JP3954845B2

JP3954845B2 - Tungsten carbide-based cemented carbide and method for producing the same

Info

Publication number: JP3954845B2
Application number: JP2001396304A
Authority: JP
Inventors: 裕久保
Original assignee: Hitachi Tool Engineering Ltd
Current assignee: Moldino Tool Engineering Ltd
Priority date: 2001-12-27
Filing date: 2001-12-27
Publication date: 2007-08-08
Anticipated expiration: 2021-12-27
Also published as: JP2003193172A

Description

【０００１】
【発明に属する技術分野】
本願発明は、超硬合金に関し、特に平均粒径が０．６μｍ以下の炭化タングステン粒子を有する、いわゆる超微粒超硬合金に関する。
【０００２】
【従来の技術】
平均粒径が１μｍ以下のＷＣ粒子を含有する超微粒超硬合金は、硬さとともに靭性も高いのでエンドミル、プリント基板用ドリル、各種せん断刃などに広範囲に用いられている。近年微細加工及び高速加工の傾向とともに超微粒合金の平均粒径も益々小さく、且つ、耐熱性、耐酸化性の高いものの要求が大となってきている。微細加工の用途に適合させるには超硬合金を構成するＷＣの粒径をより微細化させることが必要となることから、従来から周知のＶ、Ｔａ、Ｃｒなどの金属若しくはそれらの金属の化合物（炭化物、窒化物、炭窒化物など）をＷＣに対する粒成長抑制材として、単独に用いられていたものが、０．６μｍ以下の平均粒径をめざし２種以上を添加するようになってきた。例えば、特公昭６２−５６２２４号公報（特許番号１５３９９９１）ではＶとＣｒの２種を添加し、且つ、合金内に第３相が出現しないようにして靭性を劣化させない工夫が開示されている。
【０００３】
また、特許第３００８５３２号公報ではやはりＶとＣｒを複合添加し、且つ、ＶとＷを含む複合炭化物を第３相として金属結合相とＷＣの粒界に存在させることにより抗折力の向上が図れることが開示されている。特許第３０１０８５９号公報もＶとＣｒの複合添加の特許であるが、Ｃｒ炭化物や（Ｗ、Ｖ）Ｃを析出させることなくＣｒとＶの複合炭化物、より正確に記すれば（Ｃｒ、Ｖ）_２Ｃのみを素地中に分散させて、硬さと靭性の双方の向上を図ることが開示されている。３種の複合添加では特公昭６２−５６４９３号公報（特許第１４６７２９１号）においてＶとＣｒとＭｏの３種添加が開示されている。また特公昭６２−５６４９４号公報（特許第１４８７４７９号）では、ＶとＣｒと０．５〜８．０重量％のＴａＣ又は（Ｔａ、Ｎｂ）Ｃの３種の添加し、より微細な超硬合金が得られることを開示している。この場合ＴａＣ又は（Ｔａ、Ｎｂ）Ｃを主体とする固溶体炭化物相の析出相が一定量以下であれば、靭性の低下を招聘しないとされている。特公平０３−４６５３８号公報においても、ＶとＣｒと０．４〜０．５％のＴａＮｂＣの３種添加が開示されている。特許第３２０６３７５号公報においてもＶとＣｒと０．０５〜２．５％のＴａＣの複合添加によるＷＣ粒径０．７〜１．０μｍの超微粒合金が開示されている。ＷＣの平均粒径が０．６μｍ以下の、いわゆる超微粒超硬合金の耐熱性や耐酸化性を改善する方策については充分効果のある方策が開示されていないのが現状である。
【０００４】
【発明が解決しようとする課題】
