JP7486711B2 - WC-based cemented carbide and coated cutting tool using same - Google Patents
WC-based cemented carbide and coated cutting tool using same Download PDFInfo
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- 238000005520 cutting process Methods 0.000 title claims description 53
- 239000002245 particle Substances 0.000 claims description 55
- 238000000576 coating method Methods 0.000 claims description 27
- 239000011248 coating agent Substances 0.000 claims description 23
- 238000009826 distribution Methods 0.000 claims description 21
- 239000011247 coating layer Substances 0.000 claims description 18
- 229910052751 metal Inorganic materials 0.000 claims description 15
- 239000000758 substrate Substances 0.000 claims description 15
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- 239000006104 solid solution Substances 0.000 claims description 5
- 229910052804 chromium Inorganic materials 0.000 claims description 4
- 150000001875 compounds Chemical class 0.000 claims description 4
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims 1
- 229910052593 corundum Inorganic materials 0.000 claims 1
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- 239000002994 raw material Substances 0.000 description 40
- 230000000052 comparative effect Effects 0.000 description 19
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- 238000003763 carbonization Methods 0.000 description 6
- 238000005245 sintering Methods 0.000 description 6
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 5
- 229910000831 Steel Inorganic materials 0.000 description 5
- 238000005054 agglomeration Methods 0.000 description 5
- 230000007547 defect Effects 0.000 description 5
- 239000010959 steel Substances 0.000 description 5
- 239000011230 binding agent Substances 0.000 description 4
- 238000001887 electron backscatter diffraction Methods 0.000 description 4
- 229910052715 tantalum Inorganic materials 0.000 description 4
- 238000005229 chemical vapour deposition Methods 0.000 description 3
- 238000003801 milling Methods 0.000 description 3
- 239000011268 mixed slurry Substances 0.000 description 3
- 230000003287 optical effect Effects 0.000 description 3
- 238000010298 pulverizing process Methods 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- 238000005422 blasting Methods 0.000 description 2
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- 150000001247 metal acetylides Chemical class 0.000 description 2
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- 229910009043 WC-Co Inorganic materials 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
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- 239000000919 ceramic Substances 0.000 description 1
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- 238000000227 grinding Methods 0.000 description 1
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- 229910052742 iron Inorganic materials 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
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- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
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- Cutting Tools, Boring Holders, And Turrets (AREA)
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Description
本発明は、ＷＣ基超硬合金およびこれを用いた被覆切削工具に関する。 The present invention relates to a WC-based cemented carbide and a coated cutting tool using the same.
従来、金属材料等の切削加工では、高剛性、高硬度の特性を有するＷＣ基超硬合金を基材とし、耐摩耗性、耐酸化性に優れたセラミック硬質皮膜を被覆した切削工具が広く使用されている。被削材の高硬度化、高能率加工化に伴い、切削工具への負荷が増大する状況にあっては、硬質皮膜だけではなく基材である超硬合金についても、耐熱性や耐チッピング性の改善を図ることが求められている。例えば、特許文献１、２では、クロム（Ｃｒ）とタンタル（Ｔａ）を複合添加したＷＣ－Ｃｏ系超硬合金について、組織を均粒化することにより、耐チッピング性の改善を図ることが提案されている。 Conventionally, cutting tools that use a WC-based cemented carbide substrate with high rigidity and hardness and coated with a ceramic hard coating with excellent wear resistance and oxidation resistance have been widely used in cutting metal materials. In a situation where the load on cutting tools increases with the hardness and high efficiency of workpiece materials, there is a demand for improving the heat resistance and chipping resistance of not only the hard coating but also the cemented carbide substrate. For example, Patent Documents 1 and 2 propose improving the chipping resistance of WC-Co-based cemented carbide with a composite addition of chromium (Cr) and tantalum (Ta) by homogenizing the structure.
近年、金型加工の分野においては一層の低コスト化や納期の短縮化が求められており、切削加工においても切削速度の高速化や高送り条件を用いた高能率化が進められている。
しかしながら、発明者等の検討により、従来提案の超硬合金を基材とする被覆切削工具を用いたとしても、鋼等の高速切削加工、特に、軟鋼の高速加工においては、依然として、チッピングや塑性変形が発生するため、工具寿命が十分でないとの問題点を有することが確認された。
そこで、本発明者らは、鋼等の高速切削加工、特に、軟鋼の高速加工を行った際にも、基材としてチッピングや塑性変形を生じないＷＣ基超硬合金および前記ＷＣ基超硬合金を用いた被覆切削工具を提供することを解決すべき課題とした。
In recent years, there has been a demand for further cost reduction and shorter delivery times in the field of mold machining, and in cutting processes, efforts are being made to increase efficiency by increasing cutting speeds and using high feed conditions.
However, through investigations by the inventors, it has been confirmed that even when the conventionally proposed coated cutting tools using cemented carbide as a base material are used, chipping and plastic deformation still occur in high-speed cutting of steel and the like, particularly in high-speed cutting of mild steel, and therefore the tool life is insufficient.
Therefore, the inventors set out to provide a WC-based cemented carbide that does not cause chipping or plastic deformation as a substrate even when performing high-speed cutting of steel or the like, particularly when performing high-speed cutting of mild steel, and a coated cutting tool using the WC-based cemented carbide.
そして、本発明者らは、前記被覆切削工具の基材となるＷＣ超硬合金において、結合相を構成するＣｏの含有量、前記結合相に固溶するＣｒの含有量、および、前記結合相に固溶、または、組織中に分散して主成分相を構成するＴａの含有量を所定の範囲に調整し、さらに、残部であるＷＣ粒子のうち、特定の円相当粒径を有する粒子について、その平均粒径の範囲、および、円相当粒径の粒度分布における面積比の積算値が９０％となる粒径（Ｄ９０）に対して面積比の積算値が１０％となる粒径（Ｄ１０）との比（Ｄ９０／Ｄ１０）の範囲を規定するとともに、組織中にＴａの主成分相が分散することを規定することにより、鋼等の高速切削加工、特に、軟鋼の高速加工を行った際に基材に発生するチッピングや塑性変形の問題を解決できることを見出した。
また、本発明者らは、さらに、前記基材の表面に少なくとも柱状組織からなり表面側において所定の平均幅を有し、最大膜厚として含むＴｉＣＮ皮膜を有する硬質皮膜を備えること、また、加えて、前記ＴｉＣＮ皮膜の上層にＡｌ２Ｏ３皮膜を備えることにより、軟鋼の高速加工を行った際に、さらに、すぐれた耐チッピング性および耐塑性変形性を有する被覆切削工具が得られることを見出したものである。
The inventors have found that by adjusting the content of Co constituting the binder phase, the content of Cr dissolved in the binder phase, and the content of Ta dissolved in the binder phase or dispersed in the structure to form the main component phase in the WC cemented carbide that serves as the base material of the coated cutting tool within predetermined ranges, and further specifying the range of the average grain size of particles having a specific circle equivalent grain size among the remaining WC grains, and the range of the ratio (D90/D10) of the grain size (D90) at which the integrated value of the area ratio in the grain size distribution of the circle equivalent grain size is 90% to the grain size (D10) at which the integrated value of the area ratio is 10%, and specifying that the main component phase of Ta is dispersed in the structure, it is possible to solve the problems of chipping and plastic deformation that occur in the base material when high-speed cutting of steel, etc., particularly high-speed cutting of mild steel, is performed.
The inventors have also discovered that by providing a hard coating having a TiCN coating on the surface of the substrate, the hard coating having at least a columnar structure and a predetermined average width on the surface side and including the maximum film thickness, and by providing an Al 2 O 3 coating on the upper layer of the TiCN coating, a coated cutting tool having even better chipping resistance and plastic deformation resistance can be obtained when performing high-speed machining of mild steel.
