Coated cemented carbide and cutting tools having the same

Abstract

To provide a coated cemented carbide alloy with improved wear resistance and fracture resistance, resulting in a longer tool life, and a cutting tool having the same. [Solution] A coated cemented carbide comprising a cemented carbide and a coating layer formed on its surface, wherein the cemented carbide comprises a WC phase, a hard phase, and a binder phase, the WC phase contains WC, the hard phase and the binder phase each contain a predetermined compound, the content ratios of the WC phase and the binder phase are within a predetermined range, the cemented carbide comprises a surface region and an internal region extending from the surface side to the interior side, the content ratio of the hard phase is 0% by mass or more and 1.0% by mass or less of the entire surface region, the content ratio of the hard phase is greater than 1.0% by mass and 12.0% by mass or less of the entire internal region, in the surface region, the ratio A of the length of Σ2 grain boundaries to the length of the total grain boundaries between adjacent WC particles is less than 10.0%, and in the internal region, the ratio B of the length of Σ2 grain boundaries to the length of the total grain boundaries between adjacent WC particles is greater than ratio A.

Description

Technical Field

[0001] The present invention relates to a coated cemented carbide and a cutting tool having the same.

Background Art

[0002] Conventionally, it is well known that a coated cutting tool formed by vapor-depositing a coating layer with a total film thickness of 3 to 20 μm on the surface of a substrate made of cemented carbide by chemical vapor deposition is used for cutting steel, cast iron, etc. Examples of the coating layer include a coating layer composed of a single layer or a multi-layer of two or more kinds selected from the group consisting of carbides, nitrides, carbonitrides, carbon oxides, and carbonitroxides of Ti and aluminum oxide. Under such a background, there is a demand for a cemented carbide cutting tool that is more excellent in wear resistance and chipping resistance and has a long tool life.

[0003] Therefore, various proposals have been made for the purpose of providing a cemented carbide cutting tool with a long tool life. For example, in Patent Document 1, in a WC-based cemented carbide, at least one of Co and Ni is contained in an amount of 4.0% by mass or more and less than 10.0% by mass, and at least one or more selected from TiC, TaC, NbC, ZrC, HfC, and VC are contained in a total amount of 4.0% by mass or more and less than 12.0% by mass, Cr3C2 is contained in an amount of 0.0% by mass or more and less than 0.5% by mass, and the balance consists of WC and inevitable impurities. The average particle size of WC is 0.2 μm or more and 4.0 μm or less, and the ratio of the Σ2 corresponding grain boundaries of WC to the total WC / WC grain boundaries (Σ2 corresponding grain boundary ratio) is 15% or more. A WC-based cemented carbide and a cutting tool using the cemented carbide have been proposed.

[0004] Furthermore, for example, Patent Document 2 proposes a cemented carbide comprising tungsten carbide particles and a binder phase, wherein the total content of the tungsten carbide particles and the binder phase in the cemented carbide is 80 volume% or more, the content of the binder phase in the cemented carbide is 0.1 volume% or more and 20 volume% or less, and in a histogram showing the distribution of orientation difference between adjacent pairs consisting of two adjacent tungsten carbide particles in the cemented carbide, a first peak exists in the class for orientation difference of 29.5° or more and less than 30.5°, the class on the horizontal axis of the histogram represents the orientation difference and the width of the class is 1.0°, and the frequency on the vertical axis of the histogram represents the ratio of the number of adjacent pairs belonging to each class to the total number of adjacent pairs in the cemented carbide. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-139032 [Patent Document 2] International Publication No. 2023 / 139726 [Overview of the project] [Problems that the invention aims to solve]

[0006] Incidentally, in recent years, machining processes have increasingly seen a rise in speed, feed rates, and depths of cut. As a result, tool breakage is frequently observed due to cracks that originate on the surface of the coating layer of coated cutting tools due to the load on the cutting edge during machining, which then propagate into the base material, or cracks that originate in the base material due to rapid increases or decreases in cutting edge temperature, which then propagate into the coating layer.

[0007] The invention described in Patent Document 1 is said to have improved resistance to plastic deformation and excellent wear resistance because the proportion of Σ2 grain boundaries between adjacent WC particles is large. However, simply increasing the proportion of Σ2 grain boundaries may easily lead to the formation of triple points at the grain boundaries between adjacent WC particles, which may become the starting point for fracture and reduce fracture resistance, so there is room for improvement. Furthermore, in the invention described in Patent Document 2, a histogram showing the distribution of orientation differences between adjacent pairs of tungsten carbide particles shows a peak in the class of orientation differences between 89.5° and less than 90.5°, but the proportion of Σ2 grain boundaries has not been considered, so there is room for improvement in wear resistance or fracture resistance.

[0008] This invention has been made in view of the above circumstances, and aims to provide a coated cemented carbide with improved wear resistance and fracture resistance, resulting in a longer tool life, and a cutting tool having the same. [Means for solving the problem]

[0009] The inventors of this invention conducted extensive research on extending the tool life of cutting tools made of coated cemented carbide. They discovered that by configuring the coated cemented carbide in a specific way, it is possible to improve its wear resistance and fracture resistance. As a result, they found that the tool life of cutting tools made of coated cemented carbide can be extended, leading to the completion of this invention.

