Coating cutting tool

Abstract

To provide a coating cutting tool which has excellent chipping resistance, defect resistance and abrasion resistance, and a long tool life.SOLUTION: A coating cutting tool includes a base material, and a coating layer including a lower layer formed on the surface of the base material, an intermediate layer and an upper layer in this order. The lower layer and the upper layer include at least one selected from a group consisting of Ti, C, N, O and B. Average thickness of the lower layer and the intermediate layer is between 1.5 μm and 15.0 μm. The intermediate layer includes α type aluminum oxide. Average thickness of the upper layer is between 0.5 μm and 5.0 μm, average value X of spacing of cracks of the lower layer is between 0.5 μm and 10.0 μm. Average thickness Y of spacing of cracks of the intermediate layer is between 20.0 μm and 100.0 μm, average value Z of spacing of cracks of the upper layer is between 0.5 μm and 10.0 μm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a coated cutting tool.

Background Art

[0002] Conventionally, on the surface of a substrate made of a tungsten carbide-based cemented carbide, for example, a Ti compound layer such as a titanium carbide (hereinafter also referred to as TiC) layer, a titanium nitride (hereinafter also referred to as TiN) layer, a titanium carbonitride (hereinafter also referred to as TiCN) layer, a titanium oxycarbide (hereinafter also referred to as TiCO) layer, a titanium oxynitride (hereinafter also referred to as TiNO) layer, and a titanium carbon oxynitride (hereinafter also referred to as TiCNO) layer, and a coating layer composed of two or more kinds of a bilayer of an α-type aluminum oxide layer are vapor-deposited and formed by a chemical vapor deposition method, and it is well known that the coated cutting tool is used for metal cutting of metals such as steel and cast iron.

[0003] Normally, in such a coated cutting tool, since tensile stress remains in the formed coating layer, it is known that the fracture strength of the coated cutting tool decreases and it is likely to be damaged. After forming the coating layer, a technique of releasing the tensile residual stress by introducing cracks by shot peening or the like has been proposed. This technique is described in, for example, Patent Documents 1 and 2.

[0004] Patent Document 1 describes a coated cutting tool including a substrate and a coating layer formed on the surface of the substrate. Further, Patent Document 1 describes that the coating layer of the coated cutting tool has an upper layer and a lower layer, the average value X of the crack intervals of one or two layers of a compound composed of at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Si and at least one element selected from the group consisting of C, N, B, and O is 10 to 80 μm, the upper layer is formed on the surface of the lower layer, includes an aluminum oxide layer, the average value Z of the crack intervals of the aluminum oxide layer is 20 to 100 μm, and the relationship of 0 < Z - X < 90 is satisfied.

[0005] Patent Document 2 describes a surface-coated cutting tool in which a hard coating layer composed of a lower layer and an upper layer is formed on the surface of a substrate made of a tungsten carbide-based cemented carbide or a titanium carbonitride-based cermet. Patent Document 2 also describes that, among at least one Ti carbonitride layer constituting the lower layer, the layer having the thickest average layer thickness has a layer thickness of 1.5 μm or more, a crack initiation layer is formed in the Ti carbonitride layer, and a stress relaxation layer in which cracks exist with an average density of 0.2 cracks / μm or more and less than 2 cracks / μm is formed in the lower layer on the substrate side from the crack initiation layer when measured in a direction parallel to the substrate surface. Patent Document 2 also describes that in the upper layer composed of an α-type aluminum oxide layer, cracks are formed with an average density of less than 0.2 cracks / μm.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In recent years, in cutting operations, high speed, high feed rate, and deep cutting have become prominent, and the tool life has tended to decrease more than before. In order to improve the tool life, Patent Documents 1 and 2 propose releasing the tensile residual stress of the coating layer by introducing cracks by shot peening or the like after forming the coating layer.

[0008] Patent Document 1 describes a coated cutting tool including a coating layer having an upper layer and a lower layer. According to the invention described in Patent Document 1, the performance of the coated cutting tool is improved to a certain extent. However, in recent years, further improvement in chipping resistance has been demanded. Note that in Patent Document 1, the average value of the crack intervals of the Ti compound layer formed on the surface opposite to the substrate of the aluminum oxide layer in the coating layer of the coated cutting tool has not been studied. Therefore, it is not described that the average value of the crack intervals of the Ti compound layer formed on the surface opposite to the substrate of the aluminum oxide layer is 0.5 μm or more and 10.0 μm or less.

[0009] In the coating layer of the surface-coated cutting tool described in Patent Document 2, the average density of cracks in the layer composed of the α-type aluminum oxide layer formed on the outermost surface opposite to the substrate is less than 0.2 cracks / μm (when converted to the average value of crack intervals, it is more than 5 μm). When the coating layer of the surface-coated cutting tool described in Patent Document 2 has an aluminum oxide layer with an average crack interval of 20 μm or more exposed on the outermost surface opposite to the substrate, cracks are likely to occur on the surface of the coating layer during machining. Therefore, it can be said that there is room for improvement in chipping resistance and chipping resistance. Further, when an aluminum oxide layer with an average crack interval of more than 5 μm and less than 20 μm is exposed on the outermost surface opposite to the substrate, the strength of the aluminum oxide layer and the Ti carbonitride layer formed thereunder decreases. Therefore, it can be said that there is room for improvement in wear resistance and chipping resistance. Note that Patent Document 2 does not describe that the coating layer of the coated cutting tool further has a Ti compound layer on the surface opposite to the substrate of the aluminum oxide layer. Therefore, Patent Document 2 does not describe that the average value of the crack intervals of the Ti compound layer formed on the surface side opposite to the substrate of the aluminum oxide layer is 0.5 μm or more and 10.0 μm or less.

[0010] The present invention has been made to solve the above problems, and an object thereof is to provide a coated cutting tool having excellent chipping resistance, chipping resistance and wear resistance and a long tool life.

Means for Solving the Problems

[0011] To solve the problems, the present invention has the following configuration.

[0012] (Configuration 1) Configuration 1 is a coated cutting tool including a base material and a coating layer formed on the 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, the lower layer includes one or more layers of a Ti compound layer composed 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 1.5 μm or more and 15.0 μm or less, the intermediate layer includes α-aluminum oxide, the average thickness of the intermediate layer is 1.5 μm or more and 15.0 μm or less, the upper layer includes one or more layers of a Ti compound layer composed 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 upper layer is 0.5 μm or more and 5.0 μm or less, the average value X of the crack intervals of the lower layer is 0.5 μm or more and less than 10.0 μm, the average value Y of the crack intervals of the intermediate layer is 20.0 μm or more and 100.0 μm or less, the average value Z of the crack intervals of the upper layer is 0.5 μm or more and 10.0 μm or less, and it is a coated cutting tool.

[0013] (Configuration 2) Configuration 2 is the coated cutting tool of Configuration 1, wherein the average thickness of the coating layer is 8.0 μm or more and 30.0 μm or less.

[0014] (Configuration 3) Configuration 3 is the coated cutting tool of Configuration 1 or 2, wherein the upper layer includes at least a TiCN layer.

[0015] (Configuration 4) Configuration 4 is the coated cutting tool of Configuration 3, where the average thickness of the TiCN layer in the upper layer is 0.5 μm or more and 5.0 μm or less.

[0016] (Configuration 5) Configuration 5 is the coated cutting tool of any one of Configurations 1 to 4, where the difference Y - Z between the average value Y of the crack intervals and the average value Z of the crack intervals is 20.0 μm or more and 95.0 μm or less.

