Coated cutting tools

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 Art

[0002] Conventionally, it is well known that a coated cutting tool obtained 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 operations on steel, cast iron, etc. As the above coating layer, for example, a coating layer composed of a single layer selected from the group consisting of Ti carbide, nitride, carbonitride, carbonate, and carbonitratooxide and aluminum oxide or a multilayer composed of two or more of them is known.

[0003] For example, Patent Document 1 discloses a coated cutting tool including a substrate and a coating layer formed on the surface of the substrate, wherein 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 one or more Ti compound layers composed 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 α-type Al2O3. The upper layer contains TiCN. The average thickness of the lower layer is 4.0 μm or more and 10.0 μm or less. The average thickness of the intermediate layer is 3.0 μm or more and 10.0 μm or less. The average thickness of the upper layer is 1.5 μm or more and 6.5 μm or less. The ratio of the length of Σ3 grain boundaries to the total length of all grain boundaries in a specific region of the upper layer is 20% or more and 60% or less. The ratio of the particles on the (111) plane of the upper layer is 30 area% or more.

[0004] Also, for example, Patent Document 2 discloses a surface-coated cutting tool obtained by vapor-depositing a hard coating layer composed of a Ti composite carbonitride layer having an average layer thickness of 1 to 10 μm 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 ultrahigh-pressure sintered material. (a) The Ti composite carbonitride layer Composition formula: TiC X N1-X When expressed as, The condition 0.2 ≤ X ≤ 0.5 (where X represents the 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 within the measurement range of the polished surface, and the tilt angle between the normal of the {100} plane, which is the crystal plane of the crystal grain, and the normal of the normal of the polished surface is measured. The measured tilt angles within the range of 0 to 45 degrees are divided into 0.25 degree increments, and the number of inclinations within each inclination is aggregated to form a tilt angle number distribution graph in which the highest peak exists in the tilt angle inclination range of 0 to 10 degrees, and the sum of the inclinations within the range of 0 to 10 degrees accounts for 60% or more of the total number of inclinations 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 within the measurement range of the polished surface, and the inclination angle between the normal to the {100} plane, which is the crystal plane of the crystal grain, and the normal to the normal to the polished surface 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 the lattice points, and based on the measured inclination angle obtained, the distribution of lattice points (common lattice points of constituent atoms) at the interface of mutually adjacent crystal grains, in which each of the constituent atoms shares one constituent atom between the crystal grains. A surface-coated cutting tool is described, characterized in that, when the number of constituent atom co-consistent lattice point configurations in which N lattice points that do not share constituent atoms exist between the aforementioned constituent atom co-consistent lattice points is represented by ΣN+1, the sum of the distribution ratios of each individual ΣN+1 in the total ΣN+1 (however, the upper limit of N is set to 28 due to frequency) is shown in the constituent atom co-consistent lattice point distribution graph, and the sum of the distribution ratios of Σ3, Σ5, Σ7, Σ9, Σ11, and Σ13 accounts for 70% or more of the sum of the distribution ratios of the total ΣN+1. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-37150 [Patent Document 2] Japanese Patent Publication No. 2009-142972 [Overview of the project] [Problems that the invention aims to solve]

[0006] In recent years, machining processes have increasingly involved higher feed rates and deeper cuts, requiring improved tool wear resistance and chipping resistance compared to conventional methods. In particular, machining steel under high feed rates and deep cuts is increasingly subjecting coated cutting tools to heavy loads. Under such harsh cutting conditions, conventional tools are prone to crack formation and propagation during cutting, leading to chipping. This, in turn, results in a problem where tool life cannot be extended. In this context, the coated cutting tool described in Patent Document 1 requires further improvements in wear resistance and chipping resistance. Furthermore, the coated cutting tool described in Patent Document 2 does not contain an α-Al2O3 layer made of α-type aluminum oxide, and therefore its wear resistance is insufficient. In addition, the ratio of the length of the Σ11 grain boundary to the length of the CSL grain boundary has not been considered, or the ratio is not sufficiently high, leaving room for improvement in chipping resistance.