[0010] In other words, the gist of this invention is as follows: [1] A coated cemented carbide comprising a cemented carbide and a coating layer formed on the surface of the cemented carbide, The cemented carbide comprises a WC phase, a hard phase, and a binder phase. The aforementioned WC phase includes WC, The hard phase includes at least one carbide, nitride, or carbonitride selected from the group consisting of Ti, Cr, Zr, Hf, V, Nb, Ta, and Mo. The aforementioned bonded phase comprises at least one selected from the group consisting of Co, Ni, and Fe. The content of the WC phase is 75.0% by mass or more and 95.0% by mass or less based on 100% by mass of the total cemented carbide, and the content of the bonding phase is 3.5% by mass or more and 19.0% by mass or less based on 100% by mass of the total cemented carbide. The cemented carbide comprises a surface region and an internal region, extending from the surface side to the interior side. In the aforementioned surface region, the content ratio of the hard phase is 0% by mass or more and 1.0% by mass or less relative to 100% by mass of the entire surface region. In the aforementioned internal region, the content ratio of the hard phase is greater than 1.0% by mass and less than or equal to 12.0% by mass relative to 100% by mass of the entire internal region. In the aforementioned surface region, the ratio A of the length of the Σ2 grain boundary to 100% of the total grain boundary length between adjacent WC particles is less than 10.0%. In the aforementioned internal region, the ratio B of the length of the Σ2 grain boundary to 100% of the total grain boundary length between adjacent WC particles is greater than the ratio A. Coated cemented carbide. [2] The ratio of proportion B to proportion A (B / A) is 1.2 or more and 4.0 or less. [1] The coated cemented carbide described above. [3] The aforementioned percentage B is 10.0% or more and 20.0% or less. The coated cemented carbide described in [1] or [2]. [4] The aforementioned percentage A is 4.0% or more and less than 10.0%. A coated cemented carbide alloy as described in any one of [1] to [3]. [5] The average thickness of the aforementioned surface region is 10 μm or more and 30 μm or less. A coated cemented carbide alloy as described in any one of [1] to [4]. [6] The coating layer is a single layer or a stack of two or more layers containing at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, and Si, and at least one element selected from the group consisting of C, N, O, and B. The average thickness of the coating layer is 5.0 μm or more and 30.0 μm or less. The coated cemented carbide according to any one of [1] to [5]. [7] Having the coated cemented carbide according to any one of [1] to [6], Cutting tool.

Effect of the Invention

[0011] According to the present invention, it is possible to provide a coated cemented carbide having excellent wear resistance and chipping resistance and capable of extending the tool life, and a cutting tool having the same.

Brief Description of the Drawings

[0012] [Figure 1] It is a figure which shows an example of the coated cemented carbide of this embodiment.

Mode for Carrying Out the Invention

[0013] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "this embodiment") will be described in detail, but the present invention is not limited to the following embodiment. The present invention can be variously modified without departing from the gist thereof.

[0014] [Coated Cemented Carbide] The coated cemented carbide of this embodiment is a coated cemented carbide including a cemented carbide and a coating layer formed on the surface of the cemented carbide, The cemented carbide includes a WC phase, a hard phase, and a binder phase, The WC phase contains WC, The hard phase contains at least one of carbides, nitrides, or carbonitrides selected from the group consisting of Ti, Cr, Zr, Hf, V, Nb, Ta, and Mo, The binder phase contains at least one selected from the group consisting of Co, Ni, and Fe, The content ratio of the WC phase is 75.0 mass% or more and 95.0 mass% or less with respect to 100 mass% of the entire cemented carbide, The content of the binder phase is between 3.5% and 19.0% by mass, relative to 100% by mass of the total cemented carbide. The cemented carbide alloy comprises a surface region and an internal region, extending from the surface side to the interior side. In the surface region, the content of the hard phase is 0% by mass or more and 1.0% by mass or less relative to 100% by mass of the entire surface region. In the internal region, the content of the hard phase is greater than 1.0% by mass and less than or equal to 12.0% by mass relative to 100% by mass of the entire internal region. In the surface region, the ratio A of the length of the Σ2 grain boundary to 100% of the total grain boundary length between adjacent WC particles is less than 10.0%. In the interior region, the ratio B of the length of a Σ2 grain boundary to 100% of the total grain boundary length between adjacent WC particles is greater than the ratio A.

[0015] The factors that contribute to the improved wear resistance and fracture resistance of such coated cemented carbide are not fully understood, but the inventors speculate that the factors are as follows. However, the factors are not limited to these. If the WC phase contains WC, and the WC phase content is 75.0% by mass or more relative to 100% by mass of the total cemented carbide, the hardness improves, resulting in excellent wear resistance. If the WC phase content is 95.0% by mass or less, the toughness improves, resulting in excellent fracture resistance. If the binder phase contains at least one selected from the group consisting of Co, Ni, and Fe, and the binder phase content is 3.5% by mass or more relative to 100% by mass of the total cemented carbide, toughness is improved, resulting in excellent fracture resistance. If the binder phase content is 19.0% by mass or less, hardness and resistance to plastic deformation are improved, resulting in excellent wear resistance. In the surface region, if the hard phase content is 1.0% by mass or less relative to 100% by mass of the entire surface region, toughness is improved, resulting in excellent chipping resistance. In the internal region, if the hard phase content is greater than 1.0 mass% of the total internal region's mass, heat resistance and plastic deformation resistance are improved, resulting in excellent wear resistance. If the hard phase content is 12.0 mass% or less of the total internal region's mass, toughness is improved, resulting in improved chipping resistance. In the surface region, if the ratio A of the length of Σ2 grain boundaries to 100% of the total grain boundary length between adjacent WC particles is less than 10.0%, the formation of triple points at the grain boundaries between adjacent WC particles is suppressed. This reduces the number of fracture initiation points, thereby improving fracture resistance. In the internal region, if the ratio B of the length of Σ2 grain boundaries to 100% of the total grain boundary length between adjacent WC particles is greater than ratio A, the load during cutting is distributed, suppressing chipping and reducing the likelihood of uneven wear and chipping, resulting in superior wear resistance and fracture resistance.

[0016] [Carbide alloy] The cemented carbide of this embodiment contains a WC phase, a hard phase, and a binder phase. The content of the WC phase is 75.0% to 95.0% by mass, based on 100% by mass of the total cemented carbide, and the content of the binder phase is 3.5% to 19.0% by mass, based on 100% by mass of the total cemented carbide. In the cemented carbide of this embodiment, the total content of the WC phase, hard phase, and binder phase is 100.0% by mass.

[0017] In the cemented carbide of this embodiment, the content ratio (mass%) of the WC phase, binder phase, and hard phase can be determined by observing the microstructure of any cross-section with a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS) and measuring the composition of each phase of the cemented carbide using the EDS. Specifically, this can be determined by the method described in the examples below.

