JP4232198B2 - Method for manufacturing a surface-coated cemented carbide cutting tool that exhibits excellent wear resistance in high-speed cutting of non-ferrous materials - Google Patents

Description

In the present invention, a diamond-like carbon film (hereinafter referred to as a DLC film) formed by plasma CVD (chemical vapor deposition) has the same hydrogen content and a relatively high hardness. The present invention relates to a method of manufacturing a surface-coated cemented carbide cutting tool (hereinafter referred to as a coated carbide tool) that exhibits excellent wear resistance when used for high-speed cutting of non-ferrous materials such as Cu alloys.

  In general, as a coated carbide tool, a throw-away tip that is used to attach and detachably attach to the tip of a cutting tool for turning and planing of various non-ferrous materials, drills used for drilling, etc. Known as miniature drills, solid type end mills used for chamfering, grooving, shoulder processing, etc. Also, the throwaway tip is detachably attached, and cutting is performed in the same manner as the solid type end mill. The throwaway end mill tool to perform is also known.

  Further, as a coated carbide tool, a hydrogen content of 10 to 15 atomic% is formed on the surface of a substrate (hereinafter referred to as a cemented carbide substrate) made of a tungsten carbide (hereinafter referred to as WC) -based cemented carbide by a plasma CVD method. Coated carbide tools formed by vapor-depositing a DLC film with an average layer thickness of 0.6 to 1.5 μm are known, and the hydrogen content in the DLC film constituting such a coated carbide tool is high in strength (chipping resistance). It is also known that it is determined to be 10 to 15 atomic% in consideration of properties) and hardness (wear resistance).

Further, the above-mentioned coated carbide tool has the raw material gas inlet 1 on one side wall and the exhaust port 4 on the other side wall as shown in the schematic plan view and schematic front view in FIGS. 2 (a) and 2 (b), respectively. And a support body disposed along the outer peripheral portion at a predetermined distance in the radial direction from the central axis of the rotary table 5 installed in the central portion of the apparatus. The carbide substrate 6 is attached to 8 and the inside of the apparatus is evacuated, and the inside of the apparatus is held by the heater 3 installed with the front rotary table sandwiched in the apparatus while maintaining a vacuum of, for example, 8 × 10 ⁻⁵ Pa or less. For example, a bias voltage (bias power supply 7) of −500 to −1500 V is applied to the carbide substrate 6 that is heated to 200 ° C. and rotates while rotating on the rotary table, and initial plasma is generated in the apparatus. In the state, raw material For example, hydrocarbons such as acetylene (C ₂ H ₂ ) and hydrogen are introduced at a flow rate of, for example, C ₂ H ₂ : 165 to 240 cc / min and H ₂ : 50 to 125 cc / min (in this case, relative If the introduction ratio of hydrocarbons is decreased and the introduction ratio of hydrogen is increased, the hydrogen content in the DLC film increases and the hardness becomes relatively low. Increasing the hydrogen introduction ratio and reducing the hydrogen content in the DLC film results in a relatively low hardness), which is decomposed and converted into plasma (+ C ions and + H ions) To produce a DLC film containing 10-15 atomic% hydrogen and having a hardness of 18-22 GPa on the surface of the cemented carbide substrate with an average layer thickness of 0.6-1.5 μm. It is also known to be.
Japanese Patent Laid-Open No. 3-158455 JP 2001-62605 A

  In recent years, there has been a strong demand for labor saving, energy saving, and cost reduction with respect to cutting, and with this, cutting tends to increase in speed. However, in the above-mentioned conventional coated carbide tools, the DLC constituting this The coating has a relatively high hydrogen content of 10 to 15 atomic% from the aspect of emphasizing chipping resistance so that it has high strength, while sacrificing its hardness. In the present situation, the wear progresses rapidly, and as a result, the service life is reached in a relatively short time.

