Hard Coating for Cutting Tools

Abstract

The present invention relates to a cutting tool composed of a hard substrate (such as cemented carbide, cermet, ceramic, and cubic boron nitride) and a hard coating film formed on the hard substrate. The hard coating film for the cutting tool of the present invention is formed on the substrate of the cutting tool in a multilayer structure, wherein the hard coating film includes one or more coating films made of oxides and one or more coating films made of nitrides, and is characterized in that, throughout the hard coating film, the O / (O + N) ratio at the center of the cutting edge of the cutting tool is lower than the O / (O + N) ratio in a region more than 100 μm away from the center of the cutting edge.

Description

Technical Field

[0001] The present invention relates to a hard coating film formed on a hard substrate such as cemented carbide, cermet, ceramic, and cubic boron nitride (cBN) for a cutting tool. More specifically, the present invention relates to a hard coating film that extends the life of a cutting tool by controlling the content ratio of oxygen and nitrogen of the hard coating film to be different for each part of the cutting tool in a hard coating film composed of a multi-layer structure coating film including a nitride film and an oxide film. Background Art

[0002] The edge of a cutting tool is exposed to a high-temperature environment of about 1000 °C during high-speed machining of high-hardness materials, and is worn due to friction and oxidation caused by contact with a workpiece, and is also subjected to mechanical shocks such as cracks. Therefore, a cutting tool must have sufficient wear resistance and toughness.

[0003] In order to impart the required wear resistance and toughness to the cutting tool as described above, a hard coating film is formed on the surface of cemented carbide commonly used for cutting tools by chemical vapor deposition (hereinafter referred to as "CVD").

[0004] Such a hard coating film is composed of a single layer or a multi-layer of non-oxide type coating films (e.g., TiN, TiC, and TiCN), an oxide type coating film having excellent oxidation resistance (e.g., Al2O3), or a mixed layer thereof, and examples of the non-oxide type coating films include carbides, nitrides, and carbonitrides of metal elements in Groups 4, 5, and 6 of the periodic table such as TiN, TiC, TiCN, etc., and examples of the oxide type coating films include α-Al2O3 or γ-Al2O3.

[0005] Meanwhile, the functions and required physical properties of a cutting tool are slightly different depending on the part in contact with the material to be cut. For example, generally, the rake face requires oxidation resistance, wear resistance, weld resistance, etc., the edge requires oxidation resistance, heat-resistant crack resistance, delamination resistance, etc., and the flank face requires wear resistance.

[0006] In order to satisfy to some extent the physical properties required differently for each part of the cutting tool, multi-element thin films including various elements, multi-layer structure thin films composed of different material layers, or post-processing techniques have been applied, but these techniques have limitations in differentiating the physical properties of each part of the tool. Summary of the Invention

[0007] Technical Problem

[0008] An object of the present invention is to provide a hard coating film for a cutting tool, which can achieve physical properties closer to the required physical properties of the cutting edge, rake face, and flank face respectively by controlling the content ratio of oxygen and nitrogen to be different for each part to be formed in the hard coating film formed on the cutting tool, thereby extending the tool life.

[0009] Technical solution

[0010] To achieve the above object, the present invention provides a cutting tool having a hard coating film, which is a hard coating formed on a substrate of the cutting tool in a multi-layer structure, wherein the hard coating film includes one or more layers of coating films made of oxides and one or more layers of coating films made of nitrides, and in the entire hard coating film, the O / (O + N) ratio at the center of the cutting edge of the cutting tool is lower than the O / (O + N) ratio in a region more than 100 μm away from the center of the cutting edge.

[0011] Advantageous effects

[0012] In the case of a cutting tool applying the hard coating film of the present invention, the oxidation resistance and welding resistance are improved due to the increase in the O / (O + N) ratio of the rake face or flank face, and the delamination resistance is improved due to the decrease in the O / (O + N) ratio of the cutting edge portion. Description of the drawings

[0013] Figure 1 Schematically shows the structure of the hard coating film of the present invention. Detailed description of the embodiments

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0015] However, the embodiments of the present invention shown below can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. The embodiments of the present invention are provided to more comprehensively describe the present invention to those skilled in the art.

[0016] The hard coating film for a cutting tool of the present invention is formed on a substrate of the cutting tool in a multi-layer structure, wherein the hard coating film includes one or more layers of coating films made of oxides and one or more layers of coating films made of nitrides, and is characterized in that in the entire hard coating film, the O / (O + N) ratio at the center of the cutting edge of the cutting tool is lower than the O / (O + N) ratio in a region more than 100 μm away from the center of the cutting edge.

