WC-based super-hard alloy cutting tools

Abstract

This cutting tool made of WC-based cemented carbide is characterized in that: 1) said cutting tool contains 8.0-14.0 mass% of Co, 0.1-1.4 mass% of Cr3C2, and 0.6-4.0 mass% of one or more selected from among TaC, NbC, TiC, and ZrC, with the remainder consisting of WC and inevitable impurities; and 2) when the boundary length between WC grains is denoted by L1, the boundary length between a WC grain and a bonded phase or γ phase is denoted by L2, the area ratio of the bonded phase is denoted by V(%), the average grain diameter of WC grains is denoted by D (μm), the theoretical volume fraction of the γ phase is denoted by Vγ, and a WC-WC boundary length ratio is denoted by R, R=(L1) / ((L1)+(L2)), R≥(0.76-0.059×D)×(10 / V)-Vγ×0.06, and 1.0≤D≤4.0 are satisfied.

Description

[Technical Field]

[0001] The present invention relates to a cutting tool made of WC-based cemented carbide (hereinafter sometimes referred to as a WC-based cemented carbide tool). This application claims priority to Japanese application No. 2020-56624, filed on March 26, 2020. The entire contents of the Japanese application are incorporated herein by reference. [Background technology]

[0002] WC-based cemented carbide alloys are highly hard and tough, and therefore WC-based cemented carbide tools using them as tool substrates exhibit excellent wear resistance and are used as cutting tools with long life over long periods of use. Meanwhile, in recent years, various proposals have been made to further improve the cutting performance and tool life of WC-based cemented carbide tools depending on the type of work material, cutting conditions, etc.

[0003] For example, Patent Document 1 proposes a cutting tool made of a WC-based cemented carbide that satisfies the relationship B / A≦0.05, where A is the number of WC particles and B is the number of WC particles that have one or less contact points with other WC particles. The tool is said to have improved resistance to plastic deformation and a long life when used in wet continuous cutting of carbon steel and stainless steel.

[0004] Furthermore, for example, Patent Document 2 proposes a cutting tool made of a WC-based cemented carbide, which contains 10 to 13 mass% Co, a 2 to 8% Cr to Co ratio, 0.2 to 0.5 mass% TaC and / or NbC, and the remainder WC, has a hardness of 88.6 to 89.5 HRA, and has a D80 / D20 ratio of the WC cumulative grain size 80% diameter (D80) to the cumulative grain size 20% diameter (D20) in terms of area ratio on the polished surface of 2.0 to 4.0, D80 is 4.0 to 7.0 μm, and has a WC adhesion degree of 0.36 to 0.43. This tool is said to prevent adhesion of the workpiece and have improved chipping resistance when cutting difficult-to-cut materials such as stainless steel.

[0005] Furthermore, for example, in Patent Document 3, when the length of the WC-WC adhesive interface is L1 and the length of the WC-Co adhesive interface is L2, R>(0.82-0.086×D)×(10 / V) R=(L1) / ((L1)+(L2)) D: WC particle size (μm) when the area ratio of WC is 50%, 0.6≦D≦1.5 V: binder phase volume (volume%), 9≦V≦14 A cutting tool made of a WC-based cemented carbide that satisfies the above requirements has been proposed, and it is said that this tool has improved heat plastic deformation resistance and toughness when cutting Ni-based heat-resistant alloys. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6256415 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-88999 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-179433 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 an object of the present invention is to provide a cutting tool made of a WC-based cemented carbide that exhibits excellent cutting performance over long periods of use, particularly when cutting stainless steel and the like. [Means for solving the problem]

[0008] The WC-based cemented carbide cutting tool according to an embodiment of the present invention has the following features: 1)Co:8.0~14.0% by mass, Cr3C2: 0.1~1.4% by mass, One or more selected from TaC, NbC, TiC, and ZrC: 0.6 to 4.0 mass% Including, The balance is WC and unavoidable impurities, 2) The interface length between WC particles is L1, The interface length between the WC particle and the binder phase or γ phase is L2. The area ratio of the binder phase is V (%), The average particle size of WC particles is D (μm). The theoretical volume fraction of the γ phase is Vγ, When the WC-WC interface length ratio is R and R=(L1) / ((L1)+(L2)), R≧(0.76-0.059×D)×(10 / V)-Vγ×0.06, 1.0≦D≦4.0 Satisfy.

