向上させる効果を示すばかりでなく、表面処理層の耐食性および耐摩耗性を向上させる。しかし、Ｗの含有量が０．１％未満であるとその特性改善効果が認められない。一方、３０％を超えて含有させてもその効果が認められなくなるばかりでなく、部材の比重が高まり、製品重量が増大する。よって、Ｗの含有量は全組成に対して０．１〜３０％に限定する。
【００２１】
Ｎｂ、Ｚｒ、Ｔｉ、Ｔａ、ＨｆはＭｏと置換させることが可能な元素であり、母材の複硼化物に固溶するとともに一部は他の硬質粒子（硼化物、酸化物、炭化物、および窒化物）を形成し、機械的特性を向上させる。また、これらの元素は酸素との親和力が強いことから複合酸化物と結合し、より緻密で密着性に優れた表面処理層の形成に効果がある。また、これらの元素を２種以上複合含有させても単独で含有させた場合と同様な効果が得られる。しかし、含有量が０．１％未満であると改善効果が認められず、１０％を超えて含有させると焼結合金の焼結性が低下し、強度の低下を招くばかりでなく、これらの元素は高価であるためコストの上昇を招く。よってＮｂ、Ｚｒ、Ｔｉ、Ｔａ、Ｈｆの含有量は全組成に対して１種又は２種以上の合計で０．１〜１０％に限定する。
【００２２】
ＦｅはＮｉと置換可能な元素であり、表面処理層中にＦｅを複合した窒化物および酸化物皮膜を形成することで、表面処理層の自己修復性が向上する。また、安価なＦｅを使用することで、部材のコスト削減が図れる。含有量が０．１％未満であるとその改善効果が認められず、２０％を越えて含有させると、耐食性が低下するばかりでなく、母材の熱衝撃性および強度が低下する。よって、Ｆｅの含有量は全組成に対して０．１〜２０％に限定する。
【００２３】
ＣｏもＦｅと同様にＮｉと置換可能な元素であり、本発明の焼結合金の硼化物、およびＮｉ基結合相の両相に固溶し、焼結合金の熱衝撃性および高温強度を向上させる。含有量が０．１％未満であるとその改善効果が認められず、２０％を超えて含有させてもその特性向上の効果が認めらないないだけでなく、コストの上昇を招く。よって、Ｃｏの含有量は全組成に対して０．１〜２０％に限定する。ＦｅおよびＣｏは上記のように単独で含有させてもよいし、両者を含有させてもよい。両者を含有させる場合も、含有量は全組成に対して０．１〜２０％に限定する。
【００２４】
ＶはＣｒと置換させることが可能な元素であり、また、Ｃｒと同様に複硼化物中のＮｉと置換固溶し、複硼化物の結晶構造を正方晶に安定化させる効果を有する。また、Ｎｉ結合相中にも固溶し、焼結合金の耐食性、耐摩耗性、高温特性、および機械的特性を大幅に向上させる。さらに表面処理層においては、自己修復性の向上効果をもたらす。０．１％未満であるとこれらの特性改善効果が認められず、２５％を超えて含有させると、窒化物皮膜や酸化物皮膜の密着性が低下し、溶融金属や溶融樹脂への不純物混入の原因となり得る。よってＶの含有量は全組成に対して０．１〜２５％に限定する。
【００２５】
本発明の焼結合金は上記成分元素のほか、残部がＮｉで構成される。Ｎｉは複硼化物および結合相を構成する元素であり、表面処理層を構成する複合窒化物および複合酸化物の形成に必要不可欠である。本発明の焼結合金においては、Ｎｉの含有量が１０％未満であると複硼化物を十分に形成させることができないばかりか、結合相中のＮｉ含有量が不足して、焼結時に十分な液相が出現せず緻密な焼結体が得られず、強度が低下する。そのため、本発明の硬質合金にはＮｉを１０％以上含有させる必要がある。本発明の焼結合金においてＮｉを１０％以上含有させることができない場合は、許容範囲内においてＮｉ以外の各元素の含有量を減じて、１０％以上のＮｉを含有させることは言うまでもない。
【００２６】
本発明の焼結合金が含有する不可避的不純物元素の主なものはＰ、Ｓ、Ｃ、Ｓｉ、Ａｌなどであり、焼結合金の強度を維持させるためにはこれらの含有量は極力少なくすることが望ましい。これらの元素の含有量が合計で１％以下であれば、機械的特性に与える影響は比較的小さい。
【００２７】
次に本発明の製造方法について説明する。
まず母材である焼結合金の製造方法について説明する。Ｎｉ、Ｍｏ、Ｃｒ、Ｍｎ、Ｗ、Ｎｂ、Ｚｒ、Ｔｉ、Ｔａ、Ｈｆ、Ｆｅ、Ｃｏ、Ｖの１種または２種以上の元素とＢからなるＢ合金の粉末、またはこれらのＢ合金粉末とこれら元素の１種または２種以上からなる合金の粉末、またはＢ単体とＮｉ、Ｍｏ、Ｃｒ、Ｍｎ、Ｗ、Ｎｂ、Ｚｒ、Ｔｉ、Ｔａ、Ｈｆ、Ｆｅ、Ｃｏ、Ｖの単体粉末、またはＢ単体とこれらの１種または２種以上の合金からなる粉末を所定の合金組成となるように配合し、振動ボールミル等を用いて有機溶媒中で湿式粉砕後、造粒、成形し、該成形体を真空中、還元ガス中、または不活性ガス中などの非酸化性雰囲気中で液相焼結する。
【００２８】
なお、上記の焼結合金の硬質相となる複硼化物は、上記原料粉末が焼結中に反応することによって形成されるが、あらかじめＭｏおよびＮｉ、さらに上記の選択的に添加される元素からなる複硼化物、またはＢ単体の粉末とＭｏおよびＮｉさらに上記の選択的に添加される元素の粉末を炉中で反応させることにより、Ｍｏ2ＮｉＢ2型複硼化物を製造し、さらに結合組成のＮｉ、Ｍｏ、Ｆｅ、Ｃｏ、および上記の選択的に添加される元素の粉末を所定の合金組成となるように配合した粉末を用いても差し支えない。
【００２９】
上記のようにして調製した粉末を所定形状に圧粉成形した後、加熱して焼結する。焼結は通常１３７３〜１６７３Ｋの焼結温度で５〜９０分間行う。焼結温度が１３７３Ｋ未満の場合は液相が十分に出現せず、空孔の多い焼結体が得られ、十分な強度が得られない。一方、焼結温度が１６７３Ｋを超えると液相は十分に出現するものの、結晶粒が粗大化し強度が低下する。また、焼結時間が５分未満であると、元素の拡散が十分でなく、十分に高密度化しない。一方、９０分を越えて焼結してもそれ以上の強度上昇は認められず、場合によっては強度が低下することもある。以上のような液相が出現する焼結条件で焼結することにより、空孔が消失し、ほぼ１００％の密度の硬質合金が得られる。液相を出現させずに空孔を消失させる方法として、熱間静水圧プレス法、ホットプレス法、通電焼結法などがあり、これらの方法を用いても空孔を消失させることができる。またこれらの方法と液相焼結法を併用してもよい。
【００３０】
