JP7841290B2 - surface coated cutting tools - Google Patents

Description

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

To improve the cutting performance of cutting tools, there are conventional coated tools in which a coating layer is formed on the surface of a substrate such as a tungsten carbide (hereinafter referred to as WC)-based cemented carbide by vapor deposition, and these are known to exhibit excellent wear resistance.
While coated tools with the aforementioned conventional coating layer exhibit excellent wear resistance, various proposals have been made for further improvements to the coating layer.

For example, Patent Documents 1 and 2 describe a coated tool having a coating layer that includes a plurality of columnar crystals, where each of the columnar crystals 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 stacked, and this coated tool is said to have excellent wear resistance and chipping resistance.

Japanese Patent Publication No. 2019-171546 Japanese Patent Publication No. 2019-171547

This invention was made in view of the above circumstances and proposals, and in particular aims to provide a coated tool that ensures resistance to welding during the cutting of cast iron, while also possessing excellent wear resistance and chipping resistance.

A surface-coated cutting tool according to an embodiment of the present invention is
It has a substrate and a coating layer provided on the surface of the substrate,
The coating layer has a laminated layer containing one or more lamination units,
The aforementioned layered unit includes, in order from the substrate toward the tool surface, a first layer, a second layer, and a third layer.
Each of the first, second, and third layers has a substantially constant composition, without any intentional changes in composition.
The first layer is a TiC _x N _1-x with an average thickness of 0.3 μm or more and 3.0 μm or less (where the average value of x, x _avg , is 0.50 ≤ x _avg ≤ 0.65).
The second layer has an average thickness of 0.3 μm or more and 3.0 μm or less, and is TiC _y N _1-y (where the average value of y, y _avg , is 0.65 < y _avg ≤ 0.75).
The third layer is a TiC _z N _1-z with an average thickness of 0.3 μm or more and 3.0 μm or less (where the average value of z, z _avg , is 0.75 < z _avg ≤ 1.00).

Furthermore, the surface-coated cutting tool according to the above embodiment may satisfy one or more of the following items (1) to (3).

(1) The number of stacking units is 1 or more and 30 or less.
(2) The average thickness of the laminated layer is 3.0 μm or more and 16.0 μm or less.
(3) The laminate layer having one or more TiN layers, TiCNO layers, _Al₂O₃ layers, or _AlTiN layers on the tool surface side of the layer closest to the tool surface, with or without a TiCN layer.
(4) The substrate and the laminate layer have one or more layers of TiC, TiN, TiCN, and TiCNO.

The aforementioned surface-coated cutting tool, particularly in the cutting of cast iron, ensures resistance to welding while possessing excellent wear resistance and chipping resistance.

This is a schematic diagram showing a longitudinal cross-section of the coating layer of a surface-coated cutting tool according to an embodiment of the present invention.

According to the inventor's research, while the coated tools described in Patent Documents 1 and 2 exhibit excellent wear resistance and chipping resistance, they were found to have insufficient resistance to welding, particularly in the cutting of cast iron.

Upon investigating the reason, it was found _that while TiCN layers formed using hydrocarbon gases such as _C₂H₄ as the deposition gas have fine crystalline grains and therefore excellent wear resistance, the increased carbon content leads to a higher affinity with Fe contained in the workpiece, resulting in decreased resistance to welding.

The following describes in detail a coating tool according to an embodiment of the present invention.
In this specification and in the claims, when a numerical range is expressed as "M to N" (where M and N are both numerical values), it is synonymous with "M or greater, N or less," and the range includes both an upper limit (N) and a lower limit (M). When a unit is specified only for the upper limit (N), the units of the upper limit (N) and the lower limit (M) are the same.
Furthermore, the composition of compounds not expressed using a formula is not limited to stoichiometric compositions, but includes all conventionally known atomic ratios.

Figure 1 is a schematic diagram showing an example of a longitudinal cross-section of the coating layer of a surface-coated cutting tool according to an embodiment of the present invention (a cross-section perpendicular to the surface when the surface of the substrate is treated as a flat surface, ignoring minute irregularities on the substrate surface). The substrate (1) has a coating layer (10) on its surface, and the coating layer (10) has a base layer (2), a laminate layer (7), an intermediate layer (8), and an upper layer (9). The laminate layer (7) has two laminate units (6) including a first layer (2), a second layer (3), and a third layer (4). The base layer (2), intermediate layer (6), and upper layer (7) may be provided selectively, as will be described below. This embodiment will be described in detail below.

