JP7649467B2 - Surface-coated cutting tools - Google Patents

Description

The present invention relates to a surface-coated cutting tool (hereinafter sometimes simply referred to as a "coated tool") that exhibits excellent cutting performance not only in continuous high-speed cutting but also in intermittent cutting, due to the hard coating layer having excellent chipping resistance and wear resistance.

In cutting difficult-to-cut materials such as stainless steel, steels with remaining cut surfaces, and nickel-based heat-resistant alloys, cutting tools coated with AlTiN by CVD are known to exhibit high wear resistance in continuous high-speed cutting due to the hardness and oxidation resistance of the coating.
On the other hand, when the workpiece is a difficult-to-cut material such as stainless steel or nickel-based heat-resistant alloy, which has high toughness, or when cutting an unstable cutting surface where the cutting depth varies, or when cutting in a cutting region with high intermittency, the high hardness of the coating causes significant particle fall-off, leading to the progression of abnormal damage including tool breakage, and the original performance cannot be demonstrated.

In contrast, for example, in Patent Document 1, it is said that when a hard coating layer formed on a substrate surface by a chemical vapor deposition method is made of a composite nitride (TiAlN) layer or a composite carbonitride (TiAlCN) layer of Ti and Al, has a face-centered cubic structure of at least 90 volume %, has a maximum orientation index TC(111) in the (111) plane when subjected to X-ray diffraction and has a value of at least 1.5, and has a residual stress value of 0 MPa or less and -5000 MPa or more in a residual compression state, the crack resistance and wear resistance of the tool are improved.
In addition, the orientation index TC(111) of the (111) plane is derived using the measured values of the X-ray diffraction peak intensities for each of the (111), (200), (220) and (311) crystal planes of a Ti and Al complex carbonitride.

Patent Document 2 also describes that in a surface-coated cutting tool having a rake face and a flank face, the boundary between them forming a cutting edge, when the orientation index TC(111) of the (111) plane of a TiAlN layer of a specific composition and NaCl type crystal structure formed on the surface of a substrate by a CVD method exhibits a maximum value and this value satisfies 1.0<TC(111)≦4.0, a surface-coated cutting tool exhibiting excellent wear resistance and chipping resistance can be obtained.
In this case, the orientation index TC(111) of the (111) plane is derived using the measured values of the X-ray diffraction peak intensities for each of the (111), (200), (220), (311), and (222) crystal planes, which are the preferred crystal growth orientations of Ti and Al composite carbonitrides.

Special table 2018-522748 publication JP 2017-124463 A

In recent years, there has been a strong demand for labor-saving and energy-saving in cutting processing. Accordingly, there is a trend for cutting processing to become even faster and more efficient. Coated tools are required to have excellent resistance to chipping, since the shedding of particles can cause abnormal damage including tool breakage. Furthermore, for long-term use, excellent wear resistance is also required.
In addition, Patent Documents 1 and 2 propose a coated tool having both excellent fracture resistance and wear resistance, in which the crystal faces of the crystal grains of an Al, Ti composite carbonitride having a cubic crystal structure formed as a hard coating layer by a chemical vapor deposition method are oriented in the (111) plane.
However, simply orienting the crystal planes of the crystal grains of an Al, Ti composite carbonitride having a NaCl type crystal structure of a specific composition to the (111) plane and specifying the orientation index within a specific range improves the fracture resistance but reduces the wear resistance. As a result, there has been a problem in that it is not possible to achieve both fracture resistance and wear resistance, and long-term use cannot be realized.

The present invention aims to solve these problems and provide a surface-coated cutting tool that has excellent wear resistance and high chipping resistance without early wear damage even when used for a long period of time.

From the above viewpoint, the inventors have conducted extensive research to simultaneously improve and enhance the chipping resistance and wear resistance of a coated tool having a hard coating layer made of a composite carbonitride of Al and Ti formed by chemical vapor deposition, and have come to the following findings.

In other words, the inventors discovered that when forming a lower layer of a hard coating layer made of CVD-AlTiN on a tungsten carbide-based cemented carbide substrate, for example, the cutting edge rake face of the substrate can be subjected to pretreatment such as wet blasting or dry blasting, or wet blasting or dry blasting can be performed as a post-treatment after the hard coating layer is formed, or even both can be performed to intentionally impart appropriate residual stresses to the cutting edge rake face and flank face of the substrate, thereby obtaining a surface-coated cutting tool with excellent chipping resistance without reducing wear resistance.

