JP3648758B2

JP3648758B2 - Nitrogen-containing sintered hard alloy

Info

Publication number: JP3648758B2
Application number: JP10558494A
Authority: JP
Inventors: 和孝磯部; 圭一津田; 明彦池ヶ谷; 信行北川
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1994-05-19
Filing date: 1994-05-19
Publication date: 2005-05-18
Anticipated expiration: 2020-05-18
Also published as: JPH07316716A; TW379253B

Description

【０００１】
【産業上の利用分野】
本発明は、窒素含有焼結硬質合金に関し、特に、切削加工用工具の材質としての耐熱衝撃性、耐摩耗性および強度の向上を図り、かつ湿式切削への適用を可能にする窒素含有焼結硬質合金に関するものである。
【０００２】
【従来の技術】
Ｔｉを主成分とする炭窒化物などを硬質相とし、これをＮｉおよびＣｏを含む金属で結合した窒素を含有する焼結硬質合金が、切削工具として既に実用化されている。この窒素含有焼結硬質合金は、従来の窒素を含有しない焼結硬質合金に比べて硬質相が著しく微粒になり、その結果耐高温クリープ特性が大幅に改善されるため、ＷＣを主成分としたいわゆる超硬合金と並んで、切削工具として広く使用されてきている。
【０００３】
しかしながら、この窒素含有焼結硬質合金は、
▲１▼ 主成分であるＴｉの炭窒化物の熱伝導度が超硬合金の主成分であるＷＣの熱伝導度に比べて著しく小さいため、この窒素含有焼結硬質合金の熱伝導度は超硬合金の熱伝導の約２分の１であること、
▲２▼ 熱膨張係数も、熱伝導度と同様に主成分の特性値に依存するため、窒素含有焼結硬質合金の熱膨張係数は超硬合金の熱膨張係数の約１．３倍になること、
などの理由により、熱衝撃に対する抵抗が低くなる。そのため、たとえばフライス切削や角材の旋盤による切削加工、あるいは切込みが大きく変動する湿式での倣い切削などのように特に熱衝撃が厳しくなる条件下での切削においては、被覆超硬合金などに比べて、窒素含有焼結硬質合金の信頼性が低いという問題があった。
【０００４】
このような窒素含有焼結硬質合金の従来の問題点を解消するため、以下に示すようなさまざまな改良が試みられている。たとえば、特開平２−１５１３９号公報には、Ｔｉを炭化物などに換算して５０重量％以上、Ｗなどの６Ａ族元素を炭化物換算で４０重量％未満、Ｎ／（Ｃ＋Ｎ）の原子比が０．４〜０．６の窒素含有量の高いものを、焼結雰囲気を制御して表面粗さを向上させ、表層部に高い靱性と硬度とを有する改質部を形成させることが提案されている。また、特開平５−９６４６号公報には、Ｔｉを主成分とし、Ｗ，Ｍｏ，Ｃｒを炭化物換算で合計４０重量％未満含有したものを焼結後の冷却工程を制御して、表面部に内部よりも結合相の減少した領域を形成し、表面に圧縮応力を残すサーメットが開示されている。
【０００５】
【発明が解決しようとする課題】
しかしながら上記いずれの公報に開示されたサーメットにおいても、耐摩耗性および靱性は向上しているが、被覆超硬合金に比べれて耐欠損性は不十分である。また耐熱衝撃性に乏しく、特に、熱亀裂の発生や、熱衝撃および機械的衝撃の両者に起因する亀裂の進展による突発欠損が生じやすく、十分な信頼性が得られない。すなわち、このような先行技術では、コーティング工程を省略することによって製造コストが下がるものの、性能的にはそれに見合っただけのものしか発揮できない。これは、ある程度以上のＴｉの含有を前提としたいわゆるサーメットという範疇においては、欠損に対する強度向上を図ることに自ずと限界があるということを示している。
【０００６】
そこで本発明者らは、種々の切削における温度分布などの切削現象の解析と、工具内の材料成分の配置との詳細な研究を行なった結果、以下の知見を得た。
【０００７】
切削中において切削部は被削材と接触している切れ刃表面部分やすくい面の切り屑の擦過していく部分など、部分的に高温環境にさらされる。サーメットと超硬合金とを比較すると、上述のようにサーメットは熱伝導度が超硬合金の２分の１程度であるため、表面で発生する熱が内部へ拡散しにくく、表面は高温であるにもかかわらず内部では急激に温度が低下するという状態が生じる。このような状態においては一度亀裂が入ると、著しく欠損しやすくなるという問題がある。さらに、高温のサーメットが水溶性切削油によって急冷却されたり、切削空転して冷却されたりすると、その極表面部分のみが急冷されることになる。
【０００８】
サーメットと超硬合金とを比較すると、上述のようにサーメットは熱膨張係数が超硬合金の約１．３倍であるため、表層部に引張り応力が発生し、熱亀裂が非常に発生しやすくなる。いずれの特性も耐熱衝撃性では、超硬合金よりもサーメットのほうが不利である。
【０００９】
さらに、同一粒度および同一結合相量で見た場合、サーメットは超硬合金に比べて破壊靱性値も３０ないし５０％低下するため、合金内部での亀裂進展抵抗も低くなる。
【００１０】
すなわち、窒素含有焼結硬質合金において、切削仕上げ面を良好にできかつ資源的にも有利なＴｉを多量に含有したまま、熱伝導度の向上、熱膨張係数の低減、および亀裂進展抵抗の向上を図ることには、限界があるという問題があった。
【００１１】
本発明は、従来は高価な被覆超硬合金でしか使用できなかった、厳しい熱衝撃を受ける条件下での加工領域においても、表面被覆を施すことなくかつ高い信頼性を持って切削工具として使用可能な窒素含有焼結硬質合金を提供することを目的とする。
【００１２】
【課題を解決するための手段】
本発明の窒素含有焼結硬質合金は、組織的に従来の窒素含有焼結硬質合金に比べて内部にＷＣを多く存在させ、亀裂進展に対する抵抗を向上させることを狙いとしている。ＷＣを多く配合させると、従来の窒素含有焼結硬質合金においては、合金表面へのＷＣ粒子が出現して、いわゆるＰ種と呼ばれている工具材料となるが、この工具材料は切削仕上げ面の性状が低い。そのため、耐アブレッシブ摩耗性も、いわゆるサーメットや被覆超硬合金に比べると格段に劣るものとなっていた。
【００１３】
しかしながら、焼結を特定の高窒素雰囲気で行なうと、切削仕上げ面の性状を決定する、工具の最表面に存在する軟質層、すなわちいわゆる染み出し層直下から特定の深さまでの表面部分の、ＷＣ粒子を消失させ得ることが判明した。これにより、耐アブレッシブ摩耗性や耐クレーター摩耗性が大幅に向上できること、それに加えて冷却を真空などの脱炭雰囲気で行なうと、表面層付近は結合相量が減少し、それと同時に硬質相粒子にＷなどの６Ａ族金属が多く固溶する。また、結合相量勾配により熱膨張係数差に起因する表面部への圧縮応力が発生することなどの効果により合金表面が硬化し、かつ靱性を向上させることができ、その結果、耐摩耗性や靱性、耐熱衝撃性を顕著に向上させ得ることが可能になった。
【００１４】
そこで、本発明の請求項１に記載の窒素含有焼結硬質合金は、
（Ｔｉ・Ｗ_xＭ_y）（Ｃ_uＮ_1-u）（ただし、ＭはＷを除く周期律表６Ａ族金属の少なくとも１種、０＜ｘ＜１，０≦ｙ≦０．９，０≦ｕ＜０．９）およびＷＣを含む硬質相を７５重量％以上９５重量％以下、Ｎｉ，Ｃｏおよび不可避不純物を含む結合相を５重量％以上２５重量％以下含み、
Ｔｉを炭化物、窒化物あるいは炭窒化物に換算して５重量％以上６０重量％以下、周期律表６Ａ族金属を炭化物に換算して３０重量％以上７０重量％以下含有し、かつ、
前記硬質相の窒素／（炭素＋窒素）が原子比で０．２以上０．５未満であり、最表面に結合相金属とＷＣとを含む軟質層が存在し、該軟質層の直下に３μｍ以上３０μｍ以下の厚みでＷＣを含む硬質相が１体積％以下である層を有することを特徴とする。
