Surface coated cutting tool

Abstract

Provided is a surface coated cutting tool including a substrate and a coating layer, wherein: the substrate contains 4.0 to 16.0 mass% of Co and / or Ni in total, 0.0 to 0.5 mass% of Cr, 4.0 to 12.0 mass% of at least one of Ti, Ta, Nb, Zr, Hf and V, and 6.0 to 7.5 mass% of C, with the remainder comprising W and unavoidable impurities; and in crystal grains constituting a hard phase, a ratio (d99 / d50) of the cumulative equivalent circle diameter area proportion 99% grain size to the cumulative equivalent circle diameter area proportion 50% grain size is 2.0 to 2.4 in an internal cross-sectional region 300 μm or more toward the inside of the substrate from an interface between the substrate and the coating layer, and 3.0 to 4.0 in a cross-sectional region from the interface to 20 μm toward the inside of the substrate.

Description

surface coated cutting tools

[0001] The present invention relates to a surface-coated cutting tool having a coating layer and a WC-based cemented carbide substrate. This application claims priority to Japanese Patent Application No. 2024-48360, filed March 25, 2024. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] WC-based cemented carbide has high hardness and toughness, and therefore cutting tools using it as a base are known to have excellent wear resistance and long life. In recent years, various proposals have been made to further improve the cutting performance and tool life of cutting tools depending on the type of work material, cutting processing conditions, etc.

[0003] For example, Patent Document 1 describes the particle size distribution of the binder phase in the cross section of a WC-based cemented carbide substrate, where A10 is the area occupied by one binder phase particle at 10% of the cumulative particle area, and A90 is the area occupied by one binder phase particle at 90% of the cumulative particle area. ２ 0.25 μm or more ２ and an A90 / A10 ratio of 8.0 or more and less than 11.0, and the cutting tool is said to be durable in interrupted cutting.

[0004] Japanese Patent Application Laid-Open No. 2021-134364

[0005] 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 having a base body with improved resistance to plastic deformation and chipping during cutting processing, and further improved durability.

[0006] A surface-coated cutting tool according to an embodiment of the present invention has a substrate and a coating layer, wherein the substrate contains 4.0 to 16.0 mass% Co and / or Ni in total, 0.0 to 0.5 mass% Cr, 4.0 to 12.0 mass% one or more of Ti, Ta, Nb, Zr, Hf and V, 6.0 to 7.5 mass% C, and the balance being W and inevitable impurities, and the substrate has a binder phase, a hard phase and a γ phase, wherein the binder phase is mainly composed of Co and / or Ni, the hard phase is mainly composed of W carbide, and the γ phase is mainly composed of at least one cubic crystal structure carbide selected from Ti, Ta, Nb, Zr, Hf, W and V, In the crystal grains constituting the hard phase, the ratio of the cumulative equivalent circle diameter area ratio 99% grain size to the cumulative equivalent circle diameter area ratio 50% grain size (d99 / d50) is 2.0 to 2.4 in a cross-sectional region extending from the interface between the substrate and the coating layer to the interior of the substrate at a depth of 300 μm or more, and is 3.0 to 4.0 in a cross-sectional region extending from the interface to the interior of the substrate at a depth of 20 μm.

[0007] The surface-coated cutting tool has a substrate with improved resistance to plastic deformation and chipping during cutting, and has further improved durability.

[0008] 1 is a schematic diagram illustrating an observation position and an observation field by electron backscatter diffraction. 2 is a graph showing the cumulative circle-equivalent diameter area ratio (cumulative particle size distribution) of crystal grains constituting a hard phase in a cross-sectional region (surface region) from the interface between the substrate and the coating layer to 20 μm into the substrate in Example 1. 3 is a graph showing the cumulative circle-equivalent diameter area ratio (cumulative particle size distribution) of crystal grains constituting a hard phase in a cross-sectional region (internal region) from the interface between the substrate and the coating layer to 300 μm into the substrate in Example 1.

[0009] The present inventors have conducted extensive research to achieve the above-mentioned object of the invention, and as a result have discovered that the presence of a coarse hard phase in the vicinity of the substrate surface inhibits crack propagation and provides excellent resistance to plastic deformation and fracture.

