JP4282298B2

JP4282298B2 - Super fine cemented carbide

Info

Publication number: JP4282298B2
Application number: JP2002295790A
Authority: JP
Inventors: 正樹小林
Original assignee: Tungaloy Corp
Current assignee: Tungaloy Corp
Priority date: 2002-10-09
Filing date: 2002-10-09
Publication date: 2009-06-17
Anticipated expiration: 2022-10-09
Also published as: JP2004131769A

Description

【０００１】
【発明の属する技術分野】
本発明は、切削工具、耐摩耗工具、部品に使用される超微粒超硬合金に関する。例えば、本発明の超微粒超硬合金は、チップ、ドリル、エンドミル、金型、または切断刃など硬さ、耐摩耗性、強度、および／または靱性が必要とされる用途に適する。また、耐食性にも優れることから、腐食環境下で使用する耐摩耗部品やしゅう動部品にも適する。
【０００２】
【従来の技術】
従来の微粒超硬合金は、平均粒子径が０．２〜０．７μｍのＷＣ粉末とＣｏ粉末に、０．２〜２重量％のＶＣ，Ｃｒ₃Ｃ₂，ＴａＣなど粒成長抑制剤を添加し、混合した後、焼結して得られている。ＷＣの平均粒子径が１．０〜７．０μｍである粗粒超硬合金に比べ硬さと強度が共に高く、面精度、刃立性や耐摩耗性、耐溶着性などに優れるという特徴がある。そして、高硬度で高強度な微粒超硬合金を得るためには、異常成長したＷＣを含まない微細で均一な組織とする必要があり、粒成長抑制剤の成分と量やその均一分散に関する検討が数多く行われている。
【０００３】
微粒超硬合金の組成に関する先行技術としては、特開昭６３−４２３４６号公報、特開平４−２８９１４６号公報、特開平５−１１７７９９号公報などがある。また、微粒超硬合金の製造方法に関する先行技術としては、特開平０６−２１２３４１号公報、特開平１０−１１０２３５号公報などがある。さらに、結合相にニッケルを用いる微粒超硬合金には、特開昭６０−１３５５５２号公報などがある。
【０００４】
【発明が解決しようとする課題】
微粒超硬合金の組成に関する先行技術のうち、特開昭６３−４２３４６号公報には、平均粒子径が１．０μｍ以下の炭化タングステンと３〜３０％のコバルトおよび／またはニッケル中に、炭化バナジウムと炭化クロムを合計量で３〜７％の比率で固溶させた高強度超硬合金が記載されている。同様に、特開平４−２８９１４６号公報には、４〜２５重量％のコバルトおよび／またはニッケル中にバナジウムとクロムを、Ｖ／（Ｃｏ＋Ｎｉ）＝０．０１〜０．１，Ｃｒ／（Ｃｏ＋Ｎｉ）＝０．０５〜０．２の関係で含有させ、かつバナジウムとタングステンを含む複合炭化物を第３相として有する高強度高靱性超硬合金が記載されている。また、特開平５−１１７７９９号公報には、コバルト：４〜２０重量％、炭化クロム：０．３〜３．０重量％、炭化バナジウム：０．１〜３．０重量％を含有し、炭化タングステンの平均粒子径が０．８μｍ以下で、かつクロムとバナジウムの複合炭化物相が分散した炭化タングステン基超硬合金が記載されている。
【０００５】
これらの公報に記載された微粒超硬合金は、金属結合相中に溶解させたクロムとバナジウムの相乗効果によってＷＣの粒成長を抑制しようとしたものではあるが、固溶量に限界があるために、超微粒超硬合金は得られない。また複合炭化物が存在すると強度、靱性とも低下するという問題がある。特に、ニッケルを結合相とした場合には、高強度、かつ高靱性な微粒超硬合金は得られない。
【０００６】
微粒超硬合金の製造方法に関し、特開平０６−２１２３４１号公報には、酸化タングステン，酸化クロム，酸化バナジウム，酸化タンタル，モリブデンとカーボンブラックとの混合粉末を還元、炭化して複合炭化物粉末とし、これにコバルトを添加した混合粉末をプレス成形、アルゴンＨＩＰする微粒超硬合金の製造方法が記載されている。また、特開平１０−１１０２３５号公報には、結合相量に対してクロム、バナジウムの合計量が１重量％以下、ＷＣの平均粒子径が０．５μｍ以下であり、１１００〜１３５０℃，５〜２００ＭＰａで通電加圧焼結して得られる高硬度硬質合金とその製法が記載されている。
【０００７】
特開平０６−２１２３４１号公報は、粒成長抑制剤を均一に分散させることによって、粒成長を抑えたものではあるが、効果に限界がある。また、特開平１０−１１０２３５号公報は、低温での加圧焼結によって粒成長抑制を試みたものではあるが、クロム、バナジウムの添加では液相出現温度が高いために、低温焼結すると結合相が十分に分散せず強度が低下し、また通電加圧焼結法は量産品、複雑形状品、研削レス品には向かないという問題がある。
【０００８】
結合相にニッケルを用いた微粒超硬合金に関して、特開昭６０−１３５５５２号公報には、結合相が２〜２０重量％のクロムと、０．５〜１０重量％のアルミニウムと、０．５〜５重量％のチタンとを含有したニッケルからなる超微細炭化タングステン基焼結合金が記載されている。本公報は、結合相であるニッケルへのクロムとチタンとの固溶による粒成長抑制の相乗効果とアルミニウムの固溶による耐酸化性、耐熱性の改善を狙ったものではあるが、粒成長抑制効果が低く、かつ高温焼結を必要とするので超微粒超硬合金は得られ難く、またアルミニウム、チタンの固溶によって結合相が脆化して強度や靱性が向上しないという問題がある。
