Cutting tool

Abstract

The present invention provides a cutting tool comprising a base material and a coating disposed on the base material, wherein the coating includes a first layer, the first layer is formed from α-Al2O3, and the first layer is between 2 μm and 15 μm thick, inclusive. In a cross section along the normal to the interface between the base material and the coating, a ratio N2 / N1 is 0.60 or more, where N1 is the number of first grain boundaries traversed by an imaginary line L1 equidistant from the surface of the first layer or an interface on the surface side of the coating of the first layer and from the interface on the base material side of the first layer, and N2 is the number of second grain boundaries, which are grain boundaries among the first grain boundaries for which the angle to a line perpendicular to the imaginary line L1 has an absolute value of 15° or less at the position where the first grain boundary and the imaginary line L1 intersect. In the cross section along the normal to the interface between the base material and the coating, a ratio N4 / N3 and the ratio N2 / N1 satisfy the relation in expression 1, where N3 is the number of third grain boundaries traversed by an imaginary line L2 at a distance 0.5 μm away, in the direction of the base material, from the surface of the first layer or the interface on the surface side of the coating of the first layer, and N4 is the number of fourth grain boundaries, which are grain boundaries among the third grain boundaries for which the angle to a line perpendicular to the imaginary line L2 has an absolute value of 15° or less at the position where the third grain boundary and the imaginary line L2 intersect.

Description

cutting tools

[0001] The present disclosure relates to cutting tools.

[0002] Conventionally, a cutting tool has been disclosed that includes a substrate and a coating disposed on the substrate, the coating including a first layer, the first layer being α-Al ２ O ３ A cutting tool consisting of the above is used for cutting processing (Patent Document 1, Non-Patent Document 1).

[0003] International Publication No. 2015 / 114049

[0004] S. Ruppi et al. , “Influence of Process Conditions on the Growth and Texture of CVD Alpha-Alumina” Coatings 2020, 10, 158

[0005] The cutting tool of the present disclosure is a cutting tool including a substrate and a coating disposed on the substrate, the coating including a first layer, the first layer being α-Al ２ O ３ a thickness of the first layer is 2 μm or more and 15 μm or less, and in a cross section taken along a normal to an interface between the substrate and the coating, the ratio N2 / N1 of the number N2 of second grain boundaries, which are grain boundaries having an absolute value of an angle of 15° or less with respect to a line perpendicular to the imaginary line L1 at the position where the first grain boundary intersects with the imaginary line L1, to the number N1 of first grain boundaries crossed by the imaginary line L1 that is equidistant from the interface between the surface of the first layer or the surface side of the coating of the first layer and the interface between the first layer and the substrate side, is 0.60 or more, In the cross section taken along the normal to the interface between the substrate and the coating, the number N3 of third grain boundaries crossed by an imaginary line L2 that is 0.5 μm away from the surface of the first layer or the interface of the first layer on the surface side of the coating toward the substrate, and the ratio N4 / N3 of the number N4 of fourth grain boundaries that are grain boundaries that form an angle with a line perpendicular to the imaginary line L2 at the position where the third grain boundary intersects with the imaginary line L2 with an absolute value of 15° or less, and the ratio N2 / N1 satisfy the relationship of the following formula 1: 0.1≦(N2 / N1)−(N4 / N3)≦0.40 Formula 1

[0006] Fig. 1 is a schematic cross-sectional view illustrating one embodiment of the cutting tool of the present disclosure. Fig. 2 is a schematic cross-sectional view of an example of a CVD (Chemical Vapor Deposition) apparatus used in manufacturing the cutting tool of the present disclosure. Fig. 3 is an enlarged view of region III in Figs. 1 and 5. Fig. 4 is an enlarged view of region IV in Figs. 1 and 5. Fig. 5 is a schematic cross-sectional view illustrating another embodiment of the cutting tool of the present disclosure.

[0007] [Problem to be Solved by the Present Disclosure] In recent years, there has been an increasing demand for improved tool life. One important factor in improving tool life is "chipping resistance." The "chipping resistance" of a coating can be improved by performing a blasting treatment on the surface of the coating. However, when a blasting treatment is performed with the aim of imparting excellent "chipping resistance," peeling of the coating may occur, making it difficult to impart excellent "chipping resistance" to the coating. Furthermore, when a blasting treatment is performed at high pressure with the aim of imparting excellent "chipping resistance," α-Al ２ O ３ In the coating containing the layer, the α-Al ２ O ３ Since the edges of the crystals on the surface side of the coating of the layer are prone to fracture, it is difficult to perform the blasting treatment at high pressure, and it has been difficult to impart excellent chipping resistance to the coating. By imparting excellent chipping resistance to the coating, it is desired to impart excellent tool life to the cutting tool.

[0008] Therefore, an object of the present disclosure is to provide a cutting tool having an excellent tool life.

[0009] Effect of the Present Disclosure According to the present disclosure, it is possible to provide a cutting tool having an excellent tool life.

[0010] [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 disposed on the substrate, wherein the coating includes a first layer, and the first layer is made of α-Al. ２ O３ a thickness of the first layer is 2 μm or more and 15 μm or less, and in a cross section taken along a normal to the interface between the substrate and the coating, a ratio N2 / N1 of the number N2 of second grain boundaries, which are grain boundaries having an absolute value of an angle of 15° or less with respect to a line perpendicular to the imaginary line L1 at a position where the first grain boundary intersects with the imaginary line L1, to the number N1 of first grain boundaries crossed by the imaginary line L1 that is equidistant from the interface between the surface of the first layer or the surface side of the coating of the first layer and the interface between the first layer and the substrate side, is 0.60 or more, In the cross section taken along the normal to the interface between the substrate and the coating, the number N3 of third grain boundaries intersected by a virtual line L2 that is 0.5 μm from the surface of the first layer or the interface on the surface side of the coating of the first layer toward the substrate, and the ratio N4 / N3 of the number N4 of fourth grain boundaries that are grain boundaries whose absolute value of the angle with a line perpendicular to the virtual line L2 at the position where the third grain boundary intersects with the virtual line L2 is 15° or less, and the ratio N2 / N1 satisfy the relationship of the following formula 1: 0.1≦(N2 / N1)−(N4 / N3)≦0.40 Formula 1

[0011] According to the present disclosure, a cutting tool having an excellent tool life can be provided.

[0012] (2) In the above (1), the number N3 and the number N5 of fifth grain boundaries, which are grain boundaries among the third grain boundaries and which form angles with a line perpendicular to the virtual line L2 at positions where the third grain boundaries intersect with the virtual line L2, may satisfy the relationship of the following formula 2: (N5 / N3)>0.96 Formula 2 This makes it possible to provide a cutting tool with a longer tool life.

[0013] (3) In the above (1) or (2), the thickness of the first layer may be less than 8 μm, and the surface of the first layer or the surface of the first layer located at the interface with the coating on the surface side may have a surface roughness Ra of 0.03 μm or more and 0.2 μm or less. This makes it possible to provide a cutting tool with a longer tool life.

