JP7473871B2 - WC-based cemented carbide cutting tool with excellent wear resistance and chipping resistance and surface-coated WC-based cemented carbide cutting tool - Google Patents
WC-based cemented carbide cutting tool with excellent wear resistance and chipping resistance and surface-coated WC-based cemented carbide cutting tool Download PDFInfo
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- 238000005520 cutting process Methods 0.000 title claims description 67
- 239000011230 binding agent Substances 0.000 claims description 33
- 229910052804 chromium Inorganic materials 0.000 claims description 14
- 239000000203 mixture Substances 0.000 claims description 14
- 229910052758 niobium Inorganic materials 0.000 claims description 13
- 229910052715 tantalum Inorganic materials 0.000 claims description 13
- 229910052719 titanium Inorganic materials 0.000 claims description 13
- 229910052726 zirconium Inorganic materials 0.000 claims description 13
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- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 229910000838 Al alloy Inorganic materials 0.000 description 1
- 238000012935 Averaging Methods 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 229910004349 Ti-Al Inorganic materials 0.000 description 1
- 229910004692 Ti—Al Inorganic materials 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- QQHSIRTYSFLSRM-UHFFFAOYSA-N alumanylidynechromium Chemical compound [Al].[Cr] QQHSIRTYSFLSRM-UHFFFAOYSA-N 0.000 description 1
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Description
本発明は、高負荷下におけるステンレス鋼等の断続部を含む切削条件下においても、刃先が変形することなく、すぐれた耐摩耗性と耐欠損性を兼ね備えたＷＣ基超硬合金製切削工具（「ＷＣ基超硬工具」ともいう）および表面被覆ＷＣ基超硬合金製切削工具に関する。 The present invention relates to a WC-based cemented carbide cutting tool (also called a "WC-based cemented carbide tool") and a surface-coated WC-based cemented carbide cutting tool that have excellent wear resistance and chipping resistance and do not deform the cutting edge even under cutting conditions that include interrupted parts of stainless steel and the like under high loads.
ＷＣ基超硬合金は硬さが高く、また、靱性を備えることから、これを基体とするＷＣ基超硬工具は、すぐれた耐摩耗性を発揮し、また、長期の使用にわたって長寿命を有する切削工具として知られている。
しかし、近年、被削材の種類、切削加工条件等に応じて、ＷＣ基超硬工具の切削性能、工具寿命をより一段と向上させるべく、各種の提案がなされている。
WC-based cemented carbide has high hardness and toughness, and therefore WC-based cemented carbide tools using it as a base exhibit excellent wear resistance and are known as cutting tools having a long life over long periods of use.
However, in recent years, various proposals have been made to further improve the cutting performance and tool life of WC-based cemented carbide tools depending on the type of work material, cutting conditions, etc.
例えば、特許文献１では、炭化タングステン５０～９５％、残部が結合相として鉄族金属の１種または２種以上からなる超硬合金の製造方法において、焼結後の冷却工程において、該焼結温度より１００℃／分以上の冷却速度でもって超急冷し、かつミクロ組織において接触率（接触部の全面積の全粒子表面積に対する比率）が１５％以下であることを特徴とする超硬合金とすることにより、その結果として、鋼の湿式断続切削加工において、ＷＣ基超硬工具の耐欠損性を向上させる製造方法が提案されている。 For example, Patent Document 1 proposes a method for producing a cemented carbide consisting of 50-95% tungsten carbide and the remainder being one or more iron group metals as a binder phase, in which the cemented carbide is ultra-rapidly cooled at a cooling rate of 100°C/min or more from the sintering temperature in the cooling step after sintering, and the cemented carbide is characterized in that the contact ratio (the ratio of the total area of contact parts to the total particle surface area) in the microstructure is 15% or less, resulting in a manufacturing method that improves the chipping resistance of WC-based cemented carbide tools in wet intermittent cutting of steel.
また、特許文献２では、Ｃｏ量が１０～１３質量％、Ｃｏ量に対するＣｒ量の比が２～８％、ＴａＣとＮｂＣの少なくとも１種をＴａＣとＮｂＣの総量が０．２～０．５質量％となる範囲で含有し、残部がＷＣから成り、硬さが８８．６ＨＲＡ～８９．５ＨＲＡであるＷＣ基超硬工具において、研磨面上の面積比におけるＷＣ積算粒度８０％径Ｄ８０と積算粒度２０％径Ｄ２０の比Ｄ８０／Ｄ２０を２．０≦Ｄ８０／Ｄ２０≦４．０の範囲とし、また、Ｄ８０を４．０～７．０μｍの範囲とし、かつＷＣ接着度ｃを０．３６≦ｃ≦０．４３とすることにより、ステンレス鋼に代表される難削材の切削加工において、被削材の凝着を防止し耐欠損性を向上させることが提案されている。 In addition, in Patent Document 2, in a WC-based cemented carbide tool containing 10-13 mass% Co, 2-8% Cr to Co ratio, at least one of TaC and NbC in a range where the total amount of TaC and NbC is 0.2-0.5 mass%, and the remainder WC, and having a hardness of 88.6 HRA-89.5 HRA, it is proposed that the ratio D80/D20 of the WC cumulative grain size 80% diameter D80 to the cumulative grain size 20% diameter D20 in the area ratio on the polishing surface is set to a range of 2.0≦D80/D20≦4.0, D80 is set to a range of 4.0-7.0 μm, and the WC adhesion degree c is set to 0.36≦c≦0.43, thereby preventing adhesion of the workpiece and improving chipping resistance in cutting difficult-to-cut materials such as stainless steel.
特許文献３では、ＷＣ基超硬工具において、ＷＣ－ＷＣ接着界面長さをＬ１とし、ＷＣ－Ｃｏ接着界面長さをＬ２としたとき、
Ｒ＞（０．８２－０．０８６×Ｄ）×（１０／Ｖ）
の式を満足させることにより、Ｎｉ基耐熱合金の切削加工において、ＷＣ基超硬工具の耐熱塑性変形性と靱性を向上させることが提案されている。
なお、Ｒ＝（Ｌ１）／（（Ｌ１）＋（Ｌ２））
Ｄ：ＷＣ面積平均粒径（μｍ）であって、０．６≦Ｄ≦１．５の範囲である。
ここで、前記Ｄは、ＷＣの面積率が５０％となるときのＷＣの粒径をいう。
Ｖ：結合相体積（ｖｏｌ％）であって、９≦Ｖ≦１４の範囲である。
In
R>(0.82-0.086×D)×(10/V)
It has been proposed that by satisfying the above formula, the heat plastic deformability and toughness of a WC-based cemented carbide tool can be improved in cutting a Ni-based heat-resistant alloy.
In addition, R = (L1) / ((L1) + (L2))
D: WC area average grain size (μm), in the range of 0.6≦D≦1.5.
Here, D refers to the grain size of WC when the area ratio of WC is 50%.
V: binder phase volume (vol%), in the range of 9≦V≦14.
特許文献４では、ＷＣ基超硬合金製ドリルにおいて、ＷＣ基超硬合金の成分組成を、ＷＣ－ｘ質量％Ｃｏ－ｙ質量％Ｃｒ３Ｃ２－ｚ質量％ＶＣで表したとき、６≦ｘ≦１４、０．４≦ｙ≦０．８、０≦ｚ≦０．６、（ｙ＋ｚ）≦０．１ｘを満足し、また、ＷＣ基超硬合金のＷＣ接着度Ｃを、Ｃ＝１－Ｖｂ α・ｅｘｐ（０．３９１・Ｌ）で表したとき、この式におけるＷＣ基超硬合金の結合相体積率の値Ｖｂは０．１１≦Ｖｂ≦０．２５、また、（ＷＣ粒子の粒度分布の標準偏差）／（平均ＷＣ粒度）の値Ｌは０．３≦Ｌ≦０．７の範囲内であって、さらに、係数αが０．３≦α≦０．５５の値を満足するＷＣ接着度Ｃを有するＷＣ基超硬合金とすることにより、Ａｌ合金、炭素鋼等の切削加工において、硬さと剛性を低下させることなく靱性を向上させ、耐欠損性を高めたＷＣ基超硬合金製ドリルが提案されている。 In Patent Document 4, when the composition of a WC-based cemented carbide drill is expressed as WC-x mass %Co-y mass % Cr3C2 -z mass %VC, the following conditions are satisfied: 6≦x≦14, 0.4≦y≦0.8, 0≦z≦0.6, (y+z)≦0.1x. When the WC-based cemented carbide has a WC-x mass %Co-y mass % Cr3C2 -z mass % VC composition, the following conditions are satisfied: 6≦x≦14, 0.4≦y≦0.8, 0≦z≦0.6, (y+z)≦0.1x. When the WC-based cemented carbide has a WC-bonding degree C expressed as C=1- Vbα ·exp(0.391·L), the value of the binder phase volume fraction Vb of the WC-based cemented carbide in this formula is 0.11≦ Vb In addition, the value L of (standard deviation of grain size distribution of WC grains)/(average WC grain size) is within the range of 0.3≦L≦0.7, and further, the coefficient α satisfies the value of 0.3≦α≦0.55. In this way, a WC-based cemented carbide drill has been proposed which has improved toughness and enhanced chipping resistance without reducing hardness and rigidity in cutting Al alloys, carbon steels, etc.