[0018] [WC phase] In the cemented carbide of this embodiment, the WC phase contains WC, and preferably consists of WC. When the WC phase contains WC and its content is 75.0% by mass or more relative to 100% by mass of the total cemented carbide, the hardness is improved, resulting in excellent wear resistance. On the other hand, when the content of the WC phase is 95.0% by mass or less, the toughness is improved, resulting in excellent fracture resistance. From a similar viewpoint, the content of the WC phase is preferably 77.0% by mass or more and 93.5% by mass or less, and more preferably 81.0% by mass or more and 92.0% by mass or less.

[0019] In this embodiment, the content of the WC phase in the internal region is preferably 75.0% by mass or more and 95.0% by mass or less, relative to 100% by mass of the entire internal region. When the content of the WC phase in the internal region is within the above range, the effects of the present invention tend to be more effective and reliable. From a similar viewpoint, the content of the WC phase in the internal region is preferably 77.0% by mass or more and 93.5% by mass or less, and more preferably 81.0% by mass or more and 92.0% by mass or less.

[0020] [Hard phase] In the cemented carbide of this embodiment, the hard phase includes at least one carbide, nitride, or carbonitride selected from the group consisting of Ti, Cr, Zr, Hf, V, Nb, Ta, and Mo. The inclusion of such a hard phase in the cemented carbide improves its heat resistance and resistance to plastic deformation, resulting in excellent wear resistance. From a similar viewpoint, the hard phase preferably includes at least one carbide, nitride, or carbonitride selected from the group consisting of Ti, Cr, Zr, Nb, and Ta, more preferably includes at least one selected from the group consisting of TiC, TiCN, TiN, Cr3C2, ZrC, ZrN, NbC, NbN, TaC, and TaN, and even more preferably includes at least one selected from the group consisting of TiC, TiN, Cr3C2, ZrC, ZrN, NbC, and TaC.

[0021] In the cemented carbide of this embodiment, it is preferable that the hard phase content is greater than 1.0 mass% of 100 mass% of the total cemented carbide, as this improves heat resistance and plastic deformation resistance, resulting in superior wear resistance. On the other hand, it is preferable that the hard phase content is 12.0 mass% or less of 100 mass% of the total cemented carbide, as this improves toughness, resulting in improved fracture resistance. From a similar viewpoint, it is more preferable that the hard phase content is 1.5 mass% to 10.0 mass%, and even more preferable that it is 2.0 mass% to 7.0 mass%.

[0022] [Surface region and internal region] In this embodiment, the surface region is the region identified by the following analysis method. An EDS analysis is performed on a cross-section perpendicular to the surface of the cemented carbide, located 200 μm from the cutting edge of the tool towards the center of the rake face. An analysis of a 1 μm × 50 μm area, consisting of 1 μm perpendicular to the surface of the cemented carbide and 50 μm parallel to the surface, is performed sequentially from the surface to the interior of the cemented carbide, starting with the area from 1 μm from the surface to 2 μm. The area immediately preceding the point where the hard phase content exceeds 1.0 mass% is identified, and this area is defined as the surface region. If the hard phase content is 1.0 mass% or less in the analysis of the area up to 1 μm from the surface, the cemented carbide is considered to have a surface region. For example, if the area where the hard phase content first exceeds 1.0 mass% is from 20 μm to 21 μm from the surface to the interior of the cemented carbide, the thickness of the surface region is defined as 20 μm. The same analysis is performed in three fields of view, and the average thickness of the obtained surface region is taken as the average thickness of the surface region. The internal region, in the case of the above analysis, refers to the region inside the cemented carbide that is further inland than the surface region. The analytical method is not particularly limited; any method that can identify the section exceeding 1.0 mass% based on the content of the hard phase described above is acceptable.

[0023] The average thickness of the surface region is preferably 10 μm or more and 30 μm or less. When the average thickness of the surface region is 10 μm or more, toughness is improved and the material tends to have excellent fracture resistance. On the other hand, when the average thickness of the surface region is 30 μm or less, plastic deformation resistance is improved and the material tends to have excellent wear resistance. From a similar viewpoint, the average thickness of the surface region is more preferably 11 μm or more and 29 μm or less, even more preferably 13 μm or more and 28 μm or less, and even more preferably 15 μm or more and 25 μm or less.

[0024] The hard phase content in the surface region of the cemented carbide is 1.0 mass% or less relative to 100 mass% of the total surface region. When the hard phase content in the surface region is 1.0 mass% or less relative to 100 mass% of the total surface region, toughness is improved, resulting in excellent fracture resistance. From a similar viewpoint, the hard phase content in the surface region is preferably 0.0 mass% to 0.6 mass%, and more preferably 0.0 mass% to 0.4 mass%.

[0025] The content of the WC phase in the surface region of the cemented carbide is preferably within the range of 80.0% to 95.0% by mass relative to 100% by mass of the entire surface region. Furthermore, the content of the binder phase in the surface region is preferably within the range of 4.0% to 19.0% by mass relative to 100% by mass of the entire surface region. By setting the content of the WC phase and / or binder phase in the surface region within the above ranges, the effects of the present invention tend to be achieved more effectively and reliably.

[0026] The hard phase content in the internal region of the cemented carbide is between 1.0 mass% and 12.0 mass% of the total internal region (100 mass%). When the hard phase content in the internal region is greater than 1.0 mass% of the total internal region (100 mass%), heat resistance and resistance to plastic deformation are improved, resulting in excellent wear resistance. On the other hand, when the hard phase content in the internal region is 12.0 mass% or less, toughness is improved, resulting in improved fracture resistance. From a similar viewpoint, the hard phase content in the internal region is preferably between 1.5 mass% and 10.0 mass%, and more preferably between 2.0 mass% and 7.0 mass%.

[0027] In both the surface and interior regions, adjacent WC particles have grain boundaries with relatively high and relatively low energy. Typically, grain boundaries have many gaps and relatively high energy because the arrangement of atoms is irregular and random. On the other hand, some grain boundaries have regular arrangements of atoms and few gaps, and such grain boundaries have relatively low energy. A typical example of such a grain boundary with relatively low energy is the coincidence site lattice (SITE) grain boundary, also known as a corresponding grain boundary. The Σ value is known as an indicator of the degree of SITE distribution, and is defined as the ratio of the density of lattice points of two grains touching at a grain boundary to the density of coincident lattice points when both lattices are superimposed. In simple structures, grain boundaries with low SITE values ​​generally tend to have low interfacial energy and special properties. Therefore, controlling the proportion of SITE boundaries and the distribution of grain orientation differences is considered important for the properties of cemented carbide and for improving them.

