JP2004346370A

JP2004346370A - Cemented carbide

Info

Publication number: JP2004346370A
Application number: JP2003144197A
Authority: JP
Inventors: Yutaka Kubo; 裕久保
Original assignee: Hitachi Tool Engineering Ltd
Current assignee: Moldino Tool Engineering Ltd
Priority date: 2003-05-22
Filing date: 2003-05-22
Publication date: 2004-12-09
Anticipated expiration: 2023-05-22
Also published as: JP4112431B2

Abstract

<P>PROBLEM TO BE SOLVED: To further improve the deflective strength of superfine cemented carbide for coping with the fine diameter of a drill or the like as its main application. <P>SOLUTION: In the superfine cemented carbide in which the mean grain size of WC is ≤0.8 μm, the mean grain size of bonding phase grains is ≤200 μm. By adopting the constitution, the soundness in the grain boundary of the bonding phase is improved, and can be improved to a level free from influence on its deflective strength. Thus, the further improvement of the deflective strength and the reduction of variation are realized, so that the service life of a fine-diameter tool can be improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明が属する技術分野】
本発明は、超硬合金に関し、ＷＣの平均粒径が０．８μｍ以下の靭性の優れた超硬合金に関する。
【０００２】
【従来の技術】
ＷＣの平均粒径が０．８μｍ以下の超硬合金には、粒成長抑制効果を有する成分を添加する技術が、以下の特許文献１、２、３及び非特許文献４に開示されている。
【特許文献１】特開平０４−４６５３８号公報
【特許文献２】特許３０１０８５９号公報
【特許文献３】特開２０００−７１２号公報
【非特許文献４】鈴木、林、福家：粉体及び粉末冶金、９（１９７３）、１８７頁
【０００３】