Specifically, the residual stress S2 on the cutting edge rake face of the tungsten carbide based cemented carbide substrate of the surface-coated tool is set to a value smaller than the residual stress S1 on the cutting edge flank (S1>S2), and a residual stress of at least -200 MPa or less (S2≦-200 MPa) is imparted, the residual stress S1 on the cutting edge flank of the substrate is set to a value larger than the residual stress S2 (S1>S2), and the absolute value of the difference between S1 and S2 is set to a value larger than 250 MPa , and more preferably, the residual stress S2 on the cutting edge rake face is set to a residual stress of -850 MPa or less (S2≦-850 MPa), that is, a residual compressive stress of 850 MPa or more, and the residual stress S1 on the cutting edge flank of the substrate is set to a value larger than the residual stress S2 (S1>S2), and the absolute value of the difference between S1 and S2 is set to 500 This was made on the basis of the finding that by setting the value to be greater than 100 MPa , a surface-coated cutting tool having excellent fracture resistance without decreasing wear resistance and particularly suitable for turning can be obtained.
Here, when the residual stress S2 on the cutting edge rake face is, for example, "-200 MPa," this means that the residual stress S2 is a residual compressive stress and has a residual compressive stress value of 200 MPa, and when "S2≦-200 MPa" this means that "the residual stress S2 is -200 MPa or less," or in other words, "the residual compressive stress S2 is 200 MPa or more."
The same is true for the residual stress S1 on the cutting edge flank.

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,
(a) the hard coating layer has at least two layers, namely 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 21.0 μm;
(b) the lower layer is made of a Ti nitride or carbonitride and has an average layer thickness of 0.05 to 2.0 μm;
(c) the upper layer is a composite nitride layer or a composite carbonitride layer of Al and Ti, and the average layer thickness is 0.5 to 20.0 μm;
When expressed by a composition formula: (Al _X Ti _1-X ) (C _Y N _1-Y ), an average content ratio X _avg of Al to the total amount of Ti and Al in said composite nitride layer or said composite carbonitride layer and an average content ratio Y _avg of C to the total amount of C and N in said composite nitride layer or said composite carbonitride layer (wherein X _avg and Y _avg are both atomic ratios) satisfy 0.70≦X _avg ≦0.90 and 0≦Y _avg <0.05, respectively, and the composite nitride layer or composite carbonitride layer has a NaCl-type face-centered cubic crystal structure,
(d) When the residual stress on the flank of the cutting edge of the tungsten carbide based cemented carbide of the surface-coated tool is S1 and the residual stress on the rake face of the cutting edge is S2,
α) S1>S2
β) S2≦-200MPa
γ) The absolute value of the difference between S1 and S2 is greater than 250 MPa.
(2) When X-ray diffraction is performed on the upper layer, the ratio of the diffraction intensity value of the cubic (111) plane to the diffraction intensity value of the cubic (200) plane, I(111)/I(200), is
2. The surface-coated cutting tool according to claim 1, wherein the relationship of 1.0≦I(111)/I(200) is satisfied.
(3) When the residual stress on the flank of the cutting edge of the tungsten carbide-based cemented carbide of the surface-coated tool is S1 and the residual stress on the rake face of the cutting edge is S2,
α) S1>S2
β) S2≦-850MPa
γ) The absolute value of the difference between S1 and S2 is greater than 500 MPa.
It is characterized by the following.
In addition, when "to" or "-" is used in this specification to indicate a numerical range, 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.

