JP2006247779A - Coated cbn base sintered body cutting tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cutting tool, achieving a small finished surface roughness of a workpiece in cutting the workpiece made of iron material, especially hard hardness steel subjected to quenching treatment. <P>SOLUTION: In this coated cBN base sintered body cutting tool, the surface of cBN base sintered body base material containing 20 to 100 vol.% cBN is coated with a titanium compound film composed of at least one kind selected from carbide containing Ti, nitride and mutual solid solution thereof, the average film thickness of the titanium compound film is 0.1 to 10 μm, the mean particle diameter of the titanium compound film is 0.5 μm or less. This cutting tool achieves a small finished surface roughness of a workpiece. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a coated cBN-based sintered body cutting tool, and particularly to a coated cBN-based sintered body cutting tool suitable for cutting high hardness steel.

As a prior art of a coated cBN-based sintered body cutting tool, a carbide of one or two layers of periodic table 4a, 5a metal on the surface of a hard sintered body containing 20% or more of high-pressure phase type boron nitride by volume There is a coated hard sintered body having a coating layer made of nitride, oxide, boride or a composite compound thereof, or Al ₂ O ₃ (for example, see Patent Document 1).

Further, Al ₂ O ₃ having an average crystal grain size of 1 μm or less is contained in the cBN-based sintered base material, and an Al ₂ O ₃ layer having a predetermined average crystal grain size is coated to improve wear resistance. _{There is a 2} O ₃ coated cBN-based sintered body cutting tool (for example, see Patent Document 2).

JP 59-8679 A JP 2000-44370 A

In recent years, the need for longer machine life and energy savings has increased, and machine parts have been required to have high finished surface quality. The conventional coated cBN-based sintered cutting tool has been unable to sufficiently meet the demand for such high finished surface quality. For example, if an Al ₂ O ₃ film is coated on the surface of a hard sintered body containing 20% or more of high-pressure phase type boron nitride by volume, the coating of the film tends to peel off due to the low adhesion of the Al ₂ O ₃ film. For this reason, there is a problem that the roughness of the finished surface of the workpiece decreases because the minute irregularities formed by peeling off the coating during the cutting process are transferred to the workpiece. In addition, the Al ₂ O ₃ film has a problem that the surface roughness tends to increase as the film thickness increases and the particle diameter of the Al ₂ O ₃ film tends to increase. Therefore, the present invention provides a cutting tool having a small finished surface roughness of a workpiece in cutting of a workpiece, particularly in cutting of a ferrous material, and particularly of a workpiece made of hardened steel that has been quenched. The purpose is to provide.

The present inventor has been working on the development of a coated cBN-based sintered body cutting tool. When the crystal grain of the titanium compound film is made fine, the surface of the titanium compound film becomes smooth, and the boundary portion is damaged during the cutting process. The present invention has been completed by obtaining the knowledge that the cutting edge can be suppressed and the blade edge can be worn normally and the finished surface roughness of the workpiece can be reduced.

The coated cBN-based sintered cutting tool of the present invention is selected from carbides, nitrides containing Ti, and their mutual solid solutions on the surface of a cBN-based sintered base material containing 20 to 100% by volume of cBN. The titanium compound film made of at least one kind is coated, the titanium compound film has an average film thickness of 0.1 to 10 μm, and the titanium compound film has an average particle diameter of 0.5 μm or less.

The cBN-based sintered base material of the present invention contains 20 to 100% by volume of cBN, and the balance is Ti, Zr, Hf, Al, Si, V, Nb, Ta, Mo, W, Co, Mn, It is a cBN-based sintered base material containing at least one binder phase selected from carbides, nitrides, oxides, borides and their mutual solid solutions. However, when the amount of cBN contained in the cBN-based sintered base material of the present invention is 100% by volume, the cBN-based sintered base material of the present invention does not include a binder phase. When the amount of cBN contained in the cBN-based sintered base material is less than 20% by volume, the hardness decreases, so that wear significantly increases in cutting work such as high hardness steel. Therefore, the amount of cBN contained in the cBN-based sintered base material of the present invention is set to 20 to 100% by volume. In the present invention, cBN represents cubic boron nitride.