[0010] The present invention is based on these findings, and cutting tools according to embodiments of the present invention will be described below. In this specification and claims, when a numerical range is expressed as "L to M" (where L and M are both numerical values), this is synonymous with "at least L and at most M," and the range includes an upper limit (M) and a lower limit (L). When a unit is specified for only the upper limit (L), the upper limit (M) and the lower limit (L) have the same unit. The average grain size (equivalent circle diameter) of the crystal grains constituting the hard phase and γ phase is the d50 (median diameter), and the average value is the arithmetic mean value unless otherwise specified.

[0011] 1. Composition and Structure of the Substrate Details of the composition and structure of the substrate of the cutting tool according to this embodiment are as follows. The substrate is composed of three structures: a hard phase, a binder phase, and a γ layer. There are no restrictions on the shape of the substrate as long as it is the shape of the cutting tool.

[0012] (1) Co and Ni The total content of Co and / or Ni is preferably 4.0 mass % or more and 16.0 mass % or less, because when this content is satisfied, excellent resistance to plastic deformation is achieved when used as a cutting tool substrate.

[0013] Here, Co and / or Ni are present in a binder phase having crystal grains with an FCC structure or an HCP structure, and are the main components of the crystal grains of the binder phase, i.e., the total of Co and Ni accounts for 50 atomic % or more of all components constituting the binder phase. In other words, the binder phase is a phase in which the total of Co and Ni accounts for 50 atomic % or more.

[0014] The binder phase may contain W and C, which are components of the hard phase, one or more of Cr, Ti, Ta, Nb, Zr, Hf, and V, which are contained in the γ phase, and inevitable impurities. When these elements are present in the binder phase, they are presumed to be in a state of solid solution in the binder phase. The method for identifying the binder phase will be described later.

[0015] (2) Cr Cr is an optional component and may not be contained, so its content is 0.0 mass% or more and 0.5 mass% or less. Cr dissolves in the binder phase and suppresses the growth of W carbides contained mainly in the hard phase, refining the W carbides and making the W carbides contained in the substrate fine-grained and homogeneous, thereby improving the substrate's toughness and plastic deformation resistance. If the content exceeds 0.5 mass%, this function is impaired, and composite carbides of Cr and W are precipitated in the binder phase, reducing the substrate's toughness and potentially causing these carbides to become base points for chipping.

[0016] (3) Ti, Ta, Nb, Zr, Hf, V The substrate preferably contains 4.0 mass % or more and 12.0 mass % or less of one or more elements selected from Ti, Ta, Nb, Zr, Hf, and V (hereinafter sometimes referred to as M) in total. If the substrate contains less than 4.0 mass %, oxidation resistance is insufficient, and significant wear occurs due to oxidation of the hard phase during cutting, leading to the end of the substrate's life. If the substrate contains more than 12.0 mass %, toughness is insufficient, and chipping is likely to occur.

[0017] The M component exists in the γ phase as carbide crystal grains and is included as the main component of the crystal grains that make up the γ phase. The term "main component" means that the carbides of these components account for 50 atomic % or more of all the components that make up the γ phase. In addition to these carbides, the γ phase may also contain W and C contained in the hard phase, Co and Ni contained in the binder phase, and unavoidable impurities. The method for identifying the γ phase will be described later.

[0018] The average grain size (median diameter: d50) of the crystal grains constituting the γ phase is not particularly limited, but is preferably 1.0 μm or more and 3.0 μm or less. The reason for this is that if the average grain size is less than 1.0 μm, the γ phases are likely to slip between each other during cutting, resulting in insufficient plastic deformation resistance and chipping resistance, while if the average grain size exceeds 3.0 μm, sufficient wear resistance cannot be obtained.

[0019] The average grain size (d50) of the γ phase refers to the equivalent circle diameter of the crystal grains constituting the γ phase, i.e., the diameter (median diameter) when the cumulative area ratio of the diameter of a circle having the same area as the crystal grains constituting the γ phase is 50%. In other words, when a graph is plotted with the equivalent circle diameter of the crystal grains constituting the γ phase on the horizontal axis and the cumulative area ratio on the vertical axis, the equivalent circle diameter is the diameter when the cumulative area ratio is 50%. The same definition of the average grain size (d50) applies hereinafter.

