Surface-coated cutting tools with excellent fracture resistance

Abstract

To provide a surface-coated cutting tool excellent in defect resistance.SOLUTION: A surface-coated cutting tool has a hard coating layer of total average thickness of 0.55-10.5 μm which has at least two layers of a lower layer of average thickness of 0.05-1.0 μm directly contacting the surface of a tool substrate comprising a tungsten carbide-based hard metal, and an upper layer of 0.5-9.5 μm directly contacting the lower layer. The compressive residual stress value of the tool substrate is 300 MPa or more but 2,000 MPa or less. The lower layer is a Ti nitride layer or Ti carbonitride layer, and the upper layer satisfies 0.75≤Xavg≤0.90 and 0≤Yavg<0.05 when representing the composition formula of the upper layer by (AlXTi1-X)(CYN1-Y). The cutting tool includes an AlTi complex nitride or carbonitride layer having NaCl type face-centered cubic crystal structure.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] In addition to continuous high-speed cutting, the present invention relates to a surface-coated cutting tool (hereinafter sometimes simply referred to as a "coated tool") that exhibits excellent cutting performance by having a hard coating layer with excellent chipping resistance and wear resistance even in interrupted cutting.

Background Art

[0002] In the cutting of stainless steel or steel materials with a remaining welded surface, particularly in a cutting tool coated with AlTiN by the CVD method, it is known that high wear resistance is exhibited in the continuous high-speed cutting region due to its film hardness and oxidation resistance. On the other hand, in the cutting of stainless steel with high toughness of the workpiece, unstable machining such as machining of a welded cross-section with a varying depth of cut, or cutting in a highly intermittent cutting region, due to its high film hardness, significant particle detachment occurs, and abnormal damage accompanied by tool chipping progresses, resulting in the problem that the original performance cannot be exhibited.

[0003] In contrast, for example, in Patent Document 1, in a surface-coated cutting tool having a rake face and a flank face, and the boundary portion between them forming a cutting edge, the orientation index TC(111) on the (111) plane of a TiAlN layer having a specific composition and a NaCl-type crystal structure formed on the surface of the substrate by the CVD method shows a maximum value, and when the value satisfies 1.0 < TC(111) ≤ 4.0, a surface-coated cutting tool that exhibits excellent wear resistance and chipping resistance is obtained. (In deriving the orientation index TC(111) of the (111) plane, the measured values of the X-ray diffraction peak intensities for the crystal planes of (all1), (200), (220), (311), and (222), which are the crystal growth preferential orientations of the Ti, Al composite carbonitride, are used.)

[0004] In addition, Patent Document 2 discloses that a hard coating layer formed on a substrate surface by chemical vapor deposition consists of a Ti and Al composite nitride (TiAlN) layer or composite carbonitride (TiAlCN), has a face-centered cubic structure with at least 90% by volume, and when X-ray diffraction is performed, the orientation index TC(111) of the (111) plane is the largest, with a value of at least 1.5, and the residual compressive stress of the composite nitride layer or composite carbonitride layer is said to improve the crack resistance and wear resistance of the tool. (Note that the orientation index TC(111) of the (111) plane was derived using measured values ​​of X-ray diffraction peak intensities for the (111), (200), (220), and (311) crystal planes, which are the preferred crystal orientations of the Ti and Al composite carbonitride.) [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-124463 [Patent Document 2] Special Publication No. 2018-522748 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, there has been a strong demand for labor-saving and energy-saving cutting processes. Accordingly, cutting processes are becoming faster and more efficient. Coated tools are required to have excellent chipping resistance because particle shedding can cause abnormal damage, including tool breakage. Furthermore, for long-term use, excellent wear resistance is also required. Patent Documents 1 and 2 propose coated tools that combine excellent fracture resistance and wear resistance by orienting the crystal grains of an Al-Ti composite carbonitride having a cubic crystal structure, which is formed as a hard coating layer by chemical vapor deposition, in the (111) plane. However, simply orienting the crystal planes of the crystal grains of an Al, Ti composite carbonitride having a specific composition and an NaCl-type crystal structure to the (111) plane and specifying the orientation index within a specific range does not make it possible to achieve both wear resistance and fracture resistance, resulting in the problem that long-term use cannot be achieved.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to solve the above problems and to provide a surface-coated cutting tool that exhibits excellent wear resistance and chipping resistance without early wear damage even when used for a long period of time. [Means for solving the problem]

[0008] From the above viewpoint, the present inventors have conducted extensive research to improve both the fracture resistance and the wear resistance of a coated tool having a hard coating layer made of an Al-Ti composite nitride formed by chemical vapor deposition, and as a result, have obtained the following findings.

