Cutting tool

Abstract

The present invention is a cutting tool provided with a substrate and a coating film disposed on the substrate. The coating film includes a first layer disposed on the substrate and a second layer disposed directly on the first layer. The first layer has a multi-layer structure in which unit layers of two types, comprising a first unit layer and a second unit layer, are layered in alternation. The first unit layer comprises TiaAl1−a−bBbN and the second unit layer comprises TiN, where 0.30 ≤ a ≤ 0.50 and 0.005 ≤ b ≤ 0.10. In the first layer, the average percentage T1 of the number of titanium atoms to the total number of titanium and aluminum atoms is at least 60%. The average thickness of the first unit layer is at least 2 nm and no more than 50 nm, and the average thickness of the second unit layer is at least 2 nm and no more than 50 nm. In the first layer, the unit layer adjoining the second layer is the second unit layer, and the thickness of the first layer is at least 0.5 μm and no more than 5 μm. The second layer comprises TiCxN1−x, where 0.05 ≤ x ≤ 0.40. The second layer includes: a first region sandwiched between a first surface of the second layer which is on the surface side of the coating film, and a virtual plane P1 where the distance from the first surface to the second layer side is 10% of the film thickness of the second layer; and a second region sandwiched between an interface between the second layer and the first layer, and a virtual plane P2 where the distance from the interface to the second layer side is 40% of the film thickness of the second layer. In the first region, the average C1 of the percentage of the number of carbon atoms to the total number of carbon and nitrogen atoms is at least 25% and no more than 50%, and in the second region, the average C2 of the percentage of the number of carbon atoms to the total number of carbon and nitrogen atoms is at least 1% and no more than 10%. The thickness of the second layer is at least 0.5 μm and no more than 5.0 μm.

Description

cutting tools

[0001] The present disclosure relates to cutting tools.

[0002] BACKGROUND ART Conventionally, in order to improve the performance of cutting tools, development has been underway for coatings that coat the surfaces of substrates made of cemented carbide, cubic boron nitride sintered bodies, etc. (Patent Document 1).

[0003] International Publication No. 2020 / 213263

[0004] The cutting tool of the present disclosure is a cutting tool comprising a substrate and a coating provided on the substrate, wherein the coating includes a first layer provided on the substrate and a second layer provided directly on the first layer, the first layer having a multilayer structure in which two types of unit layers, consisting of a first unit layer and a second unit layer, are alternately stacked, and the first unit layer is made of Ti. ａ Al １－ａ－ｂ B ｂ the first unit layer is made of TiN, and the second unit layer is made of TiN, where 0.30≦a≦0.50 and 0.005≦b≦0.10; in the first layer, an average percentage T1 of the number of titanium atoms to the total number of titanium and aluminum atoms is 60% or more; the average thickness of the first unit layer is 2 nm or more and 50 nm or less; the average thickness of the second unit layer is 2 nm or more and 50 nm or less; in the first layer, the unit layer in contact with the second layer is the second unit layer, and the thickness of the first layer is 0.5 μm or more and 5 μm or less; and the second layer is made of TiC ｘ N １－ｘwherein 0.05≦x≦0.40, the second layer includes: a first region sandwiched between a first surface on the surface side of the coating of the second layer and an imaginary plane P1, the distance from the first surface to the second layer being 10% of the film thickness of the second layer; and a second region sandwiched between an interface between the second layer and the first layer and an imaginary plane P2, the distance from the interface to the second layer being 40% of the film thickness of the second layer, wherein in the first region, an average percentage C1 of the number of carbon atoms to the total number of carbon and nitrogen atoms is 25% or more and 50% or less, and in the second region, an average percentage C2 of the number of carbon atoms to the total number of carbon and nitrogen atoms is 1% or more and 10% or less, and the thickness of the second layer is 0.5 μm or more and 5.0 μm or less.

[0005] FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a cutting tool according to embodiment 1. FIG. 2 is an example of a first image obtained by observing the coating of the cutting tool according to embodiment 1 with a TEM. FIG. 3 is an enlarged view of the interface region between the first layer and the second layer within the frame indicated by A in FIG. 2. FIG. 4 is an example of a graph showing the results of line analysis of the coating of the cutting tool according to embodiment 1. FIG. 5 is a schematic cross-sectional view showing an example of the configuration of a film formation apparatus. FIG. 6 is a schematic cross-sectional view showing an example of the configuration of a film formation apparatus. FIG. 7 is a diagram for explaining a measurement area when measuring the diameter of the maximum inscribed circle of a crystal grain of the first layer. FIG. 8 is a diagram for explaining the positional relationship between the crystal grain and the first unit layer and the second unit layer.

[0006] [Problem to be Solved by the Present Disclosure] In recent years, there has been an increasing demand for cost reduction, and there is a demand for longer tool life. For example, cutting tools with long tool life are also required for machining stainless steel.

[0007] Therefore, an object of the present disclosure is to provide a cutting tool having a long tool life, particularly in machining stainless steel.

[0008] Effect of the Present Disclosure According to the present disclosure, it is possible to provide a cutting tool having a long tool life, particularly in machining stainless steel.

[0009] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. (1) A cutting tool of the present disclosure is a cutting tool including a substrate and a coating provided on the substrate, the coating including a first layer provided on the substrate and a second layer provided directly on the first layer, the first layer having a multilayer structure in which two types of unit layers, consisting of a first unit layer and a second unit layer, are alternately stacked, and the first unit layer is made of Ti. ａ Al １－ａ－ｂ B ｂ the first unit layer is made of TiN, and the second unit layer is made of TiN, where 0.30≦a≦0.50 and 0.005≦b≦0.10; in the first layer, an average percentage T1 of the number of titanium atoms to the total number of titanium and aluminum atoms is 60% or more; the average thickness of the first unit layer is 2 nm or more and 50 nm or less; the average thickness of the second unit layer is 2 nm or more and 50 nm or less; in the first layer, the unit layer in contact with the second layer is the second unit layer, and the thickness of the first layer is 0.5 μm or more and 5 μm or less; and the second layer is made of TiC ｘ N １－ｘ wherein 0.05≦x≦0.40, the second layer includes: a first region sandwiched between a first surface on the surface side of the coating of the second layer and an imaginary plane P1, the distance from the first surface to the second layer being 10% of the film thickness of the second layer; and a second region sandwiched between an interface between the second layer and the first layer and an imaginary plane P2, the distance from the interface to the second layer being 40% of the film thickness of the second layer, wherein in the first region, an average percentage C1 of the number of carbon atoms to the total number of carbon and nitrogen atoms is 25% or more and 50% or less, and in the second region, an average percentage C2 of the number of carbon atoms to the total number of carbon and nitrogen atoms is 1% or more and 10% or less, and the thickness of the second layer is 0.5 μm or more and 5.0 μm or less.

