JP2021146442A - Surface-coated cutting tool - Google Patents

Abstract

To provide a cutting tool which exhibits excellent cutting performance over a long period of use even in high-speed lathe-turning of spheroidal graphite cast iron.SOLUTION: A surface-coated cutting tool has a coating layer including a lower layer, an intermediate layer and an upper layer in this order toward a surface of a tool substrate. The lower layer has an average layer thickness of 2.0-20.0 μm and has at least one Ti carbonitride layer, the intermediate layer has a lower layer that has an average layer thickness of 0.1-1.5 μm and is nitride of Ti on a lower layer side and an upper layer that is carbonitride, carbonate or carbonitroxide of Ti on an upper layer side, the carbonitride, carbonate or carbonitroxide of Ti of the upper layer has an average width of crystal grains in a direction parallel to the surface of the tool substrate of 0.20 μm or less, the upper layer has an average layer thickness of 1.0-10.0 μm, when the composition is represented by composition expression: Ti1-xAlxN, 0.60≤x≤0.95 is satisfied, and the composition mainly contains crystal grains of an NaCl type face-centered cubic structure.SELECTED DRAWING: Figure 1

Description

The present invention is a surface coating cutting tool in which the hard film layer has excellent welding resistance and chipping resistance even when used for high-speed turning of spheroidal graphite cast iron, and exhibits excellent cutting performance over a long period of use. (Hereinafter, it may be referred to as a covering tool).

Generally, covering tools are used for turning and planing of various types of steel, cast iron, and other work materials, such as inserts that are detachably attached to the tip of a cutting tool, and drilling and cutting of work materials. There are drills and miniature drills, as well as solid type end mills used for surface machining, grooving, shoulder machining, etc. of work materials, and inserts can be attached and detached to perform cutting in the same way as solid type end mills. Insert type end mills and the like are known.
Conventionally, as a covering tool, for example, a tool in which a hard coating layer is formed on a tool substrate such as a WC-based cemented carbide has been known, and attention is paid to the interface between the tool substrate and the hard coating layer, and the cutting performance is improved. Various proposals have been made for the purpose of improvement.

For example, in Patent Document 1, a TiN coating layer that functions as a bonding layer is provided on a tool substrate, and a TiAlN layer (Ti and Al of Ti and Al) is provided on the TiN coating layer via a TiCN (MT-TiCN) coating layer that serves as an intermediate layer. A covering tool coated with a composite nitride layer) is described.

Further, for example, in Patent Document 2, a TiN layer having an average layer thickness of 0.1 to 1.0 μm is provided on the surface of the tool substrate, and a lower layer having an average layer thickness of 1.5 to 5.0 μm is provided on the TiN layer. TiCxN1-x (however, 0.30 ≦ x ≦ 0.80) layer and TiCyN1-y (however, 0.85 ≦ y ≦ 1.00) as an upper layer having an average layer thickness of 0.1 to 1.0 μm. Having an intermediate layer containing the intermediate layer and an N layer (however, 0.70 ≦ z ≦ 0.95) having an average layer thickness of 1.5 to 6.0 μm (AlzTi1-z) on the intermediate layer. A featured covering tool is described, which is described as having excellent chipping resistance even for high-speed, high-feed intermittent machining of steel milling.

Further, for example, Patent Document 3 has a TiCN layer as a lower layer and a TiAlCN layer as an upper layer on the surface of the tool substrate, and crystal grains having an average layer thickness of 50% or more of the total average layer thickness of the lower layers. And the crystal grains in the lower layer have a frequency distribution in which the normal line of the {422} plane of the crystal grains in the upper layer has an angle of 0 to 10 degrees with the surface of the tool substrate, which is 30% or more. Describes a covering tool having an area ratio of 50% or more of the crystal grains in the upper layer, and it is explained that this covering tool has excellent chipping resistance even for high-speed intermittent cutting of steel and cast iron. There is.