[0007] 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 chipping resistance. [Means for solving the problem]

[0008] From the above perspective, the inventors conducted extensive research on extending the tool life of coated cutting tools and found that by configuring the coating layer in a specific way, the occurrence and propagation of cracks during cutting are suppressed, resulting in excellent chipping resistance. Furthermore, the adhesion between the intermediate layer and the upper layer is also improved. As a result, it is possible to achieve high wear resistance and chipping resistance over a long period of time in intermittent machining and high-feed machining of steel, and consequently, the tool life of coated cutting tools can be extended. This led to the completion of the present invention.

[0009] In other words, the gist of this 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, an intermediate layer, and an upper layer that are sequentially laminated from the substrate side toward the surface side of the coating layer. The lower layer contains a Ti compound layer made of Ti and at least one element selected from the group consisting of C, N, O, and B. The aforementioned intermediate layer contains an α-Al2O3 layer made of α-type aluminum oxide, The upper layer contains a Ti compound layer made 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 in which the ratio of the length of the Σ11 grain boundary to the length of the CSL grain boundary in the upper layer is 25% or more. [2] The coated cutting tool according to [1], wherein, among the ratios of the lengths of Σn grain boundaries (where n is an odd number between 3 and 29) to 100% of the length of the CSL grain boundaries in the upper layer, the ratio of the length of the Σ11 grain boundary 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 total grain boundary length 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 contains 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 average thickness of the intermediate layer is 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 average thickness of the lower layer is 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 a cemented carbide, a cermet, a ceramic, or a cubic boron nitride sintered body. [Advantages of the Invention]

[0010] According to the present invention, it is possible to provide a coated cutting tool that can extend the tool life by having excellent wear resistance and chipping resistance. [Brief Description of the Drawings]

[0011] [Figure 1] It is a schematic view showing an example of the coated cutting tool of the present invention. [Embodiments for Carrying Out the Invention]

[0012] Hereinafter, embodiments 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. However, 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. Furthermore, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[0013] The coated cutting tool of this embodiment is a coated cutting tool comprising a base material and a coating layer formed on the surface of the base material, wherein the coating layer includes a lower layer, an intermediate layer, and an upper layer that are sequentially laminated from the base material 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, and 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, and the ratio of the length of the Σ11 grain boundary to the length of the CSL grain boundary in the upper layer is 25% or more.

[0014] By having the above-described configuration, the coated cutting tool of the present embodiment can improve wear resistance and chipping resistance, and as a result, can extend the tool life. The reasons for the improvement in wear resistance and chipping resistance of the coated cutting tool of the present embodiment are considered as follows. However, the present invention is not limited by the following reasons. That is, first, the coated cutting tool of the present embodiment contains, as a lower layer of the coating layer, 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. When such a lower layer is provided between the substrate of the coated cutting tool of the present embodiment and an intermediate layer containing an α-Al2O3 layer made of α-type aluminum oxide, the wear resistance and adhesion are improved. Further, since the average thickness of the entire coating layer of the coated cutting tool of the present embodiment is 10.0 μm or more, it has excellent wear resistance, while since the average thickness of the entire coating layer is 25.0 μm or less, the adhesion of the coating layer is improved, so that it has excellent chipping resistance. Also, since the average thickness of the upper layer of the coated cutting tool of the present embodiment is 1.2 μm or more, it has excellent wear resistance, while since the average thickness of the upper layer is 6.0 μm or less, the adhesion of the coating layer is improved, so that it has excellent chipping resistance. Further, the upper layer of the coated cutting tool of the present embodiment 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, and since the ratio of the length of the Σ11 grain boundary to the length of the CSL grain boundary in the upper layer is 25% or more with respect to 100% of the length of the CSL grain boundary, the generation and progression of cracks during cutting are suppressed, so that it has excellent chipping resistance, and also the adhesion between the intermediate layer and the upper layer is improved, so that high wear resistance and chipping resistance are exhibited over a long period. And by combining these configurations, it is considered that the coated cutting tool of the present embodiment has improved wear resistance and chipping resistance, and as a result, can extend the tool life.