[0010] According to the present disclosure, it is possible to provide a cutting tool having a long tool life, particularly in machining stainless steel.

[0011] (2) In the above (1), the percentage C11 of the number of carbon atoms with respect to the total number of carbon and nitrogen atoms at the interface between the second layer and the first layer, the percentage C12 of the number of carbon atoms with respect to the total number of carbon and nitrogen atoms on the imaginary plane P2, the percentage C13 of the number of carbon atoms with respect to the total number of carbon and nitrogen atoms on the imaginary plane P1, and the percentage C14 of the number of carbon atoms with respect to the total number of carbon and nitrogen atoms on the first surface may have a relationship of C11<C12<C13<C14, thereby suppressing chipping of the coating.

[0012] (3) In the above (1) or (2), the thickness of the coating may be 1.0 μm or more and 10 μm or less. When the thickness of the coating is 1.0 μm or more, the wear resistance is improved. When the thickness of the coating is 10 μm or less, the chipping resistance is improved.

[0013] [Details of the Embodiments of the Present Disclosure] Specific examples of cutting tools according to the present disclosure will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference numerals represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been appropriately changed for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0014] In the present disclosure, the notation in the form of "A to B" means A or more and B or less, and when no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0015] In the present disclosure, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is intended to include any conventionally known atomic ratio, and should not necessarily be limited to only those within the stoichiometric range.

[0016] In the present disclosure, when one or more numerical values ​​are listed as the lower limit and the upper limit of a numerical range, the combination of any one numerical value listed as the lower limit and any one numerical value listed as the upper limit is also considered to be disclosed.

[0017] In this disclosure, "comprises," "includes," "has," and variations thereof are open-ended terms. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is closed-ended. However, even a configuration expressed in closed terms may include additional elements that are normally incidental impurities or unrelated to the subject technology.

[0018] [Embodiment 1: Cutting Tool] A cutting tool according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") will be described with reference to Figure 1. As shown in Figure 1, the cutting tool 100 of Embodiment 1 is a cutting tool 100 including a substrate 10 and a coating 20 provided on the substrate 10. The coating 20 includes a first layer 21 provided on the substrate 10 and a second layer 22 provided directly on the first layer 21. The first layer 21 has a multilayer structure in which two types of unit layers, namely, a first unit layer 1 and a second unit layer 2, are alternately stacked. The first unit layer 1 is made of Ti ａ Al １－ａ－ｂ B ｂ The first unit layer 1 is made of N. The second unit layer 2 is made of TiN. Here, 0.30≦a≦0.50 and 0.005≦b≦0.10. In the first layer 21, the average percentage T1 of the number of titanium atoms relative to the total number of titanium and aluminum atoms is 60% or more. The average thickness of the first unit layer 1 is 2 nm or more and 50 nm or less. The average thickness of the second unit layer 2 is 2 nm or more and 50 nm or less. In the first layer 21, the unit layer in contact with the second layer 22 is the second unit layer 2. The thickness of the first layer 21 is 0.5 μm or more and 5 μm or less. The second layer 22 is made of TiC ｘ N １－ｘwhere x is a number between 0.05 and 0.40. The second layer 22 includes a first region 22a sandwiched between a first surface 23 on the surface side of the coating 20 of the second layer 22 and an imaginary plane P1, the distance from the first surface 23 toward the second layer 22 being 10% of the film thickness of the second layer 22; and a second region 22b sandwiched between an interface 3 between the second layer 22 and the first layer 21 and an imaginary plane P2, the distance from the interface 3 toward the second layer 22 being 40% of the film thickness of the second layer 22. In the first region 22a, the average percentage C1 of the number of carbon atoms relative to the total number of carbon and nitrogen atoms is 25% or more and 50% or less. In the second region 22b, the average percentage C2 of the number of carbon atoms relative to the total number of carbon and nitrogen atoms is 1% or more and 10% or less. The thickness of the second layer 22 is 0.5 μm or more and 5.0 μm or less.

[0019] The cutting tool of the present disclosure can have a long tool life, and the reason for this is presumably as follows.

[0020] (i) The coating of the cutting tool of the present disclosure includes a first layer having a multilayer structure in which two types of unit layers, namely, first unit layers and second unit layers, are alternately stacked. The first unit layers and second unit layers have different compositions. This makes it possible to suppress the propagation of cracks from the surface of the coating that occur during use of the cutting tool near the interface between the first unit layer and the second unit layer.

[0021] (ii) The first unit layer is Ti ａ Al １－a－ｂ B ｂThe first unit layer is made of TiAlN (0.30≦a≦0.50 and 0.005≦b≦0.10). The hardness of the first unit layer is improved by adding a small amount of boron (B) to TiAlN. The second unit layer is made of TiN. The second unit layer has excellent high-temperature stability. In the present disclosure, the first layer has a multilayer structure in which high-hardness first unit layers and second unit layers with excellent high-temperature stability are alternately stacked, thereby providing stable hardness even at high temperatures and improving crater wear resistance. Crater wear is wear that occurs mainly on the rake face of a cutting tool due to frictional heat between the cutting tool and the chips. Furthermore, the first layer has a multilayer structure in which high-hardness first unit layers and second unit layers with a lower hardness than the first unit layers are alternately stacked, thereby improving chipping resistance. Therefore, the crater wear resistance and chipping resistance of the coating are improved in a balanced manner, and the tool life of the cutting tool is extended.

[0022] (iii) The first unit layer and the second unit layer have different compositions. Therefore, the first unit layer and the second unit layer have different crystal lattices, which causes distortion of the crystal lattice in the first layer, allowing the first layer to have high hardness. Therefore, a coating including the first layer can have excellent wear resistance.

[0023] (iv) In the first layer, the average percentage T1 of the number of titanium atoms relative to the total number of titanium and aluminum atoms is 60% or more, which allows the first layer to have excellent crater wear resistance and extends the tool life of the cutting tool.