【００１５】
また、請求項２に記載の窒素含有焼結硬質合金は、上記請求項１に記載の組成において、ＷＣを含む硬質相が１体積％以下である層から、最表面からの最大深さ１ｍｍまで、内部に向かってＷＣを含む硬質相の存在量が漸次増加することを特徴とする。
【００１６】
さらに、請求項３に記載の窒素含有焼結硬質合金は、上記請求項１または２に記載の組成において、ＷＣを含む硬質相の存在量が、最表面から１ｍｍ以上の深さの内部において５体積％以上５０体積％未満であることを特徴とする。
【００１７】
本発明の請求項４に記載の窒素含有焼結硬質合金は、
（Ｔｉ・Ｗ_xＭ_y）（Ｃ_uＮ_1-u）（ただし、ＭはＴｉ，Ｗを除く周期律表４Ａ，５Ａ，６Ａ族金属の少なくとも１種、０＜ｘ＜１，０＜ｙ≦０．９，０≦ｕ＜０．９）およびＷＣを含む硬質相を７５重量％以上９５重量％以下、Ｎｉ，Ｃｏおよび不可避不純物を含む結合相を５重量％以上２５重量％以下含み、
Ｔｉを炭化物、窒化物あるいは炭窒化物に換算して５重量％以上６０重量％以下、周期律表６Ａ族金属を炭化物に換算して３０重量％以上７０重量％以下、Ｔａ，Ｎｂの合計含有量を炭化物、窒化物あるいは炭窒化物に換算して２重量％以上１５重量％以下、Ｖ，Ｚｒ，およびＨｆの合計含有量を炭化物、窒化物あるいは炭窒化物に換算して５重量％以下含有し、かつ、
硬質相の窒素／（炭素＋窒素）が原子比で０．２以上０．５未満であり、最表面に結合相金属およびＷＣを含む軟質層が存在し、該軟質層の直下に３μｍ以上３０μｍ以下の厚みでＷＣを含む硬質相が１体積％以下である層を有することを特徴とする。
【００１８】
また請求項５に記載の窒素含有焼結硬質合金は、上記請求項４に記載の組成において、前記ＷＣを含む硬質相が１体積％以下である層から、最表面からの最大深さ１ｍｍまで、内部に向かってＷＣを含む硬質相が漸次増加することを特徴とする。
【００１９】
さらに、請求項６記載の窒素含有焼結硬質合金は、上記請求項４または５に記載の組成において、前記ＷＣを含む硬質相の存在量が、最表面から深さ１ｍｍ以上の内部において５体積％以上５０体積％未満であることを特徴とする。
【００２０】
【作用】
請求項１に記載の本発明の窒素含有焼結硬質合金によれば、まず、硬質相の含有量が７５重量％以上９５重量％以下としている。これは、硬質相が７５重量％未満では耐摩耗性、耐塑性変形性の低下が著しく、９５重量％を超えると強度および靱性が不足するためである。またＴｉの含有量を炭化物などに換算して５重量％以上６０重量％以下としたのは、５重量％未満では耐摩耗性が所望のレベルに達せず、６０重量％を超えると靱性が劣化するためである。このＴｉの含有量は、５重量％以上５０重量％以下であることが望ましく、２０重量％以上５０重量％以下であることが特に望まれる。
【００２１】
周期律表６Ａ族金属を炭化物に換算して３０重量％以上７０重量％以下としたのは、３０重量％未満では所望の靱性が得られず、７０重量％を超えるとＷＣ粒子が表面にも多く残存するようになり、耐摩耗性が不十分となって好ましくないからである。この周期律表６Ａ族金属を炭化物に換算した含有量は、４０重量％以上７０重量％以下であることが望ましく、４０重量％以上６０重量％以下であることが特に望ましい。
【００２２】
また、硬質相の窒素／（炭素＋窒素）の原子比を０．２以上０．５未満としたのは、この原子比が０．２未満であると靱性および耐摩耗性ともに所望のレベルに達せず、０．５を超えると焼結性が低下し、靱性が劣化するためである。この原子比は、０．２以上０．４未満であることが望ましい。
【００２３】
さらに、ＷＣを含む硬質相がほとんど存在しない層、具体的には１体積％以下である層の厚みを、最表面の結合相金属とＷＣとからなる軟質層の直下において３μｍ以上３０μｍ以下としたのは、３μｍ未満では所望の耐アブレッシブ摩耗性および耐クレータ摩耗性を得ることができず、３０μｍを超えると亀裂進展抵抗を促進する効果が発揮されず、その結果靱性が低下するためである。
【００２４】
本発明の請求項２に記載の窒素含有焼結硬質合金によれば、ＷＣを含む硬質相が１体積％以下の層から、最表面から最大深さ１ｍｍまで、内部に向かってＷＣを含む硬質相の存在量が漸次増加することにより、ＷＣが存在する領域と存在しない領域との境界におけるＷＣ含有分布の急激な変化が防止され、その境界での残留応力の発生が緩和される。
【００２５】
本発明の請求項３に記載の窒素含有焼結硬質合金において、ＷＣを含む硬質相が、最表面から最大深さ１ｍｍ以上の内部において、５体積％以上５０体積％未満であるとしたのは、５体積％未満では所望の靱性向上効果が得られず、５０体積％では表層部分の熱衝撃に対する靱性と合金の耐塑性変形性が低下するためである。
【００２６】
さらに、上記請求項１に記載の窒素含有焼結硬質合金の硬質相の組成に代えて、請求項４に記載の組成のように、Ｗを除く周期律表６Ａ族金属に加えて、Ｔｉを除く周期律表４Ａ族金属および／または５Ａ族金属を含有し、Ｔａ，Ｎｂの合計含有量を炭化物、窒化物あるいは炭窒化物に換算して２重量％以上１５重量％以下とし、Ｖ，Ｚｒ，Ｈｆの合計含有量を炭化物、窒化物あるいは炭窒化物に換算して５重量％以下含むことによっても、請求項１に記載の組成と同様の作用効果を有する。Ｔａ，Ｎｂの炭化物等に換算した合計含有量が２重量％未満では耐クレーター摩耗性が向上せず、１５重量％を超えると耐欠損性が低下する。Ｖ，Ｚｒ，Ｈｆは高温における強度や硬度を向上させるために含有することが好ましいが、炭化物等に換算した合計含有量が５重量％を超えると、焼結性が低下し、その結果耐欠損性も低下する。
【００２７】
請求項５および６に記載の窒素含有焼結硬質合金の作用効果は、請求項２および３に記載の構造の作用効果と同様である。
【００２８】
【実施例】
以下、本発明の具体的な実施例について説明する。
【００２９】
実施例１
平均粒径が２μｍで、有芯構造の外郭部分が、反射電子顕微鏡像で純白に見え、芯部分が真っ黒に見える（Ｔｉ_0.85Ｔａ_0.04Ｎｂ_0.04Ｗ_0.07）（Ｃ_0.56Ｎ_0.44）粉末と、平均粒径が０．７μｍのＷＣ粉末と、平均粒径１．５μｍのＮｉ粉末とＣｏ粉末とを、それぞれ４５重量％、４０重量％、７重量％、８重量％の割合で、湿式混合後、型押し成形し、１０^-2Ｔｏｒｒの真空中で１２００℃で脱ガスした。その後、窒素ガス分圧３０Ｔｏｒｒで、１４５０℃で１時間焼結後、真空中で５℃／分で冷却し、試料１を形成した。この試料１のＴｉ含有量はＴｉＣＮ換算で３４重量％、Ｗ含有量はＷＣ換算で４５重量％、ＴａおよびＮｂの含有量はＴａＣ＋Ｎｂ換算で６重量％であった。またＮ／（Ｃ＋Ｎ）は、原子比で０．３となった。軟質層直下から厚さ１０μｍの領域においては、ＷＣ粒子が全く存在せず、最表面から１ｍｍの深さにおける内部のＷＣを含む硬質相の存在量は１５体積％となっていた。
【００３０】
比較のために、従来の製法によって形成したサンプルとして、試料２ないし４を形成した。試料２は、試料１と同一の型押し成形体を窒素分圧５Ｔｏｒｒ、１４００℃で焼結したものである。また、試料３は、試料２と同一の焼結体を、焼結後にＣＯ分圧２００Ｔｏｒｒで冷却したものである。また試料４は、試料２と同一の焼結体を、焼結後に窒素分圧１８０Ｔｏｒｒで冷却したものである。
【００３１】
試料２ないし４の構造は、軟質層直下のＷＣを含む硬質相の存在量が、それぞれ１０体積％、１５体積％、５体積％であった。さらに、試料１と同一原料に加えて、平均粒径１〜３μｍのＴａＣ、ＮｂＣ、ＺｒＣ、ＶＣを使用し、下記の表１に示す重量比率で配合し、試料１と同様の工程で焼結合金を形成し、表１に示す換算含有量を有する試料５ないし１０とした。Ｎｉ，Ｃｏ，ＺｒＣ，ＶＣは、換算含有量が配合組成とほぼ同じ量であるため、記載を省略した。また、このときのＮ／（Ｃ＋Ｎ）の原子比と、合金表面部の軟質層直下のＷＣを含む硬質相が１体積％以下の層の厚みと、最表面から１ｍｍにおけるＷＣを含む硬質相の存在量を、下記の表２に示した。
【００３２】
【表１】

