JP2012143828A - Surface coated cutting tool having hard coating layer with excellent toughness and chipping resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface coated cutting tool having a hard coating layer with excellent toughness and chipping resistance, and being capable of exhibiting excellent wear resistance over a long period of use.SOLUTION: The surface coated cutting tool has the hard coating layer evaporated on a surface of a tool base consisting of WC cemented carbide and TiCN-based cermet, and the hard coating layer composed of (a) a bottom layer composed of a Ti compound layer contains a modified TiCN layer and (b) a top layer composed of an aluminum oxide layer. When examining a change in the film thickness direction of an average grain size D in each thickness region at thickness intervals of 0.02 μm in the film thickness direction of the modified TiCN layer, the surface coated cutting tool has a grain crystal structure in which the average grain size D of the modified TiCN layer of the bottom layer changes periodically with a period of 0.5 μm to 5 μm along the film thickness direction because at least a plurality of thickness regions having the average grain size D of 0.5 to 1.5 μm and that of 0.05 to 0.3 μm are alternately formed along the film thickness direction of the modified TiCN layer.

Description

  The present invention provides high heat generation and high-speed heavy cutting of various steels and cast irons in which a high load acts on the cutting edge, so that the hard coating layer has excellent toughness and chipping resistance. The present invention relates to a surface-coated cutting tool that exhibits excellent cutting performance (hereinafter referred to as a coated tool).

Conventionally, generally on the surface of a substrate (hereinafter collectively referred to as a tool substrate) composed of a tungsten carbide (hereinafter referred to as WC) -based cemented carbide or titanium carbonitride (hereinafter referred to as TiCN) -based cermet. ,
(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 comprising two or more of a carbon oxide (hereinafter referred to as TiCO) layer and a carbonitride oxide (hereinafter referred to as TiCNO) layer,
(B) an aluminum oxide (hereinafter referred to as Al ₂ O ₃ ) layer in which the upper layer is 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, since the cutting performance of the above-mentioned coated tool is greatly influenced by the structure of the lower layer, some proposals have been made regarding the grain structure of the lower layer.

For example, in the cited document 1, in the coated tool in which the TiN layer is formed as the lower layer, the TiCN layer is formed as the second layer thereon, and the TiC layer, TiN layer, TiCN layer, etc. are further formed thereon, the second When the TiCN of the layer is composed of columnar crystal grains, the average crystal grain size of the TiCN is in the range of 0.1 to 1 μm when the thickness of the second layer is 4.0 μm or less, and the thickness of the second layer is When it exceeds 4.0 μm and is 20 μm or less, it is in the range of 0.5 to 3.0 μm, and the hardness of the second layer is 1600 to 2400 kg / mm ² , thereby strengthening the adhesion between the hard coating layer and the base material. On the other hand, it has been proposed to increase the toughness, peel resistance and wear resistance of the hard coating layer.

  Further, in the cited document 2, in the lower layer in which the first layer in contact with the substrate is TiN and the second layer is TiCN, the thickness of the second layer is 60% or more of the total thickness, and the particles The average particle size in the horizontal direction is 0.3 to 1.2 μm, and the average particle size in the vertical direction is at least 2.5 times the average particle size in the horizontal direction. It has been proposed to increase chipping and wear resistance.

  In the cited document 3, at least a columnar TiCN layer is formed as a lower Ti compound layer, and the TiCN columnar shape is located at a distance of 1/5 of the thickness of the TiCN layer from the upper end of the TiCN layer. The ratio between the horizontal average grain size d1 of the crystal grains and the horizontal average grain size d2 of the TiCN columnar crystal grains at a position 2/5 of the thickness of the TiCN layer from the lower end of the TiCN layer is 1 ≦ By setting d1 / d2 ≦ 1.3 and further d1 = 0.2 to 1.5 μm, both wear resistance and fracture resistance are excellent, and fracture resistance in long-time cutting including intermittent cutting It has been proposed to improve wear resistance.

