JP2006315149A - Surface coated cermet cutting tool having hard coating layer exhibiting excellent wear resistance in high-speed cutting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface coated cermet cutting tool having a hard coating layer exhibiting excellent wear resistance in high-speed cutting. <P>SOLUTION: In a coated cermet tool, the hard coating layer composed of (a) Ti compound layer having total average layer thickness of 3 to 20 μm as a lower layer and (b) α type Al<SB>2</SB>O<SB>3</SB>layer having an average layer thickness of 2 to 15 μm as an upper layer is formed by chemical vapor deposition. The α type Al<SB>2</SB>O<SB>3</SB>layer is made to be upper and lower double-layer structure composed of a reformed layer occupying 55 to 80% by the ratio with respect to an average layer thickness of whole Al<SB>2</SB>O<SB>3</SB>layer and a residual standard layer. When the inclination angle formed by a normal line of (0001) surface of crystal grains is measured by using a field emission type scanning electron microscope and an inclination angle frequency distribution graph is made by adding up the frequency existing in each division, the double-layer α type Al<SB>2</SB>O<SB>3</SB>layer shows a specific inclination angle frequency distribution graph. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention is particularly excellent when an aluminum oxide layer (hereinafter referred to as an Al ₂ O ₃ layer), which is an upper layer of a hard coating layer, is used to cut various types of steel and cast iron at high speed. The present invention relates to a surface-coated cermet cutting tool that exhibits wear resistance (hereinafter referred to as a coated cermet tool).

Conventionally, generally on the surface of a substrate (hereinafter collectively referred to as a tool substrate) composed of a tungsten carbide (hereinafter referred to as WC) -based cemented carbide or titanium carbonitride (hereinafter referred to as TiCN) -based cermet. ,
(A) As a lower layer, Ti carbide (hereinafter referred to as TiC) layer, nitride (hereinafter also referred to as TiN) layer, carbonitride (hereinafter referred to as TiCN) layer, carbon oxide (hereinafter referred to as TiCO) A Ti compound layer consisting of one or two or more layers of carbonitride oxide (hereinafter referred to as TiCNO) layers and having an overall average layer thickness of 3 to 20 μm,
(B) As an upper layer, an aluminum oxide layer (hereinafter referred to as an α-type Al ₂ O ₃ layer) having an average layer thickness of 2 to 15 μm and having an α-type crystal structure in a state of chemical vapor deposition,
A coated cermet tool formed by chemical vapor deposition of the hard coating layer composed of (a) and (b) above is known, and this coated cermet tool is used for continuous cutting and intermittent cutting of various steels and cast irons, for example. It is well known to be used in

In general, the Ti compound layer and the α-type Al ₂ O ₃ layer constituting the hard coating layer of the above-mentioned coated cermet tool have a granular crystal structure, and further, the TiCN layer constituting the Ti compound layer is the layer itself. For the purpose of improving the strength of the crystal, a vertically grown crystal formed by chemical vapor deposition at a medium temperature range of 700 to 950 ° C. using a mixed gas containing an organic carbonitride as a reaction gas in a normal chemical vapor deposition apparatus. It is also known to have an organization.
Japanese Unexamined Patent Publication No. 6-31503 Japanese Patent Laid-Open No. 6-8010

In recent years, the performance of cutting machines has been remarkable. On the other hand, there is a strong demand for labor saving and energy saving and further cost reduction for cutting work, and along with this, cutting work tends to be further accelerated. For coated cermet tools, there is no problem when this is used for continuous cutting or intermittent cutting under normal conditions such as steel or cast iron, but especially when this is used under high-speed cutting conditions, a hard coating layer Since the α-type Al ₂ O ₃ layer constituting the layer has insufficient wear resistance, the wear progresses rapidly, and the service life is reached in a relatively short time.