1. Tool base;
The tool substrate is made of a tungsten carbide-based cemented carbide. In the present invention, a residual stress of -200 MPa or less, more preferably -850 MPa or less is imparted to the cutting edge rake face of the cemented carbide substrate, thereby increasing adhesion with the hard coating layer, and the tool can be used as a cutting tool having 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.
Furthermore, by setting the residual stress value on the cutting edge rake face of the alloy substrate to -200 MPa or less, more preferably -850 MPa or less, it is possible to suppress the development of cracks during machining and to exhibit high chipping resistance.
On the other hand, as with the cutting face, the compressive residual stress increases on the flank, and if the absolute value of the difference between the residual stress value on the rake face and the residual stress value on the flank falls below 250 MPa, coating peeling is likely to occur starting from the tool flank during plastic deformation of the base material. Therefore, it is necessary that the absolute value of the difference between the residual stress value on the rake face and the residual stress value on the flank be greater than 250 MPa, and preferably greater than 500 MPa.
The residual stress can be imparted to the tool substrate by wet blasting or dry blasting as a pretreatment before the formation of a hard coating layer described later, or as a posttreatment after the formation of a hard coating layer described later.
When wet blasting or dry blasting is performed as a pretreatment before the formation of a hard coating layer, the film formation temperature can be set lower than usual to suppress relaxation of residual stress, thereby extending the life of the tool.
For example, the application of residual stress to the substrate by blasting is carried out by projecting a dry or wet blasting treatment onto the tool surface using media containing alumina, silicon nitride, or zirconia abrasive grains before or after the formation of a hard coating layer.
Blasting conditions:
Abrasive grains: ₂ grains of ZrO, ₃ grains of Al ₂ O Abrasive grain shape: spherical and/or polygonal Abrasive grain size (grain size): 125-425 μm (spherical) / <125 μm (polygonal)
Blasting pressure: 0.1-0.4MPa
Blast projection at 70-90° from the rake face. Projection time: 4-16 seconds

2. Hard coating layer;
The hardcoat layer comprises a bottom layer and a top layer, and further layers may include a top layer disposed on 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 a long period of use if the average thickness is less than 0.6 μm. On the other hand, if the average thickness exceeds 21.0 μm, peeling or chipping is likely to occur, so it is preferable to set the average thickness to 21.0 μm or less.

(a) bottom layer;
<Average layer thickness>
The lower layer is made of a Ti 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 average thickness is less than 0.05 μm. On the other hand, if the average thickness exceeds 2.0 μm, the deformation of the obtained hard coating layer becomes significant and peeling from the tool substrate occurs easily in the early stage of cutting, so the average thickness is set to 2.0 μm or less.

<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, when expressed by the composition formula TiC _Z N _1-Z , the range of 0≦Z≦0.05 is preferable.
That is, if Z is contained in an amount greater than 0.05, the hardness of the lower layer increases excessively, and peeling from the interface between the lower layer and the substrate becomes more likely to occur.

(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 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 the wear resistance is poor. On the other hand, if the average thickness exceeds 20.0 μm, the hard layer becomes too thick and peeling or chipping occurs easily during processing, so the average thickness is set to 20.0 μm or less.

<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, while 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.
Specifically, the composite nitride or composite carbonitride constituting the Al, Ti composite nitride layer or composite carbonitride layer can be expressed by the composition formula: (Al _x Ti _1-X ) (C _Y N _1-Y ). When the value of the average Al content X _avg (atomic ratio) is less than 0.70, the high-temperature hardness is insufficient and the wear resistance decreases, while when the value of X _avg (atomic ratio) exceeds 0.90, the high-temperature strength of the (Al _x Ti _1-X ) (C _Y N _1-Y ) layer itself decreases due to the relative decrease in the Ti content, making chipping and damage more likely to occur. Therefore, the value of the average Al content X _avg (atomic ratio) is specified to be in the range of 0.70 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 if the average content Y _avg (atomic ratio) of the C component is 0.05 or more, the high-temperature strength decreases, so the average content Y _avg (atomic ratio) of the C component is specified to be 0≦Y _avg <0.05.

<Crystal Orientation>
The Al or Ti composite nitride or composite carbonitride (Al _x Ti _1-x ) (C _y N _1-y ) constituting the upper layer can improve hardness by adopting a NaCl type face-centered cubic structure (hereinafter sometimes simply referred to as a "cubic structure").
That is, by forming an Al-Ti composite nitride layer or composite carbonitride layer having a high orientation in the (111) plane of a cubic crystal structure, it is possible to increase the hardness.
In addition, when the ratio I(111)/I(200) of the diffraction intensity value I(200) of the (111) plane to the diffraction intensity value I(200) of the (200) plane in the upper layer is 1.0 or more, crystal grains are less likely to fall off during processing, so it is desirable to make I(111)/I(200)≧1.0.

(c) Top layer
In the present invention, a top layer can be provided on the AlTi composite nitride layer or the AlTi composite carbonitride layer, which is the upper layer, as necessary, from the viewpoint of improving wear resistance and adapting to a wider range of processing applications.
Specifically, a layer made of an Al oxide such as α-Al ₂ O ₃ or κ-Al ₂ O ₃ , or a Ti nitride layer or carbonitride layer can be provided within the range of 4.5 μm or less.