Japanese Unexamined Patent Publication No. 2015-509858 JP-A-2018-164950 Japanese Unexamined Patent Publication No. 2016-124098

The coating tool having the hard coating layer described in Patent Documents 1 to 3 exhibits satisfactory performance in the cutting process described in each Patent Document, but is faster than spheroidal graphite cast iron having high tensile strength. It was found that when used for machining under high-load cutting conditions, the hard film layer peeled off and chipping occurred, and the life was not sufficient.

Therefore, the present invention has been made in view of such a situation, and even when subjected to high-speed turning of spheroidal graphite cast iron, it exhibits excellent peeling resistance and chipping resistance, and is excellent over a long period of use. It is an object of the present invention to provide a cutting tool that exhibits cutting performance.

In order to solve the above problems, the present inventor diligently studied the occurrence of peeling and chipping of the hard film in the high-speed turning process of spheroidal graphite cast iron. We have obtained a new finding that this abnormal growth of TiAlN is caused by crystal growth originating from the unevenness of the tool substrate and is likely to occur near the interface region between the TiCN layer and the TiAlN layer. ..

The present invention is based on this finding and is as follows.
"(1) A surface-coated cutting tool having a tool substrate and a coating layer including a lower layer, an intermediate layer, and an upper layer in this order toward the tool surface on the surface of the tool substrate.
The lower layer has an average layer thickness of 2.0 to 20.0 μm and has at least one Ti carbonitride layer.
The intermediate layer has an average layer thickness of 0.1 to 1.5 μm, with a lower layer which is a titanium nitride on the lower layer side and a titanium nitride, carbon oxide, or charcoal oxide on the upper layer side. The titanium nitride, carbon oxide, or carbon dioxide oxide of the Ti in the upper layer has an upper layer, and the average width of crystal grains in the direction parallel to the surface of the tool substrate is 0.20 μm. Below,
The upper layer has an average layer thickness of 1.0 to 10.0 μm, and when the composition is _{represented by the composition formula: Ti 1-x} Al _x N (where x represents the average composition in atomic ratio), it is 0. Mainly crystal grains having a NaCl-type face-centered cubic structure, satisfying .60 ≦ x ≦ 0.95.
A surface coating cutting tool characterized by that. "

The surface-coated cutting tool of the present invention exhibits excellent wear resistance, peeling resistance, and chipping resistance in high-load cutting accompanied by high temperature generation such as high-speed turning of spheroidal graphite cast iron.

It is a schematic diagram of the vertical cross section of the hard film layer in the surface coating cutting tool of this invention.

Hereinafter, the covering tool of the present invention will be described in more detail. In the description of the scope of claims in this specification, when the numerical range is expressed using "A to B" (both A and B are numerical values), the range is the upper limit (B) and the lower limit (A). It includes numerical values. Further, the upper limit (B) and the lower limit (A) are the same unit.

Here, in the present specification, when a compound is not represented by a composition formula, such as Ti nitride, carbide, nitride, carbon oxide, carbonitride oxide, or carbonitride, the composition is defined as. It is not necessarily limited to the stoichiometric range.

Structure and composition of hard film layer:
As schematically shown in FIG. 1, the hard film layer has three layers, a lower layer, an intermediate layer, and an upper layer, in order from the tool substrate to the tool surface, and the intermediate layer has an upper layer and a lower layer. Have.
Hereinafter, each layer will be described.

(1) Lower layer The lower layer has at least one Ti carbonitride layer, and may further contain at least one Ti carbide, nitride, carbonic acid oxide, or carbonic acid nitrogen oxide. The Ti carbonitride layer is preferably composed of columnar particles.
By having at least one Ti carbonitride layer, the upper layer formed via the intermediate layer and the tool substrate can be firmly bonded. Further, in addition to at least one Ti carbonitride layer, for example, it is preferable to have a Ti nitride layer and a Ti carbide layer as a base layer directly above the tool substrate.

