Surface coated cutting tools

Abstract

To provide coated tools that exhibit excellent resistance to chipping and breakage. [Solution] A surface-coated cutting tool having a substrate and a coating layer on the surface of the substrate, The covering layer has a lower layer and an upper layer formed on the lower layer. The aforementioned lower layer is a Ti compound layer having an average thickness of 3.0 to 20.0 μm and containing one or more layers made of TiCN. The upper layer is made of α-Al2O3 with an average thickness of 2.0 to 20.0 μm, contains sulfur, and has a sulfur content of 0.20 to 0.50 atomic percent in the region from its surface to a thickness of 0.5 μm toward the substrate, and has a residual stress of 0 to 250 MPa or less. Surface coated cutting tools.

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, for the purpose of improving the cutting performance of a cutting tool, there is a coated tool in which a coating layer is formed by vapor deposition on the surface of a substrate such as a tungsten carbide (hereinafter referred to as WC)-based cemented carbide. This coating layer exhibits excellent chipping resistance and wear resistance, and for further improvement of the coating layer, for example, a proposal has been made to add sulfur to the coating layer.

[0003] As an example thereof, Patent Document 1 describes a coated tool in which the coating layer has an α-Al2O3 layer containing sulfur, and the concentration of the sulfur decreases in the direction away from the substrate in the thickness direction of the α-Al2O3 layer, and the coated tool is said to have excellent wear resistance and slidability.

[0004] Also, as another example, Patent Document 2 describes a coated tool having one or more α-Al2O3 layers containing 100 ppm or more of sulfur and having a thickness of 1 to 25 μm, and the coated tool is said to have chipping resistance and crater wear resistance.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] This invention has been made in view of the above circumstances and proposals, and aims to provide a coating tool that exhibits superior resistance to chipping and breakage. [Means for solving the problem]

[0007] A surface-coated cutting tool according to an embodiment of the present invention is The substrate has a coating layer on its surface, The aforementioned covering layer consists of a lower layer and an upper layer formed on the lower layer. The aforementioned lower layer is a Ti compound layer having an average thickness of 3.0 to 20.0 μm and containing one or more layers made of TiCN. The upper layer is made of α-Al2O3 with an average thickness of 2.0 to 20.0 μm, contains sulfur, and has a sulfur content of 0.20 to 0.50 atomic percent in the region from its surface toward the substrate to a thickness of 0.5 μm, and a residual stress of 0 to 250 MPa or less.

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

[0009] (1) The sulfur concentration is 0.01 atomic percent or less in the region from the interface between the upper layer and the lower layer toward the surface in the thickness direction up to 0.5 μm. [Effects of the Invention]

[0010] The surface-coated cutting tool according to the above embodiment exhibits excellent resistance to chipping and fracture. [Brief explanation of the drawing]

[0011] [Figure 1] This figure schematically shows an example of a longitudinal cross-section of a surface-coated cutting tool according to an embodiment of the present invention. [Modes for carrying out the invention]

[0012] The inventors diligently investigated whether sulfur, which has been conventionally added to coating layers, could improve the fracture resistance and chipping resistance of coated tools. As a result, they obtained the novel finding that by deliberately creating a sulfur-enriched region on the surface portion of the α-Al2O3 layer that is in contact with the workpiece (the surface portion of the coated tool), and by embrittle only the surface portion of the α-Al2O3 layer, and then performing a blast treatment as a post-treatment after the coating layer has been formed, it is possible to impart appropriate residual stress to the α-Al2O3 layer, thereby improving the fracture resistance and chipping resistance of the coated tool. The present invention is based on this finding.

[0013] The present invention will be described below by providing a detailed explanation of a coating tool according to an embodiment of the present invention. In this specification and in the claims, when a numerical range is expressed as "L~M" (where L and M are both numerical values), the range includes an upper limit (M) and a lower limit (L). If a unit is specified only for the upper limit (M), then the units of the upper limit (M) and the lower limit (L) are the same.

[0014] In the claims and specification, the following wording is defined: 1) to 2) below.

[0015] 1) A longitudinal section refers to a section perpendicular to a straight line, assuming the substrate surface is free of minute irregularities.

[0016] 2) The substrate surface is a linear approximation of the boundary between the substrate and the lower layer in contact with it. That is, when the substrate has a planar surface such as an insert, elemental mapping is performed in the longitudinal section, and image processing is applied to the mapping image to find an average line for the boundary curve. The direction perpendicular to this average line is defined as the direction perpendicular to the tool substrate (the thickness direction of the coating layer).

