JP3741654B2

JP3741654B2 - Manufacturing method of high density iron-based forged parts

Info

Publication number: JP3741654B2
Application number: JP2002054244A
Authority: JP
Inventors: 尚道中村; 繁宇波; 聡上ノ薗; 政志藤長; 吉村　　隆志; 光正飯嶋; 晋小泉; 安間　　裕之
Original assignee: JFE Steel Corp; Hitachi Ltd
Current assignee: JFE Steel Corp; Hitachi Ltd
Priority date: 2002-02-28
Filing date: 2002-02-28
Publication date: 2006-02-01
Anticipated expiration: 2022-02-28
Also published as: DE10308274B4; JP2003253372A; DE10308274A1; CN1442257A; KR20030071540A; US20030215349A1

Description

【０００１】
【発明の属する技術分野】
本発明は、機械部品に用いて好適な鉄基鍛造部品の製造方法に係り、とくに鍛造荷重の低減と、密度・寸法精度の改善に関する。
【０００２】
【従来の技術】
粉末冶金技術は、複雑な形状の部品をニアネット形状でしかも高寸法精度に製造することができ、切削コストを大幅に低減できる。最近では、鉄系の粉末冶金製品（鉄基粉末製品（鉄基焼結部品))に対し、部品の小型化、軽量化のために高強度化が強く要求されている。
【０００３】
鉄基焼結部品（鉄基焼結体あるいは単に焼結体ともいう）は、鉄基金属粉に、黒鉛粉、銅粉等の合金用粉末と、ステアリン酸亜鉛、ステアリン酸リチウム等の潤滑剤とを混合し鉄基混合粉とし、ついで、この鉄基混合粉を金型に充填し圧縮成形して成形体としたのち、この成形体を焼結し焼結体とする工程により製造されるのが一般的である。得られた焼結体は、必要に応じサイジングや切削加工が施され製品とされる。また、高強度が必要な場合には、焼結体にさらに浸炭熱処理や光輝熱処理を施す場合もある。このような工程で得られた成形体の密度は、たかだか6.6 〜7.1Mg/m³程度であり、したがって、これらの成形体から得られる焼結体の密度もこの程度となる。
【０００４】
鉄基粉末製品（鉄基焼結部品）の高強度化には、成形体の高密度化による焼結部品（焼結体）の高密度化が有効である。高密度の焼結部品（焼結体）ほど、部材中の空孔が減少し、引張強さ、衝撃値、疲労強度などの機械的性質が向上する。
鉄基粉末製品（鉄基焼結部品）の密度を高密度化する成形方法として、例えば、粉末冶金法と冷間鍛造法を組合せ、ほぼ真密度に近い製品が得られる、焼結冷間鍛造方法が特開平1-123005号公報に提案されている。焼結冷間鍛造方法とは、金属粉を焼結成形したプリフォーム（予備成形品）を冷間で鍛造したのち、再焼結して高密度組成の最終製品を得る成形、加工方法である。特開平1-123005号公報に記載された技術は、表面に液状潤滑剤を塗布した冷間鍛造用焼結プリフォームをダイス内で仮圧縮成形したのち、該プリフォームに負圧を作用させて液状潤滑剤を吸引除去し、その後ダイス内で本圧縮成形し、再焼結する焼結冷間鍛造方法である。この方法によれば、仮圧縮成形前に塗布し内部に浸透した液状潤滑剤を本圧縮成形前に吸引するため、内部の微小空隙が本圧縮成形時に圧潰消滅して高密度の最終製品が得られるとしている。しかし、この方法で得られる最終焼結製品の密度は、たかだか7.5Mg/m³程度であるためその強度には限界があった。
【０００５】
一方、焼結製品（焼結体）の強度をさらに高めるためには、製品の炭素（Ｃ）濃度を増加させることが効果的である。粉末冶金法では、炭素（Ｃ）源として、黒鉛粉を原料金属粉に混合することが一般的であるが、黒鉛粉を混合した金属粉を予備成形後仮焼結（予備焼結）して成形用素材とし、さらに再圧縮成形したのち、再焼結して高強度の焼結体を得る方法が考えられる。しかし、従来の方法で仮焼結（予備焼結）を行うと、仮焼結（予備焼結）時に炭素（Ｃ）が成形用素材全体に拡散し、成形素材の硬度が増加する。このため、再圧縮成形を行うに際し、成形荷重が非常に大きくなり、しかも変形能が低下しているため所望の形状に加工できないという問題があった。したがって、高強度、高密度の製品が得られないのである。
【０００６】
このような問題に対しては、例えば、米国特許第4,393,563 号には、高温での成形を行うことなく、軸受部品を製造する方法が開示されている。この方法は、鉄粉と、鉄合金粉と、黒鉛粉と潤滑剤とを混合し、この混合粉を予備成形品に成形したのち、仮焼結し、ついで少なくとも50％の塑性加工を与える冷間鍛造を行い、その後焼結、焼鈍し、ロール加工して最終製品（焼結部材）とする工程からなっている。米国特許第4,393,563 号公報に記載された技術では、黒鉛の拡散を抑制した条件で仮焼結を行うことにより、その後の冷間鍛造で高い変形能を発現させ、成形荷重を低くすることができるとしている。しかし、米国特許第4,393,563 号公報には、仮焼結条件として、1100℃×15〜20min が推奨されており、本発明者らの実験によれば、この条件では、黒鉛が予備成形品に完全に拡散してしまい、焼結部材用素材（予備成形品）の硬さが著しく増加し、その後の冷間鍛造が困難であるということがわかった。
【０００７】