【０００９】
本発明は、上記のような問題点を解決したもので、具体的には、ニッケルを主成分とした結合相中に必然的に固溶するタングステン以外に、少なくともクロムとシリコンとボロンの３種元素を、それぞれの適量を固溶させることにより結合相の硬さ，強度，靱性を損なうことなく、焼結時のＷＣ粒成長を抑制して、ＷＣを超微粒にした超微粒超硬合金の提供を目的とする。
【００１０】
【課題を解決するための手段】
本発明者は、長年に亘り、従来の微粒超硬合金よりもさらに微粒で、かつ強度、靱性に優れた超微粒超硬合金を得るために、焼結時のＷＣ粒成長抑制について検討していたところ、結合相にニッケルを使用するとともにボロンを添加すると粒成長が抑制されること、クロムを添加すると粒成長が抑制されること、ボロンとシリコンとを同時添加して焼結温度を下げると粒成長が抑制されること、さらにクロム、シリコン、およびボロンを含むニッケル合金は硬さ、強度、および／または靱性に優れるという知見を得て、本発明を完成するに至ったものである。
【００１１】
すなわち、本発明の超微粒超硬合金は、ニッケルを主成分とする結合相と、平均粒子径：０．０５〜０．５μｍの炭化タングステンを主成分とする硬質相とからなる超微粒超硬合金において、該結合相は主成分のニッケル以外に５〜３０重量％のタングステン、少なくとも５〜１５重量％のクロム、２〜１０重量％のシリコン、および１〜５重量％のボロンを含有していることを特徴とするものである。
【００１２】
本発明の超微粒超硬合金における炭化タングステンは、平均粒子径：０．０５〜０．５μｍの超微粒ＷＣからなるものである。ＷＣは細かいほど好ましいが、原料となる超微粒ＷＣ粉末の製造が困難であり、焼結時に粒成長するためにＷＣの平均粒子径は０．０５μｍ程度が下限となる。一方、ＷＣの平均粒子径が０．５μｍを超えて大きくなると、硬さと強度が急激に低下する。粒子径が２μｍを超える粗粒ＷＣ粒子は０．１×０．１ｍｍ²の視野中に１ヶ以下であることが好ましい。なお、原料に平均粒子径が１〜７μｍの粗粒ＷＣ粉末を使用した場合には、ボロン、クロム添加による粒成長抑制効果、およびボロン、シリコン添加による焼結温度低下に伴う粒成長抑制効果は発揮できず、高硬度、高強度の超微粒超硬合金は得られない。
【００１３】
本発明の超微粒超硬合金における結合相は、Ｎｉ−Ｗ−Ｃｒ−Ｓｉ−Ｂ系合金であり、ニッケルを主成分とし、結合相全体に対して５〜３０重量％のタングステン、５〜１５重量％のクロム、２〜１０重量％のシリコン、１〜５重量％のボロンを含有しているものである。結合相中のタングステンは必然的に固溶するもので、その固溶量は、遊離炭素析出限界の高炭素合金では１０重量％、Ｎｉ₂Ｗ₄Ｃの析出限界では低炭素合金では３０重量％である。タングステンの固溶量は他元素の固溶により減少する傾向を示すため、タングステン固溶量の下限値は５重量％になる。以上のことから結合相中のタングステン量を５〜３０重量％と定めた。
【００１４】
結合相中のクロム量は、５重量％未満では結合相の強化効果および粒成長の抑制効果が少ないために硬さや強度が低下し、逆に１５重量％を超えて固溶させることは通常の焼結条件では困難であるため、５〜１５重量％と定めた。また、結合相中のシリコン量は、２重量％未満では焼結温度の低減効果が少ないために粒成長しやすく、逆に１０重量％を超えて大きくなるとＷＣと結合相の粒界に炭化ケイ素が析出して強度が低下するため、２〜１０重量％と定めた。さらに、結合相中のボロン量は、１重量％未満では粒子成長の抑制効果と焼結温度の低減効果が少ないために粒成長し易く、逆に５重量％を超えて大きくなると結合相の脆化あるいはホウ化ニッケルの析出により強度が低下するため、１〜５重量％と定めた。
【００１５】
本発明の超微粒超硬合金の結合相において、ニッケル、タングステン、クロム、シリコン、ボロン以外の元素として、耐熱性、耐食性、硬さ、強度などを向上させる目的で、結合相全体に対して５重量％以下の鉄，結合相全体に対して３重量％以下のモリブデン、および／または結合相全体に対して３０重量％以下のコバルトをニッケルに置換して含有させてもよい。すなわち、鉄とモリブデンは耐熱性や耐食性などを、コバルトは硬さや強度などを改善する。
【００１６】
本発明の超微粒超硬合金は、硬質相と結合相から構成されるが、超微粒超硬合金に含まれる結合相量は、超微粒超硬合金全体に対して５体積％未満では高温焼結が必要となり、粒成長を起こすため、硬さと強度が共に低下する。逆に４０体積％を超えて大きくなると硬さの低下が大きくなる。したがって結合相量は超微粒超硬合金全体に対して５〜４０体積％が好ましい。なお、結合相以外の残部は硬質相である。
【００１７】
硬質相としては、炭化タングステンからなる主要相のみでもよいが、クロム、コバルト、タングステン、ニッケルの炭化物、およびこれらの相互固溶体の中から選ばれた少なくとも１種からなる分散相を超微粒超硬合金全体に対して５体積％以下を含有しても好ましく、周期律表４ａ，５ａ，６ａ族元素の炭化物，窒化物，およびこれらの相互固溶体の立方晶化合物の中の少なくとも１種の立方晶相を超微粒超硬合金全体に対して５体積％以下を含有しても好ましい。