[0017] Even if the substrate has a curved surface like a drill, if the tool diameter is sufficiently large relative to the thickness of the coating layer, the boundary will be substantially flat, and the surface of the substrate can be determined using the same method as in the case of an insert. In addition, as an observation field for elemental mapping, 20 μm (length in a direction parallel to the surface of the tool substrate treated as having no minute unevenness) × 20 μm (length including the entire thickness of the coating layer) can be exemplified, and it is preferable to provide and determine a plurality of such observation fields.

[0018] 1. Coating layer In the coated tool of the present embodiment, it has an upper layer that contacts the workpiece as the coating layer, and a lower layer is provided between this upper layer and the substrate. That is, as the coating layer (4), for example, as shown in FIG. 1, one composed of the lower layer (2) can be exemplified between the substrate (1) and the upper layer (3). Hereinafter, the lower layer and the upper layer constituting the coating layer will be mainly described. Note that the composition of the compound constituting each layer described below is not limited to the stoichiometric composition.

[0019] (1) Lower layer The lower layer is a layer made of a Ti compound, that is, one or more of a layer made of a carbide, nitride, carbon oxide, and carbonitride of Ti, and necessarily has a layer made of TiCN.

[0020] The lower layer preferably has an average thickness of 3.0 to 20.0 μm. The reason is that if it is less than 3.0 μm, the excellent wear resistance of the lower layer cannot be sufficiently exhibited, while if it exceeds 20.0 μm, peeling in the coating layer is likely to occur. The average thickness of the layer made of TiCN that is necessarily included in the lower layer is more preferably 4.0 to 15.0 μm, and the average thickness of the lower layer is more preferably 5.0 to 15.0 μm.

[0021] (2) Upper layer The upper layer is an indispensable layer, a layer made of α-Al2O3, and a layer that improves chipping resistance and chipping resistance. Its average thickness is preferably 2.0 to 20.0 μm. The reason is that if it is less than 2.0 μm, the thermal stability and wear resistance of the surface layer cannot be sufficiently exhibited, while if it exceeds 20.0 μm, chipping is likely to occur. The average thickness of the upper layer is more preferably 3.0 to 15.0 μm.

[0022] Furthermore, the upper layer contains sulfur, and it is preferable that the sulfur content distribution in the region from the surface toward the substrate in the thickness direction up to 0.5 μm (the region represented as (7) in Figure 1; hereinafter sometimes referred to as the surface region) is 0.20 to 0.50 atomic percent. The sulfur content in the upper layer refers to the percentage of sulfur atoms relative to all atoms in the upper layer (atomic ratio).

[0023] When the sulfur content in the surface layer is within the aforementioned range, only the surface portion of the upper layer becomes brittle. As a post-treatment after film formation, the blast treatment allows the upper α-Al2O3 layer to acquire appropriate residual stress, improving fracture resistance and chipping resistance.

[0024] Furthermore, it is more preferable that the sulfur concentration in the region from the interface between the upper layer and the lower layer to 0.5 μm in the direction of the tool surface (the region represented as (5) in Figure 1; sometimes called the lower layer side region) be 0.01 atomic percent or less. In this case, the lower limit of the sulfur concentration may be 0.00 atomic percent. Within this sulfur concentration range, the lower and upper layers adhere firmly, improving resistance to chipping.

[0025] Here, the surface area of ​​the upper layer is as follows: In a longitudinal section, an observation area (for example, a 30 μm × 30 μm rectangular observation area) including the vicinity of the surface of the upper layer is observed using a scanning electron microscope (SEM). The surface of the upper layer is defined as the line parallel to the substrate surface that passes through the most convex part of the upper layer within the observation area. Then, with respect to this line, the region up to 0.5 μm in the thickness direction of the upper layer toward the substrate is defined as the surface layer.

[0026] Furthermore, the region of the upper layer that lies on the lower layer side is the region extending to 0.5 μm in the thickness direction of the upper layer toward its surface, relative to the approximate straight line that defines the boundary between the upper and lower layers. Here, this approximate straight line is defined as a straight line parallel to the surface of the substrate that passes through the most convex part of the lower layer.

[0027] The sulfur content in the portion of the upper layer excluding the surface and lower layer sides (referred to as the main region) is preferably 0.01 to 0.10 atomic percent. With this content, embrittlement of the upper layer does not occur, and a decrease in cutting performance can be prevented.

