Cutting Tools

Abstract

The cutting tool includes a substrate and a coating disposed on the substrate, the coating including a first layer, the first layer being made of α-Al2O3, the first layer having a thickness of 2 μm or more and 15 μm or less, and a number N1 of first grain boundaries crossed by a virtual line L1 that is equidistant from an interface of the first layer or a surface side interface of the coating of the first layer and an interface of the first layer on the substrate side in a cross section taken along a normal to the interface between the substrate and the coating, the absolute value of an angle of the first grain boundaries with respect to a straight line perpendicular to the virtual line L1 at a position where the first grain boundary and the virtual line L1 intersect is 15 a ratio N2 / N1 of the number N2 of second grain boundaries which are grain boundaries having an angle of 15° or less relative to a line perpendicular to virtual line L2 at a position where the third grain boundaries and virtual line L2 intersect to the number N3 of third grain boundaries intersected by a virtual line L2 that is 0.5 μm away from the interface on the surface of the first layer or the surface side of the coating of the first layer toward the substrate, and the ratio N4 / N3 and the ratio N2 / N1 satisfy the relationship of Formula 1.

Description

[Technical field]

[0001] The present disclosure relates to cutting tools. [Background technology]

[0002] Conventionally, cutting tools having a substrate and a coating disposed on the substrate, the coating including a first layer made of α-Al2O3, have been used for cutting (Patent Document 1, Non-Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 114049 [Non-patent literature]

[0004] [Non-Patent Document 1] S. Ruppi et al.,“Influence of Process Conditions on the Growth and Texture of CVD Alpha-Alumina” Coatings 2020,10,158 Summary of the Invention

[0005] The cutting tool of the present disclosure comprises: 1. A cutting tool comprising a substrate and a coating disposed on the substrate, The coating comprises a first layer, The first layer is made of α-Al2O3, The thickness of the first layer is 2 μm or more and 15 μm or less, 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 virtual line L1 at a position where the first grain boundaries intersect with virtual line L1, to the number N1 of first grain boundaries crossed by virtual line L1 that is equidistant from an interface of the first layer on the surface side of the first layer or the coating of the first layer and an interface of the first layer on 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, a ratio N4 / N3 of the number N4 of fourth grain boundaries, which are grain boundaries having an absolute value of an angle of 15° or less with respect to a straight line perpendicular to virtual line L2 at the position where the third grain boundaries and virtual line L2 intersect, to the number N3 of third grain boundaries crossed by virtual 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 N2 / N1 satisfy the relationship of the following formula 1. 0.1≦(N2 / N1)-(N4 / N3)≦0.40 Formula 1 [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating one embodiment of a cutting tool according to the present disclosure. [Diagram 2] 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. [Diagram 3] FIG. 3 is an enlarged view of region III in FIGS. [Figure 4] FIG. 4 is an enlarged view of region IV in FIGS. [Diagram 5] FIG. 5 is a schematic cross-sectional view illustrating another embodiment of the cutting tool of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] [Problem that this disclosure aims to solve] In recent years, the demand for improving tool life has been increasing. One important factor for improving tool life is "chipping resistance". The "chipping resistance" of a coating can be improved by performing a blasting process on the surface of the coating. However, when a blasting process is performed for the purpose of imparting excellent "chipping resistance", peeling of the coating may occur, so it may be difficult to impart excellent "chipping resistance" to the coating. In addition, when a blasting process is performed at high pressure for the purpose of imparting excellent "chipping resistance", in a coating including an α-Al2O3 layer, destruction may easily occur at the edge of the crystals on the surface side of the α-Al2O3 layer, so it may be difficult to perform a blasting process at high pressure and it may be difficult to impart excellent "chipping resistance" to the coating. It is required to impart excellent "chipping resistance" to a coating to give a cutting tool an excellent tool life.

