Coated cutting tools

Abstract

The objective is to provide a coated cutting tool that can extend tool life by having excellent wear resistance and fracture resistance. [Solution] A coated cutting tool comprising a base material and a coating layer formed on the surface of the base material, wherein the coating layer comprises, in order from the base material side toward the surface of the coating layer, a lower layer containing a specific compound layer, an intermediate layer containing an α-Al2O3 layer, and an upper layer, the upper layer containing one or more Ti compound layers made of a specific compound, and the upper layer containing at least one TiCN layer made of TiCN, the average thickness of the lower layer, intermediate layer, and upper layer being within a predetermined range, and in the cross-section of the TiCN layer in the upper layer in a direction parallel to the surface of the base material, when the total area of ​​the entire cross-section is taken as 100 area%, the ratio of the total cross-sectional area of ​​a specific region A is 30 area% or more and 70 area%, and in region A, the ratio of the total length of Σ3 grain boundaries to the total length of all grain boundaries (100%) is 30% or more and less than 60%.

Description

[Technical Field]

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

[0002] It is well known that coated cutting tools, which have been conventionally formed by depositing a coating layer with a total thickness of 3 to 20 μm onto the surface of a substrate made of cemented carbide by chemical vapor deposition, have been used for cutting steel, cast iron, and other materials. As for the coating layer, for example, a single layer or a multi-layer coating consisting of two or more types selected from the group consisting of carbides, nitrides, carbonitrides, carbonoxides, and carbonitrates of Ti, and aluminum oxide (Al2O3), is known.

[0003] For example, Patent Document 1 describes a coated cutting tool comprising a substrate and a coating layer formed on the surface of the substrate, wherein the coating layer includes a lower layer, an intermediate layer, and an upper layer in that order from the substrate side toward the surface side of the coating layer, the lower layer includes one or more Ti compound layers made of Ti and at least one element selected from the group consisting of C, N, O, and B, the intermediate layer includes an α-type Al2O3 layer made of α-type Al2O3, the upper layer includes one or more Ti compound layers made 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, and the average thickness of the upper layer is 1.00 μm or more. A coated cutting tool is described, wherein the thickness is 50 μm or less, and in the upper layer, when the total area of ​​the entire cross-section of the upper layer perpendicular to the surface of the substrate is taken as 100 area%, the ratio of the cross-sectional area (RSA1) of the region where the orientation difference A, which is the angle (in degrees) between the normal of the (220) plane of each particle having a cubic crystal structure and the normal of the surface of the substrate, is 0 degrees or more and less than 10 degrees, satisfies predetermined conditions, and in the cross-section of the upper layer perpendicular to the surface of the substrate, when the total area of ​​the entire cross-section is taken as 100 area%, the ratio of the cross-sectional area (RSA2) of the region where the orientation difference A, which is the angle (in degrees) between the normal of the (220) plane of each particle having a cubic crystal structure and the normal of the surface of the substrate, is 20 degrees or more and less than 30 degrees, satisfies predetermined conditions.

[0004] Furthermore, for example, Patent Document 2 describes a coated cutting tool comprising a substrate of cemented carbide, cermet, ceramic, steel, or cubic boron nitride, and a multilayer wear-resistant coating having a total coating thickness of 5 to 25 μm, and comprising at least two refractory coating layers deposited by chemical vapor deposition (CVD) or medium-temperature chemical vapor deposition (MT-CVD), wherein the at least two refractory coating layers comprise a first coating layer and a second coating layer deposited on each other, and the first coating layer is titanium aluminum nitride or titanium aluminum carbonitride Ti 1-u Al u C v N w(0.2≦u≦1.0, 0≦v≦0.25 and 0.7≦w≦1.15), and is deposited by CVD at a reaction temperature in a range of 600°C to 900°C, the second coating layer is made of titanium carbonitride Ti x C y N 1-y (0.85≦x≦1.1 and 0.4≦y≦0.85), and is deposited on the first coating layer by MT-CVD at a reaction temperature in a range of 600°C to 900°C, the second Ti x C y N 1-y coating layer has a columnar grain morphology, and the overall fiber texture of the Ti x C y N 1-y coating layer is characterized by a predetermined texture coefficient TC(111)>2. A coated cutting tool is described.

Prior Art Literature

Patent Literature

[0005]

Patent Literature 1

Patent Literature 2

Summary of the Invention

Problem to be Solved by the Invention

[0006] In recent cutting processing, higher speed, higher feed rate and deeper cutting have become more prominent, and there is a demand for improving the wear resistance and chipping resistance of tools more than before. In particular, in high-speed cutting of steel, there is a problem that crater wear progresses rapidly, and the tool life cannot be extended. In addition, in processing where mechanical impact and thermal impact act, chipping occurs due to particle falling off, so there is a problem that the tool life cannot be extended. The cutting tool described in Patent Literature 2 does not have an α-Al₂O₃ layer, so its wear resistance is insufficient in processing where crater wear easily progresses. Furthermore, the proportion of Σ3 grain boundaries in the TiCN layer is low, and crater wear resistance is insufficient, so there is room for improvement in wear resistance.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a coated cutting tool that can extend tool life by having excellent wear resistance and fracture resistance. [Means for solving the problem]

[0008] From the above perspective, the inventors of this invention have conducted extensive research on extending the tool life of coated cutting tools and have found that by adopting a specific configuration, wear resistance and fracture resistance can be improved, and as a result, tool life can be extended. This led to the completion of the present invention.

[0009] In other words, the present invention is as follows. <1> A coated cutting tool comprising a base material and a coating layer formed on the surface of the base material, The coating layer includes a lower layer, an intermediate layer, and an upper layer in this order, from the substrate side toward the surface side of the coating layer. The lower layer comprises one or more Ti compound layers, each consisting of a Ti compound of Ti and 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 or more and 15.0 μm or less. The aforementioned intermediate layer includes an α-Al2O3 layer made of α-type aluminum oxide, The average thickness of the aforementioned intermediate layer is 3.0 μm or more and 15.0 μm or less. The upper layer comprises one or more Ti compound layers, each consisting of a Ti compound made of Ti and at least one element selected from the group consisting of C, N, O, and B. The upper layer includes at least one TiCN layer made of TiCN, The average thickness of the upper layer is 1.0 μm or more and 6.0 μm or less. In a cross-section of the TiCN layer in said upper layer in a direction parallel to the surface of said base material, when the total area of the entire cross-section is defined as 100 area%, the ratio of the total cross-sectional area of a region A, wherein the orientation difference which is an angle formed between the normal line of the cross-section of the TiCN layer in said upper layer and the normal line of the (220) plane of the TiCN layer particles is 0 degree or more and less than 15 degrees, is 30 area% or more and 70 area% or less, A coated cutting tool, wherein in said region A, the ratio of the total length of Σ3 grain boundaries to the total length of all grain boundaries of 100% is 30% or more and less than 60%. <2> In the entire cross-section of the TiCN layer in said upper layer, the ratio of the total length of Σ3 grain boundaries to the total length of all grain boundaries of 100% is less than 30%, The coated cutting tool according to <1>. <3> The average length RSm of roughness profile elements on the surface of the intermediate layer is 5 μm or more and 20 μm or less, The coated cutting tool according to <1> or <2>. <4> The average thickness of the entire coating layer is 10.0 μm or more and 30.0 μm or less, The coated cutting tool according to any one of <1> to <3>.

