JP7570599B2 - Surface-coated cutting tools - Google Patents

Description

The present invention relates to a surface-coated cutting tool (hereinafter sometimes referred to as a coated tool).

In order to improve the cutting performance of cutting tools, there have been conventionally coated tools in which a coating layer is formed by vapor deposition on the surface of a tool substrate such as a tungsten carbide (hereinafter referred to as WC)-based cemented carbide, and these coated tools are known to exhibit excellent wear resistance.
Although the coated tools having the above-mentioned conventional coating layers are excellent in wear resistance, various proposals have been made for further improving the coating layers.

For example, Patent Documents 1 and 2 disclose a coated tool including a coating layer having a plurality of columnar crystals, each of which has a multilayer structure in which a first unit layer of TiC _x N _z-x (0.45≦x<0.70, 0.80≦z≦1.20) and a second unit layer of TiC _y N _A-y (0.70≦y≦1, 0.80≦A≦1.20) are alternately laminated, and this coated tool is said to have excellent wear resistance and chipping resistance.

JP 2019-171546 A JP 2019-171547 A

According to the inventor's investigations, the coated tools described in Patent Documents 1 and 2 have excellent wear resistance and chipping resistance, but are found to have insufficient adhesion resistance, particularly when cutting steel and cast iron.

The present invention was made in consideration of these circumstances, and aims to provide a coated tool that has excellent wear resistance and chipping resistance while ensuring adhesion resistance, particularly when cutting steel and cast iron.

The inventors have conducted extensive research into means for ensuring adhesion resistance, particularly in cutting steel and cast iron, while also providing excellent wear resistance and chipping resistance. As a result, they have discovered that a coated tool having a coating layer with a TiCN layer (upper layer) with a low C content of a predetermined average layer thickness on top of a laminate layer in which a predetermined number of TiCN layers (first layer) with a low C content and TiCN layers (second layer) with a high C content are alternately stacked can achieve the above-mentioned objective. Here, the C content range is the same for the first layer and the upper layer, and is higher for the second layer.

The present invention is based on this finding and is as follows.
"(1) A surface-coated cutting tool having a tool base and a coating layer provided on the surface of the tool base,
the covering layer has a laminate layer in which seven or more laminate unit layers are laminated and an upper layer on the upper part of the laminate layer,
the laminate unit layer has a first layer on the tool base side and a second layer on the opposite side,
The first layer has a composition represented by a composition formula: TiC _x N _1-x , where 0.50≦x≦0.60;
The second layer has a composition represented by the formula TiC _y N _1-y , where 0.65≦y≦1.00;
The composition of the upper layer is expressed by the composition formula: TiC _z N _1-z , where z is 0.50≦z≦0.60;
the laminate layer has columnar crystals, the average width of which is 130 to 300 nm;
The ratio of the average thickness of the first layer to the average thickness of the second layer, (average thickness of the first layer)/(average thickness of the second layer), is 0.5 to 3.0.
A surface-coated cutting tool comprising:
(2) The surface-coated cutting tool according to (1) above, characterized in that the upper layer has one or more layers selected from the group consisting of a TiN layer, a TiCN layer, _a TiCNO layer, an _Al2O3 layer, and an AlTiN layer.

The surface-coated cutting tool of the present invention has excellent wear resistance and chipping resistance while ensuring adhesion resistance, particularly when cutting steel and cast iron.

1 is a schematic diagram showing an example of an embodiment of a vertical cross section of a coating layer of a surface-coated cutting tool of the present invention. FIG.

In this specification and claims, when a numerical range is expressed as "M to N" (where M and N are both numerical values), the range includes an upper limit (N) and a lower limit (M), and the units of the upper limit (N) and the lower limit (M) are the same.
Furthermore, the composition of a compound not expressed by a composition formula is not limited to a stoichiometric composition, and includes all compositions of conventionally known atomic ratios.