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

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

[0010] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described. (1) The cutting tool of the present disclosure comprises: 1. A cutting tool comprising a substrate and a coating disposed on the substrate, The coating comprises a first layer, the first layer is made of α-Al2O3, The thickness of the first layer is 2 μm or more and 15 μm or less, 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 virtual line L1 at a position where the first grain boundaries intersect with virtual line L1, to the number N1 of first grain boundaries crossed by virtual line L1 that is equidistant from an interface of the first layer on the surface side of the first layer or the coating side of the first layer and an interface of the first layer on 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, a ratio N4 / N3 of the number N4 of fourth grain boundaries, which are grain boundaries having an absolute value of an angle of 15° or less with respect to a straight line perpendicular to the virtual line L2 at a position where the third grain boundaries and the virtual line L2 intersect, to the number N3 of third grain boundaries crossed by a virtual line L2 that is 0.5 μm away 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 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 have an absolute value of an angle with respect to a line perpendicular to the virtual line L2 of 45° or less at a position where the third grain boundary and the virtual line L2 intersect, may satisfy the relationship of the following formula 2. (N5 / N3)>0.96 Equation 2 This can provide a cutting tool with improved tool life.

[0013] (3) In the above (1) or (2), the thickness of the first layer is less than 8 μm; 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, thereby making it possible to provide a cutting tool having a longer tool life.

[0014] (4) In the above (1) or (2), the thickness of the first layer is 8 μm or more, 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, thereby making it possible to provide a cutting tool having 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 having a longer tool life.

[0017] [Details of the embodiment of the present disclosure] A specific example of a cutting tool according to an 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 appropriately changed for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0018] In this disclosure, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less). 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.

[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 an embodiment of the present disclosure will be described with reference to Fig. 1 and Fig. 3 to Fig. 5. Fig. 1 is a schematic cross-sectional view illustrating one embodiment of the cutting tool of the present disclosure. Fig. 3 is an enlarged view of region III in Fig. 1 and Fig. 5. Fig. 4 is an enlarged view of region IV in Fig. 1 and Fig. 5. Fig. 5 is a schematic cross-sectional view illustrating another embodiment of the cutting tool of the present disclosure. One embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") is A cutting tool 10 comprising a substrate 1 and a coating 2 disposed on the substrate 1, The coating 2 comprises a first layer 3, The first layer 3 is made of α-Al2O3, The thickness of the first layer 3 is 2 μm or more and 15 μm or less, in a cross section taken along the normal to the interface between the substrate 1 and the coating 2, 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 virtual line L1 at a position where the first grain boundaries intersect with the virtual line L1, to the number N1 of first grain boundaries crossed by a virtual line L1 that is equidistant from a surface S1 of the first layer 3 or an interface of the first layer 3 on the surface side of the coating 2, and an interface I1 of the first layer 3 on the substrate 1 side, is 0.60 or more; In the cross section taken along the normal to the interface between the substrate 1 and the coating 2, a proportion N4 / N3 of the number N4 of fourth grain boundaries, which are grain boundaries having an absolute value of an angle of 15° or less with respect to a straight line perpendicular to the virtual line L2 at the position where the third grain boundary and the virtual line L2 intersect, to the number N3 of third grain boundaries crossed by a virtual line L2 that is 0.5 μm away from the surface S1 of the first layer 3 or the interface on the surface side of the coating 2 of the first layer 3 toward the substrate 1, and the proportion 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 along the normal to the interface between the substrate 1 and the coating 2, the number N1 of first grain boundaries crossed by a virtual line L1 that is equidistant from the surface S1 of the first layer 3 or the interface on the surface side of the coating 2 of the first layer 3 and the interface I1 of the first layer 3 on the substrate 1 side, the ratio N2 / N1 of the number N2 of second grain boundaries that are grain boundaries having an absolute value of an angle of 15° or less with respect to a line perpendicular to the virtual line L1 at the position where the first grain boundary intersects with the virtual line L1 is 0.60 or more. As a result, the crystals in the first layer 3 are arranged in the same direction, so that the blasting treatment can be applied uniformly. 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 along the normal to the interface between the substrate 1 and the coating 2, the number N3 of third grain boundaries crossed by a virtual line L2 that is 0.5 μm away from the surface S1 of the first layer 3 or the interface on the surface side of the coating 2 of the first layer 3 toward the substrate 1, the proportion N4 / N3 of the number N4 of fourth grain boundaries that are grain boundaries having an absolute value of an angle of 15° or less with respect to a straight line perpendicular to the virtual line L2 at the position where the third grain boundary and the virtual line L2 intersect, and the proportion N2 / N1 satisfy the relationship of the following formula 1. 0.1≦(N2 / N1)-(N4 / N3)≦0.40 Formula 1 As a result, when performing blasting, damage to the edge of the crystals at the interface on the surface S1 of the first layer 3 or the surface side of the coating 2 of the first layer 3 is more easily suppressed, and since the blasting can be performed 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] ≪Cutting tools≫ As shown in FIG. 1 and FIG. 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 even if a part of the substrate 1 is not covered with the coating 2 or the configuration of the coating 2 is partially different, this does not deviate from the scope of this embodiment. When a part of the substrate 1 is not covered with the coating 2, the coating 2 is preferably disposed so as to cover at least the surface of the part of the substrate 1 involved in cutting. In this specification, the part of the substrate 1 involved in cutting means, depending on the size and shape of the substrate 1, a region of the substrate 1 surrounded by the cutting edge ridge and a virtual surface whose distance from the cutting edge ridge to the substrate 1 along the perpendicular to the tangent to the cutting edge ridge is, 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 cutting tools 10 such as drills, end mills, indexable cutting tips for drills, indexable cutting tips for end mills, indexable cutting tips for milling, indexable cutting tips for turning, metal saws, gear cutting tools, reamers, taps, etc.

