JP2004181618A - Surface-coated cermet cutting tool superior in high speed cutting and exhibiting heat resistant plastic deformability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-coated cermet cutting tool superior in high speed cutting, and exhibiting heat resistant plastic deformability. <P>SOLUTION: This surface-coated cermet cutting tool has a hard coating layer constituted of (a) to (d) on a surface of a cermet base body constituted of tungsten carbide group cemented carbide or titanium carbonitride group cermet. (a) A titanium nitride layer and/or a titanium carbonitride layer chemically evaporated and formed as a close contact backing layer, and having the average layer thickness of 0.1 to 2 μm. (b) A heating transformed α type aluminum oxide layer formed by transforming a crystal structure into an α type crystal structure by applying heat treatment to aluminum oxide having a κ type or θ type crystal structure in a state of being chemically evaporated and formed as a hard abrasion resistant layer, and having a structure of dispersing-distributing a heating transformed crack and the average layer thickness of 5 to 30 μm. (c) An evaporated α type aluminum oxide layer having an α type crystal structure in a state of being chemically evaporated and formed as a surface smoothing layer, and having the average layer thickness of 0.1 to 2 μm. (d) A titanium nitride layer chemically evaporated and formed as a use before-after identification layer when necessary, and having the average layer thickness of 0.1 to 2 μm. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

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【発明の効果】
表４〜６に示される結果から、本発明被覆サーメット工具１〜１２は、いずれもきわめて高い発熱を伴う鋼および鋳鉄の高速連続切削試験および高速断続切削試験でも、硬質被覆層が実質的に高強度を有し、かつα型Ａｌ_２Ｏ_３層自体のもつ高温強度および耐熱性に匹敵するすぐれた高温強度と耐熱性を具備する加熱変態α型Ａｌ_２Ｏ_３層からなるので、きわめて高い発熱を伴う鋼および鋳鉄の高速連続切削試験および高速断続切削試験でも、すぐれた耐熱塑性変形性を発揮し、この結果切刃部が正常摩耗形態をとるようになることから、すぐれた耐摩耗性を発揮するのに対して、硬質被覆層がＴｉ化合物層と蒸着α型Ａｌ_２Ｏ_３層からなる従来被覆サーメット工具１〜１２においては、前記の高速切削試験では、特に前記Ｔｉ化合物層の耐熱性不足が原因で偏摩耗の原因となる熱塑性変形が発生し、この結果摩耗進行が促進されるようになることから、比較的短時間で使用寿命に至ることが明らかである。
上述のように、この発明の被覆サーメット工具は、各種の鋼や鋳鉄などの通常の条件での連続切削や断続切削加工は勿論のこと、特に高い発熱を伴う高速切削加工に用いた場合にも、長期に亘ってすぐれた耐摩耗性を発揮するものであるから、切削加工装置の高性能化に十分満足に対応でき、かつ切削加工の一段の省力化および省エネ化、さらに低コスト化を可能とするものである。
【図面の簡単な説明】
【図１】本発明被覆サーメット工具３の硬質被覆層を構成する加熱変態α型Ａｌ_２Ｏ_３層（目標層厚：１５μｍ）のＸ線回折チャートを示す図である。
【図２】本発明被覆サーメット工具７の硬質被覆層を構成する加熱変態α型Ａｌ_２Ｏ_３層（目標層厚：１０μｍ）のＸ線回折チャートを示す図である。
【図３】本発明被覆サーメット工具９の硬質被覆層を構成する加熱変態α型Ａｌ_２Ｏ_３層（目標層厚：５μｍ）のＸ線回折チャートを示す図である。
【図４】従来被覆サーメット工具４の硬質被覆層を構成する蒸着α型Ａｌ_２Ｏ_３層（目標層厚：１５μｍ）のＸ線回折チャートを示す図である。
【図５】従来被覆サーメット工具６の硬質被覆層を構成する蒸着α型Ａｌ_２Ｏ_３層（目標層厚：１０μｍ）のＸ線回折チャートを示す図である。
【図６】従来被覆サーメット工具１０の硬質被覆層を構成する蒸着α型Ａｌ_２Ｏ_３層（目標層厚：５μｍ）のＸ線回折チャートを示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a surface-coated cermet cutting tool (hereinafter, referred to as a hard-coating layer) that exhibits excellent heat-resistant plastic deformability when cutting various steels and cast irons under high-speed cutting conditions involving high heat generation. Coated cermet tool).