特許文献１にはＣｒ、Ｖ、Ｔａの３種の添加が開示されている。また、特許文献２、特許文献３には、Ｃｒ、Ｖ添加の３相合金が開示されている。非特許文献４には、鈴木らの検討結果が開示されている。結合相の中に同一の結晶方位をもつ領域（以下、結合相粒と言う。）が存在し、該結合相粒の粒界部は結合相の最終凝固部であるために、不純物が濃縮され、粒界部は凝固収縮により、Ｃｏ量が少なくなりマイクロポアを生じやすいことを非特許文献４は開示している。
【０００４】
【発明が解決しようとする課題】
微粒超硬合金は細径のドリル、エンドミル、ルーターなどの切削工具用の素材、又は打ち抜きパンチ等の工具用材料として用いられるが、近年これらの径がますます小径化する傾向が顕著であり、これら小径工具の耐折損性を向上するためには微粒超硬合金の抗折力を更に高め強靭化することが求められている。微粒超硬合金については抗折力を高めるために、これまで、ＷＣ粒径の微粒化、粒成長抑制成分の選択、量の最適化、結合相量の最適化等がなされてきているが、更なる抗折力向上のためには、これらの適正化だけでは十分とはいえず、なお一層の向上が求められている。
【０００５】
【課題を解決するための手段】
本発明は、ＷＣの平均粒径が０．８μｍ以下である微粒超硬合金において、結合相粒の平均粒径が２００μｍ以下であることを特徴とする超硬合金である。本構成を採用することにより、靭性の優れた超硬合金を得ることができる。また、ＷＣ及び重量％で４０％以下のＣｏを成分とし、残りが粒成長抑制成分及び不可避不純物を含有することが、靭性の優れた超硬合金を得るのに好ましい。
【０００６】
【発明の実施の形態】
本発明者らは、基礎的な検討結果はあるものの、これまで注目されていなかった、結合相粒の平均粒径に着目し、この結合相粒の平均粒径を一定値以下に規定することにより、抗折力を大幅に向上させることが可能であることを見出し、本発明に至った。結合相粒の平均粒径を２００μｍ以下とすることにより、粒界部の不健全性を抗折力に影響しないレベルに健全化させることが可能である。ここで言う粒界部の健全性とは、粒界部分の不純物や粒成長抑制成分の含有量が、結合相粒内部の含有量と同等である状態の場合、健全であると言い、一方、粒界部分の不純物や粒成長抑制成分の含有量が、結合相粒内部の含有量よりも極めて多量である状態の場合、不健全であると言う。
粒成長抑制成分を含む晶出相は結合相粒界部の中でも特に粒界三重点に生じやすい。結合相粒の平均粒径が２００μｍを超えて大きい場合は、抗折力測定時に破壊の起点となり、抗折力の低下を招き、好ましくないため、結合相粒の平均粒径を２００μｍ以下に限定した。結合相粒の平均粒径が２００μｍ以下であることにより、靭性の優れた超硬合金を得ることができた。
【０００７】
ＷＣ及び重量％で４０％以下のＣｏを主成分とし、粒成長抑制成分及び不可避不純物を含有することが、優れた靭性を得るために好ましい。Ｃｏ量を４０％以下とする理由は、４０％を超えるとＣｏが多すぎることにより、超硬合金として必要な硬さがえられなくなるからである。以下に、本発明の超硬合金を実施例により詳細に説明する。
【０００８】
【実施例】
（実施例１）
組成が、Ｃｏ：８ｗｔ％、ＶＣ：０．３ｗｔ％、Ｃｒ_３Ｃ_２：０．７ｗｔ％、ＴａＣ：０．１ｗｔ％、残りＷＣ及び不可避不純物からなる超硬合金において、焼結後の冷却速度を種々変化させることにより、種々の結合相粒の平均粒径を持つ試験片を作製し、それらの抗折力を調査した。結果を表１に示す。
【０００９】
【表１】