Effect of the Invention

[0010] According to the present invention, there can be provided a coated cutting tool which has excellent wear resistance and fracture resistance and thus can extend tool life.

Brief Description of Drawings

[0011] [Figure 1] It is a schematic cross-sectional view showing an example of the coated cutting tool of the present invention.

Mode for Carrying Out the Invention

[0012] Hereinafter, modes for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary. However, the present invention is not limited to the following present embodiment. Various modifications can be made to the present invention without departing from the gist thereof. In the drawings, unless otherwise specified, the positional relationships such as up, down, left and right are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios in the drawings are not limited to the ratios shown in the figures.

[0013] The coated cutting tool of the present embodiment is a coated cutting tool comprising a base material and a coating layer formed on a surface of the base material, wherein the coating layer includes a lower layer, an intermediate layer and an upper layer in this order from the base material side toward the surface side of the coating layer; the lower layer includes one or more Ti compound layers formed of a Ti compound composed of Ti and at least one element selected from the group consisting of C, N, O and B, and the average thickness of the lower layer is 3.0 µm or more and 15.0 µm or less; the intermediate layer includes an α-Al₂O₃ layer formed of α-type aluminum oxide, and the average thickness of the intermediate layer is 3.0 µm or more and 15.0 µm or less; the upper layer includes one or more Ti compound layers formed of a Ti compound composed of Ti and at least one element selected from the group consisting of C, N, O and B, the upper layer includes at least one TiCN layer formed of TiCN, and the average thickness of the upper layer is 1.0 µm or more and 6.0 µm or less; in a cross-section of the TiCN layer in the upper layer in a direction parallel to the surface of the base material, when the total area of the entire cross-section is defined as 100 area%, a ratio (hereinafter also referred to as RSA) of the total cross-sectional area of a region A in which an orientation difference (hereinafter also referred to as orientation difference A) that is an angle formed between a normal line of the cross-section of the TiCN layer in the upper layer and a normal line of the (220) plane of particles of the TiCN layer is 0° or more and less than 15° is 30 area% or more and 70 area% or less, and in the region A, a ratio of a total length of Σ3 grain boundaries to a total length of all grain boundaries defined as 100% is 30% or more and less than 60%.

[0014] The coated cutting tool of this embodiment, by having the above configuration, can improve wear resistance and fracture resistance, and as a result, can extend tool life. The factors that improve the wear resistance and fracture resistance of the coated cutting tool of this embodiment are thought to be as follows. However, the present invention is not limited in any way by the following factors. That is, first, the coated cutting tool of this embodiment has improved wear resistance because the average thickness of the lower layer is 3.0 μm or more, which suppresses flank wear. On the other hand, the coated cutting tool of this embodiment has improved fracture resistance because the peeling of the coating layer is suppressed because the average thickness of the lower layer is 15.0 μm or less. Furthermore, the coated cutting tool of this embodiment has improved wear resistance because the average thickness of the intermediate layer is 3.0 μm or more, which suppresses crater wear. On the other hand, the coated cutting tool of this embodiment has improved fracture resistance because the peeling of the coating layer is suppressed because the average thickness of the intermediate layer is 15.0 μm or less. Furthermore, the coated cutting tool of this embodiment has improved wear resistance because the average thickness of the upper layer is 1.0 μm or more, which suppresses flank wear. On the other hand, the coated cutting tool of this embodiment has improved fracture resistance because the average thickness of the upper layer is 6.0 μm or less, which suppresses peeling of the coating layer. Furthermore, the coated cutting tool of this embodiment has improved wear resistance and fracture resistance because the upper layer includes the RSA described later on the outer layer side of the α-Al2O3 layer and a TiCN layer in which the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries in region A is controlled. Furthermore, the coated cutting tool of this embodiment has improved fracture resistance because the RSA is 30 area % or more, which suppresses particle shedding due to mechanical and thermal shocks. On the other hand, the coated cutting tool of this embodiment has improved wear resistance because the RSA is 70 area % or less. Furthermore, in this embodiment, the coated cutting tool has improved fracture resistance because the ratio of the total length of Σ3 grain boundaries to the total length of all grain boundaries in region A is 30% or more, resulting in a higher RSA of 30% or more, which further enhances the effect of suppressing particle shedding. In addition, the improved mechanical properties suppress crater wear and improve wear resistance.On the other hand, in this embodiment, the coated cutting tool has a ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries in region A of less than 60%, which suppresses grain coarsening, improves chipping resistance, and consequently improves fracture resistance. Furthermore, it is believed that the combination of these features improves the wear resistance and fracture resistance of the coated cutting tool in this embodiment, thereby extending tool life.

[0015] Figure 1 is a schematic cross-sectional view showing an example of a coated cutting tool according to this embodiment. The coated cutting tool 6 comprises a base material 1 and a coating layer 5 formed on the surface of the base material 1. The coating layer 5 has a lower layer 2, an intermediate layer 3, and an upper layer 4 laminated upwards in this order from the base material side.

[0016] The coated cutting tool of this embodiment comprises a base material and a coating layer formed on the surface of that base material. Specific examples of coated cutting tools include replaceable cutting inserts for milling or turning, drills, and end mills.

[0017] The substrate used in this embodiment is not particularly limited as long as it can be used as a substrate for a coated cutting tool. Examples of such substrates include cemented carbide, cermet, ceramics, cubic boron nitride sintered body, diamond sintered body, and high-speed steel. Among these, the substrate is preferably cemented carbide, cermet, ceramics, or cubic boron nitride sintered body because it exhibits superior wear resistance and fracture resistance, and from a similar viewpoint, the substrate is more preferably cemented carbide.

[0018] Furthermore, the substrate may have a modified surface. For example, if the substrate is made of cemented carbide, a de-β layer may be formed on its surface. Also, if the substrate is made of cermet, a hardened layer may be formed on its surface. Even if the surface of the substrate is modified in these ways, the effects of the present invention will still be achieved.