[0002]
[Prior art]
Conventionally, generally, a surface of a cermet substrate formed of a tungsten carbide (hereinafter, referred to as WC) -based cemented carbide or a titanium cermet (hereinafter, referred to as TiCN) -based cermet,
(A) As a lower layer, a Ti carbide (hereinafter, referred to as TiC) layer, a nitride (hereinafter, also referred to as TiN) layer, a carbonitride (hereinafter, referred to as TiCN) layer, all formed by chemical vapor deposition, A Ti compound layer comprising one or more of a carbonate (hereinafter, referred to as TiCO) layer and a carbonitride (hereinafter, referred to as TiCNO) layer and having a total average layer thickness of 3 to 20 μm ,
(B) a vapor-deposited α-type aluminum oxide (hereinafter referred to as Al ₂ O ₃ ) layer having an α-type crystal structure in a state formed by chemical vapor deposition and having an average layer thickness of 3 to 15 μm as an upper layer;
(C) If necessary, a TiN layer formed by chemical vapor deposition and having an average layer thickness of 0.1 to 2 μm for the purpose of identifying before and after use of the tool because it has a golden color tone,
A coated cermet tool formed by vapor-depositing the hard coating layer composed of (a) to (c) above is known, and the coated cermet tool is formed by vapor-deposited α-type Al ₂ O forming the hard coating layer. _{The three} layers have excellent high-temperature hardness and heat resistance not provided by the Ti compound layer, while the Ti compound layer has excellent strength not provided by the vapor-deposited α-type Al ₂ O ₃ layer. It is also known that, depending on the properties possessed, excellent cutting performance is exhibited in continuous cutting or interrupted cutting of, for example, various kinds of steel or cast iron (for example, see Patent Document 1).
[0003]
In general, the Ti compound layer or Al ₂ O ₃ layer constituting the hard coating layer of the above-mentioned coated cermet tool has a granular crystal structure, and the TiCN layer constituting the Ti compound layer is further improved in toughness of the layer itself. For the purpose, using a mixed gas containing an organic carbonitride, for example, CH ₃ CN as a reaction gas, and performing chemical vapor deposition at a medium temperature range of 700 to 950 ° C. using a normal chemical vapor deposition apparatus, It is also known to have a growing crystal structure (for example, see Patent Document 2).
[0004]
[Patent Document 1]
JP-A-6-31503 [Patent Document 2]
JP-A-6-8010 [0005]
[Problems to be solved by the invention]
On the other hand, in recent years, there is a strong demand for labor saving, energy saving, and further cost reduction of cutting, and along with this, cutting tends to be performed at a high speed in conjunction with high performance of a cutting apparatus. However, in the above-mentioned conventional coated cermet tool, there is no problem when this is used for continuous cutting or interrupted cutting under normal conditions such as steel or cast iron, but when this is used for high-speed cutting, it occurs at the time of cutting. Due to the high heat generated, particularly in the Ti compound layer constituting the hard coating layer, thermoplastic deformation which causes uneven wear due to insufficient heat resistance is likely to occur, and as a result, wear progress is promoted. At present, the service life is reached in a relatively short time.
[0006]
[Means for Solving the Problems]
Therefore, the present inventors have conducted research to develop a coated cermet tool in which a hard coating layer exhibits excellent heat-resistant plastic deformation properties in high-speed cutting from the above-described viewpoints.
(A) On a surface of a cermet substrate, an Al ₂ O ₃ layer having a κ-type or θ-type crystal structure is formed by vapor deposition on a surface of a cermet substrate under a normal condition under a normal condition. When heat treatment is performed under the conditions of 1100 ° C. and holding time: 2 to 10 hours, the κ-type or θ-type crystal structure of the Al ₂ O ₃ layer is transformed into an α-type crystal structure, and cracks generated by heat transformation are generated. Although the layer has a structure dispersed and distributed in the layer, the resulting heat-transformed α-type Al ₂ O ₃ layer has an excellent high-temperature hardness and heat resistance equivalent to the high-temperature hardness and heat resistance of the α-type Al ₂ O ₃ layer itself. Having the hardness and heat resistance, and having the same excellent strength as the Ti compound layer, the necessity of the Ti compound layer for securing the strength as a constituent layer of the hard coating layer is eliminated. .