このような問題に対し、例えば、特開平11-117002 号公報には、鉄を主成分とする金属粉に0.3 重量％以上の黒鉛を混合してなる金属質粉を圧粉成形して得られた、密度が7.3Mg/m³以上の予備成形体を好ましくは700 〜1000℃の温度範囲で仮焼結してなり、金属粉の粒界に黒鉛が残留している状態の組織を有する金属質粉成形素材が提案されている。この技術によれば、強度増加に必要な炭素量のみを固溶し、遊離黒鉛を残存させ、鉄粉が過度に硬化するのを防止することにより、再圧縮成形時に、低い成形荷重と高い変形能を有する成形用素材が得られるとしている。しかしながら、この方法で得られた金属質粉成形素材は、再圧縮成形工程において高い変形能を有しているが、その後の本焼結時に、残存した遊離黒鉛が消失して、細長い空孔を生ずることがあるという問題が残されていた。
【０００８】
また、特開2000-303106 号公報には、鉄を主成分とする金属粉に0.3 重量％以上の黒鉛を混合してなる金属質粉を圧粉成形して得られた、密度が7.3Mg/m³以上の予備成形体を所定の温度で仮焼結して、金属粉の粒界に黒鉛が残留している状態の組織を有する金属質粉成形素材を得る仮焼結工程と、この仮焼結工程で得られた金属質粉成形素材を再圧縮成形する再圧縮工程と、この再圧縮工程で得られた再圧縮成形体を再焼結する再焼結工程と、からなる焼結体の製造方法が提案されている。
【０００９】
また、特開平2000-355726 号公報には、合金鋼粉に、0.1 重量％以上の黒鉛を混合してなる金属質粉を圧粉成形して得られた、密度が7.3Mg/m³以上の予備成形体を所定の温度で仮焼結して、金属粉の粒界に黒鉛が残留している状態の組織を有する金属質粉成形素材とし、この金属質粉成形素材を再圧縮成形して空隙のほとんどない緻密化した組織を有する合金鋼粉塑性加工体とし、この合金鋼粉塑性加工体を所定温度で再焼結してなり、黒鉛が拡散した組織と、黒鉛が残留した組織が再焼結温度に応じて所定の割合で有する合金鋼粉再焼結加工体が示されている。
【００１０】
【発明が解決しようとする課題】
特開2000-303106 号公報、特開平2000-355726 号公報に記載された技術によれば、高密度で高強度の焼結体が得られるが、しかしながら、特開2000-303106 号公報、特開平2000-355726 号公報に記載された技術では、再圧縮成形前の素材の密度が7.3Mg/m³未満の場合、再圧縮成形方法によっては高密度でかつ高寸法精度の部品が得にくいという問題があった。
【００１１】
本発明は、上記した従来技術の問題を解決し、高密度でかつ高寸法精度の部品を低い鍛造荷重で製造可能とする、鉄基鍛造部品の製造方法を提案することを目的とする。
【００１２】
【課題を解決するための手段】
本発明者らは、上記した課題を達成するために、焼結条件と成形条件について、鋭意検討した。その結果、混合粉を予備成形したのち、添加した黒鉛を基地に拡散させる温度で、かつ低窒素雰囲気中で焼結し、あるいはさらに焼鈍を施した後、冷間での密閉鍛造または閉塞鍛造を行うことが有効であることを知見した。これにより、予備成形後の密度が低くても、高密度でかつ寸法精度が顕著に向上した鍛造部品が得られることを見出した。また、これにより、焼結後の成形（鍛造）を低い成形（鍛造）荷重で行えることも見出した。
【００１３】
本発明は、上記した知見に基づいて、さらに検討を加え完成されたものである。
すなわち、本発明は、鉄基金属粉と黒鉛粉とを含有する鉄基混合粉を、予備圧縮成形して予備圧縮成形体としたのち、該予備圧縮成形体に窒素分圧が30kPa 以下の非酸化性雰囲気中で 950℃以上1300℃以下の温度で焼結を施して、成形用素材としたのち、該成形用素材に閉塞鍛造または密閉鍛造を施し、高密度の鍛造部品とすることを特徴とする高密度鉄基鍛造部品の製造方法であり、前記鉄基金属粉が、Mn、Mo、Cr、Ni、CuおよびＶから選ばれた１種または２種以上の金属を部分拡散付着してなることが好ましく、また、本発明では、前記焼結後、さらに焼鈍を施すことが好ましく、また、本発明では、前記焼鈍が、 400℃〜 800℃の温度範囲で行うことが好ましく、また、本発明では、前記予備圧縮成形体が、7.3Mg/m³未満の密度を有することが好ましい。
【００１４】
【発明の実施の形態】
図１に、本発明の鉄基鍛造部品の製造工程の１例を示す。
原料粉末として、鉄基金属粉と、黒鉛粉、あるいはさらに合金用粉を用いる。使用する鉄基金属粉は、用途に応じ適宜選択することができ、とくに限定されないが、圧縮性の観点から本発明では、mass％で、Ｃ：0.05％以下、Ｏ：0.3 ％以下、Ｎ：0.010 ％以下を含み、残部Feおよび不可避的不純物からなる組成を有する鉄基金属粉が好適である。なお、鉄基金属粉のＯ含有量はできるだけ低くすることが圧縮成形性の観点から好ましいが、Ｏは不可避的に含有される元素であり、経済的に高価とならず工業的に実施可能なレベルである0.02mass％を下限とすることが望ましい。なお、工業的な経済性から、好ましいＯ含有量は0.03〜0.2mass ％である。また、鉄基金属粉のＮ含有量は、成形（鍛造）荷重を低減する観点からできるだけ低減することが望ましいが、工業的な経済性の観点からは、Ｎを0.010 ％以下とすることが望ましい。
【００１５】
また、本発明で使用する鉄基金属粉の粒径は、とくに限定する必要はないが、工業的に低コストで製造できる、平均粒径で30〜120 μm とするのが望ましい。なお、平均粒径は重量積算粒度分布の中点（ｄ₅₀）の値とする。
また、本発明では、上記した組成に加えてさらに、必要に応じ、Mn、Mo、Cr、Ni、CuおよびＶから選ばれた１種または２種以上を含有でき、さらに好ましくはMn：1.2mass ％以下、Mo：2.3 mass％以下、Cr：3.0 mass％以下、Ni：5.0 mass％以下、Cu：2.0 mass％以下、Ｖ：1.4 mass％以下から選ばれた１種または２種以上を含有できる。なお、Mn、Mo、Cr、Cu、Ｖのより好ましい含有量は、Mn：1.0 mass％以下、Mo：2.0 mass％以下、Cr：3.0 mass％以下、Ni：5.0 mass％以下、Cu：2.0 mass％以下、Ｖ：1.0 mass％以下である。Mn、Mo、Cr、Ni、Cu、Ｖは、いずれも焼結体の強度を増加し、あるいは焼入れ性を増加するために、必要に応じ選択して含有できる。これら合金元素は、鉄基金属粉に予合金化しても、また鉄基金属粉に部分拡散付着して部分合金化してもよく、あるいは金属粉（合金用粉）として混合してもよい。これらの内でも、部分合金化したものは、同一合金量で比べると、圧縮性に最も優れているので好ましい。しかし、いずれの場合においても、Mn：1.2mass ％、Mo：2.3 mass％、Cr：3.0 mass％、Ni：5.0 mass％、Cu：2.0 mass％、Ｖ：1.4 mass％を、それぞれ超えると、成形用素材の硬さが高くなり鍛造時の成形荷重が増大する。