[0024] (v) The coating of the cutting tool of the present disclosure is TiC ｘ N １－ｘ (0.05≦x≦0.40). The second layer has excellent lubricity. In the first region located on the surface side of the coating of the second layer, the average percentage C1 of the number of carbon atoms relative to the total number of carbon and nitrogen atoms is 25% or more and 50% or less. The first region on the surface side of the coating has extremely excellent lubricity. Therefore, even when using the cutting tool of the present disclosure to machine stainless steel, which is prone to welding, the occurrence of welding is suppressed. Therefore, the coating including the second layer has excellent welding resistance and can have excellent chipping resistance.

[0025] (vi) In the first layer, the unit layer in contact with the second layer is a second unit layer. In the second region in contact with the first layer, the average percentage C2 of the number of carbon atoms relative to the total number of carbon and nitrogen atoms is 1% or more and 10% or less. This improves adhesion between the second unit layer and the second region, and suppresses film peeling between the first layer and the second layer.

[0026] <Cutting Tool> The cutting tool of embodiment 1 is not particularly limited in shape, use, etc., as long as it is a cutting tool. The cutting tool of embodiment 1 may be, for example, a drill, an end mill, an indexable insert for milling, an indexable insert for turning, a metal saw, a gear cutting tool, a reamer, a tap, or an insert for pin milling of a crankshaft.

[0027] 1 is a schematic partial cross-sectional view showing an example of the configuration of a cutting tool according to Embodiment 1. The cutting tool 100 includes a substrate 10 and a coating 20 provided on the substrate 10. The coating 20 includes a first layer 21 provided on the substrate 10 and a second layer 22 provided directly on the first layer 21. The first layer 21 has a multilayer structure in which two types of unit layers, namely, first unit layers 1 and second unit layers 2, are alternately stacked.

[0028] <<Substrate>> The composition of the substrate is not particularly limited. The composition of the substrate may be, for example, cemented carbide, cermet, high-speed steel, ceramics, cubic boron nitride sintered body, or diamond sintered body. The substrate is preferably made of cemented carbide. This is because cemented carbide has excellent wear resistance.

[0029] A cemented carbide is a sintered body whose main component is tungsten carbide (WC) particles. The cemented carbide includes a hard phase and a binder phase. The hard phase contains WC particles. The binder phase bonds the WC particles together. The binder phase contains, for example, cobalt (Co). The binder phase may further contain titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), or the like.

[0030] The cemented carbide may contain impurities that are inevitably mixed in during the manufacturing process. The cemented carbide may also contain free carbon or an abnormal layer called an "η layer" in its structure. Furthermore, the cemented carbide may be subjected to a surface modification treatment. For example, the cemented carbide may include a de-β layer on its surface.

[0031] The cemented carbide may contain 85% by mass or more and 98% by mass or less of WC grains and 2% by mass or more and 15% by mass or less of Co. The WC grains may have an average grain size of 0.2 μm or more and 4 μm or less.

[0032] Co is softer than WC particles. As described below, the soft Co can be removed by subjecting the surface of the substrate to ion bombardment treatment. When the cemented carbide has the above composition and the WC particles have the above average particle size, appropriate irregularities are formed on the surface after the Co is removed. It is believed that forming a coating on such a surface produces an anchor effect, improving the adhesion between the coating and the substrate.

[0033] Here, the grain size of a WC grain refers to the diameter of a circle circumscribing a two-dimensional projected image of the WC grain. The grain size is measured using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). That is, the cemented carbide is cut and the cut surface is observed using an SEM or TEM. In the observed image, the diameter of the circle circumscribing the WC grain is regarded as the grain size of the WC grain. In the observed image, the grain sizes of 10 or more (preferably 50 or more, more preferably 100 or more) randomly selected WC grains are measured, and the arithmetic mean value is taken as the average grain size of the WC grains. Before the observation, it is desirable to process the cut surface with a cross section polisher (CP) or a focused ion beam (FIB) or the like.

[0034] <Coating> The coating is provided on the substrate. The coating may be provided on a portion of the surface of the substrate, or may be provided on the entire surface. However, the coating is provided on at least a portion of the surface of the substrate that corresponds to the cutting edge. In the present disclosure, the portion of the surface of the substrate that corresponds to the cutting edge means an area on the surface of the substrate that is within 0.5 mm or 2 mm from the cutting edge ridge. As long as the effects of the present disclosure are not impaired, it does not deviate from the scope of the present disclosure even if a coating is not formed on at least a portion of the portion that corresponds to the cutting edge.

[0035] The coating includes a first layer and a second layer. The first layer may be disposed directly on the substrate. The second layer may be the outermost layer of the coating. The coating may consist of a first layer disposed directly on the substrate and a second layer disposed directly on the first layer. The coating may include other layers in addition to the first and second layers, as long as the effects of the present disclosure are not impaired. For example, the coating may include one or both of a base layer disposed between the substrate and the first layer and a surface layer disposed on the outermost surface of the coating. The base layer may include at least one layer selected from the group consisting of a TiAlN layer, a TiAlSiN layer, and a TiAlBN layer. The surface layer may include at least one layer selected from the group consisting of a TiC layer, a TiN layer, and a TiCN layer.

[0036] The layer structure of the coating does not need to be uniform over the entire coating, and the layer structure may vary partially.

[0037] The thickness of the coating may be 1.0 μm or more and 10 μm or less, 1.5 μm or more and 9 μm or less, or 2.0 μm or more and 8 μm or less. The thickness of the coating refers to the sum of the thicknesses of the layers that make up the coating. Examples of "layers that make up the coating" include the first layer, second layer, base layer, and surface layer.

[0038] The thickness of each layer constituting the coating is measured by obtaining a thin section sample (hereinafter also referred to as a "cross-sectional sample") of a cross section parallel to the normal direction of the surface of the cutting tool and observing the cross-sectional sample with a scanning transmission electron microscope (STEM). An example of a scanning transmission electron microscope is the JEM-2100F (trade name) manufactured by JEOL Ltd. The cross-sectional sample is observed at a magnification of 5,000 to 10,000 times, and the thickness of each layer is measured at five locations, and the arithmetic average value is taken as the "thickness of each layer."

[0039] It has been confirmed that as long as measurements are made using the same cutting tool, there is no variation in the measurement results even if the measurement location is selected arbitrarily.

[0040] <First Layer> The first layer has a multilayer structure in which first unit layers and second unit layers are alternately stacked. The number of stacked layers is not particularly limited as long as the average thickness of each of the first unit layers and second unit layers is 2 nm to 50 nm. The number of stacked layers refers to the number of first unit layers and second unit layers included in the first layer. The number of stacked layers may be 10 to 5,000, 50 to 5,000, 250 to 2,000, or 500 to 1,000.

