SURFACE-COATED TiN-BASED CERMET CUTTING TOOL IN WHICH HARD COATING LAYER EXHIBITS EXCELLENT CHIPPING RESISTANCE

Abstract

A surface-coated TiN-based cermet cutting tool is a surface-coated TiN-based cermet cutting tool, in which a TiN-based cermet containing a TiN phase as a hard phase component is used as a body, and a hard coating layer including a titanium carbonitride layer and an aluminum oxide layer is formed on a surface, in which a linear expansion coefficient of the TiN-based cermet is set to 9.0×10.sup.−6 (/K) or more, a thermal conductivity is set to 30 (W/m.Math.K) or more, and a residual compressive stress of the hard coating layer is set to 600 to 2,000 MPa, and particularly 600 to 2,000 MPa even in an as-deposited state by adjusting component composition and the like of the TiN-based cermet.

Claims

1. A surface-coated TiN-based cermet cutting tool, comprising: a body; and a hard coating layer formed on a surface of the body, wherein a TiN-based cermet containing a TiN phase as a hard phase component is used as the body, wherein the hard coating layer includes at least one layer of a titanium carbonitride layer and an aluminum oxide layer, wherein the body has a linear expansion coefficient of 9.0×10.sup.−6 (/K) or more and a thermal conductivity of 30 (W/m.Math.K) or more, and each of the titanium carbonitride layer and the aluminum oxide layer constituting the hard coating layer has a residual compressive stress of 600 to 2,000 MPa.

2. The surface-coated TiN-based cermet cutting tool according to claim 1, wherein each of the titanium carbonitride layer and the aluminum oxide layer constituting the hard coating layer has a residual compressive stress of 600 to 2,000 MPa in an as-deposited state.

3. The surface-coated TiN-based cermet cutting tool according to claim 1, wherein the TiN-based cermet consists of 70 to 94 area % of the TiN phase, 1 to 25 area % of a Mo.sub.2C phase, and a remainder of a binder phase, a component of the binder phase consists of Fe and Ni, a total area ratio of Fe and Ni is 5 to 15 area %, and an amount of Ni with respect to a total amount of Fe and Ni is 15 to 35 mass %.

4. The surface-coated TiN-based cermet cutting tool according to claim 2, wherein the TiN-based cermet consists of 70 to 94 area % of the TiN phase, 1 to 25 area % of a Mo.sub.2C phase, and a remainder of a binder phase, a component of the binder phase consists of Fe and Ni, a total area ratio of Fe and Ni is 5 to 15 area %, and an amount of Ni with respect to a total amount of Fe and Ni is 15 to 35 mass %.

Description

DESCRIPTION OF EMBODIMENTS

[0036] Next, a surface-coated TiN-based cermet cutting tool of the present invention (hereinafter, also referred to as a “coated TiN-based cermet tool”) will be described in more detail with the following embodiments.

[0037] TiN-Based Cermet Body:

[0038] The body of the coated TiN-based cermet tool of the present embodiment is configured with a TiN-based cermet. The TiN-based cermet body has a linear expansion coefficient of 9.0×10.sup.−6 (/K) or more and a thermal conductivity of 30 (W/m.Math.K) or more by adjusting its component composition.

[0039] Here, in a case where the linear expansion coefficient of the TiN-based cermet body is less than 9.0×10.sup.−6 (/K), it is difficult to introduce a residual compressive stress of 600 MPa or more into a hard coating layer, and accordingly, sufficient chipping resistance cannot be applied. In a case where the thermal conductivity of the TiN-based cermet body is less than 30 (W/m.Math.K), the high heat of the cutting edge cannot be quickly released, and thermal impact resistance to the heat cycle of rapid heating and rapid cooling is decreased, and as a result, the life is shortened due to the generation of thermal cracks and occurrence of chipping.

[0040] Accordingly, the linear expansion coefficient of the TiN-based cermet body is set to 9.0×10.sup.−6 (/K) or more, and the thermal conductivity of the TiN-based cermet body is set to 30 (W/m.Math.K) or more.

[0041] The preferred linear expansion coefficient is 9.5×10.sup.−6 to 10.5×10.sup.−6 (/K), and the preferred thermal conductivity is 35 to 45 (W/m.Math.K).