【００１０】
結合相粒の平均粒径は、試験片を鏡面ラップ加工したのち、熱触刻法により結合相粒を現出させ、それを倍率が５０倍の写真に撮影し、画像処理により視野内の結合相粒の平均粒径を求めた。この結果より、本発明例１から４の結合相粒の平均粒径が２００μｍ以下の場合に抗折力は４３００ＭＰａ以上を示し、ほぼ一定値であるのに対して、比較例５から７の２００μｍを超える場合は、結合相粒が大きいほど、抗折力は低下することが明らかである。
【００１１】
（実施例２）
平均粒径０．６μｍのＷＣ粉末、平均粒径１．２μｍのＶＣ粉末、平均粒径１．４μｍのＣｒ_３Ｃ_２粉末、平均粒径１．３μｍのＴａＣ粉末、平均粒径０．８μｍのＣｏ粉末を原料粉末とし、これらの粉末を表２に示す組成に配合し、アトライタにてアルコールを溶媒として６時間混合した。
【００１２】
【表２】

【００１３】
混合後乾燥し、この乾燥粉を用いて、焼結後のサイズが４．５×８．５×２５ｍｍとしたＪＩＳ試験片をプレス成形した。得られた成形体を１３５０〜１４５０℃の所定の焼結温度にて、最初に６．６５Ｐａの真空度にて３０分間焼結した後、３０分間、４．９ＭＰａのＡｒ雰囲気下でシンターＨＩＰ処理を行った。シンターＨＩＰ後には強制冷却にて、１０〜１５℃／ｍｉｎの速度で冷却した。得られた焼結体を研磨し、熱触刻法にて結合相粒を現出させ、結合相粒の平均粒径を測定した。また各組成条件の試験片を３０本用いて、研削後抗折力試験を行い、抗折力値及びばらつきの評価を行った。これら抗折力測定を行った試験片につき、破壊の起点の調査を行うために、破面近傍の張力面を研磨、熱触刻法にて結合相粒を現出させ、破壊の起点と結合相粒界とが一致するかどうかにつき評価を行った。また比較例として冷却速度を５℃／ｍｉｎとした以外は実施例１と同一の条件で焼結した試験片を準備して同様な評価をした。評価結果を表２に併記する。
【００１４】
表２より、本発明例８から２０の結合相粒の平均粒径が２００μｍ以下の超硬合金は、比較例２１から２３の超硬合金に比べ、３０本の試験片の平均抗折力が高く、抗折力のばらつきを示す平均抗折力の８０％未満の本数も少ない。また、本発明例８から２０は破壊の起点と結合相粒界の一致するものもなく、結合相粒界部の健全性が大きく改善されていることがわかる。一方、比較例２１から２３の超硬合金はいずれも結合相粒の平均粒径が２００μｍを超えており、平均抗折力が低くばらつきも大きい。また破壊の起点と結合相粒界の一致するものも多く、明らかに結合相粒界の健全性が確保できていない。
【００１５】
（実施例３）
実施例２で用いた乾燥粉に溶剤及びワックスを添加して混練し、焼結後のサイズがφ３．４となるように押出し成形にて丸棒成形体を作製した。脱ワックス処理を行い、実施例２と同じ条件にて焼結を行った。得られた焼結体の結合相粒の平均粒径を実施例２と同様の測定法にて測定し、実施例２の結合相粒の平均粒径と差がないことを確認した。この丸棒素材を加工し、外径がφ０．２ｍｍ〜０．０８ｍｍのプリント基板用ドリルを作製した。
これらのドリルを用いて、表２に示す穴あけ加工条件において、各例とも５本づつ、厚さが１．６ｍｍのガラスエポキシ基板を３枚重ねた基板の穴あけ加工を行い、折損寿命の評価を行ない、平均穴あけ数を求めた。結果を表２に併記する。表２より、本発明例８から２０のドリルは３０００〜４０００穴、加工できたのに対し、比較例２１から２３のドリルは２０００台の穴数であり、折損寿命までの穴あけ数が多いことが明らかである。
【００１６】
【発明の効果】
本発明の超硬合金を適用することによって、結合相粒界部の健全性が向上し、その結果抗折力が高く、抗折力のばらつきも大幅に低減される。本発明の超硬合金を、例えばプリント基板用のドリルとして使用した場合、折損寿命も著しく改善することが明らかであり、本発明は工業上非常に有意義である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a cemented carbide, and more particularly to a cemented carbide excellent in toughness having an average particle diameter of WC of 0.8 μm or less.
[0002]
[Prior art]
Patent Literatures 1, 2, and 3 and Non-Patent Literature 4 disclose techniques for adding a component having an effect of suppressing grain growth to a cemented carbide having an average particle diameter of WC of 0.8 μm or less.
[Patent Document 1] Japanese Patent Application Laid-Open No. 04-46538 [Patent Document 2] Japanese Patent No. 3010859 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-712 [Non-Patent Document 4] Suzuki, Hayashi, Fukuya: Powder and Powder Metallurgy , 9 (1973), p. 187
Patent Literature 1 discloses three types of additions of Cr, V, and Ta. Patent Literature 2 and Patent Literature 3 disclose three-phase alloys to which Cr and V are added. Non-Patent Document 4 discloses the results of a study by Suzuki et al. A region having the same crystal orientation exists in the binder phase (hereinafter, referred to as a binder phase grain), and since the grain boundary portion of the binder phase grain is the final solidified portion of the binder phase, impurities are concentrated. Non-Patent Document 4 discloses that the amount of Co decreases at the grain boundary due to solidification shrinkage, and micropores are easily generated.
[0004]
[Problems to be solved by the invention]
Fine-grain cemented carbide is used as a material for cutting tools such as small-diameter drills, end mills and routers, or as a material for tools such as punching punches. In order to improve the breakage resistance of these small-diameter tools, it is required to further increase the bending strength of the fine-grained cemented carbide and toughen it. For fine-grain cemented carbides, in order to increase the transverse rupture strength, the WC grain size has been reduced, the grain growth inhibiting component is selected, the amount is optimized, and the amount of the binder phase is optimized. In order to further improve the transverse rupture strength, it cannot be said that these optimizations alone are sufficient, and further improvement is required.