Figure 1 is a schematic diagram showing an example of an embodiment of a longitudinal section (a section perpendicular to the surface of the tool base when the surface is treated as a flat surface, ignoring minute irregularities on the surface) of the coating layer of the surface-coated cutting tool of the present invention. On the surface of the tool base (1), the coating layer has a base layer (2), a laminate layer formed by stacking laminate unit layers including a first layer (3) and a second layer (4), an upper layer (5), and an outermost surface layer (6). This embodiment will be described in detail below.

1. Covering Layer (1) Laminated Unit Layer and Laminated Body Layer The laminated unit layer has a first layer on the tool substrate side and a second layer on the opposite side.
The composition of the first layer is preferably expressed by the composition formula TiC _x N _1-x , where 0.50≦x≦0.60;
When the composition of the second layer is expressed by the composition formula TiC _y N _1-y , it is preferable that 0.65≦y≦1.00.
The reason why it is preferable to set x and y within the above ranges is that the difference in thermal expansion coefficient due to the difference in composition becomes appropriate, and the laminate layer formed by laminating a plurality of laminate unit layers can reliably exhibit the function as a stress relaxation layer.

The average thickness of the laminate layer is preferably 4.0 to 16.0 μm, in which case the laminate layer can more reliably suppress the propagation of cracks.
In the laminate unit layer, the ratio of the average thickness of the first layer to the average thickness of the second layer, (average thickness of the first layer)/(average thickness of the second layer), is preferably 0.5 to 3.0. When it is in this range, the function as a stress relaxation layer is reliably exhibited.

The number of stacked unit layers is preferably 7 or more. There is no upper limit on the number of stacked layers, but in the example of the manufacturing method described below, the upper limit is about 50 layers due to the constraints of the manufacturing method.

The first and second layers of the laminate unit layer are both preferably fine columnar crystals, with an average width of 130 to 300 nm. If the average width is within this range, the upper layer, a TiCN layer with a low C content, described below, can also be made into fine columnar crystals, improving wear resistance and chipping resistance.

Here, the average grain width is measured as follows.
The cross section is observed with a scanning electron microscope (SEM), a line segment of at least 1 μm in length parallel to the substrate surface is drawn at a position 4 μm from the surface of the tool substrate in the thickness direction of the coating layer, the number of grain boundaries intersecting the line segment is counted, and the average grain width is calculated by dividing the length of the line segment by the number measured. The reason for the position of 4 μm is that the grain size of the crystal grains increases toward the tool surface, so the measurement was made at 4 μm.

Here, the composition of each layer is measured by cross-sectional measurement using a transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDS), and the measured values are averaged.

The surface of the tool base that is the starting point of the length in the layer thickness direction is the reference line of the interface roughness between the tool base and the coating layer (if there is a base layer, as described below, it is the base layer) in the observation image of a vertical section (almost in the layer thickness direction) that is nearly perpendicular to the tool base. In other words, when the tool base has a flat surface like an insert, element mapping is performed using EDS on the vertical section, and the interface between the coating layer and the tool base is determined by performing known image processing on the obtained element map, and the average line is arithmetically obtained for the roughness curve of the interface between the coating layer and the tool base thus obtained, and this is taken as the surface of the tool base. The direction perpendicular to this average line is taken as the direction perpendicular to the tool base (layer thickness direction).

Even if the tool base has a curved surface like a drill, if the tool diameter is sufficiently large compared to the thickness of the coating layer, the interface between the coating layer and the tool base in the measurement area will be approximately flat, so the surface of the tool base can be determined using a similar method. That is, for example, in the case of a drill, element mapping is performed using EDS on the longitudinal section of the coating layer in a section perpendicular to the axial direction, and the interface between the coating layer and the tool base is determined by performing known image processing on the obtained element map, and the average line is arithmetically determined for the roughness curve of the interface between the coating layer and the tool base thus obtained, and this is taken as the surface of the tool base. The direction perpendicular to this average line is taken as the direction perpendicular to the tool base (layer thickness direction).

