COATED CUTTING TOOL

Abstract

Coated cutting tool (4) comprising a carbide (1) and a coating layer (3) formed on the carbide (1), wherein the coated cutting tool (4) is arranged such that the coated cutting tool (4) has a rake face, a clearance face and a cutting edge line part which is located between the rake face and the clearance face, the coating layer (3) has a composite layer (2) which contains a compound with a composition represented by the following formula 1: (Al x Ti 1-x )N Formula 1, In formula 1, x represents the atomic ratio of elemental Al relative to the total of elemental Al and elemental Ti and satisfies 0.70 ≤ x ≤ 0.90. if the average thickness of the coating layer (3) in the cutting edge line part is expressed as T1 and the average thickness of the coating layer (3) in the rake face at a position 2 mm or more away from the cutting edge line part in the direction of the rake face is expressed as T2, T1 is 4.0 µm or more and 10.0 µm or less, T2 is 2.0 µm or more and 7.0 µm or less, and T2 < T1 is satisfied, and if the residual stress of the carbide (1) in the cutting edge line part is expressed as S1 and the residual stress of the carbide (1) in the rake face at a position 2 mm or more away from the cutting edge line part in the direction of the rake face is expressed as S2, S2 < S1 is satisfied.

Description

Technical field

[0001] The present invention relates to a coated cutting tool. Technical background

[0002] It is conventionally known that a coated cutting tool, which has a coating layer deposited on the surface of a hard metal substrate by a chemical vapor deposition process with a total thickness of 3 to 20 µm, is used for cutting steel, cast iron, or the like. The coating layer described above, for example, is one consisting of a single layer or two or more layers selected from the group consisting of titanium carbides, nitrides, carbonitrides, oxycarbides, oxycarbonitrides, and aluminum oxide (Al₂O₃).

[0003] Furthermore, a coated tool with a Ti-Al-based nitride layer deposited on the surface of a substrate made of cemented carbide or cubic boron nitride by a physical vapor deposition process is known, and such tools are known to exhibit excellent wear resistance. Although the conventional coated tool described above, which has a Ti-Al-based nitride layer formed by a physical vapor deposition process, exhibits relatively excellent wear resistance, cracking is likely to occur when such a tool is used under cutting conditions involving high-speed machining and intermittent loading. Therefore, various proposals for improving the coating layer have been submitted.

[0004] For example, PTL 1 describes a surface-coated cutting tool with a hard coating layer comprising at least two layers, an upper layer (α) and a lower layer (β), which are formed on the surface of a tool base made of a WC-based cemented carbide, a TiCN-based cermet, or a cBN-based ultra-high-pressure sintered body. The surface-coated cutting tool is characterized in that (a) the upper layer (α) is formed from an Al₂O₃ layer with an α-type crystal structure, (b) the lower layer (β) is formed from a Ti-Al composite nitride layer or composite carbonitride layer, (c) the Ti-Al composite nitride layer or composite carbonitride layer has at least one crystal layer with a face-centered cubic structure of the NaCl type.(d) if the thickness of the upper layer (α) in the cutting edge line is expressed as Tα1 and the thickness at a point 500 µm from the cutting edge line in the direction of the rake face is expressed as Tα2, Tα1 and Tα2 satisfy 0.0 to 5.0 µm and 1.0 to 20.0 µm respectively, and furthermore Tα1 < Tα2; and (e) if the thickness of the lower layer (β) in the cutting edge line is expressed as Tβ1 and the thickness at a point 500 µm from the cutting edge line in the direction of the rake face is expressed as Tβ2, Tβ1 and Tβ2 satisfy 1.0 to 20.0 µm respectively, and furthermore Tβ2 < Tβ1.

[0005] JP 2019-010707 A discloses a surface-coated cutting tool having a hard coating consisting of a nitride or carbonitride composite layer of Ti and Al with a face-centered cubic NaCl structure and an average layer thickness of 1.0–20.0 µm. The crystal orientation in the crystal grains is analyzed, the mean orientation difference between two adjacent measurement points in the same crystal grain is calculated, and a KAM value is determined at each measurement point. Layers in which the proportion of measurement points with a KAM value of less than 1 degree is at least 50%, and layers in which this proportion is 50% lower, are laminated. If the layer is represented by the composition (TiAl)(CN), the following conditions apply to the layer: 0.60 ≤ x ≤ 0.95 and 0 ≤ y ≤ 0.005.

[0006] JP 2004-122263 A discloses a coated cutting tool for cutting a high-precision component, shaped such that the cutting edge is sharp, the surface roughness of the cutting edge in a centerline is 0.4 µm or less, the thickness of the coating layer on the cutting face is 0.5-2 µm, and the thickness of the coating layer on the flank is 4-7 µm. US 2018 / 0347027 A1 discloses coatings that use composite architectures providing high aluminum content and high hardness for various cutting applications.For example, a coated cutting tool comprises a substrate and a coating consisting of a refractory layer applied by physical vapor deposition and adhering to the substrate, wherein the refractory layer consists of a plurality of sublayer groups, one sublayer group consisting of a titanium aluminum nitride sublayer and an adjacent composite sublayer consisting of alternating nanolayers of titanium silicon nitride and titanium aluminum nitride. List of oppositions patent literature

[0007] Patent Document 1: JP-A-2019-155570 Brief description of the invention: Technical problem

[0008] In recent cutting processes, higher speed, higher feed rates, and deeper cuts have become increasingly important, and tools must exhibit better wear resistance and fracture toughness than before. Furthermore, due to the increasing complexity of machining operations compared to the past, intermittent tool loading is becoming more prevalent. Under such harsh cutting conditions, conventional tools can fracture due to thermal cracking.

[0009] A coating layer formed by a chemical deposition process typically exhibits excellent spreading properties, and its thickness is essentially the same from the cutting edge line portion to around the center hole of the insert. Furthermore, when a Ti-Al-based nitride layer is formed by a chemical deposition process, the compressive stress of the cemented carbide substrate tends to decrease due to the low formation temperature. This is because, at low temperatures, the difference in thermal expansion between the coating layer and the cemented carbide substrate is reduced, thus decreasing the compressive stress of the cemented carbide substrate. Consequently, the resulting coated cutting tool tends to have reduced insert strength and fracture toughness.As a countermeasure against such a tendency, for example, a reduction in the insert's strength through treatments such as dry or wet blasting was prevented. However, even with simple treatments like dry or wet blasting, under the aforementioned cutting conditions, thermal cracking can occur at the corner of the insert used during processing, and such cracks can propagate to unused corners, leading to insert breakage. Consequently, it may become impossible to use unused corners for cutting. Furthermore, the occurrence of thermal cracking in the early processing phase can lead to breakage. This creates a difficulty in extending the service life of the coated cutting tool. This is presumably due to the influence of the coating layer thickness and the substrate's internal stress.

