Coated cutting tool

Abstract

Provided is a coated cutting tool capable of prolonging tool life by having excellent wear resistance and crack resistance. A coated cutting tool including a substrate and a coating layer formed on a surface of the substrate, wherein the coating layer includes, in order from a substrate side toward a surface side of the coating layer, a lower layer including a layer of a specific compound, an intermediate layer including an α-Al2O3 layer, and an upper layer. The upper layer includes one or two or more Ti compound layers composed of a specific compound. The upper layer includes at least one TiCN layer composed of TiCN. The average thickness of the lower layer, the intermediate layer, and the upper layer is within a predetermined range. In a cross section of the TiCN layer in the upper layer parallel to the substrate surface, if the total area of the entire cross section is taken as 100 area%, the total proportion of the cross-sectional area of a specific region A is 30 area% or more and 70 area% or less. In the region A, the proportion of the total length of Σ3 grain boundaries with respect to the total length of all grain boundaries is 30% or more and less than 60%.

Description

Technical Field

[0001] This invention relates to a coated cutting tool. Background Technology

[0002] Previously, coated cutting tools made by depositing a coating with a total film thickness of 3 to 20 μm on the surface of a cemented carbide substrate using chemical vapor deposition were widely known for their use in the cutting of steel, cast iron, and the like. As such coatings, for example, there are known coatings consisting of a single layer or multiple layers of one or more of a material selected from the group consisting of carbides, nitrides, carbonitrides, carbon oxides and carbonitrides of Ti, and aluminum oxide (Al₂O₃).

[0003] For example, Patent Document 1 discloses a coated cutting tool comprising a substrate and a coating formed on the surface of the substrate, the coating comprising, sequentially from the substrate side toward the surface side of the coating, a lower layer, an intermediate layer, and an upper layer. The lower layer comprises one or more Ti compound layers, the Ti compound layers being composed of Ti and at least one element selected from the group consisting of C, N, O, and B. The intermediate layer comprises an α-type Al₂O₃ layer composed of α-type Al₂O₃. The upper layer comprises one or more Ti compound layers, the Ti compound layers being composed of Ti and at least one element selected from the group consisting of C, N, and O, and at least one of the Ti compound layers in the upper layer is a TiCN layer. The average thickness of the upper layer is 1.00 µm to 6.50 µm. In the upper layer, in a cross-section of the upper layer perpendicular to the surface of the substrate, if the total area of ​​the entire cross-section is set to 100% of the area, the proportion of the cross-sectional area of ​​regions with an orientation difference A of 0 degrees or more and less than 10 degrees (RSA1) and the proportion of the cross-sectional area of ​​regions with an orientation difference A of 20 degrees or more and less than 30 degrees (RSA2) satisfy predetermined conditions. The orientation difference A is the angle formed by the normal of the (220) plane of each particle having a cubic crystal structure and the normal of the surface of the substrate, and the unit of the angle is degrees.

[0004] Furthermore, for example, Patent Document 2 discloses a coated cutting tool comprising a substrate of cemented carbide, cermet, ceramic, steel, or cubic boron nitride and a multilayer wear-resistant coating. The multilayer wear-resistant coating has a total coating thickness of 5–25 μm and comprises at least two refractory coatings deposited by chemical vapor deposition (CVD) or medium-temperature chemical vapor deposition (MT-CVD). The at least two refractory coatings comprise a first coating and a second coating deposited on top of each other. The first coating is composed of titanium aluminum nitride or titanium aluminum carbonitride Ti, wherein 0.2 ≤ u ≤ 1.0, 0 ≤ v ≤ 0.25, and 0.7 ≤ w ≤ 1.15.1- u Al u C v N w The second coating is composed of titanium carbonitride (Ti) and deposited by CVD at a reaction temperature in the range of 600°C to 900°C. x C y N 1-y The second Ti is formed and deposited on the first coating by MT-CVD at a reaction temperature in the range of 600℃ to 900℃. x C y N 1-y The coating has a columnar grain morphology and Ti x C y N 1-y The total fiber texture of the coating is characterized by a given texture coefficient TC(111) > 2.

[0005] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2024-082049 Patent Document 2: Japanese Patent Publication No. 2017-530019. Summary of the Invention

[0006] Technical issues In recent years, the cutting processes have become increasingly characterized by higher speeds, higher feed rates, and deeper cuts, demanding improved tool wear resistance and chip resistance compared to previous methods. Particularly in high-speed steel cutting, the rapid spread of crater wear hinders tool life extension. Furthermore, in machining processes involving mechanical and thermal shock, particle shedding causes defects, further complicating tool life extension. The cutting tool disclosed in Patent Document 2 does not include an α-Al₂O₃ layer; therefore, its wear resistance is insufficient in machining processes where crater wear easily spreads. Additionally, the low proportion of Σ₃ grain boundaries in its TiCN layer and insufficient resistance to crater wear leave room for improvement in its wear resistance.

[0007] The present invention was made in view of the above circumstances, and its object is to provide a coated cutting tool that can extend tool life by having excellent wear resistance and chip resistance.

[0008] Solution Based on the above viewpoints, the inventors of this invention have conducted repeated research on extending the tool life of coated cutting tools and discovered that if they are designed with a specific structure, their wear resistance and chipping resistance can be improved, thereby extending the tool life, thus completing this invention.

[0009] That is, the present invention is as follows.

[0010] <1> A coated cutting tool, wherein, The coated cutting tool includes a substrate and a coating formed on the surface of the substrate. The coating comprises, from the substrate side toward the surface side of the coating, a lower layer, an intermediate layer, and an upper layer in sequence. The lower layer comprises one or more Ti compound layers, wherein the Ti compound layers are composed of Ti and a Ti compound formed with at least one element selected from the group consisting of C, N, O and B. The average thickness of the lower layer is between 3.0 μm and 15.0 μm. The intermediate layer includes an α-Al₂O₃ layer composed of α-type alumina. The average thickness of the intermediate layer is between 3.0 μm and 15.0 μm. The upper layer comprises one or more Ti compound layers, wherein the Ti compound layers are composed of Ti and a Ti compound formed with at least one element selected from the group consisting of C, N, O and B. The upper layer includes at least one TiCN layer composed of TiCN. The average thickness of the upper layer is between 1.0 μm and 6.0 μm. In the cross-section of the TiCN layer in the upper layer parallel to the surface of the substrate, if the total area of ​​the entire cross-section is set to 100% area, then the total proportion of the cross-sectional area of ​​region A with an orientation difference of 0 degrees or more and less than 15 degrees is 30% area or more and 70% area or less. The orientation difference is the angle formed by the normal of the cross-section of the TiCN layer in the upper layer and the normal of the (220) plane of the particles of the TiCN layer. In region A, the proportion of the total length of Σ3 grain boundaries relative to 100% of the total length of all grain boundaries is more than 30% and less than 60%.

[0011] <2> according to <1> The coated cutting tool, wherein, In the entire cross-section of the TiCN layer in the upper layer, the proportion of the total length of the Σ3 grain boundaries relative to 100% of the total length of all grain boundaries is less than 30%.

[0012] <3> according to <1> or <2> The coated cutting tool, wherein, The average length RSm of the roughness curve elements on the surface of the intermediate layer is between 5 μm and 20 μm.

[0013] <4> according to <1> ~ <3> The coated cutting tool described in any one of the following statements, wherein, The average thickness of the entire coating is between 10.0 μm and 30.0 μm.