[0042] In addition, by setting the linear expansion coefficient of the TiN-based cermet body to 9.0×10.sup.−6 (/K) or more, a hard coating layer is formed on the surface of the TiN-based cermet body, and then a residual compressive stress of the hard coating layer is 600 MPa or more, thereby exhibiting excellent chipping resistance. On the other hand, in a case where the residual compressive stress is a large value exceeding 2,000 MPa, in a case where the hard coating layer is thickened (for example, in a case where the film is thickened to exceed 10 μm), self-destruction is likely to occur.

[0043] Therefore, the residual compressive stress of the hard coating layer is set to 600 MPa to 2,000 MPa and preferably 800 MPa to 1,500 MPa.

[0044] The hard coating layer of the present embodiment has the predetermined compressive residual stress in the as-deposited state, and compressive residual stress of the hard coating layer may be further additionally applied within the range of the predetermined compressive residual stress by performing the surface treatment such as sandblasting and shot peening to the surface of the hard coating layer, after forming the hard coating layer.

[0045] The hard coating layer of the coated TiN-based cermet tool of the present embodiment preferably includes at least one layer of a titanium carbonitride layer and an aluminum oxide layer formed by a chemical vapor deposition method. The residual compressive stress of the hard coating layer in this case is a residual compressive stress of the hard coating layer (for example, residual compressive stress of the titanium carbonitride layer and/or the residual compressive stress of the aluminum oxide layer) measured in a state in which the hard coating layer is coated on the surface of the body by the chemical vapor deposition method no special treatment such as sandblasting or shot peening is performed after the coating, that is, the as-deposited state.

[0046] The hard coating layer of the present embodiment preferably includes at least one layer of the titanium carbonitride layer and the aluminum oxide layer formed by the chemical vapor deposition method described above, but for other hard coating layer, it does not exclude that the hard layer well known in the related art such as a titanium compound layer such as a titanium carbide layer or a titanium nitride layer, a composite nitride layer or a composite oxide layer of titanium and aluminum, or a composite nitride layer or a composite oxide layer of chromium and aluminum is coated.

[0047] The linear expansion coefficient of the TiN-based cermet body can be measured, for example, with a dilatometer, and the thermal conductivity of the TiN-based cermet body can be measured, for example, with a xenon flash analyzer.

[0048] In addition, the residual compressive stress of the hard coating layer (preferably, titanium carbonitride layer and/or the aluminum oxide layer) can be calculated by measurement using X-ray diffraction using Cu—Kα ray (λ=1.5418 Å) as a ray source by sin.sup.2 Ψ method under conditions of a scan step: 0.013 degrees and measurement time per step: 0.48 sec/step.

[0049] Specifically, for example, in a case where the hard coating layer includes an aluminum oxide layer, the residual compressive stress can be calculated by using a diffraction peak of a (1310) plane of aluminum oxide, using a Young's modulus of 384 GPa and a Poisson's ratio of 0.232. In addition, in a case where the hard coating layer includes the titanium carbonitride layer, the residual compressive stress can be calculated by using the diffraction peak of a (422) plane of titanium carbonitride, using a Young's modulus of 475 GPa and a Poisson's ratio of 0.2.

[0050] As the TiN-based cermet having the linear expansion coefficient and thermal conductivity, for example, a TiN-based cermet consisting of 70 to 94 area % of a TiN phase, 1 to 25 area % of a Mo.sub.2C phase, and a remainder of a binder phase, in which a component of the binder phase consists of Fe and Ni, a total area ratio of Fe and Ni is 5 to 15 area %, and a amount of Ni with respect to a total amount of Fe and Ni is 15 to 35 mass % can be used.

[0051] It is generally said that a TiN-based cermet is inferior to a TiCN-based cermet in terms of sinterability and toughness, and is therefore unsuitable as a body for a surface-coated cutting tool. However, by sintering the TiN-based cermet having the component composition under the sintering conditions which will be described later, a cermet body for a surface-coated cutting tool having excellent sinterability and toughness and having a predetermined linear expansion coefficient and thermal conductivity can be manufactured.

[0052] The component composition of the TiN-based cermet will be described below.

