Cemented carbide insert for wear resistance demanding short hole drilling operations

A method of making a cutting insert comprising a cemented carbide substrate with a binder phase enriched surface zone and a coating, said substrate comprising a binder phase of Co, WC and a cubic carbonitride phase, said binder phase enriched surface zone being free of said cubic carbonitride phase and with an constant thickness around the insert, said method comprising forming a powder mixture containing WC, from about 4 to about 7 weight percent Co and from about 7 to about 10 weight percent cubic carbides of the metals from groups IVa, Va or VIa of the periodic table whereby N is added in an amount of between about 1.1 and about 1.4 of the weight of the elements from groups IVa and Va,

• mixing said powders with a pressing agent and possibly W such that the desired CW-ratio of from about 0.75 to about 0.90 is obtained,
• milling and spray drying the mixture to a powder material with the desired properties,
• compacting and sintering the powder material at a temperature of from about 1300 to about 1500° C., in a controlled atmosphere of about 5 kPa followed by cooling,
• applying conventional post sintering treatments including edge rounding and
• applying a hard, wear resistant coating comprising
• a first innermost layer of TiCxNyOz with x+y+z=1 with a thickness of from about 0.1 to about 2 μm, and with equiaxed or columnar grains with size less than about 0.5 μm using known CVD-methods
• a next layer of TiCxNyOz x+y+z=1 with a thickness of from about 2 to about 10 μm with columnar grains and with a diameter of less than-about 5 μm deposited either by MTCVD-technique using acetonitrile as the carbon and nitrogen source for forming the layer in the temperature range of from about 700 to about 900° C. or by high temperature CVD-technique, from about 1000 to about 1100° C., the process conditions being selected to grow layers with columnar grains, that is generally high process pressure of from about 0.3 to about 1 bar
• a next layer of TiCxNyOz, x+y+z=1 with z being less than or equal to about 0.5 with a thickness of from about 0.1 to about 2 μm and with equiaxed or needlelike grains with size less than or equal to about 0.5 μm, using known CVD-methods, this layer being the same as or different from the innermost layer
• an outer layer of a smooth textured α-Al2O3 layer with a thickness of from about 2 to about 10 μm and a surface roughness (Ra) of less than 0.3 μm over a measured length of 0.25 mm.