【００１８】
クロム、コバルト、タングステン、ニッケルの炭化物およびこれらの相互固溶体の中から選ばれた少なくとも１種からなる分散相として、具体的には、Ｃｒ₂₃Ｃ₆，Ｎｉ₂₃Ｃ₆，Ｎｉ₂Ｗ₄Ｃ，Ｎｉ₂Ｃｒ₄Ｃなどの複合炭化物を例示できる。Ｃｒ₂₃Ｃ₆，Ｎｉ₂₃Ｃ₆は結合相中のクロム量が過剰な場合に析出し、Ｎｉ₂Ｗ₄Ｃ，Ｎｉ₂Ｃｒ₄Ｃは超微粒超硬合金中の炭素量が低い場合に形成される。いずれも超微粒超硬合金中に均一かつ微細に分散している。しかしながら、超微粒超硬合金に含まれる分散相の量が５体積％を超えると、硬さならびに強度とも低下する傾向がみられる。
【００１９】
周期律表４ａ，５ａ，６ａ族元素の炭化物、窒化物、およびこれらの相互固溶体からなる立方晶化合物の中の少なくとも１種の立方晶相として、具体的には、タングステンを固溶した（Ｔｉ，Ｗ）Ｃ，（Ｚｒ，Ｗ）Ｃ，（Ｖ，Ｗ）Ｃ，（Ｔａ，Ｗ）Ｃ，（Ｔｉ，Ｔａ，Ｗ）（Ｃ，Ｎ）などの立方晶化合物を例示できる。例えば、立方晶相の原料としてＶＣ粉末，ＴｉＣ粉末，ＴａＣ粉末を同時添加した場合には、焼結中にＷを固溶して（Ｔｉ，Ｖ，Ｔａ，Ｗ）Ｃの組成の立方晶化合物を形成する。Ｔｉ，Ｚｒ，Ｖ，Ｔａなどを少量添加すると、焼結時に結合相へ固溶してＷＣの粒成長を抑制するとともに、常温でも結合相中に固溶して結合相の強化に役立つ。しかしながら、超微粒超硬合金に含まれる立方晶相の量が５体積％を超えると、これらの立方晶化合物が粗大化するため、超微粒超硬合金の強度が低下する傾向がみられる。
【００２０】
本発明の超微粒超硬合金の製造方法として原料粉末の混合、加圧成形、焼結の各工程を含む通常の粉末冶金法によって作製可能であるが、ＷＣ粒子径が非常に細かい超微粒超硬合金を得るため、従来の微粒超硬合金の焼結温度よりも低温で焼結させることが好ましい。すなわち、従来のＷＣ−（Ｃｏ，Ｎｉ）系微粒超硬合金の焼結温度は、１３５０〜１４５０℃であるのに対し、本発明品の超微粒超硬合金の焼結温度は、１１５０〜１３００℃が好ましい。これは、Ｎｉ−Ｓｉ−Ｂ系合金がＮｉ−７．３ｗｔ％Ｓｉ−２．２ｗｔ％Ｂ付近に１０００℃以下の３元共晶温度を有するためである。
【００２１】
原料としては、炭化タングステン粉末の粒径は細かいほど好ましく、具体的には平均粒子径０．５μｍ以下の炭化タングステン粉末が好ましい。また、原料のニッケル粉末、クロム粉末、シリコン粉末、ボロン粉末もそれぞれ粒径が細かいほど好ましい。原料としては、ホウ化ニッケル粉末、炭化クロム粉末、炭化ケイ素粉末、窒化ホウ素など粉圧、焼結時にニッケルと反応して分解・固溶し、かつ粉砕されやすい化合物を用いても良い。
【００２２】
本発明の超微粒超硬合金において、結合相の主成分であるニッケルにクロム、シリコン、ボロンが固溶する。結合相に固溶したボロンとクロムが焼結時での炭化タングステンの粒成長を抑制する。結合相に固溶したシリコンとボロンが焼結温度を低下させて炭化タングステンの粒成長を抑制するため、炭化タングステンの平均粒子径が細かい超微粒超硬合金が得られる。炭化タングステンの平均粒子径が細かくなるとともに、結合相に固溶したクロム，シリコン、ボロンのいずれも結合相の硬さと靱性を改善するため、本発明の超微粒超硬合金は従来の微粒超硬合金に比較して硬さと強度に優れる。
【００２３】
本発明の超微粒超硬合金は、チップ、ドリル、回路プリント基板加工用の小径ドリル、エンドミル、金型、または切断刃など硬さ，耐摩耗性と強度・靱性が共に必要とされる用途に適する。また、耐食性にも優れることから、腐食環境下で使用する耐摩耗性部品やしゅう動部品にも適する。
【００２４】
【実施例１】
市販されている平均粒子径が０．３μｍのＷＣ（ＷＣ／Ｆと記す），２．３μｍのＷＣ（ＷＣ／Ｍと記す），６．０μｍのＷＣ（ＷＣ／Ｃと記す），０．５μｍのＷ，１．０μｍのＮｉ，１．２μｍのＣｒ₃Ｃ₂，０．５μｍのＳｉＣ，１．３μｍのＢＮ，０．６μｍのＣｏ，１．２μｍのＦｅ，１．０μｍのＭｏ，２．０μｍのＶＣ，１．２μｍのＴｉＣ，１．０μｍのＴａＣ，０．０５μｍのカーボンブラック（Ｃと記す），０．５μｍのＡｌ，および＃３２５のＳｉ粉末を湿式ボールミルにて予備粉砕して得た２μｍのＳｉ，３μｍのＮｉ₃Ｂ（５．８重量％Ｂ）の各粉末を用いて、表１、表２に示す配合組成に秤量し、ステンレス製ポットにアセトン溶媒と超硬合金製ボールと共に挿入し、９６時間の混合・粉砕を行った後、加熱および乾燥しながら２重量％のパラフィンワックスを添加して混合粉末を得た。ここで、配合炭素量は、焼結後に遊離炭素あるいはＮｉ₂Ｗ₄Ｃ，Ｃｏ₃Ｗ₃Ｃを析出しない健全相領範囲の中央の炭素量を示す中炭素合金となるように、Ｗ粉末あるいはＣ粉末の添加により調整した。但し、本発明品６では、意識的に低炭素合金にしてＮｉ₂Ｗ₄Ｃを析出させている。
【００２５】
これらの粉末を金型に充填し、１９６ＭＰａの圧力でもって５．５×９．５×２９ｍｍの圧粉成形体を作製し、アルミナとカーボン繊維からなるシート上に設置し、雰囲気圧力１０Ｐａの真空中で、表１、表２に併記した温度でもって１時間加熱保持して、本発明品１〜１５および比較品１〜１６の超硬合金を得た。ここで、焼結温度は、３０℃刻みでおこなった焼結予備実験で焼結体の硬さおよび組織観察による結合相の分散状態から選定した。
【００２６】
【表１】

