Surface-coated cutting tool

Abstract

To provide a coated tool having a coated layer which is improved in durability.SOLUTION: In a surface-coated cutting tool, a coated layer on a substrate includes a composite nitride layer of Al and Ti of a composition that is represented by the formula (AlXTi1-X)N (Xavg being an average value of X is 0.40≤Xavg<0.60), and the composite nitride layer has an average thickness of 1.0 μm to 20.0 μm. Further, in the surface-coated cutting tool, repeated changes of a content of Al and Ti exist in composite nitride crystal grains constituting the composite nitride layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a surface-coated cutting tool (hereinafter sometimes referred to as a coated tool).

Background Art

[0002] Coated tools in which a coating layer is formed on the surface of a substrate such as tungsten carbide (hereinafter referred to as WC) - based cemented carbide are known and exhibit excellent wear resistance. And in order to improve the durability of the coated tool, various proposals have been made regarding the improvement of the coating layer.

[0003] For example, Patent Document 1 describes a coated tool having a coating layer of titanium aluminum nitride, wherein the titanium aluminum nitride coating layer has a cubic crystal structure, an aluminum content of 0.3 to 60.0% by mass, and a chlorine content of 0.01 to 2% by mass, and the coated tool is said to have high adhesion of the coating layer.

[0004] Also, for example, Patent Document 2 describes a coated tool in which two types of compounds of Ti x Al 1-x N and Ti y Al 1-y N (0 ≤ x < 0.5, 0.5 < y ≤ 1) are alternately laminated repeatedly so that the overall composition of the laminate becomes stoichiometrically aluminum-rich, and the coated tool is said to be excellent in wear resistance and have durability in high-speed cutting and cutting of high-hardness materials.

[0005] Furthermore, for example, Patent Document 3 describes a coated tool having a hard coating made of a metal nitride formed on the surface of a base material by a vapor phase synthesis method having a lattice constant 0.997 to 1.005 times that described in JCPDS and a thickness of 0.01 to 50 μm, and the coated tool is said to be excellent in wear resistance.

Prior Art Documents

Patent Documents

[0006] [[ID=4_{3}]] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-341008 [Patent Document 2] Japanese Patent Application Publication No. 7-97679 [Patent Document 3] Japanese Patent Application Publication No. 11-335813 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above circumstances and proposals, and has an object to provide a coated tool having a coating layer with improved durability in cutting processing. [Means for solving the problem]

[0008] The surface-coated cutting tool according to an embodiment of the present invention comprises: A substrate and a coating layer on the surface of the substrate are included. The coating layer is a compound of the formula: (Al X Ti 1-X )N(X, the average of X avg , 0.40≦X avg <0.60), The composite nitride layer has an average thickness of 1.0 μm or more and 20.0 μm or less, The composite nitride layer has composite nitride grains that contain repeated changes in the Al and Ti contents.

[0009] Furthermore, the surface-coated cutting tool according to the embodiment may satisfy at least one of the following requirements (1) to (3).

[0010] (1) With respect to repeated changes in the content of Al and Ti in the composite nitride crystal grains, the average change width (ΔX) of X is 0.02 to 0.25.

[0011] (2) The average interval of the repeated changes in the Al and Ti contents in the composite nitride crystal grains is 3 to 100 nm.

[0012] (3) The lattice constant a (Å) of the composite nitride crystal constituting the composite nitride layer is 0.987 × (4.1200X avg +4.2417(1-X avg )) or more, 0.997×(4.1200X avg +4.2417(1-X avg ))The following relationship must be satisfied: [Effects of the Invention]

[0013] The surface-coated cutting tool has a coating layer that is durable in cutting processing. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic view showing an example of a vertical cross section of a surface-coated cutting tool according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of repeated changes in the Al and Ti contents in composite nitride crystal grains constituting the composite nitride layer of the surface-coated cutting tool according to an embodiment of the present invention. [Figure 3] 4 is a graph showing an example of repeated changes in the Al and Ti contents in composite nitride crystal grains constituting the composite nitride layer of the surface-coated cutting tool according to an embodiment of the present invention. [Figure 4] FIG. 2 is a perspective schematic view of an example of a gas supply pipe in an example of an apparatus for manufacturing the surface-coated cutting tool according to the embodiment. [Figure 5] FIG. 5 is a cross-sectional view of the gas supply pipe of FIG. [Figure 6] 5 is a cross-sectional view showing a gas nozzle of the gas supply pipe of FIG. 4. DETAILED DESCRIPTION OF THE INVENTION

[0015] Al-Ti composite nitride layers have excellent fracture resistance due to their high hardness, and are widely used as coating layers for surface-coated cutting tools used in interrupted cutting processes. However, as the Al content increases, thermal stability decreases, and hexagonal crystals precipitate during cutting processes where the cutting edge becomes hot, resulting in reduced wear resistance.