1. Coating Layer The coating layer will be explained below.

(1) Laminated layer The laminated layer has one or more repetitions of a laminated unit of three layers, a first layer, a second layer, and a third layer, in order from the substrate side toward the tool surface.
The number of repetitions should preferably be between 2 and 30. This is because, within this range of repetitions, the aforementioned objective can be reliably achieved.

Here,
The first layer is TiC _x N _1-x (where the mean value of x, x _avg , is 0.50 ≤ x _avg ≤ 0.65),
The second layer is TiC _y N _1-y (where the mean value of y, y _avg , is 0.65 < _avg y ≤ 0.75),
The third layer is TiC _z N _1-z (where the mean value of z, z _avg , is 0.75 < z _avg ≤ 1.00),
Each is preferable.
x _avg , y _avg , and z _avg are the average values for all layers 1, 2, and 2, respectively.

The reason why it is preferable to set x _avg , y _avg , and z _avg within the above range is that within this range, the difference in thermal expansion coefficients due to differences in composition becomes appropriate, and the stress relaxation layer can be reliably exerted.

The average thickness of the first layer is between 0.3 μm and 3.0 μm.
The average thickness of the second layer is between 0.3 μm and 3.0 μm.
The average thickness of the third layer is between 0.3 μm and 3.0 μm.
This is preferable. If each layer has this average thickness, the propagation of cracks generated during machining can be suppressed more reliably (the average thicknesses of the first, second, and third layers may be the same or different). Furthermore, when the average thickness of the laminate layers is 3.0 μm or more and 16.0 μm or less, the propagation of cracks generated during machining can be suppressed even more reliably.

(2) Upper layer An upper layer may be provided on the tool surface side of the laminate, with one or more layers from among a TiN layer, a TiCNO layer, _{an Al₂O₃} layer, and an AlTiN layer, each having an average thickness of 0.1 μm or more and 20.0 μm or less, for a total average thickness of 1.0 μm or more and 25.0 μm or less (the above objectives can be achieved even without providing this upper layer). Providing this upper layer allows the coated tool to exhibit even better wear resistance and chipping resistance. Here, if the total average thickness of the upper layer is less than 1.0 μm, the function of the upper layer is not fully realized, while if it exceeds 25.0 μm, the crystal grains of the upper layer tend to coarseen, making it easier for chipping to occur.

(3) Intermediate layer An intermediate layer is more preferably provided between the laminate layer and the upper layer in order to improve the adhesion between the two layers (Figure 1 shows an embodiment in which an upper layer and an intermediate layer are provided, but even when an upper layer is provided, the intermediate layer may not be necessary). The intermediate layer is preferably a TiCNO layer, and its total average thickness is preferably 0.3 to 3.0 μm. When the average thickness is within this range, the adhesion between the laminate layer and the upper layer is further improved.

(4) Underlayment An underlayment may be provided between the substrate and the laminated layer to improve adhesion between them (the aforementioned objectives can be achieved even without it). The underlayment is preferably one or more Ti compound layers, which are TiC, TiN, TiCN, or TiCNO layers, and the average total thickness is 0.1 to 3.0 μm. When the average total thickness is within this range, the adhesion between the two is further improved.

(5) Other layers When switching the film deposition gas, a very small amount of layers other than the first layer, second layer, _third layer, _Al₂O₃ layer, AlTiN layer, TiN layer, and TiCNO layer may be produced unintentionally.

2. Substrate (1) Composition Any substrate known conventionally as a substrate of this type can be used, as long as it does not hinder the achievement of the objectives of the present invention. Examples include cemented carbide (WC-based cemented carbide, including those containing WC and Co, and further including those with carbonitrides such as Ti, Ta, and Nb added), cermet (mainly composed of TiC, TiN, TiCN, etc.), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), and cBN sintered body, and it is preferable to use any of these.

(2) Shape The shape of the base material is not particularly restricted as long as it is a shape used as a cutting tool, and examples include the shape of the insert and the shape of the drill.

3. Measurement Method (1) Composition The composition of each layer can be measured by observing at multiple locations (for example, five locations) using a transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDS), identifying each layer, measuring the composition of each layer, and averaging them.

(2) Average Thickness The average thickness of each layer constituting the coating layer can be determined by, for example, preparing a sample for observation by cutting the coating layer in a longitudinal section at an arbitrary position using a focused ion beam system (FIB), a cross-section polisher (CP), etc., and then analyzing the longitudinal section using a scanning electron microscope (SEM), a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), or energy dispersive X-ray analysis (EDX) attached to an SEM or TEM. This can be obtained by observing multiple locations (for example, five locations) using a spectrometry device, identifying each layer, measuring the thickness of each layer, and averaging the results.