【００１６】
原料粉として使用する黒鉛粉は、鍛造部品の所定の強度を確保するため、あるいは熱処理時の焼入れ性の増加を目的として、鉄基混合粉に、鉄基金属粉と黒鉛粉との合計量に対し0.03〜0.5mass ％含有されることが好ましい。黒鉛粉の含有量が、0.03mass％未満では、焼結体の強度向上効果が不足し、一方、0.5mass ％を超えると、鍛造時の圧縮荷重が過大となる。このため、鉄基混合粉における黒鉛粉の含有量は鉄基金属粉と黒鉛粉との合計量に対し0.03〜0.5mass ％とすることが好ましい。
【００１７】
また、鉄基金属粉表面への黒鉛粉の付着度を向上させるために、鉄基混合粉へワックス、スピンドル油等を添加してもよい。また、例えば、特開平1-165701号公報、特開平5-148505号公報に記載された偏析防止処理を適用し、鉄基金属質粉表面への黒鉛粉付着度を向上させることもできる。
また、鉄基混合粉には、上記した原料粉に加えて、さらに圧縮成形における成形密度の向上と金型からの抜出し力を低減する目的で、ステアリン酸亜鉛、ステアリン酸リチウム、ステアリン酸カルシウム等の金属石鹸、ステアリン酸アミド、オレイン酸アミド、エチレンビスステアロアミド等の高級脂肪酸および、ステアリン酸、オレイン酸等の高級脂肪酸、スピンドル油、タービン油、ワックス等の潤滑剤を含有できる。潤滑剤の含有量は、鉄基金属粉と黒鉛粉との合計量100 重量部に対し0.1 〜0.6 重量部とするのが好ましい。
【００１８】
なお、鉄基混合粉の混合には、通常公知な混合方法、例えばヘンシェルミキサー、コーン型ミキサー等を用いた混合方法が適用可能である。
好ましくは上記した比率で混合された鉄基混合粉は、ついで予備圧縮成形を施される。予備圧縮成形は、通常公知の圧粉成形技術、例えば金型潤滑法、分割金型による多段成形法、ＣＮＣプレス法、静圧プレス法、特開平11-117002 号公報に記載されたプレス成形法、温間成形法、あるいはこれらを組み合わせた成形方法等がいずれも適用可能である。例えば、特開平11-117002 号公報に記載されたプレス成形法によれば、原料粉末や金型を加熱することなく容易に高密度の成形体を製造することができる。
【００１９】
予備成形体の密度は、7.3Mg/m³未満とすることが好ましい。予備成形体の密度を7.3Mg/m³未満とすることにより、使用する鉄基粉末等の原料粉末の条件、予備成形条件等の制約を大幅に緩和できるという効果がある。本発明では、予備成形体の密度が7.3Mg/m³未満であっても、高密度の鍛造部品を得ることができる。本発明では、予備成形体の密度によらず、焼結、鍛造工程により、高密度鍛造部品とすることができる。なお、本発明によれば、予備成形体の密度が低いほど大幅な密度上昇が期待できる。なお、予備成形体の密度を7.3Mg/m³以上の密度としてもよいことはいうまでもない。
【００２０】
ついで、予備成形体は、焼結され、成形用素材とされる。
焼結は、窒素分圧が30kPa 以下の非酸化性雰囲気中で 950℃以上1300℃以下の温度で行う。焼結温度が 950℃未満では、黒鉛の素地への拡散が不十分のため、再結晶工程で残留した黒鉛が素地へ拡散、消失して空孔となるため、強度低下の原因となる可能性がある。一方、焼結温度が1300℃を超えても、成形性の向上効果は飽和し、これに対し製造コストが格段に増加するため、経済的に不利となる。このため、焼結温度は 950℃以上1300℃以下に限定した。
【００２１】
本発明では、焼結は、真空中、Ａｒガス中、あるいは水素ガス等の非酸化性でかつ窒素分圧が30kPa 以下である雰囲気中で行う。窒素分圧が低いほど、成形用素材のＮ含有量が低減し、その後の冷間鍛造時の鍛造荷重低減には有利となる。好ましい雰囲気としては、例えば、水素濃度が70vol ％以上の水素−窒素混合ガスがある。一方、窒素分圧が30kPa を超えると、成形用素材のＮ含有量が0.010mass ％を超えて多くなり、上記した効果が期待できなくなる。なお、焼結の処理時間は目的、条件により適宜設定できるが、通常は600 〜7200ｓの範囲とすることが好ましい。
【００２２】
また、本発明では、予備成形体に焼結を施した後に、好ましくは焼結温度より低い温度で焼鈍を行い、成形用素材としてもよい。これにより、成形用素材の圧縮性 (冷間鍛造性）が顕著に改善される。この理由については、現在までに必ずしも明確にはなっていないが、本発明者らは次のように考えている。
本発明者らの研究によれば、予備成形体に焼結を施し焼結体としたのち、焼鈍処理を施すと、成形用素材となる焼結体のＮ含有量が低減することが観測されている。これは、焼鈍処理中に焼結体内でα相への変態が進行し、Ｎの鉄合金基地への溶解度が低下するため、焼結体中のＮ含有量が低減すると推察される。この焼鈍による脱窒作用が、成形用素材の圧縮性改善の一因であると考えられる。
【００２３】
また、焼結後の焼鈍は、400 〜800 ℃の範囲の温度で行うのが好ましい。焼鈍温度が400 ℃未満あるいは800 ℃超では、Ｎ量低減効果が小さくなる。また、焼鈍時の雰囲気は、焼結時の雰囲気と同様に、非酸化性とするのがより好ましい。さらに、脱窒効率の向上のためには、焼鈍雰囲気中の窒素分圧を95 kPa以下とすることが好ましい。なお、焼鈍時の雰囲気中の窒素分圧と、焼結時の雰囲気中の窒素分圧とは必ずしも同一とする必要はない。