[0027] ≪Base material≫ Any of the conventionally known substrates 1 of this type can be used as the substrate 1. For example, the substrate 1 is preferably any of cemented carbide (WC-based cemented carbide, cemented carbide containing WC and Co, and 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, they 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 be composed of only 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 life of the cutting tool 10 tends to be shortened due to the coating 2 being too thin. On the other hand, if the thickness of the coating 2 exceeds 25 μm, chipping of the coating 2 tends to occur easily in the early cutting stage, and the life of the cutting tool 10 tends to be shortened.

[0030] The thickness of the coating 2 can be measured by observing a cross section of the coating 2 along the normal direction of the surface of the coating 2 using a scanning electron microscope (SEM). Specifically, the observation magnification of the cross section sample is set to 5,000 to 10,000 times, and the observation area is set to 100 to 500 μm 2 The thickness width is measured at three arbitrary points in one arbitrary 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 the first layer> The first layer 3 is made of α-Al2O3. "Made of α-Al2O3" means that the first layer 3 may be made of only α-Al2O3, or may contain inevitable impurities in addition to α-Al2O3, as long as the effects of the present disclosure are not impaired. 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] It is identified by X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX) that the first layer 3 is made of α-Al2O3. The content of inevitable impurities in the first layer 3 is measured by secondary ion mass spectrometry (SIMS). It has been confirmed that there is no variation in the measurement results even if the measurement points are arbitrarily selected, as long as the measurement is performed using the same cutting tool 10.

[0033] <Thickness of the 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 uniformly impart compressive residual stress to the cutting tool 10 by the blasting treatment, and therefore it is possible to impart better chipping resistance and therefore to impart a 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 may be 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 surface side of the coating 2 may have a surface roughness Ra of 0.05 μm or more and 0.2 μm or less. This makes it easier to uniformly impart compressive residual stress to the cutting tool 10 by the blasting treatment, and therefore it is possible to impart better chipping resistance and therefore to impart a better 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 may be 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 at the cutting edge R along the normal direction of the interface between the substrate 1 and the coating 2. More specifically, first, an image including the surface S1 of the first layer 3 or a surface located at the interface on the surface side of the coating 2 of the first layer 3 is obtained by imaging the cross section at the cutting edge R along the normal direction of the interface between the substrate 1 and the coating 2 using an SEM at a magnification of 1000 times. Next, in the image, an arbitrary observation field of a rectangle of 10 μm×10 μm is specified at a magnification of 10000 times. In the observation field, "the surface S1 of the first layer 3 or a surface located at the interface on the surface side of the coating 2 of the first layer 3" is assumed to pass through any pair of two opposing sides. 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" in the observation field is identified by extracting the contour information of the interface using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ) for 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 identified for any other four observation fields in the image. Next, the surface roughness Ra is identified 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. 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 same first layer 3 is measured.

[0037] <Ratio N2 / N1> In a cross section taken along the normal to the interface between the substrate 1 and the coating 2, the number N1 of first grain boundaries crossed by a virtual 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 number N2 of second grain boundaries that are grain boundaries having an absolute value of an angle of 15° or less with respect to a line perpendicular to the virtual line L1 at the position where the first grain boundary intersects with the virtual line L1 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 virtual line L1 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" is denoted as D1. Also, in Fig. 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 on the surface side of the coating 2 of the first layer 3 to the interface I1 of the first layer 3 on the substrate 1 side is equal" can be rephrased as D1 and D2 being equal.

