JP2000015514A - Twisted drill made of cemented carbide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a twisted drill having prolonged life by improving the strength and welding resistance of a cemented carbide used for the twisted drill; and by improving the welding resistance and abrasion resistance of the knife-edge of a tip blade at around its outer periphery liable to be high temperatures. SOLUTION: A twisted drill made of a cemented carbide and consisting of a B1 type solid solution phase, a WC phase, and a binder phase, consists of a solid phase, 50-70 percent by area, consisting of tungsten carbide, a solid phase, 15-30 percent by area, consisting of the B1 type solid solution phase, and the binder phase, 15-25 percent by weight, consisting of an iron-family metal. A sintered body has average grain sizes of 0.3 to 1.2 microns in the tungsten carbide phase and 0.3 to 2 microns in the B1 type solid solution phase, and a lattice constant of 3.565 to 3.575 Å in Co.

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. In addition, there are two types of cemented carbide used for twist drills. Ultra-fine-grain cemented carbide consisting of fine particles of several microns, and a cemented carbide consisting of tungsten carbide and a B-1 type solid solution in which the hard phase called tough cemented carbide equivalent to JIS P30 is used. In addition, the latter is used because of its excellent wear resistance against steel cutting.

[0003]

However, the K10
A considerable amount of cemented carbide is superior in strength on the plus side in steel cutting, but the minus side is damage to the cutting edge due to welding or the like. This welding and the like can be reduced by coating, but this is not preferable in a twist drill where re-polishing is repeated. In addition, a cemented carbide equivalent to P30 is excellent in welding and the like due to a B1 solid solution phase in which TaC, NbC, etc. are dissolved in TiC, and a minus surface has a strength of K10 due to the inclusion of Ti, etc., in steel cutting. Since the twist drill is considerably reduced, the twist drill is likely to be broken. Therefore, paying attention to the above, it is possible to achieve a satisfactory tool life by improving the strength and welding resistance of the cemented carbide as the base.

[0004]

SUMMARY OF THE INVENTION Therefore, according to the present invention, in a twisted carbide drill made of a B1-type solid solution phase, a WC phase and a binder phase, a hard phase of 50 to 70 area% of tungsten carbide and a B1-type solid solution are used. 15 to 30% by area of a hard phase composed of a phase, 15 to 30% of a binder phase composed of an iron group metal
25 wt%, and the average particle size in the sintered body is 0.3 to 1.2 microns for the tungsten carbide phase and 0.3 to 2 microns for the B1 type solid solution phase. From 3.565Å to 3.575
It is a twist drill that is Å.

[0005]

First, to improve the welding resistance of steel, the area ratio of a B1-type solid solution mainly composed of TiC or the like may be increased.
C and the like have a lower elastic modulus than WC and significantly lower bending strength including rigidity. For this reason, studies were made to reduce the amount of addition as much as possible by examining the area ratios that achieve these balances. First, attention was paid to the particle size of the B1 type solid solution, and its atomization was measured. The B1 type solid solution is Ti
The components of the FCC phase such as C, TiN, TaC, NbC, etc.
This is a solid solution in which C has penetrated, and its particle size is refined and uniformized by previously forming a solid solution of the base TiC and the like and WC. Second, the wear resistance was improved by reducing the W ratio in the B1 type solid solution. When a nitride is added to the B1 type solid solution, the solid solution of W can be suppressed, and the composition of the B1 type solid solution can be adjusted. In particular, TiN and TaN have a great effect as nitrides. The nitride is also highly effective in miniaturizing the B1 type solid solution. Third, for WC, the average particle size of the starting material is adjusted, but the particle size distribution becomes a problem,
It is difficult to equalize. For this reason, the particle size was adjusted by uniform WC particles disappearing due to WC solid solution in the B1 type solid solution. As described above, it was possible to disperse the B1 type solid solution phase sufficient for the welding resistance at the time of cutting steel, and to suppress the decrease in strength by measuring the addition amount, the composition, and the atomization.

