Coated cutting tool

Abstract

To provide a surface coated cutting tool improved in plastic deformation resistance.SOLUTION: In a surface coated cutting tool, a base body comprises a 9.0 volume% or more and 14.0 volume% or less of a bonded phase 7 containing Co, a 10.0 volume% or more and 17.0 volume% or less of a β-phase 6 containing MC or MCN (M is at least one kind of Ti, Ta, Nb and Zr) and a remnant is a hard phase 5 containing WC and includes 0.0 mass% or more and 0.5 mass% or less of Cr, which has a dephase β layer not including the β phase in which an average value of a lower end thereof is 15 μm or more and 47 μm or less, from a front surface of the base body toward the inside of the base body. In a region of 100 μm from a lower end of the dephase β layer to the inside of the base body, a ratio of an interface between the β phase occupied in the whole interface and the β phase is 1.0% or more and 7.0% or less, and a ratio of an interface between the hard phase and the β phase is 20.0% or more and 35.0% or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a surface-coated cutting tool in which a coating layer is coated on a substrate (tool substrate) made of a WC-based cemented carbide.

Background Art

[0002] WC-based cemented carbides have excellent characteristics such as mechanical strength and heat fatigue resistance, and are therefore used, for example, as the substrate of a surface-coated cutting tool with a coating layer.

[0003] On the other hand, the usage conditions of surface-coated cutting tools are becoming more energy-efficient, and higher durability such as resistance to plastic deformation is required. Therefore, proposals have been made to improve the above-mentioned characteristics of WC-based cemented carbides used as the substrate of surface-coated cutting tools.

[0004] For example, Patent Document 1 describes a WC-based cemented carbide insert that contains at least one cubic crystal of WC and a carbide or carbonitride in the binder phase, has a rich binder phase surface region, and the content of the binder phase below the rich binder phase surface region is 0.85 to 1 times the content of the binder phase inside the insert, and the content of the cubic crystal in the rich binder phase surface region is zero. The insert is said to have resistance to plastic deformation.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of the above circumstances and proposals, and an object thereof is to provide a surface-coated cutting tool with improved resistance to plastic deformation.

Means for Solving the Problems

[0007] The surface-coated cutting tool according to an embodiment of the present invention has a substrate and a coating layer on the surface of the substrate, wherein the substrate has a binder phase containing Co of 9.0% by volume or more and 14.0% by volume or less, a β phase containing MC or MCN (M is at least one of Ti, Ta, Nb, and Zr) of 10.0% by volume or more and 17.0% by volume or less, and the balance is a hard phase containing WC, contains Cr of 0.0% by mass or more and 0.5% by mass or less, and has a β-phase-free decarburized layer having an average value of 15 μm or more and 47 μm or less from the surface of the substrate toward the inside of the substrate at its lower end, to the position and in a region from the lower end of the decarburized layer to 100 μm inside the substrate, the interface ratio of the β phase to the β phase occupying the entire interface is 1.0% or more and 7.0% or less, and the interface ratio of the hard phase to the β phase is 20.0% or more and 35.0% or less at the lower end of the decarburized layer position up to 100 μm inside the substrate. That is.

[0008] Furthermore, the surface-coated cutting tool according to the embodiment may satisfy the following matters.

[0009] In the region, the average grain size of the hard phase is 1.40 μm or more and 2.10 μm or less, and the ratio of the average grain size of the hard phase to the average grain size of the β phase is 1.50 or more and 1.70 or less.

Advantages of the Invention

[0010] According to the above surface-coated cutting tool, the plastic deformation resistance is improved, and excellent tool life can be exhibited even under high-temperature and high-load cutting conditions.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0012] The present inventor conducted intensive studies to obtain a cemented carbide that achieves the above object. As a result, the following findings (1) to (3) were obtained.

[0013] (1) When analyzing the deformation of a surface-coated cutting tool that has undergone plastic deformation under high-temperature and high-load cutting conditions such as high-speed cutting, damage occurs in which the hard phase is broken starting from the interface between the hard phase and the β phase, and plastic deformation progresses due to this damage.

[0014] Here, the interface between the hard phase and the β phase refers to the interface between hard phases (hard phase / hard phase interface), the interface between the hard phase and the β phase (hard phase / β phase interface), and the interface between β phases (β phase / β phase interface).