ＷＣ粒子の微細化について述べると、ＷＣ粒子は焼結中に粒成長を起こすので、合金中のＷＣ粒子の粒径は焼結前よりも大きい。そのため粒成長抑制材を添加してＷＣの粒成長を抑制する方法の研究が進められ、Ｖが最も有効で、Ｃｒ、Ｔａ、Ｍｏも効果のあることがわかっている。平均粒径が０．６μｍ以下、願わくば０．５μｍ以下としたいならば、多量の粒成長抑制材、特に、Ｖを添加すればよいが、Ｖを多量に添加すると合金の靭性が急激に低下する。そのためＶの添加量を減らして、その結果生じる粒成長抑制効果の減少分をＣｒやＴａで補填する試み、すなわち粒成長抑制材の複合添加が行われてきたのである。しかしながら、上記の先行技術を含め発明者らが鋭意検討したところではＶとＣｒの組合せでは、焼結後の冷却中に結合相やＷＣ相とは別の第３相が析出し、それが靭性を低下させることが明らかとなった。そのため第３相が析出しない程度に添加量を少なくすると、粒成長抑制効果が希薄になる。ＶとＴａの組合せは第３相の出現がより易くなり、靭性の低下が激しい。そこで平均粒径が０．６μｍ以下、願わくば０．５μｍとした高靭性の超硬合金を得ようとするならば、ＶとＣｒとＴａの３種の添加に頼らざるを得ない。しかしながら、上述の先行技術を追試した結果、Ｔａの添加はＶとＴａの組合せ同様、靭性の低下が大きな障害となることがわかった。
【０００５】
次に、超微粒超硬合金の耐酸化性については、その主たる構成要素であるＷＣとＣｏ及び／又はＮｉはいずれも酸化開始温度が６００℃近辺で大きな違いは無い。しかし、酸化の進行速度はＷＣの方が速く、超硬合金の酸化を律速するのはＷＣといえる。しかしながらＷＣは他の金属元素を取り込む性質に乏しく、ＷＣの性質を変えることはなかなか困難である。一方、結合相であるＣｏ及び／又はＮｉについてはその性質を変化させることはＷＣよりも容易である。しかし、上述したように、超微粒超硬合金を得るために種々の添加物を用いると複炭化物と思われる新たな相が出現しそれが合金の靭性を低下させるが、さらに耐酸化性を向上させるような元素を加えると、新たな相の量がさらに多くなり著しい靭性の低下を招聘する結果となるのが一般的である。また、耐熱性についてはもともとＷＣは充分な耐熱性を有するものであるから、金属結合相を耐熱化することを考えれば十分である。以上の考察から金属結合相の耐酸化性と耐熱性の双方を向上させ、且つ、ＷＣと金属結合相以外の新たな相の出現量を増加させないか、あるいは靭性の低下を招かない性質にする添加元素を見つけ出すことができると、靭性と耐酸化性と耐熱性を具備したＷＣの平均粒径が０．６μｍ以下の超硬合金が得られることになる。換言すると、そのような性質をもたせる添加物は知られていないのが現状である。
【０００６】
【課題を解決するための手段】
そこで本発明者等は、まず靭性について、なぜＶとＣｒとＴａの３種添加が粒成長抑制効果は評価できるものの、靭性の著しい低下がなぜ起きるかの観点から種々検討した結果、結合相やＷＣ相とは明らかに異なる別の相とおぼしきものが合金全体に広がっていることが観察された。この別相とおぼしきもの（以後、出現相と記す。）はＴａ添加量とともに増加すること、同じＴａ量では低カーボン合金ほど少なく、また焼結終了後から液相消失温度までの冷却速度が速いほど減少し、場合によっては出現しなくなることがわかった。また、この出現相は量の増加に伴って抗折力値で評価される靭性が急激に低下することなどが明らかとなった。すなわち、本願発明は、Ｃｏ及びＮｉのうちの１種又は２種：２〜３０％、Ｖ：０．１〜２．０％、Ｃｒ：０．１〜２．０％、Ｔａ：０．０１％以上０．４％未満、Ｓｉ：０．１〜１．５％、を含有し、残り：炭化タングステン及び不可避不純物、からなる組成を有する超硬合金で、該超硬合金のミクロ組織は、Ｃｏ及び／又はＮｉを主体とする結合相と、平均粒径が０．６μｍ以下の炭化タングステン相と、Ｃｒ、Ｔａ、Ｖ、Ｓｉ及びＷから選ばれた１種又は２種以上の金属元素を主体とする化合物相との、３相又は３相以上を有することをを特徴とする炭化タングステン基超硬合金であり、更に、その製造方法として、焼結を加圧雰囲気又は焼結を真空雰囲気及び／又は加圧雰囲気で行い、その後急冷する製造方法である。
【０００７】
