Coated cutting tool

Abstract

To provide a coated cutting tool having superior durability in cutting of steel with a hardness of up to 40 HRC.SOLUTION: A coated cutting tool is provided, wherein a lower layer comprises an alternate lamination of a first layer of AlcTidM11-c-dN (M1 is at least one selected from Zr, Hf, V, Nb, Ta, Mo, and W, 0.50≤c≤0.55, 0.45≤d≤0.55) having crystal grains of an fcc structure, and a second layer of AleCrfM21-e-fN (M2 is at least one selected from Ti, Zr, Hf, V, Nb, Ta, Mo, and W, 0.60≤e≤0.70, 0.30≤f≤0.40) having crystal grains of an fcc structure, and an upper layer is an AlgCrhMU1-g-hN (MU is at least one selected from Ti, Zr, Hf, V, Nb, Ta, Mo, and W, 0.60≤g≤0.70, 0.30≤h≤0.40) layer having crystal grains of an fcc structure.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, coated cutting tools have been used in which a coating layer is provided by vapor deposition on a substrate such as tungsten carbide (hereinafter referred to as WC), and these coated cutting tools have been made to have high durability. In order to further improve the durability of these coated cutting tools, various proposals have been made regarding the composition and layer structure of the coating layer.

[0003] For example, Patent Document 1 describes a coated cutting tool having a coating layer in which an AlCr composite nitride layer is laminated on an AiTi composite nitride layer on a substrate. The coated cutting tool is said to have a long life due to reduced residual stress while maintaining high hardness of the coating layer and high adhesive strength between the two laminated layers. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-12564 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in consideration of the above circumstances and proposals, and aims to provide a coated cutting tool that has excellent durability even when used in cutting workpieces ranging in hardness from mild steel to steel (alloy steel) with a hardness of approximately 40 HRC. [Means for solving the problem]

[0006] A coated cutting tool according to an embodiment of the present invention comprises: A substrate and a coating layer provided on the substrate, the coating layer has a lower layer and an upper layer on the lower layer, The lower layer has a face-centered cubic lattice structure with crystal grains having an average thickness of 5 nm or more and 100 nm or less, and an average composition of Al c Ti d M1 1-c-d N (where M1 is one or more of Zr, Hf, V, Nb, Ta, Mo, W, 0.50 ≦ c ≦ 0.55, 0.45 ≦ d ≦ 0.50), and a first layer which is a composite nitride, and an average composition of Al e Cr f M2 1-e-f N (where M2 is one or more of Ti, Zr, Hf, V, Nb, Ta, Mo, W, 0.60 ≦ e ≦ 0.70, 0.30 ≦ f ≦ 0.40), and is an alternating laminate of a second layer which is a composite nitride, The upper layer has crystal grains with a face-centered cubic lattice structure, and an average composition of Al g Cr h MU 1-g-h N (where MU is one or more of Ti, Zr, Hf, V, Nb, Ta, Mo, W, 0.60 ≦ g ≦ 0.70, 0.30 ≦ h ≦ 0.40) and is a composite nitride.

[0007] The coated cutting tool according to the embodiment may satisfy the following (1).

[0008] (1) The sum of the average thickness of the lower layer and the average thickness of the upper layer is 3.5 μm or more and 6.0 μm or less.

Advantages of the Invention

[0009] The coated cutting tool has excellent durability even when used for cutting a workpiece made of steel (alloy steel) having a hardness ranging from that of mild steel to about 40 HRC.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] The present inventors have intensively studied a coated cutting tool having durability in cutting, particularly milling, using a steel (alloy steel) having a hardness of about soft steel to about 40 HRC as a workpiece. As a result, it was recognized that the durability of a coating layer in which a nitride layer containing AlCr is simply laminated on a composite nitride layer containing AlTi can be further improved.

[0012] That is, it has been found that the durability is further improved by providing a coating layer which is a composite nitride layer rich in Al and containing AlCr on the upper part of the alternating lamination with the composite nitride layer containing AlCr.

[0013] Hereinafter, the coated cutting tool according to an embodiment of the present invention will be described in more detail. In the description of this specification and the claims, when a numerical range is expressed as "L to M", this expression is synonymous with "L or more and M or less", and the range includes the upper limit value (M) and the lower limit value (L). Further, when only the upper limit value (M) is provided with a unit, the upper limit value (M) and the lower limit value (L) are in the same unit. Also, each numerical value includes a measurement error.

