JP5838805B2 - Surface coated cutting tool with excellent chipping resistance due to hard coating layer - Google Patents

Description

  In the present invention, high-speed intermittent cutting of various steels and cast irons with high heat generation and intermittent / impact loads acting on the cutting edge, the hard coating layer has excellent chipping resistance, which makes it possible to The present invention relates to a surface-coated cutting tool (hereinafter referred to as a coated tool) that exhibits excellent cutting performance over use.

Conventionally, the surface of a tool substrate (hereinafter collectively referred to as a tool substrate) generally composed of tungsten carbide (hereinafter referred to as WC) -based cemented carbide or titanium carbonitride (hereinafter referred to as TiCN) -based cermet. In addition,
(A) Ti carbide (hereinafter referred to as TiC) layer, nitride (hereinafter also referred to as TiN) layer, carbonitride (hereinafter referred to as TiCN) layer formed by chemical vapor deposition of the lower layers. A Ti compound layer consisting of one or more of a carbon oxide (hereinafter referred to as TiCO) layer and a carbonitride oxide (hereinafter referred to as TiCNO) layer,
(B) the upper layer is an aluminum oxide layer formed by chemical vapor deposition;
A coated tool formed by forming a hard coating layer composed of (a) and (b) above is known, and this coated tool is known to be used for cutting various steels and cast irons. It has been.
However, the above-mentioned coated tool has a problem that chipping or the like is likely to occur under a cutting condition in which a heavy load is applied to the cutting edge, and the tool life is short-lived. Has been made.

  For example, Patent Document 1 discloses that a hard coating layer formed on the surface of a WC-based cemented carbide substrate is composed of a single layer of TiCN or a laminate of two or more layers, and one or two of these constituent layers. (A) a crystal structure that changes from a granular crystal structure to a vertically grown crystal structure, (b) a crystal structure that changes from a granular crystal structure to a vertically grown crystal structure, and further changes from this vertically grown crystal structure to a granular crystal structure, (c ) Disclosed is a surface-coated WC-based cemented carbide cutting tool having excellent chipping resistance, which is composed of one of a crystal structure changing from a vertically grown crystal structure to a granular crystal structure, or two or more crystal structures. .

  Patent Document 2 discloses a surface-coated cutting tool in which a ceramic film is formed on the surface of a substrate made of a cemented carbide or cermet, and the ceramic coating is constituted by a single layer or a multilayer including a columnar TiCN layer. The horizontal average grain diameter d1 of the TiCN columnar crystal grains at a position that is 1/5 of the thickness of the TiCN layer from the upper end of the TiCN layer, and the distance of 2/5 of the thickness of the TiCN layer from the lower end of the TiCN layer. The ratio of the horizontal average grain size d2 of the TiCN columnar crystal grains at the position is 1 ≦ d1 / d2 ≦ 1.3, which is excellent in both wear resistance and fracture resistance, and for long-time cutting including intermittent cutting. A durable surface coated cutting tool is disclosed.

Further, Patent Document 3 discloses a surface-coated cutting tool having a hard coating layer including at least a titanium carbonitride layer on the surface of a substrate and an aluminum oxide layer as an upper layer, and hard spheres are formed on the surface of the surface-coated cutting tool. In the state of contact, the hard ball rolls around the spherical surface so that the substrate is exposed in the center of the wear mark where the surface-coated cutting tool is locally worn so that the hard ball rotates while rolling. When observed, the titanium carbonitride layer observed around the exposed substrate at the center of the wear scar is observed in the lower structure where the crack width is zero or smaller, and in the periphery of the lower structure, and cracked more than the lower structure. width is configured to large upper tissue is present, even in severe cutting conditions such as a strong impact according to the tool cutting edge, such as intermittent cutting, between the TiCN layer and the Al ₂ O ₃ layer It is possible to increase the adhesion of the hard coating layer, cutting tool life with excellent chipping resistance and wear resistance is disclosed without release occurs.

Japanese Patent Laid-Open No. 6-8009 JP-A-10-109206 JP 2005-186221 A

  In recent years, there is a strong demand for energy saving and energy saving in cutting, and along with this, coated tools have come to be used under severer conditions. For example, Patent Documents 1 to 3 show the above. Even when a coated tool is used for high-speed intermittent cutting with high heat generation and more intermittent and impact loads on the cutting edge, the thermal conductivity of the lower layer is high and the heat shielding effect is high. Since it is not sufficient, chipping and chipping are likely to occur on the cutting edge due to a high load during cutting, and as a result, the service life is reached in a relatively short time.