[0028] The residual stress (tensile residual stress) of the upper layer is preferably 0 to 250 MPa or less. This is because if it exceeds 250 MPa, the tensile residual stress causes crack propagation during cutting, leading to a decrease in fracture resistance, and if it falls below 0 MPa, the α-Al2O3 layer itself is destroyed, leading to a decrease in wear resistance and fracture resistance. The residual stress of the upper layer is more preferably 0 to 200 MPa. The residual stress in the upper layer can be controlled by known means such as blast treatment.

[0029] (3) Other layers The lower layer is formed from Ti carbides, nitrides, carbon oxides, and carbonitroxides containing TiCN, while the upper layer is formed from α-Al2O3. However, due to unintended factors such as switching of the deposition gas or subtle temperature changes, unintended compounds different from these compounds may be present in parts of the lower and upper layers. Therefore, the statement that the coating layer consists of a lower layer and an upper layer formed on the lower layer does not negate the existence of a layer containing these unintended compounds.

[0030] 2. Tool base (1)Material Any tool substrate that is conventionally known as a tool substrate of this type can be used, as long as it does not hinder the achievement of the objectives of the present invention. For example, cemented carbide (WC-based cemented carbide, including those containing WC and Co, and further including those with carbonitrides such as Ti, Ta, and Nb added), cermet (mainly composed of TiC, TiN, TiCN, etc.), or ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.).

[0031] (2) Shape The shape of the base material is not particularly restricted as long as it is a shape that can be used as a cutting tool; examples include the shape of an insert and the shape of a drill.

[0032] 3. Measurement of average thickness Here, the average thickness of each layer constituting the coating layer can be determined by, for example, preparing a longitudinal section for observation by processing the coating layer at an arbitrary position using a focused ion beam system (FIB), and then observing the longitudinal section at multiple locations (for example, 5 locations with an interval of 1.0 μm or more) in the thickness direction of the coating layer using a scanning electron microscope (SEM), transmission electron microscope (TEM), scanning transmission electron microscope (STEM), or energy dispersive X-ray spectrometry (EDX) attached to an SEM or TEM, identifying each layer, measuring the thickness of each layer, and then taking the arithmetic mean.

[0033] 4. Measurement of sulfur content in each region The average composition of each region is determined by using an electron probe microanalyzer (EPMA) to irradiate five arbitrary locations within each region with an electron beam in a longitudinal section measuring the average thickness of each layer. The analysis results of the characteristic X-rays obtained from each location are then arithmetically averaged.

[0034] 5. Measurement of residual stress The residual stress in the upper layer is measured using the sin2ψ method with an X-ray diffractometer employing CuKα rays. The diffraction peak of the α-Al2O3(1310) plane is used for the measurement, and calculations are performed using a Young's modulus of 384 GPa and a Poisson's ratio of 0.23.

[0035] 5. Manufacturing method The coated tool of this embodiment can be manufactured by forming a lower layer and an upper layer, followed by a blast treatment. These are, for example, the following manufacturing conditions.

[0036] (1) Lower layer The lower layer can be manufactured using a known chemical vapor deposition (CVD) method, so its explanation will be omitted.

[0037] (2) Upper layer The upper layer consists of three processes, each manufactured as follows: 1) First step (film formation in the lower layer region) Reaction gas composition (volume %): AlCl 3 1.0~3.0%, CO2 1.0~5.0% HCl 0.3~1.0%, H2S 0.0~1.0%, balance H2 Ambient temperature: 850~1050℃ Ambient pressure: 5~15kPa

[0038] 2) Second step (film formation on the main part) Reaction gas composition (volume %): AlCl 30.5~5.0%, CO2 2.0~10.0% HCl 0.5~3.0%, H2S 0.5~1.5%, remainder H2 Ambient temperature: 850~1050℃ Ambient pressure: 5~15kPa

[0039] 3) Third step (film formation in the surface area) Reaction gas composition (volume %): AlCl 30.5~5.0%, CO2 2.0~10.0% HCl 0.5~3.0%, H2S 2.0~3.5%, remainder H2 Ambient temperature: 850~1050℃ Ambient pressure: 5~15kPa

[0040] (3) Residual stress imposition treatment While there are no particular restrictions on residual stress imparting treatments as long as they can impart stress within the aforementioned range, blasting is one example. A blasting treatment example is a wet method in which a media containing abrasive grains of ZrO2 or Al2O3 is projected onto the tool surface. [Examples]

[0041] Next, we will describe some examples. Here, as an example of the coated tool of the present invention, we describe its application to an insert cutting tool using a WC-based cemented carbide as the base material. However, the base material can be any of the materials mentioned above, and the tool can be a drill, end mill, or the like.