[0038] In addition, "a grain boundary having an absolute value of an angle of 15° or less with respect to a line perpendicular to virtual line L1 at the intersection of the first grain boundary and virtual line L1" is a concept that includes a grain boundary GB (FIG. 3) that slopes downward to the right with respect to the line and a grain boundary GB (FIG. 4) that slopes upward to the right with respect to the line at the intersection. "A grain boundary having an absolute value of an angle of 15° or less with respect to a line perpendicular to virtual line L1 at the intersection of the first grain boundary and virtual line L1" means a grain boundary having an angle α of 15° or less in FIG. 3 and a grain boundary having an angle α of 15° or less in FIG. 4. The same applies to "a grain boundary having an absolute value of an angle of 15° or less with respect to a line perpendicular to virtual line L2 at the position where the third grain boundary and virtual line L2 intersect" described later, except that the "first grain boundary" is replaced with the "third grain boundary" and the "virtual line L1" is replaced with the "virtual line L2."

[0039] <Ratio N4 / N3> In a cross section along the normal to the interface between the substrate 1 and the coating 2, the number N3 of third grain boundaries crossed by a virtual line L2 that is 0.5 μm away from the surface S1 of the first layer 3 or the interface on the surface side of the coating 2 of the first layer 3 toward the substrate 1 may be 0.4 or more and 0.9 or less, and the number N4 of fourth grain boundaries that are grain boundaries having an absolute value of an angle of 15° or less with respect to a line perpendicular to the virtual line L2 at a position where the third grain boundary intersects with the virtual line L2 may be a ratio N4 / N3 of 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. In addition, the term "a grain boundary having an absolute angle of 15° or less with respect to a straight line perpendicular to virtual line L2 at the position where the third grain boundary and virtual line L2 intersect" is a concept that encompasses a grain boundary that slopes downward to the right with respect to the straight line at the "intersection position" and a grain boundary that slopes upward to the right with respect to the straight line.

[0040] The ratio N2 / N1 and the ratio N4 / N3 can be determined by the following method. (A1) A color map is created based on the crystal orientation of each of the crystal grains by performing an 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 areas where α-Al2O3 exists are colored white, and the other areas are colored black to obtain a first image. Next, in order to remove noise, a moving average filter with a size of 15×15 pixels (i.e., 0.3 μm×0.3 μm) is applied to the interface I1 on the substrate 1 side of the first layer 3 and the interface on the surface side of the coating 2 of the first layer 3, respectively, to smooth the first image and then perform 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 straight line L3. Next, each row of pixels in the first image that has been binarized by Otsu is observed in order from the surface side of the coating 2, and the location where the color changes from black to white is identified as 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 straight line L4 is obtained that is parallel to the straight line L3 and has the smallest sum of squares of the error in 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 straight line that is equidistant from the straight line L3 and the straight line L4 is obtained as a virtual line L1. In addition, a straight line that is 0.5 μm away from the straight line L4 toward the substrate 1 is obtained as a virtual line L2. (C1) Based on the color map created in (A1), the grain boundaries are colored black and other areas are colored white to output an image, thereby obtaining a second image. (D1) By superimposing the second image and the first image, the areas in the second image corresponding to the virtual line L1 obtained in (B1) and the areas corresponding to the virtual line L2 obtained in (B1) are identified. (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 (size of field of view: 40 μm × 25 μm) based on 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 obtained. (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 having an absolute value of an angle of 15° or less with respect to a line perpendicular to the virtual line L1 at the position where the first grain boundary and the virtual line L1 intersect, are identified. Next, N2 is divided by N1 to obtain 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 having an absolute value of an angle of 15° or less with respect to a line perpendicular to the virtual line L2 at the position where the third grain boundary and the virtual line L2 intersect, are identified. Next, N4 is divided by N3 to obtain 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 points are arbitrarily selected.