【００３３】
【表２】

【００３４】
上記各試料１ないし１０の窒素含有焼結硬質合金について、下記の表３の切削条件１ないし３を用いて切削加工を実施し、その結果下記の表４に示す判定結果を得た。
【００３５】
【表３】

【００３６】
【表４】

【００３７】
表４に示した判定結果からわかるように、請求項１または４に記載された本発明の条件を満たす組成などを有する試料１，５および６を用いた場合には、本発明の条件から外れる組成等を有する試料２ないし４および７ないし１０を用いた場合と比べて、いずれも優れた耐摩耗性、靱性および耐熱衝撃性を示している。
【００３８】
実施例２
下記の表５に示す原料粉末を用いて、それぞれの換算含有重量になるように配合および混合粉砕して、試料１１ないし２３を成形した。ここで、ＴｉＣＮ粉末は平均粒径２μｍでＣ／Ｎ原子比５／５のものを用い、その他の粉末は平均粒径１〜３μｍのものを用いた。試料１２は、Ｔａ、Ｎｂ源として平均粒径１．５μｍの（ＴａＮｂ）Ｃ粉末（ＴａＣ：ＮｂＣ＝２：１（重量比））を用い、試料１７は、Ｔｉ、Ｗ源として平均粒径２μｍの（Ｔｉ_0.8 Ｗ_0.2 ）（Ｃ_0.7 Ｎ_0.3 ）粉末を使用した。これらの固溶体原料粉末の配合量については、表５においては単体の化合物に換算して示した。各試料の配合組成については、換算含有量が配合組成とほぼ同量であるため、その記載を省略した。
【００３９】
【表５】

【００４０】
試料１１ないし２３を、１０^-2Ｔｏｒｒの真空中で３℃／分で昇温し、１２００℃で１５分間脱ガス後、窒素ガス分圧１５〜４０Ｔｏｒｒ、１４５０℃で１時間焼結後、真空中で３℃／分で１２００℃まで制御冷却した後、窒素急冷した。試料１１，１２については、同一条件での焼結後に、冷却条件を変えて、試料１１Ａないし１１Ｃおよび１２Ａないし１２Ｃを形成した。そのうち１１Ａ，１２Ａは、試料１１，１２とそれぞれ同一条件での焼結後、ＣＯ分圧１５０Ｔｏｒｒで冷却し、試料１１Ｂ，１２Ｂについては、窒素分圧２００Ｔｏｒｒで冷却し、試料１１Ｃ，１２Ｃについては１５３０℃まで昇温後１．５時間焼結した後に制御冷却したものである。
【００４１】
試料１１ないし２３および試料１１Ａないし１１Ｃ，１２Ａないし１２ＣのＮ／（Ｃ＋Ｎ）原子比と、合金表面部の軟質層直下のＷＣを含む硬質相が１体積％以下の領域の厚みと、最表面から１ｍｍの深さにおけるＷＣを含む硬質相の存在量とを、下記の表６に示した。
【００４２】
【表６】

【００４３】
表６に示した各試料について、下記の表７に示す切削条件４ないし６で切削加工を実施し、下記の表８に示す判定結果を得た。比較のため、市販の被覆超硬合金Ｐ１０グレードについても切削テストを行なった。
【００４４】
【表７】