The present inventors have, from the viewpoint as described above, focuses on coated cermet tool α type the Al ₂ O ₃ layer described above constituting the upper layer of the hard coating layer, in particular the α-type the Al ₂ O ₃ layer As a result of research to improve wear resistance,
(A) The α-type Al ₂ O ₃ layer as a hard coating layer of the above-described conventional coated cermet tool is generally a normal chemical vapor deposition apparatus,
Reaction gas composition: by _{volume%, AlCl 3: 1~5%,} CO 2: 3~7%, HCl: 0.3~3%, H 2 S: 0.02~0.4%, H 2: remainder ,
Reaction atmosphere temperature: 950-1100 ° C.
Reaction atmosphere pressure: 6-13 kPa,
The α-type Al ₂ O ₃ layer (hereinafter referred to as the standard layer) formed under the normal conditions is subjected to a field emission scanning electron microscope as shown in FIG. As shown in the schematic explanatory diagram in (b), each crystal grain having a hexagonal crystal lattice existing within the measurement range of the surface polished surface is irradiated with an electron beam, and the normal line of the surface polished surface is obtained. The inclination angle formed by the normal line of the (0001) plane, which is the crystal plane of the crystal grain, is measured, and the measurement inclination angle within the range of 45 to 90 degrees of the measurement inclination angle is set to a pitch of 0.25 degrees. When an inclination angle number distribution graph is created, which is divided for each of the areas and the frequencies existing in the respective areas are totaled, the distribution of measured inclination angles on the (0001) plane is 45 to 90 degrees as illustrated in FIG. An unbiased inclination angle number distribution graph within the range of.

(B) On the other hand, the α-type Al ₂ O ₃ layer was similarly used with a normal chemical vapor deposition apparatus,

Reaction gas composition: by _{volume%, AlCl 3: 1~5%,} CO 2: 3~7%, HCl: 0.3~3%, H 2 S: 0.02~0.4%, H 2: remainder ,
Reaction atmosphere temperature: 750 to 900 ° C.
Reaction atmosphere pressure: 20-30 kPa,
When formed under relatively low temperature and high pressure conditions (reaction gas composition is the same as the above normal conditions), the resulting α-type Al ₂ O ₃ layer (hereinafter referred to as a modified layer) is also subjected to field emission scanning. Using an electron microscope, as shown in FIGS. 1A and 1B, the surface polished surface is irradiated with an electron beam on each crystal grain having a hexagonal crystal lattice existing within the measurement range of the surface polished surface. The inclination angle formed by the normal line of the (0001) plane which is the crystal plane of the crystal grain is measured, and the measurement inclination angle within the range of 45 to 90 degrees is measured among the measurement inclination angles. When divided into pitches of 0.25 degrees and represented by an inclination angle number distribution graph obtained by summing up the frequencies existing in each of the divisions, as shown in FIG. The highest peak appears, and according to the test results, the reaction in chemical vapor deposition equipment When the atmospheric pressure is changed within the range of 20 to 30 kPa as described above, the position at which the sharpest peak appears changes within the range of 75 to 85 degrees of the inclination angle section, and the range of 75 to 85 degrees. The total number of frequencies existing in the graph occupies 45 to 65% of the total frequency in the tilt angle frequency distribution graph, and the tilt angle section falls within the range of 75 to 85 degrees in the resulting tilt angle frequency distribution graph. The modified layer in which the highest peak of shows a better abrasion resistance than the standard layer formed under the normal conditions described above.

(C) Therefore, the α-type Al ₂ O ₃ layer, which is the upper layer of the hard coating layer whose lower layer is a Ti compound layer, is 55 to 80% of the total layer thickness of the Al ₂ O ₃ layer. The upper and lower layers are composed of a modified layer and the remaining standard layer, and the surface is polished, and the modified layer has the highest peak in the tilt angle section within the range of 75 to 85 degrees. The inclination angle number distribution graph in which the total of the frequencies existing in the range of 75 to 85 degrees occupies a ratio of 45 to 65% of the entire degrees in the inclination angle number distribution graph is shown, and the standard layer is 45 to 90 degrees. Coated cermet tool composed of a double-layer α-type Al ₂ O ₃ layer showing no inclination angle distribution graph in which there is no peak over the entire measured inclination angle range in the range of , the 2-layer α type the Al ₂ O ₃ layer is relatively superior Since it consists of a modified layer with wear resistance and a standard layer with high temperature hardness, it has excellent wear resistance and high temperature hardness as the overall characteristics of the layer, so cutting is performed especially under high speed cutting conditions. Even if it goes, the whole upper layer of the hard coating layer shows an unbiased inclination angle number distribution graph within the range of the measured inclination angle of the (0001) plane corresponding to the standard layer in the range of 45 to 90 degrees. Compared to conventional coated cermet tools composed of a single-layer α-type Al ₂ O ₃ layer, the wear resistance should be improved over a long period of time.
The research results shown in (a) to (c) above were obtained.

