US Patent 7097901 Coated cutting tool insert

The present invention relates to a coated cemented carbide cutting tool insert particularly useful for turning of cast irons but also low alloyed steels at mediate to high cutting speeds. The cutting tool insert is characterised by a cemented carbide body comprising WC, cubic carbonitrides, a W-alloyed Co binder phase, a surface zone of the cemented carbide body that is binder phase enriched and nearly free of cubic carbonitride phase, and a coating including an innermost layer of TiCxNyOz with equiaxed grains, a layer of TiCxNyOz with columnar grains and at least one layer of Al2O3.