前記特許文献１にて提案されている従来のＷＣ基超硬工具によれば、冷却工程において、超急冷を行うことで、ＷＣの接着率を抑制することによって、耐チッピング性、靭性を向上し、ＷＣ基超硬工具の切削性能、工具特性の向上を図っている。
しかしながら、前記従来の工具では、ＣｒやＴａ、Ｎｂ、Ｔｉ及びＺｒのうち一種以上のγ相成分元素を合金中に含んでいないため、上記元素の結合相への固溶による強化、高温硬さの向上が足りず、基体の耐塑性変形性、耐熱性が十分でないため、靭性は向上したものの、耐塑性変形性において劣位となり、塑性変形を起因とした耐欠損性に劣るなど、高負荷下でのステンレス鋼等の断続部を含む高能率旋削加工において、工具寿命が短命であるという課題を有していた。
According to the conventional WC-based cemented carbide tool proposed in Patent Document 1, ultra-rapid cooling is performed in the cooling step to suppress the adhesion rate of WC, thereby improving chipping resistance and toughness, and thereby improving the cutting performance and tool characteristics of the WC-based cemented carbide tool.
However, in the conventional tools, since the alloy does not contain one or more of γ-phase component elements selected from Cr, Ta, Nb, Ti and Zr, strengthening due to the solid solution of the above elements in the binder phase and improvement in high-temperature hardness are insufficient, and the plastic deformation resistance and heat resistance of the base are insufficient. Therefore, although the toughness is improved, the plastic deformation resistance is inferior and the resistance to chipping caused by plastic deformation is poor. Therefore, there is a problem that the tool life is short in high-efficiency turning processing including discontinuous parts of stainless steel, etc. under high load.
前記特許文献２にて提案されている従来のＷＣ基超硬工具によれば、ＷＣ粒子の粒度分布、円形度、接着度を制御することにより、被削材との凝着を防止し、耐欠損性に優れたミーリング加工用インサートを提供している。
しかしながら、前記従来の工具では、耐欠損性を向上させるため、ＴａＣとＮｂＣが結合相中に固溶する範囲でしか含有しておらず、γ相（Ｔａ、Ｎｂ、Ｔｉ及びＺｒのうち一種以上のγ相成分元素を主として形成されるそれらの炭化物相）がＷＣ－ＷＣ粒子間に接着してＷＣ－ＷＣ界面すべりを抑制させる効果、及び高温硬さが不十分となり、ミーリング加工のような、空転時に冷却されて、刃先温度が上がりきらない加工では効果を発揮するが、特に切削時に刃先が常に高温状態となる断続部を含むステンレス鋼の高能率旋削加工においては耐塑性変形性、耐欠損性、耐摩耗性が不十分であった。
According to the conventional WC-based cemented carbide tool proposed in Patent Document 2, the particle size distribution, circularity, and adhesiveness of the WC particles are controlled to prevent adhesion to the workpiece, thereby providing an insert for milling having excellent chipping resistance.
However, in the above-mentioned conventional tool, in order to improve the chipping resistance, TaC and NbC are only contained in the range of solid solution in the binding phase, and the effect of suppressing WC-WC interface slip by bonding γ phase (carbide phase mainly formed by one or more γ phase component elements among Ta, Nb, Ti and Zr) between WC-WC particles and high-temperature hardness are insufficient. Although it is effective in processing such as milling, where the cutting edge is cooled during idling and the cutting edge temperature does not rise completely, especially in the high-efficiency turning processing of stainless steel, which includes discontinuous parts where the cutting edge is always in a high temperature state during cutting, the plastic deformation resistance, chipping resistance and wear resistance are insufficient.
前記特許文献３にて提案されている従来のＷＣ基超硬工具によれば、Ｃｏ量を減少させることなく、一定量の結合相を確保することで、靭性の低下を抑制し、ＷＣの接着比率を高めることによって、耐熱塑性変形性及び靭性を兼ね備えた、ＷＣ基超硬工具を見出している。
しかしながら、前記従来の工具では、ＷＣの接着比率が高いことで、耐塑性変形性を向上させる効果はあるものの、断続加工のような刃先の耐欠損性が求められる加工においては、切削時に発生したクラックが、靭性の低いＷＣを経由し、クラックが進展しやすく、耐欠損性が不十分であった。
According to the conventional WC-based cemented carbide tool proposed in
However, in the conventional tools described above, although the high adhesion ratio of WC has the effect of improving the resistance to plastic deformation, in processing that requires resistance to chipping of the cutting edge, such as intermittent cutting, cracks that occur during cutting tend to progress through the WC, which has low toughness, and the chipping resistance was therefore insufficient.
前記特許文献４にて提案されている従来のＷＣ基超硬工具によれば、合金中のＷＣ粒子の接着度に着目し、ＷＣ粒度分布を均粒にすることで、硬さと靭性を兼ね備えた、ＷＣ基超硬工具を見出している。
しかしながら、前記従来の工具では、耐欠損性を向上させるために、ＴａＣおよびＮｂＣを０．２％以下しか合金中に含んでいないため、γ相（Ｔａ、Ｎｂ、Ｔｉ及びＺｒのうち一種以上のγ相成分元素を主として形成されるそれらの炭化物相）がＷＣ－ＷＣ粒子間に接着してＷＣ－ＷＣ界面すべりを抑制させる効果が不十分となり、耐塑性変形性および高温硬さに劣り、高熱が発生する断続部を含むステンレス等の高能率旋削加工においては、耐塑性変形性が不十分であった。
According to the conventional WC-based cemented carbide tool proposed in Patent Document 4, a WC-based cemented carbide tool having both hardness and toughness was discovered by focusing on the degree of adhesion of WC particles in an alloy and making the WC particle size distribution uniform.
However, in the above-mentioned conventional tools, in order to improve the chipping resistance, the alloy contains only 0.2% or less of TaC and NbC, so that the effect of the γ phase (the carbide phase mainly composed of one or more γ phase component elements among Ta, Nb, Ti and Zr) adhering between WC-WC particles to suppress the WC-WC interface slip is insufficient, and the tool is inferior in plastic deformation resistance and high-temperature hardness, and in the high-efficiency turning of stainless steel and the like, which includes discontinuous parts that generate high heat, the tool has insufficient plastic deformation resistance.
そこで、本発明者らは、例えば、高負荷下でのステンレス等の断続部を含む高能率旋削切削加工等において、刃先が変形することなく、すぐれた耐欠損性および耐摩耗性を備えたＷＣ基超硬工具を提供すべく、ＷＣ基超硬合金中の複数種のＷＣ粒径の組み合わせ、ＷＣ分散性、γ相量、γ相の粒径に着目し、鋭意研究を進めたところ、次のような知見を得た。 Therefore, in order to provide a WC-based cemented carbide tool that has excellent chipping resistance and wear resistance without deforming the cutting edge, for example in high-efficiency turning cutting of stainless steel and other materials that include discontinuous parts under high load, the inventors have conducted extensive research focusing on the combination of multiple WC grain sizes in WC-based cemented carbide alloys, WC dispersion, the amount of gamma phase, and the grain size of the gamma phase, and have obtained the following findings.