  In view of the above, the inventors of the present invention have an excellent hard coating layer even when used in high-speed intermittent cutting with high heat generation and intermittent and impact loads acting on the cutting edge. As a result of earnest research on coated tools that have excellent toughness and, as a result, excellent chipping resistance and fracture resistance over long-term use, the following findings were obtained.

  That is, as a conventional hard coating layer, at least one Ti carbonitride layer comprising a Ti compound layer comprising at least one Ti carbonitride layer or two or more Ti compound layers is formed. Is formed in a columnar shape in the vertical direction as a base. Therefore, although the wear resistance is improved, the toughness of the Ti compound layer decreases as the anisotropy of the Ti carbonitride layer increases. As a result, the chipping resistance and fracture resistance could not be exhibited, and the tool life could not be satisfied.

  Therefore, the present inventors have conducted intensive research on the Ti carbonitride layer in the Ti compound layer constituting the lower layer of the hard coating layer, and found that at least one Ti carbonitride in the Ti compound layer was obtained. By allowing fine TiCN to exist in the layer in a bimodal particle size distribution, the fine TiCN having a large particle size mainly relaxes the anisotropy of the Ti compound layer, and the fine TiCN having a small particle size makes the heat of the Ti compound layer The conductivity can be suppressed and the heat shielding effect can be improved. As a result, a novel effect that the chipping resistance and chipping resistance of the hard coating layer can be drastically improved by the synergistic effect of the effect produced by the fine TiCN having a large particle size and the effect produced by the fine TiCN having a small particle size. Finding findings.

  Specifically, at least one Ti carbonitride layer constituting the lower layer is composed of a columnar vertically grown TiCN crystal structure, and fine TiCN is present in the structure in a bimodal particle size distribution. The chipping resistance and chipping resistance of the hard coating layer can be improved.

  The Ti carbonitride layer having the above-described configuration can be formed by, for example, the following chemical vapor deposition method.

On the surface of the tool base, the reaction gas composition (volume%) is TiCl ₄ : 1.7%, TDMAT (tetrakisdimethylaminotitanium): 0.01 to 0.1%, CH ₃ CN: 0.7%, N ₂ : 20%, H ₂ : the rest, the reaction atmosphere pressure is 5 to 9 kPa, the reaction atmosphere temperature is 800 to 930 ° C., and the columnar vertically grown TiCN crystal structure is formed by chemical vapor deposition. Into the reaction gas, TDMAT (tetrakisdimethylaminotitanium) is added at high and low concentrations (0.06 to 0.1%) and low concentrations (0.01 to 0.05%). By doing so, a columnar vertically grown TiCN crystal structure in which fine TiCN having a bimodal particle size distribution is present in the structure can be obtained. At this time, even if fine TiCN exists in the columnar vertically grown TiCN crystal structure, the columnar vertically grown TiCN crystal structure is not divided by controlling the maximum grain size and particle size distribution of the fine TiCN. I have found that I can grow as an organization. As a result, the toughness is improved without increasing the anisotropy of the columnar vertically grown TiCN due to the presence of the fine TiCN having a bimodal particle size distribution without reducing the toughness of the columnar vertically grown TiCN crystal structure. At the same time, the thermal conductivity is suppressed and the heat shielding effect is improved. Therefore, the chipping resistance and chipping resistance of the hard coating layer can be improved.

  Furthermore, the present inventors have conducted extensive research on the relationship between the particle size distribution of the fine TiCN present in the Ti carbonitride layer and various properties of the hard coating layer, and as a result, the particle size distribution of the fine TiCN is: It was confirmed that the best effect was achieved when the distribution was bimodal as follows.

That is, as a result of examining the relationship between the particle size distribution of fine TiCN and the film characteristics in detail, the present inventors have found that the first peak exists at 10 to 20 nm as shown in FIG. When the fine TiCN is counted for every 2 nm of fine TiCN diameter, the fine TiCN number density at the first peak is 200 to 500 / μm ² , the second peak is present at 50 to 100 nm, and the fine TiCN diameter is every 2 nm. It was found that when the fine TiCN number density in the second peak when counting fine TiCN was 10 to 30 / μm ² , the best film characteristics were exhibited.