本発明は、前記知見に基づいてなされたものであって、
「（１）質量％で、金属元素としてＣｏを８．５％以上９．５％以下、Ｃｒを０．３％以上１．０％以下、Ｔａを１．０％以上３．０％以下にて含有し、残部はＷＣと前記金属元素に固溶もしくは化合して存在する非金属元素と不可避的不純物とからなるＷＣ基超硬合金であって、
円相当の粒径が０．４μｍ以上であるＷＣ粒子の平均粒径は、１．０μｍ以上２．０μｍ以下であり、
前記平均粒径の粒度分布において面積比の積算値が９０％となる粒径Ｄ９０と面積比の積算値が１０％となる粒径Ｄ１０との比である、Ｄ９０／Ｄ１０が３．２未満であり、
組織中にＴａを主成分とする相が分散していることを特徴とするＷＣ基超硬合金。
（２） （１）に記載のＷＣ基超硬合金を基材として表面に硬質皮膜層を有する被覆切削工具。
（３） 前記硬質皮膜層は、少なくともＴｉＣＮ皮膜層を含み、前記ＴｉＣＮ皮膜層は柱状粒子を有する柱状組織からなり、前記柱状粒子の表面側における平均幅が１．０μｍ以下であり、前記硬質皮膜中にて最も厚い膜厚を有する皮膜層であることを特徴とする（２）に記載の被覆切削工具。
（４） 前記硬質皮膜層は、前記ＴｉＣＮ皮膜層の上層にＡｌ２Ｏ３皮膜層を有することを特徴とする（３）に記載の被覆切削工具。」である。
The present invention has been made based on the above findings,
"(1) A WC-based cemented carbide containing, by mass%, 8.5% to 9.5% Co, 0.3% to 1.0% Cr, and 1.0% to 3.0% Ta as metallic elements, with the balance being WC, non-metallic elements present in solid solution or in combination with the metallic elements, and unavoidable impurities,
The average grain size of WC grains having a circle-equivalent grain size of 0.4 μm or more is 1.0 μm or more and 2.0 μm or less,
D90/D10, which is the ratio of a particle size D90 at which the integrated value of the area ratio in the particle size distribution of the average particle size is 90% to a particle size D10 at which the integrated value of the area ratio is 10%, is less than 3.2;
A WC-based cemented carbide characterized in that a phase mainly composed of Ta is dispersed in the structure.
(2) A coated cutting tool having a substrate made of the WC-based cemented carbide according to (1) above and a hard coating layer on the surface thereof.
(3) The coated cutting tool according to (2), wherein the hard coating layer includes at least a TiCN coating layer, the TiCN coating layer is made of a columnar structure having columnar grains, the columnar grains have an average width of 1.0 μm or less on a surface side, and the TiCN coating layer is the coating layer having the thickest thickness in the hard coating.
(4) The coated cutting tool according to (3), wherein the hard coating layer has an Al 2 O 3 coating layer on the TiCN coating layer.
本発明によれば、軟鋼の高速加工において、耐久性に優れたＷＣ超硬合金基材およびこれを用いた被覆切削工具を提供することができる。 The present invention provides a WC cemented carbide substrate with excellent durability for high-speed machining of mild steel, and a coated cutting tool using the same.
本発明者等は、鋼等の高速加工、例えば、軟鋼の高速加工において工具寿命を大幅に改善できるＷＣ基超硬合金の組成と組織形態、さらには、硬質皮膜の組成および組織を具体的に見出したことで本発明に到達した。以下、詳細を説明する。 The inventors arrived at the present invention by specifically discovering the composition and structure of a WC-based cemented carbide, as well as the composition and structure of a hard coating, that can significantly improve tool life in high-speed machining of steel and the like, for example, in high-speed machining of mild steel. The details are described below.
［１］ＷＣ基超硬合金の組成
＜Ｃｏ含有量＞
Ｃｏは、硬質相であるＷＣ粒子を繋ぎとめる結合相であり、ＷＣ基超硬合金に高い靭性を付与する元素である。
本発明においては、軟鋼の高速加工において、優れた耐久性を再現するために、Ｃｏの含有量を狭い範囲で制御する必要があり、金属元素として、８．５質量％以上９．５質量％以下（以下、「質量％」を単に「％」と表記する）にて、添加する。
Ｃｏの含有量が８．５％未満では、超硬合金の靭性が低下する。また、組織が不均一になり易く、軟鋼の高速加工においてチッピングが発生し易くなる。一方、Ｃｏの含有量が９．５％を超えると、後述するＷＣ粒子の粒度分布を均一にしても、硬度と耐塑性変形性が低下するため、軟鋼の高速加工において、工具の耐久性が著しく低下する。
よって、Ｃｏの含有量は、８．５％以上９．５％以下と規定した。
[1] Composition of WC-based cemented carbide <Co content>
Co is a binder phase that binds together WC particles, which are a hard phase, and is an element that imparts high toughness to the WC-based cemented carbide.
In the present invention, in order to reproduce excellent durability in the high-speed machining of mild steel, the Co content needs to be controlled within a narrow range, and Co is added as a metallic element in an amount of 8.5 mass % or more and 9.5 mass % or less (hereinafter, "mass %" will be simply abbreviated as "%").
If the Co content is less than 8.5%, the toughness of the cemented carbide is reduced. In addition, the structure is easily non-uniform, and chipping is easily generated during high-speed machining of mild steel. On the other hand, if the Co content exceeds 9.5%, even if the grain size distribution of the WC particles described later is made uniform, the hardness and plastic deformation resistance are reduced, and therefore the durability of the tool is significantly reduced during high-speed machining of mild steel.
Therefore, the Co content is specified to be 8.5% or more and 9.5% or less.
＜Ｃｒの含有量＞
Ｃｒは、Ｃｏ中に固溶し、焼結過程でのＷＣ粒子の粒成長を抑制して組織を均一にする元素であり、金属元素として、０．３％以上１．０％以下にて添加する。
Ｃｒの含有量が０．３％未満では、ＷＣ粒子の粒成長が抑制されずに、ＷＣ粒子の粒度分布が不均一となり、チッピングが発生し易くなる。また、ＷＣ粒子の粒度分布が不均一になることでＣｏの分布も不均一になり、チッピングが発生し易くなる。
一方、Ｃｒの含有量が１．０％を超えると、Ｃｒを主体とする粗大な炭化物が析出して超硬合金の靭性を低下させる。
よって、Ｃｒの含有量は、０．３％以上１．０％以下とする。好ましくは、０．５％以上であり、また、好ましくは、０．８％以下である。
<Cr Content>
Cr is an element that dissolves in Co and suppresses the grain growth of WC grains during the sintering process to make the structure uniform, and is added in an amount of 0.3% to 1.0% as a metallic element.
If the Cr content is less than 0.3%, the grain growth of the WC grains is not suppressed, the grain size distribution of the WC grains becomes non-uniform, and chipping is likely to occur. In addition, the non-uniform grain size distribution of the WC grains also makes the distribution of Co non-uniform, and chipping is likely to occur.
On the other hand, if the Cr content exceeds 1.0%, coarse carbides mainly composed of Cr are precipitated, reducing the toughness of the cemented carbide.
Therefore, the Cr content is set to 0.3% or more and 1.0% or less, preferably 0.5% or more, and more preferably 0.8% or less.
＜Ｔａの含有量＞
Ｔａは、Ｃｏに固溶してＷＣ粒子の粒成長を抑制して組織を均一化する。また、組織中にＴａを主成分とする相が分散することで耐熱性を高めることができるため、金属元素として、１．０％以上３．０％以下にて添加する。
Ｔａの含有量が１．０％未満では、ＷＣ粒子の粒度分布が不均一になるとともに、組織中に分散するＴａを主成分とする相が少なく耐熱性が低下する。一方、Ｔａの含有量が３．０％を超えると、Ｔａを主成分とする相が多くなりすぎて超硬合金の靭性を低下させる。
よって、Ｔａの含有量は、１．０％以上３．０％以下とする。好ましくは、２．５％以下であり、更には、２．０％以下とすることが好ましい。
<Ta Content>
Ta dissolves in Co to suppress the grain growth of WC grains and homogenize the structure. In addition, Ta is added in an amount of 1.0% to 3.0% as a metallic element because it can improve heat resistance by dispersing a phase mainly composed of Ta in the structure.