すなわち、本発明者らは、ＷＣ基超硬工具において、ＷＣ基超硬合金中のＷＣ粒子を相対的に平均粒径が大きな粗粒ＷＣからなる粗粒ＷＣ群と相対的に平均粒径が小さな微粒ＷＣからなる微粒ＷＣ群とから構成し、粗粒ＷＣ群の平均粒径、微粒ＷＣ群の平均粒径、および、微粒ＷＣ群の平均粒径に対する粗粒ＷＣ群の平均粒径の粒径比を調整することにより、全体的には、弱いスケルトン構造の組織を得て、耐摩耗性と耐欠損性を兼ね備えたＷＣ基超硬合金製工具が得られることを知見した。
具体的には、前記微粒ＷＣ粒子群の平均粒径に対する前記粗粒ＷＣ粒子群の平均粒径の比を大きくし、粗粒ＷＣ粒子同士により形成される基本骨格の間隙部において、微粒ＷＣ粒子を粗粒ＷＣ粒子や他の微粒ＷＣ粒子との接触が少なくするよう配置することにより、合金としての硬さは維持したまま、ＷＣ粒子同士の界面長を短くし、合金中のＣｏが良好に分散した組織とすることにより、例えば、亀裂が発生した際においても、靭性の低い粗粒、微粒ＷＣ粒子を経由する直線的な亀裂の進展を抑制し、靭性の高いＣｏを主とする結合相領域を経由する割合を高め、亀裂の伝播を遅らせることにより、超硬合金の靭性が高まり、耐摩耗性を損なうことなく耐欠損性が向上することを見出したものである。
また、ＷＣ粒子同士の界面長を短くするだけでは、耐塑性変形性が低下し、切削時の刃先変形へとつながるため、ＷＣ基超硬合金中に適切な組成のγ相成分元素、適切な粒径のγ相を含むことで、γ相形成元素であるＴａ、Ｎｂ、Ｔｉ、Ｚｒのいずれか一つ以上が結合相中に含有されることにより、すぐれた耐酸化性、耐熱性、高温硬さを発揮し、かつγ相がＷＣ－ＷＣ界面に接着することで、ＷＣ－ＷＣ界面における粒界すべりを低減し、耐塑性変形性を損なうことを防ぐことを知見した。
したがって、ＷＣ基超硬合金中の粗粒ＷＣ粒子、微粒ＷＣ粒子、および、Ｃｏを含む結合相、γ相成分が前記組織を備えるＷＣ基超硬工具を、ステンレス等の高負荷下における断続を含む旋削加工等に用いた場合には、耐塑性変形性や耐摩耗性を損なわず、耐欠損性を向上させることができるため、長時間に亘って欠損を発生させることなく、正常摩耗が維持される結果、チッピング等の異常損傷の発生も抑制され、工具のさらなる長寿命化を実現することができる。
That is, the inventors have discovered that, in a WC-based cemented carbide tool, by composing the WC particles in the WC-based cemented carbide alloy into a coarse-grain WC group consisting of coarse-grain WC having a relatively large average grain size and a fine-grain WC group consisting of fine-grain WC having a relatively small average grain size, and by adjusting the average grain size of the coarse-grain WC group, the average grain size of the fine-grain WC group, and the grain size ratio of the average grain size of the coarse-grain WC group to the average grain size of the fine-grain WC group, it is possible to obtain a WC-based cemented carbide tool that has both wear resistance and chipping resistance, with an overall weak skeleton structure.
Specifically, by increasing the ratio of the average particle size of the coarse-grained WC particle group to the average particle size of the fine-grained WC particle group and arranging the fine-grained WC particles so as to reduce contact between the coarse-grained WC particles and other fine-grained WC particles in the gaps between the basic skeleton formed by the coarse-grained WC particles, the interface length between the WC particles is shortened while maintaining the hardness of the alloy, and a structure is formed in which Co in the alloy is well dispersed. For example, even when a crack occurs, the linear progress of the crack passing through the coarse and fine-grained WC particles with low toughness is suppressed, and the proportion of the crack passing through the binder phase region mainly composed of Co with high toughness is increased, thereby slowing down the propagation of the crack, thereby increasing the toughness of the cemented carbide and improving its chipping resistance without impairing its wear resistance.
Furthermore, it has been discovered that simply shortening the interface length between WC particles reduces plastic deformation resistance, leading to deformation of the cutting edge during cutting; therefore, by containing an appropriate composition of gamma phase component elements and an appropriate grain size of a gamma phase in a WC-based cemented carbide, and by containing one or more of the gamma phase forming elements Ta, Nb, Ti and Zr in the binder phase, excellent oxidation resistance, heat resistance and high-temperature hardness are exhibited, and the gamma phase adheres to the WC-WC interface, grain boundary sliding at the WC-WC interface is reduced, preventing the impairment of plastic deformation resistance.
Therefore, when a WC-based cemented carbide tool in which the coarse WC particles, fine WC particles, Co-containing binder phase, and γ-phase components in the WC-based cemented carbide alloy have the above-mentioned structure is used in intermittent turning of stainless steel or the like under high load, the resistance to fracture can be improved without impairing plastic deformation resistance and wear resistance. As a result, normal wear can be maintained without fracture over a long period of time, and the occurrence of abnormal damage such as chipping can be suppressed, thereby achieving a further extension of the tool's lifespan.
本発明は、前記知見に基づいてなされたものであって、
「（１） ＷＣ基超硬合金を基体とするＷＣ基超硬合金製切削工具において、
（ａ）前記ＷＣ基超硬合金の成分組成は、Ｃｏ：６．０～１２．０質量％、Ｃｒ３Ｃ２：０．０～１．２質量％、および、ＴａＣ、ＮｂＣ、ＴｉＣ及びＺｒＣのうちから選ばれる少なくとも１種以上を合計量にて０．６～４．０質量％含有し、残部はＷＣ及び不可避不純物とからなり、Ｃｒ３Ｃ２の質量含有率は、Ｃｏの質量含有率の１０％以下であり、
（ｂ）ＷＣ粒子は、平均粒径を比較したとき平均粒径の大きな粗粒ＷＣ群と平均粒径の小さな微粒ＷＣ群とから構成され、
（ｃ）前記ＷＣ粒子同士の界面長さＷＣ－ＷＣ界面長をＬ１、
前記ＷＣ粒子と
Ｔａ、Ｎｂ、Ｔｉ、Ｚｒのいずれか一つ以上のγ相成分元素を主として形成されるそれらの炭化物相であるγ相、および
ＷやＣ、Ｃｒ、γ相成分元素を固溶した結合相との
界面長であるＷＣ－（結合相＋γ相）界面長をＬ２
としたとき、
前記Ｌ１と前記Ｌ２の和に対する前記Ｌ１の比である比率Ｒが、（０．６６－０．０５９×Ｄ）×（１０／Ｖ）―γ相理論体積率×０．０６以上、（０．７０－０．０５９×Ｄ）×（１０／Ｖ）―γ相理論体積率×０．０６以下の値であることを特徴とするＷＣ基超硬合金製切削工具。
ここで、Ｖは、結合相の面積比率（ａｒｅａ％）、Ｄは、ＷＣ面積平均粒径（μｍ）を指し、１．０≦Ｄ≦４．０である。
（２）前記γ相の平均粒径は、０．２～４．０μｍであることを特徴とする（１）に記載のＷＣ基超硬合金製切削工具。
（３）（１）または（２）に記載のＷＣ基超硬合金製切削工具の少なくとも切れ刃には、硬質被覆層が形成されていることを特徴とする表面被覆ＷＣ基超硬合金製切削工具。」を特徴とするものである。
なお、前記（１）および（２）におけるＣｒ３Ｃ２、ＴａＣ、ＮｂＣ、ＴｉＣ、および、ＺｒＣの含有量は、ＷＣ基超硬合金の断面について測定したＣｒ量、Ｔａ量、Ｎｂ量、Ｔｉ量、Ｚｒ量を、いずれも炭化物換算した数値である。
また、本明細書中において、数値範囲を示す際に用いる「～」は、その数値の下限および上限を含むことを意味する。
The present invention has been made based on the above findings,
"(1) In a cutting tool made of WC-based cemented carbide having a substrate made of WC-based cemented carbide,
(a) The composition of the WC-based cemented carbide is Co: 6.0 to 12.0 mass%, Cr 3 C 2 : 0.0 to 1.2 mass%, and at least one selected from TaC, NbC, TiC, and ZrC in a total amount of 0.6 to 4.0 mass%, with the remainder being WC and inevitable impurities, and the mass content of Cr 3 C 2 is 10% or less of the mass content of Co,
(b) The WC grains are composed of a group of coarse WC grains having a large average grain size and a group of fine WC grains having a small average grain size, when comparing the average grain size.
( c ) The interface length between the WC grains is the WC-WC interface length L1,
The WC grains and
A gamma phase, which is a carbide phase mainly composed of one or more gamma phase component elements of Ta, Nb, Ti, and Zr, and
With a binder phase in which W, C, Cr, and γ-phase component elements are dissolved
The interface length of the WC-(binder phase + γ phase) is L2
When
A WC-based cemented carbide cutting tool, wherein a ratio R, which is a ratio of L1 to the sum of L1 and L2, is a value not less than (0.66-0.059×D)×(10/V)-theoretical volume fraction of gamma phase×0.06 and not more than (0.70-0.059×D)×(10/V)-theoretical volume fraction of gamma phase×0.06 .
Here, V is the area ratio (area %) of the binder phase, D is the area average grain size (μm) of WC, and 1.0≦D≦4.0.
(2) The WC-based cemented carbide cutting tool according to (1), characterized in that the average grain size of the γ phase is 0.2 to 4.0 μm.
