JP4112431B2

JP4112431B2 - Cemented carbide

Info

Publication number: JP4112431B2
Application number: JP2003144197A
Authority: JP
Inventors: 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: 2008-07-02
Anticipated expiration: 2023-05-22
Also published as: JP2004346370A

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、該微粒超硬合金は、重量％で４０％以下のＣｏと、残りがＷＣ、粒成長抑制成分及び不可避不純物で有り、結合相粒の平均粒径が２００μｍ以下で、試料数３０の平均抗折力が４３００ＭＰａ以上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。
【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 to which the invention belongs]
The present invention relates to a cemented carbide and relates to a cemented carbide excellent in toughness having an average WC particle size of 0.8 μm or less.
[0002]
[Prior art]
The following Patent Documents 1, 2, 3 and Non-Patent Document 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 Laid-Open No. 04-46538 [Patent Document 2]
Japanese Patent No. 3010859 [Patent Document 3]
JP 2000-712 [Non-Patent Document 4]
Suzuki, Hayashi, Fukuya: Powder and powder metallurgy, 9 (1973), p. 187
Patent Document 1 discloses the addition of three types of Cr, V, and Ta. Patent Documents 2 and 3 disclose Cr and V-added three-phase alloys. Non-Patent Document 4 discloses the results of studies by Suzuki et al. A region having the same crystal orientation in the binder phase (hereinafter referred to as a binder phase grain) exists, and the grain boundary portion of the binder phase grain is the final solidified portion of the binder phase. Non-Patent Document 4 discloses that the grain boundary portion is less likely to cause micropores due to the decrease in the amount of Co due to solidification shrinkage.
[0004]
[Problems to be solved by the invention]
Fine 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 recent years, these tendencies have become increasingly smaller. In order to improve the breakage resistance of these small-diameter tools, it is required to further increase the toughness and toughness of the fine-grain cemented carbide. In order to increase the bending strength of fine cemented carbide, the WC grain size has been reduced, the selection of grain growth inhibiting components, the amount has been optimized, the amount of binder phase has been improved, and so on. In order to further improve the bending strength, these optimizations are not sufficient, and further improvement is required.
[0005]
[Means for Solving the Problems]
The present invention provides a fine cemented carbide average grain size of WC is 0.8μm or less, the fine particle cemented carbide, 40% and less Co in weight percent, the remainder WC, grain growth suppression component and inevitable impurities The cemented carbide is characterized in that the average particle size of the binder phase grains is 200 μm or less and the average bending strength of 30 samples is 4300 MPa or more . By adopting this configuration, a cemented carbide having excellent toughness can be obtained.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Although the present inventors have a basic examination result, paying attention to the average particle diameter of the binder phase grains, which has not been noticed so far, to define the average grain diameter of the binder phase grains below a certain value. Thus, it was found that the bending strength can be greatly improved, and the present invention was achieved. By setting the average particle size of the binder phase grains to 200 μm or less, it is possible to make the unsoundness of the grain boundary part healthy to a level that does not affect the bending strength. The soundness of the grain boundary part referred to here is said to be sound when the content of impurities and grain growth inhibiting components in the grain boundary part is equivalent to the content inside the binder phase grains, When the content of impurities and grain growth inhibiting components in the grain boundary part is much larger than the content inside the binder phase grains, it is said to be unhealthy.
The crystallization phase containing the grain growth inhibiting component is likely to occur particularly at the triple boundary of the grain boundary in the bonded phase grain boundary. When the average particle size of the binder phase grains exceeds 200 μm, it becomes a starting point of fracture at the time of measuring the bending strength, leading to a decrease in the bending strength, which is not preferable. Therefore, the average particle size of the binder phase grains is limited to 200 μm or less. did. When the average particle size of the binder phase grains is 200 μm or less, a cemented carbide having excellent toughness can be obtained.
[0007]
In order to obtain excellent toughness, WC and 40% by weight or less of Co as a main component and containing a grain growth inhibiting component and inevitable impurities are preferable. The reason why the amount of Co is 40% or less is that when it exceeds 40%, too much Co cannot be obtained, and the necessary 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)
Cooling rate after sintering in a cemented carbide having a composition of Co: 8 wt%, VC: 0.3 wt%, Cr ₃ C ₂ : 0.7 wt%, TaC: 0.1 wt%, remaining WC and inevitable impurities The test pieces having various average particle sizes of the binder phase grains were produced by varying the slab, and their bending strengths were investigated. The results are shown in Table 1.
[0009]
[Table 1]