This invention was made based on the above research results, and on the surface of the tool base,
(A) As a lower layer, a Ti compound layer composed of one or more of a TiC layer, a TiN layer, a TiCN layer, a TiCO layer, and a TiCNO layer and having an overall average layer thickness of 3 to 20 μm,
(B) an α-type Al ₂ O ₃ layer having an average layer thickness of ₂ to 15 μm as an upper layer;
In the coated cermet tool formed by chemical vapor deposition of the hard coating layer composed of (a) and (b) above,
The α-type Al ₂ O ₃ layer has an upper and lower double layer structure consisting of 55 to 80% of the modified layer and the remaining standard layer in the ratio of the average layer thickness of the entire Al ₂ O ₃ layer, and a field emission type Using a scanning electron microscope, each crystal grain having a hexagonal crystal lattice existing within the measurement range of the surface polished surface is irradiated with an electron beam, and the crystal of the crystal grain is normal to the surface polished surface. Measuring the tilt angle formed by the normal line of the (0001) plane, and dividing the measured tilt angle within the range of 45 to 90 degrees of the measured tilt angles into pitches of 0.25 degrees, When expressed in the slope angle distribution graph, which is the sum of the frequencies existing in each category,
(A) In the modified layer of the α-type Al ₂ O ₃ layer, the highest peak exists in the tilt angle section within the range of 75 to 85 degrees, and the total number of frequencies existing within the range of 75 to 85 degrees. Shows an inclination angle number distribution graph occupying a proportion of 45 to 65% of the entire frequency in the inclination angle number distribution graph,
(B) In the standard layer of the α-type Al ₂ O ₃ layer, there is no peak over the entire measurement inclination angle range of 45 to 90 degrees, and the inclination angle number distribution in which the distribution of the measurement inclination angles is unbiased. Showing the graph,
The hard coating layer composed of the double layer α-type Al ₂ O ₃ layer composed of the above (A) and (B) is characterized by a coated cermet tool that exhibits excellent wear resistance in high-speed cutting. .

The reason why the numerical values of the constituent layers of the hard coating layer of the coated cermet tool of the present invention are limited as described above will be described below.
(A) Ti compound layer (lower layer)
The Ti compound layer basically exists as a lower layer of the double-layer α-type Al ₂ O ₃ layer and contributes to improving the high-temperature strength of the entire hard coating layer by its excellent high-temperature strength. The double-layer α-type Al ₂ O ₃ layer has a function of firmly adhering to any of the _two layers, thereby improving the adhesion of the hard coating layer to the tool substrate. On the other hand, if the average layer thickness exceeds 20 μm, it becomes easy to cause thermoplastic deformation especially in high-speed cutting with high heat generation, which causes uneven wear. Was determined to be 3 to 20 μm.

(B) Double layer α-type Al ₂ O ₃ layer (upper layer)
As described above, the highest peak position of the measured inclination angle in the inclination angle number distribution graph of the modified layer of the double layer α-type Al ₂ O ₃ layer is the reaction atmosphere pressure in the chemical vapor deposition apparatus, as described above, in the range of 20 to 30 kPa. When the angle is changed within the range of 75 to 85 degrees of the inclination angle section, the total of the frequencies existing in the range of 75 to 85 degrees is 45 to 65 of the entire degrees in the inclination angle distribution graph. % Of the inclination angle number distribution graph (in this case, even if the reaction atmosphere pressure is adjusted, it is not possible to occupy a frequency ratio of 65% or more). Regardless of whether the atmospheric pressure is out of the range or low, the maximum peak position of the measurement inclination angle is out of the range of 75 to 85 degrees, and the inclination angle is corresponding to this. The ratio of the frequencies existing in the range of 75 to 85 degrees in the frequency distribution graph is also less than 45% of the entire frequencies, and the desired excellent wear resistance cannot be ensured.
The double layer α-type Al ₂ O ₃ layer has excellent wear resistance and high temperature hardness due to the excellent wear resistance of the modified layer and the high temperature hardness of the standard layer. If the layer thickness of the modified layer is less than 55% in the average layer thickness of the entire Al ₂ O ₃ layer, the desired excellent wear resistance cannot be ensured, while the layer thickness is also 80%. If it exceeds 1, the high-temperature hardness will rapidly decrease and the progress of wear will accelerate, so the layer thickness of the modified layer is 55-80% of the average layer thickness of the entire Al ₂ O ₃ layer. The remainder was a double-layered structure occupying the standard layer (corresponding to the conventional α-type Al ₂ O ₃ layer).
Furthermore, if the average layer thickness of the entire double-layer α-type Al ₂ O ₃ layer is less than 2 μm, the excellent characteristics of the double layer α-type Al ₂ O ₃ layer cannot be exhibited sufficiently, while the average layer thickness exceeds 15 μm and becomes too thick. Then, since chipping (slight chipping) is likely to occur in the cutting edge portion, the overall average layer thickness is set to 2 to 15 μm.