(3) A surface-coated WC-based cemented carbide cutting tool according to (1) or (2), characterized in that a hard coating layer is formed on at least the cutting edge of the WC-based cemented carbide cutting tool.
The contents of Cr3C2 , TaC, NbC, TiC and ZrC in ( 1 ) and (2) above are the amounts of Cr, Ta, Nb, Ti and Zr measured on a cross section of the WC-based cemented carbide, all of which are converted into carbide values.
In addition, in this specification, when indicating a range of numerical values, the term "to" means that the lower limit and upper limit of the numerical value are included.
本発明のＷＣ基超硬工具および表面被覆ＷＣ基超硬合金製切削工具は、その基体を構成するＷＣ基超硬合金の成分として、Ｃｏと、ＴａＣ、ＮｂＣ、ＴｉＣおよびＺｒＣのいずれか一つ以上、および／またはＣｒ３Ｃ２を特定の組成範囲にて含有し、また、組み合わされた複数種のＷＣの粒径比、混合条件や焼結条件を制御することで、ＷＣ－ＷＣ粒子間の接触長さが短くなり、亀裂が発生した場合においても、亀裂が靭性の高い、結合相を進展する割合が高くなり、耐摩耗性を損なうことなく、耐欠損性を向上させることができる。
また、同時にγ相がＷＣ－ＷＣ界面に接着することで、ＷＣ－ＷＣ界面の粒界すべりの発生を抑制することによって、耐塑性変形性にも優れ、刃先変形起因の欠損も抑制されるため、特に、ステンレス鋼等の断続部を含む高能率旋削加工に好適であり、工具の長寿命化が達成されるものである。
The WC-based cemented carbide tool and surface-coated WC-based cemented carbide cutting tool of the present invention contain, as the components of the WC-based cemented carbide constituting the base thereof, Co and one or more of TaC, NbC, TiC and ZrC, and/or Cr3C2 in a specific composition range, and by controlling the particle size ratio, mixing conditions and sintering conditions of the multiple types of WC combined, the contact length between WC-WC particles is shortened, and even if cracks occur, the rate at which the cracks progress through the highly tough binder phase is increased, thereby improving fracture resistance without impairing wear resistance.
At the same time, the γ phase adheres to the WC-WC interface, suppressing the occurrence of grain boundary sliding at the WC-WC interface, thereby providing excellent resistance to plastic deformation and suppressing chipping due to deformation of the cutting edge. This makes the material particularly suitable for high-efficiency turning processes that include discontinuous parts of stainless steel, etc., and achieves a longer tool life.
以下、本発明について詳細に説明する。 The present invention will be described in detail below.
（１）ＷＣ基超硬合金の成分組成
＜Ｃｏ含有量＞
Ｃｏは、ＷＣ基超硬合金の主たる結合相形成成分として含有させるが、Ｃｏ含有量が６．０質量％未満では十分な靱性を保持することはできず、一方、Ｃｏ含有量が１２．０質量％を超えると急激に軟化し、切削工具として必要とされる所望の硬さが得られず、変形および摩耗進行が顕著となることから、ＷＣ基超硬合金中のＣｏ含有量を６．０～１２．０質量％と定めた。Ｃｏ含有量は、６．０～１０．０質量％の範囲を取るのがさらに好ましい。Ｃｏには、ＷやＣ、その他の不可避不純物が含まれていても良い。さらに、Ｃｒ、およびγ相成分元素であるＴａ、Ｎｂ、Ｔｉ、Ｚｒの少なくとも一種以上を含んでいてもよい。これら元素がＣｏ中に存在するときは、Ｃｏに固溶した状態であると推定される。
(1) Composition of WC-based cemented carbide <Co content>
Co is contained as a main binder phase forming component of the WC-based cemented carbide, but if the Co content is less than 6.0 mass%, sufficient toughness cannot be maintained, while if the Co content exceeds 12.0 mass%, the WC-based cemented carbide is rapidly softened, the desired hardness required for a cutting tool cannot be obtained, and deformation and wear progress become significant. Therefore, the Co content in the WC-based cemented carbide is set to 6.0 to 12.0 mass%. It is more preferable that the Co content is in the range of 6.0 to 10.0 mass%. Co may contain W, C, and other unavoidable impurities. Furthermore, it may contain Cr and at least one of Ta, Nb, Ti, and Zr, which are gamma phase component elements. When these elements are present in Co, they are presumed to be in a solid solution state in Co.
＜Ｃｒ３Ｃ２含有量＞
Ｃｒ３Ｃ２は、主たる結合相を形成するＣｏ中にＣｒとして固溶し、Ｃｏを固溶強化することで、ＷＣ基超硬合金の強度を高めることができる。
一方、Ｃｒ３Ｃ２含有量が、Ｃｏ含有量の１０％を超えて添加されると、ＣｒとＷの複合炭化物を析出するなどにより、靭性の低下や、欠損発生の起点となるおそれがあるため、Ｃｒ３Ｃ２含有量は、０．０～１．２質量％であって、かつ、Ｃｏ含有量の１０％以下とする。
< Cr3C2 content >
Cr3C2 dissolves as Cr in Co, which forms the main binder phase, and strengthens the Co through solid solution, thereby increasing the strength of the WC-based cemented carbide.
On the other hand, if the Cr3C2 content is added in an amount exceeding 10% of the Co content, it may cause a decrease in toughness or become the starting point for the generation of defects due to the precipitation of composite carbides of Cr and W, so the Cr3C2 content is set to 0.0 to 1.2 mass% and 10% or less of the Co content.
＜ＴａＣ、ＮｂＣ、ＴｉＣ、ＺｒＣ含有量＞
本発明のＷＣ基超硬合金は、その成分として、さらに、ＴａＣ、ＮｂＣ、ＴｉＣ及びＺｒＣのうちから選ばれる少なくとも１種以上を合計量で０．６～４．０質量％にて含有する。
ここで、Ｔａ、Ｎｂ、ＴｉおよびＺｒは、いずれもγ相成分元素といわれ、主たる結合相を形成するＣｏ相中に一部固溶することで、結合相の耐熱性、高温硬さを高める効果を有する。また、Ｃｏ相中に固溶せずに、合金中にこれらγ相成分元素を主とする炭化物相であるγ相（γ相成分とは別に、Ｗをさらに含んでもよい。）として存在することで、耐酸化性や耐クレーター摩耗性を向上させる効果を有し、かつＷＣ－ＷＣ界面に接着することで、ＷＣ－ＷＣ界面の粒界すべりを抑制するが、それらを炭化物換算した合計含有量が、０．６質量％未満では、効果が不十分であり、一方、４．０質量％を超えると凝集体ができやすく、欠損発生の起点となりやすくなる。
したがって、ＷＣ基超硬合金中の成分として添加するＴａＣ、ＮｂＣ、ＴｉＣ及びＺｒＣのうちから選ばれる少なくとも１種以上の合計含有量は、０．６～４．０質量％とすることが望ましい。また、γ相の平均粒径は、ＷＣ相との接触頻度が適切となる０．２～４．０μｍであることが好ましい。
ここで、γ相の平均粒径は、超硬合金の任意の表面または断面を鏡面加工し、その加工面を走査型電子顕微鏡（ＳＥＭ）で観察し、画像解析によって、少なくとも３００個の各γ相の面積を求め、その面積に等しい円の直径を算出して平均したものである。なお、鏡面加工は、例えば、集束イオンビーム装置（ＦＩＢ装置）、クロスセクションポリッシャー装置（ＣＰ装置）等を用いる。
なお、前記したＴａＣ、ＮｂＣ、ＴｉＣ、ＺｒＣに加え、Ｃｒ３Ｃ２の含有量は、ＷＣ基超硬合金についてＥＰＭＡによって測定したＣｒ量、Ｔａ量、Ｎｂ量、Ｔｉ量、Ｚｒ量を、いずれも炭化物換算した数値である。
また、γ相の理論体積率は、ＴａＣ、ＮｂＣ、ＴｉＣ、ＺｒＣの密度をそれぞれ１４．４、７．８２、４．９２、６．６６とし（［データブック 高融点化合物便覧］参照）、ＥＰＭＡによって測定されたＴａＣ、ＮｂＣ、ＴｉＣ、ＺｒＣの各含有量（質量％）を、各密度で割った数値の足し合わせた値、として求める。
<TaC, NbC, TiC, ZrC Content>
The WC-based cemented carbide of the present invention further contains, as its components, at least one selected from the group consisting of TaC, NbC, TiC and ZrC in a total amount of 0.6 to 4.0 mass %.