(2) Intermediate layer The intermediate layer has a lower layer which is a titride of Ti on the lower layer side and an upper layer which is a carbonitride, carbon oxide, or a carbonitride of Ti on the upper layer side. With such a two-layer structure, the turbulence in the growth direction of the lower Ti carbonitride starting from the unevenness of the tool substrate is divided by the TiN of the lower layer, and the crystal growth of the upper layer is transferred to the surface of the tool substrate. The direction is vertical, and abnormal growth of TiAlN, which is the upper layer described later, can be suppressed.
The upper layer of Ti carbonitride, carbon oxide, or carbonitride oxide has an average width of crystal grains in a direction parallel to the surface of the tool substrate of 0.20 μm or less. It is possible to surely divide the Ti carbonitride in the lower layer in the growth direction and suppress the abnormal growth of TiAlN in the upper layer in the interface region between the intermediate layer and the upper layer. The lower limit of the average width is not particularly limited, but when manufactured according to the manufacturing method of Examples described later, the lower limit is about 0.02 μm.

Here, the average width of the crystal grains in the direction parallel to the surface of the tool substrate is obtained as follows. That is, the polished surface of the vertical cross section of the hard film layer (the cross section perpendicular to the surface of the tool substrate) was observed in a plurality of fields with a 20000x field of view of a transmission electron microscope (TEM), and in the obtained micrograph. The number of grain boundaries intersecting a straight line of 5 μm parallel to the base material located at the center of the upper end and the lower end of the upper layer is measured at the five locations, and the inverse of the average number of grain boundaries per 1 μm of the straight line is defined as the average particle width. ..

(3) Upper layer The upper layer _{satisfies 0.60 ≦ x ≦ 0.95 when its composition is represented by the composition formula: Ti 1-x} Al _x N (where x represents the average composition by the atomic ratio). It is a TiAlN layer. The reason why x is set in this range is that if it is less than 0.60, the wear resistance is not sufficient, while if it exceeds 0.95, the amount of hexagonal precipitation increases and the hardness decreases, and the wear resistance This is because

Further, it is preferable that the TiAlN layer forming the upper layer mainly has a NaCl-type face-centered cubic structure. Here, the term "mainly in the NaCl-type face-centered cubic structure" means that the area ratio of the crystal having the NaCl-type face-centered cubic structure is 50% or more in the vertical cross section of the coating layer. Is more preferably 70% or more, more preferably 80% or more, and may be 100%.

Average film thickness of each layer:
The average film thickness of each layer constituting the hard film is 2.0 to 20.0 μm for the lower layer, 0.1 to 1.5 μm for the intermediate layer, and 1.0 to 10.0 μm for the upper layer, respectively.
The reason why the average layer thickness of the upper layer and the lower layer is set in the above range is that if it is less than the lower limit of each, excellent wear resistance cannot be exhibited over a long period of use, while if it exceeds the upper limit of each. This is because the crystal grains of the hard film tend to be coarsened, and the thickness of the entire coating layer becomes thicker, so that the effect of improving the chipping resistance cannot be obtained.
The reason why the average layer thickness of the intermediate layer is set to the above range is that if it is less than the lower limit value, a sufficient effect of dividing the turbulence in the growth direction of the Ti carbonitride in the lower layer cannot be obtained, while if it exceeds the upper limit value. This is because the above-mentioned average width exceeds 0.2 μm due to the coarsening of the crystal grains in the intermediate layer. The average layer thickness of each of the upper layer and the lower layer is not particularly limited as long as the layer thickness of the intermediate layer is within the above range and the average width of the upper layer is 0.2 μm or less.
The more preferable average thickness of each layer is 6.0 to 15.0 μm for the lower layer, 0.3 to 1.0 μm for the intermediate layer, and 3.0 to 6.0 μm for the upper layer, respectively.