To determine the average thickness, the substrate surface, which serves as the starting point for the length in the thickness direction, is defined as the reference line of the interface roughness between the substrate and the coating layer (or the underlying layer, if one exists, as described later) in the observation image of a longitudinal section (approximately in the thickness direction) perpendicular to the substrate. That is, when the substrate has a planar surface like an insert, elemental mapping using EDS is performed on the longitudinal section, and the interface between the coating layer and the substrate is determined by performing known image processing on the obtained elemental map. The average line y0 is then arithmetically calculated from the roughness curve of the interface between the coating layer and the substrate, and this is considered the surface of the substrate.

Here, the method for arithmetically determining the mean line y0 is to approximate the interface roughness by f(x) (where x is the distance in the direction parallel to the substrate surface) when the y-axis is taken in the thickness direction of the longitudinal section and the x-axis is taken perpendicular to it, and perform the calculation shown in equation [1]. Here, the length of l is preferably 4 μm or more.
Then, the direction perpendicular to this average line is defined as the direction perpendicular to the substrate (the thickness direction of the coating layer).

Furthermore, even if the substrate has a curved surface, such as a drill, if the tool diameter is sufficiently large relative to the thickness of the coating layer, the interface between the coating layer and the substrate in the measurement area will be approximately flat. Therefore, the substrate surface can be determined using a similar method. That is, for example, in the case of a drill, elemental mapping using EDS is performed on the longitudinal cross-section of the coating layer perpendicular to the axial direction. Known image processing is then applied to the obtained elemental map to determine the interface between the coating layer and the substrate. The average line of the roughness curve at this interface is then arithmetically calculated and defined as the substrate surface. The direction perpendicular to this average line is then defined as the direction perpendicular to the substrate (thickness direction).

4. Manufacturing Method The coating layer of the present invention can be manufactured, for example, by the CVD method under the following film formation conditions.

(1) Laminated layer The following percentages are volume percentages (capacity percentages).
(1-1) First layer TiCl ₄ : 1.0 to 3.0%, CH ₃ CN: 0.5 to 1.5%,
N ₂ : 13.0-40.0%, H ₂ : Residual temperature: 850-950°C
Pressure: 5.0–7.0 kPa

(1-2) Second layer TiCl ₄ : 1.0 to 2.0%, CH ₃ CN: 0.1 to 1.0%,
C ₂ H ₄ : 0.3 to 2.0%, N ₂ : 0.0 to 40.0%, H ₂ : Residual temperature: 850 to 950°C
Pressure: 5.0–7.0 kPa

(1-3) Third layer TiCl ₄ : 1.0 to 3.0%, CH ₃ CN: 0.1 to 0.8%,
C ₂ H ₄ : 2.0 to 3.0%, N ₂ : 0.0 to 15.0%, H ₂ : Residual temperature: 850 to 950°C
Pressure: 5.0–7.0 kPa

(2) Upper layer TiN layer TiCl ₄ : 2.0 to 5.0%, N ₂ : 25.0 to 35.0%, H ₂ : remaining TiC layer TiCl ₄ : 2.0 to 5.0%, CH ₄ : 5.0 to 13.0%, H ₂ : remaining TiCNO layer TiCl ₄ :0.5~3.5%, _CH3CN :0.2~1.5%,
CO: 0.1 to 0.3%, N ₂ : 35.0 to 45.0%, H ₂ : remaining AlTiN layer AlCl ₃ : 0.2 to 1.3%, TiCl ₄ : 0.1 to 0.5%,
N ₂ : 10.0 to 16.0%, NH ₃ : 2.0 to 6.0%, H ₂ : remaining Al ₂ O ₃ layers AlCl ₃ : 1.0 to 3.0%, CO ₂ : 4.5 to 6.5%,
HCl: 1.2-4.0%, H ₂ S: 0.1-0.3%, H ₂ : Residual temperature: 850-1000°C
Pressure: 4.0–30.0 kPa

(3) Intermediate TiCNO layer TiCl ₄ : 0.5 to 3.5%, CH ₃ CN: 0.2 to 1.5%,
CO: 0.1 to 0.3%, N ₂ : 35.0 to 45.0%, H ₂ : Residual temperature: 850 to 1000°C
Pressure: 5.0–30.0 kPa

(4) Substrate layers: The film deposition conditions for the TiN layer, TiC layer, and TiCNO layer are the same as for the upper layer.
TiCN layer TiCl ₄ : 1.0 to 3.0%, CH ₃ CN: 0.5 to 1.5%,
N ₂ : 13.0-18.0%, H ₂ : Residual temperature: 850-950°C
Pressure: 5.0–10.0 kPa

Next, we will describe some examples.
Here, as a specific example of the coated tool of the present invention, we will describe its application to an insert cutting tool using a WC-based cemented carbide as the base material. However, as mentioned above, the base material is not limited to a WC-based cemented carbide, and the same applies when the coated tool is applied to drills, end mills, 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 blended according to the composition shown in Table 1, wax was added, and the mixture was wet-mixed in a ball mill for 72 hours. After drying under reduced pressure, the mixture was press-molded at a pressure of 100 MPa. These compacted bodies were sintered and processed to the predetermined dimensions to produce substrates A to C made of WC-based cemented carbide with insert shapes according to ISO standard CNMA120412. Note that each powder contained trace amounts of unavoidable impurities.