3. Method for forming a hard coating layer;
(a) Method of imparting residual stress to tool substrate Residual stress can be imparted to the tool substrate by blasting (wet blasting or dry blasting) as a pretreatment before the formation of a hard coating layer described below, or as a posttreatment after the formation of a hard coating layer.
When the blast treatment is performed as a pretreatment before the formation of a hard coating layer described later, the film formation temperature can be set lower than the conventional treatment temperature to suppress the tensile stress of the hard coating layer, thereby making it possible to extend the life of the cutting tool.

(b) Method for forming the lower layer The lower layer of the hard coating layer is a compound layer made of Ti and nitrogen, or a compound layer made of Ti, nitrogen and carbon. In the first step, a chemical vapor deposition method is used, and the reaction atmosphere, such as the reaction gas composition (gas group A) and the pressure and temperature, are adjusted within appropriate ranges for each compound layer to be formed, thereby forming a TiN layer or TiCN layer with excellent adhesion.
[Film formation conditions]
1) TiN layer;
Processing method: CVD film formation Reaction gas composition (volume %)
TiCl ₄ : 3.0 to 6.0%, N ₂ : 25.0 to 35.0%, H ₂ : balance,
Reaction atmosphere pressure: 4.0 to 12.0 kPa,
Reaction atmosphere temperature: 780 to 900°C
2) TiCN layer;
Processing method: CVD film formation Reaction gas composition (volume %)
TiCl ₄ : 3.0 to 6.0%, N ₂ : 15.0 to 30.0%,
_CH4 or _CH3CN : 0.6-2.0%, _H2 : balance,
Reaction atmosphere pressure: 7.0 to 12.0 kPa,
Reaction atmosphere temperature: 780 to 900°C

(c) Method for forming upper layer Next, in the method for forming the upper layer according to the present invention, with regard to the conditions for forming the AlTi composite nitride layer or the AlTi composite carbonitride layer, for example, two types of _NH3 gas having different heating temperatures are used, and nucleation is suppressed by high-temperature ammonia gas, and crystallization is promoted, thereby making it possible to obtain coarse grains.
That is, the method for forming an AlTiN layer or an AlTiCN layer according to the present invention performs film formation by alternately repeating the second step (initial nucleus formation step), i.e., a step of forming AlTiN crystals or AlTiCN crystals that serve as initial nuclei for forming an AlTiN film or an AlTiCN film, and the third step (crystal growth step), i.e., a step of growing the AlTiN crystals or AlTiCN crystals that are the initial nuclei to form an AlTiN film or an AlTiCN film.
The film formation conditions in 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, and ammonia gas preheated at a high temperature (e.g., 300 to 450° C.) is used to promote nucleation. 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, and the ammonia gas used is changed to ammonia gas preheated at a low temperature (e.g., 50 to 250° C.), thereby suppressing nucleation and promoting crystallization, and making it possible to obtain the desired crystals.
The number of times the second and third steps are repeated is adjusted according to the target film thickness.

[Film formation conditions]
1) Second step (initial nucleation step)
Treatment method: Deposition using CVD method Reaction gas composition (volume %):
Gas group B: TiCl ₄ : 0.01 to 0.04%, AlCl ₃ : 0.01 to 0.05%,
N ₂ : 0 to 10%, C ₂ H ₄ : 0 to 0.5%, H ₂ : Remaining gas group C: NH ₃ : 0.1 to 0.8%, H ₂ : 25.0 to 35.0%,
Reaction atmosphere pressure: 4.0 to 5.0 kPa,
Reaction atmosphere temperature: 700 to 850°C
Supply cycle: 1-5 seconds,
Gas supply time per cycle: 0.15 to 0.25 seconds,
Phase difference between the supply of gas group B and the supply of gas group C: 0.10 to 0.20 seconds Preheat temperature of gas group C: 300 to 450° C.