  In addition, for the purpose of identification before and after the use of the cutting tool, a TiN layer having a golden color tone may be vapor-deposited as the outermost surface layer of the hard coating layer as necessary, but the average layer thickness in this case is It may be 0.1 to 1 μm, and if it is less than 0.1 μm, a sufficient discrimination effect cannot be obtained, while the discrimination effect by the TiN layer is sufficient for an average layer thickness of up to 1 μm.

In the coated cermet tool of the present invention, even if the double layer α-type Al ₂ O ₃ layer constituting the upper layer of the hard coating layer is subjected to cutting of various types of steel and cast iron at high speed, the double layer α-type Al _{Since the 2} O ₃ layer has excellent wear resistance and high temperature hardness, it exhibits excellent wear resistance and enables further extension of the service life.

  Next, the coated cermet tool of the present invention will be specifically described with reference to examples.

As raw material powders, WC powder, TiC powder, ZrC powder, VC powder, TaC powder, NbC powder, Cr ₃ C ₂ powder, TiN powder, and Co powder each having an average particle diameter of 1 to 3 μm are prepared. The raw material powder is blended in the blending composition shown in Table 1, added with wax, ball mill mixed in acetone for 24 hours, dried under reduced pressure, and press-molded into a green compact of a predetermined shape at a pressure of 98 MPa. The green compact is vacuum-sintered in a vacuum of 5 Pa at a predetermined temperature within a range of 1370 to 1470 ° C. for 1 hour. After sintering, the cutting edge is subjected to a honing process of R: 0.07 mm. Thus, tool bases A to F made of a WC-based cemented carbide having a throwaway tip shape specified in ISO · CNMG120408 were manufactured.

Further, as raw material powders, TiCN (mass ratio, TiC / TiN = 50/50) powder, Mo ₂ C powder, ZrC powder, NbC powder, TaC powder, WC, all having an average particle diameter of 0.5 to 2 μm. Prepare powder, Co powder, and Ni powder, blend these raw material powders into the composition shown in Table 2, wet mix with a ball mill for 24 hours, dry, and press-mold into a green compact at 98 MPa pressure The green compact is sintered in a nitrogen atmosphere of 1.3 kPa at a temperature of 1540 ° C. for 1 hour, and after sintering, the cutting edge portion is subjected to a honing process of R: 0.07 mm. Tool bases a to f made of TiCN-based cermet having a chip shape conforming to ISO standards / CNMG 120212 were formed.

Then, each of these tool bases A to F and tool bases a to f is charged into a normal chemical vapor deposition apparatus,
(A) First, Table 3 (l-TiCN in Table 3 indicates the conditions for forming a TiCN layer having a vertically elongated crystal structure described in JP-A-6-8010, and the other conditions are ordinary granularity. Under the conditions shown in Table 5 and 6 and the target layer thickness, the Ti compound layer is deposited as a lower layer of the hard coating layer under the conditions shown in Table 5).
(B) Next, under the conditions shown in Table 4, any one of the modified layers (a) to (j) and the standard layers (1) to (8) with the combinations and target layer thicknesses shown in Tables 5 and 6 The coated cermet tools 1 to 13 of the present invention were respectively produced by vapor-depositing a double layer α-type Al ₂ O ₃ layer made of any of the above as an upper layer of the hard coating layer.

For comparison purposes, the single layer α-type Al ₂ O ₃ layer, which is the upper layer of the hard coating layer, is formed on the formation conditions of the standard layers (1) to (8) shown in Table 4 (as described above, the standard The formation conditions of the layers (1) to (8) are the same as the formation conditions of the single-layer α-type Al ₂ O ₃ layer), except for the combinations shown in Table 7 and the target layer thickness. Conventional coated cermet tools 1 to 13 were produced under the same conditions as the coated cermet tools 1 to 13 of the present invention.