The present invention has been made based on the above findings,
“(1) In a surface-coated cutting tool in which a hard coating layer is provided on the surface of a tool base composed of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet,
Together with the hard coating layer is composed of a lower portion layer and the upper layer,
(A) The lower layer includes at least one Ti carbonitride layer, and has a total average layer thickness of 3 to 20 μm, a Ti compound layer composed of one layer or two or more layers,
(B) the upper layer is an aluminum oxide layer having an average layer thickness of 2 to 25 μm;
Consists of
The at least one Ti carbonitride layer constituting the lower layer of (a) has a columnar vertically grown TiCN crystal structure, in which fine TiCN exists, and the fine TiCN is It is a granular TiCN crystal phase or an amorphous TiCN phase or a mixed phase of a granular TiCN crystal phase and an amorphous TiCN phase. And the maximum particle size of the fine TiCN is 10 to 150 nm, and the particle size distribution in the lower layer of the fine TiCN has a bimodal distribution. Surface coated cutting tool.
(2) The first peak of the particle size distribution of the fine TiCN exists at 10 to 20 nm, and the fine TiCN number density in the first peak when the fine TiCN is counted for every 2 nm of the fine TiCN diameter is 200 to 500 / μm. ² and the second peak of the fine TiCN exists at 50 to 100 nm, and the fine TiCN number density in the second peak when the fine TiCN is counted for every 2 nm of the fine TiCN diameter is 10 to 30 / μm ² The surface-coated cutting tool according to (1), wherein "
It has the characteristics.

  The present invention will be described in detail below.

Lower Ti compound layer:
The lower layer composed of one or more Ti compound layers including at least one Ti carbonitride layer and having a total average layer thickness of 3 to 20 μm should be formed under normal chemical vapor deposition conditions. However, at least one Ti carbonitride layer is formed by another method as described later. The Ti compound layer constituting the lower layer itself has a high temperature strength, and the presence of the Ti compound layer makes the hard coating layer have a high temperature strength, as well as both the tool base and the upper layer made of aluminum oxide. It has an effect of firmly adhering, and thus contributing to an improvement in the adhesion of the hard coating layer to the tool substrate. However, when the total average layer thickness is less than 3 μm, the above-mentioned effect cannot be exhibited sufficiently, while the total When the average layer thickness exceeds 20 μm, chipping tends to occur. Therefore, the total average layer thickness is set to 3 to 20 μm.

At least one Ti carbonitride layer in the lower layer:
At least one Ti carbonitride layer in the lower layer has a columnar vertically grown TiCN crystal structure, and fine TiCN crystals are dispersed and distributed in the structure. By adopting such a configuration, toughness is improved and excellent chipping resistance is exhibited. However, if the maximum grain width of the columnar vertically grown TiCN crystal is smaller than 50 nm, the wear resistance over a long period of use cannot be ensured. Decreases. Therefore, the maximum particle width of the columnar vertically grown TiCN crystal is preferably 50 to 2000 nm. Further, if the aspect ratio between the maximum grain width and the maximum grain length in the film thickness direction is smaller than 5, the high wear resistance characteristic of the columnar vertically grown TiCN cannot be secured, whereas if it exceeds 50, the toughness is rather Decreases, and chipping resistance and chipping resistance decrease. Therefore, it is desirable that the aspect ratio between the maximum grain width of the columnar vertically grown TiCN crystal and the maximum grain length in the film thickness direction is 5-50. Here, the maximum particle width and the maximum particle length are, when one particle of columnar vertically grown TiCN crystal is measured, the largest value of the particle width (short side) is called the maximum particle width, The largest value (long side) is called the maximum particle length.

Furthermore, when the maximum particle size of the fine TiCN is smaller than 10 nm, the effect of dispersing and distributing the fine TiCN is not exhibited, whereas when it exceeds 150 nm, the toughness is lowered. Therefore, the maximum particle size of the fine TiCN is preferably 10 to 150 nm.

In addition to the above-described configuration, the present invention exhibits a further excellent effect when it has the following conditions. That is, when the particle size distribution in the lower layer of the fine TiCN is a bimodal particle size distribution, the lower Ti compound layer further exhibits the above-described effects. As a particularly preferred distribution form, the first peak of the distribution of fine TiCN exists at 10 to 20 nm, and the fine TiCN number density at the first peak when the fine TiCN is counted for every 2 nm of the fine TiCN diameter is 200 to 500 / present in the second peak 50~100nm the fine TiCN with a [mu] m ^2, fine TiCN number density in the second peak when the counted fine TiCN every fine TiCN diameter 2nm is at 50 to 100 / [mu] m ² . Here, the reason why the particle size and the number density in the first peak and the second peak of the bimodal particle size distribution form are determined as described above is that the heat shielding effect is sufficiently obtained when the particle size of the first peak is smaller than 10 nm. On the other hand, if the thickness exceeds 20 nm, the thermal conductivity of the film cannot be sufficiently suppressed. Further, if the particle size of the second peak is smaller than 50 nm, the toughness cannot be sufficiently improved, and if it exceeds 100 nm, the chipping resistance cannot be sufficiently improved.