[0017] (Configuration 6) Configuration 6 is the coated cutting tool of any one of Configurations 1 to 5, where the difference Y - X between the average value Y of the crack intervals and the average value X of the crack intervals is 25.0 μm or more and 95.0 μm or less.

[0018] (Configuration 7) Configuration 7 is the coated cutting tool of any one of Configurations 1 to 6, where the base material is cemented carbide, cermet, ceramics, or cubic boron nitride sintered body.

Advantages of the Invention

[0019] According to the present invention, it is possible to provide a coated cutting tool having excellent chipping resistance, defect resistance, and wear resistance, and a long tool life.

Brief Description of the Drawings

[0020]

Figure 1

Embodiments for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present invention will be specifically described. Note that the following embodiments are forms for embodying the present invention and do not limit the present invention within its scope.

[0022] <Coated Cutting Tool> As shown in Fig. 1, the coated cutting tool of the present embodiment includes a substrate 1 and a coating layer 5 formed on the surface of the substrate. Specific examples of the type of coated cutting tool include a replaceable cutting insert for milling or turning, a drill, and an end mill.

[0023] <Substrate> Examples of the substrate of the coated cutting tool of the present embodiment include cemented carbide, cermet, ceramics, cubic boron nitride sintered body, diamond sintered body, and high-speed steel. The substrate of the coated cutting tool of the present embodiment is preferably cemented carbide, cermet, ceramics, or a cubic boron nitride sintered body. Among them, when the substrate is cemented carbide or cermet, it is more preferable because of its excellent wear resistance and chipping resistance.

[0024] Note that these substrates may have their surfaces modified. For example, in the case of cemented carbide, a decarburized layer may be formed on its surface, or in the case of cermet, a surface hardened layer may be formed. Even if the surface of the substrate is modified, the effects of the present embodiment are exhibited.

[0025] <Coating layer> As shown in Fig. 1, the coating layer 5 of the present embodiment includes a lower layer 2, an intermediate layer 3, and an upper layer 4 in this order from the substrate side. The coating layer 5 of the present embodiment can include layers other than the lower layer 2, the intermediate layer 3, and the upper layer 4. However, in order to obtain a coated cutting tool having excellent chipping resistance and a long tool life, the coating layer 5 of the present embodiment preferably consists of the lower layer 2, the intermediate layer 3, and the upper layer 4.

[0026] The average thickness of the coating layer of the coated cutting tool according to this embodiment is preferably 8.0 μm or more and 30.0 μm or less, more preferably 8.4 μm or more and 29.0 μm or less, and still more preferably 12.4 μm or more and 25.3 μm or less. By the average thickness of the coating layer being below the upper limit value, the adhesion between the base material and the coating layer can be improved. Therefore, the chipping resistance of the coated cutting tool according to this embodiment can be improved, and a coated cutting tool excellent in chipping resistance can be obtained. Further, by the average thickness of the coating layer being above the lower limit value, a coated cutting tool excellent in wear resistance can be obtained.

[0027] In this specification, the "lower layer on the base material" shall include both a structure in which the lower layer is disposed in contact with the surface of the base material and a structure in which another layer is disposed between the base material and the lower layer. The same applies to the "intermediate layer on the lower layer" and the "upper layer on the intermediate layer". Note that "above" means the side farther from the base material. For example, the "intermediate layer on the lower layer" means that the intermediate layer is on the side farther from the base material than the lower layer.

[0028] <lower layer> The lower layer of the coated cutting tool according to this embodiment is disposed on the base material. The lower layer of this embodiment is preferably formed on the surface of the base material. The lower layer of this embodiment includes one or more Ti compound layers made of a Ti compound composed of Ti and at least one element selected from the group consisting of C, N, B, and O.

[0029] The lower layer of the present embodiment can include one or more Ti compound layers made of a Ti compound. Specifically, the Ti compound layer included in the lower layer of the present embodiment is preferably a Ti compound layer composed of Ti and at least one element selected from the group consisting of C, N, B, and O. As the Ti compound layer included in the lower layer, it is preferable to include at least one layer selected from the group consisting of a TiN layer made of TiN, a TiC layer made of TiC, a TiCN layer made of TiCN, a TiCO layer made of TiCO, a TiCNO layer made of TiCNO, and a TiB2 layer made of TiB2. More preferably, it includes at least one layer selected from the group consisting of a TiN layer, a TiC layer, a TiCN layer, a TiCNO layer, and a TiCO layer. Even more preferably, it includes at least one layer selected from the group consisting of a TiN layer, a TiCN layer, a TiCNO layer, and a TiCO layer. Even more preferably, it includes at least one layer selected from the group consisting of a TiN layer, a TiCN layer, and a TiCNO layer. The lower layer of the present embodiment preferably consists of two or more Ti compound layers.

[0030] The lower layer of the present embodiment preferably has a layer made of TiN or TiC (also referred to as the "A layer" in this specification) on the surface in contact with the substrate, and more preferably has a layer made of TiN. The average thickness of the A layer is preferably 0.05 μm or more and 1 μm or less, and more preferably 0.1 μm or more and 0.5 μm or less. By providing the lower layer with a predetermined A layer, a coating layer with excellent adhesion can be obtained, peeling of the coating layer is suppressed, so it is excellent in chipping resistance, and the defect resistance is further improved.

[0031] At least one layer of the lower layer of the present embodiment is preferably a layer made of TiCN (also referred to as the "B layer" in this specification). The average thickness of the B layer is preferably 1.0 μm or more and 15.0 μm or less, more preferably 1.5 μm or more and 13.5 μm or less, and even more preferably 2.0 μm or more and 13.0 μm or less. By including a TiCN layer in the lower layer, a coating layer with even better wear resistance can be obtained. The B layer can be formed on the surface of the A layer.

[0032] The lower layer of the present embodiment preferably includes a layer made of TiCNO or TiCO (also referred to as the "C layer" in this specification) between the B layer and the intermediate layer, and more preferably includes a layer made of TiCNO. The C layer is the layer that is disposed farthest from the base material among the layers constituting the lower layer. The average thickness of the C layer is preferably 0.1 μm or more and 5.0 μm or less, and more preferably 0.2 μm or more and 2.0 μm or less. By providing the lower layer with a predetermined C layer, the adhesion between the lower layer and the intermediate layer is improved, and the chipping resistance is excellent, so the defect resistance is further improved. The C layer can be formed on the surface of the B layer.

[0033] The lower layer of the present embodiment preferably consists of three layers: a predetermined A layer, a predetermined TiCN layer (B layer), and a predetermined C layer. By having the lower layer consist of the predetermined three layers, a coating layer with excellent performance can be obtained, having excellent chipping resistance, defect resistance, and wear resistance, and a coated cutting tool with a long tool life can be obtained.

[0034] The average thickness of the entire lower layer of the present embodiment is 1.5 μm or more and 15.0 μm or less, preferably 1.8 μm or more and 14.7 μm or less, and more preferably 2.4 μm or more and 13.5 μm or less. When the average thickness of the lower layer is below the above upper limit value, the adhesion of the coating layer is improved, so the chipping resistance is improved and the defect resistance is excellent. When the average thickness of the lower layer is above the above lower limit value, the wear resistance is excellent.

[0035] <Intermediate layer> The intermediate layer of the coated cutting tool of the present embodiment is disposed on the lower layer. The intermediate layer of the present embodiment is preferably formed on the surface of the lower layer.

[0036] The intermediate layer of the present embodiment preferably contains α-aluminum oxide (α-Al2O3). The intermediate layer of the present embodiment can be an aluminum oxide layer (α-Al2O3 layer) made of α-aluminum oxide.