【００２４】
また、焼鈍時間は、600 〜7200ｓの範囲とするのが好ましい。焼鈍時間が、600 ｓ未満では、窒素低減効果が少なく、また、7200ｓを超えると、効果が飽和するうえ、生産性が低下する。なお、より好ましくは、1200〜3600ｓである。
また、焼結とその後に続く焼鈍は、焼結を行った焼結炉から素材を取り出すことなく、連続して行っても何ら問題はない。焼結し、400 〜800 ℃に冷却して、そのまま焼鈍してもよい。また、焼結後、400 ℃未満まで冷却したのち、400 〜800 ℃で焼鈍してもよい。また、焼鈍は、一定の温度に均一に保持する必要はなく、例えば、400 〜800 ℃間を徐冷してもよい。徐冷する場合、上記した温度域を、通常の冷却速度で通過する時間 (約2400ｓ）に比べ、600 〜7200ｓ、好ましくは3600〜7200ｓ余分に掛かるように冷却速度を低下させてもよい。
【００２５】
ついで、成形用素材は、冷間で鍛造を施され、鍛造部品とされる。
本発明では、鍛造は密閉鍛造あるいは閉塞鍛造とする。本発明でいう「密閉鍛造」とは、成形用素材のほぼ前表面が金型表面によって拘束され、金型の隙間から素材がはみ出さないようにして行う鍛造を意味する。また、本発明でいう「閉塞鍛造」とは、素材を金型内に閉じ込めたのち、パンチ等で素材を押し、素材を金型の空間内に充満させる鍛造をいう。
【００２６】
上記した方法で得られた成形用素材に、冷間で、密閉鍛造あるいは閉塞鍛造を施すことにより、高密度でかつ寸法精度に優れた鍛造部品を、比較的低い鍛造荷重で成形できる。本発明における密閉鍛造あるいは閉塞鍛造では、成形性の向上、あるいは更なる高密度化のために金型潤滑を施すことが好ましい。金型潤滑は、鍛造前に潤滑剤を塗布する、あるいは鍛造時に固体潤滑剤を使用する通常の方法がいずれも好適である。
【００２７】
また、本発明における密閉鍛造あるいは閉塞鍛造では、金型は、密閉構造または閉塞構造の金型とし、好ましくは成形用素材と所定量のクリアランスが設定できる金型とする。クリアランスを設定することにより、鍛造時、成形用素材に所定量の塑性流動を誘起させることができ、密度をさらに向上させることができる。
【００２８】
得られた鍛造部品は、そのまま仕上加工等を施されて製品とされるか、あるいは必要に応じ再焼結および／または熱処理を施されて製品とされる。
熱処理は、目的に応じ、浸炭処理、焼入れ処理、焼戻し処理等を選択できる。例えば、ガス浸炭焼入れでは、カーボンポテンシャルが0.6 〜１％程度の雰囲気で、800 〜900 ℃程度の温度で加熱したのち、油中に焼入れするのが好ましい。また、光輝焼入れでは、焼結体の表面の高温酸化、脱炭防止のため、Ａｒガス等の不活性雰囲気、水素を含む窒素雰囲気等の保護雰囲気中で、800 〜950 ℃程度の温度に加熱したのち、油中に焼入れするのが好ましい。また、真空浸炭焼入れ、高周波焼入れでも、上記した温度範囲に加熱したのち、焼入れするのが好ましい。これらの熱処理により製品の強度を向上することができる。また、焼入れ処理後に、必要に応じ焼戻し処理を施してもよい。焼戻し温度は、130 〜250 ℃の通常公知の焼戻し温度範囲とするのが好ましい。なお、熱処理の前あるいは後に、寸法、形状の調整のために、機械加工を施してもよい。
【００２９】
【実施例】
アトマイズ純鉄粉（川崎製鉄（株）製KIP301A ）にMoO₃粉末を所定量配合し、Ｖ型混合機で15分間混合し、混合粉とした。この混合粉を水素ガス気流中で 900℃、１時間熱処理して、MoO₃粉を還元すると共に鉄粉粒子表面にMoを拡散付着し部分合金化した鉄基金属粉Ａを製造した。Mo量は化学分析により1.0mass ％であった。なお鉄基金属粉Ａは予め合金成分（予合金）としてMnを0.15mass％含有している。
【００３０】
また、水アトマイズ法にて、Mo：1.0mass ％、Mn：0.13mass％を予合金化して含有する鉄基金属粉Ｂを製造した。
鉄基金属粉Ａ、Ｂともに、Ｃ：0.01mass％、Ｏ：0.15mass％以下、Ｎ：0.01mass％以下であった。また、鉄基金属粉Ａ、Ｂともに平均粒径（ｄ₅₀）は70〜80μm の間であった。
【００３１】
上記した２種の鉄基金属粉Ａ、Ｂに、表１に示す種類と含有量の、黒鉛粉と潤滑剤とをＶ型混合機で混合し、鉄基混合粉とした。潤滑剤はステアリン酸亜鉛を用いた。
これら鉄基混合粉を金型に装入し、油圧式圧縮成形機により成形圧力を調整して予備圧縮成形し、30mmφ×13mm高さのタブレット状予備成形体とした。予備成形体の密度は6.88〜7.12Mg/m³とした。
【００３２】
得られた予備成形体に、表１に示す条件で焼結を施し、成形用素材とした。なお、一部の試料（試料No. ５〜No. ９およびNo. 11〜No. 16）では、焼結と連続して表１に示す焼鈍を行った。
ついで、得られた成形用素材を、密閉構造の金型に装入し、冷間密閉鍛造を施して円板状の鍛造部品（大きさ：φ30×13mm)(製品）とした。なお、金型はクリアランス（＝金型内径−成形用素材外径）を0.4mm とした。また、密閉鍛造時の鍛造荷重を測定した。得られた鍛造部品の密度をアルキメデス法で、硬さをロックウェル硬さ計（Ｂスケール）で、それぞれ測定した。
【００３３】
また、鍛造を行った後に、鍛造部品（製品）を観察し、製品の外周面が金型に接触した面積と金型の外周面積の比を求め、転写性を評価した。この比の値が95％以上の場合を◎、90％以上95％未満の場合を○、80％以上90％未満の場合を△、80％未満の場合を×と評価した。この値が大きいほど、寸法精度に優れているといえる。なお、製品の外周面と金型との接触の有無は、製品外周面の光沢の有無で判断した。製品と金型が接触した場合には製品外周面に光沢がでる。
【００３４】
得られた結果を表１に併記した。
【００３５】
【表１】