Upper aluminum oxide layer:
It is well known that the aluminum oxide layer constituting the upper layer has high-temperature hardness and heat resistance. However, if the average layer thickness is less than 2 μm, it should ensure wear resistance over a long period of use. On the other hand, when the average layer thickness exceeds 25 μm, the aluminum oxide crystal grains are likely to be coarsened. As a result, in addition to the decrease in high-temperature hardness and high-temperature strength, the chipping resistance, Since the deficiency deteriorates, the average layer thickness is determined to be 2 to 25 μm.

The fine TiCN in the present invention is a generic term that refers to a granular TiCN crystal phase, an amorphous TiCN phase, or a mixed phase of a granular TiCN crystal phase and an amorphous TiCN phase, and having a maximum particle size of 150 nm or less. .

Formation of fine TiCN with a bimodal particle size distribution:
The fine TiCN of the present invention can be formed by performing chemical vapor deposition under the following conditions during the formation process of the lower layer formed under normal chemical vapor deposition conditions.
That is, TDMAT, which is the core of fine TiCN, is added to the reaction gas while alternately switching between two conditions of low concentration (A condition) and high concentration (B condition), thereby providing fine particles having a bimodal particle size distribution. TiCN is formed.
Reaction gas composition (volume%):
TiCl ₄ : 1.7%,
TDMAT A condition: 0.01-0.05% B condition: 0.06-0.10%
CH ₃ CN: 0.7%,
N ₂ : 20%
H ₂ : remaining,
Reaction atmosphere pressure: 5-9 kPa
Reaction atmosphere temperature: 800-930 ° C

  In the present invention, the structure in which the fine TiCN is distributed in the columnar vertically grown TiCN crystal structure has a bimodal particle size distribution when force is applied to the columnar vertically grown TiCN crystal structure due to the presence of the fine grained TiCN. Since each columnar vertically grown TiCN crystal is displaced, a large toughness is generated and excellent chipping resistance is exhibited. In addition, the presence of fine TiCN having a small particle size suppresses the thermal conductivity of the film, thereby improving the heat shielding effect.

The coated tool of the present invention, the hard coating layer consists of a lower layer and an upper layer,
(A) The lower layer includes at least one Ti carbonitride layer, and has a total average layer thickness of 3 to 20 μm, a Ti compound layer composed of one layer or two or more layers,
(B) the upper layer is an aluminum oxide layer having an average layer thickness of 2 to 25 μm;
The at least one Ti carbonitride layer constituting the lower layer of (a) has a columnar vertically grown TiCN crystal structure, in which fine TiCN exists, and the fine particles TiCN is a granular TiCN crystal phase or an amorphous TiCN phase or a mixed phase of a granular TiCN crystal phase and an amorphous TiCN phase. The aspect ratio with the particle length is 5 to 50, the maximum particle size of the fine TiCN is 10 nm to 150 nm, and the particle size distribution form in the lower layer of the fine TiCN has a bimodal distribution. As the toughness of the coating layer is improved, the thermal conductivity is suppressed, and the heat shielding effect is improved, resulting in high heat generation of steel, cast iron, etc. Even when used for high-speed interrupted cutting where high loads and impacts are applied, it has excellent chipping resistance and fracture resistance. As a result, it exhibits excellent wear resistance over a long period of use. Long life is achieved.

The growth state of the columnar vertically grown TiCN crystal structure of at least one Ti carbonitride layer constituting the lower Ti compound layer of the present invention and the existence form of fine TiCN existing in the Ti carbonitride layer are schematically shown. FIG. It is a particle size distribution map of the fine TiCN which exists in the Ti compound layer which comprises the lower layer of this invention. It is the film | membrane structure schematic diagram which represented typically the growth state of the columnar vertically-grown TiCN crystal structure of the at least 1 layer of Ti carbonitride which comprises the lower Ti compound layer of a comparative example.