[0037] The average thickness of the intermediate layer in this embodiment is 1.5 μm or more and 15.0 μm or less, preferably 2.0 μm or more and 14.8 μm or less, and more preferably 2.5 μm or more and 13.5 μm or less. When the average thickness of the intermediate layer is not more than the above upper limit value, the adhesion of the coating layer is improved, so the chipping resistance is improved and the defect resistance is excellent. When the average thickness of the lower layer is not less than the above lower limit value, the wear resistance is excellent.

[0038] <Upper layer> The upper layer of the coated cutting tool of this embodiment is disposed on the intermediate layer. Preferably, the upper layer of this embodiment is formed on the surface of the intermediate layer. The upper layer of this embodiment includes one or more Ti compound layers composed of a Ti compound composed of Ti and at least one element selected from the group consisting of C, N, O, and B.

[0039] The upper layer of this embodiment can include one or more Ti compound layers composed of a Ti compound. Specifically, the Ti compound layer included in the upper layer of this embodiment is preferably a Ti compound layer composed of Ti and at least one element selected from the group consisting of C, N, B, and O. The Ti compound layer included in the upper layer preferably includes at least one layer selected from the group consisting of a TiN layer composed of TiN, a TiC layer composed of TiC, a TiCN layer composed of TiCN, a TiCO layer composed of TiCO, a TiCNO layer composed of TiCNO, and a TiB2 layer composed of TiB2. More preferably, it includes at least one layer selected from the group consisting of a TiN layer, a TiC layer, a TiCN layer, a TiCNO layer, and a TiCO layer. Even more preferably, it includes at least one layer selected from the group consisting of a TiN layer, a TiCN layer, a TiCNO layer, and a TiCO layer. Preferably, the upper layer of this embodiment is composed of two or more Ti compound layers.

[0040] The upper layer of this embodiment can include an L layer as the layer closest to the base material among the layers constituting the upper layer. The L layer can be a TiCNO layer, a TiCO layer, or a TiN layer. The average thickness of the L layer is preferably 0.05 μm or more and 2.0 μm or less, more preferably 0.1 μm or more and 1.0 μm or less, and still more preferably 0.2 μm or more and 0.5 μm or less. By providing the upper layer with a predetermined L layer, the adhesion between the intermediate layer and the upper layer is improved, and the chipping resistance is excellent, so the defect resistance is improved. Also, from the viewpoint of effectively and surely achieving the effect of setting the average thickness of the upper layer described later to a predetermined value or more, it is preferable.

[0041] The upper layer of this embodiment preferably includes at least a TiCN layer. At least one layer of the upper layer of this embodiment is preferably a layer made of TiCN (also simply referred to as "TiCN layer" in this specification). By including a TiCN layer in the upper layer, the effect of setting the average thickness of the upper layer described later to a predetermined value or more can be effectively and surely achieved, and a coating layer excellent in wear resistance and defect resistance can be obtained. When the upper layer has the above-described L layer, the TiCN layer can be formed on the surface of the L layer. Also, when the upper layer does not have the L layer, the TiCN layer can be formed on the surface of the above-described intermediate layer.

[0042] The average thickness of the TiCN layer in the upper layer is preferably 0.2 μm or more and 5.0 μm or less, more preferably 0.5 μm or more and 5.0 μm or less, and still more preferably 1.0 μm or more and 4.8 μm or less. When the average thickness of the TiCN layer in the upper layer is below the above upper limit value, the adhesion of the coating layer can be improved, so the chipping resistance of the coating layer is improved, and a coated cutting tool excellent in defect resistance can be obtained. When the average thickness of the TiCN layer in the upper layer is above the above lower limit value, a coating layer excellent in wear resistance can be obtained. Also, the effect of setting the average thickness of the upper layer described later to a predetermined value or more can be effectively and surely achieved, and a coating layer excellent in wear resistance and defect resistance can be obtained.

[0043] The upper layer of this embodiment can include a U layer as the layer farthest from the base material among the layers constituting the upper layer. The U layer is preferably a layer made of TiN (TiN layer). The average thickness of the U layer is preferably 0.05 μm or more and 2.0 μm or less, more preferably 0.1 μm or more and 1.8 μm or less, and still more preferably 0.1 μm or more and 0.5 μm or less. When the U layer is a TiN layer, it tends to be easier to identify the used corner. When the average thickness of the U layer of the upper layer is equal to or less than the above upper limit value, the adhesion of the coating layer can be improved, so the chipping resistance of the coating layer is improved, and a coated cutting tool with excellent defect resistance can be obtained. When the average thickness of the U layer of the upper layer is equal to or more than the above lower limit value, a coated cutting tool that can easily identify the used corner can be obtained. The U layer can be formed on the surface of the TiCN layer of the upper layer. In addition, the upper layer can be composed of two layers, an L layer and a U layer. In this case, since the upper layer does not have a TiCN layer, the U layer can be formed on the surface of the L layer. Also, the upper layer can be composed of only the U layer. In this case, since the upper layer does not have an L layer and a TiCN layer, the U layer can be formed on the surface of the intermediate layer.

[0044] The upper layer of this embodiment preferably consists of three layers, a predetermined L layer, a predetermined TiCN layer, and a predetermined U layer, or two layers, a predetermined TiCN layer and a predetermined U layer. When the upper layer consists of a plurality of predetermined layers, a coating layer with excellent performance can be obtained, and a coated cutting tool with excellent chipping resistance, defect resistance, and wear resistance and a long tool life can be obtained. In addition, the upper layer of this embodiment can consist of only a predetermined TiCN layer.

[0045] The average thickness of the entire upper layer of this embodiment is 0.5 μm or more and 5.0 μm or less, preferably 0.6 μm or more and 4.9 μm or less, more preferably 1.0 μm or more and 4.2 μm or less, and even more preferably 1.2 μm or more and 3.6 μm or less. When the average thickness of the upper layer is equal to or less than the above upper limit value, the adhesion of the coating layer is improved, so the chipping resistance is improved and the defect resistance is excellent. When the average thickness of the upper layer is equal to or more than the above lower limit value, the peeling of the coating layer, particularly the upper layer, due to the blasting treatment and the progress of cracks into the intermediate layer tend to be suppressed. Further, when the average thickness of the upper layer is equal to or more than the above lower limit value, the effect of setting the average value of the crack intervals in the upper layer described later to a predetermined value or less can be effectively and surely achieved. Furthermore, the average value of the crack intervals in the upper layer described later can be effectively and surely set to a predetermined value or more.

[0046] <Crack interval> Next, the crack intervals of the cracks in the coating layer of the coated cutting tool of this embodiment will be described. The lower layer, intermediate layer, and upper layer of the coating layer of the coated cutting tool of this embodiment have average values of predetermined crack intervals as described below. In this specification, the average value of the crack intervals in the lower layer is referred to as "average value X". Similarly, in this specification, the average values of the crack intervals in the intermediate layer and the upper layer are referred to as "average value Y" and "average value Z", respectively.

[0047] The average values X, Y, and Z of the crack intervals in the lower layer, intermediate layer, and upper layer of the coating layer can be measured as follows.