[0019] In this embodiment, the coating layer preferably has an overall average thickness of 10.0 μm or more and 30.0 μm or less. In this embodiment, the coated cutting tool tends to have improved wear resistance when the overall average thickness of the coating layer is 10.0 μm or more, and improved fracture resistance when the overall average thickness of the coating layer is 30.0 μm or less, as peeling of the coating layer is suppressed. From a similar viewpoint, it is more preferable that the overall average thickness of the coating layer be 13.0 μm or more and 28.7 μm or less, and even more preferable that it be 14.0 μm or more and 26.2 μm or less. The average thickness of each layer and the entire coating layer in the coated cutting tool of this embodiment can be determined by measuring the thickness of each layer or the entire coating layer from three or more cross-sections in each layer or the entire coating layer, and calculating the arithmetic mean.

[0020] [Lower layer] The lower layer used in this embodiment includes one or more Ti compound layers, each consisting of a Ti compound made of Ti and at least one element selected from the group consisting of C, N, O, and B. When a coated cutting tool has a lower layer between the substrate and an intermediate layer containing an α-Al2O3 layer, wear resistance and adhesion are improved.

[0021] The lower layer may consist of one layer or multiple layers (for example, two or three layers), but it is preferable that it consists of multiple layers, more preferably two or three layers, and even more preferably three layers. The Ti compound constituting the Ti compound layer included in the lower layer is preferably at least one selected from the group consisting of TiN, TiC, TiCN, TiCO, TiCNO, TiON, and TiB2, and more preferably at least one selected from the group consisting of TiN, TiC, TiCN, TiCO, and TiCNO, from the viewpoint of further improving wear resistance and adhesion. Furthermore, in the coated cutting tool of this embodiment, it is preferable that at least one of the lower layers is a TiCN layer, as this further improves wear resistance. When the lower layer consists of three layers, a TiC layer or a TiN layer may be formed as the first layer on the surface of the substrate, a TiCN layer may be formed as the second layer on the surface of the first layer, and a TiCNO layer or a TiCO layer may be formed as the third layer on the surface of the second layer. In these configurations, the lower layer may have a TiN layer formed as the first layer on the surface of the substrate, a TiCN layer formed as the second layer on the surface of the first layer, and a TiCNO layer formed as the third layer on the surface of the second layer.

[0022] The average thickness of the lower layer used in this embodiment is 3.0 μm or more and 15.0 μm or less. In this embodiment, the coated cutting tool has improved wear resistance because the average thickness of the lower layer is 3.0 μm or more, which suppresses flank wear. On the other hand, in this embodiment, the coated cutting tool has improved fracture resistance because the average thickness of the lower layer is 15.0 μm or less, which suppresses peeling of the coating layer. From a similar 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.

[0023] From the viewpoint of further improving wear resistance and fracture resistance, the average thickness of the TiC 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 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.

[0024] From the viewpoint of further improving wear resistance and fracture resistance, the average thickness of the TiCN layer in the lower layer is preferably 2.0 μm to 15.0 μm. From the same viewpoint, the average thickness of the TiCN layer in the lower layer is more preferably 3.0 μm to 14.0 μm, and even more preferably 4.0 μm to 12.5 μm.

[0025] From the viewpoint of further improving wear resistance and fracture resistance, the average thickness of the TiCNO or TiCO layer in the lower layer is preferably 0.05 μm or more and 1.50 μm or less. From the same viewpoint, the average thickness of the TiCNO 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.

[0026] The Ti compound layer in the lower layer is a Ti compound layer consisting of Ti and at least one element selected from the group consisting of C, N, O, and B, but it may also contain trace amounts of elements other than those mentioned above, as long as the effects of the lower layer are achieved.

[0027] [Middle class] The intermediate layer used in this embodiment includes an α-Al2O3 layer made of α-type aluminum oxide (α-Al2O3).

[0028] The average thickness of the intermediate layer used in this embodiment is 3.0 μm or more and 15.0 μm or less. The coated cutting tool of this embodiment has improved wear resistance because crater wear is suppressed due to the average thickness of the intermediate layer being 3.0 μm or more. On the other hand, the coated cutting tool of this embodiment has improved fracture resistance because peeling of the coating layer is suppressed due to the average thickness of the intermediate layer being 15.0 μm or less. From a similar 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.

[0029] The intermediate layer only needs to have a layer made of α-type aluminum oxide (α-Al2O3), and may or may not contain components other than α-type aluminum oxide (α-Al2O3) as long as the effects of the present invention are achieved.

[0030] 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. In this embodiment, the coated cutting tool has an average length RSm of 5 μm or more of the roughness curve elements on the surface of the intermediate layer, which increases the spacing between adjacent protrusions on the surface of the intermediate layer, suppressing the protrusions from becoming the starting point of fracture, and thus tends to improve fracture resistance. In addition, in region A described later, it tends to be easier to increase the ratio of the length of the Σ3 grain boundary to the total length of all grain boundaries (100%). On the other hand, if the average length RSm of the roughness curve elements on the surface of the intermediate layer is 20 μm or less, the unevenness of the surface of the intermediate layer improves the adhesion force with the upper layer, suppressing peeling, and thus tends to improve fracture resistance. From a similar 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. The average length RSm of the roughness curve elements on the surface of the intermediate layer can be determined by the method described in the examples below.

[0031] [Top layer] The upper layer used in this embodiment includes one or more Ti compound layers made of Ti and at least one element selected from the group consisting of C, N, O, and B, and at least one TiCN layer made of TiCN.

[0032] The upper layer used in this embodiment includes one or more Ti compound layers made of Ti and at least one element selected from the group consisting of C, N, O, and B, and includes at least one TiCN layer made of TiCN, thereby improving wear resistance. Furthermore, by including a TiCN layer on the outer layer side of the intermediate α-Al2O3 layer in which the proportion of the area occupied by region A described later and the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries in region A are controlled, wear resistance and fracture resistance are improved.

[0033] The Ti compound layers other than the TiCN layer in the upper layer are not particularly limited, but examples include a TiC layer made of TiC, a TiN layer made of TiN, a TiCO layer made of TiCO, a TiCNO layer made of TiCNO, and a TiON layer made of TiON.

[0034] The upper layer may consist of one layer or multiple layers (for example, two or three layers). When the upper layer consists of multiple layers, it is preferable to form a TiCNO layer or a TiN layer as the layer in contact with the intermediate layer, and another layer may be formed on the surface of the TiCN layer opposite the substrate. When the upper layer consists of two layers, the TiCNO layer or TiN layer may be formed as the X layer, and the TiCN layer may be formed as the Y layer on the surface of the X layer. When the upper layer consists of three layers, the TiCNO layer or TiN layer may be formed as the X layer in contact with the intermediate layer, the TiCN layer may be formed as the Y layer on the surface of the X layer, and the TiN layer may be formed as the Z layer on the surface of the Y layer.