上記のようにして得られる本発明の焼結合金は、焼結体単体としてのみ用いられるばかりでなく、鋼材と接合させて複合材として用いることも可能である。すなわち、本発明の焼結合金は超硬合金のように鋼材にロウ付けして使用するばかりでなく、ロウ材を使用することなく直接鋼材と接合させたり、鋼材表面に本発明の焼結合金の原料粉末のスラリーを塗布した後、原料粉末を焼結するとともに鋼材と拡散接合させることも可能であり、強固な接着が得られる。また、焼結と鋼材を同時に接合する焼結接合法を適用することも可能であり、鋼材は熱ダメージによる強度低下を招来することなく、複合材料をアルミニウムなどの溶融金属のダイカストマシン用部材として用いた場合、耐熱衝撃性や溶融金属に対して耐食性および耐摩耗性が必要とされる部分にのみ、本発明の焼結合金を必要最小限に用いることにより、金型などの部材を低価格で製造することが可能となる。
次に、上記のようにして得られた母材表面に形成させる表面処理層の製造方法について説明する。
【００３１】
窒化物皮膜のみを形成させる場合は、得られた母材を所望の形状に機械加工を行い、表面を洗浄脱脂した後、０．１０３〜１ＭＰａの窒素雰囲気もしくは窒素を含有する還元性雰囲気中で７７３〜１８７３Ｋの温度で５分〜５０時間保持することにより、０．５〜２０μｍの厚さの窒化物皮膜を形成させる。処理温度が７７３Ｋ未満の場合は、長時間の処理を行っても優れた耐食性および耐磨耗性が得られる十分な厚みを有する窒化物皮膜を形成することはできない。一方、１８７３Ｋを超える処理温度で処理した場合は、窒化物皮膜の剥離が生じる。処理時間が５分未満の場合は十分な厚みの窒化物皮膜の形成が認められず、５０時間を超えて処理を行っても、窒化物皮膜の成長は飽和し、剥離を生じるばかりでなく、コストの上昇につながる。よって、窒化処理は７７３〜１８７３Ｋの温度で５分〜５０時間、好ましくは９７３〜１６７３Ｋで１〜３０時間行う。雰囲気の圧力は処理槽外の大気が雰囲気中に侵入することがないように、大気圧よりも高めにする必要があり、また圧力を高めると膜厚が厚くなる傾向があるので、０．１０３〜１ＭＰａの圧力下で処理することが好ましい。このようにして０．５〜２０μｍの厚さの窒化物皮膜が得られる。窒化物皮膜の厚さが０．５μｍ未満の場合は十分な耐食性および耐磨耗性が得られず、一方２０μｍを超えると耐食性および耐磨耗性の向上効果が飽和し、経済的に有利でなくなる。
【００３２】
窒化物皮膜のみを形成させる別法として、得られた母材を所望の形状に機械加工を行い、表面を洗浄脱脂した後、まず大気中もしくは酸素雰囲気中で７７３〜１８７３Ｋの温度で５分〜５０時間保持して酸化物皮膜を形成させる。酸化物皮膜の形成手段としては、高温大気酸化法、高温湿潤水素酸化法等があるが特に限定されない。処理温度が７７３Ｋ未満の場合は、長時間の処理を行っても優れた耐食性が得られる十分な厚みを有する酸化物皮膜を形成することはできない。一方、１８７３Ｋを超える処理温度で処理した場合は、酸化物皮膜の剥離が生じる。処理時間が５分未満の場合は十分な厚みの酸化物皮膜の形成が認められず、５０時間を超えて処理を行っても、酸化物皮膜の成長は飽和し、剥離を生じるばかりでなく、コストの上昇につながる。次いで０．１０３〜１ＭＰａの窒素を含む還元性雰囲気中で７７３〜１６７３Ｋの温度で１〜４０時間保持する。このように、大気中または酸素を含む雰囲気中で加熱して酸化物皮膜を形成させ、次いで窒素を含む還元性雰囲気中で加熱すると、同一条件で窒化処理を行っても窒化処理単独の場合よりも厚い窒化物皮膜が得られ、厚膜化しやすくなる。
【００３３】
酸化物皮膜を形成させた後、窒化処理すると、窒化物皮膜は母材表面、すなわち酸化物皮膜の下層に形成される。この処理を実施する場合は、上記と同様にして母材に機械加工を施し、表面を洗浄脱脂した後、まず大気中もしくは酸素雰囲気中で７７３〜１８７３Ｋの温度で５分〜５０時間保持して０．５〜２０μｍの厚さの酸化物皮膜を形成させる。酸化物皮膜の形成手段としては、高温大気酸化法、高温湿潤水素酸化法等があるが特に限定されない。処理温度が７７３Ｋ未満の場合は、長時間の処理を行っても優れた耐食性が得られる十分な厚みを有する酸化物皮膜を形成することはできない。一方、１８７３Ｋを超える処理温度で処理した場合は、酸化物皮膜の剥離が生じる。処理時間が５分未満の場合は十分な厚みの酸化物皮膜の形成が認められず、５０時間を超えて処理を行っても、酸化物皮膜の成長は飽和し、剥離を生じるばかりでなく、コストの上昇につながる。よって、酸化処理は７７３〜１８７３Ｋの温度で５分〜５０時間、好ましくは９７３〜１６７３Ｋで１〜３０時間行う。このようにして０．５〜２０μｍの厚さの酸化物皮膜が得られる。次いで窒素を含んだ雰囲気で窒化処理を行う。窒化物皮膜は焼結合金母材と酸化物皮膜の界面に生成する。このようにして０．５〜２０μｍの厚さの窒化物皮膜の上層に酸化物皮膜を有する２層皮膜が得られる。このように窒化物皮膜上に酸化物皮膜が存在すると、酸化物が潤滑効果を示し、耐磨耗性がさらに向上する。
以下、実施例を示し本発明を具体的に説明する。
【００３４】
【実施例】
（実施例）
Ｂ粉末および金属粉末を、表１〜４に示す配合比に調整した後、振動ボールミルを用いて、アセトン中で２５時間湿式混合粉砕した。ボールミルで粉砕した後の粉末を乾燥、造粒し、得られた微粉末を所定の形状にプレス成形した後、真空度：≦１．３Ｐａの真空中で第１段加熱として１０Ｋ／分の昇温速度で昇温し、表５〜９に示す温度で表５〜９に示す時間加熱した後炉冷して焼結合金を得た。
【００３５】
【表１】
【表２】
【表３】
【表４】
【表５】
【表６】
【表７】
【表８】
【表９】
以上のようにして得られた焼結合金を所望の形状に加工し、脱脂した後、表５〜９に示す雰囲気中で表５〜９に示す加熱条件で加熱した後炉冷し、焼結合金表面に複合窒化物皮膜または複合酸化物皮膜と複合窒化物皮膜の２層皮膜からなる表面処理層を形成させた。一部の焼結合金は比較用に上記の加熱処理を施さずに、下記の特性評価に供した。
【００４５】
上記のようにして得られた表１〜９に示した焼結合金の強度、窒化物皮膜および酸化物皮膜の膜厚、耐磨耗性、耐食性、および離型性を以下のようにして評価した。
【００４６】
[強度]
焼結したままの硬質合金、および硬質合金に大気中の加熱処理を施した溶融金属用部材から試験片を切り出し、ＪＩＳ Ｈ ５５０１に基づいて抗折力（３点曲げ試験）を測定した。抗折力が大きいほど強度が優れており、１．５ＧＰａを超えるものを本発明の対象とする。結果を表１０〜１４に示す。