[0010] The surface-coated cutting tool described in PTL 1 is characterized in that, if the thickness of the lower layer (β) in the cutting edge line is expressed as Tβ1 and the thickness at a point 500 µm away from the cutting edge line in the direction of the rake face is expressed as Tβ2, then Tβ1 and Tβ2 satisfy values ​​of 1.0 to 20.0 µm and, moreover, Tβ2 < Tβ1. Such a surface-coated cutting tool is expected to be effective in improving wear resistance. Although the surface-coated cutting tool described in PTL 1 has excellent thermal insulation, since the top layer (α) is an Al2O3 layer with an α-type crystal structure, in the event of fracture, the way in which heat is transferred to the substrate differs between a part where the Al2O3 layer remains and a part where the layer has been lost.Accordingly, thermal cracking can occur, making it impossible to extend tool life. Furthermore, PTL 1 does not disclose the effect of controlling the residual stress of a carbide relative to each part of the cutting edge line and the rake face. Additionally, the process described in PTL 1 for producing a surface-coated cutting tool involves depositing a coating layer and then subjecting it to wet blasting. However, it can be difficult to impart compressive stress to a substrate through wet blasting. This is presumably due to the influence of the small size of the blasting material.

[0011] The invention was made with regard to the aforementioned prior art and one of its objectives is to provide a coated cutting tool with excellent fracture resistance, which thus enables the extension of a tool life. Solution to the problem

[0012] The inventors have conducted studies regarding the extension of the service life of a coated cutting tool. Consequently, they have determined the following and thus realized the invention. That is, if a coated cutting tool is provided with a specific design, the occurrence of thermal cracking is prevented, even under cutting conditions in which the tool is subjected to intermittent stress, thereby improving its fracture toughness. As a result, the service life of the coated cutting tools can be extended.

[0013] That is to say, the invention is as follows. [1] Coated cutting tool with a carbide and a coating layer formed on the carbide, wherein the coated cutting tool is arranged such that the coated cutting tool has a rake face, a clearance face and a cutting edge line part which is located between the rake face and the clearance face, the coating layer has a composite layer which contains a compound with a composition represented by the following formula (1): (AlxTi1−x)N (in formula (1) x represents the atomic ratio of elemental Al relative to the total of elemental Al and elemental Ti and satisfies 0.70 ≤ x ≤ 0.90), if the average thickness of the coating layer in the cutting edge line part is expressed as T1 and the average thickness of the coating layer in the rake face at a position 2 mm or more away from the cutting edge line part in the direction of the rake face is expressed as T2, T1 is 4.0 µm or more and 10.0 µm or less, T2 is 2.0 µm or more and 7.0 µm or less and T2 < T1 is satisfied, and If the residual stress of the carbide in the cutting edge line part is expressed as S1 and the residual stress of the carbide in the rake face at a position 2 mm or more away from the cutting edge line part in the direction of the rake face is expressed as S2, then S2 < S1 is satisfied. [2] Coated cutting tool according to [1], wherein the residual stress S1 is -0.5 GPa or more and 0.0 GPa or less and the residual stress S2 is -2.0 GPa or more and -0.3 GPa or less. [3] Coated cutting tool according to [1] or [2], wherein the difference T1 - T2 between the average thickness T1 and the average thickness T2 is 1.0 µm or more and 4.0 µm or less. [4] Coated cutting tool according to one of [1] to [3], wherein in the hard metal the proportion of measuring points where tungsten carbide (WC) has a KAM value of 1° or less is 90% or more and 98% or less. [5] Coated cutting tool according to one of [1] to [4], wherein the cemented carbide is based on a WC phase, contains Co in a proportion of 5.0 wt% or more and 15.0 wt% or less and Cr in a proportion of 0.3 wt% or more and 1.0 wt% or less than Cr3C2. [6] Coated cutting tool according to one of [1] to [5], wherein the coating layer has a lower layer between the hard metal and the composite layer, which contains a Ti compound comprising elemental Ti and at least one element selected from the group consisting of C, N, O and B. Advantageous effects of the invention

[0014] The coated cutting tool of the invention exhibits excellent fracture resistance and thus enables an extension of its service life. Brief description of the drawings [ Fig.1] A schematic cross-sectional view illustrating an example of the coated cutting tool of the invention. [ Fig. 2] A schematic cross-sectional view illustrating an example of a chemical vapor deposition device used in the production of the coated cutting tool of the invention to form a coating layer. [ Fig. 3] A schematic cross-sectional view to enlarge the near area of ​​a gas introduction device in the chemical vapor deposition device made of Fig. 2. Description of embodiments

[0015] In the following, one method of implementing the invention (hereinafter simply referred to as "this embodiment") is described in detail with reference to the drawings, as necessary. However, the invention is not limited to this embodiment described below. Various modifications can be made to it without deviating from the core content of the invention. Furthermore, unless otherwise indicated, the positional relationships in the drawings, such as top, bottom, right, and left, are based on the positions depicted in the drawings. Moreover, the dimensional relationships in the drawings are not limited to those illustrated.

[0016] The coated cutting tool of this embodiment comprises a carbide and a coating layer formed on the carbide and has a rake face, a clearance face, and a cutting edge line portion located between the rake face and the clearance face. The coating layer comprises a composite layer containing a compound with a composition represented by the following formula (1): (AlxTi1−x)N (in formula (1) x represents the atomic ratio of elemental Al relative to the total of elemental Al and elemental Ti and satisfies 0.70 ≤ x ≤ 0.90).

[0017] If the average thickness of the coating layer in the cutting edge line part is expressed as T1 and the average thickness of the coating layer in the rake face at a position 2 mm or more away from the cutting edge line part in the direction of the rake face is expressed as T2, then T1 is 4.0 µm or more and 10.0 µm or less, T2 is 2.0 µm or more and 7.0 µm or less and T2 < T1 is satisfied, and if the residual stress of the cemented carbide in the cutting edge line part is expressed as S1 and the residual stress of the cemented carbide in the rake face at a position 2 mm or more away from the cutting edge line part in the direction of the rake face is expressed as S2, then S2 < S1 is satisfied.

[0018] Since the coated cutting tool of this embodiment has the configuration described above, the occurrence of thermal cracking can be prevented, for example, even under cutting conditions in which the tool is intermittently subjected to high loads. Accordingly, the fracture toughness of the coated cutting tool of this embodiment can be improved, and the breakage of unused corners can also be prevented. Consequently, the tool life can be extended, and the reliability of the coated cutting tool can be increased. In the coated cutting tool of this embodiment, the factor that makes it possible to improve the fracture toughness and also prevent the breakage of unused corners is presumably as follows. However, the invention is by no means limited by the following factor.This means that, firstly, in the coated cutting tool of this embodiment, the hardness of the composite layer, which contains a compound with a composition represented by formula (1) above, improves due to solid solution hardening when the atomic ratio x of elemental Al in formula (1) above is 0.70 or more, leading to improved wear resistance. Furthermore, oxidation resistance improves with an increase in the Al content. Consequently, the crater wear resistance of the coated cutting tool of this embodiment improves, thus preventing a reduction in the strength of the cutting edge and improving the fracture toughness.Furthermore, in the coated cutting tool of this embodiment, the composite layer, which contains a compound with a composition represented by formula (1) above, includes Ti when the atomic ratio x of elemental Al in formula (1) above is 0.90 or less. Consequently, the toughness is improved, which prevents the occurrence of thermal cracking and improves the fracture toughness.

[0019] Furthermore, in the coated cutting tool of this embodiment, if the average thickness T1 of the coating layer in the cutting edge line part is 4.0 µm or more, the wear resistance is improved, and at the same time, if T1 is 10.0 µm or less, the adhesion to the carbide is improved, which can prevent the occurrence of thermal cracking and improve the fracture toughness.