In view of the above, the present inventors have focused on the DLC film of the above-mentioned conventional coated carbide tool and conducted research to further improve the wear resistance (hardness improvement). result,
(A) As shown in the schematic plan view and the schematic front view in FIGS. 1 (a) and 1 (b), respectively, a plurality of electromagnetic coils 2 are provided at predetermined intervals along the outer periphery of the side wall, and along the inner periphery of the side wall. Is also provided with a heater 3, and a plasma CVD apparatus provided with a source gas inlet 1 penetrating into the apparatus in the lateral center of the electromagnetic coil, and forming a magnetic field 9 with the electromagnetic coil, The magnetic flux density in the mounting portion of the cemented carbide substrate 6 is 50 to 300 G (Gauss) (in this case, the hydrogen content varies depending on the magnetic flux density), and the source gas from the source gas inlet 1 is only acetylene. , Except that the flow rate is a certain amount within the range of 150 to 250 cc / m, under the same conditions as the DLC film deposition conditions in the conventional plasma CVD apparatus, the hydrogen content is also 10 to 1. When a 5 atomic% DLC film is formed, the resulting DLC film will have a relatively high hardness of 25-35 GPa despite the same 10-15 atomic% hydrogen content. .
(B) In the coated carbide tool formed by vapor-depositing the DLC film of the above (a) with an average layer thickness of 0.6 to 1.5 μm, the DLC film has a hydrogen content of 10 to 15 as in the conventional DLC film. Since it contains atomic%, it has sufficient strength and retains excellent surface smoothness with a surface roughness of 30 nm or less, so it exhibits excellent chipping resistance and has a hardness of 18-22 GPa. Since it has a relatively high hardness of 25 to 35 GPa as compared with the conventional DLC coating, it has excellent wear resistance.
The research results shown in (a) and (b) above were obtained.

The present invention has been made on the basis of the above research results, and a plurality of electromagnetic coils are provided at predetermined intervals along the outer periphery of the apparatus side wall, while the electromagnetic coil is paired along the inner periphery of the apparatus side wall. Plasma CVD with a heater, and a raw material gas introduction port penetrating into the apparatus at the lateral center of the electromagnetic coil and a rotating table for mounting a carbide substrate at the center of the apparatus. Using the equipment,
The cemented carbide substrate is mounted on each of a plurality of support bodies arranged in a ring shape at a predetermined distance in the radial direction from the central axis on the rotary table, the inside of the apparatus is heated by the heater, and the rotary table A bias voltage is applied to the carbide substrate that rotates while rotating above, and an initial plasma is generated in the apparatus, and only acetylene is used as a raw material gas at a constant flow rate in the range of 150 to 250 cc / m. Introducing and decomposing this into plasma, while applying a current to the electromagnetic coil to form a magnetic field having a magnetic flux density of 50 to 300 G (Gauss) in the installation part of the cemented carbide substrate ,
Hydrogen content: 10-15 atomic%,
Hardness: 25-35 GPa,
Surface roughness: 30 nm or less,
Average layer thickness: 0.6 to 1.5 μm,
The present invention is characterized by a method for producing a coated carbide tool that exhibits excellent wear resistance in high-speed cutting of a non-ferrous material, in which a DLC film having the following characteristics is formed on the surface of the carbide substrate.

Next, the reason why the DLC film constituting the coated carbide tool is numerically limited as described above in the method of the present invention will be described.
That is, generally, the strength and hardness of the DLC film varies depending on the hydrogen content, and when the hydrogen content is less than 10 atomic%, the magnetic field film formation has a high hardness exceeding 35 GPa. The surface roughness decreases, Ra: a surface roughness of 30 nm or less cannot be ensured, and chipping (small chipping) is likely to occur during cutting. On the other hand, if the hydrogen content exceeds 15 atomic%, As a result, the high hardness of 25 GPa or more cannot be ensured even by magnetic field film formation, and the wear proceeds rapidly. By forming a film, a DLC film having a higher hardness even with the same hydrogen content is formed.
Also, if the average layer thickness of the DLC film is less than 0.6 μm, the desired wear resistance cannot be ensured over a long period of time, while if the average layer thickness exceeds 1.6 μm, chipping is performed on the cutting edge. Therefore, the average layer thickness was determined to be 1 to 10 μm.

The present invention exhibits a relatively high hardness of 25-35 GPa despite the fact that the hydrogen content of the DLC coating is 10-15 atomic%, which is the same as that of the conventional coated carbide tool, and thus various Al alloys The present invention provides a method for manufacturing a coated carbide tool that exhibits excellent wear resistance over a long period of time without causing chipping (small chipping) in high-speed cutting of copper alloy or Cu alloy.

Next, the method for producing the coated carbide tool of the present invention will be specifically described with reference to examples.

