Coated cutting tool

Abstract

To provide a coated cutting tool which has excellent abrasion resistance and chipping resistance, and thereby can extend a tool life.SOLUTION: A coated cutting tool includes a base material, and a coating layer formed on the surface of the base material, wherein the coating layer includes a lower layer and an upper layer in this order from the base material side to the surface side of the coating layer, the upper layer includes an α-Al2O3 layer, average thickness of the upper layer is 1.5 μm or more and 15.0 μm or less, the lower layer includes one or more Ti compound layers, at least the one layer of the Ti compound layers is a TiCN layer, average thickness of the TiCN layer is 3.0 μm or more and 15.0 μm or less, in the TiCN layer, when an average value of a KAM value in a first region is represented by KAM1, and an average value of the KAM value in a second region is represented by KAM2, a relation of 0.12°≤(KAM1-KAM2)≤0.50° is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] It is well known that coated cutting tools have been used for cutting steel, cast iron, etc., in which a coating layer consisting of a single layer or a multi-layer of two or more types selected from the group consisting of titanium carbide, nitride, carbonitride, carbonate, and carbonitride oxide, and aluminum oxide (Al2O3), is vapor-deposited on the surface of a cemented carbide substrate by a chemical vapor deposition method.

[0003] In Patent Document 1, the surface of a tool substrate made of a tungsten carbide-based cemented carbide or a titanium carbonitride-based cermet is coated with (a) A Ti compound layer in which the lower layer is composed of one or more layers selected from the group consisting of a Ti carbide layer, a nitride layer, a carbonitride layer, a carbonate layer, and a carbonitride-oxycarbonitride layer, each having a total average thickness of 3 to 20 μm, and at least one of these layers being a modified Ti carbonitride layer having an average thickness of 2 to 20 μm; (b) the upper layer is an aluminum oxide layer having an average layer thickness of 1 to 15 μm; In a surface-coated cutting tool having a hard coating layer formed thereon comprising the above (a) and (b), (c) For the modified Ti carbonitride layer of (a) above, a field emission scanning electron microscope and an electron backscatter diffraction pattern device are used to irradiate an electron beam onto each crystal grain having a cubic crystal lattice present within a measurement range of a polished longitudinal cross section, and measure the tilt angle formed by the normal to the (112) plane, which is the crystal face of the crystal grain, with respect to the normal to the substrate surface. Of the measured tilt angles, those within a range of 0 to 45 degrees are divided into 0.25 degree increments, and a tilt angle number distribution graph is created by tabulating the frequency within each division. The tilt angle number distribution graph shows that the total frequency within a range of 0 to 10 degrees accounts for 20 to 80% of the total frequency in the tilt angle number distribution graph. (d) A surface-coated cutting tool is described in which, for the modified Ti carbonitride layer of (a) above, an electron beam is used to irradiate each crystal grain having a cubic crystal lattice within a measurement range on a polished longitudinal cross-section surface, and the misorientation (rotation angle) between each crystal lattice is measured. If the misorientation (rotation angle) between the crystal lattices of adjacent measurement points is 5 degrees or more, the boundary between adjacent measurement points is considered to be a crystal grain boundary, and an area surrounded by a crystal grain boundary and not separated by other crystal grain boundaries is identified as the same crystal grain. Furthermore, when the average intra-grain misorientation of each crystal grain is calculated, the area ratio of crystal grains showing an intra-grain average misorientation of less than 5 degrees is 20 to 80%, while the area ratio of crystal grains showing an intra-grain average misorientation of 5 degrees or more is 20 to 80%. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6139057 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been a strong demand for labor-saving and energy-saving cutting processes, and as a result, cutting processes have become increasingly faster, with higher feed rates and deeper cuts, requiring tools to have better wear resistance and fracture resistance than ever before. In particular, in high-speed intermittent cutting, which is subject to impact loads, cracks that occur on the surface of the coating layer of conventional tools tend to propagate to the base material, causing chipping and fracture of the cutting edge, making it difficult to extend the tool life.

[0006] The coated cutting tool of Patent Document 1 does not consider the distribution of local strain in the thickness direction of the modified Ti carbonitride layer, which results in an insufficient effect in suppressing the propagation of cracks into the base material, and leaves room for improvement in fracture resistance.

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

[0008] As a result of extensive research into achieving the above object, the present inventors have discovered that by providing a coating layer in a coated cutting tool with a specific configuration, the coated cutting tool has excellent wear resistance and chipping resistance, and have thus completed the present invention.

[0009] That is, the present invention is as follows. [1] A substrate and a coating layer formed on the surface of the substrate, the coating layer includes a lower layer and an upper layer in this order from the substrate side toward the surface side of the coating layer, the upper layer includes an α-Al2O3 layer made of α-type aluminum oxide, The average thickness of the upper layer is 1.5 μm or more and 15.0 μm or less, the lower layer includes one or more Ti compound layers made of a Ti compound of Ti and at least one element selected from the group consisting of C, N, and O, and at least one of the Ti compound layers is a TiCN layer made of a carbonitride of Ti; The average thickness of the TiCN layer is 3.0 μm or more and 15.0 μm or less, A coated cutting tool in which a region of the TiCN layer extending from the substrate side toward the opposite side of the substrate is defined as a first region, a region of the TiCN layer on the opposite side of the substrate from the first region is defined as a second region, an average KAM value in the first region is defined as KAM1, and an average KAM value in the second region is defined as KAM2, satisfying the relationship of the following formula (i): 0.12°≦(KAM1-KAM2)≦0.50° (i) [2] The coated cutting tool according to [1], wherein the KAM1 is 0.40° or more and 1.00° or less. [3] The coated cutting tool according to [1] or [2], wherein the KAM2 is 0.30° or more and 0.70° or less. [4] The coated cutting tool according to any one of [1] to [3], wherein in the TiCN layer, the ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries (100%) is 15% or more and 50% or less. [5] The coated cutting tool according to any one of [1] to [4], wherein the lower layer has an average thickness of 3.0 μm or more and 15.0 μm or less. [6] The coated cutting tool according to any one of [1] to [5], wherein the coating layer has an average thickness of 5.0 μm or more and 30.0 μm or less. [7] The coated cutting tool according to any one of [1] to [6], wherein the substrate is a cemented carbide, a cermet, a ceramic, or a cubic boron nitride sintered body. [Effects of the Invention]

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

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

[0012] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary, but the present invention is not limited to the present embodiment. The present invention can be modified in various ways without departing from the gist of the invention. In the drawings, the same elements are given the same reference numerals, and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown.