【００４５】
【表８】

【００４６】
表８に示した判定結果からわかるように、請求項１または４に記載された本発明の条件を満たす組成等を有する試料１１，１２および１３ないし１７を用いた場合には、本発明の条件から外れる組成等を有する試料１１Ａないし１１Ｃ，１２Ａないし１２Ｃおよび１８ないし２３を用いた場合と比べて、いずれも優れた耐摩耗性、靱性および耐熱衝撃性を示している。
【００４７】
【発明の効果】
以上説明したように、請求項１あるいは４に記載の本発明の窒素含有焼結硬質合金によれば、硬質相の含有量を７０重量％以上とすることにより耐摩耗性、耐塑性変形性の低下を抑え、９０重量％以下とすることにより強度および靱性の不足を来すことがない。また、Ｔｉの含有量を炭化物などに換算して５重量％以上とすることにより耐摩耗性を所望のレベルに維持するととにもに、６０重量％以下とすることにより靱性の劣化を抑える。
【００４８】
また、周期律表６Ａ族金属を炭化物に換算して３０重量％以上含有することにより所望の靱性が維持され、７０重量％以下とすることにより表面でのＷＣ粒子の残存量が減少して十分な耐摩耗性を得ることができる。
【００４９】
また、硬質相の窒素／（炭素＋窒素）の原子比を０．２以上とすることにより靱性および耐摩耗性が所望のレベルに維持され、０．５以下とすることにより焼結性の低下および靱性の劣化が抑制される。
【００５０】
さらに、ＷＣを含む硬質相が１体積％以下である層の厚みを、最表面の結合相金属とＷＣとからなる軟質層の直下において３μｍ以上とすることにより所望の耐アブレッシブ摩耗性および耐クレータ摩耗性が得られ、３０μｍ以下とすることにより亀裂進展抵抗が維持されて靱性の劣化が抑えられる。
【００５１】
すなわち、請求項１あるいは４に記載の組成と構造を有することにより、表面被覆を施すことなく、切削工具用材料として優れた耐摩耗性、耐熱衝撃性および靱性を備えた窒素含有焼結硬質合金を得ることができる。
【００５２】
また、請求項２あるいは５に記載の窒素含有焼結硬質合金によれば、ＷＣが存在する領域と存在しない領域との境界で発生する残留応力は緩和され、その結果合金の強度を維持あるいは向上させることができる。
【００５３】
さらに、請求項３あるいは６に記載の窒素含有焼結硬質合金によれば、ＷＣを含む硬質相の存在量を、最表面から最大深さ１ｍｍ以上の内部において５体積％以上とすることにより所望の靱性向上効果が得られ、５０体積％以下とすることにより表層部分での熱衝撃に対する靱性と合金の耐塑性変形性が保持され、高温での過酷な切削条件下で使用される工具用材料としても優れた特性が発揮される。[0001]
[Industrial application fields]
The present invention relates to a nitrogen-containing sintered hard alloy, and in particular, nitrogen-containing sintering that improves thermal shock resistance, wear resistance, and strength as a material for a cutting tool and enables application to wet cutting. It relates to hard alloys.
[0002]
[Prior art]
Sintered hard alloys containing nitrogen in which carbonitrides mainly composed of Ti are used as a hard phase and bonded with a metal containing Ni and Co have already been put into practical use as cutting tools. In this nitrogen-containing sintered hard alloy, the hard phase becomes remarkably finer than the conventional sintered hard alloy not containing nitrogen, and as a result, the high temperature creep resistance is greatly improved. Along with so-called cemented carbide, it has been widely used as a cutting tool.
[0003]
However, this nitrogen-containing sintered hard alloy is
(1) Since the thermal conductivity of Ti carbonitride, which is the main component, is significantly smaller than that of WC, which is the main component of the cemented carbide, the thermal conductivity of this nitrogen-containing sintered hard alloy is extremely high. About half the heat conduction of hard alloys,
(2) Since the thermal expansion coefficient depends on the characteristic value of the main component as well as the thermal conductivity, the thermal expansion coefficient of the nitrogen-containing sintered hard alloy is about 1.3 times the thermal expansion coefficient of the cemented carbide. about,
For such reasons, the resistance to thermal shock is low. Therefore, compared to coated cemented carbide, for example, when cutting under conditions where thermal shock is severe, such as milling, cutting with a square lathe, or profiling in wet conditions where the depth of cut varies greatly. There was a problem that the reliability of the nitrogen-containing sintered hard alloy was low.
[0004]
In order to solve the conventional problems of such nitrogen-containing sintered hard alloys, various improvements as described below have been attempted. For example, in Japanese Patent Laid-Open No. 2-15139, Ti is converted into carbide or the like to 50 wt% or more, 6A group element such as W is less than 40 wt% in terms of carbide, and N / (C + N) atomic ratio is 0. It is proposed that a high nitrogen content of 4-0.6 is controlled to improve the surface roughness by controlling the sintering atmosphere and to form a modified portion having high toughness and hardness in the surface layer portion. Yes. Japanese Patent Laid-Open No. 5-9646 discloses a method for controlling a cooling step after sintering a material containing Ti as a main component and containing a total of less than 40% by weight of W, Mo, and Cr in terms of carbide. A cermet is disclosed that forms a region with a reduced binder phase relative to the interior and leaves a compressive stress on the surface.
[0005]
[Problems to be solved by the invention]
However, although the cermet disclosed in any of the above publications has improved wear resistance and toughness, it has insufficient fracture resistance compared to a coated cemented carbide. Further, the thermal shock resistance is poor, and in particular, the occurrence of thermal cracks and sudden defects due to the development of cracks due to both thermal and mechanical shocks are likely to occur, and sufficient reliability cannot be obtained. That is, in such a prior art, although the manufacturing cost is reduced by omitting the coating process, only the performance corresponding to the performance can be exhibited. This indicates that, in the category of so-called cermet that presupposes a certain amount of Ti content, there is a limit to improving the strength against defects.
[0006]
Therefore, as a result of detailed studies on analysis of cutting phenomena such as temperature distribution in various cuttings and arrangement of material components in the tool, the inventors have obtained the following knowledge.
[0007]
During cutting, the cutting portion is partially exposed to a high temperature environment, such as a portion where the cutting edge surface portion that is in contact with the work material is easily scraped off by a chip. Comparing cermet and cemented carbide, as mentioned above, cermet is about half the thermal conductivity of cemented carbide, so the heat generated on the surface is difficult to diffuse inside, and the surface is hot. Nevertheless, a state occurs in which the temperature rapidly decreases inside. In such a state, once a crack has occurred, there is a problem that it is extremely easy to be lost. Furthermore, when the high-temperature cermet is rapidly cooled by the water-soluble cutting oil or cooled by cutting idle, only the extreme surface portion is rapidly cooled.
[0008]
Comparing cermet and cemented carbide, as mentioned above, cermet has a thermal expansion coefficient about 1.3 times that of cemented carbide, so tensile stress is generated in the surface layer and thermal cracks are very likely to occur. Become. In any case, cermet is more disadvantageous than cemented carbide in terms of thermal shock resistance.
[0009]
Further, when viewed with the same grain size and the same amount of binder phase, cermet also has a fracture toughness value of 30 to 50% lower than that of cemented carbide, so that the crack propagation resistance inside the alloy is also lowered.
[0010]