【００４７】
[窒化物皮膜および酸化物皮膜の膜厚]
硬質合金の最表面に窒素化物皮膜または酸化物皮膜と窒素化物皮膜を形成させた焼結合金から表面皮膜を含む断面で試験片を切り出し、樹脂に埋め込んで鏡面研磨した後、倍率：３０００倍でＳＥＭ像を各試験片について３視野撮影し、窒素化物皮膜の厚さ、および酸化物皮膜の厚さを測定し、その平均値を皮膜厚さとした。結果を表１０〜１４に示す。
【００４８】
[耐磨耗性]
摩耗試験は大越式迅速摩耗試験機を用いた。これはリング・オン・プレートタイプの試験機であり、アルミニウム製の回転リングを回転させながら硬質合金で作製したブロック上の平板試験片を押し付けて摩擦し、平板試験片に生じた摩耗量、表面状態を観察し、評価した。摩耗試験では、回転リングは１Ｎの荷重をかけて１０００回転させた。結果を表１０〜１４に示す。
下記の基準で評価し、○を合格とした。
○：アルミの凝着もなく、摩耗痕の深さは１０μｍ以下
△：アルミの凝着があり、摩耗痕の深さは１０〜５０μｍ
【００４９】
[溶融金属に対する耐食性および離型性]
焼結したままの硬質合金、および硬質合金の最表面に窒化物皮膜または酸化物皮膜と窒素化物皮膜を形成させた焼結合金を１０ｍｍ×１０ｍｍ×１００ｍｍの大きさに切削加工し試験片とし、この試験片を９９３Ｋで加熱溶融したアルミニウム（ダイカスト用アルミニウム合金：ＪＩＳ−ＡＤＣ１０）中に６時間浸漬した後、試験片の長手方向に垂直な断面で切り出し、断面を光学顕微鏡で観察し、試験片が溶融アルミニウムにより表面から侵食された深さを測定し、下記の規準で耐食性および離型性（凝固後のアルミニウムからの剥離しやすさ）を評価した。
○：侵食深さ＜５μｍ、離型性良好
△：侵食深さ≧５μｍでかつ＜３０μｍ、離型性やや不良
×：侵食深さ≧３０μｍ、離型性不良
結果を表１０〜１４に示す。
【００５０】
[耐薬品性]
焼結したままの硬質合金、および硬質合金の最表面に窒化物皮膜または酸化物皮膜と窒素化物皮膜を形成させた焼結合金を１０ｍｍ×１０ｍｍ×１００ｍｍの大きさに切削加工し試験片とし、この試験片を３１３Ｋの温度保持した１０体積％のフッ化水素酸水溶液中に１０時間浸積した後、腐食の程度を肉眼観察し、下記の規準で耐薬品性を評価した。
○：腐食は認められない
△：わずかに腐食が認められる
×：局所的に腐食孔が認められる
結果を表１０〜１４に示す。
表中で１）を附したものは、特定元素を必要以上に添加しても効果の向上効果が認められないものを指す。
【００５１】
【表１０】
【表１１】
【表１２】
【表１３】
【表１４】
表１０〜１４に示すように、本発明の焼結合金材料は耐磨耗性、溶融金属に対する耐食性、離型性および耐薬品性に優れている。以下に本発明の焼結合金、およびその焼結合金の製造方法を用いて作成した機械構造部材の例を示す。
【００５７】
次に、Ｎｉ2Ｂ粉末、Ｍｏ2Ｂ5粉末、純Ｍｏ粉末、カルボニルＮｉ粉末、純Ｃｒ粉末、純Ｍｎ粉末を、表１の組成番号１６に示す成分含有量となるように配合し、振動ボールミルを用いてアセトン中で平均粒径１．０μｍとなるまで粉砕混合した。次いで混合粉を冷間静水圧成形法（ＣＩＰ）を用いて円筒状に圧粉成形した。その後、真空中で１３００℃まで昇温し２０分間保持した後炉冷し、焼結体を得た。この焼結体を所定のスリーブ形状に切削加工した後、０．１５ＭＰａの窒素雰囲気中で１１００℃で３時間加熱し、表面に窒化物皮膜を形成させた。これを合金工具鋼（ＳＫＤ６１）の外筒の内周に焼きばめし、ダイカスト用スリーブとした。このダイカスト用スリーブをアルミニウムダイカスイト装置に装填し、溶融アルミニウムの鋳込み作業に供したが、２０００回使用した後も、表面にクラック等は発生せず、磨耗も殆ど認められなかった。
【００５８】
次に、上記と同一の原料粉を上記と同一の組成となるように配合し、上記と同一条件により円筒状の焼結体を作成した。次に合金工具鋼（ＳＣＭ４４０）の芯材にこの円筒状の焼結体を嵌着し、真空中で１２００℃で２０分間加熱し、拡散接合させ、複合材を得た。この複合材の焼結体部分を射出成形用スクリューの形状に切削加工した後、０．１５ＭＰａの水素：１０％と窒素９０％からなる混合雰囲気中で１１００℃で３時間保持して窒化物皮膜を形成させた。このようにして得られた射出成形用スクリューを射出成形機に装填し、ポリプロピレンの射出成形作業に供したが、３０００回使用した後も、表面に腐食孔は発生せず、磨耗も殆ど認められなかった。
【００５９】
【発明の効果】
本発明は、Ｍｏ、Ｃｒ、Ｎｉ、Ｂ、およびさらにＭｎ、を含有させ、Ｍｏ、Ｃｒ、Ｂの含有量を一定範囲内に限定し、またはさらにＷ、Ｎｂ、Ｚｒ、Ｔｉ、Ｔａ、Ｈｆ、Ｆｅおよび／またはＣｏ、Ｖなどを適宜含有させて成る複硼化物とＮｉ基の結合相とからなる焼結合金の最表面に、窒化物皮膜、または酸化物皮膜と窒化物皮膜の２層皮膜を形成させた焼結合金材料であり、溶融金属や溶融樹脂に対する優れた耐食性、耐磨耗性、離型性、および耐薬品性を示し、射出成形機用部材や溶融金属鋳造装置用部材などの機械構造部材として好適に適用可能である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sintered alloy material and a manufacturing method thereof. More specifically, Mo2NiB2In sintered alloys mainly composed of mold double borides, the formation of nitrides or nitrides and oxides on the surface of sintered alloys has greatly improved wear resistance, corrosion resistance, and mold release properties. The present invention relates to a bonding gold material, a manufacturing method thereof, and a mechanical structural member using the sintered alloy.
