Patent ID: 7648736

Claim:
A method of making a cutting tool insert comprising a cemented carbide substrate with a binder phase enriched surface zone and a coating, the method comprising forming a powder mixture containing WC, 4-7 wt % Co, and 6-9 wt % cubic carbide forming metals from groups IVB or VB of the periodic table, wherein nitrogen is added in an amount >1.7% by weight per each wt % of the cubic carbide forming metals; mixing said powders with (a) pressing agent and (b) tungsten metal or carbon black to obtain a desired S-value; milling and spray drying the mixture to a powder material with the desired properties; compacting and sintering the powder material at a temperature of 1350-1500° C. in a controlled atmosphere followed by cooling; applying one or more post sintering treatments including edge rounding; and applying a hard, wear resistant coating by CVD- and or MTCVD-technique, wherein the cubic carbide forming metals include one or more of titanium, tantalum, niobium, vanadium, tungsten and molybdenum, wherein a ratio, by weight percent, of tantalum to niobium is 1-2.5 and a ratio, by weight percent, of titanium to niobium is 0.5-1.5, and wherein the coating comprises a first bonding layer of TiN adjacent the cemented carbide substrate, a first layer of Ti(C,N) having a thickness of from about 3 to 15 μm adjacent the first bonding layer, a second bonding layer of Ti(C,O,N) adjacent the first layer, followed by an alumina layer having a thickness of from about 3 to 15 μm, said alumina layer being composed of α-Al 2 O 3 , a further layer adjacent the alumina layer of Ti(C,N) or Ti(C,O,N) having a thickness of from about 1 to 10 μm, and a layer of TiN deposited on top of the further layer of Ti(C,N) or Ti(C,O,N), wherein a total thickness of the coating is less than 40 μm, the thickness of the first Ti(C,N) layer is 1-2 times the thickness of the alumina layer, and the thickness of the further Ti(C,N) or Ti(C,O,N) layer is 0.1-1.2 times the thickness of the first Ti(C,N) layer and 0.1-1.2 times the thickness of the alumina layer.