JP2011156637A - Surface-coated cutting tool having hard coated layer that exhibits excellent chipping resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-coated cutting tool having a hard coated layer that exhibits excellent chipping resistance in interrupted heavy-duty cutting. <P>SOLUTION: In the surface-coated cutting tool, a hard coated layer including a CrAIN layer having an average layer thickness of 0.2-2 &mu;m (when its composition formula is represented by (Cr<SB>1-X</SB>Al<SB>X</SB>)N, X is preferably 0.10-0.70 by atomic ratio.) is formed on a tool base surface of WC-based cemented carbide by vapor deposition. In the surface-coated cutting tool, the CrAIN layer has a height equal to the average layer thickness, and comprises oblong flat plate-shaped CrAIN crystal grains grown perpendicularly to the tool base surface. When a crystal grain structure in a horizontal cross-section at the depth of 0.1 &mu;m from the surface of the CrAIN layer is observed, the area ratio of the oblong flat plate-shaped CrAIN crystal grains each having a short side of 5-100 nm and an aspect ratio of 3 or more is 30% or more of the total horizontal cross-sectional area. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  Even when the hard coating layer is used under severe cutting conditions such as intermittent heavy cutting because the hard coating layer is composed of vertically long CrAlN crystal grains grown in an upright direction with respect to the tool base surface. 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 Cr and Al (hereinafter referred to as CrAlN) 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 a layer is known, and is used for continuous cutting and intermittent cutting of various steels and cast iron.
Also, for example, as shown in Patent Document 2, in a coated tool formed by physical vapor deposition of one or more hard layers made of a CrAlN layer on the surface of a tool body, at least one of the hard layers is a solid solution containing Si. Coated tools that are phase and have a crystal structure of fcc are also known.

Japanese Patent No. 3969230 Japanese Patent No. 3781374

  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. When used for intermittent heavy cutting with a load applied, 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 inventors of the present invention have made the hard coating layer a CrAlN 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 crystal grain structure of the CrAlN layer, the following knowledge was obtained.

(A) Conventionally, when forming a CrAlN layer as a hard coating layer on the surface of a tool base made of a WC cemented carbide, the tool base is attached to an arc ion plating (AIP) apparatus which is a kind of physical vapor deposition apparatus. Wearing, for example,
In-apparatus heating temperature: 390 to 450 ° C.,
DC bias voltage applied to the tool base: -20 to -50V,
Cathode electrode: Cr-Al 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 CrAlN layer (hereinafter referred to as a conventional CrAlN layer) is formed.

(B) However, the CrAlN layer is formed by, for example, applying the above-mentioned tool base to 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 view of FIG. Wearing,
Tool substrate temperature: 360 to 450 ° C.
Evaporation source: metal Cr and metal Al,
Plasma gun discharge power: 11-15 kW (relative to metal Cr),
Plasma gun discharge power: 8 to 10 kW (relative to metal Al),
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 CrAlN layer is vapor-deposited under the specific conditions of the above, the coated tool using the resulting CrAlN layer (hereinafter referred to as a modified CrAlN layer) as a hard coating layer is compared with the conventional coated tool having the CrAlN layer formed thereon. The present inventors have found that excellent fracture resistance is exhibited under high cutting and high feed intermittent cutting conditions.

(C) When the cross-sectional structure of the modified CrAlN layer was observed with a transmission electron microscope, as shown in the cross-sectional perspective view of FIG. 2, the vertical cross-section in the layer thickness direction was in an upright direction with respect to the tool base surface. In the horizontal cross section having a depth of 0.1 μm from the surface of the modified CrAlN layer, the short side is 5 to 100 nm and the aspect ratio is 3 or more. It was confirmed that certain vertical plate-like CrAlN 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 modified CrAlN 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.