そこでＴａ（Ｔａ化合物の場合はＴａ分）の適正量について厳密な調査を行ったところ、０．４％を超えると出現相が過多となり、Ｖ添加量が０．１〜２．０の範囲において充分な靭性が保てないことが明らかとなった。さらに記すれば、Ｖが０．１〜２．０％、且つ、Ｃｒが０．１〜２．０％の範囲において、いかに合金カーボン量を調整しようが、また実用範囲で冷却速度を大きくしようが、出現相の望ましい上限値を超えてしまい、充分に靭性のあるＷＣの平均粒径が０．６μｍ以下の合金が得られない。次に、耐酸化性と耐熱性については、発明者らは広範囲にわたって、その効果が得られる物質とその量を検討した結果、Ｓｉが適切であるとの結果を得た。さらに合金にＮを含有させるとＳｉの添加効果を助長させることが出来るとの結果を得た。また本発明品の製法については、焼結を加圧雰囲気中で行うと靭性のより高い合金がえられること、さらに加圧焼結後に急冷すると出現相の低減が図られ、靭性がさらに向上する結果も得た。Ｓｉの添加はＳｉを含んだ化合物でもその効果は期待できる。特に、ケイ化タンタル（Ｔａ）粉、ケイ化クロム（Ｃｒ）粉、ケイ化タングステン（Ｗ）粉などはすでにＴａ、Ｃｒ、Ｗが合金に含まれるため都合が良い。Ｎの添加はＶＮ粉、ＴｉＮ粉、Ｃｒ２Ｎ粉などが上記と同様の理由で都合が良い。
【０００８】
本願発明においてＶ（Ｖ化合物の場合はそのＶ分）は０．１〜２．０％とする。０．１％未満では充分な粒成長抑制効果が得られず、本発明の趣旨に反する。０．２％を超えると充分な靭性が得られず、抗折力が実用範囲以下に低下する。ここで抗折力の実用範囲は３０００ＭＰａ以上としたが、用途によりそれ未満でも使用可能な場合もあり、厳格に規定するものではない。Ｃｒ（Ｃｒ化合物の場合はそのＣｒ分）は０．１〜２．０％とする。０．１％未満では充分な粒成長抑制効果が得られず、本発明の趣旨に反する。０．２％を超えると充分な靭性が得られず、抗折力が実用範囲以下に低下する。Ｔａ（Ｔａ化合物の場合はそのＴａ分）は０．０１％以上０．４％未満に規定する。０．０１％未満では充分なＶ＋Ｃｒ＋Ｔａの粒成長抑制に対する相乗効果とが得られず、本発明の趣旨に反する。０．４％以上では充分な靭性が得られず、抗折力が実用範囲以下に低下する。Ｓｉ（Ｓｉ化合物の場合はそのＳｉ分）は０．１〜１．５％に規定する。０．１％未満では充分な耐酸化性と耐熱性が得られず、本発明の趣旨に反する。１．５％を超えると充分な靭性が得られない。おそらく、出現相の量が過多となるためと思われる。Ｎ（化合物の場合はそのＮ分）は２００〜１０００ｐｐｍ規定する。２００ｐｐｍ未満では充分な耐酸化性と耐熱性が感知できず、わざわざＮを添加するには及ばない。１０００ｐｐｍを超えると目下理由は不明だが充分な靭性が得られない。Ｃｏ及び／又はＮｉは２〜３０％の範囲とする。２％未満では充分な靭性が得られない。３０％を超えると超硬合金の本質的な性質の一つである硬さの低下が著しく、一部の用途を除いて実用的でない。
【０００９】
本願発明の超硬合金のミクロ組織は、金属相とＷＣ相の２相が基本であるが、製造条件によりその他の相が出現する場合がある。しかもその出現相は一つの場合も複数の場合も条件により観察される。出現相はＣｒ、Ｔａ、Ｖ及びＳｉのうちの一つ又は二つ以上の金属とＣを主体とするもので、その他時によりＣｏやＷをその構成要素とする。該出現相は製造条件により構成元素も組成比も種々変化するものなので厳密に化学組成を規定するものではない。本発明者らが鋭意検討をしたところ、該出現相がある量以上に増加すると靭性が著しく低下する。従って、本願発明のもうひとつの特徴は、Ｔａの量を規定することで該出現相の量に制限を与え、結果として靭性のあるＷＣの平均粒度が０．６μｍ以下好ましくは０．５μｍ以下の超微粒合金を得るところにある。焼結は真空雰囲気下で実施してもよいが、大気圧以上の加圧雰囲気下で行うと抗折強度が向上する。焼結性が改善されるためと推測される。加圧雰囲気下で焼結を行ったあと、炉冷ではなく、冷媒としてのガスを炉内に導入するなどして冷却速度を上げると、さらに抗折強度が向上する。金属結合相が固溶強化されたことと、基本的には靭性を劣化させる出現相の量が少なくなるためと考えられる。次いで、本発明を実施例によって詳細に説明する。
【００１０】
【実施例】
原料粉末として、平均粒径０．６μｍのＷＣ粉末、同約１μｍのＣｏ、ＶＣ、Ｃｒ_３Ｃ_２、ＴａＣ、ＣｒＳｉ_２各原料粉末を表１に示される最終組成が得られるように配合し、（ＶＣ、Ｃｒ_３Ｃ_２、ＴａＣ、ＣｒＳｉ_２はそれぞれＶ、Ｃｒ、Ｔａ、Ｓｉ量に換算して示す）成形バインダーを含んだアルコール中アトライターで１２時間混合した後、スプレードライで造粒乾燥した。
【００１１】
【表１】

【００１２】