[0016] The inventors have conducted research to prevent this deterioration in wear resistance, and as a result have found that an Al-Ti composite nitride layer with a low Al content has both superior fracture resistance and wear resistance due to its high hardness compared to known TiCN coating layers, even during cutting processes where the cutting edge becomes hot.

[0017] The inventors also found that when the Al and Ti contents in the Al-Ti composite nitride layer are repeatedly changed, the precipitation of the above-mentioned hexagonal crystals is further suppressed, and further, when a predetermined relationship is established between the lattice constant of the crystal grains constituting the Al-Ti composite nitride layer and the average composition of the Al-Ti composite nitride layer, the layer exhibits higher hardness and better wear resistance.

[0018] The present invention is based on these findings, and a surface-coated cutting tool according to an embodiment of the present invention will be described below. In this specification and claims, unless otherwise specified, the coating layer refers only to a film formed by chemical vapor deposition (CVD), and when a numerical range is expressed as "L to M" (L and M are both numerical values), this is synonymous with "not less than L and not more than M," and the range includes an upper limit (M) and a lower limit (L), and the upper limit (M) and the lower limit (L) have the same units. Furthermore, unless otherwise specified, the average value is an arithmetic average value.

[0019] 1.Coating layer FIG. 1 shows a schematic diagram of an example of a longitudinal section of a coating layer according to an embodiment of the present invention (a section perpendicular to the surface of the substrate, assuming that there are no minute irregularities on the surface of the substrate). As shown in Figure 1, a coating layer (2) is provided on a substrate (1). The coating layer (2) has a lower layer (4) provided on the substrate (1), an Al-Ti composite nitride layer (3) provided on the lower layer (4), and an upper layer (5) provided on the Al-Ti composite nitride layer (3). Here, the lower layer (4) and the upper layer (5) are provided selectively and are not essential. The following description will focus on the composite nitride layer of Al and Ti that constitutes the coating layer according to this embodiment.

[0020] 1-1. Al and Ti composite nitride layer (1) Average thickness The average thickness of the Al and Ti composite nitride layer (hereinafter sometimes referred to as the (AlTi)N layer) is preferably 1.0 μm or more and 20.0 μm or less. The reason for this is that if the average thickness is less than 1.0 μm, the (AlTi)N layer is too thin to ensure sufficient durability, while if the average thickness exceeds 20.0 μm, the crystal grains of the (AlTi)N layer tend to become coarse, making chipping more likely to occur. The average thickness of the (AlTi)N layer is more preferably 3.0 μm or more and 16.0 μm or less.

[0021] (2) Composition The (AlTi)N layer has a composition of the formula: (Al X Ti 1-X )N, the average value of X is X avg , 0.40≦X avg Preferably, X is less than 0.60. avg If the ratio is less than 0.40, the oxidation resistance of the (AlTi)N layer decreases, whereas if the ratio is 0.60 or more, the thermal stability decreases, hexagonal crystals precipitate, and the wear resistance decreases. X avg A more preferable value is 0.45 or more and 0.55 or less.

[0022] (3) Cyclic changes in Al and Ti content Observation of the crystal grains in the (AlTi)N layer using a scanning transmission electron microscope (STEM image: 200,000x magnification) reveals visible shading (see Figure 2) due to the difference in composition between Al and Ti, revealing the presence of repeated changes in the Al and Ti compositions. That is, the Al content (X) repeatedly exhibits maximum and minimum values, with regions of high Al content and regions of low Al content. Here, since Ti is the complement of the Al content (1-X), a change in the Al content also implies a change in the Ti content. While the following explanation focuses on changes in the Al content, the same applies to changes in the Ti content.

[0023] 1) Definition of cyclic changes in Al content The repeated change in Al content referred to in this specification and claims means that the Al content changes so as to alternately take maximum and minimum values, and the maximum and minimum values ​​may or may not be the same value, and the intervals between adjacent maximum and minimum values ​​may or may not be the same.