  Next, the coated tool of the present invention will be specifically described with reference to examples.

As raw material powders, WC powder, TiC powder, ZrC powder, VC powder, TaC powder, NbC powder, Cr ₃ C ₂ powder, TiN powder, and Co powder each having an average particle diameter of 1 to 3 μm are prepared. The raw material powder is blended in the blending composition shown in Table 1, added with wax, ball mill mixed in acetone for 24 hours, dried under reduced pressure, and press-molded into a green compact of a predetermined shape at a pressure of 98 MPa. The green compact is vacuum-sintered in a vacuum of 5 Pa at a predetermined temperature within a range of 1370 to 1470 ° C. for 1 hour. After sintering, the cutting edge is subjected to a honing process of R: 0.07 mm. Thus, tool bases A to E made of WC-base cemented carbide having an insert shape specified in ISO · CNMG120408 were manufactured.

In addition, as raw material powders, TiCN (mass ratio TiC / TiN = 50/50) powder, Mo ₂ C powder, ZrC powder, NbC powder, TaC powder, WC powder, all having an average particle diameter of 0.5 to 2 μm. Co powder and Ni powder are prepared, and these raw material powders are blended in the blending composition shown in Table 2, wet mixed by a ball mill for 24 hours, dried, and pressed into a compact at a pressure of 98 MPa. The green compact was sintered in a nitrogen atmosphere of 1.3 kPa at a temperature of 1540 ° C. for 1 hour, and after the sintering, the cutting edge portion was subjected to a honing process of R: 0.07 mm. Tool bases a to e made of TiCN-based cermet having an insert shape of standard / CNMG120408 were formed.

Next, a normal chemical vapor deposition apparatus is used on the surfaces of these tool bases A to E and tool bases a to e,
(A) As a lower layer of the hard coating layer, a Ti compound layer is formed by vapor deposition under the conditions shown in Tables 3 and 4 and the target layer thickness shown in Table 6.
(B) At this time, when the Ti carbonitride layer constituting the Ti compound layer was formed under the k to o conditions shown in Table 4, the TDMAT (volume%) shown in Table 4 was set at two different concentrations. The coated tools 1 to 15 of the present invention are manufactured by forming fine TiCN having a bimodal particle size distribution in the structure of the Ti carbonitride layer by alternately switching under (A condition, B condition). did.
(C) Next, a hard coating layer composed of an upper layer (aluminum oxide layer) having a target layer thickness shown in Table 6 is formed by vapor deposition.

  The Ti carbonitride layer constituting the Ti compound layer of the lower layer of the inventive coated tools 1 to 15 was observed over a plurality of fields using a scanning electron microscope (magnification 50000 times). The film structure in which fine TiCN having a bimodal particle size distribution exists in the grain boundaries and in the grains of the columnar crystals shown in the schematic diagram of the film configuration shown in FIG.

  Further, the number of fine TiCN present in the Ti carbonitride layer constituting the lower Ti compound layer of the coated tools 1 to 15 of the present invention, and the lower Ti compound layer in the direction perpendicular to the tool base. Using a scanning electron microscope (magnification 50000 times) and a transmission electron microscope (magnification 200000 times), the tool base and the horizontal direction are 10 μm in total in the thickness of Ti carbonitride layer thickness. The number density of fine TiCN (particles / μm 2) was determined for each particle size of 2 nm, and the particle size distribution form shown in the particle size distribution diagram shown in FIG. 2 was confirmed.

Furthermore, when the Ti carbonitride layer constituting the Ti compound layer constituting the lower layer of the inventive coated tools 1 to 15 was observed over a plurality of fields of view using a transmission electron microscope (magnification 200000 times), The fine TiCN was confirmed to be a granular TiCN crystal phase, an amorphous TiCN phase, or a mixed phase of a granular TiCN crystal phase and an amorphous TiCN phase.

For comparison purposes, the surfaces of the tool bases A to E and the tool bases a to e are the same as the coated tools 1 to 15 of the present invention under the conditions shown in Tables 3 and 5 and the target layer thicknesses shown in Table 7. Then, a Ti compound layer as a lower layer of the hard coating layer was formed by vapor deposition. Next, an upper layer composed of an aluminum oxide layer was formed by vapor deposition as the upper layer of the hard coating layer under the conditions shown in Tables 3 and 5 and the target layer thicknesses shown in Table 7. At this time, comparative coated tools 1 to 15 shown in Table 7 were produced by forming columnar vertically grown TiCN crystal structures without adding TDMAT.
Moreover, about the Ti carbonitride layer which comprises the Ti compound layer of the lower layer of the said comparative coating tool 1-15, when it observed over multiple visual fields using the scanning electron microscope (50000 times magnification), all are The film structure consisting of the columnar vertically grown TiCN crystal structure shown in the schematic diagram of the film structure shown in FIG. 3 was confirmed.