得られた造粒粉末を１００ＭＰａの圧力でプレス成形して圧粉体とし、この圧粉体を１０Ｐａの真空雰囲気中で焼結し、焼結体を得た。また一部は真空高温保持後Ａｒを圧力媒体として３ＭＰａの圧力による加圧焼結を実施した。更に、その一部は加圧焼結後一旦圧力媒体をのＡｒを排気し、新たに低温のＡｒガスを導入することで急速冷却を実施した。焼結温度、雰囲気などは表２に示し、適用した条件は１表に示した。
【００１３】
【表２】

【００１４】
次に、これらの各焼結体を研削して４ｍｍ×８ｍｍ×２４ｍｍのＪＩＳ抗折試験片を作成し、スパン２０ｍｍで３点曲げによる抗折力を大気中常温と真空中９７３Ｋで測定するとともに、ロックウェルＡスケール硬さ（ＨＲＡ）も測定した。また、大気中において９７３Ｋで１時間保持したのち、生成された酸化層の厚みを測定し、耐酸化性を評価した。別途走査型電子顕微鏡（ＳＥＭ）で組織観察してＷＣの平均粒径を求めた。また常温での抗折力測定後の破面をＸ線マイクロアナライザー（ＸＭＡ）で元素マッピングを行い出現相の有無を調査した。これらの結果をまとめて表１に併記する。
【００１５】
靭性についてはＶとＣｒとＴａの複合添加はそれぞれの量を規制することで、その相乗効果が顕著に現れることが実施例から分かる。比較例１はＴａ添加量が０であるため３種混合の相乗効果が無く、抗折力が３０００ＭＰａ以下と低い値を示す。靭性を落とす性質が顕著な出現相が内在するためと推測される。本発明例２〜５は、ＷＣの平均粒径は０．６μｍ以下で、且つ、抗折力３０００ＭＰａ以上を保って高靭性の合金となっている。比較例６はＴａ量が０．４％を超えたため出現相の量が増加し、抗折力が３０００ＭＰａを下回っている。比較例７はＳｉ添加量が０のため高温抗折力が１０００ＭＰａ以下、酸化物厚みが５０μｍを越え、耐熱性及び耐酸化性が改善されていない。比較例９はＳｉ量が適性範囲０．１〜１．５％を超えているため常温の抗折力が３０００ＭＰａ以下と靭性が低い。
【００１６】
本発明例１０〜１２は、ＳｉとＮが本発明の範囲内で含有されているため、常温の抗折力に加え、高温抗折力も１０００ＭＰａを超え、酸化層の厚みも３０μｍ以下で、耐熱性及び耐酸化性に優れることが分かる。比較例１３はＮ含有量が１０００ｐｐｍを超え、靭性が不足している。比較例１４はＶ添加量が０のためＷＣの平均粒径が０．６５μｍと粗大化し、粒抑制効果が希薄である。本発明例１５〜１７は、Ｖ量が本発明の範囲内、すなわち０．１〜２．０％の範囲内にあるため、粒成長と靭性の低下の双方を抑制し、超微粒で高靭性の合金となっている。比較例１８はＶが過多のため抗折力が３０００ＭＰａ以下と靭性の急激な低下が認められる。比較例１９はＣｒの添加量が０のため粒成長抑制効果が希薄なものとなっている。比較例２１はＣｒ量が過多で粒成長抑制効果は有るものの抗折力が３０００ＭＰａ以下で低靭性なものとなっている。比較例２２はＣｏが過少で充分な靭性が得られていない。比較例２５はＣｏが過多で剛性不足となり、充分な抗折強度が得られていない。その他の本発明例は、ＷＣの平均粒度が０．６μｍ、最小で０．３６μｍを達成し、また抗折力は３０００ＭＰａを維持ししている。また、高温抗折力も１０００ＭＰａを超えて、耐熱性に富むことがわかる。高温大気中に保持して生成される酸化物層の厚みも薄く、耐酸化性にも優れる。焼結後急冷すると出現相が生じなく、高い靭性が得られる。
【００１７】
【発明の効果】
以上述べたことから、本願発明の超硬合金はＷＣの粒径が極めて小さく、且つ、高い靭性と耐熱性と耐酸名性を有するもので、各種切削工具、せん断工具、小径エンドミル、プリント基板用ドリルなどに用いた場合に優れた性能を発揮する。[0001]
[Technical field belonging to the invention]
The present invention relates to a cemented carbide, and particularly to a so-called ultrafine cemented carbide having tungsten carbide particles having an average particle size of 0.6 μm or less.