The present invention has been made based on the above findings,
“(1) In a surface-coated cutting tool in which a hard coating layer composed of a CrAlN 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 CrAlN layer has a height equal to the average layer thickness, and is composed of vertically elongated CrAlN 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 CrAlN layer is observed with a transmission electron microscope, the longitudinal side having a short side of 5 to 100 nm and an aspect ratio of 3 or more. A surface-coated cutting tool characterized in that flat CrAlN crystal grains are present, and the total area occupied by the vertically long flat CrAlN crystal grains in the horizontal section is 30% or more of the total cross-sectional area.
(2) The CrAlN layer is
Composition formula: (Cr _1-X Al _X ) N
The surface-coated cutting tool according to (1), wherein the content ratio X of the Al component in the total amount with the Cr component satisfies 0.10 ≦ X ≦ 0.70 in atomic ratio. "
It has the characteristics.

  The present invention will be described below.

In the modified CrAlN layer constituting the hard coating layer of the coated tool of the present invention, the Cr component improves the high temperature strength, the Al component improves the heat resistance, and the N component has the effect of improving the layer strength. Therefore, the modified CrAlN layer comes to have high hardness, excellent heat resistance and strength, and contributes to improvement of wear resistance of the coated tool and long tool life.
As a result of performing numerous tests for forming a CrAlN layer by vapor deposition, the present inventors have formed a CrAlN layer on a tool base 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 Cr and metal Al,
Plasma gun discharge power: 11-15 kW (relative to metal Cr),
Plasma gun discharge power: 8 to 10 kW (relative to metal Al),
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 was found that a modified CrAlN layer composed of vertically long plate-like CrAlN crystal grains grown in an upright direction with respect to the tool base surface was formed when the deposition was adjusted to the specific conditions.

The modified CrAlN layer of this invention
Composition formula: (Cr _1-X Al _X ) N
When the content ratio X of the Al component in the total amount with the Cr component is less than 0.10 in atomic ratio (that is, 0.10> Al / (Cr + Al)), desired high temperature hardness and heat resistance are expected. On the other hand, if the content ratio X exceeds 0.70 (that is, Al / (Cr + Al)> 0.70), the strength of the layer itself is reduced, and the fracture resistance cannot be obtained. Therefore, the content ratio X of the Al component is desirably 0.10 to 0.70 in terms of atomic ratio.

When the structure of the modified CrAlN 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 CrAlN layer, the vertically long plate-like CrAlN crystal The height of the grains constitutes the layer thickness of the modified CrAlN layer.
Further, a horizontal cross section parallel to the tool base surface and at a depth of 0.1 μm from the surface of the modified CrAlN layer (that is, at a depth of 0.1 μm from the surface of the modified CrAlN layer and orthogonal to the layer thickness direction). In the plane), there are rectangular CrAlN crystal grains having a short side of 5 to 100 nm and an aspect ratio of 3 or more.
Moreover, in the horizontal section, the area ratio occupied by the total area of the rectangular CrAlN crystal grains is 30% or more of the total area of the horizontal section.

The average layer thickness of the modified CrAlN layer (same as the height of the vertically long plate-like CrAlN 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 CrAlN 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 CrAlN crystal grains exceeds 2 μm, the CrAlN crystal grains become coarse, surface smoothness is lost, and chipping is likely to occur.
Therefore, the average layer thickness of the modified CrAlN layer (= the height of the vertically long plate-like CrAlN crystal grains) is set to 0.2 to 2 μm.

Further, if the short side of the rectangular CrAlN crystal grains present in the horizontal cross section at a depth of 0.1 μm from the surface of the modified CrAlN layer is less than 5 nm, the toughness of the crystal grains themselves cannot be exhibited, If the side exceeds 100 nm, the crystal grain becomes coarse and complicated crystal grain boundaries cannot be introduced. Therefore, the short side of the rectangular CrAlN crystal grain is set to 5 to 100 nm.
The “short side” in the present invention refers to the size of individual CrAlN crystal grains present in a horizontal section at a depth of 0.1 μm from the surface of the modified CrAlN 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, when the aspect ratio of the rectangular CrAlN crystal grains present in the horizontal section at a depth of 0.1 μm from the surface of the modified CrAlN layer is less than 3, the shape of the crystal grains in the horizontal section is isotropic. Therefore, it becomes impossible to introduce complicated grain boundaries, so the aspect ratio of the rectangular CrAlN 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 CrAlN crystal grains present in the horizontal cross section at a depth of 0.1 μm from the surface of the modified CrAlN 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 CrAlN crystal grain area ratio is set to 30% or more.

