JP3962818B2

JP3962818B2 - Tungsten carbide based cemented carbide

Info

Publication number: JP3962818B2
Application number: JP2001387614A
Authority: JP
Inventors: 裕久保
Original assignee: Hitachi Tool Engineering Ltd
Current assignee: Moldino Tool Engineering Ltd
Priority date: 2001-12-20
Filing date: 2001-12-20
Publication date: 2007-08-22
Anticipated expiration: 2021-12-20
Also published as: JP2003183760A

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。近年微細加工の傾向とともに超微粒合金の平均粒径も益々小さいものの要求が大となってきている。そのため、従来から周知のＶ、Ｔａ、Ｃｒなどの金属ま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（特許第１５３９９９１号）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。また、特許番号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。特許番号３０１０８５９号も、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。
【０００３】
更に、３種の複合添加では、特公昭６２−５６４９３号公報（特許番号１４６７２９１）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（特許番号１４８７４７９）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。
【０００４】
【発明が解決しようとする課題】
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分かっている。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分った。
【０００５】
【課題を解決するための手段】
本発明者等は、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分った。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。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。
【０００６】
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、を含有し、残り：炭化タングステン及び不可避不純物、からなる組成を有し、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相以上有することを特徴とする超硬合金、である。
【０００７】
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、本願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、本願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、本願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。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。
【０００８】
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やＴａやＶ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０．４μｍ以下の超微粒合金を得るところにある。以下、本願発明を実施例によって詳細に説明する。
【０００９】
【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、Ｃｒ３Ｃ２、ＴａＣはそれぞれＶ、Ｃｒ、Ｔａ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。
【００１０】
【表１】

【００１１】
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。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、更に、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、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に示す。焼結においては検討結果から最適と思われる温度を選定した。出現相は焼結後の冷却速度が速いとその量が減じるので、一部冷却過程で窒素ガスによる急怜を実施した。
【００１２】
表１より、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。
【００１３】
比較例７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８〜１０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１１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１２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１４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１５は、Ｃｏが過少で充分な靭性が得られていない。比較例１８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以上を維持している。
【００１４】
【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 microfabrication, there is an increasing demand for an ultra-fine alloy whose average particle size is increasingly smaller. Therefore, conventionally known metals such as V, Ta, Cr or compounds of these metals (carbides, nitrides, carbonitrides, etc.) have been used independently as grain growth inhibitors for WC. Two or more kinds have been added aiming at an average particle size of 0.6 μm or less. For example, Japanese Examined Patent Publication No. Sho 62-56224 (Patent No. 15399991) discloses a device in which two kinds of V and Cr are added and the toughness is not deteriorated so that the third phase does not appear in the alloy. Yes. In addition, in 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 in the grain boundary of the metal bonded phase and WC as the third phase. Is disclosed. Patent No. 3010859 is also a patent for composite addition of V and Cr, but Cr and V composite carbide can be more accurately described without precipitating Cr carbide or (W, V) C (Cr, V ) only 2 _C is dispersed in the matrix, it is disclosed that improved both hardness and toughness.
[0003]
Further, regarding the three types of composite addition, Japanese Patent Publication No. 62-56493 (Patent No. 1467291) discloses the addition of three types of V, Cr, and Mo. In Japanese Examined Patent Publication No. 62-56494 (Patent No. 1487479), three kinds of V, Cr, and 0.5 to 8.0 wt% TaC or (Ta, Nb) C are added to form a finer carbide. 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.
[0004]
[Problems to be solved by the invention]
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 has been advanced, and it has been found 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. . 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 different from the binder phase and the WC phase precipitates during cooling after sintering, which increases the toughness. It became clear to reduce. 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 further testing of the above prior art, 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]
[Means for Solving the Problems]
As a result of various examinations from the viewpoint of why the addition of three kinds of V, Cr, and Ta can evaluate the effect of suppressing grain growth, but the remarkable decrease in toughness occurs, the present inventors clearly show the binder phase and the WC phase. It was observed that different different phases and objects 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. Therefore, a rigorous investigation was conducted on the appropriate amount of Ta (in the case of Ta compound, Ta), and when it exceeds 0.4%, the appearance phase becomes excessive, and the V addition amount is in the range of 0.1 to 2.0. It was revealed 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 how to increase the cooling rate within the practical range. 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.
[0006]
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 % And less than 0.4%, and the balance: tungsten carbide and inevitable impurities, and the microstructure of the cemented carbide has an average of a binder phase mainly composed of Co and / or Ni, and particle size 0.6μm or less of tungsten carbide phase, Cr, Ta, with a compound phase composed mainly of one or more metal elements selected from V and W, having three phases or three or more phases A cemented carbide, characterized by
[0007]
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. 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.
[0008]
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 appearance phase is mainly composed of one or more metals of Cr, Ta, and V and C, and sometimes Co or W is a constituent element. 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 0.4 μm or less. There is a place to obtain ultrafine alloy. Hereinafter, the present invention will be described in detail by examples.
[0009]
【Example】
As raw material powders, WC powder having an average particle diameter of 0.6 μm, and Co, VC, Cr ₃ C ₂ and TaC raw material powders of about 1 μm were blended so as to obtain the final composition shown in Table 1, (Cr3C2 and TaC are shown in terms of V, Cr and Ta, respectively) After mixing for 12 hours in an alcohol-containing attritor containing a molding binder, the mixture was granulated and dried by spray drying.
[0010]
[Table 1]

[0011]
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. Next, each of these sintered bodies was ground to prepare a 4 mm × 8 mm × 24 mm JIS bending test piece, and the bending force due to three-point bending was measured at a span of 20 mm, and Rockwell A scale hardness ( HRA) was also measured, and the structure was observed with a scanning electron microscope (SEM) to determine the average particle diameter of WC. Further, elemental mapping of the fracture surface after measuring the bending strength was performed with an X-ray microanalyzer (XMA) to investigate the presence or absence of an appearance phase. These results are summarized in Table 1. In sintering, the optimum temperature was selected from the results of the study. Since the amount of the appearance phase decreases when the cooling rate after sintering is high, a rapid cooling with nitrogen gas was performed in the partial cooling process.
[0012]
From Table 1, 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.
[0013]
In Comparative Example 7, since the V addition amount is 0, the average particle size of WC is coarsened to 0.65 μm, and the particle suppression effect is dilute. In Invention Examples 8 to 10, 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 11, since V is excessive, the bending strength is 3000 MPa or less and a rapid decrease in toughness is observed. In Comparative Example 12, since the amount of Cr added is 0, the effect of suppressing grain growth is dilute. In Comparative Example 14, 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 15, Co is insufficient and sufficient toughness is not obtained. In Comparative Example 18, 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, a minimum of 0.36 μm, and a bending strength of 3000 MPa or more.
[0014]
【The invention's effect】
From the above, the cemented carbide of the present invention has a very small WC particle size and high toughness, and when used in various cutting tools, shear tools, small diameter end mills, printed circuit board drills, etc. Excellent performance.

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% And the balance: tungsten carbide and inevitable impurities, and the microstructure of the cemented carbide has a binder phase mainly composed of Co and / or Ni and an average particle size of 0.6 μm. carbide, characterized in that it comprises the following tungsten carbide phase, Cr, Ta, with a compound phase composed mainly of one or more metal elements selected from V and W, 3-phase or three-phase or more alloy.