When the cBN group sintered body substrate of the present invention contains the same element as the element constituting the titanium compound film, the adhesion between the titanium compound film and the cBN group sintered body substrate is further increased, which is preferable. For example, when a TiAlN film is coated, it is preferable to contain Ti, Al, and N in the cBN-based sintered base material. Thus, when the same element as the element which comprises a titanium compound film | membrane is contained in a cBN group sintered compact base material, the nucleus generation | occurrence | production of a titanium compound film | membrane increases and it is thought that adhesiveness improves.

The titanium compound film of the present invention comprises at least one selected from Ti-containing carbides, nitrides, and mutual solid solutions thereof. This is because Ti-containing carbides, nitrides, and their mutual solid solutions have high adhesion to the cBN-based sintered base material and excellent wear resistance. Among them, Ti carbides, nitrides and their mutual solid solutions, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, Si composite carbides and composite nitrides of Ti And at least one selected from these mutual solid solutions, specifically, TiN, TiCN, TiC, TiAlN, TiSiN, TiCrN, TiAlSiN, TiCrSiN, TiAlCrSiN, and the like. Among these, at least one selected from TiN, TiCN, and TiAlN is more preferable, and among these, TiN is more preferable.

The titanium compound film of the present invention has an effect of filling the unevenness of the cBN-based sintered base material by making the surface of the titanium compound film itself easy to be smooth by making the average particle diameter of the titanium compound film 0.5 μm or less. Yes Smoothes the surface of the cutting tool. In addition, since the damage unit is reduced at the time of cutting, damage to the boundary portion is suppressed, the cutting edge is normally worn, and the finished surface roughness of the workpiece can be reduced over a long period of time. Of these, the average particle diameter of the titanium compound film is more preferably 0.1 μm or less. In addition, since it is difficult to make the average particle diameter of a titanium compound film less than 0.01 micrometer, practically, the average particle diameter of a titanium compound film has the preferable range of 0.01-0.5 micrometer, Among these, 0.01 Even more preferable is -0.1 μm. The average particle diameter of the titanium compound film indicates the average particle diameter of the titanium compound film in the direction parallel to the substrate. The average particle diameter of the titanium compound film is a straight line parallel to the rake face of the cBN-based sintered base material by taking a cross section of the titanium compound film by SEM observation or TEM observation, taking a photograph at approximately the center in the vertical direction of the titanium compound film. It can be determined from the number of crystal grains intersecting with. At this time, in order to accurately obtain the average particle diameter of the titanium compound film, it is preferable that the length of the straight line is 10 times or more the average particle diameter of the titanium compound film.

When the average particle size of the titanium compound film is equal to or less than the average particle size of cBN contained in the cBN group sintered body substrate, the adhesion between the titanium compound film and the cBN group sintered body substrate is improved, and the substrate surface This is preferable because it has a high effect of filling the unevenness existing in the surface.

When the average film thickness of the titanium compound film of the present invention is less than 0.1 μm, the wear resistance is reduced, and when it exceeds 10 μm, the titanium compound film is liable to be peeled off or slightly damaged, and the finished surface roughness is increased. The average film thickness was 0.1 to 10 μm. Among these, 1-5 micrometers is more preferable.

One of the uses of the coated cBN-based sintered body cutting tool of the present invention is to cut iron-based materials. Among them, the effect is particularly high when used for cutting hardened steel that has been quenched.

The titanium compound film of the present invention can be coated using a CVD method and / or a PVD method. Among these, the PVD method is preferable because finer crystal grains can be obtained than the CVD method. By appropriately selecting the coating method and conditions, the average particle size of the titanium compound film can be made 0.5 μm or less.

For example, in a thermal CVD method using TiCl ₄ and H ₂ as a source gas such as a TiCl ₄ —H ₂ —N ₂ system, the nucleus generation density is increased by increasing the amount of TiCl ₄ and H ₂ in the source gas. At the same time, by reducing the coating temperature, the growth rate of the titanium compound film can be reduced, and the average particle diameter of the titanium compound film can be reduced. In the PVD method using a Ti-based evaporation source and N ₂ gas, the average particle size of the titanium compound film can be reduced by lowering the temperature of the cBN-based sintered base material and reducing the N ₂ flow rate. . At this time, the growth rate of the titanium compound film is significantly reduced, but the growth rate of the titanium compound film can be increased by increasing the bias voltage.

Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, Si carbides, nitrides, oxides, and their mutual layers as outermost layers on the surface of the coated cBN-based sintered body cutting tool of the present invention It is more preferable to coat a hard film made of at least one selected from solid solutions because the wear resistance is improved. Among these, a hard layer made of an aluminum oxide film is more preferable because it improves oxidation resistance. A specific composition of the aluminum oxide film is Al ₂ O ₃ .

If the average film thickness of the hard film is less than 0.1 μm, the effect of covering the hard film cannot be obtained sufficiently, and if the average film thickness of the hard film exceeds 2 μm, the chipping resistance tends to decrease. The average film thickness is more preferably 0.1 to 2 μm. The hard film of the present invention can be coated using a CVD method and / or a PVD method.

When cutting is performed using the coated cBN-based sintered body cutting tool of the present invention, the finished surface roughness of the workpiece can be reduced over a long period of time.

A cBN-based sintered base material composed of cBN having an average particle size of 0.5 μm: 60% by volume and a binder phase composed of TiN and Al: the balance was sintered together with a cemented carbide base metal having a thickness of 5 mm. After sintering, it was confirmed that the cBN-based sintered base material and the cemented carbide were firmly bonded. This was processed to obtain a cBN-based sintered body cutting tool having a tool shape of JIS standard TNGA160408. A chamfer honing with a chamfer width T = 0.15 mm and a chamfer angle θ = −25 ° was performed using a diamond grindstone at the edge of the cutting edge formed by the rake face and the flank face of the cBN-based sintered body cutting tool. Further, a round honing with a radius of curvature of section R2 = 0.02 mm was applied to the portion where the flank and chamfer surface intersect.

Inventive product 1 was coated with a TiN film having an average film thickness of 4.0 μm on the surface of the cBN-based sintered body cutting tool subjected to the honing according to the conditions shown in Table 1 by the CVD method. Comparative product 1 was not coated with the honing-treated cBN-based sintered body cutting tool, and was an uncoated product. As a comparative product 2, the surface of a hoisted cBN-based sintered body was coated with a TiN film having an average film thickness of 4.0 μm by the CVD method under the conditions shown in Table 1. Inventive product 2 was coated with a TiN film having an average film thickness of 4.0 μm on the surface of the cBN-based sintered body cutting tool subjected to the honing according to the conditions shown in Table 2 by the PVD method. Inventive product 3 was obtained by coating the surface of the honing-treated cBN-based sintered body with a TiN film having an average film thickness of 4.0 μm by the PVD method under the conditions shown in Table 2.

The average grain size of the TiN film in Invention Product 1 and Comparative Product 2 is parallel to the rake face of the cBN-based sintered base material by observing the cross section of the TiN film by SEM and taking a photograph at approximately the center in the vertical direction of the TiN film. The number of crystal grains intersecting a straight line having a length of 10 μm was obtained. The average particle diameter of the TiN film in Inventions 2 and 3 is a length parallel to the rake face of the cBN-based sintered base material by TEM-observing the cross section of the TiN film and taking a photograph at approximately the center in the vertical direction of the TiN film. It was determined from the number of crystal grains intersecting a 1.0 μm straight line. These measurement results are shown in Table 1 and Table 2, respectively.

A cutting test 1 was performed on the inventive products 1 to 3 and the comparative products 1 and 2. As the evaluation of the finished surface roughness of the workpiece, the maximum height roughness Rz was used. The measuring method of Rz followed JIS standard B0601: 2001.

[Cutting test 1]
Cutting form: Continuous peripheral turning with outer diameter of 100 mm: Cylindrical hardened high hardness steel (SCM415H)
Workpiece hardness: HRC58-61
Cutting speed: 150 (m / min)
Cutting depth: 0.15 (mm)
Feed: 0.08 (mm / rev)
Cutting fluid: Not used Criteria for tool life: Cutting time when the maximum height roughness Rz of the finished surface of the workpiece is 1.6 μm or more is defined as tool life.