[0005]
[Means for Solving the Problems]
The present invention provides a fine-grained cemented carbide having an average particle size of WC of 0.8 μm or less, wherein the average particle size of binder phase particles is 200 μm or less. By employing this configuration, a cemented carbide having excellent toughness can be obtained. Further, it is preferable to obtain a cemented carbide having excellent toughness by using WC and 40% or less by weight of Co as components and the remainder containing a grain growth inhibiting component and unavoidable impurities.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
The present inventors have focused on the average particle size of the binder phase particles, which has not been noticed, although there are basic study results, and defines the average particle size of the binder phase particles to a certain value or less. As a result, it has been found that the transverse rupture strength can be greatly improved, and the present invention has been achieved. By setting the average particle size of the binder phase particles to 200 μm or less, it is possible to reduce the unsoundness of the grain boundary to a level that does not affect the transverse rupture strength. Here, the soundness of the grain boundary portion means that, when the content of the impurities and the grain growth inhibiting component in the grain boundary portion is equivalent to the content inside the binder phase grains, the soundness is defined as sound. When the content of the impurities in the grain boundary portion or the content of the grain growth suppressing component is much larger than the content in the inside of the binder phase grains, it is said that the material is unhealthy.
The crystallized phase containing the grain growth inhibiting component tends to occur particularly at the grain boundary triple point among the binder phase grain boundaries. If the average particle size of the binder phase particles is larger than 200 μm, it becomes a starting point of fracture at the time of the transverse rupture strength measurement, which causes a decrease in the transverse rupture force, which is not preferable. Therefore, the average particle size of the binder phase particles is limited to 200 μm or less. did. When the average particle size of the binder phase particles was 200 μm or less, a cemented carbide having excellent toughness could be obtained.
[0007]
It is preferable to contain WC and 40% by weight or less of Co as a main component and contain a grain growth suppressing component and an unavoidable impurity in order to obtain excellent toughness. The reason for setting the Co content to 40% or less is that if it exceeds 40%, the amount of Co is too large, so that the required hardness as a cemented carbide cannot be obtained. Hereinafter, the cemented carbide of the present invention will be described in detail with reference to examples.
[0008]
【Example】
(Example 1)
_{_{Composition, Co: 8wt%, VC:}} 0.3wt%, Cr 3 C 2: 0.7wt%, TaC: 0.1wt%, the cemented carbide consisting of the remaining WC and unavoidable impurities, cooling rate after sintering The test pieces having various average particle diameters of the binder phase particles were prepared by changing variously, and their transverse rupture strength was investigated. Table 1 shows the results.
[0009]
[Table 1]