[0024] The above formula: (Al X Ti 1-X It is more preferable that the average change width (ΔX) of X in )N is 0.02 to 0.25. This causes appropriate strain within the crystal grains having a NaCl-type face-centered cubic structure, thereby reliably improving the hardness of the coating layer. That is, if ΔX is less than 0.02, the strain is small and the coating layer may not have sufficient hardness. On the other hand, if ΔX exceeds 0.25, the strain becomes too large, increasing lattice defects and reducing the hardness of the coating layer. The average change in X (ΔX) is defined as the difference between the average of the maximum value of X and the average of the minimum value of X.

[0025] 2) Interval of repeated changes The average value of the interval between the repetition of the maximum and minimum values ​​is more preferably 3 to 100 nm, because if it is less than 3 nm or exceeds 100 nm, improvement in the hardness of the coating layer may not be expected.

[0026] 3) Surface for observing repeated changes The existence of repeated changes is confirmed by observing longitudinal sections, but their existence is not denied in observations other than longitudinal sections. For example, their existence can sometimes be confirmed even in a cross section polished from the surface side. This is the case when the repeating change has a three-dimensional structure, and the interval between the repeating changes is measured as a different value depending on how the cross section is cut. Therefore, the claims and this specification deal with repeating changes in a longitudinal cross section.

[0027] (4) Atomic ratio of (AlTi) to N In the (AlTi)N layer, the atomic ratio of the metal element (AlTi) to N (nitrogen) is (AlTi):N=0.8 to 1.2:1, but this range may be exceeded due to unintended disturbances in the film formation conditions described below.

[0028] (5) Crystal structure The (AlTi)N layer has (AlTi)N crystal grains with a NaCl-type face-centered cubic structure. The term "having (AlTi)N crystal grains with a NaCl-type face-centered cubic structure" means that crystal grains other than those with a NaCl-type face-centered cubic structure may also be present, but the presence of crystal grains other than those with a NaCl-type face-centered cubic structure is not intended. The fact that the (AlTi)N crystal grains have a NaCl-type face-centered cubic structure is confirmed using the results of an X-ray diffraction test when measuring the lattice constant, which will be described later.

[0029] (6) Lattice constant and X avg (Average Al content) An X-ray diffraction test was carried out using an X-ray diffractometer, and the profile of the measurement results was analyzed by the full pattern fitting method. After confirming that the material has a NaCl-type face-centered cubic structure, the lattice constant a of the (AlTi)N crystal grains with a NaCl-type face-centered cubic structure was calculated. The lattice constant a (Å) was found to be: 0.987×(4.1200X avg +4.2417(1-X avg )) or more 0.997×(4.1200X avg +4.2417(1-Xavg When the lattice constant a is in this range, the (AlTi)N layer has higher hardness and exhibits better wear resistance and impact resistance.

[0030] The X-ray diffraction test to determine the lattice constant a uses the 2θ-θ method with CuKα radiation. Measurement conditions are, for example, a measurement range (2θ): 15–135°, X-ray tube output: 45 kV, 40 mA, divergence slit: 0.5°, and scan step: 0.013°. To determine whether the (AlTi)N crystal has a NaCl-type face-centered cubic structure and to determine the lattice constant of the (AlTi)N crystal, reference is made to the ICDD (International Centre for Diffraction Data) Powder Diffraction File (PDF) database, PDF card number: 00-025-1495 (AlN, space group: Fm-3m(225), lattice constant: 4.1200 Å) and PDF card number: 00-038-1420 (TiN, space group: Fm-3m(225), lattice constant: 4.2417 Å).

[0031] 1-2.Other layers (1) Lower layer A lower layer having one or more Ti compound layers (not limited to stoichiometric compositions) selected from Ti nitride layers, carbide layers, and carbonitride layers, and having a total average thickness of 0.1 to 20.0 μm may be provided. Providing the lower layer between the substrate and the (AlTi)N layer improves adhesion between the substrate and the (AlTi)N layer. If the total average thickness of the lower layer is less than 0.1 μm, the improvement in adhesion by the lower layer is insufficient. On the other hand, if the total average thickness of the lower layer is greater than 20.0 μm, the crystal grains in the lower layer tend to become coarse, making chipping more likely to occur.

[0032] (2) Upper layer An aluminum oxide layer (not limited to a stoichiometric composition) having an average thickness of 0.1 to 25.0 μm may be provided on the (AlTi)N layer. The upper layer exhibits chipping resistance and wear resistance. If the total average thickness is less than 0.1 μm, the upper layer will not exhibit chipping resistance or wear resistance, while if it exceeds 25.0 μm, chipping due to the upper layer will be more likely to occur.

