Coated cutting tool

Abstract

To provide a coated cutting tool that has excellent abrasion resistance and chipping resistance, so that a service life thereof can be elongated.SOLUTION: A coated cutting tool comprises a base material and a coated layer formed on a surface of the base material. The coated layer includes a lower layer, a middle layer and an upper layer laminated in this order from the base material side toward the surface side of the coated layer. The lower layer contains a specific Ti compound layer. The middle layer contains an α-Al2O3 layer. The upper layer contains a specific Ti compound layer. An average thickness of the whole of the coated layer is 10.0 μm or more and 25.0 μm or less. An average thickness of the upper layer is 1.2 μm or more and 6.0 μm or less. A ratio of a length of a Σ11 grain boundary to a length 100% of a CSL grain boundary is 25% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] It is well known that coated cutting tools, which are formed by depositing a coating layer with a total thickness of 3 to 20 μm by chemical vapor deposition on the surface of a substrate made of cemented carbide, are used for cutting steel, cast iron, etc. As the coating layer, for example, a coating layer consisting of a single layer or a multilayer of two or more types selected from the group consisting of titanium carbides, nitrides, carbonitrides, carbonates, and carbonitride oxides, and aluminum oxide, is known.

[0003] For example, Patent Document 1 describes a coated cutting tool having a substrate and a coating layer formed on the surface of the substrate, the coating layer comprising a lower layer, an intermediate layer, and an upper layer laminated in this order from the substrate side toward the surface side of the coating layer, the lower layer containing one or more Ti compound layers formed of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B, the intermediate layer containing α-type Al2O3, and the upper layer containing TiCN, the lower layer having an average thickness of 4.0 μm to 10.0 μm, the intermediate layer having an average thickness of 3.0 μm to 10.0 μm, and the upper layer having an average thickness of 1.5 μm to 6.5 μm, the ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries (100%) in a specific region of the upper layer being 20% ​​to 60%, and the proportion of grains with a (111) plane in the upper layer being 30% by area or more.

[0004] Furthermore, for example, Patent Document 2 describes a surface-coated cutting tool in which a hard coating layer made of a Ti composite carbonitride layer having an average thickness of 1 to 10 μm is formed by vapor deposition on the surface of a tool substrate made of a tungsten carbide-based cemented carbide, a titanium carbonitride-based cermet, or a cubic boron nitride-based ultra-high pressure sintered material, (a) The Ti composite carbonitride layer is Composition formula: TiC X N1-X When expressed as 0.2≦X≦0.5 (where X represents an atomic ratio) is satisfied, (b) using a field emission scanning electron microscope, an electron beam is irradiated onto each crystal grain having a cubic crystal lattice present within a measurement range of the polished surface, and the tilt angle formed by the normal of the {100} plane, which is the crystal face of the crystal grain, relative to the normal of the polished surface is measured; among the measured tilt angles, the measured tilt angles within a range of 0 to 45 degrees are divided into sections at intervals of 0.25 degrees, and the frequency within each section is tallied to obtain a tilt angle number distribution graph in which the highest peak exists in a tilt angle section within a range of 0 to 10 degrees, and the total frequency within the 0 to 10 degree range accounts for 60% or more of the total frequency in the tilt angle number distribution graph; (c) Using a field emission scanning electron microscope, an electron beam is irradiated onto each crystal grain having a cubic crystal lattice present within the measurement range of the polished surface, and the tilt angle formed by the normal to the polished surface and the normal to the {100} plane, which is the crystal face of the crystal grain, is measured, in this case the crystal grain has a NaCl-type face-centered cubic crystal structure in which constituent atoms consisting of Ti, carbon, and nitrogen are present at lattice points, and based on the measured tilt angle thus obtained, a distribution of lattice points (constituent atom sharing lattice points) at which each of the constituent atoms shares one constituent atom between the crystal grains at the interface between adjacent crystal grains is determined. is calculated, and when a constituent atom-sharing lattice point form in which there are N lattice points (N is an even number of 2 or more in the crystal structure of an NaCl-type face-centered cubic crystal) that do not share constituent atoms between the constituent atom-sharing lattice points is represented by ΣN+1, a constituent atom-sharing lattice point distribution graph showing the distribution ratio of each ΣN+1 to the entire ΣN+1 (however, the upper limit of N is set to 28 in terms of frequency) is shown, the total of the distribution ratios of Σ3, Σ5, Σ7, Σ9, Σ11, and Σ13 accounts for 70% or more of the total distribution ratio of the entire ΣN+1. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-37150 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-142972 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent cutting processes, the trend toward higher feed rates and deeper depths of cut has become more pronounced, necessitating improved tool wear resistance and chipping resistance. In particular, cutting steel under high feed rates and deep depths of cut has increasingly placed heavy loads on coated cutting tools. Under these harsh cutting conditions, conventional tools are prone to cracks that develop and propagate during cutting, resulting in chipping. This can lead to problems that limit tool life. In light of these circumstances, the coated cutting tool described in Patent Document 1 is required to exhibit even greater wear resistance and chipping resistance. Furthermore, the coated cutting tool described in Patent Document 2 lacks an α-Al2O3 layer composed of α-type aluminum oxide, resulting in insufficient wear resistance. Furthermore, the ratio of the length of the Σ11 grain boundary to the length of the CSL grain boundary has not been examined, or the ratio is not sufficiently high, leaving room for improvement in chipping resistance.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a coated cutting tool that has excellent wear resistance and chipping resistance, thereby enabling an extension of tool life. [Means for solving the problem]

[0008] From the above perspective, the present inventors have conducted extensive research into extending the tool life of coated cutting tools. As a result, they have found that when the coating layer has a specific configuration, the generation and propagation of cracks during cutting is suppressed, resulting in excellent chipping resistance. Furthermore, the adhesion between the middle layer and the upper layer is improved, making it possible to achieve high wear resistance and chipping resistance over a long period of time in intermittent cutting or high-feed cutting of steel, and as a result, the tool life of coated cutting tools can be extended. This discovery led to the completion of the present invention.