If the Ta content is less than 1.0%, the particle size distribution of the WC particles becomes non-uniform, and the amount of the phase mainly composed of Ta dispersed in the structure is small, resulting in a decrease in heat resistance.On the other hand, if the Ta content exceeds 3.0%, the amount of the phase mainly composed of Ta becomes too large, resulting in a decrease in the toughness of the cemented carbide.
Therefore, the Ta content is set to 1.0% or more and 3.0% or less, preferably 2.5% or less, and more preferably 2.0% or less.
＜金属元素に固溶もしくは化合して存在する非金属元素と不可避的不純物＞
ＷＣ基超硬合金の残部は、主成分であるＷＣ、および、金属元素（Ｃｏ、Ｃｒ、Ｔａ）に固溶もしくは化合して存在する非金属元素と不可避的不純物である。
金属元素の固溶もしくは化合して存在する非金属元素とは、Ｃ、Ｎ等であり、光学顕微鏡観察にては遊離成分として確認されない量で存在する。
また、原料粉末や混合、焼結過程の不可避的不純物としてＦｅ、Ｎｉ、Ｎｂ、Ａｌ等を微量含有する場合がある。
<Non-metallic elements that exist as solid solutions or compounds with metallic elements and unavoidable impurities>
The balance of the WC-based cemented carbide is made up of WC as the main component, nonmetallic elements present as solid solutions or compounds with the metallic elements (Co, Cr, Ta), and unavoidable impurities.
The non-metallic elements present as solid solutions or compounds with metallic elements are C, N, etc., and are present in amounts that cannot be confirmed as free components by optical microscope observation.
Furthermore, the raw material powder may contain trace amounts of Fe, Ni, Nb, Al, etc. as unavoidable impurities during the mixing and sintering process.
［２］ＷＣ基超硬合金の組織
＜ＷＣ粒子の平均粒径＞
ＷＣ基超硬合金の硬度と靭性はトレードオフの関係にあり、硬度が増加すると靭性が低下する傾向にあり、他方、硬度が低下すると靭性が増加する傾向にある。
そして、ＷＣ基超硬合金のＣｏの含有量が同等であれば、硬度と靭性はほぼＷＣ粒子の平均粒径によって決定される。
ここでいうＷＣ粒子の平均粒径は、円相当の粒径（「円相当径」ともいう。）の平均粒径をいう。
なお、特に、ＷＣ粒子については、円相当の粒径が０．４μｍ未満の微細な粒子を含めた場合には、例えば、後述するＤ９０／Ｄ１０において、組織の均一性を正確に評価できなくなるため、円相当の粒径が０．４μｍ以上である粒子の平均粒径について規定する。
軟鋼の高速加工において、ＷＣ粒子の平均粒径が微粒になりすぎると靭性が低下してチッピングが発生する。他方、ＷＣ粒子の平均粒径が粗大になりすぎると硬度が低下して耐摩耗性が低下する。
そこで、本発明においては、円相当の粒径が０．４μｍ以上のＷＣ粒子の平均粒径を１．０μｍ以上２．０μｍ以下と規定した。好ましくは、１．２μｍ以上であり、また、好ましくは、１．８μｍ以下である。
そして、具体的には、試料を鏡面加工して、縦６０μｍ×横３０μｍ（１８００μｍ２）の範囲にある、円相当の粒径が０．４μｍ以上のＷＣ粒子の円相当の平均粒径を求めることで、ＷＣ粒子の平均粒径を精度高く評価することができる。
ＷＣ粒子の平均粒径は、ＥＢＳＤ（Ｅｌｅｃｔｒｏｎ Ｂａｃｋ Ｓｃａｔｔｅｒ Ｄｉｆｆｒａｃｔｉｏｎ：電子後方散乱回折）法を用いて測定することができる。
０．４μｍ未満のＷＣ粒子の測定についてはノイズを含むため、前述のとおり、測定対象となるＷＣ粒子の粒径を０．４μｍ以上のＷＣ粒子の円相当径の平均粒径として規定することにより評価した。なお、相当径が０．４μｍ未満の粒子が全体に占める面積率は５％以下である。
[2] Structure of WC-based cemented carbide <Average grain size of WC particles>
There is a trade-off between the hardness and toughness of WC-based cemented carbide, with an increase in hardness tending to decrease the toughness, and conversely, a decrease in hardness tending to increase the toughness.
If the Co content of the WC-based cemented carbide is the same, the hardness and toughness are determined almost entirely by the average grain size of the WC grains.
The average grain size of WC grains referred to here means the average grain size of grains equivalent to a circle (also called the "circle equivalent diameter").
In particular, with regard to WC grains, if fine grains having a circle-equivalent grain size of less than 0.4 μm are included, the uniformity of the structure cannot be accurately evaluated, for example, using D90/D10, which will be described later, so the average grain size of grains having a circle-equivalent grain size of 0.4 μm or more is specified.
In high-speed machining of mild steel, if the average grain size of WC grains is too fine, toughness decreases and chipping occurs, whereas if the average grain size of WC grains is too coarse, hardness decreases and wear resistance decreases.
Therefore, in the present invention, the average grain size of WC grains having a circle-equivalent grain size of 0.4 μm or more is specified to be 1.0 μm or more and 2.0 μm or less, preferably 1.2 μm or more, and more preferably 1.8 μm or less.
Specifically, the sample is mirror-finished and the average circle-equivalent grain size of WC grains with a circle-equivalent grain size of 0.4 μm or more within an area of 60 μm length × 30 μm width (1,800 μm2 ) is determined, thereby enabling the average grain size of the WC grains to be evaluated with high precision.
The average grain size of the WC grains can be measured by using the EBSD (Electron Back Scatter Diffraction) method.
Since the measurement of WC grains smaller than 0.4 μm includes noise, as described above, the grain size of the WC grains to be measured was evaluated by defining it as the average grain size of the circle-equivalent diameter of WC grains of 0.4 μm or more. The area ratio of grains with an equivalent diameter of less than 0.4 μm to the whole grains was 5% or less.
＜ＷＣ粒子のＤ９０／Ｄ１０＞
ここで、Ｄ９０／Ｄ１０とは、ＷＣ平均粒径の粒度分布において面積比の積算値が９０％となる粒径Ｄ９０に対する、面積比の積算値が１０％となる粒径Ｄ１０の比をいう。
本発明では、上述した組成範囲の制御に加えて、ミクロレベルの組織の均一化が重要である。上述したように、本発明のＷＣ基超硬合金は、軟鋼の高速切削において、硬度と靭性を高いレベルで確保するため、特定の平均粒径になるよう設定している。但し、同程度の平均粒径であっても、その粒度分布が広い場合には、ミクロレベルの組織が不均一となり、チッピングが発生し易くなる。
そこで、本発明では、ミクロレベルのＷＣ粒子の均一性を評価する指標として、さらに、平均粒径の粒度分布において面積比の積算値が９０％となる粒径Ｄ９０に対して、面積比の積算値が１０％となる粒径Ｄ１０の比、すなわち、Ｄ９０／Ｄ１０を用いた。この値は、仮に全ての粒子が同じ粒径であれば、Ｄ９０とＤ１０が同じ粒径となり、Ｄ９０／Ｄ１０の値は最小値の１となる。粒度分布が広い組織では、粒径が大きいＤ９０の値が大きくなる一方、粒径が小さいＤ１０の値は小さくなるので、Ｄ９０／Ｄ１０の値は１を超えて大きくなる。これに対して、Ｄ９０／Ｄ１０の値が小さいことは、粒度分布がよりシャープで均一な組織であることを示す。
但し、前述したとおり、極めて微粒なＷＣ粒子を考慮すると、微粒なＷＣ粒子は数が多いため、狙いとする１．０μｍ以上２．０μｍ以下のＷＣ粒子を正確に評価できず、Ｄ９０／Ｄ１０により組織の均一性が正確に評価できないため、組織中に均一分散している円相当の粒径が０．４μｍ未満の極めて微粒なＷＣ粒子は考慮せず、円相当径が０．４μｍ以上のＷＣ粒子について、前記Ｄ９０に対する前記Ｄ１０の比を評価することで、組織の均一性を正確に評価できることを確認した。そして、円相当の粒径が０．４μｍ以上のＷＣ粒子の平均粒径を１．０μｍ以上２．０μｍ以下とした上で、平均粒径の粒度分布において面積比の積算値が９０％における粒径Ｄ９０と面積比の積算値が１０％における粒径Ｄ１０との比であるＤ９０／Ｄ１０を３．２未満と規定することで、軟鋼の高速切削において、チッピングの発生を抑制する効果を十分に発揮できることを見出した。
好ましくは、Ｄ９０／Ｄ１０を３．０以下とすること、さらには、Ｄ９０／Ｄ１０を２．８以下とすることが好ましい。
<D90/D10 of WC particles>
Here, D90/D10 refers to the ratio of the particle size D10 where the integrated value of the area ratio is 10% to the particle size D90 where the integrated value of the area ratio is 90% in the particle size distribution of the WC average particle size.