[0033] (3) Surface layer Furthermore, TiN (not limited to a stoichiometric composition) may be provided as a surface layer on the surface of the upper layer (or at the position of the upper layer if there is no upper layer), because TiN has a golden color tone and can be used as an identification layer to distinguish, for example, whether the coated cutting tool is unused or used based on the change in the color tone of the surface of the coated cutting tool. The average thickness of this TiN layer as an identification layer may be 0.1 to 1.0 μm.

[0034] (4) Unintentional Layers When the gas pressure or temperature inside the CVD reactor becomes unstable due to an unpredictable (unintentional) cause, a very small amount of a layer different from the (AlTi)N layer, bottom layer, top layer, and surface layer may be unintentionally deposited.

[0035] 1-3.Inevitable impurities The (AlTi)N layer, lower layer, upper layer, and surface layer may contain trace amounts of Cl as an inevitable impurity. Cl is inevitably present in trace amounts when films are formed by CVD using chloride as a raw material gas. If the Cl content is 0.10 atomic % or less of the total atoms, the Cl provides the (AlTi)N layer with lubricity. In addition to the aforementioned Cl, unavoidable impurities may include unintended impurities (oxygen, carbon) that occur during the manufacturing process.

[0036] 2.Base (1)Material Any known substrate material can be used as long as it does not impede the achievement of the object of the present invention. Examples include WC-based cemented carbide (containing Co in addition to WC, and also containing carbides or nitrides of Ti, Zr, Ta, Nb, Cr, etc.), cermet (containing TiC, TiN, TiCN, etc. as its main component), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide), and cBN sintered body.

[0037] (2) Shape The shape of the substrate is not particularly limited as long as it is a shape that can be used as a cutting tool, and examples thereof include the shape of an insert and the shape of a solid tool.

[0038] 3.Measurement method The average thickness of the (AlTi)N layer of this embodiment, the content of each element, and the average change width (ΔX) of X when the content of Al and Ti are repeatedly changed are determined as follows.

[0039] (1) Average thickness Here, the average thickness of the (AlTi)N layer or the like can be determined as follows: The vertical cross section of the coating layer is polished using an ion milling device or the like. Each layer constituting the coating layer is observed using a scanning electron microscope (SEM), and the boundaries of each layer are defined based on the difference in shading. The thickness of the layer is then measured at multiple locations (e.g., five locations) and averaged to determine the average thickness of the (AlTi)N layer, etc. The definition of the substrate surface is given below.

[0040] The surface of the substrate is defined as the average line (straight line) of the interface roughness between the substrate and the coating layer in an observed image of the longitudinal section. That is, the interface between the coating layer (if a lower layer exists, use the lower layer instead of the (AlTi)N layer) and the substrate is determined from the observed image of the longitudinal section, and an average line (straight line) is drawn on the roughness curve of the interface between the coating layer and the substrate, which is defined as the surface of the substrate. The direction perpendicular to this average line is defined as the direction perpendicular to the substrate (normal direction, thickness direction of the coating layer).

[0041] Furthermore, even if the substrate has a curved surface, if the radius of curvature of the curved surface is sufficiently large compared to the thickness of the coating layer, the interface between the coating layer and the substrate in the measurement area will be approximately flat, and the surface of the substrate can be determined using a similar method.

[0042] (2) Atomic ratio of Al to Ti in the (AlTi)N layer The atomic ratio of the components constituting the (AlTi)N layer is determined as follows. The atomic ratio X of Al is measured using an electron probe microanalyzer (EPMA). The surface of the coating layer is polished to expose the (AlTi)N layer. An electron beam is irradiated onto the (AlTi)N layer from the surface side of the sample, and the average value of 10 characteristic X-ray analysis results is used.

[0043] (3) Average change in X (ΔX) when the Al and Ti contents are repeatedly changed In a longitudinal section, based on a TEM image or STEM image at 200,000x magnification, the cyclic changes in the Al and Ti content within the crystal grains are confirmed from the image shading. If the cyclic changes in the Al and Ti content within the crystal grains can be visually confirmed from the image shading as being formed in layers, as shown in Figure 2, a line analysis is performed using energy dispersive X-ray spectroscopy (EDS) across the layer where the cyclic changes in the Al and Ti content have formed. If the cyclic changes in the layered Al and Ti content cannot be visually confirmed, a line analysis is performed using energy dispersive X-ray spectroscopy (EDS) randomly in any direction.