[0009] That is, the inventors have found that when forming a lower layer of a hard coating made of CVD-AlTiN on a tungsten carbide-based cemented carbide substrate, a surface-coated cutting tool with excellent fracture resistance can be obtained by, for example, performing pretreatment such as wet blasting or dry blasting to intentionally impart an appropriate value of residual compressive stress to the substrate, or by performing posttreatment such as wet blasting or dry blasting after the formation of the hard coating to intentionally impart an appropriate value of residual compressive stress to the substrate, or by performing both of these.

[0010] The present invention has been made based on the above findings, "(1) A surface-coated cutting tool having a hard coating layer on the surface of a tool substrate made of a tungsten carbide-based cemented carbide alloy, (a) the hard coating layer has at least two layers, a lower layer directly contacting the outermost surface of the tool substrate and an upper layer directly contacting the lower layer, and the total average thickness of the hard coating layer is 0.6 to 10.5 μm; (b) the lower layer is made of a nitride or carbonitride of Ti and has an average layer thickness of 0.05 to 1.0 μm; (c) The upper layer is a composite nitride layer of Al and Ti or a composite carbonitride layer. Consists of layer, the average layer thickness of which is 0.5 to 9.5 μm; The composite nitride or composite carbonitride is Composition formula: (Al X Ti 1-X )(C Y N 1-Y ), The composite nitride or the composite carbonitride The average content ratio X of Al to the total amount of Ti and Al avg and the composite nitride or The composite carbonitride The average content ratio Y of C to the total amount of C and N avg (However, X avg , Y avg are atomic ratios), respectively, 0.75≦X avg ≦0.90, 0≦Y avg <0.05 and has a NaCl-type face-centered cubic structure only With death , (d) the value of the residual compressive stress of the tungsten carbide-based cemented carbide is 300 MPa to 2000 MPa; (e) When X-ray diffraction is performed on the upper layer, the ratio of the diffraction intensity value of the cubic (200) plane to the diffraction intensity value of the cubic (111) plane, I(111) / I(200), is The relationship 1.0≦I(111) / I(200)≦5.9 (excluding I(111) / I(200) when it is 3.5) is satisfied. A surface-coated cutting tool characterized by: (2) The value of compressive residual stress of tungsten carbide-based cemented carbide is A surface-coated cutting tool according to (1), characterized in that the surface-coated cutting tool has a compressive strength of 850 MPa to 2000 MPa. It is characterized by the following. In this specification, when a numerical range is indicated using "~" or "-", it means that the lower and upper limits of the numerical range are included. Next, the tool substrate and the hard coating layer of the coated tool of the present invention will be specifically described.

[0011] 1. Tool base; The tool substrate is made of a tungsten carbide-based cemented carbide. In the present invention, a residual compressive stress of 300 to 2000 MPa, preferably 850 to 2000 MPa, is applied to the surface of the cemented carbide substrate, thereby improving adhesion with the hard coating layer and enabling the tool to be used as a cutting tool with excellent cutting performance in terms of chipping resistance and wear resistance, not only in the continuous high-speed cutting region but also in the intermittent cutting region. By setting the residual compressive stress value at the surface of the alloy substrate to 300 MPa or more, preferably 850 MPa or more, the propagation of cracks during processing can be suppressed and high chipping resistance can be achieved, while by setting the residual compressive stress value to 2000 MPa or less, the peeling resistance effect during processing can be improved. The residual compressive stress can be imparted to the tool substrate by wet blasting or dry blasting as a pretreatment before the formation of the hard coating layer described later, or as a posttreatment after the formation of the hard coating layer described later. When wet blasting or dry blasting is performed as a pretreatment before forming a hard coating layer, the relaxation of residual compressive stress can be suppressed by setting the film formation temperature lower than usual, thereby extending the life of the tool. For example, the application of residual compressive stress to the substrate by blasting is carried out by projecting a dry or wet blasting treatment onto the tool surface using media containing abrasive grains of alumina, silicon nitride, or zirconia before or after the formation of a hard coating layer. Blasting conditions; Abrasive grains: ZrO2 grains, Al2O3 grains Grain shape: spherical and / or polygonal Abrasive grain size (grain size): 125-425 μm (spherical) / <125 μm (polygonal) Blasting pressure: 0.10-0.4MPa Projection angle relative to the normal of the rake face: 0-90 degrees Projection time: 4-16 seconds