[0053] Tin Phase:

[0054] In a case where the area ratio of the TiN phase to the TiN-based cermet body is less than 70 area %, the hardness of the body is not sufficient. On the other hand, in a case where the area ratio of the TiN phase exceeds 94 area %, fine voids (pores) are likely to be formed in the sintered structure, and the toughness is lowered. Therefore, the area ratio of the TiN phase in the TiN-based cermet body is preferably 70 to 94 area %. Compared to the TiCN-based cermet known in the related art, the TiCN-based cermet of the present embodiment increases the linear expansion coefficient and thermal conductivity to apply the residual compressive stress to the coating layer and improve the thermal impact resistance of the body, and the high linear expansion coefficient and thermal conductivity are largely caused by the properties of TiN. The linear expansion coefficient and thermal conductivity of TiC are lower than those of TiN, and TiCN has properties intermediate between TiC and TiN depending on a ratio of C and N. Therefore, in this embodiment, it is important to use TiN that does not contain C or has an extremely low C content. The area ratio of the TiN phase is more preferably 80 to 90 area %.

[0055] In the present embodiment, a cross section of the TiN-based cermet body is observed with a scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDS), and a containing element amount of an area in the obtained secondary electron image (for example, area of 100 μm.sup.2) is measured, the TiN phase, the Mo.sub.2C phase, and Fe—Ni phase are specified, the area ratio of each phase to the area is calculated, the area ratio in a plurality of areas of at least 5 or more areas are calculated, thereby setting the average value thereof as area % of each phase.

[0056] Mo.sub.2C Phase:

[0057] In a case where the area ratio of the Mo.sub.2C phase in the TiN-based cermet body is less than 1 area %, wettability between the TiN phase and the binder phase is insufficient and voids are formed in the sintered structure, and accordingly, the toughness is lowered. On the other hand, in a case where the area ratio of the Mo.sub.2C phase exceeds 25 area %, double carbides such as Fe.sub.3Mo.sub.3C phase and double nitrides such as Fe.sub.3Mo.sub.3N phase are likely to be generated, which causes a decrease in toughness. Therefore, the area ratio Mo.sub.2C phase in the TiN-based cermet body is preferably in 1 to 25 area % and more preferably 2 to 10 area %.

[0058] Binder Phase:

[0059] In a case where the area ratio of the binder phase in the TiN-based cermet body is less than 5 area %, the amount of the binder phase is small, and accordingly, the toughness of the TiN-based cermet body is lowered. On the other hand, in a case where the area ratio of the binder phase exceeds 15 area %, the amount of TiN phase, which is a hard phase component, is relatively reduced, and accordingly, the hardness required for the body cannot be ensured.

[0060] Therefore, the area ratio of the binder phase to the TiN-based cermet body is preferably 5 to 15 area % and more preferably 7 to 10 area %.

[0061] In addition, in the present invention, by setting an amount of Ni to a total amount of Fe and Ni constituting the binder phase (={Ni/(Fe+Ni)}×100) to 15 to 35 mass %, the toughness and hardness of the TiN-based cermet body can be further increased.

[0062] This is because that, in a case where the amount of Ni to the total amount of Fe and Ni (={Ni/(Fe+Ni)}×100) is less than 15 mass %, Ni is subjected to solid solution in Fe, but the hardness of the binder phase is not sufficient, since an effect of solid-solution reinforcing the binder phase is not exhibited, and on the other hand, in a case where the amount of Ni to the total amount of Fe and Ni (={Ni/(Fe+Ni)}×100) exceeds 35 mass %, intermetallic compound FeNi.sub.3 is likely to be generated, thereby lowering the toughness of the binder phase.

[0063] The amount of Ni to the total amount of Fe and Ni constituting the binder phase is more preferably 20 to 25 mass %.

[0064] Manufacturing of Coated TiN-Based Cermet Tool:

[0065] In manufacturing the coated TiN-based cermet tool of the present embodiment, for example, in order to obtain component composition and the like of each phase of the TiN phase, the Mo.sub.2C phase, and the binder phase, first, as a raw material powder, a raw material powder having components and composition, TiN: 55 to 92 mass %, Mo.sub.2C: 1 to 40 mass %, Fe: 5 to 18 mass %, Ni: 1 to 5 mass %, and mass % of Ni to the total amount of Ni and Fe (=Ni×100/(Fe+Ni)) satisfies a relationship of 15 to 35 mass % is suitably used.