[0014] (4) In the above (1) or (2), the first layer may have a thickness of 8 μm or more, and the surface of the first layer or the surface of the first layer located at the interface with the coating on the surface side may have a surface roughness Ra of 0.05 μm or more and 0.2 μm or less. This makes it possible to provide a cutting tool with a longer tool life.

[0015] (5) In any one of the above (1) to (4), the absolute value of the compressive residual stress of the first layer may be 1.5 GPa or more and 4.0 GPa or less, thereby providing a cutting tool having a longer tool life.

[0016] (6) In any one of the above (1) to (5), the orientation index TC(0 0 12) of the first layer may be greater than 4.5, thereby providing a cutting tool with a longer tool life.

[0017] [Details of the embodiment of the present disclosure] A specific example of a cutting tool according to one embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference symbols represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been changed as appropriate for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0018] In the present disclosure, the notation in the form of "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and a unit is specified only for B, the units of A and B are the same.

[0019] 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.

[0020] [Embodiment 1: Cutting Tool] A cutting tool according to one embodiment of the present disclosure will be described with reference to Fig. 1 and Figs. 3 to 5. Fig. 1 is a schematic cross-sectional view illustrating one aspect of the cutting tool according to the present disclosure. Fig. 3 is an enlarged view of region III in Figs. 1 and 5. Fig. 4 is an enlarged view of region IV in Figs. 1 and 5. Fig. 5 is a schematic cross-sectional view illustrating another aspect of the cutting tool according to the present disclosure. One embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") is a cutting tool 10 including a substrate 1 and a coating 2 disposed on the substrate 1, wherein the coating 2 includes a first layer 3, and the first layer 3 is made of α-Al. ２ O ３ the thickness of the first layer 3 is 2 μm or more and 15 μm or less, and in a cross section taken along a normal to the interface between the substrate 1 and the coating 2, the number N1 of first grain boundaries crossed by an imaginary line L1 that is equidistant from the surface S1 of the first layer 3 or the interface of the first layer 3 on the surface side of the coating 2 and the interface I1 of the first layer 3 on the substrate 1 side, is 0.60 or more, and the ratio N2 / N1 of the number N2 of second grain boundaries that are grain boundaries whose absolute value of an angle with a line perpendicular to the imaginary line L1 at the position where the first grain boundary intersects with the imaginary line L1 is 15° or less, In the cross section taken along the normal to the interface between the substrate 1 and the coating 2, the number N3 of third grain boundaries intersected by an imaginary line L2 that is 0.5 μm away from the surface S1 of the first layer 3 or the interface of the first layer 3 on the surface side of the coating 2 toward the substrate 1, the number N4 of fourth grain boundaries that are grain boundaries whose absolute value of the angle with a line perpendicular to the imaginary line L2 at the position where the third grain boundary intersects with the imaginary line L2 is 15° or less, and the ratio N4 / N3 and the ratio N2 / N1 satisfy the relationship of the following formula 1: 0.1≦(N2 / N1)−(N4 / N3)≦0.40 Formula 1

[0021] According to the present disclosure, it is possible to provide a cutting tool 10 having an excellent tool life. The reason for this is presumably as follows.

[0022] (a) In the cutting tool 10 of this embodiment, in a cross section normal to the interface between the substrate 1 and the coating 2, the ratio N2 / N1 of the number of second grain boundaries N2, which are grain boundaries whose absolute angle with a line perpendicular to the imaginary line L1 at the intersection of the first grain boundaries and the imaginary line L1 is 15° or less, to the number N1 of first grain boundaries intersected by the imaginary line L1 equidistant from the surface S1 of the first layer 3 or the interface of the first layer 3 on the surface side of the coating 2 and the interface I1 of the first layer 3 on the substrate 1 side, is 0.60 or greater. This allows the crystals in the first layer 3 to be aligned in the same direction, enabling a uniform blast treatment. As a result, the chipping resistance of the cutting tool 10 can be improved.

[0023] (b) In the cutting tool 10 of this embodiment, in a cross section taken along the normal to the interface between the substrate 1 and the coating 2, the number N3 of third grain boundaries intersected by an imaginary line L2 that is 0.5 μm away from the surface S1 of the first layer 3 or the interface of the first layer 3 on the surface side of the coating 2 toward the substrate 1, the ratio N4 / N3 and the ratio N2 / N1 of the number N4 of fourth grain boundaries that are grain boundaries whose absolute value of the angle with a line perpendicular to the imaginary line L2 at the position where the third grain boundary intersects with the imaginary line L2 is 15° or less, satisfy the relationship of the following formula 1: 0.1≦(N2 / N1)−(N4 / N3)≦0.40 Equation 1 This makes it easier to suppress damage to the edge of the crystals on the surface S1 of the first layer 3 or on the interface on the surface side of the coating 2 of the first layer 3 when performing the blasting treatment, and since it is possible to perform the blasting treatment at high pressure, it is possible to impart excellent chipping resistance to the cutting tool 10.

[0024] As described above, according to the present disclosure, a cutting tool 10 having an excellent tool life can be provided.

[0025] 1 and 5 , a cutting tool 10 according to an embodiment of the present disclosure includes a substrate 1 and a coating 2 disposed on the substrate 1. The coating 2 preferably covers the entire surface of the substrate 1, but it does not depart from the scope of this embodiment even if a portion of the substrate 1 is not coated with the coating 2 or if the coating 2 has a partially different configuration. In cases where a portion of the substrate 1 is not coated with the coating 2, the coating 2 is preferably disposed so as to cover at least the surface of the portion of the substrate 1 involved in cutting. In this specification, the portion of the substrate 1 involved in cutting refers to the region of the substrate 1 surrounded by the cutting edge ridge and an imaginary surface that is, depending on the size and shape of the substrate 1, a distance from the cutting edge ridge toward the substrate 1 along a perpendicular to the tangent to the cutting edge ridge, for example, 5 mm, 3 mm, 2 mm, 1 mm, or 0.5 mm.

[0026] The cutting tool 10 of this embodiment can be suitably used as a cutting tool 10 such as a drill, an end mill, an indexable cutting tip for a drill, an indexable cutting tip for an end mill, an indexable cutting tip for a milling process, an indexable cutting tip for a turning process, a metal saw, a gear cutting tool, a reamer, a tap, etc.

[0027] <<Substrate>> Any conventionally known substrate 1 of this type can be used as the substrate 1. For example, the substrate 1 is preferably any one of cemented carbide (WC-based cemented carbide, cemented carbide containing WC and Co, cemented carbide containing carbonitrides of Ti, Ta, Nb, etc.), cermet (mainly composed of TiC, TiN, TiCN, etc.), high-speed steel, ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), cubic boron nitride sintered body, and diamond sintered body.

[0028] It is particularly preferable to select a WC-based cemented carbide or a cermet (particularly a TiCN-based cermet) from among these various substrates 1. These substrates 1 have an excellent balance between hardness and strength, particularly at high temperatures, and therefore, when used as the substrate 1 of a cutting tool 10, can contribute to extending the life of the cutting tool 10.