[0014] Invention Effects According to the present invention, a coated cutting tool can be provided that has excellent wear resistance and chip resistance, thereby extending tool life. Attached Figure Description

[0015] Figure 1 This is a cross-sectional schematic diagram of an example of the coating cutting tool of the present invention. Detailed Implementation

[0016] Hereinafter, with reference to the accompanying drawings, a method for implementing the present invention (hereinafter also referred to as "this embodiment") will be described in detail as needed, but the present invention is not limited to the following embodiment. Various modifications can be made to the present invention without departing from its spirit. It should be noted that, unless otherwise specified, the positional relationships such as up, down, left, and right in the drawings are based on the positional relationships shown in the drawings. Furthermore, the scale of the drawings is not limited to the scale shown.

[0017] The coating cutting tool of this embodiment includes a substrate and a coating formed on the surface of the substrate. The coating, from the substrate side toward the surface side of the coating, sequentially includes a lower layer, an intermediate layer, and an upper layer. The lower layer includes one or more Ti compound layers, wherein the Ti compound layers are composed of Ti and a Ti compound formed with at least one element selected from the group consisting of C, N, O, and B. The average thickness of the lower layer is 3.0 μm to 15.0 μm or less. The intermediate layer includes an α-Al₂O₃ layer composed of α-type alumina. The average thickness of the intermediate layer is 3.0 μm to 15.0 μm or less. The upper layer includes one or more Ti compound layers, wherein the Ti compound layers are composed of Ti and a Ti compound formed with at least one element selected from the group consisting of C, N, O, and B. The upper layer includes at least one TiCN layer composed of TiCN. The average thickness of the upper layer is 1.0 μm to 6.0 μm or less. In the cross-section of the TiCN layer in the upper layer parallel to the substrate surface, if the total area of ​​the entire cross-section is set to 100% area, the total proportion (hereinafter also called RSA) of the cross-sectional area of ​​region A, where the orientation difference (hereinafter also called orientation difference A) is 0 degrees or more and less than 15 degrees, is 30% or more and 70% or less. The orientation difference is the angle between the normal of the cross-section of the TiCN layer in the upper layer and the normal of the (220) plane of the particles in the TiCN layer. In region A, the proportion of the total length of the Σ3 grain boundary relative to 100% of the total length of all grain boundaries is 30% or more and less than 60%.

[0018] The coated cutting tool of this embodiment, by possessing the above-described structure, can improve wear resistance and chipping resistance, thus extending tool life. The main reasons for the improved wear resistance and chipping resistance of the coated cutting tool of this embodiment are as follows. However, the present invention is not limited to the following reasons. Firstly, by making the average thickness of the lower layer 3.0 μm or more, the coated cutting tool of this embodiment suppresses flank wear, thereby improving wear resistance. Secondly, by making the average thickness of the lower layer 15.0 μm or less, the coated tool of this embodiment suppresses coating peeling, thereby improving chipping resistance. Furthermore, by making the average thickness of the intermediate layer 3.0 μm or more, the coated cutting tool of this embodiment suppresses crater wear, thereby improving wear resistance. Secondly, by making the average thickness of the intermediate layer 15.0 μm or less, the coated tool of this embodiment suppresses coating peeling, thereby improving chipping resistance. Furthermore, by making the average thickness of the upper layer 1.0 μm or more, the coated cutting tool of this embodiment suppresses flank wear, thereby improving wear resistance. On the other hand, the coated cutting tool of this embodiment improves chip resistance by suppressing coating peeling by making the average thickness of the upper layer 6.0 μm or less. Furthermore, the coated cutting tool of this embodiment improves wear resistance and chip resistance by including a TiCN layer on the outer side of the upper layer beyond the α-Al₂O₃ layer, and this TiCN layer controls the RSA (Relative Strength A) described later and controls the proportion of the total length of Σ₃ grain boundaries in region A that is 100% of the total length of all grain boundaries. Furthermore, the coated cutting tool of this embodiment improves chip resistance by suppressing particle shedding caused by mechanical and thermal shock by making the RSA 30% or more. On the other hand, the coated cutting tool of this embodiment improves wear resistance by making the RSA 70% or less. Furthermore, the coated cutting tool of this embodiment improves chip resistance by making the proportion of the total length of Σ₃ grain boundaries in region A that is 100% of the total length of all grain boundaries 30% or more. Furthermore, due to the improved mechanical properties, crater wear is suppressed, and wear resistance is also improved. On the other hand, the coated cutting tool of this embodiment suppresses grain coarsening and improves chipping resistance by making the proportion of the total length of Σ3 grain boundaries in region A, which is 100% of the total length of all grain boundaries, less than 60%, thereby improving chipping resistance and thus chipping resistance. Moreover, by combining these structures, the wear resistance and chipping resistance of the coated cutting tool of this embodiment are improved, and therefore, it is believed that tool life can be extended.

[0019] Figure 1This is a cross-sectional schematic diagram of an example of the coated cutting tool of this embodiment. The coated cutting tool 6 includes a substrate 1 and a coating 5 formed on the surface of the substrate 1. In the coating 5, a lower layer 2, an intermediate layer 3, and an upper layer 4 are stacked sequentially from the substrate side upwards.

[0020] The coated cutting tool of this embodiment includes a substrate and a coating formed on the surface of the substrate. Specifically, types of coated cutting tools include interchangeable cutting inserts for milling or turning, drills, and end mills.

[0021] The substrate used in this embodiment is not particularly limited as long as it can be used as a substrate for coating cutting tools. Examples of such substrates include cemented carbide, cermet, ceramic, cubic boron nitride sintered body, diamond sintered body, and high-speed steel. Among these, if the substrate is any one of cemented carbide, cermet, ceramic, and cubic boron nitride sintered body, the wear resistance and chipping resistance are superior, so it is preferred. From the same point of view, cemented carbide is more preferably the substrate.

[0022] It should be noted that the substrate can be a substrate whose surface has been modified. For example, if the substrate is made of cemented carbide, a de-β layer can be formed on its surface. Furthermore, if the substrate is made of cermet, a hardened layer can be formed on its surface. Even with such surface modification of the substrate, the effects of the present invention can still be achieved.

[0023] In this embodiment, the average thickness of the entire coating is preferably 10.0 μm or more and 30.0 μm or less. By making the average thickness of the entire coating 10.0 μm or more, the wear resistance of the coated cutting tool in this embodiment tends to be improved; by making the average thickness of the entire coating 30.0 μm or less, coating peeling is suppressed, and thus the resistance to chipping tends to be improved. From the same viewpoint, the average thickness of the entire coating is more preferably 13.0 μm or more and 28.7 μm or less, and even more preferably 14.0 μm or more and 26.2 μm or less.

[0024] It should be noted that the average thickness of each layer and the entire coating in the coating cutting tool of this embodiment can be determined by measuring the thickness of each layer or the thickness of the entire coating from three or more cross sections and calculating their arithmetic mean.

[0025] [Lower layer] The lower layer used in this embodiment includes one or more Ti compound layers, which are composed of Ti and a Ti compound formed with at least one element selected from the group consisting of C, N, O, and B. When a lower layer is included between the substrate and the intermediate layer including the α-Al₂O₃ layer, the wear resistance and adhesion of the coated cutting tool are improved.

