FINE GRAINED SINTERED CEMENTED CARBIDES CONTAINING A GRADIENT ZONE

A cemented carbide insert having high toughness and high deformation resistance at application temperatures is provided. In a coated cutting tool insert consisting a cemented carbide substrate and a coating, wherein the cemented carbide substrate comprises WC, binder phase and cubic carbide phase and has a binder phase enriched surface zone basically free of cubic carbide phase, the coated cutting tool insert is characterized in that the substrate comprises 3 to 20 wt.% of cobalt, 0.1 to 20 wt.% of vanadium and the balance 70 to 95 wt.% of WC, wherein a total content of vanadium and other cubic carbide formers from elements of the groups 4a and 5a of 1 to 20 wt.%, the WC has an average grain size of less than 1.5 mum, and free graphite does not exist in the substrate structure.