【００２７】
【表２】

【００２８】
こうして得た本発明品１〜１５および比較品１〜１６の超硬合金を＃２３０のダイヤモンド砥石で湿式研削加工し、４．０×８．０×２５．０ｍｍの形状に作製し、ＪＩＳ法による抗折力を測定して、その結果を表３、表４に示した。また、同試料の１面を平均粒子径０．３μｍのダイヤモンドペーストでラップ加工した後、ビッカース圧子を用いた荷重：９８Ｎ（本発明品２と比較品２は、１９６Ｎ）での硬さおよび破壊靱性値Ｋ１Ｃ（ＩＭ法）を測定し、その結果を表３，表４に併記した。さらに、各試料のラップ面について電界放射型走査電子顕微鏡にて組織写真を撮り、画像処理装置にて、ＷＣ，結合相，炭化クロム（Ｃｒ₂₃Ｃ₆），複合炭化物（Ｎｉ₂Ｗ₄Ｃ）などの分散相の体積，立方晶化合物などの立方晶相の体積と平均粒子径（但し、結合相は除く）を求めた。その結果を体積％に換算し表５、表６に併記し、平均粒子径は表７、表８に示す。なお、分散相の存在は、Ｘ線回折測定と走査電子顕微鏡による微少部分析で確認した。
【００２９】
【表３】

【００３０】
【表４】

【００３１】
【表５】

【００３２】
【表６】

【００３３】
【表７】

【００３４】
【表８】

【００３５】
次に、上記の抗折力試験片を超硬合金製乳鉢中で＃１００以下に粉砕し、これを５Ｎの塩酸と共にビーカーに入れて５０℃で２４時間保持することによって、超硬合金中の結合相成分のみを溶解・抽出した。各抽出液から原子吸光分析装置を用いて成分元素量を測定し、結合相の成分組成を求めた。その結果を表９、表１０に併記した。
【００３６】
【表９】