[0009] Furthermore, the WC-based cemented carbide cutting tool according to the above embodiment may satisfy either or both of the following (1) and (2).

[0010] (1) The average grain size of the γ phase is 0.2 to 4.0 μm. (2) A coating layer is formed on the cutting edge. [Effects of the Invention]

[0011] According to the above, it is possible to obtain a cutting tool made of a WC-based cemented carbide that is excellent in high-temperature hardness, plastic deformation resistance, and chipping resistance even when machining stainless steel or the like. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic diagram showing an example of the structure of a WC-based cemented carbide cutting tool according to the present embodiment. [Figure 2] FIG. 10 is a schematic diagram showing a side surface of a flank, illustrating an example of measurement of the amount of flank plastic deformation of a cutting edge. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present inventors have conducted extensive research into the WC-based cemented carbide cutting tools described in the above Patent Documents 1 to 3, and as a result have come to the following realization.

[0014] (1) In the WC-based cemented carbide cutting tool proposed in Patent Document 1, although the number of contact points between WC-WC particles is controlled to improve the plastic deformation resistance of the WC-based cemented carbide cutting tool, the plastic deformation resistance is insufficient.

[0015] (2) In the WC-based cemented carbide cutting tool proposed in Patent Document 2, the chipping resistance and adhesion resistance of the WC-based cemented carbide cutting tool are improved by controlling the WC particle size distribution, etc. However, TaC and NbC are contained only to the extent that they are solid-solubilized in the binder phase. Therefore, the γ phase they constitute adheres between WC-WC particles and acts to suppress WC-WC interfacial slip, resulting in insufficient high-temperature hardness and a short tool life when used in turning and cutting stainless steel, etc.

[0016] (3) The WC-based cemented carbide cutting tool proposed in Patent Document 3 aims to improve plastic deformation resistance by controlling the adhesive interface ratio between WC-WC particles. However, since it does not contain a gamma phase component, its high-temperature hardness is insufficient, and the focus is only on increasing the interface length ratio between WC-WC particles. Therefore, the gamma phase may not be able to fully bond between WC-WC particles and suppress grain boundary sliding of WC-WC particles, and therefore plastic deformation resistance may be insufficient when cutting stainless steel, etc.

[0017] Based on this understanding, the present inventors have conducted extensive research and have made the following findings (1) to (4) regarding cutting tools made of WC-based cemented carbide.

[0018] (1) While ensuring a predetermined amount of binder phase without reducing the Co content that forms the binder phase, When the ratio of the contact length (hereinafter referred to as the "WC-WC interface length") at the interface where WC particles with high Young's modulus come into contact with each other (hereinafter referred to as the "WC-WC interface") is increased, the WC particles act as a skeleton that prevents plastic deformation, Furthermore, by including an appropriate amount and size of gamma phase in a WC-based cemented carbide cutting tool, grain boundary sliding at the WC-WC interface is reduced, Improved plastic deformation resistance of WC-based cemented carbide cutting tools.

[0019] (2) When the average particle size of the WC particles is coarse and equal to or greater than a predetermined value, the climbing motion of edge dislocations in the binder phase is suppressed. In addition, the binder phase is solid-solution strengthened by the inclusion of Cr3C2 in the binder phase, which further improves the plastic deformation resistance of the WC-based cemented carbide cutting tool.

[0020] (3) By containing one or more of the gamma phase forming elements Ta, Nb, Ti and Zr in the binder phase, excellent oxidation resistance and high temperature hardness are exhibited.

[0021] (4) When a WC-based cemented carbide cutting tool satisfying the above (1) to (3) is used to cut difficult-to-cut materials such as stainless steel, the cutting tool has improved resistance to plastic deformation and high-temperature hardness, which reduces the occurrence of abnormal damage such as chipping caused by deformation of the cutting edge of the tool or plastic deformation. In addition, the presence of the γ phase improves oxidation resistance and high-temperature hardness, thereby achieving a longer life for the cutting tool.

[0022] Based on these findings, it was discovered that the above-mentioned problems can be solved when the ratio R (WC-WC interface length ratio) of the "WC-WC interface length" to the sum of the "WC-WC interface length" and the "WC-(binder phase or γ phase: expressed as binder phase + γ phase) interface length" in a WC-based cemented carbide cutting tool has a specific relationship with the area fraction of the binder phase, the average WC grain size, and the theoretical volume fraction of the γ phase.

