JP5397690B2 - Surface-coated cutting tool with excellent fracture resistance due to hard coating layer - Google Patents

Description

  This invention is also applicable to the case where the hard coating layer is composed of vertically flat TiSiN crystal grains grown in an upright direction with respect to the tool base surface, and is used under severe cutting conditions such as intermittent heavy cutting. The present invention relates to a tungsten carbide (hereinafter referred to as WC) -based cemented carbide surface-coated cutting tool (hereinafter referred to as a coated tool) that exhibits excellent chipping resistance and can extend the life of the cutting tool.

    In general, for coated tools, inserts that are detachably attached to the tip of a cutting tool for turning of work materials such as various types of steel and cast iron, and the inserts are detachably attached to be used for chamfering and grooving. An insert type end mill that performs cutting processing in the same manner as a solid type end mill used for processing and shoulder processing is known.

Further, for example, as shown in Patent Document 1, a composite nitride of Ti and Si (hereinafter referred to as TiSiN) is formed on the surface of a tool body composed of a tungsten carbide (hereinafter referred to as WC) based cemented carbide sintered body. A coating tool formed by physically vapor-depositing a hard coating layer composed of layers is widely known and used for continuous cutting and intermittent cutting of various steels and cast iron.
For example, as shown in Patent Document 2, in a coated tool obtained by physically vapor-depositing a hard coating layer made of a TiSiN layer on the surface of a tool body, the hard coating layer is a mixture of a crystalline phase and an amorphous layer. There is also known a coated tool which is formed as a structure and has improved crystal resistance and toughness while maintaining high hardness by defining the crystal grain size of the crystalline phase as 0.5 nm or more and less than 20 nm. .

Japanese Patent No. 3454428 Japanese Patent No. 4112296

  In recent years, the FA of cutting devices has been remarkable, and in addition, there are strong demands for labor saving, energy saving, cost reduction and efficiency for cutting, and with this, high-efficiency heavy cutting such as high feed and high cutting However, in the above-mentioned conventional coated tools, there is no particular problem when various steels and cast irons are machined under normal conditions, but there is a large intermittent / impact on the cutting edge. When it is used for intermittent heavy cutting with a heavy load, the cutting edge is likely to be damaged, and this causes the service life to be reached in a relatively short time.

  In view of the above, the present inventors have made the hard coating layer a TiSiN layer in order to show excellent fracture resistance even when used in intermittent heavy cutting and to extend the life of the coated tool. As a result of intensive studies focusing on the grain structure of the TiSiN layer, the following knowledge was obtained.

(A) Conventionally, when a TiSiN layer as a hard coating layer is formed on the surface of a tool base made of a WC cemented carbide, the above-mentioned tool base is applied to an arc ion plating (AIP) apparatus which is a kind of physical vapor deposition apparatus. For example,
In-apparatus heating temperature: 390 to 450 ° C.,
DC bias voltage applied to the tool base: -20 to -50V,
Cathode electrode: Ti-Si alloy,
Arc discharge current: 90-120A
Gas flow in the apparatus: nitrogen (N ₂ ) gas + argon (Ar) gas,
Nitrogen gas pressure in the apparatus: 1 to 5 Pa,
Under these conditions, a TiSiN layer (hereinafter referred to as a conventional TiSiN layer) is formed.

(B) However, the formation of the TiSiN layer is performed by, for example, mounting the tool base on an ion plating apparatus using a pressure gradient type Ar plasma gas, which is one type of physical vapor deposition apparatus shown in the schematic explanatory diagram of FIG. And
Tool substrate temperature: 360 to 450 ° C.
Evaporation source: metal Ti and metal Si,
Plasma gun discharge power: 8-15 kW,
Reaction gas flow rate: nitrogen _{(N 2)} gas 100 to 120 sccm,
Discharge gas: Argon (Ar) gas 30-60 sccm,
DC bias voltage applied to the tool base: +3 to +5 V,
Distance between Hearth and tool substrate: 950-1050 mm,
When the TiSiN layer is formed by vapor deposition under the specific conditions, the coated tool using the TiSiN layer formed as a result (hereinafter referred to as a modified TiSiN layer) as a hard coating layer is compared with the conventional coated tool having the TiSiN layer formed thereon. The present inventors have found that excellent fracture resistance is exhibited under high cutting and high feed intermittent cutting conditions.