[0002]
[Prior art]
Mechanical structural members such as resin injection molding machines and molten metal casting devices, particularly members used for applications requiring wear resistance, include cylinders, screws, plungers, and molding dies. As these members, those obtained by subjecting ceramics or tool steel to various surface treatments are used. Among ceramics such as sialon and alumina, sialon is particularly superior in strength, toughness, and wear resistance compared to conventional ceramics, and is applied to various engineering parts. However, it is inferior in strength to tool steel and hot tool steel such as SKD61, and when applied to a sleeve of a die casting machine, there is a problem such as cracking.
[0003]
In recent years, demands for constituent members have become stricter, and these tool steels and hot tool steels subjected to various nitriding treatments have been used. Among the nitriding treatments, coatings such as TiN and CrN by PVD and CVD are effective in improving the corrosion resistance and wear resistance, but the adhesion of the coating film to the base material is poor and defects such as heat cracks occur. Cheap. These defects shorten the life of the member and cause a reduction in the productivity of the mechanical device loaded with the member.
[0004]
Therefore, as a material having not only excellent corrosion resistance against molten metal such as molten aluminum but also thermal shock resistance superior to a ceramic material, a ternary double boride having a Ni-based binder phase is proposed (for example, specially (Kaihei 2-299740, JP-A-5-320816). However, although the Ni-based binder phase is excellent in high-temperature properties such as strength at high temperatures, it does not have sufficient corrosion resistance, such as being eroded against the molten metal or adhering to the counterpart material, and when used for a long time There was a problem in the durability of the member.
[0005]
JP-A-5-148588 and JP-A-9-217167 disclose that the corrosion resistance of a member is improved by providing an oxide film on the surfaces of steel, cast iron, and stainless steel. However, because the formed oxide film is very thin and low in hardness, it is not only applicable to plungers and sleeves that require high wear resistance, but also has poor adhesion to the base material. This may cause a problem of mixing into the molten metal due to peeling of the oxide film.
[0006]
[Problems to be solved by the invention]
In the present invention, Mo is improved in corrosion resistance and abrasion resistance to molten resin and molten metal, and has excellent release properties and also excellent chemical resistance.2NiB2It is an object of the present invention to provide a sintered alloy material mainly composed of a mold double boride, a manufacturing method thereof, and a machine structural member using the sintered alloy material.
[0007]
[Means for Solving the Problems]
The sintered alloy material of the present invention is Mo2NiB2A nitride film is formed on the outermost surface of a sintered alloy composed of a mold double boride and a Ni-based binder phase, or an oxide film is further formed on the nitride film.The nitride film is a film made of (Ni, Mo, Cr, B) mNn type composite nitride mainly composed of Mo, Cr, Ni, B metal elements and nitrogen.It is a sintered alloy material characterized by the above. It is desirable that the nitride film has a thickness of 0.5 to 20 μm, and the oxide film has a thickness of 0.5 to 20 μm.
[0008]
AndBeforeThe oxide film is preferably a film made of (Ni, Mo, Cr, B) x Oy type complex oxide mainly composed of metal elements of Mo, Cr, Ni, and B and oxygen.
[0009]
As the composition of the sintered alloy, a composition comprising 3 to 7.5% B, 21 to 79.9% Mo, 2 to 35% Cr, the balance being Ni of 10% or more, and inevitable impurities is adopted. it can. Alternatively, 0.1 to 8% of Mn is contained with respect to the total composition of the sintered alloy, and a part of the Mo content contained in the sintered alloy is set to 0. Substituting with 1-30% W, replacing part of the Mo content contained in the sintered alloy with 0.1-10% Nb with respect to the total composition, Part of the Mo content contained in the sintered alloy is replaced by 0.2 to 30% in total of both W and Nb with respect to the total composition, and the Nb content contained in the sintered alloy Substituting part or all of the amount with one or more of Zr, Ti, Ta, and Hf, and part of the Ni content contained in the sintered alloy with respect to the total composition Thus, the substitution of 0.1 to 20% in total of either one or both of Fe and / or Co is contained in the sintered alloy. Some of r content, any one of compositions of becoming replaced with 0.1 to 25% of V with respect to the total composition may be employed.
[0010]
The method for producing a sintered alloy material according to the present invention comprises heating any one of the above sintered alloys in a nitrogen atmosphere or a reducing atmosphere containing nitrogen to form a nitride film on the surface thereof.
Alternatively, any of the above sintered alloys is heated in air or in an atmosphere containing oxygen to form an oxide film on the surface, and then heated in a reducing atmosphere containing nitrogen to reduce the oxide film. To form a nitride film, or
Any of the above sintered alloys is heated in the atmosphere or in an atmosphere containing oxygen to form an oxide film on the surface, and then heated in a nitrogen atmosphere to form a nitride film under the oxide film. It is characterized by making it. It is desirable that the reducing atmosphere containing nitrogen or the pressure of the nitrogen atmosphere is 0.103 to 1 MPa.
