JP4960149B2 - Surface coated cutting tool - Google Patents

Description

  The present invention relates to a surface-coated cutting tool formed by forming a coating layer on the surface of a substrate.

  Currently, surface-coated cutting tools require wear resistance, slidability, and fracture resistance, so various coating layers are formed on the surface of a hard substrate such as a WC-based cemented carbide or TiCN-based cermet. A technique for improving the wear resistance and fracture resistance of surface-coated tools is used.

  As the coating layer, a TiCN layer or a TiAlN layer is generally widely used, but various coating layers are being developed for the purpose of improving higher wear resistance and fracture resistance.

  For example, in Patent Document 1, the TiAlN hard film coated on the surface of the substrate has a vertical / horizontal ratio of 1.5 to 7 in the crystal grain size, thereby oxidizing the TiAlN hard film at the grain boundaries. It is disclosed that the tool can be a long-life tool that can suppress the progress and is excellent in wear resistance.

  In addition, regarding a hard film composed of columnar crystals, in Patent Document 2, when a multilayer including a TiCN layer of columnar crystals is formed, the crystal width on the surface side corresponding to the upper side of the TiCN layer of columnar crystals corresponds to the lower side. It has been disclosed that by making the taper shape slightly larger than the crystal width on the substrate side, it is possible to suppress the cracks from progressing in the TiCN layer and to improve the fracture resistance of the cutting tool.

Furthermore, the applicant of the present invention disclosed in Patent Document 3 that, in a cutting tool in which a multilayer including a streaked TiCN layer formed on the surface of a substrate by a CVD method is formed, the TiCN layer is a TiCN having a small average crystal width on the substrate side. It has been proposed that the chipping resistance of the coating layer is improved by adopting a laminated structure of a layer and a TiCN layer having a large average crystal width on the upper surface thereof. Further, in Patent Document 4, by making the crystal width of the TiCN layer on the rake face a dense structure narrower than the crystal width of the TiCN layer on the flank face, a strong impact is applied to the cutting edge of the tool like interrupted cutting of cast iron. In such severe cutting conditions as described above, it has been disclosed that both the fracture resistance required for the rake face and the wear resistance required for the flank face can be satisfied.
Japanese Patent Laid-Open No. 10-315011 JP-A-10-109206 JP 2004-306246 A JP 2004-216488 A

  However, the method of simply forming the TiCN layer with a slightly larger tapered columnar shape toward the upper side as disclosed in Patent Document 2 has a limit that can prevent cracks from progressing in the TiCN layer, and cutting. There has been a demand for improved fracture resistance and improved wear resistance of tools. Further, as disclosed in Patent Document 3, a streaky TiCN layer formed by a CVD method has a laminated structure of a TiCN layer having a small average crystal width on the substrate side and a TiCN layer having a large average crystal width on the upper surface thereof. If the method and the method of making the crystal width of the TiCN layer on the rake face a dense structure narrower than the crystal width of the TiCN layer on the flank face are directly applied to the PVD coating layer formed by the PVD method, the PVD coating Since the internal stress of the coating layer itself is higher than that of the CVD coating layer, the coating layer itself may be self-destructed and chipping or peeling may occur.

  In order to further extend the life of the cutting tool, the object of the present invention is to improve the fracture resistance while suppressing the chipping of the coating layer on the rake face while taking into account the internal stress inherent in the coating layer. An object of the present invention is to provide a surface-coated cutting tool having improved tool surface wear resistance and a long tool life.

  In the surface-coated cutting tool of the present invention, the surface of the substrate is coated with a coating layer, and the ridge line portion between the rake face and the flank face is used as a cutting edge, and the thickness of the coating layer on the rake face is the flank. The coating layer is thinner than the coating layer on the surface, the coating layer is made of columnar crystals, and the average crystal width of the upper layer region located on the surface side opposite to the substrate of the coating layer is on the substrate side of the coating layer. It is composed of two layer regions that are larger than the average crystal width of the lower layer region positioned, and the ratio of the thickness of the upper layer region to the total thickness of the coating layer on the rake surface is the entire coating layer on the flank surface. It is smaller than the ratio of the thickness of the upper layer region to the film thickness, and the average crystal width of the columnar crystals on the rake face is smaller than the average crystal width of the columnar crystals on the flank face. .

  At this time, in the above configuration, a ratio of the thickness of the upper layer region to the thickness of the entire coating layer on the rake face is 20 to 50%, and the upper layer region has a ratio of the thickness of the entire coating layer on the flank surface. The thickness ratio is preferably 55 to 80%.

