Coated cutting tools

Abstract

To provide a coated cutting tool capable of extending a tool life by having excellent wear resistance and chipping resistance.SOLUTION: The coating layer includes a lower layer and an upper layer formed on a surface of the lower layer, the lower layer includes a specific Ti compound layer, a mean thickness of the lower layer is 3.0 μm or more and 15.0 μm or less, the upper layer includes an α - Al2O3 layer, a mean thickness of the upper layer is 3.0 μm or more and 15.0 μm or less, and (Σ 3 + Σ 11) / total grain boundary is 15% or more in the lower layer, Σ 11 / (Σ 3 + Σ 11) is 20% or more in the region A of the lower layer, and Σ 11 / (Σ 3 + Σ 11) is 0% or more and less than 20% in the region B of the lower layer.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] Conventionally, it is well known that a coated cutting tool formed by vapor-depositing a coating layer with a total film thickness of 3 to 20 μm on the surface of a substrate made of cemented carbide by chemical vapor deposition is used for cutting steel, cast iron, etc. As the above coating layer, for example, a single layer or a multi-layer composed of two or more layers selected from the group consisting of titanium carbide, nitride, carbonitride, carbonate, carbonitrate, and aluminum oxide is known.

[0003] In Patent Document 1, on the surface of a tool substrate composed of a tungsten carbide-based cemented carbide or a titanium carbonitride-based cermet, (a) A lower layer composed of a chemically vapor-deposited Ti compound layer containing a modified titanium carbonitride layer having an average layer thickness of at least 2 to 15 μm, (b) An upper layer composed of a modified α-type aluminum oxide layer having an average layer thickness of 1 to 15 μm and having an α-type crystal structure in a chemically vapor-deposited state, In a surface-coated cutting tool having a hard coating layer composed of the above (a) and (b), For the lower layer of (a) above, a field emission scanning electron microscope is used to irradiate each crystal grain having a face-centered cubic lattice within the measurement range of the polished cross-sectional surface of the film with an electron beam, and the inclination angle between the normals of the (001) plane and the (011) plane, which are the crystal planes of the crystal grain, with respect to the normal of the polished cross-sectional surface is measured. In this case, the crystal grain has a crystal structure of NaCl type face-centered cubic, and based on the measured inclination angle obtained, the normals of the (001) planes and the normal of the (011) plane at the interface between adjacent crystal grains are measured. The angles at which the two planes intersect are determined, and a grain boundary is defined as a case where the angles at which the normals of the (001) plane intersect and the normals of the (011) plane intersect are 2 degrees or more. The distribution of lattice points (common atom lattice points) at the interface of mutually adjacent crystal grains, in which each of the constituent atoms shares one constituent atom between the crystal grains, is calculated. The common atom lattice point morphology in which there are two lattice points that do not share constituent atoms between the common atom lattice points is represented by Σ3, and the number and position of the lower layer Σ3 corresponding grain boundaries facing the interface with the upper layer are measured. Furthermore, with respect to the upper layer of (b) above, a field emission scanning electron microscope is used to irradiate each crystal grain having a hexagonal crystal lattice within the measurement range of the polished cross-sectional surface of the film with an electron beam, and the inclination angle between the normals of the (0001) plane and the (10-10) plane, which are the crystal planes of the crystal grain, with respect to the normal of the polished cross-sectional surface is measured. In this case, the crystal grain has a corundum-type hexagonal close-packed crystal structure in which constituent atoms of Al and oxygen exist at the lattice points, respectively, and based on the measured inclination angle obtained, the normal of the (0001) plane at the interface between adjacent crystal grains is measured. The angle at which the normals of the (10-10) plane intersect is determined, and a grain boundary is defined when the angle at which the normals of the (0001) plane intersect and the normals of the (10-10) plane intersect is 2 degrees or more. The distribution of lattice points (common atom lattice points) where each of the constituent atoms shares one constituent atom between the crystal grains is calculated at the interface of mutually adjacent crystal grains, and the lattice point morphology where there are two lattice points that do not share constituent atoms between the common atom lattice points is represented by Σ3. When the number and position of the upper layer Σ3 corresponding grain boundaries facing the interface with the lower layer are measured, A surface-coated cutting tool is described, characterized in that, at the interface between the lower layer and the upper layer, the upper layer Σ3-corresponding grain boundaries are formed as continuous crystal grain boundaries for 30-70% of the lower layer Σ3-corresponding grain boundaries that exist facing the interface with the upper layer.

[0004] Furthermore, Patent Document 1 describes a method for measuring the inclination angle between the normals of the (001) plane and the (011) plane of the crystal grains, which are crystal planes of the crystal grains, by irradiating each individual crystal grain having a face-centered cubic lattice within the measurement range of the polished cross-sectional surface of the film with an electron beam, for the lower layer extending to a depth of at least 1 μm toward the substrate surface from the interface between the lower layer and the upper layer. In this case, the crystal grains have a NaCl-type face-centered cubic crystal structure, and based on the measured inclination angle obtained, the angles at which the normals of the (001) planes and the normals of the (011) planes intersect at the interfaces between adjacent crystal grains are determined. The invention describes a surface-coated cutting tool in which, when the angle at which the normals of the (001) plane intersect with each other and the normals of the (011) plane intersect is 2 degrees or more, a grain boundary is defined, and the distribution of lattice points (common lattice points of constituent atoms) in which each of the constituent atoms shares one constituent atom between the crystal grains at the interface of mutually adjacent crystal grains is calculated, and the common lattice point configuration in which there are N lattice points that do not share constituent atoms between the common lattice points of constituent atoms (however, the upper limit of N is set to 28 from the point of frequency) is represented by ΣN+1, and when the ratio of each ΣN+1 to the total ΣN+1 is calculated, the ratio of Σ3 to the total ΣN+1 in the above region is 60% or more. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2009-279693 [Overview of the project] [Problems that the invention aims to solve]

[0006] In recent years, machining processes have increasingly emphasized higher speeds, higher feed rates, and deeper cuts. Furthermore, the increased strength of workpiece materials necessitates improved tool wear resistance and fracture resistance compared to conventional methods. In particular, cast iron has become stronger in recent years to achieve thinner walls, and in machining processes, there has been an increase in high-speed cutting of cast iron and other machining operations that place heavy loads on coated cutting tools.

[0007] Against this backdrop, the surface-coated cutting tool described in Patent Document 1 has a high proportion of Σ3 grain boundaries that are continuously formed from the titanium carbonitride layer to the α-type aluminum oxide layer above it, and exhibits excellent adhesion between the titanium carbonitride layer and the α-type aluminum oxide layer. On the other hand, coated cutting tools with such a coating layer are prone to cracks that occur during processing and propagate to the substrate, resulting in chipping and defects, so there is room for improvement.