In other words, in a nitrogen-containing sintered hard alloy, the thermal conductivity is improved, the thermal expansion coefficient is reduced, and the crack propagation resistance is improved while containing a large amount of Ti, which has a good cutting finish and is advantageous in terms of resources. There was a problem that there was a limit in trying to.
[0011]
The present invention can be used as a cutting tool without applying a surface coating and with high reliability even in a processing region under severe thermal shock conditions that could only be used with expensive coated cemented carbides. An object is to provide a possible nitrogen-containing sintered hard alloy.
[0012]
[Means for Solving the Problems]
The nitrogen-containing sintered hard alloy of the present invention aims to improve the resistance to crack propagation by having a larger amount of WC in the interior than the conventional nitrogen-containing sintered hard alloy. When a large amount of WC is blended, in the conventional nitrogen-containing sintered hard alloy, WC particles appear on the alloy surface and become a so-called P-type tool material. The property of is low. For this reason, the abrasive wear resistance is also inferior to that of so-called cermet or coated cemented carbide.
[0013]
However, when the sintering is performed in a specific high nitrogen atmosphere, the WC of the soft layer existing on the outermost surface of the tool, that is, the surface portion from a position immediately below the so-called exudation layer to a specific depth, which determines the properties of the cut finish surface. It has been found that the particles can disappear. As a result, the abrasive wear resistance and crater wear resistance can be greatly improved. In addition, when cooling is performed in a decarburizing atmosphere such as a vacuum, the amount of the binder phase decreases in the vicinity of the surface layer, and at the same time, the hard phase particles A lot of Group 6A metals such as W are dissolved. In addition, the surface of the alloy can be hardened and the toughness can be improved due to the effects such as the generation of compressive stress on the surface due to the difference in thermal expansion coefficient due to the binder phase gradient. It has become possible to significantly improve toughness and thermal shock resistance.
[0014]
Therefore, the nitrogen-containing sintered hard alloy according to claim 1 of the present invention is
_{_{(Ti · W x M y)}} (C u N 1-u) ( however, M is at least one periodic table group 6A metals excluding W, 0 <x <1,0 ≦ y ≦ 0.9,0 ≦ u <0.9) and the hard phase containing WC is 75 wt% or more and 95 wt% or less, and the binder phase containing Ni, Co and inevitable impurities is contained 5 wt% or more and 25 wt% or less,
Containing 5 wt% or more and 60 wt% or less of Ti in terms of carbide, nitride or carbonitride, and containing 30 wt% or more and 70 wt% or less of the periodic table 6A group metal in terms of carbide, and
The hard phase nitrogen / (carbon + nitrogen) has an atomic ratio of 0.2 or more and less than 0.5, a soft layer containing a binder phase metal and WC is present on the outermost surface, and 3 μm immediately below the soft layer. The hard phase containing WC with a thickness of 30 μm or less has a layer of 1% by volume or less .
[0015]
Further, the nitrogen-containing sintered hard alloy according to claim 2 is the composition according to claim 1, wherein the hard phase containing WC is 1% by volume or less from the layer having a maximum depth of 1 mm from the outermost surface. The amount of hard phase containing WC gradually increases toward the inside.
[0016]
Furthermore, the nitrogen-containing sintered hard alloy according to claim 3 is the composition according to claim 1 or 2, wherein the abundance of the hard phase containing WC is 5 within a depth of 1 mm or more from the outermost surface. It is characterized by being not less than 50% by volume and not less than 50% by volume.
[0017]
The nitrogen-containing sintered hard alloy according to claim 4 of the present invention,
_{_{(Ti · W x M y)}} (C u N 1-u) ( however, M is Ti, Periodic Table 4A except W, 5A, 6A Group at least one metal, 0 <x <1,0 <y ≦ 0.9, 0 ≦ u <0.9) and 75% by weight to 95% by weight of a hard phase containing WC, and 5% by weight to 25% by weight of a binder phase containing Ni, Co and unavoidable impurities,
Ti is converted to carbide, nitride or carbonitride in the range of 5 wt% to 60 wt%, Periodic Table 6A Group metal in terms of carbide to 30 wt% to 70 wt%, and total content of Ta and Nb 2 to 15% by weight in terms of carbide, nitride or carbonitride, and 5% by weight in terms of total content of V, Zr and Hf in terms of carbide, nitride or carbonitride Containing, and
The hard phase nitrogen / (carbon + nitrogen) has an atomic ratio of 0.2 or more and less than 0.5, a soft layer containing a binder phase metal and WC is present on the outermost surface, and 3 μm or more and 30 μm immediately below the soft layer. The hard phase containing WC with the following thickness has a layer of 1% by volume or less .
[0018]
Further, the nitrogen-containing sintered hard alloy according to claim 5 is the composition according to claim 4, wherein the hard phase containing the WC is 1% by volume or less from a layer having a maximum depth of 1 mm from the outermost surface. The hard phase containing WC gradually increases toward the inside.
[0019]
Furthermore, the nitrogen-containing sintered hard alloy according to claim 6 is the composition according to claim 4 or 5, wherein the amount of the hard phase containing WC is 5 volumes in a depth of 1 mm or more from the outermost surface. % Or more and less than 50% by volume.
[0020]
[Action]
According to the nitrogen-containing sintered hard alloy of the first aspect of the present invention, first, the content of the hard phase is 75 wt% or more and 95 wt% or less. This is because when the hard phase is less than 75% by weight, the wear resistance and the plastic deformation resistance are remarkably lowered, and when it exceeds 95% by weight, the strength and toughness are insufficient. In addition, the Ti content is set to 5% by weight or more and 60% by weight or less in terms of carbide or the like. If it is less than 5% by weight, the wear resistance does not reach the desired level, and if it exceeds 60% by weight, the toughness deteriorates. It is to do. The Ti content is desirably 5% by weight or more and 50% by weight or less, and particularly desirably 20% by weight or more and 50% by weight or less.
[0021]