[0014] Hereinafter, the coated cutting tool according to an embodiment of the present invention will be described.

[0015] 1. Coating layer An example of a longitudinal section (a section perpendicular to the substrate surface when the minute unevenness on the substrate surface is treated as non-existent) of the coating layer of the coated cutting tool according to the embodiment of the present invention is schematically shown in FIG. 1. As is clear from FIG. 1, the coating layer is formed on a substrate (1) and has, in order from the substrate (1) toward the surface of the coated cutting tool, a lower layer (2) and an upper layer (3), and the lower layer (2) is an alternating lamination of a first layer (4) and a second layer (5). In FIG. 1, the first layer (4) and the second layer (5) are also alternately laminated in the white portions of the lower layer (2). Note that the underlayer and the top layer, which may be selectively provided, are not shown.

[0016] (1) Average thickness of the coating layer It is more preferable that the average thickness of the coating layer excluding the underlying layer and the top layer described below, that is, the sum of the average thickness of the lower layer and the average thickness of the upper layer is 3.5 μm or more and 6.0 μm or less. When the average thickness of the coating layer is within this range, it is possible to more reliably enhance the wear resistance while suppressing the peeling of the coating layer.

[0017] (2) Lower layer The lower layer is provided on the base material (or the underlying layer when there is an underlying layer described below) and has an alternating laminated structure of a first layer and a second layer. Each first layer and each second layer are formed to have equal thicknesses. It is preferable that this average thickness is in the range of 5 nm or more and 100 nm or less.

[0018] The preferable average thicknesses of the first layer and the second layer are 5 nm or more and 100 nm or less, whereby the adhesion between the first layer and the second layer can be enhanced. The average thicknesses of the first layer and the second layer may be the same or different. In order to maintain the adhesion of the entire coating layer and enhance the durability, it is preferable that the average thickness of the lower layer is 1.0 μm or more and 2.0 μm or less.

[0019] Both the first layer and the second layer are composite nitride layers having a face-centered cubic lattice structure containing Al. The average composition of the first layer is Al c Ti d M1 1-c-d N (where M1 is one or more of Zr, Hf, V, Nb, Ta, Mo, W, 0.50 ≤ c ≤ 0.55, 0.45 ≤ d ≤ 0.50), and the average composition of the second layer is Al e Cr f M2 1-e-f N (where M2 is one or more of Ti, Zr, Hf, V, Nb, Ta, Mo, W, 0.60 ≤ e ≤ 0.70, 0.30 ≤ f ≤ 0.40) is preferable. Here, c, d, e, and f are atomic ratios. Since c is smaller than e, the Al content in the lower layer does not become too high, suppressing the excessive refinement of the structure of the lower layer.

[0020] M1 and M2 do not necessarily have to be contained together, but may be contained to further improve wear resistance and heat resistance. When contained, the upper limits are 0.05 and 0.10 respectively in atomic ratio. M1 and M2 are more preferably W and / or Mo, and the lubricity is improved when these are contained. However, when these are contained, the total atomic ratio should be 0.05 or less. Also, although M1 and M2 are different, each of M1 and M2 may be the same as MU.

[0021] In the lower layer, the layer in contact with the base material (when there is an underlying layer described later, it is the underlying layer) may be either the first layer or the second layer. Also, the layer in contact with the upper layer may be either the first layer or the second layer. Also, the number of the first layers and the number of the second layers may be the same, or one may be one layer more than the other.

[0022] (4) Upper layer The upper layer is provided to enhance the durability of the coating layer in the cutting of alloy steel having a hardness ranging from mild steel to about 40 HRC, particularly in milling, which is the hardness range of the material to be cut. The average thickness of the upper layer is preferably 2.5 μm or more and 5.0 μm or less.

[0023] The upper layer is provided on the lower layer and is a composite nitride layer containing AlCr having a face-centered cubic lattice structure, and its average composition is Al g Cr h MU 1-g-h N (MU is one or more of Ti, Zr, Hf, V, Nb, Ta, Mo, W, 0.60 ≦ g ≦ 0.70, 0.30 ≦ h ≦ 0.40) is preferable. Here, g and h are atomic ratios. The Mu component does not necessarily have to be contained, but may be contained to further improve wear resistance and heat resistance. When contained, the atomic ratio is preferably 0.10 or less.