[0008] This invention has been made in view of the above circumstances, and aims to provide a coated cutting tool that can extend tool life by having excellent wear resistance and fracture resistance. [Means for solving the problem]

[0009] From the above perspective, the inventors conducted extensive research on extending the tool life of coated cutting tools and found that by configuring coated cutting tools in a specific way, it is possible to improve wear resistance and fracture resistance, thereby extending tool life. This led to the completion of the present invention.

[0010] In other words, the present invention is as follows. [1] A coated cutting tool comprising a base material and a coating layer formed on the surface of the base material, The coating layer includes a lower layer and an upper layer formed on the surface of the lower layer. The lower layer includes a Ti compound layer made of Ti and at least two elements selected from the group consisting of C, N, O, and B. The average thickness of the lower layer is 3.0 μm or more and 15.0 μm or less. The upper layer includes an α-Al2O3 layer made of α-type aluminum oxide, The average thickness of the upper layer is 3.0 μm or more and 15.0 μm or less. In the entire lower layer, the ratio of the sum of the lengths of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length is 15% or more. A coated cutting tool in which, when a region A is defined as a 2 μm area extending 2 μm toward the substrate from the interface between the lower layer and the upper layer, and a region B is defined as a region B toward the substrate from region A, the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region A of the lower layer is 20% or more, and the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region B of the lower layer is 0% or more and less than 20%. [2] The coated cutting tool according to [1], wherein in the region A of the lower layer, the ratio of the sum of the lengths of the Σ3 grain boundaries and the Σ11 grain boundaries to 100% of the total grain boundary length is 10% or more and 60% or less. [3] A coated cutting tool according to [1] or [2], wherein in the region B of the lower layer, the ratio of the sum of the lengths of the Σ3 grain boundaries and the Σ11 grain boundaries to 100% of the total grain boundary length is 20% or more and 70% or less. [4] The coating layer includes an adhesive layer between the lower layer and the substrate, The aforementioned adhesion layer consists of a Ti nitride layer and / or a Ti carbide layer. A coated cutting tool according to any one of [1] to [3], wherein the average thickness of the adhesion layer is 0.1 μm or more and 3.0 μm or less. [5] The coating layer further includes an outer layer on the surface of the upper layer opposite to the substrate, The outer layer is made of a compound of Ti and at least one element selected from the group consisting of C, N, O, and B. A coated cutting tool according to any one of [1] to [4], wherein the average thickness of the outer layer is 0.1 μm or more and 4.0 μm or less. [6] The coated cutting tool according to any one of [1] to [5], wherein the average thickness of the entire coating layer is 10.0 μm or more and 30.0 μm or less. [7] The coated cutting tool according to any one of [1] to [6], wherein the substrate is any one of a cemented carbide, a cermet, a ceramic, and a cubic boron nitride sintered body. [Advantages of the Invention]

[0011] According to the present invention, it is possible to provide a coated cutting tool capable of extending the tool life by having excellent wear resistance and chipping resistance. [Brief Description of the Drawings]

[0012] [Figure 1] It is a schematic cross-sectional view showing an example of the coated cutting tool of the present invention. [Figure 2] It is a schematic cross-sectional view showing another example of the coated cutting tool of the present invention. [Modes for Carrying Out the Invention]

[0013] Hereinafter, modes for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary, but the present invention is not limited to the following present embodiment. The present invention can be variously modified without departing from the gist thereof. In the drawings, the positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[0014] The coated cutting tool of this embodiment comprises a base material and a coating layer formed on the surface of the base material, wherein the coating layer includes a lower layer and an upper layer formed on the surface of the lower layer, the lower layer includes a Ti compound layer made of Ti and at least two elements selected from the group consisting of C, N, O, and B, the average thickness of the lower layer is 3.0 μm or more and 15.0 μm or less, the upper layer includes an α-Al2O3 layer made of α-type aluminum oxide, the average thickness of the upper layer is 3.0 μm or more and 15.0 μm or less, and the entire lower layer is The ratio of the total length of the Σ3 grain boundary and the Σ11 grain boundary to the total length of the grain boundary is 15% or more. When the area extending 2 μm from the interface between the lower layer and the upper layer toward the substrate is defined as region A (hereinafter also simply referred to as "region A"), and the area further toward the substrate than region A is defined as region B (hereinafter also simply referred to as "region B"), the ratio of the length of the Σ11 grain boundary to the total length of the Σ3 grain boundary and the Σ11 grain boundary in region A of the lower layer is 20% or more, and the ratio of the length of the Σ11 grain boundary to the total length of the Σ3 grain boundary and the Σ11 grain boundary in region B of the lower layer is 0% or more and less than 20%.

[0015] Figure 1 is a schematic cross-sectional view showing an example of a coated cutting tool according to this embodiment. The coated cutting tool 7 consists of a base material 1 and a coating layer 6 formed on the surface of the base material 1. In the coating layer 6, the adhesion layer 2, lower layer 3, upper layer 4, and outer layer 5 are laminated upward in this order from the base material 1 side. Furthermore, the area extending 2 μm from the interface between the lower layer 3 and the upper layer 4 toward the base material 1 side is defined as region A3a, and the area beyond region A3a toward the base material 1 side Lower layer 3 Let the range be defined as area B3b. Figure 2 is a schematic cross-sectional view showing another example of the coated cutting tool of this embodiment. The coated cutting tool 7 consists of a base material 1 and a coating layer 6 formed on the surface of the base material 1. In the coating layer 6, the lower layer 3 and the upper layer 4 are stacked upwards in this order from the base material 1 side. Furthermore, the area extending 2 μm from the interface between the lower layer 3 and the upper layer 4 toward the base material 1 side is defined as region A3a, and the area beyond region A3a toward the base material 1 side Lower layer 3 Let the range be defined as area B3b.

[0016] Figure 1 is a schematic cross-sectional view showing an example of a coated cutting tool according to this embodiment. The coated cutting tool 7 consists of a base material 1 and a coating layer 6 formed on the surface of the base material 1. In the coating layer 6, the adhesion layer 2, lower layer 3, upper layer 4, and outer layer 5 are laminated upward in this order from the base material 1 side. Furthermore, the area extending 2 μm from the interface between the lower layer 3 and the upper layer 4 toward the base material 1 is defined as region A3a, and the area further toward the base material 1 than region A3a is defined as region B3b. Figure 2 is a schematic cross-sectional view showing another example of the coated cutting tool of this embodiment. The coated cutting tool 7 consists of a base material 1 and a coating layer 6 formed on the surface of the base material 1. In the coating layer 6, the lower layer 3 and the upper layer 4 are stacked upwards in this order from the base material 1 side. Furthermore, the area extending 2 μm from the interface between the lower layer 3 and the upper layer 4 toward the base material 1 side is defined as region A3a, and the area further toward the base material 1 side from region A3a is defined as region B3b.