[0013] The coated cutting tool of this embodiment includes a substrate and a coating layer formed on the substrate surface. The coating layer includes a lower layer and an upper layer, in this order from the substrate side toward the surface side of the coating layer. The upper layer includes an α-Al2O3 layer made of α-aluminum oxide and has an average thickness of 1.5 μm to 15.0 μm. The lower layer includes one or more Ti compound layers made of a Ti compound of Ti and at least one element selected from the group consisting of C, N, and O. At least one of the Ti compound layers is a TiCN layer made of a Ti carbonitride. The TiCN layer has an average thickness of 3.0 μm to 15.0 μm. In the TiCN layer, a region extending from the substrate side to 1 μm away from the substrate is defined as a first region, and a region of the TiCN layer further away from the substrate than the first region is defined as a second region. When the average KAM value in the first region is defined as KAM1 and the average KAM value in the second region is defined as KAM2, the relationship of the following formula (i) is satisfied: 0.12°≦(KAM1-KAM2)≦0.50° (i)

[0014] The coated cutting tool of this embodiment has the above-described configuration and exhibits the following effects. However, the effects are considered to be as follows, but are not limited to these. First, the coated cutting tool of this embodiment has excellent wear resistance because the average thickness of the upper layer including the α-Al2O3 layer is 1.5 μm or more. On the other hand, the coated cutting tool of this embodiment has excellent chipping resistance and fracture resistance because the average thickness of the upper layer including the α-Al2O3 layer is 15.0 μm or less, thereby improving the adhesion of the coating layer. Furthermore, the coated cutting tool of this embodiment has excellent wear resistance because the average thickness of the TiCN layer in the lower layer is 3.0 μm or more, and can effectively and reliably achieve the effect of making the (KAM1 - KAM2) ratio 0.12° or more, as described below. On the other hand, the coated cutting tool of this embodiment has excellent chipping resistance and fracture resistance because the average thickness of the TiCN layer in the lower layer is 15.0 μm or less, thereby improving the adhesion of the coating layer.

[0015] Furthermore, in the coated cutting tool of this embodiment, when the (KAM1 - KAM2) ratio in the lower TiCN layer is 0.12° or more, cracks generated during cutting can be prevented from propagating perpendicular to the substrate surface. As a result, cracks are less likely to propagate to the substrate, improving fracture resistance. Note that "preventing propagation perpendicular to the substrate surface" does not mean suppressing crack propagation itself, but rather changing the direction of crack propagation. On the other hand, in the coated cutting tool of this embodiment, when the (KAM1 - KAM2) ratio in the lower TiCN layer is 0.50° or less, multiple cracks that propagate to the TiCN layer are less likely to connect with each other. As a result, the strength of the TiCN layer is suppressed, resulting in excellent wear resistance and fracture resistance. Note that "multiple cracks connect with each other" here means that cracks that are separated in a direction parallel to the substrate surface connect with each other. In this embodiment, the KAM (Kernel Average Misorientation) value is a numerical value indicating the local misorientation, which is the difference in crystal orientation between adjacent measurement points, in crystal orientation analysis based on electron backscatter diffraction (hereinafter referred to as "EBSD") using a scanning electron microscope, and is a parameter for quantitatively evaluating plastic deformation. A larger KAM value indicates a larger difference in crystal orientation between adjacent measurement points, which means greater plastic deformation. These combined effects result in the coated cutting tool of this embodiment having improved wear resistance and fracture resistance and a long tool life.

[0016] FIG. 1 is a schematic cross-sectional view showing an example of a coated cutting tool according to this embodiment. The coated cutting tool 5 includes a substrate 1 and a coating layer 4 formed on the surface of the substrate 1. The coating layer 4 further includes a lower layer 2 formed on the surface of the substrate 1 and an upper layer 3 formed on the surface of the lower layer 2 opposite the substrate 1.

[0017] (base material) The coated cutting tool of this embodiment includes a substrate and a coating layer formed on the surface of the substrate. Specific examples of the coated cutting tool include indexable cutting inserts for milling or turning, drills, and end mills.

[0018] The substrate in this embodiment is not particularly limited as long as it can be used as the substrate of a coated cutting tool. Examples of such substrates include cemented carbide, cermet, ceramics, cubic boron nitride sintered body, diamond sintered body, and high-speed steel. Among them, cemented carbide, cermet, ceramics, or cubic boron nitride sintered body are preferable as the substrate because they have better wear resistance and chipping resistance, and from the same viewpoint, cemented carbide is more preferable as the substrate.

[0019] The substrate may have a surface modified. For example, if the substrate is made of cemented carbide, a de-β layer may be formed on the surface. If the substrate is made of cermet, a hardened layer may be formed on the surface. Even if the surface of the substrate is modified in this way, the effects of the present invention can be achieved.