[0041] In the first layer, the unit layer in contact with the second layer is the second unit layer. In the first layer, the layer closest to the substrate may be either the first unit layer or the second unit layer.

[0042] The thickness of the first layer is 0.5 μm or more and 5 μm or less, or may be 0.6 μm or more and 4 μm or less, 0.7 μm or more and 3 μm or less, or 0.8 μm or more and 2 μm or less. When the thickness of the first layer is 0.5 μm or more, the wear resistance is improved. When the thickness of the first layer is 5 μm or less, the chipping resistance is improved.

[0043] <Average Thickness of First Unit Layer and Second Unit Layer> The average thickness of the first unit layer is 2 nm or more and 50 nm or less, and the average thickness of the second unit layer is 2 nm or more and 50 nm or less. By alternately stacking such thin layers in the first layer, crack propagation can be suppressed. If the average thickness of one or both of the first unit layer and the second unit layer is less than 2 nm, the compositions of the first unit layer and the second unit layer may be mixed, reducing the effect of suppressing crack propagation. If the average thickness of one or both of the first unit layer and the second unit layer is more than 50 nm, the effect of suppressing delamination may be reduced. The average thickness of the first unit layer and the average thickness of the second unit layer may be the same or different.

[0044] The average thickness of the first unit layer is 2 nm or more and 50 nm or less, and may be 4 nm or more and 40 nm or less, or may be 6 nm or more and 30 nm or less.

[0045] The average thickness of the second unit layer is 2 nm or more and 50 nm or less, and may be 4 nm or more and 40 nm or less, or may be 6 nm or more and 30 nm or less.

[0046] The method for measuring the average thickness of each of the first unit layer and the second unit layer is as follows. A thin section sample (hereinafter also referred to as a "cross-sectional sample") of the cross section of the cutting tool parallel to the normal direction of the surface of the cutting tool is obtained. The cross-sectional sample is observed with a scanning transmission electron microscope (STEM). An example of a scanning transmission electron microscope is the JEM-2100F (product name) manufactured by JEOL Ltd. The observation magnification of the cross-sectional sample is adjusted appropriately depending on the thickness of the first unit layer and the second unit layer. For example, the observation magnification can be approximately 1,000,000 times. The thickness is measured at five locations for one first unit layer. The arithmetic mean value of the thicknesses at the five locations of the first unit layer is calculated, and this arithmetic mean value is defined as the average thickness of the first unit layer. The thickness is measured at five locations for one second unit layer. The arithmetic mean value of the thicknesses at the five locations of the second unit layer is calculated, and this arithmetic mean value is defined as the average thickness of the second unit layer.

[0047] For each of five different first unit layers, the average thickness of the first unit layer is measured using the above procedure. The arithmetic mean value of the average thicknesses of the five first unit layers is determined. In the present disclosure, this arithmetic mean value is referred to as the average thickness of the first unit layer. For each of five different second unit layers, the average thickness of the second unit layer is measured using the above procedure. The arithmetic mean value of the average thicknesses of the five second unit layers is determined. In the present disclosure, this arithmetic mean value is referred to as the average thickness of the second unit layer.

[0048] It has been confirmed that as long as measurements are made using the same cutting tool, there is no variation in the measurement results even if the measurement location is selected arbitrarily.

[0049] <Composition of First Unit Layer and Second Unit Layer> In the cutting tool of the present disclosure, the first unit layer comprises Ti ａ Al １－ａ－ｂ B ｂ The second unit layer is made of TiN (0.30≦a≦0.50 and 0.005≦b≦0.10). The first unit layer is made of TiN. ａ Al １－ａ－ｂ B ｂ The first unit layer may contain inevitable impurities together with N. ａ Al １－ａ－ｂ B ｂ The second unit layer may be composed of TiN and unavoidable impurities. The second unit layer may contain TiN and unavoidable impurities, as long as the effects of the present disclosure are not impaired. The second unit layer may be composed of TiN and unavoidable impurities. Examples of the unavoidable impurities include carbon (C) and oxygen (O).

[0050] In the first unit layer, a may be in the range of 0.33≦a≦0.47, or 0.36≦a≦0.44.

[0051] In the first unit layer, b may be in the range of 0.01≦b≦0.09, or 0.02≦b≦0.08.

[0052] The compositions of the first unit layer and the second unit layer are measured using energy dispersive X-ray spectrometry (EDX). An EDX (TEM-DEX) attached to a transmission electron microscope (TEM) is used for composition analysis. An example of an EDX device is JED-2300 (trademark) manufactured by JEOL Ltd.

[0053] The composition analysis is performed as follows: A thin section sample (hereinafter also referred to as a "cross-sectional sample") is obtained from a cross section parallel to the normal direction of the cutting tool surface. While observing the cross-sectional sample with a TEM, EDX analysis is performed at five arbitrarily selected points within one first unit layer or one second unit layer. The first unit layer and the second unit layer can be distinguished by the difference in contrast. Here, the "five arbitrarily selected points" are selected from different crystal grains. The composition ratios of each element obtained from the measurements at the five points are arithmetically averaged to identify the respective compositions of the first unit layer and the second unit layer.

[0054] For each of the five different first unit layers, the composition of the first unit layer is determined by the above procedure. In the present disclosure, the average of the compositions of the five first unit layers is taken as the composition of the first unit layer, and based on this, Ti ａ Al １－ａ－ｂ B ｂ The a and b in N are identified. The composition of each of the five different second unit layers is identified using the above procedure. In the present disclosure, the average of the compositions of the five second unit layers is taken as the composition of the second unit layer.

[0055] It has been confirmed that as long as measurements are taken using the same cutting tool, there is no variation in the measurement results even if the measurement points are selected arbitrarily.

[0056] <<Composition of First Layer>> In the first layer, the average percentage T1 of the number of titanium atoms relative to the total number of titanium and aluminum atoms (hereinafter also referred to as "average T1") is 60% or more. This allows the first layer to have excellent crater wear resistance. The average T1 may be 60% or more and 80% or less, 63% or more and 77% or less, or 66% or more and 75% or less.

[0057] The average T1 is measured by TEM-EDX. An example of an EDX device is JED-2300 (product name) manufactured by JEOL Ltd. The average T1 is measured by the following procedure.