【００３６】
【表２】

【００３７】
本発明例（試料No.1、No.2、No.5、No.6、）は、窒素分圧の高い条件で焼結した比較例（試料No.3、No.4、No.7、No.8、）に比べて、同一鍛造荷重で成形した場合の密度が高く（すなわちより低い荷重で鍛造できる）、転写性にも優れていた（寸法精度に優れていた）。また、焼結後に、焼鈍を施した本発明例（試料No.5、No.6）は、焼鈍を施さない本発明例（試料No.1、No.2）よりも、同一鍛造荷重で成形した場合に密度が高く、転写性にも優れていた。また、焼鈍温度を 400℃〜 800℃とした本発明例（試料No. 13、No.14 、No.15)は、焼鈍温度が 300℃の本発明例（試料No.12)や焼鈍温度が 900℃の本発明例（試料No.15 、No.16)よりも、同一鍛造荷重で成形した場合に密度が高く、転写性にも優れていた。
【００３８】
また、部分合金化した鉄基金属粉Ａを用いた本発明例（試料No.1、No.5）は、予合金化した鉄基金属粉Ｂを用いた本発明例（試料No.10 、No.11)よりも同一鍛造荷重で成形した場合に密度が高く、転写性にも優れていた。
【００３９】
【発明の効果】
本発明によれば、高密度の鍛造部品を低鍛造荷重で製造でき、しかも高い寸法精度で製造でき、産業上格段の効果を奏する。
【図面の簡単な説明】
【図１】本発明の鍛造部品の製造方法の一例を示す説明図である。[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for manufacturing an iron-based forged part suitable for use in a machine part, and particularly relates to reduction of forging load and improvement of density and dimensional accuracy.
[0002]
[Prior art]
Powder metallurgy technology can manufacture parts with complex shapes in a near net shape with high dimensional accuracy, and can greatly reduce cutting costs. In recent years, there has been a strong demand for iron-based powder metallurgy products (iron-based powder products (iron-based sintered parts)) in order to reduce the size and weight of the parts.
[0003]
Iron-based sintered parts (also referred to as iron-based sintered bodies or simply sintered bodies) include iron-based metal powders, alloy powders such as graphite powder and copper powder, and lubricants such as zinc stearate and lithium stearate. And then iron-based mixed powder, and then the iron-based mixed powder is filled into a mold and compression molded to form a molded body, and then the molded body is sintered to form a sintered body. It is common. The obtained sintered body is subjected to sizing and cutting as necessary to obtain a product. In addition, when high strength is required, the sintered body may be further subjected to carburizing heat treatment or bright heat treatment. The density of the molded body obtained by such a process is at most about 6.6 to 7.1 Mg / m ³ , and therefore the density of the sintered body obtained from these molded bodies is also this level.
[0004]
To increase the strength of iron-based powder products (iron-based sintered parts), it is effective to increase the density of sintered parts (sintered bodies) by increasing the density of the compact. The higher the density of the sintered part (sintered body), the smaller the voids in the member, and the mechanical properties such as tensile strength, impact value, and fatigue strength are improved.
As a forming method to increase the density of iron-based powder products (iron-based sintered parts), for example, sintering cold forging that combines powder metallurgy and cold forging to obtain products that are close to true density A method is proposed in Japanese Patent Laid-Open No. 1-123005. The sintering cold forging method is a molding and processing method in which a preform (preliminary product) obtained by sintering metal powder is forged in a cold state and then re-sintered to obtain a final product having a high density composition. . The technique described in Japanese Patent Application Laid-Open No. 1-123005 is such that a cold forging sintered preform having a liquid lubricant applied to the surface is temporarily compression-molded in a die, and then a negative pressure is applied to the preform. This is a sintering cold forging method in which a liquid lubricant is removed by suction, and then subjected to main compression molding in a die and re-sintering. According to this method, the liquid lubricant applied and infiltrated into the interior before temporary compression molding is sucked before the main compression molding. It is supposed to be done. However, the density of the final sintered product obtained by this method is limited to about 7.5 Mg / m ³ , so its strength is limited.
[0005]
On the other hand, in order to further increase the strength of the sintered product (sintered body), it is effective to increase the carbon (C) concentration of the product. In the powder metallurgy method, as a carbon (C) source, graphite powder is generally mixed with raw metal powder. However, the metal powder mixed with graphite powder is pre-molded and then pre-sintered (pre-sintered). A method for obtaining a high-strength sintered body by re-sintering after forming a molding material and further recompression molding is conceivable. However, when pre-sintering (pre-sintering) is performed by a conventional method, carbon (C) diffuses throughout the forming material during pre-sintering (pre-sintering), and the hardness of the forming material increases. For this reason, when performing the recompression molding, there is a problem that the molding load becomes very large and the deformability is lowered, so that it cannot be processed into a desired shape. Therefore, a product with high strength and high density cannot be obtained.
[0006]
For such a problem, for example, US Pat. No. 4,393,563 discloses a method of manufacturing a bearing component without performing molding at a high temperature. In this method, iron powder, iron alloy powder, graphite powder, and lubricant are mixed, the mixed powder is formed into a preform, then pre-sintered, and then cooled to give at least 50% plastic working. It consists of a process of performing forging, then sintering and annealing, and roll processing to obtain a final product (sintered member). In the technique described in U.S. Pat. No. 4,393,563, by performing pre-sintering under the condition of suppressing the diffusion of graphite, it is possible to develop a high deformability in the subsequent cold forging and reduce the molding load. It is said. However, in US Pat. No. 4,393,563, 1100 ° C. × 15 to 20 min is recommended as a pre-sintering condition, and according to experiments conducted by the present inventors, graphite is completely contained in the preform. It has been found that the hardness of the sintered member material (preliminary product) is remarkably increased and subsequent cold forging is difficult.
[0007]
In order to deal with such problems, for example, Japanese Patent Application Laid-Open No. 11-117002 discloses a powder obtained by compacting a metal powder obtained by mixing 0.3% by weight or more of graphite with a metal powder containing iron as a main component. Further, a metal having a structure in which a preform having a density of 7.3 Mg / m ³ or more is pre-sintered preferably in a temperature range of 700 to 1000 ° C., and graphite remains in the grain boundary of the metal powder. A powder molding material has been proposed. According to this technology, only the amount of carbon necessary for increasing the strength is dissolved, leaving free graphite and preventing excessive hardening of the iron powder. It is said that a molding material having performance can be obtained. However, the metal powder molding material obtained by this method has a high deformability in the recompression molding process, but the remaining free graphite disappears during the subsequent main sintering, and elongated pores are formed. There remained a problem that could occur.
[0008]
Japanese Patent Laid-Open No. 2000-303106 discloses a powder obtained by compacting a metal powder obtained by mixing 0.3% by weight or more of graphite with a metal powder mainly composed of iron, and has a density of 7.3 Mg / a pre-sintering step of pre-sintering a preform of m ³ or more at a predetermined temperature to obtain a metal powder molding material having a structure in which graphite remains in the grain boundaries of the metal powder; A sintered body comprising: a recompression process for recompressing the metal powder molding material obtained in the sintering process; and a re-sintering process for re-sintering the recompression molded body obtained in the recompression process. The manufacturing method of this is proposed.
[0009]
Japanese Patent Application Laid-Open No. 2000-355726 discloses a powder having a density of 7.3 Mg / m ³ or more obtained by compacting metallic powder obtained by mixing 0.1% by weight or more of graphite with alloy steel powder. The preform is pre-sintered at a predetermined temperature to form a metal powder molding material having a structure in which graphite remains in the grain boundary of the metal powder, and the metal powder molding material is recompressed and molded. An alloy steel powder plastic working body having a densified structure with almost no voids, and this alloy steel powder plastic working body is re-sintered at a predetermined temperature, so that a structure in which graphite is diffused and a structure in which graphite remains are regenerated. An alloy steel powder re-sintered body having a predetermined ratio according to the sintering temperature is shown.
[0010]
[Problems to be solved by the invention]
According to the techniques described in Japanese Patent Application Laid-Open Nos. 2000-303106 and 2000-355726, high-density and high-strength sintered bodies can be obtained. In the technology described in the publication No. 2000-355726, when the density of the material before recompression molding is less than 7.3 Mg / m ³ , depending on the recompression molding method, it is difficult to obtain high density and high dimensional accuracy parts. was there.
[0011]