(C) The cross-sectional structure of the modified TiSiN layer was observed with a transmission electron microscope, and as shown in the cross-sectional perspective view of FIG. In the horizontal cross section having a depth of 0.1 μm from the surface of the modified TiSiN layer, the short side is 5 to 100 nm and the aspect ratio is 3 or more. It was confirmed that certain vertically long TiSiN crystal grains were formed in a predetermined area ratio.

(D) When the hard coating layer of the surface-coated cutting tool is composed of the above-described modified TiSiN layer of the crystal grain structure, the bending resistance of the layer is increased, the plastic deformation resistance is improved, and the crystal grain boundary is complicated. Because it is formed in an intricate manner, even when cracks occur in the hard coating layer, the resistance to crack growth increases, and as a result, high feed that places a large intermittent and impact load on the cutting edge, It has been found that even when used for high-cut intermittent heavy cutting, chipping and chipping are suppressed, and excellent cutting performance is exhibited over a long period of use.

This invention has been made based on the above findings,
In a surface-coated cutting tool in which a hard coating layer composed of a TiSiN layer having an average layer thickness of 0.2 to 2 μm is physically vapor-deposited on the surface of a tungsten carbide-based cemented carbide tool base,
The TiSiN layer has a height equal to the average layer thickness, and is composed of vertically long TiSiN crystal grains grown in an upright direction with respect to the tool base surface,
Further, when the crystal grain structure in a horizontal cross section having a depth of 0.1 μm from the surface of the TiSiN layer is observed with a transmission electron microscope, the long side is 5 to 100 nm and the aspect ratio is 3 or more. A surface-coated cutting tool characterized in that flat TiSiN crystal grains exist and the total area occupied by the vertically long flat TiSiN crystal grains in the horizontal cross section is 30% or more of the total cross-sectional area. "
It has the characteristics.

  The present invention will be described below.

In the modified TiSiN layer constituting the hard coating layer of the coated tool of the present invention, the Ti component improves the high temperature strength, the Si component improves the heat resistance, and the N component acts to improve the layer strength. Therefore, the modified TiSiN layer comes to have high hardness, excellent heat resistance and strength, and contributes to improvement of wear resistance of the coated tool and extension of the tool life.
As a result of conducting numerous tests for forming a TiSiN layer by vapor deposition, the present inventors have formed a TiSiN layer on a tool substrate by ion plating using a pressure gradient type Ar plasma gun shown in FIG. The conditions for forming are, for example,
Tool substrate temperature: 390 to 450 ° C.
Evaporation source: metal Ti and metal Si,
Plasma gun discharge power: 8-15 kW,
Reaction gas flow rate: nitrogen _{(N 2)} gas 100 to 120 sccm,
Discharge gas: Argon (Ar) gas 30-60 sccm,
DC bias voltage applied to the tool base: +3 to +5 V,
Distance between Hearth and tool substrate: 950-1050 mm,
Deposition time: 30-150 min,
It has been found that when the deposition is performed under such specific conditions, a modified TiSiN layer composed of vertically long TiSiN crystal grains grown in an upright direction with respect to the tool base surface is formed.

  In addition, when the content ratio of the Si component in the modified TiSiN layer of the present invention is less than 0.01 in terms of the atomic ratio to the total amount with the Ti component (that is, 0.01> Si / (Ti + Si)), the desired heat resistance is improved. The effect cannot be expected, while if the content ratio is similarly over 0.3 (that is, Si / (Ti + Si)> 0.3), the content ratio of the Ti component becomes relatively small, which is desirable. Therefore, the Si component content is preferably 0.01 to 0.3 in terms of atomic ratio.

When the structure of the modified TiSiN layer is observed in more detail with a transmission electron microscope, as shown in the cross-sectional perspective view of FIG. 2, in the longitudinal section in the layer thickness direction of the modified TiSiN layer, the above-described vertically flat TiSiN crystal The height of the grains constitutes the layer thickness of the modified TiSiN layer.
Also, a horizontal cross section parallel to the tool base surface and at a depth of 0.1 μm from the surface of the modified TiSiN layer (that is, at a depth of 0.1 μm from the surface of the modified TiSiN layer and orthogonal to the layer thickness direction). In the plane, there are rectangular TiSiN crystal grains having a short side of 5 to 100 nm and an aspect ratio of 3 or more.
Moreover, in the horizontal cross section, the area ratio occupied by the total area of the rectangular TiSiN crystal grains is 30% or more of the total area of the horizontal cross section.