[0009] That is, the gist of the present invention is as follows. [1] A coated cutting tool comprising a substrate and a coating layer formed on a surface of the substrate, the coating layer includes a lower layer, an intermediate layer, and an upper layer laminated in this order from the substrate side toward the surface side of the coating layer, the lower layer contains a Ti compound layer made of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B, the intermediate layer contains an α-Al2O3 layer made of α-type aluminum oxide, the upper layer contains a Ti compound layer made of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B, The average thickness of the entire coating layer is 10.0 μm or more and 25.0 μm or less, The average thickness of the upper layer is 1.2 μm or more and 6.0 μm or less, A coated cutting tool, wherein the ratio of the length of Σ11 grain boundaries to 100% of the length of CSL grain boundaries in the upper layer is 25% or more. [2] [1] The coated cutting tool according to [1], wherein the proportion of the length of the Σn grain boundary (n is an odd number of 3 or more and 29 or less) relative to 100% of the length of the CSL grain boundary in the upper layer is the largest. [3] The coated cutting tool according to [1] or [2], wherein the ratio of the length of the CSL grain boundary to 100% of the length of all grain boundaries in the upper layer is 20% or more and 60% or less. [4] The coated cutting tool according to any one of [1] to [3], wherein the upper layer includes at least a TiCN layer and / or a TiCNO layer. [5] The coated cutting tool according to any one of [1] to [4], wherein the intermediate layer has an average thickness of 3.0 μm or more and 15.0 μm or less. [6] The coated cutting tool according to any one of [1] to [5], wherein the lower layer has an average thickness of 3.0 μm or more and 15.0 μm or less. [7] The coated cutting tool according to any one of [1] to [6], wherein the substrate is any one of cemented carbide, cermet, ceramics, and cubic boron nitride sintered body. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a coated cutting tool that has excellent wear resistance and chipping resistance, thereby enabling an extension of tool life. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing an example of a coated cutting tool of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a mode 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 present embodiment. The present invention can be modified in various ways without departing from the gist of the present invention. In the drawings, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to the ratios shown in the drawings.

[0013] The coated cutting tool of this embodiment is a coated cutting tool comprising a substrate and a coating layer formed on the surface of the substrate. The coating layer comprises a lower layer, an intermediate layer, and an upper layer laminated in this order from the substrate side toward the surface side of the coating layer. The lower layer contains a Ti compound layer consisting of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B. The intermediate layer contains an α-Al2O3 layer consisting of α-aluminum oxide. The upper layer contains a Ti compound layer consisting of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B. The average thickness of the entire coating layer is 10.0 μm or more and 25.0 μm or less. The average thickness of the upper layer is 1.2 μm or more and 6.0 μm or less. The ratio of the length of the Σ11 grain boundary to the length of the CSL grain boundary (100%) in the upper layer is 25% or more.

[0014] The coated cutting tool of this embodiment, having the above-described configuration, can improve wear resistance and chipping resistance, thereby extending tool life. The factors that contribute to the improved wear resistance and chipping resistance of the coated cutting tool of this embodiment are believed to be as follows. However, the present invention is not limited by these factors. Specifically, the coated cutting tool of this embodiment includes a Ti compound layer composed of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B as the lower layer of the coating layer. The coated cutting tool of this embodiment has improved wear resistance and adhesion when such a lower layer is provided between the substrate and the intermediate layer containing an α-Al2O3 layer composed of α-aluminum oxide. Furthermore, the coated cutting tool of this embodiment has excellent wear resistance because the average thickness of the entire coating layer is 10.0 μm or more. On the other hand, the average thickness of the entire coating layer is 25.0 μm or less, which improves the adhesion of the coating layer and therefore provides excellent chipping resistance. The coated cutting tool of this embodiment has excellent wear resistance due to the upper layer having an average thickness of 1.2 μm or more, while the coating layer has excellent chipping resistance due to the upper layer having an average thickness of 6.0 μm or less. The coated cutting tool of this embodiment also has an upper layer containing a Ti compound layer composed of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B. The ratio of the length of the Σ11 grain boundary to the 100% length of the CSL grain boundary in the upper layer is 25% or more, thereby suppressing the initiation and propagation of cracks during cutting, resulting in excellent chipping resistance. Furthermore, the coated cutting tool of this embodiment also exhibits high wear resistance and chipping resistance over a long period of time due to the improved adhesion between the intermediate layer and the upper layer. The combination of these features is believed to improve the wear resistance and chipping resistance of the coated cutting tool of this embodiment, thereby extending the tool life.

[0015] 1 is a cross-sectional view showing an example of a coated cutting tool according to this embodiment. The coated cutting tool 6 includes a substrate 1 and a coating layer 5 formed on the surface of the substrate 1. The coating layer 5 includes a lower layer 2, an intermediate layer 3, and an upper layer 4 stacked in this order from top to bottom.