[0029] <Coating> The coating 2 includes a first layer 3. The coating 2 may consist solely of the first layer 3, or may include layers other than the first layer 3 ("other layers" described below) as long as the effects of the present disclosure are not impaired. The thickness of the coating 2 may be 7 μm or more and 25 μm or less, or 10 μm or more and 15 μm or less. If the thickness of the coating 2 is less than 7 μm, the coating 2 is too thin, which tends to shorten the life of the cutting tool 10. On the other hand, if the thickness of the coating 2 exceeds 25 μm, chipping of the coating 2 is likely to occur in the early stages of cutting, which tends to shorten the life of the cutting tool 10.

[0030] The thickness of the coating 2 can be measured by observing a cross section of the coating 2 along the normal direction to the surface of the coating 2 using a scanning electron microscope (SEM). Specifically, the cross section sample is observed at a magnification of 5,000 to 10,000 times, and the observation area is 100 to 500 μm ２ The thickness width is measured at any three points in any one visual field, and the average value is taken as the "thickness." The same applies to the thickness of each layer described below unless otherwise specified.

[0031] <First Layer> <Composition of First Layer> The first layer 3 is composed of α-Al ２ O ３ It consists of α-Al ２ O ３ "consisting of α-Al ２ O ３ It may consist of only α-Al, as long as the effect of the present disclosure is not impaired. ２ O ３ This means that the first layer 3 may contain inevitable impurities in addition to the above. Examples of the inevitable impurities include chlorine atoms (Cl) and sulfur atoms (S). The total content of the inevitable impurities in the first layer 3 may be, for example, 0% by mass or more and 0.10% by mass or less, or 0.01% by mass or more and 0.05% by mass or less.

[0032] The first layer 3 is α-Al ２ O ３The fact that the first layer 3 is made up of the above-mentioned components is identified by X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). The content of inevitable impurities in the first layer 3 is measured by secondary ion mass spectrometry (SIMS). It has been confirmed that, as long as measurements are performed using the same cutting tool 10, there is no variation in the measurement results even if the measurement location is arbitrarily selected.

[0033] <Thickness of First Layer> The thickness of the first layer 3 is 2 μm or more and 15 μm or less. The thickness of the first layer 3 may be 3 μm or more and 14 μm or less, 4 μm or more and 13 μm or less, or 5 μm or more and 12 μm or less.

[0034] <Surface Roughness Ra> The thickness of the first layer 3 is less than 8 μm, and the surface S1 of the first layer 3 or the surface of the first layer 3 located at the interface with the surface side of the coating 2 may have a surface roughness Ra of 0.03 μm or more and 0.2 μm or less. This makes it easier to impart uniform compressive residual stress to the cutting tool 10 by the blasting treatment, thereby imparting better chipping resistance and therefore better tool life to the cutting tool 10. When the thickness of the first layer 3 is less than 8 μm, the surface roughness Ra may be 0.03 μm or more and 0.15 μm or less, or 0.03 μm or more and 0.1 μm or less.

[0035] The thickness of the first layer 3 is 8 μm or more, and the surface S1 of the first layer 3 or the surface of the first layer 3 located at the interface with the coating 2 on the surface side may have a surface roughness Ra of 0.05 μm or more and 0.2 μm or less. This makes it easier to impart uniform compressive residual stress to the cutting tool 10 by the blasting treatment, thereby imparting better chipping resistance and therefore a longer tool life to the cutting tool 10. When the thickness of the first layer 3 is 8 μm or more, the surface roughness Ra may be 0.05 μm or more and 0.18 μm or less, or 0.06 μm or more and 0.15 μm or less.

[0036] The surface roughness Ra is measured in accordance with JIS B0601:2001 on a cross section of the cutting edge R taken along the normal direction to the interface between the substrate 1 and the coating 2. More specifically, first, an image is obtained of the cross section of the cutting edge R taken along the normal direction to the interface between the substrate 1 and the coating 2 using an SEM at a magnification of 1000x, including the surface S1 of the first layer 3 or the surface of the first layer 3 located at the interface on the surface side of the coating 2. Next, an arbitrary rectangular observation field of 10 μm × 10 μm is identified in the image at a magnification of 10,000x. In the observation field, "the surface S1 of the first layer 3 or the surface of the first layer 3 located at the interface on the surface side of the coating 2" is defined as passing through any pair of opposing sides. Next, image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ) is used to extract interface contour information for the observation field, thereby determining the "arithmetic mean roughness" of "the surface S1 of the first layer 3, or the surface located at the interface on the surface side of the coating 2 of the first layer 3" in the observation field. Next, the "arithmetic mean roughness" of "the surface S1 of the first layer 3, or the surface located at the interface on the surface side of the coating 2 of the first layer 3" is determined for any other four observation fields in the image. Next, the surface roughness Ra is determined by calculating the average value of the "arithmetic mean roughness" of "the surface S1 of the first layer 3, or the surface located at the interface on the surface side of the coating 2 of the first layer 3" in a total of five observation fields. Note that it has been confirmed that there is no variation in the measurement results even if the measurement location is arbitrarily selected, as long as the measurement is performed on the same first layer 3.

[0037] <Ratio N2 / N1> In a cross section taken along the normal to the interface between the substrate 1 and the coating 2, the ratio N2 / N1 of the number of second grain boundaries N2, which are grain boundaries whose absolute angle with a line perpendicular to the imaginary line L1 at the intersection of the first grain boundaries and the imaginary line L1 is 15° or less, to the number N1 of first grain boundaries intersected by the imaginary line L1 that is equidistant from the surface S1 of the first layer 3 or the interface of the first layer 3 on the surface side of the coating 2 and the interface I1 of the first layer 3 on the substrate 1 side, is 0.60 or more. This allows the cutting tool 10 to have excellent chipping resistance. The ratio N2 / N1 may be 0.60 or more and 1.0 or less, 0.7 or more and 1.0 or less, or 0.8 or more and 1.0 or less. 1 and 5, "the distance between the surface S1 of the first layer 3 or the interface of the first layer 3 on the surface side of the coating 2 and the virtual line L1" is denoted as D1. Also, in Figures 1 and 5, "the distance between the virtual line L1 and the interface I1 of the first layer 3 on the substrate 1 side" is denoted as D2. "The distance from the surface S1 of the first layer 3 or the interface of the first layer 3 on the surface side of the coating 2 and the interface I1 of the first layer 3 on the substrate 1 side are equal" can be rephrased as "D1 and D2 are equal."

[0038] Furthermore, the term "a grain boundary where the absolute value of the angle with respect to a line perpendicular to virtual line L1 at the position where the first grain boundary intersects with virtual line L1 is 15° or less" encompasses both a grain boundary GB ( FIG. 3 ) that slopes downward to the right with respect to the line as a reference and a grain boundary GB ( FIG. 4 ) that slopes upward to the right with respect to the line as a reference at the "intersection position." The term "a grain boundary where the absolute value of the angle with respect to a line perpendicular to virtual line L1 at the position where the first grain boundary intersects with virtual line L1 is 15° or less" refers to a grain boundary where the angle α in FIG. 3 is 15° or less and a grain boundary where the angle α in FIG. 4 is 15° or less. The same applies to the term "a grain boundary where the absolute value of the angle with respect to a line perpendicular to virtual line L2 at the position where the third grain boundary intersects with virtual line L2 is 15° or less," which will be described later, except that "first grain boundary" is replaced with "third grain boundary" and "virtual line L1" is replaced with "virtual line L2."