(2) Upper layer The upper layer is a TiCN layer, and when its composition is expressed by the composition formula _{TiCzN1 -z} , it is preferable that 0.50≦z≦0.60. When z is in this range, the affinity with the work material is reduced while retaining the columnar crystals of the lower laminate layer, and adhesion can be suppressed.
The average thickness of the upper layer is preferably 3.0 to 16.0 μm, because when the sum of the average thicknesses of the laminate layer and the upper layer is 7.0 to 20.0 μm, wear resistance can be exhibited for a long period of time.

(3) Other layers The coating layer of the present invention can achieve the above-mentioned object of the invention with only the laminate layer and the top layer, but can also include layers other than these layers. Such other layers include an outermost layer, an intermediate layer, and an undercoat layer.

(3-1) Outermost layer When a compound layer having a total average thickness of 0.1 to 20.0 μm is provided on the _upper layer as an outermost layer with a total average thickness of _1.0 to 25.0 μm, the outermost layer can exhibit even better wear resistance and chipping resistance in combination with the effects of these layers. Here, if the total average thickness of the outermost layer is less than 1.0 μm, the effect of the outermost layer is not sufficiently exhibited, while if it exceeds 25.0 μm, the crystal grains of the outermost layer are easily coarsened, and chipping is easily generated.

(3-2) Intermediate layer The intermediate layer is provided between the laminate layer and the upper layer to improve the adhesion between the two layers. The intermediate layer is preferably a TiCNO layer, and the average layer thickness is preferably 0.3 to 3.0 μm. When the average layer thickness is in this range, the adhesion between the two layers is further improved.

(3-3) Underlayer The underlayer is provided between the tool base and the laminate layer to improve the adhesion between the two layers. The underlayer is a Ti compound layer such as a TiC layer, a TiN layer, a TiCN layer, or a TiCNO layer, and the average layer thickness is preferably 0.1 to 20.0 μm. If the average layer thickness is within this range, the adhesion between the two layers is further improved.

(4) Measurement of Average Layer Thickness The average layer thickness of each layer constituting the coating layer is measured by, for example, cutting the coating layer at a longitudinal section at an arbitrary position using a focused ion beam system (FIB), a cross section polisher (CP), or the like to prepare a sample for observation, and then observing the longitudinal section using a SEM or a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), or an energy dispersive X-ray analyzer (EDX) attached to the SEM or TEM. The thickness can be obtained by observing a plurality of points (for example, five points) using a spectrometer, identifying each layer, measuring the layer thickness, and averaging the measured thicknesses.

2. Tool Base The tool base may be any of the substrates known in the art for this type of tool base, provided that they do not impede the achievement of the object of the present invention. Examples include cemented carbide (WC-based cemented carbide, WC, Co, and carbonitrides of Ti, Ta, Nb, etc.), cermets (mainly TiC, TiN, TiCN, etc.), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), and cBN sintered bodies, and any of these is preferable.

3. Manufacturing Method The coating layer of the present invention can be manufactured, for example, by the following method.

(1) Laminate Unit Layer The following percentages are by volume (volume %).
(1-1) First layer TiCl ₄ : 1.0 to 3.0%, CH ₃ CN: 0.5 to 2.0%, N ₂ : 2.0 to 30.0%, H ₂ : Residual temperature: 850 to 950°C
Pressure: 5.0 to 10.0 kPa

(1-2) Second layer TiCl ₄ : 1.0 to 3.0%, CH ₃ CN: 0.10 to 0.70%, C ₂ H ₄ : 1.1 to 3.0%, N ₂ : 0.0-40.0%, H ₂ : Residual temperature: 850-950°C
Pressure: 5.0 to 10.0 kPa

(2) Upper layer TiCl ₄ : 1.0-3.0%, CH ₃ CN: 0.5-2.0%, N ₂ : 2.0-30.0%, H ₂ : Residual temperature: 850- 950℃
Pressure: 5.0 to 10.0 kPa

Next, an embodiment will be described.
Here, as a specific example of the coated tool of the present invention, a description will be given of an insert cutting tool using a WC-based cemented carbide as the tool substrate; however, as mentioned above, the tool substrate is not limited to a WC-based cemented carbide, and the same applies when the coated tool is applied to a drill, end mill, etc.