Next, in order to improve the welding resistance, the Co content is preferably 5 to 20% by area. In this case, the carbon content of the alloy is adjusted to a lower side to prevent the chipping resistance from deteriorating. Met. That is, the lattice constant of Co continuously changes up to 3.575 ° on the low carbon side just before the decarburized phase does not appear in the cemented carbide production, and to 3.555 ° on the high carbon side just before free carbon appears. By controlling it to the low carbon side where it falls within 3.565 to 3.575 °, it was possible to prevent deterioration of chipping resistance. By setting to the low carbon side, in the ultra-fine particle carbide, in the cooling step from the liquid phase sintering step to solidification of 1250 ° C. to 1330 ° C., the WC which was dissolved in the liquid phase becomes the existing W.
Grains grow while forming crystallization plate-like WC particles on the surface of the C particles. On the low carbon side, the solidification temperature is as high as 1330 ° C., the amount of crystallized WC is small, and coalescence of WC particles due to grain growth does not easily 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 tends to crystallize into cubic grains during the cooling step, and the grains tend to coalesce during 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. In the vicinity of the center of the twist drill, crack resistance is required in order to resist cutting force generated due to low speed. Also, by controlling to the low carbon side, the Co phase dissolves a large amount of W in comparison with the high carbon side as apparent from the increase in the lattice constant. Under special cutting conditions in which the temperature is extremely high, the tool life is extremely improved and the preferable result is obtained.

Therefore, the present inventors paid attention to cracks formed at the four corners of the indentation at the time of measuring the Vickers hardness, and 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.

Next, the reason for limiting the numerical values will be described. The reason why the hard phase made of tungsten carbide is set to 50 to 70 area% is that if it is less than 50%, the B1 type solid solution phase and the binder phase are relatively too large, and particularly the rigidity is affected. On the other hand, if it exceeds 70%, the B1 type solid solution phase and the binder phase become relatively small, and particularly, the toughness is deteriorated. In addition, the hard phase composed of the B1 type solid solution phase is scattered in the tungsten carbide phase in relation to the welding resistance, and if the area is less than 15%, there is no effect on the welding resistance, and 30% is not effective. If it exceeds this, the B1 phase becomes too large and the strength is inferior. Next, C
If the content of o is less than 15 area%, the strength of the cemented carbide is low, and the twist drill is easily broken. If the content of o exceeds 25 area%, the plastic deformation resistance is deteriorated.
25 area%.

When the WC average particle size is less than 0.3 micron, the hardness of the cemented carbide becomes extremely high and the toughness is deteriorated.
If the thickness exceeds 1.2 microns, the wear resistance deteriorates.
5 microns to 1.2 microns. When the average particle size of the B1 type solid solution phase is less than 0.3 μm, the hardness of the cemented carbide becomes extremely high and the toughness is deteriorated. When the average particle size exceeds 1.2 μm, the B1 type solid solution phase has a large It is easy to propagate and the strength is reduced.
It was 2 microns. As described above, since the lattice constant of Co is lower than 3.565 ° on the high carbon side, the chipping resistance deteriorates and the solid solution strengthening of Co itself is not sufficient.
If it exceeds 575 °, a fragile decarburized phase will appear, so 3.5
65 to 3.575. Crack resistance is 60k
When it is less than g / g, sufficient strength can be maintained against the action of a cutting force that occurs accidentally, and when used as a twist drill, stable performance against chipping and breakage is exhibited.
Preferably, it is 70 kg / mm or more. Hereinafter, the present invention will be described in detail based on examples.

[0011]

Examples: Commercially available WC powder (average particle size 0.8 μm),
TiC powder (1.0 μm), TiN powder (1.0 μm)
μm), DC powder (WC / TiC = 70/30)
5 μm) and WC-TiC-
A solid solution of TiN was prepared. Solid solution is WC / TiC
/ TiN = 50/48/2, WC / TiC / TiN /
Ta (Nb) C = 50/25/5/20, dried and then subjected to a solution treatment in an N atmosphere at 1600 ° C. for 2 hours to adjust the particle size, to obtain a powder having an average particle size of 0.5 μm. It was created. Using these powders, the rest: WC, B1
It was blended so as to have a composition of 5 to 25% by volume of the solid solution and 5 to 25% by volume of the binder phase. Table 1 shows the composition and the like.

[0012]

[Table 1]

After mixing and drying with the compositions shown in Table 1, a test piece was press-formed, sintered at 1400 ° C. in a vacuum, and worked into a predetermined shape. Further, in order to confirm changes in physical properties and microstructure, the chip was polished and wrapped, and then hardness, crack resistance, and lattice constant of Co were measured. The results are also shown in Table 1. The average particle size was determined by observing the structure with an electron microscope and using the photograph. The measurement results of Invention 1 and Comparative Example 10 show that Invention 1 has an average particle size of the WC phase of 0.51 μm and a B1 solid solution of 0.9.
In Comparative Example 10, the average particle size of the WC phase was 0.5 μm.
The 53 μm, B-1 type solid solution was as coarse as 1.8 μm.