[0039] <Ratio N4 / N3> In a cross section taken along the normal to the interface between the substrate 1 and the coating 2, the ratio N4 / N3 of the number of fourth grain boundaries N4, which are grain boundaries whose absolute angle with a line perpendicular to the imaginary line L2 at the intersection of the third grain boundaries and the imaginary line L2 is 15° or less, to the number N3 of third grain boundaries intersected by the imaginary line L2 that is 0.5 μm from the surface S1 of the first layer 3 or the interface of the first layer 3 on the surface side of the coating 2 toward the substrate 1, may be 0.4 or more and 0.9 or less. This allows the cutting tool 10 to have a longer tool life. The ratio N4 / N3 may be 0.45 or more and 0.80 or less, 0.50 or more and 0.75 or less, or 0.55 or more and 0.70 or less. The term "a grain boundary at the position where the third grain boundary and the virtual line L2 intersect, the absolute value of the angle with respect to the line perpendicular to the virtual line L2 is 15° or less" is a concept that encompasses both a grain boundary that slopes downward to the right with respect to the line at the "intersection position" and a grain boundary that slopes upward to the right with respect to the line.

[0040] The ratios N2 / N1 and N4 / N3 can be determined by the following method: (A1) A color map is created based on the crystal orientation of each crystal grain by performing electron backscatter diffraction image analysis using a field emission scanning microscope on a cross section of the first layer 3 along the normal direction of the interface between the coating 2 and the substrate 1. (B1) Based on the color map created in (A1), the α-Al ２ O ３A first image is obtained by outputting the image with the areas where the first layer 3 is present as white and the other areas as black. Next, in order to remove noise, a moving average filter with a size of 15 x 15 pixels (i.e., 0.3 μm x 0.3 μm) is applied to the interface I1 on the substrate 1 side of the first layer 3 and the surface S1 of the first layer 3 or the interface on the surface side of the coating 2 of the first layer 3 to smooth the image, followed by Otsu's binarization. Next, each column of pixels in the first image after Otsu's binarization is observed in order from the substrate 1 side, and the area where the color changes from black to white is identified as the interface I1 on the substrate 1 side of the first layer 3. Next, the interface is fitted with a linear equation to obtain a line L3. Next, each column of pixels in the first image after Otsu's binarization is observed in order from the surface side of the coating 2, and the area where the color changes from black to white is identified as the interface S1 of the first layer 3 or the interface on the surface side of the coating 2 of the first layer 3. Next, a line L4 is obtained that is parallel to the line L3 and has the smallest sum of squares of the error at the "surface S1 of the first layer 3 or the interface on the surface side of the coating 2 of the first layer 3." Next, a line that is equidistant from the lines L3 and L4 is obtained as a virtual line L1. A line that is 0.5 μm away from the line L4 toward the substrate 1 is obtained as a virtual line L2. (C1) Based on the color map created in (A1), a second image is obtained by outputting an image in which the grain boundaries are colored black and the other areas are colored white. (D1) By superimposing the second image and the first image, the locations corresponding to the virtual line L1 obtained in (B1) and the virtual line L2 obtained in (B1) are identified in the second image. (E1) In the second image in which the location corresponding to the virtual line L1 obtained in (B1) and the location corresponding to the virtual line L2 obtained in (B1) are identified, the coordinates of the grain boundary are calculated by image processing for any one rectangular field of view (field of view size: 40 μm × 25 μm) using as a reference a straight line parallel to the interface I1 on the substrate 1 side of the first layer 3. Based on the coordinates, the inclination of the grain boundary (in other words, the angle of the grain boundary) is determined.(F1) In the rectangular field of view of (E1), the number N1 of first grain boundaries crossed by the virtual line L1 and the number N2 of second grain boundaries, which are grain boundaries that have an absolute value of an angle with respect to a line perpendicular to the virtual line L1 of 15° or less at the position where the first grain boundary and the virtual line L1 intersect, are identified. Next, N2 is divided by N1 to determine the ratio N2 / N1. Also, in the rectangular field of view of (E1), the number N3 of third grain boundaries crossed by the virtual line L2 and the number N4 of fourth grain boundaries, which are grain boundaries that have an absolute value of an angle with respect to a line perpendicular to the virtual line L2 of 15° or less at the position where the third grain boundary and the virtual line L2 intersect, are identified. Next, N4 is divided by N3 to determine the ratio N4 / N3.

[0041] It has been confirmed that as long as measurements are made on the same first layer 3, there is no variation in the measurement results even if the measurement location is arbitrarily selected.

[0042] <Relationship between Ratio N2 / N1 and Ratio N4 / N3> The ratio N4 / N3 and the ratio N2 / N1 satisfy the relationship of the following formula 1: 0.1≦(N2 / N1)−(N4 / N3)≦0.40 Formula 1 This makes it possible to impart excellent chipping resistance to the cutting tool 10. "(N2 / N1)−(N4 / N3)" may be 0.1 or more and 0.35 or less, 0.1 or more and 0.30 or less, or 0.1 or more and 0.20 or less.

[0043] <Ratio N5 / N3> The number N3 and the number N5 of fifth grain boundaries, which are third grain boundaries that, at the positions where the third grain boundaries intersect with virtual line L2, form angles with a line perpendicular to virtual line L2 whose absolute value is 45° or less, may satisfy the relationship in the following formula 2: (N5 / N3)>0.96 Formula 2 This makes it possible to reduce the number of third grain boundaries in the surface region of the first layer coating that form angles with a line perpendicular to virtual line L2 whose absolute value exceeds 45° at the positions where the third grain boundaries intersect with virtual line L2 (i.e., grain boundaries with a large absolute value of the angle), thereby suppressing the occurrence of coating damage and coating peeling when subjected to strong blasting, and thereby imparting a longer tool life to cutting tool 10. "N5 / N3" may be greater than 0.96 and equal to or less than 1.00, may be 0.97 or greater and equal to or less than 1.00, or may be 0.98 or greater and equal to or less than 1.00.

[0044] "N5 / N3" can be determined by the following method. It can be determined in the same way as N4 / N3, except that the number N5 of fifth grain boundaries, which are grain boundaries whose absolute angle with respect to a line perpendicular to the virtual line L2 is 45° or less, is determined, and the ratio N5 / N3 is calculated by dividing N5 by N3. Note that, as long as measurements are performed on the same first layer 3, it has been confirmed that there is no variation in the measurement results even if the measurement location is arbitrarily selected.