Here, Ta, Nb, Ti and Zr are all called γ-phase component elements, and by partially dissolving in the Co phase that forms the main binder phase, they have the effect of increasing the heat resistance and high-temperature hardness of the binder phase. In addition, by not dissolving in the Co phase but existing in the alloy as a γ-phase (which may further contain W in addition to the γ-phase component) that is a carbide phase mainly composed of these γ-phase component elements, they have the effect of improving oxidation resistance and crater wear resistance, and by adhering to the WC-WC interface, they suppress grain boundary sliding at the WC-WC interface, but if the total content of these elements converted into carbides is less than 0.6 mass%, the effect is insufficient, while if it exceeds 4.0 mass%, aggregates are likely to form and become the starting point for defect generation.
Therefore, the total content of at least one selected from TaC, NbC, TiC, and ZrC added as a component to the WC-based cemented carbide is preferably 0.6 to 4.0 mass %. The average grain size of the γ phase is preferably 0.2 to 4.0 μm, which provides an appropriate contact frequency with the WC phase.
Here, the average grain size of the γ phase is determined by mirror-finishing any surface or cross section of the cemented carbide, observing the processed surface with a scanning electron microscope (SEM), determining the area of at least 300 pieces of γ phase by image analysis, and averaging the diameters of circles equal to the areas. The mirror-finishing is performed using, for example, a focused ion beam device (FIB device), a cross-section polisher device (CP device), etc.
In addition to the above-mentioned TaC, NbC, TiC, and ZrC, the contents of Cr3C2 are values calculated by converting the amounts of Cr, Ta, Nb, Ti, and Zr measured by EPMA for the WC-based cemented carbide into carbide amounts.
The theoretical volume fraction of the γ phase is calculated by dividing the contents (mass%) of TaC, NbC, TiC, and ZrC measured by EPMA by the densities of TaC, NbC, TiC, and ZrC, which are 14.4, 7.82, 4.92, and 6.66, respectively (see [Data Book: High Melting Point Compounds Handbook]). The theoretical volume fraction of the γ phase is calculated by dividing the contents (mass%) of TaC, NbC, TiC, and ZrC by the densities, which are 14.4, 7.82, 4.92, and 6.66, respectively (see [Data Book: High Melting Point Compounds Handbook]).
（２）ＷＣ基超硬合金焼結体組織
ＷＣ基超硬合金の焼結体組織は、ＷＣ－ＷＣ界面長比率（Ｒ値）、ＷＣ面積平均粒径（Ｄ）（μｍ）、および、結合相面積比率（Ｖ）（ａｒｅａ％）、γ相理論体積率により、規定することができる。
以下では、その技術的意義および測定法について記載する。
(2) Structure of sintered WC-based cemented carbide The structure of a sintered WC-based cemented carbide can be specified by the WC-WC interface length ratio (R value), the WC area average grain size (D) (μm), the binder phase area ratio (V) (area%), and the theoretical volume fraction of γ phase.
The technical significance and measurement method are described below.
＜ＷＣ－ＷＣ界面長比率（Ｒ値）＞
本発明においては、ＷＣ－ＷＣ界面長比率（Ｒ値）を低い領域で制御し、ＷＣ同士の界面長を短くすることで、亀裂が発生した場合においても、亀裂が靭性の高い結合相中を進展する割合が高まり、耐塑性変形性や耐摩耗性を損なうことなく、耐欠損性を向上させることができるため、長時間に亘って欠損のない、正常摩耗を実現する切削工具を得ることができる。
前記ＷＣ－ＷＣ界面長比率（Ｒ値）は、ＷＣ－ＷＣ界面長をＬ１、ＷＣ－（結合相＋γ相）界面長をＬ２としたとき、
Ｒ＝（Ｌ１）／（（Ｌ１）＋（Ｌ２））により求めることができる。
すなわち、ＷＣ－Ｃｏ焼結体のイオンミリング加工面に対して、後方散乱電子回折装置（以下、ＥＢＳＤ）を備えた走査型電子顕微鏡（以下、ＳＥＭ）にてＥＢＳＤ測定、及び観察を行い、１視野２４μｍ×７２μｍの視野にてピクセルサイズを０．１μｍ×０．１μｍとし、かつＷＣ数が４０００個以上となるように複数視野観察し、前記ＷＣ－ＷＣ界面長Ｌ１、および、前記ＷＣ－（結合相（Ｃｏ、Ｃｒ、γ相成分含有）＋γ相）界面長Ｌ２を測定し、前記Ｒ＝（Ｌ１）／（（Ｌ１）＋（Ｌ２））式に導入することにより、導出することができる。
<WC-WC interface length ratio (R value)>
In the present invention, by controlling the WC-WC interface length ratio (R value) in a low range and shortening the interface length between WC, even if a crack occurs, the proportion of the crack that propagates through the highly tough bonding phase is increased, and fracture resistance can be improved without impairing plastic deformation resistance or wear resistance, so that a cutting tool that is free of fractures and achieves normal wear over a long period of time can be obtained.
The WC-WC interface length ratio (R value) is expressed as follows, where L1 is the WC-WC interface length and L2 is the WC-(binder phase+γ phase) interface length:
It can be calculated by R = (L1)/((L1)+(L2)).
That is, the ion milled surface of the WC-Co sintered compact is subjected to EBSD measurement and observation using a scanning electron microscope (hereinafter, SEM) equipped with an electron backscatter diffraction device (hereinafter, EBSD), and observation is performed in multiple fields of view with a pixel size of 0.1 μm×0.1 μm in a field of view of 24 μm×72 μm and the number of WC is 4000 or more. The WC-WC interface length L1 and the WC-(bonding phase (containing Co, Cr, and γ-phase components)+γ-phase) interface length L2 are measured, and can be derived by introducing them into the formula R=(L1)/((L1)+(L2)).
＜ＷＣ面積平均粒径（Ｄ）＞
本発明においては、ＷＣ面積平均粒径Ｄ（μｍ）を１．０μｍ以上、４．０μｍ以下と規定することにより、粗粒ＷＣへの応力集中によるクラックの進展や、クラック進展抵抗の低い微粒ＷＣによる欠損を生じにくいＷＣ基超硬合金焼結体組織を得ることができる。
ＷＣ面積平均粒径Ｄ（μｍ）は、さらに、１．６μｍ以上、３．０μｍ以下の範囲とすることが好ましい。
ここで、ＷＣ面積平均粒径Ｄ（μｍ）は、ＷＣ超硬合金の縦断面を、上記と同様にＥＢＳＤを備えたＳＥＭにてＥＢＳＤ測定、及び観察をし、画像解析によって、観察領域内における少なくとも４０００個の個々のＷＣ粒子の面積を測定し、該ＷＣ粒を同一面積の円形に近似した時の直径とともにその直径を有するＷＣ粒子が占める面積割合を算出し、各ＷＣの直径と面積割合を乗算した値の総和として求める。
<WC area average grain size (D)>
In the present invention, by specifying the WC areal average grain size D (μm) to be 1.0 μm or more and 4.0 μm or less, it is possible to obtain a WC-based cemented carbide sintered body structure that is less susceptible to crack propagation due to stress concentration in the coarse-grained WC and to chipping due to fine-grained WC that has low resistance to crack propagation.
The WC area average grain size D (μm) is further preferably in the range of 1.6 μm or more and 3.0 μm or less.
Here, the WC area average grain size D (μm) is determined by performing EBSD measurement and observation of a vertical cross section of a WC cemented carbide using an SEM equipped with EBSD as described above, measuring the areas of at least 4,000 individual WC grains in the observation area by image analysis, calculating the diameter of the WC grain when the grain is approximated as a circle of the same area, and calculating the area ratio occupied by WC grains having that diameter, and then calculating the sum of the values obtained by multiplying the diameter and area ratio of each WC grain.
＜結合相面積比率（Ｖ）＞
結合相は、主にＣｏにより構成され、その他、Ｃｒ、および、γ相形成元素である、Ｔａ、Ｎｂ、Ｔｉ、Ｚｒ元素を一部固溶して形成される。
結合相面積については、二次元平面の面積率が三次元方向においても平均的に同比率となっていることを前提として、例えば、ＷＣ基超硬合金の縦断面において、任意の視野数を選択し、各視野において、ＦＥ－ＳＥＭ（電解放出型走査型電子顕微鏡）を用い、２０００～３０００倍視野にて観察を行い、反射電子像を撮影し、画像処理にて２値化し、硬質相（ＷＣ粒子及びγ相の総称）と結合相とを分けることにより、撮影視野全体に対する結合相の面積比率を求めることができる。
<Bounded Phase Area Ratio (V)>
The binder phase is mainly composed of Co, and is formed by partially dissolving Cr and the gamma phase forming elements Ta, Nb, Ti, and Zr.