[0020] Furthermore, in the coated cutting tool of this embodiment, if the average thickness T2 of the coating layer in the rake face at a position 2 mm or more away from the cutting edge line part in the direction of the rake face is 2.0 µm or more, anomalous damage due to scratches by chips can be prevented, and at the same time, if T2 is 7.0 µm or less, a residual stress can be effectively imparted to the carbide by a treatment after the formation of the coating layer (e.g. dry blasting, shot peening).

[0021] Furthermore, in the coated cutting tool of this embodiment, wear resistance is improved when the average thickness T1 of the coating layer in the cutting edge section is greater than the average thickness T2 of the coating layer in the rake face at a position 2 mm or more away from the cutting edge section in the direction of the rake face, that is, when T2 < T1. Additionally, the occurrence of thermal cracking can be prevented. Accordingly, the occurrence of fracture that would propagate to other corners can be prevented.

[0022] Furthermore, in the coated cutting tool of this embodiment, if the residual stress S2 of the carbide in the rake face at a position 2 mm or more away from the cutting edge section in the direction of the rake face is lower than the residual stress S1 of the carbide in the cutting edge section, that is, if S2 < S1, a suppressive effect is achieved with regard to the propagation of cracks formed in the cutting edge section into the interior of the coated cutting tool during cutting operations. Accordingly, the occurrence of thermal cracking can be prevented and the fracture toughness is improved. This is presumably because the value of the residual stress S2 of the carbide in the rake face at a position 2 mm or more away from the cutting edge section in the direction of the rake face is on the compressive stress side compared to the residual stress S1 of the carbide in the cutting edge section.

[0023] Then, presumably, as a result of combining these features in the coated cutting tool of this embodiment, the fracture resistance is improved and, in addition, the breakage of unused corners can be prevented, which makes it possible to extend the service life.

[0024] Fig. Figure 1 is a schematic cross-sectional view illustrating an example of the coated cutting tool of this embodiment. A coated cutting tool 4 has a carbide 1 and a composite layer 2 (coating layer 3) which is formed on the surface of the carbide 1.

[0025] The coated cutting tool of this embodiment comprises a carbide and a coating layer formed on the carbide. Specific types of coated cutting tools include replaceable cutting inserts for milling or turning, drills, and end mills.

[0026] The cemented carbide used in this embodiment may have a modified surface. For example, a de-β layer may be formed on the surface of the cemented carbide. Even if the cemented carbide has such a modified surface, the operational effect of the invention is achieved. <Coating layer>

[0027] The coating layer for use in this embodiment comprises a composite layer containing a compound with a composition represented by the following formula (1): (Al x Ti 1-x )N (1) (in formula (1) x represents the atomic ratio of elemental Al relative to the total of elemental Al and elemental Ti and satisfies 0.70 ≤ x ≤ 0.90).

[0028] In the coated cutting tool of this embodiment, the hardness of the composite layer, which contains a compound with a composition represented by formula (1) above, is improved due to solid solution hardening when x in formula (1) above is 0.70 or more, resulting in improved wear resistance. Furthermore, oxidation resistance is improved with an increase in the Al content. Consequently, the crater wear resistance of the coated cutting tool of this embodiment is improved, thus preventing a reduction in the strength of the cutting edge and thereby improving the fracture toughness. However, in the coated cutting tool of this embodiment, Ti is present in the composite layer, which contains a compound with a composition represented by formula (1) above, when x in formula (1) above is 0.90 or less.Consequently, the toughness is improved, which can prevent the occurrence of thermal cracking and improve the fracture toughness. In this respect, x in the above formula (1) is preferably 0.71 or more and 0.89 or less, and further preferably 0.71 or more and 0.88 or less.

[0029] In the coated cutting tool of this embodiment, if the average thickness of the coating layer in the cutting edge line part is expressed as T1 and the average thickness of the coating layer in the rake face at a position 2 mm or more away from the cutting edge line part in the direction of the rake face is expressed as T2, the average thickness T1 is 4.0 µm or more and 10.0 µm or less, the average thickness T2 is 2.0 µm or more and 7.0 µm or less, and T2 < T1 is satisfied.

[0030] In the coated cutting tool of this embodiment, wear resistance is improved when the average thickness T1 is 4.0 µm or more, and simultaneously, adhesion to the carbide is improved when the average thickness T1 is 10.0 µm or less, thereby preventing thermal cracking and improving fracture toughness. In this respect, the average thickness T1 is preferably 4.4 µm or more and 9.8 µm or less, and further preferably 4.8 µm or more and 9.8 µm or less.

[0031] Furthermore, in the coated cutting tool of this embodiment, if the average thickness T2 is 2.0 µm or more, abnormal damage due to scratches from chips can be prevented, and simultaneously, if the average thickness T2 is 7.0 µm or less, residual stress can be effectively imparted to the carbide by a treatment after the formation of the coating layer (e.g., dry blasting, shot peening). In this respect, the average thickness T2 is preferably 2.0 µm or more and 6.8 µm or less, and further preferably 3.0 µm or more and 6.8 µm or less.

[0032] Furthermore, in the coated cutting tool of this embodiment, if T2 < T1, the wear resistance is improved, and the occurrence of thermal cracking can also be prevented. Accordingly, the occurrence of fracture that would reach other corners can be prevented.

[0033] Furthermore, in the coated cutting tool of this embodiment, it is preferred that the difference (T1 - T2) between the average thickness T1 and the average thickness T2 is 1.0 µm or more and 4.0 µm or less. In the coated cutting tool of this embodiment, when T1 - T2 is 1.0 µm or more, the inhibiting effect with regard to the occurrence of fracture that will reach other corners tends to be more pronounced, and at the same time, when T1 - T2 is 4.0 µm or less, the balance between wear resistance and fracture strength tends to be superior. In this respect, T1 - T2 is further preferably 1.2 µm or more and 4.0 µm or less.

[0034] Furthermore, in the coated cutting tool of this embodiment, the average thickness of the coating layer at each section can be determined by measuring the thicknesses of the coating layer at each section starting from cross-sections of the coating layer at three or more points at each section and calculating the arithmetic mean.

[0035] Furthermore, in the coated cutting tool of this embodiment, the rake face preferably has a length of 3.5 mm or more and 20.0 mm or less from the cutting edge line portion in the direction of the rake face. The length is also preferably 3.9 mm or more and 18.0 mm or less.

[0036] Furthermore, the coating layer for use in this embodiment preferably has a lower layer between the cemented carbide and the composite layer, which contains a titanium compound comprising elemental titanium and at least one element selected from the group consisting of C, N, O, and B. In the coated cutting tool of this embodiment, the wear resistance tends to improve when the coating layer has a lower layer containing a titanium compound between the cemented carbide and the composite layer. Specific examples of titanium compounds contained in the lower layer are not limited and could include, for example, a TiC layer, a TiN layer, a TiCN layer, a TiCNO layer, and the like.

[0037] The average thickness of the lower layer is preferably 0.1 µm or more and 2.0 µm or less, more preferably 0.2 µm or more and 1.5 µm or less, and even more preferably 0.2 µm or more and 1.0 µm or less. In the coated cutting tool of this embodiment, wear resistance tends to improve when the average thickness of the lower layer is within the aforementioned range. <hartmetall>

[0038] In the coated cutting tool of this embodiment, if the residual stress of the carbide in the cutting edge section is expressed as S1 and the residual stress of the carbide in the rake face at a position 2 mm or more away from the cutting edge section in the direction of the rake face is expressed as S2, then the condition S2 < S1 is met. In the coated cutting tool of this embodiment, if S2 < S1, an inhibiting effect is achieved with regard to the propagation of cracks formed in the cutting edge section into the interior of the coated cutting tool during cutting operations. Accordingly, the occurrence of thermal cracking can be prevented and the fracture toughness is improved. This is presumably because the value of the residual stress S2 lies on the compressive stress side compared to the residual stress S1.