As raw material powders, WC powder, TiC powder, VC powder, TaC powder, NbC powder, Cr ₃ C ₂ powder, and Co powder, all having an average particle diameter of 1 to 3 μm, were prepared. The mixture is blended for 96 hours with a ball mill, dried and dried, and then pressed into a green compact at a pressure of 100 MPa, and the green compact is vacuumed at 6 Pa at a temperature of 1400 ° C. for 1 hour. Sintered under holding conditions, polished, and mirror-finished cutting edge rake surface, both of which are made of WC-based cemented carbide and have a chip shape conforming to ISO standard / SPGN120308 A- 1 to A-10 were produced.

Next, eight electromagnetic coils 2 are provided at predetermined intervals along the outer periphery of the side wall shown in FIG. 1, while a heater 3 is provided in a pair with the electromagnetic coil 2 along the inner periphery of the side wall. In the central portion in the horizontal direction, a plasma CVD apparatus provided with a raw material gas inlet 1 penetrating into the apparatus is used, and the carbide substrate 6 composed of the above-described carbide substrates A-1 to A-10 is placed in acetone. In a state where the ultrasonic cleaning is performed and the substrate is dried, the rotary table 5 in the apparatus is mounted on the support body 8 arranged in a ring shape at a predetermined distance in the radial direction from the central axis thereof. The inside of the apparatus was heated to 200 ° C. with the heater 3 while evacuating the interior and maintaining a vacuum of 6.5 × 10 ⁻⁵ Pa, and 20 r. p. m. On the rotary table rotating at a rotational speed of 20r. p. m. A bias voltage of −700 V is applied to the carbide substrate 6 rotating while rotating at a rotational speed of 200 cc / acetylene (C ₂ H ₂ ) as a source gas in a state where initial plasma is generated in the apparatus. Introduced at a constant flow rate of min, decomposed and converted to plasma, while applying a predetermined current in the range of 3 to 20 A to the electromagnetic coil 2 to form a magnetic field 9 to install the cemented carbide substrate 6 Of the target layer thickness shown in Table 2 under the condition that the magnetic flux density in the part is a predetermined magnetic flux density in the range of 50 to 300 G (Gauss) (the higher the magnetic flux density, the higher the hydrogen content in the DLC film). This invention method was implemented by forming a DLC film, and this invention coated carbide tip 1-10 as this invention coated carbide tool was manufactured.

For comparison purposes, the raw material gas inlet 1 is provided on one side wall and the exhaust port 4 is provided on the other side wall shown in FIG. 1, and the heater 3 is sandwiched between the rotary table 5 installed in the center of the apparatus. Using the provided plasma CVD apparatus, the flow rates of C ₂ H ₂ gas and H ₂ gas introduced from the raw material gas inlet 1 were C ₂ H ₂ gas: 165 to 240 cc / min and H ₂ : 50 to 125 cc, respectively. The hydrogen content of the DLC film is adjusted by changing within the range of / min (in this case, if the C ₂ H ₂ gas flow rate is relatively increased and the H ₂ gas flow rate is reduced, the hydrogen content is lowered). The conventional method is carried out by forming the DLC film having the target layer thickness shown in Table 2 under the same conditions except that the magnetic field is not formed by the electromagnetic coil 2, and the conventional coated carbide tool as a conventional coated carbide tool. Hard 1 to 10 were produced.

Subsequently, the hydrogen content and hardness of the DLC coating constituting the coated carbide chips 1 to 10 of the present invention and the conventional coated carbide chips 1 to 10 obtained as a result were measured by the recoil scattering analysis method [Elastic Recoil Detection]. [Analysis] (hydrogen content) and nanoindentation method (hardness), respectively, and the surface roughness was measured using an atomic force microscope [Atomic Force Microscope]. These measurement results are shown in Table 1.
Further, when the thickness of the DLC film was measured using a scanning electron microscope (longitudinal section measurement), all showed an average layer thickness (average value of five-point measurement) substantially the same as the target layer thickness. .