[0002]
[Prior art]
Ultrafine cemented carbide containing WC particles having an average particle size of 1 μm or less has high toughness as well as hardness, and is therefore widely used in end mills, printed circuit board drills, various shearing blades, and the like. In recent years, with the trend of fine processing and high-speed processing, the average particle size of ultrafine alloy is becoming increasingly smaller, and there is an increasing demand for high heat resistance and oxidation resistance. Since it is necessary to make the grain size of WC constituting the cemented carbide finer in order to adapt to the application of microfabrication, conventionally known metals such as V, Ta, Cr, or compounds of these metals (Carbides, nitrides, carbonitrides, etc.) have been used alone as grain growth inhibitors for WC, but two or more types have been added for an average particle size of 0.6 μm or less. . For example, Japanese Patent Publication No. 62-56224 (Patent No. 1539991) discloses a device that does not deteriorate toughness by adding two kinds of V and Cr and preventing the third phase from appearing in the alloy.
[0003]
Also, in Japanese Patent No. 3008532, the bending strength is improved by adding V and Cr in combination and allowing the composite carbide containing V and W to exist as a third phase at the metal boundary and the grain boundary of WC. It is disclosed that it can be achieved. Japanese Patent No. 3010859 is also a patent for composite addition of V and Cr, but Cr and V composite carbide without precipitating Cr carbide or (W, V) C, more accurately (Cr, V) It is disclosed that only ₂ C is dispersed in the substrate to improve both hardness and toughness. Japanese Patent Publication No. 62-56493 (Patent No. 1467291) discloses the addition of three kinds of V, Cr and Mo. In Japanese Examined Patent Publication No. 62-56494 (Patent No. 1487479), three types of V, Cr, and 0.5 to 8.0% by weight of TaC or (Ta, Nb) C are added. It is disclosed that an alloy is obtained. In this case, if the precipitation phase of the solid solution carbide phase mainly composed of TaC or (Ta, Nb) C is not more than a certain amount, it is said that the toughness is not lowered. Japanese Patent Publication No. 03-46538 also discloses three types of addition of V, Cr, and 0.4 to 0.5% TaNbC. Japanese Patent No. 3206375 also discloses an ultrafine alloy having a WC grain size of 0.7 to 1.0 μm by the combined addition of V, Cr and 0.05 to 2.5% TaC. At present, no measures that are sufficiently effective are disclosed as measures for improving the heat resistance and oxidation resistance of so-called ultrafine cemented carbides having an average particle diameter of WC of 0.6 μm or less.
[0004]
[Problems to be solved by the invention]
As for the refinement of the WC particles, since the WC particles cause grain growth during sintering, the particle size of the WC particles in the alloy is larger than that before sintering. Therefore, research on a method for suppressing grain growth of WC by adding a grain growth inhibitor is advanced, and it is known that V is the most effective and Cr, Ta, and Mo are also effective. If the average grain size is 0.6 μm or less, and hopefully 0.5 μm or less, a large amount of grain growth inhibitor, especially V, may be added, but if a large amount of V is added, the toughness of the alloy decreases rapidly. To do. For this reason, attempts have been made to reduce the amount of addition of V and compensate for the resulting decrease in grain growth suppression effect with Cr or Ta, that is, combined addition of grain growth inhibitor. However, the inventors have intensively studied including the above prior art, and in the combination of V and Cr, a third phase separate from the binder phase and the WC phase precipitates during cooling after sintering, which is toughness. It became clear that it lowered. Therefore, if the addition amount is reduced to such an extent that the third phase does not precipitate, the effect of suppressing grain growth becomes dilute. The combination of V and Ta makes the appearance of the third phase easier, and the toughness is drastically reduced. Therefore, to obtain a tough cemented carbide having an average particle size of 0.6 μm or less and preferably 0.5 μm, it is necessary to rely on the addition of three types of V, Cr, and Ta. However, as a result of the above-described prior art being additionally tested, it has been found that the addition of Ta, like the combination of V and Ta, is a major obstacle to the reduction in toughness.