[0012] 2.Hard coating layer; The hard coating layer comprises a bottom layer and a top layer, and further layers may include a top layer on top of the top layer. The average thickness of the hard coating layer is set to 0.6 μm or more because adhesion, wear resistance, and chipping resistance cannot be sufficiently ensured over long-term use if it is less than 0.6 μm. On the other hand, if the average thickness exceeds 10.5 μm, peeling or chipping is likely to occur, so it is desirable to set it to 10.5 μm or less.

[0013] (a) lower layer; <Average layer thickness> The lower layer is made of titanium nitride or carbonitride and is provided directly on the tool substrate. The average thickness of the lower layer is set to 0.05 μm or more, because sufficient adhesion cannot be obtained if the thickness is less than 0.05 μm. On the other hand, if the thickness exceeds 1.0 μm, the resulting coating becomes significantly deformed and peels off from the substrate in the early stages of cutting, so the lower layer is set to 1.0 μm or less.

[0014] <Component composition> The composition of the lower layer is not particularly limited as long as it is a nitride or carbonitride of Ti, since it does not impede the object of the present invention. For example, the composition of the lower layer may be TiC Z N 1-Z When expressed as Z, the range of 0≦Z≦0.7 is preferred. That is, if Z is contained in an amount greater than 0.7, the hardness of the lower layer increases excessively, and peeling from the interface between the lower layer and the substrate tends to occur.

[0015] (b) Upper layer <Average layer thickness> The upper layer is made of a composite nitride or composite carbonitride of Ti and Al and is provided directly on and in contact with the lower layer. The average thickness of the upper layer is set to 0.5 μm or more because if it is less than 0.5 μm, the hard layer in the entire coating is insufficient and wear resistance is poor. On the other hand, if the average thickness exceeds 9.5 μm, the hard layer becomes too thick and is prone to chipping during processing, so it is set to 9.5 μm or less.

[0016] <Component composition> The upper layer is composed of an Al and Ti composite nitride layer (AlTiN layer) or a composite carbonitride layer (AlTiCN layer), and exhibits uniform wear resistance and toughness throughout the entire layer. The Ti component improves high-temperature strength, and the Al component complements high-temperature hardness and heat resistance, so that a low wear coefficient is maintained even under high-temperature cutting conditions, and excellent heat resistance can be demonstrated. The composite nitride or composite carbonitride constituting the Al-Ti composite nitride layer or composite carbonitride layer is specifically represented by the composition formula: (Al X Ti 1-X )(C Y N 1-Y ), but the average Al content X avg If the value of X (atomic ratio) is less than 0.75, the high-temperature hardness is insufficient and the wear resistance decreases. avg When the (atomic ratio) value exceeds 0.90, the relative Ti content decreases, and (Al X Ti 1-X )(C Y N 1-Y ) layer itself will have a reduced high-temperature strength, making it more susceptible to chipping and fracture. avg The value of (atomic ratio) is set to the range of 0.75 to 0.90, which is close to the maximum hardness and provides a particularly high effect. In addition, the C component has the effect of improving hardness, but the average content ratio Y avg If the atomic ratio is 0.05 or more, the high-temperature strength decreases, so the average content ratio Y avg (Atomic ratio) is 0≦Y avg It was defined as <0.05.