[0042] As raw material powders, WC powder, TiC powder, ZrC powder, TaC powder, NbC powder, Cr3C2 powder, TiN powder, and Co powder were prepared. These raw material powders were blended according to the formulation shown in Table 1, wax was added, and the mixture was ball-milled in acetone for 24 hours and then dried under reduced pressure. Subsequently, the mixture was press-molded into a compact at a pressure of 98 MPa, and this compact was vacuum-sintered in a vacuum of 5 Pa at a predetermined temperature within the range of 1370 to 1470°C for 1 hour. After sintering, substrates α and β made of WC-based cemented carbide with insert shapes according to ISO standard CNMG120408 were manufactured, respectively.

[0043] Next, a lower layer was deposited on the surface of the substrate under the conditions shown in Table 2, and an upper layer consisting of α-Al2O3 was deposited under the conditions shown in Table 3. Then, blast treatment was performed to produce Examples 1 to 8 shown in Table 5. The average thickness and sulfur concentration of the deposited coating layers are shown in Table 5.

[0044] For comparison, a lower layer was deposited on the surface of substrates A and B under the conditions shown in Table 2, and an upper layer consisting of α-Al2O3 was deposited under the conditions shown in Table 4. Then, blast treatment was performed to produce Comparative Examples 1 to 8 shown in Table 6. The average thickness of the deposited coating layer, sulfur concentration, etc., are shown in Table 6.

[0045] [Table 1]

[0046] [Table 2]

[0047] [Table 3]

[0048] [Table 4]

[0049] [Table 5]

[0050] [Table 6]

[0051] In Tables 5 and 6, the sulfur concentration (%) in the lower layer region represents the maximum sulfur concentration in the lower layer region, and the sulfur concentration (%) in the surface layer region represents the minimum sulfur concentration in the surface layer. "-" indicates that there is no applicable value, and the numbers in parentheses for each layer in the lower layer indicate the ratio (%) of the average thickness of that layer to the total average thickness of all layers (average thickness of the lower layer).

[0052] Next, cutting tests 1 and 2 were performed for Examples 1 to 8 and Comparative Examples 1 to 8 under the following cutting conditions.

[0053] Cutting Test 1 Workpiece material: JIS SCM440 with four longitudinal grooves spaced evenly along the length. Outer diameter 200mm, length 400mm, slit width 4mm Cutting speed: 400m / min Cut: 1.5mm Feed per revolution: 0.35mm Cutting time: 5 minutes Wet cutting

[0054] Cutting Test 2 Workpiece material: JIS FC300 with four evenly spaced longitudinal grooves along its length. Outer diameter 200mm, length 400mm, slit width 4mm Cutting speed: 450m / min Cutting depth: 2.0mm Feed per revolution: 0.35mm Cutting time: 5 minutes Wet cutting

[0055] The results of cutting tests 1 and 2 are shown in Table 7, respectively.

[0056] [Table 7]

[0057] In Table 7, the flank wear width (mm) refers to the flank wear width after the cutting time has elapsed, and the cutting time (minutes) refers to the cutting time (minutes) until chipping occurs and the tool reaches the end of its lifespan.

[0058] As is clear from the results in Table 7, the examples show good cutting performance, but the comparative examples experience peeling of the coating layer, chipping, or wear progression in a short time, leading to a short lifespan. [Explanation of Symbols]

[0059] 1 Base 2 Lower layer 3 Upper layer 4 Covering layer 5 Lower layer side area 6 Main areas 7 Surface area

Claims

1. A surface-coated cutting tool having a substrate and a coating layer on the surface of the substrate, The aforementioned covering layer consists of a lower layer and an upper layer formed on the lower layer. The lower layer is a Ti compound layer having an average thickness of 3.0 to 20.0 μm and containing one or more layers made of TiCN. The aforementioned upper layer is α-Al with an average thickness of 2.0 to 20.0 μm. ２ O ３ It consists of a material containing sulfur, wherein the sulfur content is 0.20 to 0.50 atomic percent in the region from its surface toward the substrate to a thickness of 0.5 μm, and the residual stress is 0 to 250 MPa or less. A surface-coated cutting tool characterized by the following features.

2. The surface-coated cutting tool according to claim 1, characterized in that the sulfur concentration is 0.01 atomic percent or less in a region from the interface between the upper layer and the lower layer toward the surface in the thickness direction up to 0.5 μm.

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