【００３７】
【表１０】

【００３８】
【発明の効果】
本発明の超微粒超硬合金は、従来の微粒超硬合金に比べて、ＷＣの平均粒子径が約１／２であり、同一結合相量の超硬合金で比較すると、硬さが約１００〜２００ＨＶ、抗折力が約１００〜３００ＭＰａも高いという効果を有する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrafine cemented carbide used for cutting tools, wear resistant tools, and parts. For example, the ultrafine cemented carbide of the present invention is suitable for applications that require hardness, wear resistance, strength, and / or toughness, such as chips, drills, end mills, molds, or cutting blades. In addition, since it has excellent corrosion resistance, it is also suitable for wear-resistant parts and sliding parts used in corrosive environments.
[0002]
[Prior art]
Conventional fine-grained cemented carbides add 0.2 to 2 wt% of grain growth inhibitors such as VC, Cr ₃ C ₂ and TaC to WC powder and Co powder with an average particle size of 0.2 to 0.7 μm And after mixing, it is obtained by sintering. Compared to coarse-grained cemented carbides with an average WC particle size of 1.0 to 7.0 μm, both the hardness and strength are high, and the surface accuracy, sharpness, wear resistance, and welding resistance are excellent. . In order to obtain a high-hardness and high-strength fine-grain cemented carbide, it is necessary to have a fine and uniform structure that does not contain abnormally grown WC, and studies on the ingredients and amounts of grain growth inhibitors and their uniform dispersion There have been many.
[0003]
As prior art relating to the composition of the fine cemented carbide, there are JP-A-63-42346, JP-A-4-289146, JP-A-5-117799, and the like. Moreover, as a prior art regarding the manufacturing method of a fine grain cemented carbide, there are Unexamined-Japanese-Patent No. 06-212341, Unexamined-Japanese-Patent No. 10-110235, etc. Further, Japanese Patent Application Laid-Open No. 60-135552 discloses a fine-grain cemented carbide using nickel as a binder phase.
[0004]
[Problems to be solved by the invention]
Among the prior arts relating to the composition of the fine cemented carbide, JP-A-63-42346 discloses vanadium carbide in tungsten carbide having an average particle size of 1.0 μm or less and 3-30% cobalt and / or nickel. And a high-strength cemented carbide in which chromium carbide is dissolved in a total amount of 3 to 7%. Similarly, JP-A-4-289146 discloses vanadium and chromium in 4 to 25% by weight of cobalt and / or nickel, V / (Co + Ni) = 0.01 to 0.1, Cr / (Co + Ni). A high-strength, high-toughness cemented carbide having a composite carbide containing vanadium and tungsten as a third phase is described. JP-A-5-117799 contains cobalt: 4 to 20% by weight, chromium carbide: 0.3 to 3.0% by weight, vanadium carbide: 0.1 to 3.0% by weight, and carbonization. A tungsten carbide-based cemented carbide in which the average particle diameter of tungsten is 0.8 μm or less and a composite carbide phase of chromium and vanadium is dispersed is described.
[0005]
The fine cemented carbides described in these publications are intended to suppress the grain growth of WC by the synergistic effect of chromium and vanadium dissolved in the metal binder phase, but the amount of solid solution is limited. In addition, an ultrafine cemented carbide cannot be obtained. Moreover, there exists a problem that both strength and toughness are lowered when composite carbide is present. In particular, when nickel is used as the binder phase, a fine cemented carbide with high strength and high toughness cannot be obtained.
[0006]
Regarding a method for producing a fine cemented carbide, Japanese Patent Laid-Open No. 06-212341 discloses that a mixed powder of tungsten oxide, chromium oxide, vanadium oxide, tantalum oxide, molybdenum and carbon black is reduced and carbonized to form a composite carbide powder. A manufacturing method of a fine cemented carbide alloy is described in which a mixed powder to which cobalt is added is pressed and argon HIP is described. Japanese Patent Application Laid-Open No. 10-110235 discloses that the total amount of chromium and vanadium is 1% by weight or less, the average particle diameter of WC is 0.5 μm or less, 1100 to 1350 ° C. A high-hardness hard alloy obtained by electrical pressure sintering at 200 MPa and its manufacturing method are described.
[0007]
Japanese Patent Laid-Open No. 06-212341 discloses a method in which the grain growth is suppressed by uniformly dispersing the grain growth inhibitor, but the effect is limited. Japanese Patent Laid-Open No. 10-110235 attempts to suppress grain growth by pressure sintering at a low temperature. However, the addition of chromium and vanadium has a high liquid phase appearance temperature. There is a problem that the phases are not sufficiently dispersed and the strength is lowered, and the electric pressure sintering method is not suitable for mass-produced products, complex shaped products, and grinding-less products.
[0008]
Regarding a fine cemented carbide using nickel as a binder phase, Japanese Patent Application Laid-Open No. 60-135552 discloses that the binder phase is 2-20 wt% chromium, 0.5-10 wt% aluminum, 0.5 wt% An ultrafine tungsten carbide based sintered alloy consisting of nickel containing ˜5 wt% titanium is described. This publication aims at the synergistic effect of grain growth suppression by solid solution of chromium and titanium in binder phase nickel and the improvement of oxidation resistance and heat resistance by solid solution of aluminum. Since the effect is low and high-temperature sintering is required, it is difficult to obtain an ultrafine cemented carbide, and there is a problem that the bonding phase becomes brittle due to the solid solution of aluminum and titanium and the strength and toughness are not improved.
[0009]
The present invention solves the above-described problems. Specifically, in addition to tungsten that inevitably dissolves in a binder phase mainly composed of nickel, at least three kinds of chromium, silicon, and boron are used. The ultrafine-grain cemented carbide with ultra-fine WC that suppresses WC grain growth during sintering without impairing the hardness, strength, and toughness of the binder phase by dissolving each element in an appropriate amount. For the purpose of provision.