[0048] First, polish from the surface of the coating layer on the side opposite to the substrate until the thicknesses of the upper layer, the intermediate layer, and the lower layer become 60 to 95% of their respective average thicknesses (for example, until they become 70 to 80% of their respective average thicknesses) to obtain a cross-section parallel to the substrate surface. Next, observe the cross-section thus obtained with a scanning electron microscope (SEM) at a magnification of 2000 times, take a plurality of observation images, and obtain a plurality of cross-section SEM photos. Next, by combining the cross-section SEM photos, obtain an SEM photo including a cross-section in the range of 200 μm in length and 300 μm in width. Next, in the obtained SEM photo, draw 10 straight lines (straight lines extending across the entire horizontal direction of the SEM photo) with a length of 300 μm or more parallel to the horizontal direction of the SEM photo at intervals of 20 μm in the vertical direction of the SEM photo. For each of the 10 straight lines, identify the intersections between the straight line and the cracks, and measure the distances between adjacent intersections. By dividing the sum of all the distances between adjacent intersections of the 10 straight lines by the number of measured intersections, the average values X, Y, and Z of the crack intervals of the cracks in each of the upper layer, the intermediate layer, and the lower layer can be calculated.

[0049] In the coating layer of the coated cutting tool of the present embodiment, the average value X of the crack intervals in the lower layer is 0.5 μm or more and less than 10.0 μm, preferably 0.6 μm or more and 9.8 μm or less, more preferably 0.7 μm or more and 8.2 μm or less, and still more preferably 0.8 μm or more and 5.2 μm or less. When the average value X of the crack intervals in the lower layer is equal to or less than the above upper limit value, the tensile residual stress in the lower layer is relaxed, so the toughness is improved and the defect resistance is improved. When the average value X is equal to or more than the above lower limit value, the strength of the lower layer is improved, so it is excellent in wear resistance and defect resistance.

[0050] In the coating layer of the coated cutting tool of the present embodiment, the average value Y of the crack intervals in the intermediate layer is 20.0 μm or more and 100.0 μm or less, preferably 26.8 μm or more and 96.0 μm or less, more preferably 31.7 μm or more and 86.4 μm or less, and still more preferably 34.8 μm or more and 85.3 μm or less. When the average value Y of the crack intervals in the intermediate layer is equal to or less than the above upper limit value, the tensile residual stress in the intermediate layer is relaxed, so the toughness is improved and the chipping resistance is improved. When the average value Y is equal to or more than the above lower limit value, the strength of the intermediate layer is improved, so it is excellent in wear resistance and chipping resistance. Further, since the decrease in the strength of the upper layer and the lower layer is suppressed, it is excellent in wear resistance and chipping resistance.

[0051] In the coating layer of the coated cutting tool of the present embodiment, the average value Z of the crack intervals in the upper layer is 0.5 μm or more and 10.0 μm or less, preferably 0.6 μm or more and 9.2 μm or less, more preferably 0.7 μm or more and 8.6 μm or less, and still more preferably 0.9 μm or more and 5.4 μm or less. When the average value Z of the crack intervals in the upper layer is equal to or less than the above upper limit value, the tensile residual stress in the upper layer is relaxed, so the toughness is improved and the chipping resistance is improved. Further, when the average value Z is equal to or less than the above upper limit value, the generation of cracks during machining is suppressed, so even if the average value of the crack intervals in the lower layer is less than 10 μm, the decrease in chipping resistance hardly occurs, and the toughness of the coating layer is further improved, so it is excellent in chipping resistance. When the average value Z is equal to or more than the above lower limit value, the strength of the upper layer is improved, so it is excellent in wear resistance and chipping resistance.

[0052] In the coating layer of the coated cutting tool of the present embodiment, the difference Y - Z between the average value Y of the crack intervals in the intermediate layer and the average value Z of the crack intervals in the upper layer is preferably 20.0 μm or more and 95.0 μm or less, more preferably 23.9 μm or more and 94.1 μm or less, and even more preferably 28.5 μm or more and 84.7 μm or less. When the difference Y - Z between the average value Y of the crack intervals in the intermediate layer and the average value Z of the crack intervals in the upper layer is equal to or less than the above upper limit value, the difference in residual stress between the upper layer and the intermediate layer becomes small, the adhesion is improved, so the chipping resistance is improved, and the defect resistance is excellent. When the difference Y - Z is equal to or more than the above lower limit value, since the decrease in the strength of the upper layer due to the introduction of cracks tends to be reduced, the wear resistance and the defect resistance are excellent.

[0053] In the coating layer of the coated cutting tool of the present embodiment, the difference Y - X between the average value Y of the crack intervals in the intermediate layer and the average value X of the crack intervals in the lower layer is preferably 25.0 μm or more and 95.0 μm or less, more preferably 25.3 μm or more and 93.8 μm or less, and even more preferably 26.0 μm or more and 85.7 μm or less. When the difference Y - X between the average value Y of the crack intervals in the intermediate layer and the average value X of the crack intervals in the lower layer is equal to or less than the above upper limit value, the difference in residual stress between the intermediate layer and the lower layer becomes small, the adhesion is improved, so the chipping resistance is improved, and the defect resistance is excellent. When the difference Y - X is equal to or more than the above lower limit value, since the decrease in strength due to the introduction of cracks into the lower layer tends to be reduced, the wear resistance and the defect resistance are excellent.

[0054] <Method for forming the coating layer> A method for forming the coating layer (lower layer, intermediate layer, and upper layer) of the coated cutting tool of the present embodiment will be described.

[0055] The coating layer of the coated cutting tool of the present embodiment can be formed through the formation process of the lower layer (Process 1), the cooling process (Process 2), the formation process of the intermediate layer and the upper layer (Process 3), the first blasting process (Process 4), and the second blasting process (Process 5). By appropriately selecting the formation conditions during the formation of the coating layer, it can be controlled to have a predetermined crack interval. In particular, by appropriately selecting the conditions of Processes 2, 4, and 5, the average values X, Y, and Z of the crack intervals can be controlled within a predetermined range.

[0056] In the following description, the composition of the source gas for forming each layer is shown in units of "mol%".

[0057] <<Process 1: Formation Process of Lower Layer>> For forming the coating layer of the coated cutting tool of the present embodiment, first, a lower layer is formed on the surface of the base material. In this specification, the formation process of the lower layer may be referred to as "Process 1".

[0058] Examples of the Ti compound layer included in the lower layer of the coated cutting tool of the present embodiment include a TiN layer, a TiC layer, a TiCN layer, a TiCNO layer, and a TiCO layer. When the lower layer consists of three layers, namely layer A, the layer composed of TiCN (layer B), and layer C, three Ti compound layers can be formed on the surface of the base material in the order of layer A, the layer composed of TiCN (layer B), and layer C.

[0059] Layer A included in the lower layer is preferably a TiN layer or a TiC layer.

[0060] The TiN layer of layer A in the lower layer can be formed by chemical vapor deposition using TiCl4, N2, and H2 as source gases. The formation conditions of the TiN layer of layer A are preferably such that the composition of the source gas is TiCl4: 5 to 10 mol%, N2: 30.0 to 50.0 mol%, the balance being H2, the temperature is 800 to 1000 °C, and the pressure is 300 to 400 hPa.

[0061] The TiC layer of the A layer in the lower layer can be formed by chemical vapor deposition using TiCl4, CH4, and H2 as source gases. The formation conditions for the TiC layer of the A layer are preferably such that the composition of the source gases is TiCl4: 1.0 to 5.0 mol%, CH4: 3.0 to 7.0 mol%, the balance being H2, the temperature is 900 to 1100 °C, and the pressure is 65 to 85 hPa.