The reason why the group 6A metal of the periodic table is 30 wt% or more and 70 wt% or less in terms of carbide is that if it is less than 30 wt%, the desired toughness cannot be obtained. This is because a large amount remains and the wear resistance becomes insufficient. The content of the Periodic Table 6A group metal converted to carbide is preferably 40% by weight or more and 70% by weight or less, and particularly preferably 40% by weight or more and 60% by weight or less.
[0022]
Moreover, the atomic ratio of nitrogen / (carbon + nitrogen) of the hard phase was set to 0.2 or more and less than 0.5. When this atomic ratio is less than 0.2, both toughness and wear resistance are at a desired level. If it exceeds 0.5 and sinterability decreases, the toughness deteriorates. This atomic ratio is desirably 0.2 or more and less than 0.4.
[0023]
Furthermore, the thickness of the layer containing almost no WC-containing hard phase, specifically, the layer having a volume of 1% by volume or less was set to 3 μm or more and 30 μm or less immediately below the soft layer composed of the outermost binder phase metal and WC. This is because the desired abrasive wear resistance and crater wear resistance cannot be obtained when the thickness is less than 3 μm, and the effect of promoting crack propagation resistance is not exhibited when the thickness exceeds 30 μm, resulting in a decrease in toughness.
[0024]
According to the nitrogen-containing sintered hard alloy according to claim 2 of the present invention, the hard phase containing WC contains hard WC from the layer of 1% by volume or less to the maximum depth of 1 mm from the outermost surface toward the inside. By gradually increasing the abundance of the phase, a sudden change in the WC content distribution at the boundary between the region where WC exists and the region where WC does not exist is prevented, and the occurrence of residual stress at the boundary is mitigated.
[0025]
In the nitrogen-containing sintered hard alloy according to claim 3 of the present invention, the hard phase containing WC is said to be 5% by volume or more and less than 50% by volume within the maximum depth of 1 mm or more from the outermost surface. This is because if it is less than 5% by volume, the desired effect of improving toughness cannot be obtained, and if it is 50% by volume, the toughness against thermal shock of the surface layer portion and the plastic deformation resistance of the alloy are lowered.
[0026]
Furthermore, in place of the composition of the hard phase of the nitrogen-containing sintered hard alloy according to claim 1, in addition to the group 6A metal of the periodic table excluding W, as in the composition according to claim 4, Ti is added. Excluding the 4A group metal and / or 5A group metal in the periodic table, the total content of Ta and Nb is 2 wt% or more and 15 wt% or less in terms of carbide, nitride or carbonitride, and V, Zr , Hf, the same effect as the composition of claim 1 can be obtained by including 5% by weight or less in terms of carbide, nitride or carbonitride. If the total content converted to Ta, Nb carbide or the like is less than 2% by weight, the crater wear resistance is not improved, and if it exceeds 15% by weight, the fracture resistance is lowered. V, Zr, and Hf are preferably contained in order to improve strength and hardness at high temperatures. However, if the total content converted to carbide or the like exceeds 5% by weight, the sinterability decreases, resulting in fracture resistance. The nature is also reduced.
[0027]
The operational effects of the nitrogen-containing sintered hard alloy according to claims 5 and 6 are the same as the operational effects of the structures according to claims 2 and 3.
[0028]
【Example】
Hereinafter, specific examples of the present invention will be described.
[0029]
Example 1
The average particle diameter is 2 μm, the outer part of the cored structure looks pure white in the reflection electron microscope image, and the core part looks black (Ti _0.85 Ta _0.04 Nb _0.04 W _0.07 ) (C _0.56 N _0.44 ) powder, average WC powder having a particle size of 0.7 μm, Ni powder and Co powder having an average particle size of 1.5 μm are wet-mixed in proportions of 45% by weight, 40% by weight, 7% by weight, and 8% by weight, respectively. The mold was molded and degassed at 1200 ° C. in a vacuum of 10 ⁻² Torr. Thereafter, sintering was performed at 1450 ° C. for 1 hour at a nitrogen gas partial pressure of 30 Torr, and then cooled at 5 ° C./min in vacuum to form Sample 1. The Ti content of Sample 1 was 34% by weight in terms of TiCN, the W content was 45% by weight in terms of WC, and the contents of Ta and Nb were 6% by weight in terms of TaC + Nb. N / (C + N) was 0.3 in atomic ratio. In the region having a thickness of 10 μm immediately below the soft layer, no WC particles were present, and the abundance of the hard phase containing WC inside at a depth of 1 mm from the outermost surface was 15% by volume.
[0030]
For comparison, Samples 2 to 4 were formed as samples formed by a conventional manufacturing method. Sample 2 was obtained by sintering the same stamped molded body as Sample 1 at a nitrogen partial pressure of 5 Torr and 1400 ° C. Sample 3 is obtained by cooling the same sintered body as Sample 2 at a CO partial pressure of 200 Torr after sintering. Sample 4 is obtained by cooling the same sintered body as that of Sample 2 at a nitrogen partial pressure of 180 Torr after sintering.
[0031]
In the structures of Samples 2 to 4, the abundance of the hard phase containing WC immediately below the soft layer was 10% by volume, 15% by volume, and 5% by volume, respectively. Furthermore, in addition to the same raw materials as Sample 1, TaC, NbC, ZrC, and VC having an average particle diameter of 1 to 3 μm are used and blended at the weight ratio shown in Table 1 below. Gold 5 was formed, and Samples 5 to 10 having the converted contents shown in Table 1 were used. Ni, Co, ZrC, and VC are omitted because the equivalent content is almost the same as the blend composition. Moreover, the atomic ratio of N / (C + N) at this time, the thickness of the hard phase containing 1% by volume or less of the hard phase containing WC immediately below the soft layer on the alloy surface, and the hard phase containing WC at 1 mm from the outermost surface The abundance is shown in Table 2 below.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
The nitrogen-containing sintered hard alloys of Samples 1 to 10 were cut using the cutting conditions 1 to 3 in Table 3 below, and as a result, the determination results shown in Table 4 below were obtained.
[0035]
[Table 3]