[0020] (4) C is added to form carbides and is mainly contained in the hard phase and γ phase. Its content is preferably 6.0 mass% or more and 7.5 mass% or less. In this content range, free carbon and W are contained in the M component and W content. ３ Co ３ If the amount of C is adjusted so that the η phase of C or the like does not exist in the substrate, a sufficient amount of carbide can be formed in the hard phase and γ phase.

[0021] (5) W W exists in the hard phase as carbide crystal grains, and is the main component of the crystal grains that make up the hard phase. That is, W carbide (mostly WC, but not limited to a stoichiometric composition. In the following description, no distinction is made between W carbide and WC) accounts for 50 atomic % or more of all the components that make up the hard phase. The hard phase may contain binder phase components, γ phase components, Cr, and unavoidable impurities that are inevitably mixed in during the manufacturing process. Furthermore, the crystal structure of the hard phase is an HCP structure, which is different from the γ phase, which has an FCC crystal structure. The method for identifying hard phases will be described later.

[0022] The average grain size of the hard phase (the circle-equivalent average grain size, d50, of the crystal grains constituting the hard phase when viewed as a whole substrate. The method for determining d50 is the same as that described above) is preferably 0.6 μm or more and 3.0 μm or less. If the average grain size (d50) is less than 0.6 μm, the propagation of cracks during cutting cannot be sufficiently suppressed. On the other hand, if it is 3.0 μm or less, plastic deformation resistance can be ensured and sufficient plastic deformation resistance is exhibited.

[0023] (6) Particle size distribution of the hard phase The ratio (d99 / d50) of the cumulative equivalent circle diameter area ratio 99% particle size (d99) of the crystal grains constituting the hard phase to the cumulative equivalent circle diameter area ratio 50% particle size (d50) of the crystal grains constituting the hard phase, which is the particle size distribution (crystal grain size distribution) of the hard phase, is 2.0 to 2.4 in an internal cross-sectional region 300 μm or more from the surface of the base toward the inside of the base (internal cross-sectional region), and is 3.0 to 4.0 in a cross-sectional region from the interface to 20 μm into the base (surface cross-sectional region).

[0024] The reasons why the numerical range of d99 / d50 is preferable in each cross-sectional region are as follows: In the surface cross-sectional region, if d99 / d50 is less than 3.0, plastic deformation of the substrate surface will result in a short life, and if it exceeds 4.0, early fracture will occur during heavy interrupted cutting with large impacts, resulting in a short life. In the internal cross-sectional region, if d99 / d50 is less than 2.0, plastic deformation inside the substrate will result in a short life during heavy cutting in which large stress acts on the substrate, and if it exceeds 2.4, early fracture will occur during heavy interrupted cutting with large impacts, resulting in a short life. In interrupted cutting in which moderate repeated impacts or thermal cycles are applied, early fracture will occur and a short life.

[0025] (7) Inevitable Impurities As described above, the hard phase, γ phase, and binder phase may contain impurities that are inevitably (unintentionally) mixed in during the manufacturing process, and the amount of such impurities is preferably 0.3% by mass or less, with the total mass of the substrate being 100% by mass.

[0026] 2. Methods for distinguishing between binder phase, hard phase, and γ phase, and measuring particle size distribution The hard phase is composed of crystal grains with an HCP structure whose main component is W carbide. The binder phase is composed of crystal grains with an FCC or HCP structure whose main component is Co and / or Ni. The γ phase is composed of crystal grains whose main component is at least one FCC carbide selected from the group consisting of Ti, Ta, Nb, Zr, Hf, W, and V. This section describes methods for distinguishing these crystal grains and measuring their areas.

[0027] (1) Cross section to be observed In order to avoid any interference with measurement by electron backscatter diffraction pattern (EBSD) described later, minute irregularities on the surface of the longitudinal cross section of the cutting tool are polished, for example, with a focused ion beam device (FIB device), to obtain a smooth cross section.

[0028] (2) Determination of the reference position As shown in Figure 1, the intersection of the extended plane of the flank and the extended plane of the rake face is defined as the cutting edge ridge, and the position 150 μm inside the rake face from this cutting edge ridge is defined as the reference position for measurement.

[0029] (3) Determining the substrate surface Then, with this reference position as the center, an observation range (a range parallel to the direction of movement of the 150 μm) with a length of 72 μm is set perpendicular to the cutting edge ridge (see Figure 1). Because the substrate surface has minute irregularities, a straight line is drawn in this observation range so that the total area of ​​the convex portions is equal to the total area of ​​the concave portions. This straight line is defined as the substrate surface.