Regarding the area of the binder phase, on the premise that the area ratio of a two-dimensional plane is on average the same ratio in three-dimensional directions, for example, an arbitrary number of fields of view is selected in the longitudinal section of a WC-based cemented carbide, and observation is performed in each field of view at a magnification of 2000 to 3000 times using an FE-SEM (field emission scanning electron microscope), a backscattered electron image is photographed, binarized by image processing, and the hard phase (a general term for WC particles and γ phase) and the binder phase are separated, whereby the area ratio of the binder phase to the entire photographed field of view can be obtained.
＜ＷＣ－ＷＣ界面長比率（Ｒ値）、結合相面積比率（Ｖ）、ＷＣ面積平均粒径（Ｄ）およびγ相理論体積率との関係＞
本発明に係るＷＣ基超硬合金は、所望の成分組成を有し、前記ＷＣ－ＷＣ界面長比率（Ｒ値）が、結合相の面積比率（∨）（ａｒｅａ％）、及びＷＣ面積平均粒径（Ｄ）（μｍ）、γ相理論体積率との関係において、Ｒは、（０．７０－０．０５９×Ｄ）×（１０／∨）―γ相理論体積率×０．０６、以下の値、かつ（０．６６－０．０５９×Ｄ）×（１０／∨）―γ相理論体積率×０．０６、以上の値、を満足するものであり、耐摩耗性、および、耐欠損性にすぐれた特性を発揮するものである。
<Relationship between WC-WC interface length ratio (R value), binder phase area ratio (V), WC area average grain size (D), and theoretical γ phase volume fraction>
The WC-based cemented carbide according to the present invention has a desired component composition, and in the relationship between the WC-WC interface length ratio (R value), the area ratio of the binder phase (V) (area %), the WC area average grain size (D) (μm), and the theoretical volume fraction of the gamma phase, R satisfies a value not greater than (0.70 - 0.059 x D) x (10/V) - theoretical volume fraction of gamma phase x 0.06 and a value not less than (0.66 - 0.059 x D) x (10/V) - theoretical volume fraction of gamma phase x 0.06, and exhibits excellent properties in terms of wear resistance and chipping resistance.
（３）ＷＣ基超硬合金の製造方法
本発明において、前記Ｒの値を満足するＷＣ基超硬合金は、例えば、以下の方法により作製することができる。
まず、準備工程として、ＷＣ粒子間にＣｏを主とする結合相を介在させ、ＷＣ同士の接触長を短くするため、ＣｏでコーティングしたＷＣ粒子（以下、ＷＣ（Ｃｏ）と記載）を用意する。そして、異なる粒径を有する２種のＷＣ（Ｃｏ）粉末を、所定の粒径比となるように配合し、さらに、所望の組成とするため、Ｃｏ粉末と、必要に応じ、Ｃｒ３Ｃ２粉末を原料粉末として配合し、さらに、ＴａＣ粉末、ＮｂＣ粉末、ＴｉＣ粉末、ＺｒＣ粉末のうちの１種以上の粉末を含有する原料粉末を加え、例えば、メディア量を減らしたアトライターや、望ましくは超音波ホモジナイザー、サイクロンミキサーなどのメディアレス長時間混合により、大きな破砕力を加えずに、ＷＣ（Ｃｏ）同士が分散するような条件で配合・混合して、混合粉末を作製する。
ついで、前記混合粉末を成形して圧粉成形体を作製し、この圧粉成形体を、例えば、加熱温度：１３５０℃以上１５５０℃以下、望ましくは１４５０℃以上１５５０℃以下、かつ、加熱保持時間：１５～１２０分、望ましくは６０～１２０分にて、高温長時間での真空雰囲気の条件で焼結し、ＣｏによるＷＣの回り込みを促進し、かつＷＣが粒成長し、ＷＣ同士が点接触することで、接触長を抑制するようにＷＣ基超硬合金を作製する。
ついで、前記ＷＣ基超硬合金を、機械加工、研削加工することにより、所望サイズ・所望形状のＷＣ基超硬工具を作製することができる。
(3) Manufacturing Method of WC-Based Cemented Carbide In the present invention, a WC-based cemented carbide satisfying the above-mentioned value of R can be manufactured, for example, by the following method.
First, in a preparation step, a bonding phase mainly composed of Co is interposed between WC particles, and in order to shorten the contact length between WC particles, WC particles coated with Co (hereinafter referred to as WC(Co)) are prepared. Then, two kinds of WC(Co) powders having different particle sizes are blended to a predetermined particle size ratio, and further, in order to obtain a desired composition, Co powder and, if necessary, Cr3C2 powder are blended as raw material powders, and further, raw material powders containing one or more of powders of TaC powder, NbC powder, TiC powder, and ZrC powder are added, and the mixture is blended and mixed under conditions such that WC(Co) particles are dispersed without applying a large crushing force by, for example, an attritor with a reduced amount of media, or preferably an ultrasonic homogenizer or a cyclone mixer, etc., for a long time without media.
Next, the mixed powder is molded to produce a powder compact, and this powder compact is sintered under conditions of a high temperature and long time in a vacuum atmosphere, for example, at a heating temperature of 1350°C to 1550°C, preferably 1450°C to 1550°C, and a heating holding time of 15 to 120 minutes, preferably 60 to 120 minutes, to produce a WC-based cemented carbide that promotes the infiltration of WC by Co, causes grain growth of WC, and brings the WC into point contact with each other, thereby suppressing the contact length.
The WC-based cemented carbide alloy is then machined and ground to produce a WC-based cemented carbide tool of a desired size and shape.
前記工程にて作製されたＷＣ基超硬工具は、ＣｏがＷＣの周囲を回り込み、かつＷＣ同士の接触が点接触となることによって、ＷＣ－ＷＣ粒子間の接触長さが短くなるため、亀裂が靭性の高い結合相中を経由する割合が高くなることで、耐摩耗性を損なうことなく、耐欠損性が向上し、長時間に亘って欠損することなく正常摩耗を維持することができる。
さらに、前記ＷＣ基超硬合金製切削工具の少なくとも切れ刃に、Ｔｉ－Ａｌ系、Ａｌ－Ｃｒ系の炭化物、窒化物、炭窒化物あるいはＡｌ２Ｏ３等の硬質皮膜を、ＰＶＤ、ＣＶＤ等の成膜法により被覆形成することにより、表面被覆ＷＣ基超硬合金製切削工具を作製することができる。
なお、表面被覆ＷＣ基超硬合金製切削工具の作製にあたり、硬質皮膜の種類、成膜法は、当業者にすでによく知られている膜種、成膜手法を採用すればよく、特に、制限するものではない。
In the WC-based cemented carbide tool produced by the above process, the Co wraps around the WC and the WC particles contact each other in a point-to-point manner, thereby shortening the contact length between WC-WC particles and increasing the proportion of cracks passing through the tough binder phase. This improves fracture resistance without impairing wear resistance, and enables the tool to maintain normal wear for a long period of time without fracture.
Furthermore, a surface-coated WC-based cemented carbide cutting tool can be produced by coating at least the cutting edge of the WC-based cemented carbide cutting tool with a hard film of Ti-Al or Al-Cr carbide, nitride, carbonitride, Al 2 O 3 , or the like by a film-forming method such as PVD or CVD.
In producing a surface-coated WC-based cemented carbide cutting tool, the type of hard coating and the coating method may be any type of coating and coating method that are well known to those skilled in the art, and are not particularly limited.
本発明のＷＣ基超硬工具および表面被覆ＷＣ基超硬合金製切削工具について、実施例により具体的に説明する。 The WC-based cemented carbide tool and surface-coated WC-based cemented carbide cutting tool of the present invention will be specifically described using examples.
（ａ）まず、焼結用の粉末として、粒径分布の異なる二種のＷＣ（Ｃｏ）粉末（粒径分布の最頻値がｒ１（μｍ）である粗粒ＷＣ（Ｃｏ）粉末と粒径分布の最頻値がｒ２（μｍ）である微粒ＷＣ（Ｃｏ）粉末）と、Ｃｏ粉末、Ｃｒ３Ｃ２粉末、ＴａＣ粉末、ＮｂＣ粉末、ＴｉＣ粉末およびＺｒＣ粉末を用意する。
また、これら前記粒径分布の異なる二種のＷＣ（Ｃｏ）粉末の配合については、粒径分布の最頻値の比、すなわち、ｒ２／ｒ１値は０．０１～０．１３を満たすことが好ましい。
表１には、各種粉末の配合組成（質量％）を示すとともに、２種類のＷＣ（Ｃｏ）粉末の平均粒径値および平均粒径比を示す。
なお、Ｃｏ粉末、Ｃｒ３Ｃ２粉末、ＴａＣ粉末、ＮｂＣ粉末、ＴｉＣ粉末、ＺｒＣ粉末の平均粒径（Ｄ５０）は、いずれも、１．０～３．０μｍの範囲内である。
(a) First, as powders for sintering, two types of WC (Co) powders having different particle size distributions (coarse-grained WC (Co) powder having a particle size distribution mode of r1 (μm) and fine-grained WC (Co) powder having a particle size distribution mode of r2 (μm)), Co powder, Cr3C2 powder, TaC powder, NbC powder, TiC powder and ZrC powder are prepared.