(B) Therefore, after a TiN layer and / or a TiCN layer are formed by vapor deposition on the surface of the cermet substrate under ordinary conditions, the above-mentioned heat-transformed α-type Al ₂ O ₃ layer is formed on the hard wear-resistant layer. A coated cermet tool formed with a vapor deposited α-type Al ₂ O ₃ layer under the same conditions for the purpose of smoothing the surface and also used for high-speed cutting accompanied by high heat generation during cutting. Since a Ti compound layer is not substantially present as a constituent layer of the hard coating layer, and the hard coating layer is substantially composed of the above-mentioned heat-transformed α-type Al ₂ O ₃ layer, the hard coating layer does not have thermoplastic deformation. To exhibit excellent wear resistance over a long period of time.
The research results shown in (a) and (b) above were obtained.
[0007]
The present invention has been made based on the results of the above-described research, and has the following features:
(A) a TiN layer and / or a TiCN layer formed by chemical vapor deposition and having an average layer thickness of 0.1 to 2 μm as an adhesion underlayer;
(B) As a hard abrasion resistant layer, Al ₂ O ₃ having a κ-type or θ-type crystal structure in a state formed by chemical vapor deposition is subjected to a heat treatment to transform the crystal structure into an α-type crystal structure, and is heated. A heat-transformed α-type Al ₂ O ₃ layer having a structure in which transformation-formed cracks are dispersed and distributed and an average layer thickness of 5 to 30 μm;
(C) a vapor deposited α-type Al ₂ O ₃ layer having an α-type crystal structure in a state formed by chemical vapor deposition and having an average layer thickness of 0.1 to 2 μm as a surface smoothing layer;
(D) a TiN layer formed by chemical vapor deposition and having an average layer thickness of 0.1 to 2 μm as a pre-use / post-use identification layer, if necessary;
The coated cermet tool having the hard coating layer composed of (a) to (d) and exhibiting excellent heat-resistant plastic deformability by high-speed cutting is characterized.
[0008]
Next, the reason why the average thickness of the constituent layers of the hard coating layer of the coated cermet tool of the present invention is limited as described above will be described.
(A) Adhesive Underlayer The adherent underlayer has an effect of improving the adhesion of the hard abrasion-resistant layer to the surface of the cermet substrate, but if the average layer thickness is less than 0.1 μm, a desired sufficient adhesion improving effect is obtained. On the other hand, the effect of improving the adhesion is sufficient when the average layer thickness is up to 2 μm. When the average layer thickness exceeds 2 μm, the occurrence of thermoplastic deformation is locally observed. Therefore, the average layer thickness was determined to be 0.1 to 2 μm.
[0009]
(B) Hard wear-resistant layer The hard wear-resistant layer substantially contributes to the improvement of the wear resistance of the cutting tool itself in a state where the hard wear-resistant layer has high strength without undergoing thermoplastic deformation even by high-temperature heating during high-speed cutting. However, if the average layer thickness is less than 5 μm, a desired long-term use life cannot be secured, while if the average layer thickness exceeds 30 μm, chipping occurs. Therefore, the average layer thickness is set to 5 to 30 μm.
[0010]
(C) surface smoothing layer above the hard wear-resistant layer, since those formed by as heat transformation treatment described above, there is a low surface smoothness condition, thus deposition α-type Al ₂ O to the surface _{Although three} layers are formed to achieve surface smoothness suitable for cutting, if the average layer thickness is less than 0.1 μm, desired surface smoothing cannot be achieved. Exceeds 2 μm, tensile stress remains when the vapor deposited α-type Al ₂ O ₃ layer (surface smoothing layer) is formed, and chipping easily occurs due to this. 0.1 to 2 μm.
[0011]
(D) Before and after use identification layer Since the TiN layer has a golden color tone as described above, it is formed by vapor deposition as necessary for the purpose of identifying before and after use of the cutting tool. If the thickness is less than 0.1 μm, a sufficient discriminating effect cannot be obtained, while the discriminating effect of the TiN layer is sufficient if the average layer thickness is up to 2 μm. It was determined to be 2 μm.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the coated cermet tool of the present invention will be specifically described with reference to examples.