  In the above configuration, the average crystal width of the columnar crystals in the upper layer region is 1.5 to 4.0 times the average crystal width of the columnar crystals in the lower layer region in the flank. desirable.

  According to the configuration of the surface-coated cutting tool of the present invention, since the thickness of the coating layer on the rake face is thinner than the thickness of the coating layer on the flank face, the chipping can withstand a large impact on the rake face. In addition, on the flank, even if there is more contact with the work material, the coating layer does not wear out and exhibits good wear resistance. In addition, the covering layer is made of columnar crystals, and the covering layer has two layer regions, specifically, the upper layer region located on the surface side opposite to the substrate has a large average crystal width, and the lower layer region located on the substrate side. Has a multilayer structure with a small average crystal width, and the ratio of the thickness of the upper layer area on the rake face is smaller than the ratio of the thickness of the upper layer area on the flank face, and further the average crystal width of the columnar crystals on the rake face is escaped. By adopting a configuration that is smaller than the average crystal width of the columnar crystals on the surface, even if a coating layer with high internal stress is formed relatively thick on the flank, the coating layer itself self-destructs and chipping and peeling occur. Good fracture resistance can be exhibited without any damage. As a result, the surface-coated cutting tool of the present invention has a long life.

  Here, in the above configuration, the ratio of the thickness of the upper layer region to the thickness of the entire coating layer on the rake face is 20 to 50%, and the ratio of the thickness of the upper layer region to the thickness of the entire coating layer on the flank is 55 to 80%. Thus, it is possible to achieve both an improvement in chipping resistance on the rake face and an improvement in wear resistance on the flank face.

  Further, in the above configuration, on the flank face, the average crystal width of the columnar crystals in the upper layer region is 1.5 to 4.0 times the average crystal width of the columnar crystals in the lower layer region. Even if the thickness is relatively large, the coating layer itself is desirable because it has a high effect of suppressing self-destruction due to internal stress.

  FIG. 1 is a schematic diagram ((a) side view, (b) (a) sectional view taken along line AA) of an end mill which is a preferred example of the surface-coated cutting tool of the present invention, and its Description will be made based on FIG. 2 ((a) rake face, (b) flank face) which are transmission electron micrographs of an example.

  According to FIG. 1, the end mill 1 is formed on the side surface in the longitudinal direction, the outer peripheral blade 4 formed at the intersecting ridge line portion of the flank 3 positioned on the outer peripheral surface and the grooved rake face 2, and the tip in the longitudinal direction. And a tip cutting edge 5 to be formed. Further, the tip cutting edge 5 is located at the intersection ridge line portion of the rake face 2 and the flank 3 on the extension of the side rake face 2 and the flank 3. A line O in FIG. 1 is a rotation axis of the end mill 1.

2 (a) and 2 (b), the surface of the substrate 6 is covered with the coating layer 7, and the coating layer 7 is composed of columnar crystals 8, which is opposite to the substrate 6 of the coating layer 7. The average crystal width w _u (w _ru , w _fu ) of the upper layer region 10 located on the surface side is larger than the average crystal width w _l (w _rl , w _fl ) of the lower layer region 11 located on the substrate 2 side of the coating layer 7. It is composed of two large layer regions. Note that the layer region in the present invention does not necessarily have a linear interface in a sectional view, and the boundary may not be clear as shown in FIG.

Further, in consideration of the respective thicknesses of the average crystal width w _rl in the average crystal width w _{r (rake} face 2 of the upper region average crystal width in 10 w _ru the rake face 2 of the lower layer region 11 of the columnar crystal 8 in the rake face 2 Value: (w _ru × T _ru + w _rl × (T _r −T _ru )) / T _r ) is the average crystal width w _f of the columnar crystal 8 on the flank 3 (the average crystal width w in the upper layer region 10 of the flank 3) _The value obtained by adding the respective thicknesses to the average crystal width w _fl in the lower layer region 11 of _fu and the flank 3: (w _fu × T _fu + w _fl × (T _f −T _fu )) / T _f ) ing.

Further, the film thickness _Tr of the covering layer 7 on the rake face 2 in FIG. 2A is smaller than the film thickness _Tf of the covering layer 7 on the flank face 3 in FIG. in the ratio of the thickness _{T ru} upper region 10 with respect to the film thickness _{T r} of the entire coating layer 7 _(T ru / T _r) is the thickness of the upper layer region 10 for covering layer 7 total thickness _{T f} at the flank face 3 _{T fu} The ratio is smaller than the ratio (T _fu / T _f ).