[0028] In the surface region of cemented carbide, if the ratio A of the length of Σ2 grain boundaries to 100% of the total grain boundary length between adjacent WC particles is less than 10.0%, the formation of triple points at the grain boundaries between adjacent WC particles is suppressed. This reduces the number of fracture initiation points, thus improving fracture resistance. On the other hand, if the ratio A is 4.0% or more, the peeling of the coating layer due to plastic deformation tends to be suppressed, thus improving wear resistance and fracture resistance. From a similar viewpoint, the ratio A is preferably 4.0% to 9.4%, and more preferably 4.1% to 9.1%.

[0029] In the internal region, the ratio B of the length of the Σ2 grain boundary to 100% of the total grain boundary length between adjacent WC particles is preferably 10.0% or more and 20.0% or less. When ratio B is 10.0% or more, the resistance to plastic deformation improves, and the material tends to have excellent wear resistance. On the other hand, when ratio B is 20.0% or less, the triple points formed at the grain boundaries between adjacent WC particles tend to be formed uniformly and dispersedly, and the material tends to have excellent fracture resistance. From a similar viewpoint, ratio B is more preferably 11.3% or more and 19.4%, and even more preferably 12.6% or more and 19.1% or less.

[0030] It is preferable that the ratio of the above ratio B to the above ratio A (B / A) is between 1.2 and 4.0. When the above ratio (B / A) is 1.2 or higher, the load during cutting is distributed, the occurrence of chipping is suppressed, and uneven wear and chipping are less likely to occur, so the wear resistance and fracture resistance tend to be even better. On the other hand, when the above ratio (B / A) is 4.0 or lower, the accumulation of strain on the surface area tends to be mitigated, and peeling of the coating layer due to plastic deformation is suppressed, so the wear resistance and fracture resistance tend to be excellent over a long period of time. From a similar viewpoint, it is more preferable that the ratio (B / A) is between 1.2 and 3.8, and even more preferable that it is between 1.8 and 3.5. In this embodiment, the proportion of each phase of the cemented carbide and the proportion of the length of the Σ2 grain boundary can be determined by the method described in the examples below.

[0031] [Binded phase] In the cemented carbide of this embodiment, the binder phase includes at least one selected from the group consisting of Co, Ni, and Fe. The inclusion of such a binder phase in the cemented carbide improves its toughness and thus its fracture resistance. From a similar viewpoint, the binder phase preferably includes at least one of Co or Ni, and more preferably Co.

[0032] In the cemented carbide of this embodiment, if the content of the binder phase is 3.5% by mass or more relative to 100% by mass of the total cemented carbide, toughness is improved, resulting in excellent fracture resistance. On the other hand, if the content of the binder phase is 19.0% by mass or less, hardness and resistance to plastic deformation are improved, resulting in excellent wear resistance. From a similar viewpoint, the content of the binder phase is preferably 4.0% by mass or more and 15.0% by mass or less, more preferably 5.0% by mass or more and 12.0% by mass or less, and even more preferably 6.0% by mass or more and 11.0% by mass or less.

[0033] In the cemented carbide of this embodiment, the Co content in the binder phase is more preferably 3.5% by mass or more and 15.0% by mass or less based on 100% by mass of the total cemented carbide. When the Co content in the binder phase is 3.5% by mass or more based on 100% by mass of the total cemented carbide, toughness is improved, and the material tends to have excellent fracture resistance. On the other hand, when the Co content is 15.0% by mass or less based on 100% by mass of the total cemented carbide, hardness and resistance to plastic deformation are improved, and the material tends to have excellent wear resistance. From a similar viewpoint, the Co content is more preferably 5.0% by mass or more and 12.0% by mass or less based on 100% by mass of the total cemented carbide, and even more preferably 6.0% by mass or more and 11.0% by mass or less.

[0034] In this embodiment, the content of the binding phase in the internal region is preferably 3.5% by mass or more and 15.0% by mass or less, relative to 100% by mass of the entire internal region. When the content of the binding phase in the internal region is within the above range, the effects of the present invention tend to be more effective and reliable. From a similar viewpoint, the content of the binding phase in the internal region is preferably 5.0% by mass or more and 12.0% by mass or less, and more preferably 6.0% by mass or more and 11.0% by mass or less.

[0035] [Coating layer] The coated cemented carbide of this embodiment comprises the cemented carbide described above and a coating layer formed on the surface of the cemented carbide. The coating layer is preferably a single layer or a laminate of two or more layers containing at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, and Si, and at least one element selected from the group consisting of C, N, O, and B. The coated cemented carbide tends to have improved wear resistance by having such a coating layer. From a similar viewpoint, the coating layer is more preferably made of at least one element selected from the group consisting of a Ti compound layer made of Ti and at least one element selected from the group consisting of C, N, O, and B, and an α-Al2O3 layer made of α-type aluminum oxide, and even more preferably made of at least one element selected from the group consisting of a TiC layer, a TiN layer, a TiCN layer, a TiCO layer, and a TiCNO layer, and an α-Al2O3 layer.

[0036] The average thickness of the entire coating layer is preferably between 5.0 μm and 30.0 μm. When the average thickness of the entire coating layer is 5.0 μm or more, the abrasion resistance tends to improve. On the other hand, when the average thickness of the entire coating layer is 30.0 μm or less, peeling of the coating layer is suppressed, and the chipping resistance tends to improve. From a similar viewpoint, the average thickness of the entire coating layer is more preferably between 8.0 μm and 25.0 μm, and even more preferably between 10.0 μm and 20.0 μm.

[0037] The coating layer may have a structure in which multiple layers with different compositions are laminated. In this case, the average thickness of each layer may be, for example, 0.1 μm to 15.0 μm, or 0.2 μm to 10.0 μm.