[0020] (covering layer) In the coated cutting tool of this embodiment, the average thickness of the entire coating layer is preferably 5.0 μm or more and 30.0 μm or less. In the coated cutting tool of this embodiment, when the average thickness of the entire coating layer is 5.0 μm or more, the wear resistance tends to be further improved. On the other hand, in the coated cutting tool of this embodiment, when the average thickness of the entire coating layer is 30.0 μm or less, the adhesion of the coating layer to the substrate is improved, so that the chipping resistance is improved and the fracture resistance tends to be even more excellent. From the same viewpoint, the average thickness of the entire coating layer is more preferably 8.4 μm or more and 28.2 μm or less, and even more preferably 11.9 μm or more and 24.5 μm or less.

[0021] (lower layer) In the coated cutting tool of this embodiment, the lower layer includes one or more Ti compound layers made of a Ti compound of Ti and at least one element selected from the group consisting of C, N, and O, and at least one of the Ti compound layers is a TiCN layer made of a carbonitride of Ti. The Ti compound layer contained in the lower layer is not particularly limited except for the TiCN layer, but examples thereof include a Ti carbide layer (hereinafter also referred to as a "TiC layer"), a Ti nitride layer (hereinafter also referred to as a "TiN layer"), a Ti carbonate layer (hereinafter also referred to as a "TiCO layer"), and a Ti carbonitride layer (hereinafter also referred to as a "TiCNO layer"). The coating layer preferably includes such a lower layer, since it further improves adhesion between the substrate and the coating layer. The lower layer may be composed of a single layer or multiple layers (e.g., two or three layers), with multiple layers being preferred, two or three layers being more preferred, and three layers being even more preferred. Furthermore, the lower layer may include a single layer of the same type of layer from among the various layers described above, or multiple layers. From the viewpoint of further improving chipping resistance and fracture resistance, the lower layer preferably includes at least one layer selected from the group consisting of a TiN layer, a TiCN layer, and a TiCNO layer. From the same viewpoint, it is even more preferable that the lower layer has a TiN layer or a TiC layer as the layer closest to the substrate (adhesion layer), a TiCNO layer or a TiCO layer as the layer closest to the upper layer (intermediate layer), and a TiCN layer between those layers, and it is particularly preferable that the lower layer has a TiN layer as the layer closest to the substrate (adhesion layer), a TiCNO layer as the layer closest to the upper layer (intermediate layer), and a TiCN layer between those layers.

[0022] In the coated cutting tool of this embodiment, the average thickness of the lower layer is preferably 3.0 μm or more and 15.0 μm or less. In the coated cutting tool of this embodiment, when the average thickness of the lower layer is 3.0 μm or more, the wear resistance tends to be excellent. On the other hand, in the coated cutting tool of this embodiment, when the average thickness of the lower layer is 15.0 μm or less, the adhesion of the coating layer is improved, so that the chipping resistance is improved and the fracture resistance tends to be excellent. From the same viewpoint, the average thickness of the lower layer is more preferably 3.8 μm or more and 14.9 μm or less, even more preferably 4.4 μm or more and 12.9 μm or less, and even more preferably 5.4 μm or more and 12.0 μm or less. Furthermore, in the coated cutting tool of this embodiment, the average thickness of the TiCN layer in the lower layer is 3.0 μm or more and 15.0 μm or less. Since the average thickness of the TiCN layer in the lower layer is 3.0 μm or more, the coated cutting tool of this embodiment has excellent wear resistance and can effectively and reliably achieve the effect of making (KAM1 - KAM2) 0.12° or more, as described below. Meanwhile, since the average thickness of the TiCN layer in the lower layer is 15.0 μm or less, the coated cutting tool of this embodiment has improved adhesion of the coating layer, resulting in improved chipping resistance and excellent fracture resistance. In addition, when the lower layer is composed of multiple layers, the average thickness of the layer (adhesion layer) closest to the substrate is preferably 0.05 μm or more and 2.0 μm or less, and more preferably 0.2 μm or more and 1.0 μm or less, particularly from the viewpoint of further improving adhesion between the lower layer or the substrate. When the lower layer is composed of multiple layers, the average thickness of the layer (intermediate layer) closest to the upper layer is preferably 0.05 μm or more and 2.0 μm or less, and more preferably 0.2 μm or more and 1.0 μm or less, particularly from the viewpoint of further improving adhesion between the upper layer (e.g., upper layer).

[0023] In the coated cutting tool of this embodiment, the region of the lower TiCN layer from the substrate side to 1 μm away from the substrate is defined as the first region, the region on the opposite side of the substrate from the first region is defined as the second region, and when the average KAM value in the first region is defined as KAM1 and the average KAM value in the second region is defined as KAM2, the relationship of the following formula (i) is satisfied. 0.12°≦(KAM1-KAM2)≦0.50° (i) In the coated cutting tool of this embodiment, when the TiCN lower layer has a (KAM1-KAM2) ratio of 0.12° or more, cracks generated during cutting can be prevented from propagating perpendicularly to the substrate surface, resulting in improved fracture resistance because the cracks are less likely to propagate to the substrate. On the other hand, in the coated cutting tool of this embodiment, when the TiCN lower layer has a (KAM1-KAM2) ratio of 0.50° or less, multiple cracks that have propagated to the TiCN layer are less likely to connect with each other, resulting in reduced strength of the TiCN layer, resulting in excellent wear resistance and fracture resistance. From the same perspective, (KAM1-KAM2) is preferably 0.13° or more and 0.47° or less, and more preferably 0.14° or more and 0.45° or less.

