CVD-COATED CEMENTED CARBIDE INSERT FOR TOUGHNESS DEMANDING SHORT HOLE DRILLING OPERATIONS

摘要

A CVD coated cutting tool insert useful for toughness demanding short hole drilling in steel is provided. In a cemented carbide insert comprising a substrate and a coating and having excellent toughness properties particularly useful for toughness demanding short hole drilling in general steels, the cemented carbide insert is characterized in that the substrate comprises WC having an average grain size of 0.5 to 1.5 mum, 8 to 11 wt.% of Co, preferably 9.5 to 10.5 wt.% of Co, and 0.2 to 0.5 wt.% of Cr, wherein the cobalt binder phase has a CW ratio of 0.80 to 0.90, and the coating comprises: - a first innermost layer of TiCxNyOz, where x+y+z=1, preferably yx and z0.8 and z=0, coaxial grains of the first innermost layer have a size of less than 0.5 mum, and a total thickness of the first innermost layer is less than 1.5 mum, preferably more than 0.1 mum; - a layer of TiCxNyOz, where x+y+z=1, preferably z=0, x0.3 and y0.3, most preferably x0.5, and the TiCxNyOz layer has columnar grains with a thickness of 1 to 8 mum, preferably 2 to 7 mum, most preferably less than 6 mum, and an average diameter of less than 5 mum, preferably 0.1 to 2 mum; a layer of Al2O3 consisting essentially of the K-phase having smooth and fine grains with a grain size of about 0.5 to 2 mum and a thickness of 0.5 to 5 mum, preferably 0.5 to 2 mum; and a further layer of TICxNyOz with a thickness of less than 1 mum, preferably 0.1 to 0.5 mum, where x+y+z=1, preferably yx and z0.3, wherein at the rake face, the outermost TiCxNyOz layer and the Al2O3-layer are fully or partially removed on 80% of the rake face area between the edge line and 100 mum inward in the direction perpendicular to the edge line.