  With the above configuration, the coating layer 7 is resistant to chipping by resisting a large impact applied to the rake face 2, and the coating layer 7 is rubbed and worn on the flank 3 although the contact surface 7 has more contact with the work material. It shows good wear resistance. Even if the coating layer 7 having high internal stress is formed relatively thick on the flank 3, the coating layer 7 itself can self-destruct and exhibit good chipping resistance without causing chipping or peeling. The end mill 1 has a long life.

Note that the crystal width w (w _ru , w _rl , w _fu , w _fl ) of the columnar crystal 8 in the coating layer 7 is intermediate between the upper layer region 10 and the lower layer region 11 of the coating layer 7 forming the columnar crystal 8. Measurement is performed with a line M (M _u , M _l ) drawn on the portion corresponding to the thickness. The average crystal width _{w t} of the columnar crystal 8 in the coating layer 7 is a line _{M (M} u, _{M l)} specifies a 100nm or more of the length L of the line _{M (M} u, _{M l)} of the length L of The number of grain boundaries that cross can be counted and calculated by length L / number of grain boundaries. The columnar crystal 8 in the present invention refers to a crystal whose crystal length in the direction perpendicular to the substrate surface is 1.5 times or more longer than the crystal width in the direction parallel to the surface of the substrate 6.

Here, the ratio (T _ru / T _r ) of the thickness T _ru of the upper layer region 10 to the film thickness T _r of the entire coating layer 7 on the rake face 2 is 20 to 50%, and the film thickness of the entire coating layer 7 on the flank 3 By setting the ratio of the thickness T _fu of the upper layer region to T _f (T _fu / T _f ) to be 55 to 80%, both the chipping resistance at the rake face 2 and the wear resistance at the flank face 3 are improved. Can be achieved. The ratio (T _r / T _f ) between the film thickness T _r of the coating layer 7 on the rake face 2 and the film thickness T _f of the coating layer 7 on the flank 3 is desirably 0.35 to 0.70. .

In the flank 3, the average crystal width w _fu of the columnar crystal 8 in the upper layer region 10 is 1.5 to 4.0 times as a ratio (w _fu / w _fl ) to the average crystal width w _fl of the columnar crystal in the lower layer region. It is desirable that the coating layer 7 itself has a high effect of suppressing self-destruction due to internal stress even if the coating layer 7 is relatively thick. Furthermore, the average crystal width w _r of the columnar crystal 8 on the rake face 2 is 0.4 to 0.7 times as a ratio (w _r / w _f ) to the average crystal width w _f of the columnar crystal 8 on the flank face. The chipping resistance on the rake face 2 and the relaxation effect on the internal stress of the coating layer 7 on the flank face 3 are desirable.

  2 is made of a nitride containing Ti and Al, the ratio of Ti to the total amount of Ti and Al in the coating layer 7 is more than the rake face 2 than the flank face. Is high, the oxidation resistance of the coating layer 7 on the rake face 2 is high, the progress of welding and wear due to oxidation can be suppressed, and the fracture resistance of the coating layer 7 on the flank face 3 is high, which occurs suddenly. As a result, it is desirable in that the end mill 1 can have a long life even under cutting conditions in which welding and defects are likely to occur.

Further, the coating layer 7 may be _a film other than the Ti _1-a Al _a N film, and besides the simple Ti _1-a Al _a N, for example, Ti _1-a-b Al _a M _b (C _x N _1-x ) (where M is one or more selected from Group 4, 5, 6 elements, rare earth elements and Si in the periodic table excluding Ti, and 0 ≦ a <1, 0 <b ≦ 1, 0 ≦ x ≦ 1)). Among them, Ti _1-a-b Al _a M _b (C _x N _1-x ) (where M is one or more selected from Group 4, 5, 6 elements, rare earth elements and Si in the periodic table excluding Ti) Yes, 0.4 ≦ a ≦ 0.65, 0 ≦ b ≦ 0.3, and 0 ≦ x ≦ 1) is desirable from the viewpoint of improving oxidation resistance, wear resistance, and fracture resistance. Further, among the above _{composition, Ti 1-a-b-} c-d Al a M b W c Si d (C x N 1-x) ( however, M is the periodic table excluding Ti 4, 5, 6 1 or more selected from group elements, rare earth elements and Si, and 0.4 ≦ a ≦ 0.65, 0 ≦ b ≦ 0.3, and 0 ≦ x ≦ 1. In this composition region, the oxidation start temperature is high, the oxidation resistance is high, the wear resistance at the time of cutting is improved, and the chipping that is likely to occur at the tip of the cutting edge can be suppressed, resulting in high fracture resistance. Further, the metal M is at least one selected from Nb, Mo, Ta, Hf, and Y. Among them, the inclusion of Nb or Mo is desirable in terms of the most excellent wear resistance and oxidation resistance.