[0015] FIG. 1 is a cross-sectional schematic view showing an example of the coated cutting tool of the present embodiment. The coated cutting tool 6 has a substrate 1, and a coating layer 5 is formed on the surface of the substrate 1. In the coating layer 5, a lower layer 2, an intermediate layer 3, and an upper layer 4 are laminated upward in this order.

[0016] 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.

[0017] The base material used 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, a base material of cemented carbide, cermet, ceramics, or cubic boron nitride sintered body is preferable because it offers superior wear resistance and fracture resistance, and from a similar viewpoint, a cemented carbide base material is even more preferable.

[0018] 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.

[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, and excellent chipping resistance because the overall average thickness of the coating layer is 25.0 μm or less improves the adhesion of the coating layer. From a similar viewpoint, 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 entire coating layer from three or more cross-sections in each layer or the entire coating layer, and calculating the arithmetic mean.

[0020] [Lower layer] The lower layer used in this embodiment contains a Ti compound layer made of Ti and at least one element selected from the group consisting of C, N, O, and B. In the coated cutting tool of this embodiment, the abrasion resistance and adhesion are improved by providing such a lower layer between the base material and the intermediate layer containing an α-Al2O3 layer made of α-type aluminum oxide.

[0021] Examples of Ti compound layers 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 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 three layers. From the viewpoint of further improving wear resistance and adhesion, the lower layer preferably contains 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 if at least one of the lower layers is a TiCN layer. Furthermore, the coated cutting tool of this embodiment tends to have further improved adhesion if at least one of the lower layers 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 if at least one of the lower layers is a TiCNO layer and the TiCNO layer is formed to be in contact with an intermediate layer containing an α-Al2O3 layer. If the lower layer consists of three layers, a TiC layer or TiN layer may be formed as the first layer on the surface of the substrate, a TiCN layer may be formed as the second layer on the surface of the first layer, and a TiCNO layer or TiCO layer may be formed as the third layer on the surface of the second layer. In this case, the lower layer may consist of a TiN layer formed as the first layer on the surface of the substrate, a TiCN layer formed as the second layer on the surface of the first layer, and a TiCNO layer formed as the third layer on the surface of the second 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 due to the average thickness of the lower layer being 3.0 μm or more. 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 when the average thickness of the lower layer is 15.0 μm or less. From a similar viewpoint, the average thickness of the lower layer is preferably 4.5 μm or more and 14.5 μm or less. twist Preferably, the particle size is between 5.5 μm and 13.0 μm. Furthermore preferable.

[0024] In the lower layer used in this embodiment, for example, the average thickness of the TiC layer 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 fracture resistance. From the same viewpoint, the average thickness of the TiC layer or TiN layer is more preferably 0.10 μm or more and 0.5 μm or less, and even more 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 fracture resistance. From the same viewpoint, the average thickness of the TiCN layer is more preferably 3.3 μm or more and 13.0 μm or less, and even more preferably 4.0 μm or more and 12.5 μm or less.

[0026] In the lower layer used in this embodiment, for example, the average thickness of the TiCNO layer 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 fracture resistance. From the same viewpoint, the average thickness of the TiCNO layer or TiCO layer is 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.

[0027] The Ti compound layer in the lower layer is a Ti compound layer consisting of Ti and at least one element selected from the group consisting of C, N, O, and B, but it may also contain trace amounts of elements other than those mentioned above, as long as the effects of the lower layer are achieved.

[0028] [Middle class] 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, because the adhesion of the coating layer is improved. From a similar 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-type aluminum oxide, and may or may not contain components other than α-type aluminum oxide (α-Al2O3) as long as it achieves the effects of the present invention.

[0031] [Top layer] The upper layer used in this embodiment contains a Ti compound layer made of Ti and at least one element selected from the group consisting of C, N, O, and B. Preferably, the upper layer contains a Ti compound layer made of Ti and at least one element selected from the group consisting of Ti and 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 Σ11 grain boundary to the length of the Σn grain boundary (n is an odd number between 3 and 29) relative to 100% of the length of the CSL grain boundary in the upper layer so that the ratio of the length of the Σn grain boundary is maximized. Furthermore, it tends to have an excellent balance of wear resistance and chipping resistance.