[0016] The coated cutting tool of this embodiment includes a substrate and a coating layer formed on the surface of the substrate. Specific examples of the coated cutting tool include indexable cutting inserts for milling or turning, drills, and end mills.

[0017] The substrate used in this embodiment is not particularly limited as long as it can be used as the substrate of a coated cutting tool.Such substrates can include, for example, cemented carbide, cermet, ceramics, cubic boron nitride sintered body, diamond sintered body and high-speed steel.Among them, if the substrate is any of cemented carbide, cermet, ceramics or cubic boron nitride sintered body, it is preferable because it has better wear resistance and chipping resistance, and from the same viewpoint, it is more preferable that the substrate is cemented carbide.

[0018] The substrate may have a surface modified. For example, if the substrate is made of cemented carbide, a de-β layer may be formed on the surface. If the substrate is made of cermet, a hardened layer may be formed on the surface. Even if the surface of the substrate is modified in this way, the effects of the present invention can be achieved.

[0019] The coating layer used in this embodiment has an overall average thickness of 10.0 μm or more and 25.0 μm or less. The coated cutting tool of this embodiment has excellent wear resistance because the overall average thickness of the coating layer is 10.0 μm or more, while the overall average thickness of the coating layer is 25.0 μm or less, improving the adhesion of the coating layer and thereby providing excellent chipping resistance. From the same perspective, the overall average thickness of the coating layer is preferably 10.5 μm or more and 24.5 μm or less, and more preferably 12.0 μm or more and 22.0 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 thickness of the entire coating layer from three or more cross sections of each layer or the entire coating layer, and calculating the arithmetic mean value.

[0020] Bottom Layer The lower layer used in this embodiment contains a Ti compound layer consisting of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B. When such a lower layer is provided between the substrate and the intermediate layer containing an α-Al2O3 layer consisting of α-aluminum oxide, the coated cutting tool of this embodiment has improved wear resistance and adhesion.

[0021] Examples of the Ti compound layer in the lower layer include a TiC layer made of TiC, a TiN layer made of TiN, a TiCN layer made of TiCN, a TiCO layer made of TiCO, a TiCNO layer made of TiCNO, a TiON layer made of TiON, and a TiB2 layer made of TiB2.

[0022] The lower layer may be composed of one layer or multiple layers (e.g., two or three layers). It is preferably composed of multiple layers, more preferably two or three layers, and even more preferably three layers. From the viewpoint of further improving wear resistance and adhesion, the lower layer preferably includes at least one layer selected from the group consisting of a TiN layer, a TiC layer, a TiCN layer, a TiCNO layer, and a TiCO layer. Furthermore, the coated cutting tool of this embodiment tends to have further improved wear resistance when at least one lower layer is a TiCN layer. Furthermore, the coated cutting tool of this embodiment tends to have further improved adhesion when at least one lower layer is a TiN layer and the TiN layer is formed on the surface of the substrate. Furthermore, the coated cutting tool of this embodiment tends to have further improved adhesion when at least one lower layer is a TiCNO layer and the TiCNO layer is formed in contact with an intermediate layer containing an α-Al2O3 layer. When the lower layer is composed of three layers, a TiC layer or a TiN layer may be formed on the surface of the substrate as a first layer, a TiCN layer may be formed on the surface of the first layer as a second layer, and a TiCNO layer or a TiCO layer may be formed on the surface of the second layer as a third layer. Among them, the lower layer may be formed on the surface of the substrate as a first layer, a TiCN layer may be formed on the surface of the first layer as a second layer, and a TiCNO layer may be formed on the surface of the second layer as a third layer.

[0023] The average thickness of the lower layer used in this embodiment is preferably 3.0 μm or more and 15.0 μm or less. The coated cutting tool of this embodiment tends to have excellent wear resistance because the average thickness of the lower layer is 3.0 μm or more. On the other hand, the coated cutting tool of this embodiment tends to have excellent chipping resistance because the average thickness of the lower layer is 15.0 μm or less, which improves the adhesion of the coating layer. From the same perspective, the average thickness of the lower layer is preferably 4.5 μm or more and 14.5 μm or less, and more preferably 5.5 μm or more and 13.0 μm or less.

[0024] In the lower layer used in this embodiment, for example, the average thickness of the TiC or TiN layer is preferably 0.05 μm or more and 1.0 μm or less from the viewpoint of further improving wear resistance and chipping resistance. From the same viewpoint, the average thickness of the TiC or TiN layer is more preferably 0.10 μm or more and 0.5 μm or less, and further preferably 0.15 μm or more and 0.3 μm or less.

[0025] In the lower layer used in this embodiment, for example, the average thickness of the TiCN layer is preferably 2.5 μm or more and 15.0 μm or less from the viewpoint of further improving wear resistance and chipping resistance, more preferably 3.3 μm or more and 13.0 μm or less, and further preferably 4.0 μm or more and 12.5 μm or less from the same viewpoint.

[0026] In the lower layer used in this embodiment, for example, the average thickness of the TiCNO or TiCO layer is preferably 0.05 μm or more and 1.4 μm or less from the viewpoint of further improving wear resistance and chipping resistance, more preferably 0.1 μm or more and 1.0 μm or less, and even more preferably 0.2 μm or more and 0.5 μm or less from the same viewpoint.

[0027] The Ti compound layer in the lower layer is a layer consisting of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B, but may contain trace amounts of components other than the above elements as long as the lower layer exhibits its desired effect.