Next, on substrates A to C, the coated tools 1 to 8 shown in Table 5 were obtained according to the conditions shown in Tables 2 and 4. Where two layers are listed in the "Layer Type" column for the upper layer, the left-hand layer is the laminated layer, and the corresponding average thickness is also indicated.

Furthermore, for comparison, coating layers were formed on the surfaces of these substrates A to C under the film formation conditions shown in Tables 3 and 4, yielding comparative example coated tools 1 to 8 shown in Table 5.

In Table 5, "-" indicates non-existence, and the layer on the right in the upper layer column is present on the coated tool surface, with its average thickness being the value on the right.

Next, for the coated tools 1-8 of the examples and coated tools 1'-8' of the comparative examples, wet cutting tests 1 and 2, as described below, were performed with the tools clamped to the tip of a tool steel cutting tool using a fixing jig, and the wear of the flank surface of the cutting edge was measured. The results of each cutting test are shown in Tables 6 and 7.

Cutting Test 1: Wet continuous outer diameter cutting workpiece: FCD700 round bar with outer diameter φ300 mm cutting speed: 300 m/min
Cut: 2.5 mm
Feed rate: 0.25 mm/rev
Cutting time: 5 minutes Cutting oil material: Water-soluble cutting oil

Cutting Test 2: Wet Intermittent End Face Cutting Workpiece Material: FCD700 Round Bar with 4 Slits, Outer Diameter φ300 mm Cutting Speed: 250 m/min
Cut: 2.0 mm
Feed rate: 0.2 mm/rev
Cutting time: 5 minutes Cutting oil material: Water-soluble cutting oil

In Tables 6 and 7, the cutting time (minutes) until the end of life of the comparative coated tool refers to the cutting time (minutes) until the tool reaches the end of life due to chipping.

As shown in Tables 6 and 7, the coated tools 1 to 8 of the examples all exhibit excellent wear resistance and chipping resistance while ensuring the welding resistance of the coating layer. Therefore, even when used for cutting cast iron, no chipping occurs, and they demonstrate excellent wear resistance over a long period. In contrast, the coated tools 1 to 8 of the comparative examples, which do not satisfy even one of the requirements specified for the coated tools of the present invention, exhibit chipping when used for cutting cast iron and reach the end of their service life in a short time.

1. Base 2. Underlayer 3. First layer 4. Second layer 5. Third layer 6. Laminated unit 7. Laminated layer 8. Intermediate layer 9. Upper layer 10. Covering layer

Claims (4)

A surface-coated cutting tool having a substrate and a coating layer provided on the surface of the substrate,
The coating layer has a laminated layer containing one or more lamination units,
The aforementioned laminated unit comprises, in order from the substrate toward the tool surface, a first layer, a second layer, and a third layer, and each of the first, second, and third layers has a substantially constant composition.
The first layer is a TiC _x N _1-x with an average thickness of 0.3 μm or more and 3.0 μm or less (where the average value of x, x _avg , is 0.50 ≤ x _avg ≤ 0.65).
The second layer has an average thickness of 0.3 μm or more and 3.0 μm or less, and is TiC _y N _1-y (where the average value of y, y _avg , is 0.65 < y _avg ≤ 0.75).
The surface-coated cutting tool is characterized in that the third layer has an average thickness of 0.3 μm or more and 3.0 μm or less of TiC _z N _1-z (where the average value of z, z _avg , is 0.75 < z _avg ≤ 1.00). The surface-coated cutting tool according to claim 1, characterized in that the number of layered units is 1 or more and 30 or less. A surface-coated cutting tool according to claim 1 or 2, characterized in that the average thickness of the laminated layer is 3.0 μm or more and 16.0 μm or less. A surface-coated cutting tool according to any one of claims ₁ to ₃ , characterized in that the layer closest to the tool surface of the laminated body has one or more layers, either via or without a TiCN layer, of a TiN layer, a TiCNO layer, an Al₂O₃ layer, or an AlTiN layer on the tool surface side of the layer closest to the tool surface.