[0011]
Furthermore, the mechanical structural member of the present invention is a mechanical structural member characterized in that a sintered alloy material created using any one of the above-described methods for producing a sintered alloy material is used as a member.
The mechanical structural member is an injection molding machine member or a molten metal casting apparatus member.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides Mo2NiB2By forming a nitride film or a two-layer film of an upper oxide film and a lower nitride film on the outermost surface of a sintered alloy mainly composed of type double boride, it is excellent for molten resin and molten metal Abrasion resistance, corrosion resistance, and releasability are imparted.
In the sintered alloy that is the base material of the mechanical structural member of the present invention, the content of B, Mo, Cr is limited to a certain range, so that the two-phase structure of the double boride and the Ni-based binder phase is sintered. It becomes a bond gold and not only provides excellent wear resistance and corrosion resistance, but also forms the above-mentioned nitride film or a surface treatment layer composed of a nitride film and an oxide film densely and stably.EspeciallyThus, it is possible to impart excellent releasability to molten resin and molten metal.
In addition, by including Mn in the base material, the mechanical properties of the base material, the corrosion resistance and self-repairing property of the surface treatment layer are improved, and by adding W, the mechanical properties of the base material, the surface treatment layer Corrosion resistance and wear resistance are improved. Furthermore, by including Nb, Zr, Ti, Ta, and Hf, the corrosion resistance and wear resistance of the surface treatment layer are improved, and by including Fe and / or Co, the thermal shock resistance and high temperature strength of the base material are improved. Will improve.
The present invention is described in detail below.
[0013]
The present inventors, before reaching the present invention, Mo2NiB2Sintered alloys mainly composed of type double borides have sufficient corrosion resistance and wear resistance to withstand in environments such as corrosive atmospheres and high temperature regions where molten resins and metals are used I found out. However, in recent years, in order to improve the performance of resins, various fillers such as glass fibers and ferrite particles have been added in large amounts, and further improvement in wear resistance of mechanical structural members has been required. Further, it has been found that, when the molten metal is in contact with the molten metal for a long time, the Ni-based binder phase reacts with the molten metal, and it is necessary to improve the corrosion resistance and the release (peeling) property. As a result of various studies, Mo2NiB2By forming a dense and stable nitride film or a surface treatment layer composed of a nitride film and an oxide film on the surface of a sintered alloy mainly composed of type double borides, the strength of the base material is maintained. It has been found that the corrosion resistance, mold release and wear resistance to molten metal and molten resin are greatly improved even when the surface hardness is increased and used for a long time.
[0014]
This is a (Ni, Mo, Cr, B) mNn type composite nitride composed mainly of metal elements of Mo, Cr, Ni, and B, which are main constituent elements of the base material, and nitrogen. It is a stable and dense film, and the oxide film is composed mainly of metal elements of Mo, Cr, Ni, and B, which are main constituent elements of the base material, and nitrogen (Ni, Mo, Cr, B) xOy. This is because the surface treatment layer constitutes a protective film and greatly improves and improves the corrosion resistance and wear resistance against the molten metal. Furthermore, by forming an oxide film in advance before forming the nitride film, and nitriding while reducing this oxide film, nitridation is promoted by the previously generated oxide layer, and the nitride film is formed. A thicker film can be formed.
[0015]
In addition to the above four elements, the sintered alloy of the present invention may selectively contain Mn, W, Nb, Zr, Ti, Ta, Hf, Fe, Co, and V. The formed nitride film or oxide film is composed of the above selectively added elements and nitrogen or oxygen in addition to Mo, Cr, Ni, and B. When the nitride or oxide does not contain Mo, Cr, Ni, or B, the bonding strength of the surface treatment layer is weak and the adhesion with the base material is reduced, so that cracks and peeling are likely to occur, and wear resistance Sex is not enough.
Specific examples of compound nitrides include (Ni, Cr)2MoThreeN, CrN, Cr2N, MoN, Mo2N, BN, etc. are mentioned. As the complex oxide, specifically, (Ni, Mo, Cr, B)2OThree, (Ni, Mo, Cr, B)ThreeOFour, (Ni, Mo, Cr, B) O, (Ni, Mo, Cr, B) OThree, (Ni, Mo, Cr, B) O2.7 ~ 2.9, (Ni, Mo, Cr, B) O2Etc.
[0016]
The above complex nitride and complex oxide are Mo2NiB2Since the double boride of the mold is obtained by nitriding or oxidizing, the base material is Mo composed mainly of Mo, Cr, Ni, and B.2NiB2It must be a sintered alloy mainly composed of type double borides.
In this sintered alloy, B is an indispensable element for forming a double boride and a surface treatment layer that become a hard phase of the base material of the sintered alloy. Moreover, the surface treatment layer containing B exhibits the effect of improving the adhesion with the base material. If the amount of B is less than 3%, the proportion of the hard phase is less than 35%, and the mechanical properties of the base material are inferior. On the other hand, if it exceeds 7.5%, the ratio of the hard phase exceeds 95%, and the strength and thermal shock resistance are lowered. Therefore, the B content is limited to 3 to 7.5%.
[0017]
Mo, like B, is an indispensable element for forming double borides and surface treatment layers. In the base material, part of the base material is dissolved in the bonded phase of the sintered alloy to improve the mechanical strength of the base material. However, if the content exceeds the appropriate amount (79.9%), M6An intermetallic compound such as C-type carbide is formed, and the strength of the base material is lowered. On the other hand, if the content is less than 21%, Ni2Since the Ni boride such as B is formed, the strength of the base material is lowered. Therefore, the Mo content is limited to 21-79.9%.
[0018]
Cr has a solid solution with Ni in the double boride and has the effect of stabilizing the crystal structure of the double boride to tetragonal crystals. It also dissolves in the Ni binder phase and greatly improves the corrosion resistance, wear resistance, high temperature characteristics, and mechanical characteristics of the sintered alloy. However, if it exceeds 35%, CrFiveBThreeAs a result, the strength of the base material is reduced. On the other hand, if it is less than 2%, the amount of Cr in the surface treatment layer becomes insufficient, and the corrosion resistance against molten metal or molten resin is reduced. Therefore, the Cr content is limited to 2 to 35%.
[0019]
Mn suppresses the grain growth of the double boride of the base material and refines the alloy structure, thereby significantly improving the mechanical properties. Further, by adding Mn, a sintered body having a good shape with little deformation during sintering can be obtained, and the effect of being made into a net is shown. Furthermore, since Mn has a strong affinity for oxygen, the surface treatment layer is made thicker and the durability of the member is improved. If the content is less than 0.1%, the effect of improving the characteristics is not recognized. If the content exceeds 8%, the mechanical properties of the base material are lowered. Therefore, the Mn content is limited to 0.1 to 8% with respect to the total composition.