  Moreover, when the cross section of each structural layer of this invention coated tool 1-15 and comparative coated tool 1-15 was measured using the scanning electron microscope (magnification 5000 times) and average layer thickness was calculated | required, all are Table 6 And an average layer thickness substantially the same as the target layer thickness shown in Table 7.

Moreover, about this invention coated tool 1-15 and comparative coated tool 1-15, similarly using the scanning electron microscope (magnification 5000 times), it comprises the Ti carbonitride layer contained in the Ti compound layer of a lower layer The maximum grain width and the maximum grain length in the film thickness direction of the columnar vertically grown TiCN crystal are measured for each of the columnar vertically grown TiCN crystals existing in a total length of 10 μm in the horizontal direction with respect to the tool base, and the average The average value of the maximum particle width and the maximum particle length in the film thickness direction was determined, and the aspect ratio was determined from these ratios.

Next, cutting test was carried out on the present coated tools 1 to 15 and comparative coated tools 1 to 15 under the conditions shown in Table 8, and the flank wear width (mm) of the cutting edge was measured in any cutting test. .
Table 9 shows the measurement results.

  From the results shown in Tables 6 and 9, in the coated tool of the present invention, the Ti carbonitride layer constituting the Ti compound layer of the lower layer of the hard coating layer has a columnar vertically grown TiCN crystal structure. The presence of fine TiCN with a bimodal particle size distribution in the structure improves toughness, suppresses thermal conductivity, and improves the heat shielding effect. In addition, even when used for high-speed intermittent machining where intermittent and shocking high loads act on the cutting edge, it has excellent chipping resistance and chipping resistance, resulting in excellent wear resistance over a long period of use. It is clear that it exhibits sex.

  On the other hand, for the comparative coated tools 1 to 15 in which the fine TiCN having a bimodal particle size distribution is not present in the Ti carbonitride layer constituting the Ti compound layer of the lower layer of the hard coating layer, In addition, when used in high-speed intermittent cutting with intermittent and shocking high loads acting on the cutting edge, it is apparent that the lifetime is reached in a short time due to the occurrence of chipping, chipping and the like.

  As described above, the coated tool of the present invention has excellent chipping resistance in high-speed intermittent cutting with high heat generation such as steel and cast iron and intermittent and impact high load acting on the cutting edge. Demonstrate fracture resistance and extend the service life, but not only for high-speed interrupted cutting conditions, but also for high-speed cutting conditions, high cutting depth, high-feed, high-speed heavy cutting conditions, etc. Of course, it is also possible.

Claims (2)

In a surface-coated cutting tool in which a hard coating layer is provided on the surface of a tool base composed of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet,
Together with the hard coating layer is composed of a lower portion layer and the upper layer,
(A) The lower layer includes at least one Ti carbonitride layer, and has a total average layer thickness of 3 to 20 μm, a Ti compound layer composed of one layer or two or more layers,
(B) the upper layer is an aluminum oxide layer having an average layer thickness of 2 to 25 μm;
Consists of
The at least one Ti carbonitride layer constituting the lower layer of (a) has a columnar vertically grown TiCN crystal structure, in which fine TiCN exists, and the fine TiCN is It is a granular TiCN crystal phase or an amorphous TiCN phase or a mixed phase of a granular TiCN crystal phase and an amorphous TiCN phase. And the maximum particle size of the fine TiCN is 10 to 150 nm, and the particle size distribution in the lower layer of the fine TiCN has a bimodal distribution. Surface coated cutting tool. The first peak of the particle size distribution of the fine TiCN exists at 10 to 20 nm, and the fine TiCN number density at the first peak when the fine TiCN is counted every 2 nm of the fine TiCN diameter is 200 to 500 / μm ^2. The second peak of the fine TiCN exists at 50 to 100 nm, and the fine TiCN number density at the second peak when the fine TiCN is counted for every 2 nm of the fine TiCN diameter is 10 to 30 / μm ^2. The surface-coated cutting tool according to claim 1, wherein