Method for measuring average layer thickness, average composition, and crystal structure:
The average film thickness can be determined by observing the vertical cross section of the hard film layer using a scanning electron microscope (SEM).
Regarding the average composition of the TiAlN layer, an electron beam microanalyzer (Electron-Probe-Micro-Analyzer: EPMA) was used to irradiate the sample whose surface was polished with an electron beam from the sample surface side, and the obtained characteristic X was obtained. The 10-point average of the line analysis results is taken as the average composition.
Regarding the crystal structure of the TiAlN layer, an electron backscatter diffraction (EBSD) was used to inject 70 degrees into each crystal grain existing within the measurement range of the polished longitudinal section of the hard film layer. An electron beam having an acceleration voltage of 15 kV at an angle is irradiated with an irradiation current of 1 nA at an interval of 0.01 μm / step. Then, by measuring the electron beam backscattered diffraction image, analyzing the crystal structure of each crystal grain, and determining the ratio of the number of pixels belonging to the NaCl-type face-centered cubic structure to the total number of identified crystal structures. , The area ratio of crystal grains having a NaCl-type face-centered cubic structure is determined. The measurement range is 50 μm in the direction parallel to the surface of the tool substrate, and the measurement range is the range including the entire thickness of the hard film layer in the vertical direction.

Tool base:
As the tool substrate, any substrate conventionally known as this type of tool substrate can be used as long as it does not hinder the achievement of the object of the present invention. For example, cemented carbide (WC-based cemented carbide, WC, as well as those containing Co and further added with carbonitrides such as Ti, Ta, Nb, etc.), cermet (TiC, It is preferably one of TiN, TiCN and the like as a main component), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide and the like), or a cBN sintered body.

Other layers (top layer)
The hard film of the present invention has sufficient wear resistance, chipping resistance, and peeling resistance even in high-speed turning of spheroidal graphite cast iron, but at least a layer containing an aluminum oxide layer is 1.0 to 25.0 μm. When provided on the TiAlCN layer as the uppermost layer in the total average layer thickness of, in combination with the effects of these layers, even more excellent wear resistance, chipping resistance, and chipping resistance are achieved. It can exhibit peelability. Here, when the total average layer thickness of the layer including at least the aluminum oxide layer is less than 1.0 μm, the effect of the layer is not sufficiently exhibited, while when it exceeds 25.0 μm, the crystal grains of the layer tend to be coarsened. Therefore, chipping is likely to occur.

Production method:
The coating of the coating tool of the present invention is carried out by, for example, the following steps using a chemical vapor deposition apparatus. The following% is a volume% (volume%), and the sum of the gas group A and the gas group B is 100% by volume in the film forming process of the upper layer.

(1) Film formation process of lower layer (TiCN layer) Reaction gas TiCl ₄ : 2.0 to 2.5%, CH ₃ CN: 0.6 to 1.0%,
N ₂ : 20-40%, H ₂ : Remaining reaction atmosphere temperature: 800-940 ° C
Reaction atmospheric pressure: 5.0 to 10.0 kPa
In addition to the TiCN layer, when a Ti compound layer, that is, any of a carbide, a nitride, a carbon oxide, or a carbon dioxide oxide of Ti is formed as a base layer, known film forming conditions are used. It may be adopted as appropriate.

(2) Intermediate layer film forming process The intermediate layer film forming process comprises an etching step, a lower layer film forming process, and an upper layer film forming process.
a Etching process Reaction gas TiCl ₄ : 4.0 to 6.0%, H ₂ : Remaining reaction atmosphere temperature: 800 to 980 ° C.
Reaction atmospheric pressure: 5.0 to 10.0 kPa
b Lower layer (TiN layer) film formation process Reaction gas TiCl ₄ : 1.5 to 2.5%, N ₂ : 45 to 65%, H ₂ : Remaining reaction atmosphere temperature: 880 to 1000 ° C.
Reaction atmospheric pressure: 12.0 to 20.0 kPa
c Upper layer (eg TiCN layer) film formation process Reaction gas TiCl ₄ : 2.0 to 2.5%, CH ₃ CN: 0.4 to 0.6%,
_{N 2: 20.0~40.0%, H 2} : balance Temperature of reaction atmosphere: 700 to 800 ° C.
Reaction atmospheric pressure: 5.0 to 10.0 kPa