[0026] The lower layer can consist of one layer or multiple layers (e.g., two or three layers), preferably multiple layers, more preferably two or three layers, and even more preferably three layers. From the viewpoint of further improving wear resistance and adhesion, the Ti compound constituting the Ti compound layer included in the lower layer is preferably at least one Ti compound selected from the group consisting of TiN, TiC, TiCN, TiCO, TiCNO, TiON, and TiB2, more preferably at least one Ti compound selected from the group consisting of TiN, TiC, TiCN, TiCO, and TiCNO. Furthermore, in the coated cutting tool of this embodiment, if at least one layer of the lower layer is a TiCN layer, the wear resistance is further improved, which is therefore preferred. When the lower layer consists of three layers, a TiC layer or a TiN layer can be formed on the surface of the substrate as the first layer, a TiCN layer can be formed on the surface of the first layer as the second layer, and a TiCNO layer or a TiCO layer can be formed on the surface of the second layer as the third layer. For the lower layer, a TiN layer can be formed on the surface of the substrate as the first layer, a TiCN layer can be formed on the surface of the first layer as the second layer, and a TiCNO layer can be formed on the surface of the second layer as the third layer.

[0027] In this embodiment, the average thickness of the lower layer is 3.0 μm or more and 15.0 μm or less. By making the average thickness of the lower layer 3.0 μm or more, the coated cutting tool of this embodiment suppresses flank wear, thereby improving wear resistance. On the other hand, by making the average thickness of the lower layer 15.0 μm or less, the coated cutting tool of this embodiment suppresses coating peeling, thereby improving resistance to chipping. From the same viewpoint, the average thickness of the lower layer is more preferably 3.5 μm or more and 14.5 μm or less, and even more preferably 4.5 μm or more and 13.0 μm or less.

[0028] From the viewpoint of further improving wear resistance and chip resistance, the average thickness of the TiC layer or TiN layer in the lower layer is preferably 0.05 μm or more and 1.00 μm or less. From the same viewpoint, the average thickness of the TiC layer or TiN layer in the lower layer is more preferably 0.10 μm or more and 0.50 μm or less, and even more preferably 0.15 μm or more and 0.30 μm or less.

[0029] From the viewpoint of further improving wear resistance and chip resistance, the average thickness of the TiCN layer in the lower layer is preferably 2.0 μm or more and 15.0 μm or less. From the same viewpoint, the average thickness of the TiCN layer in the lower layer is more preferably 3.0 μm or more and 14.0 μm or less, and even more preferably 4.0 μm or more and 12.5 μm or less.

[0030] From the viewpoint of further improving wear resistance and chip resistance, the average thickness of the TiCNO layer or TiCO layer in the lower layer is preferably 0.05 μm or more and 1.50 μm or less. Similarly, from the same viewpoint, the average thickness of the TiCNO layer or TiCO layer in the lower layer is more preferably 0.10 μm or more and 1.00 μm or less, and even more preferably 0.20 μm or more and 0.50 μm or less.

[0031] The Ti compound layer in the lower layer is a layer composed of Ti and at least one element selected from the group consisting of C, N, O and B. However, as long as the effect based on the lower layer is achieved, it may also contain trace amounts of components other than the above-mentioned elements.

[0032] [Middle Layer] The intermediate layer used in this embodiment includes an α-Al2O3 layer composed of α-type aluminum oxide (α-Al2O3).

[0033] In this embodiment, the average thickness of the intermediate layer is 3.0 μm or more and 15.0 μm or less. By making the average thickness of the intermediate layer 3.0 μm or more, the coating cutting tool of this embodiment suppresses crater wear, thereby improving wear resistance. On the other hand, by making the average thickness of the intermediate layer 15.0 μm or less, the coating peeling is suppressed, thereby improving chip resistance. From the same viewpoint, the average thickness of the intermediate layer is more preferably 4.5 μm or more and 12.5 μm or less, and even more preferably 6.0 μm or more and 10.0 μm or less.

[0034] The intermediate layer only needs to be composed of α-alumina (α-Al2O3). As long as the effect of the present invention is achieved, it may contain components other than α-alumina (α-Al2O3) or may not contain components other than α-alumina (α-Al2O3).

[0035] In this embodiment, the average length RSm of the roughness curve elements on the surface of the intermediate layer is preferably 5 μm or more and 20 μm or less. By making the average length RSm of the roughness curve elements on the surface of the intermediate layer 5 μm or more, the coating cutting tool of this embodiment increases the spacing between adjacent protrusions on the surface of the intermediate layer. Since these protrusions can be suppressed from becoming the starting point of damage, the resistance to defects tends to improve. Furthermore, in region A described later, it becomes easier to increase the proportion of the total length of the Σ3 grain boundaries, which is 100% of the total length of all grain boundaries. On the other hand, by making the average length RSm of the roughness curve elements on the surface of the intermediate layer 20 μm or less, the unevenness of the intermediate layer surface increases the adhesion between the intermediate layer and the upper layer, suppressing peeling and thus improving the resistance to defects. From the same viewpoint, the average length RSm of the roughness curve elements on the surface of the intermediate layer is more preferably 6 μm or more and 18 μm or less, and even more preferably 7 μm or more and 16 μm or less.

[0036] It should be noted that the average length RSm of the roughness curve elements in the surface of the intermediate layer can be determined by the method described in the embodiments described later.

[0037] [Upper Layer] The upper layer used in this embodiment includes one or more Ti compound layers, wherein the Ti compound layers are composed of Ti and a Ti compound formed with at least one element selected from the group consisting of C, N, O and B, and the upper layer includes at least one TiCN layer composed of TiCN.

[0038] The upper layer used in this embodiment comprises one or more Ti compound layers, wherein the Ti compound layers are composed of Ti and at least one Ti compound formed from the group consisting of C, N, O and B, and the upper layer includes at least one TiCN layer composed of TiCN, thereby improving wear resistance. Furthermore, the upper layer includes a TiCN layer on the outermost side of the α-Al₂O₃ layer compared to the intermediate layer, and this TiCN layer controls the proportion of the area occupied by region A (described later) and the proportion of the total length of Σ₃ grain boundaries in region A relative to 100% of the total length of all grain boundaries, thereby improving wear resistance and resistance to chipping.

[0039] There are no particular limitations on the Ti compound layers other than the TiCN layer in the upper layer. Examples include TiC layers made of TiC, TiN layers made of TiN, TiCO layers made of TiCO, TiCNO layers made of TiCNO, and TiON layers made of TiON.

[0040] The upper layer can consist of one layer or multiple layers (e.g., two or three layers). When the upper layer consists of multiple layers, preferably, a TiCNO layer or a TiN layer can be formed as the layer on the side in contact with the intermediate layer. Additionally, other layers can be formed on the surface of the TiCN layer away from the substrate. When the upper layer consists of two layers, a TiCNO layer or a TiN layer can be formed as layer X, followed by a TiCN layer formed on the surface of layer X as layer Y. Furthermore, when the upper layer consists of three layers, a TiCNO layer or a TiN layer can be formed as layer X on the side in contact with the intermediate layer, followed by a TiCN layer formed on the surface of layer X as layer Y, and then a TiN layer formed on the surface of layer Y as layer Z.