  Furthermore, C and N which are non-metallic components of the coating layer 7 are excellent in hardness and toughness required for the cutting tool, and in order to suppress excessive generation of droplets generated on the surface of the coating layer 7, x A particularly desirable range of (C content ratio) is 0 ≦ x ≦ 0.5. The composition of the coating layer 7 can be measured by energy dispersive X-ray spectroscopy (EDS) or X-ray photoelectron spectroscopy (XPS).

  In addition, as the substrate 6, in addition to cemented carbide or cermet composed of tungsten carbide, a hard phase mainly composed of titanium carbonitride, and a binder phase mainly composed of an iron group metal such as cobalt or nickel, silicon nitride And hard materials such as ceramics mainly composed of aluminum oxide, a hard phase made of polycrystalline diamond or cubic boron nitride, and an ultra-high pressure sintered body in which a binder phase such as ceramics or iron group metal is fired under an ultra-high pressure. Materials are preferably used.

  Further, the tool shape suitable for the present invention is such that when the coating layer 7 is formed, the flank 3 is in a direction in which the metal component is relatively straightly projected from the surface of the target to the surface of the base 6, and the rake face 2 is the target. It is possible to adopt a shape in which a metal component wraps around the surface and forms a film. Specifically, a drill, an end mill, an inner diameter machining tool having a cutting edge formed at a rod-shaped tip, and the like can be particularly preferably employed.

(Production method)
Next, the manufacturing method of the surface-coated cutting tool of the present invention will be described using the end mill 1 as an example.

  First, the tool-shaped substrate 6 is produced using a conventionally known method. Next, the coating layer 7 is formed on the surface of the substrate 6. A physical vapor deposition (PVD) method such as an ion plating method can be suitably applied as a method for forming the coating layer 7. As an example of a detailed film forming method, FIG. 3 which is a schematic diagram of an arc ion plating film forming apparatus (hereinafter, abbreviated as AIP apparatus) 20 and FIG. 3A show the rotation state of the entire sample during film forming. Referring to FIG. 4, which is a schematic view, FIG. 4B is an enlarged view of the main part of FIG. 4A in the initial stage of film formation, and FIG. 4C is an enlarged view of the main part of FIG.

The AIP apparatus 20 of FIG. 3 introduces a gas such as N ₂ or Ar into the vacuum chamber 21 from the gas inlet 22, arranges the cathode electrode 23 and the anode electrode 24, and applies a high voltage therebetween. Then, a plasma is generated, and a desired metal or ceramic is evaporated from the target 25 and ionized by the plasma to be in a high energy state, and the ionized metal is attached to the surface of the sample (end mill base 6), as shown in FIG. As shown in b), the surface of the substrate 6 is covered with the coating layer 7. Further, according to FIG. 3, the end mill main body 2 is placed in a state where a plurality of end mill bodies 2 are erected on the sample support base 26, and a plurality of towers 27 in which a plurality of stages (three stages) of the sample support bases 26 are stacked ( FIG. 3 shows two sets, and FIG. 4A shows six sets. Further, according to FIG. 3A, a heater 29 for heating the end mill body 2, a gas discharge port 30 for discharging gas out of the system, and a bias for applying a bias voltage to the end mill base 6. A power supply 31 is arranged.

Here, according to the present invention, when the end mill base 6 is first set in the film forming chamber, the axial direction (longitudinal direction) of the end mill base 6 is set with respect to the surface of the target 25 as shown in FIG. Set so that they are parallel. Then, using the target 25, the metal source is evaporated and ionized by arc discharge or glow discharge, and at the same time, nitrogen (N ₂ ) gas as a nitrogen source or methane (CH ₄ ) / acetylene (C ₂ H ₂ ) as a carbon source. By reacting with the gas, the coating layer 7 is deposited on the surface of the end mill substrate 6. Since the end mill base 6 is set in the above-mentioned direction, the flank 3 is located at a position where the metal component from the target 25 comes linearly, so that the metal component from the target 25 comes linearly. The film speed tends to increase. On the other hand, since the rake face 2 is in a form in which the metal component from the target 25 wraps around and flies in the direction of the target 25, the film forming speed tends to be slow.