[0028] [Middle layer] The intermediate layer used in this embodiment contains an α-Al2O3 layer made of α-type aluminum oxide.

[0029] The average thickness of the intermediate layer used in this embodiment is preferably 3.0 μm or more and 15.0 μm or less. The coated cutting tool of this embodiment tends to have excellent wear resistance when the average thickness of the intermediate layer containing the α-Al2O3 layer is 3.0 μm or more. On the other hand, the coated cutting tool of this embodiment tends to have excellent chipping resistance when the average thickness of the intermediate layer containing the α-Al2O3 layer is 15.0 μm or less, due to improved adhesion of the coating layer. From the same viewpoint, the average thickness of the intermediate layer is more preferably 3.5 μm or more and 14.5 μm or less, and even more preferably 4.5 μm or more and 13.5 μm or less.

[0030] The intermediate layer only needs to contain an α-Al2O3 layer made of α-aluminum oxide, and may or may not contain components other than α-aluminum oxide (α-Al2O3) as long as the effects of the present invention are achieved.

[0031] [Top layer] The upper layer used in this embodiment contains a Ti compound layer made of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B. The upper layer preferably contains a Ti compound layer made of a Ti compound of Ti, C, and at least one element selected from the group consisting of N, O, and B. Examples of the Ti compound layer in the upper layer include a TiC layer made of TiC, a TiN layer made of TiN, a TiCN layer made of TiCN, a TiCO layer made of TiCO, a TiCNO layer made of TiCNO, a TiON layer made of TiON, and a TiB2 layer made of TiB2. In particular, the upper layer preferably includes at least a TiCN layer and / or a TiCNO layer. When the upper layer includes at least a TiCN layer and / or a TiCNO layer, it tends to be easier to control the ratio of the length of the Σn grain boundary (n is an odd number between 3 and 29) to the length of the CSL grain boundary (100%) in the upper layer so that the ratio of the length of the Σ11 grain boundary is maximized. In addition, the balance between wear resistance and chipping resistance tends to be excellent.

[0032] Furthermore, in the coated cutting tool of this embodiment, the ratio of the length of the Σ11 grain boundary to the 100% length of the CSL grain boundary in the upper layer is 25% or more. In the coated cutting tool of this embodiment, the upper layer contains a Ti compound layer composed of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B. Since the ratio of the length of the Σ11 grain boundary to the 100% length of the CSL grain boundary in the upper layer is 25% or more, the initiation and propagation of cracks during cutting is suppressed, resulting in excellent chipping resistance. Furthermore, the adhesion between the intermediate layer and the upper layer is improved, resulting in high wear resistance and chipping resistance over a long period of time. From the same perspective, the ratio of the length of the Σ11 grain boundary to the 100% length of the CSL grain boundary in the upper layer is preferably 26% or more, more preferably 28% or more, and even more preferably 30% or more. Meanwhile, from the viewpoint of ease of manufacturing, the upper limit of the ratio of the length of the Σ11 grain boundary to the 100% length of the CSL grain boundary in the upper layer is preferably 60% or less. In the present application, the length of a CSL grain boundary means "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.

[0033] The upper layer in this embodiment has grain boundaries with relatively high grain boundary energy and grain boundaries with relatively low grain boundary energy. Typically, grain boundaries have many gaps due to the random arrangement of atoms, resulting in relatively high grain boundary energy. On the other hand, some grain boundaries have regular atomic arrangements with few gaps, resulting in relatively low grain boundary energy. A representative example of such grain boundaries with relatively low grain boundary energy is a coincidence site lattice grain boundary (hereinafter referred to as a "CSL grain boundary" or "CSL grain boundary"). Grain boundaries significantly affect important sintering processes such as densification, creep, and diffusion, as well as 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., grain boundary boundary orientation and grain misorientation. CSL grain boundaries play a special role. The Σ value is known as an index of the distribution of CSL grain boundaries, and is defined as the ratio of the density of crystal lattice points between two crystal grains that contact at the grain boundary to the density of lattice points that match when both crystal lattices are superimposed. In the case of simple structures, it is generally recognized 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 crystal grain misorientation is considered important for the properties and improvement of the upper layer.

[0034] Recently, 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.

[0035] For each grain in a material of interest, the crystallographic orientation is determined after indexing the corresponding diffraction pattern. EBSD, along with commercially available software, allows for relatively easy texture analysis and determination of the grain boundary character distribution (GBCD). By measuring and analyzing interfaces with EBSD, the misorientation of grain boundaries can be revealed across a large sample population of interfaces. The distribution of misorientation is typically related to the processing and / or physical properties of the material. The misorientation of grain boundaries can be derived from conventional orientation parameters such as Euler angles, angle / axis pairs, or Rodrigues vectors.

[0036] The CSL grain boundaries in the upper layer typically consist 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. Here, for example, the length of the Σ11 grain boundary refers to the total length of the Σ11 grain boundary in the field of view (specific region) observed with an SEM equipped with EBSD.

[0037] Here, "total grain boundaries" refers to the sum of all grain boundaries other than CSL grain boundaries and CSL grain boundaries. Hereinafter, 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 excluding CSL grain boundaries from all grain boundaries of the upper layer crystal grains when observed with an SEM equipped with EBSD. Therefore, the "total length of all grain boundaries" can be expressed as "the sum of the length of the CSL grain boundaries and the length of the general grain boundaries."