Furthermore, in the cited document 4, in a coated tool having at least a TiCN layer and an Al ₂ O ₃ layer as a hard coating layer, the TiCN layer is composed of a lower TiCN layer and an upper TiCN layer, and the thickness of the lower TiCN layer t1 is 1 μm ≦ t1 ≦ 10 μm, the film thickness t2 of the upper TiCN layer is 0.5 μm ≦ t2 ≦ 5 μm, and satisfies the relationship of 1 <t1 / t2 ≦ 5. Further, TiCN particles of the upper TiCN layer The average crystal width w2 is 0.2 to 1.5 μm, and the average crystal width w1 of the TiCN particles of the lower TiCN layer is 0.7 times or less of w2, thereby improving the adhesion of the hard coating layer, It has been proposed to prevent delamination and improve fracture resistance and wear resistance in intermittent cutting and the like.

JP-A-7-285001 Japanese Patent Laid-Open No. 10-15711 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 with this, the coated tool has come to be used under more severe conditions. Even when a coated tool is used for high-speed heavy cutting with high heat generation and high load acting on the cutting edge, the toughness of the lower layer is not sufficient. The current situation is that chipping tends to occur on the blade, and as a result, the service life is reached in a relatively short time.

  In view of the above, the present inventors, from the above viewpoint, have high toughness and resistance to hard coating even when used in high-speed heavy cutting with high heat generation and high load acting on the cutting edge. As a result of diligent research on a coated tool that has chipping properties and exhibits excellent wear resistance over a long period of use, the following knowledge was obtained.

  That is, the present inventors have determined that the grain structure of the hard coating layer of the coated tool, in particular, the Ti carbonitride (hereinafter referred to as TiCN) layer of the Ti compound constituting the lower layer is a columnar structure. A lower layer composed of a Ti compound layer is formed as a mixed structure of a fine-grained structure, and further, the columnar structure and the fine-grained structure are constituted as a crystal grain-structured structure that appears alternately and periodically in the layer thickness direction. It has been found that the toughness and chipping resistance of the hard coating layer composed of the lower layer and the upper layer can be improved without impairing the inherent properties of.

  And the TiCN layer (henceforth a modified TiCN layer) which has the said crystal grain structure can be formed into a film by the following chemical vapor deposition methods, for example.

For example, after depositing a TiN layer as one of the Ti compound layers constituting the lower layer on the tool base surface,
(A) A TiCN layer is deposited on the TiN layer using a TiCl ₄ —CH ₃ CN—N ₂ —H ₂ -based reactive gas,
(B) In the film forming process of (a), the introduction of the reactive gas is stopped, and at the same time, SF ₆ -based gas is introduced to perform SF ₆ etching,
(C) Next, the step (a) and the step (b) are repeated to form a TiCN layer having a target thickness.

  According to the above (a) to (c), a modified TiCN layer is formed as one of the Ti compound layers constituting the lower layer. When the microstructure of the modified TiCN layer is observed with a transmission electron microscope, It is confirmed that a crystal grain structure is formed which is composed of a mixed structure of a columnar structure and a fine grain structure, and in which the columnar structure and the fine grain structure appear periodically and alternately in the layer thickness direction.

  Then, the coated tool of the present invention in which the modified TiCN layer having the grain structure is deposited as at least one of the Ti compound layers constituting the lower layer of the hard coating layer is accompanied by high heat generation, and Even when used for high-speed heavy cutting of steel or cast iron where a high load acts on the cutting edge, the hard coating layer has excellent toughness and chipping resistance, and also exhibits excellent wear resistance over a long period of use. I found out.

This invention has been made based on the above findings,
“(1) On the surface of a tool base made of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet,
(A) The lower layer includes a Ti compound layer including at least a Ti carbonitride layer and having a total average layer thickness of 3 to 20 μm,
(B) the upper layer is an aluminum oxide layer having an average layer thickness of 1 to 25 μm;
In the surface-coated cutting tool obtained by chemical vapor deposition of the hard coating layer comprising the above (a) and (b),
The grain structure in which at least one Ti carbonitride layer constituting the lower layer of (a) has an average grain size that periodically changes in a cycle of 0.5 μm to 5 μm along the film thickness direction. A surface-coated cutting tool characterized by comprising:

  (2) The Ti compound layer of the above (a) includes at least one Ti carbonitride layer and one or two of a Ti carbide layer, a nitride layer, a carbonate layer, and a carbonitride layer. The surface-coated cutting tool according to the above (1), comprising a layer or more.