[0042] <Relationship between ratios N2 / N1 and 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 can 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 grain boundaries among the third grain boundaries and which have an absolute value of an angle with respect to a line perpendicular to the virtual line L2 of 45° or less at a position where the third grain boundary and the virtual line L2 intersect, may satisfy the relationship of the following formula 2. (N5 / N3)>0.96 Equation 2 This makes it possible to reduce the number of third grain boundaries in the surface side region of the first layer coating, in which the absolute value of the angle between the third grain boundary and the virtual line L2 and the straight line perpendicular to the virtual line L2 exceeds 45° (i.e., grain boundaries with a large absolute value of the angle), thereby suppressing the occurrence of damage to the coating and the occurrence of peeling of the coating when subjected to strong blasting, thereby imparting a better tool life to the cutting tool 10. "N5 / N3" may be greater than 0.96 and less than 1.00, may be 0.97 or more and 1.00 or less, or may be 0.98 or more and 1.00 or less.

[0044] "N5 / N3" can be determined by the following method. It can be determined in the same manner 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. It has been confirmed that there is no variation in the measurement results, even if the measurement points are arbitrarily selected, as long as the same first layer 3 is measured.

[0045] All of the third grain boundaries may have an angle of less than 45° with respect to a line perpendicular to the virtual line L2 at the position where the third grain boundary intersects with the virtual line L2. This can provide a better tool life for the cutting tool 10. The third grain boundaries may not include grain boundaries having an angle of 45° or more with respect to a line perpendicular to the virtual line L2 at the position where the third grain boundary intersects with the virtual line L2. This can provide a better tool life for the cutting tool 10.

[0046] <Compressive residual stress in the 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 better tool life. The compressive residual stress of the first layer 3 is a type of internal stress (intrinsic strain) present in the entire first layer 3, and is a stress expressed by a "-" (negative) numerical value (unit: "GPa" is used in this embodiment). Therefore, the concept of a large compressive residual stress indicates that the absolute value of the numerical value is large, and the concept of a small compressive residual stress indicates that the absolute value of the numerical value is small. In other words, the 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 may be 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" (published by Yokendo Co., Ltd., Japan Society for Materials Science, 1981)).

[0048] <First layer orientation index TC(0 0 12)> The orientation index TC(0 0 12) of the first layer 3 may be greater than 4.5. This improves the strength of the α-Al2O3 crystal grains, thereby improving the wear resistance and providing the cutting tool 10 with a longer tool life. 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 index TC(hkl) defined by the following formula 3.

[0050]

number

[0051] In formula 3, I(hkl) indicates the X-ray diffraction intensity of the (hkl) reflection plane, and I0(hkl) indicates the standard intensity according to ICDD PDF card number 00-010-0173. Furthermore, n in formula 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 the abbreviation for International Centre for Diffraction Data, and PDF (registered trademark) is the 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]

number

[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 formula 3 above to obtain formula 4 is greater than 4.5.

[0056] The above-mentioned measurement of TC(hkl) is possible by analysis using an X-ray diffraction apparatus. 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 measurement result of TC(hkl) using an X-ray diffraction apparatus is referred to as "XRD result". (conditions) Characteristic X-ray: Cu-Kα Tube voltage: 45kV Tube current: 200mA Filter: Multi-layer mirror Optics: Concentration method X-ray diffraction method: θ-2θ method When using an X-ray diffraction device, the rake face of the cutting tool is irradiated with X-rays. Normally, the rake face has irregularities while the flank face is flat. Therefore, it is preferable to irradiate the flank face with X-rays in order to eliminate disturbance factors. In particular, the X-rays are irradiated to a portion of the flank face extending within a range of about 2 to 4 mm from the cutting edge ridge. 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 face 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 were 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 an undercoat layer (FIG. 5), an intermediate layer (not shown), and a surface layer (not shown). The undercoat 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 undercoat 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. 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 fact that the underlayer is made of TiN or TiCN is measured 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 there is no variation in the measurement results even if the measurement points are arbitrarily selected, as long as the same underlayer is measured.

[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] <Middle Class> The intermediate layer may be made of TiCN. "Made of TiCN" means that the intermediate layer may be made of only 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 fact that the intermediate layer is made of TiCN is measured 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 there is no variation in the measurement results even if the measurement points are arbitrarily selected, as long as the same intermediate layer is measured.

[0064] The thickness of the intermediate layer may be 2.0 μm or more and 10 μm or less, or may be 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 be made of only TiN, or may contain inevitable impurities in addition to TiN. 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 fact that the surface layer is made of TiN is measured 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 there is no variation in the measurement results even if the measurement points are arbitrarily selected, as long as the measurement is performed on the same surface layer.

