Coated inserts for rough milling

Abstract

Coated milling insert has a WC—Co cemented carbide with a low content of cubic carbides and a highly W-alloyed binder phase and a coating including an inner layer of TiC x N y with columnar grains followed by a layer of κ-Al 2 O 3 and a top layer of TiN. The coated milling insert is particularly useful for milling of grey cast iron with or without cast skin under wet conditions at low and moderate cutting speeds and milling of nodular cast iron and compacted graphite iron with or without cast skin under wet conditions at moderate cutting speeds.

1. A method of making a milling insert comprising a cemented carbide body and a coating wherein the WC-Co-based cemented carbide body comprises WC, 7.3-7.9 wt. % Co and 1.0-1.8 wt. % cubic carbides of Ta and Nb and a highly W-alloyed binder phase with a CW-ratio of 0.86-0.94, the method comprising the steps of:
 depositing by a CVD-method a first, innermost layer of TiC x N y O z  with x+y+z=1, y>x and z<0.2 having an equiaxed grain structure with a size <0.5 μm and a total thickness of 0.1-1.5 μm;  
 depositing by a MTCVD-technique a layer of TiC x N y  with x+y=1, x>0.3 and y>0.3 with a thickness of 1-4 μm having a columnar grain structure with an average diameter of <5 μm, wherein the MTCVD-technique uses acetonitrile as a source of carbon and nitrogen for forming a layer in a temperature range of 700-900° C.;  
 depositing a layer of a smooth κ-Al 2 O 3  with a thickness of 1-2.5 μm; and  
 depositing an outer layer of TiN with a thickness of 0.5-1.0 μm.  
 
     
     
       2. The method according to the  claim 1 , wherein the cemented carbide body contains 1.4-1.7 wt. % carbides of Ta and Nb. 
     
     
       3. The method according to  claim 1 , further comprising the step of removing the outer layer of TiN along a cutting edge. 
     
     
       4. The method of making a milling insert of  claim 1 , wherein the first, innermost layer of TiC x N y O z  has y>0.8 and z=0. 
     
     
       5. The method of making a milling insert of  claim 1 , wherein the layer of TiC x N y  has x≧0.5. 
     
     
       6. A method of wet milling comprising the steps of:
 providing a cutting tool insert comprising a cemented carbide body comprising WC, 7.3-7.9 wt. % Co, 1.0-1.8 wt. % cubic carbides of Ta and Nb, and a highly W-alloyed binder phase with a CW-ratio of 0.86-0.94, a coating comprising a first, innermost layer of TiC x N y O z  with x+y+z=1, y>x and z<0.2 having an equiaxed grain structure with a size <0.5 μm and a total thickness of 0.1-1.5 μm, a layer of TiC x N y  with x+y=1, x>0.3 and y>0.3 with a thickness of 1-4 μm having a columnar grain structure with an average diameter of <5 μm, a layer of a smooth, fine-grained, 0.5-2 μm κ-Al 2 O 3  with a thickness of 1-2.5 μm, and an outer layer of TiN with a thickness of 0.5-1.0 μm;  
 operating the cutting tool insert at a speed of 70-180 m/min; and  
 feeding at a rate of 0.1-0.4 μm/tooth, wherein the wet milling is wet milling a cast iron, a compacted graphite iron or a nodular iron.  
 
     
     
       7. The method of  claim 6 , wherein the cast iron is a grey cast iron. 
     
     
       8. The method according to  claim 1 , wherein an average grain size of the WC is about  1 . 5 - 2 . 5  μm. 
     
     
       9. The method according to  claim 8 , wherein the average grain size of the WC is about  1 . 8  μm. 
     
     
       10. The method according to  claim 1 , wherein the thickness of the TiC x   N   y    layer is  2   -   2 . 7  μm.   
     
     
       11. The method according to  claim 1 , wherein the average diameter of the columnar grain structure of the TiC x   N   y    layer is  0 . 1 - 2  μm.   
     
     
       12. The method according to  claim 1 , wherein the thickness of the layer of κ- Al   2   O   3    is  1 . 2   -   1 . 7  μm.   
     
     
       13. The method according to  claim 1 , wherein the outer layer of TiN is removed along a cutting edge. 
     
     
       14. The method according to  claim 13 , wherein the layer of κ- Al   2   O   3    is at least partly removed along the cutting edge.   
     
     
       15. The method according to  claim 1 , comprising wet- blasting the coating surface with a fine - grained alumina powder or brushing the edges with a brush.   
     
     
       16. The method of  claim 6 , wherein the outer layer of TiN is removed along a cutting edge. 
     
     
       17. The method of  claim 16 , wherein the layer of κ- Al   2   O   3    is at least partly removed along the cutting edge.