[0032] Furthermore, in the coated cutting tool of this embodiment, the ratio of the length of the Σ11 grain boundary to the 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 made of Ti and at least one element selected from the group consisting of C, N, O, and B, and the ratio of the length of the Σ11 grain boundary to the length of the CSL grain boundary in the upper layer is 25% or more, which suppresses the occurrence and propagation of cracks during cutting, resulting in excellent chipping resistance, and also improves the adhesion between the intermediate layer and the upper layer, thus exhibiting high wear resistance and chipping resistance over a long period of time. From a similar viewpoint, the ratio of the length of the Σ11 grain boundary to the 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. On the other hand, from the viewpoint of ease of manufacture, the upper limit of the ratio of the length of the Σ11 grain boundary to the length of the CSL grain boundary in the upper layer is preferably 60% or less. 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.

[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. Normally, grain boundaries have many gaps and relatively high grain boundary energy because the arrangement of atoms is irregular and randomly arranged. On the other hand, some grain boundaries have regular arrangements of atoms and few gaps, and such grain boundaries have relatively low grain boundary energy. A typical example of such grain boundaries with relatively low grain boundary energy is the correspondence site lattice (CSL) grain boundary (hereinafter referred to as "CSL grain boundary" or "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, grain boundaries with low Σ values ​​are generally observed 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 upper layer and for improving them.

[0034] 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.

[0035] 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.

[0036] The CSL grain boundaries in the upper 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 the Σ11-grain boundary refers to the total length of the Σ11-grain boundaries in the field of view (a specific region) observed by a SEM equipped with EBSD.

[0037] 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 upper 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."

[0038] In the coated cutting tool of this embodiment, it is preferable that the ratio of the length of the Σ11 grain boundary is maximized among 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 in the upper layer. When the ratio of the length of the Σ11 grain boundary is maximized among 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 in the upper layer, the effect of increasing the ratio of the length of the Σ11 grain boundary to the length of the CSL grain boundary tends to be achieved more effectively and reliably.

[0039] Furthermore, in the coated cutting tool of this embodiment, the ratio of the length of CSL grain boundaries to 100% of the total grain boundary length in the upper layer is preferably 20% to 60%. In the coated cutting tool of this embodiment, if the ratio of the length of CSL grain boundaries to 100% of the total grain boundary length in the upper layer is 20% or more, the mechanical properties are improved and the progression of wear due to particle shedding is suppressed, resulting in a tendency towards excellent wear resistance. On the other hand, in the coated cutting tool of this embodiment, if the ratio of the length of CSL grain boundaries to 100% of the total grain boundary length in the upper layer is 60% or less, the coarsening of crystal grains can be suppressed, resulting in a tendency towards smaller surface roughness of the coating layer, and also a tendency towards even better wear resistance due to lower cutting resistance. From a similar viewpoint, the ratio of the length of CSL grain boundaries to 100% of the total grain boundary length 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] A 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. Methods for exposing the cross-section of the upper layer include, for example, cutting and polishing. Of these, polishing is preferred from the viewpoint of making the observation surface of the upper 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 upper 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 a flat surface (such as a flank) 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 at 70° 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 upper layer within the measurement range, using an EBSD setting of 0.1μm step size (distance between measurement points) for a measurement range of 50μm parallel to the substrate surface and the entire upper layer perpendicular to the substrate surface. At this time, the boundary between measurement points with an orientation difference of 5° or more was defined as a grain boundary.