[0038] The thickness of each layer constituting the coating layer, as well as the overall thickness of the coating layer, can be measured from the cross-sectional structure of the coated cemented carbide using an optical microscope, scanning electron microscope (SEM), or transmission electron microscope (TEM). The average thickness of each layer and the overall thickness of the coating layer in a coated cemented carbide can be determined by measuring the thickness of each layer and the overall thickness from three or more cross-sections and calculating the average value.

[0039] Furthermore, the composition of each layer constituting the coating layer can be measured from the cross-sectional microstructure of the coated cemented carbide using methods such as EDS or wavelength-dispersive X-ray spectroscopy (WDS).

[0040] [Production method of coated cemented carbide] The coated cemented carbide of this embodiment can be manufactured, for example, by the following method. The raw material powders include WC powder with an average particle size of 1.0 μm to 5.0 μm, W powder with an average particle size of 0.8 μm to 2.0 μm, C powder with an average particle size of 0.5 μm to 3.0 μm, Co powder with an average particle size of 1.0 μm to 3.0 μm, Ni powder with an average particle size of 1.0 μm to 3.0 μm, TiN powder with an average particle size of 0.7 μm to 1.5 μm, and TiCN powder with an average particle size of 0.7 μm to 1.5 μm. The following powders are prepared and blended: TiC powder with an average particle size of 0.7 μm to 1.5 μm, ZrN powder with an average particle size of 3.0 μm to 5.0 μm, ZrC powder with an average particle size of 3.0 μm to 5.0 μm, Cr3C2 powder with an average particle size of 1.0 μm to 2.0 μm, NbC powder with an average particle size of 0.8 μm to 1.2 μm, TaC powder with an average particle size of 0.8 μm to 1.2 μm, etc. (blending process).

[0041] Here, when nitrides and / or carbonitrides are used as raw material powders, surface regions tend to form more easily. Furthermore, increasing the content of nitrides and / or carbonitrides in the raw material powders also tends to increase the average thickness of the surface regions. Additionally, when W powder and C powder are used as raw materials to form the WC phase, and the proportions of W powder and C powder are increased, the above proportion B tends to increase. This is presumed to be due to the suppression of random grain boundary formation by solid-phase sintering during the first and second heating steps, and the suppression of the disappearance of Σ2 grain boundaries during subsequent liquid-phase sintering, resulting in an increase in proportion B.

[0042] Next, the required amounts of each powder are mixed together with a solvent in a wet ball mill for 5 to 15 hours to obtain a mixture (mixing step). The obtained mixture is heated and dried at a temperature of 100°C or lower while evaporating the solvent to obtain a dry mixture (drying step). 1.5% by mass of paraffin wax is added to the dry mixture and it is molded into the shape of the desired tool (molding step).

[0043] Next, the molded body obtained in the molding process is placed in a sintering furnace and heated to a temperature of 1100°C to 1300°C in a vacuum atmosphere of 70 Pa or less (first heating step). Performing the first heating step promotes degassing and tends to improve sinterability in the sintering process. Furthermore, the temperature is raised to 1400°C to 1600°C at a rate of 1°C / min to 10°C / min in an inert gas (Ar, etc.) atmosphere of, for example, 100 kPa to 1000 kPa (second heating step). After that, the sample is sintered by holding it at a temperature of 1400°C to 1600°C for 15 to 30 minutes in an inert gas (Ar, etc.) atmosphere of, for example, 60 kPa to 300 kPa (sintering step).

[0044] After the sintering process, the sample is cooled at a rate of 1°C / min to 10°C / min to a temperature below the liquidus temperature (e.g., below 1200°C) in a mixed gas atmosphere of N2 and H2 with a total pressure of 50kPa to 200kPa (first cooling step). The partial pressure ratio of N2:H2 in the mixed gas during the first cooling step may be, for example, 95:5 to 80:20. The sintered body after the first cooling step is cooled to a predetermined temperature in an inert gas atmosphere at atmospheric pressure at a controlled rate of, for example, 50°C / min, and then further cooled to room temperature (second cooling step).

[0045] Here, lowering the pressure during the sintering process tends to increase the average thickness of the surface region. Also, using H2 gas in the first cooling process and increasing the partial pressure tends to increase the ratio of proportion B to proportion A. This is presumed to be because the generation of WC nuclei is promoted, especially in the surface region, making it easier for relatively unstable random grain boundaries to form, causing proportion A to decrease significantly compared to proportion B, and consequently increasing the ratio (B / A). By controlling proportion B and the ratio (B / A) using the method described above, proportion A can also be controlled.

[0046] The method for manufacturing the coating layer in the coated cemented carbide of this embodiment is not particularly limited, but examples include chemical vapor deposition, ion plating, arc ion plating, sputtering, and ion mixing. Among these, chemical vapor deposition is even more preferable because it provides superior adhesion between the coating layer and the cemented carbide.

[0047] [Chemical vapor deposition] It is preferable to form one or more layers selected from the group consisting of a TiN layer, a TiC layer, a TiCN layer, a TiCO layer, a TiCNO layer, and an α-Al2O3 layer on the surface of the cemented carbide of this embodiment, which has been machined into a tool shape, using chemical vapor deposition. In this case, for example, one or more layers selected from the group consisting of a TiN layer, a TiC layer, a TiCN layer, a TiCO layer, and a TiCNO layer are formed as the lower layer. Next, the surface of the lower layer (if the lower layer has two or more layers, the surface of the layer furthest from the surface of the cemented carbide) is oxidized, and then an α-Al2O3 layer is formed as an intermediate layer, and then a TiCN layer and a TiN layer are sequentially formed on its surface as the upper layer.

[0048] More specifically, the lower TiN layer can be formed by chemical vapor deposition using a raw material gas composition of TiCl4: 5.0 mol% to 10.0 mol%, N2: 20.0 mol% to 60.0 mol%, and H2: the remainder, at a temperature of 850°C to 950°C and a pressure of 200 hPa to 400 hPa.

[0049] The lower TiC layer can be formed by chemical vapor deposition using a raw material gas composition of TiCl4: 1.0 mol% to 3.0 mol%, CH4: 4.0 mol% to 6.0 mol%, and H2: the remainder, at a temperature of 950°C to 1050°C and a pressure of 50 hPa to 100 hPa.