[0010]
[Means for Solving the Problems]
For many years, the present inventor has been studying the suppression of WC grain growth during sintering in order to obtain a superfine cemented carbide with finer grains and superior strength and toughness than conventional fine grained cemented carbides. When nickel is used for the binder phase and boron is added, grain growth is suppressed. When chromium is added, grain growth is suppressed. When boron and silicon are added simultaneously, the sintering temperature is lowered. The inventors have obtained the knowledge that grain growth is suppressed and nickel alloys containing chromium, silicon, and boron are excellent in hardness, strength, and / or toughness, and have completed the present invention.
[0011]
That is, the ultrafine cemented carbide of the present invention is an ultrafine cemented carbide comprising a binder phase mainly composed of nickel and a hard phase mainly composed of tungsten carbide having an average particle size of 0.05 to 0.5 μm. In the alloy, the binder phase contains 5-30 wt.% Tungsten, at least 5-15 wt.% Chromium, 2-10 wt.% Silicon, and 1-5 wt. It is characterized by being.
[0012]
Tungsten carbide in the ultrafine cemented carbide of the present invention is composed of ultrafine WC having an average particle size of 0.05 to 0.5 μm. The finer the WC, the better. However, it is difficult to produce ultrafine WC powder as a raw material, and the average particle diameter of WC is about 0.05 μm because the grain grows during sintering. On the other hand, when the average particle diameter of WC is larger than 0.5 μm, hardness and strength are drastically decreased. The number of coarse WC particles having a particle diameter exceeding 2 μm is preferably 1 or less in a visual field of 0.1 × 0.1 mm ² . When coarse WC powder having an average particle size of 1 to 7 μm is used as a raw material, the grain growth inhibiting effect due to the addition of boron and chromium, and the grain growth inhibiting effect accompanying the decrease in sintering temperature due to the addition of boron and silicon are It cannot be demonstrated, and a high-hardness, high-strength ultrafine-grained cemented carbide cannot be obtained.
[0013]
The binder phase in the ultrafine cemented carbide of the present invention is a Ni—W—Cr—Si—B alloy, nickel as a main component, 5 to 30% by weight of tungsten, and 5 to 15 based on the total binder phase. It contains 1 wt% chromium, 2-10 wt% silicon, 1-5 wt% boron. Tungsten in the binder phase inevitably forms a solid solution, and the amount of the solid solution is 10% by weight for the high carbon alloy having a free carbon precipitation limit, and 30% by weight for the low carbon alloy at the precipitation limit of Ni ₂ W ₄ C. It is. Since the solid solution amount of tungsten tends to decrease due to the solid solution of other elements, the lower limit value of the tungsten solid solution amount is 5% by weight. From the above, the amount of tungsten in the binder phase was determined to be 5 to 30% by weight.
[0014]
If the amount of chromium in the binder phase is less than 5% by weight, the strengthening effect of the binder phase and the effect of suppressing grain growth are small, so the hardness and strength are reduced. Since it is difficult under the sintering conditions, it is determined to be 5 to 15% by weight. In addition, when the amount of silicon in the binder phase is less than 2% by weight, the effect of reducing the sintering temperature is small, so that grain growth tends to occur. Conversely, when the amount exceeds 10% by weight, silicon carbide is present at the grain boundary between WC and binder phase. Was precipitated and the strength decreased, so it was determined to be 2 to 10% by weight. Further, if the boron content in the binder phase is less than 1% by weight, the effect of suppressing the grain growth and the effect of reducing the sintering temperature are small, so that the grain growth is easy. Conversely, if the amount of boron exceeds 5% by weight, the binder phase becomes brittle. Since the strength is reduced by precipitation or precipitation of nickel boride, it is set to 1 to 5% by weight.
[0015]
In the binder phase of the ultrafine cemented carbide of the present invention, as an element other than nickel, tungsten, chromium, silicon and boron, 5% of the binder phase as a whole is used for the purpose of improving heat resistance, corrosion resistance, hardness, strength and the like. The iron may be contained in an amount of not more than% by weight, not more than 3% by weight of molybdenum with respect to the whole binder phase, and / or not more than 30% by weight of cobalt with respect to the whole binder phase. That is, iron and molybdenum improve heat resistance and corrosion resistance, and cobalt improves hardness and strength.
[0016]
The ultra-fine cemented carbide of the present invention is composed of a hard phase and a binder phase. The amount of the binder phase contained in the ultra-fine cemented carbide is less than 5% by volume with respect to the entire ultra-fine cemented carbide. Since ligation is required and grain growth occurs, both hardness and strength decrease. On the contrary, when it exceeds 40 volume%, the fall of hardness will become large. Therefore, the amount of the binder phase is preferably 5 to 40% by volume with respect to the entire ultrafine cemented carbide. The balance other than the binder phase is a hard phase.
[0017]
The hard phase may be only a main phase composed of tungsten carbide, but a dispersed phase composed of at least one selected from chromium, cobalt, tungsten, nickel carbides, and their mutual solid solution is an ultrafine cemented carbide. It is preferable to contain 5% by volume or less based on the whole, and at least one cubic phase among the carbides, nitrides of the elements of Group 4a, 5a, and 6a of the periodic table, and cubic compounds of these solid solutions. It is also preferable to contain 5% by volume or less based on the whole ultrafine cemented carbide.
[0018]
