A cutting insert of a substantially horizontal cylindrical segment shape and having top and bottom surfaces with a circular segment shape. The cutting insert has a convex side and a flat side, a top cutting edge which is formed where the convex side and the top surface meet, and a bottom cutting edge which is formed where the convex side and the bottom surface meet. The cutting insert includes a hole extending from the convex side towards the flat side. The hole is positioned at a center of a surface of the flat side.

A cutting tool includes a substrate of cemented carbide having hard constituents in a metallic binder. The hard constituents include WC. The WC content in the cemented carbide is 80-95 wt %. The cemented carbide has a Fe+Ni+Co+Cr content of 3-13 wt %, an atomic ratio of 0.05<Fe/(Fe+Ni+Co+Cr)<0.35, an atomic ratio of 0.05<Ni/(Fe+Ni+Co+Cr)<0.35, an atomic ratio of 0.05<Co/(Fe+Ni+Co+Cr)<0.35 and an atomic ratio of 0.05<Cr/(Fe+Ni+Co+Cr)<0.35. The crack resistance W measured on the rake face of the cutting tool is at least 25% higher than the W measured on a cross section of the bulk area of the cutting tool.

An object of the invention is to provide a coated cutting tool whose tool life can be extended by having excellent wear resistance and fracture resistance. The coated cutting tool includes: a substrate; and a coating layer formed on a surface of the substrate, in which the coating layer includes a lower layer, an intermediate layer, and an upper layer in this order from a substrate side to a surface side of the coating layer, the lower layer includes one or more Ti compound layers formed of a specific Ti compound, the intermediate layer contains TiCNO, TiCO, or TiAlCNO, the upper layer contains α-type Al.sub.2O.sub.3, an average thickness of the lower layer is 2.0 μm or more and 8.0 μm or less, an average thickness of the intermediate layer is 0.5 μm or more and 2.0 μm or less and is 10% or more and 20% or less of a thickness of the entire coating layer, an average thickness of the upper layer is 0.8 μm or more and 6.0 μm or less, and in the intermediate layer, a ratio of a length of CSL grain boundaries to a total length 100% of a total grain boundary is 20% or more and 60% or less.

A coated tool includes a base and a coating film on the base. The coating film includes an Al.sub.2O.sub.3 layer, and a surface layer on the Al.sub.2O.sub.3 layer. The surface layer has a first erosion rate of 0.1 μm/min or less. The first erosion rate is obtained from measurement by causing a liquid A, in which 3 mass % of amorphous Al.sub.2O.sub.3 particles having a mean particle diameter of 1.1-1.3 μm is dispersed in purified water, to collide with the surface layer. The surface layer has a second erosion rate of 2.0 μm/min or more. The second erosion rate is obtained from measurement by causing a liquid B, in which 3 mass % of spherical Al.sub.2O.sub.3 particles having a mean particle diameter of 2.8-3.2 μm is dispersed in purified water, to collide with the surface layer.

A coating includes a first base layer including a nitride of at least Al and Cr, a second base layer including a nitride of at least Al and Cr overlying the first base layer, and an outermost indicator layer overlying the second base layer. The first base layer has a positive residual compressive stress gradient. The second base layer has substantially constant residual compressive stresses. The outermost indicator layer includes a nitride of Si and Me, wherein Me is at least one of Ti, Zr, Hf, and Cr. The outermost indicator layer has residual compressive stresses that are less than the residual compressive stresses of the second base layer.

A coated cutting tool includes a substrate with a rake side, a clearance side and a cutting edge, and a coating including a first layer and a second layer. The second layer includes an inner layer and an outer layer, wherein the first layer is exposed through an opening in the inner layer and the opening extends over at least a portion of the width of the cutting edge. Thereby, a double layer is provided in critical areas, whereas a single layer is provided in other areas. Preferably, the double oxide layer includes aluminum oxide layers. A method for manufacturing the coated cutting tool is also provided.

A coated cutting tool for chip forming machining of metals includes a substrate having a surface coated with a chemical vapour deposition (CVD) coating. The coated cutting tool has a substrate coated with a coating including a layer of α-Al2O3, wherein the α-Al2O3 layer exhibits a dielectric loss of 10−6≦tan δ≦0.0025, as measured with AC at 10 kHz, 100 mV at room temperature of 20° C.

A surface-coated cutting tool with a hard coating layer is provided. The hard coating layer includes at least a complex nitride or carbonitride layer (2) expressed by a composition formula: (Ti.sub.1-x-yAl.sub.xMe.sub.y)(C.sub.zN.sub.1-z), Me being an element selected from Si, Zr, B, V, and Cr. The average content ratio X.sub.avg, the average content ratio Y.sub.avg, and the average content ratio Z.sub.avg satisfy 0.60≦X.sub.avg, 0.005≦Y.sub.avg≦0.10, 0≦Z.sub.avg≦0.005, and 0.605≦x.sub.avg+y.sub.avg≦0.95. There are crystal grains having a cubic structure in the crystal grains constituting the complex nitride or carbonitride layer (2). A predetermined periodic content ratio change of Ti, Al and Me exists in the crystal grains having the cubic structure.

A cutting tool made of a cemented carbide substrate of WC, a metallic binder phase and gamma phase is provided. The cemented carbide has a well distributed gamma phase and a reduced amount of abnormal WC grains. The cutting tool has a more predicted tool life and an increased resistance against plastic deformation.

The present disclosure provides a multilayer coated cutting material having increased wear resistance at high temperatures, a method for manufacturing the same, and a cutting tool insert for mechanical machining including the same. According to an embodiment of the present disclosure, the multilayer coated cutting material includes a cemented carbide, cermet, ceramic, a cubic crystal boron nitride-based material or a hard alloy body of high-speed steel, and a cutting layer positioned on the base material and configured in multiple layers.