In the present invention, in addition to controlling the composition range described above, it is important to homogenize the micro-level structure. As described above, the WC-based cemented carbide of the present invention is set to have a specific average grain size in order to ensure high levels of hardness and toughness in high-speed cutting of mild steel. However, even if the average grain size is about the same, if the grain size distribution is wide, the micro-level structure becomes non-uniform, and chipping is likely to occur.
Therefore, in the present invention, as an index for evaluating the uniformity of WC grains at the micro level, the ratio of the grain size D10 at which the integrated value of the area ratio in the grain size distribution of the average grain size is 10% to the grain size D90 at which the integrated value of the area ratio is 90%, that is, D90/D10, is used. If all grains have the same grain size, D90 and D10 will be the same grain size, and the value of D90/D10 will be the minimum value of 1. In a structure with a wide grain size distribution, the value of D90 is large for large grains, while the value of D10 is small for small grains, so the value of D90/D10 exceeds 1 and becomes large. In contrast, a small value of D90/D10 indicates a structure with a sharper grain size distribution and a more uniform grain size distribution.
However, as mentioned above, when extremely fine WC particles are taken into consideration, the number of fine WC particles is large, so that the WC particles of the target size of 1.0 μm to 2.0 μm cannot be accurately evaluated, and the uniformity of the structure cannot be accurately evaluated by D90/D10. Therefore, it was confirmed that the uniformity of the structure can be accurately evaluated by evaluating the ratio of D10 to D90 for WC particles with a circle-equivalent diameter of 0.4 μm or more, without considering the extremely fine WC particles with a circle-equivalent diameter of less than 0.4 μm that are uniformly dispersed in the structure. Then, it was found that the effect of suppressing the occurrence of chipping can be fully exhibited in high-speed cutting of mild steel by setting the average diameter of WC particles with a circle-equivalent diameter of 0.4 μm or more to 1.0 μm to 2.0 μm, and specifying D90/D10, which is the ratio of the diameter D90 at a cumulative value of 90% of the area ratio in the particle size distribution of the average diameter, to the diameter D10 at a cumulative value of 10% of the area ratio, to less than 3.2.
It is preferable that D90/D10 is 3.0 or less, and it is further preferable that D90/D10 is 2.8 or less.
＜ＷＣ粗大粒子、凝集体（マクロ欠陥）＞
上記では、円相当径が１０μｍを超えるＷＣ粒子やＷＣ凝集体が生成しない場合について説明を行ったが、組織の一部に円相当径が１０μｍを超えるＷＣ粒子またはＷＣ凝集体、さらには、円相当径が３０μｍを超えるＷＣ粒子またはＷＣ凝集体（マクロ欠陥）を生じる場合もあるので、以下では、これらの粗大ＷＣ粒子やＷＣ凝集体が生じた場合における平均粒径の測定法について説明する。
特にマクロ欠陥が多くなるとチッピングが発生し易くなるため、円相当径が３０μｍを超えるＷＣ粒子またはＷＣ凝集体については、光学顕微鏡による組織観察において、３５００００μｍ２（５００μｍ×７００μｍ）の範囲で８個以下と規定することが好ましく、さらには、５個以下、円相当径が１０μｍを超えるＷＣ粒子またはＷＣ凝集体では、８個以下とすることが好ましい。
かかる条件を満たした上で、マクロ欠陥、および、円相当径が１０μｍを超えるＷＣ粒子およびＷＣ凝集体のない平均的な組織を有する場所を選択して平均粒径を測定する。
具体的には、試料を鏡面加工して、マクロ欠陥、および、円相当径が１０μｍを超えるＷＣ粒子およびＷＣ凝集体のない１８００μｍ２（縦６０μｍ×横３０μｍ）の範囲にある、円相当の粒径が０．４μｍ以上のＷＣ粒子の円相当の平均粒径を求めることで、ＷＣ粒子の平均粒径を精度高く評価することができる。
<Coarse WC particles and aggregates (macro defects)>
The above describes the case where WC particles or WC aggregates with an equivalent circle diameter exceeding 10 μm are not generated. However, there are also cases where WC particles or WC aggregates with an equivalent circle diameter exceeding 10 μm, and even WC particles or WC aggregates with an equivalent circle diameter exceeding 30 μm (macrodefects) are generated in part of the structure. Therefore, below, a method for measuring the average grain size when these coarse WC particles or WC aggregates are generated will be described.
In particular, since chipping is more likely to occur when there are many macro defects, it is preferable to specify that for WC grains or WC aggregates with an equivalent circle diameter exceeding 30 μm, the number be 8 or less in an area of 350,000 μm (500 μm × 700 μm) when observed by optical microscope structure, and furthermore, that the number be 5 or less, and that for WC grains or WC aggregates with an equivalent circle diameter exceeding 10 μm, the number be 8 or less.
With these conditions satisfied, a location having an average structure free of macro defects, WC grains with an equivalent circle diameter exceeding 10 μm, and WC aggregates is selected to measure the average grain size.
Specifically, the sample is mirror-finished and the average circular grain size of WC grains with a circular grain size of 0.4 μm or more within an area of 1,800 μm2 (60 μm long × 30 μm wide) that is free of macro defects, WC grains with a circular equivalent diameter exceeding 10 μm, and WC agglomerates can be determined, thereby enabling the average grain size of WC grains to be evaluated with high accuracy.
＜Ｔａ相の組織（ｄ９０／ｄ１０）＞
本発明において、組織中に分散するＴａを主成分とする相は、光学顕微鏡観察により確認することができる。Ｔａを主成分とする相はＴａに次いでＷを多く含有しており、主に炭化物や炭窒化物として存在する。組織中に分散するＴａを主成分とする相の平均粒径が小さすぎると超硬合金の耐熱性が低下し、他方、大きすぎると靭性が低下する。
そのため、組織中に分散するＴａを主成分とする相は、円相当の平均粒径を１．０μｍ以上３．０μｍとすることが好ましい。
Ｔａを主成分とする相は、金属元素としてＴａを６０質量％以上で含有し、Ｗは１～３０質量％で含有する。また、Ｔａを主成分とする相の粒度分布において、面積比の積算値が９０％における粒径をｄ９０、面積比の積算値が１０％における粒径をｄ１０とした場合、ｄ９０／ｄ１０は６．０未満であることが好ましい。更には、ｄ９０／ｄ１０は５．０以下であることが好ましい。
<Ta phase structure (d90/d10)>
In the present invention, the phase mainly composed of Ta dispersed in the structure can be confirmed by optical microscope observation. The phase mainly composed of Ta contains W in the second largest amount after Ta, and exists mainly as carbides and carbonitrides. If the average grain size of the phase mainly composed of Ta dispersed in the structure is too small, the heat resistance of the cemented carbide is reduced, whereas if it is too large, the toughness is reduced.