Further, using the samples of Examples 2 and 4 of the present invention and Comparative Example 10, a twist drill having a standard shape with two blades, an outer diameter of 8 mm, and a tip angle of 140 ° was manufactured. Was done. The cutting specifications are as follows: using a work material SCM440 (annealed material), cutting speed 60 m / min, feed speed 50
0mm / min, hole depth 24mm (3 times the drill diameter)
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 drills of Examples 2 and 4 of the present invention, separated chips were generated in the initial stage of cutting, the chip discharge property was good, smooth drilling was performed, and there was no welding or the like. In Comparative Example 10, the initial stage of cutting was performed in the same manner as in the present invention. After machining 500 holes, which are in a steady state of wear, if the film comes into contact with the chip itself due to abrasion as the amount of wear increases, in Comparative Example 10, the welded portion becomes violent, causing chipping and resulting in a long life. It became. Further, in Examples 2 and 4 of the present invention, the intersection with the outer periphery also shows normal wear,
When the machining was further continued, when the cutting edge was observed in 2000-hole machining, the wear at the intersection between the drill tip and the outer periphery increased, and although the substrate itself was involved in the cutting, normal chips were obtained. When drilling up to 3000 holes in this state and observing the tip of the twist drill, the wear near the thinning blade and the straight blade of the drill is still normal, but the intersection between the drill tip and the outer periphery has undergone plastic deformation. And had a sustainable life.

Next, using the samples of Examples 6 and 8 of the present invention and Comparative Example 12, a twist drill similar to that described above was manufactured, and after coating, a cutting test was performed. As a result, the twist drills of Examples 6 and 8 of the present invention had good chip dischargeability, could perform smooth hole drilling, and had no welding or the like. In Comparative Example 12, the initial stage of cutting was performed in the same manner as in the present invention. In Examples 6 and 8 of the present invention, even after machining of 1000 holes and 2000 holes, although the wear at the intersection of the drill tip and the outer periphery increased, the base itself was involved in the cutting, but normal chips were obtained. Had been. When drilling up to 3000 holes in this state and observing the tip of the twist drill, the wear near the thinning blade and straight blade of the drill is still normal wear, and the intersection between the drill tip and the outer periphery has not undergone plastic deformation. , A sustainable life. On the other hand, in Comparative Example 12, since the particle size of the B1 solid solution phase was coarse, 1
It was broken by repeating around 00 holes.

Next, Examples 2 and 4 of the present invention shown in Table 1 (WC
An alloy having a composition of 0.8 μm) was prepared by changing the amount of carbon. 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]

According to Table 2, among the samples in which the amount of carbon was changed, in Examples 13 to 18 of the present invention, the WC particles were rounded, grew in a square shape, and there were almost no coalesced particles. Therefore, the hardness was high, and the crack resistance was a large value. On the other hand, in Comparative Examples 19 and 22, the amount of carbon was high. The WC particles were in contact with each other, and the coalesced particles were also observed, and the crack resistance was a small value for the hardness. Further, in Comparative Examples 23 and 24, 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 19 and the like having a high carbon content, the life was shortened due to damage to the outer peripheral corners. In Comparative Example 22 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.

[0020]

The twist drill made of cemented carbide can be used with WC
Phase, B1 solid solution phase, Co phase and hard phase particle size, Co
By setting the lattice constant in a predetermined numerical range, it was possible to improve the wear resistance while maintaining the welding resistance. 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. In a twisted carbide drill made of a B1 type solid solution phase, a WC phase and a binder phase, 50 to 70 area% of a hard phase made of tungsten carbide and 15 to 30 area% of a hard phase made of a B1 type solid solution phase. And 15 to 25% by weight of a binder phase composed of an iron group metal, and the average particle size of the sintered body is from 0.3 μm to 0.3 μm.
1.2 microns, B1 type solid solution phase 0.3 microns to 2
Microns, and the lattice constant of Co is 3.565 °.
A cemented carbide twist drill characterized in that the angle is 3.575 °. 2. The cemented carbide twist drill according to claim 1, wherein the resistance to crack propagation is 60 kg / kg.
mm or more, a twist drill made of cemented carbide. 3. The twisted carbide drill according to claim 1, further comprising a hard coating and / or a lubricating coating.