[0035] The average thickness of the upper layer used in this embodiment is 1.0 μm or more and 6.0 μm or less. In this embodiment, the coated cutting tool has improved wear resistance because the average thickness of the upper layer is 1.0 μm or more, which suppresses flank wear. On the other hand, in this embodiment, the coated cutting tool has improved fracture resistance because the average thickness of the upper layer is 6.0 μm or less, which suppresses peeling of the coating layer. From a similar viewpoint, the average thickness of the upper layer is preferably 1.2 μm or more and 5.2 μm or less, and more preferably 1.5 μm or more and 4.2 μm or less.

[0036] From the viewpoint of further improving wear resistance and fracture resistance, the average thickness of the TiCN layer in the upper layer is preferably 0.5 μm to 6.0 μm. Similarly, from the same viewpoint, the average thickness of the TiCN layer in the upper layer is preferably 0.8 μm to 5.0 μm, and more preferably 1.2 μm to 4.5 μm.

[0037] From the viewpoint of further improving wear resistance and fracture resistance, the average thickness of the TiCNO layer in the upper layer is preferably 0.1 μm to 1.0 μm. From the same viewpoint, the average thickness of the TiCNO layer in the upper layer is more preferably 0.2 μm to 0.8 μm, and even more preferably 0.3 μm to 0.6 μm.

[0038] From the viewpoint of further improving wear resistance and fracture resistance, the average thickness of the TiN layer in the upper layer is preferably 0.05 μm to 1.00 μm. From the same viewpoint, the average thickness of the TiN layer in the upper layer is more preferably 0.10 μm to 0.50 μm, and even more preferably 0.15 μm to 0.25 μm.

[0039] When the upper layer used in this embodiment is in contact with the intermediate layer, the upper layer may include at least one layer selected from the group consisting of a TiN layer, a TiCO layer, a TiON layer, and a TiCNO layer as the adhesion layer on the side in contact with the intermediate layer (hereinafter also simply referred to as the "adhesion layer"). The upper layer used in this embodiment tends to have improved adhesion with the intermediate layer when it includes such an adhesion layer. From a similar viewpoint, a TiN layer or a TiCNO layer is more preferable as the adhesion layer.

[0040] In the upper layer used in this embodiment, the average thickness of the adhesion layer is preferably 0.1 μm or more and 1.0 μm or less. When the average thickness of the adhesion layer of the coated cutting tool of this embodiment is 0.1 μm or more, the adhesion between the upper layer and the intermediate layer is excellent, and the fracture resistance tends to improve. On the other hand, when the average thickness of the adhesion layer of the coated cutting tool of this embodiment is 1.0 μm or less, the wear resistance tends to improve. From a similar viewpoint, the average thickness of the adhesion 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.

[0041] The Ti compound layer in the upper layer is a Ti compound layer consisting of Ti and at least one element selected from the group consisting of C, N, and O, but it may also contain trace amounts of elements other than those mentioned above, as long as the effects of the upper layer are achieved.

[0042] In this embodiment, the coated cutting tool has a cross-section of the TiCN layer in the upper layer parallel to the surface of the substrate. When the total area of ​​the entire cross-section is taken as 100 area%, the proportion of the total cross-sectional area of ​​region A where the orientation difference A is 0 degrees or more and less than 15 degrees is 30 area% or more and 70 area% or less. In this analysis, the position for determining the ratio of the total cross-sectional area of ​​region A is defined as a cross-section exposed in a direction parallel to the surface of the substrate, at a position where 30% to 90% of the average thickness of the TiCN layer in the upper layer remains from the substrate side.

[0043] In this embodiment, the coated cutting tool has improved fracture resistance because the RSA (Resistance Factor) is 30 area% or more, which suppresses particle shedding due to mechanical and thermal shocks. On the other hand, the coated cutting tool of this embodiment has improved wear resistance because the RSA is 70 area% or less. From a similar viewpoint, it is more preferable that the RSA is 31 area% to 68 area%, and even more preferable that it is 34 area% to 62 area%. In this embodiment, RSA can be determined by the method described in the later examples.

[0044] In this embodiment, the coated cutting tool has a ratio of 30% or more in the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries in region A of the TiCN layer in the upper layer. In this embodiment, the coated cutting tool has a ratio of 30% or more in the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries in region A of the TiCN layer in the upper layer, which further enhances the effect of suppressing particle shedding due to RSA being 30% or more in area, thus improving fracture resistance. In addition, mechanical properties are improved, so crater wear is suppressed and wear resistance is also improved. On the other hand, in this embodiment, the coated cutting tool has a ratio of less than 60% in the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries in region A, which suppresses grain coarsening, improves chipping resistance, and as a result improves fracture resistance. From a similar viewpoint, in region A, the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries is preferably 35% or more and 55%, and more preferably 40% or more and 50%.

[0045] In this embodiment, the coated cutting tool has improved thermal shock resistance, and therefore tends to have improved fracture resistance. From this viewpoint, it is preferable that the ratio of the total length of Σ3 grain boundaries to 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 surface of the substrate is greater than 0% and less than 30%. From a similar viewpoint, it is preferable that the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries in the entire cross-section of the TiCN layer in the upper layer is 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%. In this analysis, the position for determining the ratio of the total length of the Σ3 grain boundaries to the total length of all grain boundaries (100%) is defined as a cross-section exposed in a direction parallel to the surface of the substrate, at a position where 30% to 90% of the average thickness of the TiCN layer in the upper layer remains from the substrate side.

[0046] In this application, the length of the CSL grain boundary refers to the "total length of the 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" among the corresponding grain boundaries indicated by a combination of Σ and a number.

[0047] The TiCN layer in the upper layer of this embodiment has grain boundaries with relatively high grain boundary energy and grain boundaries with relatively low grain boundary energy. Normally, grain boundaries have many gaps and relatively high grain boundary energy because the arrangement of atoms is irregular and randomly arranged. On the other hand, some grain boundaries have regular arrangements of atoms and few gaps, and such grain boundaries have relatively low grain boundary energy. A typical example of such grain boundaries with relatively low grain boundary energy is the correspondence site lattice (CSL) grain boundary (hereinafter also referred to as "CSL grain boundary"). Grain boundaries have a significant influence 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., the grain interface orientation and grain orientation difference. CSL grain boundaries play a special role. The Σ value is known as an indicator of the degree of distribution of CSL grain boundaries, and is defined as the ratio of the density of lattice points of two grains touching at a grain boundary to the density of lattice points that coincide when both lattices are superimposed. In the case of simple structures, it is generally observed that grain boundaries with low Σ values ​​tend to have low interfacial energy and special properties. Therefore, controlling the proportion of CSL grain boundaries and the distribution of grain orientation differences is considered important for the properties of the TiCN layer and for improving them.