[0062] The TiCN layer (B layer) of the lower layer can be formed by chemical vapor deposition using TiCl4, CH3CN, and H2 as source gases. The formation conditions for the TiCN layer (B layer) are preferably such that the composition of the source gases is TiCl4: 4 to 8 mol%, CH3CN: 0.5 to 2.0 mol%, and the balance being H2, the temperature is 750 to 950 °C, and the pressure is 60 to 80 hPa.

[0063] The C layer contained in the lower layer is preferably a TiCNO layer or a TiCO layer.

[0064] The TiCNO layer of the C layer in the lower layer can be formed by chemical vapor deposition using TiCl4, CO, N2, and H2 as source gases. The formation conditions for the TiCNO layer of the C layer are preferably such that the composition of the source gases is TiCl4: 2.0 to 6.0 mol%, CO: 0.3 to 2.0 mol%, N2: 20.0 to 50.0 mol%, and the balance being H2, the temperature is 900 to 1100 °C, and the pressure is 90 to 110 hPa.

[0065] The TiCO layer of the C layer in the lower layer can be formed by chemical vapor deposition using TiCl4, CO, and H2 as source gases. The formation conditions for the TiCO layer of the C layer are preferably such that the composition of the source gases is TiCl4: 0.5 to 2.5 mol%, CO: 1.0 to 5.0 mol%, the balance being H2, the temperature is 900 to 1100 °C, and the pressure is 70 to 90 hPa.

[0066] <<Step 2: Cooling Step>> In the method for forming the coating layer of the coated cutting tool of the present embodiment, after forming the lower layer, a cooling step is performed. In this specification, the cooling step may be referred to as "Step 2".

[0067] In the cooling process, it is preferable to cool the substrate on which the lower layer is formed to a temperature of 180 to 220°C and hold it for 50 to 70 minutes. At this time, it is preferably held in an H2 gas atmosphere with a pressure of 180 to 220 hPa. By carrying out the cooling process, cracks can be introduced into the lower layer. Also, by appropriately selecting the cooling conditions and carrying out the cooling process, a region that serves as a crack initiation point can be formed in the vicinity of the interface between the lower layer and the substrate. Therefore, by the first blasting process described later, the average value X of the crack intervals in the lower layer can be reduced.

[0068] <<Step 3: Oxidation treatment, formation process of intermediate layer and upper layer>> In the method for forming the coating layer of the coated cutting tool of the present embodiment, after the cooling process, an oxidation treatment is carried out, and then an intermediate layer and an upper layer are formed. In this specification, the oxidation treatment, the formation process of the intermediate layer and the upper layer may be referred to as "Step 3".

[0069] The oxidation treatment can be carried out by introducing CO2 gas and H2 gas at a predetermined temperature. As the oxidation treatment conditions, the composition of the gas to be introduced can be CO2: 0.2 to 1.0 mol% and the balance being H2, and it can be carried out at a temperature of 900 to 1100°C and a pressure of 50 to 70 hPa. Also, the time of the oxidation treatment is preferably 1 to 10 minutes.

[0070] By carrying out the oxidation treatment, the surface of the lower layer is oxidized, so that a coating layer excellent in adhesion between the lower layer and the intermediate layer can be obtained. Since peeling of the coating layer is suppressed, chipping resistance is excellent and defect resistance is improved.

[0071] In the method for forming the coating layer of the coated cutting tool of the present embodiment, an intermediate layer is formed on the surface of the lower layer that has been subjected to the oxidation treatment. When forming the intermediate layer, it is preferable to first carry out nucleation of the intermediate layer and then form the intermediate layer.

[0072] Nucleation of the intermediate layer can be carried out by chemical vapor deposition using AlCl3, CO, CO2, HCl, and H2 as source gases. The nucleation conditions of the intermediate layer preferably have the composition of the source gases as AlCl3: 1.0 - 5.0 mol%, CO: 0.5 - 2.0 mol%, CO2: 0.8 - 3.0 mol%, HCl: 1.5 - 5.0 mol%, and the balance being H2, at a temperature of 900 - 1100 °C and a pressure of 60 - 80 hPa.

[0073] After the nucleation of the intermediate layer, an intermediate layer made of Al2O3 is formed. The Al2O3 layer of the intermediate layer is preferably an α-type Al2O3 layer. The α-type Al2O3 layer of the intermediate layer can be formed by chemical vapor deposition using AlCl3, CO2, HCl, H2S, and H2 as source gases. As the film formation conditions, the composition of the source gases is preferably AlCl3: 2.1 - 5.0 mol%, CO2: 2.5 - 4.0 mol%, HCl: 2.0 - 3.0 mol%, H2S: 0.1 - 0.45 mol%, and the balance being H2, at a temperature of 850 - 1050 °C and a pressure of 60 - 80 hPa.

[0074] In the method for forming the coating layer of the coated cutting tool of the present embodiment, an upper layer is formed after the formation of the intermediate layer.

[0075] Examples of the Ti compound layer included in the upper layer of the coated cutting tool of the present embodiment include a TiN layer, a TiCN layer, a TiCNO layer, and a TiCO layer. When the upper layer is composed of an L layer, a TiCN layer, and a U layer, three Ti compound layers can be formed on the surface of the intermediate layer in the order of the L layer, the TiCN layer, and the U layer. Note that the upper layer can be composed of at least one of the TiCN layer and the U layer.

[0076] Among the layers constituting the upper layer, the L layer, which is the layer closest to the base material, can be a TiCNO layer, a TiCO layer, or a TiN layer.

[0077] The TiCNO layer of the L layer in the upper layer can be formed by chemical vapor deposition using TiCl4, CO, N2, and H2 as source gases. The formation conditions for the TiCNO layer of the L layer are preferably such that the composition of the source gases is TiCl4: 2.0 to 7.0 mol%, CO: 0.4 to 1.5 mol%, N2: 20.0 to 50.0 mol%, and the balance is H2, the temperature is 900 to 1100 °C, and the pressure is 80 to 120 hPa.

[0078] The TiCO layer of the L layer in the upper layer can be formed by chemical vapor deposition using TiCl4, CO, and H2 as source gases. The formation conditions for the TiCO layer of the L layer are preferably such that the composition of the source gases is TiCl4: 0.8 to 2.5 mol%, CO: 1.5 to 3.5 mol%, and the balance is H2, the temperature is 900 to 1100 °C, and the pressure is 70 to 90 hPa.

[0079] The TiN layer of the L layer in the upper layer can be formed by chemical vapor deposition using TiCl4, N2, and H2 as source gases. The formation conditions for the TiN layer of the L layer are preferably such that the composition of the source gases is TiCl4: 4.0 to 15.0 mol%, N2: 20.0 to 60.0 mol%, and the balance is H2, the temperature is 900 to 1100 °C, and the pressure is 300 to 400 hPa.

[0080] Among the layers constituting the upper layer, the layer made of TiCN (TiCN layer) formed on or above the intermediate layer above the L layer can be formed by chemical vapor deposition using TiCl4, CH3CN, and H2 as source gases. The formation conditions for the TiCN layer are preferably such that the composition of the source gases is TiCl4: 3.0 to 10.0 mol%, CH3CN: 0.5 to 2.0 mol%, and the balance is H2, the temperature is 900 to 1100 °C, and the pressure is 60 to 80 hPa.

[0081] Among the layers constituting the upper layer, the U layer, which is the layer farthest from the substrate, is preferably a layer made of TiN (TiN layer). The TiN layer of the U layer can be formed under the same conditions as the formation conditions for the TiN layer of the above-described L layer.

[0082] In the above manner, a coating layer including a lower layer, an intermediate layer, and an upper layer can be formed.