Next, in the state where the present invention coated carbide tips 1 to 10 and the conventional coated carbide tips 1 to 10 are screwed to the tip of the tool steel tool with a fixing jig,
Work material: JIS A5052 (composition is mass%, Si: 0.25%, Fe: 0.4%, Cu: 0.1%, Mg: 2.8%, Cr: 0.35%, Al and impurities: remaining) round bar,
Cutting speed: 1000 m / min. ,
Cutting depth: 8mm,
Feed: 0.4 mm / rev. ,
Cutting time: 90 minutes
Dry continuous high speed cutting test of Al alloy under the conditions of (normal cutting speed is 600 m / min.),
Work material: JIS / ADC12 (composition is, by mass%, Cu: 2.5%, Si: 10.2%, Al and impurities: remaining),
Cutting speed: 1000 m / min. ,
Cutting depth: 8mm,
Feed: 0.4 mm / rev. ,
Cutting time: 30 minutes,
The dry continuous high-speed cutting test of the Al alloy under the conditions (normal cutting speed is 600 m / min.),
Work material: JIS C2100 round bar (composition is mass%, Zn: 5.3%, Cu and impurities: remaining),
Cutting speed: 800 m / min. ,
Incision: 4mm,
Feed: 0.4 mm / rev. ,
Cutting time: 90 minutes
The dry continuous high-speed cutting test of the Cu alloy under the conditions (normal cutting speed was 300 m / min.). In any cutting test, the flank wear width of the cutting edge was measured. The measurement results are shown in Table 2.

As raw material powders, medium coarse WC powder having an average particle diameter of 5.5 μm, fine WC powder of 0.8 μm, TaC powder of 1.3 μm, NbC powder of 1.2 μm, ZrC of 1.2 μm Powder, 2.3 μm Cr ₃ C ₂ powder, 1.5 μm VC powder, 1.0 μm (Ti, W) C (mass ratio, TiC / WC = 50/50) powder, and 1 .8 μm Co powder was prepared, and each of these raw material powders was blended in the blending composition shown in Table 3, added with wax, ball milled in acetone for 24 hours, dried under reduced pressure, and then in a predetermined shape at a pressure of 100 MPa. The green compacts were press-molded, and these green compacts were heated to a predetermined temperature in the range of 1370 to 1470 ° C. at a rate of temperature increase of 7 ° C./min in a 6 Pa vacuum atmosphere. After holding at temperature for 1 hour, sintering under furnace cooling conditions 3 types of sintered carbide substrate-forming round bar sintered bodies having diameters of 8 mm, 13 mm, and 26 mm were formed, and further, the three kinds of round bar sintered bodies were ground and shown in Table 4. In combination, a carbide substrate (end mill) having a diameter of 4 mm × 13 mm, a length of 6 mm × 13 mm, a size of 10 mm × 22 mm, and a size of 20 mm × 45 mm, and a four-blade square with a twist angle of 30 degrees. ) B-1 to B-8 were produced.

Subsequently, these super-hard substrates (end mills) B-1 to B-8 were ultrasonically cleaned in acetone and dried, and then charged into the plasma CVD apparatus shown in FIG. The present invention method was carried out by forming a DLC film having the target layer thickness shown in Table 4 under the same conditions as above, and the present coated carbide end mills 1 to 8 as the present coated carbide tool were produced, respectively. .

Further, for the purpose of comparison, the above-mentioned carbide substrates (end mills) B-1 to B-8 are ultrasonically cleaned in acetone and dried, and then loaded into the plasma CVD apparatus shown in FIG. The same conditions as in Example 1 above, that is, the flow rates of C ₂ H ₂ gas and H ₂ gas introduced from the raw material gas inlet 1 were C ₂ H ₂ gas: 165 to 240 cc / min and H ₂ : 50, respectively. The DLC film having the target layer thickness shown in Table 4 under the same conditions except that the hydrogen content of the DLC film is adjusted within the range of ˜125 cc / min and the magnetic field is not formed by the electromagnetic coil 2. The conventional method was implemented by forming, and conventionally coated carbide end mills 1 to 8 as conventional coated carbide tools were manufactured, respectively.