First, Co powder, TiC powder, TaC powder, NbC powder, _{Cr3C2 powder} , and WC powder were prepared as raw material powders. These raw material powders were mixed according to the composition shown in Table 1, and wax was added and wet mixed in a ball mill for 72 hours. The mixture was dried under reduced pressure and then pressed at a pressure of 100 MPa. These powder compacts were sintered and processed to predetermined dimensions to produce tool bases A to C made of WC-based cemented carbide having an insert shape conforming to ISO standard CNMA120412.

Next, coated tools 1 to 10 of the present invention shown in Table 4 were obtained on the tool substrates A to C under the conditions shown in Table 2. The undercoat layer, intermediate layer, and outermost surface layer were formed under the conditions shown in Table 3. When two types of layers are listed in the layer type column for the outermost surface layer, the layer on the left is the upper layer, and the corresponding average layer thickness is also listed.

For comparison, coating layers were formed on the surfaces of these tool substrates A to C under the deposition conditions shown in Table 2, to obtain comparative coated tools 1 to 10 shown in Table 4. The outermost layer was deposited under the conditions shown in Table 3.

Next, wet cutting tests 1 and 2 were carried out on the coated tools 1 to 10 of the present invention and the comparative coated tools 1' to 10', all of which were clamped to the tip of a tool steel bit with a fixture, and the flank wear of the cutting edge was measured. The results of each cutting test are shown in Tables 5 and 6.

Cutting test 1: Wet continuous outer diameter cutting Workpiece: FCD700 Round bar with outer diameter of φ300 mm Cutting speed: 300 m/min
Cut: 2.5 mm
Feed rate: 0.25 mm/rev
Cutting time: 10 minutes

Cutting test 2: Wet intermittent cutting Workpiece: FCD700 Round bar with outer diameter of φ300 mm, 4 slits on end face Cutting speed: 250 m/min
Cut: 2.0 mm
Feed rate: 0.2 mm/rev
Cutting time: 10 minutes

The results shown in Tables 5 and 6 show that coated tools 1 to 10 of the present invention all have excellent wear resistance and chipping resistance while ensuring the adhesion resistance of the coating layer, and therefore do not chip even when used to cut steel or cast iron, and exhibit excellent wear resistance over a long period of time. In contrast, comparative coated tools 1 to 10, which do not satisfy even one of the requirements for the coated tools of the present invention, experience chipping when used to cut steel or cast iron, and reach the end of their useful life in a short period of time.

As mentioned above, the coated tool of the present invention exhibits excellent wear resistance and abrasion resistance while maintaining weldability over a long period of time, making it possible to provide a fully satisfactory solution for improving the performance of cutting equipment, reducing labor and energy required for cutting, and even reducing costs.

1 Tool base 2 Base layer 3 First layer 4 Second layer 5 Upper layer 6 Outermost layer

Claims (2)

A surface-coated cutting tool having a tool base and a coating layer provided on a surface of the tool base,
the covering layer has a laminate layer in which seven or more laminate unit layers are laminated and an upper layer on the upper part of the laminate layer,
the laminate unit layer has a first layer on the tool base side and a second layer on the opposite side,
The first layer has a composition represented by a composition formula: TiC _x N _1-x , where 0.50≦x≦0.60;
The second layer has a composition represented by the formula TiC _y N _1-y , where 0.65≦y≦1.00;
The composition of the upper layer is expressed by the composition formula: TiC _z N _1-z , where z is 0.50≦z≦0.60;
the laminate layer has columnar crystals, the average width of which is 130 to 300 nm;
The ratio of the average thickness of the first layer to the average thickness of the second layer, (average thickness of the first layer)/(average thickness of the second layer), is 0.5 to 3.0.
A surface-coated cutting tool comprising: 2. The surface-coated cutting tool according to claim 1, further comprising one or more of a TiN layer, a TiCN layer, a _TiCNO layer, an _Al2O3 layer, and an AlTiN layer on the upper layer.

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