[0083] <<Process 4: First Blasting Process>> In the method for forming the coating layer of the coated cutting tool according to the present embodiment, after forming the coating layer as described above, it is preferable to perform the first blasting process on the surface to be treated of the coating layer. In this specification, the first blasting process may be referred to as "Process 4".

[0084] The first blasting process can be carried out by projecting a predetermined projectile onto the surface to be treated of the coating layer under predetermined projection conditions. The first blasting process is preferably a dry blasting process. The dry blasting process refers to a process of accelerating the projectile by compressed air and projecting it onto the object to be treated.

[0085] As the projectile (media) that can be used in the first blasting process, projectiles made of rigid materials such as metals and ceramics can be used. Note that the material of the projectile is preferably a material with a lower hardness and a larger specific gravity than the material constituting the coating layer. The material of the projectile is preferably a material with a hardness lower than at least Al2O3. Specifically, it is preferable to use steel, ZrO2, etc. as the material of the projectile in the first blasting process. The shape of the projectile can be any shape. In order to generate predetermined cracks in the coating layer, the shape of the projectile is preferably spherical. The average particle size of the projectile in the first blasting process is preferably 100 to 150 μm.

[0086] The average particle size of the projectile in the first blasting process can be the particle size (average particle size: D50) of 50% of the integrated value of all particles. The same applies to other average particle sizes described in this specification. Note that the average particle size (D50) can be obtained by measuring the particle size distribution by the microtrack method (laser diffraction scattering method) and obtaining the D50 value from the results of the particle size distribution measurement. The same applies to the projectile in the second blasting process described later.

[0087] As the blasting conditions for the first blasting step, it is preferable that the projection pressure is 0.1 to 0.2 MPa, the projection angle is 70 to 90 degrees, and the projection time is 20 to 120 seconds. By using predetermined blasting conditions in the first blasting step, predetermined cracks can be generated in the coating layer.

[0088] Note that the projection angle in the first blasting step (and the second blasting step described later) means the angle when the angle is 90 degrees when projected perpendicularly to the surface of the surface to be treated. Also, when projecting a predetermined projection material onto the surface to be treated of the coating layer under predetermined projection conditions, in order to prevent the projection material from colliding with other than the surface to be treated, it is preferable to perform the operation in a state where the surface of the coating layer other than the surface to be treated is masked. The same applies to the second blasting step.

[0089] By performing the first blasting step in combination with the above-described cooling step, the average value of the crack intervals in the lower layer can be preferentially reduced compared to the intermediate layer and the upper layer. Further, since the material of the projection material has a lower hardness and a larger specific gravity than the material constituting the coating layer, the generation of cracks starting from the surface of the coating layer can be suppressed.

[0090] <<Step 5: Second Blasting Step>> In the method for forming the coating layer of the coated cutting tool of the present embodiment, after performing the first blasting step on the surface to be treated of the coating layer as described above, it is preferable to perform the second blasting step. In this specification, the second blasting step may be referred to as "Step 5".

[0091] The second blasting step can be performed by projecting a predetermined projection material onto the surface to be treated of the coating layer under predetermined projection conditions. The second blasting step is preferably a wet blasting treatment. The wet blasting treatment refers to a treatment step in which a mixed liquid of water and a projection material is accelerated by compressed air and projected onto an object to be treated.

[0092] As the projectile (media) that can be used in the second blasting process, projectiles made of rigid materials such as metals and ceramics can be used. The material of the projectile preferably has a specific gravity equal to or less than that of Al2O3 and a hardness equal to or greater than that of Al2O3. Specifically, as the material of the projectile in the second blasting process, it is preferable to use Al2O3, SiC, cBN, etc.

[0093] The shape of the projectile used in the second blasting process can be any shape. However, as will be described later, the projection angle in the second blasting process is preferably smaller than the projection angle in the first blasting process. The smaller the projection angle, the more preferentially the removal of the coating layer by the blasting process occurs. Therefore, in order to suppress the removal of the coating layer in the second blasting process, the shape of the projectile is preferably spherical rather than polygonal. The average particle size (D50) of the projectile in the second blasting process is preferably 30 to 50 μm.

[0094] As the blasting conditions in the second blasting process, the projection pressure is preferably 0.1 to 0.2 MPa, the projection angle is preferably 5 to 50 degrees, and the projection time is preferably 10 to 260 seconds. The projection angle in the second blasting process is preferably smaller than the projection angle in the first blasting process. By using predetermined blasting conditions in the second blasting process, predetermined cracks can be generated in the coating layer.

[0095] By performing the second blasting process, cracks can be preferentially introduced starting from the surface side opposite to the base material of the coating layer. Also, in the second blasting process, as the projection angle is made smaller, while suppressing the decrease in the average value of the crack intervals in the intermediate layer, the average value of the crack intervals in the upper layer can be made smaller. Also, by using a projectile made of a material having a hardness equal to or greater than that of at least Al2O3 and a specific gravity equal to or less than that of Al2O3 as the projectile, while suppressing the decrease in the average value of the crack intervals in the intermediate layer, the average value of the crack intervals in the upper layer can be made smaller.

[0096] As described above, by appropriately controlling the conditions of the cooling process (Process 2), the first blasting process (Process 4), and the second blasting process (Process 5), the average values X (lower layer), Y (intermediate layer), and Z (upper layer) of the crack intervals can be controlled within a predetermined range.

[0097] Specifically, the average value X of the crack intervals in the lower layer can be controlled by adjusting the projection time in the first blasting process or the average thickness of the entire lower layer. Specifically, by increasing the projection time in the first blasting process or decreasing the average thickness of the entire lower layer, the average value X of the crack intervals can be decreased.

[0098] Also, the average value Y of the crack intervals in the intermediate layer can be controlled by adjusting the projection angle in the second blasting process, the average thickness of the entire upper layer, and / or the average thickness thereof when a TiCN layer is formed as the upper layer. Specifically, by decreasing the projection angle in the second blasting process, increasing the average thickness of the entire upper layer, and / or increasing the average thickness of the TiCN layer in the upper layer, the average value Y of the crack intervals can be decreased.

[0099] Also, the average value Z of the crack intervals in the upper layer can be controlled by adjusting the projection time in the second blasting process. Specifically, by increasing the projection time in the second blasting process, the average value Z of the crack intervals can be decreased.

[0100] Also, the difference Y - X between the average value Y of the crack intervals in the intermediate layer and the average value X of the crack intervals in the lower layer can be controlled by adjusting the average value X of the crack intervals and the average value Y of the crack intervals. Specifically, by decreasing the average value X of the crack intervals and / or increasing the average value Y of the crack intervals, the difference Y - X of the crack intervals can be increased.

[0101] Further, the difference Y - Z between the average value Y of the crack intervals in the intermediate layer and the average value Z of the crack intervals in the upper layer can be controlled by adjusting the average value Z of the crack intervals and the average value Y of the crack intervals. Specifically, the difference Y - X of the crack intervals can be increased by decreasing the average value Z of the crack intervals and / or increasing the average value Y of the crack intervals.

Example

[0102] Hereinafter, embodiments of the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[0103] As described below, coated cutting tools of Invention Products 1 to 37 were manufactured as examples of this embodiment. Also, coated cutting tools of Comparative Products 1 to 20 were manufactured as comparative examples.

[0104] As a base material, a cemented carbide cutting insert having a CNMG120408-TM (manufactured by Tungaloy Corporation) shape and a composition of 89.2WC - 8.8Co - 2.0NbC (by mass) was prepared. After performing round honing on the cutting edge ridge line portion of this base material with an SiC brush, the surface of the base material was cleaned.