[0041] In this embodiment, the average thickness of the upper layer is 1.0 μm or more and 6.0 μm or less. By making the average thickness of the upper layer 1.0 μm or more, the coated cutting tool of this embodiment suppresses flank wear, thereby improving wear resistance. On the other hand, by making the average thickness of the upper layer 6.0 μm or less, the coated cutting tool of this embodiment suppresses coating peeling, thereby improving resistance to chipping. From the same viewpoint, the average thickness of the upper layer is preferably 1.2 μm or more and 5.2 μm or less, more preferably 1.5 μm or more and 4.2 μm or less.

[0042] From the viewpoint of further improving wear resistance and chip resistance, the average thickness of the TiCN layer in the upper layer is preferably 0.5 μm or more and 6.0 μm or less. From the same viewpoint, the average thickness of the TiCN layer in the upper layer is more preferably 0.8 μm or more and 5.0 μm or less, and even more preferably 1.2 μm or more and 4.5 μm or less.

[0043] From the viewpoint of further improving wear resistance and chip resistance, the average thickness of the TiCNO layer in the upper layer is preferably 0.1 μm or more and 1.0 μm or less. From the same viewpoint, the average thickness of the TiCNO layer in the upper layer is more preferably 0.2 μm or more and 0.8 μm or less, and even more preferably 0.3 μm or more and 0.6 μm or less.

[0044] From the viewpoint of further improving wear resistance and chip resistance, the average thickness of the TiN layer in the upper layer is preferably 0.05 μm or more and 1.00 μm or less. From the same viewpoint, the average thickness of the TiN layer in the upper layer is more preferably 0.10 μm or more and 0.50 μm or less, and even more preferably 0.15 μm or more and 0.25 μm or less.

[0045] In this embodiment, when the upper layer is in contact with the intermediate layer, the adhesive layer (hereinafter also simply referred to as the "adhesive layer") serving as the side in contact with the intermediate layer in the upper layer may include at least one layer selected from the group consisting of a layer formed of TiN, a layer formed of TiCO, a layer formed of TiON, and a layer formed of TiCNO. If the upper layer used in this embodiment includes such an adhesive layer, the adhesion between the upper layer and the intermediate layer tends to be improved. From the same viewpoint, a TiN layer or a TiCNO layer is more preferably used as the adhesive layer.

[0046] In the upper layer used in this embodiment, the average thickness of the adhesive layer is preferably 0.1 μm or more and 1.0 μm or less. For the coated cutting tool of this embodiment, if the average thickness of its adhesive layer is 0.1 μm or more, the upper layer and the intermediate layer tend to have excellent adhesion, and the resistance to chipping tends to be improved. On the other hand, for the coated cutting tool of this embodiment, if the average thickness of its adhesive layer is 1.0 μm or less, the wear resistance tends to be improved. From the same point of view, the average thickness of the adhesive layer is more preferably 0.2 μm or more and 0.8 μm or less, and even more preferably 0.3 μm or more and 0.6 μm or less.

[0047] The Ti compound layer in the upper layer is a layer composed of Ti and at least one element selected from the group consisting of C, N, O and B. However, as long as the effect based on the upper layer is achieved, it may also contain trace amounts of components other than the above-mentioned elements.

[0048] For the coating cutting tool of this embodiment, if the total area of ​​the entire TiCN layer in the upper layer parallel to the substrate surface is set to 100% area, then the total proportion of the cross-sectional area of ​​the region A with an orientation difference of 0 degrees or more and less than 15 degrees is 30% area or more and 70% area or less.

[0049] It should be noted that the analysis location of the total proportion of the cross-sectional area of ​​region A is the section exposed in the upper TiCN layer, which is located at a position from the substrate side where the remaining thickness relative to the average thickness of the upper TiCN layer is more than 30% and less than 90%, and in a direction parallel to the substrate surface.

[0050] The coated cutting tool of this embodiment improves wear resistance by suppressing particle shedding caused by mechanical and thermal shocks by achieving an RSA of 30% or more. Conversely, the coated cutting tool of this embodiment improves wear resistance by achieving an RSA of 70% or less. From the same viewpoint, an RSA of 31% or more and 68% or less is more preferred, and an RSA of 34% or more and 62% or less is even more preferred.

[0051] It should be noted that in this embodiment, the RSA can be obtained by the method described in the embodiments described later.

[0052] For the coated cutting tool of this embodiment, in region A of the TiCN layer in its upper layer, the proportion of the total length of Σ3 grain boundaries relative to 100% of the total length of all grain boundaries is 30% or more and less than 60%. By ensuring that the proportion of the total length of Σ3 grain boundaries relative to 100% of the total length of all grain boundaries in region A of the TiCN layer in this embodiment is 30% or more, the effect of suppressing particle shedding caused by an RSA of 30% or more is further improved, thus increasing resistance to chipping. Furthermore, due to the improved mechanical properties, crater wear is suppressed, and wear resistance is also improved. On the other hand, by ensuring that the proportion of the total length of Σ3 grain boundaries relative to 100% of the total length of all grain boundaries in region A is less than 60%, grain coarsening is suppressed, chipping resistance is improved, and thus resistance to chipping is increased. From the same point of view, in region A, the proportion of the total length of Σ3 grain boundaries relative to 100% of the total length of all grain boundaries is preferably 35% or more and 55% or less, and more preferably 40% or more and 50% or less.

[0053] For the coated cutting tool of this embodiment, from the viewpoint of improving thermal shock resistance and thus improving chip resistance, the proportion of the total length of Σ3 grain boundaries, which is 100% of the total length of all grain boundaries, in the entire cross-section of the TiCN layer in the upper layer parallel to the substrate surface is preferably greater than 0% and less than 30%. Similarly, from the same viewpoint, the proportion of the total length of Σ3 grain boundaries, which is 100% of the total length of all grain boundaries, in the entire cross-section of the TiCN layer in the upper layer is preferably greater than 3% and less than 25%, more preferably greater than 5% and less than 22%, and even more preferably greater than 10% and less than 20%.

[0054] It should be noted that the analytical position of the proportion of the total length of the Σ3 grain boundary relative to 100% of the total length of all grain boundaries is the cross section exposed in the upper TiCN layer, which is located at a position from the substrate side where the remaining thickness of the TiCN layer in the upper layer is more than 30% and less than 90% relative to the average thickness of the TiCN layer in the upper layer, and in a direction parallel to the substrate surface.

[0055] It should be noted that in this application, the length of the CSL grain boundary refers to the sum of the lengths of the corresponding grain boundaries represented by the combination of Σ and numbers: "Σ3 grain boundary, Σ5 grain boundary, Σ7 grain boundary, Σ9 grain boundary, Σ11 grain boundary, Σ13 grain boundary, Σ15 grain boundary, Σ17 grain boundary, Σ19 grain boundary, Σ21 grain boundary, Σ23 grain boundary, Σ25 grain boundary, Σ27 grain boundary and Σ29 grain boundary".

[0056] The TiCN layer in the upper layer of this embodiment has grain boundaries with both high and low grain boundary energies. Generally, grain boundaries have high grain boundary energies due to the irregular and disordered arrangement of atoms, resulting in numerous interstitial spaces. Conversely, some grain boundaries have lower grain boundary energies because of their regular atomic arrangement and fewer interstitial spaces. A representative example of such grain boundaries with low grain boundary energies is the Coincidence Site Lattice (CSL) grain boundary (hereinafter also referred to as "CSL grain boundary"). Grain boundaries have a significant impact on important sintering processes such as densification, creep, and diffusion, as well as on electrical, optical, and mechanical properties. The importance of grain boundaries depends on several factors, such as the grain boundary density in the material, the chemical composition of the interface, and the crystallographic structure, i.e., grain boundary plane orientation and grain orientation difference. CSL grain boundaries play a particularly important role. As an indicator of the extent of CSL grain boundary distribution, the Σ value is known, defined as the ratio of the lattice point density of two contacting grains at the grain boundary to the density of the lattice points that coincide when their lattices overlap. It is generally believed that, in simple structures, grain boundaries with low Σ values ​​tend to have low interfacial energies and unique properties. Therefore, controlling the proportion of CSL grain boundaries and the distribution of grain orientation differences is considered important for the properties of TiCN layers and for improving these properties.