[0036]
[Table 4]

[0037]
As can be seen from the determination results shown in Table 4, when Samples 1, 5 and 6 having a composition that satisfies the conditions of the present invention described in claim 1 or 4 are used, they deviate from the conditions of the present invention. Compared with the case of using samples 2 to 4 and 7 to 10 having the composition, etc., all show excellent wear resistance, toughness and thermal shock resistance.
[0038]
Example 2
Samples 11 to 23 were formed using the raw material powders shown in Table 5 below and blending, mixing and pulverizing them so as to obtain the respective converted content weights. Here, TiCN powder having an average particle diameter of 2 μm and a C / N atomic ratio of 5/5 was used, and other powders having an average particle diameter of 1 to 3 μm were used. Sample 12 uses (TaNb) C powder (TaC: NbC = 2: 1 (weight ratio)) having an average particle diameter of 1.5 μm as a Ta and Nb source, and Sample 17 has an average particle diameter of 2 μm as a Ti and W source. (Ti _0.8 W _0.2 ) (C _0.7 N _0.3 ) powder was used. About the compounding quantity of these solid solution raw material powder, in Table 5, it converted into a single compound, and showed. About the compounding composition of each sample, since the conversion content was substantially the same as the compounding composition, the description was abbreviate | omitted.
[0039]
[Table 5]

[0040]
Samples 11 to 23 were heated at a rate of 3 ° C./min in a vacuum of 10 ⁻² Torr, degassed at 1200 ° C. for 15 minutes, sintered at 1450 ° C. with a nitrogen gas partial pressure of 15 to 40 Torr, and then vacuumed. After controlled cooling to 1200 ° C. at 3 ° C./min, nitrogen quenching was performed. For samples 11 and 12, samples 11A to 11C and 12A to 12C were formed by changing the cooling conditions after sintering under the same conditions. Among them, 11A and 12A were sintered at a CO partial pressure of 150 Torr after sintering under the same conditions as Samples 11 and 12, respectively. Samples 11B and 12B were cooled at a nitrogen partial pressure of 200 Torr, and Samples 11C and 12C were 1530. After cooling to 1.5 ° C. and sintering for 1.5 hours, controlled cooling is performed.
[0041]
The N / (C + N) atomic ratio of Samples 11 to 23 and Samples 11A to 11C, 12A to 12C, the thickness of the hard phase containing WC immediately below the soft layer on the alloy surface, and the thickness of the region of 1% by volume or less, The abundance of the hard phase containing WC at a depth of 1 mm is shown in Table 6 below.
[0042]
[Table 6]