[0023] A cutting tool made of a WC-based cemented carbide according to an embodiment of the present invention will be described in detail below. In this specification and claims, when a numerical range is expressed as "L to M" (where L and M are both numerical values), the range includes the upper limit (M) and the lower limit (L), and the upper limit (M) and the lower limit (L) have the same units. The numerical values ​​also include tolerances.

[0024] 1. Ingredient composition The component composition will be explained.

[0025] (1)Co Co is contained as a constituent of the main binder phase. If the Co content is less than 8.0% by mass, the WC-based cemented carbide cutting tool will not have sufficient toughness. On the other hand, if the Co content exceeds 14.0% by mass, the WC-based cemented carbide cutting tool will rapidly soften, failing to achieve the desired hardness required for the cutting tool, and will undergo significant deformation and wear. Therefore, the Co content in the WC-based cemented carbide cutting tool is preferably 8.0 to 14.0% by mass. The Co content is more preferably 8.5 to 12.0% by mass.

[0026] The binder phase may contain W, C, and other unavoidable impurities. It may also contain Cr and at least one of Ta, Nb, Ti, and Zr, which are metallic components that make up the γ phase. When these elements are present in Co, they are presumed to be in a solid solution state in Co.

[0027] Co has two types of crystal structures, the fcc structure and the hcp structure, and binder phases containing W, C, Cr, and at least one of Ta, Nb, Ti, and Zr, which are metallic components that make up the γ phase, also have the fcc structure and the hcp structure, just like Co, which is the main binder phase component. Therefore, the binder phase regions in WC-based cemented carbide cutting tools that have these two crystal structures are called the binder phase (fcc) and the binder phase (hcp), respectively.

[0028] (2) Cr3C2 The Cr3C2 content is preferably 0.1 to 1.4 mass%. Cr3C2 dissolves as Cr in Co, which mainly forms the binder phase, and solid-solution strengthens Co, thereby increasing the strength of WC-based cemented carbide cutting tools. This effect is insufficient if the Cr3C2 content is less than 0.1 mass%, while if the Cr3C2 content exceeds 10% relative to the Co content, Cr precipitates as a complex carbide with W, which may reduce toughness or serve as a starting point for fracture. Therefore, taking into account the upper limit of the Co content of 14.0 mass%, the upper limit of the Co content is set at 1.4 mass%, which is 10% of that limit.

[0029] (3) TaC, NbC, TiC, ZrC It is preferable to contain at least one or more selected from TaC, NbC, TiC and ZrC in a total amount of 0.6 to 4.0 mass %. All of these components are also components that form the γ phase.

[0030] These metallic elements improve the high-temperature hardness of the binder phase by partially dissolving in Co, which forms the main binder phase. On the other hand, these metallic elements do not dissolve in the binder phase but exist as a γ-phase, which is a carbide phase (which may further contain W in addition to these metallic elements), thereby improving oxidation resistance and crater wear resistance, and adhering to the WC-WC interface to suppress grain boundary sliding at the WC-WC interface.

[0031] If the total content of these metal components converted into carbide (carbide in which the metal components and carbon are bonded in a 1:1 ratio) is less than 0.6 mass%, the above-mentioned function will be insufficient. On the other hand, if it exceeds 4.0 mass%, aggregates will be easily formed, which may become the starting point for the occurrence of defects. Therefore, the total content is preferably 0.6 to 4.0 mass%.

[0032] The average grain size of the γ phase is more preferably 0.2 to 4.0 μm, which allows for an appropriate contact frequency with WC particles. The average grain size of the γ phase is determined by mirror-finishing any surface or cross section of a WC-based cemented carbide cutting tool, observing the machined surface with a scanning electron microscope (SEM), and analyzing the image to determine the area of ​​at least 300 γ phases. The diameters of circles equal to the areas are then calculated and averaged. The mirror-finishing can be performed using, for example, a focused ion beam (FIB) device or a cross-section polisher (CP) device.