[0045] All of the third grain boundaries may have angles of less than 45° relative to a line perpendicular to the imaginary line L2 at the positions where the third grain boundaries intersect with the imaginary line L2. This can provide a longer tool life for the cutting tool 10. The third grain boundaries do not have to include any grain boundaries that have angles of 45° or more relative to a line perpendicular to the imaginary line L2 at the positions where the third grain boundaries intersect with the imaginary line L2. This can provide a longer tool life for the cutting tool 10.

[0046] <Compressive Residual Stress of First Layer> The absolute value of the compressive residual stress of the first layer 3 may be 1.5 GPa or more and 4.0 GPa or less. This can provide the cutting tool 10 with a longer tool life. The compressive residual stress of the first layer 3 is a type of internal stress (intrinsic strain) present throughout the first layer 3 and is expressed as a negative (-) value (unit: GPa is used in this embodiment). Therefore, a high compressive residual stress refers to a larger absolute value of the value, and a low compressive residual stress refers to a smaller absolute value of the value. In other words, an absolute value of the compressive residual stress of 1.5 GPa or more and 4.0 GPa or less means that the compressive residual stress related to the first layer 3 is -4.0 GPa or more and -1.5 GPa or less. The absolute value of the compressive residual stress of the first layer 3 may be 1.8 GPa or more and 3.5 GPa or less, or 2.0 GPa or more and 3.0 GPa or less.

[0047] The compressive residual stress of the first layer 3 can be measured by the sin2ψ method using an X-ray residual stress device (see pages 54-66 of "X-ray Stress Measurement Method" (Japan Society of Materials Science, published by Yokendo Co., Ltd. in 1981)).

[0048] <Orientation Index TC(0 0 12) of First Layer> The orientation index TC(0 0 12) of the first layer 3 may be greater than 4.5. ２ O ３ The improved strength of the crystal grains can further improve the wear resistance, thereby providing a longer tool life for the cutting tool 10. The orientation index TC(0 0 12) of the first layer 3 may be greater than 4.5 and equal to or less than 8.0, equal to or greater than 5.0 and equal to or less than 7.9, or equal to or greater than 6.0 and equal to or less than 7.9.

[0049] In this specification, the "orientation index TC(0 0 12) of the first layer 3" means the orientation index TC(0 0 12) of the (0 0 12) plane in the first layer 3, among the orientation indexes TC(hkl) defined by the following formula 3:

[0050]

[0051] In Equation 3, I(hkl) represents the X-ray diffraction intensity of the (hkl) reflection plane, and I ０ (hkl) indicates the standard intensity according to ICDD PDF card number 00-010-0173. Furthermore, n in Equation 3 indicates the number of reflections used in the calculation, which is 8 in this embodiment. The (hkl) planes used for reflection are (012), (104), (110), (0 0 12), (113), (214), (116), and (300).

[0052] ICDD (registered trademark) is an abbreviation for International Centre for Diffraction Data, and PDF (registered trademark) is an abbreviation for Powder Diffraction File.

[0053] The orientation index TC (0 0 12) of the first layer 3 in this embodiment can be expressed by the following formula 4.

[0054]

[0055] Therefore, "the orientation index TC(0 0 12) of the first layer 3 is greater than 4.5" means that the value obtained by substituting TC(0 0 12) into the above formula 3 to obtain formula 4 is greater than 4.5.

[0056] The above-described TC(hkl) can be measured by analysis using an X-ray diffraction device. TC(hkl) can be measured, for example, using Rigaku Corporation's SmartLab (registered trademark) (scan speed: 21.7° / min, step: 0.01°, scan range: 15-140°) under the following conditions. In this embodiment, the results of TC(hkl) measurement using an X-ray diffraction device are referred to as "XRD results." (Conditions) Characteristic X-rays: Cu-Kα Tube voltage: 45 kV Tube current: 200 mA Filter: Multilayer mirror Optical system: Focusing method X-ray diffraction method: θ-2θ method When using an X-ray diffraction device, X-rays are irradiated onto the rake face of a cutting tool. Since the rake face is usually uneven, while the flank face is flat, it is preferable to irradiate the X-rays onto the flank face to eliminate external disturbances. In particular, X-rays are irradiated onto a portion of the flank extending from the cutting edge ridge to a range of approximately 2 to 4 mm. This increases the reproducibility of the results. In this embodiment, the value of the orientation index TC(hkl) of the first layer 3 on the flank of the substrate is the same as the value of TC(hkl) of the first layer 3 on the rake face of the substrate.

[0057] It was confirmed that similar results could be obtained by arbitrarily selecting multiple measurement points on the same sample and performing the above measurements on each of the measurement points.

[0058] Other Layers Examples of the other layers include a base layer (FIG. 5), an intermediate layer (not shown), and a surface layer (not shown). The base layer is a layer in contact with the substrate 1. The surface layer is a layer located on the surface of the coating 2. The intermediate layer is a layer disposed between the base layer and the first layer 3 or a layer disposed between the first layer 3 and the surface layer.

[0059] <Underlayer> The underlayer may be made of TiN or TiCN. "Made of TiN or TiCN" means that the underlayer may be made of only TiN or TiCN, or may contain inevitable impurities in addition to TiN or TiCN. Here, examples of inevitable impurities include chlorine atoms (Cl), oxygen atoms (O), cobalt atoms (Co), tungsten atoms (W), nickel atoms (Ni), and boron atoms (B). The total content of inevitable impurities in the underlayer may be, for example, 0% by mass or more and 1.0% by mass or less, or 0.3% by mass or more and 0.6% by mass or less.

[0060] The underlayer is determined to be composed of TiN or TiCN by X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). The content of inevitable impurities in the underlayer is measured by secondary ion mass spectrometry (SIMS). It has been confirmed that, as long as measurements are performed on the same underlayer, there is no variation in the measurement results even if measurement locations are arbitrarily selected.

[0061] The thickness of the underlayer may be 0.1 μm or more and 2.0 μm or less, 0.5 μm or more and 1.5 μm or less, or 0.8 μm or more and 1.3 μm or less.

[0062] <Intermediate Layer> The intermediate layer may be made of TiCN. "Made of TiCN" means that the intermediate layer may consist only of TiCN, or may contain inevitable impurities in addition to TiCN. Examples of inevitable impurities include chlorine atoms (Cl), oxygen atoms (O), cobalt atoms (Co), tungsten atoms (W), nickel atoms (Ni), and boron atoms (B). The total content of inevitable impurities in the intermediate layer may be, for example, 0% by mass or more and 1.0% by mass or less, or 0.3% by mass or more and 0.6% by mass or less.

[0063] The intermediate layer is determined to be composed of TiCN by X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). The content of inevitable impurities in the intermediate layer is measured by secondary ion mass spectrometry (SIMS). It has been confirmed that, as long as measurements are performed on the same intermediate layer, there is no variation in the measurement results even if the measurement location is arbitrarily selected.

[0064] The thickness of the intermediate layer may be 2.0 μm or more and 10 μm or less, or 4.0 μm or more and 8.0 μm or less.

