Surface-coated cutting tool

Abstract

To provide a cutting tool that exhibits excellent resistance to wear and to chipping in machining stainless steel and the like.SOLUTION: A surface-coated cutting tool provided with a laminated structure having an average thickness within a range of 0.5 μm or more to 10.0 μm or less, the laminated structure being composed of alternately laminated A layers each having an average thickness of 2 nm or more and less than 50 nm and B layers each having an average thickness of 2 nm or more and less than 50 nm, wherein the A layer is constituted by an (Al1-x-yCrxMey)N (x: 0.20≤x≤0.59 in atomic ratio, y: 0.01≤y≤0.30 in atomic ratio, Me: at least one element selected from Nb, Mo, Ta, and W), and the B layer is constituted by a (Ti1-zSiz)N layer (z: 0.01≤z≤0.40 in atomic ratio).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] Conventionally, as a coated tool, for example, a coated tool in which a coating layer is formed on a substrate such as a tungsten carbide (hereinafter represented by WC) - based cemented carbide is known. And, by adjusting the composition and layer structure of this coating layer, a proposal has been made to obtain a coated tool with further improved cutting performance.

[0003] For example, Patent Document 1 discloses a coated tool including a multilayer coating layer in which a first coating layer and a second coating layer are alternately laminated in two or more layers each. The first coating layer is a coating layer containing at least Al, Cr, and N, the second coating layer is a coating layer containing Ti, Si, and N, the film thickness per layer of each of the first coating layer and the second coating layer is 1 nm or more and 20 nm or less, and a mixed structure portion in which the first coating layer and the second coating layer are mixed and which is 5% or more and 80% or less of the cross-sectional area of the multilayer coating layer exists. The coated tool is said to have excellent wear resistance even in cutting of high-hardness hardened steel.

[0004] Also, for example, Patent Document 2 discloses a first coating layer composed of Ti m Si 1-m N 1-a-b C a B b (0.7 ≦ m < 1, 0 < 1 - a - b ≦ 1) and a second coating layer composed of Al x Cr y M 1-x-y N 1-a-b C a B b (0.7 < x ≦ 0.8, 0 < y and 0 < 1 - a - b ≦ 1, M is Ti, V, Zr, Nb, Mo, Ta, W, Y, and lanthanoids (excluding Pm)) are alternately laminated. The coated tool is said to have excellent wear resistance.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-202300 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-179580 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above circumstances and proposals, and has an object to provide a cutting tool that has excellent wear resistance and chipping resistance when used for cutting stainless steel and the like. [Means for solving the problem]

[0007] The surface-coated cutting tool according to an embodiment of the present invention comprises: A substrate and a coating layer provided on the substrate, a laminated structure having an average thickness of 0.5 μm or more and 10.0 μm or less, in which A layers having an average thickness of 2 nm or more and less than 50 nm and B layers having an average thickness of 2 nm or more and less than 50 nm are alternately laminated; The A layer is (Al 1-x-y Cr x Me y )N layer (x is 0.20≦x≦0.59 in atomic ratio, y is 0.01≦y≦0.30 in atomic ratio, and Me is at least one element selected from Nb, Mo, Ta, and W), The B layer is (Ti 1-z Si z )N layer (z is an atomic ratio of 0.01≦z≦0.40).

[0008] The surface-coated cutting tool according to the above embodiment may satisfy the following (1).

[0009] (1) At the interface between the A layer and the B layer in a longitudinal cross section, the proportion of the length of the interface where the orientation difference between adjacent crystal grains of the A layer and adjacent crystal grains of the B layer is 0 degrees or more and less than 5 degrees is 50 to 100% of the total length of the interface. [Effects of the Invention]

[0010] The surface-coated cutting tool exhibits excellent wear resistance and chipping resistance even when used to cut stainless steel and the like. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of an example of a vertical cross section of a coating layer in a surface-coated cutting tool according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present inventors have conducted extensive research into coating layers in order to obtain a coated tool that has excellent wear resistance and fracture resistance even when subjected to cutting processes that apply high loads to the coating layer, such as cutting stainless steel, etc. As a result, they have made the following findings.

[0013] That is, (1) By alternately laminating (AlCr)N layers and (TiSi)N layers, both of which are less than 50 nm thick, the entire coating layer can exhibit excellent wear resistance. (2) By changing the composition of the (AlCr)N layer to (AlCrMe)N, the wear resistance and chipping resistance are further improved. (3) Wear resistance and chipping resistance are further improved by reducing the difference in crystal grain orientation between layers A and B at the interface of the longitudinal section (a section perpendicular to the surface of the substrate treated as if there were no minute irregularities on the surface of the substrate). The present invention was derived based on these findings.