[0017] The coated cutting tool of this embodiment comprises a base material and a coating layer formed on the surface of that base material. Specific examples of coated cutting tools include replaceable cutting inserts for milling or turning, drills, and end mills.

[0018] The base material in this embodiment is not particularly limited as long as it can be used as a base material for a coated cutting tool. Examples of such base materials include cemented carbide, cermet, ceramics, cubic boron nitride sintered body, diamond sintered body, and high-speed steel. Among these, the base material is preferably cemented carbide, cermet, ceramics, or cubic boron nitride sintered body because it exhibits superior wear resistance and fracture resistance, and from a similar viewpoint, the base material is more preferably cemented carbide.

[0019] Furthermore, the substrate may have a modified surface. For example, if the substrate is made of cemented carbide, a de-β layer may be formed on its surface. Also, if the substrate is made of cermet, a hardened layer may be formed on its surface. Even if the surface of the substrate is modified in these ways, the effects of the present invention will still be achieved.

[0020] In this embodiment, the average thickness of the entire coating layer is preferably 10.0 μm or more and 30.0 μm or less. When the average thickness of the entire coating layer of the coated cutting tool in this embodiment is 10.0 μm or more, it tends to have excellent wear resistance, and when the average thickness of the entire coating layer is 30.0 μm or less, the adhesion of the coating layer is improved, which improves chipping resistance and thus tends to have excellent fracture resistance. From a similar viewpoint, the average thickness of the entire coating layer is more preferably 10.6 μm or more and 29.4 μm or less, and even more preferably 12.7 μm or more and 26.2 μm or less. The average thickness of each layer and the entire coating layer in the coated cutting tool of this embodiment can be determined by measuring the thickness of each layer or the entire coating layer from three or more cross-sections in each layer or the entire coating layer, and calculating the arithmetic mean.

[0021] [Lower layer] The lower layer used in this embodiment includes a Ti compound layer made of Ti and at least two elements selected from the group consisting of C, N, O, and B.

[0022] The lower layer may consist of one layer or multiple layers (for example, two or three layers), but it is preferable that it consists of multiple layers, more preferably two or three layers, and even more preferably two layers. When the lower layer consists of two layers, the substrate side may have a TiCN layer as the first layer, and the surface of the first layer may have a TiCNO layer or a TiCO layer as the second layer. Among these, the lower layer may have a TiCN layer on the substrate side. 1 The first layer may have a TiCNO layer as the second layer on the surface of the first layer.

[0023] The lower layer may consist of one layer or multiple layers (for example, two or three layers), but it is preferable that it consists of multiple layers, more preferably two or three layers, and even more preferably two layers. When the lower layer consists of two layers, the substrate side may have a TiCN layer as the first layer, and the surface of the first layer may have a TiCNO layer or a TiCO layer as the second layer. Among these, the lower layer may have a TiCN layer as the second layer on the substrate side, and the surface of the first layer may have a TiCNO layer as the second layer.

[0024] The average thickness of the lower layer used in this embodiment is 3.0 μm or more and 15.0 μm or less. When the average thickness of the lower layer of the coated cutting tool in this embodiment is 3.0 μm or more, it exhibits excellent wear resistance, while when the average thickness of the lower layer is 15.0 μm or less, the adhesion of the coating layer is improved, improving chipping resistance and thus excellent fracture resistance. From a similar viewpoint, the average thickness of the lower layer is more preferably 4.0 μm or more and 14.5 μm or less, even more preferably 4.5 μm or more and 14.0 μm or less, and even more preferably 6.0 μm or more and 13.0 μm or less.

[0025] When the lower layer consists of two layers, the average thickness of the first layer (TiCN layer) is preferably 2.0 μm or more and 14.5 μm or less, from the viewpoint of further improving wear resistance and fracture resistance. From the same viewpoint, the average thickness of the first layer (TiCN layer) is more preferably 3.0 μm or more and 14.0 μm or less, and even more preferably 4.5 μm or more and 13.5 μm or less.

[0026] When the lower layer consists of two layers, the average thickness of the second layer (TiCNO layer or TiCO layer) is preferably 0.1 μm or more and 2.0 μm or less, from the viewpoint of further improving wear resistance and fracture resistance. From the same viewpoint, the average thickness of the second layer (TiCNO layer or TiCO layer) is more preferably 0.2 μm or more and 2.0 μm or less, and even more preferably 0.5 μm or more and 2.0 μm or less.

[0027] The lower Ti compound layer is a layer consisting of one or more of the above-mentioned layers, but may contain trace amounts of elements other than those mentioned above, as long as the effects of the present invention are achieved.

[0028] In this embodiment, the coated cutting tool has a ratio of 15% or more of the total length of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total length of grain boundaries in the entire lower layer. When the ratio of 15% or more of the total length of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total length of grain boundaries in the entire lower layer of the coated cutting tool in this embodiment is 15% or more, the proportion of grain boundaries with low grain boundary energy increases, improving resistance to plastic deformation and thus providing excellent wear resistance. On the other hand, from the viewpoint of ease of manufacture, it is preferable that the ratio of 70% or less of the total length of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total length of grain boundaries in the entire lower layer is 17% to 66%, and even more preferable that it is 23% to 59%.

[0029] In this embodiment, the coated cutting tool has a ratio of 20% or more in length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region A of the lower layer. When the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region A of the lower layer of the coated cutting tool is 20% or more, adhesion with the upper layer is improved, resulting in high wear resistance and fracture resistance over a long period of time. On the other hand, from the viewpoint of ease of manufacture, it is preferable that the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region A of the lower layer is 60% or less. From a similar viewpoint, it is more preferable that the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region A of the lower layer is 22% or more and 59%, and even more preferable that it is 28% or more and 53%.

[0030] In this embodiment, the coated cutting tool has a ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in the lower layer region B of 0% or more and less than 20%. When the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in the lower layer region B of this embodiment is 0% or more and less than 20%, the proportion of grain boundaries with low grain boundary energy increases, improving resistance to plastic deformation and thus providing excellent wear resistance. From a similar viewpoint, the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in the lower layer region B is preferably 0% or more and 19%, more preferably 0% or more and 17%, and even more preferably 0% or more and 12%.

