JP7401850B2 - surface coated cutting tools - Google Patents

Description

In particular, the present invention provides a surface-coated cutting tool whose hard coating layer has excellent adhesion resistance and chipping resistance even when used for high-speed turning of spheroidal graphite cast iron, and which exhibits excellent cutting performance over long periods of use. (hereinafter sometimes referred to as coated tools).

In general, coated tools include inserts that are removably attached to the tip of a cutting tool for turning and planing workpiece materials such as various steels and cast iron, and inserts that are used for drilling and cutting workpiece materials. There are drills, miniature drills, and solid-type end mills that are used for facing, grooving, shoulder machining, etc. of workpiece materials, and inserts can be detachably attached to perform cutting operations in the same way as solid-type end mills. Insert type end mills are known.
Conventionally, coated tools have been known that have a hard coating layer formed on a tool base such as WC-based cemented carbide, and the cutting performance has been improved by focusing on the interface between the tool base and the hard coating layer. 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 the tool base, and a TiAlN layer (Ti and Al A coated tool coated with a composite nitride layer) is described.

Further, for example, Patent Document 2 discloses that a TiN layer with an average layer thickness of 0.1 to 1.0 μm is formed on the surface of the tool base, and a lower layer with an average layer thickness of 1.5 to 5.0 μm is formed 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 with an average layer thickness of 0.1 to 1.0 μm. and an (AlzTi1-z)N layer having an average layer thickness of 1.5 to 6.0 μm (however, 0.70≦z≦0.95). A characteristic coated tool is described, and it is explained that the coated tool has excellent chipping resistance even in high-speed, high-feed interrupted machining of steel milling.

Further, for example, Patent Document 3 discloses that a tool base has a TiCN layer as a lower layer and a TiAlCN layer as an upper layer on the surface of the tool base, and crystal grains having an average layer thickness of 50% or more of the total average layer thickness of the lower layer. and the crystal grains of the lower layer have a frequency distribution in which the angle between the normal to the {422} plane of the crystal grains of the upper layer and the surface of the tool base is 30% or more in the slope section of 0 to 10 degrees, and the crystal grains of the lower layer describes a coated tool having an area ratio of 50% or more of the crystal grains in the upper layer, and explains that this coated tool has excellent chipping resistance even in high-speed interrupted cutting of steel and cast iron. There is.

Japanese Patent Application Publication No. 2015-509858 Japanese Patent Application Publication No. 2018-164950 Japanese Patent Application Publication No. 2016-124098

Although the coated tools having hard coating layers described in Patent Documents 1 to 3 exhibit satisfactory performance in the cutting operations described in each patent document, they are difficult to cut at high speed and when cutting with high tensile strength, such as spheroidal graphite cast iron. When used for machining under high-load cutting conditions, the hard coating layer peeled off and chipping occurred, and it was found that it did not have a sufficient lifespan.

Therefore, the present invention was made in view of the above circumstances, and it shows excellent peeling resistance and chipping resistance even when subjected to high-speed turning processing of spheroidal graphite cast iron, and has excellent resistance to peeling and chipping over a long period of use. The purpose is to provide cutting tools that exhibit cutting performance.

In order to solve the above-mentioned problem, the inventors of the present invention conducted intensive studies on the occurrence of peeling and chipping of the hard coating during high-speed turning of spheroidal graphite cast iron, and found that the cause of the occurrence of peeling and chipping was abnormally grown crystals of TiAlN. We obtained new knowledge that this abnormal growth of TiAlN is caused by crystal growth originating from the irregularities of the tool base, and that it tends to occur near the interface region between the TiCN layer and the TiAlN layer. .

The present invention is based on this knowledge and is as follows.
"(1) A surface-coated cutting tool having a tool base and a coating layer on the surface of the tool base including, in order, a lower layer, an intermediate layer, and an upper layer toward the tool surface,
The lower layer has at least one Ti carbonitride layer with an average layer thickness of 2.0 to 20.0 μm,
The intermediate layer has an average layer thickness of 0.1 to 1.5 μm, and includes a lower layer made of Ti nitride on the lower layer side, and a carbonitride, carbonate, or carbonitoxide of Ti on the upper layer side. The carbonitride, carbonide, or carbonitoxide of Ti in the upper layer has an average width of crystal grains of 0.20 μm in a direction parallel to the surface of the tool base. The following is true,
The upper layer has an average layer thickness of 1.0 to 10.0 μm, and the composition is expressed by the composition formula: Ti _1-x Al _x N (where x represents the average composition in atomic ratio): 0 Satisfying .60≦x≦0.95, the crystal grains are mainly of NaCl type face-centered cubic structure,
A surface-coated cutting tool characterized by: ”

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

FIG. 2 is a schematic diagram of a longitudinal section of a hard coating layer in a surface-coated cutting tool of the present invention.