[0030] (4) Observation field of view: Within this 72 μm long observation range, a 20 μm long perpendicular line is drawn from the substrate surface to the interior of the substrate, defining a rectangular surface observation field of view. Furthermore, within this 72 μm long observation range, an upper line parallel to the observation range is defined at a position 300 μm or more (e.g., 350 μm) from the substrate surface to the interior of the substrate, and a lower line parallel to the observation range is defined at a position 24 μm further inside the substrate. A rectangular internal observation field of view is defined, bounded by the observation range, the upper line, and the lower line.

[0031] In each of the surface observation field and the internal observation field, it is preferable to observe at least 300 crystal grains constituting the hard phase and at least 50 crystal grains constituting the γ phase. If it is not possible to observe these numbers in one observation field, observe fields of the same size are set at positions 150 μm or more apart in the long side direction of the rectangular observation field, and the number of observation fields is increased until 300 grains can be observed.

[0032] (5) Measurement The following measurements are carried out for the surface observation field and the internal observation field.

[0033] 1) A field emission scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) and an EBSD measurement device (for example, OIM Data Collection manufactured by AMETEK) was used to measure the area of ​​regular hexagonal pixels (center-to-center distance: 0.1 μm, area of ​​1 pixel: 0.00866 μm) at an acceleration voltage of 15 kV. ２ ) EBSD pattern and EDS data are simultaneously acquired.

[0034] 2) Next, the measurement data is read into software for analyzing the EBSD measurement results, such as OIM Analysis ver. 7.3.1 manufactured by EDAX / TSL, and the EDS count value corresponding to each element is measured for each pixel. The composition of each pixel is calculated from the obtained measurement values.

[0035] 3) That is, the average value of the EDS count values ​​of W detected from all pixels identified as HCP structure from the EBSD pattern is calculated, and pixels with W count values ​​higher than half of that average are assigned to the hard phase. Next, the average value of the EDS count values ​​of Co and Ni detected from all pixels identified as FCC structure or HCP structure is calculated, and pixels with Co and Ni EDS count values ​​higher than the average are assigned to the binder phase. The remaining pixels identified as FCC structure are assigned to the γ phase.

[0036] 4) If adjacent pixels belong to the same phase and the difference in orientation between the two pixels is 5 degrees or more, the boundary between those two pixels is considered to be the interface of a grain. If the difference in orientation is less than 5 degrees, the adjacent pixels are considered to belong to the same grain.

[0037] 5) For each phase identified as the hard phase, γ phase, and binder phase in 3), EDS measurement is again performed to confirm that the crystal grains belonging to the hard phase contain 50 atomic % or more of W carbide, that the crystal grains identified as the γ phase contain 50 atomic % or more of M carbide, and that the crystal grains identified as the binder phase contain 50 atomic % or more of Co and Ni combined. This procedure confirms the hard phase, γ phase, and binder phase. Based on the confirmed hard phase, γ phase, and binder phase, the area occupied by the average grain size (d50) of the crystal grains constituting each of the hard phase and γ phase in the observation field is calculated. The average grain size (d50) of the crystal grains constituting the hard phase and γ phase is described below.

[0038] 6) Based on the results of 5) above, calculate the diameter of a circle equal to the area of ​​at least 300 (preferably 300 to 1000) crystal grains constituting the hard phase and the γ phase, and use this as the particle size (circle equivalent diameter) of the crystal grains constituting the hard phase and the γ phase, respectively.

[0039] Next, the particle diameters of the crystal grains constituting the hard phase are plotted on the horizontal axis, and the cumulative circular equivalent area ratios of the hard phase corresponding to the particle diameters of each crystal grain on the horizontal axis are plotted on the vertical axis. The particle diameter at which the cumulative circular equivalent area ratio is 50% is defined as the average particle diameter d50 (median diameter). The particle diameter at which the cumulative circular equivalent area ratio is 99% is defined as d99. For the crystal grains constituting the hard phase, the ratio of the particle diameter d99 at which the cumulative circular equivalent area ratio is 99% to the particle diameter d50 (median diameter) at which the cumulative circular equivalent area ratio is 50% is calculated using the following formula: (d99) / (d50)×100 The average particle diameter (d50) of the crystal grains constituting the γ phase is determined in the same way as the average particle diameter (d50) of the crystal grains constituting the hard phase.