[0031] The coated cutting tool of this embodiment can effectively and reliably suppress the propagation of cracks generated during cutting into the substrate by controlling the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in regions A and B, respectively, so as to satisfy the aforementioned range.

[0032] In this embodiment, it is preferable that the coated cutting tool has a coating where the ratio of the total length of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in region A of the lower layer is 10% or more and 60% or less. When the coated cutting tool of this embodiment has a coating where the ratio of the total length of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in region A of the lower layer is 10% or more, it tends to effectively and reliably achieve the effects of improving wear resistance and fracture resistance by increasing the ratio of the length of Σ11 grain boundaries to the total length of Σ3 grain boundaries and Σ11 grain boundaries in region A, as described above. On the other hand, when the coated cutting tool of this embodiment has a coating where the ratio of the total length of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in region A of the lower layer is 60% or less, grain coarsening is suppressed, which tends to improve chipping resistance and further improve fracture resistance. From a similar viewpoint, in the lower layer region A, the ratio of the sum of the lengths of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length is more preferably 12% to 57%, even more preferably 15% to 54%, and even more preferably 20% to 48%.

[0033] In this embodiment, it is preferable that the coated cutting tool has a coating that, in the lower layer region B, has a ratio of 20% or more to 70% of the total length of the Σ3 grain boundaries and Σ11 grain boundaries relative to 100% of the total length of the grain boundaries. In this embodiment, if the ratio of 20% or more to the total length of the Σ3 grain boundaries and Σ11 grain boundaries relative to 100% of the total length of the grain boundaries in the lower layer region B, the coating cutting tool tends to have improved resistance to plastic deformation and thus better wear resistance. On the other hand, in this embodiment, if the ratio of 70% or less to the total length of the Σ3 grain boundaries and Σ11 grain boundaries relative to 100% of the total length of the grain boundaries in the lower layer region B, it tends to be easier to control the ratio of 60% or less to the total length of the Σ3 grain boundaries and Σ11 grain boundaries relative to 100% of the total length of the grain boundaries in region A. From a similar viewpoint, in the lower layer region B, the ratio of the sum of the lengths of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length is more preferably 22% to 68%, and even more preferably 24% to 61%.

[0034] In this application, the length of the CSL grain boundary refers to the "total length of the Σ3 grain boundary, Σ5 grain boundary, Σ7 grain boundary, Σ9 grain boundary, Σ11 grain boundary, Σ13 grain boundary, Σ15 grain boundary, Σ17 grain boundary, Σ19 grain boundary, Σ21 grain boundary, Σ23 grain boundary, Σ25 grain boundary, Σ27 grain boundary, and Σ29 grain boundary" among the corresponding grain boundaries indicated by a combination of Σ and a number.

[0035] The lower layer in this embodiment has grain boundaries with relatively high and relatively low energy. Normally, grain boundaries have many gaps and relatively high energy because the arrangement of atoms is irregular and random. On the other hand, some grain boundaries have regular arrangements of atoms and few gaps, and such grain boundaries have relatively low energy. A typical example of such a grain boundary with relatively low energy is the correspondence site lattice (CSL) grain boundary (hereinafter referred to as "CSL grain boundary"). Grain boundaries have a significant influence on important sintering processes such as densification, creep, and diffusion, as well as on electrical, optical, and mechanical properties. The importance of grain boundaries depends on several factors, such as the grain boundary density in the material, the chemical composition of the interface, and the crystallographic structure, i.e., the grain interface orientation and grain orientation difference. CSL grain boundaries play a special role. The Σ value is known as an indicator of the degree of distribution of CSL grain boundaries. It is defined as the ratio of the density of lattice points of two grains touching at a grain boundary to the density of lattice points that coincide when both lattices are superimposed. In simple structures, it is generally observed that grain boundaries with low Σ values ​​tend to have low interfacial energy and special properties. Therefore, controlling the proportion of CSL grain boundaries and the distribution of grain orientation differences is considered important for the properties of the lower layer and for improving them.

[0036] In recent years, a scanning electron microscope (SEM)-based technique known as electron backscatter diffraction (EBSD) has been used to study grain boundaries in materials. EBSD is based on the automated analysis of Kikuchi diffraction patterns generated by backscattered electrons.

[0037] For each crystal grain of the material under consideration, the crystallographic orientation is determined after creating an index of the corresponding diffraction pattern. Using EBSD with commercially available software, microstructure analysis and determination of grain boundary character distribution (GBCD) can be performed relatively easily. By measuring and analyzing interfaces using EBSD, the orientation difference of crystal grain boundaries in a large sample population of interfaces can be revealed. Typically, the distribution of orientation differences is related to the processing and / or properties of the material. The orientation difference of crystal grain boundaries can be obtained from common orientation parameters such as Euler angles, angle / axis pairs, or Rodrigues vectors.

[0038] The CSL grain boundaries in the lower layer typically consist of Σ3-grain boundaries, Σ5-grain boundaries, Σ7-grain boundaries, Σ9-grain boundaries, Σ11-grain boundaries, Σ13-grain boundaries, Σ15-grain boundaries, Σ17-grain boundaries, Σ19-grain boundaries, Σ21-grain boundaries, Σ23-grain boundaries, Σ25-grain boundaries, Σ27-grain boundaries, and Σ29-grain boundaries. Here, for example, the length of a Σ3-grain boundary refers to the total length of Σ3-grain boundaries in the field of view (a specific region) observed by a SEM equipped with EBSD.

[0039] Here, "whole grain boundary" refers to the sum of all grain boundaries other than CSL grain boundaries and CSL grain boundaries. Hereafter, grain boundaries other than CSL grain boundaries will be referred to as "general grain boundaries" or "random grain boundaries." General grain boundaries are the remaining grain boundaries after subtracting CSL grain boundaries from the whole grain boundaries of the lower layer grains observed with an EBS-equipped SEM. Therefore, "total length of whole grain boundaries" can be expressed as "sum of the length of CSL grain boundaries and the length of general grain boundaries."

[0040] In this embodiment, the ratio of the sum of the lengths of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in the entire lower layer, the ratio of the length of Σ11 grain boundaries to the sum of the lengths of Σ3 grain boundaries and Σ11 grain boundaries in regions A and B of the lower layer, and the ratio of the sum of the lengths of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in regions A and B of the lower layer can be calculated as follows.