[0014] The coated tool according to the embodiment of the present invention will be described in more detail below. In this specification and claims, when a numerical range is expressed using "L to M," this is synonymous with "at least L and at most M," and the range includes the numerical values of the upper limit (M) and the lower limit (L). Furthermore, when a unit is stated only for the upper limit (M), the upper limit (M) and the lower limit (L) have the same unit.

[0015] 1.Coating layer The layer structure of the coating layer of the coated tool according to an embodiment of the present invention is as shown schematically in Figure 1. It has a laminate structure (3) having a laminate unit (6) in which a base layer (2) is laminated on a substrate (1), a layer A (4) is laminated on the base layer (2), and a layer B (5) is laminated on the layer A (4). An outermost surface layer (7) is located on the laminate structure. The coating layer (8) includes the base layer (2), the laminate structure (3), and the surface layer (7). As will be described later, the undercoat layer (2) and the surface layer (7) are not essential. The white area in Figure 1 contains the laminated structure (3).

[0016] (1) A layer Layer A has an average thickness of 2 nm or more and less than 50 nm. If the average thickness is less than 2 nm, the coated tool will not be able to exhibit excellent wear resistance over long periods of use, while if the average thickness is 50 nm or more, cracks that can cause chipping, damage, etc., of the coating layer will be more likely to occur.

[0017] The average composition of the A layer is represented by the formula: (Al 1-x-y Cr x Me y )N (Me is at least one of Nb, Mo, Ta, and W), 0.20≦x≦0.59, 0.01≦y≦0.30). Al improves the high-temperature hardness of layer A, Cr improves the high-temperature toughness and high-temperature strength of layer A, and Nb, Mo, Ta, and W each improve these high-temperature hardness, toughness, and strength, and also reduce the crystal orientation difference between layer B and the composite nitride containing Ti and Si.

[0018] If the value of x is less than 0.20, crystal grains with a hexagonal structure and low hardness appear, reducing the hardness and wear resistance of Layer A. On the other hand, if the value of x exceeds 0.59, the relative Al content of Layer A as a whole decreases, making it impossible for the coating layer to ensure sufficient wear resistance. Me is at least one of Nb, Mo, Ta and W, and more preferably contains Mo. If the value of y is less than 0.01, the difference in crystal orientation with respect to layer B will not be reduced, causing strain at the interface, making it more likely to develop cracks that can cause chipping, defects, etc. On the other hand, if the value of y exceeds 0.30, the reduced proportion of Al and Cr contained in layer A will make it impossible to maintain high-temperature hardness and strength, and sufficient wear resistance will not be ensured.

[0019] According to an example of the manufacturing method described later, the ratio of (AlCrMe) to N (i.e., the ratio of metal components to nitrogen) is manufactured to be 1:1, but inevitably (unintentionally) there may be some that are not 1:1. This also applies to the composite nitride of the B layer described below.

[0020] (2)B layer Layer B has an average thickness of 2 nm or more and less than 50 nm. If the average thickness is less than 2 nm, the coated tool will not be able to exhibit excellent wear resistance over long periods of use, while if the average thickness exceeds 50 nm, Layer B will be prone to cracks that can cause chipping, defects, etc. The average thickness of layer A and the average thickness of layer B may be the same or different.

[0021] The average composition of the B layer is 1-z Si z )N, 0.01≦z≦0.40. If the value of z is less than 0.01, the layer B does not have sufficient hardness and wear resistance, whereas if the value of z exceeds 0.40, the layer B becomes amorphous and its wear resistance decreases.

[0022] (3) Laminated structure The coating layer has a laminated structure in which lamination units in which layers A and B are alternately laminated are stacked. The average thickness of the laminated structure is preferably 0.5 to 10.0 μm. If the average thickness is less than 0.5 μm, the coated tool will not be able to exhibit excellent wear resistance over long periods of use. On the other hand, if the average thickness exceeds 10.0 μm, cracks that cause chipping, damage, etc. of the coating layer will be more likely to occur. There is no restriction on the number of lamination units as long as the average thickness of each of the A layer and the B layer and the average thickness of the lamination structure are satisfied. Furthermore, the layers on the substrate side and the surface side of the laminated structure may be either layer A or layer B (only the layer on the surface side may be layer A or layer B, not a laminate unit configuration).

[0023] (4) Misorientation between adjacent grains in layer A and layer B It is more preferable that at each interface in the longitudinal section of layer A and layer B, the proportion of the length of the interface where the misorientation between adjacent crystal grains of layer A and layer B is 0 degrees or more and less than 5 degrees is 50 to 100% of the length of the entire interface. If it is less than 50%, the distortion caused by the misorientation of the crystal grains at the interface between the A layer and the B layer becomes large, and cracks that cause chipping, defects, etc., tend to occur near the interface.