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

[0068] [Embodiment 2: Manufacturing method of cutting tool] The method for manufacturing a cutting tool according to the present 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 according to the present disclosure.

[0069] The method for producing a cutting tool of this embodiment is the same as the method for producing a cutting tool of 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. Each step will be described in detail below.

[0070] ≪1st process≫ In the first step, the 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 the substrate 1 may be manufactured by a general powder metallurgy method. When the substrate 1 is manufactured by a general powder metallurgy method, for example, WC powder and Co powder are mixed by 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 molded body. The molded body is further 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 making it possible to manufacture the substrate 1 made of a WC-Co-based cemented carbide. Any substrate 1 other than the above can be prepared as long as it is a substrate 1 of this type that is conventionally known.

[0072] ≪Second process≫ In the second step, a coating is formed on the substrate 1 to obtain a cutting tool. The coating is formed, for example, by using 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 reaction vessel 53 made of heat-resistant alloy steel 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 introduction port. The gas introduction pipe is arranged to extend vertically in the internal space of the reaction vessel 53 in which the substrate setting jigs 52 are arranged, and is rotatable about the axis of the vertical direction, and is 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 constituting 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 the first embodiment, the second step can further include a step of forming the "other layer". The "other layer" can be formed by a conventional method.

[0074] <Step 2a: Step of forming the first layer by CVD method> In step 2a, the first layer is formed by the CVD method. More specifically, the substrate 1 is first 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 introduction pipe while controlling the temperature and pressure in the reaction vessel 53 within a predetermined range. As a result, 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 a portion of the nozzle 56 near 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, and are introduced into the reaction vessel 53 through different injection holes. The nozzle 56 can rotate about its axis. An exhaust pipe 59 is provided in the CVD apparatus 50, and the exhaust gas can be discharged to the outside from an exhaust port 60 of the exhaust pipe 59. The fixtures and the like in the reaction vessel 53 are usually made of graphite.

[0077] A mixed gas of AlCl3, HCl, CO2, H2S, and H2 is used as the source gas. 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 mixed gas composition, the mixed gas flow rate (i.e., the total gas flow rate), the mixed gas temperature, and the mixed gas pressure. (Condition 1) AlCl3: 2.0% by volume or more and 4.0% by volume or less HCl: 2.0% by volume or more and 4.0% by volume or less CO2: 3.0% by volume or more and 5.0% by volume or less H2S: 0.20% by volume or more and 0.60% by volume or less H2: Remaining Temperature: 950℃ or higher and 1020℃ or lower Pressure: 5kPa to 100kPa

[0078] Next, in the first injection hole 61 and the second injection hole 62, the mixed gas composition, mixed gas temperature, and mixed gas pressure conditions are set as shown in "Condition 2A" below, and in the third injection hole and the fourth injection hole, the mixed gas composition, mixed gas temperature, and mixed gas pressure conditions are set as shown in "Condition 2B" below, and film formation is performed. (Condition 2A) AlCl3: 1.9% by volume or more and 4.0% by volume or less HCl: 2.0% by volume or more and 4.0% by volume or less CO2: 4.0% by volume or more and 6.5% by volume or less H2S: 0.03% by volume or more and 0.12% by volume or less H2: Remaining Temperature: 950℃ or higher and 1020℃ or lower Pressure: 10kPa to 220kPa (Condition 2B) AlCl3: 1.5% by volume or more and 4.0% by volume or less HCl: 2.0% by volume or more and 5.0% by volume or less CO2: 3.0% by volume or more and 5.0% by volume or less H2S: 0.01% by volume or more and 0.50% by volume or less H2: Remaining Temperature: 950℃ or higher and 1020℃ or lower Pressure: 10kPa to 220kPa

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

[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 appropriately. By adjusting the deposition time of the first layer appropriately, the thickness of the first layer can be controlled.