The average layer thickness of the modified TiSiN layer (same as the height of the above-mentioned vertically long plate-like TiSiN crystal grains) is greatly influenced by the film formation time, and because the film formation time is short (for example, less than 30 minutes), the TiSiN crystal grains Is less than 0.2 μm, it is inferior in wear resistance and cannot exhibit excellent cutting performance over a long period of use, while the film formation time becomes long (for example, 150 When the height of the TiSiN crystal grains exceeds 2 μm, the TiSiN crystal grains become coarse, surface smoothness is lost, and chipping is likely to occur.
Therefore, the average layer thickness of the modified TiSiN layer (= the height of the above-mentioned vertically long tabular TiSiN crystal grains) is determined to be 0.2 to 2 μm.

In addition, when the short side of the rectangular TiSiN crystal grains present in a horizontal cross section at a depth of 0.1 μm from the surface of the modified TiSiN layer is less than 5 nm, the crystal grains alone cannot maintain sufficient strength. On the other hand, if the short side exceeds 100 nm, the crystal grains become coarse and chipping is likely to occur, so the short side of the rectangular TiSiN crystal grains is determined to be 5 to 100 nm.
As used herein, the term “short side” refers to the size of individual TiSiN crystal grains present in a horizontal section at a depth of 0.1 μm from the surface of the modified TiSiN layer, measured by a transmission electron microscope. The maximum width in the direction perpendicular to the long-side direction when the line segment indicating the measured maximum diameter of each crystal grain is the long side.

In addition, if the aspect ratio of the rectangular TiSiN crystal grains present in the horizontal cross section at a depth of 0.1 μm from the surface of the modified TiSiN layer is less than 3, the bending resistance of the layer becomes small and the desired plastic deformation resistance Therefore, the aspect ratio of the rectangular TiSiN crystal grains is determined to be 3 or more.
Here, the “aspect ratio” is a value obtained by dividing the value of the long side, which is a line segment indicating the measured maximum diameter of each crystal grain, by the value of the short side.

  Also, when the area ratio of the rectangular TiSiN crystal grains present in the horizontal cross section at a depth of 0.1 μm from the surface of the modified TiSiN layer is less than 30% of the total area of the measured horizontal cross section Since the crack propagation path is not complicated and sufficient resistance to crack propagation is not obtained and chipping is likely to occur, the rectangular TiSiN crystal grain area ratio is set to 30% or more.

  The short side value, aspect ratio value, and area ratio of the rectangular TiSiN crystal grains present in the horizontal cross section at a depth of 0.1 μm from the surface of the modified TiSiN layer are included in the deposition conditions of the modified TiSiN layer. Are affected by the film formation time, the film formation temperature and the applied DC bias voltage, the film formation temperature and the applied DC bias voltage, respectively, so that the short side value, aspect ratio value and area of the rectangular TiSiN crystal grains are affected. In order to maintain the ratio within a predetermined numerical range, it is necessary to strictly adjust the deposition time, the deposition temperature, and the applied DC bias voltage among the deposition conditions.

  In the coated tool of the present invention, the modified TiSiN layer constituting the hard coating layer is composed of vertically long TiSiN crystal grains grown in an upright direction with respect to the surface of the tool substrate, and further from the surface of the modified TiSiN layer. In the horizontal cross section having a depth of 0.1 μm, the above-mentioned vertically long tabular TiSiN crystal grains having a short side of 5 to 100 nm and an aspect ratio of 3 or more exist, and the vertically long tabular TiSiN crystal grains Since the total area occupied by the crystallized structure is 30% or more of the total cross-sectional area, the bending resistance of the modified TiSiN layer is increased, the plastic deformation resistance is improved, and the cutting edge is interrupted. Even when cracks occur in the hard coating layer during intermittent feed cutting with high feed and high depth of cut that are subject to mechanical and impact loads, the As a result, in addition to excellent high-temperature hardness, heat resistance, and high-temperature strength, chipping resistance is improved, and excellent cutting performance is demonstrated over long-term use, extending tool life. Is achieved.