[0015] In particular, the hard phase / β phase interface has low interfacial strength due to segregation of elements dissolved in the binder phase and interfacial mismatch caused by differences in crystal structure (WC, which is the main component of the hard phase, has a hexagonal crystal structure, and the main component of the β phase has a cubic crystal structure), and is easily broken by the load during cutting, causing plastic deformation of the entire cutting edge.

[0016] (2) In order to prevent defects due to crack propagation from the coating layer, even if a decarburized β layer substantially free of the β phase is provided on the substrate surface, in the region inside the substrate from the lower end thereof, since the β phase tends to aggregate during the formation of the decarburized β layer, the hard phase / β phase interface and the β phase / β phase interface are likely to increase.

[0017] (3) In this region, reducing the ratio of the hard phase / β-phase interface and the β-phase / β-phase interface can reduce the damage occurring at the interface and improve the plastic deformation resistance.

[0018] Hereinafter, embodiments of the present invention will be mainly described with a focus on the case where they are applied to inserts as surface-coated cutting tools.

[0019] 1. Structure and composition of the substrate The substrate according to this embodiment has a predetermined structure, and the structure has a binder phase, a β-phase, and a hard phase.

[0020] (1) Binder phase The binder phase contains Co and is preferably contained in an amount of 9.0% by volume or more and 14.0% by volume or less. The reason is that if it is less than 9.0% by volume, the toughness of the substrate is low and the chipping resistance is insufficient, while if it is greater than 14.0% by volume, the strength of the substrate is low and the plastic deformation resistance is insufficient. The binder phase is more preferably contained in an amount of 10.0% by volume or more and 12.0% by volume or less.

[0021] Co is the main component of the binder phase, that is, Co accounts for 50% by mass or more of all the components forming the binder phase (the definition of the main component is the same for other phases). And Co preferably contains 6.0% by mass or more and 9.0% by mass or less when viewed as the entire substrate (including those contained in the β-phase and the hard phase in addition to the binder phase). The reason is that when the content is within this range, the balance between plastic deformation resistance and toughness is excellent when used as the substrate of the surface-coated cutting tool.

[0022] Note that the binder phase may contain W and C, which are components of the hard phase, and inevitable impurities that are unavoidably mixed in during other manufacturing processes. Further, the binder phase may contain one or more of Cr, Ti, Ta, Nb, Ti, and Zr. When these elements are present in the binder phase, they are presumed to be in a solid solution state in the binder phase.

[0023] (2) β-phase The β-phase improves the oxidation resistance and crater wear resistance of the substrate and is preferably contained in an amount of 10.0% by volume or more and 17.0% by volume or less. The reason is that if it is less than 10.0% by volume, the oxidation resistance and crater wear resistance of the substrate are insufficient, while if it is more than 17.0% by volume, the toughness of the substrate decreases and the defect resistance is insufficient. More preferably, the β-phase is contained in an amount of 12.0% by volume or more and 15.0% by volume or less.

[0024] The β-phase contains MC or MCN (M is at least one of Ti, Ta, Nb, and Zr) as a main component. That is, the β-phase may contain W, which is a component of the hard phase, and inevitable impurities that are unavoidably mixed in during other manufacturing processes. And M that constitutes these MC or MCN is preferably contained in an amount of 5.0% by mass or more and 9.0% by mass or less when viewed as the entire substrate. The reason is that the wear resistance is improved within this content range.

[0025] The cubic MC or MCN is not limited to those combined in a stoichiometric ratio and includes all nitrides and carbonitrides in which M and C, M and C and N are combined.

[0026] (3) Hard phase The hard phase has WC as a main component and occupies the remainder other than the bonding phase and the β-phase. The hard phase may contain inevitable impurities. Also, the crystal structure of the hard layer is hexagonal.