Therefore, it is preferable that the phase containing Ta as a main component dispersed in the structure has an average circle-equivalent grain size of 1.0 μm to 3.0 μm.
The phase mainly composed of Ta contains 60 mass% or more of Ta as a metal element and 1 to 30 mass% of W. In addition, in the particle size distribution of the phase mainly composed of Ta, when the particle size at which the integrated value of the area ratio is 90% is d90 and the particle size at which the integrated value of the area ratio is 10% is d10, it is preferable that d90/d10 is less than 6.0. Furthermore, it is preferable that d90/d10 is 5.0 or less.
［３］ＷＣ基超硬合金を基材とする被覆切削工具
＜硬質皮膜層の形成＞
上述したＷＣ基超硬合金を基材とする切削工具に、物理蒸着法や化学蒸着法を用いて硬質皮膜を被覆することにより、さらに耐久性にすぐれた被覆切削工具を得ることができる。
軟鋼の高速加工に適用する被覆切削工具において、硬質皮膜としてＴｉＣＮ皮膜を少なくとも含み、ＴｉＣＮ皮膜を柱状組織からなり柱状粒子の表面側における平均幅を１μｍ以下、ＴｉＣＮ皮膜の膜厚を最大厚とすることが好ましい。特に、微粒組織からなるＴｉＣＮ皮膜を最大厚とすることにより、皮膜破壊が抑制され易くなる。
また、ＴｉＣＮ皮膜の効果を発揮するためには、膜厚は５．０μｍ以上であることが好ましく、他方、膜厚が厚くなり過ぎると皮膜剥離が発生し易くなるので、８．０μｍ以下であることが好ましい。
また、ＴｉＣＮ皮膜の上層には耐熱性と耐摩耗性に優れるＡｌ２Ｏ３皮膜を設けることが好ましく、その膜厚は１．０μｍ以上４．０μｍ以下であることが好ましい。
かかる皮膜構造を適用した本発明の被覆切削工具をＨＲＣ４０以下の軟鋼のミーリング加工に適用することで、特に優れた耐久性を発揮できるため好ましく、更には、切削速度２００ｍ／ｍｉｎで使用することが好ましい。
[3] Coated cutting tool using WC-based cemented carbide as a substrate <Formation of hard coating layer>
By coating a cutting tool having the above-mentioned WC-based cemented carbide as a substrate with a hard film by physical vapor deposition or chemical vapor deposition, a coated cutting tool having even greater durability can be obtained.
In a coated cutting tool applied to high-speed machining of mild steel, it is preferable that the hard coating contains at least a TiCN coating, the TiCN coating has a columnar structure, the average width of the columnar grains on the surface side is 1 μm or less, and the film thickness of the TiCN coating is a maximum thickness. In particular, by making the TiCN coating having a fine grain structure the maximum thickness, it becomes easier to suppress the coating destruction.
In order to obtain the desired effect of the TiCN film, the film thickness is preferably 5.0 μm or more. On the other hand, if the film thickness is too large, peeling of the film is likely to occur, so the film thickness is preferably 8.0 μm or less.
In addition, it is preferable to provide an Al 2 O 3 film, which has excellent heat resistance and wear resistance, on the upper layer of the TiCN film, and the film thickness thereof is preferably 1.0 μm or more and 4.0 μm or less.
The coated cutting tool of the present invention having such a coating structure is preferably used for milling mild steel of HRC 40 or less, since it exhibits particularly excellent durability, and furthermore, it is preferably used at a cutting speed of 200 m/min.
［４］ＷＣ基超硬合金の製造方法
以下に、本発明に係るミクロ組織を有するＷＣ基超硬合金の製造方法の一例を示すが、本発明の製造方法は以下の製造方法に限定されるものはない。
＜原料粉の混合工程＞
ＷＣ原料粉末の過粉砕を抑制することが有効であるため、原料粉の混合工程では、まず、ＷＣ原料粉末以外の原料粉末をまとめて混合した後、ＷＣ原料粉末を入れて混合することが好ましい。
混合条件の一例として、アトライターを用いた場合、ＷＣ原料粉末の混合は、０．５～５時間であることが好ましい。ＷＣ原料粉末以外の原料粉末の混合は、ＷＣ原料粉末の混合時間の２～５倍であることが好ましい。また、組織を均一にするとともに過粉砕を抑制するために、アトライターの回転数は８０～２００ｒｐｍが好ましい。
また、使用するＷＣ原料粉末の製造時の炭化温度が低く、微粒粉末が凝集して形成されたものを使用すると、混合工程においてＷＣ粒子が過粉砕されて組織が不均一になるため、使用するＷＣ原料粉末は、１９００℃～２２００℃で炭化処理された高温炭化原料が好ましい。
他方、原料粉末の製造時の炭化温度が高く、微粒粉末の凝集が少ないＷＣ原料粉末であっても、平均粒径が５μｍ以上になると、粉砕によって粒度分布が広がり組織が不均一になるため、その場合は、ＷＣ原料粉末はフィッシャー法で測定した平均粒径が２．０μｍ以上４．０μｍ以下で、微粒粉末の凝集が少ない粉末を用いることが好ましい。
＜焼結体の製造工程＞
焼結工程では、焼結温度を１３５０℃以上１４５０℃以下の範囲で１時間程度保持することにより、すぐれた特性を有する、ＷＣ基超硬合金を得ることができる。
[4] Manufacturing Method of WC-Based Cemented Carbide Hereinafter, an example of a manufacturing method of a WC-based cemented carbide having a microstructure according to the present invention will be described, but the manufacturing method of the present invention is not limited to the manufacturing method described below.
<Raw material powder mixing process>
Since it is effective to prevent the WC raw material powder from being excessively pulverized, in the raw material powder mixing step, it is preferable to first mix all the raw material powders other than the WC raw material powder together, and then add and mix the WC raw material powder.
As an example of mixing conditions, when an attritor is used, the mixing time of the WC raw material powder is preferably 0.5 to 5 hours. The mixing time of raw material powders other than the WC raw material powder is preferably 2 to 5 times the mixing time of the WC raw material powder. In order to homogenize the structure and prevent excessive pulverization, the rotation speed of the attritor is preferably 80 to 200 rpm.
In addition, if the carbonization temperature during production of the WC raw material powder used is low and the powder is formed by agglomeration of fine powder, the WC particles will be over-pulverized in the mixing process, resulting in a non-uniform structure. Therefore, it is preferable that the WC raw material powder used be a high-temperature carbonized raw material that has been carbonized at 1900°C to 2200°C.
On the other hand, even if the carbonization temperature during production of the raw material powder is high and the fine powder has little agglomeration, if the average particle size is 5 μm or more, the particle size distribution will widen due to grinding and the structure will become non-uniform. In that case, it is preferable to use a WC raw material powder having an average particle size of 2.0 μm or more and 4.0 μm or less as measured by the Fischer method and having little agglomeration of the fine powder.
<Manufacturing process of sintered body>
In the sintering step, the sintering temperature is maintained within the range of 1350° C. to 1450° C. for about one hour, whereby a WC-based cemented carbide having excellent properties can be obtained.
以下では、本発明を実施例により詳細に説明するが、本発明は下記の実施例により限定されるものではない。 The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples.