[0005]
Next, as for the oxidation resistance of the ultrafine cemented carbide, WC, Co and / or Ni, which are the main constituent elements, have no significant difference when the oxidation start temperature is around 600 ° C. However, the progress of oxidation is higher in WC, and it can be said that WC controls the oxidation of cemented carbide. However, WC lacks the property of incorporating other metal elements, and it is difficult to change the properties of WC. On the other hand, it is easier to change the properties of Co and / or Ni as the binder phase than WC. However, as described above, when various additives are used to obtain ultrafine cemented carbide, a new phase that appears to be a double carbide appears, which lowers the toughness of the alloy, but further improves oxidation resistance. In general, the addition of such an element results in a larger amount of new phases and a significant decrease in toughness. As for heat resistance, since WC originally has sufficient heat resistance, it is sufficient to consider making the metal bonded phase heat resistant. From the above considerations, both the oxidation resistance and heat resistance of the metal bonded phase are improved, and the appearance amount of a new phase other than WC and the metal bonded phase is not increased, or the toughness is not deteriorated. If the additive element can be found, a cemented carbide having a toughness, oxidation resistance, and heat resistance and an average particle diameter of WC of 0.6 μm or less can be obtained. In other words, the present condition is that the additive which has such a property is not known.
[0006]
[Means for Solving the Problems]
Therefore, the present inventors first conducted various studies on the toughness from the viewpoint of why the addition of three kinds of V, Cr and Ta can evaluate the grain growth suppressing effect, but causes a significant decrease in toughness. It was observed that other phases and obscurities that were clearly different from the WC phase spread throughout the alloy. This separate phase and obscured material (hereinafter referred to as the appearance phase) increases with the amount of Ta added, with the same amount of Ta, the lower the carbon alloy, the lower the cooling rate from the end of sintering to the liquid phase disappearance temperature. It was found that it decreased and disappeared in some cases. In addition, it has been clarified that the toughness, which is evaluated by the bending strength value, rapidly decreases as the amount of the appearance phase increases. That is, the present invention is one or two of Co and Ni: 2 to 30%, V: 0.1 to 2.0%, Cr: 0.1 to 2.0%, Ta: 0.01 % or more and less than 0.4%, Si: 0.1 to 1.5%, containing the remainder: in cemented carbide chromatic tungsten and unavoidable impurities carbide, a composition consisting of, the microstructure of the cemented carbide , Co, and / or a binder phase composed mainly of Ni, the average particle size of 0.6μm or less of tungsten carbide phase, Cr, Ta, 1 or two or more metal elements selected from V, Si and W the compound phase mainly composed of a tungsten carbide based cemented carbide, characterized in that it has three or more phase or 3-phase, further, the vacuum as a production method, a pressurized atmosphere or sintering sintering This is a production method in which the reaction is carried out in an atmosphere and / or a pressurized atmosphere and then rapidly cooled.
[0007]
Therefore, a rigorous investigation was conducted on the appropriate amount of Ta (in the case of Ta compound, Ta), and when it exceeded 0.4%, the appearance phase was excessive, and the V addition amount was in the range of 0.1 to 2.0. It became clear that sufficient toughness could not be maintained. Furthermore, how to adjust the amount of alloy carbon in the range where V is 0.1 to 2.0% and Cr is 0.1 to 2.0%, and also increase the cooling rate in the practical range. However, the desirable upper limit of the appearance phase is exceeded, and an alloy having a sufficiently tough WC average particle diameter of 0.6 μm or less cannot be obtained. Next, as for the oxidation resistance and heat resistance, the inventors have studied a wide range of substances and their amounts, and found that Si is suitable. Furthermore, the result that the addition effect of Si can be promoted when N was contained in the alloy was obtained. In addition, regarding the production method of the present invention, an alloy with higher toughness can be obtained when sintering is performed in a pressurized atmosphere, and further, the appearance phase is reduced by rapid cooling after pressure sintering, and the toughness is further improved. Results were also obtained. The effect of addition of Si can be expected even for a compound containing Si. In particular, tantalum silicide (Ta) powder, chromium silicide (Cr) powder, tungsten silicide (W) powder, and the like are convenient because Ta, Cr, and W are already contained in the alloy. For the addition of N, VN powder, TiN powder, Cr2N powder and the like are convenient for the same reason as described above.