Subsequently, the double-layer α-type Al ₂ O ₃ layer and the single-layer α-type Al ₂ O ₃ layer constituting the upper layer of the hard coating layer of the above-described coated cermet tool 1 to 13 of the present invention and the conventional coated cermet tool 1 to 13 Using the field emission type scanning electron microscope, an inclination angle number distribution graph was prepared.
That is, the inclination angle number distribution graph shows the modified layer of the double layer α-type Al ₂ O ₃ layer and the standard layer of the above-described coated cermet tools 1 to 13 in a state where each surface is a polished surface. Set in a lens barrel of a field emission scanning electron microscope, and an electron beam with an acceleration voltage of 15 kV at an incident angle of 70 degrees on the polished surface is irradiated with 1 nA within the measurement range of each polished surface. By irradiating each crystal grain having an existing hexagonal crystal lattice and using an electron backscatter diffraction image apparatus, a region of 30 × 50 μm is spaced at a spacing of 0.1 μm / step with respect to the normal line of the polished surface. The inclination angle formed by the normal line of the (0001) plane which is the crystal plane of the crystal grain is measured, and based on the measurement result, the measurement inclination angle within the range of 45 to 90 degrees of the measurement inclination angle is calculated. Divided every 0.25 degree pitch In addition, it was created by counting the frequencies existing in each category.
Further, the surface polished surfaces of the conventional coated cermet tools 1 to 13 of the single layer α-type Al ₂ O ₃ layer (corresponding to any one of the standard layers (1) to (8) as described above) are also subjected to the same conditions. Observed and created a tilt angle number distribution graph under the same conditions.

In the gradient angle distribution graphs of the various α-type Al ₂ O ₃ layers obtained as a result, as shown in Tables 5 to 8, double-layer α-type Al ₂ O ₃ layers of the coated cermet tools 1 to 13 of the present invention, respectively. The modified layer of the present invention shows a gradient angle distribution graph in which the distribution of the measured inclination angle of the (0001) plane shows the highest peak in the inclination angle section within the range of 75 to 85 degrees, respectively. The standard layer of the double-layer α-type Al ₂ O ₃ layer of the cermet tools 1 to 13 and the single-layer α-type Al ₂ O ₃ layer of the conventional coated cermet tools 1 to 13 have a distribution of measured inclination angles on the (0001) plane. An inclination angle number distribution graph that is unbiased within the range of 45 to 90 degrees and does not have the highest peak is shown.
Tables 5 to 7 show the entire inclination angle distribution graphs of all inclination angle numbers existing in the inclination angle sections within 75 to 85 in the inclination angle distribution graphs of the various α-type Al ₂ O ₃ layers. The percentage of
2 and 3 are graphs showing the distribution of inclination angles of the double layer α-type Al ₂ O ₃ layer and the standard layer of the coated cermet tool 2 of the present invention, and FIG. 4 is a single layer α of the conventional coated cermet tool 5. the inclination angle frequency distribution graph of the mold the Al ₂ O ₃ layer.

  Moreover, when the thickness of the constituent layer of the hard coating layer of the present invention coated cermet tools 1 to 13 and the conventional coated cermet tools 1 to 13 obtained as a result was measured using a scanning electron microscope (longitudinal section measurement) , Each showed an average layer thickness (average value of 5-point measurement) substantially the same as the target layer thickness.

Next, for the various coated cermet tools of the present invention coated cermet tool 1-13 and the conventional coated cermet tool 1-13, all of them are screwed with a fixing jig to the tip of the tool steel tool,
Work material: JIS / S45C round bar,
Cutting speed: 400 m / min. ,
Cutting depth: 1.0 mm,
Feed: 0.2 mm / rev. ,
Cutting time: 12 minutes,
Dry continuous high-speed cutting test of carbon steel under the conditions (cutting condition A) (normal cutting speed is 200 m / min.),
Work material: JIS / SNCM439 round bar,
Cutting speed: 350 m / min. ,
Cutting depth: 1.0 mm,
Feed: 0.3 mm / rev. ,
Cutting time: 9 minutes
Dry continuous high-speed cutting test (normal cutting speed is 150 m / min.) Of alloy steel under the following conditions (referred to as cutting conditions B),
Work material: JIS / FC250 round bar,
Cutting speed: 450 m / min. ,
Cutting depth: 1.0 mm,
Feed: 0.25 mm / rev. ,
Cutting time: 8 minutes,
The dry continuous high-speed cutting test (normal cutting speed is 200 m / min.) Of cast iron under the above conditions (referred to as cutting condition C), and the flank wear width of the cutting edge was measured in any cutting test. The measurement results are shown in Table 8.