[0027] (4) Measurement of the volume percentages of the bonding phase, β-phase, and hard phase The volume percentages of the bonding phase, β-phase, and hard phase are measured as follows. That is, starting from the end of the substrate surface (the cutting edge indicated by number 10 in Fig. 3), which is the intersection of the flank face and the rake face, points 300 μm away from this point in the directions of the flank face and the rake face are passed through, and the point (the point indicated by symbol X in Fig. 3) where the straight lines drawn parallel to the flank face and the rake face respectively intersect is used as the starting point. Any location in the region inside the substrate (the region indicated by symbol A in Fig. 3) partitioned by straight lines parallel to the flank face and the rake face respectively is observed by EBSD. The crystal orientation map of the observed field of view obtained by EBSD observation is analyzed to separate the bonding phase, β-phase, and hard phase. Then, the number of observed fields of view is increased until the total number of the bonding phase, β-phase, and hard phase obtained from the observation results of the observed field of view is 4000 or more, and the area percentages of the bonding phase, β-phase, and hard phase are determined. That is, when the cumulative number of the hard phase and the β-phase in one observed field of view is less than 4000, a new observed field of view is newly set in the said region, and the measurement is continued until it reaches 4000. In addition, when there are bonding phases, β-phases, and hard phases that can only be partially visually recognized at the ends of the observed field of view, they are all treated as one. And considering that the distributions of the bonding phase, β-phase, and hard phase in the vertical cross-section with respect to the cross-section taken as the observed field of view are the same, the obtained area percentage is treated as the volume percentage.

[0028] (5) Cr In order to improve the plastic deformation resistance without degrading the toughness, it is preferable to contain Cr. That is, Cr dissolves in the bonding phase and solid-solution strengthens the bonding phase. Cr may not be contained, but when it is contained, it is preferably limited to 0.5 mass% or less with respect to the substrate. Also, it is more preferably 10% or less of the Co content.

[0029] The Cr content is measured at three points by EPMA in the region where the volume percentages of the bonding phase, β-phase, and hard phase are measured by EBSD, and the average value is calculated.

[0030] (6) Unavoidable impurities As described above, the hard phase and the bonding phase may contain impurities that are inevitably (unintentionally) mixed in during the manufacturing process, and the amount thereof is preferably 0.3% by mass or less as an external number with the entire substrate being 100% by mass.

[0031] (7) β-depleted layer As shown in FIG. 1 as a cross-sectional schematic view from the substrate surface, it preferably has a β-depleted layer with an average value of the lower end thereof being 15 μm or more and 47 μm or less toward the inside thereof. to the position By having this β-depleted layer, it is possible to prevent defects in the substrate due to crack propagation from the coating layer. The β-depleted layer refers to a region where substantially no β-phase exists. Substantially no β-phase existing means that when the polished substrate cross-section is corroded with an alkaline corrosion solution such as sodium hydroxide to corrode the β-phase and observed at a magnification of 1000 times with an optical microscope, the β-phase cannot be visually recognized.

[0032] From the substrate surface to the lower end of the β-depleted layer position The length up to is, in this observation, the average value of the distances between the substrate surface and the three β-phases that are visually recognized as the shortest from the surface, that is, the shortest lengths between each of the three β-phases and the substrate surface.

[0033] Note that in the vicinity of the relief surface and the rake surface of the substrate, since denitrification may proceed excessively in the denitrification process described later, as shown in FIG. 3, the shortest length described above is measured at either the relief surface or the rake surface at a position 300 μm or more away from the intersection of the rake surface and the relief surface (the cutting edge indicated by number 10 in FIG. 3). Note that the measurement region indicated by hatching in FIG. 3 is only for visually clarifying the measurement region, and its length has no technical significance.

[0034] 2. Ratio of interfaces Next, the ratio of interfaces in the region from the lower end of the β-depleted layer position to 100 μm toward the inside of the substrate (FIG. 2 shows a cross-sectional schematic view of the structure of this region) will be described.

[0035] (1) Total interfaces As schematically shown in FIG. 2, in the substrate according to the present embodiment, there are an interface between hard phases (hard phase / hard phase interface), an interface between a hard phase and a β-phase (hard phase / β-phase interface), an interface between β-phases (β-phase / β-phase interface), an interface between a hard phase and a bonding phase (hard phase / bonding phase interface), an interface between a β-phase and a bonding phase (β-phase / bonding phase interface), and an interface between bonding phases (bonding phase / bonding phase interface). And these six types of interfaces are collectively referred to as total interfaces, and the length thereof is the total interface length.

[0036] (2) β-phase / β-phase interface ratio and hard phase / β-phase interface ratio The β-phase / β-phase interface ratio and the hard phase / β-phase interface ratio are respectively β-phase / β-phase interface ratio (%) = (interface length of β-phase / β-phase interface) / (total interface length) × 100 Hard phase / β-phase interface ratio (%) = (interface length of hard phase / β-phase interface) / (total interface length) × 100 and are defined by. Here, each interface length is a two-dimensional length in the cross section.