[0066] Then, the raw material powder satisfying the conditions described above is mixed by a ball mill, and the mixed powder is press-molded to prepare a pressed powder molded body.

[0067] Then, the pressed powder molded body is sintered in a temperature range of 1,350° C. to 1,450° C. for 30 minutes to 120 minutes while flowing a mixed gas having a hydrogen concentration of 1 to 3 volume % and a nitrogen concentration of 97 to 99 volume % (nitrogen-diluted hydrogen atmosphere), then cooled to 1,200° C. at a speed of 10° C./min, and further naturally cooled to room temperature, thereby manufacturing the TiN-based cermet body of the present embodiment having both excellent toughness and hardness.

[0068] The reason why the pressed powder molded body is sintered in the nitrogen-diluted hydrogen atmosphere is to improve the wettability between the TiN powder and Fe, which is the most component of the binder phase, and at the same time to improve the sinterability.

[0069] Next, the TiN-based cermet body is charged into a chemical vapor deposition apparatus, and a hard coating layer (preferably including a titanium carbonitride layer and/or an aluminum oxide layer) is vapor-deposited.

[0070] The total thickness of the hard coating layer is preferably 20 μm or less and more preferably 10 to 15 μm.

[0071] The vapor deposition conditions of the hard coating layer are not particularly limited, but for example, the titanium carbonitride layer can be formed under the vapor deposition conditions of

[0072] reaction gas (volume %):

[0073] TiCl.sub.4: 2%, CH.sub.3CN: 0.7%, N.sub.2: 10%, H.sub.2: remainder,

[0074] reaction pressure: 7 kPa, and

[0075] reaction temperature: 900° C.

[0076] In addition, the aluminum oxide layer can be formed under the vapor deposition conditions of

[0077] reaction gas (volume %):

[0078] AlCl.sub.3: 2.2%, CO.sub.2: 5.5%, HCl: 2.2%,

[0079] H.sub.2S: 0.2%, H.sub.2: remainder,

[0080] reaction pressure: 7 kPa, and

[0081] reaction temperature: 1,000° C.

[0082] A coated TiN-based cermet tool can be manufactured by forming the hard coating layer by vapor deposition and then machining it into a predetermined shape.

[0083] Then, by manufacturing the coated TiN-based cermet tool in the step described above, a surface-coated TiN-based cermet cutting tool in which the linear expansion coefficient of the TiN-based cermet body is 9.0×10.sup.−6 (/K) or more, the thermal conductivity is 30 (W/m K) or more, and the vapor-deposited hard coating layer has a residual compressive stress of 600 to 2,000 MPa in the as-deposited state can be obtained. Even in a case where the surface-coated TiN-based cermet cutting tool is subjected to the cutting such as a wet high-speed milling of alloy steel in which intermittent and impact mechanical loads are exerted on a cutting edge, and a thermal load (thermal impact) due to a heat cycle of rapid heating and rapid cooling is received, no abnormal damage such as chipping or fracture is generated on the cutting edge and excellent wear performance during long-term use is exhibited.

EXAMPLES

[0084] Next, the coated TiN-based cermet tool of the present invention will be described in more detail with reference to examples.

[0085] As an example of the present invention, an example in which the titanium carbonitride layer and/or the aluminum oxide layer is coated and formed on the surface of the cermet body by chemical vapor deposition as the hard coating layer, is described, but as the hard coating layer, a titanium compound layer such as a titanium carbide layer and/or a titanium nitride layer, a composite nitride layer or a composite oxide layer of titanium and aluminum, or a composite nitride layer or a composite oxide layer of chromium and aluminum can also be coated, in addition to the titanium carbonitride layer and/or the aluminum oxide layer.

[0086] As powders for manufacturing the TiN-based cermet body, a TiN powder having an average particle diameter of 10 μm, a Mo.sub.2C powder having an average particle diameter of 2 μm, a Fe powder having an average particle diameter of 2 μm, and a Ni powder having an average particle diameter of 1 μm were prepared and blended to have a blending ratio shown in Table 1, and blended so that the blending ratio of the Fe powder and the Ni powder is a blending ratio shown in Table 1, thereby preparing raw material powders 1 to 8. The average particle diameter here means a median diameter (d50).