[0017] Figure 1 Schematically shows the structure of the hard coating film of the present invention. As Figure 1As shown, a coating film made of an oxide and a coating film made of a nitride form a multilayer structure on the surface of a substrate. And in the entire hard coating film, in the region portion (shaded portion) within about 100 μm from the cutting edge center (the bent portion in the substrate) to the rake face or the flank face, the ratio of oxygen / (oxygen + nitrogen) (hereinafter referred to as O / (O + N)) is characterized by being controlled to be relatively low compared to other regions.

[0018] Meanwhile, the ratio of O / (O + N) can be uniformly formed in the region (shaded portion) within about 100 μm from the cutting edge center (the bent portion in the substrate) to the rake face or the flank face, or can be formed in a form where the ratio of O / (O + N) gradually increases continuously, intermittently, or in a mixed form from the center to the rake face or the flank face.

[0019] When the O / (O + N) of the cutting edge and the rake face or the flank face are controlled to be different from each other, the rake face or the flank face has a relatively high O / (O + N) compared to the cutting edge, and thus has improved oxidation resistance and weld resistance. Meanwhile, the cutting edge has a relatively low O / (O + N), and thus has improved delamination resistance. Through the above, the characteristics of the hard coating film can be controlled according to the respective required physical properties of the rake face (or the flank face) and the cutting edge, so that the life of the cutting tool can be extended.

[0020] In addition, in the hard coating film, when the difference between the O / (O + N) at the cutting edge center of the cutting tool and the O / (O + N) in the region more than 100 μm away from the cutting edge center is less than 0.05, the difference in physical properties between the above-mentioned cutting edge and the rake face or the flank face may be insufficient, and when it is greater than 0.15, the oxidation resistance and weld resistance of the cutting edge become too low, which is not desirable. Therefore, it is preferable to keep the difference in O / (O + N) within the range of 0.05 to 0.15.

[0021] In addition, the coating film made of an oxide and the coating film made of a nitride that constitute the hard coating film can each be a compound containing one or more elements selected from Al, Cr, Ti, Y, V, W, Ta, Nb, Mo, Zr, Hf, and Si.

[0022] In addition, when the hard coating film is formed to be as thin as having a thickness less than 0.01 μm, the thickness is too thin for the hard coating film to sufficiently protect the cutting tool, and when the thickness is greater than 20 μm, delamination and chipping, etc. may occur due to the increase in residual stress, which results in a reduction in the life of the tool instead. Therefore, it is preferable to form the thickness within the range of 0.01 μm to 20 μm.

[0023] In addition, when the total thickness of the oxide-made coating films is made thin to less than 0.01 μm, the antioxidation property is insufficient, and when the total thickness is greater than 5 μm, delamination and cracking may occur due to the increase in residual stress, and the conductivity of the coating films is significantly reduced, thereby reducing the density and adhesion of the coating films during deposition. Therefore, it is preferred to form the total thickness in the range of 0.01 μm to 5 μm, more preferably 0.01 μm to 3 μm, and most preferably 0.01 μm to 1 μm.

[0024] In addition, in the upper part and / or lower part of the coating film made of an oxide and the coating film made of a nitride, one or more layers of a compound selected from carbides, nitrides, oxides, carbonitrides, oxynitrides, oxycarbides, oxycarbonitrides, borides, boron nitrides, boron carbides, boron carbonitrides, boron oxynitrides, boron oxycarbides, boron oxycarbonitrides, and boron oxynitrides can be additionally formed, and all of these compounds contain one or more selected from Al, Cr, Ti, Y, V, W, Ta, Nb, Mo, Zr, Hf, and Si.

[0025] In addition, the coating film made of an oxide can be constituted by, for example, Al2O3, which is constituted by a cubic γ phase or a hexagonal α phase.

[0026] Embodiment

[0027] [Examples]

[0028] Preparation of Hard Coating Film

[0029] In an embodiment of the present invention, a coating film made of an oxide is formed on the surface of a hard substrate made of a sintered body such as cemented carbide, cermet, ceramic, or cubic boron nitride by using magnetron sputtering (which is a physical vapor deposition (PVD) method). In addition, a hard coating film having a multi-layer structure including a coating film made of an oxide and a coating film made of a nitride is formed by applying a hybrid PVD process that simultaneously combines arc ion plating and magnetron sputtering.