[0024] (5) Other layers (5-1) Base layer The underlayer may be, for example, a Ti compound (not limited to a stoichiometric composition) layer of one or more of Ti carbide, nitride, carbonitride, carbonate, and oxycarbonitride layers having a total average thickness of 0.1 to 2.0 μm. The underlayer strengthens adhesion between the laminated structure and the substrate.

[0025] (5-2) Surface layer The above-mentioned object can be sufficiently achieved with only the A layer and B layer, but in addition to these layers, a surface layer may be provided on top of the laminated structure.

[0026] The surface layer can be, for example, a TiN layer. Since the TiN layer has a golden yellow color tone, it can be used as an identification layer to distinguish whether the coated tool is unused or used based on the color tone change on the surface of the coated tool. The average thickness of the TiN layer serving as the discrimination layer may be, for example, 0.1 to 3.0 μm.

[0027] (5-3) Layers that may occur unintentionally In this embodiment, the films are formed so that no layers other than the base layer, layer A, layer B, and surface layer exist. However, for example, when changing the layer to be formed, an unintended change in pressure or temperature within the film forming apparatus may occur, resulting in the formation of an unintended layer different from these layers.

[0028] 2.Base (1)Material The substrate used in this embodiment can be any conventionally known substrate material as long as it does not impede the achievement of the above-mentioned object. Examples include WC-based cemented carbide (containing Co in addition to WC, and also containing carbides or carbonitrides of Ti, Ta, Nb, etc.), cermet (mainly composed of TiC, TiN, TiCN, etc.), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide), cBN sintered body, and diamond sintered body.

[0029] (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 shapes of drills, end mills, and inserts.

[0030] 3.Measurement method (1) Average thickness of each layer The average thickness of layers A, B, etc. that make up the coating layer is determined by identifying each layer A, B, etc. by element mapping in a longitudinal section (a section perpendicular to the surface of the substrate, assuming that there are no minute irregularities on the surface of the substrate) observed using an electron energy loss spectrometer (EELS) attached to a scanning transmission electron microscope (STEM) or a transmission electron microscope (TEM). At least five observation fields are set, each including 10 to 20 interfaces between layers A and B (interfaces with the base layer and surface layer may also be included), and the thickness of each layer is determined. The arithmetic mean of the thicknesses is taken as the average thickness of layers A, B, etc.

[0031] Here, the surface of the substrate is determined by observing this cross section, determining the interface between the substrate and layer A or layer B (or the underlying layer, if any) by element mapping, and arithmetically determining the average straight line of the roughness curve of the interface thus obtained, which is taken as the surface of the substrate.

[0032] (2) Composition of each layer The average composition of each of the x, y, and z layers is determined by cross-sectional observation using EELS attached to the STEM or TEM. New observations (point analysis at five locations on each layer) can be performed, but the results of EDS analysis used to determine the average thickness of each layer can also be used. The arithmetic mean of the analysis results is used to determine the average composition.

[0033] (3) Misorientation between adjacent grains in layer A and layer B The observation field is set on the longitudinal cross section so that it includes the interface between layers A and B. The observation field is a square (with its base parallel to the substrate surface) and three or more locations are set. The observation field is large enough to include 10 to 20 interfaces between layers A and B. The observation field may be the same as that used to measure the average thickness of each layer. The following measurements are performed for each observation field. This observation field is observed using EELS attached to the STEM or TEM, and the interface between layers A and B, which have different compositions, is defined. Because layers A and B are alternately stacked, there are multiple interfaces that are defined, and there are multiple endpoints of the interfaces at the left and right ends of the observation field. Next, connect the demarcated interface end point at the left edge of the observation field with the corresponding interface end point at the right edge of the observation field with a line segment. The number of line segments is the number of left edges (i.e., the number of right edges). Each of these multiple line segments is considered to be an interface line between layer A and layer B.

[0034] The crystal orientation of each crystal grain in layers A and B, which exist on either side of this interface line, is analyzed using electron backscatter diffraction pattern (EBSD) and automated crystal orientation mapping (ACOM) to obtain a crystal orientation pattern. Then, for each interface line between layers A and B, the length penetrating the region between 0 degrees and less than 5 degrees in the crystal orientation pattern is calculated, and the ratio of this length to the total length of the interface line is calculated.

[0035] The calculated ratios are then averaged to obtain the ratio of the length of the interface where the misorientation between the crystal grains of layer A and the crystal grains of layer B that are adjacent to each other at the interface in the longitudinal section is 0 degrees or more and less than 5 degrees.

[0036] The image processing performed to measure the length of the interface line is performed using image processing software, and there are no restrictions as long as it can perform the above-mentioned processing. An example of image processing software is Image J.