[0048] In recent years, a scanning electron microscope (SEM)-based technique known as electron backscatter diffraction (EBSD) has been used to study grain boundaries in materials. EBSD is based on automated analysis of Kikuchi diffraction patterns generated by backscattered electrons.

[0049] For each crystal grain of the material under consideration, the crystallographic orientation is determined after creating an index of the corresponding diffraction pattern. Using EBSD with commercially available software, microstructure analysis and determination of grain boundary character distribution (GBCD) can be performed relatively easily. By measuring and analyzing interfaces using EBSD, the orientation difference of crystal grain boundaries in a large sample population of interfaces can be revealed. Typically, the distribution of orientation differences is related to the processing and / or properties of the material. The orientation difference of crystal grain boundaries can be obtained from common orientation parameters such as Euler angles, angle / axis pairs, or Rodrigues vectors.

[0050] The CSL grain boundaries of the TiCN layer typically consist of Σ3-grain boundaries, Σ5-grain boundaries, Σ7-grain boundaries, Σ9-grain boundaries, Σ11-grain boundaries, Σ13-grain boundaries, Σ15-grain boundaries, Σ17-grain boundaries, Σ19-grain boundaries, Σ21-grain boundaries, Σ23-grain boundaries, Σ25-grain boundaries, Σ27-grain boundaries, and Σ29-grain boundaries. Here, for example, the length of a Σ3-grain boundary refers to the total length of Σ3-grain boundaries in the field of view (a specific region) observed by a SEM equipped with EBSD.

[0051] Here, "all grain boundaries" refers to the sum of all grain boundaries other than CSL grain boundaries and CSL grain boundaries. Hereafter, grain boundaries other than CSL grain boundaries will also be called "general grain boundaries" or "random grain boundaries." General grain boundaries are the remaining grain boundaries after subtracting CSL grain boundaries from the all grain boundaries of the TiCN layer when observed with an EBS-equipped SEM. Therefore, "total length of all grain boundaries" can be expressed as "the sum of the length of CSL grain boundaries and the length of general grain boundaries."

[0052] In this embodiment, the ratio of the sum of the lengths of the Σ3 grain boundaries to 100% of the total grain boundary length in the entire cross-section of the upper TiCN layer, and the ratio of the length of the Σ3 grain boundaries to 100% of the total grain boundary length in region A of the upper TiCN layer, can be calculated as follows.

[0053] A coated cutting tool is used to expose the cross-section of the upper TiCN layer in a direction parallel to the surface of the substrate, thereby obtaining an observation surface. Methods for exposing the cross-section of the upper TiCN layer include, for example, cutting and polishing. Of these, polishing is preferred from the viewpoint of making the observation surface of the TiCN layer smoother. In particular, the observation surface is preferably mirror-finished from the viewpoint of being as smooth as possible. Methods for obtaining a mirror-finish observation surface of the TiCN layer are not particularly limited, but examples include polishing using diamond paste or colloidal silica, or ion milling.

[0054] Subsequently, the observation surface is observed using a SEM equipped with EBSD. It is preferable to observe the scoop surface as the observation area.

[0055] The SEM used will be the SU6600 (manufactured by Hitachi High-Technologies Corporation) equipped with EBSD (manufactured by TexSEM Laboratories).

[0056] The normal to the observation surface is tilted 70° with respect to the incident beam, and the analysis is performed by irradiating with an electron beam at an accelerating voltage of 15kV and an irradiation current of 1.0nA. Data acquisition is performed by analyzing the crystal orientation of each TiCN particle in the upper layer using EBSD settings with a measurement range of 120μm × 120μm and a step size (distance between measurement points) of 0.1μm. At this time, grain boundaries are defined as the boundaries between measurement points where the difference in crystal orientation between adjacent measurement points is 5° or more.

[0057] Data processing is performed using commercially available software. The CSL grain boundaries corresponding to any given Σ value can be counted and confirmed by expressing them as a ratio to the total grain boundaries. From this, the length of the Σn grain boundary (n is an odd number between 3 and 29), the length of the CSL grain boundary, and the total length of the total grain boundaries in the TiCN layer are determined. Within the measurement range on the observation surface described above, a total of three fields of view are analyzed and the average value of each value is calculated. From the obtained average value, the ratio of the total length of the Σ3 grain boundaries to 100% of the total grain boundary length in the entire cross-section of the upper TiCN layer, and the ratio of the length of the Σ3 grain boundary to 100% of the total grain boundary length in region A of the upper TiCN layer can be calculated.

[0058] [Method for forming a coating layer] Examples of methods for forming each layer constituting the coating layer in the coated cutting tool of this embodiment include the following methods. However, the methods for forming each layer are not limited to these.

[0059] First, a lower layer consisting of one or more Ti compound layers is formed on the surface of the substrate. Next, the surface of the layer furthest from the substrate is oxidized. Then, a nucleus for an α-Al2O3 layer is formed on the surface of the layer furthest from the substrate, and with the nucleus formed, the α-Al2O3 layer is formed in a two-step process. Furthermore, an upper layer consisting of a Ti compound layer containing a TiCN layer is formed on the surface of the α-Al2O3 layer.

[0060] The method for forming the Ti compound layer in the lower layer is not particularly limited, but examples include the following methods. For example, a Ti compound layer consisting of a Ti nitride layer (hereinafter also referred to as the "TiN layer") in the lower layer can be formed by chemical vapor deposition using a raw material composition of TiCl4: 5.0-10.0 mol%, N2: 20-60 mol%, H2: the remainder, at a temperature of 850-950°C, a pressure of 350-450 hPa, and a gas flow rate of 40-80 L / min.

[0061] The Ti compound layer, consisting of a Ti carbide layer in the lower layer (hereinafter also referred to as the "TiC layer"), can be formed by chemical vapor deposition using a raw material composition of TiCl4: 1.5-3.5 mol%, CH4: 3.5-5.5 mol%, and H2: the remainder, at a temperature of 950-1050°C, a pressure of 70-80 hPa, and a gas flow rate of 30-70 L / min.

[0062] The Ti compound layer, consisting of a Ti carbonitride layer (hereinafter also referred to as the "TiCN layer") in the lower layer, can be formed by chemical vapor deposition using a raw material composition of TiCl4: 5.0-7.0 mol%, CH3CN: 0.5-1.5 mol%, H2: the remainder, at a temperature of 800-900°C, a pressure of 70-90 hPa, and a gas flow rate of 50-90 L / min.

[0063] The Ti compound layer, consisting of a Ti carbonitroxide layer (hereinafter also referred to as the "TiCNO layer") in the lower layer, can be formed by chemical vapor deposition using a raw material composition of TiCl4: 3.0-4.0 mol%, CO: 0.5-1.0 mol%, N2: 30-40 mol%, H2: the remainder, at a temperature of 950-1050°C, a pressure of 50-150 hPa, and a gas flow rate of 30-70 L / min.