2) Third step (crystal growth step)
Treatment method: Deposition using CVD method Reaction gas composition (volume %):
Gas group D: TiCl ₄ : 0.01 to 0.04%, AlCl ₃ : 0.01 to 0.05%,
N ₂ : 0-10%, C ₂ H ₄ : 0-0.5%, H ₂ : balance,
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 to 850°C
Supply cycle: 1-5 seconds,
Gas supply time per cycle: 0.15 to 0.25 seconds,
Phase difference between the supply of gas group D and the supply of gas group E: 0.10 to 0.20 seconds Preheat temperature of gas group E: 50 to 250° C.
In addition, the volume percentage of each gas component in the reaction gas composition (volume percentage) in each of the second and third steps indicates the volume percentage of each component calculated with the sum of gas group B and gas group C being 100 volume % in the second step, and indicates the volume percentage of each component calculated with the sum of gas group D and gas group E being 100 volume % in the third step.

The surface-coated cutting tool of the present invention imparts a predetermined range of residual stress to each of the rake face and flank face of the tool base, 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.
In particular, in turning, defects occur due to the progression of cracks from the cutting face to the flank, so a significant effect of suppressing the progression of cracks is achieved by keeping the residual stress on the cutting face at -200 MPa or less, i.e., under high compressive residual stress.
On the other hand, as with the cutting face, compressive residual stress increases on the flank, and if the absolute value of the difference between the residual stress value on the rake face and the residual stress value on the flank becomes 250 MPa or less, coating peeling becomes more likely to occur during plastic deformation of the base material. Therefore, it is necessary that the absolute value of the difference between the residual stress value on the rake face and the residual stress value on the flank be greater than 250 MPa.

FIG. 1 is a schematic 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 constituting a hard coating layer.

Next, the coated tool of the present invention will be specifically explained using examples.

As raw material powders, WC powder, TiC powder, TaC powder, NbC powder, _Cr3C2 powder and Co powder, all of which have an average particle size of 1 to ₃ μm, were prepared. These raw material powders were mixed to the composition shown in Table 1, wax was added and the mixture was ball milled in acetone for 24 hours. The mixture was then dried under reduced pressure and pressed into a green compact of a predetermined shape at a pressure of 98 MPa. This green compact was then vacuum sintered in a vacuum of 5 Pa at a predetermined temperature within the range of 1370 to 1470°C for 1 hour. After sintering, tool bases A to C made of WC-based cemented carbide having an insert shape according to ISO standard DNMG150408 were each produced.

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 in the following manner.
As described above, in the present invention, it is assumed that the cutting faces of the tool substrates A to C are subjected to a blast treatment as a pretreatment before the formation of a hard coating layer and/or a posttreatment after the formation of a hard coating layer, thereby imparting residual stress to the cutting face and flank face of the substrate (see Table 2).
Next, in the first step, one of the tool substrates A to C is placed in a chemical vapor deposition apparatus, and film formation is performed for a certain period of time under the temperature and pressure conditions described in the formation conditions (formation symbols) A to H shown in Table 3 using gas group A (TiCl ₄ , N ₂ , CH ₄ , CH ₃ CN, and the remainder H ₂ ) having the component composition shown in Table 3.

For coated tools 1 to 5 of the present invention, following the first step, in the second step (upper layer initial nucleus formation step), film formation was carried out for a certain period of time based on the gas compositions, 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 E shown in Table 4, and in the third step (upper layer crystal growth step), film formation was carried out for a certain period of time based on the gas compositions, 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, to obtain coated tools 1 to 5 of the present invention shown in Table 7.
In addition, for the coated tools 6 to 8 of the present invention, following the first process (lower layer deposition process), in the second process (upper layer initial nucleus formation process), deposition was performed under the formation conditions (formation symbols) F to H shown in Table 4, and in the third process (upper layer crystal growth process), deposition was performed under the formation conditions (formation symbols) F to H shown in Table 5.Furthermore, as the top layer, a κ-Al ₂ O ₃ layer, an l-TiCN layer or an α-Al ₂ O ₃ layer was deposited under the formation conditions shown in Table 6, thereby obtaining coated tools 6 to 8 of the present invention shown in Table 7.

For comparison purposes, comparative coated tools 1 to 5 were formed under the formation conditions (formation symbols) a to e shown in Tables 3, 4 and 5, and comparative coated tools 1 to 5 shown in Table 8 were obtained.
In addition, for comparative coated tools 6 to 8, coating was performed under the forming conditions (forming symbols) f to h shown in Tables 3, 4 and 5, and then a κ-Al ₂ O ₃ layer, an l-TiCN layer or an α-Al ₂ O ₃ layer was formed as the uppermost layer under the forming conditions (forming symbols) shown in Table 6, thereby obtaining comparative coated tools 6 to 8 shown in Table 8.