[0024] The KAM value and its average value are measured as follows. In a coated cutting tool, a cross section of the lower TiCN layer is exposed perpendicular to the surface of the substrate to obtain an observation surface. Examples of methods for exposing the cross section of the lower TiCN layer include cutting and polishing. Among these, polishing is preferred to obtain a smoother observation surface of the lower TiCN layer. A mirror-finished observation surface is particularly preferred to obtain a smoother observation surface. Methods for obtaining a mirror-finished observation surface of the lower TiCN layer include, but are not limited to, polishing using diamond paste or colloidal silica, ion milling, and the like. The region of the cross section of the lower TiCN layer extending from the substrate side to the opposite side of the substrate is defined as the first region, and the region on the opposite side of the first region from the substrate is defined as the second region. Using EBSD (manufactured by TSL), each measurement area of ​​the first and second regions is divided into regular hexagonal regions (pixels). For each divided region, a Kikuchi pattern is obtained from the backscattered electrons of an electron beam incident on the polished surface of the sample, and the pixel orientation is measured. The obtained orientation data was analyzed using the EBSD analysis software described above, and various parameters were calculated. The measurement conditions were an acceleration voltage of 15 kV, the dimensions of the measurement area were a width of 50 μm, the first area was 1 μm thick from the substrate side, the second area was the thickness of the remaining lower layer, and the distance between adjacent pixels (step size) was 0.1 μm. Adjacent pixels with an orientation difference of 5° or more from the measurement center pixel were excluded from the KAM value calculation, assuming that they were beyond the grain boundary from the single crystal in which the measurement center pixel was located. In other words, the KAM value was calculated as the average of the orientation differences between a pixel within a crystal grain and adjacent pixels located within a range from that crystal grain but not beyond the grain boundary. The KAM values ​​for all pixels comprising the entire area of ​​the measurement area were then averaged. The average KAM value was calculated by averaging the KAM values ​​averaged as described above for any five measurement areas.

[0025] In the coated cutting tool of this embodiment, the KAM1 in the lower TiCN layer is preferably 0.40° or more and 1.00° or less. When the KAM1 in the lower TiCN layer of this embodiment is 0.40° or more, the effect of (KAM1 - KAM2) being 0.12° or more tends to be effectively and reliably achieved. On the other hand, when the KAM1 in the lower TiCN layer of this embodiment is 1.00° or less, the effect of (KAM1 - KAM2) being 0.50° or less tends to be effectively and reliably achieved. From the same viewpoint, KAM1 is more preferably 0.45° or more and 0.97° or less, and even more preferably 0.52° or more and 0.92° or less.

[0026] In the coated cutting tool of this embodiment, the KAM2 of the lower TiCN layer is preferably 0.30° or more and 0.70° or less. When the KAM2 of the lower TiCN layer is 0.30° or more, the hardness of the TiCN layer is improved, and the coated cutting tool of this embodiment tends to have even better wear resistance. On the other hand, when the KAM2 of the lower TiCN layer is 0.70° or less, the toughness of the TiCN layer is improved, and the coated cutting tool of this embodiment tends to have even better fracture resistance. From the same viewpoint, the KAM2 is more preferably 0.33° or more and 0.67° or less, and even more preferably 0.39° or more and 0.65° or less.

[0027] In addition, in the coated cutting tool of this embodiment, the ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries (100%) in the lower TiCN layer is preferably 15% or more and 50% or less. In the coated cutting tool of this embodiment, when the ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries (100%) in the lower TiCN layer is 15% or more, the proportion of grain boundaries with relatively low grain boundary energy increases, improving mechanical properties and crater wear resistance, and therefore, the coated cutting tool tends to have even better wear resistance. Furthermore, since strain relaxation due to grain boundary sliding is more likely to occur, the above-mentioned (KAM1 - KAM2) value tends to be easier to control to 0.12° or more. On the other hand, in the coated cutting tool of this embodiment, when the ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries (100%) in the lower TiCN layer is 50% or less, coarsening of crystal grains can be suppressed, improving chipping resistance, and therefore, the coated cutting tool tends to have even better fracture resistance. From the same viewpoint, in the lower TiCN layer, the ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries (100%) is more preferably 16% or more and 47% or less, and even more preferably 17% or more and 42% or less. In this embodiment, the total length of all grain boundaries is the total length of the CSL grain boundaries and the lengths of the other general crystal grain boundaries.

[0028] The TiCN lower layer used in this embodiment has grain boundaries with relatively high grain boundary energy and grain boundaries with relatively low grain boundary energy. Typically, grain boundaries have many gaps due to the random arrangement of atoms, resulting in relatively high grain boundary energy. On the other hand, some grain boundaries have regular atomic arrangements with few gaps, resulting in relatively low grain boundary energy. A representative example of such grain boundaries with relatively low grain boundary energy is a coincidence site lattice grain boundary (hereinafter referred to as a "CSL grain boundary" or "CSL grain boundary"). Grain boundaries significantly affect important sintering processes such as densification, creep, and diffusion, as well as electrical, optical, and mechanical properties. The importance of grain boundaries depends on several factors, such as the grain boundary density in the material, the chemical composition of the interface, and the crystallographic structure, i.e., grain boundary boundary orientation and grain misorientation. CSL grain boundaries play a special role. The Σ value is known as an index of the distribution of CSL grain boundaries, and is defined as the ratio of the density of crystal lattice points between two crystal grains that contact each other at the grain boundary to the density of lattice points that match when both crystal lattices are superimposed. In the case of simple structures, it is generally recognized that grain boundaries with low Σ values ​​tend to have low interfacial energy and special properties. Therefore, controlling the proportion of CSL grain boundaries and the distribution of crystal grain misorientation is considered to be favorable for improving the properties of the lower TiCN layer.

[0029] Recently, a scanning electron microscope (SEM)-based technique known as electron backscatter diffraction (EBSD) has been used to study grain boundaries in materials. EBSD is based on the automated analysis of Kikuchi diffraction patterns generated by backscattered electrons.