An object of the present invention is to solve the above-described problems of the prior art, and to propose a method for manufacturing an iron-based forged part that enables a high-density and high-dimensional precision part to be manufactured with a low forging load.
[0012]
[Means for Solving the Problems]
In order to achieve the above-described problems, the present inventors diligently studied sintering conditions and molding conditions. As a result, after pre-molding the mixed powder, it is sintered in a low nitrogen atmosphere at a temperature at which the added graphite is diffused to the base, or further annealed, and then cold sealed or closed forging is performed. We found that it was effective to do. As a result, it has been found that a forged part having high density and significantly improved dimensional accuracy can be obtained even if the density after preforming is low. In addition, it has also been found that forming (forging) after sintering can be performed with a low forming (forging) load.
[0013]
The present invention has been completed with further studies based on the above findings.
That is, the present invention, after pre-compression molding an iron-based mixed powder containing iron-based metal powder and graphite powder into a pre-compression molded body, the pre-compression molded body has a nitrogen partial pressure of 30 kPa or less. Sintered at a temperature of 950 ° C or higher and 1300 ° C or lower in an oxidizing atmosphere to form a molding material, and then subject the molding material to closed or closed forging to form a high-density forged part. A method for producing a high-density iron-base forged part, wherein the iron-base metal powder is obtained by partially diffusing and attaching one or more metals selected from Mn, Mo, Cr, Ni, Cu and V. In the present invention, it is preferable to further anneal after the sintering, and in the present invention, the annealing is preferably performed in a temperature range of 400 ° C to 800 ° C, in the present invention, the preliminary compression molded article, preferred to have a density of less than 7.3 Mg / m ³ There.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, an example of the manufacturing process of the iron-base forged part of this invention is shown.
As the raw material powder, iron-based metal powder, graphite powder, or alloy powder is used. The iron-based metal powder to be used can be appropriately selected according to the application, and is not particularly limited. However, from the viewpoint of compressibility, in the present invention, it is mass%, C: 0.05% or less, O: 0.3% or less, N: An iron-based metal powder having a composition comprising 0.010% or less and the balance being Fe and inevitable impurities is suitable. In addition, it is preferable from the viewpoint of compression moldability that the O content of the iron-based metal powder is as low as possible. However, O is an element that is unavoidably contained, and can be industrially implemented without being economically expensive. It is desirable to make the level 0.02 mass% the lower limit. In view of industrial economy, the preferable O content is 0.03 to 0.2 mass%. Further, the N content of the iron-based metal powder is preferably reduced as much as possible from the viewpoint of reducing the forming (forging) load, but from the viewpoint of industrial economy, N is preferably 0.010% or less. .
[0015]
The particle size of the iron-based metal powder used in the present invention is not particularly limited, but it is desirable that the average particle size is 30 to 120 μm, which can be produced industrially at low cost. The average particle size is the value of the middle point (d ₅₀ ) of the weight integrated particle size distribution.
Further, in the present invention, in addition to the above-described composition, one or more selected from Mn, Mo, Cr, Ni, Cu and V can be contained as required, and more preferably, Mn: 1.2 mass %, Mo: 2.3 mass% or less, Cr: 3.0 mass% or less, Ni: 5.0 mass% or less, Cu: 2.0 mass% or less, V: 1.4 mass% or less . More preferable contents of Mn, Mo, Cr, Cu, V are Mn: 1.0 mass% or less, Mo: 2.0 mass% or less, Cr: 3.0 mass% or less, Ni: 5.0 mass% or less, Cu: 2.0 mass % Or less, V: 1.0 mass% or less. Mn, Mo, Cr, Ni, Cu, and V can be selected and contained as necessary in order to increase the strength of the sintered body or increase the hardenability. These alloy elements may be pre-alloyed to iron-based metal powder, may be partially diffused and adhered to iron-based metal powder, or may be partially alloyed, or may be mixed as metal powder (alloy powder). Among these, those which are partially alloyed are preferable because they are most excellent in compressibility when compared with the same alloy amount. However, in any case, if Mn: 1.2 mass%, Mo: 2.3 mass%, Cr: 3.0 mass%, Ni: 5.0 mass%, Cu: 2.0 mass%, V: 1.4 mass%, respectively, forming exceeds The hardness of the material for use increases and the forming load during forging increases.
[0016]
The graphite powder used as the raw material powder is added to the iron-based mixed powder and the total amount of iron-based metal powder and graphite powder for the purpose of ensuring the prescribed strength of the forged parts or for the purpose of increasing the hardenability during heat treatment. It is preferable to contain 0.03-0.5 mass%. When the content of graphite powder is less than 0.03 mass%, the effect of improving the strength of the sintered body is insufficient. On the other hand, when the content exceeds 0.5 mass%, the compressive load during forging becomes excessive. For this reason, it is preferable that content of the graphite powder in iron-based mixed powder shall be 0.03-0.5 mass% with respect to the total amount of iron-based metal powder and graphite powder.
[0017]
In order to improve the adhesion of the graphite powder to the surface of the iron-based metal powder, wax, spindle oil or the like may be added to the iron-based mixed powder. Further, for example, the segregation preventing treatment described in JP-A-1-65701 and JP-A-5-148505 can be applied to improve the adhesion of graphite powder to the surface of the iron-based metallic powder.
In addition to the above-mentioned raw material powder, the iron-based mixed powder further includes zinc stearate, lithium stearate, calcium stearate, etc. for the purpose of improving the molding density in compression molding and reducing the extraction force from the mold. Lubricants such as higher fatty acids such as metal soap, stearamide, oleamide, ethylene bisstearamide, higher fatty acids such as stearic acid and oleic acid, spindle oil, turbine oil, wax and the like can be contained. The content of the lubricant is preferably 0.1 to 0.6 parts by weight with respect to 100 parts by weight of the total amount of the iron-based metal powder and the graphite powder.
[0018]
For mixing the iron-based mixed powder, a generally known mixing method, for example, a mixing method using a Henschel mixer, a corn type mixer or the like can be applied.
Preferably, the iron-based mixed powder mixed in the above ratio is then subjected to preliminary compression molding. The pre-compression molding is usually performed by a conventionally known compacting technique, for example, a die lubrication method, a multistage molding method using a split die, a CNC pressing method, a hydrostatic pressing method, or a press molding method described in JP-A-11-117002. Any of a warm molding method, a molding method combining these, and the like can be applied. For example, according to the press molding method described in JP-A-11-117002, a high-density molded body can be easily produced without heating the raw material powder or the mold.
[0019]
The density of the preform is preferably less than 7.3 Mg / m ³ . By setting the density of the preform to less than 7.3 Mg / m ³ , there is an effect that the restrictions on the conditions of the raw material powder such as iron-based powder to be used, the preforming conditions, etc. can be greatly relaxed. In the present invention, a high-density forged part can be obtained even if the density of the preform is less than 7.3 Mg / m ³ . In the present invention, a high-density forged part can be obtained by a sintering and forging process regardless of the density of the preform. According to the present invention, a significant increase in density can be expected as the density of the preform is lower. Needless to say, the density of the preform may be 7.3 Mg / m ³ or more.
[0020]
Next, the preform is sintered and used as a molding material.
Sintering is performed at a temperature between 950 ° C. and 1300 ° C. in a non-oxidizing atmosphere with a nitrogen partial pressure of 30 kPa or less. If the sintering temperature is less than 950 ° C, the graphite will not be sufficiently diffused into the substrate, and the graphite remaining in the recrystallization process will diffuse into the substrate and disappear, resulting in voids, which may cause a decrease in strength. There is. On the other hand, even if the sintering temperature exceeds 1300 ° C., the effect of improving the formability is saturated, and on the other hand, the manufacturing cost is remarkably increased, which is economically disadvantageous. For this reason, the sintering temperature was limited to 950 ° C or higher and 1300 ° C or lower.
[0021]