(3) Film formation process of upper layer (TiAlN layer) Reaction gas group A NH ₃ : 0.8 to 1.6%, H ₂ : 45 to 55%
Reaction gas group B AlCl ₃ : 0.5 to 0.7%, TiCl ₄ : 0.1 to 0.3%,
N2: 0.0 to 10.0%, H ₂ : Remaining reaction atmosphere temperature: 700 to 900 ° C.
Reaction atmospheric pressure: 4.0-5.0 kPa
Reaction gas supply cycle: 1 to 5 seconds Gas supply time per cycle: 0.15 to 0.25 seconds Phase difference between gas A group supply and gas B group supply: 0.10 to 0.20 seconds

Next, an example will be described.
Here, as a specific example of the coated tool of the present invention, a tool applied to an insert cutting tool using a WC-based cemented carbide as a tool substrate will be described, but the tool substrate is limited to the WC-based cemented carbide as described above. The same applies when the tool is applied to a drill, an end mill, or the like.

First, as raw material powders, Co powder, TiC powder, ZrC powder, TaC powder, NbC powder, Cr ₃ C ₂ powder, and WC powder are prepared, and these raw material powders are blended into the blending composition shown in Table 1. Further, wax is added, wet-mixed in a ball mill for 72 hours, dried under reduced pressure, press-molded at a pressure of 100 MPa, these powder compacts are sintered, processed to a predetermined size, and ISO standard. WC-based cemented carbide tool bases A to E having an insert shape of CNMG120412 of the above were prepared.

Next, the coated tools 1 to 10 of the present invention shown in Table 7 were obtained on the tool bases A to E under the conditions shown in Tables 2 to 4 for the lower layer, the intermediate layer, and the upper layer. The film forming conditions for each of these layers are as follows.

Film formation process of lower layer (TiCN layer) Reaction gas TiCl ₄ : 2.0 to 2.5%, CH ₃ CN: 0.6 to 1.0%,
N ₂ : 20-40%, H ₂ : Remaining reaction atmosphere temperature: 800-940 ° C
Reaction atmospheric pressure: 5.0 to 10.0 kPa

Intermediate layer film formation step a Etching step Reaction gas _{Tycol 4} : 4.0 to 6.0%, H ₂ : Remaining reaction atmosphere temperature: 800 to 980 ° C.
Reaction atmospheric pressure: 5.0 to 10.0 kPa
b Lower layer (TiN layer) film formation process Reaction gas TiCl ₄ : 1.5 to 2.5%, N ₂ : 45 to 65%, H ₂ : Remaining reaction atmosphere temperature: 880 to 1000 ° C.
Reaction atmospheric pressure: 12.0 to 20.0 kPa
c Formation process of upper layer (TiCN layer) Reaction gas TiCl ₄ : 2.0 to 2.5%, CH ₃ CN: 0.4 to 0.6%,
_{N 2: 20.0~40.0%, H 2} : balance Temperature of reaction atmosphere: 700 to 800 ° C.
Reaction atmospheric pressure: 5.0 to 10.0 kPa

(3) Upper layer (TiAlN layer) film formation process Reaction gas group A NH ₃ : 0.8 to 1.6%, H ₂ : 45 to 55%
Reaction gas group B AlCl ₃ : 0.5 to 0.7%, TiCl ₄ : 0.1 to 0.3%,
N2: 0.0 to 10.0%, H ₂ : Remaining reaction atmosphere temperature: 700 to 900 ° C.
Reaction atmospheric pressure: 4.0-5.0 kPa
Reaction gas supply cycle: 1 to 5 seconds Gas supply time per cycle: 0.15 to 0.25 seconds Phase difference between gas A group supply and gas B group supply: 0.10 to 0.20 seconds

The coating tools 7 and 10 of the present invention formed the uppermost layer containing aluminum oxide under the film forming conditions shown in Table 5.