Hereinafter, the coated tool of the present invention will be explained in more detail. In addition, in this specification and claims, when a numerical range is expressed using "A to B" (A and B are both numerical values), the range is defined by the upper limit (B) and the lower limit (A). Contains numerical values. Further, the upper limit (B) and the lower limit (A) are in the same unit.

Here, in this specification, when a compound is not represented by a compositional formula, such as Ti nitride, carbide, nitride, carbonide, carbonitride oxide, or carbonitride, its composition is as follows: It is not necessarily limited to the stoichiometric range.

Structure and composition of hard film layer:
As schematically shown in Figure 1, the hard coating layer has three layers in order from the tool base toward the tool surface: a lower layer, an intermediate layer, and an upper layer, and the intermediate layer has an upper layer and a lower layer. have.
Each layer will be explained below.

(1) Lower layer The lower layer has at least one Ti carbonitride layer, and may further include at least one Ti carbide, nitride, carbonate, or carbonitride. 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 base can be firmly bonded. Further, in addition to at least one Ti carbonitride layer, it is preferable to have a Ti nitride layer and a Ti carbide layer, for example, as a base layer directly above the tool base.

(2) Intermediate layer The intermediate layer has a lower layer which is a nitride of Ti on the lower side, and an upper layer which is a carbonitride, carbonate, or carbonitride of Ti on the upper side. By adopting such a two-layer structure, the disorder in the growth direction of the Ti carbonitride in the lower layer originating from the unevenness of the tool base is interrupted by the TiN in the lower layer, and the crystal growth in the upper layer is directed to the surface of the tool base. By setting the direction perpendicularly, it is possible to suppress abnormal growth of TiAlN, which is an upper layer to be described later.
The upper layer, which is a Ti carbonitride, carbonate, or carbonitoxide layer, has an average width of crystal grains of 0.20 μm or less in a direction parallel to the surface of the tool base. It is possible to reliably disrupt the growth direction of the Ti carbonitride in the lower layer and to suppress abnormal growth of the TiAlN in the upper layer in the interface region between the intermediate layer and the upper layer. There is no particular restriction on the lower limit of this average width, but when manufactured according to the manufacturing method of the embodiment described later, the lower limit is about 0.02 μm.

Here, the average width of crystal grains in the direction parallel to the surface of the tool base is determined as follows. That is, the polished surface of a longitudinal cross section (a cross section perpendicular to the surface of the tool base) of the hard coating layer was observed in multiple fields of view using a transmission electron microscope (TEM) at a magnification of 20,000 times, and the following micrographs were obtained. At five locations, measure the number of grain boundaries that intersect with a 5 μm straight line parallel to the base material located at the center of the top and bottom ends of the upper layer, and take the reciprocal of the average number of grain boundaries per 1 μm straight line as the average grain width. .

(3) Upper layer The upper layer satisfies 0.60≦x≦0.95 when its composition is expressed by the composition formula: Ti _1-x Al _x N (where x represents the average composition in 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 will not be sufficient, whereas if it exceeds 0.95, the amount of hexagonal crystal precipitation will increase and the hardness will decrease, resulting in poor wear resistance. This is because the amount decreases.

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

Average thickness of each layer:
The average thickness of each layer constituting the hard coating is 2.0 to 20.0 μm for the lower layer, 0.1 to 1.5 μm for the middle layer, and 1.0 to 10.0 μm for the upper layer.
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, it will not be able to exhibit excellent wear resistance over a long period of use, whereas if it exceeds the upper limit of each, This is because the crystal grains of the hard coating tend to become coarse, and the thickness of the entire coating layer increases, making it impossible to obtain the effect of improving chipping resistance.
The reason why the average layer thickness of the intermediate layer is set in the above range is that if it is less than the lower limit, a sufficient effect of separating the disorder in the growth direction of Ti carbonitride in the lower layer cannot be obtained, whereas if it exceeds the upper limit, This is because the aforementioned average width exceeds 0.2 μm due to coarsening of the crystal grains in the intermediate layer. Note that the average layer thickness of the upper layer and the lower layer is not particularly limited as long as the 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 average layer thickness of each layer is more preferably 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.