In addition, in the blending of these two types of WC(Co) powders having different particle size distributions, it is preferable that the ratio of the most frequent values of the particle size distributions, that is, the r2/r1 value, satisfies 0.01 to 0.13.
Table 1 shows the blended compositions (mass %) of the various powders, as well as the average particle size values and average particle size ratios of the two types of WC(Co) powder.
The average particle size (D50) of the Co powder, Cr 3 C 2 powder, TaC powder, NbC powder, TiC powder, and ZrC powder is all within the range of 1.0 to 3.0 μm.
（ｂ）表１に示す配合組成に配合した焼結用粉末を、メディアレスのアトライター混合で回転数５０ｒｐｍ、５０時間湿式混合し、乾燥した後、１００ＭＰａの圧力でプレス成形して圧粉成形体を作製した。 (b) The sintering powders, mixed according to the composition shown in Table 1, were wet mixed in a media-less attritor mixer at a rotation speed of 50 rpm for 50 hours, dried, and then pressed at a pressure of 100 MPa to produce a powder compact.
（ｃ）ついで、これらの圧粉成形体を、表３に示す加熱温度：１４５０℃以上１５５０℃以下にて、かつ、加熱保持時間：６０～１２０分、真空雰囲気の条件で高温長時間焼結を行い、ＷＣ基超硬合金を作製した。 (c) These powder compacts were then sintered at high temperature for a long period of time in a vacuum atmosphere at a heating temperature of 1450°C to 1550°C for a heating holding time of 60 to 120 minutes, as shown in Table 3, to produce WC-based cemented carbide.
（ｄ）ついで、前記ＷＣ基超硬合金を、機械加工、研削加工し、ＣＮＭＧ１２０４０８－ＭＭのインサート形状の表５に示すＷＣ基超硬工具１～１０（以下、本発明工具１～１０という）を作製した。 (d) Next, the WC-based cemented carbide alloy was machined and ground to produce WC-based cemented carbide tools 1 to 10 (hereinafter referred to as present invention tools 1 to 10) shown in Table 5, each having an insert shape of CNMG120408-MM.
また、比較のために、表６に示すＷＣ基超硬工具１１～１８(以下、比較例工具１１～１８という)を製造した。
その製造工程では、本発明例に対し、表２、表４において、Ｃｏによるコーティングを行っていないＷＣの使用、配合組成（質量％）、混合条件、あるいは、焼結条件を変更することにより、比較例工具１１～１８を作製した。
For comparison, WC-based cemented carbide tools 11 to 18 shown in Table 6 (hereinafter referred to as comparative example tools 11 to 18) were also manufactured.
In the manufacturing process, comparative example tools 11 to 18 were produced by changing the use of WC that was not coated with Co, the compounding composition (mass%), the mixing conditions, or the sintering conditions in Tables 2 and 4 compared to the inventive examples.
ついで、本発明工具１～１０および比較例工具１１～１８のＷＣ基超硬合金の断面について、ＥＰＭＡにより、その成分であるＣｏ、Ｃｒ、Ｔａ、Ｎｂ、Ｔｉ、Ｚｒの含有量を１０点測定し、その平均値を各成分の含有量として、表５、表６に示す。
なお、Ｃｒ、Ｔａ、Ｎｂ、Ｔｉ、Ｚｒについては、それぞれの炭化物に換算して含有量を算出した。
Next, the contents of the components Co, Cr, Ta, Nb, Ti, and Zr were measured at 10 points on the cross sections of the WC-based cemented carbide of the present invention tools 1 to 10 and the comparative example tools 11 to 18 by EPMA, and the average values were taken as the contents of each component and are shown in Tables 5 and 6.
The contents of Cr, Ta, Nb, Ti, and Zr were calculated in terms of their respective carbides.
つぎに、本発明工具１～１０及び比較例工具１１～１８のＷＣ基超硬合金の断面を、ＥＢＳＤを備えたＳＥＭにて観察し、ＷＣ－ＷＣ界面長Ｌ１、および、ＷＣ－（結合相＋γ相）（結合相中にはＣｏ、Ｃｒ、一部固溶したγ相成分元素を含有）界面長Ｌ２を測定し、Ｒ＝（Ｌ１）／（（Ｌ１）＋（Ｌ２））により、ＷＣ－ＷＣ界面長比率（Ｒ値）を算出し、表５、表６に示す。 Next, the cross sections of the WC-based cemented carbide of the present invention tools 1 to 10 and the comparative example tools 11 to 18 were observed with an SEM equipped with EBSD, and the WC-WC interface length L1 and the WC-(binder phase + gamma phase) (binder phase contains Co, Cr, and partially dissolved gamma phase component elements) interface length L2 were measured. The WC-WC interface length ratio (R value) was calculated from R = (L1)/((L1)+(L2)), and is shown in Tables 5 and 6.
また、同様に、本発明工具１～１０及び比較例工具１１～１８のＷＣ基超硬合金の縦断面を、ＥＢＳＤを備えたＳＥＭにより観察し、観察領域内における個々のＷＣ粒子の面積を測定し、ＷＣ面積平均粒径Ｄ（μｍ）を求め、表５、６に示す。 Similarly, the longitudinal sections of the WC-based cemented carbide of the present invention tools 1 to 10 and the comparative example tools 11 to 18 were observed using an SEM equipped with EBSD, the area of each WC grain in the observed region was measured, and the WC area average grain size D (μm) was calculated, as shown in Tables 5 and 6.
さらに、結合相面積比率∨（ａｒｅａ％）については、本発明工具１～１０及び比較例工具１１～１８のＷＣ基超硬合金の縦断面において、任意の視野数を選択し、各視野において、ＦＥ－ＳＥＭ（電解放出型走査型電子顕微鏡）を用い、観察像を撮影し、画像処理にて２値化し、硬質相と結合相とを分け、結合相の面積比率を算出し、表５、６に示す。 Furthermore, for the binder phase area ratio ∨ (area%), an arbitrary number of fields were selected from the longitudinal sections of the WC-based cemented carbide alloys of the present invention tools 1 to 10 and the comparative example tools 11 to 18, and in each field, an observation image was taken using a FE-SEM (field emission scanning electron microscope), binarized by image processing, the hard phase and binder phase were separated, and the binder phase area ratio was calculated, as shown in Tables 5 and 6.
そして、γ相粒径については、本発明工具１～１０及び比較例工具１１～１８のＷＣ基超硬合金の縦断面において、前述した方法により、各γ相の面積を測定し、γ相の平均粒径を算出し、その結果を表５、６に示す。 The gamma phase grain size was measured by the method described above on the longitudinal sections of the WC-based cemented carbide alloys of the present invention tools 1 to 10 and the comparative example tools 11 to 18, and the area of each gamma phase was measured and the average grain size of the gamma phase was calculated. The results are shown in Tables 5 and 6.
さらに、γ相理論体積率については、本発明工具１～１０及び比較例工具１１～１８のＷＣ基超硬合金に対して、ＥＰＭＡによって測定されたＴａＣ、ＮｂＣ、ＴｉＣ、ＺｒＣの各含有量（質量％）を、各密度で割った数値の足し合わせた値として求め、その結果を表５、６に示す。 Furthermore, the theoretical volume fraction of the gamma phase was calculated by dividing the contents (mass%) of TaC, NbC, TiC, and ZrC measured by EPMA for the WC-based cemented carbide alloys of the present invention tools 1 to 10 and the comparative example tools 11 to 18 by their respective densities, and adding up the results. The results are shown in Tables 5 and 6.
＜ステンレス鋼の六角柱形状被削材の湿式外径旋削加工（正六角形断面の一辺が２０ｍｍ）＞
次いで、前記本発明工具１～１０、比較例工具１１～１８について、以下の旋削切削試験を実施した。
被削材：ＳＵＳ３０４
切削速度：１２０ｍ／ｍｉｎ
切り込み：２．０ｍｍ
送り：０．２ｍｍ／ｒｅｖ
切削時間：１０分
湿式水溶性切削油使用
上記断続部を含む六角材旋削切削試験では、切れ刃の最大逃げ面摩耗幅を測定するとともに、切れ刃の損耗状態を観察した。
表７に、この測定結果を示す。
<Wet external diameter turning of stainless steel hexagonal columnar workpiece (one side of regular hexagonal cross section is 20 mm)>
Next, the following turning and cutting tests were carried out on the tools 1 to 10 of the present invention and the comparative tools 11 to 18.