[0030] For each grain in a material of interest, the crystallographic orientation is determined after indexing the corresponding diffraction pattern. EBSD, along with commercially available software, allows for relatively easy texture analysis and determination of the grain boundary character distribution (GBCD). By measuring and analyzing interfaces with EBSD, the misorientation of grain boundaries can be revealed across a large sample population of interfaces. The distribution of misorientation is typically related to the processing and / or physical properties of the material. The misorientation of grain boundaries can be derived from conventional orientation parameters such as Euler angles, angle / axis pairs, or Rodrigues vectors.

[0031] In this embodiment, the CSL grain boundaries in the TiCN lower layer include the Σ3 grain boundary, as well as the Σ5 grain boundary, Σ7 grain boundary, Σ9 grain boundary, Σ11 grain boundary, Σ13 grain boundary, Σ15 grain boundary, Σ17 grain boundary, Σ19 grain boundary, Σ21 grain boundary, Σ23 grain boundary, Σ25 grain boundary, Σ27 grain boundary, and Σ29 grain boundary. The Σ3 grain boundary is considered to have the lowest grain boundary energy among the CSL grain boundaries in the TiCN lower layer. Here, the length of the Σ3 grain boundary refers to the total length of the Σ3 grain boundary in a field of view (a specific region) observed using an SEM equipped with EBSD. This Σ3 grain boundary has a higher density of coincidence lattice points and lower grain boundary energy than other CSL grain boundaries. In other words, the Σ3 grain boundary is a CSL grain boundary with many coincident lattice points, and two crystal grains sharing the Σ3 grain boundary behave similarly to a single crystal or twin crystal, tending to grow larger. In the coated cutting tool of this embodiment, by setting the ratio of the length of the Σ3 grain boundary to 100% of the total length of all grain boundaries in the lower TiCN layer to the above-mentioned lower limit or more, the proportion of grain boundaries with relatively low grain boundary energy increases, and strain relaxation due to grain boundary sliding becomes more likely. On the other hand, in the coated cutting tool of this embodiment, by setting the ratio of the length of the Σ3 grain boundary to 100% of the total length of all grain boundaries in the lower TiCN layer to the above-mentioned upper limit or less, coarsening of crystal grains tends to be suppressed.

[0032] Here, "total grain boundaries" refers to the sum of all grain boundaries other than CSL grain boundaries and CSL grain boundaries. Hereinafter, grain boundaries other than CSL grain boundaries will be referred to as "general grain boundaries." General grain boundaries are the remaining grain boundaries after excluding CSL grain boundaries from all grain boundaries of the grains in the lower TiCN layer when observed with an SEM equipped with EBSD. Therefore, the "total length of all grain boundaries" can be expressed as the "sum of the length of CSL grain boundaries and the length of general grain boundaries."

[0033] In this embodiment, the ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries (100%) in the lower TiCN layer can be calculated as follows.

[0034] In a coated cutting tool, the cross section of the lower TiCN layer is exposed in a direction perpendicular to the surface of the substrate to obtain an observation surface. Examples of methods for exposing the cross section of the lower TiCN layer include cutting and polishing. Among these, polishing is preferred in order to make the observation surface of the lower TiCN layer smoother. In particular, a mirror-finish observation surface is preferred in order to achieve a smoother surface. Methods for obtaining a mirror-finish observation surface of the lower TiCN layer are not particularly limited, but examples include polishing using diamond paste or colloidal silica, ion milling, etc.

[0035] Thereafter, the above observation surface is observed using an SEM equipped with EBSD. As the observation region, it is preferable to observe a flat surface (such as a rake face).

[0036] The SEM used is an SU6600 (manufactured by Hitachi High-Technologies Corporation) equipped with an EBSD (manufactured by TexSEM Laboratories).

[0037] The normal to the observation surface is tilted 70° relative to the incident beam, and analysis is performed by irradiating the electron beam with an accelerating voltage of 15 kV and a probe current of 1.0 nA. Data collection is performed at 0.1 μm / step over a 50 μm-wide area of ​​the lower TiCN layer on the observation surface. This data collection is performed over five randomly selected areas, and the average value is calculated.

[0038] Data processing is performed using commercially available software. The CSL grain boundaries corresponding to any Σ value are counted and the proportion of each grain boundary expressed as a ratio to all grain boundaries. From the above, the length of the Σ3 grain boundary, the length of the CSL grain boundary, and the total length of all grain boundaries can be calculated, and the ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries (100%) can be calculated.

[0039] (upper layer) In the coated cutting tool of this embodiment, the upper layer includes an α-Al2O3 layer made of α-aluminum oxide (hereinafter simply referred to as "α-Al2O3 layer"). When the coating layer includes such an upper layer, the wear resistance of the coating layer and the coated cutting tool increases. The upper layer may be composed of a single layer or multiple layers (for example, two or three layers manufactured by different processes).

[0040] In the coated cutting tool of this embodiment, the average thickness of the upper layer is 1.5 μm or more and 15.0 μm or less. The coated cutting tool of this embodiment has excellent wear resistance because the average thickness of the upper layer is 1.5 μm or more. On the other hand, the coated cutting tool of this embodiment has an average thickness of 15.0 μm or less, which improves the adhesion of the coating layer, thereby improving chipping resistance and resulting in excellent fracture resistance. From the same viewpoint, the average thickness of the upper layer is more preferably 2.0 μm or more and 14.5 μm or less, even more preferably 3.0 μm or more and 14.0 μm or less, and even more preferably 4.0 μm or more and 12.5 μm or less.