[0038] In the coated cutting tool of this embodiment, it is preferable that the proportion of the length of the Σn grain boundary (n is an odd number of 3 to 29) to 100% of the length of the CSL grain boundary in the upper layer be the largest. If the proportion of the length of the Σ11 grain boundary is the largest to 100% of the length of the Σn grain boundary (n is an odd number of 3 to 29) to 100% of the length of the CSL grain boundary in the upper layer, the effect of increasing the proportion of the length of the Σ11 grain boundary to 100% of the length of the CSL grain boundary tends to be more effectively and reliably achieved.

[0039] In addition, in the coated cutting tool of this embodiment, the ratio of the length of the CSL grain boundaries to 100% of the total length of all grain boundaries in the upper layer is preferably 20% to 60%. In the coated cutting tool of this embodiment, if the ratio of the length of the CSL grain boundaries to 100% of the total length of all grain boundaries in the upper layer is 20% or more, mechanical properties are improved and the progression of wear due to particle shedding is suppressed, tending to result in excellent wear resistance. On the other hand, in the coated cutting tool of this embodiment, if the ratio of the length of the CSL grain boundaries to 100% of the total length of all grain boundaries in the upper layer is 60% or less, coarsening of crystal grains can be suppressed, tending to reduce the surface roughness of the coating layer, and also, cutting resistance is reduced, tending to result in even more excellent wear resistance. From the same perspective, the ratio of the length of the CSL grain boundaries to 100% of the total length of all grain boundaries in the upper layer is more preferably 21% to 59% and even more preferably 23% to 55%.

[0040] In this embodiment, the ratio of the length of the Σ11 grain boundary to 100% of the length of the CSL grain boundary in the upper layer and the ratio of the length of the CSL grain boundary to 100% of the length of all grain boundaries can be calculated as follows.

[0041] The coated cutting tool is used to expose the cross section of the upper layer in a direction perpendicular to the surface of the substrate, thereby obtaining an observation surface. Examples of methods for exposing the cross section of the upper layer include cutting and polishing. Among these, polishing is preferred from the viewpoint of making the observation surface of the upper layer smoother. In particular, a mirror-finished observation surface is preferred from the viewpoint of achieving a smoother observation surface. The method for obtaining a mirror-finished observation surface of the upper layer is not particularly limited, but examples thereof include polishing using diamond paste or colloidal silica, ion milling, etc.

[0042] Thereafter, the above observation surface is observed using an SEM equipped with EBSD. As the observation region, it is preferable to observe a flat surface (such as a flank surface).

[0043] The SEM used is an 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° relative to the incident beam, and the analysis is performed by irradiating the electron beam with an accelerating voltage of 15 kV and a probe current of 1.0 nA. Data collection is performed by analyzing the crystal orientation of each grain in the upper layer within the measurement range, with EBSD settings of 0.1 μm step size (distance between measurement points), over a measurement range that includes 50 μm in the direction parallel to the substrate surface and the entire upper layer in the direction perpendicular to the substrate surface. Boundaries between measurement points with an orientation difference of 5° or more are considered grain boundaries.

[0045] Data processing is performed using commercially available software. The CSL grain boundaries corresponding to a given Σ value are counted and expressed as a ratio to all grain boundaries. From the above, the length of the CSL grain boundaries in the upper layer, the length of the Σn grain boundaries (n is an odd number between 3 and 29), and the total length of all grain boundaries are determined. A total of three fields of view are analyzed within the measurement range on the observation surface described above, and the average values ​​are calculated. From the obtained average values, it is possible to identify the Σn grain boundary in the upper layer with the largest length ratio among the ratios of the Σn grain boundary lengths (n is an odd number between 3 and 29) to 100% of the CSL grain boundary length. Furthermore, the ratio of the length of the Σ11 grain boundary to 100% of the CSL grain boundary length and the ratio of the length of the CSL grain boundary to 100% of the total grain boundary length can be calculated.

[0046] The average thickness of the upper layer used in this embodiment is 1.2 μm or more and 6.0 μm or less. The coated cutting tool of this embodiment has excellent wear resistance because the average thickness of the upper layer is 1.2 μm or more, while the average thickness of the upper layer is 6.0 μm or less, improving the adhesion of the coating layer and therefore excellent chipping resistance. From the same viewpoint, the average thickness of the upper layer is more preferably 1.4 μm or more and 5.9 μm or less, and even more preferably 1.6 μm or more and 5.5 μm or less.

[0047] The Ti compound layer in the upper layer is a layer consisting of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B, but may contain trace amounts of components other than the above elements as long as the upper layer exhibits its functional effects.

[0048] [External Layer] The coating layer used in this embodiment may include an outer layer on the interface of the upper layer opposite the substrate (i.e., the surface of the upper layer). Examples of the outer layer include a compound layer (different from the upper layer) composed of at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, Si, and Y and at least one element selected from the group consisting of C, N, O, and B. Such a compound layer is preferable because it tends to facilitate identification of the used corner. From a similar perspective, the outer layer is more preferably a compound layer composed of at least one element selected from the group consisting of Ti, Nb, Cr, Al, and Si and at least one element selected from the group consisting of C, N, O, and B (preferably including C and / or N), even more preferably a compound layer composed of at least one element selected from the group consisting of Ti, Cr, Al, and Si and N, and particularly preferably a TiN layer composed of TiN.