[0017] <Crystal structure> The upper layer is made of Al, Ti composite nitride or composite carbonitride (Al X Ti 1-X )(C Y N 1-Y ) can improve hardness by adopting a NaCl-type face-centered cubic structure (hereinafter sometimes simply referred to as "cubic structure"). That is, by forming a composite nitride layer or composite carbonitride layer of Al and Ti having a high orientation in the (111) plane of a cubic crystal structure, high hardness can be achieved. Furthermore, when the ratio I(111) / I(200) of the diffraction intensity value I(111) of the (111) plane to the diffraction intensity value I(200) of the (200) plane in the upper layer is 1.0 or more, the crystal grains are less likely to fall off during processing. It is defined as I(111) / I(200)≧1.0.

[0018] (c)Top layer In the present invention, a top layer can be provided on the AlTi composite nitride layer or AlTi composite carbonitride layer as the upper layer, if necessary, from the viewpoint of improving wear resistance, etc. Specifically, a layer made of an Al oxide such as α-Al2O3 or κ-Al2O3, or a Ti nitride or carbonitride layer, for example, an l-TiCN layer, can be provided in a thickness of 4.5 μm or less.

[0019] 3. Method for forming hard coating layer; (a) Method of imparting residual compressive stress to the tool substrate Residual compressive stress can be imparted to the tool substrate by wet blasting or dry blasting as a pretreatment before the formation of the hard coating layer described below, or as a posttreatment after the formation of the hard coating layer. When the blasting treatment is carried out as a pretreatment before the formation of the hard coating layer described later, the film formation temperature can be set lower than the conventional treatment temperature, thereby suppressing relaxation of the applied stress and thereby extending the life of the cutting tool.

[0020] (b) Method for forming the lower layer The lower layer of the hard coating layer is a compound layer consisting of Ti and nitrogen, or a compound layer consisting of Ti, nitrogen, and carbon. In the first step, chemical vapor deposition is used to form a TiN layer or TiCN layer with excellent adhesion by adjusting the reaction gas composition (gas group A) and the reaction atmosphere, including pressure and temperature, to appropriate ranges for each compound layer to be formed. [Film formation conditions] 1)TiN layer; Processing method: CVD film formation Reactant gas composition (volume %) TiCl4: 3.0~6.0%, N2: 25.0~35.0%, H2: remainder, Reaction atmosphere pressure: 4.0 to 5.0 kPa, Reaction atmosphere temperature: 780-900℃ 2)TiCN layer; Processing method: CVD film formation Reactant gas composition (volume %) TiCl4:3.0~6.0%, N2:15.0~30.0%, CH4 or CH3CN: 0.6-2.0%, H2: balance Reaction atmosphere pressure: 7.0 to 12.0 kPa, Reaction atmosphere temperature: 780-900℃

[0021] (c) Method for forming the upper layer <Deposition of upper layer> Next, in the method for forming the upper layer according to the present invention, the conditions for forming the AlTi composite nitride layer or AlTi composite carbonitride layer are, for example, to use two types of NH3 gas with different heating temperatures, and the high-temperature ammonia gas is used to suppress nucleation and promote crystallization, thereby obtaining coarse grains. That is, the method for forming an AlTiN or AlTiCN layer according to the present invention forms the film by alternately repeating the second step (initial nucleus formation step), i.e., the step of forming AlTiN crystals or AlTiCN crystals that serve as initial nuclei for forming an AlTiN or AlTiCN film, and the third step (crystal growth step), i.e., the step of growing the AlTiN crystals or AlTiCN crystals that serve as initial nuclei to form an AlTiN or AlTiCN film. The film formation conditions for each film formation step are outlined below. In particular, in the second step, which is the step of forming the initial nuclei of fine AlTiN or AlTiCN crystals, the following gas group B and gas group C are alternately supplied to the reactor with a phase difference to form a film. Nucleation is promoted by using ammonia gas preheated to a high temperature (e.g., 300 to 450°C). In the subsequent third step, the following gas group D and gas group E are alternately supplied to the reactor with a phase difference to form a film. By changing the ammonia gas used to ammonia gas preheated to a low temperature (e.g., 50 to 250°C), nucleation is suppressed, crystallization is promoted, and the desired crystals can be obtained. The number of times the second step and the third step are repeated is adjusted according to the target film thickness.