[0041] A coated cutting tool is used to expose the cross-section of the lower layer in a direction perpendicular to the surface of the substrate, thereby obtaining an observation surface. Methods for exposing the cross-section of the lower layer include, for example, cutting and polishing. Of these, polishing is preferred from the viewpoint of making the observation surface of the lower layer smoother. In particular, the observation surface is preferably mirror-finished from the viewpoint of being as smooth as possible. Methods for obtaining a mirror-finished observation surface of the lower layer are not particularly limited, but examples include polishing using diamond paste or colloidal silica, or ion milling.

[0042] Subsequently, the observation surface is observed using a SEM equipped with EBSD. It is preferable to observe the scoop surface as the observation area.

[0043] The SEM used will be the SU6600 (manufactured by Hitachi High-Technologies Corporation) equipped with an EBSD (manufactured by TexSEM Laboratories).

[0044] The normal to the observation surface is tilted 70° with respect to the incident beam, and the analysis is performed by irradiating the electron beam with an accelerating voltage of 15kV and an irradiation current of 1.0nA. Data acquisition is performed by analyzing the crystal orientation of each particle in the lower layer within the measurement range using an EBSD setting of 50μm in the direction parallel to the substrate surface and a measurement range that includes the entire lower layer in the direction perpendicular to the substrate surface with a step size of 0.1μm. At this time, the boundary between measurement points with an orientation difference of 5° or more is defined as a grain boundary.

[0045] Data processing is performed using commercially available software. The CSL grain boundaries corresponding to any given Σ value can be counted and confirmed by expressing them as a ratio to the total grain boundaries. From this, the length of the Σn grain boundary (n is an odd number between 3 and 29), the length of the CSL grain boundary, and the total length of all grain boundaries in the lower layer are determined. Within the measurement range on the observation surface described above, a total of three fields of view are analyzed and the average value of each value is calculated. From the obtained average value, the ratio of the sum of the lengths of the Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in the entire lower layer, the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundaries and Σ11 grain boundaries in regions A and B of the lower layer, and the ratio of the sum of the lengths of the Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in regions A and B of the lower layer can be calculated.

[0046] [Top layer] The coated cutting tool of this embodiment has a coating layer comprising a lower layer and an upper layer formed on the surface of the lower layer. The upper layer used in this embodiment includes an α-Al2O3 layer made of α-type aluminum oxide. By including an upper layer containing an α-Al2O3 layer made of α-type aluminum oxide, the coated cutting tool of this embodiment can suppress reactive wear due to oxidation of the Ti compound layer of the lower layer. As a result, the coated cutting tool of this embodiment has improved wear resistance.

[0047] The average thickness of the upper layer used in this embodiment is 3.0 μm or more and 15.0 μm or less. When the average thickness of the upper layer of the coated cutting tool in this embodiment is 3.0 μm or more, it exhibits excellent wear resistance, while when the average thickness of the upper layer is 15.0 μm or less, the adhesion of the coating layer is improved, improving chipping resistance and thus excellent fracture resistance. From a similar viewpoint, the average thickness of the upper layer is preferably 3.6 μm or more and 14.8 μm or less, and more preferably 4.2 μm or more and 14.5 μm or less.

[0048] The upper α-Al2O3 layer is made of α-type aluminum oxide, but it may contain trace amounts of components other than α-type aluminum oxide (α-Al2O3) as long as it achieves the effects of the present invention.

[0049] Furthermore, the average thickness of the adhesion layer is preferably 0.1 μm or more and 3.0 μm or less. In the coated cutting tool of this embodiment, if the average thickness of the adhesion layer is 0.1 μm or more, the Ti nitride layer and / or Ti carbide layer tend to have a uniform structure, so the adhesion of the coating layer is further improved, the chipping resistance is improved, and thus the tool tends to have excellent fracture resistance. On the other hand, in the coated cutting tool of this embodiment, if the average thickness of the adhesion layer is 3.0 μm or less, the adhesion of the coating layer is improved, the chipping resistance is improved, and thus the tool tends to have excellent fracture resistance. From a similar viewpoint, the average thickness of the adhesion layer is preferably 0.1 μm or more and 2.5 μm or less. twist Preferably, the particle size is between 0.2 μm and 1.5 μm. Furthermore preferable.

[0050] Furthermore, the average thickness of the adhesion layer is preferably 0.1 μm or more and 3.0 μm or less. In the coated cutting tool of this embodiment, when the average thickness of the adhesion layer is 0.1 μm or more, the Ti nitride layer and / or Ti carbide layer tend to have a uniform structure, which further improves the adhesion of the coating layer and improves chipping resistance, thus resulting in superior fracture resistance. On the other hand, in the coated cutting tool of this embodiment, when the average thickness of the adhesion layer is 3.0 μm or less, the adhesion of the coating layer improves and improves chipping resistance, thus resulting in superior fracture resistance. From a similar viewpoint, the average thickness of the adhesion layer is preferably 0.1 μm or more and 2.5 μm or less, and more preferably 0.2 μm or more and 1.5 μm or less.

[0051] The adhesion layer consists of a Ti nitride layer and / or a Ti carbide layer, but may contain trace amounts of components other than Ti nitride and / or Ti carbide, as long as the effects of the present invention are achieved.

[0052] Furthermore, the average thickness of the outer layer is preferably 0.1 μm or more and 4.0 μm or less. The coated cutting tool of this embodiment tends to have excellent wear resistance when the average thickness of the outer layer is 0.1 μm or more. Also, it tends to be easy to identify the corner that has been used. On the other hand, when the average thickness of the outer layer of the coated cutting tool of this embodiment is 4.0 μm or less, the adhesion of the coating layer is improved, and the chipping resistance is improved, so it tends to have excellent fracture resistance. From a similar viewpoint, the average thickness of the outer layer is preferably 0.2 μm or more and 2.0 μm or less. twist Preferably, the particle size is between 0.2 μm and 1.5 μm. Furthermore preferable.

[0053] Furthermore, the average thickness of the outer layer is preferably 0.1 μm or more and 4.0 μm or less. The coated cutting tool of this embodiment tends to have excellent wear resistance due to the average thickness of the outer layer being 0.1 μm or more. It also tends to be easy to identify the corner that has been used. On the other hand, the coated cutting tool of this embodiment tends to have excellent chipping resistance because the adhesion of the coating layer is improved and chipping resistance is improved when the average thickness of the outer layer is 4.0 μm or less. From a similar viewpoint, the average thickness of the outer layer is preferably 0.2 μm or more and 2.0 μm or less, and more preferably 0.2 μm or more and 1.5 μm or less.