[0065] <Surface Layer> The surface layer may be made of TiN. "Made of TiN" means that the surface layer may consist of only TiN, or may contain inevitable impurities in addition to TiN. Here, examples of inevitable impurities include chlorine atoms (Cl), oxygen atoms (O), cobalt atoms (Co), tungsten atoms (W), nickel atoms (Ni), and boron atoms (B). The total content of inevitable impurities in the surface layer may be, for example, 0% by mass or more and 1.0% by mass or less, or 0.1% by mass or more and 0.4% by mass or less.

[0066] The surface layer is determined to be composed of TiN by X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). The content of unavoidable impurities in the surface layer is measured by secondary ion mass spectrometry (SIMS). It has been confirmed that, as long as measurements are performed on the same surface layer, there is no variation in the measurement results even if the measurement location is arbitrarily selected.

[0067] The thickness of the surface layer may be 0.5 μm or more and 3.0 μm or less, or 1.0 μm or more and 2.5 μm or less.

[0068] [Embodiment 2: Method for manufacturing a cutting tool] A method for manufacturing a cutting tool according to this embodiment will be described with reference to Fig. 2. Fig. 2 is a schematic cross-sectional view of an example of a CVD apparatus used in manufacturing the cutting tool of the present disclosure.

[0069] The method for manufacturing a cutting tool of this embodiment is the same as the method for manufacturing a cutting tool as described in embodiment 1, and includes a first step of preparing a substrate 1 and a second step of forming a coating on the substrate 1, the second step including a step 2a of forming a first layer by a CVD method. Details of each step are described below.

[0070] <<First Step>> In the first step, a substrate 1 is prepared. As the substrate 1, the substrate 1 described in the first embodiment can be used.

[0071] For example, when a cemented carbide is used as the substrate 1, a commercially available substrate 1 may be used, or it may be manufactured by a general powder metallurgy method. When manufactured by a general powder metallurgy method, for example, WC powder and Co powder are mixed using a ball mill or the like to obtain a mixed powder. The mixed powder is dried and then molded into a predetermined shape to obtain a green body. The green body is then sintered to obtain a WC-Co based cemented carbide (sintered body). Next, the sintered body is subjected to a predetermined cutting edge processing such as honing, thereby manufacturing a substrate 1 made of a WC-Co based cemented carbide. Any substrate 1 other than those described above can also be prepared as long as it is a conventionally known substrate 1 of this type.

[0072] <<Second Step>> In the second step, a coating is formed on the substrate 1 to obtain a cutting tool. The coating is formed using, for example, a CVD apparatus 50 shown in FIG. 2 . The CVD apparatus 50 includes a plurality of substrate setting jigs 52 for holding the substrate 1 and a heat-resistant alloy steel reaction vessel 53 that covers the substrate setting jigs 52. A temperature control device 54 for controlling the temperature inside the reaction vessel 53 is provided around the reaction vessel 53. The reaction vessel 53 is provided with a gas introduction pipe having a gas inlet. The gas introduction pipe extends vertically in the internal space of the reaction vessel 53 in which the substrate setting jigs 52 are placed, and is rotatable about an axis in the vertical direction. The gas introduction pipe is also provided with a plurality of ejection holes (through holes) for ejecting gas into the reaction vessel 53. Using this CVD apparatus 50, the first layer that constitutes the coating can be formed as follows.

[0073] The second step includes a step 2a of forming a first layer by a CVD method. When the coating includes the "other layer" described in embodiment 1, the second step can further include a step of forming the "other layer." The "other layer" can be formed by a conventionally known method.

[0074] <Step 2a: Step of forming first layer by CVD method> In step 2a, the first layer is formed by CVD method. More specifically, first, the substrate 1 is placed in a substrate setting jig 52, and a source gas for the first layer is introduced into the reaction vessel 53 from a gas inlet pipe while controlling the temperature and pressure in the reaction vessel 53 within a predetermined range. In this way, the first layer is formed on the substrate 1.

[0075] A nozzle 56 having two inlets 55, 57 is disposed in the CVD apparatus 50. The nozzle 56 is disposed so as to penetrate the area in which the substrate setting jig 52 is disposed. A plurality of injection holes (a first injection hole 61, a second injection hole 62, a third injection hole (not shown), and a fourth injection hole (not shown)) are formed in the nozzle 56 in the vicinity of the substrate setting jig 52.

[0076] The gases introduced into the nozzle 56 from the inlets 55 and 57 are not mixed in the nozzle 56 either, but are introduced into the reaction vessel 53 via different injection holes. The nozzle 56 can rotate around its own axis. An exhaust pipe 59 is also provided in the CVD apparatus 50, and exhaust gases can be discharged to the outside from an exhaust port 60 of the exhaust pipe 59. The jigs and other components inside the reaction vessel 53 are usually made of graphite.

[0077] As a raw material gas, AlCl ３ , HCl, CO ２ , H ２ S, and H ２ First, in the first injection hole 61 and the second injection hole 62, film formation is performed under the following conditions (condition 1) of the composition of the mixed gas, the flow rate of the mixed gas (i.e., the total gas flow rate), the temperature of the mixed gas, and the pressure of the mixed gas: (condition 1) AlCl ３ HCl: 2.0% by volume or more and 4.0% by volume or less CO: 2.0% by volume or more and 4.0% by volume or less２ H: 3.0% by volume or more and 5.0% by volume or less ２ S: 0.20% by volume or more and 0.60% by volume or less H ２ : Remaining Temperature: 950°C or higher and 1020°C or lower Pressure: 5 kPa or higher and 100 kPa or lower

[0078] Next, in the first injection hole 61 and the second injection hole 62, the conditions of the mixed gas composition, mixed gas temperature, and mixed gas pressure are set as shown in the following "Condition 2A," and in the third injection hole and the fourth injection hole, the conditions of the mixed gas composition, mixed gas temperature, and mixed gas pressure are set as shown in the following "Condition 2B," and film formation is performed. (Condition 2A) AlCl ３ HCl: 1.9% by volume or more and 4.0% by volume or less CO: 2.0% by volume or more and 4.0% by volume or less ２ H: 4.0% by volume or more and 6.5% by volume or less ２ S: 0.03% by volume or more and 0.12% by volume or less H ２ : Remainder Temperature: 950°C or higher and 1020°C or lower Pressure: 10 kPa or higher and 220 kPa or lower (Condition 2B) AlCl ３ HCl: 1.5% by volume or more and 4.0% by volume or less; CO: 2.0% by volume or more and 5.0% by volume or less ２ H: 3.0% by volume or more and 5.0% by volume or less ２ S: 0.01% by volume or more and 0.50% by volume or less H ２ : Remaining Temperature: 950°C or higher and 1020°C or lower Pressure: 10 kPa or higher and 220 kPa or lower

[0079] The diameter Φ of the injection hole can be, for example, 1.5 mm / 2.5 mm. Note that, here, "the diameter Φ of the injection hole is 1.5 mm / 2.5 mm" can be rephrased as meaning that the minor axis of the injection hole is 1.5 mm and the major axis of the injection hole is 2.5 mm, with respect to the injection hole located in a cross section perpendicular to the longitudinal direction of the nozzle 56.