[0022] [Film formation conditions] 1) Second step (initial nucleation step) Processing method: Film formation using CVD method Reactant gas composition (vol %): Gas group B: TiCl4: 0.01 to 0.04%, AlCl3: 0.01 to 0.05%, N2: 0~10%, C2H4: 0~0.5%, H2: remainder Gas group C: NH3: 0.1-0.8%, H2: 25.0-35.0%, Reaction atmosphere pressure: 4.0 to 5.0 kPa, Reaction atmosphere temperature: 700-850℃ Supply cycle: 1~5 seconds, Gas supply time per cycle: 0.15 to 0.25 seconds, Phase difference between gas group B supply and gas group C supply: 0.10 to 0.20 seconds Gas group C preheat temperature: 300-450℃

[0023] 2) 3rd process (crystal growth process) Processing method: Film formation using CVD method Reactant gas composition (vol %): Gas group D: TiCl4: 0.01 to 0.04%, AlCl3: 0.01 to 0.05%, N2: 0~10%, C2H4: 0~0.5%, H2: remainder, Gas group E: NH3: 0.1-0.8%, H2: 25.0-35.0%, Reaction atmosphere pressure: 4.0 to 5.0 kPa, Reaction atmosphere temperature: 700-850℃ Supply cycle: 1~5 seconds, Gas supply time per cycle: 0.15 to 0.25 seconds, Phase difference between supply of gas group D and supply of gas group E: 0.10 to 0.20 seconds Preheat temperature for gas group E: 50 to 250°C In addition, the volume % of each gas component in the reaction gas composition (volume %) of each of the second and third steps indicates the volume % of each component calculated with the total of gas group B and gas group C being 100 volume % in the second step, and indicates the volume % of each component calculated with the total of gas group D and gas group E being 100 volume % in the third step. [Effects of the Invention]

[0024] The surface-coated cutting tool according to the present invention imparts a predetermined range of residual compressive stress to the surface of the tool substrate, thereby maintaining the wear resistance of the hard coating layer during cutting, enhancing the peeling resistance, suppressing the progression of cracks, and exhibiting resistance to fracture and chipping, thereby improving the tool life. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a cross-sectional view showing the relationship between a tool substrate of a coated tool according to the present invention and a lower layer (Ti(C)N layer), an upper layer (CVD-AlTiN(C) layer), and a top layer that constitute a hard coating layer. DETAILED DESCRIPTION OF THE INVENTION

[0026] Next, the coated tool of the present invention will be specifically described with reference to examples. [Example]

[0027] The raw material powders were WC powder, TiC powder, TaC powder, NbC powder, Cr3C2 powder, and Co powder, all of which had an average particle size of 1 to 3 μm. These raw material powders were blended to the composition shown in Table 1, and wax was added. The mixture was ball milled in acetone for 24 hours and dried under reduced pressure. The mixture was then pressed into a green compact of the desired shape at a pressure of 98 MPa. This green compact was then vacuum sintered in a vacuum of 5 Pa at a predetermined temperature in the range of 1370 to 1470°C for 1 hour. After sintering, tool substrates A to C made of WC-based cemented carbide and having the insert shape specified in ISO standard SEEN1203AFTN were produced.

[0028] Next, each of these tool substrates A to C was placed in a chemical vapor deposition apparatus, and coated tools 1 to 8 of the present invention were produced according to the following procedure. As described above, the present invention is premised on the assumption that tool substrates A to C are subjected to blasting, laser peening, or the like as pretreatment before forming a hard coating layer or as posttreatment after forming the lower, upper, or top layer of the hard coating layer, thereby imparting residual compressive stress (see Table 2). First, in the first step, one of tool substrates A to C is placed in a chemical vapor deposition apparatus, and film formation is carried out for a certain period of time under the temperature and pressure conditions set forth in the formation conditions (formation symbols) A to H shown in Table 3 using gas group A (TiCl4, N2, CH4, CH3CN, and the remainder H2) having the component composition shown in Table 3. Using gas group A, film formation is carried out for a certain period of time at an initial film formation temperature of 800°C to 900°C, and then the film formation temperature is lowered to 700°C to 850°C, and film formation is carried out for a certain period of time, producing a dense film.