[0010]
The average particle size of the binder phase particles can be determined by mirror lapping the test piece, exposing the binder phase particles by hot stamping, taking a 50-times photograph of the binder particles, and combining them in the visual field by image processing. The average grain size of the phase grains was determined. From these results, when the average particle size of the binder phase particles of Examples 1 to 4 of the present invention is 200 μm or less, the transverse rupture force is 4300 MPa or more, which is almost constant, whereas the transverse rupture force of Comparative Examples 5 to 7 is 200 μm. It is clear that, when it exceeds, the larger the binder phase grains, the lower the transverse rupture strength.
[0011]
(Example 2)
WC powder having an average particle size of 0.6 μm, VC powder having an average particle size of 1.2 μm, Cr ₃ C ₂ powder having an average particle size of 1.4 μm, TaC powder having an average particle size of 1.3 μm, and 0.8 μm having an average particle size of 0.8 μm Co powder was used as a raw material powder, and these powders were blended in the composition shown in Table 2 and mixed with an attritor using alcohol as a solvent for 6 hours.
[0012]
[Table 2]

[0013]
After mixing and drying, a JIS test piece having a size after sintering of 4.5 × 8.5 × 25 mm was press-formed using the dried powder. After sintering the obtained molded body at a predetermined sintering temperature of 1350 to 1450 ° C. at a vacuum degree of 6.65 Pa for 30 minutes, sinter HIP treatment is performed for 30 minutes in an atmosphere of 4.9 MPa Ar. Was done. After the sinter HIP, cooling was performed at a rate of 10 to 15 ° C./min by forced cooling. The obtained sintered body was polished, bonding phase particles were revealed by a hot stamping method, and the average particle size of the bonding phase particles was measured. Further, a bending force test after grinding was performed using 30 test pieces of each composition condition to evaluate a bending force value and variation. In order to investigate the starting point of fracture, the tensile surface near the fractured surface was polished and the bonding phase grains were exposed by the hot stamping method to investigate the starting point of fracture for the specimens subjected to these bending force measurements. Evaluation was made as to whether or not the phase grain boundaries coincided with each other. As a comparative example, a test piece sintered under the same conditions as in Example 1 except that the cooling rate was 5 ° C./min was prepared, and the same evaluation was performed. Table 2 also shows the evaluation results.
[0014]
As shown in Table 2, the cemented carbide having an average particle diameter of 200 μm or less of the binder phase particles of Examples 8 to 20 of the present invention has an average transverse rupture force of 30 test pieces as compared with the cemented carbides of Comparative Examples 21 to 23. It is high, and the number of less than 80% of the average transverse rupture force showing the variation in transverse rupture force is small. In addition, in Examples 8 to 20 of the present invention, there is no coincidence between the fracture starting point and the binder phase grain boundary, and it can be seen that the soundness of the binder phase grain boundary part is greatly improved. On the other hand, in all of the cemented carbides of Comparative Examples 21 to 23, the average grain size of the binder phase grains exceeded 200 μm, and the average bending strength was low and the dispersion was large. In addition, the fracture origin and the binder phase boundary often coincide, and the soundness of the binder phase boundary has not clearly been secured.
[0015]
(Example 3)
A solvent and a wax were added to the dry powder used in Example 2, and the mixture was kneaded, and extruded so that the size after sintering became φ3.4 to produce a round bar molded body. A dewaxing treatment was performed, and sintering was performed under the same conditions as in Example 2. The average particle size of the binder phase particles of the obtained sintered body was measured by the same measurement method as in Example 2, and it was confirmed that there was no difference from the average particle size of the binder phase particles of Example 2. This round bar material was processed to produce a printed board drill having an outer diameter of φ0.2 mm to 0.08 mm.
Using these drills, under the drilling processing conditions shown in Table 2, holes were drilled for three boards of 1.6 mm thick glass epoxy board in each case, and the evaluation of the break life was performed. And the average number of holes drilled. The results are also shown in Table 2. As shown in Table 2, the drills of Examples 8 to 20 of the present invention were able to process 3000 to 4000 holes, whereas the drills of Comparative Examples 21 to 23 were 2,000 holes, indicating that the number of holes until the break life was large. Is evident.
[0016]
【The invention's effect】
By applying the cemented carbide of the present invention, the soundness of the grain boundary portion of the binder phase is improved, and as a result, the transverse rupture strength is high, and the variation in the transverse rupture force is greatly reduced. When the cemented carbide of the present invention is used, for example, as a drill for a printed circuit board, it is clear that the break life is significantly improved, and the present invention is industrially very significant.

Claims

A fine-grain cemented carbide having an average particle size of WC of 0.8 μm or less, wherein the average particle size of binder phase particles is 200 μm or less.

2. The cemented carbide according to claim 1, wherein the cemented carbide comprises WC and 40% or less by weight of Co as a component, and the remainder is a grain growth inhibiting component and inevitable impurities.