As raw material powders, WC powders each having a predetermined average particle size in the range of 0.5 to 4 μm, (Ti, W) C (the same hereinafter, TiC / WC = 30/70 by mass ratio) powder, Ti, W) CN (TiC / TiN / WC = 24/20/56) powder, (Ta, Nb) C (TaC / NbC = 90/10) powder, Cr ₃ C ₂ powder, and Co powder, These raw material powders were blended in the composition shown in Table 1, wet-mixed in a ball mill for 72 hours, dried, and then pressed into a green compact of a predetermined shape at a pressure of 98 MPa. Medium, vacuum sintering at 1410 ° C. for 1 hour, and after sintering, a WC having a throw-away tip shape specified in ISO · CNMG120408 by subjecting the cutting edge to honing processing of R: 0.07 mm. Base cemented carbide Configured cermet substrate A~F were prepared, respectively.
[0013]
Further, as raw material powders, TiCN (TiC / TiN = 50/50 by mass ratio) powder, Mo ₂ C powder, ZrC powder, NbC powder, TaC powder, WC powder each having an average particle diameter of 0.5 to 2 μm , Co powder, and Ni powder are prepared, and these raw material powders are blended in the blending composition shown in Table 2, wet-mixed in a ball mill for 24 hours, dried, and pressed into a green compact at a pressure of 98 MPa. The green compact was sintered in a nitrogen atmosphere of 1.3 kPa at a temperature of 1540 ° C. for 1 hour, and after sintering, the cutting edge was subjected to a honing process of R: 0.05 mm to obtain an ISO. Cermet bases a to f composed of TiCN-based cermets having a chip shape of standard CNMG120412 were formed.
[0014]
Next, the surfaces of the cermet substrates A to F and the cermet substrates a to f were ultrasonically cleaned in acetone, dried, and dried using a general chemical vapor deposition apparatus under the conditions shown in Table 3. Then, a TiN layer and / or a TiCN layer having a target layer thickness shown in FIG. 4 is deposited and formed as an adhesion underlayer, and an Al ₂ O ₃ layer having a κ-type or θ-type crystal structure is deposited under the same conditions shown in Table 3. The Al ₂ O ₃ layer is subjected to a heat treatment in a hydrogen atmosphere at a temperature of 1050 ° C. for a predetermined time within a range of 2 to 10 hours to change the κ-type or θ-type crystal structure of the Al ₂ O ₃ layer to α. A heat-transformed α-type Al ₂ O ₃ layer in which the heat-transformed cracks were dispersed and distributed in the layer was formed as a hard wear-resistant layer with the target layer thickness also shown in Table 4, and Under the conditions shown and in Table 4 The present invention coated cermet tools 1 to 12 were prepared respectively by forming target layer thickness deposited α-type the Al ₂ O ₃ layer of and optionally TiN layer as each surface smoothing layer and used before and after the identification layer.
[0015]
For the purpose of comparison, the surfaces of the cermet substrates A to F and the cermet substrates a to f were ultrasonically cleaned in acetone, dried, and then dried in the same manner as in Table 3 (Table 3). 1-TiCN in No. 3 indicates conditions for forming a TiCN layer having a vertically elongated crystal structure described in Japanese Patent Application Laid-Open No. Hei 6-8008, and other conditions indicate conditions for forming a normal granular crystal structure. Under the conditions shown in Table 5, a Ti compound layer having the target layer thickness shown in Table 5 was formed by vapor deposition as the lower layer in the combination shown in Table 5; 5 a conventional coated cermet tools 1 to 12 by depositing forming average layer thickness of the deposited α-type the Al ₂ O ₃ layer and a TiN layer as required as each upper layer and used before and after the identification layer shown in Re respectively were produced.
[0016]
For the purpose of observing the difference between the heat-transformed α-type Al ₂ O ₃ layer and the vapor-deposited α-type Al ₂ O ₃ layer constituting the hard coating layer of the coated cermet tool of the present invention and the conventional coated cermet tool obtained as described above, X was used. Line diffraction was measured.
First, as a sample for X-ray diffraction measurement, a single crystal WC having a diffraction peak only on the (001) plane and the (002) plane on the X-ray diffraction chart was used as a substrate sample. The target layer thickness of the cermet tools 3, 7, and 9 is 15 μm, 10 μm, and 5 μm, and the heat-transformed α-type Al ₂ O ₃ layer, and the target layer thickness of the conventional coated cermet tools 4, 6, and 10 are also 15 μm, 10 μm. , and under the same conditions as the conditions for forming the deposited α-type _Al 2 _{O 3} layer of 5 [mu] m, the target layer thickness each 15 [mu] m, 10 [mu] m, and 5 [mu] m heating transformation α-type _Al of 2 _{O 3} layer and deposition α-type _Al 2 _{O 3} Layers were formed directly to prepare coating samples A to C of the present invention and conventional coating samples a to c.
