JP5569739B2 - Surface coated cutting tool with excellent chipping resistance - Google Patents

Description

  In the present invention, for example, even when a work material such as steel or cast iron is machined under high-speed intermittent cutting conditions with high heat generation, the hard coating layer has excellent interlayer adhesion strength, so that the chipping ( The present invention relates to a surface-coated cutting tool (hereinafter referred to as a coated tool) that exhibits excellent cutting performance over a long period of time without occurrence of microchips.

Conventionally, the surface of a tungsten carbide-based cemented carbide substrate (hereinafter referred to as a cemented carbide substrate) or a TiCN-based cermet substrate (hereinafter referred to as a cermet substrate. The cemented carbide substrate and the cermet substrate are collectively referred to as a tool substrate). In addition,
(A) a Ti compound layer composed of one or more of a TiC layer, a TiN layer, a TiCN layer, a TiCO layer, and a TiCNO layer having a total average layer thickness of 3 to 20 μm,
(B) an aluminum oxide (hereinafter referred to as Al ₂ O ₃ ) layer having an average layer thickness of 1 to 15 μm and having an α-type crystal structure in a state where the upper layer is formed by chemical vapor deposition;
A coated tool in which a hard coating layer composed of the above (a) and (b) is formed by vapor deposition is widely known (for example, Patent Document 1), and this coated tool has excellent resistance to cutting in steel or cast iron. It is known to exhibit wear.
Also known is a coated tool in which the particle width of the TiCN layer constituting the lower layer of the hard coating layer is 0.01 to 0.5 μm in order to improve the fracture resistance, impact resistance, wear resistance, etc. of the coated tool. (For example, Patent Document 2).

Japanese Patent Publication No. 50-14237 JP 2007-260851 A

In recent years, there has been a strong demand for labor saving and energy saving of cutting work, and along with this, cutting work is becoming increasingly faster and more efficient. On the other hand, hard coating is required in order to extend the tool life. Although a thicker layer is also required, high-speed intermittent cutting of steel or cast iron is performed using a conventional coated tool in which a hard coating layer consisting of a Ti compound layer as a lower layer and an Al ₂ O ₃ layer as an upper layer is formed. If it does, micro chipping, delamination, etc. will occur in the hard coating layer, and the present situation is that the service life is reached in a relatively short time due to this.

  Therefore, as a result of intensive studies on the layer structure of the hard coating layer in order to improve the chipping resistance and peel resistance of the coated tool, the present inventors have obtained the following knowledge.

Of the hard coating layer of the coated tool, the lower layer made of a Ti compound layer formed of one or more of the TiC layer, TiN layer, TiCN layer, TiCO layer and TiCNO layer is itself provided. Excellent high-temperature strength contributes to improving the high-temperature strength of the hard coating layer, and the upper layer composed of the Al ₂ O ₃ layer has excellent oxidation resistance and thermal stability and has high hardness, but generates high heat. Accordingly, in high-speed intermittent cutting in which a high load acts on the cutting edge, the adhesion strength between the lower layer and the upper layer is not sufficient, which causes micro chipping and delamination.
Therefore, in order to increase the adhesion strength between the lower layer and the upper layer, many experiments were conducted to improve the adhesion interface region of both layers. As a result, the crystal grain structure at the interface between the lower layer and the upper layer was improved. By doing so, it has been found that the interface adhesion strength between the lower layer and the upper layer can be increased.
Specifically, the average particle diameter of the crystal grains of the Ti compound layer immediately below the Al ₂ O ₃ layer is 0.5 μm or less, and the crystal grains on the lower layer side existing at the interface where the lower layer and the upper layer are adjacent to each other The lower layer and the upper layer are deposited so that the ratio b / a of the number a of (Ti compound) and the number b of crystal grains (Al ₂ O ₃ ) on the upper layer side satisfies 4 ≦ b / a ≦ 20. When formed, the strain generated at the interface between the lower layer and the upper layer is alleviated, so that the interlayer adhesion at the lower layer-upper layer interface is enhanced.
As a result, even in high-speed intermittent cutting with high heat generation and high load acting on the cutting edge, it is possible to exhibit excellent wear resistance over a long period of use without occurrence of chipping and peeling. Was found.

The present invention has been made based on the above findings,
“A hard surface composed of a lower layer having a total average layer thickness of 3 to 20 μm and an upper layer having an average layer thickness of 1 to 15 μm on the surface of a tool base made of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet In the surface-coated cutting tool in which the coating layer is formed by vapor deposition,
The lower layer is composed of one or more Ti compound layers of Ti carbide layer, nitride layer, carbonitride layer, carbonate layer and carbonitride oxide layer, and the upper layer is oxidized A ratio b / a between the number a of crystal grains on the Ti compound layer side and the number b of crystal grains on the aluminum oxide layer side, which is made of an aluminum layer and exists at an interface where the lower layer and the upper layer are adjacent to each other, 4. A surface-coated cutting tool characterized by satisfying 4 ≦ b / a ≦ 20 and further having an average particle size of crystal grains of the Ti compound layer immediately below the aluminum oxide layer of 0.5 μm or less. "
It has the characteristics.