[0008]
In the present invention, V (in the case of a V compound, V component) is 0.1 to 2.0%. If it is less than 0.1%, a sufficient grain growth suppressing effect cannot be obtained, which is contrary to the gist of the present invention. If it exceeds 0.2%, sufficient toughness cannot be obtained, and the bending strength is reduced to a practical range or less. Here, the practical range of the bending strength is set to 3000 MPa or more, but it may be used even less than that depending on the application, and is not strictly defined. Cr (in the case of a Cr compound, its Cr content) is 0.1 to 2.0%. If it is less than 0.1%, a sufficient grain growth suppressing effect cannot be obtained, which is contrary to the gist of the present invention. If it exceeds 0.2%, sufficient toughness cannot be obtained, and the bending strength is reduced to a practical range or less. Ta (in the case of a Ta compound, Ta content) is defined as 0.01% or more and less than 0.4%. If it is less than 0.01%, a sufficient synergistic effect for suppressing grain growth of V + Cr + Ta cannot be obtained, which is contrary to the gist of the present invention. If it is 0.4% or more, sufficient toughness cannot be obtained, and the bending strength is lowered to a practical range or less. Si (in the case of Si compound, Si content) is defined as 0.1 to 1.5%. If it is less than 0.1%, sufficient oxidation resistance and heat resistance cannot be obtained, which is contrary to the gist of the present invention. If it exceeds 1.5%, sufficient toughness cannot be obtained. Probably because the amount of the appearance phase becomes excessive. N (in the case of a compound, N content) is defined as 200 to 1000 ppm. If it is less than 200 ppm, sufficient oxidation resistance and heat resistance cannot be detected, and it is not enough to add N. If it exceeds 1000 ppm, the reason is currently unknown, but sufficient toughness cannot be obtained. Co and / or Ni is in the range of 2 to 30%. If it is less than 2%, sufficient toughness cannot be obtained. If it exceeds 30%, the decrease in hardness, which is one of the essential properties of cemented carbide, is remarkable, and it is not practical except for some applications.
[0009]
The microstructure of the cemented carbide of the present invention is basically two phases, a metal phase and a WC phase, but other phases may appear depending on the production conditions. Moreover, the appearance phase is observed depending on the condition in both cases. The appearing phase is mainly composed of one or more metals of Cr, Ta, V and Si and C, and Co and W are the constituent elements at other times. The appearance phase does not strictly define the chemical composition because the constituent elements and the composition ratio vary depending on the production conditions. When the present inventors diligently examined, when this appearance phase increases more than a certain amount, toughness will fall remarkably. Therefore, another feature of the present invention is that the amount of the appearance phase is limited by defining the amount of Ta. As a result, the average particle size of tough WC is 0.6 μm or less, preferably 0.5 μm or less. There is a place to obtain ultrafine alloy. Sintering may be carried out in a vacuum atmosphere, but if it is carried out in a pressurized atmosphere at atmospheric pressure or higher, the bending strength is improved. It is presumed that the sinterability is improved. After sintering in a pressurized atmosphere, bending strength is further improved by increasing the cooling rate by introducing a gas as a refrigerant into the furnace instead of furnace cooling. This is probably because the metal bonded phase was solid solution strengthened and basically the amount of the appearance phase that deteriorates toughness is reduced. Next, the present invention will be described in detail by examples.
[0010]
【Example】
As raw material powder, WC powder having an average particle size of 0.6 μm, Co, VC, Cr ₃ C ₂ , TaC, CrSi ₂ each raw material powder of about 1 μm are blended so that the final composition shown in Table 1 is obtained, (VC, Cr ₃ C ₂ , TaC, and CrSi ₂ are converted to V, Cr, Ta, and Si, respectively) After mixing for 12 hours in an alcohol-containing attritor containing a molding binder, granulate dry by spray drying did.
[0011]
[Table 1]

[0012]
The obtained granulated powder was press-molded at a pressure of 100 MPa to form a green compact, and the green compact was sintered in a vacuum atmosphere of 10 Pa to obtain a sintered body. A part of the sample was subjected to pressure sintering under a pressure of 3 MPa using Ar as a pressure medium after being kept at a high temperature under vacuum. Furthermore, a part of them was subjected to rapid cooling by evacuating Ar as a pressure medium once after pressure sintering and newly introducing low-temperature Ar gas. The sintering temperature and atmosphere are shown in Table 2, and the applied conditions are shown in Table 1.
[0013]
[Table 2]

[0014]
Next, each of these sintered bodies is ground to prepare a 4 mm × 8 mm × 24 mm JIS bending test piece, and the bending strength by bending at three points with a span of 20 mm is measured at room temperature in air and at 973 K in vacuum. Rockwell A scale hardness (HRA) was also measured. Further, after maintaining at 973 K for 1 hour in the air, the thickness of the generated oxide layer was measured to evaluate the oxidation resistance. Separately, the structure was observed with a scanning electron microscope (SEM) to determine the average particle diameter of WC. The fracture surface after measuring the bending strength at room temperature was subjected to element mapping with an X-ray microanalyzer (XMA) to investigate the presence or absence of an appearance phase. These results are shown together in Table 1.