[0087] Next, the raw material powders 1 to 8 were filled in a ball mill and mixed to prepare mixed powders 1 to 8, and the mixed powders 1 to 8 were dried and then press-molded at a pressure of 100 to 500 MPa to manufacture pressed powder molded bodies 1 to 8.

[0088] Next, the pressed powder molded bodies 1 to 8 were sintered under conditions shown in Table 2 and then cooled to room temperature, to manufacture TiN-based cermet bodies of the present invention (hereinafter referred to as “present invention bodies”) 1 to 8 shown in Table 3.

[0089] For comparison, various powders having the same average particle diameters as the tool of the present invention were blended so as to have the blending composition shown in Table 4 to prepare raw material powders 11 to 18, and then the raw material powders 11 to 18 were filled and mixed in a ball mill to prepare mixed powders 11 to 18, and the mixed powders 11 to 18 were dried and press-molded at a pressure of 100 to 500 MPa to produce pressed powder molded bodies 11 to 18. As the TiCN powder, a powder having a C:N ratio of 50:50 (herein, atomic ratio) was used.

[0090] Next, the pressed powder molded bodies 11 to 18 were sintered under conditions shown in Tables 2 and 5, and then cooled to room temperature to manufacture cermet bodies of comparative example (hereinafter, referred to as “comparative example bodies”) 11 to 18 shown in Table 6.

[0091] Next, regarding each of the present invention bodies 1 to 8 and the comparative example bodies 11 to 18, a cross section thereof was observed with a scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDS), and a containing element amount of a measurement area in the obtained secondary electron image (for example, a measurement area of 100 μm×100 μm) was measured, the TiN phase or TiCN phase, the Mo.sub.2C phase, and Fe—Ni phase were specified, the area ratio of each phase to the measurement area was calculated, the area ratios in 5 measurement areas were calculated, and the average value of these calculated values was obtained as area % of each phase in the sintered structure.

[0092] In addition, regarding the Fe—Ni phase, the Ni content and the Fe content in the phase were measured at 10 points on the Fe—Ni phase using an Auger electron spectrometer, and the obtained calculated values were averaged. From the value, the amount of Ni to the total amount of Fe and Ni (=Ni×100/(Fe+Ni)) was obtained as mass %.

[0093] Tables 3 and 6 show these values.

[0094] In addition, regarding the present invention bodies 1 to 8 and the comparative example bodies 11 to 18, alumina was used as a comparative sample and a coefficient of average linear expansion (/K), in a case where the temperature is increased from 300 K to 1,273 K at a temperature increase rate of 5° C. per minute was measured by using a dilatometer, and SUS310 was used as a comparative sample, and thermal conductivity was measured under conditions of a measurement temperature of 25° C. and Xe lamp voltage of 270 V by using a xenon flash analyzer.

[0095] Tables 3 and 6 show these values.

TABLE-US-00001 TABLE 1 Blending composition (mass %) Blending ratio Type of raw of Ni powder material TiN Mo.sub.2C Fe Ni (% by mass) powder powder powder powder powder Ni × 100/(Fe + Ni) 1 85.0 4.0 8.7 2.3 20.9 2 83.0 4.0 10.0 3.0 23.1 3 58.5 35.3 5.0 1.2 19.4 4 59.5 21.5 15.2 3.8 20.0 5 91.2 1.6 5.8 1.4 19.4 6 83.0 4.0 8.5 4.5 34.6 7 83.0 4.0 11.0 2.0 15.4 8 52.0 40.0 4.0 4.0 50.0

TABLE-US-00002 TABLE 2 Sintering condition Sintering Sintering Hydrogen Nitrogen Sintering temperature time concentration concentration condition (° C.) (min) (volume %) (volume %) 1 1400 60 2 98 2 1450 30 1 99 3 1350 120 3 97 4 1400 90 3 97