実施例１では、ＷＣ基超硬合金基材の具体的な製造方法を示すとともに、得られたＷＣ基超硬合金基材について、成分組成と組織および物性値の関係を示す。
各試料毎に、使用するＷＣ原料粉末の平均粒径、混合方法および各原料粉末の混合比率を変更し、本発明例および比較例となるＷＣ基超硬合金基材を作製した。（表１、表２を参照。）
まず、本発明例１、２、４、５では、ＷＣ原料粉末としては、２０００℃程度の高温にて炭化処理された、微粒粉末の凝集が少ないＷＣ原料粉末を原則として用い、また、本発明例３では、炭化温度が２０００℃未満であるが、凝集が少なく平均粒径が大きいＷＣ原料粉末を使用した。
次に、本発明例１～５では、ＷＣ粉末（平均粒径２．５～８．６μｍ）、Ｃｏ粉末（平均粒径１．２μｍ）、Ｃｒ３Ｃ２粉末（平均粒径が１．０μｍ）、ＴａＣ粉末（平均粒径が１．５μｍ）およびカーボン粉末を準備し、これら全原料粉末の総質量に対し２質量％のパラフィンワックスおよびエチルアルコール（水分含有量１０％未満）と、ＷＣ粉末を除く、他の原料粉末をすべて小型アトライターに装入し、回転数を１９２ｒｐｍとして、４時間混合した後、前記ＷＣ粉末を装入し、さらに１時間混合し、ＷＣ混合スラリーを作製した。
なお、粉末の平均粒径はフィッシャー法で測定した代表値である。
その後、前記ＷＣ混合スラリーを静置乾燥機にて乾燥しパン造粒器にて造粒粉末を得た。得られた造粒粉末により、ミーリング加工用インサート（ＷＤＮＴ１４０５２０－Ｂ、ブレーカを配した形状）の基材用の成形体を成形した。そして、焼結温度１４００℃にて６０分間加熱保持後、焼結温度から窒素ガスにより強制冷却して、中炭素組成のＷＣ基超硬合金からなる焼結体を作製した。
これに対し、比較例１は、ＷＣ原料粉末としては、２０００℃程度の高温にて炭化処理された、微粒粉末の凝集が少ないＷＣ原料粉末を用いるものの、Ｔａ含有粉を含むものではなく、また、比較例２～３は、ＷＣ原料粉末を高温にて炭化処理を行うものの、粒径の大きいものを用い、本発明例と同様の製造方法を用いて、ＷＣ基超硬合金からなる焼結体を作製した。
また、比較例４については、ＷＣ原料粉末を高温にて炭化処理を行うものの、粒径の大きいものを用い、ＷＣ粉末を含めて全原料粉末を同時に装入し、３時間混合したＷＣ混合スラリーを用いて、ＷＣ基超硬合金からなる焼結体を作製した。
また、比較例５は、ＷＣ原料粉末としては、発明例２などと同じく、平均粒径２．５μｍのＷＣ原料粉末を用いるものの、本発明例１～５のように、ＷＣ原料粉末以外の原料を長時間混合後、ＷＣ原料粉末を投入し、さらに混合を行うものではなく、比較例４と同じく、ＷＣ粉末を含めて全原料粉末を同時に投入し、数時間の混合後、ＷＣ基超硬合金からなる焼結体を作製するものとした。
表１に、各試料の製造に用いたＷＣ原料粉末とその混合方法を示す。
In Example 1, a specific method for producing a WC-based cemented carbide substrate is shown, and the relationship between the component composition, structure, and physical properties of the obtained WC-based cemented carbide substrate is shown.
For each sample, the average particle size of the WC raw material powder, the mixing method, and the mixing ratio of each raw material powder were changed to prepare WC-based cemented carbide substrates as examples of the present invention and comparative examples (see Tables 1 and 2).
First, in Examples 1, 2, 4, and 5 of the present invention, the WC raw material powder used was, as a rule, a WC raw material powder having little agglomeration of fine powder that had been carbonized at a high temperature of about 2000°C. In Example 3 of the present invention, a WC raw material powder having little agglomeration and a large average particle size was used, although the carbonization temperature was less than 2000°C.
Next, in Examples 1 to 5 of the present invention, WC powder (average particle size 2.5 to 8.6 μm), Co powder (average particle size 1.2 μm), Cr 3 C 2 powder (average particle size 1.0 μm), TaC powder (average particle size 1.5 μm) and carbon powder were prepared, and 2 mass% of paraffin wax and ethyl alcohol (water content less than 10%) based on the total mass of all these raw material powders, and all other raw material powders except for WC powder were charged into a small attritor, and mixed for 4 hours at a rotation speed of 192 rpm, and then the WC powder was charged and mixed for another 1 hour to prepare a WC mixed slurry.
The average particle size of the powder is a representative value measured by the Fischer method.
The WC mixed slurry was then dried in a static dryer and granulated in a pan granulator. The granulated powder was used to mold a molded body for the base material of a milling insert (WDNT140520-B, with a breaker). The molded body was then heated and held at a sintering temperature of 1400°C for 60 minutes, and then forcibly cooled from the sintering temperature with nitrogen gas to produce a sintered body made of a WC-based cemented carbide with a medium carbon composition.
In contrast, in Comparative Example 1, the WC raw material powder used was a WC raw material powder that had been carbonized at a high temperature of about 2000°C and had little aggregation of fine powder, but did not contain Ta-containing powder. In Comparative Examples 2 and 3, the WC raw material powder was carbonized at a high temperature, but one with a large particle size was used, and a sintered body made of a WC-based cemented carbide was produced using the same manufacturing method as in the present invention.
In addition, in Comparative Example 4, the WC raw material powder was carbonized at high temperature, but a powder with a large particle size was used, and all the raw material powders including the WC powder were charged at the same time and mixed for 3 hours to produce a sintered body made of a WC-based cemented carbide using the WC mixed slurry.
In Comparative Example 5, like Invention Example 2, a WC raw material powder having an average particle size of 2.5 μm was used as the WC raw material powder. However, unlike Invention Examples 1 to 5, in which raw materials other than the WC raw material powder were mixed for a long period of time, the WC raw material powder was added, and further mixing was not carried out. Instead, like Comparative Example 4, all raw material powders including the WC powder were added at the same time, and after mixing for several hours, a sintered body made of a WC-based cemented carbide was produced.
Table 1 shows the WC raw material powders used in the production of each sample and the mixing method thereof.
次に、作製された焼結体に鏡面加工を施すことにより得られた試料について、ＥＰＭＡ（ＪＥＯＬ製 ＪＸＡ－８５３０Ｆ）を用いて組織観察を行った。そして、ＥＢＳＤ（Ｅｌｅｃｔｒｏｎ Ｂａｃｋ Ｓｃａｔｔｅｒ Ｄｉｆｆｒａｃｔｉｏｎ：電子後方散乱回折）法を用いて、３０μｍ×６０μｍの範囲にある個々のＷＣ粒子の断面積を測定し、その値から円相当の粒径を求めた。これを３か所において測定を行い、円相当の粒径が０．４μｍ以上であるＷＣ粒子について、その平均粒径と、その平均粒径の粒度分布において面積比の積算値が９０％となる粒径Ｄ９０と、前記面積比の積算値が１０％となる粒径Ｄ１０と、前記粒径Ｄ９０に対する前記粒径Ｄ１０の比であるＤ９０／Ｄ１０とを求め、表２として示す。
なお、ノイズを含むため計算には含めなかった円相当径が０．４μｍ未満の粒子が全体に占める面積率は１～２％程度であった。
次いで、表３には、作製したＷＣ超硬合金の物性値（保磁力（Ｈｃ）、飽和磁化（４πσ）、硬度（ＨＲＡ））を示す。
なお、従来例１、２は軟鋼のミーリング加工に適用されている同形状の市販されているインサートである。
Next, the sintered body was mirror-finished to obtain a sample, and the structure was observed using an EPMA (JXA-8530F manufactured by JEOL). Then, the cross-sectional area of each WC grain in the range of 30 μm × 60 μm was measured using the EBSD (Electron Back Scatter Diffraction) method, and the circle-equivalent grain size was calculated from the value. This was measured at three locations, and for WC grains with a circle-equivalent grain size of 0.4 μm or more, the average grain size, the grain size D90 at which the integrated value of the area ratio in the grain size distribution of the average grain size is 90%, the grain size D10 at which the integrated value of the area ratio is 10%, and the ratio D90/D10 of the grain size D10 to the grain size D90 were calculated, and are shown in Table 2.