In the present invention, sintering is performed in a vacuum, Ar gas, or an atmosphere that is non-oxidative and has a nitrogen partial pressure of 30 kPa or less, such as hydrogen gas. The lower the nitrogen partial pressure, the lower the N content of the forming material, which is advantageous for reducing the forging load during subsequent cold forging. As a preferable atmosphere, for example, there is a hydrogen-nitrogen mixed gas having a hydrogen concentration of 70 vol% or more. On the other hand, when the nitrogen partial pressure exceeds 30 kPa, the N content of the molding material exceeds 0.010 mass%, and the above-described effects cannot be expected. In addition, although the processing time of sintering can be suitably set according to the objective and conditions, it is preferable to set it as the range of 600-7200 s normally.
[0022]
In the present invention, after the preform is sintered, it is preferably annealed at a temperature lower than the sintering temperature to obtain a molding material. Thereby, the compressibility (cold forgeability) of the forming material is remarkably improved. The reason for this is not necessarily clear up to now, but the present inventors consider as follows.
According to the studies by the present inventors, it is observed that when the preform is sintered to form a sintered body and then annealed, the N content of the sintered body that becomes the forming material is reduced. ing. This is presumed that the N content in the sintered body is reduced because the transformation into the α phase proceeds in the sintered body during the annealing treatment, and the solubility of N in the iron alloy matrix decreases. This denitrification effect due to annealing is considered to be a factor in improving the compressibility of the molding material.
[0023]
The annealing after sintering is preferably performed at a temperature in the range of 400 to 800 ° C. When the annealing temperature is less than 400 ° C. or more than 800 ° C., the effect of reducing the amount of N becomes small. The atmosphere during annealing is more preferably non-oxidizing like the atmosphere during sintering. Furthermore, in order to improve the denitrification efficiency, it is preferable to set the nitrogen partial pressure in the annealing atmosphere to 95 kPa or less. Note that the nitrogen partial pressure in the atmosphere during annealing and the nitrogen partial pressure in the atmosphere during sintering are not necessarily the same.
[0024]
The annealing time is preferably in the range of 600 to 7200 s. When the annealing time is less than 600 s, the effect of reducing nitrogen is small, and when it exceeds 7200 s, the effect is saturated and productivity is lowered. In addition, More preferably, it is 1200-3600s.
Moreover, there is no problem even if the sintering and the subsequent annealing are performed continuously without taking out the material from the sintering furnace where the sintering is performed. It may be sintered, cooled to 400 to 800 ° C., and annealed as it is. Moreover, after sintering, it may be annealed at 400 to 800 ° C. after cooling to less than 400 ° C. Moreover, annealing does not need to hold | maintain uniformly at fixed temperature, For example, you may cool slowly between 400-800 degreeC. In the case of slow cooling, the cooling rate may be lowered so that it takes 600 to 7200 s, preferably 3600 to 7200 s, in comparison with the time required for passing the above temperature range at the normal cooling rate (about 2400 s).
[0025]
Next, the forming material is cold-forged to form a forged part.
In the present invention, forging is closed forging or closed forging. The “sealed forging” as used in the present invention means forging performed in such a manner that the front surface of the molding material is almost constrained by the mold surface so that the material does not protrude from the gap between the molds. In addition, “closed forging” in the present invention refers to forging in which a material is confined in a mold and then the material is pushed by a punch or the like to fill the material in the mold space.
[0026]
By subjecting the forming material obtained by the above method to cold forging or closed forging, a forged part having high density and excellent dimensional accuracy can be formed with a relatively low forging load. In the closed forging or closed forging in the present invention, it is preferable to perform mold lubrication in order to improve moldability or further increase the density. As the mold lubrication, any ordinary method in which a lubricant is applied before forging or a solid lubricant is used during forging is suitable.
[0027]
In the closed forging or closed forging in the present invention, the mold is a mold having a closed structure or a closed structure, and preferably a mold capable of setting a predetermined amount of clearance with a molding material. By setting the clearance, a predetermined amount of plastic flow can be induced in the forming material during forging, and the density can be further improved.
[0028]
The obtained forged part is subjected to finish processing or the like as it is to obtain a product, or is subjected to re-sintering and / or heat treatment as necessary to obtain a product.
As the heat treatment, carburizing treatment, quenching treatment, tempering treatment or the like can be selected according to the purpose. For example, in gas carburizing and quenching, it is preferable to heat in an oil in an atmosphere having a carbon potential of about 0.6 to 1%, and then quench in oil. In bright quenching, in order to prevent high-temperature oxidation and decarburization of the surface of the sintered body, it is heated to a temperature of about 800 to 950 ° C in a protective atmosphere such as an inert atmosphere such as Ar gas or a nitrogen atmosphere containing hydrogen. After that, it is preferable to quench in oil. Also, in vacuum carburizing and induction hardening, it is preferable to quench after heating to the above temperature range. These heat treatments can improve the strength of the product. Moreover, you may perform a tempering process as needed after a quenching process. It is preferable that the tempering temperature is within a generally known tempering temperature range of 130 to 250 ° C. In addition, before or after the heat treatment, machining may be performed to adjust the size and shape.
[0029]
【Example】
A predetermined amount of MoO ₃ powder was mixed with atomized pure iron powder (KIP301A manufactured by Kawasaki Steel Co., Ltd.) and mixed with a V-type mixer for 15 minutes to obtain a mixed powder. This mixed powder was heat-treated in a hydrogen gas stream at 900 ° C. for 1 hour to reduce the MoO ₃ powder and to produce iron-based metal powder A in which Mo was diffused and adhered to the surface of the iron powder particles and partially alloyed. The amount of Mo was 1.0 mass% by chemical analysis. The iron-based metal powder A previously contains 0.15 mass% of Mn as an alloy component (pre-alloy).
[0030]
Moreover, the iron-based metal powder B which contains Mo: 1.0 mass% and Mn: 0.13 mass% by pre-alloying by the water atomization method was manufactured.
Both iron-based metal powders A and B had C: 0.01 mass%, O: 0.15 mass% or less, and N: 0.01 mass% or less. Further, both the iron-based metal powders A and B had an average particle diameter (d ₅₀ ) of 70 to 80 μm.
[0031]
The above-mentioned two types of iron-based metal powders A and B were mixed with graphite powder and a lubricant having the types and contents shown in Table 1 using a V-type mixer to obtain iron-based mixed powders. As the lubricant, zinc stearate was used.
These iron-based mixed powders were charged into a mold, preliminarily compression-molded by adjusting the molding pressure with a hydraulic compression molding machine, and formed into a tablet-shaped preform with a height of 30 mmφ × 13 mm. The density of the preform was 6.88 to 7.12 Mg / m ³ .
[0032]
The obtained preform was sintered under the conditions shown in Table 1 to obtain a molding material. In addition, some samples (samples No. 5 to No. 9 and No. 11 to No. 16) were annealed as shown in Table 1 continuously with the sintering.
Next, the obtained molding material was inserted into a mold having a hermetic structure and subjected to cold hermetic forging to obtain a disk-shaped forged part (size: φ30 × 13 mm) (product). The mold had a clearance (= mold inner diameter−molding material outer diameter) of 0.4 mm. Moreover, the forging load at the time of closed forging was measured. The density of the obtained forged parts was measured by the Archimedes method, and the hardness was measured by a Rockwell hardness meter (B scale).
[0033]
Further, after forging, the forged part (product) was observed, and the ratio of the area where the outer peripheral surface of the product was in contact with the mold and the outer peripheral area of the mold was determined to evaluate the transferability. A case where the value of this ratio was 95% or more was evaluated as 90, a case where it was 90% or more and less than 95%, ○, a case where it was 80% or more and less than 90%, or a case where it was less than 80%. It can be said that the larger this value, the better the dimensional accuracy. The presence / absence of contact between the outer peripheral surface of the product and the mold was determined by the presence / absence of gloss on the outer peripheral surface of the product. When the product and the mold come into contact, the outer peripheral surface of the product becomes glossy.
[0034]
The obtained results are also shown in Table 1.
[0035]
[Table 1]