[0054] The outer layer is a layer made of a compound of Ti and at least one element selected from the group consisting of C, N, O, and B. However, insofar as the effects of the present invention are achieved, it may also contain trace amounts of components other than the compound of Ti and at least one element selected from the group consisting of C, N, O, and B.

[0055] Examples of methods for forming each layer constituting the coating layer in the coated cutting tool of this embodiment include the following methods. However, the methods for forming each layer are not limited to these.

[0056] First, an adhesion layer consisting of a Ti nitride layer (TiN layer) and / or a Ti carbide layer (TiC layer) is formed on the surface of the substrate. The adhesion layer is formed, for example, by the following method.

[0057] The TiN layer can be formed by chemical vapor deposition using a raw material composition of TiCl4: 5.0-10.0 mol%, N2: 20-60 mol%, and H2: the remainder, at a temperature of 850-950°C and a pressure of 300-400 hPa.

[0058] The TiC layer can be formed by chemical vapor deposition using a raw material composition of TiCl4: 1.0-4.0 mol%, CH4: 3.0-6.0 mol%, and H2: the remainder, at a temperature of 950-1050°C and a pressure of 70-80 hPa.

[0059] Next, a lower layer consisting of a Ti compound layer is formed on the surface of the adhesion layer. If an adhesion layer is not formed, a lower layer consisting of a Ti compound layer is formed on the surface of the substrate. The lower layer is formed, for example, by performing the following steps (1), annealing, (2), and (3) in order.

[0060] [Process 1: Formation process of the lower layer - first layer (lower layer side - region B)] When forming the TiCN layer as the first layer of the lower layer (lower layer side - region B), the raw material composition is TiCl4: 6.0~8.0 mol%, CH3CN: 0.8~1.2 mol%, N2: 10.0~35.0 mol%, C2H4: 0~0.5 mol%, H2: remainder. Part or all of the first layer is formed by chemical vapor deposition at a temperature of 820~880°C and a pressure of 55~110 hPa. If the entire first layer is formed in step 1, step 2 described below does not need to be performed.

[0061] [Annealing process] Next, an annealing process is carried out with a raw material composition of C2H4: 0.5~1.5 mol%, N2: 40.0~50.0 mol%, and H2: the remainder, at a temperature of 950~1050°C and a pressure of 110~130 hPa. The duration of the annealing process is preferably 15~45 minutes.

[0062] [Step 2: Formation process of the lower layer - first layer (upper layer side - region A)] When forming the TiCN layer as the first layer of the lower layer (upper layer side - region A), the raw material composition is TiCl4: 9.0~11.0 mol%, CH3CN: 0.4~0.8 mol%, N2: 10.0~30.0 mol%, and H2: remainder. The remaining portion of the first layer is formed by chemical vapor deposition at a temperature of 980~1020°C and a pressure of 100~140 hPa.

[0063] [Step 3: Formation process of the lower layer - second layer (region A)] When forming the TiCNO layer as the second layer (region A) of the lower layer, the raw material composition is TiCl4: 9.0~11.0 mol%, CH3CN: 0.4~0.8 mol%, CO: 1.0~2.0 mol%, N2: 10.0~30.0 mol%, H2: remainder, and the second layer is formed by chemical vapor deposition at a temperature of 980~1020°C and a pressure of 100~140 hPa. When forming the TiCO layer as the second layer (region A) of the lower layer, the raw material composition is TiCl4: 5.0~7.0 mol%, CO: 2.0~3.0 mol%, H2: remainder, and the second layer is formed by chemical vapor deposition at a temperature of 980~1020°C and a pressure of 80~120 hPa. Note that if the lower layer consists of only one layer, step 3 does not need to be performed.

[0064] In step 1 (the process of forming region B) described above, the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region B of the lower layer can be controlled by adjusting, for example, the pressure and the amount of C2H4 in the raw material. Specifically, for example, by reducing the pressure in step 1, the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region B of the lower layer can be reduced. Also, for example, by increasing the amount of C2H4 in the raw material in step 1, the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region B of the lower layer can be increased.

[0065] Furthermore, in step 1 (the process of forming region B), the ratio of the sum of the lengths of the Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in region B of the lower layer can be controlled by adjusting, for example, the pressure and the amount of N2 in the raw material. Specifically, for example, by reducing the pressure in step 1, the ratio of the sum of the lengths of the Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in region B of the lower layer can be increased. Also, for example, by increasing the amount of N2 in the raw material in step 1, the ratio of the sum of the lengths of the Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in region B of the lower layer can be increased.

[0066] Furthermore, for example, by adjusting whether or not an annealing process is performed, and by adjusting each condition in steps 2 and 3 (the process of forming region A), the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region A of the lower layer can be controlled. Specifically, for example, performing an annealing process can increase the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region A of the lower layer. Also, for example, performing an annealing process and increasing the amount of TiCl4 in the raw material in steps 2 and 3 (the process of forming region A) can increase the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region A of the lower layer. Also, for example, not performing an annealing process and increasing the amount of TiCl4 in the raw material in steps 2 and 3 (the process of forming region A) tends to decrease the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region A of the lower layer. Furthermore, for example, by reducing the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region B of the lower layer, the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region A of the lower layer can also be reduced.

[0067] Furthermore, for example, by adjusting whether or not an annealing process is performed, and by adjusting each condition in steps 2 and 3 (the process of forming region A), the ratio of the sum of the lengths of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in region A of the lower layer can be controlled. Specifically, for example, performing an annealing process can reduce the ratio of the sum of the lengths of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in region A of the lower layer. Also, for example, performing an annealing process and increasing the amount of TiCl4 in the raw material in steps 2 and 3 (the process of forming region A) can reduce the ratio of the sum of the lengths of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in region A of the lower layer. Also, for example, not performing an annealing process and increasing the amount of TiCl4 in the raw material in steps 2 and 3 (the process of forming region A) tends to increase the ratio of the sum of the lengths of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in region A of the lower layer. Furthermore, for example, by increasing the ratio of the sum of the lengths of Σ3-grain boundaries and Σ11-grain boundaries to 100% of the total length of all grain boundaries in region B of the lower layer, the ratio of the sum of the lengths of Σ3-grain boundaries and Σ11-grain boundaries to 100% of the total length of all grain boundaries in region A of the lower layer can also be increased.

[0068] Furthermore, the ratio of the sum of the lengths of Σ3-grain boundaries and Σ11-grain boundaries to 100% of the total grain boundary length in the entire lower layer can be controlled by appropriately adjusting the ratio of the sum of the lengths of Σ3-grain boundaries and Σ11-grain boundaries to 100% of the total grain boundary length in each of the lower layer regions A and B.