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

[0082] <Features of the manufacturing method of the cutting tool according to the present embodiment> In the manufacturing method of the cutting tool of this embodiment, in step 2a, after performing film formation under the above-mentioned "Condition 1", film formation is performed under a combination of the above-mentioned "Condition 2A" and "Condition 2B". By combining different conditions for the growth direction of crystals, the crystal growth direction can be freely controlled, so that in a cross section along the normal to the interface between the substrate 1 and the coating, the number N1 of first grain boundaries crossed by a virtual line L1 that is equidistant from the interface on the surface of the first layer or the surface side of the coating of the first layer and the interface on the substrate 1 side of the first layer, is occupied by the number N2 of second grain boundaries that are grain boundaries whose absolute value of an angle with respect to a straight line perpendicular to the virtual line L1 is 15° or less at the position where the first grain boundary and the virtual line L1 intersect. The ratio N2 / N1 is 0.60 or more, and in the cross section along the normal to the interface between the substrate 1 and the coating, a ratio N4 / N3 of the number N4 of fourth grain boundaries, which are grain boundaries having an absolute value of an angle of 15° or less with respect to a straight line perpendicular to the virtual line L2 at the position where the third grain boundary and the virtual line L2 intersect, to the number N3 of third grain boundaries crossed by a virtual line L2 that is 0.5 μm away 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 side, and the ratio N2 / N1 can satisfy the relationship of the following formula 1. 0.1≦(N2 / N1)-(N4 / N3)≦0.40 Formula 1 As a result of extensive investigations, the present inventors have discovered that the cutting tool of the present disclosure can be realized by employing such a manufacturing method.

[0083] [Appendix 1] In the cutting tool of the present disclosure, all of the third grain boundaries may have 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] [Appendix 2] In the cutting tool of the present disclosure, the third grain boundary does not have to 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. EXAMPLES

[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] <Cutting tool manufacturing> Cutting tools according to Samples 1 to 20 and 101 to 112 were produced in the following manner.

[0087] <1st process> As the substrate, a turning insert (shape: CNMG120408N-GZ, manufactured by Sumitomo Electric Hardmetal Corp.) having the composition shown in Tables 11 and 12 was prepared.

[0088] <Second process> A base layer was formed on the surface of the substrate by carrying out a CVD method under the conditions shown in Tables 1 and 2. The deposition time was adjusted so that the base layer had a thickness as shown in Tables 11 and 12. Next, an intermediate layer was formed on the surface of the base layer by carrying out 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] The CVD method was performed to form a first layer on the surface of the intermediate layer (step 2a). In forming the first layer, the CVD method was first performed under the conditions described in Tables 3 and 4 (step I). Next, the CVD method was performed in the first and second injection holes under the conditions described in Tables 5 and 6, and the CVD method was performed in the third and fourth injection holes under the conditions described in Tables 7 and 8 to form the first layer (step II). When "-" is written in all columns of Tables 5 to 8, it means that the first layer was formed by performing only step I. When "-" is not written in all columns of Tables 5 and 6, and when "-" is written in all columns of Tables 7 and 8, it means that the first and second injection holes were used in step II, while the third and fourth injection holes were not used. The total time of step I and step II was adjusted so that the thickness of the first layer was as described in Tables 13 and 14. In addition, 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 written in all the columns of "Deposition conditions of surface layer" in Tables 9 and 10, it means that the surface layer was not formed.

[0091] Next, when a surface layer was formed on the surface of the first layer, a blasting treatment was performed on the surface of the surface layer under the following conditions: When a surface layer was not formed on the surface of the first layer, a blasting treatment was performed on the surface of the first layer under the following conditions: (conditions) Media Type:Ceramics Average media particle size: 150μm Media density: 300g / min Projection angle: 75° Projection distance: 35mm 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 observed to determine whether the coating had peeled off. The results are shown in the "Whether or Not the Coating Had Peeled Off 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] [Table 1]

[0095] [Table 2]

[0096] [Table 3]

[0097] [Table 4]

[0098] [Table 5]

[0099] [Table 6]

[0100] [Table 7]

[0101] [Table 8]

[0102]

Table 9

[0103]

Table 10

[0104]

Table 11

[0105]

Table 12

[0106]

Table 13

[0107]

Table 14

[0108]

Table 15

[0109]

Table 16

[0110]

Table 17

[0111]

Table 18

[0112] <Evaluation of cutting tool characteristics> <Composition of the undercoat layer> The composition of the base 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 "Base Layer" column in Tables 11 and 12. When the names of components are 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 components 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 names of components are listed in the "Composition" column of the "Intermediate Layer" column in Tables 11 and 12, this means that the intermediate layer is composed of the components listed in the "Composition" column of the "Intermediate Layer" column in Tables 11 and 12.