[0041] The coating layer according to this embodiment preferably further includes an outer layer on the surface of the upper layer opposite the lower layer. The outer layer is not particularly limited, but examples include a TiN layer made of Ti nitride, a TiCN layer made of Ti carbonitride, a TiC layer made of Ti carbide, a TiCNO layer made of Ti carbonitride, a TiCO layer made of Ti carbonate, and a TiB2 layer made of Ti boride. The outer layer may be a multilayer (e.g., a TiCN layer-TiN layer or a TiCNO layer-TiCN layer-TiN layer). The inclusion of such an outer layer further enhances the wear resistance of the coating layer and the coated cutting tool. It also provides improved visibility between unused and used cutting edges. Having such an outer layer as the outermost layer of the coating layer further enhances the wear resistance of the coating layer and the coated cutting tool. From the viewpoint of more effectively and reliably achieving the effect of excellent abrasion resistance, the average thickness of the outer layer is preferably 0.1 μm or more and 5.0 μm or less, more preferably 0.1 μm or more and 4.5 μm or less, and even more preferably 0.2 μm or more and 4.0 μm or less.

[0042] In this embodiment, the coated cutting tool can be obtained, for example, by the following method.

[0043] First, one or more Ti compound layers containing at least a TiCN layer are formed as a lower layer on the surface of the substrate. Next, the surface of the lower layer (if the lower layer is multiple layers, the surface of the layer farthest from the substrate) is oxidized. After that, an upper layer, which is an α-Al2O3 layer, is formed on the surface of the oxidized lower layer. Furthermore, an outer layer may be formed on the surface of the upper layer if necessary.

[0044] More specifically, for example, the lower layer is formed as a TiN layer or a TiC layer as the layer closest to the substrate (adhesion layer), a TiCNO layer or a TiCO layer as the layer closest to the upper layer (intermediate layer), and a TiCN layer is formed between those layers.

[0045] The lower TiN layer can be formed by chemical vapor deposition using a source gas composition of TiCl4: 5.0 to 10.0 mol %, N2: 20.0 to 60.0 mol %, and H2: balance, at a temperature of 850 to 950°C and a pressure of 100 to 400 hPa.

[0046] The lower TiC layer can be formed by chemical vapor deposition using a raw material gas composition of TiCl4: 1.0 to 3.0 mol%, CH4: 4.0 to 6.0 mol%, and H2: balance, at a temperature of 900 to 1000°C and a pressure of 50 to 100 hPa.

[0047] The lower TiCN layer can be formed by a two-stage chemical vapor deposition process, consisting of a first stage and a second stage. The pressure and source gas composition are the same in the first and second stages, but the temperature is varied. Specifically, the source gas composition is the same in the first and second stages, ranging from 7.0 to 11.0 mol% TiCl4, 0.8 to 1.2 mol% CH3CN, 10.0 to 25.0 mol% N2, and the remainder H2. The pressure is also the same in the first and second stages, ranging from 70 to 100 hPa. The temperature is 900 to 960°C for 20 to 60 minutes in the first stage, and 780 to 830°C in the second stage. After the first stage, the temperature is controlled to that of the second stage, and the H2 atmosphere is maintained at a pressure of 60 hPa during the temperature control. The average KAM values ​​of the first and second regions can be adjusted by forming the TiCN layer at two different temperatures or by subjecting the coating layer to wet shot blasting. Specifically, the average KAM value of the first region, KAM1, tends to increase when the temperature or time of the first stage is increased, and tends to decrease when wet shot blasting is performed. The average KAM value of the second region, KAM2, tends to decrease when the temperature or time of the second stage is decreased, and tends to decrease when wet shot blasting is performed. Furthermore, (KAM1 - KAM2) can be controlled within a desired range by forming the TiCN layer in two stages, the first and second stages, as described above, and appropriately adjusting KAM1 and KAM2 using the method described above. In addition, (KAM1-KAM2) tends to increase as the ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries in the TiCN layer (100%) increases, and also as the average thickness of the TiCN layer increases. The ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries in the TiCN layer (100%) can be controlled by adjusting the ratio of the source gas composition in the TiCN layer formation process. Specifically, for example, increasing the ratio of TiCl4 or N2 in the source gas tends to increase the ratio of the length of the Σ3 grain boundary.

[0048] The lower TiCO layer can be formed by chemical vapor deposition using a raw material gas composition of TiCl4: 1.0 to 2.0 mol%, CO: 2.0 to 4.0 mol%, and H2: balance, at a temperature of 950 to 1000°C and a pressure of 60 to 100 hPa.

[0049] The lower layer, the TiCNO layer, can be formed by chemical vapor deposition using a raw material gas composition of TiCl4: 3.0 to 5.0 mol%, CO: 0.4 to 1.0 mol%, N2: 30.0 to 40.0 mol%, and H2: balance, at a temperature of 950 to 1000°C and a pressure of 90 to 110 hPa.

[0050] The surface of the lower layer is oxidized under conditions of a gas composition of 0.1 to 1.0 mol% CO2 and the balance H2, a temperature of 970 to 1020°C, and a pressure of 50 to 70 hPa. The oxidation time is preferably 1 to 15 minutes.

[0051] After oxidation of the lower layer, aluminum oxide nuclei are formed, and the upper layer, the α-Al2O3 layer, is then formed using these nuclei. The aluminum oxide nuclei are formed by chemical vapor deposition using a source gas composition of 1.0-4.0 mol% AlCl3, 0.05-2.0 mol% CO2, 1.0-3.0 mol% CO2, 2.0-3.0 mol% HCl, and the balance H2 at a temperature of 950-1130°C and a pressure of 60-80 hPa. The upper layer, the α-Al2O3 layer, is formed by chemical vapor deposition using a source gas composition of 2.0-5.0 mol% AlCl3, 2.5-4.0 mol% CO2, 2.0-3.0 mol% HCl, 0.1-0.3 mol% H2S, and the balance H2 at a temperature of 950-1130°C and a pressure of 60-80 hPa.