[0024] (5) Other layers (5-1) Selectively provided layer Even with only the lower layer and the upper layer, the aforementioned problems can be sufficiently solved. However, in addition to these layers, a base layer may be selectively provided under the lower layer, and a top layer may be selectively provided above the upper layer.

[0025] The base layer serves to improve the adhesion between the base material and the lower layer, and examples thereof include Ti compounds such as titanium nitride and carbonitride of Ti, and composite nitrides of Al and Ti, and composite nitrides of Al and Cr. The average thickness of the lower layer may be 1.0 to 3.0 μm.

[0026] An example of the top layer is a TiN layer. Since the TiN layer has a golden color tone, for example, it can be used as an identification layer for discriminating whether the coated tool is unused or used based on the color tone change of the coated tool surface. Incidentally, the average thickness of the TiN layer as this identification layer may be, for example, 0.1 to 1.0 μm.

[0027] (5-2) Layers that may occur accidentally In this embodiment, the film is formed so that there are no layers other than the base layer, the lower layer, the upper layer, and the top layer. However, when changing the types of layers to be formed, pressure changes and temperature fluctuations in the film forming apparatus may occur unintentionally, and layers having a composition different from these layers may be accidentally formed (unintentionally) between these layers. This layer is called a layer that may occur accidentally.

[0028] 2. Substrate (1) Material The substrate used in this embodiment can be any substrate material known as long as it does not inhibit the achievement of the aforementioned purpose. For example, it is preferably any one of cemented carbide (WC-based cemented carbide, including those containing Co in addition to WC and further adding carbonitrides such as Ti, Ta, Nb, etc.), cermet (for example, those mainly composed of TiC, TiN, TiCN), ceramics (for example, titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide), cBN sintered body, or diamond sintered body.

[0029] (2) Shape The shape of the base material is not particularly restricted as long as it is a shape used as a cutting tool, and examples thereof include the shape of an insert, the shape of an end mill, and the shape of a drill.

[0030] 3. Measuring method Using a focused ion beam (FIB) apparatus, a cross-section (a plane perpendicular to the surface of the base material, assuming that there are no minute irregularities on the surface of the base material) is cut out, and for all types of layers, the thickness is measured at five locations each using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) (the observation magnification may be any magnification at which thickness measurement is possible, and it is 5,000 to 10,000 times), and the average value is taken as the average thickness of each layer. Further, by performing cross-section measurement using energy dispersive X-ray analysis (EDS) using SEM or TEM, Auger electron spectroscopy (AES), or an electron probe micro analyzer (EPMA), the composition is measured at five locations, and the average composition is calculated from the average value. Further, the crystal structure of each layer is specified from the restricted field diffraction pattern.

[0031] Here, the interface between the surface of the base material and the coating layer is determined as follows. That is, when the base material plane of the base material such as an insert is a plane, the interface between the layer immediately above the base material and the base material is determined based on the element mapping obtained using the above-described apparatus in the cross-section, and for the roughness curve connecting this interface, an average line (straight line) is arithmetically obtained, and this is taken as the surface of the base material. Further, even when the base material has a curved surface such as a drill, when the diameter of this curved surface is sufficiently large with respect to the thickness of the coating layer, the region for obtaining the above-described average line can be regarded as a substantially flat plane, so the interface between the surface of the base material and the coating layer can be obtained in the same manner as when the surface of the base material is a plane.

[0032] 4. Manufacturing method The coating layer of the present embodiment can be manufactured, for example, by the following PVD method. That is, the inside of an arc ion plating (AIP) apparatus is set to a nitrogen atmosphere, For the formation of the lower first layer, a target of AlTiM1 alloy, For the formation of the second layer, a target of AlCrM2 alloy, Furthermore, for the formation of the upper layer, a target of AlTiMU alloy is prepared, Arc discharges are sequentially generated between these targets and the anode electrode to form a lower layer (first layer, second layer) and an upper layer with a predetermined average thickness. Note that there are no restrictions on the film formation methods for the base layer and the top layer, and known methods may be used.

Example

[0033] Next, examples will be described, but the present invention is not limited to these examples.

[0034] <Example 1> As a substrate, an insert of a WC-based cemented carbide (composition: 11.5 mass% Co, 0.7 mass% Cr3C2, 2.0 mass% TaC, the balance being WC and inevitable impurities) (shape: EPNW0603TN-8 according to ISO standard) was prepared.