(3) At least one Ti carbonitride layer constituting the lower layer of the above (a) is divided into 0.02 μm thick width regions parallel to the tool base surface, and grains existing in the thick width regions When the number of boundaries is measured, and the reciprocal of the number of grain boundaries per 1 μm is defined as the average particle diameter D, the change in the average particle diameter D of each thickness width region along the film thickness direction is obtained.
A thickness width region having an average particle diameter D of 0.5 to 1.5 μm and a thickness width region having an average particle diameter D of 0.05 to 0.3 μm are alternately arranged along the film thickness direction of the layer. By forming at least a plurality of regions, the average particle diameter D of at least one Ti carbonitride layer constituting the lower layer is periodically in a cycle of 0.5 μm to 5 μm along the film thickness direction. The surface-coated cutting tool according to (1) or (2), wherein the surface-coated cutting tool has a changing grain structure. "
It has the characteristics.

The present invention will be described in detail below.
Lower Ti compound layer:
Ti compound of one or more of Ti carbide (TiC) layer, nitride (TiN) layer, carbonitride (TiCN) layer, carbonate (TiCO) layer and carbonitride oxide (TiCNO) layer The lower layer consisting of layers can be formed under normal chemical vapor deposition conditions.

Since the lower layer made of the Ti compound itself has high temperature strength, the hard coating layer has high temperature strength due to the presence of the lower layer, and the upper layer made of the tool base and Al ₂ O ₃ It adheres firmly to both, and thus has the effect of contributing to improved adhesion of the hard coating layer to the tool substrate.

However, if the total average layer thickness of the lower layer is less than 3 μm, the above-mentioned effect cannot be sufficiently exerted. On the other hand, if the total average layer thickness exceeds 20 μm, chipping is likely to occur. The layer thickness was determined to be 3-20 μm.
Lower layer modified TiCN layer:
In the present invention, at least one of the Ti compound layers constituting the lower layer is the modified TiCN layer having a crystal grain structure in which a columnar structure and a fine grain structure appear alternately and periodically. Form.

  Of course, the modified TiCN layer may be formed not only in the lower layer but in a plurality of layers in the lower layer.

  In the modified TiCN layer of the present invention, when the grain structure is observed along the layer thickness direction, the average grain diameter D of the modified TiCN layer is periodic with a period of 0.5 μm to 5 μm along the layer thickness direction. More specifically, the modified TiCN layer is divided into 0.02 μm thickness width regions parallel to the tool base surface and exists in the thickness width region. When the number of grain boundaries was measured and the change in the average grain diameter D of each thickness width region along the layer thickness direction was determined by taking the reciprocal of the number of grain boundaries per 1 μm as the average grain diameter D, the average grain diameter D Thickness range of 0.5 to 1.5 μm and thickness range of average particle size D of 0.05 to 0.3 μm are alternately at least along the thickness direction of the modified TiCN layer. It has a crystal grain structure formed in a plurality of regions.

And the toughness as the whole hard coating layer improves by forming the modified TiCN layer which has such a crystal grain structure at least in the lower layer which consists of Ti compounds, and, as a result, hard The chipping resistance and wear resistance of the coating layer can be improved.
Deposition of modified TiCN layer:
The modified TiCN layer of the present invention can be formed as at least one lower layer composed of a Ti compound layer formed under normal chemical vapor deposition conditions.
For example, using normal chemical vapor deposition equipment,
Reaction gas composition (volume%):
TiCl ₄ : 4-5%,
N _2: 30~40%,
H ₂ : residual reaction atmosphere temperature: 1020 to 1060 ° C.
Reaction atmosphere pressure: 10-30 kPa,
After depositing a TiN layer having a predetermined thickness under the conditions of
(A) On the surface of the TiN layer,
Reaction gas composition (volume%):
TiCl _4: 1~3%,
CH ₃ CN: 0.5~1.0%,
N _2: 5~15%,
H ₂ : residual reaction atmosphere temperature: 900 to 950 ° C.
Reaction atmosphere pressure: 5 to 20 kPa,
(B) Next, the introduction of the reactive gas is stopped, and instead, SF ₆ gas is added so that the gas composition is 0.1 to 2% by volume. H ₂ gas was introduced, and this SF ₆ gas was used for the following conditions:
Reaction gas composition (volume%):
SF ₆ : 0.1 to 2%,
H ₂ : residual reaction atmosphere temperature: 800 to 1050 ° C.
Reaction atmosphere pressure: 5 to 20 kPa,
The SF ₆ etching is performed for 5 to 30 minutes under the above conditions.
(C) Next, the introduction of the SF ₆ -based gas is stopped, the reaction gas (a) is introduced into the apparatus, and a TiCN layer is formed again by vapor deposition under the same conditions as (a).