[0033] The above-mentioned contents of Cr3C2, TaC, NbC, TiC, and ZrC are values ​​obtained by converting the amounts of Cr, Ta, Nb, Ti, and Zr measured for a WC-based cemented carbide cutting tool using an electron probe microanalyzer (EPMA) into the amounts of the above-mentioned carbides.

[0034] (4) WC WC is the remaining component, and may contain unavoidable impurities that are inevitably mixed in during the manufacturing process. The WC content is calculated as a carbide equivalent, assuming that W and C are combined in a 1:1 ratio.

[0035] (5) Inevitable impurities As described above, the remaining components and the binder phase may contain impurities that are inevitably mixed in during the manufacturing process, and the amount of such impurities is preferably 0.3% by mass or less, with the total amount of the WC-based cemented carbide cutting tool being taken as 100% by mass.

[0036] 2.Organization The sintered structure of WC-based cemented carbide cutting tools is determined by the WC-WC interface length ratio (R value), the WC areal mean grain size (D) (μm), the binder phase area ratio (V), and the theoretical volume fraction of the γ phase.

[0037] Details are provided below.

[0038] (1)WC-WC interface length ratio (R) Due to the high WC-WC interface length ratio (R), the WC particles with a high Young's modulus act as a skeleton that prevents plastic deformation, making it possible to obtain a WC-based cemented carbide cutting tool with excellent resistance to plastic deformation.

[0039] The WC-WC interface length ratio (R) can be calculated by the formula R = (L1) / ((L1) + (L2)), where L1 is the WC-WC interface length and L2 is the WC-(binder phase + γ phase) interface length. Here, the WC-WC interface length is the interface length between WC particles, and the WC-(binder phase+γ phase) interface length is the interface length between a WC particle and the binder phase and between a WC particle and the γ phase.

[0040] As mentioned above, the binder phase is composed mainly of Co, with W, C, Cr, and γ-phase component metal elements (Ta, Nb, Ti, Zr) dissolved therein, and the γ-phase is a carbide phase mainly composed of one or more of the γ-phase component metal elements Ta, Nb, Ti, and Zr.

[0041] The method for measuring the WC-WC interface length L1 and the WC-(binder phase+γ phase) interface length L2 will be described with reference to FIG. Specifically, the surface or cross section of a WC-based cemented carbide cutting tool is ion-milled, and the machined surface is observed using a scanning electron microscope (SEM) equipped with an electron backscatter diffraction (EBSD) device. The size of each observation field is 24 μm × 72 μm, and measurement points (represented as points, but actually regular hexagonal regions) spaced 0.1 μm apart are irradiated with an electron beam in two dimensions within the field. Multiple fields are used to identify more than 4,000 WC particles (1). Based on the EBSD pattern obtained by electron beam irradiation, the WC particles (1), the hcp binder phase (3), the fcc binder phase (4), and the γ phase (5) are identified.

[0042] In this case, since the gamma phase (5) has an fcc structure, it cannot be separated from the binder phase (fcc) (4), and is actually identified as the binder phase (fcc) (4) + gamma phase (5).

[0043] As shown in FIG. 1, when adjacent WC particles (1) have an orientation difference of 2° to 180°, the length of the interface is defined as the WC-WC interface (2) length L1. The length of the interface between the WC (1) grain and the binder phase (hcp) (3) is the WC-binder phase (hcp) interface (6) length L2-1. The length of the interface between the WC (1) grain and the (fcc binder phase (4) + gamma phase (5)) is defined as the WC-(fcc binder phase (7) + gamma phase) interface length L2-2. Furthermore, L2, which is the WC-(binder phase+γ phase) interface length, is the sum of L2-1 and L2-2.

[0044] (2) Average particle size of WC particles (D) The average particle size D (μm) of the WC particles is preferably 1.0 μm to 4.0 μm. By setting the average particle size D of the WC particles in this range, it is possible to obtain a WC-based cemented carbide sintered body structure that is less susceptible to plastic deformation due to the climbing motion of edge dislocations at high temperatures. The average particle size D (μm) of the WC particles is more preferably set in the range of 1.6 to 3.0 μm.