[0036]
[Table 2]

[0037]
Examples of the present invention (Sample No. 1, No. 2, No. 5, No. 6,) are comparative examples (sample No. 3, No. 4, No. 7, Compared to No. 8,), the density when molded with the same forging load was high (that is, it was possible to forge with a lower load), and the transferability was also excellent (excellent dimensional accuracy). In addition, the inventive examples (samples No. 5 and No. 6) that were annealed after sintering were molded at the same forging load than the inventive examples that were not annealed (samples No. 1 and No. 2). The density was high and the transferability was excellent. In addition, the present invention examples (samples No. 13, No. 14, No. 15) having an annealing temperature of 400 ° C. to 800 ° C. are the same as the present invention example (sample No. 12) having an annealing temperature of 300 ° C. Compared to the present invention examples at 900 ° C. (samples No. 15 and No. 16), the density was higher when the same forging load was formed, and the transferability was also excellent.
[0038]
Further, the present invention example using the partially alloyed iron-based metal powder A (sample No. 1, No. 5) is the present invention example using the pre-alloyed iron-based metal powder B (sample No. 10, When molded with the same forging load than No. 11), the density was high and the transferability was also excellent.
[0039]
【The invention's effect】
According to the present invention, a high-density forged part can be manufactured with a low forging load, and can be manufactured with high dimensional accuracy, which has a remarkable industrial effect.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an example of a method for producing a forged part according to the present invention.

Claims

After pre-compressing an iron-based mixed powder containing iron-based metal powder and graphite powder into a pre-compression molded body, the pre-compression molded body was subjected to a nitrogen partial pressure of 30 kPa or less in a non-oxidizing atmosphere. A high-density iron base characterized in that it is sintered at a temperature not lower than 1 ° C and not higher than 1300 ° C to form a molding material, and then the molding material is subjected to closed forging or closed forging to form a high-density forged part. Manufacturing method for forged parts.

2. The high density according to claim 1, wherein the iron-based metal powder is formed by partial diffusion adhesion of one or more metals selected from Mn, Mo, Cr, Ni, Cu, and V. 3. Manufacturing method of iron-based forged parts.

The method for producing a high-density iron-based forged part according to claim 1 or 2, further comprising annealing after the sintering.

The method for producing a high-density iron-base forged part according to claim 3, wherein the annealing is performed in a temperature range of 400 ° C to 800 ° C.

The method for producing a high-density iron-base forged part according to any one of claims 1 to 4, wherein the pre-compressed compact has a density of less than 7.3 Mg / m ³ .