From the results shown in Tables 5 to 8, the coated cermet tools 1 to 13 of the present invention each have a double layer α-type Al ₂ O ₃ layer upper and lower double layer structure modified layer, which is the upper layer of the hard coating layer. The (0001) plane tilt angle number distribution graph shows the highest peak in the tilt angle section in the range of 75 to 85 degrees, and as a result, it has relatively good wear resistance, while the standard layer is relatively Because it retains excellent high-temperature hardness, it exhibits excellent wear resistance even when cutting steel and cast iron at high speed, whereas the entire upper layer of the hard coating layer is (0001) The distribution of the measured inclination angle of the surface is unbiased within the range of 45 to 90 degrees, and shows an inclination angle number distribution graph in which the highest peak does not exist, and corresponds to any one of the standard layers (a) to (h). in the conventional coated cermet tools 1 to 13 that comprises a layer α type the Al ₂ O ₃ layer Both because of the wear resistance shortage of the single layer α type the Al ₂ O ₃ layer, a high-speed cutting conditions abrasion of the hard coating layer is accelerated significantly, it is apparent that lead to a relatively short time using life .

  As described above, the coated cermet tool of the present invention exhibits excellent wear resistance without occurrence of chipping even in continuous cutting and intermittent cutting under normal conditions such as various steels and cast irons, especially in high-speed cutting. Since it exhibits excellent cutting performance over a long period of time, it can satisfactorily respond to higher performance of the cutting device, labor saving and energy saving of cutting, and further cost reduction.

It is a schematic diagram illustrating a measurement range of the inclination angle of the case of measuring the crystal grain of the α-type the Al ₂ O ₃ layer constituting the hard coating layer (0001) plane. It is an inclination angle number distribution graph of the (0001) plane of the modified layer of the double layer α-type Al ₂ O ₃ layer constituting the hard coating layer of the coated cermet tool 2 of the present invention. It is an inclination angle number distribution graph of the (0001) plane of the standard layer of the double layer α-type Al ₂ O ₃ layer constituting the hard coating layer of the coated cermet tool 2 of the present invention. 6 is a graph showing the distribution of the number of inclination angles on the (0001) plane of a single-layer α-type Al ₂ O ₃ layer (corresponding to a standard layer) constituting a hard coating layer of a conventional coated cermet tool 5.

Claims (1)

On the surface of the tool base composed of tungsten carbide based cemented carbide or titanium carbonitride based cermet,
(A) As a lower layer, it consists of one or more of Ti carbide layer, nitride layer, carbonitride layer, carbonate layer, and carbonitride oxide layer, and has an overall average of 3 to 20 μm A Ti compound layer having a layer thickness,
(B) As an upper layer, an aluminum oxide layer having an α-type crystal structure in a chemical vapor deposited state and an average layer thickness of 2 to 15 μm,
In the surface-coated cermet cutting tool formed by chemical vapor deposition of the hard coating layer composed of (a) and (b) above,
The α-type aluminum oxide layer has an upper and lower double layer structure consisting of 55 to 80% of the modified layer and the remaining standard layer in the ratio of the average thickness of the entire aluminum oxide layer, and a field emission scanning electron microscope. The crystal grain of the crystal grain is used with respect to the normal of the surface polished surface by irradiating each crystal grain having a hexagonal crystal lattice existing within the measurement range of the surface polished surface with an electron beam (0001 ) Measure the tilt angle formed by the normal of the surface, and divide the measured tilt angle within the range of 45-90 degrees of the measured tilt angle by pitch of 0.25 degrees and exist in each section When it is represented by a tilt angle frequency distribution graph that is a sum of the frequencies to be
(A) The modified layer of the aluminum oxide layer has the highest peak in the inclination angle section within the range of 75 to 85 degrees, and the sum of the frequencies existing in the range of 75 to 85 degrees is the inclination angle. The inclination angle frequency distribution graph which occupies the ratio of 45 to 65% of the whole frequency in the number distribution graph is shown.
(B) The standard layer of the aluminum oxide layer has no peak over the entire measurement inclination angle range in the range of 45 to 90 degrees, and the distribution of the measurement inclination angle is unbiased even in any range of 45 to 90 degrees. Showing a typical inclination angle number distribution graph,
A surface-coated cermet cutting tool in which a hard coating layer characterized by comprising a double-layer α-type aluminum oxide layer comprising the above (A) and (B) exhibits excellent wear resistance in high-speed cutting.

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