[0045] Data processing is performed using commercially available software. The CSL grain boundaries corresponding to an arbitrary Σ value can be counted and confirmed by expressing them as a ratio to the total grain boundaries. From this, the length of the CSL grain boundaries, the length of the Σn grain boundaries (n is an odd number between 3 and 29) and the total length of all grain boundaries in the upper 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 "Σn grain boundary with the maximum length ratio among the ratio of the length of the Σn grain boundaries (n is an odd number between 3 and 29) to the length of the CSL grain boundaries" in the upper layer can be identified. In addition, the ratio of the length of the Σ11 grain boundaries to the length of the CSL grain boundaries and the ratio of the length of the CSL grain boundaries to the length of all grain boundaries 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, and excellent chipping resistance because the adhesion of the coating layer is improved when the average thickness of the upper layer is 6.0 μm or less. From a similar 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 Ti compound layer consisting of Ti and at least one element selected from the group consisting of C, N, O, and B, but it may also contain trace amounts of elements other than those mentioned above, as long as the effects of the upper layer are achieved.

[0048] [External layer] The coating layer used in this embodiment may include an outer layer on the interface opposite to the substrate of the upper layer (i.e., the surface of the upper layer). Examples of the outer layer include a layer of a compound consisting 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 (however, it is a different compound layer from the upper layer). It is preferable that the outer layer be such a compound layer, as it tends to make it easier to identify the corner that was used. Also, from a similar viewpoint, it is more preferable that the outer layer be a layer of a compound consisting 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 preferable that it be a layer of a compound consisting of at least one element selected from the group consisting of Ti, Cr, Al, and Si, and N, and particularly preferable that it be a TiN layer made 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 achieving the effects of the present invention more effectively and reliably, 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 by physical vapor deposition. Specific examples of methods for forming each layer include the following methods. However, the methods for forming each layer are not limited to these.

[0051] (Chemical vapor deposition) First, a lower layer consisting 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 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%, H2: the remainder, at a temperature of 850-950°C and a pressure of 350-450 hPa.

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

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

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

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

[0056] α-Al2O3, which consists of α-type aluminum oxide Layer These intermediate layers are formed, for example, by the following method.

[0057] First, the surface of the layer furthest from the substrate in the lower layer is oxidized. Then, an intermediate layer containing an α-Al2O3 layer is formed on the surface of the layer furthest from the substrate.

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

[0059] Subsequently, the α-Al2O3 layer is formed by chemical vapor deposition (film formation process) 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: the remainder, at a temperature of 950-1050°C and a pressure of 60-80 hPa.

[0060] Furthermore, an upper layer consisting of a Ti compound layer (e.g., a TiCN layer and / or a TiCNO layer) is formed on the surface of the α-Al2O3 layer (upper layer formation step).

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

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

[0063] To ensure that the ratio of the length of Σ11 grain boundaries to 100% of the length of CSL grain boundaries in the upper layer is above a specific value, for example, the pressure in the upper layer (e.g., TiCN layer and / or TiCNO layer) formation process can be controlled, or the proportion of C2H4 in the raw material composition can be controlled. More specifically, lowering the pressure in the upper layer formation process can increase the ratio of the length of Σ11 grain boundaries to 100% of the length of CSL grain boundaries in the upper layer. Also, the proportion of C2H4 in the raw material composition can be controlled. Combine Increasing this value allows for a larger ratio of the length of Σ11 grain boundaries to the length of 100% of the CSL grain boundaries in the upper layer. Furthermore, in the process of forming the upper layer (e.g., the TiCN layer and / or the TiCNO layer), by using C2H4 as the raw material composition, the ratio of the length of the Σ11 grain boundary to the length of the Σn grain boundary (where n is an odd number between 3 and 29) relative to 100% of the length of the CSL grain boundary in the upper layer tends to be maximized, thereby increasing the ratio of the length of the Σ11 grain boundary to the length of the CSL grain boundary in the upper layer.

[0064] Furthermore, in order to set the ratio of the length of CSL grain boundaries to 100% of the total grain boundary length in the upper layer to a specific range, for example, the pressure or the proportion of H2 in the raw material composition can be controlled during the upper layer (e.g., TiCN layer and / or TiCNO layer) formation process. More specifically, lowering the pressure during the upper layer formation process can increase the ratio of the length of CSL grain boundaries to 100% of the total grain boundary length in the upper layer. Also, the proportion of H2 in the raw material composition can be controlled. Combine Increasing this value allows for a larger ratio of the length of the CSL grain boundary to the total length of all grain boundaries in the upper layer.