[0058] A thin section sample (hereinafter also referred to as a "cross-sectional sample") is obtained from a cross section parallel to the normal direction of the cutting tool surface. While observing the cross-sectional sample with a TEM, EDX analysis is performed on five arbitrarily selected fields of view within the first layer to measure the percentage T of titanium atoms relative to the total number of titanium and aluminum atoms. Here, the "five arbitrarily selected fields of view" are set so that they do not overlap with one another. The area of ​​one field of view is 200 × 200 nm. In the present disclosure, the arithmetic mean of the percentages T obtained by measuring the five fields of view is defined as the average T1 in the first layer.

[0059] It has been confirmed that as long as measurements are taken using the same cutting tool, there is no variation in the measurement results even if the measurement points are selected arbitrarily.

[0060] <Positional Relationship Between Crystal Grains and First and Second Unit Layers> The positional relationship between crystal grains and first and second unit layers will be described with reference to FIG. 8 . FIG. 8 is a schematic diagram illustrating a cross section of the first layer of embodiment 1 taken along the film thickness direction. As shown in FIG. 8 , the first layer 21 has a multilayer structure in which first unit layers 1 and second unit layers 2 are alternately stacked. FIG. 8 illustrates a plurality of crystal grains 24, and the boundaries between the crystal grains 24 are indicated as crystal grain boundaries 25. Each crystal grain 24 can be composed of only a first unit layer or only a second unit layer. Furthermore, each crystal grain 24 can exist across one or more first unit layers and one or more second unit layers. That is, each crystal grain 24 can have a lamellar structure in which first unit layers and second unit layers are alternately stacked.

[0061] <<Composition of the second layer>> The second layer is TiC ｘ N １－ｘ (0.05≦x≦0.40). When x is 0.05 or more, the lubricity of the second layer is improved. When x is 0.40 or less, the oxidation resistance is improved. In the present disclosure, the second layer is ｘ N １－ｘ (0.05≦x≦0.40) means that the average composition of the entire second layer is TiC ｘ N １－ｘ This means that (0.05≦x≦0.40).

[0062] In the second layer, x may be in the range of 0.10≦x≦0.35, or 0.15≦x≦0.30.

[0063] The composition of the second layer is measured by TEM-EDX. An example of a measuring device is JEM-ARM300F2 (product name) manufactured by JEOL Ltd. The specific measuring method is as follows.

[0064] A thin section sample (hereinafter also referred to as a "cross-sectional sample") of a cross section parallel to the normal direction of the surface of the cutting tool is obtained. A region of the coating in the cross-sectional sample is observed using a TEM under conditions of an acceleration voltage of 200 V and a magnification of 500,000 to 1,000,000 times to obtain a first image.

[0065] Fig. 2 is an example of a first image. As shown in Fig. 2, in the first image, the region of the laminate of the first unit layer 1 shown in a dark color and the second unit layer 2 shown in a light color corresponds to the first layer 21, and the light-colored layer directly above the first layer 21 corresponds to the second layer 22. If the interface between the second unit layer 2 and the second layer 22 is not clear in the first image due to a difference in contrast, the position of the interface between the first layer 21 and the second layer 22, which is located toward the second layer 22 from the main surface of the first unit layer 1 closest to the second layer 22, by the thickness of the second unit layer 2, is defined as the interface 3 between the first layer 21 and the second layer 22, as shown in Fig. 3.

[0066] In the first image, a line analysis is performed along a direction perpendicular to the surface of the coating, from the surface of the coating toward the interface between the first and second layers. Based on the results of the line analysis, a graph showing changes in the titanium, carbon, and nitrogen contents is obtained. The line analysis conditions are an acceleration voltage of 200 kV and a step size of 5 nm or less.

[0067] The average composition of the second layer is determined based on the line analysis results. Five non-overlapping first images are randomly acquired from the second layer, and the above-described line analysis is repeatedly performed based on each first image to determine the average composition of the second layer. In the present disclosure, the average of the five average compositions of the second layer is defined as the composition of the second layer.

[0068] It has been confirmed that as long as measurements are made using the same cutting tool, there is no variation in the measurement results even if the measurement location is selected arbitrarily.

[0069] <<First Region and Second Region of Second Layer>> The second layer includes a first region sandwiched between a first surface on the surface side of the second layer coating and an imaginary plane P1 where the distance from the first surface to the second layer side is 10% of the film thickness of the second layer. When the second layer is provided on the outermost surface of the coating, the first surface corresponds to the surface of the coating. When a surface layer is provided on the main surface on the surface side of the second layer coating, the first surface corresponds to the interface between the second layer and the surface layer.

[0070] In the first region, the average C1 (hereinafter also referred to as "average C1") of the percentage of the number of carbon atoms relative to the total number of carbon and nitrogen atoms is 25% or more and 50% or less, or may be 33% or more and 47% or less, or may be 36% or more and 44% or less.

[0071] The second layer includes a second region sandwiched between the interface between the second layer and the first layer and an imaginary plane P2 whose distance from the interface to the second layer side is 40% of the film thickness of the second layer.

[0072] In the second region, the average C2 (hereinafter also referred to as "average C2") of the percentage of the number of carbon atoms relative to the total number of carbon and nitrogen atoms is 1% or more and 10% or less, or may be 1% or more and 9% or less, or may be 2% or more and 8% or less.

[0073] The difference between C1 and C2, C1-C2, may be 15% or more and 49% or less, or 20% or more and 40% or less.

[0074] The method for measuring the average C1 and the average C2 is as follows. Line analysis of the second layer is performed using the same method as the method for measuring the composition of the second layer described above. Figure 4 is an example of a graph showing the results of line analysis. In Figure 4, the horizontal axis (X axis) represents the distance (µm) from the surface of the coating (the measurement start point), and the vertical axis (Y axis) represents the percentage of the number of carbon atoms relative to the total number of carbon and nitrogen atoms (denoted as "C / (C+N) [%]" in Figure 4).

[0075] Based on the line analysis results, an average C of the percentage of the number of carbon atoms relative to the total number of carbon and nitrogen atoms is calculated for each of the first and second regions.

[0076] In the second layer, five first images of non-overlapping fields are arbitrarily acquired, and the above-described line analysis is repeatedly performed based on each first image to determine the average C of the percentage of the number of carbon atoms relative to the total number of carbon and nitrogen atoms in each of the first and second regions. In the present disclosure, the average C of the five first regions is referred to as the average C1 of the percentage of the number of carbon atoms relative to the total number of carbon and nitrogen atoms in the first region. In the present disclosure, the average C of the five second regions is referred to as the average C2 of the percentage of the number of carbon atoms relative to the total number of carbon and nitrogen atoms in the second region.