[0010]
The average particle size of the bonded phase grains is obtained by mirror-wrapping the test piece, then revealing the bonded phase grains by a thermal engraving method, taking a photograph with a magnification of 50 times, and bonding within the field of view by image processing. The average particle size of the phase grains was determined. From this result, when the average particle size of the binder phase grains of Invention Examples 1 to 4 is 200 μm or less, the bending strength is 4300 MPa or more, which is almost constant, whereas the 200 μm of Comparative Examples 5 to 7 is 200 μm. It is clear that the bending strength decreases as the binder phase grains increase.
[0011]
(Example 2)
WC powder with an average particle size of 0.6 μm, VC powder with an average particle size of 1.2 μm, Cr ₃ C ₂ powder with an average particle size of 1.4 μm, TaC powder with an average particle size of 1.3 μm, 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 for 6 hours using alcohol as a solvent.
[0012]
[Table 2]

[0013]
It dried after mixing, and using this dried powder, a JIS test piece having a size after sintering of 4.5 × 8.5 × 25 mm was press-molded. The obtained compact was first sintered at a predetermined sintering temperature of 1350 to 1450 ° C. at a vacuum degree of 6.65 Pa for 30 minutes, and then subjected to sintering HIP treatment in an Ar atmosphere of 4.9 MPa for 30 minutes. Went. After sinter HIP, it was cooled at a rate of 10 to 15 ° C./min by forced cooling. The obtained sintered body was polished, and bonded phase grains were exposed by a thermal contact method, and the average particle diameter of the bonded phase grains was measured. Further, 30 post-grinding bending strength tests were performed using 30 test pieces of each composition condition, and bending strength values and variations were evaluated. In order to investigate the starting point of fracture for these specimens for which the bending strength was measured, the tension surface near the fracture surface was polished, and the bonded phase grains were revealed by the thermal contact method, and bonded to the starting point of the fracture. Evaluation was made as to whether or not the grain boundaries coincided with each other. As a comparative example, a test piece sintered under the same conditions as in Example 1 was prepared except that the cooling rate was 5 ° C./min. The evaluation results are also shown in Table 2.
[0014]
From Table 2, the cemented carbide having the average particle size of the binder phase grains of Invention Examples 8 to 20 having an average particle size of 200 μm or less has an average bending strength of 30 test pieces as compared with the cemented carbide of Comparative Examples 21 to 23. The number is less than 80% of the average bending force that is high and shows variations in bending strength. Further, in Examples 8 to 20 of the present invention, there is no coincidence between the starting point of fracture 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, the cemented carbides of Comparative Examples 21 to 23 all have an average particle size of the binder phase grains exceeding 200 μm, and the average bending strength is low and the variation is large. In many cases, the starting point of the fracture coincides with the binder phase grain boundary, and clearly the integrity of the binder phase grain boundary cannot be secured.
[0015]
(Example 3)
A solvent and wax were added to the dry powder used in Example 2 and kneaded, and a round bar molded body was prepared by extrusion molding so that the size after sintering was φ3.4. Dewaxing treatment was performed, and sintering was performed under the same conditions as in Example 2. The average particle size of the binder phase grains 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 grains in Example 2. This round bar material was processed to produce a printed circuit board drill having an outer diameter of φ0.2 mm to 0.08 mm.
Using these drills, under the drilling conditions shown in Table 2, drilling was performed on five substrates each having three glass epoxy substrates each having a thickness of 1.6 mm, and evaluation of breakage life was performed. The average number of holes was determined. The results are also shown in Table 2. From Table 2, the drills of Invention Examples 8 to 20 were able to process 3000 to 4000 holes, whereas the drills of Comparative Examples 21 to 23 had 2000 holes, and the number of drills to breakage life was large. Is clear.
[0016]
【The invention's effect】
By applying the cemented carbide of the present invention, the soundness of the binder phase grain boundary is improved. As a result, the bending strength is high and the variation in the bending strength 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 breakage life is remarkably improved, and the present invention is very significant industrially.

Claims

In a fine cemented carbide having an average particle diameter of WC of 0.8 μm or less, the fine cemented carbide is 40% or less of Co by weight%, and the remainder is WC, a grain growth inhibiting component and an unavoidable impurity. A cemented carbide characterized in that an average grain size of phase grains is 200 μm or less and an average bending force of 30 samples is 4300 MPa or more .