  When the end mill base 6 has a shape with a right-handed groove while applying a high bias voltage at the initial stage of film formation, the end mill base 6 is rotated counterclockwise as shown in FIG. The film is formed while rotating. When the film is formed under these conditions, the metal component to be formed easily wraps around the rake face 2 side, so that the coating layer 7 formed on the rake face 2 and the coating layer 7 formed on the flank face 3 The film thickness is not so different. That is, in order to make the film thickness of the coating layer 7 uniform, the end mill base 6 rotates as shown in FIG. 3B while the sample support 26 rotates while the end mill base 6 rotates. The film is formed while rotating so that the sample support 26 rotates. According to the present invention, in the lower layer region 11, the rotation direction is set to a direction in which the metal component flying from the target 25 is easily caught on the rake face side, so that the configuration of the lower layer region 11 of the coating layer 7 is as described above. It is possible to control.

  Thereafter, in the later stage of film formation, as shown in FIG. 4C, the film is formed while the bias voltage is lowered and the rotation direction of the end mill base 6 is changed to the rotation opposite to the clockwise direction. When the film is formed under these conditions, the metal component to be formed is less likely to wrap around the rake face 2 side, so that the coating layer 7 formed on the rake face 2 has a coating layer 7 formed on the flank 3. It becomes thinner than the film thickness. That is, in the upper layer region 10, the configuration of the upper layer region 10 of the coating layer 7 is controlled as described above by making the direction of rotation difficult for the metal component flying from the target 25 to reach the rake face 2 side. Is possible. Note that when the bias voltage is low, the crystal of the coating layer 7 formed tends to have a large crystal width.

In the film formation, the position of the sample support base 26 is set so that the gaps d (d ₁ , d ₂ , d ₃ ) between the tip of the end mill base 6 and the upper sample support base 26 in FIG. And the end mill substrate 6 and the sample support so that the number of rotations is 3 to 6 rpm, where the number of rotations of the sample is the cycle in which the end mill substrate 6 is closest to the target 25 at each position. It is desirable to adjust the rotation speed of the base 26. In addition, the film is formed in a state where a mixed gas of nitrogen (N ₂ ) gas and argon (Ar) gas is supplied at a flow rate of argon gas to nitrogen of 1: 9 to 4: 6. The bias voltage during film formation is 70 to 200 V at the initial stage of film formation in order to produce a coating layer 7 with high hardness in consideration of the crystal structure of the coating layer and to improve the adhesion to the end mill substrate 6. It is desirable to set the film later to 30 to 125V.

  The target 25 is, for example, metal titanium (Ti), metal aluminum (Al), metal M (where M is a group selected from Group 4, 5, 6 elements of the periodic table excluding Ti, rare earth elements, and Si). It is possible to use metal targets each independently containing at least a seed), alloy targets obtained by compounding them, and mixture targets composed of these compound powders or sintered bodies.

Further, arc discharge or glow discharge is used to generate plasma, and nitrogen (N ₂ ) gas as a nitrogen source or methane (CH ₄ ) / acetylene (C ₂ H ₂ ) gas as a carbon source is used as an introduction gas. Can be used. At this time, it is desirable to use a mixed gas of nitrogen (N ₂ ) gas and argon (Ar) gas at a flow rate of argon gas to nitrogen of 0 to 4: 6.

10% by mass of metallic cobalt (Co) powder, 0.2% by mass of vanadium carbide (VC) powder, chromium carbide (Cr ₃ C ₂ ) powder with respect to tungsten carbide (WC) powder having an average particle size of 0.5 μm Was added and mixed at a ratio of 0.8% by mass, molded into a four-blade end mill shape with an outer diameter of 16 mm, and fired. And after passing through the grinding process, the surface was washed in the order of alkali, acid and distilled water to produce an end mill substrate.

Then, the substrate was set in an arc ion plating apparatus equipped with a target on which a hard layer shown in Table 1 was formed, and the substrate was heated to 500 ° C. to form a coating layer under the conditions shown in Table 1. The film forming conditions were an arc current of 150 A in a mixed gas of nitrogen gas and argon gas in an atmosphere having a total pressure of 4 Pa.