[0037] The β-phase / β-phase interface ratio (%) is preferably 7.0% or less. If it is 7.0% or less, the plastic deformation resistance of the substrate is improved. The lower limit value of the β-phase / β-phase interface ratio (%) may be 0.0%, but according to the manufacturing method described later, 1.0% becomes the lower limit value.

[0038] The hard phase / β-phase interface ratio (%) is preferably 20.0% or more and 35.0% or less. The reason is that when it is less than 20.0%, when a crack occurs, the crack does not progress along the hard phase / β-phase interface and breaks through the hard phase, so the crack does not progress linearly and is likely to be defective. On the other hand, when it is more than 35.0%, there is a lot of damage to the hard phase / β-phase interface and plastic deformation is likely to progress. The hard phase / β-phase interface ratio (%) is more preferably 25.0% or more and 30.0% or less.

[0039] The β-phase / β-phase interface ratio and the hard phase / β-phase interface ratio are measured as follows. That is, the crystal orientation map obtained from the EBSD observation results is analyzed, and the analysis is carried out until the cumulative value of the interface length of the hard phase / β phase interface is 1000 μm or more, the cumulative value of the interface length of the β phase / β phase interface is 100 μm or more, and the cumulative value of the total interface length is 3000 μm or more, and the β phase / β phase interface ratio and the hard phase / β phase interface ratio are calculated.

[0040] The observation region for calculating these interface ratios is the region from the lower end position of the β-depleted layer measured as described above to 100 μm inside the substrate. When the cumulative value of the interface length of the hard phase / β phase interface, the cumulative value of the interface length of the β phase / β phase interface, and the cumulative value of the total interface length do not reach 1000 μm or more, 100 μm or more, and 3000 μm or more, respectively, in one field of view of this observation field of view, the lower end position A new observation field of view is provided in a region 10 μm or more away in a direction parallel to the lower end, and the measurement is continued until these conditions are satisfied. In addition, when there are bonding phases, β phases, and hard phases that can only be partially visually recognized at the end of the observation field of view, they are all treated as one.

[0041] (3) Ratio of the average grain size of the hard phase to the average grain size of the β phase It is more preferable that the average grain size of the hard phase is 1.40 μm or more and 2.10 μm or less, and the ratio of the average grain sizes of the hard phase and the β phase is 1.50 or more and 1.70 or less. The reason is that when the average grain size of the hard phase is less than 1.40 μm, the defect resistance is insufficient, and when it is larger than 2.10 μm, the wear resistance may be insufficient. Also, when the ratio of the average grain sizes of the hard phase and the β phase is less than 1.50, the interface length between the hard phase and the β phase is long, the damage to the interface is large, plastic deformation is likely to progress, and when it is larger than 1.70, the amount of the β phase sandwiched between WC-WC increases, and the alloy structure becomes non-uniform due to poor dispersion of the β phase, and the tool life may become unstable.

[0042] Here, for the average particle size of the hard phase and the average particle size of the β phase, more than 4000 observable observation regions are created by combining the hard phase and the β phase. The areas of the individual hard phases and β phases are measured, and they are treated as an integral entity (integral carbide, carbonitride). The diameter of the area when the cumulative area becomes 50%, that is, the area average particle size (μm), is used.

[0043] The observation region for calculating these average particle sizes is the same as the region for obtaining the interface ratio. And when the cumulative number of the hard phase and the β phase in one observation field of view is less than 4000, a new observation field of view is provided in a region 10 μm or more away in a direction parallel to the lower end position and the measurement is continued until the number reaches 4000. In addition, when there are bonding phases, β phases, and hard phases that can only be partially visually recognized at the end of the observation field of view, they are all treated as one.

[0044] 3. Coating layer The coating layer on the substrate surface can be used without particular restrictions as long as it is a coating layer (average thickness is 5 to 20 μm) used for known surface-coated cutting tools formed by, for example, the CVD method.

[0045] 4. Manufacturing method The substrate of the surface-coated cutting tool of this embodiment can be manufactured by each process of preparing raw material powder, mixing raw material powder, molding, sintering, and machining. Here, for each process of preparing raw material powder, molding, and machining, conventionally known ones can be appropriately adopted. However, it is preferable to perform the following for the raw material powder mixing process and the sintering process.