[0064] The Ti compound layer, consisting of a Ti carbon oxide layer in the lower layer (hereinafter also referred to as the "TiCO layer"), can be formed by chemical vapor deposition using a raw material composition of TiCl4: 1.0-2.0 mol%, CO: 2.0-3.0 mol%, and H2: the remainder, at a temperature of 950-1050°C, a pressure of 50-150 hPa, and a gas flow rate of 30-70 L / min.

[0065] Furthermore, the intermediate layer consisting of an α-Al2O3 layer (hereinafter also simply referred to as the "Al2O3 layer") is formed, for example, by the following method.

[0066] First, the surface of the lower layer, the layer furthest from the substrate, is oxidized under the following conditions: the raw material composition is CO2: 0.1-1.0 mol%, H2: the remainder, the temperature is 950-1000°C, the pressure is 60-80 hPa, and the gas flow rate is 5-15 L / min (oxidation process). The preferred time for this oxidation treatment is 1-5 minutes.

[0067] Subsequently, the nuclei of the α-Al2O3 layer are formed by chemical vapor deposition using a raw material composition of AlCl3: 1.0-4.0 mol%, CO: 0.05-2.0 mol%, CO2: 1.0-3.0 mol%, HCl: 2.0-3.0 mol%, and 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 (nucleation process). The preferred duration for the nucleation process is 3-30 minutes.

[0068] Next, the first α-Al2O3 layer is formed by chemical vapor deposition using a raw material composition of AlCl3: 1.5-3.5 mol%, CO2: 0.5-2.5 mol%, HCl: 1.5-3.5 mol%, H2S: 0.10-0.40 mol%, and H2: the remainder, at a temperature of 980-1040°C, a pressure of 70-110 hPa, and a gas flow rate of 50-90 L / min (first film formation step).

[0069] The second α-Al2O3 layer is formed by chemical vapor deposition using a raw material composition of AlCl3: 1.5-3.5 mol%, CO2: 1.0-5.0 mol%, HCl: 1.5-3.5 mol%, and H2: the remainder, at a temperature of 850-940°C, a pressure of 70-110 hPa, and a gas flow rate of 50-90 L / min (second film formation step).

[0070] In order to set the average length RSm of the surface roughness curve elements in the intermediate layer to the above-mentioned specific range, for example, one can combine a first film deposition process using H2S as a raw material with a second film deposition process that does not use H2S as a raw material to deposit the intermediate layer, or control it by adjusting the temperature and the ratio of raw material composition in the second film deposition process. More specifically, combining the first and second film deposition processes tends to increase RSm. The mechanism for this is not limited to the following, but it is speculated that by combining the first and second film deposition processes, which have significantly different crystal planes that are more favorable for growth, to form the intermediate layer, some of the protrusions formed in the first film deposition process disappear during the second film deposition process, resulting in a larger RSm. Furthermore, lowering the temperature during the second film formation process tends to increase RSm. Additionally, increasing the proportion of CO2 in the raw material composition also tends to increase RSm.

[0071] Furthermore, while there are no particular limitations on the method for forming the upper layer, the following methods can be cited as examples. First, when forming an adhesion layer on the side in contact with the intermediate layer (α-Al2O3 layer), the first step in forming the upper layer is to form a Ti compound layer (adhesion layer) on the surface of the α-Al2O3 layer. Next, as the second step in forming the upper layer, a TiCN layer is formed on the surface of the adhesion layer. Furthermore, a Ti compound layer may be formed on the surface of the TiCN layer as the outermost layer of the upper layer. Alternatively, as the first step in forming the upper layer, a TiCN layer may be formed on the surface of the α-Al2O3 layer, and then as the second step in forming the upper layer, a Ti compound layer (outermost layer) may be formed.

[0072] As the first step in forming the upper layer, if, for example, a TiCNO layer is formed on the surface of the α-Al2O3 layer, it can be formed by a chemical vapor deposition method with a raw material composition of TiCl4: 7.5~9.5 mol%, CH4: 1.0~2.0 mol%, CO: 0.3~1.7 mol%, N2: 5.0~30.0 mol%, and 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.

[0073] As the first step in forming the upper layer, if, for example, a TiN layer is to be formed on the surface of the α-Al2O3 layer, it can be formed by a chemical vapor deposition method with a raw material composition of TiCl4: 6.0-10.0 mol%, N2: 10.0-30.0 mol%, H2: the remainder, at a temperature of 840-920°C, a pressure of 170-190 hPa, and a gas flow rate of 90-110 L / min.

[0074] When forming the TiCN layer as the first or second step in forming the upper layer, it can be formed by a chemical vapor deposition method with a raw material composition of TiCl4: 7.0-10.0 mol%, CH4: 0.1-2.0 mol%, CH3CN: 0.3-1.3 mol%, N2: 10.0-25.0 mol%, and 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.

[0075] Furthermore, when forming a TiN layer on the surface of the TiCN layer, it can be formed by chemical vapor deposition using a raw material composition of TiCl4: 5.0-10.0 mol%, N2: 20.0-60.0 mol%, H2: the remainder, at a temperature of 950-1050°C, a pressure of 300-400 hPa, and a gas flow rate of 50-90 L / min.

[0076] To set the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries in the cross-section of the upper TiCN layer to the above-mentioned specific range, for example, the proportion of N2 in the raw material composition in the first or second step of forming the TiCN layer as the upper layer can be controlled. More specifically, for example, increasing the proportion of N2 in the raw material composition in the first or second step of forming the TiCN layer as the upper layer tends to increase the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries in the cross-section of the TiCN layer.

[0077] In order to set the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries in region A of the upper TiCN layer to the above-mentioned specific range, for example, the proportion of N2 in the raw material composition in the first or second step of 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, increasing the proportion of N2 in the raw material composition in the first or second step of forming the TiCN layer as the upper layer tends to increase the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries in region A of the upper TiCN layer. Also, for example, increasing the average length RSm of the roughness curve elements on the surface of the intermediate layer tends to increase the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries in region A of the upper TiCN layer.

[0078] In order to set the RSA in the upper layer to the above-mentioned specific range, for example, the proportion of CH4 in the composition in the first or second step of forming the TiCN layer as the upper layer can be controlled, or the gas flow rate in the first or second step of forming the TiCN layer as the upper layer can be controlled. More specifically, for example, increasing the proportion of CH4 in the raw material composition in the first or second step of forming the TiCN layer as the upper layer tends to increase the RSA. Also, for example, increasing the gas flow rate in the first or second step of forming the TiCN layer as the upper layer tends to increase the RSA.