[0030] Specifically, the substrate is washed with wet microspray and ultrapure water, and then installed in a coating furnace in a dry state at a position radially spaced a predetermined distance from the central axis on a rotating table along the circumference. The initial vacuum pressure in the coating furnace is reduced to 8.5×10 -5Below Torr, the temperature is raised to 400°C to 600°C, and then while rotating on a rotary table in an argon (Ar) gas atmosphere, a pulsed bias voltage of -200V to -300V is applied to the rotating substrate, and ion bombardment is carried out for 30 minutes to 60 minutes. The gas pressure for coating is maintained below 50mTorr, preferably below 40mTorr, and for the substrate bias voltage during coating, it is -100V to -150V when coating an oxide film and -20V to -100V when coating a nitride film. The above coating conditions can vary according to the equipment characteristics and conditions.

[0031] More specifically, as the substrate, a cemented carbide composed of WC with an average particle size of 0.8μm and Co with a content of 10 wt% is used. The oxide coating film is made of Al2O3, and is formed under the conditions of a bias voltage of -125V (pulsed DC, 20kHz to 45kHz), a sputtering power of 20kW, injecting O2 and Ar as reaction gases and a pressure of 0.5Pa, using an Al 99.9at.% target. The nitride coating film is made of AlTiN or AlCrN, and is formed under the conditions of a bias voltage of -30V to -60V, an arc current of 100A to 150A, injecting N2 as a reaction gas and a pressure of 2.7Pa to 4.0Pa, using an AlTi(60at.% / 40at.%) target or an AlCr(64at.% / 36at.%) target. Here, an example of the present invention is constituted by applying a pulsed bias voltage of -200V to -300V for ion bombardment for 5 minutes to 10 minutes immediately after forming the oxide coating film, and a comparative example of the present invention is constituted by not performing a separate process other than coating immediately after forming the oxide coating film.

[0032] Examples and comparative examples of the present invention are manufactured under the above conditions, and basic information on the structure, thickness, and hardness of the corresponding hard coating films is shown in Table 1 below.

[0033] [Table 1]

[0034]

[0035] Analysis Results of O / (O + N) of Hard Film

[0036] Table 2 below shows the results of O / (O + N) in the coating film at the cutting edge center of the cutting tools of the samples in the examples and comparative examples analyzed by energy dispersive X-ray spectroscopy (EDX), and O / (O + N) in the coating film in the region 100 μm away from the cutting edge center. At this time, generally, the rake face of the tool is placed in a direction parallel to the target, and the flank face of the tool is placed in a direction perpendicular to the target, which can be changed according to the shape of the tool or the mounting method of the tool on the turntable. In sample numbers 1-2(R), 1-4(R), 2-2(R), and 2-4(R), the tool was mounted on the turntable such that the rake face of the tool was placed in a direction perpendicular to the target, and the flank face of the tool was placed in a direction parallel to the target.

[0037] [Table 2]

[0038]

[0039] As confirmed in Table 2 above, in the hard coating film of the examples, the value of O / (O + N) in the coating film at the cutting edge center of the cutting tool is 0.05 to 0.15 lower than the value of O / (O + N) in the coating film in the region 100 μm away from the cutting edge center (rake face or flank face) of the cutting tool. On the contrary, in the hard coating film of the comparative examples, the value of O / (O + N) in the coating film at the cutting edge center of the cutting tool is 0.01 to 0.07 higher than the value of O / (O + N) in the coating film in the region 100 μm away from the cutting edge center (rake face or flank face) of the cutting tool. That is, for the hard coating film of each example, O / (O + N) is low in the coating film at the cutting edge center of the cutting tool, and there is a more significant difference in O / (O + N) according to the position of the cutting edge.

[0040] Evaluation of Cutting Performance

[0041] To evaluate the weld resistance, delamination resistance, and chipping resistance of the hard coating films prepared as shown in Table 2, a milling test was conducted and evaluated under the following conditions.

[0042] When machining carbon steel at a low cutting speed, due to the welding of the material to be cut and the resulting built-up edge of the tool, the weld resistance of the rake face has a great influence on the cutting performance. When machining stainless steel under finish machining conditions (finish machining with a cutting depth of 1 mm or less), strain hardening is concentrated at the cutting edge portion, so the delamination resistance of this cutting edge portion has a great influence on the cutting performance. As for die steel, mechanical friction wear is the main wear type, but due to frequent chipping, the chipping resistance of the cutting edge portion also has a great influence on the cutting performance, just like its wear resistance, so that the tool can fully exhibit its original wear resistance.