[0044] The line analysis described above is performed using a measurement length that includes at least four (preferably at least six) but fewer than ten maximum and minimum values ​​of the repeated changes within a crystal grain (same grain can be used) (see Figure 3). This measurement length is divided into 500 sections for line analysis using energy dispersive X-ray spectroscopy (EDS). The average values ​​of the maximum and minimum values ​​of X are determined through line analysis. When determining the maximum and minimum values, if the measured values ​​X vary significantly, smoothing (averaging data from a certain point with data from nearby points to form a smoothly connected data set (curve)) is preferred to eliminate singular points and noise in the continuous data set. This line analysis is performed at five or more locations on one sample, and the difference between the average maximum and minimum values ​​of X in the repeated changes determined from each line analysis is defined as the average change in X (ΔX).

[0045] (4) Average spacing in repeated changes in Al and Ti content In the linear analysis of five or more points in (3) above, when measuring the maximum and minimum values ​​of X, the distance between adjacent maximum and minimum values ​​of X is also measured. The distance between adjacent maximum and minimum values ​​of X corresponding to the number of measurements of the maximum and minimum values ​​of X measured in (3) above is measured, and the average is calculated to be the average distance in the repeated changes in the Al and Ti contents.

[0046] 4. Manufacturing method 1)(AlTi)N layer The method for manufacturing the (AlTi)N layer of this embodiment includes, for example, Gas group A consisting of H2, N2, and NH3; Gas group B consisting of AlCl3, TiCl4, H2, and Ar; This can be carried out by the CVD method using

[0047] Here, gas groups A and B are supplied separately within the reaction chamber of the thermal CVD apparatus up to just before the object to be deposited, where they are mixed and reacted. This is effective for uniformly supplying gas species with high reactivity to each other across the deposition region, thereby forming a uniform coating. The detailed technical content is described, for example, in Japanese Patent Publication No. 6511798.

[0048] 2) Lower layer, upper layer and surface layer There are no restrictions on the method of manufacturing the lower layer, upper layer, and surface layer by CVD, and known methods and manufacturing conditions may be appropriately adopted. [Example]

[0049] The present invention will be described below with reference to examples, but is not limited to these examples. That is, an insert cutting tool using a WC-based cemented carbide as the substrate will be described, but the substrate may be made of any material as described above, and may have the shape of a solid tool, as described above.

[0050] 1. Manufacturing the substrate The raw material powders prepared were WC powder, TiC powder, ZrC powder, TaC powder, NbC powder, Cr3C2 powder, TiN powder, and Co powder. These raw material powders were blended according to the composition shown in Table 1, and wax was added. The mixture was ball milled in acetone for 24 hours, dried under reduced pressure, and then pressed into a green compact of the desired shape at a pressure of 98 MPa.

[0051] This green compact was then vacuum sintered, and after sintering, the cutting edge was honed to R: 0.05 mm to produce substrates A to C made of WC-based cemented carbide with the insert shape of CNMG120408-MA manufactured by Mitsubishi Materials Corporation.

[0052] 2. Film formation An (AlTi)N layer was formed on the surface of each of the substrates A to C using the CVD apparatus (see FIGS. 4 to 6) described in Japanese Patent No. 6511798, to obtain Examples 1 to 10 shown in Table 5. The film formation conditions were as shown in Table 2, and were roughly as follows:

[0053] Reaction gas composition (content of gas components is in volume %): Gas group A H2: 30.0-50.0%, N2: 1.0-2.0%, NH3: 0.5-1.5% Gas group B AlCl3: 0.10-0.30%, TiCl4: 0.10-0.30%, Ar: 1.0~2.0%, H2: remainder Reaction atmosphere pressure 4.5~5.0kPa Reaction atmosphere temperature: 750~900℃

[0054] In the CVD apparatus shown in Figs. Gas supply pipe rotation speed: 2~5 rpm Gas supply pipe nozzle angle α 180° β1 and β2 155° γ1 and γ2 55°

[0055] The lower and / or upper layers of Examples 3 to 10 were formed using a CVD apparatus normally used for forming coating layers on coated tools under the conditions shown in Table 3, and the lower and / or upper layers shown in Table 4 were formed.

[0056] For comparison, (AlTi)N layers were formed on the surfaces of substrates A to C under the film formation conditions shown in Table 2, and Comparative Examples 1 to 10 shown in Table 5 were obtained. In the manufacturing process of the comparative example, the composition of the raw material gas was changed from that of the example. The lower and / or upper layers of Comparative Examples 3 to 10 were formed using a CVD apparatus normally used for forming coating layers on coated tools, under the conditions shown in Table 3, to form the lower and / or upper layers shown in Table 4.