The area ratio of particles with a circular equivalent diameter of less than 0.4 μm, which were not included in the calculation due to noise, was about 1 to 2%.
Table 3 shows the physical properties (coercive force (Hc), saturation magnetization (4πσ), hardness (HRA)) of the produced WC cemented carbide.
Conventional examples 1 and 2 are commercially available inserts of the same shape that are used in milling of mild steel.
表２に明らかなように、所定の成分組成を有し、表１に記載された製造条件により製造された本発明例１～５は、ＷＣ相の組織において、所望の平均粒径およびシャープで均一な粒度分布（Ｄ９０／Ｄ１０値）を有していた。表３に示すように、本発明例１～５は、硬度は９０．０～９１．０ＨＲＡ、保磁力は１８０～２２０（Ｏｅ）、飽和磁化は１１～１２の範囲にあった。
本発明例１～５では、組織中に円相当の平均粒径が１．０μｍ以上３．０μｍ以下であるＴａを主成分とする相が分散し、前記Ｔａを主成分とする相の組成は、Ｔａが６０～８０質量％、Ｗが１０～３０質量％の炭化物であった。また、本発明例１において、Ｔａを主成分とする相の粒度分布において、面積比の積算値が９０％となる粒径をｄ９０、面積比の積算値が１０％となる粒径をｄ１０とした場合、ｄ９０は６．０～８．０μｍ、ｄ１０は１．５～２．０μｍ、ｄ９０／ｄ１０は４．６～５．２であった。
本発明例１、２、４、５は、高温炭化処理された平均粒径が２～３μｍ程度のＷＣ原料粉末を用いて過粉砕しないよう混合したことにより、均一な組織が得られたと推定される。また、本発明例３は高温炭化処理されたＷＣ原料粉末を使用していないが、平均粒径が大きい原料粉末を使用して過粉砕しないよう混合したことにより、他の本発明例と同様に均一な組織が得られたと推定される。
これに対し、高温炭化処理された平均粒径が５．０～６．０μｍ程度のＷＣ原料粉末を用いた比較例２、３では、ＷＣ相の組織において、Ｄ９０／Ｄ１０値が高く、粒度分布が広い組織となっていたため、やや硬度値が低かった。また比較例４、５では、ＷＣ原料粉末の過粉砕が進んだため、平均粒径が小さくなる一方、平均粒径が１０．０μｍを超える粗大な欠陥も多く発生したため、硬度および磁気特性において、安定した特性が得られなかった。
図１および図２として、本発明例１および比較例３の電子顕微鏡による組織観察写真を示す。図１より、本発明例１の組織が均一な粒径を有するＷＣ粒子からなる均粒組織であることが確認できる。他方、図２より、比較例３の組織は多くの微粒なＷＣ粒子中に粗大粒子が存在する混粒組織であることが確認できる。
As is clear from Table 2, Examples 1 to 5 of the present invention, which had the prescribed component composition and were produced under the production conditions shown in Table 1, had the desired average grain size and a sharp and uniform grain size distribution (D90/D10 value) in the WC phase structure. As shown in Table 3, Examples 1 to 5 of the present invention had a hardness in the range of 90.0 to 91.0 HRA, a coercive force in the range of 180 to 220 (Oe), and a saturation magnetization in the range of 11 to 12.
In Inventive Examples 1 to 5, a phase mainly composed of Ta having an average circle-equivalent grain size of 1.0 μm or more and 3.0 μm or less was dispersed in the structure, and the composition of the phase mainly composed of Ta was a carbide of 60 to 80 mass % Ta and 10 to 30 mass % W. In Inventive Example 1, when the grain size distribution of the phase mainly composed of Ta was such that the grain size at which the integrated value of the area ratio was 90% was d90 and the grain size at which the integrated value of the area ratio was 10% was d10, d90 was 6.0 to 8.0 μm, d10 was 1.5 to 2.0 μm, and d90/d10 was 4.6 to 5.2.
It is presumed that in invention examples 1, 2, 4, and 5, a uniform structure was obtained by using WC raw material powder with an average particle size of about 2 to 3 μm that had been subjected to high-temperature carbonization and mixing without excessive pulverization. Also, in invention example 3, although WC raw material powder that had been subjected to high-temperature carbonization was used, raw material powder with a large average particle size was used and mixed without excessive pulverization, and it is presumed that a uniform structure was obtained like the other invention examples.
In contrast, in Comparative Examples 2 and 3, which used WC raw material powder with an average particle size of about 5.0 to 6.0 μm that had been subjected to high-temperature carbonization, the WC phase structure had a high D90/D10 value and a wide particle size distribution, so the hardness value was somewhat low. In Comparative Examples 4 and 5, the WC raw material powder was over-pulverized, so the average particle size became small, but many coarse defects with an average particle size exceeding 10.0 μm occurred, so stable characteristics could not be obtained in terms of hardness and magnetic properties.
1 and 2 show electron microscope photographs of the structure of Example 1 of the present invention and Comparative Example 3. From Fig. 1, it can be seen that the structure of Example 1 of the present invention is a homogeneous grain structure made up of WC grains having a uniform grain size. On the other hand, from Fig. 2, it can be seen that the structure of Comparative Example 3 is a mixed grain structure in which coarse grains are present among many fine WC grains.
実施例２では本発明例１～３に硬質皮膜を形成した本発明例工具１～３、および、比較例２～４、および、従来例１、２に本発明例工具１～３と同じ硬質皮膜を形成した比較例工具２～４、および、従来例工具１、２について、軟鋼の高速加工における切削評価試験を実施した。
切削試験用のインサートには化学蒸着法により硬質皮膜を被覆した。
まず、柱状組織からなる柱状粒子の表面側に、平均幅が０．５μｍ～０．７μｍのＴｉＣＮを６．０μｍ被覆し、その上に３．０μｍのＡｌ２Ｏ３を被覆した。硬質皮膜の被覆後は、ウエットブラスト処理を行った。
なお、比較例工具２～４、および、従来例工具１、２は、作製した本発明例工具１～３と同様の皮膜構造であり、残留圧縮応力も同程度であることを確認した。
下記に切削条件を示し、切削試験の結果を表４に示す。なお、切削試験用インサートの工具寿命は逃げ面の最大摩耗幅が０．３ｍｍを超えたとき、もしくは、チッピング(欠損)が発生し、その幅が０．３ｍｍを超えたときまでの加工時間（ｍｉｎ）とした。
（条件）乾式加工
・工具：高速高送り用工具
・カッター型番：ＡＳＲＴ５０６３Ｒ－４
・インサート型番：ＷＤＮＴ１４０５２０－Ｂ
・刃数：１
・被削材：ＳＣＭ４４０（３２ＨＲＣ）
・切削方法：乾式のミーリング加工
・切り込み：軸方向、１．０ｍｍ、径方向、４３ｍｍ
・切削速度：２５０ｍ／ｍｉｎ
・一刃送り量：１．５ｍｍ／刃
・突出し量：１００ｍｍ
In Example 2, cutting evaluation tests were conducted in high-speed machining of mild steel for Inventive Example Tools 1 to 3, which were inventive example tools 1 to 3 with hard coatings formed thereon, Comparative Examples 2 to 4, and Conventional Example Tools 1 and 2, which were in comparative example tools 2 to 4 with the same hard coatings formed thereon as Inventive Example Tools 1 to 3, and Conventional Example Tools 1 and 2.
The inserts for the cutting tests were hard-coated by chemical vapor deposition.
First, the surface side of the columnar grains having a columnar structure was coated with 6.0 μm of TiCN having an average width of 0.5 μm to 0.7 μm, and then coated with 3.0 μm of Al 2 O 3. After coating with the hard film, wet blasting treatment was performed.