[0039] Furthermore, in the coated cutting tool of this embodiment, the residual stress S1 is preferably -0.5 GPa or more and 0.0 GPa or less. In the coated cutting tool of this embodiment, if the residual stress S1 is -0.5 GPa or more, changes in the residual stress due to heat generated during processing are more likely to be suppressed, thus preventing them from causing damage. Conversely, in the coated cutting tool of this embodiment, if the residual stress S1 is 0.0 GPa or less, the fracture toughness tends to improve. In this respect, the residual stress S1 is preferably -0.5 GPa or more and -0.1 GPa or less, and more preferably -0.5 GPa or more and -0.2 GPa or less.

[0040] Furthermore, in the coated cutting tool of this embodiment, the residual stress S2 is preferably -2.0 GPa or more and -0.3 GPa or less. In the coated cutting tool of this embodiment, if the residual stress S2 is -2.0 GPa or more, it is generally possible, due to the influence of the treatment after the formation of the coating layer, to prevent layer delamination caused by the joining of cracks in the coating layer. Conversely, in the coated cutting tool of this embodiment, if the residual stress S2 is -0.3 GPa or less, it is generally possible to prevent the propagation of thermal cracks formed in the cutting edge portion. In this respect, the residual stress S2 is preferably -1.9 GPa or more and -0.4 GPa or less, and further preferably -1.9 GPa or more and -0.5 GPa or less.

[0041] Residual stress is an internal stress (inherent strain) remaining within the coating layer. Generally, a stress represented by a numerical value with "-" (minus) is called "compressive stress," whereas a stress represented by a numerical value with "+" (plus) is called "tensile stress." In this embodiment, a higher numerical value with "+" (plus) indicates a higher residual stress, while a higher numerical value with "-" (minus) indicates a lower residual stress.

[0042] Furthermore, the residual stress can be determined by a sine 2 Ψ The residual stress can be measured using an X-ray diffractometer. Then, such a residual stress can be determined by measuring the stresses at any three points on each section (it is preferred that these points be selected to be 0.5 mm or more apart so that the stress on the section can be represented) using the sin mentioned above. 2 Ψ -Methods and determination of the average are measured.

[0043] One method for calculating strain within a crystal grain using electron backscatter diffraction (EBSD) with a scanning electron microscope is kernel average misorientation (KAM). KAM is obtained by quantifying the misorientation between an arbitrary measurement point and neighboring measurement points within a crystal grain. The KAM value is described below. [KAM value]

[0044] A KAM value is a numerical value that indicates a local misorientation, which is a crystal orientation difference between adjacent measurement points, in crystal orientation analysis based on the EBSD method. A higher KAM value indicates a greater crystal orientation difference between adjacent measurement points, and a lower KAM value indicates less local strain within the crystal grain.

[0045] In the coated cutting tool of this embodiment, the proportion of measuring points in the hard metal where tungsten carbide (WC) has a KAM value of 1° or less (hereinafter also referred to as "KAM") is C (designated) preferably 90% or more and 98% or less. A KAM C A value of 90% or more indicates that the area of ​​high local strain is small. This suggests a smaller area than the point of origin of the failure. Consequently, the fracture toughness tends to improve in the coated cutting tool of this embodiment. However, if KAM C If 98% or less is the percentage, production tends to be simple. In this respect, KAM C further preferably 90% or more and 97% or less, and even more preferably 90% or more and 96% or less.

[0046] In this embodiment, the KAM value can be measured as follows. A sample of a coated cutting tool is polished in a direction approximately parallel to the surface of the cemented carbide to expose a cross-section at a position 0.5 µm from the surface of the cemented carbide towards its interior. Using EBSD (manufactured by TSL Corporation), each measurement area of ​​the cross-section in the cemented carbide is divided into regular hexagonal measurement points (hereinafter also referred to as "pixels"). With respect to each divided pixel, a Kikuchi pattern is obtained from the reflected electrons of the electron beam incident on the cross-section (the polished area) of the sample, thereby measuring the orientations of the pixels. The obtained orientation data are analyzed using the EBSD's analysis software to calculate various parameters.The measurement conditions are defined as follows: Acceleration voltage: 15 kV, measurement area dimensions: 30 µm × 50 µm, distance between adjacent pixels (step size): 0.05 µm. An adjacent pixel whose misorientation relative to the center pixel is 5° or more is considered to be beyond the grain boundary of the individual crystal in which the center pixel is located and is therefore excluded from the calculation of a KAM value. Specifically, the KAM value is determined as the average misorientation between a given pixel within a crystal grain and adjacent pixels located in a region that is not beyond the grain boundary of the crystal grain. That is, a KAM value can be represented by the following formula (1). [Equation 1] KAM=∑j=1nαi,jn

[0047] (In formula (1) n represents the number of pixels j adjacent to any pixel i in the same crystal grain, and α i,j (stands for the crystal misorientation determined from the crystal orientation in pixel i and the crystal orientations in pixels j.)

[0048] Then, the KAM values ​​are calculated for all pixels in the hard metal, representing the entire area of ​​the measuring range. Assuming the total number of measuring points (pixels) is 100%, the proportion of measuring points (pixels) with a KAM value of 1° or less is determined. For the remaining points, a numerical value obtained by calculating the average of the proportions determined for any three arbitrary measuring ranges is used as the proportion of measuring points with a KAM value of 1° or less.

[0049] It is preferred that the cemented carbide for use in this embodiment is based on a WC phase, contains Co in a proportion of 5.0 wt% or more and 15.0 wt% or less, and Cr in a proportion of 0.3 wt% or more and 1.0 wt% or less than Cr3C2. In the cemented carbide for use in this embodiment, the toughness is improved when the Co content is 5.0 wt% or more, and thus the fracture toughness of the coated cutting tool tends to improve. Conversely, in the cemented carbide for use in this embodiment, the wear resistance of the coated cutting tool tends to improve when the Co content is 15.0 wt% or less.Furthermore, in the cemented carbide used in this embodiment, if 0.3 wt% or more of Cr is present as Cr3C2, the grain growth of tungsten carbide is inhibited, thus reducing the number of particles that act as the source of destruction. Consequently, the fracture strength of the coated cutting tool tends to improve. Conversely, in the cemented carbide used in this embodiment, if the Cr content as Cr3C2 is 1.0 wt% or less, the fracture strength of the coated cutting tool also tends to improve. The reason for this is unclear, but it is presumably due to the inhibition of Cr3C2 precipitation, which likely acts as the source of destruction.In this respect, it is further preferred that the cemented carbide for use in this embodiment is based on a WC phase, contains Co in a proportion of 5.5 wt% or more and 13.0 wt% or less, and Cr in a proportion of 0.4 wt% or more and 0.9 wt% or less than Cr3C2. It is also particularly preferred that Co is contained in a proportion of 6.1 wt% or more and 12.0 wt% or less, and Cr is contained in a proportion of 0.4 wt% or more and 0.8 wt% or less than Cr3C2. Here, the WC phase refers to a phase formed from tungsten carbide, and "based on a WC phase" means that the proportion of the WC phase in the cemented carbide is 50 wt% or more, preferably 60 wt% or more, more preferably 70 wt% or more, and even more preferably 80 wt% or more. The proportion of the WC phase in the hard metal is particularly preferably 86.0 wt% or more and 94.7 wt% or less.

