Patent ID: 7276301

Claim:
A surface-coated cermet cutting tool comprising: a hard-coating layer having a resistance to chipping, wherein the surface-coated cermet cutting tool is formed by coating, on a surface of a tool substrate made of tungsten carbide based cemented carbide or titanium carbonitride based cermet, the hard-coating layer comprising: (a) a lower layer comprising a titanium compound layer with at least one or two of a titanium carbide layer, a titanium nitride layer, a titanium carbonitride layer, a titanium carboxide layer and a titanium oxycarbonitride layer, the titanium compound layer having a total average layer thickness of 3 to 20 μm, and (b) an upper layer comprising a heat-transformed α-type Al—Zr oxide layer formed by carrying out a heat-transforming treatment in a state that a titanium oxide layer satisfying the composition formula: TiO y , (where value Y is 1.2 to 1.9 in an atomic ratio to Ti when measured by Auger Electron Spectroscopy) and having an average layer thickness of 0.05 to 1.5 μm is chemically deposited on a surface of an Al—Zr oxide layer having a κ-type or θ-type crystal structure and satisfying the composition formula: (Al 1−X Zr X ) 2 O 3 , where value X is 0.003 to 0.05 in an atomic ratio when measured by an electron probe micro-analyzer (EPMA), to transform the crystal structure of the Al—Zr oxide layer having the κ-type or θ-type crystal structure into an α-type crystal structure, wherein the heat-transformed α-type Al—Zr oxide layer is characterized by having a highest peak at an inclination angle interval in a range of 0 to 10 degrees in an inclination angle frequency-distribution graph, and a sum of frequencies in a range of 0 to 10 degrees occupies 45% or more of the total sum of frequencies in the inclination angle frequency-distribution graph, and the inclination angle frequency-distribution graph is obtained from results of radiating electron beam onto crystal grains having a hexagonal crystal lattice in a measuring range of surfaces to be polished using a field-emission-type scanning electron microscope, measuring an inclination angle of a normal line of the plane (0001) as a crystal plane in which each of the crystal grains is formed with respect to each of the polished surfaces, sorting the measured inclination angles in a range of 0 to 45 degrees among all the measured inclination angles into several intervals at a pitch of 0.25 degrees, and summing up the frequencies in each of the intervals, and wherein the heat-transformed α-type Al—Zr oxide layer has an average layer thickness of 1 to 15 μm.