[0050] The lower TiCN layer can be formed by chemical vapor deposition using a raw material gas composition of TiCl4: 6.0 mol% to 10.0 mol%, CH3CN: 0.8 mol% to 1.5 mol%, and H2: the remainder, at a temperature of 820°C to 880°C and a pressure of 60 hPa to 80 hPa.

[0051] The lower TiCO layer can be formed by chemical vapor deposition using a raw material gas composition of TiCl4: 0.5 mol% to 1.5 mol%, CO: 2.0 mol% to 4.0 mol%, and H2: the remainder, at a temperature of 950°C to 1050°C and a pressure of 60 hPa to 100 hPa.

[0052] The lower TiCNO layer can be formed by chemical vapor deposition using a raw material gas composition of TiCl4: 1.0 mol% to 5.0 mol%, CO: 0.4 mol% to 1.0 mol%, N2: 35.0 mol% to 45.0 mol%, and H2: the remainder, at a temperature of 950°C to 1050°C and a pressure of 100 hPa to 150 hPa.

[0053] The oxidation treatment is carried out under the following conditions: gas composition of CO: 0.1 mol% to 0.7 mol%, CO2: 0.2 mol% to 1.0 mol%, H2: the remainder, temperature of 970°C to 1000°C, and pressure of 40 hPa to 70 hPa. The oxidation time is preferably 1 to 5 minutes.

[0054] The intermediate α-Al2O3 layer can be formed by chemical vapor deposition using a raw material gas composition of AlCl3: 2.0 mol% to 5.0 mol%, CO2: 2.5 mol% to 4.0 mol%, HCl: 2.0 mol% to 3.0 mol%, H2S: 0.1 mol% to 0.2 mol%, and H2: the remainder, at a temperature of 950°C to 1130°C and a pressure of 60 hPa to 80 hPa.

[0055] The upper TiCN layer can be formed by chemical vapor deposition using a raw material gas composition of TiCl4: 6.0 mol% to 10.0 mol%, CH3CN: 0.5 mol% to 1.5 mol%, CH4: 1.2 mol% to 1.8 mol%, N2: 2.0 mol% to 8.0 mol%, and H2: the remainder, at a temperature of 975°C to 1025°C and a pressure of 60 hPa to 80 hPa.

[0056] The upper TiN layer can be formed by chemical vapor deposition using a raw material gas composition of TiCl4: 5.0 mol% to 10.0 mol%, N2: 20.0 mol% to 60.0 mol%, and H2: the remainder, at a temperature of 950°C to 1050°C and a pressure of 200 hPa to 400 hPa.

[0057] Furthermore, for a more specific manufacturing method, the method described in the examples below may be used.

[0058] [Cutting tools] The tools of this embodiment include the coated cemented carbide alloys described above. Aside from including these coated cemented carbide alloys, the tools of this embodiment may have the same configuration as known tools. Because the coated cemented carbide alloys of this embodiment have excellent wear resistance and fracture resistance, tools containing them can be used, for example, as cutting tools or wear-resistant tools, and are preferably used as cutting tools. The coated cemented carbide alloys of this embodiment are even more preferably used as cutting tools for carbon steel. When the coated cemented carbide alloys of this embodiment are used as cutting tools or wear-resistant tools, tool life can be extended compared to conventional methods. [Examples]

[0059] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0060] [Manufacturing of cemented carbide] As raw material powders, commercially available tungsten carbide (WC) powder with an average particle size of 3.0 μm, walnut powder with an average particle size of 1.2 μm, carbon powder with an average particle size of 1.0 μm, coco powder with an average particle size of 1.5 μm, nickel powder with an average particle size of 1.5 μm, titanium dioxide (TiN) powder with an average particle size of 1.2 μm, titanium dioxide (TiCN) powder with an average particle size of 1.2 μm, titanium dioxide (TiC) powder with an average particle size of 1.2 μm, zinc dioxide (ZrN) powder with an average particle size of 4.0 μm, zinc dioxide (ZrC) powder with an average particle size of 4.0 μm, crinoxide (Cr3C2) powder with an average particle size of 1.5 μm, nitrogen dioxide (NbC) powder with an average particle size of 1.0 μm, and crystalline carbonate (TaC) powder with an average particle size of 1.0 μm were prepared. The average particle size of the raw material powders was measured using the Fisher Sub-Sieve Sizer (FSSS) method described in ASTM standard B330.

[0061] For Inventions 1-15 and Comparative Products 1-10, the prepared raw material powders were weighed to achieve the blending compositions shown in Table 1 below. The weighed raw material powders were placed in a stainless steel pot with acetone solvent and cemented carbide balls and blended (blending step). Mixing and grinding were carried out in a wet ball mill for 8 hours to obtain a mixture (mixing step). The obtained mixture was heated and dried at a temperature of 100°C or less while evaporating the solvent to obtain a dry mixture (drying step). After adding 1.5% by mass of paraffin wax to 100% by mass of the obtained dry mixture, the mixture was press-molded into the shape of a tool at a pressure of 120 MPa using a predetermined mold to obtain a molded body of the mixture (molding step). As the mold, a mold was used in which the shape after sintering would be the ISO standard insert shape CNMG120412.

[0062] After placing the molded mixture into the sintering furnace, the temperature was raised from room temperature to 1300°C under a vacuum of 70 Pa or less (first heating step). Furthermore, the temperature was raised to the sintering temperature of 1500°C at a rate of 5°C / min under an argon gas atmosphere of 800 kPa (second heating step). Subsequently, the molded body was sintered by holding it for 20 minutes in an argon gas atmosphere at the pressures listed in Table 2 below and at the sintering temperature of 1500°C. After sintering, the sintered body was cooled to 1200°C at a rate of 5°C / min in a mixed gas atmosphere of N2 and H2 with a total pressure of 80 kPa having the partial pressure ratios listed in Table 2 below (first cooling step). Furthermore, the sintered body after the first cooling step was cooled to 900°C at a cooling rate of 50°C / min under an argon gas atmosphere at atmospheric pressure, and then further cooled to room temperature (second cooling step).

[0063] As described above, a cemented carbide alloy was fabricated in the shape of a tool. Furthermore, the cutting edge of the obtained cemented carbide alloy was honed using a SiC brush.