[0045] Here, the average grain size D (μm) of WC grains is determined by ion milling any surface or cross section of a WC-based cemented carbide cutting tool and measuring the machined surface with an SEM equipped with EBSD, as in the case of deriving the average grain size of the gamma phase. That is, measurements are taken in two dimensions at 0.1 μm intervals in a 24 μm × 72 μm field of view, and the area of ​​at least 4,000 individual WC grains within the observation area is measured by image analysis. The WC grains are approximated as circles of the same area, and the diameter and area ratio of the WC grains with that diameter are calculated. The average grain size D is then calculated as the sum of the values ​​obtained by multiplying the diameter and area ratio of each WC grain.

[0046] (3) Area ratio of binder phase (V) The area ratio of the binder phase is determined on the premise that the area ratio of the binder phase in a two-dimensional plane is the same in three-dimensional directions. On a mirror-finished surface of any surface or cross section of a WC-based cemented carbide cutting tool, multiple fields (e.g., three fields) are selected, and each field is observed at 2000 to 3000 times magnification using a field emission scanning electron microscope (FE-SEM), a backscattered electron image is taken, and the image is binarized using image processing to separate the WC particles, γ phase, and binder phase, and the area ratio of the binder phase to the entire photographed field is determined.

[0047] (4) Theoretical volume fraction of the γ phase (Vγ) The theoretical volume fraction Vγ of the γ phase is calculated by dividing the contents (mass%) of TaC, NbC, TiC, and ZrC measured by EPMA by their respective densities, assuming that the densities of TaC, NbC, TiC, and ZrC are 14.4, 7.82, 4.92, and 6.66, respectively (see "Data Book: Handbook of High Melting Point Compounds" by G. V. Samsonov and I. M. Vynicky, translated by the Japan-Soviet Press Translation Department, published by Japan-Soviet Press in December 1977).

[0048] (5) Relationship between WC-WC interface length ratio (R), binder phase area ratio (V), WC area average grain size (D), and theoretical volume fraction of γ phase (Vγ) It is preferable that the WC-WC interface length ratio (R) satisfies the relationship defined by the area ratio of the binder phase (V) (%), the area average grain size of WC (D) (μm), and the theoretical volume fraction of the gamma phase (Vγ), i.e., R≧(0.76−0.059×D)×(10 / V)−Vγ×0.06. When this relationship is satisfied, excellent properties in terms of plastic deformation resistance and chipping resistance are exhibited.

[0049] There is no particular restriction on the upper limit of R, but it is preferably 0.70, and more preferably 0.60. If R is equal to or less than this upper limit, microchipping of the cutting edge can be more reliably suppressed.

[0050] 3. Manufacturing method The WC-based cemented carbide cutting tool according to this embodiment can be produced, for example, through the following steps (1) to (3).

[0051] (1) Blend with raw powder Two types of WC powders with different particle size distributions (WC powder with the mode r1 (μm) of the particle size distribution and WC powder with the mode r2 (μm), where r1>r2) are blended in a predetermined blending ratio and a predetermined particle size ratio, and a raw material powder consisting of Co powder and Cr3C2 powder is blended, and further a raw material powder containing one or more powders of TaC powder, NbC powder, TiC powder, and ZrC powder is added.

[0052] Then, for example, by media-less mixing using an attritor with a reduced amount of media, or preferably an ultrasonic homogenizer or cyclone mixer, the materials are blended and mixed under conditions that do not apply a large crushing force, to produce a mixed powder.

[0053] In addition, it is preferable that the ratio of the mode of the particle size distribution, ie, r2 / r1, of the blend of the two types of WC powders satisfies 0.15 to 0.60.

[0054] (2) Preparation of green bodies and sintering The mixed powder is molded to produce a powder compact, which is then sintered in a vacuum atmosphere at a heating temperature of 1300 to 1450°C, preferably 1300 to 1400°C, for a heating holding time of 15 to 90 minutes, more preferably 15 to 60 minutes. This prevents changes in the shape and particle size distribution of the WC particles due to grain growth. After sintering, a solid-phase sintering step is performed in which heat treatment is performed at 1100 to 1200°C for 5 to 100 hours to enhance the adhesion between the WC particles due to grain boundary diffusion. This solid-phase sintering step may be performed immediately after sintering or after cooling has been completed. The atmosphere may be an inert gas or reducing gas, but it is preferably performed in a vacuum.

[0055] (3) Post-processing The sintered body is machined and ground to produce a WC-based cemented carbide cutting tool of a desired size and shape.