[0049] The average thickness of the outer layer is not particularly limited and may be, for example, 0.05 μm or more and 1.0 μm or less. From the viewpoint of more effectively and reliably achieving the effects of the present invention, the average thickness of the outer layer is preferably 0.1 μm or more and 0.5 μm or less, and more preferably 0.1 μm or more and 0.3 μm or less.

[0050] In the coated cutting tool of this embodiment, each layer constituting the coating layer may be formed by chemical vapor deposition or physical vapor deposition. Specific examples of the method for forming each layer include the following methods. However, the method for forming each layer is not limited to these.

[0051] (chemical vapor deposition) First, a lower layer made of one or more Ti compound layers is formed on the surface of the substrate as follows. For example, a Ti compound layer consisting of a Ti nitride layer (hereinafter also referred to as a "TiN layer") can be formed by chemical vapor deposition using a raw material composition of TiCl4: 5.0 to 10.0 mol%, N2: 20 to 60 mol%, H2: balance, at a temperature of 850 to 950°C and a pressure of 350 to 450 hPa.

[0052] A Ti compound layer consisting of a Ti carbide layer (hereinafter also referred to as a "TiC layer") can be formed by chemical vapor deposition using a raw material composition of TiCl4: 1.5 to 3.5 mol%, CH4: 3.5 to 5.5 mol%, H2: balance, at a temperature of 950 to 1050°C and a pressure of 70 to 80 hPa.

[0053] A Ti compound layer consisting of a Ti carbonitride layer (hereinafter also referred to as a "TiCN layer") can be formed by chemical vapor deposition using a raw material composition of TiCl4: 5.0 to 7.0 mol%, CH3CN: 0.5 to 1.5 mol%, H2: balance, at a temperature of 800 to 900°C and a pressure of 70 to 90 hPa.

[0054] A Ti compound layer consisting of a Ti oxycarbonitride layer (hereinafter also referred to as a "TiCNO layer") can be formed by chemical vapor deposition using a raw material composition of TiCl4: 3.0 to 4.0 mol%, CO: 0.5 to 1.0 mol%, N2: 30 to 40 mol%, H2: balance, at a temperature of 950 to 1050°C and a pressure of 50 to 150 hPa.

[0055] A Ti compound layer consisting of a Ti carbonate layer (hereinafter also referred to as a "TiCO layer") can be formed by a chemical vapor deposition method using a raw material composition of TiCl4: 1.0 to 2.0 mol%, CO: 2.0 to 3.0 mol%, and H2: balance, at a temperature of 950 to 1050°C and a pressure of 50 to 150 hPa.

[0056] The intermediate layer made of an α-Al2O3 layer (hereinafter simply referred to as an "Al2O3 layer") made of α-aluminum oxide is formed, for example, by the following method.

[0057] First, the surface of the layer farthest from the substrate among the lower layers is oxidized, and then an intermediate layer containing an α-Al2O3 layer is formed on the surface of the layer farthest from the substrate.

[0058] More specifically, the oxidation of the surface of the layer furthest from the substrate is carried out under conditions of a gas composition of 0.3 to 1.0 mol% CO2 and the balance H2, a temperature of 950 to 1050°C, and a pressure of 60 to 80 hPa (oxidation step). The oxidation treatment time is preferably 1 to 10 minutes.

[0059] Then, the α-Al2O3 layer is formed by chemical vapor deposition using a raw material gas composition of AlCl3: 2.0-5.0 mol%, CO2: 2.5-4.0 mol%, HCl: 2.0-3.0 mol%, H2S: 0.10-0.30 mol%, and H2: balance, at a temperature of 950-1050°C and a pressure of 60-80 hPa (film formation process).

[0060] Furthermore, an upper layer made of a Ti compound layer (for example, a TiCN layer and / or a TiCNO layer) is formed on the surface of the α-Al2O3 layer (upper layer forming step).

[0061] A Ti compound layer consisting of a Ti carbonitride layer (hereinafter also referred to as a "TiCN layer") can be formed by chemical vapor deposition using a raw material composition of TiCl4: 4.8 to 7.5 mol%, CH3CN: 0.4 to 1.0 mol%, C2H4: 0.6 to 1.0 mol%, N2: 5.0 to 12.5 mol%, H2: balance, at a temperature of 970 to 1020°C and a pressure of 80 to 120 hPa.

[0062] A Ti compound layer consisting of a Ti oxycarbonitride layer (hereinafter also referred to as a "TiCNO layer") can be formed by chemical vapor deposition using a raw material composition of TiCl4: 4.8 to 7.5 mol%, CO: 1.6 to 2.2 mol%, C2H4: 0.6 to 1.0 mol%, N2: 5.0 to 12.5 mol%, H2: balance, at a temperature of 970 to 1020°C and a pressure of 80 to 120 hPa.

[0063] In order to set the ratio of the length of the Σ11 grain boundary to 100% of the length of the CSL grain boundary in the upper layer to a specific value or more, for example, in the process of forming the upper layer (e.g., a TiCN layer and / or a TiCNO layer), the pressure or the proportion of C2H4 in the raw material composition can be controlled. More specifically, by lowering the pressure in the process of forming the upper layer, the ratio of the length of the Σ11 grain boundary to 100% of the length of the CSL grain boundary in the upper layer can be increased. Furthermore, by increasing the proportion of C2H4 in the raw material composition, the ratio of the length of the Σ11 grain boundary to 100% of the length of the CSL grain boundary in the upper layer can be increased. Furthermore, by using C2H4 as the raw material composition in the process of forming the upper layer (e.g., a TiCN layer and / or a TiCNO layer), the ratio of the length of the Σ11 grain boundary to the 100% length of the CSL grain boundary in the upper layer (n is an odd number between 3 and 29) can be maximized, and the ratio of the length of the Σ11 grain boundary to the 100% length of the CSL grain boundary in the upper layer can be increased.