[0037] 4. Manufacturing method The coating layer of the coated tool of this embodiment is produced, for example, by a magnetron sputtering device, using an AlTiMe target having a composition corresponding to that of the A layer as the target for depositing the A layer, and a TiSi target having a composition corresponding to that of the B layer as the target for depositing the B layer. [Example]

[0038] Next, an example will be described. Here, as an example of the coated tool of the present invention, a coated tool in the shape of a drill using a WC-based cemented carbide as a substrate will be described. However, any of the above-mentioned materials can be used for the substrate, and the same applies when the coated tool is applied to an end mill, an insert, or the like, as described above.

[0039] A drill substrate was prepared as the substrate. Specifically, the raw material powders, Co powder (10% by mass) and WC powder (90% by mass), were blended. Wax was then added and the mixture was wet mixed in a ball mill. After drying under reduced pressure, the mixture was press-molded and sintered into a green compact, which was then formed into a sintered round bar for forming the base, measuring 3.0 mm in diameter. Subsequently, a WC-based cemented carbide drill base was produced by grinding, with the groove-forming portion measuring 0.8 mm in diameter and 10.2 mm in length and a two-flute shape with a 30-degree helix angle.

[0040] Next, film formation was carried out as follows to produce coated tools of examples (hereinafter referred to as "Examples") 1 to 7. The drill base was subjected to the following treatments (1) to (4) in this order using a magnetron sputtering device.

[0041] (1) The drill base was ultrasonically cleaned in acetone and, in a dried state, was attached along its outer periphery at a position radially spaced a predetermined distance from the central axis on a rotating table in a magnetron sputtering device.

[0042] (2) The surface of the drill substrate was bombarded with argon ions.

[0043] (3) Coated tools (hereinafter referred to as Examples) 1 to 7 shown in Table 2 were produced by simultaneously applying a 0.2 ms, 830 Hz pulse between an AlCrMe alloy target for an A layer shown in Table 1 and an anode electrode, and a 4.5 ms, 37 Hz pulse between a TiSi alloy target for a B layer shown in Table 1 and an anode electrode.

[0044] On the other hand, for comparison, coated tools 1 to 8 shown in Table 2 (hereinafter referred to as "Comparative Examples") were produced using the same film-forming apparatus as in the Examples, the targets shown in Table 1, and the other film-forming conditions were the same as in the Examples.

[0045] The average thickness and average composition of layers A and B, as well as the misorientation between adjacent grains in layers A and B, were determined using the aforementioned measurement method. The misorientation measurements were performed in three different observation fields.

[0046] [Table 1]

[0047] [Table 2]

[0048] In Table 2, Comparative Example 1 did not contain any Me component.

[0049] Next, cutting tests were carried out on Examples 1 to 6 and Comparative Examples 1 to 8 under the following cutting conditions.

[0050] Cutting conditions Work material: SUS304 Cutting speed: 50m / min Feed rate: 0.025mm / rev Drilling depth: 4mm After each drilling, the damage length at the drill margin was measured, and the drilling length when the damage length reached the margin width was defined as the drilling life. The results of the cutting test are shown in Table 3. In Table 3, the life of Example 1 is set to 100%, and the life of the remaining Examples and Comparative Examples is shown as a ratio (%).

[0051] [Table 3]

[0052] As is clear from the results shown in Table 3, Examples 1 to 7 have excellent wear resistance and chipping resistance even when cutting stainless steel. In contrast, Comparative Examples 1 to 8 all had short tool lives. [Explanation of symbols]

[0053] 1 Base 2 Base layer 3 Laminated structure 4 A layer 5 B layer 6 stacking units 7 Surface layer 8 Covering layer

Claims

1. A surface-coated cutting tool having a substrate and a coating layer provided on the substrate, a laminated structure having an average thickness of 0.5 μm or more and 10.0 μm or less, in which A layers having an average thickness of 2 nm or more and less than 50 nm and B layers having an average thickness of 2 nm or more and less than 50 nm are alternately laminated; The A layer is (Al １－ｘ－ｙ Cr ｘ Me ｙ ) N layer (x is 0.20≦x≦0.59 in atomic ratio, y is 0.01≦y≦0.30 in atomic ratio, Me is at least one element selected from Nb, Mo, Ta, and W), and the B layer is (Ti １－ｚ Si ｚ )N layer (z is an atomic ratio of 0.01≦z≦0.40).

2. 2. The surface-coated cutting tool according to claim 1, wherein, in a longitudinal cross section of the interface between the A layer and the B layer, a proportion of the length of the interface where the misorientation between adjacent crystal grains of the A layer and adjacent crystal grains of the B layer is 0 degrees or more and less than 5 degrees is 50 to 100% of the total length of the interface.

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