TABLE-US-00003 TABLE 3 Component composition of body Binder phase Coefficient Type of Ni × of linear Thermal Present Type of 100/ expansion conductivity invention sintering TiN Mo.sub.2C Fe—Ni (Fe + Ni) of body of body body condition (area %) (area %) (area %) (mass %) (×10.sup.−6/K) (W/m .Math. K) 1 1 89.7 2.5 7.8 20.9 9.6 35.4 2 2 88.2 2.5 9.3 23.1 9.6 36.3 3 3 70.0 25.0 5.0 20.0 9.3 54.4 4 4 70.0 15.0 15.0 20.0 9.7 50.7 5 1 94.0 1.0 5.0 20.0 9.5 32.6 6 2 88.3 2.5 9.2 34.6 9.6 36.3 7 3 88.1 2.5 9.4 15.4 9.6 36.2 8 4 64.3 29.3 6.4 50.0 9.3 59.2

TABLE-US-00004 TABLE 4 Blending composition (% by mass) Type of Blending ratio raw of Ni powder material TiCN Mo.sub.2C Fe Ni (% by mass) powder powder powder powder powder Ni × 100/(Fe + Ni) 11 85.0 4.0 6.5 4.5 40.9 12 87.0 0.0 10.0 3.0 23.1 13 52.0 40.0 6.0 2.0 25.0 14 90.0 0.0 7.0 3.0 30.0 15 94.0 2.0 3.0 1.0 25.0 16 83.0 4.0 9.5 3.5 26.9 17 83.0 4.0 12.0 1.0 7.7 18 80.0 10.0 8.0 2.0 20.0

TABLE-US-00005 TABLE 5 Sintering condition Sintering Sintering Hydrogen Nitrogen Sintering temperature time concentration concentration condition (° C.) (min) (volume %) (volume %) 11 1400 60 0 100 12 1500 60 2 98 13 1300 120 3 97 14 1400 90 10 90

TABLE-US-00006 TABLE 6 Component composition of body Binder phase Coefficient Type of Ni × of linear Thermal comparative Type of 100/ expansion conductivity example sintering TiCN Mo.sub.2C Fe—Ni (Fe + Ni) of body of body body condition (area %) (area %) (area %) (mass %) (×10.sup.−6/K) (W/m .Math. K) 11 1 89.9 2.5 7.6 40.9 8.7 31.9 12 2 90.9 0.0 9.1 23.1 8.7 30.3 13 3 64.2 29.2 6.6 25.0 8.7 56.6 14 4 93.1 0.0 6.9 30.0 8.7 29.0 15 13 96.1 1.2 2.7 25.0 8.5 27.7 16 12 88.3 2.5 9.2 26.9 8.8 32.7 17 14 88.1 2.5 9.4 7.7 8.7 32.7 18 11 86.3 6.4 7.3 20.0 8.7 35.2

[0096] Next, the present invention bodies 1 to 8 and the comparative example bodies 11 to 18 were charged into a chemical vapor deposition apparatus, and the hard coating layers of the film types shown in Tables 7 and 8 were formed by vapor deposition with an average layer thickness shown in Tables 7 and 8 as a single layer structure or a multiple layer structure.

[0097] Here, the hard coating layer is formed by vapor deposition as a single layer structure or a multiple layer structure of up to four layers, but the number of layers is not limited, and a laminated structure of a larger number of layers may be used.

[0098] In addition, although there is no particular limitation on the vapor deposition conditions for the hard coating layer, the chemical vapor deposition conditions for titanium carbonitride and aluminum oxide in the present invention bodies 1 to 8 and the comparative example bodies 11 to 18 are as follows.

[0099] [Titanium Carbonitride]

[0100] reaction gas (volume %):

[0101] TiCl.sub.4: 2%, CH.sub.3CN: 0.7%, N.sub.2: 10%, H.sub.2: remainder,

[0102] reaction pressure: 7 kPa, and

[0103] reaction temperature: 900° C.

[0104] [Aluminum Oxide]

[0105] reaction gas (volume %):

[0106] AlCl.sub.3: 2.2%, CO.sub.2: 5.5%, HCl: 2.2%,

[0107] H.sub.2S: 0.2%, H.sub.2: remainder,

[0108] reaction pressure: 7 kPa, and

[0109] reaction temperature: 1,000° C.