[0056] (4) Formation of the coating layer A surface-coated WC-based cemented carbide cutting tool may be produced by forming a coating layer of a Ti-Al-based or Al-Cr-based carbide, nitride, carbonitride, Al2O3, or the like on at least the cutting edge portion of the WC-based cemented carbide cutting tool by a film-forming method such as PVD or CVD. In producing a surface-coated WC-based cemented carbide cutting tool, the type of coating and the method of forming the coating may be those well known to those skilled in the art. [Example]

[0057] Next, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

[0058] The examples were prepared according to the following procedure.

[0059] (1) Blend with raw powder As raw material powders for sintering, two types of WC powder with different particle size distributions (coarse-grained WC powder with a mode value of r1 (μm) in the particle size distribution and fine-grained WC powder with a mode value of r2 (μm) in the particle size distribution) were prepared, as well as Co powder, Cr3C2 powder, TaC powder, NbC powder, TiC powder, and ZrC powder.

[0060] Table 1 shows the blending compositions (mass%) of the various powders, as well as the mode and ratio of the particle size distribution of two types of WC powder. The average particle sizes (D50) of Co powder, Cr3C2 powder, TaC powder, NbC powder, TiC powder, and ZrC powder were all within the range of 1.0 to 3.0 μm. The amount of unavoidable impurities was 0.3 mass% or less, excluding the total mass of the WC-based cemented carbide cutting tool, taken as 100 mass%.

[0061] (2) Preparation of the molded body The sintering powders mixed according to the composition shown in Table 1 were wet mixed for 8 hours at a rotation speed of 50 rpm using a media-less attritor mixer, dried, and then pressed at a pressure of 100 MPa to produce a green compact.

[0062] (3) Sintering These powder compacts were sintered in a vacuum atmosphere at a heating temperature of 1340 to 1440°C for a heating holding time of 0.5 to 1.5 hours as shown in Table 3, and then solid-phase sintering was carried out continuously at 1100 to 1200°C for 10 to 100 hours to produce sintered bodies in order to increase the degree of adhesion between the WC particles due to grain boundary diffusion.

[0063] (4) Post-processing The sintered body was machined and ground to produce WC-based cemented carbide cutting tools 1 to 10 (hereinafter referred to as Examples 1 to 10) shown in Table 5, each having an insert shape of CNMG120408-GM.

[0064] For comparison, cutting tools 11 to 18 made of WC-based cemented carbide shown in Table 6 (hereinafter referred to as Comparative Examples 11 to 18) were also manufactured. In the manufacturing process, the compounding composition (mass%), mixing conditions, or sintering conditions were changed from those of the Examples as shown in Tables 2 and 4. The unavoidable impurities were 0.3 mass% or less, with the total mass of the WC-based cemented carbide cutting tool taken as 100 mass%.

[0065] Next, the contents of Co, Cr, Ta, Nb, Ti, and Zr were measured at 10 points on the cross sections of the WC-based cemented carbide cutting tools of Examples 1 to 10 and Comparative Examples 11 to 18 using an EPMA. The average values ​​were taken as the content of each component. The results are shown in Tables 5 and 6. The contents of Cr, Ta, Nb, Ti, and Zr were calculated by converting them into carbides.

[0066] Next, the cross sections of the WC-based cemented carbide cutting tools of Examples 1 to 10 and Comparative Examples 11 to 18 were observed using an SEM equipped with EBSD according to the method described above, and the WC-WC interface length L1 and the WC-(binder phase + γ phase) interface length L2 were measured, and the WC-WC interface length ratio (R value) was calculated. The WC areal average grain size D (μm) was also determined. The results are shown in Tables 5 and 6.

[0067] Furthermore, for the binder phase area ratio V (%), three visual fields containing 300 or more WC particles were selected from the cross sections of the WC-based cemented carbide cutting tools of Examples 1 to 10 and Comparative Examples 11 to 18, and the observed images were photographed using a FE-SEM (field emission scanning electron microscope) and binarized by image processing to separate the WC particles + γ phase from the binder phase, and the area ratio of the binder phase was calculated. The results are shown in Tables 5 and 6.

[0068] The grain size of the γ phase was measured by the method described above in the longitudinal cross section of the WC-based cemented carbide cutting tools of Examples 1 to 10 and Comparative Examples 11 to 18, and the average grain size of the γ phase was calculated. The results are shown in Tables 5 and 6.