[0035] For the formation of the coating layers in Invention Example 1 and Comparative Examples 1 to 7, an arc ion plating apparatus was used as described above. The target alloy was installed in the apparatus as a vapor deposition source. First, the temperature inside the arc ion plating apparatus was set to 500°C, and tool cleaning (bombardment treatment) was performed with Ar ions. Next, the pressure inside the furnace of the arc ion plating apparatus was evacuated to 5.0×10 -3 Pa or less, and N2 gas was introduced so that the furnace pressure became 3.2 Pa. Next, a bias voltage of -40 V was applied to the substrate, and current was supplied to the target alloy to form a lower layer and an upper layer on the substrate. Note that the film was formed so that the average thickness per layer of each of the first layer and the second layer with the same number of laminations was 10 nm. Table 1 shows the composition of each coating layer and the average thickness of each layer.

[0036]

Table 1

[0037] The composition and average thickness of each layer in Table 1 were measured as described above. The average thickness of the first and second layers was confirmed to be 10 nm by measuring five points per layer at a magnification of 50,000x in an observation area containing five first and second layers, averaging the measurements. The average thickness of the lower, middle, and upper layers was also measured at a magnification of 10,000x, averaging five points per layer.

[0038] In Table 1, "-" indicates that the corresponding layer was not present. Comparative Examples 2 and 3 indicate that only the layers shown in Table 1 were formed. It was confirmed that each layer in Invention Example 1 and Comparative Examples 1 to 7 had crystal grains with a face-centered cubic structure.

[0039] For Example 1 and Comparative Examples 1 to 7, cutting evaluation was performed under the following cutting conditions, and the time (in minutes: min) until the end of tool life was measured. That is, the flank wear width of the coating layer was measured every 5 minutes using an optical microscope at 100x magnification, and the machining time until the total cutting length reached 0.30 mm was defined as the tool life. However, when the flank wear width exceeded 0.30 mm at a certain measurement time, the difference between the flank wear width at the measurement time immediately before that measurement time and the flank wear width at that measurement time was proportionally distributed over the measurement time interval (5 minutes), and the time when the flank wear width reached exactly 0.30 mm was considered to be the tool life. Table 2 shows the measurement results.

[0040] Work material: S50C (18HRC) Processing method: Milling Tool model number: ASRS2032-5 Insert shape: EPNW0603TN-8 Cutting speed: 180m / min Feed per tooth: 1.5mm / tooth Axial cutting depth: 0.5 mm Radial cutting depth: 21 mm Cutting method: dry cutting

[0041]

Table 2

[0042] As is clear from Table 2, in any of the cutting tests, the time until tool life was longer and it had durability compared to any of the comparative examples in Example 1 of the present invention.

Explanation of Signs

[0043] 1 Substrate 2 Lower layer 3 Upper layer 4 First layer 5 Second layer

Claims

Claim 1 A coated cutting tool having a substrate and a coating layer provided on the substrate, wherein the coating layer has a lower layer and an upper layer on the lower layer, The lower layer has crystal grains with an average thickness of 5 nm or more and 100 nm or less and having a face-centered cubic lattice structure, and its average composition is Al ｃ Ti ｄ M1 １－ｃ－ｄ N (M1 is one or more of Zr, Hf, V, Nb, Ta, Mo, W, 0.50 ≤ c ≤ 0.55, 0.45 ≤ d ≤ 0.55) and a first layer which is a composite nitride, and its average composition is Al ｅ Cr ｆ M2 １－ｅ－ｆ N (M2 is one or more of Ti, Zr, Hf, V, Nb, Ta, Mo, W, 0.60 ≤ e ≤ 0.70, 0.30 ≤ f ≤ 0.40) and is an alternating laminate of a second layer which is a composite nitride The upper layer has crystal grains with a face-centered cubic lattice structure, and its average composition is Al ｇ Cr ｈ MU １－ｇ－ｈ N (MU is one or more of Ti, Zr, Hf, V, Nb, Ta, Mo, W, 0.60 ≤ g ≤ 0.70, 0.30 ≤ h ≤ 0.40), and is a composite nitride layer characterized in that it is a coated cutting tool. Claim 2 The coated cutting tool according to claim 1, characterized in that the sum of the average thickness of the lower layer and the average thickness of the upper layer is 3.5 μm or more and 6.0 μm or less.

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