Patent ID: 7396371

Claim:
A coated cemented carbide cutting tool insert comprising a substrate of cemented carbide having a composition comprising from about 5.0 to less than about 8.0 wt % Co, from about 3.0 to about 8.0 wt % cubic carbides of the metals Ti, Ta and Nb and possibly other carbides of the elements from group IVb, Vb or VIb of the periodic table, the addition of cubic carbide forming elements being such that the Ti/(Ti+Ta+Nb) ratio is from about 0.05 to about 0.3, from about 0.01 to about 0.2 wt % N and balance tungsten carbide (WC) having a grain size of from about 1.5 to about 3.5 μm in the as-sintered state and having a γ-phase depleted and binder phase enriched surface zone which has a depth of from about 5 to about 30 μm, and a coating having a first, innermost layer system of at least two layers of TiC x N y O z with x+y+z≦1; and the said coating having a second multilayer system comprising from about 5 to about 31 alternating layers of Al 2 O 3 and TiC x N y O z (x+y+z≦1), the Al 2 O 3 -layers having an individual layer thickness of less than about 0.6 μm and the TiC x N y O z -layers from about 0.01 to about 0.2 μm with a total thickness of the multilayer from about 1.0 to about 5.0 μm, said multilayer being exposed along the edge line and into the rake and flank face, such that the exposure on the rake face a is greater than about 0.03 and less than about 0.9 mm, the exposure on the flank face b is greater than about 0.02 and less than about 0.2 mm and a>b.