[0077] It has been confirmed that as long as measurements are made using the same cutting tool, there is no variation in the measurement results even if the measurement location is selected arbitrarily.

[0078] The second layer is a single TiC ｘ N １－ｘ In one layer, the average C1 of the first region on the surface side of the coating and the average C2 of the second region in contact with the first layer are different. ｘ N １－ｘSince the layer is made of TiN and TiCN, unlike when a two-layer structure made of a TiN layer and a TiCN layer is formed on the first layer, peeling between the TiN layer and the TiCN layer, which is likely to occur in such a two-layer structure, does not occur, and chipping of the coating is suppressed.

[0079] In the cutting tool of embodiment 1, the percentage C11 of the number of carbon atoms with respect to the total number of carbon and nitrogen atoms at the interface between the second layer and the first layer, the percentage C12 of the number of carbon atoms with respect to the total number of carbon and nitrogen atoms on the imaginary plane P2, the percentage C13 of the number of carbon atoms with respect to the total number of carbon and nitrogen atoms on the imaginary plane P1, and the percentage C14 of the number of carbon atoms with respect to the total number of carbon and nitrogen atoms on the first plane may have a relationship of C11<C12<C13<C14.

[0080] C11 may be 0% or more and 4% or less, 0% or more and 3% or less, or 0% or more and 2% or less.

[0081] C12 may be 5% or more and 15% or less, 6% or more and 14% or less, or 7% or more and 13% or less.

[0082] C13 may be 20% or more and 40% or less, 22% or more and 38% or less, or 24% or more and 36% or less.

[0083] C14 may be 41% or more and 60% or less, 41% or more and 55% or less, or 41% or more and 50% or less.

[0084] The difference between C11 and C12, C12-C11, may be 1% or more and 15% or less, or may be 3% or more and 14% or less.

[0085] The difference between C12 and C13, C13-C12, may be 5% or more and 35% or less, or 8% or more and 32% or less.

[0086] The difference between C13 and C14, C14-C13, may be 1% or more and 40% or less, or 3% or more and 35% or less.

[0087] The difference between C11 and C14, C14-C11, may be 37% or more and 60% or less, or 38% or more and 55% or less.

[0088] C11, C12, C13, and C14 are measured by the above-mentioned line analysis. First images of five non-overlapping fields of view are arbitrarily acquired on the second layer, and the above-mentioned line analysis is repeatedly performed based on each first image to measure C11, C12, C13, and C14. In the present disclosure, the average of C11 in the five fields of view corresponds to C11 at the interface between the second layer and the first layer. In the present disclosure, the average of C12 in the five fields of view corresponds to C12 in the virtual plane P2. In the present disclosure, the average of C13 in the five fields of view corresponds to C13 in the virtual plane P1. In the present disclosure, the average of C14 in the five fields of view corresponds to C14 at the first surface.

[0089] It has been confirmed that as long as measurements are made using the same cutting tool, there is no variation in the measurement results even if the measurement location is selected arbitrarily.

[0090] The second layer includes a third region sandwiched between the first region and the second region. The composition of the third region is such that the composition of the second layer is TiC ｘ N １－ｘ In the third region, the average percentage C3 of the number of carbon atoms relative to the total number of carbon and nitrogen atoms may be, for example, 10% to 30%, 12% to 25%, or 14% to 20%.

[0091] The average percentage C3 of the number of carbon atoms relative to the total number of carbon and nitrogen atoms in the third region is measured in the same manner as the average percentage C1 of the number of carbon atoms relative to the total number of carbon and nitrogen atoms in the first region described above.

[0092] <Average Thickness of Second Layer> The average thickness of the second layer is 0.5 μm or more and 5.0 μm or less, and may be 0.7 μm or more and 4.0 μm or less, or may be 1.0 μm or more and 3.0 μm or less. When the average thickness of the second layer is 0.5 μm or more, the lubricity is improved. When the average thickness of the second layer is 5.0 μm or less, the chipping resistance is improved.

[0093] <Lattice Constants of First Region and Second Region> The lattice constant of the first region of the second layer may be 4.385 Å or more and 4.405 Å or less, or may be 4.385 Å or more and 4.395 Å or less.

[0094] The lattice constant of the second region of the second layer may be 4.355 Å or more and 4.380 Å or less, or 4.355 Å or more and 4.370 Å or less. When the lattice constant of the second region is 4.355 Å or more and 4.380 Å or less, the distortion of the lattice constant of the second region with respect to the lattice constant of 4.353 Å of TiN of the second unit layer is sufficiently small, and the lattice matching is improved, thereby further improving the adhesion between the first layer and the second layer.

[0095] The lattice constants of the first and second regions are determined from the diffraction spot of the cubic crystal (111) observed in the electron diffraction pattern of the TEM. The lattice constants of the first and second regions are determined at any three points within each region. In the present disclosure, the average of the lattice constants of the three first regions corresponds to the lattice constant of the first region. In the present disclosure, the average of the lattice constants of the three second regions corresponds to the lattice constant of the second region. Observation was performed at an accelerating voltage of 200 kV and a camera length of 10 cm, and the lattice constant was calculated with an electron beam wavelength of 2.508 pm.

[0096] [Embodiment 2: Manufacturing Method of Cutting Tool] In Embodiment 2, a method of manufacturing the cutting tool of Embodiment 1 will be described. The manufacturing method of Embodiment 2 can include a step of preparing a substrate and a step of forming a coating on the substrate. Details of each step will be described below.

[0097] <<Step of Preparing a Substrate>> In the step of preparing a substrate, a substrate is prepared. The substrate described in embodiment 1 can be used as the substrate.

[0098] <<Coating Forming Process>> In the coating forming process, a coating is formed on a substrate. In the second embodiment, the coating 20 can be formed by a physical vapor deposition (PVD) method. Specific examples of PVD methods include arc ion plating (AIP), balanced magnetron sputtering (BMS), and unbalanced magnetron sputtering (UBMS). In the second embodiment, arc ion plating is preferably used.

[0099] In the AIP method, an arc discharge is generated using a target material as a cathode. This vaporizes and ionizes the target material. The ions are then deposited on the surface of the substrate 10 to which a negative bias voltage is applied. The AIP method is excellent in terms of the ionization rate of the target material.