With respect to the obtained end mill, the coating state on the rake face and the flank face contacting the outer peripheral blade was observed with a transmission electron microscope (TEM), and the structure state was confirmed. Further, the composition of the crystals constituting the coating layer was quantified by energy dispersive X-ray analysis (EDS). The results are shown in Tables 2 and 3.

  Furthermore, the cutting test was done on the following cutting conditions using the obtained end mill. The results are shown in Table 4.

Cutting method: Shoulder (milling)
Work material: SCM440
Number of revolutions: 5500 times / minute feed: 220 mm / minute cut: radial cut 0.4 mm, depth cut 2 mm
Cutting state: Water-soluble grinding fluid Evaluation method: When cutting for 10 minutes, the amount of flank wear and the chipping state at the cutting edge are measured.

  From the results shown in Tables 1 to 4, Sample Nos. In which the crystal width in the coating layer on the rake face and the flank face are the same. In No. 11, a large amount of minute chipping occurred on the rake face, and the flank wear width increased. In addition, the rake face and the flank face have the same film thickness, and are not a two-layer structure of the upper layer region and the lower layer region. 12, and the ratio of the upper layer region to the lower layer region on the rake face and flank face is the same. In No. 14, chipping occurred on the flank due to internal stress on the flank. Furthermore, the sample Nos. Having the same film thickness on the rake face and the flank face. In No. 13, chipping occurred on the rake face, and all of them had a short tool life.

  On the other hand, the sample No. In Nos. 1 to 10, the chipping resistance and wear resistance were good and the cutting performance was excellent.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic diagram about an example of the end mill which is a suitable example of the surface covering cutting tool of this invention ((a) is a side view, (b) is sectional drawing in the AA of (a)). About the suitable example of the surface covering cutting tool of this invention, (a) is a rake face, (b) is a transmission electron micrograph of a flank. In the film-forming process of the coating layer at the time of manufacturing the surface coating cutting tool of this invention, it is a schematic diagram of the arc ion plating film-forming apparatus. In the film-forming process of the coating layer when manufacturing the surface-coated cutting tool of the present invention, (a) is a schematic diagram showing the rotation state of the entire sample during film formation, and (b) is a schematic diagram of (a) at the initial stage of film formation. The principal part enlarged view, (c) is the principal part enlarged view of (a) in the film-forming late stage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 End mill 2 Rake face 3 Flank face 4 Cutting edge 6 Base body 7 Coating layer 8 Columnar crystal 10 Upper layer area 11 Lower layer area 20 AIP apparatus 21 Vacuum chamber 22 Gas inlet 23 Cathode electrode 24 Anode electrode 25 Target 26 Sample support stand 27 Tower 29 thickness w _r rake face of the upper region in the thickness T _fu flank of the upper region in the thickness T _ru rake face of the covering layer in the thickness T _f flank of the covering layer in the heater 30 gas discharge port 31 bias power T _r rake face the average crystal width w _fu flank of the columnar crystals in the average crystal width w _f flank of the columnar crystals in the lower region of the average crystal width w _rl rake face of the columnar crystals in the upper layer region in the average crystal width w _ru rake face of the columnar crystals in the Average crystal width of columnar crystals in the upper layer region in w _fl flank Average crystal width of the columnar crystals in the lower layer region d ₁ , d ₂ , d ₃ Gap between the end of the end mill body and the upper sample support

Claims (3)

A cutting tool in which a coating layer is coated on the surface of the substrate, and the cutting edge is a cross ridge line portion between the rake face and the flank face, and the thickness of the coating layer on the rake face is greater than the thickness of the coating layer on the flank face The coating layer is made of columnar crystals, and the average crystal width of the upper layer region located on the surface side of the coating layer opposite to the substrate is the average crystal width of the lower layer region located on the substrate side of the coating layer. The ratio of the thickness of the upper layer region to the film thickness of the entire coating layer on the rake face is a thickness of the upper layer region to the film thickness of the entire coating layer on the flank surface. And the average crystal width of the columnar crystals on the rake face is smaller than the average crystal width of the columnar crystals on the flank face. The ratio of the thickness of the upper layer region to the film thickness of the entire coating layer on the rake face is 20 to 50%, and the ratio of the thickness of the upper layer region to the film thickness of the entire coating layer on the flank is 55 to 80. The surface-coated cutting tool according to claim 1, wherein The average crystal width of the columnar crystals in the upper layer region is 1.5 to 4.0 times the average crystal width of the columnar crystals in the lower layer region on the flank. 2. The surface-coated cutting tool according to 2.