[0020]
W is an element that can be replaced with Mo, and not only exhibits the effect of improving the strength of the base material but also improves the corrosion resistance and wear resistance of the surface treatment layer. However, when the W content is less than 0.1%, the effect of improving the characteristics is not recognized. On the other hand, if the content exceeds 30%, not only the effect is not recognized, but also the specific gravity of the member increases and the product weight increases. Therefore, the W content is limited to 0.1 to 30% with respect to the total composition.
[0021]
Nb, Zr, Ti, Ta, and Hf are elements that can be substituted for Mo, and are dissolved in the double boride of the base material and some of the other hard particles (boride, oxide, carbide, and Nitride) and improve mechanical properties. In addition, since these elements have a strong affinity for oxygen, they bind to the composite oxide and are effective in forming a denser surface treatment layer having excellent adhesion. Further, even when two or more of these elements are combined, the same effect as that obtained when these elements are included alone can be obtained. However, if the content is less than 0.1%, the improvement effect is not recognized. If the content exceeds 10%, not only the sinterability of the sintered alloy is lowered and the strength is decreased, but also these Since the element is expensive, the cost increases. Therefore, the content of Nb, Zr, Ti, Ta, and Hf is limited to 0.1 to 10% in total with one or more of the total composition.
[0022]
Fe is an element that can be substituted for Ni, and the self-repairing property of the surface treatment layer is improved by forming a nitride and oxide film containing Fe in the surface treatment layer. Moreover, the cost of a member can be reduced by using inexpensive Fe. If the content is less than 0.1%, the improvement effect is not recognized. If the content exceeds 20%, not only the corrosion resistance is lowered, but also the thermal shock resistance and strength of the base material are lowered. Therefore, the Fe content is limited to 0.1 to 20% with respect to the total composition.
[0023]
Co, like Fe, is an element that can be substituted for Ni, and is dissolved in both the boride of the sintered alloy of the present invention and the Ni-based bonded phase to improve the thermal shock resistance and high-temperature strength of the sintered alloy. Let When the content is less than 0.1%, the improvement effect is not recognized, and when the content exceeds 20%, not only the effect of improving the characteristics is not recognized, but also the cost is increased. Therefore, the Co content is limited to 0.1 to 20% with respect to the total composition. Fe and Co may be contained alone as described above, or both may be contained. When both are contained, the content is limited to 0.1 to 20% with respect to the total composition.
[0024]
V is an element that can be substituted with Cr, and similarly to Cr, it has an effect of being substituted and dissolved with Ni in the double boride and stabilizing the crystal structure of the double boride to a tetragonal crystal. It also dissolves in the Ni binder phase and greatly improves the corrosion resistance, wear resistance, high temperature characteristics, and mechanical characteristics of the sintered alloy. Further, the surface treatment layer brings about an effect of improving self-repairability. If the content is less than 0.1%, the effect of improving these properties is not recognized. If the content exceeds 25%, the adhesion of the nitride film or oxide film decreases, and impurities are mixed into the molten metal or molten resin. Can cause Therefore, the content of V is limited to 0.1 to 25% with respect to the total composition.
[0025]
In the sintered alloy of the present invention, the balance is composed of Ni in addition to the above component elements. Ni is an element constituting a double boride and a binder phase, and is indispensable for forming a composite nitride and a composite oxide constituting a surface treatment layer. In the sintered alloy of the present invention, if the Ni content is less than 10%, the double boride cannot be sufficiently formed, and the Ni content in the binder phase is insufficient, which is sufficient at the time of sintering. A liquid phase does not appear, a dense sintered body cannot be obtained, and the strength decreases. Therefore, it is necessary to contain 10% or more of Ni in the hard alloy of the present invention. Needless to say, if the sintered alloy of the present invention cannot contain 10% or more of Ni, the content of each element other than Ni is reduced within an allowable range to contain 10% or more of Ni.
[0026]
The main inevitable impurity elements contained in the sintered alloy of the present invention are P, S, C, Si, Al, etc., and in order to maintain the strength of the sintered alloy, these contents should be reduced as much as possible. It is desirable. If the content of these elements is 1% or less in total, the influence on the mechanical properties is relatively small.
[0027]
Next, the manufacturing method of this invention is demonstrated.
First, a method for producing a sintered alloy as a base material will be described. B alloy powder composed of one or more elements of Ni, Mo, Cr, Mn, W, Nb, Zr, Ti, Ta, Hf, Fe, Co, V and B, or these B alloy powders Powder of alloy composed of one or more of these elements, or simple substance powder of B and simple substance of Ni, Mo, Cr, Mn, W, Nb, Zr, Ti, Ta, Hf, Fe, Co, V, or B A powder composed of a simple substance and one or more of these alloys is blended so as to have a predetermined alloy composition, wet pulverized in an organic solvent using a vibration ball mill or the like, granulated and molded, and the molded body Is liquid phase sintered in a non-oxidizing atmosphere such as in vacuum, in a reducing gas, or in an inert gas.
[0028]
The double boride that becomes the hard phase of the sintered alloy is formed by the reaction of the raw material powder during the sintering, and is preliminarily formed of Mo and Ni, and further from the elements that are selectively added. By reacting the double boride or the powder of B alone with the powder of Mo and Ni and the above selectively added element in a furnace, Mo2NiB2It is also possible to use a powder prepared by manufacturing a type double boride and further blending powders of Ni, Mo, Fe, Co, and the above-mentioned selectively added elements with a predetermined alloy composition. .
[0029]
The powder prepared as described above is compacted into a predetermined shape and then heated and sintered. Sintering is usually performed at a sintering temperature of 1373 to 1673K for 5 to 90 minutes. When the sintering temperature is less than 1373K, the liquid phase does not appear sufficiently, a sintered body with many voids is obtained, and sufficient strength cannot be obtained. On the other hand, when the sintering temperature exceeds 1673K, the liquid phase appears sufficiently, but the crystal grains become coarse and the strength decreases. On the other hand, if the sintering time is less than 5 minutes, the diffusion of elements is not sufficient and the density is not sufficiently increased. On the other hand, no further increase in strength is observed even after sintering for more than 90 minutes, and the strength may decrease in some cases. By sintering under the sintering conditions in which the liquid phase appears as described above, voids disappear and a hard alloy having a density of almost 100% is obtained. As a method for eliminating voids without causing a liquid phase to appear, there are a hot isostatic pressing method, a hot press method, an electric current sintering method, and the like. Even if these methods are used, voids can be eliminated. Further, these methods and the liquid phase sintering method may be used in combination.