[0100] A film formation apparatus used in the AIP method will be described with reference to Figures 5 and 6. As shown in Figure 5, the film formation apparatus 200 includes a chamber 201. The chamber 201 is provided with a gas inlet 202 for introducing a source gas into the chamber 201 and a gas exhaust port 203 for exhausting the source gas from the chamber 201 to the outside. The gas exhaust port 203 is connected to a vacuum pump (not shown). The pressure inside the chamber 201 is adjusted by adjusting the amount of gas introduced and exhausted.

[0101] A rotary table 204 is disposed within the chamber 201. A substrate holder 205 for holding the substrate 10 is attached to the rotary table 204. The substrate holder 205 is connected to the negative terminal of a bias power supply 206. The positive terminal of the bias power supply 206 is grounded.

[0102] As shown in Fig. 6, a plurality of targets 211, 212, and 213 are attached to the side wall of the chamber 201. As shown in Fig. 5, each of the targets 211 and 212 is connected to the negative pole of a DC power supply 221 or 222, respectively. The DC power supplies 221 and 222 are variable power supplies, and their positive poles are earthed. Although not shown in Fig. 5, the same applies to the target 213. Specific operations will be described below.

[0103] The substrate 10 is held by the substrate holder 205. The pressure in the chamber 201 is reduced to 1.0×10 using a vacuum pump. -4 While the turntable 204 is being rotated, the temperature of the substrate 10 is adjusted to 500° C. by a heater (not shown) attached to the film forming apparatus 200 .

[0104] Ar gas is introduced from the gas inlet 202, and the pressure inside the chamber 201 is adjusted to 3.0 Pa. While maintaining this pressure, the voltage of the bias power supply 206 is gradually changed and finally adjusted to −1000 V. Then, the surface of the substrate 10 is cleaned by ion bombardment treatment using Ar ions.

[0105] Next, if the coating includes an underlayer, the underlayer is formed on the surface of the substrate 10. For example, a TiAlN layer, a TiAlSiN layer, or a TiAlBN layer is formed on the surface of the substrate 10.

[0106] Next, a first layer is formed on the surface of the substrate 10 or the surface of the underlayer. The composition of each target material is selected to obtain the compositions of the first and second unit layers. Each target material is set in a predetermined position, nitrogen gas is introduced through the gas inlet 202, and the first layer is formed while rotating the turntable 204. When forming the first layer, the substrate temperature is set to 600 to 800°C, the nitrogen gas pressure is set to 2 to 8 Pa, the bias power supply voltage is set to -200 to -30 V (DC power supply), and an arc current of 100 to 200 A is alternately supplied to the evaporation source for forming the first unit layer and the evaporation source for forming the second unit layer. This generates metal ions from the evaporation source for forming the first unit layer and the evaporation source for forming the second unit layer. When the substrate faces the evaporation source for forming the first unit layer, the first unit layer is formed, and when the substrate faces the evaporation source for forming the second unit layer, the second unit layer is formed. When forming the second layer, the thickness of each of the first and second unit layers is adjusted by adjusting the rotation speed of the substrate. Furthermore, the thickness of the second layer is adjusted to fall within a predetermined range by adjusting the film formation time.

[0107] Next, a second layer is formed on the first layer. When forming the second layer, the substrate temperature is set to 400 to 600°C, the reactive gas pressure is set to 5.0 to 10.0 Pa, the bias power supply voltage is set to -650 to -400 V (DC power supply), and an arc current of 100 A to 200 A is alternately supplied to the evaporation source for forming the second layer. The target material is composed of Ti. The target material is set in a predetermined position, and nitrogen gas and methane gas or acetylene gas are introduced as reactive gases through the gas inlet 202. The second layer is formed while rotating the turntable 204. The flow rate ratio of methane gas or acetylene gas to nitrogen gas in the reactive gas is adjusted to increase as the time from the start of second layer formation increases. For example, when nitrogen gas and methane gas are used as the reaction gas, the flow rate ratio of the nitrogen gas and methane gas in the reaction gas is adjusted to be in the range of nitrogen gas:methane gas=10:1 to 1:1 so that the flow rate ratio of methane gas to nitrogen gas in the reaction gas increases.

[0108] Next, when the coating includes a surface layer, the surface layer is formed, for example, on the surface of the first layer.

[0109] As described above, a cutting tool having a substrate and a coating provided on the substrate can be manufactured.

[0110] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0111] <Preparation of Cutting Tools> Cutting tools were prepared as follows, and the tool life was evaluated.

[0112] A cutting tip made of cemented carbide (model number: CNMG120408 (manufactured by Sumitomo Electric Hardmetal Corporation)) was prepared as a substrate. The cemented carbide contained WC particles (90% by mass) and Co (10% by mass). The average particle size of the WC particles was 1 to 2 μm.

[0113] A coating was formed on a substrate using a film-forming apparatus having the configuration shown in Figures 5 and 6. First, the surface of the substrate was cleaned by ion bombardment treatment with Ar ions. The specific conditions for the ion bombardment treatment were as described in embodiment 2.

[0114] Next, the target materials were set at predetermined positions in the film forming apparatus, and the compositions of the respective target materials were adjusted so as to obtain the compositions of the first and second unit layers shown in Tables 3 and 4, and the compositions of the second layers shown in Tables 5 and 6.

[0115] A first layer was formed on a substrate. Specifically, nitrogen gas was introduced through a gas inlet, and first and second unit layers were alternately formed while rotating the turntable. The substrate temperature was set to 700°C, the nitrogen gas pressure to 5 Pa, and the bias power supply voltage to -50 V (DC power supply). An arc current of 150 A was alternately supplied to the evaporation source for forming the first unit layer and the evaporation source for forming the second unit layer. The thickness and number of layers of each of the first unit layer and the second unit layer were adjusted by the rotation speed of the substrate so as to obtain the number of layers listed in Tables 3 and 4. The arc current value of each target material was appropriately adjusted for several seconds before the end of the first layer deposition so that the surface of the first layer became the second unit layer.