[0050] Each composition and each proportion (wt%) in the cemented carbide for use in this embodiment are calculated as follows. The cross-sectional structures of at least three arbitrary points in the interior of the cemented carbide (e.g., a cross-sectional structure at a position at a depth of 500 µm or more from the surface towards the interior) are observed under a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS), and each composition of the cemented carbide is measured by the EDS. Based on the results, the proportion of each composition can be calculated. That is, the cemented carbide is polished in the direction orthogonal to its surface, the resulting exposed arbitrary cross-sectional structure is observed under an SEM, and using the EDS attached to the SEM, each composition and each proportion (wt%) in the cemented carbide is determined.More precisely, the arbitrary cross-sectional structure in the hard metal is observed under an EDS-equipped SEM at 2,000x to 5,000x magnification and subjected to surface analysis. Furthermore, by converting the atomic percentage of each obtained composition, the mass percentage of each can be calculated. For example, in the case of WC, a calculation is possible as follows: With the atomic ratio W:C of 1:1, the atomic percentage of WC is determined and then converted into a mass percentage. <Verfahren zum Bilden der Überzugsschicht>

[0051] In a method for forming the coating layer according to this embodiment, a composite layer containing a compound with a composition represented by formula (1) above is formed as a coating layer on the surface of a hard metal processed into a tool shape. Furthermore, if necessary, a lower layer can be formed between the hard metal and the composite layer, which consists of a Ti compound comprising elemental Ti and at least one element selected from the group consisting of C, N, O and B.

[0052] The following method, for example, can be used to form the coating layer in the coated cutting tool of this embodiment. However, the coating layer formation method is not limited to this.

[0053] The composite layer contained in the coating layer can be formed by a chemical deposition process in which the raw material composition is TiCl4: 0.2 to 0.4 mol%, AlCl3: 0.5 to 2.0 mol%, NH3: 2.0 to 4.5 mol% and H2: remainder, the temperature is 700 to 850°C and the pressure is 2.5 to 5.0 hPa.

[0054] In the case where a bottom layer consisting of a titanium compound is formed, it is possible to adjust the raw material composition, temperature, and pressure according to the desired titanium compound before forming the composite layer as described above, and then to form the bottom layer using a chemical deposition process. The following methods can be cited as concrete examples of methods for forming the bottom layer. Furthermore, in the case where a bottom layer is formed, a step of lowering the temperature to 700°C to 850°C is preferably carried out after the formation of the bottom layer to allow for the formation of a composite layer.

[0055] For example, a Ti composite layer formed from a Ti nitride layer (hereinafter also referred to as a "TiN layer") can be formed by a chemical deposition process in which the raw material composition is TiCl4: 5.0 to 10.0 mol%, N2: 20 to 60 mol% and H2: remainder, the temperature is 850 to 950°C and the pressure is 300 to 400 hPa.

[0056] A Ti composite layer formed from a Ti carbide layer (hereinafter also referred to as a "TiC layer") can be formed by a chemical deposition process in which the raw material composition is TiCl4: 1.5 to 3.5 mol%, CH4: 3.5 to 5.5 mol% and H2: remainder, the temperature is 950 to 1050°C and the pressure is 70 to 80 hPa.

[0057] A Ti composite layer formed from a Ti carbonitride layer (hereinafter also referred to as a "TiCN layer") can be produced by a chemical deposition process in which the raw material composition is TiCl4: 5.0 to 7.0 mol%, CH3CN: 0.5 to 1.5 mol% and H2: remainder, the temperature is 800 to 900°C and the pressure is 60 to 80 hPa.

[0058] A Ti composite layer formed from a Ti oxycarbonitride layer (hereinafter also referred to as a "TiCNO layer") can be formed by a chemical deposition process in which the raw material composition is TiCl4: 3.0 to 4.0 mol%, CO: 0.5 to 1.0 mol%, N2: 30 to 40 mol% and H2: remainder, the temperature is 950 to 1050°C and the pressure is 50 to 150 hPa.

[0059] A Ti composite layer formed from a Ti oxycarbide layer (hereinafter also referred to as a "TiCO layer") can be formed by a chemical deposition process in which the raw material composition is TiCl4: 1.0 to 2.0 mol%, CO: 2.0 to 3.0 mol% and H2: remainder, the temperature is 950 to 1050°C and the pressure is 50 to 150 hPa.

[0060] Fig. Figure 2 is a schematic cross-sectional view illustrating an example of a chemical vapor deposition (CVD) device used in the production of the coated cutting tool of this embodiment to form the coating layer. A CVD device 9 comprises a gas inlet device 5, a clamping device 7 on which the coated cutting tool 4 is mounted, a heating device 10, a reaction vessel 11, and a gas outlet tube 12. A raw material gas is introduced from the gas inlet device 5 into the reaction vessel 11 and, while being heated by the heating device 10, is chemically vapor-deposited on each cutting tool on the clamping device 7 to form a coating layer. The gas is then discharged from the gas outlet tube 12.

[0061] Fig. Figure 3 is a schematic cross-sectional view to enlarge the near area of ​​the gas introduction device 5 in the chemical vapor deposition device 9. Fig. 2. The raw material gas is introduced into the reaction vessel through the gas inlet device 5 from a gas outlet hole 6 and deposited on the surface of each cutting tool 4 on the clamping device 7. The thickness of the coating layer at each section can be controlled by adjusting a distance 8 between each cutting tool 4 and the clamping device 7. Specifically, in Fig. 3. The upper surface of each cutting tool 4 is a rake face. The length from the rake face to the bottom surface of the clamping device 7, on which each cutting tool 4 is mounted, and the length from the rake face on the lower surface of each cutting tool 4 to the upper surface of the clamping device, on which each cutting tool 4 is mounted, are each adjusted, thereby controlling the thickness of the coating layer on each section. For example, if the distance 8 between each cutting tool 4 and the clamping device 7 is reduced, the average thickness T2 of the coating layer in the rake face at a position 2 mm or more away from the cutting edge line portion in the direction of the rake face tends to be small relative to the average thickness T1 of the coating layer in the cutting edge line portion.Furthermore, if the pressure is reduced during the formation of a coating layer, the difference (T1 - T2) between the average thickness T2 of the coating layer in the rake face at a position 2 mm or more away from the cutting edge line part in the direction of the rake face and the average thickness T1 of the coating layer in the cutting edge line part tends to increase.

[0062] For example, the specific length of the distance 8 between each cutting tool 4 and the clamping device 7 is preferred to be 2.0 to 4.0 mm.

[0063] Furthermore, in order to control the composition represented by formula (1) above, the raw material composition must be appropriately adjusted. Specifically, as a method for controlling the ratio of Ti to Al in the raw material composition, for example, increasing the ratio AlCl3 / (AlCl3 + TiCl4) tends to increase the Al content ratio. More precisely, for example, if the ratio AlCl3 / (AlCl3 + TiCl4) in the raw material composition is set to 0.70 or more and 0.90 or less, the Al content ratio in formula (1) above can be controlled within the specific range mentioned above.