It was confirmed that the comparative example tools 2 to 4 and the conventional example tools 1 and 2 had the same coating structure as the inventive example tools 1 to 3 and had the same degree of residual compressive stress.
The cutting conditions are shown below, and the results of the cutting test are shown in Table 4. The tool life of the insert for the cutting test was defined as the machining time (min) until the maximum wear width of the flank exceeded 0.3 mm, or until chipping (fracture) occurred and its width exceeded 0.3 mm.
(Condition) Dry machining Tool: High speed, high feed tool Cutter model number: ASRT5063R-4
・Insert model number: WDNT140520-B
Number of teeth: 1
・Cutting material: SCM440 (32HRC)
Cutting method: dry milling Cutting depth: axial direction, 1.0 mm, radial direction, 43 mm
Cutting speed: 250 m/min
・Feed per blade: 1.5 mm/blade ・Protrusion: 100 mm
本発明例工具１～３は、安定した摩耗形態を示し工具寿命が最も長くなった。
比較例工具２、３は、Ｄ９０／Ｄ１０が大きいため、チッピングが発生して早期に工具寿命に達した。
比較例工具４は、平均粒径が小さく、チッピングが発生して早期に工具寿命に達した。
従来例工具１は、Ｃｏの含有量が多く、かつ、Ｔａを含有していないため、組織中にＴａを主成分とする相が分散しておらず、本発明例に比べて耐熱性が低く工具寿命が短くなった。
従来例工具２は、Ｃｏの含有量が多く、塑性変形を起こして早期に工具寿命に達した。
The inventive example tools 1 to 3 exhibited a stable wear pattern and had the longest tool life.
Comparative Example Tools 2 and 3 had a large D90/D10 ratio, and therefore chipping occurred, causing the tool to reach the end of its life early.
Comparative Example Tool 4 had a small average grain size, and chipping occurred, causing the tool to reach the end of its life early.
Conventional example tool 1 had a high Co content and did not contain Ta, so a phase mainly composed of Ta was not dispersed in the structure, and the heat resistance was lower and the tool life was shorter than that of the inventive example.
Conventional tool 2 had a high Co content and underwent plastic deformation, reaching the end of its tool life early.
実施例３では本発明例２、４、５に硬質皮膜を形成した本発明例工具２、４、５、および、比較例１および従来例１に本発明例工具２、４、５と同じ硬質皮膜を形成した比較例工具１および従来例工具１について、実施例２より、突き出しの長い条件での軟鋼の高速加工における切削評価試験を実施した。
切削試験用のインサートは化学蒸着法により実施例２と同じ硬質皮膜を被覆した。まず、柱状組織からなり柱状粒子の表面側における平均幅が０．５μｍ～０．７μｍのＴｉＣＮを６．０μｍ被覆し、その上に３．０μｍのＡｌ２Ｏ３を被覆した。硬質皮膜の被覆後は、ウエットブラスト処理を行った。
下記に切削条件を示し、切削試験の結果を表５に示す。なお、切削試験用インサートの工具寿命は逃げ面の最大摩耗幅が０．３ｍｍを超えたとき、もしくは、チッピング(欠損)が発生し、その幅が０．３ｍｍを超えたときまでの加工時間（ｍｉｎ）とした。
（条件）乾式加工
・工具：高速高送り用工具
・カッター型番：ＡＳＲＴ５０６３Ｒ－４
・インサート型番：ＷＤＮＴ１４０５２０－Ｂ
・刃数：１
・被削材：ＳＣＭ４４０（３２ＨＲＣ）
・切削方法：乾式のミーリング加工
・切り込み：軸方向、１．０ｍｍ、径方向、４３ｍｍ
・切削速度：２５０ｍ／ｍｉｎ
・一刃送り量：１．５ｍｍ／刃
・突出し量：２００ｍｍ
In Example 3, cutting evaluation tests were conducted in high-speed machining of mild steel under longer overhang conditions than in Example 2 for Inventive Example Tools 2, 4, and 5, which were formed with hard coatings as Inventive Example Tools 2, 4, and 5, and for Comparative Example Tool 1 and Conventional Example Tool 1, which were formed with the same hard coatings as Inventive Example Tools 2, 4, and 5, as Comparative Example 1 and Conventional Example Tool 1.
The inserts for the cutting test were coated by chemical vapor deposition with the same hard coating as in Example 2. First, TiCN having a columnar structure and an average width of 0.5 μm to 0.7 μm on the surface side of the columnar grains was coated with a thickness of 6.0 μm, and then Al 2 O 3 was coated with a thickness of 3.0 μm. After coating with the hard coating, wet blasting was performed.
The cutting conditions are shown below, and the results of the cutting test are shown in Table 5. The tool life of the insert for the cutting test was defined as the machining time (min) until the maximum wear width of the flank exceeded 0.3 mm, or until chipping (fracture) occurred and its width exceeded 0.3 mm.
(Condition) Dry machining Tool: High speed, high feed tool Cutter model number: ASRT5063R-4
・Insert model number: WDNT140520-B
Number of teeth: 1
・Cutting material: SCM440 (32HRC)
Cutting method: dry milling Cutting depth: axial direction, 1.0 mm, radial direction, 43 mm
Cutting speed: 250 m/min
・Feed per blade: 1.5 mm/blade ・Protrusion: 200 mm
本発明例工具２、４、５は、いずれもすぐれた工具寿命を示した。特に、Ｔａの含有量が少ない本発明例工具５は工具損傷が安定する傾向にあった。
比較例１工具は、Ｔａを含有していないため、本発明例工具２、４、５に比べると工具寿命が低下した。
従来例１工具は、Ｃｏの含有量が多く、早期に工具寿命に到達した。
All of the invention tools 2, 4 and 5 exhibited excellent tool life. In particular, the invention tool 5, which had a low Ta content, tended to have stable tool damage.
The tool of Comparative Example 1 did not contain Ta, and therefore had a shorter tool life than the tools of Inventive Examples 2, 4 and 5.
The tool of Conventional Example 1 had a high Co content and reached the end of its tool life early.
本発明に係るＷＣ基超硬合金およびこれを基材として用いた被覆切削工具は、鋼等の切削加工、特に、軟鋼の高速加工を行った際に、耐チッピング性および耐塑性変形性にすぐれるため、きわめて有用である。
The WC-based cemented carbide according to the present invention and a coated cutting tool using the same as a substrate are extremely useful because they have excellent chipping resistance and plastic deformation resistance when cutting steel and the like, particularly when cutting mild steel at high speed.
Claims (4)
円相当の粒径が０．４μｍ以上であるＷＣ粒子の平均粒径は、１．０μｍ以上２．０μｍ以下であり、
前記平均粒径の粒度分布において面積比の積算値が９０％となる粒径Ｄ９０と面積比の積算値が１０％となる粒径Ｄ１０との比である、Ｄ９０／Ｄ１０が３．２未満であり、
組織中にＴａを主成分とする相が分散していることを特徴とするＷＣ基超硬合金。 A WC-based cemented carbide containing, by mass%, as metallic elements, Co of 8.5% or more and 9.5% or less, Cr of 0.3% or more and 1.0% or less, and Ta of 1.0% or more and 3.0% or less, with the balance being WC, non-metallic elements present as solid solutions or compounds with the metallic elements, and unavoidable impurities,
The average grain size of WC grains having a circle-equivalent grain size of 0.4 μm or more is 1.0 μm or more and 2.0 μm or less,
D90/D10, which is the ratio of a particle size D90 at which the integrated value of the area ratio in the particle size distribution of the average particle size is 90% to a particle size D10 at which the integrated value of the area ratio is 10%, is less than 3.2;
A WC-based cemented carbide characterized in that a phase mainly composed of Ta is dispersed in the structure.
The coated cutting tool according to claim 3, wherein the hard coating layer has an Al2O3 coating layer on top of the TiCN coating layer.
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