Work material: SUS304
Cutting speed: 120 m/min
Cut: 2.0 mm
Feed: 0.2 mm/rev
Cutting time: 10 minutes. Wet water-soluble cutting oil was used. In the above-mentioned lathe cutting test of the hexagonal material including the interrupted portion, the maximum flank wear width of the cutting edge was measured, and the wear state of the cutting edge was observed.
Table 7 shows the results of this measurement.
また、前記本発明工具１～４、比較例工具１１～１４の切刃表面に、表８に示す平均層厚の硬質被覆層をＰＶＤ法あるいはＣＶＤ法で被覆形成し、本発明表面被覆ＷＣ基超硬合金製切削工具（以下、「本発明被覆工具」という）１～４、比較例表面被覆ＷＣ基超硬合金製切削工具（以下、「比較例被覆工具」という）１１～１４を作製した。
上記の各被覆工具について、以下に示す、ステンレス鋼の断続部を含む六角柱形状被削材の湿式外径旋削切削試験（正六角形断面の一辺が２０ｍｍ）を実施し、切れ刃の最大逃げ面摩耗幅を測定するとともに、切削加工試験後の切れ刃の損耗状態を観察した。
被削材：ＳＵＳ３０４
切削速度：１２０ｍ／ｍｉｎ
切り込み：２．０ｍｍ
送り：０．２５ｍｍ／ｒｅｖ
切削時間：１０分
湿式水溶性切削油使用
表９に、切削試験の結果を示す。
In addition, hard coating layers having average thicknesses shown in Table 8 were formed by PVD or CVD on the cutting edge surfaces of the tools 1 to 4 of the present invention and the tools 11 to 14 of the comparative examples to produce surface-coated WC-based cemented carbide cutting tools 1 to 4 of the present invention (hereinafter referred to as "coated tools of the present invention") and comparative surface-coated WC-based cemented carbide cutting tools 11 to 14 of the comparative examples (hereinafter referred to as "coated tools of the comparative examples").
For each of the above coated tools, a wet external diameter turning cutting test (each side of a regular hexagonal cross section is 20 mm) of a stainless steel workpiece containing an interrupted portion was carried out as described below. The maximum flank wear width of the cutting edge was measured, and the wear state of the cutting edge after the cutting test was observed.
Work material: SUS304
Cutting speed: 120 m/min
Cut: 2.0 mm
Feed: 0.25 mm/rev
Cutting time: 10 minutes. Wet water-soluble cutting oil was used. Table 9 shows the results of the cutting test.
表７および表９に示される試験結果によれば、本発明工具および本発明被覆工具は、ステンレス鋼の断続部を含む高能率旋削切削加工においても、欠損を発生することなく、すぐれた耐摩耗性を発揮することが分かる。
これに対して、比較例工具および比較例被覆工具は、工具が力学的衝撃に起因する欠損により短時間で寿命に至った。
The test results shown in Tables 7 and 9 show that the tool of the present invention and the coated tool of the present invention exhibit excellent wear resistance without chipping even in high-efficiency turning cutting of stainless steel including interrupted portions.
In contrast, the comparative example tool and the comparative example coated tool reached the end of their life in a short period of time due to chipping caused by mechanical impact.
以上のとおり、本発明のＷＣ基超硬工具および被覆工具は、ステンレス鋼の断続部を含む高能率旋削切削加工に供した場合、刃先変形することなく、すぐれた耐摩耗性とともに、すぐれた耐欠損性を有するが、他の被削材、切削条件に適用した場合にも、長期の使用にわたってすぐれた切削性能を発揮し、工具の長寿命化が図られることが期待される。
As described above, when the WC-base cemented carbide tool and coated tool of the present invention are used in high-efficiency turning cutting of stainless steel, including interrupted portions, they exhibit excellent wear resistance and excellent chipping resistance without causing deformation of the cutting edge. Even when used with other workpiece materials and under other cutting conditions, they are expected to exhibit excellent cutting performance over long periods of use and to extend the tool life.
Claims (3)
（ａ）前記ＷＣ基超硬合金の成分組成は、Ｃｏ：６．０～１２．０質量％、Ｃｒ３Ｃ２：０．０～１．２質量％、および、ＴａＣ、ＮｂＣ、ＴｉＣ及びＺｒＣのうちから選ばれる少なくとも１種以上を合計量にて０．６～４．０質量％含有し、残部はＷＣ及び不可避不純物とからなり、Ｃｒ３Ｃ２の質量含有率は、Ｃｏの質量含有率の１０％以下であり、
（ｂ）ＷＣ粒子は、平均粒径を比較したとき平均粒径の大きな粗粒ＷＣ群と平均粒径の小さな微粒ＷＣ群とから構成され、
（ｃ）前記ＷＣ粒子同士の界面長さＷＣ－ＷＣ界面長をＬ１、
前記ＷＣ粒子と
Ｔａ、Ｎｂ、Ｔｉ、Ｚｒのいずれか一つ以上のγ相成分元素を主として形成されるそれらの炭化物相であるγ相、および
ＷやＣ、Ｃｒ、γ相成分元素を固溶した結合相との
界面長であるＷＣ－（結合相＋γ相）界面長をＬ２
としたとき、
前記Ｌ１と前記Ｌ２の和に対する前記Ｌ１の比である比率Ｒが、（０．６６－０．０５９×Ｄ）×（１０／Ｖ）―γ相理論体積率×０．０６以上、（０．７０－０．０５９×Ｄ）×（１０／Ｖ）―γ相理論体積率×０．０６以下の値であることを特徴とするＷＣ基超硬合金製切削工具。
ここで、Ｖは、結合相の面積比率（ａｒｅａ％）、Ｄは、ＷＣ面積平均粒径（μｍ）を指し、１．０≦Ｄ≦４．０である。 In a WC-based cemented carbide cutting tool having a WC-based cemented carbide substrate,
(a) The composition of the WC-based cemented carbide is Co: 6.0 to 12.0 mass%, Cr 3 C 2 : 0.0 to 1.2 mass%, and at least one selected from TaC, NbC, TiC, and ZrC in a total amount of 0.6 to 4.0 mass%, with the remainder being WC and inevitable impurities, and the mass content of Cr 3 C 2 is 10% or less of the mass content of Co,
(b) The WC grains are composed of a group of coarse WC grains having a large average grain size and a group of fine WC grains having a small average grain size, when comparing the average grain size.
( c ) The interface length between the WC grains is the WC-WC interface length L1,
The WC grains and
A gamma phase, which is a carbide phase mainly composed of one or more gamma phase component elements of Ta, Nb, Ti, and Zr, and
With a binder phase in which W, C, Cr, and γ-phase component elements are dissolved
The interface length of the WC-(binder phase + γ phase) is L2
When
A WC-based cemented carbide cutting tool, wherein a ratio R, which is a ratio of L1 to the sum of L1 and L2, is a value not less than (0.66-0.059×D)×(10/V)-theoretical volume fraction of gamma phase×0.06 and not more than (0.70-0.059×D)×(10/V)-theoretical volume fraction of gamma phase×0.06 .
Here, V is the area ratio (area %) of the binder phase, D is the area average grain size (μm) of WC, and 1.0≦D≦4.0.
3. A surface-coated WC-based cemented carbide cutting tool according to claim 1, further comprising a hard coating layer formed on at least a cutting edge of the WC-based cemented carbide cutting tool.
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| JP2006328477A (en) | 2005-05-26 | 2006-12-07 | Hitachi Tool Engineering Ltd | Wc based cemented carbide member, and coated wc based cemented carbide member |
| JP2017148895A (en) | 2016-02-24 | 2017-08-31 | 三菱マテリアル株式会社 | Wc-based cemented carbide drill excellent in breakage resistance |
| JP2017179433A (en) | 2016-03-29 | 2017-10-05 | 三菱マテリアル株式会社 | Wc-based hard metal alloy-made tool excellent in thermal resisting plastic deformation property |
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| JP2006328477A (en) | 2005-05-26 | 2006-12-07 | Hitachi Tool Engineering Ltd | Wc based cemented carbide member, and coated wc based cemented carbide member |
| JP2017148895A (en) | 2016-02-24 | 2017-08-31 | 三菱マテリアル株式会社 | Wc-based cemented carbide drill excellent in breakage resistance |
| JP2017179433A (en) | 2016-03-29 | 2017-10-05 | 三菱マテリアル株式会社 | Wc-based hard metal alloy-made tool excellent in thermal resisting plastic deformation property |
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