[0052] The outer TiN layer can be formed by chemical vapor deposition using a raw material gas composition of TiCl4: 5.0 to 10.0 mol%, N2: 20.0 to 60.0 mol%, and H2: balance, at a temperature of 950 to 1050°C and a pressure of 300 to 400 hPa.

[0053] The outer TiCN layer can be formed by chemical vapor deposition using a raw material gas composition of TiCl4: 7.0 to 11.0 mol%, CH3CN: 0.8 to 1.2 mol%, CH4: 1.0 to 2.0 mol%, N2: 4.0 to 6.0 mol%, and H2: balance, at a temperature of 950 to 1050°C and a pressure of 60 to 80 hPa.

[0054] Furthermore, as described above, the average KAM values ​​of the first and second regions can be adjusted by performing wet shot blasting after forming the coating layer. When performing wet shot blasting, the projection pressure is 0.10 to 0.20 MPa, and particularly preferably 0.15 MPa, the projection time is 20 to 40 seconds, and particularly preferably 30 seconds, and the projection material is projected at a projection angle of 30 to 60°, and particularly preferably 45°, relative to the surface of the coating layer. From the viewpoint of easily obtaining the desired average KAM value, the projection material (media) used in wet shot blasting preferably has an average particle size of 80 to 200 μm, more preferably 80 to 150 μm, and is preferably one or more materials selected from the group consisting of Al2O3 and ZrO2.

[0055] The thickness of each layer in the coating layer of the coated cutting tool of this embodiment can be measured by observing the cross-sectional structure of the coated cutting tool using an optical microscope, a scanning electron microscope (SEM), a field emission scanning electron microscope (FE-SEM), or the like. The average thickness of each layer in the coated cutting tool of this embodiment can be determined as the arithmetic mean of measurements of the thickness of each layer at three or more locations in the vicinity of a position 50 μm from the cutting edge toward the center of the rake face of the coated cutting tool. The composition of each layer can be measured from the cross-sectional structure of the coated cutting tool of this embodiment using an energy dispersive X-ray spectrometer (EDS), a wavelength dispersive X-ray spectrometer (WDS), or the like. [Example]

[0056] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0057] The substrate was a CNMG120412-TM (Tungaloy Corporation) cutting insert made of cemented carbide with a composition of 88.5% WC-8.2% Co-1.5% TiN-1.5% NbC-0.3% Cr3C2 (by mass%). The cutting edge of the substrate was subjected to round honing with a SiC brush, and the surface of the substrate was then cleaned.

[0058] After cleaning the substrate surface, a coating layer was formed by chemical vapor deposition. First, the substrate was loaded into an externally heated chemical vapor deposition apparatus. As shown in Table 3, a TiN or TiC layer was formed as the layer closest to the substrate (adhesion layer), followed by a TiCN layer. Finally, a TiCNO or TiCO layer was formed as the layer closest to the upper layer (intermediate layer). Note that no adhesion layer was formed for Invention Product 16. Specifically, under the conditions of the source gas composition, temperature, and pressure shown in Tables 1 and 2, a lower layer with the composition shown in Table 3 was formed on the substrate surface to the average thickness shown in Table 3. Here, the TiCN layer in the lower layer was formed by a two-stage chemical vapor deposition method, a first stage and a second stage. In the first and second stages of forming the TiCN layer, the pressure and source gas composition were the same, but the temperature was varied, as shown in Table 2. After the first stage, the temperature was controlled to match that of the second stage. During the temperature control, the apparatus was filled with a H2 atmosphere at a pressure of 60 hPa. For Comparative Samples 1-3, the TiCN layer in the lower layer was formed by a single-stage chemical vapor deposition method, rather than a two-stage method. The surface of the lower layer was then oxidized for 3 minutes under the conditions shown in Table 1. After the oxidation treatment of the lower layer, aluminum oxide nuclei were formed. With these nuclei formed, the upper layer, an α-Al2O3 layer, was formed on the surface of the lower layer. Specifically, the upper layer, an α-Al2O3 layer, was formed on the surface of the lower layer after oxidation treatment under the conditions of the raw gas composition, pressure, and temperature shown in Table 1, to the average thickness shown in Table 3. For Invention Samples 20-22, an outer layer with the composition shown in Table 3 was formed on the surface of the upper layer under the conditions of the raw gas composition, temperature, and pressure shown in Table 1, to the average thickness shown in Table 3. The coating layer was then wet shot blasted for 30 seconds using the shot media shown in Table 4, at a 45° angle relative to the surface of the coating layer and a 0.15 MPa pressure. Invention Sample 24 was not wet shot blasted. In this way, coated cutting tools of invention products 1 to 24 and comparative products 1 to 12 were obtained.

[0059] [Table 1]

[0060] [Table 2]

[0061] [Table 3]

[0062] [Table 4]

[0063] [Thickness and composition of each layer] The thickness of each layer of the sample was determined as follows: using FE-SEM, the thickness was measured at three locations on the cross section of the coated cutting tool, located 50 μm from the cutting edge ridge toward the center of the rake face, and the arithmetic mean of the measurements was calculated as the average thickness. The composition of each layer of the obtained sample was measured using EDS on the cross section of the coated cutting tool, located 50 μm from the cutting edge ridge toward the center of the rake face.