[0080] The rotation speed of the nozzle 56 can be set to 1.0 rpm or more and 8.0 rpm or less. The deposition time of the first layer can be adjusted as needed. By adjusting the deposition time of the first layer as needed, the thickness of the first layer can be controlled.

[0081] <Other Steps> In addition to the above steps, the second step may include a surface treatment step such as surface grinding or blasting.

[0082] <Features of the Cutting Tool Manufacturing Method of the Present Embodiment> In the cutting tool manufacturing method of the present embodiment, in step 2a, film formation is performed under the above-mentioned "Condition 1," and then film formation is performed under a combination of the above-mentioned "Condition 2A" and "Condition 2B." This allows the crystal growth direction to be freely controlled by combining conditions for different crystal growth directions. Therefore, in a cross section along the normal to the interface between the substrate 1 and the coating, the number N1 of first grain boundaries intersected by a virtual line L1 that is equidistant from the interface of the first layer on the surface of the first layer or the surface side of the coating of the first layer and the interface of the first layer on the substrate 1 side is occupied by the number N2 of second grain boundaries that are grain boundaries whose absolute value of an angle with a line perpendicular to the virtual line L1 is 15° or less at the position where the first grain boundary intersects with the virtual line L1. The ratio N2 / N1 is 0.60 or more, and the ratio N4 / N3, which is the number of fourth grain boundaries N4, which are grain boundaries whose absolute value of an angle with a line perpendicular to virtual line L2 at a position where the third grain boundary intersects virtual line L2 is 15° or less, to the number N3 of third grain boundaries intersected by virtual line L2 that is 0.5 μm from the surface of the first layer or the interface on the surface side of the coating of the first layer toward the substrate 1 in the cross section along the normal to the interface between the substrate 1 and the coating, satisfies the relationship of the following formula 1: 0.1≦(N2 / N1)−(N4 / N3)≦0.40 Formula 1 The present inventors have found, as a result of extensive research, that the cutting tool of the present disclosure can be realized by employing such a manufacturing method.

[0083] [Supplementary Note 1] In the cutting tool of the present disclosure, all of the third grain boundaries may form angles of less than 45° with respect to a line perpendicular to the imaginary line L2 at positions where the third grain boundaries intersect with the imaginary line L2.

[0084] [Supplementary Note 2] In the cutting tool of the present disclosure, the third grain boundary does not necessarily include a grain boundary that forms an angle of 45° or more with respect to a line perpendicular to the imaginary line L2 at the position where the third grain boundary and the imaginary line L2 intersect.

[0085] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0086] <<Preparation of Cutting Tools>> Cutting tools according to Samples 1 to 20 and 101 to 112 were prepared as follows.

[0087] <First Step> A turning tip (shape: CNMG120408N-GZ, manufactured by Sumitomo Electric Hardmetal Corp.) having the composition shown in Tables 11 and 12 was prepared as a substrate.

[0088] <Second Step> An underlayer was formed on the surface of the substrate by performing a CVD method under the conditions shown in Tables 1 and 2. The deposition time was adjusted so that the underlayer had a thickness as shown in Tables 11 and 12. Next, an intermediate layer was formed on the surface of the underlayer by performing a CVD method under the conditions shown in Tables 1 and 2. The deposition time was adjusted so that the intermediate layer had a thickness as shown in Tables 11 and 12.

[0089] A first layer was formed on the surface of the intermediate layer by performing a CVD method (step 2a). In forming the first layer, first, a CVD method was performed under the conditions set forth in Tables 3 and 4 (Step I). Next, a CVD method was performed using the first and second injection holes under the conditions set forth in Tables 5 and 6, and a CVD method was performed using the third and fourth injection holes under the conditions set forth in Tables 7 and 8, thereby forming the first layer (Step II). A "-" in every column in Tables 5 to 8 means that the first layer was formed by performing only Step I. A "-" in every column in Tables 5 and 6 does not mean that the first and second injection holes were used in Step II, but the third and fourth injection holes were not. The total time for Steps I and II was adjusted so that the thickness of the first layer was as set forth in Tables 13 and 14. When both Step I and Step II were performed, the ratio of the time for Step I to the time for Step II was set to 10:1.

[0090] Next, a surface layer was formed on the surface of the first layer by performing a CVD method under the conditions shown in Tables 9 and 10. The deposition time was adjusted so that the thickness of the surface layer would be as shown in Tables 15 and 16. If "-" is entered in all of the "Deposition conditions for surface layer" columns in Tables 9 and 10, this means that no surface layer was formed.

[0091] Next, when a surface layer was formed on the surface of the first layer, the surface of the surface layer was subjected to blasting under the following conditions. When a surface layer was not formed on the surface of the first layer, the surface of the first layer was subjected to blasting under the following conditions. (Conditions) Media type: Ceramics Media average particle size: 150 μm Media concentration: 300 g / min Projection angle: 75° Projection distance: 35 mm Projection pressure: as shown in Tables 9 and 10 Time: 25 seconds Cutting tool rotation speed: 60 rpm

[0092] Next, the cutting tools after the blasting treatment were visually inspected to determine whether or not the coating had peeled off. The results are shown in the "Whether or Not the Coating Had Peeled After Blasting" column in Tables 9 and 10.

[0093] In this manner, cutting tools according to Samples 1 to 20 and 101 to 112 were produced.

[0094]

[0095]

[0096]

[0097]

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

[0110]

[0111]

[0112] <Evaluation of Cutting Tool Characteristics> <Composition of Base Layer> For each sample cutting tool, the composition of the base layer was determined by the method described in Embodiment 1. The results obtained are shown in the "Composition" column of the "Base Layer" column in Tables 11 and 12. Note that when the name of a component is listed in the "Composition" column of the "Base Layer" column in Tables 11 and 12, it means that the base layer is composed of the component listed in the "Composition" column of the "Base Layer" column in Tables 11 and 12.

[0113] <Composition of Intermediate Layer> The composition of the intermediate layer of each sample cutting tool was determined by the method described in embodiment 1. The results obtained are shown in the "Composition" column of the "Intermediate Layer" column in Tables 11 and 12. Note that when the name of a component is listed in the "Composition" column of the "Intermediate Layer" column in Tables 11 and 12, it means that the intermediate layer is composed of the component listed in the "Composition" column of the "Intermediate Layer" column in Tables 11 and 12.

[0114] <Composition of First Layer> For each sample cutting tool, the composition of the first layer was determined by the method described in Embodiment 1. The results obtained are shown in the "Composition" column of the "First Layer" column in Tables 13 and 14. Note that when the names of components are listed in the "Composition" column of the "First Layer" column in Tables 13 and 14, this means that the first layer is composed of the components listed in the "Composition" column of the "First Layer" column in Tables 13 and 14.

[0115] <Surface Roughness Ra of the Surface of the First Layer or the Surface Located at the Interface on the Surface Side of the Coating of the First Layer> The surface roughness Ra of the surface of the first layer or the surface located at the interface on the surface side of the coating of the first layer was determined by the method described in Embodiment 1. The obtained results are shown in the "Ra [μm]" column of Tables 13 and 14.