[0069] Next, an upper layer consisting of an α-Al2O3 layer is formed on the surface of the lower layer. The upper layer is formed, for example, by the following method.

[0070] First, a lower layer consisting of one or more Ti compound layers is formed on the surface of the substrate. Then, the surface of the layer furthest from the substrate is oxidized (hereinafter, this step will also be referred to as the "oxidation process"). Subsequently, an α-Al2O3 layer is formed on the surface of the oxidized layer (hereinafter, this step will also be referred to as the "film formation process").

[0071] In the oxidation treatment process, the oxidation of the surface of the layer furthest from the substrate is carried out under the following conditions: the raw material composition is CO: 0.1-0.5 mol%, CO2: 0.1-1.0 mol%, H2: the remainder, the temperature is 950-1050°C, and the pressure is 45-65 hPa. The oxidation treatment time at this time is preferably 1-5 minutes.

[0072] Then, in the film formation process, the α-Al2O3 layer is formed by chemical vapor deposition using a raw material composition of AlCl3: 2.0~4.0 mol%, CO2: 1.0~5.0 mol%, HCl: 2.0~3.0 mol%, H2S: 0.3~0.4 mol%, and H2: the remainder, at a temperature of 950~1050°C and a pressure of 60~80 hPa.

[0073] Next, an outer layer consisting of a TiN layer and / or a TiCN layer is formed on the surface of the upper layer consisting of an α-Al2O3 layer. The outer layer is formed, for example, by the following method.

[0074] The TiN layer can be formed by chemical vapor deposition using a raw material composition of TiCl4: 5.0-10.0 mol%, N2: 20-60 mol%, and H2: the remainder, at a temperature of 950-1050°C and a pressure of 300-400 hPa.

[0075] The TiCN layer can be formed by chemical vapor deposition using a raw material composition of TiCl4: 4.0-8.0 mol%, CH3CN: 0.5-2.0 mol%, N2: 3.0-7.0 mol%, and H2: the remainder, at a temperature of 950-1050°C and a pressure of 60-80 hPa.

[0076] The thickness of each layer in the coating 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, scanning electron microscope (SEM), or FE-SEM. The average thickness of each layer in the coated cutting tool of this embodiment can be determined by measuring the thickness of each layer at three or more locations near a point 50 μm from the cutting edge towards the center of the rake face of the coated cutting tool, and calculating the arithmetic mean. The composition of each 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) or a wavelength-dispersive X-ray spectrometer (WDS). [Examples]

[0077] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0078] As the base material, a cutting insert made of cemented carbide was prepared, having an insert shape of CNMA120408 (ISO standard) and a composition of 93.7%WC-6.0%Co-0.3%Cr3C2 (by mass%). After round honing of the cutting edge of this base material with a SiC brush, the surface of the base material was cleaned.

[0079] After cleaning the surface of the substrate, a coating layer was formed by chemical vapor deposition. First, the substrate was placed in an externally heated chemical vapor deposition apparatus, and under the raw material composition, temperature, and pressure conditions shown in Table 1, an adhesion layer (TiN layer or TiC layer) with the composition shown in Table 5 was formed on the surface of the substrate to the average thickness shown in Table 5. However, no adhesion layer was formed for invention 17. Next, under the raw material composition, temperature, and pressure conditions shown in Table 2, the lower side (region B) of the first layer of the lower layer with the composition shown in Table 5 was formed on the surface of the adhesion layer to an average thickness 2.0 μm less than the average thickness of the entire lower layer shown in Table 5. Subsequently, an annealing process was carried out for the time shown in Table 2 under the raw material composition, temperature, and pressure conditions shown in Table 1. However, no annealing process was carried out for comparative products 5 and 6. Subsequently, under the raw material composition, temperature, and pressure conditions shown in Table 3, the upper side (region A) of the first layer of the lower layer with the composition shown in Table 5 was formed on the surface of region B to the average thickness shown in Table 5. However, for invention 24, region A was formed only in the second layer of the lower layer. Next, under the raw material composition, temperature, and pressure conditions shown in Table 4, the second layer (region A) of the lower layer, whose composition is shown in Table 5, was formed on the surface of the first layer of the lower layer to the average thickness shown in Table 5. However, for invention 18, region A was formed only on the upper side of the first layer of the lower layer, and the second layer of the lower layer was not formed. This formed a lower layer having regions A and B. Next, an oxidation treatment was performed under the raw material composition, temperature, and pressure conditions shown in Table 1. The oxidation treatment time was 3 minutes. Then, under the raw material composition, temperature, and pressure conditions shown in Table 1, an upper layer (α-Al2O3 layer), whose composition is shown in Table 5, was formed on the surface of the oxidized lower layer to the average thickness shown in Table 5. Finally, under the raw material composition, temperature, and pressure conditions shown in Table 1, an outer layer (TiN layer or TiCN layer), whose composition is shown in Table 5, was formed on the surface of the upper layer (α-Al2O3 layer) to the average thickness shown in Table 5. Thus, coated cutting tools of inventions 1-28 and comparative products 1-12 were obtained.

[0080] The thickness of each layer in the sample was determined as follows: Using FE-SEM, the thickness was measured at three points in the cross-section near a position 50 μm from the cutting edge of the coated cutting tool toward the center of the rake face, and the arithmetic mean of these measurements was calculated as the average thickness. The composition of each layer in the obtained sample was measured using EDS in the cross-section near a position 50 μm from the cutting edge of the coated cutting tool toward the center of the rake face.

[0081] [Table 1]

[0082] [Table 2]

[0083] [Table 3]

[0084] [Table 4]

[0085] [Table 5]

[0086] [Grain boundary length] The following measurements were taken for the entire lower layer of the obtained sample, the ratio of the sum of the lengths of the Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in regions A and B (hereinafter also referred to as "(Σ3+Σ11) / total grain boundary"), and the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundaries and Σ11 grain boundaries in regions A and B of the lower layer (hereinafter also referred to as "Σ11 / (Σ3+Σ11)"). First, using a coated cutting tool, the substrate was polished in a direction perpendicular to the substrate surface until the cross-section of the lower layer was exposed to obtain an observation surface. Then, the obtained observation surface was polished using colloidal silica to obtain a mirror-polished surface. Subsequently, the observation surface described above was observed using a SEM equipped with EBSD. The scoop surface was observed as the observation area. For the SEM, we used the SU6600 (manufactured by Hitachi High-Technologies Corporation) equipped with an EBSD (manufactured by TexSEM Laboratories). The normal to the observation surface was tilted at 70° with respect to the incident beam, and the analysis was performed by irradiating the electron beam with an accelerating voltage of 15kV and an irradiation current of 1.0nA. Data acquisition was performed by analyzing the crystal orientation of each particle in the lower layer within the measurement range using an EBSD setting of 50μm in the direction parallel to the substrate surface and 0.1μm in the direction perpendicular to the substrate surface, encompassing the entire lower layer. At this time, the boundary between measurement points with an orientation difference of 5° or more was defined as a grain boundary. Data processing was performed using commercially available software. The CSL grain boundaries corresponding to any given Σ value were counted and confirmed by expressing them as a ratio to the total grain boundaries. From this, the length of the Σn grain boundary in the lower layer (n is an odd number between 3 and 29) and the total length of all grain boundaries were determined. A total of three fields of view were analyzed within the measurement range on the observation surface described above, and the average value of each value was calculated. From the obtained average values, the ratio of the sum of the lengths of the Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length in the entire lower layer, regions A and B, and the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundaries and Σ11 grain boundaries in regions A and B of the lower layer were calculated. The results are shown in Table 6.