[0029] Next, in the second step (initial nucleus formation step for the upper layer), film formation was carried out for a certain period of time based on the gas composition, supply conditions, and gas reaction conditions (pressure, temperature, process time (seconds)) of gas group B and gas group C described in the formation conditions (formation symbols) A to H shown in Table 4, and in the third step (crystal growth step for the upper layer), film formation was carried out for a certain period of time based on the gas composition, supply conditions, and gas reaction conditions (pressure, temperature, process time (seconds)) of gas group D and gas group E described in the formation conditions (formation symbols) A to E shown in Table 5, thereby obtaining coated tools 1 to 5 of the present invention shown in Table 9. In addition, for the coated tools 6 to 8 of the present invention, after the coating was formed under the forming conditions (forming symbols) F to H shown in Table 5, a κ-Al2O3 layer, an l-TiCN layer, or an α-Al2O3 layer was further formed as the top layer under the forming conditions shown in Table 6, thereby improving the surface. 7 The present invention tools 6 to 8 shown in FIG.

[0030] For comparison purposes, coatings were formed under the conditions a to e shown in Tables 3, 4 and 5 to obtain coated tools 1 to 5 as comparative examples. In addition, after forming the films under the forming conditions f to h shown in Tables 3, 4 and 5, the κ-Al2O3 layer, l-TiCN layer or α-Al2O3 layer was formed as the top layer under the forming conditions shown in Table 6. 8 Comparative Example Tools 6 to 8 shown in the table below were obtained.

[0031] Table 7 shows the residual compressive stress of the tool substrate for coated tools 1 to 8 of the present invention, the target average total thickness of the hard coating layer, the target average thickness of the lower layer and the type of film formed, the target average thickness of the upper layer, the average Al content (Xavg), the average C content (Yavg), the crystal structure and diffraction line intensity ratio (I(111) / I(200)), and the target average thickness of the top layer and the film formed. Table 8 shows the results for comparative coated tools 1 to 8 in the same manner.

[0032] The thickness of the hard coating layer of the coated tools 1 to 8 of the present invention and the coated tools 1 to 8 of the comparative examples was measured using a scanning electron microscope (magnification: 5000 times). That is, the tool was polished so that the cross section perpendicular to the substrate was exposed, and each layer was observed at a magnification of 5,000 to 20,000 times. The layer thicknesses were measured at five points within the observation field, and the average value was taken as the average layer thickness. The results are shown in Table 7 for coated tools 1 to 8 of the present invention, and in Table 8 for coated tools 1 to 8 of the comparative examples. In addition, the average Al content X of the AlTiN or AlTiCN in the upper layer avg (atomic ratio) and the average content ratio of C component Y avg The atomic ratio was determined by irradiating a polished surface of a sample with an electron beam from the surface side of the sample using an electron probe microanalyzer (EPMA, Electron-Probe-Micro-Analyser), and averaging the 10-point analysis results of the characteristic X-rays obtained. The coated tools 1 to 8 of the present invention are shown in Table 7, and the coated tools 1 to 8 of the comparative examples are shown in Table 8. avg and Y avg Indicates the value of

[0033] The crystal structures of the AlTiN and AlTiCN layers in the upper layers of the hard coating layers of the coated tools of the present invention and the comparative example can be confirmed by performing X-ray diffraction on the surface of the hard coating layer parallel to the tool substrate surface using an X-ray diffractometer with Cu-Kα radiation as the radiation source under conditions of a measurement range (2θ) of 20 to 120 degrees, a scan step of 0.013 degrees, and a measurement time per step of 0.48 seconds / step. The X-ray diffraction peaks appear between the diffraction angles of the same crystal planes shown for cubic TiN (JCPDS00-038-1420) and cubic AlN (JCPDS00-046-1200) (e.g., 36.66 to 38.53°, 43.59 to 44.77°, 61.81 to 65.18°). Furthermore, from the measured X-ray diffraction peak intensities I(hkl) for the (200) and (111) planes, the ratio I(111) of the diffraction peak intensity I(111) for the (111) plane to I(200) of the diffraction peak intensity for the (200) plane can be calculated, as I(111) / I(200). The residual stress in the tool substrate is sin 2The measurements were performed using the Ψ method with an X-ray diffractometer using Cuκα. The diffraction peak of the WC(211) plane was used for the measurements, and calculations were performed using a Young's modulus of 534 GPa and a Poisson's ratio of 0.22.