[0057] Furthermore, for comparison with conventional technology, a TiCN layer and the lower layer, lower layer and upper layer shown in Table 4 were formed on the surfaces of substrates A and C under the conditions shown in Table 3, and conventional examples 1 and 2 shown in Table 5 were produced.

[0058] For Examples 1 to 10 and Comparative Examples 1 to 10, the average thickness of each layer, the content of each element, the average change in X (ΔX), the interval between repeated changes in the content of Al and Ti, and the lattice constant a were measured using the methods described above. These results are summarized in Table 5.

[0059] [Table 1]

[0060] [Table 2]

[0061] [Table 3]

[0062] [Table 4]

[0063] In Table 4, "-" indicates that no test was performed.

[0064] [Table 5]

[0065] In Table 5, "X avg "Between the lower and upper limits of the lattice constant measured by X-ray diffraction" means that the lattice constant a (Å) measured by X-ray diffraction is between the lower limit of 0.987 × (4.1200 × avg +4.2417(1-X avg )) and the upper limit of 0.997 × (4.1200X avg +4.2417(1-Xavg )) are marked with a circle. "-" and " / " indicate that the corresponding column cannot be filled in because there was no repeated change in the Al and Ti contents. Furthermore, it was confirmed that the composite nitride crystals constituting the composite nitride layer in both the examples and comparative examples have an NaCl-type face-centered cubic structure.

[0066] Cutting test: Wet end face machining Work material: JIS SCM440 Hollow round bar (outer diameter Φ180, inner diameter Φ50) with four equally spaced grooves (width 20 mm) Cutting speed: 250m / min. Cutting depth: 2.0 mm Feed rate: 0.3mm / rev. Number of cuts: 20 passes

[0067] The results of the cutting tests are shown in Table 6. Note that for Comparative Examples 1 to 10 and Conventional Examples 1 and 2, the number of cutting passes until the end of life was caused by chipping or flank wear (life judgment criterion: flank wear width 0.4 mm).

[0068] [Table 6]

[0069] As is clear from the results shown in Table 6, all of Examples 1 to 10 had little wear, no chipping, and improved hardness and toughness, and exhibited excellent cutting performance over a long period of time. In contrast, Comparative Examples 1 to 10 and Conventional Examples 1 and 2 all had a large amount of wear or chipping occurred, and the number of cutting passes imposed in the cutting test was not met, reaching the end of their service life in a short period of time. [Explanation of symbols]

[0070] 1 Base 2 Covering layer 3 (AlTi)N layer 4 Lower layer 5 Upper layer 11 Gas supply pipe 12 Partition member 13 Center of gas supply pipe 14 Gas Group A Distribution Section 15 Gas Group B Distribution Section 16 Gas group A nozzle 17 Gas group B nozzle 18 Center of the outer peripheral opening end of the gas group A nozzle 19 Center of the outer peripheral opening end of the gas group B nozzle 20 nozzle pairs α angle β1 angle β2 angle γ1 angle γ2 angle

Claims

1. A surface-coated cutting tool having a substrate and a coating layer on a surface of the substrate, The coating layer is a compound of the formula: (Al Ｘ Ti １－Ｘ ) N(X, the average value of X ａｖｇ is 0.40≦X ａｖｇ <0.60), The composite nitride layer has an average thickness of 1.0 μm or more and 20.0 μm or less, The content of Al and Ti changes repeatedly within the composite nitride crystal grains that make up the composite nitride layer. A surface-coated cutting tool characterized by:

2. 2. The surface-coated cutting tool according to claim 1, wherein the average change width (ΔX) of X is 0.02 to 0.25 with respect to repeated changes in the contents of Al and Ti within the composite nitride crystal grains.

3. 3. The surface-coated cutting tool according to claim 1, wherein the average interval of repeated changes in the Al and Ti contents in the composite nitride crystal grains is 3 to 100 nm.

4. The lattice constant a (Å) of the composite nitride crystal constituting the composite nitride layer is 0.987 × (4.1200 × ａｖｇ +4.2417 (1-X ａｖｇ )) or more, 0.997×(4.1200X ａｖｇ +4.2417 (1-X ａｖｇ 3. The surface-coated cutting tool according to claim 1, wherein the following relationship is satisfied:

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