[0064] If the formed coating layer is subjected to dry blasting, wet blasting, or shot peening, and the conditions are adjusted accordingly, the residual stress value of the cemented carbide can be controlled. For example, under the conditions for dry blasting, the blasting media can be blasted at a pressure of 1.8 to 2.1 bar for a blasting time of 20 to 40 seconds, such that the angle of impact relative to the cemented carbide surface is 90°. For easier control of the residual stress value within the aforementioned range, the blasting media used in dry blasting is preferably at least a material with an average particle diameter of 120 to 400 µm (380 to 420 µm if the blasting media is steel), selected from the group consisting of Al₂O₃ and SiC.

[0065] In dry blasting, increasing the average particle diameter of the blasting material tends to decrease the residual stress value of the cemented carbide (compressive stress value side). Furthermore, as the impact angle approaches 45° from 90°, the residual stress S1 of the cemented carbide in the cutting edge region (compressive stress value side) tends to decrease. Additionally, increasing the blasting pressure tends to decrease the residual stress value of the cemented carbide. Finally, decreasing the blasting time tends to decrease the residual stress value of the cemented carbide.

[0066] Furthermore, when dry blasting is performed, a reduction in the thickness of the coating layer (e.g., composite layer) tends to decrease the difference between the residual stress S1 of the cemented carbide in the cutting edge portion and the residual stress S2 of the cemented carbide in the rake face at a position 2 mm or more away from the cutting edge portion in the direction of the rake face, where S2 < S1. This is presumably because, when the thickness of the composite layer (total coating layer) is smaller, the energy of dry blasting is more likely to be transferred to the cemented carbide.

[0067] Furthermore, a method for controlling the proportion of measurement points where tungsten carbide (WC) exhibits a KAM value of 1° or less in the hard metal can be, for example, a method in which the formed coating layer is subjected to dry blasting, wet blasting, or shot peening, and the conditions for this are adjusted. Specifically, a method can be described in which, during dry blasting, the blasting pressure or the type and average particle diameter of the blasting media are adjusted. More precisely, a method can be described in which, during dry blasting, the blasting pressure is set to 1.8 to 2.5 bar, and at least one material with an average particle diameter of 50 to 140 µm, selected from the group consisting of Al₂O₃ and SiC, is used as the blasting media.If the blasting pressure is set higher than the range mentioned above, or if steel is used as the blasting material (or medium) and the average particle diameter is set higher than the range mentioned above, the proportion of measurement points where tungsten carbide (WC) has a KAM value of 1° or less tends to decrease.

[0068] The thickness of the coating layer at each section of the coated cutting tool of this embodiment can be measured by observing the cross-sectional structure of the coated cutting tool using an optical microscope, a scanning electron microscope (SEM), a field emission scanning electron microscope (FE-SEM), or the like. Furthermore, the average thickness of the coating layer at each section of the coated cutting tool of this embodiment can be determined as the arithmetic mean of the thicknesses measured at three or more points at each section. Additionally, the composition of the coating layer can be measured from the cross-sectional structure of the coated cutting tool of this embodiment using an energy-dispersive X-ray spectrometer (EDS), a wavelength-dispersive X-ray spectrometer (WDS), or the like. Examples

[0069] The invention is described in more detail below with reference to examples. However, the invention is not limited to these examples.

[0070] Two types of substrates were prepared: one insert of SEET1203AGTN (hard metal with a composition of 87, 2WC-12, 0Co-0, 8Cr3C2 (all wt%), hereinafter also referred to as “substrate 1”) and one insert of SEET1203AGTN (hard metal with a composition of 93, 5WC-6, 1Co-0, 4Cr3C2 (all wt%), hereinafter also referred to as “substrate 2”). The cutting edge portion of each substrate was subjected to circular honing with a SiC brush, and then the substrate surface was washed. Furthermore, to perform the cutting test 1 described below, samples were prepared using substrate 1 (the following invention products 1 to 13 and comparison products 1 to 9), three samples for each product. In order to carry out the cutting test 2 described below, samples were prepared using substrate 2 (invention products 1 to 13 and comparison products 1 to 9), one sample for each product.Therefore, in the following method for forming a coating layer, three substrates 1 and one substrate 2, a total of four substrates, were placed simultaneously in a chemical vapor deposition device and a predetermined coating layer was formed on each substrate. [Inventory products 1 to 13 and comparison products 1 to 9]

[0071] After the surface of each substrate was washed, a coating layer was formed using a chemical vapor deposition process. First, the substrate was placed in the Fig. The externally heated chemical vapor deposition (CVD) apparatus shown in Figure 2 was inserted, and under the raw material composition, temperature, and pressure conditions shown in Table 1, a composite layer with the composition shown in Table 2 was formed on the substrate surface to the average thickness shown in Table 2. The distance between each cutting tool and the clamping device in the CVD apparatus was adjusted as shown in Table 1, thereby controlling the thickness of the coating layer (composite layer) at each section. Specifically, as shown in Figure 2, the following parameters were used: Fig. 3 to enlarge the near range of the gas introduction device in the chemical vapor deposition device, wherein the upper surface of each cutting tool 4 served as the rake face, the length from the rake face to the bottom surface of the clamping device 7 on which each cutting tool 4 was mounted, and the length from the rake face on the lower surface of each cutting tool 4 to the upper surface of the clamping device on which each cutting tool 4 was mounted, each as shown in Table 1, thereby controlling the thickness of the coating layer (composite layer) on each section.

[0072] Furthermore, after the coating layer had formed on the surface of the substrate, the coating layer surface was subjected to dry blasting using the blasting material shown in Table 3 under the blasting conditions shown in Table 3. Coated cutting tools of invention products 1 to 13 and comparison products 1 to 7 were obtained in this way.