[0065] An outer layer can be formed on the surface of the upper layer as needed, as follows. For example, a layer consisting of a Ti nitride layer (hereinafter also referred to as the "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: the remainder, 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 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 field emission scanning electron microscope (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 flank surface of the coated cutting tool, and calculating the arithmetic mean. Furthermore, the composition of each layer in the coating 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) or a wavelength-dispersive X-ray spectrometer (WDS).

[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] As the base material, a cemented carbide alloy with the composition 87.0%WC-8.6%Co-2.0%TiN-2.0%NbC-0.4%Cr3C2 (all by mass%) was prepared, machined into an insert shape of CNMG120412 (ISO standard). After round honing of the cutting edge of this base material with a SiC brush, the surface of the base material was cleaned.

[0069] [Inventions 1-25 and Comparative Products 1-10] 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 conditions of the raw material gas composition, temperature, and pressure shown in Table 1, the lower layer with the composition shown in Table 2 was formed on the surface of the substrate in the order of the first, second, and third layers, to the average thickness shown in Table 2. Next, under the conditions of a gas composition of CO2:0.5 mol%, H2:99.5 mol%, a temperature of 1000°C, and a pressure of 70 hPa, the surface of the lower layer was subjected to oxidation treatment for 5 minutes. Then, under the conditions of the raw material 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 oxidized lower layer to the average thickness shown in Table 2. Next, under the conditions of the raw material 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 inventions 22-25, an outer layer made of TiN was further formed on the surface of the upper layer to the average thickness shown in Table 2, under the raw material gas composition, temperature, and pressure conditions shown in Table 1. In this way, coated cutting tools of inventions 1-25 and comparative products 1-10 were obtained.

[0070] [Table 1]

[0071] [Table 2]

[0072] [Table 3]

[0073] [Average thickness of each layer] The average thickness of each layer in the obtained sample was determined as follows: Using FE-SEM, the thickness was measured at three points in the cross-section near a distance of 50 μm from the cutting edge of the coated cutting tool toward the center of the flank face, and the arithmetic mean of these measurements was calculated as the average thickness. The measurement results are shown in Table 2.

[0074] [Composition of each layer] The composition of each layer in the obtained sample was measured using EDS in a cross-section near the cutting edge of the coated cutting tool, at a distance of up to 50 μm from the center of the flank. 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 perpendicular to the surface of the substrate until the cross-section of the upper layer was exposed to obtain an observation surface. Furthermore, the obtained observation surface was polished using colloidal silica to obtain a mirror-finish observation surface.

[0076] Subsequently, the observation surface described above was observed using a SEM equipped with EBSD. The flank surface was observed as the observation area.

[0077] For the SEM, we used the SU6600 (manufactured by Hitachi High-Technologies Corporation) equipped with an EBSD (manufactured by TexSEM Laboratories).

[0078] 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 upper layer within the measurement range, using an EBSD setting of 0.1μm step size (distance between measurement points) for a measurement range of 50μm parallel to the substrate surface and the entire upper layer perpendicular to the substrate surface. At this time, the boundaries between measurement points with an orientation difference of 5° or more were defined as grain boundaries.

[0079] Data processing was performed using commercially available software. The CSL grain boundaries corresponding to an arbitrary Σ value were counted and confirmed by expressing them as a ratio to the total grain boundaries. From this, the lengths of the CSL grain boundaries, the Σn grain boundaries (n being an odd number between 3 and 29) and the total length of the total grain boundaries in the upper layer 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 value, the Σn grain boundary in the upper layer where the ratio of the length of the Σn grain boundary (n being an odd number between 3 and 29) to 100% of the length of the CSL grain boundaries is maximized (hereinafter also referred to as "Σn where Σn / CSL is maximized") was identified. In addition, the ratio of the length of the Σ11 grain boundaries to 100% of the length of the CSL grain boundaries in the upper layer (hereinafter also referred to as "Σ11 / CSL") and the ratio of the length of the CSL grain boundaries to 100% of the length of the total grain boundaries (hereinafter also referred to as "CSL / total grain boundary") were calculated. The results are shown in Table 4.