[0043]
Each sample shown in Table 6 was cut under the cutting conditions 4 to 6 shown in Table 7 below, and the determination results shown in Table 8 below were obtained. For comparison, a cutting test was also performed on a commercially available coated cemented carbide P10 grade.
[0044]
[Table 7]

[0045]
[Table 8]

[0046]
As can be seen from the determination results shown in Table 8, when the samples 11, 12, and 13 to 17 having the composition satisfying the conditions of the present invention described in claim 1 or 4 are used, the conditions of the present invention are used. Compared to the case of using samples 11A to 11C, 12A to 12C, and 18 to 23 having compositions deviating from the above, all show excellent wear resistance, toughness, and thermal shock resistance.
[0047]
【The invention's effect】
As described above, according to the nitrogen-containing sintered hard alloy of the present invention according to claim 1 or 4, the wear resistance and plastic deformation resistance can be improved by setting the hard phase content to 70% by weight or more. By suppressing the decrease and setting it to 90% by weight or less, there is no shortage of strength and toughness. Further, the wear resistance is maintained at a desired level by converting the Ti content to 5% by weight or more in terms of carbide and the like, and the deterioration of toughness is suppressed by setting it to 60% by weight or less.
[0048]
In addition, by containing 30% by weight or more of the group 6A metal in the periodic table in terms of carbide, desired toughness is maintained, and by making it 70% by weight or less, the remaining amount of WC particles on the surface is sufficiently reduced. High wear resistance can be obtained.
[0049]
Further, the toughness and wear resistance are maintained at desired levels by setting the atomic ratio of nitrogen / (carbon + nitrogen) of the hard phase to 0.2 or more, and the sinterability is reduced by setting it to 0.5 or less. And deterioration of toughness is suppressed.
[0050]
Furthermore, by setting the thickness of the layer having a hard phase containing WC of 1% by volume or less to 3 μm or more directly below the soft layer composed of the outermost binder phase metal and WC, desired abrasion resistance and crater resistance Abrasion is obtained, and when the thickness is 30 μm or less, crack propagation resistance is maintained and deterioration of toughness is suppressed.
[0051]
That is, the nitrogen-containing sintered hard alloy having the wear resistance, thermal shock resistance, and toughness which is excellent as a cutting tool material without having a surface coating by having the composition and structure according to claim 1 or 4. Can be obtained.
[0052]
According to the nitrogen-containing sintered hard alloy according to claim 2 or 5, residual stress generated at the boundary between the region where WC exists and the region where WC does not exist is relieved, and as a result, the strength of the alloy is maintained or improved. Can be made.
[0053]
Furthermore, according to the nitrogen-containing sintered hard alloy according to claim 3 or 6, the amount of hard phase containing WC is desired to be 5% by volume or more in the interior having a maximum depth of 1 mm or more from the outermost surface. Toughness improvement effect is obtained, and the material for tool used under severe cutting conditions at high temperature is maintained by maintaining the toughness against the thermal shock in the surface layer part and the plastic deformation resistance of the alloy by making it 50% by volume or less. As a result, excellent characteristics are exhibited.

Claims

_{_{(Ti · W x M y)}} (C u N 1-u) ( however, M is at least one periodic table group 6A metals excluding W, 0 <x <1,0 ≦ y ≦ 0.9,0 ≦ u <0.9) and the hard phase containing WC is 75 wt% or more and 95 wt% or less, and the binder phase containing Ni, Co and inevitable impurities is contained 5 wt% or more and 25 wt% or less,
Containing 5 wt% or more and 60 wt% or less of Ti in terms of carbide, nitride or carbonitride, and containing 30 wt% or more and 70 wt% or less of the periodic table 6A group metal in terms of carbide, and
The hard phase nitrogen / (carbon + nitrogen) has an atomic ratio of 0.2 or more and less than 0.5, a soft layer containing a binder phase metal and WC is present on the outermost surface, and 3 μm immediately below the soft layer. A nitrogen-containing sintered hard alloy having a layer having a thickness of 30 μm or less and a hard phase containing WC of 1% by volume or less .

2. The nitrogen-containing composition according to claim 1, wherein the abundance of the hard phase containing WC gradually increases from the layer in which the hard phase containing WC is 1% by volume or less to a maximum depth of 1 mm from the outermost surface. Sintered hard alloy.

The nitrogen-containing sintered hard alloy according to claim 1 or 2, wherein the abundance of the hard phase containing WC is 5% by volume or more and less than 50% by volume inside a depth of 1 mm or more from the outermost surface.

_{_{(Ti · W x M y)}} (C u N 1-u) ( however, M is Ti, Periodic Table 4A except W, 5A, 6A Group at least one metal, 0 <x <1,0 <y ≦ 0.9, 0 ≦ u <0.9) and 75% by weight to 95% by weight of a hard phase containing WC, and 5% by weight to 25% by weight of a binder phase containing Ni, Co and unavoidable impurities,
Ti is converted to carbide, nitride or carbonitride in the range of 5 wt% to 60 wt%, Periodic Table 6A Group metal in terms of carbide to 30 wt% to 70 wt%, and total content of Ta and Nb 2 to 15% by weight in terms of carbide, nitride or carbonitride, and 5% by weight in terms of total content of V, Zr and Hf in terms of carbide, nitride or carbonitride Containing, and
Nitrogen / (carbon + nitrogen) of the hard phase is 0.2 or more and less than 0.5 in atomic ratio, a soft layer containing a binder phase metal and WC is present on the outermost surface, and 3 μm or more immediately below the soft layer A nitrogen-containing sintered hard alloy having a layer having a thickness of 30 µm or less and a hard phase containing WC of 1 vol% or less .

The nitrogen-containing content according to claim 4, wherein the abundance of the hard phase containing WC gradually increases from the layer in which the hard phase containing WC is 1% by volume or less to a maximum depth of 1 mm from the outermost surface. Sintered hard alloy.

6. The nitrogen-containing sintered hard alloy according to claim 4, wherein the abundance of the hard phase containing WC is 5% by volume or more and less than 50% by volume in the interior having a depth of 1 mm or more from the outermost surface.