[0040] 3. Measurement of the Content of Each Component The contents of W, Co, Ni, Ti, Ta, Nb, Zr, Hf, V, Cr, and C are measured using an electron probe microanalyzer (EPMA). A sample with a ground, smooth longitudinal cross section inserted into the EPMA device is irradiated with an electron beam, and the contained components and their amounts are measured from characteristic X-rays obtained from three observation fields each measuring 100 μm (vertical) × 100 μm (horizontal), and the average of the measurement results is calculated.

[0041] 4. Coating Layer The cutting tool of this embodiment has a coating layer formed by a CVD (Chemical Vapor Deposition) method. There are no restrictions on the coating layer as long as it is a known material.

[0042] 5. Manufacturing Method The cutting tool of this embodiment can be manufactured, for example, by the following procedure. To ensure that the ratio (d99 / d50) of the cumulative equivalent circle diameter area ratio 99% grain size (d99) of the crystal grains constituting the hard phase to the cumulative equivalent circle diameter area ratio 50% grain size (d50) of the crystal grains constituting the hard phase is 2.0 to 2.4 in a cross-sectional region extending from the interface between the substrate and the coating layer to the interior of the substrate at a depth of 300 μm or more, and 3.0 to 4.0 in a cross-sectional region extending from the interface to the interior of the substrate at a depth of 20 μm, the press molding and sintering steps (2) and the heat treatment step (3), which will be described later, are important.

[0043] (1) Raw material powder and blending: As raw material powder for sintering, WC powder, Co powder, Ni powder, Cr powder, each with a Fischer diameter of 0.8 to 6.5 μm, ３ C ２ Powder, TiC powder, TaC powder, NbC powder, ZrC powder, HfC powder, VC powder, and wax are prepared, blended, and mixed using a ball mill.

[0044] (2) Press Molding and Sintering The mixed powder is dried and press molded at a pressure of, for example, 100 MPa to obtain the desired cutting tool shape after the cutting process. To ensure that WC powder with a Fischer diameter of 1.0 μm is uniformly adhered to the surface of the pressed body, the pressed body is immersed in a container filled with this WC powder. At this time, the WC powder is held to the surface of the pressed body by the wax present on the surface of the pressed body. This WC powder, together with the WC powder blended as the raw powder for sintering, then becomes a hard phase formed on the surface by sintering. Sintering is performed, for example, by holding the pressed body at a temperature in the range of 1380 to 1420°C for one hour under vacuum.

[0045] (3) Post-treatment After sintering, a surface treatment is performed to crush the hard phase present on the surface. An example of the surface treatment is wet blasting (using silicon carbide as the media). After this surface treatment, the material is held in a vacuum at a temperature between 1350 and 1380°C for approximately one hour. The crushed hard phase dissolves into the liquid binder phase and undergoes Ostwald ripening, resulting in the presence of many coarse hard phases on the substrate surface, which satisfies the distribution of the aforementioned ratio (d99 / d50). The heat-treated sintered body is then machined and ground to form the desired cutting tool shape.

[0046] (4) Formation of Coating Layer The cutting tool of this embodiment has a coating layer formed by a CVD (Chemical Vapor Deposition) method. There are no restrictions on the coating layer as long as it is a known material. However, as will be described later in the manufacturing method, for example, TiN, TiC, TiCN, Al ２ O ３ As the formation of these coating layers, a TiN layer, a TiC layer, a TiCN layer, or the like having a total thickness of 3.0 to 12.0 μm is coated at 870 to 920°C, and then the temperature is raised to 1000 to 1050°C, and then an Al layer having a thickness of 3.0 to 10.0 μm is formed. ２ O ３ An example is coating a layer.

