JP2000015513A - Cemented carbide twist drill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an anti-plastic deformation property easy to generate on the corner of an outer periphery, while keeping an anti-chipping property by specifying the Co content of a cemented carbide to a specific weight %, the average grain diameter of WC and the lattice constant of Co. SOLUTION: When a Co content is less than 5 weight %, the strength of a cemented carbide is low and a twist drill is easy to break and when it is contained beyond 12 weight %, as an anti-plastic deformation property is deteriorated, it is made to 5-12 weight %. As the WC average grain diameter is less than 0.3 μ, the hardness of the cemented carbide becomes extremely high and its toughness is deteriorated and when it exceeds 1.2 μ, as the anti-water property is deteriorated, it is made to 0.5-1.2 μ. The lattice constant of Co is made to 3.565 Å-3.575 Å, as the deterioration of the anti-chipping property and the solid solution reinforcement of Co itself are not enough at the high carbon side of less than 3.565 Å and when it exceeds 3.575 Å, as a weak decarburizing phase is appeared.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cemented carbide twist drill used for drilling and the like.

[0002]

2. Description of the Related Art Cemented carbide twist drills are widely used with the spread of MC and the like, because they have characteristics such as long life and high speed cutting as compared with high speed steel twist drills. In addition, the shape of the drill itself is high-speed
In order to cope with the high feed, a shape giving priority to the chip processing property, particularly, the discharge of the chip is used. As an example, there is Japanese Patent No. 2,674,124. In this example, a chip discharge groove is widened to provide a twist drill excellent in chip discharge property, and a twist drill adapted to high speed and high feed, which is a feature of cemented carbide.

[0003]

However, compared to high-speed steel, the cemented carbide itself has rigidity and compressive strength on the plus side and lacks bending strength on the minus side. This positive surface can be very advantageous because the twist drill is used for drilling, i.e. axial cutting. That is, since the compressive strength can be increased almost in inverse proportion to the amount of the bonding metal, the lower the amount of the bonding metal, the more advantageous. Furthermore, the cutting edge of the twist drill is a continuous cutting, the cutting temperature of the cutting edge becomes extremely high, and the tip cutting edge, especially the cutting edge of the cutting edge near the outer periphery, generates a small amount of plastic deformation, which causes micro wear. The wear is advanced by repeating the inducing, leading to the tool life. Furthermore, the vicinity of the drill rotation center has a region where the cutting speed is lower than that of the outer periphery, and it is indispensable to take measures against chipping, chipping, and the like accompanying low-speed cutting. Therefore, focusing on the above three points, it is necessary to improve the compressive strength, plastic deformation resistance, and chipping resistance of the cemented carbide as the base, especially in the vicinity of the outer periphery where the cutting edge of the tip blade becomes hot. By improving the properties and wear resistance, a satisfactory tool life can be achieved.

[0004]

SUMMARY OF THE INVENTION Generally, W of 1 μm or less is used.
An ultrafine-grain cemented carbide using C particles adds a relatively large amount of Co in order to maintain chipping resistance. Usually, the Co content is about 10 to 14% by weight. As the amount of Co increases, the plastic deformation resistance naturally deteriorates. Therefore, it is inevitable to reduce the Co content in order to improve the plastic deformation resistance. However, if the Co content is simply reduced, the strength itself also decreases, and in particular, when used in a twist drill, it is inevitable that the chipping resistance near the rotation center of the tip blade deteriorates. Therefore, according to the present invention, in a twist drill made of cemented carbide, the cemented carbide has a Co content of 5 to 12% by weight, an average particle diameter of WC of 0.3 to 1.2 microns, and Has a lattice constant of 3.565 ° to 3.575 °.

[0005]

According to the study of the present inventors, the Co content is preferably 12% by weight or less in order to improve the plastic deformation resistance.
In this case, by adjusting the carbon content of the alloy to a lower side, deterioration of chipping resistance could be prevented. In other words, the lattice constant of Co continuously changes to 3.575 ° on the low carbon side just before the decarburized phase does not appear in the production of cemented carbide, and to 3.555 ° on the high carbon side just before free carbon appears. However, by controlling to a low carbon side where it is within 3.565 to 3.575 °, deterioration of chipping resistance can be prevented.

[0006] The reason is that, in the ultra-fine particle carbide, in the cooling step from 1250 ° C. to 1330 ° C. in the latter half of the liquid phase sintering step, WC which was dissolved in the liquid phase crystallizes on the surface of the existing WC particles. The grains grow while forming plate-like WC particles.
Solidification temperature as high as 1330 ° C on low carbon side
Since the amount of carbon is small, coalescence of WC particles due to grain growth is unlikely to occur, and the shape of the particles is relatively round. On the other hand, on the high carbon side, a relatively large amount of WC becomes crystallized and becomes angular particles during the cooling step, and the particles tend to unite during the grain growth.
When the horn-like particles coalesce, the stress concentrates, and when a crack occurs, it tends to propagate, and as a result, it tends to induce chipping. This effect correlates with the chipping resistance particularly seen near the center of rotation. High compressive strength and crack resistance are required in the vicinity of the center of the twist drill in order to resist cutting resistance generated due to low speed.