Below, the hard coating layer of the coating tool of this invention is demonstrated in detail.
(A) Lower layer (Ti compound layer)
Ti composed of one or more of Ti carbide (TiC) layer, nitride (TiN) layer, carbonitride (TiCN) layer, carbonate (TiCO) layer and carbonitride oxide (TiCNO) layer The compound layer exists as a lower layer of the hard coating layer and contributes to the improvement of the high temperature strength of the hard coating layer by its excellent high temperature strength. However, when the total average layer thickness is less than 3 μm, the above-described effect is sufficiently obtained. On the other hand, if the total average layer thickness exceeds 20 μm, it becomes easy to cause thermoplastic deformation especially in high-speed intermittent cutting with high heat generation, which causes uneven wear. The thickness was determined to be 3 to 20 μm.
Moreover, when the average particle diameter of the crystal grains of the Ti compound layer immediately below the upper layer (Al ₂ O ₃ layer) exceeds 0.5 μm, the upper layer (Al ₂ O ₃ layer) and the upper layer Al ₂ O ₃ layer immediately below Since the adhesion between the Ti compound layer and the chipping resistance deteriorates, the average particle size of the crystal grains of the Ti compound layer immediately below the upper layer (Al ₂ O ₃ layer) was determined to be 0.5 μm or less.
Here, the average particle diameter refers to a crystal grain of a crystal grain of the Ti compound layer immediately below the Al ₂ O ₃ layer by drawing a line over 50 μm in a direction parallel to the surface of the carbide substrate by cross-sectional observation with a transmission electron microscope. The number of intersections with the field was counted, and the particle size was determined from the average of the lengths of the line segments.

(B) Upper layer (Al ₂ O ₃ layer)
The Al ₂ O ₃ layer constituting the upper layer is excellent in high-temperature hardness and heat resistance, and maintains wear resistance as a basic role in high-speed intermittent cutting with high heat generation.
For example, the Al ₂ O ₃ deposition pretreatment is performed on the surface of the lower layer made of the Ti compound layer by the following procedure, and then the Al ₂ O ₃ layer is formed under normal conditions, thereby satisfying the conditions defined in the present invention. A satisfactory Al ₂ O ₃ layer can be formed.
The Al ₂ O ₃ pre-deposition treatment consists of the following four stages:
First,
<< First stage >>
Reaction gas (volume%): AlCl ₃ 0.5-2%, balance Ar,
Atmospheric pressure: 30-100 Torr,
Processing temperature: 750 to 1000 ° C.
Processing time: 1-3 min. ,
After surface modification of the lower layer under the conditions of
<< Second stage >>
Atmospheric pressure: 30-100 Torr,
Atmospheric temperature: 750-1000 ° C.
In this state, the gas in the furnace is purged with Ar gas for 1 to 3 minutes.
《Third stage》
Reaction gas (volume%): CO ₂ 1-10%, balance Ar,
Atmospheric pressure: 30-100 Torr,
Processing temperature: 750 to 1000 ° C.
Processing time: 5-20 min. ,
The oxidation treatment is performed under the conditions (however, the content ratio of CO _{2 in} the reaction gas is gradually reduced as time passes)
<< Fourth Stage >>
Atmospheric pressure: 30-100 Torr,
Atmospheric temperature: 750-1000 ° C.
In this state, the furnace gas is purged with Ar gas for 1 to 3 minutes.