[0057] In recent years, techniques based on scanning electron microscopy (SEM), known as electron backscatter diffraction (EBSD), have been used to study grain boundaries in materials. EBSD is based on the automated analysis of Kikuchi diffraction patterns generated by backscattered electrons.

[0058] For each grain of the target material, the crystallographic orientation is determined after the corresponding diffraction pattern is indexed. Microstructural analysis and determination of Grain Boundary Character Distribution (GBCD) are relatively easy by using EBSD with commercially available software. By using EBSD to measure and resolve interfaces, the orientation difference of grain boundaries in sample groups with large interfaces can be clearly identified. Typically, the distribution of orientation difference is related to the material's processing and / or physical properties. The orientation difference of grain boundaries is obtained using common orientation parameters such as Euler angles, angle / axis pairs, or Rodrigues vectors.

[0059] The CSL grain boundaries of TiCN layers are typically composed of Σ3, Σ5, Σ7, Σ9, Σ11, Σ13, Σ15, Σ17, Σ19, Σ21, Σ23, Σ25, Σ27, and Σ29 grain boundaries. For example, the length of a Σ3 grain boundary is expressed as the total length of Σ3 grain boundaries in a specific area of ​​view observed by a SEM with EBSD.

[0060] The total grain boundary length is the sum of the grain boundaries other than the CSL grain boundaries and the CSL grain boundaries. Hereinafter, the grain boundaries other than the CSL grain boundaries will be referred to as "general grain boundaries" or "random grain boundaries." General grain boundaries are the grain boundaries remaining after removing the CSL grain boundaries from the total grain boundaries of the TiCN layer when observed using a SEM equipped with EBSD. Therefore, the "total length of all grain boundaries" can be expressed as the sum of the lengths of the CSL grain boundaries and the general grain boundaries.

[0061] In this embodiment, the total proportion of the length of Σ3 grain boundaries relative to 100% of the total grain boundary length in the entire cross section of the upper TiCN layer, and the proportion of the length of Σ3 grain boundaries relative to 100% of the total grain boundary length in region A of the upper TiCN layer, can be calculated in the following manner.

[0062] An observation surface is obtained by exposing a cross-section of the upper TiCN layer in a direction parallel to the surface of the substrate using a coated cutting tool. Methods for exposing the cross-section of the upper TiCN layer include, for example, cutting and grinding. Among these, grinding is preferred from the viewpoint of making the observation surface of the TiCN layer smoother. In particular, from the viewpoint of making the observation surface smoother, a mirror-like surface is preferred. Methods for obtaining a mirror-like observation surface of the TiCN layer are not particularly limited, and examples include grinding using diamond paste or colloidal silica, or ion milling.

[0063] Then, the observation surface was observed using a SEM equipped with EBSD. The rake face was preferably used as the observation area.

[0064] For SEM, use SU6600 (made by Hitachi High Technology Corporation) which has EBSD (made by TexSEM Laboratories).

[0065] The normal to the observation surface was tilted at 70° relative to the incident beam, and electron beams were irradiated under an accelerating voltage of 15 kV and an irradiation current of 1.0 nA for analysis. Within a measurement range of 120 μm × 120 μm, EBSD with a step size of 0.1 μm (distance between measurement points) was used to analyze the crystal orientation of each TiCN grain in the upper layer for data collection. At this point, the boundary between measurement points where the difference in crystal orientation between adjacent measurement points is greater than 5° was defined as a grain boundary.

[0066] Data processing was performed using commercially available software. This could be confirmed by counting the CSL grain boundaries corresponding to arbitrary Σ values ​​and expressing them as a ratio relative to all grain boundaries. Based on this method, the lengths of Σn grain boundaries (n being an odd number between 3 and 29), the lengths of CSL grain boundaries, and the total length of all grain boundaries in the TiCN layer were determined. Within the measurement range of the aforementioned observation surface, a total of three fields of view were analyzed, and the average value of each value was calculated. Based on the obtained average value, the total proportion of the lengths of Σ3 grain boundaries (representing 100% of the total grain boundary length) in the entire cross-section of the upper TiCN layer, and the proportion of the lengths of Σ3 grain boundaries (representing 100% of the total grain boundary length) in region A of the upper TiCN layer could be calculated.

[0067] [Coating Formation Methods] Examples of methods for forming the coating layers in the coated cutting tool constituting this embodiment include the following. However, the methods for forming each layer are not limited to these.

[0068] First, a lower layer consisting of one or more Ti compound layers is formed on the surface of a substrate. Next, the surface of the layer furthest from the substrate is oxidized. Then, an α-Al₂O₃ core is formed on the surface of the layer furthest from the substrate, followed by a two-stage process to form the α-Al₂O₃ layer. Further, an upper layer consisting of a Ti compound layer including a TiCN layer is formed on the surface of the α-Al₂O₃ layer.

[0069] There are no particular limitations on the method for forming the Ti compound layer in the lower layer, and the following methods can be listed as examples.

[0070] For example, the Ti compound layer in the lower layer, which consists of a Ti nitride layer (hereinafter also referred to as the "TiN layer"), can be formed by chemical vapor deposition with the following raw material composition: TiCl4: 5.0-10.0 mol%, N2: 20-60 mol%, H2: the remainder, temperature: 850-950 °C, pressure: 350-450 hPa, and gas flow rate: 40-80 L / min.

[0071] The Ti compound layer in the lower layer, consisting of a Ti carbide layer (hereinafter also referred to as the "TiC layer"), can be formed by chemical vapor deposition with the following raw material composition: TiCl4: 1.5–3.5 mol%, CH4: 3.5–5.5 mol%, H2: the remainder, temperature: 950–1050 °C, pressure: 70–80 hPa, and gas flow rate: 30–70 L / min.

[0072] The Ti compound layer in the lower layer, consisting of a Ti carbonitride layer (hereinafter also referred to as the "TiCN layer"), can be formed by chemical vapor deposition with the following raw material composition: TiCl4: 5.0–7.0 mol%, CH3CN: 0.5–1.5 mol%, H2: the remainder, temperature: 800–900 °C, pressure: 70–90 hPa, and gas flow rate: 50–90 L / min.

[0073] The Ti compound layer in the lower layer, consisting of a Ti carbon nitride oxide layer (hereinafter also referred to as the "TiCNO layer"), can be formed by chemical vapor deposition with the following raw material composition: TiCl4: 3.0-4.0 mol%, CO: 0.5-1.0 mol%, N2: 30-40 mol%, H2: the remainder, temperature: 950-1050 °C, pressure: 50-150 hPa, and gas flow rate: 30-70 L / min.

[0074] The Ti compound layer in the lower layer, which consists of a Ti carbon oxide layer (hereinafter also referred to as the "TiCO layer"), can be formed by chemical vapor deposition with the following raw material composition: TiCl4: 1.0-2.0 mol%, CO: 2.0-3.0 mol%, H2: the remainder, temperature: 950-1050 °C, pressure: 50-150 hPa, and gas flow rate: 30-70 L / min.

