US Patent RE39894 Cemented carbide insert

The present invention relates to a coated cemented carbide insert for turning of steel, like low alloyed steels, carbon steels and tough hardened steels at high cutting speeds. The cemented carbide consists of WC, 2-10 wt. % Co and 4-12 wt. % of cubic carbides of metals from groups 4, 5 or 6 of the periodic table, preferably Ti, Ta and Nb. The Co-binder phase is highly alloyed with W with a CW-ratio of 0.75-0.90. The insert has a binder phase enriched and essentially cubic carbide free surface zone A of a thickness of <20 μm and along a line C essentially bisecting the edge, in the direction from the edge to the centre of the insert, a binder phase content increases essentially monotonously until it reaches the bulk composition. The binder phase content at the edge is 0.65-0.75 times the binder phase content by volume of the bulk and the depth of the binder phase depletion is 100-300 μm, preferably 150-250 μm. The insert is coated with 3-12 μm columnar TiCN-layer followed by a 2-12 μm thick Al2O3-layer.