[0110] After forming the hard coating layer by vapor deposition, coated TiN-based cermet tools of the present invention (hereinafter, referred to as “present invention tools”) 1 to 8 shown in Table 7 and coated cermet tools of the comparative examples (hereinafter, referred to as “comparative example tools”) 11 to 18 shown in Table 8 having an insert shape of ISO standard SEEN1203AFSN were manufactured by performing grinding work.

[0111] Regarding the hard coating layer in the as-deposited state of the present invention tools 1 to 8 and the comparative example tools 11 to 18 after completing the vapor deposition, the X-ray diffraction was performed using a Cu—Kα ray (λ=1.5418 Å) as a ray source by sin.sup.2 Ψ method under the conditions of a scan step: 0.013 degrees and measurement time per step: 0.48 sec/step, and a value of the residual stress of the hard coating layer was measured and calculated.

[0112] For example, regarding the hard coating layer consisting of the aluminum oxide layer, the residual stress was calculated by using a diffraction peak of a (1310) plane, using a Young's modulus of 384 GPa and a Poisson's ratio of 0.232. For example, regarding the hard coating layer consisting of the titanium carbonitride layer, the residual stress was calculated by using a diffraction peak of a (422) plane, using a Young's modulus of 475 GPa and a Poisson's ratio of 0.2.

[0113] Tables 7 and 8 show these values.

[0114] In the tables, the residual compressive stress is shown as a positive value, and the residual tensile stress is shown as a negative value.

[0115] After the above residual stress measurement, the present invention tools 1 and 2 and the comparative example tools 1 and 2 were subjected to wet blast treatment to treat the surface of the coating layer.

[0116] The residual stresses of the TiCN layer and the Al.sub.2O.sub.3 layer of the present invention tools 1 and 2 and the comparative example tools 1 and 2 after the wet blast treatment were as follows.

[0117] Present Invention Tool 1

[0118] TiCN layer: 770 MPa (increased by 20 MPa compared to the as-deposited state)

[0119] Al.sub.2O.sub.3 layer: 1,060 MPa (increased by 40 MPa compared to the as-deposited state)

[0120] Present Invention Tool 2

[0121] TiCN layer: 1,090 MPa (increased by 30 MPa compared to the as-deposited state)

[0122] Al.sub.2O.sub.3 layer: 1,350 MPa (increased by 50 MPa compared to the as-deposited state)

Comparative Example Tool 1

[0123] TiCN layer: 240 MPa (increased by 20 MPa compared to the as-deposited state)

[0124] Al.sub.2O.sub.3 layer: 420 MPa (increased by 60 MPa compared to the as-deposited state)

Comparative Example Tool 2

[0125] TiCN layer: 540 MPa (increased by 20 MPa compared to the as-deposited state)

[0126] Al.sub.2O.sub.3 layer: 590 MPa (increased by 40 MPa compared to the as-deposited state)

TABLE-US-00007 TABLE 7 Hard coating layer First layer Second layer Third layer Fourth layer Type of Type of Average Average Average Average present present layer layer layer layer inven- inven- Type of thick- Residual thick- Residual thick- Residual thick- Residual tion tion sintering Film ness stress Film ness stress Film ness stress Film ness stress tool body condition type (μm) (MPa) type (μm) (MPa) type (μm) (MPa) type (μm) (MPa) 1 1 1 TiN 0.2 — TiCN 10.0 750 Al.sub.2O.sub.3 5.0 1020 — — — 2 2 2 TiN 0.2 — TiCN 6.0 1060 Al.sub.2O.sub.3 3.0 1300 TiN 0.2 — 3 3 3 TiN 0.2 — TiC 0.5 — Al.sub.2O.sub.3 5.0  620 — — — 4 4 4 TiN 1.0 — TiCN 5.0 1570 Al.sub.2O.sub.3 2.0 1910 — — — 5 5 1 TiN 1.0 — TiCN 12.0 700 TiN 0.1 — — — — 6 6 2 TiN 0.5 — TiCN 8.0 1250 Al.sub.2O.sub.3 4.0 1230 TiN 0.2 — 7 7 3 TiN 0.5 — TiCN 8.0 1130 TiCNO 0.2 — Al.sub.2O.sub.3 8.0 1170 8 8 4 TiN 0.5 — TiCN 5.0 920 TiCNO 0.2 — Al.sub.2O.sub.3 10.0  1060