[0030]
The sintered alloy of the present invention obtained as described above can be used not only as a single sintered body but also as a composite material by joining with a steel material. That is, the sintered alloy of the present invention is not only used by brazing to a steel material like a cemented carbide, but also directly joined to the steel material without using a brazing material, or the sintered alloy of the present invention on the surface of the steel material. After applying the slurry of the raw material powder, it is possible to sinter the raw material powder and to diffuse-bond it to the steel material, thereby obtaining strong adhesion. It is also possible to apply a sintered joining method that joins sintered and steel materials at the same time. Steel materials do not cause a decrease in strength due to thermal damage, and the composite material can be used as a member for die casting machines of molten metal such as aluminum. When used, the parts such as molds can be manufactured at low cost by using the sintered alloy of the present invention to the minimum necessary only for parts that require thermal shock resistance and corrosion resistance and wear resistance against molten metal. Can be manufactured.
Next, a method for manufacturing the surface treatment layer formed on the surface of the base material obtained as described above will be described.
[0031]
When only the nitride film is formed, the obtained base material is machined into a desired shape, the surface is washed and degreased, and then in a nitrogen atmosphere of 0.103 to 1 MPa or a reducing atmosphere containing nitrogen By holding at a temperature of 773 to 1873 K for 5 minutes to 50 hours, a nitride film having a thickness of 0.5 to 20 μm is formed. When the treatment temperature is less than 773 K, it is not possible to form a nitride film having a sufficient thickness that can provide excellent corrosion resistance and wear resistance even after long-time treatment. On the other hand, when the treatment is performed at a treatment temperature exceeding 1873K, the nitride film is peeled off. When the treatment time is less than 5 minutes, the formation of a sufficiently thick nitride film is not recognized, and even when the treatment is performed for more than 50 hours, the growth of the nitride film is saturated and peeling occurs, This leads to an increase in cost. Therefore, the nitriding treatment is performed at a temperature of 773 to 1873K for 5 minutes to 50 hours, preferably at 973 to 1673K for 1 to 30 hours. The atmospheric pressure needs to be higher than the atmospheric pressure so that the air outside the treatment tank does not enter the atmosphere, and the film thickness tends to increase when the pressure is increased. It is preferable to perform the treatment under a pressure of ˜1 MPa. A nitride film having a thickness of 0.5 to 20 μm is thus obtained. If the thickness of the nitride film is less than 0.5 μm, sufficient corrosion resistance and wear resistance cannot be obtained, while if it exceeds 20 μm, the effect of improving the corrosion resistance and wear resistance is saturated, which is economically advantageous. Disappear.
[0032]
As another method for forming only the nitride film, the obtained base material is machined into a desired shape, and after the surface is cleaned and degreased, first, in the air or in an oxygen atmosphere at a temperature of 773 to 1873 K for 5 minutes to Hold for 50 hours to form an oxide film. The means for forming the oxide film includes, but is not limited to, a high temperature atmospheric oxidation method and a high temperature wet hydrogen oxidation method. When the treatment temperature is less than 773 K, it is not possible to form an oxide film having a sufficient thickness that can provide excellent corrosion resistance even after long-time treatment. On the other hand, when the treatment is performed at a treatment temperature exceeding 1873K, the oxide film is peeled off. When the treatment time is less than 5 minutes, the formation of a sufficiently thick oxide film is not recognized, and even when the treatment is performed for more than 50 hours, the growth of the oxide film is saturated and peeling occurs, This leads to an increase in cost. Subsequently, it hold | maintains at the temperature of 773-1673K for 1 to 40 hours in the reducing atmosphere containing 0.103-1MPa of nitrogen. In this way, when heated in air or in an atmosphere containing oxygen to form an oxide film, and then heated in a reducing atmosphere containing nitrogen, even if nitriding is performed under the same conditions, nitriding alone A thick nitride film can be obtained, and it is easy to increase the film thickness.
[0033]
When the oxide film is formed and then subjected to nitriding, the nitride film is formed on the base material surface, that is, the lower layer of the oxide film. When this treatment is performed, the base material is machined in the same manner as described above, and after cleaning and degreasing the surface, it is first held in air or in an oxygen atmosphere at a temperature of 773 to 1873 K for 5 minutes to 50 hours. An oxide film having a thickness of 0.5 to 20 μm is formed. The means for forming the oxide film includes, but is not limited to, a high temperature atmospheric oxidation method and a high temperature wet hydrogen oxidation method. When the treatment temperature is less than 773 K, it is not possible to form an oxide film having a sufficient thickness that can provide excellent corrosion resistance even after long-time treatment. On the other hand, when the treatment is performed at a treatment temperature exceeding 1873K, the oxide film is peeled off. When the treatment time is less than 5 minutes, the formation of a sufficiently thick oxide film is not recognized, and even when the treatment is performed for more than 50 hours, the growth of the oxide film is saturated and peeling occurs, This leads to an increase in cost. Therefore, the oxidation treatment is performed at a temperature of 773 to 1873K for 5 minutes to 50 hours, preferably at 973 to 1673K for 1 to 30 hours. In this way, an oxide film having a thickness of 0.5 to 20 μm is obtained. Next, nitriding is performed in an atmosphere containing nitrogen. The nitride film is formed at the interface between the sintered alloy base material and the oxide film. In this way, a two-layer film having an oxide film on the upper layer of the nitride film having a thickness of 0.5 to 20 μm is obtained. When the oxide film is present on the nitride film in this manner, the oxide exhibits a lubricating effect and wear resistance is further improved.
Hereinafter, the present invention will be described in detail with reference to examples.
[0034]
【Example】
(Example)
The B powder and the metal powder were adjusted to the blending ratios shown in Tables 1 to 4, and then wet mixed and pulverized in acetone for 25 hours using a vibration ball mill. The powder after pulverization with a ball mill is dried and granulated, and the obtained fine powder is press-molded into a predetermined shape, and then the temperature is increased by 10 K / min as the first stage heating in a vacuum of ≦ 1.3 Pa. The temperature was raised at a temperature rate, and after heating for the time shown in Tables 5 to 9 at the temperatures shown in Tables 5 to 9, the furnace was cooled to obtain sintered alloys.