[0064] [Table 1]

[0065] [Table 2]

[0066] [Identification of surface area and its composition] To investigate the composition of the surface region, the microstructure of the cemented carbide perpendicular to the surface, located 200 μm from the cutting edge of the tool toward the center of the rake face, was analyzed using EDS. Analysis of a 1 μm × 50 μm area, consisting of 1 μm perpendicular to the surface and 50 μm parallel to the surface, was performed sequentially from the surface to the interior of the cemented carbide, starting with the area from 1 μm from the surface, then from 1 μm to 2 μm, and so on. The area just before the hard phase content exceeded 1.0 mass% was identified first. That is, if the hard phase content was 1.0 mass% or less in the analysis of the area up to 1 μm from the surface, the cemented carbide was considered to possess a surface region. For example, if the area identified as having a hard phase content exceeding 1.0 mass% was from 20 μm to 21 μm from the surface to the interior of the cemented carbide, the thickness of the surface region was set to 20 μm. The EDS analysis was performed by converting the mass percentage of each composition from the atomic percentage of each composition obtained. For example, in the case of WC, the atomic percentage of WC was determined by setting the atomic ratio W:C=1:1, and then converted to mass percentage. The same analysis was performed in a total of three fields of view, and the average value of the thickness of the obtained surface areas was taken as the average thickness of the surface area. These results are shown in Table 4.

[0067] [Composition of cemented carbide] The composition and percentage (mass%) of each component of the obtained cemented carbide were determined as follows: At least three arbitrary cross-sectional microstructures within the internal region of the obtained cemented carbide were observed using a scanning electron microscope (SEM) with an energy-dispersive X-ray spectrometer (EDS), and each composition was measured by EDS. From these results, the percentage of each component within the internal region of the cemented carbide was determined and considered as the overall composition of the cemented carbide. The reason for considering the composition of the internal region of the cemented carbide as the overall composition of the cemented carbide is that the proportion of the internal region in the cemented carbide is sufficiently larger than the proportion of the surface region, and it was assumed that the same value would be obtained even if both were measured together as the entire cemented carbide. As a more specific method, the cemented carbide was polished in a direction perpendicular to its surface. Among the resulting cross-sectional structures, a 50 μm × 50 μm area was observed using a scanning electron microscope (SEM), focusing on the cross-sectional structure at a depth of 200 μm from the surface of the cemented carbide towards the interior. Surface analysis was then performed using an EDS attached to the SEM to determine the composition and content (mass %) of each cemented carbide within the cemented carbide. The results are shown in Table 3.

[0068] Similarly, the phase composition of the cemented carbide alloys was investigated. All of the cemented carbide alloys obtained consisted of either a WC phase containing tungsten carbide (WC) and a bonding phase that binds the WC phase, or a WC phase containing WC, a hard phase, and a bonding phase. Furthermore, in all of the cemented carbide alloys, the main component of the bonding phase was Co and Ni, or Co.

[0069] As a result of investigating the composition of the surface region using the above method, the content of the WC phase in the surface region of the inventive product was within the range of 80.0% to 95.0% by mass relative to 100% by mass of the entire surface region. Furthermore, the content of the binding phase in the surface region of the inventive product was within the range of 4.0% to 19.0% by mass relative to 100% by mass of the entire surface region, and the content of the hard phase in the surface region of the inventive product was within the range of 0% to 1.0% by mass relative to 100% by mass of the entire surface region. Furthermore, examination of the invention revealed that the mass ratio 1 of the WC phase content in the surface region to the WC phase content in the internal region was within the range of 1.01 to 1.11. Similarly, the mass ratio 2 of the binder phase content in the surface region to the binder phase content in the internal region of the invention was within the range of 1.06 to 1.28. In particular, it was found that the above-mentioned mass ratios 1 and 2 tend to increase when the hard phase content in the cemented carbide is large, or when the average thickness of the surface region is large.

[0070] [Length of grain boundary between adjacent WC particles and length of Σ2 grain boundary] In the surface and interior regions of the cemented carbide alloy identified above, the grain boundary lengths between adjacent WC particles were measured as follows: A cemented carbide sample was polished perpendicular to its surface to expose the cross-section. The resulting cross-section was polished with colloidal silica to obtain a mirror-polished observation surface. This observation surface was observed using a Hitachi High-Technologies Corporation SU6600 SEM equipped with an EBSD (TexSEM Laboratories). The normal to the observation surface was tilted 70° with respect to the incident beam, and the analysis was performed by irradiating with an electron beam at an acceleration voltage of 15kV and an irradiation current of 1.0nA. For surface region data acquisition, assuming an average surface region thickness of 20 μm, a range of 20 μm × 50 μm (i.e., average thickness of each surface region × 50 μm) was collected using a step size (distance between measurement points) of 0.1 μm / step. This range was defined as 20 μm inward from the surface of the cemented carbide and 50 μm in a direction parallel to the surface of the cemented carbide. For internal region data acquisition, a range of 50 μm × 50 μm was collected with a step size of 0.1 μm / step, with the center of the field of view 200 μm inward from the boundary between the surface and internal regions. Data processing was performed using commercially available software. When analyzing the crystal orientation of WC particles, if the orientation difference between two adjacent measurement points was 5° or more, the boundary between those two points was defined as a grain boundary between adjacent WC particles, and the total length of the grain boundary between adjacent WC particles and the length of the Σ2 grain boundary were calculated. In both the surface region and the interior region, the ratio of the length of the Σ2 grain boundary to 100% of the total length of the grain boundaries between adjacent WC particles was calculated and designated as ratio A and ratio B. Here, the same analysis was performed for a total of three fields of view, and the average of the obtained values ​​was taken as the final value. Furthermore, the relationship between ratio A and ratio B was determined from the average of the obtained values.

[0071] The results described above are shown in Table 4. Here, regarding the average thickness of the surface region of comparative samples 1 to 3, comparative samples 1 and 2 do not contain a hard phase, and comparative sample 3 contains a hard phase but does not form a surface region, so they are indicated as "-" and "0" respectively. Furthermore, as a reference value, the results of analyzing the 10 μm × 50 μm area from the surface of the cemented carbide to a depth of 10 μm for comparative samples 1 to 3 are indicated in parentheses as the proportion A.