[0064] Furthermore, in order to set the ratio of the CSL grain boundary length to 100% of all grain boundary lengths in the upper layer within a specific range, for example, the pressure or the proportion of H in the raw material composition may be controlled in the process of forming the upper layer (e.g., a TiCN layer and / or a TiCNO layer). More specifically, lowering the pressure in the process of forming the upper layer can increase the ratio of the CSL grain boundary length to 100% of all grain boundary lengths in the upper layer. Furthermore, increasing the proportion of H in the raw material composition can increase the ratio of the CSL grain boundary length to 100% of all grain boundary lengths in the upper layer.

[0065] On the surface of the upper layer, an outer layer can be formed, if desired, as follows. For example, a layer consisting of a Ti nitride layer (hereinafter also referred to as a "TiN layer") as an outer layer can be formed by chemical vapor deposition using a raw material composition of TiCl4: 2.0 to 6.0 mol%, N2: 10.0 to 30.0 mol%, H2: balance, at a temperature of 950 to 1050°C and a pressure of 400 to 500 hPa.

[0066] The thickness of each layer in the coating layer 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. The average thickness of each layer in the coated cutting tool of this embodiment can be determined as the arithmetic mean of measurements of the thickness of each layer at three or more locations in the vicinity of a position 50 μm from the cutting edge ridge toward the center of the flank face of the coated cutting tool. The composition of each layer in the coating layer of the coated cutting tool of this embodiment can be measured from the cross-sectional structure of the coated cutting tool using an energy dispersive X-ray spectrometer (EDS), a wavelength dispersive X-ray spectrometer (WDS), or the like.

[0067] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0068] The substrate was a cemented carbide alloy machined into an insert shape conforming to ISO standard CNMG120412 and having a composition of 87.0% WC-8.6% Co-2.0% TiN-2.0% NbC-0.4% Cr3C2 (all mass%). The cutting edge of this substrate was subjected to round honing with a SiC brush, and the surface of the substrate was then cleaned.

[0069] [Invention products 1-25 and comparison products 1-10] After cleaning the surface of the substrate, a coating layer was formed by chemical vapor deposition. First, the substrate was loaded into an externally heated chemical vapor deposition apparatus. Under the conditions of the source gas composition, temperature, and pressure shown in Table 1, lower layers with the compositions shown in Table 2 were formed on the surface of the substrate in the order of first layer, second layer, and third layer, to the average thickness shown in Table 2. Next, the surface of the lower layer was subjected to an oxidation treatment for 5 minutes under conditions of a gas composition of 0.5 mol% CO2 and 99.5 mol% H2, a temperature of 1000°C, and a pressure of 70 hPa. Next, under the conditions of the source gas composition, temperature, and pressure shown in Table 1, an intermediate layer made of α-type aluminum oxide was formed on the surface of the lower layer after the oxidation treatment to the average thickness shown in Table 2. Next, under the conditions of the source gas composition, temperature, and pressure shown in Table 3, an upper layer with the composition shown in Table 2 was formed on the surface of the intermediate layer to the average thickness shown in Table 2. For invention products 22 to 25, an outer layer made of TiN was further formed on the surface of the upper layer under the conditions of the raw material gas composition, temperature and pressure shown in Table 1 to have an average thickness shown in Table 2. In this way, coated cutting tools of invention products 1 to 25 and comparative products 1 to 10 were obtained.

[0070] [Table 1]

[0071] [Table 2]

[0072] [Table 3]

[0073] [Average thickness of each layer] The average thickness of each layer of the obtained sample was determined as follows. That is, using an FE-SEM, the thickness was measured at three locations on the cross section of the coated cutting tool, located 50 μm from the cutting edge ridge toward the center of the flank face, and the arithmetic mean value was calculated as the average thickness. The measurement results are shown in Table 2.

[0074] [Composition of each layer] The composition of each layer of the obtained sample was measured using EDS on a cross section of the coated cutting tool at a position 50 μm from the cutting edge ridge toward the center of the flank face. The measurement results are shown in Table 2.

[0075] [Grain boundary length] The ratio of the length of the Σ11 grain boundary to 100% of the length of the CSL grain boundary in the upper layer of the obtained sample and the ratio of the length of the CSL grain boundary to 100% of the length of all grain boundaries were measured as follows. The coated cutting tool was polished in a direction perpendicular to the surface of the substrate until the cross section of the upper layer was exposed, and the resulting observation surface was polished with colloidal silica to obtain a mirror-like observation surface.

[0076] The above-mentioned observation surface was then observed using an SEM equipped with EBSD. The observation area was the flank face.

[0077] The SEM used was an SU6600 (Hitachi High-Technologies Corporation) equipped with an EBSD (TexSEM Laboratories).

[0078] The normal to the observation surface was tilted 70° relative to the incident beam, and the analysis was performed by irradiating the electron beam with an accelerating voltage of 15 kV and a probe current of 1.0 nA. Data collection was performed by analyzing the crystal orientation of each grain in the upper layer within the measurement range, with an EBSD setting of 0.1 μm step size (distance between measurement points), over a measurement range of 50 μm parallel to the substrate surface and including the entire upper layer in the direction perpendicular to the substrate surface. Boundaries between measurement points with an orientation difference of 5° or more were considered grain boundaries.