[0035]
[Table 1]
[Table 2]
[Table 3]
[Table 4]
[Table 5]
[Table 6]
[Table 7]
[Table 8]
[Table 9]
The sintered alloy obtained as described above is processed into a desired shape, degreased, heated in the atmosphere shown in Tables 5 to 9 under the heating conditions shown in Tables 5 to 9, and then cooled in the furnace and sintered. A surface treatment layer composed of a composite nitride film or a two-layer film of a composite oxide film and a composite nitride film was formed on the gold surface. Some sintered alloys were subjected to the following characteristic evaluation without being subjected to the above heat treatment for comparison.
[0045]
The strength of the sintered alloys shown in Tables 1 to 9 obtained as described above, the film thickness of the nitride film and the oxide film, wear resistance, corrosion resistance, and release properties were evaluated as follows. did.
[0046]
[Strength]
A test piece was cut out from the sintered hard alloy and a member for molten metal obtained by subjecting the hard alloy to heat treatment in the atmosphere, and the bending strength (three-point bending test) was measured based on JIS H5501. The greater the bending strength, the better the strength, and those exceeding 1.5 GPa are the subject of the present invention. The results are shown in Tables 10-14.
[0047]
[Film thickness of nitride film and oxide film]
A test piece was cut out from a sintered alloy in which a nitride film or oxide film and a nitride film were formed on the outermost surface of the hard alloy. The SEM image of each test piece was photographed in three fields, the thickness of the nitride film and the thickness of the oxide film were measured, and the average value was taken as the film thickness. The results are shown in Tables 10-14.
[0048]
[Abrasion resistance]
For the wear test, an Ogoshi type rapid wear tester was used. This is a ring-on-plate type testing machine. While rotating an aluminum rotating ring, a flat plate test piece on a block made of a hard alloy is pressed and rubbed, and the amount of wear and surface generated on the flat plate test piece The condition was observed and evaluated. In the abrasion test, the rotating ring was rotated 1000 times with a load of 1N. The results are shown in Tables 10-14.
Evaluation was made according to the following criteria, and ○ was accepted.
○: There is no adhesion of aluminum, and the depth of wear scar is 10 μm or less
Δ: There is adhesion of aluminum, and the depth of the wear scar is 10 to 50 μm
[0049]
[Corrosion resistance and releasability to molten metal]
A hard alloy as sintered, and a sintered alloy in which a nitride film or an oxide film and a nitride film are formed on the outermost surface of the hard alloy are cut into a size of 10 mm × 10 mm × 100 mm to obtain a test piece, This test piece was immersed in aluminum (die-cast aluminum alloy: JIS-ADC10) heated and melted at 993 K for 6 hours, then cut out in a cross section perpendicular to the longitudinal direction of the test piece, and the cross section was observed with an optical microscope. The depth of erosion from the surface by molten aluminum was measured, and the corrosion resistance and release properties (ease of peeling from the solidified aluminum) were evaluated according to the following criteria.
○: Depth of erosion <5 μm, good releasability
Δ: Depth of erosion ≧ 5 μm and <30 μm, somewhat poor releasability
×: Erosion depth ≧ 30 μm, poor releasability
The results are shown in Tables 10-14.
[0050]
[chemical resistance]
A hard alloy as sintered, and a sintered alloy in which a nitride film or an oxide film and a nitride film are formed on the outermost surface of the hard alloy are cut into a size of 10 mm × 10 mm × 100 mm to obtain a test piece, This test piece was immersed in a 10% by volume hydrofluoric acid aqueous solution maintained at a temperature of 313 K for 10 hours, and then the degree of corrosion was visually observed, and the chemical resistance was evaluated according to the following criteria.
○: Corrosion is not recognized
Δ: Slight corrosion is observed
×: Corrosion holes are observed locally
The results are shown in Tables 10-14.
Those marked with 1) in the table indicate those in which the effect of improving the effect is not recognized even if a specific element is added more than necessary.
[0051]
[Table 10]
[Table 11]
[Table 12]
[Table 13]
[Table 14]
As shown in Tables 10 to 14, the sintered alloy material of the present invention is excellent in wear resistance, corrosion resistance to molten metal, release properties, and chemical resistance. The example of the mechanical structure member created using the sintered alloy of this invention and the manufacturing method of the sintered alloy is shown below.
[0057]
Next, Ni2B powder, Mo2BFivePowder, pure Mo powder, carbonyl Ni powder, pure Cr powder, and pure Mn powder were blended so as to have the component content shown in composition number 16 of Table 1, and the average particle size of 1. in acetone using a vibration ball mill. The mixture was pulverized and mixed to 0 μm. Next, the mixed powder was compacted into a cylindrical shape by using a cold isostatic pressing method (CIP). Then, it heated up to 1300 degreeC in vacuum, hold | maintained for 20 minutes, and then cooled in the furnace, and the sintered compact was obtained. After cutting this sintered body into a predetermined sleeve shape, the sintered body was heated in a nitrogen atmosphere of 0.15 MPa at 1100 ° C. for 3 hours to form a nitride film on the surface. This was shrink-fitted to the inner periphery of the outer cylinder of alloy tool steel (SKD61) to form a die casting sleeve. This sleeve for die casting was loaded into an aluminum die casting apparatus and used for casting molten aluminum. However, after 2000 times of use, no cracks or the like were generated on the surface, and almost no wear was observed.
[0058]
Next, the same raw material powder as above has the same composition as above.To beA cylindrical sintered body was prepared under the same conditions as above. Next, this cylindrical sintered body was fitted to a core material of an alloy tool steel (SCM440), heated in a vacuum at 1200 ° C. for 20 minutes, and diffusion bonded to obtain a composite material. After the sintered portion of the composite material is cut into the shape of an injection molding screw, the nitride film is maintained at 1100 ° C. for 3 hours in a mixed atmosphere of 0.15 MPa hydrogen: 10% and nitrogen 90%. Formed. The injection molding screw thus obtained was loaded into an injection molding machine and subjected to polypropylene injection molding work. Even after 3000 times of use, no corrosion holes were generated on the surface and almost no wear was observed. There wasn't.
[0059]
【The invention's effect】
The present invention includes Mo, Cr, Ni, B, and further Mn, and limits the content of Mo, Cr, B to a certain range, or further W, Nb, Zr, Ti, Ta, Hf, A nitride film or a two-layer film of an oxide film and a nitride film is formed on the outermost surface of a sintered alloy composed of a double boride containing Ni and / or Co, V and the like and a Ni-based binder phase. Sintered alloy material with excellent corrosion resistance, wear resistance, mold release, and chemical resistance against molten metal and molten resin, such as members for injection molding machines and molten metal casting equipment It can be suitably applied as a machine structural member.
Claims (20)
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