  The short side value, aspect ratio value, and area ratio of the rectangular CrAlN crystal grains present in the horizontal cross section at a depth of 0.1 μm from the surface of the modified CrAlN layer are included in the deposition conditions of the modified CrAlN 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 CrAlN 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 CrAlN layer constituting the hard coating layer is composed of vertically long plate-like CrAlN crystal grains grown in an upright direction with respect to the tool base surface, and further from the surface of the modified CrAlN layer. In the horizontal cross section having a depth of 0.1 μm, the vertically long plate-like CrAlN crystal grains having a short side of 5 to 100 nm and an aspect ratio of 3 or more exist, and the vertically long plate-like CrAlN 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 CrAlN 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 CrAlN 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 CrAlN layer of the surface coating cutting tool of this invention is shown. The schematic diagram of the structure | tissue of the CrAlN crystal grain in the horizontal cross section of a 0.1 micrometer depth from the surface of the modified CrAlN 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, Cr ₃ C ₂ powder, and Co powder each having an average particle diameter of 1 to 3 μm are prepared, and these raw material powders are mixed in the composition shown in Table 1. Compounded, wet mixed in a ball mill for 72 hours, dried, and then pressed into a green compact at a pressure of 100 MPa. The green compact was sintered in a 6 Pa vacuum at a temperature of 1400 ° C. for 1 hour. After sintering, honing of R: 0.03 was applied to the cutting edge portion to form tool bases 1 to 10 made of WC-base cemented carbide having an ISO standard / SEEN 1203 insert shape.

Next, the tool bases 1 to 10 are ultrasonically cleaned in acetone and dried, and then attached to the ion plating apparatus using the pressure gradient type Ar plasma gun shown in FIG. Attach Cr and metal Al, 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, and then introduce Ar gas. 2.3 × 10 ⁻² Pa, the discharge power of the pressure gradient plasma gun is set to 2 kW, Ar ions are generated in the apparatus, and a bias voltage of −200 V is applied to the tool base, thereby the tool substrate to 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 45 sccm, while passing 100sccm of nitrogen gas, maintaining the pressure in the furnace to ^{3 × 10 -2 ~6 × 10 -2} Pa, the plasma beam with to generate steam of incident plasma beam metals Cr and Al metal to the evaporation source The modified CrAlN layer having the target layer thickness shown in Table 3 is vapor-deposited as a hard coating layer on the surface of the tool base fixed to the upper 1000 mm of the evaporation source. Invention surface covering inserts (hereinafter referred to as the present invention 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 CrAlN layer of the inserts 1 to 10 of the present invention.

For comparison, a comparative CrAlN layer having a target layer thickness shown in Table 5 is formed by vapor deposition on the tool bases A1 to A10 under the following conditions by a normal arc ion plating (AIP) method. 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: Cr-Al 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 is a condition for forming the conventional CrAlN layer of Comparative Example 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 inserts 1 to 10 of the present invention, vertically long plate-like CrAlN crystal grains having a height equal to the average layer thickness of the modified CrAlN layer are grown in an upright direction with respect to the tool base surface. Observation and measurement of a horizontal cross section having a depth of 0.1 μm from the surface of the CrAlN layer using a transmission electron microscope has a short side of 5 to 100 nm, an aspect ratio of 3 or more, and a total in the horizontal cross section. It was confirmed that vertically flat CrAlN crystal grains having an area of 30% or more of the total cross-sectional area were present.
FIG. 3 shows, as an example, a schematic structure diagram of CrAlN crystal grains in a horizontal cross section having a depth of 0.1 μm from the surface of the modified CrAlN layer of the insert 1 of the present invention.