[0015]
As for toughness, it can be seen from the Examples that the combined addition of V, Cr and Ta regulates the respective amounts, and the synergistic effect appears remarkably. In Comparative Example 1, since the Ta addition amount is 0, there is no synergistic effect of mixing three kinds, and the bending strength is as low as 3000 MPa or less. This is presumed to be due to the existence of a remarkable appearance phase with a characteristic of reducing toughness. In Invention Examples 2 to 5, the average particle diameter of WC is 0.6 μm or less, and a bending strength of 3000 MPa or more is maintained to be a high toughness alloy. In Comparative Example 6, since the amount of Ta exceeded 0.4%, the amount of the appearance phase increased, and the bending strength was less than 3000 MPa. In Comparative Example 7, since the Si addition amount is 0, the high temperature bending strength is 1000 MPa or less, the oxide thickness exceeds 50 μm, and the heat resistance and oxidation resistance are not improved. In Comparative Example 9, since the Si amount exceeds the suitable range of 0.1 to 1.5%, the bending strength at normal temperature is 3000 MPa or less and the toughness is low.
[0016]
In Invention Examples 10 to 12, Si and N are contained within the scope of the present invention, so that in addition to the normal temperature bending strength, the high temperature bending strength exceeds 1000 MPa, and the thickness of the oxide layer is 30 μm or less. It can be seen that the composition is excellent in resistance and oxidation resistance. In Comparative Example 13, the N content exceeds 1000 ppm and the toughness is insufficient. In Comparative Example 14, since the V addition amount is 0, the average particle diameter of WC is coarsened to 0.65 μm, and the grain suppressing effect is dilute. In Invention Examples 15 to 17, since the V amount is in the range of the present invention, that is, in the range of 0.1 to 2.0%, both the grain growth and the decrease in toughness are suppressed. It has become an alloy. In Comparative Example 18, since V is excessive, the bending strength is 3000 MPa or less and a rapid decrease in toughness is observed. In Comparative Example 19, since the amount of Cr added is 0, the effect of suppressing grain growth is dilute. In Comparative Example 21, although the Cr amount is excessive and there is a grain growth suppressing effect, the bending strength is 3000 MPa or less and low toughness. In Comparative Example 22, Co is insufficient and sufficient toughness is not obtained. In Comparative Example 25, Co is excessive and rigidity is insufficient, and sufficient bending strength is not obtained. Other examples of the present invention achieve an average particle size of WC of 0.6 μm and a minimum of 0.36 μm, and the bending strength is maintained at 3000 MPa. It can also be seen that the high temperature bending strength exceeds 1000 MPa, and the heat resistance is high. The thickness of the oxide layer produced by being held in a high-temperature atmosphere is thin and excellent in oxidation resistance. When quenched after sintering, no appearance phase occurs and high toughness is obtained.
[0017]
【The invention's effect】
From the above, the cemented carbide of the present invention has a very small WC particle size and high toughness, heat resistance and acid resistance, and is used for various cutting tools, shear tools, small diameter end mills, and printed circuit boards. Excellent performance when used in drills.

Claims

One or two of Co and Ni: 2 to 30%, V: 0.1 to 2.0%, Cr: 0.1 to 2.0%, Ta: 0.01% to 0.4% less, Si: 0.1 to 1.5%, containing the remainder: in cemented carbide chromatic tungsten and unavoidable impurities carbide, a composition consisting of, the microstructure of the cemented carbide, Co and / or Ni a binder phase composed mainly of, compound phase having an average particle diameter mainly the following tungsten carbide phase 0.6 .mu.m, Cr, Ta, V, one or more metal elements selected from Si and W And a tungsten carbide based cemented carbide characterized by having three or more phases.

The tungsten carbide base cemented carbide according to claim 1 , wherein the cemented carbide has a nitrogen content in the range of 200 to 1000 ppm.

3. A method for producing a tungsten carbide-based cemented carbide according to claim 1, wherein the tungsten carbide-based cemented carbide is sintered in a pressurized atmosphere.

In producing a tungsten carbide based cemented carbide according to claim 1 or 2, it was sintered in a vacuum atmosphere and / or pressurized atmosphere, a manufacturing method of the tungsten carbide based cemented carbide, characterized in that the subsequent rapid cooling.