After _Al 2 _{O 3} deposition pretreatment of the four steps, by depositing _{the Al} 2 _{O 3} layer in a conventional film forming method, _{the Al} 2 _{O 3} layer which satisfies the conditions defined by the present invention, i.e. The number a of Ti compound crystal grains on the lower layer side and the upper layer side existing at the interface between the lower layer (Ti compound layer) and the upper layer (Al ₂ O ₃ layer) in a cross section perpendicular to the tool base surface When the ratio b / a to the number b of Al ₂ O ₃ crystal grains is determined, an upper layer having an interface configuration in which b / a is 4 or more and 20 or less can be formed by vapor deposition.
Here, the number a of Ti compound crystal grains on the lower layer side existing at the interface between the lower layer (Ti compound layer) and the upper layer (Al ₂ O ₃ layer) and the Al ₂ O ₃ crystal grain on the upper layer side The measurement of the number b is performed by measuring a cross-section by dark field observation at 50000 times using a transmission electron microscope at 10 points of the interface between the lower layer and the upper layer, and measuring a linear distance parallel to the surface of the carbide substrate. By counting each of the number of Ti compound particles having an interface with Al ₂ O ₃ particles existing in the range of 25 μm and the number of Al ₂ O ₃ particles having an interface with Ti compound particles Can be sought.
When b / a is less than 4 for the ratio b / a of the above a and b, misfit at the lower layer-upper layer interface cannot be sufficiently relaxed, whereas b / a is If it exceeds 20, the strain between particles in Al ₂ O ₃ increases and it becomes impossible to exhibit excellent interlayer adhesion. Therefore, b / a is determined to be 4 ≦ b / a ≦ 20 .
The hard coating layer of the present invention consisting of an upper layer and a lower layer having such an interface form has excellent interlaminar adhesion due to the relaxation of the interface strain, and microchipping in high-speed intermittent cutting processing. Generation and exfoliation are suppressed.
If the average layer thickness of the upper layer is less than 1 μm, the wear resistance cannot be sufficiently exhibited over a long period of use, leading to a shortened tool life, while the average layer thickness of the upper layer exceeds 15 μm. As a result, chipping, chipping, peeling, and the like are likely to occur at the cutting edge, so the average layer thickness of the upper layer was determined to be 1 to 15 μm.

The coated tool of the present invention is a hard coating layer in which a lower layer made of a Ti compound layer and an upper layer made of an Al ₂ O ₃ layer are vapor-deposited, and the lower layer present at the adjacent interface between the lower layer and the upper layer An interface structure in which the ratio b / a of the number a of the Ti compound crystal grains on the side and the number b of the Al ₂ O ₃ crystal grains on the upper layer side satisfies 4 ≦ b / a ≦ 20 ; (Al ₂ O ₃ layer) Since the average particle diameter of the crystal grains of the Ti compound layer immediately below is 0.5 μm or less, interlaminar adhesion between the lower layer and the upper layer is particularly improved. As a result, for example, steel or Even when used for high-speed interrupted cutting with high heat, such as cast iron, where the load is applied to the cutting edge, the hard coating layer has excellent interlayer adhesion strength. Excellent wear resistance over long-term use It can be.

The interface structure schematic diagram created from the transmission electron micrograph of the interface of the lower layer of this invention coated tool 6 and an upper layer, and the value of a, b, b / a are shown. The interface structure schematic diagram produced from the transmission electron micrograph of the interface of the lower layer of the conventional coating tool 8 and an upper layer, and the value of a, b, b / a are 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 2 to 4 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 F made of a WC-based cemented carbide having a throwaway tip shape defined in ISO · CNMG 160412 were produced.

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 f made of TiCN-based cermet having standard / CNMG 160412 chip shapes were formed.

Next, each of the tool bases A to F and the tool bases a to f was charged into a normal chemical vapor deposition apparatus. First, Table 3 (l-TiCN in Table 3 is disclosed in JP-A-6-8010). The combinations shown in Table 6 under the conditions shown in Table 6 are the conditions for forming the TiCN layer having the vertically elongated crystal structure described, and other conditions for forming the normal granular crystal structure. And forming a Ti compound layer as a lower layer of the hard coating layer with a target layer thickness,
Next, under the conditions shown in Table 4, the surface of the lower layer was subjected to pretreatment for deposition of Al ₂ O ₃ ,
Next, under the conditions shown in Table 3, the Al ₂ O ₃ layer is deposited as an upper layer with the combinations and target layer thicknesses shown in Table 5,
By this, this invention coated tool 1-13 was manufactured, respectively.

For the purpose of comparison, the lower layer (Ti compound layer) and the upper layer (Al) are the same as the coated tools 1 to 13 of the present invention except that the surface of the lower layer is not pre-deposited with Al ₂ O _3. by depositing form ₂ O ₃ layer) was prepared conventionally coated tool 1-13 as shown in Table 6, respectively.

Next, by the dark field observation by a transmission electron microscope (50000 times) about 10 places near the interface between the lower layer and the upper layer of the hard coating layer of the present invention coated tools 1-13 and the conventional coated tools 1-13. Cross-sectional measurement is performed, the linear distance parallel to the surface of the carbide substrate is set to a measurement width of 25 μm, the number of Ti compound particles having an interface with Al ₂ O ₃ particles existing in the range, and the Ti compound particles and the interface The number b of Al ₂ O ₃ particles possessed was counted, and the value of b / a was determined.
Table 5 shows the values of a, b, b / a obtained above.

FIG. 1 shows a schematic diagram of an interface structure created from a transmission electron micrograph of the interface between the lower layer and the upper layer of the coated tool 6 of the present invention, and values of a, b, and b / a.
FIG. 2 shows a schematic diagram of the interface structure created from a transmission electron micrograph of the interface between the lower layer and the upper layer of the conventional coated tool 8 and the values of a, b, and b / a.