Measurement method for average layer thickness, average composition, and crystal structure:
The average film thickness can be determined by observing a longitudinal section of the hard film layer using a scanning electron microscope (SEM).
Regarding the average composition of the TiAlN layer, an electron beam was irradiated from the surface side of a sample with a polished surface using an electron beam microanalyzer (EPMA), and the obtained characteristics The 10-point average of the line analysis results is taken as the average composition.
The crystal structure of the TiAlN layer was measured using an electron backscatter diffraction (EBSD) device at 70 degrees of incidence on each crystal grain present within the measurement range of the polished longitudinal section of the hard coating layer. An electron beam with an acceleration voltage of 15 kV is irradiated with an irradiation current of 1 nA at intervals of 0.01 μm/step. Then, by measuring the electron beam backscatter diffraction image, analyzing the crystal structure of each crystal grain, and calculating the ratio of the number of pixels belonging to the NaCl type face-centered cubic structure to the total number of pixels for which the crystal structure was identified. , the area ratio of crystal grains having a NaCl type face-centered cubic structure is determined. Note that the measurement range is 50 μm in the direction parallel to the surface of the tool base, and the range including the entire thickness of the hard coating layer in the vertical direction.

Tool base:
As the tool base, any base material conventionally known as this type of tool base can be used as long as it does not impede achieving the object of the present invention. Examples include cemented carbide (WC-based cemented carbide, containing WC and Co, and also containing carbonitrides such as Ti, Ta, and Nb), cermets (TiC, It is preferable to use one of TiN, TiCN, etc. as a main component), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), or cBN sintered body.

Other layers (top layer)
The hard coating of the present invention has sufficient wear resistance, chipping resistance, and peeling resistance even in high-speed turning processing of spheroidal graphite cast iron, but the layer including at least the aluminum oxide layer has a thickness of 1.0 to 25.0 μm. When provided as the top layer on the TiAlCN layer with a total average layer thickness of It can exhibit removability. Here, if the total average layer thickness of the layers including at least the aluminum oxide layer is less than 1.0 μm, the effect of the layer will not be sufficiently exhibited, while if it exceeds 25.0 μm, the crystal grains of the layer tend to become coarse. This makes chipping more likely to occur.

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

(1) Lower layer (TiCN layer) film formation process Reactive gas TiCl ₄ : 2.0 to 2.5%, CH ₃ CN: 0.6 to 1.0%,
N ₂ : 20-40%, H ₂ : balance Reaction atmosphere temperature: 800-940°C
Reaction atmosphere pressure: 5.0-10.0kPa
In addition, when forming a Ti compound layer, that is, any one of Ti carbide, nitride, carbonate, or carbonitride oxide, as a base layer in addition to the TiCN layer, known film formation conditions are applied. It may be adopted as appropriate.

(2) Intermediate layer deposition process The intermediate layer deposition process includes an etching process, a lower layer deposition process, and an upper layer deposition process.
a Etching process Reaction gas TiCl ₄ : 4.0-6.0%, H ₂ : remainder Reaction atmosphere temperature: 800-980°C
Reaction atmosphere pressure: 5.0-10.0kPa
b Lower layer (TiN layer) film formation process Reaction gas TiCl ₄ : 1.5 to 2.5%, N ₂ : 45 to 65%, H ₂ : balance Reaction atmosphere temperature: 880 to 1000°C
Reaction atmosphere pressure: 12.0-20.0kPa
c Upper layer (e.g. TiCN layer) film formation process Reactive 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 Reaction atmosphere temperature: 700-800°C
Reaction atmosphere pressure: 5.0-10.0kPa

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

Next, examples 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 WC-based cemented carbide as the tool base will be described; however, as mentioned above, the tool base is limited to WC-based cemented carbide. The same is true when applied to tools such as drills and end mills.

First, Co powder, TiC powder, ZrC powder, TaC powder, NbC powder, Cr ₃ C ₂ powder, and WC powder were prepared as raw material powders, and these raw material powders were blended into the composition shown in Table 1. Further, wax was added and wet-mixed for 72 hours in a ball mill, dried under reduced pressure, and then press-molded at a pressure of 100 MPa. These compacts were sintered and processed to the specified dimensions to meet ISO standards. Tool bases A to E made of WC-based cemented carbide and having the insert shape of CNMG120412 were manufactured.