Next, of the present invention coated carbide end mills 1-8 and conventional coated carbide end mills 1-8, the present invention coated carbide end mills 1-3 and conventional coated carbide end mills 1-3 are as follows:
Work material: Plane dimensions: 100 mm × 250 mm, JIS A2024 with a thickness of 50 mm (composition is mass%, Cu: 4.2%, Mn: 0.6%, Mg: 1.5%, Al and Impurity: the remaining plate material,
Cutting speed: 300 m / min. ,
Incision (groove depth): 12 mm,
Table feed: 1000 mm / min,
With respect to the dry high-speed grooving test of an Al alloy under the conditions (normal cutting speed is 150 m / min.), The coated carbide end mills 4 to 6 and the conventional coated carbide end mills 4 to 6 of the present invention,
Work material: Plane dimension: 100 mm × 250 mm, thickness: 50 mm JIS AC4B (composition is mass%, Cu: 2.9%, Si: 8.5%, Al and impurities: remaining),
Cutting speed: 300 m / min. ,
Incision (groove depth): 10 mm,
Table feed: 2000mm / min,
With respect to the dry high-speed grooving test of an Al alloy under the following conditions (normal cutting speed is 150 m / min.)
Work material: Plane dimensions: 100 mm × 250 mm, thickness: 50 mm JIS C1020 (purity: 99.98 mass% pure copper) plate material,
Cutting speed: 160 m / min. ,
Cut (groove depth): 30 mm,
Table feed: 1000 mm / min,
The dry high-speed grooving test of pure copper under the above conditions (normal cutting speed is 80 m / min.), And in each grooving test, the flank wear width of the peripheral edge of the cutting edge is The cutting groove length up to 0.1 mm was measured. The measurement results are shown in Table 4.
Table 4 shows the hydrogen content, hardness, and surface roughness measured under the same conditions as in Example 1 of the DLC film. The measurement results are the results of the above-mentioned carbide substrate (end mill) B- It is the value which the DLC film formed on the surface of this using the test piece of 1-B-8 on the same conditions shows.
Furthermore, regarding the thickness of the DLC film, it was confirmed that the average layer thickness (average value of 5-point measurement) was substantially the same as the target layer thickness, as measured with a scanning electron microscope (longitudinal section measurement). It was done.

  The diameters produced in Example 2 above were 8 mm (for forming carbide substrates B-1 to B-3), 13 mm (for forming carbide substrates B-4 to B-6), and 26 mm (for carbide substrates B-). 7 and B-8)), and the diameter x length of the groove forming part is 4 mm x 13 mm (by grinding) from these three kinds of round bar sintered bodies. Carbide substrates C-1 to C-3), 8 mm × 22 mm (Carbide substrates C-4 to C-6), and 16 mm × 45 mm (Carbide substrates C-7 and C-8), and all Carbide substrates (drills) C-1 to C-8 having a two-blade shape with a twist angle of 30 degrees were produced.

Next, the cutting edges of these carbide substrates (drills) C-1 to C-8 are subjected to honing, ultrasonically cleaned in acetone, and dried, and then installed in the plasma CVD apparatus shown in FIG. The coated carbide drill of the present invention as the coated carbide tool of the present invention was carried out by forming a DLC film having the target layer thickness shown in Table 5 under the same conditions as in Example 1 above. 1 to 8 were produced.

For comparison purposes, the cutting edges of the above-mentioned carbide substrates (drills) C-1 to C-8 are honed, ultrasonically cleaned in acetone, and dried, as shown in FIG. The conventional method was carried out by charging the plasma CVD apparatus and forming the DLC film having the target layer thickness shown in Table 5 under the same conditions as in Example 1 above. Hard drills 1 to 8 were produced, respectively.