[0047] The above description includes the following additional features: (Additional Note 1) A surface-coated cutting tool having a substrate and a coating layer, wherein the substrate contains 4.0 to 16.0 mass% of one or more of Co and / or Ni in total, 0.0 to 0.5 mass% of Cr, 4.0 to 12.0 mass% of at least one of Ti, Ta, Nb, Zr, Hf, and V, 6.0 to 7.5 mass% of C, and the balance being W and inevitable impurities, and the substrate has a binder phase, a hard phase, and a γ phase, wherein the binder phase is mainly composed of Co and / or Ni, the hard phase is mainly composed of W carbide, and the γ phase is mainly composed of at least one cubic crystal structure carbide selected from Ti, Ta, Nb, Zr, Hf, W, and V, A surface-coated cutting tool characterized in that, in the crystal grains constituting the hard phase, the ratio of the cumulative equivalent circle diameter area ratio 99% grain size to the cumulative equivalent circle diameter area ratio 50% grain size (d99 / d50) is 2.0 to 2.4 in a cross-sectional region 300 μm or more inside the substrate from the interface between the substrate and the coating layer, and is 3.0 to 4.0 in a cross-sectional region 20 μm inside the substrate from the interface. (Appendix 2) A surface-coated cutting tool according to Appendices 1 or 2, characterized in that the area ratio of the binder phase in the longitudinal section is 10 to 25%.

[0048] The use of the cemented carbide for cutting tools of the present invention as a cutting tool substrate will be specifically described with reference to examples, but the present invention is not limited to these examples.

[0049] 1. Manufacturing of the Example The cutting tool of the example was manufactured by the following procedure: (1) Raw material powder and blending process First, as powder for sintering, WC powder, Co powder, Ni powder, Cr powder, each having a Fischer diameter of 0.8 to 6.5 μm, were mixed. ３ C ２ Powder, TiC powder, TaC powder, NbC powder, ZrC powder, HfC powder, and VC powder were prepared. The Fischer diameter of each powder is shown in Table 1. These powders were blended in the blending ratios shown in Table 1 and mixed using a ball mill.

[0050] (2) Press molding and sintering The mixed powder was dried and press molded at a pressure of 100 MPa to obtain a CNMG120408-MA (tool shape manufactured by Mitsubishi Materials Corporation) after the cutting process. WC powder with a Fischer diameter of 1.0 μm was uniformly attached to the surface of the press molded body. Then, sintering was performed at 1420°C for 1 hour under vacuum.

[0051] (3) Post-treatment After sintering, wet blasting was performed to crush the WC grains on the substrate surface. The wet blasting was performed under the following conditions: Pressure: 0.18 MPa, Projection time: 300 seconds, Medium: Silicon carbide with particle size #1500 as specified in JIS R 6001-1. Next, the temperature was raised to 1380°C in a vacuum and held for 1 hour. The heat-treated sintered body was then machined and ground to form the CNMG120408-MA shape.

[0052] (4) Formation of Coating Layer A coating layer was formed using a CVD method under the conditions shown in Table 2. Table 2 shows the type of layer to be formed, its average thickness, and the film formation temperature. By the above steps, cutting tools 1 to 6 of the examples shown in Table 3 (hereinafter referred to as Examples 1 to 6) were produced.

[0053] Table 3 shows the compositions, binder phase area ratios, average grain diameters (d50) of the γ phase, average grain diameters (d50) of the hard phases, and hard phase distributions (d99 / d50) of Examples 1 to 6. Figure 2 is a graph showing the cumulative equivalent circle diameter area ratios of the crystal grains constituting the hard phase in the surface region of Example 1, and Figure 3 is a graph showing the cumulative equivalent circle diameter area ratios of the crystal grains constituting the hard phase in the internal region of Example 1. In the hard phase distributions (d99 / d50) in Table 3 and Figures 2 and 3, the surface region refers to the cross-sectional region extending from the interface between the substrate and the coating layer to 20 μm into the substrate, and the internal region refers to the cross-sectional region extending from the interface between the substrate and the coating layer to 300 μm or more into the substrate.

[0054] 2. Manufacture of Comparative Example For comparison, a cutting tool of a comparative example was manufactured by the following procedure.

[0055] (1) Raw material powder and blending process First, WC powder, Co powder, Ni powder, Cr powder were used as sintering powder. ３ C ２Powder, TiC powder, TaC powder, NbC powder, ZrC powder, HfC powder, and VC powder were prepared. These powders were blended in the blending ratios shown in Table 1 and mixed using a ball mill.

[0056] (2) Press molding and sintering The mixed powder was dried and press molded at a pressure of 100 MPa to form a CNMG120408-MA (tool shape manufactured by Mitsubishi Materials Corporation) after the cutting process. WC powder with an average particle size of 1.0 μm or less was uniformly attached to the press molded body. It was then sintered in a vacuum at 1420°C for 1 hour.