[0073] The thickness of the coating layer at each section of a sample was determined as follows. Using an FE-SEM, the thicknesses at any three cross-sectional points in the cutting edge portion of the coated cutting tool and at any three cross-sectional points 2 mm or more from the cutting edge portion towards the rake face were measured, and the arithmetic mean of each was determined as the average thickness (successively designated "T1" and "T2"). The composition of the coating layer (composite layer) of the obtained sample was measured using an EDS at a cross-section close to the center of the rake face, up to 50 µm from the cutting edge portion of the coated cutting tool. These measurement results are presented in Table 2. [Table 1] sample Composite layer Distance between coated cutting tool and clamping device (mm) Temperature (°C) Pressure (hPa) Raw material composition (mol-%) AlCl3 / (AlCl3+TiCl4) TiCl4 AlCl3 NH3 H2 Invention product 1 750 3,0 0,3 1,2 3,5 95,0 0,80 3,0 Invention product 2 750 3,5 0,2 0,5 3,5 95,8 0,71 3,0 Invention product 3 700 3,0 0,3 2,0 4,0 93,7 0,87 3,0 Invention product 4 750 3,0 0,3 1,2 3,5 95,0 0,80 3,0 Invention product 5 750 2,5 0,3 1,2 2,5 96,0 0,80 3,0 Invention product 6 750 3,0 0,2 0,9 3,5 95,4 0,82 2,0 Invention product 7 750 5,0 0,3 1,2 3,5 95,0 0,80 4,0 Invention product 8 750 3,0 0,2 0,9 2,5 96,4 0,82 3,0 Invention product 9 750 4,0 0,3 1,2 3,5 95,0 0,80 3,0 Invention product 10 750 2,5 0,3 1,2 3,5 95,0 0,80 3,0 Invention product 11 750 3,0 0,3 1,3 4,0 94,4 0,81 3,0 Invention product 12 700 3,0 0,3 1,8 3,0 94,9 0,86 3,0 Invention product 13 700 3,0 0,3 1,7 3,5 94,5 0,85 3,0 Comparison product 1 750 3,0 0,5 1,0 3,0 95,5 0,67 3,0 Comparison product 2 700 3,0 0,2 2,3 3,0 94,5 0,92 3,0 Comparison product 3 750 4,0 0,3 1,2 3,0 95,5 0,80 5,0 Comparison product 4 750 2,0 0,3 1,2 5,0 93,5 0,80 3,0 Comparison product 5 900 2,0 0,3 1,2 3,0 95,5 0,80 1,0 Comparison product 6 750 5,0 0,5 2,2 3,0 94,3 0,81 6,0 Comparison product 7 750 5,0 0,3 1,2 4,0 94,5 0,80 6,0 Comparison product 8 750 5,0 0,3 1,2 4,0 94,5 0,80 6,0 Comparison product 9 750 5,0 0,3 1,2 4,0 94,5 0,80 6,0 [Table 2] sample Coating layer Composite layer (Al x Ti 1-x )N Atomic ratio x Average thickness (µm) T1 - T2(µm) thickness ratio T1 T2 Invention product 1 0,80 6,0 4,0 2,0 T2 < T1 Invention product 2 0,71 6,0 4,0 2,0 T2 < T1 Invention product 3 0,88 6,2 4,2 2,0 T2 < T1 Invention product 4 0,79 4,4 3,0 1,4 T2 < T1 Invention product 5 0,80 9,8 5,8 4,0 T2 < T1 Invention product 6 0,81 4,8 2,0 2,8 T2 < T1 Invention product 7 0,80 8,0 6,8 1,2 T2 < T1 Invention product 8 0,81 5,8 3,8 2,0 T2 < T1 Invention product 9 0,81 6,2 4,0 2,2 T2 < T1 Invention product 10 0,80 6,0 3,5 2,5 T2 < T1 Invention product 11 0,81 6,2 4,2 2,0 T2 < T1 Invention product 12 0,85 5,8 3,8 2,0 T2 < T1 Invention product 13 0,85 5,8 3,8 2,0 T2 < T1 Comparison product 1 0,65 6,0 4,0 2,0 T2 < T1 Comparison product 2 0,95 6,0 4,0 2,0 T2 < T1 Comparison product 3 0,80 3,5 3,0 0,5 T2 < T1 Comparison product 4 0,80 10,8 6,2 4,6 T2 < T1 Comparison product 5 0,79 4,6 1,4 3,2 T2 < T1 Comparison product 6 0,81 8,2 7,5 0,7 T2 < T1 Comparison product 7 0,80 6,5 6,7 -0,2 T1 < T2 Comparison product 8 0,80 4,4 5,0 -0,6 T1 < T2 Comparison product 9 0,80 4,4 5,0 -0,6 T1 < T2 [Table 3] sample Dry blasting conditions Abrasive material Beam conditions material Average particle size (µm) Angle of impact (°) Jet pressure (bar) Beam time (sec) Invention product 1 Al2O3 130 90 1,8 30 Invention product 2 Al2O3 130 90 1,8 30 Invention product 3 Al2O3 130 90 1,8 30 Invention product 4 Al2O3 120 90 1,8 20 Invention product 5 SiC 140 90 1,8 40 Invention product 6 Al2O3 120 90 1,8 20 Invention product 7 Al2O3 130 90 1,6 40 Invention product 8 Al2O3 130 90 2,1 20 Invention product 9 SiC 120 90 1,6 30 Invention product 10 Al2O3 130 90 2,1 20 Invention product 11 SiC 120 90 1,6 30 Invention product 12 Al2O3 130 90 2,1 20 Invention product 13 Steel 400 90 1,8 30 Comparison product 1 Al2O3 130 90 1,8 30 Comparison product 2 Al2O3 130 90 1,8 30 Comparison product 3 Al2O3 120 90 1,8 20 Comparison product 4 SiC 140 90 1,8 40 Comparison product 5 Al2O3 120 90 1,8 20 Comparison product 6 Al2O3 130 90 1,6 30 Comparison product 7 Al2O3 130 90 2,1 10 Comparison product 8 SiC 130 45 1,8 40 Comparison product 9 Al2O3 110 90 1,8 40 [Measurement of residual voltage]

[0074] With respect to each obtained sample, the residual stress of the hard metal was determined by a sin 2 Ψ The residual stresses were measured using an X-ray diffractometer. Stresses at any three points on the cutting edge portion were measured, and the average (arithmetic mean) was defined as the residual stress S1 of the cemented carbide. Meanwhile, stresses at any three points 2 mm or more away from the cutting edge portion in the direction of the rake face were measured, and the average (arithmetic mean) was defined as the residual stress S2 of the cemented carbide. The results are shown in Table 4. [Measurement of the KAM value]

[0075] For each sample obtained, the KAM value of the cemented carbide was measured as follows. The coated cutting tool sample was polished in a direction approximately parallel to the cemented carbide surface to expose a cross-section at a position 0.5 µm from the cemented carbide surface towards the interior of the cemented carbide. Using an EBSD (manufactured by TSL Corporation), each measurement area of ​​the cross-section in the cemented carbide was divided into regular hexagonal measurement points (hereinafter also referred to as "pixels"). For each divided pixel, a Kikuchi pattern was obtained based on the reflected electrons of the electron beam incident on the cross-section (the polished area) of the sample, thereby measuring the pixel orientations. The obtained orientation data were analyzed using the EBSD's analysis software to calculate various parameters.The measurement conditions were defined as follows: accelerating voltage: 15 kV, measurement area dimensions: 30 pm × 50 µm, distance between adjacent pixels (step size): 0.05 µm. An adjacent pixel whose misorientation relative to the center pixel was 5° or more was considered to be beyond the grain boundary of the individual crystal in which the center pixel was located and was therefore excluded from the calculation of a KAM value. Specifically, the KAM value was determined as the average misorientation between a given pixel within a crystal grain and adjacent pixels located in a region not beyond the grain boundary of the crystal grain. That is, the KAM value was calculated using the following formula (1). [Equation 2] KAM=∑j=1nαi,jn

[0076] (In formula (1) n represents the number of pixels j adjacent to any pixel i in the same crystal grain, and α i,j (stands for the crystal misorientation determined from the crystal orientation in pixel i and the crystal orientations in pixels j.)