Next, of the present invention coated carbide drills 1-8 and comparative coated carbide drills 1-8, for the present invention coated carbide drills 1-3 and comparative coated carbide drills 1-3,
Work material: Plane dimension: 100 mm × 250 mm, thickness: 50 mm JIS AC4B (composition is mass%, Cu: 2.9%, Si: 8.5%, Al and impurities: remaining),
Cutting speed: 200 m / min. ,
Feed: 0.6mm / rev,
Hole depth: 10mm,
With respect to the Al alloy wet high-speed drilling test (normal cutting speed is 80 m / min.), The coated carbide drills 4 to 6 and the comparative coated carbide drills 4 to 6 of the present invention,
Work material: Plane size: 100 mm × 250 mm, thickness: 50 mm JIS C2100 (composition is mass%, Zn: 4.9%, Cu and impurities: remaining),
Cutting speed: 300 m / min. ,
Feed: 0.6mm / rev,
Hole depth: 16mm,
With respect to the Cu alloy wet high-speed drilling cutting test under the conditions (normal cutting speed is 90 m / min.), The present invention coated carbide drills 7 and 8 and the comparative coated carbide drills 7 and 8,
Work material: Plane dimension: 100 mm × 250 mm, thickness: 50 mm JIS A5052 (composition is mass%, Si: 0.25%, Fe: 0.4%, Cu: 0.1%, Mg: 2.8%, Cr: 0.35%, Al and impurities: remaining) plate material,
Cutting speed: 220 m / min. ,
Feed: 0.7mm / rev,
Hole depth: 40mm,
We performed high-speed wet drilling test (normal cutting speed of 100 m / min.) Of Al alloy under the above conditions, and the clearance of the tip cutting edge surface in any wet drilling test (using water-soluble cutting oil) The number of drilling processes until the surface wear width reached 0.2 mm was measured. The measurement results are shown in Table 5.
Table 5 shows the hydrogen content, hardness, and surface roughness measured under the same conditions as in Example 1 of the DLC film. The measurement results show the above-mentioned carbide substrate (drill) C- It is the value which the DLC film formed on the surface of this using the test piece of 1-C-8 on the same conditions shows.
Furthermore, regarding the thickness of the DLC film, it was confirmed that the average layer thickness (average value of 5-point measurement) was substantially the same as the target layer thickness, as measured with a scanning electron microscope (longitudinal section measurement). It was done.

From the results shown in Tables 1 to 5, there is no substantial difference in the hydrogen content between the coated carbide tool of the present invention and the conventional coated carbide tool with respect to the hardness of the DLC coating, i.e., 10 to 15 for both. Despite the atomic% hydrogen content, the latter only exhibits a hardness of 18-22 GPa, whereas the former exhibits a relatively high hardness of 25-35 GPa, which results in the coatings exceeding the present invention It is clear that hard tools exhibit excellent wear resistance without high chipping (small chipping) compared to conventional coated carbide tools at high speed cutting of various Al alloys, pure copper and Cu alloys. .
As described above , according to the method of the present invention, excellent wear resistance is achieved not only when cutting under normal conditions, but also when cutting various workpieces under high-speed cutting conditions. Therefore, it is possible to produce a coated cemented carbide tool that exhibits high performance, and can satisfactorily cope with labor saving and energy saving of cutting, and further cost reduction.

The plasma CVD apparatus used for forming the DLC film of the coated carbide tool of this invention is shown, (a) is a schematic plan view, and (b) is a schematic front view. The plasma CVD apparatus used for forming the DLC film of the conventional coated carbide tool is shown, (a) is a schematic plan view, and (b) is a schematic front view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw material gas inlet 2 Electromagnetic coil 3 Heater 4 Exhaust port 5 Turntable 6 Carbide substrate 7 Bias power supply 8 Support body 9 Magnetic field

Claims (1)

A plurality of electromagnetic coils are provided at predetermined intervals along the outer periphery of the apparatus side wall, while a heater is provided in a pair with the electromagnetic coil along the inner periphery of the apparatus side wall, and the apparatus is provided at the lateral central portion of the electromagnetic coil. Using a plasma CVD apparatus provided with a turntable for mounting a cemented carbide substrate made of tungsten carbide based cemented carbide at the center of the apparatus while providing a source gas introduction port penetrating inside,
The cemented carbide substrate is mounted on each of a plurality of support bodies arranged in a ring shape at a predetermined distance in the radial direction from the central axis on the rotary table, the inside of the apparatus is heated by the heater, and the rotary table A bias voltage is applied to the carbide substrate that rotates while rotating above, and an initial plasma is generated in the apparatus, and only acetylene is used as a raw material gas at a constant flow rate in the range of 150 to 250 cc / m. Introducing and decomposing this into plasma, while applying a current to the electromagnetic coil to form a magnetic field having a magnetic flux density of 50 to 300 G (Gauss) in the installation part of the cemented carbide substrate ,
Hydrogen content: 10-15 atomic%,
Hardness: 25-35 GPa,
Surface roughness: 30 nm or less,
Average layer thickness: 0.6 to 1.5 μm,
A method of manufacturing a surface-coated cemented carbide cutting tool that exhibits excellent wear resistance in high-speed cutting of a non-ferrous material , wherein a diamond-like carbon coating having the following characteristics is formed on the surface of the cemented carbide substrate.

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