[0105] Next, the base materials of the invention products and comparative products were loaded into an external heat type chemical vapor deposition apparatus, and a coating layer was formed on the surface of the base material so as to have the compositions and average thicknesses of the coating layers (lower layer, intermediate layer, and upper layer) shown in Tables 1 to 4 (Steps 1 to 3). Thereafter, a predetermined blasting treatment was performed (Steps 4 and 5). Hereinafter, the formation conditions of each layer will be described.

[0106] <Step 1: Formation Step of Lower Layer> The lower layer having the compositions and average thicknesses shown in Tables 1 and 2 was formed on the surfaces of the base materials of the invention products and comparative products by chemical vapor deposition (Step 1). As shown in Tables 1 and 2, in all the invention products and comparative products, a lower layer composed of three layers, an A layer, a B layer, and a C layer, was formed. Table 5 shows the formation conditions of the layers for each composition in the lower layer.

[0107] <Step 2: Cooling Step> The cooling process (Process 2) was carried out on Invention Products 1 to 37 and Comparative Products 1 to 18 and 20 with the lower layer formed. Note that the cooling process was not carried out on Comparative Product 19.

[0108] In the cooling process, after the lower layer of the invention products and comparative products other than Comparative Product 19 was formed, the chamber was evacuated until it reached 30 hPa. Next, the temperature inside the chamber was lowered to 200 °C and held for 60 minutes in an H2 gas atmosphere of 200 hPa. After the cooling process of the invention products and comparative products other than Comparative Product 19 was completed, the next Process 3 was carried out.

[0109] <Process 3: Oxidation treatment, intermediate layer and upper layer formation process> The oxidation treatment, intermediate layer and upper layer formation process (Process 3) was carried out on the invention products and comparative products on which the cooling process was carried out. In the case of Comparative Product 19, after the lower layer was formed, Process 3 was carried out.

[0110] <<Oxidation treatment>> Oxidation treatment was carried out on all the invention products and comparative products. The oxidation treatment was carried out by introducing an oxidation treatment gas of CO2 gas: 0.5 mol% and H2 gas: 99.5 mol% and holding for 3 minutes under the conditions of a temperature of 1000 °C and a pressure of 60 hPa.

[0111] <<Intermediate layer formation>> The intermediate layer with the composition and average thickness shown in Tables 1 and 2 was formed on the surface of the lower layer of the invention products and comparative products by chemical vapor deposition. As shown in Tables 1 and 2, an intermediate layer made of α-type Al2O3 was formed in all the invention products and comparative products. Table 6 shows the nucleation of the intermediate layer and the film formation conditions of the α-type Al2O3 layer.

[0112] <<Upper layer formation>> The upper layers with the compositions and average thicknesses shown in Tables 3 and 4 were formed on the surface of the intermediate layer by chemical vapor deposition. As shown in Tables 3 and 4, in Invention Articles 22, 23, 26, 27, and 30 to 35 and Comparative Article 18, an upper layer composed of three layers, namely the L layer, the TiCN layer, and the U layer, was formed. Also, in Invention Articles 18 and 20, an upper layer composed only of the TiCN layer was formed. Further, in Invention Article 24, an upper layer composed only of the U layer was formed. In other Invention Articles and Comparative Articles, an upper layer composed of two layers, namely the TiCN layer and the U layer, was formed. The upper layer was formed on the intermediate layer in the order of the L layer, the TiCN layer, and the U layer. Table 7 shows the formation conditions of the L layer, the TiCN layer, and the U layer of the upper layer.

[0113] <Process 4: First Blasting Process> For the Invention Articles and Comparative Articles having the coating layers (lower layer, intermediate layer, and upper layer) formed as described above, the blasting treatment of the First Blasting Process (Process 4) was performed. However, for Comparative Article 19, the blasting treatment of the First Blasting Process was not performed.

[0114] The blasting treatment of the First Blasting Process was carried out by projecting a predetermined projectile onto the surface to be treated of the coating layer under predetermined projection conditions. The blasting treatment of the First Blasting Process was carried out as a dry blasting treatment.

[0115] As the projectile (media) of the First Blasting Process, spherical projectiles made of steel with an average particle size of 120 μm were used. As the blasting conditions of the First Blasting Process, the projection pressure was 0.15 MPa and the projection angle was 90 degrees. The projection angle means the angle when the angle is 90 degrees when projected perpendicularly to the surface of the surface to be treated. Tables 8 and 9 show the projection times of the First Blasting Process for each Invention Article and Comparative Article (excluding Comparative Article 19).

[0116] When projecting a predetermined projectile onto the surface to be treated of the coating layer under predetermined projection conditions, in order to prevent the projectile from colliding with surfaces other than the surface to be treated, the surfaces of the coating layer other than the surface to be treated were masked.

[0117] <Process 5: Second Blasting Process> After the first blasting step, the blasting process of the second blasting step (step 5) was performed on the invention products and comparative products having the coating layers (lower layer, intermediate layer, and upper layer) formed as described above. However, the blasting process of the second blasting step was not performed on the comparative product 20.

[0118] The blasting process of the second blasting step was carried out by projecting a predetermined projection material onto the surface to be treated of the coating layer under predetermined projection conditions. The blasting process of the second blasting step was carried out as a wet blasting process.

[0119] As the projection material (media) of the second blasting step, spherical projection materials made of Al2O3 with an average particle size of 40 μm were used. As the blasting conditions of the second blasting step, the projection pressure was set to 0.15 MPa. Tables 8 and 9 show the projection angles and projection times of the second blasting step for each invention product and comparative product (excluding comparative product 20). The projection angle means the angle when the angle is 90 degrees when projected perpendicularly to the surface of the surface to be treated.

[0120] When projecting a predetermined projection material onto the surface to be treated of the coating layer under predetermined projection conditions, in order to prevent the projection material from colliding with surfaces other than the surface to be treated, the surfaces of the coating layer other than the surface to be treated were masked.

[0121] Through the above steps, the coated cutting tools of the invention products and comparative products were manufactured.

[0122] <Measurement of the average thickness of each layer> For each invention product and comparative product, the average thickness of each layer of the coating layer was measured at three locations by SEM on a cross-section near the position 50 μm from the cutting edge of the coated cutting tool toward the center of the rake face, and the average value of the three locations was taken as the average thickness. Tables 1 to 4 show the average thickness of each layer of the coating layer for each invention product and comparative product.

[0123] <Measurement of the composition of each layer> The composition of each layer of the coating layer of each inventive product and comparative product was measured by using an energy-dispersive X-ray spectrometer (EDS) on the cross-section of a predetermined layer of the coated cutting tool. The crystal system of the intermediate layer was identified by X-ray diffraction measurement using a 2θ / θ focusing method optical system. Tables 1 to 4 show the composition of each layer of the coating layer (types of elements contained in each layer) of each inventive product and comparative product.

[0124] <Measurement of Crack Spacing>

[0125] The average values X, Y, and Z of the crack spacing of the coating layers (lower layer, intermediate layer, and upper layer) of the coated cutting tools of the inventive products and comparative products were measured. The measurement and calculation methods for the average values X, Y, and Z of the crack spacing of the coating layer are as follows.