Table 3 and FIG. 1 show the relationship between the cutting time of Comparative Products 1 and 2 and Invention Products 1 to 3 and the maximum height roughness Rz (μm) of the workpiece.

In comparative product 1, the finished surface roughness Rz of the workpiece increased with wear of the cutting edge. In Comparative Product 2, the average particle size of the TiN film is larger than the cBN particle size of the cBN-based sintered base material. Since the comparative product 2 developed boundary damage, the finished surface roughness of the workpiece suddenly increased. Although the comparative product 2 is coated with a TiN film, boundary damage has developed, so that the finished surface roughness of the workpiece is larger and the tool life is shorter than the comparative product 1 that is not coated with the TiN film.

Inventive products 1 to 3 have a good balance between wear resistance and boundary damage, so that the finished surface roughness can be kept smaller than those of comparative products 1 and 2. Inventive products 2 and 3 in particular had a TiN film having an average particle size of 0.1 μm or less, so the finished surface roughness was small from the beginning of cutting, and the tool life was 2.5 to 3 times that of Comparative Product 1. Among them, Invention 3 having the smallest average particle size of the TiN film maintained the roughness of the finished surface of the work piece even during the cutting process and had the longest life.

A cBN-based sintered base material composed of cBN having an average particle size of 0.5 μm: 60% by volume and a binder phase composed of TiN and Al: the balance was sintered together with a cemented carbide base metal having a thickness of 5 mm. After sintering, it was confirmed that the cBN-based sintered base material and the cemented carbide were firmly bonded. This was processed to obtain a cBN-based sintered body cutting tool having a tool shape of JIS standard TNGN160408. A chamfer honing with a chamfer width T = 0.15 mm and a chamfer angle θ = −25 ° was performed using a diamond grindstone at the edge of the cutting edge formed by the rake face and the flank face of the cBN-based sintered body cutting tool. Further, a round honing with a radius of curvature of section R2 = 0.02 mm was applied to a portion where the flank surface and the chamfer surface intersect.

Inventive product 4 was obtained by coating the surface of the cBN-based sintered body cutting tool subjected to the above honing with a TiN film having an average film thickness of 4.0 μm on the surface of the substrate by the CVD method under the conditions shown in Table 4. Inventive product 5 has a surface of the hobbed cBN-based sintered body cutting tool coated with a TiN film having an average film thickness of 2.0 μm on the surface of the substrate according to the conditions shown in Table 5 by the CVD method. An Al ₂ O ₃ film having a thickness of 2.0 μm was coated. Comparative product 3 was an uncoated product without coating the cBN-based sintered body cutting tool subjected to the honing. Comparative product 4 was obtained by coating a TiN film having an average film thickness of 4.0 μm on the surface of the cBN-based sintered body cutting tool subjected to honing under the conditions shown in Table 4 by the CVD method. In the comparative product 5, the surface of the hobbed cBN-based sintered body was coated with an Al ₂ O ₃ film having an average film thickness of 4.0 μm by the CVD method under the conditions shown in Table 6.

Inventions 4,5, TiN film in comparative product 4,5, average particle size of the Al ₂ O ₃ film, TiN film, an Al ₂ O ₃ film of the cross-section SEM observation to TiN film, the Al ₂ O ₃ film A photograph was taken at approximately the center in the vertical direction, and it was determined from the number of crystal grains intersecting a straight line having a length of 12 μm parallel to the rake face of the cBN-based sintered base material. These measurement results are shown in Tables 4, 5, and 6, respectively.

A cutting test 2 having a cutting speed higher than that of the cutting test 1 was performed on the inventive products 4 and 5 and the comparative products 3 to 5. In this cutting test, the cutting edge becomes high temperature, so the cutting tool is required to have high oxidation resistance. For the evaluation of the finished surface roughness of the workpiece, the maximum height roughness Rz was used. The measuring method of Rz followed JIS standard B0601: 2001.

[Cutting test 2]
Cutting form: Continuous peripheral turning with outer diameter of 100 mm: Cylindrical hardened high hardness steel (SCM415H)
Workpiece hardness: HRC58-61
Cutting speed: 220 (m / min)
Cutting depth: 0.15 (mm)
Feed: 0.08 (mm / rev)
Cutting fluid: Not used Tool life criteria: The cutting time when the maximum height roughness Rz of the finished surface of the workpiece is 1.6 μm or more or the missing cutting time is defined as the tool life.