  On the other hand, from Table 5, in Comparative Example Inserts 1 to 10 in which the CrAlN layer was formed by a normal arc ion plating method, columnar CrAlN crystal grains having a height equal to the average layer thickness of the conventional CrAlN layer are Growing in the upright direction with respect to the surface of the tool base, a horizontal cross section 0.1 μm high from the surface of the CrAlN 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 present invention inserts 1 to 10 and comparative example inserts 1 to 10, in a state where this is screwed to the tip of the tool steel cutter with a fixing jig,
Work material: Plane dimensions 100mm x 250mm JIS S35C plate material with a thickness of 50mm,
Cutting speed: 300 m / min. ,
Feed per tooth: 0.40 mm / tooth,
Cutting time: 2 minutes
Carbon steel dry high-speed high-feed cutting test under normal conditions (referred to as cutting condition 1) (normal cutting speed and table feed are 200 m / min. And 0.25 mm / tooth, respectively),
Work material: Plane dimensions 100 mm x 250 mm JIS / SCM440 plate material with a thickness of 50 mm,
Cutting speed: 250 m / min. ,
Feed per tooth: 0.35 mm / tooth,
Cutting time: 2 minutes
Dry high-speed high-feed cutting test of alloy steel under the following conditions (referred to as cutting condition 2) (normal cutting and feeding are 170 m / min. And 0.25 mm / blade, respectively),
Work material: Plane dimensions 100 mm x 250 mm JIS / SS400 plate material with a thickness of 50 mm,
Cutting speed: 300 m / min. ,
Feed per tooth: 0.40 mm / tooth,
Cutting time: 2 minutes
Dry high-speed high-feed cutting test of mild steel under the following conditions (referred to as cutting condition 3) (normal cutting and feeding are 250 m / min. And 0.30 mm / tooth, respectively),
In each cutting test, the flank wear width of the cutting edge was measured.
The measurement results are shown in Table 6.

  From the results shown in Tables 3, 5 and 6, in the inserts 1 to 10 of the present invention, the modified CrAlN layer constituting the hard coating layer has an average layer thickness of 0.2 to 2 μm, and on the tool base surface. On the other hand, a vertically long plate-like CrAlN crystal grain structure having the same height as the average layer thickness is formed in the upright direction, and in the horizontal cross section having a depth of 0.1 μm from the surface of the modified CrAlN layer, the short side 5-100 nm, the aspect ratio is 3 or more, the above-mentioned vertically long plate-like CrAlN crystal grains exist, and the total area occupied by the vertically long plate-like CrAlN crystal grains is 30% of the total cross-sectional area. With the crystal grain structure as described above, the bending resistance of the modified CrAlN 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 1-10, the crystal grains in the conventional CrAlN 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 CrAlN layer) is formed as a vertically long plate-like CrAlN 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 (2)

In a surface-coated cutting tool in which a hard coating layer composed of a CrAlN 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 CrAlN layer has a height equal to the average layer thickness, and is composed of vertically elongated CrAlN 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 CrAlN layer is observed with a transmission electron microscope, the longitudinal side having a short side of 5 to 100 nm and an aspect ratio of 3 or more. A surface-coated cutting tool characterized in that flat CrAlN crystal grains are present, and the total area occupied by the vertically long flat CrAlN crystal grains in the horizontal section is 30% or more of the total cross-sectional area. The CrAlN layer,
Composition formula: (Cr _1-X Al _X ) N
2. The surface-coated cutting tool according to claim 1, wherein the content ratio X of the Al component in the total amount with the Cr component satisfies 0.10 ≦ X ≦ 0.70 in atomic ratio.

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