TABLE-US-00008 TABLE 8 Hard coating layer First layer Second layer Third layer Fourth layer Type of Type of Average Average Average Average compara- compara- layer Resid- layer Resid- layer Resid- layer Resid- tive tive Type of thick- ual thick- ual thick- ual thick- ual example example sintering Film ness stress Film ness stress Film ness stress Film ness stress tool body condition type (μm) (MPa) type (μm) (MPa) type (μm) (MPa) type (μm) (MPa) 11 11 1 TiN 0.2 — TiCN 10.0 220 Al.sub.2O.sub.3 5.0 360 — — — 12 12 2 TiN 0.2 — TiCN 6.0 520 Al.sub.2O.sub.3 3.0 550 TiN 0.2 — 13 13 3 TiN 0.2 — TiC 0.5 — Al.sub.2O.sub.3 5.0 60 — — — 14 14 4 TiN 1.0 — TiCN 5.0 20 Al.sub.2O.sub.3 2.0 50 — — — 15 15 13 TiN 1.0 — TiCN 12.0 −120 Al.sub.2O.sub.3 7.0 −80 — — — 16 16 12 TiN 0.5 — TiCN 8.0 560 TiN 0.2 — — — — 17 17 14 TiN 0.5 — TiCN 8.0 470 TiCNO 0.2 — Al.sub.2O.sub.3 8.0 510 18 18 11 TiN 0.5 — TiCN 5.0 50 TiCNO 0.2 — Al.sub.2O.sub.3 10.0   50

[0127] Next, the present invention tools 1 to 8 and the comparative example tools 11 to 18 were all subjected to a wet milling test of alloy steel shown below, while being screwed to a tip of a tool steel cutter with a fixing jig, a flank face wear width of the cutting edge was measured, and a wear state of the cutting edge was observed.

[0128] Cutting Conditions:

[0129] Work material: JIS⋅SCM440 block,

[0130] Cutting speed: 800 m/min,

[0131] Depth of cut: 1.0 mm,

[0132] Feed: 0.1 nm/rev,

[0133] Cutting time: 15 minutes,

[0134] Table 9 shows the results of the cutting test.

TABLE-US-00009 TABLE 9 flank flank face State of face Wear wear wear of wear state of width cutting width cutting Type (mm) edge Type (mm) edge Present 1 0.12 No Compar- 11 0.30 Chipping invention abnormality ative tool 2 0.10 No example 12 0.25 Chipping abnormality tool 3 0.19 No 13 *8 Fracture abnormality 4 0.15 No 14 *8 Fracture abnormality 5 0.19 No 15 *2 Fracture abnormality 6 0.12 No 16 0.24 Chipping abnormality 7 0.11 No 17 0.28 Chipping abnormality 8 0.20 No 18 *7 Fracture abnormality *indicates cutting time (min) taken to the end of life.

[0135] As shown in Tables 3 and 6 to 9, in each of the present invention tools 1 to 8, the TiN-based cermet body had a predetermined linear expansion coefficient and thermal conductivity (see Table 3), and a predetermined residual compressive stress exists on the hard coating layer (see Table 7), and accordingly, even during the cutting in which intermittent and impact mechanical loads and thermal load (thermal impact) due to heat cycle of rapid heating and rapid cooling are exerted on the cutting edge, chipping for affecting the cutting life did not occur and excellent wear resistance during long-term use was exhibited (see Table 9).

[0136] On the other hand, in each of the comparative example tools 11 to 18, the TiN-based cermet body did not have the predetermined linear expansion coefficient and thermal conductivity specified in the invention (see Table 6), or the predetermined residual compressive stress did not exist on the hard coating layer (see Table 8), and accordingly, wear resistance was not sufficient, and also, tool life was shortened due to chipping of the cutting edge mainly caused by the generation and growth of thermal cracks (see Table 9).

INDUSTRIAL APPLICABILITY

[0137] Since the surface-coated TiN-based cermet cutting tool of the present invention has excellent chipping resistance and wear resistance, it can be applied not only to high-speed wet intermittent cutting but also as a cutting tool under other cutting conditions. It exhibits excellent cutting performance during long-term use, and can fully and satisfactorily respond to labor saving, energy saving, and cost reduction in cutting.