The schematic diagram of the ion plating apparatus using the pressure gradient type Ar plasma gun in order to vapor-deposit and form the hard coating layer (modified TiSiN layer) of the surface coating cutting tool of this invention is shown, (a) is a schematic front view, b) shows a schematic plan view. The cross-sectional perspective view of the hard coating layer which consists of a modified TiSiN layer of the surface coating cutting tool of this invention is shown. The structure photograph of the TiSiN crystal grain in the horizontal cross section of the depth of 0.1 micrometer from the surface of the modified TiSiN layer of this invention insert 1 is shown.

Next, the coated tool of the present invention will be specifically described with reference to examples.
In addition, although demonstrated centering on a covering insert here, it is applicable not only to a covering insert but to various covering tools, such as a covering end mill and a covering drill.

As raw material powders, WC powder, TiC powder, VC powder, TaC powder, NbC powder, Cr ₃ C ₂ powder, and Co powder, all having an average particle diameter of 1 to 3 μm, were prepared. And then wet-mixed with a ball mill for 72 hours, dried, and press-molded into a green compact at a pressure of 100 MPa. The green compact was vacuumed at 6 Pa at a temperature of 1400 ° C. for 1 hour. Sintering is carried out under the holding conditions, and after sintering, the tool bases 1 to 10 made of WC-base cemented carbide having an ISO standard / CNMG120212 insert shape are subjected to a honing process of R: 0.03 on the cutting edge portion. Formed.

Next, the tool bases 1 to 10 are ultrasonically cleaned in acetone and dried, and attached to the ion plating apparatus using the pressure gradient type Ar plasma gun shown in FIG. Attach metal Ti and metal Si, and first heat the interior of the apparatus to 390-450 ° C. with a heater while maintaining a vacuum of 1.0 × 10 ⁻³ Pa or less, then introduce Ar gas After a 2.3 × ¹⁰ -2 Pa and, by a 2kW the discharge power of the pressure gradient type plasma gun, by generating Ar ions in the device, to apply a bias voltage of -200V to the tool base body, said tool substrate by Ar bombardment for 10 minutes, then, after once 1 × ¹⁰ -3 Pa vacuum of about in the apparatus, the discharge power of the pressure gradient type Ar plasma gun and 12 kW, Ar gas Plasma 45 sccm, together with flowing 100sccm of nitrogen gas, maintaining the pressure in the furnace to ^{3 × 10 -2 ~6 × 10 -2} Pa, to generate steam of incident plasma beam metal Ti and metal Si evaporation source A modified TiSiN layer having a target layer thickness shown in Table 3 is vapor-deposited as a hard coating layer on the surface of the tool base fixed to 1000 mm above the evaporation source by ionization with a beam, thereby forming a coating tool of the present invention. Inventive surface-coated inserts (hereinafter referred to as inventive inserts) 1 to 10 were produced.
Table 2 shows a list of various conditions for ion plating using a pressure gradient type Ar plasma gun, which are conditions for forming the modified TiSiN layers of the inserts 1 to 10 of the present invention.

For comparison, the above-mentioned tool bases A1 to A10 are compared by depositing a conventional TiSiN layer having a target layer thickness shown in Table 5 by vapor deposition under the following conditions by a normal arc ion plating (AIP) method. Examples Surface-coated inserts (hereinafter referred to as comparative example inserts) 1 to 10 were produced.
In-apparatus heating temperature: 390 to 450 ° C.,
DC bias voltage applied to the tool base: -20 to -50V,
Cathode electrode: Ti-Si alloy,
Arc discharge current: 100-120A
In-apparatus gas: Nitrogen (N ₂ ) gas,
Nitrogen gas pressure in the apparatus: 1 to 5 Pa,
Table 4 shows a list of various conditions of arc ion plating (AIP), which are conditions for forming the conventional TiSiN layers of the comparative inserts 1 to 10.

Subsequently, the state of the crystal grain structure was observed using the transmission electron microscope about each hard coating layer of this invention insert 1-10 and comparative example insert 1-10.
Tables 3 and 5 show the observation results.
According to Table 3, in the present invention inserts 1 to 10, vertically long tabular TiSiN crystal grains having a height equal to the average layer thickness of the modified TiSiN layer are grown in an upright direction with respect to the tool base surface, When a horizontal cross section having a depth of 0.1 μm from the surface of the TiSiN layer was observed and measured using a transmission electron microscope, the short side was 5 to 100 nm, the aspect ratio was 3 or more, and the total in the horizontal cross section It was confirmed that vertically flat TiSiN crystal grains having an area of 30% or more of the total cross-sectional area were present.
FIG. 3 shows, as an example, a structural photograph of TiSiN crystal grains in a horizontal section having a depth of 0.1 μm from the surface of the modified TiSiN layer of the insert 1 of the present invention.