For this reason, the present inventors have paid attention to cracks generated at the four corners of the indentation when measuring the Vickers hardness, and have observed the crack propagation path in detail. In the case of the high carbon alloy, there are many angular particles, the cracks generated at the four corners of the Vickers indentation are long, and when the state is observed with a microstructure, the angular particles are broken and propagated. There is. In addition, since the low-carbon alloy has relatively round particles, the low-carbon alloy has a characteristic of propagating around the particles. As described above, in the ultrafine-grain cemented carbide, the slightly grown WC particles have a negative effect on cracks. The feature, Vicca-
The length of the cracks formed at the four corners of the
Expressed by the relationship between the total length of the book and the Vickers load. (Hereinafter referred to as crack resistance.) That is, crack resistance (kg / mm) = (Vickers load) ÷ (sum of the lengths of four cracks), and the particle is shaped like a low carbon alloy. In the case of hard, the crack length is short because the crack is difficult to propagate, so that the crack resistance is a large value. Conversely, in the high carbon alloy, stress concentration occurs in the angular particles, and the cracks are easily propagated, so that the crack length becomes longer, and thus the crack resistance becomes a small value.

[0008] Further, by controlling to a low carbon side, Co
As is clear from the increase in the lattice constant, the phase dissolves a larger amount of W than on the high carbon side. As a result, the solid solution is strengthened and the Co phase itself is hardly plastically deformed. This is extremely effective in improving the tool life and gives a favorable result. Therefore, by using an ultrafine-grained cemented carbide with low Co without deteriorating chipping resistance and simultaneously improving plastic deformation resistance and compressive strength, it can be used both near the center of rotation and near the outer periphery of the drill bit. Was also able to be a cemented carbide.

Next, the reason for limiting the numerical values will be described. Co
If the content is less than 5% by weight, the strength of the cemented carbide is low, and the twist drill is easily broken. If the content exceeds 12% by weight, the plastic deformation resistance is deteriorated. did. If the WC average particle size is less than 0.3 micron, the hardness of the cemented carbide becomes extremely high, deteriorating the toughness,
If the thickness exceeds 1.2 microns, the wear resistance deteriorates.
5 microns to 1.2 microns. If the lattice constant of Co is less than 3.565 °, the chipping resistance is deteriorated and the solid solution strengthening of Co itself is not sufficient on the high carbon side as described above, and if it exceeds 3.575 °, a fragile decarburized phase appears. Therefore, it was 3.565３3.575３. When the crack resistance is less than 70 kg /, it is possible to maintain sufficient strength against the action of a cutting force that is accidentally generated, and particularly when used as a twist drill, exhibits stable performance against chipping and breakage. Preferably, it is 90 kg / mm or more. Further, the hard film and / or the lubricating film are coated because the drill is also coated with TiN, TiN or the like to improve wear resistance, and when drilling a deep hole or the like, the lubricating film such as MoS or the like is formed on the blade groove. To reduce the resistance at the time of chip discharge. Hereinafter, the present invention will be described in detail based on examples.

[0010]

EXAMPLE Using a commercially available WC powder having an average particle diameter of 0.5 micron and a Co powder having the same micron diameter of 1 micron by a general powder metallurgy method, the cemented carbide of the present invention having a composition of 10% Co and the remaining WC powder and having a diameter of 8 mm. A twist drill was made. The physical properties of the cemented carbide after sintering are as follows: hardness HRA92, lattice constant of Co is 3.57.
0 ° and a crack resistance of 90 kg / mm were obtained. Using this alloy, 2 blades, outer diameter 8mm, tip angle 1
A twist drill having a standard shape of 40 degrees was manufactured, and after coating (TiN), a cutting test was performed. The cutting specifications are as follows: The cutting speed is 60m / m using the SCM440 (annealed material).
in, feed rate 500mm / min, hole depth 24mm
Drilling (three times the diameter of the drill) was performed using a water-soluble cutting oil. The life was determined while observing the shape of chips and the like, and checking the damage state of the cutting edge for each fixed number of processing holes.

As a result, in the twist drill according to the present invention, divided chips are generated in the initial stage of cutting, the chip discharge property is good, and smooth drilling can be performed. The chip turned into a transition break type and became a steady wear state. This chip form continued until the 3000-hole machining, and the amount of wear increased, but the intersection between the drill tip and the outer periphery showed normal wear. When the machining was further continued, chips continued to be formed after the number of drilling of 3,500 holes, the wear at the intersection of the drill tip and the outer periphery increased, and a normal chip could not be obtained. When drilling up to 4000 holes in this state and observing the tip of the twist drill, the wear near the drilling thinning blade and straight blade is still normal wear, but the intersection between the drill tip and the outer periphery has undergone plastic deformation. The life was shortened due to wear.

Next, using a conventional powder metallurgy method, a commercially available WC powder having an average particle diameter of 0.2 to 2.0 μm and a Co powder having the same 1 μm are used.
A 15% alloy was made. The WC having a particle size of less than 0.5 micron was manufactured by adding a carbide such as Cr, V, or Zr, a nitride, or the like as a grain growth inhibitor. Table 1 shows the composition and physical properties after sintering.