Table 7 shows the residual stress values of the flank and rake faces of the tool substrates of the coated tools 1 to 8 of the present invention, the target average total thickness of the hard coating layer, the target average thickness and type of film formed of the lower layer, the target average thickness of the upper layer, the average Al content (Xavg), the average C content (Yavg), the crystal structure and the diffraction line intensity ratio (I(111)/I(200)), and the target average thickness and film formed of the uppermost layer.
Similarly, Table 8 shows, for comparative coated tools 1 to 8, the residual stresses on the flank and rake faces of the tool substrate, the target average total thickness of the hard coating layer, the target average thickness and type of coating of the lower layer, the target average thickness of the upper layer, the average Al content (Xavg), the average C content (Yavg), the crystal structure and the diffraction ray intensity ratio (I(111)/I(200)), and the target average thickness of the uppermost layer.

The thickness of the hard coating layer of each of the coated tools 1 to 8 according to the present invention and the comparative coated tools 1 to 8 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 observed field of view, 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 comparative coated tools 1 to 8.
The average Al content X _avg (atomic ratio) and the average C content Y _avg (atomic ratio) of the AlTiN or AlTiCN in the upper layer were 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 obtained characteristic X-rays.
The values of X _avg and Y _avg are shown in Table 7 for the inventive coated tools 1-8 and in Table 8 for the comparative coated tools 1-8.

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

Next, with the various coated tools clamped to the tip of a tool steel cutter using a fixture, wet intermittent cutting tests of Inconel were carried out for coated tools 1 to 8 of the present invention and comparative coated tools 1 to 8, as shown below, and the maximum machining time until tool chipping was evaluated. The results are shown in Table 9.

<Cutting conditions>
Cutting test: Wet turning, intermittent cutting
Work material: Inconel 718 slit material
Outer diameter 200 mm, length 400 mm (grooved round bar material)
(4mm wide slits are evenly spaced at 50mm intervals)
Rotation speed: 80 min ^-1 ,
Cutting speed: 50m/sec. ,
Cutting depth: 0.5 mm,
Feed per blade: 0.6 mm/rev.
Cutting time: Processing until the cutting edge is chipped

As is apparent from the cutting test results shown in Table 9, the coated tool of the present invention exhibits excellent chipping resistance and wear resistance over a long period of time.

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 difficult-to-cut materials such as stainless steel, steels with remaining fused surfaces, or nickel alloys, and therefore fully satisfies the needs for high performance cutting equipment, labor-saving and energy-saving cutting, and cost reduction.

Claims (3)

A surface-coated cutting tool having a hard coating layer on a 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 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 21.0 μm;
(b) the lower layer is made of a Ti nitride or carbonitride and has an average layer thickness of 0.05 to 2.0 μm;
(c) the upper layer is a composite nitride layer or a composite carbonitride layer of Al and Ti, and the average layer thickness is 0.5 to 20.0 μm;
When expressed by a composition formula: (Al _X Ti _1-X ) (C _Y N _1-Y ), an average content ratio X _avg of Al to the total amount of Ti and Al in said composite nitride layer or said composite carbonitride layer and an average content ratio Y _avg of C to the total amount of C and N in said composite nitride layer or said composite carbonitride layer (wherein X _avg and Y _avg are both atomic ratios) satisfy 0.70≦X _avg ≦0.90 and 0≦Y _avg <0.05, respectively, and the composite nitride layer or composite carbonitride layer has a NaCl-type face-centered cubic crystal structure,
(d) When the residual stress on the flank of the cutting edge of the tungsten carbide based cemented carbide of the surface-coated tool is S1 and the residual stress on the rake face of the cutting edge is S2,
α) S1>S2
β) S2≦-200MPa
γ) the absolute value of the difference between S1 and S2 is greater than 250 MPa. When X-ray diffraction was performed on the upper layer, the ratio of the diffraction intensity value of the cubic (111) plane to the diffraction intensity value of the cubic (200) plane, I(111)/I(200), was:
2. The surface-coated cutting tool according to claim 1, wherein the relationship: 1.0≦I(111)/I(200) is satisfied. When the residual stress on the cutting edge flank of the tungsten carbide based cemented carbide of the surface-coated tool is S1 and the residual stress on the cutting edge rake face is S2,
α) S1>S2
β) S2≦-850MPa
γ) the absolute value of the difference between S1 and S2 is greater than 500 MPa .