As a dispersed phase comprising at least one selected from chromium, cobalt, tungsten, nickel carbides and their mutual solid solutions, specifically, Cr ₂₃ C ₆ , Ni ₂₃ C ₆ , Ni ₂ W ₄ C, A composite carbide such as Ni ₂ Cr ₄ C can be exemplified. Cr ₂₃ C ₆ and Ni ₂₃ C ₆ precipitate when the amount of chromium in the binder phase is excessive, and Ni ₂ W ₄ C and Ni ₂ Cr ₄ C form when the amount of carbon in the ultrafine cemented carbide is low. Is done. All are uniformly and finely dispersed in the ultrafine-grained cemented carbide. However, when the amount of the dispersed phase contained in the ultrafine cemented carbide exceeds 5% by volume, both hardness and strength tend to decrease.
[0019]
Specifically, at least one cubic phase among the cubic compounds composed of the carbides, nitrides, and their mutual solid solutions of the periodic table 4a, 5a, and 6a elements, tungsten is specifically dissolved (Ti , W) C, (Zr, W) C, (V, W) C, (Ta, W) C, and (Ti, Ta, W) (C, N). For example, when VC powder, TiC powder, and TaC powder are added simultaneously as a raw material for the cubic phase, W is solid-solved during sintering and a cubic compound having a composition of (Ti, V, Ta, W) C. Form. When a small amount of Ti, Zr, V, Ta, or the like is added, the solid phase dissolves in the binder phase during sintering to suppress WC grain growth, and at the room temperature, the solid phase dissolves in the binder phase to help strengthen the binder phase. However, when the amount of the cubic phase contained in the ultrafine cemented carbide exceeds 5% by volume, these cubic compounds are coarsened, so that the strength of the ultrafine cemented carbide tends to decrease.
[0020]
As a method for producing the ultrafine cemented carbide of the present invention, it can be produced by an ordinary powder metallurgy method including the steps of mixing raw material powder, pressure forming, and sintering. In order to obtain a hard alloy, it is preferable to sinter at a temperature lower than the sintering temperature of the conventional fine cemented carbide. That is, the sintering temperature of the conventional WC- (Co, Ni) -based fine cemented carbide is 1350 to 1450 ° C., whereas the sintering temperature of the ultra-fine cemented carbide of the present invention is 1150 to 1300. ° C is preferred. This is because the Ni—Si—B alloy has a ternary eutectic temperature of 1000 ° C. or less in the vicinity of Ni-7.3 wt% Si-2.2 wt% B.
[0021]
As the raw material, the finer the particle size of the tungsten carbide powder, the more preferable. Specifically, the tungsten carbide powder having an average particle size of 0.5 μm or less is preferable. The raw material nickel powder, chromium powder, silicon powder, and boron powder are also preferred as the particle size is finer. As raw materials, compounds such as nickel boride powder, chromium carbide powder, silicon carbide powder, boron nitride, etc., which are easily decomposed and dissolved by reacting with nickel at the time of sintering, sintering, and pulverization may be used.
[0022]
In the ultrafine cemented carbide of the present invention, chromium, silicon and boron are dissolved in nickel which is the main component of the binder phase. Boron and chromium dissolved in the binder phase suppress the grain growth of tungsten carbide during sintering. Since silicon and boron dissolved in the binder phase lower the sintering temperature and suppress the grain growth of tungsten carbide, an ultrafine cemented carbide with a fine average particle diameter of tungsten carbide can be obtained. Since the average particle diameter of tungsten carbide is reduced and chromium, silicon, and boron dissolved in the binder phase all improve the hardness and toughness of the binder phase, the ultrafine cemented carbide of the present invention is a conventional fine carbide. Excellent hardness and strength compared to alloys.
[0023]
The ultra-fine cemented carbide of the present invention is suitable for applications that require both hardness, wear resistance, strength and toughness, such as chips, drills, small diameter drills for processing printed circuit boards, end mills, dies, and cutting blades. Suitable. In addition, since it has excellent corrosion resistance, it is also suitable for wear-resistant parts and sliding parts used in corrosive environments.
[0024]
[Example 1]
WC with a mean particle size of 0.3 μm (denoted as WC / F), 2.3 μm with WC (denoted with WC / M), 6.0 μm with WC (denoted with WC / C), 0.5 μm W, 1.0 μm Ni, 1.2 μm Cr ₃ C ₂ , 0.5 μm SiC, 1.3 μm BN, 0.6 μm Co, 1.2 μm Fe, 1.0 μm Mo, 2. Obtained by pre-grinding 0 μm VC, 1.2 μm TiC, 1.0 μm TaC, 0.05 μm carbon black (referred to as C), 0.5 μm Al, and # 325 Si powder in a wet ball mill. Each powder of 2 μm Si and 3 μm Ni ₃ B (5.8 wt% B) was weighed into the composition shown in Tables 1 and 2, and acetone solvent and cemented carbide balls were placed in a stainless steel pot. After mixing and grinding for 96 hours, do not heat and dry To obtain a mixed powder by adding et 2% by weight of paraffin wax. Here, the blended carbon amount is W powder or so as to be a middle carbon alloy showing a carbon amount in the middle of a healthy phase range in which free carbon or Ni ₂ W ₄ C, Co ₃ W ₃ C is not precipitated after sintering. Adjustment was made by adding C powder. However, in the product 6 of the present invention, Ni ₂ W ₄ C is intentionally deposited as a low carbon alloy.
[0025]
These powders are filled into a mold, and a compact of 5.5 × 9.5 × 29 mm is produced with a pressure of 196 MPa, placed on a sheet made of alumina and carbon fiber, and a vacuum with an atmospheric pressure of 10 Pa. Among them, the cemented carbides of the present invention products 1 to 15 and comparative products 1 to 16 were obtained by heating and holding at the temperatures shown in Tables 1 and 2 for 1 hour. Here, the sintering temperature was selected from the hardness of the sintered body and the dispersed state of the binder phase by observation of the structure in a preliminary sintering experiment performed in increments of 30 ° C.
[0026]
[Table 1]