[0057] (3) Post-treatment After sintering, wet blasting was performed to crush the WC grains on the substrate surface. The wet blasting was performed under the following conditions. Comparative Cutting Tools 1' to 5': Pressure: 0.12 MPa, Projection Time: 60 seconds, Medium: Silicon carbide with a grain size of #240 as specified in JIS R 6001-1. Comparative Cutting Tool 6': Pressure: 0.30 MPa, Projection Time: 600 seconds, Medium: Silicon carbide with a grain size of #1500 as specified in JIS R 6001-1. Next, the temperature was raised to 1380°C in a vacuum and held for 1 hour. The heat-treated sintered body was then machined and ground to form the shape of CNMG120408-MA.

[0058] (4) Formation of Coating Layer A coating layer was formed using a CVD method under the conditions shown in Table 2. Table 2 shows the type of layer to be formed, its average thickness, and the deposition temperature. By the above steps, cutting tools 1' to 6' of the comparative examples (hereinafter referred to as Comparative Examples 1' to 6') shown in Table 3 were produced. Table 3 shows the compositions, area ratios of the binder phase, average grain size (d50) of the γ phase, average grain size (d50) of the hard phase, and distribution of the hard phase (d99 / d50) of Comparative Examples 1' to 6'.

[0059]

[0060] In Table 1, "-" indicates that no compound was added.

[0061]

[0062] In Table 2, "-" indicates that there is no corresponding layer.

[0063]

[0064] For Examples 1 to 6 and Comparative Examples 1' to 6', it was confirmed that the main component of the hard phase was W carbide, the main component of the γ phase was a cubic crystal structure carbide containing one or more elements selected from the group consisting of Ti, Ta, Nb, and Hf, and which may further contain Zr and / or V, and the main components of the binder phase were Co and Ni.

[0065] Examples 1 to 6 and Comparative Examples 1' to 6' all had a binder phase and a γ phase in addition to a hard phase, and the content of unavoidable impurities was 0.3% by mass or less, with the entire substrate being 100% by mass.

[0066] The following cutting tests were carried out on Examples 1 to 6 and Comparative Examples 1' to 6'. The results are shown in Table 4.

[0067] Cutting test: Intermittent turning of an alloy steel round bar with eight equally spaced slits in the length direction Workpiece: JIS SCM440 (HB320) round bar (with eight equally spaced slits in the length direction) Cutting speed: 90 m / min Cutting depth: 2.0 mm Feed: 0.5 mm / rev Cutting time: 5 minutes

[0068] Cutting tests were carried out four times for each sample, and the number of times that characteristic wear, fracture, and slight chipping occurred based on the cutting edge condition after the four cutting tests is recorded in Table 4. Minor chipping refers to chipping that does not interfere with the continuation of cutting work even if it occurs.

[0069]

[0070] According to the cutting test results shown in Table 4, the Examples all exhibited excellent cutting performance without any chipping in the four cutting tests, whereas the Comparative Examples all exhibited chipping in the four cutting tests, resulting in a shortened tool life.

[0071] 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 of the claims.

Claims

1. A surface-coated cutting tool having a substrate and a coating layer, wherein the substrate has a composition containing 4.0 to 16.0 mass% Co and / or Ni in total, 0.0 to 0.5 mass% Cr, 4.0 to 12.0 mass% of at least one of Ti, Ta, Nb, Zr, Hf, and V, 6.0 to 7.5 mass% C, with the balance being W and inevitable impurities, and the substrate has a binder phase mainly composed of Co and / or Ni, a hard phase mainly composed of W carbide, and a γ phase mainly composed of at least one cubic crystal structure carbide selected from the group consisting of Ti, Ta, Nb, Zr, Hf, W, and V, a ratio (d99 / d50) of a 99% cumulative equivalent circle diameter area fraction grain size to a 50% cumulative equivalent circle diameter area fraction grain size in crystal grains constituting the hard phase is 2.0 to 2.4 in a cross-sectional region extending from the interface between the substrate and the coating layer to an interior of the substrate at a depth of 300 μm or more, and is 3.0 to 4.0 in a cross-sectional region extending from the interface to an interior of the substrate at a depth of 20 μm.

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