[0043] (1) Evaluation of weldability

[0044] Material to be cut: Carbon steel (SM45C)

[0045] Sample model: SDKN1504AESN - SU

[0046] Cutting speed: 150 m / min

[0047] Feed per tooth: 0.2 mm / tooth

[0048] Depth of cut: 2 mm

[0049] (2) Evaluation of delamination resistance

[0050] Material to be cut: Stainless steel (STS316L)

[0051] Sample model: SNMX1206ANN - MF

[0052] Cutting speed: 120 m / min

[0053] Feed per tooth: 0.1 mm / tooth

[0054] Depth of cut: 1 mm

[0055] (3) Evaluation of chipping resistance

[0056] Material to be cut: Die steel (NAK80)

[0057] Sample model: ADKT170608PESR - MM

[0058] Cutting speed: 100 m / min

[0059] Feed per tooth: 0.15 mm / tooth

[0060] Depth of cut: 5 mm

[0061] The evaluation results obtained under the above conditions are shown in Table 3 below.

[0062] [Table 3]

[0063]

[0064] As confirmed in Table 3 above, compared with the hard coatings of the comparative examples, the hard coatings 1 - 2, 1 - 2(R), 1 - 4, and 1 - 4(R) in the examples have excellent weldability, delamination resistance, and chipping resistance.

[0065] The hard coating film of the embodiment has such a structure that since the O / (O+N) at the edge center is lower than that of the rake face or the flank face, the anti-delamination property and the chipping resistance of the edge part are excellent, and since the O / (O+N) of the rake face or the flank face is high, the oxidation resistance and the weld resistance are excellent. For the above reasons, compared with the hard coating film of the comparative example, the hard coating film of the embodiment has better physical properties required for each part of the tool. Therefore, it is determined to have excellent cutting performance in the milling test.

[0066] Here, in the case of Samples 1-1 and 2-1 having a double-layer structure of a nitride coating film and an oxide coating film, since the film hardness is low, the film thickness is small, and there is no outermost layer protecting the oxide coating film, the oxide coating film is rapidly consumed during processing. Therefore, the oxidation resistance and the weld resistance are reduced, resulting in relatively low cutting performance. Therefore, it can be seen that when the oxide coating film is stacked between the nitride coating films as in Samples 1-2, 1-4, 2-2, and 2-4, it is structurally stable, and when there is an O / (O+N) difference for each part of the tool as in Samples 1-2 and 1-4, it is determined to be a film structure that can best reflect the obtained effect of improving the cutting performance.

[0067] In addition to the 12 samples evaluated above, hard coating film samples having a nitride coating film containing one or more selected from Al, Cr, Ti, Y, V, W, Ta, Nb, Mo, Zr, Hf, and Si on the upper and / or lower part of a coating film made of an oxide were additionally prepared. A milling test was performed on this sample, and the evaluation results are shown in Table 4 below.

[0068] [Table 4]

[0069]

[0070] As confirmed in Table 4 above, compared with the hard coating film of the comparative example, the hard coating film of the embodiment generally has excellent weld resistance, anti-delamination property, and chipping resistance.

[0071] It can be seen that the hard coating film having a nitride coating film containing one or more selected from Al, Cr, Ti, Y, V, W, Ta, Nb, Mo, Zr, Hf, and Si on the upper and / or lower part of a coating film made of an oxide has slightly different cutting performances for each evaluation item depending on the composition and the stacking position of the nitride. As described above, by combining the compositions and structures of various materials in the coating film composed of an oxide and a nitride of the present invention, it is possible to expect to design a hard coating film suitable for the processing environment and accordingly improve the performance.

Claims

1. A hard coating film formed on a substrate of a cutting tool in a multi-layer structure, wherein: The hard coating film is formed by a physical vapor deposition (PVD) method; and The hard coating film includes one or more coating films made of oxides and one or more coating films made of nitrides on the upper and lower portions of the coating film made of oxides, wherein the coating film made of oxides is composed of Al2O3, and the Al2O3 is composed of a cubic γ phase or a hexagonal α phase; and In the entire hard coating film, the O / (O + N) ratio at the center of the cutting edge of the cutting tool is 0.05 to 0.15 lower than the O / (O + N) ratio in a region more than 100 μm away from the center of the cutting edge.

2. The hard coating film according to claim 1, wherein the coating film made of nitrides contains one or more selected from Al, Cr, Ti, Y, V, W, Ta, Nb, Mo, Zr, Hf, and Si.

3. The hard coating film according to claim 1 or 2, wherein: The total thickness of the hard coating film is 0.02 μm to 20 μm; and The total thickness of all the oxide films contained in the hard coating film is 0.01 μm to 5 μm.

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