[0126] The measurement of the average value Z of the crack spacing of the upper layer of the coating layer was performed as follows. First, until the thickness of the upper layer became 70% of the average thickness of the upper layer, polishing was carried out from the surface side of the coating layer on the side opposite to the base material to obtain a cross-section of the upper layer parallel to the base material surface. Next, the obtained cross-section of the upper layer was observed with a scanning electron microscope (SEM) at a magnification of 2000 times, and a plurality of observation images were taken to obtain a plurality of cross-section SEM photos. By combining the plurality of cross-section SEM photos, an SEM photo including a cross-section in the range of 200 μm in length and 300 μm in width was obtained. In the obtained SEM photo, 10 straight lines (straight lines extending across the entire horizontal direction of the SEM photo) with a length of 300 μm or more parallel to the horizontal direction of the SEM photo were drawn at intervals of 20 μm in the vertical direction of the SEM photo. At each of the 10 straight lines, the intersection points between the straight line and the cracks were identified, and the distances between adjacent intersection points were measured. The average value Z of the crack spacing in the upper layer was calculated by dividing the total value of all the distances between adjacent intersection points of the 10 straight lines by the number of all the intersection points measured.

[0127] The average value Y of the crack intervals in the intermediate layer of the coating layer was measured as follows. First, similar to the measurement of the crack intervals in the upper layer, until the thickness of the intermediate layer reached 80% of the average thickness of the intermediate layer, polishing was performed from the surface side of the coating layer on the side opposite to the base material to obtain a cross-section of the intermediate layer parallel to the surface of the base material. Then, similar to the measurement of the crack intervals in the upper layer, from the SEM photograph of the cross-section of the intermediate layer, the average value Y of the crack intervals of the cracks in the intermediate layer was measured and calculated.

[0128] The average value X of the crack intervals in the lower layer of the coating layer was measured as follows. First, similar to the measurement of the crack intervals in the upper layer, until the thickness of the lower layer reached 70% of the average thickness of the lower layer, polishing was performed from the surface side of the coating layer on the side opposite to the base material to obtain a cross-section of the lower layer parallel to the surface of the base material. Then, similar to the measurement of the crack intervals in the upper layer, from the SEM photograph of the cross-section of the lower layer, the average value X of the crack intervals of the cracks in the lower layer was measured and calculated.

[0129] Tables 10 and 11 show the average values X, Y, and Z of the crack intervals in the lower layer, intermediate layer, and upper layer of the coated cutting tools of the invention product and the comparative product measured as described above. Also, Tables 10 and 11 show the difference Y-Z between the average value Y of the crack intervals in the intermediate layer and the average value Z of the crack intervals in the upper layer, and the difference Y-X between the average value Y of the crack intervals in the intermediate layer and the average value X of the crack intervals in the lower layer, calculated using the average values X, Y, and Z of the crack intervals.

[0130] <Cutting Test> Cutting tests were conducted on the coated cutting tools of the invention product and the comparative product, and the chipping resistance (tool life) was evaluated. Using the coated cutting tools of the invention product and the comparative product as samples, two types of cutting tests, namely Cutting Test 1 and Cutting Test 2 described below, were conducted.

[0131] The cutting test conditions for Cutting Test 1 are as follows. [Cutting Test Conditions for Cutting Test 1] Workpiece material: S45C, Workpiece shape: A round bar with four equally spaced grooves on the outer peripheral surface, Cutting speed: 90 m / min, Cutting depth: 1.0 mm, Feed: 0.2 mm / rev, Coolant: Yes, Insert shape: CNMG120408-TM (manufactured by Tungaloy Corporation), Composition of base material: 89.2WC - 8.8Co - 2.0NbC (by mass%), Evaluation item: The tool life was defined as the time when the sample reached breakage, and the number of impacts until tool life was measured.

[0132] Tables 12 and 13 show the number of impacts and evaluation up to the tool life of Cutting Test 1. Note that for the evaluation of Cutting Test 1, when the tool life (number of impacts) was 12,000 or more, the evaluation was A; when it was 8,000 or more and less than 12,000, the evaluation was B; and when it was less than 8,000, the evaluation was C.

[0133] The cutting test conditions for Cutting Test 2 are as follows. [Cutting Test Conditions for Cutting Test 2] Workpiece material: SCM440, Workpiece shape: round bar, Cutting speed: 250 m / min, Cutting depth: 2.0 mm, Feed: 0.25 mm / rev, Coolant: Yes, Insert shape: CNMG120408-TM (manufactured by Tungaloy Corporation), Composition of base material: 89.2WC - 8.8Co - 2.0NbC (by mass%), Evaluation item: The tool life was defined as the time when the sample reached breakage or the maximum flank wear width reached 0.3 mm, and the machining time until tool life was measured.

[0134] Tables 12 and 13 show the machining time and evaluation up to the tool life of Cutting Test 2. Note that for the evaluation of Cutting Test 2, when the tool life (machining time) was 25 minutes or more, the evaluation was A; when it was 20 minutes or more and less than 25 minutes, the evaluation was B; and when it was less than 20 minutes, the evaluation was C.

[0135] <<Evaluation of Cutting Test>> All the invented products were evaluated as B or above in both Cutting Test 1 and Cutting Test 2. Therefore, it can be said that the invented products are coated cutting tools with excellent chipping resistance and defect resistance, and a long tool life.

[0136] On the other hand, for the comparative products, the evaluation in at least one of Cutting Test 1 and Cutting Test 2 was C. Therefore, it became clear that, compared with the invented products, the comparative products are coated cutting tools with insufficient chipping resistance and defect resistance, or insufficient wear resistance, and a short tool life. Also, for Comparative Products 17 and 18, chipping damage occurred in Cutting Test 2, and defects originated from this chipping damage occurred.

[0137]

Table 1

[0138]

Table 2

[0139]

Table 3

[0140]

Table 4

[0141]

Table 5

[0142]

Table 6

[0143]

Table 7

[0144]

Table 8

[0145]

Table 9

[0146]

Table 10

[0147]

Table 11

[0148]

Table 12

[0149]

Table 13

Explanation of Symbols

[0150] 1 Substrate 2 Lower Layer 3 Intermediate Layer 4 Upper Layer 5 Coating Layer 6 Coated Cutting Tool

Claims

1. A coated cutting tool including 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 this order from the substrate side, the lower layer includes one or more Ti compound layers composed 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 1.5 μm or more and 15.0 μm or less, the intermediate layer includes α-type aluminum oxide, the average thickness of the intermediate layer is 1.5 μm or more and 15.0 μm or less, the upper layer includes one or more Ti compound layers composed 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 upper layer is 0.5 μm or more and 5.0 μm or less, the average value X of the crack intervals of the lower layer is 0.5 μm or more and less than 10.0 μm, the average value Y of the crack intervals of the intermediate layer is 20.0 μm or more and 100.0 μm or less, the average value Z of the crack intervals of the upper layer is 0.5 μm or more and 10.0 μm or less. A coated cutting tool.

2. The coated cutting tool according to claim 1, wherein the average thickness of the coating layer is 8.0 μm or more and 30.0 μm or less.

3. The coated cutting tool according to claim 1 or 2, wherein the upper layer includes at least a TiCN layer.

4. The coated cutting tool according to claim 3, wherein the average thickness of the TiCN layer of the upper layer is 0.5 μm or more and 5.0 μm or less.

5. The coated cutting tool according to claim 1 or 2, wherein the difference Y - Z between the average value Y of the crack intervals and the average value Z of the crack intervals is 20.0 μm or more and 95.0 μm or less.

6. The coated cutting tool according to claim 1 or 2, wherein the difference Y - X between the average value Y of the crack intervals and the average value X of the crack intervals is 25.0 μm or more and 95.0 μm or less.

7. The coated cutting tool according to claim 1 or 2, wherein the substrate is a cemented carbide, cermet, ceramics, or cubic boron nitride sintered body.

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