In addition, with respect to the Ti compound of the lower layer of the hard coating layer of the present coated tools 1 to 13 and the conventional coated tools 1 to 13, a line is drawn over 50 μm in a direction parallel to the surface of the carbide substrate by cross-sectional observation with a transmission electron microscope. The intersection of the crystal grains of the Ti compound layer immediately below the upper layer (Al ₂ O ₃ layer) with the crystal grain boundary was counted, and the average particle diameter was determined from the average of the line segment lengths.
Table 5 shows the measured average particle diameter.

  Furthermore, when the thicknesses of the constituent layers of the hard coating layers of the present coated tools 1 to 13 and the conventional coated tools 1 to 13 were measured using a scanning electron microscope (longitudinal cross section measurement), all of the target layer thicknesses were measured. The average layer thickness (average value of 5-point measurement) was substantially the same.

Next, for the present invention coated tools 1-13 and the conventional coated tools 1-13, both are screwed with a fixing jig to the tip of the tool steel tool,
[Cutting conditions A]
Work material: JIS / SNCM420 lengthwise equal 4 round grooves with vertical grooves,
Cutting speed: 375 m / min. ,
Cutting depth: 2.4 mm,
Feed: 0.22 mm / rev. ,
Cutting time: 5 minutes
Dry high-speed intermittent cutting test of nickel chrome molybdenum steel under the conditions (normal cutting speed is 200 m / min.),
[Cutting conditions B]
Work material: JIS / FCD500 lengthwise equal length 4 round bar with groove,
Cutting speed: 365 m / min. ,
Incision: 2.45mm,
Feed: 0.31 mm / rev. ,
Cutting time: 5 minutes
Cast iron dry high-speed intermittent cutting test under the conditions (normal cutting speed is 180 m / min.),
[Cutting conditions C]
Work material: JIS / S30C lengthwise equidistant round bars with 4 vertical grooves,
Cutting speed: 370 m / min. ,
Cutting depth: 1.55mm,
Feed: 0.47 mm / rev. ,
Cutting time: 5 minutes
Carbon steel dry high-speed intermittent cutting test under normal conditions (normal cutting speed is 250 m / min.)
In each cutting test, the flank wear width of the cutting edge was measured.
The measurement results are shown in Table 7.

From the results shown in Tables 5 to 7, the coated tools 1 to 13 of the present invention have the number a of the Ti compound crystal grains on the lower layer side existing at the adjacent interface between the lower layer and the upper layer and the Al ₂ O on the upper layer side. The ratio b / a to the number b of _three crystal grains constitutes an interface structure satisfying 4 ≦ b / a ≦ 20, and the average grain size of the Ti compound layer immediately below the upper layer (Al ₂ O ₃ layer) Since the particle diameter is 0.5 μm or less, interlaminar adhesion between the lower layer and the upper layer is particularly improved, and as a result, it is used for high-speed intermittent cutting with high heat generation and high load acting on the cutting edge. Even in this case, since the hard coating layer has excellent interlayer adhesion strength, it is possible to exhibit excellent wear resistance over a long period of use without the occurrence of minute chipping or peeling on the cutting edge.
However, in the conventional coated tools 1 to 13 in which the interface structure as in the present invention is not formed between the lower layer and the upper layer of the hard coating layer, the interlayer adhesion strength of the hard coating layer under high-speed intermittent cutting conditions. Is insufficient, it is clear that micro-chipping, chipping, peeling, etc. occur in the hard coating layer and the service life is reached in a relatively short time.

  As described above, the coated tool of the present invention exhibits excellent chipping resistance and wear resistance in high-speed interrupted cutting in which a high load acts on the cutting blade with particularly high heat generation, and is used over a long period of use. Since it exhibits excellent cutting performance, high performance of the cutting device, labor saving and energy saving of cutting work, and further cost reduction can be sufficiently expected.

Claims (1)

Hard coating comprising a lower layer having a total average layer thickness of 3 to 20 μm and an upper layer having an average layer thickness of 1 to 15 μm on the surface of a tool base composed of a tungsten carbide base cemented carbide or a titanium carbonitride base cermet In a surface-coated cutting tool in which a layer is formed by vapor deposition,
The lower layer is composed of one or more Ti compound layers of Ti carbide layer, nitride layer, carbonitride layer, carbonate layer and carbonitride oxide layer, and the upper layer is oxidized A ratio b / a between the number a of crystal grains on the Ti compound layer side and the number b of crystal grains on the aluminum oxide layer side, which is made of an aluminum layer and exists at an interface where the lower layer and the upper layer are adjacent to each other, 4. A surface-coated cutting tool characterized by satisfying 4 ≦ b / a ≦ 20 and further having an average particle size of crystal grains of the Ti compound layer immediately below the aluminum oxide layer of 0.5 μm or less.

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