  On the other hand, from Table 5, in the comparative example inserts 1 to 10 in which the TiSiN layer was formed by a normal arc ion plating method, columnar TiSiN crystal grains having a height equal to the average layer thickness of the conventional TiSiN layer are Growing in the upright direction with respect to the tool base surface, a horizontal cross section 0.1 μm high from the surface of the TiSiN layer was observed and measured using a transmission electron microscope. It is understood that the presence of particles having an aspect ratio of 3 or more is not confirmed because the particles are composed of particles having a ratio of less than 2.

Next, for the above-mentioned inserts 1 to 10 and comparative example inserts 1 to 10 in the state where this is screwed to the tip of the tool steel tool with a fixing jig,
Work material: JIS · SCMnH2 lengthwise equidistant four round grooved round bars,
Cutting speed: 150 m / min. ,
Cutting depth: 3.0 mm,
Feed: 0.4 mm / rev. ,
Cutting time: 2 minutes,
Of high manganese steel under the following conditions (referred to as cutting condition 1) (normal cutting and feeding are 3 mm and 0.3 mm / rev., Respectively),
Work material: JIS · S45C lengthwise equal 4 round grooved round bars,
Cutting speed: 200 m / min. ,
Cutting depth: 3 mm,
Feed: 0.40 mm / rev. ,
Cutting time: 2 minutes,
(Continuous cutting and feeding are 3 mm and 0.20 mm / rev., Respectively)
And
In any 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 3, 5 and 6, the inserts 1 to 10 of the present invention all have a modified TiSiN layer constituting the hard coating layer having an average layer thickness of 0.2 to 2 μm, and on the tool base surface. On the other hand, a vertically long TiSiN crystal grain structure having the same height as the average layer thickness is formed in the upright direction, and in the horizontal section having a depth of 0.1 μm from the surface of the modified TiSiN layer, the short side 5-100 nm, the aspect ratio is 3 or more, the above-mentioned vertically long plate-like TiSiN crystal grains exist, and the total area occupied by the vertically long plate-like TiSiN crystal grains is 30% of the total cross-sectional area Since it has the above-mentioned crystal grain structure, the bending resistance of the modified TiSiN layer is increased, the plastic deformation resistance is improved, and the cutting blade is subjected to intermittent and impact loads. Intermittent Even when cracks occur in the hard coating layer during machining, the grain boundaries are complex and formed, so the resistance to crack growth increases, and as a result, excellent high-temperature hardness, heat resistance, In addition to the high-temperature strength, the fracture resistance is improved, the cutting performance is excellent over a long period of use, and the tool life is extended.

  On the other hand, in Comparative Example Inserts 1 to 10, the crystal grains in the conventional TiSiN layer have a low aspect ratio, the crystal grain boundaries are not formed in a complicated manner, and the resistance to the progress of cracks is weak, In intermittent cutting, it is clear that the service life is reached in a relatively short time due to defects or the like.

  As described above, in the coated tool of the present invention, the hard coating layer (modified TiSiN layer) is formed as a vertically long plate-like TiSiN crystal grain structure having a specific short diameter, aspect ratio, and area ratio. In addition to the coated inserts shown in the examples, this excellent cutting performance is not only applied to various coated tools such as coated end mills and coated drills over a long period of use. It is demonstrated.

Claims (1)

In a surface-coated cutting tool in which a hard coating layer composed of a TiSiN layer having an average layer thickness of 0.2 to 2 μm is physically vapor-deposited on the surface of a tungsten carbide-based cemented carbide tool base,
The TiSiN layer has a height equal to the average layer thickness, and is composed of vertically long TiSiN crystal grains grown in an upright direction with respect to the tool base surface,
Further, when the crystal grain structure in a horizontal cross section having a depth of 0.1 μm from the surface of the TiSiN layer is observed with a transmission electron microscope, the long side is 5 to 100 nm and the aspect ratio is 3 or more. A surface-coated cutting tool characterized in that flat TiSiN crystal grains exist and the total area occupied by the vertically long flat TiSiN crystal grains in the horizontal cross section is 30% or more of the total cross-sectional area.

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