[0072] [Table 3]

[0073] [Table 4]

[0074] [Formation of the coating layer] Using the cemented carbide alloys of inventions 1-15 and comparative products 1-10 as substrates, a coating layer was formed on the surface of the substrate by chemical vapor deposition. The method for forming the coating layer was as follows:

[0075] Each cemented carbide was placed in an externally heated chemical vapor deposition apparatus, and layers were formed in the order of the 1st, 2nd, ..., 6th layers from the surface side of the cemented carbide, so as to achieve the composition and average thickness shown in Table 5. More specifically, the coating layers were formed by chemical vapor deposition using the raw material gas composition shown in Table 6, under the process temperature and pressure conditions for each layer shown in Table 6. After forming the 1st to 3rd layers, the 3rd layer, the TiCNO layer, was subjected to oxidation treatment according to the conditions shown in Table 7. A 4th layer, the intermediate α-Al2O3 layer, was then formed on the oxidized TiCNO layer, followed by the 5th layer, the upper TiCN layer, and the 6th layer, the TiN layer, in order. After that, the sample was cooled, and after the sample temperature fell below 100°C, the sample was removed from the chemical vapor deposition apparatus. In this way, coated cemented carbide products 1 to 15 and comparative products 1 to 10 were obtained.

[0076] To determine the thickness of each layer in the sample, the following procedure was performed: Using a FE-SEM, the thickness was measured at three points in the cross-section near a position 50 μm from the cutting edge of the sample toward the center of the rake face, and the arithmetic mean of these measurements was calculated as the average thickness. The composition of each layer in the obtained sample was measured using the EDS and WDS attached to the FE-SEM in the cross-section near a position 50 μm from the cutting edge of the coated cutting tool toward the center of the rake face.

[0077] [Table 5]

[0078] [Table 6]

[0079] [Table 7]

[0080] The obtained samples were used to perform and evaluate the following cutting tests 1 and 2. The results of the evaluations are shown in Table 8.

[0081] [Cutting Test 1] ·Work material: S45C, • Cutting material shape: A round bar with four equally spaced grooves on its outer surface. ·Cutting speed: 150m / min, • Cutting depth: 1.0 mm, Feed rate: 0.3mm / rev, • Coolant: Yes, • Insert: CNMG120412 (ISO standard) • Evaluation criteria: Tool life was defined as the point at which the sample broke, and the number of impacts until tool life was measured. A longer tool life indicates superior fracture resistance. A score of A was given for impacts of 12,000 or more when fracture occurred, B for impacts of 8,000 to less than 12,000, and C for impacts of less than 8,000.

[0082] [Cutting Test 2] ·Work material: SCM440, • Cutting material shape: round bar, ·Cutting speed: 200m / min, • Cutting depth: 2.0 mm, Feed rate: 0.35 mm / rev, • Coolant: Yes, • Insert: CNMG120412 (ISO standard) • Evaluation criteria: Tool life was defined as the point at which the sample was damaged or the maximum flank wear width reached 0.3 mm. The machining time until tool life was measured. A longer tool life indicates superior wear resistance. The above machining time was evaluated as A if it was 30 minutes or more, B if it was 20 minutes or more but less than 30 minutes, and C if it was less than 20 minutes.

[0083] [Table 8]

[0084] The results shown in Table 8 indicate that the invention using the coated cemented carbide of the present invention has superior wear resistance and fracture resistance, and a longer tool life compared to the comparative product without the coating. [Industrial applicability]

[0085] The cutting tools having the coated cemented carbide of the present invention have excellent wear resistance and fracture resistance, which extends tool life compared to conventional tools, and therefore have high potential for industrial application. [Explanation of symbols]

[0086] 1...Covering layer, 2...Cemented carbide, 2a...Surface region, 2b...Inner region, 3...Covered cemented carbide.

Claims

1. A coated cemented carbide comprising a cemented carbide and a coating layer formed on the surface of the cemented carbide, The cemented carbide comprises a WC phase, a hard phase, and a binder phase. The aforementioned WC phase includes WC, The hard phase includes at least one carbide, nitride, or carbonitride selected from the group consisting of Ti, Cr, Zr, Hf, V, Nb, Ta, and Mo. The bonded phase comprises at least one selected from the group consisting of Co, Ni, and Fe. The content of the WC phase is 75.0% by mass or more and 95.0% by mass or less based on 100% by mass of the total cemented carbide, and the content of the binder phase is 3.5% by mass or more and 19.0% by mass or less based on 100% by mass of the total cemented carbide. The cemented carbide comprises a surface region and an internal region, extending from the surface side to the interior side. In the aforementioned surface region, the content ratio of the hard phase is 0% by mass or more and 1.0% by mass or less relative to 100% by mass of the entire surface region. In the aforementioned internal region, the content ratio of the hard phase is greater than 1.0% by mass and less than or equal to 12.0% by mass relative to 100% by mass of the entire internal region. In the aforementioned surface region, the ratio A of the length of the Σ2 grain boundary to 100% of the total grain boundary length between adjacent WC particles is less than 10.0%. In the aforementioned internal region, the ratio B of the length of the Σ2 grain boundary to 100% of the total grain boundary length between adjacent WC particles is greater than the ratio A. Coated cemented carbide.

2. The ratio of proportion B to proportion A (B / A) is 1.2 or more and 4.0 or less. The coated cemented carbide according to claim 1.

3. The aforementioned percentage B is 10.0% or more and 20.0% or less. The coated cemented carbide according to claim 1.

4. The aforementioned percentage A is 4.0% or more and less than 10.0%. The coated cemented carbide according to claim 1.

5. The average thickness of the aforementioned surface region is 10 μm or more and 30 μm or less. The coated cemented carbide according to claim 1.

6. The coating layer is a single layer or a laminate of two or more layers, comprising at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, and Si, and at least one element selected from the group consisting of C, N, O, and B. The average thickness of the coating layer is 5.0 μm or more and 30.0 μm or less. The coated cemented carbide according to claim 1.

7. A coated cemented carbide alloy according to any one of claims 1 to 6, cutting tools.

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