Table 7 and FIG. 2 show the relationship between the cutting time of Comparative Products 3 to 5 and Invention Products 4 and 5 and the maximum height roughness Rz (μm) of the finished surface of the workpiece.

Since the cutting test 2 was performed at a higher speed than the cutting test 1, the wear progressing speed was generally increased as compared with the cutting test 1. In Comparative product 3, the finished surface roughness of the workpiece increased with wear of the cutting edge. Comparative product 4 was coated with a TiN film, and the flank wear was smaller than that of comparative product 3, but because of the development of boundary damage, the finished surface roughness of the workpiece was large and the life was comparable to that of comparative product 3. . The comparative product 5 was coated with an Al ₂ O ₃ film, but the finished surface roughness was large from the beginning of cutting, and the finished surface roughness was further increased in 6 minutes. When the cutting edge after cutting for 6 minutes was observed, a slight peeling of the film was observed at the boundary portion during cutting. For this reason, it is considered that the finished surface roughness of the workpiece increased rapidly.

Inventive products 4 and 5 have a good balance between wear resistance and boundary damage, and the finished surface roughness can be kept smaller than those of comparative products 3 to 5. Inventive product 4 has a relatively small average grain size of TiN film of 0.2 μm, and the finished surface roughness can be maintained well from the beginning of cutting. As a result, Invention 4 was lost at the time of 10.3 minutes and reached the end of its life. As a result of observing the damage, crater wear was progressing and the dent reached the edge of the blade. From this, it is considered that the invention 4 is in a state where the cutting edge is sharpened due to crater wear, and the strength of the cutting edge is lowered to lead to a defect.

Invented product 5 coated with a multilayer film of TiN film and Al ₂ O ₃ film had a finished surface roughness at the initial stage of cutting similar to that of comparative product 1, but the increase in finished surface roughness over time was small. As a result, it had the longest life and was able to cut for 2.8 times the time of the comparative product 3. Since the TiN film has high adhesion to the cBN-based sintered body, it is difficult for peeling to occur. The Al ₂ O ₃ film is thin in order to suppress coarsening of Al ₂ O ₃ particles, but has a film thickness sufficient to exhibit oxidation resistance. Therefore, the inventive product 5 can extend the tool life while keeping the finished surface roughness of the workpiece small even in high-speed cutting.

The relationship between the cutting time of invention products 1-3 and comparative products 1 and 2 in cutting test 1 and the maximum height roughness Rz of the workpiece finish surface is shown. The relationship between the cutting time of invention products 4 and 5 and comparative products 3 to 5 in cutting test 2 and the maximum height roughness Rz of the workpiece finish surface is shown.

Claims (6)

The surface of a cBN-based sintered base material containing 20 to 100% by volume of cBN is coated with a titanium compound film composed of at least one selected from carbides, nitrides, and mutual solid solutions containing Ti. A coated cBN-based sintered body cutting tool, wherein the titanium compound film has an average film thickness of 0.1 to 10 μm, and the titanium compound film has an average particle diameter of 0.5 μm or less. The coated cBN-based sintered body cutting tool according to claim 1, wherein the titanium compound film has an average particle size of 0.1 μm or less. The coated cBN-based sintered body cutting tool according to claim 1 or 2, wherein the titanium compound film is a titanium compound film made of at least one selected from TiN, TiCN, and TiAlN. The coated cBN-based sintered body cutting tool according to any one of claims 1 to 3, wherein the cBN-based sintered body base material contains an element constituting the titanium compound film. The coated cBN-based sintered body cutting tool according to any one of claims 1 to 4, wherein an average particle diameter of the titanium compound film is equal to or less than an average particle diameter of cBN contained in the cBN-based sintered body base material. Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, Si carbide, nitride on the surface of the coated cBN-based sintered body cutting tool according to any one of claims 1 to 5. A coated cBN-based sintered cutting tool coated with a hard film made of at least one selected from oxides and their mutual solid solutions.

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