  The above steps (b) and (c) are repeated, and finally a modified TiCN layer having a target layer thickness is formed by vapor deposition.

Thereafter, a Ti compound layer required as a lower layer is formed to form a lower layer having a target layer thickness, and an Al ₂ O ₃ layer, which is an upper layer, is deposited on the upper layer by vapor deposition. By doing so, a hard coating layer is formed.
Grain structure of the modified TiCN layer:
FIG. 1 shows a schematic diagram of the crystal grain structure of the modified TiCN layer of the present invention formed under the above chemical vapor deposition conditions.

  As shown in FIG. 1, in the modified TiCN layer of the present invention, columnar TiCN grains are formed in a plurality of stages in the layer thickness direction, and at the boundaries between the upper and lower columnar TiCN grains in each stage, It has a structure in which fine-grained TiCN grains are accumulated.

  FIG. 2 shows a distribution diagram of average particle diameters in the modified TiCN layer having the grain structure of the present invention formed under the above chemical vapor deposition conditions.

  The distribution chart of the average particle diameter can be obtained by the following method.

  First, the modified TiCN layer is divided into 0.02 μm thickness width regions in parallel with the tool base surface (in FIG. 3, the sections partitioned by a plurality of parallel lines drawn parallel to the tool base surface are This corresponds to a thickness width region of 0.02 μm.) The number n of grain boundaries existing in each divided thickness width region was measured over a total of 10 μm with a transmission electron microscope (magnification 50000 times), and this n was 1 μm. It is converted into the number N (= n / 10) per grain boundary, the reciprocal of the converted value is obtained as the average particle diameter D (= 1 / N), and the average particle diameter D obtained in each thickness width region is the layer. By making a graph along the thickness direction, a layer thickness direction average particle size distribution diagram shown as FIG. 2 is created.

  And according to the grain structure of the modified TiCN layer of this invention, the thickness width in which the value of the average particle diameter D is in the range of 0.5 to 1.5 μm in the layer thickness direction average particle size distribution diagram At least a plurality of regions are formed periodically and alternately along the thickness direction of the modified TiCN layer along the thickness direction of the modified TiCN layer with the average particle diameter D being in the range of 0.05 to 0.3 μm. The

  For example, in FIG. 2, four thickness width regions in which the average particle diameter D is in the range of 0.5 to 1.5 μm are formed in the layer thickness direction, and the average particle diameter D is 0. Three thickness width regions in the range of 0.05 to 0.3 μm are formed in the layer thickness direction.

  And from this layer thickness direction average grain size distribution chart, in the modified TiCN layer of the present invention, a grain structure in which the average grain size of TiCN crystal grains periodically changes along the layer thickness direction is formed. I understand.

  In this invention, the period of change of the average particle diameter of TiCN was set to 0.5 μm to 5 μm because the period is too short when the period is less than 0.5 μm, and therefore the excellent toughness and excellent resistance to resistance of the periodic structure. This is because the chipping characteristics cannot be sufficiently exhibited, and on the other hand, when the period is 5 μm or more, the period becomes too long and the characteristics of the periodic structure cannot be sufficiently exhibited.

  In the present invention, the upper limit range of the average particle diameter D is determined to be within the range of 0.5 to 1.5 μm. When the average particle diameter is less than 0.5 μm, the difference from the average particle diameter D of the lower limit range is small This is because the characteristics of the periodic structure cannot be fully exhibited due to being too large, and on the other hand, when the thickness is 1.5 μm or more, coarse grains are formed and high toughness cannot be maintained.

  Further, the lower limit range of the average particle diameter D is determined to be in the range of 0.05 to 0.3 μm. When the average particle diameter D is less than 0.05 μm, the inter-particle strain of TiCN in the thickness width region increases and the modification This is because the high toughness of TiCN cannot be maintained due to a decrease in the adhesion of particles in the TiCN layer, while high toughness cannot be maintained due to coarse grains when the particle size is 0.3 μm or more.