[0046] In the raw material powder mixing process, the raw material powder constituting the β phase is pulverized in advance. By this pulverization, a difference occurs in the particle size ratio between the raw materials of the hard phase and the β phase, and the contact length between the hard phase and the β phase becomes short. Therefore, the ratio of the hard phase / β phase interface is reduced, and it is presumed that the β phase / β phase interface is reduced by dissolving the aggregation between raw material particles generated during the production of the raw materials.

[0047] The sintering process includes a first holding process that, after a debinding process (performed at, for example, 600 °C), is carried out at 1250 to 1400 °C for 30 to 60 minutes in a nitrogen atmosphere of 2 to 10 kPa, and -1 a second holding process that is carried out at 1420 to 1500 °C for 60 minutes in a vacuum atmosphere of 10 Pa or less. Thereafter, it is cooled to room temperature at a cooling rate of 20 °C / min or more in an inert atmosphere.

Examples

[0048] The present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

[0049] First, as powders for sintering, WC powders with an average particle size (d50) shown in Table 1 of 3.0 to 5.5 μm, Co powders with an average particle size (d50) within the range of 0.5 to 1.1 μm, and TiC powders, TiN powders, NbC powders, TaC powders, ZrC powders, Cr3C2 powders, (Ta,Nb)C powders containing Ta and Nb in a mass ratio of 9:1, (Ti,W)C powders containing Ti and W in a mass ratio of 1:1, and (Ti,W)CN powders containing Ti and W in a mass ratio of 1:1 were prepared.

[0050] Here, the TiC powders, TiN powders, NbC powders, TaC powders, ZrC powders, (Ta,Nb)C powders, (Ti,W)C powders, and (Ti,W)CN powders are raw materials for the β phase, and these are pulverized so that the specific surface area becomes 8.0 m 2 / g or more.

[0051] Also, for the WC powders, two types with different average particle sizes (the average particle size of WC1 > the average particle size of WC2) of WC1 powder and WC2 powder were prepared, and (Average particle size of WC1 powder (μm)) × (Ratio of WC1 powder in all WC powders (mass%)) + (Average particle size of WC2 powder) × (Ratio of WC2 in all WC powders (mass%)) was blended so as to be 3.0 to 5.5 μm.

[0052] That is, these powders were blended to have the composition shown in Table 2 to prepare a sintering powder. That is, after all the raw material powders were mixed with an attritor for 5 hours, they were press-molded at a pressure of 150 MPa to prepare a green compact.

[0053] Sintering was debinding was carried out at 600 °C, First holding step: held at 1350 °C (3 kPa in a nitrogen atmosphere) for 40 minutes Second holding step: held at 1450 °C (in a vacuum of 10 -1 Pa or less) for 60 minutes, Cooling: cooled at a cooling rate of 25 °C / min in an argon gas atmosphere.

[0054] Thereafter, machining and grinding were performed to machine them into the ISO shape CNMG120408, and substrates 1 to 10 (hereinafter referred to as Example substrates 1 to 10) of the surface-coated cutting tool of the example were prepared. Table 5 shows the volume % of each phase, the Cr content, the thickness of the decarburized layer, the ratio of the β-phase / β-phase interface, the ratio of the hard-phase / β-phase interface, the average particle size of the hard phase, and the average particle size of the hard phase / average particle size of the β-phase of Example substrates 1 to 10 (the measurement method is as described above).

[0055] For comparison, substrates 1 to 5 (hereinafter referred to as Comparative Example substrates 1 to 5) of the surface-coated cutting tool of the comparative example were prepared. The manufacturing process thereof was The raw material powders shown in Table 3 were prepared and blended to have the composition shown in Table 4 to prepare a sintering powder. The particle size of WC used in the blending and the specific surface area of the β-phase constituent raw material are as shown in Table 4. Without previously pulverizing the raw material powders constituting the β-phase, all the raw material powders were mixed with an attritor for 5 hours and press-molded at a pressure of 150 MPa to prepare a green compact. Thereafter, sintering was carried out with debinding at 600 °C, heating was carried out from 1200 °C to 1450 °C in a nitrogen atmosphere of 3 kPa, and without holding the temperature in this nitrogen atmosphere, it was held at 1450 °C (in a vacuum of 10 -1 Pa or less) for 60 minutes and cooled at a cooling rate of 25 °C / min in an argon gas atmosphere.