[0087] [Table 6]

[0088] Using the obtained inventions 1-28 and comparative products 1-12, cutting tests were conducted under the following conditions.

[0089] <Cutting Test 1> Workpiece material: FCD600, Workpiece shape: Cylindrical shape with a diameter of 120 mm and a length of 400 mm (four grooves evenly spaced on the outer surface of the cylinder). Cutting speed: 120m / min, Feed rate: 0.30mm / rev, Cutting depth: 2.0 mm, Coolant: Water-soluble coolant, Evaluation criteria: Tool life was defined as the point at which the sample was damaged, and the number of impacts until tool life was measured. The better the resistance to chipping, the longer the tool life.

[0090] For the number of impacts until tool life was reached in Cutting Test 1, we evaluated the number of impacts as follows: 15,000 or more was rated "A", 10,000 to less than 15,000 was rated "B", and less than 10,000 was rated "C". In this evaluation, "A" is the best, followed by "B", and "C" is the worst, meaning that "A" or "B" indicates excellent cutting performance. The results of the evaluation are shown in Table 7.

[0091] <Cutting Test 2> Workpiece material: FCD600, Workpiece shape: Disc shape with a diameter of 180 mm and a thickness of 23 mm (with a 70 mm diameter hole in the center of the disc) Cutting speed: 200m / min, Feed rate: 0.30mm / rev, Cutting depth: 2.0 mm, Coolant: Water-soluble coolant, Evaluation criteria: Tool life was defined as the point at which the sample was damaged or the maximum flank wear width reached 0.3 mm. The machining time until tool life was measured. The better the wear resistance, the longer the tool life.

[0092] For the machining time until tool life was reached in Cutting Test 2, a time of 32 minutes or more was evaluated as "A," a time of 24 minutes or more but less than 32 minutes as "B," and a time of less than 24 minutes as "C." In this evaluation, "A" is the best, followed by "B," and "C" is the worst, meaning that "A" or "B" indicates excellent cutting performance. The results of the evaluation are shown in Table 7.

[0093] [Table 7]

[0094] As shown in Table 7, the inventive product received a rating of "B" or higher in both cutting tests 1 and 2. On the other hand, the comparative product received a rating of "C" in both or either of cutting tests 1 and 2. Therefore, it can be seen that the wear resistance and fracture resistance of the inventive product are generally superior to those of the comparative product. From these results, it was found that the inventive product has superior wear resistance and fracture resistance, resulting in a longer tool life. [Industrial applicability]

[0095] The coated cutting tool of the present invention has excellent wear resistance and fracture resistance, thereby extending tool life compared to conventional tools, and from this perspective, it has potential for industrial use. [Explanation of symbols]

[0096] 1...Base material, 2...Adhesive layer, 3...Lower layer, 4...Upper layer, 5...Outer layer, 6...Coating layer, 7...Coated cutting tool, 3a...Area A, 3b...Area B

Claims

1. A coated cutting tool comprising a base material and a coating layer formed on the surface of the base material, The coating layer includes a lower layer and an upper layer formed on the surface of the lower layer. The lower layer includes a Ti compound layer made of Ti and at least two elements selected from the group consisting of C, N, O, and B. The Ti compound layer in the lower layer is a TiCN layer made of TiCN, a TiCNO layer made of TiCNO, and / or a TiCO layer made of TiCO. The average thickness of the lower layer is 3.0 μm or more and 15.0 μm or less. The upper layer is composed of α-type aluminum oxide. 2 O 3 Including layers, The average thickness of the upper layer is 3.0 μm or more and 15.0 μm or less. In the entire lower layer, the ratio of the sum of the lengths of Σ3 grain boundaries and Σ11 grain boundaries to 100% of the total grain boundary length is between 15% and 68%. A coated cutting tool in which, when a region A is defined as a 2 μm area extending from the interface between the lower layer and the upper layer toward the substrate, and a region B is defined as a region B toward the substrate from region A, the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region A of the lower layer is 20% or more and 59% or less, and the ratio of the length of the Σ11 grain boundary to the sum of the lengths of the Σ3 grain boundary and the Σ11 grain boundary in region B of the lower layer is 0% or more and less than 20%.

2. The coated cutting tool according to claim 1, wherein in the region A of the lower layer, the ratio of the sum of the lengths of the Σ3 grain boundaries and the Σ11 grain boundaries to 100% of the total grain boundary length is 10% or more and 60% or less.

3. The coated cutting tool according to claim 1 or 2, wherein in the region B of the lower layer, the ratio of the sum of the lengths of the Σ3 grain boundaries and the Σ11 grain boundaries to 100% of the total grain boundary length is 20% or more and 70% or less.

4. The coating layer includes an adhesive layer between the lower layer and the substrate, The aforementioned adhesion layer consists of a Ti nitride layer and / or a Ti carbide layer. The coated cutting tool according to claim 1 or 2, wherein the average thickness of the adhesion layer is 0.1 μm or more and 3.0 μm or less.

5. The coating layer further includes an outer layer on the surface of the upper layer opposite to the substrate, The outer layer is made of a compound of Ti and at least one element selected from the group consisting of C, N, O, and B. The coated cutting tool according to claim 1 or 2, wherein the average thickness of the outer layer is 0.1 μm or more and 4.0 μm or less.

6. The coated cutting tool according to claim 1 or 2, wherein the average thickness of the entire coated layer is 10.0 μm or more and 30.0 μm or less.

7. The coated cutting tool according to claim 1 or 2, wherein the substrate is one of a cemented carbide, a cermet, a ceramic, and a cubic boron nitride sintered body.

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