[0114] <Composition of the first layer> The composition of the first layer of each sample cutting tool was determined by the method described in embodiment 1. The results are shown in the "Composition" column of the "First Layer" column in Tables 13 and 14. When the names of components are listed in the "Composition" column of the "First Layer" column in Tables 13 and 14, it 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 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> 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 results obtained are shown in the "Ra [μm]" column of Tables 13 and 14.

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

[0117] <Compressive residual stress in the 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] <First layer orientation index TC(0 0 12)> 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 results are shown in the "TC(0012)" column of the "First Layer" column in Tables 13 and 14.

[0119] <Surface layer composition> 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. When the names of components are 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 components listed in the "Composition" column of the "Surface layer" column in Tables 15 and 16.

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

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

[0122] <Cutting test 2> Using the cutting tools of each sample, cutting tests were performed under the following cutting conditions. The cutting distance until the flank wear reached 0.2 mm was measured. The results are shown in the "Cutting test 2 [km]" column of Table 18. (Cutting conditions) Work material: FCD700 Machining: Continuous turning Cutting speed: 140m / min Feed rate: 0.3mm / rev Depth of cut: 1.5mm 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 for Samples 17 to 20, the cutting time was 210 seconds or more in Cutting Test 1, and the cutting distance was 2.5 km in Cutting Test 2. Also, although not shown in Table 18, it was confirmed that for Samples 109 to 112, at least either the cutting time of 210 seconds or more in Cutting Test 1 or the cutting distance of 2.5 km in Cutting Test 2 was not achieved.

[0125] The cutting tools of Samples 1 to 20 correspond to Examples. The cutting tools of 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 of Samples 1 to 20 have a longer tool life than the cutting tools of 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 intended from the outset 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 as limiting. The scope of the present invention is indicated by the claims, not by the embodiments and examples described above, and is intended to include the meaning equivalent to the claims and all modifications within the scope. [Explanation of symbols]

[0129] 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. 1. A cutting tool comprising a substrate and a coating disposed on the substrate, The coating comprises a first layer, The first layer is α-Al ２ O ３ It consists of: The thickness of the first layer is 2 μm or more and 15 μm or less, 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 virtual line L1 at a position where the first grain boundaries intersect with virtual line L1, to the number N1 of first grain boundaries crossed by virtual line L1 that is equidistant from an interface of the first layer on the surface side of the first layer or the coating on the surface side of the first layer and an interface of the first layer on the substrate side, is 0.60 or more, a cutting tool, in which, in the cross section taken along the normal to the interface between the substrate and the coating, a number N3 of third grain boundaries crossed by a virtual line L2 that is 0.5 μm away from a surface of the first layer or an interface on the surface side of the coating of the first layer toward the substrate, and a ratio N4 / N3 of the number N4 of fourth grain boundaries that are grain boundaries having an absolute value of an angle of 15° or less with respect to a straight line perpendicular to the virtual line L2 at a position where the third grain boundaries and the virtual line L2 intersect, and the ratio N2 / N1 satisfy the relationship of the following formula 1. 0.1≦(N2 / N1)-(N4 / N3)≦0.40 Formula 1

2. 2. The cutting tool according to claim 1, wherein the number N3 and a number N5 of fifth grain boundaries, which are grain boundaries among the third grain boundaries and have an absolute value of an angle with respect to a line perpendicular to the virtual line L2 at a position where the third grain boundary and the virtual line L2 intersect, satisfy the relationship of the following formula 2. (N5 / N3)>0.96 Formula 2

3. The thickness of the first layer is less than 8 μm; 3. The cutting tool according to claim 1, wherein a surface roughness Ra of the first layer or a surface of the first layer located at the interface with the coating on the surface side is 0.03 μm or more and 0.2 μm or less.

4. The thickness of the first layer is 8 μm or more, 3. The cutting tool according to claim 1, wherein a surface roughness Ra of the first layer or a surface of the first layer located at the interface with the coating on the surface side is 0.05 μm or more and 0.2 μm or less.

5. The cutting tool according to claim 1 or 2, wherein an 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 claim 1 or 2, wherein the first layer has a texture index TC(0 0 12) of greater than 4.5.

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