Further, for the purpose of comparison, Comparative Examples 1 to 10 shown in Table 7 were manufactured on the surfaces of the tool substrates A to E under the film forming conditions shown in Table 2. For the comparative covering tools 2, 4 and 8, the film forming conditions of the intermediate layer were the same as those of the examples, but the average layer thickness was out of the range specified in the present invention.
In Comparative Examples 7 and 10, the uppermost layer containing aluminum oxide was formed under the film forming conditions shown in Table 5.

Further, the vertical cross section of the coating layers of the coating tools 1 to 10 and the comparative coating tools 1 to 10 of the present invention was measured using SEM (magnification 5000 times), and the layer thickness of each layer was measured at 5 points in the observation field. , The average layer thickness of each layer, and the results are shown in Tables 6 and 7.
Further, the composition and crystal structure (area ratio of crystal grains of NaCl-type face-centered cubic structure) of the coating layers of the coating tools 1 to 10 of the present invention and the comparative coating tools 1 to 10 were measured by the above-mentioned methods, and Table 7 shows. Described.

Subsequently, the following cutting tests were performed on the covering tools 1 to 10 of the present invention and the comparative covering tools 1 to 10.

Work material: JIS / FCD700 round bar Cutting speed: 380 m / min
Notch: 3.0 mm
Feed: 0.35 mm / rev
Cutting time: 5 min
The results are shown in Table 8.

As is clear from the results of the cutting test shown in Table 8, all of the covering tools 1 to 10 of the present invention have excellent wear resistance, peeling resistance, and chipping resistance, and thus spheroidal graphite. Even in high-speed turning of cast iron, it exhibits excellent cutting performance over a long period of time. On the other hand, the comparative covering tools 1 to 10 which do not satisfy the matters specified in the covering tool of the present invention are chipped and have a short life when they are subjected to high-speed turning of spheroidal graphite cast iron. It has reached.

The surface-coated cutting tool of the present invention not only cuts various types of steel under normal cutting conditions, but also generates high heat and applies a large load to the cutting edge, such as spheroidal graphite cast iron. In turning, it exhibits excellent wear resistance, peeling resistance, and chipping resistance, and exhibits excellent cutting performance over a long period of time. Therefore, the performance of the cutting equipment is improved and the cutting work is labor-saving. It is also fully satisfactory for energy saving and cost reduction.

Claims (1)

A surface-coated cutting tool having a tool substrate and a coating layer including a lower layer, an intermediate layer, and an upper layer in order toward the tool surface on the surface of the tool substrate.
The lower layer has an average layer thickness of 2.0 to 20.0 μm and has at least one Ti carbonitride layer.
The intermediate layer has an average layer thickness of 0.1 to 1.5 μm, with a lower layer which is a titanium nitride on the lower layer side and a titanium nitride, carbon oxide, or charcoal oxide on the upper layer side. The titanium nitride, carbon oxide, or carbon dioxide oxide of the Ti in the upper layer has an upper layer, and the average width of crystal grains in the direction parallel to the surface of the tool substrate is 0.20 μm. Below,
The upper layer has an average layer thickness of 1.0 to 10.0 μm, and when the composition is _{represented by the composition formula: Ti 1-x} Al _x N (where x represents the average composition in atomic ratio), it is 0. Mainly crystal grains having a NaCl-type face-centered cubic structure, satisfying .60 ≦ x ≦ 0.95.
A surface coating cutting tool characterized by that.

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