[0027]
[Table 2]

[0028]
The cemented carbides of the present invention products 1 to 15 and comparative products 1 to 16 thus obtained were wet-grinded with a # 230 diamond grindstone, and formed into a 4.0 × 8.0 × 25.0 mm shape. The bending strength was measured and the results are shown in Tables 3 and 4. Further, after lapping one surface of the sample with a diamond paste having an average particle size of 0.3 μm, hardness and fracture at a load of 98 N (present product 2 and comparative product 2 is 196 N) using a Vickers indenter The toughness value K1C (IM method) was measured, and the results are also shown in Tables 3 and 4. Furthermore, a structure photograph was taken with a field emission scanning electron microscope on the lap surface of each sample, and WC, binder phase, chromium carbide (Cr ₂₃ C ₆ ), composite carbide (Ni ₂ W ₄ C) was obtained with an image processing device. The volume of the dispersed phase such as, the volume of the cubic phase such as the cubic compound and the average particle diameter (excluding the binder phase) were obtained. The results are converted to volume% and are also shown in Tables 5 and 6, and the average particle diameters are shown in Tables 7 and 8. The presence of the dispersed phase was confirmed by X-ray diffraction measurement and microscopic analysis with a scanning electron microscope.
[0029]
[Table 3]

[0030]
[Table 4]

[0031]
[Table 5]

[0032]
[Table 6]

[0033]
[Table 7]

[0034]
[Table 8]

[0035]
Next, the above-mentioned bending strength test piece was pulverized to # 100 or less in a cemented carbide mortar, and placed in a beaker with 5N hydrochloric acid and kept at 50 ° C. for 24 hours, whereby the Only the binder phase components were dissolved and extracted. The amount of component elements was measured from each extract using an atomic absorption spectrometer, and the component composition of the binder phase was determined. The results are shown in Tables 9 and 10.
[0036]
[Table 9]

[0037]
[Table 10]

[0038]
【The invention's effect】
The ultra-fine cemented carbide of the present invention has an average particle diameter of WC of about 1/2 as compared with a conventional fine-grained cemented carbide, and the hardness is about 100 when compared with a cemented carbide having the same binder phase. It has the effect that -200 HV and a bending strength are as high as about 100-300 MPa.

Claims

An ultrafine cemented carbide comprising a hard phase mainly composed of tungsten carbide having an average particle size of 0.05 to 0.5 μm and a binder phase mainly composed of nickel, wherein the ultrafine cemented carbide is composed of the ultrafine particles. 5 to 40% by volume of the binder phase with respect to the whole cemented carbide and 60 to 95% by volume of the hard phase with respect to the whole ultrafine cemented carbide, and the binder phase binds tungsten. 5 to 30% by weight with respect to the whole phase, 5 to 15% by weight with respect to the whole of the binder phase, 2 to 10% by weight of silicon with respect to the whole of the binder phase, and boron with respect to the whole of the binder phase. An ultrafine cemented carbide comprising 1 to 5% by weight , iron of 5% by weight or less with respect to the whole binder phase, molybdenum of 3% by weight or less with respect to the whole binder phase, and the balance nickel .

The ultrafine-grained cemented carbide according to claim 1, wherein 30 wt% or less of cobalt with respect to the entire binder phase is substituted for nickel.

A main phase in which the hard phase is composed of tungsten carbide having an average particle size of 0.05 to 0.5 μm, and at least one dispersed phase selected from chromium, cobalt, tungsten, nickel carbides and their mutual solid solutions; And a periodic phase table 4a, 5a, 6a group element carbide, nitride, and at least one cubic phase of a cubic compound composed of a mutual solid solution thereof, and the entire ultrafine cemented carbide alloy The content (volume%) of the main phase is a, the content (volume%) of the dispersed phase with respect to the entire ultrafine cemented carbide is b, and the content of the cubic phase with respect to the entire ultrafine cemented carbide ( The ultrafine-grained cemented carbide according to claim 1 or 2, wherein 50% a≤95, 0≤b≤5, 0≤c≤5, 60≤a + b + c≤95 are satisfied when the volume%) is expressed as c.