[0116] Next, a second layer was formed on the second unit layer of the first layer. Specifically, nitrogen gas and methane gas were introduced from the gas inlet, and the second layer was formed while the turntable was rotating. The conditions for forming the second layer of each sample were a substrate temperature of 500°C, a reactive gas pressure of 7 Pa, and an arc current of 150 A was supplied to the evaporation source for forming the second layer while the bias power supply voltage was oscillated between -600 and -500 V (DC power supply). Nitrogen gas and methane gas were introduced as reactive gases from the gas inlet 202, and the second layer was formed while the turntable 204 was rotating. As the time from the start of formation of the second layer increased, the percentage of the flow rate of methane gas relative to the total flow rate of nitrogen gas and methane gas (hereinafter referred to as the "flow rate ratio CH ４ / (N ２ +CH ４ ) was changed to the percentages shown in Tables 1 and 2 from "Start of Film Formation" to "End of Film Formation." ４ / (N ２ +CH ４ The thickness of the second layer was adjusted by the rotation speed of the substrate. By the above process, cutting tools for each sample were obtained.

[0117]

[0118]

[0119] <Evaluation> <Coating Structure> For each sample coating, the composition of the first unit layer and the second unit layer, the average thickness of each layer, the average percentage of titanium atoms (T1) relative to the total number of titanium and aluminum atoms in the first layer, the composition of the second layer, the average percentage of carbon atoms (C1) relative to the total number of carbon and nitrogen atoms in the first region, the average percentage of carbon atoms (C2) relative to the total number of carbon and nitrogen atoms in the second region, the percentage of carbon atoms (C11) relative to the total number of carbon and nitrogen atoms at the interface between the second layer and the first layer, the percentage of carbon atoms (C12) relative to the total number of carbon and nitrogen atoms on the virtual plane P2, the percentage of carbon atoms (C13) relative to the total number of carbon and nitrogen atoms on the virtual plane P1, the percentage of carbon atoms (C14) relative to the total number of carbon and nitrogen atoms on the first plane, and the lattice constants of the first and second regions were measured. The measurement methods for each item were as described in embodiment 1. The results are shown in Tables 3 to 6.

[0120]

[0121]

[0122]

[0123]

[0124] <Cutting Test 1> Turning was performed using the cutting tool of each sample under the following conditions, and the cutting time until the crater wear width reached 0.3 mm was measured. A longer cutting time indicates better crater wear resistance and a longer tool life. The results are shown in the "Cutting Time" column of "Cutting Test 1" in Tables 7 and 8.

[0125] <Cutting conditions> Workpiece: SUS316 round material Cutting speed: 150 m / min Feed rate: 0.2 mm / rev Depth of cut: 2.0 mm Wet The above cutting conditions apply to continuous turning of stainless steel.

[0126] <Cutting Test 2> Turning was performed using the cutting tool of each sample under the following conditions, and the cutting time until the width of the chipping measured from the flank face reached 0.5 mm or more was measured. A longer cutting time indicates better crater wear resistance and chipping resistance, and a longer tool life. The results are shown in the "Cutting Time" column of "Cutting Test 2" in Tables 7 and 8.

[0127] (Cutting conditions) Workpiece: SUS316 round material Cutting speed: 70 m / min Feed rate: 0.25 mm / rev Depth of cut: 1.0 mm Wet The above cutting conditions apply to intermittent turning of stainless steel.

[0128] <Evaluation Criteria for Tool Life> In the present disclosure, if the cutting time in Cutting Test 1 is 60 minutes or more and the cutting time in Cutting Test 2 is 30 minutes or more, the cutting tool is determined to have a long tool life in machining stainless steel.

[0129]

[0130]

[0131] <Discussion> The cutting tools of Samples 1 to 25 correspond to Examples. It was confirmed that these cutting tools have a long tool life when machining stainless steel.

[0132] The cutting tools of Samples 1-1 to 1-17 correspond to comparative examples, and it was confirmed that these cutting tools had insufficient tool life when machining stainless steel.

[0133] Although the embodiments and examples of the present disclosure have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined and modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0134] 1 First unit layer, 2 Second unit layer, 3 Interface, 10 Substrate, 20 Coating, 21 First layer, 22 Second layer, 22a First region, 22b Second region, 23 First surface, 24, 24a, 24b, 24c Crystal grain, 25 Crystal grain boundary, 50 Atom, 100 Cutting tool, 200 Film forming apparatus, 201 Chamber, 202 Gas inlet, 203 Gas exhaust port, 204 Rotary table, 205 Substrate holder, 206 Bias power supply, 211, 212, 213 Target material, 221, 222 DC power supply.

Claims

1. A cutting tool comprising a substrate and a coating provided on the substrate, wherein the coating includes a first layer provided on the substrate and a second layer provided directly on the first layer, the first layer having a multilayer structure in which two types of unit layers, consisting of a first unit layer and a second unit layer, are alternately stacked, and the first unit layer is made of Ti. ａ Al １－ａ－ｂ B ｂ N, the second unit layer is made of TiN, wherein 0.30≦a≦0.50 and 0.005≦b≦0.10, an average percentage T1 of the number of titanium atoms to the total number of titanium and aluminum atoms in the first layer is 60% or more, an average thickness of the first unit layer is 2 nm or more and 50 nm or less, an average thickness of the second unit layer is 2 nm or more and 50 nm or less, in the first layer, the unit layer in contact with the second layer is the second unit layer, a thickness of the first layer is 0.5 μm or more and 5 μm or less, and the second layer is made of TiC ｘ N １－ｘ wherein 0.05≦x≦0.40, the second layer includes: a first region sandwiched between a first surface on the surface side of the coating of the second layer and an imaginary plane P1, the distance from the first surface to the second layer being 10% of the film thickness of the second layer; and a second region sandwiched between an interface between the second layer and the first layer and an imaginary plane P2, the distance from the interface to the second layer being 40% of the film thickness of the second layer, wherein in the first region, an average percentage C1 of the number of carbon atoms to the total number of carbon and nitrogen atoms is 25% or more and 50% or less, and in the second region, an average percentage C2 of the number of carbon atoms to the total number of carbon and nitrogen atoms is 1% or more and 10% or less, and the thickness of the second layer is 0.5 μm or more and 5.0 μm or less.

2. The cutting tool according to claim 1, wherein a percentage C11 of the number of carbon atoms with respect to the total number of carbon and nitrogen atoms at the interface between the second layer and the first layer, a percentage C12 of the number of carbon atoms with respect to the total number of carbon and nitrogen atoms on the imaginary plane P2, a percentage C13 of the number of carbon atoms with respect to the total number of carbon and nitrogen atoms on the imaginary plane P1, and a percentage C14 of the number of carbon atoms with respect to the total number of carbon and nitrogen atoms on the first surface satisfy the relationship C11<C12<C13<C14.

3. A cutting tool according to claim 1 or 2, wherein the thickness of the coating is 1.0 μm or more and 10 μm or less.

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