[0056] Then, in the same manner as in Examples Substrates 1 to 10, the volume % of each phase, the Cr content, the thickness of the decarburized layer, the ratio of the β-phase / β-phase interface, the ratio of the hard-phase / β-phase interface, the average particle diameter of the hard phase, and the average particle diameter of the hard phase / the average particle diameter of the β-phase were measured.

[0057]

Table 1

[0058]

Table 2

[0059]

Table 3

[0060]

Table 4

[0061]

Table 5

[0062]

Table 6

[0063] For Examples Substrates 1 to 10 and Comparative Examples Substrates 1 to 6, the coating layers described in Tables 7 and 8 were formed respectively, and Examples Coated Tools 1 to 10 and Comparative Examples Coated Tools 1 to 5 were produced respectively. Then, a cutting test was conducted under the cutting conditions shown below. The results are shown in Table 9.

[0064] Cutting Conditions for the Cutting Test Workpiece: Φ200 round bar of SNCM439 Cutting speed: 100 m / min Depth of cut: 1.5 mm Feed: 1.0 mm / rev Cutting time: 0.5 minutes

[0065] In the cutting test, the following was adopted as the plastic deformation amount of the flank face of the cutting edge. That is, based on the non-deformed cutting edge ridge line before cutting, the amount by which the cutting edge ridge line was pushed in and deformed by cutting was defined as the plastic deformation amount of the flank face of the cutting edge. Specifically, as shown in Fig. 4, for the flank face (9) on the major cutting edge side of the tool, a line segment was drawn on the ridge line where the flank face (9) on the cutting edge (10) side and the rake face (8) intersect at a position sufficiently separated from the cutting edge, and this line segment was extended in the direction of the cutting edge portion. The distance (in the vertical direction of the extended line segment) between the extended line segment (12) and the cutting edge portion ridge line at the part where they are most separated was measured, and this was defined as the plastic deformation amount (11) of the flank face of the cutting edge. Also, the wear state of the cutting edge was observed after the cutting time ended.

[0066]

Table 7

[0067]

Table 8

[0068]

Table 9

[0069] As is clear from the results in Table 9, all of the coated tools in the examples had a small plastic deformation amount of the flank face that affects the tool life, exhibited excellent plastic deformation resistance without causing uneven wear or chipping. In contrast, the coated tools in the comparative examples had a large plastic deformation of the tool at a predetermined cutting time, and it was difficult to perform machining to obtain a predetermined workpiece dimension.

Explanation of reference numerals

[0070] 1 Substrate 2 Lower end of the β-depleted layer position Region of 100 μm from the β-depleted layer into the tool substrate 3 β-depleted layer 4 Coating layer 5 Hard phase 6 β-phase 7 Bonding phase 8 Scooping surface 9 Relief surface 10 Cutting edge 11 Plastic deformation amount of the relief surface of the cutting edge 12 Extended line segment A Region for measuring the area percentages of the hard phase, β layer, and bonding phase X Starting point

Claims

Claim 1 A surface-coated cutting tool having a substrate and a coating layer on the substrate, wherein the substrate has a binder phase containing Co of 9.0% to 14.0% by volume, a β phase containing MC or MCN (M is at least one of Ti, Ta, Nb, Zr) of 10.0% to 17.0% by volume, the balance being a hard phase containing WC, containing Cr of 0.0% to 0.5% by mass, has a β-phase-free decarburized layer having an average value from the substrate surface to the lower end position inside the substrate of 15 μm or more and 47 μm or less, in a region from the lower end position of the decarburized layer to 100 μm inside the substrate, the interface ratio of the β phase to the β phase in all interfaces is 1.0% or more and 7.0% or less, and the interface ratio of the hard phase to the β phase is 20.0% or more and 35.0% or less characterized in that it is a surface-coated cutting tool. Claim 2 The surface-coated cutting tool according to claim 1, characterized in that in the region, the average grain size of the hard phase is 1.40 μm or more and 2.10 μm or less, and the ratio of the average grain size of the hard phase to the average grain size of the β phase is 1.50 or more and 1.70 or less.

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