In the present invention, in the lower layer of the hard coating layer, as at least one modified TiCN layer, thickness width regions in which the average particle diameter D is within the above upper limit range and the above lower limit range appear alternately and periodically. Since it has a crystal grain structure to be produced, the high-temperature hardness of the upper layer of the Al ₂ O ₃ layer is high, even in high-speed heavy cutting with high heat generation and high load acting on the cutting edge. The excellent toughness and chipping resistance of the hard coating layer as a whole can be exhibited without impairing the heat resistance.
Upper layer Al ₂ O ₃ layer:
It is well known that the Al ₂ O ₃ layer constituting the upper layer has high-temperature hardness and heat resistance, but the average layer thickness of the upper layer made of the Al ₂ O ₃ layer of the present invention is less than 1 μm. In this case, the wear resistance over a long period of use cannot be ensured. On the other hand, if the average layer thickness exceeds 25 μm, the Al ₂ O ₃ crystal grains are likely to be coarsened. In addition to the decrease in high temperature strength, the chipping resistance at the time of high speed heavy cutting will decrease, so the average layer thickness was set to 1 to 25 μm.

In the coated tool of the present invention, as a hard coating layer, a lower layer made of a Ti compound layer and an upper layer made of an Al ₂ O ₃ layer are coated, and an average particle diameter of TiCN is formed as at least one of the lower layers. By forming a modified TiCN layer having a grain structure that periodically changes along the layer thickness direction, high heat generation occurs in steel, cast iron, etc., and a high load acts on the cutting edge. Even when used for high-speed heavy cutting, excellent toughness and chipping resistance are obtained. As a result, excellent wear resistance is exhibited over a long period of use, and the life of the coated tool is extended.

The schematic model figure of the crystal grain structure structure of the modified TiCN layer of this invention is shown. The average particle size distribution map of the layer thickness direction about the modified TiCN layer which has a crystal grain structure structure of this invention is shown. The schematic diagram of the state which partitioned the modified TiCN layer of this invention into the thickness width area | region of 0.02 micrometer with the several (imaginary) parallel line drawn | parallel with the tool base | substrate surface is shown.

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

WC powder, TiC powder, ZrC powder, VC powder, TaC powder, NbC powder, Cr ₃ C ₂ powder, TiN powder, TaN powder, and Co powder all having an average particle diameter of 1 to 3 μm are prepared as raw material powders. These raw material powders were blended into the composition shown in Table 1, added with wax, ball milled in acetone for 24 hours, dried under reduced pressure, and pressed into a green compact with a predetermined shape at a pressure of 98 MPa. The green compact was vacuum sintered at a predetermined temperature in the range of 1370 to 1470 ° C. for 1 hour in a vacuum of 5 Pa. After sintering, the cutting edge portion was R: 0.07 mm honing By processing, tool bases A to E made of WC base cemented carbide having an insert shape specified in ISO · CNMG190612 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 standard / CNMG190612 insert shapes 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,
As a lower layer of the hard coating layer, a Ti compound layer is formed by vapor deposition under the conditions shown in Table 3 and the target layer thickness shown in Table 5.

  However, in forming the Ti compound layer, at least one of them is formed by vapor deposition of the modified TiCN layer under the conditions shown in Table 4.

The modified TiCN layer is
(A) First, a TiCN layer is formed under the film forming conditions shown in Table 4,
(B) Next, under the conditions shown in Table 4, the formed TiCN layer was etched by SF ₆ for a predetermined time,
(C) The above steps (a) and (b) are repeated until a modified TiCN layer having a predetermined thickness is obtained.

After forming a lower layer having a predetermined thickness by vapor deposition, an Al ₂ O ₃ layer, which is an upper layer of the hard coating layer, is formed by vapor deposition with a target layer thickness shown in Table 5 under the conditions shown in Table 3.

  The coated tools 1 to 15 of the present invention were manufactured by vapor-depositing a hard coating layer composed of a lower layer and an upper layer shown in Table 5 by the vapor deposition.

  The modified TiCN layers of the above-mentioned coated tools 1 to 15 of the present invention were observed over a plurality of visual fields using a transmission electron microscope (magnification 50000 times). As a result, the crystal grain structure shown in the schematic diagram of FIG. Was observed.

  Similarly, using a transmission electron microscope (magnification of 50000 times), the modified TiCN layer of the present coated tool 1 to 15 in the thickness width region of 0.02 μm in the layer thickness direction as shown in FIG. The number of grain boundaries present in the thickness width region is measured, and the average particle size D is the reciprocal of the number of grain boundaries per 1 μm. The change in the average particle size D of each thickness width region along the layer thickness direction The average particle diameter distribution chart shown in FIG. 2 was created with the horizontal axis representing the average particle diameter D and the vertical axis representing the depth in the layer thickness direction.