[0075] Furthermore, the intermediate layer composed of the α-Al2O3 layer is formed, for example, by the following method.

[0076] First, the surface of the layer furthest from the substrate in the lower layer is oxidized (oxidation process) under the following conditions: raw material composition of CO2: 0.1-1.0 mol%, H2: the remainder; temperature of 950-1000℃; pressure of 60-80 hPa; and gas flow rate of 5-15 L / min. The preferred oxidation time is 1-5 minutes.

[0077] Then, the nucleus of the α-Al₂O₃ layer is formed by chemical vapor deposition (CVD) with the following raw material composition: AlCl₃: 1.0–4.0 mol%, CO: 0.05–2.0 mol%, CO₂: 1.0–3.0 mol%, HCl: 2.0–3.0 mol%, H₂: the remainder, at a temperature of 950–1050 °C, a pressure of 60–80 hPa, and a gas flow rate of 50–90 L / min. The preferred time for the nucleus formation process is 3–30 minutes.

[0078] Next, the first α-Al2O3 layer (first film formation process) is formed by chemical vapor deposition with the following raw material composition: AlCl3: 1.5-3.5 mol%, CO2: 0.5-2.5 mol%, HCl: 1.5-3.5 mol%, H2S: 0.10-0.40 mol%, H2: the remainder, temperature: 980-1040℃, pressure: 70-110 hPa, and gas flow rate: 50-90 L / min.

[0079] Then, a second α-Al2O3 layer (second film formation process) is formed by chemical vapor deposition with the following raw material composition: AlCl3: 1.5-3.5 mol%, CO2: 1.0-5.0 mol%, HCl: 1.5-3.5 mol%, H2: the remainder, temperature: 850-940℃, pressure: 70-110 hPa, and gas flow rate: 50-90 L / min.

[0080] In the intermediate layer, to control the average length RSm of the surface roughness curve elements within the aforementioned specific range, control can be achieved by, for example, by combining a first film-forming process using H2S as a raw material with a second film-forming process not using H2S as a raw material to form the intermediate layer, and / or by controlling the temperature and the proportion of raw material composition in the second film-forming process. More specifically, by combining the first and second film-forming processes, RSm tends to increase. The mechanism is speculated to be as follows, but is not limited to: since the first and second film-forming processes, which readily grow crystal planes with significantly different shapes, are combined to form the intermediate layer, a portion of the protrusions formed in the first film-forming process disappears in the second film-forming process, resulting in an increase in RSm.

[0081] Furthermore, RSm tends to increase by lowering the temperature in the second film-forming process. Even further, RSm tends to increase by increasing the proportion of CO2 in the raw material composition.

[0082] Furthermore, the method for forming the upper layer is not particularly limited, and examples such as the following can be cited. First, if an adhesive layer is formed on the side in contact with the intermediate layer (α-Al2O3 layer), as a first process for forming the upper layer, a Ti compound layer (adhesive layer) is formed on the surface of the α-Al2O3 layer. Next, as a second process for forming the upper layer, a TiCN layer is formed on the surface of the adhesive layer. Further, a Ti compound layer can also be formed on the surface of the TiCN layer as the outermost layer of the upper layer. In addition, as a first process for forming the upper layer, a TiCN layer can be formed on the surface of the α-Al2O3 layer, and then, as a second process for forming the upper layer, a Ti compound layer (outermost layer) can be further formed.

[0083] As a first process for forming the upper layer, for example, when forming a TiCNO layer on the surface of an α-Al2O3 layer, it can be formed by chemical vapor deposition with the following raw material composition: TiCl4: 7.5–9.5 mol%, CH4: 1.0–2.0 mol%, CO: 0.3–1.7 mol%, N2: 5.0–30.0 mol%, H2: the remainder, at a temperature of 860–940 °C, a pressure of 110–190 hPa, and a gas flow rate of 70–110 L / min.

[0084] As a first process for forming the upper layer, for example, when forming a TiN layer on the surface of an α-Al2O3 layer, it can be formed by chemical vapor deposition with the following raw material composition: TiCl4: 6.0–10.0 mol%, N2: 10.0–30.0 mol%, H2: the remainder, temperature: 840–920 °C, pressure: 170–190 hPa, and gas flow rate: 90–110 L / min.

[0085] As the first or second process for forming the upper layer, the TiCN layer can be formed by chemical vapor deposition with the following raw material composition: TiCl4: 7.0–10.0 mol%, CH4: 0.1–2.0 mol%, CH3CN: 0.3–1.3 mol%, N2: 10.0–25.0 mol%, H2: the remainder, at a temperature of 860–940 °C, a pressure of 110–190 hPa, and a gas flow rate of 80–110 L / min.

[0086] Furthermore, when forming a TiN layer on the surface of the TiCN layer, it can be achieved by chemical vapor deposition with the following raw material composition: TiCl4: 5.0–10.0 mol%, N2: 20.0–60.0 mol%, H2: the remainder, temperature: 950–1050 °C, pressure: 300–400 hPa, and gas flow rate: 50–90 L / min.

[0087] To ensure that the proportion of the total length of Σ3 grain boundaries, which is 100% of the total length of all grain boundaries, in the entire cross-section of the TiCN layer as the upper layer is within the aforementioned specific range, for example, the proportion of N2 in the raw material composition of the first or second process for forming the TiCN layer as the upper layer can be controlled. More specifically, for example, by increasing the proportion of N2 in the raw material composition of the first or second process for forming the TiCN layer as the upper layer, the proportion of the total length of Σ3 grain boundaries, which is 100% of the total length of all grain boundaries, in the entire cross-section of the TiCN layer tends to increase.

[0088] To ensure that the proportion of the total length of Σ3 grain boundaries, which is 100% of the total length of all grain boundaries, in region A of the upper TiCN layer is within the aforementioned specific range, for example, the proportion of N2 in the raw material composition of the first or second process for forming the TiCN layer as the upper layer can be controlled, or the average length RSm of the roughness curve elements on the surface of the intermediate layer can be controlled. More specifically, for example, by increasing the proportion of N2 in the raw material composition of the first or second process for forming the TiCN layer as the upper layer, the proportion of the total length of Σ3 grain boundaries, which is 100% of the total length of all grain boundaries, in region A of the upper TiCN layer tends to increase. Furthermore, for example, by increasing the average length RSm of the roughness curve elements on the surface of the intermediate layer, the proportion of the total length of Σ3 grain boundaries, which is 100% of the total length of all grain boundaries, in region A of the upper TiCN layer tends to increase.

[0089] In the upper layer, to keep the RSA within the aforementioned specific range, for example, the proportion of CH4 in the raw material composition of the first or second process for forming the TiCN layer as the upper layer can be controlled, or the gas flow rate in the first or second process for forming the TiCN layer as the upper layer can be controlled. More specifically, for example, by increasing the proportion of CH4 in the raw material composition of the first or second process for forming the TiCN layer as the upper layer, the RSA can tend to increase. Furthermore, for example, by increasing the gas flow rate in the first or second process for forming the TiCN layer as the upper layer, the RSA can tend to increase.