[0116] <Ratios N2 / N1, N4 / N3, and N5 / N3> For the cutting tools of each sample, the ratio N2 / N1 was determined by the method described in embodiment 1. The results obtained are shown in the "N2 / N1" column of Tables 13 and 14. For the cutting tools of each sample, the ratio N4 / N3 was determined by the method described in embodiment 1. The results obtained are shown in the "N4 / N3" column of Tables 13 and 14. For the cutting tools of each sample, the ratio N5 / N3 was determined by the method described in embodiment 1. The results obtained are shown in the "N5 / N3" column of Tables 13 and 14.

[0117] <Compressive residual stress of first layer> For the cutting tools according to Samples 17 to 20 and 109 to 112, the absolute value of the compressive residual stress of the first layer was determined by the method described in embodiment 1. The results obtained are shown in the "Compressive residual stress [GPa]" column of the "First layer" column in Table 17. Note that when "Cracks present" is written in the "Compressive residual stress [GPa]" column of the "First layer" column in Table 17, this means that the compressive residual stress could not be measured due to the occurrence of cracks in the first layer.

[0118] <Orientation index TC(0 0 12) of first layer> For the cutting tools according to each sample, the orientation index TC(0 0 12) of the first layer was determined by the method described in embodiment 1. The obtained results are shown in the "TC(0012)" column of the "First layer" column in Tables 13 and 14.

[0119] <Composition of Surface Layer> The composition of the surface layer of each sample cutting tool was determined by the method described in embodiment 1. The results obtained are shown in the "Composition" column of the "Surface Layer" column in Tables 15 and 16. Note that when the name of a component is listed in the "Composition" column of the "Surface Layer" column in Tables 15 and 16, it means that the surface layer is composed of the component listed in the "Composition" column of the "Surface Layer" column in Tables 15 and 16.

[0120] <Coating Thickness> The coating thickness of each sample cutting tool was determined by the method described in Embodiment 1. The results obtained are shown in the "Thickness [μm]" column under "Coating" in Tables 15 and 16.

[0121] <Cutting Test 1> A cutting test was performed using the cutting tools of each sample under the following cutting conditions. The cutting time until chipping occurred was measured. The results are shown in the "Cutting Test 1 [sec]" column in Table 18. (Cutting Conditions) Workpiece: FCD450 Processing: Intermittent turning Cutting speed: 450 m / min Feed rate: 0.3 mm / rev Depth of cut: 1.5 mm Cutting fluid: wet

[0122] <Cutting Test 2> A cutting test was performed using the cutting tools for each sample under the following cutting conditions. The cutting distance until flank wear reached 0.2 mm was measured. The results are shown in the "Cutting Test 2 [km]" column in Table 18. (Cutting Conditions) Workpiece: FCD700 Processing: Continuous turning Cutting speed: 140 m / min Feed rate: 0.3 mm / rev Depth of cut: 1.5 mm Cutting fluid: Wet

[0123] When the cutting time in Cutting Test 1 is 210 seconds or more and the cutting distance in Cutting Test 2 is 2.5 km or more, it means that the cutting tool has an excellent tool life.

[0124] Although not shown in Table 18, it was confirmed that Samples 17 to 20 achieved a cutting time of 210 seconds or more in Cutting Test 1 and a cutting distance of 2.5 km in Cutting Test 2. Furthermore, although not shown in Table 18, it was confirmed that Samples 109 to 112 did not achieve at least either a cutting time of 210 seconds or more in Cutting Test 1 or a cutting distance of 2.5 km in Cutting Test 2.

[0125] The cutting tools according to Samples 1 to 20 correspond to Examples. The cutting tools according to Samples 101 to 112 correspond to Comparative Examples. From the results of Cutting Test 1 and Cutting Test 2 in Table 18, it was found that the cutting tools according to Samples 1 to 20 had superior tool life compared to the cutting tools according to Samples 101 to 112.

[0126] From the above, it was found that the cutting tools according to Samples 1 to 20 had excellent tool life.

[0127] Although the embodiments and examples of the present disclosure have been described above, it is originally intended that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways.

[0128] 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 embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0129] REFERENCE SIGNS LIST 1 substrate, 2 coating, 3 first layer, 4 undercoat layer, 10 cutting tool, 50 CVD apparatus, 52 substrate setting jig, 53 reaction vessel, 54 temperature control device, 55, 57 inlet, 56 nozzle, 59 exhaust pipe, 60 exhaust port, 61 first injection hole, 62 second injection hole.

Claims

1. A cutting tool comprising a substrate and a coating disposed on the substrate, the coating including a first layer, the first layer consisting of α-Al ２ O ３ and having a thickness of 2 μm or more and 15 μm or less. In a cross-section along the normal of the interface between the substrate and the coating, for the number N1 of first grain boundaries intersected by a virtual line L1 where the distance from the surface of the first layer or the interface on the coating surface side of the first layer to the interface on the substrate side of the first layer is equal, the ratio N2 / N1 of the number N2 of second grain boundaries, among the first grain boundaries, which are grain boundaries where the absolute value of the angle with respect to a straight line perpendicular to the virtual line L1 at the position where the first grain boundary intersects the virtual line L1 is 15° or less, is 0.60 or more. In the cross-section along the normal of the interface between the substrate and the coating, for the number N3 of third grain boundaries intersected by a virtual line L2 where the distance from the surface of the first layer or the interface on the coating surface side of the first layer to the substrate side is 0.5 μm, the ratio N4 / N3 of the number N4 of fourth grain boundaries, among the third grain boundaries, which are grain boundaries where the absolute value of the angle with respect to a straight line perpendicular to the virtual line L2 at the position where the third grain boundary intersects the virtual line L2 is 15° or less, and the ratio N2 / N1 satisfy the relationship of the following formula 1. 0.1 ≦ (N2 / N1) - (N4 / N3) ≦ 0.40 Formula 1 2. The cutting tool according to claim 1, wherein the number N3 and the number N5 of the fifth grain boundaries, which are grain boundaries in the third grain boundaries and have an absolute value of the angle with respect to a straight line perpendicular to the virtual line L2 at the position where the third grain boundary intersects the virtual line L2, satisfy the following relationship of Formula 2: (N5 / N3) > 0.96 Formula 2 3. The cutting tool according to claim 1 or 2, wherein the thickness of the first layer is less than 8 μm, and the surface roughness Ra is 0.03 μm or more and 0.2 μm or less on the surface of the first layer or on the surface located at the interface on the surface side of the coating of the first layer.

4. The cutting tool according to claim 1 or 2, wherein the thickness of the first layer is 8 μm or more, and the surface roughness Ra is 0.05 μm or more and 0.2 μm or less on the surface of the first layer or on the surface located at the interface on the surface side of the coating of the first layer.

5. The cutting tool according to any one of claims 1 to 4, wherein the absolute value of the compressive residual stress of the first layer is 1.5 GPa or more and 4.0 GPa or less.

6. The cutting tool according to any one of claims 1 to 5, wherein the orientation index TC(0 0 12) of the first layer is more than 4.5.

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