[0079] The thickness of each layer in the coating of the coated cutting tool of this embodiment can be measured by observing the cross-sectional structure of the coated cutting tool using an optical microscope, scanning electron microscope (SEM), or FE-SEM. The average thickness of each layer in the coated cutting tool of this embodiment can be determined by measuring the thickness of each layer at three or more locations near a point 50 μm from the cutting edge towards the center of the flank surface of the coated cutting tool, and calculating the arithmetic mean. The composition of each layer can be measured from the cross-sectional structure of the coated cutting tool of this embodiment using an energy-dispersive X-ray spectrometer (EDS) or a wavelength-dispersive X-ray spectrometer (WDS). [Examples]

[0080] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0081] As a base material, a cutting insert made of cemented carbide was prepared, having an insert shape of CNMG120412 (ISO standard) and a composition of 87.0%WC-8.6%Co-2.0%TiN-2.0%NbC-0.4%Cr3C2 (all by mass%). After round honing of the cutting edge of this base material with a SiC brush, the surface of the base material was cleaned.

[0082] [Inventions 1-29 and Comparative Products 1-14] After cleaning the surface of the substrate, a coating layer was formed by chemical vapor deposition. First, a lower layer was formed on the surface of the substrate. Specifically, the substrate was 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, the first layer, whose composition is shown in Table 7, was formed on the surface of the substrate to the average thickness shown in Table 7. Next, under the conditions of raw material composition, temperature, pressure, and gas flow rate shown in Table 1, the second layer, whose composition is shown in Table 7, was formed on the surface of the first layer to the average thickness shown in Table 7. Then, under the conditions of raw material composition, temperature, pressure, and gas flow rate shown in Table 1, the third layer, whose composition is shown in Table 7, was formed on the surface of the second layer to the average thickness shown in Table 7. This formed a lower layer consisting of three layers.

[0083] Subsequently, as an oxidation step, the surface of the lower layer was subjected to oxidation treatment under the conditions of composition, temperature, pressure, and gas flow rate shown in Table 2. The oxidation step was performed for 3 minutes. Next, as a nucleation step, α-type aluminum oxide (α-Al2O3) nuclei were 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 step was performed for 10 minutes. Furthermore, as a first film formation step, an intermediate layer with the composition shown in Table 8 was formed on the surface of the α-type aluminum oxide (α-Al2O3) nuclei under the conditions of raw material composition, temperature, and pressure shown in Table 3 and gas flow rate shown in Table 2. For inventions 1 to 29 and comparative products 1 to 11 and 14, the time for forming the intermediate layer in the first film formation step was until the average thickness of the intermediate layer after the first film formation step reached approximately 80% of the average thickness shown in Table 8. Next, as a second film formation process, an intermediate layer with the composition shown in Table 8 was formed on the surface of the intermediate layer formed in the first film formation process, under the conditions of raw material composition, temperature, and pressure shown in Table 4, and gas flow rate shown in Table 2, to the average thickness shown in Table 8. For inventions 1 to 29 and comparative products 1 to 11 and 14, the time for forming the intermediate layer in the second film formation process was until the average thickness of the intermediate layer after the second film formation process reached the average thickness shown in Table 8. Furthermore, for inventions 1 to 29 and comparative products 1 to 11 and 14, both the first and second film formation processes for the intermediate layer were performed to form the average thickness shown in Table 8. For comparative products 12 and 13, only the first film formation process was performed, and the time for forming the intermediate layer was the time required to form the average thickness shown in Table 8.

[0084] Next, the upper layer was formed on the surface of the intermediate layer. Specifically, for inventions 1 to 26 and comparative products 1 to 14, as the first step in forming the upper layer, the X layer, whose composition is shown in Table 9, was formed on the surface of the intermediate layer to the average thickness shown in Table 9, under the conditions of raw material composition, temperature, pressure, and gas flow rate shown in Table 5. Next, as the second film formation step in forming the upper layer, the Y layer (TiCN layer), whose composition is shown in Table 9, was formed on the surface of the X layer or the surface of the intermediate layer to the average thickness shown in Table 9, under the conditions of raw material composition, temperature, pressure, and gas flow rate shown in Table 6. For inventions 27 to 29, as the first step in forming the upper layer, the Y layer (TiCN layer), whose composition is shown in Table 9, was formed on the surface of the intermediate layer to the average thickness shown in Table 9. Furthermore, for inventions 1-6, 8, 10-24, and 26, and comparative products 1-3 and 5-14, the Z layer, whose composition is shown in Table 9, was formed on the surface of the Y layer to the average thickness shown in Table 9, under the raw material composition, temperature, pressure, and gas flow rate conditions shown in Table 1. In this way, coated cutting tools for inventions 1-29 and comparative products 1-14 were obtained.

[0085] The thickness of each layer in the sample was determined as follows: Using FE-SEM, the thickness was measured at three points 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, 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 EDS 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.

[0086] [Table 1]

[0087] [Table 2]

[0088] [Table 3]

[0089] [Table 4]

[0090] [Table 5]

[0091] [Table 6]

[0092] [Table 7]

[0093] [Table 8]

[0094] [Table 9]

[0095] [RSA] The RSA of the obtained samples was calculated as follows. In the obtained samples, the cross-section of the TiCN layer of the upper layer was exposed in a direction parallel to the substrate surface, at a position where 30% to 90% of the average thickness of the TiCN layer in the upper layer remained from the substrate side. The obtained cross-section was mirror-polished, and the mirror-polished surface was observed with an electrolytic emission scanning electron microscope (FE-SEM). The azimuth difference A was measured using an electron backscattering imaging device (EBSD) attached to the FE-SEM. The total area of ​​the entire cross-section of the measured TiCN layer of the upper layer was set to 100 area%, and the ratio of the total cross-sectional area occupied by the region where the azimuth difference A is between 0 degrees and less than 15 degrees (hereinafter also referred to as region A) was defined as RSA (unit: area%). Specifically, first, the cross-sectional area of ​​region A and the cross-sectional area of ​​the region where the azimuth difference A is between 0 degrees and 45 degrees were determined. The total cross-sectional area of ​​the region between 0 degrees and 45 degrees is 100 area%. RSA was defined as the ratio of the sum of the cross-sectional areas of region A, based on these orientation differences A, to the sum of the cross-sectional areas of regions where the orientation difference A is between 0 and 45 degrees. The measurement results are shown in Table 10 below. The EBSD measurements were performed as follows: The sample was set in the FE-SEM. The sample was irradiated with an electron beam at an incident angle of 70 degrees, with an acceleration voltage of 15 kV and an irradiation current of 1.0 nA. The orientation difference A and cross-sectional area of ​​each particle were measured in a measurement range of 120 μm × 120 μm with an EBSD setting of a step size (distance between measurement points) of 0.1 μm. The cross-sectional area of ​​the upper TiCN layer within the measurement range was defined as the sum of the pixels corresponding to that area. That is, the sum of the cross-sectional areas of each region based on orientation difference A was obtained by aggregating the pixels occupied by the cross-section of the region corresponding to the orientation difference A range and converting it to area. Similar EBSD measurements were performed in a total of three fields of view within the above measurement range, and the average value of each area obtained was calculated. The RSA was calculated from the obtained average values. The results are shown in Table 10.