[0090] The thickness of each layer in the coating of the coated cutting tool of this embodiment can be determined by observing the cross-sectional microstructure of the coated cutting tool using an optical microscope, scanning electron microscope (SEM), or field emission scanning electron microscope (FE-SEM). It should be noted that the average thickness of each layer in the coated cutting tool of this embodiment can be measured at three or more locations near a position approximately 50 μm from the center of the rake face of the coated cutting tool, and the arithmetic mean can be calculated. Furthermore, the composition of each layer can be determined from the cross-sectional microstructure of the coated cutting tool of this embodiment using energy-dispersive X-ray spectroscopy (EDS) or wavelength-dispersive X-ray spectroscopy (WDS).

[0091]

Example

[0092] Prepare a cemented carbide cutting insert with the insert shape of CNMG120412 (ISO specification) and a composition of 87.0% WC, 8.6% Co, 2.0% TiN, 2.0% NbC, and 0.4% Cr3C2 (all percentages by mass) as the substrate. After rounding the cutting edge of the substrate with a SiC brush, clean the surface of the substrate.

[0093] [Inventions 1-29 and Comparative Articles 1-14] After cleaning the surface of the substrate, a coating is formed using chemical vapor deposition. First, a lower layer is formed on the surface of the substrate. Specifically, the substrate is placed in an externally heated chemical vapor deposition apparatus, and under the conditions of raw material composition, temperature, pressure, and gas flow rate shown in Table 1, a first layer with the composition shown in Table 7 is formed on the surface of the substrate with an average thickness shown in Table 7. Next, under the conditions of raw material composition, temperature, pressure, and gas flow rate shown in Table 1, a second layer with the composition shown in Table 7 is formed on the surface of the first layer with an average thickness shown in Table 7. Then, under the conditions of raw material composition, temperature, pressure, and gas flow rate shown in Table 1, a third layer with the composition shown in Table 7 is formed on the surface of the second layer with an average thickness shown in Table 7. Through the above steps, a lower layer with a three-layer structure is formed.

[0094] Then, as an oxidation process, the surface of the lower layer is oxidized under the conditions of raw material composition, temperature, pressure, and gas flow rate shown in Table 2. The oxidation process takes 3 minutes. Next, as a nucleation process, an α-type alumina (α-Al₂O₃) nucleus is formed on the surface of the oxidized lower layer under the conditions of raw material composition, temperature, pressure, and gas flow rate shown in Table 2. The nucleation process takes 10 minutes. Further, as a first film-forming process, an intermediate layer with the composition shown in Table 8 is formed on the surface of the α-type alumina (α-Al₂O₃) nucleus under the conditions of raw material composition, temperature, pressure, and gas flow rate shown in Table 3 and Table 2. It should be noted that for Inventions 1-29 and Comparative Examples 1-11 and 14, the time for forming the intermediate layer in the first film-forming process is until the average thickness of the intermediate layer after the first film-forming process reaches approximately 80% of the average thickness shown in Table 8. Next, as a second film-forming process, under the conditions of the raw material composition, temperature, and pressure shown in Table 4 and the gas flow rate shown in Table 2, an intermediate layer with the composition shown in Table 8 is formed on the surface of the intermediate layer formed in the first film-forming process, such that its average thickness is as shown in Table 8. It should be noted that for Inventions 1-29 and Comparative Examples 1-11 and 14, the time for forming the intermediate layer in the second film-forming process is until the average thickness of the intermediate layer after the second film-forming process reaches the average thickness shown in Table 8. For Inventions 1-29 and Comparative Examples 1-11 and 14, the first and second film-forming processes of the intermediate layer are performed to form the intermediate layer with the average thickness shown in Table 8. It should be noted that for Comparative Examples 12 and 13, only the first film-forming process is performed, and the time for forming the intermediate layer is the time required to form the average thickness shown in Table 8.

[0095] Next, an upper layer is formed on the surface of the intermediate layer. Specifically, for inventions 1-26 and comparative articles 1-14, firstly, as a first process for forming the upper layer, under the conditions of raw material composition, temperature, pressure, and gas flow rate shown in Table 5, an X layer with the composition shown in Table 9 is formed on the surface of the intermediate layer with an average thickness shown in Table 9. Next, as a second process for forming the upper layer, under the conditions of raw material composition, temperature, pressure, and gas flow rate shown in Table 6, a Y layer (TiCN layer) with the composition shown in Table 9 is formed on the surface of the X layer with an average thickness shown in Table 9. It should be noted that for inventions 27-29, as a first process for forming the upper layer, a Y layer (TiCN layer) with the composition shown in Table 9 is formed on the surface of the intermediate layer with an average thickness shown in Table 9. Further, for inventions 1-6, 8, 10-24, and 26, and comparative articles 1-3 and 5-14, under the conditions of raw material composition, temperature, pressure, and gas flow rate shown in Table 1, a Z layer with the composition shown in Table 9 is formed on the surface of the Y layer with an average thickness shown in Table 9. Thus, coated cutting tools of Inventions 1-29 and Comparative Examples 1-14 were obtained.

[0096] The thickness of each layer of the sample was determined using the following method: Using FE-SEM, the thickness was measured at three points in a cross-section approximately 50 μm from the edge of the coated cutting tool towards the center of the rake face, and the arithmetic mean was taken as the average thickness. Using EDS, the composition of each layer of the obtained sample was measured in a cross-section approximately 50 μm from the edge of the coated cutting tool towards the center of the rake face.

[0097] Table 1

[0098] Table 2

[0099] Table 3

[0100] Table 4

[0101] Table 5

[0102] Table 6

[0103] Table 7

[0104] Table 8

[0105] Table 9

[0106] [RSA] The RSA of the obtained sample is calculated using the following method.

[0107] In the obtained sample, a cross-section of the TiCN layer of the upper layer, parallel to the substrate surface, is exposed at a position where the thickness of the TiCN layer remaining in the upper layer from the substrate side is between 30% and 90% of the average thickness. The obtained cross-section is mirror-polished, and the mirror-polished surface is observed using FE-SEM. The orientation difference A is measured using EBSD provided with the FE-SEM. The total area of ​​the entire cross-section of the measured upper layer TiCN layer is set as 100% area, and the total proportion of the cross-sectional area occupied by the region with an orientation difference A of 0 degrees or more and less than 15 degrees (hereinafter also referred to as region A) is set as RSA (unit: area %). Specifically, firstly, the cross-sectional area of ​​region A and the cross-sectional area of ​​the region with an orientation difference A of 0 degrees or more and less than 45 degrees are calculated. It should be noted that the total cross-sectional area of ​​the region with an orientation difference A of 0 degrees or more and less than 45 degrees is set as 100% area. Among these cross-sectional areas based on orientation difference A, the ratio of the total cross-sectional area of ​​region A to the total cross-sectional area of ​​the region with an orientation difference A of 0 degrees or more and less than 45 degrees is expressed as RSA. The measurement results are shown in Table 10 below. It should be noted that the measurement method using EBSD is as follows: The sample was placed under a FE-SEM and irradiated with electron beams at an incident angle of 70 degrees, an accelerating voltage of 15 kV, and an irradiation current of 1.0 nA. Within a measurement range of 120 µm × 120 µm, using an EBSD setting of 0.1 μm step size (distance between measurement points), the orientation difference A and cross-sectional area of ​​each particle were measured. The cross-sectional area of ​​the upper TiCN layer within the measurement range is the sum of the pixels corresponding to that area. That is, the total cross-sectional area of ​​each region based on orientation difference A is calculated by adding the pixels occupied by the cross-section of the region within the orientation difference A range and then converting it into an area. Within the above measurement range, the same EBSD measurement was performed for a total of three fields of view, and then the average value of each area was calculated. The RSA was calculated based on the obtained average value. The results are shown in Table 10.