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

Lower layer (TiCN layer) film formation process Reactive gas TiCl ₄ : 2.0 to 2.5%, CH ₃ CN: 0.6 to 1.0%,
N ₂ : 20-40%, H ₂ : balance Reaction atmosphere temperature: 800-940°C
Reaction atmosphere pressure: 5.0-10.0kPa

Intermediate layer film formation process a Etching process Reaction gas TiCl ₄ : 4.0 to 6.0%, H ₂ : balance Reaction atmosphere temperature: 800 to 980°C
Reaction atmosphere pressure: 5.0-10.0kPa
b Film formation process of lower layer (TiN layer) Reaction gas TiCl ₄ : 1.5 to 2.5%, N ₂ : 45 to 65%, H ₂ : balance Reaction atmosphere temperature: 880 to 1000°C
Reaction atmosphere pressure: 12.0-20.0kPa
c Film formation process of upper layer (TiCN layer) Reactive 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 Reaction atmosphere temperature: 700-800°C
Reaction atmosphere pressure: 5.0-10.0kPa

(3) Upper layer (TiAlN layer) film formation process Reactive gas group A NH ₃ : 0.8 to 1.6%, H ₂ : 45 to 55%
Reactive gas group B AlCl ₃ : 0.5 to 0.7%, TiCl ₄ : 0.1 to 0.3%,
N2: 0.0~10.0%, _H2 : remainder Reaction atmosphere temperature: 700~900°C
Reaction atmosphere pressure: 4.0-5.0kPa
Reaction gas supply cycle: 1 to 5 seconds Gas supply time per cycle: 0.15 to 0.25 seconds Phase difference between supply of gas group A and gas B group: 0.10 to 0.20 seconds

In addition, in the coated tools 7 and 10 of the present invention, the uppermost layer containing aluminum oxide was formed under the film forming conditions listed in Table 5.

In addition, for comparison purposes, Comparative Examples 1 to 10 shown in Table 7 were manufactured on the surfaces of tool bases A to E under the film forming conditions shown in Table 2. For comparative coated tools 2, 4, and 8, the intermediate layer was formed under the same formation symbol as in the example, but the average layer thickness was outside the range defined by the present invention.
Note that in Comparative Examples 7 and 10, the uppermost layer containing aluminum oxide was formed under the film forming conditions listed in Table 5.

In addition, the longitudinal sections of the coating layers of the coated tools 1 to 10 of the present invention and the comparison coated tools 1 to 10 were measured using an SEM (magnification of 5000 times), and the layer thickness of each layer was measured at 5 points within the observation field. , the average layer thickness of each layer, and the results are shown in Tables 6 and 7.
Furthermore, the composition and crystal structure (area ratio of crystal grains with NaCl type face-centered cubic structure) of the coating layers of the coated tools 1 to 10 of the present invention and comparative coated tools 1 to 10 were measured by the method described above, and the results are shown in Table 7. Described.

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

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

As is clear from the results of the cutting tests shown in Table 8, coated tools 1 to 10 of the present invention all have excellent wear resistance, peeling resistance, and chipping resistance, so they are coated with spheroidal graphite. Demonstrates excellent cutting performance over a long period of time, even in high-speed turning of cast iron. On the other hand, when comparative coated tools 1 to 10, which do not satisfy the requirements stipulated for coated tools of the present invention, are used for high-speed turning machining of spheroidal graphite cast iron, chipping occurs and the service life ends in a short period of time. It has been reached.

The surface-coated cutting tool of the present invention can be used not only for cutting various types of steel under normal cutting conditions, but also for cutting at high speeds such as spheroidal graphite cast iron, which generates high heat and places a large load on the cutting edge. In turning processing, it exhibits excellent wear resistance, peeling resistance, and chipping resistance, and shows excellent cutting performance over a long period of time, so it can improve the performance of cutting equipment and save labor in cutting processing. The present invention can satisfactorily respond to energy saving and cost reduction.

Claims (1)

A surface-coated cutting tool having a tool base and a coating layer on the surface of the tool base including, in order toward the tool surface, a lower layer, an intermediate layer, and an upper layer,
The lower layer has at least one Ti carbonitride layer with an average layer thickness of 2.0 to 20.0 μm,
The intermediate layer has an average layer thickness of 0.1 to 1.5 μm, and includes a lower layer made of Ti nitride on the lower layer side, and a carbonitride, carbonate, or carbonitoxide of Ti on the upper layer side. The carbonitride, carbonate, or carbonitoxide of Ti in the upper layer has an average width of crystal grains of 0.20 μm in a direction parallel to the surface of the tool base. The following is true,
The upper layer has an average layer thickness of 1.0 to 10.0 μm, and the composition is represented by the composition formula: Ti _1-x Al _x N (where x represents the average composition in atomic ratio): 0 Satisfying .60≦x≦0.95, the crystal grains are mainly of NaCl type face-centered cubic structure,
A surface-coated cutting tool characterized by:

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