[0077] Then, the KAM values ​​were calculated for all pixels in the hard metal, representing the entire area of ​​the measuring range. Assuming the total number of measuring points (pixels) to be 100%, the proportion of measuring points (pixels) with a KAM value of 1° or less was determined. For the remaining measuring points, a numerical value obtained by calculating the average of the proportions determined for any three measuring ranges was used as the KAM value. Additionally, the proportion of measuring points where tungsten carbide (WC) exhibits a KAM value of 1° or less in the hard metal is defined as KAM. C The measurement results are shown in Table 4. [Table 4] sample hard metal Residual voltage (GPa) Residual stress ratio CAME C (%) S1 S2 Invention product 1 -0,3 -1,1 S2 < S1 96 Invention product 2 -0,2 -1,2 S2 < S1 95 Invention product 3 -0,3 -1,2 S2 < S1 95 Invention product 4 -0,3 -1,2 S2 < S1 96 Invention product 5 -0,3 -1,0 S2 < S1 96 Invention product 6 -0,4 -1,2 S2 < S1 94 Invention product 7 -0,2 -0,5 S2 < S1 94 Invention product 8 -0,5 -1,5 S2 < S1 94 Invention product 9 -0,1 -0,9 S2 < S1 96 Invention product 10 -0,3 -1,9 S2 < S1 94 Invention product 11 -0,2 -0,5 S2 < S1 96 Invention product 12 -0,4 -1,3 S2 < S1 90 Invention product 13 -0,4 -1,4 S2 < S1 86 Comparison product 1 -0,3 -1,1 S2 < S1 96 Comparison product 2 -0,3 -1,1 S2 < S1 96 Comparison product 3 -0,3 -1,2 S2 < S1 96 Comparison product 4 -0,1 -1,0 S2 < S1 96 Comparison product 5 -0,4 -1,5 S2 < S1 94 Comparison product 6 -0,3 0,4 S1 < S2 94 Comparison product 7 -0,3 -1,2 S2 < S1 95 Comparison product 8 -1,0 -0,8 S1 < S2 95 Comparison product 9 -0,3 -0,8 S2 < S1 79

[0078] Cutting tests were carried out using the acquired invention products 1 to 13 and comparison products 1 to 9 under the following conditions. [Cutting test 1] Deployment: SEET1203AGTN Substrate: 87.2WC-12.0Co-0.8Cr3C2 (all mass %), Workpiece: Rectangular parallelepiped SCM440, cutting speed: 250 m / min, Feed per tooth: 0.20 mm / tooth Cutting depth: 2.0 mm Coolant: Not present, Evaluation criteria: The time at which the sample splintered was defined as the service life. For three samples, it was assessed whether it was possible to use all four corners up to this service life. That is, out of a maximum of 12 corners (three samples × four corners), the number of corners from which cracks propagated to other corners upon fracture was checked. If the number of corners from which cracks propagated to other corners upon fracture was "0", such a case was classified as "A", "1" as "B", and "2 or more" as "C". The measurement results are presented in Table 5. [Cutting test 2] Deployment: SEET1203AGTN Substrate: 93.5WC-6.1Co-0.4Cr3C2 (all mass %), Workpiece: Rectangular parallelepiped FCD600, cutting speed: 300 m / min, Feed per tooth: 0.20 mm / tooth Cutting depth: 2.0 mm Coolant: Present, Evaluation criteria: The point in time at which the sample splintered or reached the maximum wear width of 0.3 mm was defined as the service life, and the processing length up to the service life was measured. If the processing length up to the service life was 12.0 m or more, the case was classified as "A", 10.0 m or more and less than 12.0 m was classified as "B", and less than 10.0 m was classified as "C". The measurement results are shown in Table 5. [Table 5] sample Cutting test 1 Cutting test 2 Number of corners where cracks spread to other corners Evaluation Processing length (m) Evaluation Invention product 1 0 A 12,0 A Invention product 2 0 A 10,5 B Invention product 3 0 A 12,5 A Invention product 4 0 A 10,5 B Invention product 5 0 A 13,5 A Invention product 6 0 A 10,0 B Invention product 7 0 A 13,0 A Invention product 8 0 A 12,5 A Invention product 9 0 A 11,5 B Invention product 10 0 A 12,5 A Invention product 11 0 A 11,0 B Invention product 12 0 A 11,0 B Invention product 13 0 A 10,0 B Comparison product 1 0 A 9,0 C Comparison product 2 1 B 6,5 C Comparison product 3 0 A 8,5 C Comparison product 4 2 C 4,0 C Comparison product 5 0 A 9,0 C Comparison product 6 2 C 8,0 C Comparison product 7 3 C 10,0 B Comparison product 8 2 C 9,0 C Comparison product 9 3 C 8,0 C

[0079] Based on the results shown in Table 5, in all the products of the invention, the number of corners from which cracks propagated to other corners upon fracture was "0", and the processing length until the service life was 10.0 m or more. In contrast, in the comparison products 4 and 6 to 9, the number of corners from which cracks propagated to other corners upon fracture was "2 or more", and in the comparison products 1 to 6 and 8 to 9, the processing length until the service life was less than 10.0 m. Thus, it is evident that the products of the invention are generally superior to the comparison products with regard to fracture strength.

[0080] The results above show that the invention products exhibited excellent fracture resistance and thus a longer service life. Industrial applicability

[0081] The coated cutting tool of the invention exhibits excellent fracture resistance and thus enables an extension of service life compared to before and is therefore commercially applicable. List of reference symbols 1 Carbide, 2 composite layer, 3 coating layers, 4 Coated cutting tool, 5 Gas inlet device, 6 gas vent holes, 7 Clamping device on which a coated cutting tool is mounted, 8 Distance between a coated cutting tool and a clamping device, 9 Chemical vapor deposition device, 10 Heating equipment, 11 reaction vessel, 12 Gas discharge pipe.< / hartmetall>

Claims

[1] Coated cutting tool (4) comprising a hard metal (1) and a coating layer (3) formed on the hard metal (1), wherein the coated cutting tool (4) is arranged such that the coated cutting tool (4) has a rake face, a clearance face and a cutting edge line part which is located between the rake face and the clearance face, the coating layer (3) has a composite layer (2) which contains a compound with a composition represented by the following formula 1: (Al x Ti 1-x )N Formula 1, In formula 1, x represents the atomic ratio of elemental Al relative to the total of elemental Al and elemental Ti and satisfies 0.70 ≤ x ≤ 0.

90. if the average thickness of the coating layer (3) in the cutting edge line part is expressed as T1 and the average thickness of the coating layer (3) in the rake face at a position 2 mm or more away from the cutting edge line part in the direction of the rake face is expressed as T2, T1 is 4.0 µm or more and 10.0 µm or less, T2 is 2.0 µm or more and 7.0 µm or less, and T2 < T1 is satisfied, and if the residual stress of the carbide (1) in the cutting edge line part is expressed as S1 and the residual stress of the carbide (1) in the rake face at a position 2 mm or more away from the cutting edge line part in the direction of the rake face is expressed as S2, S2 < S1 is satisfied. [2] Coated cutting tool (4) according to claim 1, wherein the residual stress S1 is -0.5 GPa or more and 0.0 GPa or less, and the residual stress S2 is -2.0 GPa or more and -0.3 GPa or less. [3] Coated cutting tool (4) according to claim 1 or 2, wherein the difference T1 - T2 between the average thickness T1 and the average thickness T2 is 1.0 µm or more and 4.0 µm or less. [4] Coated cutting tool (4) according to one of claims 1 to 3, wherein in the hard metal (1) the proportion of measuring points where tungsten carbide (WC) has a KAM value of 1° or less is 90% or more and 98% or less. [5] Coated cutting tool (4) according to any one of claims 1 to 4, wherein the cemented carbide (1) is based on a WC phase, contains Co in a proportion of 5.0 wt% or more and 15.0 wt% or less, and contains Cr in a proportion of 0.3 wt% or more and 1.0 wt% or less than Cr3C2. [6] Coated cutting tool (4) according to any one of claims 1 to 5, wherein the coating layer (3) has a lower layer between the hard metal (1) and the composite layer (2) which contains a Ti compound comprising elemental Ti and at least one element selected from the group consisting of C, N, O and B.

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