[0034] [Table 1]

[0035] [Table 2]

[0036] [Table 3]

[0037] [Table 4]

[0038] [Table 5]

[0039] [Table 6]

[0040] [Table 7]

[0041] [Table 8]

[0042] Next, with the various coated tools clamped to the tip of a tool steel cutter using a fixing jig, the following dry intermittent cutting test of stainless steel was carried out for the coated tools 1 to 8 of the present invention and the coated tools 1 to 8 of the comparative examples, and the maximum cutting length until tool fracture was evaluated. The results are shown in Table 9.

[0043] ≪Cutting conditions≫ Cutting test: dry face milling, center cut cutting, Work material: JIS / SUS304L 100mm wide, 400mm long block material with holes (4 holes with a diameter of 50 mm spaced 50 mm apart) Rotation speed: 968 min -1 , Cutting speed: 180m / min. Cutting depth: 1.5mm, Feed per blade: 0.25 mm / blade Cutting time: Processing until the cutting edge is chipped (evaluation ends at a maximum processing length of 8.0 m)

[0044] [Table 9]

[0045] As is clear from the cutting test results shown in Table 9, the coated tool of the present invention has a residual compressive stress of 300 MPa or more and 2000 MPa or less at the outermost surface of the tool substrate, and the hard coating layer in direct contact with the tool substrate surface comprises a lower layer of a Ti nitride or carbonitride and an upper layer of a composite nitride or composite carbonitride of Al and Ti having an NaCl-type face-centered cubic crystal structure. This prevents chipping and other problems caused by the shedding of fine crystal grains and provides excellent fracture resistance and wear resistance over a long period of time. [Industrial Applicability]

[0046] As described above, the surface-coated cutting tool of the present invention exhibits excellent wear resistance, fracture resistance, and chipping resistance not only when used in continuous cutting or intermittent cutting of ordinary steels, but also when used in intermittent cutting of stainless steels and other hard-to-cut materials on which fused surfaces remain, and therefore fully satisfies the needs for high-performance cutting equipment, labor-saving and energy-saving cutting, and cost reduction.

Claims

1. A surface-coated cutting tool having a hard coating layer on the surface of a tool substrate made of a tungsten carbide-based cemented carbide, (a) the hard coating layer has at least two layers, namely, a lower layer in direct contact with the outermost surface of the tool substrate and an upper layer in direct contact with the lower layer, and the total average thickness of the hard coating layer is 0.6 to 10.5 μm; (b) the lower layer is made of a nitride or carbonitride of Ti and has an average layer thickness of 0.05 to 1.0 μm; (c) the upper layer is a layer made of a composite nitride or composite carbonitride of Al and Ti, and has an average layer thickness of 0.5 to 9.5 μm; The composite nitride or composite carbonitride has the composition formula: (Al Ｘ Ti １－Ｘ ) (C Ｙ N １－Ｙ ) the average content ratio X of Al to the total amount of Ti and Al in the composite nitride or the composite carbonitride ａｖｇ and an average content ratio Y of C to the total amount of C and N in the composite nitride or the composite carbonitride. ａｖｇ (However, X ａｖｇ , Y ａｖｇ are atomic ratios), and 0.75≦X ａｖｇ ≦0.90, 0≦Y ａｖｇ <0.05 and has only an NaCl-type face-centered cubic crystal structure, (d) The value of the residual compressive stress of the tungsten carbide-based cemented carbide is 300 MPa or more and 2000 MPa or less; (e) When X-ray diffraction is performed on the upper layer, the ratio of the diffraction intensity value of the cubic (200) plane to the diffraction intensity value of the cubic (111) plane, I(111) / I(200), is The relationship of 1.0≦I(111) / I(200)≦5.9 (excluding the case where I(111) / I(200) is 3.5) is satisfied. A surface-coated cutting tool characterized by:

2. 2. The surface-coated cutting tool according to claim 1, wherein the tungsten carbide-based cemented carbide has a residual stress value of 850 MPa or more and 2000 MPa or less.

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