  In FIG. 2, the maximum value of the average particle diameter D in the thickness width region where the average particle diameter D is between 0.5 and 1.5 μm is the maximum value Dmax of the average particle diameter, while the average particle diameter D is The minimum value of the average particle diameter D in the thickness width region between 0.05 and 0.3 μm is set as the minimum value Dmin of the average particle diameter, and Dmax and Dmin are obtained from the average particle diameter distribution chart created as FIG. Furthermore, the distance between Dmax that appears periodically along the layer thickness direction was determined as the period C at which the micropore density changes.

  Table 6 shows the values of the maximum value Dmax, the minimum value Dmin, and the period C for the modified TiCN layer.

For comparison purposes, a Ti compound layer as a lower layer of the hard coating layer on the surfaces of the tool bases A to E and the tool bases a to e under the conditions shown in Table 3 and the target layer thickness shown in Table 7 Comparative coating tools 1 to 10 having TiCN layers shown in Table 7 were prepared by vapor-depositing Al ₂ O ₃ layers as upper layers. (The comparative coated tools 1 to 10 do not form a modified TiCN layer.)
Further, the Ti compound layer as the lower layer of the hard coating layer and the Al ₂ O ₃ layer as the upper layer are formed by vapor deposition under the conditions shown in Table 3 and the target layer thickness shown in Table 7. Comparative coated tools 11 to 15 having the TiCN layer shown in Table 7 were produced by forming a modified TiCN layer in which the average particle size of TiCN changes under the conditions shown in Table 4 in the part.

  The average particle diameter of TiCN was measured for the TiCN layer of the comparative coated tools 1 to 10 and the modified TiCN layer of the comparative coated tools 11 to 15 using a transmission electron microscope (magnification 50000 times).

  For the comparative coated tools 1 to 10, the average particle size of TiCN was almost uniform average particle size without any significant difference in the layer thickness direction.

  Table 8 shows the average particle size values that are uniform over the entire layer thickness direction for the comparative coated tools 1-10.

  For the comparative coated tools 11-15, the change in the average particle diameter over the layer thickness direction was measured as in the case of the inventive coated tools 1-15.

  Table 8 shows values of the maximum value Dmax, the minimum value Dmin, and the period C obtained for the comparative coated tools 11 to 15.

  Moreover, when the layer thickness of each component layer of this invention coated tool 1-15 and comparative coated tool 1-15 was measured using the scanning electron microscope, all are the target layer thickness shown in Table 5, Table 7, and It showed substantially the same average layer thickness.

Next, a cutting test was performed on the above-described inventive coated tools 1 to 15 and comparative coated tools 1 to 15 under the conditions shown in Table 9, and the flank wear width of the cutting edge was measured in any cutting test.

  Table 10 shows the measurement results.

From the results shown in Tables 5 to 10, in the coated tool of the present invention, as the lower layer of the hard coating layer, the average particle diameter of at least one modified TiCN is periodically 0.5 μm to 5 μm along the layer thickness direction. Even when used in high-speed heavy cutting where high load is applied to the cutting edge due to the high heat generation of steel, cast iron, etc. due to the periodically changing crystal grain structure structure, It is clear that the chipping property is excellent, and as a result, excellent wear resistance is exhibited over a long period of use.

  On the other hand, the comparative coating tools 1 to 10 in which the lower layer TiCN has a substantially uniform average particle diameter, and the comparative coating tools 11 to 15 having a grain structure outside the scope of the present invention are accompanied by high heat generation. Moreover, when used for high-speed heavy cutting in which a high load acts on the cutting edge, it is clear 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 exhibits excellent toughness and chipping resistance in high-speed heavy cutting with high heat generation such as steel and cast iron, and high load acting on the cutting edge, Although the service life can be extended, it is of course possible to use not only high-speed heavy cutting conditions but also high-speed cutting conditions and high-speed intermittent cutting conditions.

Further, in the cited document 2, in the lower layer in which the first layer in contact with the substrate is TiN and the second layer is TiCN, the thickness of the second layer is 60% or more of the total thickness, and the particles The average particle size in the horizontal direction is 0.3 to 1.2 μm, and the average particle size in the vertical direction is 2.5 times or more than the average particle size in the horizontal direction. It has been proposed to increase chipping and wear resistance.