[0108] [Grain boundary length] The following method was used to determine the total cross-section of the TiCN layer in the upper layer of the obtained sample and the total length of the Σ3 grain boundary in region A, which is 100% of the total length of all grain boundaries.

[0109] In the obtained sample, a cross-section of the TiCN layer in the upper layer, parallel to the substrate surface, was exposed at a position where the thickness of the TiCN layer remaining in the upper layer from the substrate side is between 30% and 90% of the average thickness. The obtained cross-section was mirror-polished using colloidal silica to obtain a mirror-polished surface for observation. Then, the observation surface was observed using a FE-SEM equipped with EBSD. The rake face was used as the observation area. The EBSD measurement method is as follows: The sample was placed under the FE-SEM and irradiated with electron beams at an incident angle of 70 degrees, an accelerating voltage of 15 kV, and an irradiation current of 1.0 nA. Within a measurement range of 120 µm × 120 µm, using an EBSD setting of 0.1 μm step size (distance between measurement points), the crystal orientation of each particle in the TiCN layer of the upper layer within the measurement range was analyzed. At this time, the boundary between measurement points with a crystal orientation difference of 5° or more between adjacent measurement points was considered a grain boundary.

[0110] Data processing was performed using commercially available software. The results were confirmed by counting CSL grain boundaries corresponding to arbitrary Σ values ​​and expressing them as a ratio relative to all grain boundaries. Based on this method, the total cross-section of the upper TiCN layer and the total length of Σ3 grain boundaries in region A, representing 100% of the total length of all grain boundaries, were calculated. Analysis was performed on a total of three fields of view within the measurement range of the aforementioned observation plane, and the average value of each value was calculated. The ratio of the total cross-section of the upper TiCN layer and the total length of Σ3 grain boundaries in region A, representing 100% of the total length of all grain boundaries, was calculated based on the obtained average value (hereinafter also referred to as Σ3 / total grain boundaries (%)). The results are shown in Table 10.

[0111] Table 10

[0112] [RSm] The average length RSm of the roughness curve elements on the surface of the intermediate layer of the obtained sample was determined according to the following method.

[0113] The obtained sample was immersed in a mixture of hydrofluoric acid and nitric acid for about 20 minutes to remove the upper layer, exposing the surface of the intermediate layer. Under the following conditions, the surface microstructure of the exposed intermediate layer was measured using a laser roughness measuring instrument (VK-X100, manufactured by Keyence Corporation). The results are shown in Table 11 below.

[0114] Standard: JIS B0601:2001 (ISO 4287:1997). Reference length for measurement: 50 μm Number of lines used in the measurement: 10 lines, with a spacing of 10 μm between each line.

[0115] Table 11

[0116] Using the obtained inventions 1-29 and comparative articles 1-14, cutting tests 1 and 2 were conducted under the following conditions. Cutting test 1 was a test to evaluate wear resistance, and cutting test 2 was a test to evaluate resistance to chipping. The results of each cutting test are shown in Table 10.

[0117] [Cutting Test 1] Material to be cut: SCM440 The shape of the material being cut: a round bar. Cutting speed: 250 m / min Depth of cut: 1.5mm Feed rate: 0.25 mm / rev Coolant: None Evaluation criteria: The tool life is defined as the point at which the sample is damaged or the maximum back face wear width reaches 0.3 mm. The machining time until the tool life ends is measured.

[0118] [Cutting Test 2] Material to be cut: SCM415 The shape of the material being cut: a round bar with four equally spaced grooves on its outer circumference. Cutting speed: 220 m / min Depth of cut: 1.5mm Feed rate: 0.35 mm / rev Coolant: Water-soluble coolant Evaluation criteria: The tool life is defined as the number of impacts that occur when the sample is damaged, and the number of impacts up to the tool life is measured.

[0119] For the machining time until tool life is reached in cutting test 1, 21 minutes or more is rated as "A", 15 minutes or more but less than 21 minutes is rated as "B", and less than 15 minutes is rated as "C". Furthermore, for the cumulative number of impacts until tool life is reached in cutting test 2, 12,000 or more is rated as "A", 8,000 or more but less than 12,000 is rated as "B", and less than 8,000 is rated as "C". In this evaluation, "A" represents the best, "B" represents the second best, and "C" represents the worst. The more A or B values ​​a character has, the better the cutting performance. The evaluation results are shown in Table 12.

[0120] Table 12

[0121] According to the results shown in Table 12, the invention received an "A" or "B" rating in both cutting tests 1 and 2. On the other hand, the comparative product received a "C" rating for either cutting test 1 or cutting test 2. Therefore, it can be concluded that the invention exhibits superior wear resistance and chipping resistance compared to the comparative product.

[0122] Based on the above results, it can be seen that the invention has excellent wear resistance and damage resistance, resulting in a long tool life.

[0123] Industrial availability The coated cutting tool of the present invention has excellent wear resistance and chip resistance, which can extend tool life compared with the past, and therefore has industrial applicability from this point of view.

[0124] Explanation of main component symbols 1…substrate, 2…lower layer, 3…middle layer, 4…upper layer, 5…coating, 6…coating cutting tool.

Claims

1. A coated cutting tool, wherein, The coated cutting tool includes a substrate and a coating formed on the surface of the substrate. The coating comprises, from the substrate side toward the surface side of the coating, a lower layer, an intermediate layer, and an upper layer in sequence. The lower layer comprises one or more Ti compound layers, wherein the Ti compound layers are composed of Ti and a Ti compound formed with at least one element selected from the group consisting of C, N, O and B. The average thickness of the lower layer is between 3.0 μm and 15.0 μm. The intermediate layer includes an α-Al₂O₃ layer composed of α-type alumina. The average thickness of the intermediate layer is between 3.0 μm and 15.0 μm. The upper layer comprises one or more Ti compound layers, wherein the Ti compound layers are composed of Ti and a Ti compound formed with at least one element selected from the group consisting of C, N, O and B. The upper layer includes at least one TiCN layer composed of TiCN. The average thickness of the upper layer is between 1.0 μm and 6.0 μm. In the cross-section of the TiCN layer in the upper layer parallel to the surface of the substrate, if the total area of ​​the entire cross-section is set to 100% area, then the total proportion of the cross-sectional area of ​​region A with an orientation difference of 0 degrees or more and less than 15 degrees is 30% area or more and 70% area or less. The orientation difference is the angle formed by the normal of the cross-section of the TiCN layer in the upper layer and the normal of the (220) plane of the particles of the TiCN layer. In region A, the proportion of the total length of Σ3 grain boundaries relative to 100% of the total length of all grain boundaries is more than 30% and less than 60%.

2. The coated cutting tool according to claim 1, wherein, In the entire cross-section of the TiCN layer in the upper layer, the proportion of the total length of the Σ3 grain boundaries relative to 100% of the total length of all grain boundaries is less than 30%.

3. The coated cutting tool according to claim 1, wherein, The average length RSm of the roughness curve elements on the surface of the intermediate layer is between 5 μm and 20 μm.

4. The coated cutting tool according to claim 1, wherein, The average thickness of the entire coating is between 10.0 μm and 30.0 μm.

Images