[0079] Data processing was performed using commercially available software. The CSL grain boundaries corresponding to a given Σ value were counted and confirmed by expressing the ratio to all grain boundaries. From the above, the length of the CSL grain boundaries in the upper layer, the length of the Σn grain boundaries (n is an odd number between 3 and 29), and the total length of all grain boundaries were calculated. A total of three fields of view were analyzed within the measurement range on the observation surface described above, and the average values ​​were calculated. From the obtained average values, the Σn grain boundary in the upper layer with the largest length ratio (hereinafter referred to as "Σn with the largest Σn / CSL") was identified. Additionally, the ratio of the length of the Σ11 grain boundary to 100% of the CSL grain boundary length (hereinafter referred to as "Σ11 / CSL") and the ratio of the length of the CSL grain boundary to 100% of the total grain boundary length (hereinafter referred to as "CSL / total grain boundaries") were calculated. The results are shown in Table 4.

[0080] [Table 4]

[0081] Using the obtained invention products 1 to 25 and comparison products 1 to 10, cutting test 1 and cutting test 2 were carried out under the following conditions. Cutting test 1 is a chipping test to evaluate chipping resistance, and cutting test 2 is a wear test to evaluate wear resistance. The results of each cutting test are shown in Table 5.

[0082] [Cutting test 1] Workpiece: SCM415 round bar with two equally spaced grooves on the outer surface. Cutting speed: 200m / min, Feed: 0.30mm / rev, Cutting depth: 1.5mm, Coolant: Water-soluble coolant used, Evaluation item: The tool life was determined when the sample was chipped, and the number of impacts until the tool life was reached was measured. By observing the cutting edge of the tool with a stereo microscope (100x magnification) every 500 impacts, it was confirmed that chipping, which is the starting point, occurred before the sample was chipped.

[0083] [Cutting test 2] Work material: S45C round bar, Cutting speed: 200m / min, Feed: 0.40mm / rev, Cutting depth: 2.0 mm, Coolant: Water-soluble coolant used, Evaluation items: The tool life was determined when the sample was chipped or the maximum flank wear width reached 0.3 mm, and the machining time until the tool life was reached was measured.

[0084] In Cutting Test 1 (chipping test), the number of impacts until the tool life was reached was evaluated as "A" for 15,000 or more, "B" for 10,000 or more but less than 15,000, and "C" for less than 10,000. In Cutting Test 2 (wear test), the machining time until the tool life was reached was evaluated as "A" for 40 minutes or more, "B" for 30 minutes or more but less than 40 minutes, and "C" for less than 30 minutes. In this evaluation, "A" represents the best, followed by "B" for the best, and "C" for the worst. The more A or B a sample has, the better the cutting performance. The evaluation results are shown in Table 5.

[0085] [Table 5]

[0086] From the results shown in Table 5, the chipping test and abrasion test for the inventive product were both rated "A" or "B." On the other hand, the comparative product was rated "C" in both or either the chipping test and the abrasion test. Therefore, it can be seen that the chipping resistance and abrasion resistance of the inventive product are generally superior to those of the comparative product.

[0087] From the above results, it was found that the inventive product has excellent chipping resistance and wear resistance, resulting in a long tool life. [Industrial Applicability]

[0088] The coated cutting tool of the present invention has excellent chipping resistance and wear resistance, and can therefore extend the tool life compared to conventional tools, and from this viewpoint, has industrial applicability. [Explanation of symbols]

[0089] 1...substrate, 2...lower layer, 3...intermediate layer, 4...upper layer, 5...coating layer, 6...coated cutting tool.

Claims

1. A coated cutting tool comprising a substrate and a coating layer formed on a surface of the substrate, the coating layer includes a lower layer, an intermediate layer, and an upper layer laminated in this order from the substrate side toward the surface side of the coating layer, the lower layer contains a Ti compound layer made of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B; The intermediate layer is made of α-type aluminum oxide. 2 O 3 containing a layer, the upper layer contains a Ti compound layer made of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B; The average thickness of the entire coating layer is 10.0 μm or more and 25.0 μm or less, The average thickness of the upper layer is 1.2 μm or more and 6.0 μm or less, A coated cutting tool, wherein the ratio of the length of Σ11 grain boundaries to 100% of the length of CSL grain boundaries in the upper layer is 25% or more.

2. 2. The coated cutting tool according to claim 1, wherein a ratio of the length of the Σn grain boundary (n is an odd number of 3 to 29) to 100% of the length of the CSL grain boundary in the upper layer is the largest.

3. 3. The coated cutting tool according to claim 1, wherein a ratio of the length of the CSL grain boundary to 100% of the length of all grain boundaries in the upper layer is 20% or more and 60% or less.

4. The coated cutting tool according to claim 1 or 2, wherein the top layer comprises at least a TiCN layer and / or a TiCNO layer.

5. 3. The coated cutting tool according to claim 1, wherein the intermediate layer has an average thickness of 3.0 μm or more and 15.0 μm or less.

6. 3. The coated cutting tool according to claim 1, wherein the lower layer has an average thickness of 3.0 μm or more and 15.0 μm or less.

7. 3. The coated cutting tool according to claim 1, wherein the substrate is any one of cemented carbide, cermet, ceramics, and cubic boron nitride sintered body.

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