Using these alloys, a cemented carbide twist drill having a diameter of 8 mm was manufactured, coated (TiN), and then subjected to a cutting test. First, using the same work material used in the above-described embodiment, the cutting specifications were as follows: a cutting speed of 60 m / min, a feed speed of 500 mm / min, and a hole processing of a hole depth of 24 mm (three times the diameter of the drill) were water-soluble. The test was carried out using a neutral cutting oil. The inspection was performed while confirming the damage state of the cutting edge for each constant number of machining. Table 1 shows the results.

[0014]

[Table 1]

According to Table 1, in Examples 1 to 14 of the present invention, alloys having higher hardness tend to have a longer life, but all have higher crack resistance, so that accidental breakage or the like occurs from the initial use to the stationary period. Without this, the number of processed holes was 3000 to 4500. Further, in the comparative example, the amount of Co was large,
In No. 6, the coating was damaged due to plastic deformation of the outer corner.
The test was stopped because chips were continuously formed at 250 and 500 holes due to peeling. Furthermore, 1 with less Co content
In Nos. 7 and 18, it was broken at the beginning of use.

Next, Examples 4, 5, and 6 of the present invention shown in Table 1
An alloy having a composition of (WC particles 0.5 μm) with a different amount of carbon was manufactured. The amount of carbon was converted into a lattice constant of Co from the result of the measurement of the saturation magnetic flux density. Table 2 shows the results.

[0017]

[Table 2]

From Table 2, it can be seen that among the samples in which the amount of carbon was changed, in Examples 19 to 27 of the present invention, the WC particles were rounded, grew in a square shape, and there were almost no coalesced particles. Therefore, while the hardness was high and the crack resistance was a large value, in Comparative Examples 28, 30, and 32, the amount of carbon was high. However, the WC particles came into contact with each other, and the coalesced particles were also observed, and the crack resistance was a small value in terms of hardness. Furthermore, in Comparative Examples 29, 31, and 33, since the amount of carbon was too low, an M6C phase called an eta phase was partially observed, so that the hardness was high but brittle, and the crack resistance was a small value. Next, a twist drill similar to the previous example was manufactured from these samples, and the cutting specifications were the same. The results are also shown in Table 2.

As shown in Table 2, in Comparative Example 28 and the like having a high carbon content, the life was shortened due to damage to the outer peripheral corners. In Comparative Example 29 and the like in which a decarburized layer was observed, it was broken from the shank side while the load was repeated. In this test, by specifying an appropriate amount of carbon and specifying the shape of the WC particles, stable and good results were obtained even with a cutting tool such as a twist drill which involves instability.

Subsequently, Example 24 of the present invention (Co
Using the drill of Example 27 of the present invention (Co amount 6%), the drill of Comparative Example 32, and the drills of Examples 9, 12, and 14 of Table 1 of the present invention, the cutting specifications were changed to high speed and high feed. I went. Cutting speed 100m / min, feed speed 1000mm / min
Then, a hole having a hole depth of 24 mm (three times the drill diameter) was formed using a water-soluble cutting oil. By increasing the cutting data, the load on the corner of the drill was higher, and the life of the corner was damaged. First, in Example 24 of the present invention having a WC average particle size of 0.5 μm, plastic deformation occurred at the corners with the number of processed holes of 1525, and Example 27 of the present invention (Co content 6
%), Chips began to be connected at 1825 holes. In Comparative Example 32, plastic deformation occurred at the corners with the number of processing at 100 holes. Next, in Example 9 of the present invention having a WC average particle diameter of 0.8 μm, Example 12 of the present invention having a WC average particle diameter of 1.0 μm, and Example 14 of the present invention having a WC average particle diameter of 1.2 μm, each had 2,000 holes.
There were 2200 holes and 2500 holes. In this example, by using high-speed, high-feeding specifications, an alloy having a low Co content was more excellent, and better results were obtained when WC particles were slightly coarse.

[0021]

The twist drill made of cemented carbide has a low cobalt content and a Co lattice constant within a predetermined numerical range, so that chipping resistance is maintained while plastic deformation is likely to occur at the outer corners. Properties could be improved. In particular, in a cutting tool such as a twist drill, in which cutting chips are liable to be involved and cause chipping, chipping, and the like, a stable and long-life drill can be obtained by increasing resistance to cracks.

Claims (3)

[Claims] 1. A twist drill made of cemented carbide, wherein the cemented carbide has a Co content of 5 to 12% by weight, an average WC particle size of 0.3 to 1.2 microns, and The lattice constant of Co is 3.565Å3.575Å.
A twist drill made of cemented carbide, characterized in that: 2. The cemented carbide twist drill according to claim 1, wherein the resistance to crack propagation is 70 kg / kg.
mm or more, a twist drill made of cemented carbide. 3. The cemented carbide twist drill according to claim 1, which is coated with a hard film and / or a lubricating film.