[0069] Furthermore, the theoretical volume fraction of the γ phase (Vγ) is as described above, and the results are shown in Tables 5 and 6.

[0070] [Table 1]

[0071] [Table 2]

[0072] [Table 3]

[0073] [Table 4]

[0074] [Table 5]

[0075] [Table 6]

[0076] Next, for Examples 1 to 10 and Comparative Examples 11 to 18, the following wet continuous cutting test was carried out with each of them screwed to the tip of a tool steel bit with a fixing jig.

[0077] Workpiece: JIS SUS304 (HB170) round bar Cutting speed: 100m / min Cutting depth: 2.0 mm Feed: 0.7mm / rev Cutting time: 5 minutes Using wet water-soluble cutting oil

[0078] After the wet continuous cutting test, the amount of plastic deformation on the flank of the cutting edge was measured, and the state of wear on the cutting edge was observed. The amount of plastic deformation on the flank of the cutting edge (10) was determined by drawing a line (11) on the ridge where the flank of the main cutting edge (8) and the rake face (12) intersect at a position sufficiently far from the cutting edge (9) on the flank of the main cutting edge (8) of the tool, extending the line toward the cutting edge, and measuring the maximum distance between the extended line and the ridge of the cutting edge (perpendicular to the extended line). When the amount of plastic deformation on the flank was 0.04 mm or more, the state of wear was considered to be cutting edge deformation (see Figure 2). Table 7 shows the measurement results.

[0079] [Table 7]

[0080] Furthermore, coating layers having average thicknesses shown in Table 8 were formed on the cutting edge surfaces of Examples 1 to 4 and Comparative Examples 11 to 14 by PVD or CVD to produce Examples 21 to 24 and Comparative Examples 31 to 34.

[0081] For Examples 21 to 24 and Comparative Examples 31 to 34, the wet continuous cutting test shown below was carried out, and the amount of plastic deformation on the flank of the cutting edge was similarly measured, and the state of wear of the cutting edge was observed.

[0082] Cutting conditions: Workpiece: JIS SUS304 (HB170) round bar Cutting speed: 150m / min Cutting depth: 2.0 mm Feed: 0.7mm / rev Cutting time: 5 minutes Using wet water-soluble cutting oil Table 9 shows the results of the cutting tests.

[0083] [Table 8]

[0084] [Table 9]

[0085] The test results shown in Tables 7 and 9 show that none of the examples exhibited chipping resistance and plastic deformation resistance, without causing chipping. In contrast to this, all of the comparative examples were poor in chipping resistance and plastic deformation resistance, and reached the end of their life in a short period of time.

[0086] The above-disclosed embodiments are merely illustrative in all respects and are not restrictive. The scope of the present invention is defined by the claims, not by the above-disclosed embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof. [Explanation of symbols]

[0087] 1 WC particle 2 WC-WC interface 3 Bonded phase (hcp) 4 Bonded phase (FCC) 5 γ phase 6 WC-bonded phase (hcp) interface 7 WC-(bonded phase (fcc) + γ phase) interface 8 Main cutting edge side flank 9 Cutting edge 10 Plastic deformation of flank 11 Line segment extending from the ridge where the flank and rake face intersect 12 Rake face

Claims

1. 1) Co: 8.0 to 14.0% by mass, Cr ３ C ２ :0.1~1.4 mass%, One or more selected from TaC, NbC, TiC, and ZrC: 0.6 to 4.0 mass% Including, The balance is WC and unavoidable impurities, 2) The interface length between WC particles is L1, The interface length between the WC grain and the binder phase or the γ phase is L2. The area ratio of the binder phase is V (%), The average grain size of WC grains is D (μm), The theoretical volume fraction of the γ phase is Vγ, When the WC-WC interface length ratio is R, R=(L1) / ((L1)+(L2)), R≧(0.76-0.059×D)×(10 / V)-Vγ×0.06, 1.0≦D≦4.0 WC-based cemented carbide cutting tool characterized by satisfying the following:

2. 2. The WC-based cemented carbide cutting tool according to claim 1, wherein the average grain size of the γ phase is 0.2 to 4.0 μm.

3. 3. The WC-based cemented carbide cutting tool according to claim 1, wherein a coating layer is formed on the cutting edge.

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