[0064] [Average KAM value] The average KAM values ​​of the first and second regions of the lower TiCN layer were measured as follows. First, the coated cutting tool was polished perpendicular to the substrate surface until the cross section of the lower TiCN layer was exposed, obtaining an observation surface. The obtained observation surface was then polished using colloidal silica to obtain a mirror-finished observation surface. The region of the cross section of the lower TiCN layer, extending from the substrate side toward the opposite side of the substrate, was designated as the first region, and the region opposite the substrate from the first region was designated as the second region. Using EBSD (manufactured by TSL), each measurement region of the first and second regions was divided into regular hexagonal regions (pixels). For each divided region, a Kikuchi pattern was obtained from the backscattered electrons of an electron beam incident on the polished surface of the sample, and the pixel orientation was measured. The obtained orientation data was analyzed using the EBSD analysis software, and various parameters were calculated. The measurement conditions were an acceleration voltage of 15 kV, a width of 50 μm, a first region 1 μm thick from the substrate side, and a second region the thickness of the remaining TiCN layer. The distance between adjacent pixels (step size) was 0.1 μm. Adjacent pixels with an orientation difference of 5° or more from the center pixel were excluded from the KAM calculation, assuming that they were beyond the grain boundary from the single crystal where the center pixel was located. In other words, the KAM value was calculated as the average orientation difference between a pixel within a crystal grain and an adjacent pixel located within a range not beyond the grain boundary from that crystal grain. The KAM values ​​for all pixels comprising the entire area of ​​the measurement region were then averaged. The average KAM value was calculated by averaging the KAM values ​​obtained as described above for five arbitrary measurement regions. Based on this result, the relationship between the average KAM values ​​of the first and second regions was determined. The results are shown in Table 5.

[0065] [Σ3 grain boundary length ratio] The ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries in the lower TiCN layer of the obtained sample was measured as follows. First, the coated cutting tool was polished in a direction perpendicular to the substrate surface until the cross section of the lower TiCN layer was exposed, to obtain an observation surface. The obtained observation surface was then polished using colloidal silica to obtain a mirror-like observation surface. The observation surface was then observed using an SEM equipped with EBSD. The observation area was the rake face. The SEM used was an SU6600 (manufactured by Hitachi High-Technologies Corporation) equipped with EBSD (manufactured by TexSEM Laboratories). The normal to the observation surface was tilted 70° relative to the incident beam, and the analysis was performed by irradiating the electron beam with an accelerating voltage of 15 kV and an irradiation current of 1.0 nA. Data collection was performed on a 50 μm wide area of ​​the lower TiCN layer on the observation surface at a step rate of 0.1 μm / step. This data collection was performed on five areas of the surface, and the average value was calculated. Data processing was performed using commercially available software. The CSL grain boundaries corresponding to any Σ value were counted and confirmed by expressing the proportion of each grain boundary as a ratio to all grain boundaries. From the above, the length of the Σ3 grain boundary, the length of the CSL grain boundary, and the total length of all grain boundaries were calculated, and the ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries in the lower TiCN layer (100%) was calculated. The results are shown in Table 6.

[0066] [Table 5]

[0067] [Table 6]

[0068] Using the obtained samples, cutting tests were carried out under the following conditions to evaluate chipping resistance and wear resistance. The results of each cutting test are shown in Table 7.

[0069] [Cutting test conditions] Insert: CNMG120412-TM (Tungaloy Corporation), Base material: 88.5%WC-8.2%Co-1.5%TiN-1.5%NbC-0.3%Cr3C2 (more than mass %), Work material: SCM440, Shape of workpiece: Round bar with one groove on the outer surface, Cutting speed: 300m / min, Feed: 0.2mm / rev, Cutting depth: 1.5mm, Coolant:Use, Evaluation items: The tool life was determined when the sample broke or the maximum flank wear width reached 0.3 mm, and the machining time until the tool life was reached was measured. In addition, the state of damage at the end of the tool life was confirmed using an SEM. The evaluation results obtained are shown in Table 7.

[0070] [Table 7]

[0071] As shown in Table 7, the machining time of the cutting test for the inventive products was 23 minutes or more, which was better than the machining time of the comparative products. Furthermore, the damage state at the end of the tool life was normal wear for all of the inventive products, while all of the comparative products except for comparative product 8 were chipped.

[0072] From the above results, it was found that the inventive product has excellent wear resistance and chipping resistance, resulting in a long tool life. [Industrial Applicability]

[0073] The coated cutting tool of the present invention has excellent wear resistance and fracture resistance, thereby enabling the tool life to be extended, and from this viewpoint, has industrial applicability. [Explanation of symbols]

[0074] 1...substrate, 2...lower layer, 3...upper layer, 4...coating layer, 5...coated cutting tool.

Claims

1. A substrate and a coating layer formed on the surface of the substrate, the coating layer includes a lower layer and an upper layer in this order from the substrate side toward the surface side of the coating layer, The upper layer is made of α-type aluminum oxide. 2 O 3 layer, The average thickness of the upper layer is 1.5 μm or more and 15.0 μm or less, the lower layer includes one or more Ti compound layers made of a Ti compound of Ti and at least one element selected from the group consisting of C, N, and O, and at least one of the Ti compound layers is a TiCN layer made of a carbonitride of Ti; The average thickness of the TiCN layer is 3.0 μm or more and 15.0 μm or less, A coated cutting tool in which, when a region in the TiCN layer extending from the substrate side toward an opposite side of the substrate is defined as a first region and a region on the opposite side of the substrate from the first region is defined as a second region, an average KAM value in the first region is defined as KAM1, and an average KAM value in the second region is defined as KAM2, the relationship of the following formula (i) is satisfied: 0.12°≦(KAM1-KAM2)≦0.50° (i)

2. The coated cutting tool according to claim 1 , wherein the KAM1 is equal to or greater than 0.40° and equal to or less than 1.00°.

3. The coated cutting tool according to claim 1 or 2, wherein the KAM2 is 0.30° or greater and 0.70° or less.

4. 3. The coated cutting tool according to claim 1, wherein in the TiCN layer, a ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries (100%) is 15% or more and 50% or less.

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

6. 3. The coated cutting tool according to claim 1, wherein the coating layer has an average thickness of 5.0 μm or more and 30.0 μm or less.

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

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