[0017]
Next, the X-ray diffraction measurement of the above-mentioned heat-transformed α-type Al ₂ O ₃ layer and the vapor-deposited α-type Al ₂ O ₃ layer of these coated samples was carried out by using a usual X-ray diffractometer, and Cu was placed in an X-ray tube. By irradiating the anode (target) with thermoelectrons generated from the metal W filament under the conditions of voltage: 40 kV and current: 350 mA, characteristic X-rays having a wavelength of 0.154 nm from the Cu anode surface are obtained. X-rays that generate a certain Cu-Kα ray, irradiate the characteristic X-ray to the surface of the coated sample, and diffract at an angle equal to the X-ray incident angle θ with respect to the coated sample surface among the X-rays scattered from the coated sample Was measured with an X-ray detector. The measurement results are shown in FIGS.
FIGS. 1 to 3 show X-ray diffraction charts of the heat-transformed α-type Al ₂ O ₃ layers of coating samples A to C of the present invention, and X-ray diffraction charts of vapor-deposited α-type Al ₂ O ₃ layers of conventional coating samples a to c. 4 to 6, the heating-transformed α-type Al ₂ O ₃ layer shows clear diffraction peaks on the (006) plane and the (018) plane, whereas the vapor-deposited α-type Al ₂ the O ₃ layer is clear that these (006) plane and (018) diffraction peak at a surface are not present.
[0018]
The thickness of the hard coating layer of the coated cermet tools 1 to 12 of the present invention and the conventional coated cermet tools 1 to 12 was measured by using a scanning electron microscope (similarly, vertical section measurement). However, in each case, the average layer thickness was substantially the same as the target layer thickness (average value of five-point measurements).
[0019]
Next, the above coated cermet tools 1 to 6 of the present invention and the conventional coated cermet tools 1 to 6 in a state where each of the above various coated cermet tools was screwed to the tip of a tool steel tool with a fixing jig, ,
Work material: JIS SCM440 round bar,
Cutting speed: 450m / min,
Cut: 2mm,
Feed: 0.3 mm / rev,
Cutting time: 3 minutes,
High-speed continuous cutting test of alloy steel under the following conditions:
Work material: JIS S45C lengthwise round bar with four equally spaced longitudinal grooves,
Cutting speed: 350m / min,
Cut: 1.5 mm,
Feed: 0.25 mm / rev,
Cutting time: 3 minutes,
A dry high-speed interrupted cutting test of carbon steel was performed under the following conditions.
[0020]
Further, for the coated cermet tools 7 to 12 of the present invention and the conventional coated cermet tools 7 to 12,
Work material: JIS SCM440 round bar,
Cutting speed: 500m / min,
Notch: 1 mm,
Feed: 0.2 mm / rev,
Cutting time: 3 minutes,
High-speed continuous cutting test of alloy steel under the following conditions:
Work material: JIS S45C lengthwise round bar with four equally spaced longitudinal grooves,
Cutting speed: 350m / min,
Cut: 1mm,
Feed: 0.2 mm / rev,
Cutting time: 3 minutes,
A dry high-speed intermittent cutting test was performed on carbon steel under the following conditions, and the flank wear width of the cutting edge was measured in each cutting test. Table 6 shows the measurement results.
[0021]
[Table 1]

[0022]
[Table 2]

[0023]
[Table 3]

[0024]
[Table 4]

[0025]
[Table 5]

[0026]
[Table 6]

[0027]
【The invention's effect】
From the results shown in Tables 4 to 6, the coated cermet tools 1 to 12 of the present invention have substantially high hard coating layers even in a high-speed continuous cutting test and a high-speed interrupted cutting test of steel and cast iron with extremely high heat generation. It is made of a heat-transformed α-type Al ₂ O ₃ layer having strength and excellent high-temperature strength and heat resistance comparable to the high-temperature strength and heat resistance of the α-type Al ₂ O ₃ layer itself. In high-speed continuous cutting tests and high-speed interrupted cutting tests of steel and cast iron with high heat resistance, it exhibits excellent heat-resistant plastic deformability, and as a result, the cutting edge takes on a normal wear form. relative to exert, in the conventional coated cermet tools 1 to 12 hard layer is composed of Ti compound layer and the deposition α-type Al ₂ O ₃ layer in the high-speed cutting test of the, in particular the Ti compound layer Thermal plastic deformation heat resistance insufficient cause uneven wear due to occur, since the results wear progress is to be promoted, it is clear that lead to a relatively short time service life.
