Patent attributes
The present invention relates to a cutting insert particularly for turning of stainless steel comprising a cemented carbide substrate and a post-treated coating witha substrate of cemented carbide having a composition of 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 with a Ti/(Ti+Ta+Nb) ratio of from about 0.05 to about 0.3 and balance tungsten carbide (WC) having a grain size of from about 1.5 to about 3.5 μm in the as-sintered state. Further, the substrate has a surface zone of from about 5 to about 30 μm characterized by an enrichment of binder phase and a depletion of cubic carbides,and a coating having a first, innermost layer system of one or several layers of TiCxNyOz with x+y+z≦1 with a total thickness of from about 0.7 to about 5.5 μm and a second multilayer system consisting of from about 5 to about 31 alternating layers of Al2O3 and TiCxNyOz (x+y+z≦1), preferably κ-Al2O3 and TiN, the Al2O3-layers having an individual layer thickness of less than about 0.5 μm and the TiCxNyOz-layers less than about 0.2 μm with a total thickness of the multilayer of from about 1.0 to about 5.0 μm. The multilayer is exposed along the edge line and into the rake and flank face. In an alternative embodiment the multilayer is replaced by an Al2O3-layer.