[0096] [Grain boundary length] The total length of the Σ3 grain boundaries relative to 100% of the total length of all grain boundaries in the cross-section of the TiCN layer in the upper layer of the obtained sample was measured as follows. In the obtained sample, the cross-section of the TiCN layer in the upper layer was exposed in a direction parallel to the substrate surface, at a position where the average thickness of the TiCN layer in the upper layer remained between 30% and 90% from the substrate side. The obtained cross-section was mirror-polished using colloidal silica to obtain a mirror-polished surface for observation. Subsequently, the observation surface was observed with a FE-SEM equipped with EBSD. The scoop face was observed as the observation area. The EBSD measurement was performed as follows: The sample was set in the FE-SEM. The sample was irradiated with an electron beam at an incident angle of 70 degrees, with an accelerating voltage of 15 kV and an irradiation current of 1.0 nA. The crystal orientation of each particle in the TiCN layer in the upper layer within the measurement range was analyzed using an EBSD setting of 0.1 μm step size (distance between measurement points) in a measurement range of 120 μm × 120 μm. At this time, the boundary between measurement points where the difference in crystal orientation between adjacent measurement points was 5° or more was defined as the grain boundary. Data processing was performed using commercially available software. The CSL grain boundaries corresponding to an arbitrary Σ value were counted and confirmed by expressing them as a ratio to the total grain boundaries. From this, the total length of Σ3 grain boundaries was determined relative to 100% of the total length of all grain boundaries in the entire cross-section of the upper TiCN layer and in region A. Analysis of a total of three fields of view was performed within the measurement range on the observation surface described above, and the average value of each value was calculated. From the obtained average value, the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries in the entire cross-section of the upper TiCN layer and in region A (hereinafter also referred to as Σ3 / total grain boundaries (%)) was calculated. The results are shown in Table 10.

[0097] [Table 10]

[0098] [RSm] The average length RSm of the roughness curve elements on the surface of the intermediate layer of the obtained sample was measured as follows. The obtained samples were immersed in a mixture of hydrofluoric acid and nitric acid for about 20 minutes to remove the upper layer and expose the surface of the intermediate layer. The surface texture of the exposed intermediate layer was measured using a laser roughness analyzer (VK-X100, manufactured by Keyence Corporation) under the following conditions. The results are shown in Table 11 below. Standard: JIS B0601:2001 (ISO 4287:1997), Reference length during measurement: 50 μm, Number of lines used for measurement: 10 lines spaced 10 μm apart.

[0099] [Table 11]

[0100] Using the obtained inventions 1-29 and comparative products 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 fracture resistance. The results of each cutting test are shown in Table 10.

[0101] [Cutting Test 1] Work material: SCM440, Workpiece shape: round bar, Cutting speed: 250m / min, Cutting depth: 1.5mm, Feed rate: 0.25mm / rev, Coolant: None 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, and the machining time until tool life was measured.

[0102] [Cutting Test 2] Work material: SCM415, Workpiece shape: A round bar with four equally spaced grooves on its outer surface. Cutting speed: 220m / min, Cutting depth: 1.5mm, Feed rate: 0.35mm / rev, Coolant: Water-soluble coolant, Evaluation criteria: Tool life was defined as the point at which the sample was damaged, and the number of impacts until tool life was reached was measured.

[0103] For cutting test 1, the machining time until tool life was reached was evaluated as follows: 21 minutes or more was rated "A", 15 minutes or more but less than 21 minutes was rated "B", and less than 15 minutes was rated "C". Similarly, for cutting test 2, the cumulative number of impacts until tool life was reached was evaluated as follows: 12,000 or more was rated "A", 8,000 or more but less than 12,000 was rated "B", and less than 8,000 was rated "C". In this evaluation, "A" is the best, followed by "B", and "C" is the worst. The more A or B ratings a tool has, the better its cutting performance. The results of the evaluation are shown in Table 12.

[0104] [Table 12]

[0105] As shown in Table 12, the inventive product received an "A" or "B" rating in both Cutting Test 1 and Cutting Test 2. On the other hand, the comparative product received a "C" rating in both or either Cutting Test 1 and Cutting Test 2. Therefore, it can be seen that the wear resistance and fracture resistance of the inventive product are generally superior to those of the comparative product.

[0106] Based on these results, it was found that the invention exhibits excellent wear resistance and fracture resistance, resulting in a longer tool life. [Industrial applicability]

[0107] The coated cutting tool of the present invention has excellent wear resistance and fracture resistance, thereby extending tool life compared to conventional tools, and from this perspective, it has potential for industrial use. [Explanation of symbols]

[0108] 1...Base material, 2...Lower layer, 3...Intermediate layer, 4...Upper layer, 5...Coating layer, 6...Coated cutting tool.

Claims

1. A coated cutting tool comprising a base material and a coating layer formed on the surface of the base material, The coating layer includes a lower layer, an intermediate layer, and an upper layer in this order, from the substrate side toward the surface side of the coating layer. The lower layer comprises one or more Ti compound layers, each consisting of a Ti compound of Ti and 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 or more and 15.0 μm or less. The aforementioned intermediate layer is α-Al, which consists of α-type aluminum oxide. ２ O ３ Including layers, The average thickness of the aforementioned intermediate layer is 3.0 μm or more and 15.0 μm or less. The upper layer comprises one or more Ti compound layers, each consisting of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B. The upper layer includes at least one TiCN layer made of TiCN, The average thickness of the upper layer is 1.0 μm or more and 6.0 μm or less. In the cross-section of the TiCN layer in the upper layer in a direction parallel to the surface of the substrate, if the total area of ​​the entire cross-section is taken as 100 area%, then the ratio of the total cross-sectional area of ​​region A where the orientation difference, which is the angle between the normal to the cross-section of the TiCN layer in the upper layer and the normal to the (220) plane of the particles of the TiCN layer, is 0 degrees or more and less than 15 degrees is 30 area% or more and 70 area% or less. A coated cutting tool in which, in the region A, the ratio of the total length of Σ3 grain boundaries to 100% of the total length of all grain boundaries is 30% or more and less than 60%.

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

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

4. The average thickness of the entire coating layer is 10.0 μm or more and 30.0 μm or less. The coated cutting tool according to claim 1.

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