Thereafter, a Ti compound layer required as a lower layer is formed to form a lower layer having a target layer thickness, and an Al ₂ O ₃ layer, which is an upper layer, is deposited on the upper layer by vapor deposition. By doing so, a hard coating layer is formed.
Grain structure of the modified TiCN layer:
Figure 1 shows a schematic view of a grain structure structure of the modified TiCN layer of the invention formed by the chemical vapor deposition conditions.

Further, the lower limit range of the average particle diameter D is determined to be in the range of 0.05 to 0.3 μm. When the average particle diameter D is less than 0.05 μm, the inter-particle strain of TiCN in the thickness width region increases and the modification This is because the high toughness of the TiCN layer cannot be maintained due to a decrease in the adhesion of the particles in the TiCN layer , while the high toughness cannot be maintained due to coarse grains when the particle size is 0.3 μm or more.

It shows a schematic view of a grain structure structure of the modified TiCN layer of the present invention. The average particle size distribution map of the layer thickness direction about the modified TiCN layer which has a crystal grain structure structure of this invention is shown. The modified TiCN layer of this invention is divided into 0.02 μm thickness width regions by a plurality of (virtual) parallel lines drawn in parallel to the tool base surface, and a schematic view of the partitioned state is shown.

As raw material powders, both prepared WC powder, TiC powder having an average particle size of 1 to 3 [mu] m, ZrC powder, VC powder, TaC powder, NbC powder, Cr ₃ C ₂ powder, TiN powder, your and Co powder, These raw material powders were blended in the blending composition shown in Table 1, added with wax, mixed in a ball mill for 24 hours in acetone, dried under reduced pressure, and then press-molded into a green compact of a predetermined shape at a pressure of 98 MPa, This green compact was vacuum sintered in a vacuum of 5 Pa at a predetermined temperature within a range of 1370 to 1470 ° C. for 1 hour, and after sintering, the cutting edge was subjected to a honing process of R: 0.07 mm. By applying, tool bases A to E made of a WC-base cemented carbide having an insert shape specified in ISO · CNMG190612 were produced.

In FIG. 2, the maximum value of the average particle diameter D in the thickness width region where the average particle diameter D is between 0.5 and 1.5 μm is the maximum value Dmax of the average particle diameter, while the average particle diameter D is The minimum value of the average particle diameter D in the thickness width region between 0.05 and 0.3 μm is set as the minimum value Dmin of the average particle diameter, and Dmax and Dmin are obtained from the average particle diameter distribution chart created as FIG. Further, the distance between Dmax that appears periodically along the layer thickness direction was determined as a period C in which the average particle diameter changes.

Claims (3)

On the surface of the tool base composed of tungsten carbide based cemented carbide or titanium carbonitride based cermet,
(A) The lower layer includes a Ti compound layer including at least a Ti carbonitride layer and having a total average layer thickness of 3 to 20 μm,
(B) the upper layer is an aluminum oxide layer having an average layer thickness of 1 to 25 μm;
In the surface-coated cutting tool obtained by chemical vapor deposition of the hard coating layer comprising the above (a) and (b),
The grain structure in which at least one Ti carbonitride layer constituting the lower layer of (a) has an average grain size that periodically changes in a cycle of 0.5 μm to 5 μm along the film thickness direction. A surface-coated cutting tool characterized by comprising:   The Ti compound layer of (a) includes at least one Ti carbonitride layer and one or more of Ti carbide layer, nitride layer, carbonate layer and carbonitride layer. The surface-coated cutting tool according to claim 1, comprising: The at least one Ti carbonitride layer constituting the lower layer of (a) is divided into a 0.02 μm thick width region parallel to the tool base surface, and the number of grain boundaries existing in the thick width region When the change of the average particle diameter D of each thickness width region along the film thickness direction is determined with the inverse of the number of grain boundaries per 1 μm being the average particle diameter D,
A thickness width region having an average particle diameter D of 0.5 to 1.5 μm and a thickness width region having an average particle diameter D of 0.05 to 0.3 μm are alternately arranged along the film thickness direction of the layer. By forming at least a plurality of regions, the average particle diameter D of at least one Ti carbonitride layer constituting the lower layer is periodically in a cycle of 0.5 μm to 5 μm along the film thickness direction. The surface-coated cutting tool according to claim 1, wherein the surface-coated cutting tool has a changing grain structure.