As described above, the coated cermet tool of the present invention can be used not only for continuous cutting or interrupted cutting under ordinary conditions such as various types of steel or cast iron, but also when used for high-speed cutting particularly involving high heat generation. , Which exhibits excellent wear resistance over a long period of time, so that it can respond satisfactorily to the high performance of the cutting equipment, and can further reduce the power and energy consumption of the cutting work and reduce the cost It is assumed that.
[Brief description of the drawings]
FIG. 1 is a view showing an X-ray diffraction chart of a heat-transformed α-type Al ₂ O ₃ layer (target layer thickness: 15 μm) constituting a hard coating layer of the coated cermet tool 3 of the present invention.
FIG. 2 is a view showing an X-ray diffraction chart of a heat-transformed α-type Al ₂ O ₃ layer (target layer thickness: 10 μm) constituting a hard coating layer of the coated cermet tool 7 of the present invention.
FIG. 3 is a view showing an X-ray diffraction chart of a heat-transformed α-type Al ₂ O ₃ layer (target layer thickness: 5 μm) constituting a hard coating layer of the coated cermet tool 9 of the present invention.
FIG. 4 is a diagram showing an X-ray diffraction chart of a vapor-deposited α-type Al ₂ O ₃ layer (target layer thickness: 15 μm) constituting a hard coating layer of the conventional coated cermet tool 4.
FIG. 5 is a diagram showing an X-ray diffraction chart of a vapor-deposited α-type Al ₂ O ₃ layer (target layer thickness: 10 μm) constituting a hard coating layer of the conventional coated cermet tool 6.
FIG. 6 is a diagram showing an X-ray diffraction chart of a vapor-deposited α-type Al ₂ O ₃ layer (target layer thickness: 5 μm) constituting a hard coating layer of the conventional coated cermet tool 10.

Claims (2)

On the surface of a cermet substrate composed of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet,
(A) a titanium nitride layer and / or a titanium carbonitride layer formed by chemical vapor deposition and having an average thickness of 0.1 to 2 μm as an adhesion underlayer;
(B) As a hard wear-resistant layer, aluminum oxide having a κ-type or θ-type crystal structure in a state formed by chemical vapor deposition is subjected to heat treatment to transform the crystal structure into an α-type crystal structure, and to generate heat transformation. A heat-transformed α-type aluminum oxide layer having a structure in which cracks are dispersed and distributed and having an average layer thickness of 5 to 30 μm,
(C) a vapor-deposited α-type aluminum oxide layer having an α-type crystal structure in a state formed by chemical vapor deposition and having an average layer thickness of 0.1 to 2 μm as a surface smoothing layer;
A cutting tool made of a surface-coated cermet, which exhibits excellent heat-resistant plastic deformability by high-speed cutting, formed by forming a hard coating layer composed of (a) to (c) above. On the surface of a cermet substrate composed of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet,
(A) a titanium nitride layer and / or a titanium carbonitride layer formed by chemical vapor deposition and having an average thickness of 0.1 to 2 μm as an adhesion underlayer;
(B) As a hard wear-resistant layer, aluminum oxide having a κ-type or θ-type crystal structure in a state formed by chemical vapor deposition is subjected to heat treatment to transform the crystal structure into an α-type crystal structure, and to generate heat transformation. A heat-transformed α-type aluminum oxide layer having a structure in which cracks are dispersed and distributed and having an average layer thickness of 5 to 30 μm,
(C) a vapor-deposited α-type aluminum oxide layer having an α-type crystal structure in a state formed by chemical vapor deposition and having an average layer thickness of 0.1 to 2 μm as a surface smoothing layer;
(D) a titanium nitride layer formed by chemical vapor deposition and having an average layer thickness of 0.1 to 2 μm as a pre- and post-use identification layer;
A cutting tool made of a surface-coated cermet, which exhibits excellent heat-resistant plastic deformation properties by high-speed cutting, having a hard coating layer composed of (a) to (d) above.

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