[0080] [Table 4]

[0081] Using the obtained inventions 1-25 and comparative products 1-10, cutting tests 1 and 2 were conducted under the following conditions. Cutting test 1 was a chipping test to evaluate chipping resistance, and cutting test 2 was a wear test to evaluate wear resistance. The results of each cutting test are shown in Table 5.

[0082] [Cutting Test 1] Workpiece: A round bar of SCM415 with two equally spaced grooves on its outer surface. Cutting speed: 200m / min, Feed rate: 0.30mm / rev, Cutting depth: 1.5mm, Coolant: Water-soluble coolant is used. 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. By observing the cutting edge of the tool with a stereomicroscope (100x magnification) every 500 impacts, it was confirmed that chipping, which is the starting point of chipping, occurs before the sample is damaged.

[0083] [Cutting Test 2] Workpiece material: S45C round bar, Cutting speed: 200m / min, Feed rate: 0.40mm / rev, Cutting depth: 2.0 mm, Coolant: Water-soluble coolant is used. 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, and the machining time until tool life was measured.

[0084] For the first cutting test (chipping test), the number of impacts until tool life was reached was evaluated as follows: 15,000 or more impacts was rated "A", 10,000 to less than 15,000 impacts was rated "B", and less than 10,000 impacts was rated "C". For the second cutting test (wear test), the machining time until tool life was reached was evaluated as follows: 40 minutes or more was rated "A", 30 minutes to less than 40 minutes was rated "B", and less than 30 minutes was rated "C". In this evaluation, "A" is the best, followed by "B", and "C" is the worst. The more A or B ratings a tool has, the better its cutting performance. The results of the evaluation are shown in Table 5.

[0085] [Table 5]

[0086] As shown in Table 5, the inventive product received an "A" or "B" rating in both the chipping test and the abrasion test. On the other hand, the comparative product received a "C" rating in both or either of the chipping and abrasion tests. 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] Based on these results, it was found that the invention exhibits excellent chipping resistance and wear resistance, resulting in a longer tool life. [Industrial applicability]

[0088] The coated cutting tool of the present invention has excellent chipping resistance and wear resistance, which extends tool life compared to conventional tools, and therefore has industrial applicability from this perspective. [Explanation of Symbols]

[0089] 1...Base material, 2...Lower layer, 3...Intermediate layer, 4...Upper layer, 5...Coating layer, 6...Coated cutting tool.

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, an intermediate layer, and an upper layer that are sequentially laminated from the substrate side toward the surface side of the coating layer. The lower layer contains a Ti compound layer made of Ti and at least one element selected from the group consisting of C, N, O, and B. The aforementioned intermediate layer is α-Al, which consists of α-type aluminum oxide. 2 O 3 It contains layers, The upper layer contains a Ti compound layer made of Ti and at least one element selected from the group consisting of C, N, O, and B. The Ti compound layer in the upper layer is a TiCN layer made of TiCN, or a TiCNO layer made of TiCNO. 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 in which the ratio of the length of the Σ11 grain boundary to the length of the CSL grain boundary in the upper layer is 25% or more and 58% or less.

2. The coated cutting tool according to claim 1, wherein the ratio of the length of the Σn grain boundary (where n is an odd number between 3 and 29) to the length of the CSL grain boundary in the upper layer is such that the ratio of the length of the Σ11 grain boundary is the largest.

3. The coated cutting tool according to claim 1 or 2, wherein the ratio of the length of the CSL grain boundary to 100% of the total grain boundary length 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 average thickness of the intermediate layer is 3.0 μm or more and 15.0 μm or less.

5. The coated cutting tool according to claim 1 or 2, wherein the average thickness of the lower layer is 3.0 μm or more and 15.0 μm or less.

6. The coated cutting tool according to claim 1 or 2, wherein the base material is a cemented carbide, cermet, ceramic, or cubic boron nitride sintered body.

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